Optical switch

Abstract

This optical switch connects nodes constituting a network. The optical switch comprises a first switch element including one input port and two output ports, and a second switch element including two input ports and one output port, wherein one of the output ports of the first switch element is connected to one of the input ports of the second switch element, thereby configuring an optical circuit including two input ports and two output ports.

Description

Optical switch

[0001] This disclosure relates to an optical switch, and more particularly to an optical switch that uses light for information communication.

[0002] To perform large-scale calculations on supercomputers and other systems, a technique called parallel distributed computing is used. Parallel distributed computing involves multiple processors performing calculations in parallel and exchanging information between processors during the calculation process. In some cases, a torus-shaped network is used as the network configuration to relay the communication traffic generated during the parallel distributed computing process. In particular, it is known that applying optical switches to the network allows for the scaling of the torus-shaped network. A torus network is disclosed, for example, in Non-Patent Document 1. A torus-shaped network is a connection configuration obtained by directly connecting the nodes located at both ends in each dimension, based on node connections arranged in a square mesh.

[0003] A known configuration for changing the scale of a torus-type network consists of N processors (where N is an integer greater than or equal to 2) and M optical switches (where M is an integer greater than or equal to 1), with all processors connected to the optical switches by two pairs of optical fibers. Since the M optical switches have the function of directly connecting any input / output ports, by appropriately configuring each optical switch, the corresponding M-dimensional connections can be formed, and overall, an M-dimensional torus network composed of the desired number of processors can be formed.

[0004] Jouppi, Norm, et al. "Tpu v4: An optically reconfigurable supercomputer for machine learning with hardware support for embeddings." Proceedings of the 50th Annual International Symposium on Computer Architecture. 2023.

[0005] However, in known network examples, scaling a torus network requires 2N input ports and 2N output ports on the optical switch. Therefore, large-scale torus networks require a proportionally large number of optical switches. Large-scale optical switches are difficult and expensive to manufacture. This makes the construction of large-scale torus networks difficult, and there is a demand for optical switches that can connect a large number of processors at a lower cost.

[0006] This disclosure is made in view of the above points and relates to an optical switch that is smaller and suitable for flexibly changing the scale of a torus network.

[0007] To achieve the above objective, one embodiment of the optical switch of the present disclosure is an optical switch for connecting nodes constituting a network, and includes a first switch element having one input port and two output ports, and a second switch element having two input ports and one output port, wherein one of the output ports of the first switch element is connected to one of the input ports of the second switch element, thereby forming an optical circuit having two input ports and two output ports.

[0008] This is a conceptual diagram showing a network to which an optical switch according to one embodiment of the present disclosure is applied. This is a diagram showing an example of connecting the network shown in Figure 1. This is a schematic top view of an optical switch according to one embodiment of the present disclosure. This is a diagram illustrating a configuration in which a gate circuit is provided to the optical switch shown in Figure 3. This is a diagram showing an example of a known network.

[0009] Hereinafter, an embodiment of this disclosure will be described with reference to the drawings. The drawings are intended to illustrate the configuration, arrangement, operation, effect, function, and technical concept of this embodiment, and are not intended to limit its specific configuration.

[0010] (Network) The optical circuit of this embodiment is used to connect networks to each other. Before describing the optical switch, the networks connected by the optical switch will be described below. Figure 1 is a conceptual diagram showing networks 201A and 201B to which the optical switch of this embodiment is applied. Both networks 201A and 201B are torus-type networks and have the same configuration. That is, both networks 201A and 201B are third-order (M=3) torus-type networks, and 2 M pieces, that is, 2 3 The smallest unit consists of (8) nodes, and this unit can be expanded by connecting multiple such units.

[0011] As shown in Figure 1, network 201A includes nodes A1, A2, A3, A4, A5, A6, A7, and A8. In network 201A, each node is connected to the same number of first, second, and third axes (hereinafter referred to as the X, Y, and Z axes) by cables C. Cables C in the X-axis direction are shown as dotted lines, cables C in the Y-axis direction as solid lines, and cables C in the Z-axis direction as dashed lines. Cables C in the X-axis direction are numbered 2 0 Connects different nodes. Also, cable C in the Y-axis direction has the number 2. 1 Connecting different nodes, cable C in the Z-axis direction is number 2 2 It connects different nodes. Cable C shown in Figure 1 represents a cable that includes both a transmission path and a reception path.

