JPH04280234A - Control method of polarization inversion - Google Patents

Abstract

PURPOSE:To provide an optical device having a high conversion efficiency by forming a polarization inversion structure with good controllability, and avoid the surface pollution and refractive index change to a ferroelectric material. CONSTITUTION:A voltage of 10V/mm-100kV/mm is applied so that the negative side of the spontaneous polarization of a simply polarized ferroelectric material has a negative potential and the positive side has a positive potential, a charged particle of acceleration voltage 1kV-100kV is radiated so that the current density in the irradiation surface of the ferroelectric material 1 is 1muA/mm<2>-100muA/mm<2>, and a polarization inversion structure is formed with taking at least either one of the voltage application and the charged particle radiation as a pattern corresponding to the pattern of a finally obtained polarization inversion structure.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization inversion control method suitable for application to the formation of optical devices such as optical second harmonic generating elements (hereinafter referred to as SHG elements).

0002

2. Description of the Related Art In recent years, it has been proposed to improve characteristics such as optical output by forming a periodic domain inversion structure on the surface of optical devices such as SHG elements.

For example, an SHG element generates second harmonic light of a frequency of 2ω when light of a frequency ω is introduced, and this SHG element can expand the wavelength range of single wavelength light. Accordingly, it is possible to expand the scope of use of lasers and optimize the use of laser light in each technical field. For example, by shortening the wavelength of laser light, it is possible to improve the recording density in optical recording and reproduction using laser light, magneto-optical recording and reproduction, and the like.

[0004] As such an SHG element, for example, K
So-called bulk-type SHG elements using TP, waveguide-type SHG elements that perform phase matching using a larger nonlinear optical constant, and nonlinear optical materials such as ferroelectric crystals such as LiNbO3 (LN). Cerenkov radiation type SHG that forms a linear waveguide on a single crystal substrate, inputs the fundamental wave of near-infrared light, and extracts second harmonics, such as green and blue light, from the substrate side as a radiation mode. There are elements etc.

However, the bulk type SHG element has relatively low SHG conversion efficiency due to its characteristics, and cannot use LN, which is inexpensive and provides high quality. Further, in the Cerenkov radiation type SHG element, the radiation direction of the SHG beam is in the direction into the substrate, and the beam spot has a unique shape, for example, a crescent-shaped spot, which poses problems in actual use.

In order to realize a device with high conversion efficiency,
The phase propagation speeds of the fundamental wave and the second harmonic must be made equal. As a method to do this in a pseudo manner, a method has been proposed in which the nonlinear optical constants + and - are arranged periodically (J
．． A. Armstrong, N. Bloemberge
n, et al., Phys. Rev. , 127, 1918 (19
62)). One way to achieve this is to periodically reverse the direction of the crystal (for example, crystal axis). Specific methods include, for example, cutting crystals thinly and pasting them together (Okada, Takizawa, Ieiri, NHK Technical Research, 29 (1)
, 24 (1977)), and a method of forming a periodic domain inversion structure by controlling the polarity of the applied current during crystal pulling to form periodic domains (domains).
D. Feng, N. B. Ming, J. F. Hong,
et al., Appl. Phys. Lett. 37,607 (1
980), K. Nassau, H. J. Levinst
ein, G. H. Loiacano Appl. Phy
s. Lett. 6, 228 (1965), A. Feis
st,P. Koidl Appl. Phys. Lett
．． 47, 1125 (1985)). These methods aim to form a periodic structure throughout the crystalline material. However, the method described above not only requires a large-scale apparatus, but also has the problem that it is difficult to control domain formation.

On the other hand, as a method for forming the above-mentioned periodic domain inversion structure near the surface of a crystal material, for example, T
A method for diffusing i from the crystal surface (Hiromasa Ito, Yinghai Zhang, Fumio Inaba, Proceedings of the 49th Japan Society of Applied Physics Conference 919)
(1988)) and the method of externally diffusing LiO2 (Jo
nas Webjoern, et al, IEEE P
HOTONICS TECHNOL. LETT. 1,
1989, PP316-318) has been proposed. However, with these methods, the refractive index of the domain-inverted portion changes, and the controllability of the polarization inversion shape is poor (F. Laurel et al, Integra
ted Photonics Research, Tu
12, 1989), etc. In addition, when SHG elements are formed using these methods, leakage of input light, leakage of second harmonic light, and a decrease in coupling efficiency between input light and second harmonic light may occur, resulting in so-called optical This may lead to a decrease in conversion efficiency.

[0008]

[Problems to be Solved by the Invention] Furthermore, the present applicant has previously filed Japanese Patent Application No. 1-8271 and Japanese Patent Application No. 1-184.
In the '362 patent application, we proposed a domain control method for nonlinear optical materials of ferroelectric materials. This method involves placing opposing electrodes on both opposing principal surfaces of a single-domain ferroelectric material, or placing them facing each other with an insulator interposed between them, and applying a DC voltage between the two electrodes. A periodic domain inversion structure is obtained by forming domain inversion portions.

However, in the periodic domain inversion structure formed by such a method, the ratio t/w of the polarization inversion width w to the thickness t was less than 1, as shown in FIGS. 27A and 27B. Therefore, if the periodic domain inversion structure is made finer, t
The absolute value of is small, which is smaller than the thickness of the optical waveguide. That is, for example, when the width w is set to about 1.5 μm due to a small pitch of polarization inversion, the thickness t becomes about 0.5 μm, and the thickness of the optical waveguide is reduced to about 1.0 μm.
μm, a periodic domain inversion structure is not sufficiently formed in the optical waveguide portion and its evanescent region. The effect of equalizing the phase propagation speed of waves cannot be sufficiently achieved, which is one of the reasons for hindering the improvement of SHG efficiency.

