JP2013020152A - Electromagnetic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave element that reduces an influence of aberration on electromagnetic waves of a plurality of bands having significantly different wavelengths, with a simple structure.SOLUTION: An electromagnetic wave element is configured by a composite dielectric in which a second dielectric 2 having a different dielectric constant from a first dielectric is dispersed in the first dielectric 1. The electromagnetic wave element has an effective dielectric constant almost equal to the electromagnetic wave of a predetermined first wavelength and that of a predetermined second wavelength longer than the first wavelength. The average particle size and average interspace of the second dielectric 2 is smaller than the first wavelength.

Description

  The present invention relates to an electromagnetic wave element used in two wavelength bands having greatly different wavelengths.

  A person recognizes the shape and color of an object by visible light, which is an electromagnetic wave that can be felt by the person. Further, among electromagnetic waves that cannot be felt by humans, it is possible to obtain temperature-derived information from infrared light and distance information to an object using millimeter waves. When these electromagnetic waves are used for each wavelength, information derived from temperature and distance information can be obtained.

  Therefore, various useful information can be obtained by displaying a visible light image captured by a normal camera and an image detected by infrared rays, millimeter waves, or the like in an overlapping manner. For example, if you can know the color and temperature distribution at the same time when heating foods and dishes in an oven using a visible light image and an infrared camera, this information is fed back for more efficient heating. be able to. In addition, by adding temperature distribution information to the in-vehicle camera, even a person whose clothes have been assimilated in the background can be surely recognized, leading to an improvement in the safety of the automobile.

  Here, in order to know information such as the distance and temperature of an arbitrary point of an object, in an image obtained by measuring electromagnetic waves emitted from an object with two cameras having parallax, the same point of the object is a pixel of each image. It is necessary to obtain the relationship of how the image is reflected, that is, “association”. For example, when viewing an object with two visible light cameras having parallax and “corresponding” the same point of the object in each image, calculation is performed using feature points such as the contour of the object.

  On the other hand, the substance has dispersion, and the response (refractive index, absorptance, etc.) to the electromagnetic wave varies depending on the frequency of the electromagnetic wave. In particular, slight changes in the refractive index with frequency cause aberrations, which limit the performance of electromagnetic wave elements such as lenses. For this reason, in the case of visible light, an achromatic lens system in which a plurality of lenses having positive and negative refractive powers are combined is used to remove chromatic aberration (see, for example, Patent Document 1). In addition, chromatic aberration is also suppressed by forming a diffractive surface on the surface of a lens having a curvature (see, for example, Patent Document 2).

Japanese Patent No. 4125179 Japanese Patent Laid-Open No. 10-73760

  However, when using multi-wavelength electromagnetic waves having greatly different wavelengths, different imaging elements are used corresponding to visible light, infrared light, millimeter wave, etc., and “correspondence” as the same point is It becomes more difficult. In addition, even when electromagnetic waves in a plurality of wavelength bands that are greatly different from each other can be detected by a single image sensor, an electromagnetic wave element that forms an image of an object on the image sensor is usually Therefore, the occurrence of chromatic aberration is even more problematic than when only visible light is used.

FIG. 5 is a schematic diagram for explaining chromatic aberration. In the imaging lens 101 (electromagnetic device) and an imaging system 100 consisting of image sensor 102, imaging lens 101 is designed to better imaging is performed using an electromagnetic wave having a predetermined wavelength lambda _1. Therefore, light emitted from one point on the object 103 passes through different regions of the imaging lens 101 and then converges to one point on the image 104 on the detection surface of the image sensor 102 (shown by a solid line in the figure). Light path). However, since the medium constituting the imaging lens 101 exhibits a different refractive index with respect to an electromagnetic wave having a wavelength λ ₂ that is significantly different from λ ₁ , good imaging cannot be performed with the same imaging system (dotted line in the figure). Light path). FIG. 5 shows a case where the refractive index at the wavelength λ ₂ is larger than the refractive index at the wavelength λ ₁ .

