WO2020248737A1 - 基于频谱拼接的射频线性调频信号生成方法及装置 - Google Patents

基于频谱拼接的射频线性调频信号生成方法及装置 Download PDF

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WO2020248737A1
WO2020248737A1 PCT/CN2020/087450 CN2020087450W WO2020248737A1 WO 2020248737 A1 WO2020248737 A1 WO 2020248737A1 CN 2020087450 W CN2020087450 W CN 2020087450W WO 2020248737 A1 WO2020248737 A1 WO 2020248737A1
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optical
signal
frequency
radio frequency
carrier
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PCT/CN2020/087450
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English (en)
French (fr)
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张亚梅
潘时龙
刘策
邵琨麟
李肇昱
杨悦
马丛
薛敏
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南京航空航天大学
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
    • H04B10/25137—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion using pulse shaping at the transmitter, e.g. pre-chirping or dispersion supported transmission [DST]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/5165—Carrier suppressed; Single sideband; Double sideband or vestigial

Definitions

  • the invention relates to a chirp signal generation method, in particular to a chirp signal generation method and device based on microwave photonic technology.
  • the chirp signal plays an important role in radar detection. It expands the radar spectrum range while increasing the pulse width, increasing the average transmission power and increasing the communication distance, breaking the mutual restriction between the time width and bandwidth of traditional pulse radar.
  • the time bandwidth product (TBWP) of the chirp signal is one of the important parameters of the radar detection signal. A large bandwidth can improve the range resolution of the radar, and a large time width can increase the speed resolution of the radar. Therefore, research on generating chirp signals with large TBWP is of great significance. If a chirp signal is generated in the electrical domain, due to the existence of the electronic bottleneck, the frequency in the center of the generated signal is low, the instantaneous bandwidth is small, and the system structure is also very complicated.
  • the principle of the spectrum shaping-frequency-time mapping method is to shape the spectrum of a broad-spectrum signal according to the time-domain waveform of the desired signal, and then map the shape of the frequency domain to the time domain through frequency-time mapping to obtain the desired waveform.
  • the basic idea of the microwave photon frequency doubling method is to drive the electro-optic modulator with the waveform generated in the electrical domain, and to excite different harmonic sidebands by the electro-optic nonlinear effect.
  • the microwave photon phase modulation method uses optical means to introduce a quadratic parabolic phase change to the microwave signal to obtain the required chirp signal. By performing secondary phase modulation on the optical carrier, and then beating the optical carrier to obtain the chirp signal, this method is limited by the phase modulation depth. To increase the TBWP of the signal, the modulation depth needs to be increased.
  • the time bandwidth product of the generated signal is 16. Based on this principle, Zhang Yamei and others in “Photonic generation of linear frequency-modulated waveform with improved time-bandwidth product” (Zhang, Yamei, Xingwei Ye, and Shilong Pan.
  • the above method is more effective when the number of parabolic segments is small, and when the number of segments increases to a certain extent, on the one hand, very high requirements are put on the bandwidth and sampling rate of the electric baseband waveform generator, and on the other hand, the generated signal
  • the quality of the product drops rapidly, and the time bandwidth product is difficult to further increase. How to further obtain a signal with a large time bandwidth product becomes an urgent problem to be solved.
  • the technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for generating a radio frequency chirp signal based on spectrum splicing, which can greatly increase the bandwidth range of the chirp signal.
  • a method for generating radio frequency chirp signals based on spectrum splicing The optical signal with frequency f c is divided into two paths; the first optical signal is frequency shifted to obtain a reference optical signal; the second optical signal is first converted into A multi-carrier optical signal whose frequency changes periodically.
  • the multi-carrier optical signal in each period T is formed by continuous splicing of N optical pulses with the same pulse width and an equal difference in frequency according to the frequency difference ⁇ f.
  • the original radio frequency chirp signal performs carrier suppression single-sideband modulation on the multi-carrier optical signal to obtain a light frequency modulated signal.
  • the period of the original radio frequency chirp signal is equal to the pulse width ⁇ and the slope of the optical pulse N is an integer greater than 1; finally, the optical frequency modulation signal and the reference optical signal are used for beating to obtain a radio frequency chirp signal with a bandwidth of N times the bandwidth of the original radio frequency chirp signal, and the initial frequency of the radio frequency chirp signal can pass Adjust the frequency shift amount of the first optical signal.
  • the second optical signal is converted into a periodic optical pulse signal through an optical switch, and then the optical pulse signal is input into a single frequency shift amount Is the cyclic frequency shift module of ⁇ f, and the following conditions are met: or Where T and ⁇ are the period and pulse width of the optical pulse signal, respectively, and T L is the time required for the light to travel one circle in the loop of the cyclic frequency shift module, and the multi-carrier is output from the cyclic frequency shift module Light signal.
  • the cyclic frequency shift module includes:
  • the optical combiner is used to combine the optical pulse signal with the optical signal from the optical splitter
  • the dual-parallel Mach-Zehnder modulator is driven by a radio frequency signal with the same other parameters but a phase difference of ⁇ /2, and is used to shift the frequency of the input optical signal.
  • the amount of frequency shift is the frequency of the radio frequency signal and the direction of the frequency shift Determined by the bias state of the dual parallel Mach-Zehnder modulator;
  • the optical splitter is used to divide the output signal of the dual-parallel Mach-Zehnder modulator into two paths, one is used as the output of the cyclic frequency shift module, and the other is sent to the optical combiner;
  • the optical filter is connected in series between the optical combiner and the optical splitter or connected to the output end of the cyclic frequency shift module, which is band-pass for optical signals with frequencies in f c + ⁇ f ⁇ f c +N ⁇ f , For the optical signal with frequency f c +(N+1) ⁇ f and above, it is band-stop;
  • the optical amplifier is connected in series between the optical combiner and the optical splitter.
