Microwave photon frequency hopping radar or communication signal generation method

Abstract

The invention discloses a microwave photon frequency hopping radar or communication signal generation method, and relates to the technical field of microwaves and the field of optical communication. The method is shown in a figure 1 in the specification, and comprises a laser, an optical coupler, a frequency hopping generator, a radio frequency source, a phase modulator, a Mach-Zehnder modulator, an optical band-pass filter, an optical switch, an erbium-doped optical fiber amplifier, a double-parallel Mach-Zehnder modulator, a 90-degree bridge, a photoelectric detector and a transmitting antenna. Two coherent optical frequency combs are generated by using an electro-optical modulator, the two coherent optical frequency combs are staggered at equal intervals in frequency distribution, each comb line is filtered out by using an optical band-pass filter, one comb line is used as an optical carrier to modulate a frequency hopping local oscillator signal, and the other comb line is selected as an optical carrier to modulate a radar or communication signal by using an optical switch. After combination, a frequency hopping radar or a communication signal is obtained through a photoelectric detector. According to the invention, a larger frequency hopping frequency range and smaller frequency resolution can be realized, the optical frequency comb is simple to generate, and the requirement on an optical filter is low.

Description

Technical Field

[0001] The present invention relates to the fields of microwave technology and optical communication technology, and mainly relates to microwave photonic optical frequency comb generation technology and microwave photonic frequency conversion technology. Background Art

[0002] With the rapid development of the fields of radar, communication, and electronic warfare, frequency-hopping radars and communication systems, as an important anti-jamming system, have been widely used in the military field.

[0003] Traditional electrical domain frequency-hopping systems mainly use methods mainly based on direct digital frequency synthesis (DDS) technology and phase-locked loop (PLL) technology to generate frequency-hopping signals. DDS synthesizes waveforms from the concept of phase using all-digital technology, and has advantages such as fast frequency-hopping rate and high frequency resolution, but is limited in working frequency band and has poor phase noise performance; PLL is based on the locking principle of a phase-locked loop, and changes the frequency control code to control the frequency divider to switch frequency points, and can achieve low phase noise and a large frequency range, but the working frequency band is still limited.

[0004] Currently, electronic systems such as radars and communications are developing towards high frequency bands and large bandwidths due to the problem of crowded low-frequency band spectra, and microwave photonic frequency-hopping radars and communication technologies have gradually received extensive attention. Microwave photonic technology is based on the cross-field of microwave and optics, and uses photonics methods to generate, transmit, and process microwave signals, with advantages such as large bandwidth, anti-electromagnetic interference, and low transmission loss. Currently, the more studied microwave photonic frequency-hopping schemes can be divided into three categories: the first category is the scheme based on switching the operating point of an electro-optic modulator, the second category is the scheme based on an optically injected semiconductor laser, and the third category is the scheme based on optical filtering technology. The first category of schemes controls the modulator to work at different bias points by changing the DC bias voltage input to the electro-optic modulator to generate frequency-hopping signals at different frequency points. This scheme is limited by the limited special operating points of the modulator, and the generated frequency points are also limited, usually not exceeding four; the second category of schemes is based on the single-cycle oscillation state of an optically injected semiconductor laser, and is tuned by changing the injection intensity and detuning frequency. This method has a wide tuning range, but the quality of the generated microwave signals is poor; the third category of schemes uses microwave photonic filtering technology to select different optical sidebands, and then obtains frequency-hopping signals at different frequency points through a photodetector. This method is limited by the performance of the optical filter and cannot generate frequency-hopping signals with small frequency resolution and more frequency points. Summary of the Invention

[0005] To solve the problems existing in the background art, the present invention proposes a method for generating microwave photon frequency hopping radar or communication signals. This method has three major advantages: First, this method uses multiple optical filters to filter out different comb lines of the optical frequency comb respectively, and then uses an optical switch to select different comb lines as optical carrier modulation signals to achieve the switching of the frequency hopping band, which can achieve a large frequency hopping range and a fast frequency hopping rate; Second, this method modulates the frequency hopping local oscillator signal, which can quickly switch a large number of frequency points within a certain frequency band to achieve a small frequency resolution; Third, this method generates two coherent optical frequency combs by electro-optic modulators respectively. The two optical frequency combs are equally spaced and interleaved in frequency distribution. Then, each comb line is filtered out by an optical filter respectively. Compared with using one optical frequency comb, the optical frequency comb generation method is simple, and the requirements for the bandwidth and roll-off of the optical filter are reduced by half.

