Optical interconnection communication method and system

Abstract

An optical interconnection communication method and system, relating to the field of high-speed optical interconnection in data centers. The method comprises: a binary bitstream signal to be transmitted being processed by a DSP and then changed to an analog electrical signal; outputting two paths of light by means of a laser, wherein one path serves as an optical carrier of an integrated dual-polarization coherent optical transmitter to modulate the analog electrical signal into a complex optical field signal, and the other path serves as local oscillation light to carry out time delay adjustment; carrying out coherent frequency mixing on the complex optical field signal and the local oscillation light by means of a polarization-independent coherent optical receiver, wherein the polarization state of the local oscillation light is controlled by means of feedback scrambling, so as to prevent the polarization state of the local oscillation light from falling in X and Y directions; and the electrical signal after the frequency mixing being processed by means of the DSP to restore the binary bitstream signal. The present invention is applicable to various types of modulation formats and various types of rates, and can also reduce the cost and the power consumption.

Description

An optical interconnection communication method and system TECHNICAL FIELD

[0001] The present application relates to the field of high-speed optical interconnection in data centers, and in particular to an optical interconnection communication method and system. BACKGROUND

[0002] With the emergence and popularity of new, bandwidth-intensive network applications such as HDTV (High Definition Television), VR (Virtual Reality), teleconferencing, mobile Internet, and cloud computing, network traffic is growing rapidly at a compound annual growth rate of more than 22% per year. As the cornerstone of information bearing, transmission and exchange, optical fiber communication networks will also face tremendous pressure. In particular, under the trend of 5G commercialization, the construction of DCN (Data Center Network) and CDN (Content Delivery Network) is quietly changing the distribution of large data traffic in the network. Online live streaming, video transmission, and file sharing are the main data services that occupy the majority of Internet traffic. They are mainly carried and distributed through DCN and CDN, and do not need to be transmitted through long-distance networks in most scenarios. Therefore, the network traffic load is shifting from long-haul backbone networks to medium and short distance metropolitan area networks and data centers. Research shows that global data center-related IP traffic reached 6.8 ZB (1 ZB = 10 9 TB) in 2016, and is expected to grow to 20.6 ZB by 2021, with a growth rate of about 2 times in 5 years. In particular, in cloud computing data centers, the data traffic pressure is more obvious. It is estimated that by 2021, 94% of business will be processed in cloud data centers. However, more than 70% of the traffic in data center-related networks is terminated within the data center. It is clear that short-distance (less than 2 km), high-speed optical interconnection technology will play an important role in future data transmission and carrying.

[0003] In the face of the bandwidth upgrade demand of optical interconnection in data center, capacity, power consumption and cost are three important factors. The international mainstream standard organization has made corresponding specifications for optical modules used in data center. At present, based on short wavelength VCSEL (Vertical Cavity Surface Emitting Laser) and multi-mode fiber, 10 transmits and 10 receives are realized by using multi-core MPO (Multi Push On) connector, and finally about 100G optical interconnection is completed, but its transmission distance is usually limited to about 100 meters. For the connection scene in large data center, it needs to cover 5km. At this time, it is usually necessary to upgrade to the scheme combined with DML (Directly Modulated Laser) and single-mode fiber, and to use OOK (On-Off Keying) modulation scheme, such as MSA (Multi Source Agreement) 100G CWDM4 (Coarse Wavelength Division Multiplexing) standard optical module which can support 2km, 100G transmission, but 4 sets of transceiver equipment are needed for unidirectional transmission. For the next generation 400G, 2km or so interconnection demand, EML (Electro-absorption Modulated Laser) needs to be replaced by DML on the basis of single-mode fiber, combined with high-order PAM4 (4 Pulse Amplitude Modulation) modulation technology, the number of wavelengths increases to 8, and the cost and power consumption increase significantly. For further expansion and upgrade in the future, this IMDD (Intensity Modulation Direct Detection) technology will be in a dilemma, and the module size, power consumption and cost will become a challenge.

[0004] Compared with traditional IMDD, digital coherent optical communication has become the mainstream technology of future long-distance optical communication due to its better sensitivity, higher spectral efficiency and stronger damage compensation ability, and has been deployed on a large scale. However, the existing long-distance 100G / 200G coherent DWDM (Dense Wavelength Division Multiplexing) system cannot be directly used for short-distance optical interconnection in data centers, because the number of ports in data centers is huge, and the cost of transceiver modules is extremely sensitive. At the same time, the power consumption and size of long-distance modules are large, which further limits their application in high-density optical interconnection in data centers. Therefore, how to reduce the cost and power consumption of the existing coherent optical communication system is the primary problem faced by the coherent technology for short-distance data center optical interconnection scenarios.

[0005] Currently, there are three main types of low-cost coherent optical communication technologies. The first type is to use pure analog optical signal processing to avoid using high-speed digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) and complex DSP ASICs (Digital Signal Processing Application Specific Integrated Circuit), in order to reduce cost and power consumption. However, this completely DSP-free scheme will have a large performance degradation, because it cannot compensate for the bandwidth limitations of the device, and it is difficult to adapt to higher-order modulation formats, and low complexity and no crosstalk polarization demultiplexing are one of the limiting factors for its application. [Journal of Lightwave technology, Vol. 35, no. 21, Design of Low-Power DSP-Free Coherent Receivers for Data Center Links]. The second type is to use a simplified 3x3 coupler to replace the traditional 90° coherent mixer in order to reduce the cost of some optical devices. [Journal of Lightwave technology, Vol. 36, no. 16, Comparison of low complexity coherent receivers for UDWDM-PONs]. The third type is to use a self-coherent method, in which the local oscillator light and the signal light are transmitted together from the transmitting end to the receiving end, and some method such as space division multiplexing fan-in fan-out or polarization separation is used to separate the local oscillator light from the signal light before coherent mixing. This can reduce the number and cost of lasers, and also simplify some of the DSP (Digital Signal Processing) algorithms at the receiving end [Optics Express, vol. 21, no. 2, investigating self-homodyne coherent detection in a 19 channel space-division-multiplexed transmission link]. Considering industrialization and module performance consistency, it is not difficult to find that low-cost and low-power coherent optical interconnection based on DSP is still the most expected scheme in the industry. However, in the second and third types of low-cost coherent systems, high-speed DA (digital-to-analog) and AD (analog-to-digital) sampling is involved, resulting in high power consumption, which makes it difficult to meet the power consumption requirements of data center pluggable optical modules. Reducing the system sampling rate, further simplifying the coherent DSP algorithm and architecture is a possible direction to reduce power consumption, and is also a difficult problem that needs to be solved urgently in data center high-speed coherent optical interconnection technology.

