Fiber Optics Illustrated Dictionary - Part 86 ppsx

Inthe early I990s, AT&T Bell scientists published near-field images that had been generated with a coated optical fiber probe, demonstrating that it was possible to resolve sub-wavelengt

Fiber Optics Illustrated Dictionary

or processes, and quantifies and records the results

in some form that can be further processed or

ana-lyzed Scanners, like digitizers, frequently sample

analog information and convert it to digital, or

con-vert a digital sample to a waveform for transmission

Typically the scanner does not process the

informa-tion; its job is tocapturethe information, and often

it can store that information in a variety of selectable

formats Once the information is captured, it is then

sent "live" to a processing application or stored for

later conversion or further processing Scanners are

used in a multitude of imaging and sensing

applica-tions, including those described in the Scanning

Tech-nologies chart

scanning acoustic microscopeSAM A scanning

microscope designed to assess the acoustical

prop-erties of materials at micrometer and nanometer

ranges There are different ways to approach this

problem, but in general, a SAM uses focused beams

to scan an object with some kind of detector to gauge

the result In general, SAMs have upper resolution

limits that are partly determined by Rayleigh

scatter-ing

Nearfield acoustic microscopes were developed to

overcome some of the difficulties of imaging within

the diffraction region close to a sample object They

may use electrons directed at the sample through a

chopper, with the result picked up by a scanning

elec-tron detector, or they may use laser light aimed at the

sample and detected and converted to electricity by

photodiodes (scanning probe acoustic microscope)

scanning electron microscopeSEM A type of

mi-croscope designed to magnify at levels that are

physi-cally beyond the scope of traditional optical

miscroscopes SEMs are precision instruments that

use a beam of electrons rather than a beam of light to

image a tiny section ofan object SEMS evolved from

transmission electron microscopes (TEMs),

becom-ing high-end experimental instruments in the 1940s

and commercially-practical scientific instruments in

the mid-1960s

SEMS work by accelerating electrons toward the

sample through a system of condensing lenses and

apertures such that a monochromatic beam is aimed

at the surface of the sample through a magnetic lens

The beam is moved so that it scans in a pattern that

covers the imaging area The interactions between the

electron beam and the sample are assessed and

im-aged with sensitive electron energy detectors

Mag-nifications are significantly higher than optical

scopes, up to about 15,000x

The interaction of the electron beam and the sample

results in energy changes that can be detected and are

generally interpreted so that higher energy levels

show up as brighter image regions on the monitor,

photograph, or other display medium

scanning near-field optical microscopySNOM A

more recent development in microscopy that enables

spatial resolutions below the diffraction limit oflight

characteristic offar-field optical microscopy Using

a SNOM, the investigated sample is held at a distance

smaller than the wavelength from the radiant source

Inthe early I990s, AT&T Bell scientists published near-field images that had been generated with a coated optical fiber probe, demonstrating that it was possible to resolve sub-wavelengths through small-aperture fiber optics

SNOM capability opens up new areas of research in quantum-level nanostructures without spacial aver-aging

Subsequent variations in the concept at UCSD, us-ing silver particle suspensions illuminated by a fo-cused laser instead of a fiber probe, have broadened its applications to include the study of magnetic thin film systems suitable for data storage See scanning probe microscope

SNOM Fiber Probe Simplified Example

e

A SNOMjiber probe is commonly madefrom a slen-der single-mode opticaljiber with an aluminum coat-ing The jiber may be Jabricated by jiber pulling or chemical etching methods.

Commercially, jiber probes are described in terms

oj diameter (e.g., 120 J I.m - d), the angle oJthejiber tip (e.g., 12° - b) and its length (c), as well as the optical power Jor input/output, the wavelength Jor which the probe is optimized (e.g., 480-550 11m), and the optical efficiencyJor the specijied numerical ap-erture (the uncoated tip - a) It may also be possible Jor the customer to specifY the length oj the covering that serves as a protective coating and handle (e) See

probe, photoplasticfora variation on the basic probe.

scanning probe microscopeSPM Amicroscope de-signed to facilitate the viewing ofsurface objects and 3D biological systems by means that are not readily attainable with conventional scanning near-field tech-niques for probing or manipulating surfaces SPMs are versatile instruments ranging from optical to scan-ning electron magnifications

In the mid-1990s, E Florin described a 3D scanning probe microscope that uses a 2-photon absorption process with tluorophores bound to a probe with the probe trapped by optical "tweezers" in continuous-wave mode In September 2000,V.Kley submitted a patent application for a scanning probe microscope assembly and method for making confocal, spectro-photometric, near-field, and scanning probe measure-ments and images.Inone embodiment ofthis inven-tion, a fiber optic light guide transmits light from the source to the probe.Inthe context ofa Mach-Zehnder interferometer, it is formed by two reference light sources (e.g., two lasers at different wavelengths) and two fiber optic guides See scanning near-field opti-cal microscopy

scanning rate I.The speed, in units per time period,

at which a scanning device captures information Many common technologies are expressed in terms

of inches per second Generally, for moving images,

or fidelity in conveying motion In still images, faster

scan rates may compromise the resolution or fidelity

ofan image 2 In cathode-ray tubes (CRTs), the

scan-ning rate is the speed at which the electron beam

sweeps the screen to refresh a full frame This is

usu-ally about 30 frames per second See cathode-ray

tube, frame, interlace 3 For technologies that use a

beam for scanning (antennas, radar), the rate is more

often expressed as a specified number ofsweeps over

a unit of time

scanning rate, opticalFor optical scanning of

im-ages, such as those used with computer scanners and

facsimile machines, scanning rate is often not as

im-portant as resolution In other words, the fineness of

the scan is described rather than the speed at which

it is scanned, with resolutions of 1200 to 4800 dpi

interpolated common on desktop scanners See scanner

scare-strapscolloq. Telephone line worker safety

belts

scatterv To separate, to distribute widely or

ran-domly, to disperse, to diffuse in various directions

scatter, transmissionTo diffuse or spread out in such

as way as to lose the strength or directionality of a

transmission signal In most communication

trans-missions, this is undesirable See spreading loss 3 To

enhance communications through exploiting

delib-SCC1 Specialized Common Carrier A carrier com-peting with the dominant carrier in niche markets

