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 approximately 25 μm showing highly varying reflectivity spectra, to demonstrate their single-longitudinal mode operation.
In this paper, we report a high efficiency, addressable 940 nm Vertical-Cavity Surface-Emitting Laser (VCSEL) array with a tight pitch of 10 m for a compact, low-power sensing light source. High electrical resistance of a small diameter semiconductor DBR is a major issue to obtain a high-power conversion efficiency in achieving a tight pitch VCSEL array. We have developed a highly efficient back side emitted VCSEL with intracavity contacted structure, mesa diameter of 7.5 μm, and optical aperture of 3.0 μm. The power conversion efficiency exceeded 30% from 0.5 mW to 3.5 mW in the wide power range. We also report Tx module using this highly efficient VCSEL with a tight pitch of 10 μm. The tight pitch addressable 2D VCSEL array required sophisticated process techniques because they have a small spacing of 2–3 μm between mesas. To improve productivity, we developed a new device structure decreasing the process difficulty between mesas and demonstrated 2D addressable VCSEL array arranged 64 by 64 matrix and 4096 emitters. In addition, we demonstrated addressable operation with assembled sample using Si interposer.
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.
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