High-linearity microwave photon Doppler frequency shift and arrival angle measuring device and method

Abstract

The invention provides a high-linearity microwave photon Doppler frequency shift and arrival angle measuring device. The high-linearity microwave photon Doppler frequency shift and arrival angle measuring device comprises a laser source, an optical power divider, two electric power dividers, two electric attenuators, two integrated polarization multiplexing Mach-Zehnder modulators, an optical band-pass filter, an integrated dual-polarization coherent receiver and a Balun. The invention further provides a high-linearity microwave photon Doppler frequency shift and arrival angle measuring method. According to the invention, the optical / electric power ratio is changed by adjusting the bias points of the four sub-modulators and the attenuation of the EA, so that two links with opposite nonlinearity are constructed to realize the IMD3 suppression of the system; i / Q down-conversion is realized through the dual-polarization coherent receiver, so that DFS measurement and DFS direction discrimination are realized; through phase analysis of the IF signal subjected to I / Q down-conversion, wide-angle-range AOA measurement is realized. In addition, due to the fact that BPD is used, IMD2 and common-mode noise suppression can be achieved, and therefore the system achieves DFS and AOA measurement on the basis of achieving linearization and has great advantages in the aspect of low-frequency DFS measurement.

Description

Technical Field

[0001] The present invention belongs to the technical fields of microwave photonics and microwave signal processing, and particularly relates to a high-linearity microwave photon Doppler frequency shift (DFS) and angle of arrival (AOA) measurement device and method. Background Art

[0002] Doppler frequency shift and angle of arrival measurement technologies are widely used in technologies such as electronic warfare and radar. At present, DFS and AOA estimation face several major challenges. First, in order to improve the ability to detect low-speed moving targets, a fine resolution is urgently needed. Second, the working frequency bands of current radar and communication systems cover from megahertz to dozens of gigahertz. With the development of multi-band integration, it is very difficult to measure wide-band microwave parameters by using a single electronic method or device. Due to the inherent advantages of photon technology, it is becoming an effective solution for the generation, transmission, reception processing, analysis and measurement of broadband complex microwave / millimeter wave signals.

[0003] In recent years, some schemes for simultaneously measuring the Doppler frequency shift and the angle of arrival have emerged. Among them, DFS is mainly obtained from the frequency of the intermediate frequency (IF) signal obtained by down-conversion, and there are mainly two methods for DFS direction determination, adding an electrical domain reference signal or analyzing the waveforms of two IF signals at the backend. There are also mainly two methods for AOA measurement, phase difference-power mapping and comparing the phase relationships of two IF signals. 1) A measurement method based on a parallel microwave mixer was proposed in "P Li, L Yan, J Ye, X Feng, W Pan, B Luo, X Zou, T Zhou and Z Chen. Photonic approach for simultaneous measurements of Doppler-frequency-shift and angle-of-arrival of microwave signals [J]. Optics Express, 2019, 27(6): 8709–8716.", where the Doppler frequency shift is obtained from the frequency of the intermediate frequency signal after down-conversion of the local oscillator signal and the echo signal, and the angle of arrival is obtained from the phase difference between the intermediate frequency signals. 2) A microwave photonic I / Q mixing scheme based on polarization multiplexing was proposed in "Z Tang and S Pan. Simultaneous measurement of Doppler-frequency-shift and angle-of-arrival of microwave signals for automotive radars [C]. 2019 International Topical Meeting on Microwave Photonics (MWP), 2019." to achieve DFS and AOA measurements. 3) A simple DFS and AOA estimation system was proposed in "C Huang, H Chen and E Chan. Simple photonics-based system for Doppler frequency shift and angle of arrival measurement [J]. Optics Express, 2020, 28(9): 14028–14037.", where DFS is obtained by adding an electrical reference signal and AOA is calculated by measuring the power of the intermediate frequency signal.4) "Q Jia, J Li, L Sun, D Li and J Liu. A Simple Photonics-Based Measurement Method for Microwave DFS and AOA[J]. IEEE Photonics Journal, 2022, 14(3): 1–8." Carrier-suppressed single-sideband modulation is performed using two parallel Dual-Parallel Mach-Zehnder Modulators (DPMZMs). By comparing the frequency shift and phase shift of the two-channel signals, DFS and AOA information can be obtained. Due to the introduction of the reference signal, the DFS direction can be determined.

[0004] The above solutions all have certain limitations: The method of solution (1) cannot obtain data from the perpendicular bisector of the two receiving antennas; The structure of solution (2) is relatively complex; Solution (3) requires an additional microwave source and has strict requirements for the carrier suppression ratio and phase imbalance of the optical coupler; Solution (4) uses two independent links, making it difficult to ensure the system stability. All of the above four solutions have the problem of angle ambiguity, so the AOA measurement range is limited within 90 degrees; In addition, the above solutions do not suppress the nonlinear distortion of the system, so it is difficult to extend to micro-Doppler frequency shift (mDFS) measurement. Summary of the Invention

[0005] To overcome the deficiencies of the above-mentioned prior art, the present invention provides a microwave photon Doppler frequency shift and angle of arrival measurement device with high linearity. The device includes: a laser source LD, an optical power splitter, a first electrical power splitter 1, a second electrical power splitter 2, a first electrical attenuator EA 1, a second electrical attenuator EA2, a first integrated polarization multiplexing Mach-Zehnder modulator PDM-MZM1, a first integrated polarization multiplexing Mach-Zehnder modulator PDM-MZM2, an optical bandpass filter OBPF, an integrated dual-polarization coherent receiver, and a balun; where:

[0006] The first integrated polarization multiplexing Mach-Zehnder modulator PDM-MZM1 includes: a first Mach-Zehnder modulator MZM1, a second Mach-Zehnder modulator MZM2, a first polarization beam splitter PBS1, a first polarization beam combiner PBC1, and a first polarization rotator PR1;

[0007] The second integrated polarization multiplexing Mach-Zehnder modulator PDM-MZM2 includes: a third Mach-Zehnder modulator MZM1, a fourth Mach-Zehnder modulator MZM2, a second polarization beam splitter PBS2, a second polarization beam combiner PBC2, and a second polarization rotator PR2;

