JPH08136751A - Optical waveguide and its production - Google Patents

Abstract

PURPOSE: To provide an optical waveguide in which high optical transmission efficiency is easily obtd. and to provide its production method. CONSTITUTION: This optical waveguide consists of a first layer comprising a KTP single crystal the refractive index of which is decreased and a second layer comprising a KTP single crystal having a pure compsn. on the first layer. The second layer functions as a waveguide layer. In the production method of this optical waveguide, a KTP single crystal thin film having a pure compsn. is formed by epitaxial growing on the first layer comprising a KTP single crystal the refractive index of which is decreased by substitution for a part of component elements of the crystal so that the second layer functions as a waveguide layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide and its manufacturing method, and more particularly to an optical waveguide using KTP and its manufacturing method.

[0002]

2. Description of the Related Art KTP (KTiOPO ₄ ) crystals have excellent non-linear optical characteristics, photoelectric characteristics and physical and chemical characteristics. For this reason, KTP with a pure composition
Various attempts have been made to form an optical waveguide by combining with a KTP having a higher refractive index than KTP having a pure composition by substituting a part of crystal constituent elements (hereinafter referred to as a high refractive index KTP). .

For example, Journal of Crystal Growth 112
(1991) P309-315 discloses that a high refractive index KTP (Rb _x K _1-x TiOPO ₄ , K is formed on a substrate made of pure KTP.
Ti _1-x Sn _x OPO ₄ , KTi _1-x Ge _x OPO ₄ , KT
There is disclosed a step index type optical waveguide in which a single crystal thin film of iOP _1-X As _x O ₄ etc.) is formed by a liquid phase epitaxial growth method and this high refractive index KTP single crystal thin film is used as a waveguide layer. High refractive index KTP is KTiOP
If it is _1-X As _x O ₄ , the substitution amount by As is 35%.
By setting (x = 0.35), the mismatch of the maximum lattice constant is stopped within 1%, and the waveguide layer (KTiOP _1-X As _x O ₄ layer) and the substrate under the light of wavelength 1.064 μm The refractive index difference with the layer (KTP layer) can be kept at 0.0177.

In addition, P136 and below in Artificial Crystal Science Bulletin 18 (2) (1989) shows Rb _x K _1-x TiOPO on a KTP single crystal substrate having a pure composition by a liquid phase epitaxial growth method.
A step index type optical waveguide formed by providing a ₄ single crystal thin film or a Cs _x K _1-x TiOPO ₄ single crystal thin film has been reported by Wang and Liu. According to this report, it is generally said that the replacement amount of Rb can be larger than that of Cs, and a good quality film can be produced. For example, Rb _x K _{1-x with} x = 0.5
The refractive index of TiOPO ₄ is n _x = 1.7731, n _y = 1.
7864, _nz = 1.8752, and the refractive index difference from the substrate is Δn _x = 0.009, Δn _y = 0.015, Δn _z =
It is 0.013.

[0005]

When a high refractive index KTP single crystal thin film is formed by a liquid phase epitaxial growth method,
Usually, the dip method is applied among the liquid phase epitaxial growth methods. In this case, the crystal growth conditions for the high-refractive-index KTP single-crystal thin film are more limited than those for forming a pure KTP single-crystal thin film.
The crystallinity and the uniformity of the crystal composition of the P single crystal thin film are likely to be lower than those of the pure KTP single crystal thin film. For this reason, it is difficult to obtain a conventional optical waveguide having a high refractive index KTP as a waveguide layer, which has a desired light propagation characteristic.

An object of the present invention is to provide an optical waveguide and a method of manufacturing the optical waveguide, which can easily obtain a high optical propagation efficiency.

[0007]

The optical waveguide of the present invention which achieves the above object comprises a first layer made of a KTP single crystal having a low refractive index, and a pure layer formed on the first layer. A second layer made of a KTP single crystal having a composition, and the second layer functions as a waveguide layer.

