JP3131741B2 - Method for producing lithium niobate single crystal thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium niobate single crystal thin film having a film thickness suitable for various optical materials including a thin film waveguide type second harmonic generation element.

[0002]

2. Description of the Related Art Along with the recent development of optical application technology, a shorter wavelength of a laser light source is required. This is because recording density and photosensitivity can be improved by shortening the wavelength, and application to optical devices such as optical disks and laser printers can be considered.

For this reason, the wavelength of the incident laser light is reduced to 1 /
Research has been conducted on second harmonic generation (SHG) devices that can be converted to 2.

As the second harmonic generation (SHG) element, a bulk single crystal of a nonlinear optical crystal has conventionally been used using a high-output gas laser as a light source. However, there is a strong demand for miniaturizing devices such as optical disk devices and laser printers, and gas lasers require an external modulator for light modulation, whereas semiconductor lasers can directly modulate. Semiconductor lasers have been mainly used instead of gas lasers because of their low cost and low cost. For this reason, it is necessary to obtain high conversion efficiency with a low light source output of several mW to several tens of mW.
HG elements have become necessary.

[0005] As such a nonlinear optical material for a thin film waveguide type SHG element, a waveguide in which a layer whose refractive index is changed by diffusing Ti or the like into a lithium niobate single crystal bulk has been used. It is known that a waveguide using a lithium niobate thin film formed by a high frequency sputtering method on a lithium tantalate substrate is known, but it is difficult to obtain a lithium niobate thin film having excellent crystallinity, High conversion efficiency could not be obtained.

As a method for producing a single crystal thin film having excellent crystallinity, a liquid phase epitaxial method is considered to be suitable, and various liquid phase epitaxial methods have been studied.

As a liquid phase epitaxial method for obtaining a lithium niobate thin film, for example, the following method is known.

(1) Applied Physics Letters, Vol. 2
6, No.1, the January 1975, lithium tantalate as the substrate, Li ₂ O, the V ₂ O ₅ as a flux, to form a lithium niobate thin film optical waveguide by the liquid phase epitaxial growth method, guide light Examples of waving are described.

(2) JP-B-51-9720 discloses that
A method of forming a lithium niobate thin film for an optical waveguide by a liquid phase epitaxial growth method using lithium tantalate as a substrate and Li ₂ O and V ₂ O ₅ as a flux is described.

(3) Japanese Patent Publication No. 56-47160 discloses a single crystal thin film of a Mg-containing lithium niobate / lithium tantalate solid solution on a substrate by epitaxial growth using Li ₂ O and V ₂ O ₅ as flux. Are described.

However, according to the conventionally known liquid phase epitaxial method, not only a lithium niobate single crystal having excellent crystallinity cannot be obtained on a lithium tantalate substrate, but also a liquid crystal epitaxial method particularly required for manufacturing an SHG element. It was difficult to obtain a lithium niobate single crystal having a film thickness.

The film thickness required for manufacturing the thin-film waveguide type SHG element means that the fundamental wavelength of the wavelength λ and the wavelength λ / 2 is a film thickness that can make the effective refractive index equal to the second harmonic of 2. In particular, a SHG device for a semiconductor laser is manufactured using a lithium niobate thin film formed on a lithium tantalate substrate. In this case, in order to make the effective refractive indices coincide, a lithium niobate thin film having a thickness of 5 μm or more is required.

Further, in order to obtain a high-output thin-film waveguide type SHG element, the difference in the refractive index between the substrate and the thin-film waveguide layer must be increased. For this reason, if various elements are added, there is a possibility that the optical characteristics of the waveguide layer may be deteriorated. Therefore, studies have been made to lower the refractive index of the substrate. For example, there is the following.

(4) JP-B-63-27681 discloses that a diffusion layer having a low refractive index of 3 to 6 μm is formed by diffusing vanadium pentoxide on a lithium tantalate single crystal substrate, and tantalum acid is formed thereon. A technology for epitaxially growing lithium single crystal has been disclosed.

(5) JP-B-60-34722 discloses a technique in which magnesium oxide and vanadium pentoxide are simultaneously added to a lithium tantalate single crystal substrate to epitaxially grow a lithium tantalate single crystal layer.

However, in these techniques, lithium tantalate is used as the thin film waveguide layer, and the nonlinear optical effect is inferior to lithium niobate. In addition, since the lattice constant of lithium tantalate, which is a thin film waveguide layer, cannot be changed, it is necessary to add magnesium oxide or vanadium pentoxide as long as the lattice constant of the substrate does not change. Was. Further, in the above technique, the refractive index on the substrate side must be reduced, and the variable range of the refractive index is limited.

As described above, heretofore, niobium having a large refractive index difference from the substrate and having excellent optical characteristics has a film thickness necessary for producing an optical device such as an SHG element on a lithium tantalate substrate. There was no method for practically producing lithium oxide single crystals.

The inventors of the present invention have conducted various studies to solve the above-mentioned problems, and as a result, have found that a SHG device is obtained by lattice-matching a lithium tantalate substrate and a lithium niobate single crystal thin film. Have sufficient film thickness necessary to make optical devices such as
Newly found that a lithium niobate single crystal thin film with extremely excellent optical properties, such as (the refractive index of the crystal changes when irradiated with strong light) and light propagation loss is extremely small, can be obtained practically, Proposed earlier. (Japanese Patent Application No. 1-
242285)

[0019]

As a result of further research, a single crystal thin film of lithium niobate was made of Li ₂ O,
The present inventors have found that a good product can be obtained efficiently by manufacturing from a melt having a specific composition of V ₂ O ₅ and Nb ₂ O ₅ , and have completed the present invention.

[0020]

The gist of the present invention is that Li ₂
O, the composition range of V ₂ O ₅ and Nb ₂ O ₅ is Li ₂ O-V ₂ O ₅
In the triangular diagram of the three-component system of -Nb ₂ O ₃ , A (88.9
0, 2.22, 8.88), B (55.00, 43.0).
0, 2.00), C (46.50, 51.50, 2.0
0) and D (37.50, 5.00, 57.50)
A heterogeneous element is added to at least a part of the surface of a melt containing an element indicated by a region surrounded by a composition point and having an effect of increasing the lattice constant of a lithium niobate single crystal obtained in the composition. A lithium niobate single crystal thin film lattice-matched to the substrate by contacting the lithium tantalate substrate thus prepared.

As the different element having the function of increasing the lattice constant of the lithium niobate single crystal, Na or Mg is preferable. That is, in the present invention, the lithium niobate single crystal thin film formed on the hetero element-containing lithium tantalate substrate has the Li ₂ O—V ₂ O ₅ —Nb ₂ shown in FIG.
It is formed from a melt having a composition surrounded by four points A, B, C, and D in a three-component system of O ₃ .

The lithium niobate single crystal thin film of the present invention
It must be formed on a different element-containing lithium tantalate substrate and lattice-matched to the lithium tantalate substrate. The reason is that a lithium niobate single crystal thin film and a lithium niobate single crystal thin film having extremely excellent optical characteristics due to lattice matching with the lithium tantalate substrate are formed with a thick film thickness which cannot be obtained by the prior art. Because it is done. In addition, the reason that the formed lithium niobate single crystal thin film has extremely excellent optical characteristics is that the lithium niobate single crystal thin film and the lithium tantalate substrate are lattice-matched to be integrated with the substrate, resulting in lattice distortion and distortion. This is because the film is a high-quality film having very few crystal defects, excellent crystallinity, and no microcracks.

In the prior art, since a thin film having lattice matching with the substrate could not be produced, the crystallinity of the thin film was poor, and microcracks were observed in the thin film. Therefore, scattering loss at the substrate interface and the thin film surface, and absorption loss due to the impurity mixing can be achieved by smoothing the substrate material surface and the thin film surface by polishing or chemical etching, or by using a high-purity raw material with a small impurity mixing ratio. Even if is reduced to some extent, the absorption / scattering loss at the crystal grain boundaries or the scattering loss due to microcracks is extremely large, and thus cannot be used for optical applications.

In the present invention, the means for lattice-matching the lithium niobate single crystal thin film and the lithium tantalate substrate containing a different element is not particularly limited, but sodium or magnesium or a mixture of both is used for the lithium niobate single crystal. It is advantageous to include it in the thin film.

