Multilevel optical signal packet transmission device, multilevel optical signal packet reception device, and multilevel optical signal packet transmission / reception system

Abstract

In a multilevel optical signal packet transmission device (110), n number of frames representing electrical signals are inputted to a D / A converter (114). The n number of frames are configured by adding the same header and CRC value of the header to an n number of divided data items generated on the basis of scrambled data. The D / A converter (114) converts the electrical signals of the n number of frames into one multilevel electrical signal having 2n levels. A multilevel optical transmitter (115) converts the multilevel electrical signal into a multilevel optical signal and outputs the multilevel optical signal to an optical fiber transmission line (120). The multilevel optical transmitter (115) generates the multilevel optical signal as a packet in which only the header portion has two levels.

Description

Multilevel optical signal packet transmitting device, multilevel optical signal packet receiving device, and multilevel optical signal packet transmitting / receiving system

[0001] The present invention relates to an optical transceiver for transferring data between different computers, and more particularly to a multilevel optical signal packet transmitter, a multilevel optical signal packet receiver, and a multilevel optical signal packet transmission and reception system.

[0002] Rapid increases in datacenter traffic have created a demand for high-capacity transmission systems that connect datacenters via optical transmission paths comprising optical fibers and optical amplifiers. Conventionally, dedicated Dense Wavelength Division Multiplexing (DWDM) transmission systems have been commonly used. Optical signals, such as Ethernet (registered trademark), output from servers and routers in datacenters are accommodated in transponders of DWDM transmission equipment and transmitted as DWDM signals. Furthermore, compact optical modules capable of transmitting and receiving multilevel optical signals have been developed in recent years for relatively short distances, allowing high-capacity optical signals from servers and routers to be directly accommodated in DWDM transmission equipment.

[0003] Non-Patent Document 1 discloses a technology for improving reception characteristics by electrical signal processing such as MIMO (Multiple-Input and Multiple-Output). Non-Patent Document 2 discloses that bit errors occurring in the data portion of a transmission frame can be tolerated depending on the type of application, but bit errors occurring in the header portion have a much greater impact on the application due to frame loss and must therefore be avoided. Non-Patent Document 3 discloses that in in-line amplifier systems, signal waveform distortion caused by the combined effect of higher-order group velocity dispersion (GVD) and self-phase modulation (SPM) dominates performance.

[0004] F. Hamaoka, et al., “Optical multipath network system by using diversity reception for improving transmission performance,” IEICE Comm. Exp., vol. 3, no. 8, pp. 252-257, (2014). T. Matsuda, et al., “Proposal of bit-error-tolerant transmission for flexible data transmission according to application,” IEICE Technical Report PN2023-89, pp. 107-112, (2024). T. Matsuda, et al., “Comparison between NRZ and RZ signal formats for in-line amplifier transmission in the zero-dispersion regime,” J. Lightwave Technol., vol. 16, pp. 340-348, (1998).

[0005] In recent years, it has become common for DWDM transmission equipment to use digital coherent transmission as a transmission and reception method. Digital coherent transmission eliminates the need for chromatic dispersion compensation in the optical fiber transmission line because it compensates for chromatic dispersion in the optical fiber transmission line through electrical signal processing on the receiver side.

[0006] When optical multilevel signals from a compact optical module are input and transmitted into a DWDM transmission device, optical multilevel signals are much more susceptible to chromatic dispersion than binary signals, so a dispersion compensator is required even over short distances. However, due to power consumption and size considerations, it is difficult to implement any optical or electrical chromatic dispersion compensator inside the compact optical module. Therefore, an external chromatic dispersion compensator is required, which increases cost and space, thereby negating the advantages of the compact optical module.

[0007] The technology described in Non-Patent Document 1 can improve optical noise levels in the optical domain, but cannot improve optical signal levels, and is therefore ineffective against optical signal waveform degradation due to chromatic dispersion, etc. In the technology described in Non-Patent Document 2, to avoid frame loss, which has a greater impact on the application layer than data bit errors, the transmitting side copies header information to a multi-lane signal, and the receiving side selects the header information of a frame with a correct CRC (Cyclic Redundancy Check) value from the multi-lane signal as correct, thereby correcting frame header errors and protecting the frame header. While the technology described in Non-Patent Document 2 can improve the effects of noise in the electrical (digital) domain, if the bit error rate increases dramatically due to waveform degradation, it becomes difficult not only to receive a frame with a correct CRC value, but also to recognize the beginning of a frame.

