Fiber Optics Illustrated Dictionary - Part 43 pps

Fiber Optics Illustrated Dictionary also being extended to include a set of commonly used office productivity tools. One of the more interesting aspects of GNOME is that it can be internationalized in order to make it possible for developers around the globe to create applications in the language syntax that is most com- fortable for them. One of the secondary goals of the GNOME project is to make GNOME developer tools and documentation available in every known world language (an ambitious goal but likely to result in a rich choice of options even if it is not literally achieved). GNOME also takes into consideration the maximizing of accessibility for people with disabili- ties, through the GNOME Accessibility Project. http:/ /www.gnome.org/ GNSS See Global Navigation Satellite System. GNU Acronym for "GNU's Not Unix!" A Unix work- alike developed under the aegis ofRichard Stallman of the Free Software Foundation (FSF). See Free Software Foundation, GNOME. GNU as A GNU family of assemblers used to write software code for a variety of object file formats. The original GNU assembler for the Digital Equipment Corporation (DEC) VAX system was written by Dean Elsner. Many subsequent programmers and even some commercial vendors have enhanced and main- tained the software. See Free Software Foundation. GNU C compiler GCC. A C compiler supporting ANSI standard C, C++, and Objective C. The GNU C library includes ANSI C, Unix, and POSIX functions. GNU Emacs A powerful, extensible, scriptable display editor distributed by Berkeley programmers with BSD, and by many other distributors and commercial vendors. Emacs is so powerful and so well liked by power editor users, many have half seriously re- ferred to it as an operating system. The first Emacs was written in 1975 by Richard Stallman. GNU Emacs, which was enhanced by Stallman with true LISP integrated into the editor, was introduced in the mid-1980s. GNU Emacs is widely available on Unix systems. GNU grapbicsA set of graphics utilities for plotting scientific data, with support for GNU plot files on various systems and output devices, including Post- Script, The X Window System, and Tektronix devices. GNU's BulletinA semiannual newsletter about various GNU projects, produced and distributed by the Free Software Foundation. go local A command to instruct software to connect to a local connection (usually in the same room or vicinity), usually through a serial null modem interface. GO-MVIP Global Organization for Multi-Vendor Integration Protocol. GO-MVIP is a nonprofit trade association which took over the development and promotion of MVIP in 1994, in order to assure its development and maintenance as a practical, robust common integration standard. GO-MVIP seeks to continue to develop and establish the design specifi- cations for further versions ofMVIP. See MVIP. http://www.mvip.org/ 412 Satellite Sensing Systems An artist sconception of an EROS meteorological satellite system, which was essentially the conceptfor the GOES satellites. This April 1961 drawing indicates thefield of view andorientation of the proposed AEROSgeostationarysatellite. {NOAA In Space Col- lection image.] An example of a visible image from the GOES 8 satellite on 16July 2001 with a line drawing of North America andparts of Central and South America superimposed to aid in locating geographical features. [NOAA FSL image.] GOES Geostationary Operational Environmental Satellite. A geosynchronous satellite system providing environmental monitoring data to various gov- ernmental organizations and the public. GOES systems began broadcasting, as we know it today, in 1974, having evolved out of early SMS weather satellite systems. Almost a dozen satellites were launched between the early 1968 magnetometer and infrared sensor-equipped satellites and the more so- phisticated multisensor satellites of the late 1990s. With each launch, adjustments and improvements have been made to the systems. Vertical temperature and moisture sensors were added to GOES-4, and additional signal relay capabilities were added to later GOES systems. The original GOES satellites were spin controlled, meaning that they used the physics of spinning to maintain attitude control. Since the © 2003 by CRC Press LLC mid-1990s, however, with the launching of GOES- 8, the configuration has changed to a three-axis-sta- bilized system. Ihis configuration changed not only attitude control, but also the means by which the sensors were installed and operated. Doppler radar sensors were added to the more recent satellites and have become an indispensable aspect of creating and in- terpreting weather maps. The Pacific GOES has been used for operating the Pan-Pacific Educational and Cultural Experiments (PEACESAI) to enhance medical, cultural, and educational resources in the Pacific island nations. GOES data is available to the Command and Data Acquisition Station, the National Weather Service, the Forecast Systems Laboratory (FSL) of the National Oceanic and Atmospheric Administration (NOAA), and many others. NOAA handles the operations of the satellites. GOES sensors provide continuous weather monitoring along with infonnation that can be used to estimate rainfall during more violent stonns (e.g., hurricanes) and snow accumulations and cover. Ice flows on large bodies of water can also be monitored with GOES data. Even the weather in space, in terms of various magnetic and energy particles, is monitored by GOES sensors. The GOES Space Environment Monitor (SEM) mis- sion provides a better understanding of space weather through the National Space Weather Program. Space weather forecasts aid not only in probe, shuttle, and satellite missions, but also in providing valuable cos- mological infonnation to physicists and astronomers. Satellite images with a variety of characteristics (visible, infrared, water vapor, etc.) from GOES sensors are available through the Forecast Systems Labora- tory. gold A malleable, metallic chemical element with high conductivity, which makes it useful for specialized electrical applications. Gold contacts are often found on sensitive electronics connectors in the computer and video industries. Copper and silver are also good conductors, with copper being the most widely used for electrical installations. GOLD See Global Online Directory. gold disk, gold disc 1. The master or final copy ofa product (software, music CD, laserdisc, etc.) from which mass production replicas are made. 2. A spe- ciallimited edition distribution. Collectors' edition. Gold disc music CDs sometimes are marketed as higher quality pressings with special inserts and special tracks that may not