JP2849221B2 - Optical device having channel type waveguide and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device having a channel-type waveguide and a method for manufacturing the same, and more particularly, to a method for manufacturing a crystal on a lithium tantalate single crystal substrate (hereinafter simply abbreviated as "LT substrate"). Lithium niobate single crystal thin film (hereinafter, simply abbreviated as “LN thin film”) having excellent electro-optic effect and non-linear optical characteristics.
By injecting a different element into a specific position in the T substrate, a region having a large difference in refractive index from the LN thin film is created, and a channel-type waveguide is provided. This is a proposal for an optical device to be used.

[0002]

2. Description of the Related Art As an optical device used in the above-mentioned applications, there is a conventional method in which V ₂ O ₅ is thermally diffused together with MgO into an LT substrate as proposed in Japanese Patent Publication No. 60-34722.
A structure in which an optical waveguide is formed by epitaxially growing a LiTaO ₃ thin film, and a low refraction of 3 to 6 μm by diffusing V ₂ O ₅ on the LT substrate surface as proposed in Japanese Patent Publication No. 63-27681. Having a three-layer optical waveguide in which lithium tantalate is grown by a liquid phase epitaxy method (LPE method) after forming a diffusion layer having a high refractive index, or disclosed in JP-A-1-201609. An optical device as described above, that is, `` diffuses a diffusing substance from the surface of the substrate around the ridge waveguide formed on the surface of the substrate, and changes the refractive index in the substrate at the bottom of the optical waveguide to the refractive index of the core of the optical waveguide. Ridge-type optical waveguides that enhance the confinement of light.

[0003]

However, the two prior arts use lithium tantalate as a thin film waveguide layer, and a lithium niobate thin film is formed on a lithium tantalate substrate as in the present invention. However, there is a problem that it is not possible to obtain a thin film waveguide layer having a large refractive index difference and excellent in crystallinity required for producing a high-output SHG element.

On the other hand, the optical device disclosed in Japanese Patent Application Laid-Open No. Hei 1-201609 improves the light confinement effect of the ridge waveguide by diffusing impurities into the substrate surface, but has excellent crystallinity and optical characteristics. Since a thin film waveguide layer having excellent characteristics cannot be obtained, an optical device suitable as an SHG element cannot be manufactured.

A disadvantage common to these prior arts is that a thin film for forming a lattice-matched waveguide cannot be formed on a substrate, so that the crystallinity of the thin film is poor. The occurrence of microcracks was observed in the formed thin film. For this reason, the surface of the substrate material and the surface of the thin film have to be smoothed by polishing or chemical etching or the like, or a high-purity raw material with a low impurity mixing ratio has been used. However, in these methods, even if the scattering loss at the substrate interface and the thin film surface, or the absorption loss due to impurity contamination can be reduced,
Since the absorption and scattering loss at the crystal grain boundaries is large, the light propagation loss is as large as about 3 to 5 dB / cm, and there is a problem in using it for optical applications.

An object of the present invention is to form a channel-type waveguide based on a thin-film waveguide layer having a large light confinement effect and excellent in crystallinity and optical characteristics. Overcoming the problems.

[0007]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of various studies on a method for solving the problems of the above-mentioned conventional technology, a thin film waveguide layer lattice-matched with a single crystal thin film is used to form a highly crystalline film suitable for manufacturing an SHG element or the like. It has been newly found that a single-crystal thin-film optical waveguide having a very large thickness and excellent optical characteristics such as extremely small optical damage and light propagation loss can be obtained.

On the other hand, by diffusing and containing various kinds of different elements for increasing the refractive index difference between the substrate and the thin film of the waveguide pattern portion on the lithium tantalate substrate, the refraction of the LT substrate immediately below the waveguide is reduced. It is expected that an optical device having a large difference in the refractive index between the substrate and the optical waveguide in the thin film waveguide layer can be practically obtained without impairing the characteristics of the single crystal thin film having excellent optical characteristics. Headings,
The present invention has been completed.

That is, according to the present invention, as shown in FIG.
, In the optical device formed by growing a thin-film waveguide layer 2 on the substrate 1, the lattice constant of the single crystal thin film waveguide layer, dissipate lattice matching together with that of the single crystalline substrate, the thin film waveguide layer Immediately below the formation area of the optical waveguide 3 formed therein.
The refractive index of the substrate surface 4 you location, by diffusion inclusion of dissimilar element is an optical device having a channel-type waveguide, characterized in that the relatively smaller than the region 5 which is not forming an optical waveguide 3.

