Dual-Peak Bragg Gratings Inscribed in an All-Solid Photonic Bandgap Fiber for Sensing Applications

Bragg gratings are inscribed in an all-solid photonic bandgap fiber by use of femtosecond laser irradiation. Dual-peak structure is observed in the transmission spectrum of the induced grating, which is formed by the coupling between the forward-propagating fundamental core mode and the backward-propagating core mode or supermode. Sensing characteristics of the device are investigated experimentally by employing strain and temperature tests, and similar behavior is obtained for both resonant peaks. The strain and temperature sensitivities are 0.968pm/mu epsilon and 12.01pm/degrees C, and 0.954pm/mu epsilon and 12.04pm/degrees C, for the two peaks, respectively. This device would find potential applications in real optical fiber sensing without extra reference gratings.