  In order to solve this problem, if the imaging lens 101 is configured as an achromatic electromagnetic wave element for the purpose of suppressing chromatic aberration, the apparatus becomes undesirably large. In addition, forming a diffractive surface or the like on the surface of the imaging lens 101 also causes problems such as an increase in noise and a complicated manufacturing process. Even with these improvements, chromatic aberration cannot be reduced to zero as long as the material is dispersed. In particular, when the bands of two target electromagnetic waves are greatly different, such as visible light and infrared light, visible light and millimeter wave, etc., the refractive index of the same substance changes greatly, and chromatic aberration is obtained by the above method. (See ED Palik (ed.), "Handbook of Optical Constants of Solids," Academic Press, London, UK (1998)).

  Accordingly, an object of the present invention made by paying attention to these points is to provide an electromagnetic wave element which has a simple configuration and reduces the influence of aberration on electromagnetic waves in a plurality of bands having greatly different wavelengths.

The invention of the electromagnetic wave element that achieves the above object is
An electromagnetic wave element composed of a composite dielectric material in which a second dielectric material having a different dielectric constant from the first dielectric material is dispersed in a first dielectric material,
The electromagnetic wave element has an effective dielectric constant substantially equal to an electromagnetic wave having a predetermined first wavelength and an electromagnetic wave having a predetermined second wavelength longer than the first wavelength;
The average particle diameter and average interval of the second dielectric are smaller than the first wavelength.

  Preferably, at least one of the first dielectric and the second dielectric has a resonance wavelength at which a dielectric constant changes greatly between the first wavelength and the second wavelength.

  More preferably, the electromagnetic wave element predetermines the first wavelength and the second wavelength, and sets the effective dielectric constant of the composite dielectric with respect to the electromagnetic wave of the first wavelength to the electromagnetic wave of the second wavelength. The average dielectric particle size of the second dielectric can be determined so as to be approximately equal to the effective dielectric constant of the composite dielectric with respect to

によって与えられ、ｂ，θおよびＦ（θ）は、それぞれ

により定義され、ここにおいて、ａは、前記第２の誘電体の平均的な粒径であり、ε_１およびε_２は、それぞれ前記第１の誘電体と前記第２の誘電体との誘電率であり、ｆは前記複合誘電体の全体に占める前記第２の誘電体の体積占有率であり、λは電磁波の波長である。 The effective dielectric constant corresponding to the electromagnetic waves of the first wavelength and the second wavelength is

And b, θ and F (θ) are respectively

Where a is the average grain size of the second dielectric, and ε ₁ and ε ₂ are the dielectric constants of the first and second dielectrics, respectively. F is the volume occupancy of the second dielectric in the entire composite dielectric, and λ is the wavelength of the electromagnetic wave.

  The second wavelength is preferably at least 10 times the first wavelength.

  Preferably, the electromagnetic wave element is configured as an electromagnetic wave element having a positive refractive power with respect to the electromagnetic wave having the first wavelength and the electromagnetic wave having the second wavelength.

  According to the present invention, the electromagnetic wave element is composed of a composite dielectric material in which a second dielectric material having a dielectric constant different from that of the first dielectric material is dispersed in the first dielectric material, and the first wavelength The effective dielectric constant is substantially equal to the electromagnetic wave of the second wavelength and the electromagnetic wave of the second wavelength longer than the first wavelength. Can be reduced.