Further, in the method for producing an optical waveguide of the present invention which achieves the above object, a KTP single crystal whose refractive index is lowered by substituting a part of crystal constituent elements is formed on the first layer. It is characterized in that a KTP single crystal thin film having a pure composition is epitaxially grown to form a second layer functioning as a waveguide layer.

The present invention will be described in detail below. First, the optical waveguide of the present invention will be described. This optical waveguide has a low refractive index KTP (hereinafter, low refractive index KTP).
A) a first layer of a single crystal and a second layer of a pure KTP single crystal formed on the first layer, wherein the second layer is a waveguiding layer. It functions as. Here, the low refractive index KT constituting the first layer
The P single crystal is obtained, for example, by substituting a part of the crystal constituent elements of a KTP single crystal having a pure composition, and specific examples thereof include K _1-x Na _x TiOPO ₄ (0 <x ≦ 0.5)
And the like single crystals.

In the above low refractive index KTP single crystal,
The refractive index changes depending on the substitution amount of the element. For example K
The refractive index of the _1-x Na _x TiOPO ₄ single crystal decreases as the amount of substitution with Na (value of x) increases. In Fig. 1, K _1-x Na _x TiOPO was formed on a pure KTP single crystal substrate.
_{4 When a} single crystal thin film was epitaxially grown by the dip method, the molar concentration of Na ₂ O in the flux (melt) and the refractive index of the obtained K _1-x Na _x TiOPO ₄ single crystal thin film (however, pure composition The difference with the refractive index of the KTP single crystal substrate of Δn) is shown. As described above, the refractive index of the low refractive index KTP single crystal changes according to the substitution amount of the element, so that the substitution amount of the element is within a range where the substitution element (Na or the like) can be solid-dissolved The refractive index is adjusted by appropriately selecting it according to the intended use.

In the optical waveguide of the present invention, a second layer made of KTP single crystal having a pure composition is formed on the first layer. This second layer is preferably formed by, for example, an epitaxial growth method. In order for the second layer to grow epitaxially on the first layer, the surface on the side where the second layer is formed in the first layer is preferably the (100) surface, but depending on the purpose ( It may be a 011) plane, a (201) plane, or the like. When the surface of the first layer on which the second layer is formed is a surface other than the (100) plane, the first layer is preferably formed of a low refractive index KTP single crystal substrate. When the surface of the first layer on which the second layer is formed is the (100) surface,
The first layer may be formed of a low refractive index KTP single crystal substrate or a low refractive index KTP single crystal film. When the low refractive index KTP single crystal film is used as the first layer, the surface of the first layer on which the second layer is formed is preferably the (100) surface.
The first layer is (10) of a pure KTP single crystal substrate.
It is preferably formed on the (0) plane by an epitaxial growth method. The thickness of the first layer is not particularly limited.

In the optical waveguide of the present invention, the second layer functions as a waveguide layer. Further, the optical waveguide of the present invention may be a step type two-dimensional optical waveguide or an embedded type or a ridge type three-dimensional optical waveguide. Therefore, the shape of the second layer is appropriately selected according to the type and application of the intended optical waveguide.

For example, when the target optical waveguide is a step type two-dimensional optical waveguide, the second layer is formed on the first layer in the form of a flat plate thin film. Thickness h of the second layer at this time, the refractive index n ₂ of the second layer, the refractive index of the refractive index n _1, the atmospheric gas surrounding the optical waveguide when using the optical waveguide of the first layer n ₃ (where n ₃ <n ₂ ) and the wavelength λ of the light to be propagated, the following formula (I) is used to form a single mode waveguide (TM mode or TE mode). Selected to be satisfied.

[0014]

[Equation 1]

When the target optical waveguide is a buried type three-dimensional optical waveguide, the second layer is formed in a fine line shape in the recess provided in the first layer. The film thickness and width of the second layer at this time are, for example, a wavelength λ of light to be propagated is 1.06 μm, and a refractive index difference Δn between the second layer and the first layer is 5 × 10 5. ^-3 , the film thickness is 3-4μ
m, and the width is 5 to 7 μm.

