JPH0572590A - Second harmonic wave generating element - Google Patents

Abstract

PURPOSE:To obtain the SHG element which can be easily produced and has high conversion efficiency. CONSTITUTION:The surface roughness Rmax of the thin-film waveguide layers 3 of the second harmonic generating element constituted by forming the thin-film waveguide layers 3 consisting of the single crystal of LiNO3, on an LiTaO3 substrate 1 is specified within the 10 to 10000Angstrom range. The substrate 1 and the thin-film waveguide layer 3 are so constituted as to attain lambda=0.80 to 1.15mum, noS1=2.08 to 2.17, neS2=209 to 2.30, noF1=2.20 to 2.27, and neF2=2.19 to 2.35 when the ordinary light refractive index of a basic wave laser beam of a wavelength lambda is designated as (noS1), the ordinary light refractive index of the substrate 1 when the second harmonic wave of lambda/2 is generated is designated as (noS2), the ordinary light refractive index of the thin-film waveguide layer 3 of the basic wave laser beam of the wavelength lambda is designated as (noF1), and the extraordinary light refractive index of the thin-film waveguide layer 3 when the second harmonic wave of lambda/2 is generated is designated as (neF2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film waveguide type second harmonic wave generating element (hereinafter
Abbreviated as “SHG element”), especially LiTaO
We propose an SHG device, which is characterized in that a LiNbO ₃ single crystal thin film waveguide layer having a surface roughness Rmax in the range of 10 to 10,000 A is formed on ₃ substrates.

An SHG element is an element that converts an incident laser beam having a wavelength λ into a wavelength of λ / 2 by utilizing a non-linear optical effect of an optical crystal material and outputs it. According to this SHG element, the wavelength of the output light can be converted to 1/2, so that when applied to an optical disk memory, a CD player or the like, the recording density can be increased four times. When applied to laser printers, photolithography, etc.,
It is possible to obtain high resolution.

[0003]

2. Description of the Related Art Conventionally, as such an SHG element, one using a high-output gas laser as an excitation source and using a bulk single crystal of a nonlinear optical crystal material has been known. By the way, in recent years, in optical disk devices and laser printers, there has been a strong demand for downsizing the entire device. However, since the gas laser as described above requires an external modulator for optical modulation, downsizing can be achieved. Not suitable for. Under such circumstances, the SHG element using a semiconductor laser, which is capable of direct modulation and is cheaper and easier to handle than a gas laser, has recently attracted attention.

On the other hand, even when a semiconductor laser is used as an excitation source, the output of this semiconductor laser is as small as several mW to several tens mW. For this reason, there is a strong demand for a thin film waveguide type SHG element that can be expected to have high conversion efficiency. That is, the SHG element using the thin film waveguide is 1. 1. It is possible to increase the optical power density because it is limited to the inside of the thin film waveguide. 2. The ability to interact over long distances because the light waves are confined in the thin film waveguide and do not spread. The bulk has an advantage that even a substance that cannot be phase-matched can be phase-matched by utilizing mode dispersion of a thin film.

In this respect, as a conventionally known thin film waveguide material, that is, a nonlinear optical crystal material having a nonlinear optical effect and usable for an SHG element,
LiNbO ₃ , LiTaO ₃ , KNbO ₃ , KTiOP
O ₄ (KTP), Ba ₂ NaNb ₅ O ₁₅ (BNN),
K ₃ Li ₂ Nb ₅ O ₁₅ (KLN), Ba ₂ LiNb ₅ O
₁₅ (BLN), ZnO, KTa _x Nb _{1 -x} O ₃ (KT
N), LiIO ₃ , Sr _x Ba _{1 -x} Nb ₂ O ₆ (SB
N), BaTiO ₃ , PbTiO ₃ , KH ₂ PO ₄ (K
DP), KD ₂ PO ₄ (KD ^* P), NH ₄ H ₂ PO ₄
(ADP), InPS ₄ , β-BaB ₂ O ₄ (BB
O), LiB ₃ O ₅ (LBO) and the like. Among them, LiNbO ₃ has a high nonlinear optical constant and is known as one of the most suitable materials.

[0006]

2. Description of the Related Art A method for forming a thin film waveguide layer using the LiNbO ₃ single crystal suitable as a material for a thin film waveguide has heretofore been known as a method for forming Ti thin film on a bulk single crystal of LiNbO ₃ and a proton. There is known a method of forming a layer whose refractive index is changed by performing treatments such as exchange and outdiffusion. However, in the thin-film waveguide layer obtained by these known methods, the nonlinear optical constant is reduced due to the crystallinity deterioration of this waveguide portion, and moreover, the boundary of the refractive index between this waveguide layer and the bulk single crystal layer is Is not clear, it is easy for light waves to spread from the waveguide, and it is difficult to concentrate light energy.
There is a problem that it is difficult to obtain particularly high conversion efficiency.