This is because sodium or magnesium ions or atoms have an effect of increasing the lattice constant (a-axis) of lithium niobate by substitution or doping with respect to the crystal lattice of lithium niobate. By adjusting the composition, it is possible to easily obtain lattice matching between the lithium tantalate substrate and the lithium niobate single crystal.Furthermore, sodium and magnesium not only do not impair optical characteristics at all, but magnesium This has the important effect of preventing optical damage.

When sodium and magnesium are contained, the content is 0.1 to 14.3 with respect to the lithium niobate single crystal, respectively.
It is desirable that the amount of magnesium and the amount of magnesium be 0.8 to 10.8 mol%. The reason is that when the content of sodium is less than 0.1 mol%, the lattice constant does not become large enough to be lattice-matched with the lithium tantalate substrate regardless of the amount of magnesium added. .3
On the other hand, if it exceeds mol%, the lattice constant becomes too large, and in either case, the lattice matching between the lithium tantalate substrate and the lithium niobate single crystal cannot be obtained.

When the content of magnesium is less than 0.8 mol%, the effect of preventing photodamage is insufficient, and when it exceeds 10.8 mol%, magnesium niobate-based crystals are not formed. It cannot be contained because it precipitates.

FIG. 4 shows the relationship between the sodium content and the lattice constant of the a-axis of lithium niobate, and FIG. 5 shows the relationship between the magnesium content and the lattice constant of the a-axis of lithium niobate.
Are shown below.

Regarding the sodium content, as described above, Journal of Crystal Growth, Vol.
81) On pages 572 to 576, sodium is added to lithium niobate, and Y is added by liquid phase epitaxial growth.
An example in which a sodium-containing lithium niobate thin film single crystal having a thickness of 20 μm was formed on a -cut lithium niobate substrate was described in Journal of Crystal Growth, Vol.
87) pp. 409-412 describes an example in which sodium is added to lithium niobate, and a sodium-containing lithium niobate thin film single crystal is formed on a Y-cut lithium tantalate substrate by a liquid phase epitaxial growth method. Although these documents indicate that the lattice constant of lithium niobate single crystal changes due to sodium content, it is a technology related to SAW (Surface Acoustic Wave) device, and it is used for optical characteristics and lattice matching with lithium tantalate substrate There is no description that a film having excellent optical characteristics can be obtained. In addition, the lithium niobate single crystal thin films shown in these documents are for SAW devices, and the thin film described in the former document uses lithium niobate for the substrate, and the thin film described in the latter document is However, although the thin film and the substrate are formed on the lithium tantalate substrate, but the lattice matching between the thin film and the substrate is not made,
Neither can be used as an optical material aimed at in the present application.

Further, US Pat. No. 4,093,781 describes a method in which when a lithium ferrite film is used as a substrate to form a lithium ferrite film by a liquid phase epitaxial growth method, lithium is replaced by sodium and the lattice constant is matched to that of the substrate. ing.

However, this is a technique relating to lithium ferrite and cannot be used as an optical material aimed at by the present invention, and none of these techniques impairs the novelty and inventive step of the present invention.

The reason why lithium tantalate is used as a substrate in the present invention is that the crystal system of the lithium tantalate substrate is similar to a single crystal of lithium niobate and is easy to grow epitaxially, and the lithium tantalate substrate is commercially available. Therefore, high quality products can be obtained stably.

It is necessary that at least part of the surface of the lithium tantalate substrate used in the present invention contains various different elements. Dissimilar elements refer to elements that are different from the elements that make up the substrate. Inclusion of these elements changes the lattice constant, refractive index, etc., increases the difference in the refractive index between the substrate and the thin-film waveguide layer, and increases the surface area. May be processed by mirror polishing or chemical etching.

As the different element contained on the lithium tantalate substrate, a metal element is preferable, and magnesium,
At least one selected from titanium, vanadium, chromium, iron, nickel and neodymium is desirable.

When the above-mentioned different element is contained in the lithium tantalate substrate, the different element may not be uniformly present on the entire substrate. In the present invention, a different element is added to a specific portion of the lithium tantalate substrate to form a pattern in which the refractive index of the waveguide forming portion is relatively lower than that of the non-forming portion, thereby forming niobium on the substrate. Only by forming the lithium oxide single crystal thin film in a slab shape, the lithium niobate single crystal thin film formed in the pattern portion becomes a waveguide, and a processing step for forming the waveguide can be omitted.

As a method of lowering the refractive index of the substrate at the portion where the waveguide is formed as compared with the portion where the waveguide is not formed, the refractive index of the substrate at the portion where the waveguide is formed is reduced or the refractive index of the substrate at the portion where the waveguide is not formed is increased. It is desirable.

When the heterogeneous elements are non-uniformly present, the portion corresponding to the waveguide conditions becomes a waveguide.

The content of the different element on the surface of the lithium tantalate substrate is preferably in the following composition range. Ti; 0.2 to 30 mol% Cr; 0.02 to 20 mol% Fe; 0.02 to 20 mol% Ni; 0.02 to 20 mol% Nd; 0.02 to 10 mol% Mg; 0.1 to 20 mol% V; 0.05 to 30 mol%

The above content is calculated by the formula: heterogeneous element / (LiTaO ₃ + heterogeneous element) × 100.

More preferably, Ti: 1.0 to 15 mol% Cr; 0.2 to 10 mol% Fe; 0.2 to 10 mol% Ni; 0.2 to 10 mol% Nd; 0.5 to 5 mol% Mg: 2.0 to 10 mol % V: 1.0 to 15 mol%.

The reason why the above composition range is preferable is that if the composition ratio is higher than the above range, the crystallinity of the substrate is lowered, and if the composition ratio is lower than the above range, the refractive index does not change.

Among the different elements, those having the function of increasing the refractive index of the lithium tantalate substrate are Ti, C
r, Nd, Fe, and Ni, and those having an action of lowering the refractive index are Mg and V. These elements are
The lithium tantalate substrate can contain various forms such as atoms, ions and oxides. Since these elements can change only the surface refractive index without substantially changing the properties that affect the thin film formation of the substrate, such as the surface roughness, a thin film having the same properties as a normal substrate can be formed under the same conditions. Can be manufactured.

Examples of the method for adding the different element include a liquid phase epitaxial growth method, a method in which the different element is previously mixed in the raw material of the lithium tantalate bulk single crystal, in addition to the thermal diffusion, ion exchange, and ion implantation methods. and so on. When a thermal diffusion, ion exchange, or ion implantation method is used, a diffusion layer of a different element is formed, and the diffusion layer is preferably 1 μm or more, and when the thickness of the diffusion layer is less than 1 μm, The proportion of the guided light that spreads to the substrate portion that is not diffused increases, and the refractive index required for the substrate cannot be satisfied, and sufficient characteristics as an optical waveguide may not be obtained.

In the present invention, it is particularly desirable to use the (0001) plane of a lithium tantalate substrate as the growth surface of the lithium niobate single crystal thin film.

(0001) of the lithium tantalate substrate
The plane refers to a plane perpendicular to the c-axis of lithium tantalate. The reason why it is desirable to use the (0001) plane of the lithium tantalate substrate as the growth surface of the lithium niobate single crystal thin film is that the lithium tantalate has a hexagonal crystal structure.
This is because the (0001) plane is composed of only the a-axis, and thus can be lattice-matched to the lithium niobate single crystal thin film only by changing the lattice constant of the a-axis. Further, the lattice constant (a-axis) of the lithium niobate single crystal thin film is 99.8 of the lithium tantalate substrate.
Desirably, it is 1 to 100.07%, and 99.92 to
100.03% is preferred.

For example, when the lattice constant of the lithium tantalate substrate is 5.153 °, 5.150 to 5.15
Desirably, it is 5 °. The reason is that if the lattice constant is out of the above range, it is difficult to match the lattice constants of the lithium tantalate substrate containing a different element and the lithium niobate single crystal thin film, and the lithium niobate monolithic material having excellent optical properties usable as an optical material. This is because a crystal thin film cannot be formed sufficiently thick.