It is a schematic diagram which shows the structure of the composite dielectric material which comprises the electromagnetic wave element which concerns on embodiment of this invention. 2 is a graph showing an effective dielectric constant of the electromagnetic wave element of FIG. 1 as a function of 2πa / λ. It is a schematic diagram for demonstrating the imaging performance of the imaging system to which the electromagnetic wave element of this invention is applied. It is a figure which shows typically the wavelength dependence of the dielectric constant of a dielectric material. It is a schematic diagram for demonstrating chromatic aberration.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment)
FIG. 1 is a schematic diagram showing a configuration of a composite dielectric constituting an electromagnetic wave element according to an embodiment of the present invention. In this composite dielectric, a second dielectric 2 having a dielectric constant different from that of the first dielectric 1 is dispersed in the first dielectric 1. Here, the dielectric constant of the first dielectric 1 is ε ₁ , and the dielectric constant of the second dielectric ₂ is ε ₂ . For the sake of simplicity, the second dielectrics 2 are all spheres of radius a and are not shown in the figure, but are arranged three-dimensionally to form a square lattice with period p (> a). Assume that In this case, the volume occupation ratio of the dielectric 2 occupying the whole is given by the equation (1).

Hereinafter, this f is simply referred to as volume occupancy. Such a composite dielectric is used for electromagnetic waves having two different wavelengths, and the wavelengths of the respective electromagnetic waves to be used are λ ₁ and λ ₂ in vacuum. It is assumed that the relationship (2) is established between the period p of the grating in which the second dielectric 2 is arranged and the wavelengths λ ₁ and λ _{2 of} the first and second electromagnetic waves.

In this case, an effective dielectric constant can be defined for the composite dielectric. This is called the effective dielectric constant and expressed by ε _eff . It is known that the effective dielectric constant ε _eff is expressed by equation (3) (see CL Holloway et al., IEEE Transactions on Antenna and Propagation, Vol. 51, p.2596-2603 (2003)).

  Here, F (θ) is defined by equation (4).

FIG. 2 is a graph showing the effective dielectric constant expressed by the equation (3) when λ ₁ as the first wavelength is 500 nm, with 2πa / λ ₁ as the horizontal axis. SiO ₂ (ε ₁ (λ ₁ ) = 2.14) is used as the first dielectric _{1 and} ZnS (ε ₂ (λ ₁ ) = 5.86) is used as the second dielectric 2, respectively. Was set to f = 0.268. The dielectric constants ε ₁ (λ ₁ ) and ε ₂ (λ ₁ ) of the first dielectric 1 and the second dielectric 2 are values for the wavelength λ ₁ = 500 nm. The effective dielectric constant at the left end (2πa / λ ₁ = 0) of this graph is ε ⁰ _eff (λ ₁ ) = 2.84. As 2πa / λ ₁ increases from the left end of the graph, the effective dielectric constant increases and rapidly increases and diverges in the vicinity of 2πa / λ ₁ = 1.39. This is because the dielectric sphere having a dielectric constant ε ₂ constituted by the second dielectric 2 acts as a resonator, and in this region, by adjusting the structural period of the composite dielectric, Any effective dielectric constant of 2.84 or higher can be realized.

On the other hand, when the second wavelength λ ₂ is 100 μm, the dielectric constants of the first dielectric 1 and the second dielectric 2 are ε ₁ (λ ₂ ) = 3.88 and ε ₂ (λ ₂ , respectively). ) = 9.36. Also in this case, the graph of the effective dielectric constant with respect to the second wavelength λ ₂ is a curve that diverges at a predetermined 2πa / λ _{2 as} in FIG. Here, considering that λ ₂ is 200 times λ ₁ , the value of the radius a ₂ of the second dielectric 2 where the effective dielectric constant diverges with respect to the electromagnetic wave having the second wavelength λ _2. Is considerably larger (about two digits) than the value of the radius a ₁ at which the effective permittivity diverges with respect to the electromagnetic wave having the first wavelength λ ₁ . Therefore, in the range of a satisfying 0 <2πa / λ ₁ <1.39, no divergence occurs with respect to the second wavelength λ ₂ , and the effective dielectric constant is substantially constant at ε _eff (λ ₂ ) = 4.97. Value.

