Optical transmission system, optical transmission method, transmitter and receiver

Abstract

The optical transmission system (10) of the present invention includes N directly modulated lasers that convert N-channel first electrically modulated signals into N-channel optically modulated signals and transmit them, N photodetectors that receive the N-channel optically modulated signals and convert them into N-channel second electrically modulated output signals, and at least one of a first MIMO equalizer (108) that performs an equalization process on the N-channel first electrically modulated signals to compensate for crosstalk between the N-channel first electrically modulated signals, and a second MIMO equalizer (108) that performs an equalization process on the N-channel second electrically modulated signals to compensate for crosstalk between the N-channel second electrically modulated signals, and uses matrix coefficients based on an impulse response for the equalization process. As a result, the present invention can provide an optical transmission system capable of reducing crosstalk and achieving good BER characteristics.

Description

[Technical Field]

[0001] The present invention relates to an optical transmission system, an optical transmission method, a transmitter, and a receiver that use a directly modulated laser. [Background technology]

[0002] Internet traffic in data centers and access networks is expected to increase, and Ethernet with data rates of 800 Gb / s or 1.6 Tb / s is expected to become a reality. In short-distance communications, intensity-modulated direct-detected (IMDD) systems are attracting attention due to their low cost and low power consumption.

[0003] The optical transceivers used in this IMDD system are equipped with low-power directly-modulated lasers (DMLs) and are compatible with multiple wavelength channels in wavelength division multiplexing (WDM) or spatial channels in space division multiplexing (SDM) systems. Optical transceivers compatible with WDM / SDM use photonic integrated circuits / chips (PICs), with components such as lasers, modulators, and photodetectors mounted within the same PIC.

[0004] Furthermore, the modulation format in recent standardization technology is 4-level pulse amplitude modulation (PAM). Therefore, to achieve WDM / SDM at 800 Gb / s or 1.6 Tb / s, each of the 8 or 16 channels must have a capacity of 50 GBaud or more. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 105430 [Non-patent literature]

[0006] [Non-Patent Document 1] NP Diamantopoulos, et al., “400-Gb / s DMT-SDM Transmission based on Membrane DML-Array-on-Silicon,” J. Lightw. Technol., vol. 37, no. 8, pp. 1805-1812, Apr. 2019. [Non-patent document 2] NP Diamantopoulos, et al., “4×56-GBaud PAM-4 SDM Transmission Over 5.9-km 125-μm-Clading MCF Using III-V-on-Si DMLs,” in Proc. Optical Fiber Communications Conference and Exhibition (OFC 2020), San Diego, CA, USA, 8 - 12 Mar. 2020, paper W1D.4. [Non-patent document 3] T. Fujii, et al., “Multiwavelength membrane laser array using selective area growth on directly bonded InP on SiO2 / Si,” Optica, vol. 7, no. 7, pp. 838-846, July 2020. Summary of the Invention [Problem to be solved by the invention]

[0007] When multiple components are implemented in a PIC, crosstalk increases and becomes a problem. While direct current crosstalk is relatively easy to tolerate, high-frequency crosstalk has a significant impact on the signal-to-interference and noise ratio (SINR) of PAM4 modulation. This impact becomes significant at higher data rates, where the bandwidth limitations of electronic and optoelectronic components degrade PAM4 performance.

[0008] Figures 7A-D show 54 GBaud PAM4 modulation by a low-power membrane DML on Si in an IMDD system (see Non-Patent Documents 1-3). Figures 7A and 7B show the eye patterns of the directly modulated signal with no electrical RF crosstalk and with -15 dB electrical RF crosstalk, respectively. The directly modulated signal was generated by the membrane laser on Si with a current of 13 mA.

[0009] According to measurements using a conventional DML-based PIC, RF crosstalk is approximately -15 dB (Non-Patent Documents 1 and 2). As can be seen from the simulation results of the eye patterns shown in Figures 7A and 7B, when RF crosstalk is -15 dB, PAM4 performance is significantly degraded compared to when RF crosstalk is not assumed.

