Microwave photon image frequency suppression mixing method and device based on photo-generated local oscillator

Abstract

The invention discloses a microwave photon image frequency suppression mixing method based on photo-generated local oscillation. The method comprises the following steps: S1, generating an optical carrier with a plurality of wavelength components with the same amplitude and phase; s2, dividing the optical carrier into two paths, and respectively filtering two different wavelength components with frequencies of omega 1 and omega 2 from the two paths of optical carriers; carrying out phase shift on the first path of wavelength component, and carrying out phase modulation on the second path of wavelength component by using a radio frequency signal with the frequency of omega RF; and S3, inputting the two paths of obtained optical signals into a 90-degree optical mixer, selecting two paths of mutually orthogonal optical signals from the four paths of optical signals output by the 90-degree optical mixer, respectively converting the two paths of mutually orthogonal optical signals into electric signals, and mixing the two paths of electric signals by using a 90-degree microwave bridge to obtain image frequency rejection down-conversion signals with the frequency of omega2-omega1-omegaRF. The invention further discloses a microwave photon image frequency suppression mixing device based on the photo-generated local oscillator. According to the invention, carrier-tunable broadband signal image frequency rejection frequency mixing can be realized, and a high image frequency rejection ratio is achieved.

Description

Technical Field

[0001] The present invention relates to a microwave photonic image frequency rejection mixing method, belonging to the technical field of microwave photonics. Background Art

[0002] As a core functional unit of a microwave system, a mixer converts a signal from radio frequency (RF) to intermediate frequency (IF) or vice versa through non-linear frequency conversion, and is widely used in fields such as wireless communication, radar detection, electronic countermeasure, and satellite payloads. Traditional electronic mixers are limited by the bandwidth and electromagnetic interference of semiconductor devices, and it is difficult to meet the requirements of modern broadband RF systems for high frequency, large bandwidth, and high isolation. In this context, microwave photonic mixers exhibit significant application potential due to the unique advantages of optical domain processing.

[0003] A microwave photonic mixer uses photonic technology to achieve signal modulation and frequency conversion. Its instantaneous bandwidth can reach dozens of GHz, the frequency-dependent loss is low, and it has the characteristics of anti-electromagnetic interference. In addition, the parallel processing ability of optical carriers supports multi-channel mixing, significantly reducing the system complexity. However, in a superheterodyne structure, the image frequency signal (IF) will be down-converted to the same intermediate frequency band as the target signal simultaneously, resulting in spectral aliasing and reducing the system dynamic range. Therefore, the design of an image-reject mixer (IRM) has become the key to improving the performance of microwave photonic systems.

[0004] At present, the research on microwave photonic image-reject mixers mainly focuses on two types of methods: pre-filtering method and phase cancellation method. The pre-filtering method directly filters out the image frequency signal through an optical or electrical filter. However, both methods require the filters used to have characteristics such as high center frequency, narrow passband, and steep filtering edges. These performance requirements are currently difficult to achieve simultaneously, thus limiting the operating performance of the image-reject mixer. In addition, in real application scenarios, since the signal frequency often exhibits dynamic change characteristics, this requires the filter to have corresponding frequency adjustment capabilities. However, limited by the current development level of microwave technology, there are still many technical challenges in achieving both high-performance indicators and frequency tunable characteristics of the filter (see [Strutz S J, Williams K J. An 8-18-GHz all-optical microwave downconverter with channelization[J]. IEEE Transactions on Microwave Theory and Techniques, 2001, 49(10): 1992-1995]). The phase cancellation method introduces a pair of orthogonal radio frequency signals or local oscillator signals for 90° orthogonal coupling. Through the introduced 90° phase difference, the two down-converted image frequency signals have opposite phases, and the two down-converted radio frequency signals have the same phase. After coupling, the image frequency signal is eliminated and the radio frequency signal is enhanced. This scheme uses the signal phase difference to achieve image frequency suppression, avoiding the need for high-performance filtering and multi-stage frequency conversion. In addition, when the radio frequency signal frequency changes, the microwave photonic image-reject mixer based on coherent cancellation technology can still suppress the corresponding image frequency interference, thus achieving broadband applications. However, in the implementation of the existing image-reject mixer based on the phase cancellation method, it usually requires the introduction of an electrical local oscillator signal to participate in modulation, making it difficult to obtain carrier signals with consistent amplitudes, and the image frequency rejection ratio is relatively low. The optical local oscillator scheme adopted in the present invention can not only generate carrier signals with consistent amplitudes, but also significantly expand the frequency coverage range of the local oscillator signal. Combining with the unique orthogonal modulation characteristics of the Hartley architecture, the image frequency rejection ratio of the system is improved by a breakthrough. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and provide a microwave photonic image-reject mixing method based on an optical local oscillator, which can achieve image-reject mixing of broadband signals with tunable carriers and has a high image frequency rejection ratio.

