Applications of photodiodes :

1. A reverse-biased photodiode conducts only when illuminated, assuming that the dark current is essentially zero. Due to its quick response to radi-ation and high operational speed, photodiodes are used in high-speed counting or switching applications.

2. Extensively used in an fibreoptic communication system.

3. As photosensors/photodetectors for detection of UV radiations and accurate measurement of illumination. Avalanche photodiodes have increased responsivity and can be used as photomultipliers, especially for low illumination.

4. In burglar alarm systems as normally closed switch until exposure to radiation is interrupted. When interrupted, the reverse current drops to the dark current level and sounds the alarm.

5. In an optocoupler, a photodiode is combined with a light-emitting diode to couple an input signal to the output circuit. The key advantage of an optocoupler is the electrical isolation between the input and output circuits, especially in high voltage applications. With an optocoupler, the only contact between the input and the output is a beam of light.