[0008] In view of the above background, an object of the present invention is to protect frame headers and avoid frame loss by reducing the influence of waveform degradation in optical transmission.

[0009] The multilevel optical signal packet transmission device according to the present invention receives n frames, each of which is composed of n pieces of divided data generated based on scrambled data and the same header and CRC value added to the header, and transmits the n frames of electrical signals in two ｎ and a multi-level optical transmitter that converts the multi-level electrical signal into a multi-level optical signal and outputs it to an optical fiber transmission line, wherein the multi-level optical transmitter generates the multi-level optical signal as a packet in which only the header portion is binary.

[0010] According to the present invention, the influence of waveform degradation in optical transmission is reduced, thereby protecting frame headers and avoiding frame loss.

[0011] 1 is a schematic configuration diagram of a multi-level optical signal packet transmitting and receiving system according to an embodiment of the present invention; FIG. 2 is a schematic diagram showing an example of data divided by a frame dividing unit; FIG. 3 is a schematic diagram showing an example of a frame output from a frame dividing unit; FIG. 4 is a flowchart showing a processing flow in a multi-level optical signal packet transmitting and receiving system; FIG. 5 is a schematic configuration diagram of a transmitting and receiving system used in a numerical simulation; FIG. 6 is a graph showing the relationship between transmission distance and eye opening deterioration; FIG. 7 is an eye diagram of a transmitting header signal according to a comparative example; FIG. 8 is an eye diagram of a receiving header signal according to a comparative example; FIG. 9 is an eye diagram of a transmitting header signal according to an example;

[0012] 1, a multilevel optical signal packet transmitting and receiving system 100 includes a multilevel optical signal packet transmitting device 110 and a multilevel optical signal packet receiving device 130 that is communicatively connected to the multilevel optical signal packet transmitting device 110 via an optical fiber transmission line 120.

[0013] The multilevel optical signal packet transmission device 110 includes a scrambler 111, a framer 112, a frame divider 113, a D / A converter 114, and a multilevel optical transmitter 115. The scrambler 111 scrambles input data. Scrambling refers to converting or calculating data or signals in a specific sequence or rearranging them to create a random state different from the original state without losing their contents when transmitting the data or signals. The framer 112 adds header information to the scrambled data to generate frames. The frames are binary electrical signals. The frame divider 113 copies the header information n times (n is an integer greater than or equal to 2) based on the frame generated by the framer 112, divides the scrambled data into n pieces to generate n pieces of divided data, generates n frames each having a header, a CRC value of the header, and the divided data, and inputs the electrical signals of the n frames to the D / A converter 114.

[0014] An electrical signal of n frames is input to the D / A converter 114. Each frame is composed of n pieces of divided data to which the same header and CRC value of the header are added, and each piece of divided data is generated based on scrambled data. The D / A converter 114 converts the electrical signal of n frames into two ｎ The multilevel optical transmitter 115 converts the multilevel electrical signal into a single multilevel electrical signal having a binary value. The multilevel optical transmitter 115 converts the multilevel electrical signal into a multilevel optical signal and outputs it to the optical fiber transmission line 120. The multilevel optical transmitter 115 generates the multilevel optical signal as a packet in which only the header portion is binary. The D / A converter 114 and the multilevel optical transmitter 115 correspond to a compact optical module.

[0015] The multilevel optical signal packet receiving device 130 includes a multilevel optical receiver 132, a frame combining unit 134, a deframer 136, and a descrambler 138. The multilevel optical receiver 132 receives a multilevel optical signal from the multilevel optical signal packet transmitting device 110 via the optical fiber transmission line 120 and converts the multilevel optical signal into n frames, which are electrical signals. The frame combining unit 134 checks the CRC values ​​of the n headers based on the n frames converted into electrical signals by the multilevel optical receiver 132, and combines frames using the headers of frames with correct CRC values ​​and the n divided data of each frame. The deframer 136 generates data by removing the headers from the frames combined by the frame combining unit 134. The descrambler 138 descrambles the data generated by the deframer 136.