For this reason, the present inventors have found that LiNbO₃single
Use a crystal and a laser light source with a wavelength of 0.6 to 0.94 μm
Phase matching between the fundamental laser light and the second harmonic light is obtained.
Have a specific refractive index by examining various combinations
LiTaO 3 crystal with specific refractive index on its surface
LiNbO₃A structure in which a single crystal thin film is combined as a waveguiding layer.
First, we found the conditions that enable phase matching by manufacturing,
-289599 and Japanese Patent Application No. 1-289600
Applied.

By the way, in recent years, research on green lasers has become active, and semiconductor laser pumped Nd: YAG
Laser or semiconductor laser pumped NYAB laser and KT
Development of an internal resonance type green laser in which a P single crystal or a KNbO ₃ single crystal is combined has been reported. (For example, Kubota; Electronics, Vol.36, N
o. 4, 79-82 (1991), Amano, Yokoyama et al .; Laser Research, V
ol. 18, No. 8, 634-638 (1990), Amano, Yokoyama et al .;
IEICE Technical Report, Vol.90, No. 78 (OQ
E90-30-47), 41-46 (1990), etc.)

Since this green laser has the same wavelength range as the sensitivity of an optical sensor used in a near infrared laser or the like, it does not require a great change even when it is applied to a laser disk system or the like. Only a green laser is required, which enables high density recording. Further, it is also regarded as promising as one of RGB three primary colors for realizing a next-generation high-definition display device using a laser.

However, the resonance type SHG device using a semiconductor laser pumped solid-state laser is extremely difficult to reduce in size and cost because it uses a bulk single crystal of a solid-state laser and a nonlinear optical crystal material. In addition, there is a disadvantage in that high speed modulation cannot be performed structurally. Furthermore, recently, as a light source for optical amplification of Er-doped optical fiber,
A 0.98 μm InGaAs semiconductor laser has been developed. This semiconductor laser is drawing attention as a fundamental wave light source for SHG elements that can obtain blue laser light close to green. However, it is extremely difficult to construct a resonant structure using this semiconductor laser as a fundamental wave light source, and it is extremely difficult to interact over a long distance while maintaining a high power density because a bulk single crystal is used. There is also a problem that a high SHG conversion efficiency cannot be obtained.

On the other hand, the invention previously proposed by the present inventors (Japanese Patent Application No. 1-289599 etc.) has a high SHG.
A SHG element having a single crystal thin film waveguide structure that can be expected to have a conversion efficiency and that can solve the above-mentioned drawbacks of the prior art, is a modulator suitable mainly for oscillating a blue laser,
Therefore, the conditions for producing the substrate and the single crystal thin film were such that a green laser could not be oscillated.

Therefore, the present invention relates to the above S related to the prior proposal.
The aim of the HG device is now to overcome the drawbacks of the prior art by searching for suitable conditions for obtaining a green laser.

[0013]

As a result of earnest research aimed at realizing the above-mentioned object, the inventors have found that the ordinary refractive index (noS1) of the LiTaO ₃ substrate when the wavelength of the fundamental laser light is λ (μm). and ordinary refractive index of LiNbO ₃ single crystal thin film waveguide layer (noF1), extraordinary refractive index of the definitive LiTaO ₃ substrate in generating the second harmonic wavelength λ / 2μm (neS2) and LiNbO ₃ single crystal thin film waveguide With respect to the extraordinary refractive index (neF2) of the layers, these are set within a certain numerical range, and the surface roughness of the LiNbO ₃ single crystal thin film is set within a certain numerical range.
Finding that harmonics can be generated very efficiently,
The present invention has been completed.

That is, according to the present invention, in the second harmonic generating device in which the LiNbO ₃ single crystal thin film waveguide layer is formed on the LiTaO ₃ substrate, the surface roughness R of the thin film waveguide layer is
When max is within the range of 10 to 10000Å and the fundamental wave laser beam of wavelength λ is incident, the ordinary refractive index of the substrate is (noS1), and under this incident condition, the second harmonic of λ / 2. The extraordinary refractive index of the substrate when the
2) and meanwhile, the ordinary refractive index of the thin film waveguide layer when the fundamental laser light of wavelength λ (μm) is incident is (noF1)
And the extraordinary refractive index of the thin-film waveguide layer when the second harmonic wave of λ / 2 (μm) is generated under the incident condition (ne
F2), λ, noS1, neS2, noF1, neF2
Respectively within the following numerical range; λ = 0.80 to 1.15 μm,
noS1 = 2.08 to 2.17, neS2 = 2.09 to 2.30, noF1 = 2.
The second harmonic generating element is characterized in that 20 to 2.27 and neF2 = 2.19 to 2.35. The SHG element according to the above-mentioned gist structure is beneficially a channel type in which the width of the waveguide layer is 1 to 10 μm.

[0015]

The SHG element of the present invention is characterized in that the surface roughness Rmax of the thin film waveguide layer is set within the range of 10 to 10,000 Å, and the ordinary refractive index of the substrate and the thin film waveguide layer with respect to the fundamental wave laser light, And to determine the SHG element configuration so that the numerical values of the characteristic equations of the substrate and the thin-film waveguide layer with the extraordinary refractive index for the second harmonic wavelength as a parameter fall within a specific range. It is possible to generate the second harmonic light with high conversion efficiency for the wave laser light. The details of the configuration of the present invention will be described below.

