Fiber Optics Illustrated Dictionary 1032 V-dimension ofrecorded spot In facsimile transmis- sions, the X -dimension ofrecorded spot is a means of describing variation density in terms of the mini- mum density. The largest center-to-center space be- tween recorded spots is measured in the direction of the recorded line. When it is assessed perpendicular to the recorded line, it is the V-dimension ofrecorded spot. The same principles can be applied to assess the scanning spot. YIe Acolor image information encoding scheme in which the chroma ( color) signals (C) are separated from the luminance (brightness) signals (Y). AY/C splitter cable enables the two signals to be handled separately. Yablonovitch, Eli (ca. 1947- ) A Bell research sci- entist and physics professor at Harvard and UCLA who pioneered concepts in photonic crystals, struc- tures that have significant potential for selectively controlling the behavior and wavelength filtering of light which, in turn, is valuable in the development of dense wavelength fiber-based transmission sys- tems and superfast computer systems. Yablonovitch described the structures in "Inhibited spontaneous emission in solid-state physics and electronics," in 1987, and by the early 1990s, had succeeded in pro- ducing a photonic crystal in a material with a rela- tively high refractive index (now called Yablonovite). In the mid-1990s, he collaborated with Sievenpiper et a1. in devising means to adapt the technology to longer wave lengths using 3D circuit arrangements. Yablonovitch has been awarded numerous honors for his work with photonic crystals, including the Wood Prize of the Optical Society of America. See Kawakami, Sujiro; photonic crystal. YAG See yttrium-aluminum-garnet. Vagi, Hidetsugu (1886-1976) A Japanese researcher, lab director, and educator who worked with his lab engineer, Shintaro Uda, to develop and describe a new, more sensitive directional antenna structure. See Yagi-Uda antenna. Yagi-Uda antenna A narrow bandwidth, linear, di- rectional antenna array that resembles a driven dipole antenna with branches (passive directors),- usually along one plane. The Yagi-Uda antenna improves gain with reflectors and directors (branches extend- ing out from the main rods) and works in high fre- quency ranges (radar, television, etc.). Rooftop tele- vision aerials commonly use Yagi-Uda antennas. This important antenna was designed and built ca. 1924-1926 by Shintaro U da and possibly also by Hidetsugu Vagi, Uda's lab director at Tohoku Uni- versity. The relative contributions of the two engi- neers are not clear. It was fIrst described in a paper by Vagi and Uda in 1926, but did not come to inter- national attention until it was described again by Vagi in an English language Institute of Radio Engineers (IRE) paper in 1928. Following this wider dissemi- nation of information, many called it the Vagi antenna and, ironically, it came to be more widely used in Ja- pan than abroad. U da continued to refine the design and adapted it for television reception in the mid- 1950s. An original Yagi-Uda antenna is housed in the © 2003 by CRC Press LLC Japan Broadcasting Corporation's Broadcast Mu- seum. In 1995, the antenna was awarded an IEEE Electrical Engineering Milestone. Yahoo A significant, high-profile, extensive search and information site originally developed at Stanford Univershy and established on the World Wide Web in the mid-1990s. Yahoo provides general search ca- pabilities as well as a large database of sites organized according to popular categories and topics. Yahoo also sponsors Yahoo Groups (formerly E-Groups), discussion lists. http://www.yahoo.com/ Year 2000, Y2K A designation for the electronic changeover to the new century, a circumstance that was not anticipated and accounted for by all program- mers when designing hardware, operating systems, spreadsheets, databases, backup software, schedul- ers, and the like. Many software programs and hard- ware clocks accommodated only up to the year 1999 and were not capable ofrolling over to 2000. A sig- nificant number took into consideration only the last two or three digits of the year, and thus were unable to resolve a "00" that followed a "99," for example, causing potential file and data problems for backup systems as well as various application programs. yellow alarm See yellow signal. Yellow Book CD-ROM A CD-ROM authored and written according to Yellow Book standards in ISO 9660 format, a format very common in computer mul- timedia applications. Yellow Book 1. Standard for the physical format of a CD-ROM or audio CD disk (as opposed to the logi- cal format). DVD drives are able to read CD-ROMs created according to Yellow Book standards. The Yellow Book followed from the original Red Book digital audio (CD-DA) standards. Yellow Book made it possible to store computer data in addition to au- dio data and supported up to about 650 MBytes of data. There are two subcategories, Mode 1 and Mode 2, for data with and without logical error correction (LECC). Mode 2 can support both Mode 2 and Mode 1 on a disc. See CD-ROM, ISO 9660. 2. Standards for audits of U.S. government organizations, pro- grams, and functions, and of government assistance paid to nonprofit organizations, and contractors. Yellow Book, Jargon This is a common name for the illustrated printed publication The New Hacker s Dic- tionary, which is descended from the infamous Jar- gon File. See Jargon File. Yellow Box An Apple Computer Inc. designation for an object-oriented, OS-independent developer plat- form that was initiated after NeXT was folded into Apple Computer. See Blue Box, Red Box, Rhapsody. yellow pages 1. colloq. A common name for a num- ber of business/advertising sections in various phone directories printed on yellow paper to distinguish the section from residential and government listings. Many online electronic business directories are col- loquially called the yellow pages, although British Telecom has a trademark on the name. 2. A Sun Mi- crosystems client/server protocol for system configu- ration data distribution now known as Network In- formation Service (NIS). See Network Information Service. Yellow Pages A trademark ofBritish Telecommuni- cations. yellow signal In telecommunications, an alarm con- dition, warning, or failure signal, usually in a network. The signal is often a yellow-colored light, though it may be an auditory