JPH0572589A - Second harmonic generating element - Google Patents

Abstract

PURPOSE:To allow the generation of second harmonic wave light with high conversion efficiency by specifying the surface roughness of thin-film waveguide layers and specifying the numerical values of the characteristic equations of a substrate and the thin-film waveguide layers so as to attain the values within a specific range. CONSTITUTION:The surface roughness Rmax of the thin-film waveguide layers 2, 3 of the second harmonic generating element formed with the thin-film waveguide layers 2, 3 having a nonlinear optical effect on the substrate 1 is specified within the 10 to 10000Angstrom range. The characteristics of the substrate 1 and the thin-film waveguide layers 2, 3 are specified by equation I when the ordinary light refractive index of the thin-film waveguide layers 2, 3 at the time of admitting a basic wave laser beam of a wavelength lambda into the thin-film waveguide layers 2, 3 is designated as (noF1), the extraordinary light refractive index of the substrate 1 at the time of generating the second harmonic wave under such incident conditions as (neS2) and the extraordinary light refractive index of the thin-film waveguide layers 2, 3 is designated as (neF2). The element is so constituted that the value of (A) in the equation I attains the value within a -1.22<=(A)<=1.33 range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a thin film waveguide type second harmonic wave generating element (hereinafter
"Abbreviated as" SHG element ").

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.

[0005]

However, in order to manufacture an SHG element having a thin film waveguide structure, until now, a fundamental wave laser beam having a specific wavelength λ (μm) was made incident, and the material of the substrate and the thin film at this time. The extremely inefficient work of finding the conditions under which the second harmonic is generated and determining the structure by changing the material of the waveguide layer and the film thickness thereof has been required.

In view of such inconvenience, the present inventors have previously described the wavelength λ (μm) of the fundamental laser light, the film thickness T (μm) of the thin film waveguide layer, and the fundamental laser light wavelength λ (μm). And the ordinary refractive index (noS1) of the substrate at the wavelength of the fundamental wave laser light wavelength (λμm).
1), the refractive index (neS2) of extraordinary light of the substrate at the second harmonic wavelength λ / 2 (μm) and the second harmonic wavelength (λμm)
Regarding the extraordinary refractive index (neF2) of the thin-film waveguide layer in / 2), it was found that the second harmonic can be generated very efficiently by constructing such structure so that they satisfy a specific relationship. First, Japanese Patent Application No. 1-2911
We applied for a patent as No. 22.

However, the above-mentioned technique previously proposed by the present inventors has many parameters to be adjusted for determining the structure of the SHG element, which results in the final SHG element.
In many cases, the accuracy of the device structure is lowered, which not only makes so-called fabrication difficult, but also leaves only the SHG device having low conversion efficiency.

An object of the present invention is to overcome the problems of the above-mentioned technique proposed by the present inventors in advance, and to obtain an SHG element which has high conversion efficiency with few parameters and is easy to manufacture. It is in.

[0009]

The inventors of the present invention have made extensive studies to overcome the above-mentioned problems that need to be solved, and as a result, they have more control as parameters for determining the structure of SHG devices. The easy one is the ordinary light refractive index (noF) of the thin-film waveguide layer at the fundamental laser light wavelength λ (μm).
1), the extraordinary refractive index (neS2) of the substrate at the second harmonic wavelength λ / 2 (μm) and the second harmonic wavelength λ / 2 (μm)
m) is the extraordinary refractive index (neF2) of the thin-film waveguide layer, and when these have a specific relationship, the roughness of the thin-film waveguide layer surface (R _max ) can be kept constant and the second harmonic The present invention has been completed by finding that it is extremely easy to produce a structure capable of efficiently generating

That is, according to the present invention, in the second harmonic generation device in which a thin film waveguide layer having a nonlinear optical effect is formed on a substrate, the surface roughness Rmax of the thin film waveguide layer is 10 to 10.
Within the range of 1000 Å, the ordinary refractive index of the thin-film waveguide layer when the fundamental laser light of wavelength λ is incident into this thin-film waveguide layer is (noF1), and λ / 2 under this incident condition. Second
The extraordinary refractive index of the substrate when the harmonics are generated is (neS
2) and when the extraordinary optical refractive index of the thin film waveguide layer when such a second harmonic is generated is (neF2), the characteristics of the substrate and the thin film waveguide layer have the following relationship; The second feature is that the value of (A) in the formula is within the range of −1.22 ≦ (A) ≦ 1.03.
It is a harmonic generation element.

