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A
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ABSORPTION
LOSSES
Light losses (Attenuation) normally caused by impurities such as transition
metals, neighbouring elements, water and intrinsic metal absorption.
ACCEPTANCE ANGLE
The maximum angle to the axis (centre line) of an optical fibre at which
a light ray will enter the core and be propagated. Light striking the optical
fibre at an angle greater than the Acceptance Angle will be lost.
ANALOGUE
A data format which uses continuous physical variables such as voltage amplitude
or frequency variations.
ANSI
American National Standards Institute - which co-ordinates voluntary standards
in the USA.
APEX OFFSET
The distance from the centre of the fibre core to the apex of the ferrule.
Poor apex offset results in attenuation due to increases in return loss
(reflection) & insertion loss.
ARMOUR
Extra cable protection to improve resistance to crushing, cutting and shearing
forces. The usual form is a braided steel outer jacket but tough plastic
with steel or plastic strengtheners is also used in many modern cable designs.
ASCII
American Standard Code for Information Interchange. An 8-bit code in which
letters, numbers and symbols are represented by 7-bit binary characters.
The 8th-bit is often used as a parity check.
ASYNCHRONOUS TRANSFER MODE (ATM)
The technology selected by the CCITT to deliver broadband-ISDN services.
A fast packet based technology ATM is based on a fixed packet or cell size
of 53 bytes long.
ASYNCHRONOUS TRANSMISSION
A free running transmission mode in which the time intervals between characters
may be unequal. Transmission is not synchronised with any external clock.
ATTENUATION
A loss measure for voltage, current or power (optical or electrical). The
loss in optical power along an optical fibre is measured in dB/km, and should
be quoted at a specified light wavelength. Beware when converting linear
ratios to dB, which is a logarithmic ratio. The tables for voltages and
currents are different from those referring to power.
ATTENUATOR
A device used to increase the attenuation of an Optical Fibre link, generally
used to ensure that the signal at the receive end is not too strong.
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BACKBONE
LAN
This is normally a LAN that supports internetworking between access LAN's
but exhibits a higher speed and covers a wider area than a standard LAN.
BACK REFLECTION - See Return Loss
BACKSCATTER
Scattering in directions reverse to the incident beam.
BANDWIDTH
Bandwidth is the difference between the lower and upper frequencies that
can be sent along a communication channel. When used in radio engineering,
bandwidth is quoted in cycles per second (hertz or Hz) but the word bandwidth
is now also used to specify digital data transmission channels and Hz then
refers to bits per second. The bandwidth of Ethernet, for example, is 10mhz
(mega-hertz).
BASEBAND
Used to describe a type of network in which one frequency (or bit rate)
is used to carry all information. The alternative is Broadband.
BAUD
A unit used in signalling which indicates a speed equal to the number of
shortest signal events per second. BEND LOSS
Attenuation to an optical signal that occurs when an optical fibre is bent
around a tight radius. Light effectively spills out from the core and is
lost in the cladding.
BEND RADIUS
The minimum radius around which a fibre may be curved without risk of permanent
damage resulting in excessive attenuation, or even breakage.
BER
Bit Error Rate.
BISDNB
Broadband Integrated Services Digital Network.
BIT
The commonly used abbreviation for a binary digit.
BIT ERROR RATE
The percentage of bits that are incorrectly received.
BIT TRANSFER RATE
The bit transfer rate is expressed as bits per second or bps.
BLOCK
A group of digits transmitted as a whole.
BLOWN FIBRE
Empty micro-ducts are pre-installed on-site. As, and when required, fibres
are blown into place with compressed air.
BROADBAND
The transmission of digital data streams over a wide bandwidth channel using
modulated analogue signals. Several data streams can be carried simultaneously
by using different carrier frequencies.
BS7718
Code of Practice for the installation of fibre optic cabling.
BUFFER (1)
A mechanically resilient protective coating that is applied over a fibre.
Also referred to as Secondary Coating.
BUFFER (2)
A Storage device used to compensate for a difference between rates of transmission
and receipt of data.
