Photointerrupter is also known as Optical Sensor, Photo Sensor. It can be divided into two functions: Transmission-type photo interrupter and Reflector-type photosensor.
Transmission-type photo interrupter is configured by IR and PT aligned facing each other. When it detects the infrared light blockage, it will create high/low signal.
Reflector-type optical sensor is configured by IR and PT on the same. When the infrared light is reflected by the object, Reflector-type photosensor can detects the position of object. Reflector-type photosensor is also called Photoreflector.