Laser and RF Composite Radar Detection Method and Device

Abstract

The present invention discloses a method for detecting a laser and radio frequency composite radar. The present invention combines microwave photon radar technology with lidar, generates a linear frequency modulation optical signal with a large time-bandwidth product as the lidar detection optical signal by using a cyclic frequency shift method, and multiplexes the echo signal of the lidar and the electrical signal converted by the beat frequency of the reference optical signal as the transmission signal of the radio frequency antenna, so as to ingeniously apply the lidar and the radio frequency radar in the same system, making use of their respective advantages to offset their respective disadvantages, enabling the radar system to have the characteristics of a long detection distance, a wide range, and all-weather operation, while also having the advantages of high range resolution and high velocity resolution; at the same time, the system structure is simplified, the use of devices is saved, and the requirement of the system for signal power is reduced. The present invention also discloses a device for detecting a laser and radio frequency composite radar. Compared with the prior art, the present invention combines the advantages of microwave photon radar and lidar, and has a simple system structure and a low implementation cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar, and particularly relates to a composite radar detection method combining a lidar and a radio frequency radar. Background Art

[0002] A radar can obtain information such as the distance, direction, and speed of a target by transmitting electromagnetic waves and receiving and processing the target echo signals. Due to its ability to detect targets all day and all weather and in complex environments, it is widely used in fields such as traffic monitoring, weather forecasting, resource exploration, military guidance, target tracking, and battlefield surveillance, playing an important role in both civilian and military applications.

[0003] The detection performance of a radar system is closely related to the characteristics of its transmitted waveform. The larger the bandwidth of the radar waveform, the higher the range resolution, and the larger the time width, the farther the detection range. With the continuous optimization of the radar range resolution and the continuous improvement of the detection range, it is required that the transmitted radar waveform has a large time-bandwidth product (TBWP). Therefore, how to generate a radar waveform with a large time-bandwidth product is the current research focus in the radar field. Traditional radar waveforms are mainly generated by a voltage-controlled oscillator or in the electrical domain by a digital-to-analog converter (DAC) according to the phase or amplitude information of the required signal. With the rapid development of new technologies, the operating frequency band of radars has risen to the Ka band and the W band, and the bandwidths of transmitted and received signals can reach 40 GHz or even 100 GHz. However, traditional electrical methods are limited by factors such as the clock rate and the digital-to-analog conversion rate, and the frequencies and bandwidths of the generated signals are relatively low. To generate high-frequency broadband signals with a bandwidth of several GHz or even dozens of GHz, multiple frequency multiplication and up-conversion processes are required and electromagnetic isolation measures need to be taken, resulting in high power consumption, poor stability, complex structure, and inability to meet the development needs of future radars.

[0004] Microwave photonics technology can generate high-frequency, broadband, and tunable broadband signals without multiple frequency multiplication and up-conversion operations due to its advantages such as high frequency, large bandwidth, reconfigurability, and electromagnetic interference resistance. Through reasonable design, it can also generate high-carrier-frequency and ultra-wideband multi-channel parallel signals, effectively overcoming the bottlenecks faced by pure electronic technology in generating broadband signals, such as low center frequency and small bandwidth. It is one of the research hotspots in the current field of microwave photonics. By taking advantage of the rich optical-domain spectral resources, the frequency, amplitude, and phase of signals are manipulated in the optical domain, and the generated signal bandwidth can be as high as dozens of GHz. Therefore, generating broadband signals using photonics technology has great advantages and is an inevitable development direction to break through the electronic bottleneck and achieve the generation of high-frequency, high-speed, and broadband signals. Combining microwave photonics technology with radio frequency radar systems to significantly improve radar detection performance has become a research hotspot, and different research directions have emerged, such as applying microwave photonics technologies like optoelectronic microwave generation technology, microwave optical delay and phase shift technology, microwave photon filtering technology, and all-optical sampling and quantization technology to traditional radio frequency radars; this type of radar detection system is also known as a microwave photon radar.

