Abstract: A displacement measurement sensor using the confocal principle for measuring small changes in distance to a specular target surface comprises a monochromatic light source such as a laser diode 12, an aperture, 31 an objective lens system 44 possessing spherical aberration that separates the monochromatic light at different focal distances according to the magnitude of angular deviation from the optical axis. Each distance of the target surface from the objective lens will select specific angular rays able to retrace the path through the objective lens and aperture. Each angle then will correspond to specific distance. The angle measurement is determined by detecting the light impinging on a light sensitive electronic detector array 36.

Abstract: A displacement measurement sensor using the confocal principle with an optical fiber for measuring small changes in distance to a specular target surface comprises a monochromatic light source such as a laser diode 12 coupled to a multimode optical fiber. The fiber 32 functions as both a transmitter, receiver of light ray angle information. An objective lens 40 possessing spherical aberration separates the monochromatic light at different focal distances according to the magnitude of angular deviation from the optical axis. Each distance of the target surface from the objective lens will select specific angular rays able to retrace the path through the objective lens and fiber. Each angle then will correspond to specific distance. Angular information is preserved as the light path is traced back through the fiber 32 and the angle measurement is determined by registering the light impinging on a light sensitive electronic detector array 36.