JP2000193811A - Multidimensional diffraction grating and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a multidimensional diffraction grating capable of simply obtaining nearly an equal effect to a photonic crystal by constituting a diffraction grating out of a substance of which the refractive index is changed by irradiation of an electromagnetic wave or electron beam, and multidimensionally and periodically forming territories of different refractive indexes therein. SOLUTION: Two beams of a laser beam 1 are oppositely made incident to a CdF2: Ga crystal 2, territories of different refractive index are periodically formed, to write one-dimensional diffraction grating 3 therein. The period of the written diffraction grating is decided by the wavelength of the laser beam 1, for example, in the case of the wavelength of 514.4 nm of an argon laser, it is 164 nm. Next, as shown in Fig. b, the CdF2: Ga crystal 2 is rotated by 90 deg., to write the diffraction grating 3 also in the cross direction at right angles to the previously written diffraction grating 3 as shown in Fig. c, and obtain the two-dimensional diffraction grating. Next as shown in Fig. d, the CdF2: Ga crystal 2 is further rotated by 90 deg., to write the diffraction grating 3 in the cross direction at right angles to the diffraction grating 3 as shown in Fig. e, to obtain three-dimensional diffraction grating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-dimensional diffraction grating, and more particularly to a light-reflection, light-condensing, and spectral characteristic that cannot be realized by optical components such as lenses and prisms using ordinary (natural) optical materials. To a multi-dimensional diffraction grating.

[0002]

2. Description of the Related Art A substance having a periodic change in refractive index is called a diffraction grating, and is used for various purposes such as light diffraction. An ordinary diffraction grating is one in which many straight lines are drawn at equal intervals in one direction on the surface of a glass plate or the like, which is a one-dimensional diffraction grating.

By the way, for a one-dimensional diffraction grating,
It is known that realizing a two-dimensional and three-dimensional diffraction grating can provide a new effect that cannot be obtained with a one-dimensional diffraction grating. In particular, two different optical materials having a large difference in refractive index are two-dimensional or three-dimensional with a period of about half the wavelength of light.
A dimensionally stacked structure is called a photonic crystal,
Recently, it has received special attention.

A photonic crystal has a structure in which a change in the refractive index is periodically repeated three-dimensionally in the order of half a wavelength of light, and optical components such as lenses and prisms using ordinary (natural) optical materials. Attention has been paid to the fact that it can realize light refraction and spectral characteristics that cannot be realized in such cases. In this photonic crystal, when the refractive index difference between two different optical materials is particularly large, a photonic band in which light waveguide is not allowed occurs, and by combining with a light emitting element, light emission control and various Applications are being considered. When the difference in the refractive index is small, no photonic band is generated, but as a three-dimensional diffraction grating, an abnormal diffraction phenomenon or dispersion effect of light that cannot be obtained with the ordinary optical material shown in FIG. It can be realized (see (b) in the figure).

[0005]

However, in order to actually produce a photonic crystal, it is necessary to realize a material processing technology on the order of half a wavelength of light and to realize this as a two-dimensional and three-dimensional periodic structure. There are many very difficult problems such as the point that it is not possible, and a photonic crystal at a practical level has not yet been obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multidimensional diffraction grating which can easily obtain almost the same effect as a photonic crystal by a completely new method, with respect to the above-mentioned difficulty in manufacturing a photonic crystal. It is an object of the present invention to provide a manufacturing method for realizing such a multidimensional diffraction grating structure.

[0007]

Means for Solving the Problems Photorefractive materials and compound semiconductor materials having a DX center are known to cause a change in the refractive index when irradiated with light (electromagnetic waves) or electron beams. For example, a quartz glass used for an optical fiber grating can obtain a large change in refractive index by irradiating ultraviolet rays by a photorefractive effect. In addition, AlGaAs or CdF ₂
In such compound semiconductor materials, impurities such as Si, Ge, Ga, and In doped in these materials form deep levels (DX centers), and the behavior of the DX centers formed in this manner allows It is also known that a relatively large change in the refractive index can be obtained by irradiating light. This change in the refractive index can occur locally in a very small region on the order of μm.

