Wavelength division multiplexing long-distance optical transmission link phase passive compensation method and device

Abstract

The invention discloses a wavelength division multiplexing long-distance optical transmission link phase passive compensation method and device, and the device is characterized in that a first laser is connected with an optical coupler through a cascade modulator, the cascade modulator receives a modulation signal, the optical coupler is connected with a first optical filter and a second optical filter, and the first optical filter and the second optical filter are connected with the first laser; the first optical filter is connected with a first optical wavelength division multiplexer through an optical circulator, the first optical wavelength division multiplexer is connected with a second optical wavelength division multiplexer through an optical fiber, the second optical wavelength division multiplexer is connected with an optical reflection module and a third optical filter, and the third optical filter is connected with a third optical detector. The optical circulator is connected with the power divider through the first optical detector, the second optical filter is connected with the power divider through the second optical detector, the power divider is connected with the optical modulator, and the second laser is connected with the first optical wavelength division multiplexer through the optical modulator; the invention has the advantages of stable phase, simple system, fast response and high reliability.

Description

Technical Field

[0001] The present invention relates to the field of microwave signal transmission, and particularly to a method and device for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link. Background Art

[0002] With the rapid development of atomic clock and optical fiber communication technologies, and relying on the advantages of low loss, wide bandwidth, and anti-electromagnetic interference of optical fibers, the high-stability transmission of time and frequency signals through optical fibers has become a current research hotspot and is gradually playing an increasingly important role in fields such as scientific research, astronomical observation, and national defense construction.

[0003] The frequency and time signal transmission methods mainly include wireless transmission, coaxial cable transmission, satellite transmission, optical fiber transmission, etc. The wireless signal transmission method mainly uses short-wave signals to reflect signals through the ionosphere in the atmosphere and transmit them through the atmospheric channel to the receiving antenna end, and then compare them with the clock at the receiving end to achieve signal and clock synchronization. However, the distribution, height, and structure of the ionosphere are usually random and are easily affected by factors such as atmospheric turbulence. The delay of the signal reaching the user also changes, resulting in low signal transmission accuracy, and the accuracy of clock synchronization is limited by the stability of the ionosphere.

[0004] The advantage of coaxial cable-based signal transmission is its relatively wide bandwidth, but coaxial cables have large losses, limited long-distance transmission capabilities, and the transmission delay is also affected by pressure and temperature. In addition, the cost of laying and maintaining cables is also very high.

[0005] A representative application of satellite-based time and frequency transmission is the global satellite navigation and positioning system for positioning, navigation, etc. The GPS global navigation and positioning system composed of 24 satellites has a highly stable clock reference on each satellite. By synchronizing and encoding each sub-satellite, the encoded signal is transmitted to the receiving station on the ground. Subsequently, the ground station calculates the relative delay based on the received multi-satellite encoded signals, and thus the specific position of the target can be obtained. However, affected by atmospheric disturbances, the stability of the space-ground link is poor, and it often requires long-term averaging to improve the transmission stability, which is difficult to meet the requirements of high-precision frequency transmission, and this directly affects the positioning accuracy of the system.

[0006] Optical fiber transmission has significant advantages. First, its low loss and anti-electromagnetic interference advantages make the transmission stability of frequency signals using optical fiber links much higher than other methods, especially in short-term stability, compared with atmospheric channels and satellite-to-ground channels. Second, its high bandwidth characteristics make the signal bandwidth that can be transmitted by optical fiber links very considerable. In many applications that require the transmission and reception of high-frequency, wide-bandwidth signals, such as in distributed antenna arrays for deep space exploration, high-frequency microwave / millimeter wave signals need to be transmitted and distributed, and coaxial cables or atmospheric channels cannot support the long-distance transmission of such high-frequency signals. The use of optical fibers with large transmission bandwidth, low loss, strong anti-interference, high security and stable performance can effectively avoid these problems. In addition, with the development of optical communication technology, optical devices and optoelectronic devices have become quite mature, and optical fibers have been widely laid, laying a good foundation for the use of optical fibers to transmit frequency signals.