[0005] In the actual application of radars, radio frequency radars have advantages such as long detection range and wide coverage, and are not affected by rain and snow weather, with all-weather characteristics and strong survivability in the battlefield. They are the most commonly used radar systems in current military activities. However, their resolution is restricted by the signal time width and bandwidth, generally inferior to lidar. Although lidar is easily affected by rain and snow weather, it has good directivity, strong concealment, strong anti-active interference ability, high brightness, and higher ranging accuracy and resolution, so it is widely used in many fields such as remote sensing and autonomous driving. To a certain extent, both lidar systems and radio frequency radar systems have their own advantages and disadvantages. Therefore, in practical applications, a multifunctional composite radar detection system that can take into account all-weather conditions, wide detection range, high resolution, good directivity, and strong anti-interference ability is needed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a laser and radio frequency composite radar detection method, which combines the advantages of microwave photon radars and lidars, and has a simple system structure and low implementation cost.

[0007] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0008] A laser and RF composite radar detection method generates two continuous optical carriers of the same source; frequency-shift one of the continuous optical carriers to generate a reference optical signal; for the other continuous optical carrier, first perform carrier-suppressed single-sideband modulation on it with a linear frequency-modulated electrical pulse signal to generate a linear frequency-modulated optical pulse signal, and then splice the generated linear frequency-modulated optical pulse signal into a linear frequency-modulated optical signal with a large time width and large bandwidth through cyclic frequency-shifting; divide the linear frequency-modulated optical signal into two paths, one path is used as the detection optical signal of the lidar to be emitted towards the target, and the other path is beat with a split signal of one path of the reference optical signal to obtain a double-chirped electrical signal S1; couple the lidar reflected optical signal of the target with the other split signal of the reference optical signal and convert it into an electrical signal S2, then divide it into two paths, use one path as the RF detection signal of the RF radar to be emitted towards the target, and perform a cross-correlation operation on the other path with the electrical signal S1 to obtain the detection information of the lidar on the target; perform a cross-correlation operation on the RF radar echo signal S3 of the target with the electrical signal S2 to obtain the detection information of the RF radar on the target.

[0009] Preferably, the cyclic frequency-shifting satisfies the following conditions:

[0010] The pulse width of the linear frequency-modulated optical pulse signal is equal to the loop delay of the cyclic frequency-shifting;

[0011] The pulse period of the linear frequency-modulated optical pulse signal is an integer multiple of the pulse width;

[0012] The signal bandwidth of the linear frequency-modulated optical pulse signal is equal to the frequency-shift frequency of the cyclic frequency-shifting;

[0013] The product of the pulse width of the linear frequency-modulated optical pulse signal and the frequency-shift frequency of the cyclic frequency-shifting is an integer.

[0014] Preferably, a dual-parallel Mach-Zehnder modulator operating in the carrier-suppressed single-sideband modulation mode is used to frequency-shift one of the continuous optical carriers to generate a reference optical signal.

[0015] Based on the same inventive concept, the following technical solutions can also be obtained:

[0016] A laser and RF composite radar detection device includes:

[0017] An optical carrier module for generating two continuous optical carriers of the same source;

[0018] A reference optical module for frequency-shifting one of the continuous optical carriers to generate a reference optical signal;

[0019] The cyclic frequency shift module is used to first perform carrier-suppressed single-sideband modulation on another continuous optical carrier with a linear frequency modulation electrical pulse signal to generate a linear frequency modulation optical pulse signal, and then splice the generated linear frequency modulation optical pulse signal into a linear frequency modulation optical signal with a large time width and large bandwidth through cyclic frequency shift;

[0020] The transmitting and receiving module is used to divide the linear frequency modulation optical signal into two paths, one path is used as the lidar detection optical signal to be transmitted to the target, and the other path is beat with a split signal of one path of the reference optical signal to obtain a double-chirped electrical signal S1; and couple the lidar reflected optical signal of the target with a split signal of the other path of the reference optical signal and convert it into an electrical signal S2, and then divide it into two paths, and use one path as the RF detection signal of the RF radar to be transmitted to the target; the signal processing module is used to perform a cross-correlation operation on the other path of electrical signal S2 and the electrical signal S1 to obtain the detection information of the lidar on the target, and perform a cross-correlation operation on the RF radar echo signal S3 of the target and the electrical signal S2 to obtain the detection information of the RF radar on the target.

