Method and system for generating dual-band phase coded signal based on DP-BPSK

Abstract

The present invention discloses a method and system for generating a dual-band phase-coded signal based on DP-BPSK. The system includes an LD light source, a DP-BPSK modulator, a code signal generator, a first radio frequency signal generator, a second radio frequency signal generator, and a photodetector; the DP-BPSK modulator includes a first DD-MZM, a second DD-MZM, a 90° polarization rotator, and a polarization beam combiner; the LD light source is connected to the first DD-MZM and the second DD-MZM through an optical fiber; the first DD-MZM is connected to the polarization beam combiner, the second DD-MZM is connected to the polarization beam combiner through a 90° polarization rotator, and the polarization beam combiner is connected to the photodetector; the two signals generated by the code signal generator are respectively connected to a radio frequency port of the first DD-MZM and a radio frequency port of the second DD-MZM; the first radio frequency signal generator is connected to another radio frequency port of the first DD-MZM, and the second radio frequency signal generator is connected to another radio frequency port of the second DD-MZM. The present invention utilizes a DP-BPSK modulator to generate a dual-band phase-coded signal by performing phase encoding on radio frequency signals with different frequencies in the optical domain.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication signal generation, and in particular relates to a method and system for generating a dual-band phase coded signal based on DP-BPSK (dual-polarization binary phase-shift keying, dual-polarization binary phase-shift keying modulator). Background Art

[0002] In order to improve the range resolution and speed resolution of radar, pulse compression technology is widely used in radar systems. As an important microwave waveform for pulse compression, the generation of phase-coded signals has been widely studied. In traditional technology, phase-coded signals are generated in the electrical domain using a direct digital synthesizer (DDS). However, with the development of radar technology, it is difficult to meet the radar's requirements for high frequency, large bandwidth, and large frequency tunable range using traditional methods. In order to solve these problems, technicians began to turn their attention to the optical domain, using the advantages of the optical domain such as large frequency operating range, low transmission loss, no electromagnetic interference, small system size, and light weight to perform signal generation, processing, transmission and other operations that cannot be achieved in the electrical domain.

[0003] In recent years, photonics has continuously proposed schemes for generating phase-coded microwave signals. The earliest method was achieved through spectral shaping and frequency-time mapping. Spectral shaping is achieved by a programmable spatial light modulator (SLM). The key advantage of this scheme is its high reconfigurability, which can achieve reconfigurable waveform generation. However, systems based on free-space optics are usually lossy and bulky. The second method for generating photonic phase-coded microwave signals is to control the phase difference between two coherent optical carriers and then perform frequency heterodyning at the PD. A representative scheme is that in 2007, Professor Chi Hao of Zhejiang University proposed a method for generating high-frequency phase-coded RF pulses using all-fiber components. The third method for generating photonic phase-coded microwave signals is based on the principle of vector sum, and the generation of phase-coded signals is achieved by superposition of two vectors. Its typical representative is a photonic microwave phase-coded pulse generator proposed by Lei M et al. By appropriately setting the data sequence applied to the special bias PDM-MZM, binary and quaternary phase-coded microwave pulses that are not affected by background signals can be generated.

[0004] With the continuous improvement of the requirements for radar functions, the concept of multi-band radar has been proposed. Different bands can complete different tasks under the condition of sharing some hardware platforms. Therefore, the generation of multi-band phase-coded signals has been a research hotspot in recent years. For example: Zhu D et al. proposed the generation of photonic multi-frequency phase-coded microwave signals based on polarization modulation and balanced detection in 2016; Wu D et al. proposed a photonic scheme for generating multi-frequency phase-coded microwave signals based on dual-output Mach-Zehnder modulator and balanced detection technology in 2017. In the experimental demonstration, a multi-band signal with only two frequencies was demonstrated. In addition, the use of a multi-wavelength laser source increases the cost of the system, and it is difficult to control the power of each frequency component individually unless the power of each individual wavelength of the multi-wavelength laser source can be independently controlled. Summary of the invention