The present invention realizes a multidimensional periodic structure composed of regions having different refractive indices by using the properties of the photorefractive medium and the DX material without stacking two optical materials having different refractive indices. Is what you do. Since these materials can generate a change in the refractive index according to their intensity by irradiating an electromagnetic wave or an electron beam, for example, by irradiating light with good coherence such as a laser beam, interference fringes can be obtained. And regions having different refractive indices can be periodically formed in accordance with the interference fringes. A feature of the present invention is that writing of a three-dimensional diffraction grating is performed by making full use of multiple exposure using such interference fringes.

That is, the multidimensional diffraction grating according to claim 1 is made of a substance whose refractive index changes by irradiation of an electromagnetic wave or an electron beam, and regions having different refractive indices are formed therein periodically and multidimensionally. It is characterized by being.

According to a second aspect of the present invention, in the multidimensional diffraction grating according to the first aspect, the active substance is a material having a photorefractive effect.

According to a third aspect of the present invention, there is provided the multidimensional diffraction grating according to the first aspect, wherein the active substance is DX.
It is a compound semiconductor material having a center.

According to a fourth aspect of the present invention, there is provided the multidimensional diffraction grating according to the second aspect, wherein the active substance is a quartz glass material whose refractive index changes by irradiation with ultraviolet rays.

According to a fifth aspect of the present invention, there is provided the multidimensional diffraction grating according to the third aspect, wherein the active substance is C
It is characterized in that dF ₂ is Ga.

The production of the multidimensional diffraction grating is realized by the following method. That is, in the method of manufacturing a multidimensional diffraction grating according to claim 6, by irradiating an electromagnetic wave or an electron beam to an active substance whose refractive index changes due to irradiation of an electromagnetic wave or an electron beam, the refractive index inside the active substance is reduced. Are formed in a multidimensional manner periodically to obtain a diffraction grating.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a multidimensional diffraction grating according to the sixth aspect, wherein two opposing laser beams are incident on the active substance. Write the diffraction grating, and then write the diffraction grating by irradiating two opposing laser beams from a direction orthogonal to the direction in which the laser beam was first incident.
Obtain a three-dimensional diffraction grating by obtaining two-dimensional diffraction gratings and writing the diffraction grating by injecting two opposing laser beams from directions orthogonal to the incident directions of the laser beams that have been incident so far. It is characterized by.

In this method of manufacturing a multi-dimensional diffraction grating, after writing a one-dimensional diffraction grating, the active substance is turned by 90 °.
Rotate and apply the same laser beam again, rotate it further 90 ° and similarly apply the laser beam to obtain a three-dimensional diffraction grating, or fix the active substance and change the laser light source A three-dimensional diffraction grating may be obtained (by moving).

According to an eighth aspect of the present invention, there is provided a method of manufacturing a multidimensional diffraction grating according to the sixth aspect, wherein three laser beams orthogonal to each other are respectively opposed to the laser beams. It is characterized in that three laser beams are simultaneously incident on the active substance, and a three-dimensional diffraction grating is written at a time.

According to a ninth aspect of the present invention, there is provided the method of manufacturing a multidimensional diffraction grating according to the sixth aspect, wherein the four laser beams, each having an equal angle, are formed by the active substance. And writing a three-dimensional diffraction grating consisting of a triangular grating.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a multidimensional diffraction grating and a method of manufacturing the same according to an embodiment of the present invention will be described with reference to the drawings. Here, a Ga-doped CdF ₂ crystal (active substance), which is an optical material having a DX center, is used as a substance that causes a change in the refractive index.
A grating written on this material will disappear in a few seconds at room temperature, but will last for more than a year at temperatures as low as about 150K. Therefore, it is cooled down to a low temperature of about 150K using a thermoelectric cooler, and the diffraction grating is written.

The method first introduced here as a writing method of the diffraction grating is, as shown in FIG.
Two luminous fluxes of the laser beam 1 are incident on the crystal 2 in opposition,
A region having a different refractive index is periodically formed, and a one-dimensional diffraction grating 3 is written. The period of the diffraction grating 3 to be written is determined by the wavelength of the laser beam 1, and is, for example, an argon laser.
When light having a wavelength of 514.5 nm is used, the wavelength is about 164 nm. Next, the crystal 2 is rotated by 90 ° as shown in FIG. 4B, and the diffraction grating 3 is also written in a direction orthogonal to the previously written diffraction grating 3 as shown in FIG. Get the grid. Next, as shown in (d), the crystal 2 is further rotated by 90 °, and (e)
As shown in (1), the diffraction grating 3 is also written in a direction orthogonal to the diffraction grating 3 that has been written so far to obtain a three-dimensional diffraction grating. By such a method, it is possible to obtain a multidimensional diffraction grating in which three-dimensional periodic interference fringes are written on the DX crystal.

