JP4173792B2 - Method for forming a three-dimensional photonic crystal - Google Patents

Description

  The present invention relates to a method for forming a woodpile type three-dimensional photonic crystal having a diamond crystal structure.

  As is well known to those skilled in the art, a photonic crystal has been proposed as an element for improving the performance of light emitting elements, optical circuits, and the like. A photonic crystal is a medium that exhibits a structure in which the refractive index varies with the period of the wavelength of light, and is typically a one-dimensional photonic crystal that has a simple periodic structure such as a multilayer film, or an array of holes or columns formed in a substrate. In addition to the two-dimensional photonic crystal, a three-dimensional photonic crystal having a three-dimensional mosaic structure has been proposed.

  As a method for forming a three-dimensional photonic crystal, a sequential lamination method using a semiconductor micromachining technique and a microsphere method using a large number of microspheres such as silica or polystyrene have been proposed. However, the sequential stacking method and the microsphere method are remarkably expensive due to the necessity of performing a remarkably complicated process many times. There is a problem that it is extremely difficult if not impossible to form a photonic crystal with sufficient accuracy.

In the following Patent Document 1, the present inventor irradiates a photocurable synthetic resin with two or three laser beams generated by splitting into two or three from a common laser light source, and forms a laser beam interference pattern. A method of forming a three-dimensional photonic crystal, characterized in that it is generated and cured with a photocurable synthetic resin corresponding to the laser beam interference pattern, has been proposed. According to such a method using a laser beam interference pattern, a three-dimensional photonic crystal can be formed considerably simpler and at a lower cost and with a considerably higher accuracy than the sequential lamination method and the microsphere method.
JP 2000-329920 A

  The three-dimensional photonic crystal formed by the method disclosed in the above Japanese Patent Laid-Open No. 2000-329920 previously proposed by the present inventors has a simple hexagonal lattice structure. As a three-dimensional photonic crystal, a crystal having a diamond crystal structure capable of obtaining an ideal photonic band gap, not a hexagonal lattice structure, is excellent. As a three-dimensional photonic crystal having a diamond crystal structure, Have proposed woodpile type (also called layer-by-layer type) photonic crystals and jabronovite type photonic crystals.

  The present invention has been made in view of the above-mentioned facts, and its main technical problem is that a three-dimensional photonic crystal having a diamond crystal structure, more specifically, a woodpile type three-dimensional photonic crystal, can be considerably easily and inexpensively. Also, a new and useful method that can be formed with high accuracy is applied.

As a result of earnest research, the present inventors have improved the laser light irradiation method in the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2000-329920, which has been proposed by the inventors. Found that can be achieved.

  As a method for achieving the main technical problem, the photosensitive synthetic resin is irradiated with three laser beams to generate a first laser beam interference pattern, and the photosensitive synthetic resin is irradiated with three laser beams. Forming a wood pile type three-dimensional photonic crystal having a diamond crystal structure, comprising: forming a second laser interference pattern substantially perpendicular to the first laser beam interference pattern A method is provided.

In a preferred embodiment, each of the three laser beams that generate the first laser beam interference pattern and the three laser beams that generate the second laser beam interference pattern are laser beams from a common laser light source. Are divided into three laser beams, which substantially define three sides toward the apex of the regular quadrangular pyramid, and the first laser beam interference pattern and the second laser beam interference pattern are approximately It is a two-dimensional square lattice of an elliptic cylinder array. The photosensitive synthetic resin is a photocurable synthetic resin, and it is preferable that a cured portion cured by laser light irradiation has a diamond crystal structure. Preferably, the photocurable synthetic resin is an ultraviolet curable synthetic resin, the laser light source is a near infrared pulse laser, and the photosensitive synthetic resin is cured by two-photon absorption. Advantageously, the cured portion of the photosensitive synthetic resin is used as a replica to form the three-dimensional photonic crystal from a material having a high refractive index.

  According to the present invention, a three-dimensional photonic crystal having a diamond crystal structure, more specifically, a woodpile type three-dimensional photonic crystal, can be formed considerably easily, at low cost, and with high accuracy.

  Hereinafter, preferred embodiments of the method for forming a three-dimensional photonic crystal of the present invention will be described in more detail with reference to the accompanying drawings.

