JPH10254000A - Nonlinear optical material having polarization inversion structure, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily produce a material having a polarization inversion structure large in a crystal thickness, by forming ruggedness satisfying specific conditions on a surface having polarization inversion regions. SOLUTION: The ruggedness is formed on the surface 2 having the polarization inversion regions of the nonlinear optical material 1 having the polarization inversion structure. The ruggedness is fitted to the ruggedness of the other nonlinear optical material 3 having the ruggedness on the surface having the polarization inversion structure of the same period and having the polarization inversion regions with each other. The shape of the ruggedness is not particularly limited so far as such reggedness. The depth of the ruggedness is not particularly limited if the ruggedness has the restraining force capable of fixing the positional relations of the nonlinear optical materials with each other. For example, the depth is about 0.1 to 100μm, more preferably about 1 to 100μm. The ruggedness formed on the nonlinear optical materials is eventually formed to meet the polarization inversion periods by using wet process etching when, for example, lithium niobate is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonlinear optical material having a domain-inverted structure and a method of manufacturing the same, and more particularly, to a nonlinear optical material having a domain-inverted structure and having unevenness on a surface having a domain-inverted region and a method of manufacturing the same. About the method.

[0002]

2. Description of the Related Art A nonlinear optical material is a material in which, when a voltage is applied, the refractive index of the material changes, or nonlinear polarization occurs inside the material due to the incidence of a laser beam having a strong electric field intensity. It is a material having a nonlinear optical phenomenon such as converting incident laser light into laser light of another wavelength. In particular, in the field of wavelength conversion, research has been actively conducted for the purpose of expanding the wavelength range of conventional solid-state lasers.

As a nonlinear optical material capable of polarization reversal, a ferroelectric crystal of an inorganic nonlinear optical material or an organic nonlinear optical material is used. A nonlinear optical material obtained by periodically inverting the polarization can efficiently convert the wavelength by forming a period suitable for the wavelength of light entering and exiting the material. By the way, when a non-linear optical material having a domain-inverted structure is used as a wavelength conversion crystal, if the crystal has a large thickness in the polarization direction (hereinafter referred to as “crystal thickness”), the diameter of the incident laser beam can be increased. In addition, the laser light density can be reduced, crystal breakage due to laser can be avoided, and a large output can be obtained. However, for example, when producing a domain-inverted structure having a large crystal thickness using lithium niobate or the like as a nonlinear optical material, the applied voltage required for domain-inverted becomes high when a method of applying a direct current or a pulsed high voltage from the outside is used. As a result, not only is it difficult to control the shape of the inversion structure, but also the possibility of crystal breakage due to the avalanche phenomenon increases.

Therefore, in order to obtain a nonlinear optical material having a domain-inverted structure having a large crystal thickness, a nonlinear optical material having a single polarization direction is bonded so that the polarization directions are alternated, and subjected to a high-temperature heat treatment. Diffusion bonding methods (eg, US Pat. Nos. 5,355,247 and 5,47)
No. 5,526). However, in order to obtain a wavelength conversion crystal of an arbitrary wavelength, it is necessary to determine the thickness of the wavelength conversion crystal in advance before manufacturing. Therefore, there is a problem that much time and labor are required to produce a nonlinear optical material having various kinds of domain-inverted structures.

It is also conceivable to bond a nonlinear optical material having a domain-inverted structure with another nonlinear optical material having the same domain-inverted period while observing the nonlinear optical material with an optical microscope using a double-sided exposure device or the like. However, the domain inversion period is generally several tens of μm or less, and sophisticated techniques are required to accurately adjust the period while observing with an optical microscope. Further, even if the periods are adjusted, there is no force for restraining the mutual positions, so that there is a problem that a positional shift is likely to occur in a process until bonding.

It is an object of the present invention to provide a nonlinear optical material having a domain-inverted structure with a large crystal thickness and a method for easily manufacturing such a nonlinear optical material.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, formed unevenness on a surface having a domain-inverted region of a nonlinear optical material having a domain-inverted structure, In particular, by utilizing the fact that the concavities and convexities according to the polarization inversion cycle can be easily formed by selectively etching, the sophisticated technique can easily and precisely adjust the polarization inversion cycle without requiring advanced technology, For the first time, the inventors have found that a nonlinear optical material having a large crystal thickness and a polarization inversion period can be easily manufactured, and have completed the present invention.