In contrast to such methods, a method has been proposed in which a nonlinear optical material is irradiated with an electron beam to obtain a periodic domain inversion structure with a desired pattern (R.W. Keys
,A. Loni, B. J. Luff, P. D. Town
send, others, Electronics Lette
rs lst February 1990 Vol.
．． 26 No. 3). In the case of this method, as shown in a schematic cross-sectional view in FIG. After depositing a thick Au layer, it is patterned into a desired pattern, and an electron beam is irradiated onto the patterned Au layer 63. In this method, the substrate is heated to approximately 580°C, an electric field of 10 V/cm is applied to the substrate itself in the direction of its c-axis, and
At an energy of 0 keV, electron beam irradiation is performed on 9 mm2 with a total dose of 1017, that is, about 1016 mm-2.

However, when using such a method,
A material such as an insulator or an electrode material is deposited on the surface of the LN substrate 62, which is a nonlinear optical material, and patterned, and in this state, high temperature heat treatment and voltage application at high temperature are performed. There is a risk of it getting dirty. In addition, in this case, polarization inversion is formed by out-diffusion of oxygen molecules from the LN substrate, so as with the Li out-diffusion method, changes in the composition may cause variations in the refractive index, which may cause variations in characteristics. .

The problems to be solved by the present invention are surface contamination of ferroelectric materials such as nonlinear optical materials as described above;
The object of the present invention is to obtain an optical device having a polarization inversion structure with high light conversion efficiency while avoiding changes in refractive index, and to provide a manufacturing method with good controllability of polarization inversion.

[0013]

[Means for Solving the Problems] FIG. 1 shows a schematic enlarged cross-sectional view of one manufacturing process of an example of the polarization inversion control method according to the present invention. FIG. 2 shows the manufacturing process of another example of the control method of the present invention.
Shown in schematic enlarged cross-sectional views A and B.

As shown in FIG. 1, in the control method of the present invention, a voltage of 10 V/mm to 100kV
/mm voltage is applied, and the acceleration voltage is 1kV to 100k.
V charged particles at a current density of 1 μA/mm2 to 1000 μA/mm2 on the irradiated surface of the ferroelectric material 1.
A polarization inversion structure is formed by applying at least one of voltage application and charged particle irradiation to a pattern corresponding to the pattern of the polarization inversion structure to be finally obtained.

Another control method of the present invention includes a step of irradiating charged particles onto a single-domain ferroelectric material 1, as shown in FIG. 2A, and then, as shown in FIG. 2B, and applying a voltage to the dielectric material 1.

[0016]

[Operation] As described above, according to the polarization inversion control method of the present invention, the voltage is set at 10V/10V so that the negative side of the spontaneous polarization of the single-domain ferroelectric material 1 has a negative potential and the positive side has a positive potential. mm~1
Apply a voltage of 00kV/mm and an acceleration voltage of 1kV~
Charged particles of 100 kV are applied at a current density of 1 μA/mm2 to 1000 μA/m on the irradiated surface of the ferroelectric material 1.
m2, and at least one of voltage application and charged particle irradiation is used to form a polarization inversion structure as a pattern corresponding to the pattern of the polarization inversion structure that is finally obtained. The structure could be formed with good controllability.

Such a phenomenon can be achieved by simultaneously applying a voltage and irradiating charged particles to apply an electric field to the ferroelectric material 1 and irradiating charged particles that act as a current source, that is, generate an electric field. As a result, charged particles such as electrons that have entered the ferroelectric material 1 flow like an avalanche, so that they penetrate the ferroelectric material 1 sufficiently deeply along this flow and polarization reversal occurs.

Another control method of the present invention includes a step of irradiating charged particles onto the single-domain ferroelectric material 1, as shown in FIG. 2A, and then, as shown in FIG. 2B, Although the method includes a step of applying a voltage to the ferroelectric material 1, it was possible to form a polarization-inverted structure with good controllability even when using such a control method.

In this case, charges may be accumulated on the surface of the ferroelectric material 1 due to the irradiation of the charged particles in FIG. 2A, or some of them may enter the ferroelectric material 1, and the charges may be accumulated on the surface of the ferroelectric material 1 due to the irradiation of the charged particles in FIG. Since this accumulated charge and charged particles, such as electrons, that have entered the ferroelectric material 1 flow like an avalanche, it is thought that polarization reversal occurs by penetrating, for example, the ferroelectric material 1 deeply enough along this flow. It will be done.

Furthermore, according to the control method of the present invention, since high-temperature heating is not required, deterioration and fluctuation of characteristics due to surface contamination of the ferroelectric material 1 can be avoided.

[0021] Furthermore, in the case of the above-mentioned method, unlike the conventional case of out-diffusion of Li or oxygen molecules, the composition of the ferroelectric material 1 is not changed, so that a polarization-inverted structure is obtained without a change in the refractive index. be able to.

Furthermore, since the depth at which polarization inversion can occur, that is, the thickness of the polarization inversion region can be increased compared to the conventional method, the light conversion efficiency can be increased, for example, in the above-mentioned optical waveguide type SHG element. and bulk type S
In the HG element, the selectivity of optical materials can be increased, and the manufacturing method, which has conventionally been carried out by bonding crystals, etc., can be significantly simplified.

[0023]

[Example] Below, each example of the control method of the present invention is shown in Figs. 1 to 26.
It will be described in detail with reference to a schematic enlarged sectional view, a schematic enlarged perspective view, and a manufacturing process diagram. In each example, a nonlinear optical material such as KTP, LN, LiTaO3, etc., such as LN crystal, is used as the single-domain ferroelectric material 1. By raising the temperature to, for example, about 1200° C., just below the Curie temperature, and applying an external DC voltage to the entire surface in a fixed direction, a single domain is formed that is aligned in the thickness direction of the c-axis over the entire surface.