In the optical waveguide of the present invention having the above-mentioned first layer and second layer, the waveguide layer comprises the second layer, and the second layer comprises a KTP single crystal thin film having a pure composition. Become. As for a KTP single crystal thin film having a pure composition, a film having high crystallinity and crystal composition uniformity can be easily obtained by an epitaxial growth method, and thus it is easy to form a waveguide layer having high light propagation characteristics.

Next, a method of manufacturing the optical waveguide of the present invention will be described. In the method of the present invention, as described above, the refractive index is lowered by substituting a part of the crystal constituent elements.
A KTP single crystal thin film having a pure composition is epitaxially grown on a first layer made of TP (low refractive index KTP) single crystal to form a second layer functioning as a waveguide layer.

The light propagation characteristic of the finally obtained optical waveguide has a pure composition K which functions as a waveguide layer in the optical waveguide.
In addition to being affected by the film thickness of the second layer made of the TP single crystal thin film, it is also affected by the refractive index of the low refractive index KTP single crystal used as the first layer. Then, the refractive index of the low-refractive-index KTP single crystal changes according to the substitution ratio of the element in the low-refractive-index KTP single crystal. Therefore, the composition of the low-refractive-index KTP single crystal used as the first layer is appropriately selected so that a desired refractive index can be obtained according to the light propagation characteristics required for the intended optical waveguide and the intended use.

As the above-mentioned first layer, a low refractive index KPT is used.
A single crystal substrate or a low refractive index KTP single crystal film may be used. In order to epitaxially grow the second layer on the first layer, the surface of the first layer on the side where the second layer is formed is preferably the (100) surface, but depending on the purpose ( It may be a 011) plane, a (201) plane, or the like. When the surface of the first layer on which the second layer is formed is a surface other than the (100) plane, the first layer is preferably formed of a low refractive index KTP single crystal substrate. When the surface of the first layer on which the second layer is formed is the (100) plane, the first layer may be formed of a low refractive index KTP single crystal substrate or may be formed of a low refractive index KTP single crystal substrate. It may be formed of a refractive index KTP single crystal film. When the low refractive index KTP single crystal film is used as the first layer, the surface of the first layer on which the second layer is formed is preferably the (100) surface. 1
The layer is preferably formed on the (100) plane of a KTP single crystal substrate having a pure composition by an epitaxial growth method.

Hereinafter, the method of the present invention using the low refractive index KPT single crystal substrate as the first layer (hereinafter referred to as method I) and the method of using the low refractive index KPT single crystal film (hereinafter referred to as "method I")
Method II) will be described separately.

First, the method I will be described. This method I
Then, a low refractive index KPT single crystal substrate is used as the first layer, and this low refractive index KTP single crystal substrate is formed by a method such as a uniform heating gradual cooling method which is one of flux methods, or a constant temperature growth method. It can be obtained by producing a bulk of a low refractive index KTP single crystal having a desired composition and then cutting out a plate having a desired shape from the bulk.

When a bulk of a low-refractive-index KPT single crystal is produced by a uniform heating / gradual cooling method or a constant temperature growth method, K ₂ O, K ₂ CO ₃ , KPO ₃ , and KH ₂ are used as starting materials for K.
PO _4, etc., TiO ₂ etc. as a starting material for Ti,
Starting materials for P include P ₂ O ₅ , H ₃ PO ₄ and KPO
₃ , KH ₂ PO _4, etc., and Na ₂ O, Na ₂ CO ₃ etc. can be used as starting materials for the substitutional elements (Na etc.), respectively. These starting materials are appropriately weighed according to the composition of the target low refractive index KTP single crystal.

When cutting a low-refractive-index KTP single-crystal substrate from a bulk of a low-refractive-index KTP single crystal, the surface of the substrate on which the KTP single-crystal thin film having a pure composition is to be formed is the (100) plane and the (011) The cutting direction is set according to the purpose so as to be a desired surface such as the surface or the (201) surface.

