A transmission system for radio frequency signals

Abstract

The embodiment of the application discloses a kind of transmission systems of radio frequency signal.The system includes: local end, remote end and free space link;Local end is used to send first femtosecond pulse laser to remote end, receive the second femtosecond pulse laser returned by remote end and the repetition frequency of second femtosecond pulse laser and the repetition frequency of first femtosecond pulse laser are beat frequency processing, obtain the phase factor of the phase noise of free space link, and the repetition frequency of first femtosecond pulse laser is pre-compensated based on phase factor;Remote end is used to receive the first femtosecond pulse laser sent by local end, and based on first femtosecond pulse laser, second femtosecond pulse laser is sent to local end and first femtosecond pulse laser is converted into radio frequency signal.By the application, the technical problem that high-precision radio frequency transmission under free space link cannot be realized in the related art is solved, and the technical effect of realizing high-precision transmission of radio frequency signal in free space link is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical time-frequency transfer technology, and in particular to a radio frequency signal transfer system. BACKGROUND

[0002] High-precision time-frequency signal comparison and distribution technology is of great significance in satellite positioning and navigation, deep space networking, very long baseline coherent detection and fundamental physics parameter measurement. Although the current optical fiber-based time-frequency transfer technology has matured in terms of measurement accuracy and stability, it is limited to propagation in fixed optical fiber networks. For dynamic targets, wide-area space scenarios and remote areas where it is not convenient to lay optical fibers, it is necessary to establish a higher degree of flexibility in free space links to meet the high-precision time-frequency transfer requirements in various complex scenarios.

[0003] Currently, free space time-frequency transfer technology is mainly divided into optical frequency transfer, optical carrier radio frequency transfer and optical comb transfer. The optical frequency transfer technology usually adopts active phase compensation to detect the noise of the link at the local end and pre-compensate, and then reproduce the optical frequency signal at the remote end to achieve high-stability continuous laser signal transfer. This technology generally has the advantage of high frequency transfer stability, but it usually has high requirements for the environment where the link is located. The optical carrier radio frequency transfer technology usually loads the stable radio frequency signal at the local end onto the continuous laser carrier, and detects the radio frequency phase noise of the link by optical-electric conversion. The link phase noise is eliminated by active feedback control at the local end or by mixing at the remote end. This technology usually has the advantages of simple structure and high system integration, but the frequency transfer stability of this type of technology is usually low. The optical comb transfer technology usually detects the multiple harmonics of the repetition frequency and performs post-compensation at the remote end, or sets the repetition frequency difference of the optical combs at the two stations, and uses asynchronous optical sampling technology to achieve bidirectional time-frequency transfer. This technology has high transfer accuracy, strong flexibility, and can perform synchronous transfer of time signals and frequency signals, and is the most promising technology for development and application. However, for optical comb transfer technology, the radio frequency signal is easily affected by link noise, link loss, signal strength and other factors during transmission, making it difficult to accurately reproduce the radio frequency signal at the local end at the remote end, and thus high-precision radio frequency transfer in free space links cannot be achieved.

[0004] No effective solution has been proposed to address the above problems. SUMMARY

[0005] Embodiments of the present application provide a radio frequency signal transfer system to at least solve the technical problem of not being able to achieve high-precision radio frequency transfer in free space in the related art.

[0006] According to an aspect of an embodiment of the present application, a system for transmitting a radio frequency signal is provided, comprising: a local end and a remote end, which are respectively arranged at two ends of a free space link, wherein a femto-second pulse laser is used as a transmission carrier of the radio frequency signal, the femto-second pulse laser comprising a first femto-second pulse laser and a second femto-second pulse laser; the local end is configured to send the first femto-second pulse laser to the remote end, receive the second femto-second pulse laser returned by the remote end, beat the repetition frequency of the second femto-second pulse laser with the repetition frequency of the first femto-second pulse laser to obtain a phase factor of phase noise of the free space link, and pre-compensate the repetition frequency of the first femto-second pulse laser based on the phase factor; and the remote end is configured to receive the first femto-second pulse laser sent by the local end, send the second femto-second pulse laser to the local end based on the first femto-second pulse laser, and convert the first femto-second pulse laser into the radio frequency signal.