[0006] As shown in FIG. 1 and FIG. 2, the DSP processing flow of the traditional coherent optical communication for long-distance transmission and the DSP processing flow of the traditional coherent optical communication for long-distance transmission respectively contain the part of sampling rate conversion, such as the up-sampling of FIG. 1 and the re-sampling of FIG. 2, which not only has a complex structure, but also has a large power consumption due to working under the condition of high sampling rate (more than baud rate). Especially, the calculation complexity of the functions of dispersion compensation, multi-tap adaptive equalization, frequency offset estimation and phase recovery of the receiver is large, which occupies most of the chip power consumption. Obviously, the traditional DSP architecture cannot be directly applied to the low-cost and low-power data center short-distance optical interconnection system. The modulation format of the signal is the common polarization multiplexed phase modulation or amplitude-phase modulation, such as PDM (Polarization Division Multiplexed)-PSK (Phase Shift Keying), PDM-QPSK (Quadrature Phase Shift Keying), PDM-8QAM (8-ary Quadrature Amplitude Modulation), PDM-16QAM (16-ary Quadrature Amplitude Modulation), PDM-64QAM (64-ary Quadrature Amplitude Modulation) and the like.

[0007] SUMMARY

[0008] In view of the defects in the prior art, the purpose of the present application is to provide an optical interconnection communication method and system, which is suitable for various modulation formats and various rates, and can also reduce cost and power consumption.

[0009] To achieve the above purpose, on the one hand, an optical interconnection communication method is adopted, comprising:

[0010] The binary bit stream signal to be transmitted is converted into an analog electrical signal after DSP processing; a laser is used to output two paths of light, one of which is used as an optical carrier of an integrated dual-beam coherent optical transmitter to modulate the analog electrical signal into a complex optical field signal, and the other of which is used as a local oscillator light for time delay adjustment;

[0011] The complex optical field signal and the local oscillator light are subjected to coherent mixing through a polarization-independent coherent optical receiver, wherein the polarization state of the local oscillator light is controlled through feedback disturbance to avoid the polarization state of the local oscillator light falling into the X and Y directions; the electrical signal after mixing is subjected to DSP processing to recover the binary bit stream signal.

[0012] Preferably, the digital signal processing of the binary bitstream signal to be transmitted comprises:

[0013] After the FEC encoding of the binary bitstream signal to be transmitted, independent constellation mapping is performed on the two polarization states X and Y to generate two independent complex signal streams, and then polarization diversity precoding is performed. After the precoding, the two signals are separated by quadrature, and then time domain pre-compensation is performed. The compensated signals are converted into analog signals by digital-to-analog conversion with the baud rate as the sampling rate.

[0014] Preferably, the complex signal stream generated by the constellation mapping is [X1, Y1] T , the precoded symbol stream is [X2, Y2] T , and the precoding rule is [X2, Y2] T = H·[X1, Y1] T . H is a precoding matrix, and ad-bc≠0.

[0015] Preferably, the digital signal processing of the mixed electrical signal comprises:

[0016] The mixed electrical signal is converted into a digital signal by analog-to-digital conversion and subjected to anti-aliasing filtering. The filtered signal is subjected to feedforward equalization and clock synchronization, and then single-tap adaptive equalization is performed to realize polarization demultiplexing. Then, deprecoding, demapping, and FEC decoding are performed to obtain the binary bitstream signal.

[0017] Preferably, the two signals obtained by polarization demultiplexing are [A1, B1] T , and a matrix is used to perform de-polarization diversity precoding on [A1, B1] T to obtain [A2, B2] T . The de-polarization diversity precoding rule is [A2, B2] T = H'·[A1, B1] T , where H' is the inverse matrix of the precoding matrix H.

[0018]

[0019] Preferably, the feedback scrambling control of the local oscillator light polarization state comprises:

[0020] The polarization-independent coherent light receiver divides the received local light into two branches with polarization states perpendicular to each other, and the local light in each branch is divided into two paths according to different power ratios, extracts the path with smaller optical power in each branch, obtains the power difference of the two extracted local light, and converts the power difference into a photocurrent amplitude, when the absolute value of the photocurrent amplitude is greater than a preset threshold, a control signal proportional to the absolute value is used to disturb the local light.

[0021] Preferably, the optical interconnection communication method is applicable to modulation formats including QPSK, 8QAM, 16QAM, 32QAM and 64QAM.

[0022] The optical interconnection communication method is applicable to information rates including 100G, 200G, 400G, 600G and 800G.

[0023] In another aspect, an optical interconnection communication system is provided, comprising:

[0024] A laser for outputting continuous light;

[0025] A first optical splitter for receiving the continuous light and dividing it into two paths, one of which provides an optical carrier and the other of which provides local light;

[0026] A transmitter DSP chip for converting a binary bit stream signal to be transmitted into an analog electrical signal after DSP processing;

[0027] An integrated dual-polarization coherent light transmitter for receiving the optical carrier and modulating the analog electrical signal into a complex optical field signal;

[0028] A first optical fiber channel for transmitting the complex optical field signal output by the integrated dual-polarization coherent light transmitter;

[0029] A coarse adjustable delay line for coarsely adjusting the time delay of the local light transmission line to match the length of the complex optical field signal transmission link;

[0030] A second optical fiber channel for transmitting the local light adjusted by the coarse adjustable delay line;

[0031] A polarization-independent coherent light receiver for receiving the complex optical field signal and the local light transmitted by the first optical fiber channel and the second optical fiber channel respectively and performing coherent mixing; the polarization-independent coherent light receiver includes a polarization scrambler for controlling the polarization state of the local light by feedback scrambling to avoid the polarization state of the local light falling into the X and Y directions;

[0032] A receiver DSP chip for receiving the mixed electrical signal and recovering the binary bit stream signal through DSP processing.

[0033] Preferably, the laser is a DFB laser; the splitting ratio of the first optical splitter 2 is 7:3; the coarse adjustable delay line is implemented by a single-mode optical fiber; and the first optical fiber channel and the second optical fiber channel are both common single-mode optical fibers.

[0034] Preferably, the polarization-independent coherent optical receiver comprises:

[0035] a first polarization beam splitter for splitting the complex optical field signal into two branches with mutually perpendicular polarization states;

[0036] a fine adjustable delay line for accurately adjusting the transmission time delay and optical path difference of the local light relative to the signal light, so as to ensure that the signal light and the local light satisfy the coherent length;

[0037] a second polarization beam splitter for splitting the local light into two branches with mutually perpendicular polarization states;

[0038] a polarization scrambler for receiving the local light adjusted by the fine adjustable delay line, and controlling the polarization state of the local light input to the second polarization beam splitter, so as to avoid the local light input to the second polarization beam splitter being exactly in the horizontal or vertical direction;

[0039] a second optical splitter and a third optical splitter for splitting the two local lights with polarization states in different power ratios;

[0040] a fifth balanced detector for receiving the local light with smaller power split by the second optical splitter and the third optical splitter, obtaining a power difference, and converting the power difference into an optical current amplitude output;

[0041] a controller for converting the optical current amplitude into a disturbance control signal of the polarization state of the local light, and controlling the polarization scrambler;

[0042] a mixing gain module for coherently mixing the two complex optical field signals output by the first polarization beam splitter with the local light with larger power split by the second optical splitter and the third optical splitter, respectively, to obtain real parts and imaginary parts of X and Y polarizations, respectively, and then amplifying and realizing automatic gain control.

