JPS63201042A - Production of optical device by ion exchange - Google Patents

Abstract

PURPOSE:To accurately control the ion exchanging time by heating and cooling a substrate with a molten salt without causing the variations in the refractive index of the substrate when the glass substrate is brought into contact with another high-temp. molten salt to exchange ions. CONSTITUTION:A first vessel 2 and a second vessel 4 are set in an electric heating furnace 1, a first molten salt 3 substantially without causing the variations in the refractive index of the glass substrate 6 is charged into the first vessel 2, and a second molten salt 5 for ion exchange contg. at least one kind of monovalent cation is charged into the second vessel 4. Under such a constitution, the inside of the heating furnace 1 is heated to an ion-exchange temp. while dipping the glass substrate 6 in the first molten salt 3. The glass substrate 6 is then transferred into the second molten salt 5, ions are exchanged between the molten salt 5 and the substrate to vary the refractive index in the specified region in the substrate 6, and an optical device is integrally formed in the substrate 6. When specified ion exchanging is finished, the substrate 5 is again returned into the first molten salt 3, and the inside of the heating furnace 1 is cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming optical elements such as optical waveguides in a glass substrate by ion exchange, and particularly to a method that can accurately control the ion exchange treatment time.

[Conventional technology]

An ion exchange method is known as an effective method for integrally forming optical elements such as optical waveguides and lenses in a glass substrate.

In the ion exchange method, a substrate is made of glass containing at least l@ monovalent cations, the surface of this substrate is covered with an ion permeation prevention mask material leaving an opening of a specific shape, and a high temperature molten salt is brought into contact with this surface. By exchanging ions in the substrate glass with ions in the molten salt through the mask opening, the refractive index of the substrate glass is partially changed to increase the refractive index. During the above ion exchange treatment, if a glass substrate at room temperature is brought into direct contact with a molten salt kept at a predetermined high temperature, it will cause deformation of the substrate, an abnormality in the refractive index distribution, etc. The temperature of both is gradually raised, and after reaching a predetermined ion exchange treatment temperature, it is held for a certain period of time, and then the temperature of both is lowered.

[Problem that the invention seeks to solve]

However, in the conventional method described above, even if the contact treatment time between the molten salt and the substrate glass at a constant temperature is precisely matched to the theoretically required exchange time, the actual The refractive index changes due to ion exchange even during heating or cooling processes, making it difficult to accurately control the effective ion exchange time.

That is, in the case of natural ion exchange, it was actually unavoidable than the set time.

[Means for solving problems]

In order to solve the above-mentioned conventional problems, the present invention raises or lowers the temperature of the substrate before or after the ion exchange treatment for forming an optical element, using a substrate glass different from the molten salt for the treatment. This is done by immersing the substrate in a molten salt that does not substantially change the refractive index.

The molten salt for heating or cooling the substrate used in the present invention does not need to have a composition that does not substantially prevent ion exchange with the substrate glass, and even if ion exchange occurs, the refractive index of the substrate glass will change. It is sufficient if the composition does not change substantially.

[For production]

According to the above method, there is almost no change in the refractive index that affects the characteristics of the optical element during the temperature raising or cooling process, and the contact treatment time with the original molten salt at a constant temperature is almost the effective ion exchange time. The coincidence makes it possible to precisely control the ion exchange time.

In addition, since the glass substrate is in contact with the molten salt while the temperature is rising or falling, causes of surface deterioration such as thermal shock can be eliminated to a considerable extent compared to when the glass substrate is exposed to air.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

In FIG. 1, a first container 2 and a second container are placed in an electric heating furnace l.
Containers ≠ are placed, one container 2 stores the first molten salt 3, and the other container l stores the second molten salt j.

The first molten salt 3 is for raising and lowering the temperature of the glass substrate, the second molten salt j is for ion exchange treatment, and the glass substrate 6 is subjected to a predetermined ion exchange treatment by immersion in the first molten salt j. First, it is immersed and held in the first molten salt 3.

