1. Optical Loss Budget (Example 2)
1000BASE-ZX GBIC
Ptmax = 5 dBm
Ptmin = 0 dBm
Prmax = -3 dBm
Prmin = -23 dBm
Questions:
Can you connect one GBIC to another with only a patchcord?
How can you ensure that the fiber system does not exceed the maximum loss?
Ptmax 5 dBm
Minimum Loss (dB) = 8 dB
Optical Loss Budget:
Bmax = Ptmin – Prmin
Bmin = Ptmax -Prmax
Prmax -3 dBm
Ptmin 0 dBm
Optical Power Level (dBm)
Maximum Loss (dB) = 23 dB
Prmin -23 dBm

2. Test! Basic Tests Advanced Tests Visual Fault Locator (VFL)
Optical Insertion Loss
Optical Power Levels
Advanced Tests
Optical Return Loss (ORL)
Optical Time Domain Reflectometer (OTDR)
Chromatic Dispersion (CD)
Polarization Mode Dispersion (PMD)
Optical Spectral Analysis (OSA)

3. Visual Fault Locator
VFLs provide a visible red light source useful for identifying fiber locations, detecting faults due to bending or poor connectorization, and to confirming continuity.
VFL sources can be modulated in a number of formats to help identify the correct VFL (where a number of VFL tests may be performed).
FFL-100
FFL-050

4. Advanced Tests Optical Return Loss (ORL)
Optical Time Domain Reflectometer (OTDR)
Detect, locate, and measure events at any location on the fiber link
Fiber Characterization
Determines the services that the fiber can be carry
Basic tests plus:
Chromatic Dispersion (CD)
Polarization Mode Dispersion (PMD)
Optical Spectrum Analysis (OSA)
Spectral analysis for Wavelength Division Multiplexing (WDM) systems

5. T-BERD 4000 FTTx / Access OTDR
Introduction to OTDR
It’s the single most important tester used in the installation, maintenance & troubleshooting of fiber plant
Most versatile of Fiber Test Tools
Detect, locate and measure events at any location on the fiber link
Identifies events & impairments (splices, bends, connectors, breaks)
Provides physical distance to each event/ impairment
Measures fiber attenuation loss of each event or impairment
Provides reflectance / return loss values for each reflective event or impairment
Manages the data collected and supports data reporting.
T-BERD 4000 FTTx / Access OTDR
If you can only afford one piece of test gear in your network (and it’s not a small LAN), the OTDR is the tool you will need. It will do almost everything you need to fundamentally evaluate the fiber (except for advanced test, such as PMD, CD)

6. Background on Fiber Phenomena
OTDR depends on two types of phenomena:
Rayleigh scattering
Fresnel reflections.
Light reflection phenomenon = Fresnel reflection
Rayleigh scattering and backscattering effect in a fiber

7. How does it work ?
The OTDR injects a short pulse of light into one end of the fiber and analyzes the backscatter and reflected signal coming back
The received signal is then plotted into a backscatter X/Y display in dB vs. distance
Event analysis is then performed in order to populate the table of results.
OTDR Block Diagram
Example of an OTDR trace
OTDR’s are similar in principle to:
Copper TDR
Radar
Sonar
Shoot from one end
collect reflected signal
tie round trip time to one way distance.

8. Type of Fiber and Wavelengths
Single Mode (SM)
1310 & 1550nm are primary wavelengths used in SM OTDR measurements
1625nm is used in trouble-shooting when testing on active networks is needed
Multimode (MM)
850 & 1300nm are dominant wavelengths used in MM transmission & testing
1490 FTTH operating wavelength
We believe 1490 is an unnecessary expense (to OTDR at 1490)
1550 test wavelength is fully adequate to evaluate fiber for 1490 operation

9. Dynamic Range & Injection Level
Dynamic Range determines the observable length of the fiber & depends on the OTDR design and settings
Injection level is the power level in which the OTDR injects light into the fiber under test
Poor launch conditions, resulting in low injection levels, are the primary reason for reductions in dynamic range, and therefore accuracy of the measurements
Effect of pulse width: the bigger the pulse, the more backscatter we receive
The higher the dynamic range the further the OTDR will see.
The higher the dynamic range, the more expensive the OTDR will be.
For best value determine the right module for the job.