In the SHG element according to the above-mentioned configuration, it is beneficial to use a channel type having a waveguide layer width of 1 to 10 μm.

[0012]

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.

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 in the range of 10 to 10000 Å. Is. The surface roughness was measured with a stylus type surface roughness measuring device according to JIS B0651. In the present invention, the surface roughness R
It is extremely difficult to make the value of max smaller than 10Å, and it is difficult to trap the light wave. On the other hand, when the value of the surface roughness Rmax is larger than 10000 Å, scattering loss and the like on the surface of the waveguiding layer increase and the waveguide power of the fundamental laser light decreases, so the SHG conversion efficiency decreases. , It becomes difficult to use as SHG element,
It is limited to the above.

Even in the above range of surface roughness, it is advantageous to satisfy Rmax = 10 to 1000Å in order to obtain higher conversion efficiency, and above all, Rmax = 10 to 100Å is satisfied. 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.

Next, it plays an important role in the present invention.
The characteristic formulas of the substrate and the thin film waveguide layer will be described. The refractive indices neF2 and noF that compose this characteristic formula (A)
The three parameters of 1, neS2 dominate the oscillation condition of the second harmonic (especially the phase matching condition), and the surface advance of the waveguide is the propagation loss that affects the efficiency of the second harmonic. And that is what controls the confinement efficiency. In addition, the refractive index neF2, n used as a parameter when manufacturing an SHG element that requires high accuracy.
oF1, neS2 and the surface roughness R _max of the waveguide can be measured with relatively high accuracy, and the refractive index of these can be
Since the surface roughness of the waveguide can be controlled relatively easily by adding a different element or the like and by adjusting the polishing or etching conditions, the SHG
It is convenient as a constituent parameter of the element.

According to the research conducted by the present inventors, in order for the second harmonic to oscillate, the region A (neF2 and n in FIG.
eS2), region B (difference between noF1 and noS1) overlaps or is very close to each other, or neF2 and noF1 must be close to each other. .. Therefore, for the second harmonic oscillation, it is sufficient that the above three refractive indexes neF2, neS2, and noF1 are satisfied, and it is necessary that the characteristic formula (A) consisting of these parameters satisfies a certain range. This was empirically found from many experiments. That is, the numerator of this characteristic formula (A): neF2-noF1 is n
This expresses the proximity of the values of eF2 and noF1, and this characteristic expression (A) is a relational expression representing the overlapping ratio or the proximity ratio of the area A and the area B in FIG.

In the present invention, the relationship between the characteristic expression (A) and the surface roughness described above is theoretically the relationship required to oscillate the second harmonic wave from the above-mentioned conditions of each refractive index. Although the formula (A) is obtained, which has a theoretical aspect for oscillation, the oscillation condition is obtained from the viewpoint of conversion efficiency such as confinement efficiency and propagation loss from the actual structure. The surface roughness (R _max ).

As can be seen from the above description, in the SHG element of the present invention, the wavelength of the fundamental laser light is λ (μm).
The ordinary light refractive index of the thin-film waveguide layer at
The extraordinary light refractive index of the substrate when the wavelength of the second harmonic is λ / 2 (μm) is neS2, and the extraordinary light of the thin film waveguide layer when the wavelength of the second harmonic is λ / 2 (μm) When the refractive index is neF2, the characteristic equation (A) of the substrate and the thin film waveguide layer is represented by the following equation. Then, in the above formula, it is useful that (A) shows a value within the following range; −1.22 ≦ (A) ≦ 1.03. Above all, the numerical range of the characteristic formula (A) is most advantageous when 0.11 ≤ (A) ≤ 0.32.

The wavelength (λ) of the fundamental laser light incident on the SHG element of the present invention is preferably 0.4 to 1.6 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 0.4 μm by a semiconductor laser. That is why.
On the other hand, when the fundamental wave laser light having a wavelength λ longer than 1.6 μm is used, the obtained second harmonic wavelength is 1/2 of the fundamental wave laser light. 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 wavelength (λ) of this fundamental laser light
Is relatively easy to obtain semiconductor laser light source 0.6 to 1.3 μ
m is advantageous, and in particular, the range of 0.68 to 0.98 μm is practically suitable.

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 20
This is because when the thickness is thicker than μm, the optical power density is low and the SHG conversion efficiency is low, and in any case, it is difficult to use as an SHG element. 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.

