Optical network system

Abstract

To provide an optical network system which is usable in a vehicle and the like and has improved performance.SOLUTION: An optical network system (ONWS) 1 includes a master section 3 and gateway sections (GW) 5a to 5f. The master section includes a control section 13 for controlling a first optical transmitter 11 so that a first optical signal includes transmission data constituted of repetition of a plurality of time frames and each of the plurality of time frames includes address designation information for designating any of the GWs and a plurality of pieces of packet data. Each of the GWs includes an electronic control unit 27 for receiving an electric signal output from a photoelectric conversion section 23, selecting packet data that is included in the plurality of time frames and is transmitted to the unit, and superposing the packet data on continuous light by modulating the continuous light in a period corresponding to a specific time frame before outputting it as an optical signal including data. An optical detector 19 receives the optical signal including the data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical network system that can be used in automobiles and the like. [Background technology]

[0002] Japanese Patent No. 7053028 describes an in-vehicle optical network. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7053028 Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to provide the above-mentioned in-vehicle optical network with greater scalability in terms of the number of gateways, and also to develop an optical network with improved performance, for example, in terms of temperature fluctuation and EMC performance. [Means for solving the problem]

[0005] The first invention relates to an optical network system 1 including a master unit 3 and a plurality of gateway units 5a to 5f connected to the master unit 3.

[0006] The master unit 3 has a first optical transmitter 11 that outputs a first optical signal, a control unit 13 for controlling the optical network system, a second light source 15 that outputs continuous light, and an optical detector 19.

[0007] Each of the plurality of gateway units 5a to 5f includes a first optical demultiplexing unit 21 for demultiplexing a portion of the first optical signal transmitted from the first optical transmitter 11, a photoelectric conversion unit 23 for converting the portion of the first optical signal demultiplexed by the first optical demultiplexing unit 21 into an electrical signal, and an electronic control unit 27 for receiving the electrical signal output from the photoelectric conversion unit 23 and transmitting control signals to various devices of the automobile (such as the steering wheel, engine, and windows). Furthermore, each of the plurality of gateway units 5a to 5f includes an optical modulation unit 25 for converting an electrical signal of a sensor device or the like (such as a camera or radar) connected to the electronic control unit 27 into an optical signal.

[0008] The control unit 13 of the master unit 3 The first optical transmitter 11 is controlled so that the first optical signal output from the first optical transmitter 11 includes transmission data A consisting of a repetition of multiple time frames, and each of the multiple time frames includes addressing information B that designates one of the multiple gateway units 5a to 5f, and multiple packet data C to be transmitted to all or some of the multiple gateway units 5a to 5f.

[0009] Each of the plurality of gateway units 5a to 5f The first optical demultiplexing unit 21 demultiplexes a part of the first optical signal transmitted from the first optical transmitter 11, The photoelectric conversion unit 23 converts a part of the first optical signal demultiplexed by the first optical demultiplexing unit 21 into an electrical signal, The electronic control unit 27 receives the electrical signal (data A) output from the photoelectric conversion unit 23, selects only the packet data sent to itself from among the packet data C included in multiple time frames, and transmits the signal to various devices (steering wheel, engine, windows, etc.) of the automobile connected to the electronic control unit 27. Furthermore, the electronic control unit 27 analyzes the addressing information B included in the electrical signal (data A), and if the gateway unit identified by the addressing information B is designated as a specific gateway unit and the time frame in which the electronic control unit 27 is the specific gateway unit is designated as a specific time frame, the electronic control unit 27 transmits data signals from sensor devices connected to itself (cameras, radar, etc.) to the optical modulation unit 25 during the period corresponding to the specific time frame, and modulates the continuous light sent from the second light source 15 to superimpose one or more packet data D on the continuous light. The specific gateway transmits the data D for each time frame, ultimately forming data E including the data D from each gateway.

[0010] The optical detector 19 receives an optical signal (data E) containing data that has passed through the plurality of gateway units 5a to 5f.

