Fiber Optics Illustrated Dictionary - Part 86 ppsx

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 convert a digital sample to a waveform for transmission. Typically the scanner does not process the information; its job is to capture the information, and often it can store that information in avariety ofselectable 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 applications, including those described in the Scanning Tech- nologies chart. scanning acoustic microscope SAM. A scanning microscope designed to assess the acoustical properties 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 ofdetector 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 electron 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 microscope SEM. A type of microscope designed to magnify at levels that are physi- cally beyond the scope of traditional optical miscroscopes. SEMs are precision instruments that use a beam ofelectrons rather than a beam of light to image a tiny section of an 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 microscopy SNOM. 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. 842 In the early I 990s, 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 ofresearch in quantum-level nanostructures without spacial aver- aging. Subsequent variations in the concept at UCSD, using silver particle suspensions illuminated by a focused 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 slender single-mode opticaljiber with an aluminum coating. 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 aperture (the uncoated tip - a). It may also bepossible Jor the customer to specifY the length oj the covering that serves as a protective coating andhandle (e). See probe, photoplasticfora variation on the basicprobe. scanning probe microscope SPM. A microscope designed to facilitate the viewing ofsurface objects and 3D biological systems by means that are not readily attainable with conventional scanning near-field techniques for probing or manipulating surfaces. SPMs are versatile instruments ranging from optical to scanning 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. In one embodiment of this invention, a fiber optic light guide transmits light from the source to the probe. In the 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 optical 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, © 2003 by CRC Press LLC faster scan rates are associated with higher accuracy or fidelity in conveying motion. In still images, faster scan rates may compromise the resolution or fidelity of an image. 2. In cathode-ray tubes (CRTs), the scanning rate is the speed at which the electron beam sweeps the screen to refresh a full frame. This is usually 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 aspecified number of sweeps over a unit of time. scanning rate, optical For optical scanning of images, such as those used with computer scanners and facsimile machines, scanning rate is often not as important 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-straps colloq. Telephone line worker safety belts. scatter v. To separate, to distribute widely or ran- domly, to disperse, to diffuse in various directions. scatter, transmission To diffuse or spread out in such as way as to lose the strength or directionality ofa transmission signal. In most communication transmissions, this is undesirable. See spreading loss. 3. To enhance communications through exploiting delib- erate, controlled scatter. See satellite scatter. SCC 1. Specialized Common Carrier. Acarrier com- peting with the dominant carrier in niche markets. 2. Standards Council of Canada. SCCP See Signaling Connection Control Part. SCE See Service Creation Environment. SCEP See Service Creation Environment Point. Sceptron spectral 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 stimulation, 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 aword 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 of the same diameter but different 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 of the fibers, registering the movement or lack Scanning Technologies for a Variety of Devices Application Notes scanning antenna Parts ofa moving antenna which cause the directional scanning of the antenna beam. facsimile scanner A component ofa facsimile machine which converts a sampled digital image to a waveform for transmission over phone lines. See ITU-T, facsimile, TIFF. image processing A computer input device which passes a beam over a 2D or 3D object or image, and converts it to digital data, usually a 2D raster 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 in 1968 by Hughes Aircraft for use in orbiting satellites, and first deployed in 1972 in the first Earth Resources Technology Satellite. This technology revolutionized understanding and recording ofEarth's topological and geological features. The program became Landsat in 1975. robot vision In robotics, a scanner samples visual input and processes the information in a way that provides 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 ofa particular kind, such as newly uploaded files, email, user logins, etc., or which scans processes such as network load, states, CPU usage, etc. 843 © 2003 by CRC Press LLC 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 the twisted nematic effect, this effect was studied and described by M. Schadt and W. Helfrich in "Voltage-Dependent Optical Activity ofa Twisted Nematic Liquid Crys- tal," in 1971. It is a means of modulating light through a layered liquid crystal component. Imagine a layer of nematic 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 introduced to more or less fix the alignment of the liquid 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 component 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 enables intermediary effects in the orientation of the crystals, resulting in gray scale modulation. See nematic liquid display, smectic liquid crystal. Schiifer, F.P. Along with F. 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 tunable 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, ArthurLeonard (1921- )An American! 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 , , ' 5 i are processe ~ _ ~ 2. light impulse travels from point of stimulation to both ends of fiber waveguide radiation stimulating scintillation reaction / cladding layer . 