Broadband phase noise measurement of single-frequency lasers by the short-fiber recirculating delayed self-heterodyne method

Characterization of single -frequency lasers (SFLs) requires a precise measurement of their phase noise. However, there exists a contradiction between the frequency range and laser phase noise measurement sensitivity in the delay selfheterodyne method. Achieving a broadband and highly sensitive phase noise measurement often requires overlapping the results obtained from different delay lengths. In this study, we present a precisely designed short -fiber recirculating delayed self -heterodyne (SF-RDSH) method that enables the broadband and highly sensitive laser phase noise measurement in a compact setup. By designing the length of the delay fiber based on a theoretical model, the RDSH technique with a shortest delay length of 200 m enables a highly sensitive laser phase noise measurement from 1 Hz to 1 MHz for the first time, to our knowledge. In the experiment, we demonstrate the broadband phase noise measurement of an SFL by analyzing the 1st and 10th beat notes. (c) 2024 Optica Publishing Group