WO2017028873A1

WO2017028873A1 - Interconnection network and method of routing optical signals

Info

Publication number: WO2017028873A1
Application number: PCT/EP2015/068743
Authority: WO
Inventors: Antonio D'errico; Luca Giorgi; Francesco Testa
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2015-08-14
Filing date: 2015-08-14
Publication date: 2017-02-23

Abstract

An interconnection network 40 comprising: an ingress stage 10 comprising M switch cards 12 each comprising an ingress electrical switch matrix and electrical-to-optical, E-O, conversion apparatus to convert a plurality of electrical signals from the switch matrix into respective optical signals each having a respective one of N wavelengths and to deliver the plurality of optical signals to an optical output 14; an egress stage 30 comprising M switch cards 32 each comprising an optical input 34, an egress electrical switch matrix and optical-to-electrical, O-E, conversion apparatus to convert optical signals each having a respective one of the N wavelengths into respective electrical signals and to deliver the electrical signals to the switch matrix; and an optical shuffle 42 comprising a passive fixed wavelength optical router having a cyclic wavelength response and having M input ports and M output ports, and configured to receive a plurality of optical signals at one of the input ports and to route each of said optical signals from the input port to a respective one of the output ports according to the wavelength of each optical signal, the plurality of wavelengths, N, is greater than the plurality, M, of input ports or output ports and the router is configured to route optical signals having each M^th one of the wavelengths from the selected optical shuffle input port to a same one of the output ports.

Description

INTERCONNECTION NETWORK AND METHOD OF ROUTING OPTICAL SIGNALS

Technical Field

The invention relates to an interconnection network and to a data centre comprising the interconnection network. The invention further relates to a method of routing optical signals.

Background

Datacom networks have rapidly evolved over the last decade with new requirements that demand more and more data bandwidth and more services than ever before. To fulfil the new requirements a crucial aspect is the availability of high bandwidth, low cost and scalable intra-datacentre interconnections. In conventional data centres the 1 GbE cables that connect servers to the switches present a data bottleneck that needs to be overcome. The data centre network architecture is evolving from a typical 'three-tier' architecture, composed of three layers of switches, namely access, aggregate and core, to a simpler and flatter architecture, referred to as 'spine and leaf, in which the servers of the data centre are connected to each other and interconnected to the core transport switching layer for communication between data centres. This architecture is much more effective in terms of latency, power consumption, bandwidth and scalability since the amount of data exchanged between the servers (east-west traffic) is currently much larger than the amount of traffic sent outside the data centre (north-south traffic). The spine and leaf network architecture is based on high capacity layer two, L2, switches implemented with a three stage Clos architecture, as first reported by Charles Clos, "A study of non-blocking switching networks", Bell System Technical Journal, March 1953, page 406. The high capacity L2 switches are characterized to have line cards with up to 1 Terabit throughput. An example of a data centre network is shown in Figure 1 , in which a large number of servers and storage equipment are interconnected through a high capacity Ethernet switch designed with a three stage Clos interconnection network fabric.

Currently, the I/O ports of L2 switches operating at data capacities of 10GbE and beyond (40 - 100 GbE, IEEE 802.3ba) are interconnected to the servers with optical fibres rather than electrical Ethernet cables; each optical fibre carrying a single grey optics signal generated normally by vertical-cavity surface-emitting laser, VCSEL, parallel optics interfaces. The number of I/O ports determines the number of optical fibres that are required. For a Clos matrix constructed from 12 network fabric switch, NFX, cards, having 8 switch cards in the 1^st and 3rd stages and 4 switch cards in the 2nd stage, two optical shuffles are necessary to interlace 384 bidirectional optical fibre interconnects between the 1st/3rd stage and the 2nd stage; the overall number of interconnected fibres required is 1536 (768 between the optical shuffles and the 1st/3rd stage and other 768 between the optical shuffles and the second stage). Unfortunately, the number of the optical shuffle interconnections increases with the number of interconnected switch cards.

Various solutions for simplifying the interconnection between switch cards have been proposed. For example, all electrical interconnection network fabrics in which both the switches and the interconnection are electrical. However these suffer from an electrical bottleneck which means they are not a viable solution for data signal rates of 10 Gbps and beyond. All optical interconnection network fabrics have also been proposed in which both the switches and the interconnection between the switches are optical. However, insertion losses in the optical switches dominate and require optical signal regeneration, and to achieve a scalable three stage Clos matrix architecture, inter-stage wavelength converters are needed. All these aspects restrict the practical feasibility of all-optical switching equipment due to the drawbacks in terms of footprint, cost and power consumption. To address these issues, hybrid interconnection network fabrics, in the form of electrical Ethernet switches plus optical interconnections, have been proposed. The main drawback of hybrid network fabrics is the high number of fibres needed. Each optical interconnection is supported by at least two fibres, each one carrying a single channel; one for each connection direction between the switch cards. A further approach which has been proposed is space division multiplexing in which multiple optical interconnection signals are spatially multiplexed in multicore optical fibres, MCF. The MCF must be designed to strictly match the physical characteristics of the emitting VCSEL in order to efficiently harvest the transmitted optical signal from each optical source into the respective core of the MCF. Otherwise, due to the immaturity of the MCF technology, no light can propagate with acceptable loss and crosstalk in a multimode MCF. Optical interconnections can be realized with a properly integrated structure, i.e. VCSEL plus vertically coupled MCF, but only short reaches can be covered with acceptable penalty and only if the MCF is not overly bent or stressed. Vibrations or thermal excursion can also significantly change the crosstalk between adjacent cores destroying the optical interconnection.

Summary

It is an object to provide an improved interconnection network. It is a further object to provide an improved a data centre. It is a further object to provide an improved method of routing optical signals.

A first aspect of the invention provides an interconnection network comprising an ingress stage, an egress stage and an optical shuffle. The ingress stage comprises a plurality, M, of switch cards each comprising an ingress electrical switch matrix and electrical-to- optical, E-O, conversion apparatus. The E-0 conversion apparatus is arranged to convert a plurality of electrical signals output from the ingress electrical switch matrix into respective optical signals each having a respective one of a plurality, N, of wavelengths and to deliver the plurality of optical signals to an optical output. The egress stage comprises a plurality, M, of switch cards each comprising an optical input, an egress electrical switch matrix and optical-to-electrical, O-E, conversion apparatus. The O-E conversion apparatus is arranged to convert a plurality of optical signals each having a respective one of the plurality, N, of wavelengths received from the optical input into respective electrical signals and to deliver the electrical signals to the egress electrical switch matrix. The optical shuffle is connected between the ingress stage switch cards and the egress stage switch cards. The optical shuffle comprises a passive fixed wavelength optical router having a cyclic wavelength response and having a plurality, M, of input ports, each connected to a respective switch card, and a plurality, M, of output ports, each connected to a respective switch card. The optical shuffle is configured to receive the plurality of optical signals at a selected one of the optical shuffle input ports and is configured to route each of the plurality of optical signals from the selected optical shuffle input port to a respective one of the optical shuffle output ports according to the wavelength of each optical signal. The plurality of wavelengths, N, is greater than the plurality, M, of optical shuffle input ports or optical shuffle output ports. The passive fixed wavelength optical router is configured to route optical signals having each M^th one of the plurality of wavelengths from the selected optical shuffle input port to a same one of the optical shuffle output ports.

The interconnection network may replace the prior art short-reach interconnection shuffling, realized using spatially separate, interlaced optical fibre links, with wavelength division de/multiplexed links. Instead of shuffling optical fibres, the optical links are carried by different wavelengths and these are de/multiplexed in a passive fixed wavelength optical router having a cyclic nature and a limited number of input and output ports, being less than the number of wavelengths. Configuring each passive fixed wavelength optical router in this way may enable strictly no-blocking switching operation to be achieved without the need of several multiplexing/demultiplexing stages. The interconnection network may therefore have a significantly reduced number of optical links compared to prior art network fabrics. As the interconnection network uses wavelength multiplexing any increase in the number of outputs from an electrical switch matrix simply causes an increase of the number of used wavelengths without affecting the number of physical interconnection input/output ports of the optical shuffles. The physical layer of the interconnection network may be fixed and completely passive without the need of any intelligence functionality to be operative. The interconnection network may be transparent to the overall switch card capacity since a change in the number of electrical switch matrix outputs simply changes the number of optical signals and requires no change in the number of optical outputs or in the number of optical shuffle input ports or output ports. By maintaining the same interconnection network structure low cost CAPEX and OPEX footprint and power consumption may be maintained and interconnection network may require a limited manual intervention, several orders of magnitude lower than required by the prior art network fabrics. The plurality of optical signals received at the selected one of the optical shuffle input ports may all be received at the same time or may be received at different times.

