Study On Frequency Locking Of A Femtosecond Optical Frequency Comb

In recent years, with the continuous development of science and technology, high precision time and frequency standards play a central role in the field of scientific research, national defense and so on. Optical clocks can obtain higher stability than microwave atomic clock and become one of the directions of research scientists. Femtosecond optical frequency comb plays a role of connecting the RF and optical frequency. To satisfy the requirement of research, the author mainly study the frequency locking of a femtosecond optical frequency comb in this thesis.In order to realize the frequency locking of a femtosecond optical comb, the author investigate and survey about the phase-locked loops and automatic control, and compare the characteristics of the different phase and frequency detectors and different loop filters, ultimately make the need digital phase frequency/phase detector production plan and select PID controller as the loop filter.According to characteristics of the repetition frequency of an optical frequency comb, the devices required to build the locked loop are selected. In order to realize the precision locking of an optical frequency comb, the author also investigate and survey the definition of phase noise and its measurement principle, test and analyze the phase noise of the components used in the phase-locked loop and then select the devices with the lowest noise. The phase noise of the basic devices in the phase-locked loop are given, and the results of the locked frep are also given. For the locking time up to ten hours, the Allan deviation of the frep are 3×10^-13@1s and 2.3×10^-14@100s.In view of the difficulty of locking fCEO, the digital phase/frequency detector which is needed is designed and produced independently, when designing the scheme of locking fCEO. The test results of the circuit are given, when the first edition of the circuit didn't work well, the improvement and optimization of the circuit are done, the measured results of the modified circuit are shown. The Allan deviation of the fCEO which is produced by the system of Menlo optical frequency comb are 5.5×10^-11@1s and 9.0× 10^-12@100s when it is locked by the Menlo locking system. The Allan deviation of the fCEO are 6.5×10^-11@1s and 6.4×10^-12@100s when it is locked by the homemade locking system. The Allan deviation of the fCEO which is produced by homemade optical frequency comb is 1.6×10-⁶@1s when it is locked by homemade locking system.