[0012] Therefore, in network 201A, nodes A1 and A2, A3 and A4, A5 and A6, and A7 and A8 are connected in the X-axis direction. Similarly, nodes A1 and A3, A2 and A4, A5 and A7, and A6 and A8 are connected in the Y-axis direction. Furthermore, nodes A1 and A5, A2 and A6, A3 and A7, and A4 and A8 are connected in the Z-axis direction. Thus, network 201A is a 2x2x2 torus-type network with two nodes in each of the X, Y, and Z directions.

[0013] Similarly, network 201B includes nodes B1, B2, B3, B4, B5, B6, B7, and B8. In network 201B, each node is connected to the others by cables C in the same number of directions as M in the three axes (X, Y, and Z). Cables C in the X-axis direction are shown by dotted lines, cables C in the Y-axis direction are shown by solid lines, and cables C in the Z-axis direction are shown by dashed lines. Cables C in the X-axis direction are numbered 2 0 Connects different nodes. Also, cable C in the Y-axis direction has the number 2. 1 Connecting different nodes, cable C in the Z-axis direction is number 2 2 Connect different nodes.

[0014] Therefore, in network 201B, nodes B1 and B2, B3 and B4, B5 and B6, and B7 and B8 are connected in the X-axis direction. Similarly, nodes B1 and B3, B2 and B4, B5 and B7, and B6 and B8 are connected in the Y-axis direction. Furthermore, nodes B1 and B5, B2 and B6, B3 and B7, and B4 and B8 are connected in the Z-axis direction. Thus, network 201B is a 2x2x2 torus-type network with two nodes in each of the X, Y, and Z directions.

[0015] The optical switch of this embodiment is used to connect nodes in the above-described networks 201A and 201B. Furthermore, the optical switch of this embodiment can also be used to connect network 201A and network 201B.

[0016] Here, an example of expanding the scale of a torus network by combining a plurality of minimum-unit networks will be described. FIG. 2 shows an example in which networks 201A and 201B are connected in the X-axis direction. In the network 201A shown in FIG. 2, the cable C2 (indicated by a thin broken line in the figure) that connected node A1 and node A2, node A3 and node A4, node A5 and node A6, and node A7 and node A8 is cut. Then, instead of the cut cable C2, a cable C3 (indicated by a thick broken line in the figure) that connects node A1 to node B2, node A2 to node B1, node A3 to node B4, node A4 to node B3, node A5 to node B6, node A6 to node B5, node A7 to node B8, and node A8 to node B7 is connected to the port of each node.

[0017] Through such connection, the present embodiment forms a ring network composed of four nodes: A1, A2, B1, and B2. The present embodiment also forms a ring network composed of nodes A3, A4, B3, and B4, a ring network composed of nodes A5, A6, B5, and B6, and a ring network composed of nodes A7, A8, B7, and B8. That is, when two networks 201A and 201B are connected in the X-axis direction, four sets of ring networks each composed of four nodes are formed, and the network can be expanded into a torus network with a scale of 4×2×2, which includes four nodes in the X-axis direction and two nodes each in the Y-axis direction and the Z-axis direction.

[0018] Similarly, by cutting one cable C in the Y-axis direction or Z-axis direction that connects each node and connecting a node of another network in place of the cut cable C, the present embodiment can expand the minimum-unit network also in the Y-axis direction and the Z-axis direction. When expanding nodes in the Y-axis direction, nodes whose numbers are 2 1 different from each other in networks 201A and 201B are connected. When expanding nodes in the Z-axis direction, nodes whose numbers are 2 2 different from each other in networks 201A and 201B are connected.

[0019] (Optical Switch) Next, we will describe the optical switch of this embodiment, which connects nodes included in the smallest unit network described above, or nodes included in another network. Figure 3 is a schematic top view of the optical switch of this embodiment. As described above, the optical switch 301 of this embodiment is an optical switch that connects nodes that constitute a network. A node may be a node included in one network, or a node that constitutes another network different from this network.