[0010] In conventional Ethernet standardization, the bit error rate (BER) required for forward error correction (FEC) is approximately 2.2E-4 or less, and a feed-forward equalizer (FFE) is also used.

[0011] Figure 7C shows the BER versus the number of equalizer taps when there is no electrical RF crosstalk. With an equalizer tap count of four or more, the BER decreases to about 1e-6. Thus, for this DML system, the optimal number of FFE taps is four.

[0012] Even when these four FFE taps are used, as shown in FIG. 7B, when the RF crosstalk is −15 dB, the BER deteriorates to about 1.3E−2 and does not reach the FEC threshold BER (2.2E−4).

[0013] Figure 7D shows the BER dependence on the number of electrical RF crosstalks when four taps are used. The BER deteriorates when the RF crosstalk changes from -40 dB to -10 dB, and the BER is 1.0E-4 or higher when the RF crosstalk is -22 dB or higher.

[0014] As described above, an increase in RF crosstalk causes a problem because it degrades BER and PAM4 characteristics. [Means for solving the problem]

[0015] In order to solve the above-described problems, an optical transmission system according to the present invention includes N directly modulated lasers that convert N-channel first electrical modulated signals into N-channel optical modulated signals and transmit the converted signals; N photodetectors that receive the N-channel optical modulated signals and convert them into N-channel second electrical modulated signals; and at least one of a first MIMO equalizer that performs equalization processing on the N-channel first electrical modulated signals to compensate for crosstalk between the N-channel first electrical modulated signals; and a second MIMO equalizer that performs equalization processing on the N-channel second electrical modulated signals to compensate for crosstalk between the N-channel second electrical modulated signals, wherein the equalization processing uses matrix coefficients based on an impulse response. In equation (A) represented by vector X of at least one of the first electric modulated signals of the N channels and the second electric modulated signals of the N channels, vector Y of the equalized signal, and matrix coefficient W, optimal matrix coefficients are learned so that a mean square error between vector Y simulated for vector X calculated using equation (B) and a desired output signal vector is minimized. It is characterized by the following.

[0017] An optical transmission method according to the present invention is an optical transmission method using N directly modulated lasers that convert N-channel first electrical modulated signals into N-channel optical modulated signals and transmit them, N photodetectors that receive the N-channel optical modulated signals and convert them into N-channel second electrical modulated signals, and at least one of a first MIMO equalizer to which the N-channel first electrical modulated signals are input and a second MIMO equalizer to which the N-channel second electrical modulated signals are input, the method comprising the steps of: calculating vectors of the N-channel optical modulated signals by equation (B); and calculating vectors of at least one of output signals of the first MIMO equalizer and the second MIMO equalizer. the step of calculating a vector of output signals by equation (A); the step of determining optimal matrix coefficients so that a mean square error between the calculated output signal vector and a desired output signal vector is minimized; and the step of performing an equalization process on at least one of the N-channel first electrical modulated signals and the N-channel second electrical modulated signals using the optimal matrix coefficients in at least one of the first MIMO equalizer and the second MIMO equalizer, thereby compensating for crosstalk between at least one of the N-channel first electrical modulated signals and the N-channel second electrical modulated signals.

[0018]

number

[0019] Furthermore, the present invention sendinga transmitter for transmitting N-channel analog optical modulated signals received by the receiver via the communication path in this order, the transmitter comprising: a MIMO equalizer to which the N-channel digital electrical modulated signals are input; a DA converter for converting the N-channel digital electrical modulated signals into N-channel analog electrical modulated signals; N RF drivers to which the N-channel analog electrical modulated signals are input; and N directly modulated lasers that are driven by the N-channel analog electrical modulated signals input to the N RF drivers and output the N-channel analog optical modulated signals, and the MIMO equalizer performs equalization processing on the N-channel digital electrical modulated signals using matrix coefficients based on impulse responses to compensate for crosstalk between the N-channel electrical modulated signals. In equation (A) represented by vector X of the N-channel electrical modulation signals, vector Y of the equalized signals, and matrix coefficient W, optimal matrix coefficients are learned so that the mean square error between vector Y simulated for vector X calculated using equation (B) and a desired output signal vector is minimized. It is characterized by the following.