  • a method for generating radio frequency chirp signals based on spectrum splicing The optical signal with frequency f c is divided into two paths; the first optical signal is first converted into a multi-carrier optical signal whose frequency changes periodically.
  • the multi-carrier optical signals are all formed by continuous splicing of N optical pulses with the same pulse width and the same difference in frequency according to the frequency difference ⁇ f, and then the original radio frequency chirp signal is used to perform carrier suppression on the multi-carrier optical signal.
  • the period of the original radio frequency chirp signal is equal to the pulse width ⁇ of the light pulse and the slope N is an integer greater than 1; single-sideband modulation is performed on the second optical signal with a radio frequency signal of f m to obtain a reference optical signal, f m >N ⁇ f+f 0 +k ⁇ , f 0 is the original radio frequency linear The initial frequency of the FM signal; finally, the optical FM signal and the reference optical signal are used for beating to obtain a dual chirp RF chirp signal with a bandwidth of N times the bandwidth of the original RF chirp signal.
  • the following method is used to convert the first optical signal into the multi-carrier optical signal: the first optical signal is converted into a periodic optical pulse signal through an optical switch, and then the optical pulse signal is input into a single frequency shift amount Is the cyclic frequency shift module of ⁇ f, and the following conditions are met: or Where T and ⁇ are the period and pulse width of the optical pulse signal, respectively, and T L is the time required for the light to travel one circle in the loop of the cyclic frequency shift module, and the multi-carrier is output from the cyclic frequency shift module Light signal.
  • the cyclic frequency shift module includes:
  • the optical combiner is used to combine the optical pulse signal with the optical signal from the optical splitter
  • the dual-parallel Mach-Zehnder modulator is driven by a radio frequency signal with the same other parameters but a phase difference of ⁇ /2, and is used to shift the frequency of the input optical signal.
  • the amount of frequency shift is the frequency of the radio frequency signal and the direction of the frequency shift Determined by the bias state of the dual parallel Mach-Zehnder modulator;
  • the optical splitter is used to divide the output signal of the dual-parallel Mach-Zehnder modulator into two paths, one is used as the output of the cyclic frequency shift module, and the other is sent to the optical combiner;
  • the optical filter is connected in series between the optical combiner and the optical splitter or connected to the output end of the cyclic frequency shift module, which is band-pass for optical signals with frequencies in f c + ⁇ f ⁇ f c +N ⁇ f , For the optical signal with frequency f c +(N+1) ⁇ f and above, it is band-stop;
  • the optical amplifier is connected in series between the optical combiner and the optical splitter.
  • a radio frequency chirp signal generation device based on spectrum splicing includes:
  • Light source used to generate an optical signal with a frequency f c ;
  • Optical coupler used to divide the optical signal output by the light source into two paths
  • the optical frequency shift module is used to obtain a reference optical signal after frequency shifting the first optical signal output by the light source
  • the multi-carrier generating module is used to convert the second optical signal into a multi-carrier optical signal whose frequency changes periodically.
  • the multi-carrier optical signal in each period T has the same pulse width and the same difference in frequency according to the frequency difference ⁇ f N light pulses in a progressive relationship are continuously spliced together;
  • the carrier suppression single-sideband modulation module is used to perform carrier suppression single-sideband modulation on the multi-carrier optical signal with an original radio frequency chirp signal to obtain a light frequency modulation signal.
  • the period of the original radio frequency chirp signal is equal to the light frequency modulation signal.
  • Pulse width ⁇ and slope N is an integer greater than 1;
  • the photodetector is used to beat the optical frequency modulation signal and the reference optical signal to obtain a radio frequency chirp signal with a bandwidth N times the bandwidth of the original radio frequency chirp signal, and the initial frequency of the radio frequency chirp signal can be changed by changing the first The frequency shift amount of one optical signal is adjusted.
  • the multi-carrier generating module includes:
  • Optical switch used to convert the second optical signal into a periodic optical pulse signal
  • the cyclic frequency shift module is used to perform a cyclic frequency shift of a single frequency shift of ⁇ f on the optical pulse signal output by the optical switch, and output the multi-carrier optical signal, or
  • T and ⁇ are the period and pulse width of the optical pulse signal, respectively, and T L is the time required for light to travel one circle in the loop of the cyclic frequency shift module.
  • the cyclic frequency shift module includes:
  • the optical combiner is used to combine the optical pulse signal with the optical signal from the optical splitter
  • the dual-parallel Mach-Zehnder modulator is driven by a radio frequency signal with the same other parameters but a phase difference of ⁇ /2, and is used to shift the frequency of the input optical signal.
  • the amount of frequency shift is the frequency of the radio frequency signal and the direction of the frequency shift Determined by the bias state of the dual parallel Mach-Zehnder modulator;
  • the optical splitter is used to divide the output signal of the dual-parallel Mach-Zehnder modulator into two paths, one is used as the output of the cyclic frequency shift module, and the other is sent to the optical combiner;
  • the optical filter is connected in series between the optical combiner and the optical splitter or connected to the output end of the cyclic frequency shift module, which is band-pass for optical signals with frequencies in f c + ⁇ f ⁇ f c +N ⁇ f , For the optical signal with frequency f c +(N+1) ⁇ f and above, it is band-stop;
  • the optical amplifier is connected in series between the optical combiner and the optical splitter.
  • a radio frequency chirp signal generating device based on spectrum splicing includes:
  • Light source used to generate an optical signal with a frequency f c ;
  • Optical coupler used to divide the optical signal output by the light source into two paths
  • the multi-carrier generation module is used to convert the first optical signal into a multi-carrier optical signal whose frequency changes periodically.
