Optical: systems and elements – Lens – Including a nonspherical surface
Reexamination Certificate
2002-11-12
2004-03-23
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
Including a nonspherical surface
C359S743000, C369S112010, C369S122000
Reexamination Certificate
active
06710939
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an objective lens used for an optical pick-up device and an optical pick-up device, and in particular, to an objective lens for performing recording/reproduction for optical information recording media which are different in recording density, and an optical pick-up device.
At present, there exist many kinds of optical information recording media, and the standards of these optical information recording media are established as shown in Table 1. Incidentally, hereafter (including lens data in the table), the power value of ten (for example, 2.5×10
−3
) is expressed by E (for example, 2.5×E−3).
TABLE 1
Necessary numerical
Thickness of
aperture NA
transparent base
(wave-length of
Optical disk
board (mm)
light source &lgr; nm)
CD, CD-R
1.20
0.45 (&lgr; = 780 nm)
(reproduction)
CD-R (recording,
1.20
0.50 (&lgr; = 780 nm)
reproduction)
DVD
0.60
0.60 (&lgr; = 635 nm)
Here, as the optical information recording media which are different in the recording density and required to have an interchangeability each other, there are CD and DVD. As shown in TABLE 1, these optical information recording media are different in the thickness of the transparent base board. In order to secure the interchangeability, it is necessary to correct, by any means, a spherical aberration generated by the difference of the thickness of the transparent base boards. Further, since DVD and CD are different each other in the required numerical aperture, some measures are necessary.
As the example which secures the interchangeability between DVD and CD by the objective lens, the objective lens having therein a diffractive structure is developed. As the above-mentioned objective lens, for example, there is the one in which the different diffractive structures are provided at the inside and outside of the specified distance h from the optical axis on one of the surfaces of the optical lens, and the spherical aberration is corrected for the thickness of each of the transparent base boards in an inside area, while the spherical aberration is corrected only for DVD in an outside area, and the spherical aberration is not corrected for CD, but is flared. By constructing the objective lens in the manner mentioned above, it is possible to form appropriately a light converging spot that is required for recording or reproducing of information on each optical information recording medium.
Here, concerning the flare on the outside area when CD is used, the case of an over flare and the case of an under flare are conceivable. In the case of under flare, the design makes a diffractive efficiency to be strong, causing a tendency that diffractive pitch is narrow. Accordingly, it is preferable in the design that the over flare is adopted from the view point of the diffractive efficiency.
In the optical pick-up device, an optical detecting device is generally used for judging whether the recording or reproduction of information is performed certainly or not. The optical detecting device detects the information recording light that is reflected on the surface of the optical information recording medium, and based on the result of the detection, the optical detecting device judges whether an error is caused or not. Here, the normal optical detecting device is composed of a main light receiving section, and sub light receiving sections provided on both sides of the main light receiving section, and mainly the main light receiving section reads the information recording light, while the sub light receiving section detects a tracking error.
As mentioned above, in the case that an optical surface of the objective lens is divided into two areas and the spherical aberration is corrected for the thickness of each of the transparent base boards in the inside area, while the spherical aberration is corrected only for DVD in the outside area, and that the spherical aberration is not corrected but flared for CD, a boundary of the flare light does not cover the main light receiving section and a pair of the sub light receiving sections of the optical detecting device. Accordingly, it can be said that any special problem might not happen, as far as the optical information recording media and optical detecting device are manufactured on the basis of design values.
However, in the optical information recording media, from the problem of a parts-incorporating error, when there happens the so-called disk tilt meaning that an axial line of CD is tilted to the axial line of the light converging optical system, or the so-called lens shift meaning that both of the axial lines are shifted, there is the danger that there happens a phenomenon that the boundary of the flared light is changed or the form of the flared light is distorted. The optical detecting device has essentially a function by which the tracking error is watched on the basis of the difference of the amounts of light received by the paired sub light receiving sections. However, when the above-mentioned phenomenon happens, there is the danger that an error signal is outputted, even if the tracking error does not occur.
The present invention has been achieved in view of the above-mentioned problems, and the object of the present invention is to provide an objective lens for an optical pick-up device and an optical pick-up device which can perform the recording or reproduction of information adequately for the different optical information recording media, though the construction is simple.
SUMMARY OF THE INVENTION
The objective lens for the optical pick-up device mentioned in Structure (1) is one, having
a first light source having the wavelength of &lgr;
1
and performing the recording or reproduction of information by radiating the light flux on a first optical information recording medium having the thickness of a transparent base board of t
1
,
a second light source having the wavelength of &lgr;
2
(&lgr;
1
<&lgr;
2
) and performing the recording or reproduction of information by radiating the light flux on a second optical information recording medium having the thickness of the transparent base board of t
2
(t
1
<t
2
),
a light converging optical system including an objective lens which converges the light flux irradiated from the above-mentioned first and second light sources on information recording surfaces through transparent base boards of the first and second optical information recording media, and
an optical detecting device,
wherein there are arranged three or more optical function areas in the direction to cross the optical axis,
diffractive structures are formed on an inner optical function area located at the side near the optical axis and an outer optical function area located at the side farther from the optical axis respectively,
the light flux passing through the inner optical function area is corrected in terms of spherical aberration caused, when conducting the recording or reproduction for the first and second optical information recording medium,
the light flux passing through the outer optical function area is corrected in terms of the spherical aberration caused, when conducting the recording or reproduction for the first optical information recording medium, and further, is flared, when conducting the recording or reproduction for the second optical information recording medium,
the spherical aberration of the light flux having passed through an intermediate optical function area located between the inner optical function area and the outer optical function area is discontinuous to the spherical aberration of the light flux having passed through the outer optical function area, when conducting the recording or reproduction for the second optical information recording medium,
further, the absolute value of the amount of-the spherical aberration of the light flux having passed through the intermediate optical function area and arriving at the second optical information recording medium, when conducting the recording or reproduction for the second optical
Cohen & Pontani, Lieberman & Pavane
Mack Ricky
LandOfFree
Objective lens for optical pick-up device and optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Objective lens for optical pick-up device and optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Objective lens for optical pick-up device and optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3223086