Fiber Optics Illustrated Dictionary - Part 46 ppsx

Fiber Optics Illustrated Dictionary BEe See Header Error Control. hecto- (symb. - h) ASysteme Internationale (SI) unit prefix for 100 or 10 2 • Heisenberg uncertainty principle Proposed by W. Heisenberg in 1927, the uncertainty principle has since become a fundamental principle of physics. (Heisenberg formulated a model of the structure of an atom in the 1930s which has held up well over time.) In studying movement of electronics, Heisen- berg proposed mathematically that it is not possible to determine precisely both theposition and the ve- locity ofamaterial particle at the same time. The uncertainty increases as the size of the particle de- creases. Many researchers have generalized this principle and restated it in various broader contexts, but most commonly it is brought up when describing the results of quantum experimental results. It is said that these are determined in part by the point of view and methods of the researcher. For example, iflight is studied as a particle phenomenon, it appears to behave as a particle phenomenon. If it is studied as a wave phenomenon, it appears to behave as a wave phenomenon, at least as far as the observers and measuring instruments are concerned. In other words, attempts to pin down precisely the location of an electron obscures its energy level, and vice versa, thus challenging the absolute nature of the world suggested by classical physics. Heisenberg, Werner (1901-1976)A German physicist responsible for deriving a theory of atomic structure and proposing the uncertainty principle in 1927, which has since become widely associated with his name. Heisenberg built on the work of previous physicists and mathematicians, including Hermann Weyl. For his contributions, he was awarded a Nobel prize in 1932. In the 1940s, he acted as the director to the Kaiser Wilhelm Institute for Physics. Near the end of the second World War, Heisenberg was captured by American troops and taken to Britain. When he returned to Germany, he helped found the facility that became the Max Planck Institute for Physics. Dur- ing his later years, he was working to formulate a unified field theory of elementary particles. helical antenna, helical beam antenna An antenna designed with a helical (spiral) conductor wound in acircularorpolygonal shape. The axis of the helix is usually mounted parallel to the ground. The circum- ference size of the helix in relation to one wavelength affects the angle of radiation. heliochrome [sun color] An older word for a color photograph, that is, one photographed in color as compared to one photographed in grayscale and tinted by hand using oil pigments. Color photography was not widespread until the 1960s. heliograph [sun writing] Avisual signaling system employing light signals, which was established around 1865 by H. C. Mance. The heliograph took advantage of the production of glass mirrors in the 1840s to increase the distance over which sunlight could be reflected. It used adjustable mirrors mounted 442 on tripods and could convey messages in Morse code in daylight up to about 100 miles. In the United States, leafshutter versions of the heliograph were developed to interrupt the light signals instead of directing the angle of the mirror as was done with the earlier British heliographs. Most visual signaling systems were superseded by wire telegraphy, but the heliograph survived for several decades, probablybecause itused Morse, which was then becoming widely accepted, and because it required no external power source. Since heliograph signals and microwave transmissions share some of the same line-of-sight characteristics, heliographs were resurrected to research the placement of microwave relay stations, and the heliograph is still sometimes used for military communications in regional conflicts where other means of communication are scarce. heliography [sun recording] A type of early photo- graphic process, also called sun drawing, which was pioneered by French inventor, Joseph Nicephore Niepce, in 1816. Originally Niepce used a camera similar to the camera obscura to imprint temporarily an image of light onto paper coated with silver chlo- ride. It was several years before he developed the process to the point where the image could be perma- nently preserved. See Daguerre, Louis; photography. helionics The science of the conversion of solar energy to electrical energy. heliotrope [sun turning] An early surveying instrument that employed the sun's rays to triangulate from mountain prominences. This instrument was developed and used for the highly successful engineering feat of surveying India in the 1800s. It may also have been used for signaling. It was later adapted as a heliograph by H. C. Mance in Britain and used for many decades for daylight signaling of military communications up to 100 miles. helium-neon laser, He-Ne laserA type of low power atomic gas laser, now commonly used in light shows and monitors. This laser produces warm color tones in the red-orange range but gas lasers with different gas mixes may also produce radiant energy in the blue, infrared, and ultraviolet ranges. Until semiconductor laser diodes became prevalent, this was the most common commercial laser. The helium-neon laser was described in 1959 and developed and demonstrated in December 1960 by A. Javan, not long after Townes and Schawlow had developed an optically pumped laser. The gas laser worked on a different principle from the Townes laser, converting electricity to a pure, continuous light beam by passing an electrical current through two inert gases. The light is then amplified by reflecting it between two mirrors at either ends of the laser device. The device was immediately tried for telecommunications. The day after the laser was first successfully tested, lavan's lab workers successfully used it to transmit a telephone conversation by converting voice vibrations to light pulses that were detected across the room by a sensor. In essence, the researchers had © 2003 by CRC Press LLC realized the dream of A. Graham Bell when he first invented his Photophone. Despite Bell's great excite- ment about his invention and his vision of its poten- tial, he never saw widespread commercial use of the device due to the difficulty of harnessing a consis- tent, coherent, sufficiently powerful synthetic source of light. Javan's invention, with the contributions of W. Bennett and D. Heriott, made the missing piece of technology available, a technology that since has been applied to many technologies in addition to optical communications. See carbon dioxide laser, laser history, Photophone. helium recovery In fiber optics preform fabrication and fiber pulling, helium is commonly used in many aspects of the manufacture. Contaminants are introduced into the helium at different steps along the way and one-time use of the helium is wasteful. For this reason, manufacturers such as Praxair have developed draw stations that enable the helium to be recovered, cleaned, and reused at points where lower purity helium is effective in the fiber fabrication process. See vapor deposition. helix, helical shape A spiral, continuous coil. Many types of springs employ a helix shape. In radio transmissions, a horizontal- and vertical-polarized wave combined as circular polarization, is transmitted in a helical fashion so that it can be picked up by both horizontal- and