Microwave photon fast frequency hopping signal generation system and method

Abstract

The invention discloses a microwave photon fast frequency hopping signal generation system and method. The system comprises a master laser, a light beam splitter, a slave laser, a semiconductor optical amplifier, an IQ modulator and a photoelectric detector. The main laser generates a single-frequency optical signal, and the single-frequency optical signal is modulated by the low-carrier-frequency radio-frequency signal gain switch to generate a wide-spectrum optical frequency comb; the method comprises the following steps of: dividing an optical signal into an upper branch and a lower branch through an optical beam splitter, injecting the optical signal into a slave laser through a polarization controller and a circulator to perform frequency-selecting filtering, then increasing the rejection ratio through a semiconductor optical amplifier, and loading the lower branch to a communication signal to control the phase difference between an I path and a Q path in a modulator, when carrier suppression single sideband modulation is realized, a + 1 order sideband and a-1 order sideband can be flexibly selected; and finally, beat frequency is carried out on the upper and lower branches through a photoelectric detector to realize communication signal output in a double-frequency coverage range. According to the invention, the difficulty of realizing a frequency hopping signal in a high carrier frequency and broadband range by a direct digital synthesizer in an electronic domain is greatly reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave photonics, and particularly relates to a microwave photonics fast frequency hopping signal generation system and method. BACKGROUND

[0002] With the advent of the big data era, the global spectrum resource is becoming increasingly scarce, and frequency hopping communication has been widely researched and applied in civil use due to the high spectrum resource utilization rate and other reasons. Moreover, since the carrier frequency of the frequency hopping signal constantly changes with time, the frequency hopping signal has strong anti-interference capability and plays an irreplaceable role in military secure communication. However, the traditional frequency hopping technology is mainly realized based on pure electronic methods, such as direct digital synthesis and voltage-controlled oscillator. However, due to the inherent bottleneck of electronics, the frequency hopping signal generated based on electronic methods generally has the problems of small bandwidth and low carrier frequency, and cannot solve the problems by itself.

[0003] In recent years, photons have attracted the attention of a large number of researchers due to their advantages such as high frequency band, large bandwidth and multi-channel parallel processing. Microwave photonics, which combines microwaves and light waves and is characterized by photon-assisted microwave technology, has obvious advantages in realizing the generation, processing, control and transmission of high-frequency microwave signals compared with traditional electronic schemes, and has been widely researched and gradually replaced the traditional microwave scheme in some scenarios. There are also reports on the realization of frequency hopping communication based on microwave photonics technology, which solves the problems of bandwidth and frequency in the electronic domain, but also has the disadvantages of low precision and weak anti-interference ability due to large frequency hopping bandwidth. Obviously, the traditional electronic method and the currently reported microwave photonics method have their own advantages and disadvantages, and it is difficult to simultaneously realize the frequency hopping characteristics of ultra-wideband, high precision and fast hopping speed.

[0004] Under this scenario, researchers have proposed a method based on optical and electrical joint regulation to realize the above functions. However, in the implementation process, the intermediate frequency channel bandwidth loaded by the electro-optical method is usually wide, corresponding to the comb tooth interval in the single optical comb method and the comb tooth interval difference of the upper and lower branch optical combs in the double optical comb scheme. In addition, in the existing optical comb tooth scheme, the number of comb teeth is nearly saturated, and increasing the bandwidth of the intermediate frequency signal will help to improve the overall bandwidth of the finally realized frequency hopping radio frequency signal. However, there are problems in realizing the intermediate frequency signal based on electronic methods, especially in the process of realizing high-frequency carrier frequency. Usually, a frequency multiplier is used for multiple frequency multiplication, resulting in the presence of many spurs in the frequency band, and due to the frequency hopping characteristics, fixed filters cannot be used for filtering. The signal quality of the intermediate frequency signal realized by the electronic technology as the seed source of the radio frequency frequency hopping signal will directly determine the signal quality of the radio frequency frequency hopping signal. Therefore, how to further reduce the bandwidth and upper limit of the frequency of the intermediate frequency signal without reducing the performance index is an important factor to improve the quality of the radio frequency frequency hopping signal. SUMMARY

