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Glossary

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Term Definition
L
Symbol used to designate inductance.
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Ladder rack
A rack used to hold cabling that looks like a ladder.
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Large core fiber
Usually a fiber with a core of 200 microns or more. This type of fiber is not common in structured cabling systems.
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Laser
Acronym for light amplification by stimulated emission of radiation. The laser produces a coherent source of light with a narrow beam and a narrow spectral bandwidth (about 2cm). Lasers in fiber optics are usually solid-state semiconductor types. Lasers are used to provide the high-powered, tightly controlled light wavelengths necessary for high-speed, long-distance optical fiber transmissions.
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Laser diode (LD)
A special semiconductor that emits laser light when a specific amount of current is applied. Laser diodes are typically used in higher speed applications (622Mbps to 10Gbps) such as ATM, 1000Base-LX, and SONET. The mode is usually ellipse shaped and therefore requires a lens to make the light symmetrical with the mode of the fiber, which is usually round.
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Lasing threshold
The energy level that, when reached, allows the laser to produce mostly stimulated emissions rather than spontaneous emissions.
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Lateral displacement loss
The loss of signal power that results from lateral displacement from optimum alignment between two fibers or between a fiber and an active device.
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Launch angle
In fiber-optic transmissions, the launch angle is defined as the difference between the incoming direction of the transmitting light and the alignment of the optical fiber.
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Launch cable
Used to connect fiber-optic test equipment to the fiber system.
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Launch fiber
An optical fiber used to introduce light from an optical source into another optical fiber. Also referred to as launching fiber.
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Lay
The axial distance required for one cabled conductor or conductor strand to complete one revolution around the axis around which it is cabled.
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Lay direction
The direction of the progressing spiral twist of twistedpair wires while looking along the axis of the cable away from the observer. The lay direction can be either left or right.
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Layer 2 switch
A network device that operates at the Data Link layer. The switch builds a table of MAC addresses of all connected stations and uses the table to intelligently forward data to the intended recipients.
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Layer 3 switch
A network device that can route LAN traffic (Layer 3) at a speed that is nearly as quick as a Layer 2 switch device. Layer 3 switches typically perform multiport, virtual LAN, and data pipelining functions of a standard Layer 2 switch and can also perform routing functions between virtual LANs.
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Lbf
Abbreviation for pounds force.
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