High linearity microwave photonic down-conversion receiver system based on opto-electronic oscillator

Abstract

The present application relates to the field of microwave photonics, and more particularly to a high linearity microwave photonics down-conversion receiving system based on an optoelectronic oscillator. The system comprises a laser, a first phase modulator, a first optical amplifier, a phase-shifted Bragg grating, a first photodetector, a second phase modulator, an optical filter, a second optical amplifier, and a second photodetector. The frequency of the local oscillator signal generated by the first photodetector can be tuned by changing the frequency of the laser, thereby effectively realizing the tuning of the down-converted signal output by the second photodetector. By adjusting the gain value of the first optical amplifier, the amplitude of the local oscillator spectral harmonic in the output optical signal of the first phase modulator is a specific value, thereby realizing the suppression of the third-order intermodulation distortion in the output signal, and further improving the spurious-free dynamic range of the entire down-conversion receiving system. The system has reconfigurability and high linearity, and can play a technical value in the field of radar and communication applications.

Description

Technical Field

[0001] This invention relates to the field of microwave photonics technology, and more particularly to a high-linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator. Background Technology

[0002] Microwave photonics is a new interdisciplinary field that combines photonics and microwave technology. On the one hand, it applies mature electronic technology to optical systems to collect and process signals, and on the other hand, it uses optical devices and systems to process microwave signals. Combining the great advantages of optical technology, such as low loss, large bandwidth and long distance, it greatly increases the transmission distance of high-frequency radio, and achieves the complementarity of the advantages and disadvantages of photonics and microwave technology.

[0003] Microwave photonic frequency conversion is one of the important applications of microwave photonics. Existing technologies, combining the advantages of optoelectronic oscillators (OEOs) in generating low-phase-noise, high-spectral-purity microwave signals, have proposed schemes that utilize OEOs to generate high-frequency local oscillator signals and perform optical mixing with RF input signals to achieve microwave photonic frequency conversion without an external local oscillator input. However, the improvement in spurious-free dynamic range in such schemes is still limited by the nonlinearity of the modulator. Therefore, for microwave photonic down-conversion, how to utilize OEOs to generate high-frequency tunable local oscillator signals while simultaneously achieving a spurious-free dynamic range improvement is a pressing problem that needs to be solved. Summary of the Invention

[0004] To address this issue, this invention proposes a high-linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator. This system overcomes the problem in existing technologies that cannot effectively improve the spurious-free dynamic range of the link.

[0005] To achieve the above objectives, the present invention provides a high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator, comprising:

[0006] Laser, used to output optical carrier waves;

[0007] A first phase modulator is disposed at the output end of the laser to modulate the optical carrier to generate a phase modulation signal;

[0008] A first optical amplifier is disposed at the output end of the first phase modulator to receive the phase modulation signal output by the first phase modulator and amplify the phase modulation signal; an optical beam splitter is provided at the output end of the first optical amplifier to split the phase modulation signal output by the first optical amplifier.

[0009] A phase-shifting Bragg grating is installed at one output end of the optical beam splitter and connected to the optical beam splitter through a circulator to filter the phase modulation signal output by the optical beam splitter so as to retain the optical signal of a preset wavelength.

[0010] A first photodetector is connected to both the first phase modulator and the circulator, with the port connecting the first photodetector to the circulator located downstream of the port connecting the phase-shifted Bragg grating to the circulator. This photodetector receives an optical signal of a preset wavelength output from the phase-shifted Bragg grating and beats it to generate a local oscillator signal. The generated local oscillator signal is then transmitted to the first phase modulator to modulate the optical carrier. An adjustable optical delay line is provided between the first photodetector and the circulator. A low-noise amplifier is provided between the first photodetector and the first phase modulator to amplify the local oscillator signal output from the first photodetector.

[0011] A second phase modulator is disposed at the end of the optical beam splitter away from the circulator, for receiving the modulated phase modulated signal of the beam splitter and mixing it with the radio frequency signal transmitted to the second phase modulator.

[0012] An optical filter is disposed at the output end of the second phase modulator to filter the signal output by the second phase modulator to filter out the 0th order sideband;

[0013] A second optical amplifier is disposed at the output end of the optical filter to amplify the 0th-order sideband of the optical filter output;

[0014] The second photodetector is disposed at the output end of the second optical amplifier to beat the amplified 0th-order sideband to change the down-conversion output frequency.

