JPH04247408A - Optical waveguide - Google Patents

Abstract

PURPOSE:To obtain the optical waveguide which has a high confining effect, exhibits a low propagation loss and is excellent in high electrooptical effect. CONSTITUTION:While the optical waveguide matched in the lattice of a substrate crystal and the crystal of a thin-film waveguide layer 2 is produced, this waveguide is constituted into a ridge type 1 or rib type having a relation 6.0X10<-2=W/T<=0.7X10<2> between the thickness T(mum) of the thin-film waveguide layer 2 and the width W(mum) of the thin-film waveguide layer 2. Particularly the optical waveguide of the ridge type is so designed as to have a relation 0.10<=t/T<=0.99 where the level difference of the ridge is designated as t.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to second harmonic generation (S).
The present invention relates to optical waveguides useful as optical devices such as HG) elements, optical deflectors, optical switches, optical amplifiers, and optical integrated circuits.

0002

[Prior Art] In recent years, there has been remarkable progress in optical information processing devices that utilize laser light. Among them, optical deflectors,
For optical devices such as optical modulators, optical amplification elements, and optical switches, it is essential to use high-quality optical waveguides with excellent optical properties such as electro-optic effects, nonlinear optical effects, and magneto-optic effects, and low propagation loss. be. Conventional optical waveguides that can meet these demands include (1) those in which a thin film material is sputtered onto a substrate, (2) those in which a thin film is formed on a substrate by liquid phase epitaxial growth, and (3) those in which a different element is formed on a substrate. Some proposals have been made for thermal diffusion to form a waveguide.

0003

[Problem to be solved by the invention] However, the above (
The optical waveguide (1) has a large propagation loss due to poor crystallinity, and the optical waveguide (3) has the disadvantage that it cannot be made homogeneous due to the gradient of the refractive index in the direction of diffusion of elements. Ta.

On the other hand, the optical waveguide of (2) above is
Although the above-mentioned drawbacks are not found, so far we have not been able to obtain a practical waveguide.
Applied Physics Letters” (
Vol. 24, No. 9, 1974) p42
4 to 426 Alternatively, in "Optical Integrated Circuits" P162 written by Hiroshi Nishihara, Masamitsu Haruna et al., a lithium niobate single crystal thin film is formed on a lithium tantalate substrate by a liquid phase epitaxial growth method to create an optical waveguide. Although an example has been described, such an optical waveguide has a problem in that the electro-optic constant is 1/3 smaller than that of the bulk.

[0005] Also, “Applied Physics
s Letters” (Vol.26, No.1,
January 1975), pages 8 to 10, describes an example in which a lithium niobate single crystal thin film was formed on a lithium tantalate substrate by liquid phase epitaxial growth. , results have been obtained that the propagation loss is large and it is not practical. Although the thin film formed by the liquid phase epitaxial growth method has good crystallinity, there is a problem in that the optical characteristics of the optical waveguide and the propagation loss become large.

[0006]

[Means for Solving the Problem] As a result of intensive research into the above-mentioned problems faced by the conventional technology, the present inventors have discovered that the cause of these problems is that the crystal lattice between the substrate and the thin film waveguide is completely It was determined that this was caused by a lack of matching. In order to solve this problem, it is effective to match the crystal lattices of the substrate crystal and the thin film crystal that forms the waveguide, and using a substrate and thin film waveguide that have been lattice matched in this way, it is possible to It was found that an ideal optical waveguide, which could not be obtained using conventional methods, could be obtained.

Even in such a thin film waveguide, the ridge type and rib type thin film waveguide layers have a thickness (T),
When the height (t) of the ridge or rib and the width (W) of the ridge or rib are designed to be within a certain range, that is, 6.6×10-2≦W/T≦6.7×102
The present invention was completed based on the finding that it is possible to obtain an optical waveguide that has extremely high light confinement efficiency and power density within the waveguide and can propagate light in a single mode. The power density is the value (unit: W/m2) obtained by dividing the intensity of the guided light (input light) by the cross-sectional area of the light beam.

[0008]

[Operation] The optical waveguide of the present invention is characterized in that the crystal lattices of the substrate and the thin film waveguide layer are matched to each other (lattice matching). When the substrate is lattice-matched to the thin film waveguide in this way, lattice distortion and crystal defects are extremely reduced, and a high-quality waveguide layer without microcracks can be formed.

In such lattice matching, the lattice constant of the thin film waveguide layer is 99.81 to 99.81 of the lattice constant of the substrate.
Desirably, it is 100.03%.

[0010] In the waveguide of the present invention, it is desirable that the thin film waveguide layer and the substrate contain a different element for adjusting the refractive index. The different elements contained in this thin film waveguide layer include Cr, Nd, Ti, V, Rh, Zn, and N.
At least one element selected from i and Co is desirable. In addition, as a different element to be contained in the substrate, Mg
, Ti, V, Cr, Fe, Ni, and Nd. especially,
The different element contained in the substrate may be uniformly distributed on the substrate, or may form a layer (diffusion layer) on the surface of the substrate. The thickness of the diffusion layer is preferably 0.001 to 20 μm. Note that when Mg is diffused into the substrate, the thickness of the diffusion layer is preferably 200 to 1000 Å.

In the present invention, the combination of the thin film waveguide layer and the substrate is not particularly limited, but for example, the thin film waveguide layer may include LiNbO3, α-quartz, K
TiPOO4 (KTP), β-BaB2O4 (BBO)
, KB5O8・4H2O (KB5), KH2PO4
(KDP), KD2PO4 (KD*P), NH4H2
PO4 (ADP), C5H2AsO4 (CDA), C5
D2AsO4 (CD* A), RbH2PO4 (RD
P), RbH2AsO4 (RDA), BeSO4 ・
4H2O, LiClO4・3H2O, LiClO3
, α-LiCdBO3, LiB3O5 (LBO),
Urea, etc. can be used, and as a substrate used in combination with this thin film waveguide layer, for example, LiTaO3, LiTaO
Garnets such as LiNbO3, SiO2, alumina, BeO2, ZnO2, Gd3Ga5O12, KTP, BBO, LBO, KDP, and similar compounds, soda glass, Pyrex glass, etc., on which three thin films are formed, are used.

In particular, the combination of using lithium niobate as the thin film waveguide layer and using lithium tantalate as the substrate is the most desirable form. This is because these single crystals have similar crystal structures and are easy to lattice match.

