System for transmitting radio frequency signals over optical fiber

Abstract

The application discloses a system for transmitting radio frequency signals through an optical fiber, which comprises a power divider for dividing a radio frequency input signal into at least a first radio frequency sub-signal and a second radio frequency sub-signal; a phase shifter for adjusting the phase and / or amplitude of the first radio frequency sub-signal; a first laser for generating a first laser signal according to the first radio frequency sub-signal after phase adjustment; an optical fiber transmission link for transmitting the first laser signal; a first photodetector for demodulating the received first laser signal into a radio frequency signal; an electrical coupler for dividing the radio frequency signal into the radio frequency input signal and a radio frequency feedback signal; a second laser for generating a second laser signal according to the radio frequency feedback signal; a second photodetector for demodulating the received second laser signal into a first radio frequency detection signal; and a control unit for determining a phase adjustment amount according to the second radio frequency sub-signal and the first radio frequency detection signal; and the phase shifter is used for adjusting the phase and / or amplitude of the first radio frequency sub-signal according to the phase adjustment amount.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of information communication technology, and in particular to a system for transmitting radio frequency signals through optical fiber. BACKGROUND

[0002] Radio frequency signals are widely used in many fields. Radio frequency signals are transmitted through optical fiber as a transmission medium. The radio frequency signals are modulated to the light signal of a continuous wave laser at the transmitting end and transmitted through the optical fiber. Then, the light signal is demodulated into an electrical signal at the receiving end. For some applications, a radio frequency signal as a signal source needs to be distributed to multiple remote sites synchronously, while maintaining the short-term phase noise and long-term phase stability. The phase noise level can be achieved by using a low-noise laser and a detector. However, the noise of the light signal will be deteriorated due to Rayleigh scattering and backscattering effects during the transmission of the optical fiber, and the degree is usually related to the length of the optical fiber. The change of the environmental temperature will cause the change of the refractive index of the optical fiber, resulting in the change of the optical path of the light signal, and thus causing the phase slow drift of the radio frequency signal carried by the optical carrier. How to ensure the phase stability of the radio frequency signal transmitted through the optical fiber is a technical problem to be solved by those skilled in the art. SUMMARY

[0003] The present application provides a system for transmitting radio frequency signals through optical fiber, which at least ensures the phase stability of the radio frequency signals transmitted through the optical fiber.

[0004] The present application provides a system for transmitting radio frequency signals through optical fiber, comprising:

[0005] a power divider for dividing the radio frequency input signal into at least a first radio frequency sub-signal and a second radio frequency sub-signal;

[0006] a phase shifter connected to the power divider for adjusting the phase and / or amplitude of the first radio frequency sub-signal;

[0007] a first laser connected to the phase shifter for generating a first laser signal according to the first radio frequency sub-signal after phase adjustment.

[0008] an optical fiber transmission link, a first end of the optical fiber transmission link being connected to the first laser for transmitting the first laser signal;

[0009] a first photodetector connected to a second end of the optical fiber transmission link for demodulating the received first laser signal into a radio frequency signal;

[0010] an electrical coupler connected to the first photodetector for dividing the radio frequency signal into a radio frequency input signal and a radio frequency feedback signal;

[0011] a second laser, connected with the electrical coupler, for generating a second laser signal according to the radio frequency feedback signal and inputting the second laser signal into the optical fiber transmission link from the second end;

[0012] a second photoelectric detector, connected with the first end of the optical fiber transmission link, for demodulating the received second laser signal into a first radio frequency detection signal;

[0013] a control unit, connected with the power divider and the second photoelectric detector respectively, for determining a phase adjustment amount according to the second radio frequency sub-signal and the first radio frequency detection signal;

[0014] the phase shifter is configured to adjust the phase and / or amplitude of the first radio frequency sub-signal according to the phase adjustment amount.

[0015] As an implementation manner, the control unit comprises a phase-discrimination module and a calculation module.