or textual signal or a specific data value or sequence. On gauges, there may be a yel- low band indicating a warning level, with a red band for more serious problems, such as danger levels or stop indicators. Color-coded signals are industry and even product specific but, in general, red signals are used for more serious conditions and yellow signals for localized failures or less serious warnings (conventions simi- lar to those used in railroad and traffic signals). Warn- ings may even be associated with a specific segment ofa network (e.g., fiber optic transmission link). In ATM networks alarm interfaces indicate whether alarm conditions are present. Data values are used to indicate a no alarm condition or that an incoming yellow signal, for example, has been received. Loss of frame failures are commonly signaled by alarms. Detection ofa yellow or red signal alarm in a data network may trigger other signals, such as unavail- able signal states, and timers to log the duration of an unavailable signal event. In SONET networks, a yellow signal may remotely signal a failure or help in trunk conditioning. A far end receive failure is a more specific instance of a failure detection signal in the downstream direction. In DS3 network interfaces, a yellow signal may trig- ger a yellow alarm, described in ANSI Tl.107-1989. A loss of signal, loss of frame, or alarm indication signal (AIS) may trigger a red alarm, which is cleared if there are no severely errored seconds (SESs). Com- monly, in data networks, alarms are declared after a certain number of consecutive seconds have elapsed (e.g., 2 seconds) and cleared after a certain number of seconds have elapsed (e.g., 10 seconds). yellow wire 1. A color designation used by ffiM to indicate wires used to re-establish a broken connec- tion in traces or flat cables (ribbon cables). See blue wire, purple wire, red wire. 2. A color commonly used for ring on the second phone in four-wire phone in- stallations (two wires for each phone). The corre- E~~:SI ~~~~~~~~~~a~~i~~ certification pro- I. Yes, yes key A pushbutton shortcut key on some ap- pliances or keyboards ( e.g., teletype-style) to Rrovide an affirmative response without typing ''yes. ' YIG See yttrium-iron-garnet. YIG filter A wide bandwidth filter in which a YIG crystal is positioned within the field ofa permanent magnet associated with a solenoid and tuned to the center of the frequency band. YIQ A color model originating from hardware characteristics that is used in color television transmis- sion and for some computer monitors. Y is luminosity; I and Q provide chroma signals separate from the lu- minosity in order to provide backward compatibility 1033 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary with black and white standards. On black and white (grayscale) televisions, only the Y component of the signal is displayed. See Y signal. YModem A data transfer protocol commonly used with modems developed by Chuck Forsberg as a suc- cessor to XModem. Typically faster than XModem or Kermit, though not as well supported on BBSs and at services bureaus as XModem and ZModem. YMo- dem comes in two flavors, batch and nonstop (YMo- dem-G). The batch version allows multiple files to be sent in a transmission session and wildcard char- acters for filenames are supported. When errors in transmission are frequent, YModem is able to fall back automatically to smaller packets, thus accom- modating a poor line connection, but is not compat- ible with the error correction ofXModem. See XMo- dem, ZModem. YModem-G A nonstop streaming variation of the batch-oriented YModem network communications software developed by Chuck Forsberg. YModem- G does not wait for receiver acknowledgments and does not have built-in error correction, instead it re- lies on an error-correcting modem to supply the er- ror logic. It's appropriate in situations where a good clean connection is available and speed is desired. If a problem with a bad block is encountered, the en- tire transfer is aborted. Unlike ZModem, it cannot resume a new transmission at the point at which er- rors and termination of the initial session occurred. See YModem, ZModem. yocto- y. A prefix for an SI unit quantity of 10- 2 4, or .000 000 000 000 000 000 000 001. It's a mind- bogglingly small quantity. See yotta-, zepto- yoke 1. A clamp or frame that unites or holds two parts or assemblies firmly together. 2. A coil assem- bly installed over the neck of a cathode-ray tube (CRT) to deflect the electron beam as currents pass through it. 3. A ferromagnetic assembly, without windings, that forms a permanent connection between two magnetic cores. yotta- Y. A prefix for an SI unit quantity of 10 2 4, or 1,000,000,000,000,000,000,000,000 or 1000 8 • It's a mind-bogglingly large quantity. See yocto-, zetta Young, Thomas (1773-1829) A precocious English scientist and physician who was accepted into the Royal Society when just barely in his 20s. Young be- came the foreign secretary to the Society in 1802 and retained the position for the rest of his life. In 1800, he published Experiments on Sound and Light and described his influential research into the theory of optical interference. Young lived in a period of his- tory when the wave and particle nature of light were only barely understood and still hotly debated. Fresnel was the first to really make use of the many important discoveries of Young. See interference, Newton's rings. YSZ yttrium-stabilized zirconia. A material that is usually distributed in powder fonn for manufacture into a range of products that are corrosion-resistant and readily shaped with molds. It sells for about $400 - $700 per 100 grams of powder or suspension. The material is used in the production of oxygen sensors 1034 and oxygen generation systems. See yttrium, zirconia. yttrium A metallic element similar to the rare-earth metals with which it is typically found. Yttrium ox- ide is used with Europium to make red phosphors for cathode-ray tubes. See erbium, europium, gadolinium. yttrium aluminate A substance with a low dielec- tric constant that is suitable for high-frequency ap- plications. yttrium-aluminum-garnet YAG. Acrystalline sub- stance used in laser electronics, YAG may be doped or undoped. YAG can be shaped into fibers, rods, single crystals and polycrystalline forms. It is useful in precision lasers, filter and bandgap components, and for