Fiber Optical Sensors Research Based On Chemical Etching Method

Chemical etching method is the simplest and the most popular method to make fiberoptical sensors by far, it uses corrosion solution (hydrofluoric acid solution) to etch claddingdiameter of fiber, fiber Bragg grating and long period fiber grating directly. This methoddifferent from others is no exposure. The fiber or fiber grating waveguide structure is changedduring etching process, the working process of fiber optical sensor is very sensitive tobending, temperature, strain and refractive index. It has been extensively used in the fields ofoptical communication and optical sensing. A lot of interests have been focused on chemicaletching because of their advantages such as small size, easy fabrication, good reliability, lowcost and high flexibility. This kind of method has been widely used in biochemistry, medicinalchemistry microfluidics research and related fields, which offers great prospect for scientificcommunity.Fiber optical sensors have been aroused wide range of applications, they have uniqueadvantage which broads the application scope of fiber technology, they have been become acompetitive technology in fiber sensing.This article focuses on the sensing characteristics of LMSFBG and EFPI, their sensingprinciples and applications are analyzed in theoretically and experimentally. The following arethe detail descriptions of the work:1) Depict generally on the fiber Bragg grating application and classification, and putemphases on the application in the fields of optical communication and the sensings arepresented in detail. Femtosecond laser processing and chemical etching method areintroduced simply.2) Theoretical properties for LMSFBG and EFPI are presented, The Matlab software isutilized to simulate LMSFBG and EFPI numerically. According to the simulation result, themain factor which affects LMSFBG and EFPI is analyzed.3) LMSFBG is obtained by local etching method, we study its temperature characteristicsexperimentally. The wavelengths of the two resonant peaks become0.813nm and0.733nmlonger while the temperature increases from20to90°C, and the temperature sensitivecoefficients are0.01161nm/°C and0.01047nm/℃respectively.4) EFPI sensor is made by wet chemical etching of multi-mode fiber (MMF) end-face, Westudy the temperature and strain of EFPI theoretically, an experiment is designed tomeasure of temperature and strain. In this structure EFPI is sensing head, a beam intensityof isosceles triangle is used to measure stress. The interference wavelength variation isvery small while the temperature increases from20℃to100℃. The strain increases from0μεto585με, the strain sensitivity is about0.00436nm/με, and linearity is0.999.