A method and apparatus for photonics angle of arrival measurement based on triangular wave phase modulation

Abstract

The application discloses a kind of photonic angle of arrival measurement method and device based on triangular wave phase modulation, the device of the present application, including laser source, polarization controller, double-drive Mach-Zehnder modulator, optical filter, photodetector and phase discrimination module connected in turn;Laser generates optical carrier, optical carrier enters the optical input port of double-drive Mach-Zehnder modulator by polarization controller;The direct current bias port of double-drive Mach-Zehnder modulator inputs low-frequency triangular wave signal, and the electrical input port of double-drive Mach-Zehnder modulator inputs microwave signal received by antenna;After being modulated by double-drive Mach-Zehnder modulator, optical signal enters optical filter and is filtered;The optical signal output by optical filter enters photodetector and is photoelectrically converted to obtain low-frequency electrical signal, and phase jump is obtained by phase discrimination module, and then the angle of arrival is estimated.The application utilizes low-frequency triangular wave to realize mixing, without high-frequency local oscillator signal, and the device structure is simple.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of photonics and microwave measurement technology, and is mainly applied to radar signal processing, and particularly relates to a method and device for measuring angle of arrival based on triangular wave phase modulation. BACKGROUND

[0002] The angle of arrival (AOA) of microwave signals plays an important role in satellite positioning, wireless communication, electronic warfare and other applications. The AOA can be estimated by measuring the phase difference between received signals. Using the obtained AOA information can maximize the power of the target signal, thereby improving the reception performance of the signal. In the application scenario with wide bandwidth (such as tens of gigahertz), due to the existence of electronic bottleneck, the AOA measurement method based on digital signal processing has great limitations. Microwave photonics technology with advantages of large bandwidth, low loss and anti-electromagnetic interference provides a new idea for the measurement of AOA.

[0003] At present, the angle of arrival measurement schemes based on microwave photonics mainly include the following three types:

[0004] (1) Phase-to-amplitude mapping. First, the phase of the received microwave signal is mapped to the power or direct current voltage of the output signal, and the AOA of the microwave signal is estimated by measuring the power or direct current voltage of the signal. However, the measurement error of this scheme is easily affected by the power fluctuation of the laser.

[0005] (2) Constructing a microwave photonics notch filter. A true time delay unit or a differential group delay module is used to generate a microwave photonics notch filter, and the AOA of the microwave signal is obtained by measuring the notch frequency of the output wideband signal spectrum. However, this scheme is only suitable for the measurement of wideband microwave signal AOA, and the measurement range is limited by the signal bandwidth.

[0006] (3) Down-conversion phase detection. This scheme first converts the received high-frequency microwave signal into an intermediate frequency signal through microwave photonics down-conversion technology, and then obtains the AOA of the microwave signal by measuring the phase difference information of the two intermediate frequency signals. However, this scheme needs a high-frequency local oscillator signal for down-conversion, and needs to construct two branches to compare the phase.

[0007] In view of the above status, the present application provides a method and device for measuring angle of arrival based on triangular wave phase modulation. SUMMARY

[0008] In view of the above problems existing in the prior art, the present application provides a method and device for measuring angle of arrival based on triangular wave phase modulation.

[0009] The scheme adopted by the present application to solve its technical problems is as follows:

[0010] A method for measuring the angle of arrival of a photon based on triangular wave phase modulation, comprising the following steps:

[0011] Step 1: a laser generates an optical carrier, which enters the optical input port of a double-drive Mach-Zehnder modulator through a polarization controller;

[0012] Step 2: a low-frequency triangular wave signal is input into the DC bias port of the double-drive Mach-Zehnder modulator, which introduces a pair of opposite frequency shifts to the modulated light signal of the lower arm;

[0013] Step 3: the microwave signal received by the antenna is input into the electrical input port of the double-drive Mach-Zehnder modulator;

[0014] Step 4: the modulated light signal from the double-drive Mach-Zehnder modulator enters an optical filter for filtering;

[0015] Step 5: the light signal output from the optical filter enters a photodetector for photoelectric conversion to obtain a low-frequency electrical signal, and the phase jump is obtained through a phase discrimination module, and then the angle of arrival is estimated.

