Polarization maintaining fiber coupler connection testing and alignment of the polarization axis
|Keywords||polarization-maintaining optical fiber Polarization coupling polarization extinction ratio phase modulation PZT divider filter|
The principle that the polarization coupling in Polarization-Maintaining fiber(PMF) being detected by the output polarization extinction ratio(PXR) of PMF is systematically analyzed in this dissertation. A method for the rotational alignment of PMF and another waveguide is proposed based on the principle.The experiment setup of polarization coupling detection and polarization axis alignment is designed and realized. By using this setup, the polarization coupling in PMF used in optical communication or sensors can be tested, and polarization axis of them can be aligned, which can minimize the polarization coupling caused by the junction. It has great significance for improving the performance of fiber sensors.Jones Matrix theory is used to analyze, when the PMF is aligned to another waveguide with polarization axes, the relationship of the output PXR of PMF versus the phase difference between the two polarization modes in it, and the rotational angle between the polarization axes of them. Moreover, it is proved that the output PXR is independent of the phase difference when the polarization axes of PMF and another waveguide are well rationally aligned(the rotational angle is N×90°).Based on this, PZT phase modulator is used to modulate the phase difference, stepping motor is used to turn the PMF output axis, and a proper signal processing circuit is designed to get the output PXR of PMF, sequentially, polarization coupling in PMF is obtain, and the state of the polarization axis alignment can be judged. It is found in the simulated experiment that the accuracy of rotational alignment can be better than 0.01 deg.Furthermore, the optical and circuit subsystems are designed, In the optical subsystem, coupling and focusing lens and collimating lens, fiber phase modulator, polarizing prism are designed. In the circuit subsystem, modulation power source, driving control of stepping motor, photoelectric detection circuit, preamplifier, main amplifier, filters, and divider are designed. At last, the system is experimently tested and some of influencing factors are analyzed.