2 Standards Council of Canada

SCCPSee Signaling Connection Control Part SCESee Service Creation Environment

SCEPSee Service Creation Environment Point Sceptronspectral comparative pattern recognizer.An intelligent pattern-recognition system developed in the early 1960s by Robert D Hawkins of Sperry Gy-roscope The Sceptron used quartz or glass fibers, a photocell, electrical current, and mechanical motion

to recognize a spoken word and optionally print it on

an illuminated display When exposed to audio stimu-lation, the Sceptron "learns" the sound and can then recognize it Other types of signals translated into audio frequencies can also be recognized Sceptron was able to pick out a word from human speech The fiber optic array was the most unique aspect of Sceptron's design, loosely packing about 700 fibers into 1/4 cubic inch When stimulated by mechanical excitation, the fibers, all ofthe same diameter but dif-ferent lengths, would vibrate, each at its own natural frequency A piezoelectric or electromechanical driver was provided to convert electrical signals into mechanical motion A photocell then detected the motion ofthe fibers, registering the movement or lack

Scanning Technologies for a Variety of Devices

scanning antenna Parts of a moving antenna which cause the directional scanning of the antenna

beam

facsimile scanner A component of a facsimile machine which converts a sampled digital image

to a waveform for transmission over phone lines See ITU-T, facsimile, TIFF image processing Acomputer input device which passes a beam over a2Dor3Dobject or

image, and converts it to digital data, usually a2Draster image See digitizer, optical character recognition, TWAIN

scanning radio A radio receiver that scans a range of transmission frequencies automatically,

so the user can locate and listen to conversations occurring at the time of the scan Often used to fmd emergency or cellular phone conversations

remote sensing In satellite remote sensing, a scanner employing an oscillating mirror that

captures images in strips was first proposed in1968by Hughes Aircraft for use in orbiting satellites, and first deployed in1972in the first Earth Resources Technology Satellite This technology revolutionized understanding and recording of Earth's topological and geological features The program became Landsat in1975

robot vision In robotics, a scanner samples visual input and processes the information in a

waythatprovides data useful for tracking, navigating, or object sensing Robot scanner interfaces vary widely, but often are small video cameras, light detection devices, or pattern sampling devices mounted on the robot itself Robot scanners may be simple, to detect and record light or dark areas, or complex, to capture sophisticated patterns, further processed as faces or recognized as objects

scanning software A software program that searches data for new entries of a particular kind,

such as newly uploaded files, email, user logins, etc., or which scans processes such as network load, states,CPUusage, etc

Fiber Optics Illustrated Dictionary

of movement as a dark or light spot Sceptrons were

configured in pairs, one with a reference static mask,

one as a memory mask, balanced together in a bridge

circuit See neural networks, pattern matching

Schadt-Helfrich effect Also called thetwisted

nem-atic effect,this effect was studied and described by

M Schadt andW Helfrich in "Voltage-Dependent

Optical Activity of a Twisted Nematic Liquid

Crys-tal," in 1971 It is a means ofmodulating light through

a layered liquid crystal component

Imagine a layer ofnematic liquid crystals sandwiched

between glass polarizing plates rotated 90° in

rela-tion to one another, with the crystals separated by thin

spacers A polymer or other orientation layer is

in-troduced to more or less fix the alignment of the

liq-uid crystals parallel to the plates to create a gradual

twist down through the axis between the glass plates

Light is applied to one end of the structure, through

the glass The birefringent liquid crystals guide the

linearly polarized incident light through the

compo-nent to the viewing surface on the opposite end The light emerges and the end is lit Ifvoltage is applied

to the component, it disturbs the orientation of the crystals and the polarized light is "canceled" and the viewing surface appears dark Varying the voltage en-ables intermediary effects in the orientation of the crystals, resulting in gray scale modulation See nem-atic liquid display, smectic liquid crystal

Schiifer, F.P Along withF Schmidt, and 1 Volze, Schafer published "Organic dye solution laser," in Applied Physics Letters in fall 1966, an important historic landmark in dye lasers in particular and tun-able laser technology in general In 1968, Schafer was honored for his scientific contributions with the Nernst Haber Bodenstein prize Schafer became a professor at the Max-Planck-Institut in Germany Schafer's interest in lasers never wained Thirty years later he was still publishing numerous articles on laser technologies, including short-pulse lasers

Schawlow, Arthur Leonard (1921- )AnAmerican!

