Passive phase-stable optical transmission method and system for radio frequency signals

Abstract

The present invention discloses a passive phase-stable optical transmission method of radio frequency signals, wherein an optically-carried auxiliary radio frequency signal carrying an auxiliary radio frequency signal with a frequency of f+Δf is transmitted back and forth through an optical link and then converted into an electrical signal; a microwave local oscillator signal with a frequency of 2f is mixed with the auxiliary radio frequency signal to generate an up-conversion signal, and then the up-conversion signal is mixed with the electrical signal to generate a down-conversion signal, and the down-conversion signal is modulated in the optical domain and subjected to photoelectric conversion after unidirectional transmission through the optical link, thereby achieving phase-stable transmission of the microwave local oscillator signal; wherein f is half of the frequency of the microwave local oscillator signal, and Δf is an adjustable frequency portion much smaller than f. The present invention also discloses a passive phase-stable optical transmission system of radio frequency signals. Compared with the prior art, the present invention can adjust the phase difference of the radio frequency signal before and after transmission while achieving phase-stable transmission of the radio frequency signal.

Description

Technical Field

[0001] The present invention relates to a method for phase-stable transmission of radio frequency signals, and in particular to a method and system for passive phase-stable optical transmission of radio frequency signals. Background Art

[0002] The current phase-stable transmission technology of RF phase-stable optical transmission system is mainly divided into active phase compensation and passive phase compensation. Active phase compensation can be divided into adjustable optical delay line compensation, adjustable wavelength laser compensation, microwave photon phase shifter compensation, electrical delay line / phase shifter compensation and phase-locked loop compensation; while passive phase compensation can be divided into f-2f compensation, f-3f compensation, etc.

[0003] The core idea of ​​active phase compensation stable phase transmission technology is to first extract the phase or delay jitter information in the link in real time from the signal transmitted back and forth in the link through the phase comparison module, and then drive the compensation device to compensate for the change in signal phase or delay. This method can adjust the signal phase difference between the transmitter and the receiver by controlling the compensation device. However, this method has shortcomings. On the one hand, its compensation range is limited by the phase compensation device, which is usually between tens of picoseconds and hundreds of picoseconds. When the link distance changes greatly and exceeds the capacity of the compensation device, the stable phase fails; on the other hand, the response speed of this method is usually slow.

[0004] The passive phase compensation stable phase transmission technology is based on the mixing elimination principle, or the phase conjugation principle. Generally, two optical radio frequency signals with the same phase jitter are mixed to offset the phase jitter of the optical radio frequency signal to be transmitted, or the optical radio frequency signal with phase jitter is pre-mixed with the optical radio frequency signal to be transmitted to pre-compensate the phase jitter of the optical radio frequency, and then transmitted to the remote end through the same link to obtain a phase-stable radio frequency signal. Since this method does not require feedback control of any actuator in the process of achieving stable phase transmission, it cleverly eliminates the phase jitter introduced in the transmission through mixing. Theoretically, there is no limit to its compensation range and the structure is relatively simple. However, the phase obtained by the existing passive phase compensation method is fixed. In some applications, such as beamforming, the phase difference of different nodes in the distributed system needs to be adjustable, and the existing stable phase transmission technology based on passive phase compensation is difficult to apply. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a passive phase-stable optical transmission method for radio frequency signals, which can adjust the phase difference of the radio frequency signals before and after transmission while realizing the phase-stable transmission of the radio frequency signals.

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

[0007] A passive phase-stable optical transmission method for radio frequency signals, wherein an optically-carried auxiliary radio frequency signal carrying an auxiliary radio frequency signal with a frequency of f+Δf is transmitted back and forth through an optical link and then converted into an electrical signal; a microwave local oscillator signal with a frequency of 2f is mixed with the auxiliary radio frequency signal to generate an up-conversion signal, and then the up-conversion signal is mixed with the electrical signal to generate a down-conversion signal, and the down-conversion signal is modulated in the optical domain and subjected to photoelectric conversion after unidirectional transmission through the optical link, thereby realizing phase-stable transmission of the microwave local oscillator signal; wherein f is half of the frequency of the microwave local oscillator signal, and Δf is an adjustable frequency portion much smaller than f.

