Attenuation: The decrease in magnitude of power of a signal in transmission between points. A term used for expressing the total losses on an optical fiber consisting of the ratio of light output to light input. Attenuation is usually measured in decibels per kilometer (dB/km) at a specific wavelength. The lower the number, the better the fiber. Typical multimode wavelengths are 850 and 1300 nanometers (nm); single mode, at 1300 and 1550 nm. When specifying attenuation, it is important to note if it is nominal or average, room temperature, value or maximum over operating range.
Backbone: A facility (e.g. pathway cable or conductors) between telecommunications closets or floor distribution terminals, the entrance facilities, and the equipment rooms within or between buildings.
Bandwidth: Measure of the information carrying capacity of an optical fiber normalize to an unit of MHz-km. (This term is used to specify capacity of multimode fibers only. For single mode fibers, use dispersion).
Bit: Abbreviation for binary digit; an individual digital pulse; the basic unit of computer communications.
Broadband: In general, covering a wide range of frequencies. The broadband label is sometimes used for a network that carries many different services or for video transmission.
COD (COMD): Catastrophic Optical (Mirror) Damage, a type of “sudden device failure” due to degradation of the laser mirror facet during device operation. Inherent to the physics of semiconductor surfaces the photons get absorbed at the mirror facet, which causes heat and in turn sudden growth of defects, and thus, it is “catastrophic”.
Combiner: A passive device in which optical power from several input fibers is collect at a common point.
Connection Loss: The ratio / loss of optical power (expressed as a percent) from one output port to the total output power. Also known as coupling loss.
Connector: Hardware installed on cable ends to provide physical and optical cable attachment to a transmitter / receiver or another cable. A junction which allows an optical fiber or cable to be repeatedly connected or disconnected to a device such as a source or detector.
Coupler: A device that connects three or more fiber ends, dividing one input between two or more outputs or combining two or more inputs into one output.
Coupling: Transfer of light into or out of an optical fiber (note that coupling does not require a coupler).
Coupling Loss: The ratio / loss of optical power (expressed as a percent) from one output port to the total output power. Also known as connection loss.
Cross-talk: The phenomenon where a signal transmitted on one circuit or channel of a transmission system creates an undesired effect or interference in another circuit or channel. Also called optical coupling.
Data Speed: The maximum number of bits of information, which can be transmitted per second. Typically expressed as megabits per second (Mb/s).
Data Transmission: Sending data from one place to another by means of signals over a channel.
Decibel (dB): The standard unit used to express gain or loss of optical power.
Dense Wavelength Division Multiplexing (DWDM): Wavelength Division Multiplexing (WDM), with increased available number of channels by a denser usage of the given light spectrum.
Digital Transmission: Transmission of a discrete signal (generally obtained by digitizing an analog signal) preferably by means of binary light pulses in a periodic time pattern.
Dispersion: The cause of bandwidth limitations in a fiber. Dispersion causes a broadening of input pulses along the length of the fiber. Two major types are a) mode dispersion caused by differential optical path lengths in a multimode fiber, and b) material dispersion caused by a differential delay of various wavelengths of light in a waveguide material.
Distortion: A change of signal waveform shape.
Distributed Feedback Laser (DFB): An injection laser diode, which has a Bragg reflection grating in the active region in order to suppress multiple longitudinal modes and enhance a single longitudinal mode.
Erbium Doped Fiber Amplifier (EDFA): Fiber with the element Erbium doped in small concentrations in the core of the fiber, providing the lasing medium and amplification for fiber amplifiers
Erbium Doped Waveguide Amplifier (EDWA): Silica-on-silicon integrated optical planar waveguide with the element Erbium doped in small concentrations in the waveguide providing the lasing medium and amplification for fiber amplifiers
Erbium Micro Fiber Amplifier (EMFA): Small size amplifiers which make use of new type of fiber with the element Erbium doped in high concentrations in the core of the fiber, providing the lasing medium and amplification for fiber amplifiers and reduce length of the required fiber.
Fiber (optical): Thin wire of silica (silicon dioxide), used to transmit optical information long distances. It is an optical waveguide consisting of a core and a cladding to confine the light signals.
Fiber Amplifier: A device which amplifies optical signals without first converting them to electronic form.
Fiber Optic Cable: Transmission medium using light to transmit voice, data or video through fibers made of glass, fused silica or plastic. Fiber transmissions exhibit high signal quality and high bandwidth.
Fiber Optics: Light transmission through optical fibers for communication or signaling.
Fiber-to-the-desktop: Lumics installed its first fiber-to-the-desktop transmission line to upgrade its current LAN capacity to unprecedented 1MB/s in 1Q02.
FIT: Failures In Time. FIT specifies the degradation rate in failure units per 1dB cumulative device hours, for example, 1000 FIT means 0.1% failures per 1000 hours. FIT usually varies as the device ages.