In method I, a second layer made of a KTP single crystal thin film is epitaxially grown as a waveguiding layer on the above-described low refractive index KTP single crystal substrate. At this time, when the target optical waveguide is a two-dimensional optical waveguide or a ridge-type three-dimensional optical waveguide, the surface of the low-refractive-index KTP single crystal substrate on which the pure KTP single crystal thin film is formed is A flat surface is acceptable. Further, when the target optical waveguide is a buried type three-dimensional optical waveguide, since a concave portion for forming the waveguide layer is required, the concave portion having a predetermined shape is formed by the ion sputtering method or the like.

In order to epitaxially grow the second layer made of a KTP single crystal thin film having a pure composition as a waveguiding layer on the low refractive index KTP single crystal substrate, it is preferable to use the liquid phase epitaxial growth method, and especially to use the dip method. Is preferred.

The KTP single crystal thin film having a pure composition can be formed by the dipping method, for example, as follows. First, a starting material, which is weighed according to the composition of pure KTP, is heated to obtain a flux (melt) at 850 to 950 ° C. Next, the low-refractive-index KTP single crystal substrate described above is dipped in this flux for 4 to 5 minutes, once pulled up to wash the surface with pure water, and then again dipped in the flux for 4 to 5 minutes. By repeating the immersion in the flux for 4 to 5 minutes and the surface cleaning with pure water a required number of times, the KTP single crystal thin film (second layer) of the desired composition having a pure composition can be formed into the low refractive index KTP described above. It can be formed on a single crystal substrate (first layer). In addition, KT of pure composition
Specific examples of the starting material for K, the starting material for Ti, and the starting material for P used for forming the P single crystal thin film are as follows.
Examples are the same as those mentioned in the description of the starting materials used for producing the bulk of the low refractive index KTP single crystal.

The shape of the second layer made of a KTP single crystal thin film having a pure composition which can be formed by the above method is as follows.
When the target optical waveguide is a single-mode step type two-dimensional optical waveguide, it is a flat-plate thin film. The film thickness h of the pure KTP single crystal thin film (second layer) at this time is the refractive index n of the pure KTP single crystal thin film (second layer).
₂ , the refractive index n ₁ of the low refractive index KTP single crystal substrate (first layer), the refractive index n _{3 of the} atmospheric gas surrounding the optical waveguide when the optical waveguide is used (where n ₃ <n ₂ ), And depending on the wavelength λ of the light to be propagated, it is selected so as to satisfy the above formula (I) as described in the optical waveguide of the present invention already described. Further, when the target optical waveguide is an embedded three-dimensional optical waveguide, K of pure composition is used.
The TP single crystal thin film is formed in a fine line shape so as to be embedded in the recess provided in the low refractive index KTP single crystal substrate.
At this time, the thickness and width of the KTP single crystal thin film having a pure composition (depth and width of the above-mentioned concave portion) are selected as described in the above-mentioned optical waveguide of the present invention.

In Method I, as described above, the low refractive index K
An intended optical waveguide is obtained by epitaxially growing a second layer made of a KTP single crystal thin film having a pure composition as a waveguide layer on the first layer made of a TP single crystal substrate.

Next, a method II using a low refractive index KTP single crystal film as the first layer will be described. The low-refractive-index KTP single crystal film used as the first layer in this method II is preferably epitaxially grown on a KTP single crystal substrate having a pure composition as described above. K of pure composition
Since the TP single crystal is already on the market, the KTP single crystal substrate having the above-mentioned pure composition may be a commercially available product or a substrate cut from a commercially available KTP single crystal having the pure composition. However, in method II, KT of this pure composition
Since the low refractive index KTP single crystal film is epitaxially grown on the P single crystal substrate to form the first layer, the first layer made of the low refractive index KTP single crystal film is formed in the pure KTP single crystal substrate. The crystal plane on the side of the
It is preferably a surface. On a crystal plane other than the (100) plane, it is difficult to epitaxially grow the first layer made of the low refractive index KTP single crystal film on the crystal plane.

