JPH02168207A - Forming method for curved waveguide - Google Patents

Abstract

PURPOSE:To reduce a coupling loss of a waveguide and an optical fiber by leading an ion into a curved waveguide forming area of a substrate, and subsequently, bringing the ion which is led into thermal diffusion, and leading the ion into a diffusion area of this ion. CONSTITUTION:The method is provided with a first ion leading-in process for leading an ion into a curved waveguide forming area 22 of a substrate 20, a heat treatment process for bringing the ion which is led into the substrate 20, to thermal diffusion, and a second ion leading-in process for leading the ion into a diffusion area 28 of the ion which is brought to thermal diffusion. By this thermal diffusion, a distribution of the ion in the depth direction of the substrate 20 can be extended. Also, by the ion which is brought to thermal diffusion, and the ion which is led into a second ion leading-in process, a waveguide in which a confinement action of light is strong in the waveguide width direction can be formed. In such a way, a radius of curvature is made small enough, and also, a coupling loss of the waveguide and an optical fiber is reduced.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for forming curved waveguides.

(Prior Art) Curved waveguides with various structures that can reduce loss at curved portions have been proposed. This kind of curved waveguide is described in the document IrOptical En9ineer, for example.
inq (Optical Engineering) January
ary 1988 Vol, 27 No, I p
p, 2-9 J I Like what you suggest, T1
There is a structure in which an ion exchange layer is provided at the bend of a curved waveguide formed by diffusion. Hereinafter, a method for forming this curved waveguide will be explained with reference to the drawings.

FIG. 6 is a diagram used to explain the conventional method for forming a curved waveguide. WIG-ITI
Figure (D) showing an enlarged cross-section taken along the IC line
2 is an enlarged view showing a cross section taken along the VID-VID line in FIG.

As shown in FIGS. 6A and 6C, in the conventional forming method, T1 is first diffused into the waveguide formation region of the substrate 10, for example, the LIN b 03 substrate. The Ti diffusion layer formed by this diffusion is shown with a dot and a reference numeral 12 in the figure.

Next, as shown in FIGS. 6(8) and 6(D), an ion exchange layer 14 is formed on the Ti diffusion layer 12 forming the curved portion of the curved waveguide. This ion exchange layer 14 is shown with hatching in the figure. The Ti diffusion layer 12 and/or the ion exchange layer 14 form a high refractive index region or waveguide that can substantially confine light.

The ion exchange layer 14 is formed by introducing ions, such as protons (H''), into the VTi diffusion layer 12 by ion exchange techniques.

The light confinement effect of the ion exchange layer 14 in the direction along the surface of the substrate 10 is strong, and therefore the loss at the curved portion of the waveguide is reduced.

Figure 7 is a diagram used to explain another conventional method.
A) is a plan view of the curved waveguide, and figure (B) is a cross-sectional view taken along the line ■B--■B in figure (A).

In another conventional method, a curved waveguide is formed by forming only the ion exchange layer 14 on the substrate 10, as also shown in FIGS. 7(A) and (8).

(Problem to be Solved by the Invention) However, in the above-mentioned conventional method, the Ti diffusion layer 12
The ion exchange layer 14 is formed by introducing ions into the substrate. The ion exchange rate in the TiVrA layer 12 is slow;
Therefore, there is a limit to increasing the ion concentration in the Ti diffused layer 12, and there is also a limit to the depth f (see CD in FIG. 6) into which ions can be introduced into the Ti diffused layer 12. For this reason, a curved waveguide in which the radius of curvature R of the curved portion is sufficiently small (for example, 10 mm or less) could not be obtained.

In addition, with other conventional methods, it is possible to obtain a curved waveguide with a sufficiently small radius of curvature R, but the depth 9 (see Fig. 7 (8)) of which one ion can be irradiated with respect to the substrate 10 is limited. As a result, the spread of the field distribution in the depth direction of the substrate 10 cannot be made close to the core diameter of the optical fiber, resulting in a disadvantage that the coupling loss between the waveguide and the optical fiber increases.