Therefore, by setting the radius a to an appropriate value, it is possible to make the effective dielectric constant ε _eff of the electromagnetic wave having the first wavelength λ ₁ substantially coincide with the effective dielectric constant ε _eff of the second electromagnetic wave. Specifically, in FIG. 2, when 2πa / λ ₁ = 1.18, ε _eff = 4.98. Therefore, both the wavelength λ ₁ = 500 nm and the wavelength λ ₂ = 100 μm are almost equal. The same effective dielectric constant will be obtained. Since the dielectric does not exhibit a magnetic response, the effective refractive index (effective refractive index) of the composite dielectric is equal to the square root of the effective dielectric constant. Therefore, in the above example, the composite dielectric exhibits an effective refractive index having substantially the same value for both wavelengths λ ₁ and λ ₂ .

FIG. 3 is a schematic diagram for explaining the imaging performance of the imaging system to which the electromagnetic wave element of the present application is applied. The imaging system 10 includes an imaging lens 11 and an imaging element 12. The imaging lens 11 is an electromagnetic wave element according to the present embodiment having a positive power, and forms an image 14 of the object 13 on the imaging element 12. The imaging element 12 is an element that can detect electromagnetic waves of both the _first wavelength λ ₁ and the second wavelength λ ₂ . For example, an element having sensitivity to each of the first wavelength λ ₁ and the second wavelength λ ₂ is alternately arranged on the light receiving surface in a two-dimensional array. In FIG. 3, a solid line indicates an electromagnetic wave having a _first wavelength λ ₁ (= 500 nm), and a broken line indicates an electromagnetic wave having a second wavelength λ ₂ (= 100 μm). Since the electromagnetic wave having the first wavelength λ _{1 and} the electromagnetic wave having the second wavelength λ ₂ emitted from the object have substantially the same effective refractive index, it is possible to form an image on the light receiving surface of the same image sensor 12. Thus, the chromatic aberration as shown in FIG. 5 does not occur.

In the above description, the radius a of the sphere constituting the second dielectric 2 is adjusted in the vicinity of 2πa / λ ₁ = 1.39, and the effective dielectric constant ε _eff for the electromagnetic wave having the first wavelength λ ₁ is adjusted. _{Is set} to the same value as the effective dielectric constant ε _eff of the second wavelength λ ₂ . On the other hand, the effective dielectric constant ε _eff can also be changed by adjusting the first wavelength λ ₁ in the vicinity of 2πa / λ ₁ = 1.39.

The electromagnetic wave element of the present invention utilizes the fact that the effective permittivity diverges infinitely at a wavelength at which resonance occurs between the dielectric sphere constituting the second dielectric 2 of the composite dielectric and the electromagnetic wave. That is, the first wavelength λ ₁ is set in the vicinity of the resonance wavelength, and the structure of the composite dielectric, specifically, the particle diameter of the second dielectric 2 or the first wavelength λ ₁ is adjusted to adjust the _first wavelength λ ₁ . The effective dielectric constant for the electromagnetic wave having the wavelength λ ₁ is made to coincide with the effective dielectric constant for the electromagnetic wave having the second wavelength λ ₂ . In order to enable such a design, the effective dielectric constant for the second wavelength λ ₂ must be higher than the effective dielectric constant for the first wavelength λ _{1 in} a region where resonance does not occur. The fact that this condition is generally satisfied under the condition of λ ₁ <λ ₂ will be described below based on the electrical properties of the dielectric.

FIG. 4 is a diagram schematically showing the wavelength dependence of the dielectric constant of a dielectric (see D. Palik (ed.), “Handbook of Optical Constants of Solids,” Academic Press, London, UK (1998)). ). FIG. 4 shows the real part (solid line) and imaginary part (broken line) of the dielectric constant, and there is a correlation called the Kramers-Kronig relationship between them. That is, in the region where the real part does not change much, the imaginary part takes a small value, and the dielectric is transparent (wavelength regions A, C, E). On the other hand, in the region where the real part changes, the imaginary part takes a large value, and the dielectric becomes opaque (wavelength regions B and D). There are a plurality of resonance levels in the dielectric due to the movement of electrons and phonons, each resonating with light of a specific wavelength and absorbing incident light. In the wavelength region where there is no resonance level, the real part of the dielectric constant takes a substantially constant value, but the value increases as the wavelength increases, and in the example of FIG. 4, ε _A <ε _C <ε _E. This is because all the resonance levels on the shorter wavelength side (high frequency side) than the wavelength (frequency) of the incident light are immediately polarized with respect to the electric field of the electromagnetic wave (and thus increase the value of the dielectric constant). For). That is, when two transparent regions sandwiching at least one resonance level are compared, the following equation (5) is generally satisfied regardless of the type of dielectric.

