Laser local oscillation device based on optical frequency comb and Brillouin filter

Abstract

The invention discloses a laser local oscillation device based on an optical frequency comb and a Brillouin filter, and belongs to the technical field of information transmission and processing. The device comprises a laser, an optical frequency comb generation module, a switch selection module, a frequency reference module, a DDS (Direct Digital Synthesizer) frequency synthesizer, a frequency control module, a Brillouin filter, a coupler, a photoelectric converter, an analog-to-digital converter and a stray filter. The comb spectrum laser with a fixed frequency interval is output, the center frequency of the Brillouin filter is changed by setting the pumping current of the Brillouin filter, so that a required comb spectrum obtains high gain in a passband of the filter, and after stray is filtered out through the stray filter, the laser with the selected comb spectrum frequency is output. The wide-range large-step laser local oscillator has the advantages of being high in response speed, low in cost, good in producibility and high in reliability, is suitable for achieving the wide-range large-step laser local oscillator, and is an important improvement on the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of information transmission and processing, in particular to a laser local oscillator device based on an optical frequency comb and a Brillouin filter. Background Art

[0002] Controllable adjustment of the laser local oscillator frequency is a basic requirement for optical communication, microwave photon frequency converter, laser measurement, spectrum analysis and other applications. Currently, the controllable adjustment of the laser local oscillator 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) locked to the external reference frequency, phase-locked frequency tuning can be completed by adjusting the fiber length. It has the advantages of high frequency accuracy, but it has the disadvantages of complex composition, slow response speed, large volume and power consumption. In the technology of using an optoelectronic phase-locked loop to complete the reference frequency shift using a high-stable-frequency laser as the reference light, there is a scheme that uses a radio frequency synthesizer to mix to obtain broadband controllable adjustment of the laser frequency. The frequency offset range that can be achieved is limited by the radio frequency synthesizer; there is also a scheme that uses radio frequency division in an optoelectronic phase-locked loop to achieve controllable adjustment of the laser frequency, but the division will not only cause the deterioration of the output phase noise of the optoelectronic phase-locked loop, but also the range of laser frequency movement that can be achieved is limited. In addition, there is a locking filtering scheme using an injection-locked laser for the teeth of an optical frequency comb. The frequency range that a DFB laser can lock is too wide and is power-dependent, requiring the frequency spacing of the comb teeth to be above 5 GHz to avoid mislocking. Therefore, it is not suitable for reference optical frequency offsets with frequency steps ranging from several hundred MHz to several GHz. Summary of the invention

[0003] In view of this, the present invention proposes a laser local oscillator device based on an optical frequency comb and a Brillouin filter. The present invention uses a radio frequency signal with the same step frequency as the laser local oscillator to modulate the input laser, outputs a laser (optical frequency comb) with a comb spectrum with a fixed frequency interval, and changes the center frequency of the Brillouin filter by setting the pump current of the Brillouin filter, so that a required comb spectrum is within the passband of the filter, thereby filtering out other comb spectrums, and then after further filtering out other comb spectrums through a stray filter, outputs a laser with the selected comb spectrum frequency.

[0004] In order to achieve the above object, the technical solution provided by the present invention is:

[0005] A laser local oscillator device based on an optical frequency comb and a Brillouin filter comprises a laser, an optical frequency comb generation module, a switch selection module, a frequency reference module, a DDS frequency synthesizer, a frequency control module, a Brillouin filter, a coupler, a photoelectric converter, an analog-to-digital converter, and a spurious filter; wherein:

[0006] The laser generates a frequency f 0 The narrow linewidth laser is sent to the optical frequency comb generation module;

[0007] Frequency reference module, generates frequency f c1 RF signal;

[0008] The DDS frequency synthesizer generates a frequency f under the control of the frequency control module. c2 RF signal;

[0009] The switch selection module selects the frequency f under the control of the frequency control module. c1 The RF signal or frequency is f c2 The frequency of the RF signal output by the switch selection module is recorded as f c ;

[0010] The optical frequency comb generation module, at a frequency of f c Driven by the RF signal, the frequency interval is f c The broadband comb spectrum of the laser, and the comb teeth f 0 -nf c ~f 0 +nf c The power of is approximately equal; where comb tooth i corresponds to frequency f 0 +i*f c , i=0,-1,1,-2,2,...,-n,n, n is the maximum number of comb teeth used by the laser local oscillator;