[0020] Furthermore, a receiver according to the present invention is an optical transmission system which sequentially comprises a transmitter, a communication path, and a receiver, and which receives N-channel analog optically modulated signals transmitted from the transmitter via the communication path, the receiver comprising: a photodetector array having N photodetectors which receives the N-channel analog optically modulated signals and converts them into N-channel analog electrical modulated signals; an AD converter which converts the N-channel analog electrical modulated signals into N-channel digital electrical modulated signals; and a MIMO equalizer to which the N-channel digital electrical modulated signals are input, wherein the MIMO equalizer performs equalization processing on the N-channel digital electrical modulated signals using matrix coefficients based on impulse responses to compensate for crosstalk between the N-channel electrical modulated signals. In equation (A) represented by vector X of the N-channel electrical modulation signals, vector Y of the equalized signals, and matrix coefficient W, optimal matrix coefficients are learned so that the mean square error between vector Y simulated for vector X calculated using equation (B) and a desired output signal vector is minimized. It is characterized by the following. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide an optical transmission system, an optical transmission method, a transmitter, and a receiver that can reduce crosstalk and obtain good BER characteristics. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a block diagram showing a configuration of an optical transmission system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the effect of the optical transmission system according to the first embodiment of the present invention. [Figure 3A] FIG. 3A is a diagram for explaining the effect of the optical transmission system according to the first embodiment of the present invention. [Figure 3B] FIG. 3B is a diagram for explaining the effect of the optical transmission system according to the first embodiment of the present invention. [Figure 3C] FIG. 3C is a diagram for explaining the effect of the optical transmission system according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a block diagram showing a configuration of an optical transmission system according to a first modification of the first embodiment of the present invention. [Figure 5] FIG. 5 is a block diagram showing a configuration of an optical transmission system according to a second modification of the first embodiment of the present invention. [Figure 6] FIG. 6 is a block diagram showing a configuration of an optical transmission system according to a third modification of the first embodiment of the present invention. [Figure 7A] FIG. 7A is a diagram for explaining the operation of a conventional optical transmission system. [Figure 7B] FIG. 7B is a diagram for explaining the operation of the conventional optical transmission system. [Figure 7C] FIG. 7C is a diagram for explaining the operation of the conventional optical transmission system. [Figure 7D] FIG. 7D is a diagram for explaining the operation of the conventional optical transmission system. DETAILED DESCRIPTION OF THE INVENTION

[0023] First Embodiment An optical transmission system, an optical transmission method, a transmitter, and a receiver according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 3C.

[0024] <Configuration of optical transmission system> 1, an optical transmission system 10 according to this embodiment includes a directly modulated laser (DML)-based transmitter (Tx) 101, a direct detection-based receiver (Rx) 102, and a communication path 105 connecting the transmitter 101 and the receiver 102. In the optical transmission system 10, an analog electrical modulated signal 1_1 is input to the transmitter 101, and a digital electrical modulated signal 2_1 is output from the receiver 102.

[0025] Transmitter 101 comprises, in order from the input side, a driver 103 and a laser array 104. Driver 103 comprises a plurality (N units) of RF drivers. Laser array 104 comprises a plurality (N units) of DMLs. The RF driver drives the DMLs with an RF electrical signal, and the DMLs directly modulate the output light with the RF signal, converting the electrical modulation signal into an optical modulation signal.

[0026] The communication path 105 may be an optical fiber, free space such as air, or an optical waveguide such as a PIC.

[0027] The receiver 102 includes, in order from the side connected to the communication path 105, a photodetector (PD) array 106, an analog-to-digital (AD) converter 107, and a multiple input, multiple output (MIMO) equalizer 108.

[0028] The PD array 106 includes a plurality of (N) PDs, and converts an analog optical modulation signal into an analog electrical modulation signal.

[0029] There are a plurality (N units) of AD converters 107, which convert analog electrical modulation signals into digital electrical modulation signals.