[0005] The present application aims to provide a microwave photon fast frequency hopping signal generation system and method, which fully utilizes the characteristics of the upper and lower sidebands of the IQ modulator corresponding to the phase changes of the upper and lower branch modulation signals, and which realizes the full coverage of the optical frequency comb bandwidth intermediate frequency signal by modulating the intermediate frequency signal in the bandwidth of half the optical frequency comb interval, thereby greatly reducing the carrier frequency and bandwidth requirements of the intermediate frequency hopping source in the scheme and improving the purity of the generated frequency hopping signal.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical scheme: The present application provides a microwave photon fast frequency hopping signal generation system, which comprises a master laser, an optical beam splitter, a slave laser, a semiconductor optical amplifier, an IQ modulator and a photodetector. The master laser generates a single-frequency optical signal, which is modulated by a low-carrier-frequency radio frequency signal gain switch to generate a wide-spectrum optical frequency comb; the wide-spectrum optical frequency comb has the frequency of the master laser as the center and the frequency of the low-carrier-frequency radio frequency signal as the comb interval. The optical beam splitter divides the optical frequency comb into an upper branch optical frequency comb and a lower branch optical frequency comb, which are respectively injected into the slave laser; the free oscillation frequency of the slave laser is changed by controlling the driving current to realize the frequency selection filtering of the upper branch optical frequency comb and the lower branch optical frequency comb. The semiconductor optical amplifier further suppresses the amplitudes of other optical frequencies while maintaining the power of the selected frequency, thereby realizing high-suppression-ratio filtering. The IQ modulator injects an intermediate frequency communication signal, and the frequency range of the intermediate frequency communication signal is from 0 to half of the frequency of the low-carrier-frequency radio frequency signal; by controlling the phase difference between the upper and lower branches through the IQ modulator, when the lower branch optical frequency comb after frequency selection filtering is suppressed by the intermediate frequency communication signal carrier single sideband modulation, +1 order sideband and -1 order sideband are generated. The upper branch optical frequency comb after frequency selection filtering and the lower branch optical frequency comb after the IQ modulator are coupled and sent to the photodetector; the photodetector beats the upper and lower branches, respectively, to realize two kinds of beat frequency outputs, and the upper and lower sideband limits of the two kinds of beat frequency outputs are equal; the two kinds of beat frequency outputs are spliced together to realize a double frequency coverage range of the communication signal output.

[0007] Preferably, the master laser generates a single-frequency optical signal with a signal frequency of f m which is modulated by a low-carrier-frequency radio frequency signal with a frequency of f 0 to generate a wide-spectrum optical frequency comb with f m as the center and f 0 as the comb interval.

[0008] Preferably, the optical frequency comb achieves power equivalent distribution through a 1:1 optical beam splitter.

[0009] Preferably, the system further comprises a polarization controller and a circulator, The upper branch optical signal is input into slave laser one through polarization controller one and circulator one in sequence, and slave laser one is made to work at a certain optical frequency comb frequency by adjusting the driving current, so as to realize frequency selection filtering of the upper branch optical frequency comb. The lower branch optical signal is input into slave laser two through polarization controller two and circulator two in sequence, and slave laser two is made to always work at the maximum frequency or minimum frequency of all the teeth of the optical frequency comb, so as to realize frequency selection filtering of the lower branch optical frequency comb.

[0010] Preferably, the driving current is adjusted in any of the following ways: One is to directly use an arbitrary waveform generator to realize and control the current pin of slave laser one; The other is to fix the working current of slave laser one, and at the same time, modulate the amplitude of the working current at the radio frequency.

[0011] Preferably, the system generates an initial modulated intermediate frequency communication signal based on an electronic method, and the frequency range is from 0 to half of the frequency of the low carrier frequency radio frequency signal, that is, 0- f 0 / 2.

[0012] Preferably, the tooth spacing of the wide spectrum optical frequency comb needs to be equal to or near the relaxation oscillation peak of the master laser.

