JPH06345596A - Production of ktp single crystal and optical waveguide - Google Patents

Abstract

PURPOSE:To produce a large-sized KTiOPO4 single crystal useful as a light- modulating element and with the (100) plane developed in a relatively short time and produce an optical waveguide with the single crystal as a substrate. CONSTITUTION:A seed crystal of KTiOPO4 is brought into contact with a flux consisting of 45-65mol% K2O, 25-32mol% P2O5 and 10-30mol% (TiO2)2, the flux is cooled to grow the (100) plane of the KTiOPO4 crystal preferentially, and a KTiOPO4 single crystal is produced. A substrate having the (100) plane of the single crystal is formed, the (100) plane of the substrate is brought into contact with a flux contg. a dopant M, potassium, titanium, phosphorus and oxygen to epitaxially grow the single crystal thin film of K1-xMxTiOPO4 (where M is an element or group to make the refractive index of the thin film higher than that of KTiOPO4), and an optical waveguide is produced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to KTiOPO ₄ (KT
P) Method for producing single crystal and LPE (liquid phase epitaxy)
The present invention relates to a method for manufacturing an optical waveguide by the method. More specifically, the present invention is useful as a substrate material for a light modulation element (1
The present invention relates to a method for producing a large KTP single crystal having a developed (00) plane and a method for producing an optical waveguide on the (100) plane of the KTP single crystal.

[0002]

2. Description of the Related Art KTP
It is already known to use a single crystal as a waveguide substrate for optical modulation. When a KTP single crystal is used as a waveguide substrate for optical modulation, the waveguide creation direction is limited. That is, KT
When a slab type waveguide is formed by the LPE (liquid phase epitaxy) method using P as a substrate, a uniform stacking is (10
It is formed only on the (0) plane. Therefore, the KPT single crystal as the optical modulation waveguide substrate needs to have a (100) plane. Furthermore, in order to use it as a substrate, the bottom area of the substrate is required to be, for example, about 10 × 20 mm, and a relatively large KTP single crystal is required.
Therefore, as a waveguide substrate for optical modulation, it is essential to manufacture a large KTP single crystal having a developed (100) plane.

On the other hand, as a method for producing a KTP single crystal,
The method using a phosphoric acid-based self-flux described in JP-B-1-52359 is generally used. This publication describes K ₆ (K ₆ P ₄ O ₁₃ ) flux and its surrounding composition flux (the composition is shown in FIG. 1 as points A, B and C).
It is disclosed that the KTP can be grown by a temperature gradient method or a uniform heating / grading method. However, the size of the largest KTP single crystal described in the examples of this publication is 15 × 8 × 2 mm, but the size of the (100) plane of this single crystal is unknown.

Further, Japanese Patent Publication 1-using K ₆ flux
The method described in Japanese Patent No. 52359 has been improved [Japanese Society for Crystal Growth (1992) 28aB9] to have a size larger than that of the single crystal described in, for example, about 80 to 90 mm in the c-axis direction ((100) plane It is possible to grow a KTP single crystal having a size of about 30 × 30 mm (judging from the photograph shown). That, K ₆ in solubility 950 ° C. of KTP components in K ₆ Flux
About 0.6 g per 1 g of the (K ₆ P ₄ O ₁₃ ) component, the raw material reagents mixed in this component ratio were filled in a crucible, and 9
It is heated and melted at 70 to 1000 ° C. overnight. Next, the temperature is lowered to about 950 ° C., seeding is performed at this temperature, and after seeding, the KTP single crystal is grown by slow cooling at a cooling rate of 1 to 3 ° C./day.

However, in order to grow such a large KTP single crystal as described above, a long period of about 50 days is required as a growing period. Moreover, since the KTP single crystal obtained by this method has a cubic or rectangular parallelepiped bulky form, the (100) plane having a sufficient size as a waveguide substrate for optical modulation is used when the growth is relatively short. It is impossible to cut out. Therefore, in order to obtain a large (100) plane, it is necessary to grow a relatively large KTP single crystal over a long period of time.

