Fiber Optics Illustrated Dictionary - Part 94 potx

Fiber Optics Illustrated Dictionary device-supporting software applications. TAPI can be used to create call control software for telephony devices for computerizing common functions and sought-after features. As an example, TAPI can be used to create a Caller ID-type function on a computer, with the computer answering a Caller ID-enabled phone line, assessing the Caller ID information, and perhaps relating it to a database of names or other information associated with the number and logging the call or notifying the user of the call. Since not all phone systems are equipped with TAPI interfaces, there are now third parties, such as Ryan Technologies, that provide protocol conversion modules that enable TAPI-based applications to link through the module to the phone system. In 1999, Siemens extended the utility ofTAPI by introducing a TAPI interface compatible with a national ISDN terminal. This, in conjunction with the Optiset phone, turns a computer into a powerful telephony terminal. See Telephony Services Application Programming Interface. Telephony Routing over IP TRIP. Apolicy-driven inter-administrative domain protocol for routing voice-over-Internet calls, developed by the IETF IP Telephony (iptel) working group. TRIP is independent of the signaling protocol used. It uses Border Gateway Protocol (BGP-4) to distribute routing information between administrative domains. It thus enables digital telephony calls to be routed between digital network domains and supports the exchange of routing information between providers, thus building up a forwarding information base. In August 2001, TRIP was published as an Internet Draft and, in September 2001, was submitted to the IESG for consideration as a proposed standard. TRIP may also be a part of future protocols for the propa- gation of routing information between gateways and their associated signaling servers (a process called gateway registration). Telephony Services Application Programming Interface TSAPI. A set ofguidelines developed by a group of developers, including Novell, Inc. and AT&T, for interconnecting corporate telephone sys- terns into the data network server in medium and large business networks. The specification describes the physical link that can be used to implement software- based call control from a private branch exchange (PBX) switch, for example, so that control is handled from the originating point in the local area telephone network. Thus, TAPI's call tracking capabilities make it more powerful and suitable for enterprise environ- ments than the more desktop-oriented Telephony Application Interface (TAPI). See Telephony Appli- cation Interface. telephoto, telephotography Visual information con- veyed through conventional photographs or digital photographs from data received remotely. Journalists, geographers, navigators, and others use telephotos to send or receive visual information from remote sources through wired or wireless communications, and to print them in various resolutions through pho- tographic, laser, or other means. Satellite photos of 922 the Earth's surface are extremely popular examples of telephotos. Many of the images now printed in national newspapers are telephotos sent through wireless modems by journalists using digital cameras and laptops. Teleport Communications Group TCG. At one time, a national competitive local telecommunications provider with fiber optic SONET networks in over 50 large markets, acquired in early 1998 by AT&T. teleprinter I. Teletypewriter. 2. A Western Union trade name for printing telegraph terminals. See telex. TelePrompt Project A European Community (EC) project funded by a consortium of academic and commercial groups designed to develop and further technology-based distance learning resources for Euro- pean teleworkers. The term teleworking in Europe is roughly equivalent to the term telecommuting in North America. teleran An aerial navigational guidance system employing information received through television waves and radar transmitted to aircraft by ground stations. TELESA See Telecom Services Association of Ja- pan. telesales ABritish term for telemarketing. Teletype A name trademarked by Teletype Corpora- tion for avariety ofteleprinting devices used in communications. See teletypewriter. Teletype Corporation An early printing telegraph company, the Morkrum-Kleinschmidt Corporation, which was acquired in 1930 by the Bell System and renamed Teletype Corporation. teletypesetter A machine for remotely controlling typesetting machines. When these were originally put into service, teletype machines relied on a five-unit code that was insufficient to transmit all the charac- ters needed by a similar teletypesetting machine. Thus, a six-unit signal code was developed for teletypesetters to increase the size of the character set from 32 to 64. teletypewriter TTY. A printing apparatus which, in its common form, resembles a typewriter on a ped- estal with continuous feed or tractor feed paper so that it can print unattended. Sometimes it is used to send and receive signals over phone lines and for transmitting messages or computer data in text form. The teletypewriter superseded key and sound telegraph systems because it could operate unattended, be read by individuals without knowledge ofMorse code, and achieve transmission speeds of 60 to 100 words per minute. The earliest teletype-style printers and start-stop synchronization methods were developed by Charles and Howard Krum. See Baudot code; Krum, Charles and Howard; telegraph, printing; Teletype; telex. teletypewriter code A five-unit code that employs elements ofuniform length. Start and stop pulses are used to distinguish each character in the transmissions. See Baudot code. teletypewriter exchange service Any commercial service which provides teletypewriter communica- © 2003 by CRC Press LLC tions sending and receiving services through a switching exchange. Similar in concept to a long distance telephone exchange. TWX is one such service of the Bell System, established in 1931, subsequently owned by AT&T. See Telex. Compact Television Camera A tiny television camera, not much bigger than a human hand, designed in the days when television cameras were large and heavy. The technology was designed for the demandingtask of space observation and very long-distance communications by the Marshall Space Flight Center. Similar cameras were quickly adapted for commercial telecommunications. [NASA/Marshall Space Flight Center image detail, date unknown.] television TV. A system of