[0008] Preferably, the optically-carried auxiliary radio frequency signal is obtained by the following method: up-converting a binary frequency signal of a microwave local oscillator signal using a frequency-adjustable low-frequency microwave signal with a frequency of Δf, and then modulating the obtained up-converted signal into the optical domain.

[0009] Further preferably, the up-conversion of the divided-frequency signal of the microwave local oscillator signal by using the frequency-adjustable low-frequency microwave signal with a frequency of Δf is specifically performed by using the frequency-adjustable low-frequency microwave signal to perform electrical domain IQ modulation on the divided-frequency signal of the microwave local oscillator signal.

[0010] Preferably, the optical carrier used for modulating the down-converted signal has a different frequency from the optical carrier of the optically-carried auxiliary RF signal, and a wavelength division multiplexer is used at the receiving end to separate the modulated down-converted signal from the optically-carried auxiliary RF signal.

[0011] Furthermore, the passive phase-stable optical carrier transmission method of the radio frequency signal also includes: adjusting the phase difference of the microwave local oscillator signal before and after the unidirectional transmission by adjusting the adjustable frequency part Δf.

[0012] According to the same inventive concept, the following technical solutions can also be obtained:

[0013] A passive phase-stable optical carrier transmission system for radio frequency signals, comprising a transmitter, a receiver, and an optical link connecting the transmitter and the receiver;

[0014] The transmitting end includes an optical auxiliary radio frequency signal generating module, a first photoelectric conversion module, a first mixer, a second mixer, and a first electro-optical modulator. The optical auxiliary radio frequency signal generating module is used to generate an optical auxiliary radio frequency signal carrying an auxiliary radio frequency signal with a frequency of f+Δf. The first photoelectric conversion module is used to convert the optical auxiliary radio frequency signal after being transmitted back and forth through the optical link into an electrical signal. The first mixer is used to mix a microwave local oscillator signal with a frequency of 2f with the auxiliary radio frequency signal to generate an up-conversion signal. The second mixer is used to mix the up-conversion signal with the electrical signal to generate a down-conversion signal. The first electro-optical modulator is used to modulate the down-conversion signal in the optical domain and transmit it unidirectionally to the receiving end through the optical link, wherein f is half of the frequency of the microwave local oscillator signal, and Δf is an adjustable frequency portion much smaller than f.

[0015] The receiving end includes a second photoelectric conversion module, which is used to perform photoelectric conversion on the optical down-conversion signal after unidirectional transmission, so as to achieve phase-stable transmission of the microwave local oscillator signal.

[0016] Preferably, the optical auxiliary radio frequency signal generation module includes:

[0017] An adjustable microwave source for generating a frequency-adjustable low-frequency microwave signal with a frequency of Δf;

[0018] A frequency divider, used for dividing the microwave local oscillator signal into two frequencies;

[0019] An up-conversion module, used for up-converting the binary frequency signal of the microwave local oscillator signal using the frequency-adjustable low-frequency microwave signal;

[0020] A power divider, used for dividing the up-converted signal output by the up-converter module into two paths, one of which is transmitted to the first mixer;

[0021] The second electro-optical modulator is used to modulate the frequency-converted signal on another path into the optical domain to generate an optically-carried auxiliary radio frequency signal.

[0022] Further preferably, the up-conversion module is an electrical domain IQ modulator.

[0023] Preferably, the optical carrier used for modulating the down-converted signal has a different frequency from the optical carrier of the optically-carried auxiliary RF signal, and a wavelength division multiplexer is used at the receiving end to separate the modulated down-converted signal from the optically-carried auxiliary RF signal.

[0024] Furthermore, the passive phase-stable optical transmission system of the radio frequency signal also includes:

[0025] The frequency modulation module is used to adjust the phase difference of the microwave local oscillator signal before and after unidirectional transmission by adjusting the adjustable frequency part Δf.

