A laser local oscillator device based on optical frequency comb and Brillouin filter

Abstract

This invention discloses a laser local oscillator device based on an optical frequency comb and a Brillouin filter, belonging to the field of information transmission and processing technology. The invention 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. It uses a radio frequency signal with the same step frequency as the laser local oscillator to modulate the input laser, outputting a laser with a comb spectrum having fixed frequency intervals. By setting the pump current of the Brillouin filter to change the center frequency of the filter, a desired comb spectrum can achieve high gain within the filter's passband. After spurious filtering to remove strays, the laser with the selected comb spectrum frequency is output. This invention has the advantages of fast response speed, low cost, good manufacturability, and high reliability, and is suitable for realizing wide-range, large-step laser local oscillators, representing a significant improvement over existing technologies.

Description

Technical Field

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

[0002] Controllable adjustment of the laser local oscillator frequency is a fundamental requirement for applications such as optical communication, microwave photonic frequency converters, laser measurement, and spectral analysis. Currently, controllable adjustment of the laser local oscillator frequency is mainly achieved by adjusting parameters such as laser temperature, current, and resonant cavity size. This direct tuning method suffers from drawbacks such as poor frequency accuracy, large frequency drift, and poor amplitude stability. Fiber lasers (OEOs) based on locked external reference frequencies can achieve phase-locked frequency tuning by adjusting the fiber length, offering the advantage of high frequency accuracy. However, they suffer from drawbacks such as complex composition, slow response speed, and large size and power consumption. Among the techniques for using a high-stability laser as a reference beam and employing an opto-phase-locked loop (PLL) to achieve reference frequency offset, there are schemes that utilize a radio frequency synthesizer for mixing to obtain a broadband controllable adjustment of the laser frequency. The achievable frequency offset range is limited by the radio frequency synthesizer. Another scheme utilizes radio frequency division within the PLL to achieve controllable laser frequency adjustment, but frequency division not only degrades the phase noise output of the PLL but also limits the achievable laser frequency shift range. In addition, there is a locking filtering scheme that uses injection-locked lasers for optical frequency comb teeth. The frequency range that DFB lasers can lock is too wide and is power-dependent. The frequency interval of the comb teeth must be above 5 GHz to avoid mislocking. Therefore, it is not suitable for reference light frequency offset with frequency steps in the range of 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 utilizes a radio frequency signal with the same step frequency as the laser local oscillator to modulate the input laser, outputting a laser with a comb-shaped spectrum (optical frequency comb) having fixed frequency intervals. By adjusting the pump current of the Brillouin filter to change the center frequency of the filter, the desired comb spectrum is placed within the filter's passband, thereby filtering out other comb spectra. After further filtering out other comb spectra by a stray filter, the laser with the selected comb spectrum frequency is output.

[0004] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0005] A laser local oscillator device based on an optical frequency comb and a Brillouin filter 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; wherein,

[0006] A laser generates a narrow linewidth laser with a frequency of f0, which is then fed into an optical frequency comb generation module.

[0007] The frequency reference module generates a frequency of f. c1 Radio frequency signals;

[0008] The DDS frequency synthesizer, under the control of the frequency control module, generates a frequency of f. c2 Radio frequency signals;

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

[0010] The optical frequency comb generation module, at a frequency of f c Driven by the radio frequency signal, a frequency interval of f is generated. c A broadband comb-shaped laser with comb teeth f0-nf c ~f0+nf c The power is approximately equal; where the comb tooth i corresponds to the frequency f0 + i*f c i = 0, -1, 1, -2, 2, ..., -n, n, where n is the maximum number of comb teeth used by the laser local oscillator;

[0011] The Brillouin filter includes an isolator, a Brillouin fiber, a first optical circulator, a DFB-pumped laser, a first current amplifier, and a first digital-to-analog converter. The broadband comb-spectrum laser output from the optical frequency comb generation module passes through the isolator and enters the Brillouin fiber. The other end of the Brillouin 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-pumped laser, and the output port of the first optical circulator is connected to a coupler. Data output from the frequency control module is converted into an analog signal by the first digital-to-analog converter and then enters the first current amplifier, which drives the DFB-pumped laser.

