JPH06230443A - Waveguide type second higher harmonic generating element and its production - Google Patents

Abstract

PURPOSE:To approximate the section of a polarization inversion grating to a rectangular shape and to enhance efficiency by specifying the angle formed by the periodic inversion boundary lines of polarization in an optical waveguide layer with the front surface or boundary of the optical waveguide layer to a specific range. CONSTITUTION:This second higher harmonic generating element consists of an optical substrate 51 and the ferroelectric optical waveguide layer 53 periodically arranged with polarization inversion areas having the refractive index higher than the refractive index of this optical substrate 51. The angle formed by the periodic inversion boundaries of the polarization in the optical waveguide layer 53 with the front surface or boundary of the optical waveguide layer 53 is specified to 75 to 105 deg., more preferably 85 to 95 deg.. The mismatch of the phase generated at the time the basic wave and the second higher harmonic progress in the optical waveguide layer 53 while acting on each other is efficiently compensated by specifying the angle formed by the inversion boundary lines to 75 to 105 deg., more particularly to 85 to 90 deg.. Consequently, the generation efficiency of the second higher harmonic in the optical waveguide layer 53 is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to shortening the wavelength of a light source for optical disk devices, laser printers, and other optical application devices, and in particular, semiconductor laser light having a wavelength of about 800 nm is blue with a wavelength of about 400 nm. The present invention relates to a waveguide type second harmonic generation (SHG) element that converts light into light.

[0002]

2. Description of the Related Art Electronic Letters
ics Letters) Volume 25 (1989), 731-73
On page 2, as shown in FIG. 2, Ti film is periodically formed on the lithium niobate crystal substrate 21 and heated to about 1100 ° C. to reverse the polarization of the Ti film forming portion 41, and then the proton exchange method is performed. An optical waveguide 42 is manufactured by the above method, and a polarization inversion portion in which the spontaneous polarization direction is inverted at an equal pitch on a ferroelectric material having spontaneous polarization such as incidence of the fundamental wave 23 and extraction of the second harmonic wave 24, and a proton exchange method. Is provided, and the fundamental wave 2 polarized in the z direction from one end of the optical waveguide 42 is provided.
Second harmonic wave 24 that is incident on the other side and polarized in the z direction from the other end
The method of taking out is proposed.

When lithium tantalate is used for the crystal substrate 21, a periodic proton exchange part is prepared by a proton exchange method instead of Ti diffusion and heated to about 600 ° C. to polarize only the proton exchange part layer. Has also been proposed, and a method of manufacturing the optical waveguide 42 by the proton exchange method is also proposed.

[0004]

In the method shown in FIG. 2, the polarization inversion lattice is formed by diffusing Ti or exchanging protons. Therefore, the shape of the polarization inversion lattice is the shape of the Ti diffusion layer or the proton exchange layer. , It is essentially difficult to fabricate a domain-inverted grating with a rectangular cross section.

The cross-sectional shape of the polarization inversion grating manufactured by the Ti diffusion method is substantially triangular, and the cross-sectional shape of the polarization inversion grating manufactured by the proton exchange method is approximately semicircular, so that the polarization inversion grating of an ideal rectangular cross section is used. There was a problem that the second harmonic could not be generated with the original efficiency of the SHG element having.

The object of the present invention relates to an improvement of the second harmonic generating element shown in FIG. 2, and in particular, to a waveguide type second harmonic generating element in which the cross section of the polarization inversion grating is made closer to a rectangle to improve the efficiency. It is to provide the manufacturing method.

[0007]

In order to solve the above problems, the second harmonic generation is composed of an optical substrate and a ferroelectric optical waveguide layer having a refractive index higher than that of the substrate and periodically arranged domain inversion regions. In the device, the polarization reversal boundary line in the optical waveguide layer forms an angle of 75 ° to 105 °, particularly 85 ° to 95 ° with the surface or interface of the optical waveguide layer.

A clad layer having a lower refractive index than the optical waveguide layer and a narrower width than the optical waveguide layer is provided on the optical waveguide layer.

