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Lambertian Emitter:
An emitter that radiates according to Lambert’s cosine law, which states
that the radiance of certain idealized surfaces depends on the viewing
angle of the surface. The radiant intensity of such a surface is maximum
normal to the surface and decreases in proportion to the cosine of the
angle from the normal. Given by:
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LAN (Local Area Network):
A
communication link between two or more points within a small geographic
area, such as between buildings. Smaller than a metropolitan
area network (MAN)
or a wide area
network (WAN). |
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| Large Core
Fiber:
Usually, a fiber
with a core
of 200µm or more. |
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| Large Effective Area
Fiber
(LEAF): An
optical fiber,
developed by Corning, designed to have a large area in the core,
which carries the light. |
| Laser:
Acronym for light amplification by stimulated
emission of radiation. A light source that produces, through stimulated
emission, coherent, near monochromatic light. |
| Laser Diode
(LD):
A semiconductor that
emits coherent light when forward biased. |
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Lateral Displacement Loss:
The
loss of power that results from lateral displacement of optimum
alignment between two fibers or between a fiber
and an
active device. |
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| Launch Fiber:
An
optical fiber
used to couple and condition light from an optical source
into an optical fiber. Often the launch fiber is used to create an
equilibrium mode distribution
in multimode fiber. Also called launching fiber. |
| L-Band:
The wavelength range between 1570 nm and 1610 nm used in some
CWDM
and
DWDM
applications. |
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LD:
See laser diode.
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LEAF:
See large effective area
fiber.
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Least Significant Bit: In a binary code, the bit or bit position assigned
to the smallest quantity or increment that can be represented by the
code. |
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LED:
See light-emitting diode.
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| LEC (Local Exchange
Carrier):
A local telephone company, i.e., a communications common carrier that
provides ordinary local voice-grade telecommunications service under
regulation within a specified service area. |
| LEX: Abbreviation for local exchange.
Synonym for
central office. |
| LH:
Abbreviation for long-haul. A classification of video performance under
RS-250C. Lower performance than medium-haul
or short-haul.
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| L-I Curve:
The
plot of optical output (L) as a function of current (I) which
characterizes an
electrical-to-optical converter.
A typical L-I curve is shown at right. |
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| Light:
In a strict sense, the region of the
electromagnetic spectrum
that can be perceived by human vision, designated the visible spectrum,
and nominally covering the wavelength range of 0.4 µm to 0.7 µm. In the
laser and optical communication fields, custom and practice have
extended usage of the term to include the much broader portion of the
electromagnetic spectrum that can be handled by the basic optical
techniques used for the visible spectrum. This region has not been
clearly defined, but, as employed by most workers in the field, may be
considered to extend from the near-ultraviolet region of approximately
0.3 µm, through the visible region, and into the mid-infrared region to
30 µm.
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| Light-emitting Diode (LED):
A
semiconductor that emits incoherent light when forward biased. Two types
of LED's include
edge-emitting LED's
and
surface-emitting LED's
(illustrated). |
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| Light Piping:
Use of optical
fibers to illuminate. |
| Lightguide:
Synonym for
optical fiber. |
| Lightwave:
The path of a point on a wavefront. The direction
of the lightwave is generally normal (perpendicular) to the wavefront. |
| Linear
Device:
A device for which the output is, within a given dynamic range, linearly
proportional to the input. |
| Linearity: The basic measurement of how well
analog-to-digital and
digital-to-analog conversions are performed. To
test for linearity, a mathematically perfect diagonal line is converted
and then compared to a copy of itself. The difference between the two
lines is calculated to show linearity of the system and is given as a
percentage or range of least significant bits. |
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LNB:
Abbreviation for Low Noise Block Down Converter. A
device within a satellite dish which converts X-Band
intermediate frequencies (IF) to lower
L-Band
intermediate frequencies. |
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| Local Loop:
Synonym for loop. |
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Long-haul Telecommunications:
1.
In
public switched networks,
regarding circuits that span long distances, such as the circuits in
inter-LANA,
interstate, and international communications. 2. In military use,
communications among users on a national or worldwide basis. Long-haul
communications are characterized by a higher level of users, more
rigorous performance requirements, longer distances between users,
including world wide distances, higher traffic volumes and densities,
larger switches and trunk cross sections, and fixed and recoverable
assets. Usually pertains to the U.S. Defense Communications System.
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| Longitudinal
Mode:
An
optical
waveguide
mode
with boundary condition determined along the length of the optical
cavity. |
| Loop:
1) A communication channel from a switching center
or an individual message distribution point to the user terminal
(illustrated). 2) In telephone systems, a pair of wires from a central
office to a subscriber's telephone. 3) A type of antenna used in
direction-finding equipment and in UHF reception. |
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| Loose-tube:
A type of
fiber optic cable
construction where
the fiber is contained within a loose tube in the cable jacket.
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| Loss:
The amount of a signal’s power, expressed in
dB,
that is lost in
connectors,
splices,
or fiber
defects. |
| Loss Budget:
An accounting
of overall
attenuation
in a system. See
optical link loss budget. |
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Lossless Compression:
1) Reduction of the storage size of digital data by employing one or
more appropriate algorithms in such a way that the data can be recover
without loosing integrity. 2) Reduction of the amount of data that needs
to be transmitted per unit time though an analogous real-time process
that does not compromise the ability to completely restore the data.
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| Lossy
Compression:
Reduction of the bit-rate for an image signal by using algorithms that
achieve a higher compression than lossless compression. Lossy
compression presents loss of information and artifacts that can be
ignore when comparing to original image. Lossy compression takes
advantage of the subtended viewing angle for the intended display, the
perceptual characteristics of the human eye, the statistics of image
populations, and the objective of the display. 2) Removal of
redundant bits from an image in video technology producing a minor loss
of image quality. |