In each of the following examples, regarding the plane perpendicular to the direction of spontaneous polarization of the single-domain ferroelectric material 1, the + side of the spontaneous polarization is referred to as the +c plane, and the - side is referred to as the +c plane. -c plane, the direction of spontaneous polarization is indicated by arrow d in FIGS. 1 to 26. In addition, in each example, the +c side is at a positive potential, and -
A voltage was applied so that the c-plane side had a negative potential.

In the following Examples 1 to 18, each example of a polarization inversion control method according to one of the control methods of the present invention will be described.

Example 1 In this example, as shown in FIG. 1, the -c plane is the main surface 1C,
In the case where the entire surface is divided into a single region in the thickness direction, an electrode film 4 through which charged particles such as electron beams can pass is deposited on the main surface 1C by vapor deposition, sputtering, or the like. In order for this electrode film 4 to transmit electron beams, the film thickness must be approximately several tens to 100 Å, and the material must be Al, S, etc.
It is preferable to use relatively light elements such as i and Ti.

On the other hand, on the back surface 1D of the +c surface, an electrode 5 made of Au, Ag, Cu, Al, etc. is deposited to a thickness of, for example, several hundred to several thousand angstroms by vapor deposition or sputtering.

Then, with the main surface 1C side set to a negative potential and the rear surface 1D side set to a positive potential, an applied voltage of 10V/mm to 100kV/
Apply as mm. Then, for this ferroelectric material 1, a pattern corresponding to the pattern of the required polarization inversion structure,
For example, charged particles such as an electron beam b are scanned and irradiated so as to draw a locus of a parallel strip pattern extending in a direction perpendicular to the plane of the paper in FIG. The irradiation conditions at this time are an acceleration voltage of 1 kV to 100 kV, for example 15 kV, an energy of 1 keV to 100 keV, for example 15 keV, and a current density on the main surface 1C of 1 μA/mm2 to
It was set to 1000 μA/mm2, for example, 1 μA/mm2.

Embodiment 2 Next, an example of causing polarization inversion on a plane other than the ±c plane will be described with reference to FIG. In FIG. 3, the main surface 1C of the ferroelectric material 1 is a surface along the direction of spontaneous polarization, and is polished smooth. Then, the +c plane perpendicular to the polarization direction is the side 1
With A and -c planes as side surfaces 1B, both sides 1A and 1B
The edges 1d and 1e are formed so that the main surface 1C and the main surface 1C are perpendicular to each other without being rounded. Then, electrodes 5 made of Au or the like are deposited on both side surfaces 1A and 1B.
so that they reach the edges 1d and 1e.

In this state, the polarization direction d is the same as in Example 1.
Apply a voltage with the polarity and applied voltage to the main surface 1.
Pattern irradiation of charged particles, for example, scanning irradiation of a parallel strip pattern was performed from above C to form polarization inversion on the principal surface 1C. The irradiation conditions were selected in the same manner as in Example 1.

Embodiment 3 This will be explained with reference to FIG. In FIG. 4, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and redundant explanation will be omitted. In this case, an electrode 5 made of Au or the like is placed on the side surface 1A which is the +c side.
is deposited on the side surface 1B, which becomes the -c plane, and the thickness of the film is, for example, several tens to ten so that charged particles, for example, electron beams b, can pass through.
An electrode film 4 having a thickness of about 100 Å and made of a relatively light element such as Al, Si, or Ti is deposited by vapor deposition, sputtering, or the like.

Then, the electron beam b is scanned and irradiated from above the electrode film 4 on this side surface 1B, but in this case, the edge portion 1e is
The electron beam b was irradiated onto the nearby electrode film 4 so as to form, for example, a parallel strip pattern, thereby forming polarization inversion near the edge 1e on the main surface 1C.

Embodiment 4 This will be explained with reference to FIG. In FIG. 5, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and redundant explanation will be omitted. In this case as well, polarization inversion is intended to be formed on the main surface 1C other than the ±c plane of the ferroelectric material 1 made of LN single crystal, etc., and on this main surface 1C, Au, Ag, Cu, Using materials such as Al, several dozen to
A film formed over the entire surface with a thickness of several thousand angstroms is patterned by photolithography or the like, and two parallel strip electrodes 5 are arranged in parallel. A suitable distance between the electrodes 5 is 1 μm to several hundred μm.

Then, a voltage is applied between the electrodes 5 with the same polarity and applied voltage in the polarization direction d as in Example 1, so that, for example, a parallel strip pattern is formed in the area between the electrodes 5 from the main surface 1C. Irradiation with the electron beam b was performed under the same irradiation conditions as in Example 1 to form polarization inversion in the region between the electrodes 5 on the main surface 1C.

In addition to the above polarization inversion control method, L
An SHG element can be formed by forming a proton exchange waveguide in an N single crystal. An example of the manufacturing process of the SHG element is shown in FIGS. 6A to 6D. FIG. 6A shows the polarization inversion control method described above. At this time, the electrode 5 is made of a material that is not affected by phosphoric acid or pyrophosphoric acid, such as Ta or Au/Ti. In this case, it is made of Ta, for example.

