Five-dimensional coherent detection method and receiver

Abstract

The invention discloses a five-dimensional coherent detection method and a receiver. Based on a dual-polarization 90-degree optical mixer, four pairs of balanced photoelectric detectors, a single-ended photoelectric detector and a digital domain optical field reconstruction module, complex optical field reconstruction of single-sideband or double-sideband modulation local oscillation light is realized, and beat frequency damage between local oscillation and signals is eliminated; and simultaneous coherent detection of polarization multiplexing signal light and single-sideband or double-sideband modulation local oscillation light is supported. Only one path of single-end photoelectric detector needs to be additionally arranged, extra modulation information is transmitted through local oscillation light, and the dimension of a received signal is linearly expanded to five dimensions with the lowest hardware complexity. According to the invention, the linear extension of the receiving dimension is realized with the lowest hardware complexity.

Description

Technical Field

[0001] The invention 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 Art

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

[0003] The traditional intensity modulation direct detection method modulates the information to be transmitted in the optical power dimension, and obtains the signal through the square-law detection of the photodetector at the receiving end. It has the advantages of simple structure and colorlessness, but the spectral efficiency of the receiver is limited by the modulation and demodulation process in a single dimension. On this basis, a series of direct detection methods have evolved to achieve phase and polarization diversity reception. By modulating the complex double-sideband signal on one polarization state and transmitting the unmodulated optical carrier on the other polarization state, a direct detection receiver based on the Stokes vector is constructed at the receiving end, which can expand the receiving dimension to two dimensions. Furthermore, by modulating the complex double-sideband signal on one polarization state and transmitting the single-sideband modulated signal on the other polarization state, the three-dimensional Stokes space is reversely rotated in the digital domain of the receiving end, and the signals on the two polarizations can be orthogonally restored, which increases the receiving dimension to three dimensions.

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

[0005] As the electrical bandwidth of high-speed photodetectors and analog-to-digital converters reaches a bottleneck, the signal rate that optical receivers can detect will be severely limited, so there is an urgent need to further improve detection technology. Summary of the invention

[0006] In view of the technical problems existing in the prior art and in order to expand the dimension of the received signal, the present invention aims to provide a five-dimensional coherent detection method based on single-sideband or double-sideband modulated local oscillator light and a corresponding receiver, which are potentially applicable to two application scenarios: (1) a bidirectional transmission optical interconnection scenario between data centers, in which the signal light and the local oscillator light carry four-dimensional and one-dimensional information respectively and detect them simultaneously; and (2) a bidirectional transmission laser-free optical network structure, in which the downlink four-dimensional signal light and the uplink one-dimensional signal light beat each other to achieve simultaneous reception.

[0007] The receiver of the present invention 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 present invention adopts the following technical solution:

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

[0010] The first step: using a first laser to generate an optical carrier and inputting it into a first optical transmitter, modulating the optical carrier by the signal light generated by the first optical transmitter to obtain a polarization multiplexing signal, and transmitting it in a first optical fiber channel; using a second laser to generate an optical carrier and inputting it into a second optical transmitter, performing single-sideband or double-sideband modulation on the optical carrier by the second optical transmitter to generate a first local oscillator light, and transmitting it in a second optical fiber channel;

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

[0012] Step 2: input the signal light transmitted through the first optical fiber channel into a dual-polarization 90-degree optical mixer; split the first local oscillation light transmitted through the second optical fiber channel into a second local oscillation light and a third local oscillation light through an optical splitter, input the second local oscillation light and the polarization multiplexing signal light into a dual-polarization 90-degree optical mixer, input the third local oscillation light into a single-ended photodetector, and generate a fifth electrical signal; input the outputs of the dual-polarization 90-degree optical mixer into four balanced photodetectors, respectively, to generate the first, second, third, and fourth electrical signals;

[0013] Step 3: In the digital signal processing at the receiving end, the fifth electrical signal output by the single-ended photodetector is reconstructed in the digital domain optical field to obtain the fifth digital signal, which then enters the second signal demodulation module to complete resampling, digital down-conversion, matched filtering, frame synchronization, channel equalization, down-sampling and signal demodulation;

[0014] Step 4: The first, second, third and fourth electrical signals output by the balanced photodetector are respectively divided by the conjugate of the fifth digital signal in the digital domain optical field reconstruction module to obtain the first, second, third and fourth digital signals, and then enter the first signal 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.

