JP2012037680A - Light condensation optical element, light condensation device, and photovoltaic power generation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide new light condensation means that can efficiently use light energy.SOLUTION: A light condensation optical element 10 is composed of an (A) member 11 having optical transparency and a particulate (B) member 12 having optical transparency and dispersed in the (A) member 11. When a wavelength of incident light is denoted by λ, the particle size of the (B) member is 0.1 λ to 10 λ. When light refraction index along an X axis in an electric field amplitude is denoted by nand light refraction index along a Y axis in an electric field amplitude is denoted by nin the (A) member 11, and light refraction index along an X axis in an electric field amplitude is denoted by nand light refraction index along a Y axis in an electric field amplitude is denoted by the nin the (B) member 12, the light condensation optical element 10 is so configured that the nand the nare different and the nand the nare significantly the same.

Description

  The present invention relates to an apparatus for condensing light, and more particularly to a condensing optical element that condenses light incident in a thickness direction in a side surface direction, a condensing apparatus using the condensing optical element, and a photovoltaic device.

In recent years, reduction of CO ₂ emissions has been demanded worldwide and the use of natural energy has been promoted. In the use of solar energy, solar heat energy has been used for some time with solar water heaters, etc., and a photovoltaic power generation system that converts solar light energy into electrical energy has been introduced to ordinary households. Large-scale solar power plants are also being put into practical use in various countries.

  Solar cells that convert light energy into electrical energy are classified into silicon-based, compound-based, organic-based, dye-sensitized systems, and the like in terms of photoelectric conversion material classification. A typical solar battery cell made of such a material has a power conversion efficiency of about 10 to 20%. Therefore, the radiation spectrum range of sunlight is divided into a plurality of wavelength bands, and a plurality of semiconductor layers with band gaps that are optimal for photoelectric conversion of light in each wavelength band are stacked, and the conversion efficiency to power is about 40%. Multi-junction type (also called tandem type, stacked type, etc.) solar cells have been developed.

  However, the high-efficiency solar cells as described above are extremely expensive and difficult to use except for special applications such as aerospace. In view of this, a concentrating solar cell module has been devised that condenses and enters sunlight into a small cell to reduce costs and to perform solar power generation with high efficiency. As a condensing form, a lens condensing type that condenses sunlight with a Fresnel lens or a reflecting mirror and enters the solar cell (for example, see Patent Document 1 and Patent Document 2), and fluorescent light in which fluorescent particles are dispersed Fluorescent plate condensing type (for example, refer to Patent Document 3), in which sunlight is incident on the plate and the fluorescence generated in the plate is led out and collected to the side of the plate, the hologram film and the solar battery cell are sandwiched A spectral condensing type (for example, refer to Patent Document 4) in which sunlight is incident on a plate and light diffracted by a hologram film is guided to a solar battery cell has been proposed.

JP 2005-142373 A JP 2005-217224 A US Patent Application Publication No. 2006/0107993 US Pat. No. 6,274,860

  However, each condensing method has advantages and disadvantages. For example, the lens condensing type requires a thickness corresponding to the focal length of the lens in the optical axis direction and a tracking device for matching the optical axis with the azimuth of the sun. On the other hand, the fluorescent plate condensing type and the spectral condensing type can reduce the dimension of the module in the optical axis direction and do not necessarily require a tracking device, but there is room for improvement in terms of wavelength dependency and conversion efficiency.

  This invention is made | formed in view of the above situations, and it aims at providing the new condensing means which can utilize optical energy, such as sunlight efficiently.

In order to achieve the above object, a first aspect illustrating the present invention is a condensing optical element. The condensing optical element includes a light-transmitting A member, a thickness direction in the A member (y-axis direction in the embodiment), and a first direction orthogonal to the first direction (same as the x-axis direction), And a particulate B member having light permeability dispersed in a second direction (the same as the z-axis direction). The particle diameter d of the B member has a circle equivalent diameter of 0.1λ to 10λ, where λ is the wavelength of light incident in the thickness direction. Then, the A member and the refractive index of the light electric field amplitude in the first direction n _ax, the refractive index of the light electric field amplitude in the thickness direction and n _ay, in B member, the electric field amplitude first When the refractive index of light along the direction is n _bx and the refractive index of light along the thickness direction is n _by , n _ax and n _bx are different, and n _ay and n _by are substantially Are characterized by equality. In this specification, “particle diameter” is defined by the equivalent circle diameter (diameter) by microscopy in Japanese Industrial Standard JIS Z 8901 “Test Powder and Test Particles”, and the most frequent particle with the largest frequency distribution The diameter (mode diameter) is used as the particle diameter d.