The thickness of the lithium niobate single crystal thin film is preferably 5 μm or more, more preferably 10 μm or more. In particular the lithium niobate single crystal thin film of the present invention, when used as a SHG element, the ordinary refractive index n ₀ of the lithium niobate single crystal thin film, extraordinary refractive index n _e
Are in the range of 2.24 ≦ n ₀ ≦ 2.40 and 2.0 for a laser light source (basic wavelength) having a wavelength of 0.83 μm, respectively.
<N _e <n ₀ -0.01 Scope, also with respect to the second harmonic wavelength generated (0.415μm), the ordinary refractive index n ₀ is greater than the ordinary refractive index n ₀ for the fundamental wavelength, and extraordinary refractive index n _e is preferably a ordinary refractive index n ₀ is less than the range for the fundamental wavelength.

The lithium niobate single crystal thin film of the present invention contains an element selected from Nd, Rh, Zn, Ni, Co, Ti and the like in order to change the optical characteristics such as the refractive index as required. Can also.

When an SHG device is manufactured using the lithium niobate single crystal thin film of the present invention, the transmittance of the second harmonic light is 1
It is desirable to form a wavelength-selective thin film (filter) that does not allow the fundamental laser light to pass through near 00% or directly on the light emitting end face. The reason for this is that unnecessary fundamental laser light is removed from the emitted light,
This is because only the harmonic light can be efficiently extracted. Further, by forming the wavelength-selective thin film directly on the emission end face and adjusting it so as to satisfy the antireflection condition for the second harmonic light, there is a large difference in the refractive index between the niobium lithium single crystal thin film layer and air. For this reason, it is possible to reduce the loss due to reflection occurring at the emission end face, and to improve the SHG output.

The wavelength-selective thin film may be formed at a position apart from the emission end face in the publication of the emission end face,
It may be fixed to the emission end face using an appropriate adhesive.

When the adhesive is fixed on the emission end face using the adhesive, the SHG output can be improved by adjusting the refractive index and the thickness of the adhesive so as to meet the antireflection condition for the second harmonic light. desirable.

As the wavelength-selective thin film, a color glass filter and a wavelength-selective interference film on a glass substrate are used.
Can be used.

The material of the wavelength-selective thin film is S
oxides such as iO ₂ , MgO, ZnO, Al ₂ O ₃ , LiN
A composite oxide such as bO ₃ , LiTaO ₃ , Y ₃ Ga ₅ O ₁₂ , Gd ₃ Ga ₅ O ₁₂ , or an organic substance such as PMMA MNA can be used, and a multilayer thin film in which these are stacked can also be used.

The method for producing the wavelength-selective thin film includes sputtering, epitaxial, vapor deposition, MBE (molecular beam epitaxy), MOCVD, ion plating, LB, spin coating, and dipping. Can be used.

Next, the manufacturing method of the present invention will be described.
As a method for producing the lithium niobate single crystal thin film of the present invention, a liquid phase epitaxial growth method, a sputtering method, a vapor deposition method and the like are preferable, but a liquid phase epitaxial growth method is particularly preferable. The reason for this is that it is easy to obtain a uniform film with excellent crystallinity, and as a result, it has low light propagation loss and has excellent characteristics that make full use of the nonlinear optical effect and acousto-optical effect of lithium niobate suitable as an optical waveguide. This is because the obtained lithium niobate single crystal thin film can be obtained, and the productivity is excellent.

As the liquid phase epitaxial growth method,
A lithium tantalate substrate is brought into contact with a melt made of Li ₂ O, Nb ₂ O ₅ , V ₂ O ₅ , Na ₂ O, MgO, etc., and a single crystal thin film of lithium niobate a is formed by liquid phase epitaxial growth.
It is preferable to use a method of matching the lattice constant of the axis with the lattice constant of the a-axis of the lithium tantalate substrate, since a high-quality crystal can be obtained.

In the present invention, Li ₂ O, Nb ₂ O ₅ , V ₂ O ₅ , Na ₂
The reason for using a melt made of O, MgO, or the like is that Li ₂ O and V ₂ O ₅ act as fluxes to realize liquid phase epitaxial growth of lithium niobate single crystal. In addition, by including Na and Mg in the lithium niobate single crystal thin film, the lattice constant of the a-axis of the lithium niobate single crystal thin film can be increased.
The lattice constant of the axis can be matched to the lattice constant of the a-axis of the lithium tantalate substrate, whereby a lithium niobate single crystal thin film having a large film thickness can be obtained.

In the present invention, the composition range of three components of Li ₂ O, V ₂ O ₅ and Nb ₂ O ₅ excluding Na ₂ O and MgO of the melt used in the epitaxial growth method is defined as Li ₂ O— In a triangular diagram of a three-component system of V ₂ O ₅ —Nb ₂ O ₅ , A (88.90, 2.22, 8.8)
8), B (55.00, 43.00, 2.00), C
(46.50, 51.50, 2.00) and D (37.
50, 5.00, 57.50).

Further preferred Li ₂ O, V ₂ O ₅ , Nb ₂ O ₅
The composition range of the three components is E (69.85, 21.3).
3,8.82), F (49.95, 45.02, 5.0).
3), a composition ratio indicated by a region surrounded by G (44.13, 16.76, 39.11) and H (54.72, 11.12., 34.16). Particularly preferred regions are I (57.43, 35.05, 7.52), J (49.
95, 42.53, 7.52), K (47.36, 2
6.32, 26.32) and L (56.38, 17.9).
1, 25.71).

As the composition ratio of Na ₂ O in the present invention, the molar ratio of Na ₂ O / Li ₂ O is 2.0 / 98.0-9.
It is desirable that the range satisfy 3.5 / 6.5. The reason is that when the ratio of Na ₂ O is out of the above range, the lithium niobate single crystal thin film cannot be lattice-matched with the lithium tantalate substrate containing a different element.

[0061] The Na as the composition ratio of _{2 O, Na 2 O / Li} 2 O molar ratio is 7.4 / 92.6 to 80.0 / 20.0
Is preferable, and 16.7 / 83.3 is satisfied.
It is preferable that the ratio satisfies ４８48.4 / 51.6. Further, the composition ratio of MgO is Mg
O / lithium niobate is 0.1 / 99.9 to 25.0 / 7
It is desirable that the composition range satisfy 5.0.

The reason for this is that when the ratio of MgO is lower than the above range, the effect of preventing the optical damage of Mg is insufficient, and when the ratio of MgO is higher than the above range, magnesium niobate-based crystals precipitate. This is because a lithium niobate single crystal thin film cannot be obtained.

The above-mentioned lithium niobate means a stoichiometric amount of lithium niobate that can be precipitated from a melt composition. Further, the composition ratio of MgO is preferably such that the molar ratio of MgO / lithium niobate satisfies 0.7 / 100 to 9.0 / 100, and 3.5 / 100 to 6.0 / 100.
It is preferable that the range satisfy the following.

The different elements in the thin film are: Rh; 0.05-20 mol% Zn; 0.02-30 mol% Ni; 0.1-20 mol% Co; 0.05-20 mol% Cr; 0.02-20 mol% Ti; 0.2-30 Mol% Nd; 0.02 to 10 mol% V; 0.05 to 30 mol%

As the raw material components in the present invention, oxides,
Alternatively, a compound that changes to an oxide by heating is desirable. For example, Na ₂ CO ₃ , Nb ₂ O ₅ , Li ₂ CO ₃ , V ₂
O ₅ , MgO, NaVO ₃ , NaNbO ₃ , LiVO ₃ , L
a composition of iNbO _{3 and} the like.

It is desirable to carry out the raw material components at 600 to 1300 ° C. in an air atmosphere or an oxidizing atmosphere.

According to the present invention, it is desirable that after the melt is supercooled, a different element-containing lithium tantalate substrate is brought into contact therewith and grown.

The cooling rate for bringing the melt into a supercooled state is desirably 0.5 to 300 ° C./hour.

The temperature for the growth is 600-125.
Desirably, the temperature is 0 ° C. The reason is that the melting point of lithium niobate is 1250 ° C., at which temperature crystals do not precipitate, and at 600 ° C., the melting agent (Li ₂ O—V ₂ O
This is because the raw material cannot be melted at a lower temperature than the melting point of ₅ ).

