1. Mark Ortel Sales Support Eng SCTE Member and Supporter
Fiber Optic Tests
Mark Ortel
Sales Support Eng
SCTE Member and Supporter

2. Fiber Optics Key Concepts
Agenda
Fiber Optics Key Concepts
Fiber types and Connectors
Fiber Connections: the good, the bad, and the ugly
Measurement Units
Inspection and Cleaning
Inspect Before You ConnectSM
Inspect Both Sides
Proactive Inspection
Cleaning Best Practices
Introduction to Fiber Testing
Wide variety of people on the phone – need to make sure everyone is on the same page. 2

3. Fiber Connectors are Everywhere!
Fiber optic connectors are common throughout the network as they provide the power to add, drop, move, and change the network.
Local Convergence Point
Buildings
Network Access Points
CO/Headend/MTSO
Use the phrase: Moves, adds, changes
Close slide with “connectors are everywhere”
Feeder Cables
Distribution Cables
Multi-home Units
Residential
Drop Cables

4. Inspection and Cleaning

5. Fiber Optic Connector Body
Houses the ferrule that secures the fiber in place
LC CONNECTOR
Ferrule
Thin cylinder where the fiber is mounted and acts as the fiber alignment mechanism
Ferrule
Cladding
Body
Core
The fiber connector uses a latch and key mechanism to align the fiber and prevents the rotation of ferrules of the two mated connectors.
Fiber: Cladding
Glass layer surrounding the core, which prevents the signal in the core from escaping
Fiber: Core
The critical center layer of the fiber; the conduit that light passes through

6. Anatomy of Fiber Connectors
Light is transmitted and retained in the CORE of the optical fiber by total internal reflection.
The fiber connector end face has 3 major areas – the core, the cladding and the ferrule.
Particles closer to the core will have more impact than those farther out.
Fiber End Face View
FERRULE – 1.25 or 2.5 mm
CLADDING – 125 µm
CORE – 9 µm (SM)

7. Single Fiber vs. Multi-Fiber Connectors
SINGLE FIBER CONNECTOR
MULTI-FIBER CONNECTOR
White ceramic ferrule
One fiber per connector
Common types include SC, LC, FC, and ST
Polymer ferrule
Multiple fibers in linear array (for example, 8, 12, 24, 48, and 72) in single connector providing high-density connectivity
Common type is MPO or MTP®

8. Common Single Fiber Connectors
FC connector
2.5 mm ferrule
Screw mechanism with key –aligned
Legacy – mainly used with single-mode fibers
ST Connector
Twist-lock mechanism
Legacy – mainly used with multimode fibers
SC Connector
Push-pull latching mechanism
Most widely used connector today (LAN/WAN)
LC Connector
1.25 mm ferrule
Finger latch
Fastest growing connector

9. The angle reduces the back-reflection of the connection.
Types of End Faces
PC – Physical Contact
APC – Angled Physical Contact
The angle reduces the back-reflection of the connection.
APC connectors are used in systems where back reflection is an issue such HIGH-POWER applications. Video is typically high-power, so APC connectors are found in CATV and FTTx environments.
SC - PC
SC - APC 9

10. Focus on the Connection
Bulkhead Adapter
Ferrule
Fiber
Fiber Connector
Alignment Sleeve
Alignment Sleeve
Physical Contact
Note there are two endfaces – one in the bulkhead and one on the patch cord.

11. What Makes a GOOD Fiber Connection?
The 3 basic principles that are critical to achieving an efficient fiber optic connection are “The 3 Ps”:
Light Transmitted
Perfect Core Alignment
Physical Contact
Pristine Connector Interface
Core
Cladding
CLEAN
Today’s connector design and production techniques have eliminated most of the challenges to achieving core alignment and physical contact.

12. What Makes a BAD Fiber Connection?
Today’s connector design and production techniques have eliminated most of the challenges to achieving core alignment and physical contact.
The remaining challenge is maintaining a pristine end face. As a result, CONTAMINATION is the No. 1 reason for troubleshooting in optical networks.
A single particle mated into the core of a fiber can cause significant back reflection, insertion loss, and even equipment damage.
Light
Back Reflection
Insertion Loss
Core
Cladding
Emphasis on Contamination being the No. 1 reason for troubleshooting
DIRT

