chapter 24 fiber optics and lasers © goodheart-willcox co., inc.permission granted to reproduce for...

Chapter 24

Fiber Optics and Lasers

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Objectives

• State the advantages and disadvantages of fiber-optic systems.

• Explain light theory.

• Explain causes of light energy losses in fiber-optic systems.


Objectives

• Explain the transmission of light as data.

• Explain how light is received and changed into data.

• Explain how lasers operate.

• List safety precautions to be taken when working with lasers.


Fiber Optics

• Nature of light

• Cable construction

• Attenuation

• Splices and connectors

• Transmitters

• Receivers

• Troubleshooting


Why Fiber Optics?

• Small and lightweight

• Resist corrosion and water

• Provide data security

• Immune to electromagnetic interference

• Safety from fire and explosion

• Wide bandwidth


Weight and Size

• 1/10th the weight of traditional copper wiring systems

• Aircraft and ships can carry more cargo with fiber-optic cables

• Smaller diameter than conventional systems


Corrosion and Water Resistance

• Glass and plastic are resistant to most corrosives

• Water has no effect on the light conduction capabilities

• Fiber-optic cables that run under oceans are expected to last


Security

• Fiber optics cannot be tapped into without being detected

• Cut made into the cables affects the light signal

• Far more secure than copper cable


Immunity to Electromagnetic Energy

• Fiber optics conduct light instead of electricity

• Do not need to be shielded to prevent electromagnetic interference

• Can withstand electromagnetic field of a nuclear explosion


Safety

• Fiber optics can be installed anywhere without fear of electrical sparks

• Light can be transmitted through fiber optics in place of other lamps

• Safer and cheaper than conventional electrical lamps


Bandwidth

• Light transmits at a higher frequency than electrical signals

• More signals can be transmitted at once

• Fiber optics can handle higher frequencies without losing conduction capabilities, like copper cables


The Nature of Light

• Theories of light– Light as a wave– Light as a particle

• Photons


Cable Construction

• Cladding• Buffers• Plenum areas

(Siecor Corporation, Hickory, NC)


Attenuation

• Scattering

• Dispersion

• Extrinsic losses


Scattering

• Always some impure material in the core– Causes light to reflect

• Longer cables have more signal loss

• Glass cores are better than plastic


Dispersion

• Longer fiber-optic cables have more dispersion• Receivers equipped with a digital gate can

reshape the signal


Extrinsic Loss

• Fiber-optic cables have minimum radius of bend

• Attenuation results when radius is exceeded

• Splices, couplings, and connectors are main reasons for transition signal losses


Splices and Connectors

• Glass cores must be cleaved

• Extremely sharp cutters must be used on plastic cores

• Splicing is used to transfer light directly to next cable or connector

• Fusion splices


Splices and Connectors (Cont.)

• Fresnel reflection loss – Minimized by use of sealing material with a

refraction index close to index of core material

• Temporary splices might be needed

• Pigtail splices


Fiber-Optic Transmitters

• LEDs or laser diodes• Signal can be AM

amplitude modulated or pulse modulated


Fiber-Optic Receivers

• Use photodiodes to convert light energy back to electrical energy– Avalanche photodiodes– PIN diodes– Phototransistors and photodarlingtons


Troubleshooting Fiber-Optic Systems

• Two components needed– Light transmitter– Light receiver

• Optical time domain reflectors (OTDRs)


Review

Why are fiber-optic cables resistant to corrosion?

The glass or plastic cores are resistant to corrosives


Review

What will happen to a fiber-optic cable if a cut is made into it?

The transmission of the signal is completely disrupted


Review

Why is the bandwidth of fiber-optic cables so much better than copper cables?

Because light is transmitted at a much higher frequency than electrical signals


Review

What are the two theories of light based on?

Light as a wave and light as a particle


Review

What is a photon?

A quantum of radiant energy


Review

What part of the fiber-optic cable keeps the light wave contained to the glass or plastic?

The cladding


Review

What are the units of attenuation?

Decibels (dB) or decibels per kilometer (dB/km)


Review

What is the loss of signal strength due to impurities in the core material called?

Scattering


Review

What causes extrinsic losses?

Physical factors outside the normal core


Review

What causes a fresnel reflection loss?

Differences in the refraction of two different materials joined together


Review

What are fiber-optic transmitters typically made of?

LEDs or laser diodes


Review

What are the two basic components needed to troubleshoot fiber-optic systems?

A light transmitter and a light receiver


Lasers

• Coherent light– In phase

• Incoherent light– Not in phase


Laser Construction

• Light source– Strobe lamp– Ruby tube

• Reflective surface• Emission of radiation• Lasing


Types of Lasers

• Ruby lasers– Light is pulsed, instead of continuous– Might use a liquid-nitrogen cooling system– Used for welding and cutting hard materials

• Gas lasers– Gas ionizes and produces light– Used in medical field– Used for cutting and drilling metal


Laser Applications

• Construction

• Medicine

• Supermarket checkout counters

• CD players


Lasers in Construction

• Used for measuring distances and alignment

• Used as surveying instruments

• Used as levels


Lasers in Medicine

• Used to perform many types of surgery

• Low level light helps vision

• Can view the inside of a patient

• Can be directed to the surgical area

• Used for angioplasty


Lasers at Supermarket Checkout Counters

• Nd:YAG lasers• Laser system used to

identify product codes• Light shines on a

rotating mirrored surface

• Light flashes through glass top

• Black bars in bar code absorb light


Lasers in CD Players

• Beam directed through optical lens

• Photoreceiver receives beam from CD and converts it to electrical impulses

• Tiny pits are recorded sound pattern

• Digital impulses are converted to analog signals


Other Uses of Lasers

• Private industry

• Government

• Education

• Military


Damage from Lasers

• Can be minimal and cause only temporary irritation

• Can do irreversible damage to the eye

• The light from the laser does not have to be in the visible spectrum to do damage

• Eye protection should be worn at all times


Laser Classifications

• Classified by– Maximum possible output during normal

operation– Beam width

• Class I• Class II• Class III• Class IV


Night Vision Devices

• Infrared light sources enhance available light

• Photocathodes

• Microchannel plates (MCPs)

• CCDs

• Intensifier tubes


Review

What does the acronym laser represent?

Light amplification by stimulated emission of radiation


Review

What is light consisting of all the same wavelength called?

Coherent light


Review

What is used to produce a ruby laser?

A manufactured ruby consisting of an aluminum oxide compound and chromium


Review

What three kinds of gases might be used in a gas laser?

Helium-neon, carbon dioxide (CO2), or argon


For Discussion

• Discuss what other mediums could be used to transmit data.

• List causes for the greatest signal loss in a typical fiber-optic installation.

• How might laser light transmit a voice?

chapter 24 fiber optics and lasers © goodheart-willcox co., inc.permission granted to reproduce for...

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