Optically coupled multi-node computing apparatus, method and method of transmitting optical signal

Abstract

An optically coupled multi-node computing device, method, and method for transmitting optical signals are disclosed. The optically coupled multi-node computing device includes: an integrated circuit including one or more nodes coupled to an optical network, a first node of the nodes including an optical transmitter interface and an optical receiver interface; and a first optical path of the optical network; wherein: the optical transmitter interface is configured to transmit an optical signal at a first wavelength around the first optical path in a first direction, and at least one node coupled to the optical network is configured to couple substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the optical signal at the first wavelength.

Description

[Technical Field]

[0001] This application is a divisional application of Taiwan application No. 111133768, filed on September 6, 2022. This disclosure relates to an optically coupled multi-node computing system. [Previous Technology]

[0002] Optical signals have been used to transmit data over both long and short distances (including within data centers and within individual optical devices). An example of an optical network within a device is an optical network on a chip (ONoC). There are also various optical network topologies used to connect system nodes. [Summary of the Invention]

[0003] In general, an apparatus includes: an integrated circuit including a plurality of nodes coupled to an optical network, each node including: an optical transmitter interface configured to transmit an optical signal at a location along a coupled optical path of the optical network; and an optical receiver interface configured to receive an optical signal at a location along the coupled optical path of the optical network. The apparatus includes: a first optical path of the optical network including at least a portion of a guided mode fabricated in at least one layer of the integrated circuit and configured to propagate a guided mode around a closed path; and a second optical path of the optical network including at least a portion of a guided mode fabricated in at least one layer of the integrated circuit and configured to propagate a guided mode around a closed path. The first and second optical paths overlap each other at a first set of four locations on the integrated circuit. The first optical path is coupled to two or more of the plurality of nodes at a second set of corresponding locations on the integrated circuit that are different from all locations in the first set of locations. The second optical path couples to two or more nodes in the plurality of nodes at a third corresponding position on the integrated circuit, which is different from all positions in the first and second groups of positions.

[0004] The implementation may include one or more of the following features. The first optical path may include at least a first straight segment and a second straight segment parallel to each other, wherein at least one of a plurality of nodes is coupled along the first straight segment at two or more locations in the second group, and at least one of the plurality of nodes is coupled along the second straight segment at two or more locations in the second group.

[0005] The first optical path and the second optical path can overlap each other at the four positions in the first group without switching the optical signal between the first optical path and the second optical path at any of the four positions in the first group.

[0006] At at least one of the four positions in the first group, a portion of the first optical path in the first layer of the integrated circuit may overlap with a portion of the second optical path in the second layer of the integrated circuit.

[0007] At at least one location on the integrated circuit, a portion of the second optical path may be in the first layer of the integrated circuit.

[0008] At least one of the plurality of nodes may be coupled to the first optical path at one or more locations in the second set of locations, and coupled to the second optical path at one or more locations in the third set of locations.

[0009] The first optical path and the second optical path may overlap each other, wherein at least one switch is configured to switch the optical signal between the first optical path and the second optical path at at least one of the four positions in the first group.

[0010] The first optical path and the second optical path can be fabricated in the same layer of the integrated circuit.

[0011] The switch may include at least two waveguide ring resonators located near one of the four positions in the first group where the first and second optical paths overlap.

[0012] The device may further include: a third optical path of the optical network, the third optical path including at least a portion of a guide mode fabricated in at least one layer of the integrated circuit and configured to propagate a guide mode around a closed path; and a fourth optical path of the optical network, the fourth optical path including at least a portion of a guide mode fabricated in at least one layer of the integrated circuit and configured to propagate a guide mode around a closed path. The third optical path and the fourth optical path may overlap each other at four locations in a fourth group on the integrated circuit. The third optical path is coupled to two or more nodes in a fifth group of corresponding locations on the integrated circuit, which are different from all locations in the first group of locations, the second group of locations, the third group of locations, and the fourth group of locations. The fourth optical path is coupled to two or more nodes in a sixth group of corresponding locations on the integrated circuit, which are different from all locations in the first group of locations, the second group of locations, the third group of locations, the fourth group of locations, and the fifth group of locations.

[0013] The integrated circuit may be a first integrated circuit, and the device may include a second integrated circuit, the second integrated circuit including a plurality of nodes coupled to an optical network.

[0014] The first optical path of the optical network may include at least a portion manufactured in at least one layer of the second integrated circuit.

[0015] The device may include a third integrated circuit, which includes a plurality of nodes coupled to an optical network.

[0016] The second optical path of the optical network may include at least a portion of the fabrication in at least one layer of the third integrated circuit.

[0017] At least one of the plurality of nodes coupled to the first optical path may be configured to transmit an optical signal using a first optical wavelength, and at least one of the plurality of nodes coupled to the first optical path may be configured to transmit an optical signal using a second optical wavelength different from the first optical wavelength.

[0018] The device may include a controller configured to schedule the transmission of optical signals between the nodes, wherein the controller may be configured to set the first node as a transmitter during a first time period and prevent other nodes from transmitting signals on the optical path coupled to the first node during the first time period.

[0019] Each of at least some of the nodes may include at least one of a central processing unit, a graphics processing unit, a tensor processing unit, a digital signal processor, or a matrix processor.

[0020] In another general aspect, an apparatus includes: a plurality of nodes coupled to an optical network, each node including: an optical transmitter interface configured to transmit an optical signal at a location along a coupled optical path of the optical network; and an optical receiver interface configured to receive an optical signal at a location along the coupled optical path of the optical network. The apparatus includes: a first optical path of the optical network configured to propagate a guided mode around a closed path; and a second optical path of the optical network configured to propagate the guided mode around a closed path. The first and second optical paths may overlap each other at a first set of four locations, the first optical path may couple to two or more nodes in the node at a second set of corresponding locations different from those in the first set of locations, and the second optical path may couple to two or more nodes in the node at a third set of corresponding locations different from all locations in the first and second sets of locations.

[0021] The first optical path and the second optical path can overlap each other at the four positions in the first group without switching the optical signal between the first optical path and the second optical path at any of the four positions in the first group.

[0022] The first optical path and the second optical path may overlap each other, wherein at least one switch is configured to switch the optical signal between the first optical path and the second optical path at at least one of the four positions in the first group.

[0023] The node, the first optical path, and the second optical path can be set on a single substrate.

[0024] At least some of these nodes may include integrated circuitry.

[0025] The device may include integrated circuitry, wherein the node is part of the integrated circuitry.

[0026] The first optical path and the second optical path may include planar waveguides formed on a single substrate.

[0027] The first subgroup of the node, the first portion of the first optical path, and the first portion of the second optical path can be disposed on the first substrate. The second subgroup of the node, the second portion of the first optical path, and the second portion of the second optical path can be disposed on the second substrate.

[0028] At least a portion of the first optical path may include a planar waveguide formed on the substrate.

[0029] At least a portion of the second optical path may include a planar waveguide formed on the substrate.

[0030] In another general aspect, an apparatus includes: an array of nodes; and an optical network including a first optical path and a second optical path. The first optical path is configured to propagate a guiding pattern around a first closed path, and the first optical path is optically coupled to a plurality of nodes in the array. The second optical path is configured to propagate a guiding pattern around a second closed path, and the second optical path is optically coupled to a plurality of nodes in the array. The optical network is configured such that no switch is provided between the first optical path and the second optical path, such that an optical signal traveling in the first optical path remains in the first optical path without being switched to the second optical path, and an optical signal traveling in the second optical path remains in the second optical path without being switched to the first optical path. The apparatus includes a controller configured to schedule the transmission of optical signals between the nodes through the optical network.

[0031] The implementation may include one or more of the following features. The first optical path can be optically coupled to all nodes in the array, and the second optical path can be optically coupled to all nodes in the array.

[0032] The controller can be configured to set a first node as a transmitter during a first time period, the first node can be configured to transmit optical signals on the first optical path during the first time period, and the controller can be configured to prevent other nodes from transmitting signals on the first optical path during the first time period.

[0033] The controller can be configured to set the second node as a transmitter during the first time period, the second node can be configured to transmit optical signals on the second optical path during the first time period, and the controller can be configured to prevent other nodes from transmitting signals on the second optical path during the first time period.

[0034] The array of nodes may include node rows and node columns. The first optical path may include one or more waveguide segments extending in the row direction and optically coupled to the plurality of nodes, and the second optical path may include one or more waveguide segments extending in the column direction and optically coupled to the plurality of nodes.

[0035] The first optical path may include a waveguide segment located between the nodes of the Nth row and the (N+1)th row, and may be optically coupled to all nodes of the Nth row and the (N+1)th row, where N is an integer equal to or greater than 1.

[0036] The second optical path may include a waveguide segment located between the nodes in the Mth column and the (M+1)th column, and may be optically coupled to all nodes in the Mth column and the (M+1)th column, where M is an integer equal to or greater than 1.

[0037] Each of at least some of the nodes may include at least one of a central processing unit, a graphics processing unit, a tensor processing unit, a digital signal processor, or a matrix processor.

[0038] In another general aspect, an apparatus includes: a plurality of nodes; and an optical network including a first optical path and a second optical path. The first optical path is configured to propagate a guiding pattern around a first closed path and is optically coupled to the plurality of nodes in an array. The second optical path is configured to propagate a guiding pattern around a second closed path and is optically coupled to the plurality of nodes in the array. The first and second optical paths overlap each other at at least two locations in a first set, the first optical path couples to two or more nodes in the array at corresponding locations in a second set different from the locations in the first set, and the second optical path couples to two or more nodes in the array at corresponding locations in a third set different from all locations in the first and second sets.

[0039] The implementation may include one or more of the following features. The device may include a controller configured to schedule the transmission of optical signals between nodes through the optical network. The controller may be configured to set a first node as a transmitter during a first time period and to set a first switch to a pass state or a switch state. The first node may be configured to transmit optical signals via the first switch through the first optical path during the first time period, and the controller may be configured to prevent other nodes from transmitting signals on the first optical path during the first time period.