Lattice matching, which is one of the characteristics of the present invention, will be specifically explained below using an example in which lithium niobate is used as the thin film waveguide and lithium tantalate is used as the substrate.

That is, since the a-axis lattice constant of normal lithium niobate is 5.148 Å, and the a-axis lattice constant of lithium tantalate is 5.154 Å,
It is advantageous to (1) increase the lattice constant of the LiNbO3 thin film waveguide layer, or (2) conversely decrease the lattice constant of the LiTaO3 substrate.

[0015] As the method (2) above, (a) the above L
Desirable methods include a method in which the iNbO3 thin film waveguide layer contains different elements such as Na and Mg, and (b) a method in which the Li/Nb ratio is varied. For example, considering method (a), Na and Mg atoms or ions are LiNbO3
This is because substitution or solid solution for LiNbO3 has the effect of increasing the lattice constant of LiNbO3, and as a result, by adjusting the composition of Na and Mg, LiTaO3 substrates, which generally have a large lattice constant, can be lattice matched. This is because it is possible. Note that Mg has the effect of preventing optical damage to the thin film, and is advantageous for obtaining highly efficient SHG output.

The contents of Na and Mg used to increase the lattice constant of the thin film waveguide layer are 0.1 to 14.3 mol % and 0.8 to 10 mol %, respectively, based on LiNbO3.
The content is preferably 8 mol%. This is because when the Na content is less than 0.1 mol%, lattice matching between the LiNbO3 thin film and the LiTaO3 substrate cannot be obtained regardless of the amount of Mg added; This is because if it exceeds the lattice constant, the lattice constant becomes too large, and in either case, lattice matching between the LiNbO3 thin film and the LiTaO3 substrate cannot be obtained. Moreover, the content of Mg is 0.
If it is less than 8 mol%, the effect of preventing optical damage is insufficient, and if it exceeds 10.8 mol%, LiMg
It cannot be contained because O3-based crystals will precipitate.

Next, as a lattice matching means according to method (b) above, there is a method of increasing the a-axis lattice constant of the thin film waveguide layer by changing the Li/Nb molar ratio in the LiNbO3 single crystal. It is. Li/ in this method
The molar ratio of Nb is preferably 41/59 to 56/44.

Next, as method (2) for reducing the lattice constant of LiTaO3, it is preferable to include Ti or the like in the LiTaO3 substrate. That is, this Ti is LiT
This is because Ti has the effect of reducing the lattice constant of aO3, and the amount of Ti contained is preferably 0.5 to 60 mol%.

Now, for the above-mentioned lattice matching, it is desirable to form a LiNbO3 thin film on the (0001) plane of the LiTaO3 substrate. In this way, the LiTa
The reason why it is desirable that the (0001) plane of the O3 substrate is the growth plane of the LiNbO3 thin film is that the (0001) plane is
This is because since it is composed of only the a-axis, lattice matching with the LiNbO3 thin film can be achieved simply by changing the lattice constant of the a-axis.

Note that the lattice constant (a-axis) of the LiNbO3 thin film formed on the LiTaO3 substrate is the same as that of the LiT
The lattice constant (a-axis) of the aO3 substrate is 99.81 to 100
．． 07% is preferable, and 99.92 to 100.03% is suitable. The reason for this is that when outside the above range, Li
This is because it is difficult to match the lattice constants of TaO3 and LiNbO3.

The measurement of the lattice constant necessary for the above-mentioned treatment is carried out by ordinary powder X-ray diffraction. The lattice constant is calculated by the least squares method using the 2θ values of 15 peaks of lithium niobate detected at Cu-2θ=45 to 90° and the surface index thereof. Note that in the measurement, Si is used as an internal standard.

Now, the shape of the optical waveguide of the present invention may be any form such as slab type, ridge type, rib type, loaded type, voltage induced type, etc. When applied to devices, it is desirable to use ridge-type or rib-type optical waveguides. This is because optical waveguides with these shapes have higher light confinement efficiency and are easier to process.

In the present invention, the ridge-type or rib-type optical waveguide is constructed such that the step of the ridge portion or rib portion is t (μm), and the thickness of the thin film waveguide layer is t (μm), as shown in FIG. Let T (μm) be the width of the ridge or rib part.
(μm), it is desirable to satisfy the following conditions. 6.6×10-2≦W/T≦6.7×
102...(1)
0.10≦t/T≦0.99
...(2) The reason for this is Equation (1) and Equation (2)
This is because an optical waveguide that satisfies the relational expression has extremely high power density and confinement efficiency. In addition, an optical waveguide that satisfies these conditions can easily guide light in a single mode, and is ideal for use in second harmonic generation elements, optical deflectors, optical switches, and the like.

Furthermore, the ridge portion or rib portion step t
(μm), the thickness T (μm) of the thin film waveguide layer, and the width W (μm) of the ridge or rib portion: 2.0≦W/T≦7
．． 0...(3)
0.30≦t/T≦0.80
...It is desirable that condition (4) is satisfied. In addition, the width W (μm) of the ridge portion or rib portion is
The thickness is preferably 0.1 to 100 μm.

Next, methods for manufacturing the single crystal thin film waveguide of the present invention include liquid phase epitaxial growth, sputtering,
Although a vapor deposition method is preferable, a liquid phase epitaxial growth method is particularly suitable. The reason for this is that according to the liquid phase epitaxial growth method, it is easy to obtain a homogeneous film with excellent crystallinity, and as a result, it has low optical propagation loss and is suitable as an optical waveguide. This is because the acousto-optic effect can be fully utilized.

A specific method for forming a lattice-matched LiNbO3 thin film waveguide on a LiTaO3 substrate will be described below. In the present invention, in order to lattice match the LiNbO3 thin film waveguide and the LiTaO3 substrate, Li
2 O, Nb2O5, V2O5, Na2O, Mg
A method is to use a method in which a lithium tantalate substrate is brought into contact with a melt made of O, etc., and the a-axis lattice constant of the lithium niobate single crystal thin film is matched to the a-axis lattice constant of the lithium tantalate substrate using an epitaxial growth method. , is desirable because high quality crystals can be obtained.

In carrying out such a liquid phase epitaxial growth method, the composition range of Li2O, V2O5, and Nb2O5 excluding Na2O and MgO is within the range of Li2O-V2O5-Nbb2O5 shown in FIG.
In the triangular diagram of the component system, A(88.90, 2.22,
8.88) Mol%, B (55.00, 43.00
, 2.00) mol%, C(46.50, 51.5
0, 2.00) mol%, D(11.11,80
．． 00, 8.89) mol%, E(37.50, 5
．． 00, 57.50) It is advantageous to use melts within the composition range indicated by the area enclosed by the 5 composition points of mol %.

