Short term frequency stability measurement for narrow linewidth laser by time domain self-heterodyne method

Abstract

Based on the time delay self-heterodyne method to measure the laser linewidth, the short-term linewidth variation of a narrow linewidth laser is experimentally studied and analyzed, and then a time domain self-heterodyne method is proposed to measure the short-term frequency stability of narrow linewidth laser. The Rayleigh backscattering frequency of a pulsed light propagating in an optical fiber with length of 100km is used as the local oscillation frequency with relatively long time duration to measure the frequency variation of the narrow linewidth laser. By heterodyne between the laser frequency and the local oscillation frequency, the variation of the laser frequency is presented in the heterodyne radio frequency (IF). Then the time domain data of the heterodyne IF are extracted by an oscilloscope and through short time Fourier transform the frequency from the laser in different time segments is obtained. Experimental results demonstrate that for narrow linewidth laser its frequency in short-term is randomly fluctuating with a range less than triple of the laser linewidth. The measurement and evaluation of laser short-term frequency stability benefits the application of narrow linewidth lasers in distributed optical fiber sensing area.