[0007] The key problem faced by optical fiber time-frequency transmission is that the transmission delay of optical fiber is easily affected by environmental factors such as external temperature and pressure, resulting in delay and phase instability of the transmitted signal. In particular, for long-distance optical fiber links, the length and effective refractive index of the optical fiber will also be affected by the temperature, external stress and even the rotation of the earth, which will cause the phase of the transmitted signal to be distorted. To address this problem, a large number of active phase control and compensation methods have been proposed, such as a microwave photonic Ising machine phase control system disclosed in Chinese Patent Publication No. CN117424649A. However, the above phase compensation method is affected by environmental changes, the compensated phase is unstable, and the system is complex, slow to respond, and has low reliability. Summary of the invention

[0008] The technical problem to be solved by the present invention is that the phase compensation method of the optical fiber transmission link in the prior art changes due to environmental changes, the compensated phase is unstable, and the system is complex, the response speed is slow, and the reliability is low.

[0009] The present invention solves the above technical problems through the following technical means: A method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link. The modulation signal is loaded onto the optical carrier signal output by the first laser through a cascaded modulator. The optical frequency comb signal output by the cascaded modulator is divided into two optical signals with equal power after passing through an optical coupler. One of the optical signals passes through a first optical filter to filter out the optical carrier signal and the first-order sideband signal, and is input into an optical circulator. It is multiplexed into a single optical fiber through a first optical wavelength division multiplexer and forward-transmitted to a second optical wavelength division multiplexer for demultiplexing and then enters an optical reflection module. The optical reflection module reflects the transmitted optical signal back, and after being input into the optical circulator, it is output from another port of the optical circulator to a first optical detector. After photoelectric conversion, a radio frequency signal is output; the other optical signal output by the optical coupler passes through a second optical filter to filter out the optical carrier signal and the third-order sideband signal, and is input into a second photodetector. The second photodetector outputs the third-order radio frequency signal of the modulation signal. The signals output by the first photodetector and the second photodetector are both input into a power divider for combined output; the signal output by the combined output of the power divider is loaded onto an optical modulator to modulate the optical signal output by the second laser. The modulated signal is then multiplexed into a single optical fiber through the first optical wavelength division multiplexer and forward-transmitted to the second optical wavelength division multiplexer for demultiplexing and then enters a third optical filter to filter out the first-order sideband signal and the third-order sideband signal, and then is output to a third optical detector for beat frequency output.

[0010] Further, the first laser outputs a single-wavelength laser signal as the optical carrier signal.

[0011] Further, the frequency of the modulation signal is 1 / 2 of the frequency of the radio frequency signal to be transmitted.

[0012] Further, the frequency comb interval of the optical frequency comb signal output by the cascaded modulator is the frequency of the loaded modulation signal, and the teeth of the optical frequency comb signal at least include the first-order sideband signal and the third-order sideband signal of the modulation signal.

[0013] Further, the optical reflection module is an optical mirror or another optical circulator.

[0014] Further, the two optical signals input into the first optical wavelength division multiplexer are transmitted through the same optical fiber.

[0015] Further, the second laser outputs a single-wavelength laser signal as the optical carrier and inputs it into the optical modulator.

[0016] Further, the wavelength of the second laser is different from that of the first laser, and the wavelength interval between the two is greater than 6 times the frequency of the modulation signal.

[0017] Further, the RF signal output by the first optical detector is a first-order RF signal. The first-order RF signal output by the first photodetector and the third-order RF signal output by the second optical detector are both input into a power divider for combined output.