In the above method, the single crystal becomes bulky because the KTP single crystal has a relatively uniform crystal growth rate in each axial direction when a K ₆ flux and a flux having a composition around it are used. This is because. In general,
It is known that the crystal growth rate in each axial direction changes depending on the addition of an additive to the flux, the change in the composition of the flux, the crystal growth temperature, and the like. However, hitherto, there is no known method for promoting a crystal growth rate in a specific axial direction to produce a KTP single crystal having a desired crystal plane developed in a shorter period of time.

Therefore, an object of the present invention is to provide a large-sized KTiO having a developed (100) plane, which is useful as a substrate for an optical modulator.
It is to provide a method for producing a PO ₄ single crystal in a relatively short period of time.

A further object of the present invention is to provide a method for producing an optical waveguide, in which the (100) plane natural surface of the KTiOPO ₄ single crystal obtained by the above production method is used as a substrate.

[0009]

According to the present invention, K ₂ O is 45
A 65 mol%, a P ₂ O ₅ is 25 to 32 mol%, and the flux having a composition (TiO _{2) 2} is 10 to 30 mol%, is contacted with seed crystals of KTiOPO _4, then After cooling the flux, KTiOPO
_{The present} invention relates to a method for producing a KTiOPO ₄ single crystal, which comprises preferentially growing the (100) plane of the ₄ crystal.

Further, the present invention uses the above manufacturing method to obtain K
A (100) plane substrate of TiOPO ₄ single crystal was prepared, and the (100) plane of this substrate was brought into contact with a flux containing dopants M, potassium, titanium, phosphorus and oxygen,
Single crystal thin film of K _1-x M _x TiOPO ₄ (however, the dopant M is an element or a group that makes the refractive index of the thin film higher than that of KTiOPO ₄ and x is more than 0 and less than 1) ) Is epitaxially grown, the present invention relates to a method for manufacturing an optical waveguide.

In the method of the present invention, the (100) plane is preferentially grown by adjusting the composition of the flux,
As a result, even if the thickness is sacrificed, in a relatively short period of time,
It is possible to provide a large plate-shaped KTP single crystal having a developed (100) plane, which is useful as a substrate for an optical modulator.

The present invention will be described in detail below. In the production method of the present invention, K ₂ O is 45 to 65 mol%,
P ₂ O ₅ is 25 to 32 mol%, and (TiO ₂ )
A flux having a composition in which ₂ is 10 to 30 mol% is used. By using a flux having a composition within this range, a large KTP single crystal having a developed (100) plane can be obtained. This composition is the range surrounded by the point DEFG in FIG. The compositions of points D, E, F and G are as shown in Table 1 below.

[0013]

[Table 1] ─────────────────────────────────── Point K ₂ O P ₂ O ₅ (TiO ₂ ) ₂ ─────────────────────────────────── D 45 mol% 32 mol% 22 mol% E 58. 5 mol% 32 mol% 10 mol% F 65 mol% 25 mol% 10 mol% G 45 mol% 25 mol% 30 mol% ────────────────────── ──────────────

Particularly, K ₂ O is 45 to 60, and P ₂ O
₅ is 27 to 31 mol%, and (TiO ₂ ) ₂ is 1
It is preferably 0 to 25 mol% from the viewpoint of growing the (100) plane largely and more preferentially.

In the manufacturing method of the present invention, first, a melt having the above composition is prepared. The melt is a compound serving as a K source, a Ti source, a P source, and an O source, such as KPO ₃ , K ₂ CO ₃ , and T.
It can be obtained by using iO ₂ , K ₄ P ₂ O ₇ , K ₃ PO ₄ or the like as a raw material and heating at a saturation temperature of KTP or higher. Incidentally, these raw materials are not particularly limited. The saturation temperature of KTP changes depending on the composition of the flux.
It is in the range of about 850 to 950 ° C. In addition, heating the KTP at a temperature equal to or higher than the saturation temperature can generally be performed, for example, for about 6 to 48 hours to obtain a uniform melt.