Low refractive index KTP single crystal film (first layer) epitaxially grown on a pure composition KTP single crystal substrate
Is not particularly limited, and may be of any film thickness as long as a KTP single crystal thin film (second layer) having a pure composition as a waveguide layer can be epitaxially grown thereon. .

In order to epitaxially grow the first layer made of the low refractive index KTP single crystal film on the KTP single crystal substrate having a pure composition, it is preferable to use the liquid phase epitaxial growth method, and particularly to use the dip method. .

The formation of the low refractive index KTP single crystal film by the dipping method can be performed, for example, as follows. First, the starting material, which is weighed according to the composition of the target low refractive index KTP, is heated for homogenization and heated to 950 to 1000 ° C.
After obtaining the flux (melt) of
Slowly cool to 0-950 ° C. Next, the KTP single crystal substrate having the above-mentioned pure composition is dipped in the flux after slow cooling for 4 to 5 minutes, once pulled up and the surface is washed with pure water, and then again in the flux (after slow cooling). Soak for 4 to 5 minutes. The low-refractive-index KTP single crystal film having a high degree of homogeneity is produced by repeating the dipping in the flux after slow cooling for 4 to 5 minutes and the surface cleaning with pure water a required number of times to grow the film. Can be formed on the KTP single crystal substrate. The first layer made of the low refractive index KTP single crystal film thus formed has high flatness and has a natural crystal plane (1
00), which has a flat surface which almost coincides with

In the above-mentioned dipping method, since the low refractive index KTP single crystal is a solid solution crystal, the composition of the flux is likely to change as the crystal grows, and when the composition of the flux changes, the film thickness direction is changed. The composition change occurs and the refractive index changes. Therefore, it is preferable to use a relatively large amount of flux in order to prevent the change in the refractive index. The starting material for K, the starting material for Ti, the starting material for P, and the starting material for the substituting element (Na etc.) used for forming the first layer composed of the low refractive index KTP single crystal film As specific examples, the same ones as those mentioned in the description of the starting materials used when producing the bulk of the low refractive index KTP single crystal by Method I are exemplified.

The surface of the first layer made of the low refractive index KTP single crystal film on which the second layer made of the KTP single crystal thin film having a pure composition is formed has the low refractive index KTP as the first layer. Similar to the case of using a single crystal substrate, when the target optical waveguide is a two-dimensional optical waveguide or a ridge-type three-dimensional optical waveguide, a flat surface may be used. In the case of the original optical waveguide, since a concave portion for forming the waveguide layer is required, as described in the explanation of Method I,
A recess having a predetermined shape is formed. In the method II, a second KTP single crystal thin film having a pure composition is used as a waveguide layer on the low refractive index KTP single crystal film as the first layer formed as described above by the same epitaxial growth method as in the method I. The desired optical waveguide is obtained by forming the layer of.

[0035]

In the case of a pure KTP single crystal, a film having high crystallinity and crystal composition uniformity can be easily obtained by an epitaxial growth method. Therefore, it can be obtained by forming a second layer made of a KTP single crystal thin film having a pure composition as a waveguide layer on a low refractive index KTP single crystal substrate or a first layer made of a low refractive index KTP single crystal film. In the obtained optical waveguide of the present invention, it is easy to form the second layer, which is the waveguide layer, having high uniformity of crystallinity and crystal composition. Further, since there are few scattering centers in the waveguiding layer formed of a KTP single crystal thin film having a pure composition with high uniformity of crystallinity and crystal composition, high light propagation efficiency can be obtained.

[0036]

