Research On Femtosecond Frequency Comb Repetition Frequency Control And Pulse Width Measurement

Femtosecond optical frequency combs show ultrashort pulse sequences in the time domain and equidistant comb-like multispectral spectra in the frequency domain.They have attracted the attention of scholars at home and abroad since the date of birth,and they have been used in precision spectroscopy and high-precision laser ranging.Other areas have potential significant application value.The frequency-domain key parameters of femtosecond frequency combs include the repetition frequency that characterizes the comb spacing and the bias frequency that represents the zero-order comb frequency.The frequency of any comb can be multiplied by the repetition frequency,plus the repetition frequency.The bias frequency is calculated.In order to realize the above-mentioned high-precision measurement,it is indispensable to control the frequency stabilization of the femtosecond optical frequency comb.At the same time,in order to accurately understand the time domain state of femtosecond optical combs,the measurement of pulse width is also indispensable.In view of the above two application requirements,the subject has performed the research on the repetition frequency control and pulse width measurement of femtosecond optical frequency combs.The specific contents include:1.For femtosecond optical combs affected by environmental vibration,power jitter and other factors,the repetition frequency within a certain range of rapid changes,first analyzed the basic structure of the fiber ring cavity to generate femtosecond optical frequency comb,verify the ring cavity The effect of the cavity length on the repetition frequency was designed.The cavity length adjustment mechanism based on piezoelectric ceramics was designed.A repetition frequency stabilization control unit based on analog phase lock was designed and implemented.In 5 minutes,the repetition frequency of the femtosecond frequency comb can be stably controlled within 0.20 Hz.2.In response to the problem of ambient temperature changes leading to a wide range of femtosecond frequency comb repetition frequency drift,the thermal sensitivity coefficient of the fiber ring cavity length was tested,a nd the temperature compensation requirement was determined according to the cavity length adjustment range of the piezoelectric ceramic.In order to place a constant temperature mechanism of an optical fiber ring cavity,an optical fiber ring cavity constant-temperature unit based on PID control was designed and implemented.It can realize the precise thermostatic control of the fiber ring cavity at the target temperature.At the target temperature of 18.5 °C,the precision temperature control of the optica l fiber ring cavity is achieved in the range of less than 0.12 °C.Combined with the analog phase-locked repetition frequency control unit,the stable control of the femtosecond frequency comb repetition frequency in the range of 0.20 Hz was achieved withi n one hour.3.For femtosecond optical comb pulse is too narrow,it is difficult to directly measure the pulse width problem,the use of two-photon absorption autocorrelation detection principle,first with reversed-pumped erbium-doped fiber amplifier to amplify femtosecond optical frequency comb energy,and then improve Michelson interferes with the optical path,oscillates a path mirror to form an optical path scan,detects and calculates the width of the two-photon absorption autocorrelation signal,and implements the back-calculation of the pulse width based on the correspondence between the autocorrelation signal and the pulse.A prototype was designed and implemented,and a preliminary test was conducted.