JPH05341342A - Second higher harmonic generating element and its production - Google Patents

Abstract

PURPOSE:To realize an ideal rectangular polarization inversion grid and to efficiently generate a SHG light by periodically arranging polarization inversion regions stretched from regions for starting polarization. CONSTITUTION:The proton exchanging layer of grid pattern, that is, a region for starting polarization is formed on a substrate surface by using a substrate 11 consisting of LiTaO3 or LiNbO3 and the layer is subjected to a heat treatment at >=200 deg.C within 10 minutes of holding time after forming a pattern thereon. A polarization inversion region 12 is formed under the proton exchange region by adjusting a temp. rising rate up to the heat treatment temp. to >=50 deg.C/min. and adjusting a temp. falling rate from the heat treatment temp. to >=50 deg.C/min. and the top end of the region 12 is made to an acute angle and the depth/width ratio of the polarization inversion lattice formed is also set at >1. In such a manner, SHG element having high efficiency is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to nonlinear ferroelectric optical materials such as LiTaO ₃ (hereinafter referred to as LT) and LiNbO _3.
The second harmonic generation element (hereinafter, SHG element) using a substrate (hereinafter, referred to as LN) and its manufacturing method are related to SHG.
The present invention relates to high efficiency of devices.

[0002]

2. Description of the Related Art Recently, as a compact and lightweight blue light source, attention has been paid to converting a semiconductor laser having a wavelength of 830 nm into blue light having a wavelength of 415 nm, which is half that of a semiconductor laser. For example, as described in JP-A-61-18934, an optical waveguide is formed on a LiNbO ₃ substrate by a proton exchange method (a method of partially replacing Li ions and protons of LiNbO ₃ to form an optical waveguide). However, it has been proposed that a fundamental wave be incident on one end of the above-mentioned optical waveguide to generate SHG light by Cherenkov radiation. This is shown in FIG. In FIG. 2, a channel type optical waveguide 13 is formed on the surface of a substrate 21 made of LiNbO ₃ .
When the fundamental wave incident light 14 is made incident from this one end, the Cherenkov SHG light 22 having a crescent cross section is outputted from the opposite side. Furthermore, recently, for example, Electronics
731 of Letters, 25, 11 (1989)
As discussed on page 732, a method for phase matching using polarization reversal has been proposed. That is, as shown in FIG. 3, a periodic lattice is formed on the LiNbO ₃ substrate 21 by diffusion of Ti and heated to about 1100 ° C. to invert the polarization of only the periodic lattice layer to form the triangular polarization inversion region 3.
1 is formed, and then the optical waveguide 1 is formed by the proton exchange method.
3 is produced, the fundamental wave 14 is made incident, and the SHG light 15 is taken out. When a LiTaO ₃ substrate is used, for example, Appl. Phys. Lett. 58 (24) (19
1991) As discussed in pages 2732 to 2734, as shown in FIG. 4, a periodic lattice was prepared on the substrate 11 made of LiTaO ₃ by the proton exchange method instead of Ti diffusion and heated to about 600 ° C. Then, a method of forming a semicircular domain-inverted region 41 by reversing the polarization of only the periodic lattice layer and further manufacturing the optical waveguide 13 by the proton exchange method has been attempted. Then, the fundamental wave 14 is incident on the optical waveguide 13 and the SHG light 15 is extracted.

Another conventional second harmonic generating element is an Applied Phy issued in September 1991.
The SHG device using the LT waveguide described on page 1538 of the Medical Letters and the international publication number W09.
0/04807, the waveguide structure disclosed in JP-A-4-229841, and the SHG element disclosed in JP-A-4-229841.
ELECTRONICS L, issued May 9, 1991
The SHG element described in ETTER and the like are known.

[0004]

However, the above-mentioned prior art has the following problems. In the method using Cherenkov radiation shown in FIG. 2, the beam shape of the SHG light generated as shown by 22 is crescent-shaped, and the wavefront aberration is extremely large, and it is almost impossible to narrow it down to the diffraction limit. In the method proposed for phase matching using polarization inversion shown in FIGS. 3 and 4, which is newly proposed for the above example, since SHG light is collimated light, it is extremely easy to collect light as compared with Cherenkov radiation. Has the advantage of being By the way, the generation efficiency of SHG light depends on the cross-sectional area or cross-sectional area of the polarization inversion grating and the optical waveguide, and the larger these, the better the efficiency. However, the cross-sectional shape of the domain-inverted lattice formed by the Ti diffusion method is triangular as shown at 31, and the semi-circular shape at 41 by the proton exchange method. SHG light cannot be generated with the original efficiency of the SHG element having an inversion grating.

Further, in the Ti diffusion region, there is a problem that the light damage that the refractive index changes due to strong light is likely to occur and that the nonlinear optical coefficient is lowered in the proton exchange region and the original SHG generation efficiency cannot be obtained. It was In addition, the method of proton exchange treatment that has been conventionally used is as follows. As shown in FIG. 13, a glass container 351 installed in a constant temperature bath 354 is used.
An acid 353, which is a proton source, is housed inside, and a substrate 352 is attached to the acid. In this case, the glass container 351 is attacked or protons are exchanged in all directions of the substrate depending on the acid that is the proton source, and the surface of the substrate is roughened or cracked due to the difference in the crystal orientation of the chemical damage caused by the acid. There was a problem that would end up. Further, the conventional method has a problem that the production of the polarization inversion grating and the production of the optical waveguide have to be performed twice or more in separate steps.

[0006] In addition, the Applied Physical
In the Letters SHG device, the polarization inversion grating has a width of 2.1 μm and a depth of 1.6 μm.
Since m is very shallow, it is not suitable for a high-power element, and the heat treatment temperature is as high as about 550 ° C., which is a problem. The waveguide structure of W090 / 04807 has a problem that thermal diffusion may spread in all directions because the whole is heated during the heat treatment. Further, in the SHG structure disclosed in Japanese Patent Laid-Open No. 4-229841, a domain-inverted layer having a rectangular cross section is formed by using LT, but a portion which may cause a composition change on the surface is used. Since the waveguide is formed by using the waveguide, the conversion efficiency may be deteriorated.