[0013] The application also provides a microwave photon fast frequency hopping signal generation method, which is realized based on the above microwave photon fast frequency hopping signal generation system, and the method comprises: Generating a single frequency light with a frequency of f m by the master laser, f 0 modulating the single frequency light by a low carrier frequency radio frequency signal gain switch with a frequency of f m to generate a wide spectrum optical frequency comb with a center of f 0 and a tooth spacing of M f m - Mf 0 to f m + Mf 0 ; and ​The low-power optical frequency comb is split into an upper branch optical frequency comb and a lower branch optical frequency comb by an optical beam splitter, and the upper branch optical frequency comb and the lower branch optical frequency comb are injected into slave lasers, respectively, the free oscillation frequency of the slave lasers is changed by controlling the driving current, and frequency selection filtering of the upper branch optical frequency comb and the lower branch optical frequency comb is realized; The upper branch optical frequency comb and the lower branch optical frequency comb after frequency selection filtering are both subjected to power amplification by a semiconductor optical amplifier; An initial modulated intermediate frequency communication signal is injected into an IQ modulator based on an electronic method, and the intermediate frequency communication signal has a frequency range of 0- f 0 / 2; The lower branch optical frequency comb after power amplification is injected into the IQ modulator, the phase difference of the upper branch and the lower branch is controlled by the IQ modulator, the lower branch optical frequency comb is suppressed single sideband modulated by the intermediate frequency communication signal carrier, and +1 order sideband and -1 order sideband are generated; The upper branch optical frequency comb after power amplification and the lower branch optical frequency comb after the IQ modulator are coupled and sent to a photodetector; Without changing the upper branch optical frequency comb, the upper branch and the lower branch are frequency-mixed, two kinds of frequency-mixed outputs are realized, respectively, the upper sideband limit and the lower sideband limit of the two kinds of frequency-mixed outputs are equal, the two kinds of frequency-mixed outputs are spliced together, and a communication signal output with a double frequency coverage range is realized; The working frequency of the upper branch slave laser is dynamically changed so as to work at different optical frequency comb frequencies f m - Mf 0 to f m + Mf 0 Corresponding to the change of the frequency-selected filtered optical frequency comb of the upper branch output, the radio frequency output after the upper branch and the lower branch frequency-mixing is continuously spliced on the frequency spectrum, and finally a communication signal output with a frequency range of 0- N + M +1.5) f 0 The frequency range of the frequency hopping signal is generated.

[0014] Preferably, the frequency selection filtering process comprises: The slave laser works at a certain optical frequency comb frequency by adjusting the driving current, and frequency selection filtering of the upper branch optical frequency comb is realized; The slave laser always works at the maximum frequency or the minimum frequency of all the teeth of the optical frequency comb by controlling the slave laser, and frequency selection filtering of the lower branch optical frequency comb is realized.

[0015] Compared with the prior art, the present application has the following advantages: 1. The present application realizes a broadband, high-precision and fast frequency hopping effect which is not inferior to the traditional scheme based on the simple structure of a single optical frequency comb.

[0016] 2. The optical frequency comb in this invention does not rely on the traditional complex cascaded modulator scheme; it can be achieved with just a single semiconductor laser and an external modulation radio frequency source.

[0017] 3. The gain-switching RF modulation source required by this invention has a low frequency. The traditional dual-optical frequency comb scheme uses the difference between the two optical frequency combs for broadband frequency conversion. In order to achieve broadband and large-span frequency conversion, and in order to be channelized and filtered by the optical filter, the spacing between the comb teeth of the two optical frequency combs is often around 25 GHz, which results in a high initial modulation source frequency and requires a corresponding high-power amplifier.

[0018] 4. The channelized filter of this invention is equivalently implemented by utilizing the injection-locked amplification of a semiconductor laser in the optical injection state, and its switching characteristics between different channels are also synchronously realized in the change of the laser's driving current. This is equivalent to simultaneously achieving the effects of a channelized filter and an optical switch in traditional schemes, offering significant advantages in terms of cost, complexity, size, and power consumption. Furthermore, it offers greater flexibility, without being limited by the fixed filtering bandwidth of traditional wavelength division multiplexing and demultiplexing units.

[0019] 5. In this invention, the phase change of the IQ modulator in the upper and lower branches can be achieved by changing the phase of one of the branches. This results in a fast response speed and simple control, while significantly reducing the bandwidth and frequency of the initial intermediate frequency (IF) hopping signal required. Without increasing implementation difficulty or reducing performance indicators, the requirements for the initial IF hopping signal are lowered. Simultaneously, it avoids the signal spurious problems caused by electronic methods in implementing high-frequency IF hopping signal frequency multiplication, which is closely related to the spurious signals generated during spectrum shifting to high-frequency hopping.