[0043] Preferably, the mixing gain module comprises:

[0044] a first 90° mixer for coherently mixing one of the complex optical field signals output by the first polarization beam splitter with the local light with larger power split by the second optical splitter;

[0045] a second 90° mixer for coherently mixing the other of the complex optical field signals output by the first polarization beam splitter with the local light with larger power split by the third optical splitter;

[0046] a first balanced detector and a second balanced detector, configured to convert the optical signal output by the first 90° mixer into an electrical signal, and obtain the real part and the imaginary part of the X polarization respectively;

[0047] a third balanced detector and a fourth balanced detector, configured to convert the optical signal output by the second 90° mixer into an electrical signal, and obtain the real part and the imaginary part of the Y polarization respectively;

[0048] a trans-impedance amplifier, configured to amplify the real part and the imaginary part of the X polarization and the real part and the imaginary part of the Y polarization, and realize automatic gain control.

[0049] Preferably, the second splitter and the third splitter have the same ratio, which is 95:5.

[0050] When the absolute value of the photocurrent amplitude output by the fifth balanced detector is greater than a preset threshold value, the output control electrical signal proportional to the absolute value is applied to the polarization scrambler, and the threshold value is 90% of the maximum photocurrent detected by the fifth balanced detector.

[0051] Preferably, the transmitting end DSP chip comprises:

[0052] an FEC encoding module, configured to perform FEC encoding on a binary bit stream signal to be transmitted;

[0053] a constellation map mapping module, configured to perform independent constellation map mapping on X and Y polarization states respectively according to a preset modulation format, and generate two independent complex signal streams [X1, Y1] T .

[0054] a precoding module, configured to perform polarization hierarchical precoding on the complex signal streams [X1, Y1] T , and output two precoded symbol streams [X2, Y2] T , and the precoding rule is:

[0055] [X2, Y2] T = H·[X1, Y1] T , wherein H is a precoding matrix, and ad-bc≠0.

[0056] a pre-compensation module, configured to perform time domain pre-compensation on the two precoded signals after orthogonal separation;

[0057] a DAC module, configured to perform digital-to-analog conversion on the compensated signals with a baud rate as a sampling rate, and obtain the analog electrical signal.

[0058] Preferably, the receiving end DSP chip comprises:

[0059] an ADC module for converting the mixed electrical signal into a digital signal;

[0060] two low-pass filters for respectively performing anti-aliasing filtering on the X-polarized signal and the Y-polarized signal,

[0061] two feed-forward equalizers, each corresponding to a low-pass filter, for performing feed-forward equalization on the filtered signal;

[0062] two clock recovery modules for respectively recovering the optimal sampling clock and phase from each feed-forward equalized signal;

[0063] an adaptive equalization module for performing adaptive equalization on the clock-recovered signal to achieve polarization demultiplexing and obtain two equalized signals [A1, B1] T .

[0064] a de-precoding module for performing de-polarization diversity precoding on [A1, B1] T to obtain [A2, B2] T , wherein the rule of the de-polarization diversity precoding is [A2, B2] T = H'·[A1, B1] T , wherein H' is the inverse matrix of the precoding matrix H;

[0065] two constellation diagram demapping modules for respectively demapping the signals after the de-polarization diversity precoding;

[0066] two FEC decoding modules for respectively performing FEC decoding on the demapped binary bits to recover the binary bit stream signal.

[0067] Preferably, the pre-compensation module of the sending DSP chip performs time-domain pre-compensation using a real finite impulse response filter, and the number of taps of the finite impulse response filter is less than or equal to 3.

[0068] The adaptive equalization module of the receiving DSP chip performs adaptive equalization using a single-tap 2x2 complex butterfly filter.

[0069] The DAC module and the ADC module both work at a 1x baud rate sampling speed.

[0070] The above technical solution has the following beneficial effects:

[0071] In the present application, only the sending end is provided with a laser, which, compared with the prior art, uses self-coherent technology to avoid the use of an expensive narrow-line-width laser at the receiving end, and only one laser is used at the sending end, thereby reducing the cost of a short-distance optical interconnection system.

[0072] Further, the launch end adopts a DFB (Distributed Feedback laser) laser, which generally has a larger line width, is in the order of MHz, and is cheaper than an ECL (External Cavity Laser) laser. The ECL is generally a narrow line width laser, and has a line width in the order of KHz. At present, commercial coherent optical communication systems all need an ECL laser with a line width of about 100 kHz. Therefore, the use of the DFB laser further reduces the system cost compared with other lasers.

[0073] The polarization state of the local oscillator light is controlled by using a power balance detection and a polarization scrambler in combination, so as to avoid the risk of demodulation failure when the local oscillator light is exactly X or Y polarized, to realize polarization-independent coherent reception, and to solve the difficulty of control of the polarization state of the local oscillator light in a self-coherent system.

[0074] A coarse adjustable delay line and a fine adjustable delay line are used on an optical path to adjust the optical path difference between the local oscillator light and the signal light, to ensure the matching of the coherence length, thereby avoiding the estimation of frequency offset and the recovery of phase at the receiving end, and greatly simplifying the DSP algorithm and circuit at the receiving end.

[0075] In terms of DSP, on the one hand, a baud rate sampling rate DAC and ADC conversion are used to greatly reduce the power consumption of the coherent DSP chip; on the other hand, a set of extremely simple transceiver DSP signal processing procedures are proposed to simplify the complexity of the DSP and save the chip power consumption and area.

[0076] In the launch end DSP chip, polarization diversity precoding is used to artificially introduce correlation between the signals in two polarization states, which is expected to improve the tolerance to polarization-dependent loss, and to solve the performance loss problem of low-cost devices used in a coherent system to a certain extent.

[0077] In the receiving end DSP chip, an FFE (Forward Feedback Equalizer) is used to compensate for the ISI (Inter Symbol Interference) problem caused by fiber dispersion and device bandwidth limitation, and then a single-tap butterfly filter is used to realize polarization demultiplexing, and then deprecoding is performed to recover the symbols in X and Y polarization states. The entire DSP algorithm is greatly simplified compared with the traditional coherent DSP algorithm, and all algorithm sub-modules work at a single sampling rate, so that the power consumption of the DSP chip is expected to be greatly reduced.

[0078] And, based on the DSP processing of the sending end, different high-order modulation formats such as QPSK, 8QAM, 16QAM, 32QAM, 64QAM, etc. can be applied, and multiple information rates such as 100G, 200G, 400G, 600G, 800G, etc. can be applied.

