Fiber Optic Glossary: S

s: Abbreviation for second.
Sampling Rate: The number of discrete sample measurements made in a given period of time. Often expressed in megahertz (MHz) for video.
SAP (Secondary Audio Programming): Secondary audio signal that is broadcast along with a television signal and its primary audio. SAP may be enabled through either the television, stereo VCR equipped to receive SAP signals, or an SAP receiver. SAPs may be used for a variety of enhanced programming, including providing a "video description" of a program's key visual elements, inserted in natural pauses, that describes actions not otherwise reflected in the dialog, used by visually impaired viewers. This service also allows television stations to broadcast programs in a language other than English, and may be used to receiver weather information, or other forms of "real-time" information.
SAN (Storage Area Network): Connects a group of computers to high-capacity storage devices. May be incorporated into local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN).
Saturation: 1) In a communications system, the condition in which a component of the system has reached its maximum traffic handling capacity. 2) The point at which the output of a linear device, such as a linear amplifier, deviates significantly from being a linear function of the input when the input signal is increased. 3) The degree of the chroma or purity of a color.
S-Band: The wavelength region between 1485 nm and 1520 nm used in some CWDM and DWDM applications.
SBS: See stimulated Brillouin scattering.
SC: Abbreviation for subscription channel connector. A push-pull type of optical connector that features high packing density, low loss, low backreflection, and low cost.
Scattering: The change of direction of light rays or photons after striking small particles. It may also be regarded as the diffusion of a light beam caused by the inhomogeneity of the transmitting material.
Scalable Coding: The ability to encode a visual sequence so as to enable the decoding of the digital data stream at various spatial and/or temporal resolutions.
Scalable Video: Refers to video compression that can handle a range of bandwidths, scaling smoothly over them.
Scanning: 1) In telecommunications systems, periodic examination of traffic activity to determine whether further processing is required. 2) In television, facsimile, and picture transmission, the process of successively analyzing the colors and densities of the object according to a predetermined pattern.
S-CDMA: A proprietary version of code division multiple access (CDMA). S-CDMA was developed by Terayon Corporation for data transmission across coaxial cable networks. S-CDMA scatters digital data up and down a wide frequency band and allows multiple subscribers connected to the network to transmit and receive concurrently. This method of data transmission was developed to be secure and extremely resistant to noise.
SCM: Abbreviation for subcarrier multiplexing. The process by which multiple subcarrier signals are combined onto one signal.
Scrambler: 1) A device that transposes or inverts signals or otherwise encodes a message at the transmitter to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device. Scramblers usually use a fixed algorithm or mechanism. 2) A device intended to normalize the duty cycle of a data stream to be close to 50%.
Scrambling: To transpose or invert digital data according to a prearranged scheme in order to break up the low-frequency patterns associated with serial digital signals.
SCSI: Acronym for small computer system interface. An intelligent interface device that expands a microprocessor (CPU) bus to facilitate connections to multiple peripherals (e.g., CD-ROM drives, hard drives, or scanners) and exchange data with those peripherals via a separate communications bus.
SDTV: Abbreviation for standard-definition television. Synonym NTSC television transmission.
SECAM: Abbreviation for Système Électronique Couleur avec Mèmoire. A TV standard used in various parts of the world. Delivers 625 lines at 50 frames per second.
Selfoc Lens: A trade name used by the Nippon Sheet Glass (NSG) Company for a graded-index fiber (GRIN) lens; a lens that uses refractive index gradients to focus light.
Self-phase modulation (SPM): A fiber nonlinearity caused by the nonlinear index of refraction of glass. The index of refraction varies with optical power level causing a frequency chirp which interacts with the fiber’s dispersion to broaden the pulse.
Semiconductor Optical Amplifier (SOA): A laser diode without end mirrors coupled to the fibers on both ends. Light coming in either fiber is amplified by a single pass through the laser diode. An alternative to EDFAs.
Sensitivity: See receiver sensitivity.
Serial: One bit at a time, along a single transmission path.
Serial Digital: Digital information that is transmitted in serial form. Often used informally to refer to serial digital television signals.
