CN-121983845-A - Locking method for common-cavity double-optical-comb repetition frequency difference and related equipment

CN121983845ACN 121983845 ACN121983845 ACN 121983845ACN-121983845-A

Abstract

The invention relates to the technical fields of laser frequency stable control, precise spectrum measurement and optical metering, and discloses a locking method of a common-cavity double-optical-comb repetition frequency difference and related equipment. The method comprises the steps of obtaining two paths of repetition frequency signals of the double-optical comb mode-locked laser, digitally processing the repetition frequency signals to obtain an actual frequency value, calculating a control error of an actual frequency difference and a preset target value, outputting a digital control quantity through a digital algorithm module, converting the digital control quantity into an analog signal, feeding back and adjusting the resonant cavity length of the laser, inhibiting long-term drift of the frequency difference, and carrying out reset and re-locking when the control signal and the error are monitored in real time and the safety threshold is exceeded or the laser is out of lock. The invention solves the problem of long-term drift of the repetition frequency difference caused by slow-change factors such as environmental temperature drift, mechanical disturbance, device aging and the like.

Inventors

REN JIE
CHANG HONG

Assignees

中国科学院国家授时中心

Dates

Publication Date: 20260505
Application Date: 20260113

Claims (10)

1. The method for locking the repetition frequency difference of the co-cavity double optical combs is characterized by comprising the following steps of: Acquiring two paths of repetition frequency signals output by a double-optical comb mode-locked laser, and performing digital processing on the repetition frequency signals to obtain actual frequency values of the two paths of repetition frequencies; Calculating the actual frequency difference of the two paths of repetition frequencies based on the actual frequency value, and comparing the actual frequency difference with a preset target frequency difference to obtain a frequency difference control error; inputting the frequency difference control error into a digital algorithm module for operation, and outputting a digital control quantity; Converting the digital control quantity into an analog control signal, and feeding back and adjusting the resonant cavity length of the double-optical comb mode-locked laser to inhibit long-term drift of the repeated frequency difference; And monitoring the analog control signal and the frequency difference control error in real time, and executing reset and relock operations when detecting that the preset safety threshold value is exceeded or the lock losing state is exceeded.
2. The method for locking the repetition frequency difference of the double optical combs in the common cavity according to claim 1, wherein the step of obtaining the two paths of repetition frequency signals output by the double optical comb mode-locked laser specifically comprises the steps of respectively converting the two paths of pulse signals output by the double optical comb mode-locked laser into electric pulses by utilizing two paths of photoelectric detectors, amplifying and shaping the electric pulses, and inputting the electric pulses into two high-precision frequency counters to continuously acquire the two paths of repetition frequency signals.
3. The method for locking the repetition frequency difference of the co-cavity double optical combs according to claim 1, wherein the step of digitizing the repetition frequency signals specifically comprises the step of transmitting the acquisition result of the high-precision frequency counter to the FPGA control platform in a digital form in real time through a serial communication interface, so that additional noise is avoided from being introduced in analog signal transmission.
4. The method for locking the repetition frequency difference of the co-cavity double optical combs according to claim 1, wherein the obtaining of the actual frequency values of the two paths of repetition frequencies specifically comprises the steps of carrying out average processing or sliding filtering processing on the multiple acquisition results in each sampling period in the FPGA control platform, and obtaining the actual frequency values m1 and m2 of the two paths of repetition frequencies respectively.
5. The method for locking a repetition frequency difference of a co-cavity double optical comb according to claim 1, wherein a calculation formula for calculating an actual frequency difference of two paths of repetition frequencies is as follows: Δf=m1-m2 Comparing the actual frequency difference with a preset target frequency difference to obtain a calculation formula of a frequency difference control error as follows: e(t)=Δf-Δf0 wherein m1 and m2 are actual frequency values of two paths of repetition frequencies, Δf is an actual frequency difference of the two paths of repetition frequencies, Δf0 is a preset target frequency difference, and e (t) is a frequency difference control error.
6. The method for locking the repetition frequency difference of the co-cavity double optical combs according to claim 1, wherein the digital algorithm module comprises an FPGA (field programmable gate array) for carrying out digital PID (proportion integration differentiation) operation by taking a board local oscillator clock as a time reference, and the digital algorithm module realizes simultaneous suppression of slow variation drift and rapid disturbance of the repetition frequency difference through adjustment of proportional, integral and differential parameters.
7. The method for locking the repetition frequency difference of the co-cavity double optical combs according to claim 1, wherein the step of converting the digital control quantity into the analog control signal comprises the steps of converting the digital control quantity output by the FPGA into an analog voltage signal through digital-to-analog conversion, amplifying the analog voltage signal at high voltage, loading the analog voltage signal into piezoelectric ceramics in the co-cavity double optical comb mode-locked laser, and adjusting the optical length of the laser resonant cavity through expansion and contraction of the piezoelectric ceramics.
8. A system for locking a common-cavity double optical comb repetition frequency difference, comprising: the signal acquisition and processing module is used for acquiring two paths of repetition frequency signals output by the double-optical comb mode-locked laser, and performing digital processing on the repetition frequency signals to obtain actual frequency values of the two paths of repetition frequencies; The frequency difference error calculation module is used for calculating the actual frequency difference of the two paths of repeated frequencies based on the actual frequency value, and comparing the actual frequency difference with a preset target frequency difference to obtain a frequency difference control error; the digital operation module is used for inputting the frequency difference control error into the digital algorithm module for operation and outputting digital control quantity; The feedback adjusting module is used for converting the digital control quantity into an analog control signal, feeding back and adjusting the resonant cavity length of the double-optical comb mode-locked laser and inhibiting long-term drift of the repeated frequency difference; And the state monitoring module is used for monitoring the analog control signal and the frequency difference control error in real time, and executing resetting and relock operation when detecting that the preset safety threshold value is exceeded or the lock losing state is exceeded.
9. A mobile terminal comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor implements the steps of the method for locking the co-cavity double optical comb repetition frequency difference according to any of claims 1-7 when the computer program is executed.
10. A computer readable storage medium storing a computer program, characterized in that the computer program when executed by a processor implements the steps of the method for locking the co-cavity double optical comb repetition frequency difference according to any of claims 1-7.