In an embodiment, each ingress electrical switch matrix comprises a plurality, N, of electrical output ports. The E-0 conversion apparatus is arranged to convert an electrical signal output from a respective electrical output port into a said respective optical signal.

In an embodiment, each egress electrical switch matrix comprises a plurality, N, of electrical input ports. The O-E conversion apparatus is arranged to deliver each said electrical signal to a respective one of the electrical input ports.

In an embodiment, each electrical switch matrix is an electrical packet switch matrix. In an embodiment, each ingress switch card is configured to receive input electrical signals.

In an embodiment, each ingress switch card is configured to receive input optical signals and each ingress switch card further comprises O-E conversion apparatus arranged to convert the input optical signals into corresponding electrical signals for delivery to the respective ingress electrical switch matrix.

In an embodiment, the cyclic wavelength response of the passive fixed wavelength optical router has a free spectral range, FSR, and the passive fixed wavelength optical router is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ. Each FSR of the cyclic wavelength response covers a group of optical signal wavelength consisting of a plurality, M, of the plurality of optical signal wavelengths and there is no spectral gap between adjacent groups of optical signal wavelengths. The passive fixed wavelength optical router may process a wavelength division multiplexed, WDM, comb of optical signals with a channel spacing, Δλ, and with an FSR = Μ-Δλ, and may continuously cover the full optical wavelength transmission bands, S, C and L bands, which can be used by the switch cards.

In an embodiment, the passive fixed wavelength optical router is an MxM cyclic arrayed waveguide grating, AWG. The plurality of optical signal wavelengths are optical channel wavelengths of the MxM cyclic AWG.

In an embodiment, the interconnection network further comprises an intermediate stage and a second said optical shuffle. The intermediate stage comprises a plurality, M, of switch cards provided logically between the ingress stage and the egress stage. Each switch card of the intermediate stage comprises an electrical switch matrix, an optical input, an optical output, O-E conversion apparatus and E-0 conversion apparatus. The O-E conversion apparatus is arranged to convert a plurality of optical signals each having a respective one of the plurality, N, of wavelengths received from the optical input into a respective electrical signal and to deliver the electrical signals to the electrical switch matrix. The E-0 conversion apparatus is arranged to convert a plurality of electrical signals output from the electrical switch matrix into respective optical signals each having a respective one of the plurality of wavelengths and to deliver the plurality of optical signals to the optical output. The ingress stage, the egress stage and the intermediate stage are arranged in a Clos network architecture. The optical shuffle is connected between the ingress stage switch cards and the intermediate stage switch cards and the second optical shuffle is connected between the intermediate stage switch cards and the egress stage switch cards. Each passive fixed wavelength optical router is configured to route an optical signal having a j^th wavelength of the plurality, N, of wavelengths from an i^th input port of the plurality, M, of optical shuffle input ports to a k^th output port of the plurality, M, of optical shuffle output ports according to the relationship k = j|_M + (i-1 )·

The interconnection network may implement a three stage Clos network for a strictly no-blocking switch matrix.

In an embodiment, the interconnection network comprises at least one further said intermediate stage and at least one further optical shuffle. An interconnection network comprising a higher number of switch stages may be provided, having a higher switching capacity. The interconnection network may implement a multistage Clos network for a strictly no-blocking switch matrix.

In an embodiment, each E-0 conversion apparatus comprises a plurality of E-0 converters and an optical multiplexer. Each E-0 converter is arranged to convert a respective electrical signal into a corresponding optical signal at a respective one of the plurality of wavelengths. The optical multiplexer is arranged to route each of the optical signals to the optical output. Each O-E conversion apparatus comprises a plurality of O-E converters and an optical demultiplexer arranged to route each optical signal to a respective one of the O-E converters. Each O-E converter is arranged to convert the respective optical signal into a corresponding electrical signal. Each input port of each passive fixed wavelength optical router is connected to the optical output of a respective switch card by a single respective optical waveguide and each output port of each passive fixed wavelength optical router is connected to the optical input of a respective switch card by a single respective optical waveguide.

The interconnection network may replace the prior art short-reach interconnection networks, using spatially separate, interlaced optical fibre links, with wavelength division de/multiplexed optical waveguide links. Instead of shuffling optical fibres, the optical links are carried by different wavelengths on a single optical waveguide per switch card. The interconnection network may therefore have a significantly reduced number of optical links compared to prior art network fabrics.

In an embodiment, a plurality, L, of the ingress stage switch cards each comprise a plurality, L, of optical outputs. The respective E-0 conversion apparatus of each of said plurality, L, of ingress stage cards additionally comprises a plurality, L, of optical multiplexers, each arranged to route a plurality of optical signals each having a respective one of a plurality of the plurality, N, of wavelengths to a respective one of the plurality of optical outputs. The interconnection network further comprises a plurality, L, of optical band multiplexers provided between the plurality of the ingress stage switch cards and the optical shuffle. Each optical band multiplexer comprises an optical output and a plurality, L, of optical inputs each connected to a respective optical output of the ingress stage switch cards by a single respective optical waveguide. The optical output of each optical band multiplexer is connected to a respective input port of the optical shuffle by a single respective optical waveguide.

This may enable groups of wavelengths to be routed to different optical shuffle input ports, which may further improve interconnection network scalability.

In an embodiment, each optical waveguide is one of a planar waveguide, a core of a single mode optical fibre, a core of a multimode optical fibre, or one of a plurality of cores of a multicore optical fibre. The interconnection network may replace the prior art short-reach interconnection networks, using spatially separate, interlaced optical fibre links, with wavelength division de/multiplexed optical waveguide links. Instead of shuffling optical fibres, the optical links are carried by different wavelengths on a single optical waveguide per switch card. The interconnection network may therefore have a significantly reduced number of optical connections, being optical fibres or planar waveguides, compared to prior art network fabrics. The interconnection network may therefore offer a significant reduction in optical fibre cabling cost and complexity as compared to prior art network fabrics.

In an embodiment, each switch card is configured for bidirectional operation and each input port and each output port an input/output, I/O, ports. Each optical shuffle is configured for bidirectional operation. Each ingress switch card further comprises O-E conversion apparatus, each egress switch card further comprises E-0 conversion apparatus. Each optical shuffle is configured to route a plurality of optical signals in a direction from the ingress stage to the egress stage and each optical shuffle is configured to route a plurality of optical signals in a reverse direction, from the egress stage to the ingress stage. Each optical shuffle is configured to receive a plurality of optical signals at a selected one of the optical shuffle I/O ports connect to the egress stage and is configured to route each of the plurality of optical signals from the selected optical shuffle I/O port to a respective one of the optical shuffle I/O ports connected to the ingress stage according to the wavelength of each optical signal.

In an embodiment, each passive fixed wavelength optical router is configured to route an optical signal being transmitted from the ingress stage to the egress stage having a j^th wavelength of the plurality, N , of wavelengths from an i^th I/O port of the plurality, M, of optical shuffle I/O ports on an ingress stage side of the optical shuffle to a k^th I/O port of the plurality, M, of optical shuffle I/O ports on an egress stage side of the optical shuffle according to the relationship k = j|_M + (i-1 ). Each passive fixed wavelength optical router is configured to route an optical signal being transmitted in the reverse direction, from the egress stage to the ingress stage, having a j^th wavelength of the plurality, N, of wavelengths from a k^th I/O port of the plurality, M, of optical shuffle I/O ports on the egress stage side to an i^th I/O port of the plurality, M, of optical shuffle I/O ports on the ingress stage side according to the relationship k = j|_M + (i-1 ).