[0008] The integrated dual-polarization coherent receiver includes: a third polarization beam splitter PBS3, a fourth polarization beam splitter PBS4, two 2×4 optical couplers - the first Hybrid-X and the second Hybrid-Y, 4 balanced photodetectors BPD, and 4 transimpedance amplifiers TIA; among which the 4 balanced photodetectors BPD are respectively the first BPD1, the second BPD2, the third BPD3, and the fourth BPD4; the 4 transimpedance amplifiers TIA are respectively the first TIA1, the second TIA2, the third TIA3, and the fourth TIA4;

[0009] And among which:

[0010] A laser source, which outputs a single-frequency continuous-wave laser;

[0011] An optical power splitter, which receives the single-frequency continuous-wave laser output by the laser source, splits its power into two paths and then outputs;

[0012] An electrical power splitter, which includes a first electrical power splitter 1 and a second electrical power splitter 2; the first electrical power splitter 1 is used to equally divide the received echo signal into two parts and output, and the second electrical power splitter 2 is used to equally divide the received transmit signal into two parts and output;

[0013] An electrical attenuator, which includes a first EA1 and a second EA2; the first EA1 is connected to one path of the echo electrical signal output by the first electrical power splitter 1, and by adjusting the first EA1, the power of this path of echo signal is adjusted; the second EA2 is connected to one path of the transmit electrical signal output by the second electrical power splitter 2, and is used to adjust the power of this path of transmit signal;

[0014] An integrated polarization multiplexing Mach-Zehnder modulator, which includes a first PDM-MZM1 and a second PDM-MZM2; the optical carrier output by the laser source is equally divided into two parts by the optical power splitter, and is respectively input into the first PDM-MZM1 and the second PDM-MZM2;

[0015] In the first PDM-MZM1, the optical carrier is equally divided into two parts by the first PBS1, and is respectively transmitted to the first MZM1 and the second MZM2. The other path of the echo electrical signal output by the first electrical power splitter 1 is transmitted to the first MZM1, and the echo electrical signal output by the first EA1 is transmitted to the second MZM2; the modulated optical signal output by the second MZM2 is coupled with the modulated optical signal output by the first MZM1 in the first PBC1 to output the first modulated echo signal;

[0016] In the second PDM-MZM2, the optical carrier is equally divided into two parts by the second PBS2 and respectively transmitted to the third MZM3 and the fourth MZM4. Another path of the transmitted electrical signal output by the second power divider 2 is transmitted to the third MZM3, and the transmitted electrical signal output by the second EA2 is transmitted to the fourth MZM4. The modulated optical signal output by the fourth MZM4 is coupled with the modulated optical signal output by the third MZM3 in the second PBC2 after passing through the second PR2, and the second modulated transmitted signal is output.

[0017] Optical bandpass filters, which include a first OBPF1 and a second OBPF2; the two optical bandpass filters respectively receive the first modulated echo signal and the second modulated transmitted signal output by the integrated first PDM-MZM1 and the integrated second PDM-MZM2, perform bandpass filtering on them, and respectively filter out the upper sidebands of the modulated echo signal and the modulated transmitted signal.

[0018] An integrated dual-polarization coherent receiver, which respectively receives the upper sidebands of the modulated echo signal and the modulated transmitted signal output by the first OBPF1 and the second OBPF2, performs mixing, photoelectric detection and amplification on them, and outputs four electrical signals, which are respectively represented as the first electrical signal i 1 、the second electrical signal i 2 、the third electrical signal i 3 and the fourth electrical signal i 4 ;

[0019] Baluns, which include a first balun 1 and a second balun 2; the two baluns respectively receive two of the four electrical signals output by the integrated dual-polarization coherent receiver. Among them, the first balun 1 receives the first electrical signal i 1 、the third electrical signal i 3 , and the second balun 2 receives the second electrical signal i 2 、the fourth electrical signal i 4 , respectively perform electrical domain differential processing on them, and respectively output two linearized down-converted electrical signals.

[0020] The present invention also provides a method for measuring Doppler frequency shift and angle of arrival with high linearity, which is based on the above-mentioned microwave photon Doppler frequency shift and angle of arrival measuring device with high linearity. The method includes the following steps:

[0021] Step 1: Electro-optic modulation;

[0022] The single-frequency continuous-wave laser output from the laser source is divided into two paths and respectively injected into the first PDM-MZM1 and the second PDM-MZM2.

[0023] In the first PDM-MZM1, the optical carrier is divided into two parts by the first PBS1 and connected to the first MZM1 and the second MZM2 respectively; the echo electrical signal is divided by the first power divider 1 and one path is transmitted to the first MZM1, and the other path is transmitted to the first EA1. By adjusting the EA1, the power of this path of signal is changed, so as to change the electrical power ratio of the two paths of echo signals; the echo electrical signal output by the first EA1 is transmitted to the second MZM2, and the modulated optical signal output by the second MZM2 is coupled with the modulated optical signal output by the first MZM1 in the first PBC1 to output the first modulated echo signal;

[0024] In the second PDM-MZM2, the optical carrier is divided into two parts by the second PBS2 and connected to the third MZM3 and the fourth MZM4 respectively; the transmitting electrical signal is divided by the second power divider 2 and one path is transmitted to the third MZM3, and the other path is transmitted to the second EA2. By adjusting the EA2, the power of this path of signal is changed, so as to change the electrical power ratio of the two paths of transmitting signals; the transmitting electrical signal output by the second EA2 is transmitted to the fourth MZM4, and the modulated optical signal output by the fourth MZM4 is coupled with the modulated optical signal output by the third MZM3 in the second PBC2 to output the second modulated transmitting signal;

[0025] Assume that the expression of the optical carrier is E in (t) = E c exp(j2πf c t), where f c and E c are the frequency and amplitude of the optical carrier respectively, and ω c is the angular frequency of the optical carrier; the echo signal is expressed as V e cos(2πf e t), where V e is the amplitude of the echo signal and f e is the frequency of the echo signal; at this time, the output of the PDM-MZM1 is expressed as:

[0026]