[0016] Preferably, in step 1, a laser generates an optical carrier, which enters the optical input port of a double-drive Mach-Zehnder modulator through a polarization controller. The optical field expression of the optical carrier is:

[0017]

[0018] wherein E0 and ω0 are the amplitude and angular frequency of the input optical carrier respectively, j is the imaginary unit, and t is the time.

[0019] Preferably, in step 2, a low-repetition-frequency triangular wave signal is input into the DC bias port of the double-drive Mach-Zehnder modulator, which introduces a pair of opposite frequency shifts to the modulated light signal of the lower arm. The expression of the triangular wave in a repetition period is:

[0020]

[0021] wherein A and T s are the amplitude and period of the triangular wave respectively;

[0022] The process of triangular wave phase modulation can be expressed as:

[0023] ψ(t)=(π / V π )V s (t)=±kω s t (3)

[0024] wherein V π is the half-wave voltage of the modulator, k=A / V π , and ω s =2π / Ts ,'+'and'-'correspond to the rising and falling edges of the triangular wave, respectively;

[0025] Preferably, step 3: the expression of the microwave signals received by the two antennas is:

[0026] V1(t) = V1sin(ω m t) (4)

[0027] V2(t) = V2sin(ω m t + θ) (5)

[0028] where ω m is the angular frequency of the input microwave signal, V1and V2are the peak voltages of the two signals, respectively, and θ = πsinφ is the phase difference introduced by the angle of arrival φ to the two input signals. The two microwave signals are input to the upper and lower arms of the double-drive Mach-Zehnder modulator, respectively, and the output optical field is represented as:

[0029]

[0030] where m1= πV1 / V π and m2= πV2 / V π are the modulation factors of the upper and lower arm signals, respectively;

[0031] In the case of small signal modulation, only the first-order sideband is considered. Then the output optical field can be written as:

[0032]

[0033] where J n (·) is the n-th order first kind Bessel function.

[0034] Preferably, step 4: the optical signal modulated by the double-drive Mach-Zehnder modulator enters the optical filter for filtering, and the output optical field is represented as:

[0035]

[0036] Preferably, step 5: the optical signal output by the filter enters the photoelectric converter for photoelectric conversion to obtain a low-frequency electrical signal, and the expression is:

[0037]

[0038] where η is the responsivity of the photoelectric converter, is the direct current component, is the amplitude of the alternating current component;

[0039] The phase module analyzes the electrical signal and obtains the phase jump, and further estimates the angle of arrival.

[0040] Preferably, a low-frequency triangular wave is input into the DC bias port of the double-drive Mach-Zehnder modulator to introduce a pair of fixed frequency shifts to the optical signal.

[0041] Preferably, the angle of arrival of the input microwave signal is calculated by measuring the phase jump of the output low-frequency signal.

[0042] Preferably, by analyzing the waveform and phase jump of the output signal, the system can measure the input phase difference q in the range of -180°-180°, and thus the measurement range of AOA can exceed 90° by constructing only one optical path.

[0043] Preferably, the measurement error of the system depends on the bandwidth of the oscilloscope, and the output signal bandwidth, and thus the measurement error, can be reduced by reducing the repetition frequency of the triangular wave without changing the oscilloscope.

[0044] The application also discloses a photon-based angle of arrival measurement device based on triangular wave phase modulation, which comprises, in sequence, a laser source, a polarization controller, a double-drive Mach-Zehnder modulator, an optical filter, a photodetector and a phase discriminator module; the laser source generates an optical carrier, which enters the optical input port of the double-drive Mach-Zehnder modulator through the polarization controller; a low-frequency triangular wave signal is input into the DC bias port of the double-drive Mach-Zehnder modulator, and a microwave signal received by an antenna is input into the electrical input port of the double-drive Mach-Zehnder modulator; the optical signal modulated by the double-drive Mach-Zehnder modulator enters the optical filter to be filtered; the optical signal output by the optical filter is converted into a low-frequency electrical signal by the photodetector, and the phase jump is obtained through the phase discriminator module, and thus the angle of arrival is estimated.