The seed crystal of KTiOPO ₄ used in the method of the present invention is not particularly limited. In the method of the present invention, it is preferable to use an oriented seed crystal from the viewpoint of using a seed crystal in which the X axis or the Y axis is the single crystal growth direction.

The KTiOPO ₄ seed crystal is brought into contact with the melt. Immediately after contact with the melt or after standing for a predetermined time, for example, 1 to 12 hours, cooling of the melt is started while maintaining contact. Cooling of the melt is, for example, 0.5 to 5 ° C. /
The day, preferably 1 to 3 ° C./day, is preferable from the viewpoint of obtaining a homogeneous single crystal. By cooling the melt, a KTP single crystal begins to precipitate near the tip of the seed crystal and gradually grows in the melt.

The KTiOPO ₄ seed crystal may or may not be rotated, and in the case of rotation, the rotation speed is 10 to 200 rpm, preferably 40 to 100 rpm.
Is appropriate. By rotating the seed crystal of KTiOPO ₄ , the homogeneity of the temperature and composition of the melt can be improved, and the miscellaneous products floating on the surface of the melt can be kept away from the seed crystal, and an optically good single crystal can be obtained. There is an advantage.

The growth period of the KTP single crystal according to the method of the present invention varies depending on the composition of the flux, the cooling start temperature of the melt, the cooling rate, the desired size of the KTP single crystal, and is, for example, 14 to 50 days. .

The KT which has finished the growth by stopping the cooling of the melt
The P single crystal is pulled out until it does not come into contact with the melt, then the temperature of the entire furnace is lowered to room temperature, and then taken out from the furnace. The KTP single crystal taken out of the furnace is subjected to a conventional method to remove the flux attached with water or the like. The thus obtained plate-shaped KTP single crystal with developed (100) plane is
It is used as it is or after further cutting and other operations as a substrate for a light modulation element.

Next, a method of manufacturing the optical waveguide of the present invention will be described. In the present invention, the above manufacturing method is used to produce KTi.
A (100) plane substrate of OPO ₄ single crystal is prepared. As the substrate, KTiOPO ₄ produced by the above-mentioned production method was used.
The single crystal is used as it is, or a single crystal in which at least one surface is a (100) natural surface is obtained by cutting the KTiOPO ₄ single crystal manufactured by the above manufacturing method. In addition, in the present invention, the natural surface means a surface as obtained by the method for producing a single crystal, which has not been cut or polished.

The (100) plane of this substrate is an LPE containing the dopant M, potassium, titanium, phosphorus and oxygen.
The single crystal thin film of K _1-x M _x TiOPO ₄ is epitaxially grown in contact with the working flux. Dopant M
Is not particularly limited as long as it is an element or group that makes the refractive index of the obtained thin film higher than that of the KTiOPO ₄ substrate.
Examples of such a dopant M include rubidium (Rb), thallium (Tl), lithium (Li), sodium (Na), selenium (Se), hydrogen (H), and ammonium (NH ₄ ⁺ ). . Further, the addition amount of the dopant M can be appropriately determined depending on the kind of the dopant M and the required refractive index of the thin film.

The melt of the flux for LPE is a compound serving as a potassium (K) source, a titanium (Ti) source, a phosphorus (P) source and an oxygen (O) source, and a dopant source, for example, KP.
O ₃ , K ₂ CO ₃ , TiO ₂ , K ₄ P ₂ O ₇ , K ₃ PO
₄ , Rb ₂ CO ₃ , RbPO ₃ , Li ₂ CO ₃ , Na ₂
It can be obtained by using CO ₃ , Cs ₂ CO ₃ or the like as a raw material and heating at a temperature equal to or higher than the saturation temperature of the LPE flux. Incidentally, these raw materials are not particularly limited. The saturation temperature of the LPE flux varies depending on the composition of the flux, but is in the range of about 850 to 950 ° C, for example. In addition, the heating at the saturation temperature or higher is generally, for example, about 6 to
A uniform melt can be obtained by carrying out for 48 hours.