  • the multi-carrier optical signal in each period T has the same pulse width and the same difference in frequency according to the frequency difference ⁇ f N light pulses in a progressive relationship are continuously spliced together;
  • the carrier suppression single-sideband modulation module is used to perform carrier suppression single-sideband modulation on the multi-carrier optical signal with an original radio frequency chirp signal to obtain a light frequency modulation signal.
  • the period of the original radio frequency chirp signal is equal to the light frequency modulation signal.
  • Pulse width ⁇ and slope N is an integer greater than 1;
  • the single-sideband modulation module is used to perform single-sideband modulation on the second optical signal with a radio frequency signal of f m to obtain a reference optical signal, f m >N ⁇ f+f 0 +k ⁇ , f 0 is the original radio frequency
  • the photodetector is used to beat the optical frequency modulation signal and the reference optical signal to obtain a dual chirp radio frequency chirp signal with a bandwidth of N times the bandwidth of the original radio frequency chirp signal.
  • the multi-carrier generating module includes:
  • Optical switch used to convert the first optical signal into a periodic optical pulse signal
  • the cyclic frequency shift module is used to perform a cyclic frequency shift of a single frequency shift of ⁇ f on the optical pulse signal output by the optical switch, and output the multi-carrier optical signal, or
  • T and ⁇ are the period and pulse width of the optical pulse signal, respectively, and T L is the time required for light to travel one circle in the loop of the cyclic frequency shift module.
  • the cyclic frequency shift module includes:
  • the optical combiner is used to combine the optical pulse signal with the optical signal from the optical splitter
  • the dual-parallel Mach-Zehnder modulator is driven by a radio frequency signal with the same other parameters but a phase difference of ⁇ /2, and is used to shift the frequency of the input optical signal.
  • the amount of frequency shift is the frequency of the radio frequency signal and the direction of the frequency shift Determined by the bias state of the dual parallel Mach-Zehnder modulator;
  • the optical splitter is used to divide the output signal of the dual-parallel Mach-Zehnder modulator into two paths, one is used as the output of the cyclic frequency shift module, and the other is sent to the optical combiner;
  • the optical filter is connected in series between the optical combiner and the optical splitter or connected to the output end of the cyclic frequency shift module, which is band-pass for optical signals with frequencies in f c + ⁇ f ⁇ f c +N ⁇ f , For the optical signal with frequency f c +(N+1) ⁇ f and above, it is band-stop;
  • the optical amplifier is connected in series between the optical combiner and the optical splitter.
  • the present invention breaks through the bandwidth limitation of the generated signal by the traditional method, can increase the bandwidth of the generated radio frequency signal, and increase the signal bandwidth to N times the bandwidth of the loaded radio frequency signal.
  • This device can realize the conversion of chirp signal and double chirp chirp signal.
  • FIG. 1 is a schematic structural diagram of a specific embodiment of a radio frequency chirp signal generating device according to the present invention
  • Figure 2 is a schematic diagram of the structure of a multi-carrier generation module based on a cyclic frequency shift structure
  • Figure 3 is a schematic diagram of the structure of a multi-carrier generation module based on an externally injected semiconductor laser structure
  • Figure 4 is a schematic diagram of the generated multi-carrier signal, ⁇ is the duration of any frequency optical carrier, and T is the total period;
  • Figure 5 shows the generated chirp signal
  • Fig. 6 is a schematic diagram of the frequency relationship between the optical frequency modulation signal and the single sideband modulation signal
  • Figure 7 shows the resulting dual chirp chirp signal.
  • the solution of the present invention is to convert the optical carrier into a multi-carrier optical signal formed by continuous splicing of N optical pulses whose frequency changes periodically, and then use the original radio frequency chirp signal to
  • the multi-carrier optical signal is subjected to carrier suppression single-sideband modulation to obtain a light frequency modulated signal, and finally the light frequency modulated signal and the frequency shift signal of the optical carrier are beaten to obtain a radio frequency chirp signal whose bandwidth is expanded by N times.
  • the method for generating radio frequency chirp signals based on spectrum splicing of the present invention divides an optical signal with a frequency of f c into two paths; shifts the frequency of the first optical signal to obtain a reference optical signal; divides the second optical signal
  • the signal is first converted into a multi-carrier optical signal whose frequency changes periodically.
  • the multi-carrier optical signal in each period T is continuously spliced by N optical pulses with the same pulse width and an equal difference in frequency according to the frequency difference ⁇ f.
  • the original radio frequency chirp signal is then used to perform carrier suppression single-sideband modulation on the multi-carrier optical signal to obtain a light frequency modulated signal.
  • the period of the original radio frequency chirp signal is equal to the pulse width ⁇ and the slope of the optical pulse N is an integer greater than 1; finally, the optical frequency modulation signal and the reference optical signal are used for beating to obtain a radio frequency chirp signal with a bandwidth of N times the bandwidth of the original radio frequency chirp signal, and the initial frequency of the radio frequency chirp signal can pass Adjust the frequency shift amount of the first optical signal.
  • Figure 1 shows the basic structure of a specific embodiment of the radio frequency chirp signal generating device of the present invention.
  • the device includes a laser source, two optical couplers, an optical frequency shift module, a multi-carrier generation module, a suppressed carrier single-sideband modulation module, and a photodetector.
  • the light output by the laser source is divided into two paths by the first optical coupler.
  • the optical frequency shift module shifts the frequency of the upper optical signal to obtain the reference optical signal
  • the multi-carrier generation module converts the lower optical signal into a periodic change in frequency.
