JPS63206709A - Production of flush type single mode light guide - Google Patents

Abstract

PURPOSE:To realize a flush type single mode light guide consisting of a waveguide having nearly a circular or elliptical shape without requiring electric field impression by executing heat ion exchange in both the 1st stage and 2nd stage of a stage for ion exchange and specifying the ion exchange conditions of the 1st and 2nd stages. CONSTITUTION:A glass substrate 1 contains the univalent ion selected from a group consisting of univalent alkali ion, univalent Tl ion and Ag ion for ion exchange. After a coating film 2a for controlling the ion exchange is deposited by evaporation on one face of the substrate 1, an aperture 2c of a prescribed waveguide pattern is formed thereon to form a mask film 2b. The substrate 1 which is subjected to the 1st stage of the heat ion exchange treatment in a 1st fused salt 4a then to the removal of the mask film 2b is thereafter subjected to the 2nd stage of the heat ion exchange treatment in a 2nd fused salt 4b. The ion exchange is so executed in this case that the products D1t1 and D2t2 of the 1st and 2nd effective ion exchange constants D1, D2 and ion exchange time t1, t2 satisfy the equations I and II.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a buried single-mode optical waveguide using an ion exchange method, and particularly to a method for manufacturing a single-mode optical waveguide PrT'A that does not require the application of an electric field.

[Conventional technology]

Systems and optical sensor systems require various single-mode optical devices for branching, merging, demultiplexing, and multiplexing. Several ion exchange methods are known as methods for producing these devices on glass substrates. However, in consideration of practical effects, it is desirable that the glass substrate waveguide be of a buried type, and that the electric field distribution be approximately the same so that the direct coupling with the single mode fiber is efficient. As a method close to the method for producing the above-mentioned waveguide using a conventionally known technique, there is a co-stage N electric field application ion exchange method. In this method, a mask film made of metal or the like is laminated on a glass substrate, then patterned into the shape of a waveguide, and brought into contact with molten salt while an electric field is applied to form a high refractive index part near the surface of the substrate. After the mask is removed, a second ion exchange is performed.

For the above method, for example, Springer-Ver.
[Integrated 0ptics] published by lag
H, Li1ienhof, as reported on page 11 of J.
It is explained in detail in the paper by et al.

Furthermore, Japanese Patent Publication No. 111-j973 discloses a method of creating an optical transmission path in a glass substrate in which the refractive index gradually decreases from the center toward the periphery in a cross section by performing two-step ion exchange. There is.

[Intermediate point that the invention attempts to solve]

The method of fabricating a waveguide using the application of an electric field has the problem of complicating the ion exchange process because it is necessary to apply an electric field to the blast furnace salt that is brought into contact with the front and back surfaces of the glass substrate.

Moreover, Japanese Patent Publication No. 1973/1973 does not specifically indicate the conditions for making the cross section of the push-in type waveguide circular or elliptical, nor does it specifically indicate the conditions for making the cross section a single mode waveguide.

The present invention aims to provide a novel method for manufacturing a buried single-mode optical waveguide having a circular or nearly elliptical cross section using a simple thermal ion exchange method that does not require the application of an electric field.

[Means for solving problems]

In order to solve the above problems, the present invention uses thermal ion exchange in both the first and second stages of ion exchange, and furthermore, it is necessary to realize an embedded waveguide with a circular or elliptical cross section. The ion exchange conditions for the first and second stage
It is clearly defined for each stage.

That is, the effective ion exchange constant N during the first thermionic exchange
The product Dltl of DI and ion exchange time t1 is,! <D
It is assumed that itl<30, and the effective ion exchange constant D2 and ion exchange time t2 during the second thermionic exchange! tiDzt2, 0.6<D2t
2<0.7jXDltl.

Ions for ion exchange that can be used in the present invention include monovalent alkali ions>f5J, Li, Na, Rb, Os ions, monovalent TA' ions, and Ag ions.

In addition to Ti+i, ion exchange masks include 5i0
A dielectric Wi film such as No. 2 can be used.

[For production]

Ion exchange between the glass substrate and the molten salt can be specified by the product Dt of the effective exchange constant of ions and the effective exchange time t. The effective exchange constant referred to here is an apparent diffusion constant when the movement of one ion is described by a diffusion equation when two types of ions are exchanged.

