Research On Sagnac Loop Fiber Temperature And Strain Sensor Based On SPS

Besides the advantages of general fiber optic sensors,the Sagnac loop-based modal interferometer fiber sensors have many advantages,such as simple structure,low cost and high sensitivity and so on.Recently,it is an important research direction in the field of optical fiber sensing technology in domestic.The modal interference type optical fiber based Sagnac loop sensor is usually constructed by spliced different kinds of optical fiber together or core axis of symmetry spliced the same kind optical fiber.The changes of external environmental parameters such as the temperature or strain loading on the sensing fiber,which is resulting in the interference pattern is different from the interference pattern when there is no environmental disturbance.By measuring the variation of the output interference spectrum,it can demodulate the external environmental parameters as well as their changing laws,and realize the sensing function.In this paper,a modal interference fiber structure comprising single-mode-polarization maintaining-single-mode(SPS)fiber is proposed and developed.The effects of different lengths of polarization-maintaining fibers on the interference spectrum of SPS fiber sensors are analyzed by theory and experiment.The influence of the temperature sensitivity of the SPS structure sensor has been reeled into different circle radius were inserted into Sagnac loop investigated.At the same time,in order to further improve the extinction ratio and sensitivity of the sensor resonant the trough of wave,a cascaded Sagnac loop fiber sensor based on SPS structure is proposed.The experiment also verified that the sensor can achieve simultaneous measurement of temperature and strain.The main research content of this article as follows:(1)In this paper,a Sagnac loop optical fiber sensor based on the SPS structure is developed.The influence of the polarization maintaining fiber length about the sensor sensitivity is analyzed theoretically and experimentally.The experimental results show that the number of resonant troughs of wave about SPS structure fiber based Sagnac loop optical fiber sensor increases with the increase of the polarization maintaining length.Experimental results show that the polarization maintaining fiber length has little effect on the strain sensitivity of the sensor and the strain sensitivity of all SPS structure sensors are maintained at 28.6pm/?? up and down.On the contrary,the length of PMF fiber has a significant influence on the temperature characteristics of the SPS structure sensor.When the PMF length is 15 cm,the sensor can reach a maximum sensitivity of 1.53nm/?.These researches provide the basis for optimizing the length of PMF fiber.(2)In order to further improve the sensitivity of the sensor,we investigate the temperature sensitivity dependence of the PMF length after the SPS fiber structure is reeled into a circle.Experimental results show that the temperature sensitivity of the sensor increases with radius of the circles reduce.When the radius of the circle is 3cm,the temperature sensitivity of the sensor can be increased to 1.73nm/?.(3)A cascaded Sagnac-loop fiber sensor based on SPS is proposed.The experiment confirmed that this sensor can measure temperature and strain simultaneously by measuring two resonant through wavelength or one resonant wavelength.The sensor can achieve simultaneous measurement of temperature and strain.And the cascade structure can also increase the extinction ratio of the resonant trough and improve the measurement accuracy.