[0030] The MIMO equalizer 108 is a characteristic component in this optical transmission system 10, and is used to compensate for RF crosstalk due to adjacent channels in the laser array 104, the PD array 106, and the driver 103, respectively.

[0031] In the optical transmission system 10, N DMLs of the laser array 104 are directly modulated by N-channel analog electrical modulation signals input to N RF drivers of the driving device 103 in the transmitter 101. An N-channel analog optical modulation signal is transmitted from the laser array 104, propagates through the communication path 105, and is received by N PDs of the PD array 106 in the receiver 102. The N-channel analog optical modulation signal received by the PD array 106 is converted into an N-channel analog electrical modulation signal, and then converted into a digital electrical modulation signal by N AD converters 107. The N-channel digital electrical modulation signal is input to the MIMO equalizer 108, where equalization processing is performed and then output.

[0032] Here, the MIMO equalizer 108 compensates for RF crosstalk occurring between N-channel modulation signals.

[0033] Also, when there are multiple (N-channel) signals and the number of channels is 4, 4 units each of the DML, PD, RF driver, and AD converter 107 are installed. For 8-channel signals, 8 units of each component are installed, and for 16-channel signals, 16 units of each component are installed.

[0034] <Operation of MIMO Equalizer> The operation of the MIMO equalizer 108 in the optical transmission system 10 according to this embodiment will be described below.

[0035] Assuming that the input RF signal to the MIMO equalizer 108 is vector X and the output RF signal is vector Y, their relationship is expressed by Equation (1).

[0036]

Equation

[0037] Here, W is the weight matrix of the MIMO equalizer 108 and is the reciprocal of the impulse response of the MIMO equalizer 108 in the DML transmission system.

[0038] In the MIMO equalizer 108, the number of channels is N ch , the number of taps for each channel is N taps Assume that:

[0039] TIFF0007747183000003.tif10170

[0040] The matrix coefficients (weights) W are trained to minimize the mean squared error (MSE) between Y and the known target signal.

[0041] This learning is performed using experimentally obtained measurements in a back-to-back optical system, where back-to-back refers to an experimental configuration in which the transmitter 101 and receiver 102 are directly connected, omitting the transmission path.

[0042] For example, an experimentally obtained N-channel signal X1 containing crosstalk is input to a MIMO equalizer 108 with a matrix coefficient (weight) W set to W1, and an output signal Y1 of the N-channel MIMO equalizer 108 is measured. The optimal matrix coefficient W is calculated so that the MSE between the measured N-channel output signal Y1 and the desired output signal (i.e., the output signal with the effects of crosstalk suppressed) Y0 is minimized for each channel. opt Determine.

[0043] This optimal matrix coefficient W opt By setting this in the MIMO equalizer 108, a signal equivalent to the desired output signal Y0, that is, a signal in which the influence of crosstalk is suppressed, is output.

[0044] In this way, the MIMO equalizer 108 in the optical transmission system 10 according to this embodiment performs equalization processing using matrix coefficients based on impulse responses, thereby compensating for crosstalk between multiple (N channel) signals.

[0045] <Effects> To demonstrate the effectiveness of the optical transmission system 10 according to this embodiment, a simulation was performed based on the DML-based transmitter 101. In the simulation, a typical electro-optical (EO) response of the DML shown in Fig. 2 was assumed. The DML is a membrane laser on Si, operating at a bias current of 13 mA and a -3 dB bandwidth of 20 GHz.

[0046] Figure 3A shows the number of taps in the MIMO equalizer, N taps The figure shows the simulation results of the BER performance of a 54 GBaud PAM4 signal for a 100 Mbps BER with RF crosstalk of -15 dB.

[0047] The BER decreases as the number of taps increases. When the number of taps is 1 to 3, the BER is approximately 2e-1 to 4e-2, which is the same value as when there is no crosstalk (FIG. 7C). In this way, crosstalk is reduced in the optical transmission system 10.

[0048] Furthermore, when the number of taps is increased to four, the BER decreases significantly. The BER decreases to about 3e-4 with four taps and to below 1e-4 with eight taps. Thus, good BER characteristics are obtained in the optical transmission system 10.