[0016] The phase-discrimination module determines an A component and a Φ component of a phase difference signal between the second radio frequency sub-signal and the first radio frequency detection signal according to the following relationship respectively, and the phase adjustment amount at least comprises a difference value of the Φ component between the second radio frequency sub-signal and the first radio frequency detection signal.

[0017]

[0018] Φ=arctan(Q / I);

[0019] Wherein, A is the amplitude of the radio frequency signal in the polar coordinate system, Φ is the phase of the radio frequency signal in the polar coordinate system, I is the in-phase component of the radio frequency signal in the rectangular coordinate system, and Q is the quadrature component of the radio frequency signal in the rectangular coordinate system.

[0020] As an implementation manner, an optical coupler is connected between the first end and the first laser, and a third photoelectric detector is connected with the optical coupler.

[0021] The optical coupler is configured to couple part of the first laser signal to the third photoelectric detector.

[0022] The third photoelectric detector is configured to generate a second radio frequency detection signal according to the first laser signal coupled into the third photoelectric detector.

[0023] The control unit is further configured to determine the working state of the first laser according to the second radio frequency detection signal.

[0024] As an implementation manner, an amplifier is connected between the first photoelectric detector and the electrical coupler, and the amplifier is configured to amplify the radio frequency signal output by the first photoelectric detector.

[0025] As an implementation manner, the optical fiber transmission link comprises an optical fiber, one end of the optical fiber is connected with the first optical circulator, and the other end of the optical fiber is connected with the second optical circulator.

[0026] The first optical circulator is connected with the optical coupler and the second photodetector respectively.

[0027] The second optical circulator is connected with the second laser and the first photodetector respectively.

[0028] As an implementation manner, the first constant temperature device, the second constant temperature device, the third constant temperature device and the fourth constant temperature device are provided.

[0029] The power divider is arranged in the first constant temperature device.

[0030] The phase shifter, the first laser, the first optical circulator, the second photodetector, the third photodetector and the phase discrimination module are arranged in the second constant temperature device.

[0031] The first photodetector, the second laser, the electrical coupler and the amplifier are arranged in the third constant temperature device.

[0032] The calculation module is arranged in the fourth constant temperature device.

[0033] As an implementation manner, the first constant temperature device, the second constant temperature device, the third constant temperature device and the fourth constant temperature device are provided.

[0034] As an implementation manner, the first constant temperature device, the second constant temperature device, the third constant temperature device and the fourth constant temperature device are provided.

[0035] Each temperature sensor is connected to a temperature controller, and the temperature controller controls the refrigeration capacity of the corresponding semiconductor refrigeration piece according to the collection information of each temperature sensor.

[0036] As an implementation manner, the frequency of the first laser signal and the second laser signal is different.

[0037] As an implementation manner, the frequency of the first laser signal and the second laser signal is different.

[0038] The above scheme provided by the application is that the first photoelectric detector demodulates the received first laser signal into a radio frequency signal, that is, restores the first laser signal into a radio frequency signal, the electric coupler takes out part of the restored radio frequency signal as a radio frequency feedback signal, and the second laser generates a second laser signal, which is transmitted to the transmitting end through an optical fiber transmission link and is demodulated into a first radio frequency detection signal by the second photoelectric detector, and the control unit determines the phase adjustment amount according to the second radio frequency sub-signal and the first radio frequency detection signal; and the phase shifter adjusts the phase and / or amplitude of the first radio frequency sub-signal according to the phase adjustment amount, so as to compensate for the phase slow drift of the radio frequency signal carried by the optical carrier in the optical fiber transmission, and further ensure the phase stability of the radio frequency signal transmitted through the optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0039] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the drawings:

[0040] Figure 1 A system schematic diagram for realizing radio frequency signal transmission through an optical fiber is provided for an embodiment of the application.

[0041] Figure 2 A principle diagram for determining a phase adjustment amount is provided for an embodiment of the application.

[0042] Figure 3 A system schematic diagram for realizing radio frequency signal transmission through an optical fiber is provided for another embodiment of the application.

