JPH05210132A - Polarization control method for lithium niobate and lithium tantalate and production of optical waveguide device by this method and optical waveguide device - Google Patents

Abstract

PURPOSE:To obtain polarization inversion structures with good controllability by averting the surface contamination, change in refractive index, etc., of a substrate consisting of lithium niobate LN or lithium tantalate LT. CONSTITUTION:The polarization inversion structures 30 are formed by disposing 1st and 2nd electrodes 1 and 2, in the polarization direction shown by arrows d of the substrate 10 consisting of the monodomained LN or LT, forming at least the 1st electrodes 1 to the patterns corresponding to the patterns of the polarization inversion structures 30 to be finally obtd., confining the distances between the 1st and 2nd electrodes 1 and 2 to <=200mum in the case of the LN and <=700mum in the case of the LT and impressing the voltage between these electrodes 1 and 2 in such a manner that a negative potential is attained on the negative side of the spontaneous polarization of the substrate 10 and a positive potential on the positive side in the polarization control method for the LN or LT by forming the prescribed polarization inversion structures 30 on the above-mentioned substrate 10.

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 polarization of lithium niobate and lithium tantalate, which is suitable for application to the formation of an optical device such as an optical second harmonic generating element (hereinafter referred to as SHG element). The present invention relates to an optical waveguide device manufacturing method and an optical waveguide device.

[0002]

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

For example, the SHG element generates light of the second harmonic of the frequency of 2ω when the light of the frequency ω is introduced, and the wavelength range of the single wavelength light can be expanded by the SHG element. Accordingly, it is possible to expand the range of use of lasers 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 the laser light.

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

However, the bulk-type SHG device has a relatively low SHG conversion efficiency due to its characteristics, and is inexpensive and of high quality. The above-mentioned LN and lithium tantalate LiTaO ₃ can be obtained.
(LT) cannot be used. In addition, the Cherenkov radiation type SHG element has a problem that the SHG beam is emitted in the direction toward the inside of the substrate and the beam spot shape is, for example, a crescent spot, which is a peculiar shape.

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 for simulating this, a method of periodically arranging the nonlinear optical constants + and-has been proposed (J.
A. Armstrong, N. Bloembergen, et al., Phys. Rev., 127, 1918 (1
962)). As a method of achieving this, there is a method of periodically reversing the direction of a crystal (for example, a crystal axis). As a concrete method, for example, a method in which crystals are thinly cut and bonded (Okada, Takizawa, Ieiri, NHK Technical Research, 29 (1), 24 (19)
77)), or a method of forming a periodic domain-inverted structure by forming a periodic domain by controlling the polarity of the applied current when pulling the crystal (D.Feng, NBMing, JF
Hong, et al, Appl.Phys.Lett.37,607 (1980), K.Nassau,
HJLevin-stein, GHLoiacano Appl.Phys.Lett.6,228
(1965), A.Feisst, P.Koidl Appl.Phys.Lett.47,1125 (19
85)) These methods aim to form a periodic structure throughout the crystalline material. However, the above-mentioned method not only requires a large-scale apparatus, but also has a problem that it is difficult to control polarization inversion formation.

On the other hand, as a method of forming the above-mentioned periodically poled structure near the surface of the crystalline 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)) has been proposed.

When the polarization inversion is formed by this proton exchange method, for example, as shown in FIG. 13 which is a schematic enlarged cross-sectional view of one manufacturing process thereof, it is entirely in the c-axis direction, that is, as shown in FIG.
The Ta mask layer 21 is formed on the + c plane of the substrate 10 made of, for example, LT, which is domain-domained in the polarization direction indicated by the arrow d in FIG.
Is formed in a required parallel band pattern, for example, with a pitch P of 3.6 μm and a width W of 1.8 μm.

Then, in such a state, it is placed in the container 8, immersed in phosphoric acid 19 at 260 ° C. for 50 minutes, and Li ions and protons of the LT substrate are exchanged as shown by arrows H ⁺ and Li ^+. Form an exchange layer. Then, for example, 500
The domain-inverted regions 3 can be periodically formed by performing heating at about C as shown in FIG. However, in this case, the refractive index of the domain-inverted regions 3 changes, or the depth D is smaller than the pitch of the domain-inverted regions 3,
In addition, the domain-inverted region has a triangular cross section and is poor in shape controllability (F. Laurell et al, Integrated Photonics R
esearch, Tu12,1989) etc. In addition, the metal such as the Ta mask layer 21 at the time of proton exchange may be oxidized and adhered to the substrate surface to contaminate the substrate surface.

That is, in order to ensure the above-mentioned 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 shape extending in the depth direction of the substrate 10. It is desirable that the domain-inverted regions 3 and the regions in which the domain-inverted regions do not occur are alternately formed. However, when the SHG element is formed by the above-mentioned proton exchange method, the controllability of the shape of the domain-inverted regions 3 is poor. The leakage of the input light, the leakage of the second harmonic light, the reduction of the coupling efficiency between the input light and the second harmonic light, and the like may lead to the reduction of the so-called light conversion efficiency.

[0011]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to solve the above-mentioned problems of nonlinear optical materials, especially 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, etc., and to obtain an optical waveguide device with good characteristics.