sending and receiving broadcast moving images (even if the object in the transmission isn't moving), usually in conjunction with sound, although some closed-circuit television systems don't include sound circuitry. Television broadcasts can be transmitted through air or over cables, with cable TV (CATV) increasing in popu- larity. Air transmissions are captured with a television antenna designed for a portion of the broadcast spectrum (although three-in-one antennas exist for UHF, VHF, and FM signals). At the receiving end, a television set (tuner and monitor combined), or a VCR tuner and monitor are typically used to display the broadcast. television broadcast band The various frequencies which are assigned and regulated for television broadcast transmissions. Due to the proliferation of programming and the increased availability of access through satellite transmissions, there is constant pres- sure to increase available frequencies and channels, and hundreds of programming channels are now available. See band allocations for a chart. television camera Alens-equipped, optical-sensing pickup device designed to capture moving images and transmit or pass them on to receiving, editing, and broadcast equipment. The type of signal generated by the camera varies according to the receiving or editing equipment, and varies from country to country. Television cameras have traditionally been expensive, large, heavy, analog, high-resolution apparatuses. This is all changing, with small handheld digital and Common Television Broadcast Formats Name Abbreviation Notes National Televisions Systems Committee NTSC The North American standard since the 1950s. 525 vertical lines. NTSC uses negative video modulation and FM sound. Phase Alternate Line PAL The predominant standard in the United Kingdom and parts of Western Europe since the early 1960s. 625 vertical lines. There are a number of variations of the PAL system, including PAL-B, PAL-H, PAL-M, etc. PAL uses negative video modulation and FM sound. Sequential Color and Memory SECAM Developed in France and used in North Africa, Russia, and parts of Europe since the early 1960s. 625 vertical lines. There are a number of variations of the SECAM format, including SECAM-B, SECAM-H, etc. High Definition Television HDTV Introduced in Japan and proposed as a global standard, but not readily adopted by American and other manufacturers, some of whom would prefer to enhance current standards rather than adopt a new one. 1125 vertical lines at 60 frames per second. HDTV is supported by some Internet push channels and can be viewed with an interface peripheral and a computer with a fast connection. Multiplexed Analog Components C-MAC Developed in the U.K. and recommended by the EBU as a European standard. 923 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary analog personal cameras beginning to rival the quality of traditional TV cameras for only a fraction of the price. See NTSC, PAL, SECAM. television history Television, perhaps more than any other of the major communications technologies, arose in fits and starts in the late 1800s with many geographically diverse announcements of success and few demonstrated working systems. One of the important discoveries in the history of television was the photoconductive characteristics of selenium, which responded to the amount of light hitting the surface. A French researcher, M. Senlacq, suggested in 1878 that selenium might be used to register the shapes of dark and light areas on documents. British researcher Shelford Bidwell was able to successfully transmit silhouettes by 1881, and the now famous German inventor, Paul Nipkow, after whom the Nipkow disc is named, patented an electromechani- cal television system in 1884. But the transmission of moving images and shades of gray in high enough resolutions to be practical eluded the early inventors. Although patents for television-related technologies began to appear in the late 1800s, it was not until the 1920s that television transmission and reception as we know it was demonstrated by inventors such as John L. Baird in the west and Kenjito Takayanagi in Asia. Baird's first significant success was in 1926, the same year Tekayanagi transmitted Japanese script with a cathode-ray tube. In the U.S., a precocious 15-year-old, Philo T. Farns- worth, described an idea for a television to his school- mates and reportedly showed a sketch to his teacher in 1922. In 1927 he succeeded in building a working model. Experimental television stations sprang up in the late 1920s and, by the mid-1930s, regular public broadcasting began to develop. In Europe, television images were being transmitted by 1931. Television sets were available by the late 1930s, but it took time before the technology became affordable for home use. By the late I 940s, there were at least 20 broadcast stations in North America, with hundreds of hopefuls clamoring for the limited licenses. Black and white televisions came into widespread use in the 1950s in North America and color television was common about 15 years later. By the mid-1980s, melon-sized portable televisions became inexpensive and wrist-sized consumer TVs had been developed. Commercial sponsorship provides much of the fund- ing for television in North America, thus controlling, to some extent, the type of programming which is available, influenced by majority consumer demand or perceived viewer preferences. In many other countries, television is funded and controlled by local gov- ernments. The next major step in television broadcasting was the launching of communications satellites such as the Telstar 2 in 1962 which permitted intercontinen- tal communication. Commercial application of satellite television broadcasting was pioneered by the Canadian Broadcasting Corporation through the ANIK satellite in 1972, followed in the late 1970s by 924 Turner and the Public Broadcasting System (PBS) in the U.S. In North America, satellite television broadcasts can now be received by consumers on small parabolic dishes that are served by monthly subscription services, with hundreds of potential stations available. Television is widely used for mass-media entertain- ment, education, distance monitoring, and local security monitoring. The influence oftelevision on world culture is significant and substantial, with apreponderance of the programming originating in the United States. Thus, the role models depicted through television programming and advertising sponsors have a strong effect on viewers, and implicitly promote American values, styles of dress, and cultural