CN113746546B

CN113746546B - Optical frequency comb locking method and system based on event timing

Info

Publication number: CN113746546B
Application number: CN202111296737.9A
Authority: CN
Inventors: 陈法喜; 姜海峰; 李立波; 赵侃
Original assignee: Jinan Institute of Quantum Technology
Current assignee: Jinan Institute of Quantum Technology
Priority date: 2021-11-04
Filing date: 2021-11-04
Publication date: 2022-02-15
Anticipated expiration: 2041-11-04
Also published as: CN113746546A

Abstract

The invention provides an optical frequency comb locking method and system based on event timing, which adopt a high-precision event timer to realize precise digital phase comparison, do not need a frequency synthesizer to directly measure and calculate repetition frequency F_rAnd carrier envelope phase signal frequency F_ceoWith a frequency and phase difference from the set locking frequency value, a repetition frequency F of better than 1e-14/s can be achieved by closed-loop locking_rAnd a carrier envelope phase signal frequency F of better than 5e-18/s_ceoThe locking accuracy of (2). The optical frequency comb locking method based on event timing reduces a frequency synthesizer, saves the cost of optical frequency comb equipment, improves the locking precision, and flexibly sets the repetition frequency F_rAnd carrier envelope phase signal frequency F_ceoAnd the quality of the lock within the ring can be evaluated while locking.

Description

Optical frequency comb locking method and system based on event timing

Technical Field

The invention relates to the technical field of frequency control, in particular to an optical frequency comb locking method and system based on event timing.

Background

The optical frequency comb is an important means for linking optical frequency and radio frequency, is the most effective tool for absolute optical frequency measurement so far, can accurately and simply link a microwave atomic frequency standard and an optical frequency standard,the carrier is provided for developing a frequency standard with high resolution, high precision and high accuracy, an ideal research tool is provided for scientific research directions such as precise spectrum, astronomical physics, quantum control and the like, and the carrier has wide application space in the fields of optical frequency precision measurement, atomic ion transition energy level measurement, remote signal clock synchronization, satellite navigation and the like. The application process of the optical frequency comb has a repetition frequency F_rWith carrier envelope phase signal frequency F_ceoThe two parameters are required to be accurately controlled, and the control precision directly influences the core index and the use effect of the final optical frequency comb.

For example, patent document CN111609790A discloses a method and an apparatus for processing high-precision phase frequency and phase detection signals in laser offset frequency locking. Tunable laser and femtosecond optical frequency comb pass through a beat frequency signal detection unit to obtain beat frequency signals, and the beat frequency signals are subjected to analog-to-digital sampling and then enter an FPGA development board for frequency and phase discrimination. Multiplying the beat frequency signal by a reference signal, performing low-pass filtering, obtaining a corresponding phase through a coordinate rotation arithmetic unit, performing scaling processing after phase unwrapping, outputting an error voltage signal to an analog PID controller through a digital-to-analog converter, generating a control signal by the analog PID controller to a tunable laser for closed-loop control, locking the frequency of the beat frequency signal to the reference signal, and calculating the signal-to-noise ratio, the frequency and the amplitude of the beat frequency signal.

For another example, in patent document CN103746689A, a lock detector for use in a PLL frequency synthesizer is disclosed, which includes a digital lock detector and an analog lock detector; the digital lock detector comprises a phase discrimination pulse width detector, a phase discrimination pulse period detector, an inverter INV3 and a D flip-flop DFF 4; two input ends of the analog lock detector are connected with an UP signal and a DOWN signal output by a phase frequency detector of a PLL frequency synthesizer; the analog lock detector is used for outputting a phase detection pulse signal W1 and an analog lock detection signal.

It can be seen that in the prior art, the repetition frequency F_rAnd carrier envelope phase signal frequency F_ceoThe control of the frequency synthesizer is often realized by adopting analog mixing or phase discrimination to realize frequency phase locking technology, and the technology needs to adopt a frequency synthesizerGenerating and repeating frequency F_rAnd carrier envelope phase signal frequency F_ceoTwo signals of the same frequency or fractional frequency. In order to obtain a high lock stability index, the technique puts very high demands on the frequency synthesizer, which makes it difficult to improve the lock accuracy of the optical-frequency comb. Particularly, when the radio frequency signal is used for locking the repetition frequency of the optical frequency comb, the performance index of the frequency synthesizer can only reach 1e-13/s, so that the stability of locking the repetition frequency of the optical frequency comb by using the radio frequency signal is difficult to be better than 1 e-13/s.

