FIBRE OPTICS

Mahabahu3/28/2015

1

Represented byMohammed Ebada Ahmed L-kholy

Contents :

• Construction of optical fiber

• Principle of operation

• Total internal reflection

• Types of Optical Fibers

• Medical applications of optical fiber

• Military applications of optical fiber

• Fiber Optic Sensors

Construction of optical fiber

Core-thin glass center of fiber

where light travels.

Cladding-outer optical material

surrounding the core.

Buffer coating-plastic coating

that protects the fiber.

Principle of operationFiber-optic transmission of light depends on preventing light

from escaping from the fiber.

When a beam of light encounters a boundary between two

transparent substances, some of the light is normally

reflected, while the rest passes into the new substance.

A principle called total internal reflection allows optical fibers

to retain the light they carry.

When light passes from a dense substance into a less dense

substance, there is an angle, called the critical angle, beyond

which 100 percent of the light is reflected from the surface

between substances.

Total internal reflection• At some angle, known as the critical angle θc, light traveling from a higher refractive

index medium to a lower refractive index medium will be refracted at 90° i.e. refracted along the interface.

• If the light hits the interface at any angle larger than this critical angle, it will not pass through to the second medium at all. Instead, all of it will be reflected back into the first medium, a process known as total internal reflection

Incident angle =

Types of Optical Fibers Single Mode Fibre

Multi mode optical fiber :

-Multimode Step Index Fibers- Multimode Graded Index Fibres

Single mode optical fiber

• This mode of optical fiber are used to transmit one

signal per fiber (used in telephone and cable TV).

• They have small cores(9 microns in diameter) and

transmit infra-red light from laser.

Multimode Step Index Fibers

• the index of refraction is a constant value

• The core is made from pure glass have a constant index of

refraction (n1)

• The cladding also have a constant index of refraction (n2)

n1>n2

Multimode Graded Index Fibres

The index of refraction change gradually at the area of core .

It gradually change from the center of core (n=n1 – Maximum value - )

to the seprative line between core and cladding (n=n2 – Minimum

value )

This gradually change take different shapes (triangular , parabolic )

Types Of Optical Fiber

Single-mode step-index Fiber

Multimode step-index Fiber

Multimode graded-index Fiber

n1 core

n2 cladding

no air

n2 cladding

n1 core

Variable

n

no air

Light

ray

Index profile

They sense by detecting the modulation of one or more of the

properties of light that is guided inside the fiber—intensity,

wavelength, or polarization, for instance

Physical sensors measure a variety of physiological

parameters, like body temperature, blood pressure, and

muscle displacement.

Medical applications of optical fiber :

Optical fiber sees growth as medical sensors :

Chemical sensors rely on fluorescence, spectroscopic, and

indicator techniques to identify and measure the presence of

particular chemical compounds and metabolic variables (such

as pH, blood oxygen, or glucose level). They detect specific

chemical species for diagnostic purposes, as well as monitor

the body's chemical reactions and activity.

Sensors intended for implanting or indwelling applications must be very small such

as this micro-miniature fiber-optic pressure sensor shown on a fingertip. (Courtesy of

Samba Sensors AB)

A fiber-optic intra-aortic force sensing catheter probe enables real-time monitoring of the force exerted against the heart wall by the catheter. (Courtesy of EndoSense )

The FBGs detect the force exerted against the heart wall by the stress induced on them (see Fig. 3). Force control is essential for delivering appropriate laser ablation pulses needed to produce lesions that are induced in the heart walls to reduce abnormal electric activity

Military

OCC is the premier manufacturer of military ground tactical fiber optic cable

and connectivity solutions for the U.S. military

A fully qualified ground tactical fiber optic communications

cable for military applications :

• Announcing MIL-PRF-85045/8A certified fiber optic cables. Field Proven... Now Certified. Optical Cable Corporation has always manufactured the most rugged and robust fiber optic cables for the military ground tactical market-field proven cables relied on by defense agencies around the world

• This certification was granted after subjecting these fiber optic cable products to an exhaustive series of optical, mechanical, and environmental tests to ensure full compliance to the demanding requirements of the United States military.

Coupled with deployable systems built for easy

implementation and retrieval, OCC’s military products

are designed for the needs of the soldier – rugged and

reliable – time and time again.

Why Use Fiber Optic Cable in a tactical

environment?

The 5 primary advantages of fiber optic cable over conventional coax

cable:

Repeaterless Communications

Fiber Optic – Repeaters every 16 kms (or more)

Coax – Repeaters every 500 meters

Weight

Coax cable weighs approx. 5 times more than equivalent lengths of fiber

optic cable

16 kilometers of coax cable weighs approx. 2,800 kgs, 16 kilometers of

fiber optic cable weigh approx. 550 kgs

• Higher Bandwidth • Optimized for applications requiring voice, data, and video signals

• Security • All dielectric. No signature

• Not affected by EMR

• Very difficult to tap. Reduces need for encryption

• Rugged • More rugged than coax

• No memory

Fiber Optic Sensors

Fiber optic Bragg Grating sensor principle:

The basic principle of a fiber Bragg grating (FBG) based sensor system lies in the

monitoring of the wavelength shift of the returned Bragg- signal, as a function the measured

(e.g strain, temperature and force). The Bragg wavelength is related to the refractive index

of the material and the grating pitch. Sensor system involving such grating usually work by

injecting light from a spectrally broadband source into the fiber, with the result that the

grating reflects a narrow spectral component at the Bragg wavelength, or in transmission

this component is missing from the observed spectrum.

Civil structure applications:

• Bridges

• Dams

• Tunnels and Roads

Oil & Gas:Pipelines are part of the backbone for modern community’s lifestyle and are absolutely

indispensable for transportation of water, gas, oil and all kinds of products.

Faults in these systems do not only result in service outages and financial losses but bear the

potential of spillages causing environmental pollution are even disasters accident.

Due to this, governments, engineering companies and industry associations have developed

design, operation and maintenances standards for pipelines based on which the number of leaks

could be reduced drastically since the 60’s and early 70’s of the last century.

As a result pipelines today are highly reliable and safe means of transportation.

For decades, electrical sensors have been used down hole to measure pressure, temperature, and

flow. Sensors are used to maximize production while minimizing risk to humans, the

environment and the production equipment. Fiber optic sensors are now in use where

traditional electrical sensors perform poorly or not at all. fiber optic sensors typically last longer

in these harsh environments, provide more reliable data, offer an attractive small size, and

perform in situations where actual sensor readings must be many tens of kilometers away from

the well head. Fiber Bragg Grating (FBG) optical sensors are particularly attractive as pressure

sensors and in long arrays with many temperature sensing points.

Other applications related to oil and gas where FBG sensors are ideal include monitoring

pipelines, off-shore platforms, storage facilities, tankers, and refineries. Passive fibers with long

range capability provide explosion proof monitoring of these critical assets.