Optical Add/Drop Multiplexer. A device that routes selected optical wavelengths (channels) onto or off a fiber. This is a critical ingredient of DWDM networks. Sometimes called OWAD.
Orbital Angular Momentum. The angular momentum of EM fields has two components. One is spin angular momentum (SAM), better known as wave polarization. OAM is the other. In classical mechanics, angular momentum is the product of an object’s mass and speed of rotation. Photons, however, have momentum but no mass. Their OAM is a quantum-mechanical property that can’t be described well by familiar models, but can be observed in action: the OAM of a photon imparts mechanical torque to matter upon which the photon is incident. The effect is tiny, but could be used to manipulate microscopic objects. RF sources normally emit photons with random (incoherent) OAM, so that their opposing torques, which can be either left- or right-handed, cancel one another out.
In 2012, researchers demonstrated that the OAM of RF waves can be modulated to carry information, a technology that could vastly increase the bandwidth available in a given spectrum by multiplexing subcarriers at different OAMs. Transmission required a spiral phase antenna – a dish antenna with a radial cut and a slight twist. Signals with different OAM are orthogonal, so each can be demodulated without interference from the others. This new kind of modulation is colorfully described as “twisted light” or “corkscrew beams”. The University of Glasgow has this animation that shows why.
OpenAPI Specification. A standard for describing, developing, and using HTTP-based REST APIs across multiple protocols, interfaces, and environments. It was originally called the Swagger Specification, and sometimes still is.
“Swagger” properly refers to a set of software tools for creating and documenting OAS-compliant REST APIs, and the name of the company that makes these tools.
Open Artwork System Interchange Standard. A 2004 file stream format for describing the geometric shapes that make up a photoresist mask. Along with a simplified version called OASIS.MASK, it’s an industry standard for patterns from which to produce ICs, overtaking the much older GDSII.
On-Board Diagnostics. Any of a family of self-diagnosis systems built into automotive vehicles. The newer OBD-II uses a 16-contact connector, standardized by the SAE. It’s normally under the dashboard within 2 feet of the steering wheel, and uses one of five communications protocols. This connector taps into both the ECU and the EDR.
OBD-II female connector
Some insurance companies offer lower rates to customers who plug a tracking dongle into the vehicle OBD-II port. This creates an opening to hack the vehicle.
Optical Connection Controller. A component of a client-server optical network that maintains topology and resource availability data, and assigns circuits to meet service requests.
The base 8 number system, using the digits 0-7. It’s primarily used as a more compact way of representing binary numbers. Some sources prefer it over hexadecimal (base 16) for this role because it uses only digits already familiar from base 10. Various prefixes are used to indicate that a number is octal, most often 0 (zero) or o (lower case letter O).
A 2:1 increase or decrease in a variable, usually frequency. Also refers to the bandwidth between two frequencies in which the upper is twice the lower. See decade.
OLE Custom Control. An obsolete 16/32-bit programming object using OLE in Microsoft releases of C++, Visual Basic 4.0 (32-bit) and 5.0, and other programming tools for Windows 95 and Windows NT. Introduced in 1994 to replace VBX. It uses a .ocx file name extension.
Oven-Controlled Crystal Oscillator. A very precise but power-hungry oscillator type. It draws a heating current to maintain the crystal at a fixed temperature, usually about 10° above the highest expected ambient temperature. This eliminates frequency variations due to temperature change. See XO.
Open Database Connectivity. A 1991 standard interface from Microsoft. Uses SQL statements to implement its vendor-neutral methods for accessing proprietary databases.
OpenDocument Format. An open (unlicensed) ISO standard for a set of XML-based document file types. Version 1.1 was approved in October 2006. It’s the file format for OpenOffice.org, LibreOffice, et al. Filename extensions include .odt (text), .ods (spreadsheet), .odp (presentation), .odg (graphics), and .odf (formula). Contrast OOXML.
Original Equipment Manufacturer. The actual manufacturer of hardware sold with someone else’s logo on it. Microsoft has used “OEM” to mean an edition of MS Windows for installation on a new PC, as opposed to “Upgrade”, for a PC already running an older type of Windows.
Optical-Electronic-Optical. Switching of optical signals by converting them to electronic form for de-muxing, routing, and re-muxing. This type of switch is called “opaque” because there’s no optical path through it. It’s expensive and relatively slow, but all-optical O-O-O switches are an emerging technology, still (2012) too big and too power-hungry to be practical.