10. What does an OTDR Measure ?
Distance
The OTDR measurement is based on “Time”: The round trip time travel of each pulse sent down the fiber is measured. Knowing the speed of light in a vacuum and the index of refraction of the fiber glass, distance can then be calculated.
Fiber distance = Speed of light (vacuum) X time
2 x IOR
Converts time (round trip time for signal to go out and backscatter return)

11. What does an OTDR Measure ?
Attenuation (also called fiber loss) Expressed in dB or dB/km, this represents the loss, or rate of loss between two events along a fiber span
The further the round trip of the backscatter the weaker the signal..
The X axis plots distance & Y axis plots dB signal level
It appears logically as a decreasing signal left to right over distance.

12. What does an OTDR Measure ?
Event Loss Difference in optical power level before and after an event, expressed in dB
An event is either something that was placed on purpose (splice, connector)
Or something that has happened to the fiber (bend)
Depending upon the event, It’s going to look something like the above
Fusion Splice or Macrobend
Connector or Mechanical Splice

13. What does an OTDR Measure ?
Reflectance Ratio of reflected power to incident power of an event, expressed as a negative dB value
The higher the reflectance, the more light reflected back, the worse the connection
A -50dB reflectance is better than -20dB value
Typical reflectance values
Polished Connector ~ -45dB
Ultra-Polished Connector ~ -55dB
Angled Polished Connector ~ -65dB
Reflectance relates to a specific event .
This is especially critical in high speed networks (10G+)
Or in applications that use high power lasers (RF Video overlay in FTTH)
Reflectance can cause signal degradation and needs to be managed.

14. What does an OTDR Measure ?
Optical Return Loss (ORL) Measure of the amount of light that is reflected back from a feature: forward power to the reflected power. The bigger the number in dBs the less light is being reflected.
The OTDR is able to measure not only the total ORL of the link but also section ORL
Attenuation (dB)
ORL is similar to reflectance, but instead of a single event, ORL is a measure of a section or span of overall reflected signal.
ORL of the
defined section
Distance (km)

15. Optical Return Loss (ORL)
Light reflected back to the source
PAPC
PPC PT PF
Light Source
Photo- diode
Optical return loss is the ratio of the output power of the light source to the total amount of back-reflected power (reflections and scattering). It is defined as a positive quantity.
Reflectance (dB) is the ratio of reflected power to incident power due to a single interface. It is defined as a negative quantity 
PT: Output power of the light source
PAPC: Back-reflected power of APC connector
PPC: Back-reflected power of PC connector
PF: Backscattered power of fiber
PB: Total amount of back-reflected power
ORL (dB) = 10Log > 0

16. Effects of High ORL Values
All laser sources, especially distributed feedback lasers, are sensitive to optical reflection, which causes spectral fluctuation and, subsequently, power jitter. Return loss is a measure of the amount of reflection accruing in an optical system. A -45dB reflection is equivalent to 45dB return loss (ORL). A minimum of 45-50dB return loss is the industry standard for passive components to ensure normal system operation in singlemode fiber systems.
Increase in transmitter noise
Reducing the OSNR in analog video transmission
Increasing the BER in digital transmission systems
Increase in light source interference
Changes central wavelength and output power
Higher incidence of transmitter damage
SC - PC
SC - APC
The angle reduces the back-reflection of the connection.

17. How to interpret a trace
OTDR Events
How to interpret a trace

18. How to interpret an OTDR Trace
Do step you through interpretation of an OTDR trace, we’re going to utilize content from one of our Wall posters we’ve recently developed. It’s called “Undersanding OTDRs”.
ILater in the Webex we’ll show you how you can get your own poster.
So here you see an OTDR trace w/ lots of “events”.
Let’s take a closer look at each one.

19. Front End Reflection
Connection between the OTDR and the patchcord or launch cable
Located at the extreme left edge of the trace
Reflectance:
Polished Connector ~ -45dB
Ultra-Polished Connector ~ -55dB
Angled Polished Connector up to ~ -65dB
Insertion Loss: Unable to measure
At the very beginning of the OTDR trace you see the first connection.(reflective)
Notice the spike (reflection) then a drop back down to a steady signal level.

