Research On Laser Frequency Stabilization Method Based On Femtosecond Optical Comb

This paper introduces the development and application of laser,introduces the wide application of external cavity semiconductor laser in various fields,and the importance of laser frequency stabilization in these applications.The Littrow and Littman structures of external cavity semiconductor lasers for laser frequency stabilization are introduced.The stability and reproducibility of laser frequency,the theoretical model of laser frequency stability and the factors affecting laser frequency stability are analyzed.The structure and principle of several laser frequency stabilization methods are introduced.The femtosecond optical comb system used in the experimental system is introduced.The method of laser frequency stabilization based on femtosecond comb is proposed.With the photodetector,we can detect the beat note signal between the external cavity semiconductor laser with a wavelength of 698 nm and the light output by the optical comb system.The optical signal is converted into an electrical signal.The electrical signal enters the electrical system.After signal processing,the time domain signals of frequency difference is obtained by rapid digital sampling of the beat note signal.The time domain signal is transformed by FFT in the FPGA to find the peak frequency of beat note signal,and the frequency difference between laser and comb is obtained directly.The frequency locking is realized by digital PID algorithm.In experiment,the beat frequency optical path of 698nm external cavity semiconductor laser and femtosecond optical comb is built.In the electrical part,voltage stabilized power supply,low noise power amplifier,signal limiting circuit and signal bias circuit are designed and manufactured.The parameters selection of data acquisition card and FPGA are analyzed and explained,and the electrical part is made into a FFT laser frequency locking controller.Finally,the frequency stabilization experiment of 698nm external cavity semiconductor laser was carried out.By analyzing the beat note signal data of the frequency stabilization system,it shows that the second-order stability of the system reaches about 3.6×10^-11,which meets the design requirements of the frequency stabilization system.The stability can meet the requirements of most practical applications.