Ensuring Cabling Performance in the Customer-Owned Outside Plant Keith Foord Product Manager Greenlee Communications
Introduction: Outside plant fiber networks require low reflectance terminations for high bandwidth applications. The technician needs to be able to qualify the installation to ensure that the bandwidth requirements are met. Photo: Versitron
Future Proofing your Network: Need to install a network that will provide years of service without limiting the capability of the network to handle the needs of future high bandwidth applications. Mechanical connectors limit bandwidth. Fiber has virtually unlimited bandwidth. The transmitter and receiver determine the maximum data speed and do not approach the bandwidth of the fiber.
Methods for Terminating cables in the outside plant: 1. Mechanical splicing 2. Polishing 3. Pre-polished mechanical connector 4. Splicing pre-terminated patch cords 5. Fusion splicing using Splice on Connectors (SOC)
Mechanical splices: Have inconsistent performance, sensitive to vibration Requires adhesives/matching gels High return loss (~40dB), limits bandwidth High insertion loss (~0.3dB) Long term reliability issues Polishing: Time consuming and hard to do in the field High return loss (30dB), high insertion loss (0.5dB) Subject to technician ability Photo: Shenzhen G-Tech Communication Photo: Network Cabling Help
Mechanical Connector Bandwidth limiting due to return loss Long term reliability issues High insertion loss (~0.3dB); Maximum insertion loss 0.75dB; should be validated with an OTDR or OLTS Requires fiber end to be cleaved Not suitable for outdoor installations Splicing pre-terminated patch cords Requires a splice tray to be used Approximately the same material cost as splice on connectors Requires that both fiber ends be cleaved (SOC are pre-cleaved) Photo: Fiber Instrument Sales Photo: Fiber Instrument Sales
Splice on Connectors Splice protection sleeve is located in the strain relief No splice tray is required No crimping, epoxies, matching gels Faster easier more robust installation no need to measure fiber lengths so that the splice sleeve can be mounted in a splice tray Photo: Greenlee Communications
Splice on Connectors meet the following standards: ANSI/TIA-568-C.3 TIA-604-FOCIS Telcordia GR-326-CORE
Fusion Splicing: Splicing provides consistent results for high bandwidth applications Low amount of technician training required, simple user interface Excellent return loss, typically >60dB Excellent insertion loss, typically 0.02dB SMF and 0.01dB MMF Can use pre-terminated fiber pigtails or Splice on Connectors (SOC) More economical cost per termination Splicing time = 9s, Protection shrink time = 36s (60mm)
Core alignment vs V-Groove Lower splice losses due to active alignment Two cameras and six motors align the fiber core not the outside diameter of the fiber Fiber core not in the center of the fiber causes splice losses Compensates for cladding misalignment Compensates for cladding diameter differences Each fiber manufacturer will have slightly different geometries Courtesy: Corning
Core alignment vs V-Groove Compensates for dirt in V-Groove Compensates for V-Groove damage and misalignment Even the same fiber cut and re-spliced will have higher losses since the V-Groove splicer does not know where the core of the fiber is!
Splice on Connectors Available in SC, LC, FC, ST terminations (>60dB return loss for APC versions) Inserted into the fusion splicer using fiber adapters Splice protection sleeve is located in the strain relief No splice tray is required Easier more effective cable management No crimping, epoxies, matching gels Pre-cleaved fiber ready for splicing Pre-polished fiber termini Splice protector located in strain relief
Splice on Connector Mounted in Fusion Splicer 900u Fiber Adapter SC/PC SOC in Universal Adapter Electrodes
Cost Analysis: *Single piece pricing from distribution channels Splice on Connector Connector $9.00* Labor (20 splices per hour) $2.75 Total Cost $11.75 Field Hand Polish Connector $6.00* Consumables $0.26 Labor (4 terminations per hour) $13.75 Total Cost $20.01 Mechanical Connector Connector $15.00* Labor (30 terminations per hour) $1.83 Testing $1.00 Total Cost $17.83 $55/hour ~$6 Cost Difference
Connectors must be CLEAN! Dirty connectors can cause: Complete failure Cross contamination Reduce bandwidth Permanent damage Reel type of cleaners work well Pens can clean both ferrule and bulkhead Photo: Courtesy Cletop Photo: Courtesy Greenlee Communications
Combination Cleaning Process cleans the complete end face of the widest range of debris and contamination A small amount of precision fiber optic cleaner is placed in one corner of the cleaning platform The end face is cleaned and dried in one straight-line motion Courtesy: Chemtronics
Fiber Scopes: Inspect Clean if Necessary Inspect Then Connect Replace if Necessary Validate and document that the connector is clean Micron resolution FOV most important specification must be able to view outside of the four zones
Fiber Scopes: PASS/FAIL to IEC 61300-3-5 Wireless hotspot created for interface to smart phones
Contaminates can migrate on the surface of the connector with vibration causing intermittent or total failure after installation 200X Fiber Core
Connector Zones:
Single-Mode Criteria Table Zone Description Diameter Allowable Defects (Dia) Allowable Scratches (Width) A Critical Zone 25um None visible at 200X None visible at 200x B Cladding Zone 25 to 120um Any < 2um None >3um Total of five 2um - 5um None > 10um C Adhesive Zone 120 to 130um None > 10um Any scratch OK D Contact Zone 130 to 250um None > 10um Any Scratch OK
Manual OLTS Measurements: Connect a laser to one end of the fiber and the detector to the other end to find the insertion loss of the fiber link Return loss not measured so this method is not suitable for high bandwidth links Measures the insertion loss of a fiber link at 1310nm and 1550nm Laser Source (GDLS 350) Optical Power Meter (GRP 460)
Insertion Loss Measurements using a handheld laser and power meter Zero the power meter Insert the DUT and measure the IL
Typical Report: Documents the test data, measurements with time stamp
Fully Automatic Optical Loss Test Set (OLTS) Return Loss and Insertion Loss is measured bi-directionally at all wavelengths for the entire link Need one OLTS unit on each end of the fiber link AutoTest button provides single button operation The location of the losses is not measured but is the total RL and IL for the entire link OLTS can also be used as a standalone power meter and laser source Reporting/documentation software is provided
OLTS Results Pass/Fail reporting Bi-directional measurement of insertion loss from A to B and B to A for a patch cord Summary page shows the insertion loss and return loss results for the entire link
Optical Time Domain Reflectometer (OTDR) Single ended measurement Locates individual insertion and return losses in the fiber link Full reporting documents fiber links at installation and later during troubleshooting Auto shutdown feature so that live fibers are not interrupted Out of band testing is available to test live fibers at 1625nm 930XC OTDR
Laser Probe pulse End of fiber Display Processor Coupler Detector Fiber under test Rayleigh backscatter Fresnel reflection The Optical Time Domain Reflectometer (OTDR) is an instrument that uses the inherent backscattering properties of an optical fiber to detect faults and categorize its condition. The OTDR sends high-power pulses of laser light down the fiber and captures the light that is reflected back (much like a radar system). By measuring the timing and power levels of the return pulses, the instrument correlates the reflected information with physical locations along the fiber and displays a trace that shows optical power versus distance. Attenuation of the fiber is displayed as the slope of the trace. Interruptions such as splices, connectors, bends, breaks or flaws in the fiber appear as transitions ( events ) that represent their nature and location.
Optical Time Domain Reflectometer (OTDR) Key Specifications Dynamic range; typically 32-38dB for handheld; 42dB for tablet Higher dynamic range will allow the technician to probe longer fibers or fibers with high loss events Dynamic Range is quoted at the widest pulse width, this results in the poorest resolution. Event Deadzone; typically 1-2m The ability of the OTDR to resolve between two reflective events such as poor connectors and over-layed fiber events Resolution is quoted at the narrowest pulse width, this results in the poorest dynamic range. Attenuation Deadzone; typically 4m The ability of the OTDR to measure a backscatter event (fusion splice) after a reflective event.
OTDR Trade-offs - Pulse Width Larger pulse width (more energy into the fiber) Longer distance measured Results in lower resolution Smaller pulse width (less energy into the fiber) Shorter distance measured Results in higher resolution
OTDR Trade-offs - Averaging Longer averaging time Best signal to noise Shorter averaging time Lower signal to noise
Typical OTDR Trace using Trace Viewer Software: OTDR Bulkhead *Reflective Event (not a splice) Cursors End of Fiber Some light is reflected back from the bad connection The reflected light hits the laser and is then transmitted again as signal but it is really noise (ghosting) A ghost (not real ) of the original reflection will be at 2X the original reflection Reflections will limit the bandwidth of fiber links due to ghosting effects!
Mechanical connector with high loss (but passes mechanical connector specification) and high reflection The insertion loss is <0.75dB but the return loss is > -40dB Courtesy Greenlee Communications
Mechanical connector with high loss and high reflection Return loss is hard to control and can change due to environmental conditions. Mechanical connectors and mechanical splices can move and change loss characteristic's. Courtesy Greenlee Communications
Fusion splice measurement Fusion Splice
Fusion splice measurement Fusion Splice = 0.048dB The return loss was not measureable!
SUMMARY Fusion splicing with splice on connectors is an economical solution compared to mechanical splicing, mechanical connectors and polishing fiber end faces; very short ROI Fusion splicing dramatically improves network performance when compared to mechanical connectors Mechanical connectors and splices limit bandwidth due to ghosting effects and losses OTDR technology can pinpoint reflective events that limit bandwidth
Greenlee Communications 1390 Aspen Way Vista, CA, 92081 www.greenleecommunications.com 1-800-642-2155 kfoord@greenlee.textron.com