[0027] where μ P1 is the insertion loss of the first PDM-MZM1, β 1 is the modulation index ratio introduced by the EA1, α 1 and α 2 are the DC biases of the sub-modulators the first MZM1 and the second MZM2 respectively, m e is the modulation index of the echo signal in the first PDM-MZM1, represents the output signal of the TE mode of the polarization state, represents the output signal of the TM mode; then when the transmitting signal is expressed as V t cos(2πf tt), where V t is the amplitude, f t is the frequency, and the second PDM-MZM2 output expression is obtained as follows:

[0028]

[0029] In the formula, μ P2 is the insertion loss of the second PDM-MZM2, β 2 is the ratio of the modulation index introduced by EA2, α 3 and α 4 are the DC biases of the sub-modulators, the third MZM3 and the fourth MZM4 respectively; m t is the modulation index of the transmitted signal in the second PDM-MZM2;

[0030] Step 2: Single-sideband filtering;

[0031] The first modulation echo signal and the second modulation transmission signal output by the first PDM-MZM1 and the second PDM-MZM2 are respectively transmitted to the first OBPF1 and the second OBPF2 to filter out the carrier and the lower sideband, and only the optical signal containing the upper sideband is retained, hereinafter simply referred to as the upper sideband optical signal; at this time, the output signals of the first OBPF1 and the second OBPF2 are respectively expressed as:

[0032]

[0033] In the formula, μ O1 and μ O2 are the insertion losses of the first OBPF1 and the second OBPF2 respectively; Jn(·) represents the Bessel function of the first kind of order n; higher-order Bessel functions are ignored;

[0034] Step 3: Dual-polarization coherent reception;

[0035] The two upper sideband optical signals output by the first OBPF1 and the second OBPF2 are input into the two input ports of the dual-polarization coherent receiver. The dual-polarization coherent receiver uses the internal third PBS3 and fourth PBS4 and two 2×4 optical couplers to combine these two optical signals to generate eight combinations of orthogonal polarization states. After coherent mixing, the eight optical signals are photoelectrically detected by four BPDs inside the dual-polarization coherent receiver and amplified by the TIA inside the dual-polarization coherent receiver, and four electrical signals are output, which are respectively expressed as the first electrical signal i 1 、the second electrical signal i 2 、the third electrical signal i 3 and the fourth electrical signal i 4 ;

[0036] Taking the output of the first Hybrid-X as an example, its four outputs are respectively expressed as:

[0037]

[0038]

[0039] Among them, E OBPF1-X (t) and E OBPF2-X (t) respectively represent the TE mode output signals of the first OBPF1 and the second OBPF2. After coherent mixing, the eight optical signals are detected by four BPDs through photoelectric detection and amplified by TIA. Among them, the output current of the first BPD1 - the first - path electrical signal i 1 (t) is expressed as:

[0040]

[0041] Among them, η is the responsivity of the BPD. Let α 1 =α 3 , the above formula is rewritten as:

[0042]

[0043] Similarly, let α 2 =α 4 , then the output current - the third - path electrical signal at the third BPD3 is expressed as:

[0044]

[0045] In formulas (10) and (11), the common - mode components such as the direct current and the second - order intermodulation distortion IMD2 have been eliminated by the BPD, and the differential - mode components of the frequency - converted output are amplified;

[0046] Step 4: Electrical domain linearization processing;

[0047] The first - path electrical signal i 1 output by the first TIA1 and the third TIA3 and the third - path electrical signal i 3 are subtracted in the first balun 1. The second - path electrical signal i 2 output by the second TIA2 and the fourth TIA4 and the fourth - path electrical signal i 4 are subtracted in the second balun 2 to realize a linearized measurement system;

[0048] The expression of the output current i B1 (t) of the first balun 1 is:

[0049]

[0050] In the case of small - signal input, substituting into the Bessel series expansion equation J 1 (m)≈m / 2 - m 3 / 16, where m is the modulation index, the amplitude term of the above equation is written as:

[0051]

[0052] In the formula, I B1 represents the amplitude of i B1 (t);

[0053] In the above formula, m e m t and β 1 β 2 m e m t represent the amplitude of the fundamental frequency term after frequency conversion, and represent the amplitude of the IMD3 term under two-tone derivation; since m e and m t are both less than 1, then and are approximately equal to 0. Therefore, formula (13) is approximately expressed as:

[0054]

[0055] When the condition 1 + cos(α 1 ) / 1 + cos(α 2 ) = β 1 3 β 2 is satisfied, the IMD3 component in the channel is suppressed, and the output current is re-expressed as:

[0056]

[0057] Similarly, the output currents of the second TIA2 and the fourth TIA4 are subtracted in the second balun 2. When the condition 1 + cos(α 1 ) / 1 + cos(α 2 ) = β 1 3 β 2 is satisfied, the IMD3 component in the electrical signal output by the second balun 2 is canceled, and the output current of the second balun 2 is expressed as:

[0058]

[0059] At this time, two non-linearly suppressed I / Q signals are output, and the DFS obtained from the two IF signals is f d = f t - f e , where f d represents the Doppler frequency shift. Through the phase difference of the signals in the two channels, the direction of the DFS can be identified;

[0060] Step 5: AOA measurement;

[0061] Perform phase analysis on the second electrical signal i output from the second BPD2 and the fourth BPD4 inside the dual-polarization coherent receiver, to obtain the phase difference related to AOA, and achieve large-range AOA measurement without angle ambiguity; 2 and the fourth electrical signal i 4 for the two paths, to obtain the phase difference related to AOA, and achieve large-range AOA measurement without angle ambiguity;

[0062] Assume the expression of the optical carrier is E in (t) = E c exp(j2πf c t), where f c and E c are respectively the frequency and amplitude of the optical carrier, and ω c is the angular frequency of the optical carrier; represent the two echo signals as V e cos(2πf e t) and V e In the formula, V e is the amplitude of the echo signal, f e is the frequency of the echo signal, represents the phase difference between the two echo signals; the two received echo signals are respectively input into the first MZM1 and the second MZM2 of the sub-modulator, then the output of the first PDM-MZM1 is rewritten as:

[0063]

[0064] The output of the second PDM-MZM2 remains unchanged and is expressed as:

[0065]

[0066] The two outputs are respectively expressed as:

[0067]

[0068] Analyze the phase information of the above two signals through an oscilloscope to achieve AOA measurement with nearly 360-degree angle ambiguity.

