JPH0361930A - Second harmonic wave generating element - Google Patents

Abstract

PURPOSE:To efficiently generate second harmonic waves by satisfying specific relations in the ordinary light refractive index of an LiNbO3 thin-film waveguide layer and the extraordinary light refractive indices at the wavelength of the second harmonic waves of an LiTaO3 substrate and the LiNbO3 thin-film waveguide layer. CONSTITUTION:The ordinary light refractive index nos1 at the wavelength lambdaof the basic wave laser beam of the LiTaO3 substrate of the second harmonic wave generating element (SHG element) is specified to 2.10 to 2.20 and the extraordinary light refractive index nes2 at the wavelength lambda/2 of the second harmonic wave to 2.22 to 2.28. The ordinary light refractive index nOF1 of the LiNbO3 thin-film waveguide layer at the wavelength lambdamum of the basic wave laser beam and the extraordinary light refractive index nes2 at the wavelength lambdamum/2 of the second harmonic wave of the LiTaO3 substrate and the extraordinary light refractive index neF2 at the wavelength lambdamum/2 of the second harmonic wave satisfy equation I. The SHG element having high conversion efficiency is obtd. in this way.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a second harmonic generation element having an extremely high conversion efficiency to second harmonic light.
A second harmonic generation element (hereinafter referred to as SH) in which a LiNbO film waveguide layer is formed on a 0z substrate.
Conventional technology related to (referred to as O element) SHG elements utilize the nonlinear optical effect of an optical crystal material that has a nonlinear optical effect to convert an incident laser beam of wavelength λ to a wavelength of λ/2 and output it. This element converts the wavelength of output light to 1/2, so by applying it to optical disk memories, CD players, etc., the recording density can be quadrupled, and it can also be used in laser printers, photo High resolution can be obtained by applying it to lithography and the like.

Conventionally, a bulk single crystal nonlinear optical crystal using a high-power gas laser as a light source has been used as an SHG element. However, in recent years there has been a strong demand for miniaturization of entire devices such as optical disk devices and laser printers, and gas lasers require an external modulator for optical modulation, making them difficult to miniaturize. There is a need for an SHG element that can use a semiconductor laser, which is cheaper and easier to handle than a gas laser.

In addition, when using a semiconductor laser as a light source, since the output of the semiconductor laser is low at -S from several mW to several tens of mW,
It is necessary that the SHG element is particularly capable of obtaining high conversion efficiency.

By the way, as optical crystal materials that have a nonlinear optical effect and can be used for SHG elements, lithium niobate (LiNbO:+) and lithium tantalate (LiTa
Os), KTiOPO, KNbO3, Bag Na
There are Nb5*16, Ba, LiNb0+s, etc. Among them, LiNbO5 is the most suitable because it has a high nonlinear optical constant and a small optical loss.

(Problems with the prior art) Conventionally, as a method of forming a guiding waveguide using LiNbOs material, a bulk single crystal of LiNb0+ is subjected to treatments such as Ti diffusion, proton exchange, and outdiffusion to increase the refractive index. There are known methods of forming layers with different
For waveguides obtained by these methods, it is difficult to increase the difference in refractive index from the bulk for laser light sources with short wavelengths, especially laser light sources with wavelengths of λμm or less, and the second harmonic waveguide is difficult to obtain. Phase matching for generation, that is, the refractive index (effective refractive index) of the incident laser light in the waveguide
It is extremely difficult to match the effective refractive index of the second harmonic light [Yamada, Miyazaki; Institute of Electronics, Information and Communication Engineers Technical Report, MW87-113 (1988)], and the boundary between the waveguide and the bulk is extremely difficult. Due to the lack of clarity, light waves tend to spread out from the waveguide and it is difficult to concentrate optical energy, making it difficult to obtain particularly high conversion efficiency.

