Multi-band reconfigurable broadband waveform generation device based on microwave photons

Abstract

The invention discloses a multi-band reconfigurable broadband waveform generation device based on microwave photons, belongs to the technical field of microwave photons, and solves the problems of narrow high-frequency working bandwidth and poor noise characteristic when bandwidth linear frequency modulation radar signals are generated in the prior art. By adjusting the bandwidth of the radio frequency baseband signal, the cyclic frequency shift times of the multiple optical channels and the comb tooth interval between the two optical frequency combs, the functions that the waveform frequency band of the broadband waveform is adjustable, and the frequency modulation slope and amplitude of the linear frequency modulation signal are adjustable are achieved. The multi-channel optical channel can support generation and gating of a plurality of signals with different frequency bands at the same time, each signal has independent signal reconstruction, regulation and control capabilities, the capability of adapting to different requirements of electronic information systems such as different radars for broadband waveforms is achieved, and the reconfigurable performance is high.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave photons and relates to a multi-band reconfigurable broadband waveform generating device based on microwave photons. Background Art

[0002] With the development of electronic technology, radar is facing increasingly severe threats such as anti-radiation, comprehensive electronic interference, stealth targets and low-altitude penetration. This requires radar to not only obtain basic information such as the position and speed of the target, but also have the ability to identify and image the target. Linear frequency modulation radar signals with large time-width bandwidth can improve the radar's distance and speed resolution, which is beneficial to improving the radar's concealment and anti-interference capabilities, and enhancing the radar's survivability in multiple working environments. Existing technologies include the P-3 ultra-wideband synthetic aperture radar jointly developed by the Institute of Environment at the University of Michigan and the U.S. Naval Aviation Research Center. The system uses a linear frequency modulation waveform with a bandwidth of more than 500MHz; the high-resolution SAR developed by Canada works in the X-band and uses digital technology to generate a linear frequency modulation signal with a bandwidth of 500MHz and a time width of 0.5us; the National University of Defense Technology in my country has also achieved a large-bandwidth linear frequency modulation signal with a bandwidth of 500-1000MHz and a time width of 300us in the laboratory. The document "Research on PLL Swept Frequency Broadband Signal Generation Technology" (Meng Xiangjian. National University of Defense Technology, 2014.) studies the method of PLL sweeping to generate broadband linear frequency modulation signals in response to the application needs of micro SAR, uses the circuit structure of the PLL to excite the DDS output signal, and designs and implements the Ku-band LFM signal source.

[0003] Although electronic technology has matured, the bottleneck of electronic technology has emerged as the next generation of radars has become increasingly urgent in terms of higher carrier frequencies and larger operating bandwidths. This is especially true in terms of signal generation. Currently, the electronic devices used to generate signals include frequency synthesizers and analog-to-digital converters, which have narrow high-frequency operating bandwidths and poor noise characteristics, which fundamentally limits the improvement of radar performance.

[0004] In recent years, the emerging microwave photonics uses photonic technology to generate and process microwave signals. It has the advantages of high precision and large bandwidth. It can directly realize the generation of high-stable local oscillators and arbitrary waveforms in the millimeter wave frequency band, avoid the degradation of signal quality caused by frequency doubling and up-conversion operations, and meet the requirements of broadband radar for waveforms with high frequency resolution, high speed, and large bandwidth. At the same time, the amplitude, operating frequency, and frequency modulation slope are tunable. Therefore, it is very necessary to propose a photonic broadband waveform generating device based on microwave photonic technology that can simultaneously support the generation of multiple frequency band signals and improve the performance of broadband radar. Summary of the invention

[0005] The technical solution of the present invention is used to solve the problems of narrow high-frequency working bandwidth and poor noise characteristics when generating broadband linear frequency modulation radar signals in the prior art.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] A multi-band reconfigurable broadband waveform generating device based on microwave photons, comprising a first optical frequency comb, a first optical wavelength division multiplexer, a multi-path optical channel, a second optical wavelength division multiplexer, a 2×1 optical coupler, a second optical frequency comb and an optical detector;

[0008] The output end of the first optical frequency comb is connected to the input end of the first optical wavelength division multiplexer, the multiple output ends of the first optical wavelength division multiplexer are respectively connected to the input ends of the multiple optical channels, the output ends of the multiple optical channels are respectively connected to the multiple input ends of the second optical wavelength division multiplexer, the output end of the second optical wavelength division multiplexer is connected to the first input end of the 2×1 optical coupler, the output end of the second optical frequency comb is connected to the second input end of the 2×1 optical coupler, and the output end of the 2×1 optical coupler is connected to the input end of the optical detector;

