U.S. patent application number 10/461342 was filed with the patent office on 2003-12-25 for process for preparation of optical element, electrolytic solution used for the same and apparatus for preparation of optical element.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Akutsu, Eiichi, Ohtsu, Shigemi, Shimizu, Keishi, Yatsuda, Kazutoshi.
Application Number | 20030234180 10/461342 |
Document ID | / |
Family ID | 29728232 |
Filed Date | 2003-12-25 |
United States Patent
Application |
20030234180 |
Kind Code |
A1 |
Shimizu, Keishi ; et
al. |
December 25, 2003 |
Process for preparation of optical element, electrolytic solution
used for the same and apparatus for preparation of optical
element
Abstract
Disclosed herein are a process for easily preparing an optical
element in a form of thin film which contains a functional material
whose concentration changes gradationally in an in-plane direction
and a thickness direction of a thin film, an electrolytic solution
used for the process, and an apparatus for preparing an optical
element. The process is designed to form an optical element on an
optical element preparing substrate from an electrolytic solution
containing a functional material by electrodeposition or
photovoltaic electrodeposition. The process includes a step of
changing concentration of the functional material in the
electrolytic solution in the vicinity of the optical element
preparing substrate, so that a resulting thin film changes
gradationally in the concentration of the functional material in
the in-plane direction and/or the thickness direction of the thin
film.
Inventors: |
Shimizu, Keishi;
(Nakai-machi, JP) ; Ohtsu, Shigemi; (Nakai-machi,
JP) ; Yatsuda, Kazutoshi; (Nakai-machi, JP) ;
Akutsu, Eiichi; (Nakai-machi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
29728232 |
Appl. No.: |
10/461342 |
Filed: |
June 16, 2003 |
Current U.S.
Class: |
205/80 ;
204/193 |
Current CPC
Class: |
G02F 1/065 20130101;
C25D 5/08 20130101; G02F 2202/36 20130101; C25D 1/12 20130101; C09D
5/448 20130101; C25D 1/22 20130101; C25D 13/00 20130101; B82Y 20/00
20130101; C09D 5/44 20130101 |
Class at
Publication: |
205/80 ;
204/193 |
International
Class: |
C25D 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 20, 2002 |
JP |
2002-179857 |
Claims
What is claimed is:
1. A process for preparation of an optical element comprising the
steps of: preparing a substrate having an insulating substrate and
a conductive thin film formed thereon; preparing an electrolytic
solution containing a film forming polymer decreasing solubility or
dispersibility in an aqueous liquid by a change in a pH value and a
functional material in a certain concentration; contacting the
conductive thin film with the electrolytic solution in a presence
of a counter electrode in the electrolytic solution and applying a
voltage between the conductive thin film and the counter electrode
for changing the pH value; and varying the concentration of the
functional material near the conductive thin film.
2. The process for preparation of an optical element according to
claim 1, wherein the functional material contained in the thin film
has a concentration gradation in a thickness direction of the
deposited film.
3. The process for preparation of an optical element according to
claim 1, wherein the functional material contained in the thin film
has a concentration gradation in an in-plane direction of the thin
film.
4. The process for preparation of an optical element according to
claim 1, wherein the concentration of the functional material in
the electrolytic solution is varied by a flow of another
electrolytic solution, which has a different concentration with
that of the electrolytic solution, toward the substrate in the
electrolytic solution.
5. The process for preparation of an optical element according to
claim 4, wherein the concentration of the functional material in
the electrolytic solution flown toward the substrate in the
electrolytic solution is varied with time.
6. The process for preparation of an optical element according to
claim 1, further comprising a step of transferring the deposited
film formed on the substrate to another substrate.
7. The process for preparation of an optical element according to
claim 1, further comprising a step of performing heat treatment to
the electrodeposited film.
8. A process for preparation of an optical element comprising the
steps of: preparing a substrate having an insulating substrate, a
conductive thin film and a photosemiconductive film formed thereon;
preparing an electrolytic solution containing a film forming
polymer and a functional material in a certain concentration, the
film forming polymer decreasing in solubility or dispersibility in
an aqueous liquid by a change in a pH value; contacting the
photosemiconductive film with the electrolytic solution and
applying a light to the photosemiconductive film for changing the
pH value; and varying the concentration of the functional material
near the conductive thin film.
9. The process for preparation of an optical element according to
claim 8, wherein the functional material contained in the thin film
has a concentration gradation in a thickness direction of the
deposited film.
10. The process for preparation of an optical element according to
claim 8, wherein the functional material contained in the thin film
has a concentration gradation in an in-plane direction of the thin
film.
11. The process for preparation of an optical element according to
claim 8, wherein the concentration of the functional material in
the electrolytic solution is varied by a flow of another
electrolytic solution, which has a different concentration with
that of the electrolytic solution, toward the substrate in the
electrolytic solution.
12. The process for preparation of an optical element according to
claim 11, wherein the concentration of the functional material in
the electrolytic solution flown toward the substrate in the
electrolytic solution is varied with time.
13. The process for preparation of an optical element according to
claim 8, further comprising a step of forming a thin film over an
entire surface of the substrate by application of a voltage
exceeding a Schottky barrier of the photosemiconductive film on the
optical element preparing substrate without irradiation with
light.
14. The process for preparation of an optical element according to
claim 8, further comprising a step of transferring all the thin
films formed on the substrate to another substrate.
15. The process for preparation of an optical element according to
claim 8, further comprising a step of performing heat treatment to
the deposited film.
16. An electrolytic solution as used to the method of claim 1,
comprising a film-forming polymer, which decreases in solubility or
dispersibility in an aqueous solution as a pH value changes, and a
functional material, the film-forming polymer having both
hydrophobic groups and hydrophilic groups with a number of
hydrophobic groups accounting for 30% to 80% of a total number of
hydrophobic groups and hydrophilic groups.
17. An apparatus for preparing an optical element on a substrate
having conductive thin film comprising: an electrodeposition vessel
holding an aqueous electrolytic solution, which contains a
film-forming polymer and a functional material, the film-forming
polymer decreasing in solubility or dispersibility in an aqueous
liquid as the pH value changes; a counter electrode which is placed
in the electrodeposition vessel and is electrically connected to
the conductive thin film; a unit that irradiates with light the
photosemiconductor thin film on the optical element preparing
substrate, and a mechanism to cause a flow of an aqueous
electrolytic solution, which contains a film-forming polymer and a
functional material, the film-forming polymer decreasing in
solubility or dispersibility in an aqueous liquid as a pH value
changes.
18. The apparatus for preparing an optical element according to
claim 17, further comprising a voltage applying unit that applies
voltage across the conductive thin film and the counter
electrode.
19. An apparatus for preparing an optical element on a substrate
having an electroconductive thin film comprising: an
electrodeposition vessel holding an aqueous electrolytic solution,
which contains a film-forming polymer and a functional material,
the film-forming polymer decreasing in solubility or dispersibility
in an aqueous liquid as a pH value changes; a counter electrode
which is placed in the electrodeposition vessel and is electrically
connected to the conductive thin film; a voltage application unit
that applies a voltage across the conductive thin film and the
counter electrode, and a mechanism to cause a flow of an aqueous
electrolytic solution, which contains a film-forming polymer and a
functional material, the film-forming polymer decreasing in
solubility or dispersibility in an aqueous liquid as a pH value
changes.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for preparing a
polymer thin film to be patterned in the order of micrometers. More
particularly, the present invention relates to a process for
preparing an optical element in the form of thin film which changes
in color and refractive index along its in-plane length or
thickness.