[0015] Furthermore, when the first phase modulator receives the local oscillator signal, it performs a mixing process on the local oscillator signal and the optical carrier to generate a double-sideband phase modulation spectrum.

[0016] Furthermore, the laser can output optical carriers of different frequencies to enable the first photodetector to generate a local oscillator signal of the corresponding frequency.

[0017] Furthermore, the laser, the first phase modulator, the first optical amplifier, the optical beam splitter, the second phase modulator, the optical filter, the second optical amplifier, the input terminal of the second photodetector, the optical circulator, the phase-shifted Bragg grating, the tunable optical delay line, and the input terminal of the first photodetector are connected by single-mode optical fiber.

[0018] Furthermore, the first photodetector is connected to the low-noise amplifier via an RF cable, and the low-noise amplifier is connected to the first phase modulator via an RF cable.

[0019] Furthermore, the light field output by the laser is expressed by the following formula:

[0020]

[0021] Where T M P is the attenuation coefficient generated by the transmission of the entire system. IN f is the optical power output by the laser. C Let be the optical carrier frequency, e be the exponent, j be the imaginary number, and t be the system operating time.

[0022] Set the local oscillator signal V LO =V0sin2πf LO t, where f LO V0 is the local oscillator signal frequency and V0 is the peak voltage of the local oscillator signal.

[0023] Furthermore, the laser is a distributed feedback laser.

[0024] Furthermore, both the first optical amplifier and the second optical amplifier are erbium-doped fiber amplifiers.

[0025] Furthermore, the optical beam splitter is a 1:1 power divider.

[0026] Furthermore, the operating parameters of the first phase modulator and the second phase modulator are the same.

[0027] Compared with existing technologies, the advantages of this invention are that, while keeping the radio frequency signal frequency constant, the local oscillator signal frequency can be tuned by changing the laser frequency, thereby effectively achieving down-conversion signal tuning. By adjusting the gain value of the optical amplifier, the amplitude of the local oscillator spectral harmonics in the phase modulator output optical signal is made to a specific value, thus suppressing third-order intermodulation distortion in the output signal, thereby improving the spurious-free dynamic range of the entire down-conversion receiving system. This system has reconfigurability and high linearity, and can play a technical value in radar and communication applications.

[0028] Furthermore, by using a first phase modulator to perform mixing processing on the local oscillator signal and the optical carrier, the present invention can generate a double-sideband phase modulation spectrum. At the same time, by adjusting the gain value of the first optical amplifier, the amplitude of the spectral harmonics output by the first phase modulator is maintained at a specific value, thereby achieving suppression of third-order intermodulation distortion in the output signal and improving the spurious-free dynamic range of the entire downconversion receiving system.

[0029] Furthermore, the laser can output optical carriers of different frequencies. By outputting optical carriers of different frequencies, the first photodetector can generate a local oscillator signal of the corresponding frequency. By changing the laser frequency, the local oscillator signal frequency can be tuned, thereby effectively achieving the tuning of the down-conversion signal.

[0030] Furthermore, the laser, the first phase modulator, the first optical amplifier, the optical beam splitter, the second phase modulator, the optical filter, the second optical amplifier, the input terminal of the second photodetector, the optical circulator, the phase-shifted Bragg grating, the tunable optical delay line, and the input terminal of the first photodetector are connected by single-mode optical fiber. Single-mode optical fiber has low attenuation, supports long-distance transmission, and can provide higher bandwidth than multimode optical fiber, thereby further improving the optical signal transmission efficiency.

[0031] Furthermore, the output terminal of the first photodetector, the low-noise amplifier, and the electrical input terminal of the first phase modulator are connected by an RF cable. The RF cable has a wide transmission bandwidth and low radiation loss, thereby improving the transmission efficiency of electrical signals.

[0032] Furthermore, the laser is a distributed feedback laser, which has good monochromaticity and can effectively improve spectral purity.

[0033] Furthermore, both the first and second optical amplifiers are erbium-doped fiber amplifiers. By doping the amplifiers with a certain proportion of erbium, the loss of optical signals in the communication system can be compensated, thereby effectively reducing the signal attenuation of optical signals during transmission.

[0034] Furthermore, the optical beam splitter is a 1:1 power splitter, thereby achieving proportional beam splitting of the optical field.