Fiber Optic-Based Radiation Detector

1 radiation stimulates scintillation

reaction (light emission)

_.i.'I!lIIX!lll!ls .L"L.I::;:: ~ 11- :' ': 3 TOF signalS

d

2 light impulse travels from

point of stimulation to both

ends of fiber waveguide

radiation stimulating scintillation reaction

fiber waveguide

light emissions

A radiation detector can be/abricated using opticaljiber as a transmission waveguide/or the light emilledjiom a scintillation reaction A slender, flexible jiber can be run along walls ceilings floors making it a practical alterna-tive to point-based individual detectors As radiation enters a cladded jiber doped with scintillating materials a reaction occurs in which light is emitted The light then plDpagates in both directions along the waveguide from the point(s) at which the reaction occurred Photomultipliers can be used to convert the light signal to an electrical signal and to amplify weak signals The in/ormation aniving at both endso/the waveguide canthus be plDcessed to determine the location ofthe radiation stimulus to yield usejil! information about the location duration and trajec-tory o/radiant influences in the ambient envilDnment See scintillation detector/or/urther in/ormation.

interest in spectroscopy, Schawlow studied at the

University of Toronto and Columbia University At

Columbia he met Charles Townes, with whom

be-came a collaborator in laser research From 1951 to

1961, Schawlow worked at Bell Telephone

Labora-tories on superconductivity and muclear resonance

after which he took a position as a professor at

Stan-ford University, retiring as Professor Emeritus in 1991

Schawlow has won many awards for his research,

including the National Medal of Science and the

Stuart Ballantine Medal In 1981, he was co-awarded

a Nobel Prize for his work in high-resolution

elec-tron spectroscopy that derived from the pioneer work

The Arthur Schawlow Medal of the Laser Institute

ofAmerica is named in his honor See laser history;

Townes, Charles

Scheduled TransferST A media-independent

up-per-layer protocol that was originally developed as

part ofthe HIPPI-6400 network transmission standard

schematicAdiagrammatic representation ofan

elec-trical circuit, floorplan, network, or other

intercon-nected system Electronics drawings have

conven-tions and symbols for various types of components

and connections

Schilling von Cannstedt, Pavel Lvovitch

(ca.178D-1836) A Russian diplomat posted to Germany,

Schilling invented multi-needle and single-needle

telegraph systems and a code to signal characters,

numbers, and stop/finish/continue states He

collabo-rated with S.T von Sommering, who had developed

an even earlier telegraph Schilling's telegraphs have

variously been reported as being demonstrated in

1820, 1832, and in between Given Sommering's

in-ventions around 1809, it is plausible that Schilling's

telegraph may have been demonstrated as early as

1920 See Salva i Campillo; Sommering, S.T

Schmidt, F.Along with F.P Schafer and1.Volze,

Schmidt published "Organic dye solution laser," in

AppliedPhysics Lettersin fall 1966, an important

his-toric landmark in dye lasers in particular and tunable

laser technology in general

Schott Fiber Optics, Inc.SFO A prominent

inter-national vendor of fiber optic lighting and imaging

technologies that evolved from a fiber optic research

project in 1954 (which originally became the fiber

optic division ofAmerican Optical) Through the last

half century, the company has developed glass core

and coating technologies, winding and assembly

pro-cesses, fiber drawing and faceplate fusing techniques

It has also designed and developed medical and

sci-entific instruments using fiber components

Schottky effect In a cathode-ray tube (CRT), a

ran-dom charge variation that occurs in the emission of

electrons in the strong electric field associated with

the electron-emitting cathode As an electric field is

applied there is an electron discharge from the heated

surface that reduces the amount of energy needed to

stimulate electron emission

Schottky diodeA type of efficient rectifying

com-ponent Schottky diodes are incorporated into a

number of electronic devices that require switching

may be configured as clamp diodes Schottkey diodes are found in optical beam control switching arrays and may be used as frequency doublers in RF travel-ing-wave tubes (TWTs) Synchronous rectification may now be done with field-effect transistors (FETs) rather than Schottky diodes

Schultz, Peter C.(1942- ) Schultz was educated at Rutgers University and went to work at Corning as a research scientist with a team that included D Keck and R Maurer.Inthe early 1970s, they developed a practical low-loss embodiment of fiber optics trans-mission lightguides, a technology that had eluded scientists since the early 1960s Schultz is known for having codeveloped an outside vapor deposition pro-cess in 1972 that is still a standard in the industry This led to the development ofgermania-doped fused silica

Schultzjoined SpecTran Corporation as VPofTech-nology in 1984, and later became president of tech-nology at Schultz Galileo ElectroOptics, Inc He be-came president ofHeraeus Amersil in 1988.In2000, along with Keck and Maurer, Schultz was awarded the National Medal of Technology

Schroeder, ManfredR.(1926- ) A German scien-tist and educator, Schroeder was an early researcher

in chaotic dynamics and microwave waveguides who was hired by Bell Laboratories Research in 1954 At Bell he turned his attention to the study ofspeech and hearing and headed up the acoustics and speech re-search projects from 1958 to 1969 Since Bell was a telephone company, there were many practical appli-cations for acoustics research including voice dial-ing, conferencdial-ing, speech recognition, text-to-speech applications, and more.Inconjunction with B Lo-gan, Schroeder designed a speech compressor that was made available to the American Foundation for the Blind for the Talking Book program In 1967, Schroeder was involved in the invention oflinear pre-dictive coding (LPC) and later in code-excited lin-ear prediction (CELP), important contributions to the evolution of digital voice encoding and synthesized speech While at Bell, Schroeder was named inven-tor/coinventor on 45 U.S patents

In 1969, Schroeder returned to Germany where he became a professor and lecturer in various aspects of physics, including number theory, chaos, fractals, and nonlinear dynamics He continued to work at Bell Labs for 5 months ofthe year and to maintain a strong interest in experimental acoustics, particularly in the area of generating speech through phase changes, in collaboration with H.W Strube Schroeder's studies, especially in acoustics, have been honored with sev-eral medals and awards See CELP; Harmon, Leon D.; Knowlton, Kenneth

