A novel, simple, and low-cost optical fiber temperature detection system is proposed and demonstrated in this paper, which uses the strong feedback of the Fabry-Perot Laser Diode (FP-LD) at 1550 nm to demodulate the temperature in real time in the resonator cavity. The experimental system consists of a commercial telecommunication laser source (FP-LD) and a fiber-optic Sagnac ring. In the sensing test, the change in temperature has a perfectly linear relationship with the shift of beat frequency signals (BFS). Measuring signals of different frequency will have different sensing sensitivities. System has an external photodetector (PD) in the first experiment. The temperature monitoring sensitivities is estimated to be 14.87 kHz/?C@2.49 GHz. In the second experimental system, there is no external PD, and the built-in monitor PD of FP-LD is used for photoelectric conversion. The sensitivity of the temperature sensor is 8.14 kHz/?C@1.382 GHz. In this paper, a fiber sensing system with the lowest cost and simplest structure is proposed, which consists of only a laser diode and a Sagnac ring.
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