[0069] The advantages of the present invention are as follows:

[0070] The present invention changes the optical / electrical power ratio by adjusting the bias points of four sub-modulators (MZM1, MZM2, MZM3, and MZM4) and the attenuation of the EA, constructs two links with opposite non-linearities to achieve IMD3 suppression of the system; realizes I / Q down-conversion through a dual-polarization coherent receiver to achieve DFS measurement and DFS direction discrimination; through the phase analysis of the IF signal after I / Q down-conversion, AOA measurement in a large angle range can be achieved; at the same time, due to the use of BPD, the system can also achieve IMD2 and common-mode noise suppression. Therefore, the system realizes DFS and AOA measurement on the basis of linearization, improves the measurement range and accuracy, and has great advantages in low-frequency DFS measurement. Description of the Drawings

[0071] Figure 1 It is a diagram of a high-linearity microwave photon Doppler frequency shift and angle of arrival measurement device of the present invention;

[0072] Figure 2 It is a comparison diagram of linear optimization spectra of an embodiment of the present invention;

[0073] Figure 3 It is a signal waveform diagram of DFS direction discrimination of an embodiment of the present invention;

[0074] Figure 4 It is a diagram of DFS measurement results of an embodiment of the present invention;

[0075] Figure 5 It is a diagram of AOA measurement results of an embodiment of the present invention. Detailed Embodiment

[0076] The present invention will be further described below with reference to the accompanying drawings:

[0077] The present invention provides a microwave photon Doppler frequency shift and angle of arrival measurement device with high linearity. The device includes: 1. a laser source (Laser Diode, LD); 2. an optical power splitter; 3. an electrical power splitter (the first electrical power splitter 1 and the second electrical power splitter 2 respectively); 4. electrical attenuators (Electric attenuator, EA) (the first EA 1 and the second EA2 respectively); 5. an integrated polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) (including the first PDM-MZM1 and the second PDM-MZM2), and this integrated modulator PDM-MZM is composed of two Mach–Zehnder modulators (Mach–Zehnder modulator, MZM) (the first MZM1 and the second MZM2 respectively), a polarization rotator (Polarization Rotator, PR), a polarizing beam splitter (Polarizing Beam Splitter, PBS), and a polarizing beam combiner (Polarizing Beam Combiner, PBC); 6. an optical band-pass filter (Optical Band-passFilter, OBPF); 7. an integrated dual-polarization coherent receiver (Finisar CPRV1220A), and this integrated device is composed of two PBSs (the third PBS3 and the fourth PBS4 respectively), two 2×4 optical couplers (the first Hybrid-X and the second Hybrid-Y), four balanced photodetectors (Balanced photodetector, BPD) (the first BPD1, the second BPD2, the third BPD3, the fourth BPD4 respectively), and four trans-impedance amplifiers (Trans-Impedance Amplifier, TIA) (the first TIA1, the second TIA2, the third TIA3, the fourth TIA4 respectively); 8. a balun.

[0078] 1. A laser source that outputs a single-frequency continuous-wave laser;

[0079] 2. An optical power splitter that receives the single-frequency continuous-wave laser output by the laser source, divides its power into two paths and then outputs;

[0080] 3. An electrical power splitter that includes the first electrical power splitter 1 and the second electrical power splitter 2. The first electrical power splitter 1 is used to equally divide the received echo signal into two parts and output, and the second electrical power splitter 2 is used to equally divide the received transmit signal into two parts and output.

[0081] 4. Electrical attenuator, which includes a first EA1 and a second EA2. The first EA1 is connected to an echo electrical signal of one path output by the first power splitter 1, and the power of this path of echo signal is adjusted by adjusting the first EA1. The second EA2 is connected to a transmitted electrical signal of one path output by the second power splitter 2 and is used to adjust the transmitted power of this path.

[0082] 5. Integrated polarization multiplexing Mach-Zehnder modulator, which includes a first PDM-MZM1 and a second PDM-MZM2. The single-frequency continuous optical carrier output by the laser source (hereinafter referred to as "optical carrier" for short) is equally divided into two parts by an optical power splitter and is respectively input into the first PDM-MZM1 and the second PDM-MZM2.

[0083] In the first PDM-MZM1, the optical carrier is equally divided into two parts by the first PBS1 and is respectively transmitted to the first MZM1 and the second MZM2. Another path of echo electrical signal output by the first power splitter 1 is transmitted to the first MZM1, and the echo electrical signal output by the first EA1 is transmitted to the second MZM2. The modulated optical signal output by the second MZM2 is coupled with the modulated optical signal output by the first MZM1 in the first PBC1 after passing through the first PR1, and the first modulated echo signal is output.

[0084] Similarly, in the second PDM-MZM2, the optical carrier is equally divided into two parts by the second PBS2 and is respectively transmitted to the third MZM3 and the fourth MZM4. Another path of transmitted electrical signal output by the second power splitter 2 is transmitted to the third MZM3, and the transmitted electrical signal output by the second EA2 is transmitted to the fourth MZM4. The modulated optical signal output by the fourth MZM4 is coupled with the modulated optical signal output by the third MZM3 in the second PBC2 after passing through the second PR2, and the second modulated transmitted signal is output.

[0085] 6. Optical band-pass filter, which includes a first OBPF1 and a second OBPF2. The two optical band-pass filters respectively receive the first modulated echo signal and the second modulated transmitted signal output by the integrated first PDM-MZM1 and the integrated second PDM-MZM2, perform band-pass filtering on them, and respectively filter out the upper sidebands of the modulated echo signal and the modulated transmitted signal;

[0086] 7. Integrated dual-polarization coherent receiver, which respectively receives the upper sidebands of the modulated echo signal and the modulated transmitted signal output by the first OBPF1 and the second OBPF2, performs mixing, photoelectric detection and amplification on them, and outputs four electrical signals, which are respectively represented as the first electrical signal i 1 、the second electrical signal i 2 、the third electrical signal i 3 and the fourth electrical signal i 4 ;

[0087] 8. Balun, which includes a first balun 1 and a second balun 2. The two baluns respectively receive two of the four electrical signals output by the dual-polarization coherent receiver. Among them, the first balun 1 receives the first electrical signal i 1 and the third electrical signal i 3 , and the second balun 2 receives the second electrical signal i 2 and the fourth electrical signal i 4 , respectively perform electrical domain differential processing on them, and respectively output two linearized down-converted electrical signals.