The weak interaction between light and matter is a key O-O-O problem. To address it, researchers are investigating photonic crystal (PhC) cavities, which combine very small size (a few wavelengths), high responsiveness, and the ability to confine light long enough to absorb it. Optical memory is expected to rely on materials with a refractive index that can be toggled between two states (clear/opaque) by laser pulses, although this currently requires a second laser to maintain the state.
Orthogonal Frequency Division Multiplexing. Also called COFDM (coded OFDM). A digital multi-carrier modulation (MCM) patented in 1970, and put to use 30 years later. The source data splits into parallel bit streams, each modulating its own PSK or QAM subcarrier. This uses less bandwidth than plain FDM, because the subcarriers are packed close so that their sidebands overlap. They don’t interfere because they’re mutually orthogonal, so that at each subcarrier’s spectral peak, the spectral response of all other subcarriers is zero.
Unlike conventional modulation schemes that mix a baseband data stream with an RF carrier, OFDM systems generate both the carrier and the data simultaneously within purely digital circuits using inverse FFTs. OFDM represents a conservative approach – it will operate through most types of channel interference, but will generally not provide optimum performance.
Orthogonal Frequency Division Multiple Access. Use of OFDM to transmit signals from multiple users. This technology is part of the 4G wireless standard.
Named for German physicist Georg Simon Ohm (1789-1854), and generally understood to be v = iR (voltage = current × resistance), the fundamental relation of electrical engineering. Strict literalists say that Ohm’s Law merely describes the property some materials have of electrical resistivity that doesn’t change with voltage. Certainly, it’s not a law in the absolute sense – it’s a fairly but not completely accurate description of the electrical behavior of most materials under most circumstances.
On-Line Analytical Processing. Querying databases and generating data relationships. This is NOT data mining, which is a more advanced, open-ended process that isn’t looking for specific answers.
Object Linking & Embedding. Two Microsoft “standards”, OLE1 and OLE2, for sharing data between applications and creating compound documents. Embedding means inserting a file object created by one application into another app’s document (e.g. an Excel graph in a PowerPoint presentation). It can be edited as long as its source application is available. Linking means that a document contains only a link to the object, which is stored elsewhere. Editing the original object affects all documents that link to it.
OLE 1 appeared in 1990 as a replacement for DDE, and in 1992 was added to Windows 3.1. The 1993 OLE 2 named its communication model COM (Component Object Model). Microsoft then declared that OLE was no longer an acronym, but the brand name for all their component technologies. With the 1996 introduction of ActiveX, Microsoft returned OLE to its original name and function: embedding and linking documents.
Organic Light-Emitting Diode. Made using a carbon-based compound deposited on a silicon IC chip. Active-matrix OLED displays are brighter and sharper than LCDs, with a wider viewing angle, no need for backlighting, denser pixel arrays, lower power, and thinner display panels that can even be made flexible. Since OLED pixels emit light rather than passing or blocking a backlight, they can render a deeper black when turned off. On the other hand, they do less well than LCDs with images that are mostly white.
Expectations that OLED displays would replace LCDs in the flat-panel display market, and even serve as a light source, were foiled for years by cost and durability issues, and by a NPE called Universal Display Corp. that holds many broad patents for OLED displays. In 2016, competitively priced OLED TVs began coming to market, pushing ahead of rival technologies OTFT and quantum-dot-enhanced LCD. Quantum-dot-enhanced OLED displays, abbreviated as QD-OLED, arrived in 2022.
Open Multimedia Applications Platform. A Texas Instruments family of SoC multi-core processors. An OMAP consists of a low-power ARM processor and one or more co-processors, typically DSPs. They're used primarily in mobile phones.
Object Module Format. An Intel format for object files, the intermediate form between programming-language source code and the machine language that runs on a 80x86 processor. A variant for 8051 processors is called OMF-51. Other standards of this type include COFF and ELF (2).
Object Management Group. A technology standards consortium founded in 1989 and focused on software development standards, notably UML. They’re at https://www.omg.org.
Radiating (or receiving) with uniform strength in all directions in the plane perpendicular to an antenna’s axis – not, as the name implies, in all directions. This is characteristic of dipole antennas. Contrast isotropic.
A way of representing signed binary numbers. The most significant bit is actually the sign bit, with 0 meaning positive and 1 negative. To generate a negative number, take its positive equivalent and invert every bit. For example, 00000001 is 1, so 11111110 is -1. Both 00000000 and 11111111 are 0. Twos complement notation is preferred.