The interconnection network may enable a low fibre count interconnection, low footprint, and low power consumption by using a bidirectional, passive and fixed cyclic optical shuffle to implement the multistage Clos interconnection for strictly no blocking switch.

In an embodiment, the interconnection network is an inter-line-card interconnection network. The interconnection network may connect electrical line cards or optical line cards.

A second aspect of the invention provides a data centre network comprising a plurality of data servers and an interconnection network. The interconnection network comprises an ingress stage, an egress stage and an optical shuffle. The ingress stage comprises a plurality, M, of switch cards each comprising an ingress electrical switch matrix and electrical-to-optical, E-O, conversion apparatus. The E-0 conversion apparatus is arranged to convert a plurality of electrical signals output from the ingress electrical switch matrix into respective optical signals each having a respective one of a plurality, N, of wavelengths and to deliver the plurality of optical signals to an optical output. The egress stage comprises a plurality, M, of switch cards each comprising an optical input, an egress electrical switch matrix and optical-to-electrical, O-E, conversion apparatus. The O-E conversion apparatus is arranged to convert a plurality of optical signals each having a respective one of the plurality, N, of wavelengths received from the optical input into respective electrical signals and to deliver the electrical signals to the egress electrical switch matrix. The optical shuffle is connected between the ingress stage switch cards and the egress stage switch cards. The optical shuffle comprises a passive fixed wavelength optical router having a cyclic wavelength response and having a plurality, M, of input ports, each connected to a respective switch card, and a plurality, M, of output ports, each connected to a respective switch card. The optical shuffle is configured to receive the plurality of optical signals at a selected one of the optical shuffle input ports and is configured to route each of the plurality of optical signals from the selected optical shuffle input port to a respective one of the optical shuffle output ports according to the wavelength of each optical signal. The plurality of wavelengths, N, is greater than the plurality, M, of optical shuffle input ports or optical shuffle output ports. The passive fixed wavelength optical router is configured to route optical signals having each M^th one of the plurality of wavelengths from the selected optical shuffle input port to a same one of the optical shuffle output ports.

The interconnection network may replace the prior art short-reach interconnection shuffling, realized using spatially separate, interlaced optical fibre links, with wavelength division de/multiplexed links. Instead of shuffling optical fibres, the optical links are carried by different wavelengths and these are de/multiplexed in a passive fixed wavelength optical router having a cyclic nature and a limited number of input and output ports, being less than the number of wavelengths. Configuring each passive fixed wavelength optical router in this way may enable strictly no-blocking switching operation to be achieved without the need of several multiplexing/demultiplexing stages. The interconnection network may therefore have a significantly reduced number of optical links compared to prior art network fabrics. As the interconnection network uses wavelength multiplexing any increase in the number of outputs from an electrical switch matrix simply causes an increase of the number of used wavelengths without affecting the number of physical interconnection input/output ports of the optical shuffles. The physical layer of the interconnection network may be fixed and completely passive without the need of any intelligence functionality to be operative. The interconnection network may be transparent to the overall switch card capacity since a change in the number of electrical switch matrix outputs simply changes the number of optical signals and requires no change in the number of optical outputs or in the number of optical shuffle input ports or output ports. By maintaining the same interconnection network structure low cost CAPEX and OPEX footprint and power consumption may be maintained and interconnection network may require a limited manual intervention, several orders of magnitude lower than required by the prior art network fabrics.

The plurality of optical signals received at the selected one of the optical shuffle input ports may all be received at the same time or may be received at different times.

In an embodiment, each electrical switch matrix is an electrical packet switch matrix.

In an embodiment, each ingress switch card is configured to receive input electrical signals.

In an embodiment, the cyclic wavelength response of the passive fixed wavelength optical router has a free spectral range, FSR, and the passive fixed wavelength optical router is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ. Each FSR of the cyclic wavelength response covers a group of optical signal wavelength consisting of a plurality, M, of the plurality of optical signal wavelengths and there is no spectral gap between adjacent groups of optical signal wavelengths. The passive fixed wavelength optical router may process a wavelength division multiplexed, WDM, comb of optical signals with a channel spacing, Δλ, and with an FSR = Μ-Δλ, and may continuously cover the full the full optical wavelength transmission bands, S, C and L bands, which can be used by the switch cards.

In an embodiment, each passive fixed wavelength optical router is configured to route an optical signal being transmitted from the ingress stage to the egress stage having a j^th wavelength of the plurality, N , of wavelengths from an i^th I/O port of the plurality, M , of optical shuffle I/O ports on an ingress stage side of the optical shuffle to a k^th I/O port of the plurality, M, of optical shuffle I/O ports on an egress stage side of the optical shuffle according to the relationship k = j|_M + (i-1 ). Each passive fixed wavelength optical router is configured to route an optical signal being transmitted in the reverse direction, from the egress stage to the ingress stage, having a j^th wavelength of the plurality, N, of wavelengths from a k^th I/O port of the plurality, M, of optical shuffle I/O ports on the egress stage side to an i^th I/O port of the plurality, M, of optical shuffle I/O ports on the ingress stage side according to the relationship k = j|_M + (i-1 ).

In an embodiment, the data centre network further comprises at least one data storage device and/or at least one core network router.

In an embodiment, each data server, each data storage device and each core network router comprises a line-card.

A third aspect of the invention provides a method of routing optical signals. The method comprises steps a. and b. Step a. comprises receiving a plurality of optical signals at one of a plurality, M, of input ports of a passive fixed wavelength optical router having a cyclic wavelength response and comprising a plurality, M, of output ports. Each of the plurality of optical signals has a respective one of a plurality, N, of wavelengths, and the plurality of wavelengths, N, is greater than the plurality, M, of input ports or output ports. Step b. comprises routing each optical signal from the input port to a respective one of the output ports according to the wavelength of the optical signal. Optical signals having each M^th one of the plurality of wavelengths are routed from the input port to a same one of the output ports.

The method may enable prior art short-reach interconnection network shuffling, realized using spatially separate, interlaced optical fibre links, to be replaced with wavelength division de/multiplexed links. Instead of shuffling optical fibres, the method may enable optical links to be carried by different wavelengths and these are de/multiplexed in a passive fixed wavelength optical router having a cyclic nature and a limited number of input and output ports, being less than the number of wavelengths. The method may enable strictly noblocking switching operation to be achieved without the need of several multiplexing/demultiplexing stages. The method may enable an interconnection network to have a significantly reduced number of optical links compared to prior art network fabrics. By using wavelength multiplexing any increase in the number of outputs from an electrical switch matrix simply causes an increase of the number of used wavelengths without affecting the number of physical interconnection input/output ports of the optical shuffles.

In an embodiment, the cyclic wavelength response of the passive fixed wavelength optical router has a free spectral range, FSR, and the passive fixed wavelength optical router is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ, and wherein each FSR of the cyclic wavelength response covers a group of optical signal wavelength consisting of a plurality, M, of said plurality of optical signal wavelengths and there is no spectral gap between adjacent groups of optical signal wavelengths. The method may enable a wavelength division multiplexed, WDM, comb of optical signals with a channel spacing, Δλ, and with an FSR = M- Δλ, to be routed and may continuously cover the full optical wavelength transmission bands, S, C, and L bands, which can be used by the switch cards.

In an embodiment, the passive fixed wavelength optical router is an MxM cyclic arrayed waveguide grating, AWG, and said plurality of optical signal wavelengths are optical channel wavelengths of the MxM cyclic AWG.

