Amplitude and phase stabilization transmission method and apparatus for free-space optical microwave links

Abstract

This invention discloses a method for amplitude- and phase-stable transmission of a free-space optical-carrying microwave link. The method involves transmitting a beacon optical signal from the receiver to the transmitter. After transmission through an atmospheric turbulence channel, the signal carries the fading signal from the turbulence channel. The transmitter adaptively pre-compensates the power of the optical-carrying microwave signal based on the intensity changes of the received beacon optical signal. Simultaneously, the transmitter generates a signal with the same frequency as the local oscillator signal using a voltage-controlled oscillator (VCO). At the receiver, a portion of the optical carrier micro-signal is reflected back. After photoelectric conversion at the transmitter, this micro-signal is up-converted by a frequency divider of the up-converted signal and the frequency divider of the VCO-generated signal. Finally, the phase detection error between the up-converted signal and the microwave signal to be transmitted is zero, which serves as the control target to drive the VCO to generate a phase-compensated local oscillator signal. This invention also discloses a device for amplitude- and phase-stable transmission of a free-space optical-carrying microwave link. This invention enables amplitude- and phase-stable transmission of optical-carrying microwave signals in a free-space channel.

Description

Technical Field

[0001] This invention relates to a method and apparatus for amplitude and phase stabilization transmission of a free-space optical microwave link. Background Technology

[0002] With the increase in operating frequency bands and bandwidth, distributed coherent radars demand increasingly higher synchronization accuracy in time, space, frequency, and phase, posing numerous challenges to traditional electrical synchronization technologies. Photonics technology offers advantages in achieving time, frequency, and phase synchronization of microwave signals, boasting high frequency, large bandwidth, and high accuracy. Currently, microwave frequency synchronization based on photonics technology is primarily achieved through fiber optic links. While the low-loss characteristics of fiber optics provide an excellent channel for time and frequency transmission, they also limit the system's application scenarios. Because the system is based on fiber optic networks, achieving time and frequency synchronization in complex environments and between moving platforms is difficult. Free-space optical microwave technology combines the advantages of both microwave and optical signals; however, atmospheric channels severely impact optical microwave signals. The most significant impacts include light intensity flicker caused by atmospheric turbulence, leading to jitter in received power and deterioration in transmission bandwidth, and phase velocity dispersion caused by spatial wavefront phase distortion, resulting in laser coherence degradation. These factors constitute a technical bottleneck restricting the development and application of high-speed optical microwave.

[0003] To address the amplitude and phase jitter of free-space optical microwave signals caused by the real-time and random changes in atmospheric turbulence, current amplitude jitter suppression techniques mainly employ automatic tracking and aiming, aperture averaging, and adaptive optics. Automatic tracking and aiming primarily targets beam stability, offering limited compensation for intensity flicker and power jitter caused by atmospheric turbulence. While aperture averaging can reduce intensity fluctuations to some extent, it increases system size and cost and cannot completely eliminate amplitude jitter. Adaptive optics mainly targets beam phase distortion, offering limited compensation for amplitude jitter and exhibiting high system complexity. Current phase jitter suppression techniques for space optical microwave signals can be categorized into passive and active phase compensation. Passive phase compensation primarily reduces phase noise through mixing and elimination principles, representing an open-loop, feedback-free compensation scheme. However, it cannot adapt to the dynamic changes in atmospheric turbulence in real-time, resulting in limited compensation effectiveness. Active phase compensation is a method that introduces a feedback mechanism during optical transmission to adjust the phase of the optical signal in real time, thereby suppressing the influence of phase noise. It is a closed-loop feedback control compensation scheme, but it usually requires complex optical path design and is difficult to achieve joint compensation of amplitude and phase. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for amplitude and phase stabilization transmission of optical microwave links in free space, which can simultaneously perform phase jitter pre-compensation and power pre-compensation, thereby realizing amplitude and phase stabilization transmission of optical microwave signals in free space channels.

[0005] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

[0006] A method for amplitude and phase stabilization transmission of a free-space optical microwave link includes the following steps:

[0007] Step 1: At the transmitting end, the first microwave signal generated by the voltage-controlled oscillator with the same frequency as the microwave signal to be transmitted is modulated onto the first optical carrier, and the generated first optical carrier microwave signal is transmitted to the receiving end through the free space optical carrier microwave link.

[0008] Step 2: At the receiving end, a portion of the first optical microwave signal is reflected back to the transmitting end; at the same time, a second microwave signal with the same frequency as the microwave signal to be transmitted is modulated onto the second optical carrier, and the generated second optical microwave signal is transmitted to the transmitting end through a free-space optical microwave link. The second optical carrier has a different wavelength from the first optical carrier.