[0006] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0007] A microwave photonic image-reject mixing method based on an optical local oscillator, comprising the following steps:

[0008] S1. Generate optical carriers with multiple wavelength components having the same amplitude and phase;

[0009] S2. Divide the optical carriers into two paths, and filter out two different wavelength components with frequencies ω1 and ω2 respectively from the two paths of optical carriers; perform phase shift on the first path of wavelength component, and perform phase modulation on the second path of wavelength component with a radio frequency signal having a frequency of ω RF ;

[0010] S3. Input the obtained two paths of optical signals into a 90° optical mixer, and select two mutually orthogonal paths from the four paths of optical signals output by the 90° optical mixer and convert them into electrical signals respectively, and mix these two electrical signals with a 90° microwave bridge to obtain an image frequency rejection down-converted signal with a frequency of |ω2 - ω1| - ω RF .

[0011] Preferably, the optical carriers with multiple wavelength components having the same amplitude and phase are optical frequency combs.

[0012] Preferably, perform phase shift on the first path of wavelength component through a phase modulator loaded with a DC bias voltage, and perform phase modulation on the second path of wavelength component through a phase modulator loaded with the radio frequency signal.

[0013] Based on the same inventive concept, the following technical solution can also be obtained:

[0014] A microwave photonic image frequency rejection mixing device based on optical local oscillator, comprising:

[0015] A multi-wavelength generation module for generating optical carriers with multiple wavelength components having the same amplitude and phase; a wavelength selection and modulation module for dividing the optical carriers into two paths, and filtering out two different wavelength components with frequencies ω1 and ω2 respectively from the two paths of optical carriers; performing phase shift on the first path of wavelength component, and performing phase modulation on the second path of wavelength component with a radio frequency signal having a frequency of ω RF ;

[0016] An image frequency rejection mixing module for inputting the two paths of optical signals output by the wavelength selection and modulation module into a 90° optical mixer, and selecting two mutually orthogonal paths from the four paths of optical signals output by the 90° optical mixer and converting them into electrical signals respectively, and mixing these two electrical signals with a 90° microwave bridge to obtain an image frequency rejection down-converted signal with a frequency of |ω2 - ω1| - ω RF .

[0017] Preferably, the optical carriers with multiple wavelength components having the same amplitude and phase are optical frequency combs.

[0018] Preferably, a phase modulator loaded with a DC bias voltage is used to shift the phase of the first wavelength component, and a phase modulator loaded with the RF signal is used to modulate the phase of the second wavelength component.

[0019] Preferably, each optical device in the wavelength selection modulation module is integrated on the same photonic chip.