In an embodiment, step b. comprises routing an optical signal having a j^th wavelength of said plurality, N, of wavelengths from an i^th input port of said plurality, M, of input ports to a k^th output port of said plurality, M, of output ports according to the relationship k = j|_M + (i-1 )·

A fourth aspect of the invention provides a method of routing data traffic in a data centre network. The method comprises steps i. to iii. Step i. comprises receiving a plurality of input electrical signals each carrying data traffic at an ingress electrical switch matrix and routing each input electrical signal across the ingress electrical switch matrix. Step i. additionally comprises converting each input electrical signal output from the ingress electrical switch matrix into a respective optical signal having a respective one of a plurality, N, of wavelengths, and delivering each optical signal to an optical output. Step ii. comprises routing the plurality of optical signals output at step i. according to the following steps a. and b. Step a. comprises receiving the plurality of optical signals at one of a plurality, M, of input ports of a passive fixed wavelength optical router having a cyclic wavelength response and comprising a plurality, M, of output ports. Each of the plurality of optical signals has a respective one of a plurality, N, of wavelengths, and the plurality of wavelengths, N, is greater than the plurality, M, of input ports or output ports. Step b. comprises routing each optical signal from the input port to a respective one of the output ports according to the wavelength of the optical signal. Optical signals having each M^th one of the plurality of wavelengths are routed from the input port to a same one of the output ports. Step iii. comprises converting each of the plurality of optical signals output from step ii. into a respective output electrical signal and routing each output electrical signal across an egress electrical switch matrix.

The method may enable prior art short-reach interconnection network shuffling, realized using spatially separate, interlaced optical fibre links, to be replaced with wavelength division de/multiplexed links. Instead of shuffling optical fibres, the method may enable optical links to be carried by different wavelengths and these are de/multiplexed in a passive fixed wavelength optical router having a cyclic nature and a limited number of input and output ports, being less than the number of wavelengths. The method may enable strictly no- blocking switching operation to be achieved without the need of several multiplexing/demultiplexing stages. The method may enable an interconnection network to have a significantly reduced number of optical links compared to prior art network fabrics. By using wavelength multiplexing any increase in the number of outputs from an electrical switch matrix simply causes an increase of the number of used wavelengths without affecting the number of physical interconnection input/output ports of the optical shuffles.

In an embodiment, step iii. comprises converting each of the plurality of optical signals output from step ii. into a respective intermediate electrical signal routing each intermediate electrical signal across an intermediate electrical switch matrix, and converting each intermediate electrical signal output from the intermediate electrical switch matrix into a respective further optical signal having a respective one of the plurality, N, of wavelengths. Step iii. comprises delivering the plurality of further optical signals to a second optical output and routing the plurality of further optical signals according to the steps a. and b. Step iii. comprises converting each of the plurality of optical signals output from step b. into a respective output electrical signal and routing each output electrical signal across the egress electrical switch matrix.

In an embodiment, the cyclic wavelength response of the passive fixed wavelength optical router has a free spectral range, FSR, and the passive fixed wavelength optical router is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ, and wherein each FSR of the cyclic wavelength response covers a group of optical signal wavelength consisting of a plurality, M, of said plurality of optical signal wavelengths and there is no spectral gap between adjacent groups of optical signal wavelengths. The method may enable a wavelength division multiplexed, WDM, comb of optical signals with a channel spacing, Δλ, and with an FSR = Μ-Δλ, to be routed and may continuously cover the full the full optical wavelength transmission bands, S, C and L bands, which can be used by the switch cards.

A fifth aspect of the invention provides a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement any of the above steps of the method of routing optical signals.

A sixth aspect of the invention provides a carrier containing a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement any of the above steps of the method of routing optical signals. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

A seventh aspect of the invention provides a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement any of the above steps of the method of routing data traffic in a data centre network.

An eighth aspect of the invention provides a carrier containing a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement any of the above steps of the method of routing data traffic in a data centre network. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

Brief Description of the drawings

Figure 1 is a schematic representation of a prior art interconnection network connecting servers and storage in a data centre;

Figure 2 is a schematic representation of an interconnection network according to an embodiment of the invention; Figure 3 is a schematic representation of an interconnection network according to an embodiment of the invention;

Figure 4 is a schematic representation of an interconnection network according to an embodiment of the invention;

Figure 5 is a schematic representation of an interconnection network according to an embodiment of the invention;

Figure 6 illustrates the routing of optical signals across the MxM AWG of Figure 5, in the direction from the ingress stage to the egress stage;

Figure 7 illustrates the routing of optical signals across the MxM AWG of Figure 5, in the direction from the egress stage to the ingress stage;

Figure 8 is a schematic representation of an interconnection network according to an embodiment of the invention;

Figure 9 illustrates the routing of optical signals across the first 4x4 AWG of Figure 6, in a) the direction from the ingress stage switch cards, SC, to the four ports of the AWG and b) in the reverse direction;

Figure 10 illustrates a reduction in the number of interconnecting optical fibres required by the interconnection network of Figure 8 compared to the prior art;

Figure 1 1 is a schematic representation of a switch card in the ingress stage or the egress stage of the interconnection network of Figure 8, for transmission from the switch card to the respective AWG;

Figure 12 is a schematic representation of a switch card in the ingress stage or the egress stage of the interconnection network of Figure 8, for transmission from the respective AWG to the switch card;

Figure 13 is a schematic representation of a switch card in the intermediate stage of the interconnection network of Figure 8, configured for transmission in one direction, for example from the ingress stage to the egress stage;

Figure 14 is a schematic representation of a switch card in the intermediate stage of the interconnection network of Figure 8, configured for bidirectional transmission, between the ingress stage and the egress stage;

Figure 15 is a schematic representation of a further switch card in the ingress stage or the egress stage of the interconnection network of Figure 8, configured for bidirectional transmission;

Figure 16 is a schematic representation of a further switch card in the intermediate stage of the interconnection network of Figure 8, configured for bidirectional transmission;

Figure 17 is a schematic representation of a WDM multiple transceiver of the switch card of Figure 15 or Figure 16;

Figure 18 is a schematic representation of transceiver of the WDM multiple transceiver of Figure 17; Figure 19 is a schematic representation of an interconnection network according to an embodiment of the invention;

Figure 20 is a schematic representation of data centre network according to an embodiment of the invention;

Figure 21 illustrates the steps of a method according to an embodiment of the invention of routing optical signals;

Figure 22 illustrates the steps of a method according to an embodiment of the invention of routing optical signals;

Figure 23 illustrates the steps of a method according to an embodiment of the invention of routing optical signals; and

Figure 24 illustrates the steps of a method according to an embodiment of the invention of routing data traffic in a data centre network.

Detailed description

The same reference numbers will used for corresponding features in different embodiments.

Referring to Figure 2, an embodiment of the invention provides an interconnection network 40 comprising an ingress stage 10, an egress stage 30 and an optical shuffle 42. The ingress stage 10 comprises a plurality, M, of switch cards 12 each comprising an ingress electrical switch matrix and electrical-to-optical, E-O, conversion apparatus. Each E-0 conversion apparatus is arranged to convert a plurality of electrical signals output from the ingress electrical switch matrix of the respective switch card 12 into respective optical signals and to deliver the plurality of optical signals to an optical output 14. Each of the plurality of optical signals generated by each E-0 conversion apparatus has a respective one of a plurality, N, of wavelengths; a plurality of optical signals, each having a respective one of the plurality of wavelengths, are therefore output from the respective optical output 14 of each switch card 12.

The egress stage 30 comprises a plurality, M, of switch cards 32 each comprising an optical input 34, an egress electrical switch matrix and optical-to-electrical, O-E, conversion apparatus. Each O-E conversion apparatus is arranged receive a plurality of optical signals from the optical input of the respective switch card. Each optical signal has a respective one of the plurality, N, of wavelengths. Each O-E conversion apparatus is arranged to convert each of the plurality of optical signals into a respective electrical signal and to deliver the plurality of electrical signals to the egress electrical switch matrix.

The optical shuffle 42 is connected between the ingress stage switch cards 12 and the egress stage switch cards 32. The optical shuffle 42 comprises a passive fixed wavelength optical router, referred to herein simply as an optical router, having a cyclic wavelength response and having a plurality, M, of input ports 46 and a plurality, M, of output ports 48. Each input port of the optical shuffle/optical router is connected to a respective switch card 12 of the ingress stage 10. Each output port of the optical shuffle/optical router is connected to a respective switch card 32 of the egress stage. Each optical shuffle input port 46 is configured to receive the plurality of optical signals from the respective ingress stage switch card 12. The optical shuffle 42 is configured to route each of the plurality of optical signals from the selected optical shuffle input port to a respective one of the optical shuffle output ports 48 according to the wavelength of each optical signal.