[0009] Step 3: At the transmitting end, after photoelectric conversion of the reflected signal of the first optical microwave signal, it is divided by two, and the resulting divided signal is used to upconvert the divided signal of the first microwave signal to obtain an upconverted signal with link jitter information. The upconverted signal and the microwave signal to be transmitted are phase-detected, and the phase error obtained from the phase detection is zero as the control target. The voltage-controlled oscillator is driven to generate the microwave signal to be transmitted after phase jitter pre-compensation. At the same time, the power loss of the second optical microwave signal after transmission through the free space optical microwave link is detected, and the power pre-compensation of the first optical microwave signal is performed based on the detected power loss.

[0010] Step 4: At the receiving end, photoelectric detection is performed on another part of the first optical microwave signal to obtain the microwave signal to be transmitted after phase jitter pre-compensation and power pre-compensation, thereby realizing the amplitude and phase-stable transmission of the free space optical microwave link.

[0011] Preferably, an automatic gain controller is used to pre-compensate the power of the first optical microwave signal.

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

[0013] A free-space optical microwave link amplitude and phase stabilization transmission device includes a transmitter device and a receiver device;

[0014] The transmitting device includes:

[0015] The first electro-optic modulator is used to modulate a first microwave signal generated by a voltage-controlled oscillator at the same frequency as the microwave signal to be transmitted onto a first optical carrier to generate a first optical carrier microwave signal.

[0016] The first photodetector is used to perform photoelectric conversion on the reflected signal of the first optical microwave signal;

[0017] The phase compensation module is used to perform frequency division processing on the output signal of the first photodetector, and to perform up-conversion processing on the frequency division signal of the first microwave signal using the obtained frequency division signal to obtain an up-converted signal with link jitter information. The up-converted signal and the microwave signal to be transmitted are subjected to phase detection processing, and the phase error obtained by the phase detection processing is zero as the control target to drive the voltage-controlled oscillator to generate the microwave signal to be transmitted after phase jitter pre-compensation.

[0018] The power monitoring module is used to detect the power loss of the second optical-carrying microwave signal emitted by the receiving device after transmission through the free-space optical-carrying microwave link;

[0019] The power control module is used to perform power pre-compensation on the first optical microwave signal based on the power loss detected by the power monitoring module.

[0020] The receiving device includes:

[0021] The reflection module is used to reflect a portion of the first optically transmitted microwave signal back to the transmitter.

[0022] The second electro-optic modulator is used to modulate a second microwave signal with the same frequency as the microwave signal to be transmitted onto a second optical carrier, and to transmit the generated second optical carrier microwave signal to the transmitter through a free-space optical carrier microwave link. The second optical carrier has a different wavelength from the first optical carrier.

[0023] The second photodetector is used to perform photodetection on another part of the first optical microwave signal, that is, to obtain the microwave signal to be transmitted after phase jitter pre-compensation and power pre-compensation, thereby realizing the amplitude and phase stable transmission of the free space optical microwave link.

[0024] Preferably, the power control module is an automatic gain controller.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0026] To address the amplitude jitter of free-space optical microwave signals caused by real-time random variations in atmospheric turbulence channels, this invention, based on the principle of channel reciprocity, transmits a beacon optical signal from the receiver to the transmitter. After transmission through the atmospheric turbulence channel, the signal carries the fading signal from the atmospheric turbulence channel. The instantaneous change in the intensity of the beacon optical signal received at the transmitter reflects the amplitude disturbance of the transmitted signal caused by atmospheric turbulence. Adaptive pre-compensation is performed on the power of the optical microwave signal based on the intensity change of the received beacon optical signal. To address the phase jitter of free-space optical microwave signals caused by real-time random variations in atmospheric turbulence channels, this invention is based on the principle of active phase noise cancellation. A voltage-controlled oscillator (VCO) generates an optical carrier microwave signal. At the receiving end, a portion of the optical carrier micro-signal is reflected back to the transmitting end. After photoelectric conversion, the signal is divided by two and then up-converted to obtain an up-converted signal with link jitter information. Finally, the VCO is driven and controlled with the phase detection error between the up-converted signal and the microwave signal to be transmitted being zero, thus achieving active suppression of phase jitter. This invention can simultaneously suppress amplitude and phase jitter of free-space optical carrier microwave signals caused by real-time random changes in atmospheric turbulence channels, and the system structure is simple and easy to implement. Attached Figure Description

[0027] Figure 1 This is a schematic diagram illustrating the structural principle of the amplitude and phase stabilization transmission device for the free-space optical microwave link of the present invention.

