A five-dimensional coherent detection method and receiver

Abstract

The application discloses a five-dimensional coherent detection method and a receiver. The application is based on a dual-polarization 90-degree optical mixer, four pairs of balanced photodetectors, a single-ended photodetector and a digital domain light field reconstruction module, realizes complex light field reconstruction of single-sideband or double-sideband modulated local oscillator light, eliminates beat frequency damage between the local oscillator and a signal, and supports simultaneous coherent detection of polarization multiplexed signal light and single-sideband or double-sideband modulated local oscillator light. The application only needs to additionally increase a single-ended photodetector, uses the local oscillator light to transmit additional modulation information, and linearly expands the receiving signal dimension to five dimensions with the lowest hardware complexity. The application realizes linear expansion of the receiving dimension with the lowest hardware complexity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical fiber communication, and relates to a five-dimensional coherent detection method based on single-sideband or double-sideband modulated local oscillator light and a corresponding receiver. BACKGROUND

[0002] Optical fiber communication system is an important infrastructure of modern information society, carrying more than 95% of global network traffic transmission and exchange. Optical communication detection methods include two categories of direct detection and coherent detection.

[0003] The traditional intensity modulation direct detection method modulates the information to be transmitted on the optical power dimension, and obtains the signal through the square law detection of the photodetector at the receiving end, which has the advantages of simple structure and no colorization, but the spectral efficiency of the receiver is limited by the single-dimensional modulation and demodulation process. A series of direct detection methods have been evolved to realize phase and polarization diversity reception. By modulating a complex double-sideband signal on one polarization state and transmitting an unmodulated optical carrier on the other polarization state, a direct detection receiver based on Stokes vector can be constructed at the receiving end, which can expand the receiving dimension to two dimensions. Further, by modulating a complex double-sideband signal on one polarization state and transmitting a single-sideband modulated signal on the other polarization state, inverse rotation of three-dimensional Stokes space can be performed in the digital domain at the receiving end, and the signals on the two polarizations can be orthogonally recovered, thereby increasing the receiving dimension to three dimensions.

[0004] On the other hand, coherent detection uses a local oscillator laser at the receiving end to generate an unmodulated single-frequency local oscillator light, and through a dual-polarization 90-degree optical mixer and four pairs of balanced photodetectors, phase and polarization diversity reception of the signal is simultaneously realized, thereby expanding the modulation and reception dimensions to four dimensions. Moreover, since the electrical signal is linearly proportional to the complex optical field, coherent detection can support digital domain compensation of optical fiber chromatic dispersion, nonlinearity and other channel impairments, meeting the long-distance transmission requirements.

[0005] With the development of high-speed photodetectors and analog-to-digital converters towards the bottleneck of electrical bandwidth, the signal rate that can be detected by the optical receiver will be severely limited, so it is urgent to further improve the detection technology. SUMMARY

[0006] In view of the technical problems existing in the prior art, in order to expand the receiving signal dimension, the purpose of the present application is to provide a five-dimensional coherent detection method based on single-sideband or double-sideband modulated local oscillator light and a corresponding receiver, which potentially faces two application scenarios: (1) bidirectional transmission data center interconnection scene, four-dimensional and one-dimensional information are carried by signal light and local oscillator light respectively, and are detected simultaneously; (2) bidirectional transmission laser-free optical network structure, downlink four-dimensional signal light and uplink one-dimensional signal light are frequency-mixed with each other to realize simultaneous reception.

[0007] The receiver of the application comprises a dual-polarization 90-degree optical mixer, four balanced photodetectors, a single-ended photodetector, and a digital domain optical field reconstruction module, and realizes simultaneous coherent detection of polarization multiplexed signal light and single sideband or double sideband modulated local oscillator light.