[0021] Preferably, the cyclic frequency shift satisfies the following conditions:

[0022] The pulse width of the linear frequency modulation optical pulse signal is equal to the loop delay of the cyclic frequency shift;

[0023] The pulse period of the linear frequency modulation optical pulse signal is an integer multiple of the pulse width;

[0024] The signal bandwidth of the linear frequency modulation optical pulse signal is equal to the frequency shift of the cyclic frequency shift;

[0025] The product of the pulse width of the linear frequency modulation optical pulse signal and the frequency shift of the cyclic frequency shift is an integer.

[0026] Preferably, the frequency shift module is a dual-parallel Mach-Zehnder modulator operating in the carrier-suppressed single-sideband modulation mode.

[0027] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0028] The present invention combines the microwave photon radar technology with the lidar, uses the cyclic frequency shift method to generate a linear frequency modulation optical signal with a large time-bandwidth product as the lidar detection optical signal, and multiplexes the lidar echo signal and the electrical signal converted by the beat of the reference optical signal as the RF antenna transmission signal, so as to cleverly apply the lidar and the RF radar in the same system, making up for each other's deficiencies, so that the radar system has the characteristics of long detection distance, wide range, all-weather, and at the same time has the advantages of high range resolution and high speed resolution; at the same time, it also simplifies the system structure, saves the use of devices, and reduces the requirement of the system for signal power.

[0029] The present invention further adjusts parameters such as the pulse width, pulse period, signal bandwidth, loop delay, and frequency shift of the chirped optical pulse signal in the cyclic frequency shift module to meet specific requirements, so as to ensure that the generated chirped optical signal with a large time-bandwidth product is continuous in time, frequency, and phase. Compared with the existing time-frequency domain stitching method and cyclic frequency shift method, it has lower cost, a simpler structure, and better tunability. Description of the Drawings

[0030] Figure 1 It is a schematic structural principle diagram of a specific embodiment of the laser and RF composite radar detection device of the present invention;

[0031] Figure 2 It is a schematic structural principle diagram of the optical frequency shift loop in the specific embodiment;

[0032] Figure 3 It is the time-frequency curve of the local oscillator signal generated by the beat of the photodetector 2 in the specific embodiment;

[0033] Figure 4 It is the time-domain waveform simulation of the chirped signal generated by the existing cyclic frequency shift method;

[0034] Figure 5 It is the time-domain waveform simulation of the chirped signal generated in the specific embodiment;

[0035] Figure 6 It is the cross-correlation result of the echo and the local oscillator signal when the relative delays of the lidar ranging system in the specific embodiment are 0 and 500 ps respectively. Detailed Embodiments

[0036] Aiming at the deficiencies of the prior art, the solution idea of the present invention is to generate a chirped optical signal with a large time-bandwidth product that is continuous in time, frequency, especially phase based on the cyclic frequency shift principle, and use it as the detection optical signal of the lidar. And through signal multiplexing, the electrical signal obtained by beating the lidar echo signal and the reference optical signal is used as the RF radar transmission signal, applying the lidar and the RF radar in the same system to make up for each other's deficiencies, so that the radar system has the characteristics of long detection distance, wide range, and all-weather operation, while also taking into account the advantages of high range resolution and high velocity resolution; at the same time, it can also simplify the system structure, save device usage, and reduce the requirement of the system for signal power.

[0037] The laser and RF composite radar detection method proposed by the present invention specifically includes the following steps:

[0038] Generate two continuous optical carriers of the same origin; shift the frequency of one of the continuous optical carriers to generate a reference optical signal; for the other continuous optical carrier, first perform carrier-suppressed single-sideband modulation on it with a chirped electrical pulse signal to generate a chirped optical pulse signal, and then splice the generated chirped optical pulse signal into a chirped optical signal with a large time width and large bandwidth through cyclic frequency shifting; divide the chirped optical signal into two paths, one path is used as the detection optical signal of the lidar to be emitted towards the target, and the other path is beat with a split signal of the reference optical signal to obtain a double-chirped electrical signal S1; couple the lidar reflected optical signal of the target with the other split signal of the reference optical signal and convert it into an electrical signal S2, then divide it into two paths, use one path as the RF detection signal of the RF radar to be emitted towards the target, and perform a cross-correlation operation on the other path with the electrical signal S1 to obtain the detection information of the lidar on the target; perform a cross-correlation operation on the RF radar echo signal S3 of the target with the electrical signal S2 to obtain the detection information of the RF radar on the target.

