Optical fiber frequency transmission transmitting station compatible with same frequency and harmonic waves thereof and transmission system

Abstract

The invention discloses an optical fiber frequency transmission emission station and transmission system compatible with same frequency and harmonic waves thereof, and the emission station comprises a voltage-controlled oscillator, a first electro-optical conversion unit, a first wavelength division multiplexer, a first photoelectric conversion unit, a frequency conversion network, and a low-pass filtering processing unit. And the frequency conversion network is used for receiving the microwave signal to be transmitted, the loopback microwave signal and the reference signal, performing frequency division and harmonic extraction processing on the loopback microwave signal to obtain an error signal related to the transmission delay drift of the optical fiber link and the frequency drift of the voltage-controlled oscillator, and pre-compensating the frequency to be transmitted. According to the invention, high-precision optical fiber transmission of microwave signals is realized by adopting frequency phase locking, high resolution and large-range'balance difficulty 'of a delay line are avoided, transmission of same-frequency and harmonic signals thereof is compatible, and wide application prospects are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of microwave photonics, and particularly relates to a fiber frequency transmission transmitting station and a transmission system compatible with same frequency and harmonics thereof. BACKGROUND

[0002] Time-frequency reference signals are the "invisible pulse" that sustains the precise operation of modern society. From the satellite-ground time synchronization of the Beidou-3 satellite navigation system to the nanosecond-level coordination between 5G / 6G base stations, from the wide-area phasor measurement of ultra-high voltage power grids to the microsecond-level matching of financial transactions, and from the kilometer-level laser interference of gravitational wave detection, all rely on high-stability and high-accuracy frequency and time signals. Traditional schemes use coaxial cables or microwave links for transmission, but the hundred-meter-level attenuation (>50 dB / km) and electromagnetic interference (EMI) quickly deteriorate the stability of transmission to 10 -11 (@1s) for hundreds of kilometers, which is far from meeting the higher demand of 10 -14 @order of magnitude in Shenzhen. Optical fibers, with ultra-low loss (0.17 dB / km @ 1550 nm), THz-level bandwidth, and natural anti-EMI capability, have become an ideal medium for building a wide-area time-frequency synchronization network. However, optical fibers are not "transparent pipes", and their transmission characteristics are disturbed by multiple physical fields such as environmental temperature, mechanical stress, and vibration: the temperature coefficient of 40 ps / km·℃ means that a 100 km link can produce a 80 ps drift under a 20 ℃ diurnal temperature difference; when laid in scenes such as bridges, tunnels, and mines, the random phase noise introduced by vehicle vibration and crustal microseisms can reach sub-nanosecond level, leading to a 2-3 order of magnitude deterioration in short-term stability.

[0003] To overcome the above defects, the industry has proposed bidirectional time comparison (TWTT) and round-trip time (RTT) active compensation technologies: injecting homologous or heterologous probe signals at both ends of the link, measuring the round-trip time difference in real time, and compensating with piezoelectric fiber stretchers, temperature-controlled delay lines, or acousto-optic modulators to suppress the phase noise introduced by the environment to 10 -14 @1s. However, the above methods have the following three major problems: first, Rayleigh scattering and dispersion effects require frequency shifting (usually by GHz order) of the bidirectional transmission carrier, i.e. wavelength division multiplexing to avoid the coherent superposition of backscattered light and signal light; and the mixers, frequency multipliers, and amplifiers in the frequency division multiplexing variable-frequency link will introduce additional phase noise (>10 -13Firstly, the noise of the existing frequency conversion module is accumulated linearly with the frequency conversion times, and the noise is accumulated linearly with the frequency conversion times. Secondly, the reference frequencies of different industries are significantly different: a 10 MHz cesium clock is used in a metrology laboratory, a 100 MHz output is used by a hydrogen clock, a 122.88 MHz is used by a 5G base station, and a radar system needs more than 1 GHz; the existing architecture needs to customize the frequency conversion module, the filter set and the local oscillator source for each frequency, the hardware reuse rate is low, and the cost of a single link increases exponentially with the frequency band. Thirdly, the frequency conversion module needs a high-stability local oscillator (OCXO or DRO) phase-locked reference, which causes the power consumption, volume and cost to rise simultaneously, which is not conducive to large-scale deployment in remote base stations, vehicles, ships and other restricted environments.

[0004] Therefore, how to realize cross-band, low-additive noise and high-environmental adaptability of optical fiber time-frequency transmission under the "no frequency conversion" or "universal frequency conversion" architecture has become a key bottleneck restricting the wide-area time-frequency synchronization network to be low-cost, standardized and scaled, and it is urgent to break through the "last mile" of industry application. SUMMARY

[0005] In view of the above problems of the prior art, the technical problem to be solved by the present application is to provide an optical fiber frequency transmission transmitting station compatible with the same frequency and its harmonics and a transmission system.