[0011] The Brillouin filter comprises an isolator, a Brillouin optical fiber, a first optical circulator, a DFB pump laser, a first current amplifier and a first digital-to-analog converter; the broadband comb spectrum laser output by the optical frequency comb generation module enters the Brillouin optical fiber after passing through the isolator, the other end of the Brillouin optical fiber is connected to the second input port of the first optical circulator, the first input port of the first optical circulator is connected to the DFB pump laser, and the output port of the first optical circulator is connected to the coupler; the data output by the frequency control module is converted into an analog signal by the first digital-to-analog converter and then enters the first current amplifier, and the DFB pump laser is driven by the first current amplifier;

[0012] The coupler divides the laser into two output paths, one path goes to the stray filter and the other path goes to the photoelectric converter;

[0013] A photoelectric converter converts the laser signal into a voltage signal and outputs it to an analog-to-digital converter;

[0014] The analog-to-digital converter converts the voltage signal from the photoelectric converter into a digital voltage signal and sends it to the frequency control module;

[0015] The spurious filter removes the spurious signals from the input signal and the output frequency is f 0 +if c Laser

[0016] The frequency control module completes the setting, monitoring and storage of all working parameters of the laser local oscillator; when the Brillouin filter is initially working, it controls the laser local oscillator to complete the initialization of the fixed data corresponding to each comb spectrum used by the DFB pump laser.

[0017] Furthermore, the spurious filter includes a second optical circulator, an EDF optical fiber and an FBG grating, the first port of the second optical circulator is connected to the coupler, the second port of the second optical circulator is connected to the unpumped EDF optical fiber, the other end of the EDF optical fiber is connected to the FBG grating, and the third port of the second optical circulator is used to output a frequency of f 0 +if c laser; wherein, the reflection bandwidth of the FBG grating is greater than the frequency range of the local oscillator light.

[0018] Furthermore, the spurious filter includes a second optical circulator, a DFB laser, a second current amplifier and a second digital-to-analog converter, the first port of the second optical circulator is connected to the coupler, the second port of the second optical circulator is connected to the DFB laser, and the third port of the second optical circulator is used to output a frequency of f 0 +if c The frequency control module outputs the frequency control data of the DFB laser to the second digital-to-analog converter, which is converted into an analog voltage by the second digital-to-analog converter and linearly drives the second current amplifier. The second current amplifier outputs the driving current to the DFB laser, thereby controlling the self-excitation frequency of the DFB laser through the frequency control data. When the frequency difference between the input laser and the DFB laser is appropriate to the injection power ratio, the DFB laser locks the frequency of the injected laser and filters out the spurious, and the output laser of the DFB laser is output through the third port of the second optical circulator.

[0019] Furthermore, according to different local oscillator requirements, the data output by the frequency control module to the first digital-to-analog converter is divided into two situations:

[0020] (1) The frequency control module outputs fixed data to the first digital-to-analog converter to generate a DC voltage, and the DC voltage controls the center frequency of the laser output by the DFB pump laser, and the center frequency of the pump laser determines the center frequency of the Brillouin filter;

[0021] (2) The frequency control module outputs fixed data superimposed with modulated data, wherein the fixed data controls the center frequency output by the DFB pump laser, and the superimposed modulated data is used to modulate the DFB pump laser to generate a broadband spectrum, thereby making the Brillouin filter have a broadened passband.

[0022] Furthermore, the frequency control module works as follows:

[0023] (a) Control the output frequency f of the DDS frequency synthesizer c2 For nf c1 / r, where n is the value of the maximum number of broadband comb spectra used by the local oscillator light, and r is the largest prime number less than n / 2;

[0024] (b) Control the switch selection module to output the signal of the DDS frequency synthesizer, so that the input fixed data of the first digital-to-analog converter is the budgeted corresponding broadband comb spectrum frequency f 0 +nf c1 ; Fine-tune the input fixed data of the first digital-to-analog converter until the digital voltage output by the analog-to-digital converter exceeds the threshold voltage and reaches the maximum; wherein the threshold voltage is a fixed voltage value for distinguishing whether there is a broadband comb spectrum in the passband of the Brillouin filter;