The SHG element according to the present invention has a structure in which a thin film waveguide layer is formed on a substrate. The SHG device having such a structure, that is, the SHG element in which the thin film waveguide layer is formed on the substrate, propagates the incident basic laser light only to the thin film waveguide surface, so that the light wave is confined in the thin film waveguide layer. As a result, the optical power density can be increased, and since it does not spread, it is possible to cause nonlinear interaction with the thin film waveguide layer having nonlinearity over a long distance. In addition, conventional S using bulk single crystal
There is also an advantage that even a substance that cannot be phase-matched by the HG element can be easily phase-matched by utilizing the mode dispersion of the thin film waveguide layer.

In the present invention, the thin film waveguide layer is L
An iNbO ₃ single crystal is used, and a LiTaO ₃ crystal is used as a substrate because the LiNbO ₃ single crystal has a large nonlinear optical constant, a small light loss, and a uniform film can be formed. Because you can,
LiTaO ₃ crystal, the LiNbO ₃ and a single crystal and crystal structure similar, easy to form a thin film of the LiNbO ₃ single crystal, also because easily available and inexpensive substrates with high quality.

Next, the surface roughness of the thin film waveguide layer of the SHG element of the present invention; that is, the maximum height Rmax according to the JIS B0601 standard must be within the range of 10 to 10000 Å. Is. The surface roughness is measured by J
It was measured with a stylus type surface roughness measuring device according to IS B0651. In the present invention, it is extremely difficult to make the value of the surface roughness Rmax smaller than 10Å, and it is difficult to trap the light wave. On the other hand, this surface roughness Rmax
If the value of is larger than 10,000 Å, the scattering loss on the surface of the waveguiding layer will increase, and the waveguide power of the fundamental laser light will decrease, so the SHG conversion efficiency will decrease and it will be used as an SHG element. Since it becomes difficult, the above limitation is applied.

Even within the above-mentioned surface roughness range, it is advantageous to satisfy Rmax = 10 to 1000Å in order to obtain a higher conversion efficiency, and above all, Rmax = 10 to 100Å. Is more preferred.

The surface roughness Rmax of this thin film waveguide layer
Is suitable as a control parameter for the second harmonic generation element because it can be easily measured by a stylus type surface roughness measuring instrument and can be easily controlled.

The LiTa used in the present invention is
O₃Advantageously, the substrate is a single crystal substrate. That
This LiTaO₃The surface roughness of the thin film formation surface of the substrate is
Within the range of JIS B0601 Rmax = 10 to 1000Å
Is desirable. The reason for this is that LiTaO₃Board table
Surface roughness is LiNbO₃It greatly affects the crystallinity of single crystal thin films.
Sounds, but it is extremely important to make the value of Rmax smaller than 10Å
On the other hand, while the value of Rmax is larger than 1000Å
Then, LiNbO 3 Because the crystallinity of the single crystal thin film decreases
Is.

The wavelength (λ) of the fundamental laser light incident on the SHG element of the present invention is preferably 0.80 to 1.15 μm. The reason is that it is advantageous that the fundamental laser light (λ) has a wavelength as short as possible, but it is substantially difficult to generate a laser light having a wavelength shorter than 0.80 μm by a semiconductor laser. That is why.
On the other hand, when a fundamental wave laser beam having a wavelength λ longer than 1.15 μm is used, the obtained second harmonic wavelength is half that of the fundamental wave laser beam. This is because it overlaps with the wavelength region that can be generated in the above, and the advantage of using a so-called SHG element cannot be found.

The film thickness (T) of the thin film waveguide layer constituting the SHG element of the present invention is preferably 0.1 to 20 μm. The reason is that the film thickness (T) is 0.1 μm.
This is because when the thickness is less than m, it is difficult to make the fundamental wave laser light incident and the incidence efficiency is low, and it is difficult to obtain a substantially high SHG conversion efficiency. On the other hand, this film thickness (T) is 2
This is because when the thickness is more than 0 μm, the optical power density is low and the SHG conversion efficiency is low, and it is difficult to use as an SHG element in any case. The film thickness (T) of the thin film waveguide layer is particularly preferably 0.5 to 10 μm, and particularly preferably 0.8 to 8 μm for practical use.

The SHG element of the present invention has an ordinary refractive index (noS1) of 2.08 to 2.17 at the wavelength λ (μm) of the fundamental laser light on the LiTaO ₃ substrate and a wavelength λ / of the second harmonic.
The extraordinary light refractive index (neS2) at 2 (μm) is 2.
09 to 2.30, and, definitive LiNb _O3 single crystal thin film waveguide layer ordinary refractive index at the wavelength of the fundamental wave laser beam λ (μm) (noF1) is from 2.20 to 2.27, the wavelength lambda / 2 of the second harmonic (mu
m), the extraordinary light refractive index (neF2) is 2.19 to 2.
It must be within the range of 35. The reason is that unless it is within the above range, the conversion efficiency to the second harmonic light is low and not practical.