[0008] To achieve the above object, the application adopts the following technical scheme:

[0009] A five-dimensional coherent detection method based on single sideband or double sideband modulated local oscillator light, comprising the following steps:

[0010] First step: a first laser is used to generate an optical carrier and input a first optical transmitter, the signal light generated by the first optical transmitter modulates the optical carrier to obtain polarization multiplexed signal light, which is transmitted in a first optical fiber channel; a second laser is used to generate an optical carrier and input a second optical transmitter, the second optical transmitter modulates the optical carrier to generate first local oscillator light through single sideband or double sideband modulation, which is transmitted in a second optical fiber channel;

[0011] Further, the first laser and the second laser can be the same laser or two independent lasers.

[0012] Second step: the signal light transmitted through the first optical fiber channel is input into a dual-polarization 90-degree optical mixer; the first local oscillator light transmitted through the second optical fiber channel is split into second local oscillator light and third local oscillator light by a beam splitter, the second local oscillator light and the polarization multiplexed signal light are input into the dual-polarization 90-degree optical mixer, and the third local oscillator light is input into a single-ended photodetector to generate a fifth electrical signal; the output of the dual-polarization 90-degree optical mixer is input into four balanced photodetectors respectively to generate first, second, third and fourth electrical signals;

[0013] Third step: in the digital signal processing at the receiving end, the fifth electrical signal output by the single-ended photodetector is subjected to digital domain optical field reconstruction to obtain a fifth digital signal, which then enters a second signal demodulation module to complete resampling, digital down-conversion, matched filtering, frame synchronization, channel equalization, downsampling and signal demodulation;

[0014] Fourth step: the first, second, third and fourth electrical signals output by the balanced photodetectors are respectively divided by the conjugate of the fifth digital signal in the digital domain optical field reconstruction module to obtain first, second, third and fourth digital signals, which then enter a first signal demodulation module to complete resampling, frequency offset estimation, digital down-conversion, matched filtering, frame synchronization, channel equalization, downsampling, carrier phase recovery and signal demodulation.

[0015] A coherent receiver based on single sideband or double sideband modulated local oscillator light for implementing the above method, comprising:

[0016] A light splitter module is connected with the local oscillator light input, and is used for splitting the received first local oscillator light into second local oscillator light and third local oscillator light;

[0017] A dual-polarization 90-degree optical mixer module is connected with the signal light input and the light splitter module, and is used for realizing coherent detection of the signal light and the second local oscillator light;

[0018] A single-ended photodetector module is connected with the light splitter module, and is used for realizing detection of the third local oscillator light, and generating a fifth electrical signal;

[0019] A balanced photodetector module is connected with the dual-polarization 90-degree optical mixer module, and is used for realizing photoelectric conversion, and generating first, second, third and fourth electrical signals;

[0020] A digital-domain light field reconstruction module is connected with the balanced photodetector module and the single-ended photodetector module, and is used for recovering a complex light field, and generating first, second, third, fourth and fifth digital signals.

[0021] Compared with the prior art, the present application has the following positive effects:

[0022] The method disclosed by the present application adopts single-sideband or double-sideband modulated local oscillator light to carry information, eliminates the second frequency beating damage of the local oscillator light through a single-ended photodetector and digital-domain light field reconstruction, eliminates the frequency beating interference between the local oscillator and the signal through division operation, realizes coherent detection of four-dimensional polarization multiplexed signal light and one-dimensional information carrying local oscillator light, expands the receiving dimension, and improves the receiver spectrum efficiency and channel rate. This scheme only needs to additionally increase one single-ended photodetector, and realizes linear expansion of the receiving dimension with the lowest hardware complexity. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of a coherent detection method based on single-sideband or double-sideband modulated local oscillator light according to an embodiment of the present application.

[0024] Figure 2 is a schematic diagram of a coherent receiver structure based on single-sideband or double-sideband modulated local oscillator light according to an embodiment of the present application. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below through specific embodiments and drawings.

[0026] The present application will be further described in detail below through specific embodiments and drawings. Figure 1 The implementation of the technical solution will be specifically described.