In order to relatively increase the difference in the refractive index between the substrate and the thin film, the present invention provides a method for thermally diffusing a refractive index lowering element such as Mg or V to at least the surface of the substrate in the optical waveguide forming region. On the other surface of the substrate except immediately below the optical waveguide portion, a refractive index increasing element such as Ti, Cr, Nd, Rh, Zn, Ni, Fe or Co is thermally diffused, and the refractive index of the substrate directly below the optical waveguide portion is adjusted. The area is relatively smaller than the area excluding the optical waveguide formation area. The width of the optical waveguide formation area is 0.1 mm to 100 μ
m is desirable. The thin film and the substrate are preferably an LN thin film and an LT substrate, respectively.

In the optical device, an LN thin film is grown on an LT substrate, and a channel-type waveguide is formed in the thin film. In manufacturing the optical device, the surface of the LT substrate along the waveguide is formed. Then, after containing an element that lowers the refractive index of the substrate than that which does not form a waveguide, the lithium niobate single crystal thin film formed on the substrate has a lattice constant of the hexagonal a-axis. Any one or more of the following means; Lattice constant of lithium tantalate substrate> Lattice constant of lithium niobate single crystal thin film; a. Mg or Na is contained in the lithium niobate thin film. b. Change the Li / Nb ratio of lithium niobate. c. Ti is contained in the lithium tantalate substrate. 2. When the lattice constant of the lithium tantalate substrate <the lattice constant of the lithium niobate single crystal thin film; d. Ti is contained in the lithium niobate thin film. Is manufactured by forming a film by a liquid phase epitaxial method so as to match the lattice constant of the lithium tantalate substrate according to the selection.

[0012]

The optical device of the present invention is obtained by growing an LN thin film on an LT substrate to form a channel-type optical waveguide. In particular, it is preferable that the LN thin film and the LT substrate are lattice-matched. This is because, by lattice-matching the LN thin film and the LT substrate, an LN thin film exhibiting excellent optical characteristics can be formed with a film thickness that cannot be obtained by conventional techniques. As described above, the reason why the LN thin film exhibits extremely excellent optical characteristics is that the LN thin film and the LT substrate are integrated in a lattice-matched manner, have very little lattice distortion, crystal defects, etc., have excellent crystallinity, and have a microcrack. This is because a high-quality thin film having no such properties is obtained.

In the present invention, the reason for focusing on lattice matching between the LN thin film and the LT substrate is that the lattice constant of the hexagonal a-axis of lithium niobate (5.148 °) and the lattice constant of the hexagonal a-axis of lithium tantalate are different. This is because the lattice constant (5.154 °) is close, and the following method is used. A: When the lattice constant of the LN thin film is smaller than the lattice constant (a-axis) of the LT substrate;
Including different elements in the LN thin film,
A method of increasing the lattice constant of the LN by changing the molar ratio of Li / Nb, or decreasing the lattice constant of the LT by including a different element in the LT substrate;
B: When the lattice constant of the LN thin film is larger than the lattice constant of the LT substrate; Ti is contained in the LN thin film;
This is performed by any one or more of the above methods.

First, in the above method, Na is used as a different element for lattice matching between the LN thin film and the LT substrate.
And Mg are preferred.

The reason why Na and Mg are preferable is that the Na or Mg ions or atoms have the effect of increasing the lattice constant of LN by substitution or doping with respect to the LN crystal lattice, so that the composition of Na and Mg is adjusted. As a result, the L
This is because lattice matching between the T substrate and the LN thin film can be obtained. Further, Na and Mg are preferable because they not only impair the optical characteristics at all but also have an important effect of preventing optical damage, particularly for Mg.

When Na and Mg are contained, the content is
0.1-14.3 mol% (N
a), desirably 0.8 to 10.8 mol% (Mg). The reason is that if the Na content is less than 0.1 mol%, the lattice constant cannot be increased enough to make lattice matching with the LT substrate, regardless of the presence or absence of the added amount of Mg.
If the value exceeds, the lattice constant becomes too large, and in either case, the lattice matching between the LT substrate and the LN thin film cannot be obtained.

On the other hand, if the content of Mg is less than 0.8 mol%, the effect of preventing light damage is insufficient, while if it exceeds 10.8 mol%, magnesium niobate-based crystals precipitate. This is not desirable.

The contents of Na and Mg are more preferably 0.3 to 4.8 mol% and 3.5 to 8.6 mol%, respectively, and more preferably 0.8 to 3.2 mol% and 4.5 to 5.7 mol%. It is.

Next, in the above method, the lattice constant of the hexagonal a-axis can be increased by changing the molar ratio of Li / Nb in the LN single crystal. The molar ratio of Li / Nb is desirably 41/59 to 56/44. The reason is that outside the above range, crystals such as LiNb ₃ O ₈ and Li ₃ NbO ₄ also precipitate, so that LN with excellent optical characteristics cannot be obtained.