[0045] Compared with the prior art, the application uses the phase discrimination method to measure the angle of arrival of the microwave signal, avoids the influence of the laser power fluctuation on the measurement performance and the limitation of the signal bandwidth, and uses the low-frequency triangular wave for down-mixing, which does not require a high-frequency local oscillator signal compared with the traditional down-mixing phase discrimination method, and the device structure is simple, is not affected by the electronic bottleneck, and is easy to operate and integrate. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a structure schematic diagram of a photon-based angle of arrival measurement device based on triangular wave phase modulation according to a preferred embodiment of the application.

[0047] Figure 2 is Figure 1 is a frequency spectrum schematic diagram of the signals of each node.

[0048] Figure 3 is a spectrum diagram measured by the application, the dashed line is the spectrum diagram before filtering, and the solid line is the spectrum diagram after filtering.

[0049] Figure 4 is a graph of experimental results of the present application: Figure 4 (a) is a time-domain waveform diagram measured when the input microwave signal frequency is 15GHz; Figure 4 (b) and Figure 4 (c) are respectively the measurement results and errors of the included angle when the input microwave signal frequency is changed.

[0050] Figure 5 is a flow chart of a preferred embodiment of the present application, a photonic angle of arrival measurement method based on triangular wave phase modulation. DETAILED DESCRIPTION

[0051] The embodiments of the present application will be described in detail below with specific examples, so that those skilled in the art can easily understand the technical solutions of the present application. The purpose of the present application is to overcome the limitations of the prior art, and to provide a photonic angle of arrival measurement method and device based on triangular wave phase modulation.

[0052] The photonic angle of arrival measurement method based on triangular wave phase modulation provided in the present embodiment involves components including a laser source, a polarization controller, a double-drive Mach-Zehnder modulator, an optical filter, a photodetector, and a phase discrimination module connected in sequence, and the specific connection relationship is shown in Figure 1 . The present embodiment takes 3-bit optical analog-to-digital conversion as an example, and the specific steps are as follows: Figure 5

[0053] Step 1: The laser generates an optical carrier, which enters the optical input port of the double-drive Mach-Zehnder modulator through the polarization controller. The optical field expression of the optical carrier is:

[0054]

[0055] where E0 and ω0 are the amplitude and angular frequency of the input optical carrier, respectively;

[0056] Step 2: A low-repetition-frequency triangular wave signal is input into the DC bias port of the double-drive Mach-Zehnder modulator, which introduces a pair of opposite frequency shifts to the modulated light signal of the lower arm. The expression of the triangular wave in one repetition period is:

[0057]

[0058] where A and T s are the amplitude and period of the triangular wave, respectively;

[0059] The process of triangular wave phase modulation can be expressed as:

[0060] ψ(t)=(π / V π V s (t)=±kω s t (3)​

[0061] where V π is the half-wave voltage of the modulator, k=A / V π , ω s =2π / T s , + and- correspond to the rising and falling edges of the triangular wave, respectively;

[0062] Step 3: The microwave signals received by the two antennas are input to the upper and lower arms of the dual-drive Mach-Zehnder modulator, respectively. The expressions of the microwave signals received by the two antennas are:

[0063] V1(t) = V1sin(ω m t) (4)

[0064] V2(t) = V2sin(ω m t+θ) (5)

[0065] where ω m is the angular frequency of the input microwave signal, V1and V2are the peak voltages of the two signals, respectively, and θ=πsinφ is the phase difference introduced by the angle φ to the two input signals;

[0066] The two microwave signals are input to the upper and lower arms of the dual-drive Mach-Zehnder modulator, respectively, and the output optical field is represented as:

[0067]

[0068] where m1=πV1 / V π and m2=πV2 / V π are the modulation factors of the upper and lower arms, respectively;

[0069] In the case of small signal modulation, only the first-order sideband is considered. Then the output optical field can be written as:

[0070]

[0071] where J n (n) is the n-th order first kind Bessel function;