[0012]

FIG. 1 shows an enlarged schematic cross-sectional view of one manufacturing process of an example of a polarization control method according to the present invention. As shown in FIG. 1, the present invention provides a method for controlling the polarization of lithium niobate in which a predetermined domain-inverted structure 30 is formed on a substrate 10 made of single-domain lithium niobate (LN). The first and second electrodes 1 and 2 are arranged in the polarization direction, and at least the first electrode 1 is formed in a pattern corresponding to the pattern of the polarization inversion structure 30 to be finally obtained. The distance T between 1 and 2 is 2
The first and second electrodes 1, 2 are
In between, a voltage is applied so that the negative side of the spontaneous polarization of the substrate 10 becomes a negative potential and the positive side becomes a positive potential to form the polarization inversion structure 30.

In another polarization control method of the present invention, one example of the manufacturing process is shown in FIG. 2, and a predetermined process is performed on a substrate 10 made of lithium niobate single-domained in the in-plane direction. In the method of controlling the polarization of lithium niobate for forming the polarization inversion structure 30, the first and second electrodes 1 and 2 are arranged in the polarization direction on the one main surface of the substrate 10, and at least the first electrode 1 Is the first and second electrodes 1 in a pattern corresponding to the pattern of the finally obtained domain-inverted structure 30,
The distance between the two is 7 μm to 200 μm, and
A voltage is applied between the first and second currents 1 and 2 at a temperature of not less than 0 ° C. so that the negative side of the spontaneous polarization of the substrate 10 becomes a negative potential and the positive side becomes a positive potential, and the polarization inversion structure 30 is formed.
To form.

In the present invention, in each of the above polarization control methods, the voltage applied between the first and second electrodes 1 and 2 is 1
5 kV / mm or more.

Furthermore, in the present invention, in each of the above polarization control methods, the voltage applied between the first and second electrodes 1 and 2 is a pulse voltage composed of at least two pulses.

Further, according to the present invention, in each of the polarization control methods described above, a voltage is applied between the first and second electrodes 1 and 2 in a state where the entire substrate 10 is immersed in an insulating liquid.

Furthermore, in the method for manufacturing an optical waveguide device of the present invention, a polarization inversion structure is formed by the above-mentioned method for controlling the polarization of lithium niobate.

The optical waveguide device of the present invention has an enlarged schematic perspective view of one example thereof, as shown in FIG.
An optical waveguide 11 is formed on a substrate 10 made of lithium niobate, which is divided into single domains in the axial direction, and a domain-inverted structure 30 is periodically formed in the optical waveguide direction of the optical waveguide 11, and the domain-inverted structure 30 is formed. The thickness in the c-axis direction of 200μ
It is configured as m or less.

In another polarization control method of the present invention, as shown in FIG. 1 which is a schematic enlarged cross-sectional view of an example thereof, a substrate 10 made of single-domain lithium tantalate (LT) is used.
In the method for controlling the polarization of lithium tantalate for forming a predetermined polarization inversion structure 30, the first and second electrodes 1 and 2 are arranged in the polarization direction of the substrate 10, and at least the first electrode 1 is the final electrode. To form a pattern corresponding to the pattern of the domain-inverted structure 30 obtained in a desired manner, and the distance T between the first and second electrodes 1 and 2 is set to 700 μm or less.
A voltage is applied between the second electrode 1 and the second electrode 2 so that the negative side of the spontaneous polarization of the substrate 10 becomes a negative potential and the positive side becomes a positive potential to form the domain-inverted structure 30.

Further, another polarization control method of the present invention is, as shown in FIG. 2 of one manufacturing process thereof, a substrate 10 made of lithium tantalate single-domained in the in-plane direction,
In the method for controlling the polarization of lithium tantalate which forms a predetermined polarization inversion structure 30, the first and second electrodes 1 and 2 are arranged in the polarization direction on one main surface of the substrate 10, and at least the first electrode is provided. 1 is formed in a pattern corresponding to the pattern of the finally obtained domain-inverted structure 30 with the distance between the first and second electrodes 1 and 2 being 700 μm or less, and 150
A voltage is applied between the first and second electrodes 1 and 2 so that the negative side of the spontaneous polarization of the substrate 10 is a negative potential and the positive side thereof is a positive potential at a temperature of not less than 0 ° C.
To form.

The present invention also provides a method for controlling the polarization of lithium tantalate as described above, wherein the first and second electrodes 1, 2 are
The voltage applied between them is set to 15 kV / mm or more.

Further, according to the present invention, in the above-described polarization control method for lithium tantalate, the voltage applied between the first and second electrodes 1 and 2 is a pulse voltage composed of at least two pulses.

Further, according to the present invention, in each of the above-described methods for controlling the polarization of lithium tantalate, a voltage is applied between the first and second electrodes 1 and 2 with the entire substrate 10 immersed in the insulating liquid.

Furthermore, in the method of manufacturing the optical waveguide device of the present invention, the polarization inversion structure is formed by the above-mentioned polarization control method of lithium tantalate.

Further, the optical waveguide device of the present invention has a schematic enlarged perspective view of an example thereof, as shown in FIG.
An optical waveguide 11 is formed on a substrate 10 made of lithium tantalate which is single-domained in the axial direction, and a polarization inversion structure 30 is periodically formed in the optical waveguide direction of the optical waveguide 11, and this polarization inversion structure 30 is formed. C-axis thickness of 700
Configured to be less than or equal to μm

[0026]

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

This is probably because of the following reasons. That is, in general, such as LN single crystal and LT single crystal,
Ferroelectric material (fr) whose crystal is destroyed when high voltage is applied
In ozenferroelectrics), it is said that polarization inversion does not occur even if a voltage that does not cause crystal breakdown is applied, and conventionally, polarization inversion is caused by application of a relatively low voltage that does not cause crystal breakdown. It was That is, in order to reduce the coercive electric field, at a high temperature of about 600 ° C,
A relatively low electric field with respect to a thick substrate having a thickness of about 1 mm or more in the c-axis direction, that is, several V / mm to several hundred V /
An electric field of about mm was applied to form polarization inversion.

