Fiber Characteriztion Measurements and Testing

8/2/2019 Fiber Characteriztion Measurements and Testing

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Fiber Characterization, Measurementsand Testing

Roger [email protected]



Why?



Broadband ExplosionBroadband Worldwide

0

50

100

150

200

250

300

350

400

450

500

2001 2002 2003 2004 2005 2006 2007 2008 2009

Year

S u b s c r i b e r s ( M i l l i o n s ) FTTx

Wireless

HFC

DSL



Network Architecture

ROADMNetwork

OC-192

Edge Router

AccessRouters

OC-192

Access Network

ENIU

MSPP

MSPP

IP DSLAM

Residentialaccessnetwork

ONT

CMTS

FTTTower(IEEE802.16 WiMAX)

FibreAccess(xPON)

CATVAccess

EnterpriseCustomer

MetroNetwork

SuperHead-End

Video Service OfficeLocal Content

CopperAccess

GigE

GigE

GigE

GigE

10GigE

10GigE

10/100M Eth.

Long Haul

Interconnection(OC-192/OC-768) or 10GigE over

)



Traffic rebalancing

ROADM

Network

Congested area



Disaster Recovery

ROADM

Network



40Gbps

100Gbps

10Gbps40Gbps

100Gbps

10Gbps

The entire network must be tested

for longest path and highest rate



Fiber Characterization

What tests make up “Fiber Characterization”?

1. Connector Inspection

2. Optical Loss – Insertion Loss3. Optical Return Loss including Reflectance

4. Chromatic Dispersion

5. Polarization Mode Dispersion



Fiber Connector Performance

RL = 14dB

NC IL<1dB RL = 12dB

PC IL<.7dB RL > 30dB

SUPER PC

SPC IL<0.5dB RL > 40dBULTRA PC

UPC IL<0.5dB RL > 50dB

8º APC IL<0.5dB RL > 60dB

FIBER TO AIR

NON-CONTACT

PHYSICAL

CONTACT

ANGLEDPHYSICAL

CONTACT

PTPIPR

PI PTPR1PR2

PT

PR3

PI

PR3

PI = Incident Power PR1 = Reflected Power (1st Face)

PT = Transmitted Power PR2 = Reflected Power (2nd Face)

PR = Reflected Power PR3 = Slight Scattered Power Reflected From Imperfect Faces

PI PTPR1

8º

PI

8º

PTPR3

PR3

Insertion Loss (IL) Return Loss



Connectors: Handling & Care!!! Warning !!!

Angle Polished Connectors cannot be connected

with flat polished connectors!



Connector Cleaning and Inspection

Inspection techniques:A microscope or fiber probe can be used to inspect connectors

A microscope will act as a magnifying glass, if you inspect a connector on a livefiber, permanent damage can be done to your eyes!

Using a fiber probe is the safest way to inspect a connector



Physically Damaged End-Face

Physical damages to the end face of a connector will bepermanent and it will in most cases require a connector

replacement. Scratches can generate high loss, butmore importantly, cause reflectance that can causetransmitter issues.



Connector Cleaning and Inspection

WHOA

Permanently Damaged



!!!CLEAN YOUR CONNECTORS!!!Facts

90% of all transmission

problems are because ofdirty or damaged connectors

Careful inspection, handlingand most of all CLEANINGcan fix or eliminate mostproblems

Use of a patch cord on the test

equipment will increase thelife of the front connector.

Clean the ferrule! Remove theadapter if possible. Don’t just

push dirt into the interface.



Optical Loss and Insertion Loss

Insertion Loss – the loss of optical energy resulting from the insertion of a

component or device in an optical path

Optical Loss - Difference in power level between the transmitting source and

the receiving power meter. Should comply with the link loss budget.

The total optical system/link loss is the sum of the insertion loss (IL) of the

OLT connector, WDM coupler, splices, fiber attenuation, splitter, ONTconnector and any bad connector matings

Should be tested at all operating wavelengths

Fiber loss is of great importance for installed fiber links sincefiber attenuation (loss of power) directly determines the total loss

and thus the quality of a transmission system.



• LASER output = 0 dBm (1 milliwatt).