[0005] In view of the above situation, the present invention uses a DP-BPSK modulator to generate a dual-band phase-coded signal by phase-coding RF signals with different frequencies in the optical domain, and provides a method and system for generating a dual-band phase-coded signal based on DP-BPSK.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A system for generating dual-band phase coded signals based on DP-BPSK comprises an LD light source, a DP-BPSK modulator, a code signal generator, a first radio frequency signal generator, a second radio frequency signal generator, and a photodetector; the DP-BPSK modulator comprises a first DD-MZM, a second DD-MZM, a 90° polarization rotator, and a polarization beam combiner; the LD light source is connected to the first DD-MZM and the second DD-MZM through an optical fiber; the first DD-MZM is connected to the polarization beam combiner, the second DD-MZM is connected to the polarization beam combiner through a 90° polarization rotator, and the polarization beam combiner is connected to the photodetector; two signals generated by the code signal generator are respectively connected to a radio frequency port of the first DD-MZM and a radio frequency port of the second DD-MZM; the first radio frequency signal generator is connected to another radio frequency port of the first DD-MZM, and the second radio frequency signal generator is connected to another radio frequency port of the second DD-MZM.

[0008] The system structure of the present invention is simple. It realizes the generation of dual-band phase-coded signals by only one integrated modulator, breaking through the limitation of a single frequency band. Moreover, the phase of the dual-band phase-coded signal generated by the present invention is only related to the polarity of the digital signal generated by the code generator, and there is no requirement for the power of the digital signal and the radio frequency signal, so the whole system does not need an amplifier. In addition, since the present invention does not involve wavelength-related devices such as filters, the frequency tunable range of the system is improved.

[0009] Furthermore, the light source is an LD light source, and the light wave emitted by the semiconductor laser is expressed as: E in (t) = E 0 exp(jω c t), where E 0 Expressed as the electric field amplitude of the input optical carrier, ω c is the center frequency of the input optical carrier.

[0010] Furthermore, DP-BPSK is an integrated modulator, which is internally composed of DD-MZM, DD-MZM, 90° polarization rotator and polarization combiner, with a total of four RF ports, two DC biases, and the upper and lower paths are in different polarization states.

[0011] Furthermore, the first RF signal generator generates a first RF signal of cos(2πf 1 t), where f 1 is the frequency of the radio frequency signal. Since the present invention has no special requirements on the amplitude of the radio frequency signal, the radio frequency signal does not need to be amplified.

[0012] Furthermore, the second RF signal generator generates a second RF signal of cos(2πf 2 t), where f 2 This is the frequency of the RF signal and also does not require amplification.

[0013] Furthermore, the code signal generator generates two digital signals, wherein the rates of the two digital signals are consistent and both are f 1 / 6. Since the phase change of the phase-encoded signal of the present invention is only related to the polarity of the digital signal, the digital signal does not need to be amplified.

[0014] Furthermore, after the modulated signal passes through the photodetector, the optical signal is converted into an electrical signal.

[0015] Furthermore, the two DD-MZM DC biases inside DP-BPSK are biased at the maximum transmission point, that is, V DC1 =V DC2 =0.

[0016] The present invention also discloses a method for generating a dual-band phase coded signal of the system, comprising the following steps:

[0017] S1.LD light source generates continuous light wave, which enters DP-BPSK modulator through optical fiber;

[0018] S2. The RF signal generated by the first RF signal generator is loaded on the first DD-MZM inside the DP-BPSK modulator;

[0019] S3. The RF signal generated by the second RF signal generator is loaded on the second DD-MZM inside the DP-BPSK modulator;

[0020] S4. The code signal generator generates two digital signals as input voltage signals which are loaded on the first DD-MZM and the second DD-MZM of the DP-BPSK modulator respectively;

[0021] S5. Input the output modulated signal into the photodetector through the polarization beam combiner inside the DP-BPSK modulator.

[0022] Compared with the existing technical solutions for generating phase coded signals, the method and system technical solutions for generating dual-band phase coded signals based on DP-BPSK of the present invention have a simple system structure and meet the generation of dual-band phase coded signals at the same time. There are no wavelength-related devices in the entire system, the frequency tunable range is large, and the generation of phase coded signals is only related to the polarity of the digital signal and has nothing to do with the amplitude. Therefore, there is no need for amplification in the entire system, which simplifies the entire system, and the generated dual-band phase coded signals have potential application value in multi-band radar systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the system structure for generating dual-band phase coded signals based on DP-BPSK;

[0024] Figure 2 This is the simulation result of dual-band phase-coded pulse signal generation based on DP-BPSK Figure 1 .

[0025] Figure 3 This is the simulation result of dual-band phase-coded pulse signal generation based on DP-BPSK Figure 2 .