[0040] The first node can be configured to transmit an optical signal at a first wavelength around the first optical path in a first direction, and at least one node coupled to the optical network can be configured to couple substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the optical signal at the first wavelength transmitted by the first node.

[0041] The first node may include an optical transmitter interface and an optical receiver interface. The optical transmitter interface may be configured to transmit a first optical signal at a first wavelength along a portion of a first closed path, and to transmit a second optical signal at a second wavelength along a portion of the first closed path. The optical receiver interface may be configured to receive an optical signal at a third wavelength from a location along the first closed path.

[0042] The second node may include an optical transmitter interface and an optical receiver interface. The optical transmitter interface may be configured to transmit an optical signal at the third wavelength along a portion of the first closed path, and is configured to transmit an optical signal at the second wavelength along a portion of the first closed path. The optical receiver interface may be configured to receive an optical signal at the first wavelength from a location along the first closed path.

[0043] The third node may include an optical transmitter interface and an optical receiver interface. The optical transmitter interface may be configured to transmit an optical signal at the first wavelength onto the first closed path, and is configured to transmit an optical signal at the third wavelength onto the first closed path. The optical receiver interface may be configured to receive an optical signal at the second wavelength from a location along the first closed path.

[0044] The plurality of nodes may include at least a first node, a second node, and a third node coupled to the first closed path. The plurality of nodes may be configured to communicate on the first optical network using a plurality of wavelengths including at least a first wavelength, a second wavelength, and a third wavelength.

[0045] The first node may include: an optical transmitter interface configured to transmit a first optical signal at the first wavelength onto the first closed path; an optical receiver interface configured to simultaneously detect a second optical signal at a second wavelength and a third optical signal at a third wavelength from the first closed path; and demodulation circuitry coupled to the optical receiver interface of the first node. The demodulation circuitry may be configured to determine, for a plurality of time slots, a mapping between a plurality of amplitude levels detected during the time slot and binary symbols modulated onto each of the second and third optical signals.

[0046] The second node may include: an optical transmitter interface configured to transmit the second optical signal onto the first closed path; an optical receiver interface configured to simultaneously detect multiple optical signals at wavelengths different from the second wavelength from the first closed path; and demodulation circuitry coupled to the optical receiver interface of the second node. The demodulation circuitry may be configured, for multiple time slots, to determine a mapping between multiple amplitude levels detected during the time slot and binary symbols modulated onto each of the multiple optical signals detected by the optical receiver interface of the second node.

[0047] In another general aspect, an apparatus includes: an array of nodes; and an optical network including a first optical loop and a second optical loop, wherein the first optical loop is optically coupled to all nodes in the array, and the second optical loop is optically coupled to all nodes in the array. The apparatus includes a controller configured to schedule the transmission of optical signals between the nodes via the optical network. The controller is configured to allow only one node to broadcast an optical signal via the first optical loop during a first time period, and to prevent other nodes from transmitting optical signals via the first optical loop during the first time period; to allow only one node to broadcast an optical signal via the second optical loop during a second time period, and to prevent other nodes from transmitting optical signals via the second optical loop during the second time period.

[0048] The controller can be configured to schedule the first node and the second node to communicate with each other through the first optical loop during the third time period, schedule the third node and the fourth node to communicate with each other through the second optical loop during the third time period, and prevent other nodes from sending optical signals on the first optical loop and the second optical loop during the third time period.

[0049] For example, no switch is provided between the first and second optical loops, such that an optical signal traveling in the first optical loop remains in the first optical loop without being switched to the second optical loop, and an optical signal traveling in the second optical loop remains in the second optical loop without being switched to the first optical loop; and the optical signal is transmitted between nodes through the optical network.

[0050] Each node may include: an optical transmitter interface configured to transmit an optical signal at a first location along a first optical loop or a second optical loop; and an optical receiver interface configured to receive an optical signal at a second location along the first optical loop or the second optical loop. The first optical loop and the second optical loop may overlap each other at a first set of four locations, the first optical loop may couple to two or more nodes in the node at a second set of corresponding locations different from all locations in the first set of locations, and the second optical loop may couple to two or more nodes in the plurality of nodes at a third set of corresponding locations different from all locations in the first set of locations and all locations in the second set of locations.

[0051] Each of at least some of the nodes may include at least one of a central processing unit, a graphics processing unit, a tensor processing unit, a digital signal processor, or a matrix processor.

[0052] In another general aspect, an apparatus includes: an array of four rows and four columns of nodes, a first optical loop, and a second optical loop. The first optical loop includes a first optical path segment located between the first and second rows, and a second optical path segment located between the third and fourth rows. The second optical loop includes a third optical path segment located between the first and second columns, and a fourth optical path segment located between the third and fourth columns. Each node in the first and second rows is optically coupled to the first optical path segment, each node in the third and fourth rows is optically coupled to the second optical path segment, each node in the first and second columns is optically coupled to the third optical path segment, and each node in the third and fourth columns is optically coupled to the fourth optical path segment.

[0053] In another general aspect, a method includes transmitting an optical signal from a first node to a second node via an optical network. Each node includes: an optical transmitter interface configured to transmit the optical signal at a location along a coupled optical path of the optical network; and an optical receiver interface configured to receive the optical signal at a location along the coupled optical path of the optical network. The method includes: a closed-path propagation guidance mode around a first optical path of the optical network; and a closed-path propagation guidance mode around a second optical path of the optical network. The first and second optical paths overlap each other at a first set of four locations, the first optical path couples to two or more nodes in the node at a second set of corresponding locations different from those in the first set of locations, and the second optical path couples to two or more nodes in the node at a third set of corresponding locations different from all those in the first and second sets of locations.

[0054] In another general aspect, an apparatus includes: an integrated circuit including one or more nodes coupled to an optical network, and a first optical path of the optical network. The first node of the one or more nodes includes: an optical transmitter interface configured to transmit an optical signal at a first location along the coupled optical path of the optical network; and an optical receiver interface configured to receive an optical signal at a second location along the coupled optical path of the optical network. The first optical path of the optical network is fabricated in at least one layer of the integrated circuit and configured to propagate at least a portion of a guided mode around a closed path. The optical transmitter interface in the first node is configured to transmit an optical signal at a first wavelength around the first optical path in a first direction. At least one node coupled to the optical network is configured to couple substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the optical signal at the first wavelength transmitted by the optical transmitter interface of the first node.

[0055] The implementation may include one or more of the following features. A node coupled to the optical network and configured to couple substantially all remaining optical power from the first optical path at the first wavelength may include a first node.

[0056] The optical transmitter interface in the first node may include a light source, which is coupled to the first optical path through an optical structure that transmits an optical signal at a first wavelength from the light source to the first position.

[0057] The optical transmitter interface of the first node may include an optical power termination structure, which receives substantially all remaining optical power coupled from the first optical path at the first wavelength at the first location via the optical structure.

[0058] The optical structure may include at least two ring resonators, wherein the optical signal is at a first wavelength and the remaining optical power propagates around each ring resonator in opposite directions.

[0059] The optical receiver interface may include an optical splitter configured to couple a portion of the optical power propagating through the second location to one or more detectors.

[0060] The one or more detectors include a plurality of detectors, and the optical receiver interface includes an optical structure configured to couple optical power at different wavelengths to different corresponding detectors of the plurality of detectors.

[0061] A node coupled to the optical network and configured to couple substantially all remaining optical power at the first wavelength from the first optical path may include a second node of one or more nodes on the integrated circuit.

[0062] The second node may include: an optical transmitter interface configured to transmit an optical signal at a third location along a coupled optical path of the optical network; and an optical receiver interface configured to receive an optical signal at a fourth location along a coupled optical path of the optical network.

[0063] The optical receiver interface in the second node can be configured to couple substantially all remaining optical power at the first wavelength from the first optical path.

[0064] Nodes coupled to the optical network and configured to couple substantially all remaining optical power at the first wavelength from the first optical path may include nodes outside the integrated circuit.

[0065] In another general aspect, an apparatus includes: a plurality of nodes coupled to an optical network, and a first optical path of the optical network configured to propagate a guided mode around a closed path. The first node of the plurality of nodes includes: an optical transmitter interface configured to transmit an optical signal at a first location along the coupled optical path of the optical network; and an optical receiver interface configured to receive an optical signal at a second location along the coupled optical path of the optical network. The optical transmitter interface in the first node is configured to transmit an optical signal at a first wavelength around the first optical path in a first direction. At least one node coupled to the optical network is configured to couple substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the optical signal at the first wavelength transmitted by the optical transmitter interface of the first node.

[0066] The implementation may include one or more of the following features. The node and the first optical path may be disposed on a single substrate.

[0067] At least some of these nodes may include integrated circuits.

[0068] The device may include integrated circuitry, wherein the node is part of the integrated circuitry.

[0069] The first optical path may include a planar waveguide formed on a single substrate.

[0070] The first subgroup of the node and the first portion of the first optical path can be disposed on the first substrate, and the second subgroup of the node and the second portion of the first optical path can be disposed on the second substrate.

[0071] In another general aspect, a method includes: transmitting an optical signal at a first wavelength from a first node to a second node via an optical network including a first optical path configured to propagate a guiding mode around a closed path. The first node is configured to transmit the optical signal around the first optical path in a first direction. At least one node coupled to the optical network couples substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the optical signal at the first wavelength transmitted by the first node.

[0072] The implementation may include one or more of the following features. The at least one node coupled to the optical network and configured to couple substantially all remaining optical power from the first optical path at the first wavelength may include a first node.

