Perspectives for Parallel Optical Interconnects

This monograph is a result of the ESPRIT Basic Research Working Group 3199, WOIT (Workshop on Optical Information Technology) that gathers most of the European Universities active in the field of Optical Computing. The volume discusses the applicability of parallel optical interconnects to computer architectures.

1 Perspectives for parallel optical interconnects: introduction.- 1.1 Optical Interconnects and ESPRIT BRA WOIT.- 1.2 What are optical interconnects?.- 1.3 Optical interconnects: how ?.- 1.3.1 Passive devices.- 1.3.2 Active devices.- 1.3.3 Schemes for parallel optical interconnects.- 1.3.4 Limits of optical interconnects.- 1.4 Optical interconnects: why ?.- Acknowledgements.- References.- First Section: Components.- 1.1 Passive interconnect components.- 2 Free space interconnects.- 2.1 Introduction: 3D optical interconnects.- 2.2 Optical free space channels and their implementations.- 2.2.1 Diffraction and degrees of freedom.- 2.2.2 Two basic interconnect setups.- 2.3. Limitations.- 2.3.1 Compactness.- 2.3.2 Alignability.- References.- 3 Reflective and refractive components.- 3.1 Introduction and concept.- 3.1.1 Definition of reflective and refractive components.- 3.1.2 Reflection and refraction for interconnect components.- 3.2 Interconnects with microlens arrays.- 3.2.1 Introduction.- 3.2.2 Interconnection density provided by miniature lenses beyond the paraxial approximation.- 3.2.3 Concluding remarks.- 3.3 Refractive microlens arrays.- 3.3.1 Fields of application.- 3.3.2 Geometry and parameters of microlenses.- 3.3.3 The different fabrication processes.- 3.3.4 Concluding remarks.- References.- 4 Diffractive components: holographic optical elements.- 4.1 Introduction.- 4.2 Types of holographic optical elements.- 4.2.1 Thin holograms.- 4.2.2 Thick holograms.- 4.3 Holographic materials for fixed interconnects.- 4.4 Design of holographic optical elements.- 4.4.1 The hologram phase function.- 4.4.2 Astigmatism and Bragg condition.- 4.4.3 Optimum design for imaging elements.- 4.4.4 Analysis of holographic optical elements.- 4.5 Diffraction efficiency of volume holograms recorded with one or multiple object beams.- 4.5.1 Diffraction efficiency of single volume gratings.- 4.5.2 Simultaneous recording of N object waves.- 4.5.3 Sequential recording of N object waves.- 4.6 Fabrication methods and selected examples.- 4.6.1 Optimized holographic optical elements.- 4.6.2 Sequentially recorded multifacet elements.- 4.6.3 Simultaneously recorded multifacet elements.- 4.6.4 Simultaneous recording of fan-out elements.- 4.6.5 Sequential recording of fan-out elements.- 4.7 Conclusions.- References.- 5 Diffractive components: computer-generated elements.- 5.1 Diffractive optical elements.- 5.2 Design of diffractive optical elements.- 5.2.1 The phase function of diffractive components.- 5.2.2 Optimum design for imaging and beam shaping.- 5.3 Diffraction theory.- 5.3.1 Approximate diffraction theory.- 5.3.2 Rigorous diffraction theory.- 5.3.3 Rigorous modal theory for one-dimensional lamellar gratings.- 5.4 Fabrication technology for diffractive optical elements.- 5.4.1 Primary pattern fabrication.- 5.4.2 Pattern transfer.- 5.4.3 Direct writing of continuous microreliefs.- 5.4.4 Replication techniques.- 5.5 Selected experimental results for DOEs.- 5.5.1 Lenslet arrays.- 5.5.2 Fan-out elements.- 5.6 Future perspectives for diffractive optical elements.- References.- 6 Characterization of Interconnection Components.- 6.1 Introduction.- 6.2 Characterization of the surface structure.- 6.2.1 Macrostructure measurements.- 6.2.2 Microstructure measurements.- 6.3 Characterization of optical performance.- 6.3.1 Wave aberration measurement and related merit functions.- 6.3.2 Calibration problems.- 6.3.3 Direct PSF measurements.- 6.3.4 Angle measurement of reflective/refractive and diffractive deflectors.- 6.3.5 Diffraction efficiency of volume HOE, CGH.- 6.4 Characterization of index profiles.- 6.5 Conclusion.- References.- 1.2 Active interconnect components.- 7 Optoelectronic semiconductor devices.- 7.1 Introduction.- 7.2 Semiconductor materials and growth techniques.- 7.2.1 III–V compound semiconductors.- 7.2.2 Crystal growth techniques.- 7.3 Basic device trends.- 7.3.1 Basic heterostructures.- 7.3.2 Towards lower-dimensional structures.- 7.3.3 Lattice-mismatched heterostructures.- 7.4. Optoelectronic device arrays.- 7.4.1 Introduction.- 7.4.2 Progress in edge-emitting diode lasers.- 7.4.3 Surface-emitting laser arrays.- 7.4.4 Self-electrooptic effect device arrays and vertical-to-surface transmission electrophotonic devices.- 7.5 Summary.- References.- 8 Spatial light modulators for interconnect switches.- 8.1 Introduction.- 8.2 Mechanisms for Spatial Light Modulation.- 8.2.1 Refractive Modulation.- 8.2.2 Absorptive Modulation.- 8.2.3 Mechanical Modulation.- 8.3 Examples of Spatial Light Modulators.- 8.3.1 Refractive SLMs.- 8.3.2 Absorptive SLMs.- 8.3.3 Mechanical SLMs.- 8.3.4 Optical Discs as SLMs.