Coherent Mixing Interference Based Sensors for Characterizing Movement of a Watch Crown

An electronic watch includes a housing, a user-operable watch crown mounted to the housing, an electromagnetic radiation source emitting a beam of electromagnetic radiation toward a watch crown surface, and a sensor. The beam of electromagnetic radiation depends on a coherent mixing of electromagnetic radiation within a resonant cavity of the electromagnetic radiation source. The coherent mixing includes a mixing of a first amount of electromagnetic radiation generated by the electromagnetic radiation source and a second amount of electromagnetic radiation redirected into the resonant cavity by the watch crown surface. The sensor measures a first parameter of the beam of electromagnetic radiation and determines, using the measurement of the first parameter, a value of a second parameter characterizing movement of the watch crown. The second parameter may include a direction of rotation or speed of rotation of the watch crown, or other parameters.