The reason why it is advantageous to use a melt having such a composition range is that it facilitates lattice matching between the LiNbO3 single crystal thin film made of Na and Mg and the LiTaO3 substrate, and improves the optical properties of the resulting LiNbO3 single crystal thin film. This is because a LiNbO3 single-crystal thin film of good quality can be obtained with excellent properties and particularly low optical propagation loss.

[0029] Furthermore, excluding the above Na2O and MgO,
The composition range of Li2O, V2O5, and Nb2O5 is Li2O-V2O5-Nb2O5 shown in Fig. 3.
In the triangular diagram of the three-component system, F(49.49, 4
5.46, 5.05) mol%, G(11.11,
80.00, 8.89) mol%, H (42.81,
22.94, 34.25) mol %, the composition ratio is preferably surrounded by three composition points, and further, the Li2
The composition range of O-V2O5-Nb2O5 is I(47.64, 4
6.12, 6.24) mol%, J(27.01,
64.69, 8.30) mol%, K(36.71,
37.97, 25.32) mol%, L(44.05,
32.97, 22.98) mol %, the range surrounded by the four composition points is suitable, and further M(45.36,
46.45, 8.19) mol%, N (32.89,
57.05, 10.06) mol%, O(36.71,
44.30, 18.99) mol%, P(44.
The range surrounded by the four composition points of 95, 40.54, 14.51) mol % is optimal.

[0030] Furthermore, the composition ratio of Na2O in the present invention is Na2O/Li2O in molar ratio of 2.0/
It is desirable that the range satisfies 98.0 to 93.5/6.5. This is because if the proportion of Na2O deviates from the above molar ratio range, it is difficult to lattice match the LiTaO3 substrate and the LiNbO3 single crystal thin film. As the composition ratio of Na2O, the molar ratio is Na2O/
Li2O is 7.4/92.6 to 80.0/20.
It is desirable that the range satisfies 0, and 16.7/83
．． It is preferable that the range satisfies 3 to 48.4/51.6.

Next, regarding the composition ratio of MgO, the molar ratio of MgO/LiNbO3 is 0.1/99.
It is desirable that the composition range satisfies 9 to 25.0/75.0. The above-mentioned LiNbO3 means the theoretical amount of lithium niobate that can be precipitated from the melt composition. This is because if the proportion of MgO is lower than the above range, the optical damage prevention effect of Mg is insufficient, and if the proportion of MgO is higher than the above range, magnesium niobate crystals will precipitate.

Furthermore, as the composition ratio of MgO, the value of MgO/LiNbO3 in molar ratio is 0.7/100
The composition range preferably satisfies 9.0/100 to 3.5/100, and preferably 3.5/100 to 6.0/100.

Next, in the present invention, LiTaO
After adding a different element to at least part of the surface of the three substrates, it is desirable to form a LiNbO3 single crystal thin film that is lattice-matched to the LiTaO3 substrate. Methods for adding the different elements include thermal diffusion, ion exchange, ion implantation, etc., as well as liquid phase epitaxial growth, a method of pre-mixing different elements in the raw material of a single crystal, (raw material addition method), etc. can be used.

In particular, when the thermal diffusion, ion exchange, or ion implantation method is used, a diffusion layer of a different element is formed, and the thickness of the diffusion layer is preferably 0.001 to 20 μm. The reason for this is that the thickness of the diffusion layer is 0.001μ.
If the diameter is less than 20 μm, the proportion of the guided light that spreads to the parts of the substrate where different elements are not diffused increases, making it impossible to satisfy the refractive index required for the substrate.
This is because if it exceeds 100%, the crystallinity deteriorates and sufficient characteristics as an optical waveguide cannot be obtained.

[0035] After the substrate is heated for thermal diffusion of the dissimilar element, it is desirable to bring it into contact with a melt for liquid phase epitaxial growth while keeping it heated. The reason for this is that if the substrate is cooled after thermal diffusion and then heated again for liquid phase epitaxial growth, the crystallinity of the substrate will deteriorate. It is preferable that the thermal diffusion is performed using preheating in the same furnace as the melt is heated.

In the present invention, the melt composition is as follows:
Nb2O5, V2O5, Li2O, Na2O and M
In addition to gO, Nd, Rh, Zn, Ni, C
Oxides of elements selected from O, Ti, etc. can be used.

Furthermore, in the present invention, by changing the Li/Nb molar ratio in the LiNbO3 single crystal, Li
As a method for lattice matching the NbO3 single crystal thin film and the LiTaO3 substrate, a liquid phase epitaxial growth method is used, and at least K2O, V205 is used as the melt for this purpose.
, Li2O, Nb2O5 is advantageously used. The reason for this will be explained below.

[0038] The K2O and V2O5 act as a melting agent (flux). K2O, V2O as a melting agent
5 can prevent the supply of Li from the melting agent, so by changing the composition ratio of Li2O and Nb2O5 in the raw materials, the Li/Nb molar ratio of the precipitated LiNbO3 single crystal can be changed. Can be done. When the Li/Nb molar ratio changes, the a-axis lattice constant also changes, so the a-axis lattice constant of the LiNbO3 single crystal thin film can be controlled by controlling the composition ratio of Li2O and Nb2O5 in the raw materials, and LiNbO3 Single crystal thin film and Li
The TaO3 substrate can be lattice matched.

[0039] The above K2O, V205, Li2O,
The melt consisting of Nb2O5 contains Na2O and MgO.
may be added. This is because the a-axis lattice constant of the LiNbO3 single crystal thin film can be increased by adding MgO or Na2O.

The melt composition has a molar ratio of Li2O/N
It is desirable that b2O is 43/57 to 56/44, and preferably 43/57 to 50/50. This is because if the temperature is outside the above range, crystals such as LiNb3O8, which have a different crystal structure from the LiNbO3 single crystal, will precipitate.

In addition, the composition ratio of K2O and V205 is such that the theoretical amount of LiNbO3 single crystal that can be precipitated from the melting agent (KVO3 equivalent)/raw material composition consisting of K2O and V205 is 25/75 to 75/ It is desirable that the range satisfies 25. This is because if it is out of the above range, the crystal structure of the precipitated LiNbO3 single crystal will change and the optical properties will deteriorate.

