GB2240682A

GB2240682A - An optical interconnect assembly

Info

Publication number: GB2240682A
Application number: GB9002435A
Authority: GB
Inventors: Robert Charles Goodfellow; Martin Goodwin
Original assignee: GEC Marconi Ltd; Plessey Co Ltd; Marconi Co Ltd
Current assignee: Plessey Co Ltd; BAE Systems Electronics Ltd
Priority date: 1990-02-03
Filing date: 1990-02-03
Publication date: 1991-08-07
Anticipated expiration: 2010-02-03
Also published as: GB2240682B; GB9002435D0

Abstract

An optical interconnect assembly comprising a plurality of silicon integrated circuits (1, 2, 3, 4) which are connected electrically, optically and mechanically to an optoelectronic substrate (5) having a plurality of optoelectronic components (7) formed thereon, said components (7) being interconnected by optical waveguides (8) also formed on said substrate (5). <IMAGE>

Description

AN OPTICAL INTERCONNECT ASSEMBLY This invention relates to an optical interconnect assembly employing an active optoelectronic motherboard substrate to provide the optical-electrical data transducers for silicon integrated circuits and the interconnection optical pathways between them.

High speed and high density interconnection of ICs gives rise to problems of power dissipation (for high speed because of the need to rapidly charge and discharge long capacitive lines), crosstalk (because of the inductive coupling), topology (because electrical connectors cannot cross like optical waveguides) and of complexity (because conductor widths impact signalling capacity, loss and crosstalk). Application of optics presents the means to overcome these limitations. Previous implementations of optical interconnect have involved depositing passive waveguiding structures on the surface of the integrated circuit itself or have employed free-space holographic data paths. The interconnect assembly described here enables an active integrated optical circuit to provide the data exchange and power distribution functions - the so called optical motherboard.This invention achieves this without requiring complex post-processing of the integrated circuit or alteration of existing well-established foundry processes.

According to the invention there is provided an optical interconnect assembly comprising a plurality of silicon integrated circuits (1, 2, 3, 4) which are connected electrically, optically and mechanically to an optoelectronic substrate (5) having a plurality of optoelectronic components (7) formed thereon, said components (7) being interconnected by optical waveguides (8) also formed on said substrate (5).

Preferably said optoelectronic components include laser diodes, waveguide modulators, wavelength selective devices, photodetectors and waveguide switches and said optoelectronic components include neural network processing nodes, array processing circuits, cellular logic processing nodes and circuits requiring high bandwidth interconnection.

The waveguides and optoelectronic components may form a global, local and clock distribution interconnect between said silicon integrated circuits.

The invention will now be described further by way of example with reference to the accompanying drawings in which: Figures la and lb illustrate plan view and side view of one embodiment of the optical motherboard assembly comprising four integrated circuits on an active optoelectronic substrate; Figure 2 illustrates an alternative embodiment of an optical motherboard assembly comprising two integrated circuits on a conventional substrate, and an active optoelectronic superstrate; Figure 3 illustrates a plan view of - an active motherboard assembly configured to provide a data bus between four integrated circuit; and, Figure 4 illustrates a plan view of an active motherboard assembly configured to provide clock signal distribution to four integrated circuits.

In the configuration shown in figures la and ib four integrated circuits, 1, 2, 3 and 4 are electrically and mechanically connected to an active optoelectronic substrate 5. The optoelectronic substrate contains a plurality of detector elements 7 associated with data input points on the integrated circuits. The detector elements and modulator elements are optically linked by a channel waveguide interconnection pattern 8, fed by a separate semiconductor light source 9. Data can thus be transferred from an output point on circuit 1 to a corresponding input point on any of the circuits 1, 2, 3 or 4.

One means of achieving the electrical and mechanical connection between the integrated circuits and the optoelectronic motherboard substrate is the use of solder bonds 10.

An alternative implementation of the optical motherboard has the detector elements formed in the integrated circuits themselves.

In this case the optical signal is deflected vertically down from the waveguide to the integrated circuit, which can be achieved by forming a suitably designed diffraction grating or angled facet on the waveguide. This implementation is appropriate when detectors cannot be realised directly in the chosen optoelectronic material system.

Table 1 lists several (but not all) suitable optoelectronic material systems in which the optical motherboard can be realised.

