Effect of macro-bending on resonant wavelength and intensity of long-period gratings in photonic crystal fiber

We report the spectral characteristics of CO₂-laser inscribed long-period gratings (LPGs) in endlessly single mode photonic crystal fiber (PCF) subject to macro-bending. The coupling modes as a result of bending were studied by examining the shifts of resonant wavelengths, the splits of attenuation bands, and the variation in coupling strength of the transmission spectra. A bending coefficient of ∼ 27.9 nm·m was determined in the PCF at 180° rotational orientation relative to the point of laser inscription in the curvature range from 2.6 m^-1 to 3.5 m ^-1. Compared with conventional fiber LPGs fabricated using the same method, the PCF-based LPGs possess higher sensitivity both to bending and orientation, making them promising for sensor applications.