Furthermore, the composition ratio of MgO is
/ The theoretical amount of LiNbO3 single crystal that can be precipitated from the raw material composition is 0.01/100 to 30/10 in molar ratio.
It is desirable that the range satisfies 0. This is because if the molar ratio is outside the above range, magnesium niobate crystals will precipitate.

Furthermore, it is advantageous for the composition ratio of K2O and V205 to be K2O and V205 =1/1 in terms of molar ratio.

In the present invention, in manufacturing an optical waveguide, it is important to bring the melt into a supercooled state and then bring it into contact with a lithium tantalate substrate for growth. The surface roughness of the lithium tantalate single crystal thin film forming surface is JIS
B0601, Rmax = 300 to 1000 Å is desirable. The reason for this is that it is extremely difficult to reduce the value of Rmax to less than 3000 Å, and the value of Rmax is
This is because when the thickness exceeds 000 Å, the crystallinity of the lithium niobate single crystal thin film decreases.

In the present invention, the lithium niobate single crystal thin film has an a-axis lattice constant of 5.128 to 5.150 Å.
In the case of lattice matching with a single crystal substrate having a hexagonal crystal structure in the range of 20 to 30, it is desirable to include Ti in the lithium niobate single crystal thin film. The reason for this is that Ti atoms or ions have the effect of reducing the lattice constant of the lithium niobate substrate and can be lattice matched to the substrate.
As a method for this, Li2O, V2 O5, Nb
A melt consisting of 2O5, TiO2 can be used.

The growth rate of the lithium niobate single crystal thin film of the present invention is preferably 0.01 to 1.0 μm/min. This is because if the growth rate is faster than this, waviness will occur in the lithium niobate single crystal thin film, and if the growth rate is slower than this, it will take time to grow the thin film.

In the case shown in FIG. 2, the surface of a commercially available lithium tantalate substrate is optically polished.
The relationship between the contents of Na and Mg in the thin film and the a-axis lattice constant of lithium niobate was investigated by immersing the thin film in a melt with different Mg compositions and performing liquid phase epitaxial growth.

In the present invention, a of the LiTaO3 substrate is
Lattice matching can be achieved by adjusting the lattice constant of the axis by adding a different element to match the lattice constant of the a-axis of the LiNbO3 single crystal. As a method to reduce the a-axis lattice constant of the lithium tantalate substrate,
It is desirable to contain Ti atoms or ions. This is because Ti atoms or ions have the effect of reducing the a-axis lattice constant of the lithium tantalate substrate. From this point of view, when the Ti atoms or ions are contained, the content is preferably 0.2 to 30 mol % based on the lithium tantalate single crystal. Further, as a method for manufacturing the lithium tantalate substrate to which the above-mentioned different element is added and the a-axis lattice constant is adjusted, the CZ (Czochralski) method is preferable. Raw materials used under this method include, for example, lithium carbonate, tantalum pentoxide, titanium oxide, vanadium pentoxide.

Further, the a-axis lattice constant of the lithium tantalate substrate can be increased by adding a different element such as sodium.

In the present invention, after manufacturing a single crystal thin film that is lattice-matched to the substrate as described above, the single crystal thin film is subjected to optical polishing, chemical etching, etc. to adjust the film thickness.

Furthermore, the light input and output portions are processed into optical waveguides by polishing the end faces to prevent light reflection and scattering.

Further, a ridge type or rib type optical waveguide can be processed by conventional methods such as photolithography and dry etching.

Further, in the optical waveguide of the present invention, the surface roughness of the thin film waveguide layer is JIS B0601 Rmax = 0.0.
02 to 0.300, and the end surface roughness of the thin film waveguide layer is JIS B0601 Rmax = 0.002 to 0.
．． 400 is desirable. The reason for this is that within the above range, scattering of guided light is suppressed, incidence efficiency is improved, and propagation loss is reduced.

By the way, in general, in order for lithium niobate or lithium tantalate single crystals to have optically useful properties such as electro-optic effects and nonlinear optical effects, they must be heated to temperatures above the Curie point during the manufacturing process. It is necessary to heat and apply an electric field to pole the crystal. However, it is known that single crystals such as lithium niobate and lithium tantalate containing different elements cannot be easily poled. However, the lithium niobate single crystal thin film obtained by the production method of the present invention is always polarized even if the lithium tantalate substrate is in a polarized state or electrically neutralized by polarization inversion. It exhibits various properties such as extremely excellent electro-optic effects and nonlinear optical effects.

Therefore, the lithium niobate single crystal thin film and the lithium tantalate substrate of the present invention do not require a poling process, so they can be easily manufactured. This method has the advantage that a lithium tantalate substrate containing different elements can be used.

When the optical waveguide of the present invention is used in a second harmonic generation element (SHG element), the wavelength of the fundamental laser beam (λμm), the thickness of the thin film waveguide layer (Tμm), the fundamental wave laser Ordinary refractive index of the substrate (n0S1) at the optical wavelength (λμm), ordinary refractive index of the thin film waveguide layer (n0F1) at the fundamental laser light wavelength (λμm), and abnormality of the substrate at the second harmonic wavelength (λμm/2) Optical refractive index (n
It is desirable that the extraordinary optical refractive index (neF2) of the thin film waveguide layer at the second harmonic wavelength (λμm/2) is expressed by one of the following relational expressions.

The optical waveguide of the present invention can be applied to all known waveguide-type optical devices such as optical modulators such as SHG elements, optical deflectors, optical switches, optical amplification elements, and optical integrated circuits.

[0058]

[Example] Example 1 (1) Li2CO3 51 mol%, V2O5 39
mol %, Nb2O5 10 mol %, and 4 for the theoretical amount of LiNbO3 that can be precipitated from the melt composition.
A mixture of 3 mol% Na2CO3 and 7 mol% MgO added to the theoretical amount of LiNbO3 that can be precipitated from the melt composition was placed in an iridium crucible and grown in an epitaxial growth apparatus under an air atmosphere. The contents of the crucible were melted by heating to 1100°C to obtain a melt. Next, this molten body is propelled using a propeller.
The mixture was stirred for 12 hours at a rotation speed of 200 rpm.