[0006] To solve the above technical problems, the present application provides the following technical solutions: An optical fiber frequency transmission transmitting station compatible with the same frequency and its harmonics comprises A voltage-controlled oscillator for generating a microwave signal to be transmitted; A first electro-optical conversion unit for modulating the microwave signal to be transmitted into the optical domain to form a first optical signal as an optical carrier microwave signal to be transmitted; A first wavelength division multiplexer for coupling the optical carrier microwave signal to be transmitted into an optical fiber transmission link and extracting a loopback optical carrier microwave signal from the optical fiber transmission link; the loopback optical carrier microwave signal is obtained by a receiving station after frequency division and harmonic extraction processing of a received optical carrier microwave signal and then looped back to the transmitting station; A first optoelectronic conversion unit for restoring the loopback optical carrier microwave signal to the microwave domain to obtain a first microwave signal as a loopback microwave signal; A frequency conversion network for receiving the microwave signal to be transmitted, the loopback microwave signal and a reference signal, and performing frequency division and harmonic extraction processing on the loopback microwave signal to obtain an error signal related to the transmission delay drift of the optical fiber link and the frequency drift of the voltage-controlled oscillator; and A low-pass filter processing unit for low-pass filtering the error signal output by the frequency conversion network and outputting the error signal to the control end of the voltage-controlled oscillator.

[0007] Further, the first electro-optical conversion unit comprises A first laser for generating a first optical carrier; and The first electro-optical modulator is configured to modulate the microwave signal to be transmitted to the first optical carrier by low-bias voltage control to form a suppressed carrier optical microwave signal to be transmitted; The first photoelectric conversion unit comprises The first optical amplifier is configured to amplify the power of the loopback optical microwave signal; and The first photodetector is configured to restore the amplified loopback optical microwave signal to the microwave domain to obtain a loopback microwave signal.

[0008] Further, by selecting the parameters of the frequency division and harmonic extraction process of the restored received optical microwave signal at the receiving station and the parameters of the frequency division and harmonic extraction process of the loopback microwave signal by the frequency conversion network, the error signal is a direct current signal.

[0009] Further, the frequency conversion network comprises The third filter amplification unit is configured to filter and amplify the loopback microwave signal; The power divider is configured to divide the filtered and amplified loopback microwave signal into two paths to obtain a first loopback microwave signal and a second loopback microwave signal; The first electrical processing unit is configured to frequency divide and extract harmonics from the first loopback microwave signal and up-convert the frequency of the microwave signal to be transmitted output by the voltage-controlled oscillator to obtain a first mixed signal; The second electrical processing unit is configured to down-convert the frequency of the second loopback microwave signal and a reference signal to obtain a second mixed signal; and The phase comparison unit is configured to extract the phase difference between the first mixed signal and the second mixed signal to obtain an error signal.

[0010] Further, the process of frequency dividing and extracting harmonics from the restored received optical microwave signal at the receiving station is as follows: first, filter to extract the second harmonic of the optical microwave signal to be transmitted, then divide the frequency of the second harmonic by ten, and then filter to extract the third harmonic from the signal after the frequency division by ten; The process of frequency dividing and extracting harmonics from the first loopback microwave signal by the first electrical processing unit is as follows: first, divide the frequency of the first loopback microwave signal by three, and then filter to extract the second harmonic from the signal after the frequency division by three; The error signal V 8 is expressed as follows:

[0011] wherein, ω 0 represents the angular frequency of the reference signal; ω ω0 represents the angular frequency of the microwave signal to be transmitted by the voltage-controlled oscillator, and ω 0= 2ω ; τf a one-way transmission delay of the optical fiber transmission link; θ 0 represents an initial phase of the reference signal; represents an initial phase of the to-be-transmitted microwave signal of the voltage-controlled oscillator.

[0012] Further, the first electrical processing unit comprises a first frequency divider for frequency dividing the first loopback microwave signal to obtain a second microwave signal; a second filter-amplification unit for filtering and amplifying the second microwave signal to extract a harmonic of the second microwave signal to obtain a third microwave signal; a first frequency mixer for mixing the third microwave signal and the to-be-transmitted microwave signal output by the voltage-controlled oscillator to obtain a fourth microwave signal; and a first filter-amplification unit for filtering the fourth microwave signal, extracting an up-conversion thereof, and performing amplification processing to obtain a first mixed signal; the second electrical processing unit comprises a reference signal generation unit for outputting a reference signal; a second frequency mixer for mixing the second loopback microwave signal and the reference signal to obtain a fifth microwave signal; and a fourth filter-amplification unit for filtering the fifth microwave signal, extracting a down-conversion thereof, and performing amplification processing to obtain a second mixed signal.

[0013] Further, the reference signal generation unit comprises a harmonic generator for generating a comb spectrum signal according to an input standard signal and outputting; and a first filter for filtering the comb spectrum signal to extract a harmonic of the required standard signal as a reference signal provided to the second frequency mixer.

[0014] A fiber frequency transmission system compatible with a same frequency and harmonics thereof, comprising a transmitting station adopting the fiber frequency transmission transmitting station compatible with a same frequency and harmonics thereof according to any one of the above; an optical fiber transmission link for connecting the transmitting station and a receiving station, transmitting the to-be-transmitted optical carrier microwave signal output by the transmitting station to the receiving station, and loopbacking the third optical signal output by the receiving station to the transmitting station; and the receiving station for receiving the optical carrier microwave signal transmitted by the transmitting station from the optical fiber transmission link, and performing photoelectric conversion, frequency division, and harmonic extraction processing to obtain an output microwave signal and a ninth microwave signal, and modulating the ninth microwave signal to an optical domain to form a third optical signal and couple into the optical fiber transmission link.