[0026] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0027] The present invention realizes passive phase-stable transmission of optical radio frequency by using existing passive phase compensation technology. By introducing a microwave auxiliary signal whose frequency can be adjusted within a certain range, the phase of the final received signal changes with the frequency of the microwave auxiliary signal. Therefore, the required specific phase difference can be obtained by adjusting the frequency of the microwave auxiliary signal, thereby realizing arbitrary adjustment of the phase difference between the receiving end and the transmitting end. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the principle of the technical solution of the present invention;

[0029] Figure 2 It is a specific implementation structure of the passive phase-stabilized optical carrier transmission system of the present invention;

[0030] Figure 3 It is a schematic diagram of the integration of the signal after steady-state transmission intercepted from the sampling oscilloscope within 5 minutes when the microwave auxiliary signal frequency is 2.0 GHz;

[0031] Figure 4 This is a schematic diagram of the integration of the signal after steady-state transmission captured from a sampling oscilloscope within 5 minutes when the microwave auxiliary signal frequency is 2.0GHz+8.334kHz. DETAILED DESCRIPTION

[0032] In view of the shortcomings of the prior art, the solution of the present invention is to achieve passive phase-stabilized transmission of optical radio frequency based on the existing passive phase compensation technology, by introducing a microwave auxiliary signal whose frequency can be adjusted within a certain range, so that the phase of the final received signal changes with the frequency of the microwave auxiliary signal. Therefore, the required specific phase difference can be obtained by adjusting the frequency of the microwave auxiliary signal, thereby realizing arbitrary adjustment of the phase difference between the receiving end and the transmitting end.

[0033] The passive phase-stable optical carrier transmission method of radio frequency signals of the present invention is as follows:

[0034] After the optically-carried auxiliary radio frequency signal carrying the auxiliary radio frequency signal with a frequency of f+Δf is transmitted back and forth through the optical link, it is converted into an electrical signal; a microwave local oscillator signal with a frequency of 2f is mixed with the auxiliary radio frequency signal to generate an up-conversion signal, and then the up-conversion signal is mixed with the electrical signal to generate a down-conversion signal, and the down-conversion signal is modulated in the optical domain and subjected to photoelectric conversion after unidirectional transmission through the optical link, thereby realizing the phase-stable transmission of the microwave local oscillator signal; wherein f is half of the frequency of the microwave local oscillator signal, and Δf is an adjustable frequency part that is much smaller than f.

[0035] The passive phase-stable optical carrier transmission system of radio frequency signals proposed by the present invention comprises a transmitting end, a receiving end and an optical link connecting the transmitting end and the receiving end;

[0036] The transmitting end includes an optical auxiliary radio frequency signal generating module, a first photoelectric conversion module, a first mixer, a second mixer, and a first electro-optical modulator. The optical auxiliary radio frequency signal generating module is used to generate an optical auxiliary radio frequency signal carrying an auxiliary radio frequency signal with a frequency of f+Δf. The first photoelectric conversion module is used to convert the optical auxiliary radio frequency signal after being transmitted back and forth through the optical link into an electrical signal. The first mixer is used to mix a microwave local oscillator signal with a frequency of 2f with the auxiliary radio frequency signal to generate an up-conversion signal. The second mixer is used to mix the up-conversion signal with the electrical signal to generate a down-conversion signal. The first electro-optical modulator is used to modulate the down-conversion signal in the optical domain and transmit it unidirectionally to the receiving end through the optical link, wherein f is half of the frequency of the microwave local oscillator signal, and Δf is an adjustable frequency portion much smaller than f.

[0037] The receiving end includes a second photoelectric conversion module, which is used to perform photoelectric conversion on the optical down-conversion signal after unidirectional transmission, so as to achieve phase-stable transmission of the microwave local oscillator signal.