Disclosure of Invention

In order to solve the technical problems, the invention provides an optical frequency comb locking method and system based on event timing, which adopt a high-precision event timer to realize precise digital phase comparison, and do not need a frequency synthesizer to directly measure and calculate repetition frequency F_rAnd carrier envelope phase signal frequency F_ceoWith a frequency and phase difference from the set locking frequency value, a repetition frequency F of better than 1e-14/s can be achieved by closed-loop locking_rAnd a carrier envelope phase signal frequency F of better than 5e-18/s_ceoThe locking accuracy of (2).

The optical frequency comb locking method based on event timing reduces a frequency synthesizer, saves the cost of optical frequency comb equipment, improves the locking precision, and flexibly sets the repetition frequency F_rAnd carrier envelope phase signal frequency F_ceoAnd the quality of the lock within the ring can be evaluated while locking.

An optical frequency comb locking method based on event timing comprises the following steps:

the method comprises the following steps: passing the optical part of the optical frequency comb through F_rIncluding repetition frequency F of controller output_rThe optical signal of frequency and phase information is input to a first photodetector, and converted to include a repetition frequency F_rWhile passing the optical part of the optical comb through F_ceoOutput of the controller containing carrier envelope phase frequency F_ceoThe optical signal of the frequency and phase information is input to a second photoelectric detector and converted into an optical signal containingCarrier envelope phase frequency F_ceoElectrical signals of frequency and phase information of;

step two: the first adjustable band-pass filter and the second adjustable band-pass filter respectively filter the electric signals output by the first photoelectric detector and the second photoelectric detector;

step three: outputting the reference frequency signal into two paths of signals which are respectively used as the reference frequency signals of a first event timer and a second event timer;

step four: event timer one will include repetition frequency F after filtering_rThe electrical signal containing the frequency and phase information is subjected to M frequency division, and the event timer II is used for filtering the electrical signal containing the carrier envelope phase frequency F_ceoThe electrical signal of frequency and phase information of (a) is divided by N;

step five: event timer measures the electrical signal divided by M, divides the frequency to F_rThe value at the time of each rising edge of the electrical signal,/M, is denoted tr_iEvent timer two measures the electrical signal divided by N, and divides the frequency into F_ceoThe time value of each rising edge of the/N electrical signal is denoted as tc_jThe phase difference calculator is based on tr_iCalculating the repetition frequency F_rReal-time frequency signal and repetition frequency F_rSet value F_rsetPhase error P between_EFriThe second phase difference calculator is according to tc_jCalculating carrier envelope phase frequency F_ceoReal-time frequency signal and carrier envelope phase frequency F_ceoSet value F_ceosetPhase error P between_EFceoi，

The phase error P_EFriThe calculation method of (2) is as follows:

；

the phase error P_EFceoiThe calculation method of (2) is as follows:

；

wherein M, N is frequency division number, i and j are specific time;

step six: digital regulator based on phase error P_EFriCalculating a digital-to-analog converter for controlling the repetition frequency F_rThe first digital-to-analog converter outputs an analog signal according to the control quantity DA1, and drives the F through the first driver_rA controller for realizing a repetition frequency F of the optical part of the optical frequency comb_rControl of real-time frequency of (a); two data phase errors P of digital regulator_EFceoiCalculating the envelope phase frequency F of the second control carrier of the digital-analog converter_ceoAccording to the control quantity DA2, the second digital-analog converter outputs an analog signal according to the control quantity DA2, and drives F through the second driver_ceoA controller for realizing carrier envelope phase frequency F of optical frequency comb_ceoControl of real-time frequency of (a);

step seven: repeating the fifth step and the sixth step to realize the repetition frequency F of the optical part of the optical frequency comb_rAnd carrier envelope phase frequency F_ceoIs controlled precisely.

