Learn

Making sense out of complex Pro A/V and Broadcast technologies.

edu

Guide

Fiber Optic Cables

and Connectors

An educational resource published by Communications Specialties, Inc..

Learn how easy it is to terminate and fabricate your own

fiber optic cables and what types of fiber and fiber jackets

are available.

commspecial.com



edu

Guide

Making sense out of complex Pro A/V and Broadcast technologies.

Communications Specialties, Inc. is committed

to increased education and knowledge in the Pro A/V

and Broadcast industries.

We hope that you enjoy reading – and learning! –

with our eduGuide series of educational resources.

For additional information on these and other industry

related technologies, please visit us at

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©2009 Communications Specialties, Inc. All Rights Reserved.

Specifications, claims or other product information contained in this document are subject to

change without notice. This document may not be reproduced, in whole or in part, without the

express written consent of Communications Specialties, Inc.,

Fiberlink, Pure Digital Fiberlink, the starburst logo, Scan Do and Deuce are registered trademarks

of Communications Specialties, Inc. CSI and the triangle designs are trademarks of

Communications Specialties, Inc.

October 8, 2009



Introduction

In the design of a fiber optic transmission system, the first step is to determine

which transmitters and receivers are best suited to the signal type. The best

way to find the right system is to compare data sheets and consult with sales

engineers to find which products best meet the system specifications. Once

this is done, the next consideration is the choice of the fiber optic cable itself,

the optical connectors to be used and the method of attaching these

connectors. This portion of the system design is not so straightforward and is

shrouded in a great deal of misunderstandings and fear of complex “glass

grinding” techniques by the inexperienced. This booklet should clarify several

misconceptions about fiber cable and termination.

Cable Construction

Like copper wire, fiber optic cable is available in many physical variations.

There are single and multiple conductor constructions, aerial and direct burial

styles, plenum and riser cables and even ultra-rugged military type tactical

cables that will withstand severe mechanical abuse. Which cable one chooses

is, of course, dependent upon the application.

Regardless of the final outer construction however, all fiber optic cable

contains one or more optical fibers. These fibers are protected by an internal

construction that is unique to the type of fiber optic cable. The two most

common protection schemes in use today are to enclose the tiny fiber in a

loose fitting tube or to coat the fiber with a tight fitting buffer coating.

In the loose tube method the fiber is enclosed in a plastic buffer-tube that is

larger in inner diameter than the outer diameter of the fiber itself. This tube is

sometimes filled with a silicone gel to prevent the buildup of moisture as well.

Since the fiber is basically free to “float” within the tube, mechanical forces

acting on the outside of the cable do not usually reach the fiber.

Cable containing a loose buffer-tube fiber is generally very tolerant of axial

forces of the type encountered when pulling through conduits or where

constant mechanical stress is present such as cables employed for aerial use.

Since the fiber is not under any significant strain, loose buffer-tube cables

exhibit low optical attenuation losses.

In the tight buffer construction, a thick coating of a plastic-type materials

applied directly to the outside of the fiber itself. This results in a smaller overall

diameter of the entire cable and one that is more resistant to crushing or

overall impact-type forces. Because the fiber is not free to “float” however,

tensile strength is not as great. Tight buffer cable is normally lighter in weight

and more flexible than loose-tube cable and is usually employed for less

Introduction to Fiber Optic Cables and Connectors

3



severe applications such as within a building or to interconnect individual

pieces of equipment.

Figure 1 - Basic Fiber Optic Cable Construction - loose tube

and tight buffer fiber optic cable.

Buffer Tube

Outer Jacket

KEVLAR Strength

Members

Optical Fiber

Buffer

Coating

Figure 2 - Types of Fiber Optic Cable - single and two conductor fiber optic

cables, as well as a more complex multi-fiber cable. Note that the two

conductor cable is similar to the common AC powerline electrical cable.

Outer Jacket

Optical Fiber

Kevlar Strength Member

Buffer Tube

Ridged Fiberglass Central Strength Member

Single Cable

Dual Core Cable

Quad Core Cable

As can be seen from the diagram, in all cases the fiber/buffer tube is first

enclosed in a layer of synthetic yarn such as Kevlar for strength. An outer

jacket of PVC or similar material is then extruded over everything to protect

the inside of the cable from the rigors of the operating environment. In

multifiber cables, an additional strength member is also often added.