[0039] The laser and RF composite radar detection device proposed by the present invention includes:

[0040] An optical carrier module for generating two continuous optical carriers of the same origin;

[0041] A reference optical module for shifting the frequency of one of the continuous optical carriers to generate a reference optical signal;

[0042] A cyclic frequency shift module for, for the other continuous optical carrier, first performing carrier-suppressed single-sideband modulation on it with a chirped electrical pulse signal to generate a chirped optical pulse signal, and then splicing the generated chirped optical pulse signal into a chirped optical signal with a large time width and large bandwidth through cyclic frequency shifting;

[0043] A transmission and reception module for dividing the chirped optical signal into two paths, using one path as the detection optical signal of the lidar to be emitted towards the target, and the other path is beat with a split signal of the reference optical signal to obtain a double-chirped electrical signal S1; and coupling the lidar reflected optical signal of the target with the other split signal of the reference optical signal and converting it into an electrical signal S2, then dividing it into two paths, using one path as the RF detection signal of the RF radar to be emitted towards the target; a signal processing module for performing a cross-correlation operation on the other path of the electrical signal S2 with the electrical signal S1 to obtain the detection information of the lidar on the target, and performing a cross-correlation operation on the RF radar echo signal S3 of the target with the electrical signal S2 to obtain the detection information of the RF radar on the target.

[0044] The linear frequency modulation signal (LFM) is a commonly used waveform signal in current radar systems. Currently, the main methods for generating linear frequency modulation signals based on microwave photonics technology include the spectral shaping - frequency - time mapping method, the frequency doubling method, the optical injection semiconductor laser method, the phase modulation method, and the time - frequency domain stitching method. The spectral shaping - frequency - time mapping method shapes the spectrum of a wide - spectrum light source according to the waveform of the required signal, and then maps the shape in the frequency domain to the time domain to obtain the desired waveform. Its advantages are large bandwidth and tunability; its disadvantages are that limited by device precision, the time width of the generated signal is small, and the fineness of the signal waveform is very poor, making it difficult to meet the radar requirements. The frequency doubling method uses the baseband linear frequency modulation signal generated in the electrical domain to drive an electro - optic modulator. Different harmonic sidebands are excited by the electro - optic nonlinear effect, and different sidebands are selected for beating to obtain a signal with a center frequency and bandwidth that are multiples of the baseband signal. Its advantages are simple structure and easy operation; its disadvantages are that it has high requirements for the baseband radar waveform generator and the spurs increase sharply. The optical injection semiconductor laser method is based on the principle that when the frequency detuning between the master laser and the slave laser remains unchanged, the frequency (or wavelength) of the microwave signal obtained by beating between the master and slave lasers is linearly related to the optical injection intensity of the master laser. Its disadvantages are that the phase noise deteriorates exponentially, the spurs increase sharply, and the efficiency decreases exponentially with the bandwidth and frequency doubling coefficient. The phase modulation method introduces a quadratic parabolic phase change to the microwave signal by using optical means to obtain the required linear frequency modulation signal. Its disadvantage is that limited by the modulator power, the time - bandwidth product of the generated linear frequency modulation signal is small, making it difficult to meet the requirements. The time - frequency domain stitching method combines the characteristics of rich optical domain spectral resources and flexible electrical domain signal generation. It generates a linear frequency modulation signal by electrical methods, and after frequency conversion and delay line delay using an optical frequency comb, it is stitched in the time - frequency domain to obtain a linear frequency modulation signal with a large bandwidth and a large time width. The time - frequency domain stitching method has advantages such as large bandwidth, high flexibility, tunable frequency, and reconfigurable waveform compared with other methods; its disadvantages are that it requires phase locking of double optical frequency combs with different frequency intervals, the structure is complex, and the programmable optical filter used is expensive.

