Research On Sensing Principle And Application Based On The S-bend Fiber

Compared with ordinary single optical fibers,S-bend fiber is a special structure of optical fiber.S-bend fiber can couple the fundamental core mode to cladding modes or reverse.Study on sensing application of the simple S-bend fiber,it's with advantage of simple structure,easy fabricate,high sensitivity,could be used to fabricate various kinds of optical fiber sensor.The main research contents of this paper are as follows:1.Referred to academic papers and literature of S-bend fiber sensor at home and abroad.this thesis introduced the development background,transmission principle,demodulation method and application prospect of S-bend fiber sensor.It also introduced the classification,production and its application of the S-bend fiber sensor,especially carried on the detailed classification according to the producing methods;and its advantages and disadvantages of each type is commented.2.A sensing structure of a long period grating etched on a S-bend fiber has been proposed.This paper introduces the mainly welding methods of S-bend fiber,theoretical analysis of it's working principle,the field distribution of core and cladding is simulated,The frequency spectrum of interference spectrum is analyzed,the frequency characteristics of the interference spectrum is also analyzed.3.The principle of sensor's micro-displacement measurement is introduced.When micro displacement experiments were carried out,the curve of the resonance wavelength was plotted,and the fitting curve of micro displacement with changes of wavelength or intensity is plotted.4.The sensing structure of a long period grating etched on the S-bend fiber is used to measure the temperature and curvature.The correlation principle of curvature and temperature measurement is analyzed,and the sensing and measuring of curvature and temperature are realized.The experimental results show that the sensor has good sensitivity.5.In the design system demodulation circuit,filtering and amplifying circuit were designed.Control unit based on STM32 was designed,and software was also designed,The detection error range of the system is within the range of 0.5dBm.