[0003] 2. Description of the Related Art:
[0004] There is known a conventional method for patterning a
polymer thin film in the order of micrometers. This method has
steps of coating a flat substrate with a photocurable resin (as a
raw material for polymer thin film) by spin coating or the like,
exposing the coated film after drying to ultraviolet rays, and
developing the cured film. A similar method is also used for a
polymer thin film formed from a non-photocurable resin. In this
case, the polymer thin film is coated with a photocurable resin in
the same way as mentioned above and the coated film is patterned by
exposure and development.
[0005] These methods work well in preparation of a polymer thin
film containing a functional material, such as fine particles
(e.g., pigment and highly refractive material), molecules (e.g.,
dye), and polymer of a different kind, which is uniformly dispersed
therein. However, with these methods, it is impossible to prepare a
polymer thin film in which the concentration of the functional
material changes stepwise or continuously along its in-plane length
or thickness, because the polymer thin film itself is formed
uniformly by spin coating. It is possible to prepare a thin film in
which the concentration of the functional material changes along
its thickness, if coating is repeated several times with coating
solutions each containing the functional material in different
concentrations. In this case, the variation of concentration is
stepwise and it is difficult to change the concentration
continuously.
[0006] By the way, the present inventors proposed processes for
forming an image with high resolution and for preparing a color
filter from an electrodeposition material containing a coloring
agent by electrodeposition or photovoltaic electrodeposition at a
low voltage. Details of these processes are disclosed in Japanese
Published Unexamined Patent Applications Nos. Hei 10-119414,
11-189899, 11-15418, 11-174790, 11-133224, and 11-335894. These
methods are characterized by simplicity in preparation of colored
film with high-resolution. They are used mainly in the application
area of liquid crystal display units.
[0007] The above-mentioned photovoltaic electrodeposition process
and its related technology make it possible to continuously change
the concentration of the functional material in the film (such that
the concentration of the functional material increases in
proportion to the film thickness) if an adequate control is exerted
on at least one of such variables as (a) bias voltage to be
applied, (b) duration of irradiation with light, and (c) intensity
of light for irradiation. Consequently, with this process, we can
obtain a thin film in which the concentration of the functional
material continuously changes in the in-plane direction. On the
other hand, however, it poses some problems. That is, the resulting
polymer thin film is poor in flatness and cannot be transferred to
another surface satisfactorily because the thicker part of the thin
film tends to blur. Needless to say, this process does not give a
thin film in which the concentration of the functional material
changes continuously in the thickness direction.
[0008] There is a conventional process called photobleaching which
permits the concentration of the functional material to change from
place to place in a polymer thin film. This process employs special
molecules which change in color or disappear upon irradiation with
light having a specific wavelength. This process gives a uniformly
thick thin film (such as the one produced by spin coating) in which
the refractive index changes from place to place. This process,
however, is not generally acceptable because the material for
photobleaching is limited.
[0009] As mentioned above, there has been no process for preparing
a polymer thin film and a patterned polymer thin film which is made
up mainly of a polymer and which contains a functional material
(such as pigment fine particles, dye, and highly refractive fine
particles) such that the concentration of the functional material
changes continuously along the in-plane length or the thickness of
the thin film.
SUMMARY OF THE INVENTION
[0010] The present invention was completed in view of the-foregoing
and provides a process for preparation of an optical element, an
electrolytic solution used for the process, and an apparatus for
preparation of the optical element. According to the present
invention, the optical element is a polymer thin film containing a
functional material such that the concentration of the functional
material changes somewhat stepwise or continuously in the in-plane
and/or thickness direction. According to the present invention, the
process permits easy production of such an optical element.
[0011] The foregoing is dealt with by providing a process for
preparation of an optical element, an electrolytic solution used
for the process, and an apparatus for preparation of the optical
element as follows.
[0012] One aspect of the present invention resides in a process for
preparation of an optical element which includes the steps of:
preparing a substrate having an insulating substrate and a
conductive thin film formed thereon; preparing an electrolytic
solution containing a film forming polymer decreasing in solubility
or dispersibility in an aqueous liquid as a pH value changes and a
functional material in a certain concentration; contacting the
conductive thin film with the electrolytic solution in a presence
of a counter electrode in the electrolytic solution and applying a
voltage between the conductive thin film and the counter electrode
for changing the pH value; and varying the concentration of the
functional material near the conductive thin film.
[0013] Another aspect of the present invention resides in a process
for preparation of an optical element which includes the steps of:
preparing a substrate having an insulating substrate, a conductive
thin film and a photosemiconductive film formed thereon; preparing
an electrolytic solution containing a film forming polymer
decreasing in solubility or dispersibility in an aqueous liquid as
a pH value changes and a functional material in a certain
concentration; contacting the photosemiconductive film with the
electrolytic solution and applying a light to the
photosemiconductive film for changing the pH value; and varying the
concentration of the functional material near the conductive thin
film.
[0014] Another aspect of the present invention resides in an
apparatus for preparing an optical element on a substrate having
conductive thin film, including: an electrodeposition vessel
holding an aqueous electrolytic solution, which contains a
film-forming polymer and a functional material, the former
decreasing in solubility or dispersibility in an aqueous liquid as
the pH value changes; a counter electrode which is placed in the
electrodeposition vessel and is electrically connected to the
conductive thin film; a unit that irradiates with light the
photosemiconductor thin film on the optical element preparing
substrate, and a mechanism to cause a flow of an aqueous
electrolytic solution, which contains a film-forming polymer and a
functional material, the former decreasing in solubility or
dispersibility in an aqueous liquid as a pH value changes.
[0015] Another aspect of the present invention resides in an
apparatus for preparing an optical element on a substrate having an
clectroconductive thin film, including: an electrodeposition vessel
holding an aqueous electrolytic solution, which contains a
film-forming polymer and a functional material, the former
decreasing in solubility or dispersibility in an aqueous liquid as
a pH value changes; a counter electrode which is placed in the
electrodeposition vessel and is electrically connected to the
conductive thin film; a voltage application unit that applies a
voltage across the conductive thin film and the counter electrode,
and a mechanism to cause a flow of an aqueous electrolytic
solution, which contains a film-forming polymer and a functional
material, the former decreasing in solubility or dispersibility in
an aqueous liquid as a pH value changes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Preferred embodiments of the present invention will be
described in detail on the followings, wherein:
[0017] FIG. 1 is a diagram showing the steps of preparing the
optical element according to one embodiment of the present
invention.
[0018] FIGS. 2A and 2B are a plan view and a sectional view,
respectively, of the optical element obtained by the process of the
present invention,
[0019] FIG. 3 is a schematic diagram showing the apparatus to
prepare the optical element by using a projection exposure
unit.
[0020] FIG. 4 is a schematic diagram showing the apparatus to
prepare the optical element by using a proximity exposure unit.
[0021] FIG. 5 is a schematic diagram showing the apparatus to
prepare the optical element by using a scanning laser exposure
unit.
[0022] FIG. 6 is a schematic diagram showing the apparatus to
prepare the optical element by electrodeposition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] According to the present invention, the process for
preparation of an optical element is based the technology disclosed
in Japanese Published Unexamined Patent Applications Nos. Hei
10-119414, 11-189899, 11-15418, 11-174790, 11-133224, and
11-335894. This technology is designed to form a thin film by
electrodeposition or photovoltaic electrodeposition. The process of
the present invention is characterized by performing
electrodeposition in such a way that the concentration of the
functional material in the electrolytic solution changes in the
vicinity of the optical element preparing substrate so that the
resulting thin film contains the functional material whose
concentration gradationally changes. The following deals mainly
with optical waveguides (of core-cladding type) and lenses as the
typical examples of the optical element.