[0015] Further, the receiving station comprises a second wavelength division multiplexer, configured to extract the optical microwave signal from the optical fiber transmission link as a second optical signal, and couple the third optical signal into the optical fiber transmission link; a second photoelectric conversion unit, configured to restore the second optical signal to the microwave domain to obtain a sixth microwave signal; a fifth filter amplification unit, configured to filter the sixth microwave signal, extract a harmonic signal thereof and perform amplification processing to obtain a seventh microwave signal; a second frequency divider, configured to divide the seventh microwave signal to obtain an eighth microwave signal; a second filter, configured to filter the eighth microwave signal to extract a signal at a required frequency point as an output microwave signal from a first output end thereof, and extract a harmonic signal of the eighth microwave signal to obtain a ninth microwave signal from a second output end thereof; and a second electro-optical conversion unit, configured to modulate the ninth microwave signal to the optical domain to form the third optical signal.

[0016] Further, the optical fiber transmission link is a single-fiber bidirectional serial link formed by connecting a plurality of bidirectional relay stations in series through an optical fiber link; the bidirectional relay station comprises an optical relay station and / or an electrical relay station, the optical relay station comprises a bidirectional optical amplification unit, and the electrical relay station comprises an optical-electric conversion unit and an electric-optical conversion unit connected in series.

[0017] In the present application, the conventional method of using a delay line for phase compensation in the current frequency transmission system is changed, and frequency pre-compensation is used to realize high-precision optical fiber transmission of standard signals, which not only avoids the high resolution and large range of "balance dilemma" of the delay line, but also can be compatible with the transmission of the same frequency and its harmonic signals, and can output additional frequency points comprehensively, to meet the application requirements of different scenes. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and serve to explain the principles of the application, and do not limit the application in any way. In the drawings: Figure 1 The structural block diagram of an embodiment of the optical fiber frequency transmission transmitting station compatible with the same frequency and its harmonics of the present application.

[0019] Figure 2 The structural block diagram of a frequency conversion network.

[0020] Figure 3 The structural block diagram of an embodiment of the optical fiber frequency transmission system compatible with the same frequency and its harmonics of the present application.

[0021] Figure 4 The structural block diagram of a receiving station.

[0022] The description reference signs are as follows: frequency conversion network 11; low pass filter processing unit 12; voltage controlled oscillator 13; first laser 14; first electro-optical modulator 15; first wavelength division multiplexer 16; first optical amplifier 17; first photoelectric detector 18; phase comparison unit 111; first filter amplification unit 112; first mixer 113; second filter amplification unit 114; first frequency divider 115; third filter amplification unit 116; power divider 117; fourth filter amplification unit 118; second mixer 119; first filter 110; harmonic generator 1111; transmitting station 1; receiving station 2; second wavelength division multiplexer 21; second optical amplifier 22; second photoelectric detector 23; fifth filter amplification unit 24; second frequency divider 25; second filter 26; second laser 27; second electro-optical modulator 28; optical fiber transmission link 3; bidirectional relay station 31. DETAILED DESCRIPTION

[0023] The embodiments of the present application are described below through specific concrete examples, the figures provided in the following examples only schematically illustrate the basic concept of the present application, and the following examples and features in the examples can be combined with each other without conflict.

[0024] Please refer to Figure 1 , Figure 1 The structural block diagram of an embodiment of the transmitting station compatible with the optical fiber frequency transmission of the same frequency and its harmonics of the present application. The transmitting station compatible with the optical fiber frequency transmission of the same frequency and its harmonics of the present application of the present embodiment comprises voltage controlled oscillator 13, first electro-optical conversion unit, first wavelength division multiplexer 16, first photoelectric conversion unit, frequency conversion network 11 and low pass filter processing unit 12.

[0025] The voltage controlled oscillator 13 is used to generate the microwave signal to be transmitted, and the output end of the voltage controlled oscillator 13 is respectively electrically connected with the first input end of the frequency conversion network 11 and the input end of the first electro-optical conversion unit.

[0026] The first electro-optical conversion unit is used for modulating the microwave signal to be transmitted into the optical domain to form a first optical signal as the optical carrier microwave signal to be transmitted. In the embodiment, the first electro-optical conversion unit comprises a first laser 14 and a first electro-optical modulator 15. The first laser 14 is used for generating a first optical carrier; and the first electro-optical modulator 15 is used for modulating the microwave signal to be transmitted into the first optical carrier through low-bias voltage control to form the optical carrier suppressed microwave signal to be transmitted. The optical input end of the first electro-optical modulator 15 is connected with the optical output end of the first laser 14, and the radio frequency input end is electrically connected with the output end of the voltage-controlled oscillator 13 as the input end of the first electro-optical conversion unit.

[0027] The first wavelength division multiplexer 16 is used for coupling the optical carrier microwave signal to be transmitted into the optical fiber transmission link 3, and extracting the loopback optical carrier microwave signal from the optical fiber transmission link 3. The loopback optical carrier microwave signal is obtained by the transmitting station 1 after the receiving station 2 performs frequency division and harmonic extraction processing on the restored received optical carrier microwave signal. The first channel end of the first wavelength division multiplexer 16 is connected with the optical output end of the first electro-optical modulator 15, the second channel end is connected with the optical input end of the first opto-electric conversion unit, and the common end is connected with the optical fiber transmission link 3.