In the present invention, as the growth surface of the lithium niobate single crystal thin film, the lithium tantalate substrate (0
It is desirable to use the (001) plane.

At the time of the growth, it is desirable to rotate the substrate. This is because by rotating the substrate, crystals having uniform characteristics and film thickness can be formed.

Preferably, at least the surface of the lithium tantalate substrate containing a different element is optically polished and then subjected to a chemical etching treatment. The thickness of the lithium niobate single crystal thin film of the present invention, which crystallizes on a heterogeneous element-containing lithium tantalate substrate, is determined by appropriately selecting the contact time between the substrate and the melt and the temperature of the melt.
Can be controlled. In the present invention, as the melt _{composition, Nb 2 O 5, V 2} O 5, LiO 2, Na 2 O, MgO
In addition, oxides of elements selected from Nd, Rh, Zn, Ni, Co, Ti and the like can be used.

FIG. 2 is a sectional view of a lithium niobate thin film lattice-matched by adding 1 mol of Na and 6 mol of Mg to a lithium tantalate substrate containing a different element in the method of the present invention.
Shown in FIG. 3 shows an X-ray diffraction diagram at this time. At this time, the lattice constant was 5.1535 °.

Next, an embodiment of the present invention will be described.

Example 1 (1) 44.4 mol% of Na ₂ CO _3, 44.4 mol of Li ₂ CO ₃
Mol%, V ₂ O ₅ 5.6 mol%, Nb ₂ O ₅ 5.6 mol%,
MgO was added in an amount of 5 mol% based on the theoretical amount of LiNbO _{3 that} can be precipitated from the raw material composition (MgO / LiNbO ₃ =
5/95), and the mixture was placed in a platinum crucible and heated to 1100 ° C. in an air atmosphere in an epitaxial growth and growth apparatus to dissolve the contents of the crucible. Next, the melt was stirred with a propeller at a rotation speed of 150 rpm for 20 hours.

(2) Chamfering a 1 mm thick lithium tantalate substrate (R side: JIS B0701 R 0.5)
After that, an MgO layer having a thickness of 250 ° was formed by RF sputtering, and thermally diffused at 940 ° C. to form a diffusion layer having a thickness of 250 °. The surface ordinary light refractive index of the diffusion portion was lower by 0.015 than in the case where MgO was not diffused. Also,
The surface roughness of the substrate surface is determined according to JIS B0601 Rmax =
170 degrees.

(3) After the melt was gradually cooled to 938 ° C. at a cooling rate of 60 ° C. per hour, the substrate was cooled at 938 ° C. for 5 hours.
It was preheated for 0 minutes and immersed in the melt for 20 minutes while rotating at 100 rpm. The growth rate of lithium niobate was 0.7 μm / min.

(4) The substrate material is pulled up from the melt, and the melt is shaken off at a rotation speed of 1,000 rpm for 30 seconds, and then gradually cooled to room temperature at 1 ° C./min. A sodium and magnesium-containing lithium niobate single crystal thin film having a thickness was obtained.

(5) The amounts of sodium and magnesium contained in the obtained lithium niobate single crystal thin film were 1 mol% and 6 mol%, respectively. The refractive index measured at an incident light wavelength of 1.15 μm is 2.225 ± 0.0
01. The lattice constant (a-axis) is 5.155 °,
The surface roughness of lithium niobate is determined according to JIS BO601.
Rmax = 1000 °.

Example 2 (1) 69 mol% of Li ₂ CO _3, 16 mol% of V ₂ O ₅ , Nb
A mixture of 15 mol% of ₃ O _{5 and} 2.60 and 6 mol% of Cr ₂ O ₃ , Na ₂ CO ₃ , and MgO, respectively, based on the theoretical amount of LiNbO _{3 that} can be precipitated from the melt composition is put into a platinum crucible. Then, the contents of the crucible were dissolved by heating to 1100 ° C. in an air atmosphere in an epitaxial growth and growth apparatus.
(Na ₂ O / Li ₂ O = 45/69, MgO / LiNbO
₃ = 6/94)

(2) The melt was gradually cooled to 916 ° C. at a cooling rate of 60 ° C. per hour. After optically polishing the (0001) plane of the lithium tantalate single crystal having a thickness of 1.5 mm, chamfering (C plane: JIS B0701 C0.7) was performed, and then a 500 Å thick V film was formed by RF sputtering.
After forming the film, it was thermally diffused at 970 ° C. to form a diffusion layer of 500 ° and then chemically etched to obtain a substrate material. The surface roughness of this substrate is JIS B0601
Rmax = 300 °. This substrate material had an ordinary light refractive index reduced by 1 × 10 ⁻³ as compared with a substrate material that does not diffuse V. The substrate material was immersed in the melt for 15 minutes while rotating at 100 rpm. The growth rate of lithium niobate was 0.60 μm /.

(3) The substrate material is pulled up from the melt, and the melt is shaken off at a rotation speed of 1000 rpm for 30 seconds, and then gradually cooled to room temperature at a rate of 1 ° C./min. A chromium, sodium, and magnesium-containing lithium niobate single crystal thin film having a thickness of 9 μm was obtained.

(4) The amounts of chromium, sodium and magnesium contained in the obtained lithium niobate single crystal thin film were 2 mol%, 7 mol% and 7 mol%, respectively. The lattice constant (a-axis) of the thin film is 5.155 °, and the refractive index measured at an incident light wavelength of 1.15 μm is 2.230 ± 2.
It was 0.001. The surface roughness of lithium niobate is
JIS BO601 Rmax = 1000 °.

Example 3 (1) 37.8 mol% of Li ₂ CO ₃ , 15 mol% of V ₂ O ₅ ,
Nb ₃ O ₅ 2.8 mol%, Na ₂ CO ₃ 44.4 mol% addition, precipitatable from the melt composition and TiO _2, MgO Li
15.3 mol% respectively based on the theoretical amount of NbO _3, 3
The mixture with the mol% added was placed in an iridium crucible, and was placed in an epitaxial growth and growth apparatus under an air atmosphere at 1100.
C. to dissolve the contents of the crucible. Next, the melt was subjected to 12 rpm using a propeller at a rotation speed of 200 rpm.
Allowed to stir for hours.

(2) The melt was gradually cooled to 915 ° C. at a cooling rate of 60 ° C. per hour. The (0001) plane of the lithium tantalate single crystal was optically polished to a thickness of 1.8 mm, and then chamfered (C plane JIS B0701 C05). After forming an MgO film having a thickness of 1000 ° and a width of 5 μm by photolithography and RF sputtering, it was thermally diffused at 920 ° C. to obtain a substrate material having an MgO diffusion channel having a width of 5 μm. The thickness of the diffusion layer was about 2 μm. This channel part is MgO
Has an ordinary light refractive index of 15 × 10 ⁻³ as compared with a portion where the light is not diffused.
Had decreased. Further, the surface roughness is measured according to JIS BO601.
Rmax = 300 °. 915 ° C
And then immersed in the melt for 17 minutes while rotating at 100 rpm. The growth rate is 1.94
μm / min.

(3) The substrate material is pulled up from the melt, and the melt is shaken off at a rotation speed of 1000 rpm for 30 seconds, and then at a cooling rate of 300 ° C. per hour to the Curie temperature of the lithium tantalate single crystal. After slowly cooling and keeping at that temperature for 1 hour, the temperature is gradually cooled to room temperature at a cooling rate of 60 ° C. for 1 hour, and a sodium-magnesium-containing lithium niobate single crystal thin film having a thickness of about 33 μm is formed on the substrate material. Obtained.

(4) The amounts of sodium, magnesium and titanium contained in the obtained lithium niobate single crystal thin film were 1.2 mol%, 4 mol% and 8 mol%, respectively.
Met. The lattice constant (a-axis) is 5.155 °, and the refractive index measured at an incident light wavelength of 1.15 μm is 2.239 ±.
It was 0.001.