The purpose of this invention is to solve the problems of the conventional method mentioned above,
It is an object of the present invention to provide a method for forming a curved waveguide that can sufficiently reduce the radius of curvature and reduce coupling loss with an optical fiber.

(Means for Solving the Problems) In order to achieve this object, the curved waveguide forming method of the present invention includes a first ion introduction step of introducing ions into the curved waveguide forming region of the substrate, and a step of introducing ions into the curved waveguide forming region of the substrate. It is characterized by comprising a heat treatment step for thermally diffusing the introduced ions, and a second ion introduction step for introducing ions into the diffusion region of the thermally diffused ions.

(Function) According to such a formation method, ions are first introduced into the curved waveguide formation region of the substrate in the first ion introduction step, and then the ions introduced into the substrate are thermally diffused in the heat treatment step. This thermal diffusion can widen the distribution of ions in the depth direction of the substrate.

Next, in a second ion introduction step, ions are introduced into the diffusion region of the thermally diffused ions. A waveguide with a strong light confinement effect in the waveguide width direction can be formed by the thermally diffused ions and the ions introduced in the second ion introduction step.

(Examples) Examples of the present invention will be described below with reference to the drawings. Note that the drawings are merely shown schematically to the extent that the present invention can be understood, and therefore the shapes, dimensions, and arrangement values of each component are not limited to the illustrated examples.

1(A) to 1(D) are cross-sectional views showing step by step the main steps in an embodiment of the present invention, and FIG. 2(A)
- (D) are plan views showing step by step the main steps in an embodiment of the present invention.

Figure 1 (A) is the construction A-IA in Figure 2 (A).
Figure 1 (B) is a cross section taken along the I B-I B line in Figure 2 (B), and Figure 1 (C) is a cross section taken along the IC-IC line in Figure 2 (C). Figure 1 (D) shows a cross section along the IQ-ID line in Figure 2 (D), and roughly shows Figure 2 (A), CB), (C) and C.
D) are respectively shown in Fig. 1 (A), (B), (C) and (D
) shows the process at the same stage.

In this embodiment, first, for example, iNbx is used as the substrate 10.
8 Ta+-x○3 substrates (○≦X≦1) are prepared.

As shown in Figure 1 (A) and Figure 2 (A),
Seven masks 24 are formed on the substrate so that the substrate surface 20a of the curved waveguide forming region 22 of the substrate 20 is exposed and seven portions of the substrate 20 other than the region 22 are exposed. The mask 24 may be, for example, a two-layer mask made of Cr and SiO2 that are laminated sequentially from the substrate side, a mask made of Cr, or a mask made of A! This is a mask etc.

Next, as shown in FIGS. 1(B) and 2(B), ions are introduced into the curved waveguide forming region 22 of the substrate 20 (
(first iontophoresis step). The region into which ions were introduced in this step (first 0-person region) is shown with the reference numeral 26 and hatching in the figure.

In the ion introduction process of this embodiment, the substrate 20 is immersed in a molten salt (for example, a molten salt of benzoic acid or a molten salt of birophosphoric acid), and ion exchange PA is performed as usual. Ions (e.g. protons H”) are transferred to the substrate 2.
Introduced into 0. At this time, the temperature of the molten salt is set to 250, for example.
Keep at °C.

Next, as shown in FIGS. 1(C) and 2(C), the substrate 20 is taken out from the molten salt and cleaned.

Next, the ions introduced into the substrate 20 in the first ion introduction step are thermally diffused (heat treatment step). The region 12 (dispersion Kt) in which ions are diffused in this step is indicated by the reference numeral 28 and an open circle in the figure.

In the heat treatment process of this embodiment, the heating temperature of the substrate 20 is set to a temperature higher than the holding temperature of the molten salt during ion introduction, for example, 4.
The temperature should be around 00°C. By arbitrarily setting the heating temperature and heating time in the heat treatment step, the ions in the first introduction region 26 are diffused in the depth direction of the substrate 20, so that the ion distribution in the depth direction of the substrate 20 can be set arbitrarily and suitably. It can be expanded widely. Moreover, the distribution of ions in the depth direction can be made wider than before.

