JP2008158017A - Electrode for producing domain-inverted structure, method for producing electrode, apparatus for producing domain-inverted structure, and method for producing domain-inverted structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for producing a domain inversion structure capable of easily forming a uniform periodic domain inversion region over a wide range.
SOLUTION: Electrodes (2, 3) respectively disposed on two opposing surfaces with respect to a dielectric substrate 1 having a nonlinear optical effect, each electrode (2) disposed on each of the two opposing surfaces. , 3) has at least one electrode (2) having a predetermined electrode pattern for producing a domain-inverted structure in which the polarization direction is inverted by applying an electric field to the dielectric substrate, and the conductive fine particles 5 It is characterized in that a material containing is used.
[Selection] Figure 1

Description

  The present invention relates to an electrode for producing a domain-inverted structure, a method for producing the electrode, an apparatus for producing a domain-inverted structure, and a method for producing a domain-inverted structure.

Ferroelectric crystals such as LiNbO ₃ and LiTiO ₃ have a non-linear optical effect and are used for laser light wavelength conversion elements. In particular, an optical element (wavelength conversion element) having a polarization inversion structure that satisfies the quasi phase matching (QPM) condition by periodically inverting the polarization direction is a second harmonic with respect to laser light in a wide wavelength range. Wave generation (SHG) and optical parametric oscillation (OPO) can be performed.

  As a form of this wavelength conversion element, there are a waveguide type in which a region having a width of about several μm is inverted in the vicinity of the substrate surface, and a bulk type in which the entire cross section of the substrate is used by inversion throughout the thickness direction of the substrate Are being considered. In the waveguide type, since light is concentrated in a narrow waveguide region of about several μm, it is possible to convert the wavelength of incident laser light having a relatively low energy with high efficiency. On the other hand, the bulk type can perform wavelength conversion with respect to a beam diameter larger than that of the waveguide type. Therefore, it is possible to obtain a high output light by entering a high-energy laser beam. The bulk type is also easy to align.

  In the production of these wavelength conversion elements, the waveguide type is relatively simple because only the vicinity of the surface of the dielectric substrate needs to be inverted, but the bulk type has a wide beam passing range of several tens of μm, Since it is necessary to reverse the polarization in the thickness direction of the substrate also, it is not easy.

  The bulk-type wavelength conversion element is manufactured by forming a predetermined electrode pattern on both surfaces (called + Z plane and -Z plane, or + C plane and -C plane) of a substrate having a uniform polarization direction, and applying a voltage. This is done by reversing the polarization direction of the portion sandwiched between the electrodes.

  However, in order to fabricate an element with high wavelength conversion efficiency, the inversion region must be fabricated with high accuracy with respect to the design value. In particular, since the bulk type assumes a larger incident beam diameter than the waveguide type, it is necessary to invert the polarization of a thick substrate uniformly over a wide range. Various manufacturing methods have been studied for these problems.

  Patent Document 1 discloses a method in which the occurrence of polarization reversal of unnecessary portions is suppressed by degrading the crystallinity of the surface of the + Z plane so that short-period polarization reversal can be easily formed. Further, Patent Document 2 discloses that a + Z plane electrode for applying an electric field for polarization reversal is divided into a plurality of segments having a period wider than a target period, and an electric field is individually applied to finely divide the electrode. A method for producing a domain-inverted structure with a simple period is shown. In Patent Document 3, the + Z plane side on which an electrode having a predetermined pattern is vacuumed to prevent discharge between the electrodes, and the −Z plane side is set to atmospheric pressure and corona charged to generate an electric field. A method for producing a domain-inverted structure with a fine period by applying is shown.