priorities to all parts of the globe. See Baird, John Logie; Farnsworth, Philo T.; Nipkow, Paul Gottlieb; Nipkow disc; Takayanagi, Kenjito; television; television camera; Zworykin, Vladimir. television relay Astation designed to pass on a television broadcast signal to the next station so the signal is protected from loss. The relayed signal is not intended for reception by viewers until it reaches the destination station. television signal The coding of images can be accomplished in a number of ways, and there are several standards, each of which is preferred in a different part of the world. Common formats related to the broadcast and display of moving image signals are shown in the Common Broadcast Formats chart. telework Work at home or at satellite locations made possible through computer and telecommunications technologies. In 1988, Jack M. Nilles proposed a broad definition oftelework as " all work-related substitutions oftelecommunications and related information technologies for travel," thus, employerl employee interactions across distance through new technologies. This term is more common in Europe and is roughly equivalent to the term telecommuting in North America. See ADVANCE Project, European Community Telework Forum, TelePrompt Project. telex teleprinter exchange. Generic term for a communications service developed near the end of the second world war that uses teletypewriters to transmit through wire lines and automatic exchanges to produce a wlitten message at the destination. In Eu- rope, this technology used audio frequencies over phone lines. See Baudot code, Telex, Western Union. Telex A global message service established in the United States by Western Union in the early 1960s. This was competitive with AT&T's TWX service. Telkes, Maria Aphysicist who did pioneer work in the development of solar energy in the early part of the 20th century. Solar energy has subsequently become an extremely important power source for or- biting communications satellites. Telnet Protocol Awidely supported 8-bit, byte-oriented network protocol for remote terminal access, originating from the days of the ARPANET. Telnet allows the user to log on to another system through a TCP/IP network, and perform file functions and other © 2003 by CRC Press LLC activities. Telnet is spelled in lowercase when used as a command to launch a remote utility that uses the Telnet Protocol. The form of the Telnet command is: telnet [IP_address/host_name] [port] (with the command entered in lower case). See RFC 318, RFC 854, RFC 855 to RFC 861 (various options). TELSTAR 1 A historically significant low-altitude communications satellite that broadcast microwave transmissions and tracked satellites in the 1960s. This AT&T endeavor is claimed to be the first active communications satellite, launched 10 July 1962 by the United States, although some RCA engineers launched a transmissions satellite earlier. It is the first transponder-equipped satellite. Prior to this, satellites were passive transmitters, but the use of transponders for amplifying the signals was preferred from this time on, and some satellites now include as many as ten transponders. The TELSTAR had some early problems that were fixed in 1962; it ceased function- ing in 1963. By 1964, two more TELSTAR satellites had been successfully launched and TELSTAR 3-D was launched in the mid-1980s. Telstar Communications Satellite The Telstar 3-Dsatellite being put into Earth orbit from thepayloadbay of the Space Shuttle Discovery in the mid-1980s. [NASA/JSC image detail.} TEM wave transverse electromagnetic wave. template 1. Apattern, guide, table, or mold used to provide the basic configuration, format, or design for creating a new version, or multiple versions of a project with few or no changes. A template is intended to save time by automating the creation of new versions. A word processing template can be used to set up documents which are reissued frequently with only minor changes (e.g., form letters). TemporaryMobile Station Identifier TMSI. A dynamically assigned mobile station identifier (MSID). TENET See Texas Educational Network. tensile strengthAdescriptor for the greatest amount of longitudinal stress that can be borne by a particular material before it will rip apart. The units used to describe this property vary from industry to industry. It is an important factor in many manufacturing and industrial applications. tension testerAn industrial device that tests the tension parameters in a newly spliced fiber optic cable assembly. This is often sold as an option to a cladding alignment splicer. See cladding alignment splicer. tera- T. A prefix for an SI unit quantity of 10 12 , or 1,000,000,000,000. It's a trillion, a very large quantity, but considering there are now hard drives with terabytes of storage space, it's not as big as it used to be. It comes from the Greek root terat or teras mean- ing "monster." See peta-, pico TERENA Trans-European Research and Education Networking Association. A European network evolv- ing from the European Academic and Research Net- work (EARN) and the Reseaux Associes pour la Re- cherche Europeenne (RARE). TERENA was established from the merger of these organizations in 1994 to promote and participate in the high quality international information infrastructures to benefit research and education. TERENA includes members from more than three dozen countries, as well as a number of high-profile computer developers/vendors, and the CERN and ACMWF international treaty organizations. TERENA has been responsible for BITNET support in Europe including data collection and the distribution of nodes and routing tables. See BITNET. terminal 1. An endpoint, extremity. 2. Aconducting device, often a small metal post or receptacle, pro- vided for facilitating a good electrical connection. 3. A device or system which provides remote access to a central computer. 4. An endpoint in a communications line, or one which can be, but is not neces- sarily, extended to other circuits. Terminal Adapter TA. A device available in various configurations from anumber of vendors ,which provides protocol adaptation and interfacing with an ~~Fl~~:i~i~~~:~~~::~~~::s~~~~ ,. Terminal EndpointIdentifier TEl. An identifier for distinguishing between several different devices using the same ISDN transmission links. Values may be dynamically assigned to TEIs ranging from 0 to 126. Fixed TEIs are assigned values between 0 and 63. The value of 127 is reserved for TEl broadcast, which aids in carrying out management functions. An ISDN device must be assigned at least one unique TEl value, either by preassignment or dynamically, by the local exchange, as needed (sometimes called Auto TEl). The TEl Management Protocol is used to dynamically assign values in a request/response inter- action. Dynamic allocation is usually used on point- to-multipoint links but may be used on point-to-point links terminating office In atransmission such as a phone call or telegraph message, the terminating office is the switching center which is the final one that connects directly to the subscriber line or other receiver of the communications. In Internet dialup communications, the local ISP would be considered the terminating office. 