For this reason, the present inventors used L i N b O3 material and a 0.8 μm band semiconductor laser light source,
We investigated various combinations that can achieve phase matching between the fundamental wave light and the second harmonic light, and discovered that LiTa with a specific refractive index
os single crystal and Li with a specific refractive index on its surface
We discovered the conditions that would enable phase matching with a structure in which a NbOs thin film was combined as a waveguide layer, and first filed a patent application in 1983-
No. 160804 was filed.

However, the previous invention has an extremely narrow scope of application as it can only use a 0.8 (TM band) semiconductor laser as a fundamental wave laser light source, and furthermore,
Since the refractive index of a substance varies with wavelength in a -J'llQ manner, it could not be applied to laser light sources of different wavelengths.

Therefore, the present inventors used LiNbO as a material and developed a 5r(
As a result of intensive research on the conditions of the G element, LiTa0z
This is a second harmonic generation element in which a LiNbOsfm film waveguide layer is formed on a substrate, and the ordinary refractive index (na3
2) and the value of the extraordinary refractive index (nesz) at the second harmonic wavelength (λμm/2) is set in a specific range, and the ordinary refractive index (no □), Li
Extraordinary refractive index (nus□) at the second harmonic wavelength (λμm/2) of the TaO5 substrate and extraordinary refractive index (n,,□) at the second harmonic wavelength (λμm/2) of the LiNbO3 film waveguide layer ) by satisfying a certain relation to
The present invention was completed based on the novel discovery that second harmonics can be generated extremely efficiently.

(Means to solve the problem) In the present invention, LtNb○ is formed on a LiTaO3 substrate.

A second harmonic generation element formed by a thin film waveguide layer, in which L i T a○ is the fundamental laser light wavelength of the substrate (
The ordinary refractive index (no, +) at λμm) is 2.10
~2.20, the extraordinary refractive index (na32) at the second harmonic wavelength (λttm/2) is 2.22-2.28, and the fundamental laser light wavelength (
This SHG element is characterized in that the ordinary refractive index (nox) at the wavelength of the second harmonic (λμm) and the extraordinary refractive index (n5r8) at the second harmonic wavelength (λμm/2) are expressed by the following relational expression.

(Function) The structure of the SHG element of the present invention is that L
It is necessary that an iNb0sF# film waveguide layer is formed.

The reason why it is necessary for the structure of the SHG element to be such that a thin film waveguide layer is formed on a substrate is that the second harmonic light in an SHG element that has a thin film waveguide layer formed on a substrate is Generation has the advantages of being able to utilize the energy of light concentrated in a thin film, and because the light waves are confined within the thin film and do not spread out, interactions can occur over long distances. This is because SHG elements that use conventional bulk materials have the advantage of being able to achieve phase matching by utilizing the mode dispersion of thin films even with materials that cannot be phase matched. LiNb0. as a wave layer. The reason why it is necessary to use LiNb0. LiTaO3 has a large nonlinear optical constant, low optical loss, and can form a uniform film.Also, LiTaO3 has a similar crystal structure to the LiNbO5, and the LiTaO3 has a similar crystal structure to the LiNbO5.
This is because it is easy to form a thin film of b○, and it is easy to obtain high quality and inexpensive crystals.

Note that the L i T a Ox substrate is advantageously a single crystal substrate.

In the SHG element of the present invention, the ordinary refractive index (n, , ) of the LiTaO3 substrate at the fundamental laser light wavelength (λ) is 2.
．． 10 to 2620, the extraordinary refractive index (na32) at the second harmonic wavelength (λ/2) is 2.22 to 2.28, and the Li at the fundamental laser light wavelength (λμm) is
Ordinary refractive index (netl) of NbOs thin film waveguide layer
, the second harmonic wavelength (λμm
/2) and the extraordinary refractive index (n, Ft) at the second harmonic wavelength (λμm/2).
) must satisfy the following relational expression. .

The reason is that the ordinary refractive index (n.,) of the LiTaO3 substrate at the fundamental laser light wavelength (λμm) is 2.1.
0 to 2.20, the extraordinary refractive index (n1□) at the second harmonic wavelength (λμm/2) is 2.22 to 2.28,
Moreover, by creating a structure that satisfies the above relational expression, it is possible to obtain an SHG element with extremely high conversion efficiency.

