CN111786726A - Radio frequency optical transmission system and method for phase-stable transmission - Google Patents
Radio frequency optical transmission system and method for phase-stable transmission Download PDFInfo
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Abstract
The invention relates to a radio frequency optical transmission system for stable phase transmission, which comprises: the optical transmission unit is used for outputting a first optical signal and a second optical signal, wherein the first optical signal and the second optical signal are homologous light, and the first optical signal and the second optical signal have frequency difference; an optical receiving unit receiving the first optical signal and splitting a part of the first optical signal to form a third optical signal; and the phase discrimination unit is converted to obtain a first radio frequency signal and a second radio frequency signal, and a phase difference signal is obtained based on the first radio frequency signal and the second radio frequency model. And the central processing unit generates a control signal based on the phase difference signal, and the light emitting unit receives the control signal and regulates and controls the first light signal. Make the frequency shift of optical domain replace the frequency reduction on the electric domain, the cost of this application on equipment has reduced, can not just need readjust the system setting because of the signal frequency change simultaneously, the practicality that improves greatly.
Description
Technical Field
The present invention relates to the field of radio frequency optical transmission, and in particular, to a phase-stabilized transmission radio frequency optical transmission system and method.
Background
The radio frequency optical transmission (ROF) technology is a new development meeting the requirements of high-speed and high-capacity wireless communication, combines light communication with wireless communication, uses optical fibers as a transmission medium, realizes transmission of broadband wireless signals, fully exerts the advantages of small attenuation of optical fiber transmission, long distance, strong anti-interference capability and the like, and can be widely applied to the fields of satellite communication, broadband radio frequency microwave signal transmission, electronic countermeasure, airborne, carrier-borne communication and the like.
Due to the characteristics of the optical fiber, transmission delay is easily changed due to environmental interference, so that the phase of a radio frequency signal loaded on the broadcast is jittered. With the continuous maturity of radio frequency optical transmission technology, the application field and scale are continuously enlarged, and the influence of phase jitter brought by transmission is more and more prominent.
In order to solve the technical problem, in the prior art, a path of dot frequency signal is usually returned to a transmitting end along with a path of normally output dot frequency signal after the dot frequency signal passes through an optical fiber of the same path, mixed with an initial dot frequency signal, phase-discriminated, and compensated by using an electronic phase discriminator. However, in this technical solution, the electronic phase discriminator has the problems of narrow working bandwidth and low phase detection precision for high-frequency signals, and the high requirement for the performance of the photodetector greatly increases the system cost.
Disclosure of Invention
Therefore, it is necessary to provide a phase-stable transmission rf optical transmission system and method, which have the advantages of large compensation range, high working bandwidth, high detection accuracy and high applicability.
A phase-stabilized transmission radio frequency optical transmission system, comprising:
the optical transmission unit is used for outputting a first optical signal and a second optical signal, wherein the first optical signal and the second optical signal are homologous light, and the first optical signal and the second optical signal have frequency difference;
an optical receiving unit receiving the first optical signal and splitting a part of the first optical signal to form a third optical signal;
the conversion phase demodulation unit is used for receiving the second optical signal and the third optical signal, coupling the second optical signal and the third optical signal to obtain a fourth optical signal, filtering the fourth optical signal to obtain a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal, converting the-1 order optical sideband of the fourth optical signal into a first radio frequency signal, converting the +1 order optical sideband of the fourth optical signal and the fourth optical signal into a second radio frequency signal, and obtaining a phase difference signal based on the first radio frequency signal and the second radio frequency model;
and the central processing unit is used for receiving the phase difference signal and generating a control signal based on the phase difference signal, and the light emitting unit is used for receiving the control signal and regulating and controlling the first light signal.
In one embodiment, the light emitting unit includes:
the optical signal modulation unit is used for modulating the initial optical signal according to the initial radio frequency signal;
the emission light splitting unit is connected with the optical signal modulation unit and is used for splitting the initial optical signal into two paths, wherein one path is an initial first optical signal, and the other path is an initial second optical signal;
and the compensation unit is connected with the emission light splitting unit and electrically connected with the central processing unit, receives the initial first optical signal and the control signal, pre-compensates the initial first optical signal based on the control signal to generate and output the first optical signal.