Furthermore, ELECTRONICS LETT
In the SHG element described in ER, a polarization inversion layer is formed on an LN substrate by using an electron beam.
When the electron beam is used as described above, since the inversion layer is formed by the electron beam, there is a possibility that the crystal uniformity in the depth direction of the inversion layer cannot be ensured. The present invention has been made to pay attention to the above problems and to solve them effectively.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to manufacture a domain-inverted grating in an ideal rectangular shape. The object of the present invention is to realize an ideal rectangular domain-inverted grating by producing, for example, a spike-shaped domain-inverted region whose tip is periodically acutely angled as shown in FIG.
It is an object of the present invention to provide a second harmonic generation element capable of generating highly efficient SHG light. It should be noted that the term spike-like used in the present application is merely used to indicate a state in which the tip is made into an acute angle. The presence of spike domains in the LiTaO ₃ or LiNbO ₃ substrate is
For example, J. Appl. Phys. vol. 46, No.
3 (1975), as is well known, at page 1063, but until now there was no means to control the spiked domains. The present invention intends to achieve a high-efficiency SHG element by artificially controlling the generation of the domain-inverted region whose tip is formed into an acute angle, and utilizing the property of extending perpendicularly to the c-axis direction of the substrate. ..

Then, when we examined the conditions for realizing a domain-inverted region with a sharp tip, LiT
It has been found that the aforesaid regions often appear when the aO ₃ or LiNbO ₃ substrate undergoes a relatively rapid thermal history. This is because the magnitude of polarization changes abruptly in response to a rapid thermal change, and an effective electric field is generated around the domain wall. Therefore, the spike domain is the direction of polarization. It is considered to grow along the c-axis. Therefore, it is considered that the same phenomenon may possibly generate spike-like domains not only due to thermal change but also due to stress, for example. We have come to think that this spike-like domain can be arranged periodically if the polarized bud region is formed periodically. It is considered that there is a possibility that as a bud of the domain, a region in which the magnitude of polarization or the direction thereof is locally different from that of the peripheral portion may be the bud of the domain.

Based on the above idea, in order to form a domain-inverted grating whose tip is periodically acutely angled on the LiTaO ₃ or LiNbO ₃ substrate upper surface, after forming periodically polarized bud regions on the substrate surface, Heat treatment is performed at an appropriate temperature rising / falling rate to form a domain-inverted region having a periodic tip with an acute angle, and then an optical waveguide is formed on the surface in a direction orthogonal to the above-mentioned region. It was thought that a domain-type polarization inversion grating could be formed, and as a result, a highly efficient SHG element could be realized. Further, the optical waveguide may be formed after removing the buds in the domain left on the surface by polishing or the like. The depth of the domain-inverted region having an acute tip is preferably larger than the depth of the optical waveguide. Therefore, the depth of the domain-inverted grating is larger than the width in the periodic direction, that is, the depth of the domain-inverted grating /
It is desirable that the width ratio exceeds 1. The width of the domain-inverted grating in the periodic direction is selected according to the wavelength of the light to be used, but a desirable rectangular domain-inverted grating by making it approximately equal to the width of the polarization bud region formed on the surface in the range of approximately 1 μm or more and 10 μm or less. Can be realized.

In the heat treatment for forming the domain-inverted regions, it is desirable to perform a temperature change rate of 50 ° C./minute or more during one or both of the temperature increase to the heat treatment temperature and the temperature decrease from the heat treatment temperature. In addition, a sprout domain-inverted region having a period matching the lattice pattern is formed by forming a sprout region, that is, a lattice pattern, on the surface of the substrate, which is a sprout of polarization inversion, and extending the domain-inverted region from this sprout region. Can be formed. Further, in some cases, the width of the lattice pattern in the periodic direction is 1 μm or more and 10 μm or less, and the width of the spike-shaped domain-inverted region is substantially equal to the width of the lattice pattern. Further, it is also possible to form a lattice-patterned proton exchange layer on the surface of the substrate and perform heat treatment. Further, the heat treatment after the formation of the lattice-patterned proton exchange layer,
Heat treatment temperature is 200 ° C or higher and heat treatment time is 10
Within minutes

Another object of the present invention is to form an ideal rectangular domain-inverted lattice in a uniform composition region where the original characteristics of the material can be exhibited, and to manufacture a highly efficient SHG element. That is, the object of the present invention is to realize an ideal rectangular domain-inverted lattice by producing a domain-inverted region extending from the polarization bud region, which is a proton exchange region, as shown in FIG. It is to generate SHG light.

In order to form a periodic domain inversion region from a polarization bud region, which is a proton exchange region, on the surface of a LiTaO ₃ or LiNbO ₃ substrate, first, an optical waveguide is formed on the substrate surface, and a periodic waveguide by proton exchange is formed. After forming the lattice pattern, heat treatment is performed at an appropriate temperature rising / falling rate to extend the domain inversion region from the bud region, whereby a substantially rectangular domain inversion lattice can be formed in the optical waveguide. As a result, a highly efficient SHG element can be realized.

Further, according to the present invention, in order to form a periodically domain-inverted region in a uniform composition region of a LiTaO ₃ or LiNbO ₃ substrate, a proper lattice elevating and lowering is formed when forming a periodic lattice pattern by proton exchange. By giving a thermal history of temperature velocities, a domain-inverted region with a sharp tip with a periodic tip is formed, and then, as it is or after re-heat treatment, an optical waveguide is produced, whereby a substantially rectangular shape is formed in the optical waveguide. A type domain inversion grating can be formed. Further, as shown in FIG. 15, as the method of the proton exchange treatment, the acid is retained on the substrate surface by using the surface tension of the acid which is the proton exchange source, and a rapid thermal history is provided by a directional heating means such as a plate type heater. By carrying out the proton exchange on only one surface of the crystal substrate while applying the magnetic field, it is possible to form a domain-inverted region whose tip is periodically acute. Also, platinum is used as the substrate holder because it has good thermal conductivity and is not easily attacked by the proton source, acid, and its shape is plate-shaped or dish-shaped to protect the heater when acid spills. As a result, it was thought that a highly efficient SHG element could be easily realized.

Another object of the present invention is to manufacture a highly efficient SHG device in which an ideal rectangular domain-inverted grating and an optical waveguide are easily manufactured by one-time photolithography. That is, the object of the present invention is to realize an ideal rectangular polarization inversion lattice by producing a polarization inversion lattice extending from a proton exchange region (bud region) as shown in FIG. By doing so, an element for generating highly efficient SHG light can be manufactured in a simple process.

Another object of the present invention is to provide a second harmonic generation element in which the width of the polarization inversion grating and the width of the waveguide are formed to be the same, and a method for manufacturing the same. The present invention is also characterized in that after the formation of the periodically poled lattice, heat treatment is performed to increase the refractive index of the proton exchange region on the substrate surface to form an optical waveguide. The present invention further provides that the heat treatment temperature is 20.
It is characterized in that the temperature is 0 ° C. or higher and the heat treatment time is within 20 minutes.