The plurality of wavelengths, N, is greater than the plurality, M , of optical shuffle input ports or optical shuffle output ports. The passive fixed wavelength optical router is configured to route optical signals having each M^th one of the plurality of wavelengths from the selected optical shuffle input port to a same one of the optical shuffle output ports. So, for example, the first wavelength is routed from the first input port to the first output port, the second wavelength is routed from the first input port to the second output port, the third wavelength is routed from the first input port to the third output port and so on up to the M^th wavelength which is routed to the M^th output port. The (1 +M)^th wavelength is routed from the first input port to the first output port, the (2+M)^th wavelength is routed from the first input port to the second output port, and so on cyclically up to the N^th wavelength.

In an embodiment, each ingress stage switch card 12 is configured for bidirectional operation and each egress stage switch card 32 is configured for bidirectional operation. Each input port and each output port is an input/output, I/O, port. The passive fixed wavelength optical router of the optical shuffle 42 is configured for bidirectional operation. Each ingress switch card 12 further comprises O-E conversion apparatus and each egress switch card 32 further comprises E-0 conversion apparatus. The optical shuffle is configured to route a plurality of optical signals in a direction from the ingress stage 10 to the egress stage 30 and to route a plurality of optical signals in a reverse direction, from the egress stage to the ingress stage. The optical shuffle is configured to receive a plurality of optical signals at a selected one of the optical shuffle I/O ports 48 connect to the egress stage 30 and is configured to route each of the plurality of optical signals from the selected optical shuffle I/O port to a respective one of the optical shuffle I/O ports 46 connected to the ingress stage according to the wavelength of each optical signal.

In a further embodiment, the cyclic wavelength response of the passive fixed wavelength optical router has a free spectral range, FSR, and is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ. Each FSR of the cyclic wavelength response covers a group of optical signal wavelengths consisting of a plurality, M, of the N optical signal wavelengths. There is no spectral gap between adjacent groups of optical signal wavelengths.

An embodiment of the invention provides an interconnection network 50, as illustrated in Figure 3, which is similar to the interconnection network 10, with the following modifications. In this embodiment, the passive fixed wavelength optical router is a cyclic arrayed waveguide grating 52 having M input ports 46 and M output ports 48, referred to as an MxM cyclic AWG. The plurality, N, of optical signal wavelengths are optical channel wavelengths of the MxM cyclic AWG. The cyclic response of the AWG 52 has a free spectral range, FSR, and is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ. Each FSR covers a plurality, M, of the N optical signal wavelengths, giving the AWG an FSR of M Δλ. There is no spectral gap FSRs, i.e. between adjacent groups of M optical signal wavelengths.

Figure 4 shows an interconnection network 60 which is similar to the interconnection network 10, with the following modifications. In this embodiment, the interconnection network additionally comprises an intermediate stage 20 and a second optical shuffle 44.

The intermediate stage comprises a plurality, M, of switch cards 22 provided logically between the ingress stage 10 and the egress stage 30. Each switch card 22 of the intermediate stage comprises an electrical switch matrix, an optical input 24, an optical output 26, O-E conversion apparatus and E-0 conversion apparatus.

Each O-E conversion apparatus is arranged to convert a plurality of optical signals each having a respective one of the plurality, N, of wavelengths received from the optical input 24 of the respective switch card 22 into a respective electrical signal and to deliver the electrical signals to the electrical switch matrix. Each E-0 conversion apparatus is arranged to convert a plurality of electrical signals output from the electrical switch matrix of the respective switch card 22 into respective optical signals each having a respective one of the plurality of wavelengths and to deliver the plurality of optical signals to the optical output 26.

The ingress stage 10, the egress stage 30 and the intermediate stage 20 are arranged in a Clos network architecture. The optical shuffle 42 is connected between the ingress stage switch cards 12 and the intermediate stage switch cards 22 and the second optical shuffle 44 is connected between the intermediate stage switch cards 22 and the egress stage switch cards 32. Each input port 46 of the optical shuffle 42 is configured to receive the plurality of optical signals output from the respective ingress stage switch card 12. Each input port 46 of the second optical shuffle 44 is configured to receive the plurality of optical signals output from the respective intermediate stage switch card 22. Each optical shuffle 42, 44 is configured to route each of the plurality of optical signals from the selected optical shuffle input port 46 to a respective one of the optical shuffle output ports 48 according to the wavelength of each optical signal.

Figure 5 shows an interconnection network 70 which is similar to the interconnection network 60 of the previous embodiment, with the following modifications. In this embodiment, each optical shuffle is an MxM cyclic AWG 52, 54. Using a cyclic MxM AWG with a proper FSR equal to Μ Δλ as optical shuffle enables direct connections between optical links pertinent to different switch cards.

Each ingress stage switch card 12 is configured for bidirectional operation, each intermediate stage switch card 22 is configured for bidirectional operation and each egress stage switch card 32 is configured for bidirectional operation. Each input port and each output port is an input/output, I/O, port. Each MxM cyclic AWG 52, 54 is configured for bidirectional operation. Each ingress switch card 12 further comprises O-E conversion apparatus and each egress switch card 32 further comprises E-0 conversion apparatus.

Each MxM AWG 52, 54 is configured to route a plurality of optical signals in a direction from the ingress stage 10 towards the egress stage 30 and to route a plurality of optical signals in a reverse direction, from the egress stage towards the ingress stage.

Figure 6 illustrates the wavelength distribution at each port of an MxM AWG 52, 54 when M WDM combs of N wavelengths are received on a first side of the AWG. Each MxM AWG 52, 54 is configured to route an optical signal, having a j^th wavelength of the plurality, N, of wavelengths, being transmitted from the ingress stage towards the egress stage from an i^th I/O port of the plurality, M, of optical shuffle I/O ports 46 on a first side to a k^th I/O of the plurality, M, of optical shuffle I/O ports 48 on a second side of the MxM AWG according to the relationship

k = j|_M + (i-1 ).

As illustrated in Figure 7, each MxM AWG is additionally configured to route an optical signal being transmitted in the reverse direction, from the egress stage towards the ingress stage, from a k^th I/O port of the plurality, M, of optical shuffle I/O ports 48 on the second side to an i^th I/O port of the plurality, M, of optical shuffle I/O ports 46 on the first side according to the relationship

k = j|_M + (i-1 ),

where j is the wavelength of the optical signal. The j|_M, j modulo M , value represents the cyclic nature of the MxM AWG.

Figure 8 shows an interconnection network 80 which is similar to the interconnection network 70 of the previous embodiment, with the following modifications. In this embodiment, each of the ingress stage 10, the intermediate stage 20 and the egress stage 30 comprises four switch cards 66, 68, 72. Each optical shuffle is a 4x4 cyclic AWG 62, 64. Each optical signal generated at each switch card 66, 68, 72 has one of 48 wavelengths. From each switch card of the ingress stage 10 and the egress stage 30 a single optical fibre carries a WDM bidirectional comb of 48 wavelengths from/toward the optical shuffle, AWG 62, 64. The 48 wavelengths are able to be the same for all of the switch cards. From each switch card 68 of the intermediate stage two optical fibre are used to carry two equal WDM bidirectional combs of 48 wavelengths, to and from the ingress and egress stages.

Each I/O port of each 4x4 AWG 62, 64 is connected to the optical I/O port of a respective switch card 66, 68, 72 by a single respective optical fibre 89 and each I/O port of each 4x4 AWG is connected to the optical I/O port of a respective switch card by a single respective optical fibre 89.

The three stages of the interconnection network 80, namely the ingress stage 10, the intermediate stage 20 and the egress stage 30, are arranged in a three stage Clos architecture to provide a strictly no-blocking interconnection network. The interconnection network 80 provides:

a) Transformation of a physical fibre connection by wavelength division multiplexing technology in combination with a cyclic modular optical wavelength router to implement a strictly no blocking switch that tears down the number of interconnecting cables, i.e. fibre patch cords, that are required;

b) Fully operative physical layer without the need of any intelligence and control; c) Highly scalable with any increase in channel capacity;

d) Highly scalable with the number of I/O ports on the interconnected switch cards.

