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 isn’t 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 • R&E 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 expen$ive 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