nt 1310 unit 9

Topics: Optical fiber, Laser Pages: 8 (2641 words) Published: August 11, 2015
NT 1310
Physical Networking

Unit 9
Assignment 1 : Transmitters.
Exercise 1 : Light Sources and Companents
LAB 1 : New Building – Optical – Network

Amir R. Ghattas

The differences between LED and Laser Transmitters
LED
LED (Light-Emitting Diode) is a two-lead semiconductor light source. It resembles a basic p-n junction diode (is a boundary or interface between two types of semiconductor material, p-type and n-type, inside a single crystal of semiconductor., which emits light when activated. When a fitting voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semi-conductor. An LED is often small in area (less than 1 mm2) and integrated optical components may be used to shape its radiation pattern. Appearing as practical electronic components in 1962, [9] the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still frequently used as transmitting elements in remote-control circuits, such as those in remote controls for a wide variety of consumer electronics. The first visible-light LEDs were also of low intensity, and limited to red. Modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.

Laser Transmitter
A laser transmitter projects a beam of laser light outward while raising and lowering the beam. The beam may define a conical surface of varying inclination. The transmitter includes a laser source that directs a beam generally vertically, and a beam diverting element. The beam diverting element is positioned in the path of the beam, intercepting the beam and redirecting it. The beam emerges from the transmitter as a non-vertical beam that is raised and lowered. The diverting element may include a pair of mirrors configured as pentagrams, with one of the mirrors pilotable. Alternatively, the diverting element may include a plurality of micro mirrors. Also, the diverting element may include a conical reflector and an annular lens which is cyclically raised and lowered. The beam may be raised and lowered cyclically according to a predetermined schedule, or it may be raised and lowered non-cyclically. Laser transmitters have been used in a variety of ways in the construction and surveying industries. In a typical application at a construction site, a laser transmitter projects a plane of laser light for use as a position reference by workers, and by various machines carrying laser receivers. The machines may be operated by workers who view position displays, or may be operated automatically or semi-automatically by control systems that respond to the measured positions and elevations, and to a database of desired positions and elevations. The machines may also carry other position detection devices, such as GPS receivers or the like, for supplementing or augmenting the laser system measurement of position. Lasers are monochromatic (single color wavelength), collimated (non-divergent) and coherent (wavelengths in- phase) in contrast, LED's are neither coherent nor collimated and generate a broader band of wavelengths (multiple). In addition, a significant difference between the two is the power output. The peak power output of lasers is measured in watts, while that of LED’s is measured in milliwatts. Also, LED's usually have a 50% duty cycle, meaning that they are "on" 50% of the time and "off" 50% of the time regardless of what frequency (pulses per second) setting is used.

Exercise 1 Light Source and Components

1. Forward biased led—A basic LED light source is a semiconductor diode with a p region. When the LED is forward biased (a positive voltage is applied to the p region and a negative voltage to the n region), current flows through the LED. As current flows...
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