Further, regarding the above methods, as a method of reducing the lattice constant of the a-axis of the LT substrate,
It is desirable to contain Ti. The reason for this is that Ti atoms or their ions have the effect of reducing the lattice constant of the a-axis of the LT substrate.

When the above-mentioned Ti atom or its ion is contained, the content thereof is based on the LT single crystal.
It is preferably 0.2 to 30 mol%. The reason is that Ti
When the content of is less than 0.2 mol%, the lattice constant does not become small enough to allow lattice matching with the LN single crystal, and when it exceeds 30 mol%, on the contrary, the lattice constant becomes too small. This is because lattice matching between the LT substrate and LN cannot be obtained.

In the above case, it is necessary to reduce the lattice constant of the a-axis of the LN single crystal thin film.
In order to lattice-match with the LT substrate adjusted to the range of 128 to 5.173 °, it is desirable to include Ti in the LN thin film. The reason is that Ti atom or its ion is L
This is because it has the effect of reducing the lattice constant of the a-axis of the N thin film. Therefore, in this case, the LN thin film is a
The lattice constant of the axis will be adjusted in the range of 5.128 to 5.173mm.

The substrate used in the present invention is:
The crystal structure is hexagonal and the lattice constant of the a-axis is 5.128 to 5.
Within the range of 173 °, lattice matching with the LN thin film is easy, and the shape of the substrate is a flat, rod-like, fibrous, etc. substrate such as Al ₂ O ₃ , ZnO, MgO, Gd ₃ Ga ₅ O ₁₂ ,
Although lithium tantalate and the like can be used, lithium tantalate is particularly suitable. The reason for this is that the crystal system of the lithium tantalate single crystal is similar to the lithium niobate single crystal, and is easy to epitaxially grow.

The LT substrate used in the present invention includes:
A material in which various elements are contained and whose lattice constant, refractive index, and the like are changed, or a material whose surface is treated by chemical etching or the like can be used. The surface roughness of the LT substrate on which the LN thin film is formed is JIS B0601, R _max = 300.
Desirably, it is 1000 mm. The reason for this is that it is extremely difficult to make the value of R _max less than 300 °, and if the value of R _max exceeds 1000 °, the crystallinity of the LN thin film decreases.

It is desirable to use a (0001) plane perpendicular to the c-axis of the LT substrate as a growth surface of the LN thin film. The reason is that the lithium tantalate has a hexagonal crystal structure and the (0001) plane is lattice-matched only with the a-axis. Therefore, the lattice matching with the LN thin film can be performed only by changing the lattice constant of the a-axis. Because it is convenient.

The lattice constant of such an LN thin film is
Desirably, 99.81 to 100.07%, 99.92 to 100.07%.
03% is preferred. For example, the lattice constant of the LT substrate is 5.
If it is 153 mm, it is desirable that it be 5.150-5.155 mm. The reason for this is that when the lattice constant is out of the range,
This is because it is difficult to match the lattice constants of the LT substrate and the LN thin film, and it is not possible to form a sufficiently thick LN thin film having excellent optical characteristics that can be used as an optical material.

Further, the LN thin film of the present invention has Cr, Nd,
It is effective to include at least one selected from Rh, Zn, Ni, Co, Ti, and V.

Next, in the present invention, the substrate is provided with at least a surface such that a refractive index of a pattern forming region where an optical waveguide is formed is relatively smaller than that of a region excluding the pattern forming region. It is necessary to include a heterogeneous element in a part thereof, whereby an optical waveguide is formed in the thin film without losing the characteristics of the thin film, which is an important feature of the present invention. .

That is, by injecting a different element into at least the surface of the substrate by a method such as thermal diffusion,
Mainly change (decrease) the refractive index of this substrate
Therefore, the difference in the refractive index between the substrate and the thin film waveguide can be increased.

In the case of the LT substrate and the LN thin film, the different element is used for a purpose different from the element for lattice-matching the LT substrate and the LN thin film.
Mg or V, or at least one metal element selected from Ti, Cr, Nd, Rh, Zn, Ni, Fe, Co and the like is desirable.

Of the above-mentioned different elements, Mg and V, when diffused on the surface of the LT substrate, lower the refractive index there.
Cr, Nd, Rh, Ni, Fe and Co conversely increase the refractive index.
Therefore, Mg or V is thermally diffused into the LT substrate substrate (channel portion) directly below the optical waveguide forming portion in the LN thin film, and Cr,
It can be said that it is preferable to include one or more elements of Nd, Rh, Zn, Ni, Fe and Co by thermal diffusion.