[0045] In order to generate a linear frequency modulation optical signal with a large time - bandwidth product that is continuous in time, frequency, and especially phase, the present invention further improves on the existing cyclic frequency shift method. Specifically, the cyclic frequency shift is made to satisfy the following conditions:

[0046] The pulse width of the linear frequency modulation optical pulse signal is equal to the loop delay of the cyclic frequency shift;

[0047] The pulse period of the linear frequency modulation optical pulse signal is an integer multiple of the pulse width;

[0048] The signal bandwidth of the linear frequency modulation optical pulse signal is equal to the frequency shift of the cyclic frequency shift;

[0049] The product of the pulse width of the linear frequency modulation optical pulse signal and the frequency shift of the cyclic frequency shift is an integer.

[0050] For the convenience of public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment in conjunction with the accompanying drawings:

[0051] The basic structure of the laser and radio frequency composite radar detection device in this embodiment is as Figure 1 shown. First, a narrow linewidth laser generates a continuous optical carrier and enters an optical coupler 1, which is split into two paths. One path enters a DPMZM (dual parallel Mach-Zehnder modulator) 1. By making DPMZM1 operate in the suppressed carrier single sideband modulation mode, frequency shifting of the input optical signal is achieved. The frequency shift can be arbitrarily tuned by changing the frequency of the applied radio frequency signal. The frequency-shifted optical signal serves as a reference optical signal. The other optical carrier signal enters an optical switch constructed by cascading a Mach-Zehnder modulator and a filter. An arbitrary waveform generator (AWG) is used to modulate a chirped electrical pulse signal to the Mach-Zehnder modulator, and the Mach-Zehnder modulator is made to operate at the minimum transmission point to suppress the carrier and even-order sidebands. Then, one of the positive and negative first-order sidebands is selected and output through the filter. In this way, the optical switch generates a chirped optical pulse signal, and the pulse width and period of this chirped optical pulse signal are consistent with those of the chirped electrical pulse signal.

[0052] Next, the chirped optical pulse signal output by the optical switch is input into the frequency shift loop for cyclic frequency shifting. Common devices for frequency shifting optical signals are acousto-optic modulators (AOMs) and dual parallel Mach-Zehnder modulators. The acousto-optic modulator utilizes the acousto-optic effect to diffract the laser to achieve the frequency shift effect. Its advantages are high frequency shift accuracy and good frequency shift effect. Its disadvantages are that it is limited by the crystal material, the frequency shift amount is severely limited, usually between dozens of megahertz and several hundred megahertz, and its frequency shift direction is fixed and cannot be changed. The dual parallel Mach-Zehnder modulator utilizes electro-optic intensity modulation to excite higher-order sidebands and achieves the frequency shift effect by adjusting the phase relationship between the sidebands. Its advantages are that the frequency shift can be arbitrarily tuned by changing the frequency of the applied radio frequency signal, and the frequency shift direction can be changed by adjusting the bias voltage. Its disadvantages are that there are too many variables to control, the bias point is prone to drift, and the suppression of the carrier and sidebands is not large enough. Each of these two methods has its own advantages and disadvantages.

[0053] In this embodiment, a dual parallel Mach-Zehnder modulator is selected as the frequency shift device in the frequency shift loop; as Figure 2As shown in the figure, the frequency-shifted loop includes four parts: an optical coupler 6, a dual-parallel Mach-Zehnder modulator 2, an optical coupler 7, and an optical amplifier. By adjusting the parameters, the following conditions are satisfied: the pulse width of the chirped optical pulse signal is equal to the loop delay of the cyclic frequency shift; the pulse period of the chirped optical pulse signal is an integer multiple of the pulse width; the signal bandwidth of the chirped optical pulse signal is equal to the frequency shift of the cyclic frequency shift; the product of the pulse width of the chirped optical pulse signal and the frequency shift of the cyclic frequency shift is an integer. In this case, the output of the frequency-shifted loop is a large time-width and large bandwidth chirped optical signal that is continuously spliced in time, frequency, and phase; it can be expressed by the formula:

[0054]

[0055] where τ is the pulse width of the chirped optical pulse signal, T L is the loop delay of the cyclic frequency shift, T s is the pulse period of the chirped optical pulse signal, f s is the frequency shift of the cyclic frequency shift, B is the bandwidth of the chirped optical pulse signal, and M and N are non-zero integers.