BUS
Cabling, carrying signals around inside a computer or between computers
and other devices.
BYTE
A binary string which is normally of 8 bits. |
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CABLE
A cable construction whereby one or more optical fibres are contained within
a jacket, which may also contain a variety of strengthening and other protective
materials.
CATV
Community Antenna (Access) TeleVision.
CCITT
Comite Consultatif International de Telegraphique et Telephonique - an international
organisation which devises and recommends standards for international telecommunications.
CCTV
Closed Circuit Television.
CHANNEL
A communication path for transmission of data between two points.
CHROMATIC DISPERSION
Pulse spreading in an optical fibre caused by variations in light propagation
with wavelength. The sum of waveguide dispersion and material dispersion.
CLADDING
The low refractive index material that surrounds the core of an optical
fibre and ensures the internal reflection on which propagation of light
signals depends.
COHERENT BUNDLE
Optical fibres that are packed in a coherent bundle retain fixed relative
positions at each end and can transmit an optical image. Used extensively
in flexible endoscopes (fibrescopes).COHERENT COMMUNICATIONS
A transmission system in which the phase relationships of signals are known
and controlled, leading to higher bandwidths.
CONNECTOR
Termination component installed on ends of fibre optic cables. It provides
physical attachment and optical coupling to further cables, transmitters,
receivers and other devices.
CONTENTION SYSTEM
A communications network in which two or more stations have equivalent status
and contend for access to the transmission medium.
CORE
The centre, light guiding part of an optical fibre. The refractive index
is higher than that of the cladding, to ensure propagation of optical signals.
CORE ECCENTRICITY
A measure of the displacement of the centre of a core relative to the cladding
centre.
CORE ELLIPTICITY
A measure used to indicate a core's deviation from roundness.
COUPLER
An optical component which splits or combines optical communication channels.
COUPLING
Transfer of light into or out of an optical fibre, (not implying the use
of a coupler).
CRITICAL ANGLE
The limiting angle at which a light ray will be totally internally reflected.
CROSS TALK
Interference signal between communication channels.
CSMA
Carrier Sense Multiple Access. A network access procedure whereby before
transmitting to the network a station checks for the presence of a carrier
signal showing that the network is already being used. Transmission only
starts if no other carrier is detected.
CSMA/CD
Carrier Sense Multiple Access with Collision Detection. A type of network,
(e.g. Ethernet), in which all connected devices monitor continuously. If
a transmitted message overwrites one already on the network a collision
is detected and the message is re-transmitted.
CUT-OFF WAVELENGTH
The longest wavelength at which a singlemode fibre can transmit two modes. |
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DATALINK
In fibre optics, a transmitter, optical fibre cable and receiver that transmits
digital date between two points.
DATA RATE
The rate at which BITs of information are transmitted along a fibre.
DATA SIGNALLING RATE
The rate at which data bits can be transmitted, measured in bits per second
(bps).
DBMS
Decibels relative to a power level of 1mW.
DECIBEL (dB)
A logarithmic comparison of power levels, (optical or electrical), voltages
and currents.
DEMODULATION
Re-creation of an original data stream from a modulated signal.
DEMULTIPLEXING
Splitting up a multiplexed signal into its component parts.
DEMUX
De-multiplexer
DETECTOR
In fibre optics, a device that generates an electrical signal when illuminated
by light. Examples are photodiodes and phototransistors.
DIGITAL
A series of coded pulses that, according to their absence or presence, can
carry streams of data. Their format may use either discrete or separate
physical levels.
DIGITAL SIGNAL
A signal encoded in discrete levels, typically binary 1 and binary 0.
DIODE
An electronic device which lets current flow in one direction only. Diodes
used in fibre optics include light emitters, (LED's and laser diodes) and
detectors (photodiodes).
DIRECTIONAL COUPLER
An optical fibre coupler where light at the input ports is only transferred
to one or more defined output ports.
DISPERSION
Dispersion causes a broadening of pulses as they are propagated along an
optical fibre, causing limitations in bandwidth.