Schweigger, Johann Salomon Christoph (1779-1857) A German physicist who contributed substan-tially to the development of the galvanometer and is credited as the first inventor of a practical version of the galvanometer Schweigger studied electromag-netism and observed in the early 1800s that current passing through a coil could increase the magnetic

Fiber Optics Illustrated Dictionary

influence ofa needle Building on the work of0rsted,

Schweigger continued with his research on

electro-magnetism and various configurations ofconductors

and, by 1920, had developed an electromagnetic

mul-tiplier that could detect very small amounts

ofattrac-tion or repulsion, thus developing a practical means

for detecting and measuring galvanic current See

galvanometer

scintillation Areaction that occurs when a charged

particle with sufficient energy impacts a material

which can be stimulated to emit energy in the optical

spectrum as the electrons return to a nonexcited state

Exposing certain materials to ionizing radiation

causes a scintillation reaction in which the materials

fluoresce

Scintillation may be stimulated intentionally or may

occur naturally and may be desirable or undesirable,

depending upon the circumstances There is a branch

of climatology that studies and predicts ionospheric

scintillation patterns, which is of importance to

sat-ellite systems maintenance and radio wave

propaga-tion

Inpractical applications in the fiber optics industry,

scintillation is the process ofconverting

electromag-netic energy outside the optical spectrum into light

energy See ionization, scintillator

scintillation, ionospheric Areaction that occurs

when electromagnetic energy passes through the

Earth's ionosphere (such as a space probe

communi-cation, marine distress call, or orbiting satellite

ra-dio transmission) and encounters small irregularities

in the plasma density along the path traveled,

result-ing in phase and intensity fluctuations Some of the

radiant energy is absorbed and reemitted in the

opti-cal spectrum

Ionospheric scintillation is an important factor in

ra-dio signals that are reflected off or through the

iono-sphere Scintillation can cause signal degradation,

loss oflock conditions, fade, and cycle irregularities

Solar flares, which effect the ionosphere, can

influ-ence the degree of scintillation that might occur at

particular times Scintillation indexes have been

de-veloped to give a quick-glance idea of the level of

scintillation that might be expected to occur in a

par-ticular equatorial sector at a selected frequency This

information can be combined with NOAA space

en-vironment data to generate scintillation graphs For

example, an intensity index ofO.S or higher indicates

moderate to high scintillation conditions

scintillation detector Adevice that detects light

emissions from a scintillation reaction, that is, one

in which electromagnetic radiation is absorbed and

reemitted in the optical spectrum The detector then

uses a photocathode to convert the light energy into

electrical energy so that it can drive various

measure-ment and display components to provide useful

in-formation Fiber optics may be used to direct the light

from the scintillator to the phototube (e.g., through a

fiber optic arrayfaceplate)or from the phototube to

the processing components

Since electromagnetic energy occurs in a very broad

range offrequencies, materials may be chosen to

cre-ate a scintillation reaction within specific frequency ranges (or to be more sensitive within those frequency ranges) For example, thallium-doped sodium iodide may be used in gamma ray detectors

The energy level of the electromagnetic particle in part determines the magnitude of the ionization re-action and the intensity of the scintillation rere-action, enabling the strength of the energy to be calculated

A discriminator may further be used to isolate pulses within a particular amplitude range

Nishiura and Izumi have described an interesting type

of fiber-based radiation detector It is comprised of

an optical fiber doped with scintillating materials which emit light energy when stimulated by radia-tion that is propagated through the length ofthe fiber

to both ends Detectors at each end of the fiber use differences in signal arrival times (time offlight

-TOF) to calculate the location of the radiation expo-sure on the fiber path Thus, the fiber line can be con-veniently installed along a wall or ceiling and can be

as long as the light is able to travel through the fiber core In contrast to point-source detectors, it can de-tect radiation intensities along the length ofthe cable The hardware interfaces with a software signal pro-cessing application to provide a visual display and numeric readouts of the radiant energy detected by the system

Scintillation detectors are used for scientific and medical imaging, industrial safety devices (e.g., ra-diation detectors), and ionospheric interference pre-dictors See scintillation

scintillator Acomponent for converting energy from

a high-energy charged particle such as X-radiation or gamma radiation into light energy Thereafter opti-cal fibers can optionally be used to direct the light (or a portion of the light) to a phototube or photo-multiplier tube that further converts the signal to an electrical charge

Scintillators are generally fabricated from materials with excellent light-transmitting characteristics, good temperature tolerance, and sufficient stability for ac-complishing the task at hand A high index ofrefrac-tion is usually desirable and rapid decay of the exci-tation phase when a charged particle hits the scintil-lator generally permits a finer resolution for the pro-cessing of subsequent particles Typically, the scin-tillator, and any associated light-sensitive components such as photomultiplier tubes, are shielded from ex-traneous light by dark housings and tape to seal the cracks

There are many materials with scintillating proper-ties, including liquids, gases, powders, and single crystals (e.g., yttrium-aluminum-garnet - VAG) Powder scintillators are typically mixed and bound

to a glass substrate Liquid scintillators may be a mix-ture of chemicals in a mineral oil suspension Com-mercially available plastic scintillators are common There may be a tradeoff between the response time and the longevity of scintillating materials Some of the powdered materials may have quick response times, but will lose effectiveness over time with exposure to radiation Single crystal scintillators have

than some other scintillating materials.

