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超高速フォトダイオードとその通信技術への応用

電子情報通信学会和文論文誌Cに優れたレター論文を発表した

電子情報通信学会和文論文誌Cに優れたレター論文を発表した

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/LPT.2020.3007415

Language：English   Publishing type：Research paper (scientific journal)  

Nonlinear compensation for indoor visible light communication systems with carrierless amplitude and phase modulation
Although there are enormous available bandwidths for license-free visible light communication (VLC), a relatively narrow modulation bandwidth of LED is still an obstacle for further application. The carrierless amplitude and phase (CAP) modulation is a high spectral efficiency modulation technology which has begun to draw more attention in recent years. However, to meet the illumination of indoor VLC, the nonlinear interference is quite serious because of multipath fading channels. Thus, the spectrum efficiency of VLC with CAP modulation is greatly limited by these nonlinear effects. In this paper, the nonlinear distortion of indoor VLC systems, which was introduced by the nonlinearity of analog device and multipath fading channel, has been analyzed. Therefore, the problem we are trying to solve is to study an adaptive digital equalizer at CAP modulation which can efficiently mitigate nonlinearity of indoor VLC. The simulation result shows that the adaptive digital decision-feedback equalizer is an effective solution that can mitigate inter-symbol interference and improve the receiver performance efficiently.

DOI： 10.7567/1347-4065/ab1fd8

Language：English  

700 GHz terahertz wave beam combination by optical phase control

DOI： 10.7567/1347-4065/ab26aa

Language：Japanese  

波長可変分布活性DFBレーザの波長切替幅400GHz(3.2nm)での高速高安定化を目指してレーザモデルの高精度化を行った。モデルをもとに設計したフィードフォワード／フィードバック併用制御により100ns以下の波長切替時間と切替後の波長安定性を実現した。

Language：Japanese  

半導体光増幅器(SOA)における注入電流変化に対する光位相変化を測定するためにマッハ・ツェンダ干渉計型強度変調器を模した測定系を光ファイバで構成し、かつ光ファイバ長の揺らぎの影響を受けない測定法を提案している。本測定により、SOAの注入電流に対する光位相変化を高精度で測定でき、本測定法が有効である事を確認した

Language：English  

For phase stabilization of two-tone coherent millimeter-wave/microwave carrier generation, two types of phase detection schemes were devised based on lightwave interferometric technique, the Mach-Zehnder interferometric method and the pseudo Mach-Zehnder interferometric method. The former system showed clear eye patterns at both OOK and PSK modulations of 1 Gbit/s on the 12.5-GHz carrier. The latter system demonstrated the error-free transmission at OOK modulation of 11 Gbit/s on the 100-GHz carrier.

DOI： 10.1587/transele.e99.c.1048, 10.7567/1347-4065/ab26aa_references_DOI_5YmyZzbRIm9Zdn1o04YvQNbqpIi

Language：English   Publishing type：Research paper (international conference proceedings)  

The lasers for the flexible-grid wavelength division multiplexing (WDM) system are required to have high precision of wavelength stability. Previously, we proposed the wavelength-controlling system of the Distributed FeedBack Laser Diode (DFB-LD) with the photomixing technique and a microwave filter to precisely measure the optical frequency error from the target value. To enlarge the wavelength-capture range, we improve the system to detect the wavelength error with two different microwave filters in parallel. Experimental results show that the wavelength-capture range is extended up to 4 GHz while the wavelength error is still kept within ±50 MHz.

DOI： 10.7567/JJAP.55.08RB10

Language：English  

Sub-microsecond wavelength stabilization of tunable lasers with the internal wavelength locker
We proposed a method of accelerating the wavelength stabilization after wavelength switching of the Tunable Distributed Amplification (TDA-) DFB laser using the internal wavelength locker to reduce the size and the cost of wavelength control system. The configuration of the wavelength stabilization system based on this locker was as follows. At the wavelength locker, the light intensity after an optical filter is detected as a current by the photodiodes (PDs). Then, for estimating the wavelength, the current is processed by the current/voltage-converting circuit (IVC), logarithm amplifier (Log Amp) and Field Programmable Gate Array (FPGA). Finally, the laser current is controlled to tune to the desired wavelength with reference to the estimated wavelength. With this control system the wavelength is stabilized within 800 ns after wavelength switching which is even faster than that with the conventional control system.

DOI： 10.7567/JJAP.55.08RB07

Language：English  

Fast wavelength switching with tunable distributed amplification distributed feedback laser by feedforward control technique
We proposed the way to accelerate the wavelength switching at the TDA-DFB laser based on the feedforward control. From experimental lasers’ responses, we designed and simulated the feedforward controllers using MATLAB/Simulink so as to reduce the time for wavelength stabilization. We applied this technique to two different situations; one is for the laser drive circuit with a large output current and 50-ns rise time, and the other is for that with a moderate output current and 5-ns rise time. In both situations, we showed the improvement of the wavelength switching times which were from 450 ns to 150 ns and 75 ns to 35 ns, respectively. From these results, it is confirmed that the proposed control technique is efficient for possible practical applications.

DOI： 10.7567/JJAP.53.08MB11

Language：Japanese  

高周波キャリアを二光波のビート信号で生成する光学系をマッハ・ツェンダ干渉計として構成し，干渉光強度の安定化制御で高周波キャリアの位相安定化を行う方法を提案している．実験により10 Hz以下の位相ゆらぎが低減され本提案の有効性が確認された．

Publisher：Optics Communications  

We propose a cost-effective THz wireless communication scheme for future femtocell networks that leverages either direct gain modulation (DGM) or cross gain modulation (XGM) of a semiconductor optical amplifier (SOA) to convert coaxially or optically carried data into intensity-modulated THz waves, respectively. This architecture, based on an SOA and a uni-traveling-carrier photodiode (UTC-PD), has advantages over typical THz modulation schemes involving a resonant tunneling diode or an electro-optic modulator combined with a UTC-PD. Consequently, it facilitates the seamless convergence of hybrid fiber-coaxial networks to THz radio access networks with low cost, straightforward monolithic integration, and a more compact footprint. Furthermore, we experimentally verified the possibility of non-return-to-zero on–off keying wireless communication over 0.5 m in the 300 GHz band, achieving real-time transmission of 4 Gbit/s for coaxial access via an SOA's DGM and 10 Gbit/s for fiber access via the SOA's XGM. Notably, these data rates were attained by simple non-coherent THz intensity demodulation based on a Fermi-level managed barrier diode while meeting the 7% hard-decision forward error correction (HD-FEC) threshold (3.4×10−3). Finally, we conducted an analysis of the merits and drawbacks of the proposed THz communication scheme based on the combination of an SOA and a UTC-PD, discussed bottlenecks that hinder further rate improvement, and explored possibilities for optimization. In conclusion, this scheme is crucial for realizing future ultra-high-speed wireless networks that seamlessly connect to fiber-coaxial networks.

DOI： 10.1016/j.optcom.2024.130724

Scopus

Language：Japanese  

This article presents research trends in terahertz-wave wireless communications as well as our research results on terahertz wave phase management in an optical domain at photomixing technology, such as power combining, beam steering and phase stabilization for multi-level phase modulation.

DOI： 10.14923/transelej.2023jci0017

CiNii Research

Publisher：Electronics (Switzerland)  

Advancements in semiconductor devices, such as Uni-travelling-carrier photodiodes (UTC-PDs), have played a significant role in the development of Terahertz communication technology. However, the persistent challenge is the limited output power from a single UTC-PD required for practical transmission distances. To enhance the output power, we propose and demonstrate a novel Terahertz wave power combining technique using a photomixer device comprising two arrayed UTC-PDs monolithically integrated with a microstrip line-based 2 × 1 Wilkinson power combiner and a patch antenna on a Silicon Carbide (SiC) substrate at 300 GHz. When the two UTC-PDs are activated at photocurrents of 8 mA and 10 mA, the device exhibits a 7.3 dB increase in power relative to the power obtained when only the 8 mA UTC-PD is activated, and a 4.4 dB increase in power relative to the power obtained with the 10 mA UTC-PD. This implies that power can be enhanced by a factor of N2 if the photocurrent is multiplied by N. Additionally, we demonstrate that the UTC-PD output saturation depends on the space charge effect, which modulates the electric field in the depletion region and results from critical charge density of about 80 kA/cm2 for the device in this work.

