JP3303346B2 - Method for controlling polarization of lithium niobate and lithium tantalate, method for manufacturing optical waveguide device using the same, and optical waveguide device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the polarization of lithium niobate and lithium tantalate suitable for forming an optical device such as an optical second harmonic generation element (hereinafter referred to as an SHG element). And a method of manufacturing an optical waveguide device using the method.

[0002]

2. Description of the Related Art In recent years, it has been proposed to improve the characteristics such as light output by forming a periodically domain-inverted structure on a surface of an optical device such as an SHG element.

For example, an SHG element generates second harmonic light having a frequency of 2ω when light having a frequency of ω is introduced. This SHG element can expand the wavelength range of single-wavelength light. Accordingly, it is possible to expand the range of use of the laser and optimize the use of laser light in each technical field. For example, the recording density can be improved in optical recording / reproducing, magneto-optical recording / reproducing, etc. using laser light by shortening the wavelength of laser light.

As such an SHG element, for example, K
So-called bulk type S using TP (KTiOPO ₄ )
A linear waveguide is formed on a single crystal substrate made of a nonlinear optical material such as an HG element or a waveguide type SHG element that performs phase matching using a larger nonlinear optical constant, such as lithium niobate LiNbO ₃ (LN). There is a Cherenkov radiation type SHG element or the like in which a fundamental wave of near-infrared light is input thereto and the second harmonic, for example, green or blue light is emitted from the substrate side in a radiation mode.

[0005] However, the bulk type SHG element has a relatively low SHG conversion efficiency due to its characteristics, and the above-mentioned LN and lithium tantalate LiTaO _{3, which} are inexpensive and high in quality, can be obtained.
(LT) cannot be used. Further, the Cherenkov radiation type SHG element emits the SHG beam in the direction of the substrate, and the beam spot has a peculiar shape, for example, a crescent-shaped spot, and has a problem in actual use.

To realize a device with high conversion efficiency,
The phase propagation velocities of the fundamental wave and the second harmonic must be equal. As a method of simulating this, a method of periodically arranging the non-linear optical constants + and-has been proposed (J.
A. Armstrong, N. Bloembergen, et al., Phys. Rev., 127, 1918 (1
962)). As a method of realizing this, there is a method of periodically inverting the direction of a crystal (for example, a crystal axis). As a specific method, for example, a method of cutting and laminating a crystal thinly (Okada, Takizawa, Ieiri, NHK Technical Research, 29 (1), 24 (19
77)) or a method of forming a periodically domain-inverted structure by controlling the polarity of a current applied during crystal pulling to form a periodic domain (domain) (D. Feng, NBMing, JF
Hong, et al, Appl. Phys. Lett. 37, 607 (1980), K. Nassau,
HJ Levin-stein, GHLoiacano Appl.Phys.Lett.6,228
(1965), A. Feisst, P. Koidl Appl. Phys. Lett. 47, 1125 (19
85)). These methods aim at forming a periodic structure throughout the crystalline material. However, the above-described method not only requires a large-scale apparatus, but also has a problem that it is difficult to control the polarization inversion.

On the other hand, as a method of forming the above periodically poled structure near the surface of the crystal material, for example, a method of exchanging protons and Li to raise the temperature to near the Curie temperature (Kiminori Mizuuchi, Kazuhisa Yamamoto and Tetsu)
o Taniuchi, Appl. Phys. Lett., 59, 1538 (1991)).

In the case where the polarization inversion is formed by this proton exchange method, for example, as shown in a schematic enlarged sectional view of one manufacturing process in FIG.
In FIG. 5, a Ta mask layer 21 is formed on the + c plane of the substrate 10 made of, for example, LT, which is single-domained in the polarization direction indicated by the arrow d.
Is formed on a required parallel band pattern, for example, with a pitch P of 3.6 μm and a width W of 1.8 μm.

In this state, it is placed in the vessel 8 and immersed in phosphoric acid 19 at 260 ° C. for 50 minutes to exchange Li ions and protons on the LT substrate as shown by arrows H ⁺ and Li ^+. An exchange layer is formed. Then, for example, 500
By performing heating at about ° C., the domain-inverted regions 3 can be periodically formed as shown in FIG. However, in this case, the refractive index of the domain-inverted region 3 changes, or the depth D is small with respect to the pitch of the domain-inverted region 3,
In addition, the domain-inverted region has a triangular cross section and is poor in controllability of the shape (F. Laurell et al, Integrated Photonics R
esearch, Tu12, 1989). Further, there is a possibility that a metal such as the Ta mask layer 21 at the time of proton exchange is oxidized on the substrate surface and contaminates the substrate surface.

That is, in order to reliably perform the above-described phase matching, it is desirable that the depth D of the domain-inverted region 3 is large, and its cross-sectional shape is a stripe extending in the depth direction of the substrate 10. It is desirable that the domain-inverted regions 3 and the regions where domain-inversion does not occur are formed alternately. However, when the SHG element is formed by the above-described proton exchange method, the controllability of the shape of the domain-inverted regions 3 is poor. In addition, there is a possibility that the so-called light conversion efficiency is reduced by causing a leak of the input light, a leak of the second harmonic light, and a decrease in the coupling efficiency between the input light and the second harmonic light.

[0011]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to solve the above-mentioned nonlinear optical materials, in particular, LN.
In addition, it is possible to obtain a domain-inverted structure with good controllability by avoiding surface contamination of LT, change in refractive index, and the like, and to obtain an optical waveguide device having good characteristics.

[0012]

According to the present invention, there is provided a method for controlling the polarization of lithium niobate for forming a predetermined domain-inverted structure on a substrate made of lithium niobate in a single domain. Disposing the first and second electrodes,
At least the first electrode is formed in a pattern corresponding to the pattern of the domain-inverted structure to be finally obtained, the distance between the first and second electrodes is set to 200 μm or less, and between the first and second electrodes, A voltage is applied such that the negative side of the spontaneous polarization of the substrate is at a negative potential and the positive side is at a positive potential to form a domain-inverted structure.

[0013]

Further, according to the present invention, in the above-mentioned polarization control method, the voltage applied between the first and second electrodes may be 15 kV /
mm or more.

Further, according to the present invention, in each of the above-described polarization control methods, the voltage applied between the first and second electrodes is a pulse voltage composed of at least two or more pulses.

Further, according to the present invention, in each of the above-mentioned polarization control methods, the first and second substrates are immersed in an insulating liquid.
A voltage is applied between the electrodes. Further, according to the present invention, in each of the above-described polarization control methods, the second electrode is formed so as to cover almost entirely the negative side of the spontaneous polarization of the substrate.

