Laser local oscillation device realized by using optical frequency comb and photoelectric phase-locked loop

Abstract

The invention discloses a laser local oscillation device realized by using an optical frequency comb and a photoelectric phase-locked loop, and belongs to the technical field of information transmission and processing. The device comprises a radio frequency module, an optical frequency comb generation module, a photoelectric phase-locked loop and a frequency control module, can perform radio frequency signal modulation with fixed frequency on input laser, and outputs comb-shaped frequency spectrum laser with fixed frequency intervals to enter the photoelectric phase-locked loop; by setting the parameters of the photoelectric phase-locked loop, the frequency corresponding to the specified comb teeth in the optical frequency comb can be locked, the interference of other comb teeth can be filtered out, and the local oscillation laser taking the radio frequency signal as the step can be output. According to the invention, ultrahigh-frequency, ultra-wide-bandwidth and large-frequency stepping local oscillation laser can be output. The system has the advantages of simplicity in implementation, high response speed, high integration degree, low resource consumption and the like, and is an important improvement on the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of information transmission and processing, and in particular to a laser local oscillator device realized by using an optical frequency comb and a photoelectric phase-locked loop. Background Art

[0002] Controllable frequency adjustment of the laser local oscillator is a basic requirement for optical communications, microwave photonic frequency converters, laser measurement, spectrum analysis and other applications. Currently, the controllable adjustment of laser frequency is mainly achieved by adjusting the temperature, current, resonant cavity size and other parameters of the laser. This direct tuning method has the disadvantages of poor frequency accuracy, large frequency drift and poor amplitude stability. Based on the fiber laser (OEO) that locks the external reference frequency, phase-locked frequency tuning can be completed by adjusting the fiber length. It has the advantage of high frequency accuracy, but it has the disadvantages of complex composition, slow response speed, large size and power consumption. Using a high-stable frequency laser as the reference optical frequency, there are mainly the following solutions in the technology of using an optoelectronic phase-locked loop to complete the controllable offset of the reference frequency:

[0003] (1) The broadband controllable adjustment of the laser frequency is obtained by using a radio frequency synthesizer for radio frequency mixing. Its performance is completely dependent on the radio frequency synthesizer and cannot give full play to the advantages of the optoelectronic phase-locked loop.

[0004] (2) The controllable adjustment of the laser frequency is achieved by using RF frequency division in an optoelectronic phase-locked loop. However, frequency division will not only cause the deterioration of the output phase noise of the optoelectronic phase-locked loop, but also the controllable frequency offset range that can be achieved is limited.

[0005] (3) An injection-locked laser is used to lock the teeth of an optical frequency comb. However, the frequency range of injection locking is too wide. The frequency interval of the comb teeth must be more than ten GHz to avoid mislocking. Therefore, it is not suitable for reference optical frequency offset with frequency steps ranging from several hundred MHz to several GHz. Summary of the invention

[0006] In view of this, the present invention proposes a laser local oscillator device realized by using an optical frequency comb and an optoelectronic phase-locked loop. The present invention modulates a radio frequency signal of a fixed frequency (several hundred MHz to several GHz) on the input laser, outputs a comb-shaped spectrum laser (optical frequency comb) with a fixed frequency interval into the optoelectronic phase-locked loop, and by setting the parameters of the optoelectronic phase-locked loop, the frequency corresponding to the specified comb teeth in the optical frequency comb can be locked, and the interference of other comb teeth can be filtered out, and the local oscillator laser with the radio frequency signal as the step can be output.

[0007] In order to achieve the above object, the technical solution provided by the present invention is:

[0008] A laser local oscillator device realized by using an optical frequency comb and an optoelectronic phase-locked loop, comprising an optical frequency comb generation module and an optoelectronic phase-locked loop, including a radio frequency module, an optical frequency comb generation module, an optoelectronic phase-locked loop and a frequency control module, wherein:

[0009] The radio frequency module includes a first frequency reference module, a DDS frequency synthesizer, and a switch; the switch selects signals from the first frequency reference module and the DDS frequency synthesizer under the control of the frequency control module, and outputs corresponding signals to the optical frequency comb generation module;

[0010] The frequency control module completes the parameter setting, monitoring and storage of the laser local oscillator device;