While most fiber optic cables are manufactured of totally non-conductive

materials, there are some cable that employ steel tape-wound outer jackets

for rodent resistance (direct burial types) or metallic strength members such

as steel wire for aerial (telephone pole) use. There are even fiber optic cables

with imbedded copper electrical conductors for transferring power to remote

electronic packages.

4

Introduction to Fiber Optic Cables and Connectors



Optical Fiber

Whether loose-buffer or tight-buffer, the actual glass fiber used in any fiber

optic cable only comes in one of two basic types, multimode fiber for use

over short to moderate transmission distances (up to about 2 Km) and single

mode fiber for use over distances that are generally greater than 2 Km.

Communications grade multimode fiber normally comes in two sizes, 50

micron core and 62.5 micron core, the latter being the size most commonly

available. The outer diameter of both is 125 microns and both use the same

connector size. Single mode fiber comes in only one size, 8-10 microns for the

core diameter and 125 microns for the outer diameter. Connectors for single

mode fiber are not the same as those designed for multimode fiber but can

look the same as we will soon discuss.

Figure 3 - Two types of optical fiber: step-index and graded-index fibers

Cladding

Core

Light

Step-Index Fiber

Core

Light

Graded-Index Fiber

Step index fiber has a core of ultra-pure glass surrounded by a cladding layer

of standard glass with a higher refractive index. This causes light traveling

within the fiber to continually “bounce” between the walls of the core much

like a ball bouncing through a pipe. Graded index fiber on the other hand

operates by refracting (or bending) light continually toward the center of the

fiber like a long lens. In a graded index fiber the entire fiber is made of ultra-

pure glass. In both types of fiber however, the light is effectively trapped and

does not normally exit except at the far end.

Losses in an optical fiber are the result of absorption and impurities within

the glass as well as mechanical strains that bend the fiber at an angle that

is so sharp that light is actually able to “leak out” through the cladding

region. Losses are also dependent on the wavelength of the light employed

in a system since the degree of light absorption by glass varies for different

wavelengths. At 850 nanometers, the wavelength most commonly used in

short-range transmission systems, typical fiber has a loss of 3 to 4 dB per

kilometer of length. At 1310 nanometers this loss drops to under 2 dB per

kilometer and at 1550 nanometers, the loss is a dB or so.

Introduction to Fiber Optic Cables and Connectors

5



The last two wavelengths are therefore obviously used for longer transmission

distances. The losses described above are independent of the frequency

or data rate of the signals being transmitted. There is another loss factor

however that is frequency (and wavelength) related and is due to the fact that

light can have many paths through the fiber. This is commonly referred to as

dispersion.

Figure 4 - shows the mechanism of this loss through step-index fiber

Short Path

Long Path

Various Light Path Lengths Through a Fiber

A straight light path through a fiber is shorter than one that travels with

maximum “bouncing”. This means that for a fast rise-time pulse of light, some

paths will result in light reaching the end of the fiber sooner than through

other paths. This causes a smearing or spreading effect on the output rise-

time of the light pulse which limits the maximum speed of light changes that

the fiber will allow. Since data is usually transmitted by pulses of light, this in

essence, limits the maximum data rate of the fiber.

The spreading effect for a fiber is expressed in terms of MHz per kilometer.

Standard 62.5 micron core multimode fiber usually has a bandwidth limitation

of 160 MHz per kilometer at 850 nanometers and 500 MHz per kilometer at

1310 nanometers due to its large core size compared to the wavelength of

the propagated light. Single mode fiber, because of its very small 8 micron

core diameter has a bandwidth of thousands of MHz per kilometer at 1310

nanometers. For most low frequency applications however, the loss of light

due to absorption will limit the transmission distance rather than the pulse

spreading effect.

6

Introduction to Fiber Optic Cables and Connectors



Optical Connectors

Since the tiny core of an optical fiber is what transmits the actual light, it is

imperative that the fiber be properly aligned with emitters in transmitters,

photo-detectors in receivers and adjacent fibers in splices. This is the function

of the optical connector. Because of the small sizes of fibers, the optical

connector is usually a high precision device with tolerances on the order of

fractions of a thousandth of an inch.

Although there are many different styles available the most common optical

cable connector in current use is the ST type shown in figure 5.