The method of manufacturing an optical waveguide device according to the present invention is an optical waveguide device comprising: forming a predetermined domain-inverted structure on a substrate made of single domain lithium niobate; and forming an optical waveguide on the substrate. In the manufacturing method of
The first and second electrodes are arranged in the polarization direction of the substrate, and at least the first electrode is formed in a pattern corresponding to the finally obtained pattern of the domain-inverted structure, and the distance between the first and second electrodes Is set to 200 μm or less, and a voltage is applied between the first and second electrodes so that the negative side of the spontaneous polarization of the substrate has a negative potential and the positive side has a positive potential to form a domain-inverted structure. An optical waveguide is formed in a region where the domain-inverted structure is formed.

The optical waveguide device according to the present invention has c
An optical waveguide is formed on a substrate made of lithium niobate that is single-domaind in the axial direction, and a domain-inverted structure is formed periodically in the optical waveguide direction of the optical waveguide. The thickness or the length is set to 200 μm or less.

Further, the present invention provides a method for controlling the polarization of lithium tantalate to form a predetermined domain-inverted structure on a substrate made of lithium domain tantalate in a single domain. The electrodes are arranged to form at least a first electrode in a pattern corresponding to the pattern of the domain-inverted structure to be finally obtained. The distance between the first and second electrodes is set to 700 μm or less, and the first and second electrodes are formed. A voltage of 15 kV / mm or more is applied between the electrodes to set the negative side of the spontaneous polarization of the substrate to a negative potential and the positive side to a positive potential to form a domain-inverted structure.

[0020]

[0021]

According to the present invention, in the above-described method for controlling the polarization of lithium tantalate, the voltage applied between the first and second electrodes is a pulse voltage composed of at least two or more pulses.

Further, according to the present invention, in the above-mentioned method for controlling the polarization of lithium tantalate, a voltage is applied between the first and second electrodes while the entire substrate is immersed in an insulating liquid. According to the present invention, in each of the above-described methods for controlling the polarization of lithium tantalate, the second electrode is formed so as to cover substantially the entire negative side of the spontaneous polarization of the substrate.

Further, the present invention provides a method of manufacturing an optical waveguide device in which a predetermined domain-inverted structure is formed on a substrate made of a single-domain lithium tantalate, and then an optical waveguide is formed on the substrate. First and second electrodes are arranged in the polarization direction, and at least the first electrode is formed in a pattern corresponding to the pattern of the finally obtained domain-inverted structure;
The distance between the first and second electrodes is set to 700 μm or less, and between the first and second electrodes, the negative side of the spontaneous polarization of the substrate is set to a negative potential, and the positive side is set to a positive potential. m
A voltage of m or more is applied to form a domain-inverted structure, and an optical waveguide is formed in a region of the substrate where the domain-inverted structure is formed.

The optical waveguide device according to the present invention has c
An optical waveguide is formed on a substrate made of lithium tantalate that is single-domaind in the axial direction, and a domain-inverted structure is formed periodically in the optical waveguide direction of the optical waveguide. Is set to 700 μm or less, and this domain-inverted structure is formed over substantially the entire thickness or the entire length in the c-axis direction in the region where the domain-inverted structure is formed on the substrate.

[0026]

According to the polarization control method of the present invention described above, the shape of the domain-inverted region can be formed with good controllability and without crystal deterioration.

This is considered to be due to the following reason. That is, in general, such as LN single crystal and LT single crystal,
A crystal is destroyed when a high voltage is applied.
ozenferroelectrics), it is said that polarization inversion does not occur even when a voltage that does not cause crystal breakdown occurs. Conventionally, polarization inversion occurs by applying a relatively low voltage that does not cause crystal breakdown. Was. That is, in order to lower the coercive electric field, at a high temperature of about 600 ° C.,
A relatively low electric field for a substrate whose thickness in the c-axis direction is as thick as about 1 mm or more, for example, several V / mm to several hundred V /
An electric field of about mm was applied to form domain inversion.

However, as a result of the present inventors' earnest studies, it has been found that the above-described crystal breakdown is caused by the thickness of the substrate in the c-axis direction, that is, the distance between the electrodes. 4 and 5 show the substrate thickness dependence of the polarization inversion electric field and the crystal breakdown electric field of the lithium niobate LN and lithium tantalate LT single crystal substrates, respectively. In this case, sample 1 was an LN single crystal manufactured by Yamaju Ceramics, sample 2 was an LN single crystal manufactured by Crystal Technology, sample 3
As an example, an LN single crystal manufactured by Mitsui Kinzoku Co., Ltd., and an LT single crystal manufactured by Yamaju Ceramics Co., Ltd. were used as a sample 4. By changing the substrate thickness, an electric field where polarization inversion started to be formed (polarization inversion electric field) and crystal destruction began to occur. The electric field (crystal breakdown electric field) was measured. In the figure, Δ, ○, □, and Δ represent samples 1 to 3, respectively.
The inversion electric field of ▲, ▲, ●, ■ and ▼ are samples 1 to 4, respectively.
5 shows the breakdown electric field of the semiconductor device.

As can be seen from FIGS. 4 and 5, the reversal electric field is almost constant and is about 15 to 20 kV / mm.
On the other hand, the breakdown electric field decreases with an increase in the substrate thickness, and falls below the inversion electric field when the substrate thickness is about 200 μm in the case of LN and about 700 μm in the case of LT. Therefore, when the substrate thickness is LN, it is 200 μm, and when it is LT, it is 7 μm.
If it exceeds 00 μm, it is considered that the crystal is destroyed before the polarization inversion occurs, and it becomes impossible to perform the polarization inversion operation.

On the other hand, when the substrate thickness is 2 in LN,
In the case of 00 μm or less and LT of 700 μm or less,
Since there are regions (represented by hatched regions A and B in FIGS. 4 and 5) which are equal to or larger than the inversion electric field and equal to or smaller than the breakdown electric field, when a substrate having such a relatively small thickness is used, an appropriate electric field is required. It seems that by applying the voltage, a domain-inverted structure can be favorably obtained without causing crystal breakage. In addition, in this case, since the domain inversion occurs between the electrodes 1 and 2, the shape thereof has a greater depth than the width and the pitch, and the domain-inverted structure 30 having a desired shape can be obtained.

