A Fiber Ring Cavity Laser Temperature Sensor Based on Polymer-Coated No-Core Fiber as Tunable Filter

A fiber ring cavity laser temperature sensor is presented and demonstrated. The sensor probe consists of a fiber Bragg grating (FBG) and a heterostructure based on polymer-coated no-core fiber (NCF), and this probe also functions as a wavelength-selective component in the fiber laser system. There are multimode interference and antiresonance effects in the NCF coated with high refractive index polymer. Embedding this sensing head into an Er-doped fiber ring cavity laser system is helpful to improve the spectral quality and the detection limit (DL). The passband peak position of the heterostructure filter and FBG filter varies with the temperature, which leads to the corresponding shift in the output laser wavelengths. Experimental investigation achieves a maximum sensitivity of −3.155 nm/°C in the temperature range from −4 °C to 47 °C, and the DL is calculated as 0.005 °C. It should be noted that there are several measurement intervals in this temperature range, which can be distinguished by the cascaded FBG to obtain the accurate temperature value. Moreover, the sensor with a smaller NCF diameter has a higher temperature sensitivity. The proposed sensor can meet the actual demands of mesoscale ocean phenomena and microregion temperature detection in seawater, and it provides references for improving the sensing capability of optical methods in ocean detection and other practical application.