  However, even when the above-described method for producing a domain-inverted structure is used, it is not easy to form a domain-inverted region that is uniform over a wide range. The domain-inverted region does not occur uniformly under the + electrode, but the domain-inverted region sparsely formed under the + electrode grows in the Z-plane direction and −Z-plane direction with the application time. This has been observed experimentally. Once the nuclei are formed, the charge tends to concentrate, so the part where the nuclei were first formed spreads over time, and as a result, only the periphery of the part where the nuclei were first formed is inverted. It becomes a state like this. Therefore, how to perform nucleation uniformly is important for forming a uniform domain-inverted region over a wide area.

In order to solve this problem, Patent Document 4 shows that a domain-inverted region serving as a nucleus can be easily formed by forming the end portion of the electrode pattern into a fine bent shape. However, in the element for generating visible and ultraviolet light by SHG, since the period of polarization inversion is about several μm, it is very difficult to fabricate the structure of the pattern end, making it difficult to produce the electrode pattern. There was a problem.
JP 2000-147484 A JP 2003-307758 A JP-A-7-72521 JP 2003-5236 A

  The present invention is intended to solve the above-described problems, and an electrode for producing a domain-inverted structure and an electrode production method capable of easily forming a uniform periodic domain-inverted region over a wide range It is another object of the present invention to provide a device for manufacturing a domain-inverted structure and a method for manufacturing a domain-inverted structure.

  In order to achieve the above object, the invention according to claim 1 is an electrode disposed on two opposing surfaces of a dielectric substrate having a nonlinear optical effect, and is disposed on each of the two opposing surfaces. At least one of the electrodes to be formed has a predetermined electrode pattern for producing a polarization reversal structure that reverses the polarization direction by applying an electric field to the dielectric substrate, and includes a conductive fine particle Is used.

  According to a second aspect of the present invention, in the electrode according to the first aspect, the conductive fine particles have a size in the range of 50 nm to 200 nm.

  According to a third aspect of the present invention, in the electrode for producing a domain-inverted structure according to the first or second aspect, the conductive fine particles have a needle-like structure.

  According to a fourth aspect of the present invention, there is provided a method for producing an electrode having a predetermined electrode pattern for producing a domain-inverted structure on a dielectric substrate having a nonlinear optical effect, wherein an insulator is provided on the surface of the dielectric substrate. A groove is made of a material, and the electrode pattern is formed by filling the groove with a material containing conductive fine particles.

  The invention according to claim 5 is a method for producing an electrode having a predetermined electrode pattern for producing a domain-inverted structure on a dielectric substrate having a nonlinear optical effect, wherein the photosensitive substrate contains conductive fine particles. A resin film is formed on a dielectric substrate, and a photosensitive resin containing conductive fine particles is processed by photolithography to form an electrode pattern.

  According to a sixth aspect of the present invention, a domain-inverted structure is fabricated on a dielectric substrate having a nonlinear optical effect by using the domain-inverted structure fabrication electrode according to any one of the first to third aspects. Is a device for manufacturing a domain-inverted structure.

  The invention according to claim 7 is the apparatus for producing a domain-inverted structure according to claim 6, further comprising a heating means for heating the dielectric substrate while an electric field is applied to the dielectric substrate. It is a feature.

  The invention described in claim 8 is the apparatus for producing a domain-inverted structure according to claim 6, further comprising ultraviolet irradiation means for irradiating the dielectric substrate with ultraviolet rays while applying an electric field to the dielectric substrate. It is characterized by being.

  According to a ninth aspect of the present invention, a domain-inverted structure is fabricated on a dielectric substrate having a nonlinear optical effect by using the domain-inverted structure fabrication electrode according to any one of the first to third aspects. A method for producing a domain-inverted structure characterized by the following.

  According to the first to third aspects of the present invention, the electrodes are disposed on the two opposing surfaces of the dielectric substrate having the nonlinear optical effect, and are disposed on the two opposing surfaces, respectively. At least one of the electrodes has a predetermined electrode pattern for producing a polarization reversal structure that reverses the polarization direction by applying an electric field to the dielectric substrate, and a material containing conductive fine particles is used. Therefore, nucleation of domain inversion can be promoted and uniform nucleation can be performed over a wide range, and thereby a uniform domain inversion structure (periodic domain inversion region) can be easily formed over a wide range. it can.