Therefore, the substrate is made of magnesium-doped lithium niobate, and the optical waveguide layer is made of lithium niobate, or lithium niobate having a smaller amount of magnesium doped than the substrate. Alternatively, the substrate is made of lithium tantalum niobate, and the optical waveguide layer is made of lithium niobate or lithium tantalum niobate having a larger amount of niobium than the substrate.

The cladding layer is made of ZnO or S.
iO ₂ .

Further, the substrate may be potassium titanate phosphate or potassium arsenic phosphate arsenate, and the optical waveguide layer may be potassium arsenate titanate or potassium arsenate phosphate titanate having a larger amount of arsenic than the substrate. Alternatively, the substrate may be potassium titanate phosphate or potassium rubidium titanate phosphate, and the optical waveguide layer may be rubidium titanate phosphate or potassium rubidium potassium titanate having a larger amount of rubidium than the substrate.

In this case, the cladding layer is made of SiO ₂
And

Further, an optical waveguide layer is formed on a substrate having periodically poled portions by a process including at least liquid phase epitaxial growth.

At this time, the film growth temperature for liquid phase epitaxial growth is set to 800 ° C. or lower, and particularly 750 ° C. or lower.

Further, when the optical waveguide layer is magnesium-doped lithium niobate, lithium niobate, or lithium tantalum niobate, the flux used for liquid phase epitaxial growth is vanadium pentoxide, boron trioxide, or fluorine. Lithium iodide, or potassium fluoride, or vanadium pentoxide and potassium oxide,
Alternatively, vanadium pentoxide and sodium oxide, boron trioxide and molybdenum trioxide, or boron trioxide and tungsten trioxide are used.

When the optical waveguide layer is potassium arsenic phosphate titanate, potassium arsenate titanate, potassium rubidium phosphate titanate or rubidium titanate phosphate, the flux used for liquid phase epitaxial growth is Tungsten trioxide, molybdenum trioxide, or potassium phosphorous arsenate is used.

[0017]

[Operation] The periodically reversal boundary line of polarization in the optical waveguide layer is
The angle formed with the surface or interface of the optical waveguide layer is 75 ° to 1
By setting the angle to be 05 °, particularly 85 ° to 95 °, it is possible to efficiently compensate for the phase mismatch that occurs when the fundamental wave and the second harmonic travel in the optical waveguide layer while interacting with each other. As a result, the second harmonic generation efficiency in the optical waveguide layer is improved.

Further, by providing a clad layer having a lower refractive index than the optical waveguide layer and a narrower width than the optical waveguide layer on the optical waveguide layer, the light distribution can be made symmetrical in the vertical direction. Can be efficiently confined in the optical waveguide layer. As a result, the generation efficiency of the second harmonic in the optical waveguide layer is further improved.

Further, the substrate is made of magnesium-doped lithium niobate, the optical waveguide layer is made of lithium niobate, or lithium niobate having a smaller magnesium doping amount than the substrate, and the domain-inverted portions are periodically provided in advance. By the process of liquid phase epitaxial growth of the optical waveguide layer on the substrate at a film growth temperature of 800 ° C. or less, particularly 750 ° C. or less, the periodically inversion boundary line of polarization in the optical waveguide layer is formed on the surface or the interface of the optical waveguide layer. The angle formed can be 75 ° to 105 °, especially 85 ° to 95 °.

Alternatively, the substrate is made of lithium tantalum niobate, the optical waveguide layer is made of lithium niobate or lithium tantalum niobate having a larger amount of niobium than that of the above substrate, and a domain-inverted portion is periodically provided on the substrate. By the step of performing liquid phase epitaxial growth of the optical waveguide layer at a film growth temperature of 800 ° C. or less, particularly 750 ° C. or less, the angle at which the periodically inversion boundary line of the polarization in the optical waveguide layer forms the surface or the interface of the optical waveguide layer. 75 ° to 105 °, especially 85
It can be in the range of 90 ° to 95 °.

