Full Evaluation of Polarization Characteristics of Multifunctional Integrated Optic Chip With High Accuracy

The polarization characteristics of the multifunctional integrated optic chip (MFIOC) are fully evaluated with high accuracy by using optical coherence domain polarimetry based on white light interferometer. Two polarization maintaining (PM) fibers, serving as extended fibers, are spliced to the PM pigtails of the MFIOC with polarization axes aligned. By launching light at 45° to the birefringence axes of the lead-in extended PM fiber, the beams along the fast and slow axes of the birefringent waveguides interfere after a 45° polarization analyzer and an optical path correlator. The polarization extinction ratio (PER) and birefringence of the LiNbO
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Y-waveguide, the birefringence of the PM pigtails, and the crosstalks at the connection points between the Y-waveguide and the PM pigtails can be simultaneously obtained from the amplitudes and positions of the corresponding interference peaks. The characteristic peak of the Y-waveguide's PER is shifted out of the interference peak of the light source ripple by selecting proper length of the extended fibers. The extended fibers also brings in two additional cross-coupling points at the ends of the PM pigtails, which are used for calculating the birefringence of the PM pigtails. In addition, the alignment type between the PM pigtails and the birefringent Y-waveguide is identified according to the position of the characteristic peak of the Y-waveguide's PER. Theoretical model based on Jones matrix is built to describe the characteristic peaks of the MFIOC. Two MFIOCs with different alignment angle between the PM pigtails and the Y-waveguide are experimentally tested. Results show that the PER resolution of the proposed method can achieve nearly −90 dB and the dynamic range of the test system is about 90 dB.