JPH0348831A - Domain control method for nonlinear ferroelectric optical material - Google Patents

Abstract

PURPOSE:To obtain an exact periodic domain inversion structure by disposing counter electrodes on both sides of a nonlinear ferroelectric optical material formed as a single domain in-between, forming at least one thereof as the patterns corresponding to the periodic domain inversion structures and impressing a DC voltage between the electrodes formed in such a manner. CONSTITUTION:Parallel and stripe-shaped rugged patterns 3 corresponding to the patterns of the periodic domain structures to be formed on the 1st nonlinear ferroelectric optical element material 1 are formed by reactive ion etching, etc., on the main surface 2a consisting of +C surface of the 2nd nonlinear ferroelectric optical element material 2. The main surface 2a formed with the rugged patterns 3 is then butted and superposed on the main surface 1a consisting of the +C surface of the 1st material and the heat resistant electrodes 9, 9 are disposed to face each other on both sides of the materials 1, 2 in-between. A DC power source 4 is then turned on with the material 2 side as + to impress the DC voltage between the materials 1 and 2. The periodic domain inversion structure parts 5a corresponding to the patterns 3 of the substrate 2 are generated on the main surface 1a side of the material 1 in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to a nonlinear ferroelectric device suitable for application to, for example, the formation of periodic domain inversion grooves in an optical second harmonic generation device (hereinafter referred to as an SHG device). The present invention relates to a domain control method for an optical material body.

[Summary of the invention]

The present invention relates to a domain control method for a nonlinear ferroelectric optical material body, and the present invention relates to a domain control method for a nonlinear ferroelectric optical material body, and the present invention relates to a domain control method for a nonlinear ferroelectric optical material body. overlapping the second nonlinear ferroelectric optical material body so that its uneven pattern is in contact with the first nonlinear ferroelectric optical material body,
By applying a required DC voltage between the first and second nonlinear ferroelectric optical material bodies, a domain inversion portion is locally formed in the first nonlinear ferroelectric optical material body, By doing so, it is possible to reliably form the domain inversion portion of the fine pattern using a simple device and operation.

[Conventional technology]

SHG devices using Cerenkov radiation have been proposed (for example, Noguchi, Sansui: Applied Physics 56.1637 (1)
987)). However, in this SHG element, the radiation direction of the beam is in the direction of the substrate, and the beam spot has a unique shape, for example, a crescent-shaped spot, which poses problems in actual use. On the other hand, by making the waveguide structure a periodic domain inversion structure in which the domain is inverted to an odd multiple of the coherent length, SHG is able to obtain a highly efficient output with a circular or elliptical beam spot shape. Please see Hiromasa I, Yinghai Zhang, et al., Proceedings of the 49th Japan Society of Applied Physics Conference Proceedings 919 (1988)).

As a method for performing domain inversion, there is a method of controlling current during crystal pulling (D, Feng
, N.B., Ming, J.F., Hong, et al., Ap.
plied Phys+cs Letters, 37
．． 607 (1980), K, Na5sau, H,1
Evinstein, G.H., Loiacono
, Applied Physics Letter
s 6.228 (1965), A. Fe1sst,
P, Koidl.

Applied Physics Letters 4
7. 1125 (1985>) However, such a method not only requires a large-scale apparatus, but also has problems in that it is difficult to control domain formation.

Further, as another method of domain inversion, for example, a method of diffusing T1 can be considered, but in this case, there is a problem that the refractive index of the domain inverted portion changes, resulting in a large number of SH wave beams.

[Problem to be solved by the invention]

The present invention is a simple device, that is, without the need for a large-scale device, by a simple operation, and without causing a change in the refractive index of the domain inversion region. The purpose is to make it possible to form an inverted structure of a target domain.

For this purpose, a domain control method for nonlinear ferroelectric optical materials was previously proposed in Japanese Patent Application No. 1-8271 filed by the present applicant. In this method, counter electrodes are placed on both opposing principal surfaces of a single-domain nonlinear ferroelectric optical material, and at least one of them is formed into a pattern corresponding to a periodic domain inversion structure. By applying a DC voltage between both electrodes, domain inversion parts are locally formed, thereby forming a periodic domain inversion structure. In this method, an electrode is directly attached to the nonlinear ferroelectric optical material crystal substrate, or the electrodes are brought into direct contact with each other, and a voltage is applied between opposing electrodes. However, due to the high-temperature heating performed to lower the coercive electric field of the material body, atoms of the constituent materials of the nonlinear optical material body and atoms serving as the electrodes may diffuse into each other, leading to disadvantages such as the risk of impairing the purity of the optical material body. be.

The present invention aims to solve the above-mentioned inconvenient problems.