[0011] The optical frequency comb generation module, at a frequency of f c Driven by an RF signal, the frequency is f 0 The narrow line width laser is modulated to generate a frequency interval of f c The broadband comb spectrum signal light, and the comb teeth f 0 +mf c ~f 0 +nf c The power of is approximately equal; where f 0 +mf c is the minimum operating frequency of the laser local oscillator device, f 0 +nf c is the maximum operating frequency of the laser local oscillator device, m and n are integers, and the frequency f 0 +i*f c Corresponding to comb tooth i, i=0,-1,1,-2,2,...,-n,n;

[0012] The photoelectric phase-locked loop includes a DFB laser, an optical combiner, an optical coupler, a photodetector, an intermediate frequency filtering and amplifying module, a second frequency reference module, a frequency detector, a phase detector, a limiting loop filter, a frequency control module, an analog-to-digital converter, a frequency control module, an adder, and a current amplifier; wherein:

[0013] The frequency of the DFB laser output is f v Laser

[0014] The optical coupler divides the laser output from the DFB laser into two paths, one path enters the optical combiner, and the other path is used as the output light of the laser local oscillator device;

[0015] The optical combiner converts the frequency f transmitted by the optical coupler into v The laser and the comb spectrum signal from the optical frequency comb generation module are photosynthesized into a mixed optical signal;

[0016] The photodetector converts the mixed optical signal into a mixed electrical signal;

[0017] The intermediate frequency filtering and amplifying module filters and amplifies the mixed frequency electrical signal to obtain an intermediate frequency signal;

[0018] The second frequency reference module outputs the phase detection frequency f pd The signal is given to the frequency detector and phase detector;

[0019] The phase detector frequency of the second frequency reference module is f pd The signal and the intermediate frequency signal from the intermediate frequency filtering and amplification module are subjected to frequency and phase discrimination. The output of the frequency and phase detector enters the limiting loop filter, where the phase discrimination frequency is f pd The signal has the same center frequency as the intermediate frequency signal;

[0020] The output of the limiting loop filter is divided into two paths, one path is converted into a digital signal by an analog-to-digital converter and enters the frequency control module, and the other path is added with the voltage output by the digital-to-analog converter in an adder;

[0021] The output voltage of the adder enters the current amplifier and is converted into a driving current, and the driving current drives the DFB laser to generate laser;

[0022] When the photoelectric phase-locked loop is in the initial stage of operation, the frequency control module controls the entire laser local oscillator device to obtain the input control data of the digital-to-analog converter corresponding to each comb tooth used, and accordingly establishes a control data table corresponding to the comb teeth m to n;

[0023] When the photoelectric phase-locked loop works in a locked state, the lock detection signal output by the frequency detector is sent to the frequency control module, and the frequency control module monitors the operation of the phase-locked loop.

[0024] Furthermore, after the optoelectronic phase-locked loop is locked, the DFB laser outputs a laser frequency f v Equal to f 0 +if c +f pd , where i is the number of comb teeth selected.

[0025] Furthermore, in the initial stage of operation of the photoelectric phase-locked loop, the frequency control module controls the entire laser local oscillator device to obtain the input control data of the digital-to-analog converter corresponding to each comb tooth used, and accordingly establishes a control data table corresponding to the comb teeth m to n, specifically in the following manner:

[0026] (1) The frequency control range of the limiting loop filter output is less than f pd / 2;

[0027] (2) Find the digital-to-analog converter data corresponding to comb tooth n, specifically:

[0028] (21) Set the output frequency f of the DDS frequency synthesizer c2For nf c1 / r 1 , the control switch selects the signal of the DDS frequency synthesizer, and sets the digital-to-analog converter data to work at the comb frequency f 0 +nf c1 At the 4000A, adjust the DAC data until the optoelectronic phase-locked loop is locked, and then fine-tune the DAC data to make the limiting loop filter output at the ideal voltage, where n is the maximum comb value of the local oscillator frequency, r 1 Take the largest prime number less than n / 2;

[0029] (22) Control the output frequency f of the DDS frequency synthesizer c2 For nf c1 / r 2 , observe whether the optoelectronic phase-locked loop is locked or not, where r 2 Take the smallest prime number greater than n / 2;

[0030] (221) If the optoelectronic phase-locked loop cannot lock, the output frequency f of the DDS frequency synthesizer is controlled c2 For nf c1 / r 1 , adjusting the digital-to-analog converter data until the optoelectronic phase-locked loop locks to a different locking point, then fine-tuning the digital-to-analog converter so that the limiting loop filter outputs an ideal voltage, and then proceeding to step (22);

[0031] (222) If the optoelectronic phase-locked loop is locked, but the output of the limiting loop filter deviates from the ideal voltage by more than the threshold, then execute step (221);

