Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-06-21
2001-02-20
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C349S200000, C349S077000
Reexamination Certificate
active
06191881
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a variable focal length lens panel and fabricating the same wherein the variable focal length lens panel can be used as a lens, for example, for an optical pickup used both in a compact disc (CD) and a digital video disc (DVD) in an optical disc drive.
2. Description of the Related Art
There has been conventionally developed a liquid crystal lens capable of varying a focal length by an applied voltage, which is, for example, disclosed in Japanese Patent Laid-Open Publication No. H4-240817.
As shown in
FIG. 9
, a variable focal length lens disclosed in this publication has such structure that 320×220 pixels are arranged in a lattice shape by transparent electrodes in a display area
41
which is recorded as a phase type Fresnel zone plate
42
of a liquid crystal space optical modulator
40
, and ECB (electrically controlled birefringence) mode liquid crystal is sealed in the display area
41
.
The liquid crystal space optional modulator
40
has a light wave modulation characteristic such that when a voltage is applied to the transparent electrodes, laser beams undergo continuous phase modulation in the range of 0 to 2&pgr;. At the time of such phase variation, by applying a voltage signal V
s
that effects every pixel with a phase modulation corresponding to the spatial coordinates thereof, laser beams
43
which incident on the liquid crystal spatial optional modulator
40
undergo a phase modulation by respective pixels, and concentrated on a focal point Fa on the optical axis as shown in FIG.
10
. Further, if a different voltage signal V
s
is applied, the light-concentrating position of the laser beams
43
can be moved to a point Fb on the optical axis.
However, the publication set forth above merely discloses a theoretical construction, it does not disclose concrete shapes and constructions of the respective transparent electrodes serving as the variable focal length lens and does not disclose the explanation of materials in the embodiment, hence it is not practicable.
A liquid crystal lens is also disclosed in Japanese patent Laid-Open Publication No. H3-2840. Briefly explaining this liquid crystal lens, it comprises a liquid crystal, a control electrode for applying a voltage to the liquid crystal, and a fixed electrode, wherein the control electrode is composed of circular or concentric ring-shaped transparent electrode bands
47
and insulating bands
46
for insulating between the transparent electrode bands
47
, as shown in FIG.
11
. Respective transparent electrode bands
47
are independently wired.
Polarizers may be disposed at both sides of the liquid crystal panel. If polarizers are not disposed, when a voltage is applied to the transparent electrode bands
47
, the liquid crystal panel turns the direction of polarization of incident light 90° while the incident light passes thereby in the areas where the transparent electrode bands exist, and permits incident light to pass through as it is in the other areas.
Accordingly, light beams which emerge out from the liquid crystal lens can form images independently without interfering with one another on the same point, wherein the focal length thereof is varied by a voltage applied to the transparent electrode bands
47
.
However, practicable concrete shapes and materials are not disclosed, and a method of fabricating the liquid crystal lens is indistinct, and hence the liquid crystal lens shown in this publication has not been put into operation.
As mentioned above, the conventionally proposed variable focal length lenses are theoretical or principled and do not specify practicable concrete shapes and constructions, and methods of fabricating the same are not disclosed, so that they have not been put to practical use.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to solve the problems described above and to provide a variable focal length lens panel which is practicable for a lens used in an optical pickup of an optical disc drive, and a method of fabricating the variable focal length lens panel at low cost.
To achieve the above objects, the variable focal length lens panel according to the invention is structured as follows.
The variable focal length lens panel comprises a transparent first substrate and a transparent second substrate, a circular transparent electrode provided on the first substrate at the center thereof, a plurality of annular transparent electrodes which are disposed outside the circular transparent electrode concentrically and narrowed in width and interval as they are directed outward, extension electrodes which extend crosswise outward from the circular transparent electrode across the plurality of annular transparent electrodes, an external terminal electrode disposed at a portion close to a periphery of the first substrate so as to connect respective outer ends of the extension electrodes with one another, and a first alignment layer provided at least on an area where the circular transparent electrode and the annular transparent electrodes are formed.
Further, a transparent electrode is provided on an entire surface of the second substrate, and a second alignment layer is provided on the transparent electrode, wherein an alignment direction of the first alignment layer and that of the second alignment layer are parallel with each other.
The first substrate and the second substrate are kept at a given interval with the transparent electrodes thereon facing each other by a plurality of gap members provided on an area outside an outermost electrode of the annular transparent, and the substrates are bonded to each other by a seal member provided on the external terminal electrode, and a nematic liquid crystal is sealed in a gap between the first substrate and the second substrate.
With such a construction, it is possible to vary the focal length with high performance.
Further, with such a construction the gap members are not dispersed in the concentric annular transparent electrodes, the inferior alignment caused by the passing of the diffracted light through the periphery of the gap members is reduced, thereby varying the focal length with high performance.
Further, it is preferable to provide a seal member having an aperture at a part thereof annularly between the first and second substrates so as to surround the outer periphery of an outermost electrode of the annular transparent electrodes.
It is preferable to set a pretilt angle formed on the surfaces of the first and second alignment layers is in the range of 1.0° to 2.5°.
Further, the nematic liquid crystal sealed in the gap between the first substrate and the second substrate is not doped with a chiral material.
Still further, if there is established a relation of &Dgr;nd=(&lgr;/2)+n&lgr; (n is 0 or a positive integer) between a value &Dgr;nd which is a product of a cell gap d formed between the first substrate and the second substrate and a birefringence &Dgr;n of the nematic liquid crystal sealed between the first substrate and the second substrate and a wavelength &lgr; of laser beams to be used, light can be efficiently utilized.
The method of fabricating a variable focal length lens panel according to the invention has following steps.
(1) a step of providing a circular transparent electrode on a transparent first substrate at the center thereof, a plurality of annular transparent electrodes which are disposed outside the circular transparent electrode concentrically and narrowed in width and interval as they are directed outward, extension electrodes which extend crosswise outward from the circular transparent electrode across the plurality of annular transparent electrodes, and an external terminal electrode disposed at a portion close to the periphery of the first substrate so as to connect respective outer ends of the extension electrodes with one another;
(2) a step of providing a first alignment layer at least on an area of the first substrate where the circular transparent electrode and the annular t
Armstrong, Westerman Hattori, McLeland & Naughton
Citizen Watch Co. Ltd.
Sugarman Scott J.
Thompson Tim
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