[0006] The technical solution adopted by the present invention is: The device includes a laser LD, an optical coupler OC, a frequency hopping generator, a radio frequency source, a phase modulator PM, a Mach-Zehnder modulator MZM, an optical bandpass filter OBPF, an optical switch OS, an erbium-doped fiber amplifier EDFA, a dual-parallel Mach-Zehnder modulator DPMZM, a 90-degree hybrid coupler, a photodetector PD, and a transmitting antenna. As shown in the accompanying drawings of the specification Figure 1 shown, it is characterized in that: The continuous optical carrier output by the laser is divided into two paths, the upper path and the lower path, by the optical coupler OC1. The upper path is first connected to the input end of the PM, and then connected to MZM1. The output end of MZM1 is divided into m paths by OC2 and respectively connected to m OBPFs. One of the paths is directly connected to the input end of EDFA1, and the other m - 1 paths are connected to the input end of the optical switch. The lower path is connected to the input end of MZM2. The output end of MZM2 is divided into n paths by OC3 and respectively connected to n OBPFs. The output ends of the n OBPFs are all connected to the input end of the optical switch OS. The output end of EDFA1 is connected to the input end of DPMZM1. The frequency hopping generator generates a frequency hopping local oscillator signal, which is loaded onto the two radio frequency ports of DPMZM1 through the first 90-degree hybrid coupler. The output end of the optical switch is connected to the input end of DPMZM2 through EDFA2. The radar or communication signal is loaded onto the two radio frequency ports of DPMZM2 through the second 90-degree hybrid coupler. The output ends of DPMZM1 and DPMZM2 are connected to OC4. After combining, they are connected to the input end of PD, and the output end of PD is connected to the transmitting antenna.

[0007] DPMZM is an integrated device, which consists of two parallel sub-MZMs and a main MZM.

[0008] The frequency hopping generator described above can use a commercial frequency hopping signal transmitting chip to transmit a frequency hopping local oscillator signal, and the required frequency range of the frequency hopping local oscillator signal is half of the frequency interval of a single optical frequency comb.

[0009] The described optical switch has a specification of (n + m - 1)×1, that is, there are n + m - 1 input ports and 1 output port. The switching rate of a commercial high-speed optical switch can reach the ns level. By controlling the optical switch to select different channels, the transmission frequency band of the frequency-hopping signal can be quickly switched.

[0010] When the present invention works, it includes the following steps: (1) The optical carrier emitted by the laser is divided into two paths, the upper path and the lower path, by the optical coupler OC1. (2) In the upper path, the PM and MZM1 are cascaded. The radio frequency signal RF1 is loaded onto the radio frequency port of the PM, and the radio frequency signal RF2 is loaded onto the radio frequency port of the MZM1. The MZM1 operates at the minimum point. By controlling the frequencies and powers of the radio frequency signals RF1 and RF2, an m-line optical frequency comb is generated, where m is an even number, and the frequency interval of the optical frequency comb is f. (3) The output of the MZM1 is divided into m paths by the OC2. Each path is connected to an OBPF. The center frequencies of the m OBPFs are respectively aligned with the comb lines of each optical frequency comb and filter them out. The outermost, i.e., the first comb line with the lowest frequency, is directly connected to the input end of the EDFA1, and the remaining m - 1 paths are respectively connected to the input ends of the optical switch. (4) In the lower path, the radio frequency signal RF3 is loaded onto the radio frequency port of the MZM2. The MZM2 operates at a non - special point. By adjusting the frequency and power of the radio frequency signal RF3 and the bias voltage of the MZM2, an n - line optical frequency comb is generated, where n is an odd number, and the frequency interval of the optical frequency comb is f. The m - line optical frequency comb and the n - line optical frequency comb generated in the upper and lower paths show equidistant interleaving in the frequency distribution. (5) The output of the MZM2 is divided into n paths by the OC3. Each path is connected to an OBPF. The center frequencies of the n OBPFs are respectively aligned with the comb lines of each optical frequency comb and filter them out. The outputs of the n OBPFs are respectively connected to the input ends of the optical switch. (6) The output of the EDFA1 is connected to the DPMZM1. The frequency - hopping local oscillator signal with a frequency - hopping range of 0~f / 2 is generated by the frequency - hopping generator and is loaded onto the two radio frequency ports of the DPMZM1 through the first 90 - degree hybrid coupler. The two sub - modulators of the DPMZM1 operate at the minimum point, and the main modulator operates at the quadrature point, modulating the frequency - hopping local oscillator signal on one side of the optical carrier. (7) By setting the optical switch, one path is selected from the m + n - 1 paths and amplified by the EDFA2. (8) The output of the EDFA2 is connected to the DPMZM2. The radar or communication signal is loaded onto the two radio frequency ports of the DPMZM2 through the second 90 - degree hybrid coupler. The two sub - modulators of the DPMZM2 operate at the minimum point, and the main modulator operates at the quadrature point, modulating the radar or communication signal on one side of the optical carrier. (9) The outputs of DPMZM1 and DPMZM2 are combined through OC4 and then connected to the PD for optoelectronic conversion, and then the frequency-hopping radar or communication signal is transmitted through the transmitting antenna. (10) The tuning speed of the optical switch can reach the nanosecond level. By quickly switching the tuning optical switch between different channels, a frequency-hopping radar or communication signal with full-spectrum frequency agility can be generated.

