JPH0580376A - Nonlinear optical material - Google Patents

Abstract

PURPOSE:To obtain a non-doped nonlinear optical material of waveguide structure having a high optical-damage threshold value and a nonlinear optical effect almost equivalent to LiNbO3 by laminating the thin-film crystal of KNbO3 on a substrate having a lower refractive index than KNbO3. CONSTITUTION:The thin film crystal 2 is laminated on any one face 1 among the (110) face of spinel, the (112bar0) face and (112bar1) face of quartz crystal, the (010) face and (100) face of KTP or the (110) face of MgO. The obtained optical material is reduced in lattice mismatching, enhanced in proof stress to light and increased in the optical-damage threshold value, the nonlinear optical constant is increased, and the wavelength conversion effect is improved. The optical material is used for the wavelength conversion element, optical switch, light modulator, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical material used as a wavelength conversion element, an optical switch, an optical modulator or the like in a light source device for a high density optical disc, an information processing device such as an optical arithmetic device or the like.

[0002]

2. Description of the Related Art Nonlinear optical effects are the same as nonlinear optical materials,
Even if light sources having the same light output are used, the more the light is confined in a region as narrow as possible, in other words, the larger the spatial density of the light incident on the nonlinear medium, the greater the effect. For this reason, the structure of the nonlinear optical material should be a waveguide structure, and in the optical waveguide, the step-like change in the refractive index at the interface between the substrate and the optical waveguide laminated on the substrate facilitates design and characteristics. This is preferable from the viewpoint of controllability, and from this point of view, a waveguide is deposited in a thin film on a substrate having a refractive index smaller than that of the waveguide material itself, rather than being formed by an impurity diffusion method, an ion exchange method, or the like. It can be said that it is more preferable to use the waveguide or the channel type waveguide manufactured by etching the thin film.

As a conventional non-linear optical material satisfying these conditions, a LiTaO ₃ substrate or sapphire (α-
On the Al ₂ O ₃ ) substrate by LPE (Liquid Phase Epitaxial) method
Some have deposited LiNbO ₃ thin film crystals (OQE88-4
3). LiNbO ₃ has a large non-linear optical constant indicating the strength of the non-linear optical effect, is chemically stable, and has excellent characteristics when used in, for example, a wavelength conversion element.

[0004]

However, the LiNbO ₃ thin film crystal is about 30 MW / cm ^{2 in} the case of laser light having a so-called optical damage threshold of 1.06 μm, which is a level at which its ferroelectricity is destroyed by light energy. There was a problem that it was lower than other materials. As a means to solve this, MgO is added to the substrate.
There has been proposed a method of increasing the optical damage threshold value by doping Al.

However, this method has a drawback that it is difficult to adjust the MgO component ratio, and it is not easy to satisfy such a component ratio particularly in the crystal growth process by the sputtering method. The present invention has been made to solve such conventional problems, and provides a non-linear optical material having a waveguide structure that is non-doped, has a high optical damage threshold, and has a non-linear optical effect similar to that of LiNbO _3. It is intended to be provided.

[0006]

In the nonlinear optical material according to the present invention, in order to solve the problems], in the nonlinear optical material formed by depositing a KNbO ₃ thin-film crystal on a substrate having a refractive index less than the refractive index of the KNbO _3, The KNbO ₃ thin film crystal is a {110} plane of spinel, a {112 bar 0} plane of crystal, and a {112 bar 1 plane.
} Plane, KTP {010} plane, {100} plane, or MgO {1
It is characterized in that it is deposited on any one of the 10} planes.

[0007]

[Function] In the present invention, spinel, crystal, KTP (KTiO)
KNb on the surface of the substrate formed by either PO ₄ ) or MgO
Since the O ₃ thin film crystal is laminated, the lattice mismatch is small, the proof stress against light is greatly increased, the optical damage threshold value is increased, and the nonlinear optical constant is also increased to improve the wavelength conversion effect. ..

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. (Embodiment 1) FIG. 1 is a schematic view showing a nonlinear optical material of a thin film waveguide structure according to the present invention, in which 1 is a substrate and 2 is K.
It shows a waveguide made of NbO ₃ thin film crystal. The substrate 1 is made of a material having a refractive index smaller than that of KNbO ₃ , for example, spinel (MgO.Al ₂ O ₃ ), and a waveguide 2 made of a KNbO ₃ thin film crystal on its (110) plane. To
It is deposited by the RF magnetron sputtering method or the like.

An example of the deposition conditions of KNbO ₃ thin film crystals is as follows. Spinel belongs to the cubic system and has a lattice constant of 8.02Å at room temperature.
The substrate 1 is obtained by cutting along the (110) plane as shown in (a). FIG. 2 (a) is an explanatory view showing a unit cell of spinel and its (110) plane. In the figure, 3 is a basic unit cell of spinel, and 4 is a spinel (110) plane (shown by hatching). is there.
Next, this substrate 1 is maintained at about 600 ° C. in an atmosphere having a gas pressure ratio of Ar: O ₂ = 1: 1, and a thin film of KNbO ₃ single crystal having a RF power density of about 1 w / cm ² and a thickness of 1 μm is deposited.

FIG. 2B is an explanatory diagram showing oxygen atoms 11 of the spinel and oxygen atoms 12 of the KNbO ₃ thin film crystal laminated on the (110) plane of the spinel, with the latter projected onto the former. The arrangement of spinel oxygen atoms 11 is 4.01Å in the [001] direction and 2.84Å in the [11 bar 0] direction as shown in Fig. 2 (d).
Has become a cycle. On the other hand, the arrangement of oxygen atoms 12 of KNbO ₃ has a period of 3.97Å in the b-axis direction and a period of 5.70Å in the a-axis direction as shown in Fig. 2 (c). As shown in (b), 1.0% in the b-axis direction of KNbO ₃ ,
It becomes about 0.35% in the a-axis direction, and relatively good matching of mutual oxygen atoms is possible.

