| As a typical application of white light interferometer,optical coherence domain polarization measurement system has become an important tool for evaluation of distributed polarization mode coupling.Optical coherence domain polarization measurement system shows outstanding advantages,such as high detection sensitivity,wide dynamic range,and long distance measuring devices.It has been widely used in polarization maintaining fiber(PMF)manufacturing,integrated optical devices testing,and distributed sensing.Especially,the polarization evaluation of key devices in gyro and their manufacture will be greatly developed with the help of optical coherence domain polarization test technique to keep up with the rapid development of fiber optic gyro.Some researches on the white light interferometer and optical fiber smart structure have been studied in our previous work.Here,we continue to intensively research into the polarization mode coupling theory analysis,system performance improvement,and typical polarization device applications.Firstly,we proposed an optical path tracing method to simplify the theoretical analysis of polarization transmission behavior in birefringent devices.Secondly,we enhanced the dynamic range of measurement system based on analyzing the noise of white light interferometer.Thirdly,we in-depth studied the PMF with multiple coupling points utilizing the proposed optical path tracing method.Then,we proposed a differential delay line structure to suppress the mechanical fluctuation and extend the scanning optical path.Additionally,some practical applications,such as the two-channel testing method for Y-junction,have been done with the above theoretical analysis.Some details are listed as follows:(1)An optical path tracing method was proposed to simplify the analysis of polarization transmission behavior in birefringent devices.We analyzed the phenomenon of polarization coupling based on the graphical method and enumeration method.(2)We firstly proposed a method to improve dynamic range of polarization mode coupling measurement system based on white light interferometer beyond 100 dB.We analyzed the inherent noises in detail and overcame the limitation of interference beat noise.This method can dramatically improve the dynamic range through eliminating interference beat noise and enhancing the interference signal intensity simultaneously.(3)We proposed a strategy to readily identify high-order interference introduced by polarization mode couplings of multiple perturbations in PMF.We enhanced the optical path tracking method and derived the general formulas of high-order interference.It isdemonstrated the suppression and enhancement conditions for the high-order interferences by altering the spliced angle between PMF under test and polarizers' pigtails.All the characteristic interferograms including realistic coupling points and high-order interferences could be distinguished through just four measurements.(4)We firstly proposed a differential scanning delay line to extend scanning length and improve measurement accuracy of optical coherence domain polarimetry.The delay line is based on the symmetrical structure and coupling between the two independent graded refractive index lenses.We analyzed the polarization mode coupling model with the measurement error caused by the GRIN-lens-based delay line,and the single GRIN-lens and differential GRIN-lens are both discussed.(5)We proposed dual-channel polarization mode measurement systems for the Y-junction.In the first configuration,the Y-junction is directly employed as a beam coupler to construct the interferometer.In the other configuration,the dual-channel optical coherence domain polarization system contains a function of self-calibration.The characteristics of Y-junction — chip polarization extinction ratio,the polarization crosstalk of output coupling points,split ratio,and the temperature coefficient of chip birefringence were measured in static and dynamic conditions. |
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