Further, in the second step, the center frequency of the first tunable bandpass filter is preset at F_rSet value of (F)_rset+/-1 MHz, the central frequency of the second adjustable band-pass filter is preset at the carrier envelope phase frequency F_ceoSet value of (F)_ceoset±1MHz。

Further, in the third step, the reference frequency signal is locked to the standard frequency signal of the external radio frequency reference signal, and the range is 100MHz to 200 MHz.

Further, in the fourth step, the selection principle of the frequency division values M and N is as follows: at the guaranteed repetition frequency F_rAnd carrier envelope phase frequency F_ceoOn the premise that the frequency values after frequency division are all smaller than or equal to 20MHz, the smaller the values of M and N are, the better the frequency division is.

A locking system for implementing an event timing based optical-frequency comb locking method, comprising:

an optical-frequency comb optical portion comprising F_rController and F_ceoA controller for controlling the operation of the electronic device,said F_rThe controller is used for outputting a signal containing a repetition frequency F_rOf frequency and phase information of said optical signal, said F_ceoThe controller is used for outputting a frequency F containing a carrier envelope phase_ceoThe frequency and phase information of;

the first photoelectric detector and the second photoelectric detector are respectively connected with F_rController and F_ceoA controller for respectively including the repetition frequencies F_rAnd contains the carrier envelope phase frequency F_ceoThe optical signal of the frequency and phase information is converted into an electrical signal;

the first adjustable band-pass filter and the second adjustable band-pass filter are respectively connected with the output ends of the first photoelectric detector and the second photoelectric detector and are used for respectively filtering the electric signals output by the first photoelectric detector and the second photoelectric detector;

an event timer is connected with the output end of the first tunable band-pass filter, and the output end of the first tunable band-pass filter contains the repetition frequency F_rThe second event timer is connected with the output end of the second adjustable band-pass filter, and the phase frequency F containing the carrier envelope and output by the second adjustable band-pass filter_ceoThe electrical signal of (a) is subjected to N frequency division;

the phase difference calculator I is connected with the output end of the event timer I and used for calculating the repetition frequency F_rReal-time frequency signal and its set value F_rsetPhase error P between_EFri(ii) a The second phase difference calculator is connected with the output end of the second event timer and used for calculating the carrier envelope phase frequency F_ceoReal-time frequency signal and its set value F_ceosetPhase error P between_EFceoi；

A digital regulator connected with the output end of the phase difference calculator I and used for regulating the phase difference according to the phase error P_EFriCalculating the repetition frequency F_rThe second digital regulator is connected with the output end of the second phase difference calculator and is used for calculating the phase difference according to the phase error P_EFceoiCalculating carrier envelope phase frequency F_ceoThe control amount DA 2;

the first digital-to-analog converter is connected with the output end and the root of the first digital regulatorThe analog signal is output according to the control quantity DA1, and is input to F of the optical part of the optical-frequency comb through a driver_rA controller for realizing the repetition frequency F_rReal-time frequency phase control; the second digital-to-analog converter is connected with the output end of the second digital regulator, outputs an analog signal according to the control quantity DA2 and inputs the analog signal into the F of the optical part of the optical frequency comb through the second driver_ceoA controller for realizing carrier envelope phase frequency F_ceoReal-time frequency phase control.

Further, the repetition frequency F is changed by a phase difference calculator_rSet value of (F)_rsetSetting the center frequency of the first tunable bandpass filter at F_rset1MHz, realizing a repetition frequency F of combing the optical frequency of the optical part_rLocking on the new set frequency value; changing carrier envelope phase frequency F by phase difference calculator_ceoSet value F_ceosetSetting the center frequency of the second tunable bandpass filter at F_ceoset+/-1 MHz, realizing the carrier envelope phase frequency F of the optical part of the optical frequency comb_ceoLocking onto the new set frequency value.

Further, a driver I converts the voltage signal outputted from the phase difference calculator I into an F signal suitable for driving the optical part of the optical frequency comb after passing through a digital regulator I and a digital-to-analog converter I_rA high voltage signal of the controller; the second driver converts the voltage signal output by the second phase difference calculator into F suitable for driving the optical part of the optical frequency comb after passing through the second digital regulator and the second digital-to-analog converter_ceoA current signal of the controller.