In one embodiment, the optical transmitting unit further includes an acousto-optic frequency shifter, and the acousto-optic frequency shifter receives the initial second optical signal and down-converts the initial second optical signal to output the second optical signal.
In one embodiment, the optical signal modulation unit comprises a Mach-Zehnder modulator, and the modulator generates a carrier-suppressed double-sideband modulation signal by adjusting the bias voltage.
In one embodiment, the light receiving unit includes a receiving optical splitting unit, configured to receive the first optical signal, one output end of the receiving optical splitting unit is connected to the light receiving unit and outputs the third optical signal, and the other output end is configured to output a fifth optical signal.
In one embodiment, the light receiving unit further includes:
the receiving optical detector is connected with one output end of the receiving optical splitting unit to receive the fifth optical signal and convert the fifth optical signal into a third radio frequency signal;
the impedance matching circuit and the radio frequency amplifying circuit are sequentially connected in series, the impedance matching circuit is electrically connected with the receiving optical detector and receives the third radio frequency signal, and the radio frequency amplifying circuit processes the third radio frequency signal to output a far-end radio frequency signal.
In one embodiment, the switching phase detection unit includes:
an optical coupler for coupling the second optical signal and the third optical signal to obtain the fourth optical signal;
an optical filter for filtering the fourth optical signal and outputting a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal;
the phase discrimination optical detector is used for converting a-1 order optical sideband of the fourth optical signal into the first radio frequency signal and converting a +1 order optical sideband of the fourth optical signal into the second radio frequency signal;
the phase discriminator, the phase discriminator with the phase discrimination light detector electricity is connected, receives first radio frequency signal with second radio frequency signal, and based on first radio frequency signal with second radio frequency signal obtains the phase difference signal, the output of phase discriminator with central processing unit electricity is connected, exports the phase difference signal extremely central processing unit.
In one embodiment, the optical coupler includes at least two input terminals, one input terminal is connected to the light emitting unit and receives the second optical signal, the other input terminal is connected to the light receiving unit and receives the third optical signal, and an output terminal of the optical coupler is connected to the optical filter and outputs the fourth optical signal to the optical filter.
In one embodiment, the optical filter is a multi-window programmable optical filter.
A radio frequency optical transmission method of phase-stable transmission comprises the following steps:
providing a first optical signal and a second optical signal based on an optical transmitting unit, wherein the first optical signal and the second optical signal are homologous light, and a frequency difference exists between the first optical signal and the second optical signal;
conducting the first optical signal to an optical receiving unit, and splitting a part of the first optical signal to form a third optical signal;
coupling the second optical signal and the third optical signal to obtain a fourth optical signal, wherein the fourth optical signal is filtered by an optical filter and then outputs a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal; converting-1 order optical sidebands of the fourth optical signal into a first radio frequency signal, converting +1 order optical sidebands of the fourth optical signal into a second radio frequency signal, and obtaining a phase difference signal based on the first radio frequency signal and the second radio frequency signal;
generating a control signal based on the phase difference signal, and regulating the first optical signal based on the control signal.
In one embodiment, the providing the first optical signal and the second optical signal based on the light emitting unit specifically includes:
providing an initial optical signal;
dividing the initial optical signal into two paths, wherein one path is an initial first optical signal, and the other path is an initial second optical signal;
pre-compensating the initial first optical signal based on the control signal to generate the first optical signal;
and performing frequency reduction processing on the initial second optical signal to obtain the second optical signal.
Has the advantages that:
by the technical scheme of the invention, the optical domain frequency shift replaces the frequency reduction in the electrical domain, all processing before the +1 order optical sideband and the-1 order optical sideband of the fourth optical signal are converted into the first radio frequency signal and the second radio frequency signal is the processing of the optical signal, no complex electric device is needed, the complexity of the system and the overall cost are reduced, the central processing unit controls the light emitting unit to regulate and control the first optical signal based on the phase difference signal, so that the working bandwidth is improved, the phase detection precision of the high-frequency signal is also improved, compared with the high requirement on the performance of the photoelectric detector in the prior art, the cost of the device is reduced, meanwhile, the system setting cannot be readjusted due to the change of the signal frequency, the practicability is greatly improved, and the method has the advantages of large compensation range, high working bandwidth, high detection precision and high applicability.