  In particular, in the invention according to claim 3, in the electrode for producing a domain-inverted structure according to claim 1 or 2, the conductive fine particles have a needle-like structure. Even when the amount is reduced, the charge can be moved uniformly in the material, and the nucleation density can be easily adjusted. That is, even when the density at which the domain-inverted nuclei are formed is lowered, a uniform domain-inverted structure can be formed.

  According to a fourth aspect of the present invention, there is provided a method for producing an electrode having a predetermined electrode pattern for producing a domain-inverted structure on a dielectric substrate having a nonlinear optical effect, wherein the electrode has a surface on the surface of the dielectric substrate. An electrode of an electrode for producing a domain-inverted structure in which a highly uniform domain-inverted region can be formed by forming a groove with an insulator material and embedding the groove with a material containing conductive fine particles to form the electrode pattern. A conventional photolithography technique can be used for the production of the pattern, and the electrode pattern can be formed easily (simplely).

  According to a fifth aspect of the present invention, there is provided a method for producing an electrode having a predetermined electrode pattern for producing a domain-inverted structure on a dielectric substrate having a non-linear optical effect, wherein the photosensitive substrate contains conductive fine particles. Inverted structure that can form highly uniform domain-inverted regions by forming an electrode pattern by forming a conductive resin film on a dielectric substrate and processing the photosensitive resin containing conductive fine particles by photolithography The electrode pattern of the electrode for production can be produced only by photolithography, and the electrode pattern can be formed easily (simplely).

  Further, according to the invention described in claims 6 to 9, the electrode for polarization inversion structure fabrication according to any one of claims 1 to 3 is used to polarize a dielectric substrate having a nonlinear optical effect. Since the inversion structure is manufactured, uniform nucleation can be performed over a wide range, and thus, a uniform domain inversion structure with less unevenness over a wide range can be easily manufactured.

  Particularly, in the invention according to claim 7, in the apparatus for manufacturing a domain-inverted structure according to claim 6, the apparatus further includes a heating unit that heats the dielectric substrate while applying an electric field to the dielectric substrate. As a result, the electric field strength necessary for the polarization inversion can be reduced, so that the polarization inversion structure for the thick dielectric substrate can be easily manufactured.

The invention according to claim 8 is the apparatus for producing a domain-inverted structure according to claim 6, further comprising ultraviolet irradiation means for irradiating the dielectric substrate with ultraviolet rays while applying an electric field to the dielectric substrate. In addition, since the electric field intensity required for polarization reversal can be reduced by ultraviolet irradiation, it is easy to produce a polarization reversal structure for a thick dielectric substrate.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The present invention relates to a dielectric substrate having a nonlinear optical effect, which is an electrode disposed on each of two opposing surfaces, and at least one of the electrodes disposed on each of the two opposing surfaces is A material having a predetermined electrode pattern for producing a polarization inversion structure that inverts the polarization direction by applying an electric field to the dielectric substrate and containing conductive fine particles is used.

  Here, silver (Ag) or the like is used as the conductive fine particles, and the conductive fine particles have a size in the range of 50 nm to 200 nm. Examples of the material containing conductive fine particles include a conductive resin and an adhesive. In these materials, current flows through the conductive fine particles. When such a material is used as an electrode material for producing a domain-inverted structure, charges are concentrated at the point where the conductive fine particles are in contact with the dielectric substrate, and a domain-inverted nucleus is easily formed. Since the contact points between the conductive fine particles and the surface of the dielectric substrate are evenly distributed in the range in which the electrodes are formed, nucleation is likely to occur in many places within the range in which the electrodes are formed. A uniform domain-inverted region with little unevenness along the electrode pattern can be formed.