[0018] The present invention further provides a wavelength-division multiplexing long-distance optical transmission link phase passive compensation device. The device applies the above method of the claims. The device includes a first laser, a second laser, a cascaded modulator, an optical coupler, a first optical filter to a third optical filter, a first photodetector to a third photodetector, a power divider, an optical modulator, an optical circulator, a first optical wavelength-division multiplexer, a second optical wavelength-division multiplexer, and an optical reflection module. The first laser is connected to the optical coupler via the cascaded modulator. The cascaded modulator receives a modulation signal. The optical coupler is respectively connected to the first optical filter and the second optical filter. The first optical filter is connected to the first optical wavelength-division multiplexer via the optical circulator. The first optical wavelength-division multiplexer is connected to the second optical wavelength-division multiplexer via an optical fiber. The second optical wavelength-division multiplexer is connected to the optical reflection module and the third optical filter. The third optical filter is connected to the third photodetector. The optical circulator is connected to the power divider via the first photodetector. The second optical filter is connected to the power divider via the second photodetector. The power divider is connected to the optical modulator. The second laser is connected to the first optical wavelength-division multiplexer via the optical modulator.

[0019] The advantages of the present invention are as follows:

[0020] (1) Based on microwave photon transmission technology, the present invention adopts a dual-wavelength multiplexing transmission technology. By obtaining the phase change in the optical fiber link through a round-trip transmission link and then through beat-frequency pre-modulation, the phase stability of the transmitted RF signal can be achieved. The passive compensation method adopted is not affected by environmental changes. The system architecture is a fully analog real-time automatic compensation, without the need for a complex feedback control circuit, with a fast response speed and high reliability.

[0021] (2) Through the wavelength-division multiplexing method, the present invention obtains the phase change in the optical fiber link through a single-wavelength round-trip transmission link, and then through modulation on another wavelength optical signal, and finally through the method of beat-frequency cancellation, the elimination of the phase change caused by the influence of the environment on the optical transmission link is realized.

[0022] (3) The two optical signals of the present invention are transmitted through the same optical fiber, which ensures the consistency of the phase changes caused by environmental influences such as temperature and stress in the passive compensation during the long-distance transmission process. At the same time, the optical fiber after demultiplexing by the wavelength-division multiplexer is also as short as possible to reduce the compensation error of the system. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of a wavelength-division multiplexing long-distance optical transmission link phase passive compensation device disclosed in an embodiment of the present invention. Detailed implementation manners

[0024] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] As Figure 1 shown, an embodiment of the present invention provides a method and apparatus for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link. The apparatus includes a first laser, a second laser, a cascaded modulator, an optical coupler, a first optical filter, a second optical filter, a third optical filter, a first optical detector, a second optical detector, a third optical detector, a power splitter, an optical modulator, an optical circulator, a first optical wavelength division multiplexer, a second optical wavelength division multiplexer, a transmission optical fiber, an optical reflection module, etc.

[0026] The first laser outputs a single-wavelength laser signal as an optical carrier signal and inputs it into the cascaded modulator. The optical carrier signal E 1 has the following expression:[[]]

[0027]

[0028] where A is the amplitude of the optical carrier signal, w 1 is the angular frequency of the optical carrier signal, is the initial phase of the optical carrier signal.

[0029] The modulation signal is loaded onto the optical carrier signal output by the first laser through the cascaded modulator. The frequency of the loaded modulation signal is 1 / 2 of the radio frequency signal frequency f m to be transmitted. The optical signal output by the cascaded modulator is an optical frequency comb signal. The frequency comb interval is the frequency of the loaded modulation signal. The comb teeth include at least the 1st and 3rd sidebands of the modulation signal. Its expression E 10 is as follows:[[]]

[0030]

[0031] Only the 1st and 3rd sidebands are retained in the above expression, and other sideband terms are omitted. Where A 1 , A 3 correspond to the amplitudes of the 1st and 3rd sideband signals respectively, and θ represents the initial phase of the radio frequency signal to be transmitted.

