Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：{mdpi} {ag}  

<jats:p>In this paper, we introduce how gallium nitride-based (GaN-based) VCSELs with curved mirrors have evolved. The discussion starts with reviewing the fundamentals of VCSELs and GaN-based materials and then introducing the curved-mirror cavity’s principle and history and the latest research where the structure is applied to GaN-based materials to form VCSELs. We prepared these parts so that readers understand how VCSELs with this cavity work and provide excellent characteristics such as efficiency, life, stabilized mode behavior, etc. Finally, we discussed the challenges and prospects of these devices by touching on their potential applications.</jats:p>

DOI： 10.3390/photonics10040470

Scopus

Authorship：Lead author,　Corresponding author   Publisher：Proceedings of SPIE the International Society for Optical Engineering  

We report the latest progress of gallium nitride-based vertical-cavity surface-emitting lasers (VCSELs) containing a curved mirror. Highly uniform and efficient devices were developed. The average threshold current was 0.64 mA with a standard deviation of 0.043 mA. The peak wall-plug efficiency and output power were 13.4 % and 7.6 mW at operating currents of 5.2 mA and 12.8 mA, respectively. We obtained green VCSELs with milliwatt-class outputs and a wall-plug efficiency of 3.7%. We also report the progress of VCSELs with a single-cavity filtering mirror and a cavity length of ~25 μm showing highly varying reflectivity spectra, to demonstrate their single-longitudinal mode operation.

DOI： 10.1117/12.2647047

Scopus

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} publishing  

<jats:title>Abstract</jats:title>
<jats:p>This study obtained highly uniform and efficient GaN-based vertical-cavity surface-emitting lasers (VCSELs) with curved mirror from a single wafer. The average threshold current (Ith) and the optical output power (Pmax) of 14 nominally identical chips measured up to 7 mA were 0.64 mA and 4.5 mW, respectively. The standard deviations of Ith and Pmax were 0.043 mA and 0.23 mW, respectively. Additionally, the best chip shows maximum values of wall plug efficiency and output power of 13.4% and 7.6 mW, respectively, at 5.2 mA and 12.8 mA operating currents.</jats:p>

DOI： 10.35848/1882-0786/acace8

Scopus

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer science and business media {LLC}  

<jats:title>Abstract</jats:title><jats:p>We report a self-induced spatially-coherent dot array consisting of fourteen units of vertical-cavity surface-emitting modes that exhibit spatially uniform spectra. A 47.5 µm total beam width and 0.5° narrow emission are achieved using an oblong cavity enclosed with a flat top mirror, cylindrically curved bottom mirror, and side facet. Notably, terminating the side of the cavity with a perpendicular facet enhances the horizontal propagation, which couples with the vertical resonance in each dot, similar to the case of master lasers in injection-locked lasers that delocalize the modes. Conventional semiconductor lasers, edge-emitting lasers, and vertical-cavity surface-emitting lasers have a Fabry–Pérot cavity; furthermore, emission and resonance are in identical directions, limiting the beam width to micrometers. Though the present structure has the same scheme of propagation, the right-angled facet synchronizes the modes and drastically expands the beam width.</jats:p>

DOI： 10.1038/s41598-022-26257-0

Scopus

Authorship：Corresponding author  

DOI： 10.1109/ISLC51662.2021.9615750

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：{IOP} publishing  

<jats:title>Abstract</jats:title>
<jats:p>A single cavity filtering mirror with a highly varying reflectivity spectrum was used to demonstrate a single longitudinal mode operation for a VCSEL with a ∼25 <jats:italic>μ</jats:italic>m cavity length. The 443.5 nm lasing peak had an SMSR of 42 dB at 9 mA, 70 kA cm<jats:sup>−2</jats:sup>. Increasing the number of DBR pairs between the VCSEL and filtering mirror cavity reduced the simulated optical standing wave in the mirror cavity by 57% and experimentally gave a 42% increase in the slope efficiency to achieve 2.56 mW at 7 mA from a device with a 4 <jats:italic>μ</jats:italic>m aperture with a single longitudinal mode.</jats:p>

DOI： 10.35848/1882-0786/ac7697

Scopus

Authorship：Lead author,　Last author,　Corresponding author  

Publisher：Conference Digest IEEE International Semiconductor Laser Conference  

A single cavity filtering mirror was used to demonstrate single longitudinal mode operation for a VCSEL with a ∼25 μm cavity length. The 443.5 nm lasing peak had an SMSR of 42 dB at 9 mA, 70kA/cm2.

DOI： 10.23919/ISLC52947.2022.9943331

Scopus

Publisher：Proceedings of SPIE the International Society for Optical Engineering  

Many applications benefit from single mode operation of vertical-cavity surface-emitting lasers (VCSELs) due to the need for a consistent beam profile and wavelength. While long cavity VCSELs have demonstrated good results in recent years, with examples of sub 1mA thresholds for devices with blue and green emission, the mode has not been fully controlled. Traditionally, VCSELs, with their short cavities, inherently maintain single longitudinal mode operation while struggling with multi-lateral modes. However, the use of a long cavity device with a curved mirror provides the opposite challenges for mode control, as the lateral mode can be controlled with the lens curvature, but the long cavity length allows for multiple longitudinal modes. In this paper, we will present the use of a filtering mirror with a highly varying reflectivity spectrum for obtaining single longitudinal mode operation up to 2mW and 50 kA/cm². The filtering mirror reflectivity leads to significant mirror loss for adjacent longitudinal modes. Thus, by engineering the beam profile with the lens and filtering the longitudinal modes with the mirror structure, we are able to control the output shape, divergence angle, and wavelength stability of the device. This mode control, along with the low thresholds and lifetimes greater than 2000 hours, shows the potential of the long cavity structure for a variety of applications.

DOI： 10.1117/12.2606537

Scopus

Publisher：Proceedings of the International Display Workshops  

Highly efficient and uniform GaN-VCSELs with curved mirrors were obtained. The peak WPE and output power were 13.4% and 7.6 mW. This talk also reviews the latest progress of the green VCSELs.

Scopus

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：IEEE Photonics Journal  

We report a narrow divergence angle in a blue gallium-nitride-based visible vertical-cavity surface-emitting laser (GaN-VCSEL) with a curved mirror. This device exhibited continuous-wave operation at a wavelength of 447.9 nm. The full-width at half-maximum divergence angle of the 8 μm-aperture VCSEL was 3.9° when the device was operated at a current of 1.2 × Ith, where Ith is the threshold current. In this type of cavity, the radius of curvature (ROC) of the curved mirror determines the near-field pattern (NPF) and far-field pattern (FFP). The authors fabricated devices having ROC up to 988 μm, which is more than 10 times greater than the ROC of the mirror used in the previously reported structures, allowing this narrow emission. The I-L characteristics showed that the Ith value increased with increasing ROC. The present study investigates the mechanism behind this tendency in detail.

DOI： 10.1109/JPHOT.2022.3165665

Scopus

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