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

[0016] An optical splitter module, connected to the local oscillator light input, and used to split the received first local oscillator light into a second local oscillator light and a third local oscillator light;

[0017] A dual-polarization 90-degree optical mixer module is connected to the signal light input and the optical splitter module to realize coherent detection of the signal light and the second local oscillation light;

[0018] A single-ended photodetector module, connected to the optical splitter module, for detecting the third local oscillation light and generating a fifth electrical signal;

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

[0020] The digital domain light field reconstruction module is connected to the balanced photodetector module and the single-ended photodetector module, and is used to restore the complex light field and generate the first, second, third, fourth and fifth digital signals.

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

[0022] The method of the present invention uses single-sideband or double-sideband modulated local oscillator light to carry information, eliminates secondary beat frequency damage of local oscillator light through single-ended photodetector and digital domain light field reconstruction, eliminates beat frequency interference between local oscillator and signal through division operation, and simultaneously realizes coherent detection of four-dimensional polarization multiplexing signal light and local oscillator light carrying one-dimensional information, expands the receiving dimension, and improves the receiver's electrospectral efficiency and channel rate. This solution only requires an additional single-ended photodetector to achieve linear expansion of the receiving dimension with minimal hardware complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It 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 invention.

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

[0025] The present invention is further described in detail below through specific embodiments and drawings.

[0026] The following is a schematic diagram of this embodiment Figure 1 Provide specific instructions for the implementation of the technical solution.

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

[0028] Step 2: Split the first local oscillator light in the second optical fiber channel into the second local oscillator light and the third local oscillator light through an optical splitter, input the polarization multiplexing signal light and the second local oscillator light in the first optical fiber channel into a dual-polarization 90-degree optical mixer, and input them into the first to fourth balanced photodetectors after polarization and phase diversity, and obtain four different electrical signal components after difference through four balanced detectors: the first electrical signal I1, the second electrical signal I2, the third electrical signal I3, and the fourth electrical signal I4. Then input these four electrical signals into the digital domain optical field reconstruction module; input the third local oscillator light into a single-ended photodetector to generate the fifth electrical signal I5 and input it into the digital domain optical field reconstruction module;

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

[0030]

[0031] Wherein, H{·} represents the Hilbert transform, and ln(·) represents the logarithm operation of the natural base.

[0032] If the first local oscillation 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, down-sampling and signal demodulation;

[0035] Step 4: In the digital domain light field reconstruction module, for the first, second, third and fourth electrical signals, reconstruct the corresponding first, second, third and fourth digital signals D 1 / 2 / 3 / 4 as follows

[0036] D1=I1 / conj(D5)

[0037] D2=I2 / conj(D5)

[0038] D3=I3 / conj(D5)

[0039] D4=I4 / conj(D5)

[0040] Here, conj(·) represents a complex conjugate operation.

[0041] Subsequently, the reconstructed first, second, third and fourth digital signals are input into a signal 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 The figure is a schematic diagram of the structure of a coherent receiver based on single-sideband or double-sideband modulated local oscillator light corresponding to the above method.

[0043] The receiver structure includes: a splitter module, connected to the local oscillator light input, used to split the local oscillator light into a second intrinsic light and a third local oscillator light; a dual-polarization 90-degree optical mixer module, connected to the signal light input and the splitter module, used to achieve mixing of the signal light and the second local oscillator light to generate 8 optical signals; a first, second, third, and fourth balanced photodetector modules, connected to the dual-polarization 90-degree optical mixer module, used to convert the input optical signal into a first, second, third, and fourth electrical signal output; a single-ended photodetector module, connected to the splitter module and the second coherent receiver module, used to convert the input third local oscillator light into a fifth electrical signal output; and a digital domain optical field reconstruction module, connected to the first, second, third, and fourth balanced photodetector modules and the single-ended photodetector module, used to convert 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 invention rather than to limit the same. A person skilled in the art may modify or make equivalent substitutions for the technical solutions of the present invention without departing from the spirit and scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A five-dimensional coherent detection method, comprising the steps of: 1) The transmitting end uses a first laser to generate an optical carrier and inputs it into a first optical transmitter, modulates the optical carrier by a signal generated by the first optical transmitter, obtains polarization multiplexed signal light and inputs it into a first optical fiber channel; A second laser is used to generate an optical carrier and input the optical carrier into a second optical transmitter, and the optical carrier is subjected to single-sideband or double-sideband modulation by the second optical transmitter to generate a first local oscillator light and input the first local oscillator light into a second optical fiber channel; 2) The receiving end inputs the polarization multiplexing signal light after being transmitted through the first optical fiber channel into a dual-polarization 90-degree optical mixer, divides the first local oscillation light after being transmitted through the second optical fiber channel into a second local oscillation light and a third local oscillation light through an optical splitter, and inputs the second local oscillation light into the dual-polarization 90-degree optical mixer; the dual-polarization 90-degree optical mixer performs polarization and phase diversity on the input polarization multiplexing signal light and the second local oscillation light, and inputs them into four balanced photodetectors respectively, generating a first electrical signal I1, a second electrical signal I2, a third electrical signal I3, and a fourth electrical signal I4; the third local oscillation 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 inputs it into the second signal demodulation module to complete resampling, digital down-conversion, matched filtering, frame synchronization, channel equalization, down-sampling 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, respectively, to obtain the corresponding first digital signal D1, the second digital signal D2, the third digital signal D3, and the fourth digital signal D4, and inputs them into the 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 according to claim 1, characterized in that If the first local oscillation light is a single-sideband signal, then the formula A fifth digital signal D5 is obtained, wherein H{·} represents Hilbert transform, and ln(·) represents the logarithm operation of the natural base.