reinforcing fiber in composite materials. When YAG is doped with cerium, it can be used to produce scintillation. A YAG scintillating crystal has a long lifespan and is useful in electron microscopy. See scintillator. yttrium-aluminum-perovskite YAP. A crystalline substance used as a scintillating material in electron microscopy, YAP has high light-emitting properties and good resistance to high temperatures and radia- tion damage. YAP has a faster decay time than yt- trium-aluminum-garnet (YAG). YAP is versatile in terms of emitted spectrum (may not require replace- ment of an existing photomultiplier) and long-lived, capable of outliving the lifespan of the instrument for which it is producing a scintillation material (e.g., electron microscope). yttrium-iron-garnet YIG. A crystal used in the manufacture of amplifiers, filters, multiplexors, etc. that is used with a variable magnetic field to tune wideband microwave circuits. See YIG filter. Yukawa, Hideki (1907-1981) A Japanese physicist who proposed a new nuclear force- field theory and a massive nuclear particle, the meson. The existence of the meson was verified by Cecil Powell a couple of decades later. Yukawa furthered the nuclear pro- cess ofK capture, the absorption of an innermost en- circling electron. This theory, too, was subsequently confirmed. Yukawa received the Nobel Prize in Phys- ics in 1949 for his significant contributions to the un- derstanding of quantum mechanics. yuppie young urban/upwardly mobile professional. Atakeoff on the term hippie from the sixties, a yup- pie was generally someone born into a home with good financial resources or who was ambitious and was likely to enjoy a prosperous living. yurt A sturdy, circular, temporary, mobile shelter of Asian origin. Yurts are used on work sites where shel- ter for equipment and workers is needed during con- struction or installation work. In the author's town, little yurts have been popping up around the various road construction sites under which new fiber optic cables are being installed. YUV A color encoding scheme to accommodate hu- man visual systems which are less sensitive to color variations than to intensity variations (particularly in individuals who are color blind). Thus, YUV uses full bandwidth to encode luminance (Y) and half band- width to encode chroma (UV). See Y IC. yV V-matrix ofa vacuum tube. © 2003 by CRC Press LLC Z 1. symb. impedance. See impedance. 2. abbrev. Zulu time. See Zulu time. 3. abbrev. Zebra time. See Zebra time. 4. symb. zetta See zetta. 5. The name ofa formal specification language for describing and modeling computing systems, based on axiomatic set theory and predicate calculus. Z was developed at Ox- ford University in the early 1980s. Z axis A reference baseline or vector within a coor- dinate system, most often associated by convention with rectangular or Cartesian coordinates. The Z axis is oriented perpendicular to the X and Y axes in a three-dimensional system. See Cartesian coordinates, X axis, Y axis. Z axis modulation The varying of the intensity of an electron stream in a cathode-ray tube (CRT) by manipulating the cathode or control grid. Z code In telegraphy, a system of shortcut codes re- lated to short phrases to save transmissions time. Z codes were those prefixed with "Z," a rarely used let- ter, to reduce the chance of confusing them with the content ofa message. For example, ZFB meant "Your signal is Failing Badly." Z Fiber A commercial pure silica core optical fiber developed by Sumitomo Electric Industries, Ltd. (SEI) which held the record for low loss at attenua- tion of 0.154 dBlkm from 1986 to 2002, when it was succeeded by a new fiber by the same company. Z Fiber is suitable for repeaterless submarine dense wavelength division multiplex (DWDM) transmis- sions applications. See Sumitomo Electric Industries, Z-PLUS Fiber. Z force The pressure sensitivity of touch-activated devices, such as touchscreen monitors or touch-sen- sitive pads, as are often used in kiosks. Z Series Recommendations A series of ITU -T rec- ommended guidelines for programming languages and general software aspects of telecommunications systems. These guidelines are available for purchase from the ITU- T. Since ITU- T specifications and rec- ommendations are widely followed by vendors in the telecommunications industry, those wanting to maxi- mize interoperability with other systems, or conform to software conventions widely used, need to be aware of the information disseminated by the ITU- T. A full list of general categories is listed in Appendix C and specific series topics are listed under indi- vidual entries in this dictionary, e.g., B Series Rec- ommendations. See Z Series Recommendations chart. Z-80 The Zilog Z-80 8-bit computer microprocessor was released in 1976 by the Zilog Corporation and was quickly incorporated into many control and ro- botics applications, and into a number of popular microcomputers such as the Tandy Radio Shack Model I and LNW-80 computers. While it was ca- pable of clock rates up to 2.5 MHz, implementations of 1.4 to 2.4 were common. The Z-80 evolved from the Intel 8080 with which it was more or less compatible; it was faster, with more instructions, not all ofwhich were used to ensure compatibility with 8080 systems. The Z-80 has a simple register structure, including index registers and an accumulator, and is capable of 16-bit address- ing through 8-bit double register pairs, something not found on most of the other microprocessing chips that were incorporated into 8-bit microcomputers at the time. Many hobbyists acquired their first machine lan- guage and assembly language programming skills on the Z-80 chip. The original Z-80 was followed by faster versions, such as the Z-80A, Z-80B, and oth- ers, and has been used for over two decades in many control applications such as robotics and satellite te- lemetry, due to its simple efficiency, low cost, and practical instruction set. See TRS-80. z-fold, zigzag fold, fanfold A term for a type of fold often used in continuous-feed forms and other com- puter printouts. The name is derived from the shape of three sheets ofpaper that alternately fold one way or the other along the perforations. Z-marker See zone marker. Z·PLUS FiberA commercial pure silica core opti- cal fiber with fluorine-doped silica cladding, devel- oped by Sumitomo Electric Industries, Ltd. (SEI) which