Humidity sensor based on intracavity sensing of fiber ring laser

A humidity sensor based on the intracavity sensing of a fiber ring laser is proposed and experimentally demonstrated. In the fiber ring laser, a humidity-sensitive fiber-optic multimode interferometer (MMI), fabricated by the single-mode-no-core-single-mode (SNCS) fiber coated with Agarose, works as the wavelength-selective filter for intracavity wavelength-modulated humidity sensing. The experiment shows that the lasing wavelength of the fiber laser has a good linear response to ambient humidity from 35%RH to 95%RH. The humidity sensitivity of −68 pm/%RH is obtained with a narrow 3 dB bandwidth less than 0.09 nm and a high signal-to-noise ratio (SNR) 60 dB. The time response of the sensor has been measured to be as fast as 93 ms. The proposed sensor possesses a good stability and low temperature cross-sensitivity.