CN111064515A - Optical fiber transmission system - Google Patents
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 64
- 230000005540 biological transmission Effects 0.000 title claims abstract description 60
- 230000003287 optical effect Effects 0.000 claims abstract description 92
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
- H04B10/2519—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion using Bragg gratings
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
- H04B10/25133—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion including a lumped electrical or optical dispersion compensator
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Abstract
The invention discloses an optical fiber transmission system, comprising: the QPSK optical signal transmitting unit and the QPSK optical signal receiving unit transmit DP-QPSK optical signals through the optical fiber transmission link, the tail end of the optical fiber transmission link, which is connected with the QPSK optical signal receiving unit, is provided with an optical fiber Bragg grating for performing dispersion compensation on the signals in an optical domain, the output end of the optical fiber Bragg grating is connected with the input end of the QPSK optical signal receiving unit, the output end of the QPSK optical signal receiving unit is connected with the input end of the DSP signal processing module, and the DSP signal processing module is internally provided with a dispersion compensation unit for performing dispersion compensation on the signals in an electrical domain. Through the double dispersion compensation of the signals in the optical domain and the electrical domain, the loss of the optical fiber signals in long-distance transmission can be effectively compensated, and the communication quality of optical fiber transmission is improved.
Description
Technical Field
The invention relates to the field of optical signal transmission, in particular to an optical fiber transmission system.
Background
With the continuous development of communication technology, wired and wireless broadband access users will continue to grow rapidly and the bandwidth demand of a single user will increase exponentially in a long period of time in the future, while broadband applications such as HDTV, internet of things, cloud computing and the like are emerging continuously, transmission bandwidth will also continue to increase, and operators face a situation that bandwidth increment is not increased, so that a backbone network will face huge transmission pressure for a long time in the future. Polarization-multiplexed quadrature phase shift keying (DP-QPSK) based on coherent light becomes the mainstream technology of high-speed optical communication transmission, the dispersion problem in optical fiber communication is the main factor of signal degradation, and especially with the increase of speed and the increase of transmission distance, the dispersion problem in optical fiber communication is more serious, and the communication quality is seriously affected.
Disclosure of Invention
The present invention is directed to at least one of the technical problems in the prior art, and therefore, an object of the present invention is to provide an optical fiber transmission system, which can perform dispersion compensation on signals and improve the communication quality of optical fiber transmission.
The technical scheme adopted by the invention is as follows:
an optical fiber transmission system comprising: the QPSK optical signal transmitting unit and the QPSK optical signal receiving unit transmit DP-QPSK optical signals through the optical fiber transmission link, the tail end of the optical fiber transmission link, which is connected with the QPSK optical signal receiving unit, is provided with an optical fiber Bragg grating for performing dispersion compensation on the signals in an optical domain, the output end of the optical fiber Bragg grating is connected with the input end of the QPSK optical signal receiving unit, the output end of the QPSK optical signal receiving unit is connected with the input end of the DSP signal processing module, and the DSP signal processing module is internally provided with a dispersion compensation unit for performing dispersion compensation on the signals in an electrical domain.
The optical fiber transmission system according to the embodiment of the invention has at least the following technical effects: generating a DP-QPSK optical signal through a QPSK optical signal transmitting unit, arranging an optical fiber Bragg grating at the tail end of an optical fiber transmission link, and performing dispersion compensation on the DP-QPSK optical signal in an optical domain; meanwhile, the output end of the QPSK optical signal receiving unit is connected with a DSP signal processing module, and the dispersion compensation is carried out on the signal in the electric domain through a dispersion compensation unit in the DSP signal processing module. Through the double dispersion compensation of the signals in the optical domain and the electrical domain, the loss of the optical fiber signals in long-distance transmission can be effectively compensated, and the communication quality of optical fiber transmission is improved.
According to some embodiments of the present invention, the QPSK optical signal transmitting unit includes a laser transmitter, a first polarization beam splitter, two IQ modulators, a random code generator, and a polarization beam combiner; the output end of the laser transmitter is connected with the input end of a first polarization beam splitter for splitting an optical signal into two beams of polarized light polarized along X and Y, the output end of the first polarization beam splitter is respectively connected with the input ends of two IQ modulators for respectively inputting one beam of polarized light, the random code generator is respectively connected with the input ends of the two IQ modulators for providing random code elements to enable the IQ modulators to generate QPSK modulated optical signals, the output ends of the two IQ modulators are respectively connected with the input end of a polarization beam combiner for combining the two beams of QPSK modulated optical signals into one beam of DP-QPSK optical signals, and the output end of the polarization beam combiner is connected with an optical fiber transmission link for outputting DP-QPSK optical signals.