Following the heat treatment process, the diffusion region 2 of thermally diffused ions
81 Introducing ions (second ion introduction step), the region into which ions were introduced in this step (second introduction region),
In the figure, the reference numeral 30 and hatching are shown.

In the second ion introduction step of this embodiment, the substrate 20 is immersed in a molten salt and ion exchange is performed in a conventional manner, thereby introducing ions into the substrate 20. On this occasion,
The temperature of the molten salt is maintained at, for example, 250° C., and the substrate 20 is held in this molten salt for 1 to 3 hours.

A high refractive index region that can substantially confine light is formed by the diffusion region 28 and the Tsuta 9M region 30, and this high refractive index region constitutes a waveguide.

Following the second ion implantation step, the mask 24 is removed from the substrate, thus obtaining a substrate 20 with a curved waveguide having a predetermined shape.

By forming a waveguide with the diffusion region 28 and the second introduction region 30, it is possible to obtain a waveguide with greater light confinement in the direction along the substrate surface than conventional ones,
Therefore, even when a curved waveguide having a curved portion with a smaller radius of curvature than the conventional one, for example, 10 mm or less, loss can be reduced to a level suitable for practical use.

In addition, by widening the ion distribution in the depth direction of the substrate in the heat treatment process, the spread of the field distribution in the depth direction of the substrate 20 can be made closer to the core diameter of the optical fiber than before. The coupling loss between the optical fiber and the optical fiber can be reduced compared to the conventional method.

Fig. 3 is a diagram showing the loss characteristics of the curved waveguide formed in this example, and the vertical axis of Fig. 3 is the loss (dB/ra).
d) and the horizontal axis indicate the radius of curvature R (mm).

In Figure 3, the dotted line indicates the wavelength λ of the guided light.
This is a curve showing loss characteristics when a single mode waveguide is formed with 1.3 urn and t in the waveguide (corresponding to the width of the region 22, see FIG. 2(A)) being 7 um. λ
When a single mode waveguide is formed by the conventional method with = 1.3 um and t = 7 um, the radius of curvature is approximately 0 ~
In the region of 3mm, there is a loss so large that it cannot be measured, and when R = 4.7um, the loss is approximately 6d.
B/rad, and the loss can be reduced the most.

Roughly speaking, the curve shown by the dashed line in Figure 3 is λ0.85.
Loss characteristics when a single mode waveguide is formed with um and t=7um! The curve showing λ and the curve showing solid line are λ
This is a curve showing loss characteristics when a single mode waveguide is formed with =0.63 um and t = 7 um.

In addition, the first straight 8 was achieved only by Ti diffusion! A dedicated waveguide is formed, and a second straight waveguide is formed by the diffusion region 28 and the second introducing region 30 as in this embodiment, and the wavelength λ and width t of these waveguides are the same, and these straight waveguides are formed. When the loss of the J waveguide was compared, the loss of the second straight waveguide increased more than the loss of the first straight waveguide, but this increase was 5 dB or less. Among these losses, we calculated the coupling loss with the optical fiber by considering the propagation loss, and found that the coupling loss of the second straight waveguide is worse than the coupling loss of the first straight waveguide, but this deterioration is less than 12 dB. We were able to.

A third straight waveguide was formed by ion exchange only with the same wavelength λ and width t, and the coupling loss between this third straight waveguide and the first straight waveguide was compared. The coupling loss of the waveguide is 10 dB lower than that of the first straight waveguide.
It got worse soon.

In the embodiment described above, the second introduction region 30 was formed over the entire curved waveguide forming region 22, but the second introduction region 3
The arrangement position of the second introduction region 30 is not limited to this, but can be any suitable position that can improve the confinement of light in the direction along the substrate surface (waveguide width direction). may be provided in part or all of the region 22. Hereinafter, other examples of the arrangement position of the second introduction region will be explained with reference to FIGS. 4 and 5. In the following description, points that are different from the embodiments described above will be explained, and detailed explanations of points similar to the embodiments described above will be omitted.