However, it has been clarified by the inventors of the present invention that the above-mentioned 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 reversal electric field and the crystal breakdown electric field of the lithium niobate LN and lithium tantalate LT single crystal substrates, respectively. In this case, as sample 1, LN single crystal manufactured by Yamaju Ceramics, as sample 2, LN single crystal manufactured by Crystal Technology, and sample 3
As an LN single crystal manufactured by Mitsui Kinzoku Co., Ltd. and an LT single crystal manufactured by Yamaju Ceramic Co., Ltd. as sample 4, the electric field (polarization reversal electric field) and the crystal breakdown start to occur by changing the substrate thickness. The electric field (crystal breakdown electric field) was measured. In the figure, △, ○, □, and ▽ are samples 1 to 1, respectively.
Inversion electric field of 4, ▲, ●, ■ and ▼ are samples 1 to 4 respectively
Shows the breakdown electric field.

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 as the substrate thickness increases, and falls below the reversal electric field when the substrate thickness is 200 μm for LN and 700 μm or more for LT. Therefore, if the substrate thickness is LN, it is 200 μm, and if it is LT, it is 7 μm.
If the thickness exceeds 00 μm, the crystal is destroyed before the polarization inversion occurs, and the polarization inversion operation cannot be performed.

On the other hand, in LN, the thickness of the substrate is 2
In case of less than 00 μm and less than 700 μm in LT,
Since there is a region (represented by hatched regions A and B in FIGS. 4 and 5) that is equal to or greater than the reversal electric field and equal to or less than the breakdown electric field, an appropriate electric field is required when using a substrate having such a relatively thin thickness. By applying the voltage, it is considered that a polarization inversion structure can be satisfactorily obtained without causing crystal breakdown. Moreover, in this case, polarization inversion occurs between the electrodes 1 and 2, so that the shape has a larger depth than the width and the pitch, and the polarization inversion structure 30 having a desired shape can be obtained.

On the other hand, in the case of using the substrate 10 made of lithium niobate LN or lithium tantalate LT that is single-domained in the in-plane direction, the first and the first polarization directions on one main surface of the substrate 10 are used. The two electrodes 1 and 2 are formed at least as a pattern corresponding to the pattern of the domain-inverted structure 30 finally obtained by the first electrode 1, and in particular, the distance between the first and second electrodes 1 and 2 is 200 for LN
The polarization inversion structure could be similarly formed with good controllability by forming it to have a thickness of less than or equal to μm and, in the case of LT, to less than or equal to 700 μm. In this case, the domain-inverted structure 30 could be accurately formed by setting the temperature at the time of applying the voltage to 150 ° C. or higher.

For LN and LT substrate materials having a substrate thickness of 100 μm, electrodes are formed on the main surface and the back surface to make the interelectrode distance 100 μm, and a DC voltage of 1.5 kV is 40
When applied for a minute, a domain-inverted structure could be formed without causing crystal breakdown. Therefore, although there is a variation in the reversal electric field in FIGS. 4 and 5, it is understood that the polarization reversal structure can be surely obtained by setting the applied electric field to 15 kV / mm or more.

Further, by applying two or more pulse voltages as the applied voltage, it was possible to form the domain-inverted structure without causing crystal breakdown in the same manner.

Further, by applying a voltage while these substrates are immersed in an insulating liquid, it is possible to suppress the discharge between the electrodes adhered to the surface of the substrate even when a high voltage is applied, and it is possible to accurately reverse the polarization. The structure could be formed.

According to each polarization control method as described above, the crystal breakdown can be reliably avoided by applying an electric field of 15 kV / mm or more with the distance between the electrodes being 200 μm or less for LN and 700 μm or less for LT. Therefore, it is not necessary to heat to about 500 ° C. to 1200 ° C. in order to reduce the coercive electric field, and the polarization inversion can be formed at room temperature. Therefore, it is possible to avoid the inconvenience such as the contamination of the crystal caused by depositing or contacting the electrodes while heating and the change in the refractive index due to the proton exchange, and the change in the characteristics can be avoided.

In the optical waveguide device formed by such a polarization control method, as shown in FIG. 3, the polarization inversion structure 30 in which the optical waveguide 11 is provided has a thickness in the c-axis direction of 200 μm or less at LN. , LT is 700 μm or less, and by adopting such a configuration, it is possible to form a periodic domain-inverted structure without causing a change in characteristics as described above, and surely a quasi phase. S with good matching and good SHG conversion efficiency
An HG element can be obtained.

[0037]

EXAMPLES Each example of the polarization control method of the present invention will be described in detail below. In each case, a periodic polarization inversion 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 an optical waveguide device of a high efficiency SHG element. Indicates. Further, in each of the examples, the substrate 10 is divided into single domains 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 surface in the c-axis direction. I went to.