DOI： 10.3390/electronics13132661

Scopus

Publisher：Optics Communications  

Reconfigurable Intelligent Surfaces (RISs), proposed as innovative units, possess the potential to establish reliable connections in Underwater Optical Wireless Communication (UOWC) systems, where direct transmission (DT) experiences significant weakening due to dynamic channel conditions. In this paper, we examine the performance of a UOWC system consisting of an RIS and a modulating retroreflector (MRR), referred to as the RIS-assisted MRR-UOWC system. The channel is affected by a combination of path loss, gamma–gamma (G–G) turbulence, and pointing error (PE). The considered system employs the spectral-power-efficient L-ary Quadrature Amplitude Modulation Multi-Pulse Pulse-Position Modulation (LQAM-MPPM) technique. For our system performance measures, we present upper-bound (UB) and approximate UB expressions for the average bit-error rate (BER) of LQAM-MPPM signals. These expressions are used to analyze the system's performance. Performance metrics are established by deriving the Probability Density Function (PDF), Cumulative Distribution Function (CDF), and Moment-Generating Function (MGF) for the end-to-end signal-to-noise ratio (SNR), resulting from the sum of products of independent but not identically distributed (i.ni.d) channel coefficients. The results of our study indicate that the LQAM-MPPM scheme surpasses traditional schemes.

DOI： 10.1016/j.optcom.2024.130444

Scopus

Publisher：Japanese Journal of Applied Physics  

Photomixing is one of the promising THz-wave generation methods. A conventional photomixing system with two lasers results in increasing the volume and power consumption of the system. For downsizing the system and reducing its power consumption, we have previously proposed a method to generate a THz-wave by a single wavelength-tunable laser. This technique can generate a quasi-continuous THz wave as well as a pulsed THz wave, based on which we are studying toward pulse frequency-amplitude modulation as a multi-level modulation method. In this paper, we have successfully generated a THz wave with frequency modulation between 286 GHz and 322 GHz by a single wavelength-tunable laser.

DOI： 10.35848/1347-4065/ad37c3

Scopus

Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

We explored the potential of an optoelectronic frequency hopping system within the 300 GHz band, leveraging a tunable distributed feedback laser array and uni-traveling carrier photodiode. Our experiments successfully achieved a 10-channel terahertz (THz) frequency hopping, marking a significant advancement in THz secure communication technologies. Notably, the system exhibited a rapid frequency-hopping capability with a short transition time of 0.8 ms between channels, ranging from 288 to 331 GHz. Further, we conducted data transmission tests at a rate of 5 Gbit s⁻¹ across several channels. The results were promising, showing each channel maintained a clear eye pattern and a low bit error rate, crucial factors for reliable and secure data transmission. These findings not only demonstrate the efficacy of our system but also open new avenues for high-speed, secure THz communication.

DOI： 10.35848/1347-4065/ad3926

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Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/ad3926/pdf

Publisher：International Journal of High Speed Electronics and Systems  

A terahertz (THz) wave generator for multiplying the output power from arrayed photomixers is developed. The generator is composed of two uni-traveling carrier photodiodes (UTC-PDs) as the photomixers, a 2 × 1 T-junction power combiner and a microstrip rectangular patch antenna on a silicon carbide (SiC) substrate in which photocurrents of 300 GHz from the UTC-PDs are combined to be fed to the antenna. Experimental results show that the output power is multiplied by 5.8 dB (approximately fourfold) compared to that of a single UTC-PD. This advancement has the potential for further multiplication of THz power by cascaded combining of a larger number of UTC-PDs.

DOI： 10.1142/S0129156424400251

Scopus

Publisher：2024 International Conference on Electronics Packaging, ICEP 2024  

We designed a terahertz wave power combiner which combines high-frequency currents from each photomixer in a micro strip line and investigated the feasibility of terahertz wave power combining. The designed terahertz power combiner was fabricated on silicon carbide (SiC) substrate because of its high thermal conductivity, which prevents thermal damage to the UTC-PD at high photocurrent. The UTC-PDs was activated with a bias voltage of -1.0 V and a photo current of 8 mA. Experimental results show that the output power of four photo mixers is multiplied by 11 dB (approximately 13 times) compared to that of a single photomixer, which confirms a great advantage of arrayed photomixers as a current source. In addition, the THz waves was higher without narrowing the beam width, compared to using the method of arrayed antennas with UTC-PDs.

DOI： 10.23919/ICEP61562.2024.10535617

Scopus

Publisher：2024 Optical Fiber Communications Conference and Exhibition, OFC 2024 - Proceedings  

We proposed a photonic frequency-hopping physical-secure Terahertz-wave communication system driven by a high-speed wavelength tunable laser and a photomixer, and experimentally demonstrated a frequency-hopping time of less than 25 ns at 300-GHz band.

Scopus

Publishing type：Research paper (scientific journal)   Publisher：Journal of Infrared, Millimeter, and Terahertz Waves  

THz technology has the potential to revolutionize various fields, including high-speed wireless communication, medical imaging, and spectroscopy. One challenge facing THz technology, however, is the limited output power (on the order of microwatts) of photonic THz sources (e.g., uni-traveling-carrier photodiode). Researchers are therefore exploring THz beam steering techniques to maximize their power effectiveness. To this end, we propose a photonic THz beam steering method that utilizes fiber chromatic dispersion, eliminating the need for energy-consuming active electronics. This paper explains its basic operating principle, fabrication and performance analysis of the associated THz array antenna, and demonstrates the feasibility of achieving a 300 GHz beam steering within 10∘ by means of dispersion-varied polarization-maintaining fibers. In conclusion, the present scheme can greatly enhance the power efficiency of photonic THz sources, and enable the potential advantages of seamless integration with fiber-optic networks, including reduced complexity, simplified operation, low power consumption, and cost-effectiveness.

DOI： 10.1007/s10762-024-00975-0

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

As a high-frequency carrier, the terahertz (THz) wave is essential for achieving high-data-rate wireless transmission due to its ultra-wide bandwidth. Phase stabilization becomes crucial to enable phase-shift-based multilevel modulation for high-speed data transmission. We developed a Mach–Zehnder interferometric phase stabilization technique for photomixing, which has proved a promising method for phase-stable continuous THz-wave generation. However, this method faced inefficiencies in generating phase-modulated THz waves due to the impact of the phase modulator on the phase stabilization system. By photomixing, which is one of the promising methods for generating THz waves, the phase of the generated THz waves can be controlled in the optical domain so that the stability of the generated THz wave can be controlled by photonics technologies. Thus, we devised a new phase stabilization approach using backward-directional lightwave, which is overlapped with the THz wave generation system. This study presented a conceptual and experimental framework for stabilizing the phase differences of optical carrier signals. We compared the optical domain and transmission performances between forward-directional and backward-directional phase stabilization methods. Remarkably, our results demonstrated error-free transmission at a modulation frequency of 3 Gbit/s and higher.

DOI： 10.3390/electronics12153366

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Future wireless communications require higher security as well as a higher data rate. We have been studying physically secured wireless transmission systems and previously proposed encryption/decryption techniques based on the AND operation caused by coherent detection between two encrypted data sequences on two different terahertz carriers. Furthermore, we suggested that by employing the XOR operation as the decryption, the proposed system can be made more secure because XOR increases the computational complexity for eavesdroppers to recover the plaintext. In this paper, we propose the XOR operation between two data sequences on FSK-modulated terahertz waves. By constructing the XOR encryption transmitters/receivers, which consisted of high-speed wavelength tunable lasers and arrayed uni-traveling-carrier photodiodes (UTC-PDs), we successfully demonstrated the XOR operation between two data sequences on 200 GHz waves from the two transmitters.

DOI： 10.3390/electronics12122629

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

Terahertz (THz) pulses with picosecond-level duration are generated and enhanced by fabricating arrayed InP/InGaAs unitraveling-carrier photodiodes (UTC-PDs) with integrated planar bowtie antennas. We experimentally demonstrated THz pulses generation from an UTC-PD with a duration of 10ps and 25GHz repetition rate. Compared with those of an individual UTC-PD excited at a photocurrent of 3mA and dc bias voltage of -1.5V, the pulsed THz waves generated from three arrayed UTC-PDs exhibited a 7-dB power enhancement gain after optical time alignment through optic-fiber delay lines. Experimental results indicate that this optoelectronic THz pulses generation based on arrayed UTC-PDs can achieve scalable directional gain and low-profile assembly. Enhanced THz pulses generation will be beneficial for the applications of quasi-time-domain THz spectroscope and pulse-based THz communications.

DOI： 10.1109/tthz.2023.3251736

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Authorship：Last author,　Corresponding author  

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Language：Others  

Publisher：Photonics  

The photomixing of two lightwaves is one of the promising methods of generating a terahertz (THz) wave. The conventional photomixing system consisting of two lasers and a modulator results in large transmitter volumes and high power consumption. To solve this issue, we devised a novel THz wave generation and modulation system based on photomixing using a single wavelength-tunable laser in combination with delayed self-multiplexing. We successfully demonstrated the feasibility of 300-GHz wave generation and modulation.