[0027] Step 1: A first laser is used to generate an optical carrier, which is input into a first optical transmitter for modulation to generate polarization multiplexed signal light [S x , S y ] T , wherein Sx and S y are X-polarized and Y-polarized optical signal components, respectively. The first optical fiber channel is used for transmitting the optical signal components to a receiving end; a second laser is used for generating an optical carrier, and a second optical transmitter is used for generating a first local oscillator light C+S C , wherein C is an optical carrier component, and S C is a single sideband or double sideband modulated optical signal, which is transmitted to the receiving end through a second optical fiber channel.

[0028] Second step: the first local oscillator light in the second optical fiber channel is divided into a second local oscillator light and a third local oscillator light by a beam splitter. The polarization multiplexed signal light in the first optical fiber channel and the second local oscillator light are input into a dual-polarization 90-degree optical mixer, and then input into a first to fourth balanced photodetector after polarization and phase diversity. Four different electrical signal components are obtained after the four balanced photodetectors are subtracted: a first electrical signal I1, a second electrical signal I2, a third electrical signal I3, and a fourth electrical signal I4. The four electrical signals are input into a digital domain optical field reconstruction module; the third local oscillator light is input into a single-ended photodetector to generate a fifth electrical signal I5, which is input into the digital domain optical field reconstruction module.

[0029] Third step, through the digital domain optical field reconstruction module, the fifth electrical signal I5 is reconstructed into a complex optical field, i.e., a fifth digital signal D5. If the first local oscillator light is a single sideband signal, the reconstructed fifth digital signal D5 is as follows

[0030]

[0031] , wherein H{·} represents Hilbert transform, and ln(·) represents natural logarithm operation.

[0032] If the first local oscillator light is a double sideband signal, the reconstructed fifth digital signal D5 is as follows

[0033]

[0034] Subsequently, the reconstructed fifth digital signal is input into a signal demodulation module to complete resampling, digital down-conversion, matched filtering, frame synchronization, channel equalization, downsampling, and signal demodulation.

[0035] Fourth step, in the digital domain optical field reconstruction module, for the first, second, third, and fourth electrical signals, the corresponding first, second, third, and fourth digital signals D 1 / 2 / 3 / 4 are reconstructed as follows

[0036] D1 = I1 / conj(D5)

[0037] D2 = I2 / conj(D5)

[0038] D3 = I3 / conj(D5)

[0039] D4 = I4 / conj(D5)

[0040] Wherein, conj(·) represents taking complex conjugate operation.

[0041] Subsequently, the reconstructed first, second, third and fourth digital signal input signals are input into a demodulation module to complete resampling, frequency offset estimation, digital down-conversion, matched filtering, frame synchronization, channel equalization, down-sampling, carrier phase recovery and signal demodulation.

[0042] Figure 2 A schematic diagram of a coherent receiver structure based on single-sideband or double-sideband modulation local oscillator light corresponding to the above method.

[0043] The receiver structure comprises: a splitter module connected to the local oscillator light input, for splitting the local oscillator light into second local oscillator light and third local oscillator light; a dual-polarization 90-degree optical mixer module connected to the signal light input and the splitter module, for realizing mixing of the signal light and the second local oscillator light to generate eight optical signals; first, second, third and fourth balanced photodetector modules connected to the dual-polarization 90-degree optical mixer module, for converting the input optical signals into first, second, third and fourth electrical signal outputs; a single-end photodetector module connected to the splitter module and a second coherent receiver module, for converting the input third local oscillator light into a fifth electrical signal output; a digital domain optical field reconstruction module connected to the first, second, third, fourth balanced photodetector modules and the single-end photodetector module, for converting the first, second, third, fourth and fifth electrical signals into first, second, third, fourth and fifth digital signals.

