Radiation hard optical link for slhc
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Radiation-Hard Optical Link for SLHC. W. Fernando, K.K. Gan, A. Law, H.P. Kagan, R.D. Kass, S. Smith The Ohio State University. M.R.M. Lebbai, P.L. Skubic University of Oklahoma. June 28, 2007. Outline. l Introduction l Bandwidth of micro twisted-pair cables

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Radiation-Hard Optical Link for SLHC

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Radiation-Hard Optical Link for SLHC

W. Fernando, K.K. Gan, A. Law, H.P. Kagan, R.D. Kass, S. Smith

The Ohio State University

M.R.M. Lebbai, P.L. Skubic

University of Oklahoma

June 28, 2007




lBandwidth of micro twisted-pair cables

lBandwidth of fusion spliced SIMM-GRIN fiber

lRadiation hardness of PIN/VCSEL arrays

lResults on MT-style optical packages based on BeO



ATLAS Pixel Opto-Link Architecture

lATLAS is a detector studying pp collisions of 14 TeV at CERN

upixel detector is innermost tracker

udetector upgrade planned for Super-LHC in 2015

a upgrade based on current pixel link architecture

to take advantage of R&D effort and production experience?

micro twisted pairs decouple

pixel and opto module production

a simplify both production

8 m of rad-hard/low-bandwidth

SIMM fiber fusion spliced to 70 m


GRIN fiber


R&D Issues for SLHC

lbandwidth of ~ 1 Gb/s is needed

ucan micro twisted pair transmit at this speed?

ucan fusion spliced SIMM/GRIN fiber transmit at this speed?

lcan PIN/VCSEL arrays survive SLHC radiation dosage?


Bandwidth of Micro Twisted Pairs

(current pixel cable)

lcurrent pixel cable with thick insulation is quite optimum!


Eye Diagrams

127 m cable

100 m current pixel cable

140 cm

140 cm

60 cm

640 Mb/s

1280 Mb/s

ltransmission at 640 Mb/s is adequate

ltransmission at 1280 Mb/s may be acceptable

l127 m cable is slightly better


Bandwidth of Fusion Spliced Fiber

8 + 80 m spliced SIMM/GRIN fiber

1 m GRIN fiber

2 Gb/s

ltransmission up to 2 Gb/s looks adequate


Radiation Level at SLHC

lOptical link of current pixel detector is mounted on patch panel:

amuch reduced radiation level:

uSi (PIN) @ SLHC:

n2.5 x 1015 1-MeV neq/cm2

n4.3 x 1015 p/cm2 or 114 Mrad for 24 GeV protons


n14 x 1015 1-MeV neq/cm2

n2.7 x 1015 p/cm2 or 71 Mrad for 24 GeV protons

uabove estimates include 50% safety margin


Requirements for PIN/VCSEL


uWhat is responsivity after irradiation?

uWhat is rise/fall time after irradiation?


udriver chip most likely be fabricated with 0.13 mm process

nnominal operating voltage is 1.2 V

nthick oxide option can operate at 2.5 V

aVCSELs must need < 2.3 V to produce 10 mA or more

uWhat is rise/fall time after irradiation?

uWhat is optical power after irradiation?

uWhat current is needed for annealing?


PIN Responsivity

lresponsivity decreases by 65% after SLHC dosage


VCSEL LIV Characteristics






6ULM requires higher voltage to operate

lall arrays have very good optical power


VCSEL Power vs Dosage


lOptowell survives to SLHC dosage

lmore VCSELs might survive with more annealing during irradiation


Opto-Pack Development

lcurrent pixel detector uses Taiwan optical packages

nVCSEL mounted on PCB with poor heat conduction

nmicro soldering of 250 mm leads is difficult

lOhio State develops new opto-pack for SLHC

nuses BeO base with 3D traces for efficient heat removal

nwire bond to driver/receiver chip




Results on Opto-Packs

l30 VCSEL/PIN opto-packs have been fabricated

uall VCSEL opto-packs have good coupled power

aprinciple of new opto-pack has been demonstrated

1 cm

MT ferrule

VCSEL array

Ceramic guide pin



lmicro twisted-pair cable of current ATLAS pixel detector

can be usedfor transmission up to 1 Gb/s

lfusion spliced SIMM/GRIN fiber can transmit up to 2 Gb/s

lPIN responsivity decreases by 65% after SLHC dosage

lOptowell VCSEL survives SLHC dosage

acurrent opto-link architecture satisfies SLHC requirements

lcompact MT-style opto-pack based on BeO has been developed


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