  • the multi-carrier optical signal in each period T is continuously spliced by N optical pulses with the same pulse width and the same difference in frequency according to the frequency difference ⁇ f, and then the carrier single-sideband modulation is suppressed
  • the module uses the original radio frequency chirp signal to perform carrier suppression single sideband modulation on the multi-carrier optical signal to obtain a light frequency modulated signal.
  • the period of the original radio frequency chirp signal is equal to the pulse width ⁇ and the slope of the optical pulse N is an integer greater than 1; the second optical coupler combines the optical frequency modulation signal with the reference optical signal and converts it into an electrical signal by a photodetector, that is, the beat frequency of the two is realized, and the bandwidth is N times the original A radio frequency chirp signal with a bandwidth of the radio frequency chirp signal, and the initial frequency of the radio frequency chirp signal can be adjusted by changing the frequency shift amount of the first optical signal.
  • the multi-carrier generation module can be implemented in a variety of structures, such as a cyclic frequency shift structure or an externally injected semiconductor laser structure.
  • the optical frequency shift module can be realized by an acousto-optic modulator or a dual-parallel Mach-Zehnder modulator (DPMZM). In order to increase the amount of frequency shift, the DPMZM method is preferred.
  • the frequency shift range of the acousto-optic modulator is on the order of MHz.
  • the frequency shift range of the DPMZM method is in GHz.
  • the Multi-carrier generation module based on cyclic frequency shift structure.
  • the multi-carrier generation module includes a cascaded optical switch and a cyclic frequency shift module.
  • the optical switch is used to convert the downstream optical signal into a periodic optical pulse signal;
  • the cyclic frequency shift module is used for Perform a cyclic frequency shift with a single frequency shift of ⁇ f on the optical pulse signal output by the optical switch, and output the multi-carrier optical signal, or
  • T and ⁇ are the period and pulse width of the optical pulse signal, respectively, and T L is the time required for light to travel one circle in the loop of the cyclic frequency shift module.
  • the cyclic frequency shift module is a loop constructed based on the optical frequency shift module.
  • the optical frequency shift module can adopt various existing technologies.
  • the present invention preferably adopts the cyclic frequency shift module implemented based on DPMZM, which specifically includes :
  • the optical combiner is used to combine the optical pulse signal with the optical signal from the optical splitter
  • the dual-parallel Mach-Zehnder modulator is driven by a radio frequency signal with the same other parameters but a phase difference of ⁇ /2, and is used to shift the frequency of the input optical signal.
  • the amount of frequency shift is the frequency of the radio frequency signal and the direction of the frequency shift Determined by the bias state of the dual parallel Mach-Zehnder modulator;
  • the optical splitter is used to divide the output signal of the dual-parallel Mach-Zehnder modulator into two paths, one is used as the output of the cyclic frequency shift module, and the other is sent to the optical combiner;
  • the optical filter is connected in series between the optical combiner and the optical splitter or connected to the output end of the cyclic frequency shift module, which is band-pass for optical signals with frequencies in f c + ⁇ f ⁇ f c +N ⁇ f , For the optical signal with frequency f c +(N+1) ⁇ f and above, it is band-stop;
  • the optical amplifier is connected in series between the optical combiner and the optical splitter.
  • FIG. 2 shows a preferred implementation of the multi-carrier generating module.
  • the optical switch in this embodiment is composed of MZM.
  • MZM has only a DC bias
  • E MZM cos ⁇ E in
  • the clock signal is controlled to make ⁇ at 0 versus The two points are alternately changed to realize the switch function.
  • other existing optical switches can also be used.
  • the optical signal with frequency f c enters the loop (the input light is ), control the DC bias voltage of the DPMZM and the phase of the two loaded radio frequency signals to suppress the carrier single sideband (CS-SSB) modulation of the light.
  • CS-SSB carrier single sideband
  • the two RF ports of the DPMZM are loaded with the same frequency of the RF signal with a phase difference of 90°. Assuming that the upper channel is loaded with a cosine signal and the lower channel is loaded with a sine signal, the upper channel output is:
  • an optical amplifier such as an erbium-doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA)
  • EDFA erbium-doped fiber amplifier
  • SOA semiconductor optical amplifier
  • the finally obtained multi-carrier optical signal is shown in Figure 4.
  • Figure 3 shows the multi-carrier generation module based on the externally injected semiconductor laser structure.
  • the specific details of this structure are described in "Flexible frequency-hopping microwave generation by dynamic control of optically injected semiconductor laser” (Zhou, Pei, et al. .”Flexible frequency-hopping microwave generation by dynamic control of optically injected semiconductor laser.” IEEE Photonics Journal 8.6 (2016): 1-9.), so I won’t repeat it here.
  • ⁇ is a constant.
  • k needs to have a specific value:
  • the optical frequency shift module modulate the light emitted by the laser source with a frequency f m , and f m >N ⁇ f+f 0 +k ⁇ radio frequency signal, making the light
  • the instantaneous frequency of the FM signal falls between the frequency of the laser source and the frequency of the first-order sideband, as shown in Figure 6, and the obtained single-sideband modulation signal and the light FM signal are beaten at the same time.
  • the radio frequency signals of two frequencies are obtained, namely the double chirped chirp signal as shown in Figure 7.

