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Prepared by:

Muhammad Azam

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OutlinesWhat is OTDR?

Basic principle o operation!

Basic re"uirements or setup o OTDR! Types o OTDRs a#ailable!

 Testin$ usin$ OTDR

 Trace Analysis

%imitations

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What is OTDR?OTDR 'Optical Time Domain Re(ectometer) is a

#ersatile portable instrument that is used *idely toe#aluate the characteristics o an installed +ber optic

lin,!

-t also measures optical +ber parameters such asattenuation. len$th. optical connector and splices loss!

OTDR technolo$y is desi$ned to pro#ide a sin$leended test o any cable!

OTDR undamentally is an Optical RADAR!

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Basic operational principle

OTDR %A0R

0i$nalprocessor and

displayPhotodetector

2iber under test

Return0i$nals

Optical3irculator

-nputsi$nal

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OTDR 0etup

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OTDR 0etup6 RA78 The +rst one to consider is 9Ran$e or distance o +ber to test!

Many OTDRs ha#e automatic len$th detection unctions. but i

the len$th is ,no*n. the user can set the ran$e manually! The

ran$e settin$ should be ad;usted to no less than 1!5 to &< the

+ber span under test!

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Ran$e>!

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OTDR 0etup6 Pulse Width

%on$er pulse *idths are used or lon$er ran$e tests! As distance

increases. pulse *idth must $o up. other*ise traces *ill appear

9noisy and rou$h!

0imilarly. short traces *ill be inconclusi#e i lon$ pulse *idths are

used 'e#ents may be missed or clipped)!@

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Pulse Width>

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OTDR 0etup6 -nde< o

Reraction -n re#ie*. the -nde< o Reraction is a *ay o measurin$ thespeed o li$ht in a material! %i$ht tra#els astest in a

#acuum. such as outer space! The actual speed o li$ht in a

#acuum is /. ,ilometers per second. or 1@=. milesper second! -nde< o Reraction is calculated by di#idin$ the

speed o li$ht in a #acuum by the speed o li$ht in some

other medium!

Index of Refraction = Speed of Light in a Vacuum

  Speed of Light in a Medium

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-nde< o Reraction>- the 8roup -nde< o Reraction '8-R) settin$ in the OTDR

does not match that o the +ber under test. the results *ill

sho* incorrect distances as a result!

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OTDR 0etup6 A#era$in$

 TimeA#era$in$ time reers to ho* lon$ the user allo*s the de#ice tota,e samples 'ho* lon$ the test 9runs)! The lon$er thetestin$Ca#era$in$ time allo*ed. the better the result!

#entually. enou$h data is a#era$ed or a $ood test and

continuin$ to test *ont yield any more o an accurate result!

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OTDR 0etup6 A#era$in$

 Time>

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OTDR Types

Most common OTDRs use a 9console desi$n allo*in$ the user to

up$rade or s*ap bet*een MM and 0M modules!

 These oEer similar analytical eatures to the lab "uality OTDRs. but

are more ru$$ed and +eld portable! 2iles can be sa#ed to #arious

media and later do*nloaded to a P3! 14

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Micro OTDRs

Micro6OTDRs are the ne

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OTDR Testin$8enerates a baseline trace: A 9#isual o the

lin,!

3an identiy and e#aluate speci+c e#ents in

the lin,!

3able acceptance tool!

2ault location tool!

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 Troubleshootin$ Tools

Fsed

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OTDR Trace Analysis

3onnect the OTDR to a launch 'suppressionCreerence) cable!

 The secondary end o the launch cable *ill be connected to

an access panel at one end o the +ber optic span under test!

Optionally. a recei#e cable can be attached at the ar end! 1@

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Obser#ations on display

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 Trace Analysis>!

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 Trace Analysis>!Most commonly. users manipulate t*o cursors. 9A and 9B.to illustrate *hat is reerred to as 9t*o point loss on an

OTDR result!

 This can be used to sho* loss in a sin$le e#ent or in a

$roup o e#ents! These cursors can be indi#idually mo#ed

let and ri$ht to speci+c points on the result!

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 Trace Analysis>!

Fse cursorCmar,ers to isolate indi#idual e#ents. such as the

repair splice location 'abo#e)>

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 Trace Analysis>!

>or the t*o point loss 'attenuation) o an entire net*or,

span 'abo#e)> &/

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 Trace Analysis>!

>or the physical len$th o a +ber span 'abo#e)!

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OTDR %imitations The limited distance resolution o the OTDR ma,es it #ery

hard to use in a %A7 or buildin$ en#ironment *here cables

are usually only a e* hundred meters lon$!

 The OTDR has a $reat deal o diGculty resol#in$ eatures in

the short cables o a %A7 and is li,ely to sho* H$hostsH rom

re(ections at connectors. *hich conuses the user!

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