Nonlinear modification of the laser noise power spectrum induced by a frequency-shifted optical feedback

TL;DR

This paper investigates how frequency-shifted optical feedback nonlinearly affects laser noise spectra and relaxation oscillation frequencies, combining theoretical, numerical, and experimental approaches to reveal the underlying dynamics.

Contribution

It introduces a comprehensive analysis of the nonlinear coupling between stationary and transient laser dynamics under frequency-shifted feedback, supported by theoretical, numerical, and experimental validation.

Findings

Relaxation frequency depends on feedback strength.

Noise power spectrum reveals the transfer modulation function.

Theoretical predictions align well with experimental data.

Abstract

In this article, we study the non-linear coupling between the stationary (i.e. the beating modulation signal) and transient (i.e. the laser quantum noise) dynamics of a laser subjected to frequency shifted optical feedback. We show how the noise power spectrum and more specifically the relaxation oscillation frequency of the laser are modified under different optical feedback condition. Specifically we study the influence of (i) the amount of light returning to the laser cavity and (ii) the initial detuning between the frequency shift and intrinsic relaxation frequency. The present work shows how the relaxation frequency is related to the strength of the beating signal and the shape of the noise power spectrum gives an image of the Transfer Modulation Function (i.e. of the amplification gain) of the nonlinear-laser dynamics.The theoretical predictions, confirmed by numerical resolutions, are in good agreements with the experimental data.