• Power meter measures -3 dBm at far end.

• 0 dBm minus -3 dBm = 3 db

• Link loss is 3 db (Not 3 dBm).

Link Loss, dBm vs. dB



OTDR-Optical Time Domain Reflectometer

a break point

splice and connector losses point-to-point distances total cable length

connector quality (Return Loss)

attenuation of the fiber

It is optical radar and can measure:

Installation and Commissioning

Maintenance.

Emergency RestorationFiber identification.Characterization

An OTDR is used for fiber:



How does an OTDR work?

FusionSplice

Bend ConnectorPair

Crack FiberEnd

Mechanical

Splice

Fiber Network

OTDR Measurement Display R e l a t i v e P o w e r ( d B )

Optical Time Domain Reflectometer

Laser

Coupler

PulseGenerator

Detector

Analyzing Circuitry + Display"Intelligence"



Fiber events and their trace representation

Backscatter

Mechanical Spliceor Connector

Air gap

Crack

Loss

Reflection

(Non-Reflective)

Broken fiber-endCleaved end oropen connector

(Reflective)

Reflection non reflective

Bend

Loss

Fusion Splice



If the “bend radius” of the fiber isexceeded, a loss of light will occur

The Longer wavelengths will tend to travel

in the core-cladding interface; thereforehigher loss will be observed at thesewavelengths if the fiber is bent.

A macrobend can be identified bymeasuring the loss at multiple wavelengths

(e.g., 1310 and 1550 nm). If the loss ishigher at longer wavelengths, chances arethat there is a macrobend along the fiber.

Macrobend



Visual Fault Locator—VFLMacrobendings:

A Visual Fault Locator (VFL) can be used to find macrobendings:

Bad splices will also shine using a VFL:



Macrobend Trace

Loss through splice:

1310 - .100 dB

1550 - .699 dB1625 – 1.299 dB



A measure of the total energy reflected back to the source byall the interfaces due to a variation of the index of refraction

(IOR), breaks, voids, backscatter, etc, created inside acomponent or along a link.Comes from the amount of energy lost within componentsand fiber due to back reflections

We use the term « ORL » when speaking of the amount ofenergy returned by a section or an entire linkExpressed as a positive value

ORL [dB] = Pincident [dBm] – Preflected [dBm]

OPTICAL RETURN LOSS (ORL) (dB)



Will come from abrupt changes in the IOR: Fiber break, mechanicalsplice, bulkheads, connectors, etc

We use the term « reflectance » when speaking of the amount of energyreturned by specific points within the network

Expressed as a negative value

Reflectance [dB] = Preflected [dBm] - Pincident [dBm]

(Fresnel) Back Reflections (-dB)

Fiber section

Patch Panel

Fiber sectionFiber section

Connector

Patch Panel

Mec. Splice

Connectorreflectance: -45dB

Mechanical splicereflectance: -45dB

Connectorreflectance: -55dB



Fiber section

Fiber section

Patch Panel

Mechanical splice

Testing System ORL

C.O.

DropSplitter

Reflectance = Link ORL

ITU Recommendations for ORLOC-3: 20 dB

OC-12: 20 / 24 dBOC-48: 24 dBOC-192: 27 dBFTTx: 32 dB with Analog Video



Dynamic Range

Pulse Width

Dead Zone

Launch Cables

Key Performance Parameters



Dynamic Range - What Distance Can I Measure?

The maximum distance you can measure depends onthe attenuation of the fiber

and the dynamic range of your OTDR.

To measure long fibers, or fast measurements onshort fibers, you want a high dynamic range.

Small Dynamic Range Large Dynamic Range0 km200 km 200 km



Pulse Width- Affecting Dynamic Range & Deadzone

Short Pulse Long Pulse

Long Pulses Width provides:Travel further down the fiberImprove the signal-to-noise ratio

(SNR)Result in less resolution

Result in longer dead zones

Short Pulse Width provides:Short distance down the fiberLowe SNR

Better resolutionShorter dead zones



Event and Attenuation Dead Zones

Attenuation Deadzone

Event Deadzone

1.5dB

0.5 dB

Event dead zone

The event or reflective dead zonerepresents the minimum distancebetween the beginning of a reflective

event and the point where aconsecutive reflective event should

clearly be recognized.