[0028] The first opto-electric conversion unit is used for restoring the loopback optical carrier microwave signal into the microwave domain to obtain a first microwave signal as the loopback microwave signal. In the embodiment, the first opto-electric conversion unit comprises a first optical amplifier 17 and a first photoelectric detector 18. The first optical amplifier 17 is used for performing power amplification on the loopback optical carrier microwave signal; and the first photoelectric detector 18 is used for restoring the power amplified loopback optical carrier microwave signal into the microwave domain to obtain the loopback microwave signal. The optical input end of the first optical amplifier 17 is connected with the second channel end of the first wavelength division multiplexer 16 as the input end of the first opto-electric conversion unit, and the optical output end of the first optical amplifier 17 is connected with the optical input end of the first photoelectric detector 18. The radio frequency output end of the first photoelectric detector 18 is electrically connected with the second input end of the frequency conversion network 11.

[0029] The frequency conversion network 11 is used for receiving the microwave signal to be transmitted, the loopback microwave signal and the reference signal through the first input end, the second input end and the third input end respectively, performing frequency division and harmonic extraction processing on the loopback microwave signal, extracting the error signal related to the optical fiber link transmission delay drift and the frequency drift of the voltage-controlled oscillator 13 itself, and outputting from the output end.

[0030] The low-pass filter processing unit 12 is used for low-pass filtering the error signal output by the frequency conversion network 11 and outputting to the control end of the voltage-controlled oscillator 13 to change the output frequency of the voltage-controlled oscillator 13. The input end of the low-pass filter processing unit 12 is electrically connected with the output end of the frequency conversion network 11, and the output end of the low-pass filter processing unit 12 is electrically connected with the control end of the voltage-controlled oscillator 13.

[0031] Please refer to Figure 2 , the frequency conversion network 11 can include a third filter amplification unit 116, a power divider 117, a first electrical processing unit, a second electrical processing unit and a phase comparison unit 111.

[0032] The third filter amplification unit 116 is used for filtering and amplifying the loopback microwave signal. The input end of the third filter amplification unit 116 is electrically connected with the radio frequency output end of the first photodetector 18 as the second input end of the frequency conversion network 11; and the output end of the third filter amplification unit 116 is electrically connected with the input end of the power divider 117.

[0033] The power divider 117 is used for dividing the filtered and amplified loopback microwave signal into two paths to obtain a first loopback microwave signal and a second loopback microwave signal. The first loopback microwave signal is output from the first output end of the power divider 117 to the first electrical processing unit, and the second loopback microwave signal is output from the second output end of the power divider 117 to the second electrical processing unit.

[0034] The first electrical processing unit is used for frequency dividing and harmonic extracting the first loopback microwave signal and up-converting the to-be-transmitted microwave signal output by the voltage-controlled oscillator 13 to obtain a first mixed signal.

[0035] The second electrical processing unit is used for down-converting the second loopback microwave signal with the reference signal to obtain a second mixed signal.

[0036] The phase comparison unit 111 is used for extracting the phase difference of the first mixed signal and the second mixed signal to obtain the error signal. The first input end and the second input end of the phase comparison unit 111 are electrically connected with the output ends of the first electrical processing unit and the second electrical processing unit respectively, and the output end of the phase comparison unit 111 is electrically connected with the input end of the low-pass filter processing unit 12 as the output end of the frequency conversion network 11.

[0037] The first electrical processing unit can include a first frequency divider 115, a second filter amplification unit 114, a first frequency mixer 113 and a first filter amplification unit 112.

[0038] The first frequency divider 115 is used to divide the first loopback microwave signal to obtain the second microwave signal. The input terminal of the first frequency divider 115 is electrically connected to the first output terminal of the power divider 117, and the output terminal is electrically connected to the input terminal of the second filter amplification unit 114.

[0039] The second filtering and amplification unit 114 is used to filter and amplify the second microwave signal and extract the harmonics of the second microwave signal to obtain the third microwave signal.

[0040] The first mixer 113 is used to mix the third microwave signal and the microwave signal to be transmitted output by the voltage-controlled oscillator 13 to obtain the fourth microwave signal. The first input terminal of the first mixer 113 is electrically connected to the output terminal of the voltage-controlled oscillator 13 as the first input terminal of the frequency conversion network 11. The second input terminal of the first mixer 113 is electrically connected to the output terminal of the second filter amplification unit 114. The output terminal of the first mixer 113 is electrically connected to the input terminal of the first filter amplification unit 112.

[0041] The first filtering and amplifying unit 112 is used to filter the fourth microwave signal, extract its up-conversion frequency, and amplify it to obtain the first mixing signal. The output terminal of the first filtering and amplifying unit 112 is electrically connected to the first input terminal of the phase comparison unit 111 as the output terminal of the first electrical processing unit.

[0042] The second electrical processing unit includes a reference signal generation unit, a second mixer 119, and a fourth filtering and amplification unit 118.