[0073] In another general aspect, an apparatus includes: a first optical network configured to propagate a guided mode around a first closed path; and at least a first node, a second node, and a third node coupled to the first closed path. The first node includes: an optical transmitter interface configured to transmit an optical signal at a first wavelength to the second node along a portion of the first closed path, and configured to transmit an optical signal at a second wavelength to the third node along a portion of the first closed path; and an optical receiver interface configured to receive an optical signal at a third wavelength from a location along the first closed path. The second node includes: an optical transmitter interface configured to transmit an optical signal at a third wavelength to the first node along a portion of the first closed path, and configured to transmit an optical signal at the second wavelength to the third node along a portion of the first closed path; and an optical receiver interface configured to receive an optical signal at the first wavelength from a location along the first closed path. The third node includes: an optical transmitter interface configured to transmit an optical signal at the first wavelength onto the first closed path, and configured to transmit an optical signal at the third wavelength onto the first closed path; and an optical receiver interface configured to receive an optical signal at the second wavelength from a location along the first closed path.

[0074] Implementations may include one or more of the following features. The device may also include a second optical network configured to propagate a guidance pattern around a second closed path, wherein the third node is coupled to the second closed path.

[0075] The device may also include a fourth node coupled to the second closed path.

[0076] The device may also include a third optical network configured to propagate a guided pattern around a third closed path, wherein the fourth node is coupled to the third closed path.

[0077] The device may also include at least a fifth node and a sixth node coupled to the third closed path.

[0078] The fifth node may include: an optical transmitter interface configured to transmit an optical signal at a second wavelength to the sixth node along a portion of the third closed path, and configured to transmit an optical signal at a third wavelength to the fourth node along a portion of the third closed path; and an optical receiver interface configured to receive an optical signal at a first wavelength from a location along the third closed path. The sixth node may include: an optical transmitter interface configured to transmit an optical signal at a first wavelength to the fifth node along a portion of the third closed path, and configured to transmit an optical signal at a third wavelength to the fourth node along a portion of the third closed path; and an optical receiver interface configured to receive an optical signal at a second wavelength from a location along the third closed path. The fourth node may include: an optical transmitter interface configured to transmit an optical signal at a second wavelength onto the third closed path, and configured to transmit an optical signal at a first wavelength onto the third closed path; and an optical receiver interface configured to receive an optical signal at a third wavelength from a location along the third closed path.

[0079] The optical receiver interface of the first node can also be configured to receive an optical signal at the second wavelength from a position along the first closed path.

[0080] In another general aspect, an apparatus includes: a first optical network configured to propagate a guiding pattern around a first closed path; a second optical network configured to propagate a guiding pattern around a second closed path; a switching node coupled to the first closed path and the second closed path; and a plurality of nodes configured to communicate between the plurality of nodes using a first wavelength group through the first optical network, and to communicate with the switching node using a second wavelength different from the first wavelength group through the first optical network.

[0081] The implementation may include one or more of the following features. The plurality of nodes may include a first node and a second node, the first node and the second node being coupled to the first closed path but not to the second closed path, the first node may include an optical transmitter interface configured to transmit an optical signal at a first wavelength to the second node along a portion of the first closed path, the optical transmitter interface of the first node may be configured to transmit an optical signal at a second wavelength to the switching node along a portion of the first closed path, and the first node may include an optical receiver interface configured to receive an optical signal at a third wavelength from a location along the first closed path.

[0082] The second node may include: an optical transmitter interface configured to transmit an optical signal at a third wavelength to the first node along a portion of the first closed path, the optical transmitter interface of the second node may be configured to transmit an optical signal at a second wavelength to the third node along a portion of the first closed path, and the second node may include an optical receiver interface configured to receive an optical signal at the first wavelength from a location along the first closed path.

[0083] The switching node may include: an optical transmitter interface configured to transmit an optical signal at the first wavelength onto the first closed path, the optical transmitter interface of the switching node may be configured to transmit an optical signal at the third wavelength onto the first closed path, and the switching node may include an optical receiver interface configured to receive an optical signal at the second wavelength from a position along the first closed path.

[0084] In another general aspect, a method is provided for transmitting optical signals among a plurality of nodes coupled to an optical network configured to propagate a guided pattern around a closed path. The method includes: at each node in a subgroup of the plurality of nodes, transmitting an optical signal from that node to other nodes in the subgroup using a unique wavelength from a wavelength group allocated to that node for transmission within the subgroup. The method includes: at each node in the subgroup, receiving an optical signal from other nodes in the subgroup using a wavelength from the wavelength group other than the unique wavelength allocated to that node for transmission within the subgroup. The method includes: at a node not in a subgroup of the plurality of nodes, communicating with each node in the subgroup using a wavelength not in that wavelength group.

[0085] In another general aspect, an apparatus includes: a first optical network configured to propagate a guided pattern around a first closed path; and a plurality of nodes, including at least a first node, a second node, and a third node coupled to the first closed path. The plurality of nodes are configured to communicate on the first optical network using a plurality of wavelengths including at least a first wavelength, a second wavelength, and a third wavelength. The first node includes: an optical transmitter interface configured to transmit a first optical signal at the first wavelength onto the first closed path; an optical receiver interface configured to simultaneously detect a second optical signal at the second wavelength and a third optical signal at the third wavelength from the first closed path; and demodulation circuitry coupled to the optical receiver interface of the first node. The demodulation circuitry is configured to determine, for a plurality of time slots, a mapping between a plurality of amplitude levels detected during the time slot and binary symbols modulated onto each of the second and third optical signals. The second node includes: an optical transmitter interface configured to transmit the second optical signal onto the first closed path; an optical receiver interface configured to simultaneously detect multiple optical signals at wavelengths different from the second wavelength from the first closed path; and demodulation circuitry coupled to the optical receiver interface of the second node. The demodulation circuitry is configured to determine, for multiple time slots, a mapping between multiple amplitude levels detected during those time slots and binary symbols modulated onto each of the multiple optical signals detected by the optical receiver interface of the second node.

[0086] The implementation may include one or more of the following features. The third node may include: an optical transmitter interface configured to transmit the third optical signal onto the first closed path; an optical receiver interface configured to simultaneously detect multiple optical signals at wavelengths different from the third wavelength from the first closed path; and a demodulation circuit coupled to the optical receiver interface of the third node. The demodulation circuit may be configured to determine, for multiple time slots, a mapping between multiple amplitude levels detected during the time slot and binary symbols modulated onto each of the multiple optical signals detected by the optical receiver interface of the third node.

[0087] This binary symbol can correspond to a non-return-to-zero (NRZ) binary symbol.

[0088] For the demodulation circuitry coupled to the optical receiver interface of the first node, the plurality of amplitude levels detected during the time slot, including four amplitude levels, may include: a first amplitude level corresponding to approximately zero power in the second optical signal and approximately zero power in the third optical signal; a second amplitude level corresponding to a first predetermined power in the second optical signal and approximately zero power in the third optical signal; a third amplitude level corresponding to approximately zero power in the second optical signal and a second predetermined power in the third optical signal; and a fourth amplitude level corresponding to a third predetermined power, which is substantially equal to the sum of the first predetermined power in the second optical signal and the second predetermined power in the third optical signal.

[0089] The first node may further include: a second optical receiver interface configured to simultaneously detect multiple optical signals at wavelengths different from the first wavelength, the second wavelength, and the third wavelength from the first closed path. The first node may further include a second demodulation circuit coupled to the second optical receiver interface of the first node and configured to determine, for multiple time slots, a mapping between multiple amplitude levels detected during the time slot and binary symbols modulated onto each of the multiple optical signals detected by the second optical receiver interface of the first node.

[0090] The plurality of nodes may include a node. The demodulation circuitry coupled to the optical receiver interface of the first node may include at least a detector, each detector being configured to determine, for a plurality of time slots, a mapping between at least four amplitude levels detected during the time slot and binary symbols modulated onto each of at least two optical signals.

[0091] The plurality of nodes may include a node, and the demodulation circuitry of the optical receiver interface coupled to the first node may be configured to determine, for the plurality of time slots, a mapping between at least a few amplitude levels detected during the time slot and a binary symbol modulated to each of the at least a few optical signals.

[0092] The first node can be configured to couple substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the first optical signal transmitted by the optical transmitter interface of the first node.

[0093] In another general aspect, an apparatus includes: a first optical network configured to propagate a guided pattern around a first closed path; and a plurality of nodes, including at least a first node coupled to the first closed path. The plurality of nodes are configured to communicate on the first optical network using a plurality of wavelengths including at least a first wavelength, a second wavelength, and a third wavelength. The first node includes: an optical transmitter interface configured to transmit a first optical signal at the first wavelength onto the first closed path; an optical receiver interface configured to simultaneously detect a second optical signal at the second wavelength and a third optical signal at the third wavelength from the first closed path; and demodulation circuitry coupled to the optical receiver interface of the first node. The demodulation circuitry is configured to determine, for a plurality of time slots, a mapping between a plurality of amplitude levels detected during the time slot and binary symbols modulated onto each of the second and third optical signals.

[0094] The implementation may include one or more of the following features. The plurality of nodes may include a second node, the second node comprising: an optical transmitter interface configured to transmit the second optical signal onto the first closed path; an optical receiver interface configured to simultaneously detect from the first closed path a plurality of optical signals at wavelengths different from the second wavelength; and a demodulation circuit coupled to the optical receiver interface of the second node. The demodulation circuit is configured to determine, for a plurality of time slots, a mapping between a plurality of amplitude levels detected during the time slot and binary symbols modulated onto each of the plurality of optical signals detected by the optical receiver interface of the second node.

[0095] In another general aspect, a method includes transmitting a first optical signal at a first wavelength onto a first closed path at a first node coupled to a first optical network configured to propagate a guiding mode around a first closed path; simultaneously detecting a second optical signal at a second wavelength and a third optical signal at a third wavelength from the first closed path at the first node; and determining, for a plurality of time slots, a mapping between a plurality of amplitude levels detected during the time slots and binary symbols modulated onto each of the second and third optical signals.