[0044] The above embodiments are only used to illustrate the technical solutions of the present application rather than limit it, and the ordinary skilled in the art can modify or equivalently replace the technical solutions of the present application without departing from the spirit and scope of the present application, the protection scope of the present application should be subject to the claims.

Claims

1. A method of five-dimensional coherent detection, comprising the steps of: 1) a first laser is used to generate an optical carrier and input into a first optical transmitter, a signal generated by the first optical transmitter modulates the optical carrier to obtain a polarization multiplexed signal light and input into a first optical fiber channel; a second laser is used to generate an optical carrier and input into a second optical transmitter, the second optical transmitter modulates the optical carrier to generate a first local oscillator light by single sideband or double sideband modulation and input into a second optical fiber channel; 2) a receiving end inputs the polarization multiplexed signal light transmitted through the first optical fiber channel into a dual polarization 90-degree optical mixer, inputs the first local oscillator light transmitted through the second optical fiber channel into a beam splitter to obtain a second local oscillator light and a third local oscillator light, and inputs the second local oscillator light into the dual polarization 90-degree optical mixer; the dual polarization 90-degree optical mixer inputs the polarization multiplexed signal light and the second local oscillator light into four balanced photodetectors after polarization and phase diversity to generate a first electrical signal I1, a second electrical signal I2, a third electrical signal I3 and a fourth electrical signal I4; the third local oscillator light is input into a single-ended photodetector to generate a fifth electrical signal I5; 3) the receiving end performs digital domain optical field reconstruction on the fifth electrical signal I5 to obtain a fifth digital signal D5 and input it into a second signal demodulation module to complete resampling, digital down conversion, matched filtering, frame synchronization, channel equalization, downsampling and signal demodulation; 4) the receiving end divides the first electrical signal I1, the second electrical signal I2, the third electrical signal I3 and the fourth electrical signal I4 by the conjugate of the fifth digital signal D5 to obtain corresponding first, second, third and fourth digital signals D1, D2, D3 and D4, and input them into a first signal demodulation module to complete resampling, frequency offset estimation, digital down conversion, matched filtering, frame synchronization, channel equalization, downsampling, carrier phase recovery and signal demodulation.

2. The method of claim 1, wherein, If the first local light is a single sideband signal, the fifth digital signal D5 is obtained by the formula H{D4}·ln(D4) 3. The method of claim 1, wherein, If the first local light is a double sideband signal, the fifth digital signal D5 is obtained by the formula ​ 4. The method according to claim 1 or 2 or 3, characterized in that, The first laser and the second laser are the same laser or two independent lasers.

5. A five-dimensional coherent detection receiver, characterized by The system comprises a beam splitter module, a dual polarization 90-degree optical mixer module, a single-ended photodetector module, four balanced photodetector modules, a digital domain optical field reconstruction module, a first signal demodulation module and a second signal demodulation module; The beam splitter module is configured to receive the first local oscillator light and divide it into the second local oscillator light and the third local oscillator light, input the second local oscillator light into the dual polarization 90-degree optical mixer and input the third local oscillator light into the single-ended photodetector module; The dual polarization 90-degree optical mixer module is configured to input the second local oscillator light and the polarization multiplexed signal light transmitted through the first optical fiber channel into the four balanced photodetector modules after polarization and phase diversity; The four balanced photodetector modules are configured to perform photoelectric conversion on the input signals to generate the first electrical signal I1, the second electrical signal I2, the third electrical signal I3 and the fourth electrical signal I4 and input them into the digital domain optical field reconstruction module; The single-ended photodetector module is configured to generate the fifth electrical signal I5 according to the input third local oscillator light and input it into the digital domain optical field reconstruction module. ​ The digital domain light field reconstruction module is configured to perform digital domain light field reconstruction on the fifth electrical signal I5 to obtain a fifth digital signal D5 and input the fifth digital signal D5 to the second signal demodulation module. The first electrical signal I1, the second electrical signal I2, the third electrical signal I3 and the fourth electrical signal I4 are divided by the conjugate of the fifth digital signal D5 respectively to obtain corresponding first, second, third and fourth digital signals D1, D2, D3 and D4, and the first, second, third and fourth digital signals D1, D2, D3 and D4 are input to the first signal demodulation module. The first signal demodulation module is configured to sequentially perform resampling, frequency offset estimation, digital down-conversion, matched filtering, frame synchronization, channel equalization, downsampling, carrier phase recovery and signal demodulation on the input signal. The second signal demodulation module is configured to sequentially perform resampling, digital down-conversion, matched filtering, frame synchronization, channel equalization, downsampling and signal demodulation on the input signal. The signal modulated by the first optical transmitter on the optical carrier is a polarization multiplexed signal light; the signal modulated by the second optical transmitter on the optical carrier is a first local oscillator light.