In order to obtain particularly high conversion efficiency, it is advantageous to satisfy T(netl nas□), and in particular, T(no
□ −n1□ ) is preferably satisfied.

The SHG element of the present invention has an ordinary refractive index (na32
) is 2.10 to 2. ．． 20. Second harmonic wavelength (λμm/
The extraordinary refractive index (nus2) in 2) is 2.22 to 2
．． Must be 28.

The reason is that the ordinary refractive index (netl) at the fundamental laser light wavelength and the extraordinary refractive index (na32) at the second harmonic wavelength of the LiTaO3 substrate are preferably as low as possible, but are lower than the above refractive index range. LiT
This is because it is difficult to obtain an aO5 substrate, and on the other hand, SH has a high conversion efficiency when the refractive index is higher than the above range.
This is because it becomes difficult to obtain a G element.

LiNb0. The thin film waveguide layer and the LiTaO3 substrate are made of Na, Cr.

It is advantageous to use a material whose refractive index is adjusted by containing different elements such as Mg, Nd, Ti, and V.

By incorporating Na, Cr, Nd, Ti, etc. into the LjNbOsfi film waveguide layer and the LiTaO3 substrate, the LiNbOspi film waveguide layer and the LiTaO3 substrate are
The refractive index of the O3 substrate can be increased, and Mg, V
By containing the above-mentioned LiNb0. The refractive index of the thin film waveguide layer and the LiTaO3 substrate can be lowered.

The content of Na is preferably 0.1 to 10 mo1%. The reason for this is that the Na content is lomo1%.
If it exceeds LiNb0. Thin film waveguide layer or L
This is because the optical properties of the iTaO5 substrate deteriorate, and when Q is lower than 1 mo 1%, the refractive index hardly changes, so in either case it cannot be a practical SHG element. The content of Na is 0.8 m
01% to 2mo1% is suitable.

Further, the Cr content is preferably 0.02 to 20 mo1%. The reason for this is that when the Cr content exceeds 20 mo1%, a LiNbOs thin film waveguide layer or an L This is because the optical properties of the i T a Ox substrate will deteriorate, and if it is lower than 0°1 mo1%, the refractive index will hardly change, so in either case it will not be a practical SHG element. Said Cr
The content of 0.2 mo1% to 10 mo1% is especially suitable.

Further, the content of Mg is preferably 0.1 to 20m01%. The reason for this is that if the Mg content exceeds 20 mo1%, the optical properties of the LiNbO5 thin film waveguide layer or LiTaO5 substrate will deteriorate, and if the Mg content is lower than O11 mo1%, it will prevent light damage. This is because, in either case, it will not be a practical SHG element because it has almost no effect. The Mg content is preferably 2.0 mo1% to 10 mo1%.

The Ti content is preferably 0.2 to 30 mo1%. The reason for this is that the Ti content is 30 mo1%.
If it exceeds LiNb0. Thin film waveguide layer or L
iTaO3! This is because the optical properties of the S plate deteriorate,
Moreover, if it is lower than 0.2 mo1%, the refractive index hardly changes, and in any case, it will not be a practical SHG element. Among others, the content of Ti is 1.
0mo1% to 15mo1% is suitable.

The Nd content is preferably 0.02 to 10 mol%. The reason for this is that the Nd content is 10 mol%.
%, L i N b Oz thin film waveguide layer,
Alternatively, the optical properties of the LiTaO5 substrate deteriorate, and if it is lower than 0.02mol%, the refractive index hardly changes, so in either case, practical SHG
This is because it does not become an element. The content of Nd is preferably 0.5mo 1% to 5mo 1%.

The content of V is preferably 0.05 to 30 mo1%. The reason for this is that the grain content of the above ① is 30mol1.
This is because if it exceeds 0.05mol%, crystals with different structures will precipitate in the LiNbO5 thin film waveguide layer or LiTaO3 substrate, deteriorating the optical properties.
If it is lower, the refractive index will hardly change, so in any case, it will not be a practical SHG element.