[0049] In Figure 3B and C, the number of taps is N taps The eye patterns and BER of a 54 GBaud PAM4 signal are shown for four and eight channels.

[0050] Number of taps N taps When there are four taps, a better eye pattern can be obtained compared to when there is crosstalk (Fig. 7B). taps With 8, the BER is 6.1E-5, which is below the FEC threshold of the Ethernet link.

[0051] In this way, in the optical transmission system 10, crosstalk can be reduced and good BER characteristics can be obtained by using a MIMO equalizer with at least one tap. Furthermore, it is desirable for the MIMO equalizer to have four or more taps, which can significantly reduce crosstalk and obtain good BER characteristics.

[0052] According to the optical transmission system, optical transmission method, transmitter and receiver of the present embodiment, crosstalk can be reduced by the MIMO equalizer, and good BER characteristics can be obtained.

[0053] In addition, it can reliably transmit signals of 400 Gb / s or more over short distances of up to about 2 km with low power consumption.

[0054] In particular, when the transmitter and receiver in the optical transmission system according to this embodiment are mounted on a photonic integrated circuit or chip (PIC), signals of 400 Gb / s or more can be transmitted reliably over short distances with low power consumption. Here, either the transmitter or the receiver may be mounted on a PIC.

[0055] <Variation 1> An optical transmission system, an optical transmission method, a transmitter, and a receiver according to a first modification of the first embodiment of the present invention will be described with reference to FIG.

[0056] 4, an optical transmission system 20 according to the present first modification includes a DML-based transmitter (Tx), a direct detection-based receiver (Rx), and a communication path 205 connecting the transmitter 201 and the receiver 202. In the optical transmission system 20, a digital electrical modulated signal is input to the transmitter 201, and the digital electrical modulated signal is output from the receiver 202.

[0057] The transmitter 201 includes, in order from the input side, a DA (Digital-to-Analog) converter, an RF driver, and a laser array 204. The receiver 202 includes, in order from the side connected to the communication path 205, a PD array 206, an AD converter 207, and a MIMO equalizer 208. The other configurations are the same as those in the first embodiment.

[0058] In optical transmission system 20, N-channel digital electrical modulated signals input to N DA converters 209 in transmitter 201 are converted into N-channel analog electrical modulated signals and input to N RF drivers. As in the first embodiment, N-channel analog optical modulated signals are transmitted from laser array 204 and propagated through communication path 205. Subsequently, the N-channel analog optical modulated signals are received by PD array 206 in receiver 202, converted into N-channel analog electrical modulated signals, and subjected to equalization processing by MIMO equalizer 208, which outputs digital electrical modulated signals. Here, MIMO equalizer 208 compensates for RF crosstalk occurring between the N-channel modulated signals.

[0059] According to the optical transmission system, optical transmission method, transmitter and receiver of this modification, crosstalk can be reduced by the MIMO equalizer, and good BER characteristics can be obtained, as in the first embodiment.

[0060] <Variation 2> An optical transmission system, an optical transmission method, a transmitter, and a receiver according to a second modification of the first embodiment of the present invention will be described with reference to FIG.

[0061] 5, an optical transmission system 30 according to the second modification of this embodiment includes a DML-based transmitter (Tx), a direct detection-based receiver (Rx), and a communication path 305 connecting the transmitter 301 and the receiver 302. In the optical transmission system 30, a digital electrical modulated signal is input to the transmitter 301, and the digital electrical modulated signal is output from the receiver 302.

[0062] The transmitter 301 includes, in order from the input side, a MIMO equalizer 308, a DA converter 309, an RF driver, and a laser array 304. The receiver 302 includes, in order from the side connected to the communication path 305, a PD array 306 and an AD converter 307. The other configurations are the same as those in the first embodiment.