[0011] The optical modulation section 25 preferably includes a differential optical phase modulator. The optical detector 19 preferably detects the optical signal E containing data by a direct detection method including optical delay interference.

[0012] The optical modulation section 25 preferably includes a differential optical phase modulator. The master unit 3 preferably further includes a second demultiplexing unit 31 for demultiplexing the continuous light. The photodetector 19 preferably uses the continuous light demultiplexed by the second demultiplexing section 31 as local light and performs homodyne detection. [Effects of the Invention]

[0013] The advantages of the present invention will be explained in the following examples. For example, the optical network of the present invention can be more scalable in terms of the number of gateways. Furthermore, the optical network of the present invention has improved performance in terms of temperature fluctuations and EMC performance. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of an optical network system. [Figure 2] FIG. 2 is a conceptual diagram for explaining transmission data and optical signals. [Figure 3] FIG. 3 is a block diagram showing an example of the configuration of an optical network system different from that shown in FIG. [Figure 4] FIG. 4 is a conceptual diagram showing a configuration example of an OMEGA optical network system according to the first embodiment. [Figure 5] FIG. 5 is a conceptual diagram showing a configuration example of a SiPhON optical network system according to the second embodiment. [Figure 6] FIG. 6 is a conceptual diagram illustrating an example of the configuration of an optical network system according to an embodiment. [Figure 7] FIG. 7 is an explanatory diagram comparing the network expandability of the embodiment and SiPhON. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and includes appropriate modifications of the embodiments described below within the scope obvious to those skilled in the art.

[0016] Fig. 1 is a block diagram showing an example of the configuration of an optical network system. As shown in Fig. 1, the optical network system 1 includes a master unit 3 and multiple gateway units 5a to 5f. The master unit 3 and the gateway units 5a and 5f are connected to each other by, for example, optical fibers. The multiple gateway units 5a to 5f are also connected to each other by, for example, optical fibers. An example of the optical fiber is a single-mode optical fiber.

[0017] The master unit 3 has a first optical transmitter 11 that outputs a first optical signal, a control unit 13 for controlling the optical network system, a second light source 15 that outputs continuous light, and a photodetector 19. The first optical transmitter 11 may directly modulate the first light source (LD) or may have an optical intensity modulator. The photodetector (PD) 19 may be a known one as appropriate.

[0018] The control unit 13, for example, controls the optical network and includes an AI processor that recognizes objects in camera images and the like, and a high-performance computer (HPC) that controls autonomous driving. The system sends information from cameras, radars, and other devices connected to each gateway unit to a processor within the control unit 13 via a photodetector 19, which recognizes obstacles and the like. This information is sent to the HPC within the control unit 13, and the system 1 determines whether autonomous driving is necessary, generates control signals for the steering wheel, brakes, etc., and transmits the control signals via the first optical transmitter 11 to the gateway to which the device to be controlled is connected.

[0019] Each of the multiple gateway units 5a to 5f includes a first optical demultiplexing unit 21, an opto-electrical conversion unit 23, an optical modulation unit 25, and an electronic control unit 27. The first optical demultiplexing unit 21 is an element for demultiplexing a portion of the first optical signal transmitted from the first optical transmitter 11. Elements for demultiplexing a portion of an optical signal are well known. A well-known optical demultiplexer can be used as the first optical demultiplexing unit 21. The opto-electrical conversion unit 23 is an element for converting a portion of the first optical signal demultiplexed by the first optical demultiplexing unit 21 into an electrical signal. The portion of the first optical signal demultiplexed by the first optical demultiplexing unit 21 is input to the opto-electrical conversion unit 23 via an optical waveguide, an optical fiber, or the like. The optical signal input to the opto-electrical conversion unit 23 is then converted into an electrical signal, and a control signal is sent via the electronic control unit 27 to a device connected to the electronic control unit 27. The optical modulation unit 25 is a component that converts electrical signals from sensors (cameras, radar, etc.) connected to the electronic control unit 27 into optical signals by modulating continuous light transmitted from the second light source 15. The optical modulation unit 25 may include, for example, a known optical modulator. Examples of known optical modulators include an intensity modulator and a phase modulator. The optical modulator may also be a waveguide-type optical modulator. The optical modulation unit 25 preferably includes a differential optical phase shift keying (DPSK) device. The optical modulator is preferably a thin-film LN modulator (TFLN modulator). This phase modulator preferably has electrodes along an optical waveguide and can adjust the phase of light propagating through the optical waveguide by adjusting the voltage applied to the electrodes. The intensity modulator generally uses an MZI (Molded Zone Interleaving) type waveguide. For example, the MZI requires optical demultiplexing and multiplexing, and it is desirable to use a heater to adjust the optical phase in response to changes in temperature, etc.

