1. Fiber Optic Cables Design
Session 2:
Fiber Optic Cables Design
In this session we will discuss
Different types of cables
Cable specification
Guidelines for fiber optic design and installation
Optical cable pulling

2. Fiber Optic Components
Hardware provides the mounting, protection, etc. for connectors or splices
Cable protects fibers in the application environment
Connectors join fibers or connect to active devices so they can be disconnected for rerouting, testing, etc.
Splices join two fibers permanently
Test equipment checks performance
Now let’s take a look at the components of a fiber optic system. We’ll examine each of these in detail and look at their installation.
FOTM, Chapter 4-7, DVVC, Chapter 12-13

3. Main parts of a bare fiber
Main parts of a cable
(Polymer
coating
+ Buffer)
Kevlar
Main parts of a bare fiber

4. Two Buffer Types Loose buffer and tight buffer
Loose-tube cable, used in the majority of outside-plant installations in North America.
tight-buffered cable, primarily used inside buildings.

5. Tight vs. loose buffer

6. Property of loose buffer
Loose buffered cables are constructed so the fibers are decoupled from tensile forces that the cable may experience during installation and operation. Loose-buffered cables have the following characteristics:
More robust than tight buffered cables for outdoor applications.
Optimized and proven for long outdoor runs.
Less expensive than indoor cable per fiber-meter, specifically at fiber counts above 24.
Have high fiber counts.
Have better packing density.

7. Advantages of Loose-Buffer Cable
A hard color-coded plastic buffer tubes having an inside diameter several times that of the fiber.
Excess fiber length (relative to buffer tube length) insulates fibers from stresses of installation and environmental loading.
Less temperature sensitive
Loose-tube cables typically are used for outside-plant installation in aerial, duct and direct-buried applications.
Yarn (Kevlar) strength members keep the tensile load away from the fiber.

8. Tight-Buffered Cable The buffer is in direct contact with the fiber.
The tight-buffered design provides a rugged cable structure to protect individual fibers during handling, routing and connectorization.
More temperature sensitive
This design is suited for "jumper cables" which connect outside plant cables to terminal equipment, and also for linking various devices in a premises network.
Multi-fiber, tight-buffered cables often are used for intra-building, risers, general building and plenum applications.

9. Advantage of tight buffer cable
Tight-buffered fiber generally have a 900 um plastic coating applied directly to the fiber.
Increased physical flexibility.
Smaller bend radius for low fiber-count cables.
Easier handling characteristics in low fiber counts
The two typical constructions of tight-buffered cables are:
Distribution design, which has a single jacket protecting all the tight buffered fibers.
Breakout design, which has an individual jacket for each tight-buffered fiber.

10. Strength members-Handling the Load
The strength member bears tensile load, ensuring that it does not transfer to the fiber.
To be effective, strength members must have lower net elongation than that of the optical fibers they protect. For example, glass fibers usually elongate 0.5 to 1.0% before breaking, so strength members used for glass fibers must elongate even less.
Most common materials are Kevlar aramid yarn, steel and fiber glass epoxy rods. These materials are distinguished by such unique properties as wet strength, abrasion resistance and flexibility.

11. Selecting the Proper Jacket
The outer jacket is the remaining critical component of a fiber optic cable.
Based on the environmental protection required for the application.
Chemical resistant
Temperature requirement: from -60oC to 200oC
Fire safety
Meets the requirement of National Electrical Code (NEC) and Underwriters Laboratories (UL)

12. Example of jacketing materials
PVC - This family of plastics is commonly used for jacketing because of its unique combination of properties,
low combustibility,
toughness,
weatherability, and
dimensional stability.
It is versatile and can be formulated for demanding applications.