Serial Digital Interface (SDI): A 10-bit, scrambled, polarity independent interface, based on a 270 Mb/s data rate, with common scrambling for both component ITU-R 601, composite digital video, and four channels of (embedded) digital audio. Most new broadcast digital equipment includes SDI.
Serial Digital Transport Interface (SDTI): Another name for SMPTE 305M. Allows faster-than-real-time transfers between various servers and between acquisition tapes, disk-based editing systems and servers. Supports both 270 Mb/s and 360 Mb/s data rates.
Set-top Box: See STB.
SH: Abbreviation for short-haul. A classification of video performance under RS-250B/C. Higher performance than long-haul or medium-haul.
Sheath: An outer protective layer of a fiber optic cable. Also called the cable jacket.
Shot Noise: Noise caused by current fluctuations arising from the discrete nature of electrons.
Si: Abbreviation for silicon. Generally used in detectors. Good for short wavelengths only (e.g., < 1,000 nm).
Sideband: Frequencies distributed above and below the carrier that contain energy resulting from amplitude modulation. The frequencies above the carrier are called upper sidebands, and the frequencies below the carrier are called lower sidebands.
Silica Glass: Glass made mostly of silicon dioxide, SiO₂, used in conventional optical fibers.
Signal-to-Noise Ratio (SNR): The ratio of the total signal to the total noise which shows how much higher the signal level is than the level of the noise. A measure of signal quality.
Simple Network Management Protocol (SNMP): The Internet standard protocol for network management software. It monitors devices on the network, and gathers device performance data for management information data bases (MIB).
Simplex: Single element (e.g., a simplex connector is a single-fiber connector).
Simplex Cable: A term sometimes used for a single-fiber cable.
Simplex Transmission: Transmission in one direction only.
Single Attachment Concentrator: A concentrator that offers one attachment to the FDDI network.
Single-Line Laser: See single-longitudinal mode laser.
Single-Longitudinal Mode Laser (SLM): An injection laser diode which has a single dominant longitudinal mode. A single-mode laser with a side mode suppression ratio (SMSR)< 25 dB.
Single-Mode (SM) Fiber: A small-core optical fiber through which only one mode will propagate. The typical diameter is 8-9 microns.
Single-Mode Laser Diode (SMLD): See single-longitudinal mode laser.
Single-Mode Optical Loss Test Set (SMOLTS): An optical loss test set for use with single-mode fiber.
SI Units: Abbreviation for Système Internationale (in English, International System of Units), commonly known as the metric system.
SLED: See surface-emitting diode.
SLM: See single-longitudinal mode laser.
Slope Efficiency (SE): This is the mean value of the incremental change in optical power for an incremental change in forward current when the device is operating in the lasing region of the optical power output versus forward current curve. Also referred to as differential efficiency.
SMF: Abbreviation for single-mode fiber.
SMA: A threaded type of optical connector. One of the earliest optical connectors to be widely used. Offers poor repeatability and performance.
Smart Structures: Also smart skins. Materials containing sensors (fiber optic or other types) to measure their properties during fabrication and use.
SMD: Abbreviation for surface-mount device. See SMT.
SMPTE: Abbreviation for Society of Motion Picture and Television Engineers. Organization that publishes ANSI-approved standards, recommended practices, and engineering guidelines for the motion picture and television industry.	http://www.smpte.org
SMPTE 259M: Television standard, written by the Society of Motion Picture and Television Engineers (SMPTE), that describes a serial digital interface (SDI) for 10-bit 4:2:2 component and 4f_sc composite digital transport.
SMPTE 310M: Television standard, written by the Society of Motion Picture and Television Engineers (SMPTE), that describes a synchronous serial interface for MPEG-2 digital transport streams.
SMT: Abbreviation for surface-mount technology. An electronics manufacturing technique.
S/N: See signal-to-noise ratio.
SNR: See signal-to-noise ratio.
SOA: See semiconductor optical amplifier.
Soliton Pulse: An optical pulse having a shape, spectral content, and power level designed to take advantage of nonlinear effects in an optical fiber waveguide, for the purpose of essentially negating dispersion over long distances.
