Research On Optical Subcarrier Vibration Measurement Technology

Laser Doppler measurement technology is widely used in the field of velocity and vibration measurement because of its high precision and no direct contact with the object being measured.However,the roughness of the measured object cause the efficiency of the heterodyne detection of the echo laser signal to be affected,that is,the decoherence effect.In this paper,a scheme of vibration detection for rough targets using optical subcarrier is designed,which avoids the decoherence effect in laser heterodyne detection.The principle of optical subcarrier vibration measurement is to use the microwave signal to modulate the intensity of the laser signal,to transmit the subcarrier of the light to the measured object,and to detect the echo signal directly by the photodetector.The Doppler shift is extracted from the echo signal to obtain the vibration information of the target.An overall vibration measurement scheme is designed,which is divided into optical subcarrier modulation transmitting system and echo signal receiving and processing system.The two optical intensity modulation modes of direct and indirect modulation are compared and analyzed.The indirect modulation mode using the MZ electro-optic modulator as the external modulator is selected.The working mode of the MZ modulator is deeply studied.The result of the simulation experiment of the optical subcarrier modulation system in this design is obtained by using optisystem.It is in conformity with the expectation.The structure of homodyne and heterodyne reception is compared and analyzed,and a set of heterodyne reception architecture is designed.The selection principles of the main components,light sources,modulators and photodetectors in the scheme are analyzed in combination with their important parameters.In the aspect of Doppler signal processing,the FFT algorithm and the Welch method in classical power spectrum estimation are studied deeply.The two algorithms and the Welch algorithms with different window functions are compared.All kinds of algorithms are simulated and analyzed by MATLAB software.Finally,the MATLAB is used to simulate the optical subcarrier vibration measurement system,and the simulation experiment is carried out by using the optical subcarrier of the 1GHz to the target of the 1KHz vibration amplitude of 1mm,and the good results are obtained without noise and noise.