The present invention is further characterized in that in the heat treatment, a temperature change rate of 50 ° C./min or more is included in one or both of a temperature increase to a treatment temperature and a temperature decrease from the treatment temperature. The present invention further provides that the acid is pyrophosphoric acid, phosphoric acid,
It is characterized by using benzoic acid and stearic acid. Another object of the present invention is to add L containing MgO of 1 mol% or more.
By using a T substrate, a second harmonic generation element having excellent light transmittance is provided.

[0018]

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

(Embodiment 1) FIG. 1 is a configuration and operation explanatory view showing an embodiment of an SHG element according to the present invention, FIG.
(H) is a figure which shows the manufacturing process of the said SHG element. 6 and 7 are photographs showing a spike-shaped polarization inversion grating, and FIG. 8 is a photograph showing a conventional semicircular polarization inversion grating. In FIG. 1, 11
Is a LiTaO ₃ single crystal substrate whose surface is the −c plane, and the direction of spontaneous polarization is downward. Reference numeral 12 is a portion where the polarization is inverted, for example, in a spike shape, and the polarization direction is upward in this portion. M. Didomenico Jr. Et al. Journal of Applied Physics
s Vol. 40, No. 2 According to page 720 to 734 of the nonlinear optical coefficient code LiNbO ₃ or LiTa
In the case of a ferroelectric crystal of the space group R3c such as O _3, the direction of spontaneous polarization agrees. Therefore, it can be said that the nonlinear optical coefficients of the substrate and the optical waveguide layer of this example are also periodically inverted. Reference numeral 13 is a channel type optical waveguide, which is a fundamental wave, SH
G light also propagates while being confined in this portion. The incident fundamental wave 14 is polarized in the direction perpendicular to the crystal surface. Reference numeral 15 denotes SHG light generated in the optical waveguide layer portion, which is also polarized in a direction perpendicular to the crystal surface.

Next, the method of forming the domain inversion grating of the present invention will be described with reference to FIG. As shown in FIG. 5A, LiT
A substrate 11 is prepared in which the -Z (c) plane of the aO ₃ substrate is polished to about 1/10 of the laser light wavelength λ. Figure 5
As shown in (b), a Ta film 51 is formed on the −Z surface of the substrate 11 by 30 nm sputtering. As shown in FIG. 5C, a photoresist 52 was spin-coated on the Ta film 51, and the photoresist 52 was patterned by a normal photolithography technique using a photomask having a window for a portion where the polarization reversal 12 was performed. The pattern period of the photomask is adjusted to the period of SHG light generated at 1 to 10 μm. Using the photoresist 52 patterned as shown in FIG. 5D as a mask, the Ta film 51 is patterned by dry etching or wet etching by RIE using CF ₃ Cl gas. Figure 5
As shown in (e), the photoresist 52 is removed with acetone, and the proton exchange is performed at 260 ° C. for 3 times with pyrophosphoric acid.
By performing the process for 0 to 60 minutes, a polarization bud region (hereinafter referred to as a proton exchange region or exchange layer) 53 is formed. Figure 5
As shown in (f), the Ta film 51 is etched with an aqueous solution of NaOH. As shown in FIG. 5 (g), the polarization inversion layer extends downward with the proton exchange layer 53 as a nucleus or sprout by inserting the substrate on which the proton exchange layer 53 is formed into an electric furnace and performing heat treatment. A spike-shaped domain-inverted region 12 having a sharp tip is formed on the substrate. The heat treatment conditions are a temperature of 540 ° C., a holding time of 0.5 minutes, a temperature rising rate up to the heat treatment temperature of 50 ° C./min or more, and a temperature lowering rate from the heat treatment temperature of 50 ° C./min or more to cause spike-like polarization reversal. A region, that is, a domain-inverted grating 12 was produced. The depth was larger than the optical waveguide depth formed on the substrate surface and smaller than the substrate thickness. In addition, the width is almost equal to the width of the proton exchange pattern, and a substantially rectangular polarization inversion grating can be realized within the range of the depth of the optical waveguide. In addition, the polarization inversion grating 12
The depth / width ratio is larger than 1, so that the waveguide area can be increased to cope with a large output.
In this case, particularly when used as a bulk type SHG element, SHG light can be efficiently generated.
The effect of the depth / width ratio of the grating 12 exceeding 1 is similarly exhibited in all other embodiments described later. If the heat treatment time is longer than, for example, 5 minutes, the spike-shaped polarization inversion grating 12 formed disappears. Therefore, the holding time is set to a time during which the polarization inversion grating 12 does not disappear, for example, within 5 minutes. After forming the spike-shaped inversion lattice 12 as shown in FIG. 5 (h), the proton exchange layer 54 on the substrate surface is removed by polishing, and then the substrate surface is made orthogonal to the polarization inversion lattice by a normal proton exchange method. An optical waveguide was produced. The waveguide direction of the optical waveguide is as shown in FIGS. 5A to 5F in the direction perpendicular to the periodic direction of the domain-inverted grating, and finally the waveguide end face is optically polished to manufacture the SHG element. Further, the optical waveguide may be manufactured while the proton exchange layer remains. FIG. 6 is a cross-sectional photograph of the produced spike-shaped polarization inversion grating. A high-efficiency SHG element can be realized by polishing the upper part of the proton exchange layer and the inverted portion of the spike-like polarization inversion lattice until the distance between the substrate portion becomes 1: 1 and then forming an optical waveguide on the substrate surface.

A spike-shaped polarization inversion grating was produced by the above-described production method, and an optical waveguide was produced without polishing the substrate surface.
An SHG element having an element length of 1 cm was produced. SH manufactured using a titanium-sapphire laser as the light source of the fundamental wave
When a fundamental wave with a wavelength of 830 nm is incident on the G element, 4
A 15 nm blue SHG light was obtained. The SHG light output at this time is 2.8 mW, and the standardized SHG efficiency is 10% /
It was W · cm ² . The polarization inversion grating produced at this time had a polarization inversion grating close to an ideal rectangular shape as shown in FIG. 7, and the tip had a spike shape.

For comparison, another SHG element was manufactured under the same conditions as in Example except that the heat treatment time was increased to 10 minutes. Observation of the cross section of the domain-inverted grating produced at this time revealed a semicircular shape as shown in FIG. Then SH
The G light output was measured in the same manner as in the example, and SH at this time was measured.
G light output is 0.1 mW and standardized SHG efficiency is 4%
/ W · cm ² . From this, it was found that the use of the spike-shaped polarization inversion grating is useful for a highly efficient SHG element. In the above embodiment, the polarization inversion grating has been described as having a spike shape.
Needless to say, the present invention is not limited to this, and the same applies to the examples described later.

