Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2001-08-28
2002-11-05
Hindi, Nabil (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112010, C369S112090
Reexamination Certificate
active
06477130
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pick-up apparatus with two light sources. More specifically, the present invention relates to an optical pickup apparatus capable of utilizing two respective light sources, each having a different wavelength, for reading two respective types of optical discs, and wherein, no photo detector adjustment is required in order to read each type of disk.
2. Description of the Related Art
FIG. 5
shows the general structure of a conventional optical pick-up apparatus. A light ray radiating from a laser diode
11
is collimated by a collimator lens
12
and its beam form is shaped by a beam shaping prism
13
. It passes through a beam splitter
14
and is deflected 90 degrees by a deflective prism
15
. It is then focused by an objective lens
16
and radiated on an optical disc
17
as a minute optical spot. Recording, reproducing and erasing information on the optical disc
17
are carried out by this optical spot.
A light ray reflected off of the optical disc
17
is collimated by the objective lens
16
again, and its path is deflected 90 degrees by the deflective prism
15
. It is reflected by the beam splitter
14
and is focused by a focusing lens
18
. Cylindrical lens
19
provides astigmatism and the light ray is received on photo detector
20
. It is photo detector
20
that detects the information signal and the servo signal as used within the optical pick-up apparatus.
Recent attempts to increase optical disc capacity have led to the practice of shortening the wavelength of the light source used to read these higher capacity discs. In general, the illuminated spot radial on an optical disc is proportional to the wavelength &lgr; of the light source used to read the disc, and the capacity of the optical disc is inversely proportional to the square of the wavelength &lgr;. Notwithstanding the trend toward using shorter wavelengths, there do exist optical disc drives that depend on the longer wavelengths. For example, the disc drive might depend on a reflective rate of the optical disc and also on the recording power. In such instances, it is impossible to reproduce and record information on a conventional disc by using a light source with a shortened wavelength.
Accordingly, for the purpose of establishing compatibility between conventional discs and optical discs has larger capacities, an optical disc drive might have two different kinds of light sources. One light source has a short wavelength (e.g., 650 nm), the other light source has a conventional wavelength (e.g., 785 nm). The simplest way to realize such a combined disc drive is to employ two separate pick-up apparatuses, each of which employs a light source having a different wavelength. However, in this case, such a drive would become too large and too expensive to be practical.
On the other hand, both the size and cost of such a combined arrangement could be reduced if two separate light sources, each having a different wavelength, could be processed using one common optical arrangement.
FIG. 6
shows such a conventional optical pick-up apparatus. The optical parts depicted in
FIG. 6
are common to those optical parts depicted within the optical pick-up device of
FIG. 5
, the only difference being the light source
21
. For example, a first light source comprising a laser diode (LD) chip having a wavelength of 650 nm and a second light source comprising a laserdiode (LD) chip having a wavelength of 785 nm are separated by a very small distance which ranges from scores to hundreds of nanometers (nm). One light source, in the light source portion
21
, is located on the optical axis of the collimator lens
12
, a ray from this light source travels as a solid line of FIG.
6
. The other light source, in the light source portion
21
, is located such that it is slightly departed from the optical axis of the collimator lens
12
, a ray from this light source travels as a dotted line of FIG.
6
. These two light sources are used selectively.
For example, an optical information recording and reproducing apparatus, as disclosed in Japanese unexamined patent (KOKAI) No. 06-259804, comprises a first light source, a second light source, an optical beam composing means for composing rays from respective light sources on the same optical path, an optical arrangement which makes a beam from the first light source focused on the first optical disc and makes a beam from the second light source focused on the second optical disc, and photo detectors for receiving reflective rays from both the first optical disc and the second optical disc.
In the
FIG. 6
optical pick-up apparatus, one light source, in the light source portion
21
, is located on the optical axis of the collimator lens
12
, the other light source in the light source portion
21
, is located such that it is slightly departed from the optical axis of the collimator lens
12
. A light ray radiating from the collimator lens
12
, which is departed from its optical axis, is incident to the inclining of that light ray from the objective lens. Furthermore, since aberration occurs and it is difficult to form a good optical illuminated spot on the optical disc
17
, and also, since two rays having different wavelengths reflected on the optical disc are incident to the converging lens
18
with different angles, the incident respective positions of the reflected light rays on the photo detector
20
are different. Therefore, when adjustments are made to the photo detector
20
for a light ray having one wavelength, a servo signal detected by the photo detector for a ray having a different wavelength necessarily has an offset component.
Thus, there exists a need for an apparatus and method which allows for the use of a single optical arrangement for utilizing light rays of differing wavelengths to read optical discs of different respective capacities, and wherein optical signals received by the photo detector as reflected from the respective optical discs do not contain an offset component.
SUMMARY OF THE INVENTION
The present invention overcomes the problems associated with the prior art and provides a method and apparatus for utilizing light rays of differing wavelengths to read optical discs of different respective capacities. The present invention serves to prevent aberration of the minute optical spot used to read the respective optical discs and also serves to eliminate an offset component with respect to the signals received by the photo detector, as reflected from the respective optical discs.
REFERENCES:
patent: 6084845 (2000-07-01), Mizuno
patent: 6256272 (2001-07-01), Yoon
patent: 06259804 (1994-06-01), None
Dickstein , Shapiro, Morin & Oshinsky, LLP
Ricoh & Company, Ltd.
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