The photodetector is also called an optical receiver. It converts the variation in optical power into a corresponding variation in the electric current. As compare to the optical transmitter the design of optical receiver is more complicated just because the receiver must detect weak, distorted signals and then make decisions on what type of data was sent based on an amplified version of this totally distorted signal.
Photodiodes are one type of photodetector, is capable of converting light into either voltage or current. That depends upon the mode of operation. In photodetector cut off wavelength and quantum efficiency can be defined as λc and ȵ
The requirement of the ideal photodetector
- High sensitivity at the operating wavelength
- Spectral response: This parameter also describe the efficiency of the photodetector as a function of wavelength.
- Size: Photodetector size must be small
- Voltage: It must be work on small voltage
- High fidelity: The received signal must be reproduced as it as far as possible
- Cost: Cost of the photodetector must be less
- Noise: Minimum noise must be introduced by the detector device
- Stability: Performance characteristics of photodetector should not change with a change in ambient conditions
Types of photodetector
- LDR
- the p-n junction semiconductor photodetector
- Traveling wave photodetector
- PIN diode
- Avalanche photodiode
- Phototransistor