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Testing Optical Fiber Links

In Premises Networks. Noyes Fiber Systems. Horizontal Segment. Backbone Segment. Testing Optical Fiber Links. A. A. A. A. Work Area Outlet. Main Patch Panel. B. B. B. B. Optical Fiber Link. Outline. Optical Fiber Links — Overview Parameters — What should I test?

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Testing Optical Fiber Links

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  1. In Premises Networks Noyes Fiber Systems Horizontal Segment Backbone Segment Testing Optical Fiber Links A A A A Work Area Outlet Main Patch Panel B B B B Optical Fiber Link Testing Optical Fiber Links in Premises Networks — November 2000

  2. Outline • Optical Fiber Links — Overview • Parameters — What should I test? • Industry Standards — Which should I use? • Test Equipment — What do I need? • Procedures • Light source and power meter • Certification test set • OTDR • Troubleshooting Testing Optical Fiber Links in Premises Networks — November 2000

  3. Optical Fiber Links and Link Segments TIA-568 defines an optical fiber linksegment as: “… the cable, connectors, and splices between two optical fiber patch panels.” Testing Optical Fiber Links in Premises Networks — November 2000

  4. Optical Fiber Optical Fiber Link Segment Adapter Connector Splice A B Patch panel or outlet Patch panel Testing Optical Fiber Links in Premises Networks — November 2000

  5. Optical Fiber Links • In structured cabling systems, links may include horizontal and backbone segments. • All links defined in TIA-568 are duplex (one fiber for each direction of transmission). • Optical fiber channels include the patch cords that connect equipment to each end of every link. Testing Optical Fiber Links in Premises Networks — November 2000

  6. HorizontalSegment Backbone Segment Outlet Horizontal Patch Panel Work Area Splice Telecom Closet Main Patch Panel Network Equipment Equipment Room Horizontal and BackboneLink Segments Testing Optical Fiber Links in Premises Networks — November 2000

  7. Channel Link Outlet Horizontal Patch Panel Work Area Splice Telecom Closet Main Patch Panel Network Equipment Equipment Room Link vs. Channel Which Do I Certify ? Fiber patch cords add negligible loss (and NO CROSS-TALK!). So in fiber optic networks, unlike CAT5/6 networks, youcertify the link not the channel. Testing Optical Fiber Links in Premises Networks — November 2000

  8. Rx Rx Tx Tx Splice “NIC”(Network Interface Card in a PC) Network Equipment(Hub, switch, etc.) TIA-568 Link — Detailed View Channel Link PatchCord Horizontal Segment PatchCord Backbone Segment PatchCord A A A A A A A B B B B B B MainPatch Panel Outlet HorizontalPatch Panel Testing Optical Fiber Links in Premises Networks — November 2000

  9. Plug • A-side: OUTPUT • B-side: INPUT • Jack • A-side: INPUT • B-side: OUTPUT A A B Patch Cord Link Segment B TIA-568 Link Polarity • TIA-568 defines a duplex (2-fiber) system with patch cord “plugs” and wall or panel “jacks.” • Every plug and jack has an A and B side: Testing Optical Fiber Links in Premises Networks — November 2000

  10. Equipment Patch Cord (1 Flip) Equipment Patch Cord (1 Flip) Link (1 Flip) A A A A A A A A Rx Rx Tx Tx B B B B B B B B EquipmentJacks EquipmentJacks Patch CordPlugs Patch PanelJacks Patch CordPlugs TIA-568 Link Polarity (cont.) • Every plug and jack must mate A to A and B to B. • Every link segment and patch cord must have one “flip” from A to B and B to A. Testing Optical Fiber Links in Premises Networks — November 2000

  11. Parameters Testing Optical Fiber Links in Premises Networks — November 2000

  12. Fiber Parameters Include … • Attenuation (insertion loss per km) • Bandwidth (LED and laser) • Insertion loss caused by bending • Group Index of Refraction (GIR) • … and more. Testing Optical Fiber Links in Premises Networks — November 2000

  13. Connector Parameters Include … • Insertion loss • Return loss (reflectance) • Loss over temperature and humidity • Loss increase after “N” connection cycles • … and more. Testing Optical Fiber Links in Premises Networks — November 2000

  14. Typical Fiber Optic Field Measurements • Link Certification • Insertion loss • Length • OTDR trace • Troubleshooting • Equipment output power • Link insertion loss • Link continuity (flash light or red laser) • Link fault-locating (red laser or OTDR) Testing Optical Fiber Links in Premises Networks — November 2000

