Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
2001-01-11
2003-06-10
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave directional modulation
Reexamination Certificate
active
06577434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable focal position spatial modulation device. More specifically, the present invention relates to the variable focal position spatial modulation device which is appropriately employed for, for example, a liquid crystal lens.
2. Description of the Related Arts
There have conventionally been a plastic mold Fresnel plate, a photographic dry plate type diffraction grating, a glass plate marking-off type diffraction grating, a photographic dry plate type hologram and a photoresist type hologram, in each of which the transmission or reflection optical path is fixed in the manufacturing stage.
As a technique for deflecting the transmission or reflection optical path, there are, for example, the following techniques.
Japanese Non-examined Patent Publication No. HEI 10-62609 proposes a microlens capable of adjusting the focal position. This changes the focal position of one lens and is effective only in the case of a small-diameter pupil lens. If the microlens is simply increased in dimension, then the necessary spherical surface (aspherical surface) cannot be obtained. Therefore, it is presumable that the practicality is difficult.
U.S. Pat. No. 5,839,001 discloses a technique for providing a deflection means for deflecting an incident optical path with a power. However, the lens power is not changed, and the pupil of the imaging lens cannot be effectively used.
A technique capable of forming a microlens array and changing the focal position is disclosed in O plus E, Vol. 20, No. 10, p.1118-1124, October 1998, “Liquid Crystal Microlens”. However, only a lens having a diameter of several tens to several hundreds of micrometers can be formed.
Japanese Patent No. 2628630 (Japanese Non-examined Patent Publication No. SHO 62-170933) discloses a system in which electrodes are arranged in a concentric shape and varied voltages are successively applied to the ring-shaped electrodes. However, this system is a method for controlling the alignment and the refractive power between electrodes with liquid crystals held between them, and no description is provided for the alignment displacement and refractive power displacement between the ring-shaped electrodes. The alignment therebetween is tilted and the refractive power is varied by the influence of the electrodes between the ring-shaped electrodes. This portion generates an unnecessary refractive power and becomes a factor for generating flare.
Japanese Non-examined Patent Publication No. HEI 9-304748 discloses a technique with a multi-ring-shaped structure for producing a lens effect by reducing the electrode width in the radial direction from the center to the periphery. The technique is designed so as to have a variation in the refractive power between an electrode and an electrode. However, the alignment is tilted and the refractive power is varied by the influence of the electrodes in a portion between the multi-ring-shaped electrodes, and this portion generates an unnecessary refractive power and generates flare. The upper and lower electrodes are asymmetrically arranged and only one electrode voltage is provided. However, this is not intended to solve the problem of flare.
Conventionally, as a “bifocal lens system” capable of varying the focal position with a small device, the use of liquid crystals has been proposed. This produces a lens effect by forming electrodes on two substrates and varying the refractive index of the liquid crystals between the electrodes with interposition of the liquid crystals by arranging the electrodes in a multi-ring-like shape. This system utilizes the phenomena that no lens effect is produced as a result of the alignment of the liquid crystals parallel to the substrate when no electric field is applied and that the refractive power is varied as a result of the change of the alignment angle of the liquid crystals when an electric field is applied.
Although the method of controlling the alignment and the refractive power between the electrodes with interposition of the liquid crystals have been described, the behavior of the alignment displacement and the refractive power displacement generated between the ring-shaped electrodes has not been described. In practice, the alignment is tilted and the refractive index is varied by the influence of the electrodes between the ring-shaped electrodes, and this portion generates an unnecessary refractive power and becomes a factor for generating flare.
The generation of the flare causes the erroneous detection of sensing in focus detection and so on, and the flare causes degradation in image quality when used in an imaging system. This means that the lens does not produce a good performance.
The space between the electrodes with interposition of the liquid crystals has a constant refractive index, and the total refractive index of the device becomes a quantized refractive index of each ring. Due to these two factors, the lens does not realize a good performance.
FIGS. 1A through 1D
show a conventional liquid crystal lens.
As shown in the schematic sectional view of
FIG. 1A
, a liquid crystal lens
500
is obtained by sealing liquid crystals
530
with substrates
510
and
520
that are arranged parallel and seal members
538
and
539
. Electrodes
511
,
512
,
521
and
522
and alignment films
518
and
528
are arranged on mutually opposite surfaces of the substrates
510
and
520
. The electrodes
511
and
512
and the electrodes
521
and
522
are formed in a ring shape concentric to an optical axis O and arranged opposite to each other. Then, in an electrode opposition region P between the opposite electrodes, the alignment of the liquid crystals
530
is varied by an electric field with an applied voltage, allowing the refractive index to be controlled to a specified refractive index. However, it has been considered that the alignment of the liquid crystals
530
is not varied and no refractive power is present in the adjacent electrode non-opposition region N where no electrodes face each other.
For the above reasons, the region N and the region P have different refractive indexes, and the refractive index of the liquid crystal lens
500
has an intermittent quasi-rectangular distribution as shown plainly in FIG.
1
B. In other words, as shown in
FIG. 1C
, the liquid crystal lens
500
corresponds to a Fresnel lens that has a plurality of linear lens surface elements
540
. Then, as shown in
FIG. 1D
, a luminous flux
552
that has passed through the electrode opposition region P forms an image at a focal point
550
, whereas a luminous flux
554
that has passed through the electrode non-opposition region N forms no image at the focal point
550
, leading to a degraded image forming characteristics.
In practice, refraction occurs even if the alignment of the liquid crystals
530
is not varied (even with a horizontal alignment) since the refractive index is different from that of air. Furthermore, due to the electric fields generated between the electrodes, the alignment not only varies in the electrode opposition region P, but exerts some influence on an expanded region. In particular, due to the latter, the refractive index gradually increases in the electrode non-opposition region N with an increasing distance from the electrode opposition region P, consequently producing a power.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a variable focal position spatial modulation device which realizes a satisfactory image forming performance.
In order to achieve the above object, according to one aspect of the present invention, there is provided a variable focal position spatial modulation device, comprising: a variable refractive index material that is arranged inside a luminous flux and that is able to deflect an incident light; a plurality of electrode pairs arranged at intervals in one of a concentric shape, a concentric oval shape and an unequally magnified concentric oval shape, in which a pair of electrodes of e
Epps Georgia
Hanig Richard
McDermott & Will & Emery
Minolta Co. , Ltd.
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