13. Industrial Cable Standards
5 cable types have emerged as de facto standards
Simplex and Duplex (Zipcord) cable
Distribution cable
Breakout cable
Loose-tube cable
Hybrid or composite cable

14. Simplex Cables
With an outer diameter of 1.7 mm to 3.0 mm contain semi-tight tubes in a PVC jacket.
Product properties
tight bending radius
rugged design
assembled with spring-loaded connectors
buffering material is self-extinguishing, non-toxic and halogen-free
Installation load – short term, 250 lb
Operating load – long term, 10 lb (simplex)

15. Duplex Cables
Consist of two single-fiber cables (semi-tight tube with strain relief and jacket). Duplex cables are used for indoor applications.
Product properties
tight bending radius
rugged design
can be assembled with spring-loaded connectors
Buffering materials are self-extinguishing, non-toxic and halogen-free

16. Fiber Optic Ribbon Cable
Large fiber counts

17. Tight Buffer/Distribution Cables
Small-tight packed
Several tight-buffer fibers under the same jacket
Used for short and dry conduit runs and riser and plenum applications.
Not individually reinforced – with only one Kevlar for all fibers.
1, 2 to .

18. Breakout Cables
Consist of 4 to 12 simplex single-fiber cables around a central strength member and unified in a single cable by a second outer jacket.
More expansive
Product properties
rugged design
can be assembled with spring-loaded connectors
Buffering materials are self-extinguishing, non-toxic and halogen-free

19. Loose-Tube/Outdoor Cables
This cable group includes jellyfree cables, non-armored multi-fiber loose tube cables, glass-armored multi-fiber loose tube cables and steel-armored multi-fiber loose tube cables.
Applications
Overhead – strung from telephone poles
Direct burial – placed directly in a trench dug in the ground and covered
Indirect burial – inside a duct or conduit
Submarine –underwater

20. Composite/Hybrid cables
integrate fiber optic and energy conductors in one jacket. The installation of two cables is thus avoided.
Properties
Combination of fiber-optic cables with copper power cables
jacket material selection same as with fiber-optic cables (e.g. flame-retardant, halogen free)
Field of application
as data and power cable for industry, LAN, video, telephone, customer-specific applications, etc.

21. Review: identify the typea b
Because of the wide variety of conditions to which they are exposed, optical fibers have to be encased in several layers of protection. The first of these layers is the primary buffer coating, a thin protective coating made of ultraviolet curable acrylate ( a plastic), which is applied to the glass fiber as it is being manufactured. This thin coating provides moisture and mechanical protection.
The next layer of protection is a buffer, that is typically extruded over this coating to further increase the strength of the single fibers. This buffer can be either a loose tube or a tight tube.The next layer is a strength member, usually an aramid fiber, that can be used for pulling the cable. Finally, the entire cable is covered by a jacket designed to withstand the environment into which the cable is going to be installed.
Tight buffer (a zipcord is shown), distribution and breakout cables are used indoors. Outdoors, loose tube cable is used to allow filling the cable with water-blocking materials to protect the fibers from moisture.
FOTM, Chapter 4,5,913, DVVC, Chapter 11 c d

22. Specifying Fiber Optic Cable
Specifying the proper cable requires two major considerations:
1. How the cable will be installed.
2. What environment it will be facing after installation.

23. Installation Specs Max recommended installation load:
1 fiber: lbs
Multifiber (6-12) cables: lbs
Direct buried: 600 lbs
Min recommended installation bending radius:
>20x the cable diameter
Cable diameter
Recommended temperature ranges for installation
Recommended temperature ranges for storage

24. Environmental Specifications
Temperature
Long term bend radius (10x the cable dia.)
Electrical codes (NEC)
Long term tensile load
Flame resistance
Rodent penetration (armored)
Water resistance (filled and blocked)
Crush loads
Abrasion resistance
Resistance to chemicals
Impact resistance
Vibration
Specifying the proper cable requires two major considerations:
1. How the cable will be installed.
2. What environment it will be facing after installation.
These are simply guidelines to consider when looking for a cable for any particular installation. Different manufacturers have different cable designs for applications - and mayber different designs than other manufacturers.
Therefore it is preferable to talk to several manufacturers when choosing a cable, especially in unusual situations.
FOTM, Chapter 4,5,913, DVVC, Chapter 11