[0012] The coupler splits the laser into two outputs, one of which goes into a stray filter and the other into a photoelectric converter;

[0013] The photoelectric converter converts the laser signal into a voltage signal and outputs it to the analog-to-digital converter.

[0014] The analog-to-digital converter converts the voltage signal from the photoelectric converter into a digital voltage signal, which is then sent to the frequency control module.

[0015] A spurious filter removes spurious signals from the input signal, and its output frequency is f0 + if. c The laser;

[0016] The frequency control module completes the setting, monitoring, and storage of all operating parameters of the laser local oscillator; when the Brillouin filter is initially working, it controls the laser local oscillator to complete the initialization of 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 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 an unpumped EDF fiber, the other end of the EDF 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 The laser; wherein the reflection bandwidth of the FBG grating is greater than the frequency range of the local oscillator.

[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 f0+if. c The frequency control module outputs the frequency control data of the DFB laser to the second digital-to-analog converter, which converts it into an analog voltage and linearly drives the second current amplifier. The second current amplifier outputs a drive 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 stray light. The output laser of the DFB laser is output through the third port of the second optical circulator.

[0019] Furthermore, depending on the different requirements of the local oscillator, the data composition output from the frequency control module to the first digital-to-analog converter falls into two categories:

[0020] (1) The frequency control module outputs fixed data to the first digital-to-analog converter to generate 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.

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

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

[0023] (a) Controlling the output frequency f of the DDS frequency synthesizer c2 for nfc1 / r, where n is the value of the maximum number of broadband comb spectra used by the local oscillator, and r is the largest prime number less than n / 2;

[0024] (b) The control switch selects the output signal of the DDS frequency synthesizer, so that the input data of the first digital-to-analog converter is fixed at the budgeted corresponding broadband comb frequency f0+nf. c1 Fine-tune the fixed input 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 its maximum; where the threshold voltage is a fixed voltage value that distinguishes whether there is a broadband comb spectrum in the passband of the Brillouin filter.

[0025] (c) Select the output of the frequency reference module by controlling the switch selection module, and observe whether the digital voltage output by the analog-to-digital converter exceeds the threshold voltage.

[0026] If so, 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 via the switch selection module, and then the fixed input data of the first digital-to-analog converter is adjusted. At the same time, the digital voltage output of the analog-to-digital converter is detected. If the digital voltage exceeds the threshold voltage, the fixed input data of the first digital-to-analog converter is finely adjusted. After finding the peak point of the digital voltage, the output of the frequency reference module is selected via the switch selection module again, and it is detected whether the digital voltage exceeds the threshold voltage at this time. This process is repeated until a fixed input data of the first digital-to-analog converter is found, which makes the digital voltage exceed the threshold voltage when the DDS frequency synthesizer and the frequency reference module drive the optical frequency comb generation module. This fixed input data of the first digital-to-analog converter is the initialization data corresponding to comb tooth n.

[0028] (d) Let k = 1;

[0029] (e) Control switch selection module output frequency f c1 The input fixed data of the first digital-to-analog converter is finely adjusted in the direction of the nk comb 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 (nk)f c1 / r k Select the output of the DDS frequency synthesizer using the switch selection module, and observe f. c2 Can the digital voltage output by the analog-to-digital converter exceed the threshold voltage? If it does, then the current fixed input data of the first digital-to-analog converter is the initialization data corresponding to the nk comb tooth; otherwise, repeat this step until the initialization data corresponding to the nk comb tooth is found; where r kChoose the prime number that is closest to (nk) / 2;

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

[0031] As can be seen from the above description, the beneficial effects of the present invention are as follows:

[0032] 1. This invention uses a Brillouin filter based on an optical frequency comb to select comb teeth and add a stray filter, thereby realizing ultra-wideband frequency shifting of the laser frequency in steps of comb tooth intervals, and enabling ultra-high frequency, ultra-wideband laser local oscillators with settable frequencies.

[0033] 2. This invention employs a method for comb tooth selection and calibration based on Brillouin filters, which can accurately calibrate the control parameters of each application comb tooth in the optical frequency comb.

[0034] 3. This invention provides two methods for implementing stray filters: one is the implementation method using an injection-locked laser with a large power output, and the other is the implementation method using a simple unpumped EDF fiber for stray absorption. These two methods can be applied to different application scenarios.