  15. What Is Not Typically Measured in the Field • Bandwidth — fiber bandwidth is measured at the factory and not impacted by installation practices. • Return Loss — optical return loss (reflection) does not significantly impact LAN transceivers (but can impact telco equipment and so is measured in telco/CATV networks). • Cross-talk — Cross-talk is never a fiber optic problem! Testing Optical Fiber Links in Premises Networks — November 2000

  16. Power and Insertion Loss — What You Really Need to Know • Power is normally expressed in dBm: PdBm = dB relative to one milliwatt = 10 log10 (Pwatts/1 mW) • Insertion loss in dB is the difference between input and output power, when both powers are expressed in dBm. • “Attenuation” is fiber insertion loss in dB/km. • The insertion loss of passive components, such as optical fiber and connectors, is always positive. Testing Optical Fiber Links in Premises Networks — November 2000

  17. 1 km of optical fiber Fiber Insertion Loss Example PIN = - 20 dBm POUT = - 23 dBm Insertion Loss = PIN - POUT = -20 dBm - (-23) dBm = 3 dB Attenuation = 3 dB/km. Testing Optical Fiber Links in Premises Networks — November 2000

  18. Optical Fiber Connection (mated connector pair) Connection Insertion Loss Example PIN = - 20 dBm POUT = - 20.75 dBm Insertion Loss = PIN - POUT = -20 dBm - (-20.75) dBm = 0.75 dB Testing Optical Fiber Links in Premises Networks — November 2000

  19. Insertion Loss as a Ratio PIN (watts)/ POUT (watts)Insertion Loss (dB)1:1 (no loss) 0 dB 2:1 3 dB 4:1 6 dB 10:1 10 dB 100:1 20 dB 1 000:1 30 dB 10 000:1 40 dB • Insertion Loss (dB) = 10 x Log [ PIN (watts) / POUT (watts) ] Testing Optical Fiber Links in Premises Networks — November 2000

  20. PIN = - 20 dBm PREFL = - 45 dBm Optical Fiber Link What Is Optical Return Loss? • Fiber optic link optical return Loss, or ORL, expressed in dB, is the difference between input and reflected power, when both powers are expressed in dBm. Optical Return Loss = PIN – PREFL = -20 dBm - (-45) dBm = 25 dB Testing Optical Fiber Links in Premises Networks — November 2000

  21. Optical Return Loss (cont.) • The ORL of an event, such as a connection, is measured using an OTDR as “reflectance”. • To make things complicated, reflectance in dB, is the negative of ORL in dB. • 10Mb/s, 100 Mb/s, and even Gigabit Ethernet systems are not very sensitive to reflection so the ORL of premises network links is not normally measured. • In the future, however, field measurement of ORL in premises networks may become more important because of 10 Gigabit Ethernet and higher rate systems. Testing Optical Fiber Links in Premises Networks — November 2000

  22. Pulses In Pulses Out High bandwidth Fiber Low bandwidth Fiber Pulses In Pulses Out What About Bandwidth? • High bandwidth fiber has low dispersion. Testing Optical Fiber Links in Premises Networks — November 2000

  23. Bandwidth (cont.) • Bandwidth is an important fiber parameter. • Bandwidth is expressed in units of MHz “dot” km, for example 500 MHzkm (not MHz “per” km) • Bandwidth may also be specified as a guaranteed operating distance for a given bit rate, for example “Gigabit Ethernet guaranteed to 1000 meters” • Because bandwidth is not impacted by installation practices it is not normally measured in the field. • However, it is a critical to specify bandwidth or guaranteed operating distance when ordering optical fiber cable. Testing Optical Fiber Links in Premises Networks — November 2000

  24. Standards Testing Optical Fiber Links in Premises Networks — November 2000

  25. Cabling Standardssuch as: Application Standardssuch as: TIA-568-B* (North America) ISO 11801 (International) EN 50173 (European) 10Base-FL 100Base-FXFDDI ATM Fibre Channel 1000Base-SX and LX * Replaced TIA-568-A in 2000. Fiberoptic Standards • There are two types of fiber optic standards: Testing Optical Fiber Links in Premises Networks — November 2000

  26. Example Cabling Standard: TIA-568-B • TIA-568-B specifies the following maximum values on 62.5 m multimode fiber in backbone links: • Fiber attenuation at 850 nm: 3.50 dB/km* • Fiber attenuation at 1300 nm: 1.50 dB/km • Loss per connection (mated pair): 0.75 dB • Loss per splice (mechanical or fusion): 0.3 dB * In TIA-568-A, max. fiber attenuation at 850 nm was 3.75 dB/dm Testing Optical Fiber Links in Premises Networks — November 2000