In general, the effective exchange chamber vkD is a function of temperature, so D
Strictly speaking, the i product is determined by integration.

By setting the Di product in the first and second stage ion exchange treatments within the above-mentioned range, a single mode optical waveguide with a nearly circular cross section can be obtained.

〔Example〕

FIG. 1 is a cross-sectional view showing step-by-step an embodiment of the present invention.

l is a glass substrate, containing Na and K as monovalent ions for ion exchange at a total of 510
g, consisting of a polished high-quality glass plate with BgO3 as the main network-forming oxide.

A T film with a thickness of about 1 μm is deposited on one side of the glass substrate l by sputtering.
A single film to be covered 2a is deposited, and openings 2C of a predetermined waveguide pattern are formed in this coating film Ja by photolithography and etching steps to form a mask film 2b.

The glass substrate l coated with the mask film 2b described above is immersed in a first melting salt <<a to perform a first-stage thermal ion exchange treatment.

The first molten salt powder a held in a crucible 3 placed in an electric furnace (not shown) is connected to a mask film xby of a glass substrate l.
It is used to increase the refractive index in the vicinity of the open loco C provided in c, and is a molten salt containing at least one first ion selected from the group consisting of heptavalent ions.

In addition to sulfate or nitrate, chloride salt is added to the molten salt solution as necessary to ensure uniform ion exchange and to prevent damage to the glass substrate.

After completing the second stage thermal ion exchange treatment, the mask film 2b is removed from the surface of the substrate l, and the substrate l from which the mask film has been removed is immersed in a second molten salt lIb to perform the second stage thermal ion exchange treatment. Perform ion exchange treatment.

The second melting chamber Ilb is used to reduce the refractive index near the surface of the glass substrate l, and is a molten salt containing at least one second ion selected from the group consisting of heptavalent ions. .

Here, the first ion and the second ion must have at least opposite effects on the glass substrate l to change the refractive index.

After completing the second stage thermionic exchange treatment, an embedded waveguide portion 5 is formed within the glass substrate l.

In the above example, Tl ions were used as the first ions and Tl ions were used as the second ions. 1st
The molten salt +a is a nitrate containing Tl ions, and the second molten salt +b is a sulfate containing ions. The temperature at which the ion exchange was performed was set at 1M degrees, which is around the glass transition point, where the ion exchange constant is large and the glass substrate l does not undergo any deformation such as warping.

Next, the ion exchange conditions in the present invention will be explained in detail.

The ion exchange between the glass substrate and the molten salt can be specified by @Dt, which is the effective exchange constant PD of ions and the effective mixing time ν time t.

The effective exchange constant referred to here is an apparent diffusion constant when the movement of one ion is described by a diffusion equation when two types of ions are exchanged.

In general, the effective exchange constant is a function of temperature, so fa
Strictly speaking, t is determined by integration.

In the examples, the ion exchange conditions for the first and second stages were discussed using the combinations shown in Table 1 (conditions are expressed as Dt products).

As shown in Table 1, the dimensions of the waveguide cross section are long axis /lI-, ? /μm1 short axis, r-13μm is obtained.

When the maximum refractive index difference is set to about o, ooq in this waveguide dimension, the waveguide becomes a single mode, and the coupling efficiency can be made relatively good for a single mode 7 eyer.

In the sample shop 6, the waveguide dimensions are too large, making it difficult to form a single mode waveguide.

In the sample stores 7 to IO, the ion exchange in the second stage progresses too much, and the waveguide dimensions become smaller, and at the same time, the maximum concentration region of the first ions becomes significantly smaller.

That is, while the waveguide cross-sectional shapes of samples A/ to &6 were generally suitable, all of the samples A7 to A/0 were inappropriate.

FIG. 2 shows the refractive index distribution of the waveguide section 5 obtained in sample Aj.

If the combination of experimental conditions is shown graphically, it will look like No. JrgJ. The ○, Δ, and X marks in the figure represent "suitable,""slightlyunsuitable," and "unsuitable," respectively.

If the Dt of the first stage ion exchange is not 3 or more, the cross-sectional dimension of the waveguide will be too small (the long axis will be IOμmH degrees or less),
Also, if it is not 30 or less, it is too large.