[0031]

For each of the substrate materials LN and LT having a substrate thickness of 100 μm, electrodes are formed on the main surface and the back surface to make the distance between the electrodes 100 μm and to apply a DC voltage of 1.5 kV to 40 μm.
When applied for minutes, a domain-inverted structure could be formed without causing crystal destruction. Therefore, although the inversion electric field varies in FIGS. 4 and 5 described above, it can be seen that the polarization inversion structure can be reliably obtained by setting the applied electric field to 15 kV / mm or more.

Furthermore, by applying two or more pulse voltages as applied voltages, a domain-inverted structure could be formed without causing crystal breakdown.

By applying a voltage while immersing these substrates in an insulating liquid, even when a high voltage is applied, discharge between the electrodes attached to the substrate surface can be suppressed, and the polarization inversion can be accurately achieved. The structure could be formed.

According to each of these polarization control methods, it is possible to reliably avoid crystal breakage by applying an electric field of 15 kV / mm or more by setting the distance between the electrodes to 200 μm or less in LN and 700 μm or less in LT. Therefore, it is not necessary to heat the substrate to about 500 ° C. to 1200 ° C. in order to lower the coercive electric field, and the domain inversion can be formed at room temperature. Therefore, it is possible to avoid inconveniences such as contamination of the crystal caused by attaching or contacting the electrode while heating and fluctuation of the refractive index due to proton exchange, and to avoid fluctuation of characteristics.

As shown in FIG. 3, in the optical waveguide device formed by such a polarization control method, the thickness of the polarization inversion structure 30 in which the optical waveguide 11 is provided in the c-axis direction is not more than 200 μm in LN. , LT is 700 μm or less. With such a configuration, a periodic domain-inverted structure can be formed without causing a change in characteristics as described above. S that has been matched and has good SHG conversion efficiency
An HG element can be obtained.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, each example of the polarization control method of the present invention will be described in detail. In each case, a periodic domain-inverted structure is formed on a substrate 10 made of LN single crystal or LT single crystal, and an optical waveguide is formed in this portion to obtain a highly efficient SHG element optical waveguide device. Is shown. In each of the examples, the single domainization of the substrate 10 is performed by, for example, raising the temperature to, for example, about 600 ° C. immediately below the Curie temperature, and applying an external DC voltage in a certain direction over the entire c-axis direction. I went along.

In each of the following embodiments, the direction of spontaneous polarization is indicated by arrow d, and the direction of polarization of the domain-inverted region is indicated by arrow h.
Indicated by First, in the following Examples 1 to 8, a case where a domain-inverted structure is formed on a lithium niobate substrate will be described.

Embodiment 1 A description will be given with reference to a schematic enlarged perspective view of FIG. In this case, the substrate 10 is formed as a single domain in the entire thickness direction, and the first electrode 1 made of Al, Au, or the like is formed on the main surface 1S on the positive side of the polarization, for example, in a comb-like pattern. The second electrode 2 is entirely covered on the back surface 1R on the negative side of the polarization.

In this example, the entire substrate 10 is immersed in a container 8 in a fluorocarbon high voltage solution such as Fluorinert (trade name, manufactured by Sumitomo 3M) or an insulating solution 9 such as silicon oil. A voltage is applied such that the positive side, that is, the first electrode 1 side has a positive potential, and the negative side of polarization, that is, the second electrode 2 side has a negative potential, and a polarization inversion structure of a pattern corresponding to the comb-tooth pattern of the first electrode 1 is applied. Was formed. At this time, the electric field applied to the substrate 10 is desirably selected within the range of the region A described with reference to FIG. Reference numeral 5 denotes a power supply.

In this case, the thickness of the substrate 10 is 98 μm, the voltage is 2.1 kV, and 1 ms is applied.
A domain-inverted structure 30 having a fine period of about 3 μm can be obtained. Further, domain-inverted regions are formed over the comb teeth of the electrodes 1 and 2, that is, over the entire thickness of the substrate 10.
The depth could be increased with respect to the pitch P. Further, by applying a voltage in the insulating liquid 9 in this manner, a discharge between the electrodes 1 and 2 can be reliably avoided, and a domain-inverted structure can be obtained with good controllability without causing crystal destruction. Was.

Then, as shown in FIG. 3, an optical waveguide 11 was formed on the main surface 1S of the substrate 10 to form an optical waveguide device. The optical waveguide 11 is formed by patterning a mask made of, for example, Ta or the like by applying photolithography or the like to portions other than the portion where the waveguide 11 is formed, and heating the optical waveguide 11 to 200 ° C. for about 20 minutes using the mask as a mask. It can be formed by dipping in phosphoric acid. Then, after removing the mask, the end face 12 of the optical waveguide is optically polished to obtain an optical waveguide device, that is, an SHG element.

In this case, since the periodic domain-inverted structure 30 having no change in characteristics such as a change in the refractive index and having a large depth with respect to the pitch is obtained, the quasi-phase matching is ensured. Thus, an SHG element having high light conversion efficiency can be obtained.

Embodiment 2 A description will be given with reference to a schematic enlarged perspective view of FIG. 6, parts corresponding to those in FIG. 1 are denoted by the same reference numerals.
Also in this case, the substrate 10 is formed into a single domain entirely in the thickness direction, the thickness is set to 200 μm or less, and the first surface made of Al or the like is formed on the main surface 1S on the positive side of the polarization. In this case, the second electrode 2 having a comb-like pattern made of Al or the like is also formed on the back surface 1R on the negative side of the polarization, and the comb-tooth portion is formed on the main surface 1
It is formed so that the substrate 10 is sandwiched between the upper surface S and the lower surface 1 so as to face each other. In the same manner as in the first embodiment, a voltage is applied by setting the positive side of polarization, that is, the first electrode 1 side to a positive potential, and setting the negative side of polarization, that is, the second electrode 2 side to a negative potential. The domain-inverted structure 30 having a pattern corresponding to the comb-tooth pattern was formed. Also in this case, the magnitude of the electric field is selected in the same manner as in the first embodiment, and the domain-inverted structure 30 is formed without causing crystal destruction and over the comb teeth of the electrodes 1 and 2, that is, over the entire thickness of the substrate 10. Was formed, and the depth could be increased with respect to the pitch.

Also in this case, the first embodiment described above
Similarly to the above, an optical waveguide device can be formed by forming an optical waveguide on the main surface 1S by a proton exchange method or the like,
An SHG element with high light conversion efficiency can be obtained.

Embodiment 3 A description will be given with reference to a schematic enlarged perspective view of FIG. 7, parts corresponding to those in FIG. 6 are denoted by the same reference numerals, and redundant description will be omitted. In this case, the second electrode 2 is entirely formed on the rear surface 1R of the substrate 10, and also in this example, the pattern corresponds to the pattern of the first electrode 1 as in the fifth embodiment. The domain-inverted structure 30 of the pattern could be obtained, and the depth could be increased with respect to the pitch.