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

Example 1 An explanation will be given with reference to the schematic enlarged perspective view of FIG. In this case, in the case where the substrate 10 is entirely divided into single domains in the thickness direction, 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 tooth pattern. And the second electrode 2 is deposited on the entire back surface 1R on the negative side of the polarization.

In this example, the entire substrate 10 is polarized while being immersed in the container 8 in a fluorocarbon high-voltage resistant liquid such as Fluorinert (trade name, manufactured by Sumitomo 3M) or an insulating liquid 9 such as silicon oil. A voltage is applied with the positive side, that is, the first electrode 1 side as a positive potential, and the negative side of polarization, that is, the second electrode 2 side, as a negative potential, and a voltage is applied, and the polarization inversion structure of the pattern corresponding to the comb tooth pattern of the first electrode 1 is applied. Formed. At this time, the electric field applied to the substrate 10 is preferably selected within the range of the area A described in FIG. 4, that is, at least 15 kV which is higher than the reversal electric field and lower than the breakdown electric field. Reference numeral 5 indicates a power source.

In this case, the thickness of the substrate 10 is 98 μm, the voltage is 2.1 kV, and the voltage is applied for 1 ms.
A domain-inverted structure 30 having a fine period of about 3 μm can be obtained, and a domain-inverted region is formed over the comb teeth of each 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 the voltage in the insulating liquid 9 as described above, the discharge between the electrodes 1 and 2 can be surely avoided, and the polarization inversion structure can be obtained with good controllability without causing crystal breakdown. It was

Then, as shown in FIG. 3, an optical waveguide 11 was formed on the main surface 1S of the substrate 10 to prepare an optical waveguide device. The optical waveguide 11 is patterned by, for example, a proton exchange method, that is, a mask made of Ta or the like is patterned by applying photolithography or the like to a portion other than the portion where the waveguide 11 is formed, and this is used as a mask and heated to 200 ° 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, since there is no change in characteristics such as a change in refractive index and a periodic domain-inverted structure 30 having a large depth with respect to the pitch can be obtained, quasi-phase matching is surely performed. As a result, an SHG element having high light conversion efficiency can be obtained.

Example 2 Description will be given with reference to the schematic enlarged perspective view of FIG. 6, parts corresponding to those in FIG. 1 are designated by the same reference numerals.
In this case as well, the substrate 10 is formed into a single domain over the entire surface 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. Electrode 1 is patterned in a comb-teeth pattern, and in this case, the second electrode 2 having a comb-teeth pattern also made of Al or the like is formed on the back surface 1R on the negative side of the polarization, and the comb-teeth portion is the main surface 1.
It is formed so that the substrate 10 is sandwiched between the upper surface S and the rear surface 1 so as to face each other. Then, as in Example 1 described above, a voltage is applied with the positive side of the polarization, that is, the first electrode 1 side as a positive potential, and the negative side of the polarization, that is, the second electrode 2 side as a negative potential, to apply the voltage to the first electrode 1 A domain-inverted structure 30 having a pattern corresponding to the comb-teeth pattern was formed. Also in this case, the magnitude of the electric field is selected in the same manner as in Example 1 so that the crystal inversion does not occur and the domain-inverted structure 30 is formed over the comb teeth of each 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 is also used.
Similarly, an optical waveguide can be formed on the main surface 1S by a proton exchange method or the like to prepare an optical waveguide device,
An SHG element with high light conversion efficiency can be obtained.

Embodiment 3 Description will be given with reference to the schematic enlarged perspective view of FIG. In FIG. 7, parts corresponding to those in FIG. 6 are designated by the same reference numerals, and redundant description will be omitted. In this case, the second electrode 2 is entirely formed on the back surface 1R of the substrate 10, and this example also corresponds to the pattern of the first electrode 1 as in the case of the fifth embodiment. It was possible to obtain the domain-inverted structure 30 of the pattern and further to make the depth large with respect to the pitch.

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

Fourth Embodiment A description will be given with reference to FIG. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and duplicate description will be omitted. 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 indicated by the arrow d of the substrate 10, and the side wall surfaces in the longitudinal direction thereof are a side surface 1A composed of the positive side of polarization and a side surface 1B composed of the negative side. It is composed of This side surface 1A and 1
A first electrode 1 and a second electrode 2 made of Al or the like are formed as a comb-teeth pattern over B and the upper side surface 1E adjacent thereto by a manufacturing process described later. At this time, the comb-teeth part is located on both side surfaces 1A and 1B from both upper side surfaces 1E
The comb-teeth tips on both side surfaces 1A and 1B are arranged opposite to both ends of the main surface 1S. 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 structure, 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 form the polarization inversion region 3 in the ridge 6, and each comb tooth is formed. Polarization inversion structure 3 of the pattern corresponding to the pattern of the tip
I was able to get 0.

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

Then, 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.
Pattern.

Subsequently, as shown in FIG. 8C, the substrate 10 is etched from the main surface 1S by 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. 1E is exposed to form the ridge 7. At this time, the height of the ridge 6 is set to about 2 μm by controlling the etching depth with respect to the substrate 10.

Further, as shown in FIG. 8D, Al, A
Metal layer 34 made of, for example, Al such as u, Pt, K, Li
Are covered and formed on the entire surface of the ridge 6 by vapor deposition, sputtering or the like.

