1. 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

2. Introduction Multistage architecture: parallel computers, switching networks Dense optical interconnect: interconnection folded in 2D… Optical Multistage Architecture Paradigm +

3. Fiber-Modules vs. Free-Space Fibers have better efficiency than holograms for long-range interconnections. No cross-talk in 3D, just like free-space optics, Interconnect space-invariance not required 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

4. 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

5. … 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 processor interconnection network with four- dimensional hypercube topology. 2D output data flow … One or more reconfigurable modules The network must provide (at least) four cube permutations c 1, c 2, c 3, c 4 - Asynchronously for each processor - Synchronously (weak interconnection) - In a time-slotted manner

6. 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

7. 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

8. A C : Rem: Dynamic alignment is tightly coupled with dynamic reconfiguration of the interconnect. Cf. Naruse’s presentation. A C : Rem: Dynamic alignment is tightly coupled with dynamic reconfiguration of the interconnect. Cf. Naruse’s presentation. Cascaded Multi-permutation Module Paradigm Interleaved fiber-based permutation modules: …small mechanical/optical perturbation produces a drastic change of the interconnection pattern Cascaded multi-permutation modules: …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.

9. Exchange permutation for N=16=2 4 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  (1) ) 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. [slide not shown in main presentation]

10. c3c3 c4c4 c2c2 c1c1 c2c2 c1c1 c3c3 c4c4 Example: Multistage Spanned Hypercube …topology is mapped on a plane (2D 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}

11. 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)

12. id.id C 1. C 2 id. C 2 C 1. id. =. =. =. = c2c2 c1c1 c3c3 c4c4 [slide not shown in main presentation]

13. 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 this simple cascaded architecture. …displacement is 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

14. Conclusion Design and characterization of integrated 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 [ 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)

15. Electro-optical reconfiguration of the interconnection module. nanosecond range reconfiguration time ! Interconnection + optical function modules Mixed interconnections, and other all optical functions (ex.: delay lines) Further research directions