High precision measurement technology for beat length of birefringence optical fiber

Based on hybrid Sagnac interferometer formed with single directional coupler and polarization maintaining fiber (PMF) under test, a high precision measurement technology for beat length of birefringence fiber is proposed. The measure error is analyzed and the optimum measure condition is defined. With the high performance optical sensing interrogator technology, the beat length measure precision can be better than 0.001 mm. The verify test is made experimentally. The beat length stability of PMF and polarization maintaining photonic crystal fiber (PM PCF) has been measured and compared too. The result proves the excellent birefringence temperature stability of PM PCF.