Research On Temperature And Strain Sensor Based On Special Fiber And Sagnac Ring Structure

With the rapid growth of the global economy,the demand for coal resources has further increased in China.The shallow coal resources are difficult to meet the needs of economic development.Mining deep coal resources on a large scale has become an inevitable trend in the development of China's coal industry.However,there are many potential safety hazards in the mining process,which may cause heavy casualties and economic losses if not discovered in time.At present,the traditional electrical sensors have been widely used in colliery monitoring system.But electrical sensors have some disadvantages,such as front power supply,susceptible to electromagnetic interference and short transmission distance,it has limitations when used in flammable and explosive environments such as coal mines.On the contrary,the optical fiber sensors have obvious advantages such as no front power supply,resistance to electromagnetic interference,corrosion resistance,high sensitivity and high precision,which is suitable for coal mine safety management and monitoring system.Moreover,for coal mine safety management and monitoring,temperature and strain are two important parameters.In this paper,the methods to improve temperature and strain sensitivity of the optical sensor are studied intensicely.Two kinds of optical fiber temperature and strain sensors are designed and fabricated.The thin core polarization maintaining fiber(TPMF)and the TPMF-thin core photosensitive fiber(TPSF)structures were introduced into the fiber Sagnac interferometer(FSI),respectively.Furthermore,to further improve temperature and strain sensitivity of the sensor,a highly sensitive optical fiber temperature and strain sensor based on the cascade structure of FSI and polarization mode interferometer(PMI)is proposed.The temperature and strain sensitivity of these three sensing structures is significantly improved.The research contents as follows:1.A kind of optical fiber Sagnac interferometric temperature and strain sensor with enhanced sensitivity based on the TPMF is fabricated.Utilizing the core mismatch during fusion splicing of TPMF and fibers with different core diameters,the influence of different lengths of TPMF on the temperature and strain sensitivity are experimentally studied.The results show that the length of the TPMF has significant influence on the temperature sensitivity of the sensor,but almost no influence on the strain sensitivity.The highest temperature sensitivity(-1.70 nm/?)can be obtained with 3 cm TPMF;the lowest temperature sensitivity(-1.52nm/?)can be obtained with 15 cm TPMF,the highest strain sensitivity(23.07 pm/??)can be obtained with 12 cm TPMF.2.A kind of optical fiber Sagnac interferometric temperature and strain sensor based on core diameter mismatched is is fabricated.The proposed sensor is fabricated with TPMF and TPSF fused and introduced into Sagnac ring.Utilizing the core mismatch during fusion splicing of Ge-B doped TPSF and fibers with different core diameters,the influence of different lengths of TPSF on the temperature and strain sensitivity are experimentally studied.The length of the TPMF remains unchanged at 10 cm.The results show that the length of the TPSF has obvious influence on the temperature sensitivity of the sensor,but almost don't have influence on the strain sensitivity.The highest temperature sensitivity(-1.93 nm/?)can be obtained with 12 cm TPSF;The lowest temperature sensitivity(-1.46 nm/?)and the highest strain sensitivity(36.92 pm/??)can be obtained with 16 cm TPSF.3.An optical fiber temperature and strain sensor is proposed,which introducs Elliptical core polarization maintaining fiber(ECPMF)into the Sagnac ring as a reference interferometer.The sensor consists of a reference interferometer FSI and a sensing interferometer PMI.Utilizing that the reference interferometer FSI is insensitive to temperature,strain,bending,and torsion,the temperature and strain sensitivity of a single PMI,a single FSI,and cascade sensors are studied by simulation and experiment.The results show that single FSI is relatively insensitive to temperature and strain.While the temperature and strain sensitivity of the cascaded sensor is 11.12 times(-15.56 nm/?)and 11.81 times(154.04 pm/??)higher than that of the single PMI,respectively.The simulation result is 11.34 times,which is basically consistent with the experimental results.Based on the above analysis,the sensors proposed in this paper overcomes the shortcomings of traditional electrical sensors,which play a positive role in promoting public safety industries such as coal mine management and monitoring.Meanwhile,these sensors can be applied to aerospace,medicine and health,marine development,safety monitoring and other fields in the future.