Accurate evaluation of self-heterodyne laser linewidth measurements using Wiener filters

TL;DR

This paper presents an improved Wiener filter-based post-processing method for self-heterodyne laser linewidth measurements, effectively reducing artifacts and accurately estimating intrinsic linewidth even with high detector noise.

Contribution

It introduces a Wiener filter approach that eliminates reconstruction artifacts and offers a new method for intrinsic linewidth estimation in noisy measurement conditions.

Findings

Artifact-free FN-PSD reconstruction using Wiener filters

Accurate intrinsic linewidth estimation under high noise

Effective in simulated laser noise scenarios

Abstract

Self-heterodyne beat note measurements are widely used for the experimental characterization of the frequency noise power spectral density (FN-PSD) and the spectral linewidth of lasers. The measured data, however, must be corrected for the transfer function of the experimental setup in a post-processing routine. The standard approach disregards the detector noise and thereby induces reconstruction artifacts, i.e., spurious spikes, in the reconstructed FN-PSD. We introduce an improved post-processing routine based on a parametric Wiener filter that is free from reconstruction artifacts, provided a good estimate of the signal-to-noise ratio is supplied. Building on this potentially exact reconstruction, we develop a new method for intrinsic laser linewidth estimation that is aimed at deliberate suppression of unphysical reconstruction artifacts. Our method yields excellent results even in the presence of strong detector noise, where the intrinsic linewidth plateau is not even visible using the standard method. The approach is demonstrated for simulated time series from a stochastic laser model including 1/f-type noise.