Also in this case, in the first embodiment described above.
Similarly to the above, an optical waveguide device can be formed by forming an optical waveguide on the main surface 1S by a proton exchange method or the like,
An SHG element with high light conversion efficiency can be obtained.

Embodiment 4 A description will be given with reference to FIG. In FIG. 2, portions corresponding to FIG. In this example, a convex portion, that is, a ridge 6 is formed on the substrate 10. The longitudinal direction of the ridge 6 is selected so as to be orthogonal to the spontaneous polarization direction of the substrate 10 as indicated by the arrow d, and the longitudinal side wall surface has a side surface 1A composed of the positive side of polarization and a side surface 1B composed of the negative side. It consists of. This side 1A and 1
A first electrode 1 and a second electrode 2 made of Al or the like are formed in a comb-like pattern on the upper surface B and on the upper side surface 1E adjacent thereto by a manufacturing process described later. At this time, the comb tooth portions are on both side surfaces 1A and 1B from both upper side surfaces 1E.
So that the tips of the comb teeth on both side surfaces 1A and 1B are arranged opposite to both ends of the main surface 1S. And the thickness T of the ridge 6 in the width direction.
Is selected to be 200 μm or less, and the distance between the first and second electrodes 1 and 2 is selected to be 200 μm or less.

In such a configuration, a voltage is applied so that the first electrode 1 side has a positive potential and the second electrode 2 side has a negative potential, thereby forming a domain-inverted region 3 in the ridge 6 and Polarized structure 3 of the pattern corresponding to the pattern at the tip
0 could be obtained.

FIGS. 8A to 8D show an example of a method for forming the ridge 6 on the substrate 10 and forming the electrodes 1 and 2 of a required pattern on the longitudinal side surfaces 1A and 1B as described above.
Shown in As shown in FIG. 8A, after a resist 31 is entirely coated and baked on the main surface 1S of the substrate 10 where the domain inversion is to be formed, a mask layer 32 made of Ni, Cr, or the like is deposited by vapor deposition, sputtering, or the like. Then, after a resist 33 is applied thereon and baked, the resist 33 remains in a required portion where the ridge 6 is to be formed, that is, in this case, the resist 33 has a required width T in a polarization direction indicated by an arrow d. The pattern having a longitudinal direction perpendicular to the paper surface of No. 8 is exposed and developed by application of photolithography or the like to be patterned.

As shown in FIG. 8B, the mask layer 32 and the resist 31 are formed by anisotropic etching such as RIE (reactive ion etching) using the resist 33 as a mask.
Is patterned.

Subsequently, as shown in FIG. 8C, the substrate 10 is etched from above the main surface 1S using the mask layer 32 as a mask by anisotropic etching such as RIE, and the side surfaces 1A and 1B and the upper side surface adjacent thereto are etched. 1E is exposed to form a ridge 7. At this time, the height of the ridge 6 is set to about 2 μm by controlling the etching depth of the substrate 10.

Further, as shown in FIG.
Metal layer 34 made of, for example, Al such as u, Pt, K, and Li
Is formed over the entire surface of the ridge 6 by vapor deposition, sputtering or the like.

Next, after the metal layer 34 is patterned into the comb-like pattern shown in FIG. 2 by anisotropic etching such as RIE, the resist 21 is immersed in a solvent such as acetone to remove the resist 21. As shown in FIG. 6, only the metal layer 34 on the ridge 6 is lifted off, and the first comb-shaped first portions adjacent to the upper surface 1E from the side surfaces 1A and 1B, respectively.
Electrode 1 and the second electrode 2 can be formed.

In this case, a waveguide is formed in the ridge 6 by a proton exchange method or the like before or after the above-described voltage application step for polarization inversion, and the first electrode 1 and the second electrode 2 are removed. Thus, an SHG element can be obtained.

As described above, when the ridge 6 is formed on the substrate 10 and electrodes are applied to the side surfaces 1A and 1B to apply a voltage, an electric field component which is not parallel to the spontaneous polarization,
That is, the electric field component that does not directly affect the polarization inversion can be greatly reduced. In the case of the substrate 10 such as an LN crystal, an electric field component that is not parallel to the direction in which the spontaneous polarization occurs exerts a large stress on the material. Therefore, by reducing such an electric field component, the crystal breakage of the substrate 10 can be more reliably performed. Can be avoided.

When the domain inversion is formed by such a configuration, each domain inversion region 3 can be formed over the entire thickness of the ridge 6. Therefore, by appropriately selecting the depth of the waveguide, the domain-inverted structure 30 can be formed over the entire thickness of the waveguide or more, and with almost no crystal breakage. Is used as an SHG element, light conversion efficiency such as SHG efficiency can be increased.

Fifth Embodiment A description will be given with reference to a schematic enlarged perspective view of FIG. 9, parts corresponding to those in FIG. 2 are denoted by the same reference numerals, and redundant description will be omitted. Also in this case, the voltage is applied while the entire substrate 10 in the fourth embodiment described in FIG. 2 is immersed in the insulating liquid 9 in the container 8 as in the first embodiment described in FIG. . Also in this case, the width on the ridge 6, that is, the first electrode 1 and the second electrode 2
The interval T between them was selected to be 7 μm or more and 200 μm or less, and a voltage was applied by selecting an electric field within the range of the region A in FIG. Also in this case, a domain-inverted structure 30 having a pattern corresponding to the comb-tooth pattern is formed between the tips of the comb teeth of the first electrode 1 and the second electrode 2, and an optical waveguide (not shown) is formed thereon. By forming, a SHG element having high light conversion efficiency could be obtained. Further, by applying an electric field in the insulating liquid 9 in this manner, the electrodes 1 and 2 are formed in the same manner as in the first embodiment.
In this way, it was possible to reliably avoid the discharge during the period.

