阅读说明：本技术 双光梳多倍频因子频谱扩展调频信号产生系统及实现方法 (Double-optical-comb multi-frequency-multiplication-factor frequency spectrum spreading frequency modulation signal generation system and implementation method ) 是由 高永胜 王武营 王鑫圆 谭庆贵 高许岗 樊养余 齐敏 于 2019-12-03 设计创作，主要内容包括：本发明提供了一种双光梳多倍频因子频谱扩展调频信号产生系统及实现方法,激光器和直接数字合成器为倍频模块中提供光载波和线性调频信号,倍频模块实现电信号的光电转换及倍频,光频梳模块生成五线光频梳,五路光信号分别注入到五个并联的PD中进行光电探测,对得到的电信号进行频谱拼接,即可实现10/20倍频的线性调频信号频谱扩展。本发明有效地实现高频率、大带宽线性调频信号的产生,并且具有结构简单,频率捷变和通道干扰小的特点；采用了最新的微波光子学技术,融合了多倍频和光频梳技术,拓展了原始电线性调频信号载频和带宽的范围,显著降低了对电线性调频信号频率和带宽的要求。(The invention provides a double-optical-comb multi-frequency-multiplication factor frequency spectrum spreading frequency modulation signal generation system and an implementation method, wherein a laser and a direct digital synthesizer provide optical carriers and linear frequency modulation signals for a frequency multiplication module, the frequency multiplication module realizes photoelectric conversion and frequency multiplication of electric signals, the optical frequency comb module generates a five-line optical frequency comb, the five optical signals are respectively injected into five parallel PDs for photoelectric detection, and the obtained electric signals are subjected to frequency spectrum splicing, so that 10/20 frequency-multiplied linear frequency modulation signal frequency spectrum spreading can be realized. The invention effectively realizes the generation of high-frequency and large-bandwidth linear frequency modulation signals and has the characteristics of simple structure, frequency agility and small channel interference; the latest microwave photonics technology is adopted, the frequency multiplication and optical frequency comb technology is fused, the range of the carrier frequency and the bandwidth of the original electric linear frequency modulation signal is expanded, and the requirements on the frequency and the bandwidth of the electric linear frequency modulation signal are obviously reduced.)

1. A double-optical comb multi-frequency multiplication factor frequency spectrum spread frequency modulation signal generation system is characterized in that:

the double-optical-comb multi-frequency-multiplication factor frequency spectrum spreading frequency modulation signal generation system comprises a laser, a Direct Digital Synthesizer (DDS), a frequency multiplication module, an optical frequency comb module and a frequency spectrum spreading module, wherein the laser and the direct digital synthesizer provide optical carriers and linear frequency modulation signals for a Mach-Zehnder modulator (MZM) in the frequency multiplication module, and the output port of the DDS is a point a; the frequency doubling module realizes photoelectric conversion and frequency doubling of an electric signal, adjusts the bias voltage of a MZM direct current port, enables the MZM to work in a carrier suppression mode, and modulates an input linear frequency modulation signal onto a 1-order or 2-order optical sideband of an optical carrier, so that 2/4 frequency doubling signals are generated after PD, and the output port of the frequency doubling module is a point b; the optical frequency comb module generates a five-line optical frequency comb, an optical signal output by the frequency doubling module is firstly input into an arrayed waveguide grating (AWG1) for wavelength separation, and the AWG has a wavelength demultiplexing function, so that two sidebands with different wavelengths in the optical signal are separated; two output ports of the AWG1 are marked as a point c and a point d respectively, two paths of optical signals output by the AWG1 are injected into an X-MZM and a Y-MZM in an optical frequency comb module respectively, then, the input power of a local oscillator signal and the direct current bias voltage of the MZM are adjusted, the power of output optical carriers, the power of +/-1 order optical sidebands and the power of +/-2 order optical sidebands are equal, and therefore the generation of a five-line optical frequency comb is achieved, the output port of the X-MZM is marked as an e, and the output port of the Y-MZM is marked as an f; the spectrum expansion module realizes photoelectric conversion and spectrum splicing of optical signals, and the AWG2 in the spectrum expansion module has functions similar to those of AWG1 and is used for wavelength separation of five-wire optical comb signals, so that five paths of optical signals with different wavelengths are obtained at five output ports of the AWG2 and are marked by g, h, i, j and k respectively; the five paths of optical signals are respectively injected into five parallel PDs for photoelectric detection, and the obtained electric signals are subjected to frequency spectrum splicing, so that 10/20 frequency-doubled chirp signal frequency spectrum spreading can be realized.