[0032] The optical frequency comb signal output by the cascaded modulator is divided into two optical signals with equal power after passing through an optical coupler. One of the optical signals passes through a first optical filter to filter out the optical carrier signal and the first-order sideband signal and is input into an optical circulator. After passing through the circulator, it is transmitted forward through one fiber. The expression of the forward-transmitted signal is:

[0033]

[0034] The above-mentioned optical signal is input into a first optical wavelength division multiplexer after passing through the circulator, multiplexed into one fiber for forward transmission. After long-distance transmission, it is input into a second optical wavelength division multiplexer for demultiplexing, output from the corresponding wavelength channel and then enters an optical reflection module. The optical signal entering the optical reflection module is reflected back and continues to be transmitted backward along the original path in the original fiber. The optical reflection module can be implemented using an optical mirror, an optical circulator, etc.

[0035] The backward-transmitted optical signal is input into the optical circulator and then output from the other port of the optical circulator and connected to a first photodetector. After photoelectric conversion, a radio frequency signal is output. Then, the phase change of the radio frequency signal caused by the influence of the environment through the round-trip optical transmission link, and the expression of the radio frequency signal is:

[0036] e 1u =a 1u cos(f m t / 2+θ / 2+2ΔT*f m / 2)=a 1u cos(f m t / 2+θ / 2+ΔT*f m )

[0037] where a 1u is the amplitude of the converted radio frequency signal, and ΔT is the time change after the signal passes through the one-way optical fiber transmission link.

[0038] The other optical signal output by the optical coupler passes through a second optical filter to filter out the optical carrier signal and the third-order sideband signal. This signal is then input into a second photodetector to output the third-order radio frequency signal of the modulation signal. The expression of the third-order radio frequency signal of the modulation signal is:

[0039] e 3u =a 3u cos(3f m t / 2+3θ / 2)

[0040] The first-order radio frequency signal and the third-order radio frequency signal respectively output by the aforementioned first photodetector and second photodetector are both input into a power divider for combined output. The expression of the output signal of the power divider is:

[0041] e sum =a1u cos(f m t / 2 + θ / 2 + ΔT*f m ) + a 3u cos(3f m t / 2 + 3θ / 2)

[0042] The second laser outputs a single - wavelength laser signal as an optical carrier. The wavelength of the second laser is different from that of the first laser, and the wavelength interval should be at least greater than 6 times the modulation signal frequency. The optical signal output by the second laser is input into an optical modulator. The RF signal output by the multiplexer combination of the foregoing power divider is loaded on the modulator, and the signal after modulating the optical signal output by the second laser also passes through the first optical wavelength division multiplexer and is multiplexed into the transmission optical fiber for forward transmission.

[0043] The foregoing forward - transmitted signal passes through long - distance optical fiber transmission and then passes through the second optical wavelength division multiplexer for demultiplexing. After outputting from the corresponding wavelength channel, it is connected to the third optical filter, and the 1st - order and 3rd - order sideband signals are filtered out and output to the third optical detector for beat - frequency output. The signal output by the third optical detector is expressed as:

[0044] e 0 = a 0 cos[3f m (t + ΔT) / 2 + 3θ / 2 - f m (t + ΔT) / 2 + θ / 2 - ΔT*f m = a 0 cos(f m t + θ)

[0045] Thus, the phase change generated by the influence of the environment on the optical transmission link is offset. The phase change in the transmission link does not exist in the finally output RF signal, thus ensuring the output of a phase - stable RF signal of the system. The finally output RF signal is twice the frequency of the modulation signal.

[0046] It should be noted that the two optical signals input into the first optical wavelength division multiplexer are transmitted through the same optical fiber, ensuring the consistency of the phase changes caused by environmental influences such as temperature and stress for passive compensation during long - distance transmission. However, at the same time, it should also be noted that the optical fiber after demultiplexing by the second optical wavelength division multiplexer should be as short as possible to reduce the compensation error of the system.