[0088] The present invention also provides a high linearity Doppler frequency shift and angle of arrival measurement method, which is based on the above measurement device. This method includes the following steps:

[0089] Step 1: Electro-optic modulation;

[0090] The single-frequency continuous wave laser output from the laser source is split into two paths and then respectively injected into the first PDM-MZM1 and the second PDM-MZM2.

[0091] In the first PDM-MZM1, the optical carrier is divided into two parts by the first PBS1 and respectively connected to the first MZM1 and the second MZM2. The echo electrical signal is split by the first power splitter 1, and one path is transmitted to the first MZM1, and the other path is transmitted to the first EA1. By adjusting EA1, the power of this path signal is changed, thereby changing the electrical power ratio of the two echo signals. The echo electrical signal output by the first EA1 is transmitted to the second MZM2. The modulated optical signal output by the second MZM2 is coupled with the modulated optical signal output by the first MZM1 in the first PBC1 to output the first modulated echo signal.

[0092] Similarly, in the second PDM-MZM2, the optical carrier is divided into two parts by the second PBS2 and respectively connected to the third MZM3 and the fourth MZM4. The transmitted electrical signal is split by the second power splitter 2, and one path is transmitted to the third MZM3, and the other path is transmitted to the second EA2. By adjusting EA2, the power of this path signal is changed, thereby changing the electrical power ratio of the two transmitted signals. The transmitted electrical signal output by the second EA2 is transmitted to the fourth MZM4. The modulated optical signal output by the fourth MZM4 is coupled with the modulated optical signal output by the third MZM3 in the second PBC2 to output the second modulated transmitted signal.

[0093] Assume that the expression of the optical carrier is E in (t) = E c exp(j2πf c t), where f c and E c are respectively the frequency and amplitude of the optical carrier, and ω c is the angular frequency of the optical carrier. The echo signal is expressed as V ecos(2πf e t), where V e is the amplitude of the echo signal, and f e is the frequency of the echo signal. At this time, the output of PDM-MZM1 can be expressed as:

[0094]

[0095] where μ P1 is the insertion loss of the first PDM-MZM1, β 1 is the modulation index ratio introduced by EA1, α 1 and α 2 are the DC biases of the sub-modulators the first MZM1 and the second MZM2 respectively, m e is the modulation index of the echo signal in the first PDM-MZM1, represents the output signal of the TE mode of the polarization state, represents the output signal of the TM mode. Then when the transmitted signal is expressed as V t cos(2πf t t), where V t is the amplitude and f t is the frequency, similarly, the output expression of the second PDM-MZM2 can be obtained:

[0096]

[0097] where μ P2 is the insertion loss of the second PDM-MZM2, β 2 is the modulation index ratio introduced by EA2, α 3 and α 4 are the DC biases of the sub-modulators the third MZM3 and the fourth MZM4 respectively; m t is the modulation index of the transmitted signal in the second PDM-MZM2.

[0098] Step 2: Single-sideband filtering;

[0099] The first modulated echo signal and the second modulated transmitted signal output by the first PDM-MZM1 and the second PDM-MZM2 are respectively transmitted to the first OBPF1 and the second OBPF2 to filter out the carrier and the lower sideband, and only the optical signal containing only the upper sideband is retained, hereinafter simply referred to as the upper sideband optical signal. At this time, the output signals of the first OBPF1 and the second OBPF2 can be respectively expressed as:

[0100]

[0101] where μ O1 and μ O2They are the insertion losses of the first OBPF1 and the second OBPF2 respectively. Jn(·) represents the Bessel function of the first kind of order n. Considering the finite modulation index, the higher-order Bessel functions are ignored.

[0102] Step 3: Dual-polarization coherent reception;

[0103] Input the two upper-sideband optical signals output from the first OBPF1 and the second OBPF2 into two input ports of a dual-polarization coherent receiver. The dual-polarization coherent receiver (Finisar, CPRV1220A) uses two internal PBSs (the third PBS3 and the fourth PBS4) and two 2×4 optical couplers (the first Hybrid-X and the second Hybrid-Y) to combine these two optical signals, generating eight combinations of orthogonal polarization states. After coherent mixing, the eight optical signals are photoelectrically detected by four BPDs (the first BPD1, the second BPD2, the third BPD3, and the fourth BPD4) inside the dual-polarization coherent receiver, and are all amplified by TIAs (the first TIA1, the second TIA2, the third TIA3, and the fourth TIA4) inside the dual-polarization coherent receiver, outputting four electrical signals, which are respectively represented as the first electrical signal i 1 、the second electrical signal i 2 、the third electrical signal i 3 and the fourth electrical signal i 4 . The description of the dual-polarization coherent receiver corresponds to the device manual and is well-known to those skilled in the art.

[0104] Taking the output of the first Hybrid-X as an example, its four outputs are respectively represented as:

[0105]

[0106] Among them, E OBPF1-X (t) and E OBPF2-X (t) respectively represent the TE-mode output signals of the first OBPF1 and the second OBPF2. After coherent mixing, the eight optical signals are photoelectrically detected by four BPDs and are all amplified by TIAs. Among them, the output current of the first BPD1 - the first electrical signal i 1 (t) can be represented as:

[0107]

[0108] Among them, η is the responsivity of the BPD. Let α 1 = α 3 , the above formula can be rewritten as:

[0109]

[0110] Similarly, let α 2 = α4 Then the current-output third-channel electrical signal output from the third BPD3 terminal can be expressed as:

[0111]

[0112] In formulas (10) and (11), common-mode components such as direct current and second-order intermodulation distortion (IMD2) have been eliminated by the BPD, and the differential-mode components of the frequency-converted output are amplified.

[0113] Step 4: Electrical domain linearization processing;

[0114] The first-channel electrical signal i output from the first TIA1 and the third TIA3 1 and the third-channel electrical signal i 3 are subtracted in the first balun 1, and the second-channel electrical signal i output from the second TIA2 and the fourth TIA4 2 and the fourth-channel electrical signal i 4 are subtracted in the second balun 2, finally realizing a linearized measurement system.