The thickness of a scintillating layer depends upon

the application In electron microscopy, for example,

itmay vary from 0.5 - 1.0 mm

Scintillation may be configured through the use of

discrete crystals, bonded layers, or planar arrays

con-sisting of strips, rectangles, trapezoids, etc

Scintillators are used in electron microscopy,

medi-cal and dental imaging systems such as computer

to-mography (CT) and X-ray machines, and a number

of experimental physics instruments They may be

bonded to fiber optic faceplates to jointly control and

guide light emissions to electronic imaging

compo-nents See faceplate, fiber optic; P-47; phototube

SCQAn AT&T specialized network maintenance

organization providing a single point of contact for

resolving customer network faults

SCQ UnixThe Santa Cruz Operation's adaptation of

Unix See Unix, UNIX

scope 1 Generic term for any visual enlargement

mechanism typically viewed through a narrow

aper-ture, such as a microscope, telescope, or periscope

2 colloq.Ageneric term for a bounded display device

representing abstracted data that would otherwise be

invisible to human eyes Radar scopes enable

trans-lation ofreflected radio signals into visual signals that

are positionally displayed and oscilloscopes enable

electrical signals to be displayed as waveform

repre-sentations See oscilloscope

SCP1 Satellite Communications Processor 2 See

Service Control Point See Signaling System 7 (SS7)

3 See Session Control Protocol

SCR1 silicon-controlled rectifier 2 See sustainable

cell rate See cell rate for chart 3 System Clock

Ref-erence A synchronization time reference used, for

example, in MPEG decoding

scramblerA device which rearranges or distorts a

data communication or broadcast transmission to

pro-vide a measure ofsecurity A descrambler is required

at the end of the transmission to convert the

infor-mation back into comprehensible form Scrambling

is a type ofencryption, although the termencryption

tends to be associated more with sophisticated data

encryption schemes, and scrambling is associated

more with the simple rearrangement ofa few

param-eters, such as inverting audio frequencies Black

mar-ket descramblers are common, especially for

televi-sion broadcast signals, since scrambling schemes are

easier to decode than sophisticated key encryption

algorithms Scrambling and encryption are

some-times combined to maximize security Scramblers are

most commonly used to protect pay services like

cable channels, but they are sometimes used to disrupt

the transmissions of others, such as communications

in war zones or traffic radar detectors

Scribner, Charles Ezra(1858-1926) An American

inventor and engineer, Scribner was chief engineer

at Western Electric, after joining the firm at the age

of 18 He had already patented a telegraph receiver

at that age, and eventually held over 440 patents, more

than any other single man in electrical history One

telephone switchboard Scribner founded the West-ern Electric engineering department, which later evolved into Bell Telephone Laboratories

SCRLSee Signal Corps Laboratories

scroll barA graphical user interface (GUI) device which serves two purposes: to indicate additional in-formation beyond what can be seen in the current win-dow or box, and to allow the user to scroll up and down (or across) the contents of the box by clicking

on and dragging the scroll bar or by clicking on ar-row indicators at either end of the scroll bar A well-designed scroll bar may have a third function - to give

a proportional idea of how much information is be-ing viewed or hidden Displaybe-ing a scalbe-ing drag area

to match the size proportional to the total of the in-formation contained in the listing, helps the viewer

to perceive whether a little or much is hidden from view

Some scroll bars are designed so the scrolling speed accelerates the longer the listing and the longer the user holds down the scroll bar This type ofselectively accelerated scroll can be very handy and is perceived

by most users as natural and comfortable

SCSISee Small Computer System Interface

SCSI connectorAn electrical/data connector sup-porting the data transmission requirements of the Small Computer System Interface (SCSI) standard

Traditionally, most SCSI devices (hard drives, car-tridge drives, scanners, etc.) were connectedwith

DB-25 or 50-pin flat connectors However, more recent SCSI-2 devices use a connection with finer pins See Small Computer System Interface

Common SCSI Connectors

Traditionally, DB-25 (top left) and 50-pinjlat con-nectors (top right) have been used to interconnect SCSI devices or to connect them to the host or peripheral card associated with the host Since SCSI devices can

be daisy-chained, it is important to terminate the last device in the chain A common 25-pin SCSI termina-tor is shown (bottom).

••.•••.•<::••••:• • • ~I.

}

;:!ii

Fiber Optics Illustrated Dictionary

SCT Secretaria de Comunicaciones y Transportes A

state agency given jurisdiction over communications

for Mexico in the 1938 Law of General Means of

Communications It has played an important role in

regulation and public services in Mexico's

telecom-munications history In 1992, telecomtelecom-munications

were transferred to the Telecomunicaciones de Mexico

SCTE I See serial clock transmit external 2 See

Society ofCable Telecommunications Engineers, Inc

SCTP See Stream Control Transmission Protocol

SDL See Specification and Design Language

SDLC See Synchronous Data Link Control

SDLLC SDLC Logical Link Control A Cisco

Sys-tems IOS feature which can provide translation

be-tween Synchronous Data Link Control (SDLC) and

IEEE 802.2 type 2

SDH See Synchronous Digital Hierarchy

SDN See Software Defmed Network

SDNS See Secure Data Network System

SDPI.See Service Data Point 2 See Service

Dis-covery Protocol 3 See Session Data Protocol 4 See

Session Description Protocol 5 See Simple

Discov-ery Protocol

SDSL single-line DSL One of a number of optional

configurations ofDigital Subscriber Line

telecommu-nications services SDSL is intended to provide a

ba-sic DSL option delivering 1.544 Mbps data rates in

both the upstream and downstream directions over

existing copper twisted-pair wireline connections

See Digital Subscriber Line

SDTI See Serial Data Transport Interface

SDTP See Serial Data Transport Protocol

Se symb selenium See selenium.