Embodiments of the present invention will be described below. Example 1 (Fabrication of Optical Waveguide by Method I) The composition of the melt (flux) is (K ₂ O, P ₂ O ₅ , TiO ₂ ).
₂ , Na ₂ O) = (44.4, 33.8, 20.4,
Low refractive index KT adjusted to 1.5) (mol%)
Large platinum crucible (diameter 140m
m, depth 140 mm) up to 80% of its volume. Then, the crucible filled with the raw material is heated to 95
A melt was prepared by uniformly melting and mixing the raw materials in the crucible at 0 to 1000 ° C., and then the melt was gradually cooled to about 890 ° C. over about 180 minutes and left at this temperature. Next, a seed crystal for producing a single crystal (having an orientation suitable for producing a substrate) is set so that the Y axis of this seed crystal is perpendicular to the liquid surface of the melt, and seeding is carried out for a while. After that, it was gradually cooled to the saturation temperature of 885 ° C. over about 180 minutes. After that, it is slowly cooled at a rate of 1 ° C./day, and a crystal is grown for about 40 days to obtain a low refractive index KTP having a Z-axis length of about 80 mm.
Single crystal (K _1-x Na _x TiOPO ₄ single crystal (0 <x ≦ 0.
5)) bulk was obtained. Then, from the above bulk, parallel to the (011) plane of the bulk, 15 × 20 × 0.5 mm
The low refractive index KTP single crystal substrate was obtained by cutting out the substrate.

Next, the composition of the melt (flux) is (K ₂
O, P ₂ O ₅ , TiO ₂ ) = (45.7, 33.8, ₂ )
0.4) (mol%) of pure composition adjusted to K
The raw material for TP single crystal is uniformly melt-mixed in the crucible,
A 5 ° C. melt was obtained. Then, the low refractive index KTP single crystal substrate was dipped in this melt for 4 to 5 minutes, and was once pulled up to wash the surface with pure water, and then again immersed in the melt.
Soaked for ~ 5 minutes. By this operation, the above low refractive index KT
Main surface of first layer composed of P single crystal substrate ((100)
A second layer composed of a pure KTP single crystal thin film having a film thickness of 7 to 10 μm was formed on the surface.

Thereafter, the surface of the low refractive index KTP single crystal substrate on which a KTP single crystal thin film having a pure composition is formed is washed with pure water, and further, both ends in the longitudinal direction of the substrate are polished to obtain the purpose. A two-dimensional optical waveguide was obtained. In this optical waveguide, the second layer made of a KTP single crystal thin film having a pure composition functions as a waveguide layer. In addition, KT of pure composition
The refractive index difference Δn between the second layer made of the P single crystal thin film and the first layer made of the low refractive index KTP single crystal substrate was 0.01.

When 633 nm light of a helium neon laser was made incident on this optical waveguide by the prism coupling method and this light was propagated, a single mode (TE
Mode, TM mode) was confirmed. Moreover, when the light attenuation coefficient was measured, it was about 0.07 db /
It was cm.

Example 2 (Fabrication of Optical Waveguide by Method II) First, K of pure composition having a size of 40 × 10 × 0.5 mm was prepared.
A TP single crystal substrate was prepared. This substrate is a (100) substrate. In addition, the composition of the melt (flux) is (K ₂ O,
P ₂ O ₅ , TiO ₂ , Na ₂ O) = (45.2, 33.
8,20.4,0.7) (mol%) adjusted to have a low refractive index KTP single crystal raw material with a diameter of 80 mm and a depth of 8
A melt was prepared by putting it in a 0 mm crucible and uniformly melt-mixing it in a crystal growth furnace set at about 950 ° C. for about 12 hours. This melt is about 1 after stabilization.
The temperature was lowered to about 883 ° C. over 80 minutes, and it was left for a while until the temperature became stable.

Then, the KTP single crystal substrate having the above-mentioned pure composition is dipped in the above melt after the temperature is stabilized for 4 to 5 minutes,
The surface was once pulled up and washed with pure water, and then again immersed in the melt for 4 to 5 minutes. By repeating this operation 2 to 3 times, a first layer made of a low refractive index KTP single crystal film having a film thickness of less than 100 μm was formed on the KTP single crystal substrate having the pure composition. The composition of this low refractive index KTP single crystal film was K _1-x Na _x TiOPO ₄ (0 <x ≦ 0.5). Moreover, the flatness of this film was high.

Next, a KTP single crystal melt having a pure composition was prepared under the same conditions as in Example 1, and this melt was used in the same manner as in Example 1 to perform the above-described low refractive index KTP single crystal film. KTP of pure composition with a thickness of 10 μm ± 5 on the first layer consisting of
A second layer composed of a single crystal thin film was formed.