Various non-linear optical materials are used for the substrate and the thin film waveguide layer in the present invention. As the substrate, for example, LiNbO ₃ , LiTaO ₃ ,
LiB ₃ O ₅ (LBO), Gd ₃ Ga ₅ O ₁₂ (GGG),
α-Al ₂ O ₃ , KTiOPO ₄ (KTP), β-BaB
₂ O ₄ (BBO), KH ₂ PO ₄ (KDP), KNbO
₃ , Sr _x Ba _1-x Nb ₂ O ₆ (SBN), K ₃ Li ₂ N
b ₅ O ₁₅ (KLN), KTaO ₃ , MgO, ZnO, S
Materials such as rTiO ₃ , KH ₂ PO ₄ (KDP) and similar compounds thereof, SiO ₂ , soda glass and Pyrex glass are used. Examples of the thin film waveguide layer include LiNbO ₃ and LiTa.
O ₃ , KNbO ₃ , KTiOPO 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), Zn
O, KTa _x Nb _1-x O ₃ (KTN), LiIO ₃ , S
r _x Ba _1-x Nb ₂ O ₆ (SBN), BaTiO ₃ , P
bTiO ₃ , KH ₂ PO ₄ (KDP), KD ₂ PO
₄ (KD ^* P), NH ₄ H ₂ PO ₄ (ADP), InP
S ₄ , β-BaB ₂ O ₄ (BBO), LiB ₃ O ₅ (L
A material such as BO) is used.

Materials for the substrate and thin film waveguide layer include:
It is desirable to adjust the refractive index of each element by incorporating different elements such as Na and Cr, Mg, Nd, Zn, Ni, Ti and V. It should be noted that the Na, Cr, Mg, Nd, Zn, Ni, Ti, V are added to the substrate or the thin film waveguide layer.
As a method of containing a different element such as, a raw material of the material and a different element or a different element compound are mixed in advance, and a thin film waveguide layer is formed on the substrate by a liquid phase epitaxial growth method, or the substrate And thin film waveguide layers,
It is desirable to use a diffusion method for diffusing different elements such as Na, Mg, Nd, Zn, Ni, Ti, and V.

A substrate suitable for the production of the SHG element of the present invention
As a combination of a thin film and a thin film waveguide layer / substrate,
NN / α-Al₂O₃, LiNbO₃/ GGG, LiN
bO₃/ MgO, SBN / α-Al₂O₃, KLN / α
-Al₂O₃, ADP / KDP, BBO / α-Al₂O
₃Etc. are suitable. And in such a combination
But as a substrate LiTaO₃As a single crystal or thin film waveguide layer
LiNbO₃Combinations using single crystals are particularly preferred
is there. The reason for this is that the LiNbO₃Single crystal is nonlinear light
High scientific constant, low light loss, uniform thinness
It can be mentioned that a film can be prepared, and LiTaO₃single
The crystal is LiNbO₃Similar in crystal structure to single crystal
And the LiNbO 3 It is easy to form a thin film of single crystal, and
In addition, it is easy to obtain high quality and inexpensive crystals.

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 incident light into the waveguide, and the incident efficiency is low.
This is because the HG conversion efficiency also becomes low. On the other hand, the larger the width is, the higher the incidence efficiency is, 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.

[0028]

【Example】

Example 1-1 When the wavelength (λ) of the fundamental wave laser light is 0.98 μm, the ordinary refractive index (noS1) when the fundamental wave laser light of this wavelength is incident is 2.141, and 1mm thick Z-cut LiTaO ₃ single crystal substrate 1 with extraordinary refractive index (neS2) of 2.225 when 2 harmonics are generated
The ordinary refractive index (noF1) when the fundamental laser light of wavelength (λ) is incident is 2.235, and the extraordinary refractive index (neF2) when the second harmonic is generated under this incident condition is shown above. 2.
A LiNbO ₃ single crystal thin film 2 containing 243 of Na and Mg dissolved in 1 and 5 mol% respectively was grown to a thickness of 2.60 μm by a liquid phase epitaxial growth method. The surface roughness of this thin film is JIS B0601 Rmax = 200Å
Met. The above-mentioned LiNbO ₃ single crystal thin film in which Na and Mg are dissolved in solid solutions of 1 and 5 mol% respectively is described in International Application No.
PCT / JP90 / 01207 (International Publication Number WO
91/04360), and the a-axis lattice constant of the LiNbO ₃ single crystal thin film is 5.15.
The lattice constant of a-axis of 37Å and LiTaO ₃ is 5.1538Å, and both are lattice-matched. Further, an etching mask having a width of 5 μm is formed on the single crystal thin film with a photoresist film, and then a channel type waveguide layer 3 is formed by ion beam etching, and further, both end faces are optically polished to remove the light from the end face. The SHG element is capable of entering and exiting light. In this SHG element, the equation (A) in the relational expression is
It was equivalent to the case of 0.44. For this SHG element, a semiconductor laser with a wavelength of 0.98 μm and 50 mW was
When the SHG conversion efficiency when incident on the a, Mg solid solution LiNbO ₃ single crystal thin film was measured, it was 15.4%, and a high SHG conversion efficiency was obtained.

