JP2003270688A - Wavelength conversion element and periodical polarization inversion structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength conversion element which is provided with a periodical polarization inversion structure of higher resolution while suppressing reduction of the conversion efficiency. <P>SOLUTION: The wavelength conversion element is provided with an optical waveguide 15A and a periodical polarization inversion structure 20 formed in the optical waveguide 15A, and the periodical polarization inversion structure 20 has a polarization inversion part 22 and a polarization non-inversion part 24 alternately arranged, and each polarization inversion part 22 includes a first polarization inversion part 22A and a second polarization inversion part 22B having different design widths. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to formation of a periodically poled structure that can be used for manufacturing an optical waveguide device suitable for a second harmonic generation device of a quasi phase matching system.

[0002]

2. Description of the Related Art In general optical information processing technology, in order to realize high-density optical recording, a blue light laser capable of stably oscillating blue light having a wavelength of about 400 to 430 nm with an output of 30 mW or more is required. There is competition for development. As a blue light source, an optical waveguide type wavelength conversion element is expected, which is a combination of a laser that oscillates red light as a fundamental wave and a second harmonic generation element in which a QPM grading is formed.

In the wavelength conversion element, QPM grading is realized by a periodically poled structure having a predetermined period, and a so-called voltage application method is known as a method of forming the periodically poled structure. FIG. 9 is a perspective view schematically showing a process of forming the periodically poled structure 20 in the ferroelectric single crystal substrate 1 by the voltage application method.

In this method, an off-cut substrate 1 made of a ferroelectric single crystal is used. Since the direction B of the ferroelectric single crystal forming this substrate is inclined at a predetermined angle, for example, 5 ° with respect to the front surface 1A and the back surface 1B, this substrate 1 is called an offcut substrate.

A first electrode 30 and a third electrode 6 are formed on the front surface 1A of the substrate 1, and a second electrode (uniform electrode) 5 is formed on the back surface 1B. The first electrode 30 is a comb-shaped electrode composed of a plurality of elongated electrode pieces 34 arranged periodically and an elongated feeding electrode 32 connecting the many electrode pieces 34.
The third electrode 6 is composed of an elongated counter electrode piece 6A,
The counter electrode piece 6A is provided so as to face the tip of the electrode piece 34.

First, the entire substrate 1 is polarized in the direction B, that is, the non-polarization inversion direction 4B. Then, for example, when a voltage of V1 is applied between the first electrode 30 and the third electrode 6 and a voltage of V2 is applied between the first electrode 30 and the second electrode 5, the polarization inversion part 22 gradually progresses from the tip of each electrode piece 34 in parallel with the direction B. The polarization inversion direction 4A, which is the polarization direction of the polarization inversion part 22, is the non-polarization inversion direction 4A.
It is the opposite of B. It should be noted that a non-polarization inversion portion 24 that is not polarization-inverted is formed at a position that does not correspond to the electrode piece 34, that is, between the adjacent polarization inversion portions 22. In this way, the periodic domain-inverted structure 20 in which the domain-inverted portions 22 and the non-domain-inverted portions 24 are alternately arranged is formed.

[0007]

A periodically poled structure 20
Since the cycle of is determined by the electrode piece 34 of the first electrode 30, it is necessary to improve the cycle resolution of the electrode piece 34 in order to improve the resolution of the polarization inversion cycle. Since each electrode piece 34 is formed by the patterning of the mask (reticle) manufacturing apparatus, the resolution of the period of the electrode piece 34 is determined by the patterning resolution. That is, the resolution of the periodically poled structure 20 is determined by the patterning resolution of the mask manufacturing apparatus.

However, if an attempt is made to improve the patterning resolution of the mask manufacturing apparatus, the cost will increase significantly. As another method, if a stepper exposure apparatus is used, it is possible to manufacture the first electrode 30 having the electrode piece 34 having a higher resolution than in the case of using a mask manufacturing apparatus, but the cost is also significantly increased. Resulting in.

An object of the present invention is to form a periodically poled structure having a high resolution and a low cost while suppressing a decrease in conversion efficiency.