The composite dielectric according to the present embodiment includes a first dielectric 1 and a second dielectric 2, and at least one of the first dielectric 1 and the second dielectric 2 is the first dielectric By having a resonance wavelength between which the dielectric constant changes greatly between the wavelength of 1 and the second wavelength, the composite dielectric as a whole can satisfy the equation (5). Further, according to the refractive index of SiO ₂ , it is known that the relationship of the formula (5) is established if the wavelength band of the normal electromagnetic wave is different by about 10 times (for example, D. Palik (ed.), “Handbook of Optical Constants of Solids, "Academic Press, London, UK (1998)).

In the above embodiment, it is calculated that the effective dielectric constant of the composite dielectric is given in FIG. 2 for λ ₁ (= 500 nm) of the relatively short first wavelength, but the left end (2πa of this graph) The effective dielectric constant at / λ ₁ = 0) is ε ⁰ _eff (λ ₁ ) = 2.84. On the other hand, when the same calculation is performed at a relatively long wavelength λ ₂ (= 100 μ), the effective dielectric constant at 2πa / λ ₂ = 0 is ε ⁰ _eff (λ ₂ ) = 4.97. Therefore, since ε ⁰ _eff (λ ₁ ) <ε ⁰ _eff (λ ₂ ), the effective permittivity is made to coincide with electromagnetic waves of both wavelengths in the range of 0 <2πa / λ ₁ <1.39. be able to.

Thus, even in the composite dielectric, the relationship of ε ⁰ _eff (λ ₁ ) <ε ⁰ _eff (λ ₂ ) inevitably holds if λ ₁ <λ ₂ shown in equation (5). The composite dielectric of the present invention can be configured using many types of dielectrics regardless of the types of the dielectrics 1 and 2.

As described above, according to the present embodiment, the electromagnetic wave element is formed by dispersing the second dielectric 2 having a dielectric constant different from that of the first dielectric 1 in the first dielectric 1. Since it is composed of a composite dielectric and has an effective dielectric constant substantially equal to the electromagnetic wave of the first wavelength λ _{1 and} the electromagnetic wave of the second wavelength λ ₂ longer than the first wavelength λ ₁ , With such a configuration, it is possible to reduce the influence of aberration on electromagnetic waves in a plurality of bands having greatly different wavelengths, and to have excellent imaging performance with respect to both electromagnetic waves. Therefore, when the electromagnetic wave element of the present invention is applied to the imaging apparatus, the pixels in the same position of the image are the same point of the object to be observed with respect to the electromagnetic waves having different wavelengths, so It becomes unnecessary, and the whole apparatus can also be comprised simply.

Further, in the imaging system of FIG. 3 configured using the electromagnetic wave element according to the present embodiment, the operating wavelengths λ ₁ and λ ₂ are set at the time of manufacturing the electromagnetic wave system, and good imaging performance is obtained for both. However, even if the imaging performance is deteriorated due to a manufacturing error or an environmental change, it can be easily corrected by slightly changing the first wavelength λ ₁ for illuminating the object, for example. It also has the effect of being able to. This is based on the characteristic that the effective permittivity changes greatly in the vicinity of 2πa / λ ₁ = 1.39, and is an effect that cannot be obtained with a normal dielectric lens in which the permittivity changes only slowly with respect to the wavelength. It is.