Description

Locking method for common-cavity double-optical-comb repetition frequency difference and related equipment Technical Field The invention relates to the technical fields of laser frequency stable control, precise spectrum measurement and optical metering, in particular to a locking method of a common-cavity double-optical-comb repetition frequency difference and related equipment. Background The double optical comb technology is taken as a core technology with ultrahigh precision measurement potential, plays an important role in a plurality of high-end scientific fields such as precise spectrum measurement, optical frequency calibration, femtosecond laser ranging and the like, the measurement precision of the double optical comb technology directly depends on stable repetition frequency difference between two paths of coherent optical comb signals, and the stable repetition frequency difference is a core premise for realizing high-precision data sampling. In early implementations of dual optical comb systems, two independent optical frequency combs were typically employed for co-ordination. Because the two independent optical frequency combs are in different environments, the influence of the environmental noise is obviously different, so that the mutual dryness of the two optical frequency combs is difficult to ensure. To obtain high enough mutual dryness, a frequency or phase locking system with high bandwidth and complex structure must be configured, which severely limits the wide popularization and practical application of the double optical comb measurement technology [G. Ycas; F. R. Giorgetta; E. Baumann; I. Coddington; D. Herman; S. A. Diddams; N. R. Newbury, "High-coherence mid-infrared dual-comb spectroscopy spanning 2.6 to 5.2μm," Nature Photonics, 2018, 12(4): 202-208.]. In order to solve the defect of independent optical comb-connected cube, a common-cavity double-optical comb mode-locking laser becomes an important development trend in the field of double-optical comb light sources in recent years. The core design idea of the laser is to maintain two mode-locked laser oscillations in the same resonant cavity or partially share the two resonant cavities which are organically combined, and through the structural design, the environmental noise affecting the cavity length can be automatically counteracted, so that the inherent mutual coherence [S. M. Link; A. Klenner; M. Mangold; C. A. Zaugg; M. Golling; B. W. Tilma; U. Keller, "Dual-comb modelocked laser,"Optics Express, 2015, 23(5): 5521-5531.], of two optical combs is greatly improved, and the stability of the repetition frequency difference of the two optical combs is improved by several orders of magnitude. However, in practical application scenarios such as double optical comb spectrum, double optical comb ranging, etc., extremely high requirements are put on the stability of the double optical comb repetition frequency difference, and not only excellent short-term stability, but also long-term stability meeting high standards are required. The problem of long-term slow drift still exists in the repetition frequency difference of the existing common-cavity double-optical-comb mode-locked laser, and how to realize long-term stable locking of the double-optical-comb repetition frequency difference in a method as simple as possible is an important scientific problem to be solved in the current field. In view of the above technical problems, some related solutions have been proposed in the prior art, but all have obvious drawbacks: Rong Siju et al, in the infrared and laser engineering (2022, 51 (11): 20220108) disclose a "dual optical comb repetition frequency difference asynchronous locking technique", a core solution of the prior art, which is to lock against the repetition frequency difference of two independent dual optical comb mode-locked lasers, whose technical implementation relies on complex radio frequency signal generation and processing systems. For a common-cavity double-optical comb mode-locked laser with a compact structure and high inherent mutual coherence, the scheme is still complicated, cannot adapt to the application scene of the common-cavity structure, and is not beneficial to practical popularization. A phase-stabilized double optical comb interferometer technique based on an analog phase-locked loop and a pre-feedback is disclosed in Nature Communications by z Chen et al (2018, 9 (1): 3035). According to the technical scheme, on the basis of locking the repetition frequencies of two paths of optical combs to stable radio frequency references respectively, the acousto-optic frequency shifter is utilized for actively compensating the relative offset frequency, and although higher mutual dryness can be realized, a very complex electronic system and an optical system are involved, so that the whole system is huge and high in cost, and the application cost is too high for a co-cavity double-optical comb mode-locking laser.