Linewidth characteristics of narrow linewidth lasers with high-sweeping linearity

As a continuously tunable laser with high-sweeping linearity, narrow linewidth lasers have excellent coherence properties that make them indispensable for the improvement of the spatial resolution of optical frequency domain reflection (OFDR) technology. In order to investigate the linewidth characteristics of narrow linewidth lasers with high-sweep linearity, this paper reviews the measurement and calculation methods of linewidth. The theoretical analysis of the linewidth is also carried out, and a delayed self-heterodyne measurement system based on the non-equilibrium Mach-Zehnder (M-Z) interferometer structure is built. The experimental results show that the steady-state linewidth of the laser is 178 kHz, and the fluctuation range of the dynamic linewidth is 150-200 kHz. In order to balance the speed and accuracy of linewidth measurement, the linewidth values at receiver bandwidth of 10 kHz, 30 kHz and 100 kHz are analyzed. Analyze the linewidth spreading generated by the laser during continuous frequency tuning, compensate the deviation between the real value of linewidth and the measured value by controlling the step amount of the laser wavelength tuning to keep the output power stable and reduce the measurement error caused by the linewidth spreading. This study not only improves the knowledge of linewidth characteristics, but also have important practical significance for OFDR research.