[0096] An implementation may include one or more of the following features. The method may include: transmitting a second optical signal onto a first closed path at a second node coupled to the first optical network; simultaneously detecting multiple optical signals at wavelengths different from the second wavelength from the first closed path; and determining, for multiple time slots, a mapping between multiple amplitude levels detected during the time slot and binary symbols modulated onto each of the multiple optical signals detected by the optical receiver interface of the second node.

[0097] Details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages of the invention will become apparent and readily understood from the description, drawings, and claims.

[0098] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict with a patent application or its publication, this specification (including the definitions) shall prevail.

Implementation Method

[0100] Figure 1A shows a schematic diagram of an example of an optically coupled multi-node computing system 100A. System 100A includes 16 nodes (labeled 0 to 15) (e.g., 106a, 106b, 106c, 106d, collectively referred to as 106) coupled to an optical network comprising overlapping unidirectional optical loops 102 and 104 that provide optical signal flows for transmitting optical signals between different pairs of nodes 106. For example, each optical loop 102, 104 can be implemented as an optical waveguide formed on an integrated platform to propagate guided modes around a closed path. In this example, the paths of optical loops 102, 104 overlap at four locations (e.g., 108) where they overlap, without any switching elements. Therefore, if the waveguides at these overlapping locations are fabricated in different layers of a photonic integrated circuit without physical intersection, optical signals can pass through these overlapping locations without significant loss. Alternatively, if the waveguides do intersect each other at the overlapping locations, the optical signal can pass through these overlapping locations with relatively small loss (e.g., 0.05 dB–0.1 dB at each intersection).

[0101] Exemplarily, optical loops 102 and 104 of the optical network can serve as a first optical path and a second optical path, respectively. The first optical path of the optical network includes at least a portion of a guided mode fabricated in at least one layer of the integrated circuit and configured to propagate a guided mode around a closed path; and the second optical path of the optical network includes at least a portion of a guided mode fabricated in at least one layer of the integrated circuit and configured to propagate a guided mode around a closed path. Exemplarily, the first optical path and the second optical path can be fabricated in different layers without physical intersection. Optionally, the first optical path and the second optical path can also be fabricated in the same layer.

[0102] Node 106 can be configured as a computing node, comprising one or more processors, as well as other optical, electronic, or optoelectronic circuitry, which may be integrated into an integrated circuit for each node or into a single integrated circuit comprising all 16 nodes. The processors may include one or more digital central processing units (or cores) and / or one or more photonic computing modules such as optoelectronic matrix multiplication modules, as described, for example, in U.S. Patent Application 16 / 431,167, filed June 4, 2019, and U.S. Patent Application 17 / 204,320, filed March 17, 2021 (provided in Appendix A), both of which are incorporated herein by reference. In this example, each node is coupled to two optical loops 102 and 104 via a corresponding pair of transmitter and receiver modules 110. For example, transmitter and receiver modules 110 may be coupled to locations on the optical loops using a ring resonator 116. In this example, each node 106 is optically coupled to two loops 102 and 104, so an optical signal can travel from one node to any other node in a single hop. Here, the term "hop" generally refers to the transmission of an optical signal from one node or switch to another. Therefore, if an optical signal travels directly from node A to node B, that is one hop. If an optical signal travels from node A to node B via a switch node or intermediate node C, that is two hops. The divided bandwidth of this implementation is: * Tx / Rx BW * # wavelength.

[0103] Here, N represents the number of nodes, Tx / Rx BW represents the transmit bandwidth (Tx BW) or receive bandwidth (Rx BW) (usually Tx BW = Rx BW), and #wavelength represents the number of wavelengths used to transmit signals between nodes 106. The partitioned bandwidth generally refers to the maximum bandwidth between any two nodes 106 in system 100A. For any two nodes in system 100A, the maximum bandwidth between these two nodes will be at least this partitioned bandwidth. For a pair of nodes, the maximum bandwidth between the two nodes in this pair may be greater than this partitioned bandwidth. The partitioned bandwidth is a measure of the transmission bottleneck in the system, therefore a larger partitioned bandwidth is generally preferred.

[0104] In some implementations, each node transmits an optical signal using a specified wavelength, and different nodes transmit optical signals using different wavelengths. For example, node 0 transmits an optical signal using wavelength WL0, node 1 transmits an optical signal using wavelength WL1, ..., node 15 transmits an optical signal using wavelength WL15. When nodes 1 through 15 receive an optical signal with wavelength WL0, nodes 1 through 15 know that the optical signal was transmitted from node 0. Similarly, when nodes 0 and 2 through 15 receive an optical signal with wavelength WL1, nodes 0 and 2 through 15 know that the optical signal was transmitted from node 1. Each node can decide whether to further process the optical signal or ignore it upon receiving it. In this example, each node broadcasts the optical signal to other nodes, and the other nodes determine how to process the received signal.

[0105] Because there are two optical loops 102 and 104, each node can transmit a first optical signal on optical loop 102 and a second optical signal on optical loop 104 during the same time slot. Compared to having only one optical loop, having two optical loops 102 and 104 increases the communication bandwidth between nodes.

[0106] In some embodiments, the number of wavelengths used by nodes for optical signal transmission is less than the number of nodes. Two or more nodes share the same wavelength when transmitting optical signals. System 100A includes a controller for scheduling optical signal transmissions between nodes sharing the same wavelength on the same loop. For example, suppose nodes 0 to 3 use wavelength WL0 to transmit optical signals, nodes 4 to 7 use wavelength WL1, nodes 8 to 11 use wavelength WL2, and nodes 12 to 15 use wavelength WL3. The controller can schedule data transmissions at different times through the optical loop by different nodes sharing a single wavelength. For example, the controller can configure one of nodes 0 to 3 to transmit an optical signal with wavelength WL0 in the loop in time slot 0, configure one of nodes 4 to 7 to transmit an optical signal with wavelength WL1 in the loop in time slot 0, configure one of nodes 9 to 11 to transmit an optical signal with wavelength WL2 in the loop in time slot 0, and configure one of nodes 12 to 15 to transmit an optical signal with wavelength WL3 in the loop in time slot 0.

[0107] Because there are two optical loops 102 and 104, each node may transmit a first optical signal on optical loop 102 and a second optical signal on optical loop 104 during the same time slot. It is also possible for the first node to transmit the first optical signal on optical loop 102 and the second node to transmit the second optical signal on optical loop 104 during the same time slot when the first and second nodes share the same transmission wavelength.

[0108] In some embodiments, multiple nodes share the same transmission wavelength, and system 100A includes a controller for scheduling optical signal transmissions between nodes 106. The controller also informs the intended recipients of the signal so that the receiver nodes know they should expect to receive the signal in a specific time slot. For example, the controller can schedule data transmissions between different pairs of nodes via an optical loop at different times. The controller can configure a first node (e.g., node 1) as a transmitter on the optical loop and a second node (e.g., node 10) as a receiver on the optical loop during a first time period t1, and prevent other nodes from transmitting optical signals on the same optical loop during the first time period t1. The controller can configure a third node (e.g., node 3) as a transmitter on the optical loop and a second node (e.g., node 0) as a receiver on the optical loop during a second time period t2, and prevent other nodes from transmitting optical signals on the same optical loop during the second time period t1, and so on. Because there are two optical loops 102 and 104, it is possible for the first node to send a first optical signal to the second node on optical loop 102 and for the third node to send a second optical signal to the fourth node on optical loop 104 during the same time period. Having two optical loops 102 and 104 increases the communication bandwidth between nodes compared to having only one optical loop.

[0109] System 100A includes an array of four rows and four columns of nodes. Optical loop 102 includes a first waveguide portion extending between the first and second column nodes and optically coupled to each node in the first and second columns. Optical loop 102 includes a second waveguide portion extending between the third and fourth column nodes and optically coupled to each node in the third and fourth columns. Thus, optical loop 102 is optically coupled to each node in the array of nodes. Optical loop 104 includes a first waveguide portion extending between the first and second row nodes and optically coupled to each node in the first and second rows. Optical loop 104 includes a second waveguide portion extending between the third and fourth row nodes and optically coupled to each node in the third and fourth rows.

[0110] Figure 1B shows a schematic diagram of an example of an optically coupled multi-node computing system 100B. System 100B includes 16 nodes (labeled 0 to 15) (e.g., 118a, 118b, 118c, 118d, collectively referred to as 118) coupled to an optical network comprising overlapping unidirectional optical loops 102 and 104 that provide optical signal streams for transmitting optical signals between different pairs of nodes 118. In this example, overlapping locations include switches 120a, 120b, 120c, 120d (collectively referred to as 120) configured to transmit optical signal streams between the two optical loops 112 and 114. Therefore, in this example, each node 118 is coupled to only one of the optical loops 112 or 114, and if the optical signal does not pass through switch 120, the optical signal can travel from one node to any other node in a single hop, or if the optical signal travels along the path through switch 120, it can travel from one node to any other node in two hops. Furthermore, optical crosstalk between optical loops 112 and 114 can be reduced by the presence of the switch. The divided bandwidth of this implementation is also: * Tx / Rx BW * # Wavelength

[0111] In some embodiments, system 100B includes a controller for scheduling optical signal transmission between nodes 118 and configuring switches 120 to enable optical signals to be transmitted from transmitters to receivers. For example, to enable node 1 to send optical signals to node 4, the controller configures switches 120b, 120d, and 120c to a passing state (see Figures 4A and 5A), such that optical signals can pass through the optical loop 114 from node 1 to switch 120b, from switch 120b to switch 120d, from switch 120d to switch 120c, and from switch 120c to node 4. To enable node 1 to send optical signals to node 5, the controller configures switches 120b and 120d to a pass-through state and switch 120c to a switch-to-switch state (see Figures 4B and 5B). This allows the optical signal to pass through optical loop 114 from node 1 to switch 120b, from switch 120b to switch 120d, from switch 120d to switch 120c, and through optical loop 112 from switch 120c to node 5. Alternatively, the controller can configure switch 120b to a switch-to-switch state and switches 120d and 120c to a pass-through state, allowing the optical signal to pass through optical loop 114 from node 1 to switch 120b, from switch 120b to switch 120d, from switch 120d to switch 120c, and through optical loop 112 from switch 120c to node 5.