[0009] The optical channel includes an optical switch, an optical modulator, an optical filter and a frequency shift unit connected in sequence; the frequency shift unit includes a 2×2 optical coupler, an optical amplifier and an acousto-optic frequency shifter; the first output end of the 2×2 optical coupler is connected to the input end of the optical amplifier, the output end of the optical amplifier is connected to the input end of the acousto-optic frequency shifter, and the output end of the acousto-optic frequency shifter is connected to the first input end of the 2×2 optical coupler;

[0010] The input end of the optical switch serves as the input end of the optical channel, the RF input end of the optical modulator receives the RF baseband signal, the output end of the optical filter is connected to the second input end of the 2×2 optical coupler, and the second output end of the 2×2 optical coupler serves as the output end of the optical channel.

[0011] Furthermore, the first optical frequency comb outputs a multi-tooth signal, the number of teeth of the first optical frequency comb corresponds to the number of output channels of the first optical wavelength division multiplexer, and the passband center frequency of each output end of the first optical wavelength division multiplexer corresponds one-to-one to each tooth wavelength of the first optical frequency comb.

[0012] Furthermore, the first optical wavelength division multiplexer divides the wavelengths of the multi-comb signal output by the first optical frequency comb, and outputs the optical comb signal corresponding to each comb wavelength from each output end of the first optical wavelength division multiplexer.

[0013] Furthermore, the optical modulator uses the optical comb signal input into the optical modulator as an optical carrier signal, inputs the corresponding radio frequency baseband signal into the optical modulator for modulation, and outputs an optical modulated signal.

[0014] Furthermore, the optical filter is used to filter out the optical carrier signal and retain the single-sideband optical modulation signal.

[0015] Furthermore, the first input end of the 2×2 optical coupler receives the optical modulated signal after being frequency-shifted by the acousto-optic frequency shifter, the second input end of the 2×2 optical coupler receives the optical modulated signal after being filtered by the optical filter, the first output end of the 2×2 optical coupler outputs the optical modulated signal for cyclic frequency shifting, which is input into the acousto-optic frequency shifter for cyclic frequency shifting after being amplified by the optical amplifier, and the second output end of the 2×2 optical coupler outputs the coupled linear frequency modulation signal.

[0016] Furthermore, the frequency shift amount of the acousto-optic frequency shifter is the same as the bandwidth of the radio frequency baseband signal modulated by the optical channel.

[0017] Furthermore, the second optical wavelength division multiplexer is used to combine the linear frequency modulation signals output by multiple optical channels, the linear frequency modulation signal output by the second optical wavelength division multiplexer is input to the first input end of the 2×1 optical coupler, and the second optical frequency comb inputs the output multi-comb signal to the second input end of the 2×1 optical coupler, and then inputs the optical detector after coupling by the 2×1 optical coupler.

[0018] Furthermore, the second optical frequency comb has the same number of teeth as the first optical frequency comb, but different tooth intervals.

[0019] The advantages of the present invention are:

[0020] The present invention is based on microwave photonic technology, combined with wavelength multiplexing and optical cyclic frequency shifting, to generate photonic broadband waveforms. By adjusting the bandwidth of the RF baseband signal, the number of cyclic frequency shifts of multiple optical channels, and the comb tooth spacing between two optical frequency combs, the waveform frequency band of the broadband waveform can be adjusted, and the frequency modulation slope and amplitude of the linear frequency modulation signal can be adjusted. The multiple optical channels can simultaneously support the generation and selection of multiple signals of different frequency bands. Each signal has the ability of independent signal reconstruction and regulation, and has the ability to adapt to different requirements of different radar and other electronic information systems for broadband waveforms, and has strong reconfigurable performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural diagram of a multi-band reconfigurable broadband waveform generating device based on microwave photons according to the first embodiment of the present invention;

[0022] 2(a) to (c) are schematic diagrams of the waveform generating device according to the first embodiment of the present invention generating signals under different conditions. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0025] Embodiment 1

[0026] like Figure 1 As shown, specifically, a multi-band reconfigurable broadband waveform generating device based on microwave photons is disclosed, comprising a first optical frequency comb, a first optical wavelength division multiplexer, a multi-path optical channel, a second optical wavelength division multiplexer, a 2×1 optical coupler, a second optical frequency comb and an optical detector;

[0027] The output end of the first optical frequency comb is connected to the input end of the first optical wavelength division multiplexer, the multiple output ends of the first optical wavelength division multiplexer are respectively connected to the input ends of multiple optical channels, the output ends of the multiple optical channels are respectively connected to the multiple input ends of the second optical wavelength division multiplexer, the output end of the second optical wavelength division multiplexer is connected to the first input end of the 2×1 optical coupler, the output end of the second optical frequency comb is connected to the second input end of the 2×1 optical coupler, and the output end of the 2×1 optical coupler is connected to the input end of the optical detector.