vertical-polarized antennas. Hellman-MerkleA trapdoor knapsack cryptography system principally designed by Ralph Merkle, with input from Martin Hellman, who was a collaborator with Whitfield Diffie on another cryptography system. The Hellman-Merkle scheme was found to be breakable and was reported as such in 1982. See Diffie-Hellman. Hello Protocol In Open Shortest Path First Protocol (OSPF), a mechanism for establishing and maintain- ing neighbor relationships. It may also be used for dynamic neighbor discovery on broadcast networks. The Hello Protocol elects the designated router on networks with at least two attached routers. Helmholtz, Hermann von (1821-1894) A German physicist who expressed relationships between fundamental phenomena, such as heat and light, by treat- ing them as manifestations of a single force, a concept we now associate with energy. Helmholtz further sought to generalize the concepts put forth by James Joule. Helmholtz encouraged the work of Heinrich Hertz, who became one of the true pioneers in the discovery of the physical existence and properties of radiant energy (radio waves). The Hermann Helmholtz Association of German Research Centers (HGF) continues Hermann Helmholtz's tradition by supporting research on sci- entific' technological, and biomedical topics through a consortium of centers. See Hertz, Heinrich. http://www.helmholtz.de/ henry A unit of inductance in a circuit (self-inductance or mutual inductance of two circuits) such that the electromotive force of one volt is produced when the inducing current varies at the rate of one ampere per second. Named after Joseph Henry. Henry Ford Museum & Greenfield Village The largest indoor/outdoor museum complex in the U.S. providing authentic historical artifacts and educational activities. Among other fields, it features ex- hibits on the history oftransportation and communication, including Thomas Edison's Menlo Park Labo- ratory. The Henry Ford Museum is located in Dearborn, MI. http://www.hfmgv.org/ Henry magnet Joseph Henry experimented with electromagnets in the 1820s and 1830s, creating a number of different configurations. The Henry magnet is a type of experimental magnet, powered by a 9uan- tity battery, that he called a "quantity magnet.' The horseshoe-shaped magnet was wrapped with several layers of insulated wire connected in parallel. Henry also experimented with a magnet powered by an in- tensity magnet that could power devices at a distance. Henry based his magnets on his studies of electro- magnetism and the work of previous magnet researchers. As an improvement to earlier attempts, Henry's powerful quantity magnet could transform enough electrical energy into mechanical energy to be useful. Thus, Henry himself experimented with the practicability of the electromagnet for powering ru- dimentary telegraphic systems and he communicated his ideas to many eminent inventors who built upon his ideas and put them into commercial use. See Henry, Joseph. Henry, Joseph (1797-1878) A gifted American physicist who began experimenting with magnetism in 1927, Henry produced a high-power industrial electromagnet in 1931. He incorporated his various discoveries into many practical devices, including telegraphs, relays, and electromagnetic motors. Joseph Henry actively encouraged and assisted other researchers, in addition to carrying on experiments himself, a fact not always publicly acknowledged by the many inventors who benefited from his generos- ity. Morse, Wheatstone, and many other inventors were assisted by the information communicated on both sides of the Atlantic by Joseph Henry. Joseph Henry advocated a science and research fo- cus for the great Smithson endowment that eventu- ally became the Smithsonian Institution, and he was appointed its first Secretary in 1878. He also co- founded the U.S. National Academy of Sciences. The henry, a unit of inductance, is named after him (1891 ). See Henry magnet. HEP high energy physics. HEPIC High Energy Physics Information Center. An informational link among worldwide HEP resources to assist researchers in locating sources and resources. One of the services is a global search facility for searching across HEP Web servers that is updated about once per month. HEPIC is funded by the U.S. Department of Energy Division of High Energy Phys- ics. It is supported by the Fermilab Computing Divi- sion. http://www.hep.net/ hermetic seal A seal that is airtight and leaktight, and is sometimes used to preserve a gaseous environment, inside a sealed device, that is different from the gaseous composition outside. Hermetic seals are generally 443 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary intended to be permanent. Hermetic sealing is used in a variety of industries, including electronics and electrical installation. Herrold, Charles D. "Doc" (1875-1948) An Ameri- can inventor and educator, Herrold is one of the first experimenters to transmit voice over distance. He did this through Station FN in the Garden City Bank Building, beginning in 1909. He became known by amateurs for his station SJN broadcasts. When Lee de Forest's transmitter failed, Herrold provided music and news to the 1915 World's Fair about 50 miles away. He had other interests as well and was awarded a patent for the Arc Phone in 1915. In 1922, he was broadcasting at 833 kHz through station KQW from San Jose, California. See KDKA, radio history. hertz Hz. A unit of frequency expressed as one cycle per second, named after H. R. Hertz. Hertz antennaAn antenna system that uses distributed capacitance to determine its resonant frequency, which, in turn, is influenced by the physical length of the antenna. This antenna is used in applications where ground reflection is not a necessary factor for its functioning. Unlike Marconi antennas, a Hertz antenna is not dependent on the ground or the body ofa vehicle as a resonant conductor. This type of antenna is common for television and frequency modulated (PM) broadcasts. See antenna, Marconi antenna. Hertz, Heinrich Rudolf (1857-1894) A German physicist who demonstrated important properties of electromagnetic radiation, discoveries that later experimenters applied to facilitate the transmission of radiant energy. By 1887, the physical existence of radio waves had been established. He also contrib- uted a streamlined reformulation of Maxwell 's equa- tions that was widely accepted The Hertz antenna and hertz unit of frequency are named after him. See Helmholtz, Hermann. Hertzian waves Electromagnetic waves in the range from about 10kHz to 30,000 GHz. James Clerk-Max- well had proposed that rapidly vibrating electric cur- rents would emit waves, and Hertz experimentally confirmed this proposition. The waves are named after him. See radio wave. Hertzstark, Curt (1902-1988) A Viennese inventor who devised handheld calculator technology that was patented in the late 1930s, but wasn't produced until the mid-1940s. Its accuracy apparently rivaled many modem devices. See Zuse, Konrad. hetero- Prefix for different, other, not usual. It is often used to describe a mix or variety. heterodyne l'. t. To produce a beat between two frequencies, which could be of various kinds: audio, optical, or radio. In radio heterodyning, an electrical beat can be selectively created and controlled by heterodyning a received signal current with a steady introduced current. The frequency thus formed can then be further