3. The method according to claim 1, characterized in that If the first local oscillation light is a double-sideband signal, then the formula A fifth digital signal D5 is obtained.

4. The method according to claim 1, 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 in that: It includes a beam splitter module, a dual-polarization 90-degree optical mixer module, a single-ended photodetector module, four balanced photodetector modules, a digital domain light field reconstruction module, a first signal demodulation module and a second signal demodulation module; in The optical splitter module is used to receive the first local oscillation light and split it into the second local oscillation light and the third local oscillation light, and input the second local oscillation light into the dual-polarization 90-degree optical mixer and input the third local oscillation light into the single-ended photodetector module; The dual-polarization 90-degree optical mixer module is used to perform polarization and phase diversity on the input second local oscillation light and the polarization multiplexing signal light after being transmitted through the first optical fiber channel, and then input them into four balanced photodetector modules respectively; The four balanced photodetector modules are used to perform photoelectric conversion on the input signals, respectively generate a first electrical signal I1, a second electrical signal I2, a third electrical signal I3, and a fourth electrical signal I4, and input them into the digital domain light field reconstruction module; The single-ended photodetector module is used to generate a fifth electrical signal I5 according to the input third local oscillation light and input the fifth electrical signal I5 to the digital domain light field reconstruction module; The digital domain light field reconstruction module is used 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 into 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 the corresponding first digital signal D1, the second digital signal D2, the third digital signal D3, and the fourth digital signal D4, and inputting them into the first signal demodulation module; The first signal demodulation module is used to perform 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 in sequence; The second signal demodulation module is used to perform resampling, digital down-conversion, matched filtering, frame synchronization, channel equalization, down-sampling and signal demodulation on the input signal in sequence; The optical carrier is modulated by a signal generated by the first optical transmitter to obtain polarization multiplexed signal light; and the optical carrier is single-sideband or double-sideband modulated by the second optical transmitter to generate the first local oscillator light.

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

7. A five-dimensional coherent detection system, characterized in that: It includes a sending end and a receiving end, where The transmitting end is used to generate an optical carrier using a first laser and input the optical carrier into a first optical transmitter, modulate the optical carrier by a signal generated by the first optical transmitter, obtain polarization multiplexed signal light and input the signal light into a first optical fiber channel; A second laser is used to generate an optical carrier and input the optical carrier into a second optical transmitter, and the optical carrier is subjected to single-sideband or double-sideband modulation by the second optical transmitter to generate a first local oscillator light and input the first local oscillator light into a second optical fiber channel; The receiving end includes a beam splitter module, a dual-polarization 90-degree optical mixer module, a single-ended 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 optical splitter module is used to receive the first local oscillation light and split it into the second local oscillation light and the third local oscillation light, and input the second local oscillation light into the dual-polarization 90-degree optical mixer and input the third local oscillation light into the single-ended photodetector module; The dual-polarization 90-degree optical mixer module is used to perform polarization and phase diversity on the input second local oscillation light and the polarization multiplexing signal light after being transmitted through the first optical fiber channel, and then input them into four balanced photodetector modules respectively; The four balanced photodetector modules are used to perform photoelectric conversion on the input signals, respectively generate a first electrical signal I1, a second electrical signal I2, a third electrical signal I3, and a fourth electrical signal I4, and input them into the digital domain light field reconstruction module; The single-ended photodetector module is used to generate a fifth electrical signal I5 according to the input third local oscillation light and input the fifth electrical signal I5 to the digital domain light field reconstruction module; The digital domain light field reconstruction module is used 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 into 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 the corresponding first digital signal D1, the second digital signal D2, the third digital signal D3, and the fourth digital signal D4, and inputting them into the first signal demodulation module; The first signal demodulation module is used to perform 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 in sequence; The second signal demodulation module is used to perform resampling, digital down-conversion, matched filtering, frame synchronization, channel equalization, down-sampling and signal demodulation on the input signal in sequence.

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