DISTRIBUTED SYSTEM
A system containing two or more intelligent stations linked by a communication
network.
DOPANT
In fibre optics, a material such as germanium or boron oxide that is added
to silica to change the refractive index.
DUAL RING (FDDI DUAL RING)
A pair of counter rotating logical rings.
DUPLEX TRANSMISSION
Simultaneous independent transmission in both directions over a communication
link, sometimes over the same fibre.
DUTY CYCLE
When applied to a periodic waveform, this is a measure of the effect of
a pulsed input to a device. Normally expressed as the ratio of on time to
total cycle time.
DYNAMIC RANGE
In opto-electronics, the maximum operating power range expressed in dB. |
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EDGE
LIGHT EMITTING DIODE (ELED)
An LED that emits light from its edge which can be coupled into an optical
fibre more efficiently than light from a conventional LED.
EIA
Electronic Industry Association.
ERROR RATE
The ratio of incorrectly received data (bits, characters or blocks) to the
total amount of transmitted data.
ESCON
Enterprise System CONnectivity.
ETHERNET
A network using CSMA/CD which is widely used for LANs. Most Ethernets use
coaxial cable but optical fibres are usually specified for links between
buildings, to avoid risk of lightning damage and EMI, and to provide electrical
isolation.
EXPANDED BEAM CONNECTOR
A connector in which the diameter of a beam of light emerging from a fibre
is expanded, then focused onto the core of another fibre. |
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FACEPLATE
A rigid array of short fibres fused together to form the face of a cathode
ray tube.
FAST ETHERNET
A similar topology to traditional Ethernet operating at 100Mb/s.
FDDI
Fibre optic Distributed Data Interface.
FERRULE
A tube, housed within a connector, in which the central bore contains and
aligns the optical fibre.
FIBRE OPTIC DISTRIBUTED DATA INTERFACE (FDDI)
A standard for a 100Mb/s fibre optic local area network.
FIBRE OPTIC SYSTEM
In Datacoms and Telecoms a system employing fibre optic cable to transmit
data, voice and video signals.
FIBRE OPTICS
The branch of optical, communication and electronic technologies concerned
with the transmission of electromagnetic radiation through thin fibres made
of transparent material such as glass, fused silica and plastic.
FIBRE UNDERCUT OR PROTRUSION
It is the distance of the fibre end face relative to the spherical surface
of the ferrule. Typically ±50nm, excessive undercut adversely effects
both Back Reflection and Insertion Loss, whereas excessive protrusion can
lead to fibre damage or even component failure in service.
FLUX
The level of power passing either to, from or through a surface measured
on energy per unit time.
FREQUENCY DIVISION MULTIPLEXING
Multiplexing of signals by assigning a different carrier frequency to each
and then combining in a single signal.
FREQUENCY MODULATION
Changing the carrier wave frequency according to changes in an information
stream.
FRESNEL REFLECTION
Reflection of light at the end of an optical fibre caused by the difference
of refractive index between the fibre core and the media (often air) with
which it is interfacing.
FTTC
Fibre To The Curb.
FTTH
Fibre To The Home.
FUNDAMENTAL MODE
The lowest order mode of a waveguide.
FUSED (FUSION) SPLICE
Splice in which two optical fibres are fused together by a heat process. |
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GATEWAY
A device that interconnects two communication networks and transfers messages
between them by translating protocols, buffering data rates and accommodating
different physical interfaces such as connectors and cables. A gateway might
by used to link a network using optical fibres with a coaxial cable based
system.
GHz (GIGAGHERTZ)
Measure of frequency equal to 109 hertz.
G.I
Graded Index
GRADED INDEX FIBRE
Optical fibre with a refractive index profile that is maximum at the centre
and decreases until it matches the index of the cladding at the core/cladding
interface. Light rays are thus re-focused in the core. They travel more
quickly in the lower index regions of the core, which reduces modal dispersion. |
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HALF-DUPLEX
TRANSMISSION
Transmission in either direction along a communications link, but not in
both directions simultaneously.