[0028] The optical channel includes an optical switch, an optical modulator, an optical filter and a frequency shifting unit connected in sequence; the frequency shifting unit includes a 2×2 optical coupler, an optical amplifier and an acousto-optic frequency shifter; the first output end of the 2×2 optical coupler is connected to the input end of the optical amplifier, the output end of the optical amplifier is connected to the input end of the acousto-optic frequency shifter, and the output end of the acousto-optic frequency shifter is connected to the first input end of the 2×2 optical coupler.

[0029] The input end of the optical switch serves as the input end of the optical channel, the RF input end of the optical modulator receives the RF baseband signal, the output end of the optical filter is connected to the second input end of the 2×2 optical coupler, and the second output end of the 2×2 optical coupler serves as the output end of the optical channel.

[0030] Furthermore, the first optical frequency comb outputs a multi-tooth signal, the number of teeth of the first optical frequency comb corresponds to the number of output channels of the first optical wavelength division multiplexer, and the passband center frequency of each output end of the first optical wavelength division multiplexer corresponds one-to-one to each tooth wavelength of the first optical frequency comb.

[0031] In this embodiment, the first optical frequency comb is used to output a plurality of optical comb tooth signals, and the optical comb tooth signals include a plurality of optical signals with different frequencies and uniformly distributed frequencies. The optical frequency comb can generate regularly spaced frequency lines (i.e., optical comb tooth signals), and each optical comb tooth is actually a separate frequency signal. These frequency lines can cover a wide frequency range and are very precisely spaced. The optical frequency comb generates a series of precisely spaced frequency lines by emitting extremely short, repetitive light pulses. Each pulse contains a combination of a large number of different frequencies, forming a frequency comb, which is used to emit a light beam containing widely and evenly distributed frequencies, showing the characteristics of a wide spectrum. The laser emitted by the optical frequency comb covers a plurality of different frequencies, and the different frequencies are strictly and evenly distributed, forming a plurality of sharp and evenly spaced spectral lines. By precisely controlling the phase and frequency of the laser, the coherence between different pulses can be maintained.

[0032] Furthermore, the first optical wavelength division multiplexer divides the wavelengths of the multi-comb signal output by the first optical frequency comb, and outputs the optical comb signal corresponding to each comb wavelength from each output end of the first optical wavelength division multiplexer.

[0033] In this embodiment, the first optical frequency comb output includes N optical comb signals with different frequencies and uniform frequency distribution. The optical comb signals are wavelength-divided into N optical comb signals with different frequencies by the first optical wavelength division multiplexer. The output end of each first optical wavelength division multiplexer outputs a comb signal corresponding to the center frequency of the channel and inputs it into the optical channel of the corresponding frequency band.

[0034] Furthermore, the optical switch is used to control the on and off of each optical comb signal, so as to select the signal according to the needs of the device.

[0035] In this embodiment, the optical fiber input end of the optical modulator is connected to the output end of the optical switch, the optical fiber output end of the optical modulator is connected to the input end of the optical filter, the RF input end of the optical modulator is used to receive the RF baseband signal, the optical comb signal input into the optical modulator is used as the optical carrier signal, and the corresponding RF baseband signal is input into the optical modulator for modulation. In this embodiment, the RF baseband signal input into the optical modulator is set according to the waveform input required by the corresponding device, and the N optical channels can input the same RF baseband signal or different RF baseband signals, and the frequencies of the optical carrier signals on the N optical channels are different.

[0036] Furthermore, the optical filter is used to filter out the optical carrier signal and retain the single-sideband optical modulation signal. When the RF baseband signal is modulated onto the optical comb signal, modulation sidebands will be generated on both sides of each optical signal frequency. If the passband bandwidth of the optical channel is equal to or greater than the interval between the optical comb teeth, the modulation sidebands of adjacent optical comb teeth may overlap into adjacent optical channels, resulting in signal interference and performance degradation. Since the output values ​​of the two sidebands will be different after interference, their superposition will affect the threshold judgment of the output optical power value in the later stage, and it is impossible to judge whether the frequency band of the signal falls within the corresponding frequency interval. Therefore, the optical signal after filtering by the optical filter can only pass a single optical sideband, so that each channel only transmits its corresponding optical comb tooth and its sideband, accurately controlling the transmission of the signal, thereby improving the overall efficiency and signal quality of the device.