Next, after patterning the metal layer 34 into the comb-like pattern shown in FIG. 2 by anisotropic etching such as RIE, the resist 21 is removed by immersing it in a solvent such as acetone, and the like shown in FIG. 8E. As shown in FIG. 7, only the metal layer 34 on the ridge 6 is lifted off, and the first comb-shaped first adjacent side surfaces 1A and 1B are adjacent to the upper side surface 1E.
The 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 voltage application step for forming the polarization inversion described above, and the first electrode 1 and the second electrode 2 are removed. Thus, an SHG element can be obtained.

In this way, when the ridge 6 is formed on the substrate 10 and the electrodes are attached 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, it is possible to greatly reduce the electric field component that does not directly affect the polarization reversal. The substrate 10 such as an LN crystal has a large stress exerted on the material by an electric field component that is not parallel to the direction in which the spontaneous polarization occurs. Therefore, by reducing such an electric field component, the crystal breakdown of the substrate 10 can be more reliably performed. It can be avoided.

When the domain inversion is formed by such a structure, each domain inversion region 3 can be formed over the entire thickness of the ridge 6. Therefore, by properly selecting the depth of the waveguide, it is possible to form the domain-inverted structure 30 over the entire thickness of the waveguide or a depth greater than that, and with almost no crystal destruction. When used as an SHG element, light conversion efficiency such as SHG efficiency can be improved.

Embodiment 5 Description will be given with reference to the schematic enlarged perspective view of FIG. In FIG. 9, parts corresponding to those in FIG. 2 are designated 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 Example 4 described in FIG. 2 is immersed in the insulating liquid 9 in the container 8 as in Example 1 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 the voltage was applied by selecting the electric field within the region A in FIG. 4 as in the above-mentioned examples. Also in this case, a polarization inversion structure 30 having a pattern corresponding to the comb tooth pattern is formed between the comb tooth tips of the first electrode 1 and the second electrode 2, and an optical waveguide (not shown) is formed thereon. By forming the, it was possible to obtain an SHG element with high light conversion efficiency. 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.
It was possible to reliably avoid the discharge during the period.

Embodiment 6 Description will be given with reference to the schematic enlarged perspective view of FIG. In this case, the substrate 10 made of lithium niobate single-domained in the in-plane direction indicated by the arrow d is used, and the negative side of the polarization 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-shaped pattern is deposited and formed, while a second electrode 2 made of Al or the like is entirely deposited and formed on the side surface 1B on the positive side of polarization by vapor deposition, sputtering or the like. Become. 5 is a power supply. Even in this case, the entire substrate 10 is covered with the Fluorinert (Sumitomo 3
The voltage is applied in a state of being immersed in a CFC-based high voltage resistant liquid such as manufactured by M Co., etc. or an insulating liquid 9 such as silicon oil. At this time, the pitch P of the first electrodes 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 so that the electrode 1 side has a negative potential and the second electrode 2 side has a positive potential, and a pulse voltage with a width of 100 μs is applied twice or more, for example, five times, so that crystal destruction or the like is almost eliminated It is possible to obtain the domain-inverted structure 30 having a pattern corresponding to the comb-teeth pattern of the first electrode 1 without occurring.

Embodiment 7 Description will be given with reference to a schematic enlarged perspective view of FIG. 11
In FIG. 10, parts corresponding to those in FIG. In this case, the first electrode having the comb-teeth pattern is formed on the side surface 1A on the positive polarization side of the substrate 10 made of lithium niobate, and the second electrode having the comb-teeth pattern is formed on the main surface 1S on the negative polarization side. 2 is an example formed by applying photolithography or the like after being deposited by vapor deposition, sputtering, etc., so that the comb-teeth tips of the electrodes 1 and 2 face each other on the main surface 1S and the side surface 1A. It is 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, which corresponds to the comb tooth pattern of the first electrode 1 and the second electrode 2. A domain-inverted structure 30 having such a pattern was formed. Also in this case, the width and pitch of the tips 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.

Example 8 Description will be given with reference to the schematic enlarged perspective view of FIG. In this case, the substrate 10 made of lithium niobate single-domained in the direction indicated by the arrow d is used as an example, and the first electrode 1 and the second electrode 2 are arranged in the polarization direction on the one main surface 1S. To place. In this case, the first electrode 1 and the second electrode 2 made of Al or the like are both formed by depositing by vapor deposition, sputtering, etc., and then patterned by applying photolithography or the like into a comb tooth shape. Width W at the tip
Is 1 μm, the pitch P is, for example, 2 μm, the distance L between the comb tooth tips of the electrodes 1 and 2 is 100 μm, the thickness T of the substrate 10 is about 1 mm, and the comb tooth tips of the electrodes 1 and 2 are Are arranged so as 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, under the 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 electrode on the positive side between the first electrode 1 and the second electrode 2. The voltage is 2.6 kV so that the second electrode 2 has a positive potential.
As a pulse voltage having a width of 100 μs is applied twice or more, for example, five times to form the polarization inversion region 3 extending from the tip of the comb tooth of the first electrode 1, and the tip of the comb tooth of the first electrode 1 is formed. The periodic domain-inverted structure 30 having a pattern corresponding to the partial pattern could be formed with almost no crystal destruction. Moreover, the discharge between the electrodes 1 and 2 could be reliably avoided.