[0115] The output current i B1 (t) of the first balun 1 is expressed as:

[0116]

[0117] In the case of small-signal input, substituting into the Bessel series expansion equation J 1 (m)≈m / 2 - m 3 / 16, where m is the modulation index, the amplitude term of the above equation can be written as:

[0118]

[0119] In the formula, I B1 represents the amplitude of i B1 (t).

[0120] In the above formula, m e m t and β 1 β 2 m e m t represent the amplitudes of the fundamental frequency terms after frequency conversion, and can represent the amplitudes of the IMD3 terms under two-tone derivation. Since m e and m t are both less than 1, then and are approximately equal to 0. Therefore, formula (13) can be approximately expressed as:

[0121]

[0122] When the condition (1 + cos(α 1 )) / (1 + cos(α 2 )) = β 1 3 β 2 is satisfied, the IMD3 component in the channel is suppressed, and at this time the output current can be re-expressed as:

[0123]

[0124] Similarly, the output currents of the second TIA2 and the fourth TIA4 are subtracted in the second balun 2. When the condition (1 + cos(α 1 )) / (1 + cos(α 2 )) = β 1 3 β 2 is satisfied, the IMD3 component in the electrical signal output by the second balun 2 is canceled, and the output current of the second balun 2 is expressed as:

[0125]

[0126] At this time, two non-linearly suppressed I / Q signals are output, and from the two IF signals, the DFS is f d = f t - f e , where f d represents the Doppler frequency shift, and the direction of the DFS can be identified through the phase difference between the signals of the two channels.

[0127] Step 5: AOA measurement;

[0128] Perform phase analysis on the second electrical signal i 2 and the fourth electrical signal i 4 output by the second BPD2 and the fourth BPD4 inside the dual-polarization coherent receiver, and the phase difference related to the AOA can be obtained to achieve large-range AOA measurement without angular ambiguity.

[0129] Assume that the expression of the optical carrier is E in (t) = E c exp(j2πf c t), where f c and E c are the frequency and amplitude of the optical carrier respectively, and ω c is the angular frequency of the optical carrier. Express the two echo signals as V e cos(2πf e t) and V e In the formula, Ve is the amplitude of the echo signal, f e is the frequency of the echo signal, represents the phase difference between two echo signals. The two received echo signals are respectively input into the first MZM1 and the second MZM2 of the sub-modulator. At this time, the output of the first PDM-MZM1 can be rewritten as:

[0130]

[0131] The output of the second PDM-MZM2 remains unchanged and is expressed as:

[0132]

[0133] The two outputs are respectively expressed as:

[0134]

[0135] The meanings of all symbols in step 5 are the same as those explained above. By analyzing the phase information of the above two signals with an oscilloscope, the AOA measurement without angular ambiguity of nearly 360 degrees can be realized.

[0136] To verify the feasibility and effectiveness of the present invention, the VPI optical simulation platform is used to verify the signal generation function and the performance of the generated signal of the present device.

[0137] Set the output optical carrier frequency of the laser source to 193.4 THz and the output optical power to 16 dBm; the half-wave voltage of the PDM-MZM is set to 3.5 V; the responsivity of the dual-polarization coherent receiver is 0.45 A / W, and the TIA amplification power is 18 dB.

[0138] First, verify the linearization performance of the present invention. At this time, it mainly aims at the mDFS measurement scenario, that is, the echo signal contains both DFS and mDFS signals at the same time. Use dual-tone signals with frequencies of 10.3 GHz and 10.5 GHz to simulate the received echo signal, and the transmit signal frequency is 10 GHz and the power is 10 dBm. Here, it is assumed that mDFS and DFS are 0.3 GHz and 0.5 GHz respectively for convenient spectrum observation. In fact, the DFS value is much smaller than this value. For comparison, the present invention also simulates the basic down-conversion technology based on DPMZM (only including LD, DPMZM, erbium-doped fiber amplifier and photodetector (PD)). The spectrum results of the two groups of links are as Figure 2As shown, where the dashed line is the result of a typical DPMZM-based scheme. It can be seen that in addition to the two-tone down-converted signals at 0.3 and 0.5 GHz in the link at this time, IMD3 signals are also generated at two frequency points of 0.1 GHz and 0.7 GHz, as well as IMD2 at 0.2 GHz, the second-harmonic down-converted signal at 0.4 GHz, and the DC component. These non-linear signals are all relatively close to the DFS, so they will affect the measurement results. In particular, the IMD2 component is the closest to the DFS signal and has a relatively large power. The figure shows the spectral results based on the system in this section. It can be seen that at this time, the above non-linearities have been suppressed, only containing the frequency to be measured, without the interference of spurious components.

[0139] To verify the DFS direction discrimination performance, the transmitted signal is set to 10 GHz with a power of 10 dBm. First, the echo signal is set to 10.5 GHz, that is, DFS is +0.5 GHz. The result is as Figure 3 (a) shown. At this time, the Q-channel signal leads the I-channel by 90 degrees, and the DFS direction is positive. Subsequently, the echo signal is set to 9.5 GHz, that is, DFS is -0.5 GHz. The result is as Figure 3 (b) shown. At this time, the Q-channel signal lags behind the I-channel by 90 degrees, and the DFS direction is negative.

[0140] Next, verify the DFS measurement effect. The transmitted signal is set to 10 GHz with a power of 10 dBm. DFS changes from -100 KHz to 100 KHz at a step of 10 KHz, and the output signal is subjected to spectral analysis. The DFS measurement results can be obtained as Figure 4 shown. Figure 4 The squares in the figure are the measured DFS, and the stars are the measurement errors. It can be seen that the measurement error of DFS fluctuates between -0.1 - 0.1 Hz.

[0141] To further evaluate the AOA measurement performance. The transmitted signal frequency is set to 10 GHz, and the power is set to 10 dBm. At the same power, the frequency of the echo signal is changed to 10.5 GHz, and the phase shifter is used to simulate the phase difference between the two antennas from -170 to 180 degrees in steps of 10 degrees. The measured phase differences are represented by solid circles in Figure 5 . For the convenience of comparison, the theoretical phase difference values are also shown by solid lines in the figure. The measurement errors at each phase difference are shown by stars in Figure 5 . It can be seen that the error of the phase difference is between ±0.02 degrees.