(5) The obtained lithium niobate single crystal thin film is vertically polished with respect to an MgO diffusion channel having a width of 5 μm, laser light is incident on the end surface, and a near-field pattern of emitted light is obtained. Observation of the laser beam confirmed that the laser light was well confined on the MgO diffusion channel having a width of 5 μm. The surface roughness of the surface of the obtained lithium niobate single crystal thin film was measured according to JIS BO601R.
max = 1000 °.

[0089] Example _{4 (1) V 2 O 5} 44 mole%, Nb ₃ O ₅ 4 mol%, Li ₂ C
A mixture of 52 mol% of O _3, 5 mol% each of MgO and Na ₂ CO ₃ with respect to the theoretical amount of LiNbO ₃ capable of precipitating from the melt composition was put into an iridium crucible, and the mixture was placed in an epitaxial growth growth apparatus under an air atmosphere. At 110
The contents of the crucible were dissolved by heating to 0 ° C. (Na ₂
O / Li ₂ O = 7.4 / 52, MgO / LiNbO ₃ = 5
/ 95)

(2) The melt was gradually cooled to 941 ° C. at a cooling rate of 60 ° C. per hour. The (0001) plane of the lithium tantalate single crystal is optically polished to a thickness of 1.0 mm, chamfered (R plane: JIS BO701 R0.1), and the diffusion layer is formed by photolithography and RF sputtering. 400 with a 5 μm wide window
After forming the Ti film of Å, the substrate was thermally diffused at 950 ° C., and a substrate having a 5 μm wide Ti non-diffusion channel was used as a substrate material. The thickness of the diffusion layer was about 3 μm. The Ti diffused portion has an ordinary light refractive index of 10 × compared to the channel portion.
10 ^-3 had increased. Surface roughness is JIS BO601
Rmax = 100 °. This substrate material is heated to 941 ° C.
For 30 minutes, and immersed in the melt for 15 minutes while rotating at 100 rpm. The growth rate of the lithium niobate single crystal thin film was 0.53 μm / min.

(3) The substrate material is pulled up from the melt, the melt is shaken off at a rotation speed of 1000 rpm for 30 seconds, and then gradually cooled to room temperature at a cooling rate of 60 ° C. per hour. Then, a sodium and magnesium-containing lithium niobate single crystal thin film having a thickness of about 8 μm was obtained.

(4) The amounts of sodium and magnesium contained in the obtained lithium niobate single crystal thin film were 1 mol% and 6 mol%, respectively. The lattice constant (a-axis) was 5.153 °, and the refractive index measured at an incident light wavelength of 1.15 μm was 2.227 ± 0.001.

(5) The obtained lithium niobate single-crystal thin film is vertically polished with respect to a 5 μm wide Ti non-diffusion channel, laser light is incident on the end surface, and a near-field pattern of emitted light is obtained. When the electron beam was observed, it was confirmed that the laser light was well confined on the Ti undiffused channel having a width of 5 μm. The surface roughness of the surface of the obtained lithium niobate single crystal thin film was measured according to JIS BO601Rm.
ax = 1000 °.

[0094] Example _{5 (1) Li 2 CO 3} 50.0 mol%, V ₂ O ₅ 30.0 mol%, Nb ₂ O ₅ 20.0 _{mol%, Na 2 CO 3, MgO} , N
Mixtures containing 50.4 mol%, 4.5 mol%, and 0.8 mol% of d ₃ O ₅ added to the theoretical amount of LiNbO _{3 that} can be precipitated from the melt composition are put into an iridium crucible, and epitaxially grown and grown. The contents of the crucible were dissolved by heating to 1100 ° C. in an air atmosphere in the apparatus. (Na ₂ O / Li ₂ O = 40/50, MgO / LiN
bO ₃ = 4/96)

(2) After the melt was gradually cooled to 929 ° C. at a cooling rate of 60 ° C. per hour, the (0001) plane of the lithium tantalate single crystal was optically polished and chemically etched to a thickness of 0.6 mm. After chamfering (C surface: JIS B0
701 C0.1), and then a Ni film having a thickness of 400 ° was formed by RF sputtering, and then thermally diffused at 1000 ° C. to obtain a substrate material. The diffusion layer was about 3000 °. This substrate material had an ordinary light refractive index increased by 2 × 10 ⁻³ as compared with a portion where Ni was not diffused. The surface roughness of this substrate material is JIS BO601 Rmax = 100 °
Met. The substrate material was immersed in the melt for 7 minutes while rotating at 100 rpm. The growth rate of the lithium niobate single crystal thin film was 1.86 μm /.

(3) The substrate material is pulled up from the melt, and the melt is shaken off at a rotational speed of 1000 rpm for 30 seconds, rapidly cooled to 600 ° C. at 20 ° C./min, and then cooled to 1 ° C.
/ Min at a cooling rate of / min.
A sodium and neodymium-containing lithium niobate single crystal thin film having a thickness of μm was obtained. The surface roughness of the surface of the obtained lithium niobate single crystal thin film was determined according to JIS BO601Rmax =
1000Å.

(4) The amounts of sodium, magnesium and neodymium contained in the obtained lithium niobate single crystal thin film were 2 mol%, 5 mol% and 0.4 mol%, respectively. The lattice constant (a-axis) is 5.155 °, and the refractive index measured at an incident light wavelength of 1.15 μm is 2.227 ±.
It was 0.001.

[0098] Example _{6 (1) Na 2 CO 3} 47.4 mol%, Li ₂ CO ₃ 23.7
Mol%, V ₂ O ₅ 4.2 mol%, Nb ₃ O ₅ 24.7 mol%, which can precipitate of TiO ₂ from the melt composition LiNb
The mixture added at 12.0 mol% with respect to the theoretical amount of O ₃ was placed in an iridium crucible, and heated to 1100 ° C. in an air atmosphere in an epitaxial growth and growth apparatus to dissolve the contents of the crucible.

(2) The melt was gradually cooled to 893 ° C. at a cooling rate of 60 ° C. per hour. After optically polishing the (0001) plane of the lithium tantalate single crystal having a thickness of 1.7 mm,
By photolithography and RF sputtering, an MgO film having a thickness of 800 ° and a width of 5 μm and an MO film having a width of 5 μm were formed.
After a Cu film having a thickness of 400 ° was formed on portions other than the gO film, thermal diffusion was performed at 1000 ° C. to form a diffusion layer having a thickness of about 2000 °. Next, a substrate having an MgO diffusion channel having a width of 5 μm was chemically etched to obtain a substrate material. The ordinary light refractive index of the channel portion where MgO is diffused and the portion where Cu is diffused other than the channel portion are reduced by 10 × 10 ⁻³ and increased by 1 × 10 ^−3, respectively, as compared with the substrate material which does not diffuse anything. Was. The surface roughness is JIS B
O601 Rmax = 500 °. The substrate material was preheated at a height of 10 mm from the melt at 893 ° C. for 60 minutes, and then immersed in the melt for 12 minutes while rotating at 100 rpm. The growth rate was 0.58 μm / min.

(3) The substrate material is pulled up from the melt, and the melt is shaken off at a rotation speed of 1000 rpm for 30 seconds, and then gradually cooled to room temperature at a cooling rate of 2 ° C./min. A sodium and titanium-containing lithium niobate single crystal thin film having a thickness of 7 μm was obtained.

(4) The amounts of sodium and titanium contained in the obtained lithium niobate single crystal thin film were 2.5 mol% and 5.0 mol%, respectively. The lattice constant (a-axis) was 5.153 °, and the refractive index measured at an incident light wavelength of 1.15 μm was 2.241 ± 0.001. The surface roughness of the surface of the obtained lithium niobate single crystal thin film is
JIS BO601Rmax = 2000 °.

(5) The obtained lithium niobate single crystal thin film is polished perpendicularly to an MgO diffusion channel having a width of 5 μm, laser light is incident on the end surface, and near-field pattern of emitted light is obtained. Observation of the laser beam confirmed that the laser light was well confined on the MgO diffusion channel having a width of 5 μm.

Example 7 (1) The surface of the LiNbO ₃ single crystal thin film obtained in Example 1 was mirror-polished to produce a slab type waveguide using the LiNbO ₃ thin film as a waveguide layer.

(2) The thickness of the slab type waveguide is adjusted by ion beam etching to a phase matching thickness of 2.50 μm ± 2.
Adjusted to 0.05 μm.