Further, said F_rThe controller comprises a piezoelectric ceramic piece and an electro-optical modulator, wherein F_ceoThe controller is a pump laser tube of the seed laser.

Has the advantages that: optical frequency comb locking method based on event timing, and event timer is used for repeating frequency F_rAnd carrier envelope phase frequency F_ceoThe frequency phase measurement without dead zone realizes precise digital phase comparison, the single comparison precision is better than 3ps, the comparison rate is more than 20MHz, the locking bandwidth better than 1MHz can be realized, and the method can be applied to a frequency-free synthesizerFlexible setting of repetition frequency F in case of a failure of a power supply_rAnd carrier envelope phase frequency F_ceoThe locking frequency of (1). Through experiments, the optical frequency comb locking method based on event timing can realize the repetition frequency F superior to 1e-14/s_rFrequency phase measurement and control accuracy, and F is better than 5e-18/s_ceoThe locking accuracy of (2). At the same time as the event timer is counting the repetition frequency F_rAnd carrier envelope phase frequency F_ceoPerforming frequency-phase measurements without dead zones, i.e. evaluating the quality of the lock in the loop while locking, for a repetition frequency F_rThe evaluated frequency stability platform is superior to 8e-18/100000s, and the carrier envelope phase frequency F_ceoThe frequency stability plateau evaluated was better than 1e-12/100000 s.

The terms used herein are explained as follows:

the optical frequency comb is based on mode-locked femtosecond pulse laser technology and can conveniently, reliably and accurately lock the optical frequency to the reference frequency. The basic principle is as follows: the output of the pulse laser is a series of ultrashort pulses with equal intervals in the time domain, the pulse width is generally several to dozens of femtoseconds, the repetition frequency is several hundred MHz to several GHz, and the pulse laser is an optical comb consisting of a series of equally spaced spectral lines in the frequency domain, and the interval between every two comb teeth is equal to the repetition frequency of the femtosecond laser.

An event timer is a device for measuring the arrival time of a recording pulse. The basic principle is as follows: the event timer runs a system time inside, and when the detected pulse signal arrives, the arrival time of the rising edge or the falling edge of the pulse is accurately recorded. The single measurement resolution of the event timer can reach ps magnitude, and the maximum timing rate is about 20MHz when the frequency is not divided.

M-division or N-division, since the maximum timing rate of the event timer is around 20MHz, and F_rAnd F_ceoOften in the order of hundreds of MHz, pair F in order for the event timer to function properly_rPerforming frequency division of M, F_ceoThe measured signal input to the event timer is within a reasonable range by dividing by N. M and N are each such that F_rAnd F_ceoThe smallest positive integer less than 20MHz after frequency division.

The carrier envelope phase is a very important parameter of the periodic-magnitude laser pulse, and is a relative phase between the maximum value of the periodic-magnitude pulse envelope and the maximum value of electric field oscillation under the envelope.

Drawings

FIG. 1 is a flow chart of an event timing based optical-frequency comb locking method of the present invention;

FIG. 2 is a schematic diagram of the overall structure of an event timing-based optical-frequency comb locking system according to the present invention;

fig. 3 is a schematic illustration of the electrical signal of the present invention being divided.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the following is a more detailed description of the present invention with reference to the accompanying drawings by way of examples, but the embodiments of the present invention are not limited thereto. It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The term "comprising", without further limitation, means that the element so defined is not excluded from the group consisting of additional identical elements in the process, method, article, or apparatus that comprises the element.

Referring to fig. 1, it is a flow chart of the locking method of optical-frequency comb based on event timing of the present invention, comprising the following steps:

1. passing the optical part of the optical frequency comb through F_rIncluding repetition frequency F of controller output_rThe optical signal of the frequency and phase information is input to the first photodetector PD and converted to include the repetition frequency F_rWhile passing the optical part of the optical comb through F_ceoOutput of the controller containing carrier envelope phase frequency F_ceoThe optical signal of frequency and phase information is input to a second photodetector PD and converted into a signal containing a carrier envelope phase frequency F_ceoOf frequency and phase informationAn electrical signal.

