Fiber Optics Flashcards by Gieselle Esguerra

is essentially a waveguide for light

Optical Fiber

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index of refraction of the cladding is ___ that of the core, causing rays of light leaving the core to be refracted back into the core

Less Than

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LASER meaning:

Light Amplification by Stimulated Emission of Radiation

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Advantages of optical fiber include:

Greater bandwidth than copper
Lower loss
Immunity to crosstalk
No electrical hazard

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Optical fibers work on the principle of

Total Internal Reflection

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is closely related to the critical angle and is often used in the specification for optical fiber and the components that work with it

Numerical Aperture

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is twice that given by the numerical aperture

Angle of Acceptance

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Multimode propagation will cause ____, which results in the spreading of pulses and limits the usable bandwidth

Dispersion

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Types of index profiles:

Step-Index

- Graded-Index

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the index of refraction changes radically between the core and the cladding

Step-Index

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is a compromise multimode fiber, but the index of refraction gradually decreases away from the center of the core

Graded-Index

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increases with the bandwidth of the light source

Dispersion

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Basic types of fiber-optic cables: (2)

loose tube cable

- tight-buffer cable

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all the stress of cable pulling is taken up by the cable’s strength members and the fiber is free to expand and contract with temperature

loose tube cable

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are cheaper and generally easier to use

tight-buffer cable

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Splice & Connector Losses:

Axial or angular misalignment
Air gaps between the fibers
Rough surfaces at the ends of the fibers

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is a permanent connection

Splice

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is a removable connection

Connector

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Coupler Construction (2)

transmissive coupler

- reflective coupler

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Optical emitters operate on the idea that electromagnetic energy can only appear in a discrete amount known as a ___

Quantum

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is form of junction diode that is operated with forward bias

LED

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generate coherent, intense light of a very narrow bandwidth

Laser Diode

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The most common optical detector used with fiber-optic systems is the ___

PIN diode

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PIN diode is operated in ___

Reverse bias mode

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The creation of electron-hole pairs due to the absorption of a photon of incoming light may set off avalanche breakdown, creating up to 100 more pairs

Avalanche Photodiode (APD)

band of light frequencies that is too high to be seen by the human eye with wavelengths ranging between 770nm and 10^6 nm

Infrared

band of light frequencies to which the human eye will respond with wavelengths ranging between 390 nm and 770 nm

Visible

band of light frequencies that are too low to be seen by the human eye with wavelengths ranging between 10 nm and 390 nm

Ultraviolet

The coating helps protect the fiber from moisture, which reduces the possibility of occurrence of a detrimental phenomenon called ___ or static fatigue cause by high humidity

Stress Corrosion

Types of optical fibers commonly used today: (3)

- plastic core and cladding - glass core, plastic cladding (or PCS - plastic-clad-silica) - glass core, glass cladding (or SCS - silica-clad-silica)

Process of decaying from one energy level to another energy level is called ___

Spontaneous decay or spontaneous emission

Is the science of measuring only light waves that are visible to the human eye

Photometry

Measures light throughout the entire electromagnetic spectrum

Radiometry

How a light ray reacts when it meets the interface of two transmissive materials that have different indexes of refraction

Snell's Law

Defined as the minimum angle of incidence at which a light ray may strike the interface of two media and result in an angle of refraction of 90 degrees or greater

Critical Angle

Defined as the maximum angle in which external light rays may strike the air/glass interface and still propagate down the fiber

Acceptance angle or Acceptance cone half-angle

Closely related to acceptance angle and is the figure of merit commonly used to measure the magnitude of the acceptance angle

Numerical Aperture (N.A.)

Simply means path

Mode

has a central core with a uniform refractive index

Step-index Fiber

Has no cladding and the refractive index of the core is nonuniform, it is highest in the center of the core and decreases gradually with distance toward the outer edge

Graded-index Fiber

Type of optical fiber configurations: (3)

- single-mode step index optical fiber - multimode step-index optical fiber - multimode graded-index optical fiber

Predominant losses in optical fiber cables: (6)

- absorption loss - material or Rayleigh scattering loss - chromatic or wavelength dispersion - radiation loss - modal dispersion - coupling loss

The light rays that escape represent loss in light power called __

Rayleigh scattering loss

Occurs as a result of differences in the thermal contraction rates between the core and cladding material

Microbending

Is caused by the differences in the propagation times of light rays that take different paths down a fiber

Modal dispersion OR Pulse spreading

Characteristics of Light Detectors: (4)

- responsivity - dark current - transit time - spectral response - light sensitivity

A measure of the conversion efficiency of a photodetector; Its the ratio of the output current of a photodiode to th input optical power and has the unit of A/W

Responsivity

The leakage current that flows through a photodiode with no light input

dark current

The time it takes a light-induced carrier to travel across the depletion region of a seminconductor

transit time

range of wavelength values that a given photodiode will respond

spectral response

The minimum optical power a light detector can receive and still produce a usable electrical output signal

Light Sensitivity

bandwidth of an analog communications system as a percentage of its carrier frequency

bandwidth utilization ratio

Materials commonly used for the buffer jacket include: (6)

- steel - fiberglass - plastic - flame-retardant polyninyl chloride (FR-PVC) - Kevlar Yarn - Paper

Wavelengths that are refracted the most

Violet

Wavelengths that are refracted the least

Red

indicates what signal frequency can be propagated down through a given distance of fiber cable and is expressed mathematically as the product of distance and bandwidth

Bandwidth length product (BLP) or Bandwidth distance product (BDP)

Losses caused by imperfect physical connections

Coupling Loss

Lateral or axial displacement between two pieces of adjoining fiber cables

Lateral Displacement

Sometimes called END SEPARATION; When splices are made, the fibers should actually touch

Gap Displacement/Misalignment

Loss that if less than 2deg, will be 0.5 dB

Angular Displacement/Misalignment

Loss incurred if the ends of 2 adjoining fibers are not polished and fit together squarely

Imperfect Surface Finish

Type of laser that use a mixture of helium and neon enclosed in a glass tube

Gas Lasers

Type of laser that uses organic dyes enclosed in a glass tube for an active medium

Liquid Lasers

Type of laser that uses a solid, cylindrical crystal such as ruby for the active medium

Solid Laser

Type of laser that ae made from semiconductore p-n junctions and are commonly called ILDs

Semiconductor Laser

Fiber Optics Flashcards

(65 cards)