(2) The melt was slowly cooled to 915°C at a cooling rate of 60°C per hour. The (0001) plane of lithium tantalate single crystal is optically polished to a thickness of 1.8 mm.
After that, chamfering (C side) was performed. The film thickness is 1000 Å by photolithography and RF sputtering method.
After forming an MgO 2 film, it was thermally diffused at 920° C., and a material having an MgO 2 diffusion layer of 1000 Å was used as a substrate material. When the fundamental laser light wavelength λ is 0.78 μm, the ordinary refractive index (nos1) of this substrate is 2.151
, the extraordinary refractive index at the second harmonic λ/2 (nes2
) was 2.261. In addition, the surface roughness is JIS
B0601 Rmax = 300 Å. This substrate material was preheated at 915° C. for 30 minutes and then immersed in the melt for 17 minutes while rotating at 100 rpm. The growth rate was 1.94 μm/min.

(3) The substrate material was pulled up from the melt, rotated at a rotational speed of 1000 rpm for 30 seconds to shake off the melt, and then a lithium tantalate single crystal was cooled at a cooling rate of 300° C. per hour. Curie temperature (
650 °C), kept at that temperature for 1 hour, and then slowly cooled to room temperature at a cooling rate of 60 °C per hour to deposit a layer of lithium mononiobate containing Na and Mg on the substrate material with a thickness of about 16 μm. A crystal thin film was obtained.

(4) The amounts of Na and Mg contained in the obtained lithium niobate single crystal thin film were 2.
The mol% was 6 mol%. In addition, the lattice constant of the thin film (
a-axis) is 5.155 Å, and the incident light wavelength λ is 0.83 μm.
The ordinary refractive index measured at (noF1) is 2.264
, the extraordinary refractive index at the second harmonic λ/2 (neF2
) was 2.263. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B0601 R.
max = 300 Å.

(5) The obtained lithium niobate single crystal thin film was optically polished and subjected to ion beam etching.
After the thickness was set to 7 μm, a Ti waveguide pattern was formed by photolithography and RF sputtering, and after ion beam etching was performed using this as an etching mask, the Ti etching mask was removed, and further ion beam etching was performed. By polishing the end face of the wave path and setting the surface roughness to JIS B0601 Rmax = 400 Å, the width is 10 μm and the film thickness is 2.50 ± 0.05.
A ridge-type waveguide with a height difference of 2.0 μm was created. The surface roughness of the lithium niobate single crystal thin film is determined by JIS
B0601 Rmax = 300 Å.

[0063] In the optical waveguide created in the above example, 8
When 30 nm light was guided, generation of 415 nm second harmonic light (SHG) was confirmed. This waveguide is single mode, and the above equation (5), (6
) The SHG element shown in the formula is as follows.

Example 2 (1) Na2CO3 12.8 mol%, V2O5
40 mol%, Nb2O5 10 mol%, and Li2
37.2 mol% CO3 and 5 mol% MgO based on the theoretical amount of LiNbO3 that can be precipitated from the melt composition.
A mixture obtained by adding the above was placed in a platinum crucible and heated to 1100° C. in an air atmosphere in an epitaxial growth growth apparatus to melt the contents of the crucible to obtain a melt. This melt was then stirred using a propeller at a rotational speed of 150 rpm for 20 hours.

(2) After chamfering (R surface) a 1 mm thick lithium tantalate substrate, a 250 Å thick MgO
The layer was sputtered and thermally diffused at 940° C. to form a 250 Å thick diffusion layer. The refractive index is Mg
It was 0.015 lower than when O was not diffused. In addition, the surface roughness of the substrate surface is determined according to JIS B0601 R.
max = 170 Å.

(3) After slowly cooling the melt to 938°C at a cooling rate of 60°C per hour, the substrate is heated to 93°C.
It was preheated at 8° C. for 50 minutes and immersed in the melt for 20 minutes while rotating at 100 rpm. The growth rate of lithium niobate was 0.7 μm/min. (4) Pull up the substrate material from the melt and rotate at 1
After shaking off the melt by rotating at 000 rpm for 30 seconds, it was cooled to 700 °C at 1 °C/min.
℃ to 600 ℃ at a rate of 0.1 ℃/min, and then from 600 ℃ to room temperature at a rate of 1 ℃/min to form a lithium niobate single crystal thin film containing Na and Mg with a thickness of approximately 10 μm on the substrate material. I got it.

(5) The amounts of Na and Mg contained in the obtained lithium niobate single crystal thin film were each 1
The mol% was 6 mol%. In addition, the lattice constant of the thin film (
a-axis) was 5.153 Å, and the refractive index measured at an incident light wavelength of 1.15 μm was 2.231 ±0.001. The surface roughness of lithium niobate is JIS B0601
Rmax = 500 Å.

(6) The obtained lithium niobate single crystal thin film was optically polished and subjected to ion beam etching.
After making the thickness 9 μm, in the same manner as in Example 1,
Width 8μm, film thickness 3.65μm±0.05μm, step
A 1.5 μm ridge-type waveguide was created. At this time, the surface roughness of lithium niobate is JIS B0601 Rm
ax = 500 Å, the roughness of the waveguide end face is JIS
B0601 Rmax = 500 Å. This waveguide was a single mode, and the configuration of the element shown in equations (5) and (6) was as follows. t/T=0.4 W/T=2.2

Example 3 (1) 30 mol% Na2 CO3, Li2 CO
3 20 mol%, V2O5 40 mol%, Nb2O
5. A mixture containing 10 mol% of MgO and 5 mol% of MgO added to the theoretical amount of LiNbO3 that can be precipitated from the melt composition (MgO/Nb2O5 = 10/95) was placed in a platinum crucible, and the mixture was placed in an epitaxial growth growth apparatus. The contents of the crucible were melted by heating to 1000° C. in an air atmosphere to obtain a melt.

(2) Heat the obtained melt at 60°C per hour.
It was slowly cooled to 907°C at a cooling rate of . The (0001) plane of a lithium tantalate single crystal containing Na was optically polished, chemically etched to a thickness of 1.0 mm, and further chamfered (C-plane) to be used as a substrate material. Surface roughness is JIS B0601 Rmax = 300 Å
Met. The amount of Na contained in this substrate material was 4
It was mol%. Further, the lattice constant (a-axis) of the substrate material was 5.163 Å. The substrate material was preheated for 30 minutes at a height of 15 mm above the melt and then immersed in the melt for 7 minutes while rotating at 100 rpm. The growth rate of lithium niobate single crystal thin film is 1.14 μm
/minute.

