Fiber Bragg grating in seven core fiber fabricated with infrared femtosecond laser pulses and a phase mask

Fibre Bragg grating (FBG) is inscribed into a seven core optical fibre by use of femtosecond laser side illumination. Multiple peaks in the reflection and transmission spectrum are observed, which result from the Bragg resonance of the core mode and cladding mode by phase match condition. The grating spectra exhibit linear response to rising temperature, and a sensitivity of 12 pm/°C is achieved between room temperature and 1000°C. Such a Bragg grating is promising to find applications in harsh environments.