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 alternative 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 waveguidefrom the point(s) at which the reaction occurred. Photomultipliers can be used to convert the light signal to an electrical signal and to amplify weaksignals. The in/ormation aniving at both endso/the waveguide canthus beplDcessed to determine the location of the 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. 844 © 2003 by CRC Press LLC Canadian physicist and laser pioneer with a strong interest in spectroscopy, Schawlow studied at the University of Toronto and Columbia University. At Columbia he met Charles Townes, with whom became 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 aposition as aprofessor 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 electron spectroscopy that derived from the pioneer work. The Arthur Schawlow Medal of the Laser Institute of America is named in his honor. See laser history; Townes, Charles. Scheduled Transfer ST. A media-independent upper-layer protocol that was originally developed as part of the HIPPI -6400 network transmission standard. schematicA diagrammatic representation of an electrical 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, PavelLvovitch (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 inventions 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 and 1. Volze, Schmidt published "Organic dye solution laser," in Applied Physics Letters in fall 1966, an important historic landmark in dye lasers in particular and tunable laser technology in general. Schott Fiber Optics, Inc. SFO. Aprominent international 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 of American Optical). Through the last half century, the company has developed glass core and coating technologies, winding and assembly processes, fiber drawing and faceplate fusing techniques. It has also designed and developed medical and scientific 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 diode A type ofefficient rectifying component. Schottky diodes are incorporated into a number ofelectronic devices that require switching or voltage control components. In TTL circuits they 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. In the early 1970s, they developed a practical low-loss embodiment of fiber optics transmission lightguides, a technology that had eluded scientists since the early 1960s. Schultz is known for having codeveloped an outside vapor deposition process in 1972 that is still a standard in the industry. This led to the development of germania-doped fused silica. Schultzjoined SpecTran Corporation as VPofTech- nology in 1984, and later became president of technology at Schultz Galileo ElectroOptics, Inc. He became president of He rae us Amersil in 1988. In 2000, along with Keck and Maurer, Schultz was awarded the National Medal of Technology. Schroeder, Manfred R. (1926- ) A German scientist 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 of speech and hearing and headed up the acoustics and speech research projects from 1958 to 1969. Since Bell was a telephone company, there were many practical applications for acoustics research including voice dial- ing, conferencing, speech recognition, text-to-speech applications, and more. In conjunction 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 of linear pre- dictive coding (LPC) and later in code-excited linear prediction (CELP), important contributions to the evolution of digital voice encoding and synthesized speech. While at Bell, Schroeder was named inventor/coinventor on 45 U.S. patents. In 1969, Schroeder returned to Germany where he became aprofessor 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 of the year and to maintain a strong interest in experimental acoustics, particularly in the area ofgenerating 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 ofapractical version of the galvanometer. Schweigger studied electromag- netism and observed in the early 1800s that current passing through a coil could increase the magnetic 845 © 2003 by CRC Press LLC 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 multiplier 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 anonexcited 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 abranch ofclimatology that studies and predicts ionospheric scintillation patterns, which is ofimportance to satellite systems maintenance and radio wave propaga- tion. In practical applications in the fiber optics industry, scintillation is the process ofconverting electromagnetic energy outside the optical spectrum into light energy. See ionization, scintillator. scintillation, ionospheric A reaction that occurs when electromagnetic energy passes through the Earth's ionosphere (such as a space probe communication, marine distress call, or orbiting satellite radio transmission) and encounters small irregularities in the plasma density along the path traveled, resulting in phase and intensity fluctuations. Some of the radiant energy is absorbed and reemitted in the optical spectrum. Ionospheric scintillation is an important factor in radio signals that are reflected off or through the ionosphere. Scintillation can cause signal degradation, loss of lock conditions, fade, and cycle irregularities. Solar flares, which effect the ionosphere, can influence the degree ofscintillation that might occur at particular times. Scintillation indexes have been developed to give a quick-glance idea of the level of scintillation that might be expected to occur in apar- ticular equatorial sector at a selected frequency. This information can be combined with NOAA space environment data to generate scintillation graphs. For example, an intensity index ofO.S or higher indicates moderate to high scintillation conditions. scintillation detector A device 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 information. Fiber optics may be used to direct the light from the scintillator to the phototube (e.g., through a fiber optic array faceplate) or from the phototube to the processing components. Since electromagnetic energy occurs in a very broad range offrequencies, materials may be chosen to cre- 846 