Research On The Key Technology Of Optical Coherence Domain Polarization Systerm

Polarization Maintaining Fiber (PMF) can maintain the polarization state of the lighttransmitted in it, and has better compatibility with single mode fiber, so it is widely used inoptical fiber sensing, optical communication and many other fields. When PMF is affected bytemperature, pressure, torsion, the electromagnetic field, internal strain and other factors, thepolarization coupling will happen in it, which affects its polarization maintaining, thus affectsthe performance of their application systems.There are many methods to detecting the polarization coupling of the PMF，manyresearch institutes and companies in the domestic and foreign have also studied in this area,and some of them have already produced some instruments. Currently, the main contents ofthe study is to improve the measurable length of PMF and increase the dynamic range of thetesting, to reduce the spatial resolution and shorten the measurement time.Based on white light interferometry, we built an all-fiber Optical Coherence DomainPolarization (OCDP) system, and have studied a number of key technologies in this system,and looked for the solutions to improve detection accuracy of the system through thecontinuous theoretical and experimental study. The details are as follows:1. Studyed the way of noise suppression in OCDP systems from theory and methods.We have analysed the generation mechanism of noise which affecting the system performance,such as Rayleigh scattering noise, shot noise, optical coherent noise and so on. We also haveanalysed the impact of interference caused by the choice of light source. Here we proposed amethod that using differential detection method to reduce the light RIN noise, the systemnoise floor is-84dB after these works.2. Proposed the method of expanding the optical path scanning in OCDP. Through thepolarization maintaining fiber optical switch and motorized positioning system, we achieved awide range of scan. Here the optical path scanning range we have achieved is800mm.3. Proposed a method to compensate the birefringence dispersion of the PMF. First weanalyzed the influence of the dispersion in OCDP, and then, according to the principle ofbirefringence dispersion, we proposed a method which is changing the scanning direction toreduce the effect of birefringence dispersion when scanning long distance PMF. 4. Verified that temperature could affect the birefringence of polarization maintainingfiber. After testing the position of coupling point in different temperature based on OCDP, wefound that the position decreased when temperature increased, Therefore, it proved that thebirefringence of the PMF increases with decreasing temperature.