The interconnection network 80 is based on multiplexing a plurality of optical signals, each carrying a respective communications traffic flow, on a single waveguide or fibre core thus reducing the number of fibre necessary to interconnect the switch cards with the AWG. Single mode optical fibres may be used to enable bidirectional propagation between the AWGs and the switch cards, to further reduce the number of fibres and simplify the manual configuration and the deployment of fibres in interconnection network. Using a cyclic MxM AWG, wavelength division multiplexing and bidirectional propagation, only one optical fibre is required to connect each switch card with the respective AWG. At each port of the cyclic MxM AWG, N (even much greater than M) different wavelengths can go bi-directionally in and out without interfering.

Figure 9a illustrates the shuffling of the optical signals, according to their wavelengths, as they are routed by the first AWG 62 from the ingress switch cards, SC1 1 , SC12, SC13, SC14, towards the intermediate stage switch cards 68. Figure 9b illustrates the shuffling of the optical signals, according to their wavelengths, as they are routed by the first AWG 62 in the opposite direction, from intermediate stage switch cards SC21 , SC22, SC23, SC24 towards the ingress switch cards, SC1 1 , SC12, SC13, SC14.

Figure 10 illustrates the impact of the interconnection network 80 as compared to prior art in terms of fibre count versus switch matrix dimensions, i.e. the number of switch cards in each of the ingress stage and the egress stage. The interconnection system simplification provided by the interconnection network 80 leads to a strong reduction in the number of I/O ports for the switch matrix and in the number of interconnecting fibre cables (around 100 times lower in case of single mode fibre use thanks to bidirectional transmission on the same fibre) while maintaining the switch throughput. The third line of Figure 10 illustrates the number of optical connections within the interconnection network 80, 1536 in this example of 48 wavelengths and four switch cards in each stage, and compares the 16 optical fibres requires by the interconnection network 80 of this embodiment with the 1536 optical fibres that would be required by a prior art network fabric having a three stage Clos fabric with four switch cards in each stage. The interconnection network 80 therefor reduces the number of optical fibres required by a factor of 96. Figure 1 1 illustrates a switch card 66 for use in the egress stage 30 of the interconnection network 80 of Figure 8. The switch card 66 is for transmission from the switch card to the respective AWG.

The switch card 66 comprises an electrical switch matrix 81 and E-0 conversion apparatus 82. The electrical switch matrix 81 has 48 output ports 88. The E-0 conversion apparatus comprises 48 E-0 converters 84 and an optical multiplexer 86. Each E-0 converter is arranged to receive a respective electrical signal from a respective one of the output ports 88 of the electrical switch matrix and is arranged to convert the electrical signal into a corresponding optical signal at a respective one of the 48 wavelengths. The optical multiplexer 86 is arranged to receive the 48 optical signals output from the E-0 converters and is arranged to route the 48 optical signals to the optical output 14.

Figure 12 illustrates a switch card 72 for use in the egress stage 30 of the interconnection network 80 of Figure 8. The switch card 72 is for transmission from the AWG 64 to the switch card.

The switch card 72 comprises an electrical switch matrix 90 and O-E conversion apparatus 92. The electrical switch matrix 90 has 48 input ports 98. The O-E conversion apparatus comprises an optical demultiplexer 96 and 48 O-E converters 94. The optical demultiplexer 96 is arranged to receive optical signals at the 48 wavelengths from the AWG 64 and is arranged to route each of the optical signals to at respective one of the O-E converters. Each O-E converter is arranged to receive a respective optical signal from the demultiplexer 96 and is arranged to convert the optical signal into a corresponding electrical signal, which is delivered to a respective one of the input ports 98 of the electrical switch matrix 90.

Figure 13 illustrates a switch card 68 for use in the intermediate stage 20 of the interconnection network 80 of Figure 8. The switch card 68 is for transmission in the direction from ingress stage to the egress stage, or vice versa.

The intermediate stage switch card 68 comprises an electrical switch matrix 90, an optical input 24, an optical output 26, O-E conversion apparatus 92 and E-0 conversion apparatus 82.

The electrical switch matrix 90 has 48 input ports and 48 output ports. The O-E conversion apparatus 92 comprises an optical demultiplexer 96 and 48 O-E converters 94. The optical demultiplexer 96 is arranged to receive optical signals at the 48 wavelengths from the AWG 62 and is arranged to route each of the optical signals to at respective one of the O- E converters. Each O-E converter is arranged to receive a respective optical signal from the demultiplexer 96 and is arranged to convert the optical signal into a corresponding electrical signal, which is delivered to a respective one of the input ports of the electrical switch matrix 90. The E-0 conversion apparatus comprises 48 E-0 converters 84 and an optical multiplexer 86. Each E-0 converter is arranged to receive a respective electrical signal from a respective one of the output ports of the electrical switch matrix 90 and is arranged to convert the electrical signal into a corresponding optical signal at a respective one of the 48 wavelengths. The optical multiplexer 86 is arranged to receive the 48 optical signals output from the E-0 converters and is arranged to route the 48 optical signals to the optical output 26.

Figure 14 illustrates a switch card 100 for use in the intermediate stage 20 of the interconnection network 80 of Figure 8. The switch card 100 is configured for bidirectional transmission, both in the direction from ingress stage to the egress stage, and vice versa. The switch card 100 of this embodiment is similar to the switch card 68 of the previous embodiment, with the following modifications.

Each of the AWG 62, 64 input ports and each of the AWG output ports are input/output, I/O, ports, and each of the input ports and the output ports of the electrical switch matrix are input/output, I/O, ports. The switch card input 24 is an input/output and the switch card output 26 is an input/output.

The E-0 conversion apparatus 82 additionally comprises an optical demultiplexer 106 and 48 O-E converters 102. The optical demultiplexer 96 is arranged to receive optical signals at the 48 wavelengths from the AWG 62 and is arranged to route each of the optical signals to at respective one of the O-E converters. Each O-E converter 102 is arranged to receive a respective optical signal from the demultiplexer 96 and is arranged to convert the optical signal into a corresponding electrical signal, which is delivered to a respective one of the input ports of the electrical switch matrix 90. The optical multiplexer 86 and the optical demultiplexer 106 are connected to the switch card input/output 26 through a first optical circulator 109.

The O-E conversion apparatus 92 additionally comprises an optical multiplexer 108 and 48 E-0 converters 104. Each E-0 converter 104 is arranged to receive a respective electrical signal from a respective one of the output ports of the electrical switch matrix 90 and is arranged to convert the electrical signal into a corresponding optical signal at a respective one of the 48 wavelengths. The optical multiplexer 108 is arranged to receive the 48 optical signals output from the E-0 converters 104 and is arranged to route the 48 optical signals to the optical input/output 24. The optical multiplexer 108 and the optical demultiplexer 96 are connected to the switch card input/output 24 through a second optical circulator 109.

Figure 15 illustrates an alternative switch card 1 10 for use in the ingress stage 10 or in the egress stage 30 of the interconnection network 80 of Figure 8. The switch card 1 10 is configured for bidirectional operation.

The switch card 1 10 comprises 48 input optical fibres 1 12, 48 output optical fibres 120, a 10Gb/s transmitter optical subassembly and receiver optical subassembly, TOSA/ROSA, 124, an electrical switch matrix 1 14, a wavelength division multiplexed, WDM, multiple transceiver 1 16, and an optical output 14.

The electrical switch matrix 1 14 comprises 48 10 Gb/s electrical I/O ports 122 connected to the TOSA/ROSA 124 by a first electrical link 1 18a and a further 48 10 Gb/s electrical I/O ports 126 connected to the WDM multiple transceiver 1 16 by a second electrical link 1 18b.

The TOSA 124 is arranged to receive 48 input optical signals from the input optical fibres 1 12 and is arranged to convert each into a respective corresponding electrical signal. The electrical signals are delivered from the TOSA to the I/O ports 122 of the electrical switch matrix 1 14. The ROSA 124 is arranged to receive 48 output electrical signals from the electrical switch matrix I/O ports 122 and convert each electrical signal into a respective corresponding output optical signal.