[0032] (223) If the optoelectronic phase-locked loop is locked and the output of the limiting loop filter does not deviate from the ideal voltage by more than the threshold, then record the current digital-to-analog converter data to the position corresponding to n in the control data table;

[0033] (3) Set i=n-1 and find the DAC data corresponding to comb tooth i;

[0034] (4) controlling the switch to select the output of the first frequency reference module, so that the digital-to-analog converter data is fine-tuned unidirectionally from the determined i+1 to i, until the optoelectronic phase-locked loop is locked again from being unlocked, and then fine-tuning the digital-to-analog converter data so that the deviation between the output of the limiting loop filter and the ideal voltage does not exceed a threshold value;

[0035] (5) Control the output frequency f of the DDS frequency synthesizer c2 If c1 / r i , control the switch to select the output of the DDS frequency synthesizer and observe whether the optoelectronic phase-locked loop is locked or not. iTake a prime number near i / 2 that is not equal to i / 2; when i is a negative number, the frequency f c2 If c1 / r i The absolute value of

[0036] If the optoelectronic phase-locked loop cannot be locked, or the deviation between the output of the limiting loop filter and the ideal voltage exceeds the threshold, return to step (4);

[0037] If the optoelectronic phase-locked loop is locked and the deviation between the output of the limiting loop filter and the ideal voltage does not exceed the threshold, the current digital-to-analog converter data is recorded to the position corresponding to i in the control data table;

[0038] (6) Set i = i-1, and repeat steps (4) to (6) until i <m。

[0039] Furthermore, when the photoelectric phase-locked loop converts the working comb tooth frequency, the frequency control module first controls the phase-locked loop to open the loop, and presets the limiting loop filter to the ideal voltage, and then reads the table data corresponding to the new working comb tooth from the control data table and writes it into the digital-to-analog converter, and then closes the phase-locked loop after the current amplifier output is stable.

[0040] Furthermore, when the photoelectric phase-locked loop works in a locked state, the locking detection signal output by the frequency detector is sent to the frequency control module, and the frequency control module monitors the operation of the phase-locked loop in the following specific manner:

[0041] The output voltage of the limiting loop filter is converted into a digital voltage value by an analog-to-digital converter and transmitted to the frequency control module;

[0042] The frequency control module calculates the deviation between the digital voltage value and the ideal voltage, averages multiple deviations and then compensates them to the control data table corresponding to the current comb tooth, and uses the compensated table data the next time the comb tooth is used;

[0043] If it is monitored that the deviation between the current digital voltage value and the ideal voltage exceeds the threshold, the drift excess information is sent to the host system. Under the control of the host system, the frequency control module sets the digital-to-analog converter data to the compensated data, or slowly fine-tunes the digital-to-analog converter data until the deviation between the output voltage of the limiting loop filter and the ideal voltage does not exceed the threshold.

[0044] It can be seen from the above description that the beneficial effects of the present invention are:

[0045] 1. The present invention is based on the design of the output after comb-tooth selection filtering of the optical frequency comb, which realizes ultra-wideband frequency shifting of the laser frequency with the comb-tooth interval as a step, and can realize ultra-high frequency, ultra-wideband and high-precision adjustable frequency laser local oscillator.

[0046] 2. The present invention adopts a comb-tooth selection amplification implementation method based on a superheterodyne optoelectronic phase-locked loop, which can be flexibly designed by taking advantage of the high maturity of the phase-locked loop technology and the wide selection of optoelectronic devices.

[0047] 3. The present invention has the advantages of low requirements on the amplitude-frequency flatness of the optical frequency comb signal, high spurious suppression, stable output optical power, and automatic tracking of laser frequency drift.

[0048] 4. The present invention has the advantages of high integration, low cost, good manufacturability, high reliability, small size and low power consumption, and can be used as a key component of a microwave photonic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 It is a principle block diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0052] A laser local oscillator device realized by using an optical frequency comb and an optoelectronic phase-locked loop, such as Figure 1 As shown, it includes an optical frequency comb generation module, a first frequency reference module, a DDS frequency synthesizer, a switch, a DFB laser, an optical combiner, an optical coupler, a photodetector, an intermediate frequency filtering and amplification module, a second frequency reference module, a frequency detector, a limiting loop filter, a frequency control module, an analog-to-digital converter, a frequency control module, an adder, and a current amplifier. The device uses the step frequency f of the laser local oscillator to generate a frequency comb. c1 The same RF signal at the input frequency f 0 The laser is modulated, and the output has a fixed frequency interval f c1 The laser (optical frequency comb) with a comb spectrum is locked by the optical phase-locked loop with a frequency of f after setting the parameters corresponding to the i-th comb tooth of the superheterodyne optical phase-locked loop. 0 +if c1 The comb teeth are filtered out to filter out other comb teeth, and the output frequency is f 0 +if c1The figure shows the initial parameters of the optical phase-locked loop corresponding to each comb tooth. The f output by the DDS frequency synthesizer is used under the control of the frequency control module. c2 Perform comb parameter correction at the initial stage of the local oscillator.