[0024] The process of the present invention makes it possible to
easily prepare a thin-film optical element in which the
concentration of the functional material changes gradationally. The
advantage of this process is that the concentration changes
continuously instead of stepwise (as in the conventional
technology) and moreover the concentration changes not only in the
thickness direction but also in the in-plane direction. A
combination of these modes of change may give a three-dimensional
gradation. In addition, the thin film proper which is formed by
deposition is flat and uniform in thickness regardless of the
changing concentration of the functional material therein. This
facilitates transfer and eliminates blurs and other defects.
[0025] The electrodeposition process basically has a step of
preparing a substrate for electrodeposition, which is made up of an
insulating substrate and a conductive thin film formed thereon, in
an aqueous electrolytic solution, which contains a film-forming
polymer and a functional material, the former decreasing in
solubility or dispersibility in an aqueous liquid as the pH value
changes, in such a way that at least the conductive thin film comes
into contact with the electrolytic solution, and a step of applying
a voltage across the conductive thin film and its counter
electrode, thereby causing the materials to deposit on the
conductive thin film.
[0026] The photovoltaic electrodeposition process utilizes
photoelectromotive force that is generated in a photosemiconductor
thin film. It has a step of preparing a substrate for photovoltaic
electrodeposition, which is made up of an insulating substrate and
a conductive thin film and a photosemiconductor thin film
sequentially laminated thereon, in an aqueous electrolytic
solution, which contains a film-forming polymer and a functional
material, the former decreasing in solubility or dispersibility in
an aqueous liquid as the pH value changes, in such a way that at
least the photosemiconductor thin film comes into contact with the
electrolytic solution, and a step of applying a voltage across the
photosemiconductor thin film and its counter electrode in a
selected region while irradiating the selected region in the
photosemiconductor thin film with light, thereby causing the
materials to deposit on the selected region of the
photosemiconductor thin film.
[0027] The electrodeposition process and photovoltaic
electrodeposition process make it possible to accurately form an
optical element having fine patterns without the necessity of
applying a high voltage (over 5 V). Whereas the conventional
process that uses a photosensitive resin to prepare an optical
element needs a thin film with an accurately controlled thickness
on the substrate and poses a problem with alkaline waste liquids
resulting from etching, the process of the present invention makes
it possible to easily control the thickness of the thin film by
adjusting the duration of light irradiation or voltage application
and needs no etching for patterning (and hence poses no
environmental problem).
[0028] The process for preparation of an optical element which is
based on photovoltaic electrodeposition will be described first in
the following. This process uses an optical element preparing
substrate, which is made up of an insulating substrate and a
conductive thin film and a photosemiconductor thin film
sequentially laminated thereon. The insulating substrate includes
glass plate, quartz plate, plastic film, epoxy resin sheet, and the
like. The conductive thin film includes those of ITO, indium oxide,
nickel, and aluminum. The photosemiconductor thin film includes
titanium oxide thin film, zinc oxide thin film, and the like, which
will be explained in the following. Incidentally, the insulating
substrate and conductive thin film should be transparent to light
in the case where the photosemiconductor thin film is irradiated
with light through the insulating substrate. This is not applied to
the case in which irradiation with light is carried out through the
electrolytic solution.
[0029] The electrolytic solution will be explained later because it
is used in common for the photovoltaic electrodeposition process
and the electrodeposition process.
[0030] The term "selected region" as used in the present invention
denotes the entire region as well as the partial region in the
optical element preparing substrate. For example, in the case where
a cladding layer is formed on the entire surface of the substrate,
the selected region means the entire surface which is irradiated
with light.
[0031] The process of the present invention may be applied in the
following manner to the preparation of an optical element including
a cladding layer and a core layer laminated on one the-other.
First, the cladding layer is formed on the entire surface from the
electrolytic solution for the cladding layer. Second, the selected
region (or the entire surface) of the substrate is irradiated with
light. Third, the core layer is formed on the selected region (or
the core-forming region) from the electrolytic solution for the
core layer. Finally, the selected region is irradiated with light.
Another cladding layer may be formed on the core layer by repeating
the same steps as above without drying the cladding layer and the
core layer. The resulting optical element is made up of a lower
cladding layer, a core layer, and an upper cladding layer.
[0032] Moreover, the above-mentioned cladding layer may also be
formed by electrodeposition even though irradiation with light is
replaced by application of a voltage exceeding the Schottky barrier
of the photosemiconductor thin film on the optical element
preparing substrate. This process is simpler because it dispenses
with the step for exposure.
[0033] The process for preparing an optical element according to
the present invention will be illustrated below with reference to
the accompanying drawings. FIGS. 1A to 1D show the steps of
preparing a waveguide in which a cladding layer is formed on the
entire surface of a substrate, with a core layer interposed between
them, the core layer containing a functional material (such as fine
particles to control the refractive index) such that its
concentration changes gradationally in the thickness direction.
[0034] FIG. 1A shows an example of the optical element preparing
substrate 10, which has an insulating substrate 12, a conductive
film 14, and a photosemiconductor thin film 16. FIG. 1B shows a
cladding layer 18 (not yet dried) which has been formed from an
electrolytic solution for the cladding layer. The entire surface of
the cladding layer 18 has been irradiated with light or
alternatively it has been given a voltage exceeding the Schottky
barrier of the photosemiconductor thin film.
[0035] FIG. 1C shows a core layer 20 formed in the selected region
on the cladding layer 18 (not yet dried) from an electrolytic
solution for the core layer. The core layer 20 has been irradiated
with light. The core layer contains the functional material such
that its concentration gradationally changes. This is accomplished
by changing the concentration of the functional material in the
electrolytic solution in the vicinity of the optical element
preparing substrate, as mentioned later. In the case where the
functional material is fine particles to control the refractive
index, the resulting core layer has a refractive index which
changes from place to place. FIG. 1C shows that the concentration
of the functional material is high at the center of the thickness
of the core layer.
[0036] FIG. 1D shows an additional cladding layer 22 (not yet
dried) which has been formed on the core layer 20 (not yet dried)
from an electrolytic solution for the cladding layer. The entire
surface of the cladding layer 20 has been irradiated with light or
alternatively it has been given a voltage exceeding the Schottky
barrier of the photosemiconductor thin film. The desired optical
element is completed by drying these layers.
[0037] The foregoing example demonstrates a case in which the core
layer has the gradation of concentration. Needless to say, there
may be another case in which the cladding layer or both the core
layer and the cladding layer have the gradation of
concentration.
[0038] FIGS. 2A and 2B show an example of an optical element (such
as lens) which is characterized in that the concentration of the
functional material in the thin film changes in the in-plane
direction. FIGS. 2A and 2B show how the concentration of the
functional material decreases in going from the center to the
periphery in the flat circular thin film 24 formed on the optical
element preparing substrate 10. The change of concentration is
represented by the density of dots.
[0039] The above-mentioned photovoltaic electrodeposition process
may employ an optical element preparing substrate made up of a
conductive substrate and a photosemiconductor thin film formed
thereon. The conductive substrate may be the one which is formed
from at least one member selected from iron, nickel, zinc, copper,
or titanium, or compounds thereof, or mixtures thereof. The
conductive substrate may also include conductive plastics film.
[0040] The photosemiconductor may be formed from titanium oxide or
zinc oxide by the process mentioned later. Alternatively, it is
also possible to form a photosemiconductor thin film on a plate of
metallic titanium or zinc by oxidation of its surface. In this
case, the optical element preparing substrate or the deposition
substrate is made up of a conductive substrate and a
photosemiconductor thin film formed thereon.