2. Due to the inclusion of the repetition frequency F_rAnd an electrical signal containing carrier envelope phase frequency F_ceoThe electrical signals of the frequency and phase information of (2) include electrical signals of other frequencies, so it is necessary to filter the electrical signals output by the photodetector PD i and the photodetector PD ii by the tunable bandpass filter i and the tunable bandpass filter ii, respectively, and output electrical signals including the repetition frequency F_rAnd an electrical signal containing carrier envelope phase frequency F_ceoThe frequency and phase information of the electrical signal, facilitating subsequent frequency division and event timing. The center frequency of the first tunable bandpass filter is set in advance at a repetition frequency F_rSet value of (F)_rset+/-1 MHz, preferably 200MHz +/-1 MHz, and the central frequency of the second adjustable band-pass filter is set in advance at the carrier envelope phase frequency F_ceoSet value of (F)_ceoset. + -. 1MHz, preferably 270 MHz. + -. 1 MHz.

3. And outputting the reference frequency signal into two paths of signals which are respectively used as the reference frequency signals of the event timer I and the event timer II and used for referencing the clock of the event timer so as to time. The reference frequency signal is generally 100 MHz-200 MHz, and can be locked on a standard frequency signal of an external radio frequency reference signal, such as an atomic clock signal with high stability; in the preferred embodiment, the reference frequency signal is chosen to be 100 MHz. The reference frequency signal is preferably output by a high stability crystal oscillator.

4. Event timer one will include repetition frequency F after filtering_rThe electrical signal containing the frequency and phase information is subjected to M frequency division, and the event timer II is used for filtering the electrical signal containing the carrier envelope phase frequency F_ceoThe electrical signal of frequency and phase information of (a) is divided by N; to ensure that the two event timers can properly make measurements.

An event timer is a device used to measure and record the arrival time of a signal, and when the measured signal arrives, the arrival time of the rising or falling edge of the signal is accurately recorded. The single measurement resolution of the event timer can reach ps magnitude, and the maximum timing rate without frequency division is about 20 MHz. Therefore, the event timer is internally provided with the programmable frequency divider, and the frequency of the arriving signal is divided by M or N, so that the frequency range of the input signal can be increased.

The division values M and N are selected in such a way that the repetition frequency F is guaranteed_rAnd carrier envelope phase frequency F_ceoOn the premise that the frequency values after frequency division are all less than or equal to 20MHz, the values of M and N need to be as small as possible. In a preferred embodiment, the value of M is 10, and the value of N is 15, when the center frequency of the first tunable bandpass filter is preset to 200MHz, and the center frequency of the second tunable bandpass filter is preset to 270MHz, the center frequency includes the repetition frequency F_rThe electrical signal is divided to obtain a signal with a repetition frequency of 20MHz and containing a carrier envelope phase frequency F_ceoThe frequency of the electrical signal is divided to obtain a signal with 18MHz of carrier envelope phase frequency.

5. Event timer measures the electrical signal divided by M, divides the frequency to F_rThe value at the time of each rising edge of the electrical signal,/M, is denoted tr_iEvent timer two measures the electrical signal divided by N, and divides the frequency into F_ceoThe time value of each rising edge of the/N electrical signal is denoted as tc_j. Referring to fig. 3, a schematic diagram of the electrical signal being divided.

Phase difference calculator I according to tr_iCalculating the repetition frequency F_rReal-time frequency signal and repetition frequency F_rSet value F_rsetPhase error P between_EFriThe second phase difference calculator is according to tc_jCalculating carrier envelope phase frequency F_ceoReal-time frequency signal and carrier envelope phase frequency F_ceoSet value F_ceosetPhase error P between_EFceoi。

The phase error P_EFriThe calculation method of (2) is as follows:

；

the phase error P_EFceoiThe calculation method of (2) is as follows:

；

wherein 10 is a value of the frequency division number M, 15 is a value of the frequency division number N, and i and j are specific moments.

