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Due to the cheap price and availability, most of the devices use LED as the light source. LED (Light emitting Diode) is a semiconductor that produces light when current is passed through them.
Figure 4: LED construction
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The light detector is the component used to detect the light produced by the light source. They are commonly known as photodiode or phototransistor. Due to its capability of sensing the different pulses of light they are known as receiver. There best application is in the receiver end of the optical fiber data transmission. The transponder connected with it converts the light sensed by these detectors to electrical pulses.
Figure 5: Spectral Response of light detector
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