2. College of Science, Harbin Engineering University, Harbin, Heilongjiang 150001, China;
3. College of Information and Communications Engineering, Harbin Engineering University, Harbin, Heilongjiang 150001, China;
4. College of Electronic Engineering and Automation, Guilin University of Electronic Technology, Guilin, Guangxi 541004, China
Overview: The polarization crosstalk, also termed polarization mode coupling, of a fiber optic polarization component and device refers to the optical power coupling that occurs at a disturbance point between the two orthogonal polarized modes propagating in it. The distributed polarization crosstalk along with the light propagation direction is directly responsible for the optical polarization properties, for example, the polarization, elliptical polarization, and depolarization properties. It also indirectly reflects the manufacturing technique and the state of the ambient environment, for example, the stress and strain at the joint and fixed position, as well as the temperature. Thus, it is the comprehensive embodiment of the intrinsic performance of the fiber optic polarization component or device and the influence of environment. It is expected to be a general characteristic parameter for online testing, diagnosis, and evaluation of the performance of the fiber optic polarization component and device.
The optimal measurement method for distributed polarization crosstalk till now is the optical coherence domain polarimetry (OCDP). It is based on the white light interferometry and accurately measures the position and amplitude of the distributed polarization crosstalk using a scanning white light interferometer to realize interference between different polarized modes. It has the merits of ultra-high sensitivity, ultra-wide dynamic range, and ultra-long measurable length. Over the past decade, our research group developed suppression technique for interferometric beat noise to enhance the dynamic range beyond 100 dB, developed suppression technique for insertion loss fluctuation of optical delay line to reduce the measurement resolution below 0.2 dB, developed range extension technique of the optical delay line to enlarge the measurement length over 5 km, and so on.
This review takes the polarization maintaining fiber coil and multifunctional integrated optical modulator as examples of distributed polarization crosstalk measurement and application. Firstly, the measurement principle of distributed polarization crosstalk based on the OCDP is introduced. Secondly, the measurement error sources and corresponding suppression methods are reviewed. Thirdly, the accurate measurement results of the fiber optic polarization component and device at different temperature are demonstrated. In the end, it outlooks the development of distributed polarization crosstalk measurement considering the complicated and changeable operation environment of the fiber optic polarization component and device, as well as the semi-closed and closed light path measurement.