13. Contamination and Signal Performance
FIBER CONTAMINATION AND ITS EFFECT ON SIGNAL PERFORMANCE
CLEAN CONNECTION
Back Reflection = dB
Total Loss = dB 1
DIRTY CONNECTION
Back Reflection = dB
Total Loss = 3.2 dB 3
CLEAN Connection vs. DIRTY Connection
This OTDR trace illustrates a significant decrease in signal performance when dirty connectors are mated.
Make connection to link budget.
Make the point that where the contamination is makes a difference

14. Illustration of Particle Migration
11.8µ
15.1µ
10.3µ
Core
Cladding
Actual fiber end face images of particle migration
Emphasis on what happens over time with a little bit of contamination never being caught.
Even though the contamination at the beginning was not in the core, it can easily migrate to the core.
Each time connectors are mated, particles around the core become displaced, causing them to migrate and spread across the fiber surface.
Particles larger than 5 µm usually explode and multiply upon mating.
Large particles can create barriers (air gaps) that prevent physical contact.
Particles smaller than 5 µm tend to embed into the fiber surface creating pits and chips.

15. Particle Migration and Signal Performance
-70
-60
-50
-40
-30
-20
Baseline/ Initial Contamination
1st Mating
2nd Mating
3rd Mating
Actual fiber end face images of particle migration
Importance is where the contamination is.
For each successive mating, actual dB values increase as signal performance decreases
Dirt particles near or on the fiber core significantly affect signal performance

16. PITS (permanent damage)
Dirt Damages Fiber!
Mating dirty connectors embeds the debris into the fiber.
Light
Back Reflection
Insertion Loss
Core
Cladding
PITS (permanent damage)
DIRT
Mating force of 2.2 lb over 200 um diameter gives 45,000 psi.
Once embedded debris is removed, pits and chips remain in the fiber.
These pits can also prevent transmission of light, causing back reflection, insertion loss and damage to other network components.
Most connectors are not inspected until the problem is detected… AFTER permanent damage has already occurred.

17. Types of Contamination
Fiber end faces should be free of any contamination or defects, as shown below:
Single-mode Fiber
Common types of contamination and defects include the following:
Dirt
Oil
Pits & Chips
Scratches

18. Contamination Categories
LOOSE
Most contamination comes from dry particles that have fallen onto the end face or have been “placed” there during handling
BONDED
Most stubborn particles are held in place with grease, oils, or dried residue from a wet cleaning process
MATED
Particles on the end face of a connector can also become embedded into the glass if mated with another connector
CONTAMINATION MUST BE CLEANED from the end face prior to mating in order to optimize the efficiency of an optical signal or interconnect

19. Inspect Before You Connectsm
Follow the simple “INSPECT BEFORE YOU CONNECT” process to ensure fiber end faces are clean prior to mating connectors. 19

20. Inspect, Clean, Inspect, and Go!
Fiber inspection and cleaning are SIMPLE steps with immense benefits. 1
Inspect
■ Use a probe microscope to INSPECT the fiber.
– If the fiber is dirty, go to Step 2, Clean.
– If the fiber is clean, go to Step 4, Connect. 2
Clean
■ If the fiber is dirty, use a simple cleaning tool to CLEAN the fiber surface. 3
Re-inspect 4
Connect
■ If the fiber is clean, CONNECT the connector.
NOTE: Be sure to inspect both sides (patch cord “male” and bulkhead “female”) of the fiber interconnect.
■ Use a probe microscope to RE-INSPECT (confirm fiber is clean).
– If the fiber is still dirty, repeat Step 2, Clean.
– If the fiber is clean, go to Step 4, Connect.

21. Inspect and Clean Both Connectors in Pairs!
Inspecting BOTH sides of the connection is the ONLY WAY to ensure the connector will be free of contamination and defects.
Inspection is contact-free. Discuss or have separate slide.
Patch Cord (Male) Inspection
Bulkhead (Female) Inspection
Patch cords are easy to access and view compared to the fiber inside the bulkhead (or test equipment or network equipment) which are frequently overlooked. The bulkhead side may only be half of the connection, but it is far more likely to be dirty and problematic.