HANDSHAKE SIGNALS
Signals used to request permission to send messages, and to acknowledge
the receipt of data transfers.
HDTV
High Definition Television.
HEAD END
The central distribution point in a broadband data highway or cable television
system.
HERMAPHRODITE CONNECTOR
A connector pair in which each part includes both pins (male) and sockets
(female).
HERTZ (Hz)
Unit of frequency, in cycles per second.
HUB
A multi- port repeater used in Ethernet environments to distribute data
to multiple users. |
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IEE
The Institution of Electrical Engineers (British).
IEEE
The Institution of Electrical and Electronics Engineers (USA). IEEE Committee
802 and its various sub-committees define interface and communication standards
for networks.
INDEX MATCHING MATERIAL
Normally a gel or liquid with a refractive index that is almost equal to
the core index. Normally used to reduce reflections at a fibre end face.
INDEX OF REFRACTION
The ratio of the speed of light in a vacuum to the speed in a media such
as glass or air.
INDEX PROFILE
Curve of the refractive index over the cross section of an optical waveguide.
INFRARED
The band of electromagnetic wavelengths between 700nm to about 1mm. The
transmission of light in glass optical fibres is most efficient in the infrared,
at wavelengths from 1100nm to 850nm.
INSERTION LOSS
The extra optical attenuation caused by the insertion of a component into
an optical system.
INTEGRATED OPTICS
Design and application of optical devices that perform several functions
on a single substrate.
INTEGRATED OPTOELECTRONICS
Integration of optical and electronic devices on the same chip.
INTRINSIC LOSSES
Losses in a splice that arise from differences in the two fibres being joined
together.
ISDN
Integrated Services Digital Network. A public network in which a single
subscriber interface provides a variety of communication services for voice
and data.
ISO
International Standards Organisation.
ISOLATOR
A two part component having greater attenuation in one direction than the
other often used to prevent return reflections in a transmission path. |
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JACKET
A layer of material surrounding an optical fibre but not bonded to it; part
of the cable, not of the fibre. |
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KEVLAR
A strong synthetic material used widely as strength members within optical
fibre cables. The name is a trademark of Dupont. |
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LAN
Local Area Network.
LARGE CORE FIBRE
An optical fibre with core diameter greater than 100 micron.
LASER
Light Amplification by Stimulated Emission of Radiation. In fibre optics,
laser diodes are widely used as light emitters, especially in singlemode
and long haul systems. Light from laser diodes covers only a narrow band
of wavelengths so that dispersion caused by differing light velocities in
an optical fibre is substantially reduced.
LD
Laser Diode.
LED
Light Emitting Diode.
LIGHT
Electromagnetic radiation visible to human eye; also applied to invisible
near infrared radiation that carries signals in most optical fibre systems.
LIGHT DETECTOR
In fibre optics a semiconductor device that can detect light and transform
this into an electrical output.LIGHTGUIDE
Optical fibre or fibre bundle.
LOCAL AREA NETWORK
A data communications network serving a limited area such as a building
or factory site.
LOCAL LOOP
The subscriber link in a telephone network.
LONG HAUL NETWORK
A network that carries data between towns and cities involving long distances.
Distances may be up to several hundred miles. Optical fibres are extensively
used for this application.
LOOPBACK
Diagnostic test where the transmitted signal is returned to the sending
device after passing through a datacomms link or network.
LOOSE TUBE
A protective tube loosely surrounding an optical fibre or cable which is
often filled with protective gel.
LOSS
Attenuation of an optical signal, usually measured in dB.
LOSS BUDGET
An account showing the overall loss in an optical fibre link, compared with
the minimum received power specified at the receiver and the power available
from the transmitter. Because losses are usually expressed in dB, a logarithmic
expression, a simple approach need only involve addition and subtraction. |
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MACROBENDING
Bend of radius much larger than the fibre core as opposed to micro-bending.
MACROBENDING LOSS
Loss in an optical fibre due to bends of radius larger than the fibre diameter.
MAN
Metropolitan Area Network.
