Fiber Testing

1
Fiber Testing

• Perspective!
• Fiber is just one part of overall system
• Modulation rates
• Laser characteristics
• Receiver characteristics
• Distance requirements
• Fiber types and interfaces
• Must test to specifications designed into the
  system
• High transmission speeds and longer fiber spans
  make testing and verification much more critical
  than most Quilt engineers have ever had to deal,
  with even just a few years ago.
• Performance depends upon total optical
  charactization
• Fiber (types, distances, etc)
• Equipment (e.g. OADMs, DCMs, etc)

2
Fiber Characterization

• Testing prior to placing in service
• Measure end to end distance
• Verify splice conformance and identify poor
  cross-connects
• Identify high reflectance points
• Attenuation by segment
• Different fiber types exhibit different loss
• Measure each fiber
• Both directions
• At both 1310 nm and 1550 nm (assuming only SM
  fibers)
• Dispersion
• These days we should measure both Chromatic
  Dispersion and Polarization Mode Dispersion
• Wan segments may need DCM how much depends on
  application specifics (WDM? Laser types? Fiber
  type? Distance?)

3
Equipment

• Field optical testset platform which supports
  multiple modules (e.g. Exfo FTB400)
• Optical Time Domain Reflectometer (OTDR) module
• Used often for repair verification so make it
  small and portable
• Chromatic Dispersion module/testset
• OC48 and higher speed interfaces vary
  dramatically
• Polarization Mode Dispersion module/testset
• Should have this for 10gig (or higher) WAN
  segments
• Optical Spectrum Analyzer (OSA)
• Required for WDM systems
• Useful for non-WDM problem resolution as well

4
Equipment

• Cleaning
• Testing is pointless on dirty fiber
• Cletop (or equivalent) fiber termination cleaner
  (for male components such as SC/FC/LC connectors)
• Swabs (for female components such as bulkhead
  connectors and ports)
• Handheld fiber inspection microscope (male
  components)
• Fiber port camera for female ports
• Compressed air canisters for blowing out
  components

5
Fiber Operation and Maintenance

• Who owns the fiber?
• Owner typically is responsible for operational
  maintenance and repair of WAN fiber
• They may have more than just your fiber in the
  bundle, have access to conduit, etc.
• You (fiber customer) may be required to assist in
  maintenance and/or repair by providing access to
  your facilities for testing, verifying repairs
  are made to specification and on time, etc.
• A repair at 3am in a manhole on a busy street
  needs to be tested then not the next day after
  they button up the manhole.
• A re-splice may cost several thousand dollars!
  And significant haedaches
• There may be several providers along your path
• You will need to identify where a failure is
  occuring in order to notify the correct provider
  for action
• OTDR simplifies this process.
• Includes patch fibers, laterals, concatenations
  along entire path

6
Fiber O M

• Fiber engineering
• Aerial vs buried
• Hanging fiber is often easier to repair
• Experience shows mtbf for hanging fiber is really
  pretty good
• SMF28 vs other (e.g. TW, TWrs, LEAF, etc)
• SMF optimized for 1310nm operation not WDM
• SMF works fine for WDM in reduced span, simple
  WDM networks
• Be careful of ZDSF and fiber planted before
  1993/94
• ZDSF not good for WDM systems, old fiber had PMD
  issues
• Diverse, collapsed, or unprotected
• Obviously, diversity minimizes operational impact
  of physical fiber outages

7
Fiber O M

• Splicing vs Patching
• Splicing must be done well
• If you must be responsible for splicing, make
  sure you have good equipment and skilled
  personnel doing it
• A good fiber tech is worth their weight in
• Splicing provides much better connections
• Better media transferal
• Less reflectance
• Less loss across interfaces
• Splicing reduces risk of inadvertent disconnects
• But makes testing more difficult in case of
  repairs

8
Fiber O M

• Patch fiber and cross-connects
• Cross-connects generate 90 (or more) of fiber
  outages
• Patch fibers are dirty or mechanically faulty
• Poorly seated at connections
• These fibers are most often fiddled with
• In POPs, fiber trays are full, fiber pulls
  inadvertently crimp existing fibers in trays, etc.

9
Fiber termination

• Termination should be done by qualified personnel
  
• No such thing as saving money here this isnt
  building your own Cat5 cable
• SC? FC? LC?
• UPC or APC?
• UPC is conventional flat fiber Ultra Polished
  Connector
• APC is Angle Polished reduced reflectance
  often advisable for high speed or very sensitive
  optical engineering (DWDM, 10gig, etc)
• Try to standardize, but not completely possible
• Have tested patch cables and adapter cables in
  varying lengths (LC-SC, FC-SC, etc.)

10
WARNING!!! Do not gaze into fiber with remaining
eye!
11
Active Optics

• New equipment is required by law to have an
  Automatic Power Disable feature for high power
  lasers
• Turns down laser in case of optical LoS
• Some WDM systems are launching at 5 db (!)
• Amplified systems particularly Raman amps
  will significantly boost this power further
• Protects field personnel from exposure to errant
  laser energy during repair, testing, or fiber
  crossconnecting process
• RE community needs to consider these as real
  occupational safety issues need to explore and
  establish appropriate safety procedures.

12
Metro Fiber Considerations

• Access, Access, Access
• Points of Presence 24x7access for your techs,
  and for other techs (other fiber providers,
  service providers, etc)
• Some fiber pops and/or huts require special
  safety training for techs (e.g. RR huts, highway
  huts, etc.)
• Security
• Security is extremely important, but
• Too much can be onerous and unworkable
• Design your POPs with security and access in
  mind
• E.g. Cage space and/or suites provide
  appropriate security while allowing significant
  flexibility
• If you invest in long term fiber, expect to grow
  at your POP arrange expansion space early so
  that it grows in a consolidated space.

13
Personnel

• Optical Engineers are things we must develop.
• Metro and regional fiber networks designed for
  very high performance DWDM systems require
  significantly different engineering
  specializations than campus networks.
• We need to hire more junior engineers and train
  them for metro/regional networking requirements
• Hiring these skills is expenive and difficult
• Existing senior engineers are both
  over-subscribed and expensive filling the
  pipeline with new blood will help control these
  costs over the long term, and provide the breadth
  and scope of skills we need to architect,
  engineer, contract, deploy, operate, and maintain
  the new infrastructure.

14
Fiber Operations Maintenance

• Record keeping
• A good RON will create a database containing all
  the information associated with fiber facilities
• Segment identifiers, provider, POCs,
• A-Z ends down to the bay, shelf, and position,
  termination types, length
• Fiber characteristics type of fiber, measured
  loss, dispersion (CD/PMD)
• Higher layer circuit connections
• Customer identifier, pocs, etc.
• Concatenated segments,
• Cross-connects end to end