Fiber Testing Basics and FTTX Application

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Fiber Testing Basics and FTTX Application
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Fiber Testing Basics and FTTX Application

• Fiber Testing Basics
• Optical Loss and Insertion Loss
• Optical Return Loss and Reflectance
• Connector Quality
• OTDR Trace Analysis
• FTTX Testing Overview and Challenges
• Construction Phase
• Installation/Turn Up Phase
• Troubleshooting after the Fiber Plant is
  Active
• Conclusion

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Testing Changes

• System Managers, Manufacturers and Engineers are
  looking for
• Bidirectional Tests
• Optical Loss
• Optical Return Loss
• OTDR Traces
• Connector Inspection
• Better Documentation (Characterization of Fiber)
• Basic OTDR Trace Analysis from the Technicians

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Installation Testing Optical Loss and Insertion
Loss

• Bidirectional end to end loss measurement
• Optical Loss - Difference in power level (loss)
  between the transmitting source and the receiving
  power meter
• Insertion Loss the loss of optical energy
  resulting from the insertion of a component or
  device in an optical path
• The total optical system/link loss is the sum of
  the insertion loss (IL) of the OLT connector, WDM
  coupler, splices, fiber attenuation, splitter,
  ONT connector and any bad connector mating
• Should comply with the link loss budget
• Optical splitters are the greatest contributor to
  loss
• Should be tested at all operating wavelengths
  especially when the network includes older
  cables. This is because fibers designed for use
  at 1550 nm may not have been previously qualified
  for use at 1490 nm and may show higher
  attenuation than expected.

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OPTICAL RETURN LOSS (ORL) (dB)

• A measure, from one end, of the total energy
  reflected back to the source by all the
  interfaces due to a variation of the index of
  refraction (IOR), breaks, voids, backscatter,
  etc, created inside a component or along a link.
• Comes from the amount of energy lost within
  components and fiber due to back reflections
• We use the term  ORL  when speaking of the
  amount of energy returned by a section or an
  entire link
• Expressed as a positive value
• ORL dB Pincident dBm Preflected dBm

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Optical Return Loss (ORL)

• What contributes to Optical Return Loss?
• Rayleigh backscattering
• intrinsic to the fiber and cannot be
  completely eliminated.
• Fresnel back reflections
• caused by different network elements (mainly
  connectors and components) with air/glass or
  glass/glass interfaces and can always be improved
  by special care or better designs.

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Fresnel Back Reflections (-dB)

• Will come from abrupt changes in the IOR Fiber
  break, mechanical splice, bulkheads, connectors,
  etc
• We use the term  reflectance  when speaking of
  the amount of energy returned by specific points
  within the network
• Expressed as a negative value
• Reflectance dB Preflected dBm - Pincident
  dBm

Connector reflectance -55dB
Connector reflectance -45dB
Mechanical splice reflectance -45dB
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ORL (dB)A few examples
Testing Loss and ORL
Reflectance rayleigh Link ORL
Drop
C.O.
Fiber section
Mechanical splice
OC-3 20 dB OC-12 20 / 24 dB OC-48 24
dB OC-192 27 dB FTTx 32 dB
with Analog Video
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Facts Concerning ORL

• The higher the ORL the better the system will
  perform
• ORL testing is vital to ensure the system is not
  reflecting too much power
• ITU recommends a minimum ORL of
• OC-3 20 dB
• OC-12 20 / 24 dB
• FTTx 32 dB
• OC-48 24 dB
• OC-192 27 dB with Analog
  Video
• Should be tested at all operating wavelengths
  (1310/1490/1550)
• Poor ORL can facilitate
• Strong fluctuations in laser output power
• Interference at the receiver end
• Lower carrier-to-noise ratio in analog systems
  which leads to distortions on video systems
• Higher BER in digital systems
• Potential permanent damage to the laser (EDFA
  )

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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 live fiber, permanent
damage can be done to your eyes! Using a fiber
probe is the safest was to inspect a connector
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OTDR Testing

• What does an OTDR do? What can it tell me about
  the fiber under test?
• A detailed map of each fiber.
• Location and Type of each event (fusion splice,
  connector, patch panel, etc.).
• Optical Loss of the span and Insertion Loss of
  the Event.
• Attenuation of each fiber section.
• Optical Return Loss of the span and Reflectance
  Value and Insertion Loss of each connector.
• Macrobends.

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Macrobend

• If the bend radius of the fiber is exceeded, a
  loss of light will occur
• The Longer wavelengths will tend to travel in the
  core-cladding interface therefore higher loss
  will be observed at these wavelengths if the
  fiber is bent.
• A macrobend can be identified by measuring the
  loss at multiple wavelengths (e.g., 1310 and 1550
  nm). If the loss is higher at longer wavelengths,
  chances are that there is a macrobend along the
  fiber.

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FTTX Optical Testing

• How do these measurements and testing procedures
  apply to FTTX?
• What are the challenges specific to FTTX?
• What are the common questions about FTTX?