In each of the above-mentioned examples, the polarization inversion structure is formed on the lithium niobate LN substrate to obtain the optical waveguide device. 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, can 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, which is the light source, is 6 μm.
It is about m or more, and by increasing the width of the waveguide end face 12, the coupling efficiency can be improved. In this case, by setting the distance between the electrodes to be about 7 μm or more, the domain-inverted structure 30 can be reliably formed even in the vicinity of the waveguide end face 12, and such coupling efficiency can be achieved without impairing the conversion efficiency. It is possible to improve.

Further, in this case, by increasing the distance between the electrodes and widening the region where the domain-inverted structure is formed, it is possible to increase the alignment margin of the patterning when forming the waveguide, and it is possible to fabricate. This facilitates the formation of a plurality of waveguides.

Further, it is difficult to accurately form the polarization inversion period in units of Å, but for example, patterning is performed so that the tip of one electrode is oblique to the tip of the other electrode, and the distance between electrodes is reduced. By gradually changing from a large value to a large value, the width and the pitch of each polarization inversion region can be slightly changed in the waveguide direction, and the quasi phase matching in the SHG element described above can be surely performed. Even in this case, the distance between the electrodes is 7 μm or more and 10 to 100 μm.
By adjusting the degree, patterning can be facilitated.

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

In this example, the entire substrate 10 is polarized while being immersed in the container 8 in a fluorocarbon high-voltage resistant liquid such as Fluorinert (manufactured by Sumitomo 3M Co., Ltd.) or an insulating liquid 9 such as silicon oil. A voltage is applied with the positive side, that is, the first electrode 1 side as a positive potential, and the negative side of polarization, that is, the second electrode 2 side, as a negative potential, and a voltage is applied, and the polarization inversion structure of the pattern corresponding to the comb tooth pattern of the first electrode 1 is applied. Formed. At this time, the electric field applied to the substrate 10 is preferably selected within the range of the region B described in FIG. 5, that is, the reversal electric field of about 15 kV or more 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 with a voltage of 2.6 kV, a domain-inverted structure 30 having a fine period of about 3.6 μm can be obtained, and further, the comb-teeth portion of each electrode 1 and 2 can be obtained. That is, the domain-inverted regions were formed over the entire thickness of the substrate 10, and the depth could be increased with respect to the pitch P thereof. Further, by applying the voltage in the insulating liquid 9 as described above, the discharge between the electrodes 1 and 2 can be surely avoided, and the polarization inversion structure can be obtained with good controllability without causing crystal breakdown. It was

Then, as shown in FIG. 3, an optical waveguide 11 was formed on the main surface 1S of the substrate 10 to prepare an optical waveguide device. This optical waveguide 11 is patterned by, for example, a proton exchange method, that is, a mask made of, for example, Ta, is applied to the portion other than the portion where the waveguide 11 is formed by patterning by photolithography or the like, and this is used as a mask and heated 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, since there is no change in characteristics such as a change in the refractive index and the periodic domain-inverted structure 30 having a large depth with respect to the pitch can be obtained, the quasi-phase matching is surely performed. As a result, an SHG element having high light conversion efficiency can be obtained.

Tenth Embodiment A description will be given with reference to FIG. 6, parts corresponding to those in FIG. 1 are designated by the same reference numerals. In this case as well, the substrate 10 is formed into a single domain over the entire surface in the 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. Electrode 1 is patterned in a comb-teeth pattern, and in this case, the second electrode 2 in the comb-teeth 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-teeth portion is the main surface 1S. The upper surface and the back surface 1R are formed so as to face each other so as to sandwich the substrate 10 therebetween. Then, as in the first embodiment, the positive side of polarization, that is, the first electrode 1 side is a positive potential, and the negative side of polarization, that is, the second electrode 2 is.
A voltage was applied with the side being a negative potential, and a domain-inverted structure 30 having a pattern corresponding to the comb-teeth pattern of the first electrode 1 was formed. Also in this case, the magnitude of the electric field is selected in the same manner as in Example 1 so that the crystal inversion does not occur and the domain-inverted structure 30 is formed over the comb teeth of each 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 is also used.
Similarly, an optical waveguide can be formed on the main surface 1S by a proton exchange method or the like to prepare an optical waveguide device,
An SHG element with high light conversion efficiency can be obtained.

Embodiment 11 An explanation will be given with reference to FIG. In FIG. 7, parts corresponding to those in FIG. 6 are designated by the same reference numerals, and redundant description will be omitted. In this case, the second electrode 2 is entirely formed on the back surface 1R of the substrate 10 by this method.
Similarly to the above, the 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 described above is also used.
Similarly, an optical waveguide can be formed on the main surface 1S by a proton exchange method or the like to prepare an optical waveguide device,
It is possible to obtain an SHG element with high light exchange efficiency.

Embodiment 12 A description will be given with reference to FIG. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and duplicate description will be omitted. 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 indicated by the arrow d of the substrate 10, and the side wall surface in the longitudinal direction is polarized. 1A on the positive side and 1B on the negative side. On this side surface 1A and 1B,
8A described above over the upper side surface 1E adjacent to these.
The first electrode 1 and the second electrode 2 made of Al or the like are formed as a comb-shaped pattern by the manufacturing steps described in E to E. At this time, the comb teeth are formed so as to extend from both upper side surfaces 1E to both side surfaces 1A and 1B, and the tip ends of the comb teeth on both side surfaces 1A and 1B are arranged to face both ends of the main surface 1S. To do so. 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 structure, 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 form the polarization inversion region 3 on the ridge 6, and each comb tooth is formed. Polarization inversion structure 3 of the pattern corresponding to the pattern of the tip
I was able to get 0.

