Optical encoder disks and strips are components of rotary and linear encoders, respectively. They are usually made of metal, plastic, glass, or paper.

Optical encoders are sensors that translate either rotary or linear mechanical motion into electrical signals. They are used for a wide array of high-accuracy motion control, positioning, and measurement applications. The manufacture of encoder disks and strips involves cutting slots in the material, or printing alternating dark and light areas. Disks are paired with a light emitting diode (LED) and an optical detector to "read" slot patterns as they pass in front of the LED light source. Encoders may detect both the speed and direction that an encoder disk or strip is moving and return position information to a circuit.

Rotary encoder disks and strips may incorporate several different patterns made by printing or cutting alternating dark and light areas. Quadrature, a common technique, offsets two sets a half line-width apart to produce four counts per line. Other types of patterns permit different types of output signals from the optical encoder. As a rule, the resolution or counts per revolution of an encoder disk or strip depend on the slot pattern's placement.

Greater quantities of slots are necessary as the need for control increases, since slot width is the determining factor with regards to encoder precision. Typical applications involve systems that sense the position of a moving part or rotating shaft. They are often used to determine the exact position and current direction of force actuators, such as DC motors. Many actuators tend to exhibit over- and under-shoot depending upon the applied load.

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