[0025] (c) controlling the switch selection module to select the output of the frequency reference module and observing whether the digital voltage output by the analog-to-digital converter exceeds the threshold voltage;

[0026] If yes, the current input fixed data of the first digital-to-analog converter is the initialization data corresponding to comb tooth n;

[0027] If not, the output of the DDS frequency synthesizer is selected through the switch selection module, and then the input fixed data of the first digital-to-analog converter is adjusted, and the digital voltage output by the analog-to-digital converter is detected at the same time. If it is found that the digital voltage exceeds the threshold voltage, the input fixed data of the first digital-to-analog converter is fine-tuned, and after the digital voltage peak point is found, the output of the frequency reference module is selected through the switch selection module to detect whether the digital voltage exceeds the threshold voltage at this time; this is repeated until the input fixed data of the first digital-to-analog converter is found, so that when the DDS frequency synthesizer and the frequency reference module drive the optical frequency comb generation module, the digital voltage can exceed the threshold voltage, and the input fixed data of the first digital-to-analog converter is the initialization data corresponding to the comb tooth n;

[0028] (d) Let k = 1;

[0029] (e) Control switch selects module output frequency f c1 , the input fixed data of the first digital-to-analog converter is fine-tuned in the direction of the nk comb teeth until the digital voltage output by the analog-to-digital converter becomes the first peak value exceeding the threshold voltage; then, the output frequency f of the DDS frequency synthesizer is controlled c2 for (nk)f c1 / r k , the switch selection module selects the output of the DDS frequency synthesizer and observes f c2Can the digital voltage output by the analog-to-digital converter exceed the threshold voltage? If so, the current fixed input data of the first digital-to-analog converter is the initialization data corresponding to the nk comb teeth. Otherwise, repeat this step until the initialization data corresponding to the nk comb teeth is found. Wherein, r k Take the prime number closest to (nk) / 2;

[0030] (f) Let k=k+1, and repeat steps e and f until the initialization and storage of fixed data corresponding to all comb teeth are completed.

[0031] It can be seen from the above description that the beneficial effects of the present invention are:

[0032] 1. The Brillouin filter of the optical frequency comb of the present invention selects the comb teeth plus the stray filter mode, realizes the ultra-wideband frequency shift of the laser frequency with the comb tooth interval as the step, and can realize the laser local oscillation of ultra-high frequency and ultra-wideband adjustable frequency.

[0033] 2. The present invention adopts a method for comb tooth selection and calibration based on a Brillouin filter, which can accurately calibrate the control parameters of each applied comb tooth of the optical frequency comb.

[0034] 3. The present invention provides two methods for realizing spurious filters, namely, a method for realizing an injection-locked laser with a relatively high power output, and a method for realizing spurious absorption by a simple unpumped EDF optical fiber. These two methods can be suitable for different application scenarios.

[0035] 4. The present invention can be implemented using mature optical devices and electrical devices. The equipment manufactured based on this principle has the advantages of low cost, good manufacturability, fast frequency conversion speed, high reliability, etc., and can be used as a key component of a microwave photonic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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.

[0037] Figure 1This is a principle block diagram of a laser local oscillator device based on an optical frequency comb and a Brillouin filter in an embodiment of the present invention. In the figure, an ultra-wideband comb spectrum laser is first realized based on the optical frequency comb, and then the comb spectrum is selected and amplified based on the Brillouin filter, and finally the spurious filtering based on the non-pumped EDF fiber is performed, so that a pure single-frequency laser is obtained after frequency shifting, wherein the adjustment of the center frequency of the Brillouin filter is achieved by changing the frequency of the pump laser. The figure also provides an auxiliary module for detecting the correctness of the selected comb teeth.

[0038] Figure 2 This is a principle block diagram of another spurious filter in an embodiment of the present invention. In the figure, an injection-locked laser is formed based on a DFB laser. The laser input to the injection-locked laser filters out other unselected comb spectrum spurious after locking. The frequency range of injection locking can be controlled by adjusting the driving current of the DFB laser. The driving current of the DFB laser can be realized by the digital frequency control module by controlling the input data of DAC2. DETAILED DESCRIPTION

[0039] 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.