[0016] [Details of Each Part of the System] In the multilevel optical signal packet transmitting device 110, the scrambler 111 determines a scrambled signal for data using, for example, a predetermined generating polynomial that uses information on the signal several bits earlier, so as to prevent excessively long successions of "0"s or "1"s in the data. The framer 112 generates, for example, a frame F0 as shown in FIG. 2A by adding header information to the scrambled data. In FIG. 2A, data D0 is the scrambled data. In the frame dividing unit 113, the number n of copies of the header information is the same as the number of divisions of data D0. For example, if n is 4, the frame dividing unit 113 divides data D0 in frame F0 into data D1, data D2, data D3, and data D4, as shown in FIG. 2A. That is, the frame dividing unit 113 generates four divided data pieces from data D0.

[0017] 2B, the frame divider 113 duplicates the header in frame F0 by the number of divided data pieces. For example, if n is 4, the frame divider 113 further adds a header CRC value of 1 and data D1 to the duplicated header to generate frame F1. The frame divider 113 adds a header CRC value of 2 and data D2 to the duplicated header to generate frame F2. The frame divider 113 adds a header CRC value of 3 and data D3 to the duplicated header to generate frame F3. The frame divider 113 adds a header CRC value of 4 and data D4 to the duplicated header to generate frame F4. Here, CRC values ​​1 to 4 are different from each other. The frame dividing unit 113 divides and interleaves the generated n frames into a plurality of lanes L1, L2, ..., Ln, and transmits them to the multilevel optical transmitter 115. The number of lanes is the same as the number n of copies of the header information.

[0018] Also, for example, if n is 4, 2 ｎ= 16, the multilevel optical transmitter 115 converts the 16-level multilevel electrical signal into a multilevel optical signal using an electrical / optical conversion function. The multilevel optical transmitter 115 generates the multilevel optical signal as a packet in which only the header portion of this multilevel optical signal is binary. The data portion of this packet is 16-level. The multilevel optical transmitter 115 transmits the multilevel optical signal to the optical fiber transmission line 120.

[0019] In the multilevel optical signal packet receiving device 130, the multilevel optical receiver 132 converts the multilevel optical signal from the optical fiber transmission line 120 into n frames, which are electrical signals, using an optical / electrical conversion function. The multilevel optical receiver 132 interleaves and divides the generated n frames into multiple lanes L1, L2, ..., Ln, and inputs them to the frame synthesizing unit 134.

[0020] The frame synthesizer 134 checks whether the CRC values ​​of each of the n frames are correct and free of bit errors. For example, if n is 4, as shown in Fig. 2B, the frame synthesizer 134 synthesizes the data D1 to D4 of each of the four frames F1 to F4 into the header of a frame (e.g., frame F1) with a correct CRC value, thereby generating frame F0 (see Fig. 2A).

[0021] If the frame synthesis unit 134 determines that all n frames do not have correct CRC values, a frame loss occurs, but the probability of this occurring can be made sufficiently small by setting n to an appropriate value.

[0022] When the frame synthesizing unit 134 synthesizes frame F0 (see FIG. 2A ), the deframer 136 removes the header from this frame F0 to generate data D0. Note that in FIG. 2A , data D0 is scrambled data. Similar to the scrambler 111 on the transmitting side, the descrambler 138 descrambles the data D0 using, for example, a predetermined generator polynomial that uses information on the signal several bits earlier. As a result, when transmitting a digital signal (data), a process is performed on the receiving side to stably extract a clock signal from the received signal. Note that the descrambled data is output from the multilevel optical signal packet receiving device 130. If, for example, a server is connected downstream of the multilevel optical signal packet receiving device 130, the server executes a predetermined program using the output data.

[0023] [Operation of Multilevel Optical Signal Packet Transmitting and Receiving System] Next, the processing flow in the multilevel optical signal packet transmitting and receiving system 100 according to the embodiment will be described with reference to Fig. 3 (and Fig. 1 as appropriate). In the multilevel optical signal packet transmitting device 110, the scrambler 111 scrambles the data to be transmitted (step S1). Then, the framer 112 adds header information to the scrambled data to generate frames (step S2). Then, the frame dividing unit 113 divides the scrambled data and adds a duplicated header and a CRC value of the header to each divided data, thereby generating n frames (step S3).

