Sony Corporation

Takatoshi Yamada

Jin Sato

Motoo Aiba

Kyu Kanno

Satoshi Kawakita

Takeshi Mizuno

Norio Fukasawa

A diffraction element for diffracting a particular wavelength of incident optical beam includes: a base section made from a first resin and provided with a predetermined diffraction pattern; and a cover section made from a second resin and covering the diffraction pattern, wherein a rate of change of refraction index of the first resin is substantially the same as a rate of change of refraction index of the second resin in a temperature range between a first temperature and a second temperature.

Diffraction element, objective lens unit, optical pickup and optical disc apparatus

The first and second materials of the diffraction element are selected such that the first material's refraction indexes n(&#x3bb;), n(&#x3bb;) and n(&#x3bb;) for the first, second and third wavelengths &#x3bb;and &#x3bb;and the second material's refraction indexes n(&#x3bb;), n(&#x3bb;) and n(&#x3bb;) for the first, second and third wavelengths &#x3bb;and &#x3bb;satisfy one of the conditions (1) or (2).

Diffraction element, objective lens unit, optical pickup, optical disc apparatus and design method for diffraction element

An objective lens is configured of a first crown-glass lens and a second flint-glass lens, whereby it can exhibit substantially identical optical properties at a plurality of recording/reproducing light source wavelengths, particularly, in both 650 nm and 405 nm wavelength bands. Also, by maximizing the difference in glass transition point between the first and second lenses, one of the first and second lenses having a higher glass transition point is molded first, to allow that first molded lens to serve as a mold tool for molding the other lens. This dispenses with the steps of aligning and adhesive bonding the two lenses, whereby this objective lens can be used at a plurality of wavelengths as a single objective lens, and thus an information recording/reproducing apparatus can be of a simple configuration.

Objective lens and optical pickup apparatus, information recording/reproducing apparatus

An optical lens composed of a transparent material, wherein one surface thereof on a light source side is a convex aspherical surface of rotation symmetry defined by a function relative to the radial distance from an optical axis. The aspherical surface is shaped to be a curved one without any stepped region with regard to the radial direction in the defined area, and has a portion where the derivatives of the function are discontinuous at a predetermined radial position. Although not equipped with an iris diaphragm, this optical lens is capable of eliminating an incident light beam outside the optical effective surface thereof without deteriorating the optical characteristics.

Growing community of inventors

Kanagawa, Japan

Takatoshi Yamada