[0007] Optionally, the local end comprises a first femto-second optical comb, a first fiber loop, a first fiber stretcher, a first optical terminal, a first servo controller, and a first piezoelectric driver, wherein a first end of the first femto-second optical comb is connected with a first end of the first fiber loop, a second end of the first fiber loop is connected with a first end of the first fiber stretcher, a second end of the first fiber stretcher is connected with a first end of the first optical terminal, a second end of the first optical terminal is connected with the free space link, a first end of the first servo controller is connected with a first end of the first piezoelectric driver, and a second end of the first piezoelectric driver is connected with a third end of the first fiber stretcher.

[0008] Optionally, the first femto-second pulse laser generated by the first femto-second optical comb is sent to the remote end after passing through the first fiber loop, the first fiber stretcher, and the first optical terminal; and the first servo controller adjusts the repetition frequency of the first femto-second pulse laser through the first piezoelectric driver and the first fiber stretcher.

[0009] Optionally, the local end comprises an atomic clock, wherein a first end of the atomic clock is connected with a second end of the first femto-second optical comb; and the repetition frequency of the first femto-second pulse laser generated by the first femto-second optical comb is directly locked to a radio frequency signal of the atomic clock.

[0010] Optionally, the local end comprises a first photodetector, a frequency synthesizer and a first frequency mixer, wherein a first end of the first photodetector is connected with the third end of the first fiber-optic circulator, a second end of the first photodetector is connected with a first end of the first frequency mixer, a first end of the frequency synthesizer is connected with the second end of the atomic clock, a second end of the frequency synthesizer is connected with a second end of the first frequency mixer, and a third end of the first frequency mixer is connected with the second end of the first servo controller.

[0011] Optionally, the first photodetector converts the radio frequency signal corresponding to the second femtosecond pulse laser into a first target radio frequency signal, the frequency synthesizer locked to the atomic clock outputs a second target radio frequency signal, and the first frequency mixer mixes the first target radio frequency signal and the second target radio frequency signal to obtain a mixed error signal as an input signal of the first servo controller.

[0012] Optionally, the remote end comprises a second optical terminal, a fiber coupler, a fiber mirror and a second photodetector, wherein a first end of the second optical terminal is connected with the free-space link, a second end of the second optical terminal is connected with a first end of the fiber coupler, a second end of the fiber coupler is connected with the fiber mirror, and a third end of the fiber coupler is connected with the second photodetector; wherein the second optical terminal receives the first femtosecond pulse laser, and splits the first femtosecond pulse laser through the fiber coupler to form two beams of light, one of which is reflected by the fiber mirror and returns to the local end along the original path, and the other of which is converted into the radio frequency signal by the second photodetector.

[0013] Optionally, the remote end comprises a second optical terminal, a second fiber-optic circulator, a fiber-optic coupler, a second fiber-optic stretcher, a second photo-detector, a third photo-detector, a second piezoelectric driver, a second frequency mixer, and a second servo controller, wherein a first end of the second optical terminal is connected with the free-space link, a second end of the second optical terminal is connected with a first end of the second fiber-optic circulator, a second end of the second fiber-optic circulator is connected with a first end of the fiber-optic coupler, a third end of the second fiber-optic circulator is connected with a first end of the second photo-detector, a second end of the fiber-optic coupler is connected with a first end of the second fiber-optic stretcher, a third end of the fiber-optic coupler is connected with a first end of the third photo-detector, a second end of the second fiber-optic stretcher is connected with the second femto-second optical comb, a third end of the second fiber-optic stretcher is connected with a first end of the second piezoelectric driver, a second end of the second piezoelectric driver is connected with a first end of the second servo controller, a second end of the second photo-detector is connected with a first end of the second frequency mixer, a second end of the third photo-detector is connected with a second end of the second frequency mixer, and a third end of the second frequency mixer is connected with a second end of the second servo controller.

[0014] Optionally, a repetition frequency of the second femto-second pulsed laser generated by the second femto-second optical comb and a repetition frequency of the first femto-second pulsed laser generated by the first femto-second optical comb are locked to different radio frequency signal sources, respectively.

[0015] Optionally, the repetition frequency of the femto-second pulsed laser carries phase noise introduced by the free-space link.