processed by amplification, as in repeater stations or filtering. See beat, beat frequency, heterodyne repeater. heterodyne repeater A frequency repeating system commonly used in the propagation of radio signals that uses heterodyning to create an intermediate fre- 444 quency through demodulation, which is amplified, modulated, and retransmitted over the next leg. This technique is less subject to distortion and loss through modulation/demodulation than baseband repeating. Heterodyne repeating may be used in conjunction with baseband repeating if the signal is traveling through several legs and some channels need to be dropped off at the baseband stations. See Armstrong, Edwin H.; baseband repeater. heterojunction In semiconductors, a common dynamic junction, usually of p-n type, in which the materials on either side of the junction are substantially different. See homojunction, p-n junction. beterojunction laserA semiconductor laser component that has been designed to reduce losses resulting from light diffraction within the optical reflective cavity by engineering the p-n junction width and the index of refraction of the cavity. By replacing some of the materials in the junction so that the junction is not homogenous, the index of refraction can be reduced to retain more light within the reflective optical cavity, reducing losses. This is more efficient than the traditional homojunction laser diode. It is also possible to retain the materials in the junction but replace the materials in the p-n regions, but this may be so effective in confining the light energy within the cavity that it may damage the component. There is a happy medium between laser efficiency in terms of producing photons, and confinement in- efficiency to allow the light to escape from the cavity before it damages the component itself. Larger optical cavities with different layers are one strategy for increasing efficiency without destroying the component from within. See homojunction laser, semiconductor laser. heuristic problem-solvingAn exploratory problem- solving strategy that employs successive trial and evaluation of the results in such a way that the results can be used in the subsequent trials to "home in" on a solution. Heuristics are often used in artifi- cial intelligence programs where the result is not known in advance, and where brute force methods are inappropriate due to the large number of possible choices and outcomes. Chess playing programs, for example, use a combination of heuristics to handle novel situations and databases of known moves and strategies. Heuristics are common in robotics, where a robot may have to interact with an unknown or un- predictable environment. See algorithmic problem- solving, brute force problem-solving, neural network. Hewlett, William R. (1913-2001) An American inventor and business tycoon, Bill Hewlett was a founder of Hewlett-Packard along with David Pack- ard. An instrumentation engineer, Bill Hewlett invented an audio oscillator which was used by Disney Studios in the production of Fantasia. He was a past president and director of the Institute of Radio Engi- neers (now the IEEE), an honorary trustee of the Cali- fornia Academy of Sciences, and held many other professional and civic leadership positions. A promi- nent Silicon Valley pioneer and philanthropist, Hewlett was known personally by many of the promi- © 2003 by CRC Press LLC nent personalities in the emerging small-scale computer revolution. Hewlett-Packard Company HP. In 1938, Dave Packard and Bill Hewlett, both graduates ofStanford University, began working out of a garage in Palo Alto, California. Their first product, an audio oscillator resulting from Bill Hewlett's research of nega- tive feedback, was designed to test sound equipment. It was a new type of design, utilizing an incandes- cent bulb to provide variable resistance. This product was followed by a harmonic wave analyzer. Their first big client was Walt Disney Studios. Disney or- dered eight oscillators for the production of the movie Fantasia. From these beginnings, Hewlett and Packard formed apartnership on New Year's Day in 1939; a toss ofa coin decided the company name. HP was officially incorporated in 1947. Since then Hewlett-Packard has become a well- known supplier ofcalculators, computers, software, printers, and other accessories to the computing industry. The firm is known for good quality products (their calculators have been known to survive the "drop-kick" test) and a corporate culture that seems to produce happier employees than many other companies in the industry. In 1996, David Packard, successful businessman and philanthropist, died at the age of83, followed by Wil- liam R. Hewlett, in 200 I. HF, hf I. hands free. 2. See high fidelity. 3. See high frequency. HFC See Hybrid Fiber Coax. Hi band A video standard developed by the Sony Corporation in 1989 to support 500 lines of resolution on a TV screen. This resolution falls between NTSC and High Definition Television (HDTV). See Hi8mm. Hi-Band IRAn infrared-remote technology used for remotely controlling a variety of consumer devices such as car stereo systems. Hi-OVIS Highly Interactive Optical Visual Infor- mation System. AJapanese cable television delivery system employing different types of cable for different parts of the service network. Hi8mm A high-quality, analog, tape-based compact video system developed by Sony, Hi8mm became especially popular in the late 1990s. Hi8mm has many benefits, including small cassettes, only 2.5 x 3.6 in. for two hours of recording/playback at regular speeds. The long play time gives Hi8mm an advantage over S- VHSc (compact S- VHS). The small cassette format enables video camcorders and playback decks to be compact as well. The sound quality is excellent, compared to older technologies, and features stereo sound, though not all Hi8mm camcorders have two microphones. The video resolution of 400 lines and signal-to-noise ratio of 40 to 50 dB are equal to S- VHS and far superior to 240-line 35 to 45 dB VHS formats. F or analog recording, Hi8mm is likely to remain a viable, favorite format for a while longer, but digital camcorders are catching on quickly and will probably supersede Hi8 as it offers 500+ lines ofresolu- tion, CD-quality sound, and digital nonlinear editing capabilities without conversion. HiFD A 3.5-in. floppy diskette system developed jointly by Sony and Fujifilm, introduced in 1997. HiFDs are double-sided, with a magnetic storage capacity of up to 200 megabytes. hibernation A resting state, one of low energy usage and activity. A term often applied to the sleep mode on portable computers, which powers down during times of low activity to extend battery life. Hi- bernation has also long been applied to software applications that lie dormant waiting for some event causing them to become active, or to run at a higher priority level. The event that rouses the program can be many things, including the time of day, input from an interface device such as the mouse or keyboard, activity of users, or data from another program. See sleep mode. hickey A spot, halo, or other imperfection in the ink or toner of a printout caused by undesired extrane- ous particles, dried ink, etc. Hicks, John Wilbur"Will"An American physicist and inventor, Hicks was one of the many optical researchers who worked at one time at American Opti- cal. After leaving the company to cofound Mosaic