SEAL Simple and Efficient Adaptation Layer See

asynchronous transfer mode in the Appendix for

in-formation about ATM adaptation layers

seal n. I.Apart designed to tightly close or close off

a part, adjoining parts, or a container Seals are

some-times used to make parts air- or watertight 2 A

se-curity/tamper device designed to indicate whether the

parts adjoining or underlying the seal have been

opened or altered It is common for technical

ponents such as hard drives, internal parts to

com-puters, and warranteed parts to be sealed by a plastic

or metallic adhesive seal, or a dot of colored paint or

resin Breaking the seal may void a warranty

search engine A software application designed to

search and retrieve information from a database

ac-cording to user-specified parameters or keywords

SeeWAIS

search engine, Web A software application

com-bined with a Web site to provide search and retrieval

of a great variety of information, such as newsgroup

postings, personal or business names and addresses,

individual Web pages, or Web site topics Many

in-clude advanced search features with logical

opera-tions for more specific or complex searches

Consid-ering the millions of sites on the Web, Web search

engines are indispensable See Appendix C for a list

ofWeb search engine sites

SECAM sequential couleur avec memoire; sequential

color with memory Acomposite color television

stan-dard developed in France and used also in the French colonies and western regions of the former USSR.It supports up to 625 scanlines at 50 cycles per second

at a frame rate of25 per second at 4.42MHz,with an inverted signal that makes it incompatible with PAL, the other common fOlmat in Europe, and NTSC, the format used in North America

second 1.A briefunit of time defined as 1I60th ofa minute in reference to a solar day 2 A unit of time, designated in 1967 by the General Conference of Weights and Measures, as the duration of 9,192,631,770 periods of the radiation correspond-ing to the transition between the two hyperfine lev-els of the ground state of the cesium-I 33 atom See atomic clock

Second/Secondary Audio Program SAP Asecond-ary source of audio, usually a better quality audio or similar-quality audio provided in another language, that can be selectively chosen by a listener/viewer Section Terminating Equipment STE In SONET networking, the STE may be a terminating network element or a regenerator between any two adjacent network elements (such as line repeaters or lightwave terminals) It can originate, access, and/or modify the section overhead, or terminate it, if needed See SONET, Synchronous Transport Signal

Secure Data Network System SDNS A system which incorporates the SDNS Message Security Pro-tocol (MSP), developed as a cooperative project be-tween government and industry participants and sponsored by the U.S National Security Agency (NSA) MSP was specified to be integrated into the

XAOO Message Handling System (MRS) environment.

Secure HTTP, Secure Hypertext Transfer Proto-col S-HTTP A security-enhanced version of HTTP introduced in the mid-1990s The original experimen-tal version was designed to support multiple public-key algorithms, although a 1997 revision designates the Diffie-Hellman algorithm as the default It is sometimes called HTTP/SSL SSL was originally developed for transmitting private documents through the Internet via a browser (e.g., Netscape) and was later standardized as a transport layer security stan-dard See Hypertext Transfer Protocol, RFC 2616, RFC 2660, RFC 2716, RFC 2817

Secure Multipurpose Internet Mail Extension See SIMIME

Secure Public Networks Act SPNA An act of the U.S Senate (S 909) introduced by Senators McCain and Kerrey, in 1997 The Act would make it lawful for U.S persons to use encryption, regardless of al-gorithm, encryption key length, or implementation; however, it differs from the Security and Freedom through Encryption (SAFE) Act in that it would re-quire U.S persons to use government-approved third-party encryption key escrow agents to hold spare cop-ies of every encryption key This type of key recov-ery system has been brought forward numerous times

in the last few years and has always met with strong debate from the business community and privacy advocates

SPNA made it unlawful to use encryption to further

generally unlawful to decrypt communications

with-out authority This effort was one ofthe few bills

sup-ported by Louis Freeh, Director of the FBI Exports

would be limited to encryption products with 56-bit

keys or less It established a relationship between

digital signature certificates and key escrow systems

The act was approved by the Senate Commerce

Com-mittee in May 1997 but was not brought to a full

Sen-ate vote due to a number of other options that were

introduced See Encryption for the National Interest

Act, Security and Freedom through Encryption Act

Security and Freedom through Encryption Act

SAFE Important legislation proposed as alternative

policy for protecting security and personal privacy

while still promoting electronic commerce.Itwas a

long process to work out the terms of SAFE,

begin-ning in 1995 In February 1997, the SAFE Act was

introduced with the same terms as H.R 3011,

pro-posed in 1996 The 1997 bill sought to ensure that

Americans could use any type of encryption

any-where in the world and would be permitted to sell any

type of encryption domestically It further sought

penalties against unlawful use ofencryption and

pro-moted the relaxation of export controls over

encryp-tion algorithms and encrypencryp-tion-related products

Through committees, the text of the original

Goodlatte and Lofgren bill was significantly changed

Introduced into the U.S House ofRepresentatives as

H.R 695, in 1997, the bill amended title 18, U.S

Code to " affirm the rights ofUnited States persons

to use and sell encTXption and to relax export

con-trols on encryption ' As with other privacy-related

bills, there was significant debate and the bill was

competitive with others, including the Secure Public

Networks Act

In May 1997, the House Judiciary Committee

unani-mously approved SAFE, while agreeing to three

amendments In June, the House International

Rela-tions Subcommittee on International Economic

Policy and Trade approved SAFE by a majority

Amendments and input from the House Intelligence

Committee followed, with consideration of the

Oxley-Manton amendment to criminalize the

domes-tic use of strong encryption This amendment drew

much debate from citizens and law professionals

By the 1999 106th Congress, there were two versions

of the proposal H.R 850 dealt largely with the

ex-port of encryption products and had many

implica-tions for the Export Administration Act of 1979 Since

itwas frrst introduced, it broadened and became more

lenient in terms of restrictions on personal and

busi-ness use of encryption, essentially opening the door

not only to using any encryption products but also in

exporting them It appears that the advocacy of

pri-vacy rights supporters and the competitive needs of

U.S exporters swung the pendulum in this direction

The Act subsequently went through many

commit-tees for markups and, in some cases, adoption

Under the tenns of the Act, it is lawful for persons

specified in the Act to sell any encryption, regardless

of the algorithm, in interstate commerce Thus, there

cryption keys, for example It further states that the federal government and individual states may not re-quire key escrow/key recovery information as was previously proposed in other bills