[0016] In the embodiment of the present application, the transmission system of the radio frequency signal comprises a local end, a remote end and a free space link, the local end and the remote end are respectively arranged at two ends of the free space link, wherein the femtosecond pulse laser is used as a transmission carrier of the radio frequency signal, the femtosecond pulse laser comprises a first femtosecond pulse laser and a second femtosecond pulse laser; the local end is configured to send the first femtosecond pulse laser to the remote end, receive the second femtosecond pulse laser returned by the remote end, and perform beat processing on a repetition frequency of the second femtosecond pulse laser and a repetition frequency of the first femtosecond pulse laser to obtain a phase factor of phase noise of the free space link, and pre-compensate the repetition frequency of the first femtosecond pulse laser based on the phase factor; the remote end is configured to receive the first femtosecond pulse laser sent by the local end, send the second femtosecond pulse laser to the local end based on the first femtosecond pulse laser, and convert the first femtosecond pulse laser into a radio frequency signal. That is, the embodiment of the present application utilizes the femtosecond pulse laser which goes back and forth in the free space link, the repetition frequency signal of which carries the phase noise in the free space link, the repetition frequency signal of the returned femtosecond pulse laser is detected to perform beat processing with the repetition frequency signal of the local end to obtain the phase factor of the phase noise of the free space link, and the repetition frequency of the local end is actively pre-compensated, and the photoelectric conversion of the femtosecond pulse laser is performed to accurately reproduce the radio frequency signal of the local end at the remote end, thereby solving the technical problem that the high-precision radio frequency transmission under the free space link cannot be realized in the related art, and achieving the technical effect of realizing the high-precision transmission of the radio frequency signal in the free space link. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which are included to provide a further understanding of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and serve to explain the present application. In the drawings:

[0018] Figure 1 A schematic diagram of a transmission system of a radio frequency signal provided by the embodiment of the present application is shown in FIG. 1;

[0019] Figure 2 A schematic diagram of a transmission system of a radio frequency signal provided by the optional embodiment of the present application is shown in FIG. 2;

[0020] Figure 3 A schematic diagram of another transmission system of a radio frequency signal provided by the optional embodiment of the present application is shown in FIG. 3. DETAILED DESCRIPTION

[0021] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish different objects, rather than to limit a specific order.

[0023] According to one aspect of the present invention, a radio frequency signal transmission system is provided. Figure 1 This is a schematic diagram of a radio frequency signal transmission system provided in an embodiment of the present invention, as shown below. Figure 1 As shown, the radio frequency signal transmission system includes: a local end 12, a remote end 14, and a free space link 16. The local end 12 and the remote end 14 are respectively located at the two ends of the free space link 16. The femtosecond pulse laser is used as the transmission carrier of the radio frequency signal. The femtosecond pulse laser includes a first femtosecond pulse laser and a second femtosecond pulse laser.

[0024] Local terminal 12 is used to send a first femtosecond pulse laser to remote terminal 14, receive a second femtosecond pulse laser returned by remote terminal 14, and perform beat frequency processing on the repetition frequency of the second femtosecond pulse laser and the repetition frequency of the first femtosecond pulse laser to obtain the phase factor of the phase noise of the free space link 16, and pre-compensate the repetition frequency of the first femtosecond pulse laser based on the phase factor.

[0025] The remote end 14 is used to receive the first femtosecond pulse laser sent by the local end 12, and send the second femtosecond pulse laser to the local end 12 based on the first femtosecond pulse laser, and convert the first femtosecond pulse laser into a radio frequency signal.

[0026] It should be noted that the local end 12 can be used as the master station and the remote end 14 can be used as the slave station; the first femtosecond pulse laser is the femtosecond pulse laser emitted from the first femtosecond optical comb of the local end 12; the second femtosecond pulse laser is the femtosecond pulse laser reflected by the fiber optic mirror of the remote end 14 or the femtosecond pulse laser emitted from the second femtosecond optical comb of the remote end 14.

[0027] In the above embodiment of the present application, the transmission system of the radio frequency signal utilizes femtosecond pulse laser to and from the free space link, the repetition frequency signal of which carries the phase noise in the free space link, the repetition frequency signal of the returned femtosecond pulse laser is detected, beat processing is performed with the repetition frequency signal at the local end, the phase factor of the phase noise of the free space link is obtained, active pre-compensation is performed on the repetition frequency at the local end, and the radio frequency signal at the local end is accurately reproduced at the remote end through photoelectric conversion of the femtosecond pulse laser, thereby solving the technical problem that high-precision radio frequency transmission under the free space link cannot be realized in the related art, and achieving the technical effect of realizing high-precision transmission of the radio frequency signal under the free space link.