The WDM multiple transceiver is arranged to receive 48 output electrical signals from the electrical switch matrix I/O ports 126 and is arranged to convert each output electrical signal into a corresponding optical signal at a respective one of the 48 wavelengths. The WDM multiplex transceiver is further arranged to receive a plurality of optical signals, each having a respective one of the 48 wavelengths, from the switch card I/O port 14, and is arranged to convert each optical signal into a respective corresponding electrical signal.

Figure 16 illustrates an alternative switch card 130 for use in the intermediate stage

20 of the interconnection network 80 of Figure 8. The switch card 130 is configured for bidirectional operation.

The switch card 130 comprises a first I/O port 24, a second I/O port 26, a first WDM multiple transceiver 134, a second WDM multiple transceiver 138 and an electrical switch matrix 132.

The electrical switch matrix 132 comprises 48 10 Gb/s electrical I/O ports 122 connected to the first WDM multiple transceiver 134 by a first electrical link 136a and a further 48 10 Gb/s electrical I/O ports 126 connected to the second WDM multiple transceiver 138 by a second electrical link 136b.

Each WDM multiple transceiver 134, 138 is arranged to receive 48 electrical signals from the electrical switch matrix I/O ports 122, 126 and is arranged to convert each output electrical signal into a corresponding optical signal at a respective one of the 48 wavelengths. Each WDM multiplex transceiver is further arranged to receive a plurality of optical signals, each having a respective one of the 48 wavelengths, from one of the switch card I/O ports 14, 26 and is arranged to convert each optical signal into a respective corresponding electrical signal.

Figure 17 shows a WDM multiple transceiver 1 16, 134, 138 of Figures 15 and 16 in more detail. The WDM multiple transceiver 1 16, 134, 138 comprises three WDM transceivers 140, three optical couplers, OC, 146 and a band/power coupler 148.

Each WDM transceiver 140 has an output 142 and an input 144 coupled via an optical coupler 146 to the band/power coupler 148. Each WDM transceiver 140 comprises a transmitter side connected to the output 144 and a receiver side connected to the input 146. The transmitter side comprises a laser array 150, a modulator array 152 and an optical multiplexer 154, and the receiver side comprises an optical demultiplexer 158 and a photodetector, PD, array 156, as shown in Figure 18. The laser array 150 comprises 16 lasers each operable at a respective one of the 48 wavelengths; the lasers of each WDM transceiver operating using a respective one third, i.e. 16, of the 48 wavelengths. The modulator array 152 comprises 16 optical modulators, each configured to modulate the optical signal generated by the respective laser with data traffic to be transmitted. The photodetector array 156 comprises 16 photodetectors each arranged to receive an optical signal having a respective one of the 16 wavelengths and convert the optical signal into a corresponding respective electrical signal.

The band/power coupler 148 is configured to route the optical signals at each of the 16 wavelengths to the optical output 138.

Figure 19 shows an interconnection network 160 which is similar to the interconnection network 80 of the previous embodiment, with the following modifications. In this embodiment, each of the ingress stage switch cards 162 comprises four optical I/O ports 164. The interconnection network 160 additionally comprises four optical band de/multiplexers 166 provided between the ingress stage switch cards 162 and the first 4x4 AWG 62 and a further four optical band de/multiplexers 166 provided between the egress stage switch cards 172 and the second 4x4 AWG 64.

The E-O/O-E conversion apparatus of each of the ingress stage cards additionally comprises four optical de/multiplexers, each arranged to route a plurality of optical signals each having a respective one four sub-sets of the 48 wavelengths to and from a respective one of the four optical I/O ports. For example, each optical multiplexer may be arranged to route optical signals in respective subset of 12 of the 48 wavelengths. The optical fibre connections from only the first ingress stage switch card, SC1 1 , to the four de/multiplexers 166 are shown for reasons of clarity.

Similarly, each of egress stage switch cards 172 comprises four optical I/O ports164.

The E-O/O-E conversion apparatus of each of the egress stage cards additionally comprises four optical de/multiplexers, each arranged to route a plurality of optical signals each having a respective one four sub-sets of the 48 wavelengths to and from a respective one of the four optical I/O ports. The optical fibre connections from only the first egress stage switch card, SC31 , to the four de/multiplexers 166 are shown for reasons of clarity.

Each optical band de/multiplexer 166 comprises four of optical I/O ports on one side, each connected to a respective optical I/O port of the respective ingress stage switch card or of the respective egress stage switch card by a respective optical waveguide, and one optical I/O port on the other side, connected to a respective I/O port of the respective AWG 62, 64 by a respective optical waveguide.

Figure 20 shows a data centre network 200 according to an embodiment of the invention. The data centre network comprises a plurality of data servers 210 and an interconnection network 40, 50, 60, 70, 80, 160, as described in any of the above embodiments. The steps of a method 300 according to an embodiment of the invention of routing optical signals are shown in Figure 21 . The method 300 comprises steps a. and b.

Step a. comprises receiving a plurality of optical signals 302 at one of a plurality, M, of input ports of a passive fixed wavelength optical router. The passive fixed wavelength optical router has a cyclic wavelength response and comprises a plurality, M, of output ports. Each of the plurality of optical signals has a respective one of a plurality, N, of wavelengths, the plurality of wavelengths, N, being greater than the plurality, M, of input ports or output ports.

Step b. comprises routing each optical signal 304 from the input port to a respective one of the output ports according to the wavelength of the optical signal. Optical signals having each M^th one of the plurality of wavelengths are routed from the input port to a same one of the output ports.

In an embodiment, the cyclic wavelength response of the passive fixed wavelength optical router has a free spectral range, FSR, and is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ. Each FSR of the cyclic wavelength response covers a group of optical signal wavelengths consisting of a plurality, M, of the N optical signal wavelengths. There is no spectral gap between adjacent groups of optical signal wavelengths.

The steps of a method 310 according to an embodiment of the invention of routing optical signals are shown in Figure 22. The method 310 of this embodiment is similar to the method 300 of the previous embodiment, with the following modifications. In this embodiment, step a. comprises receiving a plurality of optical signals 302 at one of a plurality, M, of input ports of an MxM cyclic AWG 312. The plurality of optical signal wavelengths are optical channel wavelengths of the MxM cyclic AWG. The cyclic response of the AWG 52 has a free spectral range, FSR, and is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ. Each FSR covers a plurality, M, of the N optical signal wavelengths, giving the AWG an FSR of M Δλ. There is no spectral gap FSRs, i.e. between adjacent groups of M optical signal wavelengths.

The steps of a method 320 according to an embodiment of the invention of routing optical signals are shown in Figure 23. The method 320 of this embodiment is similar to the method 300, with the following modifications.

In this embodiment, step b. comprises routing an optical signal 324 having a j^th wavelength of the plurality, N , of wavelengths from an i^th input port of the plurality, M, of input ports to a k^th output port of the plurality, M, of output ports according to the relationship

k = j|_M + (i-1 ).

Figure 24 shows the steps of a method according to an embodiment of the invention of routing data traffic in a data centre network.

The method 400 comprises steps i. to iii. Step i. 402 comprises: receiving a plurality of input electrical signals each carrying data traffic at an ingress electrical switch matrix;

routing each input electrical signal across the ingress electrical switch matrix;

converting each input electrical signal output from the ingress electrical switch matrix into a respective optical signal having a respective one of a plurality, N , of wavelengths;

and delivering each optical signal to an optical output.

Step ii. comprises routing the plurality of optical signals output at step i. according to the method of routing an optical signal 300, 310, 320 described above.

Step iii. comprises converting each of the plurality of optical signals output from step ii. into a respective output electrical signal and routing each output electrical signal across an egress electrical switch matrix 404.

Figure 25 shows the steps of a method 410 according to a further embodiment of the invention of routing data traffic in a data centre network. The method 410 of this embodiment is similar to the method 400 of the previous embodiment.

In this embodiment, the method 410 comprises the following additional steps between steps ii. and iii. :

converting each of the plurality of optical signals output from step ii. into a respective intermediate electrical signal;

routing each intermediate electrical signal across an intermediate electrical switch matrix;

converting each intermediate electrical signal output from the intermediate electrical switch matrix into a respective further optical signal having a respective one of the plurality, N , of wavelengths;

routing the plurality of further optical signals according to the method of routing an optical signal 300, 310, 320 described above.