[0020] The optical switch 301 includes two switch elements 301A and 301B. Switch element 301A has one input port a and two output ports b and c. Switch element 301B has two input ports d and e and one output port f. One of the output ports b and c of switch element 301A (output port c in Figure 3) is connected to one of the input ports of switch element 301B (input port d in Figure 3). With this configuration, switch elements 301A and 301B constitute an optical switch 301 that includes multiple optical circuits 321 to 328, each having two input ports and two output ports. The multiple optical circuits 321 to 328 connect eight (2) third-order (M-order) networks. 3 It consists of ) optical circuits and is integrated as a waveguide-type optical device. In this embodiment, switch element 301A corresponds to the first switch element, and switch element 301B corresponds to the second switch element.

[0021] Furthermore, the optical switch 301 provides a function to connect nodes to each other in any of the M-directions (axes), and each optical switch 301 is equipped with two cables: one for connecting to a node within network 201A or network 201B, and another for connecting to an optical switch in another network. In order to provide such inter-node connection functionality, the optical switch 301 in this embodiment has two MIt includes optical circuits. In this embodiment, since a minimum first-order network is constructed, M is an integer of 1 or greater. As shown in Figures 1 and 2, the network of this embodiment is third-order, so there are 8 (2 3 The optical circuits 321 to 328 are included. As shown in Figure 3, optical circuit 322 includes switch elements 302A and 302B. Optical circuit 323 includes switch elements 303A and 303B, optical circuit 324 includes switch elements 304A and 304B, optical circuit 325 includes switch elements 305A and 305B, optical circuit 326 includes switch elements 306A and 306B, and optical circuit 327 includes switch elements 307A and 307B. Furthermore, optical circuit 328 includes switch elements 308A and 308B.

[0022] Next, using Figure 3, we will specifically explain how the optical switch 301 connects to nodes in network 201A or to nodes in network 201B. First, when connecting nodes in network 201A along the X-axis, if the node number is 2 0 Transmitters and receivers from different nodes are connected. Therefore, the transmitter of node A1 shown in Figure 1 is connected to one input port a of the optical circuit 321, and the receiver of node A2 is connected to output port f.

[0023] Similarly, the transmitter of node A2 is connected to input port a of optical circuit 322, and the receiver of node A1 is connected to output port f. Furthermore, the transmitter of node A3 is connected to input port a of optical circuit 323, and the receiver of node A4 is connected to output port f. The transmitter of node A4 is connected to input port a of optical circuit 324, and the receiver of node A3 is connected to output port f. Furthermore, the transmitter of node A5 is connected to input port a of optical circuit 325, and the receiver of node A6 is connected to output port f. The transmitter of node A6 is connected to input port a of optical circuit 326, and the receiver of node A5 is connected to output port f. The transmitter of node A7 is connected to input port a of optical circuit 327, and the receiver of node A8 is connected to output port f. The transmitter of node A8 is connected to input port a of optical circuit 328, and the receiver of node A7 is connected to output port f. With this connection, this embodiment allows node A1 to be connected to node A2, node A3 to node A4, node A5 to node A6, and node A7 to node A8, respectively, using two cables for transmission and reception.

[0024] Furthermore, the optical switch of this embodiment can connect nodes of the network 201A not only in the X-axis direction, but also in the Y-axis and Z-axis directions. When connecting nodes in the Y-axis direction, the number is 2 1Different nodes are connected to each other. Specifically, the transmitter of node A1 is connected to input port a of optical circuit 321, and the receiver of node A3 is connected to output port f. The transmitter of node A3 is connected to input port a of optical circuit 322, and the receiver of node A1 is connected to output port f. Furthermore, the transmitter of node A2 is connected to input port a of optical circuit 323, and the receiver of node A4 is connected to output port f. The transmitter of node A4 is connected to input port a of optical circuit 324, and the receiver of node A2 is connected to output port f. Furthermore, the transmitter of node A5 is connected to input port a of optical circuit 325, and the receiver of node A7 is connected to output port f. The transmitter of node A7 is connected to input port a of optical circuit 326, and the receiver of node A5 is connected to output port f. The transmitter of node A6 is connected to input port a of optical circuit 327, and the receiver of node A8 is connected to output port f. The transmitter of node A8 is connected to input port a of optical circuit 328, and the receiver of node A6 is connected to output port f. With these connections, this embodiment allows nodes A1 and A3, A2 and A4, A5 and A7, and A6 and A8 to be connected by two cables, one for transmission and one for reception.