According to some embodiments of the invention, the IQ-modulator consists of two MZM-modulators and one 90 ° PM-modulator for forming the in-phase and quadrature two-way non-return-to-zero pulsed electrical signal I, Q.
According to some embodiments of the present invention, an erbium-doped fiber amplifier is further disposed between the end of the optical fiber transmission link and the fiber bragg grating for amplifying the DP-QPSK optical signal.
According to some embodiments of the present invention, a filter is further disposed between the QPSK optical signal receiving unit and the fiber bragg grating.
According to some embodiments of the present invention, the QPSK optical signal receiving unit includes a second polarization beam splitter, two mixers, a local oscillator laser, and a photodetector, the second polarization beam splitter being configured to separate the received DP-QPSK optical signal into polarization-multiplexed orthogonal signals; the output end of the second polarization beam splitter is respectively connected with the input ends of the two frequency mixers, the output end of the local oscillator laser is respectively connected with the input ends of the two frequency mixers, and the frequency mixers are used for carrying out 90-degree frequency mixing on orthogonal signals and local oscillator signals; the output end of the frequency mixer is connected with the input end of the photoelectric detector to convert the frequency-mixed signals into electric signals, and the output end of the photoelectric detector is connected with the input end of the DSP signal processing module.
According to some embodiments of the present invention, the DSP signal processing module further includes an a/D conversion unit, an IQ orthogonality compensation unit, a clock recovery unit, an adaptive equalization unit, a polarization demultiplexing unit, a phase/frequency offset estimation unit, and a decoding decision unit, where the a/D conversion unit, the IQ orthogonality compensation unit, the clock recovery unit, the dispersion compensation unit, the adaptive equalization unit, the polarization demultiplexing unit, the phase/frequency offset estimation unit, and the decoding decision unit are sequentially connected, the IQ orthogonality compensation unit is configured to perform orthogonal normalization processing on the signal, the clock recovery unit is configured to keep the synchronization between the electrical signal in the DSP signal processing module and the clock frequency of the QPSK optical signal transmitting unit, the adaptive equalization unit is configured to eliminate nonlinear loss, and the polarization demultiplexing unit is configured to separate out the signal in a polarization state, the phase/frequency offset estimation unit is used for eliminating phase and frequency deviation between the local oscillator laser signal and the carrier signal, and the decoding decision unit is used for recovering the carrier signal into an original data signal.
According to some embodiments of the invention, the IQ orthogonality compensation unit performs an orthogonal normalization process on the signal using a GOSP orthogonality compensation algorithm.
According to some embodiments of the invention, the adaptive equalization unit eliminates non-linear losses by a unity impulse response filter.
According to some embodiments of the invention, the dispersion compensation unit performs color gamut compensation on the signal using a frequency domain dispersion compensation algorithm.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
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The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic block diagram of an optical fiber transmission system according to an embodiment of the present invention;
fig. 2 is a schematic block diagram of a QPSK optical signal transmitting unit according to an embodiment of the present invention;
fig. 3 is a schematic block diagram of a QPSK optical signal receiving unit according to an embodiment of the present invention;
fig. 4 is a functional block diagram of a DPS signal processing module in an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
In the description of the present invention, if there are first and second described only for the purpose of distinguishing technical features, it is not understood that relative importance is indicated or implied or that the number of indicated technical features or the precedence of the indicated technical features is implicitly indicated or implied.
Referring to fig. 1, an optical fiber transmission system of the present invention includes: the QPSK optical signal transmitting unit 100, the optical fiber transmission link 200, the QPSK optical signal receiving unit 300, and the DSP signal processing module 400, the QPSK optical signal transmitting unit 100 generates DP-QPSK optical signals to enter the optical fiber transmission link 200 for transmission, the middle part of the optical fiber transmission link 200 is a conventional optical fiber transmission device, a receiving end of the optical fiber transmission device is sequentially connected with an erbium-doped optical fiber amplifier 220, an optical fiber bragg grating 210, and a filter 230, the erbium-doped optical fiber amplifier 220 amplifies the optical signals to reduce loss during optical fiber transmission, the optical fiber bragg grating 210 performs dispersion compensation on the signals in an optical domain, and the compensation principle is D (λ) L + DFBG(λ) ═ 0, where D (λ) is the wavelength of the fiberThe dispersion coefficient of λ; l is the transmission distance of the optical fiber transmission link 200; dFBG(λ) is the total amount of dispersion of a single fiber bragg grating.
