JP2003177441A - Optical waveguide element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an optical waveguide structure in which damage to a substrate is made small, to provide a simultaneous production method of a fine polarization structure such as a periodic polarization structure or the like and the optical waveguide structure and an optical waveguide element which is manufactured using the methods indicated above, eliminates the necessity of heating by the heater used to countermeasure optical damage and realizes a stable wavelength conversion even in the room temperature operations. <P>SOLUTION: In the relationship of a refractive index elliptical body at a y surface (a 'b' axis cross section) of an optical waveguide region 21 and a 90° polarization region 22, the refractive index of the region 21 becomes higher than the refractive index of the region 22 along the x direction of the coordinates of the regions 22 and 21. Therefore, by inserting polarized waves of the x direction of the coordinates, light beams are confined in and the region 21 is used as an optical waveguide. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an element having an optical waveguide structure in a single crystal. In particular, the present invention relates to an element that has an optical waveguide structure and a periodic polarization inversion structure and has a wavelength conversion function that can convert the wavelength of input light into light having another wavelength.

[0002]

2. Description of the Related Art In the field of communication using optical fibers, large capacity and high speed data transmission is required. Especially wavelength multiplexing (W
DM) and optical time division multiplexing (OTDM) are promising in that the transmission capacity of an optical fiber can be significantly increased, and a wavelength control technique for accurately controlling a plurality of carrier wavelengths and a certain carrier wavelength are different. A wavelength conversion technology for converting to a carrier wavelength becomes important.

For example, in an existing optical communication network,
Optical transmission of a single wavelength with a carrier wavelength in the 1.3 μm band, where optical fiber loss is small, is the mainstream, and is generally laid for the purpose of replacing telephone communication networks in cities. on the other hand,
In a trunk line optical communication network connecting cities, wavelength-multiplexed optical transmission having a carrier wavelength of 1.5 μm, which is suitable for wavelength-multiplexed transmission, is the mainstream.

When connecting both optical communication networks, since carrier wavelengths are different from each other, an optical signal flowing through one network is first converted into an electrical signal and then converted into an optical signal using a carrier wavelength compatible with the other network. There is a need to. Then, the performance of optical communication is limited by the capability of electric signal processing.

Therefore, if the carrier wavelength of one network can be directly converted to the carrier wavelength of the other network, electrical signal processing is eliminated and high performance of optical communication can be effectively maintained. Therefore, an optical mixing technique for converting the carrier wavelength is indispensable.

In such wavelength conversion, second harmonic generation (SHG) and sum frequency generation (SF) due to the nonlinear optical effect are performed.
G), difference frequency generation (DFG), parametric conversion, etc. are used, and therefore a material having a high nonlinear optical effect is desired.

As a related prior art, Japanese Patent Laid-Open No. 10-2
13826 and JP 2000-10130 are related papers (Ming-Hsien CHOU, et al., I).
EICETRANS. ELECTRON., VOL.E83-C, NO.6, p.869, JUNE 20
00), Reference 2 (CQXu, et al., Journal Applied Physic
s, VOL.87, NO.7,2000), Reference 3 (Kurihara, Solid State Physics, p.7)
5, Vol.29, No.1,1994), and reference 4 (Furukawa, Sato, Journal of Japan Society for Crystal Growth, p.277, Vol.17, No.3 & 4, 1990).

In Reference 1, PPLN having a waveguide structure
Optical mixing by difference frequency generation using a (periodically-poled lithium niobate) element is described. In Reference 2, QPM (Quasi-Phase Matching: Lithium Niobate LiNbO3) is used.
A quasi-phase matching element is a type of optical damage (Photorefractive dama) in which high-intensity light causes a local electric field due to free carrier absorption, causing a large fluctuation in the nonlinear optical constant.
ge) is described. Documents 3 and 4 also relate to lithium niobate. In the case of performing wavelength conversion in this way, lithium niobate, which has a high nonlinear optical effect, has been conventionally used in many cases.