be included on a regular copy of the CD. gold number, custom number, vanity number A phone number specifically selected so that it is easy to remember, particularly if the letters associated with the number spell out a word or other mnemonic. There is typically an extra fee associated with get- ting a gold number. Sometimes people get lucky, and their number just happens to be easy to remember or to spell something interesting. Goldstone Deep Space Communication Complex One of the complexes of the NASA Deep Space Net- work (DSN) that provides radio communications for interplanetary spacecraft. The complex is further used for radio astronomy and radar observations of our solar system and the universe beyond. Other complexes in the Network are located in Madrid, Spain, and Canberra, Australia. See Deep Space Network. Deep Space Communication Complex Large beam waveguide parabolic antennas at the Goldstone Deep Space Communication Complex in the Mojave Desert in Goldstone, California. The 34- meter dishes are used for astronomical research and radio space communications. [NASAIJPL image, 1990.J GOME See Global Ozone Monitoring Experiment. GOME Data Processor GDP. A ground segment system designed to process data from the satellite- based Global Ozone Monitoring Experiment (GOME). Raw data is processed by the GDP into Levell radianceslreflectances and Level 2 trace gas quantities data that are made available to interested parties. A number of images and other data sets are also available, some of which may be downloaded by FIP. The GDP was jointly designed and developed by Gennan, Dutch, and U.S. organizations and is ad- ministrated by the European Space Agency (ESA). Processing is handled at the DFD, the German Re- mote-Sensing Data Center. See Global Ozone Moni- toring Experiment. GOMS See Geostationary Operational Meteorologi- cal Satellite. goniometer A detection instrument that can be set at a range of angles, sometimes in selected increments (or with optional heads), to assess the different patterns of light scattered from a sample. The results are useful in industrial analysis of materials such as poly- mers and particulate composites. Fiber optics enable the probing surface to be separate from the rest of the electronics. Goniometers may be built into spectrometers although some newer fiber optic spectrometers don't require traditional goniometers. Gooch, Daniel (1816-1889) An English locomotive engineer and businessman who aided in the installation of the fITst successful permanent telegraph cable link between North America and the British Isles. At arelatively young age, Gooch was appointed the locomotive superintendent of the Great Western Rail- way (GWR). In 1840, Gooch contacted gifted engineering designer Isambard K. BruneI about designing an engine works for GWR (this association between the two talented engineers was to take an interesting tum more than a decade later). Using new 413 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary technology and the results of experiments in atmospheric resistance, Gooch designed locomotives that could travel at faster speeds than previous models. He was also a supporter of wide gauge technology, despite the trend to smaller gauges. Gooch designed more than 300 locomotives in his career as an engineer. In the 1860s, Gooch resigned his position with GWR to put his efforts into telegraphic communications. He became Chairman of the Telegraph Construction and Maintenance Company and a director of the Anglo- American Company. In the meantime, BruneI had been designing the Great Eastern (originally the Leviathon). The Great Eastern was purchased by Gooch and his colleagues for cable laying and was instrumental in laying the first transatlantic communications cable, the feat that Gooch is best known for, despite his many other accomplishments. See Great Eastern. good condition In many rating systems, a product with minimal abrasions from wear and tear, and mechanisms that are in good working order. Good condition does not describe the age of the product or its remaining useful life. Often intermediary between fair condition and excellent or like new condition. goodputAgeneric measurement of network data suc- cessfully received, effective throughput; in contrast, discarded cells, or transmitted cells in a congested link, are called badput. See cell rate, throughput. Goodwin, Hannibal(1822-1900) An American min- ister and inventor who created celluloid film in 1885 and received a patent for rollable film in 1887. For many years, motion picture films were known as celluloids, and individual animation frames used to create frame-by-frame animation are still known by the abbreviated form cells. gopher The command for initiating a Gopher client on a text-based system is "gopher" (all lower case), and "xgopher" is a similar client command that works with The X Window System. See Gopher. GopherA document system developed by P. Lindner, M. McCahill, B.Alberti, F.Anklesaria, andD. Torrey at the University ofMinnesota in the early 1990s to provide a local campus information server. The Go- pher service quickly grew to become a worldwide resource. It is a client/server distributed document delivery system, i.e., a means of locating information on the Internet through a simple menu-like text interface (or graphical Gopher client) or of sending information through electronic mail. It is also possible to set bookmarks, Gopher information locations that are frequently used. Links to various Gopher servers together comprise a virtual community known as Gopherspace. The Gopher text menu interface is being superseded by graphical Web interfaces. See Veronica, RFC 1436. Gopherspace The Gopher document system is com- posed of many widely distributed document reposi- tories and Internet services in Cyberspace. Hence, the Gopher facilities online are called "Gopherspace" by many their users. See Gopher. GORIZONT A Russian geostationary telecommunications satellite launched in 1996. 