Embodiment 6 A description will be given with reference to a schematic enlarged perspective view of FIG. In this case, the substrate 10 made of lithium niobate which is single-domained in the in-plane direction indicated by an arrow d is used, and the polarization side on the main surface 1S is made of Al or the like by applying photolithography or the like. A first electrode 1 having a comb-like pattern is formed by deposition, while a second electrode 2 made of Al or the like is entirely formed on the positive side surface 1B of polarization by vapor deposition, sputtering, or the like. Become. 5 is a power supply. Also in this case, the entire substrate 10 is transferred to Florinert (Sumitomo 3) in the container 8.
The voltage is applied in a state of being immersed in a CFC-based high-voltage resistant liquid such as a product of M Corporation or an insulating liquid 9 such as silicon oil. At this time, the pitch P of the first electrode 1 is 2
μm, the width W is 1 μm, the distance L between the tips of the electrodes 1 and 2 on the main surface 1S is 100 μm, and the thickness T of the lithium niobate 10 is 1 mm.
The voltage is set to 2.6 kV, and a pulse voltage having a width of 100 μs is applied twice or more, for example, five times so that the electrode 1 side has a negative potential and the second electrode 2 side has a positive potential. It is possible to obtain the domain-inverted structure 30 having a pattern corresponding to the comb-tooth pattern of the first electrode 1 without occurrence.

Embodiment 7 A description will be given with reference to a schematic enlarged perspective view of FIG. FIG.
In FIG. 10, the portions corresponding to those in FIG. In this case, a first electrode of a comb-like pattern is provided on the positive side surface 1A of the substrate 10 made of lithium niobate, and a second electrode of a comb-like pattern is further provided on the main surface 1S of the negative side of the polarization. 2 is formed by vapor deposition, sputtering or the like, and then formed by application of photolithography or the like. The tips of the comb teeth of these electrodes 1 and 2 are opposed to each other over the main surface 1S and the side surface 1A. Make it patterned. Also in this case, the voltage is applied while the entire substrate 10 is immersed in the insulating liquid 9 in the container 8. In such a configuration, a voltage is applied so that the first electrode 1 side has a positive potential and the second electrode 2 side has a negative potential to correspond to the comb pattern of the first electrode 1 and the second electrode 2. The polarization inversion structure 30 having the pattern shown in FIG. Also in this case, the width and pitch of the tip of the comb teeth and the magnitude of the voltage were selected in the same manner as in Example 6, and the domain-inverted structure 30 could be obtained with almost no crystal destruction.

Eighth Embodiment A description will be given with reference to a schematic enlarged perspective view of FIG. In this case, an example in which the substrate 10 made of lithium niobate which is single-domained in the direction shown by the arrow d is used, and the first electrode 1 and the second electrode 2 Place. In this case, the first electrode 1 and the second electrode 2 made of Al or the like are both formed by being deposited by, for example, vapor deposition, sputtering, or the like, and then patterned by applying photolithography or the like to form a comb-like shape. Tip width W
, The pitch P is, for example, 2 μm, the distance L between the tips of the comb teeth of the electrodes 1 and 2 is 100 μm, the thickness T of the substrate 10 is about 1 mm, and the tips of the comb teeth of the electrodes 1 and 2 Are arranged to face each other.

Also in this case, the voltage is applied while the entire substrate 10 is immersed in the insulating liquid 9 in the container 8. In such a configuration, at a temperature of 150 ° C. or higher, the first electrode 1 on the negative side of the spontaneous polarization of the substrate 10 has a negative potential and the first side on the positive side between the first electrode 1 and the second electrode 2. Voltage of 2.6 kV so that the second electrode 2 has a positive potential.
As a result, a pulse voltage having a width of 100 μs is applied twice or more, for example, five times to form a domain-inverted region 3 extending from the tip of the comb teeth of the first electrode 1, and the tip of the comb teeth of the first electrode 1 is formed. The periodic domain-inverted structure 30 having a pattern corresponding to the pattern of the portion could be formed with almost no crystal destruction or the like. In addition, discharge between the electrodes 1 and 2 was reliably avoided.

In each of the above-described examples, an optical waveguide device is obtained by forming a domain-inverted structure on a lithium niobate LN substrate. In this case, the distance between the electrodes is set to 7 μm or more. As a result, the coupling efficiency with the semiconductor laser, which is the light source of the guided light, could be improved more reliably. That is, as shown in FIG. 3, the width Wg of the optical waveguide 11 is about 3 μm, but the diameter of the near field pattern of the semiconductor laser as the light source is 6 μm.
m or more, and by increasing the width at the waveguide end face 12, the coupling efficiency can be improved. In this case, by setting the distance between the electrodes to about 7 μm or more, the domain-inverted structure 30 is surely formed even in the vicinity of the waveguide end face 12, and such a coupling efficiency can be obtained without impairing the conversion efficiency. Can be improved.

Also, in this case, by increasing the distance between the electrodes and making the region where the domain-inverted structure is formed wider, it is possible to increase the alignment tolerance of the patterning in forming the waveguide. This facilitates the formation of a plurality of waveguides.

Further, it is difficult to form a polarization inversion cycle with high accuracy in units of Å. For example, patterning is performed so that the tip of one electrode is oblique to the tip of the other electrode to reduce the distance between the electrodes. By gradually changing the width from the large to the small, the width and the pitch of each domain-inverted region can be changed by a small amount in the waveguide direction, and the quasi-phase matching in the above-described SHG element can be surely performed. Also in this case, the distance between the electrodes is 7 μm or more and 10 to 100 μm.
By setting the degree, patterning can be facilitated.

Next, in the following Examples 9 to 16,
A case where a domain-inverted structure is formed on a lithium tantalate substrate will be described. Example 9 Example 9 will be described with reference to FIG. In this case, the substrate 10 made of lithium tantalate is entirely domain-divided in the thickness direction, and Al, Au is formed on the main surface 1S on the positive side of the polarization.
The first electrode 1 is patterned into, for example, a comb-like pattern, and the second electrode 2 is entirely covered on the back surface 1R on the negative side of the polarization.

In this example, the polarization of the substrate 10 is immersed in a container 8 in a fluorocarbon high voltage solution such as Fluorinert (trade name, manufactured by Sumitomo 3M) or an insulating solution 9 such as silicon oil. A voltage is applied such that the positive side, that is, the first electrode 1 side has a positive potential, and the negative side of polarization, that is, the second electrode 2 side has a negative potential, and a polarization inversion structure of a pattern corresponding to the comb-tooth pattern of the first electrode 1 is applied. Was formed. At this time, the electric field applied to the substrate 10 is desirably selected within the range of the region B described with reference to FIG. 5, that is, about 15 kV or more of the inversion electric field and less than the breakdown electric field.

In this case, the thickness of the substrate 10 is 100 μm,
By applying a pulse having a width of 100 μs five times at a voltage of 2.6 kV, a domain-inverted structure 30 having a fine period of about 3.6 μm can be obtained. That is, a domain-inverted region was formed over the entire thickness of the substrate 10, and the depth could be increased with respect to the pitch P. Further, by applying a voltage in the insulating liquid 9 in this manner, a discharge between the electrodes 1 and 2 can be reliably avoided, and a domain-inverted structure can be obtained with good controllability without causing crystal destruction. Was.