FIG. 6B shows the proton exchange waveguide manufacturing process.
For example, a reaction solution 9 such as pyrophosphoric acid or phosphoric acid in a container 8
The ferroelectric material 1 is immersed in the ferroelectric material 1, and proton exchange is performed as shown by the arrow e in the figure. In this case, the electrode 5 can be used as a mask for proton exchange, that is, the electrode 5 can be created and the mask for proton exchange can be created, so that the process can be simplified. There is no need for a mask alignment configuration for creating the waveguide 2, making it possible to create the so-called self-contained waveguide.
Alignment (automatic alignment) can be achieved, and the waveguide 2 can be precisely created on the periodic domain structure.

Then, as shown in FIG. 6C, the unnecessary electrode 5 is removed by etching or the like. For example, in the case of Ta, NaOH:H2O2:H2O = 3:1:7 is 7
It is removed by etching using an etching solution heated to 0°C. Further, when the electrode 5 is formed of Au/Ti, it can be removed by etching with aqua regia.

Thereafter, as shown in FIG. 6D, annealing is performed at, for example, 400.degree. C. for several tens of minutes to recover the nonlinear optical constants that were lowered due to the proton exchange described in FIG. 6B. In this way, an optical device such as an SHG element with quasi-phase matching can be obtained.

Embodiment 5 This will be explained with reference to FIG. In this example, as shown in FIG. 7, a convex portion 7 is formed facing the main surface 1C of the ferroelectric material 1 other than the ±c plane where polarization inversion is to be formed. Convex part 7
It is desirable that the longitudinal direction of is selected to be perpendicular to the direction of spontaneous polarization shown by arrow d. When selected in this way, the longitudinal side wall surface of the convex portion 7 is constituted by a side surface 1A consisting of the +c plane of the ferroelectric material 1 and a side surface 1B consisting of the -c plane. On these side surfaces 1A and 1B, an electrode 5 made of Au or the like is formed, for example, over the upper side surface 1E adjacent to these side surfaces 1A and 1B, respectively, by a manufacturing process to be described later. And between this electrode 5 -c plane, that is, the side surface 1
A voltage is applied so that B has a negative potential and the +c plane, that is, the side surface 1A, has a positive potential. Then, the electron beam b is irradiated onto the region where polarization inversion between the electrodes 5 is to be formed, for example, in a parallel strip pattern. The applied voltage, acceleration voltage of the electron beam, and current density at this time were selected in the same manner as in Example 1.

As described above, the convex portion 7 is formed on the ferroelectric material 1.
FIG. 8 shows an example of a method for forming a substrate and further forming electrodes on the longitudinal sides 1A and 1B. As shown in FIG. 8A, main surface 1C of ferroelectric material 1 where polarization inversion is to be formed.
A resist 11 made of AZ4210 (manufactured by Hoechst, trade name) or the like is applied over the entire surface, and after baking in hot air at about 80° C. for 30 minutes, a mask layer 12 made of Ni, Cu, etc. is deposited. The film is deposited to a thickness of approximately several thousand angstroms by sputtering or the like. After that, TSMR8900 (
After coating and baking a resist 13 made of a material such as (manufactured by Tokyo Ohka Co., Ltd., trade name) in the same manner as the resist 11 described above, the resist 13 is left in the required areas where the convex portions 7 are to be formed, that is, in this case, in the direction of the arrow d. It has the required width in the polarization direction shown in Figure 8.
A pattern whose longitudinal direction was perpendicular to the plane of the paper was exposed and developed using photolithography or the like, and then post-baked in hot air at 120° C. for 30 minutes.

Next, as shown in FIG. 8B, ECR-RIE
Using a (electron cyclotron resonance reactive ion etching) device or the like, the mask layer 12 and the resist 11 are etched using Ar ions, for example, shown by arrow c, using the resist 13 as a mask.
pattern.

Next, as shown in FIG. 8C, ECR-RI
Using a patterned mask layer 12 as a mask, the ferroelectric material 1, for example, LN single crystal, is etched using an ion gas such as C2F6 or C3F8, as shown by arrow c in the figure, from the +c plane using an E device or the like. Aspect 1
The convex portion 7 is formed by exposing the side surface 1B consisting of the A and -c planes and the upper side surface 1E adjacent thereto.

Then, as shown in FIG. 8D, a metal layer 14 made of Al, Au, Ag, Cu, etc. is deposited over the entire surface of the convex portion 7 by vapor deposition, sputtering, or the like.

Next, as shown in FIG. 8E, this metal layer 14
By soaking the ferroelectric material 1 coated with the ferroelectric material 1 in a solvent such as acetone and removing the resist 11, only the metal layer 14 on the convex portion 7 is lifted off, and the metal layer 14 is removed from the side surfaces 1A and 1B adjacent to the upper side surface 1E, respectively. Then, the electrode 5 is formed.

The above is a method for forming polarization inversion on the ferroelectric material 1 having the convex portions 7.
It can be applied to SHG in which a proton exchange waveguide or a Ti diffusion waveguide is formed on an LN single crystal. Figures 9A-D
This shows a case where the domain control method according to the fifth embodiment described above is applied to a method of manufacturing an optical device such as an SHG element having a proton exchange waveguide formed therein.

First, as shown in FIG. 9A, a ferroelectric material 1 made of LN single crystal or the like is immersed in a reaction solution 9 made of phosphoric acid, pyrophosphoric acid, etc. at about 200° C., so that protons are generated as shown by arrow e. The waveguide 2 is created by performing the exchange.

Next, this ferroelectric material 1 is annealed in a furnace 10 at about 400°C. By annealing, the nonlinear optical constants decreased by the proton exchange treatment can be restored. After this, the step of forming the convex portion 7 of the ferroelectric material 1 and the formation of the electrode 5 explained with reference to FIGS. 8A to 8D are performed.

Then, as shown in FIG. 9C, voltage application and electron beam irradiation are performed under the same conditions as in Example 5 described in FIG. 7 to form a periodic domain inversion structure.