414 GoS grade of service. A phrase to describe service levels, which usually are individually defined on an industry basis. See class ofservice. GOS See Global Observing System. GOSIP Government Open Systems Interconnection Profile. A U.S. government version of the Open Sys- tems Interconnection system which is required in many government data network installations. Gosling, James Gosling is best known for his con- tributions to the Java programming language, developed at Sun Microsystems, Inc. He was associated with Bill Joy, Mike Sheradin, and Patrick Naughton on Project Stealth in 1991. Project Stealth's goal was to develop a distributed network in which the various electronic devices could intercommunicate. See Java; Joy, William. Goubau 1958 Wave-Guiding Patent This selection of diagrams from Goubau spatent accompanies his description of a method for transmitting a substantially cylindrical wave beam by re- setting the cross-sectional amplitude and phase distribution of the beam at intervals that are large com- paredto the beam radius. Goubaufurther describes a mechanism tophase-correctelementsinterceptingthe beam to effect repetitions of the cross-sectional amplitude and phase distribution, as desired. The dia- gram illustrates some of the phase-correcting lenses for accomplishing his goals. Goubau, GeorgJohann ErnstApioneerresearcher into hollow optical waveguides utilizing lenses as a © 2003 by CRC Press LLC means to guide light. Goubau submitted a patent application for an invention to transmit electromagnetic wave beams, in November 1958 (U.S. #3,101,472). In 1961, he coauthored "On the ~ided propagation of electromagnetic wave beams' in IEEE Transac- tions and continued lens guide research with a number of scientists through the 1960s. See Dicke, Robert. Gould, Gordon (1920- ) An American engineer, Gould has been involved in maser/laser technology since the late 1950s. Gould studied optics at Yale Uni- versity and later began a Ph.D. in physics at Colum- bia University, where Charles Townes was a professor. Townes had been conducting historic research on masers (microwave amplification) since the early 1950s. In 1957, Townes and Gould discussed the concept of using light amplification rather than microwave amplification for developing lasers. Gould was an ambitious student who wanted to earn a patent for a historic invention. After discussions with Towne about patent application procedures, he left graduate school to work for TRG, worked on a prototype and filed a patent, in 1959. The patent was initially denied due to the earlier patent of lasers developed by Townes and Schawlow because Gould, at the time, could not produce substantive written or prototypic proof of lasers invented in 1958 But, after a subsequent legal battle, some of the claims were accepted and a patent was awarded in 1977 giving him rights to royalties for certain laser technologies. In 1967 Gould accepted a professorship at the Poly- technic Institute of New York where he established and promoted laser research. Gould supports educa- tion in optics. See Dicke, Robert; laser; laser history. Gouy, Louis-Georges (1854-1926) A French physi- cist and educator who described thermal motion in ions in support of molecular theories that applied to an electrical double layer associated with planar sur- faces, now called the Gouy-Chapman theory. The theory, while flawed in some of its assumptions, ap- plies reasonably well for certain aqueous solutions, but does not hold up as well for small distances and high surface potentials (e.g., edges). Gouy balance An instrument for assessing the mag- netization ofa paramagnetic substance (one with unpaired electrons) as compared to the gravitational at- traction of a counterweight, named after Louis- Georges Gouy. In other words, a device for determining magnetic susceptibility. Differences in apparent mass of a sample may be assessed in and out of a magnetic field. The number of unpaired electrons of a sample may be determined as the force with which a paramagnetic compound is attracted to the magnet is related to the number of unpaired electrons and can be compared with substanced with known parameters. A Gouy balance utilizes large magnets mounted stationary opposite a movable sample. Contemporary replacements for the Gouy balance do it the other way around, with movable magnets balanced on either side ofa stationary sample. Gouy phase shift A shift in the Gaussian mode that occurs when the beam passes through a focal point (sometimes called the beam waist), named after Louis-Georges Gouy. The phase shift has been used as a means to split and statistically observe radiant energy characteristics and has been described as a mechanism for accelerating fast pulses. However, observation of the phenomenon was mainly of math- ematical interest until the late 1990s, when systems were designed capable of transmitting in the terahertz (THz) frequencies-yielding beams that could be assessed for both amplitude and phase. This enables the Gouy phase shift to be more readily observed and in- terferometrically plotted. See tilt locking. Government Emergency Telecommunications Service GETS. A service of the U.s. National Com- ~~i:~t~t~f:~~::!~!~;~1~;~:~;~:~ ~~ I. works by authorized users. GETS provides emergency access and processing in local and long-distance telephone networks through a dialing plan and personal identification number (PIN). GETS services are provided through major long-distance networks, local networks, and leased networks through a uni- versal access number and common telephone devices (desk phone, cell, phone, fax line, etc.). Once authen- ticated through the PIN, the caller receives special handling that may include priority and/or enhanced routing. See National Communications System. http://gets.ncs.gov/ Government Information Locator Service GILS. An ISO standard metadata scheme for describing government information resources with the intent of streamlining the management of information for ef- ficient search and retrieval. GILS is an open, cost- effective, scalable data standard to facilitate the search for collections of information and specific information within a collection. GILS extensions allow specific categories of data to be managed and searched. GILS is based on the ISO 23950 search standard and can be approached in somewhat the same way as information searching may be approached in a reference library. See Dublin Core, In- ternational Development Markup Language. http://www.access.gpo.gov/su _ docs/ gil s/index.html GPF See general protection fault. GPRS See General Packet Radio Service. GPS See Global Positioning System. GPS Control Segment A general overall category of the GPS system which comprises a main tracking station, in Schriever (formerly Falcon) Air Force Base, Colorado, and subsidiary tracking stations worldwide as part of the U.S. Department of Defense's Global Positioning System. The tracking stations take the signals from the satellites and incorporate them into orbital models that are further used to compute precise, individual, orbital data and clock corrections. Portions of this orbital ephemeris are sent via radio transmissions to GPS receivers. See GPS Space Segment, GPS User Segment. GPS Navigation Data Satellites in the Global Posi- tioning System (GPS) send out two microwave carrier signals, one of which provides navigation information in the form of a series