[0035] 4. This invention can be implemented using mature optical and electrical devices. Equipment manufactured based on this principle has advantages such as low cost, good manufacturability, fast frequency conversion speed, and high reliability, and can be used as a key component of microwave photonic systems. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a block diagram illustrating the principle of a laser local oscillator device based on an optical frequency comb and a Brillouin filter, according to an embodiment of the present invention. The diagram first realizes an ultra-wideband comb-spectrum laser based on the optical frequency comb, then performs comb spectrum selection and amplification based on a Brillouin filter, and finally performs stray filtering based on a pump-free EDF fiber, thus obtaining a frequency-shifted, pure single-frequency laser. The center frequency of the Brillouin filter is adjusted by changing the frequency of the pump laser. An auxiliary module for detecting the correctness of the selected comb teeth is also shown in the diagram.

[0038] Figure 2This is a block diagram of another spurious filter in an embodiment of the present invention. The diagram uses an injection-locked laser composed of a DFB laser. The laser light input to the injection-locked laser filters out other comb spurious signals that were not selected after locking. The injection-locked frequency range can be controlled by adjusting the driving current of the DFB laser. The driving current of the DFB laser can be controlled by the digital frequency control module by controlling the input data of DAC2. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

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

[0041] The frequency reference module generates a frequency of f. c1 The radio frequency signal has a frequency of f c1 The radio frequency signal is the step frequency of the laser local oscillator;

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

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

[0044] The laser generates a narrow linewidth laser with a frequency of f0, which enters the optical frequency comb generation module.

[0045] The optical frequency comb generation module, at a frequency of f c Driven by a radio frequency signal, a frequency interval of f is generated. c A broadband comb-spectrum laser, with comb teeth f0-nf c ~f0+nf c The power is approximately equal, where frequency f0 corresponds to comb tooth 0, and frequency f0+f c Corresponding to comb tooth 1, frequency f0-f c Corresponding to comb tooth -1, frequency f0+2f c Corresponding to comb teeth 2, etc., n is the maximum number of comb teeth used by the laser local oscillator;

[0046] In existing technologies, the frequency interval is f. cThere are many methods for optical frequency combing. In this embodiment, a mature MZM modulator can be used to form a PM modulator, which is then connected in series with an IM modulator to generate an optical frequency comb.

[0047] Generally, the comb spectrum is symmetrical about f0, and the local oscillator may only use f0-nf. c ~f0+nf c A portion of the combing pattern.

[0048] In the Brillouin filter, the combed laser light passes through an isolator and enters the Brillouin fiber. 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, and the third port of the optical circulator C1 outputs 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 constitute the standard configuration of a Brillouin filter. With a suitable Brillouin fiber and DFB-pumped laser, it can provide a gain of over 40dB for the selected comb signal while not amplifying other interfering comb signals. Therefore, the Brillouin filter simultaneously performs comb selection and amplification.

[0050] Depending on the different design requirements, Brillouin fiber can be selected as either single-mode fiber or highly nonlinear fiber.

[0051] The output laser of the coupler is split into two paths. One path enters the first port of the optical circulator C2, and the other path enters the photoelectric converter, which converts it 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 within the current Brillouin filter passband. By controlling the center frequency of the Brillouin filter, direct feedback information can be obtained through the digital voltage. For example, the presence of a comb spectrum within the Brillouin filter passband can be determined using the digital voltage. Observing the digital voltage to its maximum while adjusting the center frequency of the Brillouin filter indicates that the filter's center frequency coincides with the comb spectrum.

[0053] The second port of optical circulator C2 is connected to a spurious filter. After filtering out spurious signals, the output frequency at the third port of optical circulator C2 is f0+if. c The laser.

[0054] Depending on the local oscillator requirements, the data composition output from the frequency control module to the first digital-to-analog converter DAC1 varies, including the following cases:

[0055] (1) The frequency control module can output fixed data to the first digital-to-analog converter DAC1 to generate 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 shift.

[0057] When calibrating the fixed data corresponding to the first digital-to-analog converter DAC1 for each comb spectrum, the frequency control module needs to output only fixed data to DAC1.