[0020] 6. In this invention, a semiconductor optical amplifier is used to further improve the suppression ratio of channelization filtering; 7. This invention is no longer limited to generating ultra-wideband, high-precision, fast frequency-hopping signals based on purely electronic or microwave photonic methods. Instead, it fully utilizes the advantages of both methods to simultaneously generate ultra-wideband signals that are both high-precision and fast frequency-hopping. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the microwave photonic fast frequency hopping signal generation system provided by the present invention; Figure 2 The single-frequency light from the main laser in this invention is filtered by a frequency of... f 0 A schematic diagram of a broadband optical frequency comb generated after gain switching modulation of a low carrier frequency radio frequency signal; Figure 3 This is the spectrum of the upper branch optical signal output after being filtered by a channelized laser in this invention. Figure 4 is the optical spectrum diagram of the upper branch optical signal output after the semiconductor optical amplifier and the channel filter in the present application; Figure 5 is the schematic diagram of the intermediate frequency communication signal modulated to the IQ modulator in the present application; Figure 6 is the optical spectrum diagram of the lower branch optical signal output after the channel filter from the second laser in the present application; Figure 7 is the optical spectrum diagram of the lower branch optical signal output after the semiconductor optical amplifier and the channel filter in the present application; Figure 8 is the optical spectrum diagram of the optical signal output from the second laser after the carrier suppression ±1 order single sideband modulation of the IQ modulator in the present application; Figure 9 is the schematic diagram of the frequency spectrum output after the beat frequency of the photodetector in the present application; Figure 10 is the optical spectrum diagram of the upper branch optical signal output after the channel filter from the first laser and the semiconductor optical amplifier when the first laser works at different optical frequency comb frequencies in the present application; Figure 11 is the RF frequency hopping splicing spectrum diagram output after the beat frequency of the spectrum diagram output by controlling the channelization laser of the upper branch in the present application. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings and examples. The examples described below by reference to the accompanying drawings are illustrative and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0023] In the description of the present application, it should be noted that the terms "upper", "lower", "front", "back", "end", "bottom", "side" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or components referred to must have a particular orientation, therefore cannot be understood as a limitation of the present application.

[0024] In the present application, unless otherwise explicitly specified and limited, the terms "connection", "installation" and the like should be understood broadly, for example, it can be fixed connection, it can also be direct connection, or it can be connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0025] Second, the present application is called "one embodiment" or "embodiments" refers to a specific feature, structure or characteristics that can be included in at least one implementation of the present application. In this specification, "in one embodiment" does not mean the same embodiment, nor is it a separate or selective embodiment that excludes other embodiments.

[0026] The specific embodiments of the present application are described in further detail below with reference to the accompanying drawings. The following embodiments are used to illustrate the present application, but not to limit the scope of the present application.