If the optical waveguide layer is the above-mentioned magnesium-doped lithium niobate, lithium niobate, or lithium tantalum niobate, the flux is vanadium pentoxide, boron trioxide, lithium fluoride, or Liquid phase epitaxial growth can be performed by using potassium fluoride, vanadium pentoxide and potassium oxide, vanadium pentoxide and sodium oxide, boron trioxide and molybdenum trioxide, or boron trioxide and tungsten trioxide.

Further, from the refractive index, ZnO is added to the cladding layer.
Alternatively, SiO ₂ can be used.

Alternatively, the substrate may be potassium titanate phosphate or potassium arsenic phosphate titanate, and the optical waveguide layer may be potassium arsenate titanate or potassium arsenate phosphate titanate having a larger arsenic amount than the substrate, and the polarization inversion part is previously prepared. The optical waveguide layer is formed on the substrate on which the film growth temperature is 80
The angle at which the periodically inversion boundary line of polarization in the optical waveguide layer forms a surface or an interface of the optical waveguide layer at 75 ° to 105 °, especially at 85 ° C., by the step of liquid phase epitaxial growth at 0 ° C. or less, particularly 750 ° C. or less. It can be in the range of 90 °

Alternatively, the substrate may be potassium titanate phosphate or potassium rubidium phosphate titanate, and the optical waveguide layer may be rubidium titanate phosphate or potassium rubidium titanate phosphate having a larger amount of rubidium than the substrate, and the polarization reversal portion is previously prepared. The periodic inversion boundary line of the polarization in the optical waveguide layer is formed on the substrate by periodically performing liquid phase epitaxial growth at a film growth temperature of 800 ° C. or less, particularly 750 ° C. or less on the substrate. The angle with the surface or interface of the layer is 75 ° to 105 °, especially 85 °
It can be in the range of 90 ° to 95 °.

If the optical waveguide layer is potassium arsenic phosphate titanate, potassium titanate arsenate, potassium rubidium titanate potassium or rubidium titanate phosphate, the flux is tungsten trioxide or Liquid phase epitaxial growth can be performed by using molybdenum trioxide or potassium arsenic phosphate.

Further, due to the refractive index, the cladding layer is made of SiO 2.
₂ can be used.

[0027]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a sectional view of the second harmonic generating element, FIG.
Is an operation explanatory view thereof, FIG. 4 is a manufacturing process drawing thereof, and FIG. 5 is a view showing a relationship between a shape of a domain inversion portion and a film growth temperature.

An object of the present invention is to improve the efficiency by making the cross sectional shape of the periodically poled grating of the second harmonic generating element close to a rectangle.

Therefore, consider the structure shown in FIG. A ridge-type optical waveguide layer 53 is provided on the + c surface of the substrate 51, and in the optical waveguide layer 53, spontaneous polarization upward portions 57 and downward polarization portions (polarization inversion regions) 58 are periodically arranged.
Also, a similar configuration may be formed on the -c plane.

Reference numeral 56 denotes a polarization reversal portion provided in the substrate to form the polarization reversal region, and the polarization direction with respect to the substrate is reversed.

The domain-inverted region 56 is formed by, for example, Ti diffusion, ion exchange, EB drawing method, direct electric field application (poling) method or the like.

The optical waveguide layer 53 can be formed by a liquid phase epitaxial growth method, a vapor phase growth method such as sputtering, or a solid phase growth method such as epitaxial growth by melting.

Next, a method of forming the spontaneous polarization portion 58 into a shape close to a rectangle will be described.

In the present invention, the polarization inverting portion 56 is provided on the substrate 51 and then the optical waveguide layer 53 is formed. As shown in FIG.
The shape of the domain-inverted portion 58 depends on the film growth temperature.
The boundary line for periodically reversing polarization in the optical waveguide layer at an angle of 00 ° C. or lower forms an angle of 75 ° to 105 ° with the boundary line between the substrate and the optical waveguide layer, and the cyclic line for polarization in the optical waveguide layer at 750 ° C. The boundary line is 85 ° with the boundary line between the substrate and the optical waveguide layer.
The angle is 95 °. From FIG. 5, at 800 ° C. or higher, the shape of the domain-inverted portion 58 rapidly approaches a triangular shape obtained by Ti diffusion.

