Low-Loss Low-Back-Reflection Coupling of Hollow-Core Photonic Bandgap Fiber with Integrated-Optic Circuit in Fiber Optic Gyroscope

Photonic bandgap fiber-optic gyroscope has excellent environment adaptability and shows great prospect. The coupling between hollow-core photonic bandgap fiber coil and integrated-optic circuit is a crucial technology in photonic bandgap fiber-optic gyroscope. A low-loss low-back-reflection method for the coupling between a hollow-core photonic bandgap fiber and integrated-optic circuit is proposed. The end-face of the hollow-core photonic bandgap fiber only needs to be flat-cleaved with a general fiber cleaver. The optimal coupling angle is determined and experimentally verified to overcome the effect caused by the air gap between angle-cleaved integrated-optic circuit and flat-cleaved hollow-core photonic bandgap fiber end-face. Experimental results reveal that the coupling loss and back-reflection of the hollow-core photonic bandgap fiber with the integrated-optic circuit are better than 3.2 dB and -43 dB, respectively. Compared with conventional butt coupling and fusion splicing, the coupling performance of the proposed method is significantly improved, which can achieve low-loss, low-back-reflection, and high reliability. The method provides a foundation for the coupling between hollow-core photonic bandgap fiber coil and integrated-optic circuit in fiber optic gyroscope.