MANCHESTER ENCODING
A self-clocking data encoding technique. If an o is sent, a low to high
transition occurs halfway through the bit period; conversely if a 1 is sent,
a high to low transition occurs. There is at least one signal transition
in every bit.
MARGIN
Allowance for attenuation in addition to that allowed for in system design.
MATERIAL DISPERSION
Pulse dispersion in an optical fibre caused by variation of refractive index
with wavelength.
Mbit/s Mbps, Mb/s
Mega Bits per Second = 106 bits per second; 106bps.
MECHANICAL SPLICE
A splice in which optical fibres are joined mechanically but not fused together.
MEDIA INTERFACE CONNECTOR (MIC)
A mated connector pair providing attachment between an FDDI node and a fibre
cable plant. Referred to as FDDI connector.
Mhz (MEGAHERTZ)
Unit of frequency equal to 106 hertz.
MIC
Media Interface Connector used to describe the duplex FDDI plug.
MICROBENDING
Tiny bends in a fibre that increases loss by allowing spillage of light
from the core.
MICROMETRE (um)
10-6 metre
MICRON (um)
A micrometre.
MINIMUM BEND RADIUS
See Bend Radius
MODAL DISPERSION
Dispersion caused by the difference in time taken by different modes to
travel along a multimode fibre.
MODE
A permitted electromagnetic field pattern in an optical fibre.
MODE FIELD DIAMETER
The diameter of the one mode of light that is being propagated in a singlemode
fibre.
MODE SCRAMBLER
A unit containing one or more optical fibres in which strong mode coupling
occurs. Normally used as a means of providing a mode distribution independent
of source characteristics.
MODE STRIPPER (OR CONDITIONER OR FILTER)
A device that removes high order modes in a multimode fibre, to standardise
conditions for measurement.
MODEM
MOdulator-DEModulator. A device which accepts a serial stream of bits as
input and produces a modulated analogue signal as output; and vice-versa.
MODULATION
A coding method allowing controlled variation, with time, of any property
of a wave for the purpose of transferring information.
MONCHROMATIC
A single wavelength.
MULTI-DROP LINE
A single communications line to which more than one node is attached.
MULTICHANNEL CABLE
Optical cable containing more than one optical fibre.
MULTIMODE DISTORTION
The distortion of a signal in a wave-guide resulting from the superposition
of modes with differing delays.
MULTIMODE FIBRE
Optical fibre with a core size that permits propagation of non-axial rays.
Usually described by referring to core diameter and cladding diameter, e.g.
62.5/125.
MULTIPLEXING
Combining several data channels so that a composite signal can be transmitted
over a single communications link.
MUX
Multiplexer. |
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NA
Numerical Aperture.
NANOMETRE (ns)
10-9 metre.
NANOSECOND (ns)
10-9 second.
NETWORK TOPOLOGY
The physical and logical arrangement of interconnections between network
stations. Most optical fibre networks have star or ring topologies, and
their derivatives, because of the difficulty in making a T-junction in optical
fibre, needed for a highway configuration.
nm
Nanometre=10-9 metre.
NIC
Network Interface Card.
NODE
A point within a communications network at which data is received or from
which it is sent. Interconnection points within a network are also called
nodes.
NRZ
No Return to Zero. A digital code in which the signal level is low for 0
and high for 1 but does not return to zero between successive bits. Important
in fibre optic data transmission because the 0 level at the receiver end
of a link can be substantially higher than the dark current level.
ns
Nanosecond=10-9 second.
NUMERICAL APERTURE (NA)
The sine of the acceptance angle of a fibre, multiplied by the refractive
index of the medium from which the light is entering (which is 1 for air).
It can be shown that NA= n12 -n22 for light entering from air, (n1 and n2
are the refractive indexes of core and cladding respectively). |
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OEM
Original Equipment Manufacturer.
OPEN SYSTEMS INTERCONNECTION REFERENCE MODEL
A seven-layer model, produced by the ISO, which defines the hierarchy and
standard procedures for operating a communications system that provides
open access between network stations.
