Technical Seminar

Yaswanth

G12761A041

2

Fiber Optic Technology

Contents:Introduction HistoryConstruction Principle WorkingClassificationsApplicationAdvantagesDisadvantages

Introduction:

We hear about fiber-optic cables whenever people talk about the telephone system, the cable TV system or the Internet.

We are increasing ability to transmit more information, more quickly and over longer distances.

An optical fiber (or fiber) is a glass or plastic fiber that carries light along its length . Fiber Optics is overlap of applied science and engineering.

What are Fiber Optics?

Fiber optics (optical fibers) are long, thin strands of very pure glass about the diameter of a human hair.

They are arranged in bundles called optical cables and used to transmit light signals over long distances.

History:1880: Alexander G. Bell

transmit sound waves over beam of light

1930: TV image through uncoated fiber cables Few years later image through a single glass fiber

1951: Flexible fiberscope: Medical applications

1956: The term “fiber optics” used for the first time

1960: Laser invented

1967: New Communications medium: cladded fiber

1970s & 1980s : High quality sources and detectors

1990: Deployment of SONET systems

Construction:

Optical Fiber consists of 3 regions

1.Core – thin glass center of the fiber where light travels.

2.Cladding – outer optical material surrounding the core

3.Buffer Coating – plastic coating that protects the fiber.

Principle:

The principle behind the transmission of the light waves in an Optical Fiber is “Total Internal Reflection”

The angle of refraction at the interface between two media is governed by Snell’s law:

2211 sinsin θnθn

Angle of incidence < critical angle

Angle of incidence = critical angle Angle of incidence > critical angle

Refraction, Critical angle , Total internal reflection

Working:When light traveling in a dense medium hits a boundary at a steep angle (larger than the "critical angle “for the boundary), the light will be completely reflected. This phenomenon is called total internal reflection.

Total internal reflection occurs when light enters fromhigher refractive index to lower refractive index material, i. e from glass to air total internal reflection is possible but it is not possible in air to glass.

In Figure we see that where the angle 01 is greater than the critical value the ray is refracted into the cladding and will ultimately be lost outside the fiber. This is loss.

In Figure we see that for rays where angle01 is less than a Critical value then the ray will propagate along the fiber and will be “bound” within the fiber.

n2 cladding

n2 claddingn1 core

AcceptanceCone

-If the angle too large light will be lost in cladding- If the angle is small enough the light reflects into core and propagates

qC

Acceptance Cone

n2 cladding

n2 claddingn1 core

AcceptanceCone

Acceptance angle, qc, is the maximum angle in whichexternal light rays may strike the air/Fiber interfaceand still propagate down the Fiber with <10 dB loss.Note: n1 belongs to core and n2 refers to cladding)

22

21

1sin nnC

qC

Acceptance Angle

Transmission of signal:The light in a fiber-optic

cable travels through the core by constantly bouncing from the cladding and the principle called total internal reflection.

Hence the cladding does not absorb any light from the core.

Types of Optical Fibers:

Material used

Mode of transmission

Refractive index profile

GlassFiber

PlasticFiber

Singlemode

Multimode

StepIndex

GradedIndex

Classification based on “Material Used”

Classification based on “Modes of Transmission”

Classification based on “Refractive Index profile”

Application: Fiber Optic Communication

Process of Fiber Optic Communication

Advantages:

Less signal degradationLess ExpensiveLite weightDigital SignalsNon-FlammableHigher carrying CapacityThinnerLow PowerUse Light Signals

Disadvantages

Higher initial cost in installationInterfacing costStrength

Lower tensile strengthRemote electric powerMore expensive to repair/maintain

Tools: Specialized and sophisticated