Fabrications, Inc., with P. Kiritsy, in the late 1950s, he was approached by John Johnson about the po- tential of fiber optic filaments for lengthening alight path through fiber optics rather than through longer tubes. Hicks succeeded in pulling optical fibers, in making fiber-based vacuum assemblies and, in col- laboration with B. Gardner, in developing fiber optic faceplates (arrays of aligned bundles of fibers) which were all significant innovations at the time. He maintained close ties with American Optical (AO). In 1961, he worked with Elias Snitzer at AO to dem- onstrate the dielectric waveguide properties of optical fibers so small, they would carry light in a single wavelength mode. Hicks' interest in fiber optics hasn't waned. Many of his visions of fiber have come true and he continues to promote an optimistic viewpoint ofwidespread data-over-fiber availability. He has been involved with a number of companies and has continued to ten- der proposals for fiber-based technologies through American Micro-Optical, Inc. See Johnson, John; Kawakami, Shojiro; Kao, Charles K.; Snitzer, Elias. hierarchyA group of items, people, or processes or- dered according to some type of structure or rank, usually top-down or bottom-up. Ahierarchy may be nested. Hierarchies are generally designed to facilitate the location of some item within the hierarchy or to simplify the understanding of its contents. People in an organization, and files or discussion groups on a computer or network system are often assigned positions within hierarchies. High Altitude Long Endurance HALE. Pilotless platform crafts intended to float above commercial aircraft at about 20,000 meters, which have been proposed as two-way communications links capable of carrying phased antenna arrays. The HALE systems 445 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary are experimental and a number ofsystems from helium to jet-engine propulsion have been proposed. The cost relative to traditional satellites makes HALE transceivers attractive to developers. Actual deploy- ment of these systems has to take normal aircraft safety and traffic patterns into consideration. high ASCII There really isn't such a thing, since ASCII defines the lower 128 characters ~O to 127), but "high ASCII" and "extended ASCII' are often used to describe characters above decimal values of 127, which are different on each system. See extended ASCII. high bandwidth slang Descriptive of a person with high level, wide-ranging intellectual abilities. The author first heard this phrase in the early 1980s among hard-core programming friends in computer users groups and suspects it originated spontaneously in a number of places and subsequently spread through networks such as Fidonet. Other computer-related terms that have been applied metaphorically to human intelligence include high baud rate, high clock speed, and multitasking. high bit-rate Digital Subscriber Line HDSL. A digital transmissions technology that can transmit DS-l or E-l transmissions for longer distances over the traditional, unshielded twisted-pair wire that is widely installed in telephone circuitry. HOSL is typically used in digital loop carrier systems, private branch networks, and cellular antenna systems. Un- like earlier technologies, HDSL transmits over mul- tiple lines without repeaters and uses techniques to pack more information in less bandwidth. It provides rates up to 1.544 Mbps over DS-l or 2.048 Mbps over E1in the 80 to 240 kHz bandwidth range. See Digi- tal Subscriber Line, DS High Definition Television HDTV. In 1987, the F ed- eral Communications Commission (FCC) acknowledged that the NTSC television was out of date and formed an Advisory Committee on Advanced Tele- vision SeIVice (ACATS) to recommend a revised television standard for the U.S. Most of the improved systems proposed to the FCC were analog or hybrid analog/digital. The FCC stated a preference for a si- mulcast HDTV system and identified four digital systems. These were extensively analyzed, leading to an ACATS recommendation that digital HDTV should be adopted. In 1993 an alliance was formed in cooperation with ACATS to create an HDTV system, re- leasing specifications in 1994. high Earth orbit HEO. An orbiting region around the Earth into which certain types ofcommunications satellites are launched. There are advantages and disadvantages to high orbits. The main advantage is that it takes fewer satellites to provide global coverage. Disadvantages include the higher cost of launching, the higher amplification needed for signals to travel the greater distances, and the effects of radiation. The lifespans of high-orbit satellites tend to be around twelve to fifteen years. Most high-orbit satellites travel at about 20,000 to 40,000 kilometers outside earth. High Earth orbit satellites are typically used for geostationary satellites such as the u.s. Global 446 Positioning System (GPS). See low Earth orbit, Glo- bal Positioning System, medium Earth orbit. high fidelity Aplayback system that reproduces the original so well that it is indistinguishable, or almost indistinguishable, from the original source. This quality is often accomplished through fast transmission and wide bandwidths. In audio systems, high fidelity is frequently abbreviated hi-fl. high frequency A signal frequency defined as the range from 3 to 30 MHz. High Level Data Link Control HDLC. An lTU-T standard bit-orienteddata link layer communications protocol originally developed by ISO for managing synchronous serial transmissions over a link connection. In HDLC there are separate bit patterns for control and data representation. high level language Acomputer programming language at the user level, designed to be as close to a natural language as possible and generalizable to a variety of platforms. FORTRAN, BASIC, and co- BOL are probably the best-known and most widely used high level languages. High level languages are often interpreted, but may be compiled for the spe- cific platforms on which they will be running. As languages become closer to machine level, they also tend to be more symbolic and, thus, more difficult to read and write. They also increase in platform-depen- dency. For contrast, see assembly language, low level language, machine language. high pass filter A filter designed so it doesn't pass waves below a specified cutoff frequency (greater than zero), and the transmission band extends upward indefinitely from that cutoff point. See low pass filter. High Performance Computing Act An act of the U.S. Congress which was passed in 1991 to facilitate and promote the development and evolution of interconnected computer networks serving educational institutions, research laboratories, and industry. High Sierra standard A compact disc standard introduced in 1986 by the High Sierra Group (named after the hotel and casino at which the group met). It was subsequently adopted by ECMA (ECMA-119) and ISO (ISO 9660) and released with slight revi- sions. See ISO 9660. High Speed Data Unit HSDU. Aphysical data communications device to provide a high-speed data channel together with control signals from, for example, a serial connection. HSDU may be software configurable and may operate in synchronous or asynchronous modes or both. High SpeedInternetAccessA summary of infonna- tion published about high speed Internetworking, published monthly by Information Gatekeepers, Inc. high speed