[0010]

[Means for Solving the Problems] In order to solve the above-mentioned object,
The present invention is a wavelength conversion element comprising an optical waveguide and a periodically domain-inverted structure formed in the optical waveguide, wherein the periodically domain-inverted structure is composed of alternately arranged domain-inverted regions and non-polarized regions. A polarization inversion part, and the polarization inversion part includes a first polarization inversion part and a second polarization inversion part having different design widths.

Further, according to the present invention, the first electrode is arranged on one surface of the substrate made of a ferroelectric material, and the second electrode is arranged on the substrate at a position facing the first electrode. Then, a method of forming a periodic domain inversion structure by applying a voltage between the first electrode and the second electrode, wherein the first electrode is one electrode piece having a different design width. And having the other electrode piece.

This makes it possible to form a periodic domain-inverted structure with low cost and higher resolution, while suppressing a decrease in conversion efficiency. The design width means the width of a mask or reticle for forming the polarization inversion portion and the electrode piece. The accuracy of the width of the mask or reticle depends on the type of exposure apparatus.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present embodiment will be described below with reference to the drawings. FIG. 1 is a diagram showing a periodically poled structure 20 according to an embodiment of the present invention. The periodically poled structure 20 is provided on the substrate 1. The substrate 1 is composed of a ferroelectric single crystal. The substrate 1 is adhered to the fixing substrate 7 via the bonding layer 8.

On one surface 1B of the substrate 1, flat plate portions 16 and 1 are provided.
7 and a ridge type optical waveguide element 15 are formed.
16A of the flat plate portion 16 and 17A of the flat plate portion 17 are processed surfaces. The optical waveguide element 15 is provided with an optical waveguide 15A, and the optical waveguide 15A is provided with a periodic domain-inverted structure 20 in which domain-inverted portions 22 and non-domain-inverted portions 24 are alternately arranged.

The polarization inversion section 22 is polarized in the polarization inversion direction 4A, and the non-polarization inversion section 24 is in the non-polarization inversion direction 4B.
Is polarized to. The plurality of polarization inversion parts 22 and the non-polarization inversion parts 24 are formed in parallel with each other.

Further, the polarization inversion section 22 has a first polarization inversion section 22A and a second polarization inversion section 22B, and the first polarization inversion section 22A and the second polarization inversion section 22B are arranged alternately. Has been done. The first domain-inverted portion 22A has a narrower design width than the second domain-inverted portion 22B. Here, the design width is a length in a direction perpendicular to the polarization inversion direction 4A.

FIG. 2 shows the periodically poled structure 20 shown in FIG.
First polarization inversion part 22A and second polarization inversion part 22
It is an enlarged view of the vicinity of B. As shown in FIG. 2, the periodic domain-inverted structure 20 includes a first domain-inverted part 22A, a first non-domain-inverted part 24A, a second domain-inverted part 22B, and a second non-domain-inverted part 24B in this order. It has an array of repeating units. Here, the design width of the first polarization inversion section 22A is A, the design width of the second polarization inversion section 22B is (A + C), and the first non-polarization inversion section 24A and the second non-polarization inversion section 24.
The design widths of B are both B. That is, the second domain-inverted portion 22B has a wider design width by C than the first domain-inverted portion 22A.

The period of the periodically poled structure 20 will be described with reference to FIG. One period of the periodic domain-inverted structure 20 is determined by the arrangement interval of the domain-inverted portions 22. Here, the arrangement interval is the length from the center position of the design width of the polarization inversion portion 22 to the center position of the design width of the polarization inversion portion 22 next arranged via the adjacent non-polarization inversion portion 24. .

The periodically poled structure 20 according to the present embodiment.
The first interval 28A from the first polarization reversal portion 22A to the second polarization reversal portion 22B in (1) is (A / 2 + B + (A + C) / 2) = A + B + C / 2. Similarly, the second interval 28B from the second polarization inversion portion 22B to the first polarization inversion portion 22A is ((A + C) / 2 + B + A / 2) = A + B + C / 2.