As described in Reference 2, lithium niobate causes a large shift in the quasi-phase matching wavelength in minutes with the passage of time from the start of light incidence, resulting in a large intensity of the wavelength-converted output light. fluctuate. The magnitude and period of such intensity fluctuations are irregular, and artificial control is almost impossible, which is a disadvantage in application. However, the optical damage of lithium niobate has a crystal temperature of 80 ° C to 200 ° C.
It has been found that it can be alleviated by keeping it high to some extent, and a heater for crystal heating is indispensable as a countermeasure.

However, the presence of such a heater causes an increase in size, complexity, and power consumption of the device when it is applied to optical communication and the like. Further, in order to improve the wavelength conversion efficiency, it is necessary to use a waveguide. As a process for forming a waveguide, an element diffusion method of titanium or Zn of a lithium niobate crystal, or a proton exchange method by a low temperature process of a lithium tantalate crystal is known. However, these waveguide forming steps must be performed by heat treatment or the like before or after the step of forming the periodically poled structure, and the number of steps is extremely large in forming the wavelength conversion element, so that the cost, It took a lot of time.

On the other hand, potassium niobate is a material which has not only a large nonlinear optical effect but also an extremely low optical damage effect. In order to use potassium niobate for wavelength conversion in the optical communication band, it is necessary to create a periodically poled structure and perform QPM. Moreover, in order to improve the conversion efficiency, it is necessary to form a waveguide.

However, since the potassium niobate crystal has a phase transition temperature of around 200 ° C., the element diffusion method of titanium or Zn of the lithium niobate crystal accompanied by the above heat treatment cannot be used. Further, it is not possible to fabricate an optical waveguide by a simple method such as a proton exchange method by a low temperature process of lithium tantalate crystal.

A He + ion implantation method has been known as a method for forming a waveguide for potassium niobate. (Strohkendl et.al. J.Appl.Phys., Vol
69, No1, 84 (1991)) Acceleration 2MeV, 4Dose 2nd harmonic (SHG:
It is reported as a waveguide for generating SHG light having a wavelength of 490 nm) or generating a SHG light having a wavelength of 430 nm from a fundamental wave having a wavelength of 860 nm. (Pliska et.al .; J.Appl. Phys.Vol.8
4, No. 3, 1186 (1998)) Propagation loss is small for light with a fundamental wave wavelength of 1 μm or less, but when the fundamental wave wavelength is long, the propagation loss increases due to the tunneling effect on the substrate. Propagation loss for a fundamental wave having a wavelength of 1.55 μm is 10 dB / cm or more, and it hardly functions as a waveguide. Further, since the implantation energy is high, there is a problem that the substrate is damaged and the nonlinear optical effect is reduced. In addition, the polarization inversion voltage of potassium niobate crystal occurs at a voltage that is significantly lower than that of lithium niobate crystal, so when injecting charged ions, the substrate is charged and the polarization inversion structure is partially However, it cannot be used as a method for producing a waveguide having a periodically poled structure. (Pliska et.al .;
J.Opt.Soc.Am.B, vol15, No2, 628 (1998))

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical waveguide structure which causes less damage to a substrate during manufacturing, and a periodic polarization inversion structure which does not require heating by a heater as a measure against optical damage and is stable even at room temperature operation. An object is to provide an optical waveguide device capable of realizing wavelength conversion.

[0015]

The present invention is an optical waveguide element comprising a ferroelectric substrate provided with an optical waveguide, wherein the polarization direction of a region forming the optical waveguide and the polarization direction of a region sandwiching the optical waveguide. Are different from each other, the refractive index of the region in which the optical waveguide is formed is higher than the refractive index of the regions sandwiching the optical waveguide.

Further, the present invention may be provided with a periodic polarization inversion structure so as to cross the light traveling direction of the optical waveguide.