Drawings
Fig. 1 is a schematic structural diagram of an rf optical transmission system showing phase-stable transmission according to an embodiment of the present invention;
fig. 2 is a flowchart of an rf optical transmission method showing phase-stationary transmission according to an embodiment of the present invention.
Reference numerals: 10. a light emitting unit; 11. an optical signal modulation unit; 12. an emission spectroscopic unit; 13. a compensation unit; 14. an acousto-optic frequency shifter; 20. a light receiving unit; 21. a receiving light splitting unit; 22. receiving a light detector; 23. an impedance matching circuit; 24. a radio frequency amplification circuit; 30. a conversion phase discrimination unit; 31. an optical filter; 32. a phase discrimination photodetector; 33. a phase discriminator; 34. an optical coupler; 40. a central processing unit.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "vertical", "horizontal", "inner", "outer", etc. indicate orientations or positional relationships based on methods or positional relationships shown in the drawings, and are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
The radio frequency optical transmission (ROF) technology is a new development meeting the requirements of high-speed and high-capacity wireless communication, combines light communication with wireless communication, uses optical fibers as a transmission medium, realizes transmission of broadband wireless signals, fully exerts the advantages of small attenuation of optical fiber transmission, long distance, strong anti-interference capability and the like, and can be widely applied to the fields of satellite communication, broadband radio frequency microwave signal transmission, electronic countermeasure, airborne, carrier-borne communication and the like.
Due to the characteristics of the optical fiber, transmission delay is easily changed due to environmental interference, so that the phase of a radio frequency signal loaded on the broadcast is jittered. With the continuous maturity of radio frequency optical transmission technology, the application field and scale are continuously enlarged, and the influence of phase jitter brought by transmission is more and more prominent.
In the prior art, a path of point frequency signal is usually returned to a transmitting end along with a normally output point frequency signal after the point frequency signal passes through an optical fiber of the same path, mixed with an initial point frequency signal, phase-discriminated, and compensated by an electronic phase discriminator. However, in this technical solution, the electronic phase discriminator has the problems of narrow working bandwidth and low phase detection precision for high-frequency signals, and the high requirement for the performance of the photodetector greatly increases the system cost.
In order to solve the above problem, as shown in fig. 1, the present invention provides a phase-stable transmission rf optical transmission system, including: the optical transmitter includes an optical transmitting unit 10 configured to output a first optical signal and a second optical signal, where the first optical signal and the second optical signal are homologous light and have a frequency difference; an optical receiving unit 20 receiving the first optical signal and splitting a part of the first optical signal to form a third optical signal; the conversion phase discrimination unit 30 receives the second optical signal and the third optical signal, couples the second optical signal and the third optical signal to obtain a fourth optical signal, filters the fourth optical signal to obtain a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal, converts the-1 order optical sideband of the fourth optical signal into a first radio frequency signal, converts the +1 order optical sideband of the fourth optical signal into a second radio frequency signal, and obtains a phase difference signal based on the first radio frequency signal and the second radio frequency model; and a central processing unit 40 receiving the phase difference signal and generating a control signal based on the phase difference signal, and the light emitting unit 10 receiving the control signal and regulating the first light signal.
Through the above technical solution, when the first optical signal sent by the optical transmitting unit 10 is transmitted to the optical receiving unit 20, because phase jitter is introduced due to environment conversion, the optical receiving unit 20 divides the first optical signal into one path to form a third optical signal, converts-1 order optical sidebands of the second optical signal and the third optical signal into a first radio frequency signal, converts +1 order optical sidebands of the second optical signal and the third optical signal into a second radio frequency signal, and a phase difference obtained by comparing the two radio frequency signals can reflect the phase jitter introduced in the transmission process, and the central processing unit 40 can regulate and control the first optical signal based on a control signal formed by the phase difference signal. The technical scheme of the invention enables the optical domain frequency shift to replace the frequency reduction in the electrical domain, all processing before converting the second optical signal and the third optical signal into the first radio frequency signal and the second radio frequency signal is to process the optical signals, complex electric devices are not needed, the complexity and the overall cost of the system are reduced, the central processing unit 40 controls the light emitting unit 10 to regulate and control the first optical signal based on the phase difference signal, the working bandwidth is improved, the phase detection precision of the high-frequency signal is also improved, compared with the high requirement on the performance of the photoelectric detector in the prior art, the cost of the device is reduced, the system setting does not need to be readjusted due to the change of the signal frequency, the practicability is greatly improved, and the device has the advantages of large compensation range, high working bandwidth, high detection precision and high applicability.