2. A method for implementing a system for spread spectrum generation of a frequency modulated signal using the dual optical comb multiple frequency multiplier of claim 1, comprising the steps of:

step 1: the optical signal output by the laser and the chirp signal output by the DDS are respectively expressed as:

step 2: in the frequency doubling mode, the optical signal at the output b point of the frequency doubling module is represented as:

wherein m is the modulation index, J_n(. cndot.) is a first class of nth order Bessel function;

in the quadruple frequency mode, the optical signal at the output b point of the frequency doubling module is represented as:

and step 3: the optical signal output by the frequency doubling module is input into the AWG1, the upper and lower optical sidebands are separated, the wavelengths of the upper and lower optical sidebands are different, the AWG separates according to the wavelength, and the c-point optical signal is expressed as follows in a frequency doubling mode:

expressed in quadruple frequency mode as:

the optical signal at point d is represented in the frequency doubling mode as:

in the quadruple frequency mode can be expressed as:

the optical signal output by the AWG1 is input into an optical frequency comb module and used as an optical carrier wave with the frequency f_LO1And f_LO2Are respectively input to the RF ports of the X-MZM and the Y-MZM as drive signals, f_LO1And f_LO2The frequency difference of (a) is the same as the bandwidth of the chirp signal; in the X-MZM, the local oscillator signal is represented as: s_LO1(t)＝V_LO1·sin(ω_LO1t) wherein V_LO1And ω_LO1Amplitude and angular frequency of the local oscillator signal, respectively; the carrier, positive-negative first-order sideband and positive-negative second-order sideband of the X-MZM output are:

wherein the content of the first and second substances,

adjusting the power and DC bias of the input local oscillator signal to make E₀|＝|E_±1|＝|E_±2If, then, at point e, a frequency interval of f is generated_LO1The five-line optical comb signal of (1);

in Y-MZM, the local oscillator signal is denoted S_LO2(t)＝V_LO2·sin(ω_LO2t) in which V_LO2And ω_LO2Amplitude and angular frequency of the local oscillator signal, respectively, the output carrier, positive and negative first-order sidebands and positive and negative second-order sidebandsRespectively, the following steps:

adjusting the power and DC bias of the input local oscillator signal to make E₀|＝|E_±1|＝|E_±2If, then at point f, a frequency interval of f is generated_LO2The five-line optical comb signal of (1);

and 4, step 4: and after combining the optical signals of the point e and the point f, inputting the combined optical signals into an AWG2 for channel separation, and then inputting the optical signals of the five channels into a PD for photoelectric detection to finally obtain a 10/20 frequency-doubling spectrum-expanded chirp signal.

Technical Field

The invention relates to the field of radar detection, in particular to a frequency spectrum spreading frequency modulation signal generation system and an implementation method.