[0142] In summary, the above-described embodiments are only examples of the present invention and are not solely used to define the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several equivalent deformations and substitutions can be made based on the disclosed content of the present invention. The laser wavelength and power, radio frequency signal frequency and power, modulator bias point, etc. can all be changed. These equivalent deformations, substitutions, and adjustments of the frequency range should also be regarded as within the protection scope of the present invention.

Claims

1. A high linearity microwave photon Doppler frequency shift and arrival angle measurement device, characterized in that: The device comprises: a laser source LD, an optical power divider, a first electric power divider 1, a second electric power divider 2, a first electric attenuator EA1, a second electric attenuator EA2, a first integrated polarization multiplexing Maximizer modulator PDM-MZM1, a first integrated polarization multiplexing Maximizer modulator PDM-MZM2, an optical bandpass filter OBPF, an integrated dual-polarization coherent receiver, and a balun; wherein The first integrated polarization multiplexing Maxwell gain modulator PDM-MZM1 includes: a first Maxwell gain modulator MZM1, a second Maxwell gain modulator MZM2, a first polarization beam splitter PBS1, a first polarization beam combiner PBC1, and a first polarization rotator PR1; The second integrated polarization multiplexing Magnetron modulator PDM-MZM2 includes: a third Magnetron modulator MZM1, a fourth Magnetron modulator MZM2, a second polarization beam splitter PBS2, a second polarization beam combiner PBC2, and a second polarization rotator PR2; The integrated dual-polarization coherent receiver includes: a third polarization beam splitter PBS3, a fourth polarization beam splitter PBS4, two 2×4 optical couplers - a first Hybrid-X and a second Hybrid-Y, four balanced photodetectors BPD, and four transimpedance amplifiers TIA; wherein the four balanced photodetectors BPD are respectively a first BPD1, a second BPD2, a third BPD3, and a fourth BPD4; and the four transimpedance amplifiers TIA are respectively a first TIA1, a second TIA2, a third TIA3, and a fourth TIA4; And among them: A laser source, which outputs a single-frequency continuous-wave laser; An optical power splitter receives the single-frequency continuous wave laser output by the laser source, splits the power into two paths and then outputs the power; The electric power divider comprises a first electric power divider 1 and a second electric power divider 2; the first electric power divider 1 is used to divide the received echo signal into two parts and output them, and the second electric power divider 2 is used to divide the received transmission signal into two parts and output them; The electric attenuator includes a first EA1 and a second EA2; the first EA1 is connected to an echo electric signal output by the first electric power divider 1, and the power of the echo signal is adjusted by adjusting the first EA1; the second EA2 is connected to a transmission electric signal output by the second electric power divider 2, and is used to adjust the transmission power of the transmission signal; An integrated polarization multiplexing Maxwell gain modulator includes a first PDM-MZM1 and a second PDM-MZM2; an optical carrier output by a laser source is equally divided into two parts by an optical power divider and input into the first PDM-MZM1 and the second PDM-MZM2 respectively; In the first PDM-MZM1, the optical carrier is equally divided into two parts by the first PBS1 and transmitted to the first MZM1 and the second MZM2 respectively. The other echo electrical signal output by the first electrical power divider 1 is transmitted to the first MZM1, and the echo electrical signal output by the first EA1 is transmitted to the second MZM2. The modulated optical signal output by the second MZM2 is coupled with the modulated optical signal output by the first MZM1 in the first PBC1 after passing through the first PR1, and the first modulated echo signal is output. In the second PDM-MZM2, the optical carrier is equally divided into two parts by the second PBS2 and transmitted to the third MZM3 and the fourth MZM4 respectively. The other transmission electrical signal output by the second electrical power divider 2 is transmitted to the third MZM3, and the transmission electrical signal output by the second EA2 is transmitted to the fourth MZM4; the modulated optical signal output by the fourth MZM4 is coupled with the modulated optical signal output by the third MZM3 in the second PBC2 after passing through the second PR2, and a second modulated transmission signal is output; An optical bandpass filter, comprising a first OBPF1 and a second OBPF2; the two optical bandpass filters respectively receive a first modulated echo signal and a second modulated transmission signal output by the integrated first PDM-MZM1 and the integrated second PDM-MZM2, perform bandpass filtering on them, and filter out upper sidebands of the modulated echo signal and the modulated transmission signal respectively; An integrated dual-polarization coherent receiver receives the modulated echo signal and the upper sideband of the modulated transmission signal output by the first OBPF1 and the second OBPF2, performs frequency mixing, photoelectric detection and amplification on the signals, and outputs four electrical signals, which are respectively represented as a first electrical signal i1, a second electrical signal i2, a third electrical signal i3 and a fourth electrical signal i4; The balun includes a first balun 1 and a second balun 2; the two baluns respectively receive two of the four electrical signals output by the integrated dual-polarization coherent receiver, wherein the first balun 1 receives the first electrical signal i1 and the third electrical signal i3, and the second balun 2 receives the second electrical signal i2 and the fourth electrical signal i4, performs electrical domain differential processing on them respectively, and outputs two linearized down-converted electrical signals respectively.

