optocouplers are available in the IC form MCT2E is the standard optocoupler IC which
is used popularly in many electronic application.
This input is applied between pin 1& pin 2. An
infrared light emitting diode is connected between these pins.
The infrared radiation from the LED gets focused on
the internal phototransistor.
The base of the phototransistor is generally left
open. But sometimes a high value pull down resistance is connected from the
Base to ground to improve the sensitivity.
The block diagram shows the
opto-electronic-integrated ciruit (OEIC) and the major components of a
fiber-optic communication facility.