[0011] This solution proposes a method for generating a microwave photonic frequency-hopping radar or communication signal. Two coherent optical frequency combs are generated through an electro-optic modulator. The two optical frequency combs are equally spaced and interleaved in frequency distribution. Each comb line is filtered out by an optical bandpass filter respectively. The outermost comb line is used as the optical carrier to modulate the frequency-hopping local oscillator signal through DPMZM1, and the remaining comb lines are connected to the optical switch. The optical switch selects one of them as the optical carrier to modulate the radar or communication signal through DPMZM2. The outputs of DPMZM1 and DPMZM2 are combined and then the frequency-hopping radar or communication signal is obtained through the PD.

[0012] This solution meets the requirements of a larger frequency-hopping range and more frequency-hopping points for frequency-hopping radars and communication systems. The optical switch is used to realize the switching of the frequency-hopping band, and the frequency-hopping generator is used to realize the switching of the frequency points within the band. The two cooperate to switch simultaneously to generate a frequency-hopping radar or communication signal with full-spectrum frequency agility. The two coherent optical frequency combs generated by this solution are equally spaced and interleaved in frequency distribution. Each comb line is filtered out by an optical bandpass filter respectively. Compared with a single optical frequency comb, the method for generating the optical frequency comb is simple, the requirements for the bandwidth and roll-off of the optical bandpass filter are reduced by half, and at the same time, the system has high frequency adjustability and strong scalability. Description of the Drawings

[0013] Figure 1 It is a schematic diagram of the principle of a method for generating a microwave photonic frequency-hopping radar or communication signal according to the present invention. Figure 2 Taking a coherent five-line optical frequency comb and six-line optical frequency comb as examples, the spectral diagrams of each part in the schematic diagram are shown. Figure 3 In (a), it is the time-frequency diagram of the generated 25 - 30 GHz frequency-hopping communication signal, Figure 3 In (b), it is the time-frequency diagram of the generated 50 - 55 GHz frequency-hopping communication signal. Detailed Embodiment

[0014] The following details the embodiments of the present invention with reference to the drawings: These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0015] As shown in the drawings of the specification Figure 1As shown in the figure, in this embodiment, it includes a laser LD, an optical coupler OC, a frequency hopping generator, a radio frequency source, a phase modulator PM, a Mach-Zehnder modulator MZM, an optical bandpass filter OBPF, an optical switch OS, an erbium-doped fiber amplifier EDFA, a dual-parallel Mach-Zehnder modulator DPMZM, a 90-degree hybrid, a photodetector PD, and a transmitting antenna. As shown in the accompanying drawings of the specification Figure 1 As shown, its characteristics are as follows: The continuous optical carrier output by the laser is divided into two paths, the upper path and the lower path, by the optical coupler OC1. The upper path is first connected to the input end of the PM, and then connected to MZM1 to generate a 6-line optical comb. Through OC2, it is divided into 6 paths and respectively connected to 6 OBPFs. One path is directly connected to the input end of EDFA1, and the remaining 5 paths are connected to the input end of the optical switch. The lower path is connected to MZM2 to generate a 5-line optical comb. Through OC3, it is divided into 5 paths and respectively connected to 5 OBPFs. The output ends of the 5 OBPFs are all connected to the input end of the optical switch OS. The output end of EDFA1 is connected to the input end of DPMZM1. The frequency hopping generator generates a frequency hopping local oscillator signal, which is loaded onto the two radio frequency ports of DPMZM1 through the first 90-degree hybrid for suppressed-carrier single-sideband modulation. The optical switch selects one path from 10 inputs, amplifies it through EDFA2, and connects it to the input end of DPMZM2. The radar or communication signal is loaded onto the two radio frequency ports of DPMZM2 through the second 90-degree hybrid for suppressed-carrier single-sideband modulation. The output ends of DPMZM1 and DPMZM2 are connected to OC4 for combining, and then through PD for photoelectric detection to obtain the frequency hopping radar or communication signal, which is transmitted through the transmitting antenna.