[0056] Then, through an optical filter, the noise and unwanted optical sidebands in the chirped optical signal are filtered out. After that, it is divided into two paths by a coupler 2. One path enters an optical circulator as the detection optical signal of the lidar, and the other path is used as the local oscillator signal of the lidar.

[0057] Among them, the detection optical signal is input to port 1 of the optical circulator, output from port 2, and then enters an optical antenna, where the light in the optical fiber is converted into spatial light and emitted. After the detection optical signal detects the target, it returns along the original path. The returned optical signal is input from port 2 of the optical circulator through the optical antenna. The optical circulator separates it from the original optical signal, and the returned optical signal is output from port 3. This returned optical signal carries the detection information of the lidar.

[0058] As Figure 1 shown, the present invention multiplexes the echo signal of the lidar, that is, the lidar echo signal output from port 3 of the circulator and a path of reference optical signal separated from the optical coupler 3 are input to the optical coupler 4 for coupling, and beat at the photodetector 1 to obtain an electrical signal S2 carrying the detection information of the lidar. This chirped electrical signal is input to the transmitting antenna and transmitted. After being reflected by the target and received, the receiving antenna obtains an electrical signal S3 carrying the detection information of the RF radar.

[0059] Another path of reference optical signal separated from the optical coupler 3 and the chirped optical local oscillator signal separated from the optical coupler 2 are input to the optical coupler 5 for coupling, and beat at the photodetector 2 to obtain a reference electrical signal S1 for lidar detection.

[0060] The reference signal S1 generated by the photodetector 2, the electrical signal S2 carrying the lidar detection information generated by the photodetector 1, and the electrical signal S3 carrying the RF radar detection information received by the receiving antenna are input into a real-time oscilloscope for acquisition; the detection information of the target by the lidar can be obtained after performing cross-correlation processing on the two signals S1 and S2, and the detection information of the target by the RF radar can be obtained after performing cross-correlation processing on the two signals S2 and S3.

[0061] For a moving target, when the dual-parallel Mach-Zehnder modulator 1 does not modulate the optical carrier separated by the optical coupler 1, there is only one peak in the pulse after cross-correlation processing, which only carries the coupled information of the target's distance and speed. When the dual-parallel Mach-Zehnder modulator 1 modulates the optical carrier separated by the optical coupler 1 and satisfies the condition of generating a V-shaped double-chirp signal (shifting the optical carrier to a certain frequency in the middle of the linearly chirped optical signal) or an X-shaped double-chirp signal (the modulation output is two optical carriers falling on both sides of the linearly chirped optical signal frequency range) by beating with the linearly chirped optical signal generated by the cyclic frequency shift module, the pulse signal after cross-correlation processing contains two peaks, and the target's speed information and distance information can be respectively solved after calculation. Therefore, the DPMZM1 should be adjusted so that the frequency-shifted optical signal output by it beats with the linearly chirped optical signal generated by the cyclic frequency shift module to generate a double-chirped electrical signal.

[0062] The following is a further analysis from the principle:

[0063] A path of optical carrier signal emitted by the laser enters an optical switch implemented by cascading a Mach-Zehnder modulator and a filter. If the optical carrier expression entering the modulator is E0 = cos(ω0t), an arbitrary waveform generator (AWG) is used to input a linearly chirped pulse s(t) to the modulator, which can be expressed as:

[0064]

[0065] where ω m is the starting frequency of the signal, τ is the pulse width of the signal, T s = Pτ is the signal period, k = B / 4τ is the chirp rate of the signal, B is the bandwidth, and rect[x] is a rectangular window function, specifically:

[0066]

[0067] According to the working principle of the Mach-Zehnder modulator, the output can be expressed as:

[0068]

[0069] where, Vπ is the half-wave voltage of the modulator, V DC is the bias voltage, which is expanded by Bessel series as:

[0070]

[0071] where m = π / 2V π , if V is controlled DC such that and only small-signal modulation is considered, then Equation (5) can be rewritten as:

[0072]

[0073] It can be seen that the output of the modulator only has positive and negative first-order sidebands. After filtering out one of the sidebands with an optical filter, Equation (6) can be written as:

[0074]

[0075] Thus, a chirped optical pulse signal is generated, and its pulse width and period are consistent with those of the single-frequency pulse signal applied to the modulator.