[0079] In conclusion, the application finally realizes the beneficial effect of realizing low-cost, high-speed and low-power short-distance optical interconnection, which is very suitable for the optical interconnection scene in the data center which is sensitive to cost and power consumption. BRIEF DESCRIPTION OF DRAWINGS

[0080] Fig. 1 is a schematic diagram of the DSP processing flow of the sending end of the conventional coherent optical communication for long-distance transmission;

[0081] Fig. 2 is a schematic diagram of the DSP processing flow of the receiving end of the conventional coherent optical communication for long-distance transmission;

[0082] Fig. 3 is a schematic diagram of the single-tap adaptive equalizer structure of the embodiment of the application;

[0083] Fig. 4 is a schematic diagram of the optical interconnection communication system of the embodiment of the application;

[0084] Fig. 5 is a schematic diagram of the implementation principle of the polarization-independent coherent optical receiver;

[0085] Fig. 6 is a schematic diagram of the DSP chip of the sending end of the embodiment of the application;

[0086] Fig. 7 is a schematic diagram of the DSP chip of the receiving end of the embodiment of the application;

[0087] Fig. 8 is a schematic diagram of the local oscillator polarization control flow of the embodiment of the application;

[0088] Fig. 9 is a QPSK constellation diagram of the embodiment of the application;

[0089] Fig. 10 is an 8QAM constellation diagram of the embodiment of the application.

[0090] Reference signs:

[0091] 1-laser, 2-first optical splitter, 3-coarse adjustable delay line, 4-integrated dual-polarization coherent optical transmitter, 5-DSP chip of the sending end, 6-first fiber channel, 7-polarization-independent coherent optical receiver, 8-DSP chip of the receiving end, 9-second fiber channel;

[0092] 51-FEC encoding module, 52-constellation diagram mapping module, 53-pre-encoding module, 54-pre-compensation module, 55-DAC module;

[0093] 700-mixing gain module, 701-first polarization beam splitter, 702-first 90° mixer, 703-first balanced detector, 704-second balanced detector, 705-transimpedance amplifier, 706-second 90° mixer, 707-third balanced detector, 708-fourth balanced detector, 709-second optical splitter, 710-third optical splitter, 711-second polarization beam splitter, 712-fifth balanced detector, 713-controller, 714-polarization scrambler, 715-precision adjustable delay line;

[0094] 81-ADC module, 82-low pass filter, 83-feed forward equalizer, 84-clock recovery module, 85-adaptive equalization module, 86-decoding module, 87-constellation demapping module, 88-FEC decoding module. DETAILED DESCRIPTION

[0095] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0096] An embodiment of an optical interconnection communication method is provided, specifically comprising:

[0097] In the transmitting direction, the binary bit stream signal to be transmitted is converted into an analog electrical signal after DSP processing. A laser is used to provide a direct current optical carrier for optical interconnection communication, and also as a local oscillator light for coherent detection. Specifically, the laser outputs two optical signals, one of which is used as an optical carrier of an integrated dual-coherent optical transmitter, and the analog electrical signal obtained by DSP processing is modulated into a complex optical field signal; the other is used as a local oscillator light for time delay adjustment. The time delay of the local oscillator light transmission line can be adjusted by a coarse adjustable delay line to match the length of the complex optical field signal transmission link, so as to ensure that the complex optical field signal and the local oscillator light are near the coherence length.

[0098] In the receiving direction, the above-mentioned complex optical field signal and local oscillator light are received by a polarization-independent coherent optical receiver, and coherent mixing is performed to move the modulated signal to the baseband to obtain a baseband electrical signal. The polarization state of the local oscillator light is controlled by feedback polarization scrambling to avoid the polarization state of the local oscillator light falling into the X and Y directions, thereby causing the loss of data in one of the polarization states, and ensuring correct demodulation of polarization multiplexed data. The electrical signal after mixing is processed by DSP to recover the binary bit stream signal. After mixing, four electrical signals are obtained, which are two X-polarized and Y-polarized electrical signals and their respective in phase and quadrature.

[0099] The polarization state of the local oscillation light controlled by the feedback disturbance specifically comprises: the polarization-independent coherent light receiver divides the received local oscillation light into two polarization state perpendicular branches, the local oscillation light in each branch is divided into two paths according to different power ratios, the path with smaller optical power of the local oscillation light in each branch is extracted, the power difference of the extracted two paths of the local oscillation light is obtained, and the power difference is converted into a photocurrent amplitude; when the absolute value of the photocurrent amplitude is greater than a preset threshold, a control signal proportional to the absolute value is used to disturb the local oscillation light.

[0100] Based on the above embodiment, a DSP processing embodiment in the transmission direction and the receiving direction is further provided. The binary bit stream signal to be transmitted is processed by digital signal processing, specifically comprising the steps of:

[0101] S101. The binary bit stream signal to be transmitted is subjected to FEC (Forward Error Correction) encoding.

[0102] S102. The data after FEC encoding is subjected to independent constellation mapping for X and Y two polarization states (i.e. horizontal and vertical two polarization states) according to a preselected modulation format, to generate two independent complex signal streams [X1, Y1] T .

[0103] S103. The complex signal streams [X1, Y1] T are subjected to polarization diversity precoding, to output two precoded symbol streams [X2, Y2] T ; the precoding rule is:

[0104] [X2, Y2] T = H·[X1, Y1] T , wherein, is a precoding matrix, and ad-bc≠0 is satisfied.

[0105] S104. The two precoded signals are subjected to orthogonal separation, to obtain corresponding four signals, which represent the real part and the imaginary part of the X and Y polarization states respectively, and then are subjected to time domain pre-compensation by an FIR (Finite Impulse Response) filter in a real number field respectively, to adjust the relative time delay between the signals and compensate for the bandwidth of part of the optoelectronic devices.

[0106] Preferably, to ensure low complexity and power consumption, the number of taps of the FIR is not more than 3.

[0107] S105. The four signals after pre-compensation are sent into a DAC for digital-to-analog conversion with a baud rate as a sampling rate, to obtain an electrical signal to be modulated.

[0108] In the receiving direction, the mixed electrical signal is processed by digital signal processing, which includes the following steps:

[0109] S201. The four-way electrical signal output by the polarization-independent coherent receiver is converted into four-way digital signals by analog-to-digital conversion at a sampling rate of the baud rate.

[0110] S202. The four-way digital signals are processed by digital anti-aliasing filtering with a low-pass filter to remove signal spectrum aliasing that may be caused by single sampling.

[0111] S203. The filtered signals are pre-fed and equalized to compensate for the influence of inter-symbol interference (ISI) caused by bandwidth limitation and short-fiber dispersion, and the time difference between channels.