FIG. 4 is a diagram for explaining the arrangement values of the second introduction region, and FIG. 4 (A) is a curve formed in the same manner as in the above-mentioned embodiment] A plan view and a diagram (B) of a substrate provided with a wave path. Figure (A)
FIG. 2 is a sectional view taken along the line VB-VB in FIG. Note that the same components as those in the above-described embodiments are designated by the same reference numerals.

In the example shown in FIG. 4, the second introduction region 30 is, for example, a portion that corresponds to a curved portion of the curved waveguide, and the center of curvature of the curved portion O.
It is provided in the area 22 on one side of the side.

In this example as well, a waveguide with strong light confinement in the waveguide width direction can be formed.

FIG. 5 is also a diagram for explaining the arrangement position of the 21st observation area, and FIG. 8) is shown in figure (
It is a sectional view taken along the VB-VB line in A). It should be noted that the same components as those in the above-mentioned embodiments are denoted by the same reference numerals.

In the example shown in FIG. 5, the second introduction region 30 is divided into, for example, a region 22 corresponding to the curved portion of the curved waveguide and a region 32 outside the region 22 and on the side of the center of curvature O (center side region). establish. Even in this example, a waveguide with strong light confinement in the width direction of the waveguide can be formed. , the forming material can be changed as desired.

In addition, in the above-mentioned embodiments, specific materials and numerical conditions were cited and explained in order to deepen the understanding of the present invention, but these are only examples, and therefore the materials and numerical conditions must be considered within the scope of the purpose of the present invention. It can be changed as desired.

(Effects of the Invention) As is clear from the above description, according to the curved waveguide forming method of the present invention, ions are introduced into the curved waveguide forming region of the substrate in the first ion introduction step, and then The ions introduced into the substrate in the heat treatment step are thermally diffused.Next, in the second ion introduction step, ions are introduced into the diffusion region of the thermally diffused ions to form a curved wave path.

Thermal diffusion in the heat treatment process can widen the distribution of ions in the depth direction of the substrate, and as a result, the field distribution in the depth direction of the substrate can be brought closer to the core diameter of the optical fiber. Therefore, the coupling loss between the waveguide and the optical fiber can be reduced compared to the conventional method.

In addition, by forming a curved waveguide with the thermally diffused ions and the ions introduced in the second ion introduction step, a waveguide with a larger light confinement effect in the width direction of the waveguide than before can be obtained. be able to. Therefore, even when forming a curved waveguide having a curved portion with a radius of curvature smaller than that of the conventional one, for example, 10 mm or less,
Loss can be reduced to a level suitable for practical use.

[Brief explanation of the drawing]

Figures 1 (A) to (D) are cross-sectional views for explaining the invention in detail, Figures 2 (A) to (D) are plan views for explaining the invention in detail, and Figure 3 is an embodiment. A diagram showing the loss characteristics of a waveguide formed by the method of FIG. 6(A) to 6(D) are diagrams illustrating the conventional method, and FIG. 7(A) to (B) are diagrams explaining the conventional method. It is a figure provided for explanation of another method. 20...Substrate, 22...Curved waveguide forming region 26...First introduction region, 28...Diffusion region 3
0...Second introduction area, 32...Center side area. Patent source Oki Electric Industry Co., Ltd. Plan view for explanation of the example Fig. 2 Radius of curvature R (mm) 0.5 Waveguide loss characteristics Fig. 2 Fig. 2 Arrangement position of the second introduction region Fig. 4 Arrangement values of the second introduction area] Fig. 5 Fig. 6 Fig. 6 Explanatory diagram of other conventional methods Fig. 7

Claims (1)

[Claims] (1) A first ion introduction step of introducing ions into the curved waveguide forming region of the substrate, a heat treatment step of thermally diffusing the ions introduced into the substrate, and introducing ions into the diffusion region of the thermally diffused ions. A method for forming a curved waveguide, comprising: a second ion introduction step.