[0043] Figure 4 A system schematic diagram for realizing radio frequency signal transmission through an optical fiber is provided for another embodiment of the application. DETAILED DESCRIPTION

[0044] The application will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and not to limit the application. In addition, it should be noted that only parts related to the application are shown in the drawings for ease of description.

[0045] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict. The application will be described in detail below with reference to the drawings and embodiments.

[0046] As shown in Figure 1 The system for realizing radio frequency signal transmission through an optical fiber provided by the embodiment of the application comprises:

[0047] The power divider 1 is used for dividing the radio frequency input signal into at least a first radio frequency sub-signal and a second radio frequency sub-signal; the power divider 1 can be selected according to actual needs to divide the radio frequency signal into 2, 3, 4, 6, 8 or 12 radio frequency sub-signals; in this example, the radio frequency signal is divided into two radio frequency sub-signals, which are the first radio frequency sub-signal and the second radio frequency sub-signal.

[0048] The phase shifter 2 is connected with the power divider 1 and is used for adjusting the phase and / or amplitude of the first radio frequency sub-signal; in this example, the phase shifter 2 adopts IQ (In-phase Quadrature-phase) modulation, and the phase detection module 31 in the following adopts IQ demodulation.

[0049] The first laser 6 is connected with the phase shifter 2 and is used for generating a first laser signal according to the first radio frequency sub-signal after phase adjustment; each laser referred to herein is, for example but not limited to, a distributed feedback fiber laser (DFB-FL).

[0050] The fiber transmission link 8 has a first end connected with the first laser 6 and is used for transmitting the first laser signal; the first laser signal produced by the first laser 6 is coupled into the fiber transmission link 8 for transmission. One side of the first laser 6 is set as a transmitting end.

[0051] The first photodetector 9 is connected with a second end of the fiber transmission link 8 and is used for demodulating the received first laser signal into a radio frequency signal; each photodetector referred to herein is, for example but not limited to, an intrinsic PN junction photodiode, a PIN junction photodiode or an APD avalanche diode, etc. The first photodetector 9 is set as a receiving end.

[0052] The electrical coupler 11 is connected with the first photodetector 9 and is used for dividing the radio frequency signal into a radio frequency input signal and a radio frequency feedback signal;

[0053] The second laser 12 is connected with the electrical coupler 11 and is used for generating a second laser signal according to the radio frequency feedback signal and inputting the second laser signal into the fiber transmission link 8 from the second end;

[0054] The second photodetector 5 is connected with the first end of the fiber transmission link 8 and is used for demodulating the received second laser signal into a first radio frequency detection signal;

[0055] The control unit 3 is connected with the power divider 1 and the second photodetector 5 respectively and is used for determining a phase adjustment amount according to the second radio frequency sub-signal and the first radio frequency detection signal;

[0056] The phase shifter 2 is configured to adjust the phase and / or amplitude of the first radio frequency sub-signal according to the phase adjustment amount.

[0057] The first photoelectric detector 9 demodulates the first laser signal into a radio frequency signal, that is, restores the first laser signal into a radio frequency signal, the electrical coupler 11 takes out part of the restored radio frequency signal as a radio frequency feedback signal, and the second laser 12 generates a second laser signal, which is transmitted to the transmitting end through the optical fiber transmission link 8 and demodulated into a first radio frequency detection signal by the second photoelectric detector 5. The control unit 3 determines the phase adjustment amount according to the second radio frequency sub-signal and the first radio frequency detection signal. The phase shifter 2 adjusts the phase and / or amplitude of the first radio frequency sub-signal according to the phase adjustment amount, so as to compensate for the phase slow drift of the radio frequency signal carried by the optical carrier in the optical fiber transmission, and further ensure the phase stability of the radio frequency signal transmitted through the optical fiber.

[0058] As an implementation manner, referring to Figure 2 , the control unit 3 comprises a phase discrimination module 31 and a calculation module 32. The calculation module 32 can be a software implementation manner, which can run in a CPU, FPGA, etc.