DOI： 10.3390/photonics10040369

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Scopus

Language：Japanese  

We have previously demonstrated beam steering of terahertz waves generated from arrayed photomixers by mechanically adjusting the optical phase. This time, we succeeded in electronically controlling the beam steering angle with an accuracy of less than 10° using an optical phased array that can adjust the optical phase electrically.

DOI： 10.14923/transelej.2022jcl0007

CiNii Research

Publishing type：Research paper (international conference proceedings)   Publisher：2023 35th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2023  

We designed and assessed a power combiner-radiator complex for integration with 300-GHz-band arrayed photomixers. The device consists of a microstrip-line based combiner (Wilkinson combiner or a T-junction combiner) and a patch antenna. Simulation results show an increase of the radiated power by 2.54 dB with a Wilkinson combiner and 2.94 dB with a T-junction combiner in comparison to a conventional single port-fed device. The results further show realized directional gains of 4.85 dBi and 5.04 dBi for the complex based on a Wilkinson combiner and a T-junction combiner, respectively. Additionally, the Wilkinson combiner gives better return loss and isolation between the input ports than the T-junction combiner, while the T-junction combiner has a better radiation efficiency of 85% compared to 77% of the Wilkinson combiner.

DOI： 10.23919/URSIGASS57860.2023.10265384

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Publisher：International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz  

We developed a fiber-coupled uni-traveling-carrier photodiode (UTC-PD) array chip for the purpose of combining the generated THz waves, and the feasibility of 300 GHz beam steering with the aid of a genetic algorithm is demonstrated in this work. Not only is this algorithm capable of automatically compensating for the optical path difference arising from the inconsistent lengths of coupled fibers, but it can also calculate the optimal phase shift in each channel for deflecting the THz beam to a predetermined angle. The implementation of this optimization algorithm in THz beam steering provides an attractive solution for efficient THz wireless communication or imaging applications in a large-scale UTC-PD array.

DOI： 10.1109/IRMMW-THz57677.2023.10299236

Scopus

Publisher：2023 Opto-Electronics and Communications Conference, OECC 2023  

We designed and analyzed the performance of a 2 by 1 coupled line Wilkinson combiner-antenna device for arrayed photomixers at 300 GHz. Simulation results showed that there is a 2.59 dB increase in total radiated THz-wave power when the coupled line Wilkinson combiner is used to integrate two identical UTC-PDs and feed their output power into an antenna, compared to a single-port feed for a single UTC-PD. Additionally, there is a -21.5 dB isolation between the feed ports and a realized gain of 4.8 dBi in the +z (theta = 0) direction. Furthermore, the quarter wavelength lines for the designed combiner covers a half area of 0.1 × 0.055 mm2 compared to the conventional Wilkinson combiner.

DOI： 10.1109/OECC56963.2023.10209621

Scopus

Publishing type：Research paper (international conference proceedings)   Publisher：28th Microoptics Conference, MOC 2023  

We demonstrated an optoelectronic frequency hopping system in the 300-GHz band using a tunable DFB laser array and an antennas-integrated UTC-PD chip. The experimental result exhibited a fast-hopping speed of 4.4 GHz/ms in the 300-330 GHz range, which shows great potential for THz secure communication.

DOI： 10.23919/MOC58607.2023.10302896

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DOI： 10.1364/OFC.2023.M3D.4

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Publishing type：Research paper (international conference proceedings)   Publisher：2023 Optical Fiber Communications Conference and Exhibition, OFC 2023 - Proceedings  

We developed a THz-wave power-combination and beam-steering system driven by an optoelectronic phased array. The 300-GHz waves from an antenna-coupled InP/InGaAs UTC-PD array are combined with 16-dB gain and steered continuously over a 30° range.

DOI： 10.23919/OFC49934.2023.10116084

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Publisher：28th Microoptics Conference, MOC 2023  

We designed a novel terahertz wave power combiner which combines high-frequency currents from each photomixer in a micro strip line. The experimental result showed that the combined power increases super-linearly with the number of the photomixers, which for the first time confirms a great advantage of photomixing as a current source.

DOI： 10.23919/MOC58607.2023.10302740

Scopus

Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of SPIE - The International Society for Optical Engineering  

To exploit the extremely wide bandwidth in the THz region for ultra-high-speed wireless communication, UTC-PD-based THz emitters enjoy a wide bandwidth and high linearity, but face challenges in increasing power due to saturation effects and thermal effects. We designed a 16-way WR3 power combiner for 12 dB gain using the Y-branch structure in the 300 GHz band. Additionally, a 37.7 dBi gain reflector-integrated diagonal horn antenna was developed for a pencil beam at 300 GHz. Furthermore, ongoing efforts are dedicated to manufacturing them with 3D printing technique.

DOI： 10.1117/12.2647226

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Publisher：2023 35th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2023  

Higher-frequency carriers are inevitable for higher-speed wireless communication. To maximize their advantage, phase stabilization is an essential technology for phaseshift-based multi-level modulation. At photomixing, which has been a promising way for continuous THz-wave generation, we have devised a Mach-Zehnder interferometric phase stabilization method. However, the serious drawback of the method is the ineffectiveness for a phase-modulated THz wave. This time, we invent a phase stabilization system with a backward-direction lightwave overlapping on the THz-wave generation system. A conceptual and experimental setup of phase detection and phase stabilization is presented in this paper. The stabilization system is revealed to be effective at above a couple of Gbit/s.

DOI： 10.23919/URSIGASS57860.2023.10265667

Scopus

Publisher：ICECOM 2023 - 24th International Conference on Applied Electromagnetics and Communications  

This paper presents our strategic approaches for increasing data rates of terahertz (THz) wireless communications using photonics-based transmitters and receivers and shows recent results in the 300-GHz-band.

DOI： 10.1109/ICECOM58258.2023.10367950

Scopus

Publisher：28th Microoptics Conference, MOC 2023  

Based on our devising THz-wave-generation method by photomixing using single wavelength-Tunable laser, we design a pulse frequency modulation system. Experimental results show the feasibility of pulsed THz wave generation with different frequencies. Together with the use of a wavelength selective switch, the system can be developed into pulse frequency-Amplitude modulation.

DOI： 10.23919/MOC58607.2023.10302887

Scopus

Language：Japanese  

The photomixing technique is a promising method of terahertz-wave generation. However, the conventional method uses two lasers, which results in a large space and high-power consumption. We devised a photomixing system using a single wavelength-tunable laser. We successfully demonstrated the system at 300 GHz using a reflection-type transversal filter laser.

DOI： 10.14923/transelej.2022jcl0003

CiNii Research

Language：Others  

Authorship：Last author,　Corresponding author  

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

In this study, generating and enhancing THz continuous/pulsed waves is achieved by fabricating a monolithic InP substrate chip of arrayed photomixers, where each photomixer includes an InP/InGaAs uni-traveling-carrier photodiode (UTC-PD) with integrated 1 × 4 planar slot antennas (PSAs). Through optoelectronic time-aligned and-gradient delays of lightwaves that couple to arrayed photomixers, the radiated THz waves yield both quantitative gain and spatial directional gain. To generate continuous 300 GHz waves, each UTC-PD is excited at a photocurrent of 3 mA to attain-15.79 dBm THz power that exhibits 12 dB combined gain by four arrayed UTC-PDs. Whereas,-17.71 dBm THz pulse generation with a duration of 25 ps can be achieved at the same optical pump power. The results show that the power enhanced gain of THz pulses is around 10 dB, which is less than that of continuous THz waves, because a part of the generated frequency components of the THz pulse is significantly deteriorated by bandwidth-limited PSAs. Furthermore, by means of optoelectronic time-gradient delay with frequency-independent characteristics, we successfully demonstrate steering of continuous and pulsed THz waves repeatedly in a range of 30° and 20°, respectively. In conclusion, strengthening directional THz power by beam-combining and-steering with arrayed photomixers is a promising technique for effective generation of continuous/pulsed THz waves.

DOI： 10.1109/jlt.2022.3204113

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Language：Japanese  

Evaluation of High-Security Wireless Communication System Utilizing AND Operation Between Two Data
We have proposed a method to improve physical layer security of wireless communication by radiating two data from different locations. In this system, a receiver can decode original data by implementing AND operation between two data. This time, we confirmed feasibility of proposed system by implementing AND operation between two light waves.