[0024] The D / A converter 114 then converts the electrical signal into a multi-level electrical signal based on each frame (step S4). The multi-level optical transmitter 115 then converts the multi-level electrical signal into a multi-level optical signal (step S5). The multi-level optical transmitter 115 then outputs the multi-level optical signal to the optical fiber transmission line 120 (step S6).

[0025] In the multilevel optical signal packet receiving device 130, the multilevel optical receiver 132 receives the multilevel optical signal from the optical fiber transmission line 120 (step S7). The multilevel optical receiver 132 converts the multilevel optical signal into n frames (step S8). The frame combining unit 134 checks each CRC value and combines the frames (step S9). The deframer 136 removes the header from the frame (step S10). The descrambler 138 descrambles the data (step S11).

[0026] Example In order to confirm the effects of the multilevel optical signal packet transmitting and receiving system 100 according to the embodiment, a numerical simulation for verification was performed using the system configuration shown in Fig. 4. In this simulation, a 100G compact optical module using two 25Gbaud (Giga baud) 50G-PAM4 (Pulse-Amplitude Modulation) signals was assumed, and the eye opening penalty (EOP) when transmitting 25Gbaud 50G-PAM4 signals was evaluated by numerical simulation.

[0027] [System Configuration of Simulation] The transmission / reception system 200 shown in Fig. 4 simulates the multilevel optical signal packet transmission / reception system 100 shown in Fig. 1, and includes a D / A converter 214, a PAM4 optical transmitter 215, a single mode optical fiber 220, an optical amplifier 231, a PAM4 optical receiver 232, and an EOP evaluation unit 233. Here, the single mode optical fiber is abbreviated as "SMF" in the figure, and the optical amplifier is abbreviated as "AMP" in the figure.

[0028] The D / A converter 214 corresponds to the D / A converter 114 in Fig. 1. The PAM4 optical transmitter 215 corresponds to the multilevel optical transmitter 115 in Fig. 1. The single-mode optical fiber 220 corresponds to the optical fiber transmission line 120 in Fig. 1. The optical amplifier 231 is inserted on the receiving side to compensate for loss in the single-mode optical fiber 220. The PAM4 optical receiver 232 corresponds to the multilevel optical receiver 132 in Fig. 1. The EOP evaluation unit 233 is a calculation unit that performs calculations to evaluate eye opening degradation.

[0029] In this simulation, the number of lanes, n, was assumed to be 2. Data D1 and data D2 are binary data simulating header information. Data D1 is input to the D / A converter 214 from lane L1, and data D2 is input to the D / A converter 214 from lane L2. In the present invention, data D1 and data D2 are the same binary data. The binary data D1 and data D2 are converted into a multilevel signal (four-level signal) by the D / A converter 214, and the PAM4 optical transmitter 215 generates an optical multilevel signal. After transmitting through the single-mode optical fiber 220, the optical amplifier 231 compensates for losses in the single-mode optical fiber 220 and inputs it to the PAM4 optical receiver 232.

[0030] The EOP evaluation unit 233 calculates the eye pattern of the received signal relative to the transmitted signal when a binary header signal according to the present invention is transmitted and received (Example). The EOP evaluation unit 233 calculates the eye pattern of the received signal relative to the transmitted signal when a multi-level (four-level) header signal according to conventional technology is transmitted and received (Comparative Example). The EOP evaluation unit 233 calculates the eye opening degradation with respect to the transmission distance for the Example and Comparative Example. Note that a method for evaluating eye opening degradation is described in Non-Patent Document 3.

[0031] [Eye Opening Degradation] Figure 5 is a graph showing the relationship between transmission distance and eye opening degradation. In the graph, the horizontal axis represents transmission distance [km]. The vertical axis represents eye opening degradation [dB]. Eye opening degradation was calculated when the transmission distance was 4, 8, 12, 16, and 20 km. In Figure 5, white circles represent the calculation results for the comparative example, and black circles represent the calculation results for the example. However, when the transmission distance was 20 km, waveform degradation was so great that calculation was not possible for the comparative example.