As another method, as shown in FIG. 3, a total of six laser beams 1 of three laser beams orthogonal to each other and laser beams respectively opposed to the laser beams are simultaneously incident on the crystal 2. Then, a method of writing the three-dimensional diffraction grating 3 at a time is also conceivable.

Alternatively, as another method, as shown in FIG. 4, a laser beam 1 incident on a material on which the diffraction grating 3 is written has four laser beams 1 all having the same angle. A method of writing the three-dimensional diffraction grating 3 is also conceivable. In any of the above methods, a three-dimensional diffraction grating can be obtained inside the crystal by appropriately adjusting the intensity of writing light and the exposure time (exposure amount).

By using the multidimensional diffraction grating and the method of manufacturing the multidimensional diffraction grating according to the present embodiment, refraction of light, which cannot be obtained particularly with optical components such as lenses and prisms using ordinary (natural) optical materials, can be obtained. Since dispersion characteristics can be realized, if optical components such as a lens and a prism are made by this, the size can be significantly reduced, and the device can be used in a wavelength multiplexing optical communication system or the like.

[0024]

According to the multidimensional diffraction grating and the method for manufacturing the multidimensional diffraction grating of the present invention, refraction and dispersion of light which cannot be obtained particularly with optical components such as lenses and prisms using ordinary (natural) optical materials. Since the characteristics can be realized, if optical components such as a lens and a prism are made by this, the size can be significantly reduced, and the device can be used in a wavelength multiplexing optical communication system or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing refraction of light by a prism;
(A) is a diagram showing refraction of light by a normal optical material,
(B) is a diagram showing refraction of light by the photonic crystal.

FIG. 2 is a diagram illustrating a method for manufacturing a multidimensional diffraction grating according to one embodiment of the present invention.

FIG. 3 is a view illustrating a method for manufacturing a multidimensional diffraction grating according to another embodiment of the present invention.

FIG. 4 is a view illustrating a method for manufacturing a multidimensional diffraction grating according to another embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 laser beam 2 CdF ₂ : Ga crystal (active substance) 3 diffraction grating

Claims (9)

[Claims] 1. A multidimensional diffraction grating comprising a substance whose refractive index changes by irradiation of an electromagnetic wave or an electron beam, wherein regions having different refractive indices are formed therein periodically and multidimensionally. 2. The multidimensional diffraction grating according to claim 1, wherein said active substance is a material having a photorefractive effect. 3. The multidimensional diffraction grating according to claim 1, wherein the active substance is a compound semiconductor having a DX center. 4. The multidimensional diffraction grating according to claim 2, wherein the active substance is quartz glass whose refractive index changes when irradiated with ultraviolet rays. 5. The multidimensional diffraction grating according to claim 3, wherein the active substance is CdF ₂ : Ga. 6. An active substance whose refractive index changes by irradiation of an electromagnetic wave or an electron beam is irradiated with an electromagnetic wave or an electron beam to form a region having a different refractive index in the active substance in a multidimensional manner. A method for producing a multidimensional diffraction grating, comprising: obtaining a diffraction grating by: 7. The method for manufacturing a multi-dimensional diffraction grating according to claim 6, wherein two opposing laser beams are incident on the active substance to write a one-dimensional diffraction grating, and then the laser beam is first applied. A two-dimensional diffraction grating is obtained by writing a diffraction grating by injecting two opposing laser beams from a direction perpendicular to the direction in which the laser beam is incident. By writing a diffraction grating by injecting two opposing laser beams from orthogonal directions, 3
A method for producing a multidimensional diffraction grating, comprising obtaining a two-dimensional diffraction grating. 8. The method for manufacturing a multidimensional diffraction grating according to claim 6, wherein three laser beams orthogonal to each other and three laser beams respectively opposed to said laser beams are simultaneously incident on said active substance. And writing a three-dimensional diffraction grating at a time. 9. The method of manufacturing a multidimensional diffraction grating according to claim 6, wherein four laser beams having the same angle formed by each of the light beams are incident on the active substance, and the three-dimensional diffraction grating is formed of a triangular grating. And a method for manufacturing a multidimensional diffraction grating.