The content of V is 2.0 mo1% to 10 mo
1% is preferred.

Note that the content is L i N b Os or
It is expressed as mo1% of the foreign element with respect to L i T a 03.

As a method for obtaining the LiNb0zfl film waveguide layer containing a different element such as Na, Cr, Mg, Nd, Ti, V, etc., the raw material and the different element or 5'! Seed element compounds are mixed and Li is grown by liquid phase epitaxial growth method.
LiNb0. on TaO3 substrate. Methods of forming thin film waveguide layers, sputtering method, metal chemical deposition (MOCV)
D) method, molecular beam epixiety (MBE) method, or the above Li Ta Oz substrate or LiNbO5
Various methods can be used, such as a method of diffusing different elements such as Na, Cr, Mg, Nd, Ti, and V into the thin film waveguide layer, and an ion implantation method.

The SHG element of the present invention has a fundamental laser light wavelength (λμ
m) is preferably 0.68 to 0.94 μm.

The reason is that it is advantageous for the fundamental wave laser light (λμm) to have a wavelength as short as possible;
This is because it is substantially difficult to generate laser light with a wavelength shorter than 0.68 μm using a semiconductor laser, whereas when using a fundamental laser light with a wavelength longer than 0.94 μm, the resulting Since the wavelength of the second harmonic is 1/2 that of the fundamental laser beam, this is a wavelength range that can be relatively easily generated directly by a semiconductor laser, and there is no advantage to using an S It G element. It is. Wavelength (λ) of the fundamental laser beam
is 0.78~, which is relatively easy to obtain a semiconductor laser light source.
0.386 μm is advantageous, especially 0.82 to 0.0386 μm.
84 μm is practically suitable.

II of the L i N b Os thin film waveguide layer of the SHG device of the present invention! It is preferable that ff(T) is in the range of 0.3 to 16 μm.

The reason is that the film W-(T) of the thin film waveguide layer is 0°3
If it is thinner than 16 μm, it is difficult to make the fundamental laser beam incident and the incidence efficiency is low, making it difficult to obtain substantially high SHG conversion efficiency.On the other hand, if it is thicker than 16 μm, the optical power density is low. , 5HGi conversion efficiency becomes low, making it difficult to use as an SHG element in either case. The thickness of the thin film waveguide layer is preferably 0. 5 to 10 μm is advantageous, especially 1
~8 μm is practically suitable.

In the SHG element of the present invention, the incident angle (θ) of the fundamental laser beam with respect to the optical axis (Z axis) of the thin film waveguide layer is 0±15°.
Alternatively, it is preferably within the range of 90±15°.

The reason is that the incident angle (θ) of the fundamental wave laser beam is 5
This is because within the above range, the conversion efficiency to the second harmonic is extremely high. It is particularly advantageous for the incident angle of the fundamental laser beam to be within the range of 0±5° or 90±5°.

Furthermore, the SHG element of the present invention is advantageously of a channel type having a width of 1 to 10 μm.

The reason why a channel type SHG element is advantageous is that the optical power density can be higher than that of a slab type.
Also, the reason why it is advantageous for the width to be 1 to IO μm is that if the width is smaller than λμm, it is difficult to introduce the incident light into the waveguide, and the incidence efficiency is low, so the SHG conversion efficiency is also low. On the other hand, the larger the width, the higher the incidence efficiency is, but if it is larger than 10 μm, the optical power density decreases, and the SHG conversion efficiency decreases.

The method for manufacturing the channel-type SHO element includes, for example, forming a thin film waveguide layer on a substrate by a method such as sputtering or liquid phase epitaxial growth, and then applying photolithography and RF on the thin film waveguide layer. A method such as forming a Ti waveguide backbone by sputtering and performing ion beam etching using this as an etching mask to create a channel type SHG element can be used.

Examples of the present invention will be described in detail below.