Then, as shown in FIG. 3, an optical waveguide 11 was formed on the main surface 1S of the substrate 10 to form an optical waveguide device. The optical waveguide 11 is patterned by, for example, a proton exchange method, that is, by patterning a mask made of, for example, Ta by applying photolithography or the like to a portion other than the portion where the waveguide 11 is to be formed, and using this as a mask, heating to 260 ° C. for about 20 minutes. It can be formed by dipping in phosphoric acid. Then, after removing the mask, the end face 12 of the optical waveguide is optically polished to obtain an optical waveguide device, that is, an SHG element.

In this case, a periodic domain-inverted structure 30 having no change in characteristics such as a change in refractive index and having a depth greater than the pitch can be obtained. Thus, an SHG element having high light conversion efficiency can be obtained.

Embodiment 10 A description will be given with reference to FIG. 6, parts corresponding to those in FIG. 1 are denoted by the same reference numerals. Also in this case, the substrate 10 is formed as a single domain in the entire thickness direction, the thickness is set to 700 μm or less, and the first surface made of Al or the like is formed on the main surface 1S on the positive side of the polarization. In this case, the second electrode 2 of the comb-like pattern made of Al or the like is also formed on the back surface 1R on the negative side of the polarization, and the comb-tooth portion is formed on the main surface 1S. The upper and lower surfaces 1R are formed so as to be opposed to each other so as to sandwich the substrate 10 therebetween. As in the first embodiment, the positive side of the polarization, that is, the first electrode 1 side is set to the positive potential, and the negative side of the polarization, that is, the second electrode 2 is set.
A voltage was applied with the negative side being a negative potential to form a domain-inverted structure 30 having a pattern corresponding to the comb pattern of the first electrode 1. Also in this case, the magnitude of the electric field is selected in the same manner as in the first embodiment, and the domain-inverted structure 30 is formed without causing crystal destruction and over the comb teeth of the electrodes 1 and 2, that is, over the entire thickness of the substrate 10. Was formed, and the depth could be increased with respect to the pitch.

Also in this case, in the first embodiment described above.
Similarly to the above, an optical waveguide device can be formed by forming an optical waveguide on the main surface 1S by a proton exchange method or the like,
An SHG element with high light conversion efficiency can be obtained.

Embodiment 11 A description will be given with reference to FIG. 7, parts corresponding to those in FIG. 6 are denoted by the same reference numerals, and redundant description will be omitted. In this case, the second electrode 2 is formed on the entire back surface 1R of the substrate 10 by adhesion.
Similarly to the above, a domain-inverted structure 30 having a pattern corresponding to the pattern of the first electrode 1 could be obtained, and the depth could be increased with respect to the pitch.

Also in this case, the first embodiment is used.
Similarly to the above, an optical waveguide device can be formed by forming an optical waveguide on the main surface 1S by a proton exchange method or the like,
An SHG element having high light exchange efficiency can be obtained.

Embodiment 12 A description will be given with reference to FIG. In FIG. 2, portions corresponding to FIG. In this example, a projection or ridge 6 is formed on the substrate 10, and the longitudinal direction of the ridge 6 is selected to be orthogonal to the spontaneous polarization direction of the substrate 10 as indicated by an arrow d, and the longitudinal side wall surface is polarized. And a side surface 1A composed of a positive side and a side surface 1B composed of a negative side. On these sides 1A and 1B,
8A described above over the upper side 1E adjacent to these.
The first electrode 1 and the second electrode 2 made of Al or the like are formed as a comb-like pattern by the manufacturing steps described in FIGS. At this time, the comb teeth portion is formed so as to extend from both upper side surfaces 1E to both side surfaces 1A and 1B, and furthermore, the comb tooth tip portions on both side surfaces 1A and 1B are arranged opposite to both ends of main surface 1S. So that And this ridge 6
The thickness T in the width direction is selected to be 700 μm or less, and the distance between the first and second electrodes 1 and 2 is selected to be 700 μm or less.

In such a configuration, a voltage is applied so that the first electrode 1 side has a positive potential and the second electrode 2 side has a negative potential, thereby forming a domain-inverted region 3 on the ridge 6 and Polarized structure 3 of the pattern corresponding to the pattern at the tip
0 could be obtained.

Also in this case, before or after the above-described voltage application step for polarization inversion, a waveguide is formed in the ridge 6 by the proton exchange method or the like, and the first electrode 1 and the second electrode 2 are formed. Is removed to obtain an SHG element.

As described above, when the ridge 6 is formed on the substrate 10 and electrodes are applied to the side surfaces 1A and 1B and a voltage is applied, an electric field component that is not parallel to spontaneous polarization, ie, polarization inversion occurs. An electric field component having no direct influence can be greatly reduced. Also in the LT crystal, the electric field component not parallel to the direction in which the spontaneous polarization occurs exerts a large stress on the material. Therefore, by reducing such an electric field component, it is possible to more reliably avoid the destruction of the substrate 10 as a result. Can be.

When domain inversion is formed by such a configuration, each domain inversion region 3 can be formed over the entire thickness of the ridge 6. Therefore, also in this case, as in Embodiment 4 described above, by appropriately selecting the depth of the waveguide, the polarization can be achieved over the entire thickness of the waveguide or more, and with almost no crystal breakdown. The inversion structure 30 can be formed, and when this is used as an SHG element, light conversion efficiency such as SHG efficiency can be increased.

Embodiment 13 A description will be given with reference to FIG. 9, parts corresponding to those in FIG. 2 are denoted by the same reference numerals, and redundant description will be omitted. Also in this case, the voltage is applied while the entire substrate 10 in the twelfth embodiment described in FIG. 2 is immersed in the insulating liquid 9 in the container 8 as in the ninth embodiment described in FIG. . Then, the width on the ridge 6, that is, the interval T between the first electrode 1 and the second electrode 2 is selected to be equal to or less than 700 μm. A voltage was applied by selecting an electric field. Also in this case, a domain-inverted structure 30 having a pattern corresponding to the comb-tooth pattern is formed between the tips of the comb teeth of the first electrode 1 and the second electrode 2, and an optical waveguide (not shown) is formed thereon. By forming, a SHG element having high light conversion efficiency could be obtained. Further, by applying the electric field in the insulating liquid 9 in this manner, it was possible to reliably avoid the discharge between the electrodes 1 and 2 as in the first embodiment.