[0112] In some embodiments, the controller can evaluate the switch configuration to determine whether only one pair of nodes can communicate with each other during a time period, or whether two pairs of nodes can communicate with each other during that time period. If the switch is configured to cause optical loops 112, 114 to form a single optical path during a first time period, then only two nodes can communicate with each other on that optical path during that first time period. If the switch is configured to cause optical loops 112, 114 to form two separate optical paths during a second time period, then the first and second nodes can communicate with each other, and the third and fourth nodes can communicate with each other during that second time period.

[0113] In some embodiments, each switch 120 switches the optical signal to allow the optical signal to either continue traveling on the same optical loop or switch to a different optical loop without further processing. In some embodiments, such as in a larger optical network where the optical signal can pass through a large number of switches resulting in significant signal attenuation, one or more switches may provide optical amplification to improve the signal level. In some embodiments, one or more switches may convert the received optical signal into an electrical signal, process the electrical signal using electronic circuitry, convert the electrical signal back into an optical signal, and transmit the optical signal to a next destination.

[0114] Other examples of such optically coupled multi-node computing systems can be implemented. For example, in some embodiments, there may be subgroups containing overlapping positions of switches. Moreover, multiple optical loops oriented vertically (e.g., in the y-direction) and horizontally (e.g., in the x-direction) can be combined such that any two optical loops overlap each other at four locations. Figure 2A shows an example of an arrangement 200A with four optical loops, wherein the four optical loops are first to fourth optical paths, and the four optical loops include two horizontal loops 130 having long straight sections extending in the x-direction and two vertical loops 132 having long straight sections extending in the y-direction. Figure 2B shows an example of another arrangement 200B with four optical loops, which includes two horizontal loops 140 and two vertical loops 142, wherein a switch 144 is provided at each location where two loops overlap.

[0115] Figure 2C shows an example of a unidirectional loop optical network 200C with six optical loops, including two horizontal loops 130 with long straight sections extending in the x-direction, two vertical loops 132 with long straight sections extending in the y-direction, and two diagonal loops 134 and 136. Diagonal loop 134 allows nodes in the upper right quadrant of the node array to communicate with nodes in the lower left quadrant. Diagonal loop 136 allows nodes in the upper left quadrant of the node array to communicate with nodes in the lower right quadrant.

[0116] Figure 2D shows an example of a unidirectional loop optical network 200D with a right optical loop, which includes two horizontal loops 130 with long straight sections extending in the x-direction, two vertical loops 132 with long straight sections extending in the y-direction, and four diagonal loops 136. The diagonal loops 134 allow nodes in the upper right quadrant of the node array to communicate with nodes in the lower left quadrant. The diagonal loops 136 allow nodes in the upper left quadrant of the node array to communicate with nodes in the lower right quadrant. Compared to the unidirectional loop optical network 200C, the unidirectional loop optical network 200D has a higher transmission bandwidth in the diagonal direction.

[0117] Additionally, if there are subgroups of adjacent nodes fabricated on different photonic integrated circuits (PICs), the PICs can be interconnected to provide a closed path by interconnecting portions of the optical loop with optical fibers or fiber bundles, as shown in arrangement 300A in FIG3A. Arrangement 300A includes four PICs, with the upper left photonic integrated circuit clockwise to the lower left photonic integrated circuit, and clockwise from the first to the fourth integrated circuit, respectively. Each integrated circuit may include multiple nodes coupled to the optical network. The corresponding ends of portions of the loop waveguide 150 are interconnected via segments of optical fiber 152. This technique can be used to scale up the system.

[0118] Figure 3B illustrates an example of a unidirectional loop optical network 300B, which includes a partial loop waveguide 150 interconnected by segments of optical fibers 152 extending in the x and y directions. The unidirectional loop optical network 300B also includes a partial loop waveguide 154 interconnected by segments of optical fibers 156 extending diagonally. The diagonal partial loop waveguide 154 and the segments of optical fibers 156 allow nodes in the upper right photonic integrated circuit (second integrated circuit) to communicate with nodes in the lower left photonic integrated circuit (fourth integrated circuit), and allow nodes in the upper left photonic integrated circuit (first integrated circuit) to communicate with nodes in the lower right photonic integrated circuit (third integrated circuit).

[0119] Exemplarily, the first optical path of the optical network includes at least a portion fabricated in at least one layer of the second integrated circuit. The second optical path of the optical network includes at least a portion fabricated in at least one layer of the third integrated circuit. Various types of switches can be used at overlapping locations. In some embodiments, two ring resonators 162, 164 are used to form switch 160. Switch 160 has a pass state shown in FIG. 4A and a switch state shown in FIG. 4B. In the pass state, the optical signal 170 traveling on waveguide 166 continues on waveguide 166, and the optical signal 172 traveling on waveguide 168 continues on waveguide 168. In the switch state, the optical signal 174 traveling on waveguide 166 is switched to waveguide 168, and the optical signal 176 traveling on waveguide 168 is switched to waveguide 166. For example, when a switch with the transmission and switching states shown in Figures 4A and 4B is used in the optical loop arrangement of Figure 2B, and the switch is in the switching state, the optical signal will switch from the horizontal loop to the vertical loop, or from the vertical loop to the horizontal loop. Given the narrow bandwidth of the ring resonator, this type of switch can be used to switch a single wavelength at a time. The ring resonator can be tuned, or a separate pair of rings can be pre-configured for each wavelength.

[0120] In some embodiments, a Mach-Zehnder interferometer (MZI) is used to form a switch. This switch has the pass-through state shown in FIG. 5A and the switch state shown in FIG. 5B. Given the wide bandwidth of the MZI, this type of switch can be used to switch multiple wavelengths simultaneously (e.g., all wavelengths).

[0121] Figures 6A and 6B illustrate different states of the receiver / transmitter module 110, which includes both an optical receiver interface (Rx) 180 and an optical transmitter interface (Tx) 182. In the state of Figure 6A, the optical receiver interface Rx 180 is configured to couple substantially all optical power in the received optical signal 188 to the photodetector (PD) 184, and the optical transmitter interface Tx 182 is configured to modulate the light from the light source 186 to provide the optical signal 186 that has been modulated with data. The dashed lines indicate the states of the corresponding waveguides in which substantially no optical power propagates. In the state of Figure 6B, the optical receiver interface Rx 180 is configured to allow the input optical signal 190 to pass through without being coupled and detected, and the optical transmitter interface Tx 182 is configured to prevent any optical signal from being sent onto the coupled optical path. Measurement photodiodes (MPDs) 192 and 194 can be used to verify the tuning of the ring resonator used for coupling the transmitted / received optical signals. In the state shown in Figure 6A, measurement photodiode 192 should measure a low signal, and measurement photodiode 194 should measure a low signal. In the state shown in Figure 6B, measurement photodiode 192 should be idle and not measure any signal, and measurement photodiode 194 should measure a high signal.

[0122] Figure 7 illustrates another example of an optically coupled multi-node computing system 700 comprising multiple wafers and using four different wavelengths for inter-wafer communication. In this example, system 700 includes four wafers (labeled 1 to 4) 702a, 702b, 702c, 702d (collectively referred to as 702), which are interconnected (e.g., via optical fiber 704) to communicate over a unidirectional loop optical network 722. For example, each wafer 702 may represent an optical communication interface for a computing node (not shown). Each wafer includes an optical receiver interface Rx 706 and an optical transmitter interface Tx 708. In this example, each wafer 702 is configured to use different laser wavelengths for transmission (i.e., wavelengths 1 to 4) and is configured to receive each of the three remaining wavelengths in a corresponding photodetector coupled by a corresponding ring resonator tuned to those wavelengths. For example, chip 702a is configured to transmit data using laser wavelength 1, chip 702b is configured to transmit data using laser wavelength 2, chip 702c is configured to transmit data using laser wavelength 3, and chip 702d is configured to transmit data using laser wavelength 4.

[0123] The optical receiver interface 706 of each chip 702 includes a photodetector 706 for detecting received optical signals. The optical receiver interface 706 includes an optical splitter 714 having a first branch 718 and a second branch 720. The optical splitter splits the received optical signals, and a portion of the received optical power (e.g., 25%) is sent to the first branch 718, and the remaining portion of the received optical power (e.g., 75%) is sent to the second branch 720. The optical signal in the first branch 718 is coupled to the photodetector 706.

[0124] The optical transmitter interface Tx 708 includes a pair of ring resonators 710 configured to both couple the transmitted optical signal (originating from the optical transmitter interface Tx 708) in an appropriate direction to the optical network 722, and couple substantially all received optical power in the second branch 720 at the same allocated wavelength (e.g., from the same transmitted signal, after it has propagated around the loop) to the optical terminator 712 to prevent the received optical power from interfering with the transmitted optical signal. The coupled (received) optical power propagates in opposite directions around the pair of ring resonators 710 into the optical terminator 712.

[0125] Referring to Figure 8A, the example optical communication interface 800 can be used in an optical system that communicates between various optical communication interfaces using five wavelengths. The optical communication interface 800 includes a wafer 802 similar to wafer 702 of Figure 7, but wafer 802 includes four photodetectors in its optical receiver interface instead of the three photodetectors used in wafer 702. Wafer 802 includes an optical transmitter interface 810 and an optical receiver interface 804. The optical transmitter interface 810 uses one wavelength, and the optical receiver interface 804 has a separate group of ring resonators 806 and photodetectors 808 for each remaining wavelength in the system. In this example, the optical transmitter interface 810 uses wavelength 1. The optical receiver interface 804 includes four groups of ring resonators 806, each group of ring resonators 806 being designed to couple a specific wavelength from 2 to 5 to a corresponding photodiode 808.