2. A high-linearity Doppler frequency shift and arrival angle measurement method, which is based on the above-mentioned high-linearity microwave photon Doppler frequency shift and arrival angle measurement device, characterized in that: The method comprises the following steps: Step 1: electro-optic modulation; The single-frequency continuous wave laser output from the laser source is split into two paths and injected into the first PDM-MZM1 and the second PDM-MZM2 respectively; In the first PDM-MZM1, the optical carrier is divided into two parts by the first PBS1, and connected to the first MZM1 and the second MZM2 respectively; the echo electrical signal is divided by the first electrical power divider 1, and one path is transmitted to the first MZM1, and the other path is transmitted to the first EA1, and the signal power of the path is changed by adjusting EA1, thereby changing the electrical power ratio of the two paths of echo signals; the echo electrical signal output by the first EA1 is transmitted to the second MZM2, and the modulated optical signal output by the second MZM2 is coupled with the modulated optical signal output by the first MZM1 in the first PBC1 after passing through the first PR1, and the first modulated echo signal is output; In the second PDM-MZM2, the optical carrier is divided into two parts by the second PBS2, and connected to the third MZM3 and the fourth MZM4 respectively. The transmission electrical signal is transmitted to the third MZM3 in one way after being split by the second electrical power divider 2, and the other way is transmitted to the second EA2. The signal power of the way is changed by adjusting EA2, thereby changing the electrical power ratio of the two transmission signals. The transmission electrical signal output by the second EA2 is transmitted to the fourth MZM4, and the modulated optical signal output by the fourth MZM4 is coupled with the modulated optical signal output by the third MZM3 in the second PBC2 after passing through the second PR2, and the second modulated transmission signal is output. Assume that the expression of the optical carrier is E in (t) = E c exp(j2πf c t), where f c and E c are the frequency and amplitude of the optical carrier, ω c is the angular frequency of the optical carrier; the echo signal is represented by V e cos(2πf e t), where V e is the echo signal amplitude, f e is the echo signal frequency; at this time, the output of PDM-MZM1 is expressed as: In the formula, μ P1 is the insertion loss of the first PDM-MZM1, β1 is the ratio of the modulation index introduced by EA1, α1 and α2 are the DC bias of the first MZM1 and the second MZM2 of the sub-modulator, respectively, and m e is the modulation index of the echo signal in the first PDM-MZM1, represents the polarization state TE mode output signal, represents the TM mode output signal; when the transmission signal is represented by V t cos(2πf t t), where V t is the amplitude, f t For frequency, the second PDM-MZM2 output expression is obtained: In the formula, μ P2 is the insertion loss of the second PDM-MZM2, β2 is the ratio of the modulation index introduced by EA2, α3 and α4 are the DC bias of the third MZM3 and the fourth MZM4 of the sub-modulator respectively; m t is the modulation index of the transmitted signal in the second PDM-MZM2; Step 2: Single sideband filtering; The first modulated echo signal and the second modulated transmit signal output by the first PDM-MZM1 and the second PDM-MZM2 are transmitted to the first OBPF1 and the second OBPF2 respectively, for filtering out the carrier and the lower sideband, and retaining the optical signal containing only the upper sideband, hereinafter referred to as the upper sideband optical signal; at this time, the output signals of the first OBPF1 and the second OBPF2 are respectively expressed as: Where μ O1 and μ O2 are the insertion losses of the first OBPF1 and the second OBPF2, respectively; Jn(·) represents the first-order n-order Bessel function; higher-order Bessel functions are ignored; Step 3: Dual polarization coherent reception; Input the two sideband optical signals output by the first OBPF1 and the second OBPF2 into the two input ports of the dual-polarization coherent receiver. The dual-polarization coherent receiver combines the two optical signals by using the third PBS3 and the fourth PBS4 and two 2×4 optical couplers therein to generate eight combinations of orthogonal polarization states. After coherent mixing, the eight optical signals are photoelectrically detected by four BPDs inside the dual-polarization coherent receiver and amplified by the TIA inside the dual-polarization coherent receiver to output four electrical signals, which are respectively represented as the first electrical signal i1, the second electrical signal i2, the third electrical signal i3 and the fourth electrical signal i4; Taking the output of the first Hybrid-X as an example, its four outputs are expressed as follows: Among them, E OBPF1-X (t) and E OBPF2-X (t) represent the TE mode output signals of the first OBPF1 and the second OBPF2 respectively. After coherent mixing, the eight optical signals are photoelectrically detected by four BPDs and amplified by TIA. The output current of the first BPD1 - the first electrical signal i1(t) is expressed as: Where η is the responsiveness of BPD, let α1 = α3, and rewrite the above formula as: Similarly, let α2=α4, then the current output by the third BPD3 terminal - the third electrical signal is expressed as: In equations (10) and (11), the common-mode components such as DC and second-order intermodulation distortion IMD2 have been eliminated by the BPD, and the differential-mode components of the frequency conversion output are amplified; Step 4: Electrical domain linearization processing; The first electrical signal i1 and the third electrical signal i3 outputted by the first TIA1 and the third TIA3 are subtracted in the first balun 1, and the second electrical signal i2 and the fourth electrical signal i4 outputted by the second TIA2 and the fourth TIA4 are subtracted in the second balun 2, so as to realize a linearized measurement system; The output current i of the first balun 1 B1 (t) is expressed as: In the case of small signal input, substitute the Bessel series expansion equation J1(m)≈m / 2-m 3 / 16, m is the modulation index, then the amplitude term of the above equation is written as: In the formula, I B1 Indicates i B1 The magnitude of (t); In the above formula, m e m t and β1β2m e m t represents the amplitude of the fundamental frequency term after frequency conversion, and represents the amplitude of IMD3 term under two-tone derivation; due to m e and m t If both are less than 1, then and is approximately equal to 0, so formula (13) is approximately expressed as: When the conditions are met When , the IMD3 component in the channel is suppressed, and the output current is re-expressed as: Similarly, the output currents of the second TIA2 and the fourth TIA4 are subtracted in the second balun 2. When the condition is met When , the IMD3 component in the electrical signal output by the second balun 2 is cancelled, and the output current of the second balun 2 is expressed as: At this time, two nonlinear suppressed I / Q signals are output, and the DFS obtained from the two IF signals is f d =f t -f e , where f d It represents Doppler frequency shift. Through the phase difference of the signals of the two channels, the direction of DFS can be identified. Step 5: AOA measurement; Perform phase analysis on the second electrical signal i2 and the fourth electrical signal i4 output by the second BPD2 and the fourth BPD4 inside the dual-polarization coherent receiver to obtain the phase difference related to AOA, so as to achieve wide-range AOA measurement without angle ambiguity; Assume that the expression of the optical carrier is E in (t) = E c exp(j2πf c t), where f c and E c are the frequency and amplitude of the optical carrier, ω c is the angular frequency of the optical carrier; the two echo signals are represented as V e cos(2πf e t) and Where V e is the echo signal amplitude, f e is the echo signal frequency, Represents the phase difference between the two echo signals; the two received echo signals are input into the first MZM1 and the second MZM2 of the sub-modulator respectively, then the output of the first PDM-MZM1 is rewritten as: The output of the second PDM-MZM2 remains unchanged and is expressed as: The two outputs are expressed as: The phase information of the above two signals is analyzed by an oscilloscope to achieve nearly 360-degree AOA measurement without angle ambiguity.

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