OPTICAL FIBRE
A cylindrical core of flexible transparent material surrounded by a tubular
cladding of material with a lower refractive index. Light enters at one
end of the optical fibre and emerges at the other end, after propagation
by internal reflection along the core.
OPTICAL TIME DOMAIN REFLECTOMETER (OTDR)
An instrument that measures transmission characteristics of an optical fibre
by sending a short pulse and measuring the return signals resulting from
backscatter and reflections.
OPTICAL WAVEGUIDE
Any structure that can guide light along a preset path. One example is an
optical fibre. Optical wave-guides can also be formed from solid material.
OPTOELECTRONIC
A technology-encompassing device that's function as electrical-to-electrical
transducers capable of: responding to optical power; the emission or modification
of optical radiation; and the utilisation of optical radiation for their
internal operation.
OSI
Open System Interconnection. |
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PACKET
A unit of information, comprising a group of bits including data and control
elements, which is switched and transmitted as a composite.
PATCHCORD
A length of (Usually) ruggedised fibre with a connector at both ends.
PARITY CHECK
A means of detection transmission errors.
PASSIVE COUPLER
A coupler that divides a light input between output ports without adding
any light power.
PATCHBOX (PatchPanel)
A cable termination enclosure which allows demountable interconnection between
the discrete fibres in a cable or to another patchbox. Allows signal routing
to be re-configured as required.
PCS FIBRE
Plastic-Clad Silica fibre.
PEAK WAVELENGTH
The wavelength at which the optical power of a source is at its maximum.
PHASE MODULATION
Modulation of the phase angle of a signal in accordance with an input signal.
(Used in both optical and electrical circuits).
PHOTODETECTOR
A detector that converts a light input into an electrical output signal.
PHOTODIODE
A diode which acts as a photodetector.
PHOTON
The quantum of electromagnetic radiation. The phenomenon of light can be
described as a series of photons; this is an alternative to wave theory.
PHOTOTRANSISTOR
A transistor in which an amplified current is generated when light falls
on the base-collector junction.
PHYSICAL LAYER
Layer 1 of the OSI model, which specifies mechanical and functional characteristics
between nodes. Relevant to optical fibre links.
PICOSECOND
10-12 second
PIGTAIL
A length of optical fibre or cable attached to a connector or component
intended to facilitate jointing between that component and another optical
fibre or component. Usually buffered fibre only with a connector at 1 end
only - the other is spliced.
PIN PHOTODIODE
A fast linear photodetector, widely used in fibre optic receivers.
PLANAR WAVEGUIDE
A step-index multimode fibre in which a silica core is surrounded by a plastic
cladding with lower refractive index.
PLENUM
The air handing space between walls, under structural floors, and above
drop ceilings, which can be used to route intrabuilding cabling.
PLENUM CABLE
A cable whose flammability and smoke characteristics allow it to be routed
in a plenum area without being enclosed in a conduit.
PMD
Physical Media Independent as defined by ANSI X3T9.5 document.
POLARIZATION MAINTAINING OPTICAL FIBRE
Optical fibre which maintains the polarization of incoming light.
POLARIZED LIGHT
Light for which the electrical vector of the electromagnetic field has been
oriented, instead of being at random.
PORT
Hardware entity at each end of the link.
PREFORM
A cylindrical rod of glass from which an optical fibre is drawn. The preform
is fabricated with refractive index variations and other characteristics
that are maintained in the drawn fibre.
PRIMARY COATING
A thin plastic coating applied to the outer cladding of an optical fibre
to protect from contamination and abrasion.
PROTOCOL
A set of rules for operating a communications system.
PULSE DISPERSION
The lengthening of a pulse as it travels along an optical fibre.
PULSE SPREADING
Pulse dispersion. |
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RAY
A geometric representation of a light path through an optical medium-a line
normal to the wave front indication the direction of radiant energy flow.
RADIUS OF CURVATURE
The radius across the mating face of a ferrule, used in connectors. Optically,
assures low I.R & R.L
RECEIVER (IN FIBRE OPTICS).