[0043] The reference signal generation unit is used to output a reference signal. In this embodiment, the reference signal generation unit includes a harmonic generator 1111 and a first filter 1110. The harmonic generator 1111 is used to generate a comb-shaped spectrum signal based on the input standard signal and output it; the first filter 1110 is used to filter the comb-shaped spectrum signal and extract the harmonics of the required standard signal as a reference signal to provide to the second mixer 119. The input terminal of the harmonic generator 1111 is used to input a stable microwave signal as a standard signal, and the output terminal of the harmonic generator 1111 is electrically connected to the input terminal of the first filter 1110.

[0044] The second mixer 119 is used to mix the second loopback microwave signal and the reference signal to obtain the fifth microwave signal. The first input terminal of the second mixer 119 is electrically connected to the output terminal of the first filter 1110, the second input terminal of the second mixer 119 is electrically connected to the second output terminal of the power divider 117, and the output terminal of the second mixer 119 is electrically connected to the input terminal of the fourth filter amplification unit 118.

[0045] The fourth filtering and amplification unit 118 is used to filter the fifth microwave signal, extract its down-conversion frequency, and amplify it to obtain the second mixing signal. The output terminal of the fourth filtering and amplification unit 118 is electrically connected to the second input terminal of the phase comparison unit 111 as the output terminal of the second electrical processing unit.

[0046] Using the above structure, by selecting the parameters (i.e., division ratio and harmonic order) for frequency division and harmonic extraction processing when restoring the received optical microwave signal at the receiving station 2, and the parameters (i.e., division ratio and harmonic order) for frequency division and harmonic extraction processing of the loopback microwave signal by the frequency conversion network 11, the error signal can be made into a DC signal that does not change with time, that is:

[0047] in, ω 0 represents the angular frequency of the reference signal; ω This represents the angular frequency of the microwave signal to be transmitted by the voltage-controlled oscillator 13; τ f This represents the one-way transmission delay of fiber optic transmission link 3 (i.e., the transmission delay from transmitting station 1 to receiving station 2). θ 0 indicates the initial phase of the reference signal; This indicates the initial phase of the microwave signal to be transmitted by the voltage-controlled oscillator 13. When this DC signal is kept constant by phase-locked loop, 2 2 = ( If (where is a constant), the signal received by the receiving station can be expressed as: That is, the phase of the signal received by the receiving station and the transmission delay of the optical fiber link. It is unrelated to achieving high-precision fiber optic frequency transmission.

[0048] In this embodiment, the receiving station 2 restores the received optical microwave signal and performs frequency division and harmonic extraction processing. The process can be as follows: first, the second harmonic of the restored optical microwave signal is extracted by filtering; then, the second harmonic is divided into ten harmonics; and finally, the signal after ten harmonics is filtered to extract the third harmonic.

[0049] The process of the first electrical processing unit performing frequency division and harmonic extraction on the first loopback microwave signal can be as follows: first, the first loopback microwave signal is divided into three parts by three, and then the signal after frequency division is filtered to extract the second harmonic. That is, the first frequency divider 115 divides the first loopback microwave signal into three parts to obtain the second microwave signal; the second filtering and amplification unit 114 extracts the second harmonic of the second microwave signal to obtain the third microwave signal, i.e.

[0050] ω0=2ω Of course, the frequency division ratio and harmonic order mentioned above are only values ​​in a specific example. In other embodiments, the frequency division ratio and harmonic order can also take other values.

[0051] Please see Figure 3 , Figure 3 This is a structural block diagram of an embodiment of the fiber optic frequency transmission system compatible with both the same frequency and its harmonics according to the present invention. The fiber optic frequency transmission system compatible with both the same frequency and its harmonics in this embodiment includes a transmitting station 1, a fiber optic transmission link 3, and a receiving station 2. The transmitting station 1 can be a fiber optic frequency transmission transmitting station compatible with both the same frequency and its harmonics as described in any of the above embodiments.

[0052] The optical fiber transmission link 3 is used to connect the transmitting station 1 and the receiving station 2, transmitting the optical microwave signal to be transmitted from the transmitting station 1 to the receiving station 2, and looping the third optical signal output from the receiving station 2 back to the transmitting station 1. In this embodiment, the optical fiber transmission link 3 is a single-fiber bidirectional series link formed by connecting multiple bidirectional repeater stations 31 in series via an optical fiber link. The bidirectional repeater station 31 may include multiple optical repeater stations and / or electrical repeater stations. The optical repeater station may adopt a bidirectional optical amplification unit, and the electrical repeater station may adopt a structure of a series photoelectric conversion unit and an electro-optical conversion unit.

[0053] The receiving station 2 is used to receive the optical microwave signal transmitted by the transmitting station 1 from the optical fiber transmission link 3, and after photoelectric conversion, frequency division and harmonic extraction processing, it obtains the output microwave signal and the ninth microwave signal, and modulates the ninth microwave signal into the optical domain to form the third optical signal and couples it into the optical fiber transmission link 3.

[0054] Please see Figure 4 The receiving station 2 may include a second wavelength division multiplexer 21, a second photoelectric conversion unit, a fifth filtering and amplification unit 24, a second frequency divider 25, a second filter 26, and a second electro-optical conversion unit.