Optical Network Unit. A telephone system drop-box in a subscriber neighborhood where a fiber-optic line from the central office links with local loops to individual subscribers.
Out-of-Order Execution. A set of three techniques for boosting CPU performance by changing the order in which it executes instructions:
dataflow analysis – Re-arranging instructions for optimal execution speed
multiple-branch prediction – Predicting the instructions most likely to be sent next
speculative execution – Executing the instructions predicted by multiple-branch prediction in parallel, so that if one of the branch predictions is correct, the results will already be in progress or complete when that instruction is received
Object-Oriented Programming. See programming language. Popular OO languages include C++ (a superset of C), Smalltalk (a syntactically simpler language with several dialects, including VisualWorks, Smalltalk/V, Visual Smalltalk, and Visual Age), and Java (C++ syntax with some Smalltalk features, including garbage collection and no pointers).
Office Open XML. Microsoft proprietary specification for a set of XML-based document file types. MS Office 2007 is only a partial implementation, supplanting the binary formats of Office 2003 and earlier. Filename extensions include .docx (document), .xlsx (spreadsheet), and .pptx (presentation). Contrast ODF.
Operational Amplifier. A very common DC-coupled analog circuit that greatly amplifies the voltage differential between its two inputs. The ideal op-amp has infinite gain, hence no voltage differential across its input terminals and no current flow into either input. A non-inverting op-amp circuit has signal input on the non-inverting (+) terminal, and output in phase with input. An inverting op-amp circuit has signal input on the inverting (-) terminal, and output 180° out of phase with input. Note that in both of these cases, output feeds back to the inverting input.
Like all amplifiers, the op-amp is powered, but the images above omit supply voltage inputs to keep things simple. To analyze an op-amp circuit, write a node equation for each input terminal, treat the op-amp as ideal by setting v- = v+, and solve the equations together.
A logic circuit output that uses the open (i.e., not connected internally to a positive voltage) collector terminal of a bipolar transistor. To function, it requires an external pull-up resistor to a positive voltage. This configuration allows multiple outputs to be wired together (a wired-OR circuit): all of the outputs are normally pulled high (logic 0), but if any one of them goes active low (logic 1) by sinking current, all of them will be pulled low. This implements a logical OR. It’s very useful for data buses. Compare push-pull.
Also called current-source. A logic circuit output that uses the open (i.e. not connected internally) emitter terminal of a bipolar transistor. To function, it requires an external pull-down resistor to a negative voltage. When the transistor is off (logic low), the output is pulled low externally; when on, the transistor pulls the output high. This is the output type for ECL.
IEEE plug-and-play standard (P1275) that specifies a processor-independent mechanism for a system to interrogate expansion devices, configure them for the system, and install appropriate device drivers.
Open Graphics Library. The open-source standard computer graphics API, dating to 1992, and still dominant on Unix and Linux platforms. Microsoft initially supported it, but dropped it in favor of its own Direct3D (part of DirectX) after Windows NT.
An Intel hard-drive cache technology released in 2017. An Optane module connects to a system M.2 port and provides a faster cache for SATA hard drives than a cache built into the drive itself.
Offset Quadrature Phase Shift Keying. Also called SQPSK (Staggered QPSK). A type of QPSK with one of the bit streams delayed by 1 bit period, which is half a symbol period. Because the resultant signal never undergoes a 180° phase shift, it reduces the unwanted sidelobes that cause out-of-band interference. This is important in nonlinear devices. The amplitude envelope of the signal has a maximum 3 dB fluctuation.
Open Radio Access Network. An international alliance of telecom companies and organizations working toward the technology for post-5G mobile networks. They’re at https://www.o-ran.org. The term also refers to a standard developed by the 3GPP for interfaces within the RANs that carry 5G mobile-phone traffic. It’s pushed primarily by wireless service providers, who want to ensure interoperability between RAN equipment from different manufacturers.
A subsidiary of Orbital Sciences Corp. that provides worldwide low-rate data (not voice) services, particularly two-way paging and E-mail, through value-added resellers (VARs). The satellite links are simple bent-pipe relays. As of 2003, they have a global network of ground stations (4 in the US), and 30 LEO satellites in 6 different orbits (four at 825 km altitude, with one of these equatorial and the other three inclined at 45° to the equator, and two at 780 km altitude with inclinations 70° and 108°). The ground stations use 148-149.9 MHz uplink and 137-138 MHz downlink, both OQPSK at 57.6 kb/s. The mobile units use the same frequencies and symmetric differential PSK (SDPSK), at 2.4 kb/s uplink and 4.8 or 9.6 kb/s downlink. The dependence on ground stations means many areas of the world aren’t covered. Compare Globalstar, ICO, Inmarsat, Iridium.
