Refractive Index Fiber Laser Sensor by Using Tunable Filter Based on No-Core Fiber

A novel refractive index fiber laser sensor based on a fiber Bragg grating (FBG) integrated with a section of no-core fiber (NCF) is proposed and experimentally demonstrated. The oscillating wavelength of the fiber laser is only decided by the central wavelength of the FBG that is insensitive to the surrounding refractive index (SRI). However, the output power of the fiber laser varies with the SRI because the laser output is filtered by the edge of the bandpass filter (BPF) formed by the multimode interference (MMI) effect in the NCF, which is sensitive to the SRI. By measuring the variation of the output power, a cost-effective power detection RI sensor could be realized. The fiber laser sensor has a linear relationship with SRI and a sensitivity of 113.73 dB/RIU in the RI range of 1.333–1.4076.