That is, the present invention provides a nonlinear optical material having a domain-inverted structure having irregularities satisfying the following condition (1) on a surface having a domain-inverted region; This is a mode in which the unevenness of another nonlinear optical material having an inversion structure and having unevenness on the surface having the domain-inverted region is fitted to each other. Two or more nonlinear optical materials described above, a nonlinear optical material having a domain-inverted structure having a structure fitted in the unevenness with each other, the nonlinear optical material described above, having a domain-inverted structure of the same period, And a method of manufacturing a nonlinear optical material having a domain-inverted structure, wherein another nonlinear optical material having irregularities on a surface having a domain-inverted region is fitted through the irregularities of the other. A method for manufacturing a nonlinear optical material having the above-described domain-inverted structure, wherein the formed concavities and convexities are formed by etching or machining, and a method for manufacturing a nonlinear optical material having the above-described domain-inverted structure, wherein the etching is wet etching. The nonlinear optical material is lithium niobate, and the solvent used for wet etching is a mixture of hydrofluoric acid and nitric acid or hydrofluoric acid. The manufacturing method of the nonlinear optical material having the domain-inverted structure described above, the manufacturing method of the nonlinear optical material having the domain-inverted structure wherein the etching is dry etching, and the machining is performed from dicing, spraying, and ultrasonic processing. The present invention relates to a method for manufacturing a nonlinear optical material having the above-described domain-inverted structure, which is one type of machining selected from the group consisting of:

[0009]

FIG. 1 shows an embodiment of a nonlinear optical material having a domain-inverted structure according to the present invention. Surface 2 having domain-inverted region of nonlinear optical material 1 having domain-inverted structure
Are formed with irregularities. The irregularities have a domain-inverted structure with the same period, and have a form in which the irregularities of another nonlinear optical material 3 having irregularities on the surface having the domain-inverted regions are fitted to each other. Here, a surface having a domain-inverted region means a surface in which a portion where the polarization direction is periodically inverted is exposed, and having a domain-inverted structure having the same period means that one of the domain-inverted structures is used. The width 4 of the domain-inverted region and the period 6 of the domain-inverted region of the nonlinear optical material having the structure (width 4 of the domain-inverted region)
And the width 5 of the non-polarization-inverted region) and the width and the reversal period of the domain-inverted region of the nonlinear optical material having the other domain-inverted structure.

The unevenness formed on the nonlinear optical material can be formed on the surface having the domain-inverted region by a method such as etching or machining. The method of forming the unevenness by etching is, for example, as follows. A non-linear optical material 7 (for example, lithium niobate) having a domain-inverted structure shown in FIG. 2 is coated with a mixed solution of hydrofluoric acid and nitric acid or a solvent such as hydrofluoric acid on the flat and bottom surfaces of the material (hereinafter referred to as By etching the “perpendicular surface”, one axial direction as shown in FIG. 3 (Z direction in FIG. 3)
Then, the one-way polarized surface is selectively etched (hereinafter also referred to as “selective etching”), and the surface orthogonal to the polarization direction becomes the non-linear optical material 8 having an uneven shape according to the polarization inversion period.

[0011] Examples of the etching method include ion etching, dry etching and wet etching. The ion etching is a method in which inactive ions collide with a non-linear optical material surface in a vacuum to remove surface substances and form irregularities. Dry etching is a method in which a surface substance is removed by a reaction between a reactive gas (for example, carbon tetrachloride gas or the like) and the material to form irregularities, which is also called reactive ion etching. Wet etching is a method in which a nonlinear optical material is immersed in a solvent such as a strong acid to remove surface substances and form irregularities. Among them, wet etching is preferable because an etching mask is not required and selective etching can be performed.

When the nonlinear optical material is, for example, lithium niobate, the solvent used for wet etching may be a mixed solution of hydrofluoric acid and nitric acid or a strong acid such as hydrofluoric acid. In a mixed acid of hydrofluoric acid (HF) and nitric acid (HNO ₃ ), the mixing ratio (volume ratio) is preferably HF: HNO ₃ = 1: 2.
When wet etching is performed, surface treatment of the nonlinear optical material is not particularly performed, and irregularities corresponding to the polarization inversion cycle can be formed by simply immersing the material in the solvent.

As the machining, for example, dicing,
Injection processing, ultrasonic processing and the like can be mentioned, and among them, dicing is preferable because it is easy to form irregularities. More specifically, dicing refers to shaping a surface orthogonal to the polarization direction and / or a surface parallel to the polarization direction of a nonlinear optical material having a domain-inverted structure using a dicing blade or the like to form irregularities. . Injection processing is a method in which abrasive grains are sprayed on a sample to obtain an arbitrary processing shape, and ultrasonic processing is a method in which a cutting tool is applied to a sample and processing is performed according to the shape of the tool while flowing abrasive grains. It is.

