Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1998-04-07
2002-05-14
Psitos, Aristotelis M. (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044320, C369S112020
Reexamination Certificate
active
06388967
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal driving signal generating apparatus for driving liquid crystal and an optical disk reproducing apparatus having the liquid crystal driving signal generating apparatus.
2. Description of the Related Art
In recent years, a digital video disk (DVD) has been proposed as an information recording (reproducing) medium with a large capacity exceeding a compact disk (hereinafter referred to as “CD”).
The DVD, which is an optical disk with the same diameter as that of the CD, that is, 12 cm, employs the wavelength of a laser light source of 650 nm which is shorter than that of 780 nm employed in the CD and further employs an objective lens with the numerical aperture of 0.6 which is larger than that of 0.45 employed in the CD.
Further, the DVD employs MPEG2 as the data compression algorithm.
Since the DVD has been improved in this manner as compared with the CD, it is possible to store digital data of about 5 giga byte on one side of a disk.
However, it has been said that a reproducing apparatus for reproducing a DVD, which is a high density medium much more than the CD, requires a control means for controlling the inclination, that is, the tilt angle of the disk surface relative to the optical axis of an optical pickup.
The applicant of the present application has already proposed in Japanese Patent Unexamined Application No. Hei 9-128785 that the aberration of the wave surface caused by the inclination of the disk surface and the variation of the disk thickness is corrected by using a liquid crystal panel.
To be more concrete, this proposal is characterized in that a liquid crystal panel for the aberration correction split into a predetermined configuration is disposed on the optical axis of a laser beam, whereby the aberration of the wave surface caused by the inclination of the disk surface and the variation of the disk thickness is corrected by controlling a refractive index of each of the split portions.
FIG. 8
shows an example of an optical disk reproducing apparatus using such a theory.
In
FIG. 8
, a laser beam radiated from a laser light source
1
is reflected by a half mirror
2
.
The laser beam reflected by the half mirror
2
passes through a liquid crystal panel
3
and applied to an objective lens
4
, which in turn forms a laser beam spot on an optical disk
5
.
The reflection light reflected by the optical disk
5
passes again the objective lens
4
, liquid crystal panel
3
and half mirror
2
, and then converged on a photo receptor
7
by a condenser lens
6
.
A tilt sensor
8
for detecting the inclination of the optical disk
5
is provided in adjacent to a pickup. The tilt sensor
8
is provided with one light emitting portion and two light receiving portions so that light irradiated from the light emitting portion on the optical disk
5
is reflected thereby and received as reflection light by the respective light receiving portions.
An adder
10
detects a difference between the outputs from the respective light receiving portions and supplies the difference as a tilt error signal to an analog-to-digital (A/D) converter
11
.
The tilt error signal is converted into a digital value by the A/D converter
11
and supplied to a central processing unit (CPU)
17
.
Upon occurrence of the tilt error, the CPU
17
outputs to a gain adjuster
13
a control signal for correcting the wave surface aberration caused by the tilt error.
An oscillation circuit
12
outputs a reference signal whose duty ratio is set to be 50(%) like a rectangular wave, for example.
The gain adjuster
13
adjusts an amplification degree of the reference signal supplied from the oscillation circuit
12
under the control of the CPU
17
.
Thus, a driving signal inputted into the liquid crystal panel
3
is a signal with a duty ratio of 50% whose voltage amplitude is adjusted in accordance with the inclination of the disk.
The liquid crystal panel
3
is formed by sealing liquid crystal between two transparent glass substrates.
FIGS. 9A and 9B
are diagrams showing an example of the configuration of the liquid crystal panel
3
.
FIG. 9B
is a cross sectional view of the liquid crystal panel
3
, and
FIG. 9B
is a plan view of the liquid crystal panel
3
.
Transparent electrodes
302
a,
302
b
such as indium tin oxide (ITO) electrodes are deposited on the inner surface of transparent glass substrates
301
a,
301
b.
At least one of the transparent electrodes
302
a
,
302
b
has the electrode configuration split longitudinally and latitudinally into electrode portions as shown in FIG.
9
B. Each of the electrode portions thus split is connected to corresponding one of the gain adjuster
13
so that voltages applied to the electrode portions are controlled under the control of the CPU
17
.
Orientation films
303
a,
303
b
for providing the liquid crystal with predetermined molecule orientation are formed on the inner surfaces of the transparent electrodes
302
a,
302
b.
Liquid crystal
304
is sealed between the orientation films
303
a
,
303
b.
The liquid crystal
304
is liquid crystal having birefringence effect such that a refractive index (n
1
) of the liquid crystal molecule M to the optical axis direction differs from a refractive index (n
2
) thereof to the direction opposite to the optical axis direction. Thus, the liquid crystal may be nematic liquid crystal, for example.
FIGS. 11A
to
11
C are diagrams showing changes in the orientation of liquid crystal when voltage applied to the liquid crystal
304
is changed.
FIG. 11A
shows the orientation of the liquid crystal molecule M when the voltage applied to the liquid crystal is zero, while
FIGS. 11B and 11C
show the orientations of the liquid crystal molecule when alternative voltage is applied to the liquid crystal. In this case, the applied voltages are in a relation of e1<e2.
In this manner, the orientation of the liquid crystal molecule M can be controlled from the horizontal direction to the vertical direction by changing the alternative voltage applied thereto.
In
FIGS. 11A
to
11
C, the respective portions of the liquid crystal
304
corresponding to all the split electrode portions are oriented to the same direction since the same control voltage is applied to the respective split electrode portions. However, it is possible to set suitable refractive indexes (n
1
-n
2
) for the respective portions of the liquid crystal
304
corresponding to the respective electrode portions by separately controlling the voltage applied to the respective electrode portions split longitudinally and latitudinally.
When the refractive index of the liquid crystal is changed, it is possible to provide a light beam passing through the liquid crystal with an optical path difference given by the following expression.
optical path difference=&Dgr;
n×d
where &Dgr;n represents a changed value of the refractive index and d represents the thickness of the liquid crystal
304
.
This means that the light beam passing through the liquid crystal is provided with a phase difference given by the following expression.
phase difference=&Dgr;
n×d×
(2&pgr;/&lgr;)
where &lgr; represents a wavelength of the light beam.
Accordingly, it is possible to correct the wave surface aberration caused by the inclination of the disk by controlling the refractive indexes n of the respective portions of the liquid crystal corresponding to the split electrode portions so as to cancel the aberration caused in the objective lens
4
.
In the liquid crystal driving signal generating apparatus for controlling the voltage amplitude of the driving signal, there arises a problem that how the control of the voltage amplitude of the driving signal for driving liquid crystal is realized.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances, and therefore an object of the present invention is to provide a novel liquid crystal driving signal generating apparatus.
Another object of the present invention i
Abe Hiroaki
Furukawa Jun-ichi
Murao Noriaki
Tateishi Kiyoshi
Pioneer Corporation
Psitos Aristotelis M.
Sughrue & Mion, PLLC
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