[0040] A laser local oscillator device based on an optical frequency comb and a Brillouin filter, such as Figure 1 As shown, including:

[0041] Frequency reference module, generates frequency f c1 The RF signal with frequency f c1 The RF signal is the step frequency of the laser local oscillator;

[0042] The DDS frequency synthesizer generates a frequency f under the control of the frequency control module. c2 The RF signal with frequency f c2 The RF signal is used for the center frequency calibration of the Brillouin filter;

[0043] The switch selection module, under the control of the frequency control module, selects the frequency f c1 Or frequency f c2 The frequency of the RF signal output by the switch selection module is recorded as f c ;

[0044] The laser generates a frequency f 0 The narrow linewidth laser enters the optical frequency comb generation module;

[0045] The optical frequency comb generation module, at a frequency of f c Driven by the RF signal, the frequency interval is f cA broadband comb spectrum (comb spectrum) of laser light, with comb teeth f 0 -nf c ~f 0 +nf c The power is approximately equal, where the frequency f 0 Corresponding to comb tooth 0, frequency f 0 +f c Corresponding to comb tooth 1, frequency f 0 -f c Corresponding to comb tooth -1, frequency f 0 +2f c corresponding to comb teeth 2, etc., n is the maximum number of comb teeth used by the laser local oscillator;

[0046] In the prior art, the frequency interval is f c There are many methods for optical frequency comb. In this embodiment, a mature MZM modulator can be used to form PM modulation and then cascade IM modulation to generate an optical frequency comb.

[0047] In general, the comb spectrum is about f 0 Symmetrical, the local oscillator may only use f 0 -nf c ~f 0 +nf c A part of the score.

[0048] In the Brillouin filter, the combed laser enters the Brillouin fiber after passing through the isolator. The other end of the Brillouin fiber is connected to the second port of the optical circulator C1. The first port of the optical circulator C1 is connected to the DFB pump laser. The third port of the optical circulator C1 is output to the coupler. The first digital-to-analog converter DAC1 converts the data output by the frequency control module into an analog signal, which then enters the first current amplifier. The first current amplifier is used to drive the DFB pump laser.

[0049] The above components are the standard configuration of the Brillouin filter. With the appropriate Brillouin fiber and DFB pump laser, a gain of more than 40dB can be provided to the selected comb signal, and other interfering combs are not amplified. Therefore, the Brillouin filter simultaneously completes the selection and amplification of the comb.

[0050] Brillouin optical fiber can be selected as single-mode optical fiber or highly nonlinear optical fiber according to different design requirements.

[0051] The output laser of the coupler is divided into two paths, one path enters the first port of the optical circulator C2, and the other path enters the photoelectric converter and is converted into a voltage signal. The voltage signal is converted into a digital voltage by the analog-to-digital converter ADC and then sent to the frequency control module.

[0052] The digital voltage output by the analog-to-digital converter ADC represents the power of the laser in the current Brillouin filter passband. After controlling the center frequency of the Brillouin filter, direct feedback information can be obtained through the digital voltage. For example, the digital voltage can be used to determine whether there is a comb spectrum in the Brillouin filter passband. When the digital voltage is observed to be maximum while adjusting the center frequency of the Brillouin filter, it represents the overlap between the center frequency of the filter and the comb spectrum.

[0053] The second port of the optical circulator C2 is connected to a stray filter. After the stray is filtered out, the output frequency at the third port of the optical circulator C2 is f 0 +if c of laser.

[0054] Depending on the requirements of the local oscillator, the data output by the frequency control module to the first digital-to-analog converter DAC1 has different compositions, including the following:

[0055] (1) The frequency control module can output fixed data to the first digital-to-analog converter DAC1 to generate a DC voltage. The DC voltage controls the center frequency of the output laser of the DFB pump laser. The center frequency of the pump laser determines the center frequency of the Brillouin filter.

[0056] The center frequency f of the Brillouin filter b Equal to the center frequency f of the pump laser p Subtract the Brillouin frequency shift.

[0057] When calibrating each comb spectrum to correspond to the fixed data of the first digital-to-analog converter DAC1 , the frequency control module is required to output only the fixed data to DAC1 .