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FTTX Testing Application and Challenges Outline

• Typical topologies
• Deployment phases
• Construction testing
• Optical Loss and Insertion Loss - Bidirectional
• Reflectance and Optical Return Loss -
  Bidirectional
• OTDR
• Connector Quality
• Service activation   
• Power Level Verification ONT Requirements
• Connector Quality
• Troubleshooting   
• Most common troubleshooting methods

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Deployment Requirements and Challenges

• Access Networks
• Deployment Requirements and Challenges
• Typical topologies
• Testing
• Loss, reflectance and ORL
• ORL vs. video feed
• OTDR Macrobends
• Connector Quality
• Testing Procedures to Overcome Challenges   
• At the link level most common test methods
• System activation and operation at the
  premises/ONU level
• Troubleshooting PONs

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Typical Topologies One and Cascaded Splitters
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Deployment Requirements and Challenges

• Access Networks
• Deployment Requirements and Challenges
• Typical topologies
• Testing Construction Phase
• Optical Loss, Reflectance and ORL
• ORL vs. video feed
• OTDR Macrobends
• Connector Quality
• Testing Procedures to Overcome Challenges   
• At the link level most common test methods
• System activation and operation at the
  premises/ONU level
• Troubleshooting PONs

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Installation Testing Optical Loss and Insertion
Loss

• Bidirectional end to end loss measurement
• Optical Loss - Difference in power level (loss)
  between the transmitting source and the receiving
  power meter
• Should comply with the link loss budget (ranging
  from 20 to 30dB)
• Optical splitters are the greatest contributor to
  loss
• All operating wavelengths should be tested

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ORL vs. Video Feed

• Why should ORL be reduced to a minimum?
• ORL is the total amount of light reflected back
• Strong fluctuations in laser output power
• Distortions in analog video signals (multipath
  interference (MPI))
• Higher bit-per-error rate (BER) in digital
  systems
• Potential permanent damage to the laser.
• ITU recommends ORL of 32 dB or better in FTTX

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Connector inspection at DROP and Premises
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Construction testing OTDR characterization (Drop
? C.O. )

• Complete upstream link characterization including
  splitter

Drop terminal
Splitter
Patch panel
C.O. Patch panel End of link
Splice tray
Splice tray
C.O.
OLT
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FTTH Network Testing Methods OTDR Testing
through splitters
Required OTDR Characteristics for Testing PONs
Standard OTDR Blind after splitter

• High dynamic range
• Short dead zones
• Dual or triple-wavelength testing
  (1310/1490/1550nm)
• Fast Recovery
• FTTx ready software

PON-Optimized OTDR Clear trace after splitter
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FTTH Service-Activation

• Access Networks
• Deployment Requirements and Challenges
• Typical topologies
• Testing Construction Phase
• Loss, reflectance and ORL
• ORL vs. video feed
• Macrobends
• Testing Procedures to Overcome Challenges   
• System activation and operation
• Troubleshooting FTTH live PONs

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PON/ FTTx Testing

• Subscriber Activation Scenario
• ONT is installed
• Drop fiber is installed (can be
  pre-connectorized)
• ONT is powered up
• Each optical signal is measured (must meet
  power-level criteria)

Activation phase
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FTTH Live PON Troubleshooting (In-Service)

• Access Networks
• Deployment Requirements and Challenges
• Typical topologies
• Testing
• Loss, reflectance and ORL
• ORL vs. video feed
• Macrobends
• Testing Procedures to Overcome Challenges   
• At the link level most common test methods
• System activation and operation at the
  premises/ONU level
• Troubleshooting FTTH Live PONs

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FTTH Live PON Troubleshooting (In-Service)

• Low Power at ONT
• If a section of the fiber is defective, an OTDR
  can be used to locate the break or macrobend.
• The fiber must be disconnected at the FDH or CO
  to ensure that no signal is present.
• Note Only dark fibers can be tested with regular
  OTDRs!
• The OTDR can be connected at the FDH or ONT
  location.

What about active spliced networks?
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In-service PON testing Out-of-band filtered OTDR
Step 1
Step 2
Maintenance troubleshooting phase Out-of-band
filtered OTDR in-service PON testing
PPM-350B Filtered FTTH / PON Power Meter
FTB 1650/1625 nm filtered OTDR In-Service
Testing on FTTH live networks
Troubleshooting phase
Live incoming signal (1310 / 1550) optimal
efficiency range of operation lt -15 dBm
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FTTH Live PON Troubleshooting (In-Service)
Typical Problems and Test Solutions

• No communication between OLT and ONT
• PON power meter to verify optical signals.
• OTDR to localize break.
• Increased BER
• If a signal level is out of the transmission
  window (above or under), BER may increase.
• The PON power meter is the best tool to monitor
  each signal level.
• OTDRs can be used to localize fault (possible
  macrobend).
• Macrobend
• A VFL can be used to find and correct macrobends
  in splice trays.
• OTDRs can be used to detect and localize problem.
• Bad Connectors
• A fiber probe can be used to find and clean dirty
  connectors.

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Conclusion

• System Managers, Engineers and Manufacturers are
  looking for more than the Optical Loss
  measurement.
• They are under pressure to characterize their
  fiber plant during the construction phase due to
  increased demands from the equipment they are
  installing and the services they are offering.
• Documentation is becoming a priority.
• Technicians capable of getting the most of their
  equipment has become a must.

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Questions?

• Thank You
• Tony Lowe
• Technical Sales Specialist
• tony.lowe_at_exfo.com
• Exfo.com