Application of wavelet denoising in 3×3 phase demodulation linewidth measurement system

Abstract

Narrow linewidth lasers have important applications in optical communication and sensing. To accurately measure the linewidth, we built a laser linewidth measurement system based on 3×3 coupler. It uses the demodulation algorithm of Differential Cross Multiplication to get the phase noise, and then obtains the linewidth value according to the β-separation line method. At the same time, we introduced wavelet denoising in the signal processing in order to reduce the influence of low frequency noise. Two wavelet bases, db4 and sym11, which were more effective for this system were identified through simulation, and experiments were conducted using a 2 μm band laser. The results prove that the frequency noise power spectral density and linewidth values are reduced after using wavelet denoising.