[0020] More preferably, the multi-wavelength generation module, the wavelength selection modulation module, and the image frequency rejection mixing module are assembled in the same package through a micro-assembly process, and the electrical signal interconnection between the optical system and the electrical system is realized through microstrip lines or gold wire leads.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] By introducing a multi-wavelength generation module, the present invention significantly expands the frequency operating range of the optically generated local oscillator, and does not require the participation of an electrical local oscillator signal, greatly reducing the system complexity; the present invention adopts a wavelength selection modulation mechanism to perform phase modulation on specific wavelength components in the optically generated local oscillator signal, and then combines it with another wavelength component and inputs it into a photodetector to complete photoelectric conversion; this design scheme based on phase modulation has unique advantages, and its theoretical analysis shows that the optical beat frequency process will not generate radio frequency (RF) signals, thus effectively solving the problem of RF signal leakage; the microwave photonic image frequency rejection mixing architecture of the present invention can realize carrier-tunable broadband signal image frequency rejection mixing and has a high image frequency rejection ratio. Description of the Drawings

[0023] Figure 1 It is a schematic structural principle diagram of a preferred embodiment of the microwave photonic image frequency rejection mixing device based on the optically generated local oscillator of the present invention; wherein (a) is a structural diagram and (b) is a schematic diagram of the principle;

[0024] Figure 2 It is a simulation result diagram of selecting a local oscillator signal from an optical frequency comb, wherein (a) is a generated optical frequency comb spectrum diagram; (b) is a spectrum diagram after wavelength selection;

[0025] Figure 3 It is an electrical spectrum diagram of the mixing simulation result of the preferred embodiment of the present invention;

[0026] Figure 4 It is a simulation result diagram of the image frequency rejection effect of the preferred embodiment of the present invention. Detailed Embodiments

[0027] Aiming at the deficiencies of the prior art, the solution idea of the present invention is to combine a multi-wavelength generation module with a wavelength selection modulation mechanism to greatly expand the frequency operating range of the optically generated local oscillator, reduce RF signal leakage, and improve the image frequency rejection ratio without the participation of an electrical local oscillator signal.

[0028] The microwave photonic image frequency suppression mixing method based on optical local oscillator generation proposed by the present invention includes the following steps:

[0029] S1. Generate an optical carrier with multiple wavelength components having the same amplitude and phase;

[0030] S2. Divide the optical carrier into two paths, and filter out two different wavelength components with frequencies ω1 and ω2 respectively from the two paths of optical carriers; phase-shift the first path of wavelength components, and use a radio frequency signal with a frequency of ω RF to perform phase modulation on the second path of wavelength components;

[0031] S3. Input the two obtained optical signals into a 90° optical mixer, select two mutually orthogonal paths from the four output optical signals of the 90° optical mixer and convert them into electrical signals respectively, and mix these two electrical signals with a 90° microwave bridge to obtain an image frequency suppression down-converted signal with a frequency of |ω2 - ω1| - ω RF .

[0032] The microwave photonic image frequency suppression mixing device based on optical local oscillator generation proposed by the present invention includes:

[0033] A multi-wavelength generation module that generates an optical carrier with multiple wavelength components having the same amplitude and phase;

[0034] A wavelength selection and modulation module for dividing the optical carrier into two paths, and filtering out two different wavelength components with frequencies ω1 and ω2 respectively from the two paths of optical carriers; phase-shifting the first path of wavelength components, and using a radio frequency signal with a frequency of ω RF to perform phase modulation on the second path of wavelength components;

[0035] An image frequency suppression mixing module for inputting the two optical signals output by the wavelength selection and modulation module into a 90° optical mixer, selecting two mutually orthogonal paths from the four output optical signals of the 90° optical mixer and converting them into electrical signals respectively, and mixing these two electrical signals with a 90° microwave bridge to obtain an image frequency suppression down-converted signal with a frequency of |ω2 - ω1| - ω RF .