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

[0059] When operating from the local oscillator, the Brillouin filter's broadened passband prevents the input light frequency f0 from drifting with the center frequency of the DFB-pumped laser, thus avoiding deterioration of the Brillouin filter characteristics. For high-frequency stable f0 and DFB-pumped lasers, a wideband output signal is not required.

[0060] Depending on the different system requirements, such as Figure 1 Stray filters can be implemented using unpumped EDF fibers:

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

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

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

[0064] In addition, such as Figure 2 Stray filters can also be implemented using injection-locked DFB lasers:

[0065] The second port of optical circulator C2 is connected to the DFB laser. 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, it linearly drives the second current amplifier. The second current amplifier outputs a drive 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 stray light. The output laser of the DFB laser is output through the third port of optical circulator C2.

[0066] The Brillouin filter provides a large gain (above 40dB) for the selected comb spectrum, which can achieve the injection power ratio required by the DFB laser. Other comb spectrum spurious signals cannot achieve the same injection power ratio. Therefore, the comb spectrum selected by the Brillouin filter is locked within a suitable frequency difference range (up to 4GHz to 30GHz).

[0067] Once injected and locked, the output laser power of a DFB laser remains stable and independent of the input laser power. Because the injection-locked frequency difference range is wide, the DFB laser only requires simple calibration of 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 operating parameters of the laser local oscillator; during the initial operation of the Brillouin filter, it controls the laser local oscillator to initialize the fixed data corresponding to each comb spectrum used by the DFB pump laser, specifically in the following manner:

[0069] (1) After the local oscillator operating parameters stabilize, control the output frequency f of the DDS frequency synthesizer. c2 for nf c1 / r;

[0070] This step only begins after the frequency control module has monitored and stabilized the operating parameters of the laser local oscillator, such as voltage, current, and temperature.

[0071] (2) The control switch selects the output signal of the DDS frequency synthesizer, so that the input data of the first digital-to-analog converter DAC1 is fixed at the corresponding comb frequency f0+nf of the budget. 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 its maximum.

[0072] Where n is the maximum number of combs used by the local oscillator, r can be a maximum prime number less than n / 2, and the threshold voltage is a fixed voltage value that distinguishes whether there is a comb within the passband of the Brillouin filter.

[0073] The estimated comb frequency f0+nf c1The corresponding fixed input data for DAC1 can be either the fixed input data of DAC1 corresponding to the comb spectrum n from the last calibration, or the input control data of DAC1 corresponding to the comb spectrum n calculated based on the hardware design.

[0074] Each local oscillator has an optimal r value, and using the largest prime number less than n / 2 is more universally applicable. Furthermore, a smallest prime number greater than n / 2 can be used for further confirmation, but this is unnecessary for most local oscillators. For example, when n is 80, an r value of 37 can be chosen.

[0075] Brillouin filtering provides a power gain of over 40dB for the comb spectrum, considering the amplitude unevenness of the comb spectrum and f. c The threshold voltage can usually be more than 20 times the interference comb voltage to account for the fluctuations caused by different factors.

[0076] (3) Select the output of the frequency reference module by controlling the switch selection module, and observe 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, then 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, then 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, then the current input fixed data of DAC1 is the initialization data corresponding to the comb tooth n.

[0079] frequency nf c1 The r-th comb spectrum and frequency f of / r c1 If the nth comb spectrum passes through a narrow-band (bandwidth around 30MHz) Brillouin filter and causes the digital voltage output by the ADC to exceed the threshold voltage, then the center frequency of the Brillouin filter controlled by the current input fixed data of DAC1 is determined to be frequency f. c1 The fixed data corresponding to the generated comb teeth n.

[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 fixed input data of DAC1 while detecting the digital voltage. If the digital voltage is found to exceed the threshold voltage, the fixed input data of DAC1 is finely adjusted to find the peak point of the digital voltage. Then, it is detected whether the digital voltage exceeds the threshold voltage when the RF output of the frequency reference module drives the optical frequency comb module. This continues until a fixed input data of DAC1 is found that can make the digital voltage exceed the threshold voltage when both the DDS frequency synthesizer and the frequency reference module drive the optical frequency comb module. Then, the fixed input data of DAC1 is the initialization data corresponding to the comb tooth n.

