Objective lens for optical pick-up
US6191889A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 28, 1999 |
| Grant date | Feb 20, 2001 |
| Priority date | — |
| Expiry date | May 28, 2019 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/1372
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
An objective lens includes a refractive lens having a positive refractive power, and a diffractive grating having a plurality of concentric ring-shaped steps that are formed on at least one lens surface of the refractive lens. The objective lens is a biconvex plastic lens of which first and second surfaces are aspherical. A diffractive grating is formed on the first surface of the objective lens. The diffractive grating is similar to a Fresnel lens, it is formed as many concentric rings each of which has a wedge sectional shape. The boundary between the adjacent rings is a step to give a predetermined optical path difference. The diffractive grating has wavelength dependence such that spherical aberration varies in the undercorrected direction as wavelength of incident light increases.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.