Fiber Optic Glossary: N

n: Abbreviation for nano. One billionth or 10^-9.
N: Abbreviation for Newtons. Measure of force generally used to specify fiber optic cable tensile strength.
nA: Abbreviation for nanoamp. One billionth of an Amp or 10^-9 Amps.
NA: See numerical aperture.
NAB: Abbreviation for National Association of Broadcasters. A trade association that promotes and protects the interests of radio and television broadcasters before Congress, federal agencies and the Courts.	http://www.nab.org/
NA Mismatch Loss: The loss of power at a joint that occurs when the transmitting half has a numerical aperture greater than the NA of the receiving half. The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector.
National Electric Code^® (NEC): A standard governing the use of electrical wire, cable and fixtures installed in buildings; developed by the American National Standards Institute (ANSI), sponsored by the National Fire Protection Association (NFPA), identified by the description ANSI/NFPA 70-1990.	http://www.ansi.org/
NCTA: Abbreviation for National Cable Television Association. The major trade association for the cable television industry.	http://www.ncta.com/
NDSF: See non dispersion-shifted fiber.
Near-end Crosstalk (NEXT, RN): The optical power reflected from one or more input ports, back to another input port. Also known as isolation directivity.
Near Infrared: The part of the infrared near the visible spectrum, typically 700 nm to 1500 nm or 2000 nm; it is not rigidly defined.
NEMA: Abbreviation for National Electrical Manufacturers Association. Organization responsible for the standardization of electrical equipment, enabling consumers to select from a range of safe, effective, and compatible electrical products.	http://www.nema.org/
NEP: See noise equivalent power.
Network: 1) An interconnection of three or more communicating entities and (usually) one or more nodes (illustrated). 2) A combination of passive or active electronic components that serves a given purpose.
Network Topology: The specific physical, i.e., real, logical, or virtual, arrangement of the elements of a network. Common network topologies include a bus (or linear) topology, a ring topology, and a hybrid topology, which can be a combination of any two or more network topologies. Illustrated to the right is a bus topology utilizing tee couplers to connect a series of stations that listen to a single backbone of cable.
NF: See noise figure.
NFPA: Abbreviation for National Fire Protection Association. Publisher of the National Electrical Code®, and 300 other codes and standards through a full, open-consensus process.	http://www.nfpa.org/Home/index.asp
nm: Abbreviation for nanometer. One billionth of a meter or 10^-9 meters.
Node: 1) A terminal of any branch in network topology or an interconnection common to two or more branches in a network. 2) One of the switches forming the network backbone in a switch network. 3) A point in a standing or stationary wave at which the amplitude is a minimum.
Noise: 1) An undesired disturbance within the frequency band of interest; the summation of unwanted or disturbing energy introduced into a communications system from man-made and natural sources. 2) A disturbance that affects a signal and that may distort the information carried by the signal. 3) Random variations of one or more characteristics of any entity such as voltage, current, or data.
Noise Equivalent Power (NEP): The noise of optical receivers, or of an entire transmission system, is often expressed in terms of noise equivalent optical power.
Noise Figure (NF): The ratio of the output signal-to-noise ratio to the input signal-to-noise ratio for a given element in a transmission system. Used for optical and electrical components.
Non Dispersion-shifted Fiber (NDSF): The most popular type of single-mode fiber deployed. It is designed to have a zero-dispersion wavelength near 1310 nm.
Nonlinearity: The deviation from linearity in an electronic circuit, an electro-optic device or a fiber that generates undesired components in a signal. Examples of fiber nonlinearities include SBS, SRS, FWM, SPM, XPM, and Intermodulation.
Non Zero-dispersion-shifted Fiber (NZ-DSF): A dispersion-shifted single-mode fiber that has the zero-dispersion wavelength near the 1550 nm window, but outside the window actually used to transmit signals. This strategy maximizes bandwidth while minimizing fiber nonlinearities.
NRZ: Abbreviation for nonreturn to zero. A common means of encoding data that has two states termed “zero” and “one” and no neutral or rest position.
ns: Abbreviation for nanosecond. One billionth of a second or 10^-9 seconds.
NTSC: 1) Abbreviation for National Television Systems Committee. The organization which formulated the NTSC system. 2) Standard used in the U.S. that delivers 525 lines at 60 frames per second.
Numerical Aperture (NA): The light-gathering ability of a fiber; the maximum angle to the fiber axis at which light will be accepted and propagated through the fiber. NA = sin a, where a is the acceptance angle. NA also describes the angular spread of light from a central axis, as in exiting a fiber, emitting from a source, or entering a detector.
nW: Abbreviation for nanowatt. One billionth of a Watt or 10^-9 Watts.
Nyquist Frequency: The lowest sampling frequency that can be used for analog-to-digital conversion of a signal without resulting in significant aliasing. Normally, this frequency is twice the rate of the highest frequency contained in the signal being sampled. Also called Nyquist rate.
NZ-DSF: See non zero-dispersion-shifted fiber.