Furthermore, LiTaO₃Substrate fundamental wave laser
The ordinary refractive index (noS1) at the wavelength of light λ (μm) is 2.
09 to 2.14, the difference in the wavelength λ / 2 (μm) of the second harmonic
Ordinary refractive index (neS2) is 2.12 to 2.23, and LiNb
O 3 Wavelength of fundamental wave laser light of single crystal thin film waveguide layer λ (μ
Ordinary refractive index (noF1) in m) is 2.22 to 2.24, second
Extraordinary light refractive index (n at wavelength λ / 2 (μm) of harmonics
More preferably, eF2) is in the range of 2.21 to 2.26.
It

LiNbO having the above-mentioned refractive index₃
Single crystal thin film waveguide layer and LiTaO 3 substrates are Na,
Heterogeneous elements such as Cr, Mg, Nd, Zn, Ni, Ti, V
Use the one whose refractive index is adjusted by containing the element.
It is advantageous to use.

Now, LiTaO₃On the substrate, the Na,
Heterogeneous elements such as Cr, Mg, Nd, Zn, Ni, Ti, V
LiNbO containing element₃Form a single-crystal thin-film waveguide layer
As a method of
Liquid phase epitaxial growth by mixing different element compounds
LiTaO by long method 3 LiNbO on the substrate₃Single crystal thin film
Waveguide layer forming method, sputtering method, metallization
Deposition (MOCVD) method, Molecular beam epitaxy (M
BE method etc. can be applied. In addition, the Li
TaO₃Substrate or LiNbO 3 Single crystal thin film waveguiding layer
Different Na, Mg, Nd, Zn, Ni, Ti, V, etc.
As a method of incorporating the seed element, a diffusion method or ion implantation
Various methods such as a method can be used.

Now, the SHG element of the present invention is advantageously a channel type in which the width of the waveguide layer is 1 to 10 μm. The channel type SHG element is advantageous because the optical power density can be made higher than that of the slab type. The reason why the width is 1 to 10 μm is advantageous is that if the width is smaller than 1 μm, it is difficult to introduce the incident light into the waveguide and the incident efficiency is low.
This is because the conversion efficiency will also be low. On the other hand, the incident efficiency is higher as the width is larger, but if it is larger than 10 μm, the optical power density is lowered and the SHG conversion efficiency is lowered.

As a method of manufacturing the SHG element according to the present invention, a thin film waveguide layer is formed on a substrate by a method such as a sputtering method or a liquid phase epitaxial growth method, and the thin film waveguide layer is formed on the thin film waveguide layer. A method of producing a channel type SHG element by forming a Ti waveguide pattern by photolithography and RF sputtering, and ion beam etching using this as an etching mask is advantageously suitable.

[0030]

【Example】

Example 1-1 When the wavelength (λ) of the fundamental laser light is 1.15 μm, the ordinary refractive index (noS1) when the fundamental laser light of this wavelength is incident is 2.133. On a 1 mm thick Z-cut LiTaO ₃ single crystal substrate 1 having an extraordinary refractive index (neS2) of 2.194 when two harmonics are generated,
The ordinary refractive index (noF1) is 2.225 when the fundamental wave laser light of wavelength (λ) is incident, and the extraordinary refractive index (neF2) is 2.208 when the second harmonic is generated under this incident condition. A LiNbO ₃ single crystal thin film 2 containing 1 mol% and 5 mol% of solid solution of Na and Mg, respectively, was grown to a thickness of 1.43 μm by a liquid phase epitaxial growth method. The surface roughness of this thin film was JIS B0601 Rmax = 200Å.
It should be noted that L containing 1.5 mol% of Na and Mg dissolved therein
iNbO ₃ single crystal thin film is international application number PCT / JP90
/ 01207 (International publication number WO 91/04360
No.), a LiNbO ₃
The a-axis lattice constant of the single crystal thin film is 5.1537Å, LiTaO
The lattice constant of the a-axis of the _three single crystal substrates is 5.1538Å, and both are lattice-matched.

Further, a photoresist is formed on the single crystal thin film.
An etching mask with a width of 5 μm is formed by the strike film,
Channel type waveguide by ion beam etching
Layer 3 is formed, and the end faces on both sides are optically polished to form the end faces.
The SHG element is capable of further entering and exiting light. This SHG element
30mW He-Ne laser with wavelength of 1.15μm
And Na, Mg solid solution LiNbO 3 incident on single crystal thin film
The SHG conversion efficiency in this case was 12.3%,
It was confirmed that the SHG element had high conversion efficiency.

Example 1-2 An SHG element similar to the example 1-1 was prepared, except that the thickness of the LiNbO ₃ single crystal thin film was 3.29 μm. The surface roughness of this thin film was JIS B0601 Rmax = 500Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 1-1, it was 5.4%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 1-3 Same as Example 1-1, except that LiNbO 3 single crystal
An SHG element having a thin film thickness of 3.70 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 1000Å
there were. This SHG element is the same as in Example 1-1.
The SHG conversion efficiency was measured to be 1.6%.
It was confirmed to be a highly efficient SHG element.