held the record for low loss at attenuation of 0.154 dB/km from 1986 to 2002, when it was suc- ceeded by a new fiber by the same company. The Z- fibers are widely used in repeaterless submarine cable installations. See Sumitomo Electric Industries, Ltd., Z Fiber. Z++ Just as e++ is seen as a more recent, object-ori- ented derivative of the C programming language, Z ++ 1035 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary is an object-oriented extension of Z, a formal speci- fication language for describing computing systems. SeeZ. Zl A historically important pioneer home-brewed binary relay computer developed in Germany in the mid-1930s by Konrad Zuse. While this was a signifi- cant pioneering computer construction, it was largely unknown outside of Germany due to the second World War and, as such, did not significantly influ- lTU-T Z Series Reeommendations Recom. Z.I 00 S~<;i~c~tioll~lIid description lan~e{$PL) Z.lOS SDLcom.biried with ASN.lmodules (SDLlASN.l) ZJ 06 '. GOmtnol1itl~rchange fonnatfqr" SDL Z.107 SDl.,withembeddedASN.l Z.l09 SDLcoml)ilJedwith UML Z.l 10 Criteriaforuseof formal description techniquesl.lY ITU-T Z.120 Message sequence chart (MSC) Z.130 ITI!0bject<ietinitio~ language Z.140 Jlu:~r~tll1tj,t~bttlaJ' combmed:, notation'V'e~i9q3 ·(TTCN 3);(1ore language Z.141 Jberre~~dTabular ColIlbitled NotationversiotJ 3 (TTCN"3): '[abul8fpr~entation fonnat Z.200········: CHII.L::1'11e[fU. T Progranlmitlg Language Z.30t Introduction to the CCITIman- machine language Z.302 Themeta-ltltlguage for describing MMLsyntQ.and dialogue proced~~::.;: ' . . Z.311 Iptrpd1.lpp~~~Q:syntax .• and,9j~lQgue· . procedure~' Z.312 BfiSic f01'lJlatlay()ut Z.314. The character.set and basic. elements Z.315 Input{cotnp1~pd}languagesyr1taJt. sp~~ificati9g . Z.3t6·. Ol1tputJ81i~gf:sYntaxspecification Z.317 Man-macb.i!l.edialogue procedures Z.321 Introductionto the extended MML for visual display terminals Z.322 Capabilities of visual display terminals Z.323 'Man-~cl:!W~igteraction Z.331 >Introductioltto:the specification of the.man-macnineinterface Z.332 Methodologyfortbe specification of the man-machine interface - General 1036 ence the industry abroad. It is noteworthy that it was built in an apartment, rather than in a university re- search facility as were other pioneercomputing plat- forms. See Zuse, Konrad. Z3 A historic programmable, general purpose com- puter, developed by Konrad Zuse. The Z3 was re- leased in 1941. See ZI, Zuse, Konrad. zap slang To eradicate data, to bum out a circuit, or to apply charge to an object or environment. It may or may not be intentional, and can result from power fluctuations such as those caused by lightning (which is probably where the term originated). You can zap a file to kill specific data (or the whole file), you can zap food in a microwave, and you can zap or "fry" a circuit by accidentally shorting it. The tenn is occa- sionally used to indicate a quick change, such as the changing of a TV station with a remote, but this di- lutes the meaning of the term and is better avoided (unless perhaps it's a lightning fast change) as zap is intended to describe an action or event that is poten- tially dangerous, lethal, or destructive, especially where electricity is involved. See kill. zapper 1. A device for applying a sudden stimulus such as electricity or heat that affects an immediate change such as a burn or incision. Examples include shock devices such as a stun gun or a laser torch or scalpel. 2. A software utility that causes something to be instantly altered or removed, such as a file zapper that may be designed to seek out and perma- nently eradicate the entries of customers who have not purchased anything for more than a year. ZBLANAheavy metal fluoride glass used in the fab- rication of fibers, ZBLAN is fluorine with zirconium, barium, lanthanum, aluminum, and sodium (Zr, Ba, La,Al, Na), sometimes called fluorozirconate. Fibers manufactured with ZBLAN have low attenuation and good transmission properties. Compared to silica- based glass, ZBLAN supports a broader spectrum of wavelengths, from ultraviolet to infrared. It is also possible to dope ZBLAN fibers for use as fiber am- plifiers. By 1998, D. Tucker at the NASA/Marshall Space Flight Center had reported that ZBLAN does not crystalize as readi ly, and is clearer, ifconstructed in a near-weightless environment away from Earth's gravity. This leads to a remarkably pure, clear fiber and ZBLAN's transmission properties approach that which is considered theoretically best. ZBLAN sig- nificantly outperfonns silica glasses in the regions above which they "top off' at wavelengths of about 2.3 fl. ZBLAN is capable oftransmitting wavelengths of up to 4.5 fl and higher. In actual use, ZBLAN is currently limited to short distances, but with im- proved fabrication processes to prevent or reduce crystallization, the potential of ZBLAN for fiber com- munications in a broad spectrum of wavelengths is excellent. Scientists point out that the whole process doesn't have to take place at zero "g" to take advantage of space-based ZBLAN optical fiber. The fiber preforms could be created in space, with the filaments pulled back on Earth. See prefonn, vapor deposition process. © 2003 by CRC Press LLC ZBLAN Low Gravity Fiber-Pulling Experiments 4.0 1.5 io 2.5 3.0 15 w.v.length (1ft1cs'aM) 0.5 100.00 Comparison of ZBLANfibers pulled at 0 G (left) and 1 G (right) aboard alow-gravity experiment con- ducted by the NASA/Marshall Space Flight Center. Bubbles and other defects in the example on the right will scatter optical signals and interfere with traansmission. The pure, uncrystallized opticalfiber on the left has the potential to transmitt 100 times more data than traditional silica-based optical fibers. [NASA/Marshall photos.J ZBLAN - Silica Comparison Opticalfibers made from ZBLAN rather than silica exhibit aprofile of efficiencyfarcloser to the theoreti- cal best. NASA has been conducting research into pull- ing ZBLANfibers in space where conditions can be createdfor reducing crystallization. [NASA/Marshall Space Flight Center, 1998.J 10,000.00 I I A miniaturefurnace designed to study ZBLAN op- tical fiberpulling under low gravity conditions aboard a KC-135 aircraft. It is operated here by Guy Smith of the University of Alabama in collaboration with Dr. Dennis Tucker of the Marshall Space Flight Cen- ter, in experiments conducted in 1999. 