[0032] When the condition for reception is an eye opening degradation of 3 dB or less, it is expected that transmission will become difficult due to frame loss caused by waveform degradation when the transmission distance is 12 km in the comparative example. In contrast, in the example, frame loss can be avoided even when the transmission distance is 20 km or more. This shows that the example is suitable for long-distance transmission of 20 km or more.

[0033] [Eye Diagrams] Fig. 6A is an eye diagram of a transmission header signal according to a comparative example. Fig. 6B is an eye diagram of a reception header signal according to a comparative example. Fig. 6C is an eye diagram of a transmission header signal according to an example. Fig. 6D is an eye diagram of a reception header signal according to an example. The horizontal axis of each eye diagram indicates the period in arbitrary units (au). The vertical axis indicates the amplitude in arbitrary units. Figs. 6B and 6D show the received waveforms after 12 km transmission.

[0034] As shown in Figures 6A and 6B, in the comparative example in which a multilevel (four-level) header signal is transmitted, the eye pattern is significantly degraded due to the effects of chromatic dispersion. In contrast, as shown in Figures 6C and 6D, in the example in which a binary header signal is transmitted, the eye pattern is less degraded.

[0035] [Effects] As described above, the multilevel optical signal packet transmitting device 110 receives n frames, each of which is made up of n (n is an integer of 2 or more) pieces of divided data generated based on scrambled data and has the same header and header CRC value added thereto, and transmits the n frames of electrical signals in two ｎ The multi-level optical transmitter 115 is characterized by generating the multi-level optical signal as a packet in which only the header portion is binary.

[0036] By doing this, the multilevel optical signal packet transmitter 110 receives n frames, each consisting of a header, a CRC value, and a data portion, and is therefore able to reduce the effects of noise in the electrical domain (digital). Furthermore, while transmitting a multilevel signal as is is susceptible to the effects of chromatic dispersion, the multilevel optical signal packet transmitter 110 converts only the header portion of the multilevel signal into a binary signal, thereby suppressing waveform degradation of the header portion due to the effects of chromatic dispersion during transmission. This allows the multilevel optical signal packet transmitter 110 to reduce frame loss due to bit errors in the header portion of the frame. Therefore, the multilevel optical signal packet transmitter 110 can protect frame headers and avoid frame loss by reducing the effects of waveform degradation during optical transmission.

[0037] The multi-level optical signal packet transmitting device 110 is characterized by comprising a scrambler 111 that scrambles data, a framer 112 that adds header information to the scrambled data to generate a frame, and a frame dividing unit 113 that, based on the frame generated by the framer 112, duplicates the header information n times, divides the scrambled data into n pieces to generate n pieces of divided data, generates n frames each having a header, a CRC value of the header, and the divided data, and inputs the electrical signals of the n frames to a D / A converter 114.

[0038] By doing this, the multilevel optical signal packet transmission device 110 scrambles only the data portion before framing, rather than scrambling the entire frame as in the past. Therefore, the header information added to the data portion by the framer 112 is not scrambled. The frame division unit 113 holds n pieces of header information copied to each of the n lanes. In this way, the multilevel optical signal packet transmission device 110 can generate a multilevel signal while holding the header information copied to the multiple lanes, and can convert only the header portion of the multilevel signal into a binary signal.

[0039] The multilevel optical signal packet receiving device 130 is characterized by comprising: a multilevel optical receiver 132 that receives a multilevel optical signal from the multilevel optical signal packet transmitting device 110 via the optical fiber transmission line 120 and converts the multilevel optical signal into n frames that are electrical signals; a frame combining unit 134 that checks the CRC values ​​of n headers based on the n frames converted into electrical signals by the multilevel optical receiver 132 and combines frames using the headers of frames with correct CRC values ​​and the n divided data of each frame; a deframer 136 that generates data by removing the headers from the frames combined by the frame combining unit 134; and a descrambler 138 that descrambles the data generated by the deframer 136.

[0040] By doing this, the multilevel optical signal packet receiving device 130 receives the multilevel optical signal as a packet in which only the header portion is binary. The received multilevel optical signal has suppressed waveform deterioration in the header portion due to the influence of chromatic dispersion during transmission. This allows the multilevel optical signal packet receiving device 130 to correctly recognize the beginning of a frame, making it possible to improve the bit error rate of the header portion.