[0016] In this embodiment, the specific implementation steps of the method are as follows: Step 1: The laser generates a continuous optical carrier, which is then divided into two paths, the upper path and the lower path, by the optical coupler OC1. Step 2: In the upper path, PM and MZM1 are cascaded. The sine signal RF1 with a frequency of 20 GHz output by the radio frequency source is loaded onto the radio frequency port of the PM. The power of RF1 is adjusted to generate a 3-line optical frequency comb with a frequency interval of 20 GHz. The sine signal RF2 with a frequency of 5 GHz output by the radio frequency source is loaded onto the radio frequency port of MZM1. MZM1 operates at the minimum point to generate a 6-line optical comb with a frequency interval of 10 GHz. The spectrogram is as shown in Figure 2 Figure (a) in it. Step 3: In the lower path, the sine signal RF3 with a frequency of 10 GHz output by the radio frequency source is loaded onto the radio frequency port of MZM2. MZM2 operates at a non-special point. The power of RF3 and the bias voltage of MZM2 are adjusted to generate a 5-line optical comb with a frequency interval of 10 GHz. The spectrogram is as shown in Figure 2 Figure (b) in it. The generated 5-line optical frequency comb and 6-line optical frequency comb show equally spaced interleaving in the frequency distribution. Step 4: The output of MZM1 is divided into 6 paths by OC2, and each path is connected to an OBPF. The center frequencies of the 6 OBPFs are respectively aligned with the comb lines of each optical frequency comb and filtered out. The leftmost first optical frequency comb is directly connected to the input end of EDFA1 and amplified by EDFA1. The spectrogram is as shown in Figure 2 Figure (c) therein, and the remaining 5 paths are respectively connected to the input ends of the optical switch. Step 5: The output of MZM2 is divided into 5 paths by OC3, and each path is connected to an OBPF. The center frequencies of the 5 OBPFs are respectively aligned with each comb line and filtered out. The outputs of the 5 OBPFs are respectively connected to the input ends of the optical switch. Step 6: By setting the optical switch, 1 path is selected from 10 inputs for output. Here, the 3rd one of the 5-line optical frequency combs is selected and amplified by EDFA2. The spectrogram is as shown in Figure 2 Figure (d) therein. Step 7: The output of EDFA1 is connected to DPMZM1. The frequency-hopping local oscillator signal with a frequency range of 0 - 5 GHz emitted by the frequency-hopping generator is loaded onto the two RF ports of DPMZM1 through the first 90-degree hybrid. The two sub-modulators of DPMZM1 operate at the minimum point, and the main modulator operates at the quadrature point, modulating the frequency-hopping local oscillator signal on the left sideband of the optical carrier. The spectrogram is as shown in Figure 2 Figure (e) therein. Step 8: The output of EDFA2 is connected to DPMZM2. The 16QAM signal with a center frequency of 150 MHz and a bandwidth of 200 MHz is loaded onto the two RF ports of DPMZM2 through the second 90-degree hybrid. The two sub-modulators of DPMZM2 operate at the minimum point, and the main modulator operates at the quadrature point, modulating the communication signal on the right sideband of the optical carrier. The spectrogram is as shown in Figure 2 Figure (f) therein. Step 9: The outputs of DPMZM1 and DPMZM2 are combined by OC4 and then connected to the PD for optoelectronic conversion to obtain the frequency-hopping communication signal. The electrical spectrogram is as shown in Figure 2 Figure (g) therein, and then it is transmitted through the transmitting antenna to complete the transmission. Step 10: The generated frequency-hopping communication signal has a frequency range of 25 - 30 GHz, and the time-frequency diagram is as shown in Figure 3 Figure (a) therein. Switch the optical switch to select another channel, and the generated frequency-hopping communication signal has a frequency range of 50 - 55 GHz, and the time-frequency diagram is as shown in Figure 3 Figure (b) therein. Step 11: The tuning speed of the optical switch can reach the ns level. By tuning the optical switch to quickly switch between different channels, a frequency-hopping communication signal with full-spectrum frequency agility can be generated.

