CTS Session 01 Basic

8/3/2019 CTS Session 01 Basic

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Fundamental Law of Optics



Session 01 References

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Chapter 1, 2, 3



• Light normally goes in straight lines but lenses andmirrors can deflect it.

• It was proven that (Wheeler) that light can go aroundcorners.

Light Propagation

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•o a n erna re ec ons can gu e g a ong a g assrod.

• An optical fiber guides light in a manner similar to avery thin glass rod.

• Optical fiber can guide it around corners.



Light Propagation

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Characteristics of Fiber

• Optical Fiber evolved from devices developed to guidelight which normally go in straight lines.

• In some cases or applications, lights must go aroundcorners.

• Light phenomenon called total internal reflections can

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con ne g ns e ransparen ma er a an gu e a ongthe material.• A very thin glass rod is called an optical fiber can guide

light.

• Total reflection occurs when light travelling in onemedium tries to enter a medium with lower refractiveindex.



• Coating fiber with certain material resulted in a

cladded fiber.• Cladding is protecting the core fiber with

transparent material of lower refractive index.• Clad fibers were the ke develo ment in makin


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fiber optic suitable for practical application.• Invention of laser stimulated interest in optical

communications.• Optical fibers have very high bandwidth.• Glass fibers are inherently strong allowing their use

in outdoor cables.




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• Fiber optics has revolutionized telecommunications

by supplying tremendous bandwidth whichpreviously was in short supply.

• Fiber optics technology is still developing andcontinue to dominate the telecommunication


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industry.• The telecommunication network distributes and

transmits information.• Communication system consists of pipes

(transmission system) that transmit signal andswitches that directs them to their destination.



• Light is one type of electromagnetic radiation. It is apart of the EM spectrum with a distinct range of


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wave eng , requenc es an p o on energ es.• Optical wavelengths include near ultraviolet, visible,

and near infrared.• Light can be viewed.



Basic of Optics

• Duality• Wave Length

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•ave ase n er erence• Refractive

• Total internal reflection



• Light can be considered as Electromagnetic waves orparticles called photons (duality concept).

• A photon is a quantum of Electromagnetic energy.• A light wave consists of electric and magnetic fields.• A single photon is a short packet of waves.• The li ht carried in fiber o tic communications

Basic of Optics

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system can be viewed as either a wave or a particle.• Light waves add or subtract amplitude depending on

their relative phase.• Refraction occurs when light changes speed as it

goes between two materials; the path of the lightbends.



Basic of Optics

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• Refractive index is the speed of light in vacuumdivided the speed of light in a material.

η = (c vacuum /cmaterial)

• The angle of incidence (I) at the surface and the angleof refraction R of the transmitted li ht determine the

Basic of Optics

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bending.• Snell low describes the bending:

ηi sin(I) = ηr sin(R)

• Total reflection occurs when light in a high indexmaterial hits a boundary of a material of lowerrefractive index at a glancing angle.



Basic of Optics

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Light Guiding

• Cladding• Im urities

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• Core cladding• Confinement angle



• Key elements of optical fiber are core and cladding.

• Core is the inner part of the fiber and claddingsurrounds it.

• Light is guided in the core of an optical fiber by total

Light Guiding

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.

• The angle over which a fiber accepts light depends onthe refactive indexes of the core and cladding.

• The acceptance angle is the angle over which lightentering the fiber will be guided along the core.

NA = √√√√(ηc2 – ηcl

2)



Light Guiding

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Light Guiding

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Light Guiding

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Core9 µm



• An optical fiber will pick up some light from any lightsource.

• Coupling light efficiently into the fiber requires

focusing and aligning onto the core within theacceptance angle of the fiber.

• Light source size and alignment are critical in

Light Collection

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co ec ng g n a er core.• For communication system it is more efficient to use a

light source that is close to the fiber core size such assemiconductor laser or LED (for larger core).

•Transferring light between fiber requires carefulalignment; hence, joining the ends of optical fibersrequires careful alignment and tight tolerances.

• Transfer losses must be considered.



Light Collection

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Fiber for Transmission

• Degradation

• Attenuation• Dispersion• Crosstalk

•

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• Bandwidth• Mechanical Strength

• Cross section• Transmission Capacity



• Attenuation, dispersion, and cross talk can degradesignals transmitted by fibers.

• Absor tion scatterin and li ht leaka e are the

Fiber Attenuation

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component of fiber attenuation.• Atoms within the fiber scatter light out of the core.• Attenuation of a fiber is the product of the length times

the characteristic loss in decibels per kilometer.



• Optical fibers are unique in transmitting high speedsignals with low attenuation,whereas the attenuationof copper wires increases with signal frequency.

• Dispersion limits fiber transmission bandwidth• Cross talk is the leakage of signals between nominally

independend channels.

Bandwidth and Dispersion

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• on near n erac ons e ween op ca c anne s n esame fiber can cause cross talk.

• Electronics play important roles in fiber opticequipment

• Transmitter wavelength depends on the applicatonrequirements.• A receiver converts an optical signal into electronic

form.



Parameters

Major fiber properties Attenuation as a function of wavelength. Collection of light into fiber (coupling). Transmission modes.

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Transmission capacity and pulse spreading. Operating Wavelength. Tolerances for splicing, connecting, temperature,

abuse.

Cost.

Documents

CTS Session 01 Basic