| 摘要 |
PURPOSE:To increase both diffracting and focusing functions for the light given from a light source and to miniaturize an optical disk pickup, by using a micro- Fresnel lens containing concentric grating parts in place of an objective. CONSTITUTION:The laser light is converted into parallel beams by a collimator lens 3 and turned 90 deg. round a polarizing axis by a 1/4 wavelength plate 5 after passing through beam splitters 4A and 4B. Then the parallel beams pass through a micro-Fresnel lens 12 containing concentric grating parts 14 having rectangular sections and formed on the upper side of a transparent substrate 13. Therefore an incident planar wave A is turned into a spherical wave B by diffraction, and therefore the spot diameter (d) of the laser light is minimized at a focal point F1. In this case, the F-number of the lens 12 is reduced to decrease the diameter (d). Several hundreds of the parts 14 are formed with their roughness decreased toward the circumference part from the center, and the pitches are set at 1mum- several mum at the circumference part. |