[0028] In an exemplary embodiment, the above-mentioned local end 12 comprises a first femtosecond optical comb, a first fiber optical circulator, a first fiber stretcher, a first optical terminal, a first servo controller and a first piezoelectric driver, wherein the first end of the first femtosecond optical comb is connected with the first end of the first fiber optical circulator, the second end of the first fiber optical circulator is connected with the first end of the first fiber stretcher, the second end of the first fiber stretcher is connected with the first end of the first optical terminal, the second end of the first optical terminal is connected with the free space link 16, the first end of the first servo controller is connected with the first end of the first piezoelectric driver, and the second end of the first piezoelectric driver is connected with the third end of the first fiber stretcher.

[0029] It should be noted that the first femtosecond pulse laser generated by the first femtosecond optical comb is transmitted to the remote end 14 after passing through the first fiber optical circulator, the first fiber stretcher and the first optical terminal; and the first servo controller adjusts the repetition frequency of the first femtosecond pulse laser through the first piezoelectric driver and the first fiber stretcher.

[0030] Further, the above-mentioned local end 12 comprises an atomic clock, wherein the first end of the atomic clock is connected with the second end of the first femtosecond optical comb; wherein the repetition frequency of the first femtosecond pulse laser generated by the first femtosecond optical comb is directly locked to the radio frequency signal of the atomic clock.

[0031] Further, the above-mentioned local end 12 comprises a first photodetector, a frequency synthesizer and a first frequency mixer, wherein the first end of the first photodetector is connected with the third end of the first fiber optical circulator, the second end of the first photodetector is connected with the first end of the first frequency mixer, the first end of the frequency synthesizer is connected with the second end of the atomic clock, the second end of the frequency synthesizer is connected with the second end of the first frequency mixer, and the third end of the first frequency mixer is connected with the second end of the first servo controller.

[0032] It should be noted that the first photodetector converts the radio frequency signal corresponding to the second femtosecond pulse laser into a first target radio frequency signal, a frequency synthesizer locked to an atomic clock outputs a second target radio frequency signal, the first frequency mixer mixes the first target radio frequency signal and the second target radio frequency signal to obtain a mixed error signal as an input signal of the first servo controller.

[0033] In an exemplary embodiment, the remote end 14 includes a second optical terminal, a fiber coupler, a fiber mirror and a second photodetector, wherein a first end of the second optical terminal is connected with the free space link 16, a second end of the second optical terminal is connected with a first end of the fiber coupler, a second end of the fiber coupler is connected with the fiber mirror, and a third end of the fiber coupler is connected with the second photodetector; wherein the second optical terminal receives the first femtosecond pulse laser and splits the first femtosecond pulse laser into two beams through the fiber coupler, one of the two beams is reflected by the fiber mirror and returns to the local end 12 along the original path, and the other beam is converted into a radio frequency signal by the second photodetector.

[0034] In an exemplary embodiment, the remote end 14 includes a second optical terminal, a second fiber circulator, a fiber coupler, a second fiber stretcher, a second photodetector, a third photodetector, a second piezoelectric driver, a second frequency mixer and a second servo controller, wherein a first end of the second optical terminal is connected with the free space link 16, a second end of the second optical terminal is connected with a first end of the second fiber circulator, a second end of the second fiber circulator is connected with a first end of the fiber coupler, a third end of the second fiber circulator is connected with a first end of the second photodetector, a second end of the fiber coupler is connected with a first end of the second fiber stretcher, a third end of the fiber coupler is connected with a first end of the third photodetector, a second end of the second fiber stretcher is connected with the second femtosecond optical comb, a third end of the second fiber stretcher is connected with a first end of the second piezoelectric driver, a second end of the second piezoelectric driver is connected with a first end of the second servo controller, a second end of the second photodetector is connected with a first end of the second frequency mixer, a second end of the third photodetector is connected with a second end of the second frequency mixer, and a third end of the second frequency mixer is connected with a second end of the second servo controller.