[0041] Oxidation may be accomplished inexpensively by heating at a
high temperature in the air or by anodization. In other words, it
is possible to form a transparent semiconductor thin film without
using the expensive sputtering method. Incidentally, it is
desirable that the unoxidized part of the underlying metal
substrate should be coated with an insulating film to avoid
formation of an unnecessary electrodeposition film thereon.
[0042] Now, the process for preparation of an optical element which
is based on electrodeposition will be described in the following.
This process uses an optical element preparing substrate, which is
made up of an insulating substrate and a conductive thin film or a
patterned conductive thin film formed thereon. The optical element
preparing substrate is arranged in an aqueous electrolytic
solution, which contains a film-forming polymer and a functional
material, the former decreasing in solubility or dispersibility in
an aqueous liquid as the pH value changes, in such a way that at
least the conductive thin film comes into contact with the
electrolytic solution. Then a voltage is applied across the
conductive thin film and its counter electrode, so that the
materials deposit on the conductive thin film. During voltage
application, the concentration of the functional material in the
electrolytic solution is changed in the vicinity of the optical
element preparing substrate. Thus, the resulting thin film contains
the functional material gradationally. The foregoing process may be
used to form on the optical element preparing substrate a core
layer in which the concentration of the functional material changes
gradationally.
[0043] The insulating substrate may be the same one as used in the
photovoltaic electrodeposition method. The patterned conductive
thin film may be formed by patterning the conductive film in the
usual way or coating the conductive substrate with an insulating
film so that a conductive part is exposed in a desired pattern.
These substrates may be used to form the cladding layer or core
layer by the electrodeposition process.
[0044] The optical element prepared as mentioned above may be
transferred to another substrate in the following manner.
[0045] First, the method of transferring the optical element
prepared by photovoltaic electrodeposition to an optical element
substrate is explained. (The optical element in this case denotes
the core layer and the cladding layer individually or in
combination.) The substrate to which transfer is made may be the
one which functions also as a cladding layer. In this way it is
possible to reduce the total number of steps including the step of
electrodeposition. If an optical element is prepared by repeating
transfer of the core layers and cladding layers, which have been
formed separately by electrodeposition, there may be the
possibility that loss increases at the interface between the core
layer and the cladding layer and the resulting waveguide is
slightly deformed.
[0046] The optical element substrate includes those of glass, epoxy
resin, and the like which are in general use. The optical element
substrate which functions also as a cladding layer includes
polyethylene film, polyester film, polycarbonate film, acrylic
resin film, fluoropolymer film, and the like.
[0047] The cladding layer or core layer formed by electrodeposition
as mentioned above may also be transferred to another substrate. In
this case, the substrate should preferably be one which functions
as the cladding layer.
[0048] Transfer of an optical element (which has been prepared by
the above-mentioned photovoltaic electrodeposition) to another
substrate may be accomplished easily if a release layer is
previously formed on the optical element preparing substrate. This
release layer obviates the necessity of using heat or pressure at
the time of transfer and hence eliminates the possibility of damage
to the substrate and optical element.
[0049] The release layer should preferably be one which has a
critical surface tension not higher than 30 dyne/cm and has no
influence on electrodeposition current. Its typical examples
include commercial fluoropolymer spray for waterproofing, silicone
resin, silicone oil, and unsaturated fatty acid such as oleic
acid.
[0050] The electrodeposition uses a film-forming polymer which
decreases in solubility or dispersibility in an aqueous liquid as
the pH value changes. Such a material is exemplified by a substance
which preferably contains such ionic groups as carboxyl group and
amino group in the molecule. These groups change in ionic
dissociation as the pH value changes. However, the presence of
ionic groups is not necessarily essential, and the polarity of
ionic groups does not matter.
[0051] The property that solubility or dispersibility in an aqueous
liquid decreases as the pH value changes is important for the
film-forming polymer from the standpoint of the mechanical strength
of the thin film (optical element). Examples of such a material
include ionic polymers having ionic groups as mentioned above. The
ionic polymer should be highly soluble or dispersible in an aqueous
liquid (with or without pH adjustment) and also highly
transparent.
[0052] The polymer should have both hydrophilic groups and
hydrophobic groups in the molecule so that it decreases in
solubility or dispersibility in an aqueous solution as the pH value
changes. Examples of the hydrophilic groups include carboxyl group
(anionic) and amino group (cationic) which are capable of
ionization. (These groups are simply referred to as "ionizable
groups" hereinafter.) A polymer having carboxyl groups dissolves in
an aqueous solution when the pH value is in the alkaline region
because the carboxyl groups dissociate. On the other hand, it
precipitates out in the acid region because the carboxyl groups do
not dissociate any longer.
[0053] The hydrophobic groups in the polymer permit the polymer to
separate out (in the form of thin film) instantaneously as the pH
value changes and hence the dissociated groups become non-ionic.
The hydrophobic groups absorb the fine particles to control
refractive index and help the polymer to disperse while the optical
element is being prepared according to the present invention as
mentioned later. The hydrophilic group also includes hydroxyl
groups in addition to the ionizable groups.
[0054] The polymer having both hydrophobic groups and hydrophilic
groups should preferably be one in which the number of hydrophobic
groups accounts for 30% to 80% of the total number of hydrophobic
groups and hydrophilic groups. The one in which the number of
hydrophobic groups is less than 30% of the total number of
hydrophobic groups and hydrophilic groups gives rise to a film
which is easily soluble and poor in water resistance and strength.
The one in which the number of hydrophobic groups is more than 80%
of the total number of hydrophobic groups and hydrophilic groups is
poor in solubility in an aqueous solution and hence it gives rise
to an electrolytic solution which is viscous or turbid with
precipitation. It is more desirable that the number of hydrophobic
groups should account for 55 to 70% of the total number of
hydrophobic groups and hydrophilic groups. The polymer containing
hydrophobic groups in such a range forms film efficiently at a low
clectrodeposition potential of the order of photoelectromotive
force and gives rise to a stable electrolytic solution.
[0055] An example of the above-mentioned polymer is a copolymer
made up of a polymerizable monomer having hydrophilic groups and a
polymerizable monomer having hydrophobic groups.
[0056] Examples of the polymerizable monomer having hydrophilic
groups include methacrylic acid, acrylic acid, hydroxyethyl
methacrylate, acrylamide, maleic anhydride, fumaric acid, propionic
acid, itaconic acid, and derivatives thereof, but they are not
limited thereto. Of these examples, methacrylic acid and acrylic
acid are useful hydrophilic monomers because they contribute to the
film-forming efficiency due to pH changes.
[0057] Examples of the polymerizable monomer having hydrophobic
groups include alkene, styrene, a-methylstyrene, a-ethylstyrene,
methyl methacrylate, butyl methacrylate, acryronitrile, vinyl
acetate, ethyl acrylate, butyl acrylate, lauryl methacrylate, and
derivatives thereof. These examples are not limitative. Of these
examples, styrene and c-methylstyrene are useful hydrophobic
monomers because they contribute to the hysteresis characteristics
for re-dissolution.
[0058] A preferred polymer used in preparation of the optical
element according to the present invention is a copolymer made up
of acrylic acid or methacrylic acid, as the monomer containing
hydrophilic groups, and styrene or c-styrene, as the monomer
containing hydrophobic groups.
[0059] The process for preparing the optical element according to
the present invention uses a polymer which is made up of
polymerizable monomers each containing hydrophilic groups and
hydrophobic groups. This polymer should preferably be a copolymer
which contains hydrophilic groups and hydrophobic group in a
certain ratio as specified above. There may be more than one kind
each of hydrophilic groups and hydrophobic groups.
