White light interferometry for pigtail polarization crosstalk of Ti-diffused LiNbO₃ integrated optic phase modulator

A new test method for the pigtail polarization crosstalk of the Ti-diffused LiNbO₃ integrated optic phase modulator (Ti:LiNbO₃ IOPM) is proposed based on the white-light interferometry. The white light interference intensity as a function of the alignment angle between the integrated optic chip and the polarization-maintaining pigtail and the azimuth of the polarizer is theoretically analyzed. It is shown by the digital simulation that the pigtail polarization crosstalk of the IOPM can be obtained by the peaks of the interference envelope associated with the polarization coupling points of the IOPM. The pigtail polarization crosstalk of the Ti:LiNbO₃ IOPM is tested by utilizing the white light interferometry, and the apparent interference peaks are exhibited at the polarization coupling points. The input and output pigtail polarization crosstalk are -34.5 dB and -23.3 dB respectively at room temperature, and decrease as the temperature rises from -40°C to 60°C. The feasibility of the white light interferometry is verified by the experimental results.