The shape of the above-mentioned unevenness is such that it has a domain-inverted structure having the same period and is fitted to the unevenness of another nonlinear optical material having unevenness on the surface having the domain-inverted region. There is no particular limitation.

The depth of the unevenness is not particularly limited as long as there is a binding force capable of fixing the positional relationship between the nonlinear optical materials.
For example, about 0.1-100 μm, preferably 1-10
It is about 0 μm.

In the case of using lithium niobate, for example, the unevenness formed on the nonlinear optical material is necessarily formed in accordance with the polarization inversion cycle by using wet etching. Lithium niobate, lithium tantalate, and the like tend to have a crystal structure in which the spontaneous polarization direction coincides with the Z-axis direction as the crystal axis direction. It has the feature that the direction and the-direction are reversed. Therefore, when the polarization is reversed, a + Z plane and a -Z plane (a plane generally perpendicular to the crystal axis) appear periodically on the same surface. + Z
Since the atomic arrangement is different between the surface and the -Z surface, if a specific etching solution is used, a difference occurs in the etching rate, and irregularities are naturally formed. Especially for lithium niobate,
By inverting the Z-axis, the Y-axis and the X-axis, which are orthogonal to the Z-axis, can also be inverted in the same manner, and selective etching can be performed not only on the Z-plane but also on the Y-plane and the X-plane. Irregularities are formed. Therefore, there is no need to labor for forming irregularities so that the domain-inverted regions of the two nonlinear optical materials newly coincide with each other. However, when performing machining such as dicing, when the irregularities have a domain-inverted structure of the same period, and are fitted with the irregularities of another nonlinear optical material having irregularities on a surface having a domain-inverted region. In addition, it is necessary to align the inverted portions of the materials so that they always coincide with each other.

The non-linear optical material having two or more domain-inverted structures having the irregularities is fitted through the irregularities on the surface orthogonal to the polarization direction of the material, so that the non-linear optical materials are fitted in the irregularities. A nonlinear optical material having a domain-inverted structure having a structure can be obtained. Further, irregularities are formed on the front surface and the rear surface (hereinafter, also referred to as “plane parallel to the polarization direction”) of the material, and the irregularities on the surface parallel to the polarization direction and / or orthogonal to the polarization direction. The non-linear optical material having the domain-inverted structure having the structure fitted in the unevenness can be obtained by fitting through the unevenness of the surface.
The method of forming irregularities on a plane parallel to the polarization direction is the same as the method of forming irregularities on a plane perpendicular to the polarization direction described above. FIG. 4 shows a nonlinear optical material having a domain-inverted structure having a fitted structure using unevenness of a surface orthogonal to the polarization direction of the material, and FIG. 3 shows a nonlinear optical material having a domain-inverted structure having a fitted structure by utilizing unevenness of a flat surface and unevenness of a surface orthogonal to a polarization direction.

In order to manufacture a nonlinear optical material having a domain-inverted structure having a fitted structure as shown in FIG. 5, first, irregularities are formed on a plane parallel to the polarization direction of the material and a plane perpendicular to the polarization direction. It is necessary to form a material having irregularities on the four surfaces. In order to form irregularities on the four surfaces of the nonlinear optical material having a domain-inverted structure, the entire material may be immersed in a mixed solution of hydrofluoric acid and nitric acid and a solvent such as hydrofluoric acid.

As a method of manufacturing a nonlinear optical material having a domain-inverted structure having a fitted structure, for example, a nonlinear optical material having two domain-inverted structures having the above-mentioned unevenness on a surface having a domain-inverted region is fitted. As an example, a method in which the unevenness of one nonlinear optical material and the unevenness of the other nonlinear optical material are engaged with each other so as to engage with each other, and then a method of pressing and pressurizing. It can be obtained by a method such as diffusion bonding at a temperature equal to or lower than the Curie point, a method of bonding the interface between materials with an adhesive having a refractive index similar to that of the nonlinear optical material, or the like. The thickness of the nonlinear optical material having the domain-inverted structure with the fitted structure is
It is 1 mm or more, preferably about 1 to 20 mm.