[0059] The phase discrimination module 31 determines the A component and the Φ component of the phase difference signal between the second radio frequency sub-signal and the first radio frequency detection signal according to the following relationship, and the phase adjustment amount at least comprises the difference between the Φ components of the second radio frequency sub-signal and the first radio frequency detection signal.

[0060]

[0061] Φ = arctan (Q / I) ;

[0062] Wherein, A is the amplitude of the radio frequency signal in the polar coordinate system, Φ is the phase of the radio frequency signal in the polar coordinate system, I is the in-phase component of the radio frequency signal in the rectangular coordinate system, and Q is the quadrature component of the radio frequency signal in the rectangular coordinate system.

[0063] The second radio frequency sub-signal and the first radio frequency detection signal are IQ demodulated by the phase discrimination module 31, and the I component and the Q component of the phase difference signal between the second radio frequency sub-signal and the first radio frequency detection signal are output, and the A component and the Φ component corresponding thereto are obtained according to the above formula, and at least the difference of the Φ component between the second radio frequency sub-signal and the first radio frequency detection signal is determined as the phase adjustment amount. Since the second laser signal is generated based on the first laser signal, it is equivalent to that the second laser signal is transmitted twice in the optical fiber transmission link 8, so the phase slow drift is twice of the phase slow drift of the received end radio frequency signal, and therefore half of the phase error is compensated in the phase. Of course, in actual situation, there are also errors caused by other measurement systems, in order to obtain more accurate compensation, the phase adjustment amount can be determined by the PID (Proportional Integral Derivative; proportional-integral-differential) algorithm.

[0064] As shown in Figure 2 , the second radio frequency sub-signal and the first radio frequency detection signal are input to the phase discrimination module 31, the phase discrimination module 31 IQ demodulates the second radio frequency sub-signal and the first radio frequency detection signal, and outputs the I component and the Q component of the phase difference signal between the second radio frequency sub-signal and the first radio frequency detection signal, and obtains the A component and the Φ component corresponding thereto according to the above formula, and at least the difference of the Φ component between the second radio frequency sub-signal and the first radio frequency detection signal is determined as the phase adjustment amount, and after analog-to-digital conversion ADC, input to the CPU / FPGA for calculation, and after digital-to-analog conversion DAC, the corresponding I / Q amount to be compensated is obtained and input to the phase shifter 2 for compensation.

[0065] In addition, in this scheme, the phase adjustment amount is determined based on the IQ demodulation and IQ modulation mode, which can perform phase discrimination within 360°, and accordingly can perform phase compensation within 360°.

[0066] As an implementation manner, referring to Figure 3 , in order to monitor the working state of the first laser 6, so that the first laser 6 can be found in time when it fails, and timely maintenance can be performed, an optical coupler 7 is connected between the first end and the first laser 6, and the optical coupler 7 is connected with a third photodetector 4;

[0067] The optical coupler 7 is used for coupling part of the first laser signal to the third photodetector 4;

[0068] The third photodetector 4 is used for generating a second radio frequency detection signal according to the first laser signal coupled into the third photodetector 4;

[0069] The control unit 3 is also configured to determine the working state of the first laser 6 according to the second radio frequency detection signal. For example, according to the strength of the second radio frequency detection signal, it is determined whether the working state of the first laser 6 is normal or abnormal.

[0070] As an implementation manner, an amplifier 10 is connected between the first photodetector 9 and the electrical coupler 11, and the amplifier 10 is configured to amplify the radio frequency signal output by the first photodetector 9.

[0071] As an implementation manner, the optical fiber transmission link 8 includes an optical fiber 82, one end of the optical fiber 82 is connected to a first optical circulator 81, and the other end is connected to a second optical circulator 82; the optical circulator has multiple ports, and the multiple ports have non-reciprocal characteristics. When an optical signal is input from any port, it can be output from the next port in a predetermined order with very small loss, and the loss of the port to all other ports is very large, becoming a non-communicating port.

[0072] The first optical circulator is connected with the optical coupler 7 and the second photodetector 5 respectively;

[0073] The second optical circulator is connected with the second laser 12 and the first photodetector 9 respectively.