[0060] The functional material used in the present invention
include fine particles to control refractive index, fine particles
of pigment, dye, and electrically conductive fine particles.
[0061] The fine particles to control refractive index are either
those of high refractive index which are added to the core layer
and those of low refractive index which are added to the cladding
layer. The former are exemplified by titanium oxide and zinc oxide
and the latter are exemplified by magnesium fluoride.
[0062] The above-mentioned fine particles should have a
number-average particle diameter of 0.2 to 150 nm, preferably 2 to
20 nm, so that they readily disperse in the electrolytic solution
and keep clear the electrodeposited film. With a number-average
particle diameter smaller than 0.2 nm, the fine particles are high
in production cost and poor in quality uniformity. On the other
hand, with a number-average particle diameter larger than 150 nm
(which is one-tenth of the wavelength (1.5 .mu.m) used for
communications), the fine particles produce adverse effects such as
decreased clarity, internal irregular reflection, and internal
loss.
[0063] For adjustment of refractive index, the above-mentioned
functional material may be selected from one kind of film-forming
polymer which differs in refractive index from the main
film-forming polymer.
[0064] According to the present invention, the process for
preparing the optical element should work in such a way as to give
a thin film in which the content of the functional material changes
gradationally in the thickness direction. To achieve the foregoing,
it is necessary to change the concentration of the functional
material in the electrolytic solution in the vicinity of the
optical element preparing substrate (or in the vicinity of the
conductive thin film or photosemiconductor thin film, or in the
vicinity of a thin film if it has already been formed). One way to
meet this requirement is made to flow a secondary electrolytic
solution toward the optical element preparing substrate in a
primary electrode deposition solution, the former differing from
the latter in the concentration of the functional material. If the
concentration of the functional material is to be uniform in the
in-plane direction of the resulting thin film, it is necessary to
keep uniform the concentration of the functional material in the
electrolytic solution in the vicinity of the entire film-forming
region of the optical element preparing substrate. The foregoing
may be achieved by making a flow of the electrolytic solution whose
shape conforms to the film-forming region, or by causing the
electrolytic solution to flow through small holes evenly arranged
over the film-forming region. For example, in the case where a core
optical waveguide is to be formed, the foregoing is achieved by
flowing the electrolytic solution toward the core-forming region on
the optical element preparing substrate through slits or small
holes which are arranged in conformity with the core shape. If a
voltage is applied to the film-forming region while the
electrolytic solution is flowing, the electrolytic solution, which
differs in the concentration of the functional material from its
surrounding one, comes into contact with the optical element
preparing substrate. Thus the resulting electrodeposited thin film
has a different concentration of the functional material than it
would have if the surrounding electrolytic solution alone were
used.
[0065] If it is desirable to form a thin film on a previously
formed thin film (the former differing from the latter in the
concentration of the functional material) as in the case where a
core layer is formed subsequently on a cladding layer, it is not
necessary to entirely replace the electrolytic solution in the
vessel (for example, replacing the solution for the cladding layer
with the solution for the core layer). Instead, it is only
necessary to flow a second electrolytic solution, which differs
from a first one in the concentration of the functional material,
toward the film-forming region. In this way it is possible to form
a thin film with a different concentration of the functional
material on a previously formed thin film. The result is process
simplification and cost reduction.
[0066] An alternative process is also possible which employs plural
electrolytic solutions differing in the concentration of the
functional material. In this case the electrolytic solutions are
sequentially made to flow toward the optical element preparing
substrate so that the concentration of the functional material
changes with time in the vicinity of the substrate. The thus formed
thin film changes gradationally in the concentration of the
functional material. If the electrolytic solution is made to flow
in such a way that the concentration of the functional material
therein changes continuously, the resulting thin film will contain
the functional material in continuously changing concentrations.
For example, if plural electrolytic solutions are made to flow in
an adequate order with respect to the concentration of the
functional material, it would be possible to form a core layer in
which the concentration of the functional material is higher at its
center. Alternatively, if plural electrolytic solutions are flown
continuously such that the concentration of the functional material
gradually increases and then a voltage is applied steadily (with
the flow of the electrolytic solution suspended), the concentration
of the functional material to be electrodeposited decreases. Thus,
in this way it is possible to form a core layer in which the
concentration of the functional material is higher at its center.
(The concentration of the functional material is lower in the
previously formed cladding layer than in the core layer.)
[0067] An adequate flow rate of the electrolytic solution should be
0.1 to 10 mm/s so that the flow does not damage the deposited film
and the concentration of the functional material changes in
proportion to the film-forming rate.
[0068] The above-mentioned process gives rise to a thin film which
is flat and uniform in thickness regardless of the changing
concentration of the functional material. Therefore, the thin film
permits transfer easily and has few blurs and flaws.
[0069] According to the present invention, the process for
preparation of an optical element may be modified in the way of
changing the concentration of the functional material in the
electrolytic solution in the vicinity of the optical element
preparing substrate, so that the resulting thin film contains the
functional material whose concentration changes gradationally in
the in-plane direction of the thin film. The foregoing is achieved
by causing the electrolytic solution to flow in such a way that the
concentration of the functional material changes in the in-plane
direction. To be concrete, such a flow is made by directing an
electrolytic solution, which differs in the concentration of the
functional material from its surrounding electrolytic solution,
toward a specific part of the film-forming region on the optical
element preparing substrate. The flow made in this manner impinges
upon the substrate and then spreads along the substrate surface and
eventually diffuses into its surrounding electrolytic solution.
Thus the concentration of the functional material in the
electrolytic solution in the vicinity of the substrate changes in
the direction in which the electrolytic solution flows along the
substrate. It is also possible to produce a thin film in which the
content of the functional material changes in the in-plane
direction if plural electrolytic solutions, which differ in the
concentration of the functional material from one another, are
directed toward the optical clement preparing substrate from plural
outlets.
[0070] It is also possible to form an optical element in which the
concentration of the functional material differs
three-dimensionally if the above-mentioned methods for gradation in
the thickness direction and the in-plane direction of the
functional material are combined with each other.
[0071] A detailed mention is made below of the process and
apparatus for preparing the optical element of the present
invention.
[0072] FIG. 3 is a schematic diagram showing an example of the
apparatus for preparing the optical element by the photovoltaic
electrodeposition process.
[0073] There is shown a vessel 80 holding an electrolytic solution
20, in which is placed an optical element preparing substrate 10
(formed of a transparent insulating substrate 12 and a transparent
conductive film 14 and a photosemiconductor thin film 16
sequentially laminated thereon) such that at least the
photosemiconductor thin film 16 comes into contact with the
electrolytic solution 20. Above the electrolytic solution is an
exposure system (of projection type) has a first image-forming
optical lens 73, a photomask 71, a second image-forming optical
lens 72, and a light source (not shown) which are arranged from the
side of the vessel 80. The light source emits a beam of light 70
which passes through the second image-forming lens 72 and forms an
image at the photomask 71. The photomask 71 produces a patterned
beam of light which passes through the first image-forming lens 73
and forms an image on the surface of the photosemiconductor thin
film.