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Abstract

本发明公开了一种基于频谱拼接的射频线性调频信号生成方法。本发明将光载波转换为频率呈周期性变化的N个光脉冲连续拼接而成的多载波光信号，然后用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，最后用光线性调频信号与光载波的移频信号进行拍频即可得到带宽扩大为N倍的射频线性调频信号。本发明还公开了一种基于频谱拼接的射频线性调频信号生成装置。相比现有技术，本发明可生成带宽大幅提高的线性调频信号或双啁啾线性调频信号。

Description

基于频谱拼接的射频线性调频信号生成方法及装置 技术领域
本发明涉及一种线性调频信号生成方法，尤其涉及一种基于微波光子技术的线性调频信号生成方法及装置。
背景技术
线性调频信号在雷达探测中有着重要作用，它在扩展雷达频谱范围的同时增加脉冲宽度，提高平均发射功率以及加大通信距离，突破了传统脉冲雷达时宽与带宽相互制约的关系。线性调频信号的时间带宽积(TBWP)是雷达探测信号的重要参数之一，大带宽可以提高雷达的距离分辨率，大时宽可以提高雷达的速度分辨率。因此，研究产生具有大TBWP的线性调频信号具有重要意义。若在电域中产生线性调频信号，由于电子瓶颈的存在，产生信号的中心内频率低，瞬时带宽小，系统结构也很复杂。随着微波光子技术的发展，利用电光调制技术产生微波信号因其噪声小，带宽大而受到广泛研究。目前，依据工作原理可划分为频谱整形-频时映射法、微波光子倍频法和微波光子调相法，频谱拼接法四种。频谱整形-频时映射法，其原理是对宽谱信号的光谱根据所需信号的时域波形进行整形，然后通过频时映射将频域的形状映射到时域，得到所需波形。微波光子倍频法，其基本思路是利用电域产生的波形驱动电光调制器，由电光非线性效应激发出不同谐波边带，选取其中不同的边带拍频，可得到宽带、高频线性调频信号，从而增加波形的中心频率和带宽。张方正等人在“Photonics-based real-time ultra-high-range-resolution radar with broadband signal generation and processing”(Zhang,Fangzheng,Qingshui Guo,and Shilong Pan."Photonics-based real-time ultra-high-range-resolution radar with broadband signal generation and processing."Scientificreports 7.1(2017):13848.)中将线性调频信号调制到双平行马赫增德尔调制器(DPMZM)上，调节偏置电压，只保留偶数阶边带，送入光电探测器(PD)拍频，得到带宽扩大4倍的线性调频信号。微波光子调相法，通过使用光学手段对微波信号引入二次抛物线型的相位变化，得到所需的线性调频信号。通过对光载波进行二次相位调制，之后再与光载波拍频得到线性调频信号，但是这种方法受限于相位调制深度，要提升信号的TBWP，需要提高调制深 度，对于调制深度为π时，产生的信号的时间带宽积为16。基于这种原理张亚梅等人在“Photonic generation of linear frequency-modulated waveform with improved time-bandwidth product”(Zhang,Yamei,Xingwei Ye,and Shilong Pan."Photonic generation of linear frequency-modulated waveform with improved time-bandwidth product."2015 International Topical Meeting on Microwave Photonics(MWP).IEEE,2015.)中提出了用分段法进行二次相位调制，将要调制上的抛物线分段，然后放大到电光调制器所能承受的且引入相移为2π整数倍的功率，利用相位可折叠卷绕的特性，等效增加相位调制的调制深度，从而将所产生的信号的时间带宽积提高了45倍。此后她们又在“Photonic generation of linear-frequency-modulated waveforms with improved time-bandwidth product based on polarization modulation”(Zhang,Yamei,et al."Photonic generation of linear-frequency-modulated waveforms with improved time-bandwidth product based on polarization modulation."Journal of Lightwave Technology 35.10(2017):1821-1829.)中提出了基于偏振调制器的分段抛物线调制法，将信号的时间带宽积提高了500倍。频谱拼接法，是将某一段频率范围分成几小段，在每一小段上调制上线性调频信号，然后拼接起来，组成带宽更大的线性调频信号。陈文娟等人在“Photonics-based reconfigurable multi-band linearly frequency-modulated signal generation”(Chen,Wenjuan,et al."Photonics-based reconfigurable multi-band linearly frequency-modulated signal generation."Optics express 26.25(2018):32491-32499.)中提出了利用梳齿不对齐的双光频梳，在一组上调制上线性调频信号，和另一组拍频，拼接，产生大带宽的线性调频信号。
上述方法在抛物线分段数较少的时候较为有效，而当分段数增加到一定程度时，一方面对电基带波形发生器的带宽、采样率提出了非常高的要求，另一方面所产生的信号的质量急速下降，时间带宽积难以进一步提高。如何进一步得到大时间带宽积的信号成为亟待解决的问题。
发明内容
本发明所要解决的技术问题在于克服现有技术不足，提供一种基于频谱拼接的射频线性调频信号生成方法，可大幅提高线性调频信号的带宽范围。
本发明具体采用以下技术方案解决上述技术问题：
一种基于频谱拼接的射频线性调频信号生成方法，将频率为f c的光信号分为两路；对第一路光信号进行移频后得到参考光信号；将第二路光信号首先转换为频率呈周期性变化的多载波光信号，每一周期T中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成，然后用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
Figure PCTCN2020087450-appb-000001
N为大于1的整数；最后用光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的射频线性调频信号，且所述射频线性调频信号的初始频率可通过改变第一路光信号的移频量进行调整。
优选地，使用以下方法将第二路光信号转换为所述多载波光信号：将第二路光信号通过光开关转换为周期性的光脉冲信号，然后将光脉冲信号输入单次移频量为Δf的循环移频模块，并令以下条件得到满足：
Figure PCTCN2020087450-appb-000002
或
Figure PCTCN2020087450-appb-000003
其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所需时间，则从循环移频模块输出所述多载波光信号。
进一步优选地，所述循环移频模块包括：
光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双平行马赫曾德尔调制器的偏置状态决定；