Also in this case, a waveguide is formed in the ridge 6 by the Pronto exchange method or the like before or after the voltage application step for forming the polarization inversion, and the first electrode 1 and the second electrode 2 are formed. Can be 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 to apply a voltage, an electric field component which is not parallel to the spontaneous polarization, that is, a polarization inversion, is generated. It is possible to greatly reduce the electric field component that has no direct influence. Even in the LT crystal, the 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 electric field component, the destruction of the substrate 10 as a result can be more surely avoided. You can

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

Embodiment 13 A description will be given with reference to FIG. In FIG. 9, parts corresponding to those in FIG. 2 are designated 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 Example 12 described in FIG. 2 is immersed in the insulating liquid 9 in the container 8 as in Example 9 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 700 μm or less, and as in each of the above-described examples, within the range of the region B in FIG. A voltage was applied by selecting the electric field. Also in this case, a polarization inversion structure 30 having a pattern corresponding to the comb tooth pattern is formed between the comb tooth tips of the first electrode 1 and the second electrode 2, and an optical waveguide (not shown) is formed thereon. By forming the, it was possible to obtain an SHG element with high light conversion efficiency. Further, by applying the electric field in the insulating liquid 9 as described above, it was possible to surely 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 single-domained in the in-plane direction indicated by the arrow d is used, and the negative side of polarization on the main surface 1S is made of Al or the like by application of photolithography or the like. A first electrode 1 having a comb-like pattern is deposited and formed, and a second electrode 2 made of Al or the like is entirely formed on the positive side surface 1B of the one electrode.
Is formed by vapor deposition, sputtering, or the like.
Also in this case, the voltage is applied while the entire substrate 10 is immersed in the fluorocarbon high withstand voltage such as Fluorinert (trade name, manufactured by Sumitomo 3M Co., Ltd.) in the container 8 or the insulating liquid 9 such as silicon oil. is there.

At this time, the pitch P of the first electrodes 1 is 2 μm.
m, the width W is 1 μm, the distance L between the tip ends of the comb teeth of each 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
With a voltage of 5.2 kV so that the side of the second electrode 2 has a negative potential and the side of the second electrode 2 has a positive potential, a pulse voltage having a width of 100 μs is applied twice or more, for example, five times, and crystal destruction or the like hardly occurs. It is possible to obtain the domain-inverted structure 30 having a pattern corresponding to the comb tooth pattern of the first electrode 1.

Embodiment 15 A description will be given with reference to FIG. 11, parts corresponding to those in FIG. 10 are designated by the same reference numerals, and redundant description will be omitted. In this case, the first electrode 1 having the comb-teeth pattern is formed on the side surface 1A on the positive polarization side of the substrate 10 made of lithium tantalate, and the first electrode 1 having the comb-teeth pattern is formed on the main surface 1S on the negative polarization side. In the example in which two electrodes 2 are deposited by vapor deposition, sputtering or the like and then formed by application of photolithography or the like, the tip end portions of the comb teeth of each of the electrodes 1 and 2 are the main surface 1
Patterning is performed so as to face each other over S and the side surface 1A. Even in this case, the substrate 1
The voltage is applied in a state where the whole 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, which corresponds to the comb tooth pattern of the first electrode 1 and the second electrode 2. A domain-inverted structure 30 having such a pattern was formed. Also in this case, the width and pitch of the tips 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, the substrate 10 made of lithium tantalate single-domained in the in-plane direction indicated by the arrow d is used as an example, and the first electrode 1 and the second electrode 1 in the polarization direction on the one main surface 1S are used. The electrode 2 is arranged. In this case A
The first electrode 1 and the second electrode 2 made of 1 or the like are both formed by deposition by vapor deposition, sputtering, etc., and then patterned into a comb tooth shape by application of photolithography, etc. Width W is, for example, 1μ
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.
The distance between the electrodes 1 and 2 is about m, 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, under the 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 electrode on the positive side between the first electrode 1 and the second electrode 2. The voltage is set to 5.2 kV so that the second electrode 2 has a positive potential.
As a pulse voltage having a width of 200 μs is applied twice or more, for example, five times to form the polarization inversion region 3 extending from the tip of the comb tooth of the first electrode 1, and the tip of the comb tooth of the first electrode 1 is formed. The periodic domain-inverted structure 30 having a pattern corresponding to the partial pattern could be formed with almost no crystal destruction. Moreover, the discharge between the electrodes 1 and 2 could be reliably avoided.

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

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

When the substrate is subjected to proton exchange and irradiation of charged particles such as an electron beam prior to voltage application,
The polarization in the substrate is easily inverted, and the voltage value required for the polarization inversion can be reduced.

Further, as the applied electric field, for example, when a DC voltage added with an AC component of a waveform pattern whose amplitude is gradually attenuated is used, the polarization in the substrate is disturbed, thereby facilitating the inversion of the polarization. You can also Further, by properly selecting the width and the number of times of application using the pulse voltage, it is possible to form the domain-inverted region having the required width and depth.

[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 the electric field is applied is appropriately selected, and the electric field of the reversal electric field or more and the breakdown electric field or less is set. By applying, it is possible to reliably form a domain-inverted structure having a depth corresponding to the distance between the electrodes without causing crystal breakdown.