[0025] Furthermore, when connecting nodes along the Z-axis, the number is 2 2Different nodes are connected to each other. Specifically, the transmitter of node A1 is connected to input port a of optical circuit 321, and the receiver of node A5 is connected to output port f. The transmitter of node A5 is connected to input port a of optical circuit 322, and the receiver of node A1 is connected to output port f. Furthermore, the transmitter of node A2 is connected to input port a of optical circuit 323, and the receiver of node A6 is connected to output port f. The transmitter of node A6 is connected to input port a of optical circuit 324, and the receiver of node A2 is connected to output port f. Furthermore, the transmitter of node A3 is connected to input port a of optical circuit 325, and the receiver of node A7 is connected to output port f. The transmitter of node A7 is connected to input port a of optical circuit 326, and the receiver of node A3 is connected to output port f. Furthermore, the transmitter of node A4 is connected to input port a of optical circuit 327, and the receiver of node A8 is connected to output port f. Furthermore, the transmitter of node A8 is connected to input port a of optical circuit 328, and the receiver of node A4 is connected to output port f. With these connections, this embodiment allows nodes A1 and A5, A2 and A6, A3 and A7, and A4 and A8 to be connected by two cables, one for transmission and one for reception.

[0026] The above explanation pertains to network 201A shown in Figures 1 and 2. However, it goes without saying that the same method can be used to connect nodes in the X, Y, and Z axes for network 201B, which is a similar minimum-unit network. The node connections in network 201B can be explained by replacing "node A" with "node B" in the above explanation. When connecting the two networks 201A and 201B in the X, Y, and Z axes, 2M optical switches 301 are required. In this embodiment, 6 optical switches are required to connect networks 201A and 201B in the tertiary direction.

[0027] (Network Expansion) Next, we will describe how to expand a torus-type network using the optical switch of the present invention. The optical switch used for network expansion is equipped with switch elements 301A to 308A internally, and of these switch elements, eight (2 M The output ports are connected to a series of cables and brought out to the outside. The device also includes internal switch elements 301B to 308B, and eight input ports of these switch elements that are not connected to switch elements 301A to 308A are connected to a series of optical cables and brought out to the outside. Here, the "series of optical cables" are optical cables that maintain a relative order and connect without crossing, and may be, for example, tape fibers with two or more optical cores bundled together.

[0028] Here, we will first explain an example of extending network 201A and network 201B in the X-axis direction. In this explanation, we will distinguish between connections between nodes within network 201A or network 201B, which will be referred to as "direct connection," and connections to nodes in the other network, which will be referred to as "non-direct connection."

[0029] This embodiment connects the eight output ports of the optical switch 301 applied to network 201A, which are not directly connected to the nodes, with the eight input ports of the optical switch 301 applied to network 201B, which are not directly connected to the nodes, without crossing them. Furthermore, this embodiment connects the eight output ports of the optical switch 301 applied to network 201B, which are not directly connected to the nodes, with the eight input ports of the optical switch 301 applied to network 201A, without crossing them.

[0030] The above connection enables a non-direct connection between node A1 of network 201A and node B2 of network 201B. Additionally, non-direct connections become possible between node A2 of network 201A and node B1 of network 201B, node A3 of network 201A and node B4 of network 201B, node A4 of network 201A and node B3 of network 201B, node A5 of network 201A and node B6 of network 201B, node A6 of network 201A and node B5 of network 201B, node A7 of network 201A and node B8 of network 201B, and node A8 of network 201A and node B7 of network 201B.

[0031] At this point, the X-axis connection shown in Figure 3 is realized, forming a ring network consisting of four nodes: A1, A2, B1, and B2. Similarly, a ring network is formed consisting of nodes A3, A4, B3, B4, A5, A6, B5, B6, and A7, A8, B7, and B8. As a result, four sets of ring networks are formed, thereby expanding the smallest unit network into a 4x2x2 torus-shaped network with four nodes in the X-axis direction and two nodes each in the Y-axis and Z-axis directions. Such expansions can be further carried out in the Y-axis and Z-axis directions.