The melt is, for example, 0 to 5 ° C. above the saturation temperature.
The temperature is set low and the (100) natural surface of the KTP substrate is brought into contact. The contact with the melt is preferably performed after equilibration with the melt temperature of the KTP substrate in order to prevent cracking due to thermal strain of the KTP substrate. The contact time of the KTP substrate with the melt can be appropriately set in consideration of the melt temperature (difference from the saturation temperature) and the like depending on the film thickness required for the obtained single crystal thin film. The film thickness of the single crystal thin film is appropriately determined depending on the wavelength of light to be propagated, the difference in refractive index between the substrate and the thin film, etc., for example, in a waveguide for single moat propagation.

Usually, the contact time of the KTP substrate with the melt is
For example, it is about 1 to 120 minutes. Further, the KTP substrate may or may not be rotated, and when it is rotated, the rotation speed is appropriately set to about 40 to 100 rpm. By rotating the KTP substrate, the homogeneity of the temperature and composition of the melt can be increased, and miscellaneous products floating on the surface of the melt can be kept away from the substrate, and an optically good single crystal thin film can be obtained.

After the growth of the single crystal thin film is completed, the KTP substrate is pulled up to a position where it does not come into contact with the melt, and then the temperature of the entire furnace is lowered to room temperature and then taken out from the furnace. The KTP substrate taken out from the furnace is subjected to a conventional method to remove the flux attached with water or the like to obtain a waveguide.

[0027]

According to the method for producing a KTiOPO ₄ single crystal of the present invention, a large plate-like KTP single crystal having a (100) plane developed can be produced in a relatively short period of time. The obtained KTP single crystal has high optical homogeneity and (100)
Since it is a plane substrate, it is useful as a substrate material for an optical modulator, particularly as a substrate for forming a slab type waveguide by a liquid phase epitaxial method. Furthermore, according to the manufacturing method of the present invention, KT
An optical waveguide thin film layer can be formed on the (100) plane of P to obtain a waveguide for an optical modulator.

[0028]

EXAMPLES The present invention will now be described in more detail with reference to examples.

Example 1 123 g of potassium phosphate (KPO ₃ ) and titanium oxide (T
26 g of iO ₂ ) and 24 g of potassium carbonate (K ₂ CO ₃ ).
100m diameter which mixed and maintained at 970-1000 degreeC
It was supplied 6 to 7 times to a crucible having a height of m and a height of 100 mm to obtain a melt. This melt was kept at this temperature for 12 to 24 hours to form a homogeneous melt. This melt had a composition of K ₂ O of 51.
5 mol%, P ₂ O ₅ is 31.5 mol%, and (TiO ₂ ) ₂ is 17.0 mol%.
Indicate.

After homogenizing the melt, the temperature of the melt was set to 927 ° C., the seed crystal was slowly soaked, left for a while (4 to 5 hours), and then gradually cooled at a cooling rate of 1 ° C./day. . The seed crystal used had a length of about 10 mm, a width of about 5 mm, and a thickness of about 5 mm (the seed crystal axis was the Y axis). When annealing was continued for 6 days in this state, crystals grew mainly in the direction perpendicular to the Y-axis,
A transparent plate-shaped single crystal with a developed (100) plane was obtained. The size of the (100) plane of this single crystal is about 30 mm x about 10 mm
And the thickness was about 5 mm.

Examples 2 to 6 Fluxes having the compositions shown in Table 2 (points t, u, v in FIG. 2)
w, x), a seed crystal temperature, a cooling rate, and a growth time were used to grow a single crystal. Table 2 shows the dimensions and thickness of the (100) plane of the obtained single crystal.

