Transcript Title Here - SCTE Penn

Optical Loss Budget (Example 2)
 1000BASE-ZX GBIC
Optical Power Level (dBm)
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–
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 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
Ptmin = 0 dBm
Prmax = -3 dBm
Prmin = -23 dBm
Ptmax 5 dBm
Minimum Loss (dB) = 8 dB
Prmax -3 dBm
Ptmin 0 dBm
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Maximum Loss (dB) = 23 dB
Prmin -23 dBm
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Optical Loss Budget:
Bmax = Ptmin – Prmin
Bmin = Ptmax -Prmax
Test!
 Basic Tests
– Visual Fault Locator (VFL)
– Optical Insertion Loss
– Optical Power Levels
 Advanced Tests
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–
–
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2
Optical Return Loss (ORL)
Optical Time Domain Reflectometer (OTDR)
Chromatic Dispersion (CD)
Polarization Mode Dispersion (PMD)
Optical Spectral Analysis (OSA)
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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-050
3
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
FFL-100
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
4
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
Introduction to OTDR
It’s the single most important tester used in the
installation, maintenance & troubleshooting of fiber plant
T-BERD 4000 FTTx / Access OTDR
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.
5
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
Background on Fiber Phenomena
OTDR depends on two types of phenomena:
- Rayleigh scattering
- Fresnel reflections.
Rayleigh scattering and
backscattering effect in a fiber
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Light reflection phenomenon =
Fresnel reflection
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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
7
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Example of an OTDR trace
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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
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
What does an OTDR Measure ?
 Event Loss
Difference in optical power level before and after an event,
expressed in dB
Fusion Splice or
Macrobend
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Connector or
Mechanical Splice
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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
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 Polished Connector
~ -45dB
 Ultra-Polished Connector
~ -55dB
 Angled Polished Connector
~ -65dB
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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.
Attenuation (dB)
The OTDR is able to measure not only the total ORL of the link but
also section ORL
ORL of the
defined section
Distance (km)
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
Optical Return Loss (ORL)
 Light reflected back to the source
PPC
PAPC
PAPC
PAPC
Light
Source
Photodiode
PF
PF
PF
PT
PT: Output power of the light source
ORL (dB) = 10Log (
PT
)> 0
PB
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
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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
–
–

Increase in light source interference
–

Reducing the OSNR in analog video transmission
Increasing the BER in digital transmission systems
Changes central wavelength and output power
Higher incidence of transmitter damage
SC - PC
SC - APC

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The angle reduces the back-reflection of the
connection.
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OTDR Events
How to interpret a trace
How to interpret an OTDR Trace
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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
Ultra-Polished Connector
Angled Polished Connector
Insertion Loss:
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~ -45dB
~ -55dB
up to ~ -65dB
Unable to measure
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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
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Connector
A connector mechanically mates
2 fibers together and creates a
reflective event
Reflectance:
 Polished Connector
~ -45dB
 Ultra-Polished Connector
~ -55dB
 Angled Polished Connector
Insertion Loss:
up to ~ -65dB
~ 0.5dB
(loss of ~0.2dB w/ very good connector)
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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)
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Reflectance:
None
Insertion Loss:
Small gain
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Fusion Splices
Direction A-B
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Direction B-A
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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)
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Reflectance:
None
Insertion Loss:
Varies w/ degree
of bend & wavelength
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Mechanical Splice
A Mechanical Splice mechanically aligns
two fibers together using a self-contained
assembly.
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Reflectance:
~ -35dB
Insertion Loss:
~ 0.5dB
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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)
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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.
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Reflectance:
Lower than echo source
Insertion Loss:
None
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Typical Attenuation Values








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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)
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
Best Practices with OTDRs
Performing an OTDR Test
1. Inspect & Clean connector end faces (patch cords
& bulkheads (including test instrument)
2. Set up instrument for test environment
3. Test
4. View trace/table of results
5. Store / Report Results
6. Further analysis optional
(for advanced users)
30
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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
Short Pulse:
•
•
•
•
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More Resolution
Shorter Dead Zones
Less Dynamic Range
More Noise
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100ns
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Long Pulse:
•
•
•
•
Less Resolution
Wider Dead Zones
More Dynamic Range
Less Noise
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
20s
32
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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.
33
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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:
1. Determine the longest span you will be testing w/ this
module
2. Determine the expected link loss budget this will
translate to
3. 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)
34
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
Example: Link Loss / OTDR Module selection calculation
Calculation
Factors
Link example & calculations
Longest span length 75km
1550nm
dB
dB
24.75
15
+1
+1
Avg fiber span loss
0.33dB/km @ 1310nm x 75 = 24.75dB
0.20dB/km @ 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
+ 1.5
+ 1.5
dB adjustment
OTDR module DR
Recommend allowing 6 dB for splice loss
measurement
+6
+6
= 33.25
= 23.5
Dynamic Range requirement for Module
35
1310nm
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
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
36
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
TB6000/8000 OTDR Distance Chart
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JDSU CONFIDENTIAL & PROPRIETARY INFORMATION
Fiber Characterization
Step-by-step review