[0026] Among them, 1. LD light source; 2. DD-MZM (dual-drive Mach-Zehnder modulator); 3. DD-MZM (dual-drive Mach-Zehnder modulator); 4. 90° polarization rotator; 5. Polarization beam combiner; 2, 3, 4, and 5 together constitute the DP-BPSK modulator; 6. Code signal generator; 7. RF signal generator; 8. RF signal generator; 9. Photodetector. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0028] According to the existing phase coding signal generation technology, the present invention utilizes the DP-BPSK modulator and completes the generation of the dual-band phase coding signal through two internally integrated DD-MZMs with different polarization states.

[0029] Example 1

[0030] like Figure 1 As shown, the system for generating dual-band phase coded signals based on DP-BPSK in this embodiment includes: LD light source 1, DD-MZM2, DD-MZM3, 90° polarization rotator 4, polarization beam combiner 5, code signal generator 6, RF signal generator 7, RF signal generator 8, and photodetector 9. DD-MZM2, DD-MZM3, 90° polarization rotator 4, and polarization beam combiner 5 together constitute a DP-BPSK modulator.

[0031] LD light source 1 is connected to DD-MZM 2 and DD-MZM3 of DP-BPSK modulator through optical fiber; DD-MZM2 is connected to polarization beam combiner 5, DD-MZM3 is connected to polarization beam combiner 5 through 90° polarization rotator 4, polarization beam combiner 5 is connected to photodetector 9, and the modulated signal is input to photodetector 9. The DP-BPSK modulator is internally divided into two DD-MZMs with different polarization states, and the two signals generated by code signal generator 6 are respectively connected to one RF port of the two DD-MZMs; two RF signal generators 7 and 8 are respectively connected to the other RF port of the two DD-MZMs.

[0032] Example 2

[0033] This embodiment is based on the method for generating a dual-band phase coded signal of the system in Embodiment 1, and the specific steps are as follows:

[0034] Step S1, a continuous wave light source generated by a semiconductor laser (LD) 1, the emitted light wave is expressed as: E in (t) = E 0 exp(jω c t), where E 0 Expressed as the electric field amplitude of the input optical carrier, ω c is the center frequency of the input optical carrier;

[0035] Step S2, the radio frequency signal generated by the first radio frequency signal generator 7 is loaded on the first DD-MZM2 inside the DP-BPSK modulator;

[0036] Step S3, the radio frequency signal generated by the second radio frequency signal generator 8 is loaded on the second DD-MZM3 inside the DP-BPSK modulator;

[0037] Step S4, the code signal generator 6 generates two digital signals as input voltage signals and loads them respectively on the first DD-MZM2 and the second DD-MZM3 of the DP-BPSK modulator;

[0038] Step S5, inputting the output modulated signal into the photodetector 9 through the polarization beam combiner 5 inside the DP-BPSK modulator.

[0039] Steps S2 to S5 are the input and output processes of the modulator, and the specific theoretical derivation is as follows:

[0040]

[0041] Among them, ω c is the center frequency of the LD output optical carrier, ω 1 and ω 2 are the frequencies of the RF signals generated by the two RF signal sources, β 1 and β 2 is the modulation depth β of the RF signal 1 =πV 1 / V π , β 2 =πV 2 / V π

[0042] V 1 、V 2 is the amplitude of the input RF signal, φ 1 ,φ 2 is the phase caused by DC bias, γ 1 , γ 2 is the modulation depth of the input digital signal, s 1 (t), s 2 (t) is the input digital signal.

[0043] Expand the above expression using Bessel function to get:

[0044]

[0045] Among them, J n Represents the Bessel function expansion coefficient. Since it is a small signal modulation, the high-order sidebands can be ignored.

[0046] Let φ 1 =φ 2 =0, the modulated signal after PD can be expressed as:

[0047] i 1 =E x *E x * αJ 1 (β)cos(ω 1 t)sin(γ 1 s 1 (t))+J 0 (β)cos(γ 1 s 1 (t))

[0048] i 2 =E y *E y * αJ 1 (β)cos(ω 2 t)sin(γ 2 s 2 (t))+J 0 (β)cos(γ 2 s 2 (t))

[0049] When 1 (t)={1,-1},s 2 When (t) = {1, -1}, a dual-band phase-coded signal is generated after passing through PD.

[0050] Figure 2 represents the 3 GHz phase coded signal generated by simulation, Figure 3 It represents the 6 GHz phase coded signal generated by simulation.

