Chapter 8: FIBER OPTIC COMMUNICATIONS

Chromatic Dispersion

It occurs to non-coherent light sources where light contains combination of different wavelengths and can only occur in single mode.

Attenuation

It results in a reduction in the power of the light wave as it travels down the cable.

Planck's Law

It states that when visible light or high frequency electromagnetic radiation illuminates a metallic surface, electrons are emitted (Photoelectric effect).

Buffer Jacket

It surrounds the protective coating and provides the cable additional protection against abrasion and shock.

Solid Laser

It uses solid cylindrical crystal such as Ruby for an active medium.

Splicing

permanently attaching the end of one optical fiber cable to another.

Optical Fiber

It is the medium, channel or path where light signals travel.

Fiber Optics

It is the science, study, or technology dealing with light transmission.

Polyurethane Outer Jacket

It is where the entire cable assembly is contained.

Radiometry

It measures light throughout the entire electromagnetic spectrum.

Critical Angle

It is the minimum angle of incidence at which light ray may strike the interface of two media and result in an angle or refraction of 90 degrees.

Heinrich Lamm

A German scientist successfully transmitted images through a single glass fiber.

Photometry

It is the science of measuring only light waves that are visible to the human eye.

Light sensitivity

It is the minimum optical power a light detector can receive and still produce a usable electrical output signal.

Spectral Response

It is the range of wavelength values that can be used for a given photodiode.

Infrared absorption

It is the result of photons of light that are absorbed by the atoms of the glass core molecules.

Dark Current

It is the leakage current that flows through a photodiode with no light input.

Cladding

It is the material of lower refractive index that surrounds the core.

Acceptance Angle

It is the maximum angle between the axis of an optical fiber and a ray of light entering the fiber.

Class II

Class of laser that applies to visible light lasers.

Class III

Class of laser that is considered safe if handled carefully, with restricted beam viewing.

Class IV

Class of laser that is highest and most dangerous class of laser, even reflections are hazardous.

Class I

Class of laser that is safe under all conditions of normal use.

Responsivity

It is the measure of conversion efficiency of a photodetector. It is the ratio of the output current of photodiode to the input optical power.

Strength members

Encapsulates the buffer jacket which increases the tensile strength of the overall cable assembly.

Theodore Maiman

He built the first optical maser in late 50s.

Narinder Singh Kapany

He coined the term fiber optics in 1956. He was from England who was regarded as the father of fiber optics.

Absorption Loss

Impurities in the fiber absorb the light and convert it to heat.

Alexander Graham Bell

In 1880 he experimented the transmission of sound waves over a beam of light using a device known as photophone.

Abraham van Heel, Harold Hopkins, Narinder Singh Kapany

In 1950s they experimented with light transmission through bundles of fibers. Their study led to the development of flexible fiberscope.

Modal Dispersion

Is caused by the difference in the propagation times of light ray that take different path down the fiber, and can only occur in multimode fibers.

Numerical Apperture

Is described as the light gathering ability of an optical fiber. A figure of merit commonly used to measure the magnitude of the acceptance angle.

Acceptance Cone

Is produced after rotating the acceptance angle around the fiber axis.

Avalance Photodiode (APD)

It has a PIPN structure, more sensitive than PIN diode, and require less amplification.

Gas Laser

It has mixture or helium and neon enclosed in a glass tube.

Liquid Laser

It has organic dyes enclosed in a glass tube for an active medium.

LED (light-emitting diode)

It is a PN junction diode that is usually made up of aluminum gallium arsenide or gallium arsenide phosphide.

Loose Tube Configuration

It is a cable configuration in which each fiber is contained in a protective tube; inside the tube, a polyurethane compound encapsulate the fiber which prevents the intrusion of water.

Constrained Fiber Configuration

It is a cable configuration wherein the fiber is surrounded by a primary and secondary buffer comprised of Kevlar yarn.

Multiple Strands Configuration

It is a cable configuration which includes a steel central member and a layer of Mylar tape wrap.

PIN Diode

It is a depletion layer photodiode and is probably the most common device used as a light detector in fiber optic communications system.

Microbend

It is a miniature bend or geometric imperfection along the axis of the fiber which represents the discontinuity in the fiber.

Protective Coating

It is a special lacquer, silicone or acrylate coating that is generally applied to the outside of the cladding.

Edge-Emitting LED

It is a variation of heterojunction LED. Its emitting surface is a stripe.

Burrus Etched-Well Surface-Emitting LED

It is a variation of homojunction LED. It is surface-emitting LED having an etched-well that helps in concentrating the emitted light into a very small area.

Optical Power

It is also known as radiant flux. It measures the rate at which electromagnetic waves transfer light energy.

Ion Resonance Absorption

It is caused by OH ions in the material.

Constant-Radius Bend

It is caused by excessive pressure and tension and generally occur when fibers are bent during handling or installation.

Ultraviolet absorption

It is caused by valence electrons in the silica material from which the fibers are manufactured.

Light Intensity

It is described in terms of luminous flux density in lumens per unit area.

Material Scattering Loss

It is due to the imperfections in the fiber that are formed during manufacturing process. When light strike these impurities they are diffracted, this is known as Rayleigh scattering loss.

Semiconductor Laser

It is made from semiconductor PN junctions and are commonly ILD.

PCS (Plastic-Clad-Silica)

It is made of a glass core and a plastic cladding.

SCS (Silica-Clad-Silica)

It is made up of a glass core and glass cladding.

PSP (Plastic-Clad-Plastic)

It is made up of a plastic core and a plastic cladding.

Bending Loss

It is predominantly caused by small bends and kinks in the fiber.

ILD (Injection Laser Diode)

It is similar to LED except that it operates in a higher threshold.

Ultraviolet

It is the band of frequencies that are too high to be seen by the human eye with wavelengths ranging between 10 nm and 390 nm.

Infrared

It is the band of high frequencies that is too low to be seen by the human eyes with wavelengths ranging between 770 nm and 10^6 nm.

Visible

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

Index Profile

It is the graphical representation of the value of the refractive index across the fiber.

Core

It is the internal material of the fiber, specifically the central part of the fiber where the light propagates.

Window

Refers to the range of wavelength that can be satisfactorily used in an optical fiber.

Step Index

The core is surrounded by an outside cladding with uniform refractive index less than that of the core.

Graded Index

The index of refraction of the core is not constant, instead it varies smoothly and continuously over the diameter of the core.

Multimode

The light travels in two or more paths, and its core has larger diameter.

Single mode

The light travels only in one path, and its core has smaller diameter.

Prismatic Reflection

The spectral separation of white light.

Heterojunction LEDs

They are edge emitters. It consists of a PN junction in which the two sides of the junction are made of different materials.

Kapron, Keck, & Maurer

They are from Corning Glass Works in Corning, New York who developed an optical fiber with losses less than 2 dB/km.

Homojunction LEDs

They are surface emitters. It consists of a PN junction made from two different mixtures of same type of atoms.

George Bockham and Charles Kuen Kao

They proposed a new communication medium using cladded fiber cables.

John Baird and Clarence Hansell

They were granted patents for scanning and transmitting television images through uncoated fiber cables.

Charles Townes & Arthur Schawlow

They wrote a paper describing how it was possible to use stimulated emission of light waves as well as microwaves.