Birefringent Axes Aligning System for Electro-optic Probe Fabrication Using Polarization Maintaining Fiber

Fabrication method of a fiber optic electric field sensing probe using polarization maintaining fiber (PMF) is described including a birefringent axes aligning system. The sensing probe is basically a fiber-coupled Fabry-Perot resonator where a thin birefringent wafer of LiTaO3 with an external cavity is mounted onto the end of PMF. An optical wave from a superluminescent laser diode after a linear polarizer parallel to the slow axis of the PMF is made to enter the LiTaO3 crystal with polarization parallel to its extraordinary axis and the reflected optical wave is detected after passing through a polarization analyzer. By measuring a minimum value of a ratio of the reflected optical power at 90° to that of 0° of analyzer, we successfully demonstrated that the angular accuracy of the slow axis of the PMF with respect to the extraordinary axis of the LiTaO3 can be evaluated. Aligning both axes precisely, the electro-optic effect associated with LiTaO3 and polarization is optimized with greater stability. Long term stability of the fabricated PMF sensing probe was enhanced by about 3 times compared to that of a conventional single mode fiber one. As a result of uncertainty analysis, the method we proposed has an overall angular uncertainty of 1° when the used fiber optic components have polarization angle tolerance of 1°.