22. Proactive vs. Reactive Inspection
PROACTIVE INSPECTION:
Visually inspect fiber connectors at every stage of handling BEFORE mating them.
Connectors are much easier to clean prior to mating, before embedding debris into the fiber.
REACTIVE INSPECTION:
Visually inspect fiber connectors AFTER discovering a problem, typically during troubleshooting.
By this time, connectors and other equipment may have suffered permanent damage.
Dirty Fiber PRIOR to Mating
Fiber AFTER Cleaning
Fiber AFTER Mating and Numerous Cleanings
Dirty Fiber PRIOR to Mating
Common mistake is to reactively inspect fiber endfaces 22

23. Benefits of Proactive Inspection
PROACTIVE INSPECTION is quick and easy, with indisputable benefits
Reduce Network Downtime
Active network = satisfied customers
Reduce Troubleshooting
Prevent costly truck rolls and service calls
Optimize Signal Performance
Network components operate at highest level of performance
Prevent Network Damage
Ensure longevity of costly network equipment 23

24. Cleaning Best Practices
Many tools exist to clean fiber
Many companies have their own “best practices”
Dry clean first. If that does not clean, then try wet cleaning.
Always finish with dry cleaning!
Whatever cleaning equipment you use, make sure it is designed for fiber optic cleaning.

25. Light Transmission

26. Optical Communications
Communication technology, developed in the 70s, that sends optical signals down hair-thin strands of glass fiber
Transmitter
Receiver
Light Rays
Fiber
Fiber optics is a communication technology developed in the 1970s and became widely deployed by the 1990s. It is now the primary transport medium in all types of telecommunications networks. Very simply, fiber optic communication transmits optical signals down very thin glass fiber strands to a receiver. 26

27. Optical Fiber Types 2 Types Multimode Single-mode
Two basic types of fiber optic cables are used: Multimode and Single-mode. Details of how light travels down these two types of fiber will be addressed on the following two slides. Physically, both fiber types are made up of a glass core surrounded by a glass cladding. A protective buffer then covers the fiber that is typically stripped off when terminating a fiber.
The core of a multimode fiber is either 50 or 62.5 microns wide.
The core of a single-mode fiber is typically 9 microns wide.
Both multimode and single-mode fiber cores are surrounded by a 125 micron cladding.
The buffer takes the total diameter of the fiber to either 250 or 900 microns.
Note that these examples show simplex fiber cables. Multi-strand fiber cables also exist. 27

28. Fiber Types MM
Fiber carries numerous light rays (mode) simultaneously through the fiber.
Light traveling through multimode fiber takes multiple paths or modes, which causes the light pulses to spread out or disperse. The result of this pulse spreading is that multimode fiber cannot carry high bit rates over long distances. Multimode fiber is typically found in local area networks working at 850 or 1300 nanometers. While the fiber optic cable itself is not significantly cheaper than single-mode fiber, the light sources are. Multimode fiber uses LEDs or VCSEL (cheap lasers) as light sources compared to lasers for single-mode fiber.
Refractive index: Measures the speed of light in a material. For example, n1 and n2 are the respective refractive index of the cladding and the core, and n1<n2 is the condition for the light traveling down the fiber.
Fiber channel and Ethernet are most common applications
High attenuation
850 to 1300 nm transmission wavelengths
Local networks (<2 km)
Limited bandwidth
LAN/Industry 28

29. Fiber carries a single light ray (mode).
Fiber Types SM
Fiber carries a single light ray (mode).
Low attenuation
1260 to 1660 nm transmission wavelengths
Access/medium/long haul networks (>200 km)
Nearly infinite bandwidth
Telecom/CATV
FTTx
CWDM/DWDM
Outside plant fiber optic cable uses single-mode fiber. Working at 1310, 1550, and other wavelengths in the 1260 to 1660 nanometer range, single-mode fiber can carry very high bit rates over long distances. Because the core of the fiber is so small, light can only take a single path through it, minimizing the amount of dispersion.
Single-mode fiber is also used in wavelength division multiplexing systems, which have multiple wavelengths of light traveling on the same fiber.
Ethernet/FICON on SM is popular in enterprise 29

30. Measurement Units dBm unit is decibels relative to 1 mW of power
dBm is an ABSOLUTE measurement
dB is a RELATIVE measurement
1 mW = 0 dBm Tx
Relative Power (dB) =10*Log
2 dB
1 dB
Loss = 8 dB
Absolute Power (dBm) =10*Log
5 dB
When we move into the section that discusses testing, the difference between dB and dBm will become critical. Simply put, dBm is an ABSOLUTE measurement: 1 mW equals 0 dBm, while dB is a relative measurement.
The diagram on the right side of the slide illustrates this. At the top a transmitter is generating 0dBm – an absolute value. At the bottom a receiver is receiving -8 dBm, again an absolute value. Between the transmitter and the receiver are two fiber optic cables and a single fiber connector that, combined, create a loss of 8 dB—a relative value. In other words, loss is never referred to in dBm because it is always a relative value. We could change the transmitted level to +8 dBm and the received level would then become 0 dBm, because the relative amount of loss is still 8 dB.
Make note of loss shown at connection – want connector to be about .75dB of loss – most volatile point
-8 dBm Rx
0 dBm
-3 dBm
-20 dBm
-40 dBm
1 mW
0.5 mW
0.01 mW mW 30

