Precise laser linewidth measurement by feature extraction with short-delay self-homodyne.

We propose a precision measurement method of laser linewidth based on short-delay self-homodyne, using the second peak-valley difference (SPVD) feature of the coherent power spectrum to fit laser linewidth. The SPVD model of the self-homodyne coherent envelope spectrum was established. One-to-one correspondence among the values of SPVD, the delay length, and the laser linewidth was determined theoretically and through simulations, while the reliability and stability of the method was verified experimentally. By comparing the detected results, it is found that the fitted laser linewidth obtained by the self-homodyne system is closer to its true value than that obtained by the self-heterodyne system. Hence, the simpler structure of the short-delay self-homodyne coherent envelope laser linewidth measurement method proposed is expected to substitute the previous laser linewidth measurement method, including complex short-delay self-heterodyne coherent envelope laser linewidth measurement method and traditional self-homodyne/heterodyne laser linewidth measurement method, to achieve more precise laser linewidth value.