The number of output data points on the integrated circuit that can be assessed by the optical motherboard is determined by the modulator packing density and electrical and optical crosstalk considerations. Practical waveguide modulators currently have widths of approximately 40m. Consequently on a lcm2 integrated circuit 200 high speed data channels can be realised. The power to drive the optical modulator depends on the data rate and type of modulator. The current devices require approximately 1 volt for a lpF capacitance. Hence at 100 Mbit/s a single output takes approximately 0.1mW which is favourable compared with the 25 (or so) mW required for the electrical case equivalent.

Figure 2 shows an alternative construction for the optical motherboard. In this case, the two or more integrated circuits 12 and 13 are mounted conventionally onto a passive substrate 14. The optoelectronic motherboard substrate 15 is mounted on top of the two integrated circuits forming an optical waveguide bridge between them. Again one possible means of connecting the silicon integrated circuits and the optoelectronic substrate is solder-bonds, 16. This geometry allows more efficient heat-sinking of the silicon integrated circuits and could be more appropriate for high power devices.

Figure 3 shows one application of the optical motherboard, comprising four integrated circuits, 17, 18, 19 and 20, mounted onto the optoelectronic substrate 21. The waveguide pattern 22, modulators 23 and detectors 24 are laid out to provide an optical data bus between the four integrated circuits. The low propagation loss associated with waveguide modulators allows this databus to be extended to larger numbers of integrated circuits.

Figure 4 shows a second application of the optical motherboard for providing clock signal distribution to the four (or more) integrated circuits 25. The optoelectronic substrate 26 contains a branching waveguide pattern 27 connecting a single modulated semiconductor light source 28 to detectors 29 on each of the integrated circuits.The direct integration of laser sources and detectors with the waveguides in the optical motherboard allow large margins to be achieved between launched signal power and receiver sensitivity, and can be used to achieve high degrees of signal fanout.

Substrate Waveguides Modulator Coupling to Detector Glass Ion Exchange Deposited e-o polymer Surface grating Si - on IC Polyimide Deposited e-o polymer Surface grating Si - on IC Deposited SiO2 Deposited e-o polymer Surface grating Si - on IC Silicon Polyimide Deposited e-o polymer Surface grating Si - on IC or substrate Deposited SiO2 Deposited e-o polymer Surface grating si - on IC or substrate Sods Lime Glass Deposited e-o polymer Leaky guide Si - on IC or substrate Lithium Niobate Ion Exchange Lithium niobate Surface grating Si - on IC GaAs GaAs GaAs quantum Well Waveguide GaAs or ga InAs Inp Inp Quantum well type Waveguide Ga InAs Ceramic Polyimide Deposited e-o polymer Surface grating Si - on IC Deposited SiO2 Deposited e-o polymer Surface grating Si - on IC TABLE 1

Claims

CLAIMS 1. An optical interconnect assembly comprising a plurality of silicon integrated circuits (1, 2, 3, 4) which are connected electrically, optically and mechanically to an optoelectronic substrate (5) having a plurality of optoelectronic components (7) formed thereon, said components (7) being interconnected by optical waveguides (8) also formed on said substrate (5).
2. An assembly according to claim 1, in which said plurality of silicon integrated circuits are connected by flip-chip solder bonds to the components formed on the optoelectronic substrate.
3. An assembly according to claim 1 or 2, in which said plurality of optoelectronic components include laser diodes, waveguide modulators, wavelength selective devices, photodetectors and waveguide switches.
4. An assembly according to claim 1 or 2, in which said plurality of silicon integrated circuits include neural network processing nodes, array processing circuits, cellular logic processing nodes and circuits requiring high bandwidth interconnection.
5. An assembly according to any one of the preceding claims, in which said optoelectronic substrate is formed in III-V semiconductor material.
6. An assembly according to any one of claims 1 to 4, in which said substrate is formed in lithium niobate.
7. An assembly according to any one of claims 1 to 4, in which said substrate is formed using an electrooptic organic polymer.
8. An optical interconnect assembly according to any one of the preceding claims, in which said waveguides integrated circuits and optoelectronic components form a data distribution bus between said silicon integrated circuits.
9. An optical interconnect assembly according to any one of claims 1 to 7, in which said waveguides and optoelectronic components form a global interconnect between said silicon integrated circuits.
10. An optical interconnect assembly according to any one of claims 1 to 7, in which said waveguides and optoelectronic components form a local interconnect between said silicon integrated circuits.
11. An optical interconnect assembly according to any one of claims 1 to 7, in which said waveguides and optoelectronic components form a clock distribution interconnect between said silicon integrated circuits.
12. An optical interconnect assembly substantially as hereinbefore described with reference to the accompanying drawings.