[0047] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link, characterized in that: The modulation signal is loaded on the optical carrier signal output by the first laser through the cascade modulator. The optical frequency comb signal output by the cascade modulator is divided into two optical signals of equal power after passing through the optical coupler. One of the optical signals passes through the first optical filter, filters out the optical carrier signal and the first-order sideband signal, and inputs into the optical circulator. The optical signal is multiplexed into an optical fiber through the first optical wavelength division multiplexer and forwardly transmitted to the second optical wavelength division multiplexer for demultiplexing and then enters the optical reflection module. The optical reflection module reflects the transmitted optical signal back, inputs into the optical circulator, and then outputs from the other port of the optical circulator to the first optical detector, and outputs the radio frequency signal after photoelectric conversion. The other optical signal output by the optical coupler The optical signal passes through the second optical filter, filters out the optical carrier signal and the third-order sideband signal, and is input into the second photodetector. The second photodetector outputs the third-order radio frequency signal of the modulated signal. The signals output by the first photodetector and the second photodetector are both input into the power divider for combined output. The combined output signal of the power divider is loaded onto the optical modulator, and the optical signal output by the second laser is modulated. The modulated signal is then multiplexed into an optical fiber through the first optical wavelength division multiplexer and forwardly transmitted to the second optical wavelength division multiplexer for demultiplexing, and then enters the third optical filter, filters out the first-order sideband signal and the third-order sideband signal, and then is output to the third optical detector for beat frequency output.

2. A method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link according to claim 1, characterized in that: The first laser outputs a single-wavelength laser signal as an optical carrier signal.

3. The method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link according to claim 1, characterized in that: The frequency of the modulation signal is 1 / 2 of the frequency of the radio frequency signal to be transmitted.

4. The method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link according to claim 1, characterized in that: The frequency comb interval of the optical frequency comb signal output by the cascade modulator is the frequency of the loaded modulation signal, and the comb teeth of the optical frequency comb signal at least include the first-order sideband signal and the third-order sideband signal of the modulation signal.

5. The method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link according to claim 1, characterized in that: The light reflection module is a light reflection mirror or another light circulator.

6. The method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link according to claim 1, characterized in that: The two optical signals input into the first optical wavelength division multiplexer are transmitted through the same optical fiber.

7. The method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link according to claim 1, characterized in that: The second laser outputs a single-wavelength laser signal as an optical carrier which is input into the optical modulator.

8. The method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link according to claim 1, characterized in that: The wavelength of the second laser is different from that of the first laser, and the wavelength interval between the two is greater than 6 times the frequency of the modulation signal.

9. The method for passive phase compensation of a wavelength division multiplexing long-distance optical transmission link according to claim 1, characterized in that: The radio frequency signal output by the first photodetector is a first-order radio frequency signal. The first-order radio frequency signal output by the first photodetector and the third-order radio frequency signal output by the second photodetector are both input into the power divider and combined for output.

10. A wavelength division multiplexing long-distance optical transmission link phase passive compensation device, characterized in that: The device applies the method described in any one of claims 1 to 9, and comprises a first laser, a second laser, a cascade modulator, an optical coupler, a first optical filter to a third optical filter, a first optical detector to a third optical detector, a power divider, an optical modulator, an optical circulator, a first optical wavelength division multiplexer, a second optical wavelength division multiplexer and an optical reflection module, wherein the first laser is connected to the optical coupler via the cascade modulator, the cascade modulator receives a modulated signal, the optical coupler is respectively connected to the first optical filter and the second optical filter, the first optical filter is connected to the first optical wavelength division multiplexer via the optical circulator, the first optical wavelength division multiplexer is connected to the second optical wavelength division multiplexer via an optical fiber, the second optical wavelength division multiplexer is connected to the optical reflection module and the third optical filter, the third optical filter is connected to the third optical detector, the optical circulator is connected to the power divider via the first optical detector, the second optical filter is connected to the power divider via the second optical detector, the power divider is connected to the optical modulator, and the second laser is connected to the first optical wavelength division multiplexer via the optical modulator.

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