[0063] In optical transmission system 30, N-channel digital electrical modulated signals input to MIMO equalizer 308 of transmitter 301 undergo equalization processing and are input to N DA converters 309. Subsequently, the N DA converters 309 convert the signals into N-channel analog electrical modulated signals and input them to N RF drivers. N-channel analog optical modulated signals are transmitted from laser array 304 driven by N RF drivers, propagate through communication path 305, and are received by PD array 306 in receiver 302. They are then converted into N-channel digital electrical modulated signals by AD converter 307 and output. Here, MIMO equalizer 308 compensates for RF crosstalk that occurs between the N-channel modulated signals.

[0064] According to the optical transmission system, optical transmission method, transmitter and receiver of this modification, crosstalk can be reduced by the MIMO equalizer, and good BER characteristics can be obtained, as in the first embodiment.

[0065] <Variation 3> An optical transmission system, an optical transmission method, a transmitter, and a receiver according to a third modification of the first embodiment of the present invention will be described with reference to FIG.

[0066] 6, an optical transmission system 40 according to a third modification of this embodiment includes a DML-based transmitter (Tx), a direct detection-based receiver (Rx), and a communication path 405 connecting the transmitter 401 and the receiver 402. In the optical transmission system 40, a digital electrical modulated signal is input to the transmitter 401, and an analog electrical modulated signal is output from the receiver 402.

[0067] Transmitter 401 includes, in order from the input side, a MIMO equalizer 408, a DA converter 409, an RF driver, and a laser array 404. Receiver 402 includes a PD array 406. This differs from Modification 2 in that receiver 402 does not include an AD converter after PD array 406, and the output is an analog electrical modulated signal. Other configurations and operations are the same as those of Modification 2.

[0068] According to the optical transmission system, optical transmission method, transmitter, and receiver according to this modification example, similar to the first embodiment, crosstalk can be reduced by the MIMO equalizer, and good BER characteristics can be obtained.

[0069] As described above, the optical transmission system according to this embodiment and its modification example includes N direct modulation lasers, N photodetectors, and a MIMO equalizer. Here, the N direct modulation lasers convert N-channel electrical modulation signals (first electrical modulation signals) into N-channel optical modulation signals and transmit them. The N photodetectors receive the N-channel optical modulation signals and convert them into N-channel electrical modulation signals (second electrical modulation signals). The MIMO equalizer performs equalization processing on either one of the N-channel first electrical modulation signals and the N-channel second electrical modulation signals using matrix coefficients based on the impulse response. Thereby, crosstalk between signals of either one of the N-channel first electrical modulation signals and the N-channel second electrical modulation signals is compensated.

[0070] <Second Embodiment> The optical transmission system, optical transmission method, transmitter, and receiver according to the second embodiment of the present invention will be described.

[0071] <Configuration of Optical Transmission System> As shown in FIG. 1, the optical transmission system according to this embodiment includes a DML-based transmitter (Tx), a direct detection-based receiver (Rx), and a communication path connecting the Tx and the Rx, and has the same configuration as the first embodiment.

[0072] <Operation of MIMO Equalizer> Similar to the first embodiment, when the RF signal of vector X is input, the MIMO equalizer in the optical transmission system according to this embodiment outputs the RF signal of vector Y as shown in Equation (1). The coefficients of matrix W are learned by minimizing the MSE between Y and a known target signal based on a learning algorithm.

[0073] In this embodiment, a simulation including RF crosstalk is used in the learning.

[0074] In this simulation, first, the output of the DML including crosstalk is calculated as an N-channel signal vector X1.

[0075] Here, the output power of the DML is simulated by taking into account crosstalk between adjacent lasers via leakage bias current from one channel to the adjacent channel. In this numerical simulation, we use the rate equation for the carrier density, expressed as Eq. (2).

[0076]

number

[0077] where t is time, N is the carrier density in the DML, and η i is the quantum efficiency, q is the charge density, and V is the volume of the active layer of the DML. XT are the instantaneous currents of the applied signal and crosstalk, respectively. R(N) is the carrier recombination factor, G is the gain, and S is the photon density.

[0078] The calculation of I(t) also assumes a 54 GBaud PAM4 signal shaped by a root-raised cosine (RRC) filter with a roll-off factor of 0.1.