1037 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary ZBTSI See zero byte time slot interchange. Zebra time, Z time The same as Greenwich Mean Time. See Greenwich Mean Time, Z. Zeeman effect An effect observed in 1896 on the structure of gas spectrum lines when subjected to the influence of a moderately strong magnetic field. It was observed by Pieter Zeeman that sharp spectral lines split into multiple closely spaced lines. This early puzzle gave rise to a number of lines of research in quantum physics. The number of lines is gener- ally three, although anomalous effects have been ob- served and even stronger magnetic fields can cause some spectral lines to emerge. The Zeeman effect is a useful tool in a number of ar- eas of science including the study oflaser light. It intrigues quantum physicists and is used by astro- physicists to map the magnetic field strengths of so- lar effects and to study other galactic magnetic fields. The Zeeman effect is often described along with the Stark effect (the influence of strong electrical fields on spectral lines). See Stark effect. ZenAn Asian Buddhist system ofbelief that encour- ages meditation and self-discipline, and the attain- ment of enlightenment through direct intuitive expe- rience. See Zen mail. Zen mail A tongue-in-cheek descriptive phrase for computer communications that erroneously (or de- liberately) arrive with no content in the body of the message. See Zen. zener current In an intense electric field, a current through an insulator sufficient to excite an electron from the valence band to the conduction band. zener diode An electronic component that behaves like a rectifier below a certain voltage, but exhibits a sudden increase in current-carrying capacity above a specific voltage level (zener value) and a corre- sponding decrease in dynamic resistance resulting in a reverse breakdown. The dual nature (di-) makes it possible to represent conducting and nonconducting (or very low conducting) states as a binary system and the breakdown under reverse bias (functioning as an open circuit) is particularly useful as a refer- ence circuit or as ashutoff circuit to respond to power surges above a certain voltage threshold. Doping is a manufacturing process in which elements such as rare earth elements are introduced into a sub- stance (e.g., fiber optic cable) to improve its quali- ties for a particular purpose such as the transmission of laser light. Doping is also used in semiconductors to influence their conducting qualities. Heavy dop- ing in p-n junctions, for example, results in very thin depletion layers that hinder impact ionization but fa- cilitate quantum tunneling and the flow of current. This, in turn, leads to zener breakdown which is somewhat related to avalanche breakdown from im- pact ionization, as may occur in lightly doped p-n junctions. Zener diodes are used in voltage regulators and power supplies and help prevent electrostatic discharge in a wide variety of semiconductor technologies. They are becoming especially important in the mobile commu- nications industry because small portable devices 1038 become vulnerable to voltage surges/static electric- ity when they are connected to other devices such as network cables, docks. Tiny zener diodes capable of absorbing static surges are thus being incorporated into mobile phones, pagers, etc. zenereffectAreverse-current breakdown effect that occurs at a semiconductor or insulatorjunction in the presence ofa high electric field. See zener current, zener diode. Zenith Corporation One of the early entrants to the radio industry, Zenith was founded in 1931 by a ra- dio amateur and soon became a major manufacturer. Zenith now promotes consumer flat-screen, large-size television/media screens. Too bad the commercials aren't as classy as the products. ZEONEX A commercial tradename for ZION Technology's implementation of cyclic olefin poly- mer. See cyclic olefin polymer. zeppelin antenna Ahorizontally oriented antenna, which is a multiple ofahalf wavelength in length with a two-wire transmission coming into one end, which is also a multiple ofahalf wavelength. zepto- A standard metric prefix of the Systeme In- temationale (SI). The zepto unit is used in scientific measurement requiring very small numbers and rep- resents 1000- 7 in decimal. See zetta zero balancingA telephone service accounting tech- nique in which a specific dollar quantity is distrib- uted over a large category of calls. The total base price of all the calls within the category is used to calcu- late an adjustment percentage so the full dollar amount produces a zero balance (rounding errors are not permitted). zero beat In electronics and acoustics, a condition during which two combined frequencies match, and consequently do not create a beat. zero beat reception, homodyne reception In radio transmission reception, a system that uses locally generated voltage at the receiving end of the trans- mission, which is the same frequency as the original carrier and combines it with the incoming signal. See beat reception, heterodyne. zero bias 1. In a cathode-ray tube (CRT), the absence of any difference in potential between the cathode and its control grid. 2. In teletypewriter transmission cir- cuits, zero bias is a state in which the length of the received signal matches the length of the transmit- ted signal. zero bit insertion, bit stuffing In data communica- tions, the process of inserting a zero bit after a series of one bits in order to specify a distinct break or change. Thus, the beginning or ending ofa frame is not misconstrued. This is sometimes used in place of control signals. zero compression A data compression technique in which nonsignificant leading zeros are removed. zero fIllA data manipulation technique in which ze- ros are inserted into a file or transmission without affecting the meaning of the data. See zero bit in- sertion. zero dispersion In an optical waveguide, physical characteristics that result in the propagating © 2003 by CRC Press LLC phenomena traveling in step with one another from one end of the link to another (without dispersing). This situation is actually somewhat difficult to achieve, especially in long haul fiber optic links car- rying multiple wavelengths. Due to the different reflective lines of travel of dif- ferent light beams, they tend to arrive at the endpoint at different