Research On Optical System Compensation Technology In Surface Topography Measurement By Optical Fiber Sensors

Because optical fiber sensors have simple structure,small size,corrosion resistance,electromagnetic interference resistance,and high sensitivity,it is widely used in surface topography,micro-displacement,and other measurements.Among them,the reflective intensity-modulation optical fiber sensor is the simplest and most easily realized sensor,so it become a subject of extensive research.It uses the optical fiber as the transmission medium,and the change of the light intensity caused by the external signal,testing the light intensity by the photoelectric detection element to measure each parameter.For the measurement in surface topography measurement by reflective intensity-modulated optical fiber sensor(RIM-FOS),this paper has deeply studied optical system construction,modeling of RIM-FOS transmission characteristics,design of optical intensity compensation method,and experimental verification.Firstly,according to the basic structure of RIM-FOS,an optical system is constructed,and analyzing the basic characteristics of each device and choosing the parameter of them.In the light path construction,the coupling efficiency of the light source and the fiber is analyzed deeply,and a combined lens coupling system is proposed.By using ZEMAX of optical design software,the simulation analysis results in about 78.5% coupling efficiency,which greatly reduces the loss energy of the light source output power by coupling.According to the basic working principle of RIM-FOS,this paper uses Gaussian distribution hypothesis of fiber exit intensity distribution,and establishes a mathematical model of the receiving optical power of the receiving fiber.Simultaneously this paper analyzes the impact of factors such as output power fluctuation of the light source on the light receiving characteristics of RIM-FOS.Then a new type of unequal distance dislocation type tri-optical fiber dual-optical path compensation structure was designed.Through simulation analysis of the light intensity compensation effect,the effect of light source output power fluctuation and other factors on the measurement accuracy can be effectively eliminated.This paper proposes a method of the neural network compensation,which doesn't set the optical path of the splitting reference beam.The neural network is used to predict the output power of the light source over a period of time,which is used for the neural network to compensate the reference signal in the structure,thereby achieving light intensity compensation.Finally,the output characteristics of the light source and the stability of the output power were experimentally tested,and the long-term output power stability of the semiconductor laser was 0.49%.At the same time,the two compensation methods were verified experimentally.The experimental results showed that the neural network compensation method can effectively improve the accuracy of displacement measurement.