  27. Example Application Standard:Gigabit Ethernet • IEEE 802.3z (Gigabit Ethernet) specifies the following maximum values on 62.5 m, 200 MHz-km multimode optical fiber links when using 850 nm (SX) sources: • Insertion loss: 2.60 dB • Distance: 275 m Testing Optical Fiber Links in Premises Networks — November 2000

  28. Standards (cont.) • There are only a few cabling standards • In North America, TIA-568-B is the primary commercial building cabling standard. • But there are many applications standards including: 10, 100, and 1000 Mb/s Ethernet, FDDI, ATM, Fibre Channel and more. • And new application standards like 10 Gb/s Ethernet are in development. Testing Optical Fiber Links in Premises Networks — November 2000

  29. Which standard(s) should I use? • It is very possible for a link to meet the requirements of a cabling standard, like TIA-568, and not meet the requirements of a high-speed application like Gigabit Ethernet. • Therefore,every optical fiber link should meet the applicable cabling standard and the toughest application standardit must support. Testing Optical Fiber Links in Premises Networks — November 2000

  30. TIA-568-B vs. GBE Example • Referring to the earlier link example assume: • connector specs: 0.6 dB loss per connection • fusion splice loss: 0.1 dB • fiber specs: 62.5 um, 200 MHzkm, 3 dB/km • horizontal segment length: 90 M • backbone segment length: 150 M • Does this link meet TIA-568-B and will it support 1000Base-SX (850 nm) ? Testing Optical Fiber Links in Premises Networks — November 2000

  31. Example (cont.) HorizontalPatch Panel MainPatch Panel Outlet Splice A A A A 0.1 dB B B B B Rx Tx Tx 0.6 dB 0.6 dB Rx 0.6 dB 0.6 dB 90 m 150 m HorizontalSegment BackboneSegment Certification Test Set (Main Unit) Certification Test Set (Remote Unit) Testing Optical Fiber Links in Premises Networks — November 2000

  32. Example (cont.) • TIA-568-B requirements are met: • Horiz. length = 90 M (90 M max) • Horiz. Loss = 1.47* dB (2 dB max.) • BB length = 150 m (2000 m max.) • BB fiber attenuation = 3 dB/km (3.50 dB/km max.) • BB connector loss = 0.6 dB (0.75 dB max.) • BB splice loss: = 0.1 dB (0.3 dB max) • Total link loss: = 3.22** dB (4.33*** dB max.) * Horizontal segment loss = 0.09 km x 3 dB/km + 2 x 0.6 dB = 1.47 dB** Total link loss = 1.47 dB + 3 dB/km x .15 km + 2 x .6 + .1 = 3.22 dB*** TIA-568-B limit = 2 dB + 3.50 dB/km x .15 km + 2 x .75 + .3 = 4.33 dB Testing Optical Fiber Links in Premises Networks — November 2000

  33. Example (cont.) • But not all 1000Base-SX requirements are met: • Link length = 90 m + 150 m = 240 m (275 m max.) • Link loss = 0.24 km x 3 dB/km + 4 x 0.6 dB + 0.1 dB = 0.72 dB + 2.5 dB = 3.22 dB (2.60 dB max.) Testing Optical Fiber Links in Premises Networks — November 2000

  34. Example (cont.) • Could this link support 1000Base-SX? • Yes, by using lower-loss connectors. • For example by using connectors with an average loss of 0.4 dB then: • Total link loss = 0.72 dB + 4 x 0.4 dB + 0.1 dB = 0.72 + 1.7 dB = 2.42 dB (2.60 dB max.) Testing Optical Fiber Links in Premises Networks — November 2000

  35. Important Conclusion: • Multimode fiber links may have to exceed the requirements of TIA-568-B in order to support high speed applications like Gigabit Ethernet. FUTURE SHOCK: 10 Gigabit and even 100 Gigabit Ethernet are being discussed by the standards bodies. So high-bandwidth fiber, low-loss connectors, and good installation practices will be even more critical in the future. Testing Optical Fiber Links in Premises Networks — November 2000

  36. Test Equipment Testing Optical Fiber Links in Premises Networks — November 2000

  37. Basic Test Kit • Light source — 850/1300 nm LED source may be used to measure insertion loss on multimode and singlemode links found in premises networks. • Optical power meter — Measures optical power and optical fiber insertion loss. • Microscope — 200x recommended to inspect connector polish and cleanliness • Flashlight — to check continuity on multimode fiber links (will not work well on singlemode fiber) Testing Optical Fiber Links in Premises Networks — November 2000