[0020] The control unit 13 of the master unit 3 transmits a control signal for automatic driving to the first optical transmitter 11. The first optical transmitter 11 then controls the first optical signal and outputs the control signal to the gateway. FIG. 2 is a conceptual diagram for explaining transmission data and optical signals. The first optical signal includes transmission data A consisting of a repetition of multiple time frames, and each of the multiple time frames includes addressing information B that designates one of the multiple gateway units 5a to 5f and multiple packet data C to be transmitted to all or some of the multiple gateway units 5a to 5f. The first optical signal output by the first optical transmitter 11 constitutes the DD (down data)-Plane in the embodiment described below and may be low-speed (for example, 1 Gbps or more and 10 Gbps or less). The first optical signal may be broadcast to all gateways belonging to the system 1.

[0021] An example of the operation of each of the plurality of gateway units 5a to 5f will be described. The first optical demultiplexing unit 21 demultiplexes a portion of the first optical signal transmitted from the first optical transmitter 11. The demultiplexed portion of the first optical signal is transmitted to the photoelectric conversion unit 23. The remainder of the demultiplexed first optical signal is output toward the next gateway.

[0022] Then, the photoelectric conversion unit 23 converts into an electrical signal a part of the first optical signal demultiplexed by the first optical demultiplexing unit 21. The photoelectric conversion unit 23 outputs the obtained electrical signal (data A) to the electronic control unit 27. The electronic control unit 27 selects only the packet data sent to itself from the packet data C (for example, Ether packets) included in a plurality of time frames. Furthermore, the electronic control unit 27 recognizes address specification information B present for each time frame of data A. If this specification information B matches its own GW number, the electronic control unit 27 transmits sensor information from connected sensors to the optical modulation unit 25. Continuous light (CW) transmitted from the second light source 15 is sequentially superimposed with data from GWs specified for each time frame to form data E, which is then transmitted to the optical detection unit 19. The second light source 15 to the optical detection unit 19 constitute a UD (updater)-Plane in the embodiment described below, and is preferably a broadband (>10G). The specification of this GW may be controlled by a timetable. By changing the frequency at which each GW is specified, the bandwidth allocation for each GW can be freely set / changed.

[0023] 1, the optical modulation unit 25 preferably includes a differential optical phase shift keying (DPSK) device. Also, in this system 1, the optical detector 19 preferably detects the optical signal E containing data by a direct detection method. In this case, the optical detector 19 includes an optical delay interferometer and detects the optical signal E.

[0024] FIG. 3 is a block diagram showing an example of the configuration of an optical network system different from that shown in FIG. 1. The same components of the optical network system 1 shown in FIG. 3 as those shown in FIG. 1 will be described below, and a detailed description thereof will be omitted. In the optical network system 1 shown in FIG. 3, the master unit 3 further includes a second demultiplexing unit 31 for demultiplexing continuous light. The optical detector 19 performs homodyne detection using the continuous light demultiplexed by the second demultiplexing unit 31 as local light. The continuous light output from the second light source 15 is demultiplexed by the second demultiplexing unit 31. One of the continuous lights demultiplexed by the second demultiplexing unit 31 is output to a gateway, as in the optical network system 1, and data is superimposed on it at each gateway. The resulting data is returned to the optical detector 19 as data E. Meanwhile, the remaining continuous light demultiplexed by the second demultiplexing unit 31 is input directly to the optical detector 19 without passing through a gateway, and is used as local light. In this embodiment as well, it is preferable that the optical modulation section 25 includes a differential optical phase shift modulator (DPSK modulator). [Example]