  That is, according to the present invention, with respect to a dielectric substrate having a nonlinear optical effect, at least one of the electrodes respectively disposed on two opposing surfaces is polarized by applying an electric field to the dielectric substrate. Since a material having a predetermined electrode pattern for producing a domain-inverted structure for reversing the direction and containing conductive fine particles is used, nucleation of domain-inversion is promoted and uniform nucleation is performed over a wide range. Accordingly, a uniform domain inversion structure (periodic domain inversion region) can be easily formed over a wide range.

  Next, with reference to FIG. 1 and FIG. 2, an electrode for producing a domain-inverted structure and a method for producing the domain-inverted structure of the present invention will be described.

FIG. 1 is a diagram showing an example of a dielectric substrate on which an electrode pattern is formed. In the example of FIG. 1, LiNbO ₃ doped with 5 mol% of MgO (hereinafter referred to as MgO: LN) is used for the dielectric substrate 1. In addition, an electrode 2 having a comb-like electrode pattern is formed on the + Z plane of the substrate 1, and an electrode 3 having no pattern is formed on the -Z plane. The electrode 2 formed on the + Z plane is made of a resin material that is made conductive by mixing conductive fine particles 5. In the example of FIG. 1, spherical particles are used as the conductive fine particles 5.

  FIG. 2 is a diagram illustrating a state in which a voltage is applied to the MgO: LN substrate 1 of FIG. FIGS. 3A to 3D are diagrams showing changes in the domain-inverted regions when a voltage is applied to the MgO: LN substrate 1 of FIG. 1 via the electrodes 2 and 3. Referring to FIGS. 3A to 3D, at the interface between the MgO: LN substrate 1 and the electrode 2, electric charges concentrate on the portion where the conductive fine particles 5 are in contact. For this reason, polarization-reversed nuclei 6 are easily generated at the contact portions between the conductive fine particles and MgO: LN. The polarization inversion nuclei 6 generated in the electrode portion grow in the order of FIGS. 3A, 3B, 3C, and 3D along with the application time of the electric field, and finally, as shown in FIG. Thus, the domain-inverted region 7 along the electrode pattern of the electrode 2 is formed. Since such a portion exists uniformly over the entire electrode 2 on the + Z plane side, unevenness of the nucleation position hardly occurs. Therefore, a uniform domain inversion structure can be formed over the entire surface on which the electrode 2 is formed. Further, when the electric field is applied, if the substrate 1 is heated or irradiated with ultraviolet rays, the electric field strength required for the polarization inversion is reduced, so that a polarization inversion structure can be formed on the thicker substrate 1.

  4 and 5 are diagrams showing an example of an electrode manufacturing method (electrode pattern manufacturing method) according to the present invention.

In the method of FIG. 4, first, a groove 11 is formed on the dielectric substrate 1 with an insulating material 10 (FIGS. 4A and 4B), and the groove 11 is embedded with a material 12 containing conductive fine particles. (FIG. 4 (c)). Here, as the insulator material 10, a photoresist may be used, or an SiO ₂ film or the like is formed on the surface of the dielectric substrate 1, and the groove 11 is formed by photolithography and etching. good. In the case of using a photoresist, it is necessary to select a solvent that does not dissolve the resist as a solvent for a material containing conductive fine particles. The size of the conductive fine particles needs to be sufficiently small with respect to the grooves 11, but in recent years, nanoscale fine particles are manufactured using various metals, and the pitch of the electrode pattern is about several μm. Even if it is narrow, they can be used. Specifically, the polarization inversion period studied for wavelength conversion ranges from 1.8 μm (UV light generation with SHG and SFG) to 40 μm (infrared light generation with OPO), and the groove period is The size of the fine particles is preferably about 1/100 of the groove. That is, the size of the conductive fine particles (for example, silver fine particles) is preferably about 50 nm to 200 nm.