In this case, the relationship between the refractive indices is n _ax <n _bx and n _bx > n _by , or n _ax <n _bx and n _ax <n _ay , or n _ax > It can be configured that n _bx and n _bx <n _by , or n _ax > n _bx and n _ax > n _ay .

Further, when the electric field amplitude at the A member of the refractive index of the light in the second direction and n _az, the refractive index of the light electric field amplitude in the second direction in the B member has a n _bz, and n _az You may comprise so that _nbz may become substantially equal.

In the A member and the B member, the size parameter α defined by (π × d × n _ax ) / λ is preferably 1.5 ≦ α ≦ 40, and more preferably 2 ≦ α ≦ 20. preferable. Further, the particle diameter d of the B member is desirably 20 μm or less.

  The density of the B member dispersed in the A member is incident on the surface of the condensing optical element in the thickness direction, and is scattered by the plurality of B members and travels toward the back surface of the condensing optical element. Can be set to be totally reflected on the back surface.

  The 2nd mode which illustrates the present invention is a condensing device. The condensing apparatus of the 1st structure form contained in this aspect is the condensing optical element in any one of Claims 1-11, and the reflection provided along the back surface in the back surface side of this condensing optical element A mirror, and a polarization plane rotating element that is provided between the condensing optical element and the reflecting mirror and rotates the polarization plane of the light that has been transmitted twice by 90 degrees.

  The condensing apparatus of the 2nd structure form contained in this aspect is the 1st condensing optical element in any one of Claims 1-11, and the 2nd in any one of Claims 1-11. A second condensing optical element on the back side of the first condensing optical element in the first direction of the second condensing optical element (second condensing optical element in the embodiment). The element is arranged so that the x-axis direction of the element is parallel to the second direction of the first light-collecting optical element (same as the z-axis direction of the first light-collecting optical element).

  The condensing apparatus of the 3rd structure form contained in this aspect is the 1st condensing optical element in any one of Claims 1-11, and the 2nd in any one of Claims 1-11. A second condensing optical element on the back side of the first condensing optical element in the first direction of the second condensing optical element (second condensing optical element in the embodiment). The first condensing element is disposed so that the x-axis direction of the element is parallel to the first direction of the first condensing optical element (same as the z-axis direction of the first condensing optical element). A polarization plane rotating element is provided between the optical element and the second condensing optical element to rotate the polarization plane of the transmitted light by 90 degrees.

  A third aspect illustrating the present invention is a photovoltaic device. A photovoltaic device according to a first configuration included in this aspect includes a condensing optical element according to any one of claims 1 to 11 and light guided in a first direction by the condensing optical element (for example, implementation) And a photoelectric conversion element (for example, a solar cell in the embodiment) that photoelectrically converts light guided to the + x side and the −x side in the x-axis direction in the embodiment.

  A photovoltaic device according to a second configuration included in this aspect includes a condensing optical element according to any one of claims 1 to 11 and light guided in a first direction by the condensing optical element (for example, implementation) Light guided to the + x side and −x side in the x-axis direction in the embodiment) (for example, solar cells in the embodiment) and light guided in the second direction by the condensing optical element (For example, light guided to + z side and −z side in the z-axis direction in the embodiment) and a photoelectric conversion element that performs photoelectric conversion.

The photovoltaic device of the 3rd composition form contained in this mode is the condensing device according to claim 12,
And a photoelectric conversion element that photoelectrically converts light guided in the first direction by the condensing optical element (for example, light guided to the + x side and the −x side in the x-axis direction in the embodiment).