It is preferable that the ferroelectric substance is any of orthorhombic crystals, tetragonal crystals and monoclinic crystals, and it is more preferable that the ferroelectric substance is potassium niobate.

As described above, the conventional method for producing an optical waveguide on a ferroelectric material is to use titanium or Zn on a lithium niobate crystal.
And the like, a proton exchange method for a lithium tantalate crystal, and a He + ion implantation method for a potassium niobate crystal. In all of these, a region having a chemically changed refractive index was produced. .

In the present invention, the optical waveguide structure can be obtained by using a new idea of physically changing the polarization structure without using the conventional chemical change.

The optical waveguide structure of the present invention is shown in FIG. FIG. 1A shows an outline view of the shape of the ferroelectric substrate 4 before the optical waveguide is manufactured. The + c axis direction of the crystal axis is the polarization direction, and the directions of the a, b, and c axes that are the crystal axes before fabrication are taken as x, y, and z coordinates, respectively. FIG. 1B shows the polarization structure of the ferroelectric substrate 4 after the optical waveguide is manufactured. In the figure, the polarization direction of the optical waveguide region 21 (+ c axis direction) and the polarization direction of the 90 ° polarization region 22 (+ c axis direction) form 90 ° with each other. The polarization direction (+ c axis direction) of the optical waveguide region 21 can be either ± z direction in coordinates, and the polarization direction of the 90 ° polarization region 22 (+ c axis direction) can be in ± x directions.

In this case, the propagation direction of light in the optical waveguide is the y-direction (b-axis direction) on the coordinate axis. Therefore, in the following, y
Consider a case where light propagates in the direction (b-axis direction). FIG. 1 shows the relationship between the optical waveguide region 21 and the 90 ° polarized region 22 in this structure in the y-plane (b-axis cross section) of the refractive index ellipsoid.
It shows in (c). As shown in FIG. 1C, in the 90 ° polarization region 22 and the optical waveguide region 21, in the x direction of the coordinates,
The refractive index of the optical waveguide region 21 becomes higher than that of the 90 ° polarized region 22. From this, the light can be confined by introducing the polarized wave in the x direction of the coordinates, and the optical waveguide region 21 can be used as an optical waveguide. In this way, the refractive index of the optical waveguide region in the polarization direction is larger than that of the polarization inversion region, so that it has a remarkable guiding function for polarized light. Furthermore, the polarization of the optical waveguide region 21 can be taken in any of the ± z directions of the coordinates. From this, it is possible to fabricate a fine polarization structure such as the above-mentioned periodic polarization inversion structure in the optical waveguide region 21.

Next, a method of manufacturing a new optical waveguide structure using the above 90 ° polarized region 22 will be described below. FIG. 2 shows a schematic enlarged schematic view of one manufacturing process of an example of the optical waveguide structure manufacturing method according to the present invention. As shown in FIG. 2, the present invention is an optical device that forms a predetermined optical waveguide structure on a ferroelectric substrate 4 having a polarization that is divided into domains so that the + z direction of coordinates is the polarization direction (+ c axis direction). In the method for producing a waveguide structure, the electrodes 1 and 2 of the first and second electrodes are arranged on the substrate 4, and a pattern is formed on at least one of the first and second electrodes 1 and 2, The manufacturing circuit is configured such that the negative side of the polarization direction (+ c axis direction) of the substrate 4 is the negative electrode and the positive side is the positive electrode between the second electrode 1 and the second electrode 1 and 2. An optical waveguide structure is produced by applying an electric field between the electrodes 2 of. It is assumed that the electrode pattern is formed on either or both of the first and second electrodes.

The electrode pattern 31 for forming the optical waveguide may have any shape such as a straight line, a curved line, an obtuse angle, or an acute angle, but in order to accurately manufacture the 90 ° polarization region 22 forming the optical waveguide. , Which have a right angle to a straight line portion such as a straight line having a side parallel to the y direction (b axis direction light propagation direction) as shown in FIG. Is desirable. The relationship between the first and second electrodes 1 and 2 of the electrode pattern 31 for forming the optical waveguide is as shown in some examples in FIG. In both cases, the same pattern may be formed, or the patterns on both sides may be displaced.