The filter 230 is configured to send the filtered DP-QPSK optical signal to the QPSK optical signal receiving unit 300, an output end of the QPSK optical signal receiving unit 300 is connected to an input end of the DSP signal processing module 400, and a dispersion compensation unit 410 is disposed in the DSP signal processing module 400 and configured to perform dispersion compensation on the signal in an electrical domain, preferably, in this embodiment, the dispersion compensation unit 410 performs color gamut compensation on the signal by using a frequency domain dispersion compensation algorithm.
A QPSK optical signal transmitting unit 100 is used for generating a DP-QPSK optical signal, an optical fiber Bragg grating 210 is arranged at the tail end of an optical fiber transmission link 200, and dispersion compensation is carried out on the DP-QPSK optical signal in an optical domain; meanwhile, the output end of the QPSK optical signal receiving unit 300 is connected to the DSP signal processing module 400, and the dispersion compensation unit 410 in the DSP signal processing module 400 performs dispersion compensation on the signal in the electrical domain. Through the double dispersion compensation of the signals in the optical domain and the electrical domain, the loss of the optical fiber signals in long-distance transmission can be effectively compensated, and the communication quality of optical fiber transmission is improved.
Referring to fig. 2, the QPSK optical signal transmitting unit 100 includes a laser transmitter 110, a first polarization beam splitter 120, two IQ modulators 130, a random code generator 140, and a polarization beam combiner 150; the output end of the laser transmitter 110 is connected to the input end of the first polarization beam splitter 120, the laser transmitter 110 converts the original data signal into an optical signal and inputs the optical signal to the first polarization beam splitter 120(PBS), the output end of the first polarization beam splitter 120 is connected to the input ends of the two IQ modulators 130, the random code generator 140(PRBS) is connected to the input ends of the two IQ modulators 130, the output ends of the two IQ modulators 130 are connected to the input end of the polarization beam combiner 150(PBC), and the output end of the polarization beam combiner 150 is connected to the optical fiber transmission link 200.
The IQ modulator 130 consists of two MZM modulators and one 90 ° PM modulator to form a co-directional and quadrature two-way non-return-to-zero pulsed electrical signal I, Q.
The working process of the QPSK optical signal transmitting unit comprises the following steps:
the laser transmitter 110 converts an original data signal into an optical signal and inputs the optical signal into a first polarization beam splitter 120, the first polarization beam splitter 120 splits the optical signal into two beams of polarized light polarized along X and Y, the two beams of polarized light are respectively input into an IQ modulator 130 as a modulation light source, a random code element provided by a random code generator 140(PRBS) is subjected to serial-parallel conversion and then is divided into two columns of random code elements and respectively input into an IQ modulator, the IQ modulator 130 is composed of two MZM modulators and a 90 ° PM modulator, taking an X branch as an example, an optical signal X modulated by one MZM modulator is input into an IQ modulatorQOptical signal X phase-shifted by 90 DEG with another MZM modulator and a 90 DEG PM modulatorIThe coupling is a path of QPSK modulated optical signal, and the two IQ modulators respectively input a bundle of QPSK modulated optical signals into the polarization beam combiner 150 and combine the bundle of DP-QPSK optical signals into a bundle of DP-QPSK optical signals, which is then transmitted to the optical fiber transmission link 200.
Referring to fig. 3, the QPSK optical signal receiving unit 300 includes a second polarization beam splitter 310, two mixers 320, a local oscillator laser 330, and a photodetector 340, wherein an output end of the second polarization beam splitter 310 is connected to input ends of the two mixers 320, respectively, and an output end of the local oscillator laser 330 is connected to input ends of the two mixers 320, respectively; preferably, in the present embodiment, both the mixers 320 adopt 90 ° optical mixers; the output terminals of the two mixers 320 are connected to the input terminal of the photodetector 340, and the output terminal of the photodetector 340 is connected to the input terminal of the DSP signal processing block 400.
The working flow of the QPSK optical signal receiving unit 300 is as follows:
the DP-QPSK optical signal is separated into polarization-multiplexed quadrature signals by the second polarization beam splitter 310 (PBS); similarly, the local oscillator signal provided by the local oscillator laser 330 is also split into two local oscillator signals in orthogonal polarization states, the 90 ° optical mixer performs 90 ° coherent mixing on the orthogonal signal and the local oscillator signal, and each optical signal after mixing is converted into four paths of electrical signals X by the photodetector 340I1、XQ1、YI1And YQ1And then input to the DSP signal processing block 400.