- 8.4 Examples of SLM-Based Switching Networks.- 8.4.1 Vector-Matrix Processor Interconnect (MILORD).- 8.4.2 Matrix-Matrix Processor Interconnect (OCPM).- 8.4.3 Spatial Switching with Nonlinear F-P Cavity Devices.- 8.4.4 S-SEED Photonic Switching Fabrics.- 8.5 Summary.- Acknowledgements.- References.- 9 Reprogrammable Components: Photorefractive Materials.- 9.1 Introduction.- 9.2 The photorefractive effect.- 9.2.1 Grating formation and storage.- 9.2.2 Main parameters.- 9.3 Photorefractive materials.- 9.3.1 Passive applications.- 9.3.2 Active applications.- 9.4 Conclusion.- References.- 10 Acousto-optic devices.- 10.1 Fundamentals of acousto-optics.- 10.2 Acousto-optic Bragg deflectors.- 10.3 Interconnect capabilities of bulk devices.- 10.4 Surface acoustic wave devices.- 10.5 Conclusions.- References.- Second Section: Interconnection schemes and systems.- 2.1 Parallel schemes.- 11 Density of parallel optical interconnects.- 11.1 Introduction.- 11.2 Topology.- 11.3 Parallelism.- 11.4 Randomness.- 11.5 Crosstalk.- 11.6 Space sharing.- 11.7 Beam combination.- 11.8 Heat.- 11.9 Tolerances.- 11.10 Conclusions.- Acknowledgement.- References.- 12 Interconnects with optically thin elements.- 12.1 Introduction.- 12.2 Fourier plane array generators.- 12.3 Space variant Interconnections.- 12.3.1 1 to N2 Mappings.- 12.3.2 N to N Mappings.- 12.4 Space invariant interconnections.- 12.5 Free-space optical switching systems.- 12.5.1 Optical crossbar architectures.- 12.5.2 Scalable free-space optical crossbars.- 12.6 Compact parallel optical interconnections.- 12.6.1 Minimum optical interconnection volume.- 12.6.2 Compact Fourier plane optical interconnections.- 12.6.3 Fresnel plane interconnections.- 12.7 Conclusions: future directions for parallel optical interconnections.- References.- 13 Interconnects with optically thick elements.- 13.1 Introduction.- 13.2 Diffraction properties of thick gratings.- 13.2.1 Geometrical approach to the Bragg condition and grating thickness criterion.- 13.2.2 Phase and absorption gratings.- 13.2.3 Example of uniform index transmission gratings.- 13.2.4 Recording and reading out thick gratings.- 13.3 Superimposed gratings recorded in thick media: limitation of the interconnect capacity by the Bragg degeneracy.- 13.3.1 Bragg degeneracy.- 13.3.2 Interconnects between a 1D input and a 2D output array.- 13.3.3 Interconnects between two 2D arrays: sampling grids.- 13.3.4 Gratings recorded at one wavelength and read out at another wavelength.- 13.4 Limitations inherent to volume holographic interconnects.- 13.4.1 Successive diffractions and cross talk.- 13.4.2 Fidelity of the interconnections.- 13.4.3 Temporary conclusion.- 13.5 Interconnect capacities of existing materials.- 13.5.1 Introduction.- 13.5.2 Storage capacity of a BaTiO3 photorefractive crystal.- 13.5.3 Data rate-Capacity trade off.- 13.6 Correlators and memories.- 13.6.1 Correlators.- 13.6.2 Optical memories.- 13.7 Self aligning interconnects.- 13.7.1 Introduction.- 13.7.2 Self aligning interconnect with a phase conjugate mirror.- 13.7.3 Self aligning interconnection with two dynamic media.- 13.7.4 Self aligning interconnection with the double phase conjugate mirror.- 13.8 Conclusion.- References.- 14 Theory of interconnection networks.- 14.1 Applications of interconnection networks.- 14.1.1 Classification of interconnection networks.- 14.1.2 Static connection topologies.- 14.1.3 Dynamic connection topologies.- 14.1.4 Minimum number of switching elements in non-blocking networks.- 14.1.5 Arbitration in the case of address conflicts.- 14.2 Concepts and experiments for free-space optical interconnections.- 14.2.1 Experiments for multistage networks.- 14.2.2 Optical implementations of a crossbar network.- References.- 2.2 Limits.- 15 Limitations and scaling laws in parallel optoelectronic interconnections.- 15.1 Introduction.- 15.2 Basic concepts.- 15.3 Data multiplexers/demultiplexers.- 15.4 Data transmitters.- 15.4.1 Active emitters.- 15.4.2 Modulators.- 15.4.3 Conclusions for Transmitters.- 15.5 The optical channel(s).- 15.6 Data receivers.- 15.6.1 Receivers without amplification.- 15.6.2 Noise limited receivers.- 15.7 The optoelectronic data link.- 15.7.1 Data link with a receiver without amplification.- 15.7.2 Data link with a noise limited receiver.- 15.7.3 Comparison.- 15.8 Examples.- 15.8.1 A parallel system at the noise limit.- 15.8.2 A high-speed system with high light levels.- 15.9 Conclusions.- References.- 16 Comparison between electrical and optical interconnects.- 16.1 Introduction.- 16.2 Optical intracomputer communication systems.- 16.2.1 Sources and detectors.- 16.2.2 Optical channels.- 16.3 Analysis of interconnect limitations in VLSI systems.- 16.3.1 Introduction.- 16.3.2 Technological constraints in VLSI.- 16.3.3 Architectural constraints.- 16.4 Optical and electrical interconnects.- 16.4.1 Connectivity density considerations.- 16.4.2 Bandwidth consideration.- 16.4.3 Power consideration.- 16.4.4 Discussion and conclusion.- References.- Contributors.