Optical Proximity Switch

Optical Proximity switch offer non-contact sensing of almost any substance or object up to a range of 10 meters. These sensors consist of a light source (usually an LED, light emitting diode, in either infrared or visible light spectrum) and a detector (photodiode). Due to the high intensity infra-red energy beam, these sensors have major advantages over other opto-electronic systems when employed in dusty enviroments. With their focused beam and long range, opto-electronic sensors are increasingly used in applications where other sensing techniques are lacking in sensing distance or accuracy. 
These are available in a variety of modes including:
1) Infrared Proximity (Diffuse Reflective)
2) Transmitted Beam (Thru-beam)
3) Retroreflective (Reflex)
4) Polarized Retroreflective (Polarized Reflex)
5) Fiber Optic
6) Background Rejection