From the above, the rectangular cross section as shown in FIG.
Optical Waveguide Layer 53 Having Periodic Polarization Inverted Grating of Almost Rectangular Section
Can be formed.

The second harmonic generating element of the present invention can be manufactured by combining materials.

For example, magnesium doped lithium niobate is used, and lithium niobate or lithium niobate containing less magnesium than the substrate is used for the optical waveguide layer.

It is also possible to use tantalum-lithium niobate for the substrate and lithium niobate for the optical waveguide layer, or tantalum-lithium niobate having a higher niobium content than the substrate.

Furthermore, the substrate may be potassium titanate phosphate or potassium arsenic phosphate arsenate, and the optical waveguide layer may be potassium arsenate titanate or potassium arsenate phosphate titanate having a larger amount of arsenic than the substrate.

Alternatively, the substrate may be potassium titanate or potassium rubidium titanate, and the optical waveguide layer may be rubidium titanate or potassium rubidium titanate having a larger amount of rubidium than the substrate.

The extraordinary refractive index of lithium niobate of the above-mentioned substrate with respect to light having a wavelength of 633 nm is, for example, 2.203 in a commercially available congruent composition, and, for example, 5 mol% of niobium doped with magnesium is used. The extraordinary light refractive index of lithium oxide is 2.192 (H. Tama
da, Journal of Applied Physics, Vol. 70, N
o. 5 (1991), pp 2536-2541).
The extraordinary light refractive index of lithium tantalate with respect to light having a wavelength of 633 nm is 2.180 (see Hiroshi Nishihara's "Optical Integrated Circuit" p178).

Furthermore, it is known that both the extraordinary refractive index of tantalum / lithium niobate increases monotonically with the amount of niobium (NTT Technology Transfer Co., Ltd., "Improvement of Crystal Quality of Oxide Ferroelectric Material". Research ”Chapter 3).

Both lithium niobate and lithium tantalate are special cases of tantalum lithium niobate.

Similarly, potassium arsenate phosphate titanate has a refractive index which increases with the amount of arsenic. Utilizing this relationship, the potassium arsenate titanate optical waveguide layer is grown in liquid phase epitaxial growth on the potassium arsenate phosphate titanate substrate. Has been reported (LK Chheng et al., Journal of Cry.
stal Growth magazine, Vol. 112 (1991), pp3
09-315).

Both potassium titanate phosphate and potassium arsenate titanate are special cases of potassium arsenate phosphate titanate.

Similarly, in the case of potassium rubidium titanate phosphate, the refractive index increases with the amount of rubidium, and an example of forming an optical waveguide by exchanging a part of potassium ion of potassium titanate phosphate with rubidium ion is reported. (JDBierlein et al., Conference on Lase
rs and Electro-Optics (1991) Proceedings, CMH
13).

Both potassium titanate and rubidium titanate are special cases of potassium rubidium titanate.

FIG. 4 is a process diagram of a method of manufacturing the second harmonic generating element by liquid phase epitaxial growth and ion milling.

First, a 5 mol% MgO-doped LiNbO ₃ substrate 5 whose + c surface is optically polished as shown in FIG. 4A is used.
1 is ultrasonically cleaned in acetone and pure water and dried quickly.

Then, as shown in FIG. 7B, a 30 Å Ti film 81 is formed on the + c surface by sputtering.

Then, as shown in FIG. 7C, the Ti film 81 is formed.
A photoresist 82 is coated on the top by a spinner, and the photoresist 82 is patterned using a photoresist having a domain-inverted portion opened therein (FIG. 4 (d)).

Next, the Ti film 81 is patterned by RIE using CF ₃ Cl gas using the photoresist as a mask to remove the photoresist 82 (FIG. 4).
(E)). The pattern cycle of the photomask is 1 μm.
It is adjusted to the period of SHG light generated from m to 10 μm.