20. Dead Zones
Attenuation Dead Zone (ADZ) is the minimum distance after a reflective event that a non-reflective event can be measured (0.5dB)
In this case the two events are more closely spaced than the ADZ, and shown as one event
ADZ can be reduced using shorter pulse widths
Event Dead Zone (EDZ) is the minimum distance where 2 consecutive unsaturated reflective events can be distinguished
In this case the two events are more closely spaced than the EDZ, and shown as one event
EDZ can be reduced using shorter pulse widths
At some point you’ve probably heard people talk about dead zones.
Where w/ your mobile phone, a dead zone is a spot where you can’t hear, an OTDR dead zone is an area where you cannot see true signal.
It’s caused by reflective events (connector, mechanical splice)
Within the definition of Dead Zone, there are two categories:
ADZ & EDZ (above)

21. Connector
A connector mechanically mates 2 fibers together and creates a reflective event
Reflectance:
Polished Connector ~ -45dB
Ultra-Polished Connector ~ -55dB
Angled Polished Connector up to ~ -65dB Insertion Loss: ~ 0.5dB
(loss of ~0.2dB w/ very good connector)
A connector causes a reflection (air gap) which.
An angled connector will have a much lower spike than a non-angled (PC type)

22. Fusion Splices
A Fusion Splice thermally fuses two fibers together using a splicing machine
Reflectance: None
Insertion Loss: < 0.1dB
A “Gainer” is a splice gain that appears when two fibers of different backscatter coefficients are spliced together (the higher coefficient being downstream)
Fusion splices are the standard method of splicing fibers today.
You won’t see them as much in LANs as you will in public networks.due to distances.
Reflectance: None
Insertion Loss: Small gain

23. Fusion Splices Direction A-B Direction B-A
Biggest chalenge w/ OTDR’s here is getting the loss of the event accurate. If you need optimum accuracy you’ll need to shoort both directions.

24. Macrobend Macrobending results from physical bending of the fiber.
Bending Losses are higher as wavelength increases.
Therefore to distinguish a bend from a splice, two wavelengths are used (typically 1310 & 1550nm)
Here we’re only covering Macrobends; but…
You’ll also here the two terms
Macrobend & Microbend - Same result, but different causes…
Macrobending loss refers to loss from physical bending of the fiber
Microbending loss is caused by pressure resulting in changing the physical shape fo the glass at a particular spot (core deformation)
Reflectance: None
Insertion Loss: Varies w/ degree of bend & wavelength

25. Mechanical Splice
A Mechanical Splice mechanically aligns two fibers together using a self-contained assembly.
Don’t see too many of these anymore.
Looks like a connector because it’s a mechanical connection w/ an air gap.
This has been replaced for the most part by the fusion splice.
Reflectance: ~ -35dB
Insertion Loss: ~ 0.5dB

26. Fiber End or Break
A Fiber End or Break occurs when the fiber terminates.
The end reflection depends on the fiber end cleavage and its environment.
Reflectance: PC open to air ~ -14dB
APC open to air ~ - 35dB
Insertion Loss: High (generally)
An OTDR cannot tell you whether the end of the fiber is the real end or a cut or break.
The signals look the same, so here you have to use your knowledge of the network.
”How long is it supposed to be?”
“ “Am I shooting the correct fiber?”

27. Ghosts
A Ghost is an unexpected event resulting from a strong reflection causing “echos” on the trace
When it appears it often occurs after the fiber end.
It is always an exact duplicate distance from the incident reflection.
Ghosts are what they sound like (unless you believe in Ghosts)
The are artifacts that show up on the trace that aren’t really there.
But you can spot a ghost if you know what to look for…
Now OTDRs have Ghost detect features that you can use to help identify them.
Reflectance: Lower than echo source
Insertion Loss: None

