A Novel Birefringent Photonic Crystal Fiber and Its Application to Curvature Measurement

We demonstrate a curvature sensor with a newly designed photonic crystal fiber of high birefringence (Hi-Bi PCF). The proposed PCF has two large air holes in the outer cladding region that give rise to core ellipticity during the fabrication process. The curvature sensor is based on the PCF Sagnac interferometer, the output spectrum shift of which provides information on the PCF curvature. It turns out that the curvature sensitivity depends on the bending directions with respect to the large-air-hole alignment. For the two orthogonal bending directions, the curvature sensitivities near 1480 nm are -1.87 nm/m-1 (parallel to the axis of the two large air holes) and 1.24 nm/m-1 (perpendicular to the axis of the two large air holes), respectively, and are also insensitive to environmental temperature variation. The proposed curvature sensor may be useful in thin structural deflection measurement.