optical sources by fiber optic in indonesia.pptx

optical source

1. Optical sources and transmitter

2. We know that electrical signals (in the form of voltage or current) have to be converted into optical signals (light pulses) at the transmitter end in an optical fiber communication system . So , the fundamental function of an optical source is to transform electrical energy (i.e., the current ) into an equivalent optical energy (i.e., light pulse) as efficiently as possible . T here are mainly two types of optical sources : monochromatic incoherent sources such as LEDs , monochromatic coherent sources such as laser diodes .

3. T he major requirements for an optical source are : Ideally, the light output must be focused (i.e., highly directional) so that it can be launched into an optical fiber efficiently. The size and configuration of an optical source should be compatible so as to couple light efficiently into an optical fiber . The optical source must have linear output. This means that the output optical signal should be in direct proportion to the input electrical signal so as ensure minimum noise and distortion. Optical sources should be able to generate optical signals at wavelengths where the fiber attenuation is minimum. Moreover, optical pulse dispersion should be low so that optical detectors can operate efficiently

4. Optical sources must emit sufficient optical power so as to compensate for transmission losses due to fiber cable as well as the connectors used in the link. This is required in order to ensure adequate optical power level necessary to operate the optical detector at the receiver end. Optical sources should be capable of providing signal modulation over a wide bandwidth ( ranging from audio frequencies to several GHz). However, they should have narrow linewidth so as to produce negligible fiber dispersion. Optical sources must generate a stable output optical signal which should not vary with operating temperature and other environmental conditions. Optical sources should be highly reliable and inexpensive.

5. Review of Semiconductor Physics silicon has four electrons in its outermost shell, by which it makes covalent bonds with its neighboring atoms, as shown in Fig. below. These electrons are somewhat loosely bound. An electron can gain energy by external means , such as thermal energy, to break the covalent bond and, thereby, contribute to the conduction band .