Minimum reflection channel in amplifying random media

TL;DR

This study numerically investigates how coherent amplification affects the minimum reflection channel in disordered media, revealing that gain can enhance destructive interference to further reduce light reflection.

Contribution

It demonstrates that optical gain can be tuned to optimize destructive interference in the minimum reflection channel, leading to reduced reflectance in random media.

Findings

Minimum reflection can be further reduced by optical gain.

Gain can slow or reverse the increase in reflectance.

Interference effects dominate over amplitude growth in certain conditions.

Abstract

We present a numerical study on the minimum reflection channel in a disordered waveguide and its modification by coherent amplification of light. The minimum reflection channel is formed by destructive interference of quasi-normal modes at the front surface of the random medium. While the lowest reflection eigenvalue increases with gain in most random realizations, the minimum reflection channel can adjust its modal composition to enhance the destructive interference and slow down the growth of reflectance with gain. Some of the random realizations display a further reduction of the minimum reflectance by adding optical gain. The differential amplification of the modes can make their destructive interference so effective that it dominates over the amplitude growth of the modes, causing the reflectance to drop with gain. Therefore, the interplay between interference and amplification makes it possible to further minimize light reflection from a strong scattering medium by introducing optical gain.