[0058] (2) The frequency control module can output fixed data superimposed with modulated data, wherein the fixed data controls the center frequency output by the DFB pump laser, and the superimposed modulated data can modulate the DFB pump laser to generate a broadband spectrum, thereby making the Brillouin filter have a broadened passband.

[0059] When the local oscillator is working, the Brillouin filter has a widened passband to prevent the input optical frequency f 0 The center frequency drift of the DFB pump laser causes the Brillouin filter characteristics to deteriorate. For high frequency stability f 0 With DFB pump lasers, it is not necessary to output broadband signals.

[0060] Depending on the system requirements, such as Figure 1 , the spurious filter can be realized using unpumped EDF fiber:

[0061] The second port of the optical circulator C2 is connected to the unpumped EDF fiber, the other end of the EDF fiber is connected to the FBG grating, and the third port of the optical circulator C2 is output, wherein the reflection bandwidth of the FBG grating is slightly larger than the frequency range of the local oscillator light.

[0062] Unpumped EDF fiber has different absorption characteristics for different frequency components in the input laser signal according to their power, and can suppress other interference combs other than the higher power selected comb by more than 25dB. The reflection filter of FBG grating can further filter out the interference combs outside the working bandwidth of the local oscillator.

[0063] The use of unpumped EDF fiber has the advantages of simplicity and reliability, but will cause attenuation of the selected comb spectrum.

[0064] In addition, if Figure 2 , the spurious filter can also be implemented using an injection-locked DFB laser:

[0065] The second port of the optical circulator C2 is connected to the DFB laser, and the frequency control module outputs the frequency control data of the DFB laser to the second digital-to-analog converter DAC2. After being converted into an analog voltage by the second digital-to-analog converter DAC2, the second current amplifier is linearly driven, and the second current amplifier outputs a driving current to the DFB laser. The self-excitation frequency of the DFB laser can be controlled by the frequency control data. When the frequency difference between the input laser and the DFB laser is appropriate to the injection power ratio, the DFB laser can lock the frequency of the injected laser and filter out strays, and the output laser of the DFB laser is output through the third port of the optical circulator C2.

[0066] The Brillouin filter has a large gain (more than 40dB) for the selected comb spectrum, which can achieve the injection power ratio required by the DFB laser, while other comb spectrum spurious cannot reach the injection power ratio. Therefore, the comb spectrum selected by the Brillouin filter is locked within the appropriate frequency difference range (up to 4GHz to 30GHz).

[0067] After the DFB laser is injection locked, the output laser power is stable and has nothing to do with the input laser power. Since the injection locked frequency difference range is wide, the DFB laser only needs to simply calibrate the frequency control data of the second digital-to-analog converter DAC2 corresponding to each comb spectrum.

[0068] The frequency control module completes the setting, monitoring and storage of all working parameters of the laser local oscillator. When the Brillouin filter is initially working, it controls the laser local oscillator to complete the initialization of the fixed data corresponding to each comb spectrum used by the DFB pump laser. The specific method is as follows:

[0069] (1) After the local oscillator operating parameters are stable, control the output frequency f of the DDS frequency synthesizer c2 For nfc1 / r;

[0070] The frequency control module starts this step only after the voltage, current, temperature and other working parameters of the laser local oscillator are monitored and stabilized.

[0071] (2) Control the switch selection module to output the signal of the DDS frequency synthesizer, so that the input fixed data of the first digital-to-analog converter DAC1 is the corresponding comb frequency f 0 +nf c1 , fine-tune the input fixed data of the first digital-to-analog converter DAC1 until the digital voltage output by the ADC exceeds the threshold voltage and reaches the maximum.

[0072] Among them, the value of n is the value of the maximum number of comb spectra used by the local oscillator light, r can be the largest prime number less than n / 2, and the threshold voltage is a fixed voltage value for distinguishing whether there is a comb spectrum in the passband of the Brillouin filter.

[0073] The estimated comb frequency f 0 +nf c1 The corresponding fixed input data of DAC1 may be the fixed input data of DAC1 corresponding to the comb spectrum n calibrated last time, or the input control data of DAC1 corresponding to the comb spectrum n calculated according to the hardware design.