Attenuation dead zone

The attenuation or non-reflective deadzone is the minimum distance afterwhich a consecutive reflective event

and attenuation measurement can bemade.



Launch Cable – Yes or No for OTDR measurement

Launch cables:

A Launch cable is used if user wants to measure the first or

last connector of an optical link.It allows the OTDR to have a power reference before andafter the connector in order to measure it.

Standard available lengths are will vary from 200 meters to

1500 meters

Launch cable



Without a Launch Cable (Pulse Suppressor Box):

The loss of thefirst connector ofthe link is NOT

measured




With a Launch Cable (Pulse Suppressor Box):

The loss of thefirst connector of

the link ismeasured

Fiber sectioncorresponding to

PSB box




Non-Linear EffectsCD, PMD, 2nd order PMD

Attenuation problems: Output power,receiver sensitivity, link loss, ORL

10 Gig10 Gig

40 Gig40 Gig

100 Gig100 Gig

1 Gig1 Gig

1 megabit1 megabit

Physical Layer–Dominant Sources of Signal Degradation



Dispersion dangerDispersion is a complex physical phenomenon whichresults in light pulses being spread out in the timedomain as they pass down an optical fiber.

It is an intrinsic property of the fiber physical layer.

At low transmission speeds the inter bit gap means thesystems are intolerant of this pulse spreading.

At higher speeds (10G and above), it can have acatastrophic effect.



TT

Dispersion in a transmission

10% 10%



Effects of Dispersion



Dispersion and BER



So what … ?

DispersionCD/PMD

Pulsebroadening

In the physical layer At the transport layer

SLA penaltiesInability to operate at

high speed(extreme)

Significant delaysand expense ininstallation &

commissioning

BIT Errors and BERT

issues

Business issues



Source wavelengths do not propagate at the same speed throughglass, thus they arrive at different times

A pulse transmitted in such way suffers a spread, calledDispersion, limiting the transmission bandwidth.

λλλλ1 λλλλ2 λλλλ3 λλλλ1 λλλλ2λλλλ3

λλλλ1 λλλλ3

PulsePulse Spreading

Chromatic Dispersion



n2 n1

A pulse transmitted in such medium suffers abroadening, a dispersion, limiting the signaltransmission bandwidth.

T

TTB = DL∆λ

where ∆λ = sourcelinewidth

ex. 100 MHz (0.0008 nm)

Chromatic Dispersion

P

λ

-80 -75 -70 -65 -60 -55 -50 -45 -40

-20 -15 -10 -5 0 5 10 15 20



DFB LASER

mw

Ghz

DFB LASER direct modulation



P u l s e d e l a y

( p s )

λλλλ (nm)

λλλλ0000

zero dispersion wavelength

C h r o m

a t i c D i s p e r s i o

n

( p s / n m k

m )

λλλλ (nm)

+0

_

S 0

s l o p e

a t z e r o

d i s p e r s i o

n

λλλλ0000zero dispersion wavelength

Chromatic dispersion issues

Different wavelengths different velocities

The slope of this

Gives this

vg vg



Fiber Attenuation and Dispersion



Dispersion of new Fiber Types

+2

+4

- 2

- 4

Lucent

TrueWave

Corning LS

G.653

C

h r o m a t i c D i s p e r s i o n ( p s / n m

- k m )

Lucent

TrueWave

Balanced +

Lucent

TrueWave

Balanced -

1530 1540 1550 1560 1570

EDFA L-bandS-band EDFA CEDFA C--bandband

Corning

MetroCor

Reduced Slope

Corning LEAF

SMF-28e

+17



OC-12 =>633Mbps => T= 1608 ps => 10%=160ps

GigE =>1.25Gbps => T= 800ps => 10%=80ps

OC-48 =>2.488Gbps => T= 402 ps => 10%=40ps

OC-192 =>9,953Gbps => T= 100.5 ps=> 10%=10ps

10GigE WAN =>9.953Gbps => T= 100.5 ps=> 10%=10ps

10GigE LAN =>10.3Gbps => T= 97 ps => 10%=9.7ps

OTN =>10.709Gbps => T= 93.4 ps => 10%=9.3ps

OC-768 =>39.808Gbps => T= 25.1 ps => 10%=2.5ps

CD Limits in a transmission



Polarization Mode Dispersion:The light is an electro-magnetic wave

The light consists of

electric field - E

magnetic field - Htravelling in time (ωωωω) and space (k) along the axis of propagation (Z).