times. Different frequencies in the same lightguide (e.g., in multimode fiber) also will have different travel speeds due to their different energy levels and characteristics. In addition, the wave- lengths of the lightwaves are not usually coincident with acoustical vibrations that occur in the cable ex- cept at certain specific frequencies. Thus, various types of dispersion almost invariably occur and, in fact, tend to be detrimental to the composition of the signal at the endpoint (it's usually advantageous for related signals to arrive at the same time). Thus, zero dispersion often a design goal in the en- gineering and construction of fiber optic communi- cations systems. However, there are situations where radiant energy in a cable will travel without disper- sion and may be in phase with energy that could cause noise. In very short cable lengths, there may not be sufficient distance/time for the different parts ofa sig- nal to shift from one another, especially if the lightguide is very straight and little internal reflec- tion is necessary to channel the light. In a carefully engineered cable where graded index fiber is used to compensate for differences in reflectivity and travel time in different wavelengths, dispersion may be minimized and approach zero. Thus, there is a bal- ance between trying to achieve zero dispersion and interference factors that may impinge upon the sig- nal when it reaches that level. See dispersion, zero- dispersion wavelength. zero-dispersion slope In a single-mode optical fiber, for example, the rate of change of dispersion at the zero-dispersion wavelength relative to the light beam's wavelength. zero-dispersion wavelength (symb. - A o ) In an op- tical waveguide, the wavelength( s) at which material disperson and waveguide dispersion cancel one an- other, in the sense that they are in phase. When un- wanted wavelengths move in step with operational wavelengths, significant interference can occur. The Aois sometimes called the "dispersion window." In dispersion-unshifted silica-based optical fibers, the A o occurs at about 1.3 Jlm, in dispersion-shifted fibers at about 1.55 Jlm. Dispersion-shifting may be accom- plished by doping the fiber. It is important to under- stand the disperion wavelength phenomenon so as to avoid undesired nonlinear interference and modula- tion instability. It is also possible to achieve high data transmission rates near this frequency, so it helps to know just where that point lies. Dispersion-shifted fiber (DSF) shifts the zero-disper- sion point from 1310 to 1550 nm to move it out of the phase range. However, four-wave mixing may occur in these fibers, so they are more suitable for single-channel systems than others. To gain the ad- vantages of dispersion-shifted fiber while avoiding the disadvantages of four-wave mixing, nonzero dis- persion-shifted fiber was developed (e.g., OFS's TrueWave RS fiber). Dispersion-compensatingfiber (DCF) is another spe- cialized type of fiber useful for endlink connections because it has a high negative dispersion value that reverses chromatic dispersion. Zero-dispersion wavelength parameters have tradi- tionally been difficult to measure precisely, hinder- ing the development ofa reference standard. Mechels et al. have described the development ofa frequency- domain phase-shift system intended to reduce sys- tematic A o measurement errors. See dispersion. zero insertion force ZIF. A type of socket used in integrated circuits that allows a chip to be inserted without undue pressure. A lever or screw is then pushed or turned to secure the component so that it is not dislodged due to bumping or transit. This type of socket costs more than standard pres- sure sockets and tends to be used in specialized sys- tems such as test systems or with specific chips that are larger or more expensive. zero level A level established in order to have a ref- erence from which to judge further states or activi- ties of sounds and signals for observation, calibra- tion, or testing. The definition of zero level is tech- nology specific. zero potential The potential of the Earth, used as a reference measure. zero power peripheral A device that requires very little power and consequently can draw that power from the primary device to which it is attached, or from the circuit with which it is associated. Some mo- dems and most telephones take their power from the phone line, unless they have extra features (e.g., speakerphone) requiring additional power. Zero power peripherals are favored in constrained spaces and mobile communications as they are often less bulky than standard peripherals with power sup- plies, and easier to attach, since extra electrical out- lets are not required. zero punch A punch located specifically in the third row from the top ofa punch card. See Hollerith card, punch card. zero shift, zero drift A descriptive measure of the amount of shift or drift that has occurred from the original setting or calibration point, at a subsequent point in time. See zero stability. zero stability The ability of an instrument to retain its original state or settings over time, that is, to wi th- stand zero shift. Zero stability is generally considered a desirable characteristic. See zero shift. zero stuffing See zero bit insertion. zero suppression The elimination of zeros that are not meaningful. Zero suppression is often used to in- crease the readability of information with leading zeros, for formatting or transmission purposes, which would otherwise be distracting or confusing to a hu- man reader. In these cases, the zeros are often re- placed with a blank (a space character on printouts). Tables and columnar data (like financial statements) are usually printed with zero suppression. 