Example 1-2 An SHG element similar to the example 1-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 4.34 μm. The surface roughness of this thin film is JISB0601 Rmax = 300
It was Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 1-1, it was 3.1%.
It was confirmed that the SHG element had high conversion efficiency.

Example 1-3 An SHG element similar to the example 1-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 5.83 μm. The surface roughness of this thin film is JISB0601 Rmax = 100
It was Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 1-1, it was 6.9%,
It was confirmed that the SHG element had high conversion efficiency.

Example 2-1 When the wavelength (λ) of the fundamental wave laser light is 0.67 μm, the ordinary refractive index (noS1) when the fundamental wave laser light of this wavelength is incident is 1.764, and under this incident condition The fundamental wave laser light of wavelength (λ) is incident on a 0.5 mm thick R-cut α-Al ₂ O ₃ single crystal substrate with an extraordinary light refractive index (neS2) of 1.794 when the second harmonic is generated. The ordinary optical refractive index (noF1) is 2.270, and the extraordinary optical refractive index (neF2) is 2.427 when the second harmonic is generated under this incident condition.
It was grown to a thickness of 0.42 μm. The surface roughness of this thin film is
JIS B0601 Rmax = 1000Å. Furthermore, a width of 5 is formed on the single crystal thin film by a photoresist film.
A μm etching mask is formed, and then ion beam etching is performed to form a channel type waveguide layer.
The end faces on both sides were optically polished to obtain an SHG element capable of entering and exiting light from the end faces. This SHG element corresponds to the case where the expression (A) in the relational expression is 0.25. Regarding this SHG element, SHG when a semiconductor laser of wavelength 0.67 μm, 50 mW is incident on the KLN single crystal thin film
When the conversion efficiency was measured, it was 5.4%, and a high SHG conversion efficiency was obtained.

Example 2-2 An SHG element similar to the above Example 2-1 was prepared, except that the KLN single crystal thin film had a thickness of 0.64 μm. The surface roughness of this thin film was JIS B0601 Rmax = 2000Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 2-1, it was 1.2%, 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 KLN single crystal thin film had a thickness of 1.26 μm. The surface roughness of this thin film was JIS B0601 Rmax = 1100Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 2-1, it was 1.8%, 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 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.
1mm thick X-cut LiTaO₃Waves on a single crystal substrate
Ordinary refractive index when a long (λ) fundamental laser beam is incident
(NoF1) is 2.232, and the second harmonic is generated under this incident condition.
Extraordinary light refractive index (neF2) when generated is 2.235
LiNbO Liquid phase epitaxial growth method for 3 single crystal thin films
Was grown to a thickness of 5.15 μm. Surface roughness of this thin film
That is, JIS B0601 Rmax = 150Å.
 Further, a photoresist film is formed on the single crystal thin film.
Forming an etching mask with a width of 5 μm, and then
Beam etching to form a channel-type waveguide layer.
In addition, both ends are optically polished and light enters and exits from the ends.
The SHG element is capable of This SHG element is related to the above
The formula (A) in the formula corresponds to the case of 0.12.
It was About this SHG element, wavelength 1.06μm, 100mW
Of YAG laser of LiNbO₃Incident on a single crystal thin film
The SHG conversion efficiency in this case was 13.3%,
High SHG conversion efficiency was obtained.