  In the method of FIG. 5, conductive fine particles are directly mixed with a photosensitive resin, and patterning is performed by photolithography (FIGS. 5A, 5B, and 5C). This method can produce an electrode pattern more easily than the method of FIG. However, in this case, it is necessary to adjust the amount of conductive fine particles to be mixed to such an extent that light that is sufficiently exposed when photolithography is performed can be transmitted.

  In the above-described example, spherical particles are used as the conductive fine particles, but the conductive fine particles are not limited to spherical particles, and those having an arbitrary shape can be used. For example, the conductive fine particles can be needle-shaped. FIG. 6 shows an electrode 2 formed of a material in which acicular conductive fine particles 5 are mixed. Carbon nanotubes can be used as the needle-like conductive fine particles. When using needle-shaped conductive fine particles, the electrode can be made conductive even with a smaller mixing amount than when using spherical conductive fine particles, so the density of nucleation should be reduced as necessary. This is advantageous in cases where it is desired to increase the light transmittance as shown in FIG.

The present invention can be used for an element having a polarization inversion structure in a visible light laser light source, a photo printer, a display, a terahertz laser light source, and the like.

It is a figure which shows an example of the dielectric substrate in which the electrode pattern was formed. It is a figure which shows a mode that a voltage is applied via an electrode to the MgO: LN board | substrate of FIG. It is a figure which shows the change of a polarization inversion area | region when a voltage is applied to the MgO: LN board | substrate of FIG. 1 via an electrode. It is a figure which shows the example of the manufacturing method (electrode pattern manufacturing method) of the electrode of this invention. It is a figure which shows the example of the manufacturing method (electrode pattern manufacturing method) of the electrode of this invention. It is a figure which shows the electrode formed with the material which mixed the acicular electroconductive fine particles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dielectric substrate 2, 3 Electrode 5 Conductive fine particle 10 Insulator material 11 Groove 12 Material containing conductive fine particle

Claims (9)

An electrode disposed on two opposing surfaces with respect to a dielectric substrate having a nonlinear optical effect, and at least one of the electrodes respectively disposed on the two opposing surfaces is a dielectric substrate An electrode for producing a domain-inverted structure having a predetermined electrode pattern for producing a domain-inverted structure in which the polarization direction is inverted by applying an electric field to the electrode, and comprising conductive fine particles. 2. The electrode for producing a domain-inverted structure according to claim 1, wherein the conductive fine particles have a size in a range of 50 nm to 200 nm. 3. The electrode for producing a domain-inverted structure according to claim 1 or 2, wherein the conductive fine particles have a needle-like structure. A method for producing an electrode having a predetermined electrode pattern for producing a domain-inverted structure on a dielectric substrate having a nonlinear optical effect, wherein a groove is made of an insulating material on the surface of the dielectric substrate. A method for manufacturing an electrode, wherein the electrode pattern is formed by embedding with a material containing conductive fine particles. A method for producing an electrode having a predetermined electrode pattern for producing a domain-inverted structure on a dielectric substrate having a nonlinear optical effect, wherein a photosensitive resin containing conductive fine particles is formed on the dielectric substrate. A method for producing an electrode, wherein a photosensitive resin containing conductive fine particles is processed by photolithography to form an electrode pattern. A device for producing a domain-inverted structure, wherein the domain-inverted structure is produced on a dielectric substrate having a nonlinear optical effect, using the electrode for producing a domain-inverted structure according to any one of claims 1 to 3. . 7. The apparatus for producing a domain-inverted structure according to claim 6, further comprising heating means for heating the dielectric substrate while an electric field is applied to the dielectric substrate. 7. The apparatus for producing a domain-inverted structure according to claim 6, further comprising ultraviolet irradiation means for irradiating the dielectric substrate with ultraviolet rays while applying an electric field to the dielectric substrate. Production device. A method for producing a domain-inverted structure, comprising: producing a domain-inverted structure on a dielectric substrate having a nonlinear optical effect using the electrode for domain-inverted structure production according to any one of claims 1 to 3. .

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