[0035] It should be noted that the repetition frequency of the second femtosecond pulse laser generated by the second femtosecond optical comb and the repetition frequency of the first femtosecond pulse laser generated by the first femtosecond optical comb are respectively locked to different radio frequency signal sources; in addition, the repetition frequency of the femtosecond pulse laser carries the phase noise introduced by the free space link 16.

[0036] The optional embodiments of the present application are described in detail below.

[0037] The optional embodiment of the present application provides a transmission system of radio frequency signals, which utilizes femtosecond pulse laser as a transmission carrier of the radio frequency signals, locks the repetition frequency of the femtosecond laser on a stable radio frequency signal source, transmits the femtosecond pulse laser back and forth between two stations, makes the repetition frequency of the femtosecond pulse laser carry the phase noise introduced by the free space link, mixes the degraded repetition frequency signal with a reference signal at a local end to obtain a phase factor of the phase noise of the free space link, and modulates the phase factor on the repetition frequency of the femtosecond optical comb on the basis to realize the pre-compensation of the link noise and the high-precision stable transmission of the repetition frequency radio frequency signal.

[0038] Figure 2 The optional embodiment of the present application provides a schematic diagram of a transmission system of radio frequency signals, as shown in Figure 2 The repetition frequency f r of the femtosecond optical comb 1 (corresponding to the first femtosecond optical comb) of the local end master station is directly locked on a stable radio frequency signal r f of an atomic clock. The femtosecond pulse laser emitted by the femtosecond optical comb 1 passes through an optical fiber ring 1 (corresponding to the first optical fiber ring), an optical fiber stretcher 1 (corresponding to the first optical fiber stretcher) and an optical terminal 1 (corresponding to the first optical terminal) and is emitted into a free space link for propagation, wherein a servo controller 1 (corresponding to the first servo controller) of the local end changes the repetition frequency of the femtosecond pulse laser through a piezoelectric driver 1 (corresponding to the first piezoelectric driver) and the optical fiber stretcher 1, which is equivalent to adding a compensation phase Therefore, the repetition frequency of the femtosecond pulse laser emitted by the optical terminal 1 can be expressed as During the link transmission process, the femtosecond pulse laser signal is affected by atmospheric turbulence, and the repetition frequency introduces link phase noise The femtosecond pulse laser reaches the remote slave station and is received by an optical terminal 2 (corresponding to the second optical terminal) and is split by an optical fiber coupler, part of which is reflected by an optical fiber mirror and returns along the original light path, and the other part is converted by a photodetector 2 (corresponding to the second photodetector) to output a radio frequency signal The femtosecond pulse laser reflected by the optical fiber mirror propagates through the free space link again, further degrading its repetition frequency, and according to the laser link reciprocity principle, the repetition frequency of the femtosecond pulse laser signal returned to the local end master station can be expressed as The signal passes through the optical fiber stretcher 1 again and adds a compensation signal After photoelectric conversion by a photodetector 1 (corresponding to the first photodetector), a radio frequency signal is output On the basis, a frequency synthesizer locked on the local end atomic clock outputs a radio frequency signal f rThis signal is from the same repetition frequency as the femtosecond optical comb 1. Therefore, the radio frequency signal f output by the frequency synthesizer is... r The radio frequency signal output by photodetector 1 The input mixer 1 (corresponding to the first mixer mentioned above) performs mixing, and the resulting error signal... As the input signal to servo controller 1, after the servo loop is locked, the error signal Eliminated, i.e. Therefore, the radio frequency signal output from the remote slave station This enables highly stable long-distance transmission of radio frequency signals.