[0027] In conjunction Figure 1 , the present application provides a microwave photon fast frequency hopping signal generation system, the system mainly includes a master laser, an optical beam splitter, a polarization controller, a circulator, a semiconductor optical amplifier, a slave laser, an IQ modulator and a photodetector, Specifically, The master laser generates a single-frequency optical signal, which is modulated by a low-frequency RF signal gain switch to generate a multi-tooth optical frequency comb with high carrier-to-noise ratio near the frequency, and the optical frequency comb tooth spacing corresponds to the modulated RF signal frequency; The optical frequency comb is equally divided by a 1:1 optical beam splitter, and the optical frequency comb is divided into two branches, which are used as frequency hopping frequency conversion local oscillator photon source and frequency hopping signal modulation photon source; The upper branch optical signal passes through the polarization controller one and the circulator one in turn and is input into the slave laser one, and the slave laser one is adjusted to work at a certain optical frequency comb frequency, at this time, due to the injection locking amplification effect, the output optical signal of the slave laser one only realizes power amplification of the corresponding tooth, that is, the channelization filtering effect is realized; It should be noted that by changing the corresponding free oscillation frequency of the slave laser one and enabling it to step jump each time to correspond to a certain frequency of the upper optical frequency comb, channelization filtering of different frequency combs or optical signals can be realized at different times. The polarization state of the signal light injected into the slave laser one is controlled and adjusted by the polarization controller, so that efficient injection locking can be realized; In order to further improve the frequency selection filtering effect and suppress other frequency combs, the frequency selection filtered optical frequency comb is input into the semiconductor optical amplifier one to further improve the power of the required frequency signal and suppress the amplitude of other frequency signals, thereby realizing high rejection ratio filtering; The lower branch optical signal is input into the slave laser two through the polarization controller two and the circulator two, and the working current of the slave laser two is controlled to remain unchanged, so that the slave laser two always works at the maximum frequency or minimum frequency of all the teeth of the optical frequency comb, and the power of the channel light is amplified through injection locking amplification; In order to further improve the frequency selection filtering effect and suppress other frequency combs, the frequency selection filtered optical frequency comb is input into the semiconductor optical amplifier one to further improve the power of the required frequency signal and suppress the amplitude of other frequency signals, thereby realizing high rejection ratio filtering; The initial modulated intermediate frequency communication signal based on the electronic method is injected into the IQ modulator, and the frequency range is from 0 to half of the low carrier frequency radio frequency modulation source frequency; The lower branch optical signal is injected into the IQ modulator, and the single optical signal output from the laser two will be suppressed single sideband modulated by the intermediate frequency frequency hopping signal carrier, the phase difference of the I and Q two paths in the IQ modulator bridge control modulator is flexibly controlled, so that when the carrier suppressed single sideband modulation is realized, the +1 order sideband and -1 order sideband can be flexibly selected; at the same time, due to the different phase differences, the lower branch optical signal and the upper branch optical signal are respectively at 90° and -90°, which will cause the +1 order sideband and -1 order sideband effects; The upper branch optical signal and the lower branch optical signal through the IQ modulator are coupled and sent to the photodetector, the upper and lower branch frequencies are obtained without changing the upper branch optical signal, and the upper and lower sideband limits of the two outputs are equal due to the intermediate frequency communication signal starting from 0 GHz, so that the two frequency outputs are spliced together, thereby realizing the output of the communication signal with double frequency coverage. With the continuous change of the output optical signal after the channelization filtering of the upper branch, the radio frequency output after the upper and lower branch frequency can be spliced on the spectrum, and finally the wideband frequency hopping signal generation is realized.

[0028] In the application, the free oscillation wavelength of the laser one needs to be efficiently switched over time, so the operating current of the laser one needs to be continuously changed with the different carrier frequency requirements of the frequency hopping signal, and the frequency hopping pattern corresponds to the driving current pattern of the laser one. There are two ways to change the driving current, one is to directly use an arbitrary waveform generator to realize and control the current pin of the laser, and the other is to fix the operating current of the laser, and modulate the amplitude of the operating current at its radio frequency.

[0029] In the application, the intermediate frequency communication signal is loaded by using the IQ electro-optic modulator. By controlling the phase difference of the intermediate frequency communication signals in the upper and lower branches of the IQ modulator and selecting +90° and -90°, the spectrum output by the IQ modulator corresponds to carrier suppressed single sideband +1 order sideband and -1 order sideband modulation, respectively, so that the same comb tooth of the upper branch can realize spectrum shift of the intermediate frequency signal to different carrier frequencies after frequency mixing, and the maximum and minimum frequencies of the two radio frequency hopping signals after spectrum shift are equal, so that spectrum splicing can be realized, which is equivalent to realizing the output of the frequency hopping signal with twice the bandwidth of the initial input intermediate frequency signal, and the required bandwidth of the intermediate frequency signal is greatly reduced.

[0030] In this invention, the switching speed of the frequency hopping signal is determined by two factors: first, the switching speed of the frequency hopping signal in the lower branch, which is determined by electronic technology; and second, the switching speed of the broadband frequency-converted local oscillator optical signal provided by the upper branch, which corresponds to the response speed after each current adjustment of the laser 1, and is determined by photonics technology.

[0031] The high-carrier-frequency hopping signal ultimately achieved in this invention originates from the beat frequency of the optical signal comb selected by the channelization filter of the upper branch and the suppressed single-sideband modulation signal of the signal optical carrier of the lower branch. For the comb of the upper branch, when the current is changed, the output single comb tooth will jump at different optical frequency comb tooth frequencies, and the spacing between adjacent comb teeth is exactly equal to twice the bandwidth of the modulated intermediate frequency signal. Therefore, when adjacent comb teeth of the channelized output of the upper branch beat with the signal of the lower branch, the output frequency hopping signal can be spliced ​​in the spectrum. This achieves a wide-span, ultra-wideband, and continuous radio frequency frequency hopping signal, and the final frequency hopping signal bandwidth is the product of the number of comb teeth + 0.5 and the comb tooth spacing. The precision of the frequency hopping signal is determined by the minimum frequency hopping interval of the initial input intermediate frequency signal.