The shape of the electrode according to the present invention does not depend on the material of the material as long as it is a patterned electrode. For example, using photolithography for pattern formation,
LiCl, KCl are formed on the insulating layer 5 such as a metal electrode made of Al, Au or the like formed by a lift-off method, and a photoresist or the like whose period is formed by photolithography.
Liquid electrodes using an electrolytic solution such as the above as an electrode, or an electrode manufactured by combining two of these photoresist and metal electrode.

Next, a method for simultaneously producing the above-mentioned new optical waveguide structure using the 90 ° polarization region 22 and a fine polarization structure such as a periodic polarization inversion structure using the 180 ° polarization region will be described below. In FIG. 7A, the 90 ° polarization region 2 described above is used.
A structure having a new optical waveguide structure using 2 and a fine polarization structure such as a periodic polarization inversion structure with a 180 ° polarization region is shown. As shown in FIG. 7 (a), the above-mentioned structure is 90 °.
It has an optical waveguide region 21 surrounded by a polarization region 22. Further, as shown in FIG. 7B, the inside of the optical waveguide region 21 forms a fine polarization structure 23 in which regions 10 oriented in the + z direction and regions 11 oriented in the −z direction are periodically arranged. . When light is propagated in the y direction in the optical waveguide region 21 having the structure shown in FIG. 7A, the optical waveguide region 21 can function as an optical waveguide having the function of the fine polarization structure 23 such as periodic polarization inversion by the 180 ° polarization structure. You can

Next, one example of a manufacturing process of the simultaneous manufacturing method of the fine polarization structure 23 such as periodic polarization inversion and the optical waveguide structure according to the present invention will be described with reference to the schematic enlarged schematic view shown in FIG. According to the present invention, as shown in FIG. 2, a polarization forming a predetermined polarization structure is formed on a ferroelectric substrate 4 having polarization divided into single domains so that the + z direction of coordinates is the polarization direction (+ c axis direction). In the method for simultaneously producing a single-crystal polarization structure and an optical waveguide structure having, the substrate 1 has electrodes 1 of the first and second electrodes,
And 2 are arranged to form a pattern on at least one electrode of the first or second electrodes 1 and 2, and the polarization direction of the substrate 4 (+ c axis direction) between the first and second electrodes 1 and 2. Of the polarization inversion structure and the optical waveguide structure by constructing a manufacturing circuit such that the negative side of the electrode is the negative electrode and the positive side of the electrode is the positive electrode, and applying an electric field between the first electrode 1 and the second electrode 2. Are produced at the same time. The electrode pattern is formed on either or both of the first and second electrodes 1 and 2 in FIG.

In the present invention, the electrode pattern 31 for forming the optical waveguide may have any shape such as a straight line, a curved line, an obtuse angle or an acute angle, but the 90 ° polarized region 22 forming the optical waveguide is produced with high precision. To do this, for example, see FIG.
It is desirable to have a right angle with a straight line portion such as a straight line shape having sides parallel to the y direction (light propagation direction of the b axis direction) as shown in (a), a side perpendicular to the x direction, a lattice shape, or a rectangular shape. First and second electrode patterns 31 for forming an optical waveguide
As shown in FIG. 6 (b), the relationship between the electrodes 1 and 2 is that when one side is a full surface electrode, when both sides are formed with the same pattern, or when both sides of the electrode are displaced. Either is fine.