[0032]

[Table 2]

Example 7 (Production of Optical Waveguide) a) Charge of Reagent to Crucible As raw material, 44.9, manufactured by Shiratsu Chemical Laboratory Co., Ltd., potassium methanephosphate (KPO ₃ ), 134.9 g, rare metallic (stock) ) Made of 4N, titanium oxide (TiO ₂ ) 27.4
g, 3N manufactured by Mitsuwa Chemical Co., Ltd., and 36.5 g of rubidium carbonate (RbCO ₃ ) were mixed and melt-mixed in a crucible-type electric furnace kept at 1000 ° C. to give an inner diameter of 50 mm and a height. A 70 mm platinum crucible was charged.
(80% charge amount)

B) Immersion of Substrate The crucible charged as described above is set in a predetermined LPE electric furnace (manufactured by Vacuum Metallurgy Co., Ltd.) and heated to 1000
Further melt-mixed at 0 ° C. Next, the single crystal obtained in Example 1 was cut to obtain a (100) plane substrate ((10
0) Surface dimension 10 mm x 20 mm, thickness 1 mm) is attached to the tip of the dipping shaft, lowered at a speed of about 20 mm / min to prevent the substrate from cracking due to thermal strain, and stopped at the surface of the liquid to bring the substrate temperature and solution temperature. Was equilibrated. (At this time, the substrate was almost vertical to the liquid surface, and the lower end was in contact with the liquid.) About 10 minutes, the (100) surface substrate with the natural surface and the back surface was subjected to the liquid temperature setting of 957 ° C. (saturation). Temperature 9
After dipping for 46 minutes at 60 ° C.), the substrate was pulled up and cooled to room temperature (the substrate rotation speed was 30 rpm).
As a result, on the natural surface, crystal growth having the characteristics of the natural surface was realized, and a homogeneous transparent film was formed. The film thickness is about 100
was μm. The composition of the obtained thin film is K _1-x Rb _x Ti
OPO ₄ (x = 0.3) and the refractive index is n _x = 1.
7727, n _y = 1.7863, was n _z = 1.8755. On the other hand, on the polished surface, a heterogeneous layer consisting of fine striations was formed.

Example 8 Obtained by cutting the single crystal obtained in Example,
A (100) plane substrate (the (100) plane having a dimension of 10 mm × 20 mm and a thickness of 1 mm) in which the front surface is a natural surface and the back surface is a polished surface
Was immersed for 35 minutes under the liquid temperature setting of 957 to 958 ° C (saturation temperature of 960 ° C). (Substrate rotation speed is 30 rp
m) As a result, as in Example 7, a homogeneous transparent film was formed on the natural surface. The film thickness at this time was about 80 μm.

[Brief description of drawings]

FIG. 1 shows a composition range of a flux described in JP-B-1-52359 and a composition range of a flux for producing a KTiOPO ₄ single crystal of the present invention.

FIG. 2 shows an enlarged view of the composition range of the flux for producing a KTiOPO ₄ single crystal of the present invention and the composition of each flux used in the examples.

Claims (4)

[Claims] 1. K ₂ O is 45 to 65 mol%, and P ₂
In a flux having a composition in which O ₅ is 25 to 32 mol% and (TiO ₂ ) ₂ is 10 to 30 mol%, K
Contacting a seed crystal of TiOPO _4, then cooling the flux method of KTiOPO ₄ single crystals, characterized in that to preferentially grow (100) plane of KTiOPO ₄ crystals. 2. The flux has a composition in which K ₂ O is 45 to 60 mol%, P ₂ O ₅ is 27 to 31 mol%, and (TiO ₂ ) ₂ is 10 to 25 mol%. The manufacturing method according to claim 1. 3. The production method according to claim 1, wherein a seed crystal of KTiOPO ₄ is brought into contact with a flux having a temperature of 850 to 950 ° C., and the temperature of the flux is cooled at 1 to 5 ° C./day. 4. KTi is produced using the manufacturing method according to claim 1.
A substrate having a (100) plane of an OPO ₄ single crystal was prepared,
The (100) plane of this substrate was brought into contact with a flux containing the dopant M, potassium, titanium, phosphorus and oxygen to form a single crystal thin film of K _1-x M _x TiOPO ₄ (however, the dopant M is the refractive index of the thin film). Is an element or a group that makes the refractive index higher than that of KTiOPO ₄ , and x is a number greater than 0 and less than 1) is epitaxially grown.