Refers to sets of signals, codewords, or vectors whose cross-correlation product (the integral of the product of any two set members over time) is zero, such as sin(ωt) and cos(ωt). This means they can’t interfere with one another. Sets of mutually orthogonal signals are used in many types of modulation, such as orthogonal M-ary FSK and OFDM. Simple example: 1 kbaud FSK is orthogonal if its tones are at 10 kHz and 11 kHz. Bi-orthogonal means any two members of the set have a cross-correlation of either 0 or –1. Orthonormal means orthogonal with unity vector length. Compare antipodal.
Operating System. A software program that runs other programs. There have been many operating systems since the early 1950s, most of them now discarded and forgotten. PC and workstation systems that are or have been popular include Unix, VMS, MS-DOS, Mac OS, Amiga, Windows, OS/2, Solaris, OS X, and GNU/Linux. More compact operating systems for tablets and smartphones include Android, iOS, and Windows RT. There are also embedded operating systems, but only embedded device programmers deal with them.
Operating systems are classed by capability as either single-tasking or multi-tasking, and by interface as either CLI or GUI.
O-scope for short. Instrument for displaying and measuring oscillations of signal voltage. Researchers were building them as early as the 1890s, but the modern instrument, with triggered waveform capture and a default display that uses the horizontal x-axis for time and the vertical y-axis for voltage, took shape after WWII. Contrast logic analyzer, network analyzer, and spectrum analyzer.
Open Software Foundation. A consortium formed by IBM, DEC, HP, et. al. in reaction to the AT&T/Sun pact to develop a Unix standard that favored Sun’s hardware. They created the Motif GUI and toolkit for X Window.
Open Systems Interconnect. A model for packet-switched networks with virtual circuits, released by the ISO in 1983, for which reason it’s called both the OSI model and the ISO model. The ITU-T adopted it as X.200. It defines a complete set of protocols, and a 7-layer network, from highest to lowest:
7. Applications – protocols that user applications (browsers, word processors, file transfer, games, etc.) employ to connect with network services
6. Presentation – operating system, device drivers, data format and encryption
5. Session – opens links between apps across the network
4. Transport – data flow control, and ensuring that the lowest three layers are working
By the mid-1990s, the success of the Internet and its freely available TCP/IP protocol suite had made the OSI protocols irrelevant. The OSI model is still widely used to describe networks.
Open Source Initiative. A non-profit corporation (http://opensource.org) founded in 1998 to support open-source software development. They have both common ground and philosophical disagreements with the older FSF.
Organic Thin-Film Transistor. Slower but cheaper than standard transistors. Many organic semiconductors are photoconductive under visible light, so they have potential applications in flat-panel displays. They typically have problems with stability and making electrical contacts. See OLED.
One-Time Password. A password that’s valid for only a short period of time, commonly 30 seconds. It’s generated by a device the user physically possesses, such as a smartphone or a battery-powered token generator, using the current time and a secret key stored in the device. The server that validates the password has to have the same generating algorithm and secret key associated with the user’s access credentials. See MFA.
Off-The-Record. A protocol for providing end-to-end encryption to online chat sessions. Each user runs an OTR-capable chat client, and they connect through a chat server. For even better anonymity, connect to the chat server via a darknet connection.
Ovonic Unified Memory. Sort of named for Stanford Ovshinsky, patent 1966, and also called chalcogenide RAM (C-RAM). The first phase-change memory (PCM) technology. Its material is a chalcogenide alloy typically containing germanium, antimony, tellurium, and/or sulfur. Cost and temperature-tolerance issues have limited its commercial use so far (2011).
Using a separate, non-traffic network (or frequencies) for the control signals that manage network (or channel) connections. Compare with in-band signaling.
Open Verification Methodology. Application for testing FPGA designs. It uses SystemVerilog, but can also handle designs created in Verilog, VHDL, and SystemC. See UVM.
Optical cross-Connect. An optical switch, one of the key ingredients of a DWDM network. It switches different wavelengths (channels) among multiple fibers.