[0051] The invention discloses a method and system technical solution for generating a dual-band phase coded signal based on DP-BPSK. Compared with the existing technical solution for generating a phase coded signal, the system structure is simple and the generation of dual bands is satisfied. There is no wavelength-related device in the whole system, the frequency tunable range is large, and the generation of the phase coded signal is only related to the polarity of the digital signal and has nothing to do with the amplitude. Therefore, no amplification is required in the whole system, which simplifies the whole system. The generated dual-band phase coded signal has potential application value in multi-band radar systems.

[0052] The above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A system for generating dual-band phase coded signals based on DP-BPSK, characterized in that: The invention comprises an LD light source (1), a DP-BPSK modulator, a code signal generator (6), a first radio frequency signal generator (7), a second radio frequency signal generator (8), and a photodetector (9); the DP-BPSK modulator comprises a first DD-MZM (2), a second DD-MZM (3), a 90° polarization rotator (4), and a polarization beam combiner (5); the LD light source (1) is connected to the first DD-MZM (2) and the second DD-MZM (3) via an optical fiber; the first DD-MZM (2) and the polarization beam combiner (5) are connected to each other via an optical fiber. The first DD-MZM (2) and the second DD-MZM (3) are connected to each other, the second DD-MZM (3) is connected to the polarization beam combiner (5) through a 90° polarization rotator (4), and the polarization beam combiner (5) is connected to the photodetector (9); the two signals generated by the code signal generator (6) are respectively connected to a radio frequency port of the first DD-MZM (2) and a radio frequency port of the second DD-MZM (3); the first radio frequency signal generator (7) is connected to another radio frequency port of the first DD-MZM (2), and the second radio frequency signal generator (8) is connected to another radio frequency port of the second DD-MZM (3); The DP-BPSK modulator is an integrated modulator with four RF ports, two DC biases, and two channels in orthogonal polarization states; The radio frequency signal generated by the first radio frequency signal generator is cos(2πf1t), where f1 is the frequency of the radio frequency signal; The radio frequency signal generated by the second radio frequency signal generator is cos(2πf2t), where f2 is the frequency of the radio frequency signal; The DC bias of the first DD-MZM and the second DD-MZM in the DP-BPSK modulator are both biased at the maximum transmission point, that is, V DC1 =V DC2 =0; The code signal generator generates two parallel digital signals, and the rates of the two digital signals are consistent and are f1 / 6; The input and output derivation process of the DP-BPSK modulator is as follows: Among them, ω c is the center frequency of the LD output optical carrier, ω1 and ω2 are the frequencies of the RF signals generated by the two RF signal sources, β1 and β2 are the modulation depths of the RF signals, β1 = πV1 / V π , β2=πV2 / V π , V1, V2 are the amplitudes of the input RF signals, φ1, φ2 are the phases caused by DC bias, γ1, γ2 are the modulation depths of the input digital signals, s1(t), s2(t) are the input digital signals; Expand the expression using Bessel functions to get: Among them, J n represents the Bessel function expansion coefficient; Let φ1=φ2=0, the modulated signal after PD is expressed as: i1=E x *E x * αJ1(β)cos(ω1t)sin(γ1s1(t))+J0(β)cos(γ1s1(t)); i2=E y *E y * αJ1(β)cos(ω2t)sin(γ2s2(t))+J0(β)cos(γ2s2(t)); When s1(t) = {1, -1}, s2(t) = {1, -1}, a dual-band phase-coded signal is generated after PD.

2. The system for generating a dual-band phase coded signal based on DP-BPSK according to claim 1, characterized in that: The light wave emitted by the LD light source is expressed as: E in (t) = E0exp(jω c t), where E0 represents the electric field amplitude of the input optical carrier, ω c is the center frequency of the input optical carrier.

3. The system for generating dual-band phase coded signals based on DP-BPSK according to claim 1, characterized in that: After passing through the photodetector, the modulated output optical signal is converted into an electrical signal.

4. A method for generating a dual-band phase coded signal according to any one of claims 1 to 3, characterized in that: The steps include: S1.LD light source (1) generates a continuous light wave, which enters the DP-BPSK modulator through the optical fiber; S2. The RF signal generated by the first RF signal generator (7) is loaded on the first DD-MZM (2) inside the DP-BPSK modulator; S3. The RF signal generated by the second RF signal generator (8) is loaded on the second DD-MZM (3) inside the DP-BPSK modulator; S4. The code signal generator (6) generates two digital signals as input voltage signals, which are loaded on the first DD-MZM (2) and the second DD-MZM (3) of the DP-BPSK modulator respectively; S5. The output modulated signal is input into the photodetector (9) through the polarization beam combiner (5) inside the DP-BPSK modulator.

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