Example 1-1 Thickness 0.5 +++ m by liquid phase eviaxial method
) Various thicknesses of T on LiTaO single crystal substrate
i, Mg, Na (each 5.5.2 molX) solid solution LiNb
S
It was made into an HG element. Fundamental laser light wavelength λ is 0.837
When it is 1 m, the ordinary refractive index (no!+) of the LiTaO3 single crystal substrate is 2.151. The ordinary refractive index (nOF+) of the LiNbO5 single crystal thin film waveguide layer is 2.273, and the extraordinary refractive index (n@St) of the LiTaO3 single crystal substrate at the second harmonic λ/2 is 2°263, at λ/2. Extraordinary optical refractive index (n1l) of LiNbO5 single crystal thin film waveguide layer
F! ) was 2.267.

This SHG element is null nss! In the SHO element, Ti, l'1g, Na solid Ig
L i N b O.

The thickness of the thin film was 2.02 μm.

Regarding this SHO element, the wavelength is 0.83μm, 40m
When the SHC conversion efficiency was measured when the W semiconductor laser was incident at an angle of 90'' to the crystal axis (Z axis) of the single crystal thin film, it was 21.2%, which was a very high efficiency. .

Example 1-2 Basically the same as Example 1-1, but using Ti.

Mg, Na solid solution LiNb0. An SHG element with a thin film thickness of 9.8 μm was created.

When we measured the SHC conversion efficiency when a 40 mW semiconductor laser with a wavelength of 0.83 μm was incident on this SHO element at an angle of 90' to the crystal axis (Z axis) of the single crystal thin film, it was 1.7%. Therefore, a sufficiently high efficiency was obtained as an SHG element.

Example 1-3 Basically the same as Example 1-1, but using Ti.

1 yen of Mg, Na solid content LiNbO5 thin film is 0.7
A SHG element with a diameter of μm was manufactured.

Regarding this SHG element, the wavelength is 0.83μm, 40m
When the SHC conversion efficiency was measured when a W semiconductor laser was incident at an angle of 90'' to the crystal axis (Z axis) of a single crystal thin film, it was 1.8%.

Sufficiently high efficiency was obtained as an element.

Example 2-1 Y with a thickness of 0.51111 by RF sputtering method
VzO with a thickness of λμm on a cut LiTa01 single crystal substrate
A 1FJ film was formed, and ■ was diffused into the surface layer of the LiTaO3 single crystal using a thermal diffusion method. Fundamental laser light wavelength λ is 017
8 μm, ■The ordinary refractive index (no7) of the diffused LiTaO3 substrate is 2.153, and ■The extraordinary refractive index of the diffused LiTaO5 substrate at the second harmonic λ/2 (nas,
) was 2.272.

On this substrate, various thicknesses of Mg and Nd (5 mo1%, 2 mo1%, respectively) were grown by liquid phase epitaxial growth.
) A solid solution LiNbO3 single crystal a film was grown. The surface was mirror-polished and the end faces on both sides were mirror-polished to make it possible for light to enter and exit from the end faces to form a SHG element. When the fundamental laser light wavelength λ is 0.78 μm, ? 1g, Nd solid solution 1.1
The ordinary refractive index (nov+) of the Nboz thin film waveguide layer is 2.
281, Mg, Nd solid solution L at second harmonic λ/2
The extraordinary refractive index (ne□) of the iNbO3 thin film waveguide layer is 2.
It was 276.

This SHO element is n@F! n*5Z The thickness of the Mg, Nd solid solution LiNb0z thin film of the SHO element was 2.10 μm.

Regarding this SHG element, wavelength Q, 787zm, 40m
When the SHG conversion efficiency was measured when a W semiconductor laser was incident at an angle of 90° to the crystal axis (Z axis) of the single crystal thin film, it was 19.0%, and a very high efficiency was obtained.