of time-lagged data 415 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary frames sent over a specific time period. Subframes are also included for checking data integrity. The satellites are equipped with atomic clocks, and clock data parameters are sent and related to GPS time. Orbits are described by transmitting regularly updated ephemeris data. See Global Positioning System, Uni- versal Coordinated Time. GPS Operational Constellation The system of over 20 more-or-less evenly spaced, orbiting satellites (some of which are spares), equipped with atomic clocks, in the Global Positioning System (GPS) Space Segment. These satellites orbit the Earth twice a day at about 11,000 miles altitude, transmitting information used in the U.S. Department of Defense's Glo- bal Positioning System. The orbital planes are in- clined at about 55 degrees in relation to Earth's equa- torial plane. From anyone point on Earth, it is generally possible to locate between five and eight satellites, four or five of which are typically used to compute location and timing information. The satellites transmit two microwave carrier signals; the L1 frequencies carry the navigation message (with data describing the orbit and clock parameters) and SPS code signals, and the L2 frequencies monitor ionospheric delay ofPPS receivers. See Global Positioning Sys- tem. GPS receiver/display A fixed or mobile Global Po- sitioning System (GPS) device that interprets GPS information and computes graphics, text, locations, maps, or other displays that provide the user information about position, time, and sometimes velocity. A graphical display oflatitude and longitude is common. Receivers vary from room-sized systems to small handheld units from $180 up to hundreds of thousands of dollars. GPS consoles are used by sur- veyors, have been combined with map databases to provide car consoles, and have also been incorporated into 'smart cars' that can steer themselves. It is not unrealistic to predict that someday small GPS systems will be designed into wristwatch-style personal locators for travellers, sales representatives, hikers, et a1. See Global Positioning System, Intelligent Ve- hicle Highway System. GPS Space Segment Ageneral overall category of the GPS system that consists of GPS satellites de- ployed and administered by the U.S. Department of Defense as part of its Global Positioning System. See GPS Control Segment, GPS User Segment. GPS translatorA Global Positioning System trans- lating capability to support technologies that require precise positioning and trajectory tracking data. This type of data is ofimportance to missiles and rockets and other high-velocity acceleration devices. Trans- lator GPS systems support midcourse corrections, safety operations, and downrange tracking. They are a cost-effective option to certain radar tracking systems and a higher-accuracy option to portable GPS receiver systems. Avehicle or interceptor device installed with a GPS translator captures the GPS signals, translates them to an appropriate communications frequency, and transmits them to a ground-based station for further 416 processing. The use of ground-based stations also makes it possible to store the data in larger storage media for subsequent playback and analysis, a capability that is impractical in most on-site GPS devices. IEC is a commercial vendor of GPS translators that has been providing and developing the technology since the 1980s. It has supplied translator systems to both the U.S. Navy and the U.S. Air Force. IEC has recently introduced a family ofdigital GPS translators that can support encryption for greater security, and it is developing a smaller, more powerful Trans- lated GPS Range System (TGRS), in cooperation with the Air Force. GPS User SegmentAgeneral overall category of the GPS system that includes GPS receivers and users of the U.S. Department ofDefense's Global Position- ing System. See GPS Control Segment, GPS Space Segment. Grade 1 to 5 twisted pair See twisted pair cable. Grade Bsignal Aradio-frequency broadcasting signal defined by the Federal Communications Commis- sion (FCC). It is a measure of the strength of a tele- vision broadcasting station's signal at a specific location. The purpose of the rating is to define minimum acceptable standards of quality for viewing purposes in the context of defining whether a specific subscriber is served or unserved by the signal. When the Satellite Home Viewer Improvement Act (SHVIA) was passed in 1999, it included a require- ment that the FCC re-evaluate the Grade B signal standard to determine if it should be changed or re- placed with something else for determining whether a household is unserved (unable to receive a signal of an acceptable level). Since it is impractical to go out and measure radio signal strengths in the vicinity ofevery subscriber in the U.S., the FCC created a computer model for satellite companies and televi- sion stations to predict whether a given household is served or unserved. This computer model went through several versions in order to include the effects ofbuildings, terrain, and land cover variations that could impede radio-frequency signals. If the pre- dicted model is under dispute, a person may request a waiver from local TV stations serving the area. If the waiver is granted, the person becomes eligible to receive distant signals. If the parties cannot agree whether a subscriber is served or unserved, the American Radio Relay League (ARRL) has been designated as an indepen- dent, neutral entity for arbitrating and designating the party, with input from the satellite provider and TV station, to conduct a field test of signal strength. grade ofservice GoS. A service level indicator evalu- ated on an industry basis according to the type of service provided. In some industries a hierarchical category scale is applied to various levels or definitions ofservice. In telecommunications, grade ofservice is typically described in statistical terms related to the speed and probability of connecting, and the characteristics of the connection, etc. See class ofservice, quality of service. graded index GI. A designation for a fiber waveguide © 2003 by CRC Press LLC that has had its propagation characteristics for certain wavelengths altered by the deliberate inclusion of dopant materials in the fiber. Thus, undesirable effects such as dispersion can be mitigated in multi- mode fibers (especially those for longer distances) by selectively controlling the speeds at which the light beams travel within certain portions of the fiber. Beams that reflect in the lightguide at steeper angles normally would take longer to traverse the distance than beams that