Referring to fig. 4, the DSP signal processing module 400 is further provided with an a/D conversion unit 420, an IQ orthogonality compensation unit 430, a clock recovery unit 440, an adaptive equalization unit 450, a polarization demultiplexing unit 460, a phase/frequency offset estimation unit 470, and a decoding decision unit 480, wherein the a/D conversion unit 420, the IQ orthogonality compensation unit 430, the clock recovery unit 440, the dispersion compensation unit 410, the adaptive equalization unit 450, the polarization demultiplexing unit 460, the phase/frequency offset estimation unit 470, and the decoding decision unit 480 are sequentially connected.
The DSP signal processing module 400 repairs and compensates transmission damage of the optical fiber transmission link 200, the a/D conversion unit 420 converts the analog electrical signal into a digital signal, and the IQ orthogonality compensation unit 430 performs orthogonal normalization processing on the signal by using a GOSP orthogonality compensation algorithm to compensate IQ non-orthogonality; because the sampling clock of the a/D conversion unit 420 and the clock of the QPSK optical signal transmitting unit 100 output data are independent, so that the clock at the transmitting and receiving ends has differences in frequency and phase, the clock recovery unit 440 is required to synchronize the electrical signal in the DSP signal processing module with the clock frequency of the QPSK optical signal transmitting unit.
The operation flow of the dispersion compensation unit 410 is: the method comprises the steps of dividing a time domain signal into a plurality of sections, carrying out FFT (fast Fourier transform) on the time domain signal of each section, transforming the time domain signal into a frequency domain, multiplying the time domain signal by a frequency domain transmission function G (z, w) to obtain a dispersion-compensated frequency domain signal, and carrying out IFFT (inverse fast Fourier transform) on the frequency domain signal to change the signal from the frequency domain to the time domain.
Wherein the frequency domain transfer function is formulated as
Wherein j is an imaginary unit, and D (lambda) is the dispersion coefficient of the optical fiber at the wavelength lambda; l is the transmission distance of the optical fiber transmission link 200, c is the speed of light, and w is a frequency component of the optical carrier.
After performing color gamut compensation on the signal, the adaptive equalization unit 450 eliminates non-linear loss through the unit impulse response filter, the polarization demultiplexing unit 460 is configured to separate the signal in the polarization state, in this embodiment, the polarization demultiplexing unit 460 separates the signal in the polarization state by using a dish filter, the phase/frequency offset estimation unit 470 eliminates phase and frequency deviation between the local oscillation laser signal and the carrier signal, and a blind phase search algorithm or an M _ Rife algorithm may be used. The decoding decision unit 480 restores the signal of each I, Q branch to a carrier phase signal, and then restores the signal to the original data signal by the decision device.
By adopting the DSP signal processing module 400 of the embodiment of the invention to carry out IQ orthogonality compensation, clock recovery, dispersion compensation, nonlinear loss elimination and phase/frequency difference estimation compensation on the electric signal, the damage of optical fiber transmission is greatly eliminated, and the optical fiber communication quality in high-speed and long-distance application scenes is further improved.
In the description herein, reference to the description of the terms "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples," etc., means that a particular feature or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
Claims (10)
1. An optical fiber transmission system, comprising: a QPSK optical signal transmitting unit (100), an optical fiber transmission link (200), a QPSK optical signal receiving unit (300) and a DSP signal processing module (400), the QPSK optical signal transmitting unit (100) and the QPSK optical signal receiving unit (300) transmit DP-QPSK optical signals through an optical fiber transmission link (200), the end of the optical fiber transmission link (200) connected with the QPSK optical signal receiving unit (300) is provided with an optical fiber Bragg grating (210) for performing dispersion compensation on the signal in the optical domain, the output end of the fiber Bragg grating (210) is connected with the input end of a QPSK optical signal receiving unit (300), the output end of the QPSK optical signal receiving unit (300) is connected with the input end of the DSP signal processing module (400), a dispersion compensation unit (410) is arranged in the DSP signal processing module (400) and is used for carrying out dispersion compensation on signals in an electrical domain.
2. The optical fiber transmission system according to claim 1, wherein: the QPSK optical signal transmitting unit (100) comprises a laser transmitter (110), a first polarization beam splitter (120), two IQ modulators (130), a random code generator (140) and a polarization beam combiner (150); the output end of the laser transmitter (110) is connected with the input end of the first polarization beam splitter (120) for splitting the optical signal into two beams of polarized light along the X polarization and the Y polarization, the output end of the first polarization beam splitter (120) is respectively connected with the input ends of two IQ modulators (130) for respectively inputting a beam of polarized light, the random code generator (140) is respectively connected with the input ends of the two IQ modulators (130) for providing random code elements to enable the I Q modulator to generate QPSK modulated optical signals, the output ends of the two IQ modulators (130) are respectively connected with the input end of the polarization beam combiner (150) for combining the two QPSK modulated optical signals into one DP-QPSK optical signal, the output end of the polarization beam combiner (150) is connected with the optical fiber transmission link (200) for outputting DP-QPSK optical signals.