[0025] (Background / Purpose) To achieve autonomous driving, it is necessary to quickly and accurately repeat the following processes: "recognition" of surrounding information using cameras and radar, "decision" using that information by a high-performance computer (HPC), and "control" of autonomous driving based on that decision information. In this "recognition," "decision," and "control" loop, it is the "in-vehicle network" that transmits large amounts of information accurately and with low latency, and to achieve fully autonomous driving, it is necessary to satisfy all of the following requirements.

[0026] Zoning Architecture Current in-vehicle networks use a "domain-based network" in which multiple networks (e.g., CAN, LIN, MOST) operating on different protocols for various functions and applications, such as control systems, body systems, information systems, and safety systems, are spread throughout the vehicle like a spider's web. However, as the number of microcontrollers (electronic control units: ECUs) controlling each component increases, network complexity, bandwidth shortages, weight, and cost become major issues. Therefore, to achieve autonomous driving, it is essential to transition to a "zone-based network" in which the vehicle interior is divided into multiple zones and each zone is equipped with a gateway (GW). Conventional networks are divided into zones, and cameras and other sensors are connected to the nearest GW. Data is then transferred via a high-speed in-vehicle network to the HPC in the master device. Furthermore, for autonomous driving at level 4 and above, vehicles will be equipped with numerous cameras, radars, and other devices, requiring scalability in the number of zones (GWs). Since the number of cameras, radars, and other devices connected to each GW varies, the bandwidth allocated to each GW must be freely adjustable.

[0027] High-capacity and asymmetric communication Conventional 2K cameras have difficulty identifying distant signs, etc., so 4K cameras (approximately 10Gbps per unit, as they are used uncompressed) are necessary. Therefore, in the future, a high-capacity network of 100Gbps class will be required to transmit data from the GW to the HPC, but conversely, the transfer of control commands from the HPC to the GW only requires a capacity of a few Gbps, so the realization of asymmetric communication with excellent energy efficiency is required.

[0028] Low latency and timeliness Latency in in-vehicle networks is an extremely important characteristic because it causes delays in decision-making and control. Furthermore, control timing (timeliness) is also an important parameter, and it is necessary to reduce fluctuations in delay time.

[0029] Environmental resistance / EMC performance (Electro-Magnetic Compatibility) In-vehicle networks are required to operate in extremely harsh environments, including a wide temperature range of -40 to 125°C, and with vibration, oil, water, dust, etc. Furthermore, with the increasing speed of in-vehicle networks, the increase in ECUs, the shift to EVs, and advances in connectivity (V2X), the interior of the vehicle is becoming saturated with "electromagnetic noise," and there is an ever-increasing demand for "EMC performance" that is not affected by or emits electromagnetic noise.

[0030] Reliability, long life, redundancy Failure of an in-vehicle network can directly lead to accidents and loss of life, making it a critical issue for autonomous driving. In addition to reducing the failure rate (extending the lifespan) of the entire network system, it is essential to have a mechanism that allows safe operation to continue by quickly switching to a backup device / line in the unlikely event of a failure (redundancy).

[0031] low power consumption Since power consumption affects the driving range of an EV, a highly energy-efficient network that is proportional to the amount of data transferred is required.