As described above, in the periodic domain-inverted structure 20 according to this embodiment, the first domain-inverted portions 22A and the second domain-inverted portions 22B having different design widths are arranged. Polarization inversion part 22A and second polarization inversion part 22B
Is constant (A + B + C / 2). That is,
The periodically poled structure 20 of the present embodiment has a period (A + B + C / 2) in design.

The period of the periodically poled structure 20 is (A
+ B + C / 2), for example, the first polarization inversion unit 2
2A, the second polarization inversion part 22B, the first non-polarization inversion part 2
When the resolutions of 4A and the second non-polarization inversion part 24B are both x, and C is an odd multiple of x, the resolution of the period (A + B + C / 2) of the periodic domain inversion structure 20 is x / 2. Becomes As described above, the periodic domain-inverted structure 20 according to the present embodiment can have a period with a resolution higher than that of the first domain-inverted portion 22A and the second domain-inverted portion 22B.

For example, A = 0.3 μm and B = 2.5 μm
And C = 0.1 μm, the periodically poled structure 2
The cycle of 0 (A + B + C / 2) is 2.85 μm.
In this way, the first polarization inversion unit 2 having a resolution of 0.1 μm
In the periodic domain-inverted structure 20 in which 2A and the second domain-inverted portions 22B are arranged, a period having a resolution of 0.05 μm can be formed.

The method of forming the periodically poled structure 20 in this embodiment will be described below. Periodically poled structure 20
Is formed on the substrate 1 made of a ferroelectric single crystal by the voltage application method described in FIG.

FIG. 3 is a diagram for explaining a method of forming the periodically poled structure 20 in the present embodiment. First electrode 30 used for forming the periodically poled structure 20
Has one electrode piece 34A having a different design width, the other electrode piece 34B, and the power feeding electrode 32 connecting the plurality of one electrode pieces 34A and the plurality of other electrode pieces 34B, respectively. One electrode piece 34A and the other electrode piece 34B
Are alternately arranged in a direction perpendicular to the polarization inversion direction 4A.

For example, when a voltage of V1 is applied between the first electrode 30 and the third electrode 6 and a voltage of V2 is applied between the first electrode 30 and the second electrode 5, The polarization inversion part 22A and the second polarization inversion part 22B gradually progress in the polarization inversion direction 4A from the tips of the one electrode piece 34A and the other electrode piece 34B, respectively. Thereby, the periodic domain-inverted structure 20 in which the domain-inverted portions 22 and the non-domain-inverted portions 24 are alternately arranged is formed. In this periodic domain-inverted structure 20, first domain-inverted portions 22A and second domain-inverted portions 22B are further arranged alternately.

FIG. 4 is an enlarged view of the vicinity of one electrode piece 34A and the other electrode piece 34B of the first electrode 30 shown in FIG. As shown in FIG. 4, in the first electrode 30, one electrode piece 34A and the other electrode piece 34B are alternately connected to the power feeding electrode 32. Further, between the one electrode piece 34A and the other electrode piece 34B, a first spacing portion 38A and a second spacing portion 38B that space them are alternately provided. That is, in the first electrode 30, an arrangement in which one electrode piece 34A, the first spacing portion 38A, the other electrode piece 34B, and the second spacing portion 38B are sequentially set as a repeating unit is repeated. .

Here, the design width of the one electrode piece 34A is A, the design width of the other electrode piece 34B is (A + C), and the design widths of the first spacing portion 38A and the second spacing portion 38B are B. . That is, the other electrode piece 34B has a wider design width by C than the one electrode piece 34A. Thus, one electrode piece 34A and the other electrode piece 34 having different design widths are provided.
By using the first electrode 30 having B, the periodic domain-inverted structure 20 having the first domain-inverted part 22A and the second domain-inverted part 22B having different design widths can be formed.

Since the first electrode 30 is formed by patterning using a mask, the design width A of the one electrode piece 34A of the first electrode 30 and the first spacing portion 38A.
The resolution of the design width B of the second spacing portion 38B and the design width (B + C) of the other electrode piece 34B are both determined by the patterning resolution.