networkingThis is arelative phrase and will change as the technology advances but, in the mid-1990s, high speed networking was generally considered to be around or over 100 Mbps. Examples of high speed networktechnologies include asynchronous transfer mode (ATM), Fast Ethernet, and Fiber Distributed Data Interface (FOOl). High Speed Technology HST. A U.S. Robotics pro- prietary, high-speed, full duplex signaling and error © 2003 by CRC Press LLC control transmission protocol. U.S. Robotics manu- factures modems complying with this protocol and some dual-standard modems that are both HST and V.32 bis capable. See Microcom Networking Proto- col, modem, V Series Recommendations. High Speed Token-Ring HSTR. An enhanced commercial Token-Ring technology developed by Inter- national Business Machines (ffiM). HSTR can run Token-Ring and Ethernet on one medium, support source routing through data packet headers, and was based on existing standards, including Fibre Chan- nel. Aimed at a market similar to Ethernet, HSTR appears to be primarily supported by those upgrad- ing legacy Token-Ring systems. See Token-Ring. high usage groups In the telephone industry, high usage groups are trunks between main switching of- fices that are established as priority routes to handle the majority of transmissions. High usage trunk groups are intended to hand off overflow traffic to alternate trunks. See erlang. high-threshold logic HTL. A concept used in physics and electronics especially with regard to computer circuit designs. Voltage thresholds are voltage levels at which more or less voltage may have no further effect or at which more or less voltage (at the high or low thresholds, respectively) could damage a system or render it inoperable. They are also points at which state changes may occur due to unconditioned or noisy signals. In transistor-based devices, the threshold voltage is related to performance levels and is often used to control the characteristics and opera- tion ofa system. Conventionally, on portable devices, lowered power is associated with degraded performance and power leakage. However, the use of high- threshold transistors is seen as one means to extend battery life on low-power devices, such as cellular phones, while in standby power mode without ad- versely affecting performance. High-Density Bipolar 3 See HDB3. High-performance Network Forum HNF. Devel- opers and promoters of the HIPPI GSN standards. European High-performance Network Forum (EHUG) works in cooperation with HNF and coor- dinates an annual network technical symposium. http://www.hnt:org/ high-resolution direct core monitoring HDCM. A commercial software imaging process for fiber optic fusion splicing systems such as the Micro-Core™ Alignment Fusion Splicer. It facilitates core alignment prior to splicing and splice loss estimates after splicing. highllow tariffA charge that is selectively made according to a type or level of service. For example, some Internet Service Providers (ISPs) charge different rates for connection time depending upon the speed at which the subscriber's modem connects. A bulletin board service (BBS) may quote two levels of service depending upon whether or not the user wants to access the games sections. In phone services, two prices may be quoted for a subscriber call, one cost per minute over high density trunks and a different cost per minute over low density trunks. HIPERLAN high-performance radio local area network. A European standard for local area networks (LAN s) that are interconnected through radio frequency transmissions rather than through wires. Un- like North American radio-based LANs, that are largely based on sharing unlicensed 900-MHz and 2.4-GHz spectrums, HIPERLAN was allocated dedicated spectrums in the 5.15- to 5.30- and 17.1- to 17.3-GHz frequency regions by CEPT, in 1992. A draft standard was developed by ETSI and presented as a functional specification in 1995. The availability of dedicated bandwidth increases the probability of reliable service with less chance of outside interference. See air interface, local area wireless network. HIPPI High Performance Parallel Interface. HIPPI is a point-to-point high speed data transfer technology created at Los Alamos in the 1980s. HIPPI oper- ates over twisted-pair copper cable for distances up to 25 to 50 meters (longer with cascaded switches) and distances up to 300 meters, or 10 kilometers over multimode or single-mode fiber cables. HIPPI was originally developed for supercomputing applications but is starting to be adapted to other en- vironments with the dramatic drop in price of the technology, particularly the switches. Transmission speeds include 800 Mbps and 1.6 Gbps (simplex or duplex). HIPPI can be employed with SaNEr over distances and over satellite transmission links. HIPPI is an ANSI standard with a series of documents spell- ing out the standard and its various switching and encapsulation characteristics. See HIPPI-6400. HIPPI-6400, SuperIDPPI High Performance Par- allel Interface. Officially it is now known as Giga- byte System Network (GSN). A very high bandwidth, low latency network transmission technology which offers gigabytes-per-second transfer rates, much faster than the capacity of Gigabit Ethernet, ATM, or Fibre Channel. Based on the HIPPI standard, but with enhancements in error correction and lower latency rates, HIPPI-6400 uses a fixed-length cell of32 bytes. Transfer rates that are as fast as, or faster than, the internal workings of an individual computer on a network will change computing in a significant way. With this development, the network is no longer a bottleneck and individual computers attached to the network can theoretically function as individual parts of the same organism, that is, as a massively parallel computing system. Fast transfer rates with high bandwidth also make it easy to support a diverse variety of protocols, providing flexibility. SuperHIPPI can support applications like uncompressed digital movies and HDTV signals. See HIPPI, Scalable Coherent In- terface. Hirschowitz, Basil Isaac (1925- )A South African physician and educator who traveled first to the U.K., then to the U.S. where he became a professor ofmedi- cine. Hirschowitz visited Hopkins and Kapany in London at the time they were conducting pioneer research on the use of fiber optics for medical viewing instruments, in 1954. Along with C. Wilbur Peters, he undertook aproject to develop a flexible fiber optic endoscope, hiring Larry Curtiss to assist in the work. The resulting instrument aligned the optical 447 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary fibers by embedding them in a glass matrix with a low refractive index to facilitate total internal reflection. The instrument was first used with a patient in 1957. The Hirschowitz endoscope is now in the Smithsonian Institution collection. See Kapany, N; Hopkins, H. Historic Speedwell Located in New Jersey, this museum features telegraph history through the daily life of the Vail family and their association with Samuel Morse. Morse had a close association with the Vail family who provided space, materials, and expertise to assist him in fabricating the inventions for which he is known. The Vail family is also known for the great success bf AT &1. See Vail, Alfred; Vail, Theo- dore. hits I. A quantitative expression of the number of system or application accesses ofa specified type within a specified time period. 