In terms ofexport, a highly contentious issue, SAFE stipulates that the Secretary of Commerce (with con-currence from the Secretary of Defense) has exclu-sive authority to control computer-related exports, in-cluding information security products, except for military uses The Secretary would carry out a one-time 15-day technical review of entities wanting to export encryption-related products, after which no export licenses would be required, except where na-tional security might be involved (e.g., per the Trad-ing with the Enemy Act) This is a significant change over previous policies that strictly limited encryption key lengths, for example Pressure from the industry and competition from foreign bodies providing en-crypted products and encryption algorithms were probably the basis for this change of heart The Act expressly stated that nothing in the Act shall limit the authority of the President under the International Emergency Economic Powers Act, the Trading with the Enemy Act, or the Export Administration Act of

1979 Thus, there would continue to be prohibitions

on the export ofencryption products to countries " that have been determined to repeatedly~rovide sup-port for acts of international terrorism '

To satisfy the concerns of law enforcement person-nel, who increasingly worry that the ability ofcrimi-nals to engage in surreptitious, global communica-tions is outstripping the ability of law enforcement

to monitor these communications, a stipulation in the Act stated that the Attorney General " shall com-pile, and maintain in classified form, data on the in-stances in which encryption has interfered with, impeded, or obstructed the ability of the Department

of Justice to enforce the criminal laws of the United States." SAFE prohibits the use ofencryption for hid-ing messages related to criminal acts See Anti-Ter-rorism Act of 2001, E-Privacy Act, Secure Public Networks Act

Security AssociationsSAse Elements for containing information for the execution of network security services such as Internet Protocol (IP) layer services (authentication, encapsulation, etc.), transport layer

or applications layers services, or protection of ne-gotiation-related network traffic See Internet Secu-rity Association and Key Management Protocol Security Multiparts specificationA specification for secure messages, separating the content data from the signature, and formatting them as multiple parts

of a MIME communication See S/MIME, RFC1847

Security Protocols for Sensor Networks SPINS Based upon the premise that in the future, wireless networks will be comprising millions of small self-organizing sensors, Perrig, Szewczyk et al have pro-posed a set of security protocols to explore security issues in sensor networks

The SPINS work has arisen out of the SmartDust

.

,

t

Fiber Optics Illustrated Dictionary

multi-hop networks ofsmall, low-power, sensor devices are

being built utilizing the TinyOS event-driven

oper-ating system It was discovered that workstation

mod-els ofsecurity were impractical in a low-power,

multi-sensor environment, including Diffie-Hellman

algo-rithms and digital signatures There simply is not

enough resource space to implement the usual methods

other shared key algorithms could be used The

tight version ofthe Timed, Efficient, Streaming,

Loss-tolerant Authentication Protocol) to provide

authen-ticated streaming broadcast; on SNEP (Secure

Net-work Encryption Protocol) for data confidentiality,

two-party data authentication, and data freshness; and

on an authenticated routing protocol using SPINS

building blocks Results of the project indicate that

it is feasible to add security to severely

resource-con-strained sensor networks through symmetric

cryptog-raphy

Seebeck, Thomas Johann(1770-1831) A German

researcher who described thermoelectrical effects in

1823, after observing a connection between

electric-ity and heat This observation is now exploited in the

fabrication of many types of semiconductor

compo-nents, such as thermocouples, and is called the

Seebeck effect See thermocouple

seek timeAquantified description ofthe time it takes

to locate specified information In software, for

ex-ample, this could be expressed as the average time

in milliseconds or clock cycles it takes for a specific

tool to locate queried information from a database of

a given size In hard storage devices, it could be

ex-pressed as the average time it takes for the read head

to position itself on the track where the information

lies Industry definitions of seek times exist for

spe-cific types and sizes of devices

segmentation and reassemblyA common process

in packet-based networking ofdividing up the

pack-ets so they can be individually processed or routed,

and reassembling them at the receiving end to recreate

the original message or transmission

seizeTo take control of a circuit or system so it

can-not be used by others Computer files are sometimes

seized and locked so that the data cannot be

inadvert-endy modified simultaneously by more than one user

This helps protect data integrity Transmission circuits

may be seized to prevent interference on the line or

to preserve privacy

Selective Sequence Control ComputerSSEC The

successor to the Automatic Sequence Control

Calcu-lator, better known as the Harvard Mark I, instigated

by IBM in 1948 By this time a number of different

designers and manufacturers were getting involved

in the development and marketing oflarge-scale

puting machines and IBM was motivated by the

com-petition Machines built around this time represent a

transitional evolution from calculator/tabulators to

computing machines in common understanding

selenium(symb - Self A photoconductive element

(AN 34) first isolated in the early 1800s, selenium's

light-sensitive properties were noted by British sci-entists in 1873, which subsequently led to many of

trans-missions using selenium The properties of selenium provided A Graham Bell with the idea of transmit-ting sound via light which led to the invention of the Photophone