In the above-mentioned embodiments, the structure in which the KNbO ₃ thin film crystal is formed on the (110) face of the spinel is shown, but the present invention is not limited to this, and the face {110} equivalent thereto may be used. Although MgO.Al ₂ O ₃ having a mixed crystal ratio of 1: 1 is shown as the spinel, it goes without saying that spinel having a different mixed crystal ratio may be used. As a result of investigating the light damage threshold value of Example 1 as described above, it was found that the light damage threshold value of 35
It was confirmed to be about 0 MW / cm ² .

(Embodiment 2) Although not specifically shown in this embodiment, quartz is used as the substrate and
KNb on the 12 bar 0) surface using LPE (liquid crystal epitaxial) method
Waveguides made of O ₃ thin film crystals were laminated. KNbO ₃
An example of the deposition conditions of the thin film crystal is shown below with specific numerical values.

First, the crystal is shown in FIG. 3 (a) (112 bar 0).
Cut the surface to obtain the substrate. FIG. 3 (a) is an explanatory view showing a unit lattice and its (112 bar 0) plane, in which 5 is a basic unit lattice of crystal, and 6 is a crystal (112 bar 0) plane (hatched and shown. ). The crystal lattice constant is 4.91 on the a-axis.
Å, 5.40Å on the c-axis, and is a trigonal crystal at room temperature, but since it can be equivalently expressed as a hexagonal crystal, it is represented as a hexagonal crystal in FIG. 3 (a).

Next, this substrate and K ₂ O--Nb ₂ O ₅ --V ₂ O
A KNbO ₃ thin film crystal (single crystal) having a film thickness of 1 μm or more was laminated by the LPE method using a ₅ type material at a growth temperature of about 1000 ° C. Not only the (112 bar 0) plane of the crystal, but also the {112 bar 0} plane including this, or the (112 bar 1) plane, or the equivalent {112 bar 1} plane including this, KNbO ₃ Similar effects can be obtained by depositing thin film crystals.

FIG. 3B shows the oxygen atom 13 of the crystal and (1
Oxygen atoms in KNbO ₃ thin film crystal deposited on the (12 bar 0) plane 12
It is explanatory drawing which projects and shows the latter on the former. The arrangement of oxygen atoms 13 in the crystal is 5.40Å in the [0001] direction shown in Fig. 3 (d).
The cycle is also 4.25Å in the [11 bar 00] direction. The arrangement of oxygen atoms 12 of KNbO ₃ is shown in Example 1.
As shown in. Therefore, the lattice mismatch is KNb
It becomes 5.5% in the a-axis direction of O ₃ and 7.0% in the b-axis direction, and it is possible to match the oxygen atoms on the a-axis and the b-axis of quartz and KNbO ₃ .

In the above-described Example 1, the spinel was used as the substrate 1, the waveguide 2 of KNbO ₃ thin film crystal was used on the (110) plane 4 thereof, and in Example 2, quartz was used as the substrate (112 bar 0 ) The structure in which KNbO ₃ thin film crystals are laminated on the surface 6 has been described, but the material of the substrate is not particularly limited to these, and KTP (KTiOPO ₄ ), MgO or the like may be used.
If KTP is used as the substrate, its (010) plane, (100) plane
If KNbO ₃ thin film crystals are laminated on the planes or their equivalent {010} planes, {100} planes, and when MgO is used, on their (110) planes or their equivalent {110} planes. Good.

Next, as a substrate, spinel (Mg
Table 1 shows the lattice mismatch when O · Al ₂ O ₃ ), quartz (SiO ₂ ), KTP, and MgO are used.

[0018]

[Table 1]

The nonlinear optical constants (pm / V) of the nonlinear optical material according to the present invention and the conventional nonlinear optical material are shown in Table 2.

[0020]

[0021]

In the nonlinear optical material according to the present invention as described above, according to the present invention, since a KNbO ₃ thin-film crystal on a substrate having a refractive index less than the refractive index of the KNbO ₃ are then stacked, KNbO ₃ thin film The present invention is excellent in that the optical damage threshold, which is the level at which the ferroelectricity of the crystal is impaired, is increased, the nonlinear optical constant is also large, and excellent characteristics are obtained when used in wavelength conversion elements, optical switches, optical modulators, etc. It has a great effect.

[Brief description of drawings]

FIG. 1 is a schematic view of a nonlinear optical material according to the present invention.

FIG. 2 is an explanatory diagram showing a matching mode of a unit cell of spinel and oxygen atoms.

FIG. 3 is an explanatory diagram showing a matching mode of a unit cell of quartz and oxygen atoms.

[Explanation of symbols]

1 substrate 2 waveguide consisting of KNbO ₃ thin film crystal 3 unit cell of spinel 4 (110) face of spinel 5 unit lattice of crystal 6 (112 bar 0) face of crystal 11 oxygen atom of spinel 12 oxygen atom of KNbO ₃ thin film crystal 13 Quartz oxygen atoms

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Nonaka 2-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Takao Yamaguchi 2-18th Keihanhondori, Moriguchi-shi, Osaka Sanyo Denki Within the corporation

Claims (1)

[Claims] 1. A nonlinear optical material formed by laminating a waveguide made of KNbO ₃ thin-film crystal on a substrate having a refractive index less than the refractive index of the KNbO _3, which is the waveguide K
NbO ₃ thin film crystals are spinel {110} planes, crystal {112 bar 0} planes, {112 bar 1} planes, and KTP {01} planes.
A non-linear optical material characterized by being deposited on any of the 0} plane, the {100} plane, or the MgO {110} plane.