Frequency: The number of cycles per unit of time, denoted by Hertz (Hz). Thus 1 Hz=1 cycle per second.
Gigabit-Per-Second (Gb/s): One billion (more accurate: 1024x1024x1024) bits per second.
Insertion Loss: Additional loss in a system when a device such as a connector is inserted, equal to the difference in signal level between the input and output.
Isolator: Prevents the amplified signal from reflecting back upstream, where it would increase noise and decrease efficiency.
Laser: Light Amplification by Stimulated Emission of Radiation. A device, which generates and amplifies electromagnetic oscillations at wavelengths between the far infrared and ultraviolet. Like any electromagnetic oscillator, a laser oscillator consists of two basic elements: an amplifying (active) medium and a regeneration or feedback device (resonant cavity). A laser’s amplifying medium can be a gas, semiconductor or dye solution etc; feedback is typically from two mirrors. Distinctive properties of the electromagnetic oscillations produced include monochromaticity high intensity, small beam divergence and phase coherence. As a description of a device ‘laser’ refers to the active medium plus all equipment necessary to produce the effect of lasing.
Laser Diode: A semiconductor device that emits coherent light when forward biased. It is widely used as light sources and pump lasers for amplifiers in optical networks.
Local Area Network (LAN): A geographically limited communications network intended for the local transport of data, video and voice.
Long Haul Telecommunications: Long-distance telecommunication links.
Megabit-Per Second (Mb/s): One million (strictly: 1024x1024) bits per second.
Median Life (years): ML, the time, when the cumulated device failure reaches 50%. Sloppy speaking, in ML’s time period, about half of the operating devices are expected to fail most probably.
Milliwatts (mW): A unit of measure (of power) equal to one thousandth of a watt.
MTTF (years): Mean Time To Failure, the statistical expectation value of Time To Failure (TTF). In standard lifetime estimates (log-normal, Weilbull) the relation holds: ML < MTTF, i.e. median life is shorter than mean time to failure.
Multiplexing: A technique that combines voice frequency circuits by interleaving the signals into time or frequency slots for transport over higher speed transmission systems.
Nm (Nanometer): A unit of measure equal to one billionth of a meter.
Receiver: A detector and electronic circuitry to change optical signals to electrical signals.
Regenerator: A device that receives a fiber optic signal and regenerates it for retransmission, used in very long fiber optic links.
Single Mode Fiber: An optical waveguide (or fiber) in which the signal travels in one ‘mode’. The fiber has a small core diameter.
Singlemode or Multimode: Singlemode fibers produce almost mathematically perfect Gaussian beams. A collimated Gaussian beam behaves very differently from a multimode beam. Gaussian beams maintain collimation over a certain distance, often called the beam confocal parameter which varies from a fraction of a millimeter for very small collimators to meters for large beam collimators. The center of the beam confocal parameter is called the beam waist. It is very important to define the position of the beam waist to achieve optimum performance. The beam waist can be adjusted for a collimator with a given size. The longer the focal length, the larger the tuning range. What is important to remember is that doubling the focal length would quadruple the tuning range and the beam confocal parameter. Multimode “collimators” on the other hand really never collimate the beam. They simply form an image of the fiber core at the certain distance. Therefore, it is critical to define the image distance between the pairing collimators.
Source: A transmitting LED or laser diode, which produces an information-carrying optical signal, when properly driven (with electrical energy).
Spherical or Chromatic Aberration: Almost all polished lenses form flat and spherical surfaces which limit the lens` ability to focus a Gaussian optical beam into a diffraction limited spot. The technical term for this behavior is spherical aberration. As a result, the coupling efficiency between collimator pairs made with spherical lenses are far from optimum. Aspherical lenses use a slightly modified surface contour to significantly reduce spherical aberration. They are ideal for most applications with single wavelength or relatively small bandwidth. When two beams with far different wavelengths come into a single lens, either spherical or aspherical, their focal distances are different, often called chromatic aberration. Achromatic doublets are frequently used to reduce the effect.
Sudden failure: unpredictable device failure, mostly originating from gradual growing microscopic defects that lead to catastrophic rapid degradation during device operation. Life estimates due to sudden failures are only possible to a certain degree of confidence using statistical sample testing.
Transmission Loss: Total loss encountered in transmission through a system.
Transmitter: A driver and a source used to convert electrical signals into optical signals.
TTF: Time To Failure. The time passed until the device suffers total failure and needs to be replaced. TTF is related to either “sudden failure” or “wear out”.
Wavelength: A parameter of the light wave. It is the distance (in meters) between two adjacent peaks in a wave.
Wavelength Division Multiplexing (WDM): A technique to combine many signals of different wavelengths of light on a single optical fiber.
Wear out: Failure mechanism related to gradual degradation of performance (such as light power of a laser), can be monitored over time and is predictable in contrast to so-called “sudden failures”.