SNR Improvement of Optical Frequency Domain Polarimetry Against Laser Frequency Sweep Nonlinearity

A high-precision measurement of distributed polarization crosstalk (DPC) is necessary for developing the device with an ultrahigh polarization extinction ratio of even more than 80 dB. Optical frequency domain polarimetry (OFDP) is a novel DPC measurement method with a potential ultra-wide dynamic range. The degradation of dynamic range caused by interference phase error is a common issue in optical frequency domain measurement techniques. In this work, we enhanced the dynamic range by solving the phase error problem induced by the laser frequency sweep nonlinearity to improve the measurement precision of weak polarization crosstalk. The aliasing issue caused by the fluctuation of the frequency sweep rate is the primary reason for the limited dynamic range. We proposed a modified dynamic range limit model of OFDP considering the aliasing issue. The experimental results agree with the inflection points predicted by the modified dynamic range limit model. Under the guidance of the model, we achieved a dynamic range of more than 115 dB with different optical path differences of the interferometer and various sweep rates of the laser. Compared to the DPC measurement method with a dynamic range of 100 dB, the measurement repeatability is improved from 7.0 dB to <1.0 dB for polarization crosstalk less than −95 dB.