Then, the above substrate is put into a diffusion furnace and the temperature is about 80.
Heat treatment is performed at about 1100 ° C. for about 10 minutes in an Ar atmosphere containing water vapor through a warm water bubbler at a temperature of about 100 ° C. At the time of cooling, the atmosphere was changed to O ₂ containing water vapor. As a result, the domain inversion part 56 is formed on the + c surface of the substrate 51 as shown in FIG.

Then, an optical waveguide layer of a LiNbO ₃ single crystal thin film is formed on the + c surface of the substrate 51 by the liquid phase epitaxial crystal growth method.

The melt during the epitaxial growth was made of 50.0 mol% lithium carbonate Li ₂ CO ₃ as a raw material,
2.5 mol% niobium pentoxide Nb ₂ O ₅ , 47.5 mol%
The respective powders of vanadium pentoxide V ₂ O ₅ of 1. were weighed and mixed, then put in a platinum crucible and melted at 900 ° C.

Then, after maintaining at a temperature of 1200 ° C. in an electric furnace at a temperature of 1200 ° C. for 10 hours, the melt was cooled to 720 ° C. at a cooling rate of 50 ° C./h, and a Pt stirrer was used at 60 rpm. Stir for 3 hours to homogenize.

Next, this melt was cooled to 690 ° C. at a cooling rate of 30 ° C./h, and the substrate shown in FIG. 6 (f) was brought into contact with it for 33 minutes to obtain a film thickness of 3 μm shown in FIG. The optical waveguide layer 53 of the LiNbO ₃ thin film is grown.

Next, the above sample was placed in an electric furnace at 30 ° C.
Slowly cool to room temperature at a cooling rate of / h.

When the optical waveguide layer is the above lithium niobate, magnesium-doped lithium niobate, or lithium tantalum niobate, the flux material in the epitaxial growth of the above optical waveguide layer 53 is 5 In addition to vanadium oxide, use boron trioxide, lithium fluoride, potassium fluoride, vanadium pentoxide and potassium oxide, vanadium pentoxide and sodium oxide, boron trioxide and molybdenum trioxide, or boron trioxide and tungsten trioxide. May be.

When the optical waveguide layer 53 is potassium arsenic phosphate titanate, potassium titanate arsenate, potassium rubidium titanate phosphate, or rubidium titanate phosphate, the flux material is tungsten trioxide. Alternatively, molybdenum trioxide, potassium arsenic phosphate, or the like may be used.

The optical waveguide layer 53 (single crystal thin film) and the substrate 5
When the domain 1 is etched with an etching solution of nitric acid: hydrofluoric acid = 1: 1, the polarization part 57
And 58 are the same as the polarization direction of the corresponding substrate 51, and the interface thereof is substantially perpendicular to the interface between the optical waveguide layer 53 and the substrate 51 (FIG. 4 (g)).

Finally, a channel part was produced. First, the photoresist was patterned using a photoresist having only the channel portion as a light shielding portion, and then the thin film was etched by 2 μm by ion milling using this photoresist as a mask. The channel width is 3 μm.
Then, the photoresist was removed to produce a channel part. The ion milling device used in this step has a structure in which a plasma chamber has a plurality of permanent magnets arranged on the outer periphery of a conical hollow vacuum container, and ions generated in the plasma generation chamber are an acceleration electrode, a deceleration electrode, It is a structure that is drawn out by three electrodes of a ground electrode. Therefore, the spatial density distribution of ions is uniform, the directivity is extremely high, and etching with extremely high precision is possible.

In the above channel portion, when the optical waveguide layer is the above-mentioned lithium niobate, magnesium-doped lithium niobate, or lithium tantalum niobate, for example, ZnO or SiO ₂ is sputtered on the optical waveguide layer. It can be formed into a loading type by forming a film or an embedded type by proton exchange.

If the optical waveguide layer is potassium arsenate phosphate titanate, potassium potassium arsenate titanate or rubidium potassium titanate phosphate, or rubidium titanate phosphate, for example, SiO ₂ is sputtered on the optical waveguide layer. It can also be manufactured as a loading type by filming, or as an embedded type by ion exchange of Rb, Tl and the like.

