Abstract: As the linewidth of the laser under test approaches or even breaks through 1 kHz, the length of the delay fiber in the delay self-heterodyne measurement method needs to be lengthened properly, so that the measurement results are affected by 1/f noise. In this paper, the influences of 1/f noise on the measurement accuracy of laser linewidth in the order of kHz and below using the delayed self-heterodyne method based on a short delay fiber, and the corresponding suppression technique, are investigated. Our research results show that 1/f noise has a greater influence on the central part of the delay self-heterodyne power spectrum measured by the delay self-heterodyne method using short delay fiber, so that by selecting the difference of the coherent envelope peak and valley far from the center of the self-heterodyne power spectrum to retrieve the laser linewidth, the influence of 1/f noise can be effectively avoided, thereby obtaining a more accurate linewidth of the measured laser. Furthermore, by measuring the fiber laser linewidths in the order of kHz and below, and comparing them with the integral linewidths obtained from the β-separation line based on the frequency noise spectrum, the effectiveness of the 1/f noise compensation method is verified.

Key words: fiber laser, linewidth measurement, delayed self-heterodyne, 1/f noise