光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻；
光放大器，串接于光合路器与光分路器之间。
基于相同的发明思路还可以得到以下技术方案：
一种基于频谱拼接的射频线性调频信号生成方法，将频率为f c的光信号分为 两路；将第一路光信号首先转换为频率呈周期性变化的多载波光信号，每一周期中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成，然后用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
Figure PCTCN2020087450-appb-000004
N为大于1的整数；用频率为f m的射频信号对第二路光信号进行单边带调制，得到参考光信号，f m＞N·Δf+f 0+kτ，f 0为原始射频线性调频信号的初始频率；最后用光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的双啁啾射频线性调频信号。
优选地，使用以下方法将第一路光信号转换为所述多载波光信号：将第一路光信号通过光开关转换为周期性的光脉冲信号，然后将光脉冲信号输入单次移频量为Δf的循环移频模块，并令以下条件得到满足：
Figure PCTCN2020087450-appb-000005
或
Figure PCTCN2020087450-appb-000006
其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所需时间，则从循环移频模块输出所述多载波光信号。
进一步优选地，所述循环移频模块包括：
光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双平行马赫曾德尔调制器的偏置状态决定；
光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻；
光放大器，串接于光合路器与光分路器之间。
一种基于频谱拼接的射频线性调频信号生成装置，包括：
光源，用于生成频率为f c的光信号；
光耦合器，用于将光源输出的光信号分为两路；
光移频模块，用于对光源输出的第一路光信号进行移频后得到参考光信号；
多载波生成模块，用于将第二路光信号转换为频率呈周期性变化的多载波光信号，每一周期T中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成；
抑制载波单边带调制模块，用于用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
Figure PCTCN2020087450-appb-000007
N为大于1的整数；
光电探测器，用于对光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的射频线性调频信号，且所述射频线性调频信号的初始频率可通过改变第一路光信号的移频量进行调整。
优选地，所述多载波生成模块包括：
光开关，用于将第二路光信号转换为周期性的光脉冲信号；
循环移频模块，用于对光开关输出的光脉冲信号进行单次移频量为Δf的循环移频，并输出所述多载波光信号，
Figure PCTCN2020087450-appb-000008
或
Figure PCTCN2020087450-appb-000009
其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所需时间。
进一步优选地，所述循环移频模块包括：
光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双平行马赫曾德尔调制器的偏置状态决定；
光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻；
光放大器，串接于光合路器与光分路器之间。
一种基于频谱拼接的射频线性调频信号生成装置包括：
光源，用于生成频率为f c的光信号；
光耦合器，用于将光源输出的光信号分为两路；
多载波生成模块，用于将第一路光信号转换为频率呈周期性变化的多载波光信号，每一周期T中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成；
抑制载波单边带调制模块，用于用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
Figure PCTCN2020087450-appb-000010
N为大于1的整数；
单边带调制模块，用于用频率为f m的射频信号对第二路光信号进行单边带调制，得到参考光信号，f m＞N·Δf+f 0+kτ，f 0为原始射频线性调频信号的初始频率；
光电探测器，用于对光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的双啁啾射频线性调频信号。
优选地，所述多载波生成模块包括：
光开关，用于将第一路光信号转换为周期性的光脉冲信号；
循环移频模块，用于对光开关输出的光脉冲信号进行单次移频量为Δf的循环移频，并输出所述多载波光信号，
Figure PCTCN2020087450-appb-000011
或
Figure PCTCN2020087450-appb-000012
其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所需时间。
进一步优选地，所述循环移频模块包括：
光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双平行马赫曾德尔调制器的偏置状态决定；
光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻；
光放大器，串接于光合路器与光分路器之间。
相比现有技术，本发明技术方案具有以下有益效果：
一、本发明突破了传统方法对产生的信号的带宽限制，可以提高所产生的射频信号的带宽，将信号带宽提升为所加载射频信号带宽的N倍。
二、本装置可以实现线性调频信号和双啁啾线性调频信号的转换。
附图说明
图1为本发明射频线性调频信号生成装置的一个具体实施例的结构示意图；
图2为基于循环移频结构的多载波生成模块结构示意图；
图3为基于外注入半导体激光器结构的多载波生成模块结构示意图；
图4为所产生的多载波信号示意图，τ为任一频率光载波的持续时间，T为总周期；
图5为所产生的线性调频信号；
图6为光线性调频信号与单边带调制信号之间的频率关系示意图；
图7为产生的双啁啾线性调频信号。
具体实施方式
为了大幅度提高射频线性调频信号的带宽，本发明的解决思路是将光载波转换为频率呈周期性变化的N个光脉冲连续拼接而成的多载波光信号，然后用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，最后用光线性调频信号与光载波的移频信号进行拍频即可得到带宽扩大为N倍的射频线性调频信号。
具体而言，本发明基于频谱拼接的射频线性调频信号生成方法，将频率为f c的光信号分为两路；对第一路光信号进行移频后得到参考光信号；将第二路光信号首先转换为频率呈周期性变化的多载波光信号，每一周期T中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成， 然后用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
Figure PCTCN2020087450-appb-000013
N为大于1的整数；最后用光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的射频线性调频信号，且所述射频线性调频信号的初始频率可通过改变第一路光信号的移频量进行调整。
为了便于公众理解，下面通过具体实施例并结合附图来对本发明的技术方案进行详细说明：