925 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary TERMITE Aterminology database which contains all tenns appearing in printed glossaries of the Inter- national Telecommunication Union (lTD) since 1980, contributed by a variety of industry professionals, including technical editors and translators. English, French, Spanish, and Russian source tenns are in- cluded. Access to the database is available through Telecom Infonnation Exchange Services (TIES). ITU activities are now also being archived in this database. http://www.itu.int/search/wais/Tennite/ terminator Aphysical device or setting to indicate the end ofa data path in a connection in which more devices may be added. If a chain is not terminated, the end of the system is seen as an open port and the system either continues to try to send signals to (and to expect signals from) another device that isn't there or, in fiber optic networks, to experience undesirable back reflection and instability. SCSI-format cartridge drives sometimes have autotermination built in to the device and the user may have to use a specified port on the device, if it is the last in the chain. Some devices tenninate internally with a setting on a switch or a small internal or external dipswitch. Other devices, such as scanners and external hard drives, are terminated with an external tenninator attached to one of the SCSI input/output connection mounts. Internal hard drives are often terminated with a set of resistors that can be removed or, in some cases, with jumpers. Most SCSI chains can be tenninated with standard 50- or 68-pin SCSI tenninators, but there are excep- tions, including aproprietary "black" SCSI tenninator distributed by Apple Computer for some of their older computers and certain Apple laser printers that support font storage on attached hard drives. On an Ether network using "thin" cables (1 ObaseT), a tenninator is required on each end of the data bus if the chain or "ring" is not closed. If"thick" Ether (1 Obase2) connections to a plug-and-play hub in a star topology are used, separate tennination is not required. In a wired network, devices such as SCSI-fonnat CD- ROM drives, hard drives, and scanners can be chained along the same data path, but atenninator is required on the end device (usually the one farthest from the motherboard) to prevent the system from seeking devices beyond the last one. Failure to terminate a SCSI chain can cause immediate or sporadic problems with data access on the chained devices. In a fiber optic network, the problem of back reflection can be even more serious than in wired networks. Many aspects of wired networks are designed to handle signals in two directions along one wire. Even when separate wires are used, the strength of the data signal is controlled such that damage to components is unlikely (possible, but not common). In fiber optic networks, an open, untenninated port may allow laser light to escape, which can be a danger to eyes. Improper closing ofa fiber port can result in the laser light being reflected back down the waveguide in the wrong direction. This not only disrupts the path and amplitude of the light data signals, but also may 926 interrupt or damage the laser source. Passive tenninators are most common, but advance- ments in networking and greater demands on the technology are giving rise to various types ofactive ter- minators. Longer cable runs and higher data rate per- fonnance may be accompanied by higher noise sen- sitivity that may be mitigated by active tenninators with voltage regulation. Active SCSI tenninators may autoselect between low-voltage differential (LVD) and single-ended (SE) modes. Because of the extra electronics, active tenninators are sometimes a little larger than passive tenninators commonly cost about 50% more than their passive counterparts. Fiber optic tenninators come in a variety of fonnats, including SC and FC and generally follow Telcordia standards. Some fiber tenninators are doped and are typically sold to support specific wavelength ranges. Many of them resemble standard fiber connectors but they are designed to eliminated back reflection rather than to facilitate the attachment of another length of cable or device. Terrestrial Digital Service TDS. Acommercial private digital data transmission service offered by MCI to subscribers over local exchange carrier (LEC) TI, DS-3 systems. Thus, customers would have fast transmission links to MCI Services. There was some de- bate over this service option through the Federal Communications Commission (FCC). TESe Technology Subcommittee. tesla Ameter-kilogram-second unit of magnetic flux density equivalent to one weber per square meter. Named after Nikola Tesla. Tesla coil An air-core transfonner for creating high- voltage discharges at very high frequencies. Tesla, Nikola (1856-1943) An engineer and inventor born in Smiljan Lika (Austria-Hungary) who developed the alternating current induction motor, an essential part ofalternating current distribution systems. Tesla began his research in Hungary, and then emigrated to the United States in 1884. He created a number of unique inventions and also improved upon those of others. In America, Nikola Tesla and Thomas Edison came into regular contact with one another, not always with happy consequences, and an enmity grew between the two men. When it was proposed in 1912 that the Nobel prize be awarded jointly to Edison and Tesla, Tesla eschewed any association with Edison, and the prize went to a Swedish scientist instead. Tesla's inventive mind turned power generated devices into interesting applications such as aircraft power systems and robotic submarines. In 1888, he was awarded a patent for an electromagnetic motor. Tesla eamed more than 700 patents in his lifetime and produced many more unpatented ideas and inventions. Tesla was somewhat temperamental and eccentric. One of his most practical contributions was the