The connector consists of a precision pin that houses the actual fiber,

a spring-loaded mechanism that presses the pin against a similar pin in a

mating connector (or electro-optic device) and a method of securing and

strain-relieving the outer jacket of the fiber optic cable. ST connectors are

available for both multimode and single mode fibers. The main difference

between the two is the precision of the central pin. Since this difference is not

readily noticeable, care must be taken to use the correct connector. This is

especially true with pre-terminated connectors, such as the Corning Unicam

Connector System.

Figure 5 - The ST-style Optical Connector

Precision Connector

Pin (spring loaded)

Body & Locking

Mechanism

Strain Relief

Boot

Locating Tip

Fiber Optic Cable

The traditional method for attaching optical connectors consists of first

stripping the jacket from the fiber cable with tools that are almost exact

equivalents of those used for electrical cable. Once this is done the strength

members are trimmed and inserted into various restraining grommets or

sleeves. For loose-tube fibers, the buffer tube is then removed, exposing

the actual fiber. For tight-buffer fibers, the buffer coating is removed with

a precision stripping tool that looks like a small wire stripper. The process,

up to this point is still similar to preparing copper wire. It is when the bare

Introduction to Fiber Optic Cables and Connectors

7



fiber is exposed that the differences (compared to copper wire) occur. The

stripped fiber is now coated with a quick drying epoxy resin and inserted into

a precision hole or groove in the connector pin.

Then the strain relieving components are assembled and the basic connector

is ready for finishing. At this point the end of the bare fiber is protruding

from the front of the connector pin. The pin is placed in a special tool that is

then used to cleave or cut the tiny glass fiber flush with the end of the pin.

This takes a second or two. Next the connector is placed into a small jig and

run over two or three grades of fine lapping film, the equivalent of ultra-

fine sandpaper. This completes the polishing of the fiber and the optical

connector is ready for use. The complete task, not including the 5 minutes

of epoxy drying time, takes anywhere from 5 to 10 minutes per connector

depending on the skill level of the person. Figure 6 shows the various steps

involved in installing conventional ST connectors.

Many people have reservations about “connectorizing” fiber optic cable

due to problems they have heard about concerning the “grinding and

polishing of glass”. When one realizes that the “grinding and polishing” takes

less than a minute, and is done within a simple fool-proof fixture, the mystery

quickly evaporates. In fact, assembling an ST style optical connector is, in

reality no more demanding a task than assembling an older style electrical

BNC. Once one is completely familiar with the process, (which takes from 30

minutes to an hour to learn) the longest time interval involved in the finishing

process is waiting for the epoxy to cure.

Never-the-less the reservations continue. As a result, several connector

manufacturers manufacture so-called “quick-crimp” optical connectors.

These devices are installed with various mechanical clamp arrangements

and hot melt or instant bond adhesives (or, in some cases no chemical

adhesive at all). Some of these connectors, such as the Corning Unicam

Connector System, are even provided with a pre-polished length of optical

fiber in the tip there by eliminating the finishing step altogether. The

performance and reliability of this system is on par with the traditional “grind

and polish” system and is now in common use.

Other optical connectors that are available include the LC, SC and FCPC.

All are similar in that they position the fiber within a close tolerance tip which

then mates with an equally precise device on the other end. They really only

differ from each other in the mechanical way that the connectors mate to

each other. In any event all optical connector manufacturers provide detailed,

easy to follow step-by-step installation procedures for their respective

connectors.

8

Introduction to Fiber Optic Cables and Connectors



Figure 6 - Traditional steps involved in installing conventional ST connectors

1) Slide boot and crimp tube over end of fiber

Fiber

Boot

Crimp Tube

2) Strip fiber optic cable to dimensions shown

Kevlar

Buffer

Bare Fiber

0.3”

0.6”

1.5”

3) Cleave and apply epoxy

Apply Epoxy

Here

Note that with the Corning Unicam Connector System or the

Fiberlink® 6202 Field Termination Kit you do not need to perform

any grinding or polishing and there is no need for any epoxies or glues.

4) Assemble and crimp

Crimp

5) Complete the cable assembly

Introduction to Fiber Optic Cables and Connectors

9



Other issues in the eduGuide Series

Introduction to Fiber Optics

Undisputably, fiber is the future. Learn all about the benefits

of fiber optic technology in this easy-to-read guide.

Advantages of Digital Fiber Optics

Examine how digital signals over fiber are accomplished,

the phenomenal results they achieve, and how cost-effective it is.

Fiber Optic Cables, Connectors and Integration

Learn how easy it is to terminate and fabricate your own fiber optic cables,

what types of fiber and fiber jackets are available and how to design

and integrate a fiber optic system.