(3) The slab type waveguide obtained in the above (1) and (2) was subjected to photolithography to a width of 10 μm.
A ridge-type channel waveguide having a thickness of 2.50 μm ± 0.05 μm and a step of 1 μm was prepared.

(4) Both end faces of the channel type waveguide obtained in (3) are mirror-polished by buff polishing so that light can enter and exit from the end faces to obtain a second harmonic generation (SHG) element. .

(5) The SHG element formed of the channel waveguide formed in the above (4) was precisely aligned with the light emitting region of the semiconductor laser and one end face of the channel waveguide. Thereafter, the semiconductor laser chip and the SHG element were fixed on the silicon block using an ultraviolet curing resin. Further, wires are bonded to the electrodes on the upper and lower surfaces of the semiconductor laser so that driving power can be supplied.

(6) The semiconductor laser and the SH
After integrating the G element, it is placed in a metal hermetically sealed package, and the external pins and wires are electrically connected so that operating power can be supplied by the external pins. A cap provided with a window was put on, and the inside was hermetically sealed in a high-purity nitrogen gas atmosphere. When the operating voltage at which the output from the semiconductor laser is 48.0 mW is applied to the hermetically sealed package type device produced using the SHG device comprising the LiNbO ₃ thin film of the present invention, the glass window The output of the second harmonic was 2.0 mW, and the output of the semiconductor laser was 0.1 μW, so that the second harmonic could be efficiently extracted.

Example 8 (1) 45.9 mol% of Na ₂ CO ₃ , Li ₂ CO ₃ 3
6.8 mol%, V ₂ O ₅ 2.7 mol%, Nb ₂ O ₅ 1
4.6 mol%, and 4 mol% of MgO based on the theoretical amount of LiNbO _{3 that} can be precipitated from the melt composition (MgO 3)
/ Nb ₂ O ₅ = 4/96) is placed in a platinum crucible and placed in an epitaxial growth and growth apparatus under an air atmosphere.
The contents of the crucible were dissolved by heating to 1100 ° C.

(2) The melt was gradually cooled to 907 ° C. at a cooling rate of 60 ° C. per hour. The optically polished (0001) plane of sodium-containing lithium tantalate single crystal is chemically etched to a thickness of 1.0 mm, and further chamfered (C plane JIS B0701 C0.5) as a substrate material. did. Surface roughness is JISB0601R
max = 300 °. The amount of sodium contained in this substrate material was 4 mol%. The lattice constant (a-axis) of the substrate material was 5.163 °. The substrate material was preheated from the melt at a height of 15 mm for 30 minutes, and then immersed in the melt for 7 minutes while rotating at 100 rpm. The growth rate of the lithium niobate single crystal thin film was 1.14 μm / min.

(3) The substrate material is pulled up from the melt, and the melt is shaken off on the melt for 30 seconds while rotating at a rotation speed of 1000 rpm, and then the lithium tantalate single crystal is cured at a cooling rate of 5 ° C./min. Slowly cool down to the temperature, hold at that temperature for 1 hour, then slowly cool down to room temperature at a cooling rate of 60 ° C. per hour, and place sodium and magnesium-containing lithium niobate single crystal crystals of about 8 μm thickness on the substrate material A thin film was obtained.

(4) The amounts of sodium and magnesium contained in the obtained lithium niobate single crystal thin film were 1.2 mol% and 5 mol%, respectively. Also,
The lattice constant (a-axis) of the single crystal thin film is 5.154 °, and the refractive index measured at an incident light wavelength of 1.15 μm is 2.229 ± 2.
It was 0.001. The surface roughness of the surface of the obtained lithium niobate single crystal thin film was measured according to JIS B0601Rmax.
= 2000 °.

Example 9 (1) Li ₂ CO ₃ 60 mol%, V ₂ O ₅ 20 mol%,
Nb ₂ O ₅ 20 mole%, added 4 mol% of MgO based on the theoretical amount of precipitation can be LiNbO ₃ from the melt composition _{(MgO / LiNbO 3 = 4/} 96), deposition of TiO ₂ from the melt composition A mixture added to a platinum crucible at 16 mol% based on the theoretical amount of possible LiNbO ₃ was placed at 1100 ° C. in an epitaxial growth and growth apparatus under an air atmosphere.
Until the contents of the crucible were dissolved.

(2) The melt was gradually cooled to 932 ° C. at a cooling rate of 60 ° C. per hour. The (0001) plane of lithium-tantalate single crystal containing titanium was optically polished, then chemically etched to a thickness of 0.8 mm, and further chamfered (R plane: JIS B0701R0.5) as a substrate material. The amount of titanium contained in the substrate material was 9 mol%. Surface roughness is JIS B0601
Rmax = 100 °. The lattice constant (a-axis) of the substrate material was 5.146 °. While rotating this substrate material in the melt at 100 rpm, 18
Soak for minutes. The growth rate of the lithium niobate single crystal thin film was 0.72 μm / min.

(3) The substrate material is pulled up from the melt, and the melt is shaken off on the melt for 30 seconds while rotating at 1000 rpm, and then gradually cooled to room temperature at a cooling rate of 1 ° C./min. A titanium and magnesium-containing lithium niobate single crystal thin film having a thickness of about 13 μm was obtained thereon.

(4) The amounts of titanium and magnesium contained in the obtained lithium niobate single crystal thin film were 8 mol% and 5 mol%, respectively. The single crystal thin film has a lattice constant (a-axis) of 5.145 ° and an incident light wavelength of 1.1.
The refractive index measured at 5 μm was 2.233 ± 0.001. The surface roughness of the surface of the obtained lithium niobate single crystal thin film was determined according to JIS B0601Rmax = 2000 °.
Met.

Example 10 (1) 26.0 mol% of Na ₂ CO ₃ , Li ₂ CO ₃ 3
LiNb capable of precipitating 6.0 mol%, V ₂ O ₅ 25 mol%, Nb ₂ O ₅ 13 mol%, and MgO from the melt composition
0 ₃ of the mixture was added 5 mol% based on the theoretical amount in an air atmosphere in an epitaxial growth apparatus put in a platinum crucible and the contents dissolved in the crucible was heated to 1100 ° C..

(2) The melt was gradually cooled to 935 ° C. at a cooling rate of 60 ° C. per hour. Alumina (α-Al ₂ O ₃ )
After the (0001) plane of the single crystal was optically polished, it was chemically etched to a thickness of 2 mm to obtain a substrate material. The surface roughness was JIS B0601 Rmax = 200 °. This substrate material is 935 from the melt at a height of 10 mm.
After preheating at 45 ° C. for 45 minutes, 100 rpm
Immersion for 12 minutes while rotating. The growth rate of the lithium niobate single crystal thin film was 1.08 μm / min.

(3) The substrate material is pulled up from the melt, and the melt is shaken off on the melt for 30 seconds while being rotated at a rotation speed of 1000 rpm, then rapidly cooled at a rate of 20 ° C./min, and then cooled at 1 ° C./min. It was gradually cooled to a room temperature at a cooling rate to obtain a sodium, magnesium and lithium niobate-containing single crystal thin film having a thickness of about 13 μm on the substrate material.

(4) The amounts of sodium and magnesium contained in the obtained lithium niobate single crystal thin film were 1 mol% and 6 mol%, respectively. The lattice constant (a-axis) of the single crystal thin film is 5.153 °, and the refractive index measured at an incident light wavelength of 1.15 μm is 2.236 ± 0.0.
01. The surface roughness of the surface of the obtained lithium niobate single crystal thin film was JIS B0601Rmax = 14.
It was 00 $.

Example 11 (1) 26.0 mol% of Li ₂ CO ₃ , Nb ₂ O ₅
0 mol% K ₂ CO ₃ 22.5 mol% V ₂ O ₅ 22.
Li capable of depositing 5 mol% of MgO from the melt composition
A mixture containing 5 mol% of the theoretical amount of NbO ₃ was placed in a platinum crucible and heated to 1100 ° C. in an air atmosphere in an epitaxial growth and growth apparatus to dissolve the contents of the crucible.