2. The number of attempts of illegal entry to a system within a specified time. This information is used to gauge security needs and adjust procedures, if necessary. 3. The number of successful accesses ofa database or a Web site. HNF See High-performance Network Forum. HNS See Hughes Network Systems. HOBIS Hotel Billing Information System. Hockham, Gearge A. Along with Charles K. Kao, Hockham authored "Dielectric-Fiber Surface Waveguides for Optical Frequencies" in Proc. IEEE (1966). Together they promoted the concept of re- moving impurities from optical transmission glass to reduce loss and increase transmission, an idea that made fiber links apractical reality. Hodgson, James (1672-1755) A British mathema- tician and lecturer, Hodgson was evangelizing scien- tific achievements at an important time in history when many significant historical figures, including Isaac Newton, Defoe, Hauksbee, and Boyle, were in- fluencing the future of science and trade. Hodgson had been an assistant to the Astronomer Royal Flamsteed since 1696, but left that position in late 1702 to become a lecturer. Hodgson was versed in natural philosophy, experimental science, and mathematics, and joined Francis Hauksbee the Elder at the Royal Society during its leadership by Newton. In 1703, he became a fellow of the Society. As a lecturer, Hodgson advertised seminars in as- tronomy and philosophy promoting the discoveries of members of the Royal Society and demonstrated experiments. Hodgson began to write technology books by 1704 and apparently also tutored in the sciences. Hauksbee, ademonstrator for the Society, had an interest in these lecturers and the two began to work together, thus creating a forum for practical embodiments of Newton's theories and some of Hawksbee's own inventions. In 1706, Hodgson published The theory of navigation demonstrated. In 1709 he became a mathematics master at the Royal Mathematical-School in Christ-Hospital. In 1736, he published The Doctrine ofFluxtions Founded on Sir Isaac Newton s Method, one of the early textbooks on calculus. 448 Hodgson was an important impetus in bringing experimental science (which was still a relatively re- cent concept) and mathematics to the common man, primarily merchants, navigators, and tradespeople who recognized the value of new technologies to their professions. He was also one of the first to voice the basic principles of sonar, suggesting that sound could be used to estimate the distances of ships at sea and ofland objects. See Hauksbee the Elder, Francis. Hoff, Marcian Edward (Ted), Jr. (1937- ) An American engineer who, in response to a request from a Japanese company for a calculator chip, designed the Intel 4004, in 1971. This highly significant invention was the first commercially successful micropro- cessor chip, and it launched the microcomputer industry. Hoffbecame a manager in the Applications Research division of Intel Corporation in 1968 and joined the 4004 development project. In 1983, he became Vice President of Atari, Inc., which was well known at the time for home computer systems and, in 1984, was awarded the IEEE Centennial Medal. In 1990, he was appointed ChiefTechnologist at FTI Teklicon, Inc. hold I. To pause, to cause to remain in a particular position or situation. 2. While attempting a computer login, the user may be queued or put on hold until fewer users are on the system. This hold usually mani- fests as a pause after typing the username or after typing the usemame and password. On popular archive sites, there may be a hold period or increased lag time while accessing a system. Sometimes it's better to log on later during off-peak hours, or to find a less busy mirror site, if one exists. 3. On phone systems where the receptionist is busy with other calls, or the auto- mated system is queuing the caller for the next available operator, the user is usually put on hold, sometimes for extraordinarily unreasonable lengths of time (especially if it's a long-distance call). On systems that don't have music or a recording informing you that you are in the queue, it is sometimes difficult to know if you are still on hold or have been cut off. On multiline systems, a call can often be put on hold by one individual and picked up by another (line hold). On some systems, the hold call can be continued only on the main console or by the person originally put- ting the call on hold (exclusive hold). Hold Recall An optional telephone feature that alerts you to the fact that someone is on hold. On most multiline systems and some residential phones, the line on hold will be identified by a flashing LED or, on more sophisticated systems, with beeps or voice messages. hold time 1. In circuits, the time interval after the clocking ofa trigger circuit during which data must remain unaltered. 2. In welding or soldering, the time during which the welded object must be held relatively steady in order for the weld or solder to harden. 3. In telephony, the length of time a caller is kept waiting, and waiting holding beam A diffused electron stream used to re- generate charges applied to the surface of a storage tube. © 2003 by CRC Press LLC holding coil In a communications circuit, an addi- tional coil in a relay for each direction ofa transmission that can be opened or closed independently of the main circuit to enable a single circuit to accom- modate alternate two-way communications. holding gun In an electron storage tube, the source of the electrons that make up the holding stream. holding time In telecommunications, the entire du- ration of a call from the time the connection is re- quested until it is completed and disconnected. The actual time during which the connection is established is only a portion of the holding time, although it's usually the time that is billed. Holding time is important, for example, in tracking sales calls. How long does the sales representative or telemarketer actually stay on the line trying to connect a call and handle the entire transaction, as opposed to the amount of time actually spent with the customer? If there is a large discrepancy, another method may need to be tried. Holding time is also important in computer or telephone circuit planning and management because the time spent connecting and queuing the caller may affect capacity and efficiency as much as that portion of the call during which the communication takes place. holding trunk In telephone communications, a queue wherein a call is held until availability is established or an alternate route is found. holiday factor A concept in service and retail industries (including Internet services) that accommodates changes in rates of service use or product purchase during holidays. The transportation, retail, and telecommunications industries tend to have patterns of higher usage during holidays and need to factor in extra staff, lines, products, etc. to handle the demand. Holidays may also create decreased demand, in which case shutdown or reduction of unneeded systems may result in cost savings. Hollerith card Historically, a sturdy, rectangular, piece of card stock organized into rows and columns that were individually labeled and further organized into sections. A circular hole was punched in the card to select the coded data in that region of the card. The punched holes could later be read and decoded to re- assemble the original information. This concept