[0032] It should be noted that the number of teeth in the optical frequency comb is related to the power and frequency of the gain-switched modulated semiconductor laser. The higher the power, the better, but at the same time, it is necessary to control the main laser to prevent it from entering a chaotic state; the frequency needs to be near the relaxation oscillation peak of the main laser.

[0033] Since the total bandwidth of the final frequency hopping signal is related to the number of comb teeth and the tooth spacing of the optical frequency comb, the larger the tooth spacing, the better. The tooth spacing corresponds to or is close to the relaxation oscillation frequency of the main laser. Therefore, in order to improve the bandwidth of the final frequency hopping signal and reduce the requirements for the RF signal power in the gain switching state, a laser with a larger relaxation oscillation frequency and a higher small signal modulation response at that position is selected.

[0034] Using the above technical solution, during the processing of the upper and lower branches, a light-injected semiconductor laser is used for channelized filtering and frequency selection, followed by a semiconductor optical amplifier to further improve the filtering effect. Furthermore, since the optical signals of both upper and lower branches originate from the same source, the signal quality of the beat frequency is good.

[0035] The present invention adopts the above-mentioned technical solution, and by making full use of the characteristic that the ±1st order sideband in the IQ modulator responds quickly with the phase change of the upper and lower branch modulation signals, it significantly reduces the requirements for the initial intermediate frequency hopping signal while realizing the generation of ultra-wideband, large-span, continuous high-precision microwave photonic fast frequency hopping signals, thereby reducing the implementation difficulty and improving the signal quality.

[0036] Based on the above system, the method for generating microwave photonic fast frequency hopping signals is implemented as follows: Step 1, the main laser generates a frequency of...f m Single-frequency light, with a frequency of f 0 The low carrier frequency radio frequency signal is modulated by gain switching to generate a signal near this frequency. f m Centered on the comb teeth, with a spacing of 1 / 25mm between the comb teeth. f 0 A broadband optical frequency comb, with the comb tooth spacing corresponding to the frequency of the modulated radio frequency signal, has the following spectrum: Figure 2 As shown, Figure 2 Figure (a) shows the spectrum of the main laser, and Figure (b) shows the spectrum of the main laser powered by a laser with a frequency of [missing value]. f 0 The output spectrum of the low carrier frequency RF signal after gain switching modulation, assuming a total of 2M+1 comb teeth and a comb tooth frequency range of... f m - Mf 0 ~f m + Mf 0 In the picture, f m - Nf 0 Let N be any optical frequency comb frequency, where N = 0, ±1, ±2, ..., ±M.

[0037] Step 2: The optical frequency comb is split into two paths by a 1:1 optical beam splitter to serve as the upper and lower branch frequency hopping conversion local oscillator photon source and the frequency hopping signal modulation photon source.

[0038] Step 3: The upper branch optical signal is sequentially input to the slave laser through polarization controller one and circulator one. The slave laser is adjusted to operate at a certain optical frequency comb frequency. Due to the injection-locked amplification effect, the signal power at that frequency will be significantly enhanced, while the power of other output optical signals remains unchanged or is suppressed due to mode competition. This achieves frequency-selective filtering from multiple optical frequency comb teeth to a single optical frequency comb signal. The optical signal output from the slave laser is as follows: Figure 3 As shown, only the corresponding comb teeth achieve power amplification, i.e., frequency selective filtering effect.

[0039] Step 4: The frequency-selective filtered optical frequency comb is further amplified by a semiconductor optical amplifier to increase the power of the desired frequency signal while suppressing the amplitude of other frequency signals, achieving a high rejection ratio filter; the result is as follows. Figure 4 As shown.

[0040] Step 5: Generate an initial modulated intermediate frequency (IF) communication signal based on electronic methods. The frequency range is from 0 to half the frequency of the aforementioned low-carrier frequency (RF) signal, and the corresponding spectrum is as follows: Figure 5 As shown.

