Ultra-narrow-linewidth measurement utilizing dual-parameter acquisition through a partially coherent light interference.

Laser linewidths of the order of 100 Hz are challenging to measure with existing technology. We propose a simple, efficient method to measure ultra-narrow linewidths using dual-parameter acquisition based on partially coherent light interference. The linewidth is obtained using two parameters that are easily extracted from the power spectrum. This method reduces the influence of 1/f noise by utilizing a kilometer-order-length delay fiber and is independent of the fiber-length error for a general situation. Simulation results show that, for a length error less than 10%, the total linewidth measurement error is less than 0.3%. Experimental results confirm the feasibility and superior performance of this method.