As understanding of the capabilities of selenium evolved, it came to be used in television cameras It

is sensitive to heat and light in varying degrees, de-pending upon other factors, and has important recti-fication properties; it can be used to convert AC to

DC power In solid-state electronics, selenium is a p-type semiconductor See Baird, John; Photophone Selenium Cells - Historic Forenmners

A selection ofsome of the selenium cells designed

by Tainter and Be// in the process of inventing the Photophone, a means oftransmitting sounds by light Selenium was a light-sensitive material with rectify-ing properties that were exploitedfor sound and im-age communications [U.S patent#235,497, J880.}

self-electro-optic effect device SEED A quantum well-based photonic optical device used for photo-nic switching, developed in the AT&T Bell Labora-tories in 1987 This multi-element device, when bi-ased by an external voltage, creates an external field that shifts the wavelength of the onset of absorption

to vary Optical sensors can be used with a SEED system to detect the resulting light This suggests the possibility of developing light-based switching mechanisms and optical logic SEED latches were described in the late 1980s and the first SEED de-vices were created in the late 1980s and early 1990s

In December 1989, Bell Labs announced the devel-opment ofa very high-capacity gallium-arsenide pho-tonic integrated circuit capable ofprocessing 2 kbits ofoptical information in parallel Each element in the chip array is a Symmetric-SEED (S-SEED) which

Illumination from a low-power light beam can be

used with the S-SEED to cause it to switch in less

than a billionth of a second This has important

im-plications for parallel processing, as complete arrays

can be simultaneously accessed

With the spread ofoptical communications

technolo-gies, scientists have been seeking ways to make the

physical transmission path all-optical SEED

ele-ments have possibilities as optical memory cells once

the means to combine them more effectively into

ar-rays as been worked out This, in turn, could support

the development of an all-optical switching

mecha-nism (e.g., an optical ATM switch)

Within the U.S Navy, 1 Bechtel has described

re-search on logic systems for solving Boolean

equa-tions based on a Symmetric-SEED (S-SEED) system

A single light source could potentially be split into a

matrix of light beams, which are then modulated by

a Symmetric-SEED-based spatial modulator and the

individual members in the array reset according to

Boolean inputs The value ofthe remaining member,

unaffected by inputs, would correspond to the

Bool-ean solution with the result signaled by a matrix of

equal intensity light beams onto a detector

U.K researchers, with help from a grant from the

European Union, have developed a digital optical

network for image processing based upon

self-linear-ized SEED (SL-SEED) concepts By exploiting the

fact that SEED responsivity can be increased by

ap-plication of voltage, a feedback loop can be

estab-lished The modulator photocurrents and detector

in-fluence one another until the photocurrents of both

match The photocurrent is proportional to the input

light minus the reflected light The detector

photo-current is proportional to the control light input

Con-trol can then be "subtracted" from the signal For

im-age processing, an element must then interact with

neighboring elements See electroabsorption,

quan-tum well, Stark effect

SEM See scanning electron microscope

semaphoreA visual signaling system employing

movable apparatus like arms or flags Individual

sym-bols, words, or instructions are made to correspond

to distinct positions of the arms or flags While

elec-tronic communications have superseded most

sema-phore systems, they are still sometimes preferred in

situations where electronic messages might be

over-heard See Chappe, Claude

semaphore, programming1.Anaccess or exclusion

indicator, such as a variable flag Semaphores are

useful for controlling file locks to preserve data

in-tegrity In other words, they can be used to prevent

multiple users from accessing a file simultaneously

and changing data in a way that could disrupt the

in-formation or corrupt the data 2 A low-level integer

variable having only nonzero values; a primitive

which can be used for synchronization in concurrent

processing implementations

semiconductorA material widely used in

electron-ics due to its relative balance of electrical conducting

and insulating properties (hence the name

semicon-talline in structure, and their properties of enabling

or impeding the flow of current are used in design-ing solid state electronic circuitry

Materials commonly used to create semiconductor components include silicon, germanium, and gallium arsenide Doping, the addition ofother elements, may

be part of the fabrication of semiconductors to fur-ther control and enhance their properties Current flow in semiconductors is commonly controlled by electricity, but may also be controlled by the influ-ence of light or magnetic fields Semiconductors are important materials used in the manufacture of inte-grated circuits See inteinte-grated circuit

Semiconductor Industry Association SIA The leading U.S trade association for the microchip in-dustry, established in 1977 by pioneers in the indus-try The SIA promotes and supports the competitive-ness of the U S semiconductor industry and repre-sents its membership through input to government representatives It also researches and reports on pos-sible health hazards related to the semiconductor in-dustry

In 1982, the SIA formed Semiconductor Research Corporation (SRC) to plan, direct, and fund precom-petitive silicon research projects at major academic institutions.In1985, the organization submitted in-put to the U.S government regarding the balancing oftrade practices between Japan and the U.S In 1987, SIA formed SEMATECH, a consortium of chip manufacturers dedicated to improving semiconduc-tor manufacturing technologies In 1997, the Focus Center Program was established to engage in long-term research to ensure the long-long-term viability ofthe industry

Semaphoric Optical Signaling System

France had an extensive system ofsemaphore sig-naling before the telegraph was invented Limited vis-ibility in bad weather and the needfor constant moni-toring were two disadvantages ofthis system.

semiconductor laserA compact laser comprising layers of semiconductor and other components A crystalline compound ofgallium and arsenic (gallium-arsenide - GaAs) is used to make semiconductor