Optical Fiber Strain Sensor Based On Open-cavity Structure

Due to the needs of precision measurement,biochemical testing,engineering mechanics and other fields,optical fiber micro-cavity interferometer is widely studied.Compared to the conventional fiber interferometer,it has the merits of ultra-small small size and ultra-high sensitivity.In this paper,the large offset splicing technology was used as the preparation method to explore the strain-sensitive characteristics of the micro-cavity fiber interferometer.The multimode assisted micro-cavity structure was optimized,and the tapered micro-cavity strain interferometer based on arc discharge technology was proposed and the strain characteristics were tested.The main contents are as follows:(1)Based on Mach-Zehender and Fabry-Perot interference,the working principle of micro-cavity was analyzed.Using beam propagation method,the beam expansion effect of multimode open-cavity structure is simulated.The offset and length of open-cavity was analyzed.Also its temperature and strain sensing characteristics were theoretically studied.(2)The single-mode based open-cavity interferometer was fabricated.By adjusting the offset value,the transmissive and reflective open-cavity structures were prepared,respectively.And the strain test was conducted and the experimental results showed that the sensitivities of reflective and transmissive structures were 1.35 pm/?? and 1.775pm/??,with the linearity of 0.99.However,due to the lost energy in opening cavity,the periodicity of spectraum was worsened when the cavity length is longer than 500 ?m.(3)In order to improve the preparation efficiency,the multimode-assisted open-cavity interferometer was proposed.The simulation and experimental results showed that the preparation efficiency can be improved by the introduction of multimode fiber.In addition,the multimode-assisted tapered open-cavity interferometer was fabricated and compared by one-and two-step arc discharge technique.Then the strain characteristics were studied and the results show that the strain wavelength sensitivity is negatively proportional to the waist diameter of taper,and higher responses were obtained in the two-step discharged structures.The maximum wavelength sensitivity reaches 48.6 pm/?? in the range from 0 to 110 ??,when the waist diameter is about 30 ?m.