1. Testing Optical Fiber Links
In Premises Networks
Noyes Fiber Systems
Horizontal Segment
Backbone Segment 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 link segment as:
“… the cable, connectors, and splices between two optical fiber patch panels.”
Testing Optical Fiber Links in Premises Networks — November 2000

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

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

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

9. 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:
Plug
A-side: OUTPUT
B-side: INPUT
Jack
A-side: INPUT
B-side: OUTPUT A B
Patch Cord
Link Segment
Testing Optical Fiber Links in Premises Networks — November 2000

10. 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. Rx Tx
Equipment
Link (1 Flip)
Patch Cord (1 Flip) A B
Patch Panel Jacks
Patch Cord Plugs
Equipment Jacks
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. Fiber Insertion Loss Example
PIN = - 20 dBm
POUT = - 23 dBm
1 km of optical fiber
Insertion Loss = PIN - POUT
= -20 dBm - (-23) dBm
= 3 dB
Attenuation = 3 dB/km.
Testing Optical Fiber Links in Premises Networks — November 2000

18. Connection Insertion Loss Example
PIN = - 20 dBm
POUT = dBm
Optical Fiber Connection (mated connector pair)
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
Insertion Loss (dB) = 10 x Log [ PIN (watts) / POUT (watts) ]
PIN (watts) / POUT (watts) Insertion Loss (dB) :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
Testing Optical Fiber Links in Premises Networks — November 2000

20. Why Use dBm to Express Power ?
dBm is a convenient unit to express the small power levels used in fiber optic communication systems:
Power (watts) Power (dBm)
0.1 W + 20 dBm
0.01 W + 10 dBm
0.001 W (1 mW) dBm
0.1 mW dBm
0.01 mW dBm
0.001 mW dBm
mW dBm
mW - 50 dBm
Testing Optical Fiber Links in Premises Networks — November 2000

21. 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.
PIN = - 20 dBm
PREFL = - 45 dBm
Optical Fiber Link
Optical Return Loss = PIN – PREFL
= -20 dBm - (-45) dBm
= 25 dB
Testing Optical Fiber Links in Premises Networks — November 2000

22. 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

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

24. 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

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

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

27. 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: dB/km
Loss per connection (mated pair): 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

28. 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

29. 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

30. 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 standard it must support.
Testing Optical Fiber Links in Premises Networks — November 2000

31. 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: 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

32. Horizontal Patch Panel
Example (cont.)
Horizontal Patch Panel
Main Patch Panel
Outlet
Splice A A A A
0.1 dB B B B B Rx Tx Tx
0.6 dB
0.6 dB
0.6 dB
0.6 dB Rx
90 m
150 m
Horizontal Segment
Backbone Segment
Certification Test Set (Main Unit)
Certification Test Set (Remote Unit)
Testing Optical Fiber Links in Premises Networks — November 2000

33. TIA-568-B requirements are met:
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 = 3.22 dB *** TIA-568-B limit = 2 dB dB/km x .15 km + 2 x = 4.33 dB
Testing Optical Fiber Links in Premises Networks — November 2000

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

35. Could this link support 1000Base-SX?
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 dB
= dB = 2.42 dB (2.60 dB max.)
Testing Optical Fiber Links in Premises Networks — November 2000

36. 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

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

38. 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

39. 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

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

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

42. 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

43. 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

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

45. Measuring Optical Fiber Link Loss
Outlet Tx Rx
Light Source
Optical Power Meter
Horizontal Patch Panel
Splice
Main Patch Panel A B
2 dB
Horizontal Segment
Backbone Segment
-20 dBm
-22 dBm
Testing Optical Fiber Links in Premises Networks — November 2000

46. 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

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

48. Certifying (Loss + Length)
240 m
Outlet Rx Tx
Main Unit
Remote Unit
Horizontal Patch Panel
Splice
Main Patch Panel A B
2dB 2dB
240 m
PASS
Horizontal Segment
Backbone Segment
-20 dBm
-22 dBm
-22 dBm
-20 dBm
Testing Optical Fiber Links in Premises Networks — November 2000

49. Using an OTDR To 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

50. (to generate a baseline trace)
Using an OTDR
(to generate a baseline trace)
Work Area Outlet
Horizontal Patch Panel
Splice
Main Patch Panel A B
Horizontal Segment
Backbone Segment
Launch
Cable (Fiber Box)
Receive
Cable (Fiber box)
OTDR SM MM
Testing Optical Fiber Links in Premises Networks — November 2000

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

52. Why is an OTDR So Useful? Because it can: Generate a baseline trace
Measure link insertion loss* and length,
Measure event insertion loss, return loss (reflectance), and location (connections and splices)
Fault locate
* However a light source and optical power meter are the most accurate tools for measuring insertion loss.
Testing Optical Fiber Links in Premises Networks — November 2000

53. Troubleshooting a failed fiber link
Measure equipment output power.
Verify connectivity using a visual fault identifier (also called a VFI or red laser).
Measure end-to-end link loss.
Fault-locate using an OTDR:
Generate a trace.
Look for breaks, or events with excessive loss
Compare with baseline trace if available
Testing Optical Fiber Links in Premises Networks — November 2000

54. Example Fault: (Fiber break)
Network Equipment
Work Area
Outlet
Main Patch Panel
Equipment Room
Horizontal Patch Panel
Telecom Closet
Splice
Link Failure
Alarm !
Break
Testing Optical Fiber Links in Premises Networks — November 2000

55. Measure Transmitter Output Level (Using an Optical Power Meter)
Optical Power Meter (OPM)
Equipment output levels look okay.
- 8 dBm
Network Equipment
Outlet
Main Patch Panel
Horizontal Patch Panel
Telecom Closet
Splice
Testing Optical Fiber Links in Premises Networks — November 2000

56. Verify Connectivity (Using a VFI or “red laser”)
Network Equipment
Work Area
Outlet
Main Patch Panel
Equipment Room
Horizontal Patch Panel
Telecom Closet
Splice
Visual Fault
Identifier
(VFI)
No light seen at link output.
NOTE: A VFI or “red laser” generates visible light at about 650 nm.
Testing Optical Fiber Links in Premises Networks — November 2000

57. or … Verify Connectivity (Using a light source and power meter)
Network Equipment
Work Area
Outlet
Main Patch Panel
Equipment Room
Horizontal Patch Panel
Telecom Closet
Splice
Light Source
Low
Optical Power
Meter
Testing Optical Fiber Links in Premises Networks — November 2000

58. Fault-Locate (Using an OTDR)
Network Equipment
Work Area
Outlet
Main Patch Panel
Equipment Room
Horizontal Patch Panel
Telecom Closet
Splice
Launch
Cable
Receive
Cable
OTDR MM
Testing Optical Fiber Links in Premises Networks — November 2000

59. OTDR Trace Showing Break at 120 m
Distance to fault ( 120 m)
Fault !
250 50
100
150
200 -2 -1 -3 -4 -5
Relative Power (dB)
Distance (m) A B
Baseline
Trace
New Trace
Testing Optical Fiber Links in Premises Networks — November 2000

60. Questions?
Testing Optical Fiber Links in Premises Networks — November 2000