[0037] In this embodiment, the 2×2 optical coupler in the frequency shift unit receives the optical modulated signal after the frequency shift output by the acousto-optic frequency shifter through the first input end, and receives the optical modulated signal after filtering by the optical filter through the second input end. The first output end of the 2×2 optical coupler amplifies the optical modulated signal through the optical amplifier, and then finely shifts the frequency of the single-sideband optical modulated signal through the acousto-optic frequency shifter. The frequency shift amount is the same as the bandwidth of the RF baseband signal modulated by the optical channel. The acousto-optic frequency shifter is set according to the needs of the device to form a fixed-length loop branch in the frequency shift unit. The frequency shift amount generated in each cycle is fixed, and the coupled linear frequency modulation signal is output through the second output end of the 2×2 optical coupler. Further, in this embodiment, the frequency modulation slope of the linear frequency modulation signal can be tuned by controlling the frequency shift amount, so that multiple optical pulse trains with different frequencies can be output in a single optical channel.

[0038] Furthermore, the acousto-optic frequency shifter is used to shift the frequency of the single-sideband optical modulated signal in each cycle, which can not only avoid the coherent superposition of multiple cycles of the same-frequency signal in the loop branch, but also continuously shift the frequency of the single-sideband optical modulated signal, thereby completing the frequency linear tuning required for the linear frequency modulation signal.

[0039] Furthermore, the optical amplifier is used to control the gain within the loop branch. Since the optical coupler and acousto-optic frequency shifter in the loop branch have losses, by changing the gain of the optical amplifier, the balance between loss and gain in the loop branch can be achieved, thereby increasing the number of cycles of the single-sideband optical modulated signal in the loop branch.

[0040] Furthermore, the second optical wavelength division multiplexer is used to combine the linear frequency modulation signals output by N optical channels, the combined optical signal output by the second optical wavelength division multiplexer is input to the first input end of the 2×1 optical coupler, and the second optical frequency comb inputs the output multi-comb signal to the second input end of the 2×1 optical coupler, and then inputs the optical detector after coupling by the 2×1 optical coupler.

[0041] In this embodiment, the second optical frequency comb has the same number of teeth as the first optical frequency comb, but the tooth spacing is different. In this embodiment, the tooth spacing of the second optical frequency comb can be adjusted according to the needs of the device, and the multi-tooth signal output by the second optical frequency comb is coupled with the combined optical signal. Since the multi-tooth signal contains signals of multiple frequency bands, multiple RF signals of different frequency bands can be generated by beating the optical detector.

[0042] As shown in Figure 2(a), specifically, if the RF baseband signals of optical channels 1 to N are the same, the bandwidth is f B , the number of cyclic frequency shifts of the N optical channels is M, and the tooth spacing of the second optical frequency comb is set to differ from the tooth spacing of the first optical frequency comb by Mf B , then the output RF signal of N optical channels is shown in Figure 2(a), and the bandwidth can be MNf B Generation of ultra-wideband signals.

[0043] As shown in Figure 2(b), if the bandwidths of the RF baseband signals of optical channels 1 to N are different and are loaded on N optical channels in time-sharing order, the output of RF signals of different frequency bands can be achieved in time-sharing. By setting the number of cyclic frequency shifts of each optical channel and setting a certain frequency interval between the frequency comb interval of the second optical frequency comb and the frequency comb interval of the first optical frequency comb, the output RF signal of the device can be as shown in Figure 2(b), indicating that the bandwidth and start and end frequencies of the signals in different time periods can be adjusted.

[0044] As shown in FIG2(c), if the bandwidths of the RF baseband signals of optical channels 1 to N are different but are simultaneously loaded on N optical channels, by setting the number of cyclic frequency shifts of each optical channel and a certain frequency interval between the frequency comb interval of the second optical frequency comb and the frequency comb interval of the first optical frequency comb, the output RF signal of the device can be as shown in FIG2(c), and RF signals of multiple frequency bands, different bandwidths, and different start and end frequencies can be simultaneously output within the same period of time.