25. Six NEC770 Ratings These 6 ratings are:
OFN optical fiber non-conductive
OFC optical fiber conductive
OFNG or OFCG general purpose
OFNR or OFCR riser rated cable for vertical
runs
OFNP or OFCP plenum rated cables for air-
handling areas
OFN-LS low smoke density

26. Cable Ratings and Markings
All premises cables must carry identification and ratings per the NEC (National Electrical Code) paragraph 770.
Cables without markings should never be installed indoors as they will not pass inspections!
Inspectors are not inspecting fiber for electrical safety (unless the cable is conductive), but are inspecting for conformance with fire codes.
FOTM, Chapter 4,5,913, DVVC,Chapter 12

27. Fiber Optic Cable Selection Criteria
Cost
Proper for the application (building, riser, plenum, aerial, direct burial, submarine, etc.)
Enough fiber for redundancy, upgrades
Meets environmental requirements
Choose hardware to fit cable needs
Choice of cables
Other factors to be considered when choosing a fiber optic cable are:
1. Current and future bandwidth requirements.
2. Acceptable attenuation rate.
3. Length of cable.
4. Cost of installation.
5. Mechanical requirements (ruggedness, flexibility, flame retardance, low smoke, cut- through resistance).
6. UL/NEC requirements.
7. Signal source (coupling efficiency, power output, receiver sensitivity).
8. Connectors and terminations.
9. Cable dimension requirements.
10. Physical environment (temperature, moisture, location).
11. Compatibility with any existing systems.
FOTM, Chapter 4,5,913, DVVC, Chapter 11

28. Four Ways to Future-Proof
Install the best multimode fiber
Include spare fibers
Include singlemode fibers in multimode cable
Include fibers in copper cables (rare)

29. Cable Designs - Indoor Short distances - breakout cable
Longer lengths -distribution cable
All dielectric
Plenum PVC if available
Performance Specifications
Tensile load: lbs max.
Temperature range: -10 to +60 C
Strength members: Kevlar®
Jacket: UL Rated
Do not install cable indoors without UL Fire Rating!
Breakout cable is larger and more expensive, but for short distances it offers more ruggedness and the ability to be terminated without the need for patch panels or termination boxes, saving that cost.
For most backbone cables, distribution cables have a smaller size for the number of fibers, easing pulling of the cable, and are terminated in patch panels or boxes to protect the fibers.
Remember that indoor cables must meet UL ratings!
FOTM, Chapter 4,5,913, DVVC, Chapter 11

30. Cable Designs - Outdoor
Loose tube
Water-blocked gel-filled (dry water-blocked
cable is now also available)
Consider ribbon for high fiber count
All dielectric
Performance Specifications
Tensile load when installed: 600 lbs max.
Strength members: fiberglass & Kevlar®
Temperature range -40 to +60 C
Rodent resistance: armor or innerduct
Jacket: black polyethylene (UV stability)
All outdoor cables are loose tube to allow inclusion of water-blcoking compounds. Most are gels but some dry water-blcoking cables are available (using materials developed for disposable diapers!)
Outdoor direct buried installations will either be armored or installed in conduit to prevent rodent (or other critter) damage.
Cables pulled through conduit must be chosen for the proper pulling tension, properly lubricated and pulled with some form of limiter (breakaway swivel or tension-contolled puller).
FOTM, Chapter 4,5,913, DVVC,Chapter 12

31. Outside Plant Installation
Outside plant installations require more hardware (and more investment in the tools and test equipment.) and even splicing vans are the tools of the trade for OSP contractors.
FOTM, Chapter 9,12,13,15, DVVC, Chapter 11, 15
Outside plant installations require more tools and test equipment, such as pullers, splicers, OTDRs, etc.

32. Outside Plant Installation
all singlemode fiber with high fiber counts.
optimized for resisting moisture and rodent damage.
Long distances mean cables are fusion spliced together, since cables are not made longer than about 4 km (2.5 miles)
Connectors (SC, ST or FC styles) on factory made pigtails are spliced onto the end of the cable.
After installation, every fiber and every splice is tested with an OTDR.

