Reconfigurable optical interconnections using multi-permutation-integrated fiber modules JSAP conference, 27 March 2003 Alvaro Cassinelli *, Makoto Naruse **,***, Masatoshi Ishikawa *, and Fumito Kubota **. Univ. of Tokyo *, Communications Research Laboratory **, JST PRESTO *** output input Introduction. In previous work we explored a way to alleviate wiring congestion in massively interconnected multi-chip architectures using cascaded optoelectronic arrays and fiber-based, plane-to-plane (2D) optical interconnection modules [1]. The target application for these modules was packet-switching using a buffered, highly scalable multistage interconnection network. We study here multi-permutation modules containing a set of independent addressable permutations. Addressing can be done by minute mechanical displacement of the modules (figure). Cascading these modules without intermediate optoelectronic arrays gives a transparent multistage architecture adequate for circuit switching in weak-interconnected multiprocessors. Introduction Multistage architecture: parallel computers, switching networks Dense optical interconnect: interconnection folded in 2D Optical Multistage Architecture Paradigm + Fiber-Modules vs. Free-Space Fiber have better efficiency (than holograms) for long-range interconnections. no cross-talk in 3D, just like free-space optics, No space-invariance possible. Theoretically more volume efficient than free-space Precise and robust alignment possible multiple interleaved permutations possible. Maybe hard to build? Boring, but not a fundamentally difficult (can be automated, can be done by layers). Alignment of both output and input needed Power dissipation may be a fundamental limitation, but we are far from these limits 2D folded perfect shuffle permutation module (2) wave-guide arrays for fixed, point-to-point and space variant interconnections are an interesting alternative to free-space optics Interconnection module Elementary Processor Array VCSEL array Photo- detector array 2D input data flow Fixed inter-stage interconnections FIXED interconnections Optoelectronic processing/switching useful for pipeline processing of data (eg. FFT) or packet switching. or reconfigurable inter-stage interconnections Reconfigurable Interconnection module 2D input data flow High bandwidth transparent circuit-switched networks for permutation routing in multi-processors Reconfigurable Interconnection module c2c2 c1c1 c3c3 c4c4 16 processors interconnected using the four-dimensional hypercube topology. The network provides four cube permutations c 1, c 2, c 3, c 4 2D output data flow One or more reconfigurable modules Cascaded Multi-permutation Module Paradigm Interleaved fiber-based permutation modules: A C : Rem: Dynamic alignment is tightly coupled with dynamic reconfiguration of the interconnect. Cf. Naruses presentation. A C : Rem: Dynamic alignment is tightly coupled with dynamic reconfiguration of the interconnect. Cf. Naruses presentation. A small mechanical or optical perturbation can produce a drastic change of the interconnection pattern from input to output! Cascaded multi-permutation modules: This architecture simplifies module design (bi-permutations), while maintaining whole network interconnection capacity. Cascaded optical permutation modules output input {c 2, id} A multistage version of most direct topologies (hypercube, cube-connected-cycles, deBruijn) can be implemented using specially designed interconnection modules. Unfolded Folded [ exchange (k) ] (k) {b n, b k+1, b k, b k-1, b 2, b 1 } If k n/2, ( (1) and (2) ) exchange only rows: (1) (2) (3) (4) If k>n/2, ( (3) and (4) ) exchange only columns. The modules are just the same than previous ones, rotated. Only two modules are needed Module design: layered modules [slide not shown in main presentation] Example: exchange (cube) permutation for N=2 4 For N=4=2 1 x2 1 (n=2) we have : (1) = id (2) = row (1). col (1).L = L For N=8=2 2 x2 1 (n=3) we have : (1) = id (2) = row (2) (new) (3) = row (2). col (1).L = row (2). L For N=2=2 1 x2 0 (n=1) we have : (1) = row (1) = id For N=16=2 2 x2 2 (n=4) we have : (1) = id (2) = row (2) (3) = row (2). col (1).L = row (2). L (4) = row (2). col (2).L = row (2). R row (2). L.. But is not always so simple: shuffle permutation [slide not shown in main presentation] c3c3 