[0039] Considering the significant losses in laser link transmission over long distances, which often result in low femtosecond laser signal strength and consequently weak radio frequency signal strength output from the slave photodetector 2, this invention can... Figure 2 Further improvements were made based on this foundation to achieve... Figure 3 The figure shows a free-space radio frequency transmission system based on a femtosecond optical comb, suitable for long-distance transmission links. Figure 3 A schematic diagram of another radio frequency signal transmission system provided as an optional embodiment of the present invention, as shown below. Figure 3 As shown, the master station system structure remains unchanged, while the slave station adds a femtosecond optical comb 2 (corresponding to the second femtosecond optical comb mentioned above), a servo controller 2 (corresponding to the second servo controller mentioned above), a photodetector 3 (corresponding to the third photodetector mentioned above), an optical fiber circulator 2 (corresponding to the second optical fiber circulator mentioned above), and a mixer 2 (corresponding to the second mixer mentioned above). Since the repetition frequencies of the slave station femtosecond optical comb 2 and the master station femtosecond optical comb 1 are locked to different radio frequency sources, the repetition frequency of the femtosecond optical comb 2 can be expressed as: in, This represents the repetition rate phase difference between the two optical combs. Similar to the master station principle, the femtosecond pulse laser from the slave station, after modulation by fiber stretcher 2, has a repetition frequency that can be expressed as... A portion of the femtosecond pulsed laser light passes through an optical fiber coupler into photodetector 3, where it undergoes photoelectric conversion to output a radio frequency signal. Another portion is transmitted to the main station via fiber optic coupler, fiber optic circulator 2, and optical terminal 2. Simultaneously, the femtosecond pulsed laser from the main station undergoes photoelectric conversion by photodetector 2 to obtain a radio frequency signal. The mixed signal of the output signal of photodetector 2 and the output signal of photodetector 3 is used as the input error signal of servo controller 2, that is... Servo controller 2 outputs phase compensation signal Feedback control is provided for the piezoelectric actuator 2 and the fiber optic stretcher 2. It is worth noting that in this embodiment, the master station receives a femtosecond pulsed laser signal from the slave station, which is then converted into a radio frequency signal by the photodetector 1. The signal is mixed with the radio frequency signal f r The mixing result is taken as the input error signal of the servo controller 1, i.e. Thus, the locking loops are formed in the master station and the slave station respectively. It can be seen that, in the case that both the stations are locked, That is, Therefore, the radio frequency signal output by the photoelectric detector 3 of the slave station can be expressed as That is, the high-stability remote transmission of the radio frequency signal is realized. Since the radio frequency signal output by the photoelectric detector 3 is directly generated by the femtosecond pulse laser of the femtosecond comb 2, the intensity of the signal will not decrease with the increase of the link distance, and thus the signal is very suitable for long-distance transmission link.

[0040] Further, Figure 2 The slave station in the system is suitable as a terminal of the time-frequency transmission comparison system, and the master station in the system is suitable as a relay station of the time-frequency transmission comparison system. Figure 3 The slave station in the system is suitable as a terminal of the time-frequency transmission comparison system, and the master station in the system is suitable as a relay station of the time-frequency transmission comparison system. Figure 2 , Figure 3 The master station and the slave station in the system are combined to form a network topology, so as to meet more extensive time-frequency transmission comparison requirements.

[0041] In the above embodiments of the present application, the description of each embodiment has its own focus, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0042] In the several embodiments provided by the present application, it should be understood that the present application can be implemented in other manners. The above-described apparatus embodiments are merely schematic, and the division of units is merely a logical function division, and there can be another division manner in actual implementation, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units shown or discussed can be indirect coupling or communication connection through some interfaces, and can be electrical or other forms.

[0043] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., can be located in one place or distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purposes of the embodiments.

[0044] In addition, each function unit in each embodiment of the present application can be integrated in one processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software function unit.

[0045] The above is only the preferred embodiment of the present application, and it should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A radio frequency signal transmission system, characterized in that, include: The system includes a local end, a remote end, and a free space link, wherein the local end and the remote end are respectively located at both ends of the free space link, and a femtosecond pulse laser is used as the transmission carrier of radio frequency signals, and the femtosecond pulse laser includes a first femtosecond pulse laser and a second femtosecond pulse laser. The local end is used to send the first femtosecond pulse laser to the remote end, receive the second femtosecond pulse laser returned by the remote end, and perform beat frequency processing on the repetition frequency of the second femtosecond pulse laser and the repetition frequency of the first femtosecond pulse laser to obtain the phase factor of the phase noise of the free space link, and pre-compensate the repetition frequency of the first femtosecond pulse laser based on the phase factor. The remote end is configured to receive the first femtosecond pulse laser transmitted by the local end, and based on the first femtosecond pulse laser, transmit the second femtosecond pulse laser to the local end, and convert the first femtosecond pulse laser into the radio frequency signal.

