Optical track sensing device

An optical sensor consisting of a nearly monochromatic point source such as a light emitting diode (LED) (102,401) or a vertical cavity surface emitting laser (VCSEL) which is mounted on a multiple element detector (103). When this sensor is placed near a moving object (107) with a reflective periodic pattern (302) on its surface (such as an optical disk), it can produce a signal which can be used to control the position of the object. Unlike other sensors which often use lenses to project the light emitted by the light source onto the object and collect the light reflected (106) from the object and project them onto a photodector, this new sensor performs the tasks of object illumination and light collection without the use of any optical component. A self-imaging principle is used by placing the detector on the self-imaging plane of the object to detect the motion of the object. In order to detect the periodic signal in the self-image of the periodic object, the detector element is covered with a grating (412,414) structure having the same period or two times the period of the object.