After this, as shown in FIG. 9D, the electrode 5
is removed by etching with NaOH aqueous solution, hydrochloric acid, aqua regia, etc. In this way, optical devices such as SHG elements can be manufactured. In this case, especially by creating the convex portion 7 for creating the periodic polarization inversion structure, the ridge-shaped waveguide 2 can be formed at the same time, so the manufacturing process can be simplified. Furthermore, the periodic polarization inversion structure and the waveguide can be formed with high precision in a self-aligned manner, that is, without mask alignment or the like.

FIG. 10 shows a method for manufacturing an optical device such as an SHG element in which the waveguide 2 is formed by the Ti diffusion method.
First, as shown in FIG. 10A, a Ti layer 15 is deposited on the main surface 1C of a ferroelectric material 1 such as LN single crystal to a thickness of about several hundred angstroms by vapor deposition, sputtering, or the like.

[0051] Next, T
A waveguide 2 is formed by diffusing i into a ferroelectric material 1. At this time, it is desirable to introduce oxygen and water vapor to prevent oxygen deficiency in the ferroelectric material 1 and external diffusion of LiO2.

After that, as shown in FIGS. 10C and D, the same manufacturing process as that explained in FIGS. 9C and D is carried out,
An optical device such as an SHG element having the Ti diffusion waveguide 2 can be obtained.

In Examples 1 to 5 described above, an example was explained in which a voltage was applied to the entire surface of the ferroelectric material 1 and charged particles were irradiated in a desired pattern. In Examples 6 to 12, cases will be described in which electrodes of a desired pattern are formed and a voltage is applied locally to the electrodes.

Example 6 In this example as well, when LN single crystal is used as the ferroelectric material 1, as shown in FIG.
Then, an electrode film 4 is formed on the main surface 1C by vapor deposition, sputtering, or the like. This electrode film 4 has a thickness of, for example, approximately several tens to 100 Å, and is made of a relatively thin film such as Al, Si, or Ti so that charged particles such as electron beams can pass through the ferroelectric material 1 without much loss. Formed by light elements. On the other hand, after a metal layer made of Au, Ag, Cu, Al, etc. is deposited on the entire surface of the back surface 1D made of the +c plane by vapor deposition, sputtering, etc., for example, The electrodes 5 are formed by patterning a parallel strip pattern extending in a direction perpendicular to the paper plane of FIG. 11 by a lift-off method or the like by applying photolithography or the like. This electrode 5 does not necessarily need to transmit electron beams, and its film thickness is preferably several hundred to several thousand angstroms.

Then, a voltage is applied so that the main surface 1C side, which is the -c plane, has a negative potential, and the back surface 1D, which is the +c plane, has a positive potential, and charged particles, such as electron beams b, are irradiated from above the main surface 1C. The conditions of the applied voltage, the acceleration voltage of the electron beam, and the irradiation current density at this time are selected to be the same as in Example 1. At this time, the electron beam b is irradiated with a pattern corresponding to the pattern deposited on the back surface 1D.

Embodiment 7 This will be explained with reference to FIG. 12. In FIG. 12, parts corresponding to those in FIG. 11 are denoted by the same reference numerals, and redundant explanation will be omitted. This example is a case where the electrode film 4 is formed in a pattern corresponding to the region where polarization inversion is to be obtained on the main surface 1C side to which charged particles are irradiated, and the film thickness is the same as that of the electrode film 4 in Example 6.
After depositing the metal layer with the material, a desired pattern, for example, a parallel strip pattern extending in a direction perpendicular to the plane of the paper in FIG. A shaped electrode film 4 is formed. On the other hand, on the back surface 1D on the +c side, Au, Ag, Cu, Al, etc. are deposited over the entire surface by vapor deposition, sputtering, etc. to a thickness of several hundred to several thousand angstroms, similar to the electrode 5 in Example 6. to obtain the electrode 5. This electrode 5 does not necessarily need to be transparent to charged particles.

A voltage was applied to the ferroelectric material 1 under the same conditions as in Example 6, and charged particles were irradiated to form a polarization-inverted structure. At this time, charged particles such as electron beams b are uniformly irradiated over the entire surface of the ferroelectric material 1 from above the main surface 1C, or are scanned and irradiated in a desired pattern to form a desired pattern of polarization inversion.

Embodiment 8 This example corresponds to Embodiment 2 explained with reference to FIG. 3, and will be explained with reference to FIG. Figure 3 in Figure 13
The same reference numerals are given to corresponding parts and redundant explanation will be omitted. In this case, the electrode 5 made of Au, Ag, Cu, Al, etc. is entirely deposited on the side surface 1A made of the +c plane forming the electrode 5 by vapor deposition, sputtering, etc., and the other side surface 1A is made of the +c plane. That is, the electrode 5 on the side surface 1B consisting of the −c plane
For example, a pattern corresponding to the polarization inversion of a parallel strip pattern to be formed on the main surface 1C is patterned in a comb shape using an etching method, a lift-off method, etc. by applying photolithography or the like. At this time, edges 1d and 1e are formed so that the main surface 1C and side surface 1B of the ferroelectric material 1 are perpendicular to each other without being rounded.
At points d and 1e, the tip of each electrode 5 is attached. The film thickness is preferably several hundred to several thousand angstroms.

Then, a voltage is applied between the electrodes 5 under the same conditions as in Example 1, and charged particles such as electron beams b are irradiated from above the main surface 1C under the same irradiation conditions as in Example 1 to form polarization inversion. do. At this time, the electron beam b may be irradiated over the entire surface, or may be irradiated in a scanning manner over a region where the required polarization inversion is to be formed. Furthermore, in the illustrated example, the comb-shaped electrode 5 is provided on the side surface 1B side which is the -c plane of the ferroelectric material 1, but the comb-shaped electrode 5 may be provided on the +c plane side. A voltage is applied by setting the comb-shaped electrode 5 side at a positive potential.