adaptation of alternating current into everyday applications. His colleague, George Westinghouse, further implemented many ofTesla's ideas. The tesla unit of magnetic flux is named after him. © 2003 by CRC Press LLC TESP See Telecommunications Electric Service Pri- ority. test board A switching panel used for making temporary connections in conjunction with the panel or equipment being tested. By diverting some of the signals through the test panel, problems can sometimes be more easily isolated or identified. A test clip can also be used for the purpose of making quick temporary connections. See breadboard, shunt. testjack/plugA connecting hole in acircuit or panel for inserting a corresponding plug Gack) and cable for making temporary connections for testing and maintenance. Test jacks and plugs come in many shapes and sizes depending upon what type of circuit is tested. A telephone test set is a portable telephone handset that has clips for temporary attach- ments to a conducting line or test jacks for temporary insertion into in a test jack plug frame. test jack frame TJF. In private branch exchange (PBX) telephone systems, a frame for inserting test cables for maintenance and testing, usually mounted in or near the main PBX cabinet and terminating the cabinet connections. test pattern Any pattern generated for a particular transmission medium that indicates the integrity of the various characteristics of its signal, which may include resolution, signal strength, stability, linear- ity, contrast, brightness, colors, sound range and quality, etc. 2. In video editing, a series of bands of specific colors. 3. In television broadcasting and television set calibration and diagnosis, a pattern (known to some as the Indian head pattern) which includes particular lines and line widths, ellipses, tonal gra- dations, and numerical values that allow the diagnos- tician to determine problems and make adjustments. This test pattern was frequently used in the 1950s and 1960s by local stations as a visual signal to viewers to indicate that there was no programming currently in progress, although this use has greatly declined due to the multitude of programming now available. tetrodeA four-element vacuum tube. The three-element tube, called a triode, was developed by Lee de Forest. This no doubt inspired experimenters to try other configurations. The four-element tube followed, consisting ofa filament, plate, and two grids rather than one. The second grid, the tetrode or screen grid, was positioned between the first grid and the electron-attracting plate (anode). Texas Educational Network TENET. A Texas education communications infrastructure dedicated to fostering educational innovation and excellence among educators and students. TENET developed through the collaboration of the Department of In- formation Resources, the Texas Education Agency, and the University of Texas. TENET provides various resources, including publications, discussion fo- rums, and professional development seminars and facilities. http://www.tenet.edu/tenet-info/main.html TFT See thin film transistor. TFTP See Trivial File Transfer Protocol. TFTP Multicast Option A protocol option for the Trivial File Transfer Protocol (TFTP) to enable multiple clients to concurrently receive the same file through multicast packets to increase network efficiency. TFTP Multicast Option was submitted as an Experimental RFC by A. Emberson in February 1997. See Trivial File Transfer Protocol, RFC 2090. theremin An electronic musical instrument incorpo- rating radio frequency oscillators in which two similar frequencies were combined to provide a lower, human-audible frequency. This was done by combining a reference frequency with a variable frequency. The theremin was played by interposing a hand to vary the capacitance between two projecting elec- trodes, thus controlling the pitch and volume. It was first constructed in 1920 and became popular in the late 1920s. The process of mixing signals of slightly different frequencies is called heterodyning and was incorpo- rated into many radios over the next couple of de- cades. A transistor version of the theremin still exists' and Mystery Science Theater 3000 fans are fa- miliar with its eerie sounds. It was named after its inventor Leon Theremin, who originally called his invention an "retherphone." See heterodyning, Theremin, Leol1'. Theremin, Leon (1896-1993) A Russian engineer and inventor who devised electronic musical instruments, most notably the "retherphone" (theremin) while a student at the University of Petrograd. He traveled to America in 1927 to playa concert, and 2 years later licensed the Radio Corporation of America (RCA) to manufacture a"thereminvox." While in the U.S., Theremin also experimented with multimedia concerts, combining light shows and dance with the theremin music, later returning to do research at the University of Moscow. See theremin. thermal noise Random noise arising from heat generated by the motion of charged particles. Thermal noise in electrical circuits is undesirable if it inter- feres with transmission. thermal circuit breakerAbreaker mechanism that trips when heat generated by excessive current ex- pands the conductor. See circuit breaker. thermion An electrically charged particle (a positive or negative ion) emitted from a heat source. See thermoelectron. thermionic emission The emission of electrically charged particles under the influence of heat. Ther- mionic emissions are characteristic of hot cathode- ray tubes. Cathodes without thermionic emissions are called cold cathodes. thermionic valve See vacuum tube. thermistor An electrical resistor comprising a semiconductor with a high, nonlinear temperature coefficient. The resistance of the semiconductor varies suf- ficiently in relation to the temperature to make it useful in a number of applications. See thermostat. thermocouple, thermaljunctionA device that measures temperature at the junction ofa pair ofjoined wires employing dissimilar materials, with the difference in potential proportional to the temperature, determined by an instrument connected to the other ends of the wires. 