  The photovoltaic device of the 4th, 5th structure form contained in this aspect WHEREIN: The light (For example, the light guide | induced to the 1st direction in the condensing apparatus of Claim 13 or 14 and a 1st condensing optical element) Photoelectric conversion element that photoelectrically converts light guided to + x side and −x side in the x-axis direction in the embodiment) and photoelectric conversion of light guided in the first direction in the second condensing optical element (same as above) And a second photoelectric conversion element.

In the condensing optical element of the first aspect of the present invention, the particulate B member is dispersed in the transparent A member, and the particle diameter of the B member is a circle when the wavelength of incident light is λ. The equivalent diameter d is 0.1λ to 10λ. In the A member and the B member, when the electric field amplitude is set to n _ax and n _bx respectively for the refractive index of the light along the first direction and n _ay and n _by for the refractive index of the light along the thickness direction, respectively. Unlike the light field amplitude along the first direction and n _bx and n _ax, the optical electric field amplitude in the thickness direction and the n _ay and n _By substantially equal constructed. Here, the A member and the B member, since the refractive index n _bx and n _ax of the light electric field amplitude in the first direction is different from the electric field amplitude entering the wavelength conversion optical element along a first direction The B member appears as particles to the light.

  The condensing optical element according to the first aspect of the present invention is based on the Mie scattering theory because the particle diameter of the B member dispersed in the A member is on the same order as the wavelength λ of the incident light. According to the above, in the light incident on the condensing optical element in the thickness direction, the light of the polarization component along the first direction is scattered in a predetermined angle range every time the B member is encountered, and the first direction is obtained by repeating this. The ratio of the light traveling to the + side and the light traveling to the − side along the line increases. For light traveling along the first direction (light whose electric field amplitude is along the second direction), there is no substantial difference in refractive index between the A member and the B member. The light passes through the A member and the B member so as to propagate in the medium, and is condensed on the + side or the − side in the first direction. Therefore, according to this invention, the new condensing means which can utilize optical energy, such as sunlight efficiently, can be provided.

  The condensing device according to the second aspect of the present invention is configured to condense the light of the polarization component transmitted through the condensing optical element again with the same / or the second condensing optical element. For this reason, the condensing apparatus which can utilize light energy, such as sunlight, with high efficiency with a thin and simple structure can be provided.

  The photovoltaic device according to the third aspect of the present invention includes the above-described condensing optical element or condensing device, and a photoelectric conversion element that photoelectrically converts the collected light. For this reason, the photovoltaic device which can utilize light energy, such as sunlight efficiently, with a thin and simple structure can be provided.

1 is an external perspective view of a photovoltaic device 1 illustrating an embodiment of the present invention. It is typical sectional drawing seen in the II-II arrow direction attached to FIG. 1, and is explanatory drawing which shows a mode that the advancing direction of light changes by scattering. It is explanatory drawing which shows the relationship of the refractive index ellipse in the condensing optical element 10 of a 1st structure form. In the figure, (a) shows the case where the B member 12 has birefringence, and (b) shows the case where the A member 11 has birefringence. It is explanatory drawing which shows the relationship of the refractive index ellipse in the condensing optical element 20 of a 2nd structure form. In the figure, (a) shows the case where the B member 22 has birefringence, and (b) shows the case where the A member 21 has birefringence. It is explanatory drawing which shows typically the relationship between the incident angle of light and scattering in the condensing optical element 10 of a 1st structure form. It is explanatory drawing which shows typically the relationship between the incident angle of light and scattering in the condensing optical element 20 of a 2nd structure form. It is a graph which illustrates light scattering distribution in case a particle diameter is 0.15 micrometer. It is a graph which illustrates light scattering distribution in case a particle diameter is 0.3 micrometer. It is a graph which shows the scattering distribution of FIG.7 and FIG.8 with a different display form. It is a graph group which shows the change of the scattering distribution of light when a size parameter is changed. It is a graph which shows the relationship between a size parameter and the ratio of backscattering with respect to forward scattering. It is a graph which shows the relationship between a size parameter and a scattering angle. It is a graph which shows the relationship between a size parameter when a volume is made constant, and a scattering coefficient. It is a graph which shows the relationship between the refractive index of particle | grains, and a scattering cross section in 1st Example. It is the table | surface which put together the relationship between the incident angle to particle | grains, and each parameter | index in 1st Example. It is the simulation data which calculated what kind of angle distribution the perpendicularly incident light in a 1st Example becomes in a scattering step. It is a graph which shows the relationship between the refractive index of particle | grains, and a scattering cross section in 2nd Example. It is the table | surface which put together the relationship between the incident angle to particle | grains, and each parameter | index in 2nd Example. It is the simulation data which calculated what kind of angle distribution the perpendicularly incident light in a 2nd Example becomes in a scattering step. It is the table | surface which put together the relationship between the incident angle to particle | grains, and each parameter | index in a comparative example. It is the simulation data which calculated what kind of angle distribution the perpendicularly incident light in a comparative example becomes in a scattering step. It is a schematic block diagram of the condensing device 60 of the 1st structural example. It is a schematic block diagram of the condensing apparatus 80 of the 3rd structural example. It is a conceptual diagram which illustrates the extraction method of the light energy from a condensing optical element.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view of a photovoltaic device 1 illustrating an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view as viewed in the direction of arrows II-II appended in FIG. For the sake of clarity, a coordinate system consisting of an x-axis, a y-axis, and a z-axis that are orthogonal to each other is defined and shown in FIG. The y axis is the thickness direction of the condensing optical element 10, the x axis and the z axis are two axes perpendicular to each other in the plane of the condensing optical element, and FIG. 2 is a plane that includes the x axis and the y axis and is perpendicular to the z axis. This corresponds to a schematic cross-sectional view cut along (xy plane). For convenience of explanation, the posture shown in FIG. 2 is sometimes referred to as up, down, left, and right, but the placement posture is arbitrary.