[0074] In FIG. 3, there is also shown a plate 100 which permits
another electrolytic solution which differs in the concentration of
the functional material from the electrolytic solution 20 to flow
at a controlled flow rate. There are shown a flow outlet 102 formed
in the plate 100, a container 106 to hold the electrolytic
solution, and a pump 104 to steadily feed under pressure the
electrolytic solution from the container 106. These components
constitute the flow-forming mechanism. The electrolytic solution is
discharged from the flow outlet 102 at an-adequate flow rate which
is controlled by the pump. The pump, which causes a flow as
mentioned above, may be any commercial one which produces the
desired flow rate even though it sometimes suffers pulsation. The
flow outlet 102 of the plate 100 discharges an electrolytic
solution which differs in the concentration of the functional
material from the electrolytic solution 20, so that the
concentration of the functional material changes in the
electrolytic solution in the vicinity of the optical element
preparing substrate. The flow outlet should be positioned such that
it is a certain distance away from the position where the thin film
is formed on the optical element preparing substrate. The distance
should be about 0.2 to 10 mm in order to prevent the flow outlet
from coming into contact with the substrate and in order to ensure
a uniform flow rate.
[0075] In this embodiment, the plate 100 functions also as a
counter electrode 91, which is electrically connected to a voltage
application unit 90 such as a potentiostat that applies a bias
voltage. The voltage application unit 90 is connected further to a
reference electrode 92 such as a saturated calomel electrode, and
is constituted in a tripolar manner. The voltage application unit
90 is connected further to the conductive film 14 of the substrate
on which the thin film is formed. Needless to say, the counter
electrode may be installed separately in an adequate position in
the vessel 80 without it functioning also as the plate.
Incidentally, application of a bias voltage from the voltage
application unit is not necessary and hence the voltage application
unit itself is not necessary in the case where photoelectromotive
force is strong enough to change the hydrogen ion concentration
required for film deposition. However, it is desirable to install
the voltage application unit so that the process works
satisfactorily for any film-forming substrate under any
electrodeposition condition.
[0076] The method of forming a flow of the electrolytic solution is
disclosed in the specification of Japanese Unexamined Patent
Application No. 2001-353725 filed by the present applicant. This
method can be used in the present invention.
[0077] The preparation of the optical element is illustrated below
by way of example. In this example, an optical waveguide is
prepared by using the photovoltaic electrodeposition apparatus as
shown in FIG. 3. This optical waveguide is made up of a cladding
layer (lower), which is laminated on the entire surface of a
substrate, a core layer, and a cladding layer (upper), which is
laminated on the entire surface of a substrate. The core layer
contains a functional material (fine particles to control
refractive index) such that its concentration changes in the
thickness direction.
[0078] The process starts with filling the vessel 80 with the
electrolytic solution 20 from which the lower cladding layer is
formed. The lower cladding layer is formed on the entire surface of
the substrate by application of a voltage across the voltage
application unit 90 and the counter electrode 91 (the plate 100),
without irradiation with light. This voltage is higher than the
Schottky barrier of the photosemiconductor thin film on the
substrate on which the optical element preparing substrate.
[0079] Then, the photomask 71 for the core layer is set as shown in
FIG. 3. The container 106 to hold the electrolytic solution is
filled with the electrolytic solution for the lower core layer, and
the electrolytic solution is allowed to flow out of the outlet 102
at a controlled flow rate. Subsequently, the photosemiconductor
thin film 16 is exposed to light by the exposure unit in such a way
that the light forms an image in the selected region on the surface
thereof. Simultaneously with exposure, a bias voltage is applied by
the voltage application unit 90. The bias voltage should be high
enough so that the sum of the bias voltage and the
photo-electromotive force generated in the photosemiconductor thin
film exceeds the threshold voltage necessary for film deposition.
Application of the bias voltage greatly changes the hydrogen ion
concentration of the electrolytic solution in the vicinity of the
selected region which has been exposed. Since the above-mentioned
electrolytic solution contains an electrodepositing material which
decreases in solubility or dispersibility in an aqueous solution as
the hydrogen ion concentration changes, an electrodeposition film
(lower core layer) containing fine particles to control refractive
index separates out on the surface of the lower cladding layer as
the result of decrease in solubility in the electrolytic solution
near the selected region. After that, irradiation with light and
voltage application are suspended. Subsequently, the electrolytic
solution for the core layer in the container 106 to hold the
electrolytic solution is replaced by the electrolytic solution for
the upper core layer. The latter solution differs from the former
solution in the concentration of fine particles to control
refractive index. The replaced electrolytic solution is allowed to
flow out of the outlet 102 and irradiation with light and
application of bias voltage are carried out in the same way as
mentioned above, so that a thin film (upper core layer) is formed.
Thus there is formed the core layer in which the content of fine
particles to control refractive index changes gradationally in the
thickness direction. Incidentally, in the case where the liquid
flow forming mechanism is so constructed as to continuously flow
electrolytic solutions differing in the concentration of the
functional material, it is not necessary to suspend irradiation
with light and replace the electrolytic solution for the upper core
in the container to hold the electrolytic solution as mentioned
above after the lower core layer has been formed. Instead, all that
is necessary is to permit the electrolytic solution for the upper
core to flow continuously.
[0080] Then, the electrolytic solution in the electrolytic vessel
80 is replaced with the electrolytic solution for the upper
cladding layer. The upper cladding layer is formed, without
irradiation with light, over the entire surface in the same way as
the lower cladding layer.
[0081] A mention is made below of another apparatus for preparing
the optical element by photovoltaic electrodeposition. FIG. 4 is a
schematic diagram showing another apparatus for preparing the
optical element which is the same as that shown in FIG. 3 except
that it employs an exposure unit of proximity exposure type. The
apparatus shown in FIG. 4 is designed such that the photomask is
placed near the photosemiconductor thin film (or in contact with
the insulating substrate). Therefore, it gives a highly resolved
pattern without resorting to an exposure system having a focusing
optical system and reflecting optical system (mirror) unlike the
apparatus shown in FIG. 3. The exposure unit 75 may be that of
parallel light type or contact type. The light source for
irradiation may be a uniformly emitting Hg--Xe lamp. In this case,
it is desirable that the insulating substrate be thinner than 0.2
mm so that the diffraction of light is minimized.
[0082] For preparation of the optical element, this apparatus is
operated in the same way as that shown in FIG. 3. In addition,
photovoltaic electrodeposition may be performed over the entire
surface of the optical element preparing substrate by irradiation
with light in order to form the lower and upper cladding
layers.
[0083] FIG. 5 is a schematic diagram showing another apparatus for
preparing the optical element. This apparatus is the same as that
shown in FIG. 3 except that it employs a laser writing unit of
scanning type as the exposure unit. In FIG. 5, there is shown the
laser writing unit 78 which emits He--Cd laser or the like.
[0084] In addition, FIG. 6 is a schematic diagram showing another
apparatus for preparing the optical element by electrodeposition.
This apparatus is the same as those shown in FIGS. 3 to 5 except
that it does not have the exposure unit.
[0085] According to the present invention, the process for
preparation of the optical element should preferably be followed by
a step of heat treatment after all the optical elements have been
formed. This heat treatment reduces the transmission loss of the
finished optical element.
[0086] Incidentally, "all the optical elements" means one or all
optical elements in the case where one or more optical elements
(for example, more than one core layer and more than one cladding
layer) are formed. "After all the optical elements have been
formed" means that "after the optical element has been formed by
deposition" in the case where the optical element is formed on the
optical element-preparing substrate by (photo)-electrodeposition
and the thus obtained optical element is used as such as the
optical element. However, it is usually understood that the
above-mentioned heat treatment follows a drying step to remove
water from the optical element. "After . . . " also means "after
the optical element has been transferred to the optical element
substrate" in the case where the process for preparation of the
optical element involves transfer to the optical element
substrate.
[0087] The optical element formed by (photo)-electrodeposition
usually contains a trace amount of water caught in the film.
Therefore, the optical element formed by deposition is dried to
remove water from the film. Removal of water results in film
defects (such as pinholes) in the optical element. This is a
possible cause that increases the transmission loss of the optical
element. It is expected that the above-mentioned heat treatment
repairs such defects and smoothens the surface of the optical
element and reduces the surface roughness of the core-clad
interface, thereby decreasing the transmission loss.