Also, the Dt of the second stage ion exchange is 7! of the Dt of the first stage! If it is less than %, the waveguide section will virtually disappear, and if it is less than 0.6, the second stage ion exchange will not be effective.
In other words, the waveguide does not become a buried type, but becomes a nearly semicircular waveguide.

Therefore, the effective ion exchange constant D during the first thermionic exchange
The product Di tl of 1 and the ion exchange time tl is 3 times Dl
tl×3Q, and the effective ion exchange constant D2 during the second thermionic exchange
The product D2t2 of and ion exchange time t2 is 0.6 < p2
t2<0.7! ;XDlt, it is necessary to set it to 1.

More preferably, in the first ion exchange, j <D
It is recommended that the following conditions be satisfied: ltl <, /j.

As described above, an embedded circular or elliptical waveguide can be obtained, but experiments have shown that in order to create a single mode waveguide, the refractive index difference of the waveguide needs to be 0.00 J to o, oos. I understand more.

Note that it is desirable for the refractive index difference to be small when the cross-sectional size of the waveguide is large, and for the refractive index difference to be large when the cross-sectional size of the waveguide is small, from the viewpoint of electric field distribution matching with the single mode fiber.

Generally, the desired waveguide parameters are approximately 10-. 20μm1 short axis, r-tsμm1 refractive index difference 0.
00J~o, oos.

In order to create a predetermined refractive index difference, it is necessary to select the alkali content and molten salt composition of the glass substrate. Generally, when the alkali content of the glass substrate is high, it is desirable to reduce the content of ions, which are holes contributing to the refractive index, in the molten salt composition. On the other hand, when the alkali content of the glass substrate is low, it is desirable to increase the content of ions that serve as holes contributing to the refractive index in the molten salt composition.

- As an example, waveguide diameter/fX10μm1 refractive index difference o, o
oII is recommended.

〔Effect of the invention〕

According to the present invention, it is possible to realize an embedded single-mode waveguide using thermionic exchange method, which was previously impossible.

The method of the present invention has the advantage that ion exchange is very simple because it does not require the application of an electric field, and it also has the advantage of reducing tklfM on the glass surface and non-uniformity of the waveguide, which tend to occur with the electric field application method. .

Therefore, the method for manufacturing a buried single-mode optical waveguide according to the present invention is extremely suitable for inexpensive mass production.

[Brief explanation of the drawing]

Fig. 1 is a gloss diagram showing step by step an embodiment of the present invention.
IiU is a cross-sectional view showing an example of the ion concentration distribution of the ion exchange waveguide obtained by the method of the present invention, and Figure 3 shows the product of the effective ion exchange constant and ion exchange time of the first and second stages and the waveguide dimensions. It is a diagram showing suitability and unsuitability. l...Glass substrate cb...Mask film 2C...Waveguide pattern opening≠a...First molten salt qb... Second
Melting #! Hani... Waveguide Figure 1 Figure 2

Claims (2)

[Claims] (1) Forming a mask film for ion exchange control on a glass substrate containing monovalent ions selected from the group consisting of monovalent alkali ions, monovalent Tl ions, and Ag ions as ion exchange ions; , forming a predetermined waveguide pattern on the mask film, and immersing the glass substrate at high temperature in a molten salt containing at least one first monovalent ion that changes the refractive index of the glass substrate. and removing the mask into a molten salt containing at least one second monovalent ion that changes the refractive index of the glass substrate in a direction opposite to that of the first ions. A two-step thermionic exchange method consisting of a second thermionic exchange process by immersing a heated glass substrate at a high temperature, the first
Let the product D_1・t_1 of the effective ion exchange constant D_1 during the second thermionic exchange and the ion exchange time t_1 be 3≦D_1t_1≦30, and the effective ion exchange constant D_ during the second thermionic exchange
The product D_2t_2 of 2 and ion exchange time t_2 is 0.6≦
A method for manufacturing a buried single mode optical waveguide satisfying D_2t_2≦0.75×D_1t_1. (2) Claims in which the first monovalent ion is an ion containing at least one of Tl or Cs ions, and the second monovalent ion is an ion containing at least one of Na or K ions. 2. A method for manufacturing an embedded single-mode optical waveguide according to item 1.