1039 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary zero transmission level reference point For an ar- bitrarily selected point in a circuit, a level reading that is subsequently used against which to measure trans- mission levels in other points of the circuit or at the same point at another time. In telephone transmis- sions, the reference point is frequently selected at the location of the source of the transmission. zero usage customerA listed subscriber who has not used the network to which he or she has access. zero water peak fiber A type of optical communi- cations fiber first commercially released by OFS in 2002. This fiber pennanently eliminates a water peak that typically occurs at 1400 nm while preserving the 1300 nm wavelength band, thus substantially increas- ing capacity over traditional single-mode fibers car- rying E-band coarse wavelength division (CWDM) multiplexed transmissions. zerofI1I, zeroize To insert the zero character into un- used storage locations. This is done for a variety of reasons: for fonnatting, for creating space savers, and sometimes as a delay mechanism to match up trans- mission speeds with output speeds of slower output devices (printers, facsimile machines, etc.). zetta- Z. A standard metric prefix of the Systeme In- ternationale (SI). The zetta unit is used in scientific measurement requiring very large numbers and rep- resents 10 21 or 1,000,000,000,000,000,000,000 or 1000 7 in decimal. See yotta-, zepto ZIF See zero insertion force. Zimmermann, Philip R. A software engineer and cryptography specialist, best known for developing the Pretty Good Privacy (PGP) encryption scheme based upon the Blowfish technology, Zimmennann is the founder ofPGP, Inc. He is a software engineer with a long history of experience in cryptography, data security, data communications, and realtime em- bedded systems development. Zimmennann has been honored with numerous hu- manitarian awards due to his contribution to the safe- guarding of personal privacy, including the 1996 Norbert Wiener Award, the 1995 Pioneer Award from the Electronic Frontier Foundation, and many more. Zimmennann is a member of the International Asso- ciation of Cryptologic Research, the Association for Computing Machinery (ACM), and others. See Blow- fish, PGP Inc., Pretty Good Privacy. zinc (symb. - Zn) A malleable, light-bluish, active, metallic element (AN - 30) with a relatively high electropotential, useful in plating, dipping, and gal- vanizing, to prevent corrosion in other metals. It tends to be brittle and difficult to work with above and be- low 100 - 150 0 C. Combined with copper, it fonns brass. It is used for piping, construction accessories, and household items. zinc-fluoride (symb. - ZnF , F 2Zn1) A white, crys- talline zinc compound. Zinc-fluoride is one ofa num- ber of zinc compounds suitable for use in ZBLAN- type high-quality optical glass applications. See ZBLAN. zinc-oxide (symb. - ZnO, 0IZn1) A white, crystal- line zinc compound (familiar in commercial sun screens and antiseptive ointments) that is widely used 1040 in optics. Historically, zinc was used in early voltaic cells (the forerunners to modem batteries) such as the Daniell cell. See Daniell battery. At some wavelengths, ZnO is transparent. It is used in deposition processes, photocopier photoconductive surfaces, light-emitting diode components, and blue lasers. The material behaves differently when it in- teracts with gas molecules, making it suitable for the detection of flammable gases. It may be used to im- prove the physical properties of rubber. When zinc- oxide is combined with aluminum (AI), fluoride (F), or indium (In), it can function as an electrically-con- ducting oxide in optoelectronic applications. New fabrication applications for ZnO are being de- vised. In January 2002, Eagle-Picher Technologies announced the successful development of p-type thin film layers created from ZnO by a molecular beam epitaxy (MBE) process. This has potential for detec- tors and light-emitting diode and laser illuminators in the ultraviolet (UV) range. The addition of Mag- nesium (Mg) brings the spectral range even deeper into the UV spectrum. zinc-selenide (symb. - ZnSe, Se 1 Zn 1 ) An amber-to- reddish-colored crystalline zinc compound that has good unifonnity and transmission properties, as well as low bulk absorption ratings, though it is more brittle and subject to cracking than glass. In commer- cial applications, it transmits in the ca. 0.5 - 15 J.lm range and is popular for laser optics in the infrared spectrum. Zinc-selenide is used in lenses for carbon-dioxide lasers and certain guidance systems and spectro- scopes. It has also been used in experimental photo- conductive semiconductor switching circuits. Com- pounds similar to zinc-selenide are sometimes used in vertical-cavity surface-emitting lasers (VCSELs). zip v. To bundle up or compress a file or set of files, usually for transferring or archiving. The tenn is now commonly used for any such processing (zipping) of files, regardless of the archive utility used, but origi- nally referred to programs called gzip and PKZIP. See arc, compress, gzip, PKZIP. ZIP Zone Infonnation Protocol. zipped See zip, gzip, PKZIP. zirconia A substance exhibiting different molecular structures at different temperature ranges. Oxides may be combined with zirconia to reduce structural changes that occur at different production tempera- tures. Once stabilized, the material becomes highly resistant to temperature-induced phase transitions. Zirconia is customarily made by injecting zirconium- dioxide powder into molds and grinding the molded components to industry standards. Zirconia is a versatile material that is made into a ce- ramic for use in many industries, including the fabri- cation ofjoint prosthesis for surgical implantation. The material is favored for ferrules for fiber optic joint support due to its strength, resistance to environmen- tal erosion, and low insertion loss qualities; though some companies are now creating plastic ferrules with good optical performance. See ferrule, zirco- nium oxide. See YSZ. © 2003 by CRC Press LLC zirconium oxide A tan- or beige-colored substance with high refractory properties, low thermal conduc- tivity, low friction coefficents, and high heat toler- ance. Zirconium oxide is strong, versatile, and chemi- cal and corrosion-resistant. It is created by stabiliz- ing zirconia crystals to resist structural changes at different temperatures. The material is suitable for the production of ceramic ferrules for fiber optic connec- tors and, when combined with metal leads, can pro- vide illumination for spectrometers. It is also used in oxygen-sensing components. See zirconia. Ziv See Lempel-Ziv. ZModem A fast, flexible, error-correcting, full-du- plex file transfer data transmission protocol similar to XModem and YModem, but with updates and en- hancements. YModem and ZModem were written by Chuck Forsberg. ZModem is well supported by various telecommu- nications programs, and many BBSs and service