[0112] S204. The signals after pre-fed equalization are clock-synchronized to restore the optimal sampling clock and phase, and the clock-synchronization algorithm needs to work at a single sampling rate.

[0113] S205. As shown in FIG. 3, Xin, Yin, Xin', and Yin' represent input and output signal vectors of adaptive equalizers X and Y for two polarization states, respectively, and Wxx, Wxy, Wyx, and Wyy are four sets of tap coefficients of the butterfly filter, representing the influence of X polarization input on X polarization output, the influence of Y polarization input on X polarization output, the influence of X polarization input on Y polarization output, and the influence of Y polarization input on Y polarization output, respectively. According to certain tap adaptive updating rules and updating periods, single-tap adaptive equalization is implemented to realize polarization demultiplexing, and the two-way signals after equalization are [A1, B1] T .

[0114] Preferably, a single-tap adaptive filter is used to adaptively equalize the signals after clock recovery, such as a single-tap 2x2 complex butterfly filter.

[0115] S206. A matrix is used to perform depolarization diversity precoding processing on [A1, B1] T to obtain [A2, B2] T , and the rule of depolarization diversity precoding is [A2, B2] T = H'·[A1, B1] T , where H' is the inverse matrix of the precoding matrix H.

[0116] S207. According to a pre-selected modulation format, the demapping of the signals after precoding is completed, and the recovered symbols are converted into binary bits.

[0117] S208. The binary bits after demapping are FEC-decoded to recover the binary data stream at the transmitting end.

[0118] Preferably, the number of taps used in the feedforward equalization in S205 is no more than 10, and the tap adaptive updating criterion can be constant modulus algorithm (CMA), multi-modulus algorithm (MMA), cascaded multi-modulus algorithm (CMMA), or least mean square error algorithm (LMS). The tap coefficient updating period of the single-tap adaptive filter is no less than 10 symbol periods.

[0119] As shown in FIG. 4, the application also proposes an embodiment of an optical interconnection communication system, which can implement at least one of the above-mentioned methods. The system comprises a transmitting end and a receiving end. The transmitting end comprises a laser 1, a first optical splitter 2, a coarse adjustable delay line 3, an integrated dual-polarization coherent light transmitter 4, a transmitting end DSP chip 5, a first fiber channel 6, and a second fiber channel 9. The receiving end comprises a polarization-independent coherent light receiver 7 and a receiving end DSP chip 8. The transmitting end and the receiving end are connected through two fiber channels.

[0120] The output of the laser 1 is connected to the first optical splitter 2. The outputs of the first optical splitter 2 are connected to the integrated dual-polarization coherent light transmitter 4 and the coarse adjustable delay line 3, respectively. The integrated dual-polarization coherent light transmitter 4 is also connected to the transmitting end DSP chip 5 and the first fiber channel 6. The other port of the coarse adjustable delay line 3 is connected to the second fiber channel 9. The other ends of the first fiber channel 6 and the second fiber channel 9 are connected to the signal light and the local oscillator light interfaces of the polarization-independent coherent light receiver 7, respectively. The output electrical interface of the polarization-independent coherent light receiver 7 is connected to the receiving end DSP chip.

[0121] The laser 1 is used to output continuous light, which provides a direct current optical carrier for the optical interconnection system and also serves as the local oscillator light for coherent detection. Preferably, the line width of the laser 1 is no less than 10 MHz. The laser 1 preferably adopts a DFB (Distributed Feedback laser).

[0122] The first optical splitter 2 is used to divide the output of the laser 1 into two paths, so as to control the distribution ratio of the optical carrier and the local oscillator light power. Preferably, the splitting ratio of the first optical splitter 2 is greater than 6:4 and less than 8:2.

[0123] The transmitting end DSP chip 5 is used to convert the binary bit stream signal to be transmitted into an analog electrical signal after encoding, constellation mapping, and appropriate pre-compensation, so as to drive the integrated dual-polarization coherent light transmitter 4. The DAC used in the transmitting end DSP chip 5 works at a 1-times baud rate sampling rate, so as to reduce the power consumption of the system.

[0124] The integrated dual-polarization coherent light transmitter 4 is used to modulate the analog electrical signal into a polarization multiplexed complex optical field signal, i.e., signal light, so as to complete the conversion of the signal to be transmitted from the electrical domain to the optical field.

[0125] The first optical fiber channel 6 is used as a low-loss transmission medium for transmitting the modulated signal light.

[0126] The coarse adjustable delay line 3 is used for adjusting the time delay of the local light transmission line to match the length of the optical signal transmission link, so as to ensure that the signal light and the local light are in the vicinity of the coherence length.

[0127] The second optical fiber channel 9 is used as a low-loss transmission medium for transmitting the local light signal adjusted by the coarse adjustable delay line 3.

[0128] Further, the lengths of the first optical fiber channel 6 and the second optical fiber channel 9 are substantially equal and do not exceed 5 kilometers.

[0129] The polarization-independent coherent light receiver 7 is used for coherently mixing the local light with the signal light, moving the modulated signal to the baseband, and obtaining a baseband electrical signal. Further, the polarization-independent coherent light receiver 7 realizes feedback scrambling, thereby automatically adapting the input local light in any polarization state.

[0130] The receiving end DSP chip 8 is used for converting the received baseband electrical signal into a digital signal, and then performing certain digital signal processing, such as impairment equalization and compensation, polarization demultiplexing, demodulation and decoding, and finally restoring the binary data stream at the transmitting end. The ADC of the receiving end DSP chip 8 also works at a 1-fold baud rate sampling rate, so as to reduce the power consumption of the system.

[0131] As shown in FIG. 5, an embodiment of the polarization-independent coherent light receiver 7 in the above-described embodiment is provided, and the internal structure thereof specifically comprises a first polarization beam splitter 701, a second polarization beam splitter 709, a third polarization beam splitter 710, a second polarization beam splitter 711, a fifth balanced photodetector 712, a controller 713, a scrambling device 714, a fine adjustable delay line 715, and a mixing gain module 700. The mixing gain module 700 is composed of a first 90° mixer 702, a first balanced photodetector 703, a second balanced photodetector 704, a transimpedance amplifier 705, a second 90° mixer 706, a third balanced photodetector 707, and a fourth balanced photodetector 708.

[0132] The input of the first polarization beam splitter 701 is used as a signal light input port of the polarization-independent coherent light receiver 7, one end of the fine adjustable delay line 715 is used as a local light input port of the polarization-independent coherent light receiver 7, and the output of the transimpedance amplifier 705 is used as an electrical signal output port of the polarization-independent coherent light receiver 7.