[0053] Assume the frequency is f 0 The narrow linewidth laser enters the optical frequency comb generation module at a frequency of f c The frequency interval of the optical frequency comb generation module is f c The broadband comb spectrum signal light, and the comb teeth f 0 +mf c ~f 0 +nf c The power of is approximately equal, where f 0 +mf c is the minimum operating frequency of the laser local oscillator, f 0 +nf c is the maximum operating frequency of the laser local oscillator, m and n are integers, and the number of the comb teeth is the frequency f 0 Corresponding comb tooth 0, frequency f 0 +f c Corresponding comb tooth 1, frequency f 0 -f c Corresponding comb tooth -1, frequency f 0 +2f c Corresponding to comb tooth 2 and so on, and so on.

[0054] Here, m and n can be positive integers, negative integers or zero. In the following, n is assumed to be a positive integer. If m and n are negative integers or |m|>n, equivalent substitution can be performed.

[0055] The optoelectronic phase-locked loop works as follows:

[0056] (1) The frequency of the channel coupled by the DFB laser is f v The laser and the input comb spectrum signal light enter the optical combiner to form a mixed optical signal, which enters the photodetector and is converted into a mixed frequency electrical signal; the other frequency of the signal coupled out by the DFB laser is f v The laser is used as the output light of the laser local oscillator.

[0057] After the comb spectrum output by the optical frequency comb generation module enters the superheterodyne optoelectronic phase-locked loop for processing, the DFB laser outputs the selected comb tooth replica frequency. The superheterodyne optoelectronic phase-locked loop plays the role of selecting the comb spectrum and filtering out other comb spectra.

[0058] Here, the DFB laser can expand the loop bandwidth of the phase-locked loop by serially connecting an acousto-optic frequency shifter, a PM modulator, etc., or lasers such as SG-DBR lasers can be used instead of the DFB laser, but these solutions are relatively complicated.

[0059] (2) The mixed electrical signal is filtered and amplified by the intermediate frequency module to obtain the intermediate frequency signal. The frequency reference 2 outputs the phase detection frequency f pd The signal and the intermediate frequency signal are frequency- and phase-detected in the frequency detector, where the center frequency of the intermediate frequency filter and the phase-detection frequency are f pd Similarly, after the loop is locked, the intermediate frequency filter can effectively eliminate the clutter generated by other comb teeth mixing, such as f c1 -f pd To have a suppression of more than 50dB, pd Take f c1 / 4 is more appropriate.

[0060] In the embodiment, f pd Can be in 0~f c1 / 2, taking into account the filter design and phase-locked loop frequency discrimination characteristics, etc. pd In f c1 / 5~f c1 / 3 is a good value, where f pd Take f c1 / 4 has a better balance.

[0061] (3) The output of the frequency detector and phase detector enters the limiting loop filter. The limiting loop filter has filtering parameters designed according to the characteristics of the phase-locked loop. The center voltage of the output voltage after limiting is an ideal voltage, which can be changed to the ideal voltage instantaneously under control. The basis for selecting the limiting voltage range is that the change range of the DFB laser frequency controlled by the limited voltage output is not greater than 0.5f c1 The lock detection signal output by the frequency detector and phase detector is sent to the frequency control module.

[0062] It should be noted that in the embodiment, the control range of the output voltage of the limiting loop filter can be less than f c1 Choose from a wide range, taking into account the design requirements of each module of the phase-locked loop, and select 0.5f c1 When calibrating the input control data of the comb teeth corresponding to the analog-to-digital converter DA, you can choose to reduce the limit voltage range, such as taking 0.25f c1 .

[0063] (4) The output of the limiting loop filter is divided into two paths. One path is converted into a digital signal by an analog-to-digital converter (AD) and enters the laser frequency control module. The other path is added to the output voltage of the digital-to-analog converter (DA) in an adder. The output voltage of the adder enters a current amplifier and is converted into a drive current. The drive current drives the DFB laser to generate laser light. Adjusting the output voltage of the adder can control the DFB laser to output laser light in the required frequency range.