[Means to solve the problem]

The present invention provides a first nonlinear ferroelectric optical material (1) having a single domain as shown in FIG.
a) has an uneven pattern (3) on at least one main surface (2a).
) is formed into a single-domain nonlinear second nonlinear ferroelectric optical material body (2), and its concavo-convex pattern (3) is
is one main surface (1) of the first nonlinear ferroelectric optical material (1)
Lay them out so that they touch a). And these first
and second nonlinear ferroelectric optical material bodies (1) and (2)
By turning on the DC power supply (4) in between and applying the required DC voltage, the domain of the pattern corresponding to the uneven pattern (3) is inverted as shown in FIG. 3A and as shown by the broken line in FIG. The portion (5a) is locally formed on one principal surface (1a) of the first nonlinear ferroelectric material body (1).

These first and second nonlinear ferroelectric optical material bodies (1)
and [2) can be made of the same material and have a single domain structure with the C axis in the thickness direction.

The concavo-convex pattern (3) for the second nonlinear ferroelectric optical material body (2) is formed on its +0 main surface (2a),
The principal surface (2a) consisting of this +0 plane and the principal surface (1a) consisting of the +0 plane of the first nonlinear ferroelectric optical material body (1) are superimposed so as to be in contact with each other, and the above-mentioned DC voltage is applied. Lectures at the Tohoku Branch Federation Conference of Related Academic Societies on the Second Nonlinear Ferroelectricity with Concave and Convex Patterns (3) Collection 2
F5 (1986, 8)) is applied with the optical material body (2) side as the positive electrode side.
It is.

[Effect]

According to such a method, the contact portion between the crystal substrates, that is, the portion where the first nonlinear ferroelectric optical material body (1) contacts the second nonlinear ferroelectric material body (2), that is, the uneven pattern Domain inversion occurs at (3) the contact portion with the convex portion). That is, the main surface (1a) side of the +0 surface of the first nonlinear ferroelectric optical material body (1) is positive, and the main surface (1b) side formed by the −C plane on the opposite side is negative. When a DC voltage is applied, polarization inversion proceeds from the +0 plane to the 10 plane of the optical crystal substrate, which causes the polarization to change from the convex part of the concavo-convex pattern (3) of the second nonlinear ferroelectric optical material body (2). Polarization inversion, that is, domain inversion occurs on the main surface (1a) of the first nonlinear ferroelectric optical material (1) that is in contact with the first nonlinear ferroelectric optical material (1). This can be seen, for example, in Ando and Nakamura, who described a polarization reversal method for optical crystal substrates using only heat treatment.
Embodiment] An example of the case where the method of the present invention is used to obtain a Cerenkov radiation type SHG element having a periodic domain inversion structure will be described.

In this case, as shown in FIGS. 2B and A, it consists of two substrates having a C axis in the thickness direction of a lithium niobate (LiNbO3) crystal with a large nonlinear coefficient, for example, the main surface (1a) and (2i). ) side as the +0 plane, that is, first and second nonlinear ferroelectric optical material bodies (1) and (2) made into a single domain having a C axis (two axes) in the thickness direction are prepared. These nonlinear ferroelectric optical materials (1) and (2) can be made into single domains by, for example, raising the temperature to about 1200°C below the IJ temperature and applying an external DC voltage across the entire surface in the thickness direction. By applying , it is possible to form domains with the C axis aligned in the thickness direction over the entire surface.

In the present invention, the period to be formed in the first nonlinear ferroelectric optical material body (1) is formed on the main surface (2a) consisting of the +0 plane of the second nonlinear ferroelectric optical material body (2). A concavo-convex pattern (3) is formed in a striped parallel arrangement corresponding to the pattern of the target domain structure. The uneven pattern (3) can be formed by etching using photolithography, for example. That is, a photoresist is applied over the entire surface of the second nonlinear ferroelectric optical material body (2) on one main surface (2a) consisting of the +0 surface, and subjected to pattern exposure and development treatment to form a resist pattern that will become an etching mask. However, using this resist pattern as a mask, it can be formed by chemical wet etching or dry etching such as RrE (reactive ion etching).

Then, the main surface (2a) having this uneven pattern (3)
As shown in FIG. 1, the first nonlinear ferroelectric optical material body (1) is aligned and superimposed on one main surface (1a) consisting of the +0 plane. Heat-resistant electrodes (8) and (9) are placed between these nonlinear ferroelectric optical material bodies (1) and (2).
) are placed facing each other. Heat-resistant ^β is provided between these electrodes (8) and (9) and each material body (1) and (2) as necessary.
The plate-shaped electrodes (8) and (9) are arranged through the insulators (6) and (7) such as 203, or the plate-shaped insulator (6)
) and (7), respectively, by depositing film-like electrodes (8) and (9) on these electrodes (8) and (9).
) may be opposed to both material bodies (1) and (2) via insulators (6) and (8). Then, with the second nonlinear ferroelectric optical material body (2) as the + side, the DC power source [4] is turned on to apply a DC voltage between the two material bodies [1] and (2). In this case, the voltage applied is, for example, 1000 to 1200
℃For example in an atmosphere of 1040℃, for example in air
6) 300V to the extent that no dielectric breakdown occurs in (7),
Apply for 1 hour. In this way, as shown in FIG. 3A, the uneven pattern ( Periodic domain inversion structure (5) corresponding to 3)
) occurs at a depth of approximately 30 μm. Then the first and second
electrodes (8) and (9) are excluded.