bu- reaus use it. ZModem includes fallback and dynamic adjustment of packet size, which is important if the connection is a line with fluctuating characteristics. One of ZModem's most valuable features is its ability to re- sume a file transfer that has been aborted. With al- most all earlier desktop serial file transfer programs, if the line was interrupted or the file transfer aborted 99% of the way through, the program would start again from the beginning when reconnected, rather than resuming from where it left off. ZModem can detect a partial file, establish a new starting point at the end of the partial file, and continue transmitting until the transfer is completed or interrupted. If you've ever spent a couple of hours transferring a very large file on a slow link and lost it when the trans- mission was almost complete, you will appreciate ZModem's "resume" feature. See XModem, YMo- demo ZOG A high-performance frame- and link-based hypertext system designed for local area networks (LANs) developed at Carnegie Mellon University. It has evolved into a commercial product called Knowl- edge Management System (KMS). zone 1. An area, usually contiguous, which mayor may not be self-contained; or has some common char- acteristics within itself; or which is distinguished as different, in some way, from the surrounding area; or which is assigned on the basis of size, population, or some other economic or practical characteristic (as in shipping zones). 2. A section of computer storage allocated for a particular purpose. 3. In telephone communications, a specified area outside the local ex- change. 4. In cellular phone communications, a zone consisting of adjacent cells is called a cluster. 5. A region in which communications are banned or im- peded, called a blackout zone. 6. Aphysical or vir- tual region of access within a network, sometimes de- lineated by physical structures such as aworkstation or router. See firewall. zone, optical recognition A region manually speci- fied by the user, or automatically detected and en- closed by the optical recognition software, that cor- responds to aparticular type of information. For ex- ample, some optical document recognition systems, and some of the better optical character recognition systems, can distinguish columns and page numbers, images and formulas, and scan each separately from the others. Some software facilitates the preconfiguration of zones in a template. Order prior- ity for the zones may be assigned. In this way a long document, such as a book in which most of the pages are identical in format, can be scanned without re- setting the zones each time. Zones in Optical Recognition Many optical recognition programs will automati- cally determine zones or allow them to be manually configured. This allows theflow of text, and separa- tion of graphics and text to be handled more efficiently by the software, as in this Caere Omnipage example. zone, punch card One of three specific positions on the top ofa punch card. See punch card, zone punch. zone blanking Turning offa cathode-ray tube (CRT) at a point in the sweep of an antenna. zone cabling A cabling architecture designed for open office systems in which various physical zones are designated and cabled so that office desks and equipment can be moved around without ever being too far from the various necessary outlets and con- nectors. zone marker, Z-marker Avertically radiating bea- con oflight that signals a zone above a radio station transceiver. zone method A wire installation ceiling distribution system in which the space above rooms is organized 1041 © 2003 by CRC Press LLC . Industries, Ltd. (SEI) which held the record for low loss at attenuation of 0.154 dB/km from 1986 to 2002, when it was suc- ceeded by a new fiber by the same company. The Z- fibers are widely used in repeaterless submarine cable installations. See Sumitomo Electric Industries, Ltd., Z Fiber. Z++ Just as e++ is seen as a more recent, object-ori- ented derivative of the C programming language, Z ++ 1035 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary is an object-oriented extension of Z, a formal speci- fication. A o ) In an op- tical waveguide, the wavelength( s) at which material disperson and waveguide dispersion cancel one an- other, in the sense that they are in phase. When un- wanted wavelengths move in step with operational wavelengths, significant interference can occur. The Aois sometimes called the "dispersion window." In dispersion-unshifted silica-based optical fibers, the A o occurs at about 1.3 Jlm, in dispersion-shifted fibers at about 1.55 Jlm. Dispersion-shifting may be accom- plished by doping the fiber. It is important to under- stand the disperion wavelength phenomenon so as to avoid undesired nonlinear interference and modula- tion instability. It is also possible to achieve high data transmission rates near this frequency, so it helps to know just where that point lies. Dispersion-shifted fiber (DSF) shifts the zero-disper- sion point from 1310 to 1550 nm to move it out of the phase range. However, four-wave mixing may occur in these fibers, so they are more suitable for single-channel systems than others. To gain the ad- vantages of dispersion-shifted fiber while avoiding the disadvantages of four-wave mixing, nonzero dis- persion-shifted fiber was developed. A o ) In an op- tical waveguide, the wavelength( s) at which material disperson and waveguide dispersion cancel one an- other, in the sense that they are in phase. When un- wanted wavelengths move in step with operational wavelengths, significant interference can occur. The Aois sometimes called the "dispersion window." In dispersion-unshifted silica-based optical fibers, the A o occurs at about 1.3 Jlm, in dispersion-shifted fibers at about 1.55 Jlm. Dispersion-shifting may be accom- plished by doping the fiber. It is important to under- stand the disperion wavelength phenomenon so as to avoid undesired nonlinear interference and modula- tion instability. It is also possible to achieve high data transmission rates near this frequency, so it helps to know just where that point lies. Dispersion-shifted fiber (DSF) shifts the zero-disper- sion point from 1310 to 1550 nm to move it out of the phase range. However, four-wave mixing may occur in these fibers, so they are more suitable for single-channel systems than others. To gain the ad- vantages of