∆τ

∆τ

z,tz,t

TT

slow axisslow axis

tt

fast axisfast axis

Polarization Mode Dispersion



Fiber defects Manufacturing (Rare) Installation generated

– twists, strains,bends.

EnvironmentalConstraints

Fiber defects Manufacturing (Rare) Installation generated

– twists, strains,bends.

EnvironmentalConstraints

Geometric Internal Stress

Lateral Pressure

Bend

Heat

Wind (aerialfibers)

What causes PMD?






Asymmetries inAsymmetries in fiberfiber core geometry and/or stress distribution createcore geometry and/or stress distribution create fiberfiber locallocalbirefringence.birefringence.

A "real"A "real" fiberfiber is a randomly distributed addition of these localis a randomly distributed addition of these local birefringentbirefringent portions.portions.




PMD and DGDDGD MAXDGD MAX

2 * PMD2 * PMD



M. Karlsson, et al., IEEE. J. Lightwave Techn.127 km buried DSF

!"#

#$%&!&

'

%(#)*(&+,

,

-

#$%&!&

'

%(#)*(&+,

,

-

On day five – 10gig services are

impacted by PMD

On day twentyfive – 10 Gigservices are

OK.

PMD vs. Wavelength: Long-term Variability



Proposed PMD coefficient for a 99.994% probability that thepower penalty will be less than 1 dB for 0.1 of the bit period

Bit rate

(Gb/s)

2.5

10

2040

100

Average DGD

(ps)

PMD coefficient

400 km fiber (ps/km½)

40

10

52.5

1

≤≤≤≤ 2.0

≤≤≤≤ 0.5

≤≤≤≤0.25

0.125

0.06

PMD Limits in a transmission



FTB-5700: Single-ended dispersion analyzer

FTB 5700 Si l d d di i l



FTB-5700 Single-ended dispersion analyzer



SOA

PBS

CD feature explained - 1

TunableFilter

OSA-like

In-Out

Grating

Motor

S-C-L Band

Scrambler



PBS

Scrambler

CD feature explained - 2

S-C-L Band

Check delay at

given Lambda

SOA

TunableFilter

Preparesnext lambda



Based on reflectometry8 measurements, different lambdas.Different distance (IOR variation)

FTB-5700: FOTP-168



SOA

PBS

Scrambler

PMD feature explained - 1

TunableFilter

OSA-like

In-Out

Grating

Motor

S-C-L Band

Pair of close lambdas,random SOP in FUT



SOA

PBS

Scrambler

PMD feature explained - 2

TunableFilter

Measure Local Delay

S-C-L Band

Preparesnext pair

FTB 5700 method: TIA FOTP 243:



FTB 5700 method: TIA-FOTP-243:

SSA (SOP Scrambling Analysis).

t

tPMD



FTB 5700 single ended capability

Connectors

Connectors

or

splices

5km 7km 8km 3km 15km 5km

Test 1

STARTPMD = 12ps

Disconnect

orbreak the splice

here

Test 2

PMD = 11.7ps

Test 3

PMD = 3.1ps

11.3ps!!

FTB 5800/5500B



FTB-5800/5500B: Dual-ended dispersion analyzer



Source

Oscillator DUT or FUT

Optical filteringPhasemeter

FTB-5800 method: FOTP-169Approved Phase shift method

FTB 5500B: FOTP 124A



Broadband

SourcePolarizer

Interferometer

Mirror

Analyzer

PBS

Detectors

FUT

FTB 5500B: FOTP-124A

ps

%Generalized Interferometric method (GINTY)



Thank you!

Questions?

Roger [email protected]

805-217-0170

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Fiber Characteriztion Measurements and Testing

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