JPH03259204A - Optical wavegiide substrate by diffusion of material for increasing refractive index - Google Patents

Abstract

PURPOSE:To obtain excellent optical characteristics by diffusing a material for decreasing the refractive index into a substrate deeper than the waveguide formed by diffusing a material for increasing the refractive index into the substrate and shallower than in a surface waveguide layer. CONSTITUTION:Ti is thermally diffused into the waveguide forming region of the LiNbO3 substrate 1, by which the Ti diffused waveguide 2 is formed. The surface waveguide layer 3 is then formed deeper than the Ti diffused waveguide layer 2. Further, MgO is additionally diffused in a dry atmosphere to form the low-refractive index layer 3a deeper than the Ti diffused waveguide 2 and shallower than the surface waveguide layer 3. Since the surface waveguide layer 3 is formed with the sufficient depth, the control of the depth of this diffusion is relatively easily executed. The respective layers are, therefore, formed in such a state that the waveguide 2 of the refractive index is enclosed circumferentially with the low-refractive index 3a and the high-refractive index layer 3b remains under the low-refractive index layer 3a. The optical waveguide having the good property to confine light is thus obtd. The excellent optical characteristics are obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an optical waveguide substrate used for optical integrated circuits or optical functional devices.

“Prior Art” A Ti-diffused L iN bo 3 waveguide fabricated by thermally diffusing Ti into a L i N bo s substrate is
Useful as a single mode waveguide. Also, LiNbO
Since the third crystal is an EO (electro-optic) crystal, the optical properties of the waveguide layer can be controlled by applying an electric field, and therefore it can be applied to optical switches, optical modulators, or mode converters. .

Now, in the process of manufacturing a Ti-diffused LiNbO5 optical waveguide, when Ti is thermally diffused in a dry atmosphere, Ti is diffused into the LiNbO5 substrate and at the same time LttO is released from the crystal surface (hereinafter, this phenomenon LitO
(called out-diffusion). When LiO is diffused out, a surface waveguide layer with a high refractive index is formed on the surface of the LiNbO3 substrate due to the escape of LiO, which causes a problem in that the confinement of extraordinary rays from the outside becomes weak. .

On the other hand, when Ti diffusion is performed in a wet atmosphere, L
Outward diffusion of izo is suppressed to some extent. in particular,
A method has been reported in which Ti is thermally diffused in a purged atmosphere of Ar or N containing water vapor at a temperature of around 1000°C. However, even when such a method is used, a surface waveguide layer is still formed at a depth of several microns from the surface of the LiNbO3 substrate. FIG. 3 illustrates a cross-sectional view of a Ti-diffused LiN b Os waveguide taken along a plane perpendicular to the optical propagation axis when Ti is diffused in a wet atmosphere as described above. In this figure, l
is an L zN bos substrate, 2 is a waveguide formed by Ti diffusion, and 3 is a surface waveguide layer formed by out-diffusion of Lizo. When the surface waveguide layer 3 is formed in this manner, the light propagating through the waveguide 2 leaks laterally (arrows La and Lb), and the confinement of light within the waveguide 2 becomes weaker. In particular, as shown in FIG. 4, the leakage of light in the lateral direction (arrow Lc) increases at locations where the waveguide 2 is curved. Furthermore, since the depth of the Ti diffused waveguide 2 is on the order of several μm, like the surface waveguide layer 3, the optical characteristics of the Ti diffused waveguide are adversely affected.

Therefore, a method has been proposed in which Ti is diffused in a wet atmosphere to form a waveguide as described above, and then MgO is additionally diffused. According to this method, by doping MgO, the refractive index of the surface waveguide layer is reduced and light confinement within the waveguide is improved, and the refractive index distribution within the waveguide is improved. This provides the effect that the spot shape of the propagating light becomes approximately circular.

"Problems to be Solved by the Invention" However, when Ti is diffused in a wet atmosphere, the thickness of the surface waveguide layer formed on the substrate cannot be controlled; is also highly sample dependent. Therefore, as described above, when additional diffusion of MgO is performed, if the depth to which MgO is diffused is not appropriate, there is a problem that the optical characteristics of the waveguide deteriorate. For example, as shown in FIG. 5(a), the MgO diffusion layer 3a is connected to the waveguide 2.
If it is formed shallower than this, the bottom of the waveguide 2 will still be in contact with the surface waveguide layer 3 having a high refractive index, resulting in light leakage through this bonding surface. Furthermore, as shown in FIG. 5(b), when the diffusion of MgO proceeds deeper than the surface waveguide layer 3, a low refractive index layer 1b having a lower refractive index than the LiNbO3 substrate is formed under the surface waveguide layer 3. It will be done. As a result,
The refractive index of the surface waveguide layer 3 in which MgO is diffused is n3, and the refractive index of the low refractive index layer 1b below the surface waveguide layer 3 is n+b.
When the refractive index of the LiN bo 3 substrate l is nl, the relationship n+b<n+<ns holds, and light propagates through the surface waveguide layer 3.