[0079] Next, the matrix coefficient W is set to W1, and the calculated signal vector X1 is used to calculate the signal vector Y1 of N channels as the output of the MIMO equalizer according to equation (1).

[0080] Finally, the optimum matrix coefficients W are calculated so that the MSE between the calculated signal vector Y1 and the desired output signal vector (i.e., the vector of the output signal with the crosstalk effect suppressed) Y0 is minimized for each channel. opt Determine.

[0081] This optimal matrix coefficient W opt By setting this in the MIMO equalizer, a signal equivalent to the desired output signal Y0, that is, a signal in which the influence of crosstalk is suppressed, is output.

[0082] In this way, the MIMO equalizer in the optical transmission system according to this embodiment performs equalization processing using matrix coefficients based on impulse responses obtained by simulation.

[0083] According to the optical transmission system, optical transmission method, transmitter and receiver of this embodiment, crosstalk can be reduced by the MIMO equalizer, and good BER characteristics can be obtained, as in the first embodiment.

[0084] In the optical transmission system according to this embodiment, the same configuration as in the first embodiment is used, but the same configuration as in Modifications 1 to 3 of the first embodiment may also be used.

[0085] As described above, the optical transmission system according to this embodiment includes N directly modulated lasers, N photodetectors, and a MIMO equalizer. Here, the N directly modulated lasers convert N-channel electrical modulated signals (first electrical modulated signals) into N-channel optical modulated signals and transmit them. The N photodetectors receive the N-channel optical modulated signals and convert them into N-channel electrical modulated signals (second electrical modulated signals). The MIMO equalizer performs equalization processing on either the N-channel first electrical modulated signals or the N-channel second electrical modulated signals using matrix coefficients based on an impulse response. This compensates for crosstalk between either the N-channel first electrical modulated signals or the N-channel second electrical modulated signals.

[0086] The optical transmission system, optical transmission method, transmitter and receiver according to the embodiments of the present invention can handle both digital signals and analog signals.

[0087] In the optical transmission system, optical transmission method, transmitter, and receiver according to the embodiments of the present invention, examples have been shown in which learning is performed using experimentally obtained measurements and simulations, but this is not limiting and learning may also be performed using a known learning algorithm for an equalizer.

[0088] In the optical transmission system, optical transmission method, transmitter, and receiver according to the embodiments of the present invention, an example has been shown in which a MIMO equalizer is provided in either the transmitter or the receiver, and equalization processing is performed on either the first electrical modulated signal or the second electrical modulated signal, but this is not limiting, and a MIMO equalizer may be provided in both the transmitter and the receiver, and equalization processing may be performed on both the first electrical modulated signal and the second electrical modulated signal.

[0089] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the optical transmission system, optical transmission method, transmitter, and receiver configurations have been shown, but the present invention is not limited to these examples. Anything that can demonstrate the functions and effects of the optical transmission system will suffice. [Industrial Applicability]

[0090] The present invention relates to an optical transmission system, an optical transmission method, a transmitter, and a receiver, and can be applied to short-distance communications in data centers and the like. [Explanation of symbols]

[0091] 10 Optical Transmission Systems 101 Transmitter 102 Receiver 103 Drive unit 104 Laser Array 105 Communication Channel 106 Photodetector Array 107 AD converter 108 MIMO equalizer

Claims

1. N direct modulation lasers that convert N-channel first electrical modulation signals into N-channel optical modulation signals and transmit the converted signals; N photodetectors that receive the N-channel optical modulated signals and convert them into N-channel second electrical modulated signals; at least one of a first MIMO equalizer that performs equalization processing on the N-channel first electric modulated signals to compensate for crosstalk between the N-channel first electric modulated signals, and a second MIMO equalizer that performs equalization processing on the N-channel second electric modulated signals to compensate for crosstalk between the N-channel second electric modulated signals; The equalization process uses matrix coefficients based on an impulse response, In equation (A) represented by a vector X of at least one of the N-channel first electric modulated signals and the N-channel second electric modulated signals, a vector Y of the equalized signal, and the matrix coefficient W, The optimal matrix coefficients are learned so that the mean square error between the vector Y simulated for the vector X calculated using equation (B) and the desired output signal vector is minimized. An optical transmission system comprising: [Equation 1] [Equation 2]