[0076] Another signal split by optical coupler 1 enters dual-parallel Mach-Zehnder modulator 1 for modulation. The dual-parallel Mach-Zehnder modulator is composed of two push-pull Mach-Zehnder modulators (MZMs) placed in parallel. If the input optical carrier expression is: E a (t) = Acos(ω0t), where ω0 is the angular frequency of the optical carrier and A is the amplitude of the input optical carrier. According to the working principle of the dual-parallel Mach-Zehnder modulator, the output signal is:

[0077]

[0078] where the radio frequency signal amplitude is 2V A , the angular frequency is ω, V π is the half-wave voltage, is the phase difference introduced by the radio frequency signal, is the phase difference introduced by the three bias voltages, m = πV A / 2V π is the modulation coefficient.

[0079] Expanding Equation (8) by Bessel series gives:

[0080]

[0081] By controlling the three bias voltages such that the output signal can be simplified to:

[0082]

[0083] Equation (10) shows that there is only one first-order sideband and one third-order sideband left in the output, and the third-order sideband can be suppressed by adjusting the radio frequency signal voltage 2V A to make J1(m) >> J3(m).

[0084] Therefore, by changing the three bias voltages, the phase difference of the radio frequency signal, and the output voltage, the carrier single sideband can be suppressed, and only one first-order sideband remains in the output, thereby realizing frequency shifting of the input optical signal. The frequency shifting frequency can be arbitrarily tuned by changing the frequency of the applied radio frequency signal.

[0085] Input the chirped optical pulse output by the optical switch into the optical frequency shifting loop for cyclic frequency shifting, and make the system satisfy

[0086] Equation (1). In this case, the output of the cyclic frequency shifting module can be expressed as:

[0087]

[0088] Equation (11) represents the generation of an optical chirped signal with a large time-bandwidth product. Its starting frequency is ω0 + ω m , and the bandwidth is PB. It can be seen that the signal is the splicing of the signal generated by the original optical switch in time and frequency, and due to τf s = N, so the phase difference at the splicing point is indicating that the phase is also continuous. This is particularly important. Compared with the current methods: the time-frequency domain splicing method requires phase locking of double optical frequency combs with different frequency intervals, which is costly and has a complex structure; the common cyclic frequency shifting method usually can only ensure that the chirped signal generated by splicing is continuous in time and frequency, but the phase is not necessarily continuous; the scheme adopted in the present invention has great advantages.

[0089] Take T s = 5 μs, τ = 500 ns, f s = 1 GHz, ω m = 2 GHz. When the time-frequency curve is made through matlab simulation as Figure 3 shown, the bandwidth range after splicing is 2 GHz - 26 GHz, indicating that the present scheme generates a chirped signal that is continuous in time and frequency through cyclic frequency shifting. At the same time, the time-domain waveforms of the chirped signals generated by the existing cyclic frequency shifting method and the present scheme are respectively simulated, and the results are as Figure 4 , Figure 5 shown. It can be seen that this cyclic frequency shifting scheme has the advantage of continuous phase compared with the existing cyclic frequency shifting method.

[0090] Finally, the reference signal S1 generated by the photodetector 2, the electrical signal S2 carrying the lidar detection information generated by the photodetector 1, and the electrical signal S3 carrying the RF radar detection information received by the receiving antenna are input into a real-time oscilloscope for acquisition; after performing cross-correlation processing on the two signals S1 and S2, the detection information of the lidar on the target can be obtained, and after performing cross-correlation processing on the two signals S2 and S3, the detection information of the RF radar on the target can be obtained.

[0091] To verify the effectiveness of the technical solution of the present invention, the ranging functions of the lidar and the RF radar of the lidar and RF composite radar detection device of the present invention were respectively simulated and verified. The simulation of the lidar specifically uses a method of adding an optical delay to simulate the distance information of the lidar detecting an object. When the optical delay is 0 and the optical delay is 500 ps respectively, the cross-correlation pulse images of the echo signal and the local oscillator signal are made, and the results are as Figure 6 shown. The time coordinates corresponding to the peaks are 500.1 ns and 500.6 ns respectively. That is to say, the change amount of the loop delay is consistent with the change amount of the time coordinate of the cross-correlation pulse peak. Therefore, the ranging ability of the lidar can be proved.