Embodiment 9 This example corresponds to Embodiment 3 explained in FIG. 4, and will be explained with reference to FIG. Figure 4 in Figure 14
The same reference numerals are given to corresponding parts and redundant explanation will be omitted. In this case, charged particles, for example, electron beams b, are irradiated from above the side surface 1A consisting of the -c plane, and the electrode film 4 on this side surface 1A is designed to allow the charged particles to pass through without much loss. The same material as the electrode film 4 in 1,
Deposit with a certain thickness. Then, on the side surface 1B consisting of the +c plane, A
A metal layer made of u, Ag, Cu, Al, etc., with a thickness of several hundred to several thousand Å
After the film has been adhered to a certain degree, it is formed into a desired comb-like pattern by photolithography or the like, similar to the electrode 5 in Example 8.

Then, a voltage is applied under the same conditions as in Example 1, and a charged particle such as an electron beam b is applied under the same irradiation conditions as in Example 1 to the surface on which polarization inversion is to be formed, that is, near the main surface 1C from above the side surface 1A. is irradiated to form polarization inversion corresponding to the electrode pattern. At this time, the electron beam b may be irradiated over the entire surface, or may be irradiated in a scanning manner over a region where the required polarization inversion is to be formed.

Embodiment 10 This example corresponds to the above-mentioned embodiment 9 explained in FIG. 14, and will be explained with reference to FIG. 15. In FIG. 15, parts corresponding to those in FIG. 14 are designated by the same reference numerals, and redundant explanation will be omitted. In this case, the side surface 1B on the -c plane side
An electrode film 4 through which charged particles, for example, electron beam b, can pass is formed on the electrode film 4 in a desired pattern, for example, a comb-like pattern, in which polarization inversion is to be formed, and the electron beam b is irradiated from above this electrode film 4. The applied voltage and irradiation conditions at this time are as described in Example 1 above.
By selecting the same conditions as above, polarization inversion is formed on the main surface 1C.

Embodiment 11 This example corresponds to Embodiment 4 explained in FIG. 5, and will be explained with reference to FIG. Figure 5 in Figure 16
The same reference numerals are given to corresponding parts, and redundant explanation will be omitted. In this case, each electrode 5 is formed in a comb-like pattern by applying photolithography or the like so that the tips of the comb teeth are arranged in close proximity to each other. By forming such a pattern, the electric field within the ferroelectric material 1 generated by applying a voltage between the electrodes 5 is distributed, or for example, the electric field is made to exist locally. And electron beam b
from the main surface 1C where the polarization inversion structure is to be formed,
Alternatively, scanning irradiation is performed in a parallel strip pattern across the comb tooth tips of the electrodes 5 to form a polarization inversion structure corresponding to the shape of the electrode pattern.

In this case as well, the polarity and magnitude of the applied voltage in the polarization direction d, as well as the acceleration voltage and irradiation current density of the irradiated electron beam b, are selected in the same manner as in Example 1.

In this case, the shape of the electrode 5 may be such that one side is flat and the other is comb-shaped, as shown in FIG. 17, and the shape of the tip of the comb teeth is as shown in FIGS. 18A and B
Various shapes can be taken, such as an acute angle shape as shown in FIG. 18C or a circular arc shape as shown in FIG. 18C.

Embodiment 12 This example corresponds to Embodiment 5 described in FIG. 7, and will be explained with reference to FIG. 19. Figure 7 in Figure 19
The same reference numerals are given to corresponding parts, and redundant explanation will be omitted. In this case, each electrode 5 has a comb-like pattern, and its comb-teeth tips are formed from the upper surface 1E of the ferroelectric material 1 to the side surfaces 1A and 1B of the convex portion 7. Then, it is formed by photolithography or the like so that the tips of the comb teeth on each side surface 1A and 1B are arranged opposite to both ends of the main surface 1C. By forming such a pattern, the electric field within the ferroelectric material 1 generated by applying a voltage between the electrodes 5 is distributed, or for example, the electric field is made to exist locally. Then, the electron beam b is applied to the entire main surface 1C on which the polarization inversion structure is to be formed, or to the electrode 5.
A parallel strip pattern is scanned and irradiated so as to span between the tips of the comb teeth to form a polarization inversion structure corresponding to the shape of the electrode pattern.

In this case as well, the polarity and magnitude of the applied voltage, as well as the acceleration voltage and irradiation current density of the irradiated electron beam b, are selected in the same manner as in Example 1.

In this case, as in Example 5, when forming a proton exchange waveguide or a Ti diffusion waveguide, there is an advantage that the formation of the ridge type waveguide and the formation of the convex portion 7 can be performed at the same time. have The manufacturing process in this case is shown in Figure 8.
The process is almost the same as that described in , but a comb patterning process of the electrode 5 is inserted between FIG. 8D and FIG. 8E.

Next, in Examples 13 to 18, cases in which polarization inversion is obtained by depositing an insulator in a desired pattern on a ferroelectric material will be described. In each example, in order to save the effort of selectively and precisely irradiating charged particles, such as electron beams, an insulator with a desired pattern is formed and the electron beams are selectively masked by this. SiO2, Si3N4, resist, etc. are suitable as the insulator, and the patterning can be performed by photoresist technology, etching method, or lift-off method. The thickness of the insulator is preferably several thousand Å to several tens of μm.

