Optoelectronics is the technology which combines optics and electronics. The devices based on this technology are known as Optoelectronics devices. These devices are of two types which are light-generating optoelectric devices and light-sensitive devices.
Examples of Light generating Optoelectronics devices
The best known types of light-generating optoelectric devices are:
- The ordinary tungsten filament lamp.
- Light-emitting diode (LED).
- The multi segment LED array.
- And the neon or gas discharge lamp.
- Some special types of light generating devices includes the cathode ray tube (CRT) and the LASER.
Examples of Light Sensitive Optoelectronics devices
- Light-sensitive devices include photodiodes and phototransistors. They have optosensitive conductivity.
- Light sensitive resistors which have optosensitive resistivity.
- Solar or photovoltaic cells which are optosensitive voltage generators.
- Some specialist devices such as opto-isolators and opto-reflectors combine both light generating and light-sensing units in a single package.
Applications of Optoelectronics Devices
- These devices are setup for generating a wide variety of stationary or moving visual displays.
- Optoelectronics devices finds application to provide an automatic switching or alarm action. It can be in the presence or absence of a visible or invisible light source. Or to provide a similar action when a person or object moves within the range of a generated light source.
- They also finds applications to provide remote-control action via an infra-red light generator and a remotely placed detector.
- In some applications, fiber optic cables can be used to form a low loss closed circuit. These circuits are connecting link between modulated light generator and a matching remotely placed light-sensitive device and thus forming an interference free data link.
Any light source can emits energy only over a certain range of frequencies or wavelengths. A graph of energy output plotted against either frequency or wavelength is called the emission spectrum for a given light source.
A light-sensitive device is sensitive only for a certain range of radiation frequencies. A graph between device current, voltage, or resistance plotted against frequency is known as its spectral response. For a given photosensitive material, there is a minimum radiation frequency (or maximum wavelength) that can produce effect and this frequency is known as the threshold frequency.
Terminologies related to Optoelectronics devices
The total light energy output, or luminous flux from a source is defined as the total quantity of light energy emitted per second from a luminous body. It is represented by symbol F or ф and is measured is ‘milliwatts’ or in lumens, where 1 lumen = 1.496 mW. The conception of luminous flux help us to specify the output and efficiency of a given light source.
Luminous intensity in any given direction is the luminous flux emitted by the source per unit solid angle, measured in direction in which intensity is required. It is denoted by symbol I and is measured in candela (Cd) or lumens per steradian. Total lumens given out by the source of one candela is 4π lumens.
When the light falls upon any surface, the phenomenon is called the illumination. Illumination is defined as the number of lumens falling on the surface per unit area. It is denoted by symbol E and is measured in lumens per square meter, or lux or meter-candle. If a flux of lumens fall on surface of area A. the illumination of that surface is
E = ф/A lumens/meter square or lux (lx).
The above light generating and light sensitive devices like Light dependent Resistor, Photoconductive Cells, Photodiode, Photovoltaic Cells, Photo Transistors, Light Emitting Diodes, Liquid Crystal Displays, Seven-Segment Displays and Optocouplers are discussed in later articles.