have a "straight shot" through the guide. However, by gradually changing the index of refraction of the lightguide out towards the outer di- ameters to enable faster propagation in this region, it is possible to compensate for the longer travel path. GI fiber operates in the O-band region around 1300 nm. See dispersion, light speed, stepped index. gradient Gradual change in elevation, color, or tex- ture along an axis. Gradual blend or transition. See gradient fill. gradient fiU A common feature of paint programs that allows the user to fill a defined area with graduated tones ranging from one specified color or shade of gray to another. The number of colors in the palette and the two end-tones selected will affect the smooth- ness and visual appeal of the transition, with more tones generally creating a more pleasing effect. Ra- dial fills can be used to simulate 3D surface areas, as lighter areas appear as highlights. Graham Act A U.S. 1921 act in which telephone companies were granted exemptions to the provisions of the Shennan Antitrust Act. It enabled AT&T, especially, to expand and exert further monopolistic control over the telephone networks. See the Kings- bury Commitment, Modified Final Judgment. Gramme, Zenobe Theophile (1826-1901) A Bel- gian engineer who emigrated to France, Gramme developed a direct current (DC) generator, featuring a ring armature in 1869 and 1870. Together with Hippolyte Fontaine, Gramme opened a factory called Societe des Machines Magneto-Electriques Gramme. In 1873, at the Vienna Exposition, it was noticed by a mechanic that an electrical connection from another generator could power the armature of the first generator, thus exhibiting the characteristics ofa motor. It was an important historical advancement in industrial and transportation technologies. grandfather clause A previously existing object, structure, statute, ownership right, or policy that may continue despite subsequent restrictions or regulations that would prevent its creation or continuance. A grandfather clause grants a type of pardon, special permission, or immunity. For example, military sur- plus purchased by a civilian in the 1960s may be regu- lated in the 1990s such that similar items may not be purchasable by current civilians (such as radiation bunkers). If the ownership is protected by a grandfather clause, when restrictions are imposed or rein- stated, current civilian owners might not have to give up the property (but also may not be able to sell it, except perhaps back to the government). Building codes are often subject to grandfather clauses. If you purchase a house built in 1920, it may not be subject to the same offset, materials, or safety regulations as current structures. Voting and immigration laws have certain grandfather clauses. Immigrants to the country prior to a certain date do not require the same documents and eli- gibility requirements as later immigrants. In telecommunications, phones and various electronic components built or installed before a certain date may not have to meet all current Federal Communi- cations Commission (FCC) regulations. grandfathered in Instated or installed before certain restrictions or regulations were put in place that would otherwise prevent creation, installation, or operation. ;~:~;:~~~!~~~:~~~~~:;n::;'k:~~~~~~ *~: • graphechon can store an electrical charge pattern, similar to the functioning of an iconoscope, and re- cover the pattern at different scanning rates. graphic equalizer A component providing a set of controls for adjusting the tonal qualities at several frequencies in an audio system, usually a music system. The equalizer is not a stand-alone component; it works in conjunction with other components such as receivers, phonographs, tape players, CD players, etc. It frequently has a series of vertical analog sliders for making individual adjustments. GraphicalKernel System GKS. An official standard for 2D graphics in the mid-1980s, evolved from the Core. A 3D extension was subsequently developed, and GKS-3D became a standard in 1988. See Core, PHIGS. graphical user interface GUI. A way of facilitating communication between a human and a device, usually a computing machine, by presenting the information in the form of visual metaphors. Agraphical user interface works in conjunction with a variety of physical input devices, including speech recognition hardware, mice, keyboards, stylus pens, touchscreens, and joysticks. They provide a means to select and control the various visual elements, which commonly include menus, drag bars, buttons, icons, and window gadgets. Video games like Pong were early electronic adaptations of simple GUIs. Many of the earliest applied GUI ideas in general use today were developed at Xerox PARC and incorporated by Apple Computer into the Macintosh operating system. graphics accelerator A chip or circuit board integrated into a computer system to relieve the CPU of some of the functions related to the processing and display of graphics. Graphics tend to be computing intensive, and sharing the load can significantly speed the display and refresh of images. Graphics accelerators are often sold as peripheral cards that can be plugged into a slot. See graphics coprocessor. graphics controller, graphics display processor Specialized computer hardware to improve raster displays by taking some of the load from the CPU. Graphics controllers can speed up scan conversion, and the composition, display, and movement of graphics images and primitives. See cathode-ray tube, frame buffer. 417 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary graphics coprocessor A chip designed to speed computer graphics composition, display, or refresh by sharing the load with the system CPU. Coprocessors are sometimes designed for very specific tasks, such as updating a screen, or storing and displaying graphics primitives, hardware sprites, and the like. Unlike graphics accelerators, which are often sold to con- sumers as optional system-enhancing peripherals, graphics coprocessors are more commonly sold integrated into the system, often on the motherboard. See graphics accelerator. Standardized Recording/Playback Fonnats VHS Super-VHS Hi-8mm CD+G laserdisc The variety of standardized recording andplayback media for graphics and multimedia products is increasing. Some of the more common formats supporting both images and sound are shown here. It may be that D VD-related formats, which hold more information in less space, will eventually supersede most or all of the above technologies. graphics device interface GO!. Physical and virtual connections between graphics hardware components and the computer CPU. Since graphics applications