Example 3-2 An SHG device similar to that of Example 3-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 7.04 μm. The surface roughness of this thin film is JISB0601 Rmax = 1000
It was Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 3-1, it was 3.3%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 3-3 An SHG device similar to that of Example 3-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 8.17 μm. The surface roughness of this thin film is JISB0601 Rmax = 1200.
It was Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 3-1, it was 2.8%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 4-1 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 1.753, and the second harmonic wave is generated under this incident condition.
Extraordinary refractive index (neS2) of 1.761 when wavelength is generated
0.5 mm thick C-cut α-Al 2 O 3 Single crystal substrate
When the fundamental laser light of wavelength (λ) is incident on
The optical refractive index (noF1) is 2.227, and the second
Extraordinary refractive index (neF2) is 2.21 when harmonics are generated
8 is LiNbO₃RF single crystal thin film
Was grown to a thickness of 2.24 .mu.m. This thin film table
The surface roughness is JIS B0601 Rmax = 100 Å
It was Furthermore, a photoresist film is formed on this single crystal thin film.
An etching mask having a width of 5 μm is formed, and then the mask is formed.
On-beam etching to make a channel type waveguide layer,
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. This SHG element is
Equation (A) in the equation is equivalent to the case of -0.020
there were. About this SHG element, wavelength 1.15μm, 30
mW He-Ne laser, LiNbO₃For single crystal thin film
When SHG conversion efficiency when incident is measured, it is 7.9
%, And high SHG conversion efficiency was obtained.

Example 4-2 The same as Example 4-1 except that LiNbO was used. 3 single crystal
An SHG element having a thin film thickness of 3.52 μm was produced.
The surface roughness of this thin film is JIS B0601Rmax = 11
It was 00Å. About this SHG element, Example 4-1
When the SHG conversion efficiency was measured in the same manner as above, it was 1.7%.
Therefore, it is recognized that the SHG element has high conversion efficiency.
It was

Example 4-3 An SHG device similar to that of Example 4-1 was prepared, except that the LiNbO ₃ single crystal thin film had a thickness of 4.48 μm. The surface roughness of this thin film is JISB0601 Rmax = 800
It was Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 4-1, it was 3.9%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 5-1 Z-cut Li having a thickness of 1 mm was formed by the RF sputtering method.
TaO₃Form a 1000Å thick V film on a single crystal substrate,
LiTaO by thermal diffusion method₃Diffuse V into the single crystal surface
It was When the fundamental laser light wavelength (λ) is 0.84 μm,
Ordinary refractive index (no when entering this fundamental wave laser light)
S1) is 2.130, and the second harmonic wavelength is generated under this incident condition.
The extraordinary light refractive index (neS2) at that time was 2.229.
The wavelength on this substrate was measured by the liquid phase epitaxial growth method.
Ordinary refractive index when (λ) fundamental laser light is incident
(NoF1) is 2.248, and the second harmonic is generated under this incident condition.
The extraordinary light refractive index (neF2) when is generated is 2.294.
Zn and Mg dissolved in 2 and 5 mol% respectively
LiNbO 3 Single crystal thin film was grown to a thickness of 1.94 μm.
It was The surface roughness of this thin film is JIS B0601 Rma.
x = 150Å. Furthermore, on this single crystal thin film,
Form an etching mask with a width of 5 μm using a photoresist film.
Channel, then ion beam etching
As a rectangular waveguiding layer, and further optically polish the end faces on both sides.
The SHG element is capable of entering and exiting light from this end face. this
In the SHG element, when the expression (A) in the above relational expression is 0.71
Was equivalent to. For this SHG element,
A 0.84 μm long, 100 mW semiconductor laser was used for Zn
Melt LiNbO₃SHG conversion when incident on a single crystal thin film
The efficiency was measured to be 13.8%, which is a high SHG conversion effect.
The rate was obtained.

Example 5-2 An SHG device similar to that of Example 5-1 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 is JISB0601 Rmax = 200
It was Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 5-1, it was 9.2%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 5-3 An SHG device similar to that of Example 5-1 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 is JISB0601 Rmax = 1200.
It was Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 5-1, it was 2.6%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 6-1 When the wavelength (λ) of the fundamental laser light is 0.78 μm,
Ordinary Refractive Index When Injecting Fundamental Wave Laser Light of Various Wavelengths
(NoS1) is 1.454, and the second harmonic is generated under this incident condition.
The extraordinary light refractive index (neS2) when generated is 1.471.
1mm thick SiO 2 RF sputtering method on the substrate
Therefore, when the fundamental laser light of wavelength (λ) is incident,
The photorefractive index (noF1) is 2.287, and the second
The extraordinary light refractive index (neF2) is 2.36 when harmonics are generated.
A BNN single crystal thin film of 0 was grown to a thickness of 0.72 μm.
Let The surface roughness of this thin film is JIS B0601 R
It was max = 100Å. 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 the end face of the lever. This
In the SHG element of, the formula (A) in the relational expression is 0.082
It was the case. About this SHG element
A semiconductor laser with a wavelength of 0.78 μm and 50 mW
The SHG conversion efficiency when incident on a single crystal thin film was measured.
It was 20.4%, and high SHG conversion efficiency was obtained.