Example 2-2 Basically the same as Example 2-1, except that Mg+Nd solid solution LiNb0. S H with a thin film thickness of lO, 4 μm
For the G element, a 40 mW semiconductor laser with a wavelength of 0.78 μm is set at 90° to the crystal axis (Z axis) of the single crystal 7N film.
When the SHC conversion efficiency was measured when incident at an angle of 1.3%, a sufficiently high efficiency was obtained as an SHG element.

Example 2-3 The SH was basically the same as Example 2-1, but the thickness of the MgNcl LiNb0sfl film was 0.5 μm.
For the G element, a 40 mW semiconductor laser with a wavelength of 0.78 μm is placed at 90° with respect to the crystal axis (Z axis) of the light source single crystal thin film.
When the SHG conversion efficiency was measured when the light was incident at an angle of .degree., it was 1.7%, which was a sufficiently high efficiency as an SHG element.

Example 3-1 L'1gO with a thickness of λμm was deposited on an X-cant LiTaO3 single crystal substrate with a thickness of 0.511111 by the RF sub-lid method.
Form a thin film, diffuse Mg into the surface layer of the LiTaO5 single crystal using thermal diffusion method, and adjust the fundamental laser light wavelength λ to 0.9 μm.
Then, the ordinary refractive index (n.31) of the Mg-diffused LiTaO3 single crystal substrate is 2.141, and the second harmonic λ/2
The ordinary refractive index (na32) of the diffused LiTaO3 single crystal substrate was 2°245.

On this substrate, various thicknesses of Mg, Nd'(5,5motχ) solid solution LiNb0 were grown by liquid phase epitaxial growth.
z The nine surfaces on which the single-crystal thin film was grown are mirror-polished, and the end faces on both sides are mirror-polished to allow light to enter and exit from the end faces.SH
It was used as a C element.

When the fundamental laser light wavelength λ is 0.9 μm, Mg,
Ordinary refractive index of Nd solid solution LiNbO5 single crystal thin film waveguide layer (
nor+) is 2.285, Mg, Nd solid solution LiNb0. at the second harmonic λ/2. The extraordinary refractive index (n*vz) of the single crystal thin film waveguide layer was 2.263.

This SHO element is n*F! noil Mg, Nd solid solution LjNb03 single crystal thin film thickness 2.1
For the SHG element with a wavelength of 3 μm, the wavelength is 0.9 μm,
A 40mW semiconductor laser is aligned with the crystal axis (Z axis) of a single crystal thin film.
When the SHG conversion efficiency was measured at an angle of 0°, it was 26.2%, which is a very high SHG conversion efficiency.
Conversion efficiency was obtained.

Example 3-2 Basically the same as Example 3-1, except that the S H
In the G element, the thickness of the Mg, Nd solid solution LiNb0 thin film was 14.0 μm.

A 40 mW semiconductor laser with a wavelength of 0.9 um is attached to this 5IIG element at 0@
The SHG conversion efficiency when incident at an angle of 1.6% was measured, and a sufficiently high efficiency was obtained as an SHG element.

Example 3-3 Basically the same as Example 3-1, but with Mg.

Nd solid content LiNb0. For an SHG element with a thin film thickness of 0.7 μm, a 40 mW semiconductor laser with a wavelength of 0.9 μm is set at 0° with respect to the crystal axis (Z axis) of the single crystal thin film.
When the SHO conversion efficiency was measured when the light was incident at an angle of 2.0%, a sufficiently high efficiency was obtained as an SHG element.

Example 4-1 Various thicknesses of Mg were deposited on a Z-cut LiTaO3 single crystal substrate with a thickness of 0.5 +a- by liquid phase epitaxial growth.
A solid solution LiNb0i single crystal thin film with O (2 mo1%) was grown.

The surface was mirror-polished and the end faces on both sides were mirror-polished to allow light to enter and exit from the end faces, thereby forming an SHG element.

When the fundamental laser light wavelength λ is 0.83 μm, Li
The ordinary refractive index (na31) of the TaO3 single crystal substrate is 2.
141, the ordinary refractive index (nOF+) of the LiNbO3 single crystal thin film waveguide layer at λ is 2.273, and the second harmonic λ/
The extraordinary refractive index (n
a32) is 2.263, LiNb0. at λ/2.
The extraordinary refractive index (n*Ft) of the single crystal thin film waveguide layer is 2.
It was 267.