6. The receiver of claim 5, characterized in that If the first local light is a single sideband signal, the fifth digital signal D5 is obtained by the formula ; wherein H{·} represents Hilbert transform, and ln(·) represents natural base logarithm operation; if the first local light is a double sideband signal, the fifth digital signal D5 is obtained by the formula .

7. A five-dimensional coherent detection system, characterized in that The system comprises a sending end and a receiving end. The sending end is configured to generate an optical carrier by using a first laser and input the optical carrier to a first optical transmitter, modulate the optical carrier by a signal generated by the first optical transmitter to obtain a polarization multiplexed signal light and input the polarization multiplexed signal light to a first optical fiber channel. The sending end is configured to generate an optical carrier by using a first laser and input the optical carrier to a first optical transmitter, modulate the optical carrier by a signal generated by the first optical transmitter to obtain a polarization multiplexed signal light and input the polarization multiplexed signal light to a first optical fiber channel. The receiving end comprises a beam splitter module, a dual-polarization 90-degree optical mixer module, a single-end photodetector module, four balanced photodetector modules, a digital domain light field reconstruction module, a first signal demodulation module and a second signal demodulation module. The beam splitter module is configured to receive the first local oscillator light and split the first local oscillator light into a second local oscillator light and a third local oscillator light, input the second local oscillator light to the dual-polarization 90-degree optical mixer and input the third local oscillator light to the single-end photodetector module. The dual-polarization 90-degree optical mixer module is configured to input the second local oscillator light and the polarization multiplexed signal light transmitted through the first optical fiber channel to the four balanced photodetector modules after polarization and phase diversity. The four balanced photodetector modules are configured to perform photoelectric conversion on the input signals to generate first, second, third and fourth electrical signals I1, I2, I3 and I4 respectively and input the first, second, third and fourth electrical signals I1, I2, I3 and I4 to the digital domain light field reconstruction module. The single-end photodetector module is configured to generate a fifth electrical signal I5 according to the input third local oscillator light and input the fifth electrical signal I5 to the digital domain light field reconstruction module. The digital domain light field reconstruction module is configured to perform digital domain light field reconstruction on the fifth electrical signal I5 to obtain a fifth digital signal D5 and input the fifth digital signal D5 to the second signal demodulation module. and dividing the first electrical signal I1, the second electrical signal I2, the third electrical signal I3 and the fourth electrical signal I4 by the conjugate of the fifth digital signal D5 respectively to obtain corresponding first digital signal D1, second digital signal D2, third digital signal D3 and fourth digital signal D4, and inputting the first digital signal D1, the second digital signal D2, the third digital signal D3 and the fourth digital signal D4 to the first signal demodulation module; The first signal demodulation module is used for sequentially performing resampling, frequency offset estimation, digital down-conversion, matched filtering, frame synchronization, channel equalization, down-sampling, carrier phase recovery and signal demodulation on the input signal. The second signal demodulation module is used for sequentially performing resampling, digital down-conversion, matched filtering, frame synchronization, channel equalization, down-sampling and signal demodulation on the input signal.

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