[0035] Furthermore, the parameters of the first phase modulator and the second phase modulator are the same, thereby effectively improving the consistency and reliability of the system modulation. Attached Figure Description

[0036] Figure 1 This is a block diagram of the high linearity microwave photonic downconversion receiving system based on an optoelectronic oscillator as described in this invention. Detailed Implementation

[0037] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0038] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0039] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0040] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] Please see Figure 1The diagram shows a structural block diagram of the high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to the present invention. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to the present invention includes a laser, a first phase modulator, a first optical amplifier, an optical beam splitter, a phase-shifting Bragg grating, a first photodetector, a second phase modulator, an optical filter, and a second photodetector. The laser is used to output an optical carrier wave. A first phase modulator is disposed at the output end of the laser to modulate the optical carrier wave to generate a phase modulation signal. A first optical amplifier is disposed at the output end of the first phase modulator to receive the phase modulation signal output by the first phase modulator and amplify the phase modulation signal. An optical beamsplitter is disposed at the output end of the first optical amplifier to split the phase modulation signal output by the first optical amplifier. A phase-shifted Bragg grating is disposed at one output end of the optical beamsplitter and connected to the optical beamsplitter via a circulator to filter the phase modulation signal output by the optical beamsplitter to retain an optical signal of a preset wavelength. A first photodetector is connected to both the first phase modulator and the circulator, with the port of the first photodetector connected to the circulator located downstream of the port of the phase-shifted Bragg grating connected to the circulator. This photodetector receives the optical signal of the preset wavelength output by the phase-shifted Bragg grating and beats it to... The optical transducer generates a local oscillator signal and sends the generated local oscillator signal to a first phase modulator to modulate the optical carrier. An adjustable optical delay line is provided between the first photodetector and the circulator. A low-noise amplifier is provided between the first photodetector and the first phase modulator to amplify the local oscillator signal output by the first photodetector. A second phase modulator is located at the end of the optical beamsplitter furthest from the circulator to receive the modulated phase-modulated signal from the beamsplitter and mix it with the radio frequency signal sent to the second phase modulator. An optical filter is located at the output of the second phase modulator to filter the signal output by the second phase modulator to filter out the 0th-order sideband. A second optical amplifier is located at the output of the optical filter to amplify the 0th-order sideband output by the optical filter. A second photodetector is located at the output of the second optical amplifier to beat the amplified 0th-order sideband to change the down-conversion output frequency.

[0042] When the system is running, the laser output frequency is f. C The optical carrier wave is input to the first phase modulator for modulation, generating a phase-modulated signal. The modulation index of the local oscillator signal is controlled by adjusting the gain of the first optical amplifier. The frequency of the local oscillator signal required by the system is obtained by adjusting the distance between the laser frequency and the notch frequency of the phase-shifted Bragg grating. After phase-to-intensity modulation conversion is completed by phase-shifted Bragg grating filtering, the signal is beat-frequency generated in the first photodetector to produce a frequency of f.LO The local oscillator signal is amplified by a low-noise amplifier and then input into the first phase modulator to modulate the optical carrier, forming a closed loop. Afterward, the modulated signal output from the first phase modulator is amplified and used as the carrier input to the second phase modulator, modulated with a frequency of f. RF The radio frequency signal is modulated, mixed, and then filtered out by an optical filter to obtain the 0th-order sideband. The output signal frequencies are f0 and f1 respectively. C f C -f RF +f LO and f C +f RF -f LO Finally, the 0th-order sideband enters the second photodetector and beats to achieve down-conversion signal output. The frequency of the output down-converted signal is the frequency difference between the local oscillator signal and the radio frequency signal, i.e., f. RF -f LO When the output RF signal frequency remains constant, the local oscillator signal frequency can be tuned by changing the laser frequency, thereby achieving the tuning of the down-conversion signal.

[0043] This invention includes a first phase modulator, which, upon receiving the local oscillator signal, performs frequency mixing on the local oscillator signal and the optical carrier to generate a double-sideband phase modulation spectrum. By adjusting the gain value of the first optical amplifier, the amplitude of the local oscillator spectrum harmonics in the output optical signal of the first phase modulator is made to a specific value, thereby suppressing third-order intermodulation distortion in the output signal and improving the spurious-free dynamic range of the entire down-conversion receiving system.

