Research On Quadrature Demodulation Digital Pound-Drever-Hall Techniques Of Frequency Stabili-Zation

Laser has widely applications in the fields such as precision metrology,gravitational wave detection and information science,due to its obvious characteristics of high brightness,good monochromatics and coherence.If the optical atomic clock is realized by use of laser,the time and length standards can reach a higher accuracy.However,the laser frequency stability directly determines the accuracy of the optical atomic clock.Therefore,it is of great significance to investigate the techniques of laser frequency stabilization.The Pound-Drever-Hall(PDH)frequency stabilization method has the advantages of good stability and rapid response,which can easily obtain tre laser output of narrow linewidth,being generally used as frequency stabilization method.In this thesis,a scheme of the quadrature demodulation digital PDH frequency stabilization has been designed,as compared with the traditional PDH frequency stabilization system,the scheme avoids the use of a phase shifter and has the lower electronic noise,being favorable to improve the laser frequency st,ability.The main research contents of this thesis are as follows:First,according to the composition and working principle of the traditional PDH frequency stabilization system,the quadrature demodulation digital PDH frequency stabilization scheme has been designed,and its feasibility has been analyzefd.Secondly,the hardware circuits of digital quadrature demodulation have been designed,including amplification circuit,frequency selecting circuit and FPGA-based data processing module,The RMatlab software has been used to simulate the functions and parameters of the hardware module.The source code design,logic function,pin configuration and layout had been simulated and verified on the Quartus ? software.The correctness of the design mocdule timing and waveform has been verified by the Modelsim software.Thirdly.an experiment system of the quadrature demodulation digital PDH frequency stabilization of the single-frequency all-solid-state laser has been established,and a experimental study of the laser frequency discrimination has been implemented.Using the Signal Tap ? software to demonstrate the hardware design.The laser has been phase-modulated on a condition of single-longitudinal mode oscillation,and the error signal of the frequency drift has been detected by a photodetector,the error signal has been pre-processed by the amplification circuit and frequency selection circuit,it has been collected by high-speed ADC module,and then processed by FPGA using the method of quadrature demodulation.The frequency discrimination curve has been obtained by the Matlab software.The experimental results show that the maximum deviation of laser frequency is 10.444MHz,and the frequency discrimination sensitivity is 100.43mV/MHz.Finally,the errors sources of the experimental system have been analyzed,mainly including both optical noises such as residual amplitude modulation,pattern matching,and hardware noises produced by the DDS spectrum and ADC conversion.