For example, as shown in FIG. 381, for example, birophosphoric acid is applied to the main surface (1a) side of the material body (1) having the periodic domain inversion structure (5) and then thermally diffused, or hot phosphoric acid is applied, for example. An optical waveguide (10) having a refractive index larger than that of the material body (1) is formed by immersing it in acid and performing proton substitution. In this way, a structure in which the periodic domain inversion structure (5) enters the optical waveguide (10) can be obtained, but as another example, as shown in FIG. 382, the periodic domain inversion structure (5) A material body (1
) is provided with an optical waveguide (10) on one principal surface (1a) of a non-linear or linear material layer having a low absorption rate for the fundamental wave and a higher refractive index than the material body (1). The ratio of T1 to the sum of and Ta is Ti/(Ti +T
a) (atomic %) is 0 <Ti/(Ti + Ta) 5
60 (atomic %), or may be formed by evaporation deposition, epitaxial growth, or the like of hydrogenated silicon, titanium dioxide, arsenic glass, zinc sulfide, zinc oxide, or the like.

In this way, it is possible to configure an SHG element in which the periodic domain inversion structure portion (5) is formed, for example, across the waveguide direction.

〔Effect of the invention〕

As described above, according to the present invention, the domain inversion structure (
5) is avoided, the electrode is prevented from coming into direct contact with the main surface (1a) of the nonlinear ferroelectric optical material body (1) to form the second nonlinear ferroelectric material body (1), for example. Since the optical material bodies (2) are brought into contact with each other, even if they are exposed to high heat while in contact with each other, the inconvenience of variations in properties due to mutual diffusion is avoided, and the electrodes are brought into direct contact. Inconveniences such as deterioration of purity due to mutual diffusion of atoms in the case of the present invention are avoided.

In addition, when insulators (6) and (7) are interposed between each electrode (6) and (7) and the nonlinear ferroelectric optical material body (1) and (2), the optical material body especially A nonlinear ferroelectric optical material body (1) forming a domain inversion structure (5)
), crystal damage etc. caused by the flow of current can be avoided, making it possible to construct an SHG element with good characteristics.

Further, according to the method of the present invention, a second nonlinear ferroelectric optical material body (2) separate from the first nonlinear ferroelectric optical material body (1) forming the domain inversion structure (5) is provided. The domain inversion part (5a) of the domain inversion structure part (5) is caused by collision.
), the second nonlinear ferroelectric optical material body (
2) can be used repeatedly to form domain inversion structures [5] for a large number of first nonlinear ferroelectric optical material bodies (1). In addition, this second nonlinear ferroelectric optical material body (2) is simply balanced with the first nonlinear ferroelectric optical material body (1) that is to form the domain inversion structure (5). In this work, it is possible to avoid the inconvenience of forming electrode patterns one by one, and it is possible to simplify the apparatus and the work, thereby improving mass productivity. In addition, since the domain inversion structure portion (5) is reliably formed in a pattern corresponding to the uneven pattern (3) formed on the second nonlinear ferroelectric optical material body (1), when patterning the electrode, As such, it is possible to avoid the risk of the pattern being distorted during heating, and even with a fine pattern, the desired domain inversion structure (5) can be reliably constructed with good reproducibility.

Further, in the method of the present invention, the domain inversion portion (5a) is made of Ti.
Since it is not formed by such doping, the refractive index does not change in this domain inversion 1 (3a), and problems such as a large number of SH wave beams caused by this can be avoided.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the domain inversion control method used to explain the method of the present invention, and FIG.
and a sectional view of the second nonlinear ferroelectric optical material body, and FIG. 3 is an enlarged linear sectional view of each step in an example in which the method of the present invention is applied to obtain a Cerenkov radiation type SHG element. (1) and (2) are first and second nonlinear ferroelectric optical material bodies, (3) is an uneven pattern, and (8) and (9) are electrodes. Agent Hide Hitomatsu Kuma Mori Domain Lord 1 I paid off the wholesale power of the busy confectionery 50 Diagram 1 ■ Line? / Figure 2 of H body φ breakage diagram for promoting dielectric material

Claims (1)

[Scope of Claims] A second single-domain nonlinear ferroelectric optical material body, wherein a first nonlinear ferroelectric optical material body is single-domained, and a concavo-convex pattern is formed on at least one principal surface. are superimposed so that their uneven patterns are in contact with one principal surface of the first nonlinear dielectric optical material body, and a required DC voltage is applied between the first and second nonlinear ferroelectric optical material bodies. A domain control method for a nonlinear ferroelectric optical material body, comprising locally forming a domain inversion part of a pattern corresponding to the uneven pattern on the one principal surface of the first nonlinear ferroelectric optical material body. .