JPH0216484B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves forming a mask layer for blocking ion passage in a desired pattern on the surface of a transparent member made of glass or a similar material, and performing ion exchange or The present invention relates to a method of manufacturing a refractive index distribution type transparent member in which a refractive index distribution according to the desired pattern is obtained in the transparent member by performing ion diffusion.

Conventionally, as an optical splitter or optical demultiplexer used for optical communications, etc., a converging rod lens is placed at the output end of an optical fiber to make the output light from the optical fiber almost parallel light, and a space in which this parallel light travels is used. A prism, a mirror, or an interference filter has been inserted into the output end face of the focusing rod lens, or a vapor-deposited film has been directly formed on the end face of an optical fiber. However, such a structure requires a considerable number of man-hours to manufacture and has drawbacks such as poor reproducibility.

Therefore, a mask layer for blocking ion passage is formed on a glass substrate, etc., and after etching this mask layer into a desired pattern, the glass substrate is immersed in high-temperature molten salt to melt the cations constituting the modified oxide of the glass. A refractive index distribution according to the desired pattern is formed in the glass substrate by ion exchange with alkali ions in the salt, or by diffusing ions in the molten salt into the glass substrate while applying an electric field. It has been proposed to configure an optical branching device or an optical demultiplexer by using this method.

When forming a desired refractive index distribution in a glass substrate using the above-mentioned ion exchange method or electric field application ion diffusion method, titanium or aluminum has traditionally been used as a mask layer to prevent the passage of ions. Metals such as these were used to form a film by vapor deposition, sputtering, etc. on the surface of a glass substrate.

However, this type of metal mask requires high-temperature molten salt,
For example, when it comes into contact with nitrates or sulfates, it becomes oxidized and often fails to function as a mask to prevent the passage of ions, which was its initial purpose. In particular, in the electric field applied ion diffusion method, the molten salt decomposes rapidly, so the metal mask is easily oxidized and cannot function as a mask, making it impossible to form the desired pattern of refractive index distribution correctly. Ta.

The present invention is intended to solve the above-mentioned problems, and is to form a refractive index distribution in a desired pattern in a transparent member made of glass or other similar materials by an ion exchange method or an electric field applied ion diffusion method. In the method, by using an ion layer that sufficiently functions to prevent the passage of ions in areas other than a predetermined area on the surface of the transparent member, it is possible to obtain a desired good refractive index distribution. This is what I did.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 is a schematic longitudinal cross-sectional view of an electric field application ion diffusion device for explaining the method according to the present invention for forming a refractive index distribution in a glass substrate by an electric field application ion diffusion method. As the glass substrate 1, optical glass or the like can normally be used, and here BK-
Optical glass commonly referred to as No. 7 was used.

On one surface of the glass substrate 1, a mask layer 2 having a desired pattern for blocking the passage of ions is deposited in advance by sputtering or the like.
Note that in order to form the mask layer 2 in a desired pattern on the glass substrate 1 in advance, the mask layer 2 is first formed over the entire surface of one side of the glass substrate 1. In this case, in order to increase the adhesion strength between the glass substrate 1 and the mask layer 2, sputtering is preferable to the vapor deposition method. Next, as shown in FIGS. 2 and 3, an ion layer 2 is formed using a known photolithography technique.
By partially etching the mask layer 2, a desired pattern is formed on the mask layer 2 to form openings 3 through which ions pass.

Next, the glass substrate 1 is placed in the electric field application ion diffusion device shown in FIG. In this case, glass substrate 1
is placed on a support frame 1b placed in a molten salt container, and a cylindrical frame portion 1a having a cross section substantially the same as that of the substrate is formed integrally with the glass substrate 1 in advance, or It is preferable to attach this glass substrate 1 to the frame portion 1a after forming the above-described desired pattern.

In the apparatus shown in FIG.
For example, molten salt of AgNO ₃ alone or
Molten salt of TlNO ₃ alone or Tl ₂ SO ₄ , K ₂ SO ₄ ,
A mixed molten salt containing three salts of ZnSO ₄ or the like can be used. However, although Ag ions have a small radius and thus have a fast diffusion speed, they have the disadvantage of easily generating colloids, which can cause coloring.
In addition, Tl ions are desirable because they contribute to the largest increase in the refractive index among monovalent ions, but nitrates have a low melting temperature of 206°C and evaporate rapidly, so TlNO ₃ cannot be used in the electric field applied ion diffusion method. is not very desirable. On the other hand, Tl ₂ SO ₄ , K ₂ SO ₄ , ZnSO ₄
The above-mentioned salt was used in this example because a liquid mixed in a ratio of 30%:30%:40% by mole has a melting temperature of 400°C and is suitable for the electric field applied ion diffusion method. In addition, in order to apply an electric field, the glass substrate 1
An anode electrode 6 is in the molten salt 4 in contact with the mask layer 2.
A cathode electrode 7 was placed in the molten salt 5 in contact with the surface opposite to the mask layer 2.

