Groove depth estimation system using diffractive groove effects

摘要

Groove depth estimation apparatus provides an incident light beam which illuminates the surface of a grooved disc with a light spot that spans a plurality of convolutions of the groove. The structure of the groove convolutions serves as a diffraction grating which reflects the incident light beam into a plurality of diverging beams of light. A photodetector provides measurements of the light power in the respective reflected beams. Calculator circuits are provided for deriving from the photodetector measurements estimation of the average groove depth in the region illuminated by the light spot.