3. The optical fiber transmission system according to claim 2, wherein: the IQ modulator (130) consists of two MZM modulators and one 90 ° PM modulator for forming a co-directional and quadrature two-way non-return-to-zero pulsed electrical signal I, Q.
4. The optical fiber transmission system according to claim 1, wherein: an erbium-doped fiber amplifier (220) is further arranged between the tail end of the optical fiber transmission link (200) and the fiber Bragg grating (210) and is used for amplifying DP-QPSK optical signals.
5. The optical fiber transmission system according to claim 1, wherein: a filter (230) is further arranged between the QPSK optical signal receiving unit (300) and the fiber Bragg grating (210).
6. The optical fiber transmission system according to claim 1, wherein: the QPSK optical signal receiving unit (300) comprises a second polarization beam splitter (310), two mixers (320), a local oscillator laser (330) and a photoelectric detector (340), wherein the second polarization beam splitter (310) is used for separating a received DP-QPSK optical signal into polarization-multiplexed orthogonal signals; the output end of the second polarization beam splitter (310) is respectively connected with the input ends of the two mixers (320), the output end of the local oscillator laser (330) is respectively connected with the input ends of the two mixers (320), and the mixers (320) are used for mixing the orthogonal signal and the local oscillator signal by 90 degrees; the output end of the mixer (320) is connected with the input end of the photoelectric detector (340) for converting the mixed signal into an electric signal, and the output end of the photoelectric detector (340) is connected with the input end of the DSP signal processing module (400).
7. The optical fiber transmission system according to claim 1, wherein: the DSP signal processing module (400) is also internally provided with an A/D conversion unit (420), an IQ orthogonality compensation unit (430), a clock recovery unit (440), an adaptive equalization unit (450), a polarization demultiplexing unit (460), a phase/frequency offset estimation unit (470) and a decoding decision unit (480), wherein the A/D conversion unit (420), the IQ orthogonality compensation unit (430), the clock recovery unit (440), the dispersion compensation unit (410), the adaptive equalization unit (450), the polarization demultiplexing unit (460), the phase/frequency offset estimation unit (470) and the decoding decision unit (480) are sequentially connected, the IQ orthogonality compensation unit (430) is used for carrying out orthogonal normalization processing on signals, the clock recovery unit (440) is used for keeping the clock frequency of an electric signal QPSK in the DSP signal processing module and a QPSK optical signal transmitting unit synchronous, the adaptive equalization unit (450) is used for eliminating nonlinear loss, the polarization demultiplexing unit (460) is used for separating signals in a polarization state, the phase/frequency offset estimation unit (470) is used for eliminating phase and frequency deviation between a local oscillator laser signal and a carrier signal, and the decoding decision unit (480) is used for restoring the carrier signal into an original data signal.
8. The fiber optic transmission system of claim 7, wherein: the IQ orthogonality compensation unit (430) adopts a GOSP orthogonality compensation algorithm to carry out orthogonal normalization processing on the signals.
9. The fiber optic transmission system of claim 7, wherein: the adaptive equalization unit (450) eliminates non-linear losses by a unity impulse response filter.
10. The optical fiber transmission system according to any one of claims 1 or 7, wherein: the dispersion compensation unit (410) performs color gamut compensation on the signal by using a frequency domain dispersion compensation algorithm.
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| 曹圣皎等: "相干光OFDM通信系统中的IQ补偿和相位估计", 《光通信研究》 * |
| 郭显成，陈坤: "DP-QPSK相干光传输系统性能分析", 《信息通信》 * |
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| CN111934761B (en) * | 2020-08-12 | 2022-04-12 | 长春理工大学 | A high-speed coherent laser communication device against atmospheric turbulence based on few-mode parallel mixing |
| CN113098592A (en) * | 2021-03-31 | 2021-07-09 | 北京百度网讯科技有限公司 | Signal processing method and signal processing system |
| CN115941043A (en) * | 2022-11-21 | 2023-04-07 | 深圳华迅光通科技有限公司 | An optical communication module and an optical communication system using the optical communication module |
| CN117254859A (en) * | 2023-11-17 | 2023-12-19 | 鹏城实验室 | Coherent light transmission method and coherent light transmission system |
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