927 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary Semiconductor thermocouple assemblies are fabricated by connecting two dissimilar metals and interconnecting the thermocouples in series. Materials with a high thermoelectric coefficient are typically used (e.g., antimony). When the junctions are dissimilar (e.g., different metals), the difference in heat absorption can be used to generate voltage, thus signaling the detection of heat. Treating one of the metals to increase its absorption through chemicals or col- oring may magnify the effect (improve signal-to- noise ratio). See potentiometer; pyroelectric detec- tor; Seebeck, Thomas; thermopile. thermocouple wire A wire used with a thermocouple which is made of iron or particular alloys calibrated to the appropriate specifications. thermodynamics The art and science ofheat-related phenomena, their properties and relationships. thermoelectron An electron (negative thermion) emitted from a heat source. See thermion. thermography Aprinting process in which nondry- ing inks are treated to simulate a raised, engraved surface. After passing through the press, the ink is dusted with a compound which, after the excess is removed, is exposed to heat, causing it to fuse with the ink to form a raised surface. thermopile A component with broadband absorption characteristics suitable for detecting radiation such as infrared light. Thermopile detectors are fabricated from multiple thermocouple devices connected in series. They may be made with wired junctions or film junctions, with film versions generally provid- ing advantages of size, portability, and response times over larger wired assemblies. See photodetector, thermocouple. thermoplastic A material with industrial significance because it can be heated and reshaped and rehardened by cooling. It has various uses including insulating and information recording. Contrast with thermoset. thermoset Aresin or plastic material which can be shaped and cured, but once this has been done, can- not be reshaped and cured again, as with thermoplastic. Contrast with thermoplastic. thermostat 1. Asensing and regulating device trig- gered by temperature which is useful in turning machines on or off, for controlling fire safety devices such as alanns and sprinklers, and for regulating heating and cooling systems. 2. A device which regulates temperature, by measuring it and controlling heating equipment (or heating and cooling equipment) in order to maintain the temperature at the setting selected on the thennostat. This is usually accomplished by triggering the heating circuit when the temperature varies a certain amount below or above the desired setting. Thermostats that can be programmed for specific temperatures at scheduled times during the day are increasingly common. Temperature regulation (cooling) in large supercomputing implementations is important. See thermistor. THF See tremendously high frequency. thin film A very fine layer or combined layers used to enhance or change the properties ofa material. Thin films are typically "grown" in chemical vapor deposi- 928 tion processes. There are many different types of film and their structure depends upon the chemicals used, the properties and combination of the component layers, temperature, and other fabrication parameters. Thin films can be grown with low dielectric constants, making them suitable for use in integrated circuits and as filters (e.g., DWM ONU filters). Magnetic thin films have unusual megnetotransport properties useful for the development of sensing devices and magnetic recording technologies. Thin films can be grown at high temperatures for use in superconductivity research. Thin films have thousands of applications as filters, dielectric mirror surfaces, barrier layers, polarizing layers, and more. Thin films can be deposited on fiber optic filaments to filter a signal or prevent backreflection. Antireflecting coatings for optical lenses in eyeglasses and imaging devices can be made with thin films. Calculators and wristwatches use sili- con thin-film solar chargers. Traditionally, thin film-treated wafers were placed between fiber endfaces to filter the light crossing from one fiber to the next. However, it has been suggested that better performance is possible by stacking between 20 and 150 layers of alternating highllow re- fractive-index films onto a substrate and using this thin film component in place oftreated wafers. See sputtering. See Fiber Optic Probes diagram. thin film transistor TFT. Atechnology used in display devices which creates a correspondence between a transistor and pixel on the screen so that pixels can be independently controlled. Used in color (RGB) active matrix LCD panels. This technology has been applied to portable display projectors and similar devices. Thompson, Joseph John (1856-1940) An English experimenter who investigated electricity and X-rays. He was awarded a Nobel prize in physics in 1906 for gaseous conductivity ofelectricity. Thompson, Ken (1943- )Principal developer, along with Dennis M. Ritchie, of the Unix operating system in 1969. It is quite a distinction considering its widespread use and utility. Unix has since evolved through extensive support by the programming community and exists in a variety of forms, although all bear similar features. Thompson also authored B, which was a predecessor to C. See Unix, UNIX. Thompson, William See Lord Kelvin. Thomson, Elihu (1853-1937) Inventor of one of the first alternating current (AC) generators, in 1878. At the time, the predominant form of power was direct current (DC). This was a significant achievement because it enabled the transmission of much higher volt- ages, necessary to cross some of the distances desired. Improvements to the concept were soon developed by William Stanley. Thomson also experimented, in 1892, with electric arcs. He collaborated with Sebastian de Ferranti and William Stanley in the development of the transformer. thread 1. In piping, a helical indentation used to match and secure separate sections. 2. One of a number of continuing elements, themes, or trains of © 2003 by CRC Press LLC 2110 Fiber Optic Probes and Thin Film Filter Technologies 2120 Figures 27a - 27cfrom a patent developed by M. Wach et al. show different views of a fiber optic light-scattering probe consisting of a tightly aligned multifiber ring sUlTounding a centralfiber. Stepped index silica core/cladding fibers are suitable for this type of device. The centralfiber, insulated by a light-bloc/dngfilm or coating, may be used to deliver light while the surrounding ringfibers detect it or vice versa. Figure 80 illustrates the application of thin- film filtering to a complex contoured suiface (in this case the cone-shapedendface of a fiber filament that is coupled with anotherfiber). Filters such as the one illustratedin Figure 80 can help reduce back reflection at coupledjoints. Index-matching epoxy or gel can be used to fill in the gap betweenfibers. .z!!!jz'- 55 E Figures 55a - 55e illustrate how different configurations are possible for manipulating light through adjoining segments of a multifiberprobe. Various endfacepolishes, angles, and thin film filters make itpossible to use the basic idea in a variety of applications. [Diagrams adaptedfrom USPTO patent #6,416,234, submitted August 2000.J 929 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary thought related to a common forerunner. 