The nonlinear optical materials used in the present invention include LiTaO ₃ (LT), LiNbO ₃ (LN), K
TiOPO ₄ (KTP), LiNbP ₄ O ₁₂ (LN
P), KNbO ₃ (KN), BaNaNb ₅ O ₁₅ (BN
N), KTiOAsO ₄ (KTA), β-BaB ₂ O ₄
(BBO), LiB ₃ O ₇ (LBO) and KH ₂ PO
₄ Inorganic nonlinear optical materials such as (KDP), metanitroaniline (mNA), 2-methyl-4-nitroaniline (MNA), 4-bromo-4′-methoxychalcone (chalcone), dicyanovinylanisole, 5-dimethyl-1- (4-nitrophenyl) pyrazole (DM
NP), N-methoxymethyl-4-nitroaniline (M
MNA), 4'-nitrobenzylidene-3-acetamino-4-methoxyaniline (MNBA), L-arginine phosphate monohydrate (LAP), 2-adamantylamino-5-nitropyridine (AANP) and Pauld An organic nonlinear optical material such as a polymer may be used.

As the inorganic nonlinear optical material, the domain-inverted shape is uniform over the entire domain-inverted region, the shape is maintained up to the back surface of the crystal substrate, and the material properties are good (the nonlinear optical constant is large). It is preferable to use LT, LN and KTP from the viewpoint of high wavelength conversion efficiency.

As the organic nonlinear optical material, MNB is preferred because of its good material properties (large nonlinear optical constant).
It is preferred to use A, MNA and chalcone.

The method for producing the inorganic nonlinear optical material is not particularly limited. For example, in the case of LiNbO ₃ single crystal,
A melt pulling method in which a seed of LiNbO ₃ crystal is brought into contact with a melt of Li ₂ O and Nb ₂ O ₅ and the seed is slowly pulled up to grow LiNbO ₃ as a single crystal using the seed as a nucleus.

The method for producing an organic nonlinear optical material includes a melting method in which a crystal is grown from a melt having a crystal composition and a melt method in which an organic substance is heated to a temperature equal to or higher than the melting point and then slowly cooled to grow the crystal. For example, AANP can be produced by a melt method in which nitrogen gas and AANP powder are sealed in a glass ampule, heated to a temperature equal to or higher than the melting point of AANP in a furnace, and then the temperature is lowered to grow crystals.

The nonlinear optical material used in the present invention may contain impurities. Impurities that can be included in the inorganic nonlinear optical material include rare earth elements, metal oxides, metal elements, and the like. Examples of impurities that can be contained in the organic nonlinear optical material include organic dyes. Also,
Impurities may be doped into the nonlinear optical material depending on the required characteristics of the product.

Examples of the rare earth elements include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, lutetium and the like. Examples of the metal oxide include magnesium oxide. Examples of the metal element include iron, nickel, chromium, cobalt, aluminum, titanium and zinc.

The method of doping the nonlinear optical material with impurities is performed by a method known per se. For example, in the case of an inorganic nonlinear optical material, it is performed simultaneously with its growth, or a heat treatment is performed by depositing a doping material on the crystal surface. And diffusing it inside the crystal. In the case of an organic non-linear optical material, a method of performing the same at the time of its growth or a method of diffusing it from the surface of the material may be used.

A method for manufacturing a nonlinear optical material having a domain-inverted structure is as follows. When a voltage is applied via an electrolytic solution to a nonlinear optical material structure including a nonlinear optical material, an insulating film provided on one surface of the material at an interval, and a conductive film covering the surface of the material and the insulating film. ,
The voltage applied to the nonlinear optical material is reduced by the partial pressure of the insulating film, and polarization inversion occurs selectively only in the portion without the insulating film. In this way, a nonlinear optical material in which the domain-inverted region and the non-domain-inverted region of the nonlinear optical material are arranged at a certain interval is obtained.

The width of the domain-inverted region and the non-domain-inverted region is arbitrarily designed according to the characteristics of the product, and is usually 1 to 100 μm.
m. The width of the domain-inverted region and the width of the non-domain-inverted region may be the same or different, but it is preferable that the ratio between the domain-inverted region and the non-domain-inverted region is 1: 1.

[0030]

EXAMPLES Examples and comparative examples are shown below, but the present invention is not limited by these examples. Example 1 A mixture of hydrofluoric acid (50 mol%) and nitric acid (60 mol%) in a ratio of 1 to 2 (volume ratio) was used. At 60 ° C., a LiNbO ₃ crystal having a domain-inverted structure (inversion ratio of 50%, polarization) As a result of immersing the Z plane (width of the inversion region: width of the non-polarization inversion region = 1: 1) for 2 minutes, unevenness corresponding to the polarization inversion cycle was obtained at a depth of 0.03 μm. After bonding two obtained LiNbO ₃ crystals having a domain-inverted structure having irregularities, they were joined in a heat treatment furnace at 500 ° C. to obtain a 1000 μm-thick LiNbO ₃ crystal having a domain-inverted structure.