This S II G element is n*F! n@sM In the above SHG element, the thickness of the MgO solid solution LiNb03a film was set to 2.0λμm.

Second S I (for G element, wavelength 0.83 μm, 40
The SHG conversion efficiency when a mW semiconductor laser was incident at an angle of 90'' with respect to the crystal axis (Z axis) of the single crystal thin film was measured and was 21.2%, indicating a very high efficiency.

Example 4-2 Basically the same as Example 4-1, except that the thickness of the MgO solid solution LiNb0sFI film was 17.8 μm.
A G element was created.

When we measured the SHG conversion efficiency when a 40 mW semiconductor laser with a wavelength of 0.83 μm was incident on this SHG element at an angle of 90° to the crystal axis (Z axis) of the single crystal thin film, it was 1.7%. Therefore, a sufficiently high efficiency was obtained as an SHG element.

Example 4-3 Basically the same as Example 4-1, but with Mg0UI
SH where the thickness of the A-soluble LvbosfW film was 0.5 μm
A G element was manufactured.

Regarding this SHG element, the wavelength is 0.83μm, 40m
When the SHG conversion efficiency was measured when a W semiconductor laser was incident at an angle of 90'' to the crystal axis (Z axis) of a single crystal thin film, it was 1.8%, which was a sufficiently high efficiency as an SHG element. It was done.

Example 5-1 X with a thickness of 0.5 mm by liquid phase epitaxial growth method
) Nd of various thicknesses on a LiTaO3 single crystal substrate
(5mo1%) solid solution LiNb0. The surface on which the single-crystal thin film was grown was mirror-polished, and the end faces on both sides were mirror-polished to enable light to enter and exit from the end faces, producing an SHG element. When the fundamental laser light wavelength λ is 0.9 μm, L at λ
The ordinary refractive index (na31) of the iTaO3 single crystal substrate is 2
．． Ndl1 at 141 λ! If the ordinary refractive index (no□) of the molten LiNb0z thin film waveguide layer is 2.285, λ/2
The extraordinary refractive index (nm
s*) is 2°245, Nd solid solution LiN at λ/2
b0. The extraordinary refractive index (fl*Fl) of the thin film waveguide layer is 2
．． It was 263.

This SHO element is n@F! -ns! ! The thickness of the Nd solid solution LiNbO5 thin film of the SHC element was set to 2°13 μm.

Regarding this SHC element, the wavelength is 0.9 μm and 40 m.
When the SHO conversion efficiency was measured when a W semiconductor laser was incident at an angle of Oo with respect to the crystal axis (Z axis) of the single crystal thin film, it was 26.2%, and a very high efficiency was obtained.

Example 5-2 Basically the same as Example 5-1, but with Nd solid solution Li
For a SHO device with a NbO5 thin film of 14.0 pm, SHG when a 40 mW semiconductor laser with a wavelength of 0.9 μm is incident at an angle of 0° to the crystal axis (Z axis) of the single crystal thin film. When we measured the conversion efficiency, it was 1.6.
%, and a sufficiently high efficiency was obtained as an SHG element.

Example 5-3 Basically the same as Example 5-1, but using Nd solid? 9
SHG conversion when a 40 mW semiconductor laser with a wavelength of 0.9 μm is incident at an angle of 0° to the crystal axis (Z axis) of the single crystal thin film for a SHO device made of LiNbO with a thin film thickness of 0.7 μm. When the efficiency was measured, it was 2.0%.
Therefore, a sufficiently high efficiency was obtained as an SHG element.

Example 6-1 Y with a thickness of 0.5 on by liquid phase epitaxial growth method
(l) of various thicknesses on a LiTaO3 single crystal substrate
Il.