First, for comparison with the method according to the present invention, the thickness of the mask layer 2 created by sputtering was
Ti of 1.5μm (usually in the range of 1 to 2μm)
Regarding the glass substrate 1 made of only metal, the first
Ion diffusion was performed by applying an electric field in the mixed salt using the apparatus shown in the figure. As a result, the Ti metal film was oxidized to form a TiO ₂ film in 30 minutes, and at the same time, ions were diffused over the entire surface of the mask layer 2 side of the glass substrate 1, making it unable to function as a mask. .

Next, according to the present invention, as clearly shown in FIG.
A 0.2 μm thick SiO ₂ film 9 was further formed by sputtering on the 1.5 μm Ti metal film 8 to form a two-layer film, and the same test as in the comparative example described above was conducted for 6 hours. Incidentally, although a crack appeared in the SiO ₂ film 9, the Ti metal film 8 was not oxidized, retained its initial metallic luster, and functioned satisfactorily as a mask.

Note that in order to form the Ti metal film 8 and the SiO ₂ film 9 into desired patterns, various methods can be employed using known photolithography techniques. For example, Ti may be applied to the entire surface of one side of the glass substrate 1.
After forming the metal film 8 and the SiO ₂ film 9 in sequence, these films 8 and 9 can be sequentially etched into a desired pattern, or after forming the Ti metal film 8 in the desired pattern, the SiO ₂ film can be etched. It is also possible to form 9 and etch it.

Next, for comparison with the method according to the present invention, a SiO ₂ film with a thickness of approximately 1 μm was directly deposited on the glass substrate 1 by sputtering, and after desired patterning was performed, the same process was performed as in the comparative example described above. When ion diffusion was performed by applying an electric field, a high refractive index layer was formed on the entire surface of the glass substrate 1 on the mask layer 2 side, and SiO ₂
It has also become clear that a mask alone cannot function as a mask.

From the above tests, the Ti metal film functions as a mask layer for blocking ion passage, but it oxidizes and forms TiO ₂
It was discovered that once it becomes a film, it does not function as a mask. On the other hand, when a SiO ₂ film is attached on top of a Ti metal film, the SiO ₂ film allows ions to pass through but not O ₂ gas, etc., so the SiO ₂ film prevents the Ti metal film from oxidizing. This two-layer film was found to be useful as a mask in the electric field applied ion diffusion method. Note that the oxide film or nitride film used to prevent oxidation of the metal film usually has a different expansion coefficient from the underlying metal, so it is not recommended to make it too thick to prevent peeling.
A thickness of about 0.3 μm is sufficient.

Although the present invention has been described above with reference to Examples, the present invention is not limited to these Examples.
Various modifications are possible based on the technical idea of the present invention.

For example, a two-layer film in which a Si ₃ N ₄ film is formed on a Ti metal film by the CVD method, a two-layer film in which an SiO ₂ film is formed on an Al metal film or a Cr metal film is used as the mask layer 2. When similar tests were conducted, it was found that all of them functioned satisfactorily as masks. In addition, the electric field applied ion diffusion method is particularly useful as it takes 1/3 to 1/4 of the processing time compared to the ion exchange method, so in the above explanation, only the electric field applied ion diffusion method was explained, but the present invention It goes without saying that the method can be applied to forming a refractive index distribution on a transparent member such as a glass substrate using the ion exchange method.

As described above, when forming a desired pattern of refractive index distribution in a transparent member by ion exchange or ion diffusion, the present invention combines a metal film and an oxide film or nitride film laminated on the metal film. Since the mask layer for blocking ion passage consisting of a layered film is formed, the passage of ions can be extremely well blocked by the mask layer, thereby obtaining a desired good refractive index distribution. I can do it.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention using an electric field applied ion diffusion method, in which Fig. 1 is a schematic vertical cross-sectional view of an electric field applied ion diffusion device, and Fig. 2 is a cross-sectional view of the glass substrate shown in Fig. 1. A partial plan view, FIG. 3 is a sectional view taken along the line -- in FIG. Regarding the symbols used in the drawings, 1...
... glass substrate, 2 ... mask layer, 3 ... opening,
It is.

Claims (1)

[Claims] 1. By forming a mask layer for blocking ion passage in a desired pattern on the surface of a transparent member, and performing ion exchange or ion diffusion through the openings of this mask layer, the desired pattern is formed in the transparent member. In a method for manufacturing a refractive index distribution type transparent member that obtains a refractive index distribution according to A method for producing a gradient index transparent member, characterized in that the ion exchange or ion diffusion is performed after forming the ion passage blocking mask layer consisting of a double layer film or a nitride film.