Example 2-1 When the wavelength (λ) of the fundamental laser light is 0.98 μm,
Ordinary Refractive Index When Injecting Fundamental Wave Laser Light of Various Wavelengths
(NoS1) is 2.141, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neS2) when is generated is 2.225.
1mm thick X-cut LiTaO 3 Waves on a single crystal substrate
Ordinary refractive index when a long (λ) fundamental laser beam is incident
(NoF1) is 2.238, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neF2) when is generated is 2.255.
LiNbO₃Liquid phase epitaxial growth of single crystal thin film
It was grown to a thickness of 2.79 μm by the method. The surface of this thin film
The roughness was JIS B0601 Rmax = 1000Å. It
In addition, the width of a photoresist film on this single crystal thin film
An etching mask of 5 μm is formed, and then an ion mask is formed.
Channel etching to form a channel-type waveguide layer
In addition, the end faces on both sides are optically polished so that light can enter and exit from the end faces.
It was a possible SHG element. For this SHG element,
A 0.98 μm long, 50 mW semiconductor laser is used for LiNbO. 3 single
When measuring the SHG conversion efficiency when incident on a crystalline thin film
4.8%, which is an SHG element with high conversion efficiency.
Was recognized.

Example 2-2 An SHG device similar to that of Example 2-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 3.80 μm. The surface roughness of this thin film is JISB0601 Rmax = 200Å
Met. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 2-1, it was 10.5%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 2-3 An SHG device similar to that of Example 2-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 5.71 μm. The surface roughness of this thin film is JISB0601 Rmax = 800Å
Met. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 2-1, it was 7.0%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 3-1 When the wavelength (λ) of the fundamental laser light is 1.06 μm,
Ordinary refractive index (n
oS1) is 2.137, and the second harmonic is emitted under this incident condition.
Abnormal refractive index (neS2) of 2.209
1mm Z-cut LiTaO 3 Wavelength on single crystal substrate
Ordinary refractive index when the fundamental laser light of (λ) is incident
(NoF1) is 2.230, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neF2) when is generated is 2.225.
1 mol% and 5 mol% solid solution of Na and Mg, respectively
LiNbO₃Liquid phase epitaxial growth of single crystal thin film
It was grown to a thickness of 2.72 μm by the method. The surface of this thin film
The roughness was JIS B0601 Rmax = 100Å. It
In addition, the width of a photoresist film on this single crystal thin film
Form a 5μm etching mask, then ion beam
Channel etching to form a channel-type waveguide layer
In addition, the end faces on both sides are optically polished so that light can enter and exit from the end faces.
It was a possible SHG element. For this SHG element,
A YAG laser with a length of 1.06 μm and a power of 100 mW is used to solidify Na and Mg.
Melt LiNbO₃SHG conversion when incident on a single crystal thin film
When the efficiency was measured, it was 25.3%, and S with high conversion efficiency
It was confirmed to be an HG device.

Example 3-2 The same as Example 3-1 except that LiNbO was used. 3 single crystal
An SHG element having a thin film thickness of 5.81 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 1100Å
there were. This SHG element is the same as in Example 3-1.
The SHG conversion efficiency was measured to be 11.8%.
It was confirmed to be a highly efficient SHG element.

Example 3-3 The same as Example 3-1 except that LiNbO was used. 3 single crystal
An SHG element having a thin film thickness of 6.46 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 1000Å
there were. This SHG element is the same as in Example 3-1.
The SHG conversion efficiency was measured to be 3.5%.
It was confirmed to be a highly efficient SHG element.

Example 4-1 Z-cut LiTaO having a thickness of 1 mm RF on 3 single crystal substrates
Form a V film with a thickness of 1000Å by the sputtering method, and
iTaO 3 Diffuse V into the surface of single crystal by thermal diffusion method
It was If the wavelength (λ) of the fundamental laser light is 0.98 μm
When the fundamental laser light of this wavelength is incident,
The folding rate (noS1) is 2.121, which is the second highest value under this incident condition.
The extraordinary refractive index (neS2) when a harmonic is generated is 2.185.
Became. On this substrate, the fundamental wave laser light of wavelength (λ)
The ordinary light refractive index (noF1) when incident on is 2.235.
Optical anisotropy when the second harmonic is generated under the conditions of incidence
The folding rate (neF2) is 2.243, Zn and Mg are respectively
2 mol%, 5 mol% solid-dissolved LiNbO 3 Single crystal thin film
To a thickness of 2.88 μm by liquid phase epitaxial growth
I grew it. The surface roughness of this thin film is JIS B0601.
Rmax = 150Å. Furthermore, on this single crystal thin film
An etching mask with a width of 5 μm is formed by the photoresist film.
Formed and then ion beam etching
It is a channel waveguide layer, and both end faces are optically polished.
The SHG element is capable of entering and exiting light from its end face. This
Of SHG device of 0.98μm wavelength, 50mW semiconductor
Laser, Zn, Mg solid solution LiNbO 3 For single crystal thin film
The SHG conversion efficiency when incident is 13.9%
And it is recognized that the SHG element has high conversion efficiency.
It was

Example 4-2 Same as Example 4-1 except that LiNbO 3 single crystal
An SHG element having a thin film thickness of 4.44 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 1100Å
there were. This SHG element is the same as in Example 4-1.
The SHG conversion efficiency was measured to be 3.0%.
It was confirmed to be a highly efficient SHG element.

