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

Multistage architecture:

parallel computers,

switching networks

Dense optical interconnect:

interconnection folded in 2D…

Optical Multistage Architecture Paradigm

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Shuffle interconnectionExchange switch

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Shuffle interconnectionExchange switch

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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

Interconnection module

Interconnection module

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

c2

c1

c 3 c4

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 c1, c2 , c3, c4

- Asynchronously for each processor

- Synchronously (weak interconnection)

- In a time-slotted manner

Time slotted permutation switching

Time slot

Permutation appearance period

time

Red link Blue link Green link Orange link

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Burst Interconnects

Computationone-stage(ex. 1 ms)

Burst interconnection within “short” time slot

(Ex. 10Gbps, 100nsec 1kbit)

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Interconnection switching interval

(Ex. 1ms)＝

…Slow switching okay

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

outputinput

{c2, id}

A multistage version of most direct topologies (hypercube, cube-connected-cycles, deBruijn) can be implemented using specially designed interconnection modules.

Exchange permutation for N=16=24

Unfolded

Folded

[ exchange (k) ]

(k)

{bn, … bk+1, bk, bk-1, … b2, b1}

{bn, … bk+1, bk, bk-1, … b2,b1}

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]

c3

c4

c2

c1

c2

c1

c 3 c4

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…

{c2, id}{c1, id}

{c3, id}{c4, id}

Channels are single mode fibers: MFD = 9.5 mGrad 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 mo

dule

Input second module

{c2, id}input output

{c2, id}

{c1, id}

Displacement stage (piezo)

id.id

C1. C2

id. C2

C1. id

. =

. =

. =

. =

c2

c1

c 3 c4

[slide not shown in main presentation]

Input (exit VCSEL array)

Output first two modules (CCD image)

id.id

C1. C2

id. C2

C1. 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

{c2, id}{c1, id}

Alignment tolerance: 5 m (half peak power).

Displacement pitch for commutation: 125 m

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)

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)

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Further research directions