[0041] Step 6: The lower branch establishes a stable frequency-modulated photon source. The optical signal from the lower branch is sequentially input to the slave laser two via polarization controller two and circulator two. The operating current of the slave laser two is kept constant, always operating at the maximum or minimum frequency of all teeth of the optical frequency comb. After injection-locked amplification, the power of the light in this channel is amplified, and its output spectrum is as follows: Figure 6 As shown.

[0042] Step 7: The frequency-selective filtered optical frequency comb is then passed through a semiconductor optical amplifier to achieve high rejection ratio filtering; the result is as follows. Figure 7 As shown.

[0043] Step 8: The lower branch optical signal is injected into the IQ modulator. The IQ modulator controls the phase difference between the upper and lower branches. The single optical signal output from laser two will be suppressed by the intermediate frequency communication signal carrier for single-sideband modulation. Simultaneously, due to the different phase differences at 90° and -90°, two effects will occur: +1st-order sideband and -1st-order sideband, respectively. The corresponding spectra are as follows: Figure 8 As shown, Figure 8 Figure (a) shows a schematic diagram of the -1st order sideband, and Figure (b) shows a schematic diagram of the +1st order sideband.

[0044] Step 9: Without changing the optical signal of the upper branch, implement two different beat frequency outputs for the upper and lower branches respectively, such as... Figure 9 Figure (a) shows the -1st order sideband beat frequency, and Figure (b) shows the +1st order sideband beat frequency. Since the intermediate frequency communication signal starts from 0 GHz, the upper and lower sideband limits of the two outputs are equal, thus achieving a frequency-hopping signal generation effect with double the bandwidth, such as... Figure 9 Figure (c) in the middle.

[0045] Step 10: Dynamically change the operating frequency of laser one to make it operate at different optical frequency comb frequencies. f m - Mf 0 to f m + Mf 0 The channelized filter output spectrum of the corresponding branch will also change continuously, such as Figure 10 As shown.

[0046] Step 11: As the optical signal output after channelization filtering of the upper branch changes continuously, the radio frequency output after frequency beat of the upper and lower branches can be continuously spliced ​​on the spectrum, ultimately achieving 0-(N+M+1.5). f 0 Frequency hopping signal generation within a frequency range, such as Figure 11 As shown.

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A microwave photonic fast frequency hopping signal generation system, characterized in that, include: Master laser, optical beam splitter, slave laser, semiconductor optical amplifier, IQ modulator, and photodetector; The main laser generates a single-frequency optical signal, which is modulated by a gain switch of a low-carrier-frequency radio frequency signal to generate a broadband optical comb. The broadband optical comb is centered on the frequency of the main laser and the frequency of the low-carrier-frequency radio frequency signal is used as the spacing between the comb teeth. The optical beam splitter divides the optical frequency comb into an upper branch optical frequency comb and a lower branch optical frequency comb. The upper branch optical frequency comb and the lower branch optical frequency comb are respectively injected into the slave laser. By controlling the driving current to change the free oscillation frequency of the slave laser, frequency selective filtering of the upper branch optical frequency comb and the lower branch optical frequency comb is achieved. The semiconductor optical amplifier further enhances the power of the frequency-selective filtered optical frequency while suppressing the amplitude of other optical frequency signals, achieving high suppression ratio filtering. The IQ modulator injects an intermediate frequency (IF) communication signal, the frequency range of which is from 0 to half the frequency of the low carrier frequency radio frequency signal; the phase difference between the upper and lower branches is controlled by the IQ modulator, and when the optical frequency comb of the lower branch after frequency selection and filtering is modulated by the carrier-suppressed single sideband of the IF communication signal, a +1 order sideband and a -1 order sideband are generated. The upper branch optical frequency comb after frequency selection and filtering and the lower branch optical frequency comb after IQ modulator are coupled and sent to the photodetector. The photodetector beats the upper and lower branches, respectively realizing two beat frequency outputs. The upper and lower sideband limits of the two beat frequency outputs are equal. The two beat frequency outputs are spliced ​​together to realize the communication signal output with double frequency coverage.

2. The microwave photonic fast frequency hopping signal generation system according to claim 1, characterized in that, The main laser generates a signal frequency of: f m A single-frequency optical signal with a frequency of f 0 After gain switching modulation of the low carrier frequency radio frequency signal, a signal is generated. f m Centered on, with comb teeth spaced as f 0 A broadband optical frequency comb.

3. The microwave photonic fast frequency hopping signal generation system according to claim 1, characterized in that, The optical frequency comb achieves power equivalent distribution through a 1:1 optical beam splitter.