In the present invention, the electrode pattern 32 for producing the fine polarization structure 23 such as the periodic polarization reversal may have any shape such as a straight line, a curved line, an obtuse angle or an acute angle.
In order to accurately manufacture the 180 ° -polarized structure region that forms the finely polarized structure, for example, y as shown in FIG. 6A is used.
It is desirable to have a right angle with a straight line portion such as a straight line having a side parallel to the x direction, a lattice shape, or a rectangular shape, which is perpendicular to the direction (b-axis direction light propagation direction). In the present invention, the relationship between the first and second electrodes 1 and 2 of the electrode pattern 32 for producing the finely polarized structure 23 such as periodic polarization inversion is shown in FIG.
As shown in (c), it is preferable that one side is a full-scale electrode or both sides have the same pattern.

The shape of the electrode according to the present invention does not depend on the material of the electrode as long as it is a patterned electrode. For example, using photolithography for pattern formation,
LiCl, KCl are formed on the insulating layer 5 such as a metal electrode made of Al, Au or the like formed by a lift-off method, and a photoresist or the like whose period is formed by photolithography.
Liquid electrodes using an electrolytic solution such as the above as an electrode, or an electrode manufactured by combining two of these photoresist and metal electrode. In addition, the above-described patterned electrode may be manufactured by using either the first or second electrode 1 or 2, or both of them.

An optical waveguide structure could be produced by the above-described method for producing an optical waveguide structure. Furthermore, by the method for simultaneously producing a fine polarization structure such as a periodic polarization structure and an optical waveguide structure according to the present invention, a fine polarization structure such as a periodic polarization inversion structure and an optical waveguide structure could be produced simultaneously. This eliminates the need for means such as ion implantation, and thus does not cause damage to the crystal. This is due to the phenomenon described below.

In FIG. 2, a patterned electrode is formed on the first electrode 1 of the substrate 4, and the electric field required to reverse the polarization direction (+ c axis direction) from the + z direction to the −z direction of the coordinates is first.
Was applied between the electrode 1 and the second electrode 2. As a result, surprisingly, in addition to the region having the polarization direction (+ c axis direction) in the ± z axis direction of the coordinate, the region having the polarization direction (+ c axis direction) in the ± x axis direction, that is, FIG. It was confirmed that a plate-like 90 ° polarization region 22 having a surface parallel to the y-axis of the coordinates and inclined by ± 45 ° from the z-plane was formed similarly to the structure shown in FIG. When the substrate 4 was further etched with hydrofluoric acid for 10 minutes, the optical waveguide region 21 had a 180 ° polarization structure in which the polarization direction (+ c axis direction) was the ± z axis direction of the coordinates, and a fine polarization structure corresponding to the pattern electrode. It has been confirmed that they have both.

The reason for this is considered as follows. When an electric field equal to or more than the electric field required to invert the polarization direction (+ c axis direction) by 180 ° is applied to the substrate 4, an oblique component of the electric field causes an electric field necessary to rotate the polarization direction (+ c axis direction) by 90 °. Since it is larger, it is possible to fabricate a 90 ° polarization region other than 180 ° polarization, an optical waveguide structure can be produced, and a fine polarization structure such as periodic polarization inversion and an optical waveguide structure can be produced at the same time. It seems to be.

As described above, an optical waveguide structure having a 90 ° polarization structure can be manufactured by applying an electric field parallel to the polarization direction (+ c-axis direction). Further, as described above, by applying an electric field in parallel with the polarization direction (+ c-axis direction) using the electrode with the fine pattern,
It was found that a structure having both a fine polarization structure 23 such as a periodic polarization structure having an 80 ° polarization structure and an optical waveguide structure having a 90 ° polarization structure can be manufactured at the same time.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Potassium niobate (KN) is used as a ferroelectric substrate 4, cut perpendicular to the polarization direction (+ c-axis direction), and a photoresist is applied as an insulating layer 5 to one main surface of the polarization. Then, the pattern is formed by photolithography, the first electrode 1 of the saturated LiCl aqueous solution, and the second electrode 2 in which only the saturated LiCl aqueous solution is in contact with the substrate 4.

