Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-07-12
2001-04-17
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S245000, C349S025000, C349S028000, C349S113000
Reexamination Certificate
active
06219170
ABSTRACT:
BACKGROUND OF THE INVENTIONE
1. Field of the Invention
The present invention relates to a light modulation device, and more particularly to a light modulation device which is capable of modulating light in the infrared wavelength region to the visible ray region and performing exposure and display using light in the foregoing region.
2. Description of the Related Art
Hitherto, devices for modulating light, exposing a photosensitive material to light or performing display by using the modulate include an electro-optical crystal, such as LN (lithium niobate: LiNbO3), KDP (potassium phosphate: KH2PO4) or ADP (ammonium phosphate: NH4H2PO4), using the Pockels effect or electro-optical crystal, such as PLZT, mainly using the Kerr effect.
The foregoing liquid crystal devices, which can be operated at low voltage, however, suffer from unsatisfactorily low response speed and excessive dependency on the environment including temperature. TN (Twist Nematic) type liquid crystal and birefringent liquid crystal, which are main types of the liquid crystal, must be used with a polarizing plate. Thus, there arises a problem of light absorption owning to the polarizing plate.
As a new light modulation device, which is capable of overcoming the foregoing problems, a technique has been disclosed in Japanese Patent Laid-Open No. 9-179082. As shown in
FIG. 16
, dielectric substances
113
, such as PZT or PLZT, are, in a space between glass substrates
111
and
112
, held between transparent electrodes
114
and
15
. Then, voltage is applied so that light modulation is performed. The principle which is used to perform the light modulation is as follows: when the space between the two transparent electrodes is not applied with voltage, penetration of light is permitted. When voltage is applied to the space, electrons are charged in the cathode side of the transparent electrode. Thus, the density of electrons is raised so that light is reflected by the transparent electrode adjacent to the cathode. The foregoing method enables light modulation to be performed without the polarizing plate.
In the foregoing light modulation process, the density of electrons required to perform the light modulation is raised as the wavelength of light is shortened. Therefore, enlargement of the number of electrons, which must be charged, is required to induce raising of the density of electrons in the light modulation device. To operate the device, the electrostatic capacity between the electrodes must be enlarged. Therefore, the foregoing dielectric substance must be a material, for example, PZT or PLZT which is a ceramic-type high dielectric-constant substance, having a significantly high dielectric constant. The foregoing materials having the high dielectric constant, however, cannot easily be formed into a thin film having a stable dielectric constant. Therefore, there arises a problem in that the density of electrons around the transparent electrode cannot stably be controlled.
In recent years, light modulation devices using the field-optical effect of the semiconductor or control of the density of carriers in a p-n junction structure have been developed. All of the developed devices are arranged to perform light modulation in the vicinity of the wavelength near an end of light absorption by using band gap energy. There has not been developed a device of a type for performing the light modulation in the visible ray region or changing the reflectance of light in the foregoing region.
An electric optical crystal is able to perform a high-speed response and is free from excessive dependency on the environment. However, an electric optical crystal of a type using the Pockels effect requires very high operating voltage. An electric optical crystal of a type using the Kerr effect can be operated at relatively low voltage which is excessively higher than that required for the liquid crystal device. What is worse, the electric optical crystal cannot be used to form a precise array structure. Since the electric optical crystal requires a polarizing plate, there arises a problem of absorption of light due to the provided polarizing plate.
SUMMARY OF THE INVENTION
To overcome the foregoing problems experienced with the conventional light modulation devices, an object of the present invention is to provide a light modulation device, an exposing device and a display unit each having a simple structure, capable of quickly and stably operating even at low voltage and corresponding to visible rays to infrared rays.
To achieve the foregoing object, a light modulation device of one of the embodiments in the present invention comprises: a semiconductor layer formed on the upper surface of a lower transparent electrode; and an upper transparent electrode formed on the upper surface of the semiconductor layer through an insulating layer, wherein an electric field for depleting carriers of the semiconductor layer is applied to a space between the upper transparent electrode and the lower transparent electrode so as to change at least either of reflectance of light or adsorptance of light
Further, a light modulation device of one of other embodiments in the present invention comprises: a first semiconductor layer made of an n-type semiconductor material or a p-type semiconductor material and formed on the upper surface of a lower transparent electrode; a second semiconductor layer formed on the upper surface of the first semiconductor layer and made of the p-type semiconductor material when the first semiconductor layer is made of the n-type semiconductor and made of the n-type semiconductor material when the first semiconductor layer is made of the p-type material; and an upper transparent electrode formed on the upper surface of the second semiconductor layer, wherein an electric field for depleting carriers of the semiconductor layers is applied to a space between the upper transparent electrode and the lower transparent electrode so as to change at least either of reflectance of light or adsorptance of light.
The light modulation device such as disclosed in the embodiments of this invention is arranged to be applied with an electric field, which depletes carriers of the semiconductor layer, to the space between the upper transparent electrode and the lower transparent electrode to change at least either of adsorptance of light or reflectance of light. Therefore, when the electric field is applied, the light modulation device permits penetration of incident light. When the electric field is not applied, the light modulation device absorbs or reflects incident light, that is, inhibits penetration. The above-mentioned light modulation device has the foregoing light modulation characteristic.
REFERENCES:
patent: 5384649 (1995-01-01), Takimoto et al.
patent: 5583676 (1996-12-01), Akiyama et al.
Ichihashi Mitsuyoshi
Kimura Koichi
Epps Georgia
Fuji Photo Film Co. , Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Thompson Timothy
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