Optical propagation loss of light having a wavelength of 830 nm was measured by the cutback method with respect to the optical waveguide manufactured by the above process, and a good value of 0.5 dB / cm was obtained.

The optical waveguide length of the sample is 10 mm, and the vertical length is 5 m.
A second harmonic wave generation experiment was performed by cutting with m and optically polishing the vertical side.

In the above experiment, the titanium-sapphire laser light 11 was condensed on the end face of the channel portion by the objective lens 12, the data was placed on the copper block to which the Peltier element was connected, and the temperature was monitored by the thermocouple. First, the temperature is 25 ℃
Then, the wavelength of the laser light source was set so that the generation efficiency of the second harmonic was maximized.

As a result, 4 mW with a fundamental wave input of 40 mW
The second harmonic output of was obtained, and the efficiency considering Fresnel reflection loss was 11.8%. This value is sufficiently higher than the conventional value.

Further, when estimated from the above result, the output 20
When a high power semiconductor laser of 0 mW is coupled to an optical waveguide with a coupling efficiency of 50%, the second harmonic generation efficiency is 30%,
A second harmonic output of 30 mW is obtained, which means that it can be sufficiently used as a light source for writing and reproducing on a magneto-optical disc or a phase change optical disc.

[0071]

According to the present invention, the domain of the periodically poled substrate is transferred by the LPE method to form the periodic spontaneous domain-inverted region of the rectangular cross section in the optical waveguide. A highly efficient second harmonic generation element can be manufactured.

[Brief description of drawings]

FIG. 1 is a sectional view of a second harmonic generation element according to the present invention.

FIG. 2 is a perspective view of a second harmonic generation element using conventional polarization inversion.

FIG. 3 is a configuration diagram of a light source using the second harmonic generation element of the present invention.

FIG. 4 is a manufacturing process diagram of a second harmonic generation element of the present invention.

FIG. 5 is a graph showing the relationship between the shape of the polarization inversion portion and the film growth temperature.

[Explanation of symbols]

11 ... Laser, 12 ... Optical system (objective lens), 1
3, 23 ... Fundamental wave, 19, 24 ... Second harmonic wave, 51
... substrate, 53 ... optical waveguide layer, 57 ... polarization non-inversion part,
56, 58 ... polarization inversion part, 41, 81 ... Ti film, 82 ...
Photoresist.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenchi Ito 1-280 Higashi Koigokubo, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor Hisao Kurosawa 5200 Sankejiri, Kumagaya-shi, Saitama Hitachi Metals Co., Ltd. Inside the Magnetic Materials Laboratory (72) Inventor Masazumi Sato 5200 Sankejiri, Kumagaya-shi, Saitama Hitachi Metals Co., Ltd. Inside the Magnetic Materials Laboratory (72) Inventor Fumio Futanda 5200 Sangajiri, Kumagaya, Saitama Inside the Hitachi Materials Co., Ltd. (72) Inventor Kohei Ito 5200 Sankejiri, Kumagaya City, Saitama Hitachi Metals Co., Ltd.

Claims (14)