DOI： 10.14923/transelej.2022jcl0001

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/LPT.2021.3137808

Language：Others   Publishing type：Research paper (scientific journal)  

We proposed a new control method of the tunable distributed feedback (DFB) laser array (TLA) to realize high-speed optical switching by changing the injection current without sacrificing reliability. Previous studies of high-speed wavelength switching at DFB lasers achieved a sub-second switching time by injecting a large current to the active layer. However, a large injection current caused laser degradation that seriously reduced laser lifetime and reliability. In this paper, based on fast wavelength switching by injection current control, a new switching method was proposed that reduces an averaged injection current by increasing temperature. We successfully demonstrated 400-GHz-wide wavelength switching, which is the maximum tuning range of a single DFB laser in the TLA, with a switching time of 130 ms and reduced the injection current from 402 to 52 mA. Thus, we were able to greatly improve the reliability and increase the lifetime of the TLA by 60 times.

DOI： 10.1109/LPT.2021.3137808

Publisher：OECC/PSC 2022 - 27th OptoElectronics and Communications Conference/International Conference on Photonics in Switching and Computing 2022  

We proposed a physical layer secure wireless communication system using AND operation. In this paper, we demonstrate data transmission based on AND operation between two 300-GHz-band signals from two transmitters.

DOI： 10.23919/OECC/PSC53152.2022.9850185

Scopus

Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

Terahertz-wave has been attracting attention for high-speed wireless communication and photomixing is considered to be a promising method for generating terahertz-waves. Since the output power of the conventional InGaAsP-based photomixer saturates due to its lower voltage resistance, an InGaN-based photomixer with higher voltage resistance is under investigating. One of the essential technologies of InGaN-based photomixing is two-tone single-mode lightwave. In this paper, we devised a method to make a two-tone lightwave using a 405-nm laser and a periodic optical filter. We successfully demonstrated the two-tone lightwaves for four different terahertz bands.

Scopus

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Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

We had previously proposed a physically encrypted Terahertz (THz) communication system based on AND operation between two signals and confirmed the effectiveness of the decryption. In this paper, by utilizing uni-traveling carrier photodiodes (UTC-PDs) arrays with 4 × 4 slot antennas as transmitters and coherent detection at the receiver, we experimentally demonstrated the feasibility of the proposed system with 500 Mbit/s data transmission on 300-GHz band.

Scopus

Web of Science

Publisher：Proceedings of SPIE - The International Society for Optical Engineering  

6G/beyond 5G technologies should meet the requirement for both high speed and high security. We have focused on terahertz (THz) waves for high-speed transmission, and by photomixing, we have demonstrated power enhancement and beam steering. In terms of the security of wireless transmission, physical-layer security becomes an important issue. We have proposed a novel wireless communication system based on beam steering and coherent detection. In this system, two different data encoded from original data on two THz beams are radiated from two different locations and are overlapped at a target area by beam steering. Then, a receiver at the area implements logical AND operation between the two data as a result of coherent detection, which deduces the original data. This time, as a feasibility confirmation, we performed logical AND operation between two data on different lightwaves and measured the bit error rate of the deduced original data. Experimental results showed that the original data is deduced exactly from the two encoded data when the amplitude ratio between the two data is smaller than 5. This indicates that the acceptable ratio between the distances from two different transmitters would be up to 5. Experimental results also showed that the bit error rate suddenly deteriorates when the time slots of the two data are shifted by 0.7 bits This indicates that the receivable area is limited in several centimeters square for a 1-Gbit/s data.

DOI： 10.1117/12.2606717

Web of Science

Scopus

Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of SPIE - The International Society for Optical Engineering  

To realize a high-speed high-reliability wavelength switching at future WDM networks, we proposed the injection-current/temperature cooperative control method of the tunable-distributed-feedback (DFB) laser array (TLA) for avoiding a large injection current, which is the primary cause of laser degradation. We successfully demonstrated a full-C-band wavelength switching within 124 ms by rapid increase of the injection current and following gradual decrease of the injection current to avoid laser aging. Compared to the conventional control method, the meantime to failure of the TLA in the proposed method is estimated to be extended by 44 times.

DOI： 10.1117/12.2604422

Web of Science

Scopus

researchmap

Publishing type：Research paper (international conference proceedings)   Publisher：OECC/PSC 2022 - 27th OptoElectronics and Communications Conference/International Conference on Photonics in Switching and Computing 2022  

Taking advantage of photomixing technique, we successfully demonstrated the generation of pulsed THz waves with a repetition rate of 5, 10, and 25 GHz, as well as their enhancement by 10 dB using 4-arrayed UTC-PDs.

DOI： 10.23919/OECC/PSC53152.2022.9849992

Scopus

researchmap

Publisher：OECC/PSC 2022 - 27th OptoElectronics and Communications Conference/International Conference on Photonics in Switching and Computing 2022  

TLA have succeeded in improving reliability through current/temperature cooperative control. We aim to obtain the equation relating temperature, current, and wavelength required for feed-forward control to improve the wavelength switching speed.

DOI： 10.23919/OECC/PSC53152.2022.9850042

Scopus

Publisher：Proceedings of the 10th International Japan-Africa Conference on Electronics, Communications, and Computations, JAC-ECC 2022  

In this letter, outage probability of terahertz (THz) link between two unmanned aerial vehicles (UAVs) is analytically and numerically investigated. Composite fading statistical model is developed considering joint effects of multipath fading, angle of arrival (AoA), and pointing-errors. The derived expression for outage probability is used to illustrate the misleading results in case of neglecting UAV antenna orientation fluctuations. In addition, effect of antenna half power beam width (HPBW) on maximum achievable link length under constraint of threshold outage probability is numerically investigated. Derived expression is validated by comparing analytical results with Monte Carlo (MC) simulation and they show high degree of agreement.

DOI： 10.1109/JAC-ECC56395.2022.10044033

Scopus

Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of the 10th International Japan-Africa Conference on Electronics, Communications, and Computations, JAC-ECC 2022  

We analyzed the performance of a microstrip patch antenna fed by a 2 by 1 Wilkinson power combiner at 300 GHz. Simulation results show that a 2.54 dB gain in total radiated power can be achieved when the Wilkinson power combiner is used to feed the antenna compared to a single-port power feed. Results further show that the combiner provides a good isolation of -21.5 dB between the input ports. Additionally, the peak power in the +z (theta =0) direction for both xz and yz planes increases by 4.8 dB.

DOI： 10.1109/JAC-ECC56395.2022.10043902

Scopus

researchmap

Publisher：Asia Communications and Photonics Conference, ACP  

The performance of modulating retro-reflector underwater optical wireless communication systems with the spectral-power-efficient L-ary quadrature amplitude modulation multi-pulse pulse-position modulation (LQAM-MPPM) technique is investigated. Our results reveal that the LQAM-MPPM technique outperforms conventional ones.

DOI： 10.1109/ACP55869.2022.10089065

Web of Science

Scopus

Publisher：OECC/PSC 2022 - 27th OptoElectronics and Communications Conference/International Conference on Photonics in Switching and Computing 2022  

A photonics-based control system to stabilize the phases of the optical signal for terahertz wave phase modulation is introduced. The analysis of the phase modulator with inverse direction lightwave is successfully presented.

DOI： 10.23919/OECC/PSC53152.2022.9850107

Scopus

Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

High-frequency carriers have been widely used in recent wireless communication. To comply with this situation, a phase-stable wave carrier generation is an essential technology. We devised a phase stabilization system for photomixing-based THz wave phase modulation with an inverse pilot lightwave. A stable 300-GHz phase modulated wave was successfully generated and transmitted, testifying to the effectiveness of the proposed system.

Scopus

Web of Science

Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

We proposed a high speed intensity modulation system of THz waves with a low voltage signal by combining a wavelength-tunable laser and photomixing technology. We demonstrated 150 Mbit/s intensity modulation of THz waves at 2 Vpp by using an RTF laser as a wavelength tunable laser.

Scopus

Web of Science

Language：Others   Publishing type：Research paper (scientific journal)  

— For photonic-based continuous THz-wave generation for a wireless communication, a fiber-based configuration has been used. Without the fiber-optics, THz-wave generation system could be minimized by monolithic integration. Thus, based on the monolithic integration, a THz-wave generator consisting of arrayed light sources and arrayed photomixers was proposed. Arrayed light sources that can be operated at 600 GHz were designed and fabricated. Experimental results showed that the light sources have a practically uniform optical output. And then, 600-GHz power combining and directional gain were obtained in combination with arrayed photomixers.