Example 6-2 An SHG element similar to the above Example 6-1 was prepared, except that the BNN single crystal thin film had a thickness of 1.13 μm. The surface roughness of this thin film was JIS B0601 Rmax = 1200Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 6-1, it was 4.3%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 6-3 An SHG device similar to that of Example 6-1 was prepared, except that the BNN single crystal thin film had a thickness of 1.30 μm. The surface roughness of this thin film was JIS B0601 Rmax = 150Å. When the SHG conversion efficiency of this SHG element was measured in the same manner as in Example 6-1, it was 11.3%, and it was confirmed that the SHG element had a high conversion efficiency.

Example 7-1 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 is
The extraordinary light refractive index (neS2) when it occurs is 2.209
1mm thick X-cut LiTaO 3 Wavelength on single crystal substrate
Ordinary refractive index when the fundamental laser light of (λ) is incident
(NoF1) is 2.232, and the second harmonic is generated under this incident condition.
Extraordinary light refractive index (neF2) when generated is 2.235
LiNbO₃Liquid phase epitaxial growth method for single crystal thin film
Was grown to a thickness of 5.15 μm. Surface roughness of this thin film
That is, JIS B0601 Rmax = 5000Å.
Furthermore, a width of a photoresist film is applied 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 and the light enters and exits from this end face.
The SHG element is capable of This SHG element is related to the above
The formula (A) in the formula corresponds to the case of 0.12.
It was About this SHG element, wavelength 1.06μm, 100mW
Of YAG laser of LiNbO₃Incident on a single crystal thin film
The SHG conversion efficiency in this case was 3.3%.
Therefore, high SHG conversion efficiency was obtained.

Example 7-2 The same as Example 7-1 except that LiNbO was used. 3 single crystal
An SHG element having a thin film thickness of 7.04 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 7000
It was Å. About this SHG element,
Similarly, when the SHG conversion efficiency was measured, it was 0.8%.
Therefore, it is recognized that the SHG element has high conversion efficiency.
It was

Example 7-3 Same as Example 7-1 except that LiNbO 3 single crystal
An SHG element having a thin film thickness of 8.17 μm was produced. This
The surface roughness of the thin film is JIS B0601 Rmax = 6000
It was Å. About this SHG element,
Similarly, when the SHG conversion efficiency was measured, it was 0.7%.
Therefore, it is recognized that the SHG element has high conversion efficiency.
It was

Comparative Example 1 When a fundamental wave laser beam having a wavelength (λ) of 1.06 μm is incident
The ordinary refractive index (noS1) of the mushroom is 2.137, and under this incident condition
Refractive index (neS2) of extraordinary light when the second harmonic is generated at
Is 2.209, 1mm thick X-cut LiTaO₃Single bond
When fundamental wave laser light of wavelength (λ) is incident on the crystal substrate
The ordinary refractive index (noF1) of the mushroom is 2.232, and under this incident condition
The extraordinary light refractive index (neF2) when the second harmonic is generated
2.235 is LiNbO₃Liquid crystal epitaxy
It was grown to a thickness of 5.15 μm by the charl growth method. this
The surface roughness of the thin film is JIS B0601 Rmax = 1100
It was 0Å. In addition, the photoresist on this single crystal thin film
An etching mask with a width of 5 μm is formed by the strike film,
Ion beam etching
A wave layer is formed, and the end faces on both sides are optically polished.
The SHG element is capable of further entering and exiting light. This SHG
The element corresponds to the case where the expression (A) in the above relational expression is 0.12.
It was something. This SHG element has a wavelength of 1.06μ
m, 100 mW YAG laser, LiNbO 3 single crystal thin
When the SHG conversion efficiency when incident on the film was measured, it was 0.
013%, and a practical SHG element cannot be obtained.
won.