Example 4-3 The same as Example 4-1 except that LiNbO was used. 3 single crystal
An SHG element having a thin film thickness of 6.05 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 500Å
Met. This SHG element was the same as in Example 4-1.
Similarly, the SHG conversion efficiency was measured to be 6.6%.
It was confirmed that the SHG element had a high conversion efficiency.

Example 5-1 When the wavelength (λ) of the fundamental laser light was 1.15 μm,
Ordinary Refractive Index When Injecting Fundamental Wave Laser Light of Various Wavelengths
(NoS1) is 2.133, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neS2) when is generated is 2.194.
Z-cut LiTaO with a thickness of 1 mm 3 Waves on a single crystal substrate
Ordinary refractive index when a long (λ) fundamental laser beam is incident
(NoF1) is 2.227, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neF2) when is generated is 2.218.
LiNbO Liquid phase epitaxial growth of 3 single crystal thin films
It was grown to a thickness of 2.08 μm by the method. The surface of this thin film
The roughness was JIS B0601 Rmax = 100Å. It
In addition, the width of a photoresist film on this single crystal thin film
An etching mask of 5 μm is formed, and then an ion mask is formed.
Channel etching to form a channel-type waveguide layer
In addition, the end faces on both sides are optically polished so that light can enter and exit from the end faces.
It was a possible SHG element. For this SHG element,
A He-Ne laser with a length of 1.15 μm and 30 mW is used for LiNbO.
₃Measure the SHG conversion efficiency when incident on a single crystal thin film
It is 8.5%, which is an SHG element with high conversion efficiency.
Was recognized.

Example 5-2 An SHG element similar to the example 5-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 3.42 μm. The surface roughness of this thin film was JIS B0601 Rmax = 90Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 5-1, it was 1.7%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 5-3 The same as Example 5-1 except that LiNbO was used. 3 single crystal
An SHG element having a thin film thickness of 5.23 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 100Å
there were. This SHG element is the same as in Example 5-1.
The SHG conversion efficiency was measured to be 1.1%.
It was confirmed to be a highly efficient SHG element.

Example 6-1 Y-cut LiTaO having a thickness of 1 mm RF on 3 single crystal substrates
Forming 1000Å thick MgO film by sputtering method
And LiTaO₃MgO was formed on the surface of the single crystal by the thermal diffusion method.
Diffused. The wavelength (λ) of the fundamental laser light is 1.06 μm
And when a fundamental laser beam of this wavelength is incident
Has an ordinary refractive index (noS1) of 2.117,
Refractive index (neS2) when the second harmonic is generated at
Was 2.169. Inject fundamental laser light onto this substrate
Ordinary refractive index (noF1) is 2.230 when
Extraordinary refractive index when the second harmonic is generated under the conditions
(NeF2) is 2.225, Zn and Mg are 2.5 each
LiNbO dissolved in mol%₃Liquid crystal epitaxy of single crystal thin film
It was grown to a thickness of 2.72 μm by the axial growth method.
The surface roughness of this thin film is JIS B0601 Rmax = 150
It was Å. Furthermore, a photoresist is formed on this single crystal thin film.
An etching mask with a width of 5 μm is formed by the strike film,
Ion beam etching
Corrugated layer, and then further polish the end faces on both sides by optical polishing
The SHG element is capable of further entering and exiting light. This SHG element
YAG laser with wavelength of 1.06 μm and 100 mW
Zn, Mg solid solution LiNbO 3 incident on single crystal thin film
The SHG conversion efficiency in this case was 25.3%,
It was confirmed that the SHG element had high conversion efficiency.

Example 6-2 An SHG device similar to that of Example 6-1 was prepared, but the thickness of the LiNbO ₃ single crystal thin film was 4.23 μm. The surface roughness of this thin film was JIS B0601 Rmax = 100Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 6-1, it was 5.4%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 6-3 The same as Example 6-1 except that LiNbO was used. 3 single crystal
An SHG element having a thin film thickness of 5.80 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 200Å
there were. This SHG element is the same as in Example 6-1.
The SHG conversion efficiency was measured to be 11.9%.
It was confirmed to be a highly efficient SHG element.