31. Optical power is lost as light travels along fibers
Attenuation
Optical power is lost as light travels along fibers
Primarily caused by absorption and scattering
Usually expressed in dB or dB/km.
Source
RECEIVER
Pin
(Emitted power)
Power variation
Pout
(Received power)

32. Absorption and Scattering
Absorption: Light is absorbed due to chemical properties or natural impurities in the glass. Accounts for about 5% of total loss.
Scattering is the loss of a light signal from the fiber core caused by impurities or changes in the index of refraction of the fiber. Accounts for about 95% of total loss.
Pure Glass=Si O2 Si O Cu
Imperfections
Light scattered
Impurities

33. Bending Losses Microbending Macrobending
Microbending losses are due to microscopic fiber deformations in the core-cladding interface caused by induced pressure on the glass
Macrobending
Macrobending losses are due to physical bends in the fiber that are large in relation to fiber diameter
Attenuation due to bending is increases with wavelength (e.g. greater at 1550nm than at 1310nm)

34. Spectral Attenuation 190 THz 50 THz Attenuation (dB/km)
Cut-off wavelength for singlemode fiber 4 3
OH-
absorption
Peak
Attenuation (dB/km)
OH- 2
OH- 1
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
Wavelength (µm)
1st Window
S- Band 1460 to 1530nm
L-Band 1565 to 1625nm
O Band (2nd Window )
U- Band to 1675 nm
C-Band 1530 to 1565 nm (3rd window)
E-Band 1360 to 1460nm

35. Loss Process Coupling Junction Impurities Macro or Absorption micro
Input
Output
Impurities
Scattering
Loss
Injection
Absorption
Junction
Coupling
Macro or
micro
bending
loss

36. Sources Characteristics LEDs Lasers Output Power
Linearly proportional to drive current
Proportional to current above the threshold
Current
Drive Current: 50 to 100 mA Peak
Threshold Current: 5 to 40 mA
Speed
Slower
Faster
Wavelengths Available
0.66 to 1.65 µm
0.78 to 1.65 µm
Spectral Width
Wider ( nm FWHM)
Narrower ( nm to 10 nm FWHM)
Fiber Type MM
SM, MM
Ease of Use
Easier
Harder
Lifetime
Longer
Long
Cost
Low
High

37. Detectors
Photodiodes: different spectral characteristics depending on the type of semiconductor  different wavelength settings/calibration in power meter
Si: Silicon
GE: Germanium
InGaAs: Indium Gallium Arsenide
S (A/W)
850
1310
1550
(nm) GE
InGaAs
0.5
1625 Si
Values for temp = 0°C
Values for temp = 23°C Si GE
InGaAs
Meas. Range nm nm nm
Characteristics
Only for MM fibers
For general use
Recommended for 1625nm

38. Difference between maximum input and minimum sensitivity.
Dynamic Range
Difference between maximum input and minimum sensitivity.
Typical power meter dynamic ranges:
+20 dBm to -70 dBm for Telephony
+30 dBm to -55 dBm for CATV
-20 dBm to -60 dBm for LAN

39. Optical Loss Budget
Maximum loss = Minimum power output of source minus minimum acceptable power level of receiver
Minimum loss = Maximum power output of source minus maximum acceptable power level of receiver
Ptmax
Minimum Loss (dB)
Prmax
Optical Loss Budget:
Bmax = Ptmin – Prmin
Bmin = Ptmax -Prmax
Ptmin
Optical Power Level (dBm)
Maximum Loss (dB)
Prmin

40. Optical Loss Budget (Example 1)
1000BASE-LX GBIC
Ptmax = -3 dBm
Ptmin = -9.5 dBm
Prmax = -3 dBm
Prmin = -19 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 -3 dBm
Minimum Loss (dB) = 0 dB
Optical Loss Budget:
Bmax = Ptmin – Prmin
Bmin = Ptmax -Prmax
Prmax -3 dBm
Ptmin -9.5 dBm
Optical Power Level (dBm)
Maximum Loss (dB) = 18.5 dB
Prmin -19 dBm