4. A microwave photonic fast frequency hopping signal generation system according to claim 2, characterized in that, The system also includes: a polarization controller and a circulator. The upper branch optical signal is sequentially input to the slave laser through polarization controller one and circulator one. By adjusting the driving current, the slave laser is made to operate at a certain optical frequency comb frequency, thereby achieving frequency selective filtering of the upper branch optical frequency comb. The lower branch optical signal is sequentially input to the slave laser through polarization controller two and circulator two, controlling the slave laser two to always operate at the maximum or minimum frequency of all comb teeth of the optical frequency comb, thereby realizing frequency selective filtering of the lower branch optical frequency comb.

5. A microwave photonic fast frequency hopping signal generation system according to claim 4, characterized in that, Adjust the drive current using any of the following methods: One method is to directly use an arbitrary waveform generator to implement and control the current pin of laser one; Another method is to fix the operating current from the laser and modulate the amplitude of the operating current at its radio frequency.

6. The microwave photonic fast frequency hopping signal generation system according to claim 1, characterized in that, The system generates an initially modulated intermediate frequency (IF) communication signal based on electronic methods, with a frequency range from 0 to half the frequency of the low carrier frequency radio frequency signal, i.e., 0- f 0 / 2.

7. The microwave photonic fast frequency hopping signal generation system according to claim 1, characterized in that, The spacing between the comb teeth of the broadband optical frequency comb must be equal to or near the relaxation oscillation peak of the main laser.

8. A method for generating microwave photonic fast frequency hopping signals, characterized in that, Based on the microwave photonic fast frequency hopping signal generation system according to claim 1, the method includes: The frequency is generated by the main laser. f m Single-frequency light, with a frequency of f 0 The low carrier frequency radio frequency signal is modulated by gain switching and then generated with f m Centered on, with comb teeth spaced as f 0 A broadband optical frequency comb; assuming a total of 2 comb teeth. M +1, then the frequency range of the broadband optical comb is f m -Mf 0 to f m +Mf 0 ; The low-power optical frequency comb is divided into an upper branch optical frequency comb and a lower branch optical frequency comb by an optical beam splitter. The upper branch optical frequency comb and the lower branch optical frequency comb are injected into the slave laser respectively. By controlling the driving current to change the free oscillation frequency of the slave laser, frequency selective filtering of the upper branch optical frequency comb and the lower branch optical frequency comb is achieved. Both the upper and lower branch optical frequency combs after frequency selection and filtering are amplified by a semiconductor optical amplifier; An intermediate frequency (IF) communication signal, initially modulated using electronic methods, is injected into an IQ modulator. The IF communication signal has a frequency range of 0- f 0 / 2; The power-amplified lower branch optical frequency comb is injected into the IQ modulator. The phase difference between the upper and lower branches is controlled by the IQ modulator. The lower branch optical frequency comb is suppressed by the intermediate frequency communication signal carrier single sideband modulation to generate +1 order sideband and -1 order sideband. The upper branch optical frequency comb, after power amplification, is coupled to the lower branch optical frequency comb via IQ modulator and sent to the photodetector. Without changing the optical frequency comb of the upper branch, two beat frequency outputs are achieved for the beat frequencies of the upper and lower branches respectively. The upper and lower sideband limits of the two beat frequency outputs are equal. The two beat frequency outputs are spliced ​​together to achieve communication signal output with double frequency coverage. Dynamically change the operating frequency of the laser in the upper branch to make it work at different optical frequency comb frequencies. f m -Mf 0 to f m + Mf 0 The optical frequency comb after frequency selection and filtering of the corresponding upper branch output changes, and the RF output after frequency beating by the upper and lower branches is continuously spliced ​​in the spectrum, ultimately achieving 0 to ( N + M +1.5) f 0 Frequency hopping signal generation within a frequency range.

9. A method for generating microwave photonic fast frequency hopping signals according to claim 8, characterized in that, The frequency selective filtering process includes: By adjusting the driving current, the laser is made to operate at a certain optical frequency comb frequency, thus achieving frequency selective filtering of the upper branch optical frequency comb. By controlling the laser to always operate at the maximum or minimum frequency of all comb teeth of the optical frequency comb, frequency selective filtering of the lower branch optical frequency comb can be achieved.

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