In an alternative embodiment, the light emitting unit 10 includes: an optical signal modulation unit 11, configured to modulate an initial optical signal according to an initial radio frequency signal; the emission light splitting unit 12 is connected with the optical signal modulation unit 11 and is used for splitting the initial optical signal into two paths, wherein one path is an initial first optical signal, and the other path is an initial second optical signal; and the compensation unit 13 is connected with the emission light splitting unit 12 and electrically connected with the central processing unit 40, and the compensation unit 13 receives the initial first optical signal and the control signal, pre-compensates the initial first optical signal based on the control signal to generate and output the first optical signal.
In an alternative embodiment, the optical signal modulation unit 11 includes a mach-zehnder modulator and a laser, and the modulator generates a carrier-suppressed double-sideband modulation signal by adjusting the bias voltage. The Mach-Zehnder modulator is connected with the laser through an optical fiber, a laser optical signal emitted by the laser is input into the Mach-Zehnder modulator, and an initial radio frequency signal enters the Mach-Zehnder modulator to modulate the laser optical signal. And adjusting the direct current bias voltage of the Mach-Zehnder modulator to enable the Mach-Zehnder modulator to work at the lowest point of a transmission curve so as to generate the initial optical signal with suppressed carrier. The emission light splitting unit 12 may be an optical splitter, and the emission light splitting unit 12 splits the initial optical signal into two parts, one part becomes the initial first optical signal, and the other part becomes the initial second optical signal, because the initial first optical signal and the initial second optical signal are originally the same as the initial optical signal, the phases of the two are the same.
The compensation unit 13 includes, but is not limited to: light-adjustable delay line, temperature control optical fiber, piezoelectric ceramic optical fiber, optical fiber stretcher, electric-adjustable delay line, temperature-controllable box, etc. One input end of the compensation unit 13 receives the initial first optical signal, and the other receiving end receives the control signal sent by the central processing unit 40, compensates the initial first optical signal according to the control signal, and outputs the first optical signal from the output end of the compensation unit 13.
In an optional embodiment, the optical transmitting unit 10 further includes an acousto-optic frequency shifter 14, the acousto-optic frequency shifter 14 receives the initial second optical signal and down-converts the initial second optical signal to output a second optical signal, and the down-conversion of the second optical signal by the acousto-optic frequency shifter 14 is more stable than the down-conversion in the electrical domain.
In an alternative embodiment, the light receiving unit 20 includes a receiving optical splitting unit 21 for receiving the first optical signal, one output terminal of the receiving optical splitting unit 21 is connected to the light receiving unit 20 and outputs the third optical signal, and the other output terminal is used for outputting the fifth optical signal. The receiving and splitting unit 21 may be an optical splitter, and an input end of the receiving and splitting unit 21 is connected to an output end of the compensation unit 13 through an optical fiber to receive the first optical signal output by the compensation unit 13. The receiving and splitting unit 21 splits the first optical signal into two paths, one path is a third optical signal, the other path is a fifth optical signal, one output end of the receiving and splitting unit 21 is connected with the conversion phase discrimination unit 30 through an optical fiber, and the third optical signal is transmitted to the conversion phase discrimination unit 30 through the optical fiber.
In an alternative embodiment, the light receiving unit 20 further includes: the receiving optical detector 22 is connected to an output end of the receiving and splitting unit 21 to receive the fifth optical signal and convert the fifth optical signal into a third radio frequency signal; the impedance matching circuit 23 and the radio frequency amplifying circuit 24 are sequentially connected in series, the impedance matching circuit 23 is electrically connected with the receiving optical detector 22 and receives a third radio frequency signal, and the radio frequency amplifying circuit 24 processes the third radio frequency signal to output a far-end radio frequency signal.