[0036] For the convenience of public understanding, the technical solution of the present invention will be described in detail below through a preferred embodiment in conjunction with the accompanying drawings:

[0037] The structural principle of the microwave photonic image frequency suppression mixing device in this embodiment is as Figure 1As shown, it includes three parts: a multi-wavelength generation module, a wavelength selection modulation module, and an image frequency rejection mixing module. Among them, the multi-wavelength generation module is used to generate optical carriers with multiple wavelength components having the same amplitude and phase. The wavelength selection modulation module is used to divide the optical carrier into two paths, and filter out two different wavelength components with frequencies ω1 and ω2 respectively from the two paths of optical carriers; perform phase shift on the first path of wavelength component, and use a radio frequency signal with a frequency of ω RF to perform phase modulation on the second path of wavelength component. The image frequency rejection mixing module is used to input the two paths of optical signals output by the wavelength selection modulation module into a 90° optical mixer, and select two orthogonal paths from the four paths of optical signals output by the 90° optical mixer and convert them into electrical signals respectively, and mix these two electrical signals with a 90° microwave bridge to obtain an image frequency rejection down-converted signal with a frequency of |ω2 - ω1| - ω RF , and finally realize image frequency rejection mixing.

[0038] As Figure 1 shown in (a) of [reference], the multi-wavelength generation module in this embodiment generates an optical frequency comb with multiple optical comb teeth, and the amplitude and phase of each optical comb tooth are the same but the wavelengths are different.

[0039] As Figure 1 shown in (a) of [reference], the wavelength selection modulation module in this embodiment includes a 1×2 optical splitter, an optical filter 1, a phase modulator 1, an optical filter 2, and a phase modulator 2; the optical frequency comb output by the multi-wavelength generation module is divided into two paths by the 1×2 optical splitter; one path above is filtered by the optical filter 1 to filter out one optical comb tooth, and then input into the phase modulator 1 to be modulated by a DC signal, so as to realize phase shift, and the phase shift amount can be adjusted by the intensity of the DC signal; the other path below is filtered by the optical filter 2 to filter out another optical comb tooth, and then input into the phase modulator 2 to be modulated by a radio frequency signal. In addition, in order to improve the system integration degree, each optical device in the wavelength selection modulation module in this embodiment is integrated on the same photonic chip, and the specific integration process can adopt existing photonic integration processes such as photonic monolithic integration technology, photonic heterogeneous integration technology, photonic heterogeneous integration technology, and micro-assembly process; the photonic chip can adopt a chip based on indium phosphide, silicon, thin film lithium niobate, or thin film lithium tantalate; the optical coupling between the photonic chip and other modules can adopt coupling methods such as fiber connection, photonic wire bonding connection, and lens coupling.

[0040] As Figure 1As shown in (a) of [the figure], the image frequency rejection mixer module in this embodiment includes a 90° optical mixer, a photodetector 1, a photodetector 2, and a 90° microwave bridge; the two output optical signals of the two phase modulators in the wavelength selection modulation module are respectively input into the two input ends of the 90° optical mixer, and two orthogonal outputs of the four outputs of the 90° optical mixer are respectively converted into electrical signals by the photodetector 1 and the photodetector 2, and then mixed by the 90° microwave bridge to output an image frequency rejection mixer signal.

[0041] To further improve the system integration and reduce the volume, the multi-wavelength generation module, the wavelength selection modulation module, and the image frequency rejection mixer module can be assembled in the same package through a micro-assembly process, and the electrical signal interconnection between the optical system and the electrical system is realized through microstrip lines or gold wire leads.

[0042] The working principle of this embodiment is as shown in Figure 1 (b) of [the figure], specifically as follows:

[0043] Assume that the frequencies of the two optical comb teeth filtered by the optical filter 1 and the optical filter 2 are ω1 and ω2 respectively, and the signal expressions are

[0044] E1(t) = A0 exp(jω1t)

[0045] E2(t) = A0 exp(jω2t)

[0046] where A0 is the amplitude of the local oscillator optical signal. The above two local oscillator optical signals can generate a photo-generated local oscillator signal with a frequency of ω LO = |ω2 - ω1| in the photodetector. One of the local oscillator light waves (the component with a frequency of ω2 is selected in the text) passes through the down-path phase modulator and is modulated by loading a radio frequency signal with a frequency of ω RF . If the modulation form is small-signal modulation, the output signal of the down-path phase modulator is