[0074] Each local oscillator has an optimal r value. It is more generally applicable to use the largest prime number less than n / 2. In addition, the smallest prime number greater than n / 2 can be used for further confirmation, but this is not necessary for most local oscillators. For example, when n is 80, the r value can be 37.

[0075] The Brillouin filter has a power gain of more than 40dB for the comb spectrum. Considering the uneven amplitude of the comb spectrum and f c Due to the fluctuations caused by different interferences, the threshold voltage can usually be more than 20 times the interference comb voltage.

[0076] (3) The control switch selection module selects the output of the frequency reference module and observes whether the ADC output digital voltage exceeds the threshold voltage.

[0077] The output frequency of the frequency reference module is a fixed frequency f c1 If the digital voltage output by the ADC is lower than the threshold voltage, there is no comb spectrum in the passband of the Brillouin filter. If the digital voltage output by the ADC is higher than the threshold voltage, there is a comb spectrum in the passband of the Brillouin filter.

[0078] (301) If the digital voltage output by the ADC exceeds the threshold voltage, the current fixed input data of DAC1 is the initialization data corresponding to the comb tooth n.

[0079] Frequency nf c1 / r's rth root comb spectrum and frequency f c1The nth root comb spectrum of passes through a narrowband (bandwidth of about 30MHz) Brillouin filter, and the digital voltage output by the ADC exceeds the threshold voltage, then the center frequency of the Brillouin filter controlled by the current fixed input data of DAC1 is determined to be frequency f c1 The generated comb tooth n corresponds to fixed data.

[0080] (302) If the digital voltage output by the ADC is lower than the threshold voltage, the switch selection module selects the output of the DDS frequency synthesizer, and then adjusts the DAC1 input fixed data while detecting the digital voltage. If it is found that the digital voltage exceeds the threshold voltage, the DAC1 input fixed data is fine-tuned to find the digital voltage peak point, and then detects whether the digital voltage exceeds the threshold voltage when the RF output of the frequency reference module drives the optical frequency comb module; this is done until a DAC1 input fixed data is found that can make the digital voltage exceed the threshold voltage when the DDS frequency synthesizer and the frequency reference module drive the optical frequency comb module. In this way, the DAC1 input fixed data is the initialization data corresponding to the comb tooth n.

[0081] Using nf c1 When driving the optical frequency comb module, the comb spectrum interval is greater than f c1 More than twice as large, it is easier to find f 0 +nf c1 .

[0082] First find the frequency f 0 +nf c1 The corresponding fixed input data of DAC1 needs to be explored in a larger range. The larger the comb spectrum interval, the easier it is to find. However, it is difficult to realize nf c1 / rThe more troublesome it is, the more trade-offs there are.

[0083] (4) Let k=1.

[0084] (5) Control switch selection module output frequency f c1 , the input fixed data of the first digital-to-analog converter is fine-tuned in the direction of the nk comb teeth until the digital voltage output by the analog-to-digital converter becomes the first peak value exceeding the threshold voltage; then, the output frequency f of the DDS frequency synthesizer is controlled c2 for (nk)f c1 / r k , the switch selection module selects the output of the DDS frequency synthesizer and observes f c2 Can the digital voltage output by the analog-to-digital converter exceed the threshold voltage? If so, the current fixed input data of the first digital-to-analog converter is the initialization data corresponding to the nk comb teeth. Otherwise, repeat this step until the initialization data corresponding to the nk comb teeth is found. Wherein, r k Take the prime number closest to (nk) / 2.

[0085] When the initialization data corresponding to the comb tooth n is correct, this step can usually be verified once.

[0086] For a smaller number of teeth, it is better to use the largest prime number less than (n-1) / 2 than the smallest prime number greater than (n-1) / 2. For example, for a comb number of 6, use 6f c1 / 5 is obviously better.

[0087] (6) Let k=k+1, and repeat steps 5 and 6 until the initialization and storage of fixed data corresponding to all comb teeth are completed.

[0088] In particular, when obtaining the initialization data of comb number 4 and -4, use f c2 4f c1 / 3 for verification; when obtaining the initialization data of comb number 3, -3, use f c2 3f c1 / 2 for verification; when obtaining the initialization data of comb number 2, -2, use f c2 2f c1 Check; when obtaining the initialization data of comb number -1, 0, 1, no f is required c2 Correction.