In an alternative embodiment, the transition phase detection unit 30 includes: an optical coupler 34 for coupling the second optical signal and the third optical signal to obtain a fourth optical signal; an optical filter 31 for filtering the fourth optical signal and outputting a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal; the phase discrimination optical detector 32 is configured to convert a-1 order optical sideband of the fourth optical signal into a first radio frequency signal, and convert a +1 order optical sideband of the fourth optical signal into a second radio frequency signal; the phase detector 33, the phase detector 33 is electrically connected with the phase detection photodetector 32, receives the first radio frequency signal and the second radio frequency signal, and obtains a phase difference based on the first radio frequency signal and the second radio frequency signal, an output end of the phase detector 33 is electrically connected with the central processing unit 40, and outputs a phase difference signal to the central processing unit 40.
In an alternative embodiment, the optical coupler 34 comprises at least two input terminals, one input terminal is connected to the light emitting unit 10 and receives the second optical signal, the other input terminal is connected to the light receiving unit 20 and receives the third optical signal, the output terminal of the optical coupler 34 is connected to the optical filter 31, and outputs the fourth optical signal to the optical filter 31, the optical filter 31 outputs the +1 order optical sideband and the-1 order optical sideband of the fourth optical signal after filtering, therefore, when the first radio frequency signal and the second radio frequency signal are obtained, the high-frequency third optical signal is not processed to obtain the high-frequency radio frequency signal, instead, the-1 order optical sideband of the fourth optical signal is converted into the first radio frequency signal, the +1 order optical sideband of the fourth optical signal is converted into the second radio frequency signal, and the obtained first radio frequency signal and the second radio frequency signal do not need to be subjected to frequency reduction processing in an electrical domain in subsequent processing.
The optical filter 31 is a multi-window programmable optical filter 31, the second optical signal and the second optical signal pass through an optical coupler 34 to form a fourth optical signal, the fourth optical signal is sent into the optical filter 31 for filtering to obtain two paths of optical signals with different wavelengths, each path of optical signal includes two optical carriers with similar wavelengths, and two central passband frequencies of the optical filter 31 are respectively close to the upper and lower sideband frequencies of the carrier suppressed double-sideband modulation signal output by the optical signal modulation unit 11. Two output ends of the optical filter 31 are respectively connected with the two phase discrimination photodetectors 32 through optical fibers, and a-1 order optical sideband of the fourth optical signal and a +1 order optical sideband of the fourth optical signal are respectively sent into the two phase discrimination photodetectors 32 to be converted into a first radio frequency signal and a second radio frequency signal.
The phase difference between the first radio frequency signal and the second radio frequency signal can be obtained by comparing the first radio frequency signal and the second radio frequency signal through the phase discriminator 33, that is, the phase difference between the third optical signal and the second optical signal is obtained, and the phase jitter introduced when the radio frequency signals are transmitted in a link is obtained. The output voltage of the phase detector 33 is determined by the phase difference between the second optical signal and the third optical signal, and the output voltage is the phase difference signal. The central processing unit 40 can utilize the phase difference signal to control the compensation unit 13 to compensate the initial first optical signal through a compensation algorithm to generate a first optical signal, pre-compensate the phase jitter introduced by the environmental transformation, and finally obtain an output far-end radio frequency signal with stable phase at the far end, so as to implement phase-stable transmission, where the central processing unit 40 includes but is not limited to: microprocessors, programmable logic controllers, field programmable gate arrays, operational amplifiers, analog circuits, and the like.
As shown in fig. 2, the present invention further provides a phase-stabilized transmission rf optical transmission method, including the following steps:
step S10: providing a first optical signal and a second optical signal based on the optical transmitting unit 10, wherein the first optical signal and the second optical signal are homologous light, and a frequency difference exists between the first optical signal and the second optical signal;
step S20: conducting the first optical signal to the optical receiving unit 20 and splitting a portion of the first optical signal to form a third optical signal;
step S30: coupling the second optical signal with the third optical signal to obtain a fourth optical signal, and outputting a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal after the fourth optical signal is filtered by the optical filter 31; converting a-1 order optical sideband of the fourth optical signal into a first radio frequency signal, converting a +1 order optical sideband of the fourth optical signal into a second radio frequency signal, and obtaining a phase difference signal based on the first radio frequency signal and the second radio frequency signal;
step S40: a control signal is generated based on the phase difference signal, and the first optical signal is regulated based on the control signal.