[0133] The two outputs of the first polarization beam splitter 701 are connected to one input port of the first 90° mixer 702 and the second 90° mixer 706 respectively; one output port of the second optical splitter 709 and the second optical splitter 710 is connected to the other input port of the first 90° mixer 702 and the second 90° mixer 706 respectively. The four outputs of the first 90° mixer 702 are connected to the input ports of the first balanced detector 703 and the second balanced detector 704 respectively. The four outputs of the second 90° mixer 706 are connected to the input ports of the third balanced detector 707 and the fourth balanced detector 708 respectively. The outputs of the first balanced detector 703, the second balanced detector 704, the third balanced detector 707 and the fourth balanced detector 708 are connected to the trans-impedance amplifier 705.

[0134] The input of the second polarization beam splitter 711 is connected to the output of the depolarizer 714, and its two outputs are connected to the inputs of the second optical splitter 709 and the third optical splitter 710 respectively. The other output ports of the second optical splitter 709 and the third optical splitter 710 are connected to the input of the fifth balanced detector 712. The output of the fifth balanced detector 712 is connected to the input of the controller 713, and the output of the controller 713 is connected to the control port of the depolarizer 714. The input of the depolarizer 714 is connected to the output of the fine-tunable delay line 715.

[0135] The fine-tunable delay line 715 is used to finely adjust the transmission time delay and optical path difference of the two optical paths of the local light and the signal light, so as to ensure that the signal light and the local light meet the coherent length.

[0136] The first polarization beam splitter 701 is used to divide the complex optical field signal (i.e. the signal light) into two branches with mutually perpendicular polarization states.

[0137] The second polarization beam splitter 711 is used to divide the local light into two branches with mutually perpendicular polarization states.

[0138] The depolarizer 714 is used to control the polarization state of the local light input to the second polarization beam splitter 711, so as to avoid the polarization state of the local light entering the second polarization beam splitter 711 falling into the X and Y directions, i.e. to avoid the local light being exactly in the horizontal or vertical direction.

[0139] The second optical splitter 709 and the third optical splitter 710 are used to split the two local lights with different power ratios, and the local light with smaller power is sent to the fifth balanced detector 712.

[0140] The fifth balanced detector 712 is used to receive the local light with smaller power split by the second optical splitter and the third optical splitter respectively, extract the power difference of the polarization-split local light, and convert it into an optical current amplitude output.

[0141] The controller 713 is configured to convert the photoelectric current amplitude into a disturbance control signal of the local oscillator light polarization state, and control the disturbance device 714 in a certain manner to realize polarization disturbance.

[0142] The mixing gain module 700 is configured to coherently mix the two complex light field signals output by the first polarization beam splitter 701 with the local oscillator light with greater power output by the second light splitter 709 and the third light splitter 711 respectively, and then obtain the real part and the imaginary part of the X and Y polarizations respectively, amplify and realize automatic gain control. Further, the internal structure and specific functions are as follows:

[0143] The first 90° mixer 702 is configured to coherently mix the complex light field signal output by the first polarization beam splitter 701 with the local oscillator light with greater power output by the second light splitter 709.

[0144] The second 90° mixer 706 is configured to coherently mix the other complex light field signal output by the first polarization beam splitter 701 with the local oscillator light with greater power output by the third light splitter 710.

[0145] The first balanced detector 703 and the second balanced detector 704 are configured to convert the optical signal output by the first 90° mixer 702 into an electrical signal, and obtain the real part and the imaginary part of the X polarization respectively.

[0146] The third balanced detector 707 and the fourth balanced detector 708 are configured to convert the optical signal output by the second 90° mixer 706 into an electrical signal, and obtain the real part and the imaginary part of the Y polarization respectively.

[0147] The transimpedance amplifier 705 is configured to amplify the real part and the imaginary part of the X polarization and the real part and the imaginary part of the Y polarization, and realize automatic gain control.

[0148] The polarization-independent coherent light receiver 7 realizes feedback disturbance by detecting the differential power signals of the second light splitter 709 and the third light splitter 710, so as to automatically adapt to the local oscillator light with any polarization state input.

[0149] As shown in FIG. 6, the process of controlling the disturbance device 714 by the controller 713 in a certain manner specifically includes:

[0150] S301. The fifth balanced detector 712 detects the optical power difference of the local oscillator light with smaller output power of the third light splitter 709 and the fourth light splitter 710, and converts the optical power difference into a photoelectric current amplitude output.

[0151] S302. Taking the absolute value of the photoelectric current amplitude output by the fifth balanced detector 712.

[0152] S303. The controller 713 judges whether the absolute value is greater than a pre-set threshold value, if yes, go to S304; if no, return to S301. Preferably, the threshold value is 90% of the maximum photocurrent detected by the fifth balance detector 712.

[0153] S304. The controller 713 outputs a control electrical signal proportional to the above-mentioned absolute value, to the perturber 714.

[0154] S305. The perturber 714 perturbs the input local oscillator light polarization state according to the size of the received control electrical signal.

[0155] In the above-mentioned optical interconnection communication system, preferably, the laser 1 is a DFB laser with a nominal line width of 10 MHz and an output power of 16 dBm. The splitting ratio of the first optical splitter 2 is 7:3. The coarse adjustable delay line 3 is realized by a single-mode optical fiber with a length of 1 to 5 meters. The first optical fiber channel 6 and the second optical fiber channel 9 are both ordinary single-mode optical fibers with a length of 2 kilometers. The second optical splitter 709 and the third optical splitter 710 have the same ratio, both being 95:5.

[0156] As shown in FIG. 7, an embodiment of the transmitter DSP chip 5 in an optical interconnection communication system is provided. The transmitter DSP chip 5 specifically includes an FEC encoding module 51, a constellation map mapping module 52, a pre-encoding module 53, a pre-compensation module 54, and a DAC module 55.

[0157] The FEC encoding module 51 is used to perform FEC encoding on a binary bit stream signal to be transmitted.

[0158] The constellation map mapping module 52 is used to perform independent constellation map mapping on X and Y two polarization states respectively according to a pre-set modulation format, to generate two independent complex signal streams [X1, Y1] T .

[0159] The pre-encoding module 53 is used to perform polarization hierarchical pre-encoding on the complex signal streams [X1, Y1] T , to output two pre-encoding symbol streams [X2, Y2] T , and the pre-encoding rule is:

[0160] [X2, Y2] T = H·[X1, Y1] T , where H is a pre-encoding matrix, and ad-bc≠0.

[0161] The pre-compensation module 54 is used to obtain four signals corresponding to the real and imaginary parts of X and Y polarizations after the two pre-coded signals are separated by quadrature, and then pre-compensate in time domain to adjust the relative time delay between the signals and compensate for the bandwidth of the optoelectronic devices. Preferably, the pre-compensation module 54 uses a real finite impulse response filter (FIR) to pre-compensate in time domain; to ensure low complexity and power consumption, the number of taps of the FIR is no more than 3.

[0162] The DAC module 55 is used to convert the compensated signals into analog electrical signals at a sampling rate of 1 times the baud rate.