When the above-mentioned different elements are contained in the LT substrate or the LN thin film, the respective lattice constants and the refractive indexes change simultaneously, so that the respective contents must be adjusted as described later.

The thickness of the diffusion layer of the different element thermally diffused into the substrate by these methods is desirably 0.01 to 20 μm. The reason is that when the thickness of the diffusion layer is less than 0.01 μm,
Since the proportion of guided light that spreads to the substrate portion where the heterogeneous element is not diffused increases, the refractive index required for the substrate cannot be satisfied, and the light trapping effect is reduced, and exceeds 20 μm. In this case, since the crystallinity is reduced, sufficient characteristics as an optical waveguide cannot be obtained.

As described above, the different element is added to a specific portion of the substrate (the optical waveguide forming region and / or a peripheral portion other than the portion) so that the refractive index of the waveguide forming portion becomes non-conductive. It is possible to form a pattern relatively lower than the wave path forming portion. Therefore, only a thin film having excellent crystallinity and optical characteristics is simply formed on the substrate in a slab shape, and a part of the thin film formed in the pattern portion becomes an optical waveguide. A special processing step for forming the waveguide can be omitted.

It should be noted that each of the above-mentioned different elements which lowers or raises the refractive index of the substrate can change only the surface refractive index without substantially changing the characteristics affecting the thin film formation of the substrate, such as the surface roughness. Since it can be changed, a thin film having the same characteristics as a normal substrate can be manufactured under the same conditions.

The amount of the different element contained on the LT substrate surface (intrusion due to thermal diffusion) is desirably in the following composition range. Refractive index lowering element Mg: 0.1-20 mol% V: 0.05-30 mol% Refractive index raising element Ti: 0.2-30 mol% Cr: 0.02-20 mol% Fe: 0.02 20 mol% Ni: 0.02 to 20 mol% Nd: 0.02 to 10 mol% Rh: 0.02 to 20 mol% Co: 0.02 to 15 mol% Zn: 0.02 to 20 mol% The content is different element / (LiTaO ₃ + different element) × 10
It is calculated with 0.

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 LT substrate is reduced, and if the composition ratio is lower than the above range, the refractive index does not change.

Further, it is more preferable that the content of the different element be within the following range. Refractive index lowering element Mg: 2.0 to 10 mol% V: 1.0 to 15 mol% Refractive index raising element 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% Rh: 0.2 to 10 mol% Co: 0.2 to 8 mol% Zn: 0.2 to 10 mol%

The above-mentioned different elements can be contained in the LT substrate in various forms such as atoms, ions and oxides.

Next, the production method of the present invention is described by using an LN thin film, LT
An example in which an optical device composed of a substrate is manufactured will be described. The LT substrate to which the above-mentioned different element is added and the lattice constant of the hexagonal a-axis is adjusted (5.128 to 5.173Å) is used.
Using a raw material such as lithium carbonate, tantalum pentoxide, titanium oxide, or vanadium pentoxide, heat and dissolve it in an iridium crucible or a platinum-rhodium crucible and pull up as a lithium tantalate single crystal, such as the Czochralski method (CZ method) Prepare at

Next, in order to make the refractive index of the optical waveguide pattern forming region (channel portion) of the LT substrate thus obtained smaller than that of the LN thin film, the optical waveguide pattern portion (channel portion) is formed. ) Or other portions are made to contain a different element having the above-described action of lowering or increasing the refractive index by a method such as thermal diffusion. Thereafter, an LN thin film lattice-matched to the LT substrate is formed.

Examples of the method of incorporating the different element into the substrate surface include a method of diffusing by heating, an ion exchange method, an ion implantation method, a liquid phase epitaxial growth method (LPE growth method), a raw material addition method, and the like. Can be used.

In this treatment, it is desirable that after the substrate is heated for thermal diffusion of different elements, the substrate is brought into contact with the melt for LPE growth in the heated state. The reason is that if the substrate is cooled after thermal diffusion and heated again for LPE growth, the crystallinity of the substrate is reduced.

This thermal diffusion is desirably 850 ° C. to 1000 ° C. This is because diffusion does not proceed at a temperature lower than 850 ° C., and at a temperature higher than 1000 ° C., the crystallinity of the substrate is reduced and Li is diffused out. Further, the time of the thermal diffusion is preferably 0.5 to 20 hours.

In the liquid phase epitaxial method, L
Before bringing the T substrate into contact with the melt, it is desirable that the LT substrate be preheated in advance. The reason for this LT
This is because the substrate is very susceptible to thermal shock.

It is desirable that such a raw material component is heated and melted at 600 to 1300 ° C. in an air atmosphere or an oxidizing atmosphere. The melt is brought into a supercooled state and then brought into contact with an LT substrate to grow. The cooling rate for bringing the melt into a supercooled state is preferably 0.5 to 300 ° C./hour.

