Optimization of phase noise testing algorithm for extremely narrow linewidth

Phase noise refers to the random phase fluctuation in the laser system. Calculating laser phase noise requires large datasets, leading to inefficiency. For optimizing, we apply I/Q demodulation and multi-threading with window functions, discrete Fourier transforms and cross power spectral density. Additionally, the cross power spectral density enable to reduce the impact of measurement system. This method converts the real signal into a complex one via the Hilbert transform, removes the carrier with linear fitting, and calculates phase noise through cross power spectral density.