Optical distance sensors are the culmination of decades of research and development (R&D) in the field of optoelectronics. This subset of photonics is concerned with the application of electronic devices that detect, emit, and modulate light to accomplish an extremely diverse range of functions. In the context of distance measurement: Light is used to measure the distance of a sensor to an obstacle or surface.
This is a companion discussion topic for the original entry at https://community.robotshop.com/blog/show/optical-distance-sensors-principles-applications