3. In programming, a flexible process organization mechanism by which individual processes can use common resources, but continue to operate unimpeded by other threads, if needed, in order to improve program efficiency or to increase simultaneous access to various system or applications resources. Common in object- oriented systems. thread, discussion In online newsgroups, a topic of conversation characterized by the same (or similar) subject line, and theme and direction ofdiscussion. Threads are a very convenient way to follow one line of thought through the myriad opinions discussed in the general context ofa news group. Good newsread- ing software will organize threads into groups and subgroups much the same way computer directories (folders) are organized on the computer operating system. Thus, the user can selectively open and read, or close and ignore, a thread. three finger salute slang A descriptive phrase for rebooting the operating system (without powering down the system) with three designated keys held down simultaneously for MS-DOS/lntel-based IBM- licensed systems (Ctrl-Alt-Delete) and Amigas. throughput Production; output; nonredundant information or items ofrelevance moving through a system. Throughput is used in industrial and computing industries to describe the efficiency ofa system or end-result ofa communication (how much infonnation got through). The measurement of throughput is quite specific to the system and infonnation or objects being trans- ferred, so there are few generalized standards for time intervals or total data against which to compare the throughput (end result). Nevertheless, relative measures of throughput, as compared to another manu- facturer, another type of machine, or when processed in a different manner, can be very useful in tuning a production line system. Relative measures of data throughput in different parts of a network, or over different data protocols or operating systems, simi- larly can be used to improve the configuration and efficiency ofa computer network. TI-99/4 A Texas Instruments home computer introduced early in 1980. It featured 16 Kbytes RAM, sound capabilities, 16-color graphics on a 13-inch color monitor, extended TI BASIC, and cartridge-like solid state program modules for a list price of$1150 U.S. TIA See Telecommunications Industry Association. Till See tone in band. TIC See Token-Ring interface coupler. ticket In telecommunications, a record ofa transaction or paid toll, fare, or fee. The ticket indicates either that the transaction has been confinned and it's OK to bill the client, or that the transaction and bill- ing have both taken place (as in many credit card transactions). Tickets traditionally were on paper, but electronic tickets are becoming prevalent, with online transactions sometimes going directly through to the credit card company from the vendor without any slips or other paper confinnations. tickler In computer applications, a program designed 930 to hibernate until a certain time or until certain events take place, and then become active to remind the user of something timely or important, such as appoint- ments, anniversaries, events, etc. These applications have variously been called ticklers, reminders, and naggers. tickler, electronic In electronics, a feedback or re- generation device consisting of two small coils connected in an electron tube, one to the anode (in series), the other to the grid-circuit. tie n. Fastener, electrical strap, bundler. Astrip, usually ofplastic or Velcro™, to hold wires away from one another, bundle them together, or fix them in place, sometimes to a post or other secure structure. tie line I. In power systems, transmission lines that connect neighboring systems. 2. In telecommunications, a line for directly tying two telephone or telegraph connections together without going through a public switching center, often called a "dedicated" line. For example, the President might have a tie line connected directly to top advisors that doesn't go through any outside switches or connections, to en- sure security, reliability, and speed for the connection. In the days before telephone switching centers and central offices connected local telephone subscribers, tie lines were common. For example, in the 1800s, a dozen telephone or telegraph tie lines might be wired out ofa single office to connect it with other local businesses. The streets were often cluttered with hundreds of lines running between windows and buildings and the utility poles holding the lines were com- plexly wired and difficult to maintain. Tie lines are still used for a variety ofsecurity and business-related purposes. They are especially useful in office complexes composed of several buildings that have a large volume of calls between the buildings. A tie line may be set up to connect directly simply by lifting the handset or pushing a button, as in a hot line. A tie tmnk connects to telephone switching systems such as two private branch exchange (PBX) systems and may require dialing access code prefixes reserved for that purpose on aparticular system or the system may be locally automated to inter- pret an extension number to be translated into a tie line call. With the evolution of voice over digital data networks, the concept of tie lines has been adapted to computer networking. Access concentrators can be used to consolidate separate voice and data lines used for communications within a company into a single network and voice over network communications can then replace traditional telephone tie lines. Thus, ex- isting Frame Relay links used for data, for example, could also be used for voice communications, remov- ing the need for dedicated phone lines. tie trunkA telephone (or telegraph) line directly connecting private branch exchanges (PBXs). See tie line. tie line control system In power distribution, a system for administering the amount of electrical energy purchased by asubscriber (usually an industrial complex) from a utility company. © 2003 by CRC Press LLC tie wrap A plastic, fabric, jute or other type of tie material used for holding together a bundle of cables for ease of placement or movement as a unit. Plastic tie wraps sometimes have a hook mechanism that catches and holds the tie when it is cinched tight. Velcro brand tie wraps are easy to unwrap and read- just, if needed. TIES 1. Telecom/Information Equipment and Ser- vices. A government-to-government program which provides u.s. and Russian support for the expansion of international commerce in high technology. This is a subgroup under the U.S Russia Business Devel- opment Committee (BDC). 