  Referring to FIG. 1, in a preferred embodiment of the method of the present invention for forming a woodpile photonic crystal, a glass cell 4 which may be a rectangular or cubic shape filled with a photosensitive synthetic resin 2. Prepare. The photosensitive synthetic resin 2 is preferably an uncured photocurable synthetic resin, particularly an ultraviolet curable synthetic resin. As an ultraviolet curable synthetic resin which can be used conveniently, the ultraviolet curable synthetic resin currently marketed as a brand name "SCR500" from Nippon Synthetic Rubber Co., Ltd. can be mentioned, for example.

  The glass cell 4 is held in a required state by an appropriate holding means (not shown), and the first surface (lower surface in FIG. 1) S1 of the photosensitive synthetic resin 2 filled in the glass cell 4 is numbered as a whole. The three laser beams LB1, LB2, and LB3 are irradiated by the laser beam irradiation means indicated by 6. In the illustrated embodiment, the laser light irradiation means 6 includes a common laser light source 8, two splitters 10 and 12, and four reflecting mirrors 16, 18, 20 and 24. The laser light source 8 is preferably a laser light source that emits a near-infrared pulse laser, such as a titanium sapphire (Ti: Sapphire) laser. The pulsed laser light emitted from the laser light source 6 is split into two laser lights by the splitter 10, and one of the two split laser lights is reflected by the reflecting mirror 16 to reach the splitter 12, and further by the splitter 12. The light is split into two laser beams LB1 and LB2, and the other is reflected by the reflecting mirror 18 to become laser beam LB3. The laser beam LB1 is reflected by the reflection mirror 24 and applied to the first surface S1 of the synthetic resin 2. The laser beam LB2 is reflected by the reflection mirror 20 and the reflection mirror 24 and is applied to the first surface S1 of the synthetic resin 2. The laser beam LB3 is reflected by the reflection mirror 24 and applied to the first surface S1 of the synthetic resin 2.

  The optical path lengths of the laser beams LB1, LB2, and LB3 from the laser light source 6 to the first surface S1 of the synthetic resin 2 are set to be substantially the same. Further, an ND filter (not shown) is inserted in the optical paths of the laser beams LB1, LB2, and LB3. By adjusting the ND filter, the intensities of the light beams of the laser beams LB1, LB2, and LB3 are made substantially the same. ing. Further, the three laser beams LB1, LB2 and LB3 reflected by the reflecting mirror 24 and applied to the first surface S1 of the synthetic resin 2 define three sides of the regular quadrangular pyramid, and the regular quadrangular pyramid. Is positioned on the first surface S <b> 1 of the synthetic resin 2. When the first surface S1 of the synthetic resin 2 is irradiated with such three laser beams LB1, LB2, and LB3, the laser interference pattern 26 shown in FIG. A laser beam interference pattern 26 that is a two-dimensional square lattice of the array 28 is generated. When the synthetic resin 2 is an ultraviolet curable synthetic resin and the laser beam generated by the laser light source 8 is a near infrared pulse laser, the synthetic resin 2 is cured according to the laser beam interference pattern 26 by two-photon absorption. Thus, a number of substantially elliptical column arrays 30 (FIG. 3) are cured. When a number of substantially elliptical column arrays 30 are cured by two-photon absorption, only the vicinity of the peak value of the pulse laser contributes to the curing. The interval between adjacent rods in the laser beam interference pattern 26 is defined by the inclination angle α of the three laser beams LB1, LB2, and LB3 that define a regular quadrangular pyramid. When the inclination angle α is increased, the interval is decreased.

  When the irradiation of the above-described three laser beams LB1, LB2, and LB3 on the first surface S1 of the synthetic resin 2 is completed, the glass cell 4 filled with the synthetic fiber 2 is formed as shown by a two-dot chain line in FIG. Similarly, three laser beams LB1, LB2, and LB3 are irradiated onto the second surface S2 that is rotated 90 degrees and is substantially perpendicular to the first surface S1 of the synthetic resin 2. Therefore, the laser beam interference pattern 26 that is a two-dimensional square lattice of the substantially elliptical column array 28 is generated also on the second surface S2 of the synthetic resin 2, and thus a large number of substantially elliptical column arrays 32 (FIG. 3) are cured. . Regarding the synthetic resin 2, the laser beam interference pattern 26 generated by the three laser beams LB1, LB2, and LB3 irradiated to the second surface S1 is the three laser beams LB1 irradiated to the second surface S2. , LB2 and LB3 are substantially perpendicular to the laser light interference pattern 26 generated. In other words, three laser beams LB1 for the second surface S2 with respect to a large number of substantially elliptical column arrays 30 that are cured by irradiation of the three laser beams LB1, LB2, and LB3 for the first surface S1. A large number of substantially elliptical column arrays 32 that are cured by the irradiation of LB2 and LB3 are substantially vertical, and each of the large number of substantially elliptical column arrays 32 is adjacent to a specific direction (vertical direction in FIG. 3). It can be extended. Therefore, when the synthetic resin 2 in the glass cell 4 is taken out and the uncured portion is removed by washing with, for example, an ethanol solution, a woodpile photonic crystal 34 as shown in FIG. 3 is formed. Such a woodpile type three-dimensional photonic crystal 34 has a diamond crystal structure having an ideal photonic band gap.

