OptOELECTRONICS
Optoelectronics is the branch of electronics which deals with optics as well as electronics. It works on the principle of conversion of light energy into electricity. Optoelectronics encompasses the study, design and manufacture of hardware devices that convert electrical signals into photon signals and vice versa. Any device that operates as an electrical-to-optical or optical-to-electrical transducer is considered an optoelectronic device.
Classification of Optical Devices
Optical devices can be classified into 3 types –
1. Light Emitters – These devices give out light when excited electrically. They are also known as light sources.
Examples – LED, Laser diode, etc.
2. Light detectors or sensors – These devices convert light into some form of electrical energy or they will modify some electrical property such as resistance.
Examples – LDR, Photodiode, Phototransistor, Solar cell, etc.
3. Optocouplers or Optoisolators – These devices are formed by combining a light source and light detector into one device. Optocouplers will couple the signal from one point to another but isolate them physically.
Photon Absorption Mechanism
1. When light is incident on a semiconductor, the photons may be absorbed by the semiconductor or they may propagate though the semiconductor without getting absorbed.
2. Whether the photons may get absorbed or not depends on the band gap energy (Eg)
3. If Photon energy(E) < Eg,
Photons get absorbed, no light transmitted through the semiconductor and it is transparent.
4. If Photon energy(E) > Eg,
Photons will interact with the valence electrons and impart energy to them. These electrons cross the energy band gap and enter the conduction band. In doing so, they create holes at the valence band thus create electron-hole pairs.
5. As the electron-hole pair gets created, the excess energy may give the electron/hole additional kinetic energy.
6. This energy is dissipated in the form of heat.