It is desirable that the temperature of the Curie point of the lithium tantalate substrate is maintained for a certain period of time or cooled at a rate of 0.1 to 5 ° C./min. The reason for this is that the generation of cracks due to the phase transition of the crystal at the Curie point can be prevented.

Preferably, at least one side of the lithium tantalate substrate is optically polished and then subjected to chemical etching.

The thickness of the lithium tantalate substrate is 0.5
Desirably, it is ~ 2.0 mm. The reason is that a substrate thinner than 0.5 mm is liable to crack, and a substrate thicker than 2.0 mm has a problem of a pyroelectric effect, and is charged by heating or polishing, so that polishing debris and the like are easily attached and scratches are easily generated. Because.

Next, an LN thin film is grown on the surface of the LT substrate thus obtained. As a method of this growth, an LPE growth method, a sputtering method, a vapor deposition method, or the like is applied, and an LPE growth method (liquid phase epitaxial growth method) is particularly preferable. The reason is that it is easy to obtain a homogeneous film with excellent crystallinity, and as a result, light propagation loss is small and suitable as an optical waveguide. In addition, the nonlinear optical effect, electro-optical effect, acousto-optical effect, etc. of lithium niobate single crystal This is because an LN thin film having excellent properties that can be fully utilized can be obtained, and the productivity is also excellent.

As the LPE growth method, Li ₂ O, Nb
_{A method in} which the LT substrate is brought into contact with a melt composed of ₂ O ₅ , V ₂ O ₅ , Na ₂ O, MgO, etc., and the lattice constant of the a-axis of the LN thin film is matched with the lattice constant of the a-axis of the LT substrate by LPE growth. Is used because a high quality crystal can be obtained.

The thickness of the LN thin film can be controlled by appropriately selecting the contact time between the LT substrate and the melt and the temperature of the melt.

The growth rate of this LN thin film is 0.01 to 1.0 μm.
m / min is desirable. The reason is that when the speed is higher than 1.0 μm / min, the LN thin film undulates, and when the speed is lower than 0.01 μm / min, it takes time to grow the LN thin film.

In the present invention, the melt composition used for LPE growth includes Nb ₂ O ₅ , V ₂ O ₅ , Li ₂ O,
In addition to Na ₂ O and MgO, oxides of elements selected from Nd, Rh, Zn, Ni, Co, Ti and the like can be used.

The LN thin film obtained in this way is referred to as LT
The method of lattice matching with the substrate is as described above. For example, the LN thin film and the LT substrate can be lattice matched by changing the molar ratio of Li / Nb in the lithium niobate single crystal. As a specific method,
It is advantageous to use the LPE growth method and to use a composition consisting of at least K ₂ O, V ₂ O, Li ₂ O, Nb ₂ O ₅ as the melt for this purpose. The reason for this is that K ₂ O and V ₂ O act as a melting agent. By using K ₂ O and V ₂ O as the flux, the supply of Li from the flux can be prevented.
By changing the composition ratio of Li ₂ O, Nb ₂ O _{5 in} the raw material,
The molar ratio of Li / Nb of the precipitated lithium niobate single crystal can be changed.

When the molar ratio of Li / Nb changes, the lattice constant of the a-axis also changes. Therefore, the lattice constant of the lithium niobate single crystal thin film on the a-axis is changed to Li ₂ O, Nb ₂ O ₅ in the raw material. By controlling the composition ratio, the LN thin film and the LT substrate are lattice-matched.

In the present invention, the lattice constant of the a-axis of the LN thin film is already adjusted to the range of 5.128 to 5.173 °.
Ti may be contained in the LN thin film for lattice matching with the T substrate. As a method for this, a composition mainly composed of Li ₂ O, V ₂ O ₅ , Nb ₂ O ₅ , and TiO ₂ is used as a melt in LPE growth, and the LT substrate is brought into contact with the melt. Is advantageous in that the LPE growth is performed and the lattice constant of the a-axis of the LN thin film is matched with the lattice constant of the a-axis of the LT substrate.

In particular, when the lithium niobate single crystal thin film of the present invention is used as an SHG element,
Ordinary refractive index n _O of the N film, extraordinary refractive index n _e is the wavelength
Against 0.83μm laser source (fundamental wavelength), ranges of _{2.25 ≦ n O ≦ 2.40, 2.0} <n e <n O -0.01 Scope, also with respect to the second harmonic wavelength generated (0.415Myuemu) extraordinary refractive index n _e Te it is desirable that the ordinary refractive index n _O lesser extent with respect to the second harmonic.

