Optical waveguides – Planar optical waveguide – Thin film optical waveguide
Reexamination Certificate
1999-08-27
2001-11-27
Ullah, Akm E. (Department: 2874)
Optical waveguides
Planar optical waveguide
Thin film optical waveguide
C385S014000, C385S037000, C385S129000
Reexamination Certificate
active
06324329
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P10-242403 filed Aug. 28, 1998 which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photocatalyst excitation apparatuses.
2. Description of the Related Art
Conventional photocatalyst materials showing catalytic functions by irradiation of light include titanium dioxide, tungsten oxide, vanadium oxide, zirconium oxide, zinc oxide, zinc sulfide, and tin oxide. Recently, titanium dioxide (TiO
2
) has attracted attention due to high oxidative decomposition ability, antifouling properties, and hydrophobicity thereof.
Photocatalyst excitation apparatuses using such photocatalysts have various structures depending on the use. In general, as shown in
FIG. 6
, a TiO
2
photocatalyst layer
82
is formed on a substrate
80
composed of a tile, glass or plastic and is irradiated with excitation light
84
for the photocatalyst, such as ultraviolet light, from the upper side.
When the TiO
2
photocatalyst layer
82
is irradiated with the excitation light
84
, electrons are excited by the photoelectric effect so that electrons and holes are generated and migrate to the surface of the TiO
2
photocatalyst layer
82
. Electrons reduce oxygen in air to form superoxide ions (O
2
−
), whereas holes degrade water adsorbed on the surface to form hydroxyl radicals (.OH). The superoxide ions and hydroxyl radicals are called activated oxygen species and show strong oxidizing effects.
When organic contaminants adhere to the TiO
2
photocatalyst layer
82
, superoxide ions deprive the organic compound of carbon whereas hydroxyl radicals deprive the organic compound of hydrogen to decompose the organic compound. The decomposed carbon and hydrogen are oxidized to form carbon dioxide and water. Oxidative decomposition of and antifouling properties to organic substances are thereby shown.
In the above conventional photocatalyst excitation apparatus, solar light containing ultraviolet light or ultraviolet light emitted from an artificial light source is used as the excitation light
84
which is incident on the photocatalyst layer
82
.
Since a light source separately placed at the exterior of the photocatalyst excitation apparatus is used in such a case, the excitation light
84
may be absorbed or scattered in media such as air and moisture which are present between the light source and the TiO
2
photocatalyst layer
82
. Thus, the excitation light
84
for the photocatalyst may be attenuated when it reaches the TiO
2
photocatalyst layer
82
. Accordingly, the optical power from the light source is not effectively used.
When solar light is used as the excitation light
84
, the luminous power of the solar light significantly depends on the weather out of doors, and the solar light is shaded or diminished indoors. Thus, the TiO
2
photocatalyst layer
82
does not stably work as the photocatalyst.
When a nondirectional light source such as a fluorescent lamp is used as the light source of the excitation light
84
, some part of the light is scattered and is not incident on the TiO
2
photocatalyst layer
82
. Thus, the optical power of the light source is not effectively used. When a highly directional light source such as a semiconductor laser or a light emitting diode (LED) is used, mismatch of the irradiating zone of the light source and the position of the TiO
2
photocatalyst layer
82
causes dissipation of the light from the light source to regions other than the TiO
2
photocatalyst layer
82
. Thus, the optical power of the light source also cannot be effectively used.
When an ultraviolet light source is used as the light source for the excitation light, which is radiated towards regions other than the TiO
2
photocatalyst layer
82
, may reach the eyes and skin. Thus, the effects on human bodies, particularly the possibility of melanoma carcinogenesis concerns. When the photocatalyst excitation apparatus is used in products, in which people view for a long time, such as a Braun-tube screen of a television set and a windshield of an automobile, the above hazards will be severe problems.
When an artificial light source is used as the light source for the excitation light, a space is required for independently placing the light source. Thus, the possibility of the use of the photocatalyst excitation apparatus is limited and the esthetics thereof may be deteriorated.
In general, the activity of the catalyst increases as the thickness of the TiO
2
photocatalyst layer
82
increases. When light with a wavelength which has large absorption in the TiO
2
photocatalyst layer
82
is used as the excitation light
84
, the light is absorbed in a shallow region near the surface of the TiO
2
photocatalyst layer
82
, and thus uniform excitation is not achieved in the deep region. When light with a wavelength which has small absorption in the TiO
2
photocatalyst layer
82
is used as the excitation light
84
, the TiO
2
photocatalyst layer
82
is uniformly excited from the surface to the deep region, but the excitation efficiency is not high due to low light absorption. Accordingly, even if the thickness of the TiO
2
photocatalyst layer
82
is sufficiently increased to enhance the activity, the increased thickness is not effectively used in any case.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a photocatalyst excitation apparatus which can effectively use the optical power of a light source, shows stable photocatalytic effects having high efficiency, does not require an independent space for the placement causing restriction of use, and can prevent adverse effects of ultraviolet light on human bodies.
A first aspect of the present invention is a photocatalyst excitation apparatus including a substrate, a light guide layer formed on the substrate, a light source for emitting excitation light for a photocatalyst towards the light guide layer, and a photocatalyst layer formed on the light guide layer, the excitation light emitted from the light source passing through the light guide layer and the leakage light from the light guide layer activating the photocatalyst layer, wherein the light source comes into close contact with the end face of the light guide layer.
In the first aspect, the light guide layer is formed on the substrate, and the photocatalyst layer is formed on the light guide layer. When the substrate used transmits the excitation light and has a smooth surface compared to the wavelength of the excitation light for the photocatalyst, the layered configuration of the substrate, the light guide layer, the photocatalyst layer, and an air layer in contact with the photocatalyst layer can be considered to be a multimodal four-layer step-type slab light guide. Thus, the excitation light incident on the light guide layer passes through the light guide layer and leaks from the light guide layer to illuminate the entire rear face of the photocatalyst layer. Since the illuminating light travels through a long distance in the photocatalyst layer, the overall photocatalyst layer is activated with high efficiency.
Since the light source comes into close contact with the end face of the light guide layer, the excitation light emitted from the light source is effectively incident on the light guide layer. Since there is no medium such as air or moisture between the light source and the photocatalyst layer, there is no loss of the luminous power due to light absorption and scattering in the medium. Thus, the apparatus can significantly effectively use the optical power of the light source. When a material absorbing less of the excitation light is used for the light guide layer, the loss of the luminous power due to light absorption in the light guide layer is reduced.
Since external environments do not affect this apparatus, unlike the use of solar light as the excitation light, the photocatalyst layer shows stable photocatalytic effects.
When ultraviole
Connelly-Cushwa Michelle R.
Sonnenschein Nath & Rosenthal
Sony Corporation
Ullah Akm E.
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