SONET: Abbreviation for synchronous optical network transport system. An interface standard widely used by the telecom industry where OC-3 is the lowest current rate (155.5 Mb/s), and OC-768 is the highest rate being contemplated (39.808 Gb/s). Valid rates increase by a factor of four from the OC-3 rate up to OC-768.
Source: In fiber optics, a transmitting LED or laser diode, or an instrument that injects test signals into fibers.
Span Engineering: The process of designing a DWDM transmission span to achieve the required performance based on fiber type, the transmission distance, amplifier spacing, noise, power, and channel count.
Spectral Efficiency: The number of data bits per second that can be transmitted in a one Hertz bandwidth range.
Spectral Width: A measure of the extent of a spectrum. For a source, the width of wavelengths contained in the output at one half of the wavelength of peak power. Typical spectral widths are 50 to 160 nm for an LED and less than 5 nm for a laser diode.
Spectral Width, Full Width, Half Maximum (FWHM): The absolute difference between the wavelengths at which the spectral radiant intensity is 50 percent of the maximum power.
Splice: A permanent connection of two optical fibers through fusion or mechanical means.
Splitter: see Coupler.
Splitting Ratio: The ratio of power emerging from two output ports of a coupler.
SPM: See self-phase modulation.
SRS: See stimulated Raman scattering.
ST: Abbreviation for straight tip connector. Popular fiber optic connector originally developed by AT&T.
Stabilized Light Source: An LED or laser diode that emits light with a controlled and constant spectral width, center wavelength, and peak power with respect to time and temperature.
Star Coupler: A coupler in which power at any input port is distributed to all output ports.
Star Network: A network in which all terminals are connected through a single point, such as a star coupler or concentrator.
STB: Abbreviation for set-top box. An auxiliary device that usually sits on top of or adjacent to a television receiver used in direct analog or digital satellite transmission and digital television to view the signals on an analog TV. Converter boxes are becoming obsolete as old model televisions requiring a converter are replaced by modern televisions, which incorporate a converter into the television. Also called a set-top converter.
Step-index Fiber: Fiber that has a uniform index of refraction throughout the core that is a step below the index of refraction in the cladding.
Stimulated Brillouin Scattering (SBS): The easiest fiber nonlinearity to trigger. When a powerful light wave travels through a fiber it interacts with acoustical vibration modes in the glass. This causes a scattering mechanism to be formed that reflects much of the light back to the source.
Stimulated Raman Scattering (SRS): A fiber nonlinearity similar to SBS but having a much higher threshold. This mechanism can also cause power to be robbed from shorter wavelength signals and provide gain to longer wavelength signals.
Strength Member: The part of a fiber optic cable composed of aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.
Submarine Cable: A cable designed to be laid underwater.
Subscriber Loop: Also called local loop. The link from the telephone company central office (CO) to the home or business (customer premises).
Sun Fade: In satellite systems, the loss of a satellite signal that occurs when energy from the sun overpowers the satellite's signal. Also called sun transit or sun outage.
Supertrunk: A cable that carries several video channels between facilities of a cable television company.
Surface-emitting Diode: A simple and inexpensive LED design that emits light from its flat surface rather than its side with emission spread over a wide angle.
Surround Sound: More commonly referred to as Dolby Digital, a standard for high-quality digital audio that is used for the sound portion of video stored in digital format, especially videos stored on DVD-ROMs. Dolby Digital delivers 6 channels in the 5:1 format: left, right, and center screen channels, separate left and right sounds, and a subwoofer channel.
Switch: 1) In communications systems, a mechanical, electro-mechanical, or electronic device for making, breaking, or changing the connections in or among circuits. 2) Synonym for central office, switching center. 3) In communications systems, to transfer a connection from one circuit to another.
Synchronization Pulse: 1) A signal derived from the composite or combination of the horizontal and vertical drives. 2) A pulse used to achieve or maintain synchronism, usually applied to analog signals. (The term "synchronization bit" is usually applied to digital data streams.) Commonly called the sync pulse. See also composite sync.
Synchronous: A data signal that is sent along with a clock signal. A system in which events, such as signals, occur at evenly spaced time durations. Opposite of asynchronous.