Enhancement of slope efficiency of a dually modulated photonic-crystal surface-emitting laser over a wide range of emission angles by introducing a backside reflector

Abstract

Dually modulated photonic-crystal surface-emitting lasers (DM-PCSELs) are a new type of semiconductor laser that enable on-chip, mechanical-free, high-power, high-beam-quality 2D beam scanning over a wide field of view. These lasers are attracting attention for application in light detection and ranging, and the improvement of their slope efficiency is desired for this application. Thus far, the highest experimentally demonstrated slope efficiency is approximately 0.4 W/A at wavelengths of around 940 nm, which was limited by the fact that roughly half of the laser light was emitted toward and absorbed by the backside electrode. In this work, in order to improve the slope efficiency of DM-PCSELs, we utilize the light emitted toward the backside of the device by introducing a distributed Bragg reflector (DBR) as a backside reflector. In consideration of this laser’s ability to emit beams over a wide field of view, we design laser structures that facilitate a commensurate enhancement of efficiency at various emission angles. Next, we discuss the effect of the DBR on the confinement of transverse modes in thickness direction as well as the suppression of higher-order transverse modes. Then, we analyze the emission characteristics of a DM-PCSEL with a DBR and calculate that the theoretical slope efficiency is enhanced to 0.7–0.8 W/A, which is twice that of the device without a DBR, over a wide range of emission angles from 0° to 30°. We then fabricate the devices and experimentally demonstrate the emission of a single-lobed beam with a high slope efficiency of 0.7–0.8 W/A.