[0064] If the output voltage of the frequency detector is directly sampled by high-speed AD, and the high-speed DA output voltage is directly sent to the current amplifier, the Figure 1 The analog-to-digital converter, Figure 1 The limiting loop filter and adder can be implemented in the digital domain by DSP, FPGA and other chips using digital algorithms. This has flexible functional design, but has poor spurious performance and high cost.

[0065] Figure 1 The analog limiting loop filter and adder in the circuit can be realized by using devices such as operational amplifiers, which has the advantages of mature technology, simple circuit, fast locking speed, low cost and good spurious performance.

[0066] Furthermore, after the optoelectronic phase-locked loop is locked, the DFB laser outputs a laser frequency f v Equal to f 0 +if c +f pd , where i is the number of comb teeth selected.

[0067] The amplitude output variation of the local oscillator light coupled out by the DFB laser is small, the polarization is controllable and it is independent of the amplitude and polarization of the locking comb teeth.

[0068] Furthermore, in the initial stage of operation of the photoelectric phase-locked loop, the laser frequency control module controls the entire local oscillator device to obtain the DA input control data corresponding to each comb tooth used, and accordingly establishes a control data table corresponding to the comb teeth m to n. The specific steps include:

[0069] After the phase-locked loop locks any comb tooth, the data in the control data table corresponding to the comb tooth passes through the DA, so that the output voltage of the limiting loop filter is close to the ideal voltage. This step can only be completed after the voltage, temperature and other conditions of the entire laser local oscillator device are stable and the entire laser local oscillator device cooperates.

[0070] (1) Make the frequency control range of the limiting loop filter output smaller than f pd / 2.

[0071] This step is designed to improve the identification accuracy of the photoelectric phase-locked loop lock correction frequency. The frequency control range is f pd / 4 is better.

[0072] (2) Find the DA data corresponding to comb tooth n.

[0073] Search from the highest positive integer n, using nf c1 / r 1 With nf c1 / r 2 For all comb teeth with negative numbers, we should start from the smallest negative number.

[0074] (20) Set the output frequency f of the DDS frequency synthesizer (DDS) c2 For nf c1 / r 1 , control switch to select DDS f c2 output, set the DA data to work at the comb frequency f 0 +nf c1 At this point, adjust the DA data until the optoelectronic phase-locked loop is locked, and then fine-tune the DA data to make the limiting loop filter output the ideal voltage. Where n is the maximum comb value of the local oscillator frequency, r 1 The largest prime number that can be less than n / 2.

[0075] Working at frequency f 0 +nf c1 The budgeted DA data of the comb teeth may be the DA data corresponding to the comb tooth n calibrated last time, or may be the DA data corresponding to the comb tooth n calculated according to the hardware design.

[0076] In fact, the DDS can be part of other modules in a large system and can also be used as a correction source during initial calibration.

[0077] When n is negative, nf c1 / r 1 With nf c1 / r 2 The result needs to be taken as the absolute value.

[0078] (21) Control the output frequency f of DDS c2 For nf c1 / r 2 , observe whether the photoelectric phase-locked loop is locked or not. 2 The smallest prime number greater than n / 2 can be selected. Different laser local oscillators each have an optimal set of r 1 、r 2 .

[0079] Different local oscillator devices have an optimal set of n 1 、r 2 , but using prime numbers near n / 2 is more generally adaptable.

[0080] (22) If the optoelectronic phase-locked loop cannot lock, control the output frequency f of the DDS c2 For nf c1 / r 1 , adjust the DA data until the optoelectronic phase-locked loop locks to a different locking point, then fine-tune the DA to make the limiting loop filter output the ideal voltage, and then continue with the previous step.

[0081] Wrong lock other comb teeth such as f 0 +(n-1)f c1 、f 0 +(n+1)f c1 etc., cannot satisfy the simultaneous nf c1 / r 1 、nf c1 / r 2 Comb teeth interval locking. Follow these steps to determine whether the lock is accurate. 0 +nf c1 .

[0082] (23) If the optoelectronic phase-locked loop is locked, but the limiting loop filter output deviates from the ideal voltage by a large margin, proceed to the previous step.

[0083] According to system design and selection 1 、r 2 This situation may occur when the phase difference comb teeth n is large. A properly designed system has a DDS output frequency f c2 For nf c1 / r 1 When locked, the output frequency of the DDS is f c2 For nf c1 / r 2 Also an ideal locking point.