[0074] As an implementation manner, as Figure 4 In order to reduce system noise and temperature-induced measurement error, the system for transmitting radio frequency signals through an optical fiber further includes a first thermostat device 21, a second thermostat device 22, a third thermostat device 23, and a fourth thermostat device 24.

[0075] The power divider 1 is arranged in the first thermostat device 21;

[0076] The phase shifter 2, the first laser 6, the first optical circulator, the second photodetector 5, the third photodetector 4, and the phase discrimination module 31 are arranged in the second thermostat device 22;

[0077] The first photodetector 9, the second laser 12, the electrical coupler 11, and the amplifier 10 are arranged in the third thermostat device 23;

[0078] The calculation module 32 is arranged in the fourth thermostat device 24.

[0079] Each of the above components is arranged in the corresponding thermostat device. By controlling the temperature of the thermostat device, the temperature of the transmitting end and the receiving end can be controlled within a target precision range, for example, but not limited to, a precision control of ±0.01℃, or even a precision higher than ±0.01℃. Avoiding noise and phase slow drift caused by temperature changes.

[0080] As a possible implementation, a semiconductor refrigeration sheet 26 is arranged in each of the first constant temperature device 21, the second constant temperature device 22, the third constant temperature device 23 and the fourth constant temperature device 24, and the temperature in each constant temperature device is controlled by controlling the refrigeration power of the semiconductor refrigeration sheet 26.

[0081] As a possible implementation, a temperature sensor is arranged in each of the first constant temperature device 21, the second constant temperature device 22, the third constant temperature device 23 and the fourth constant temperature device 24.

[0082] Each temperature sensor is connected to a temperature controller 25, which controls the refrigeration power of the corresponding semiconductor refrigeration sheet 26 according to the collected information of each temperature sensor. Since the above power divider 1, the phase shifter 2, the first laser 6, the first optical circulator, the second photodetector 5, the third photodetector 4 and the phase detection module 31, the first photodetector 9, the second laser 12, the electrical coupler 11 and the amplifier 10, the calculation module 32 and the like all emit heat into the corresponding constant temperature device, the temperature in each constant temperature device is collected by the temperature sensor, and the refrigeration power of the semiconductor refrigeration sheet 26 is controlled according to the temperature change, so as to ensure that the temperature in each constant temperature device is relatively constant.

[0083] As a possible implementation, the frequency of the first laser signal is different from that of the second laser signal.

[0084] As a possible implementation, the frequency of the first laser signal is different from that of the second laser signal by 1GHz to 50GHz.

[0085] When transmitting the same wavelength optical signals in the same optical fiber in the forward and reverse directions, Rayleigh scattering will cause the phase noise of the transmitted signals to deteriorate, affecting the quality of the transmitted radio frequency signals. In this scheme, the frequency of the first laser signal is different from that of the second laser signal to reduce noise and improve the quality of the radio frequency signals. At the same time, the wavelength difference between the first laser signal and the second laser signal cannot be too large. If the wavelength difference is too small, Rayleigh scattering effect will still occur, and if the wavelength difference is too large, the phase difference caused by the wavelength difference will be greater than the phase slow drift caused by temperature, which will result in the inability to accurately measure the system phase slow drift. For example, in this example, a single-mode optical fiber with a dispersion parameter of about 17ps / km / nm is used, the frequency of the first laser signal is different from that of the second laser signal by 1GHz to 50GHz, and the influence on the application with a transmission length of 2km is less than 0.2ps. If the transmission length is fixed, the signal delay phase is fixed, and the dispersion phase change caused by the slow drift length can be ignored.

[0086] It should be understood that the above-mentioned directional or positional relationships expressed by terms "center", "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like are based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0087] The above description is merely the preferred embodiments of the present application and the explanation of the technical principles applied. It should be understood by those skilled in the art that the scope of the application involved in the present application is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combinations of the above technical features or their equivalent features without departing from the inventive concept. For example, the technical solutions formed by mutually replacing the above-mentioned features with the technical features disclosed in the present application (but not limited to) having similar functions.