[Claims] 1. A second harmonic generation device comprising an optical substrate and a ferroelectric optical waveguide layer having a refractive index higher than that of the substrate and periodically arranged polarization inversion regions, wherein a polarization period in the optical waveguide layer is The waveguide type second harmonic generation element, wherein the angle of the inversion boundary line with the surface or interface of the optical waveguide layer is set to 75 ° to 105 °. 2. A second harmonic generation device comprising an optical substrate and a ferroelectric optical waveguide layer having a refractive index higher than that of the substrate and periodically arranged domain inversion regions, wherein the polarization period in the optical waveguide layer is The waveguide type second harmonic generation device, wherein the angle between the optically inverted boundary line and the surface or interface of the optical waveguide layer is 85 ° to 95 °. 3. The waveguide according to claim 1, wherein a clad layer having a lower refractive index than the optical waveguide layer and a narrower width than the optical waveguide layer is provided on the optical waveguide layer. Type second harmonic generation element. 4. The method according to claim 1, 2 or 3,
The substrate or the cladding layer is made of magnesium-doped lithium niobate (LiNbO ₃ ), and the optical waveguide layer is made of lithium niobate, or lithium niobate having a smaller magnesium doping amount than the substrate or the clad layer. Waveguide type second harmonic generator. 5. The method according to claim 1, 2 or 3,
Lithium tantalum niobate (LiTa _x Nb _1-x O ₃ ; 0 ≦ x ≦ 1) is used as the substrate or the cladding layer, and tantalum niobium having a larger amount of niobium is used as the optical waveguide layer than the lithium niobate or the substrate or the clad layer. A waveguide-type second harmonic wave generating element, which is made of lithium oxide. 6. A waveguide type second harmonic generation element according to claim 4 or 5, wherein ZnO or SiO ₂ is used for the cladding layer. 7. The method according to claim 1, 2 or 3,
The substrate or the clad layer is potassium titanate phosphate (KTiOPO ₄ ) or potassium arsenic phosphate titanate (KTiOAs _x P _{1 -x} O ₄ ; 0 ≦ x ≦ 1), and the optical waveguide layer is potassium arsenate titanate (KTiOAs). KTiOAsO ₄ ) or a second harmonic generation element of the waveguide type characterized by using potassium arsenate phosphate titanate having a larger amount of arsenic than the substrate or the clad layer. 8. The method according to claim 1, 2 or 3,
The substrate or the cladding layer is potassium titanate phosphate (KTiOPO ₄ ) or potassium rubidium titanate phosphate (Rb _x K _1-x TiOPO ₄ ; 0 ≦ x ≦ 1), and the optical waveguide layer is rubidium titanate phosphate ( RbTiO
PO ₄ ) or a ruthenium potassium phosphate titanate having a larger amount of rubidium than the substrate or clad layer, and a waveguide type second harmonic generation device. 9. A waveguide type second harmonic wave generating element according to claim 7, wherein SiO ₂ is used for the cladding layer. 10. A method of manufacturing a second harmonic generation device having a ferroelectric optical waveguide layer in which domain-inverted regions are periodically arranged, wherein a domain-inverted portion is periodically provided in the substrate, and the optical waveguide layer is formed as described above. A method of manufacturing a waveguide type second harmonic generation element, comprising at least a step of performing liquid phase epitaxial growth on a substrate. 11. The method for manufacturing a waveguide type second harmonic generation element according to claim 10, wherein the film growth temperature in liquid phase epitaxial growth is 800 ° C. or lower. 12. The method of manufacturing a waveguide type second harmonic generation element according to claim 10, wherein the film growth temperature of the liquid phase epitaxial growth is 750 ° C. or lower. 13. The optical waveguide layer according to claim 10, 11 or 12, wherein the optical waveguide layer is magnesium-doped lithium niobate, lithium niobate, or lithium tantalum niobate. Vanadium oxide (V ₂ O ₅ ),
Or boron trioxide (B ₂ O ₃ ), lithium fluoride (LiF), potassium fluoride (KF), or vanadium pentoxide (V ₂ O ₅ ) and potassium oxide (K ₂ O),
Or vanadium pentoxide (V ₂ O ₅ ) and sodium oxide (Na ₂ O), or boron trioxide (B ₂ O ₅ ) and molybdenum trioxide (MoO ₃ ), or boron trioxide (B)
₂ O ₃ ) and tungsten trioxide (WO ₃ ), a method for manufacturing a waveguide type second harmonic wave generating element. 14. The optical waveguide layer according to claim 10, wherein the optical waveguide layer is potassium arsenic phosphate titanate,
Or potassium arsenate titanate, potassium rubidium titanate phosphate, or rubidium titanate phosphate, and the flux used for liquid phase epitaxial growth is tungsten trioxide (WO ₃ ) or molybdenum trioxide (MoO ₃ ), Or potassium arsenic phosphate (KA
s _x P _1-x O ₄ ; 0 ≦ x ≦ 1).