DOI： 10.1109/LPT.2021.3124826

Language：Japanese  

Feasibility Demonstration of Encrypted Wireless Communication by Utilizing AND Operation between Two Carriers via Coherent Detection
Utilizing the characteristics that the coherent detection can perform AND operation between two RF signals, we devised a new encryption method for wireless communication at the physical layer. We confirmed the AND operation via heterodyne detection of two 300-GHz band carriers, and the principle of the reception method of the devised system was demonstrated.

DOI： 10.14923/transelej.2021JCL0002

Language：English  

DOI： 10.1016/j.ijleo.2021.167203

Language：English  

DOI： 10.1364/OE.423308

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English  

Full-range wavelength switching at tunable distributed amplification-DFB laser with high-accuracy feedforward control

DOI： 10.1049/ell2.12122

Language：English  

As a physically secured wireless communication method, a novel configuration which deduces ANDed data decoded from heterodyne detection between two wireless data streams was proposed. As a feasibility experiment, the demonstration of a heterodyne AND operation was conducted by devising an optical system to emulate our novel wireless system. Experimental results testified the principle of our proposed physical layer security.

DOI： 10.1587/elex.18.20210008

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1049/ell2.12122

Language：Japanese  

High-Speed Wavelength Switching Control at Tunable Laser based on Nonlinear Model
To realize high-speed 800-GHz-wide wavelength switching with TDA (tunable distributed amplification)-DFB laser, we developed a higher-accuracy model accounting for the laser nonlinearity. By combining the feedforward control based on our nonlinear model and the feedback control, a high-speed wavelength switching time of 30 ns and long-term wavelength stabilization was achieved.

DOI： 10.14923/transelej.2020jcl0009

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

High-Speed Wavelength Switching at TDA-DFB Laser Based on a Nonlinear Model
In order to realize a high-speed optical switch for optical packet switching (OPS), we have been focused on a wavelength routing optical switch consisting of tunable lasers and an arrayed waveguide grating (AWG), and have studied high-speed wavelength switching of a tunable distributed amplification (TDA)-distributed feedback (DFB) laser. Previously, we achieved high-speed wavelength switching by feedforward control based on linear control theory. In this article, to realize higher-speed wavelength switching, we proposed a more accurate control model based on the nonlinearity of the TDA-DFB laser. We applied our nonlinear model to 400-GHz-wide and 600-GHz-wide wavelength switching and realized high-speed wavelength switching times of 33 ns and 39 ns, respectively.

DOI： 10.1109/LPT.2020.3026739

Language：Others   Publishing type：Research paper (other academic)  

In order to realize a high-speed wavelength switching of the TDA-DFB laser at a wide switching width, we developed an accurate control model accounting for the laser nonlinearity. We applied our nonlinear model to 400-GHz-wide and 600-GHz-wide switching and achieved a switching time within 50 ns.

DOI： 10.1109/OECC48412.2020.9273522

Language：Others   Publishing type：Research paper (other academic)  

We optimized the current/temperature cooperative control to improve the reliability of the tunable distributed feedback laser array (TLA) at high-speed wavelength switching. We demonstrated a 2-ms wavelength switching with a practically low average injection current.

DOI： 10.1109/OECC48412.2020.9273595

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/LPT.2020.3007415

Language：English  

Language：Others   Publishing type：Research paper (other academic)  

We devise cooperative control of injection current and temperature for wavelength switching at the DFB-LD. Prompt change of the current makes high-speed switching and gradual cooperative change of current/temperature results in wavelength stabilization at lower current. Experiment shows a switching within 31 ms as well as long term stabilization with the current of less than 100 mA.

DOI： 10.23919/MOC46630.2019.8982899

Language：Others   Publishing type：Research paper (other academic)  

The TDA-DFB laser has nonlinearity on the current-wavelength characteristic and needs high accuracy control model for realizing high-speed wide-range switching We designed a nonlinear model for high-speed 600-GHz-wide wavelength switching and showed the feasibility of this control model for much wider range switching.

DOI： 10.23919/MOC46630.2019.8982905

Language：Others   Publishing type：Research paper (other academic)  

Beam-steering is an effective method for future terahertz-wave wireless communications because the power is concentrated to a certain direction. A 2×8 optical phased array was designed and fabricated using a silica-based lightwave circuit for THz phase control, and 450-GHz-wave beam-steering with 1 kHz repetition was demonstrated.

Language：Others   Publishing type：Research paper (other academic)  

The multi-dimensional carrierless amplitude and phase (MD-CAP) modulation is a high spectral efficiency modulation technology which has begun to draw more attention in recent years. Meanwhile, how to improve the energy efficiency is also an important issue within the limited bandwidth. In this paper, a 3D-CAP modulation with trellis coded constellation has been proposed. At the premise of increasing the transmission bandwidth, the bit error rate is reduced through the unified design of channel coding and modulation.

DOI： 10.23919/PS.2019.8818137

Language：Japanese  

Language：English  

DOI： 10.15017/2195853

Language：Others  

DOI： 10.7567/jjap.57.08pd04

Language：Japanese  

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.1117/12.2287326

Language：Others   Publishing type：Research paper (other academic)  

With the increasing popularity of LED lighting and a growing demand for bandwidth in wireless communication, the visible light communication (VLC) is one of the promising scheme for addressing the bottleneck in the emerging broadband access networks. For research in the field of VLC focused on solutions of contradiction between massive available bandwidth and limited modulation bandwidth of LED, the purpose of this paper is to design an VLC experiment platform with characteristics of high flexibility and rapid productization. As a result, this platform not only expand the concept of software defined communication, but has the advantage of simple structure and low cost.

DOI： 10.23919/MOC.2017.8244620

Language：Others   Publishing type：Research paper (other academic)  

We propose a novel THz wave phase control system consisting of an optical device whose chromatic dispersion changes the phase difference between two lightwaves for photomixing. Our devised Mach-Zehnder modulation technique reveals the feasibility of full-range THz wave phase control with the semiconductor phase modulator.

DOI： 10.1109/OECC.2017.8114812

Language：Others   Publishing type：Research paper (other academic)  

We devise an optical-to-wireless media conversion method by XGM at the SOA aiming for a future use at a THz-wave access. We investigate the XGM characteristics and the performance of our proposed media conversion method. We configure the media-converted data transmission system and demonstrate an error free transmission.

DOI： 10.23919/MOC.2017.8244486

Language：Others   Publishing type：Research paper (other academic)  

We constructed the linear wavelength sweeping system with 2-μm-band distributed Bragg reflector laser for the second-harmonic-detection wavelength modulation spectroscopy. Using our devised linearity evaluation method with a germanium etalon filter, we experimentally confirmed that the nonlinearity of the laser can be efficiently compensated.

DOI： 10.23919/MOC.2017.8244604

Language：Others   Publishing type：Research paper (other academic)  

For fast wavelength switching within the full available wavelength range of the tunable laser array, we investigated a wavelength stabilizing method after switching on the injection current to the laser's active layer. Experimental results demonstrated that our feedback controller dramatically reduced wavelength switching time from 800 μs to 2.0 μs.

DOI： 10.23919/MOC.2017.8244600

Language：English   Publishing type：Research paper (other academic)  

We have previously proposed a synchronous THz-wave combiner with linearly arrayed power sources. With four arrayed photomixers we experimentally confirmed directional gain of 5.9 dB. In this paper, for exerting full performance of the array effect, we configured for the first time two-dimensionally arrayed THz-wave combiner and demonstrated a power gain of 4.8 dB compared to the linear array.

Language：English  

A THz-wave interferometer was devised for measurement of the THz-wave phase shift. In this measurement system, the relative phase shift is deduced from the interference between the THz waves generated by two photomixers. Experimental results with this interferometer revealed that the semiconductor phase modulator could be used as a THz-wave phase shifter by utilizing its chromatic dispersion.

Language：Others   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (other academic)  

This paper presents a design and fabrication of 4 x 4 one-sided directional slot array antenna on indium phosphide (InP) substrate for 0.3 THz (300 GHz) wireless link. The antenna has top antenna metal layer and bottom floating metal layer. Polyimide dielectric layer is stacked between each metal layer. The antenna is placed on the deep etched InP substrate. By optimizing the length of the bottom floating metal layer, one-sided directional radiation can be realized. The branched coplanar wave guide (CPW) transmission line is connected to each antenna element with the same electrical length. The size of the 4 x 4 array antenna is 2,730 mu m x 3,000 mu m with uni-traveling-carrier photodiodes, DC bias and ground lines. Simulated realized gain in peak direction of the proposed antenna is 11.7 dBi. The transmission measurement is carried and measured received power.

DOI： 10.1117/12.2248859

Language：Others   Publishing type：Research paper (other academic)  

For the purpose of sub-millisecond wavelength switching, the feedforward current control technique was applied to the DFB laser. At the switching from 191.2 THz to 191.0 THz, our designed controller successfully reduced the wavelength switching time of the tunable DFB laser array down to 800 μs.

