Lec-4 Laser Diode (22-03-07)

Lec-4 Laser Diode (22-03-07) - Photonic Network By Dr. M H...

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Unformatted text preview: Photonic Network By Dr. M H Zaidi aser D iode L ight emitters are a key element in any fiber optic system. This component converts the electrical signal into a corresponding light signal that can be injected into the fiber. The light emitter is an important element because it is often the most costly element in the system, and its characteristics often strongly influence the final performance limits of a given link. Figure 1 - Laser Diodes Convert an Electrical Signal to Light Photonic Network By Dr. M H Zaidi Laser diodes are complex semiconductors that convert an electrical current into light. The conversion process is fairly efficient in that it generates little heat compared to incandescent lights. Five inherent properties make lasers attractive for use in fiber optics. 1. They are small. 2. They possess high radiance (i.e., They emit lots of light in a small area). 3. The emitting area is small, comparable to the dimensions of optical fibers. 4. They have a very long life, offering high reliability. L aser D iode Photonic Network By Dr. M H Zaidi 5. They can be modulated (turned off and on) at high speeds. Table 1 offers a quick comparison of some of the characteristics for lasers and LEDs. These characteristics are discussed in greater detail throughout this article and the article on light- emitting diodes. L aser D iode able 1 - Comparison of LEDs and Lasers Characteristics LED Lasers Output Power Linearly proportional to drive current Proportional to current above the threshold Current Drive Current: 50 to 100 mA Peak Threshold Current: 5 to 40 mA Coupled Power Moderate High Speed Slower Faster Output Pattern Higher Lower Bandwidth Moderate High Wavelengths Available 0.66 to 1.65 μm 0.78 to 1.65 μm Spectral Width Wider (40-190 nm FWHM) Narrower (0.00001 nm to 10 nm FWHM) Fiber Type Multimode Only SM, MM Ease of Use Easier Harder Lifetime Longer Long Cost Low ($5-$300) High ($100-$10,000) Photonic Network By Dr. M H Zaidi L aser diodes are typically constructed of GaAlAs (gallium aluminum arsenide) for short- wavelength devices. Long-wavelength devices generally incorporate InGaAsP (indium gallium arsenide phosphide). L aser D iode Photonic Network By Dr. M H Zaidi Laser Diode Performance Characteristics S everal key characteristics lasers determine their usefulness in a given application. These are: Peak Wavelength: This is the wavelength at which the source emits the most power. It should be matched to the wavelengths that are transmitted with the least attenuation through optical fiber. The most common peak wavelengths are 1310, 1550, and 1625 nm....
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This note was uploaded on 06/03/2011 for the course IT ISE808 taught by Professor Mr.tayyab during the Spring '11 term at College of E&ME, NUST.

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Lec-4 Laser Diode (22-03-07) - Photonic Network By Dr. M H...

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