[Outline of photovoltaic power generation equipment]
In order to grasp the outline of the whole apparatus, first, the whole outline will be described with the photovoltaic power generation apparatus 1 using the condensing optical element 10 of the first configuration form as a main example. The photovoltaic device 1 includes a condensing optical element 10 (20) that condenses light incident in the thickness direction, and a photoelectric conversion element that photoelectrically converts the light collected by the condensing optical element and guided to the end. 50. The illustrated configuration form shows a configuration example in which the condensing optical element 10 (20) is formed in a plate shape. As the photoelectric conversion element 50, various known elements can be used. For example, the photoelectric conversion element 50 can be configured by using the various types of solar cells described above.

[Outline of condensing optical element]
The condensing optical element 10 (20) is mainly composed of an A member 11 (21) that transmits sunlight and a particulate B member 12 (22) having light permeability dispersed in the A member. Is done. The particle diameter of the B member is set such that the equivalent circle diameter d is about 0.1λ to 10λ, where λ is the wavelength of light incident on the condensing optical element. Here, when the wavelength λ of the light to be condensed in the condensing optical element has a width, the particle diameter d of the B member is 1/10 of the shortest wavelength λmin in the wavelength band and 10 of the longest wavelength λmax. Can be doubled. Specifically, when collecting sunlight, the radiation spectrum of sunlight is approximately 400 nm to 1800 nm, and the particle diameter d of the B member can be 40 nm to 1.8 μm.

  The B member is uniformly dispersed (as viewed macroscopically) as a whole in the x-axis direction, the y-axis direction, and the z-axis direction. However, in FIG. Only the B member 12 on the optical path of the light is shown. Note that the distribution density of the B member is appropriately set according to the material, shape, and use conditions of the A member and the B member. This will be described in detail later.

In the condensing optical element 10 (20), the refractive index characteristics of the A member and the B members 11, 12 (21, 22) are different, and at least one of the A member and the B member has birefringence. . In this specification, in the A member, the polarization direction is in the xy plane and the electric field amplitude is in the x-axis direction, the refractive index of the light is n _ax , the polarization direction is in the xy plane, and the electric field amplitude is in the y-axis direction. _Assume that the refractive index of light is _nay , and the refractive index of light whose polarization direction is in the yz plane and whose electric field amplitude is in the z-axis direction is _naz . Similarly, in the B member, the refractive index of light in which the polarization direction is in the xy plane and the electric field amplitude is in the x-axis direction is n _bx , and the refraction of light in the polarization direction is in the xy plane and the electric field amplitude is in the y-axis direction. rate the n _by, the polarization direction electric field amplitude of the refractive index in the z-axis direction of the light and n _bz in the y-z plane.

