Line-width measurement of DFB laser based on frequency shift delay self-heterodyning method

In order to measure the line-width of distributed feedback(DFB) diode single mode semiconductor laser, novel optical fiber self-heterodyne measurement scheme based on Mach-Zehnder interference structure was adopted and a set of all fiber time-delay self-heterodyne measurement system was designed. After theoretical analysis, narrow band line-width measurement system with time-delay fiber length of 900m, 3000m and 6000m was set up. A DFB single mode laser source with center wavelength of 1550nm and nominal line-width of 800kHz was tested. The measured line-width values of laser were 951.566kHz, 832.471kHz and 802.221kHz respectively. The designed scheme is verified by simulation. The results show that, compared with the simulation results, narrowband line-width measurement system with the length of 6000m is optimal, and its error is within 3%, which proves the rationality and accuracy of self-heterodyne interference principle. All fiber frequency shift delay self-heterodyne method has advantages and practical value for measuring the line-width of DFB lasers.