For step S10, the following steps are included:
step S101: providing an initial optical signal;
step S102: dividing the initial optical signal into two paths, wherein one path is an initial first optical signal, and the other path is an initial second optical signal;
step S103: pre-compensating the initial first optical signal based on the control signal to generate a first optical signal;
step S104: and performing frequency reduction processing on the initial second optical signal to obtain a second optical signal.
Specifically, the first optical signal and the second optical signal are output through the light emitting unit 10, and the light emitting unit 10 includes: an optical signal modulation unit 11, a transmitting light splitting unit 12, a compensation unit 13 and an acousto-optic frequency shifter 14. The optical signal modulation unit 11 includes a mach-zehnder modulator and a laser, the mach-zehnder modulator is connected with the laser through an optical fiber, a laser optical signal emitted by the laser is input into the mach-zehnder modulator, and an initial radio frequency signal enters the mach-zehnder modulator to modulate the laser optical signal. And adjusting the direct current bias voltage of the Mach-Zehnder modulator to enable the Mach-Zehnder modulator to work at the lowest point of a transmission curve so as to generate the initial optical signal with suppressed carrier. The emission light splitting unit 12 may be an optical splitter, and the emission light splitting unit 12 splits the initial optical signal into two parts, one part becomes the initial first optical signal, and the other part becomes the initial second optical signal, because the initial first optical signal and the initial second optical signal are originally the same as the initial optical signal, the phases of the two are the same.
The compensation unit 13 includes, but is not limited to: light-adjustable delay line, temperature control optical fiber, piezoelectric ceramic optical fiber, optical fiber stretcher, electric-adjustable delay line, temperature-controllable box, etc. One input end of the compensation unit 13 receives the initial first optical signal, and the other receiving end receives the control signal sent by the central processing unit 40, compensates the initial first optical signal according to the control signal, and outputs the first optical signal from the output end of the compensation unit 13.
The acousto-optic frequency shifter 14 receives the initial second optical signal, performs frequency reduction processing on the initial second optical signal, and outputs a second optical signal, and the frequency reduction of the second optical signal by the acousto-optic frequency shifter 14 is more stable than that of the frequency reduction in the electrical domain.
For step S20, specifically, the light receiving unit 20 includes a light receiving and splitting unit 21 for receiving the first optical signal, one output terminal of the light receiving and splitting unit 21 is connected to the light receiving unit 20 and outputs the third optical signal, and the other output terminal is used for outputting the fifth optical signal. The receiving and splitting unit 21 may be an optical splitter, and an input end of the receiving and splitting unit 21 is connected to an output end of the compensation unit 13 through an optical fiber to receive the first optical signal output by the compensation unit 13. The receiving and splitting unit 21 splits the first optical signal into two paths, one path is a third optical signal, the other path is a fifth optical signal, one output end of the receiving and splitting unit 21 is connected with the conversion phase discrimination unit 30 through an optical fiber, and the third optical signal is transmitted to the conversion phase discrimination unit 30 through the optical fiber.
As for step S30, specifically, the second optical signal and the third optical signal may be coupled by an optical coupler 34, the optical coupler 34 includes at least two input ends, one input end is connected to the optical transmitting unit 10 and receives the second optical signal, the other input end is connected to the optical receiving unit 20 and receives the third optical signal, the output end of the optical coupler 34 is connected to the optical filter 31 and outputs the fourth optical signal to the optical filter 31, and the optical filter 31 filters and outputs the +1 order optical sideband and the-1 order optical sideband of the fourth optical signal, so that when the first radio frequency signal and the second radio frequency signal are obtained, instead of processing the high-frequency third optical signal to obtain a high-frequency radio frequency signal, the-1 order optical sideband of the fourth optical signal is converted into the first radio frequency signal, the +1 order optical sideband of the fourth optical signal is converted into the second radio frequency signal, and the obtained first radio frequency signal and the second radio frequency signal do not need to be subjected to frequency domain down-conversion in subsequent processing And (6) processing.