In this example, since the light propagation direction is the y-direction (b-axis direction) of the coordinates, as shown in FIG. 7C, an electrode for producing the fine polarization structure 23 such as periodic polarization reversal. Of the electrode 31 for forming the optical waveguide are arranged in the x-direction and the x-direction is arranged in parallel with the y-direction.
It was arranged perpendicular to the direction and parallel to the y direction. The width of the electrode is 10
μm, the electrode interval was 100 μm. The opposing electrodes were full-scale electrodes.

In this example, the electrode pattern 32 for producing a finely polarized structure such as periodic polarization inversion has a width of the electrode portion of the electrode pattern 32 of 15 μm, and a width of the photoresist insulating layer 5 portion of 15 μm. The shape is such that the total period is 30 μm.

In this example, the substrate is sandwiched by silicone rubber and an acrylic plate, and the space between the acrylic plate and the substrate is filled with a LiCl saturated aqueous solution. At the time of filling, degassing is performed so that bubbles are not left on the surface of the substrate.

Next, by applying an electric field between the substrates by a power source, a fine polarization structure 23 such as a periodically poled structure having a 180 degree polarization structure shown in FIG. 7A and an optical waveguide structure having a 90 degree polarization structure. Were simultaneously produced. In this case, the thickness of the substrate 4 is 1 mm and the thickness of the photoresist is 8 mm.
μm, the electrode 1 has a positive potential and the electrode 2 has a negative potential, and an electric field of about 300 V / mm is about 50 ms, about 350
An attempt was made to fabricate the above-mentioned structure by three methods of applying an electric field of V / mm of about 9 ms and an electric field of about 400 V / mm of about 5 ms.

An example of the result is shown in FIG. FIG. 3 is an optical micrograph observed from the y-plane (b-axis cross section). Figure 3
As shown in the photograph of FIG.
As shown in (c), the optical waveguide region 21 was formed by the 90 ° polarization region 22. (A jagged black part can be seen along the upper edge of the substrate, which is a chip made when the cross section is cut.) The width of the 90 ° polarization region 22 is very narrow (<1 μm).
However, it was found that the difference in refractive index is large enough to confine light.

Further, the formed substrate 4 was etched with hydrofluoric acid for 10 minutes to confirm the formation state of the fine polarization structure 23 such as the periodic polarization inversion structure of the 180 ° polarization structure. An example of the result is shown in FIG. Figure 4 is the coordinate z
It is an optical microscope photograph after etching of the surface perpendicular to the axis, that is, the surface that was the first electrode 1. In the black-and-white pattern parallel to the x-axis direction, the black region 11 is the region having the −z direction polarization direction, and the white region 10 is the region having the + z direction polarization direction. Further, the straight stripes parallel to the y-axis direction are the portions where the formed 90 ° polarization regions 22 appear on the surface, and an optical waveguide can be formed between these 90 ° polarization regions 22. As shown in FIG. 4, in the optical waveguide region 21 sandwiched by the 90 ° polarization regions 22, the fine polarization structure 23 can be finely formed. As shown in the photograph of FIG. 4, with any of the application methods, a periodic polarization inversion structure having a 180 ° polarization structure with a period of 30 μm was formed in the optical waveguide region 21 as shown in FIG. 7A. From the above results,
An optical waveguide structure using a 90 ° -polarized structure can be manufactured by the electric field application method, and further, an optical waveguide structure using the 90 ° -polarized structure and a fine polarization structure such as periodic polarization reversal by the 180 ° -polarized structure can be simultaneously formed. It was possible to make.

According to the present invention, the optical waveguide can be provided not only on the surface of the substrate but also inside the substrate.
By providing four electrode patterns for forming the domain-inverted regions and performing the polarization process, the optical waveguide region surrounded by 90 ° polarization regions 22 on the four sides inside the substrate 4 made of crystal as shown in FIG. 21 is formed.

Although the above explanation has been mainly given by taking the KNbO ₃ crystal as an example, the orthorhombic and tetragonal crystals of KTiOPO ₄ and Ba are used.
It goes without saying that it can also be applied to TiO ₃ , RbTiOPO ₄ , LiB ₃ O _{5, and the} like.