[0038] In order to facilitate public understanding, the technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0039] The basic principle of the technical solution of the present invention is as follows Figure 1 As shown in the figure, the solid line represents the circuit and the dotted line represents the optical path. Assuming that the microwave local oscillator signal with a frequency of 2f needs to be transmitted, it can be expressed as f. are the frequency and initial phase of the microwave local oscillator signal respectively; Figure 1 As shown, the frequency is f+Δf and the initial phase is Auxiliary RF signal It is divided into two paths, one of which is modulated in the optical domain to generate an optically-carried auxiliary RF signal, and the other is mixed with a microwave local oscillator signal to realize up-conversion, wherein f is half of the frequency of the microwave local oscillator signal, and Δf is an adjustable frequency part that is much smaller than f; the optically-carried auxiliary RF signal is converted to the electrical domain after being transmitted back and forth through the optical link and mixed with the up-conversion signal to realize down-conversion, and the down-conversion signal is modulated in the optical domain and transmitted unidirectionally to the receiving end through the optical link; the receiving end performs photoelectric conversion on the optically-carried down-conversion signal after unidirectional transmission, so as to realize the stable phase transmission of the microwave local oscillator signal, and the phase difference adjustment of the microwave local oscillator signal before and after unidirectional transmission can be realized by adjusting Δf.

[0040] Figure 2 A specific implementation structure of the passive phase-stabilized optical carrier transmission system of the present invention is shown; Figure 2As shown, the passive phase-stabilized optical carrier transmission system of this embodiment includes a transmitter, a receiver and an optical link connecting the two; the transmitter includes a signal source, a binary divider, an electrical domain IQ modulator, a power divider, a mixer 1, a mixer 2, a laser 1, a laser 2, a modulator 1, a modulator 2, an optical coupler, a photodetector 1, and an optical circulator 1; the receiver includes an optical circulator 2, a wavelength division multiplexer, and a photodetector 2; the optical link in this embodiment is an optical fiber link. Figure 2 As shown, the microwave local oscillator signal S1 to be transmitted generated by the signal source is divided into two paths, one for up-conversion; the other is divided by a two-way frequency divider, and then the frequency-adjustable low-frequency signal is processed by an electrical domain IQ modulator to obtain a frequency-adjustable microwave auxiliary signal S a The microwave auxiliary signal is divided into two paths through the power divider. One path is mixed with the microwave local oscillator signal to be transmitted to generate an up-conversion signal S2. The other path is modulated to the optical carrier generated by the laser 1 through the modulator 1 to generate a detection optical signal. After being transmitted back and forth through the optical fiber link, the detection optical signal is converted into an electrical signal S on the photodetector 1. ar ; The electrical signal S ar The down-converted signal S3 is mixed with the up-converted signal S2, and is modulated onto the optical carrier generated by the laser 2 through the modulator 2. After unidirectional transmission through the same optical fiber link as mentioned above, it is detected on the photodetector 2 to generate the electrical signal S4.

[0041] In order to transmit the detection optical signal and the optical carrier down-conversion signal simultaneously through the same optical fiber, in this embodiment, laser 1 and laser 2 output optical carriers of different wavelengths, and the two are separated by a wavelength division multiplexer at the receiving end.

[0042] The frequency-adjustable microwave auxiliary signal undergoes one round-trip transmission in the optical fiber link, while the microwave local oscillator signal only undergoes one unidirectional transmission in the optical fiber link. The transmission delay of the microwave auxiliary signal after the round-trip transmission is twice the unidirectional transmission delay of the microwave local oscillator signal, and the initial frequency of the frequency-adjustable microwave auxiliary signal is half the frequency of the microwave local oscillator signal. After two mixings, the frequency of the microwave local oscillator signal remains unchanged, but a phase conjugate term corresponding to the transmission delay at that moment is introduced into the phase. Therefore, after the signal is modulated onto an optical carrier and transmitted unidirectionally through the same optical fiber link, the phase of the electrical signal recovered by the photodetector is not affected by the optical fiber link, thereby realizing stable phase transmission of optically-carried radio frequency; the frequency of the microwave auxiliary signal is adjusted within a certain range, so that the phase of the finally received signal changes accordingly, thereby the required specific phase difference can be obtained by adjusting the frequency of the microwave auxiliary signal, thereby realizing arbitrary adjustment of the phase difference between the receiving end and the transmitting end.