[0028] Figure 2 This is a schematic diagram of the structural principle of the phase compensation module. Detailed Implementation

[0029] To address the shortcomings of existing technologies, this invention addresses the issue of simultaneously suppressing phase jitter and amplitude jitter. For amplitude jitter in free-space optical microwave signals caused by real-time random variations in the atmospheric turbulence channel, this invention, based on the principle of channel reciprocity, transmits a beacon light signal from the receiver to the transmitter. After transmission through the atmospheric turbulence channel, the signal carries the fading signal from the atmospheric turbulence channel. The instantaneous change in the intensity of the beacon light signal received at the transmitter reflects the amplitude disturbance of the transmitted signal caused by atmospheric turbulence. Adaptive pre-compensation is performed on the power of the optical microwave signal based on the intensity change of the received beacon light signal. To address phase jitter in microwave signals, this invention is based on the principle of active phase noise cancellation. A voltage-controlled oscillator (VCO) generates a signal with the same frequency as the local oscillator signal (the microwave signal to be transmitted). At the receiving end, a portion of the optical carrier micro-signal is reflected back to the transmitting end, then converted by photoelectric conversion and subjected to a frequency division process. This divided signal is then up-converted with the frequency-divided signal generated by the VCO, resulting in an up-converted signal containing link jitter information. Finally, with the phase detection error between this up-converted signal and the microwave signal to be transmitted being zero, a proportional-integral controller drives the VCO to generate an error signal to achieve pre-compensation for phase jitter in the microwave signal to be transmitted, thus realizing active suppression of phase jitter.

[0030] The amplitude and phase stabilization transmission method for free-space optical microwave links proposed in this invention includes the following steps:

[0031] Step 1: At the transmitting end, the first microwave signal generated by the voltage-controlled oscillator with the same frequency as the microwave signal to be transmitted is modulated onto the first optical carrier, and the generated first optical carrier microwave signal is transmitted to the receiving end through the free space optical carrier microwave link.

[0032] Step 2: At the receiving end, a portion of the first optical microwave signal is reflected back to the transmitting end; at the same time, a second microwave signal with the same frequency as the microwave signal to be transmitted is modulated onto the second optical carrier, and the generated second optical microwave signal is transmitted to the transmitting end through a free-space optical microwave link. The second optical carrier has a different wavelength from the first optical carrier.

[0033] Step 3: At the transmitting end, after photoelectric conversion of the reflected signal of the first optical microwave signal, it is divided by two, and the resulting divided signal is used to upconvert the divided signal of the first microwave signal to obtain an upconverted signal with link jitter information. The upconverted signal and the microwave signal to be transmitted are phase-detected, and the phase error obtained from the phase detection is zero as the control target. The voltage-controlled oscillator is driven to generate the microwave signal to be transmitted after phase jitter pre-compensation. At the same time, the power loss of the second optical microwave signal after transmission through the free space optical microwave link is detected, and the power pre-compensation of the first optical microwave signal is performed based on the detected power loss.

[0034] Step 4: At the receiving end, photoelectric detection is performed on another part of the first optical microwave signal to obtain the microwave signal to be transmitted after phase jitter pre-compensation and power pre-compensation, thereby realizing the amplitude and phase-stable transmission of the free space optical microwave link.

[0035] The amplitude and phase stabilization transmission device for free-space optical microwave links proposed in this invention includes a transmitting end device and a receiving end device;

[0036] The transmitting device includes:

[0037] The first electro-optic modulator is used to modulate a first microwave signal generated by a voltage-controlled oscillator at the same frequency as the microwave signal to be transmitted onto a first optical carrier to generate a first optical carrier microwave signal.

[0038] The first photodetector is used to perform photoelectric conversion on the reflected signal of the first optical microwave signal;

[0039] The phase compensation module is used to perform frequency division processing on the output signal of the first photodetector, and to perform up-conversion processing on the frequency division signal of the first microwave signal using the obtained frequency division signal to obtain an up-converted signal with link jitter information. The up-converted signal and the microwave signal to be transmitted are subjected to phase detection processing, and the phase error obtained by the phase detection processing is zero as the control target to drive the voltage-controlled oscillator to generate the microwave signal to be transmitted after phase jitter pre-compensation.