[0092] For the simulation of RF radar ranging, an electrical delay is specifically added to simulate the distance information of the target object. Its verification method is the same as that of the lidar ranging system. Within a certain error range, the ranging ability of the system can also be verified.

Claims

1. A laser and radio frequency composite radar detection method, characterized in that Generate two continuous optical carriers of the same origin; perform frequency shift on one of the continuous optical carriers to generate a reference optical signal; for the other continuous optical carrier, first perform carrier-suppressed single-sideband modulation on it with a chirped electrical pulse signal to generate a chirped optical pulse signal, and then splice the generated chirped optical pulse signal into a chirped optical signal with a large time width and large bandwidth through cyclic frequency shift, and the cyclic frequency shift satisfies the following conditions: The pulse width of the chirped optical pulse signal is equal to the loop delay of the cyclic frequency shift; The pulse period of the chirped optical pulse signal is an integer multiple of the pulse width; The signal bandwidth of the chirped optical pulse signal is equal to the frequency shift of the cyclic frequency shift; The product of the pulse width of the chirped optical pulse signal and the frequency shift of the cyclic frequency shift is an integer; Divide the chirped optical signal into two paths, one path is used as the detection optical signal of the lidar to be emitted to the target, and the other path is beat with a split signal of one path of the reference optical signal to obtain a double-chirped electrical signal S1; couple the lidar reflected optical signal of the target with the other split signal of the reference optical signal and convert it into an electrical signal S2, then divide it into two paths, use one path as the RF detection signal of the RF radar to be emitted to the target, and perform a cross-correlation operation on the other path with the electrical signal S1 to obtain the detection information of the lidar on the target; Perform a cross-correlation operation on the RF radar echo signal S3 of the target and the electrical signal S2 to obtain the detection information of the RF radar on the target.

2. The laser and radio frequency composite radar detection method according to claim 1, wherein Use a dual-parallel Mach-Zehnder modulator operating in the carrier-suppressed single-sideband modulation mode to perform frequency shift on one of the continuous optical carriers to generate a reference optical signal.

3. A laser and radio frequency composite radar detection device, characterized in that, Comprising: An optical carrier module for generating two continuous optical carriers of the same origin; A reference optical module for performing frequency shift on one of the continuous optical carriers to generate a reference optical signal; A cyclic frequency shift module for, for the other continuous optical carrier, first performing carrier-suppressed single-sideband modulation on it with a chirped electrical pulse signal to generate a chirped optical pulse signal, and then splicing the generated chirped optical pulse signal into a chirped optical signal with a large time width and large bandwidth through cyclic frequency shift, and the cyclic frequency shift satisfies the following conditions: The pulse width of the chirped optical pulse signal is equal to the loop delay of the cyclic frequency shift; The pulse period of the chirped optical pulse signal is an integer multiple of the pulse width; The signal bandwidth of the chirped optical pulse signal is equal to the frequency shift of the cyclic frequency shift; The product of the pulse width of the chirped optical pulse signal and the frequency shift of the cyclic frequency shift is an integer; The transmitting and receiving module is used to divide the chirped optical signal into two paths. One path is used as the detection optical signal of the lidar to be transmitted to the target, and the other path is mixed with one split signal of the reference optical signal to obtain the double-chirped electrical signal S1; and the lidar reflected optical signal of the target is coupled with the other split signal of the reference optical signal and converted into an electrical signal S2, and then it is divided into two paths. One path is used as the RF detection signal of the RF radar to be transmitted to the target; the signal processing module is used to perform a cross-correlation operation on the other electrical signal S2 and the electrical signal S1 to obtain the detection information of the lidar on the target, and perform a cross-correlation operation on the RF radar echo signal S3 of the target and the electrical signal S2 to obtain the detection information of the RF radar on the target.

4. The laser and radio frequency composite radar detection device according to claim 3, wherein The frequency shift module is a dual-parallel Mach-Zehnder modulator operating in the carrier-suppressed single-sideband modulation mode.

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