The optical filter 31 is a multi-window programmable optical filter 31, the second optical signal and the second optical signal pass through an optical coupler 34 to form a fourth optical signal, the fourth optical signal is sent into the optical filter 31 for filtering to obtain two paths of optical signals with different wavelengths, each path of optical signal includes two optical carriers with similar wavelengths, and two central passband frequencies of the optical filter 31 are respectively close to the upper and lower sideband frequencies of the carrier suppressed double-sideband modulation signal output by the optical signal modulation unit 11.
Two output ends of the optical filter 31 are respectively connected with the two phase discrimination photodetectors 32 through optical fibers, and a-1 order optical sideband of the fourth optical signal and a +1 order optical sideband of the fourth optical signal are respectively sent into the two phase discrimination photodetectors 32 to be converted into a first radio frequency signal and a second radio frequency signal. The phase difference between the first radio frequency signal and the second radio frequency signal can be obtained by comparing the first radio frequency signal and the second radio frequency signal through the phase discriminator 33, that is, the phase difference between the third optical signal and the second optical signal is obtained, and the phase jitter introduced when the radio frequency signals are transmitted in a link is obtained.
For step S40, specifically, the output voltage of the phase detector 33 is determined by the phase difference between the second optical signal and the third optical signal, and the output voltage is the phase difference signal. The central processing unit 40 may be utilized to control the compensation unit 13 to compensate the initial first optical signal through a compensation algorithm based on the phase difference signal to generate a first optical signal, and to pre-compensate the phase jitter introduced by the environmental transformation, and finally obtain an output far-end radio frequency signal with a stable phase at the far end, so as to implement phase-stable transmission.
By the technical scheme of the invention, the optical domain frequency shift replaces the frequency reduction in the electrical domain, all processing before the +1 order optical sideband and the-1 order optical sideband of the fourth optical signal are converted into the first radio frequency signal and the second radio frequency signal is the processing of the optical signal, no complex electric device is needed, the complexity of the system and the overall cost are reduced, the central processing unit 40 controls the light emitting unit 10 to regulate and control the first optical signal based on the phase difference signal, so that the working bandwidth is improved, the phase detection precision of the high-frequency signal is also improved, compared with the high requirement on the performance of the photoelectric detector in the prior art, the cost of the device is reduced, meanwhile, the system setting cannot be readjusted due to the change of the signal frequency, the practicability is greatly improved, and the method has the advantages of large compensation range, high working bandwidth, high detection precision and high applicability.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above examples only show some embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (11)
1. A phase-stabilized transmission radio frequency optical transmission system, comprising:
the optical transmission unit is used for outputting a first optical signal and a second optical signal, wherein the first optical signal and the second optical signal are homologous light, and the first optical signal and the second optical signal have frequency difference;
an optical receiving unit receiving the first optical signal and splitting a part of the first optical signal to form a third optical signal;
the conversion phase demodulation unit is used for receiving the second optical signal and the third optical signal, coupling the second optical signal and the third optical signal to obtain a fourth optical signal, filtering the fourth optical signal to obtain a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal, converting the-1 order optical sideband of the fourth optical signal into a first radio frequency signal, converting the +1 order optical sideband of the fourth optical signal and the fourth optical signal into a second radio frequency signal, and obtaining a phase difference signal based on the first radio frequency signal and the second radio frequency model;
and the central processing unit is used for receiving the phase difference signal and generating a control signal based on the phase difference signal, and the light emitting unit is used for receiving the control signal and regulating and controlling the first light signal.
2. The phase-stable transmission radio-frequency optical transmission system according to claim 1, wherein the light emitting unit includes:
the optical signal modulation unit is used for modulating the initial optical signal according to the initial radio frequency signal;
the emission light splitting unit is connected with the optical signal modulation unit and is used for splitting the initial optical signal into two paths, wherein one path is an initial first optical signal, and the other path is an initial second optical signal;
and the compensation unit is connected with the emission light splitting unit and electrically connected with the central processing unit, receives the initial first optical signal and the control signal, pre-compensates the initial first optical signal based on the control signal to generate and output the first optical signal.