(3) Pull up the substrate material from the melt, shake it off by rotating it for 30 seconds at a rotational speed of 1000 rpm, and then cool the lithium tantalate single crystal at a cooling rate of 5° C./min. Curie temperature (645
℃), kept at that temperature for 30 minutes, and then gradually cooled to room temperature at a cooling rate of 60℃ per hour to deposit a single crystal of lithium niobate containing Na and Mg with a thickness of about 7 μm on the substrate material. A thin film was obtained.

(4) The amounts of Na and Mg contained in the obtained lithium niobate single crystal thin film were 7 mol % and 6 mol %, respectively. Furthermore, the lattice constant (a-axis) of the single crystal thin film is 5.163 Å, and the incident light wavelength is 1.15 μ.
The refractive index measured in m was 2.232 ±0.001. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B0601 Rmax = 800
It was Å.

(5) The obtained lithium niobate single crystal thin film was optically polished and subjected to ion beam etching.
After the thickness was set to 7 μm, a width of 5 μm was obtained using the same method as in Example 1.
μm, film thickness 2.30±0.02 μm, step difference 1.0 μm
A ridge-type waveguide was created. The surface roughness of the lithium niobate single crystal thin film is JIS B0601 Rmax
= 100 Å, and the roughness of the end face of the waveguide is according to JIS
B0601 Rmax = 100 Å. This waveguide is single mode, and as described in (5) and (6) above.
The element configuration of the equation was as follows. t/T=0.4 W/T=2.2

Example 4 (1) Li2CO3 49 mol%, V2O5 41
mol%, Nb2O5 10 mol%, and the theoretical amount of LiNbO3 that can be precipitated from the melt composition.
Based on 43 mol% Na2CO3 and the theoretical amount of LiNbO3 that can be precipitated from the melt composition, 6 mol%
of NgO 2 was placed in an iridium crucible and heated to 1100° C. in an epitaxial growth and growth apparatus under an air atmosphere to melt the contents of the crucible to obtain a melt. This melt was then stirred using a propeller at a rotational speed of 200 rpm for 12 hours.

(2) The melt was slowly cooled to 915°C at a cooling rate of 60°C per hour. The (0001) plane of lithium tantalate single crystal is optically polished to a thickness of 1.8 mm.
After that, chamfering (C side) was performed. By photolithography and RF sputtering method, the film thickness is 1000 Å,
A MgO film with a width of 5 μm was formed. Next, this substrate was brought close to the melt in the epitaxial growth apparatus at 2.67 cm/min, and preheating and thermal diffusion were performed simultaneously. The thickness of the diffusion layer was 1000 Å. The substrate material was immersed in the melt for 17 minutes while rotating at 100 rpm. The growth rate was 1.94 μm/min.

(3) Pull up the substrate material from the melt, shake it off by rotating it at a rotational speed of 1000 rpm for 30 seconds, and then cool it at a cooling rate of 300° C. per hour to the Curie temperature of the lithium tantalate single crystal. (6
After cooling slowly to 50℃ and keeping at that temperature for 1 hour,
The mixture was gradually cooled to room temperature at a cooling rate of 60° C. per hour to obtain a lithium niobate single crystal thin film containing Na and Mg with a thickness of about 21 μm on the substrate material.

(4) The amounts of Na and Mg contained in the obtained lithium niobate single crystal thin film were 2 mol% and 5 mol%, respectively. In addition, the lattice constant of the thin film (a
The refractive index measured at an incident light wavelength of 1.15 μm was 2.231 ±0.001. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B0601 Rmax = 900 Å.

(5) The obtained lithium niobate single crystal thin film was optically polished and subjected to ion beam etching.
．． After the thickness was set to 8 μm, a width of 15 μm, a film thickness of 5.70±0.05 μm, and a step difference of 3.6 μm was obtained using the same method as in Example 1.
A ridge-type waveguide of m was obtained. The surface roughness of the obtained lithium niobate single crystal thin film was determined according to JIS B0601.
Rmax = 300 Å, the roughness of the waveguide end face is JI
S B0601 Rmax = 400 Å. This waveguide is single mode, and as described in (5) and (6) above.
The element configuration shown in the formula was as follows. t/T=0.6 W/T=2.6

Example 5 (1) Li2CO3 21.0 mol%, Nb2O5
34.0 mol%, K2CO3 22.5 mol%
, 22.5 mol % of V2O5, and 5 mol % of MgO based on the theoretical amount of LiNbO3 that can be precipitated from the melt composition was placed in a platinum crucible and grown in an epitaxial growth apparatus under an air atmosphere. The contents of the crucible were melted by heating to 1100° C. to obtain a melt.

(2) This melt was slowly cooled to 893°C at a cooling rate of 60°C per hour. The (0001) plane of lithium tantalate single crystal is optically polished to a thickness of 1.5 mm.
And so. Surface roughness is JIS B0601 Rmax =
It was 400 Å. The substrate material was then preheated at 893° C. 15 mm above the melt and then immersed in the melt for 11 minutes while rotating at 100 rpm. The growth rate of the lithium niobate single crystal thin film was 0.54 μm/min.

(3) The substrate material was pulled up from the melt, rotated at a rotational speed of 1000 rpm for 30 seconds to shake off the melt, and then heated at a cooling rate of 1° C./min for 63 minutes.
The substrate was cooled to 0 °C, then cooled from 630 °C to 600 °C at a rate of 0.2 °C/min, and further slowly cooled to room temperature at a rate of 1 °C/min. A crystal thin film was obtained. The lattice constant (a-axis) of this single crystal thin film is 5.154 Å, and the refractive index measured at an incident light wavelength of 1.15 μm is 2.
．． 231 ±0.001. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B06.
01 Rmax = 1400 Å.

(4) The obtained lithium niobate single crystal thin film was optically polished and made to a thickness of 1.5 μm by reactive ion beam etching, and then processed to a width of 5 μm and a film thickness of 5 μm using the same method as in Example 1. 1.21±0.02μm, step 0
．． A 9 μm ridge-type waveguide was obtained. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B06.
01 Rmax = 1300 Å, and the roughness of the end face of the waveguide was JIS B0601 Rmax = 1000 Å. This waveguide is single mode, and as described in (5) above,
The configuration of the element shown in formula (6) was as follows. t/T=0.7 W/T=4.1

Example 6 (1) 26.8 mol% Na2CO3, Li2CO
3 23.2 mol%, V2O5 38.0 mol%,
Nb2O5 12.0 mol% A mixture prepared by adding 12.0 mol% TiO2 to the theoretical amount of LiNbO3 that can be precipitated from the above-mentioned melt composition was placed in an iridium crucible, and the mixture was heated for 1100 min in an air atmosphere in an epitaxial growth apparatus. The contents of the crucible were melted by heating to 0.degree. C. to obtain a melt.