[0088] The above-mentioned heat treatment is not specifically
restricted in temperature and duration so long as it reduces the
transmission loss of the optical element. The heating temperature
may be determined in consideration of the glass transition
temperature and flow point of the film-forming polymer.
[0089] For efficient heat treatment, the heating temperature should
preferably be higher than the flow point of the polymer. "Plow
point" means that defined in "Method for testing polymers"
(Lectures on Polymer Technology, vol. 14, pp. 364 to 369, compiled
by Institute of Polymer Science, issued by Chijin Shokan, 1963).
The polymer used in the present invention should be one which has a
flow point in the range of 50 to 200.degree. C., preferably 80 to
150.degree. C., and more preferably 110 to 130.degree. C.
[0090] The heating temperature may be lowered or the heating time
may be reduced if pressure is applied to the optical element at the
time of heat treatment.
[0091] The above-mentioned polymer for electrodeposition should be
one which has a refractive index ranging from 1.45 to 1.6 and is
transparent in its deposited state. It suits the optical element
because it does not absorb the light with a wavelength of 0.8 to
1.6 .mu.m which is used for the optical element.
[0092] Moreover, the polymer after dissolution in water to give the
electrolytic solution does not absorb UV light; therefore, it
permits the photosemiconductor to be irradiated with UV light for
patterning through the electrolytic solution. In addition, it is
capable of electrodeposition with a low potential (5V or below).
This facilitates forming the electrodeposition pattern with the
photoelectromotive force generated by the photosemiconductor.
EXAMPLES
[0093] The present invention will be described in more detail with
reference to the following examples which are not intended to
restrict the scope thereof.
Example 1
[0094] This example demonstrates the preparation of an optical
waveguide of clad-core-clad structure. (The cladding layer is
formed by application of a voltage exceeding the Schottky barrier
of the photosemiconductor instead of irradiation with light.)
[0095] (1) Preparation of Electrolytic Solution for Clad
[0096] In 100 g of pure water was dispersed 5 g of styrene-acrylic
acid copolymer (having a molecular weight of 13,000, a molar ratio
of 65:35 for styrene and acrylic acid, and an acid value of 150).
[This copolymer will be referred to as "electrodepositable polymer
A" hereinafter.] To the resulting dispersion was added
dimethylaminoethanol in a ratio of 180 ml/l. (This reagent is a
water-soluble liquid having a boiling point no lower than
110.degree. C. and a vapor pressure no higher than 100 mmHg.) The
resulting solution was given tetramethylammoniumhydroxide and
ammonium chloride so that it had pH 7.8 and a conductivity of 8
mS/cm. The thus obtained solution was used as the electrolytic
solution from which the cladding layer was formed.
[0097] (2) Preparation of Electrolytic Solution 1 for Cure
[0098] In 100 g of pure water were dispersed 5 g of
electrodepositable polymer A (mentioned above) and 5 g of titanium
oxide having a particle diameter of 2 nm. To the resulting
dispersion was added dimethylaminoethanol in a ratio of 180 mmol/l.
The resulting solution was given tetramethylammoniumhydroxide and
ammonium-chloride so that it had pH 7.8 and a conductivity of 8
mS/cm. The thus obtained solution was used as an electrolytic
solution 1 from which the core was formed.
[0099] (3) Preparation of Electrolytic Solution 2 for Core
[0100] The same procedure to prepare the electrolytic solution 1
for the core was repeated except that the amount of titanium oxide
was increased to 25 g to prepare an electrolytic solution 2 for the
core.
[0101] (4) Preparation of Optical Element Preparing Substrate
[0102] An alkali-free #7059 glass substrate (0.5 mm thick)
underwent sputtering for coating with a transparent ITO conductive
film (100 nm thick) and further underwent RF sputtering for coating
with TiO.sub.2 film (200 nm thick).
[0103] (5) Preparation of Optical Waveguide
[0104] An apparatus for photovoltaic electrodeposition was used
which has a mechanism to flow the electrolytic solution as shown in
FIG. 4. The plate has a slit-like outlet corresponding to the core
to be formed. The plate was used as the counter electrode
(platinum) and a TiO.sub.2 electrode was used as the working
electrode for the saturated calomel electrode. The photomask 71 has
an opening corresponding to the core to be formed. The exposure
unit is that of proximity exposure type (made by Yamashita Denso
Co., Ltd.). The outlet in the plate is 1 mm away from the substrate
on which the core is formed.
[0105] First, the electrodeposition vessel was filled with the
electrolytic solution for the cladding layer (mentioned above). A
bias voltage of 3.5 V was applied for 10 seconds to the working
electrode, without the exposure unit emitting light. Thus there was
formed the lower cladding layer (5 .mu.m thick) over the entire
TiO.sub.2 surface.
[0106] With the optical element preparing substrate remaining in
the electrodeposition vessel, the electrolytic solution 2 for the
core started to flow at a flow rate of 0.1 mm/s toward the core
forming position from the slit-like outlet in the plate. After 10
seconds, with a bias voltage (1.8 V) applied to the working
electrode, the exposure unit was activated to emit UV light (365 nm
in wavelength and 50 mW/cm.sup.2 in intensity) for 15 seconds.
There was formed a lower core layer (5 .mu.m thick and 10 .mu.m
wide) only on that region of the cladding layer which was
irradiated with UV light.
[0107] Irradiation with UV light and application of bias voltage
were suspended. The electrolytic solution was replaced with the
electrolytic solution 1 for the core. The electrolytic solution 1
started to flow at a flow rate of 0.1 mm/s toward the core forming
position from the slit-like outlet in the plate. After 10 seconds,
with a bias voltage (1.8 V) applied to the working electrode, the
exposure unit was activated to emit UV light (365 nm in wavelength
and 50 mW/cm.sup.2 in intensity) for 15 seconds. There was formed
an upper core layer (5 .mu.m thick and 10 .mu.m wide) on the lower
core layer.
[0108] The electrolytic solution in the vessel was replaced with
the electrolytic solution for the clad (mentioned in (1) above).
Without irradiation with light from the exposure unit, a bias
voltage of 4 V was applied to the working electrode for 35 seconds.
There was formed the upper cladding layer (8 .mu.m thick) over the
entire surface.
[0109] The optical element preparing substrate was taken out of the
electrodeposition vessel and then washed by dipping in pure water
for 3 minutes so as to remove a trace amount of residual salt from
the film. Washing was followed by drying with clean air. Thus the
substrate for optical waveguide was completed.
[0110] The thus obtained optical waveguide was cut to a length of
50 mm by using a dicing saw. The sample was tested for insertion
loss. The transmission loss of the sample was about 5 dB for a
wavelength of 0.85 .mu.m.
Example 2
[0111] The optical waveguide prepared in Example 1 underwent heat
treatment at 140.degree. C. for 3 minutes. The heat-treated sample
was tested for transmission loss in the same way as in Example 1.
The result indicated that the heat treatment reduced transmission
loss by about 1.5 dB. A probable reason for this is that the heat
treatment removes a few pinholes remaining in the film of the
optical waveguide..
[0112] The optical waveguide constructed as mentioned above
produces a profound effect of confining light even though its
cladding layer is thin in the thickness direction. This leads to an
improvement in transmission loss over the conventional optical
waveguide of simple step-index type.