[0084] (24) If the optoelectronic phase-locked loop is locked and the limiting loop filter output is at the ideal voltage, the current DA data is recorded to the corresponding position n in the control data table.

[0085] After finding the highest working comb tooth, DA data of each comb tooth is corrected from high to low. In theory, the comb teeth found in sequence have a high accuracy rate.

[0086] (3) Initially, let n-1 be i and find the DA data corresponding to comb tooth i.

[0087] When searching from the smallest negative number m, we should set m+1 to i.

[0088] (30) Control switch to select frequency reference f c1Output, so that the DA data changes unidirectionally from the determined i+1 to i, until the optoelectronic phase-locked loop goes from unlocked to locked, and then fine-tunes the DA data to make the limiting loop filter at the ideal voltage.

[0089] (31) Control the output frequency f of DDS c2 If c1 / r i , control switch to select DDS f c2 Output, observe whether the photoelectric phase-locked loop is locked or not, where r i A prime number near i / 2 that is not equal to i / 2 can be selected; when i is a negative number, the frequency f c2 If c1 / r i The result needs to be the absolute value.

[0090] (32) If the optoelectronic phase-locked loop cannot be locked, or the limiting loop filter output deviates greatly from the ideal voltage, then repeat step (30).

[0091] (33) If the optoelectronic phase-locked loop is locked and the limiting loop filter output is at the ideal voltage, the current DA data is recorded to the corresponding position i in the control data table.

[0092] Since vibration and temperature affect the stability of the optoelectronic phase-locked loop system, when n is large, the output frequency f of the DDS needs to be adjusted. c2 If c1 / r i Verification ensures the accuracy of the control data table. Here, a prime number is used to verify the working frequency once.

[0093] (34) Search for the DA data corresponding to the lower comb tooth i-1, assuming that i-1 is i, and repeat step (30) until the lowest comb tooth m is used.

[0094] For i to be a negative number, it does not affect the correctness of the above process.

[0095] (35) When i takes the value of 2, 1, 0, -1, or -2, the DA data can be changed unidirectionally from i+1 to i. After the optoelectronic phase-locked loop loses lock, the loop can be locked again. Then, the DA can be fine-tuned to make the limiting loop filter output the ideal voltage. The current DA data can be recorded as the comb selection control table data corresponding to i.

[0096] For example, when the value of i is 1, the DA data can be changed unidirectionally from i=2 to i=1. After the photoelectric phase-locked loop loses lock, it can be locked again, and then the DA can be fine-tuned to make the limiting loop filter output the ideal voltage. The current DA data can be recorded as the DA data corresponding to i=1.

[0097] For example, when the value of i is -1, the DA data can be changed unidirectionally from i=0 to i=-1. After the photoelectric phase-locked loop loses lock, it can be locked again, and then the DA can be fine-tuned to make the limiting loop filter output the ideal voltage. The current DA data can be recorded as the DA data corresponding to i=-1.

[0098] Furthermore, when the photoelectric phase-locked loop converts the working comb frequency, the frequency control module first controls the phase-locked loop to open the loop, and presets the limiting loop filter to the ideal voltage, and then reads the table data corresponding to the new working comb from the control data table and writes it into DA, and then closes the phase-locked loop after the current amplifier output is stable.

[0099] The main purpose of this process is to speed up the phase-locked loop's locking time and prevent the phase-locked loop from mislocking other comb teeth.

[0100] Furthermore, when the optoelectronic phase-locked loop is operating in a locked state, the frequency control module monitors the operation of the phase-locked loop. The specific monitoring process is as follows:

[0101] The output voltage of the limiting loop filter is converted into a digital voltage value by an analog-to-digital converter, and the deviation between the digital voltage value and the ideal voltage is calculated. The deviation is averaged and compensated to the control data table corresponding to the current comb tooth, and the compensated table data is used the next time the comb tooth is used.

[0102] This can correct the input laser frequency f 0 DFB laser frequency drift over time.

[0103] If it is monitored that the deviation between the current digital voltage value and the ideal voltage exceeds the limit value, the drift excess information is sent to the system's overall control. Under the system control, the frequency control module of the local oscillator sets the DA data to the compensated data, or slowly fine-tunes the DA data until the deviation between the output voltage of the limiting loop filter and the ideal voltage is controlled within an appropriate range.

[0104] Different systems have different requirements for the laser local oscillator, and the methods of handling the deviation between the digital voltage value and the ideal voltage are also different.