2. N RF drivers that, in turn, drive the N directly modulated lasers; the N directly modulated lasers; a transmitter comprising: In order, the N photodetectors; N AD converters; the second MIMO equalizer; a receiver comprising: a communication path connecting the transmitter and the receiver; The optical transmission system according to claim 1 , comprising:

3. in turn, the first MIMO equalizer; N D / A converters; N RF drivers for driving the N directly modulated lasers; the N directly modulated lasers; a transmitter comprising: a receiver including the N photodetectors; a communication path connecting the transmitter and the receiver; The optical transmission system according to claim 1 , comprising:

4. At least one of the transmitter and the receiver is mounted on a PIC.

4. The optical transmission system according to claim 2 or 3.

5. N direct modulation lasers that convert N-channel first electrical modulation signals into N-channel optical modulation signals and transmit the converted signals; N photodetectors that receive the N-channel optical modulated signals and convert them into N-channel second electrical modulated signals; at least one of a first MIMO equalizer to which the N-channel first electrical modulated signals are input and a second MIMO equalizer to which the N-channel second electrical modulated signals are input; An optical transmission method using calculating a vector of the N-channel optical modulated signals according to equation (B); calculating a vector of an output signal of at least one of the first MIMO equalizer and the second MIMO equalizer according to equation (A); determining optimal matrix coefficients such that the mean square error between the calculated output signal vector and a desired output signal vector is minimized; performing an equalization process on at least one of the N-channel first electrical modulated signals and the N-channel second electrical modulated signals using the optimum matrix coefficients in at least one of the first MIMO equalizer and the second MIMO equalizer, thereby compensating for crosstalk between at least one of the N-channel first electrical modulated signals and the N-channel second electrical modulated signals; An optical transmission method comprising: [Equation 3] [Equation 4]

6. In an optical transmission system comprising, in order, a transmitter, a communication path, and a receiver, The transmitter transmits N-channel analog optical modulated signals received by the receiver via the communication path, a MIMO equalizer to which N-channel digital electrical modulated signals are input; a DA converter that converts the N-channel digital electrical modulation signals into N-channel analog electrical modulation signals; N RF drivers to which the N-channel analog electrical modulation signals are input; N directly modulated lasers that are driven by N-channel analog electrical modulation signals input to the N-channel RF drivers and output the N-channel analog optical modulation signals; Equipped with the MIMO equalizer performs an equalization process on the N-channel digital electrical modulation signals using matrix coefficients based on an impulse response to compensate for crosstalk between the N-channel electrical modulation signals; In equation (A) represented by the vector X of the N-channel electrical modulation signals, the vector Y of the equalized signals, and the matrix coefficients W, The optimal matrix coefficients are learned so that the mean square error between the vector Y simulated for the vector X calculated using equation (B) and the desired output signal vector is minimized. A transmitter characterized by: [Equation 5] [Equation 6]

7. In an optical transmission system comprising, in order, a transmitter, a communication path, and a receiver, The receiver receives N-channel analog optical modulated signals transmitted from the transmitter via the communication path, a photodetector array having N photodetectors for receiving the N-channel analog optical modulated signals and converting them into N-channel analog electrical modulated signals; an AD converter that converts the N-channel analog electrical modulation signals into N-channel digital electrical modulation signals; a MIMO equalizer to which the N-channel digital electrical modulated signals are input; Equipped with the MIMO equalizer performs an equalization process on the N-channel digital electrical modulation signals using matrix coefficients based on an impulse response to compensate for crosstalk between the N-channel electrical modulation signals; In equation (A) represented by the vector X of the N-channel electrical modulation signals, the vector Y of the equalized signals, and the matrix coefficients W, The optimal matrix coefficients are learned so that the mean square error between the vector Y simulated for the vector X calculated using equation (B) and the desired output signal vector is minimized. A receiver characterized by: [Equation 7] [Equation 8]

Images