That is, when the resolution of the mask is x,
When C is an odd multiple of x, the resolution of one electrode piece 34A and the other electrode piece 34B of the first electrode 30 is x / 2. Therefore, by using the first electrode 30, it is expected that the periodic domain-inverted structure 20 having the resolution of x / 2 is formed. Therefore, for example, the resolution of the mask in the mask manufacturing apparatus is 0.1 μm.
When the difference C between the one electrode piece 34A and the other electrode piece 34B is an odd multiple of 0.1 μm, the periodic domain-inverted structure 20 having a resolution of 0.05 μm can be formed. . Further, for example, the resolution of the mask is 0.01
μm, one electrode piece 34A and the other electrode piece 34A
When the difference C from B is an odd multiple of 0.01 μm,
The periodically poled structure 20 having a resolution of 0.005 μm can be formed. As described above, by using the first electrode 30 having the one electrode piece 34A and the other electrode piece 34B such that the difference C is an odd multiple of the mask resolution, the cycle of half the resolution of the mask is obtained. The domain-inverted structure 20 can be formed.

FIG. 5 is an enlarged view of a main part of the first electrode 40 having a shape different from that of the first electrode 30 described in FIGS. 3 and 4. In the first electrode 40 shown in FIG. 5, the one electrode piece 44A and the other electrode piece 44B have the same design width, and the first separation provided between the one electrode piece 44A and the other electrode piece 44B. The design widths of the portion 48A and the second spacing portion 48B are different. The design width of the one electrode piece 44A and the other electrode piece 44B is A, the design width of the first spacing portion 48A is B, and the design width of the second spacing portion 48B is (B + C). That is, the second separating portion 48B is the first separating portion 4
Compared to 8A, the design width is wider by C.

The first spacing 47A between the electrode pieces 44 is (A / 2 + B + A / 2) = A + B. Further, the second interval 47B is ((A / 2 + (B + C) + A / 2) = A + B + C.) Thus, the first interval 47A and the second interval 4
7B is different, the average of the two intervals is (A + B
+ C / 2), which is equal to that of the first electrode 30 in the present embodiment. Therefore, also in the first electrode 40, similarly to the first electrode 30, it is possible to form a periodic domain-inverted structure having a cycle having a resolution half that of patterning in the mask manufacturing apparatus.

Periodic polarization inversion structure 2 in the present embodiment
0 has higher period accuracy than the periodically poled structure formed by using the first electrode 40 shown in FIG.
It is possible to obtain a QPM grading with a good y ratio and form a second harmonic generating element with an output high of several%. This is probably because the width of each electrode piece actually formed is a value slightly deviated from the designed value. For example, when the difference between the design width of one electrode piece and the design width of the other electrode piece is set to 0.1 μm, if this design value is faithfully transferred to the electrode piece, the conversion efficiency is considerably reduced. Should be. However, the difference in the width of the electrode pieces actually formed is
It is considerably smaller than 0.1 μm, and as a result, it is considered that the reduction in conversion efficiency is suppressed.

In the first electrode, it suffices that one electrode piece and the other electrode piece are arranged as a repeating unit with a set in which m pieces and n pieces are arranged, respectively. That is, it suffices that one electrode piece is arranged in m number and then the other electrode piece is arranged in n number, and m and n are limited to the present embodiment (m = 1, n = 1). Not done. In addition,
In this case as well, the design width of the spacing portion is constant.

Further, in the periodic domain-inverted structure, it is sufficient that the first domain-inverted portions and the second domain-inverted portions are arrayed as a repeating unit in which m and n arrays are arrayed. That is, it is sufficient that m first polarization inversion parts are arranged and then n second polarization inversion parts are arranged. For m and n, this embodiment (m = 1, n =
It is not limited to 1). Also in this case, the design width of the non-polarization inversion part is constant.

From the point of obtaining high output, m and n
Is preferably 10 or less, and m + n is preferably 15 or less.

FIG. 6 shows the substrate 1 on which the periodically poled structure 20 is formed by the voltage application process shown in FIG. As shown in FIG. 6, the optical waveguide 15A can be formed in the substrate 1 along the periodically poled structure 20. The forming method is not particularly limited, but a titanium diffusion method and a proton exchange method are preferable.