[0045] The present invention is based on microwave photonic technology, combined with wavelength multiplexing and optical cyclic frequency shifting, to generate photonic broadband waveforms. By adjusting the bandwidth of the RF baseband signal, the number of cyclic frequency shifts of multiple optical channels, and the comb tooth spacing between two optical frequency combs, the waveform frequency band of the broadband waveform can be adjusted, and the frequency modulation slope and amplitude of the linear frequency modulation signal can be adjusted. The multiple optical channels can simultaneously support the generation and selection of multiple signals of different frequency bands. Each signal has the ability of independent signal reconstruction and regulation, and has the ability to adapt to different requirements of different radar and other electronic information systems for broadband waveforms, and has strong reconfigurable performance.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-band reconfigurable broadband waveform generator based on microwave photons, characterized in that: It includes a first optical frequency comb, a first optical wavelength division multiplexer, a multi-path optical channel, a second optical wavelength division multiplexer, a 2×1 optical coupler, a second optical frequency comb and an optical detector; The output end of the first optical frequency comb is connected to the input end of the first optical wavelength division multiplexer, the multiple output ends of the first optical wavelength division multiplexer are respectively connected to the input ends of the multiple optical channels, the output ends of the multiple optical channels are respectively connected to the multiple input ends of the second optical wavelength division multiplexer, the output end of the second optical wavelength division multiplexer is connected to the first input end of the 2×1 optical coupler, the output end of the second optical frequency comb is connected to the second input end of the 2×1 optical coupler, and the output end of the 2×1 optical coupler is connected to the input end of the optical detector; The optical channel includes an optical switch, an optical modulator, an optical filter and a frequency shift unit connected in sequence; the frequency shift unit includes a 2×2 optical coupler, an optical amplifier and an acousto-optic frequency shifter; the first output end of the 2×2 optical coupler is connected to the input end of the optical amplifier, the output end of the optical amplifier is connected to the input end of the acousto-optic frequency shifter, and the output end of the acousto-optic frequency shifter is connected to the first input end of the 2×2 optical coupler; The input end of the optical switch serves as the input end of the optical channel, the RF input end of the optical modulator receives the RF baseband signal, the output end of the optical filter is connected to the second input end of the 2×2 optical coupler, and the second output end of the 2×2 optical coupler serves as the output end of the optical channel.

2. The multi-band reconfigurable broadband waveform generating device based on microwave photons according to claim 1 is characterized in that: The first optical frequency comb outputs a multi-tooth signal, the number of teeth of the first optical frequency comb corresponds to the number of output channels of the first optical wavelength division multiplexer, and the passband center frequency of each output end of the first optical wavelength division multiplexer corresponds one-to-one to each tooth wavelength of the first optical frequency comb.

3. The multi-band reconfigurable broadband waveform generating device based on microwave photons according to claim 2 is characterized in that: The first optical wavelength division multiplexer divides the wavelengths of the multi-comb signal output by the first optical frequency comb, and outputs the optical comb signal corresponding to each comb wavelength from each output end of the first optical wavelength division multiplexer.

4. The multi-band reconfigurable broadband waveform generating device based on microwave photons according to claim 1 is characterized in that: The optical modulator uses the optical comb signal input into the optical modulator as an optical carrier signal, inputs the corresponding radio frequency baseband signal into the optical modulator for modulation, and outputs an optical modulated signal.

5. The multi-band reconfigurable broadband waveform generating device based on microwave photons according to claim 1 is characterized in that: The optical filter is used to filter out the optical carrier signal and retain the single-sideband optical modulation signal.

6. The multi-band reconfigurable broadband waveform generating device based on microwave photons according to claim 5 is characterized in that: The first input end of the 2×2 optical coupler receives the optical modulated signal after being frequency-shifted and output by the acousto-optic frequency shifter, the second input end of the 2×2 optical coupler receives the optical modulated signal after being filtered by the optical filter, the first output end of the 2×2 optical coupler outputs the optical modulated signal for cyclic frequency shift, which is input into the acousto-optic frequency shifter for cyclic frequency shift after being amplified by the optical amplifier, and the second output end of the 2×2 optical coupler outputs the coupled linear frequency modulation signal.

7. The multi-band reconfigurable broadband waveform generating device based on microwave photons according to claim 6 is characterized in that: The frequency shift amount of the acousto-optic frequency shifter is the same as the bandwidth of the radio frequency baseband signal modulated by the optical channel.

8. The multi-band reconfigurable broadband waveform generating device based on microwave photons according to claim 1 is characterized in that: The second optical wavelength division multiplexer is used for combining linear frequency modulation signals output by multiple optical channels. The linear frequency modulation signal output by the second optical wavelength division multiplexer is input to the first input end of the 2×1 optical coupler. The second optical frequency comb inputs the output multi-comb signal to the second input end of the 2×1 optical coupler, and then inputs the signal to the optical detector after coupling by the 2×1 optical coupler.

9. The multi-band reconfigurable broadband waveform generating device based on microwave photons according to claim 8, characterized in that: The second optical frequency comb has the same number of comb teeth as the first optical frequency comb, but different comb tooth intervals.

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