[0089] The fixed data of DAC1 corresponding to each comb spectrum i is stored. When the working comb spectrum i is changed, the fixed data corresponding to the new i is retrieved from the stored data and set to DAC1.

[0090] In summary, the present invention uses a radio frequency signal with the same step frequency as the laser local oscillator to modulate the input laser, outputs a comb spectrum laser with a fixed frequency interval, and changes the center frequency of the Brillouin filter by setting the pump current of the Brillouin filter, so that a required comb spectrum obtains high gain in the passband of the filter, and then outputs the laser of the selected comb spectrum frequency after the stray is filtered out by the stray filter. The present invention has the advantages of fast response speed (us level), low cost, good manufacturability and high reliability, is suitable for realizing a wide range and large step laser local oscillator, and is an important improvement on the prior art.

[0091] 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 based on an optical frequency comb and a Brillouin filter, characterized in that: It includes a laser, an optical frequency comb generation module, a switch selection module, a frequency reference module, a DDS frequency synthesizer, a frequency control module, a Brillouin filter, a coupler, a photoelectric converter, an analog-to-digital converter, and a spurious filter; among them, The laser generates a narrow linewidth laser with a frequency of f0 and feeds it into the optical frequency comb generation module; Frequency reference module, generates frequency f c1 RF signal; The DDS frequency synthesizer generates a frequency f under the control of the frequency control module. c2 RF signal; The switch selection module selects the frequency f under the control of the frequency control module. c1 The RF signal or frequency is f c2 The frequency of the RF signal output by the switch selection module is recorded as f c ; The optical frequency comb generation module, at a frequency of f c Driven by the RF signal, the frequency interval is f c The broadband comb spectrum of the laser, and the comb teeth f0-nf c ~f0+nf c The power of the comb teeth i corresponds to the frequency f0+i*f c , i=0,-1,1,-2,2,...,-n,n, n is the maximum number of comb teeth used by the laser local oscillator; The Brillouin filter comprises an isolator, a Brillouin optical fiber, a first optical circulator, a DFB pump laser, a first current amplifier and a first digital-to-analog converter; the broadband comb spectrum laser output by the optical frequency comb generation module enters the Brillouin optical fiber after passing through the isolator, the other end of the Brillouin optical fiber is connected to the second input port of the first optical circulator, the first input port of the first optical circulator is connected to the DFB pump laser, and the output port of the first optical circulator is connected to the coupler; the data output by the frequency control module is converted into an analog signal by the first digital-to-analog converter and then enters the first current amplifier, and the DFB pump laser is driven by the first current amplifier; The coupler divides the laser into two output paths, one path goes to the stray filter and the other path goes to the photoelectric converter; A photoelectric converter converts the laser signal into a voltage signal and outputs it to an analog-to-digital converter; The analog-to-digital converter converts the voltage signal from the photoelectric converter into a digital voltage signal and sends it to the frequency control module; The spurious filter removes the spurious signals from the input signal, and the output frequency is f0+if c Laser The frequency control module completes the setting, monitoring and storage of all working parameters of the laser local oscillator; when the Brillouin filter is initially working, it controls the laser local oscillator to complete the initialization of the fixed data corresponding to each comb spectrum used by the DFB pump laser.

2. A laser local oscillator device based on an optical frequency comb and a Brillouin filter according to claim 1, characterized in that: The stray filter comprises a second optical circulator, an EDF optical fiber and an FBG grating, wherein the first port of the second optical circulator is connected to the coupler, the second port of the second optical circulator is connected to the unpumped EDF optical fiber, the other end of the EDF optical fiber is connected to the FBG grating, and the third port of the second optical circulator is used to output a frequency of f0+if c laser; wherein, the reflection bandwidth of the FBG grating is greater than the frequency range of the local oscillator light.