[0055] The second wavelength division multiplexer 21 is used to extract the received optical microwave signal from the optical fiber transmission link 3 as a second optical signal; and to couple a third optical signal into the optical fiber transmission link 3. The common terminal of the second wavelength division multiplexer 21 is connected to the optical fiber transmission link 3, the first channel terminal is connected to the input terminal of the second photoelectric conversion unit, and the second channel terminal is connected to the output terminal of the second electro-optical conversion unit.

[0056] The second photoelectric conversion unit is used to restore the second optical signal to the microwave domain to obtain the sixth microwave signal. The second photoelectric conversion unit includes a second optical amplifier 22 and a second photodetector 23. The second optical amplifier 22 amplifies the second optical signal; the second photodetector 23 restores the amplified second optical signal to the microwave domain to obtain the sixth microwave signal. The optical input terminal of the second optical amplifier 22 is connected to the first channel terminal of the second wavelength division multiplexer 21, and the optical output terminal is connected to the optical input terminal of the second photodetector 23; the radio frequency output terminal of the second photodetector 23 is electrically connected to the input terminal of the fifth filter amplification unit 24.

[0057] The fifth filtering and amplifying unit 24 is used to filter the sixth microwave signal, extract its harmonic signals, and amplify them to obtain the seventh microwave signal. The output terminal of the fifth filtering and amplifying unit 24 is electrically connected to the input terminal of the second frequency divider 25. In this embodiment, the fifth filtering and amplifying unit 24 extracts the second harmonic signal of the sixth microwave signal and amplifies it to obtain the seventh microwave signal.

[0058] The second frequency divider 25 is used to divide the seventh microwave signal to obtain the eighth microwave signal. The output terminal of the second frequency divider 25 is electrically connected to the input terminal of the second filter 26. In this embodiment, the second frequency divider 25 divides the seventh microwave signal by ten times to obtain the eighth microwave signal.

[0059] The second filter 26 is used to filter the eighth microwave signal, extract the signal at the desired frequency (e.g., the frequency corresponding to the standard signal or other frequency signals) and output it from its first output terminal as the output microwave signal of the receiving station 2; and extract the harmonic signal of the eighth microwave signal to obtain the ninth microwave signal, which is output from its second output terminal to the second electro-optic modulator 28. In this embodiment, the second filter 26 extracts the third harmonic signal of the eighth microwave signal to obtain the ninth microwave signal.

[0060] The second electro-optic conversion unit is used to modulate the ninth microwave signal into the optical domain to form a third optical signal. The second electro-optic conversion unit includes a second laser 27 and a second electro-optic modulator 28. The second laser 27 is used to generate a second optical carrier; the second electro-optic modulator 28 is used to modulate the ninth microwave signal onto the second optical carrier through quadrature bias voltage control to form the third optical signal. The optical input terminal of the second electro-optic modulator 28 is connected to the optical output terminal of the second laser 27. The third optical signal is looped back to the transmitting station 1 via the optical fiber transmission link 3 to obtain... The working principle of this embodiment is as follows: Please see Figures 1 to 4 The voltage-controlled oscillator 13 of transmitter station 1 outputs an angular frequency of 1. ω and initial phase is microwave signal to be transmitted V 1:

[0061] microwave signal to be transmitted V 1. After low-bias modulation by the first electro-optic modulator 15, the wavelength is... λ The light is transmitted to the receiving station 2 via the first optical carrier wave 16 and coupled to the optical fiber transmission link 3 through the first wavelength division multiplexer 16. In this embodiment, the wavelength of the first optical carrier wave is... λ 1 = 1550.12 nm. Of course, the wavelength of the first optical carrier can also take other values.

[0062] Receiving station 2 receives wavelength 21 via the second wavelength division multiplexer 21. λ The optical microwave signal 1 is recovered to the microwave domain to obtain the sixth microwave signal. The second harmonic of the sixth microwave signal is then extracted by the fifth filtering and amplification unit 24 and amplified to obtain the seventh microwave signal. V 2:

[0063] Use the second frequency divider 25 to pair the seventh microwave signal V 2. The signal is divided into ten frequencies to obtain the eighth microwave signal; then, the eighth microwave signal is filtered by the second filter 26 to extract the signal at the desired frequency (e.g., the frequency corresponding to the standard signal and signals at other frequency points) as the output microwave signal of the receiving station 2; and the third harmonic signal of the eighth microwave signal is extracted to obtain the ninth microwave signal as the loopback signal. V 3:

[0064] Loopback signal V 3 is orthogonally modulated to a wavelength of 3 by the second electro-optic modulator 28. A third optical signal is formed on the second optical carrier, and coupled to the optical fiber transmission link 3 via the second wavelength division multiplexer 21, thereby looping back to the transmitting station 1. In this embodiment, the wavelength of the second optical carrier... λ 2 = 1550.92nm. Of course, the wavelength of the second optical carrier can also take other values.