tend to be CPU intensive, it is very common for other graphics hardware (accelerator cards, frame buffers, blitters, etc.) to be incorporated into a system to facilitate the fast creation, display, and refresh of images on a variety of output devices. graphics engine The part ofa computer architecture supporting the graphics functions of the machine, particularly graphics composition, buffering, display, and fast refresh. Graphics engines are typically designed to handle many of the functions in hardware, so there is a minimum of on-the-spot software cal- culations. Enhanced graphics standards and graphics engines are being developed to support features such as realtime animation; hardware pan, zoom, compression/decompression; instant resolution- switching; and video signal support. Graphics Environment Manager GEM. One of the first graphical user interfaces (Gills) developed by Gary Kildall's Digital Research, the same company 418 that created the popular CP 1M text -based operating system in the 1970s. GEM was fIrst demonstrated publicly at the COMDEX computer industry trade show in 1983 and shipped a few months later. The interface greatly resembled the Macintosh interface that Apple had developed after observing development research at the Xerox PARC laboratories. GEM did not become widely distributed, with the excep- tion of providing a front-end to Xerox's Ventura Pub- lisher, a desktop publishing programming that was widely used for documentation page layout on Intel- based microcomputers in the later 1980s. Graphics Interchan~e Format GIF. (GIF ought to be pronounced "gif given that the G stands for "graphics," but its author apparently uses "jif.") GIF is aproprietary raster graphics format introduced by CompuServe, Inc. in 1987. It is an 8-bit graphics format developed with the patented Lempel-Ziv- Welch (LZW) compression, whose implementation requires a royalty agreement from Unisys Corporation. The level of compression varies with the type of image and number of colors, but 3 or 4 times compression ratios are common on a typical color image. Due to patent issues, CompuServe agreed in 1994 to secure a license agreement to distribute the LZW technology and issued the Graphics Interchange Format De- veloper Agreement to provide software developers permissions under CompuServe's software license agreement with Unisys. GIF is particularly suitable for images that have a small number of distinct colors, as opposed to images that have a great variety of subtle color changes. It also handles line art, grayscale images (through color palette gray matching), and sharp color boundaries better than formats optimized for other characteristics. Because GIF is a 256-color fonnat rather than a 24-bit color format ( 1.6 million colors), 24-bit images will be dithered and adjusted and may not fully satisfy the needs of the user. GIP will support transparency, which is sometimes desired in order for a background image to be displayed behind the GIF image or through parts of the GIP image as though there were holes. Transparency is often used by Web designers to produce special effects in Web pages, such as buttons with irregularly shaped edges. GIF is one of the three most common graphics formats supported by World Wide Web browsers, the other two being PNG and JPEG. PNG is an open, nonproprietary format, developed to supersede GIP. In January 1995, CompuServe announced the GIF24 proj ect for designing a replacement format for the original 8-bit GIP, and a month later officially announced that Portable Network Graphics (PNG) would be used as the basis for GIF24. Support for GIF users is provided on the CompuServe Graphics Support Forum (GO GRAPHSUPPORT). See Lempel-Ziv- Welch, Portable Network Graphics. graphics library GL. The writing of graphics routines for computers is time intensive and specialized. F or that reason, many companies decide to purchase graphics libraries rather than to write their own. These © 2003 by CRC Press LLC library routines consist ofa collection of commonly used graphics primitives and actions (lines, circles, dots, fills, patterns, etc.) that can be dynamically called from the graphics library or compiled and linked into the software executables as needed. graphics mode Asetting on dual-display mode systems (typically older IBM-compatibles) that permits the access and display of individually addressable pixels for the rendering of images and graphics characters. Some systems distinguish between text and graphics modes and will display only in one mode or the other. With faster processors, the trend is toward the more flexible graphics modes, with graphics characters. This frees the user from having to select a mode and switch between them. Graticule Examples [ [ Graticules are overlay templates used for a wide variety of alignment and calibration purposes, especially in scientific viewing and measuringinstnlments, video titling. and the evaluation of video images. They are also used to display and analyze field positions in videotapes of team sports. graticuie graphical reticule 1. A diagnostic and measurement overlay screen used with cathode-ray tubes (CRTs). The screen is calibrated and placed on the front of the tube, with the tube image showing through so the relationship of the displayed image to the screen can be observed. Agraticule may also be used with a spectrum analyzer, for analyzing band- width, with the analyzer calibrated to a specified number ofgraticule units. 2. A microscopic component incorporated into some eyepieces that provides an ar- rayed reference field for observation and count esti- mates of fibrous or particulate specimens (e.g., as- bestos fibers). In this context, it is often called a reticule. It is useful in fabrication, contamination test- ing, and quality assurance. 