  After irradiating the first surface S1 of the synthetic resin 2 with the three laser beams LB1, LB2, and LB3, the glass cell 4 is rotated by 90 degrees, and the three laser beams LB1 are applied to the second surface S2 of the synthetic resin 2. Instead of irradiating with LB2 and LB3, if desired, the entire surface of the laser beam irradiation means 6 or a part of its constituent elements is appropriately moved with respect to the glass cell 4 so that the second surface of the synthetic resin 2 S2 can be irradiated with three laser beams LB1, LB2, and LB3.

The structure shown in FIG. 3 formed from a cured synthetic resin can be used as it is as a woodpile type three-dimensional photonic crystal, but the photonic crystal is formed from a material having a high refractive index. It is hoped that. Therefore, the structure shown in FIG. 3 formed from a cured synthetic resin is used as a so-called replica, and is made from a material having a high refractive index, for example, titanium oxide (TiO ₂ ) or silicon oxide (SiO ₂ ). It is preferable to form a woodpile type three-dimensional photonic crystal having a structure as shown in FIG.

  In the case described above, the laser beam interference pattern 26 as shown in FIG. 2 due to laser beam interference, that is, the laser beam interference pattern 26 which is a two-dimensional square lattice of the substantially elliptical column (column having a substantially elliptical cross section) array 28. However, the ratio of the minor axis to the major axis of the substantially elliptical shape of the laser interference pattern 26 is that of the intensity of the laser beam LB2 and the intensity of the laser beam LB3 with respect to the intensity of the laser beam LB1 by adjusting the ND filter. It can be controlled by changing the ratio. For example, when the intensity of the light beam of the laser beam LB1 is about several times the intensity of the light beams of the laser beam LB2 and the laser beam LB3, the laser interference pattern 26 changes from a substantially elliptical column array to a substantially cylindrical array.

The simple figure which shows the laser beam irradiation mode for forming a woodpile type three-dimensional photonic crystal. The figure which shows the laser beam interference pattern produced | generated by the laser beam irradiation in FIG. The simplified perspective view which shows the formed woodpile type | mold three-dimensional photonic crystal.

Explanation of symbols

2: photosensitive synthetic resin 6: laser beam irradiation means 26: laser beam interference pattern 34: woodpile type three-dimensional photonic crystal

Claims (5)

Irradiating the photosensitive synthetic resin with three laser beams to generate a first laser beam interference pattern, and irradiating the photosensitive synthetic resin with three laser beams to the first laser beam interference pattern Forming a second laser interference pattern substantially perpendicular to the method, and forming a woodpile type three-dimensional photonic crystal having a diamond crystal structure. Each of the three laser beams that generate the first laser beam interference pattern and the three laser beams that generate the second laser beam interference pattern split the laser beam from the common laser light source into three. Three sides of the side substantially toward the apex of the regular quadrangular pyramid, and the first laser beam interference pattern and the second laser beam interference pattern are two-dimensional in a substantially elliptic cylinder array. The method of claim 1, wherein the method is a square lattice. The method according to claim 1, wherein the photosensitive synthetic resin is a photocurable synthetic resin, and a cured portion cured by laser light irradiation has a diamond crystal structure. 4. The method of claim 3, wherein the photocurable synthetic resin is an ultraviolet curable synthetic resin, the laser light source is a near infrared pulsed laser, and the photosensitive synthetic resin is cured by two-photon absorption. The method according to claim 3 or 4, wherein the three-dimensional photonic crystal is formed from a material having a high refractive index by using the cured portion of the photosensitive synthetic resin as a replica.

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