[0072] Step 4: The optical signal modulated by the dual-drive Mach-Zehnder modulator enters the optical filter for filtering, and the output optical field is represented as:

[0073]

[0074] Step 5: The optical signal output by the optical filter enters the photodetector for photoelectric conversion to obtain a low-frequency electrical signal, and the expression is:

[0075]

[0076] in It refers to the responsivity of the photoelectric converter. The DC component, The amplitude of the AC component;

[0077] The phase detection module consists of an oscilloscope and a digital signal processing program. The signal waveform acquired by the oscilloscope is input into the digital signal processing program. The program analyzes the waveform to determine the sign of the phase transition (positive if both sides of the transition point are peaks; negative if both sides are troughs). It then calculates the time difference τ0 between the two peaks or troughs, and finally obtains the input phase difference θ (when the phase transition is positive, θ = kω). s τ0 / 2; When the phase jumps to negative, θ=(2π-kω) s The magnitude of τ0) / 2) is then determined based on the mapping relationship between the angle of arrival φ and the phase difference θ, φ = sin -1 (θ / π) estimates the angle of arrival.

[0078] Figure 2 The diagram shows the spectrum of the signals obtained in steps 3, 4, and 5. It can be seen that when the triangular wave is at the rising edge and the falling edge, the phase of the final signal is different. Therefore, within one repetition period, the phase can jump from +θ to -θ.

[0079] Figure 3 The images show the spectra before and after filtering. It can be seen that the power ratio of the filtered first-order sideband to the optical carrier and the second-order sideband is greater than 20dB.

[0080] Figure 4 (a) is the time-domain waveform measured when the input microwave frequency is 15 GHz. It can be seen that the signal waveform changes with θ, and its phase jump is related to θ. Figure 4 (b) and (c) show the measurement results and errors of the angle of arrival when the frequency of the input microwave signal is changed. It can be seen that when the frequency of the input microwave signal is between 12 GHz and 18 GHz, the measurement range of the angle of arrival is -70.8 degrees to 70.8 degrees, and the measurement error is less than ±2 degrees.

[0081] like Figure 5As shown, the embodiment discloses a photon-based angle of arrival measurement device based on triangular wave phase modulation, which comprises a laser source, a polarization controller, a double-drive Mach-Zehnder modulator, an optical filter, a photodetector and a phase discrimination module connected in sequence; the laser generates an optical carrier, which enters the optical input port of the double-drive Mach-Zehnder modulator through the polarization controller; the direct current bias port of the double-drive Mach-Zehnder modulator inputs a low-frequency triangular wave signal, and the electrical input port of the double-drive Mach-Zehnder modulator inputs a microwave signal received by an antenna; the modulated optical signal enters the optical filter for filtering; the optical signal output by the optical filter enters the photodetector for photoelectric conversion to obtain a low-frequency electrical signal, and the phase jump is obtained through the phase discrimination module, and then the angle of arrival is estimated.

[0082] In the embodiment, the laser adopts DX2 of ID Photonics, the polarization controller adopts 1550003112 of 3PMPC, the DDMZM adopts FTM7937EZ / 202 of Fujitsu, the electrical signal source 1 adopts SMB100A of Rohde & Schwarz, the electrical signal source 2 adopts 1435F of Ceyear, the function generator (generating a triangular wave) adopts DG1022Z of RIGOL, the optical filter (FBG filter) is produced by aos, the photodetector adopts 10G-A-FA of CONQUER, the spectrometer adopts AQ6370D of Yokogawa, and the oscilloscope adopts DS1104Z of RIGOL.

[0083] In the embodiment, the microwave signals received by the two antennas are respectively input to the two electrodes of the double-drive Mach-Zehnder modulator for modulation; a low-repetition-frequency triangular wave is input to the direct current bias end of the modulator for phase modulation, and the result is that a pair of opposite frequency shifts are introduced to the optical signal in a repetition period; the modulated signal enters the optical band-pass filter for filtering, and the filtered first-order sideband signal contains two frequency components; the photodetector performs photoelectric conversion on the filtered optical signal to generate an intermediate frequency signal with periodic phase jump, the phase discrimination module is used for collecting low-speed electrical signals and analyzing phase jump, and finally the angle of arrival of the microwave signal is obtained. Compared with the traditional down-mixing phase discrimination method, the scheme of the application realizes mixing by using a low-frequency triangular wave, without the need for a high-frequency local oscillator signal, and at the same time, the device structure is simple, is not affected by the electronic bottleneck, is easy to operate and integrated.