[0126] In systems using an odd number of wavelengths (e.g., 2N+1, where N is an integer), the remaining 2N wavelengths can be detected individually (as in this example) or by fewer photodetectors within a wavelength subgroup (as shown in the optical receiver interface 850 of Figure 8B). In this example, there are still 5 wavelengths, but only 2 photodetectors 852 are present instead of the 4 photodetectors 808 used in the example of Figure 8A. Each photodetector 852 receives optical signals from two pairs of ring resonators 854.

[0127] In some embodiments, the system uses PAM4 modulation to modulate optical signals transmitted at optical communication interfaces or between wafers to have four different predetermined amplitude levels. Each photodetector 852 is connected to a corresponding demodulation circuit (PAM4 RX) 856, which is configured to perform PAM-4 demodulation on the four different predetermined amplitude levels of the received optical signal. Since two different wavelengths are combined onto a single photodetector 856, the optical power amplitude levels are added incoherently (i.e., without interference). As the optical signal travels along the optical loop 722, a portion of the optical power is split by each wafer encountered along the optical loop 722. The more wafers the optical signal encounters, the greater the amount of optical power split, and the smaller the remaining optical power. Considering the coupling ratio of the directional coupler / splitter in each wafer 702, and the corresponding number of times a given signal (at a given wavelength) from a given wafer is split before being received at that wafer, there will be a different unique amplitude level associated with each wafer / wavelength.

[0128] Figures 9A to 9C include tables showing exemplary values ​​of the power levels of optical signals with various wavelengths when the optical signal passes through various numbers of wafers. Figure 9A includes a table 900 showing examples of the power levels of optical signals with various wavelengths when the optical signal passes through various numbers of wafers. The values ​​in Table 900 are normalized to a maximum value of 1. The example in Figure 9A assumes that wafer 1 uses wavelength 1 for the transmission of the optical signal. Similarly, wafers 2 to 5 use wavelengths 2 to 5 for the transmission of the optical signal, respectively. If wafer 1 sends an optical signal with wavelength 1 and amplitude 1 to wafer 2, the power level of the optical signal with wavelength 1 received at wafer 2 is 0.7. If wafer 1 sends an optical signal with amplitude 1 to wafer 3, passing through wafer 2 along the way, the power level of the optical signal with wavelength 1 received at wafer 3 is 0.7 * 0.7 = 0.49. If chip 1 sends an optical signal with an amplitude of 1 to chip 4, passing through chips 2 and 3, the power level of the optical signal with a wavelength of 1 received at chip 4 will be 0.73 = 0.343. If chip 1 sends an optical signal with an amplitude of 1 to chip 5, passing through chips 2 to 4, the power level of the optical signal with a wavelength of 1 received at chip 5 will be 0.74 = 0.2401. Similarly, if chip 2 sends an optical signal with a wavelength of 2 and an amplitude of 1 to chip 3, the power level of the optical signal with a wavelength of 2 received at chip 3 will be 0.7. If chip 2 sends an optical signal with an amplitude of 1 to chip 1, passing through chips 3 to 5, the power level of the optical signal with a wavelength of 2 received at chip 1 will be 0.2401.

[0129] Figure 9B is Table 902, which shows the obtained amplitude level and normalized amplitude level (normalized to the maximum amplitude 1), which is obtained from the mapping of wavelengths (labeled WL#) received at each of the two receivers (RX0, RX1) at each wafer shown in Table 904 of Figure 9C. Using this scheme, multiple optical signals at different wavelengths from different corresponding transmitting wafers can be detected simultaneously on a single photodetector, thereby reducing the total number of photodetectors required. In this example, wafer 1 includes receivers RX0 and RX1. Receiver RX0 detects wavelengths WL3 and WL5, and receiver RX1 detects wavelengths WL2 and WL4. Wafer 2 includes receivers RX0 and RX1, wherein receiver RX0 detects wavelengths WL1 and WL4, and receiver RX1 detects wavelengths WL3 and WL5. Wafer 3 includes receivers RX0 and RX1, wherein receiver RX0 detects wavelengths WL2 and WL5, and receiver RX1 detects wavelengths WL1 and WL4. Chip 4 includes receivers RX0 and RX1, wherein receiver RX0 detects wavelengths WL1 and WL3, and receiver RX1 detects wavelengths WL2 and WL5. Chip 5 includes receivers RX0 and RX1, wherein receiver RX0 detects wavelengths WL2 and WL4, and receiver RX1 detects wavelengths WL1 and WL3.

[0130] As shown in Figure 9B, if the receiver RX0 of chip 1 detects an optical signal with an amplitude of approximately 1.043, it can be inferred that the received signal is '1' at wavelength WL3 and '1' at wavelength WL5. If the receiver RX0 of chip 1 detects an optical signal with an amplitude of 0.7, it can be inferred that the received signal is '1' at wavelength WL5 and '0' at wavelength WL3. If the receiver RX0 of chip 1 detects an optical signal with an amplitude of 0.343, it can be inferred that the received signal is '1' at wavelength WL3 and '0' at wavelength WL5. If the receiver RX0 of chip 1 detects an optical signal with an amplitude of 0, it can be inferred that the received signal is '0' at wavelength WL3 and '0' at wavelength WL5.

[0131] If receiver RX1 of chip 1 detects an optical signal with an amplitude of 0.7301, it can be inferred that the received signal is '1' at wavelength WL2 and '1' at wavelength WL4. If receiver RX1 of chip 1 detects an optical signal with an amplitude of 0.49, it can be inferred that the received signal is '1' at wavelength WL4 and '0' at wavelength WL2. If receiver RX1 of chip 1 detects an optical signal with an amplitude of 0.2401, it can be inferred that the received signal is '1' at wavelength WL2 and '0' at wavelength WL4. If receiver RX1 of chip 1 detects an optical signal with an amplitude of 0, it can be inferred that the received signal is '0' at wavelength WL2 and '0' at wavelength WL4. The analog signals detected at receivers RX0 and RX1 of chips 2 to 5 can be converted to digital values ​​in a similar manner.

[0132] Figure 10 illustrates another example of an optically coupled multi-node computing system 1000. In this example, eight computing nodes 1002 are optically connected via a loop optical network 1004 and electrically connected in one of two Fast Peripheral Component Interconnect (PCIE) networks 1006a, 1006b (collectively referred to as 1006), controlled by corresponding PCIE switches 1008a, 1008b (collectively referred to as 1008) having ports 1010 for connection to other systems (e.g., host systems). There is also a ninth node 1012, which has a switch 1014 optically connected to the eight computing nodes 1002 in the same loop optical network 1004. The loop optical network 1004 may be, for example, a dense wavelength division multiplexed (DWDM) ring network providing all-to-all direct routing between the computing nodes 1002 and the switch node 1012. Laser source 1016 (e.g., a comb laser) can provide light of different wavelengths, which are then modulated by individual nodes 1002. Laser source 1016 transmits laser light through waveguide nodes, for example, similar to the examples shown in Figures 7 and 8A (except that the laser source is external to the nodes). Alternatively, in other examples, each node 1002, 1012 may include or be coupled to its own laser source.

[0133] Figure 11 illustrates an example of optical transmitter (TX) and receiver (RX) interfaces included in each node 1002, 1012 for coupling optical signals to and from the loop optical network 1004. In this configuration, each compute node 1002 includes a processing engine (PE) 1100, which is assigned a unique laser wavelength (L#) for transmission to other compute nodes 1002 and is configured to receive each other wavelength used by the compute node 1002. Each compute node 1002 is connected to a TX interface for transmission on the unique laser wavelength (one of wavelengths L0 to L7) assigned to that compute node 1002. For example, PE 0 is connected to a TX interface configured to transmit an optical signal with wavelength L0, PE 1 is connected to a TX interface configured to transmit an optical signal with wavelength L1, PE 2 is connected to a TX interface configured to transmit an optical signal with wavelength L2, and PE 7 is connected to a TX interface configured to transmit an optical signal with wavelength L7. Each processing engine is connected to a TX interface configured to transmit an optical signal with a common laser wavelength (L8) to the switch node 1012. Only one processing engine transmits an optical signal with wavelength L8 in any given time slot. The switch node 1012 transmits and receives signals at wavelength L8 when communicating with the compute node 1002.

[0134] Switch node 1012 also includes another set of optical receiver RX and optical transmitter TX interfaces for communication on different loop optical networks 1102. In this example, there are eight switch nodes 1012 configured such that when a switch node 1012 communicates with other switch nodes 1012 on the loop optical network 1102, each switch node 1012 is configured to transmit on a unique laser wavelength (one of wavelengths L0 to L7) assigned to that switch node 1012. For example, switch node 0 is configured to transmit an optical signal of wavelength L0 on the loop optical network 1102, switch node 1 is configured to transmit an optical signal of wavelength L1 on the loop optical network 1102, switch node 2 is configured to transmit an optical signal of wavelength L2 on the loop optical network 1102, and switch node 7 is configured to transmit an optical signal of wavelength L7 on the loop optical network 1102.

[0135] Figure 12 illustrates an example of a rack optical system 1200, which includes racks for eight optically coupled multi-node computing systems (e.g., 1000a, 1000b, 1000c (collectively referred to as 1000)). Each system 1000 includes a chassis and is connected to another loop optical network 1202 of the rack via corresponding switch interfaces in their switch nodes. For communication on the loop optical network 1202, each system 1000 includes switches for different wavelengths assigned to subgroups of eight of nine wavelengths. For example, a switch in system 1000a can use wavelength 1 to communicate with other systems 1000 on the loop optical network 1202. Similarly, switches in systems 1000b and 1000c can use wavelengths 1 and 2, respectively, to communicate with other systems 1000 on the loop optical network 1202. Each computing node 1002 in system 1000 is 3 hops away from any other computing node 1002 in another system 1000 (e.g., node A in system 1 to switch 1 in system 1, switch 1 in system 1 to switch 2 in system 2, and switch 2 in system 2 to node B in system 2).