[0041] The multi-level optical signal packet transmitting and receiving system 100 is characterized by comprising a multi-level optical signal packet transmitting device 110 and a multi-level optical signal packet receiving device 130 that is communicatively connected to the multi-level optical signal packet transmitting device 100 via an optical fiber transmission path 200.

[0042] By doing so, the multilevel optical signal packet transmitting and receiving system 100 can directly accommodate a small optical module using a multilevel optical signal in a DWDM system as light, enabling frame-lossless transmission without a chromatic dispersion compensator. Therefore, by using the multilevel optical signal packet transmitting and receiving system 100, economic benefits can be expected due to the sharing of transmission paths and the reduction of transponders. For example, even a 100GbE-LR4 small optical module using two 25 Gbps 50G-PAM4 signals, which is originally capable of 10 km transmission, can avoid frame loss in 10 km transmission and enable bit error-tolerant transmission depending on the application.

[0043] The present invention is not limited to the above-described embodiments, and many modifications can be made by a person of ordinary skill in the art within the technical concept of the present invention. For example, if it is desired to further reduce bit errors in the header section, this can be achieved by parallelizing the optical multilevel signal by wavelength multiplexing, as in Non-Patent Document 2. When parallelizing the optical multilevel signal by wavelength multiplexing, multiple signals (for example, m≧2) of the n lanes shown in FIG. 1 are arranged in a row. In this case, the lane number is L ｍ，ｎ (m≧2, n≧2). That is, the total number of lanes is expressed as the product of n and m. In this case, the multilevel optical transmitter 11 can be identified by 2 ｎ A multilevel optical signal having m wavelengths is sent from the optical fiber transmission line 120 to the multilevel optical receiver 132 .

[0044] 100 Multilevel optical signal packet transmitting and receiving system 110 Multilevel optical signal packet transmitting device 111 Scrambler 112 Framer 113 Frame dividing unit 114 D / A converter 115 Multilevel optical transmitter 120 Optical fiber transmission line 130 Multilevel optical signal packet receiving device 132 Multilevel optical receiver 134 Frame combining unit 136 Deframer 138 Descrambler 200 Transmitting and receiving system 214 D / A converter 215 PAM4 optical transmitter 220 Single mode optical fiber 231 Optical amplifier 232 PAM4 optical receiver 233 EOP evaluation unit F0, F1, F2, F3, F4 Frame

Claims

1. n frames are input, each of which is composed of n divided data pieces generated based on scrambled data, with the same header and CRC value added to the header, and the electrical signals of the n frames are divided into two ｎ a multi-level optical signal packet transmitting device comprising: a D / A converter that converts the multi-level electrical signal into a single multi-level electrical signal having a binary value; and a multi-level optical transmitter that converts the multi-level electrical signal into a multi-level optical signal and outputs the multi-level optical signal to an optical fiber transmission line, wherein the multi-level optical transmitter generates the multi-level optical signal as a packet in which only a header portion is binary.

2. The multilevel optical signal packet transmitting device according to claim 1, comprising: a scrambler that scrambles data; a framer that generates a frame by adding header information to the scrambled data; and a frame dividing unit that, based on the frame generated by the framer, makes n copies of the header information and divides the scrambled data into n pieces to generate the n pieces of divided data, generates n frames each having a header, a CRC value of the header, and divided data, and inputs the electrical signals of the n frames to the D / A converter.

3. A multilevel optical signal packet receiving device comprising: a multilevel optical receiver that receives the multilevel optical signal via the optical fiber transmission line from the multilevel optical signal packet transmitting device according to claim 1 or 2 and converts the multilevel optical signal into n frames that are electrical signals; a frame combining unit that checks the CRC values ​​of n headers based on the n frames converted into electrical signals by the multilevel optical receiver and combines frames using the headers of frames with correct CRC values ​​and the n divided data of each frame; a deframer that generates data by removing the headers from the frames combined by the frame combining unit; and a descrambler that descrambles the data generated by the deframer.

4. A multilevel optical signal packet transmission and reception system comprising: a multilevel optical signal packet transmission device according to claim 1 or claim 2; and a multilevel optical signal packet reception device according to claim 3, which is communicatively connected to said multilevel optical signal packet transmission device via an optical fiber transmission line.

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