3. The phase-stable transmission radio-frequency optical transmission system according to claim 2, wherein the optical transmission unit further includes an acousto-optic frequency shifter, and the acousto-optic frequency shifter receives the initial second optical signal, down-converts the initial second optical signal, and outputs the second optical signal.
4. The phase-stabilized transmission radio-frequency optical transmission system according to claim 2, wherein the optical signal modulation unit includes a mach-zehnder modulator, and the modulator generates a carrier-suppressed double-sideband modulation signal by adjusting a bias voltage.
5. The phase-stable transmission radio-frequency optical transmission system according to claim 1, wherein the optical receiving unit includes a receiving splitter unit configured to receive the first optical signal, one output end of the receiving splitter unit is connected to the optical receiving unit and outputs the third optical signal, and the other output end is configured to output a fifth optical signal.
6. The phase-stable transmission radio-frequency optical transmission system according to claim 5, wherein the optical receiving unit further includes:
the receiving optical detector is connected with one output end of the receiving optical splitting unit to receive the fifth optical signal and convert the fifth optical signal into a third radio frequency signal;
the impedance matching circuit and the radio frequency amplifying circuit are sequentially connected in series, the impedance matching circuit is electrically connected with the receiving optical detector and receives the third radio frequency signal, and the radio frequency amplifying circuit processes the third radio frequency signal to output a far-end radio frequency signal.
7. The phase-stabilized transmission radio-frequency optical transmission system according to claim 1, wherein the switching phase detection unit includes:
an optical coupler for coupling the second optical signal and the third optical signal to obtain the fourth optical signal;
an optical filter for filtering the fourth optical signal and outputting a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal;
the phase discrimination optical detector is used for converting a-1 order optical sideband of the fourth optical signal into the first radio frequency signal and converting a +1 order optical sideband of the fourth optical signal into the second radio frequency signal;
the phase discriminator, the phase discriminator with the phase discrimination light detector electricity is connected, receives first radio frequency signal with second radio frequency signal, and based on first radio frequency signal with second radio frequency signal obtains the phase difference signal, the output of phase discriminator with central processing unit electricity is connected, exports the phase difference signal extremely central processing unit.
8. The phase-stable transmission radio-frequency optical transmission system according to claim 7, wherein the optical coupler includes at least two input ends, one input end is connected to the light emitting unit and receives the second optical signal, the other input end is connected to the light receiving unit and receives the third optical signal, and an output end of the optical coupler is connected to the optical filter and outputs the fourth optical signal to the optical filter.
9. The phase-stable transmission radio frequency optical transmission system according to claim 8, wherein the optical filter is a multi-window programmable optical filter.
10. A radio frequency optical transmission method of phase-stable transmission is characterized by comprising the following steps:
providing a first optical signal and a second optical signal based on an optical transmitting unit, wherein the first optical signal and the second optical signal are homologous light, and a frequency difference exists between the first optical signal and the second optical signal;
conducting the first optical signal to an optical receiving unit, and splitting a part of the first optical signal to form a third optical signal;
coupling the second optical signal and the third optical signal to obtain a fourth optical signal, wherein the fourth optical signal is filtered by an optical filter and then outputs a +1 order optical sideband and a-1 order optical sideband of the fourth optical signal; converting-1 order optical sidebands of the fourth optical signal into a first radio frequency signal, converting +1 order optical sidebands of the fourth optical signal into a second radio frequency signal, and obtaining a phase difference signal based on the first radio frequency signal and the second radio frequency signal;
generating a control signal based on the phase difference signal, and regulating the first optical signal based on the control signal.
11. The phase-stable transmission radio-frequency optical transmission method according to claim 10, wherein providing the first optical signal and the second optical signal based on the optical transmitting unit specifically includes:
providing an initial optical signal;
dividing the initial optical signal into two paths, wherein one path is an initial first optical signal, and the other path is an initial second optical signal;
pre-compensating the initial first optical signal based on the control signal to generate the first optical signal;
and performing frequency reduction processing on the initial second optical signal to obtain the second optical signal.
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