CLAP: a Crosstalk and Loss
Analysis Platform for Optical
Interconnects
Special session on
Silicon Photonics Interconnects:
an Illusion or a Realistic Solution?
Mahdi Nikdast1, Luan H. K. Duong1, Jiang Xu1, Sébastien Le Beux2,
Xiaowen Wu1, Zhehui Wang1, Peng Yang1, and Yaoyao Ye1
1The
Hong Kong University of Science and Technology
2Lyon Institute of Nanotechnology
NOCS 2014, Ferrara, Italy
Outline
 Introduction
 Crosstalk in basic optical elements
 Analytical models for the crosstalk and SNR
 CLAP: Crosstalk and Loss Analysis Platform
 Case study
 Summary
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The road to
Optical Interconnects
 Limitations of metallic interconnects in electronic
NoCs:
 Parasitic resistance and capacitance
 High latency and power dissipation, and low bandwidth
 Consume kilowatts of power to achieve the communication
bandwidth that will be required by multiprocessor systemson-chip (MPSoCs) by 2020 using the 14 nm process
[Beausoleil, Proc. of IEEE’ 2008]
 ITRS* [ITRS (2000)] has pointed out the urgent need for
new intra-chip interconnection technologies
IBM ICON (Intra-Chip Optical Network)
3D-integated chip consists of several layers
*International Technology Roadmap for Semiconductors
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Optical Interconnects
The Present and The Future
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Optical Interconnects
The Present and The Future
Roadmap of Industrial photonics technologies (source: HP)
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Why is Considering Crosstalk Noise
Important?
 Crosstalk noise is an intrinsic characteristic of
photonic devices widely used in optical NoCs
 Crosstalk noise is very small at the device level,
and it has been ignored at the router and network
levels!
 But, what if it cannot be ignored ?
 What is the impact of crosstalk noise on large scale ONoCs?
 What is the worst-case and the average Signal-to-Noise Ratio
(SNR) in an ONoC?
 …
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Crosstalk in Basic Optical
Elements
 Inter-channel crosstalk
 Crosstalk signal is at a wavelength sufficiently different
from the desired signal’s wavelength
 Intra-channel crosstalk
 Crosstalk signal is at the same wavelength as that of the
desired signal or sufficiently close to it
 Cascading a wavelength demultiplexer (demux) with a
wavelength multiplexer (mux), optical switches
 Can be coherent and incoherent
 Cannot be removed by filtering
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Basic Optical Elements
 We consider first-order incoherent and coherent
crosstalk
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Basic Optical Elements II
 Optical modulator
and photodetector
models as a part
of the E-O and O-E
interfaces
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Hierarchical Systematic
Crosstalk Noise Analysis
Network Level
Router Level
Device Level
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Analytical Models for Crosstalk
 Let’s consider a parallel switching element as an
example:
[S. Xiao, Opt. Express’ 2007]
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Notation
Definition
Pin
Input power
Kp0
Crosstalk per MR
(OFF)
Lp0
Crosstalk per MR
(ON)
λMR
MR’s resonant
wavelength
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Signal-to-Noise Ratio (SNR) in
Optical Interconnects
 We have studied the SNR in optical interconnect
architectures:
 Analysis of the worst-case and the average signal power,
crosstalk noise power, and SNR
 Different optical interconnect architectures: mesh-based,
folded-torus-based, fat-tree-based, and ring-based
ONoCs using WDM
 Indicated the scalability constraints and power efficiency
in different architectures
 Integrated the analytical models into a newly developed
Crosstalk and Loss Analysis Platform (CLAP)
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Crosstalk and Loss Analysis
Platform (CLAP)
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Some of CLAP’s Capabilities
 Analyzes the signal power, crosstalk noise power,
and SNR in arbitrary ONoC architectures of any
network size
 New version (v3.0) includes Coherent crosstalk
analysis
 Optical router analyzer (higher orders of crosstalk)
 Provides the worst-case and the average results
 Available online with documentation:
 http://www.ece.ust.hk/~eexu
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Case Study
 SUOR (Sectioned Un-directional Optical Ring)
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Summary
 Studied the worst-case and the average crosstalk
noise and SNR in optical interconnects
 Developed CLAP, an automated crosstalk and loss
analysis platform that can analyze the signal power,
crosstalk noise power, and SNR in different optical
interconnect architectures
 Crosstalk noise is a critical issue, which restricts the
scalability of optical interconnects and damages the
SNR
 Different optical interconnect architectures have
different SNR performances
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Other Useful Tools and
Resources
 An open tool for heterogeneous multiprocessor research and
development:
COSMIC: Heterogeneous Multiprocessor Benchmark Suite
 An open tool for networks-on-chip based on real applications:
MCSL: Realistic Network-on-Chip Traffic Patterns
 An open tool for optical interconnect network research and
development:
OTemp: Optical Thermal Effect Modeling Platform
 We also maintain a bibliography on inter/intra-chip optical
interconnect networks:
Inter/Intra-Chip Optical Network Bibliography
All are available: http://www.ece.ust.hk/~eexu
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Acknowledgements
 Current group members
 Prof. Jiang Xu, Xiaowen Wu, Zhehui Wang, Xuan Wang, Zhe
Wang, Luan Duong, and Peng Yang
 Past members
 Dr. Mahdi Nikdast, Dr. Yaoyao Ye, Dr. Weichen Liu, Prof.
Sébastien Le Beux
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Thanks!
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