[0043] Specifically, it is assumed that the microwave local oscillator signal generated by signal source 2 is S1:

[0044]

[0045] Among them, are the initial frequency and phase of the microwave local oscillator signal respectively;

[0046] The microwave auxiliary signal generated by signal source 1 is S a :

[0047]

[0048] Among them, Δf, are the continuously changing frequency and phase of the microwave auxiliary signal respectively;

[0049] The electrical signal detected by the photodetector 1 after the microwave auxiliary signal is transmitted back and forth once is S ar :

[0050]

[0051] Where τ is the delay of one-way transmission;

[0052] Microwave local oscillator signal S1 and microwave auxiliary signal S a The up-conversion signal S2 is:

[0053]

[0054] The up-converted signal S2 and the electrical signal S detected by the photodetector ar Down-converting to get signal S3:

[0055]

[0056] After the down-converted signal S3 is unidirectionally transmitted through the same optical fiber link, the electrical signal detected by the photoelectric detector 2 is S4;

[0057]

[0058] It can be seen that the phase jitter introduced by the optical fiber link is eliminated, while the frequency variation within a certain range introduced by the microwave auxiliary signal is converted into the corresponding phase difference.

[0059] In order to verify the technical effect of the present invention, the following experiments were conducted:

[0060] First, we built a unidirectional 2000m optical fiber link using Figure 2 The system architecture shown performs phase-stabilized transmission and step-by-step adjusts the phase difference between the transmitter and the receiver. Figure 3 This is the integral of the signal received by the receiving end within 5 minutes when the auxiliary signal is 2 GHz. It can be seen that its phase is stable. Figure 4is the integral of the signal received by the receiver within 5 minutes when the auxiliary signal is 2GHz+8.334kHz. It can be seen that its phase is also stable, but different from Figure 3 Compared with the conventional microwave auxiliary signal, the phase is offset, which shows that by continuously adjusting the frequency of the microwave auxiliary signal, the received signal has a phase difference that changes accordingly, while the delay τ introduced by the optical fiber link is a fixed value. Therefore, the required specific phase difference can be obtained by adjusting the frequency of the microwave auxiliary signal, thereby realizing the arbitrary adjustable phase difference between the receiving end and the transmitting end.

[0061] It can be deduced from the above formula that the frequency of the auxiliary signal is adjusted to 2 GHz, 2 GHz + 2.779 kHz, 2 GHz + 5.557 kHz, 2 GHz + 8.334 kHz, 2 GHz + 11.11 kHz, and 2 GHz + 13.89 kHz, so that the phase difference between the receiving end and the transmitting end can be stepped from 0 to 100° at intervals of 20°.

[0062] In summary, it can be seen that the technical solution of the present invention can not only realize passive phase-stabilized transmission of optical radio frequency, but also adjust the frequency of the microwave auxiliary signal within a certain range, so that the final received signal obtains a phase difference that changes accordingly. Therefore, a specific phase difference can be obtained by adjusting the frequency of the microwave auxiliary signal, thereby realizing arbitrary adjustment of the phase difference between the receiving end and the transmitting end.