[0081] Use nf c1 When driving the optical frequency comb module, the comb spacing ratio f c1 More than twice the size makes it easier to find f0+nf c1 .

[0082] First search for frequency f0+nf c1 The corresponding DAC1 input data requires a relatively large range of trial and error; the larger the comb interval, the easier the search, but implementing nf... c1 The more complicated / r becomes, the more you need to weigh the pros and cons.

[0083] (4) Let k = 1.

[0084] (5) Control switch selector module output frequency f c1 The input fixed data of the first digital-to-analog converter is finely adjusted in the direction of the nk comb 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 (nk)f c1 / r k Select the output of the DDS frequency synthesizer using the switch selection module, and observe f. c2 Can the digital voltage output by the analog-to-digital converter exceed the threshold voltage? If it does, then the current fixed input data of the first digital-to-analog converter is the initialization data corresponding to the nk comb tooth; otherwise, repeat this step until the initialization data corresponding to the nk comb tooth is found; where r k Choose the prime number that is closest to (nk) / 2.

[0085] If the initialization data corresponding to comb tooth n is correct, this step can usually be verified successfully on the first try.

[0086] For a smaller number of comb teeth, using the largest prime number less than (n-1) / 2 is less desirable than using the smallest prime number greater than (n-1) / 2. For example, for a comb tooth count of 6, using 6f would be preferable. c1 / 5 is clearly better.

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

[0088] Specifically, when obtaining the initialization data for the comb tooth count of 4 and -4, f is used. c2 4f c1 / 3 is used for verification; when obtaining the initial data for the comb tooth count of 3 and -3, f is used. c2 For 3f c1 / 2 is used for verification; when obtaining the initial data for the number of comb teeth 2 and -2, f is used. c2 For 2f c1Perform verification; when obtaining initial data of comb tooth count -1, 0, 1, f can be omitted. c2 Correction.

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

[0090] In summary, this invention utilizes an radio frequency signal with the same step frequency as the laser local oscillator to modulate the input laser, outputting a laser with a comb spectrum at fixed frequency intervals. By adjusting the pump current of the Brillouin filter to change its center frequency, the desired comb spectrum achieves high gain within the filter's passband. After spurious emissions are filtered out by a stray filter, the laser with the selected comb spectrum frequency is output. This invention offers advantages such as fast response speed (µs level), low cost, good manufacturability, and high reliability. It is suitable for realizing wide-range, large-step laser local oscillators and represents a significant improvement over existing technologies.

[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 this 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 this invention should be included within the protection scope of this invention.

Claims

1. A laser local oscillator device based on an optical frequency comb and a Brillouin filter, characterized in that, This 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 which, A laser generates a narrow linewidth laser with a frequency of f0, which is then fed into an optical frequency comb generation module. The frequency reference module generates a frequency of f. c1 Radio frequency signals; The DDS frequency synthesizer, under the control of the frequency control module, generates a frequency of f. c2 Radio frequency signals; The switch selection module, under the control of the frequency control module, selects the frequency f. c1 The radio frequency signal or frequency is f c2 The frequency of the radio frequency signal output by the switch selection module is denoted as f. c ; The optical frequency comb generation module, at a frequency of f c Driven by the radio frequency signal, a frequency interval of f is generated. c A broadband comb-shaped laser with comb teeth f0-nf c ~f0+nf c The power is approximately equal; where the comb tooth i corresponds to the frequency f0 + i*f c i = 0, -1, 1, -2, 2, ..., -n, n, where n is the maximum number of comb teeth used by the laser local oscillator; The Brillouin filter includes an isolator, a Brillouin fiber, a first optical circulator, a DFB-pumped laser, a first current amplifier, and a first digital-to-analog converter. The broadband comb-spectrum laser output from the optical frequency comb generation module passes through the isolator and enters the Brillouin fiber. The other end of the Brillouin 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-pumped laser, and the output port of the first optical circulator is connected to a coupler. Data output from the frequency control module is converted into an analog signal by the first digital-to-analog converter and then enters the first current amplifier, which drives the DFB-pumped laser. The coupler splits the laser into two outputs, one of which goes into a stray filter and the other into a photoelectric converter; The photoelectric converter converts the laser signal into a voltage signal and outputs it to the analog-to-digital converter. The analog-to-digital converter converts the voltage signal from the photoelectric converter into a digital voltage signal, which is then sent to the frequency control module. A spurious filter removes spurious signals from the input signal, and its output frequency is f0 + if. c The laser; The frequency control module completes the setting, monitoring, and storage of all operating parameters of the laser local oscillator; when the Brillouin filter is initially working, it controls the laser local oscillator to complete the initialization of fixed data corresponding to each comb spectrum used by the DFB pump laser.

