Inversed Vernier effect based single-mode laser emission in coupled microdisks

TL;DR

This paper investigates the mechanism behind single-mode laser emission in coupled microdisks, confirming the role of internal coupling and the inversed Vernier effect through experimental and theoretical analysis.

Contribution

It provides the first experimental confirmation of the inversed Vernier effect as the mechanism for single-mode operation in coupled microdisks.

Findings

Mode numbers are nearly single-mode over a wide power range.

Laser spectra show the first peak is mainly from one disk.

Internal coupling dominates the observed single-mode behavior.

Abstract

Recently, on-chip single-mode laser emission has attracted considerable research attention due to its wide applications. While most of single-mode lasers in coupled microdisks or microrings have been qualitatively explained by either Vernier effect or inversed Vernier effect, none of them have been experimentally confirmed. Here, we studied the mechanism for single-mode operation in coupled microdisks. We found that the mode numbers had been significantly reduced to nearly single-mode within a large pumping power range from threshold to gain saturation. The detail laser spectra showed that the largest gain and the first lasing peak were mainly generated by one disk and the laser intensity was proportional to the frequency detuning. The corresponding theoretical analysis showed that the experimental observations were dominated by internal coupling within one cavity, which was similar to the recently explored inversed Vernier effect in two coupled microrings. We believe our finding will be important for understanding the previous experimental findings and the development of on-chip single-mode laser.