Analysis of thermal instability for fiber backscatter phase and intensity.

In this Letter, we utilize the speckle model to measure the average random scattering rate of fiber backscatter and analyze its dependence on length, yielding a linear fitting coefficient of 0.23 ppm/m for a PM980-XP fiber. We incorporate the temperature coupling effect into the model and validate the model's accuracy by examining the distribution of the change rate of the backscattering rate relative to the temperature and the amplitude spectral density of the backscattered power.

Suppression of frequency-mixing effect for pm-level heterodyne interferometers based on "zero coupling" optical path length control.

Optical path length (OPL) noise resulting from stray light significantly constrains interferometry displacement measurements in the low-frequency band. This paper presents an analytical model considering the presence of stray light in heterodyne laser interferometers. Due to the cyclic nonlinear coupling effect, there will be some special OPLs of stray light, minimizing the frequency-mixing impact to zero.