As is clear from the above description, according to the present embodiment, it is possible to realize an ideal rectangular domain-inverted lattice by producing a domain-inverted lattice, and to realize a highly efficient SH.
An SHG element that can generate G light can be realized. Further, although the LT substrate has been mainly described in the above-mentioned embodiments, the same operational effect is produced also for the LN substrate. In addition, in all of the embodiments described below, the same operational effects are also exhibited in the LN substrate.

(Embodiment 2) In the above embodiment, the optical waveguide is formed after the domain-inverted region is formed. However, these forming procedures may be reversed as described below, or the proton exchange region may be left. Hereinafter, the second embodiment of the present invention will be described in detail. FIG. 9 is a configuration and operation explanatory view showing an embodiment of an SHG element according to the present invention, and FIGS. 10A to 10G are views showing a manufacturing process of the SHG element. FIG. 11 is a photograph showing a polarization inversion lattice formed outside the proton exchange region, and FIG. 12 is a photograph showing a semicircular polarization inversion lattice.

In FIG. 9, 11 is a LiTaO ₃ single crystal substrate whose surface is the −c plane, and the direction of spontaneous polarization is downward. Reference numeral 12 denotes a proton exchange region (polarization bud region) 16 in which polarization is a compositional modulation region, and a portion formed other than that.
The polarization direction is upward in these portions. Reference numeral 13 is a channel type optical waveguide, and the fundamental wave and SHG light are also confined and propagated in this portion. The incident fundamental wave 14 is polarized in the direction perpendicular to the crystal surface. Reference numeral 15 denotes SHG light generated in the optical waveguide layer portion, which is also polarized in a direction perpendicular to the crystal surface.

Next, the method of forming the domain inversion grating of the present invention will be described with reference to FIG. L as shown in FIG.
A substrate 11 having an optical waveguide 13 formed on the -Z (c) plane of an iTaO ₃ substrate by a proton exchange method is prepared. As shown in FIG. 10, except that the waveguide 13 is first formed.
The steps shown in (b) to (10) g are operated in the same manner as the steps shown in FIGS. 5 (b) to 5 (g) in the first embodiment. The depth of the domain-inverted lattice or the region 12 manufactured as described above was larger than the depth of the optical waveguide and the proton exchange layer formed on the surface of the substrate and smaller than the thickness of the substrate. In addition, the width is almost equal to the width of the proton exchange pattern, and it was possible to realize a substantially rectangular polarization inversion grating in the range of the depth of the optical waveguide. Finally, the SHG element is manufactured by optically polishing the end face of the waveguide. Also in this case, as in Example 1, if the holding time during the heat treatment is longer than, for example, 5 minutes, the spike-shaped polarization inversion grating 12 formed disappears, so that the polarization inversion grating 12 disappears during the holding time. No time, for example, within 5 minutes.

A polarization inversion grating was produced by the above-described production method, and an SHG element having an element length of 1 cm was produced. When a fundamental wave was incident on this element using the same titanium-sapphire laser as used in Example 1, the same SH as in Example 1 was obtained.
It was possible to obtain G light output and standardized efficiency. The polarization reversal grating produced at this time had an ideal polarization reversal grating close to a rectangular shape as shown in FIG. 11, and the tip had a spike shape.

Next, for comparison, another SHG element was produced in which only the proton exchange region was polarization-inverted. Observation of the cross section of the domain-inverted grating produced at this time revealed a semicircular shape as shown in FIG. Next, when the SHG light output was measured in the same manner as in the example, the SHG light output at this time was 0.1 mW.
And the normalized SHG efficiency was 4% / W · cm ² . As a result, using a spike-shaped polarization inversion grating,
It was found that it is useful for a highly efficient SHG device to fabricate a polarization inversion lattice in a region other than the proton exchange region. As is clear from the above description, according to the present embodiment, it is possible to realize an ideal rectangular polarization inversion lattice by producing a polarization inversion lattice in a region other than the proton exchange region, and it is possible to realize a highly efficient SHG. An SHG element that can generate light can be realized.

(Embodiment 3) In the previous embodiment, the proton exchange operation and the spike-shaped polarization inversion lattice formation operation are performed in separate steps. However, as shown below, these operations are performed simultaneously. May be. Hereinafter, the third embodiment of the present invention will be described in detail. FIG. 14 is a diagram showing a method of proton exchange heat treatment, and FIGS. 15 (a) to 15 (g) are diagrams showing a manufacturing process of the SHG element. FIG. 16 is a photograph showing a polarization inversion lattice formed outside the proton exchange region, and FIG. 17 is a photograph showing a semicircular polarization inversion lattice. In this embodiment, finally, an SHG element having the same structure as that of the second embodiment shown in FIG. 9 is formed. Therefore, as described above, in FIG. 9, 11 is the LiTaO ₃ single crystal substrate whose surface is the −c plane, and the direction of spontaneous polarization is downward. Reference numeral 12 denotes a proton exchange region 16 in which the polarization is a composition modulation region and a portion formed in the other portion. In these portions, the polarization direction is upward. Reference numeral 13 is a channel type optical waveguide, which is a fundamental wave, SH
G light is also confined and propagated in this portion. The incident fundamental wave 14 is polarized in the direction perpendicular to the crystal surface. Reference numeral 15 denotes SHG light generated in the optical waveguide layer portion, which is also polarized in a direction perpendicular to the crystal surface.

Next, the proton exchange treatment will be described.
By proton exchange by immersing the substrate or the like in an acidic solution, H ⁺ ions enter the substrate from the surface of the substrate and are exchanged with Li of the substrate to form a composition change layer. Particularly, the dissociation constant of phosphoric acid is higher than that of benzoic acid (C ₆ H ₅ COOH, melting point 121 ° C., boiling point 250 ° C.) by two to three orders of magnitude, and the concentration of H is high, so that the degree of composition change is large. Further, it is possible to perform high-temperature treatment with a liquid up to about 300 ° C., and the evaporation amount is extremely small, and controllability and workability are good. Further, since it is soluble in water, it is possible to wash the sample, the container and the jig. Pyrophosphoric acid (H ₄ P ₂ O ₇ , melting point 61 ° C., boiling point 300 ° C.) was used as phosphoric acid. In FIG. 14, LiTaO whose surface is the −Z plane
_{3 The} single crystal substrate 11 is placed on a platinum plate 62 which is a substrate holder, and a few drops of pyrophosphoric acid 63 are held on the substrate 11 by utilizing surface tension. 6 on the directional heating means heated to the proton exchange temperature, for example, the plate type heater 64.
The second substrate holder is placed, and this is heated in one direction, that is, the back surface, and proton exchange is performed for several minutes to several hours. Here, the directional heating means means a heating means capable of heating the substrate from one side thereof. After the proton exchange, the substrate is taken out and washed with water to remove 63 of pyrophosphoric acid. As a result, the proton exchange layer 65 is formed only on one surface of the substrate 11. All proton exchange was performed in the atmosphere. In addition, for selective proton exchange, Ta that does not melt in pyrophosphoric acid is used.
It is possible to make a lattice mask by applying a film to the substrate surface and performing photolithography. Here, the substrate holder 62 is made of platinum, which has good thermal conductivity and is not easily attacked by acid as a proton source, and its shape is plate-like or dish-like for protecting the heater when acid is spilled.

