Demonstration of critical coupling in an active III-nitride microdisk photonic circuit on silicon

TL;DR

This paper demonstrates critical optical coupling in active III-nitride microdisk photonic circuits on silicon, highlighting efficient energy transfer, lasing behavior, and the effects of fabrication on device performance for integrated blue-light sources.

Contribution

It presents the first detailed analysis of critical coupling and phase matching in active III-nitride microdisk circuits on silicon, with insights into lasing thresholds and fabrication impacts.

Findings

Critical coupling achieved at short gap sizes and thin waveguides.

Whispering gallery mode lasing demonstrated across various parameters.

Output sensitivity strongly depends on coupling and processing effects.

Abstract

On-chip microlaser sources in the blue constitute an important building block for complex integrated photonic circuits on silicon. We have developed photonic circuits operating in the blue spectral range based on microdisks and bus waveguides in III-nitride on silicon. We report on the interplay between microdisk-waveguide coupling and its optical properties. We observe critical coupling and phase matching, i.e. the most efficient energy transfer scheme, for very short gap sizes and thin waveguides (g = 45 nm and w = 170 nm) in the spontaneous emission regime. Whispering gallery mode lasing is demonstrated for a wide range of parameters with a strong dependence of the threshold on the loaded quality factor. We show the dependence and high sensitivity of the output signal on the coupling. Lastly, we observe the impact of processing on the tuning of mode resonances due to the very short coupling distances. Such small footprint on-chip integrated microlasers providing maximum energy transfer into a photonic circuit have important potential applications for visible-light communication and lab-on-chip bio-sensors.