The slotted optical switch, sometimes known as opto switch or optical switch but not to be confused with the optical component, is a device comprising a photoemitter (e.g. LED) and a photodetector (e.g. photodiode) mounted in a single package so that the photoemitter normally illuminates the photodetector, but an opaque object can be inserted in a slot between them so as to break the beam. Associated circuitry is provided which changes state when the beam is interrupted. For example, the carriage of a computer printer may be fitted with a projection which interrupts the beam of a slotted switch when it reaches the end of its travel, causing circuitry to react appropriately. Another application of the slotted switch is in the type of computer mouse with a rotating ball. The ball measures distances moved by rotating orthogonal shafts which drive optical chopper wheels turning in the slots of slotted switches.^[1]

This device uses the same basic components as an opto-coupler, but is operated by manipulating the light path instead of the photoemitter input.

Illustrations and data on slotted optical switches are to be found in catalogues and manufacturers' data sheets.^[2]