Next, the method of forming the domain inversion grating of the present invention will be described with reference to FIG. As shown in FIG.
An iTaO ₃ substrate 11 is prepared. The following steps shown in FIGS. 15B to 15D are operated in exactly the same manner as the steps shown in FIGS. 5B to 5D in the first embodiment. Then, as shown in FIG. 15E, the photoresist 72 is removed with acetone, and pyrophosphoric acid is used to remove the photoresist 72.
The proton exchange heat treatment shown in No. 4 is performed at 260 ° C. for 30 to 60
By doing so, the spike-shaped polarization inversion region 12 is formed at the same time as the proton exchange region 16 is formed. Figure 1
When the substrate holder 62 is placed on or removed from the heater 64 of No. 4, the substrate 11 undergoes a rapid thermal change. At this time, the temperature rise rate up to the proton exchange treatment temperature is 50 ° C./min or more, and the temperature decrease rate from the heat treatment temperature is 50 ° C./min or more, so that the spike-shaped polarization inversion region, that is, the polarization is generated outside the proton exchange region 16. The inversion grating 12 could be produced. Figure 15
As shown in (f), the Ta film 51 is etched with an aqueous solution of NaOH. As-is or re-heat treatment at temperature 400
Hold time at 0.5 ° C for 0.5 minutes, heat-up temperature up to 5
It is performed at 0 ° C / min or more, and the rate of temperature decrease from the heat treatment temperature is 50
By carrying out at a temperature of not less than ° C / min, it is possible to suppress the decrease of the nonlinear optical constant due to the proton exchange. Then, an optical waveguide is manufactured. The depth of the produced polarization inversion lattice is larger than the depth of the optical waveguide and the proton exchange layer formed on the substrate surface and smaller than the substrate thickness, and its width is almost equal to the width of the proton exchange pattern, and the range of the depth of the optical waveguide. Was able to realize a substantially rectangular polarization inversion grating. Finally, the SHG element is manufactured by optically polishing the end face of the waveguide. Further, the influence of the nonlinear optical constant due to the proton exchange may be prevented by removing the proton exchange layer region by polishing before forming the waveguide.

As described above, according to this embodiment, since the polarization inversion lattice 12 can be formed at the same time as the proton exchange, the subsequent heat treatment becomes unnecessary and the number of steps can be reduced. In addition, since the heating is performed in one direction, that is, from the back surface of the substrate during the proton exchange, the direction of thermal diffusion can be controlled and a good polarization inversion lattice can be formed, as compared with the case where the entire heating is performed in a heating furnace or the like. .. A polarization inversion grating was produced by the above-described production method, and an SHG element having an element length of 1 cm was produced. When a fundamental wave was incident on this element using the same titanium-sapphire laser as that used in Example 1, the same SHG light output and standardized SHG efficiency as in Example 1 could be obtained. The polarization inversion grating produced at this time had an ideal polarization inversion grating close to a rectangular shape as shown in FIG. 16 (a), and the tip had a spike shape.

Further, FIG. 16B shows that LiTaO ₃ was used as a substrate in the above operation, proton exchange using pyrophosphoric acid was carried out at 260 ° C. for 30 minutes, and then proton exchange heat treatment was carried out at 440 ° C. for 0.5 minutes. The crystal structure of the obtained product is shown. In addition, FIG. 16C shows that LiNbO ₃ was used as the substrate in the above operation, proton exchange using pyrophosphoric acid was performed at 230 ° C. for 16 minutes, and then heat treatment was performed for 7 hours.
The crystal structure after 0.5 minutes at 00 ° C is shown. According to these, although the thickness of the proton exchange layer is 1 μm or less, the domain-inverted region deeply extends from the proton exchange layer into the substrate and reaches a length of 40 μm or more. It turns out that the tip is thin and sharp and has a good spike shape.

Next, for comparison, another SHG element was produced in which only the proton exchange region was polarization-inverted. Observation of the cross section of the domain-inverted grating produced at this time revealed a semicircular shape as shown in FIG. Next, when the SHG light output was measured in the same manner as in the example, the SHG light output at this time was 100 nW.
And the normalized SHG efficiency was 4% / W · cm ² . From this, it was found that a highly efficient SHG element can be easily realized by producing a spike-shaped polarization inversion lattice in a region other than the proton exchange region during the proton exchange heat treatment. As is clear from the above description, according to this example, it is possible to realize an ideal rectangular polarization inversion lattice by producing a polarization inversion lattice in a region other than the proton exchange region during the proton exchange heat treatment, An SHG element capable of generating highly efficient SHG light can be easily realized.

(Embodiment 4) In Embodiment 3 above, the formation of the polarization inversion grating and the formation of the optical waveguide were carried out in separate steps. However, as shown below, this is performed only once by photolithography. It may be formed by. Hereinafter, the fourth embodiment of the present invention will be described in detail. FIG. 18 is a configuration and operation explanatory view showing an embodiment of an SHG element according to the present invention,
19 (a) to 19 (g) are views showing a manufacturing process of the SHG element. FIG. 20 is a photograph showing a polarization inversion lattice extended from the proton exchange region, and FIG. 21 is a photograph showing a semicircular polarization inversion lattice.

In FIG. 18, 11 is a LiTaO ₃ single crystal substrate whose surface is the −c plane, and the direction of spontaneous polarization is downward. 12 is a proton exchange region which is a composition modulation region 16
Inverted polarization formed at the same time, and the polarization direction is upward in these portions. 13 is a channel type optical waveguide, and the fundamental wave and SHG light are also confined and propagated in this portion. The incident fundamental wave 14 is polarized in the direction perpendicular to the crystal surface. Reference numeral 15 denotes SHG light generated in the optical waveguide layer portion, which is also polarized in a direction perpendicular to the crystal surface.