[0059]

EXAMPLES Example 1 (1) Li ₂ CO ₃ (50 mol%), V ₂ O ₅ (40 mol%), Nb ₂ O ₃ (10 mol%), and LiNbO which can be precipitated from the melt composition the amount of Na ₂ CO ₃ which corresponds to 43 mol% relative to ₃ of theory, and 7 mol% based on the theoretical amount of precipitation can be LiNbO ₃ from the melt composition
The mixture obtained by adding MgO 2 was placed in an iridium crucible and dissolved by heating to 1100 ° C. in an epitaxial growth apparatus under an air atmosphere. Next, the melt in the crucible was stirred with a propeller at a rotation speed of 200 rpm for 12 hours. The melt is cooled at a rate of 60 ° C./hour to 915
The temperature was gradually cooled to ° C.

(2) As shown in FIG. 2, first , the (0001) plane of the lithium tantalate single crystal is optically polished to a thickness of 1.8 mm, and then a chamfered (C 0.5) substrate material 1 is prepared. I
Was. Next, a sputtering mask 6 is formed on the surface of the substrate material 1 by photolithography.
The surface is made of Mg with a thickness of 1000mm and a width of 5μm by RF sputtering.
An O film (different element layer 7) is formed, and the sputtering
After removing the disk 6, the above-mentioned remaining in the optical waveguide forming region
By heating at 920 ° C. to thermally diffuse the dissimilar element layer 7 to the substrate surface, a 1000 μm thick , 5 μm wide
To form a MgO diffusion channel 8. In the MgO diffusion channel 8 , the ordinary light refractive index was reduced by 15 × 10 ^{-3 as} compared with the region 5 where MgO was not diffused. The surface roughness was JIS B0601 R _max = 300 °. This substrate material 1
Was preheated at 915 ° C for 30 minutes and then obtained in the step (1).
In in the melt crucible is, while rotating at 100rpm
Soaked for 17 minutes. The growth rate was 1.94 μm / min.

(3) The substrate material is pulled up from the melt in the crucible, and the melt is shaken off by rotating at a rotation speed of 1000 rpm for 30 seconds. Then, the Curie temperature of the lithium tantalate single crystal at a cooling rate of 300 ° C. per hour (650 ° C.), hold at that temperature for 1 hour, then slowly cool down to room temperature at a cooling rate of 60 ° C. in one hour, and place a 33 μm thick LN thin film containing Na and Mg on the substrate material ( A thin-film waveguide layer 2) was obtained. (4) The amounts of Na and Mg contained in the obtained LN thin film were 2 mol% and 6 mol%, respectively. The refractive index measured at a lattice constant (a-axis) of 5.155 ° and an incident light wavelength of 1.15 μm was 2.231 ± 0.001.

[0062] (5) the LN thin film obtained is subjected to a end face polished perpendicular to the MgO diffusion channel portion of width 5μm formed on the substrate, thereby forming an optical waveguide 3. When a laser beam was incident on the end face of the waveguide and the near-field pattern of the emitted light was observed, the laser light was Mg of 5 μm width.
It was confirmed that O was well confined in the diffusion channel. The surface roughness of the obtained waveguide surface is JI
S B0601 R _max = 1000 ° In this way, light can be confined only by diffusing a different element into the substrate, and processing like the conventional ridge-type or rib-type waveguide is not required.

[0063] Example _{2 (1) Na 2 CO 3} 12.8 mol%, V ₂ O ₅ 40 mole%, Nb ₂ O ₅ 10 mole%, the Li ₂ CO ₃ 37.2 mol%, allows deposition of MgO from the melt composition A mixture obtained by adding 5 mol% to the theoretical amount of LiNbO ₃ was placed in an iridium crucible, and heated to 1100 ° C. in a liquid phase epitaxial growth apparatus under an air atmosphere to dissolve the contents of the crucible. The above melt per hour
It was gradually cooled to 941 ° C at a cooling rate of 60 ° C.

(2) Next, the (0001) plane of the LT single crystal was optically polished to a thickness of 1.0 mm, and then chamfered (R0.5). The surface was subjected to photolithography and RF sputtering. Then, a Ti film having a thickness of 400 ° having a gap (channel forming portion) having a width of 5 μm was formed, and then thermally diffused at 950 ° C. As a result, a substrate material having a channel portion having a width of 5 μm and not diffusing Ti on the LT substrate surface was obtained. The thickness of the Ti diffusion layer other than the channel portion was 400 mm. In addition,
The Ti diffused portion (the portion other than the channel portion) had an ordinary light refractive index increased by 2 × 10 ⁻³ as compared with the channel portion.
The surface roughness was JIS B0601 R _max = 100 °. After preheating this substrate material at 950 ° C for 30 minutes,
Dipping for 15 minutes while rotating at pm. The growth rate of the lithium niobate single crystal thin film was 0.53 μm / min.