[0084] Other contents of the embodiment can refer to the foregoing method embodiment.

[0085] The above merely describes the preferred embodiments of the present application and the principles of the applied technology. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and that various obvious changes, modifications and substitutions can be made by those skilled in the art without departing from the scope of the present application. Therefore, although the present application has been described in detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the appended claims.

Claims

1. A method of triangle wave phase modulation based photonic angle of arrival measurement, characterized in that, The method comprises the following steps: Step 1: a laser generates an optical carrier, and the optical carrier enters an optical input port of a double-drive Mach-Zehnder modulator through a polarization controller; Step 2: a low-frequency triangular wave signal is input into a direct current bias port of the double-drive Mach-Zehnder modulator; Step 3: a microwave signal received by an antenna is input into an electrical input port of the double-drive Mach-Zehnder modulator; Step 4: the modulated optical signal is filtered by an optical filter; Step 5: the optical signal output by the optical filter is photoelectrically converted into a low-frequency electrical signal by a photodetector, and a phase jump is obtained through a phase discrimination module, and then an angle of arrival is estimated.

2. The method of claim 1, wherein the method is based on a triangular wave phase modulation. In step 1, an optical field expression of the optical carrier is: （1） wherein, and are the amplitude and the angular frequency of the input optical carrier, respectively.

3. The method of claim 2, wherein the method is based on a triangular wave phase modulation. In step 2, an expression of the triangular wave in a repeating period is: （2） wherein and are the amplitude and period of the triangular wave, respectively; A triangular wave phase modulation process is represented as: （3） wherein is the half-wave voltage of the modulator, , +, and - correspond to the case where the triangular wave is at the rising and falling edges, respectively.

4. The method of claim 3, wherein the method is based on a triangular wave phase modulation. In step 3, expressions of the microwave signals received by two antennas are: （4） （5） wherein is the angular frequency of the input microwave signal, and are the peak voltages of the two signals, respectively, is the angle of arrival is the phase difference introduced to the two input signals; The two microwave signals are input into the upper and lower arms of the electrical input port of the double-drive Mach-Zehnder modulator, and an output optical field is represented as: （6） wherein, and are the modulation factors of the upper and lower arm signals, respectively; In the case of small signal modulation, only a first-order sideband is considered, and the output optical field is written as: （7） wherein is the first kind Bessel function of order one.

5. The method of claim 4, wherein the phase modulation is based on a triangular wave. In step 4, the modulated optical signal is filtered by the optical filter, and an output optical field is represented as: （8）。 6. The method of claim 5, wherein the method is based on a triangular wave phase modulation. In step 5, the filtered optical signal is photoelectrically converted into a low-frequency electrical signal by the photodetector, and an expression of the low-frequency electrical signal is: （9） wherein is the responsivity of the photoelectric converter, is the direct current component, is the amplitude of the alternating current component.

7. A photonics angle of arrival measurement device based on triangular wave phase modulation, characterized by The method comprises a laser source, a polarization controller, a double-drive Mach-Zehnder modulator, an optical filter, a photodetector and a phase discrimination module which are sequentially connected; the laser generates an optical carrier, and the optical carrier enters an optical input port of the double-drive Mach-Zehnder modulator through the polarization controller; a low-frequency triangular wave signal is input into a direct current bias port of the double-drive Mach-Zehnder modulator, and a microwave signal received by an antenna is input into an electrical input port of the double-drive Mach-Zehnder modulator; The modulated optical signal is filtered by the optical filter; the optical signal output by the optical filter is photoelectrically converted into a low-frequency electrical signal by the photodetector, and a phase jump is obtained through the phase discrimination module, and then an angle of arrival is estimated.

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