Demonstration of Parametric Instability suppression through optical feedback

TL;DR

This paper demonstrates a method to suppress parametric instability in a long optical cavity by using optical feedback with mode matching and phase control, combining theoretical analysis and experimental validation.

Contribution

It introduces a novel optical feedback technique that actively suppresses high order optical modes to prevent parametric instability in large-scale cavities.

Findings

Successful suppression of parametric instability with a gain of approximately 2.5

Effective mode matching and phase control achieved in the feedback loop

Experimental results confirm theoretical predictions of instability suppression

Abstract

We demonstrate the suppression of parametric instability using through optical actuation in an electro-optical feedback loop, stabilising the high order optical mode content in an 80 metre long Fabry-Perot cavity. The loop suppression of the high order mode is achieved by injecting a high order mode with the same frequency and opposite phase. Frequency matching is achieved by measuring the beat note signal between the fundamental and high order mode in transmission of the cavity and applying that signal to an electro-optical modulator to create the required frequency sideband. Spatial mode matching of the sideband to the high order mode is accomplished through the inherent mode overlap between the input injected beam and the high order mode of the cavity. The paper presents the theoretical analysis and experimental demonstration of parametric instability suppression, for an instability which would normally ring up with a parametric gain of approximately 2.5.