Step iii. comprises converting each of the plurality of optical signals output after routing the optical signals into a respective output electrical signal and routing each output electrical signal across the egress electrical switch matrix.

A further embodiment of the invention provides a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement any of the above steps of the method of routing optical signals.

A further embodiment of the invention provides a carrier containing a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement any of the above steps of the method of routing optical signals. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium. A further embodiment of the invention provides a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement any of the above steps of the method of routing data traffic in a data centre network.

A further embodiment of the invention provides a carrier containing a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement any of the above steps of the method of routing data traffic in a data centre network. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Claims

1. An interconnection network comprising:

an ingress stage comprising a plurality, M, of switch cards each comprising an ingress electrical switch matrix and electrical-to-optical, E-O, conversion apparatus arranged to convert a plurality of electrical signals output from the ingress electrical switch matrix into respective optical signals each having a respective one of a plurality, N, of wavelengths and to deliver the plurality of optical signals to an optical output;

an egress stage comprising a plurality, M, of switch cards each comprising an optical input, an egress electrical switch matrix and optical-to-electrical, O-E, conversion apparatus arranged to convert a plurality of optical signals each having a respective one of the plurality, N, of wavelengths received from the optical input into respective electrical signals and to deliver the electrical signals to the egress electrical switch matrix; and

an optical shuffle connected between the ingress stage switch cards and the egress stage switch cards, the optical shuffle comprising a passive fixed wavelength optical router having a cyclic wavelength response and having a plurality, M, of input ports, each connected to a respective switch card, and a plurality, M, of output ports, each connected to a respective switch card, the optical shuffle being configured to receive the plurality of optical signals at a selected one of the input ports and configured to route each of the plurality of optical signals from the selected optical shuffle input port to a respective one of the optical shuffle output ports according to the wavelength of each optical signal,

wherein the plurality of wavelengths, N, is greater than the plurality, M, of optical shuffle input ports or optical shuffle output ports and the passive fixed wavelength optical router is configured to route optical signals having each M^th one of the plurality of wavelengths from the selected optical shuffle input port to a same one of the optical shuffle output ports.

2. An interconnection network as claimed in claim 1 , wherein the cyclic wavelength response of the passive fixed wavelength optical router has a free spectral range, FSR, and the passive fixed wavelength optical router is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ, and wherein each FSR of the cyclic wavelength response covers a group of optical signal wavelength consisting of a plurality, M, of the plurality of optical signal wavelengths and there is no spectral gap between adjacent groups of optical signal wavelengths.

3. An interconnection network as claimed in claim 2, wherein the passive fixed wavelength optical router is an MxM cyclic arrayed waveguide grating, AWG, and the plurality of optical signal wavelengths are optical channel wavelengths of the MxM cyclic AWG.

4. An interconnection network as claimed in any preceding claim, further comprising an intermediate stage and a second said optical shuffle, the intermediate stage comprising a plurality, M, of switch cards provided logically between the ingress stage and the egress stage, each switch card of the intermediate stage comprising: an electrical switch matrix; an optical input; an optical output; O-E conversion apparatus arranged to convert a plurality of optical signals each having a respective one of the plurality, N, of wavelengths received from the optical input into respective electrical signals signal and to deliver the electrical signals to the electrical switch matrix; and E-0 conversion apparatus arranged to convert a plurality of electrical signals output from the electrical switch matrix into respective optical signals each having a respective one of the plurality, N, of wavelengths and to deliver the plurality of optical signals to the optical output, and wherein the ingress stage, the egress stage and the intermediate stage are arranged in a Clos network architecture with the optical shuffle connected between the ingress stage switch cards and the intermediate stage switch cards and the second optical shuffle connected between the intermediate stage switch cards and the egress stage switch cards, and each passive fixed wavelength optical router is configured to route an optical signal having a j^th wavelength of the plurality, N, of wavelengths from an i^th input port of the plurality, M, of optical shuffle input ports to a k^th output port of the plurality, M, of optical shuffle output ports according to the relationship k = j|_M + (i-1 )■

5. An interconnection network as claimed in any preceding claim, wherein:

each E-0 conversion apparatus comprises a plurality of E-0 converters, each arranged to convert a respective electrical signal into a corresponding optical signal at a respective one of the plurality of wavelengths and an optical multiplexer arranged to route each of the optical signals to the optical output; and

each O-E conversion apparatus comprises a plurality of O-E converters and an optical demultiplexer arranged to route each optical signal to a respective one of the O-E converters, each O-E converter being arranged to convert the respective optical signal into a corresponding electrical signal, and wherein each input port of each passive fixed wavelength optical router is connected to the optical output of a respective switch card by a single respective optical waveguide and each output port of each passive fixed wavelength optical router is connected to the optical input of a respective switch card by a single respective optical waveguide.

6. An interconnection network as claimed in claim 5, wherein:

a plurality, L, of the ingress stage switch cards each comprise a plurality, L, of optical outputs and the respective E-0 conversion apparatus of each of the plurality, L, of ingress stage cards additionally comprises a plurality, L, of optical multiplexers each arranged to route a plurality of optical signals each having a respective one of a plurality of the plurality, N, of wavelengths to a respective one of the plurality of optical outputs; and further comprising a plurality, L, of optical band multiplexers provided between the plurality of the ingress stage switch cards and the optical shuffle, each optical band multiplexer comprising an optical output and a plurality, L, of optical inputs each connected to a respective optical output of the ingress stage switch cards by a single respective optical waveguide and the optical output of each optical band multiplexer being connected to a respective input port of the optical shuffle by a single respective optical waveguide.

A data centre network comprising:

a plurality of data servers; and

an interconnection network as claimed in any preceding claim.

A method of routing optical signals, the method comprising steps:

a. receiving a plurality of optical signals at one of a plurality, M, of input ports of a passive fixed wavelength optical router having a cyclic wavelength response and comprising a plurality, M, of output ports, each of the plurality of optical signals having a respective one of a plurality, N, of wavelengths, wherein the plurality of wavelengths, N, is greater than the plurality, M, of input ports or output ports; and

b. routing each optical signal from the input port to a respective one of the output ports according to the wavelength of the optical signal, wherein optical signals having each M^th one of the plurality of wavelengths are routed from the input port to a same one of the output ports.

A method as claimed in claim 8, wherein the cyclic wavelength response of the passive fixed wavelength optical router has a free spectral range, FSR, and the passive fixed wavelength optical router is configured to route a plurality of optical signal wavelengths separated by a channel spacing, Δλ, and wherein each FSR of the cyclic wavelength response covers a group of optical signal wavelength consisting of a plurality, M, of said plurality of optical signal wavelengths and there is no spectral gap between adjacent groups of optical signal wavelengths.

A method as claimed in claim 9, wherein the passive fixed wavelength optical router is an MxM cyclic arrayed waveguide grating, AWG, and said plurality of optical signal wavelengths are optical channel wavelengths of the MxM cyclic AWG.

A method as claimed in any of claims 8 to 10, wherein step b. comprises routing an optical signal having a j^th wavelength of said plurality, N, of wavelengths from an i^th input port of said plurality, M, of input ports to a k^th output port of said plurality, M, of output ports according to the relationship k = j|_M + (i-1 ).

A method of routing data traffic in a data centre network, the method comprising steps: i. receiving a plurality of input electrical signals each carrying data traffic at an ingress electrical switch matrix, routing each input electrical signal across the ingress electrical switch matrix, converting each input electrical signal output from the ingress electrical switch matrix into a respective optical signal having a respective one of a plurality, N, of wavelengths, and delivering each optical signal to an optical output;

ii. routing the plurality of optical signals output at step i. according to the method of any of claims 8 to 1 1 ;

iii. converting each of the plurality of optical signals output from step ii. into a respective output electrical signal and routing each output electrical signal across an egress electrical switch matrix.

A computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to implement the method according to any one of claims 8 to 12.

A carrier containing the computer program of the previous claim, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.