[0136] Figure 13 illustrates an example of a clustered optical system 1300 comprising eight rack optical systems (e.g., 1200a, 1200b (collectively referred to as 1200)), wherein each rack optical system 1200 includes eight multi-node computing systems 1000. In this example, the clustered optical system 1300 includes eight rows of multi-node computing systems 1000 and eight columns of multi-node computing systems 1000. The clustered optical system 1300 includes a loop optical network, such as 1302a, 1302b (collectively referred to as 1302), wherein each loop optical network 1302 connects the multi-node computing systems 1000 in rows. Each multi-node computing system 1000 is connected to the loop optical network 1202 and the loop optical network 1302 via a corresponding switch interface in its switch node, thereby allowing the multi-node computing system 1000 to communicate with any other multi-node computing system 1000 in the clustered optical system 1300.

[0137] Each multi-node computing system 1000 includes a switch node comprising two distinct sets of switch interfaces for connecting to these additional loop optical networks 1202, 1302. One set of switch interfaces is used to connect to other multi-node computing systems 1000 in the same rack optical system 1200 via the loop optical network 1202, and the other set of switch interfaces is used to connect to other multi-node computing systems 1000 in the same row of different rack optical systems 1200.

[0138] In order to communicate between each row of the cross-rack optical system 1200 on the loop optical network 1302, the switches of each rack optical system 1200 are assigned to different wavelengths of a subgroup of 8 wavelengths out of 9 wavelengths. Each computing node 1002 in the rack / frame is 4 hops away from any other computing node 1002 in another rack / frame (e.g., node A in system 1 of rack 1 to switch 1 of system 1 of rack 1, switch 1 of system 1 of rack 1 to switch 2 of system 1 of rack 2, switch 2 of system 1 of rack 2 to switch 3 of system 2 of rack 2, switch 3 of system 2 of rack 2 to node B of system 2 of rack 2).

[0139] For example, in rack 1, a switch in system 1 can send a signal with wavelength 1 to other systems in rack 1 via loop optical network 1202a, a switch in system 2 can send a signal with wavelength 2 to other systems in rack 1 via loop optical network 1202a, and so on. A switch in system 1000 of rack 1 can communicate with other systems 1000 in rack 1 via loop optical network 1202a using wavelengths 1 to 8, and communicate with other systems 1000 in racks 2 to 8 via wavelength 9. In rack 2, a switch in system 1 can send a signal with wavelength 2 to other systems in rack 2 via loop optical network 1202b, a switch in system 2 can send a signal with wavelength 3 to other systems in rack 2 via loop optical network 1202b, and so on. The switches in system 1000 of rack 2 can communicate with other systems 1000 in the same rack using wavelengths 2 to 9 on loop optical network 1202b, and with other systems 1000 in racks 1 and 3 to 8 using wavelength 1. The switches in system 1000 of rack 3 can communicate with other systems 1000 in rack 3 using wavelengths 3 to 9 and 1 on loop optical network 1202c, and with other systems 1000 in racks 1, 2 and 4 to 8 using wavelength 2, and so on.

[0140] In some embodiments, multiple optically coupled multi-node computing systems can be formed on multiple corresponding layers of a substrate to increase the node density in a given volume. For example, a first optically coupled multi-node computing system can be formed on a first layer or a first set of layers in the substrate, and a second optically coupled multi-node computing system can be formed on a second layer or a second set of layers in the substrate. For example, each multi-node computing system includes N nodes, so the two multi-node computing systems have a total of 2N nodes. The first node having circuitry in the first layer or the first set of layers includes transmitter and receiver modules on the second layer or the second set of layers, which allow the first node to communicate with nodes on the second layer or the second set of layers via a loop optical network in the second layer or the second set of layers. The circuitry of the first node on the first layer or the first set of layers is electrically coupled to the transmitter and receiver modules on the second layer or the second set of layers via vertical contacts (such as vias). This design allows any node among the 2N nodes to optically communicate with any node among the other 2N nodes via one of the optical networks in the first and second optically coupled multi-node computing systems. In a similar manner, three or more optically coupled multi-node computing systems can be formed on three or more corresponding layers or groups of layers of a substrate.

[0141] In some examples, multiple optically coupled multi-node computing systems can be formed on multiple corresponding substrates stacked vertically to increase the node density in a given volume. For example, a first optically coupled multi-node computing system can be formed on a first substrate, and a second optically coupled multi-node computing system can be formed on a second substrate. For example, each multi-node computing system includes N nodes, so the two multi-node computing systems have a total of 2N nodes. The first node on the first substrate includes transmitter and receiver modules on the second substrate, which allow the first node to communicate with nodes on the second substrate via a loop optical network on the second substrate. The circuitry of the first node on the first substrate is electrically coupled to the transmitter and receiver modules on the second substrate via vertical contacts extending vertically across the first and second substrates. This design allows any node in the 2N nodes to optically communicate with any node in the other 2N nodes via one of the optical networks in the first and second optically coupled multi-node computing systems. In a similar manner, three or more optically coupled multi-node computing systems can be formed on three or more corresponding substrates.

[0142] In some embodiments, multiple optically coupled multi-node computing systems having any of the designs shown in Figures 1B to 8B can be formed on multiple corresponding layers or groups of layers in a substrate, or on multiple substrates stacked vertically together, or on a combination thereof.

[0143] The number of nodes and optical loops in a multi-node computing system may differ from the example above. For example, n1 horizontal optical loops (with parallel straight waveguide segments extending in the x-direction) and n2 vertical optical loops (with parallel straight waveguide segments extending in the y-direction) may be used, where n1 is different from n2.

[0144] Some of the systems, components, and / or functional operations described in this specification may be implemented in digital electronic circuitry, including structures and their structural equivalents disclosed in this specification, or in computer software, firmware, or hardware, or in a combination of one or more of them. Embodiments of the subject matter described in this specification may be implemented using one or more modules of computer program instructions encoded on a computer-readable medium for execution by or control of the operation of a data processing device. The computer-readable medium may be a manufactured product such as a hard disk drive in a computer system or an optical disc sold through retail channels, or an embedded system. The computer-readable medium may be acquired separately and subsequently encoded with one or more modules of computer program instructions, such as by transmitting one or more modules of computer program instructions over a wired or wireless network. The computer-readable medium may be a machine-readable storage device, a machine-readable storage substrate, a memory device, or a combination of one or more of the above.

[0145] A computer program (also known as a program, software, software application, script, or code) may be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and may be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program may be stored as part of a file that stores other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to said program, or in multiple coordinated files (e.g., a file that stores one or more modules, subprograms, or code portions). A computer program may be deployed to execute on a single computer or on multiple computers located on a website or distributed across multiple websites and interconnected by a communication network.

[0146] The processes and logic flows described in this specification can be executed by one or more programmable processors that execute one or more computer programs to perform functions by manipulating input data and producing outputs. The processes and logic flows can also be executed by dedicated logic circuits, and the device can also be implemented as dedicated logic circuits, such as FPGAs (Field Programmable Gate Arrays) or ASICs (Application-Specific Integrated Circuits).

[0147] Although this disclosure has been described in conjunction with certain embodiments, it should be understood that this disclosure is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, and the scope of the claims should be interpreted in the broadest possible sense to include all such modifications and equivalent structures permitted by law. [Simplified Explanation of the Diagram]

[0099] This disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be emphasized that, according to common practice, the various features in the drawings are not drawn to scale. Instead, for clarity, the dimensions of the various features have been arbitrarily enlarged or reduced. Figures 1A and 1B are schematic diagrams of an example optically coupled multi-node computing system. Figures 2A, 2B, 2C, and 2D are schematic diagrams of an example optical loop arrangement. Figures 3A and 3B are schematic diagrams of an example interconnection of multiple photonic integrated circuits. Figures 4A and 4B are schematic diagrams of different states of an example switch. Figures 5A and 5B are schematic diagrams of different states of an example switch. Figures 6A and 6B are schematic diagrams of different states of an example receiver / transmitter module for a node. Figure 7 is a schematic diagram of an example optically coupled multi-node computing system. Figure 8A is a schematic diagram of an example optical communication interface. Figure 8B is a schematic diagram of an example optical receiver interface. Figures 9A, 9B, and 9C are tables for simultaneously receiving values ​​of multiple wavelengths. Figure 10 is a schematic diagram of an example optically coupled multi-node computing system. Figure 11 is a schematic diagram of the interface portion of an optically coupled multi-node computing system. Figure 12 is a schematic diagram of an example rack-mounted optical system. Figure 13 is a schematic diagram of an example cluster (pod) optical system. The same reference numerals and names denote the same elements in each figure.

Claims

1. An optically coupled multi-node computing device, comprising: An integrated circuit including one or more nodes coupled to an optical network, a first node of the one or more nodes including: an optical transmitter interface configured to transmit an optical signal at a first location along a coupled optical path of the optical network; and an optical receiver interface configured to receive an optical signal at a second location along the coupled optical path of the optical network; and a first optical path of the optical network including at least a portion of a guided mode fabricated in at least one layer of the integrated circuit and configured to propagate around a closed path; wherein: the optical transmitter interface in the first node is configured to transmit an optical signal at a first wavelength around the first optical path in a first direction, and at least one node coupled to the optical network is configured to couple substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the optical signal at the first wavelength transmitted by the optical transmitter interface of the first node.

2. The apparatus as claimed in claim 1, wherein, The nodes coupled to the optical network and configured to couple substantially all remaining optical power from the first optical path at the first wavelength include the first node.

3. The apparatus as claimed in claim 2, wherein, The optical transmitter interface in the first node includes a light source, which is coupled to the first optical path through an optical structure that transmits the optical signal at the first wavelength from the light source to the first location.