[0065] Transmitter 1 receives wavelength 16 via the first wavelength division multiplexer 16. The optical signal is used to obtain the loopback optical carrier microwave signal. The loopback optical carrier microwave signal is then recovered to the microwave domain to obtain the loopback microwave signal. V 4:

[0066] The loopback microwave signal V4. After being filtered and amplified by the third filtering and amplification unit 116, the power is divided into two paths: the first loopback microwave signal and the second loopback microwave signal. The first loopback microwave signal is divided into three frequencies by the first frequency divider 115, then filtered by the second filtering and amplification unit 114 to extract its second harmonic, and then amplified to obtain the third microwave signal. V 5:

[0067] Third microwave signal V 5. The microwave signal to be transmitted output by the voltage-controlled oscillator V 1. Perform up-conversion to form the first mixer signal V 6:

[0068] The standard signal, after being processed by the comb-shaped spectrum signal generated by the harmonic generator 1111, is filtered by the first filter 1110 to extract the required harmonics and obtain the reference signal. V 0:

[0069] For example, when the microwave signal to be transmitted V angular frequency of 1 ω When the frequency is 500MHz and the standard signal frequency is 100MHz, the center frequency of the first filter 1110 can be 1000MHz, thus obtaining the angular frequency. ω 0 is a reference signal for 1000MHz V 0. The center frequency of the second filter 26 can be 100MHz or 300MHz, thus filtering out a microwave signal with a frequency of 300MHz (i.e., the third harmonic signal of the eighth microwave signal) as the ninth microwave signal; and filtering out a microwave signal with a frequency of 100MHz as the output microwave signal of the receiving station 2, realizing the frequency transmission of the standard signal. Of course, by changing or increasing the center frequency of the second filter 26, microwave signals at other frequencies can also be obtained.

[0070] Second loop microwave signal and reference signal V 0 performs down-conversion to form the second mixer signal. V 7:

[0071] The two mixed signals are compared in phase in phase comparison unit 111 to form an error signal. V 8, and through error signals V 8 drives the voltage-controlled oscillator 13. Due to the limitations of this embodiment... ω 0= 2ωTherefore, the error signal is a DC signal. When this DC signal is kept constant through phase-locked loop, (2) 2 ) is a constant At this time, the phase of the signal received by receiving station 2 is related to the transmission delay of optical fiber transmission link 3. τ f This means that high-precision fiber optic frequency transmission has been achieved. At this point, receiving station 2 receives the seventh microwave signal obtained after post-processing. V 2 can be represented as

[0072] In this embodiment, the traditional method of using delay lines for phase compensation in current frequency transmission systems is changed. Frequency phase-locked loop pre-compensation is used to achieve high-precision fiber optic transmission of standard signals. This not only avoids the high resolution and wide-range "balance dilemma" of delay lines, but also can be compatible with the transmission of signals of the same frequency and their harmonics. In addition, it can output additional frequency points to meet the application needs of different scenarios.

[0073] The above embodiments merely illustrate preferred implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. A fiber optic frequency transmission transmitter compatible with both co-frequency and harmonic frequencies, characterized in that, include A voltage-controlled oscillator is used to generate microwave signals to be transmitted. The first electro-optical conversion unit is used to modulate the microwave signal to be transmitted into the optical domain to form a first optical signal as the optical carrier microwave signal to be transmitted. The first wavelength division multiplexer is used to couple the optical microwave signal to be transmitted into the optical fiber transmission link, and to extract the loopback optical microwave signal from the optical fiber transmission link; the loopback optical microwave signal is obtained by the receiving station performing frequency division and harmonic extraction processing on the received optical microwave signal and then looping it back to the transmitting station. The first photoelectric conversion unit is used to restore the loopback optical carrier microwave signal to the microwave domain and obtain the first microwave signal as the loopback microwave signal. The frequency conversion network is used to receive the microwave signal to be transmitted, the loopback microwave signal, and the reference signal, and to perform frequency division and harmonic extraction processing on the loopback microwave signal to obtain error signals related to the transmission delay drift of the optical fiber link and the frequency drift of the voltage-controlled oscillator itself. as well as The low-pass filter processing unit is used to perform low-pass filtering on the error signal output by the frequency conversion network and then output it to the control terminal of the voltage-controlled oscillator.

2. The fiber optic frequency transmission transmitting station compatible with both its own frequency and harmonics as described in claim 1, characterized in that: The first electro-optic conversion unit includes A first laser is used to generate a first optical carrier. as well as The first electro-optic modulator is used to modulate the microwave signal to be transmitted onto the first optical carrier through a low bias voltage control, thereby forming a suppressed carrier optical microwave signal to be transmitted. The first photoelectric conversion unit includes The first optical amplifier is used to amplify the power of the loopback optical carrier microwave signal; as well as The first photodetector is used to restore the amplified loopback optical microwave signal to the microwave domain to obtain the loopback microwave signal.

3. The fiber optic frequency transmission transmitting station compatible with both its own frequency and harmonics as described in claim 1, characterized in that: By selecting the parameters for frequency division and harmonic extraction processing when restoring the received optical microwave signal at the receiving station, and the parameters for frequency division and harmonic extraction processing of the loopback microwave signal by the frequency conversion network, the error signal is made into a DC signal.