(3) Next, 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 60 ° C. per hour. A Na, Mg-containing LN thin film having a thickness of about 8 μm was obtained on the material. (4) The amounts of Na and Mg contained in the obtained LN 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 2.231 ± 0.001. (5) The obtained LN thin film was polished at an end face perpendicular to a channel portion of a 5 μm wide Ti undiffused portion to form a waveguide. Laser light is incident on the end face of this waveguide,
Observation of the near-field pattern of the emitted light confirmed that the laser light was well confined on the 5 μm wide Ti undiffused channel. The surface roughness of the surface of the obtained waveguide was JIS B0601 R _max = 1000 °.
As described above, light can be confined only by diffusing a different element into the substrate, and processing like a conventional ridge or rib type waveguide is not required.

[0066] Example _{3 (1) Na 2 CO 3} 25.8 mol%, Li ₂ CO ₃ 24.2 mol%, V ₂ O ₅
A mixture obtained by adding 40.0 mol%, Nb ₂ O ₃ 10.0 mol%, and TiO ₂ to the stoichiometric amount of LiNbO ₃ capable of precipitating from the melt composition was added to an iridium crucible, and the mixture was placed in an air atmosphere. The contents of the crucible were dissolved by heating to 1100 ° C. in an epitaxial growth and growth apparatus. The obtained melt was gradually cooled to 893 ° C. at a cooling rate of 60 ° C. per hour.

(2) Next, (0) of the lithium tantalate single crystal
After the surface (001) is optically polished to a thickness of 1.7 mm, the thickness is 800 mm by photolithography and RF sputtering.
After forming a MgO film having a width of 5 μm and a Cu film having a thickness of 400 ° on portions other than the MgO film having a width of 5 μm, the film was thermally diffused at 1000 ° C. to form a 400 μm diffusion layer. Then 5μm wide MgO
The diffusion channel was chemically etched to obtain a substrate material. The ordinary light refractive index of the channel portion in which MgO was diffused and the portion in which Cu was diffused other than the channel portion decreased by 10 × 10 ⁻³ and increased by 1 × 10 ^−3, respectively, as compared with the substrate material in which nothing was diffused. Was. The surface roughness is JIS B0601
R _max = 500 °. This substrate material is removed from the melt by 10
After preheating at 893 ° C for 60 minutes at a height of 10 mm, 10
It was immersed for 12 minutes while rotating at 0 rpm. 0.58 growth rate
μm / min.

(3) Next, the substrate material is pulled up from the melt.
And shake off the melt at 1000 rpm for 30 seconds.
After cooling, slowly cool to room temperature at a cooling rate of 2 ° C / min.
An LN thin film containing Na and Ti having a thickness of about 7 μm was obtained on the material. (4) Amount of Na and Ti contained in the obtained LN thin film
Was 4.6 mol% and 5.0 mol%, respectively. Also,
Measured at a lattice constant (a-axis) of 5.153 mm and an incident light wavelength of 1.15 μm
The obtained refractive index was 2.241 ± 0.001. (5) Transfer the obtained LN thin film to an MgO diffusion channel with a width of 5 μm.
The end face is polished perpendicular to the
Incident and observed near-field pattern of emitted light
However, the laser beam is a 5μm wide MgO diffusion channel.
It was confirmed above that it was well confined. Get
The surface roughness of the waveguide surface is JIS B0601 R _max= 2000Å
Met. In this way, the substrate contains different elements
Light can be confined by light
This eliminates the need for processing such as the waveguide described above.

[0069] precipitatable Example _{4 (1) Na 2 CO 3} 12.8 mol%, V ₂ O ₅ 40 mole%, Nb ₂ O ₃ 10 mol%, Li ₂ CO ₃ 37.2 mol%, the MgO from the melt composition A mixture obtained by adding 5 mol% to the theoretical amount of LiNbO ₃ was placed in an iridium crucible and heated to 1100 ° C. in an epitaxial growth and growth apparatus under an air atmosphere 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) Next, after chamfering (R 0.5) the LT substrate having a thickness of 1 mm, a 250ÅMgO layer was formed by RF sputtering, and then the LT substrate was epitaxially grown and grown at 2.67 cm / min. The pre-heating and thermal diffusion were performed at the same time by approaching the melt. The surface roughness of the LT substrate surface was JIS B0601 _Rmax = 170 °. (3) After slowly cooling the melt to 938 ° C. at a cooling rate of 60 ° C. per hour, preheating the LT substrate at 938 ° C. for 50 minutes, and immersing the melt in the melt for 20 minutes while rotating at 100 rpm. did. The growth rate of lithium niobate was 0.7 μm / min.