4. The apparatus as claimed in claim 3, wherein, The optical transmitter interface of the first node includes an optical power termination structure, which receives substantially all remaining optical power coupled from the first optical path at the first wavelength at the first location via the optical structure.

5. The apparatus as claimed in claim 4, wherein, The optical structure includes at least two ring resonators, wherein the optical signal is at the first wavelength, and the remaining optical power propagates around each of the ring resonators in opposite directions.

6. The apparatus as claimed in claim 2, wherein, The optical receiver interface includes an optical splitter configured to couple a portion of the optical power propagating through the second location to one or more detectors.

7. The apparatus as claimed in claim 6, wherein, The one or more detectors include a plurality of detectors, and the optical receiver interface includes an optical structure configured to couple optical power at different wavelengths to different corresponding detectors of the plurality of detectors.

8. The apparatus as claimed in claim 1, wherein, The nodes coupled to the optical network and configured to couple substantially all remaining optical power from the first optical path at the first wavelength include second nodes on the integrated circuit.

9. The apparatus as claimed in claim 8, wherein, The second node includes: an optical transmitter interface configured to transmit an optical signal at a third location along a coupled optical path of the optical network, and an optical receiver interface configured to receive an optical signal at a fourth location along the coupled optical path of the optical network.

10. The apparatus as claimed in claim 9, wherein, The optical receiver interface in the second node is configured to couple substantially all remaining optical power at the first wavelength from the first optical path.

11. The apparatus as claimed in claim 1, wherein, The nodes coupled to the optical network and configured to couple substantially all remaining optical power at the first wavelength from the first optical path include nodes outside the integrated circuit.

12. An optically coupled multi-node computing device, comprising: A plurality of nodes coupled to an optical network, wherein a first node of the plurality of nodes includes: an optical transmitter interface configured to transmit an optical signal at a first location along a coupled optical path of the optical network; and an optical receiver interface configured to receive an optical signal at a second location along the coupled optical path of the optical network; and a first optical path of the optical network configured to propagate a guided mode around a closed path; wherein the optical transmitter interface of the first node is configured to transmit an optical signal at a first wavelength around the first optical path in a first direction, and at least one node coupled to the optical network is configured to couple substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the optical signal at the first wavelength transmitted by the optical transmitter interface of the first node.

13. The apparatus as claimed in claim 12, wherein, The node and the first optical path are disposed on a single substrate.

14. The apparatus as claimed in claim 12 or 13, wherein, At least some of the nodes each include integrated circuitry.

15. The apparatus as claimed in claim 12 or 13, wherein the apparatus includes integrated circuitry, The node is part of the integrated circuit.

16. The apparatus as claimed in claim 13, wherein, The first optical path includes a planar waveguide formed on the single substrate.

17. The apparatus as claimed in claim 12, wherein, The first subgroup of the node and the first portion of the first optical path are disposed on the first substrate, and the second subgroup of the node and the second portion of the first optical path are disposed on the second substrate.

18. An optically coupled multi-node computation method, comprising: An optical signal at a first wavelength is transmitted from a first node to a second node via an optical network, the optical network including a first optical path configured to propagate a guided mode around a closed path; wherein the first node is configured to transmit the optical signal around the first optical path in a first direction, and at least one node coupled to the optical network couples substantially all remaining optical power at the first wavelength from the first optical path to prevent interference with the optical signal at the first wavelength transmitted by the first node.

19. The method as described in claim 18, wherein, The at least one node coupled to the optical network and configured to couple substantially all remaining optical power from the first optical path at the first wavelength includes the first node.

20. An optically coupled multi-node computing device, comprising: A first optical network, configured to propagate a guidance pattern around a first closed path; The system comprises a plurality of nodes, including at least a first node, a second node, and a third node coupled to the first closed path, wherein the plurality of nodes are configured to communicate on the first optical network using a plurality of wavelengths including at least a first wavelength, a second wavelength, and a third wavelength; the first node comprises: an optical transmitter interface configured to transmit a first optical signal at the first wavelength onto the first closed path; an optical receiver interface configured to simultaneously detect a second optical signal at the second wavelength and a third optical signal at the third wavelength from the first closed path; and a demodulation circuit coupled to the optical receiver interface of the first node and configured to determine, for a plurality of time slots, a mapping between a plurality of amplitude levels detected during the time slots and binary symbols modulated onto each of the second and third optical signals; and the second node comprises: an optical transmitter interface configured to transmit the second optical signal onto the first closed path. An optical receiver interface configured to simultaneously detect multiple optical signals at wavelengths different from the second wavelength from the first closed path, and a demodulation circuit coupled to the optical receiver interface of the second node, and configured to determine, for multiple time slots, a mapping between multiple amplitude levels detected during the time slots and binary symbols modulated onto each of the multiple optical signals detected by the optical receiver interface of the second node, wherein the first node is configured to couple substantially all remaining optical power at the first wavelength from the first closed path to prevent interference with the first optical signal transmitted by the optical transmitter interface of the first node.

21. The apparatus as claimed in claim 20, wherein, The third node includes: an optical transmitter interface configured to transmit the third optical signal onto the first closed path; an optical receiver interface configured to simultaneously detect multiple optical signals at wavelengths different from the third wavelength from the first closed path; and a demodulation circuit coupled to the optical receiver interface of the third node and configured to determine, for multiple time slots, a mapping between multiple amplitude levels detected during the time slots and binary symbols modulated onto each of the multiple optical signals detected by the optical receiver interface of the third node.

22. The apparatus as claimed in claim 20, wherein, The binary symbol corresponds to the non-return-to-zero (NRZ) binary symbol.

23. The apparatus as claimed in claim 20, wherein, For the demodulation circuitry coupled to the optical receiver interface of the first node, the plurality of amplitude levels detected during the time slot, comprising a group of four amplitude levels, include: a first amplitude level corresponding to approximately zero power in the second optical signal and approximately zero power in the third optical signal; a second amplitude level corresponding to a first predetermined power in the second optical signal and approximately zero power in the third optical signal; a third amplitude level corresponding to approximately zero power in the second optical signal and a second predetermined power in the third optical signal; and a fourth amplitude level corresponding to a third predetermined power, the third predetermined power being substantially equal to the sum of the first predetermined power in the second optical signal and the second predetermined power in the third optical signal.

24. The apparatus as claimed in claim 20, wherein, The first node further includes: a second optical receiver interface configured to simultaneously detect multiple optical signals at wavelengths different from the first wavelength, the second wavelength, and the third wavelength from the first closed path; and a second demodulation circuit coupled to the second optical receiver interface of the first node and configured to determine, for multiple time slots, a mapping between multiple amplitude levels detected during the time slots and binary symbols modulated onto each of the multiple optical signals detected by the second optical receiver interface of the first node.

25. The apparatus as claimed in claim 20, wherein, The plurality of nodes includes a node, and the demodulation circuitry coupled to the optical receiver interface of the first node includes at least a detector, each of the detectors being configured to determine, for a plurality of time slots, a mapping between at least four amplitude levels detected during the time slots and binary symbols modulated onto each of at least two optical signals.

26. The apparatus as claimed in claim 20, wherein, The plurality of nodes includes a node, and the demodulation circuitry coupled to the optical receiver interface of the first node is configured to determine, for a plurality of time slots, a mapping between at least a plurality of amplitude levels detected during the time slots and binary symbols modulated onto each of at least a plurality of optical signals.

27. An optically coupled multi-node computing device, comprising: A first optical network, configured to propagate a guidance pattern around a first closed path; The system includes multiple nodes, including at least a first node coupled to the first closed path, wherein the multiple nodes are configured to communicate on the first optical network using multiple wavelengths including at least a first wavelength, a second wavelength, and a third wavelength; and wherein the first node includes: an optical transmitter interface configured to transmit a first optical signal at the first wavelength onto the first closed path; an optical receiver interface configured to simultaneously detect a second optical signal at the second wavelength and a third optical signal at the third wavelength from the first closed path; and a demodulation circuit coupled to the optical receiver interface of the first node and configured to determine, for multiple time slots, a mapping between multiple amplitude levels detected during the time slots and binary symbols modulated onto each of the second and third optical signals, wherein the first node is configured to couple substantially all remaining optical power at the first wavelength from the first closed path to prevent interference with the first optical signal transmitted by the optical transmitter interface of the first node.

28. The apparatus as claimed in claim 27, wherein, The plurality of nodes includes a second node, the second node comprising: an optical transmitter interface configured to transmit the second optical signal onto the first closed path; an optical receiver interface configured to simultaneously detect a plurality of optical signals at wavelengths different from the second wavelength from the first closed path; and a demodulation circuit coupled to the optical receiver interface of the second node and configured to determine, for a plurality of time slots, a mapping between a plurality of amplitude levels detected during the time slots and a binary symbol modulated onto each of the plurality of optical signals detected by the optical receiver interface of the second node.

29. An optically coupled multi-node computation method, comprising: At a first node coupled to a first optical network, a first optical signal at a first wavelength is transmitted onto a first closed path, the first optical network being configured to propagate a guided mode around the first closed path; at the first node, a second optical signal at a second wavelength and a third optical signal at a third wavelength are simultaneously detected from the first closed path; and for a plurality of time slots, a mapping is determined between a plurality of amplitude levels detected during the time slots and binary symbols modulated onto each of the second and third optical signals, wherein the first node couples substantially all remaining optical power at the first wavelength from the first closed path to prevent interference with the first optical signal.

30. The method of claim 29, comprising, at a second node coupled to the first optical network: transmitting the second optical signal onto the first closed path; simultaneously detecting from the first closed path a plurality of optical signals at wavelengths different from the second wavelength; and determining, for a plurality of time slots, a mapping between a plurality of amplitude levels detected during the time slots and binary symbols modulated onto each of the plurality of optical signals detected by the optical receiver interface of the second node.

Images