Research Of Optical System In Fiber Polarization Coupling Analyzer Based On White-light Interferometry

Polarization maintaining fiber (PMF) has been widely applied in optical fiber sensors. Fiber-optic gyro is one of the important applications. But spurious polarization coupling caused by many factors will affect the performance of PMF, and therefore reduce fiber-optic gyro's quality and measuring precision. Fiber polarization coupling analyzer researched by this thesis is used to detect the coupling position and intensity of spurious polarization coupling point along the PMF. The instrument is based on white-light interferometry. The optical system of this instrument is designed in this thesis.The major achievements of this thesis are as follows:1,Analyze the influence of light source's spectral width on the coherence and the intensity change of coherence field, and select the light source with proper spectral width upon the system resolution.2,Explain the two parts of white-light interferometer: sensing interferometer and reference interferometer during design.3,Analyze the transmission of the light wave through the optical system, and deduce the formula for position and intensity of polarization coupling, and analyze the rotating angle's effect on the measurement precision of coupling intensity.4,Design the optical system of polarization coupling analyzer. Figure out the aperture and focus length of expanding lens and focusing lens. Design the polarization prism from combination of its two part, the optical axis direction, cutting angle and the air-gap thickness. Figure out the scanning arm's length of Michelson interferometer upon the range of the instrument.5,Estimate the wavefront error of the whole optical system, and select a proper defocus length to improve the wavefront error, and then check the system's aberration after defocus.6,Make a experiment on PMF, and calculate the coupling intensity and position along the PMF. Verify the correctness and feasibility of the principle of the instrument in practice. The innovations of this thesis are as follows:1,Analyze the coherent character of white-light interferometer from the viewpoint of coherent optics, and clarify the influence of light source's spectral width on the coherence and the intensity change of coherence field, also discuss the principle of selecting low-coherence light source.2,Discuss the overall configuration of detector, system-structure and light source from the viewpoint of geometric optics and the aberration theory. Consider the match of the aberration and the detector's area as well as the wavefront error.3,Clarify that fiber polarization interferometer functions as sensing interferometer, and digital scanning Michelson interferometer as reference interferometer, which explains the double interferometer system theory of white-light interferometry.