Some Issues Of Wavelength Encoding Fiber Optical Position Sensor With Varied Line-space Grating

In these years,lots of optical position sensors are generally needed where electromagnetic sensors can't work for the magnetic and electrical interference.A number of Linear position Fiber Optic Sensors has emerged in the program of FLASH(Fly-By-Light Advanced Systems Hardware) sponsored by U.S.A in 1970s. Since 1990s,the fiber optical sensors have attracted enormous interest in our country, which may replace the electromagnetic sensors in special applications.A wavelength encoded fiber optic position sensor has been investigated,in which the sensing element is a diffraction grating with a linear variation in period over its length.When illuminated with a broadband optical source at a fixed angle of incidence,linear translation of the grating always lead to a linear shift in the wavelength of the detected signals collected at a fixed angle.Based on the information coming from the papers which can be got,some researchers have worked out the first wavelength encoded fiber optic position sensor prototype employing varied line-space grating in our country through several years' hard work.The following work is to develop an engineering sample sensor.This thesis focuses on the optical system of the wavelength encoding fiber optical position sensor with varied line-space grating and presents optimum parameters as well as design methods which can avoid some problems during the manufacture of the engineering sample sensor.The main contents of this thesis are summarized as follows:1.Research on wavelength encoded fiber optic position sensor's optical systemThe optics system of the sensor,including the varied line-space grating,the input and output fibers,was analyzed using the design method of the monochromator.Theoretic analysis for the varied line-space grating shows that the focusing characteristic is special for the sensor.For high resolution and high frequency response,the new design for the sensor should consider the varied line-space grating's focusing characteristic.The differences were analyzed using the optical designing soft-Zemax.The calculation method for the fiber's diameter is presented in this part. How does the optic spectrometer's resolution influence the sensor's displacement resolution,and the method choosing the optimized spectrometer is also discussed in this part.2.Theoretic error analysis of the engineering sample sensor's systemThe error coming from the guide has a significantly effect on the displacement measure error.To improve the whole performance,single-mirror was replaced by dual-mirrors,and the novel configuration makes the sensor insensitive to the guide errors.A theoretic analysis on the results of engineering sample sensor's test was conducted,and solutions for solving the existence problems were proposed.3.Optimization for the angle sensor's optical system and fabrication method of the cylindrical varied line-space gratingA wavelength encoded fiber optic angle position sensor was optimized using a cylindrical varied line-space grating.And the method for fabricating of cylindrical varied line-space grating was proposed with holographic-electroplating method. Firstly,a metal varied line-space grating on the Ni foil with a thickness of 100μm was prepared using the holographic-electroplating method.Then,a cylindrical varied line-space grating was made by fixing the metal grating on a cylinder.The main innovations of this paper include:The theoretical analysis and experimental study on the optical system of wavelength-encoding-fiber optical position sensor with varied line-space grating were conducted,and the optimum methods for the fabrication of high resolving power sensor were proposed;an error analysis was carried out for the engineering sample sensor,and the single-mirror was replaced by dual-mirrors,which made the sensor insensitive to the guide errors;the cylindrical varied line-space grating for the angle sensor was fabricated using the holographic- electroplating method.