Language：English   Publishing type：Research paper (scientific journal)  

A multicode optical code-division multiplexing (OCDM) is proposed to support the dynamic changes in the requested traffic demand in OCDM networks by adapting the number of allocated codes according to the requested transmission rate. In order to support time-variant data rates and multiservice transmissions; a multicode variable-weight 2D one-coincidence frequency hopping code/optical orthogonal code (OCFHC/OOC) is employed as the signature code in the proposed system. Two multicode assignment methods, namely, random multicode assignment (RMA) policy and uniform multicode assignment (UMA) policy, are presented. For each code assignment method, we drive the probability density function (pdf) of the number of active codes in each wavelength group. The bit error probability (BEP), the probability of degradation, and the blocking probability are derived as network performance key parameters. The proposed system has a simplified routing and code assignment process with a lower blocking probability. Our numerical results indicate that the network teletraffic capacity and blocking probability can be improved significantly using UMA policy and call admission control.

DOI： 10.1109/TCOMM.2015.2512922

Language：Others   Publishing type：Research paper (other academic)  

The lasers for the WDM system with the flexible grid need to have highly accurate wavelength tuning and stability. Instead of using optical filters, we propose the microwave photonics approach with photo-mixing technique and the laser current controlling. Experimental results show that the optical frequency is stabilized with the accuracy of 0.05GHz.

DOI： 10.1109/MOC.2015.7416475

Language：English   Publishing type：Research paper (other academic)  

For high-power THz wave generation by photomixing of two lightwaves, we proposed the synchronous power combiner which consists of eight-arrayed photomixers/antennas and the THz phase control system. We experimentally confirmed the effectiveness of the power combination by synchronizing the phases of the THz wave by the mechanical optical delay lines and also demonstrated the same functionality at the lightwave-circuit-based optical phase control system. We found that the directional gain is increasing with increasing the number of photomixers from two to three and it reached up to 4.5 dB.

DOI： 10.1117/12.2212017

Language：English  

This paper presents a novel design of 300 GHz band 1 x 4 one-sided directional slot dipole array antenna fed by coplanar waveguide (CPW) on indium phosphide (InP). The proposed antenna has four antenna elements and branched CPW structure to achieve a high antenna gain and a sharp beam. We fabricated and measured the array antenna. In the EM simulation, forward directional peak gain is 7.35 dBi. The measured reflection coefficient is agreed with the simulation results.

DOI： 10.34385/proc.37.s2.1.1

Language：English   Publishing type：Research paper (scientific journal)  

Optical code-division multiplexing (OCDM) systems use short pulses compared with bit-duration to achieve high transmission rate. The use of short pulses poses several problems as a result of group velocity dispersion (GVD), intersymbol interference (ISI) (due to avalanche photodiode (APD) buildup time), and receivers limited bandwidth. In this paper, an OCDM system employing code-shift keying (CSK) and overlapping pulse-position modulation (OPPM) signaling is proposed and theoretically investigated. By using CSK while maintaining same data rate, the chip duration can be increased to counteract the GVD effect in 2D OCDM systems. Moreover, by increasing the chip duration, the chip rate is decreased and the stringent requirement on receiver bandwidth is relaxed. In addition, using overlapping property in OPPM allows for further chip duration increase. We consider using correlation receivers with hard-limiters and APDs at the receiver side. The bit error probability (BEP) of the proposed system is derived taking into account the impacts of APD noise, thermal noise, GVD, ISI, and multiple-access interference (MAI). A performance comparison between OOK-, PPM-, OPPM-OCDM and the proposed system is carried out. Our results reveal that the use of CSK/OPPM-OCDM with data rate constraint allows the reduction of MAI, GVD and ISI effects with improved spectral efficiency.

DOI： 10.1109/TCOMM.2015.2467372

Language：English   Publishing type：Research paper (other academic)  

There has been a growing interest in the application of terahertz (THz) waves to broadband wireless communications. Particularly, use of THz waves at frequencies above 275 GHz is one of the big concerns among researchers, because these frequency bands have not yet been allocated for specific active services, and there is a possible opportunity to utilize extremely large bandwidths for ultra-broadband wireless communications. In this paper, we describe photonics-based approaches to realizing most practical and robust 300-GHz-band wireless links to meet and explore realworld applications at the earliest opportunity as a technology driver. We present enabling technologies for a real-time 50-Gbit/s transmission at over 20-m distance.

DOI： 10.1145/2800795.2800824

Language：Others  

DOI： 10.7567/jjap.53.08mb09, 10.7567/jjap.55.08rd04_references_DOI_Tdkkh8ulZvCb0YVD8qOC3zLOGvM

Language：English   Publishing type：Research paper (scientific journal)  

Wide-band high-efficiency optical-to-electrical conversion stimulus probe heads have been developed for testing large-signal responses of high-speed electronic devices, Two types of such probes were demonstrated using a 155-mu m 85-GHz-bandwidth waveguide p-i-n photodiode, The type-I probe employs a simple semirigid coaxial cable with a bias network for the electrical-signal transmission, resulting in a very low modal dispersion of <1.0 ps, The highest -3-dB bandwidth of 60 GHz was obtained for an output voltage of 250 mV(p-p), and was maintained beyond 50 GHz for output voltages of up to 400 mV(p-p). The type-II probe employs a broad-band InP high electron-mobility transistor distributed amplifier that boosts the electrical output signal amplitude over 1 Vp-p. The -3-dB bandwidth is 40 (35) GHz for output voltages up to 500 (1000) mV(p-p).

Language：English   Publishing type：Research paper (scientific journal)  

Ultrafast optical signal measureent using optoelectronic techniques

DOI： 10.1023/A:1006964727065

Language：English   Publishing type：Research paper (scientific journal)  

We developed a highly efficient, broad-band optoelectronic stimulus probe head employing a 1.55-μm waveguide p-i-n photodiode (WGPD). The novel multimode waveguide structure of the WGPD and optical lens-based rigid coupling assembly yielded a very high responsivity of 0.75 A/W. The OE probe has an effective 3-dB bandwidth of 50 GHz which is currently limited by the frequency dispersion of the CPW used in the probe. 2-mW, 64-Gb/s RZ optical pulse patterns were successfully able to be converted to 200 mVpp electrical pulses.

DOI： 10.1109/68.481134

Language：English   Publishing type：Research paper (scientific journal)  

A novel ultrafast optical pulse-pattern signal measurement technique using a fast photodetector and electro-optic sampling is demonstrated. The technique can measure 100Gbit/s optical pulse-pattern signals with high sensitivity and polarisation independence.

Language：English   Publishing type：Research paper (scientific journal)  

A mushroom-mesa structure is proposed to reduce the CR-time constant which originates from the waveguide photodiode structure. Experimental results at a 1.55-mum wavelength show that the multimode waveguide p-i-n photodiode with mushroom-mess structure has an electrical 3-dB bandwidth of more than 75 GHz in the frequency domain and an electrical 3-dB bandwidth of 110 GHz in the time domain. The external quantum efficiency is 50&#37; or 0.63 A/W, which leads to a record bandwidth-efficiency product of 55 GHz for long wavelength p-i-n photodetectors.

Language：English   Publishing type：Research paper (scientific journal)  

The response of ultrafast photodetectors at 1.55mum wavelength has been measured by electro-optic sampling using adiabatically compressed soliton pulses. 750fs-duration pulses with no wings were used to both pump and probe the waveguide pin photodiode. The measured bandwidth of the photodiode is more than 110 GHz, which is the highest value for a detector operating at 1.55 mum.

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2017.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名城大学   Country：Japan  

Event date： 2017.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名城大学   Country：Japan  

Event date： 2017.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名城大学   Country：Japan  

Event date： 2017.3

Language：English  

Venue：San Diego   Country：United States  

We achieved 600-GHz-wave power combination with directional gain by optically phase tuning of arrayed photomixers. Using this phase control technique for phase shift, we also demonstrated the beam steering within an angle of 35 degrees.