A device that detects an optical signal and converts it into an electrical
signal.
REDUNDANCY
Built-in duplication of a vital part of a system that can take over if a
fault occurs.
REFRACTION
The bending of light as it passes between materials of different refractive
index.
REFRACTIVE INDEX
Ratio of the speed of light in a vacuum to the speed of light in a material.
REFRACTIVE INDEX GRADIENT
The change in refractive index with distance from the longitudinal axis
of a graded index optical fibre.
REGENERATOR
A receiver-transmitter unit that detects a weak optical signal, cleans and
amplifies it, then sends the regenerated signal on through a further length
of optical fibre.
REPEATER
In a fibre system, an opto-electronic device or module that receives an
optical signal, converts it to electrical form, amplifies it (or in the
case of a digital signal, reshapes, retimes or otherwise reconstructs it
and retransmits it in optical fibre).
RESPONSIVITY
The ratio of detector output (electrical) to input (optical), usually measured
in micro-amps (electrical) per micro-watt (optical).
RETURN LOSS
The power returned down a fibre after reflection from a component. Usually
expressed in dB, as a proportion of through power.
RIBBON CABLE
A cable in which many optical fibres are embedded in parallel, in a plastic
sheath, to form a ribbon-like structure. Electrical conductors may also
be included.
RING CABLE
Interconnection of nodes in a network to form a complete ring.
RISE TIME
The time taken for a signal (optical or electrical) to rise from low level
to peak value (usually taken as the time from 10% to 90% of peak).
RUGGEDISED
A cable construction comprising a secondary coated fibre surrounded with
Kevlar and then an outer sheath, usually about 2-3mm in diameter. |
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SCATTERING
LOSSES
Losses in optical fibres caused by the material of the fibre or by imperfections.
SECONDARY COATING
See Buffer (1).
SELFOC LENS
Trade name used by Nippon Sheet Glass Company for a graded index fibre lens.
SERIAL TRANSMISSION
A method of transmission in which each bit of information is sent sequentially
on a single channel.
SHEATH
The outer protective layer of an optical fibre cable.
SIGNAL-TO-NOISE-RATIO
The ratio of signal to noise (measured in dB).
SILICA GLASS
Glass made mostly of silicon dioxide, used in optical fibres.
SIMPLEX TRANSMISSION
Operation of a communication channel in one direction only.
SINGLE-FREQUENCY LASER
A laser that emits a range of wavelengths that are so close together that
they can be considered as a single wavelength.
SINGLEMODE FIBRE
A low loss optical fibre with a core diameter of 2 to 8 microns. Only one
mode is transmitted at the wavelength of interest.
SKEW RAY
A light ray that never intersects the axis of a fibre while being internally
reflected.
SNELL'S LAW
The law of refraction when a light ray passes between two Media, usually
expressed as:
n1 sin q1 = n2 sin q2
where n1 and n2 are the refractive indices of the media and q1 and q2 are
angles, in the two media, between the ray of light and the normal to the
interface.
SONET
Synchronous Optical NETwork
SOURCE
Device that converts an electrical signal carrying information into a corresponding
optical signal for transmission by an optical fibre, usually an LED or laser
diode.
SOURCE OPTICAL POWER
The mean level of power emitted by a light source.
SPECTRAL WIDTH
The range wavelengths emitted by a source.
SPEED OF LIGHT
Approx.2.998x108 metres/second (in vacuum).
SPLICE
A permanent junction between two fibre ends. (See also Fused Splice or Mechanical
Splice).
SPLITTING RATIO
The ratio of power emerging from two ports of a coupler.
STAR CONNECTED NETWORK
A network in which each of the secondary stations is connected to a single
primary station by a dedicated point-to-point link.
STAR COUPLER
A coupler with more than three ports.
STEP INDEX FIBRE
A fibre in which the refractive index of the core is uniform across its
diameter.
STIMULATED EMISSION
An occurrence created in a semiconductor laser diode when photons stimulate
available excess charge carriers to the emission of further photons. The
emitted light is identical in wavelength and phase with the incident light
- thus producing a coherent source.