[0032] In order to achieve 100G-class transmission capacity (e.g., 25G x 4 lanes, 50G x 2 lanes) in the above-mentioned zone division network, various high-speed in-vehicle communication standards, including in-vehicle Ethernet, have been considered in recent years from both electrical and optical perspectives. In electrical networks, inexpensive UTP (Unshielded Twisted Pair) cables have been used until now, but in recent years, more expensive coaxial cables and STP (Shielded Twisted Pair) cables have come to be used. IEEE802.3cy (Beyond 10G) was established as the standard for in-vehicle Ethernet in 2023. However, at a transmission speed of 25 Gbps, even with STP, the transmission distance is only 11 m, which falls short of the 15 m required for in-vehicle use. For electrical transmissions of 10 Gbps or more, transmission loss in the high-frequency range and EMC (Electromagnetic Compatibility) are major issues. In optical networks, the IEEE802.3cz (Multi-Gigabit Optical Automotive Ethernet, commonly known as OMEGA) standard, which will use silica-based multimode optical fiber (OM3 GI-50) for the first time, was established in 2023. The light source is a 980nm VCSEL, the modulation method is NRZ for transmission speeds of 25Gbps, and PAM4 for transmission speeds of 50Gbps, with a transmission distance of 40m. The dividing line between electricity and optical technology is generally said to be 100 Gbps·m, and optical technology is considered advantageous for transmission distances of 4 m or more at 25 Gbps. Therefore, a transition to optical networks is expected to achieve the high speeds (25 Gbps or more), high EMC performance, and transmission distances (15 m or more) required for highly automated driving. However, no in-vehicle optical network fully satisfies all of the above requirements. This embodiment aims to provide a "high-performance, highly reliable in-vehicle optical network" that satisfies all the requirements for fully automated driving by using a new communication method.

[0033] (Reference example 1) This article explains the configuration and challenges of IEEE802.3cz (OMEGA), which was standardized in 2023. OMEGA allows for various network topologies, including star, tree, and ring (daisy chain) topologies. Figure 4 shows an example of a configuration with six gateways connected in a daisy chain. The master device with the HPC is connected to the gateways, and the gateways are connected via optical transceivers using VCSELs (vertical cavity surface-emitting lasers) and multimode fiber. Two lanes are assumed for redundancy. In this case, the entire system will be equipped with 28 VCSELs (24 of which are operational). The links indicated by dotted lines in the figure are initially blocked by Spanning Tree Protocol (STP, a protocol that prevents data from flowing continuously). However, they become active when another link fails, enabling continuous autonomous operation. Compared to telecommunications, OMEGA offers superior speed, transmission distance, and EMC performance, but it has the following issues.

[0034] Reliability and laser life Of all the components used in optical networks, the laser (VCSEL) has the highest failure rate, and therefore, a decrease in reliability (lifespan) is a major issue for OMEGA, which is equipped with a large number of optical transceivers. Generally, the lifespan of a VCSEL is halved for every 10°C increase in temperature, and it deteriorates rapidly in inverse proportion to the seventh power of the current density. There are concerns that laser failures will occur frequently in OMEGA in high-temperature environments.

[0035] Delay time, delay fluctuation In OMEGA, large delays and delay variations occur due to the multiple electrical switches that are used. In in-vehicle networks, the timing of control is important, and it is necessary to reduce delay variations through priority control using QoS.

[0036] Dealing with asymmetric communication In an autonomous driving in-vehicle network, the upstream GW (cameras, etc.) to HPC requires a large capacity of 100G, while the downstream HPC (control commands, etc.) to GW only requires a bandwidth of a few Gbps, resulting in extremely asymmetric communication. However, in a link using optical transceivers, the upstream and downstream bandwidths are equivalent, resulting in a series of dummy packets in downstream communication, which is extremely wasteful.

[0037] Power consumption Optical transceivers must constantly generate clocks, so they must constantly send dummy signals even when there is no real data. Furthermore, the GW contains electrical switches and numerous Drivers / TIAs, which consumes a lot of power.