6. Digital regulator PID according to phase error P_EFriCalculating a digital-to-analog converter for controlling the repetition frequency F_rThe first digital-to-analog converter outputs an analog signal according to the control quantity DA1, and drives the F through the first driver_rThe controller realizes the repetition frequency F of the optical part of the optical frequency comb_rControl of real-time frequency of (a); two data phase error P of digital regulator PID_EFceoiCalculating the envelope phase frequency F of the second control carrier of the digital-analog converter_ceoAccording to the control quantity DA2, the second digital-analog converter outputs an analog signal according to the control quantity DA2, and drives F through the second driver_ceoThe controller realizes the carrier envelope phase frequency F of the optical frequency comb optical part_ceoControl of real-time frequency.

Due to F in the optical part of the optical-frequency comb_rThe control part needs high-voltage driving signals, so that the first driver converts voltage signals output by the first phase difference calculator into voltage signals suitable for driving the F in the optical part of the optical frequency comb after passing through the first digital regulator PID I and the first digital-to-analog converter I_rAnd controlling the high voltage signal of the part. In a preferred embodiment, the driver is a voltage amplifier.

The driver is used for converting the voltage signal output by the phase difference calculator II into F suitable for driving the optical part of the optical frequency comb after passing through the digital regulator PID II and the digital-to-analog converter II_ceoControlling the current signal of part to finally realize F_ceoThe current control of the control part, in the preferred embodiment, the driver is the current controller.

7. Repeating the fifth step and the sixth step, namely realizing the repetition frequency F of the optical frequency comb optical part_rAnd carrier envelope phase frequency F_ceoPrecise control of the frequency phase. It should be noted that this step is repeated for long term drift and short term disturbances of the system, so that the system achieves high accuracy。

The experiment proves that the invention can realize the repetition frequency F with the stability superior to 1e-14/s by adopting the optical frequency comb locking method based on the event timing_rFrequency phase measurement and control accuracy of (2) and carrier envelope phase frequency F with stability better than 5e-18/s_ceoThe locking accuracy of (2). At the same time as the event timer is counting the repetition frequency F_rAnd carrier envelope phase frequency F_ceoPerforming frequency-phase measurements without dead zones, i.e. evaluating the quality of the lock in the loop while locking, for a repetition frequency F_rThe evaluated frequency stability platform is superior to 8e-18/100000s, and the carrier envelope phase frequency F_ceoThe frequency stability plateau evaluated was better than 1e-23/100000 s. The stability value is the stability calculated by the Allan variance algorithm and is an important evaluation index in the time-frequency field. The frequency stability table refers to the frequency stability calculated by the long time axis, that is, the stability is no longer superior to the two stability values even if the time axis is longer.

Referring to fig. 2, there is shown a schematic diagram of an overall structure of a locking system for implementing an event timing-based optical-frequency comb locking method according to the present invention, the locking system including:

an optical-frequency comb optical part 10 comprising F_rControllers 10-1 and F_ceoController 10-2, said F_rThe controller is used for outputting a signal containing a repetition frequency F_rOf frequency and phase information of said optical signal, said F_ceoThe controller is used for outputting a frequency F containing a carrier envelope phase_ceoThe frequency and phase information of;

in a preferred embodiment, F_rThe controller comprises a piezoelectric ceramic wafer PZT for controlling the length of the optical cavity and an electro-optical modulator EOM, F_ceoThe controller is a pump laser tube of the seed laser. Specifically, F_rThe controller changes the position of the reflector in the piezoelectric ceramic piece PZT by controlling the length of the piezoelectric ceramic piece PZT to change the optical path so as to achieve the purpose of changing the cavity length, and modulates the phase, the amplitude, the intensity and the polarization state of an optical signal by controlling the refractive index of an electro-optical crystal in the electro-optical modulator EOM to change. F_ceoThe controller changes the laser power by changing the current of the pump laser tube, so that the dispersion of the laser in the cavity is changed, and the carrier envelope frequency difference is changed.

F is respectively connected with the first photoelectric detector PD 14 and the second photoelectric detector PD13_rControllers 10-1 and F_ceoTwo outputs of the controller 10-2 for respectively containing the repetition frequency F_rAnd contains the carrier envelope phase frequency F_ceoThe optical signal of the frequency and phase information is converted into an electrical signal; outputs are respectively composed of repetition frequencies F_rAnd carrier envelope phase frequency F_ceoOf the electrical signal of (a).