3. Areference grid or out- line image superimposed over a still or moving image to aid in analyzing or understanding the image or making sure it is within certain tolerances (e.g., the correct aspect ratio). This is especially useful for mapping, video element alignment (to avoid undes- ired clipping oftitles or images), and video transfer to other media with the increasing variety of different video formats (NTSC aspect ratios, widescreen, picture-in-picture, etc.). A graticule is the same ba- sic concept as a reticule, but is more often used to assess recorded images, as in cartography or video, as opposed to real specimens as might be viewed with scientific devices, especially microscopes and tele- scopes. See graticule library, reticule. graticuie library A set ofpredesigned graticules for use as reference, calibration, or counting templates for superimposing over an image or text. A simple example ofa graticule is a reticular grid on a piece of mylar that is placed over a picture to provide reference marks for hand copying the picture. More so- r:£:~~~~~{~~~~~~~:;r~~~~:~ • images or magnified viewing fields. For example, a graticule with reference marks for scale and for indi- cating the outlines of an antarctic icefield as it looked in 1970, could be superimposed over a s~tellite image of the icefield as it looks today. User-designed graticule templates could be included as part of a graticule library database for custom applications or future use. See graticule. grating A series of narrow ordered slits or grooves specifically designed and oriented so they reflect electromagnetic waves in a spread or concentrated pattern in a desired direction. For some types ofgrat- ings, the period of the grating (the distance from one facet to the next) can be "tuned" to selectively admit or reflect optical wavelengths. Other types ofgrat- ings depend upon the shape of the corrugations to control light in a particular diffraction order. Thus, gratings are useful as filtering mechanisms. Antenna reflectors sometimes incorporate grating designs. Gratings have existed for centuries for a wide variety ofpurposes. However, most grating components intended for use in scientific instruments have been developed since 1900. Diffraction gratings as they are used in modern components have been manufactured in a number of ways since the 1960s. They are now regularly incorporated into fiber optic filament and semiconductor components to act as lightwave filters. Gratings can be produced mechanically in a variety ofmaterials or photographically in layered films. A photographic interference grating is arecording ofa stationary interference fringe field (sometimes called aholographic grating). Since gratings are often fabricated on thin films with fine tolerances and densities, it is necessary to match the light source with the structure. It may be necessary to lower the light intensity or increase the thick- ness of the grating and associated component layers in order to prevent the light (which is often laser light) from melting the grating. See blazed grating, Bragg grating, diffraction, echelle grating, Fresnel lens, interference grating, ruled grating. grating arrow In scientific and engineering diagrams illustrating grating components with asymmetric corrugations, an indication of the orientation of the grating. For example, in asawtooth-shaped grating (e.g., a blazed grating), the arrow would be oriented from 419 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary the peak to the more distant trough (the one farthest from and connected to that peak) along the grating normal (typically illustrated along the horizontal [X] axis). grating equation In the context of diffraction gratings, an equation that enables the ordered angles of reflected incident light to be calculated and modeled. Thus, sine =sine + mA.ld with q representing the light source's incident angle upon a diffraction grating, at a wavelength of! and a grating period (the distance from one corrugation to the next) of d, q, rep- resents the diffraction angle such that the sin of the diffraction angle is equal to the sin of the angle of incidence plus the incident wavelength divided by the grating period. The structure ofdiffraction gratings and their effectiveness is in part due to the "tuning" of the angles to interact in desirable ways with specific wavelengths. See diffraction, grating, Wood anomaly. grating, fiber optic A series of grooves in a fiber optic filament intended to control the propagation oflight as it passes through the grating. For example, a grating can help control the direction of the lightwave, the wavelength(s) of the propagated light, or both. The grating is "etched" or "written" into the fiber and the fiber may be strained at the time the grating is Wl;t- ten. Multiple overlapping gratings may be used to further condition the propagating lightwave. Long-period gratings may provide phase-matched coupling from transfering power from one optical mode to another within a fiber (e.g., between guiding and cladding modes). Permanent long-period gratings are typically laser written through an amplitude mask. Adjustable long-period gratings may be mechanically written through pressure that produces nonpermanent microbends. Fiber gratings are used in sensors, scientific instruments, and fiber optic communication networks. See Bragg grating, grating. gravity cell, crowfoot cell A type of voltaic wet cell suitable for providing small currents at a constant electromotive force. It derives its name from the way the lower and upper chemical solutions (e.g., copper sulphate over zinc sulphate) align themselves in relation to each other. Gray, Elisha (1835-190 I) Aphysicist and inventor who developed many early telegraph technologies at about the same time Alexander Graham Bell was working to develop a harmonic telegraph. Gray was mechanically apt and had publicly demonstrated an early version ofa harmonic telegraph, a device to send tones over wire, before Bell applied for a patent for his version. Gray filed a caveat for a patent the same day as Bell filed for the patent on what is now Mechanically Impressed Adjustable Grating LI:CU-i-i~:j ~~ , lIel 09 1 r'~'~~'~"'AAO"""~ elastic 1- 1 pressure I I component ,- I I I flber-t- I grating +- I support I I L ~ A long-period adjustable grating designed by L. Mollenauer of Lucent Technologies, Inc. pmvides an alternative to pemJanent gratings. Instead of writing the grating into the stlucture of a single-modejiber; as is traditional, thefiber is impressed into an external mechanical grating ''form'' to inlfVduce microbends into thejiber that cause thepmpagatinglight to be conditioned for certain specified wavelengths. In other words, only selected wavelengths will escape the jiltering process and continue pmpagating along the transmission path. By inlfVducinga series of impressedgratings into the path. selectivity can befurther controlled. With this type of configuration, dynamic changes in the wavelength selectivity andgain equalization are possible. This may be practical for many situations where smallgratingperiods (the distance between cO/rugations) are not required. 