Claims

1. A system for transmission of radio frequency signals over optical fiber, characterized by, include: A power divider is used to split an RF input signal into at least a first RF sub-signal and a second RF sub-signal. A phase shifter, connected to the power divider, is used to adjust the phase and / or amplitude of the first radio frequency sub-signal; A first laser, connected to the phase shifter, is used to generate a first laser signal based on the phase-adjusted first radio frequency sub-signal; An optical fiber transmission link, wherein the first end of the optical fiber transmission link is connected to the first laser and is used to transmit the first laser signal; A first photodetector is connected to the second end of the optical fiber transmission link and is used to demodulate the received first laser signal into a radio frequency signal. An electrical coupler, connected to the first photodetector, is used to separate the radio frequency signal into a radio frequency input signal and a radio frequency feedback signal; A second laser, connected to the electrical coupler, is used to generate a second laser signal based on the radio frequency feedback signal and transmit it from the second end into the optical fiber transmission link. The second photodetector is connected to the first end of the optical fiber transmission link and is used to demodulate the received second laser signal into a first radio frequency detection signal. The control unit is connected to the power divider and the second photodetector respectively, and is used to determine the phase adjustment amount based on the second radio frequency sub-signal and the first radio frequency detection signal; The phase shifter is used to adjust the phase and / or amplitude of the first radio frequency sub-signal according to the phase adjustment amount; The control unit also includes a computing module and a phase detection module; The optical coupler is connected to a third photodetector; The optical coupler is used to couple a portion of the first laser signal to the third photodetector; The third photodetector is used to generate a second radio frequency detection signal based on the first laser signal coupled into the third photodetector; The control unit is also configured to determine the operating state of the first laser based on the second radio frequency detection signal; An amplifier is connected between the first photodetector and the electrocoupler, and the amplifier is used to amplify the radio frequency signal output by the first photodetector. The optical fiber transmission link includes an optical fiber, one end of which is connected to a first optical circulator and the other end of which is connected to a second optical circulator. The first optical circulator is connected to the optical coupler and the second photodetector respectively, and the optical coupler is connected between the first end and the first laser. The second optical circulator is connected to the second laser and the first photodetector, respectively; The phase shifter, the first laser, the first optical circulator, the second photodetector, the third photodetector, and the phase detection module are disposed in the second constant temperature device; The first photodetector, the second laser, the electrocoupler, and the amplifier are disposed in the third constant temperature device; The power divider is located in the first temperature control device; the computing module is located in the fourth temperature control device.

2. The system for transmission of radio frequency signals over optical fiber as claimed in claim 1 wherein, The phase detection module determines the A component and Φ component of the phase difference signal between the second radio frequency sub-signal and the first radio frequency detection signal according to the following relationship, and the phase adjustment amount includes at least the difference of the Φ component between the second radio frequency sub-signal and the first radio frequency detection signal; Where A is the amplitude of the radio frequency signal in the polar coordinate system, Φ is the phase of the radio frequency signal in the polar coordinate system, I is the in-phase component of the radio frequency signal in the rectangular coordinate system, and Q is the quadrature component of the radio frequency signal in the rectangular coordinate system.

3. The system for transmitting radio frequency signals via optical fiber according to claim 1, characterized in that, The first, second, third, and fourth temperature control devices are all equipped with semiconductor cooling chips.

4. The system for transmitting radio frequency signals via optical fiber according to claim 3, characterized in that, Temperature sensors are installed in the first, second, third, and fourth temperature control devices. Each of the temperature sensors is connected to a temperature controller, which controls the cooling capacity of the corresponding thermoelectric cooler based on the information collected by each of the temperature sensors.

5. The system for transmitting radio frequency signals via optical fiber according to any one of claims 1-4, characterized in that, The first laser signal has a different frequency than the second laser signal.

6. The system for transmitting radio frequency signals via optical fiber according to claim 5, characterized in that, The first laser signal and the second laser signal have a frequency difference of 1 GHz to 50 GHz.

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