33. Fiber Optic Installations - Premises
Premises applications usually mean lots of cables - both copper and fiber - terminated in telecom rooms.
FOTM, Chapter 9,12,13,15, DVVC, Chapter 11, 15

34. Premise Cable Installation
multimode in short lengths (a few hundred feet), with 2 to 48 fibers per cable typically.
Some users install hybrid cable with both multimode and singlemode fibers.
Splicing is not needed.
Most connectors are SC or ST style. Termination is by installing connectors directly on the ends of the fibers, primarily using adhesive technology.
Testing is done my a source and meter, but every installer has a flashlight type tracer to check fiber continuity and connection.

35. Prism Dispersion
For visible light, most transparent materials (e.g. glasses) have:
1 < n (red) < n (yellow) < n (blue)
that is, refractive index n decreases with increasing wavelength λ.
At the interface of such a material with air, predicted by Snell's law, the blue light, with a higher refractive index, will be bent more strongly than red light, resulting in the well-known rainbow pattern.

36. Dispersion in Fiber
No power is lost due to dispersion, but the peak power has been reduced.
Dispersion distorts both analog and digital signals.
Dispersion is normally specified in nanoseconds per kilometer.
input
output

37. Pulse spreading
The data which is carried in an optical fibre consists of pulses of light energy following each other rapidly.
There is a limit to the highest frequency, i.e. how many pulses per second which can be sent into a fibre and be expected to emerge intact at the other end. This is because of a phenomenon known as pulse spreading which limits the "Bandwidth" of the fibre.

38. Different Types of Dispersion
Dispersion is the spreading of a light pulse as it travels down the length of an optical fiber.
Dispersion limits the bandwidth or information carrying capacity.
There are 4 main types of dispersion:
Modal dispersion
Material dispersion
Waveguide dispersion
Polarization mode dispersion

39. Dispersion and Chirp
Dispersion produces a frequency chirp in the bit pulse

40. Dispersion Compensation

41. 1. Modal dispersion input Output ?
A well defined pulse of single wavelength is coupled into a multimode step-index fiber. Compare two modes in travel time –
One along optical axis
One close to the critical angle
Which one moving faster?
What will happen to the pulse shape?

42. Modal Dispersion Occurs only in multimode fibers
Due to the different path for each mode in a fiber and consequently each mode arrives at the other end of the fiber at different time
Typical modal dispersion is about nanoseconds/km
Modal dispersion can be reduced by using
a single mode fiber – a single path
a smaller core diameter – less modes
a graded-index fiber - ?

43. Graded-index vs. step-index fiber
In a graded-index fiber, the light rays that follow longer paths travel at a faster speed and arrive at the other end of the fiber at nearly the same time as the rays follow shorter paths.

44. 2. Material (chromatic) dispersion
n = c/v, v changes for each wavelength
Different wavelengths (colors) travel at different speeds through even a single mode fiber
The amount of dispersion of a fiber depends
The spectrum range of the light injected
The nominal operating wavelength

45. Dispersion vs. Wavelength
zero-dispersion wavelength. For standard single-mode fibers, this is in the region of 1310 nm.
zero-dispersion wavelength means maximum information-carrying capacity.

46. Anomalous and normal dispersion
In a standard SMF:
the dispersion D > 0 for l >1.31 mm
this is called anomalous dispersion
Shorter l components travel faster than for longer l components
the dispersion D < 0 for l <1.31 mm
this is called normal dispersion
Longer l components travel faster than for shorter l components

47. Consequences of pulse spreading
The Bandwidth is the highest number of pulses per second, that can be carried by the fiber without loss of information due to pulse spreading.
Frequency Limit (Bandwidth)
If signal pulses follow each other too fast (max frequency), then by the time they reach the end fibre they will have merged together and become indistinguishable. This is unacceptable for digital systems which depend on the precise sequence of pulses as a code for information.

48. Consequences of pulse spreading
Distance Limit
A given length of fibre, as explained above, has a maximum frequency (bandwidth) which can be sent along it.
If we want to increase the bandwidth for the same type of fibre we can achieve this by decreasing the length of the fibre.
Another way of saying this is that for a given data rate there is a maximum distance which the data can be sent.