STRAIN MEMBER (STRENGTH MEMBER)
The part of an optical fibre cable which ensures that no strain is imposed
on the fibres. Materials used include steel and synthetic yarns.
SUBSCRIBER LOOP
The link to individual subscribers in a telephone network.
SUPERTRUNK
A cable that carries several video channels between facilities, in a cable
TV or data communication network.
SURFACE EMITTING DIODE
An LED which emits light from its surface rather than from its edge.
SYNCHRONOUS TRANSMISSION
A transmission method in which the synchronising of characters is controlled
by timing or clock signals. Transmitters and receivers operate continuously
at the same frequency.
SYSTEM NETWORK ARCHITECTURE (SNA)
A communication system that links intelligent terminals to large computers,
developed by IBM. |
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T |
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T-COUPLER
A coupler with three ports.
TDM
Time-Division Multiplexing.
THRESHOLD CURRENT
The minimum current needed to sustain laser action in a laser diode.
TIGHT BUFFER
A material tightly surrounding a fibre in a cable, holding it rigidly in
place.
TIME DIVISION MULTIPLEXING
Digital multiplexing by taking one pulse at a time from separate signals
and combining them into a signal bit stream.
TOKEN
A unique bit sequence which permits a station to transmit to a token ring
network.
TOKEN RING NETWORK
A network which can only be accessed by a station that is allocated the
token, which is passed around the network in a predetermined sequence.
TOTAL INTERNAL REFLECTION
Total reflection of light back into a medium when it strikes the interface
with another medium having lower refractive index.
TRANSCEIVER
A combined transmitter and receiver.
TRANSMISSION LOSS
Total loss suffered by a lightwave through a system due, for example, to
the attenuation created by the fibre, connectors, splices etc.
TRANSMISSION MEDIA
The physical media through which communication signal are transmitted, for
example optical fibre, coaxial cable, twisted pairs.
TRANSMITTER
An optoelectronic unit comprising a driver and source which can change electrical
signals into optical signals.
TRANSIENT LOSS
An interruption to data flow caused by transient 'spikes' incurred usually
due to abnormal movement of fibres carrying the signal causing micro / macro
bends and corrupting data flow. (See B.E.R)
TRANSPARENCY
A communication system which is transparent imposes no restrictions on the
code or bit patterns in the information being transmitted.
TREE COUPLER
A coupler which distributes light signals to several output ports. |
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U |
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ULTRAVIOLET
Electromagnetic waves with wavelengths around 100 to 400mm.
UTP
Unshielded Twisted Pair. Copper cable. |
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V |
|
VISIBLE
LIGHT
Electromagnetic radiation that is visible to the human eye, at wavelengths.
VISIBLE RADIATION
Radiation (light) visible to the human eye. |
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W |
|
WAVEGUIDE
A device which constrains or guides the propagation of electromagnetic waves
along a path defined by the construction of the guide. Optical fibres are
a form of optical waveguide.
WAVEGUIDE DISPERSION
Dispersion arising from the dependence of the speed of light on wavelength
due to the geometrical properties of the fibre.
WAVELENGTH
Electromagnetic energy is transmitted in the form of a sinusoidal wave.
The wavelength is the distance covered by one cycle.
WAVELENGTH DIVISION MULTIPLEXING
A technique for increasing the capacity of a fibre channel by combining
optical signals at two different wavelengths.
WDM
Wavelength Division Multiplexing.
WIDE AREA NETWORK
Communication network covering long distances, often using some public network
facilities.
WINDOWS
When referred to fibre, indicates the three commonly used attenuation minima.
1st, 2nd and 3rd windows refer to 850nm, 1310nm and 1550nm regions respectively. |
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Z |
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ZERO
DISPERSION WAVELENGTH
Wavelength at which net chromatic dispersion of an optical fibre equals
zero. This happens when wavelength dispersion cancels out material dispersion.
ZIRCONIA
Ceramic material used for making ferrules in fibre optic connectors. |