This invention was made in view of the above circumstances,
It is an object of the present invention to provide an optical waveguide substrate using diffusion of a high refractive index material that has excellent optical properties and can be manufactured stably.

"Means for Solving the Problems" The present invention forms a waveguide on the surface of a substrate by diffusing a high refractive index material onto the substrate in a dry atmosphere. , deeper than the waveguide, and shallower than the surface waveguide layer formed with the formation of the waveguide, and is characterized by having a low refractive index material diffused therein.

"Operation" In the case of the above configuration, the relationship of the depth of the waveguide, the depth of the low refractive index layer, and the depth of the surface waveguide layer is established, and light propagates only within the waveguide. In addition, since both the high refractive index material and the low refractive index material are diffused in a dry atmosphere, it is easy to control the depth relationships of each layer as described above, and a high yield can be achieved during manufacturing. can get.

Embodiment An optical waveguide substrate using diffusion of a high refractive index material according to an embodiment of the present invention will be described below. In this example, L
Ti is used as a high refractive index material for the iNbO3 substrate.
The case where MgO is diffused as a material for lowering the refractive index will be explained as an example. In addition to L iN b Os, the substrate materials include L iT ao 2 and PLZT.

It is possible to use an oxide dielectric material such as S B N ST iB ao 3, ZnO, or a glass material such as quartz glass or optical glass. In addition to Ti, high refractive index materials used as waveguide materials include T11SFe, Ag
, La, Y, etc. can be used. In addition to MgO, materials for lowering the refractive index include Na, O1LitO
It is possible to use lBed, F, B2O2, etc.

Now, with reference to FIG. 1, a method of manufacturing an optical waveguide substrate according to this embodiment will be explained. First, for example, by a lift-off method, a waveguide formation region of the LiN bos substrate 1 is
Ti is selectively sputtered. Next, Ti is thermally diffused in a dry atmosphere. As a result, Figure 1 (
As shown in a), the Ti diffused waveguide 2 is formed and LizO is diffused out to form a surface waveguide layer deeper than the Ti diffused waveguide 2 with a thickness of about 100 μm. 3 is formed. When looking at the distribution of refractive index within the surface waveguide layer 3 with the surface waveguide layer 3 formed deeply in this way, the refractive index is low near the surface and reaches its maximum at a considerable depth from the surface. There is. Therefore, light does not propagate within the surface waveguide layer 3 unless the light is introduced from a position deeper than the position where the refractive index is maximum.

Next, additional diffusion of MgO is performed in a dry atmosphere, and a second
As shown in Figure (b), deeper than the Ti diffusion waveguide 2,
Moreover, a low refractive index layer 3a is formed shallower than the surface waveguide layer 3. This diffusion depth can be controlled relatively easily because the surface waveguide layer 3 is formed with a sufficient depth. As a result, the high refractive index waveguide 2 is surrounded by the low refractive index layer 3a, and each layer is formed with the high refractive index layer 3b remaining below the low refractive index layer 3a. An optical waveguide with good light confinement properties can be obtained.

"Effects of the Invention" As explained above, according to the present invention, by diffusing a high refractive index material onto a substrate in a dry atmosphere, a waveguide is formed on the surface of the substrate, and a waveguide is formed on the surface of the substrate. Since the low refractive index material is diffused in the atmosphere deeper than the waveguide and shallower than the surface waveguide layer formed with the formation of the waveguide, it has excellent optical properties and , it is possible to realize an optical waveguide substrate by diffusion of a high refractive index material that can be manufactured at a high yield.

[Brief explanation of drawings]

FIG. 1 shows Ti-diffused LiNb0 according to an embodiment of the present invention.
．． FIG. 2 is a diagram illustrating the method of manufacturing an optical waveguide, FIG. 2 is a diagram showing the refractive index distribution in the surface waveguide layer 3 in the same example, and FIG.
5 to 5 are diagrams for explaining the problems of Ti-diffused L i N bo 3 manufactured by the conventional manufacturing method. Figure 1 To) +1) 1 1...L iN bo , substrate, 2...
・Ti diffusion waveguide, 3...Surface waveguide layer, 3a・
...Low refractive index layer, 3b...High refractive index layer.

Claims (1)

[Claims] A waveguide is formed on the surface of the substrate by diffusing a high refractive index material into the substrate in a dry atmosphere, and a waveguide is formed deeper than the waveguide in the dry atmosphere. An optical waveguide substrate by diffusion of a high refractive index material, characterized in that the low refractive index material is diffused shallower than the surface waveguide layer formed in conjunction with the formation of the waveguide.