[0044] The present invention is equipped with a laser output optical carrier. When the radio frequency signal frequency remains unchanged, the local oscillator signal frequency can be tuned by changing the laser frequency, thereby effectively achieving the tuning of the down-conversion signal.

[0045] Specifically, the laser output frequency is f C The optical carrier wave is input to the first phase modulator for modulation, generating a modulated signal. This signal then passes through the first optical amplifier and optical beam splitter, and is converted from phase to intensity modulation by a circulator and a phase-shifting Bragg grating. The reflected optical signal is transmitted to the first photodetector for photoelectric demodulation, generating a beat frequency of f. LO The local oscillator signal is amplified by a low-noise amplifier and then transmitted to the first phase modulator to form a photoelectric oscillation loop. After the photoelectric oscillator self-excites, the first phase modulator outputs a phase modulation spectrum with double sides. The gain value of the first optical amplifier is further adjusted to make the spectrum harmonic amplitude of the first phase modulator output a specific value, thereby achieving the suppression of third-order intermodulation distortion in the output signal and improving the spurious-free dynamic range of the entire downconversion receiving system.

[0046] Please continue reading. Figure 1 The laser output is connected to the optical input of the first phase modulator. The output of the first phase modulator is connected to the input of the first optical amplifier. The output of the first optical amplifier is connected to the input of the optical beamsplitter. The output 1 of the optical beamsplitter is connected to port 1 of the optical circulator. Port 2 of the optical circulator is connected to the phase-shifted Bragg grating. Port 3 of the optical circulator is connected to the input of the tunable optical delay line. The output of the tunable optical delay line is connected to the input of the first photodetector. The output of the first photodetector is connected to the input of the low-noise amplifier. The output of the low-noise amplifier is connected to the electrical input of the first phase modulator to form a closed loop. The output 2 of the optical beamsplitter is connected to the optical input of the second phase modulator. The output of the second phase modulator is connected to the input of the optical filter. The output of the optical filter is connected to the input of the second optical amplifier. The output of the second optical amplifier is connected to the input of the second photodetector. Adjacent components are connected by single-mode optical fiber or radio frequency cable.

[0047] Specifically, the laser, the first phase modulator, the first optical amplifier, the optical beam splitter, the second phase modulator, the optical filter, the second optical amplifier, the input terminal of the second photodetector, the optical circulator, the phase-shifting Bragg grating, the tunable optical delay line, and the input terminal of the first photodetector are connected by single-mode optical fiber.

[0048] Specifically, the output of the first photodetector, the low-noise amplifier, and the electrical input of the first phase modulator are connected by an RF cable.

[0049] This invention sets a laser output optical carrier, and the optical field output by the laser is expressed by the following formula:

[0050]

[0051] Where T M P is the attenuation coefficient generated by the transmission of the entire system. IN f is the optical power output by the laser. C Let be the optical carrier frequency, e be the exponent, j be the imaginary number, and t be the system operating time.

[0052] Set the local oscillator signal V LO =V0sin2πf LO t, where f LO V0 is the peak voltage of the local oscillator signal, where V0 is the local oscillator signal frequency. The gain of the optical amplifier is calculated from the amplitude of the local oscillator signal, thereby directly realizing the tunable down-conversion of the RF signal and simultaneously improving the spurious-free dynamic range of the down-conversion receiving system.

[0053] Specifically, assume the input two-tone signal is: V = V1[sin(2πf1t) + sin(2πf2t)], where f1 and f2 are the frequencies of the two-tone signal, V1 is the peak voltage of the two-tone signal, and V is the half-wave voltage of the first phase modulator and the second phase modulator. π For consistency, the modulation index of the local oscillator signal is m0 = πV LO / V π The expression for the optical carrier modulated by two phase modulators is:

[0054]

[0055] The modulation index of the second phase modulator is m1 = πV0 / V π The current obtained by demodulation from the output of the second photodetector is:

[0056]

[0057] in Let n, p, r, and s be the responsivity of the second photodetector, where n, p, r, and s are all integers. Let the required intermediate frequency f be... IF1 =f1-f LO f IF2 =f2-f LO When only frequency point 2f is considered IF1 -f IF2 The third-order intermodulation signal at T ff Let be the attenuation coefficient, then the third-order current term output at this frequency can be expressed as:

[0058]

[0059] F(t) is a current term function. When the third-order intermodulation distortion is completely suppressed, I IMD3 =0, and at the same time, the fundamental frequency current component I F Since ≠0, the condition for the modulation index m0 of the first phase modulator can be obtained. Therefore, the gain value of the optical amplifier can be obtained through the amplitude of the local oscillator signal, thereby directly realizing the tunable down-conversion of the radio frequency signal and simultaneously improving the spurious-free dynamic range of the down-conversion receiving system.

