Optical Backplanes -Fantasy or Reality?

Beth MurphyScott Schaeffer

Paper Outline

• Definition of a “Backplane”

• Overview of Backplane Technologies

• Advantages of an Optical Backplane

• Components of a Typical Optical Backplane

• Optical Backplane Applications & Examples

• The Future of Copper Backplanes

• Cost Comparison of Copper vs. Optical Backplane

Definition of a “Backplane”

• Traditional Copper Laminate BasedBackplane

• Laminate Backplanes Interconnectedwith Copper Cables

• Optical Backplanes

“Backplane” Path

SERDES SERDESSingle CuBackplane

Traditional

SERDES SERDESCu

Backplane

Multi-Rack Cu Cabled

CuBackplane

Cu Cable

SERDES SERDESSingle CuBackplane

Multi-Level

ModulatorDe-

Modulator

SERDES SERDES

Optical Backplane

FOXCVR

FOXCVR

FO CableOpticalBackplaneFO Cable

Definition of a Logical Backplane

Limitations of Traditional Copper Backplanes

• FR-4 Laminate Backplanes• Laminate Based Backplanes Interconnected

by Copper Cable– 1.25 Gbps– 2.5 Gbps– 10 Gbps

Approximate Amplitude vs. Length Curves at 1.25 Gbps

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.5 5 10 20 30 40 50

Length in Meters

Am

plit

ud

e

22 AWG Shielded Quad, 150 Ohm

28 AWG Shielded Quad, 150 Ohm

26 AWG Shielded Pair, 100 Ohm

30 AWG Shielded Pair, 100 Ohm

26 AWG Coax, 50 Ohm

30 AWG Coax, 50 Ohm

38 AWG Coax, 50 Ohm

Length vs. Attenuation at 1.25 Gbps

Approximate Amplitude vs. Length Curves at 2.5 Gbps

0.20.30.40.50.60.70.80.9

1

1.5 5 10 20 30 40 50

Length in Meters

Am

plit

ud

e

22 AWG Shielded Quad, 150 Ohm

28 AWG Shielded Quad, 150 Ohm

26 AWG Shielded Pair, 100 Ohm

30 AWG Shielded Pair, 100 Ohm

26 AWG Coax, 50 Ohm

30 AWG Coax, 50 Ohm

38 AWG Coax, 50 Ohm

Length vs. Attenuation at 2.5 Gbps

0 2 4 6 8 10 1 20

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

Len

gth,

met

ers

Un e qu a liz e d 22AWGEqualiz e d 22AW G

Data Rate

Len

gth

in m

eter

sLength vs. Data Rate to 12.5 Gbps

Advantages of an Optical Backplane

• Native Optical Domain

• Reach (or Length)

• Obsolescence Proofing and Performance

• Scalability

Applications for Optical Backplanes

• Applications in the Optical Domain

• Applications Replacing Copper where Reachis the Driver

• Applications Replacing Copper wherePerformance is the Driver

Optical Backplane Technologies

• Polymer Waveguide

• Optical Fiber Circuit

Polymer Waveguide

ADVANTAGES:• Low signal skew & distortion• Noise immunity• Very low crosstalk• Frequency independent loss• DWDM Multiplexing• 12-60 channel LIGHTRAY MPX connectors• Waveguide multi-channel connectors• Mandatory in purely optical systems such as OXC

Polymer Waveguide

OPTICAL POLYMERSConcept:

– Films or coatings– 25-50 micron density– Multilevels possible– Light “channels” formed by imaging process

Development needs:– Vector routing (“Bends”)– Inter level connection– Low Loss

Optical Fiber Circuit

• Fiber Equivalent of a Copper Backplane

Optical Fiber Circuit

Components of a Typical Optical Backplane

• Transceiver

• System Card Fiber Cable Assembly

• Backplane Connectors

• Optical Fiber Circuit

SYSTEM CARDELECTRICAL/MECHANICAL BACKPLANE

Optical Backplane

Blindmate Optical Connectors

Ribbon Cables

Electrical Connectors

Optical Transceivers

900 um Buffer Fiber

Typical Optical Backplane System Components

Examples of Optical Backplanes

• Inter-Rack Optical Backplanes

SYSTEM CARDELECTRICAL/MECHANICAL BACKPLANE

Optical Backplane

Blindmate Optical Connectors

Ribbon Cables

Electrical Connectors

Optical Transceivers

900 um Buffer Fiber

Optical Backplane “Inter-Rack” Components

Examples of Optical Backplanes

• Inter-Rack Optical Backplanes

• Intra-Rack Optical Backplanes

SYSTEM CARDELECTRICAL/MECHANICAL BACKPLANE

Optical

Backplane

Blindmate Optical Connectors

Ribbon Cables

Electrical Connectors

Optical Transceivers

900 um Buffer Fiber

Optical Backplane “Intra-Rack” Components

Examples of Optical Backplanes

• Inter-Rack Optical Backplanes

• Intra-Rack Optical Backplanes

• Inter-Device “Optical Backplanes”

SYSTEM CARDELECTRICAL/MECHANICAL BACKPLANE

Optical Backplane

Blindmate Optical Connectors

Ribbon Cables

Electrical Connectors

Optical Array Devices

System Card Optical Circuit

“Inter-Device” Optical Circuit Components

Fully Integrated Optical Backplane System

System Card

Blindmate Optical Connectors

Ribbon Cables

Electrical Connectors

To NextRack/Shelf

Electrical/MechanicalBackplane

OpticalBackplane

Premise/UserInterface

Optical Array Devices

System Card Optical Circuit

OpticalCross

Connect

OpticalCross

Connect

RibbonCable

Breakout

The Future of Copper Backplanes

• New Laminates

• Next Generation Copper BackplaneInterconnects

• Multi-Level Signaling

The Effect of NewLaminates at 4.8 Gbps

Fig 10

The Effect of NewLaminates at 9.6 Gbps

• Backplane Interconnects for 10 GbpsApplications– Plated Through-hole Capacitance and

Inductance are the Bottleneck– Coaxial Performance at Non-coaxial

Density– Footprint Loss vs. Density

4 Level Pulse Amplitude Modulation PAM

Multi-Level Signaling

DataRate /

ChannelTechnology

CopperBackplane* see Note 1

Copper Cables Fiber –Std. SFF Optics Device

** see Note 2

Fiber –Array

Cost /Gbps

~ $1.83-$7.05

~$30 ~$106 ~$116

1.25

Gbp

s

Reach <~36” 30m 22 AWGShielded Quad withHSSDC likeinterconnect

220m IEEE 802.3z (MMF) 300m HIPPI 6400 (MMF)

Cost /Gbps

~ $.92-$3.53 $10 $180 TBD

2.5

Gbp

s

Reach <~24” 18m 22 AWGShielded Quad withHSSDC likeinterconnect

3-5 km (SMF) TBD

Cost /Gbps

~$.92-$3.53(RO4350)

$4

5 G

bps

Reach <~24”” 14m 22 AWGShielded Quad withHSSDC likeinterconnect

TBD TBD

TBD

Cost/Gbps

~$.46-$1.76(RO4350)

$2 $1060

10 G

bps

Reach TBD 8m 22 AWG ShieldedQuad with HSSDClike interconnect

TBD TBD

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