[0032] In the above expansion, this embodiment allows the wiring between optical switches provided within the smallest unit network to be done with two sets of non-crossing 8-core optical fibers. Therefore, this embodiment allows two 1-input 2-input optical switches. M A small optical switch that integrates two units, M By applying 2M units to each node, the smallest possible network unit can be connected in the X, Y, and Z axes. Therefore, this embodiment provides a torus-type network that is economical and easy to expand, using optical switches composed of a small number of switch elements, and requiring minimal wiring work.

[0033] (Optical gate circuit) In the present embodiment described above, when an optical switch is manufactured using a silica-based planar lightwave circuit, if a Mach-Zehnder interferometer is used as a switch element, a difference may occur in extinction ratio characteristics between two ports. Here, non-direct connection for connecting nodes within a minimum unit network requires lower optical loss than direct connection for connecting nodes within the network. For this reason, in the present embodiment, of the two ports, the port with more excellent extinction ratio characteristics is applied to a port for non-directly connecting a node, and the other port is used as a port for connecting a node by direct connection. Further, in such a configuration, when the extinction ratio of the optical switch is insufficient for direct connection of nodes, a gate switch can be inserted as necessary to improve the extinction ratio.

[0034] FIG. 4 is a diagram for explaining the aforementioned gate switch (optical gate circuit). FIG. 4 shows eight optical circuits 321 to 328, and all of the optical circuits 321 to 328 are configured in the same manner. Therefore, in the present embodiment, the description of the optical circuit 321 is substituted for the description of the other optical circuits 322 to 328. The gate switch is provided between an input port of an optical circuit and a switch element, between an output port and a switch element, or between switch elements constituting an optical circuit. The gate circuit only needs to have a configuration that switches on and off the light (signal) passing through the switch element in the optical circuit.

[0035] The optical circuit shown in FIG. 4 shows an example in which the optical circuit 321 is configured by a 1×2 switch element 312 and a 2×1 switch element 313, and switch elements 311 and 314 functioning as a gate switch are added thereto. The switch element 312 and the switch element 314 correspond to the optical circuit 301A shown in FIG. 3, and the switch element 311 and the switch element 313 correspond to the optical circuit 301B. Thick lines in the figure indicate signals input to and output from the optical circuit 301A, and thin lines indicate signals input to and output from the optical circuit 301B.

[0036] The routes indicated by horizontal lines in the switch elements 311 to 314 in Fig. 4 are routes with excellent extinction ratio characteristics (no optical signal leakage in the off state), and can improve the extinction ratio characteristics of the entire route. The routes indicated by diagonal lines are routes with inferior extinction ratio characteristics (optical signal leakage in the off state), and reduce the extinction ratio characteristics of the entire route.

[0037] The route that is input from the input port a and output via the output port b does not cause light leakage in the process of passing through the switching element once, and is a high-characteristic route used for non-direct connection of nodes. On the other hand, the route where light is input from the input port a and output from the output port c, and the route where light is input from the input port d and output from the output port f pass through the high-characteristic route indicated by the horizontal line once due to the provision of the switch elements 311 and 314, and the extinction ratio is improved at this time. According to this embodiment, the direct connection route of the optical switch 301 passes through a route with excellent extinction ratio characteristics twice, and the non-direct connection route passes through such a route once. Therefore, the route between the transmitter and the receiver passes through a route with excellent extinction ratio characteristics twice. As described above, in this embodiment, a gate switch for improving the extinction ratio is inserted into the optical switch 301, so that the characteristics of the optical switch can be improved.

[0038] (Comparative Example) As a comparative example to the optical circuit of the present embodiment described above, a configuration in which an optical switch is applied to a known network to change the scale of a torus network will be described. Fig. 5 is a diagram showing an example of a known network. The network shown in Fig. 5 includes N (N is an integer of 2 or more) processors P501 to P50N, and optical switches S401 to S40M (M is an integer of 1 or more). All of the processors 501 to 50N are connected to the optical switches 401 to 40M via two pairs of optical fibers. Since the optical switches 401 to 40M have a function of directly connecting any input and output ports, appropriate settings for each optical switch can form a connection of a corresponding dimension, and overall form an M-dimensional torus network configured with a desired number of processors.

[0039] For example, in a one-dimensional torus network, or ring-shaped network, N processors 501 to 50N each have 2 pairs of optical fibers (2 for transmission and 2 for reception), and all of these optical fibers are connected to an optical switch 401. In such a configuration, by appropriately configuring the optical switch 401, N processors can be connected in a ring shape. Furthermore, multiple rings can be created to form any number of ring networks (N ÷ 2 or less) in which fewer than N processors are connected (the minimum number of processors in a ring is 2).