c4c4 c2c2 c1c1 c2c2 c1c1 c3c3 c4c4 Example: Multistage Spanned Hypercube topology mapped on a plane (optical interconnects, VLSI integration) spanned hypercube using four bi-permutation modules four-dimensional hypercube connected multiprocessor {c 2, id} {c 1, id} {c 3, id} {c 4, id} Spanned version of a 4-dimensional weak- interconnected hypercube (16 nodes, 1 bit wide data-bus). It uses four bi-permutation modules, each providing a cube permutation and the identity, which gives a total of 2 4 =16 global permutations for the whole network. Alternatively, using only two of these modules, one can implement an hypercube of dimension 2, with a four bit wide data-bus. Time slotted permutation switching Time slot Permutation appearance period time Red link Blue link Green link Orange link Interconnect 1 Interconnect 2 Interconnect 3 Interconnect N Interconnect 1 Interconnect 2 Interconnect 3 Interconnect N Interconnect 1 Interconnect 2 Interconnect 3 Interconnect N time Burst Interconnects Computation one-stage (ex. 1 ms) Burst interconnection within short time slot (Ex. 10Gbps, 100nsec 1kbit) Interconnect 1 Interconnect 2 Interconnection switching interval (Ex. 1ms) Slow switching okay Channels are single mode fibers: MFD = 9.5 m Grad diameter 125 m 1 m NA: 0.1 0.01 Module Prototype is not integrated as a single block Experiment Setup using two bi-permutation modules. Output (to CCD) Input (from VCSEL array) Exit first module Input second module {c 2, id} input output {c 2, id} {c 1, id} Displacement stage (piezo) Input (exit VCSEL array) Output first two modules (CCD image) id.id C 1. C 2 id. C 2 C 1. id Preliminary results Inter-module Coupling Efficiency: 1.7dB (no additional optics, matching oil or antireflection coating). Validation of simple cascaded architecture. displacement operated manually using a piezo-stage {c 2, id} {c 1, id} Alignment tolerance: 5 m (half peak power). Displacement pitch for commutation: 125 m Conclusion Design and characterization of multi-permutations modules Architectural considerations: Modularity / scalability / reusability of modules and systems Input/output module alignment Micro-lenses, fibers with round ends. Modules built from fiber bundles. Active alignment using electromechanical modules Applications: Transparent time division multiplexed permutation network with relatively slow switching time (ms range) Buffered architecture using bi-permutation modules for packet routing. Simulation results are encouraging and besides control simplicity, an additional advantage is that MEMS actuators could be used in AC mode (at their resonant frequencies). [ Ongoing research ] A C : Multi-function modules: the use of optical fiber modules fits well with the all optical approach; for instance, one can imagine a module with several different interconnection patterns, but also other optical-functions like optical delay lines: However, in all-optical networks the switches may be very fast (electro optical devices, not MEMS), because the delay time for avoiding the drop of ATM cells is ?? for a typical Gigabit network!!! A C : Multi-function modules: the use of optical fiber modules fits well with the all optical approach; for instance, one can imagine a module with several different interconnection patterns, but also other optical-functions like optical delay lines: However, in all-optical networks the switches may be very fast (electro optical devices, not MEMS), because the delay time for avoiding the drop of ATM cells is ?? for a typical Gigabit network!!! The switching fabric studied here provides a limited number of long-range, all- optical interconnections useful for high throughput massively interconnected multiprocessors requiring relatively slow switching time (ms range) Electro-optical reconfiguration of the interconnection module. nanosecond range reconfiguration time Interconnection + optical function modules Mixed interconnections, and other optical functions (ex.: delay lines!) Further research directions References: [1] Cassinelli et al., JSAP [2] Naruse et al., JSAP spring meeting [3] Goulet et al., OJ2000, pp All optical switching (modules with integrated permutations and directional couplers for instance) must be used if switching speed needs to be orders of magnitude higher. Proposed all-optical bi-permutation switch module