Background

The linear frequency modulation signal has the advantages of large instantaneous bandwidth, high range resolution and high moving target detection characteristic, and can be widely used in pulse compression radars and electronic warfare systems. The broadband linear frequency modulation signal with longer duration is used, larger energy can be transmitted with smaller peak power, the problem of power saturation in a transmitter in the pulse radar is avoided, and the requirement on the complexity of a system is reduced. Thus, longer detection distances, higher spatial resolution, and lower probability of interception and interference can be achieved using broadband chirp signals. The traditional linear frequency modulation signal generation method based on Direct Digital Synthesis (DDS) is limited by frequency dependence of electronic devices, generates linear frequency modulation signals with high frequency and large bandwidth (the general frequency is less than 10GHz, and the bandwidth is less than 2GHz), often needs multiple frequency mixing and filtering, causes complex system structure and deteriorated signal quality, and has the defects of high cost, poor reconfigurability, low power efficiency and large size and weight, and seriously restricts the detection precision and the resolution capability of a radar system.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a double-optical-comb multi-frequency-multiplication factor frequency spectrum spreading frequency modulation signal generation system and an implementation method. The traditional linear frequency modulation signal generation method based on Direct Digital Synthesis (DDS) is limited by an electronic bottleneck, the frequency of the generated linear frequency modulation signal is generally lower than 10GHz, the bandwidth is lower than 2GHz, and the defects of complex structure, high price, low efficiency and large size exist. In order to solve the problem, the invention realizes the frequency multiplication spectrum expansion of the linear frequency modulation signal 10/20 by using the optical frequency comb and the frequency multiplication technology, reduces the requirements on the frequency and the bandwidth of a DDS generated signal, and has the advantages of simple structure, easy realization, reconfiguration and small interference.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a double-optical-comb multi-frequency-multiplication factor frequency spectrum spreading frequency modulation signal generation system comprises a laser, a Direct Digital Synthesizer (DDS), a frequency multiplication module, an optical frequency comb module and a frequency spectrum spreading module, wherein the laser and the direct digital synthesizer provide optical carriers and linear frequency modulation signals for a Mach-Zehnder modulator (MZM) in the frequency multiplication module, and the output port of the DDS is a point a; the frequency doubling module realizes photoelectric conversion and frequency doubling of an electric signal, adjusts the bias voltage of a MZM direct current port, enables the MZM to work in a carrier suppression mode, and modulates an input linear frequency modulation signal onto a 1-order or 2-order optical sideband of an optical carrier, so that 2/4 frequency doubling signals are generated after PD, and the output port of the frequency doubling module is a point b; the optical frequency comb module generates a five-line optical frequency comb, an optical signal output by the frequency doubling module is firstly input into an arrayed waveguide grating (AWG1) for wavelength separation, and the AWG has a wavelength demultiplexing function, so that two sidebands with different wavelengths in the optical signal are separated; two output ports of the AWG1 are marked as a point c and a point d respectively, two paths of optical signals output by the AWG1 are injected into an X-MZM and a Y-MZM in an optical frequency comb module respectively, then, the input power of a local oscillator signal and the direct current bias voltage of the MZM are adjusted, the power of output optical carriers, the power of +/-1 order optical sidebands and the power of +/-2 order optical sidebands are equal, and therefore the generation of a five-line optical frequency comb is achieved, the output port of the X-MZM is marked as an e, and the output port of the Y-MZM is marked as an f; the spectrum expansion module realizes photoelectric conversion and spectrum splicing of optical signals, and the AWG2 in the spectrum expansion module has functions similar to those of AWG1 and is used for wavelength separation of five-wire optical comb signals, so that five paths of optical signals with different wavelengths are obtained at five output ports of the AWG2 and are marked by g, h, i, j and k respectively; the five paths of optical signals are respectively injected into five parallel PDs for photoelectric detection, and the obtained electric signals are subjected to frequency spectrum splicing, so that 10/20 frequency-doubled chirp signal frequency spectrum spreading can be realized.

The implementation method of the double-optical-comb multi-frequency-multiplication factor frequency spectrum spread frequency-modulated signal generation system comprises the following steps:

step 1: optical information output by laserThe sign and the chirp output by the DDS are expressed as:

and s (t) ═ V_Ssin(ω_St+kπt²) (ii) a Wherein E is_cIs the electric field strength, ω, of the optical carrier_cAngular frequency, V, of optical carrier_S、ω_SAnd k is the amplitude, angular frequency and chirp slope of the chirp signal, respectively;

step 2: in the frequency doubling mode, the optical signal at the output b point of the frequency doubling module is represented as:

wherein m is the modulation index, J_n(. cndot.) is a first class of nth order Bessel function;

in the quadruple frequency mode, the optical signal at the output b point of the frequency doubling module is represented as:

and step 3: the optical signal output by the frequency doubling module is input into the AWG1, the upper and lower optical sidebands are separated, the wavelengths of the upper and lower optical sidebands are different, the AWG separates according to the wavelength, and the c-point optical signal is expressed as follows in a frequency doubling mode:

expressed in quadruple frequency mode as:

the optical signal at point d is represented in the frequency doubling mode as:

in the quadruple frequency mode can be expressed as:

the optical signal output by the AWG1 is input into an optical frequency comb module and used as an optical carrier wave with the frequency f_LO1And f_LO2Are respectively input to the RF ports of the X-MZM and the Y-MZM as drive signals, f_LO1And f_LO2The frequency difference of (a) is the same as the bandwidth of the chirp signal; in the X-MZM, the local oscillator signal is represented as: s_LO1(t)＝V_LO1·sin(ω_LO1t) wherein V_LO1And ω_LO1Amplitude and angular frequency of the local oscillator signal, respectively; the carrier, positive-negative first-order sideband and positive-negative second-order sideband of the X-MZM output are:

wherein the content of the first and second substances,

in order to be the modulation index,

is a direct current offset angle;

adjusting the power and DC bias of the input local oscillator signal to make E₀|＝|E_±1|＝|E_±2If, then, at point e, a frequency interval of f is generated_LO1The five-line optical comb signal of (1);

in Y-MZM, the local oscillator signal is denoted S_LO2(t)＝V_LO2·sin(ω_LO2t) in which V_LO2And ω_LO2The amplitude and angular frequency of the local oscillator signal are respectively, and the output carrier, positive and negative first-order sidebands and positive and negative second-order sidebands are respectively:

adjusting power of input local oscillator signalAnd DC bias voltage, so that | E₀|＝|E_±1|＝|E_±2If, then at point f, a frequency interval of f is generated_LO2The five-line optical comb signal of (1);

and 4, step 4: and after combining the optical signals of the point e and the point f, inputting the combined optical signals into an AWG2 for channel separation, and then inputting the optical signals of the five channels into a PD for photoelectric detection to finally obtain a 10/20 frequency-doubling spectrum-expanded chirp signal.

The invention has the advantages of effectively realizing the generation of high-frequency and large-bandwidth linear frequency modulation signals, and having the characteristics of simple structure, frequency agility and small channel interference. The invention adopts the latest microwave photonics technology, integrates the frequency multiplication and optical frequency comb technology, expands the range of the carrier frequency and bandwidth of the original electric linear frequency modulation signal, and obviously reduces the requirements on the frequency and bandwidth of the electric linear frequency modulation signal. Therefore, the invention can better meet the requirements of military pulse compression radar and electronic warfare, has important effect on improving the detection distance and resolution of the radar, and has wide application prospect.

Drawings

Fig. 1 is a schematic diagram of the generation of a dual optical comb multiple frequency multiplication factor based spectrum spread chirp signal in the present invention.

Fig. 2 is an electrical spectrum of the original chirp signal output by the DDS of the present invention.

FIG. 3 is a spectrum of a signal after microwave photon frequency doubling according to the present invention.

Fig. 4 is a graph of the upper and lower sideband spectra of the AWG1 output of the present invention.

FIG. 5 is a diagram showing the spectrums of the output signals of X-MZM and Y-MZM of the present invention, wherein (a) is the spectrum at point e, and (b) is the spectrum at point f.

Fig. 6 is an electrical spectrum of a chirped signal after spectral spreading according to the present invention (center frequency 13GHz, bandwidth 10 GHz).

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

The invention combines the microwave technology and the photonics technology, and realizes the high-quality processing of microwave signals by utilizing the inherent advantages of large bandwidth, tunability and electromagnetic interference resistance of the photonics technology. The method is based on the microwave photon five-line optical frequency comb and multiple frequency technology, utilizes the MZM (Mach-Zehnder modulator), the array waveguide grating, the photoelectric detector and other photoelectric devices, can realize the frequency multiplication spectrum expansion of the linear frequency modulation signal 10/20, obviously reduces the frequency and bandwidth requirements on the DDS, and has the advantages of frequency agility, electromagnetic interference resistance and small channel interference.

A double-optical-comb multi-frequency-multiplication factor frequency spectrum spreading frequency modulation signal generation system comprises a laser, a Direct Digital Synthesizer (DDS), a frequency multiplication module, an optical frequency comb module and a frequency spectrum spreading module, wherein the laser and the direct digital synthesizer provide optical carriers and linear frequency modulation signals for a Mach-Zehnder modulator (MZM) in the frequency multiplication module, and the output port of the DDS is a point a; the frequency doubling module realizes photoelectric conversion and frequency doubling of an electric signal, adjusts the bias voltage of a MZM direct current port, enables the MZM to work in a carrier suppression mode, and modulates an input linear frequency modulation signal onto a 1-order or 2-order optical sideband of an optical carrier, so that 2/4 frequency doubling signals are generated after PD, and the output port of the frequency doubling module is a point b; the optical frequency comb module generates a five-line optical frequency comb, an optical signal output by the frequency doubling module is firstly input into an arrayed waveguide grating (AWG1) for wavelength separation, and the AWG has a wavelength demultiplexing function, so that two sidebands with different wavelengths in the optical signal are separated; two output ports of the AWG1 are marked as a point c and a point d respectively, two paths of optical signals output by the AWG1 are injected into an X-MZM and a Y-MZM in an optical frequency comb module respectively, then, the input power of a local oscillator signal and the direct current bias voltage of the MZM are adjusted, the power of output optical carriers, the power of +/-1 order optical sidebands and the power of +/-2 order optical sidebands are equal, and therefore the generation of a five-line optical frequency comb is achieved, the output port of the X-MZM is marked as an e, and the output port of the Y-MZM is marked as an f; the spectrum expansion module realizes photoelectric conversion and spectrum splicing of optical signals, and the AWG2 in the spectrum expansion module has functions similar to those of AWG1 and is used for wavelength separation of five-wire optical comb signals, so that five paths of optical signals with different wavelengths are obtained at five output ports of the AWG2 and are marked by g, h, i, j and k respectively; the five paths of optical signals are respectively injected into five parallel PDs for photoelectric detection, and the obtained electric signals are subjected to frequency spectrum splicing, so that 10/20 frequency-doubled chirp signal frequency spectrum spreading can be realized.