[0105] In summary, the present invention can modulate the input laser with a fixed frequency radio frequency signal, output a laser (optical frequency comb) with a comb spectrum with a fixed frequency interval, enter the optoelectronic phase-locked loop, and lock the frequency corresponding to the specified comb teeth in the optical frequency comb by setting the parameters of the optoelectronic phase-locked loop, and filter out the interference of other comb teeth, and output the local oscillator laser with the radio frequency signal as the step. The present invention can output a large-step (more than several hundred MHz) local oscillator laser with ultra-high frequency (up to THz) and ultra-wide bandwidth signals. The present invention has the advantages of simple implementation, fast response speed, low spurious, and low resource consumption, and is an important improvement on the prior art.

[0106] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples. Any omissions, modifications, equivalent substitutions, improvements, etc. made to the above embodiments within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A laser local oscillator device realized by using an optical frequency comb and an optoelectronic phase-locked loop, characterized in that: It includes a radio frequency module, an optical frequency comb generation module, an optoelectronic phase-locked loop and a frequency control module, wherein: The radio frequency module includes a first frequency reference module, a DDS frequency synthesizer, and a switch; the switch selects signals from the first frequency reference module and the DDS frequency synthesizer under the control of the frequency control module, and outputs corresponding signals to the optical frequency comb generation module; The frequency control module completes the parameter setting, monitoring and storage of the laser local oscillator device; The optical frequency comb generation module, at a frequency of f c Driven by an RF signal, the narrow linewidth laser with a frequency of f0 is modulated to generate a frequency interval of f c The broadband comb spectrum signal light, and the comb teeth f0+mf c ~f0+nf c The power of is approximately equal; among them, f0+mf c is the minimum operating frequency of the laser local oscillator device, f0+nf c is the maximum operating frequency of the laser local oscillator device, m and n are integers, and the frequency f0+i*f c Corresponding to comb tooth i, i=0,-1,1,-2,2,...,-n,n; The photoelectric phase-locked loop includes a DFB laser, an optical combiner, an optical coupler, a photodetector, an intermediate frequency filtering and amplifying module, a second frequency reference module, a frequency detector, a phase detector, a limiting loop filter, a frequency control module, an analog-to-digital converter, a frequency control module, an adder, and a current amplifier; wherein: The frequency of the DFB laser output is f v Laser The optical coupler divides the laser output from the DFB laser into two paths, one path enters the optical combiner, and the other path is used as the output light of the laser local oscillator device; The optical combiner converts the frequency f transmitted by the optical coupler into v The laser and the comb spectrum signal from the optical frequency comb generation module are photosynthesized into a mixed optical signal; The photodetector converts the mixed optical signal into a mixed electrical signal; The intermediate frequency filtering and amplifying module filters and amplifies the mixed frequency electrical signal to obtain an intermediate frequency signal; The second frequency reference module outputs the phase detection frequency f pd The signal is given to the frequency detector and phase detector; The phase detector frequency of the second frequency reference module is f pd The signal and the intermediate frequency signal from the intermediate frequency filtering and amplification module are subjected to frequency and phase discrimination. The output of the frequency and phase detector enters the limiting loop filter, where the phase discrimination frequency is f pd The signal has the same center frequency as the intermediate frequency signal; The output of the limiting loop filter is divided into two paths, one path is converted into a digital signal by an analog-to-digital converter and enters the frequency control module, and the other path is added with the voltage output by the digital-to-analog converter in an adder; The output voltage of the adder enters the current amplifier and is converted into a driving current, and the driving current drives the DFB laser to generate laser; When the photoelectric phase-locked loop is in the initial stage of operation, the frequency control module controls the entire laser local oscillator device to obtain the input control data of the digital-to-analog converter corresponding to each comb tooth used, and accordingly establishes a control data table corresponding to the comb teeth m to n; When the photoelectric phase-locked loop works in a locked state, the lock detection signal output by the frequency detector is sent to the frequency control module, and the frequency control module monitors the operation of the phase-locked loop.

2. The laser local oscillator device realized by using an optical frequency comb and an optoelectronic phase-locked loop according to claim 1, characterized in that: After the optoelectronic phase-locked loop is locked, the DFB laser outputs the laser frequency f v equal to f0+if c +f pd , where i is the number of comb teeth selected.