In another method, as shown in FIG.
The fixing substrate 7 is bonded to the front surface 1A of the substrate 1 via the bonding layer 8. Preferably, before this, the first electrode 30, the second electrode 5, and the third electrode 6 are removed from the substrate 1. At the stage of FIG. 7, the periodically poled structure 20 is formed near the surface 1A of the substrate 1.

The next step will be described with reference to FIG. After the periodic domain inversion structure 20 is formed, the back surface 1B of the substrate 1 is formed.
The side is ground to thin the substrate 1. At this stage, it is difficult to make the substrate 1 thin enough to confine light in the thickness direction. Therefore, the substrate 1 is processed and removed while leaving the ridge type optical waveguide 15A shown in FIG. That is, the edges 15B at both ends of the optical waveguide 15A shown in FIG.
To the edge 15C, the removed portions 18B and 18C at both ends thereof are removed. At this stage, the very thin flat plate portions 16 and 17 shown in FIG. 1 are left on the substrate 1 after the removal portions 18B and 18C are removed. During this processing, the thickness of the optical waveguide 15A is adjusted. Such processing can be performed by, for example, a dicing processing apparatus or a laser processing apparatus, but mechanical processing such as dicing processing is preferable.

In the above embodiment, the substrate 1 is bonded to the fixing substrate 7 by the bonding layer 8. In this case, the refractive index of the bonding layer 8 is preferably lower than that of the substrate 1, and the bonding layer 8 is preferably amorphous. The difference between the refractive index of the bonding layer 8 and the refractive index of the substrate 1 is preferably 5% or more, more preferably 10% or more.

The material of the bonding layer 8 is preferably organic resin or glass (particularly preferably low melting glass). Examples of the organic resin include acrylic resin, epoxy resin, silicone resin and the like. As the glass, a low melting point glass containing silicon oxide as a main component is preferable.

The type of the ferroelectric single crystal is not limited. However, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), lithium niobate-
Lithium tantalate solid solution and K ₃ Li ₂ Nb ₅ O ₁₅ single crystals are particularly preferable.

In order to further improve the optical damage resistance of the three-dimensional optical waveguide in the ferroelectric single crystal, magnesium (M
g), one or more metal elements selected from the group consisting of zinc (Zn), scandium (Sc) and indium (In) can be contained, and magnesium is particularly preferable.

From the viewpoint that the polarization inversion characteristics (conditions) are clear, a lithium niobate single crystal, a lithium niobate-lithium tantalate solid solution single crystal, or a material obtained by adding magnesium to these is particularly preferable.

A rare earth element can be contained as a doping component in the ferroelectric single crystal. This rare earth element acts as an additive element for laser oscillation. The rare earth elements include Nd, Er, Tm, Ho,
Dy and Pr are preferred.

As a material for forming the mask pattern for forming the periodically poled structure 20, resist and Si are used.
The O _2, Ta and the like. A photolithography method can be exemplified as a method for forming the mask pattern.

As the material of the electrode used in the voltage application method, Al, Au, Ag, Cr, Cu, Ni, Ni-Cr, Pd and Ta are preferable.

The material of the fixing substrate 7 is not particularly limited as long as it has a predetermined structural strength. However, it is preferable that physical properties such as a thermal expansion coefficient are close to those of the optical waveguide, such as lithium niobate (LiNbO ₃ ), lithium tantalate (LiT).
_aO-3), lithium niobate - lithium tantalate solid _solution, each single crystal of K ₃ Li ₂ Nb _{5 O 15} particularly preferred.

When the element of the present invention is used as a second harmonic generator, the harmonic wavelength is 330-1600n.
m is preferred, and 400-430 nm is particularly preferred.

In each of the above examples, the ferroelectric single crystal substrate is, for example, a 5 ° off-cut substrate, but the off-cut angle is not particularly limited. Particularly preferably, the off-cut angle is 1 ° or more, or 20 ° or less.