Although the description has been limited to the single crystal material, it goes without saying that a material epitaxially grown on the substrate can also be applied.

[0044]

According to the present invention, an optical waveguide can be obtained in which the substrate is not damaged during manufacturing. Further, it is possible to fabricate an optical waveguide structure that does not damage the substrate without losing the fine polarization structure such as the periodic polarization inversion structure, and it is possible to fabricate the fine polarization structure such as the periodic polarization structure and the optical waveguide structure at the same time. Further, it is possible to provide an optical waveguide device that can realize stable wavelength conversion even at room temperature operation without the need for a heater for light damage. The practical and industrial effects of the present invention are great in improving these device characteristics and saving power.

[Brief description of drawings]

1A is a schematic diagram of a ferroelectric substrate before fabrication of an optical waveguide, FIG. 1B is a conceptual diagram of an optical waveguide structure having a 90 ° polarization structure, and FIG. 1C is an optical waveguide structure having a 90 ° polarization structure and refraction in each region. It is a figure showing an ellipsoid.

FIG. 2 is a schematic enlarged schematic view of one manufacturing process in the method for producing an optical waveguide structure and the method for simultaneously producing a fine polarization structure such as periodic polarization inversion and an optical waveguide structure in the present invention.

FIG. 3 is an optical micrograph of an optical waveguide structure having a 90 ° polarization structure manufactured by an electric field application method, observed from the y direction.

FIG. 4 is an optical microscope photograph of a periodically poled structure formed by a 180 ° -polarized structure manufactured by an electric field application method, observed from the z direction before manufacturing.

FIG. 5 is a diagram showing an example of an electrode structure for producing an optical waveguide structure. (A) Schematic view of z plane (b) Schematic view from y plane

FIG. 6 is a diagram showing an example of an electrode structure for simultaneously producing an optical waveguide structure and a fine polarization structure such as a periodic polarization structure. (A) Schematic view of z plane (b) Schematic view from y plane (c)
Schematic view from the x-plane

FIG. 7 (a) is a schematic view of a structure having both a novel optical waveguide structure using a 90 ° polarization region and a fine polarization structure such as a periodic polarization inversion structure with a 180 ° polarization region. (B) A schematic view of a fine polarization structure such as a periodic polarization reversal structure due to a 180 ° polarization region in the optical waveguide region. (C) It is a schematic diagram of the pattern of the electrode used in embodiment.

FIG. 8 is a diagram showing an optical waveguide device having an optical waveguide region formed inside a crystal.

[Explanation of symbols]

1st electrode 2 Second electrode 4 substrates 5 insulating layers 6 power supply Area with polarization direction in 10 + z axis direction 11-A region having a polarization direction in the z-axis direction 21 Optical Waveguide Area 22 90 ° domain 23 Finely polarized structure such as periodic polarization structure 31 Electrode pattern for forming optical waveguide 32 Electrode pattern for producing finely polarized structure

Claims (5)

[Claims] 1. An optical waveguide device comprising a ferroelectric substrate provided with an optical waveguide, wherein the polarization direction of a region forming the optical waveguide and the polarization direction of a region sandwiching the optical waveguide are different from each other. An optical waveguide element characterized in that a refractive index of a region to be formed is made higher than a refractive index of a region sandwiching the optical waveguide. 2. The optical waveguide element according to claim 1, wherein an angle formed by a polarization direction of a region sandwiching the optical waveguide and a polarization direction of a region forming the optical waveguide is 90 °. 3. The optical waveguide element according to claim 1, further comprising a periodic polarization inversion structure that crosses the light traveling direction of the optical waveguide. 4. The optical waveguide device according to claim 1, wherein the ferroelectric substance is any of orthorhombic crystals, tetragonal crystals and monoclinic crystals. 5. The optical waveguide device according to claim 4, wherein the ferroelectric substance is potassium niobate.