28. Typical Attenuation Values
0.2 dB/km for singlemode fiber at 1550 nm
0.35 dB/km for singlemode fiber at 1310 nm
1 dB/km for multimode fiber at 1300 nm
3 dB/km for multimode fiber at 850 nm
0.05 dB for a fusion splice
0.3 dB for a mechanical splice
0.5 dB for a connector pair (FOTP-34)
Splitters/monitor points (varys with component)

29. Best Practices with OTDRs

30. Performing an OTDR Test
Inspect & Clean connector end faces (patch cords & bulkheads (including test instrument)
Set up instrument for test environment
Test
View trace/table of results
Store / Report Results
Further analysis optional (for advanced users)

31. Key OTDR Setup Parameters for Manual Operation
Pulse Width
Controls the amount of light injected into the fiber
A short pulse width enables high resolution and short dead zones, but limited dynamic range
A long pulse width enables high dynamic range but less resolution and longer dead zones
5ns
1µs
So, if you go to manual, there are three key parameters that you need to set:
The first is pulse width.
Short Pulse:
More Resolution
Shorter Dead Zones
Less Dynamic Range
More Noise
Long Pulse:
Less Resolution
Wider Dead Zones
More Dynamic Range
Less Noise
100ns

32. Key OTDR Setup Parameters for Manual Operation
Acquisition Time (Averaging)
Length of time the OTDR takes to acquire and average the data points
Increasing acquisition time improves the dynamic range w/o affecting the resolution or dead zones. 5s
30s
In addition you need to set the averaging time.
Today seconds is most common, but sometimes you may want to use a shorter pulse to see more detail and you may need to average longer to get a cleaner trace.
20s

33. Key OTDR Setup Parameters for Manual Operation
Index of Refraction (IOR)
The IOR converts time, measured by the OTDR, to distance, which is displayed on the trace
Entering the appropriate value into the OTDR will ensure accurate length measurements for the fiber.
You may also need to set the IOR
There is more fiber in cable (fiber length) than there is cable (cable length).
This is called an overlength factor.
You can optimize the distance accuracy of the OTDR by referencing a known cable length to the OTDR and set the IOR to match the physical reference.

34. How to select the right OTDR Test Module
OTDR modules are primarily specified in terms of dynamic range
Select the optimum test module as follows:
Determine the longest span you will be testing w/ this module
Determine the expected link loss budget this will translate to
Select the module by subtracting 6 dB from the rated dynamic range of the module (this is the range of the unit to view backscatter signal or measure a splice loss)
Picking the right module is important to help minimize your investment while making sure you have the right range to manage your fiber network.

35. Example: Link Loss / OTDR Module selection calculation
Calculation Factors
Link example & calculations
Longest span length
75km
Avg fiber span loss
1310nm x 75 = 24.75dB
1550nm x 75 = 15dB
Connector Loss
Typically 2 connectors per span
2 x 0.5dB each = 1dB
Splice Loss
Typically < 0.1dB per splice w/ 1 splice per 5 km of fiber
75 / 5 = 15 splices x 0.1dB each = 1.5dB
dB adjustment OTDR module DR
Recommend allowing 6 dB for splice loss measurement
1310nm
1550nm dB
24.75 15
+ 1
+ 1.5
+ 6
= 33.25
= 23.5
I’ve included this handy-dandy guide in an attempt to simplify the process.
Once you have the number (for each wavelength), select the module w/ the value that corresponds to the calculation (or the closest one above it).
For example, w/ the values above, I would select the JDSU MR module (40/38dB) which is our lowest dynamic range single mode module w/ the best dead zone performance.
Dynamic Range requirement for Module

36. Tools to Optimize OTDR testing
Launch Cable
Using a launch cable allows the characterization of the connector at the origin of the link.
This shifts the first connector outside the dead zone of the OTDR connector
The last connector can also be measured by using a receive cable
About Launch Cables
Launch cables are typically 100 – 1,000 meters in length.
The length required depends upon the dead zone performance of the OTDR. A minimum 2x the attenuation dead zone length is recommended, although in practice, most are much longer
Launch cables allow you to see the near end connector,
Using these at both ends (receive cable) can allow a fairly accurate link loss measurement to be performed (as the connector losses at both ends can be measured.

37. TB6000/8000 OTDR Distance Chart

38. Fiber Characterization
Step-by-step review