After that, the surface of the KTP single crystal substrate having the pure composition, which has been formed to the KTP single crystal thin film having the pure composition, is washed with pure water, and further, both ends in the longitudinal direction of the substrate are polished to obtain the object. A two-dimensional optical waveguide was obtained. In this optical waveguide, the second layer made of a KTP single crystal thin film having a pure composition functions as a waveguide layer. In addition, KT of pure composition
The refractive index difference Δn between the second layer made of the P single crystal thin film and the first layer made of the low refractive index KTP single crystal film was 0.006.

When 633 nm light of a helium neon laser was made to enter this optical waveguide in the same manner as in Example 1 and this light was propagated, propagation as a single mode (TE mode, TM mode) was confirmed. Further, when the light attenuation coefficient was measured by the same method as in Example 1, it was about 0.0
It was 9 db / cm.

Example 3 (Production of Optical Waveguide by Method II) First, a KTP single crystal substrate having a pure composition and the same shape as that used in Example 2 was prepared. This substrate is a (100) substrate. The composition of the melt (flux) is (K
₂ O, P ₂ O ₅ , TiO ₂ , Na ₂ O) = (44.4,3
3.8, 20.4, 1.5) (mol%) of the low refractive index KTP single crystal raw material was put into a crucible having a diameter of 80 mm and a depth of 80 mm and heated under the same conditions as in Example 2. And melt-mixed to prepare a melt. After stabilizing this melt, the temperature was lowered to about 885 ° C. over about 180 minutes, and the melt was left for a while until the temperature became stable.

Then, the KTP single crystal substrate having the above-mentioned pure composition was immersed in the above-mentioned melt after the temperature was stabilized, and washed with pure water under the same conditions as in Example 2 to obtain the above-mentioned pure composition. A first layer made of a low refractive index KTP single crystal film having a film thickness of less than 100 μm was formed on a KTP single crystal substrate. The composition of this low refractive index KTP single crystal film is K _1-x Na _x TiOPO _4.
(0 <x ≦ 0.5). Moreover, the flatness of this film was high.

Next, a melt for a KTP single crystal thin film having a pure composition was prepared under the same conditions as in Example 1, and this melt was used in the same manner as in Example 1 to prepare the above low refractive index KTP single crystal. K of pure composition with a thickness of 15 μm ± 5 on the first layer of the film
A second layer composed of a TP single crystal thin film was formed.

After that, the surface of the KTP single crystal substrate having the above pure composition, which has been formed to the KTP single crystal thin film having the pure composition, is washed with pure water, and further, both ends in the longitudinal direction of the substrate are polished to obtain the object. A two-dimensional optical waveguide was obtained. In this optical waveguide, the second layer made of a KTP single crystal thin film having a pure composition functions as a waveguide layer. In addition, KT of pure composition
The refractive index difference Δn between the second layer made of the P single crystal thin film and the first layer made of the low refractive index KTP single crystal film was 0.01.

When 633 nm light of a helium neon laser was incident on this optical waveguide in the same manner as in Example 1 and this light was propagated, propagation as a single mode (TE mode, TM mode) was confirmed. Further, when the light attenuation coefficient was measured by the same method as in Example 1, it was about 0.0
It was 7 db / cm.

Example 4 (Production of Optical Waveguide by Method II) First, a KTP single crystal substrate having a pure composition and the same shape as that used in Example 2 was prepared. This substrate is a (100) substrate. The composition of the melt (flux) is (K
₂ O, P ₂ O ₅ , TiO ₂ , Na ₂ O) = (42.9,3
3.8, 20.4, 3.0) (mol%), the low refractive index KTP single crystal raw material was put into a crucible having a diameter of 80 mm and a depth of 80 mm, and heated under the same conditions as in Example 2. And melt-mixed to prepare a melt. After the stabilization, the melt was cooled to about 879 ° C. over about 180 minutes, and was left for a while until the temperature became stable.