[0040] The power monitoring module is used to detect the power loss of the second optical-carrying microwave signal emitted by the receiving device after transmission through the free-space optical-carrying microwave link;

[0041] The power control module is used to perform power pre-compensation on the first optical microwave signal based on the power loss detected by the power monitoring module.

[0042] The receiving device includes:

[0043] The reflection module is used to reflect a portion of the first optically transmitted microwave signal back to the transmitter.

[0044] The second electro-optic modulator is used to modulate a second microwave signal with the same frequency as the microwave signal to be transmitted onto a second optical carrier, and to transmit the generated second optical carrier microwave signal to the transmitter through a free-space optical carrier microwave link. The second optical carrier has a different wavelength from the first optical carrier.

[0045] The second photodetector is used to perform photodetection on another part of the first optical microwave signal, that is, to obtain the microwave signal to be transmitted after phase jitter pre-compensation and power pre-compensation, thereby realizing the amplitude and phase stable transmission of the free space optical microwave link.

[0046] To facilitate public understanding, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings:

[0047] The present invention provides an amplitude- and phase-stabilized transmission device for a free-space optical microwave link, such as... Figure 1 As shown, it includes transmitting equipment and receiving equipment; the transmitting equipment includes laser 1 (wavelength λ1), electro-optic modulator, power control module, power detection module, phase compensation module, photodetector, optical circulator, and wavelength division multiplexer; the receiving equipment includes wavelength division multiplexer, Faraday mirror, laser 2 (wavelength λ2), optical circulator, and photodetector.

[0048] The specific working process of this device is as follows:

[0049] Step 1: At the transmitting end, the first microwave signal generated by the voltage-controlled oscillator with the same frequency as the microwave signal to be transmitted is modulated onto the first optical carrier with wavelength λ1 output by the laser 1. The generated first optical carrier microwave signal is transmitted to the receiving end through the free space optical carrier microwave link after passing through the power control module.

[0050] Step 2: At the receiving end, the Faraday mirror reflects part of the first optical microwave signal back to the transmitting end; at the same time, the second microwave signal with the same frequency as the microwave signal to be transmitted is modulated onto the second optical carrier with wavelength λ2 output by the laser 2, and the generated second optical microwave signal is transmitted to the transmitting end through the free space optical microwave link;

[0051] Step 3: At the transmitting end, the photodetector performs photoelectric conversion on the reflected signal of the first optical microwave signal separated by the wavelength division multiplexer, and then sends it to the phase compensation module; the specific structure of the phase compensation module is as follows: Figure 2 As shown, a frequency divider is used to divide the first microwave signal output from the voltage-controlled oscillator by two, and another frequency divider is used to divide the first microwave signal by two. Then, a mixer is used to mix the two divided signals to achieve up-conversion, resulting in an up-converted signal with link jitter information. A phase detector is used to perform phase detection between the up-converted signal and the microwave signal to be transmitted, and the phase error signal output by the phase detector is input to a proportional-integral controller. The proportional-integral controller uses the zero phase error obtained from the phase detection as the control target, and drives the voltage-controlled oscillator to generate the microwave signal to be transmitted after phase jitter pre-compensation. At the same time, the second optical microwave signal with a wavelength of λ2 separated by the wavelength division multiplexer is sent to the power monitoring module. The power monitoring module detects the power loss of the second optical microwave signal after transmission through the free-space optical microwave link. The power control module performs power pre-compensation on the first optical microwave signal based on the power loss detected by the power monitoring module. In this embodiment, the power control module uses an automatic gain controller.

[0052] Step 4: At the receiving end, the photodetector performs photodetection on another part of the first optical microwave signal, that is, it obtains the microwave signal to be transmitted after phase jitter pre-compensation and power pre-compensation, thereby realizing the amplitude and phase stable transmission of the free space optical microwave link.

[0053] The technical principle of the above phase compensation is further explained below:

[0054] At the transmitting end, a voltage-controlled oscillator (VCO) generates a signal with the same frequency as the microwave signal to be transmitted (microwave local oscillator signal), and its expression is:

[0055]

[0056] Where ω0 and These represent the angular frequency and phase of the signal generated by the VCO. A portion of this signal is then divided to generate a frequency-divided signal:

[0057]

[0058] Another portion is loaded onto an electro-optic modulator, where the first optical carrier is intensity modulated and then transmitted through a free-space optical-microwave link. The receiving end returns the signal to the transmitting end via a Faraday mirror, where it is then converted by photoelectric conversion and divided by two. The expression for this is:

[0059]

[0060] in The phase jitter is introduced by the space optical link; two frequency-divided signals are mixed to generate an up-converted signal:

[0061]

[0062] Subsequently, phase detection was performed with the microwave local oscillator signal, which is:

[0063]

[0064] in The phase of the microwave local oscillator signal; during phase detection, the following is achieved:

[0065]

[0066] Therefore, the microwave signal to be transmitted, after phase jitter pre-compensation, is generated by driving the VCO through a PI (Proportional-Integral Controller) as follows:

[0067]

[0068] After being transmitted again via the space optical link, the signal recovered by the receiving end is:

[0069]

[0070] It can be observed that the signal does not carry phase jitter introduced by the space optical link, thus achieving coherence with the microwave local oscillator signal at the transmitting end.

Claims

1. A method for amplitude- and phase-stable transmission of a free-space optical microwave link, characterized in that, Includes the following steps: Step 1: At the transmitting end, the first microwave signal generated by the voltage-controlled oscillator with the same frequency as the microwave signal to be transmitted is modulated onto the first optical carrier, and the generated first optical carrier microwave signal is transmitted to the receiving end through the free space optical carrier microwave link. Step 2: At the receiving end, a portion of the first optical microwave signal is reflected back to the transmitting end; at the same time, a second microwave signal with the same frequency as the microwave signal to be transmitted is modulated onto the second optical carrier, and the generated second optical microwave signal is transmitted to the transmitting end through a free-space optical microwave link. The second optical carrier has a different wavelength from the first optical carrier. Step 3: At the transmitting end, after photoelectric conversion of the reflected signal of the first optical microwave signal, it is divided by two, and the resulting divided signal is up-converted with the divided signal of the first microwave signal to obtain an up-converted signal with link jitter information. The up-converted signal and the microwave signal to be transmitted are phase-detected, and the phase error obtained from the phase detection is zero as the control target. The voltage-controlled oscillator is driven to generate the microwave signal to be transmitted after phase jitter pre-compensation. At the same time, the power loss of the second optical microwave signal after transmission through the free space optical microwave link is detected, and the power pre-compensation of the first optical microwave signal is performed based on the detected power loss. Step 4: At the receiving end, photoelectric detection is performed on another part of the first optical microwave signal to obtain the microwave signal to be transmitted after phase jitter pre-compensation and power pre-compensation, thereby realizing the amplitude and phase-stable transmission of the free space optical microwave link.

2. The amplitude- and phase-stable transmission method for a free-space optical-microwave link as described in claim 1, characterized in that, The power pre-compensation of the first optical carrier microwave signal is performed using an automatic gain controller.

3. A amplitude- and phase-stabilized transmission device for a free-space optical microwave link, comprising a transmitting end device and a receiving end device; characterized in that, The transmitting device includes: The first electro-optic modulator is used to modulate a first microwave signal generated by a voltage-controlled oscillator at the same frequency as the microwave signal to be transmitted onto a first optical carrier to generate a first optical carrier microwave signal. The first photodetector is used to perform photoelectric conversion on the reflected signal of the first optical microwave signal; The phase compensation module is used to perform frequency division processing on the output signal of the first photodetector, and to perform up-conversion processing on the frequency division signal of the first microwave signal using the obtained frequency division signal to obtain an up-converted signal with link jitter information. The up-converted signal and the microwave signal to be transmitted are subjected to phase detection processing, and the phase error obtained by the phase detection processing is zero as the control target to drive the voltage-controlled oscillator to generate the microwave signal to be transmitted after phase jitter pre-compensation. The power monitoring module is used to detect the power loss of the second optical-carrying microwave signal emitted by the receiving device after transmission through the free-space optical-carrying microwave link; The power control module is used to perform power pre-compensation on the first optical microwave signal based on the power loss detected by the power monitoring module. The receiving device includes: The reflection module is used to reflect a portion of the first optically transmitted microwave signal back to the transmitter. The second electro-optic modulator is used to modulate a second microwave signal with the same frequency as the microwave signal to be transmitted onto a second optical carrier, and to transmit the generated second optical carrier microwave signal to the transmitter through a free-space optical carrier microwave link. The second optical carrier has a different wavelength from the first optical carrier. The second photodetector is used to perform photodetection on another part of the first optical microwave signal, that is, to obtain the microwave signal to be transmitted after phase jitter pre-compensation and power pre-compensation, thereby realizing the amplitude and phase stable transmission of the free space optical microwave link.

4. The amplitude- and phase-stabilized transmission device for a free-space optical microwave link as described in claim 3, characterized in that, The power control module is an automatic gain controller.

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