was born out of the cards used to store loom patterns on Jacquard looms. In the 1920s, ffiM, the evolution- ary heir to the Hollerith Tabulating Company, introduced a patented rectangular hole that made it possible to encode almost twice as much information as the original round hole cards. Hollerith cards were used to store historic computing machine code in the days before tape, diskette, and hard drive storage. The punched card was, in effect, a binary storage system with the unpunched or punched locations representing off or on and corre- sponding to no or yes responses to a predefined parameter. As the storage capacity of these cards was quite limited, many cards were needed to store a body of information. Punch cards, in general, can be fully punched and read in again with mechanical or optical devices, or partially punched to provide a record without the mess and waste of chad and read again with sensing devices. In the case of Hollerith cards, the punched cards were read by an electrical reader that completed acircuit and activated a relay when a pin passed through a portion of the card with a hole. With the use of gang punches with selectable tem- plates, up to 40,000 cards a day could be punched. The computer cards commonly used in library books, until bar codes became prevalent in the 1990s, are descended from Hollerith cards. See Hollerith Elec- trical Tabulating Machine, Jacquard 100m, zero punch. Hollerith code A 12-1evel code designed by Herman Hollerith in 1889 for use on Hollerith cards which, in tum, were used with the Hollerith Electrical Tabu- lating Machine. The card is sectioned and labeled and the code was implemented in the form of holes punched at specified intervals in designated rows and columns, with each column correspondin~ to an alphabetic or numeric character, in order to form a semipermanent record that could be read and interpreted in the future. This code was widely used in early computing days to store program instructions and data. Over time, variations were developed and EAI and ANSI standards were established to govern the configuration of the cards, holes, and data encod- ing. Hollerith code survived much longer than the Hol- lerith Machine, which was superseded by electronic computers. Hollerith code continued to be used in microfilm records, e.g., for storing microfilm image data and is still covered in Information Technology (IT) courses. For the processing of textual information, it has been superseded by other systems, including EBCDIC and ASCII. See Hollerith Electrical Tabulating Machine. Hollerith Electrical Tabulating Machine A mechanical-electrical data processing mechanism for quickly and accurately recording and classifying individual data from avariety of sources. It was developed by Herman Hollerith in the early 1880s. Hollerith's machine came to prominence when it was selected (over a system developed by A. Graham Bell) to tally the results of the 11th U.S. Census, in 1890. Before Hollerith's invention, it had taken almost a decade to process the results ofa U.S. census. With the use of the Tabulating Machine by the Popu- lation Division of the Census Office, thousands of entries could be tabulated in a single day, thus greatly expediting the recording of over 60 million cards, one for each person included in the census. The 1890 census was processed in only a year. The Census Office continued to use the Hollerith Machine for further statistical analysis of specialized groups within the population. For example, in 1901, Bell was using the Hollerith machine to compile and process information from the census relating to the blind and deaf, with assistance from his wife on se- lecting and organizing the format and priorities related to the data (an important aspect of setting up 449 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary the punch configuration and tabulation). After the census, other organizations with statistical tabulating needs looked into the use of the machine, including accounting and transportation firms. There were two main aspects to the Hollerith Ma- chine: the adjustable punching mechanism for creating the data cards and the electrical pin-based reading mechanism for processing the cards, activating relays, and incrementing a counter. The letters and numbers organized on the punch mechanism's keyboard could be altered to suit the type of data that were being entered. The Hollerith Machine received much publicity as a result of the 1890 census and caught the attention of other institutions, especi~illy statistical and auditing companies and departments. Variations and improve- ments were developed, with the tabulating and sorting functions sometimes implemented separately and sometimes housed in one unit. The Hollerith mechanical tabulating mechanism was to be an important impetus in the development of advanced calculators, the forerunners to early computers. See Harvard Mark I; Hollerith, Herman; In- ternational Business Machines. Hollerith Tabulating Data Card A sample of a punchedHollerith card in which the cardhas been organized in sections and labeled with alphabetic or numeric markers. [Railroad Gazette, April 1895.] Hollerith, Herman (1860-1929) An American engineer who devised a historic tabulating machine, in 1884, which he further developed with the concept of punched cards as an information storage medium. In 1889 he received apatent for his machine to compile statistics (U.S. #395,782). Hollerith was subsequently contracted to carry out the storing and reading of U.S. census information, beginning with the 1890 U.S. census. Following the success of this invention, he fonned the Tabulating Machine Company, in 1896, to market the technology. In 1911, it was merged with other companies to become the Com- puter Tabulating Recording Company, the historic beginnings of International Business Machines (mM). See Hollerith Electrical Tabulating Machine. hologram A type of imaging using lasers, based on the recording of an optical interference pattern 450 produced by the interaction of two or more waves from the same source. The effect of viewing a holo- graphic image is a sort of 3D, when moving the head around and focusing on different parts of the image. In most cases, it is not fully a 3D effect, as the image is usually recorded on some flat (with transparent depth) medium such as glass or transparent plastic (although the technology itself is not limited to this form ofpresentation). The image is typically more ethereal than a photograph, since it is viewed through "layers" of the transparent medium. Projected ho- lographic images hold great promise for 3D virtual reality, and scientists have been working on holo- graphic memory modules for computers that poten- tially can store enormous amounts ofinformation in small three-dimensional components. It has been suggested that human memory may share some functional similarities with holograms. Hollerith Tabulating System The Hollerith Electric Tabulating System showing the punch on a movable arm poised over the card holder and a lettered and numbered keyboard hole alignments for the various data that were to be entered and stored on punched cards. [The Manufac- turer andBuilder, J( 22, 1890.J A Hollerith reader, the sorting and tabulating mechanism that was used to process the individual cards intostatisticaldata once they hadbeenpunched with information relevant to the application. [Rail- road Gazette, April 1895.