[0060] Preferably, the laser is a distributed feedback laser, which has good monochromaticity and can effectively improve spectral purity.

[0061] Preferably, both the first optical amplifier and the second optical amplifier are erbium-doped fiber amplifiers. By doping the amplifier with a certain proportion of erbium, the loss of optical signals in the communication system can be compensated, thereby effectively reducing the signal attenuation of optical signals during transmission.

[0062] Preferably, the optical beam splitter is a 1:1 power splitter, thereby achieving proportional beam splitting of the optical field.

[0063] Preferably, the parameters of the first phase modulator and the second phase modulator are the same, thereby effectively improving the consistency and reliability of the system modulation.

[0064] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator, characterized in that, include: Laser, used to output optical carrier waves; A first phase modulator is disposed at the output end of the laser to modulate the optical carrier to generate a phase modulation signal; A first optical amplifier is disposed at the output end of the first phase modulator to receive the phase modulation signal output by the first phase modulator and amplify the phase modulation signal; an optical beam splitter is provided at the output end of the first optical amplifier to split the phase modulation signal output by the first optical amplifier. A phase-shifting Bragg grating is installed at one output end of the optical beam splitter and connected to the optical beam splitter through a circulator to filter the phase modulation signal output by the optical beam splitter so as to retain the optical signal of a preset wavelength. A first photodetector is connected to both the first phase modulator and the circulator, with the port connecting the first photodetector to the circulator located downstream of the port connecting the phase-shifted Bragg grating to the circulator. This photodetector receives an optical signal of a preset wavelength output from the phase-shifted Bragg grating and beats it to generate a local oscillator signal. The generated local oscillator signal is then transmitted to the first phase modulator to modulate the optical carrier. An adjustable optical delay line is provided between the first photodetector and the circulator. A low-noise amplifier is provided between the first photodetector and the first phase modulator to amplify the local oscillator signal output from the first photodetector. A second phase modulator is disposed at the end of the optical beam splitter away from the circulator, for receiving the modulated phase modulated signal of the beam splitter and mixing it with the radio frequency signal transmitted to the second phase modulator. An optical filter is disposed at the output end of the second phase modulator to filter the signal output by the second phase modulator to filter out the 0th order sideband; A second optical amplifier is disposed at the output end of the optical filter to amplify the 0th-order sideband of the optical filter output; The second photodetector is disposed at the output end of the second optical amplifier to beat the amplified 0th-order sideband to change the down-conversion output frequency.

2. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, When the first phase modulator receives the local oscillator signal, it performs a mixing process on the local oscillator signal and the optical carrier to generate a double-sideband phase modulation spectrum.

3. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, The laser can output optical carriers of different frequencies, which are used to enable the first photodetector to generate a local oscillator signal of the corresponding frequency.

4. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, In the system, adjacent components used to transmit optical signals are connected by single-mode optical fiber.

5. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, The first photodetector is connected to the low-noise amplifier via an RF cable, and the low-noise amplifier is connected to the first phase modulator via an RF cable.

6. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, The light field output by the laser is expressed by the following formula: Where T M P is the attenuation coefficient generated by the transmission of the entire system. IN f is the optical power output by the laser. C Let be the optical carrier frequency, e be the exponent, j be the imaginary number, and t be the system operating time. Set the local oscillator signal V LO =V0 sin2πf LO t, where f LO V0 is the local oscillator signal frequency and V0 is the peak voltage of the local oscillator signal.

7. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, The laser is a distributed feedback laser.

8. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, Both the first optical amplifier and the second optical amplifier are erbium-doped fiber amplifiers.

9. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, The optical beam splitter is a 1:1 power splitter.

10. The high linearity microwave photonic down-conversion receiving system based on an optoelectronic oscillator according to claim 1, characterized in that, The first phase modulator and the second phase modulator have the same operating parameters.

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