1χNa, 5molXMg, 1molXNd) Solid solution LiNb0. Single crystal thin films were grown. 'The surface was mirror-polished and the end faces on both sides were mirror-polished to allow light to enter and exit from the end faces, thereby forming an SHG element.

When the fundamental laser light wavelength λ is 0.78 μm, Li
The ordinary refractive index (na31) of the TaO3 single crystal substrate is 2.
153, the ordinary refractive index (nor+) of the (Na, Mg, Nd) solid solution LiNbO3 film waveguide layer is 2.281, and the extraordinary refractive index (n*sM) of the LiTaO3 single crystal substrate at the second harmonic wavelength λ/2 is 2.281. ) is 2.272, (Na, gate g,
Nd) Extraordinary optical refractive index (n
aWt) was 2.276. This SHG element is naWt n@t! In the SHC element, (Na, Mg, Nd)
The thickness of the solid solution LiNbOx thin film was 2.10 μm.

A 40 mW semiconductor laser with a wavelength of 0.78 μm is applied to this SHC element at a 90° angle with respect to the crystal axis (Z axis) of the single crystal thin film.
When the SHG conversion efficiency was measured at an angle of 19.0°, it was 19.0%, and a very high efficiency was obtained.

Example 6-2 Basically the same as Example 6-1, but (Na, Mg
, Nd) For a SHG element with a solid solution ttNbosl film thickness of 10.4 μm, wavelength of 0.78 μm, 40 mW
When the SHG conversion efficiency was measured when a semiconductor laser was incident at an angle of 90'' with respect to the crystal axis (Z axis) of the single crystal thin film, it was 1.3%, which is a sufficiently high efficiency as an SHC element. was gotten.

Example 6-3 Basically the same as Example 6-1, but (Na, Mg
) The thickness of the solid solution LiNbO31 film was 0.5 μm.
For the HC element, a 40 mW semiconductor laser with a wavelength of 0.78 μm is applied at 90° to the crystal axis (Z axis) of the single crystal thin film.
When the SHG conversion efficiency was measured when the light was incident at an angle of 1.7%, it was 1.7%, which was a sufficiently high efficiency as an SHG element.

(Effects of the Invention) As described above, according to the present invention, extremely high SHC
, LiNbO5 on LiTaO3 substrate with conversion efficiency
It is possible to provide an SHG element in which a thin film waveguide layer is formed.

Claims (1)

[Claims] 1. A second harmonic generation element in which a LiNbO_3 thin film waveguide layer is formed on a LiTaO_3 substrate, which
The ordinary refractive index (n_a_3_1) at the fundamental laser light wavelength (λμm) of the aO_3 substrate is 2.10 to 2.20.
, the extraordinary refractive index (n_a_3_2) at the second harmonic wavelength (λμm/2) is 2.22 to 2.28, and the ordinary refractive index (n_a_F_1) of the LiNbO_3 thin film waveguide layer at the fundamental laser light wavelength (λμm) is 2.22 to 2.28. ), LiTaO
The extraordinary refractive index (n_a_3_2) at the second harmonic wavelength (λμm/2) of the _3 substrate and the extraordinary refractive index (n_a_F_2) at the second harmonic wavelength (λμm/2) of the LiNbO_3 thin film waveguide layer have the following relationship. A second harmonic generation element characterized by being represented by the following formula. 2.0≦(n_0_F_1−n_a_3_2)/(n_
The second harmonic generating element according to claim 1, wherein a_3_2)≦30.02, and the LiNbO_3 film waveguide layer has a thickness of 0.1 to 20 μm. 3. The fundamental laser light wavelength (λ) is 0.68 to 0.
The second harmonic generating element according to claim 1, which has a thickness of 94 μm. 4. The incident angle (θ) of the fundamental wave laser beam with respect to the optical axis (Z axis) of the thin film waveguide layer is 0±15° or 90±1
2. The second harmonic generating element according to claim 1, wherein the angle is 5°. 5. The second harmonic generating element according to claim 1, wherein the second harmonic generating element is a channel type having a width of 1 to 10 μm.