Event date： 2016.11

Language：Japanese  

Venue：東京 機械振興会館   Country：Japan  

Event date： 2016.10

Language：English  

Venue：UC Berkeley   Country：United States  

Event date： 2016.10

Language：English  

Venue：UC Berkeley   Country：United States  

Event date： 2016.10

Language：English  

Venue：UC Berkeley   Country：United States  

Event date： 2016.10

Language：English  

Venue：UC Berkeley   Country：United States  

Event date： 2016.10

Language：English  

Venue：UC Berkeley   Country：United States  

Event date： 2016.9

Language：English  

Venue：宮崎大学   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：宮崎大学   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：北海道大学   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：北海道大学   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：北海道大学   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：北海道大学   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：北海道大学   Country：Japan  

Event date： 2016.7

Language：English  

Venue：朱鷺メッセ   Country：Japan  

Event date： 2016.7

Language：English  

Venue：朱鷺メッセ   Country：Japan  

Event date： 2016.4

Language：Japanese  

Venue：リゾーピア熱海   Country：Japan  

Event date： 2016.4

Language：Japanese  

Venue：リゾーピア熱海   Country：Japan  

Event date： 2016.4

Language：Japanese  

Venue：リゾーピア熱海   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2016.2

Language：English   Presentation type：Oral presentation (general)  

Venue：San Fransisco   Country：United States  

Event date： 2016.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名城大学   Country：Japan  

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢しいのき迎賓館   Country：Japan  

Event date： 2015.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

The wavelength control system with the internal wavelength locker of the tunable lasers is configured so as to accelerate the wavelength detection speed. With this control system the wavelength is stabilized within 3.8 µs after wavelength switching which is even faster than that with the conventional control system.

Other Link： http://www.moc2015.com/

Event date： 2015.10

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：Fukuoka   Country：Japan  

The lasers for the WDM system with the flexible grid need to have highly accurate wavelength tuning and stability. Insteadof using optical filters, we propose the microwave photonics approach with photo-mixing technique and the laser current controlling. Experimental results show that the optical frequency is stabilized with the accuracy of 0.05GHz

Event date： 2015.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

We propose a power combiner of the synchronous terahertz waves for generating a higher coherent terahertz output power. The combiner consists of arrayed photomixers with bowtie-antennas. The experimental results show terahertz waves synchronized by the combiner results sum of the powers from photomixers and the directional gain of about 2 dB.

Other Link： http://www.moc2015.com/

Event date： 2015.6 - 2015.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Shanghai   Country：China  

We present the method of the high-speed wavelength switching of the tunable distributed amplification (TDA-) DFB laser by feedforward control. We designed and simulated the feedforward controller to accelerate the wavelength switching. A switching time of less than 100 ns with a frequency deviation of less than 1 GHz was achieved at switching toward 400-GHz spaced channels. The results indicate the feasibility of the TDA-DFB laser for future wavelength routing systems.

Other Link： http://www.oecc2015.sjtu.edu.cn/

Event date： 2015.6 - 2015.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Shanghai   Country：China  

We devised a phase stabilization technique at optoelectronic carrier generation applicable for the future THz wireless transmission. In this presentation we demonstrate at the first time that our technique using a Mach-Zehnder interferometric configuration is effective for the optoelectronic carrier for phase-shift keying signals as well as that for on-off keying signals by using an 1-Gbit/s binary-phase-shift keying transmission on a 12.5-GHz optoelectronic carrier.

Other Link： http://www.oecc2015.sjtu.edu.cn/

Event date： 2015.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

The lasers for the future WDM system such as the flexible grid need to have highly accurate wavelength tuning which corresponds to the optical frequency stability within ±0.1 GHz. Instead of the use of the conventional wavelength locker which detects the optical frequency with optical filters, we propose the microwave photonics approach in which the beat signals are generated by photo-mixing with reference lights and filtered by the microwave filter. In this method the frequency accuracy depends on the accuracy of the microwave filter. Experimental results show that the optical frequency is stabilized at the grid with the accuracy of ±0.1 GHz by using the microwave filter.

Event date： 2015.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka   Country：Japan  

We present a phase stabilization system of optoelectronic carrier generation for the future THz wireless transmission. The system has a Mach-Zehnder interferometric configuration and we transmitted 1-Gbit/s data at a 12.5-GHz carrier to confirm the effectiveness of the concept. We found that the noise floor which had been observed at the BER characteristics in our previous work disappeared with an optimized control and attained an error free performance.

Event date： 2015.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：立命館大学、草津市   Country：Japan  

UTC-PDアレイと光位相調整器によるコヒーレントテラヘルツ波発生デバイスの試作

Event date： 2015.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：立命館大学、草津市   Country：Japan  

モジュール内蔵波長ロッカを用いたフィードバック制御による TDA-DFBレーザの高速波長切替

Event date： 2015.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：立命館大学、草津市   Country：Japan  

マッハ・ツェンダ干渉計型二光波間位相安定化法によるPSK変調キャリアの位相雑音低減

Event date： 2015.3

Language：Japanese  

Venue：立命館大学、草津市   Country：Japan  

マッハ・ツェンダ干渉計型二光波間位相安定化法によるPSK変調キャリアの位相雑音低減

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Event date： 2014.11

Language：English  

Venue：Sendai   Country：Japan  

The lasers for the flexible grid need to have highly accurate wavelength tuning which corresponds to the optical frequency stability within ±0.1 GHz. Instead of the use of the conventional wavelength locker which detects the optical frequency with optical filters, we propose the microwave photonics approach in which the beat signals are generated by photo-mixing with reference lights and filtered by the microwave filter. In this method the frequency accuracy depends on the accuracy of the microwave filter. Experimental results show that the optical frequency is stabilized at the grid with the accuracy of ±0.1 GHz by using the band elimination filter which has the 3-dB bandwidth of 0.1 GHz.

Event date： 2014.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長崎市   Country：Japan  

Event date： 2014.10

Language：English  

Venue：Sapporo   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島大学   Country：Japan  

光バースト、光パケットシステムなどの波長ルーティングシステム発展のためには、より高速に波長切替可能な光源が必要となってくる。我々はこれまでに、制御層への電流変化により波長が変化するTDA(Tunable Distributed Amplifier) DFBレーザについて、フィードフォワード(FF)制御を導入することによってより、長波長ある波長安定状態から制御層電流を増加し短波長側(光周波数の増大方向制御層電流増加)への波長切替において応答高の速化を実現してきた[2]。本稿では短波長側への切替に加えて制御層電流を減少した長波長側(光周波数の増大方向) (制御層電流減少)への波長切替応答高速化を目指しについても、FF制御を導入することでそれぞれ波長切替時間35 ns、30 nsを実現したことと、切替応答について考察を行ったのでが高速化されたことについて報告する。

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島大学、徳島市   Country：Japan  

基準光との光差周波を用いた半導体レーザの高精度波長安定化

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島大学、徳島市   Country：Japan  

フィードフォワード/フィードバック切替型制御による波長可変レーザの高速波長安定化

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島大学、徳島市   Country：Japan  

TDA-DFBレーザの波長切替応答高速化の検討

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

フィードフォワード制御によるTDA-DFBレーザの波長切替高速化と光スイッチ動作

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島大学、徳島市   Country：Japan  

Event date： 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Jeju   Country：Korea, Republic of  

Aiming fast wavelength switching for the tunable distributed amplification (TDA-) DFB lasers, the transfer function is deduced from the transient response and then the feedforward controller is designed. Experimental results show that the wavelength can be accurately stabilized within 35 ns and 30 ns when the optical frequency changes from 192.8 THz to 193 THz and vice versa, respectively.

Event date： 2014.7

Language：English   Presentation type：Oral presentation (general)  

Venue：San Diego   Country：United States  

For fast wavelength switching of TDA-DFB lasers, the feedforward controller is designed. Experimental results show switching times of 35 ns and 30 ns when the optical frequency changes from 192.8 THz to 193.0 THz and vice versa

Event date： 2014.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Nice   Country：France  

We propose a Mach-Zehnder interferometric phase detection for low phase noise subterahertz(THz) carrier frequency generation. In this scheme, phase fluctuation between two optical signals can be detected as the interference between their optical sidebands. Experimental result shows that, by controlling the interference to be constant, the phase noise is successfully reduced, which indicates effectiveness of the proposed method.