Embodiment 13 This example corresponds to Embodiment 4 explained in FIG. 5, and will be explained with reference to FIG. In FIG. 20, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and redundant explanation will be omitted. In this case, an insulator 6 is deposited, for example, in a parallel strip pattern in this case, on a region where no polarization reversal occurs between the parallel plate-shaped electrodes 5 on the main surface 1C, and charged particles are applied to the entire surface in Example 1. Polarization inversion was formed by irradiation under the same conditions as above.

Embodiment 14 This example corresponds to Embodiment 5 explained in FIG. 6, and will be explained with reference to FIG. In FIG. 21, parts corresponding to those in FIG. 6 are designated by the same reference numerals, and redundant explanation will be omitted. In this case as well, the insulator 6 is deposited, for example, in a parallel strip pattern on the area on the main surface 1C where no polarization reversal occurs between the electrodes 5, and charged particles are applied over the entire surface under the same conditions as in Example 1. irradiation to form polarization inversion.

Embodiment 15 This example corresponds to Embodiment 2 explained with reference to FIG. 3, and will be explained with reference to FIG. In FIG. 22, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and redundant explanation will be omitted. In this case as well, an insulator 6 is deposited on the main surface 1C in a region where no polarization reversal occurs between the electrodes 5, for example in a parallel strip pattern, and charged particles are applied to the entire surface in the same manner as in Example 1. Irradiation was performed under certain conditions to form polarization inversion.

Furthermore, in Examples 16 to 18 below, desired domains are formed according to the electric field distribution depending on the shape of the electrode 5, and an insulator 6 is further formed to selectively mask charged particles, such as electron beams b. The aim is to increase the selectivity of regions where polarization inversion occurs by changing the distribution of the electric field and the distribution of electron beam irradiation. It is desirable that the material, film thickness, etc. of the insulator be selected in the same manner as in Examples 13 to 15 described above, and the patterning thereof can be formed by the same method.

Embodiment 16 This example corresponds to Embodiment 8 explained with reference to FIG. 13, and will be explained with reference to FIG. In Figure 23, Figure 1
The same reference numerals are given to the parts corresponding to 3, and redundant explanation will be omitted. In this case, the insulator 6 is deposited, for example, in a parallel strip pattern on the region on the principal surface 1C where polarization inversion does not occur, that is, the region covering the portion where the comb tooth tips of the comb-shaped electrode 5 are not formed. Example 1
Polarization inversion was formed by irradiation under the same conditions as above. Note that in the illustrated example, the comb-shaped electrode 5 is provided on the side surface 1B side which is the -c plane of the ferroelectric material 1, but the comb-shaped electrode 5 may be provided on the +c plane side. is a comb-shaped electrode 5
A voltage is applied with the side at a positive potential.

Embodiment 17 This example corresponds to Embodiment 11 explained with reference to FIG. 16, and will be explained with reference to FIG. In FIG. 24, parts corresponding to those in FIG. 16 are designated by the same reference numerals, and redundant explanation will be omitted. In this case, an insulator 6 is deposited, for example, in a parallel strip pattern on a region where polarization inversion does not occur on the main surface 1C, that is, on a region other than the comb-teeth portion of the comb-shaped electrode 5, so that the charged particles are covered over the entire surface. Irradiation was performed under the same conditions as in Example 1 to form polarization inversion. In this case as well, the shape of the electrode 5 formed on the main surface 1C of the ferroelectric material 1 is as shown in FIGS.
Various patterns can be adopted as shown in 8A to 8C.

Embodiment 18 This example corresponds to Embodiment 12 explained with reference to FIG. 19, and will be explained with reference to FIG. 25. In FIG. 25, parts corresponding to those in FIG. 19 are given the same reference numerals, and redundant explanation will be omitted. In this case as well, the insulator 6 is coated on the main surface 1C in a region where the polarization of the electrode 5 does not occur, that is, on the region between the portions where the comb teeth are not formed, for example, in a parallel strip pattern, so that the entire surface is covered. Charged particles were irradiated under the same conditions as in Example 1 to form polarization inversion.

Next, another polarization inversion control method according to the present invention will be described in detail with reference to FIGS. 2A and 26A and 26A and B. In each example, LN is used as the ferroelectric material 1.
In the case where a single crystal is used, and the polarization direction is made into a single domain in the entire thickness direction by the same method as in Examples 1 to 18, the main surface 1C consisting of the -c plane.
Polarization inversion is created by irradiating charged particles, such as electron beams b, from above.

Example 19 As shown in FIG. 2A, the electron beam b is irradiated from the main surface 1C of the ferroelectric material 1 in a desired pattern, that is, for example, a parallel strip pattern extending in a direction perpendicular to the paper plane of FIG. 2A. The beam is scanned and irradiated so as to draw a trajectory. Irradiation conditions such as the acceleration voltage and irradiation current density of the electron beam b at this time are selected in the same manner as in Example 1.

Next, as shown in FIG. 2B, an electrode 5 is formed over the entire surface of the main surface 1C of the ferroelectric material 1 and the back surface 1D consisting of the +c plane. This electrode 5 is made of Au, Ag
, Cu, Al, etc., and is deposited to a thickness of several hundred to several thousand angstroms by vapor deposition, sputtering, or the like. Then, a voltage is applied between the electrodes 5 so that the main surface 1C side has a negative potential and the back surface 1D side has a positive potential to form polarization inversion. The applied voltage at this time is selected in the same manner as in the first embodiment.