(2) The melt was gradually cooled to 893 ° C. at a cooling rate of 60 ° C. per hour. The (0001) plane of the lithium tantalate single crystal was optically polished to a thickness of 1.5 mm, and an MgO film having a thickness of 800 ° and a width of 5 μm was formed by photolithography and RF sputtering.
After a Cu film having a thickness of 400 ° was formed on the portion other than the MgO film of m, the film was thermally diffused at 1000 ° C. The diffusion layer is made of Mg
Both O and CuO were about 2000 °. Then, width 5μ
Those having m MgO diffusion channels were chemically etched to obtain a substrate material. The channel portion where MgO is diffused and the portion where Cu is diffused other than the channel portion are:
The ordinary light refractive index was decreased by 10 × 10 ⁻³ and increased by 1 × 10 ^−3, respectively, as compared with the substrate material in which none was diffused.
The surface roughness was JIS B0601Rmax = 400 °. This substrate material is placed at a position of 15 mm
Preheat at 93 ° C, then 100 rpm in the melt
Immersion for 11 minutes while rotating. The growth rate of the lithium niobate single crystal thin film was 0.54 μm / min.

(3) The substrate material is pulled up from the melt, and the melt is shaken off at a rotation speed of 1000 rpm for 30 seconds, and then gradually cooled to room temperature at a cooling rate of 1 ° C./min. A MgO-containing lithium niobate single crystal thin film having a thickness of about 6 μm was obtained. The lattice constant (a-axis) is 5.153
Å, the refractive index measured at an incident light wavelength of 1.15 μm is 2.
230 ± 0.001. The surface roughness of the surface of the obtained lithium niobate single crystal thin film was measured according to JIS B0601.
Rmax = 1400 °.

Example 12 (1) 50 mol% of Li ₂ CO _3, 30 mol% of V ₂ O ₅ , Nb
20 mol% of ₃ O _{5 and} 86 mol% of Na ₂ CO ₃ with respect to the theoretical amount of LiNbO _{3 that} can be precipitated from the melt composition,
A mixture of MgO and 0.2 mol% based on the theoretical amount of LiNbO _{3 that} can be precipitated from the melt composition is put into an iridium crucible, and heated to 1100 ° C. in an air atmosphere in an epitaxial growth and growth apparatus, and the crucible content is increased. Was dissolved. Next, the melt was stirred for 12 hours at a rotation speed of 200 rpm using a propeller.

(2) The melt was gradually cooled to 915 ° C. at a cooling rate of 60 ° C. per hour. The (0001) plane of the lithium tantalate single crystal was optically polished to a thickness of 1.8 mm, and then chamfered (C plane: JIS B0701 C0.1). An MgO film having a thickness of 1000 ° and a width of 5 μm was formed by photolithography and RF sputtering. Then, the substrate was brought close to the melt in the epitaxial growth and growth apparatus at 2.67 cm / min, and preheating and thermal diffusion were performed simultaneously. The thickness of the diffusion layer was about 4000 °. This substrate material was immersed in the melt for 17 minutes while rotating at 100 rpm. The growth rate is 1.94 μm
/ Min.

(3) The substrate material is pulled up from the melt, the melt is shaken off at a rotational speed of 1000 rpm for 30 seconds, and then the temperature of the single crystal of lithium tantalate single crystal at a cooling rate of 300 ° C. per hour. Slowly cooled to room temperature at a cooling rate of 60 ° C. in one hour, and a sodium-magnesium-containing lithium niobate single crystal thin film having a thickness of about 33 μm is formed on a substrate material. I got

(4) The amounts of sodium and magnesium contained in the obtained lithium niobate single crystal thin film were 1.2 mol% and 0.3 mol%, respectively. The lattice constant (a-axis) is 5.155 ° and the incident light wavelength is 1.15.
The refractive index measured in μm was 2.228 ± 0.001.

(5) The obtained lithium niobate single crystal thin film is vertically polished with respect to an MgO diffusion channel having a width of 5 μm so that laser light is incident on the end surface and a near-field pattern of emitted light is obtained. Observation of the laser beam confirmed that the laser light was well confined on the MgO diffusion channel having a width of 5 μm. The surface roughness of the surface of the obtained lithium niobate single crystal thin film was measured according to JIS BO601R.
max = 900 °.

Example 13 (1) 50 mol% of Li ₂ CO _3, 40 mol% of V ₂ O ₅ , Nb
₂ O ₅ 10 mole%, a Na ₂ CO ₃ with respect to precipitation theoretical amount of LiNbO _3, added 45 mol% of MgO with respect to precipitation theoretical amount of LiNbO _3, put the mixture was added 7 mol% platinum crucible Then, the contents of the crucible were dissolved by heating to 1100 ° C. in an air atmosphere in an epitaxial growth and growth apparatus.

(2) The melt was gradually cooled to 918 ° C. at a cooling rate of 60 ° C. per hour. After optically polishing the (0001) plane of the lithium tantalate single crystal, an MgO film having a thickness of 1000 ° and a width of 5 μm is formed by photolithography and RF sputtering, and then thermally diffused at 1000 ° C. to a width of 5 μm. A substrate having an MgO diffusion channel was used as a substrate material. The diffusion layer was about 1 μm. In this channel portion, the ordinary light refractive index was reduced by 15 × 10 ⁻³ as compared with the portion where MgO was not diffused. The substrate material was immersed in the melt for 9 minutes while rotating at 100 rpm.
The growth rate was 2.1 μm / min.

(3) The substrate material is pulled out of the melt, and the melt is shaken off at 1000 rpm for 30 seconds on the melt, and then gradually cooled to room temperature, and about 19 μm thick sodium and magnesium are placed on the substrate material. A lithium-containing lithium niobate single crystal thin film was obtained.

(4) The amounts of sodium and magnesium contained in the obtained lithium niobate single crystal thin film were 2 mol% and 6 mol%, respectively. The lattice constant (a-axis) was 5.155 °, and the refractive index measured at an incident light wavelength of 1.15 μm was 2.229 ± 0.001.

(5) The obtained lithium niobate single crystal thin film is polished perpendicularly to an MgO diffusion channel having a width of 5 μm, laser light is incident on the end surface, and a near-field pattern of emitted light is obtained. Observation of the laser beam confirmed that the laser light was well confined on the MgO diffusion channel having a width of 5 μm.

[0134] Example _{14 (1) Na 2 CO 3} 12.8 mol%, Li ₂ CO ₃ 37.2
Mol%, V ₂ O ₅ 40.0 mol%, Nb ₂ O ₅ 10.0 mol%, the Nd ₂ O ₃ relative to the theoretical amount of precipitated LiNbO _3,
The mixture to which 0.8 mol% was added was put into a platinum crucible, and 1100 ° C. in an air atmosphere in an epitaxial growth and growth apparatus.
Until the contents of the crucible were dissolved.

(2) The melt was gradually cooled to 927 ° C. at a cooling rate of 60 ° C. per hour, and the (0001) plane of the lithium tantalate single crystal was optically polished. After forming the Ni film of
After thermally diffusing at a temperature of ° C., a material chemically etched was used as a substrate material. The diffusion layer was about 6000 °. This substrate material had an ordinary light refractive index increased by 1 × 10 ⁻³ compared to a substrate material that did not diffuse Ni. This substrate material was immersed in the melt for 7 minutes while rotating at 100 rpm.
The growth rate was 1.57 μm / min.

(3) The substrate material is pulled up from the melt, and the melt is shaken off at 1000 rpm for 30 seconds on the melt, then slowly cooled to room temperature, and about 11 μm thick sodium or neodymium is placed on the substrate material. A lithium-containing lithium niobate single crystal thin film was obtained.

(4) The amounts of sodium and neodymium contained in the obtained lithium niobate single crystal thin film were 1.2 mol% and 0.4 mol%, respectively. The lattice constant (a-axis) is 5.153 ° and the incident light wavelength is 1.15 μm.
Was 2.232 ± 0.001.

Embodiment 15 This embodiment is basically the same as Embodiment 1 except that MgO
Was added, the Na content in the lithium niobate single crystal thin film grown by liquid phase epitaxial was changed by changing the amounts of Na ₂ CO ₃ and LiaCO ₃ . In addition, (a) of the lithium niobate single crystal corresponding to each Na content
Is measured using powder X-ray diffraction. The relationship between the content of Na in the lithium niobate single crystal thin film and the lattice constant of the a-axis is shown in FIG. An example is shown in FIG.