420 © 2003 by CRC Press LLC considered to be the first telephone, thought of as a speaking telegraph at the time. In 1867, Gray developed a new telegraph relay instrument. In collaboration with his partner, Enos M. Barton, Gray organized the Western Electric Manu- facturing Company in 1869 and expanded by buy- ing out the Ottawa, Illinois Western Union offices. Late in 1873, Gray reports having noticed different vibratory properties in human tissue (an idea pio- neered by Meucci) and described the placing ofa gal- vanometer in the circuit with a microphone for transmitting human speech through wires. This observation resulted in a patent application that was not accepted until three years later as Gray had to substi- tute animal tissue for human to satisfy the Patent Of- fice. Gray filed a patent similar to Bell's only hours after Bell, and his company was later purchased by Bell. In the 1880s, telegraphs that would transmit hand- writing were developed and Gray patented a telau- tograph which could lift the pen between letters per- mitting more natural characters to be transcribed, and sold the rights to a company founded with his name. See telephone history. Gray, Stephen (1666-1736) An English experi- menter who authored an article for Philosophical Transactions in 1720, describing various investiga- tions of attractive properties and light-producing properties of various "electrics." He discovered that a substance electrified by friction could pass this property to another substance. He enlarged on the prior work of Gilbert, demonstrating that Gilbert's "non-electrics" could conduct electricity from one body to another and could be electrified if insulated with a conductor. His association with the Royal Society of London indicates that he was likely familiar with the work and writings ofF. Hauksbee, and he continued some of the interesting lines of inquiry first investigated by Hauksbee. In the late 1720s, Gray began a fruitful collaboration with Granville Wheler, a member of the Royal Soci- ety. Gray and Wheler were to discover that substances could be roughly divided into additional substances that readily conducted "electric virtues" and those that did not. See inductance. Gray& BartonA telecommunications company established by Elisha Gray and Enos Barton in 1869 when Elisha Gray bought out George Shawk's interest in the partnership. The physical facility was an electric shop abandoned by the Western Union Tele- graph Company. In 1872, it became Western Elec- tric Company, which supplied components to the Western Union Telegraph Company and later became an exclusive manufacturer for the Bell System. See Graybar Electric Company, Inc.; Western Electric Company. gray market product One of several types of products that are not fully endorsed by the manufacturer. Examples include a product sold by an unauthorized distributor; a product that might be second rate in some way, which nonnally wouldn't be sold by repu- table dealers; or a return item that is promoted as be- ingnew. GrayTelephonePay Station CompanyA company fonned to commercialize the rotary payphones that were common from about 1930 to the 1960s. Graybar Electric Company, Inc. A spinoff of the Western Electric Company in 1925, this company handled electrical distribution. The name derives from the original founders of the Gray & Barton company, founded by Elisha Gray and Enos Barton in 1869. In 1928-1929, the employees purchased the company from Western Electric Company, and it is still one of the largest employee-owned companies in the United States. Graybar Electric continues to do business after more than sixty years, globally sup- plying almost a million different electrical and telecommunications products. See Gray & Barton, West- ern Electric Company. grayline The region in any particular place where the Sun is rising or setting. This infonnation is of interest to those trying to detennine a radio signal transmissions path using the characteristics of the Earth's ionosphere to help propagate the signal. There are software programs containing extensive databases of thousands of cities, designed to generate a grayline chart and display a world clock to assist amateur and professional radio operators in sending and receiv- ing radio communications. Some grayline generators also include azimuth projection maps (Great Circle maps) which can help the user detennine where radio signals may be arriving from different parts of the world, depending upon location and time of day. See ionosphere. grayscale Visual infonnation represented in shades of gray, i.e., with no color. In computing tenns, many people confuse the terms monochrome and grayscale. Monochrome refers to one active color, whether it be white, black, green, or amber. Many older computer monitors were monochrome monitors. Grayscale refers to two or more (typically 16 to 64) shades of gray typically ranging between white and black. Grayscale monitors are less expensive than color and are very suitable for desktop publishing and other black and white and grayscale print-related applications. grayscale monitorA monitor capable of displaying a variety of levels of light intensities (usually between 16 and 64), which are perceived as shades of gray. grazing incidence An angle that is perpendicular or nearly perpendicular to a reference surface's normal such that an incident wave within the grazing incidence tolerances is reflected off the surface. For re- flection at very low grazing angles that are almost parallel to the surface in an internal resonating cav- ity, a very highly reflective surface and short high- energy wavelengths (e.g., X-rays) are generally required. However, external resonators/reflectors have been used with wavelengths in the optical region. Assemblies with two adjacent dielectric materials with different indexes of refraction may exploit grazing angles to achieve total internal or external reflec- tance, depending upon the relationship of the conduc- tive materials. 421 © 2003 by CRC Press LLC . Grating LI:CU-i-i~:j ~~ , lIel 09 1 r'~'~~'~"'AAO"""~ elastic 1- 1 pressure I I component ,- I I I flber-t- I grating +- I support I I L ~ A long-period adjustable. An English locomotive engineer and businessman who aided in the installation of the fITst successful permanent telegraph cable link between North America and the British Isles. At arelatively young age, Gooch was appointed the locomotive superintendent of the Great Western Rail- way (GWR). In 1840, Gooch contacted gifted engineering designer Isambard K. BruneI about designing an engine works for GWR (this association between the two talented engineers was to take an interesting tum more than a decade later). Using new 413 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary technology and the results of experiments in atmospheric. Satellites in the Global Posi- tioning System (GPS) send out two microwave carrier signals, one of which provides navigation information in the form of a series of time-lagged data 415 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary frames sent over

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