The next proton exchange treatment is carried out in exactly the same manner as in the case of the third embodiment described above, using pyrophosphoric acid or the like. The acid used for the proton exchange is phosphoric acid,
It can be easily analogized that the use of benzoic acid and stearic acid is also possible.

Next, the method of forming the polarization inversion grating and the optical waveguide of the present invention will be described with reference to FIG. The figure is a cross-sectional view of the optical waveguide and the polarization inversion grating portion. A LiTaO ₃ substrate 11 is prepared as shown in FIG. Below, FIG.
The steps shown in FIGS. 19B to 19D are the same as those shown in FIG.
The procedure is exactly the same as the steps shown in FIGS. 5 (b) to 5 (d) in Example 1 except that a photomask having a window width of 2 to 6 μm is used. Then, as shown in FIG. 19E, the photoresist 72 is removed with acetone, and the proton exchange heat treatment shown in FIG. 14 of the third embodiment is performed at 260 ° C. for 30 to 6 with pyrophosphoric acid.
By performing the process in 0 minutes, the proton-exchanged region or exchange layer 16 is formed, and at the same time, the spike-shaped polarization inversion layer 12 is formed. The substrate 11 undergoes a rapid thermal change when the substrate holder 62 is placed on or removed from the heater 64 shown in FIG. At this time, the temperature rising rate up to the proton exchange treatment temperature is 50 ° C /
The proton exchange region 16 and the spike-like domain-inverted region, that is, the domain-inverted lattice 12 can be produced by performing the heating for 5 minutes or more and the temperature decrease rate from the heat treatment temperature at 50 ° C./minute or more. As shown in FIG. 19F, the Ta film 51 is etched with an aqueous solution of NaOH. The heat treatment is performed at a temperature of 380 ° C. for a holding time of 5 minutes, the temperature rising rate up to the heat treatment temperature is 50 ° C./min or more, and the temperature lowering rate from the heat treatment temperature is 50 ° C./min or more to increase the refractive index of the proton exchange part. Higher to form an optical waveguide. Further, it is possible to suppress the decrease of the nonlinear optical constant due to the proton. If the heat treatment time is 20 minutes or more, the diffusion of protons becomes too large and the loss of the optical waveguide becomes large. The depth of the produced polarization inversion lattice is larger than the depth of the optical waveguide and the proton exchange layer formed on the surface of the substrate and smaller than the thickness of the substrate, and its width is almost equal to the width of the proton exchange pattern, and the range of the depth of the optical waveguide. Was able to realize a substantially rectangular polarization inversion grating. Finally, the SHG element is manufactured by optically polishing the end face of the waveguide.

A polarization inversion grating was produced by the above-described production method, and an SHG element having an element length of 1 cm was produced. When a fundamental wave was incident on this element using the same titanium-sapphire laser as used in Example 1, the same SH as in Example 1 was obtained.
It was possible to obtain G light output and standardized SHG efficiency. The polarization inversion grating produced at this time had an ideal polarization inversion grating close to a rectangular shape as shown in FIG. 20, and the tip had a spike shape. In particular, in FIG. 20, unlike in FIG. 6 of the first embodiment, it is found that the domain-inverted gratings are clearly separated from each other at the upper end portion without contacting each other and have a good structure.

Next, for comparison, another SHG element in which only the proton exchange region was polarization-inverted was prepared. Observation of the cross section of the domain-inverted grating produced at this time revealed a semicircular shape as shown in FIG. Next, when the SHG light output was measured in the same manner as in the example, the SHG light output at this time was 100 nW.
And the normalized SHG efficiency was 4% / W · cm ² . From this, it was found that the spike-shaped polarization inversion grating extending outside the proton exchange region during the proton exchange heat treatment and the waveguide can be easily manufactured in one photolithography process, and a highly efficient SHG element can be realized. It was Further, the proton exchange region serving as a sprout of the spike-shaped domain has a higher refractive index by heat treatment as shown in FIG. 22, and can be configured as an optical waveguide.
That is, in order to form a periodically domain-inverted region in a uniform composition region of a LiTaO ₃ or LiNbO ₃ substrate,
When a periodic lattice pattern is formed by proton exchange, a thermal history of an appropriate rate of temperature increase / decrease is applied to form a periodic spike-like domain-inverted region, and then reheat treatment is applied to make the proton-exchange region optically transparent. If the waveguide is used, a substantially rectangular polarization inversion grating can be formed in the optical waveguide.
By using this method, the polarization inversion grating and the optical waveguide can be produced by only one photolithography. In this case, as a method of the proton exchange treatment, for example, a plate type heater is used as shown in FIG.

As is clear from the above description, according to this example, an ideal rectangular domain-inverted lattice is formed by producing a spike-shaped domain-inverted lattice that extends outside the proton-exchange region during the proton-exchange heat treatment. Can be realized 1
It is possible to easily realize an SHG element capable of generating highly efficient SHG light in one photolithography process.

(Embodiment 5) SH is obtained by forming a spike-shaped polarization inversion grating as shown in each of the above embodiments.
The generation efficiency of G light can be increased, but the addition efficiency of SHG light can be further increased by adding Mg to the substrate material as described below.

The fifth embodiment of the present invention will be described in more detail below. A sample was prepared by the following manufacturing method. First, by the Czochralski method, about 5 kg of LiTaO ₃ was placed in a crucible made of iridium having a diameter of 100 mm and a depth of 120 mm.
Raw material powder (The raw material used for the growth is 4 N purity Li ₂ O, Ta
It is a mixture of ₂ O ₅ and MgO powder. ) Was melted by high frequency heating to form a melt, and then seeding was performed, and a 2-inch single crystal was grown in a predetermined orientation for about 3 days. The growth rate at this time is 1-2 mm /
h, the rotation speed is 10 to 20 rpm. Next, the crystal grown by the above method was subjected to single domainization treatment. For example, a Pt electrode plate is provided so as to face the crystal in the Z-axis direction through a conductive powder that is non-reactive with the crystal, and the crystal is inserted into an electric furnace to perform a single domainization process. Then, from each crystal, a square block with each edge parallel to the x-axis direction, the y-axis direction, and the z-axis direction and having a size of 10 × 10 × 10 mm ³ was cut out, and each surface thereof was mirror-polished. Alternatively, a 2-inch wafer was made from each crystal. In this way, a lithium tantalate single crystal was prepared and examined for light transmission characteristics.