[0163] As shown in FIG. 8, the receiver DSP chip 8 includes an ADC module 81, two low-pass filters 82, two feed-forward equalizers 83, two clock recovery modules 84, an adaptive equalization module 85, a de-pre-coding module 86, two constellation demapping modules 87, and two FEC decoding modules 88.

[0164] The ADC module 81 is used to convert the four electrical signals output by the polarization-independent coherent receiver 7 into four digital signals at a sampling rate of 1 times the baud rate.

[0165] The two low-pass filters 82 are used to perform anti-aliasing filtering on the X and Y polarization signals, respectively, to remove signal spectrum aliasing that may be caused by single sampling.

[0166] The two feed-forward equalizers 83 each correspond to a low-pass filter 82 and perform feed-forward equalization on the filtered signals; the equalization compensates for the impact of inter-symbol interference (ISI) caused by limited system bandwidth and short-distance fiber dispersion, and can also compensate for the time difference between channels.

[0167] The two clock recovery modules 84 each recover the best sampling clock and phase for the signal after feed-forward equalization; the clock synchronization algorithm needs to work at a single sampling rate.

[0168] The adaptive equalization module 85 is used to perform adaptive equalization on the signal after clock recovery to achieve polarization demultiplexing and obtain two equalized signals [A1, B1] T .

[0169] The de-pre-coding module 86 uses a matrix to perform de-polarization diversity pre-coding on [A1, B1] T to obtain [A2, B2] T The rule for de-polarization diversity pre-coding is [A2, B2] T = H'·[A1, B1] T , where H' is the inverse matrix of the pre-coding matrix H.

[0170] Two constellation demapping modules 87 demap the signals after the completion of the encoding.

[0171] Two FEC decoding modules 88 perform FEC decoding on the demapped binary bits to recover the binary bit stream signals.

[0172] Based on the above system, a use embodiment of the DSP processing is provided. In this embodiment, the baud rate is 32 Gbaud, and the modulation format used is polarization multiplexing QPSK, i.e. PDM-QPSK signal, the constellation diagram and bit mapping method of which are shown in Fig. 9. The polarization diversity precoding matrix is The number of taps used by the feedforward equalizer 83 is 7, and the single-tap adaptive filter used by the adaptive equalization module 85 uses a multi-modulus algorithm (MMA) for tap adaptive updating, and the tap coefficient updating period is equal to every 16 symbol periods.

[0173] Based on the above system, another use embodiment of the DSP processing is provided. In this embodiment, the baud rate is 42 Gbaud, and the modulation format used is polarization multiplexing 8QAM, i.e. PDM-8QAM signal, the constellation diagram and bit mapping method of which are shown in Fig. 10. Fig. 10 shows a special 8QAM, which is a subset of the 16QAM constellation points, and it is different from the common square or circular 8QAM because it has the largest minimum Euclidean distance, thus having better BER performance under AWGN. The bit-to-symbol mapping relationship defines a unique corresponding method of the binary bits to the complex signal symbols. The polarization diversity precoding matrix is The number of taps used by the feedforward equalizer is 9, and the single-tap adaptive filter uses a multi-modulus algorithm (MMA) for tap adaptive updating, and the tap coefficient updating period is equal to every 16 symbol periods.

[0174] The present application is not limited to the above embodiments, and for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements are also considered to be within the scope of protection of the present application. The contents not described in detail in the specification are the prior art known to those skilled in the art.

Claims

1. A method for optical interconnection communication, characterized in that, comprising: Converting the binary bit stream signal to be transmitted into an analog electrical signal after being processed by a DSP; Using a laser to output two beams of light, one as the optical carrier of an integrated dual-polarization coherent optical transmitter to modulate the analog electrical signal into a complex optical field signal, and the other as the local oscillator light for time delay adjustment; Performing coherent mixing on the complex optical field signal and the local oscillator light through a polarization-independent coherent optical receiver, wherein the polarization state of the local oscillator light is controlled by feedback polarization perturbation to avoid the polarization state of the local oscillator light falling into the X and Y directions; the mixed electrical signal is processed by a DSP to recover the binary bit stream signal.

2. The optical interconnection communication method according to claim 1, characterized in that, The digital signal processing of the binary bit stream signal to be transmitted includes: After the binary bit stream signal to be transmitted is subjected to FEC encoding, independent constellation mapping is performed on the X and Y polarization states to generate two independent complex signal streams, and then polarization diversity precoding is performed. The two precoded signals are orthogonally separated and then subjected to time domain pre-compensation. The compensated signal is subjected to digital-to-analog conversion at the baud rate as the sampling rate to obtain the analog electrical signal.

3. The optical interconnection communication method according to claim 2, characterized in that: The complex signal stream generated by the constellation diagram mapping is [X 1 , Y 1 T , and the symbol stream after precoding is [X 2 , Y 2 T . The rule of precoding is [X 2 , Y 2 T = H · [X 1 , Y 1 T , is the precoding matrix and satisfies ad - bc ≠ 0.​​​​ 4. The optical interconnection communication method according to claim 3, characterized in that, The digital signal processing of the mixed electrical signal includes: The mixed electrical signal is converted from analog to digital and subjected to anti-aliasing filtering. The filtered signal is subjected to feedforward equalization and clock synchronization, and then single-tap adaptive equalization is performed to achieve polarization demultiplexing, and then de-precoding, de-mapping and FEC decoding are performed to obtain the binary bit stream signal.

5. The optical interconnection communication method according to claim 4, characterized in that: The two signals obtained by polarization demultiplexing are [A 1 , B 1 T . Using a matrix to perform depolarization diversity precoding processing on [A 1 , B 1 T to obtain [A 2 , B 2 T . The rule of the depolarization diversity precoding is: [A 2 , B 2 T = H'·[A 1 , B 1 T , where H' is the inverse matrix of the precoding matrix H.​​​​​ 6. The optical interconnection communication method according to claim 1, characterized in that, The feedback polarization perturbation to control the polarization state of the local oscillator light includes: The polarization-independent coherent optical receiver divides the received local oscillator light into two branches with perpendicular polarization states. The local oscillator light of each branch is divided into two paths according to different power ratios, and the path with the smaller optical power separated from the local oscillator light of each branch is extracted, and the power difference between the two extracted local oscillator lights is obtained, and the power difference is converted into the amplitude of the photocurrent. When the absolute value of the photocurrent amplitude is greater than a preset threshold, the local oscillator light is perturbed by a control signal proportional to the absolute value.

7. The optical interconnection communication method according to any one of claims 1-6, characterized in that: The modulation formats applicable to the optical interconnection communication method include QPSK, 8QAM, 16QAM, 32QAM and 64QAM; The information rates applicable to the optical interconnection communication method include 100G, 200G, 400G, 600G and 800G.