As the substrate 1, so-called X-cut substrate, Y-cut substrate and Z-cut substrate can be used. X
When a cut substrate or a Y-cut substrate is used, the second electrode may be provided on one surface 1A instead of being provided on the back surface 1B, and a voltage may be applied between the first electrode and the second electrode. it can. In this case, the third electrode may be omitted, but may be left as a floating electrode. When using a Z-cut substrate, a second electrode can be provided on the back surface 1B and a voltage can be applied between the first electrode and the second electrode. In this case, the third electrode is not always necessary, but it may be left as a floating electrode.

[0051]

EXAMPLES The device of FIG. 1 was formed according to the process described with reference to FIGS. 3, 4 and 6-8.
Specifically, a substrate 1 having a diameter of 3 inches and a thickness of 0.5 mm and made of 5% magnesium-doped lithium niobate single crystal was prepared. Substrate 1 is a 5 ° off-cut Y substrate. On this substrate 1, a first electrode 30, a second electrode 5, and a third electrode 6 made of metal tantalum were formed by photolithography. Here, on the reticle, one electrode piece 3 of the first electrode 30 is used.
The design width of 4A was 0.3 μm, and the design width of the other electrode piece 34B was 0.4 μm. As a result, the actual widths of the one electrode piece 34A and the other electrode piece 34B in the first electrode 30 are 0.411 μm and 0.
It was 453 μm. Further, the actual width of the separating portion 38 is
The average was 2.389 μm. The distance between the electrode piece 34 and the third electrode 6 was 300 μm.

Although it depends on the performance of the stepper exposure apparatus used, the designed widths of the two electrode pieces 34A and 34B of 0.3 μm and 0.4 μm are different from each other when the exposure apparatus used is disassembled. The difference between the widths of the electrode pieces on the reticle is 0.1 μm, while the difference between the electrode pieces actually formed is about 0.0 μm as shown above.
It is as small as 4 μm. If the width of the electrode piece is formed according to the design of the reticle, the conversion efficiency of the SHG output will be reduced, but since the difference in the width of the actually formed electrode piece is small, it will be evenly spaced from the electrode piece. It was possible to make the reduction in conversion efficiency extremely small as compared with the case where the width of the part is configured. Further, when the voltage application described below was performed, the difference in the width of polarization inversion formed at the electrode pieces 34A and 34B was further reduced, and the reduction in conversion efficiency could be almost eliminated. However, the electrode pieces 34A and 3
When the design width of 4B is 1 μm or more, the electrode piece is formed with the width designed by the reticle.

A pulsed voltage of 2.0 kV (pulse width 20 msec, 25 Hz, pulse number 4 times, upper limit value of applied current: 2 mA) was generated from the power supply to form the periodically poled structure 20. When the voltage is applied about 4 times, the depth from the tip of each electrode piece 34 is lowered vertically downward from the surface of the substrate 1.
The polarization inversion of 2.5 μm was formed periodically.

Next, the substrate 1 was cut and polished along a plane perpendicular to the polarization direction B of the substrate, the cross section was etched using a mixed solution of hydrofluoric acid and nitric acid, and a photograph of the cross section was taken. A periodic domain-inverted structure having the domain-inverted pattern shown in FIG. 1 was formed.

Using this device, a titanium-sapphire laser was used to generate the second harmonic. Phase matching wavelength is 850nm, second harmonic wavelength is 425nm
Met. The SHG conversion efficiency was about 830% / W. When the incident output of the fundamental wave was 100 mW, a 30 mW second harmonic output was obtained, and no characteristic deterioration due to optical damage was observed in the second harmonic.

[0056]

As described above, according to the present invention, it is possible to form a periodic domain inversion structure having a period of higher resolution while suppressing a decrease in conversion efficiency.

[Brief description of drawings]

FIG. 1 is a periodically poled structure 2 according to an embodiment of the present invention.
It is a figure which shows 0.

FIG. 2 is an enlarged view of a first domain-inverted portion 22A and a second domain-inverted portion 22B of the periodic domain-inverted structure 20 shown in FIG.

FIG. 3 is a diagram for explaining a method of forming the periodically poled structure 20.