} home In computer interfaces that distinguish regions © 2003 by CRC Press LLC of the screen for different functions, one comer is usually designated as the home position, that is, a position to where a pointing device may return, or where a cursor might start again after the region has been cleared or a new window opened. On English language-based systems, for example, the home position in a text window is usually the top left corner. If the text were being typed in another language that tracks from right to left, such as Hebrew, the home position would be the top right of the window or screen, or bottom right if it is bottom to top reading. In PostScript page layout programming, the home position is generally considered the bottom left comer, as it is with a number ofprinter graphics languages. Some systems have a home key as a one-step shortcut to position the cursor in the home position. home ATM network HAN. A broadband home network providing connectivity with a variety of services and devices (computers, television, appliances, etc.). See ATM Forum, fiber to the home, RBB. home page A World Wide Web concept referring to the fIrst, primary, or main page ofa set of hypertext linked pages on a particular host, or belonging to a particular individual or organization. Web pages are not inherently hierarchical, since any page can link to any other, but humans tend to grasp concepts more easily when information is organized in a top-down or bottom-up manner, and home pages reflect our preference for this type of organizational structure. A home page serves as ajumping off point, table of contents, or general site information map to help navi- gate the rest of the links. Commercial sites tend to have home pages that showcase product information and entice the user to explore the rest of the site. Per- sonal sites often show family relations, professional credentials, and personal interests. Educational home pages usually provide information on course offer- ings, faculty, and facilities. See HTML, hypertext, World Wide Web. home run A centralized wiring topology, like a star topology, in which cables to individual units or con- soles all lead back to the central switching system. Most private branch systems, almost all key systems, and many of the smaller computer network systems have this type of cabling arrangement. In home run wiring, which has little or no redundancy, a severed line will cut off the end station from all other stations. See topology. Homebrew Computer Club A historic, influential, electronic thinktank and tinkerer's organization, founded in California in 1975. Steve Wozniak is one of the most famous of the Homebrew members. The Altair was demonstrated at a Homebrew meeting, with homebrewers jumping on the opportunity to write applications for this early computer. homeostasis A state in which there is a tendency to- ward balance, stability, or equilibrium. A state in which there is no change. homing I. Zeroing in on an intended destination or target. 2. Approaching an intended destination by holding some parameter of navigation constant (with the exception ofaltitude). 3. In guidance systems, transmitting, receiving, and evaluating signals in order to locate a target. Bats and missiles use homing systems. 4. In telecommunications, homing is the se- lection ofa route through which a call can be set to the next switching center, especially in toll systems, which may pass through several specified switching stations. homodyne reception See zero beat reception. homojunction A mechanism within a semiconductor in which the layers comprising either side of the junction are substantially formed of one material. For dynamic processes to occur within traditional semiconductors (those dependent upon materials rather than the composition of the layers), however, there needs to be some difference between the two layers associated with the junction such as differences in con- ductivity or doping. Doping, the impregnation of impurities with particular properties, creates a dynamic imbalance between the layers to facilitate energy transfer and release of photons, for example and it can reduce the contact resistance between the semiconductor and a metal contact, creating an n-n+junction. See heterojunction. homojunction laser A basic semiconductor laser with a single semiconductor material for the p-n junction doped to produce the dynamic energy transfer effects of the junction. The index of refraction is controlled by the type and amount of doping. This produces an effective laser, but some of the light is lost due to diffraction, so it is not of the highest efficiency. See heterojunction laser, semiconductor laser. Honeywell Kitchen Computer Honeywell, in a blaze of optimism that is unique in entrepreneurial history, introduced one oftheir Series 16 computers as a home computer for the kitchen through the Neiman Marcus catalog for $10,000, in 1969. It could store recipes, was programmable, and included kitchen accessories. To put the price in perspective, it cost roughly the same as four new cars or a small starter home, or five years' gross wages for a person earning minimum wage. Even now, almost halfa cen- tury later, there are few computers in kitchen envi- ronments, and it would be incredibly difficult to sell one for the modem equivalent of $80,000. As you might expect, the Kitchen Computer flopped. The Series-16 computers, from which the Kitchen Computer was born, were originally designed by Computer Control Company and bought out by Hon- eywell. They were released at about the same time as the Digital Equipment Corporation (DEC) PDP-8 minicomputers. The Series-16 computers included the DDP-116 (1965), the DDP-516 (1966), and the DDP-316 (1969). The DDP-316 was essentially a physically reduced-size version of the DDP-516. By 1960s standards, the 316 line would probably be considered minicomputers, as they had 16-bit registers, with core memory and a memory read/write time of between 1 and 2 microseconds, which was pretty good compared to the low-cost microcomputers that came out a decade later. The main unit of the smaller models was about the size ofa deep 17" CRT moni- tor. Like the later Altair, the units had lots of switches 451 © 2003 by CRC Press LLC . designed by Computer Control Company and bought out by Hon- eywell. They were released at about the same time as the Digital Equipment Corporation (DEC) PDP-8 minicomputers. The Series-16 computers included the DDP-116 (1965), the DDP-516 (1966), and the DDP-316 (1969). The DDP-316 was essentially a physically reduced-size version of the DDP-516. By 1960s standards, the 316 line would probably be considered minicomputers, as they had 16-bit registers, with core memory and a memory read/write time of between 1 and 2. leaving the company to cofound Mosaic Fabrications, Inc., with P. Kiritsy, in the late 1950s, he was approached by John Johnson about the po- tential of fiber optic filaments for lengthening alight path through fiber optics rather than through longer tubes. Hicks succeeded in pulling optical fibers, in making fiber- based vacuum assemblies and, in col- laboration. intended to float above commercial aircraft at about 20,000 meters, which have been proposed as two-way communications links capable of carrying phased antenna arrays. The HALE systems 445 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary are experimental and a