Scan Converters Buyer’s Guide

Everything you need to evaluate and decide on the perfect Scan Converter.

Video Scaling

A comprehensive overview of the technology, how it works

and when to use this technology effectively.

Advanced Video Scaling

Easy explanations of Inverse 3:2 Pulldown, Anamorphic Scaling and Other

Confusing Concepts.

Other Educational Resources

commspecial.com

Visit our website for online education resources, product literature and more!

Pure Digital Fiberlink® Application Brief – Everyday Pro A/V

This application brief illustrates the benefits of using Pure Digital Fiberlink®

in any Pro A/V installation. Regardless of your Pro A/V market specialty,

this Application Brief is a valuable guide to integrating and specifying

Pure Digital Fiberlink® products.

Pure Digital Fiberlink® Intelligence Brief – Government/Military

Detailed analysis of how Pure Digital Fiberlink® has become the solution of

choice for mission critical government, intelligence and military applications.

If you are involved in this market segment, this document will prove to be

valuable during your next project specification.

10

Introduction to Fiber Optic Cables and Connectors



Introduction to Fiber Optic Cables and Connectors

11



12

Introduction to Fiber Optic Cables and Connectors



Introduction to Fiber Optic Cables and Connectors

13



About Communications Specialties, Inc.

Communications Specialties, Inc. (CSI) is an award-winning, Long Island

based company that manufactures and sells a variety of products for the

distribution, conversion or transmission of television and computer video

signals, including fiber optic transmission systems, scan converters and video

scalers.

The company was founded in 1983 by veterans of the broadcast industry.

Since then, CSI has managed to consistently design innovative products that

are used worldwide by Fortune 500 Companies and Government Agencies in

a variety of markets such as Broadcast, Professional A/V, Videoconferencing,

Education, Home Theater, Security, ITS, Industrial Monitoring, Digital Signage,

Government/Military and more!

The

Pure Digital Fiberlink®

line offers an extensive and affordable family

of fiber optic transmission systems for the Professional A/V marketplace

and includes several ground-breaking products for the transmission of

high-resolution RGB signals. Systems for point-to-point and

point-to-multipoint signal distribution make these products highly

desirable for any Pro A/V applications.

Our premier product line, the

Scan Do®

family of computer to video scan

converters, has redefined industry standards in computer video to NTSC/

PAL technology with unsurpassed performance in its price range. All models

support high resolutions and refresh rates and are VGA and Mac® compatible.

The feature-rich and versatile Scan Do family offers the widest range of scan

converters on the market.

The award-winning,

Deuce®

video scalers convert NTSC and PAL to high-

resolution, non-interlaced video and offer a far superior and affordable

alternative to line doubling and quadrupling. The new generation of Deuce

products offer a wide range of non-interlaced resolutions and refresh rates

for every application, from professional A/V installations to home theater,

including a model designed especially for use with HDTV displays.

In addition, CSI manufactures a comprehensive selection of distribution

amplifiers, VGA monitor, keyboard and mouse extenders and accessories for

our entire product line.

14

Introduction to Fiber Optic Cables and Connectors



Communications Specialties and its products have been the recipient of

numerous industry awards. In 2005, the Pure Digital Fiberlink® 7220 Series

for high-resolution RGB and Stereo Audio was honored as one of the AV

industry’s best technological innovations of the year by receiving a “rAVe

Radical Product of the Year” award as “Best New Analog Signal Processing

Product”. The rAVe email newsletter is published by professional audiovisual

industry veterans and is read industry-wide.

Among CSI’s many other awards are AV Video Magazine’s Platinum Award

(given to Scan Do® Ultra and Deuce®) and the Video Systems’ Vanguard Award

(given to Deuce).

The company is headquartered in the United States on Long Island, New York,

with Sales Offices in Florida, Indiana and Virginia. Research, development,

design, engineering, manufacturing and customer support operations

are performed at the New York headquarters. Other locations include

Communications Specialties Pte Ltd (CSPL) - a wholly owned subsidiary office

in Singapore that provides support to distributors in the Far East and Pacific

Rim.

Our in-house sales department handles complete product-line sales directly

to end-users as well as to an international network of representatives and

resellers. All of our products are backed by an exceptional warranty.

Introduction to Fiber Optic Cables and Connectors

15



Learn

Making sense out of complex Pro A/V and Broadcast technologies.

edu

Guide

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