(2) The melt was slowly cooled to 893°C at a cooling rate of 60°C per hour. After optically polishing the (0001) plane of a lithium tantalate single crystal with a thickness of 1.7 mm, a MgO film with a thickness of 800 Å and a width of 5 μm and a film other than the MgO film with a width of 5 μm were formed using photolithography and RF sputtering. Cu with a thickness of 400 Å
After forming the film, it was thermally diffused at 1000°C and heated to 400°C.
A diffusion layer of Å was formed. Then, a material having an MgO 2 diffusion channel with a width of 5 μm was chemically etched and used as a substrate material. The ordinary refractive index of the channel part in which MgO is diffused and the part in which Cu is diffused other than the channel part is 10× compared to the substrate material without any diffusion.
It was decreased by 10-3 and increased by 1x10-3. Also,
Surface roughness is JIS B0601 Rmax = 500 Å
Met. After preheating this substrate material at 893 °C for 60 minutes at a height of 10 mm above the melt,
Soaked for 12 minutes while rotating at rpm. The growth rate was 0.58 μm/min.

(3) The substrate material was pulled up from the melt, rotated at a rotational speed of 1000 rpm for 30 seconds to shake off the melt, and then heated at a cooling rate of 2°C/min to 654°C.
After cooling to 645 °C and keeping the temperature constant for 1 hour, it was slowly cooled to room temperature at a rate of 2 °C/min, and about 7μ was deposited on the substrate material.
A lithium niobate single crystal thin film containing Na and Ti with a thickness of m was obtained.

(4) The amounts of Na and Ti contained in the obtained single crystal thin film of lithium niobate were 4.6 mol% and 5.0 mol%, respectively. Also, the lattice constant (a-axis) is 5.153 Å, and the incident light wavelength is 1.15 μm.
The refractive index measured was 2.241 ±0.001. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B0601 Rmax = 2000 Å
Met.

(5) The obtained lithium niobate single crystal thin film was optically polished and made to a thickness of 5.3 μm by reactive ion beam etching, and then a film with a width of 10 μm was formed using the same method as in Example 1. Thickness 4.85±0.05μm, step 2
．． A 7 μm ridge-type waveguide was obtained. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B06.
01 Rmax = 1500 Å, and the roughness of the end face of the waveguide was JIS B0601 Rmax = 1400 Å. This waveguide was single mode. And the above (
The element configuration shown in equations 5) and (6) was as follows. t/T=0.6 W/T=2.1

Example 7 (1) Using Li2CO3, Ta2O5, and TiO2 as raw materials, a lithium tantalate single crystal containing 8.8 mol% of Ti was pulled by the CZ method. Next, a substrate was cut out from this single crystal. The lattice constant of the a axis is 5.14
It was 7 Å.

(2) Li2CO3 40.2 mol%,
V2O5 46.0 mol%, Nb2O5 13.
8 mol%, LiNbO3 that can be precipitated from the melt composition
A mixture of 5.6 mol% MgO based on the theoretical amount of LiNbO and 6.25 mol% TiO2 based on the theoretical amount of LiNbO3 that can be precipitated from the melt composition was placed in an iridium crucible. The contents of the crucible were melted and a melt was obtained by heating the crucible to 1100°C in an air atmosphere in an epitaxial growth apparatus.

(3) The melt was slowly cooled to 893°C at a cooling rate of 60°C per hour. After optically polishing the (0001) plane of a lithium tantalate single crystal with a thickness of 1.7 mm, a MgO film with a thickness of 800 Å and a width of 5 μm and a film other than the MgO film with a width of 5 μm were formed using photolithography and RF sputtering. 400 Å thick Cr
After forming the film, it was thermally diffused at 1000°C and heated to 400°C.
A diffusion layer of Å was formed. Then, a material having an MgO 2 diffusion channel with a width of 5 μm was chemically etched and used as a substrate material. The ordinary refractive index of the channel part in which MgO is diffused and the part in which Cr is diffused other than the channel part is 10× compared to the substrate material without any diffusion.
It was decreased by 10-3 and increased by 1x10-3. Also,
Surface roughness is JIS B0601 Rmax = 500 Å
Met. After preheating this substrate material at 893 °C for 60 minutes at a height of 10 mm above the melt,
Soaked for 12 minutes while rotating at rpm. The growth rate was 0.58 μm/min.

(4) The substrate material was pulled up from the melt, rotated at a rotational speed of 1000 rpm for 30 seconds to shake off the melt, and then slowly cooled to room temperature at a cooling rate of 2° C./min. A lithium niobate single crystal thin film containing Mg and Ti with a thickness of about 7 μm was obtained on top.

(5) The amounts of Mg and Ti contained in the single crystal thin film of lithium niobate obtained were as follows:
They were 5.0 mol% and 5.0 mol%. Also, the lattice constant (a-axis) is 5.147 Å, and the incident light wavelength is 1.15 μ.
The refractive index measured in m was 2.241 ±0.001. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B0601 Rmax = 2000
It was Å.

(6) The obtained lithium niobate single crystal thin film was optically polished and made to a thickness of 5.3 μm by reactive ion beam etching, and then processed to a width of 10 μm and a film thickness of 10 μm using the same method as in Example 1. 4.85±0.05μm, step 2.
A 7 μm ridge-type waveguide was obtained. The surface roughness of the obtained lithium niobate single crystal thin film was determined according to JIS B060.
1 Rmax = 1500 Å, the roughness of the waveguide end face is:
JIS B0601 Rmax = 1400 Å. This waveguide is single mode, and as described in (5) above.
, (6) The element configuration shown in equation (6) was as follows. t/T=0.6 W/T=2.1

Comparative Example 1 (1) Li2CO3 51 mol%, V2O5 39
mol %, Nb2O5 10 mol %, and 4 for the theoretical amount of LiNbO3 that can be precipitated from the melt composition.
3 mol% Na2CO3 and 7 mol% M based on the theoretical amount of LiNbO3 that can be precipitated from the melt composition.
The mixture containing gO was placed in an iridium crucible and heated for 1 hour under an air atmosphere in an epitaxial growth apparatus.
The contents of the crucible were melted by heating to 100° C. to obtain a melt. Next, this molten material was heated using a propeller for 200 min.
The mixture was stirred for 12 hours at a rotation speed of rpm.