3. The laser local oscillator device based on an optical frequency comb and a Brillouin filter according to claim 1, characterized in that: The spurious filter comprises a second optical circulator, a DFB laser, a second current amplifier and a second digital-to-analog converter, wherein the first port of the second optical circulator is connected to the coupler, the second port of the second optical circulator is connected to the DFB laser, and the third port of the second optical circulator is used to output a frequency of f0+if c The frequency control module outputs the frequency control data of the DFB laser to the second digital-to-analog converter, which is converted into an analog voltage by the second digital-to-analog converter and linearly drives the second current amplifier. The second current amplifier outputs the driving current to the DFB laser, thereby controlling the self-excitation frequency of the DFB laser through the frequency control data. When the frequency difference between the input laser and the DFB laser is appropriate to the injection power ratio, the DFB laser locks the frequency of the injected laser and filters out the spurious, and the output laser of the DFB laser is output through the third port of the second optical circulator.

4. The laser local oscillator device based on an optical frequency comb and a Brillouin filter according to claim 1, characterized in that: According to different local oscillator requirements, the data output from the frequency control module to the first digital-to-analog converter is divided into two situations: (1) The frequency control module outputs fixed data to the first digital-to-analog converter to generate a DC voltage, and the DC voltage controls the center frequency of the laser output by the DFB pump laser, and the center frequency of the pump laser determines the center frequency of the Brillouin filter; (2) The frequency control module outputs fixed data superimposed with modulated data, wherein the fixed data controls the center frequency output by the DFB pump laser, and the superimposed modulated data is used to modulate the DFB pump laser to generate a broadband spectrum, thereby making the Brillouin filter have a broadened passband.

5. The laser local oscillator device based on optical frequency comb and Brillouin filter according to claim 1, characterized in that: The frequency control module controls the laser local oscillator to complete the initialization of the fixed data corresponding to each comb spectrum used by the DFB pump laser, and its working mode is as follows: (a) After the local oscillator operating parameters are stable, control the output frequency f of the DDS frequency synthesizer c2 For nf c1 / r, where r is the largest prime number less than n / 2, and n is the value of the maximum number of broadband comb spectra used by the local oscillator light; (b) Control the switch selection module to output the signal of the DDS frequency synthesizer, so that the input fixed data of the first digital-to-analog converter is the budgeted corresponding broadband comb spectrum frequency f0+nf c1 ; Fine-tune the input fixed data of the first digital-to-analog converter until the digital voltage output by the analog-to-digital converter exceeds the threshold voltage and reaches the maximum; wherein the threshold voltage is a fixed voltage value for distinguishing whether there is a broadband comb spectrum in the passband of the Brillouin filter; (c) controlling the switch selection module to select the output of the frequency reference module and observing whether the digital voltage output by the analog-to-digital converter exceeds the threshold voltage; If yes, the current input fixed data of the first digital-to-analog converter is the initialization data corresponding to comb tooth n; If not, the output of the DDS frequency synthesizer is selected through the switch selection module, and then the input fixed data of the first digital-to-analog converter is adjusted, and the digital voltage output by the analog-to-digital converter is detected at the same time. If it is found that the digital voltage exceeds the threshold voltage, the input fixed data of the first digital-to-analog converter is fine-tuned, and after the digital voltage peak point is found, the output of the frequency reference module is selected through the switch selection module to detect whether the digital voltage exceeds the threshold voltage at this time; this is repeated until the input fixed data of the first digital-to-analog converter is found, so that when the DDS frequency synthesizer and the frequency reference module drive the optical frequency comb generation module, the digital voltage can exceed the threshold voltage, and the input fixed data of the first digital-to-analog converter is the initialization data corresponding to the comb tooth n; (d) Let k = 1; (e) Control switch selects module output frequency f c1 , the input fixed data of the first digital-to-analog converter is fine-tuned in the direction of the nk comb teeth until the digital voltage output by the analog-to-digital converter becomes the first peak value exceeding the threshold voltage; then, the output frequency f of the DDS frequency synthesizer is controlled c2 for (nk)f c1 / r k , the switch selection module selects the output of the DDS frequency synthesizer and observes f c2 Can the digital voltage output by the analog-to-digital converter exceed the threshold voltage? If so, the current fixed input data of the first digital-to-analog converter is the initialization data corresponding to the nk comb teeth. Otherwise, repeat this step until the initialization data corresponding to the nk comb teeth is found. Wherein, r k Take the prime number closest to (nk) / 2; (f) Let k=k+1, and repeat steps e and f until the initialization and storage of fixed data corresponding to all comb teeth are completed.

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