Scott Cumston 5/15/2013
NGT1310 Wednesday 165
Instructor: Robert Freid
Physical Networking Unit 9 Assignments
Unit 9 Exercise 1 – Definitions for Light Sources and Components
Forward Biased LED - When an LED is forward biased, the anode is connected to positive
and cathode is connected to negative terminal of the supply, then current flows through the
LED, just like in a regular diode.
Incoherent Light – Light in which the electric and magnetic fields of photons are completely
random in orientation.
Laser – An 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. Used to
provide the high-powered, tightly controlled light wavelengths necessary for high-speed,
long-distance optical fiber transmissions.
Output Pattern – The LED and laser semiconductors used in fiber-optic light sources are
packaged to couple as much light as possible into the core of the optical fiber. The LED has
a wide output pattern compared to a laser and does not couple all its light energy into the
core of a multimode optical fiber. The output pattern of a laser light source is very narrow,
allowing a majority of the light energy to be coupled into the core of a single-mode or
multimode optical fiber.
Output Power – Amount of power a component, circuit or system can deliver to a load.
Modulation Speed – The modulation speed of a light source is just one factor that can limit
the performance of a fiber-optic communication system.
Core Diameter Mismatch – This occurs when the core diameter of the transmitting fiber (t)
is larger than the core diameter of the fiber at the receiving end (r).
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