Example 7-1 Z-cut LiTaO having a thickness of 1 mm RF on 3 single crystal substrates
Forming 1000Å thick MgO film by sputtering method
And LiTaO₃MgO was formed on the surface of the single crystal by the thermal diffusion method.
Diffused. The wavelength (λ) of the fundamental laser light is 0.84 μm
And when a fundamental laser beam of this wavelength is incident
Has an ordinary refractive index (noS1) of 2.130,
Refractive index (neS2) when the second harmonic is generated at
Was 2.229. On this substrate, the fundamental wave of wavelength (λ)
Ordinary refractive index (noF1) when entering laser light is 2.24
8 when the second harmonic is generated under this incident condition
Extraordinary light refractive index (neF2) is 2.294, Na, Mg
LiNbO dissolved in 1 mol% and 5 mol% respectively₃single
Crystal thin film is 1.94μm by liquid phase epitaxial growth method
Grown to a thickness of. The surface roughness of this thin film is JIS
B0601 Rmax = 200Å. Furthermore, this single crystal
Etching of 5 μm width with a photoresist film on the thin film
Mask and then ion beam etching
A more channel-type waveguiding layer with both end faces
SHG element that is optically polished and allows light to enter and exit from its end face
And About this SHG element, wavelength 0.84μm, 80
An mW semiconductor laser is used as a solid solution of Na and Mg. 3 single
When measuring the SHG conversion efficiency when incident on a crystalline thin film
The SHG element has a high conversion efficiency of 13.8%.
Was recognized.

Example 7-2 An SHG device similar to that of Example 7-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 2.92 μm. The surface roughness of this thin film was JISB0601 Rmax = 560Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 7-1, it was 9.2%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 7-3 An SHG device similar to that of Example 7-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 3.40 μm. The surface roughness of this thin film was JIS B0601 Rmax = 200Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 7-1, it was 2.6%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 8-1 When the wavelength (λ) of the fundamental laser light was set to 1.06 μm,
Ordinary Refractive Index When Injecting Fundamental Wave Laser Light of Various Wavelengths
(NoS1) is 2.137, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neS2) when is generated is 2.209.
Z-cut LiTaO with a thickness of 1 mm₃Waves on a single crystal substrate
Ordinary refractive index when a long (λ) fundamental laser beam is incident
(NoF1) is 2.230, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neF2) when is generated is 2.225.
1 mol% and 5 mol% solid solution of Na and Mg, respectively
LiNbO Liquid phase epitaxial growth of 3 single crystal thin films
It was grown to a thickness of 2.72 μm by the method. The surface of this thin film
The roughness was JIS B0601 Rmax = 5000Å.
Furthermore, a photoresist film is applied on this single crystal thin film.
Form an etching mask with a width of 5 μm,
Channel etching to form a channel-type waveguide layer
In addition, the end faces on both sides are optically polished so that light can enter and exit from the end faces.
It was a possible SHG element. For this SHG element,
A YAG laser with a length of 1.06 μm and a power of 100 mW was used for solidification of Na and Mg.
Melt LiNbO 3 SHG conversion when incident on a single crystal thin film
When the efficiency was measured, it was 6.3%, and the conversion efficiency was high.
It was confirmed to be an HG device.

Example 8-2 The same as Example 8-1, except that LiNbO 3 single crystal
An SHG element having a thin film thickness of 5.81 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 7000Å
there were. This SHG element is the same as in Example 8-1.
The SHG conversion efficiency was measured to be 3.0%.
It was confirmed that the SHG element had high efficiency.

Example 8-3 The same as Example 8-1, except that LiNbO was used. 3 single crystal
An SHG element having a thin film thickness of 6.46 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 7000Å
About this existing SHG element, as in Example 8-1
The SHG conversion efficiency was measured and found to be 0.9%.
It was confirmed that the SHG element had a high rate.

Comparative Example 1 When the wavelength (λ) of the fundamental laser light is 1.06 μm,
Ordinary Refractive Index When Injecting Fundamental Wave Laser Light of Various Wavelengths
(NoS1) is 2.137, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neS2) when is generated is 2.209.
Z-cut LiTaO with a thickness of 1 mm 3 Waves on a single crystal substrate
Ordinary refractive index when a long (λ) fundamental laser beam is incident
(NoF1) is 2.230, and the second harmonic wave is generated under this incident condition.
The extraordinary light refractive index (neF2) when is generated is 2.225.
1 mol% and 5 mol% solid solution of Na and Mg, respectively
LiNbO Liquid phase epitaxial growth of 3 single crystal thin films
It was grown to a thickness of 2.72 μm by the method. The surface of this thin film
The roughness is JIS B0601 Rmax = 12000 Å
It was Furthermore, a photoresist film is formed on this single crystal thin film.
Form an etching mask with a width of 5 μm and then
Channel-type waveguide layer by ion beam etching,
Furthermore, the end faces on both sides are optically polished and light enters and exits from the end faces.
The SHG element is capable of firing. About this SHG element
Then, a YAG laser with a wavelength of 1.06 μm and 100 mW was
Mg solid solution LiNbO 3 SH when incident on a single crystal thin film
The measured G conversion efficiency is 0.025%, which is practical
It could not be used as an SHG element.