2. See Telecom Informa- tion Exchange Services. TIFF Tag Image File Format. A very widely used platform- and application-independent, lossless, color, raster image file format that encodes the data as strips or bands. The TIFF format is used in faxes, image processing programs, scanned files, and many graphics creation programs. It is well supported by service bureaus and the printing and graphics design industries. Files are often identified by the. TIF or . tiff file extensions. Creation of the format took into consideration the needs of the desktop-publishing industry and other related graphics applications, with the goal of making image information broadly interchangeable. TIFF was created to be extensible so that it may accom- modate future needs. TIFF has gone through a number of major revisions but, in general, fields are identified with unique tags so that various applications can elect to include or exclude particular fields depending upon their needs and capabilities. The core fields comprise Baseline TIFF. A TIFF file consists of three main parts: an image file header, a directory of fields, and the file data. Descrip- tions and definitions of baseline and extended fields are documented in the TIFF Technical Notes (TTN). An adaptation called TIFF-FX has been defined for facsimile applications. See facsimile, scanner, TIFF-FX, TWAIN. TIFF-FX A subset of TIFF adapted to generating documents with minimal, lossless grayscale and color attributes for use as facsimile messages. The format uses some of the Baseline TIFF fields in addition to extensions pertinent to facsimile transmissions. Since the format can be used over both traditional and host- based transmissions media, TIFF -FX is suitable as a downwardly compatible, standardized facsimile format for data network communications. Profile S (TIFF-S) is a subset of TIFF, related to TIFF-FX, that defines a minimal black-and-white format to enable fast easy transmission of simple facsimile documents. Profile F (TIFF-F) is a slightly extended version of Profile S that is still restricted to black-and-white transmissions. TIFF -F was originally introduced by Joe Campbell and a group of fax experts; then, in 1998, with increased interest in Internet faxing con- nectivity, it was formally described by the IETF In- ternet Fax Working Group. In essence, the image data to be faxed are compressed and inserted into a TIFF -FX file with the informa- tional fields encoded with data specific to the image. The byte order is from least to most significant (an important detail, since the full TIFF specification can be set to either big- or little-endian and conversion may be necessary before transmitting as a TIFF-FX variant). While the full TIFF specification is somewhat flexible in terms of the ordering and structure offields, TIFF-FX recommends that multiple image file directories (IFDs) be organized as a linked list. The MIME Content Type for these files is image/tiff. The Application parameter is TIFF -REG (optional). See IFax device, image file directory, TIFF, RFC 2301, RFC 2306. TIIAP See Telecommunications and Information Infrastructure Assistance. tiling 1. In printing, a technique for printing a large image on pieces of paper that are small, relative to the size of the image. Commonly used for billboards, banners, and wall-sized murals. Most computer printers have options for tiling, in order to print large images on letter sized paper. 2. In digital image display, a visual artifact common to heavily compressed images which causes a blocky, mosaic-like appearance to otherwise smooth lines and transitions. See DCT, JPEG. tilt locking A method of frequency-locking a laser beam to an optical cavity by misaligning the laser with respect to the resonating cavity such that a non- resonant spatial mode is produced. An assessment of the interference between the carrier and the spatial mode yields a quantum noise-limited frequency dis- criminator. Tilt locking uses interference between the carrier field and a directly reflected phase reference signal (e.g., a non-resonant higher-order spatial mode). Thus, the encoding/decoding of spatial modes is optical rather than electro-optic. Interference between the two spatial modes may be assessed by detecting the reflected beam on a two- element split photodiode such that each lobe of a transverse electromagnetic (TEM) mode is incident to a separate side of the photodiode. The error signal is derived by subtracting the photocurrents from each side of the photodiode. Tilt locking may be useful for frequency stabilization, conversion, or interferometric gravitational wave detection. TIMA See Interactive Media Alliance, The. TIME Time Protocol. A network date/time protocol submitted as an RFC in May 1983 by Postel and Harrenstien. TIME provides a site-independent, machine-readable date and time. The Time service provides the time in seconds since midnight January 1, 1900. This is useful for systems that do not have a built-in date/time clock and for systems that need to be coordinated to preserve or aid data integrity or process administration. TIME can be accessed through port 37 over Transmission Control Protocol (TCP) or over the User Datagram Protocol (UDP). See RFC 868. time code A system of encoding timing information on a recording medium, usually along with the information that is being stored. This technique is 931 © 2003 by CRC Press LLC . Nikola Tesla. Tesla coil An air-core transfonner for creating high- voltage discharges at very high frequencies. Tesla, Nikola (185 6-1 943 ) An engineer and inventor born in Smiljan Lika (Austria-Hungary) who developed the alternating. designated keys held down simultaneously for MS-DOS/lntel-based IBM- licensed systems (Ctrl-Alt-Delete) and Amigas. throughput Production; output; nonredundant information or items ofrelevance moving through a system. Throughput is used in industrial and computing industries to describe the efficiency. Fiber Optics Illustrated Dictionary device-supporting software applications. TAPI can be used to create call control software for telephony devices for computerizing

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