(4) Pulling up the substrate material from the melt,
After shaking off the melt on the melt at 1000 rpm for 30 seconds, slowly cool to room temperature at 1 ° C / min.
Thus, an LN thin film containing Na and Mg having a thickness of m was obtained. (5) The amounts of Na and Mg contained in the obtained LN thin film were 1 mol% and 5 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 2.231 ± 0.001. The thickness of the MgO 2 diffusion layer of the substrate was 255 °. The surface roughness of the LN were JIS B0601 R _max = 1400Å.

(6) A ridge channel having a width of 5 mm was formed on the obtained LN thin film by photolithography and dry etching, and the end face was polished perpendicular to the channel to form a waveguide. Laser light was incident from the end face of the waveguide portion and the near-field pattern of the emitted light was observed. As a result, it was confirmed that the laser light was well confined in a channel having a width of 5 μm. The confinement efficiency of the waveguide is the same as that of the conventional ridge waveguide.
1.5 times.

[0073]

As described above, according to the present invention, L
Since the T substrate and the LN thin film are lattice-matched, the crystallinity and optical characteristics of the optical waveguide layer are basically excellent, and under the relationship between such a substrate and the thin film, the LT substrate has: It is possible to obtain SH without impairing the above-mentioned characteristics only by containing a different element smaller than the refractive index of the optical waveguide forming portion.
An optical device suitable as a G element or the like can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a perspective view of an optical device of the present invention.

FIG. 2 is a manufacturing process diagram of the optical device of the present invention.

[Description of Signs] 1 Thin-film waveguide layer 2 Substrate 3 Optical waveguide 4 Region of substrate forming optical waveguide 5 Region of substrate not forming optical waveguide 6 Sputtering mask 7 Heterogeneous element layer formed by RF sputtering 8 Heterogeneous Element diffusion layer

Claims (6)

(57) [Claims] In an optical device having a thin film waveguide layer formed on a substrate, there is no bending in an optical waveguide forming region of the substrate.
Optical device, characterized in that Oriritsu were relatively smaller than the refractive index of the base plate surface area has such an optical waveguide is formed. 2. In an optical device having a lithium niobate single crystal thin film formed on a lithium tantalate substrate, a lattice constant of the lithium niobate single crystal is lattice-matched to that of the lithium tantalate single crystal. Along with the refractive index of at least the surface of the lithium tantalate substrate, which corresponds to the optical waveguide forming region formed in the lithium niobate single crystal thin film, by diffusing and containing different elements, the refractive index of the substrate in the region where the optical waveguide is not formed. An optical device having a channel-type waveguide, which is also relatively small. 3. The lithium tantalate substrate surface in the optical waveguide portion forming region contains a refractive index lowering element such as Mg or V, or the substrate surface other than the optical waveguide portion forming region contains
Include a refractive index increasing element such as Ti, Cr, Nd, Rh, Zn, Ni, Fe or Co, and make the refractive index of the lithium tantalate substrate, which corresponds to the optical waveguide forming region, higher than that of the region where the optical waveguide is not formed. The optical device according to claim 1, wherein the optical device is made smaller. 4. The method according to claim 1, wherein at least one surface of the substrate has a refractive index of a substrate corresponding to a region where an optical waveguide is formed, and a refractive index of the other region.
An element that makes the refractive index smaller than the substrate refractive index of the region is formed on the optical waveguide forming region or other region portion of the substrate.
Be contained in, then, a method of manufacturing an optical device, which comprises forming a thin film waveguide layer on a substrate of this. 5. In manufacturing an optical device in which a lithium niobate single crystal thin film is formed on a lithium tantalate substrate, at least one surface of the lithium tantalate substrate has a refractive index of a substrate in an optical waveguide forming region. said There is containing an element to be relatively smaller than that of the area not forming the optical waveguide, further, the lattice constant of the hexagonal a-axis of the base plate
Lattice constant of lithium niobate single crystal thin film matches
Thus, Mg in the lithium niobate single crystal thin film
Or liquid phase epitaxial growth containing Na
And a method for manufacturing an optical device having a channel-type waveguide. 6. The lithium tantalate substrate surface immediately below the optical waveguide portion contains 1) a refractive index lowering element such as Mg or V, or 2) Ti, A refractive index increasing element such as Cr, Nd, Rh, Zn, Ni, Fe or Co may be contained, or the refractive index of the lithium tantalate substrate corresponding to the optical waveguide forming region may be changed to lithium niobate single crystal by at least one of the methods. The optical device according to claim 5, wherein the optical device is smaller than the thin film.