| Modern manufacturing tends to be on the nanometer scale,so the accuracy and performance requirements for sensors are also increasing.For Instance,the next-generation manufacturing process for the mobile phones chips will be 7nm process,lending to the facts that the universal micro-scale measurement technology is far from meeting the manufacturing and measurement requirements of these smart devices.In order to achieve high-precision and high-resolution measurement,the traditional method is to use He-Ne laser interferometry,but it is expensive,complex and environmentally sensitive.The emergence of white light interferometry exactly right breaks these limits of laser interferometry.In the past 10 years,white light interferometry technology has deeply crossed with fiber-optic transmission technology to form a new type of fiber-optic white-light interference sensor technology.Due to its high measurement resolution,stable measurement performance and absolute measurement,this technology has been the one of hot research spots widely followed by inside and outside.In this paper,a studied is proceeded that is about the application of fiber white light interferometry in the displacement sensing field,and a corresponding micro-displacement measurement system with a large range is designed based on this.A wide-spectrum semiconductor laser is used as the system light source,and white light is introduced into the optical fiber path,which is sequentially subjected to beam modulation and beam demodulation in the optical path,and finally a white light interference pattern is formed.The position of the center fringe of the white light interference pattern changes with the change of the external displacement input.The Measurements of the displacement input can be obtained by detecting the position of the center fringe by the photoelectric conversion module.In the aspect of optical hardware implementation,the measured displacement is introduced by the change of Fabry-Perot(F-P)cavity's length,and the modulation of the white light beam is realized by the multi-beam interference effect of the F-P cavity.Through above steps,the displacement information is included in the white light beam.Demodulation is achieved by the Fizeau-wedge.At the bottom of the Fizeau-wedge,the central fringe of the white light interference pattern appears only where the wedge thickness exactly matches the cavity length of the F-P cavity.In order to enable the photoelectric conversion module to accurately detect the position of the central fringe of the white light interference pattern,the necessary signal processing on the interference signal is performed.Based on the existing relevant theory,this paper proposes a new composite structure of white light interference signal intensity distribution,and uses power exponential operation to preprocess white light interference signal,which improves the quality of interference pattern.Moreover,for precisely locating the central fringe of white light interference pattern,various center-of-gravity methods are compared to find the most appropriate method to achieve the location of central fringe.Finally,combined with the characteristics of designed system,the differential light intensity center-of-gravity method was chosen to locate the central fringe of the white light interference pattern.For verifying the feasibility of the micro-displacement measurement system designed by this paper and testing its measurement performance,the relevant experimental platform was built,and the optical path part of the system was adjusted reasonably.The interference spot associated with the optical path difference was successfully obtained.Then,through joint debugging with modules such as photoelectric conversion,signal processing,and data acquisition,the displacement value is finally obtained.The experimental results show that the theoretical resolution of the system can reach 150 nm,the measurement range can reach 0.2mm,whose repeatability and linearity are good,with a large range expansion potential. |
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