Scanning device including plastic high-numerical aperture objective

• US 20040120053A1
• Filed: 10/21/2003
• Published: 06/24/2004
• Est. Priority Date: 04/25/2001
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Hendriks, Bernardus Hendrikus Wilhelmus
• Granted Patent: US 7,239,459 B2
• Time in Patent Office: Days
• US Class Current: 359/719
• CPC Class Codes: G11B 7/1374 Objective lenses optical objectives per se G02B9/00
• CPC Class Codes: G11B 7/13922 passive
• CPC Class Codes: G11B 7/22 Apparatus or processes for the manufacture of optical heads, e.g. assembly

Abstract

An optical scanning device for scanning an information layer (104) of an optical record carrier (102) includes a radiation source (110) for generating a radiation beam (108) and a high-NA objective system (118) for converging the radiation beam on the information layer. The objective system includes a first lens (116) and a second lens (117). The first lens and the second lens are made of plastic. The signs of the temperature-dependence of the spherical aberration of the first and second lens are different and the magnitudes of the temperature-dependence of the spherical aberration of the two lenses is substantially equal such that the temperature-dependence of the spherical aberration of the objective system as a whole is reduced to less than 30 mλ OPDrms for a temperature change of 30 K.

Claims

1. An optical scanning device for scanning an information layer of an optical record carrier, the device including a radiation source for generating a radiation beam having a wavelength λ

and an objective system having a numerical aperture larger than 0.65 for converging the radiation beam on the information layer, the objective system including a first and a second lens both made of plastic, characterized in that

the first and second lens each have a temperature-dependence of the spherical aberration imposed on the radiation beam, the signs of the dependence of the first and second lens being different and the magnitudes of the dependence of the first and second lens being substantially equal such that the temperature-dependence of the spherical aberration of the objective system is reduced to less than 30 mλ

OPDrms for a temperature change of 30 K.

2. The optical scanning device according to claim 1, including a detection system for converting radiation coming from the information layer to an information signal, and an information processing unit for error correction of the information signal.

3. An objective system having a numerical aperture larger than 0.65 for focussing a radiation beam having a wavelength λ

and including a first and a second lens both made of plastic, characterised in that the first and second lens each have a temperature-dependence of the spherical aberration imposed on the radiation beam, the signs of the dependence of the first and second lens being different and the magnitudes of the dependence of the first and second lens being substantially equal such that the temperature-dependence of the spherical aberration of the objective system is reduced to less than 30 mλ

OPDrms for a temperature change of 30 K.

4. The objective system according to claim 3, wherein the first lens has a magnification β

smaller than 0.2 and the second lens has a magnification β

larger than 0.2.

5. The objective system according to claim 4, wherein the second lens has a magnification β

in the range from 0.3 to 0.6.

6. The objective system according to claim 4, wherein the first lens is made of a material having a higher refractive index than the material of which the second lens is made.

7. The objective system according to claim 4, wherein the first lens is made of COC and the second lens is made of PMMA, and the magnification of the second lens is in the range from 0.4 to 0.5.

8. A method for manufacturing an objective system having a numerical aperture larger than 0.65 for focussing a radiation beam having a wavelength λ

and including a first and a second lens both made of plastic, including the steps of

designing the objective system to have a temperature-dependence of the spherical aberration of less than 30 mλ

OPDrms for a temperature change of 30 K by making the signs of the temperature-dependence of the spherical aberration of the first and second lens different and the magnitudes of the temperature-dependence of the first and second lens substantially equal,

manufacturing the first and second lens according to the design and

assembling the first and second lens to an objective system.

9. The method according to claim 8, wherein the sign of the temperature-dependence of the spherical aberration of the first and second lens is set by giving the first lens a magnification β

smaller than 0.2 and the second lens a magnification larger than 0.2.

10. The method according to claim 8, wherein the first and second lens are manufactured using injection moulding.