图1显示了本发明射频线性调频信号生成装置的一个具体实施例的基本结构。如图1所示，该装置包括激光源、两个光耦合器、光移频模块、多载波生成模块、抑制载波单边带调制模块、光电探测器。激光源输出的光被第一个光耦合器分为两路，光移频模块对上路光信号进行移频后得到参考光信号，多载波生成模块将下路光信号转换为频率呈周期性变化的多载波光信号，每一周期T中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成，然后抑制载波单边带调制模块用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
Figure PCTCN2020087450-appb-000014
N为大于1的整数；第二个光耦合器将光线性调频信号与参考光信号合为一路后经光电探测器转换为电信号，即实现了两者的拍频，得到带宽为N倍原始射频线性调频信号带宽的射频线性调频信号，且所述射频线性调频信号的初始频率可通过改变第一路光信号的移频量进行调整。
其中的多载波生成模块可采用多种结构实现，例如基于循环移频结构或基于外注入半导体激光器结构。光移频模块可采用声光调制器或双平行马赫增德尔调制器(DPMZM)等实现，为了提高移频量，优选采用DPMZM的方式，声光调制器的移频范围在MHz量级，而DPMZM方法的移频范围在GHz。
基于循环移频结构的多载波生成模块多载波生成模块包括级联的光开关和循环移频模块，光开关用于将下路光信号转换为周期性的光脉冲信号；循环移频模块用于对光开关输出的光脉冲信号进行单次移频量为Δf的循环移频，并输出 所述多载波光信号，
Figure PCTCN2020087450-appb-000015
或
Figure PCTCN2020087450-appb-000016
其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所需时间。
所述循环移频模块是基于光移频模块所构建的一个环路，其中的光移频模块可采用现有的各种技术，本发明优选采用基于DPMZM实现的循环移频模块，其具体包括：
光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双平行马赫曾德尔调制器的偏置状态决定；
光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻；
光放大器，串接于光合路器与光分路器之间。
图2显示了多载波生成模块的一个优选实现方案，本实施例中的光开关由MZM构成，当MZM只有直流偏置时，其输出为E MZM＝cosφE in，控制时钟信号，使φ在0与
Figure PCTCN2020087450-appb-000017
两个点交替变化，即可实现开关功能，当然，其它现有光开关也可使用。打开光开关后，频率为f c的光信号进入环路中(输入光为
Figure PCTCN2020087450-appb-000018
)，控制DPMZM的直流偏压以及加载的两个射频信号的相位即可对光进行抑制载波单边带(CS-SSB)调制。DPMZM的两射频端口加载的射频信号频率相同，相位相差90°，设其上路加载的是余弦信号，下路加载的是正弦信号，则上路输出为：
Figure PCTCN2020087450-appb-000019
调节上路直流偏压，使得
Figure PCTCN2020087450-appb-000020
根据小信号近似，又得到：
Figure PCTCN2020087450-appb-000021
同理，得到下路的输出信号：
Figure PCTCN2020087450-appb-000022
再调节第三个直流偏置，使上下两路分别相移
Figure PCTCN2020087450-appb-000023
和
Figure PCTCN2020087450-appb-000024
整个DPMZM的输出为：
Figure PCTCN2020087450-appb-000025
这样就实现了CS-SSB，等效于进行移频处理。
设光在环路中环绕一圈的时间为τ，为了不让光的前部与光的尾部发生干涉，需要控制光开关的打开时间也为τ。则在经过nτ时间之后，光场
Figure PCTCN2020087450-appb-000026
为了保证产生信号的功率一定，环路中包含一个光放大器(例如掺铒光纤放大器(EDFA)或半导体光放大器(SOA))，对每转一圈的光损耗进行补偿。将光滤波器设置为对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻。在环路中环绕的时间为T＝Nτ。经过时间T后，光路中将不再有信号，此时打开光开关，使原始光信号再次进入环路，由此可以看出光开关的开关周期为T。最终得到的多载波光信号如图4所示。
图3显示了基于外注入半导体激光器结构的多载波生成模块，该结构的具体细节由周沛等人在"Flexible frequency-hopping microwave generation by dynamic control of optically injected semiconductor laser"(Zhou,Pei,et al."Flexible frequency-hopping microwave generation by dynamic control of optically injected semiconductor laser."IEEE Photonics Journal 8.6(2016):1-9.)中给出，此处不再赘述。
通过抑制载波单边带调制模块对图4所示的多载波光信号调制上一个周期为τ的线性调频信号，设该信号为
Figure PCTCN2020087450-appb-000027
之后再与参考光信号合束，送入PD，则得到输出信号：
Figure PCTCN2020087450-appb-000028
其中，ψ为常数。为了能够顺利拼接，k需要有特定的取值：
f 0+Δf+kτ＝2Δf+f 0
Figure PCTCN2020087450-appb-000029
这样，我们就得到了带宽相对加载的线性调频信号扩大N倍的线性调频信号，如图5所示。
此外，如果我们将光移频模块替换成单边带调制模块，给激光源发出的光调制上一个频率为f m，且f m＞N·Δf+f 0+kτ的射频信号，使得光线性调频信号的瞬时频率均落在激光源频率与一阶边带的频率之间，如图6所示，然后用所得到的单边带调制信号与光线性调频信号拍频，便可以在同一时刻得到两个频率的射频信号，即如图7所示的双啁啾线性调频信号。

Claims (12)

  1. 一种基于频谱拼接的射频线性调频信号生成方法，其特征在于，将频率为f c的光信号分为两路；对第一路光信号进行移频后得到参考光信号；将第二路光信号首先转换为频率呈周期性变化的多载波光信号，每一周期T中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成，然后用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
    Figure PCTCN2020087450-appb-100001
    N为大于1的整数；最后用光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的射频线性调频信号，且所述射频线性调频信号的初始频率可通过改变第一路光信号的移频量进行调整。
  2. 如权利要求1所述射频线性调频信号生成方法，其特征在于，使用以下方法将第二路光信号转换为所述多载波光信号：将第二路光信号通过光开关转换为周期性的光脉冲信号，然后将光脉冲信号输入单次移频量为Δf的循环移频模块，并令以下条件得到满足：
    Figure PCTCN2020087450-appb-100002
    或
    Figure PCTCN2020087450-appb-100003
    其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所需时间，则从循环移频模块输出所述多载波光信号。
  3. 如权利要求2所述射频线性调频信号生成方法，其特征在于，所述循环移频模块包括：
    光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
