Temperature Self-Compensation High-Resolution Refractive Index Sensor Based on Fiber Ring Laser

In this letter, a temperature self-compensation high-resolution refractive index (RI) sensor based on intracavity intensity-modulated sensing in a fiber ring laser is demonstrated. A fiber-optic multimode interferometer based on single-mode-no-core-single-mode fiber structure is cascaded with a fiber Bragg grating and used as a reflected sensing head to enhance intensity-modulated depth. It is inserted in a fiber ring laser as a wavelength selective filter and the intracavity intensity-modulated RI sensing is induced for the output intensity of the fiber laser. Furthermore, because the lasing wavelength of the sensor system is sensitive to temperature but insensitive to external RI, the temperature self-compensation measurement can be realized. The RI sensitivity is measured to be -4.98 mW/RIU from 1.3349 to 1.3665. Correspondingly, the relative intensity sensitivity achieves -196.1 dB/RIU from 1.3349 to 1.3544 and -744.6 dB/RIU from 1.3544 to 1.3665. The resolution of the fiber laser sensor is obtained as high as 2 × 10
^-10
RIU with the signal-to-noise ratio more than 55 dB.