Research On Dual-source Locked Dual-frequency Laser

In recent years,with the rapid development of ultra-precision machining and manufacturing industry,laser interferometry technology with its non-contact,high precision,traceability and other characteristics,has been the mainstream technology means of ultra-precision displacement measurement and precise positioning.And the dual-frequency laser measurement using heterodyne interference measurement principle,with better anti-interference ability and higher measurement accuracy,so it has been widely used.As the core component of heterodyne interferometry,the performance of dual-frequency lasers directly affects the accuracy of interferometric measurements.Based on traditional coaxial double-frequency laser interferometer has the nonlinear error of frequency aliasing,and the dual-band light frequency offset range is limited,it is proposed to research a dual-band light space separation and the frequency offset range adjustable system of new non coaxial dual frequency laser,based on the traditional coaxial double-frequency laser interferometer in double-frequency introducing the nonlinear error of frequency aliasing,dual-band light limited frequency offset range,research a dual-band light space separation and the frequency offset range adjustable system of non-coaxial dual frequency laser,it is called dual light source locked dual frequency in this paper.Combine the space separation interferometer built the heterodyne interferometry system,and verify the performance of the non-coaxial dual frequency laser by experiments.The research contents are as followed:?1?According to the principle of heterodyne interferometry and the space separation interferometer structure,analyzing the displacement measurement error caused by frequency and frequency drift and the error model.The influence of the parameters of frequency difference on the measurement accuracy is revealed.In addition,considering the electronic subdivision error and measuring the optical path structure,analysis of the performance indicators of the frequency difference accuracy and stability needed to achieve the sub-nanometer measurement accuracy;?2?For the dual light source locking system,the beat signal contains noise,the amplitude is small and the waveform is not ideal and other problems,I have designed a high precision low drift bias signal preconditioning circuit to achieve the light beat signal high-precision filtering,amplification and shaping processing in the target frequency band.On this basis,the design of multi-cycle synchronous frequency measurement based on the high-precision digital frequency measurement module to achieve the measured frequency band within the accurate measurement;?3?The controlled object has several problems,such us long time delay,large inertia in the control,using step identification method to obtain the mathemat ical model of controlled object,according to the proportional gain,thermal inertia,time delay and other related parameters,designed and implemented based on the algorithm of Smith-PI frequency offset locking frequency stabilization system,and the Simulink simulation toolbox is used to simulate the control parameters and provide a reference for the actual control parameters?On this basis,a high precision digital frequency stabilization controller is designed.The process of controlling from preheating control,double mode heat and stability control to frequency lock control is realized,and the precision and repeatability of frequency-difference locking is guaranteed.Setting up the dual light source frequency locking frequency stabilization experiment device,according to the target frequency difference control parameters of different frequency bands,testing the frequency difference locking effect.The experimental results show that when the dual-source-locked dual-frequency laser is designed with 5MHz,10 MHz,20MHz,30 MHz and 40 MHz as the preset target frequency difference,the dithering in 24 h is less than ±90k Hz,frequency difference stability is better than 3.8×10^-10/24 h.