[0040] Furthermore, by adding two pairs of optical fibers (two for transmission and two for reception) to each of the N processors P501 to P50N, and connecting all of these optical fibers to the optical switch S402, the N processors can be connected in a ring configuration even via the optical switch S402, provided that the settings are configured correctly. In addition, multiple rings can be created, and any number of additional ring networks (N ÷ 2 or less) can be formed, each connecting fewer than N processors. In other words, since the network can be constructed so that each of the N processors P501 to P50N belongs to two different ring networks, it is also possible to construct a two-dimensional torus network.

[0041] By increasing the number of optical switches by one in this way, the number of dimensions of the torus can be increased by one, and an M-dimensional torus network can be formed using M optical switches. Known optical switches for changing the scale of such a torus-type network required having a number of ports roughly equal to the total number of nodes in the network.

[0042] (Effects) As described above, the optical switch of the present invention is composed of two small switch elements. MAn M-order network can be connected using these two-input, two-output optical circuits. Therefore, the optical switch of this embodiment can have significantly fewer ports compared to the comparative example described above. Consequently, the optical switch of this embodiment can form a large-scale network at a smaller size and lower cost than the configuration of the comparative example. Furthermore, applying silica-based planar optical circuit technology, which involves forming a silica glass waveguide on a silicon substrate and driving it by the thermo-optic effect, can particularly enhance economic efficiency.

[0043] Furthermore, in the optical switch of this embodiment, ports for connecting to nodes within the network and ports for connecting to another minimal unit network are arranged alternately. For connecting such ports, a multi-core connector consisting of tape fiber and MPO connectors can be used, for example. If the optical switch is manufactured using silica-based planar optical wave circuit technology, and every other port is brought out with tape fiber and connected with the above-mentioned multi-core connector, the work required for connection can be simplified.

[0044] Furthermore, in the optical switch of this embodiment, the output port may be folded back to the input side, and the tape fiber used for connecting the smallest unit networks may be integrated for both transmission and reception. With such a configuration, the number of components can be reduced, and economic benefits can be further enhanced.

[0045] Although the above embodiment explains that a torus-type network can be realized economically and easily expanded by using the optical switch of this embodiment, the applications of the optical switch of the present invention are not limited to torus-type networks. For example, in the description so far, the optical switch of the present invention has been described as 2 M I gave an example of a torus-shaped network with 1 node and 1 transceiver on each node, but what if we changed this to a network with 2 nodes and 2 transceivers on each node? M-1 When used in conjunction with individual transceivers, it can also be used as an optical switch to realize a multiplex ring network that is economical and easy to expand with minimal wiring work.

[0046] As described above, the optical switch according to this embodiment can provide the function of economically changing the scale of a torus-type network with a small number of switch elements. In torus-type networks, which are often adopted as one of the efficient network configurations in supercomputers, this optical switch is expected to be put into practical use as an optical switch suitable for customizing the network size, i.e., the number of processors used, to an optimal value according to the amount of computation to be performed.

[0047] A1-A8, B1-B8, Nodes 201A, 201B, Network 301, Optical Switches / Circuits 321-328, S401-S40M, Optical Switches P501-P50N

Claims

1. An optical switch for connecting nodes constituting a network, comprising: a first switch element having one input port and two output ports; and a second switch element having two input ports and one output port, wherein one of the output ports of the first switch element is connected to one of the input ports of the second switch element, thereby constituting an optical circuit having two input ports and two output ports.

2. The optical circuit is divided into two M The optical switch according to claim 1, which includes a number and in which M is an integer of 1 or more.

3. Of the first switch elements, two that are not connected to the second switch element. M The output ports are connected to a series of cables and brought out to the outside, and of the second switch elements, two are not connected to the first switch element. M The optical switch according to claim 2, wherein each of the input ports is connected to a series of cables and brought out to the outside.

4. The optical switch according to claim 1, further comprising an optical gate circuit for switching an optical signal on and off between at least one of the following: between the input / output port of the optical circuit and the first switch element, between the input / output port of the optical circuit and the second switch element, and between the first switch element and the second switch element.

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