Polarization Maintaining Fiber Coupler Extinction Ratio Improvement In Technology Research

Along with the development of coherence optical fiber communication, the required performance level of polarization-maintaining-fiber (PMF) connector is higher and higher. There are some technical difficulties for PMF connector relatively with common single-mode-fiber (SMF) one. Polarization extinction ratio (PER) is an important parameter used to describe the ability of an optical fiber or other component to maintain an incident polarization state. Currently, in the influence of inevitable connecting stresses induced by design and manufacture, PER is lower than 30 dB mostly and the first pass-yield of 25 dB standard is quite low, just around 60 %～70 %. PER is researched roundly and systematically in this dissertation through one perpetual PMF connector used for DSDBR tunable laser. Series of improvements are described, PER is higher than 30 dB for most connectors, and the first-pass yields reach 85 %. This dissertation mainly described three items. Firstly, two measurements of PER are compared through experiments. Secondly, the improvements of encapsulation technology and internal structure design are set forth. Finally, environment measurement are designed and analyzed. The research work and experimental results in this dissertation are listed as follow:1) The research of two PER measurementsBased on different representations of monochromatic plane wave's polarization state, there are two methods for PER measurement, one is rotating polarizer method; the other is Poincare sphere method. The former is direct method with narrow testing range, and the detected light-power varies sinusoidal. The latter is indirect, and can be realized using adjustable temperature, pressure or incident light-wavelength with consistent results. Experiments show that the latter is more stable for fluctuation of both incident light-wavelength and power.2) Modifications of PMF connector's encapsulation technology to improve PERBased on the influence of photo-elastic effect on optical fiber birefringence, PER can be improved through modifications of encapsulation technology which reduce the stress of fiber. Two items are discussed. Firstly, the difference of influence on PER for two material, Crown-glass BK7 and Zirconia-ceramics, are compared through finite element model (FEM) and experiments. Secondly, more reasonable and effective solidifying program of epoxy adhesive is set up. Experiments demonstrate 15 % improvement of PER first-pass yield using the technology mentioned above.3) The innovative internal structure design to improve PERAlso based on photo-elastic effect principle, PER can be improved through internal structure design including larger radius of ceramic hole, shorter length of hole and addition at ceramic bottom. Experiments are designed and the results indicate an evident improvement and the PER are higher than 30 dB for most devices.4) All of improvements are verified by certain environment measurementsdefined by international document GR326-CORE which especial for optical connector. Measurements'results indicate improved PMF connector can suffer adverse circumstances, but show PER isn't stable enough.There are some shining points in this dissertation which no related reports found until now. Firstly, optimized curing program at 45℃or 55℃can improve PER meanwhile save curing time. Secondly, lengthen ferrule hole and add its transition part at bottom are beyond current standard structure which can improve PER.