[0017] Taking the above example, an electro-optic modulator is used to generate a 5-line optical frequency comb and a 6-line optical frequency comb with a frequency interval of 10 GHz each. The frequency distributions of the two optical frequency combs are equally spaced and interleaved. At the same time, a frequency hopping local oscillator signal in the 5 GHz frequency range is generated by a frequency hopping generator, and a frequency hopping range of 50 GHz can be achieved. The frequency resolution depends on the frequency resolution of the frequency hopping local oscillator signal.

[0018] In summary, the above-described embodiments are only examples of the present invention and are not intended to limit the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several equivalent deformations and substitutions can be made based on the disclosed content of the present invention. The generation method, the number of lines, the frequency interval of the optical frequency comb, and the frequency range of the frequency hopping local oscillator signal can all be changed. These equivalent deformations, substitutions, and adjustments of the frequency range should also be regarded as the protection scope of the present invention.

Claims

1. A method for generating a microwave photon frequency hopping radar or communication signal, comprising a laser diode LD, an optical coupler OC, a frequency hopping generator, a radio frequency source, a phase modulator PM, a Mach-Zehnder modulator MZM, an optical bandpass filter OBPF, an optical switch OS, an erbium-doped fiber amplifier EDFA, a dual-parallel Mach-Zehnder modulator DPMZM, a 90-degree hybrid, a photodetector PD, and a transmitting antenna, characterized in that: The continuous optical carrier output by the laser is divided into two paths, the upper path and the lower path, by the optical coupler OC1. The upper path is connected to the PM and then cascaded with MZM1. MZM1 operates at the minimum point. By controlling the frequencies and powers of the radio frequency signals RF1 and RF2 applied to the PM and MZM1, an m-line optical frequency comb is generated. The frequency interval of the optical frequency comb is f. The output of MZM1 is divided into m paths by OC2. Each path is connected to an OBPF. The center frequency of the OBPF is aligned with each comb line. The outermost comb line with the lowest frequency is connected to EDFA1 and amplified by EDFA1. The outputs of the remaining m - 1 OBPFs are connected to the input of the optical switch OS. The lower path is connected to the input of MZM2. MZM2 operates at a non - special point. By controlling the DC bias voltage applied to MZM2 and the frequencies and powers of the radio frequency signal RF3, an n - line optical frequency comb is generated. The frequency interval of the n - line optical frequency comb is f. The n - line optical frequency comb and the m - line optical frequency comb are equally spaced and interleaved in frequency distribution. The output of MZM2 is divided into n paths by OC3. Each path is connected to an OBPF. The center frequency of the OBPF is aligned with each comb line. The outputs of the n OBPFs are all connected to the input of the optical switch OS. The optical switch selects one path from the input m + n - 1 paths. The output of EDFA1 is connected to the input of DPMZM1. The frequency - hopping generator generates a frequency - hopping local oscillator signal with a frequency range from 0 to f / 2, which is applied to the two radio - frequency ports of DPMZM1 through the first 90 - degree hybrid. The two sub - modulators in DPMZM1 operate at the minimum point, and the main modulator operates at the quadrature point. The output of the optical switch is amplified by EDFA2. The output of EDFA2 is connected to the input of DPMZM2. The radar or communication signal is applied to the two radio - frequency ports of DPMZM2 through the second 90 - degree hybrid. The two sub - modulators in DPMZM2 operate at the minimum point, and the main modulator operates at the quadrature point. The outputs of DPMZM1 and DPMZM2 are combined through OC4 and connected to the PD for optoelectronic conversion to generate a frequency - hopping radar or communication signal, which is transmitted via the transmitting antenna. This method realizes the switching of the frequency - hopping frequency band by switching the optical switch and realizes the switching of more frequency points within the frequency band by modulating the frequency - hopping local oscillator signal generated by the frequency - hopping generator. The two cooperate and switch simultaneously to generate a frequency - hopping radar or communication signal with full - spectrum frequency agility.

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