2. The transmission system according to claim 1, characterized in that, The local terminal includes a first femtosecond optical comb, a first fiber circulator, a first fiber stretcher, a first optical terminal, a first servo controller, and a first piezoelectric driver. The first end of the first femtosecond optical comb is connected to the first end of the first fiber circulator, the second end of the first fiber circulator is connected to the first end of the first fiber stretcher, the second end of the first fiber stretcher is connected to the first end of the first optical terminal, the second end of the first optical terminal is connected to the free space link, the first end of the first servo controller is connected to the first end of the first piezoelectric driver, and the second end of the first piezoelectric driver is connected to the third end of the first fiber stretcher.

3. The transmission system according to claim 2, characterized in that, The first femtosecond pulse laser generated by the first femtosecond optical comb is transmitted to the remote end after passing through the first fiber circulator, the first fiber stretcher and the first optical terminal; and the first servo controller adjusts the repetition frequency of the first femtosecond pulse laser through the first piezoelectric driver and the first fiber stretcher.

4. The transmission system according to claim 2, characterized in that, The local terminal includes an atomic clock, wherein a first end of the atomic clock is connected to a second end of the first femtosecond optical comb; wherein the repetition frequency of the first femtosecond pulse laser generated by the first femtosecond optical comb is directly locked to the radio frequency signal of the atomic clock.

5. The transmission system according to claim 4, characterized in that, The local terminal includes: a first photodetector, a frequency synthesizer, and a first mixer, wherein a first end of the first photodetector is connected to a third end of the first fiber optic circulator, a second end of the first photodetector is connected to a first end of the first mixer, a first end of the frequency synthesizer is connected to a second end of the atomic clock, a second end of the frequency synthesizer is connected to a second end of the first mixer, and a third end of the first mixer is connected to a second end of the first servo controller.

6. The transmission system according to claim 5, characterized in that, The first photodetector converts the radio frequency signal corresponding to the second femtosecond pulse laser into a first target radio frequency signal, the frequency synthesizer locked to the atomic clock outputs a second target radio frequency signal, and the first mixer mixes the first target radio frequency signal and the second target radio frequency signal to obtain a mixed error signal as the input signal of the first servo controller.

7. The transmission system according to claim 1, characterized in that, The remote end includes a second optical terminal, a fiber coupler, a fiber mirror, and a second photodetector. The first end of the second optical terminal is connected to the free-space link, the second end of the second optical terminal is connected to the first end of the fiber coupler, the second end of the fiber coupler is connected to the fiber mirror, and the third end of the fiber coupler is connected to the second photodetector. The second optical terminal receives the first femtosecond pulse laser and splits it into two beams through the fiber coupler. One beam is reflected by the fiber mirror and returns to the local end along the original path, while the other beam is converted into the radio frequency signal by the second photodetector.

8. The transmission system according to claim 2, characterized in that, The remote end includes a second optical terminal, a second fiber optic circulator, a fiber optic coupler, a second fiber optic stretcher, a second photodetector, a third photodetector, a second piezoelectric driver, a second mixer, a second servo controller, and a second femtosecond optical comb. The first end of the second optical terminal is connected to the free-space link; the second end of the second optical terminal is connected to the first end of the second fiber optic circulator; the second end of the second fiber optic circulator is connected to the first end of the fiber optic coupler; the third end of the second fiber optic circulator is connected to the first end of the second photodetector; the second end of the fiber optic coupler is connected to the first end of the second fiber optic stretcher; the third end of the fiber optic coupler is connected to the first end of the third photodetector; the second end of the second fiber optic stretcher is connected to the second femtosecond optical comb; the third end of the second fiber optic stretcher is connected to the first end of the second piezoelectric driver; the second end of the second piezoelectric driver is connected to the first end of the second servo controller; the second end of the second photodetector is connected to the first end of the second mixer; the second end of the third photodetector is connected to the second end of the second mixer; and the third end of the second mixer is connected to the second end of the second servo controller.

9. The transmission system according to claim 8, characterized in that, The repetition frequency of the second femtosecond pulse laser generated by the second femtosecond optical comb and the repetition frequency of the first femtosecond pulse laser generated by the first femtosecond optical comb are respectively locked to different radio frequency signal sources.

10. The transmission system according to any one of claims 1 to 9, characterized in that, The repetition frequency of the femtosecond pulse laser carries phase noise introduced by the free space link.

Images