Then, the KTP single crystal substrate having the above-mentioned pure composition was immersed in the above-mentioned melt after the temperature was stabilized, and washed with pure water under the same conditions as in Example 2 to obtain the above-mentioned pure composition. A first layer made of a low refractive index KTP single crystal film having a film thickness of less than 100 μm was formed on a KTP single crystal substrate. The composition of this low refractive index KTP single crystal film is K _1-x Na _x TiOPO _4.
(0 <x ≦ 0.5). Moreover, the flatness of this film was high.

Next, a melt for a KTP single crystal thin film having a pure composition was prepared under the same conditions as in Example 1, and this melt was used in the same manner as in Example 1 to prepare the low refractive index KTP single crystal. K of pure composition with a thickness of 13 μm ± 5 on the first layer of the film
A second layer composed of a TP single crystal thin film was formed.

After that, the surface of the KTP single crystal substrate having the pure composition, which has been formed to the KTP single crystal thin film having the pure composition, is washed with pure water, and further, both ends in the longitudinal direction of the substrate are polished to obtain the object. A two-dimensional optical waveguide was obtained. In this optical waveguide, the second layer made of a KTP single crystal thin film having a pure composition functions as a waveguide layer. In addition, KT of pure composition
The refractive index difference Δn between the second layer made of the P single crystal thin film and the first layer made of the low refractive index KTP single crystal film was 0.02.

When 633 nm light of a helium neon laser was incident on this optical waveguide in the same manner as in Example 1 and this light was propagated, propagation as a single mode (TE mode, TM mode) was confirmed. Further, when the light attenuation coefficient was measured by the same method as in Example 1, it was about 0.0
It was 8 db / cm.

[0055]

As described above, in the optical waveguide of the present invention, a waveguiding layer is formed by a single crystal thin film which is easy to obtain a film having high uniformity of crystallinity and crystal composition, that is, a KTP single crystal thin film having a pure composition. Are formed. Since the KTP single crystal thin film having a pure composition has few scattering centers, the present invention makes it possible to easily provide an optical waveguide having a high light propagation efficiency.

[Brief description of drawings]

FIG. 1 K _1-x Na _x TiOPO ₄ epitaxially grown on a KTP single crystal substrate of pure composition by a dip method.
The refractive index of the single crystal (however, the difference Δn between the refractive index of the KTP single crystal substrate having a pure composition) and Na ₂ in the flux used
It is a graph which shows the relationship with the molar concentration of O.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G02B 6/12 M

Claims (8)

[Claims] 1. A first layer made of a KTP single crystal having a low refractive index, and a pure composition of K formed on the first layer.
An optical waveguide comprising a second layer made of TP single crystal, and the second layer functions as a waveguide layer. 2. The optical waveguide according to claim 1, wherein the first layer is a substrate or a film made of a KTP single crystal whose refractive index is lowered by substituting a part of crystal constituent elements. 3. The optical waveguide according to claim 1 or 2, wherein the first layer is made of K _1-x Na _x TiOPO ₄ single crystal (0 <x ≦ 0.5). 4. A KTP single crystal thin film having a pure composition is epitaxially grown on a first layer made of KTP single crystal whose refractive index is lowered by substituting a part of crystal constituent elements to function as a waveguide layer. And a second layer for forming the optical waveguide. 5. The method according to claim 4, wherein as the first layer, a substrate or a film made of KTP single crystal whose refractive index is lowered by substituting a part of crystal constituent elements is used. 6. The composition of the first layer is K _1-x Na _x TiOPO.
_{It is 4} (0 <x <0.5), Claim 4 or Claim 5 which is.
The method described in. 7. The method according to claim 4, wherein the propagation characteristics of light in the waveguide layer are controlled by controlling the substitution ratio of elements in the first layer. 8. The first layer is a film epitaxially grown on a KTP single crystal substrate having a pure composition by a dip method, and the dip method repeats dipping in a melt and surface cleaning with pure water to form a film. The method according to any one of claims 4 to 7, which is to grow.