Wiener-Filter Enhanced Estimation of the Intrinsic Laser Linewidth from Delayed Self-Heterodyne Beat Note Measurements

Narrow-linewidth lasers exhibiting low phase noise are core elements of coherent optical communication systems, gravitational wave interferometers and emerging quantum technologies (e.g., optical atomic clocks, matter-wave interferometers, ion-trap quantum-computers etc.). For many of these applications, the performance depends critically on the laser's intrinsic (Lorentzian) linewidth [1], which is typically obscured by additional
$1/f\text{-like}$
technical noise. Because of this so-called flicker noise, the laser linewidth alone is not a well-defined quantity and needs to be specified for a given measurement time. For a detailed characterization of the frequency noise exhibited by the laser, the measurement of the frequency noise power spectral density (FN-PSD) is required.