New Focus 1480 User manual

USER’S GUIDE
15-GHz & 25-GHz
Photodetectors
Models1480&1481
IncludesModel1481-50
Thesephotodetectorsaresensitivetoelectrostatic
dischargesandcouldbepermanentlydamagedif
subjectedeven to smalldischarges. Groundyour-
selfadequatelypriortohandlingthesedetectorsor
makingconnections.Agroundstrapprovidesthe
mosteffectivegroundingandminimizesthe
likelihoodofelectrostaticdamage.
NEW FOCUS, Inc.
2630Walsh Ave.• Santa Clara,CA 95051-0905• USA
phone:[phone] • Fax:[phone]
e-mail:[e-mail] • www.newfocus.com
®
®
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Warranty
NewFocus,Inc. guaranteesitsproductstobefreeofdefectsforoneyear from
thedateofshipment.Thisisinlieuofallotherguarantees,expressedorimplied,
anddoes notcoverincidentalorconsequentialloss.
Copyright 2000,NewFocus,Inc.Allrights reserved.
The symbolandNEWFOCUS,Inc.are registeredtrademarks
ofNEWFOCUS,Inc.
DocumentNumber 151095Rev.A
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15-GHz & 25-GHz Photodetectors Contents • 3
Contents
Operation 5
Introduction .... ..... ..... ..... ..... ..... .. ... .. ... .. .. 5
HandlingPrecautions..... ..... .. ... .. ..... ..... ..... ... 6
QuickStart.... ..... ..... ..... ..... ..... .. ... .. ..... .... 7
CheckingtheBatteryand OffsetVoltage .... ..... ..... ... 8
MakingtheMicrowaveConnection... .. ..... ..... ..... .. 9
ConnectingtheDetectorto theOpticalInput ... ..... .... 9
Characteristics 11
PhotodetectorCharacteristics ... .. ..... ..... ..... ..... . 11
Bias-MonitorCharacteristics ..... ..... ..... ..... ..... .. 12
Responsivity .. ..... ..... ..... ..... ..... ..... .. ... .. ... 12
Troubleshooting 13
TestingthePhotodiode . ..... ..... ..... .. ... .. ... .. .... 13
CheckingtheDC-OffsetVoltage.. ..... ..... ..... .. ... .. 13
BasicOpticalTest.. ..... .. ... .. ... .. ..... ..... ..... .... 13
CleaningtheFiberConnector ... ..... ..... ..... ..... ... 14
CustomerService 17
TechnicalSupport.. ..... ..... ..... ..... ..... .. ... .. ... 17
Service..... ..... .. ... .. ..... ..... ..... ..... ..... ..... . 17
AppendixI:MicrowaveConnectors 19
AppendixII:InsidethePhotodetector 20
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4 • Contents NEW FOCUS, Inc.
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15-GHz & 25-GHz Photodetectors Operation • 5
Operation
Introduction
High-speedmeasurementsareeasywiththe Models
1480and1481photodetectormodules.These
modulesconvertyouropticalsignalstoelectronic
signals,ineffectgivingeveryhigh-speed/high-
frequencyinstrumentinyourlabanopticalinput.
Eachmoduleconnectsdirectlytothe testinstrument
oramplifier,eliminatingtheneedforcoaxialcables,
whichcouldseriouslydistortpicosecondpulsesand
attenuatemicrowavesignals.The optical signalis
deliveredtothephotodiodeinthemodulethrougha
multimodeoptical fiber.Moreover,thephotodiode
biascircuitand batteryareself-contained,eliminating
thehassleofexternalpowersuppliesandexpensive
biasnetworksandreducingthe possibilityof
photodiodedamageduetoovervoltage.
TheModels1480and1481useaGaAsPINphotodiode
designedforhighresponsivityinthe 780–870-nm
wavelengthrange.Thehigh-speedcircuitryproducesa
cleanimpulseresponse,makingthesemodelsidealfor
digitalcommunicationmeasurements.A 50- Ω
terminatingresistorminimizeselectricalreflections,
whichhelpstominimize ringingwhen usedwith
amplifiers whichmay nothave perfect50- Ω inputs.
TheModel1480hasaninternal62.5-µmmultimode
fiberwhichdeliverstheinputlighttothe65-µm-
diameterphotodiode,permittingtheuse ofdelivery
fibers with corediametersof62.5µm orsmaller,
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6 • Operation NEW FOCUS, Inc.
includingsingle-modefibers.Theinternalfiberis
anglepolishedforlowbackreflection.
TheModel1481hasaninternalsingle-modefiber,
whichisanglepolishedtoreducebackreflections.The
Model1481-50hasaninternal50-µmmultimodefiber
andusesaGRINlens toimagethefiberoutputonto
the25-µmphotodiodeusedin thesemodels.The
opticalelementsareanti-reflectioncoatedforlowback
reflectionat850nm.
Figure 1:
Models
1480 & 1481
photodetector
modules
Handling Precautions
Wheneverhandlingthephotoreceiver,makesureto
followthese precautions:
• Priortohandlingthedetectorormaking
connections,besuretogroundyourself
adequately—evensmallelectrostaticdischarges
couldpermanentlydamagedthedetector.A
groundstrapprovides the mosteffective
groundingandminimizesthe likelihoodof
electrostaticdamage.