  38. Additional Test Equipment • Certification Test Set • Fastest way to certify duplex optical fiber links. • Measures loss, length, and provides PASS/FAIL results • Very useful in high fiber count installations. • OTDR (Optical Time-Domain Reflectometer) • Generates a baseline trace. • Very useful fault-locator. • Only way to measure events such as connections and splices. • Visible (red) laser • Very useful troubleshooter—highlights breaks and bad connectors. • Highlights bends in singlemode fibers. • Check continuity on multimode or singlemode fibers. Testing Optical Fiber Links in Premises Networks — November 2000

  39. Scratch goes near the core! Dirt particles Fiber Core (singlemode) Using an Optical Fiber Scope Ferrule Testing Optical Fiber Links in Premises Networks — November 2000

  40. Fiber Core (multimode) Using an Optical Fiber Scope (cont.) Ferrule Body oil(don’t touch the connector end-face!) Testing Optical Fiber Links in Premises Networks — November 2000

  41. Setting Up Your Light Source and Optical Power Meter • Turn on light source and optical power meter and allow them to warm-up per User’s Guide. • Set reference (typically once per day): • Attach clean Tx jumper to source • Connect other end of Tx jumper to meter. • Set reference level. • Disconnect Tx jumper from optical power meter (Do NOT remove jumper from light source!) Testing Optical Fiber Links in Premises Networks — November 2000

  42. Light Source / Power Meter (cont.) • Check jumpers: • Attach the Rx jumper to power meter • Connect the Tx and Rx jumpers using an adapter. • Verify loss is less than or equal to a typical connection loss (e.g.  0.4 dB) • Attach light source and meter to opposite ends of the fiber link under test (see diagram). • Measure loss in dB • Repeat for other fibers … keep connectors clean! Testing Optical Fiber Links in Premises Networks — November 2000

  43. Adapter Tx jumper Rx jumper Tx Rx Tx Rx 0 dB 0.4 dB Light Source Optical PowerMeter Light Source Optical PowerMeter 1) Set reference 2) Check jumpers One-Jumper Reference Method Testing Optical Fiber Links in Premises Networks — November 2000

  44. -22 dBm HorizontalPatch Panel MainPatch Panel -20 dBm Outlet Splice A A A A B B B B Tx HorizontalSegment BackboneSegment Rx 2dB Light Source Optical PowerMeter Measuring Optical Fiber Link Loss Testing Optical Fiber Links in Premises Networks — November 2000

  45. Using a Certification Test Set • Attach clean Tx jumpers to Main and Remote • Connect the other end of each Tx jumper to the Rx port on the other unit. • Set reference (typically once per day). • Check jumpers. • Set up Auto Test rule. • Connect Main and Remote to the link under test. • Test and store results (two fibers per Auto Test). Testing Optical Fiber Links in Premises Networks — November 2000

  46. Remote Tx Jumper Adapters Remote Rx Jumper Main Tx Jumper Main Rx Jumper Rx Tx Rx Rx Tx Tx Tx Rx 0dBm 0.4 dBm Main Unit Remote Unit Main Unit Remote Unit 1) Set reference 2) Check jumpers One-Jumper Reference Method Testing Optical Fiber Links in Premises Networks — November 2000

  47. 240 m -20 dBm HorizontalPatch Panel MainPatch Panel -22 dBm Outlet -22 dBm Splice -20 dBm A A A A B B B B Rx Tx Tx Rx HorizontalSegment BackboneSegment 2dB 2dB 240 m PASS Main Unit Remote Unit Certifying (Loss + Length) Testing Optical Fiber Links in Premises Networks — November 2000

  48. Using an OTDRTo Generate a Baseline Trace • Turn on OTDR and allow it to warm-up per User’s Guide. • Attach launch cable to OTDR port and receive cable to far-end of fiber link under test • Both must have the same fiber type as link under test. • Set wavelength, pulse width, range, number of averages, etc. • Or, use automatic setup features of the OTDR • Run test, save trace, move to next fiber Testing Optical Fiber Links in Premises Networks — November 2000

  49. Work AreaOutlet HorizontalPatch Panel MainPatch Panel Splice A A A A B B B B HorizontalSegment BackboneSegment Receive Cable (Fiber box) MM SM Launch Cable(Fiber Box) OTDR Using an OTDR (to generate a baseline trace) Testing Optical Fiber Links in Premises Networks — November 2000

  50. LaunchCable Horiz.Seg. BackboneSegment Term.Cable Example OTDR Trace Link Length ( 130 m) A B 0 One Connection(Loss  0.4 dB) -1 Link Loss ( 2.1 dB) Two Connections (Loss  0.8 dB) -2 RelativePower(dB) Splice(Loss  0.1 dB) -3 -4 -5 0 50 100 150 200 250 Distance (m) Testing Optical Fiber Links in Premises Networks — November 2000

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