3. The laser local oscillator device realized by using an optical frequency comb and an optoelectronic phase-locked loop according to claim 1, characterized in that: In the initial stage of operation of the photoelectric phase-locked loop, the frequency control module controls the entire laser local oscillator device to obtain the input control data of the digital-to-analog converter corresponding to each comb tooth used, and accordingly establishes a control data table corresponding to the comb teeth m to n, specifically in the following manner: (1) The frequency control range of the limiting loop filter output is less than f pd / 2; (2) Find the digital-to-analog converter data corresponding to comb tooth n, specifically: (21) Set the output frequency f of the DDS frequency synthesizer c2 For nf c1 / r1, control switch selects the signal of DDS frequency synthesizer, sets the digital-to-analog converter data to work at the comb frequency f0+nf as budgeted c1 At, adjust the digital-to-analog converter data until the optoelectronic phase-locked loop is locked, and then fine-tune the digital-to-analog converter data to make the limiting loop filter output at the ideal voltage, where n is the maximum comb value of the local oscillator frequency, and r1 is the largest prime number less than n / 2; (22) Control the output frequency f of the DDS frequency synthesizer c2 For nf c1 / r2, observe whether the optoelectronic phase-locked loop is locked or not, where r2 takes the smallest prime number greater than n / 2; (221) If the optoelectronic phase-locked loop cannot lock, the output frequency f of the DDS frequency synthesizer is controlled c2 For nf c1 / r1, adjust the digital-to-analog converter data until the optoelectronic phase-locked loop locks to a different locking point, then fine-tune the digital-to-analog converter to make the limiting loop filter output an ideal voltage, and then continue with step (22); (222) If the optoelectronic phase-locked loop is locked, but the output of the limiting loop filter deviates from the ideal voltage by more than the threshold, then execute step (221); (223) If the optoelectronic phase-locked loop is locked and the output of the limiting loop filter does not deviate from the ideal voltage by more than the threshold, then record the current digital-to-analog converter data to the position corresponding to n in the control data table; (3) Set i=n-1 and find the DAC data corresponding to comb tooth i; (4) controlling the switch to select the output of the first frequency reference module, so that the digital-to-analog converter data is fine-tuned unidirectionally from the determined i+1 to i, until the optoelectronic phase-locked loop is locked again from being unlocked, and then fine-tuning the digital-to-analog converter data so that the deviation between the output of the limiting loop filter and the ideal voltage does not exceed a threshold value; (5) Control the output frequency f of the DDS frequency synthesizer c2 If c1 / r i , control the switch to select the output of the DDS frequency synthesizer and observe whether the optoelectronic phase-locked loop is locked or not. i Take a prime number near i / 2 that is not equal to i / 2; when i is a negative number, the frequency f c2 If c1 / r i The absolute value of If the optoelectronic phase-locked loop cannot be locked, or the deviation between the output of the limiting loop filter and the ideal voltage exceeds the threshold, return to step (4); If the optoelectronic phase-locked loop is locked and the deviation between the output of the limiting loop filter and the ideal voltage does not exceed the threshold, the current digital-to-analog converter data is recorded to the position corresponding to i in the control data table; (6) Set i = i-1, and repeat steps (4) to (6) until i <m。 4. The laser local oscillator device realized by using an optical frequency comb and an optoelectronic phase-locked loop according to claim 1, characterized in that: When the photoelectric phase-locked loop converts the working comb tooth frequency, the frequency control module first controls the phase-locked loop to open the loop, and presets the limiting loop filter to the ideal voltage, then reads the table data corresponding to the new working comb tooth from the control data table and writes it into the digital-to-analog converter, and then closes the phase-locked loop after the current amplifier output is stable.

5. The laser local oscillator device realized by using an optical frequency comb and an optoelectronic phase-locked loop according to claim 1, characterized in that: When the photoelectric phase-locked loop works in a locked state, the lock detection signal output by the frequency detector is sent to the frequency control module, and the frequency control module monitors the operation of the phase-locked loop in the following specific manner: The output voltage of the limiting loop filter is converted into a digital voltage value by an analog-to-digital converter and transmitted to the frequency control module; The frequency control module calculates the deviation between the digital voltage value and the ideal voltage, averages multiple deviations and then compensates them to the control data table corresponding to the current comb tooth, and uses the compensated table data the next time the comb tooth is used; If it is monitored that the deviation between the current digital voltage value and the ideal voltage exceeds the threshold, the drift excess information is sent to the host system. Under the control of the host system, the frequency control module sets the digital-to-analog converter data to the compensated data, or slowly fine-tunes the digital-to-analog converter data until the deviation between the output voltage of the limiting loop filter and the ideal voltage does not exceed the threshold.

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