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The principle and design of high-resolution sensors are of great significance in the development of fiber-optic sensors. In this article, a general method based on intracavity sensing of fiber ring laser (FRL) is proposed for high-resolution measurement, and a high-resolution temperature sensing system is experimentally demonstrated. The theoretical model for intracavity sensing of FRL is presented. In the sensing system, a fiber-optic Sagnac loop is inserted into an FRL for temperature measurement, which performs as the filter and sensing head simultaneously. Because the filter characteristics of the Sagnac loop is modulated by temperature, the intracavity intensity-modulated sensing is induced for the output power of the FRL. With the method based on intracavity sensing, the temperature resolution level of the sensing system has been improved from 10−3 °C–10−6 °C. The stability and measurement errors are also measured. The proposed method can be extensible to similar fiber-optic sensors to improve measurement resolution.

A multi-direction bending sensor based on the 18-core photonic crystal fiber (PCF) is demonstrated in this paper. The design of the sensor is discussed theoretically and experimentally. The PCF serves as the laser gain medium and the sensing medium simultaneously in the fiber laser sensor. The operating wavelength of the proposed PCF laser sensor is about 1032.32 nm. A CMOS image capture system is used to acquire the distribution of supermodes in the PCF laser. Based on the normalized intensity distribution of supermodes, six directions can be measured. The sensor also shows the ability to measure bending radius within 0.11 m. Then, the thermal effects of the bending sensor have been analyzed and the sensing system shows a low temperature crosstalk.

In this paper, a curvature sensor based on fiber ring laser with Sagnac loop is proposed and experimentally demonstrated. The Sagnac loop is inserted into a fiber ring laser used as the sensing element and the filter. The intracavity sensing is induced in the fiber laser with the filtering characteristic of the Sagnac loop modulated by the curvature. The intracavity sensing system is used to narrow the corresponding 3-dB band-width and enhance the resolution of the curvature sensor. With the intracavity intensity modulation method, the output power of the fiber ring laser sensor will change with an increase in curvature. The curvature range from 0 m−1 to 5.6865 m−1 has been measured and the highest curvature resolution of 6 × 10−8 m−1 is obtained. Based on the intracavity sensing system, the curvature resolution level has been enhanced from 10−4 m−1 to 10−8 m−1. The stability and measurement errors of the system are also studied and analyzed.