An example of this result is shown in FIG. The SAW-grade lithium tantalate single crystal containing a large amount of transition metal impurities such as iron in the range of several to ten and several ppm has large light absorption in a wide wavelength range of 300 to 500 nm. The lithium tantalate single crystal (referred to as an optical grade) in which transition metal impurities such as iron, manganese, and chromium are reduced to 1 ppm or less has a smaller light absorption at 300 to 500 nm than a crystal having much iron, but 400 nm. 40 because there is absorption below
The light transmittance is insufficient as a substrate for generating blue SHG light of 0 nm or less. Further, in the crystal in which 1 mol% of MgO is added, the fundamental absorption edge moves to the short wavelength side by about 2 nm,
When the amount of addition was increased, the fundamental absorption edge became closer to the short wavelength side.
In particular, the remarkable effect of adding MgO is a wavelength of 280 to 40.
This is an improvement in the light transmittance at 0 nm, and if this substrate is used, the wavelength of the basic light is 800 nm or less, for example, 78 nm.
390nm emission SHG using 0nm semiconductor laser
The device becomes feasible. If MgO is added in an amount of about 5 mol%, 700 nm light is used as the basic light and 350
It is also possible to emit light in the vicinity of nm, expanding its application range.

Therefore, a polarization inversion lattice was formed by the method shown in FIG. 24 using a lithium tantalate single crystal whose optical transparency was improved by adding MgO and an undoped lithium tantalate single crystal as substrates. The method of manufacturing the SHG substrate using the LT substrate to which MgO is added uses the same steps as those used in Example 2 in FIGS. 10A to 10G. The depth of the polarization inversion grating thus formed was larger than the depth of the optical waveguide formed on the surface of the substrate and smaller than the thickness of the substrate. The width was almost equal to the width of the proton exchange pattern. After the polarization inversion grating 12 was formed, the proton exchange layer on the substrate surface was removed by polishing, and an optical waveguide was formed on the substrate surface by the usual proton exchange method. Finally, the SHG element is manufactured by optically polishing the end face of the waveguide.

An optical waveguide was prepared in the above-mentioned polarization inversion grating to prepare an SHG device having a device length of 1 cm. When a titanium-sapphire laser was used as a light source of the fundamental wave and a fundamental wave having a wavelength of 820 nm was made incident on the produced SHG element, 410 nm blue SHG was obtained. At this time, when the polarization inversion grating has a rectangular cross section and the polarization inversion region has a depth larger than the width in the periodic direction, the SHG light output is 15
High output SHG light at mW is obtained and power density 165
A stable output was obtained at KW / cm ² . When the output of SHG light was evaluated using a semiconductor laser with a wavelength of 780 nm as a fundamental wave by changing the period of the polarization inversion grating, a single crystal of lithium tantalate containing MgO with improved light transmittance at a wavelength of 280 to 400 nm was evaluated. The device used as the substrate provided an output of SHG light of about 1.5 mW. on the other hand,
An element using a non-doped lithium tantalate single crystal as a substrate could only obtain an SHG light output of 0.7 mW because the substrate has a large light absorption.

Depending on the heat treatment time, when the cross section of the manufactured domain-inverted lattice is observed, it may have a rectangular shape. When the depth of the domain-inverted region such as the rectangular shape is larger than the width in the periodic direction, the shape ratio of the domain-inverted portion to the non-inverted portion with respect to the incident direction of light becomes 1: 1. Become. On the other hand, when the manufacturing method of polarization inversion, such as the heat treatment time, is changed, the cross section of the manufactured polarization inversion lattice may become semicircular when observed. When the depth of the domain-inverted region such as a semi-circular shape is smaller than the width in the periodic direction, the shape ratio of the domain-inverted portion and the non-inverted portion with respect to the incident direction of light deviates from perfect 1: 1. Therefore, sufficient SHG light cannot be emitted.

An optical waveguide was formed in the above-described polarization inversion lattice of the lithium tantalate single crystal to which MgO was added, and an SHG element having an element length of 1 cm was prepared. When a titanium-sapphire laser was used as a light source of the fundamental wave and a fundamental wave having a wavelength of 820 nm was incident on the manufactured SHG element, 410
A blue SHG light of nm was obtained. At this time, when the cross section of the polarization inversion grating is rectangular and the depth of the polarization inversion region is larger than the width in the periodic direction, the SHG light output is 15 mW, and the high output SHG light is obtained. 165 kW / c
A stable output was obtained at m ² .

On the other hand, when the cross section of the domain inversion grating is semicircular and the depth of the domain inversion region is smaller than the width in the periodic direction,
9 mW SHG light was obtained. As a result, a polarization inversion lattice is formed in the lithium tantalate single crystal, and preferably, the cross section has a rectangular shape, and when the depth of the polarization inversion region is larger than the width in the periodic direction, the incidence of light is increased. It was found that the shape ratio of the domain-inverted part to the non-inverted part with respect to the direction was 1: 1 and it was useful for a highly efficient SHG element. In particular, by adding MgO to the substrate material, the basic absorption edge can be shifted to the edge wavelength side, a highly efficient SHG element can be realized, and its application range can be expanded.

An optical modulator was manufactured by using the crystal of the present invention whose optical damage strength was improved by adding MgO as a substrate and making light emitted from a laser light source incident on an electro-optic crystal to change the phase of the light. Was confirmed to be stable. According to the present invention, a lithium tantalate single crystal having excellent light transmittance in a short wavelength band of 400 nm or less can be obtained for the first time. As a result, a lithium tantalate single crystal can be used as a substrate for an optical element that uses short-wavelength light of 400 nm or less, and the stability and high output of an SHG element can be improved by utilizing the large nonlinear optical constant of the lithium tantalate single crystal. The characteristics can be improved.

Further, preferably, the LT single crystal containing 1 mol% or more of MgO has a basic absorption edge shifted to the short wavelength side as compared with a non-added crystal, the color of the crystal disappears, and the color of the crystal changes to colorless and transparent. did. Further, the obtained lithium tantalate single crystal having excellent light transmittance was processed into a wafer and used as a substrate of an optical element, and the polarization direction of the lithium tantalate single crystal was periodically inverted. By creating a structure in which the depth is larger than the width in the periodic direction, SHG light can be generated with the original efficiency of the SHG element having an ideal polarization inversion grating with a rectangular cross section.

With the above structure, the light transmission characteristics of the crystal can be greatly improved, and various optical elements such as a wavelength conversion element, an optical modulator and an optical deflector which use short wavelength light can be stably operated. I was able to do it. There is no limitation on the means for growing a single crystal in carrying out the present invention, and it is generally the Czochralski method, and in some cases, the Bridgman method, the floating zone method or the fiber pedestal method can be used for the growth. is there.