Example 3
[0113] (1) Preparation of Electrolytic Solution for Clad
[0114] In 100 g of pure water was dispersed 5 g of styrene-acrylic
acid copolymer (having a molar ratio of 20:80 for styrene and
acrylic acid, an acid value of 160, and a molecular weight of
12,000). [This copolymer will be referred to as "electrodepositable
polymer B" hereinafter.] To the resulting dispersion was added
dimethylaminoethanol in a ratio of 180 ml/l. The resulting solution
was given tetramethylammoniumhydroxide and ammonium chloride so
that it had pH 7.8 and a conductivity of 8 mS/cm. The thus obtained
solution was used as the electrolytic solution from which the
cladding layer was formed.
[0115] (2) Preparation of Electrolytic Solution 1 for Core
[0116] In 100 g of pure water were dispersed 5 g of
electrodepositable polymer A (used in Example 1) and 5 g of
electrodepositable polymer B (mentioned above). To the resulting
dispersion was added dimethylaminoethanol in a ratio of 180 mmol/l.
The resulting solution was given tetramethylammoniumhydroxide and
ammonium chloride so that it had pH 7.8 and a conductivity of 8
mS/cm. The thus obtained solution was used as an electrolytic
solution 1 from which the core layer was formed.
[0117] (3) Preparation of Electrolytic Solution 2 for Core
[0118] The same procedure to prepare the electrolytic solution 1
for the core was repeated except that the amount of
electrodepositable polymer B was increased to 25 g to prepare an
electrolytic solution 2 for the core.
[0119] (4) Preparation of Optical Element Preparing Substrate
[0120] An alkali-free #7059 glass substrate (0.5 mm thick)
underwent sputtering for coating with a transparent ITO conductive
film (100 nm thick) and further underwent RF sputtering for coating
with TiO.sub.2 film (200 nm thick).
[0121] (5) Preparation of Optical Waveguide
[0122] An apparatus for photovoltaic electrodeposition was used
which has a mechanism to flow the electrolytic solution which-is
the same one as used in Example 1.
[0123] First, the electrodeposition vessel was filled with the
electrolytic solution for the cladding layer (mentioned in (1)
above). A bias voltage of 3.5 V was applied for 10 seconds to the
working electrode, without the exposure unit emitting light. Thus
there was formed the lower cladding layer (5 .mu.m thick) over the
entire TiO.sub.2 surface.
[0124] With the optical element preparing substrate remaining in
the electrodeposition vessel, the electrolytic solution 2 for the
core started to flow at a flow rate of 0.1 mm/s toward the core
forming position from the slit-like outlet in the plate. After 10
seconds, with a bias voltage (1.8 V) applied to the working
electrode, the exposure unit was activated to emit UV light (365 nm
in wavelength and 50 mW/cm.sup.2 in intensity) for 15 seconds.
There was formed a lower core layer (5 .mu.m thick and 10 .mu.m
wide) only on that region of the cladding layer which was
irradiated with UV light.
[0125] Irradiation with UV light and application of bias voltage
were suspended. The electrolytic solution was replaced with the
electrolytic solution 1 for the core (mentioned in (2) above). The
electrolytic solution 1 started to flow at a flow rate of 0.1 mm/s
toward the core forming position from the slit-like outlet in the
plate. After 10 seconds, with a bias voltage (1.8 V) applied to the
working electrode, the exposure unit was activated to emit UV light
(365 nm in wavelength and 50 mW/cm.sup.2 in intensity) for 15
seconds. There was formed an upper core layer (5 .mu.m thick and 10
.mu.m wide) only on that region of the TiO.sub.2 surface which was
irradiated with UV light.
[0126] The electrolytic solution in the vessel was replaced with
the electrolytic solution for the clad (mentioned in (1) above).
Without irradiation with light from the exposure unit, a bias
voltage of 4 V was applied to the working electrode for 35 seconds.
There was formed the upper cladding layer (8 .mu.m thick) over the
entire surface.
[0127] The optical element preparing substrate was taken out of the
electrodeposition vessel and then washed by dipping in pure water
for 3 minutes so as to remove a trace amount of residual salt from
the film. Washing was followed by drying with clean air. Thus the
substrate for optical waveguide was completed.
[0128] The thus obtained optical waveguide was cut to a length of
50 mm by use of a dicing saw. The sample was tested for insertion
loss. The transmission loss of the sample was about 4.5 dB for a
wavelength of 0.85 .mu.m.
Example 4
[0129] The optical waveguide prepared in Example 3 underwent heat
treatment at 140.degree. C. for 3 minutes. The heat-treated sample
was tested for transmission loss in the same way as in Example 3.
The result indicated that the heat treatment reduces transmission
loss by about 1.5 dB.
[0130] The optical waveguide constructed as mentioned above
produces a profound effect of confining light even though its
cladding layer is thin in the thickness direction. This leads to an
improvement in transmission loss over the conventional optical
waveguide of simple step-index type.
Example 5
[0131] This example demonstrates the preparation of an optical
element preparing substrate and a circular thin film (10 mm in
diameter) formed thereon.
[0132] The optical element preparing substrate is the same one as
used in Example 1. The optical element was prepared by use of an
apparatus provided with the scanning laser exposure unit (He--Cd
laser) as shown in FIG. 5. This exposure unit has an optical system
which spirally scans the entire surface of the substrate at a rate
of 0.05 mm/s with an He--Cd laser beam focused to a spot diameter
of 100 .mu.m. The electrolytic solution flowed from a round outlet
(1 mm in diameter) formed in the plate. The outlet is 1 mm away
from the substrate on which the thin film is formed.
[0133] The electrodeposition vessel was filled with the
electrolytic solution for the cladding layer (which is the same one
as used in Example 1). The electrolytic solution for the cladding
layer (which is the same one as used in Example 1) was made to flow
at a rate of 0.1 mm/s from the outlet toward the center of the
round area of the substrate on which a round thin film is formed.
After 10 seconds, the round area was spirally scanned (around the
center) with an He--Cd laser from a position 10 mm away from the
center. Thus there was formed a round thin film, 10 mm in diameter
and 1 .mu.m thick. (See FIG. 2.) This thin film has refractive
indices of 1.7 at its center and 1.5 at its periphery. With the
refractive index continuously changing from the center to the
periphery, this thin film is expected to find use as a lens.
Example 6
[0134] The sample obtained in Example 5 was passed through two
rolls (roll surface temperature: 170.degree. C.; linear pressure:
300 g/cm; and linear speed: 20 mm/s) under pressure with heating
under the following conditions, with a separately prepared
polyethylene film (0.2 mm thick) placed on the round thin film.
This rolling step made it possible to form on the polyethylene film
a round polymeric thin film which has a distribution of refractive
index. The round thin film formed in Example 5 was so flat that it
was easily transferred without deformation.
[0135] The process according to the present invention permits easy
preparation of an optical element with a thin film which contains a
functional material with gradationally changing concentrations. The
change of concentration is not stepwise as in the conventional
technology but is moderate or continuous. In addition, the change
of concentration takes place not only in the thickness direction
but also in the in-plane direction of the thin film. Combination of
changing concentrations in two directions gives a three-dimensional
gradation. The thin film formed by deposition is flat (with a
uniform thickness) despite the changing concentration of the
functional material, and hence it can be transferred easily without
appreciable blurring and defect. Moreover, the distribution of the
functional material is more accurate than that achieved by the
conventional technology which employs a developing sleeve to make
inorganic conductive fine particles to unevenly distribute in the
resin (as disclosed in Japanese Published Unexamined Patent
Applications No. Hei 8-160737).
[0136] The entire disclosure of Japanese Patent Application No.
2002-179857 filed on Jun. 20, 2002 including specification, claims,
drawings and abstract is incorporated herein by reference in its
entirety.
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