[0047]

[0048] Another local oscillator light wave (the component with a frequency of ω1 is selected in the text) controls the phase of the optical carrier of this path by changing the DC bias point of the up-path phase modulator, and the output signal of the up-path phase modulator is:

[0049]

[0050] where V DC and V PM are the DC bias voltage and the half-wave voltage of the phase modulator respectively, and J (i) is the i-th order Bessel function. The signals output from the up-path and the down-path are then input into the 90° optical mixer, and the output optical signal can be expressed as:

[0051]

[0052] Take E OUT1 , E OUT3 The signal is input into the photodetector for beat frequency to obtain the required down-converted microwave signal. The image frequency suppression module uses the Hartley structure of image frequency suppression down-conversion to achieve image frequency suppression mixing. If E OUT1 Obtained by beat frequency where A1 is the amplitude of E R and is the phase of E S . E OUT3 Obtained by beat frequency where A2 is the amplitude of E L and is the phase of E L . It can be seen that E S and E L are a set of orthogonal signals. Assuming that there is an image frequency signal E J , then there is E L - E R＝ E J - E L . Input into a 90° microwave bridge, and after one signal is phase-shifted by 90° and coupled with the other path, the output signal is:

[0053]

[0054] Or

[0055]

[0056] It can be seen from formula (1.5) that when the image frequency signal and the radio frequency signal are input into this mixing structure together, the final output signal is only down-converted to the intermediate frequency signal generated by mixing the radio frequency signal and the local oscillator signal (or the intermediate frequency signal generated by mixing the image frequency signal and the local oscillator), realizing image frequency suppression mixing.

[0057] To verify the technical effects of the technical solution of the present invention, the above specific embodiments were subjected to simulation verification. The specific simulation conditions are as follows: The optical carrier wavelength emitted by the laser is set to 1550 nm, and the power is 18 dBm. An RF signal with a modulation frequency of 6 GHz is modulated on the MZM; through high-precision band-pass filtering, five optical carriers with strict amplitude and phase consistency are extracted from the generated signal, and a typical comb tooth structure of an equivalent optical frequency comb is successfully constructed based on this scheme, and then an accurate simulation of the optical local oscillator signal is realized. The output signal is divided into two paths by a 1×2 optical power splitter and sent to an optical band-pass filter for selection. The extinction ratio of the filter is set to 40 dB. A chirped signal with a frequency of 7-9 GHz is applied to the upper PM. The two signals are mixed and output through a 90° optical mixer at the output end. A set of quadrature mixing output ports are selected. In this simulation scheme, the signal output ports of 0° and 90° are selected. The two signals are respectively input into a photodetector PD with a responsivity of 0.65 A / W for beat frequency, and finally the two output signals pass through a 90° microwave bridge. The obtained signal is observed through a spectrum analyzer and an oscilloscope. When analyzing the image rejection ratio, according to the input local oscillator signal in this system being 10 GHz and the RF signal being a chirped signal with a frequency of 7-9 GHz, the input image frequency signal is a chirped signal with a frequency of 17-19 GHz.

[0058] Figure 2 Shows the simulation result data of the local oscillator signal selection of the optical frequency comb. The generated optical frequency comb teeth are as Figure 2 (a) shown. Select the second and fourth comb teeth from left to right to obtain the local oscillator signal of the local mixing system, that is, ω LO = 16 GHz. Figure 2 (b) shows the spectrogram after the two optical wavelengths with different frequencies are selected by the upper and lower optical band-pass filters.

[0059] Figure 3 Shows the simulation result data of the mixing collected by the spectrum analyzer. It can be clearly observed that the frequency component ω LO generated by the beat frequency of the two optical carriers. The frequency characteristics of this spurious component are independent of the RF frequency input to the system, and its value is only determined by the frequency difference between the two selected comb teeth. Therefore, it can be eliminated by an electrical domain filter, and the required ω LO - ω RF can also be observed, representing the realization of downconversion.

