Fiber optics101

Fiber OpticsECE 422L

2013

• Consultation Time: 2:30 – 4:30 PM

• Main Book:

• Fiber Optics Communications Technology

– by Djafar K. Mynbaev

• OPTICAL FIBER COMMUNICATION

– SUDHEESH

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UM Core Values

Excellence

Honesty and Integrity

Teamwork

Innovation

History

• Willebrord Snell

– a Dutch mathematician who in 1621 wrote the formula

for the principle of refraction

• Daniel Colladon and Jaques Babinet

– First demonstrated in the 1840s, The light-guiding

principle behind optical fibers

• John Tyndall (Irish inventor)

– offering public displays using water-fountains .

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History

• Alexander Graham Bell

– In 1880, demonstrated his photophone, one of the first

true attempts to carry complex signals with light. It was

also the first device to transmit signals wirelessly.

• William Wheeler

– in 1880, the same year that Bell’s photophone made its

debut, used pipes with a reflective coating inside that

guided light from a central arc light throughout a house.

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History

• Brian O’Brien,

– President of the Optical Society of America

– In 1951 suggested to use a surrounding, or

“cladding,” the fiber with a layer of material

with a lower refractive index.

• Narinder Kapany coined the term fiber

optics

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History

• In 1966 Charles K. Kao and George

Hockham proposed optical fibers at STC

Laboratories (STL), Harlow, when they

showed that the losses of 1000 db/km in

existing glass (compared to 5-10 db/km in

coaxial cable) was due to contaminants,

which could potentially be removed.

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History

• AT&T and GTE

– The first full-scale commercial application of

fiber optic communication systems occurred in

1977

– Use fiber optic telephone systems for

commercial customers.

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Fiber Optics

• Is a glass or plastic fiber designed to guide light

along its length by confining as much light as

possible in a propagating form.

• Are widely used in fiber-optic communication,

which permits transmission over longer distances

and at higher data rates than other forms of wired

and wireless communications.

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Principles of Fiber Optic Transmission

• The Fiber Optic Link

components

– Transmitter

– Receiver

– The optical fiber

– The connectors

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• Transmitter

– converts an electrical signal into light energy to

be carried through the fiber optic link.

– The signal could be generated by a computer, a

voice over a telephone, or data from an

industrial sensor.

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The Fiber Optic link

• Receiver

– Is an electronic device that collects light energy

and converts it into electrical energy, which can

then be converted into its original form.

– The receiver typically consists of a photo

detector to convert the received light into

electricity, and circuitry to amplify and process

the signal.

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• Optical Fibers

– Carry light energy from the transmitter to the

receiver. An optical fiber may be made of glass

or plastic, depending on the requirements of the

job that it will perform.

– The advantage: can carry light around corners

and over great distances.

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• Connectors

– Attached to the optical fiber

and allows it to be mated to

the transmitter or receiver to

provide solid contact.

– Must align the fiber end

precisely with the light

source or receiver to prevent

signal loss.

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Basic Principles of Light

• All light is a form of electromagnetic

energy.

• Electromagnetic energy is emitted by any

object that has a temperature above absolute

zero , which means that the atoms in the

object are in motion.

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• The energy takes two forms:

– an electrical field and a magnetic field, formed

at right angles to each other and at right angles

to their path of travel,

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• Light travels at lower velocities through

various materials or media such as the

earth’s atmosphere, glass, plastic, and

water.

• A medium’s optical density, which is

different from its physical density,

determines how quickly light passes

through it.

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Refraction

• the bending of light as it

passes from one material

into another.

• occurs when light waves

change speed as they cross

the boundary between two

materials with different

optical densities.

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• Light slows down

at a denser medium

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Refraction

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Refraction Index

Refraction of Light

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Model used to calculate Refraction

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• Snell’s law

• n1sinθ1 = n2sinθ2

Critical Angle

• The incident angle required to produce

a refracted angle of 90°.

• As the incident ray moves from normal

toward the critical angle, less and less

of the incident ray’s energy is carried

into the refracted ray.

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Critical Angle

• Incidence angle < Critical angle

n1n2

𝜃1

𝜃2

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Critical Angle

• Incidence angle =

Critical angle

• At the critical angle,

all of the incident

ray’s energy is

refracted along the

interface.

n1n2

𝜃1

𝜃2 = 90𝑜

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Critical Angle

• Incidence angle >

Critical angle

• As the incident

angle exceeds

90°, the light is

reflected

n1n2

𝜃1 𝜃2

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Solving for Critical Angle

θc = arcsin (n2 ÷ n1)

• So if we want to know the critical angle of

an optical fiber having a core RI of n1 = 1.51

and a cladding RI of n2 = 1.46:

θc = arcsin(1.46 ÷ 1.51) = 75.211°

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Total Internal Reflection

• Occurs when

Incidence angle >

critical angle

• All light reflects back

toward the incident

medium

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Total Internal Reflection

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Sample Problem

• Calculate the critical angle of an optical

fiber with a core RI of 1.48 and a

cladding RI of 1.46.

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Fresnel Reflections

• Reflected at an angle equal to the angle of

incidence.

• The greater the difference in RI between the

two materials, the more light will be

reflected.

• You experience Fresnel reflection whenever

you look through a window and see a faint

reflection of yourself in the glass.

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• Augustin Fresnel determined how to

calculate the amount of light lost through

Fresnel reflection

• equation: ρ = ((n1 – n2) ÷ (n1 + n2))2

– where ρ is the amount of light reflected and n is

the RI of the medium.

• To calculate the loss in decibels

– dB = 10Log10 (1 – ρ)

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Fresnel Reflections

Sample

• Calculate the dB loss due to Fresnel

reflection of a light from the air entering

a fiber core with an RI of 1.48.

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Reference

• Fiber Optics Communications Technology

– by Djafar K. Mynbaev

• OPTICAL FIBER COMMUNICATION

– SUDHEESH

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Fiber optics101

Education

Transcript of Fiber optics101