Comparative Example 2 An ordinary light having a wavelength (λ) of 0.67 μm, an ordinary refractive index (noS1) of 2.310 when a fundamental laser beam is incident, and an abnormal light when a second harmonic is generated under this incident condition. Refractive index (neS2)
Is 2.350, the ordinary refractive index (noF1) is 2.270 when the fundamental wave laser light of wavelength (λ) is incident on the R-cut α-Al ₂ O ₃ single crystal substrate of 0.5 mm thickness and containing different elements.
Then, the KLN single crystal thin film having an extraordinary light refractive index (neF2) of 2.427 when the second harmonic is generated under this incident condition,
It was grown to a thickness of 0.42 μm by the RF sputtering method. The surface roughness of this thin film is JIS B0601 R
It was max = 10000Å. Further, an etching mask having a width of 5 μm is formed on the single crystal thin film with a photoresist film, and then a channel type waveguide layer is formed by ion beam etching. The SHG element is capable of entering and exiting light. In this SHG element, the expression (A) in the above relational expression is 2.
It was equivalent to 04. For this SHG element, a semiconductor laser with a wavelength of 0.67 μm and 50 mW was
When the SHG conversion efficiency when incident on the N single crystal thin film was measured, it was 0.005%, and a practical SHG element could not be obtained.

Comparative Example 3 The ordinary refractive index (noS1) when a fundamental laser beam having a wavelength (λ) of 0.83 μm is 2.151, and the extraordinary refractive index when a second harmonic is generated under this incident condition. (NeS2) is 2.
The ordinary refractive index (noF1) is 2.270 when the fundamental laser light of wavelength (λ) is incident on the X-cut LiTaO ₃ single crystal substrate of 261 which is 0.5 mm in thickness. A LiNbO ₃ single crystal thin film in which 1 mol% of Nd and Na each having an extraordinary refractive index (neF2) of 2.263 when solid state was generated was grown by a liquid phase epitaxial growth method. As a result of electron microscope observation, it was found that the thickness was 3 μm. On this thin film, by photolithography,
Further, a Ti thin film pattern was formed, and then ion beam etching was performed to form steps. When the step difference was measured with a step meter, it was 0.80 μm. By removing the Ti thin film and further observing with an electron microscope, the film thickness T shown in FIG.
As a result of obtaining the ratio of the step difference t and the thickness T, the thickness T was 2.96 μm. Further, ion beam etching is performed and electron microscope observation is performed, and the thickness T is obtained from the ratio of the thickness T and the step t shown in FIG.
The thickness was adjusted to 80 μm. The end surface of the waveguide was mirror-polished to allow light to enter and exit from the end surface, thus forming an SHG element. This SHG element corresponds to the case of {(λ + 0.1) N ₁ / (λ ³ T)} = 0.2. However, In this SHG element, a semiconductor laser having a wavelength of 0.83 μm and a power of 50 mW was incident at an incident angle of 90 ° with respect to the optical axis (Z axis) of the Nd, Na solid solution LiNbO ₃ single crystal thin film.
When the conversion efficiency was measured, it was 18.8%, and it was confirmed that the SHG element had an extremely excellent SHG conversion efficiency.
However, for this SHG element, measurement of the film thickness T was very troublesome.

[0052]

As described above, according to the present invention, it is possible to obtain an SHG element having a thin film waveguide structure which is easy to manufacture and has an extremely high SHG conversion efficiency.

[Brief description of drawings]

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

FIG. 2 is a wavelength dispersion curve of LiTaO ₃ and LiNbO ₃ when a LiNbO ₃ thin film is formed on a LiTaO ₃ substrate.

[Explanation of symbols]

 1 substrate 2 thin film 3 waveguiding layer

Claims (2)

[Claims] 1. A second harmonic generation device comprising a thin film waveguide layer having a non-linear optical effect formed on a substrate, wherein the thin film waveguide layer has a surface roughness Rmax in the range of 10 to 10,000 Å. , The ordinary refractive index of the thin-film waveguide layer when a fundamental-wave laser beam having a wavelength λ is incident on it (no
F1), the extraordinary optical refractive index of the substrate when generating the second harmonic of λ / 2 under this incident condition is (neS2), and the thin film when such second harmonic is generated. When the extraordinary refractive index of the waveguiding layer is (neF2), the characteristics of the substrate and the thin film waveguiding layer are the following relational expressions; The second feature is that the value of (A) in the formula is within the range of −1.22 ≦ (A) ≦ 1.03.
Harmonic generator. 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.