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟大学   Country：Japan  

光バースト/パケットスイッチングの実現に向けて高速かつ高精度に波長切替可能な波長可変レーザ(TDA-DFBレーザ)の研究が行われている。我々はデジタル制御による複雑な系の安定化の実現可能性に注目し、フィードフォワード(FF)制御とフィードバック(FB)制御を組み合わせることでFBループ周期よりも高速に波長安定化できることを報告した。本稿では、波長可変レーザおよびその周辺回路を含むシステム全体の特性に基づいた最適なFB制御パラメータの設計とその検証を行ったので報告する。

Event date： 2014.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場   Country：Japan  

光通信の大容量化に向けてフレキシブルグリッドが注目されている。フレキシブルグリッドでは6.25GHz間隔で配置された光周波数を中心に帯域粒度12.5GHzの任意の幅のスロットを配置できるため高密度な波長多重伝送が可能となるが、グリッド間隔が6.25GHzと狭いためレーザーには±0.1GHz以内の精度での波長安定化が必要となる。本研究では、フレキシブルグリッドから半周期ずらした基準光群と被測定光の差周波を波長誤差検出信号として用い、高精度にレーザーの波長を安定化する方法を検討した。

Event date： 2014.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟大学   Country：Japan  

光バーストシステムや光パケットシステムには波長可変範囲が広く高速波長切替が可能な光源が求められる。その候補の一つとしてTDA (Tunable Distributed Amplification）-DFBレーザが開発されている。熱ドリフト補償器を集積したTDA-DFBレーザでは波長切替時の熱ドリフトを抑制し0.31 usまでの高速波長切替が実現できている。我々はフィードフォワード制御により駆動回路の立ち上がり時間を高速化し、波長切替時間150 nsを実現した。本稿ではさらに高速な回路を設計し、それに適合したフィードフォワード制御によって波長切替時間50 ns以下を実現したので報告する。

Event date： 2013.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

The wavelength stabilization based on the digitally controlled thermal-drift canceler is proposed and experimentally demonstrated. The tunable distributed amplification (TDA-) DFB laser controlled by this canceler reaches the targeted wavelength within a microsecond and keeps it stably.

Event date： 2013.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

The feedforward controller is designed and demonstrated to accelerate the wavelength switching for the tunable distributed (TDA) DFB lasers. The controller has an impulse overshoot waveform so as to induce prompt transition of short time phenomena. The controlled laser shows a wavelength switching time of 150 ns which shows effectiveness of the proposed technique.

Event date： 2013.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡工業大学   Country：Japan  

FF制御とFB制御を組み合わせた制御法を考案し、これをTDA-DFBレーザに適用した。実験により、熱ドリフトを補償することで320nsの高速な波長安定化を確認した。

Event date： 2013.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡工業大学   Country：Japan  

波長切替高速化を目的にTDA-DFBレーザの波長切替特性のモデル化とフィードフォワード制御の設計を行った。実際に制御系を作製し波長切替150 nsを実現した。

Event date： 2024.3

Language：Others  

Venue：Yokohama   Country：Japan  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2023.12

Language：Japanese  

Venue：仙台   Country：Japan  

Event date： 2023.12

Language：Japanese  

Venue：仙台   Country：Japan  

Event date： 2023.12

Language：Japanese  

Venue：東京   Country：Japan  

Event date： 2023.12

Language：Japanese  

Venue：東京   Country：Japan  

Event date： 2023.12

Language：Japanese  

Venue：東京   Country：Japan  

Event date： 2023.12

Language：Japanese  

Venue：東京   Country：Japan  

Event date： 2023.9

Language：Others  

Country：Other  

Event date： 2023.9

Language：Others  

Country：Other  

Event date： 2023.9

Language：Others  

Country：Other  

Event date： 2023.9

Language：Others  

Country：Other  

Event date： 2023.9

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Event date： 2023.9

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Event date： 2023.9

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Event date： 2023.9

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Event date： 2023.9

Language：Others  

Country：Other  

Event date： 2023.9

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Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Event date： 2023.9

Language：Others  

Country：Other  

Event date： 2023.9

Presentation type：Oral presentation (invited, special)  

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Event date： 2023.9

Language：Others  

Country：Other  

Event date： 2023.6

Language：Japanese  

Venue：渋川   Country：Japan  

Event date： 2023.6

Language：Japanese  

Venue：渋川   Country：Japan  

Event date： 2023.6

Language：Japanese  

Venue：渋川   Country：Japan  

Event date： 2023.6

Language：Japanese  

Venue：渋川   Country：Japan  

Event date： 2023.6

Language：Japanese  

Venue：渋川   Country：Japan  

Event date： 2022.9

Language：Others  

Country：Other  

Event date： 2022.9

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Event date： 2022.9

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Event date： 2022.9

Language：Others  

Country：Other  

Event date： 2022.9

Language：Others  

Country：Other  

Event date： 2022.9

Language：Others  

Country：Other  

Event date： 2022.9

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Event date： 2022.9

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Event date： 2022.9

Language：Others  

Country：Other  

Event date： 2022.9

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Event date： 2022.6

Language：Others  

Country：Other  

Event date： 2022.6

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Event date： 2022.6

Language：Others  

Country：Other  

Event date： 2022.6

Language：Others  

Country：Other  

Event date： 2022.6

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Event date： 2022.6

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Event date： 2022.3

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2022.3

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Italy  

Event date： 2022.3

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2022.3

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2022.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2022.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2022.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2022.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.8

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.12

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.12

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.12

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Japan  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島 (online)   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島 (online)   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島 (online)   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei (online)   Country：Taiwan, Province of China  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei (online)   Country：Taiwan, Province of China  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei (online)   Country：Taiwan, Province of China  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei (online)   Country：Taiwan, Province of China  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei (online)   Country：Taiwan, Province of China  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei (online)   Country：Taiwan, Province of China  

Event date： 2020.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡 (online)   Country：Japan  

Event date： 2020.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡 (online)   Country：Japan  

Event date： 2020.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡 (online)   Country：Japan  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：佐賀   Country：Japan  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：佐賀   Country：Japan  

Event date： 2020.9

Language：English   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2020.8

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco (online)  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Singapore   Country：Singapore  

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：富山市   Country：Japan  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：富山市   Country：Japan  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan   Country：Korea, Republic of  

Event date： 2019.9 - 2019.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan   Country：Korea, Republic of  

Event date： 2019.9 - 2019.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan   Country：Korea, Republic of  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan   Country：Korea, Republic of  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan   Country：Korea, Republic of  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan   Country：Korea, Republic of  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Dublin   Country：Korea, Republic of  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪府豊中市   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪府豊中市   Country：Japan  

Event date： 2019.9 - 2019.8

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2019.4 - 2020.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：群馬県   Country：Japan  

Event date： 2019.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：群馬県   Country：Japan  

Event date： 2019.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：群馬県   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Seoul   Country：Korea, Republic of  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.1

Language：English  

Country：Japan  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2018.11

Language：Japanese  

Venue：福岡   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei   Country：Taiwan, Province of China  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei   Country：Taiwan, Province of China  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Taipei   Country：Taiwan, Province of China  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Event date： 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：TOYAMA   Country：Japan  

Event date： 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：TOYAMA   Country：Japan  

Event date： 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：TOYAMA   Country：Japan  

Event date： 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：TOYAMA   Country：Japan  

Event date： 2018.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Jeju   Country：Korea, Republic of  

Event date： 2018.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：湯河原   Country：Japan  

Event date： 2018.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：湯河原   Country：Japan  

Event date： 2018.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：湯河原   Country：Japan  

Event date： 2017.11

Language：English  

Venue：Tokyo   Country：Japan  

For fast wavelength switching within the full available wavelength range of the tunable laser array, we investigated a wavelength stabilizing method after switching on the injection current to the laser's active layer. Experimental results demonstrated that our feedback controller dramatically reduced wavelength switching time from 800 μs to 2.0 μs.

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

We investigated the ability to tilt the terahertz wave beam at arrayed photomixers. Experimental demonstration showed that optical phase control enabled us to make a beam steering of a 300-GHz terahertz wave in a range of 25 degrees.

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

With the increasing popularity of LED lighting and a growing demand for bandwidth in wireless communication, the visible light communication (VLC) is one of the promising scheme for addressing the bottleneck in the emerging broadband access networks. For research in the field of VLC focused on solutions of contradiction between massive available bandwidth and limited modulation bandwidth of LED, the purpose of this paper is to design an VLC experiment platform with characteristics of high flexibility and rapid productization. As a result, this platform not only expand the concept of software defined communication, but has the advantage of simple structure and low cost.

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

We devise an optical-to-wireless media conversion method by XGM at the SOA aiming for a future use at a THz-wave access. We investigate the XGM characteristics and the performance of our proposed media conversion method. We configure the media-converted data transmission system and demonstrate an error free transmission.

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

We propose a measurement method of the optical pulse width at high-repetition frequencies. It consists of simple components such as a self-delayed interferometer and an optical power meter. We generated 50-GHz repetition pulses by superposing several lightwaves with 50-GHz spacing, and measured their pulse width with this measurement system.

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

We constructed the linear wavelength sweeping system with 2-μm-band distributed Bragg reflector laser for the second-harmonic-detection wavelength modulation spectroscopy. Using our devised linearity evaluation method with a germanium etalon filter, we experimentally confirmed that the nonlinearity of the laser can be efficiently compensated.

Event date： 2017.7 - 2017.8

Language：English