The substrate 6 is 5i02. Besides BzO3 and divalent cation oxides, about 10% Na2O and about 3
It consists of a glass with a composition containing 20%.

One side of the substrate B is coated with a Ti thin film, leaving an opening for a predetermined optical waveguide pattern.

The first melt jfiJ is NaNO3:KNO3−/0
: It is a mixed salt prepared at a ratio of 3:3, and even if it contacts the glass substrate 6 in a molten state, the Na:to ratio is the same as the Na:to ratio inside the glass substrate, so it is substantially ion-free. No exchange occurs. As the first molten salt 3, in addition to the above composition, a mixed salt of NaNO3 and KNO3, etc., which does not substantially change the refractive index of the glass substrate B even if ion exchange occurs, can be used.

In addition, as the glass substrate 6, TI! When using an oxide containing ions that increase the refractive index, such as or Os, a molten salt containing sulfate or nitrate of Tl or Cs can be used as the first molten salt 3. good. Preferably, the composition of the first molten salt 3 is such that it contains cations in substantially the same content ratio as the monovalent cations that can be ion-exchanged contained in the glass substrate.

With the substrate B immersed in the first molten salt 3 as described above, the temperature inside the heating furnace L is raised, and when the predetermined ion exchange treatment temperature is reached, the substrate 6 is immersed in the second molten salt 3 as shown in FIG. Molten salt!
Move inside.

Second molten salt! is a mixed salt prepared in the ratio of TlNO3:NaNO3-2:. When it comes into contact with the glass substrate 6 in a molten state, mainly Na in the glass substrate 6 and Tl in the molten salt j partially undergo ion exchange. The refractive index increases.

In addition to the composition described above, various mixed salts containing ions that increase or decrease the refractive index of the glass substrate B can be used as the second molten salt j.

Then, after immersing it in the molten salt for a certain period of time and performing the prescribed ion exchange treatment, the substrate is reused! is returned to the first French molten salt 3 and the temperature inside the heating furnace is lowered.

In the above-mentioned example, the molten salt was immersed in a molten salt having a composition different from that for ion exchange treatment during both the temperature raising and temperature lowering processes, but the J! i! Seed molten salt molten salt pickling may also be performed.

In addition to the above-mentioned composition, the glass substrate 6 may be made of, for example, TI.
! A borosilicate glass containing K.20 can also be used, and the composition K is not particularly limited. Furthermore, as monovalent ions for ion exchange, in addition to the aforementioned Na1K and TJ, O8,
Rb and Ag can also be used.

〔Effect of the invention〕

According to the present invention, the ion exchange time can be controlled to a positive value, and the actual ion exchange time can be sufficiently shortened regardless of the time required to raise or lower the temperature. Optical elements with extremely small cross-sectional areas, such as single-mode optical waveguides, which could not be manufactured using the ion exchange method, can also be formed in a substrate with high precision.

[Brief explanation of the drawing]

The drawings show one embodiment of the invention, and FIG. 1 shows a solution for heating a substrate prior to ion-exchange treatment. 7 is a sectional view showing the salt immersion stage, and FIG. 2 is a sectional view showing the ion exchange treatment stage. /... Heating furnace Ko, II... Molten 1i!
! Broken container 3...Metal i for raising (or lowering) the temperature of the substrate
! l! Salt j... Molten salt for ion exchange treatment 6...
・・・Glass substrate

Claims (1)

[Claims] A high-temperature molten salt containing at least one type of monovalent cation is brought into contact with the surface of the glass substrate, and the refractive index of a specific region within the glass substrate is changed by exchanging the ions with ions in the glass. In a method for manufacturing an optical element by ion exchange, in which an optical element is integrally formed in a substrate by changing the ion exchange temperature, the ion exchange treatment by contacting with the molten salt or (
and) an ion exchange characterized in that at least part of the subsequent temperature raising or (and) temperature lowering treatment of the substrate is performed by immersing the substrate in another molten salt that does not substantially change the refractive index of the substrate. A method for manufacturing an optical element.