[0038] (Reference example 2) Next, we will explain conventional SiPhON (Patent Document 1). SiPhON (Fig. 5) has a completely separate data plane (D-Plane) and control plane (C-Plane). It operates using a ring-type network configuration connected by single-mode fiber and a fixed-length optical frame switching method. In the C-Plane, a low-speed optical signal transmitted from a master device is partially branched to each gateway, broadcasting addresses, commands, and a common clock signal to all gateways. In the D-Plane, only the master device is equipped with a laser, and each gateway is equipped with an integrated device consisting of a Mach-Zehnder optical modulator and a photodetector (PD). This optical integrated device switches between receive mode, transmit mode, and through mode on a time frame basis depending on the applied bias voltage, thereby transmitting and receiving data between the master and gateway. For example, when gateway 1 is addressed by the C-Plane and the command is in receive mode, the transmitted data from the master stored in the D-Plane time frame is received by the PD in the optical integrated device and sent to the electronic control unit as an electrical signal. Furthermore, when GW1 is addressed and the command is in send mode, data is transmitted from GW1 to the master by modulating the CW light in the next time frame with the optical modulator. In other GWs with mismatched addresses specified by the C-Plane, the optical integrated device is set to through mode, allowing the optical signal to pass through as is.

[0039] The advantages of conventional SiPhON are summarized below. In SiPhON, only the master device is equipped with a laser, and the gateway does not have any light source. Because the master device has an HPC, temperature control is required to maintain a certain temperature (e.g., below 60°C). The laser can also be cooled, which significantly extends the laser's lifespan (more than several decades). Furthermore, extremely high reliability can be achieved by switching to a backup laser in the event of a main laser failure. Furthermore, because light passes directly through the optical integrated device at each gateway without using an electrical switch, latency is extremely low. Furthermore, there is no need for traffic control using higher-level protocols such as QoS, and latency fluctuations are extremely low, resulting in excellent timeliness. Furthermore, by changing the C-Plane receive and transmit mode assignments, it is possible to freely set and change the upstream and downstream bandwidths and the bandwidth allocation to each gateway.

[0040] As described above, SiPhON has significant advantages over OMEGA in terms of reliability (long life), low latency, asymmetric communication, etc. However, the following issues need to be resolved. 1. The optical integrated devices used in SiPhON use MZ optical modulators, and due to their large optical loss, optical signals passing through many gateways become extremely weak. In addition, intensity modulation (NRZ) is used as the modulation method, and as the signal speed increases, the receiving sensitivity on the receiving side (direct detection) deteriorates. This makes it difficult to increase the number of gateways, and there are problems with the scalability of the network. 2. With SiPhON, light passes through each gateway as it is, so it is less susceptible to electromagnetic noise than OMEGA, improving EMC performance. However, when passing through multiple gateways, intensity noise is added due to temperature fluctuations and electromagnetic noise, which causes a deterioration in reception sensitivity.

[0041] Example 1 The present invention provides a new in-vehicle optical network that solves the problems of SiPhON while maintaining its advantages. Figure 6 is a conceptual diagram showing an example of the configuration of an optical network system according to the present invention. In this embodiment, in order to efficiently execute the asymmetric communication unique to in-vehicle networks, the downstream (Master → GW) Down-Data Plane (DD-Plane) and the upstream (GW → Master) Up-Data Plane (UD-Plane) are completely separated. These planes operate using an all-optical frame switching method based on a fixed-length time frame, similar to SiPhON (the system described in Patent Document 1), and the Master-GW and GW-GW connections are made via silica-based single-mode optical fiber. The operation and role of each plane are explained below.

[0042] DD (Down-Data)-Plane (Data transmission from Master to GW) The DD-Plane (dotted outer frame) transmits low-speed (e.g., 2.5Gbps-NRZ) optical signals and broadcasts them to all gateways by tapping a portion of the optical signal at each gateway. Therefore, the signal is transmitted directly from the Master to all gateways. The DD-Plane's key role is to specify gateways operating in the UD-Plane (control plane role). The gateway's designated address is stored at the beginning of each time frame, and the designated gateway then sends data within the time frame on the UD-Plane. This gateway designation is controlled by a timetable, and by changing the frequency at which each gateway is designated, it is possible to freely set and change the bandwidth allocation for each gateway. The gateway address is followed by an Ether packet addressed to the gateway from the Master, and each gateway receives only packets that match its own MAC address (data forwarding role). Another role of the DD-Plane is to distribute the universal clock. Since all GWs receive the same optical signal, they can operate at the same clock frequency (the role of clock synchronization).