Embodiment 14 A description will be given with reference to FIG. In this case, the substrate 10 made of lithium tantalate is used. The substrate 10 is made of lithium tantalate which is single-domaind in the in-plane direction indicated by an arrow d. A first electrode 1 having a comb-like pattern is formed on the second electrode 2 entirely made of Al or the like on the positive side surface 1B of the one electrode.
Is formed by deposition, sputtering or the like.
Also in this case, a voltage is applied while the entire substrate 10 is immersed in an insulating liquid 9 such as a fluorocarbon-based high voltage such as Fluorinert (trade name, manufactured by Sumitomo 3M) or a silicone oil in a container 8. is there.

At this time, the pitch P of the first electrode 1 is 2 μm.
m, the width W is 1 μm, the distance L between the tips of the comb teeth of the electrodes 1 and 2 on the main surface 1S is 200 μm, and the thickness T of the substrate 10 is 1 mm. 1
By applying a pulse voltage of 5.2 kV and applying a pulse voltage having a width of 100 μs twice or more, for example, five times so that the negative electrode potential becomes the negative potential and the second electrode 2 side becomes the positive potential, crystal breakage and the like hardly occur. The domain-inverted structure 30 having a pattern corresponding to the comb pattern of the first electrode 1 can be obtained.

Fifteenth Embodiment A description will be given with reference to FIG. 11, parts corresponding to those in FIG. 10 are denoted by the same reference numerals, and redundant description will be omitted. In this case, the first electrode 1 having a comb-like pattern is provided on the positive side surface 1A of the polarization of the substrate 10 made of lithium tantalate, and the first electrode 1 having the comb-like pattern is further provided on the main surface 1S having the negative polarity. In this example, two electrodes 2 are formed by application of photolithography or the like after being deposited by vapor deposition, sputtering, or the like.
The patterning is performed so as to be opposed to each other on S and the side surface 1A. Also in this case, the substrate 1
The voltage application is performed in a state where the entirety 0 is immersed in the insulating liquid 9 in the container 8. In such a configuration, a voltage is applied so that the first electrode 1 side has a positive potential and the second electrode 2 side has a negative potential to correspond to the comb pattern of the first electrode 1 and the second electrode 2. The polarization inversion structure 30 having the pattern shown in FIG. Also in this case, the width and pitch of the tip of the comb teeth and the magnitude of the voltage were selected in the same manner as in Example 14, and the domain-inverted structure 30 could be obtained with almost no crystal destruction.

Embodiment 16 A description will be given with reference to FIG. In this case, an example is shown in which a substrate 10 made of lithium tantalate which is single-domained in the in-plane direction indicated by an arrow d is used, and the first electrode 1 and the second electrode 1 are arranged in the polarization direction on one main surface 1S. The electrode 2 is arranged. In this case A
The first electrode 1 and the second electrode 2 are formed by, for example, vapor deposition, sputtering, and the like, and then formed by comb-shaped patterning by application of photolithography or the like. Is 1 μm, for example.
m, the pitch P is, for example, 2 μm, the distance L between the tips of the comb teeth of the electrodes 1 and 2 is 200 μm, and the thickness T of the substrate 10 is 1 m.
m and are arranged such that the tips of the comb teeth of the electrodes 1 and 2 face each other.

Also in this case, the voltage is applied while the entire substrate 10 is immersed in the insulating liquid 9 in the container 8. In such a configuration, at a temperature of 150 ° C. or higher, the first electrode 1 on the negative side of the spontaneous polarization of the substrate 10 has a negative potential and the first side on the positive side between the first electrode 1 and the second electrode 2. Voltage of 5.2 kV so that the second electrode 2 has a positive potential.
As a result, a pulse voltage having a width of 200 μs is applied twice or more, for example, five times to form the domain-inverted region 3 extending from the tip of the comb teeth of the first electrode 1, and the tip of the comb teeth of the first electrode 1 is formed. The periodic domain-inverted structure 30 having a pattern corresponding to the pattern of the portion could be formed with almost no crystal destruction or the like. In addition, discharge between the electrodes 1 and 2 was reliably avoided.

Incidentally, in the above-described embodiment, 15 kV /
A field-inverted structure was formed by applying an electric field of
The upper limit of the applied electric field, that is, the upper limit of the electric field that causes crystal destruction, varies greatly depending on the minute difference in the chemical composition ratio of each crystal substrate sample, the application time of the electric field, and the like. However, in order to reliably avoid crystal breakage and accurately form a domain-inverted structure with a fine pitch and width, 100 kV /
mm or less.

In each of Examples 1 to 16 described above, the electrode is directly formed on the substrate 10. In each case, an insulating layer is provided between the electrode and the substrate 10. It may be provided to apply a voltage.

In the case where the substrate is irradiated with charged particles such as proton exchange and electron beam prior to voltage application,
The polarization in the substrate is easily inverted, and the voltage required for the polarization inversion can be reduced.

Further, as the applied electric field, for example, when a DC voltage to which an AC component of a waveform pattern whose amplitude is gradually attenuated is used, the polarization in the substrate is disturbed, thereby easily inverting the polarization. You can also. Furthermore, by appropriately selecting the width and the number of times of application using a pulse voltage, a domain-inverted region having a required width and depth can be formed.

[0090]

As described above, according to the method for controlling the polarization of lithium niobate and lithium tantalate according to the present invention, the distance between the electrodes to which an electric field is applied is appropriately selected, and the electric field between the inversion electric field and the breakdown electric field is less than the breakdown electric field. Is applied, it is possible to reliably form a domain-inverted structure having a depth corresponding to the distance between the electrodes without causing crystal breakage.

For example, when the present invention is applied to an LN or LT substrate having a single domain in the thickness direction, a domain-inverted structure can be formed with good shape controllability in the depth direction. On the other hand, the LN divided into a single domain in the in-plane direction can reliably form domain inversion by applying an appropriate electric field to the LT substrate with the positive side of polarization as a positive potential and the negative side as a negative potential. In particular, for example, when a convex portion such as a ridge is formed on a substrate and an electrode is applied so as to sandwich the convex portion and a voltage is applied, the polarization inversion has a length corresponding to the thickness of the convex portion. The structure can be obtained, and the shape controllability of the domain-inverted structure can be improved.

Therefore, according to the method of manufacturing an optical waveguide device of the present invention in which a domain-inverted structure is formed by using such a control method and an optical waveguide is further formed to constitute an optical waveguide device, quasi-phase matching is ensured. As a result, an SHG element having high light conversion efficiency can be obtained.