The first adjustable band-pass filter 15 is connected with the output end of the first photodetector PD 14, the second adjustable band-pass filter 16 is connected with the output end of the second photodetector PD13, and the first adjustable band-pass filter 15 and the second adjustable band-pass filter 16 respectively filter the electric signals output by the first photodetector PD 14 and the second photodetector PD 13.

The reference frequency signal outputs two signals which are respectively used as frequency references of the event timer I19 and the event timer II 20. The event timer one 19 is connected with the output end of the tunable bandpass filter one 15, and the tunable bandpass filter one 15 outputs a signal containing the repetition frequency F_rThe second event timer 20 is connected with the output end of the second tunable band-pass filter 20, and the second tunable band-pass filter 20 outputs a signal containing a carrier envelope phase frequency F_ceoTo ensure that the two event timers can properly make measurements.

The first phase difference calculator 23 is connected with the output end of the first event timer 19, the second phase difference calculator 24 is connected with the output end of the second event timer 20, and the first phase difference calculator 23 is used for calculating the repetition frequency F_rReal-time frequency signal and its set value F_rsetPhase error P between_EFriThe second phase difference calculator 24 is used for calculating the carrier envelope phase frequency F_ceoReal-time frequency signal and its set value F_ceosetPhase error P between_EFceoi；

The digital regulator PID one 21 is connected with the phase difference calculator one 23An output terminal for being according to P_EFriCalculating the repetition frequency F_rAnd the control quantity DA1 is inputted to the digital-to-analog converter one 17, and the analog signal outputted from the digital-to-analog converter one 17 is inputted to F of the optical-frequency comb optical portion 10 through the driver one 11_rA control section for realizing a repetition frequency F_rReal-time frequency phase control.

The second digital regulator PID 22 is connected with the output end of the second phase difference calculator 24, and the second digital regulator PID 22 is according to P_EFceoiCalculating carrier envelope phase frequency F_ceoAnd the control quantity DA2 is inputted to the second digital-to-analog converter 18, and the analog signal outputted from the second digital-to-analog converter 18 is inputted to F of the optical-frequency comb optical portion 10 through the second driver 12_ceoA control part for realizing carrier envelope phase frequency F_ceoReal-time frequency phase control.

The first driver converts the voltage signal output by the first phase difference calculator into F suitable for driving the optical part of the optical frequency comb after passing through the first digital regulator PID and the first digital-to-analog converter_rHigh voltage signal of controller. The second driver converts the voltage signal output by the second phase difference calculator into F suitable for driving the optical part of the optical frequency comb after passing through the second digital regulator PID and the second digital-to-analog converter_ceoA current signal of the controller.

By varying the repetition frequency F_rSet value of (F)_rsetThe system automatically sets the center frequency of the first tunable band-pass filter to F_rsetThe repetition frequency F of the optical frequency combing optical system can be realized by +/-1 MHz_rLocking on the new set frequency value; by varying the carrier envelope phase frequency F_ceoSet value F_ceosetThe system automatically sets the center frequency of the second tunable bandpass filter to F_ceosetThe carrier envelope phase frequency F of the optical frequency comb optical system can be realized by +/-1 MHz_ceoLocking onto the new set frequency value.

For the system embodiment, since it basically corresponds to the method embodiment, reference may be made to the partial description of the method embodiment for relevant points. The above-described system embodiments are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

The foregoing is directed to embodiments of the present invention, and it is understood that various modifications and improvements can be made by those skilled in the art without departing from the spirit of the invention.