[0043] UD (Up-Data)-Plane (Data transmission from GW to Master) Like conventional SiPhONs, only the master device has a light source (LD); each gateway does not have any. Furthermore, because the master device has a high-performance computer (HPC), its temperature must be controlled below a certain level. The LD can also be cooled in the same way, enabling an extremely long service life. Furthermore, if the main LD fails, a backup LD takes over, providing redundancy to prevent network interruptions. The CW light from the LD passes through the optical phase modulators in all gateways and is sent directly to the master without any OEO conversion. At this time, as mentioned above, data is transmitted from the electronic control unit of the gateway designated by the DD-Plane. This drives the optical phase modulator, which superimposes the data onto the time frame as an optical DPSK (Differential Phase-Shift Keying) signal at 25 Gbps per lane. For example, a thin-film LN modulator (x-cut TFLN), which has seen remarkable development in recent years, is used as the optical phase modulator. Optical phase modulators using TFLN have the advantages of extremely low optical loss (less than 3 dB), high speed, small size, low drive voltage, high temperature operation, and low cost, and in recent years have been increasingly applied to optical transceivers for data centers. Optical signals with data stored on each time frame are coherently received (homodyne detection) at the master.

[0044] The differences between this embodiment and SiPhON (Patent Document 1) are summarized as follows. In this embodiment, differential phase shift keying (DPSK) is used instead of optical intensity modulation (NRZ). MZI-type optical intensity modulators, which are generally used for optical intensity modulation, require optical demultiplexing and multiplexing, resulting in large optical loss. In addition, arm phase adjustment using a heater is required, but control over the wide temperature range required for vehicles is difficult. On the other hand, optical phase modulators are composed of a single optical waveguide, so optical loss is extremely small and temperature control is not required at all.

[0045] In SiPhON, the system is divided into a C-Plane and a D-Plane, where the C-Plane specifies the address of the gateway and the operation of the receive mode (downstream) / transmit mode (upstream), and the D-Plane performs the upstream / downstream data transfer. In this embodiment, the system is divided into a DD-Plane and a UD-Plane, where the DD-Plane performs the address of the gateway (the function of the C-Plane in conventional SiPhON) and the downstream data transfer (Master to Gateway), and the UD-Plane performs the upstream data transfer (GW to Master). This eliminates the need for bias control for mode switching, which was previously required, and also makes it possible to remove the photodetector (PD) in the optical integrated device.

[0046] Conventional NRZ signals are directly affected by temperature changes and electromagnetic noise on a bit-by-bit basis as they pass through multiple gateways, resulting in a deterioration of receiver sensitivity. On the other hand, this example uses a DPSK signal that represents 1 / 0 by the phase difference between adjacent bits. Therefore, if there is gradual temperature change or electromagnetic noise of about several GHz, adjacent bits will be subject to the same phase noise, making it possible to cancel the phase noise on the receiving side, and a significant improvement in EMC performance can be expected.

[0047] Conventional optical intensity modulation requires direct detection at the optical receiving end, which leads to degradation of receiver sensitivity as transmission speeds increase. Optical phase modulation, on the other hand, can significantly improve sensitivity through coherent reception. However, in conventional optical communications, the goal is to transmit data over long distances, making it extremely difficult to generate local light (LO) with the exact same wavelength as the optical signal at the receiving end. Conventional optical communications necessitate heterodyne detection using expensive, power-hungry digital signal processors (DSPs). In contrast, the optical network described in this example is a highly specialized network in which light transmitted from the master returns to the master. Therefore, by tapping a portion of the light from the LD light source and using it as LO light, homodyne detection, which has superior receiver sensitivity to heterodyne, can be easily applied. Furthermore, this eliminates the need for a DSP and allows the DPSK signal to be converted back to the original NRZ signal using a phase diversity method using low-power analog circuits.