The optical waveguide device of the present invention can be formed by the above-described manufacturing method of the present invention without causing crystal destruction, contamination, etc., and has a polarization having a depth greater than the width and pitch in the c-axis direction. It is possible to realize an optical waveguide device such as an SHG element and an optical modulator having an inverted structure and high light conversion efficiency.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one manufacturing process of an example of a polarization control method.

FIG. 2 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization control method.

FIG. 3 is a schematic enlarged perspective view of an example of the optical waveguide device of the present invention.

FIG. 4 is a view showing the substrate thickness dependence of the polarization reversal electric field and the crystal breakdown electric field of lithium niobate.

FIG. 5 is a diagram showing the substrate thickness dependence of the polarization reversal electric field and the crystal breakdown electric field of lithium tantalate.

FIG. 6 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization control method.

FIG. 7 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization control method.

FIG. 8 is a process chart of another example of the polarization control method.

FIG. 9 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization control method.

FIG. 10 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization control method.

FIG. 11 is a schematic enlarged perspective view showing one manufacturing process of another example of the polarization control method.

FIG. 12 is a schematic enlarged perspective view showing one manufacturing process of another example of the polarization control method.

FIG. 13 is a process chart of an example of a polarization control method by proton exchange.

FIG. 14 is a schematic enlarged cross-sectional view of a domain-inverted region obtained by a proton exchange method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st electrode 2 2nd electrode 1S principal surface 1R back surface 3 Polarization inversion area 5 Power supply 8 Container 9 Insulating liquid 10 Substrate 11 Optical waveguide 12 Waveguide end surface 30 Polarization inversion structure

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI G02F 1/37 G02B 6/12 M (56) References JP-A-3-31828 (JP, A) JP-A-3-132628 ( JP, A) JP-A-4-3128 (JP, A) Albert A. Ballman, H .; Brown, Ferroselect ric Domain Reversal in Lithium Matatalate, Ferroelectric trics, vol. 4, pp. 189-194 (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/29-7/00

Claims (13)

(57) [Claims] 1. A method for controlling the polarization of lithium niobate in which a predetermined domain-inverted structure is formed on a substrate made of single domain lithium niobate, wherein the first and second electrodes are arranged in a polarization direction of the substrate. Placed,
At least the first electrode is formed in a pattern corresponding to the finally obtained pattern of the domain-inverted structure, the distance between the first and second electrodes is 200 μm or less, and the distance between the first and second electrodes is A method of controlling the polarization of lithium niobate, wherein a voltage is applied such that the negative side of the spontaneous polarization of the substrate is at a negative potential and the positive side is at a positive potential to form a domain-inverted structure. 2. The method for controlling the polarization of lithium niobate according to claim 1, wherein the voltage applied between the first and second electrodes is 15 kV / mm or more. 3. The method for controlling polarization of lithium niobate according to claim 1, wherein the voltage applied between the first and second electrodes includes at least two pulses. 4. The lithium niobate according to claim 1, wherein a voltage is applied between the first and second electrodes while the entire substrate is immersed in an insulating liquid. Polarization control method. 5. The niobic acid according to claim 1, wherein the second electrode is substantially entirely coated on the negative side of the spontaneous polarization of the substrate. How to control the polarization of lithium. 6. A method for manufacturing an optical waveguide device, comprising forming a predetermined domain-inverted structure on a substrate made of single domain lithium niobate and then forming an optical waveguide on the substrate, wherein the polarization direction of the substrate is First and second electrodes are arranged on
At least the first electrode is formed in a pattern corresponding to the pattern of the domain-inverted structure finally obtained, the distance between the first and second electrodes is 200 μm or less, and the distance between the first and second electrodes is A voltage is applied such that the negative side of the spontaneous polarization of the substrate is a negative potential and the positive side is a positive potential to form a domain-inverted structure, and an optical waveguide is formed in a region of the substrate where the domain-inverted structure is formed. A method of manufacturing an optical waveguide device. 7. An optical waveguide is formed on a substrate made of lithium niobate having a single domain in the c-axis direction, and a domain-inverted structure is periodically formed in an optical waveguide direction of the optical waveguide. An optical waveguide device, wherein the thickness or the length in the c-axis direction of the domain-inverted structure is 200 μm or less. 8. A method for controlling the polarization of lithium tantalate to form a predetermined domain-inverted structure on a substrate made of single domain lithium tantalate, wherein the first and second electrodes are arranged in the direction of polarization of the substrate. Placed,
At least the first electrode is formed in a pattern corresponding to the finally obtained domain-inverted structure pattern, the distance between the first and second electrodes is 700 μm or less, and the distance between the first and second electrodes is The negative side of the spontaneous polarization of the substrate is set to a negative potential, and the positive side is set to a positive potential.
A polarization control method for lithium tantalate, wherein a polarization inversion structure is formed by applying a voltage of V / mm or more. 9. The method of claim 8, wherein the voltage applied between the first and second electrodes comprises at least two pulses. 10. The polarization control of lithium tantalate according to claim 8, wherein a voltage is applied between the first and second electrodes while the entire substrate is immersed in an insulating liquid. Method. 11. The lithium tantalate according to claim 8, 9 or 10, wherein the second electrode is substantially entirely deposited on the negative side of the spontaneous polarization of the substrate. Polarization control method. 12. A method of manufacturing an optical waveguide device, comprising: forming a predetermined domain-inverted structure on a substrate made of single-domain lithium tantalate, and then forming an optical waveguide on the substrate; First and second electrodes are arranged on
At least the first electrode is formed in a pattern corresponding to the pattern of the domain-inverted structure finally obtained, the distance between the first and second electrodes is set to 700 μm or less, and the distance between the first and second electrodes is The negative side of the spontaneous polarization of the substrate is set to a negative potential, and the positive side is set to a positive potential.
A method for manufacturing an optical waveguide device, comprising applying a voltage of V / mm or more to form a domain-inverted structure, and forming an optical waveguide in a region of the substrate where the domain-inverted structure is formed. 13. An optical waveguide is formed on a substrate made of lithium tantalate having a single domain in the c-axis direction, and a domain-inverted structure is formed periodically in the optical waveguide direction of the optical waveguide. The thickness or length in the c-axis direction of the domain-inverted structure is 700 μm.
m or less, and wherein the domain-inverted structure is formed over substantially the entire thickness or the entire length in the c-axis direction in a region of the substrate where the domain-inverted structure is formed.