Long-period fiber grating based on inner microholes in optical fiber.

A new, to the best of our knowledge, type of long-period fiber grating based on inner microholes in an optical fiber core is proposed and demonstrated. The device is fabricated by first using a femtosecond laser to write a series of vertical short line structures in the core of a single-mode fiber, followed by discharge of the short line areas with a fusion splicer. Owing to the high temperature generated, the line structure rapidly expands and forms an inner microhole. The device is found to have good high temperature sustainability up to 1000°C, with a sensitivity of approximately 13 pm/°C and its strain and bending sensitivities are approximately -1.57 pm/µÉ› and -5.198 dB/m-1, in the ranges of 0-800 µÉ› and 0-0.77 m-1, respectively. It is expected that the device can contribute to the multi-parameter sensing and detection of high temperature in harsh environments.