[0048] Figure 7 shows the network scalability of this example. In SiPhON, the presence of an optical modulator in the Master reduces the output optical intensity of the Master, and the optical loss at each GW is large. Furthermore, the receiving sensitivity of direct detection at the Master is poor, so the maximum number of GWs that can be connected is four. On the other hand, in this example, the Master does not require an optical modulator, and the optical loss of the optical phase modulator at each GW is small. Furthermore, the ability to use homodyne detection significantly improves receiving sensitivity, and even if eight or more GWs are connected, the Master can still receive signals satisfactorily. [Industrial Applicability]

[0049] The optical network of the present invention has significant advantages over IEEE802.3cy (B10G: electrical) and IEEE802.3cz (OMEGA: optical), which will be standardized in 2023. Furthermore, in the embodiments, when using a silica single-mode optical fiber with low optical loss, it has the advantage of being able to be deployed over a wide area of ​​several kilometers. Therefore, the "high-performance, highly reliable all-optical network" of the present invention can be deployed in various infrastructure facilities, including autonomous vehicles, which require a high level of safety, as well as aircraft, ships, robot control, home networks, medical equipment, and B5G networks. [Explanation of symbols]

[0050] 1 Optical Network System 3 Master Section 5a~5f Gateway section 11 First optical transmitter (11) 13 Control Unit 15 Second Light Source 19 Photodetector 21 First optical demultiplexing unit 23 Photoelectric conversion unit 25 Optical modulation section 27 Electronic Control Unit 31 Second branching section

Claims

1. A master unit (3), The master unit (3) and a plurality of gateway units (5a to 5f) connected thereto are included. An optical network system (1), The master unit (3) The optical network system (1) includes a first optical transmitter (11) that outputs a first optical signal, a control unit (13) for controlling the optical network system (1), a second light source (15) that outputs continuous light, and an optical detector (19), Each of the plurality of gateway units (5a to 5f) The optical transmitter (11) includes a first optical demultiplexing section (21) for demultiplexing a part of a first optical signal transmitted from the first optical transmitter (11), a photoelectric conversion section (23) for converting the part of the first optical signal demultiplexed by the first optical demultiplexing section (21) into an electrical signal, an optical modulation section (25) for modulating continuous light transmitted from a second light source (15), and an electronic control unit (27) for receiving the electrical signal output from the photoelectric conversion section (23) and controlling the optical modulation section (25), The control unit (13) controlling the first optical transmitter (11) so that a first optical signal output from the first optical transmitter (11) includes transmission data configured of a repetition of a plurality of time frames, each of the plurality of time frames including addressing information specifying one of the plurality of gateway units (5 a to 5 f) and a plurality of packet data to be transmitted to all or some of the plurality of gateway units (5 a to 5 f); Each of the plurality of gateway units (5a to 5f) A first optical demultiplexing unit (21) demultiplexes a part of the first optical signal transmitted from the first optical transmitter (11), The photoelectric conversion unit (23) converts a part of the first optical signal demultiplexed by the first optical demultiplexing unit (21) into an electrical signal, the electronic control unit (27) receives the electrical signal output from the photoelectric conversion unit (23), selects only the packet data sent to itself from the packet data included in the plurality of time frames, analyzes addressing information included in the electrical signal, and designates the gateway unit specified by the addressing information as a specific gateway unit, and designates the time frame for which itself is a specific gateway unit as a specific time frame, and controls the optical modulation unit (25) so that, during a period corresponding to the specific time frame, the optical modulation unit (25) modulates the continuous light to superimpose one or more packet data on the continuous light and outputs the superimposed data as an optical signal including data; The optical detector (19) receives an optical signal including the data that has passed through the plurality of gateway units (5a to 5f). Optical network system (1).

2. An optical network system (1) according to claim 1, The optical modulation unit (25) includes a differential optical phase modulator, The optical detector (19) detects the optical signal containing the data by a direct detection method including optical delay interference.

3. An optical network system (1) according to claim 1, The optical modulation unit (25) includes a differential optical phase modulator, The master unit (3) further includes a second demultiplexing unit (31) for demultiplexing the continuous light, The optical detector (19) uses the continuous light demultiplexed by the second demultiplexing section (31) as local light and performs homodyne detection.

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