(2) The melt was slowly cooled to 915°C at a cooling rate of 60°C per hour. The (0001) plane of lithium tantalate single crystal is optically polished to a thickness of 1.8 mm.
After that, chamfering (C side) was performed. By photolithography and RF sputtering method, the film thickness is 1000 Å,
After forming an MgO 2 film with a width of 5 μm, it was thermally diffused at 920° C., and a material having an MgO 2 diffusion channel of 1000 Å and a width of 5 μm was used as a substrate material. The thickness of the diffusion layer is 1
000 Å. This channel part has an ordinary refractive index of 15 x 10-3 compared to the part where MgO is not diffused.
It was decreasing. In addition, the surface roughness is JIS B0601 R
max = 300 Å. This substrate material is 9
After preheating for 30 minutes at 15 °C, 100
Soaked for 17 minutes while rotating at rpm. The growth rate was 1.94 μm/min.

(3) Pull up the substrate material from the melt and place it on the melt for 30 seconds at a rotation speed of 1000 rpm.
After shaking off the melt, it was slowly cooled to room temperature at a cooling rate of 300° C. per hour to obtain a single crystal thin film of lithium niobate containing Na and Mg with a thickness of about 37 μm on the substrate material.

(4) The amounts of Na and Mg contained in the obtained lithium niobate single crystal thin film were 2 mol% and 6 mol%, respectively. The lattice constant (a-axis) of the thin film was 5.155 Å, and the refractive index measured at an incident light wavelength of 1.15 μm was 2.231 ±0.001.

(5) The obtained lithium niobate single crystal thin film was optically polished and plasma etched to 3.80
After obtaining a thickness of μm, a width of 4 m was obtained using the same method as in Example 1.
A ridge-type waveguide with a film thickness of 3.53±0.05 μm and a step difference of 0.1 μm was obtained. The surface roughness of the obtained lithium niobate single crystal thin film was JIS B0601 Rma
x = 1000 Å. Also, in this example, the above (
The element configuration shown in formulas 5) and (6) was as follows. t/T=0.02 W/T=1133

Note that the optical propagation loss of the optical waveguide shown in this comparative example was 1.8 dB/cm. Furthermore, in this comparative example, the optical power density was low because it was not possible to confine light to the ridge portion.

Comparative Example 2 (1) Li2CO3 51 mol%, V2O5 39
A mixture consisting of 10 mol% of Nb2O5 was placed in an iridium crucible and heated to 1100° C. in an epitaxial growth growth apparatus under an air atmosphere to melt the contents of the crucible to obtain a melt. This melt was then stirred for 12 hours using a propeller at a rotational speed of 200 rpm.

(2) The melt was slowly cooled to 915°C at a cooling rate of 60°C per hour. The (0001) plane of lithium tantalate single crystal is optically polished to a thickness of 1.8 mm.
After that, chamfering (C side) was performed. After preheating this substrate material at 915 °C for 30 minutes, 10
It was immersed for 17 minutes while rotating at 0 rpm. The growth rate was 1.94 μm/min.

(3) The substrate material was pulled up from the melt, rotated at a rotational speed of 1000 rpm for 30 seconds, the melt was shaken off, and then slowly cooled to room temperature at a cooling rate of 300° C. per hour. A lithium niobate single crystal thin film with a thickness of about 2 μm was obtained.

(4) The obtained lithium niobate single crystal thin film was optically polished and plasma etched to a thickness of 1.0μ.
A slab-type waveguide with a thickness of m was obtained. The surface roughness of the lithium niobate single crystal thin film is JIS B0601 Rm
ax = 1000 Å.

[Results of Examples and Comparative Examples] Above, Examples 1-
Regarding No. 7, the lithium niobate single crystal thin film of the present invention of the obtained optical waveguide was subjected to a prism bonding method to obtain a wavelength of 0.
．． The optical propagation loss for a semiconductor laser beam of 83 μm and the Pockels constant, which is also an electro-optic constant, were measured by placing a sample in a Mach-Zehnder interferometer, and the results are shown in Tables 1 and 2 together with the results of Comparative Example 2.

Table 3 shows the results of measuring the light confinement efficiency at the ridge portion of the waveguide for Examples 1 to 7 and Comparative Example 1. Table 1 Propagation loss Table 2 Electro-optic effect

Table 3 Confinement efficiency of light in ridge part

[
Example 8 This example describes a method similar to that of Example 1, in which LiNb
Slab-type or ridge-type (same shape as Example 1) waveguides were formed in the O3 thin film and LiTaO3 substrate by adding different elements as shown in Table 4, respectively, and the propagation loss of these waveguides was calculated. It was measured. Table 4 shows the results.
Shown below. Table 4 Different elements in the substrate and thin film and propagation loss The numbers in the formula are propagation loss (dB/cm)

[0108]

As explained above, the optical waveguide of the present invention has high confinement efficiency, low propagation loss, and excellent optical properties such as electro-optic effect. Therefore, it is useful when applied to various optical devices such as optical modulators, optical deflectors, optical amplification elements, and optical switches.

[Brief explanation of the drawing]

[Figure 1] Schematic diagram of a ridge-type optical waveguide

[Figure 2] Graph showing the relationship between the Na content in the LiNbO3 waveguide and the a-axis lattice constant

[Figure 3] Li2O-V2 O5 -Nb2O5 triangular diagram

[Explanation of symbols]

1 Ridge part 2 Thin film waveguide layer 3 Board

Claims (5)

[Claims] 1. An optical waveguide characterized in that a substrate crystal and a crystal of a thin film waveguide layer are lattice matched. 2. An optical waveguide having a ridge-type or rib-type thin film waveguide layer, wherein the thickness of the thin film waveguide layer is T(
The width W (μm) of the thin film waveguide layer is 6.6×10−
An optical waveguide characterized by having a relationship such as 2≦W/T≦6.7×102. 3. The optical waveguide according to claim 2,
Among them, for the ridge type, the ridge part step t (μm) and the thin film waveguide layer thickness T (μm) are 0.10
An optical waveguide characterized by having a relationship such as ≦t/T≦0.99. 4. The optical waveguide according to claim 2, wherein the substrate and the thin film waveguide layer are lattice matched. 5. Any one of claims 1, 2, 3 and 4, wherein the substrate is made of lithium tantalate single crystal, and the thin film waveguide layer is made of lithium niobate single crystal. The optical waveguide according to item 1.