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 reaction and the intensity of the scintillation reaction, enabling the strength of the energy to be calculated. Adiscriminator 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 radiation that is propagated through the length of the fiber to both ends. Detectors at each end of the fiber use differences in signal arrival times (time of flight - TOF) to calculate the location of the radiation exposure on the fiber path. Thus, the fiber line can be con- veniently installed along awall 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 detect radiation intensities along the length of the cable. The hardware interfaces with a software signal processing 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., radiation detectors), and ionospheric interference pre- dictors. See scintillation. scintillatorAcomponent for converting energy from ahigh-energy charged particle such as X-radiation or gamma radiation into light energy. Thereafter optical fibers can optionally be used to direct the light (or a portion of the light) to a phototube or photomultiplier 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 of refrac- tion is usually desirable and rapid decay of the excitation phase when a charged particle hits the scintillator generally permits a finer resolution for the processing of subsequent particles. Typically, the scintillator, 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 properties, 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 tradeoffbetween the response time and the longevity ofscintillating 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 © 2003 by CRC Press LLC long life spans, but may have slower response times than some other scintillating materials. The thickness ofa scintillating layer depends upon the application. In electron microscopy, for example, it may 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, medical 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 components. See faceplate, fiber optic; P-47; phototube. SCQ An AT&T specialized network maintenance organization providing a single point of contact for resolving customer network faults. SCQ Unix The Santa Cruz Operation's adaptation of Unix. See Unix, UNIX. scope 1. Generic term for any visual enlargement mechanism typically viewed through a narrow aperture, such as a microscope, telescope, or periscope. 2. colloq. A generic term for a bounded display device representing abstracted data that would otherwise be invisible to human eyes. Radar scopes enable translation of reflected radio signals into visual signals that are positionally displayed and oscilloscopes enable electrical signals to be displayed as waveform repre- sentations. See oscilloscope. SCP 1. Satellite Communications Processor. 2. See Service Control Point. See Signaling System 7 (SS 7). 3. See Session Control Protocol. SCR 1. 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. scrambler A device which rearranges or distorts a data communication or broadcast transmission to provide a measure of security. Adescrambler is required at the end of the transmission to convert the information back into comprehensible form. Scrambling is a type of encryption, although the term encryption tends to be associated more with sophisticated data encryption schemes, and scrambling is associated more with the simple rearrangement ofa few parameters, such as inverting audio frequencies. Black mar- ket descramblers are common, especially for television broadcast signals, since scrambling schemes are easier to decode than sophisticated key encryption algorithms. Scrambling and encryption are sometimes 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 ofothers, 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 of his most significant inventions was the multiple telephone switchboard. Scribner founded the West- ern Electric engineering department, which later evolved into Bell Telephone Laboratories. SCRL See Signal Corps Laboratories. scroll bar A graphical user interface (GUI) device which serves two purposes: to indicate additional information 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. Awell- designed scroll bar may have a third function - to give a proportional idea of how much information is being viewed or hidden. Displaying a scaling drag area to match the size proportional to the total of the information 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 of selectively accelerated scroll can be very handy and is perceived by most users as natural and comfortable. SCSI See Small Computer System Interface. SCSI connector An 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 connected with 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 connectors (top right) havebeen usedto interconnect SCSI devices or to connect them to the host or peripheral cardassociatedwith 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). 847 ••.•••.• <:: •••• :•. ~ .•.•. I. }. ;:!ii © 2003 by CRC Press LLC 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 telecommunications history. In 1992, telecommunications were transferred to the Telecomunicaciones de Mexico. SCTE I. See serial clock transmit external. 2. See Society of Cable 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 between 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. SDP I. 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 ofa number ofoptional configurations of Digital Subscriber Line telecommunications 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 information about ATM adaptation layers. seal n. I. A part designed to tightly close or close off a part, adjoining parts, or a container. Seals are sometimes used to make parts air- or watertight. 