The implementation method of the double-optical-comb multi-frequency-multiplication factor frequency spectrum spread frequency-modulated signal generation system comprises the following steps:

step 1: the optical signal output by the laser and the chirp signal output by the DDS are respectively expressed as:

and s (t) ═ V_Ssin(ω_St+kπt²) (ii) a Wherein E is_cIs the electric field strength, ω, of the optical carrier_cAngular frequency, V, of optical carrier_S、ω_SAnd k is the amplitude, angular frequency and chirp slope of the chirp signal, respectively;

step 2: in the frequency doubling mode, the optical signal at the output b point of the frequency doubling module is represented as:

wherein m is the modulation index, J_n(. cndot.) is a first class of nth order Bessel function;

in the quadruple frequency mode, the optical signal at the output b point of the frequency doubling module is represented as:

and step 3: the optical signal output by the frequency doubling module is input into the AWG1, the upper and lower optical sidebands are separated, the wavelengths of the upper and lower optical sidebands are different, the AWG separates according to the wavelength, and the c-point optical signal is expressed as follows in a frequency doubling mode:

expressed in quadruple frequency mode as:

the optical signal at point d is represented in the frequency doubling mode as:

in the quadruple frequency mode can be expressed as:

the optical signal output by the AWG1 is input into an optical frequency comb module and used as an optical carrier wave with the frequency f_LO1And f_LO2Are respectively input to the RF ports of the X-MZM and the Y-MZM as drive signals, f_LO1And f_LO2Frequency difference of (1) and line

The bandwidths of the chirp signals are the same; in the X-MZM, the local oscillator signal is represented as: s_LO1(t)＝V_LO1·sin(ω_LO1t) of 10, V_LO1And ω_LO1Amplitude and angular frequency of the local oscillator signal, respectively; the carrier, positive-negative first-order sideband and positive-negative second-order sideband of the X-MZM output are:

wherein the content of the first and second substances,

in order to be the modulation index,

is a direct current offset angle;

adjusting the power and DC bias of the input local oscillator signal to make E₀|＝|E±₁|＝|E±₂If, then, at point e, a frequency interval of f is generated_LO1The five-line optical comb signal of (1);

in Y-MZM, the local oscillator signal is denoted S_LO2(t)＝V_LO2·sin(ω_LO2t) in which V_LO2And ω_LO2Amplitude and angular frequency of the local oscillator signal, respectively, the carrier, positive and negative first-order sidebands andthe positive and negative second-order sidebands are respectively:

adjusting the power and DC bias of the input local oscillator signal to make E₀|＝|E_±1|＝|E_±2If, then at point f, a frequency interval of f is generated_LO2The five-line optical comb signal of (1);

and 4, step 4: and after combining the optical signals of the point e and the point f, inputting the combined optical signals into an AWG2 for channel separation, and then inputting the optical signals of the five channels into a PD for photoelectric detection to finally obtain a 10/20 frequency-doubling spectrum-expanded chirp signal.

In the invention, LD (laser diode) is a laser diode which can output polarized light, AWG (arrayed waveguide grating) is an arrayed waveguide grating which is used for separating the upper and lower optical sidebands of a frequency doubling signal; dds (direct digital synthesis) is a direct digital synthesizer for generating an original chirp signal; MZM (Mach-Zehnder modulator) is Mach-Zehnder modulator, can produce 2/4 double frequency signal and five-line optical frequency comb; pd (photo detector) is a detector that can convert optical signals into electrical signals.