Effects of Spatially Nonuniform Gain on Lasing Modes in Weakly Scattering Random Systems

TL;DR

This paper investigates how nonuniform optical gain affects lasing modes in one-dimensional random systems, revealing complex mode interactions and the emergence or disappearance of modes due to gain distribution changes.

Contribution

It provides a numerical analysis of the impact of spatially nonuniform gain on lasing modes, including mode mixing and the creation or loss of modes, without considering gain saturation or mode competition.

Findings

Nonuniform gain causes significant changes in lasing modes.

Mode mixing increases as gain distribution becomes more nonuniform.

New lasing modes can appear or disappear with changing gain distribution.

Abstract

A study on the effects of optical gain nonuniformly distributed in one-dimensional random systems is presented. It is demonstrated numerically that even without gain saturation and mode competition, the spatial nonuniformity of gain can cause dramatic and complicated changes to lasing modes. Lasing modes are decomposed in terms of the quasi modes of the passive system to monitor the changes. As the gain distribution changes gradually from uniform to nonuniform, the amount of mode mixing increases. Furthermore, we investigate new lasing modes created by nonuniform gain distributions. We find that new lasing modes may disappear together with existing lasing modes, thereby causing fluctuations in the local density of lasing states.