Linewidth measurement of Littrow structure semiconductor laser with improved methods

In this Letter, the frequency noise spectrum is analyzed in the experiment of the laser linewidth measurement. The power spectrum of three most widely used laser linewidth measurement methods, i.e., the heterodyne measurement, the self-homodyne measurement and the self-heterodyne measurement, are restudied both theoretically and experimentally. A scheme adopting an avalanche photodetector (APD) in the delayed self-heterodyne (DSHT) method is proposed, and an indirect determined result is given.