Embodiment 16 This embodiment is basically the same as Embodiment 12 except that Mg
A single-crystal lithium niobate thin film was grown without doping O and changing the ratio of LiaCO ₃ and Nb ₃ O _{5 in} the raw material. Next, the lattice constant of the a-axis of the lithium niobate single crystal corresponding to each Li / Nb ratio was measured using powder X-ray diffraction, and the relationship between the lattice constant of the a-axis in the lithium niobate single crystal thin film was determined. Is shown in FIG.

Example 17 (1) Li ₂ CO ₃ 50 mol%, V ₂ O ₅ 40 mol%, Nb
10 mol% of ₃ O ₅ , TiO ₂ is added to the theoretical amount of LiNbO _{3 which} can be precipitated from the melt composition,
The raw material mixture was prepared. Each mixture was placed in a platinum crucible and heated to 1100 ° C. in an epitaxial growth and growth apparatus under an air atmosphere to dissolve the contents of the crucible.

(2) The melt was gradually cooled to 932 ° C. at a cooling rate of 60 ° C. per hour. After optically polishing the (0001) plane of lithium-tantalate single crystal containing titanium, it was chemically etched to a thickness of 0.8 mm to obtain a substrate material. The amount of titanium contained in the substrate material was 9 mol%. Surface roughness is JIS BO601
Rmax = 100 °. This substrate material is 100r
It was immersed in the melt while rotating at pm.

(3) The substrate material was pulled up from the melt, and the melt was shaken off on the melt for 30 seconds while rotating at 1000 rpm, and then gradually cooled to room temperature at a cooling rate of 1 ° C./min. FIG. 6 shows the relationship between the content of Ti in the lithium niobate single crystal thin film obtained from each raw material and the lattice constant of the a-axis of the lithium niobate single crystal thin film.

Embodiment 18 This embodiment is basically the same as Embodiment 1 except that Na ₂
By changing the amounts of CO ₃ and Li ₂ CO ₃ , the Na content in the lithium niobate single crystal thin film grown by liquid phase epitaxial was changed. The content of MgO was 5 mol%. The a-axis lattice constant of the lithium niobate single crystal corresponding to each Na content was measured using powder X-ray diffraction, and the Na content in the lithium niobate single crystal thin film and the a-axis lattice constant were measured. The relationship between the constants is shown in FIG. FIG. 7 shows the relationship between Na and the lattice constant of the a-axis of the niobate single crystal thin film when MgO is not doped for comparison.

Example 19 (1) Li ₂ CO ₃ 50 mol%, V ₂ O ₅ 40 mol%, Nb
₃ O ₅ 10 mol%, LiNbO that can be precipitated from the melt composition
A mixture in which the added amount of MgO was changed with respect to the theoretical amount of ₃ was placed in a platinum crucible to prepare a mixture having a different composition. Subsequently, the contents of the crucible were dissolved by heating to 1100 ° C. in an air atmosphere in an epitaxial growth and growth apparatus. Further, the melt was stirred with a propeller at a rotation speed of 100 rpm for 12 hours.

(2) The (0001) plane of the lithium tantalate single crystal having a thickness of 2 mm is optically polished, chemically etched, and chamfered (R plane JIS; B0701 R0.5).
Was done. The melt is cooled at a rate of 60 ° C./hour to 9
After gradually cooling to 15 ° C., the substrate was preheated at 915 ° C. for 30 minutes, and then immersed in the melt for 8 minutes while rotating at 100 rpm. The growth rate of lithium niobate is 1
μm / min.

(3) The substrate material is pulled up from the melt, and the melt is shaken off at a rotation speed of 1000 rpm for 30 seconds, and then gradually cooled to room temperature at a rate of 1 ° C./min. A magnesium-containing lithium niobate single crystal thin film having a thickness of 3 mm was obtained.

(4) The a-axis lattice constant of the obtained magnesium-containing lithium niobate single crystal was measured by X powder diffraction, and the relationship between the a-axis lattice constant and the content of MgO is shown in FIG. In Examples 15 to 19, the purpose was not to match the lattice, but the relationship between the lattice constant of the a-axis of the lithium niobate single crystal thin film obtained by liquid phase epitaxial growth and the composition of lithium niobate was examined. However, lithium niobate and the substrate are not always lattice-matched. For the lithium niobate single crystal thin film of the present invention obtained in Examples 1 to 14 (excluding 7), the light propagation loss with respect to a semiconductor laser having a wavelength of 0.83 μm by the prism coupling method;
The Pockels constant was measured with a Mach-Zehnder interferometer, and the results are shown in Table 1. Also, in the same manner as in Example 1,
Table 2 shows the light propagation loss of the thin films obtained by adding different elements to the thin film and the substrate, respectively. The heterogeneous element diffusion layer of the substrate is
It is about 1 μm.

[0148]

[Table 1]

[0149] The comparative example is an Applied Physic.
s Letters, vol. 24, no. 9,197
4 This is the value described in P424.

[0150]

[Table 2]

[0151]

As described above, according to the present invention, a lithium niobate single crystal thin film lattice-matched to a substrate is prepared from a melt composed of Li ₂ O—V ₂ O ₃ —Nb ₂ O ₃ having a specific composition range. By manufacturing, it is possible to form a lithium niobate single crystal thin film having extremely excellent optical characteristics, which has not been obtained conventionally, and a sufficient thickness necessary for use as an optical device. It is not only optimal as a constituent material of an SHG element, but also useful as a constituent material of an optical device.

[0152]

[Brief description of the drawings]

FIG. 1 shows Li ₂ O—V ₂ O ₃ —N used in the present invention.
FIG. ₃ is a triangular diagram showing a composition range of a melt composed of b ₂ O ₃ .

FIG. 2 shows a (0001) of a lithium tantalate single crystal substrate
The schematic diagram which shows a surface.

FIG. 3 is a photograph showing a cross section of a lithium niobate thin film formed on a lithium tantalate single crystal substrate when lattice-matched.
It is a photograph taken.

FIG. 4 is an X-ray diffraction diagram of the lithium niobate of the present invention when lattice matched.

FIG. 5 shows the lattice constant of the a-axis of lithium niobate thin film and Na
Of content

FIG. 6 shows lattice constant of a-axis and Mg of lithium niobate thin film.
Of content

FIG. 7 is a schematic view of a second harmonic generation device obtained in Example 7.

[Explanation of symbols]

 Reference Signs List 1 wavelength-selective filter 2 sealing cap 3 SHG device 4 fixing base 5 semiconductor laser chip 6 heat sink 7 base 8 lead pin

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-95242 (JP, A) JP-A-50-92300 (JP, A) JP-A-3-218997 (JP, A) JP-A-4- 12095 (JP, A) JP-A-5-178692 (JP, A) JP-B 51-9720 (JP, B2) JP-B 56-47160 (JP, B2) JP-B 63-27681 (JP, B2) JP-B-60-34722 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) C30B 1/00-35/00 CA (STN)

Claims (3)

(57) [Claims] The composition of Li ₂ O, V ₂ O ₅ and Nb ₂ O ₅ is represented by A (88.90, 2) in a ternary diagram of a ternary system of Li ₂ O—V ₂ O ₅ —Nb ₂ O ₃ . .22, 8.88), B (5
5.00, 43.00, 2.00), C (46.50,
51.50, 2.00) and D (37.50, 5.0).
0, 57.50), which is surrounded by four composition points,
In addition, a lithium tantalate substrate having a different element added to at least a part of its surface is brought into contact with a melt containing an element having an effect of increasing the lattice constant of the lithium niobate single crystal obtained in the composition. And manufacturing a lithium niobate single crystal thin film lattice-matched with the substrate on the substrate. 2. The different element having the function of increasing the lattice constant of a lithium niobate single crystal is Na.
4. The method for producing a lithium niobate single crystal thin film according to claim 1. 3. A dissimilar element having an effect of increasing the lattice constant of a lithium niobate single crystal is Mg.
4. The method for producing a lithium niobate single crystal thin film according to claim 1.