Claims

1. An optical frequency comb locking method based on event timing is characterized by comprising the following steps:

the method comprises the following steps: passing the optical part of the optical frequency comb through F_rIncluding repetition frequency F of controller output_rThe optical signal of frequency and phase information is input to a first photodetector, and converted to include a repetition frequency F_rWhile passing the optical part of the optical comb through F_ceoOutput of the controller containing carrier envelope phase frequency F_ceoThe optical signal of the frequency and phase information is input to a second photoelectric detector and converted into a phase frequency F containing a carrier envelope_ceoElectrical signals of frequency and phase information of;

step four: event timer one will include repetition frequency F after filtering_rThe electric signal of the frequency and phase information is subjected to M frequency division, and an event timer is twoThe filtered envelope phase frequency F containing the carrier_ceoThe electrical signal of frequency and phase information of (a) is divided by N;

The phase error P_EFriThe calculation method of (2) is as follows:

；

the phase error P_EFceoiThe calculation method of (2) is as follows:

;

wherein M, N is frequency division number, i and j are specific time;

step six: digital regulator based on phase error P_EFriCalculating a digital-to-analog converter for controlling the repetition frequency F_rThe first digital-to-analog converter outputs an analog signal according to the control quantity DA1, and drives the F through the first driver_rA controller for realizing a repetition frequency F of the optical part of the optical frequency comb_rControl of real-time frequency of (a); two data phase errors P of digital regulator_EFceoiCalculating the envelope phase frequency F of the second control carrier of the digital-analog converter_ceoControl quantity DA2, numberThe second analog converter outputs an analog signal according to the control quantity DA2, and drives F through the second driver_ceoA controller for realizing carrier envelope phase frequency F of optical frequency comb_ceoControl of real-time frequency of (a);

2. The method as claimed in claim 1, wherein in the second step, the center frequency of the tunable bandpass filter is preset to F_rSet value of (F)_rset+/-1 MHz, the central frequency of the second adjustable band-pass filter is preset at the carrier envelope phase frequency F_ceoSet value of (F)_ceoset±1MHz。

3. The method as claimed in claim 1, wherein the reference frequency signal is locked to the standard frequency signal of the external RF reference signal in the third step, and the range is 100MHz to 200 MHz.

4. The method as claimed in claim 1, wherein the division values M and N are selected according to the following rules: at the guaranteed repetition frequency F_rAnd carrier envelope phase frequency F_ceoOn the premise that the frequency values after frequency division are all smaller than or equal to 20MHz, the smaller the values of M and N are, the better the frequency division is.

5. A locking system for implementing the event timing based optical-frequency comb locking method according to any one of claims 1 to 4, comprising:

an optical-frequency comb optical portion comprising F_rController and F_ceoController, said F_rThe controller is used for outputting a signal containing a repetition frequency F_rOf frequency and phase information of said optical signal, said F_ceoThe controller is used for outputting a frequency F containing a carrier envelope phase_ceoThe frequency and phase information of;

the first digital-to-analog converter is connected with the output end of the first digital regulator, outputs an analog signal according to the control quantity DA1 and inputs the analog signal into the F of the optical part of the optical-frequency comb through the first driver_rA controller for realizing the repetition frequency F_rReal-time frequency phase control; the second digital-to-analog converter is connected with the output end of the second digital regulator, outputs an analog signal according to the control quantity DA2 and inputs the analog signal into the F of the optical part of the optical frequency comb through the second driver_ceoA controller for realizing carrier envelope phase frequency F_ceoReal-time frequency phase control.

6. Locking system according to claim 5, characterized in that the repetition frequency F is changed by a phase difference calculator_rSet value of (F)_rsetSetting the center frequency of the first tunable bandpass filter at F_rset1MHz, realizing a repetition frequency F of combing the optical frequency of the optical part_rLocking on the new set frequency value; changing carrier envelope phase frequency F by phase difference calculator_ceoSet value F_ceosetSetting the center frequency of the second tunable bandpass filter at F_ceoset+/-1 MHz, realizing the carrier envelope phase frequency F of the optical part of the optical frequency comb_ceoLocking onto the new set frequency value.

7. The locking system of claim 5, wherein the driver converts the voltage signal outputted from the phase difference calculator into a voltage signal suitable for driving F in the optical portion of the optical comb after passing through the digital regulator and the digital-to-analog converter_rA high voltage signal of the controller; the second driver converts the voltage signal output by the second phase difference calculator into F suitable for driving the optical part of the optical frequency comb after passing through the second digital regulator and the second digital-to-analog converter_ceoA current signal of the controller.

8. The locking system of claim 5, wherein F_rThe controller comprises a piezoelectric ceramic piece and an electro-optical modulator, wherein F_ceoThe controller is a pump laser tube of the seed laser.