Claims

1. A passive phase-stabilized optical transmission method for radio frequency signals, characterized in that: After the optically-carried auxiliary radio frequency signal carrying the auxiliary radio frequency signal with a frequency of f+Δf is transmitted back and forth through the optical link, it is converted into an electrical signal; the microwave local oscillator signal with a frequency of 2f is mixed with the auxiliary radio frequency signal to generate an up-conversion signal, and then the up-conversion signal is mixed with the electrical signal to generate a down-conversion signal, and the down-conversion signal is modulated in the optical domain and subjected to photoelectric conversion after unidirectional transmission through the optical link, thereby realizing the phase-stable transmission of the microwave local oscillator signal; wherein f is half of the frequency of the microwave local oscillator signal, and Δf is an adjustable frequency part much smaller than f; the optically-carried auxiliary radio frequency signal is obtained by the following method: up-converting the two-frequency signal of the microwave local oscillator signal with a frequency-adjustable low-frequency microwave signal with a frequency of Δf, and then modulating the obtained up-conversion signal into the optical domain; the up-conversion of the two-frequency signal of the microwave local oscillator signal with a frequency-adjustable low-frequency microwave signal with a frequency of Δf is specifically performing electrical domain IQ modulation on the two-frequency signal of the microwave local oscillator signal with the frequency-adjustable low-frequency microwave signal.

2. The passive phase-stabilized optical transmission method of radio frequency signals as claimed in claim 1, characterized in that: The optical carrier used for modulating the down-converted signal has a different frequency from that of the optical carrier of the optically-carried auxiliary radio frequency signal. The down-converted signal and the optically-carried auxiliary radio frequency signal are separated after modulation at the receiving end through a wavelength division multiplexer.

3. The passive phase-stabilized optical transmission method of radio frequency signals according to claim 1, further comprising: The phase difference adjustment of the microwave local oscillator signal before and after unidirectional transmission is achieved by adjusting the adjustable frequency part Δf.

4. A passive phase-stable optical transmission system for radio frequency signals, comprising a transmitter, a receiver, and an optical link connecting the transmitter and the receiver; characterized in that: The transmitting end includes an optical auxiliary radio frequency signal generating module, a first photoelectric conversion module, a first mixer, a second mixer, and a first electro-optical modulator. The optical auxiliary radio frequency signal generating module is used to generate an optical auxiliary radio frequency signal carrying an auxiliary radio frequency signal with a frequency of f+Δf. The first photoelectric conversion module is used to convert the optical auxiliary radio frequency signal after being transmitted back and forth through the optical link into an electrical signal. The first mixer is used to mix a microwave local oscillator signal with a frequency of 2f with the auxiliary radio frequency signal to generate an up-conversion signal. The second mixer is used to mix the up-conversion signal with the electrical signal to generate a down-conversion signal. The first electro-optical modulator is used to modulate the down-conversion signal in the optical domain and transmit it unidirectionally to the receiving end through the optical link, wherein f is half of the frequency of the microwave local oscillator signal, and Δf is an adjustable frequency portion much smaller than f. The receiving end includes a second photoelectric conversion module, which is used to perform photoelectric conversion on the optical down-conversion signal after unidirectional transmission, so as to achieve the stable phase transmission of the microwave local oscillator signal; the optical auxiliary radio frequency signal generation module includes: an adjustable microwave source, which is used to generate a frequency-adjustable low-frequency microwave signal with a frequency of Δf; A frequency divider, used for dividing the microwave local oscillator signal into two frequencies; An up-conversion module, used for up-converting the two-frequency signal of the microwave local oscillator signal with the frequency-adjustable low-frequency microwave signal; the up-conversion module is an electrical domain IQ modulator; The power divider is used to divide the up-converted signal output by the up-converter module into two paths, one of which is transmitted to the first mixer; the second electro-optical modulator is used to modulate the other up-converted signal into the optical domain to generate an optically-carried auxiliary RF signal.

5. The passive phase-stabilized optical transmission system of radio frequency signals as claimed in claim 4, characterized in that: The frequency of the optical carrier used for modulating the down-converted signal is different from that of the optical carrier of the optically-carried auxiliary radio frequency signal. The down-converted signal and the optically-carried auxiliary radio frequency signal are separated after modulation through a wavelength division multiplexer at the receiving end.

6. The passive phase-stabilized optical transmission system of radio frequency signals as claimed in claim 4, characterized in that: Also includes: The frequency modulation module is used to adjust the phase difference of the microwave local oscillator signal before and after unidirectional transmission by adjusting the adjustable frequency part Δf.

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