K.K. Gan IWORID-8 1

Bandwidths of Micro Twisted-Pair Cables and Fusion Spliced SIMM-GRIN Fibers

K.K. GanThe Ohio State University

July 5, 2006

K.K. Gan IWORID-8 2

Outline

Introduction

Bandwidth of micro twisted-pair cables

Bandwidth of fusion spliced SIMM-GRIN fibers

Measurement of VCSEL characteristics

Summary

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ATLAS Pixel Opto-Link Architecture

ATLAS is a detector studying pp collisions of 14 TeV at CERNpixel detector is innermost subsystemdetector upgrade planned for Super-LHC in 2015

current optical link of pixel detector transmits signal at 80 Mb/sopto-link production is decoupled from module production

transmit signal to/from module with micro twisted pairsuse PIN/VCSEL arrays coupled to robust fiber ribbonuse 8 m of rad-hard/low-bandwidth SIMM fiber fusionspliced to 70 m rad-tolerant/medium-bandwidth GRIN fibersimplify opto-board productionupgrade based on current pixel link architectureto take advantage of R&D effort and production experience?

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R&D Issues for SLHC

bandwidth of ~ 640 Mb/s is neededcan micro twisted pair transmit at this speed?can fusion spliced SIMM/GRIN fiber transmit at this speed?

can PIN/VCSEL arrays survive SLHC radiation dosage?

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Bandwidth of Micro Twisted Pairs

bandwidth of 3 micro twisted-pair wires were compared:38 AWG/100 µm, 2 turns/cm (current pixel cable)36 AWG/127 µm, 2 turns/cm36 AWG/127 µm, 4 turns/cm

0

200

400

600

800

1000

50 70 90 110 130 150Length (cm)

Ris

e Ti

me

(20%

- 80

%) (

ps)

AWG 38, 5 TPIAWG 36, 5 TPIAWG 36, 10 TPI

2 T/cm2 T/cm4 T/cm

current pixel cable is the best!

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Eye Diagrams at 350 Mb/s

140 cm pixel cable

Skewclear 60 cm pixel cable

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Eye Diagrams at 650 Mb/s

60 cm pixel cable

140 cm pixel cable

Skewclear

transmission at 650 Mb/sis adequate

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Eye Diagrams at 1.3 Gb/s

60 cm pixel cable

140 cm pixel cable

Skewclear

transmission at 1.3 Gb/sis marginal

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Using Skewclear in Pixel Detector?

A picture is worth a thousand words…

60 µm wires

Skewclear

Skewclear is too big for pixel detector

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Bandwidth of Fusion Spliced Fiber

29 m spliced SIMM/GRIN fiber20 m GRIN fiber

2 Gb/s

transmission up to 2 Gb/s looks adequate

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Requirements for VCSELVCSEL driver chip most likely be fabricated with 0.13 µm process

operating voltage is 1.2 Vthick oxide option can operate at 2.5 VVCSEL must need < 2.3 V to produce 10 mA or more

What is VCSEL optical power after irradiation?Can VCSEL be annealed after irradiation?

What VCSEL current is needed for annealing?

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Rise/Fall Time of VCSELs

all VCSELs have similar rise timeULM has somewhat slower fall time

0

40

80

120

160Rise TimeFall Time

Tim

e (p

s)

ULM OptowellAOC Finisar

(20-80%)

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I-L and I-V Characteristics

somewhat high voltage needed to drive VCSELvery good optical power

ULM850-00-TT-HSMAPP

0.0

0.5

1.0

1.5

2.0

2.5

0 2 4 6 8 10 12 14Current (mA)

Volta

ge (V

)

0

500

1000

1500

2000

2500

Opt

ical

Pow

er ( µ

W)

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I-L and I-V Characteristics

AOC HFE419X-441

0.0

0.5

1.0

1.5

2.0

2.5

0 2 4 6 8 10 12Current (mA)

Volta

ge (V

)

0

500

1000

1500

2000

2500

Opt

ical

Pow

er ( µ

W)

good optical powercandidate for irradiation study

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I-L and I-V Characteristics

Optowell TP85-LCP0N

0.0

0.5

1.0

1.5

2.0

2.5

0 2 4 6 8 10 12Current (mA)

Volta

ge (V

)

0

500

1000

1500

2000

2500

Opt

ical

Pow

er ( µ

W)

very good optical powercandidate for irradiation study

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Summarymicro twisted-pair cable of current ATLAS pixel detectorcan be used for transmission up to 1 Gb/sfusion spliced SIMM/GRIN fiber can transmit up to 2 Gb/s

current opto-link infrastructure satisfies SLHC requirementtwo VCSEL candidates identified for irradiationwith 24 GeV protons at CERN this August