| In recent years,with the rapid development of ultrafast optical technology,a technology called femtosecond laser frequency comb has become the focus of many scientific research scholars.The femtosecond laser frequency comb has excellent time-frequency characteristics and ultra-high resolution.It has broad application prospects in high-end equipment manufacturing,industrial measurement,and other fields that rely on high-precision absolute distance measurement.The dual-comb ranging system developed from femtosecond laser frequency comb generates reference interference signal and measurement interference signal through an asynchronous optical sampling of two optical combs with a small repetition rate difference,The time information can be obtained and the distance can be calculated according to the envelope peak position of the two interference signals.The system has the characteristics of fast speed,high resolution,and high precision.Although the distance measurement system based on dual-comb light source has greatly developed the distance measurement technology,there are still many problems to be solved in the system,such as the stability of repetition rate and poor repetition rate,the sustainability of system operation,the miniaturization and portability of the system and so on.In this thesis,various factors affecting the stability of repetition frequency and repetition frequency difference of dual-comb ranging system are studied and analyzed.The temperature control,integration,and miniaturization of the system are designed.The locking loop is designed and built based on phase-locked loop technology to realize the precise locking of repetition rate and repetition rate difference.The dual-comb ranging experiment is carried out.The main research contents of this paper are as follows:(1)Aiming at the problem that temperature,environmental disturbance,pump source current,and other factors affect the repetition frequency stability of femtosecond laser frequency comb,a temperature control scheme is designed to accurately control the temperature in the laser cavity atą0.2?;Through mechanical integration design,a compact double optical comb system is obtained.The system is isolated from the external environment with a high-density aluminum plate,which improves the stability of the system;Through experimental analysis,the best working current of the pump source is 1000m A.(2)Aiming at the problem of controlling the repetition rate of femtosecond laser frequency comb,the relationship between the cavity length and repetition rate of femtosecond laser frequency comb is studied and analyzed,and piezoelectric ceramics is selected to control the cavity length;Through experiments,the jitter range of the repetition rate of the dual-comb system under free operation within 24 hours is 1.37574k Hz.According to the jitter range,the appropriate piezoelectric ceramics are selected and the installation mode is designed.It is tested that the maximum range of the tunable repetition rate of the piezoelectric ceramics selected in this subject is 1.58k Hz,which is greater than the jitter range of the repetition rate,which proves that the control of the repetition rate can be realized.(3)Aiming at the problem of femtosecond laser frequency comb repetition rate locking,two femtosecond laser frequency comb repetition frequency locking systems based on the same reference signal source are designed based on the principle of phase-locked loop,Through the noise analysis of the locking loop,appropriate key devices are selected to build the locking system,and finally the repetition rate locking of two femtosecond laser frequency combs is realized;When the average time is 1s,the Allan deviation of the repetition rate of the dual-comb is 1.074×10-13and 1.841×10-13.When the average time is100s,the Allan deviation of the repetition rate of the dual-comb reaches 4.4×10-14 and7.86×10-14.(4)Aiming at the problem that the stability of the repetition rate difference affects the ranging results in the dual-comb ranging system,The influence of the dual-comb system on ranging when the repetition rate difference is not locked is studied and analyzed,which realizes the precise locking of the repetition rate difference.When the average time is 1s,the Allan deviation of the repetition rate difference is 1.8×10-13.When the average time is 100s,the Allan deviation of repetition rate difference reaches 1.579×10-14.To miniaturize the dual-comb ranging system,the asynchronous locking device with different repetition rates is integrated and encapsulated.After locking the repetition rate difference,we cooperated with other students in the research group to carry out the dual-comb ranging experiment,and finally realized a single measurement of 4.85?m,and when the average time reaches 19ms,the ranging accuracy can be improved to 271nm,The ranging accuracy meets the needs of absolute distance measurement application in the industrial field. |
PDF Full Text Request