4 is one electrode piece 34 of the first electrode 30 shown in FIG.
It is an enlarged view of A and the other electrode piece 34B vicinity.

5 is an enlarged view of a main part of a first electrode 40. FIG.

FIG. 6 is a diagram showing a state in which the second electrode 5 is formed on the substrate 1 in the method of forming the periodically poled structure 20.

FIG. 7 is a diagram showing a state in which the fixing substrate 7 is formed on the substrate 1 in the method of forming the periodically poled structure 20.

FIG. 8 shows a method of forming the periodically poled structure 20.
It is a figure which shows the state before grinding the back surface 1B.

FIG. 9 is a diagram for explaining a method of forming a periodically poled structure 20 in a conventional example.

[Explanation of reference numerals] 1 substrate 1A front surface 1B back surface
4A Polarization inversion direction 4B Non-polarization inversion direction 5 Second electrode
6 Third electrode 6A Counter electrode piece 7 Fixing substrate 8
Bonding layer 15 Optical waveguide element 15A Optical waveguide 15B, 15C Edge 16, 17 Flat plate portion 16A, 17A Processed surface
18B, 18C removal part 20 periodic polarization inversion structure 22 polarization inversion part 22A first polarization inversion part 22B second polarization inversion part
24 non-polarization inversion part 24A first non-polarization inversion part 24B second non-polarization inversion part 28
A first interval 28B second interval 3
0 first electrode 32 feeding electrode 34
Electrode piece 34A One electrode piece 34B
The other electrode piece 37A The first interval 37
B second spacing 38A first spacing portion
38B 2nd spacing part 40 1st electrode 42 Feed electrode 44
A One electrode piece 44B Other electrode piece 47A First interval
47B Second spacing 48A First spacing portion 48B Second spacing portion

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Makoto Iwai             2-56, Sudacho, Mizuho-ku, Nagoya-shi, Aichi             Inside Hon insulator Co., Ltd. F-term (reference) 2K002 AB12 CA03 DA06 FA27 GA04                       HA20

Claims (10)

[Claims] 1. A wavelength conversion element comprising an optical waveguide and a periodic domain-inverted structure formed in the optical waveguide, wherein the periodic domain-inverted structure comprises alternating domain-inverted regions. A wavelength conversion element, comprising: a non-polarization inverting part, wherein the polarization inverting part includes a first polarization inverting part and a second polarization inverting part having different design widths. 2. The difference between the design width of the first domain-inverted portion and the design width of the second domain-inverted portion is an odd multiple of about 0.1 μm. Wavelength converter. 3. The difference between the design width of the first domain-inverted portion and the design width of the second domain-inverted portion is an odd multiple of about 0.01 μm. Wavelength converter. 4. The periodic domain-inverted structure is formed by using an electrode formed using a mask, and a difference between a design width of the first domain-inverted portion and a design width of the second domain-inverted portion. Is an odd multiple of the precision of the mask, The wavelength conversion element according to claim 1, wherein 5. The wavelength conversion element according to claim 1, wherein a design width of the non-polarization inversion portion is substantially constant. 6. A first electrode is arranged on one surface of a substrate made of a ferroelectric material, and a second electrode is arranged on the substrate at a position facing the first electrode. A method for forming a periodically poled structure by applying a voltage between one electrode and the second electrode, wherein the first electrode is one electrode piece and another electrode having different design widths. A method of forming a periodically poled structure, comprising: a piece. 7. The method according to claim 6, wherein the difference between the design width of the one electrode piece and the design width of the other electrode piece is an odd multiple of about 0.1 μm. 8. The method according to claim 6, wherein the difference between the design width of the one electrode piece and the design width of the other electrode piece is an odd multiple of about 0.01 μm. 9. The first electrode is formed using a mask, and the difference between the design width of the one electrode piece and the design width of the other electrode piece is an odd multiple of the accuracy of the mask. 7. The method according to claim 6, characterized by: 10. The method according to claim 6, wherein a distance between the one electrode piece and the other electrode piece adjacent to each other in the first electrode is substantially constant. The method described.