[0060] Figure 4 Shows the simulation result diagram of the image rejection effect of the present invention. The downconverted signal ω LO - ω RFObservation was carried out. When the input was the image frequency signal in the range of 17 - 19 GHz, the output of the spectrum analyzer of the input image frequency signal was compared with the output result of the spectrum analyzer of the input radio frequency signal. It was obtained that the image frequency rejection ratio of this system was 53.7 dB·Hz2 / 3, verifying the feasibility and reliability of the technical solution of the present invention in the processing of broadband signals. At the same time, it had excellent image frequency rejection characteristics, providing a new solution for the design and implementation of high-performance microwave photonic mixers.

Claims

1. A microwave photon mirror frequency suppression mixing method based on optically generated local oscillator, characterized in that: The following steps are involved: S1. Generate an optical carrier with multiple wavelength components having the same amplitude and phase; S2, dividing the optical carrier into two paths, and filtering out two different wavelength components with frequencies ω1 and ω2 from the two optical carrier paths respectively; The first wavelength component is phase shifted with a frequency of ω RF The radio frequency signal performs phase modulation on the second wavelength component; S3, input the obtained two optical signals into a 90° optical mixer, and select two mutually orthogonal optical signals from the four optical signals output by the 90° optical mixer and convert them into electrical signals respectively, and mix the two electrical signals with a 90° microwave bridge to obtain a frequency of |ω2-ω1|-ω RF The image frequency of the down-converted signal is suppressed.

2. The microwave photon mirror frequency suppression mixing method based on photogenerated local oscillator according to claim 1, characterized in that: The optical carrier with multiple wavelength components having the same amplitude and phase is an optical frequency comb.

3. The microwave photon mirror frequency suppression mixing method based on optically generated local oscillator according to claim 1, characterized in that: The first wavelength component is phase-shifted by a phase modulator loaded with a DC bias voltage, and the second wavelength component is phase-modulated by a phase modulator loaded with the radio frequency signal.

4. A microwave photon mirror frequency suppression mixing device based on optically generated local oscillator, characterized in that: include: A multi-wavelength generation module, used for generating optical carriers with multiple wavelength components having the same amplitude and phase; A wavelength selective modulation module, used for dividing the optical carrier into two paths, and filtering out two different wavelength components with frequencies ω1 and ω2 from the two optical carrier paths respectively; The first wavelength component is phase shifted with a frequency of ω RF The radio frequency signal performs phase modulation on the second wavelength component; The image frequency suppression mixing module is used to input the two optical signals output by the wavelength selection modulation module into the 90° optical mixer, and select two mutually orthogonal optical signals from the four optical signals output by the 90° optical mixer and convert them into electrical signals respectively, and mix the two electrical signals with a 90° microwave bridge to obtain a frequency of |ω2-ω1|-ω RF The image frequency of the down-converted signal is suppressed.

5. The microwave photon mirror frequency suppression mixing device based on optically generated local oscillator according to claim 4, characterized in that: The optical carrier with multiple wavelength components having the same amplitude and phase is an optical frequency comb.

6. The microwave photon mirror frequency suppression mixing device based on optically generated local oscillator according to claim 4, characterized in that: The first wavelength component is phase-shifted by a phase modulator loaded with a DC bias voltage, and the second wavelength component is phase-modulated by a phase modulator loaded with the radio frequency signal.

7. The microwave photon mirror frequency suppression mixing device based on optically generated local oscillator according to claim 4, characterized in that: The optical devices in the wavelength selection modulation module are integrated into the same photonic chip.

8. The microwave photon mirror frequency suppression mixing device based on optically generated local oscillator according to claim 7, characterized in that: The multi-wavelength generation module, the wavelength selection modulation module, and the image frequency suppression mixing module are assembled in the same tube shell through a micro-assembly process, and the electrical signal interconnection between the optical system and the electrical system is achieved through microstrip lines or gold wire leads.

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