    双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双平行马赫曾德尔调制器的偏置状态决定；
    光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
    光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻；
    光放大器，串接于光合路器与光分路器之间。
  4. 一种基于频谱拼接的射频线性调频信号生成方法，其特征在于，将频率为f c的光信号分为两路；将第一路光信号首先转换为频率呈周期性变化的多载波光信号，每一周期中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成，然后用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
    Figure PCTCN2020087450-appb-100004
    N为大于1的整数；用频率为f m的射频信号对第二路光信号进行单边带调制，得到参考光信号，f m＞N·Δf+f 0+kτ，f 0为原始射频线性调频信号的初始频率；最后用光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的双啁啾射频线性调频信号。
  5. 如权利要求4所述射频线性调频信号生成方法，其特征在于，使用以下方法将第一路光信号转换为所述多载波光信号：将第一路光信号通过光开关转换为周期性的光脉冲信号，然后将光脉冲信号输入单次移频量为Δf的循环移频模块，并令以下条件得到满足：
    Figure PCTCN2020087450-appb-100005
    或
    Figure PCTCN2020087450-appb-100006
    其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所需时间，则从循环移频模块输出所述多载波光信号。
  6. 如权利要求5所述射频线性调频信号生成方法，其特征在于，所述循环移频模块包括：
    光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
    双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双平行马赫曾德尔调制器的偏置状态决定；
    光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
    光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及 以上频率的光信号为带阻；
    光放大器，串接于光合路器与光分路器之间。
  7. 一种基于频谱拼接的射频线性调频信号生成装置，其特征在于，包括：
    光源，用于生成频率为f c的光信号；
    光耦合器，用于将光源输出的光信号分为两路；
    光移频模块，用于对光源输出的第一路光信号进行移频后得到参考光信号；
    多载波生成模块，用于将第二路光信号转换为频率呈周期性变化的多载波光信号，每一周期T中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成；
    抑制载波单边带调制模块，用于用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
    Figure PCTCN2020087450-appb-100007
    N为大于1的整数；
    光电探测器，用于对光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的射频线性调频信号，且所述射频线性调频信号的初始频率可通过改变第一路光信号的移频量进行调整。
  8. 如权利要求7所述射频线性调频信号生成装置，其特征在于，所述多载波生成模块包括：
    光开关，用于将第二路光信号转换为周期性的光脉冲信号；
    循环移频模块，用于对光开关输出的光脉冲信号进行单次移频量为Δf的循环移频，并输出所述多载波光信号，
    Figure PCTCN2020087450-appb-100008
    或
    Figure PCTCN2020087450-appb-100009
    其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所需时间。
  9. 如权利要求8所述射频线性调频信号生成装置，其特征在于，所述循环移频模块包括：
    光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
    双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双 平行马赫曾德尔调制器的偏置状态决定；
    光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
    光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻；
    光放大器，串接于光合路器与光分路器之间。
  10. 一种基于频谱拼接的射频线性调频信号生成装置，其特征在于，包括：
    光源，用于生成频率为f c的光信号；
    光耦合器，用于将光源输出的光信号分为两路；
    多载波生成模块，用于将第一路光信号转换为频率呈周期性变化的多载波光信号，每一周期T中的多载波光信号均由脉宽相同而频率按频率差Δf呈等差递进关系的N个光脉冲连续拼接而成；
    抑制载波单边带调制模块，用于用原始射频线性调频信号对所述多载波光信号进行载波抑制单边带调制，得到光线性调频信号，所述原始射频线性调频信号的周期等于所述光脉冲的脉宽τ且斜率
    Figure PCTCN2020087450-appb-100010
    N为大于1的整数；
    单边带调制模块，用于用频率为f m的射频信号对第二路光信号进行单边带调制，得到参考光信号，f m＞N·Δf+f 0+kτ，f 0为原始射频线性调频信号的初始频率；
    光电探测器，用于对光线性调频信号和参考光信号进行拍频，得到带宽为N倍原始射频线性调频信号带宽的双啁啾射频线性调频信号。
  11. 如权利要求10所述射频线性调频信号生成装置，其特征在于，所述多载波生成模块包括：
    光开关，用于将第一路光信号转换为周期性的光脉冲信号；
    循环移频模块，用于对光开关输出的光脉冲信号进行单次移频量为Δf的循环移频，并输出所述多载波光信号，
    Figure PCTCN2020087450-appb-100011
    或
    Figure PCTCN2020087450-appb-100012
    其中T、τ分别为所述光脉冲信号的周期、脉宽，T L为光在所述循环移频模块的环路中走一圈所 需时间。
  12. 如权利要求11所述射频线性调频信号生成装置，其特征在于，所述循环移频模块包括：
    光合路器，用于将所述光脉冲信号与来自光分路器的光信号进行合路；
    双平行马赫曾德尔调制器，其被其余参数相同但相位相差π/2的射频信号驱动，用于对所输入光信号进行移频，移频量为所述射频信号的频率，移频的方向由双平行马赫曾德尔调制器的偏置状态决定；
    光分路器，用于将双平行马赫曾德尔调制器的输出信号分为两路，一路作为所述循环移频模块的输出，一路送入所述光合路器；
    光滤波器，串接于光合路器与光分路器之间或者接在所述循环移频模块的输出端，其对于频率在f c+Δf～f c+N×Δf光信号为带通，对于频率为f c+(N+1)×Δf及以上频率的光信号为带阻；
    光放大器，串接于光合路器与光分路器之间。
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