Example 2 On a LiNbO ₃ crystal having a domain-inverted structure, a precision dicing saw (trade name: DAD2SP-67, manufactured by Disco Corporation) was used, with a resin diamond blade, a groove width of 300 μm, a depth of 50 μm, and a period. As a result of forming irregularities at intervals of 300 μm, irregularities corresponding to the polarization inversion cycle
Obtained at a depth of 10 μm. Two obtained LiNbO ₃ crystals having a domain-inverted structure having irregularities were bonded together with a photocurable adhesive to obtain a 1000 μm-thick LiNbO ₃ crystal having a domain-inverted structure.

[0032]

The nonlinear optical material having the domain-inverted structure of the present invention has irregularities on the surface having the domain-inverted region.
This material can be easily and precisely fitted with another nonlinear optical material having a domain-inverted structure of the same period and having unevenness on the surface having the domain-inverted region, and matching the domain-inverted period. . Therefore, a non-linear optical material having a domain-inverted structure with a large crystal thickness can be obtained easily and with high precision without requiring advanced technology. Therefore, if a non-linear optical material having a domain-inverted structure with a large crystal thickness is used as the wavelength conversion crystal, the incident laser beam diameter can be increased, and as a result, the laser light density can be reduced,
Crystal breakage by laser can be prevented, and high output can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a nonlinear optical material having a domain-inverted structure of the present invention.

FIG. 2 is a diagram illustrating a nonlinear optical material having a domain-inverted structure in which no irregularities are formed.

FIG. 3 is a diagram showing a nonlinear optical material having a domain-inverted structure in which a polarization plane in one direction in one axial direction is selectively etched.

FIG. 4 is a diagram illustrating a nonlinear optical material having a domain-inverted structure having a fitted structure via unevenness on a surface orthogonal to the polarization direction of the nonlinear optical material having a domain-inverted structure.

FIG. 5 is a diagram showing a nonlinear optical material having a domain-inverted structure having a fitted structure via unevenness of a surface parallel to the polarization direction of the nonlinear optical material having a domain-inverted structure.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 Nonlinear optical material having domain-inverted structure 2 Surface having domain-inverted region 3 Nonlinear optical material having domain-inverted structure having unevenness on surface having domain-inverted region 4 Width of domain-inverted region 5 Width of non-domain-inverted region 6 Nonlinear Polarization reversal period of optical material 7 Non-linear optical material having domain-inverted structure without unevenness 8 Non-linear optical material having domain-inverted structure with unevenness on surface having domain-inverted region

Claims (8)

[Claims] 1. A nonlinear optical material having a domain-inverted structure having irregularities satisfying the following condition (1) on a surface having a domain-inverted region. (1) A configuration in which the irregularities have a domain-inverted structure of the same period and are fitted to the irregularities of another nonlinear optical material having irregularities on the surface having the domain-inverted region. 2. A nonlinear optical material having a domain-inverted structure in which two or more nonlinear optical materials according to claim 1 have a structure fitted to each other with unevenness. 3. The non-linear optical material according to claim 1, and another non-linear optical material having a domain-inverted structure having the same period and having irregularities on a surface having a domain-inverted region through irregularities formed by each other. A method for manufacturing a nonlinear optical material having a domain-inverted structure, wherein 4. The method for manufacturing a nonlinear optical material having a domain-inverted structure according to claim 3, wherein the irregularities formed on the nonlinear optical material are formed by etching or machining. 5. The method for manufacturing a nonlinear optical material having a domain-inverted structure according to claim 4, wherein the etching is wet etching. 6. The production of a nonlinear optical material having a domain-inverted structure according to claim 5, wherein the nonlinear optical material is lithium niobate, and the solvent used for wet etching is a mixed solution of hydrofluoric acid and nitric acid or hydrofluoric acid. Method. 7. The method for manufacturing a nonlinear optical material having a domain-inverted structure according to claim 4, wherein the etching is dry etching. 8. The method for manufacturing a nonlinear optical material having a domain-inverted structure according to claim 4, wherein the machining is one kind of machining selected from the group consisting of dicing, injection machining, and ultrasonic machining.