2. A security/tamper device designed to indicate whether the parts adjoining or underlying the seal have been opened or altered. It is common for technical components such as hard drives, internal parts to com- puters, and warranteed parts to be sealed by aplastic or metallic adhesive seal, or a dot ofcolored paint or resin. Breaking the seal may void a warranty. search engine A software application designed to search and retrieve information from a database according to user-specified parameters or keywords. SeeWAIS. search engine, Web A software application combined with a Web site to provide search and retrieval ofa great variety ofinformation, such as news group postings, personal or business names and addresses, individual Web pages, or Web site topics. Many include 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 of Web search engine sites. SECAM sequential couleur avec memo ire; sequential color with memory. A composite color television stan- 848 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 4.42 MHz, 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 levels of the ground state of the cesium-I 33 atom. See atomic clock. Second/SecondaryAudio Program SAP. Asecond- ary source ofaudio, 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 between 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 experimental 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 standard. See Hypertext Transfer Protocol, RFC 2616, RFC 2660, RFC 2716, RFC 2817. Secure Multipurpose InternetMail 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 algorithm, encryption key length, or implementation; however, it differs from the Security and Freedom through Encryption (SAFE) Act in that it would require U.S. persons to use government-approved third- party encryption key escrow agents to hold spare cop- ies ofevery encryption key. This type of key recovery 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 © 2003 by CRC Press LLC the commission of a criminal offense and made it generally unlawful to decrypt communications without authority. This effort was one of the 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. It was 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, proposed 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 ofexport controls over encryption algorithms and encryption-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 of United States persons to use and sell encTXption and to relax export controls 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 export of encryption products and had many implica- tions for the Export Administration Act of 1979. Since it was frrst introduced, it broadened and became more lenient in terms ofrestrictions on personal and business 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 privacy rights supporters and the competitive needs of U.S. exporters swung the pendulum in this direction. The Act subsequently went through many committees 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 would no longer be restrictions on the lengths of encryption keys, for example. It further states that the federal government and individual states may not require 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 ofDefense) has exclu- sive authority to control computer-related exports, including information security products, except for mili tary 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 national security might be involved (e.g., per the Trad- ing with the Enemy Act). This is asignificant 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 of encryption products to countries " that have been determined to repeatedly ~rovide support for acts ofinternational terrorism ' To satisfy the concerns of law enforcement person- nel, who increasingly worry that the ability of crimi- nals to engage in surreptitious, global communications is outstripping the ability of law enforcement to monitor these communications, astipulation 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 ofJustice to enforce the criminal laws of the United States." SAFE prohibits the use of encryption for hid- ing messages related to criminal acts. See Anti- Ter- rorism Act of 2001, E-Privacy Act, Secure Public Networks Act. SecurityAssociations SAse 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 specification A specification for secure messages, separating the content data from the signature, and formatting them as multiple parts of a MIME communication. See S/MIME, RFC 1847. 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 proposed a set ofsecurity protocols to explore security issues in sensor networks. The SPINS work has arisen out of the SmartDust 849 © 2003 by CRC Press LLC i nn •. ,. o' ~I.l;'. . .', . , t Fiber Optics Illustrated Dictionary program at u.s. Berkeley, in which prototype multi- hop networks of small, low-power, sensor devices are being built utilizing the TinyOS event-driven oper- ating system. It was discovered that workstation mod- els of security were impractical in a low-power, multi- sensor environment, including Diffie-Hellman algorithms and digital signatures. There simply is not enough resource space to implement the usual methods. RCS was chosen as the cryptographic primitive, but other shared key algorithms could be used. The researchers have presented information on Jl TESLA (a tight version of the Timed, Efficient, Streaming, Loss- tolerant Authentication Protocol) to provide authenticated 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 electricity and heat. This observation is now exploited in the fabrication of many types of semiconductor components, such as thermocouples, and is called the Seebeck effect. See thermocouple. seektimeA quantified description of the time it takes to locate specified information. In software, for example, 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 expressed 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 specific types and sizes of devices. segmentation and reassembly A common process in packet-based networking of dividing 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. seize To take control ofa circuit or system so it cannot 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 Computer SSEC. 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 of large-scale computing machines and IBM was motivated by the competition. 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 850 light-sensitive properties were noted by British scientists in 1873, which subsequently led to many of the important pioneer experiments in television transmissions using selenium. The properties of selenium provided A. Graham Bell with the idea of transmitting 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, depending upon other factors, and has important rectification 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 of some of the selenium cells designed by Tainter and Be// in the process of inventing the Photophone, a means of transmittingsounds by light. Selenium was a light-sensitive material with rectify- ingproperties that were exploited for sound and image communications. [U.S. patent #235,497, J880.