Comparative Example 2 Z-cut LiTaO having a thickness of 1 mm RF on 3 single crystal substrates
Form a V film with a thickness of 1000Å by the sputtering method, and
iTaO 3 V is diffused on the surface of the single crystal by the thermal diffusion method.
It was If the wavelength (λ) of the fundamental laser light is 0.98 μm
When the fundamental laser light of this wavelength is incident,
The folding rate (noS1) is 2.181, which is the second highest value under this incident condition.
The extraordinary refractive index (neS2) when a harmonic is generated is 2.185.
Met. On this substrate, the fundamental wave laser light of wavelength (λ)
The ordinary light refractive index (noF1) when incident on is 2.235.
Optical anisotropy when the second harmonic is generated under the conditions of incidence
The folding rate (neF2) is 2.243, Zn and Mg are respectively
2 mol%, 5 mol% solid-dissolved LiNbO₃Single crystal thin film
To a thickness of 2.88 μm by liquid phase epitaxial growth
I grew it. The surface roughness of this thin film is JIS B0601.
Rmax = 10000Å. Furthermore, this single crystal thin film
On top of that, an etching mask with a width of 5 μm is formed by a photoresist film.
Disk, then by ion beam etching
Channel-type waveguiding layer
Polished to be an SHG element that allows light to enter and exit from its end face
It was About this SHG element, wavelength 0.98μm, 50mW
Semiconductor laser of Zn, Mg solid solution LiNbO 3 single crystal
Measurement of SHG conversion efficiency when incident on a thin film
0.014%, which is a practical SHG element.
There wasn't.

Comparative Example 3 Mg (5 mol%) solid solution LiNbO ₃ single crystal thin films having various thicknesses were grown on a Z-cut LiTaO ₃ single crystal substrate having a thickness of 0.5 mm by a liquid phase epitaxial growth method. After mirror polishing the surface,
As a result of observation with an electron microscope, it was found that the thickness was 3 μm. This film is subjected to T by the usual photolithography.
An i thin film pattern was formed. This thin film was subjected to ion beam etching to form steps. When the step difference was measured with a step meter, it was 0.80 μm. Next, the Ti thin film was removed, and further observation with an electron microscope was carried out to obtain the ratio between the film thickness T and the step t shown in FIG. 1 to obtain the film thickness T. As a result, the film thickness T was 2.96 μm. .. Further, ion beam etching was performed, and electron microscope observation was performed. The thickness T was determined from the ratio of the thickness T and the step t shown in FIG. 1, and the thickness T was adjusted to 1.80 μm. The end faces on both sides were mirror-polished to obtain an SHG element capable of entering and exiting light from the end faces. When the fundamental laser light wavelength λ is 0.94 μm, Li
Ordinary refractive index (noS1) of TaO ₃ single crystal substrate is 2.180, LiNb
The ordinary refractive index (noF1) of the O ₃ single crystal thin film waveguide layer is 2.271,
The extraordinary refractive index (neS2) of the LiTaO ₃ single crystal substrate at the second harmonic wavelength λ / 2 was 2.261, and the extraordinary refractive index (neF2) of the LiNbO ₃ single crystal thin film waveguide layer was 2.268. This SH
G element is Also, The SHG conversion efficiency of this SHG element was 0.80% when a semiconductor laser with a wavelength of 0.94 μm and a wavelength of 40 mW was incident at an incident angle of 90 ° with respect to the crystal axis (Z axis) of the single crystal thin film. The measurement of the film thickness was troublesome.

[0058]

As described above, according to the present invention, L
iTaO 3 LiNbO on single crystal substrate₃Forming a thin film waveguide layer
Ordinary refraction of this substrate and the thin film waveguide layer
By adjusting the refractive index and the extraordinary light refractive index within the specified range,
Easy SHG element with extremely high SHG conversion efficiency
It can be manufactured, and in particular, it can generate a green laser with high efficiency.
You can

[Brief description of drawings]

FIG. 1 is a schematic diagram of an SHG element of the present invention.

[Explanation of symbols]

 1 substrate 2 thin film 3 waveguiding layer

Claims (2)

[Claims] 1. A second harmonic generation device comprising a LiNbO ₃ single crystal thin film waveguide layer formed on a LiTaO ₃ substrate, wherein the thin film waveguide layer has a surface roughness Rmax of 10 to 10000 Å.
And the ordinary refractive index of the substrate is (noS1) when a fundamental laser beam of wavelength λ is incident, and λ /
The extraordinary refractive index of the substrate when the second harmonic of 2 is generated is (neS2), and the ordinary refractive index of the thin film waveguide layer when the fundamental laser light of wavelength λ (μm) is incident. Is (noF1) and the extraordinary refractive index of the thin-film waveguide layer is (neF2) when the second harmonic of λ / 2 (μm) is generated under the incident condition, then λ, noS1, neS2, no
A second harmonic generation element characterized in that F1 and neF2 are within the following numerical ranges, respectively. Note λ = 0.80 to 1.15 μm noS1 = 2.08 to 2.17 neS2 = 2.09 to 2.30 noF1 = 2.20 to 2.27 neF2 = 2.19 to 2.35 2. The second harmonic generating element according to claim 1, wherein the second harmonic generating element is a channel type having a waveguide layer width of 1 to 10 μm.