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 that is single-domained in the in-plane direction can surely form the polarization inversion by applying an appropriate electric field to the LT substrate with the positive side of the polarization being the positive potential and the negative side being the negative potential. In particular, for example, when a convex portion such as a ridge is formed on a substrate and electrodes are applied so as to sandwich the convex portion and a voltage is applied, polarization inversion of a length corresponding to the thickness of the convex portion is performed. 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 the polarization inversion structure is formed by using such a control method and the optical waveguide is further formed to constitute the optical waveguide device, the quasi phase matching is surely performed. It is possible to obtain an SHG device having high light conversion efficiency.

The optical waveguide device of the present invention can be formed by the above-described manufacturing method of the present invention without causing crystal breakage, contamination, etc., and has a polarization 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 which has an inversion structure and has a high light conversion efficiency.

[Brief description of drawings]

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

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

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

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

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

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

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

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

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

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

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

FIG. 12 is a schematic linear enlarged perspective view showing another manufacturing process 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 an enlarged schematic cross-sectional view of a domain-inverted region by a proton exchange method.

[Explanation of symbols]

 1 1st electrode 2 2nd electrode 1S Main surface 1R Back surface 3 Polarization inversion region 5 Power supply 8 Container 9 Insulating liquid 10 Substrate 11 Optical waveguide 12 Waveguide end face 30 Polarization inversion structure

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G02F 1/37 7246-2K

Claims (14)

[Claims] 1. A method for controlling the polarization of lithium niobate, wherein 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 at least 200 μm. A method for controlling polarization of lithium niobate, wherein a polarization inversion structure is formed by applying a voltage so that the negative side of the spontaneous polarization of the substrate is a negative potential and the positive side thereof is a positive potential. 2. A method for controlling the polarization of lithium niobate, which comprises forming a predetermined domain-inverted structure on a substrate made of lithium niobate that is single-domained in the in-plane direction, comprising: A first electrode and a second electrode, and at least the first electrode has a pattern corresponding to the pattern of the finally obtained domain-inverted structure, and the distance between the first and second electrodes is 7 μm to 200 μm. And a voltage is applied between the first and second electrodes so that the negative side of the spontaneous polarization of the substrate is a negative potential and the positive side is a positive potential. A polarization control method for lithium niobate, characterized in that a polarization inversion structure is formed. 3. The method for controlling polarization of lithium niobate according to claim 1 or 2, wherein the voltage applied between the first and second electrodes is 15 kV / mm or more. 4. The lithium niobate according to claim 1, 2 or 3, wherein the voltage applied between the first and second electrodes comprises at least two pulses. Polarization control method. 5. The voltage is applied between the first and second electrodes in a state where the entire substrate is immersed in an insulating liquid, wherein the voltage is applied between the first electrode and the second electrode. 4. The method for controlling the polarization of lithium niobate according to item 4. 6. An optical waveguide device, characterized in that a polarization inversion structure is formed by the method of controlling the polarization of lithium niobate according to claim 1, claim 2, claim 3, claim 4, or claim 5. Manufacturing method. 7. An optical waveguide is formed on a substrate made of lithium niobate single-domained in the c-axis direction, and a domain-inverted structure is periodically formed in the optical waveguide direction by the optical waveguide. An optical waveguide device, wherein the thickness of the domain-inverted structure in the c-axis direction is 200 μm or less. 8. A method of controlling the polarization of lithium tantalate in which a predetermined domain-inverted structure is formed on a substrate made of single-domain lithium tantalate, wherein the first and second electrodes are arranged in the 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 700 μm or less, and the distance between the first and second electrodes is at least 700 μm. In the method of controlling polarization of lithium tantalate, a voltage is applied so that the negative side of the spontaneous polarization of the substrate is a negative potential and the positive side of the substrate is a positive potential to form a polarization inversion structure. 9. A method of controlling the polarization of lithium tantalate in which a predetermined domain-inverted structure is formed on a substrate made of lithium tantalate single-domained in the in-plane direction, the polarization direction on one main surface of the substrate. A first electrode and a second electrode, and at least the first electrode has a pattern corresponding to the pattern of the finally obtained domain-inverted structure so that the distance between the first and second electrodes is 700 μm or less. At a temperature of 150 ° C. or higher, a voltage is applied between the first and second electrodes such that the negative side of the spontaneous polarization of the substrate is a negative potential and the positive side is a positive potential. A polarization control method for lithium tantalate, which is characterized in that an inverted structure is formed. 10. The method for controlling polarization of lithium tantalate according to claim 8, wherein the voltage applied between the first and second electrodes is 15 kV / mm or more. 11. The lithium tantalate according to claim 8, wherein the voltage applied between the first and second electrodes comprises at least two pulses. Polarization control method. 12. The method according to claim 8, wherein a voltage is applied between the first and second electrodes in a state where the entire substrate is immersed in an insulating liquid.
Alternatively, the method for controlling the polarization of lithium tantalate according to claim 11. 13. An optical waveguide device, wherein a polarization inversion structure is formed by the method for controlling the polarization of lithium tantalate according to claim 8, claim 9, claim 10, claim 11, or claim 12. Manufacturing method. 14. An optical waveguide is formed on a substrate made of lithium tantalate single-domained in the c-axis direction, and a domain-inverted structure is periodically formed in the optical waveguide direction by the optical waveguide. An optical waveguide device, wherein the polarization inversion structure has a thickness in the c-axis direction of 700 μm or less.