8. An optical interconnection communication system, characterized in that, comprising: A laser for outputting continuous light; A first optical splitter for receiving the continuous light and dividing it into two paths, one path providing an optical carrier and the other path as the local oscillator light; A transmitting end DSP chip for converting the binary bit stream signal to be transmitted into an analog electrical signal after being processed by a DSP; An integrated dual-polarization coherent optical transmitter for receiving the optical carrier and modulating the analog telecommunication signal into a complex optical field signal; A first optical fiber channel for transmitting the complex optical field signal output by the integrated dual-polarization coherent optical transmitter; A coarse adjustable delay line for coarsely adjusting the time delay of the local oscillator optical transmission line to match the transmission link length of the complex optical field signal; A second optical fiber channel for transmitting the local oscillator optical signal adjusted by the coarse adjustable delay line; A polarization-independent coherent optical receiver for receiving the complex optical field signal and the local oscillator optical signal respectively transmitted by the first optical fiber channel and the second optical fiber channel and performing coherent mixing; the polarization-independent coherent optical receiver includes a polarization scrambler for controlling the polarization state of the local oscillator optical signal through feedback polarization scrambling to prevent the polarization state of the local oscillator optical signal from falling into the X and Y directions; A receiving-end DSP chip for receiving the mixed electrical signal and recovering the binary bit stream signal through DSP processing.

9. The optical interconnection communication system according to claim 8, characterized in that: The laser is a DFB laser; the splitting ratio of the first optical splitter 2 is 7:3; the coarse adjustable delay line is implemented by a single-mode optical fiber; the first optical fiber channel and the second optical fiber channel are both ordinary single-mode optical fibers.

10. The optical interconnection communication system according to claim 8, characterized in that, The polarization-independent coherent optical receiver includes: A first polarization beam splitter for splitting the complex optical field signal into two branches with perpendicular polarization states; A fine adjustable delay line for precisely adjusting the transmission time delay and optical path difference of the local oscillator optical signal relative to the signal optical signal to ensure that the signal optical signal and the local oscillator optical signal satisfy within the coherent length; A second polarization beam splitter for splitting the local oscillator optical signal into two branches with perpendicular polarization states; A polarization scrambler that receives the local oscillator optical signal adjusted by the fine adjustable delay line and controls the polarization state of the local oscillator optical signal input to the second polarization beam splitter to prevent the local oscillator optical signal entering the second polarization beam splitter from being exactly horizontal or vertical; A second optical splitter and a third optical splitter for splitting the two local oscillator optical signals with polarization states in different power ratios; A fifth balanced detector for receiving the local oscillator optical signals with smaller power respectively split by the second optical splitter and the third optical splitter, obtaining the power difference, and converting it into an optical current amplitude output; A controller for converting the optical current amplitude into a perturbation control signal of the local oscillator optical signal polarization state and controlling the polarization scrambler; A mixing gain module for coherently mixing the two complex optical field signals output by the first polarization beam splitter with the local oscillator optical signals with larger power respectively split by the second optical splitter and the third optical splitter, and then respectively obtaining the real part and the imaginary part of the X and Y polarizations, amplifying and realizing automatic gain control.

11. The optical interconnection communication system according to claim 10, characterized in that, The mixing gain module includes: A first 90° mixer for coherently mixing one of the complex optical field signals output by the first polarization beam splitter with the local oscillator optical signal with larger power split by the second optical splitter; A second 90° mixer for coherently mixing the other complex optical field signal output by the first polarization beam splitter with the local oscillator optical signal with larger power split by the third optical splitter; The first balanced detector and the second balanced detector are used to convert the optical signals output by the first 90° mixer into electrical signals, respectively obtaining the real part and the imaginary part of the X polarization; The third balanced detector and the fourth balanced detector are used to convert the optical signals output by the second 90° mixer into electrical signals, respectively obtaining the real part and the imaginary part of the Y polarization; The transimpedance amplifier is used to amplify the real part and the imaginary part of the X polarization and the real part and the imaginary part of the Y polarization and implement automatic gain control.

12. The optical interconnection communication system according to claim 10, characterized in that: The ratios of the second optical splitter and the third optical splitter are the same, both being 95:5; When the absolute value of the photocurrent amplitude output by the fifth balanced detector is greater than a preset threshold, an output control electrical signal proportional to the magnitude of the absolute value acts on the polarization scrambler, and the threshold is 90% of the maximum photocurrent detected by the fifth balanced detector.

13. The optical interconnection communication system according to claim 8, characterized in that, The transmitting end DSP chip includes: The FEC encoding module is used to perform FEC encoding on the binary bit stream signal to be transmitted; The constellation mapping module is used to perform independent constellation mapping for the X and Y polarization states respectively according to a preset modulation format, generating two independent complex signal streams [X 1 , Y 1 T ;​ Precoding module, configured to perform polarization hierarchical precoding on the complex signal stream [X 1 , Y 1 T and output two precoded symbol streams [X 2 , Y 2 T , and the precoding rule is:​​ [X 2 ,Y 2 T =H·[X 1 ,Y 1 T , ​​ is a precoding matrix, satisfying ad - bc ≠ 0. The pre-compensation module is used to perform time-domain pre-compensation on the two pre-coded signals after orthogonal separation; The DAC module is used to perform digital-to-analog conversion on the compensated signal at the baud rate as the sampling rate to obtain the analog electrical signal.

14. The optical interconnection communication system according to claim 13, characterized in that, The receiving end DSP chip includes: The ADC module is used to convert the mixed electrical signal into a digital signal; Two low-pass filters are used to perform anti-aliasing filtering processing on the X polarization signal and the Y polarization signal respectively, Two feed-forward equalizers, each corresponding to a low-pass filter, perform feed-forward equalization on the filtered signal; Two clock recovery modules are used to recover the optimal sampling clock and phase for each feed-forward equalized signal respectively; Adaptive equalization module, which performs adaptive equalization on the signal after clock recovery to achieve polarization demultiplexing and obtain two equalized signals [A 1 , B 1 T .​ The depolarization diversity precoding module uses a matrix to process [A 1 , B 1 T for depolarization diversity precoding to obtain [A 2 , B 2 T . The rule of the depolarization diversity precoding is: [A 2 , B 2 T = H' · [A 1 , B 1 T , where H' is the inverse matrix of the precoding matrix H;​​​​ Two constellation diagram demapping modules are used to demap the signals that have completed depolarization diversity precoding respectively; Two FEC decoding modules are used to perform FEC decoding on the demapped binary bits respectively to recover the binary bit stream signal.

15. The optical interconnection communication system according to claim 14, characterized in that: The pre-compensation module of the transmitting end DSP chip performs time-domain pre-compensation using a real-domain finite impulse response filter, and the number of taps of the finite impulse response filter is less than or equal to 3; The adaptive equalization module of the receiving end DSP chip performs adaptive equalization using a single-tap 2x2 complex butterfly filter; Both the DAC module and the ADC module operate at a sampling rate of 1 times the baud rate.