• DonotovertorquethemicrowaveK-connector.
Excessivetorquecandamage connectors.
• Makesuretheopticalconnectorisclean and
undamagedbeforeconnectingittothedetector
module.
Optical Input
Off On Batt
Chk
Bias
Monitor
FC/PC connector
for fiber optic input
Bias-monitor port—output
is equal to photodiode current
times 1000 Ω, for 1 mV/µA.
Power switch
Battery-check button—
press to apply the photo-
diode bias voltage to
the bias-monitor port.
2.00 (50.8)
2.25 (57.1)
2.00
(50.8)
Output K-connector
3.14 (79.8)
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15-GHz & 25-GHz Photodetectors Operation • 7
Quick Start
UsetheModels1480and1481high-speedGaAs
photodetectormodulesfor detectinglightinthe
wavelengthrangefrom400to870nm.Eachmoduleis
50- Ω terminatedandhasaninternalbatteryandbias
circuitry tomakeitself-contained—noadditional
powersupplyorbias circuitryisneeded.
Tooperatethemodule,followthesequick-start
instructionsorconsulttheothersectionsofthis
manualfor moredetail.
1. Takeproperprecautionstoavoidelectrostatic
damagetothe photodiode.(See“HandlingPrecau-
tions”onpage6.)
2. Removethemodulefromitscase.
3. Turnonpowerusingthe“Off/On”switch.
Ifyouare usingthedetectorforthefirst time,oryou
wishtocheckthebatteryandDCoffset,performsteps
4,5and6
4. Connectavoltmetertothe“BiasMonitor”SMA
connector.
5. Pressthe“BattChk”button.Thevoltageshouldbe
atleast3.5V.
6. Releasethe“BattChk”button.Withoutanoptical
input,thevoltageshouldbelessthan10mV.
7. Connectthephotodetectormoduletoyour
measurementinstrument,beingcarefulnotto
over-torquetheK-connector.Theinstrumentmust
havea50- Ω inputimpedance.
8. Checkthattheopticalpoweremergingfromyour
fiberisbelowthecwSaturationPower, as
appropriate, to ensure detectorlinearityandto
avoiddetectordamage.(See “Characteristics” on
page11 . )
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8 • Operation NEW FOCUS, Inc.
9. Connectyouropticalfibertotheconnectoronthe
detectormodule.
10. Whenfinishedusingthe module,turnoffthe
powertopreserve batterylife.
Ifanyofthesestepspresentproblemsoryouwould
likemoreinformation,pleaseconsulttheremainderof
thismanual.
Checking the Battery and OffsetVoltage
Thebatteryandoffsetvoltageshouldbechecked
regularlytoensureproperfunctioningofthe detector.
1. Turnonthemoduleusingthepowerswitch.
2. Connectthe“Bias Monitor”porttoavoltmeter.
3. Press andholdthe “BattChk”buttonandobserve
thebias-monitoroutput.Thephotodiodebias
voltageismomentarilyappliedtothe“Bias
Monitor”SMAconnector.Areadingof5Vonthis
connectoristypical with anewbattery; the
batteryshouldbe replaced whenthevoltage
reaches3.5V.
4. Releasethe“BattChk”buttonandobservethe
voltagelevel onthevoltmeter.Withoutanoptical
input,thisvoltageis the DCoffsetplusdark
current. This“darkvoltage”shouldbeless than
10mV.
5. Ifneeded, keepthevoltmeterconnectedtothe
moduletooptimizecouplingtothefiber.
Replacing the battery
1. Turnoffthemoduleandremovethetwoscrews
onthebackpanelwithaPhillipsscrewdriver.(See
Figure1onpage6.)
2. Removethebackpanelandreplacethebattery.
3. Replacethebackpanel.
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15-GHz & 25-GHz Photodetectors Operation • 9
4. Checkthebatterylevelasdescribed above.
Making the Microwave Connection
1. Connectthephotoreceivermodule’smicrowave
connector toa testinstrumentthathasa50- Ω
input,suchasanoscilloscopeorspectrumana-
lyzer, ortoanother50- Ω load.Ifnecessary, usea
high-frequencycable(best performanceis
achievedwithoutacable).
2. Toavoidconnectordamageand signaldistortion,
besurethatthecableandtheinstrumentyou
intendtoconnecttothemodulehavecompatible
connectors.See “AppendixI:Microwave
Connectors”onpage19 fora listofcompatible
connectors.
Connecting the Detector to the Optical Input
1. Measurethepeak powerinthefiberpriortocon-
nectiontothe moduletobesureitis within the
safeoperatingrange(see“PhotodetectorCharac-
teristics”onpage11).
2. Connectthefiber-opticcabletothe fiber-optic
inputonthedetectormodule.Ifneeded,theBias
Monitormaybeusedtooptimizecouplingtothe
fiber.
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10 • Operation NEW FOCUS, Inc.
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