Embodiment 20 In FIGS. 26A and 26B, parts corresponding to those in FIGS. 2A and 2B are given the same reference numerals, and repeated explanation will be omitted. In this case, as shown in FIG. 26A, a voltage is applied after irradiating the electron beam b under the same conditions as in FIG. 2A, but as shown in FIG. 26B, the entire ferroelectric material 1 is placed in a container. 8
A voltage is applied while the device is immersed in an insulating liquid 21 made of Fluorinert or the like. By applying a voltage in such an insulating liquid 21, discharge between the electrodes can be reliably avoided, so a sufficiently large voltage can be applied to the ferroelectric material 1. Therefore,
By applying high voltage in the insulating liquid 21, polarization inversion can be formed as a clearer pattern.

[0081] When voltage is applied in the insulating liquid 21 in this manner, polarization reversal can be caused without irradiation with charged particles by selecting an appropriate voltage that is sufficiently large. . Therefore, for example, the electrodes 5 on the ferroelectric material 1 are formed in a pattern corresponding to a desired polarization inversion pattern, and the required voltage is applied in the insulating liquid 21 only in the region where the polarization inversion is to be formed. By applying this, it is possible to form a desired pattern of polarization inversion without irradiating charged particles.

In particular, Examples 2 to 5 and Examples 8 to 1
As shown in 8, when the plane on which the polarization inversion is formed is other than the ±c plane of the ferroelectric material 1, that is, the polarization inversion is formed on the so-called X plate or Y plate, and the waveguide 2 is formed in this part. In this case, a TE waveguide mode SHG element can be obtained. Since a normal laser diode emits TE wave oscillation, it is possible to improve the coupling efficiency with the laser diode and facilitate coupling with the laser diode.

In each of the above-mentioned examples, irradiation was performed using an electron beam as a charged particle, but for example, when LN single crystal is used as a ferroelectric material, various other methods such as Li+ ion irradiation may be used. Charged particles can be used.

[0084]

Effects of the Invention As described above, according to the polarization reversal control method of the present invention, polarization reversal is formed without high-temperature heating, so deterioration and fluctuation of characteristics due to surface contamination of the ferroelectric material 1 can be avoided. Moreover, unlike the conventional Li out-diffusion method, the composition of the ferroelectric material 1 is not changed, so a polarization inversion structure can be obtained without changing the refractive index.

[0085] Furthermore, compared to the case of charged particle irradiation alone, by applying an appropriate voltage, the contrast between regions where polarization reversal occurs and regions where no polarization reversal occurs becomes clearer. can be measured.

Furthermore, since the depth of polarization inversion can be increased compared to the conventional method, the above-mentioned optical waveguide type SH
The light conversion efficiency can be increased in optical devices such as G elements, and the selectivity of optical materials can be increased in optical devices such as bulk type SHG elements. It is possible to greatly simplify the manufacturing method that was previously carried out by the above methods.

Further, as mentioned above, the ± of the ferroelectric material 1
When forming polarization inversion on a plane other than the c-plane, that is, the so-called X plate or Y plate, and forming the waveguide 2 in this part,
We were able to obtain a TE waveguide mode SHG device and improve the coupling efficiency with the laser diode.
Coupling with a laser diode can be facilitated.

[Brief explanation of the drawing]

FIG. 1 is a schematic enlarged cross-sectional view showing one manufacturing process of an example of the polarization inversion control method according to the present invention.

FIG. 2 is a manufacturing process diagram showing an example of the manufacturing process of another polarization inversion control method according to the present invention.

FIG. 3 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 4 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 5 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 6 is a manufacturing process diagram showing an example of a method for manufacturing an optical device.

FIG. 7 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 8 is a manufacturing process diagram showing another example of the polarization inversion control method according to the present invention.

FIG. 9 is a manufacturing process diagram showing another example of a method for manufacturing an optical device.

FIG. 10 is a manufacturing process diagram showing another example of a method for manufacturing an optical device.

FIG. 11 is a schematic enlarged cross-sectional view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 12 is a schematic enlarged sectional view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 13 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 14 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 15 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 16 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 17 is a schematic enlarged top view showing an example of an electrode shape.

FIG. 18 is a schematic enlarged top view showing another example of the electrode shape.

FIG. 19 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 20 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 21 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 22 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 23 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 24 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 25 is a schematic enlarged perspective view showing a manufacturing process of another example of the polarization inversion control method according to the present invention.

FIG. 26 is a manufacturing process diagram showing another example of the polarization inversion control method according to the present invention.

FIG. 27 is a schematic enlarged cross-sectional view showing a conventional periodic domain inversion structure.

FIG. 28 is a schematic enlarged cross-sectional view showing an example of a conventional method for manufacturing a periodic domain inversion structure.

[Explanation of symbols]

1 Ferroelectric material 1C Main surface 1D back side 1d Edge 1e Edge 1A side 1B Side 1E Top side 2 Waveguide 3 Polarization inversion structure 3A Polarization inversion 4 Electrode film 5 Electrode 6 Insulator 7 Convex part 8 Container 9 Reaction liquid 10 Furnace 21 Insulating liquid

Claims (2)

[Claims] Claim 1: A voltage of 10 V/voltage is applied so that the negative side of the spontaneous polarization of the single-domain ferroelectric material has a negative potential and the positive side has a positive potential.
A voltage of 1 μA/mm to 100 kV/mm is applied, and charged particles with an accelerating voltage of 1 kV to 100 kV are applied at a current density of 1 μA/mm to 1000 μA/mm on the irradiated surface of the ferroelectric material.
μA/mm2, and at least one of the voltage application and the charged particle irradiation is formed in a pattern corresponding to the pattern of the polarization inversion structure to be finally obtained, so that the polarization inversion structure is formed. A polarization reversal control method characterized by: 2. Polarization inversion characterized by comprising the steps of irradiating charged particles onto a single-domain ferroelectric material, and then applying a voltage to the ferroelectric material. Control method.