Li ₂ CO ₃ and Ta ₂ O used as raw materials
The compounding ratio of ₅ is desirable from the viewpoint of single crystal growth because it is easy to obtain a high quality single crystal with a normal congruent composition, but it is necessary to change the refractive index of the single crystal substrate depending on the device application. Sometimes. In such a case Li
_A desired single crystal substrate can be obtained by changing the compounding ratio of ₂ CO ₃ and Ta ₂ O ₅ . Although it is desirable to add the element at the time of mixing in order to make the raw material uniform, it may be added to the raw material melt.

[0054]

As described above, according to the present invention, the following excellent operational effects can be exhibited. According to the present invention, an ideal rectangular polarization reversal grating is realized by forming a polarization reversal region having a sharp tip and forming a polarization reversal grating having a depth / width ratio of more than 1. And an SHG element capable of generating highly efficient SHG light can be realized. Further, according to the present invention, it is possible to realize an ideal rectangular polarization inversion lattice by producing a polarization inversion lattice extended from the proton exchange region (polarization bud region), and to achieve high efficiency. An SHG element capable of generating SHG light can be realized. Further, according to the present invention, it is possible to realize an ideal rectangular polarization inversion lattice by producing a polarization inversion lattice in a region other than the proton exchange region during the proton exchange heat treatment,
An SHG element capable of generating highly efficient SHG light can be easily realized. Furthermore, according to the present invention, it is possible to realize an ideal rectangular polarization inversion lattice by producing a polarization inversion lattice with a sharp tip extending outside the proton exchange region during the proton exchange heat treatment. It is possible to easily realize the SHG element capable of generating highly efficient SHG light in the photolithography process. Further, the polarization inversion lattice and the waveguide extending outside the proton exchange region during the proton exchange heat treatment can be manufactured by one photolithography process. Further, according to the present invention, it was possible to obtain a lithium tantalate single crystal having excellent light transmittance in a short wavelength band of 400 nm or less. As a result, a lithium tantalate single crystal can be used as a substrate for an optical element that uses short-wavelength light of 400 nm or less, and the stability and high output of the SHG element can be improved by utilizing the large nonlinear optical coefficient of the lithium tantalate single crystal. The characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a structural diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional SHG element using Cherenkov radiation.

FIG. 3 is a conventional SHG using a triangular polarization inversion grating.
It is a figure which shows an element.

FIG. 4 is a diagram showing a conventional SHG element using a semicircular polarization inversion grating.

5 (a) to 5 (h) are diagrams showing a method for manufacturing a spike-shaped polarization inversion grating according to the present invention.

FIG. 6 is a photograph showing a crystal structure of a spike-shaped polarization inversion lattice.

FIG. 7 is a photograph showing a crystal structure of a spike-shaped polarization inversion lattice.

FIG. 8 is a photograph showing a crystal structure of a semicircular polarization inversion lattice.

FIG. 9 is a structural diagram for explaining an embodiment of the present invention.

10 (a) to 10 (g) are diagrams showing a method of manufacturing a spike-shaped polarization inversion grating according to the present invention.

FIG. 11 is a photograph showing a crystal structure of a spike-shaped polarization inversion lattice outside the proton exchange region.

FIG. 12 is a photograph showing a crystal structure of a semicircular polarization inversion lattice.

FIG. 13 is a diagram showing a conventional proton exchange method.

FIG. 14 is a diagram showing a proton exchange heat treatment according to the present invention.

15 (a) to 15 (g) are diagrams showing a method for manufacturing a spike-shaped polarization inversion grating according to the present invention.

FIG. 16 is a photograph showing a fine pattern in which a spike-shaped polarization inversion lattice outside the proton exchange region is formed on the substrate.

FIG. 17 is a photograph showing a fine pattern in which a semicircular domain-inverted grating is formed on a substrate.

FIG. 18 is a structural diagram for explaining an example of the present invention.

19 (a) to 19 (g) are diagrams showing a method of manufacturing a spike-shaped polarization inversion grating and an optical waveguide according to the present invention, respectively.

FIG. 20 is a photograph showing a fine pattern formed on a substrate showing a proton exchange region and a spike-shaped polarization inversion lattice.

FIG. 21 is a photograph showing a fine pattern formed on a substrate showing a semicircular polarization inversion grating.

FIG. 22 is a diagram showing a refractive index of a proton exchange waveguide with respect to heat treatment time.

FIG. 23 is a diagram showing the light transmission characteristics of various lithium tantalate single crystals and lithium niobate single crystals.

[Explanation of symbols]

11,511 Substrate (LiTaO ₃ ) 12 Spike-shaped polarization inversion region 13 Channel type optical waveguide 14 Fundamental incident light 15 SHG output light 21 Substrate (LiNbO ₃ ) 22 Cherenkov SHG light 31 Triangular polarization inversion region 41 Semicircular polarization inversion Area 51 Ta film 52 Photoresist 53 Proton exchange area 54 Polishing removal area 62 Platinum substrate holder 63 Pyrophosphoric acid 64 Plate type heater 65 Proton exchange layer 71 Ta film 72 Photoresist 351 Glass container 352 Substrate 353 Acid 354 Thermostat

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Furukawa 5200 Mikkaji, Kumagaya-shi, Saitama Hitachi Metals Co., Ltd. Magnetic Materials Research Institute (72) Kohei Ito 5200 Mikkaji, Kumagaya, Saitama Hitachi Metals Co., Ltd. In-house (72) Inventor Masazumi Sato 5200 Mikkaji, Kumagaya-shi, Saitama Hitachi Metals Co., Ltd.Magnetic Materials Research Laboratories (72) Inventor Kazutomi Kawamoto 292 Yoshida-cho, Totsuka-ku, Yokohama-shi Kanagawa ) Inventor Kenji Itoh, 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd.

Claims (3)

[Claims] 1. A polarization bud region periodically formed on a substrate, and a polarization inversion region extending from the bud region and having a sharp tip, the polarization bud region and the polarization. The polarization inversion lattice formed by the inversion region has a depth / width ratio of 1
A second harmonic generation element characterized by exceeding. 2. A polarization inversion region extending from a polarization bud region periodically formed on a substrate and having a sharp tip, and a conductor formed on the substrate after removing the polarization bud region. A second harmonic generation element having a waveguide, wherein a depth / width ratio of a polarization inversion grating formed by the polarization inversion region exceeds 1. 3. A method for manufacturing a second harmonic generating element, wherein periodically formed polarization bud regions are formed on a substrate, and then polarization inversion regions are extended from the polarization bud regions to form sharp edges. And a depth / width ratio of a domain-inverted grating formed by the polarization bud region and the domain-inverted region is greater than 1, a method of manufacturing a second harmonic generation element.