  Such an imaging system using a composite dielectric as an imaging lens functions particularly effectively in, for example, a fluorescence microscope, a laser scanning microscope, a scanning near-field optical microscope, and an optical recording system that use monochromatic light for imaging. . Alternatively, the electromagnetic wave element of the present invention can also be applied to an optical recording system that needs to read and write recording media of different standards such as CD, DVD and Blue-ray with a single system. Furthermore, when a new system such as holographic memory or two-photon recording is incorporated in the future, it can be applied as a technique for correcting aberrations of an optical system that reads and writes recording media in a wider wavelength band.

In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible. For example, in the above-described embodiment, the composite dielectric is configured by arranging the dielectric balls of the second dielectric in a square lattice pattern on the first dielectric, but the composite dielectric according to the present invention is used. The effect of the electromagnetic wave element using the same can be obtained regardless of the shape and arrangement of the first dielectric and the second dielectric. The reason is that, in a structure in which dielectric spheres smaller than the wavelength are dispersed, the effective dielectric constant is the dielectric constant of the dielectric constituting the dielectric sphere (ε ₁ and ε _{2 in the} above embodiment) and the volume occupation ratio f. This is because it depends on the size and arrangement of the dielectric sphere (see, for example, F. Capolino (ed.), "Metamaterials Handbook-Theory and Phenomena of Metamaterials," CRC Press, NW (2009), Chapter 9). ). Therefore, the second dielectric in the composite dielectric is not limited to a spherical shape, and does not need to be regularly arranged like a square lattice.

  In the above embodiment, the electromagnetic wave element is an imaging lens having a positive power. However, the electromagnetic wave element may have a negative power, or a plurality of electromagnetic wave elements may be used in combination. Also good. The bands of the first wavelength and the second wavelength are not limited to visible light and infrared light, and can be various combinations including terahertz waves, millimeter waves, microwaves, and the like. Further, the electromagnetic wave element according to the present invention can be applied to various uses such as data writing to and reading from an imaging system or a recording medium, electromagnetic wave detection, or processing using electromagnetic waves. is there.

DESCRIPTION OF SYMBOLS 1 1st dielectric material 2 2nd dielectric material 10 Imaging system 11 Imaging lens 12 Imaging device 13 Object 14 Imaging device 100 Imaging system 101 Imaging lens 102 Imaging device 103 Object 104 Image

Claims (6)

An electromagnetic wave element composed of a composite dielectric material in which a second dielectric material having a different dielectric constant from the first dielectric material is dispersed in a first dielectric material,
The electromagnetic wave element has an effective dielectric constant substantially equal to an electromagnetic wave having a predetermined first wavelength and an electromagnetic wave having a predetermined second wavelength longer than the first wavelength;
The electromagnetic wave element, wherein an average particle diameter and an average interval of the second dielectric are smaller than the first wavelength.   At least one of the first dielectric and the second dielectric has a resonance wavelength in which a dielectric constant changes greatly between the first wavelength and the second wavelength. The electromagnetic wave element according to claim 1.   The first wavelength and the second wavelength are determined in advance, and the effective dielectric constant of the composite dielectric with respect to the electromagnetic wave of the first wavelength is defined as the effective dielectric constant of the composite dielectric with respect to the electromagnetic wave of the second wavelength. The electromagnetic wave element according to claim 1 or 2, wherein the electromagnetic wave element is generated by determining an average particle size of the second dielectric so as to be substantially equal to the first dielectric material. The effective dielectric constant corresponding to the electromagnetic waves of the first wavelength and the second wavelength is

And b, θ and F (θ) are respectively

Where a is the average grain size of the second dielectric, and ε ₁ and ε ₂ are the dielectric constants of the first and second dielectrics, respectively. 4 is a volume occupancy ratio of the second dielectric material occupying the entire composite dielectric material, and λ is a wavelength of the electromagnetic wave. Electromagnetic wave element.   The electromagnetic wave element according to any one of claims 1 to 4, wherein the second wavelength is at least 10 times the first wavelength. The electromagnetic wave element according to any one of claims 1 to 5, which has a positive refractive power with respect to the electromagnetic wave having the first wavelength and the electromagnetic wave having the second wavelength.

Images