Linewidth study of the frequency-modulated laser based on the delayed self-heterodyne scheme

We investigate the linewidth of the frequency-modulated laser (FML) by using the delayed self-heterodyne (DSH) method. We deduce the expression of the linewidth theoretically and arrive at the conclusion that the linewidth of the FML measured by DSH method is the convolution of the spectrum of the output of the heterodyne interferometer with an ideal monofrequency laser under modulation and the natural linewidth of the laser. Experiments are carried out and the testing linewidths are in agreement with the theoretical results. The properties of the linewidth of the FML are analyzed based on the conclusion obtained and its guidance for application is discussed.

► We study the linewidth of the frequency-modulated laser based on the DSH method.
► A mathematical expression is deduced to describe the linewidth of the FML.
► The work lay a foundation for the linewidth analysis and control.
► We point out potential use of the FML in reduction of interferometric noise.
► We give advices on the frequency deviation test based on the linewidth analysis.