2. The laser local oscillator device based on an optical frequency comb and a Brillouin filter according to claim 1, characterized in that, The stray filter includes a second optical circulator, an EDF 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 an unpumped EDF fiber, the other end of the EDF 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 The laser; wherein the reflection bandwidth of the FBG grating is greater than the frequency range of the local oscillator.

3. A laser local oscillator device based on an optical frequency comb and a Brillouin filter according to claim 1, characterized in that, 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 f0 + if. c The frequency control module outputs the frequency control data of the DFB laser to the second digital-to-analog converter, which converts it into an analog voltage and linearly drives the second current amplifier. The second current amplifier outputs a drive 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 stray light. The output laser of the DFB laser is output through the third port of the second optical circulator.

4. A laser local oscillator device based on an optical frequency comb and a Brillouin filter according to claim 1, characterized in that, Depending on the local oscillator requirements, the data output from the frequency control module to the first digital-to-analog converter consists of two types: (1) The frequency control module outputs fixed data to the first digital-to-analog converter to generate 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. (2) The frequency control module outputs fixed data superimposed with modulation data. The fixed data controls the center frequency of the DFB pump laser output, and the superimposed modulation data is used to modulate the DFB pump laser to generate a broadband spectrum, thereby giving the Brillouin filter a broadened passband.

5. A laser local oscillator device based on an optical frequency comb and a Brillouin filter according to claim 1, characterized in that, The frequency control module controls the laser local oscillator to initialize the fixed data corresponding to each comb spectrum used by the DFB pump laser. Its working mode is as follows: (a) After the local oscillator operating parameters stabilize, 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; (b) The control switch selects the output signal of the DDS frequency synthesizer, so that the input data of the first digital-to-analog converter is fixed at the budgeted corresponding broadband comb frequency f0+nf. c1 Fine-tune the fixed input 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 its maximum; where the threshold voltage is a fixed voltage value that distinguishes whether there is a broadband comb spectrum in the passband of the Brillouin filter. (c) Select the output of the frequency reference module by controlling the switch selection module, and observe whether the digital voltage output by the analog-to-digital converter exceeds the threshold voltage. If so, 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 via the switch selection module, and then the fixed input data of the first digital-to-analog converter is adjusted. At the same time, the digital voltage output of the analog-to-digital converter is detected. If the digital voltage exceeds the threshold voltage, the fixed input data of the first digital-to-analog converter is finely adjusted. After finding the peak point of the digital voltage, the output of the frequency reference module is selected via the switch selection module again, and it is detected whether the digital voltage exceeds the threshold voltage at this time. This process is repeated until a fixed input data of the first digital-to-analog converter is found, which makes the digital voltage exceed the threshold voltage when the DDS frequency synthesizer and the frequency reference module drive the optical frequency comb generation module. This fixed input data of the first digital-to-analog converter is the initialization data corresponding to comb tooth n. (d) Let k = 1; (e) Control switch selection module output frequency f c1 The input fixed data of the first digital-to-analog converter is finely adjusted in the direction of the nk comb 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 (nk)f c1 / r k Select the output of the DDS frequency synthesizer using the switch selection module, and observe f. c2 Can the digital voltage output by the analog-to-digital converter exceed the threshold voltage? If it does, then the current fixed input data of the first digital-to-analog converter is the initialization data corresponding to the nk comb tooth; otherwise, repeat this step until the initialization data corresponding to the nk comb tooth is found; where r k Choose the prime number closest to (nk) / 2; (f) Let k = k + 1, and repeat steps e and f until the initialization and storage of all fixed data corresponding to the comb teeth are completed.

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