Fiber Bragg grating inscription in multi-core photonic crystal fiber by femtosecond laser

The inscription of fiber Bragg grating (FBG) in a pure-silica multi-core photonic crystal fiber (PCF) using femtosecond laser and phase mask is reported. Three resonant dips are observed in the transmission spectrum due to the multiple supermodes transmitted in the PCF. The induced refractive index modulation of 2.2 × 10−4 is achieved for a peak power density of 4.8 × 1013 W/cm2 without any fiber sensitization. The experimental results show that type II grating is inscribed and it has high thermal stability. The temperature corresponding to 50% decrease in transmission loss of the FBG is about 970 °C. The central wavelengths of the three dips linearly shift with pressure sensitivity of −4.8 pm/MPa and strain sensitivity of 1.2 pm/με. This FBG will find applications in optical fiber sensing under high temperature.