} self-electro-optic effect device SEED. A quantum well-based photonic optical device used for photonic 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 which, in turn, causes the intensity of transmitted light 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 devices were created in the late 1980s and early 1990s. In December 1989, Bell Labs announced the development ofa very high-capacity gallium-arsenide photonic integrated circuit capable of processing 2 kbits of optical information in parallel. Each element in the chip array is a Symmetric-SEED (S-SEED) which © 2003 by CRC Press LLC can function as a logic gate, memory cell, or switch. Illumination from a low-power light beam can be used with the S-SEED to cause it to switch in less than a billionth ofa second. This has important im- plications for parallel processing, as complete arrays can be simultaneously accessed. With the spread ofoptical communications technologies, scientists have been seeking ways to make the physical transmission path all-optical. SEED elements have possibilities as optical memory cells once the means to combine them more effectively into arrays as been worked out. This, in turn, could support the development of an all-optical switching mechanism (e.g., an optical ATM switch). Within the U.S. Navy, 1. Bechtel has described research 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 of the 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 application of voltage, a feedback loop can be established. The modulator photocurrents and detector influence one another until the photocurrents ofboth match. The photo current 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 image processing, an element must then interact with neighboring elements. See electroabsorption, quantum well, Stark effect. SEM See scanning electron microscope. semaphore A visual signaling system employing movable apparatus like arms or flags. Individual symbols, words, or instructions are made to correspond to distinct positions of the arms or flags. While electronic communications have superseded most semaphore systems, they are still sometimes preferred in situations where electronic messages might be over- heard. See Chappe, Claude. semaphore, programming 1. An access or exclusion indicator, such as a variable flag. Semaphores are useful for controlling file locks to preserve data integrity. 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 information or corrupt the data. 2. Alow-level integer variable having only nonzero values; a primitive which can be used for synchronization in concurrent processing implementations. semiconductor A material widely used in electronics due to its relative balance of electrical conducting and insulating properties (hence the name semiconductor). Semiconductor materials are typically crystalline in structure, and their properties ofenabling or impeding the flow ofcurrent 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 further control and enhance their properties. Current flow in semiconductors is commonly controlled by electricity, but may also be controlled by the influence of light or magnetic fields. Semiconductors are important materials used in the manufacture of integrated circuits. See integrated circuit. Semiconductor Industry Association SIA. The leading U.S. trade association for the microchip industry, established in 1977 by pioneers in the industry. 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 possible health hazards related to the semiconductor industry. In 1982, the SIA formed Semiconductor Research Corporation (SRC) to plan, direct, and fund precom- petitive silicon research projects at major academic institutions. In 1985, the organization submitted input to the U.S. government regarding the balancing of trade practices between Japan and the U.S. In 1987, SIA formed SEMATECH, a consortium of chip manufacturers dedicated to improving semiconductor manufacturing technologies. In 1997, the Focus Center Program was established to engage in long- term research to ensure the long-term viability of the industry. Semaphoric Optical Signaling System France had an extensive system of semaphore signaling before the telegraph was invented. Limitedvis- ibility in badweatherandthe needfor constant moni- toring were two disadvantages of this system. semiconductor laser A compact laser comprising layers of semiconductor and other components. A crystalline compound of gallium and arsenic (gallium- arsenide - GaAs) is used to make semiconductor 851 © 2003 by CRC Press LLC . Adaptation Layer. See asynchronous transfer mode in the Appendix for information about ATM adaptation layers. seal n. I. A part designed to tightly close or close off a part, adjoining parts, or a container. Seals are sometimes used to make parts air- or watertight. 2. A security/tamper device designed to indicate whether the parts. , t Fiber Optics Illustrated Dictionary program at u.s. Berkeley, in which prototype multi- hop networks of small, low-power, sensor devices are being built utilizing the TinyOS event-driven oper- ating system. It was discovered that workstation mod- els of security were impractical in a low-power, multi- sensor environment, including Diffie-Hellman algorithms and digital signatures. There simply is not enough resource space to implement the usual methods. RCS was chosen as the cryptographic primitive, but other shared key algorithms could be used. The researchers have presented information on Jl TESLA (a tight version of the Timed, Efficient, Streaming, Loss- tolerant Authentication Protocol) to provide authenticated 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,. Transfer ST. A media-independent upper-layer protocol that was originally developed as part of the HIPPI -6 400 network transmission standard. schematicA diagrammatic representation of an electrical circuit, floorplan, network, or other

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