4. The fiber optic frequency transmission transmitting station compatible with both the same frequency and its harmonics as described in any one of claims 1 to 3, characterized in that: The frequency conversion network includes The third filtering and amplification unit is used to filter and amplify the loopback microwave signal; A power divider is used to split the filtered and amplified loopback microwave signal into two paths, resulting in a first loopback microwave signal and a second loopback microwave signal. The first electrical processing unit is used to perform frequency division and harmonic extraction processing on the first loop microwave signal and then up-convert it with the microwave signal to be transmitted output by the voltage-controlled oscillator to obtain the first mixed signal. The second electrical processing unit is used to downconvert the second loopback microwave signal and the reference signal to obtain the second mixing signal. as well as The phase comparison unit is used to extract the phase difference between the first and second mixing signals to obtain the error signal.

5. The fiber optic frequency transmission transmitting station compatible with both its own frequency and harmonics as described in claim 4, characterized in that, The process of frequency division and harmonic extraction of the restored received optical microwave signal by the receiving station is as follows: first, the second harmonic of the optical microwave signal to be transmitted is extracted by filtering; then, the second harmonic is divided into ten harmonics; and finally, the signal after ten harmonics is filtered to extract the third harmonic. The process of the first electrical processing unit performing frequency division and harmonic extraction on the first loop microwave signal is as follows: first, the first loop microwave signal is divided into three parts, and then the second harmonic is extracted from the divided signal by filtering. Error signal V The expression for 8 is as follows: in, ω 0 represents the angular frequency of the reference signal; ω This represents the angular frequency of the microwave signal to be transmitted in the voltage-controlled oscillator, and ω 0= 2ω ; τ f This indicates the one-way transmission delay of an optical fiber transmission link; θ 0 indicates the initial phase of the reference signal; This indicates the initial phase of the microwave signal to be transmitted by the voltage-controlled oscillator.

6. The fiber optic frequency transmission transmitting station compatible with both its own frequency and harmonics as described in claim 4, characterized in that: The first electrical processing unit includes The first frequency divider is used to divide the first loopback microwave signal to obtain the second microwave signal; The second filtering and amplification unit is used to filter and amplify the second microwave signal and extract the harmonics of the second microwave signal to obtain the third microwave signal. The first mixer is used to mix the third microwave signal and the microwave signal to be transmitted output by the voltage-controlled oscillator to obtain the fourth microwave signal. as well as The first filtering and amplification unit is used to filter the fourth microwave signal, extract its up-conversion frequency, and amplify it to obtain the first mixing signal. The second electrical processing unit includes Reference signal generation unit, used to output reference signal; The second mixer is used to mix the second loopback microwave signal and the reference signal to obtain the fifth microwave signal; as well as The fourth filtering and amplification unit is used to filter the fifth microwave signal, extract its down-conversion frequency, and amplify it to obtain the second mixing signal.

7. The fiber optic frequency transmission transmitting station compatible with both its own frequency and harmonics as described in claim 6, characterized in that: The reference signal generation unit includes A harmonic generator is used to generate and output a comb-shaped spectrum signal based on an input standard signal. as well as The first filter is used to filter the comb-shaped spectrum signal and extract the harmonics of the required standard signal as a reference signal to provide to the second mixer.

8. A fiber optic frequency transmission system compatible with both co-frequency and harmonic frequencies, characterized in that: include The transmitting station adopts the fiber optic frequency transmission transmitting station compatible with the same frequency and its harmonics as described in any one of claims 1 to 7; An optical fiber transmission link is used to connect a transmitting station and a receiving station, to transmit the optical microwave signal to be transmitted from the transmitting station to the receiving station, and to loop back the third optical signal output from the receiving station to the transmitting station. as well as The receiving station is used to receive the optical microwave signal transmitted from the transmitting station from the optical fiber transmission link, and to perform photoelectric conversion, frequency division and harmonic extraction processing to obtain the output microwave signal and the ninth microwave signal, and to modulate the ninth microwave signal into the optical domain to form the third optical signal and couple it into the optical fiber transmission link.

9. The fiber optic frequency transmission system compatible with both the same frequency and its harmonics as described in claim 8, characterized in that: The receiving station includes The second wavelength division multiplexer is used to extract the optical microwave signal from the optical fiber transmission link as the second optical signal, and to couple the third optical signal into the optical fiber transmission link. The second photoelectric conversion unit is used to restore the second optical signal to the microwave domain to obtain the sixth microwave signal; The fifth filtering and amplification unit is used to filter the sixth microwave signal, extract its harmonic signals and amplify them to obtain the seventh microwave signal. The second frequency divider is used to divide the seventh microwave signal to obtain the eighth microwave signal; The second filter is used to filter the eighth microwave signal and extract the signal at the required frequency point as the output microwave signal from its first output terminal. And the harmonic signal of the eighth microwave signal is extracted to obtain the ninth microwave signal, which is then output from its second output terminal; as well as The second electro-optical conversion unit is used to modulate the ninth microwave signal into the optical domain to form the third optical signal.

10. The fiber optic frequency transmission system compatible with both the same frequency and its harmonics as described in claim 8, characterized in that: The optical fiber transmission link is formed by connecting multiple bidirectional repeater stations in series via optical fiber links to form a single-fiber bidirectional serial link; the bidirectional repeater station includes an optical repeater station and / or an electrical repeater station, the optical repeater station includes a bidirectional optical amplification unit, and the electrical repeater station includes a photoelectric conversion unit and an electro-optical conversion unit connected in series.

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