  Here, in FIG. 2, if the polarization state of light whose electric field amplitude is parallel to the paper surface is p-polarized light, and the polarization state of light whose electric field amplitude is perpendicular to the paper surface is s-polarized light, the electric field amplitude is in the xy plane. The light in the x-axis direction is p-polarized light traveling in the y-axis direction, and the light having the polarization direction in the xy plane and the electric field amplitude in the y-axis direction is p-polarized light traveling in the x-axis direction. Further, light whose polarization direction is in the yz plane and whose electric field amplitude is in the z-axis direction is s-polarized light traveling in the y-axis direction.

In this case, different from the n _ax and n _bx, n _ay and the n _By the A member and the B member is set to be substantially equal. Note that n _ay and n _by are substantially equal means a refractive index relationship in which p-polarized light traveling in the x-axis direction is not significantly scattered or refracted by the B member. The case where the difference in refractive index is 0.05 or less.

In such a condensing optical element 10 (20), for p-polarized light that enters the element from above and proceeds in the y-axis direction, n _ax and n _bx are different from each other. Therefore, the B member 12 (22) Are recognized as particles. At this time, how the p-polarized light traveling in the y-axis direction is affected by the presence of the B member is handled by handling the wavelength of the p-polarized light traveling in the y-axis direction in the medium (A member) (λ / N _ax ) and the particle diameter d of the particles (B member) dispersed in the medium.

  Specifically, when the particle diameter d of the B member is sufficiently smaller than the wavelength of light propagating in the A member, the Rayleigh scattering theory can be applied. On the other hand, when the particle diameter d of the B member is on the same order as the wavelength of light propagating through the A member, the theory of Mie scattering can be applied. When the particle diameter d of the B member is sufficiently larger than the wavelength of light propagating through the A member, the theory of geometric optics is applied.

  In the present embodiment, the particle diameter d of the B member 12 (22) is set to a circle-equivalent diameter of about 0.1λ to 10λ, and is on the same order as the wavelength of light propagating through the A member, which is a medium. It is. Therefore, the theory of Mie scattering can be basically applied to the relationship between the light propagating through the A member and the B member in the condensing optical element 10 (20).

  However, in the condensing optical element 10 (20), at least one of the A member and the B members 11, 12 (21, 22) has birefringence, and the orientation of the principal axis of the birefringence (the ray is abnormal). The presence / absence of scattering and the light scattering direction are deflected in accordance with the relationship between the direction of the fast axis or slow axis as light) and the polarization direction of the light traveling through the A member.

For simplification, either the A member or the B member has positive birefringence (birefringence in which the refractive index of extraordinary light is higher than the refractive index of ordinary light), and the main axis of birefringence is uniaxial. Think about the case. In this case, n _ax and n _bx are different (n _ax ≠ n _bx ), and n _ay and n _by are substantially equal (n _{ay ≈n by} ). The main axis of birefringence is in the x-axis direction. There are two cases, the case of orientation and the case of orientation in the y-axis direction.

FIG. 3 shows the relationship between the refractive index ellipse 30 of the A member and the refractive index ellipse 35 of the B member when the principal axis of birefringence is oriented in the x-axis direction. In FIG. 3, (a) shows the case where the B member has positive birefringence, and (b) shows the case where the A member has positive birefringence. What is shown with hatching in the figure is the refractive index circle of the A member and the B member in the yz plane. As can be seen from both figures, when the main axis of birefringence is oriented in the x-axis direction, not only n _ay and n _by but also n _az and n _bz are substantially equal, and n _ay = n _az ≈n _by = N _bz Thus, as a typical example of the case where the principal axis of uniaxial anisotropic birefringence is oriented in the x-axis direction, the case where the B member has birefringence as shown in FIG. The condensing optical element 10 will be described.

On the other hand, FIG. 4 shows the relationship between the refractive index ellipse 40 of the A member and the refractive index ellipse 45 of the B member when the main axis of birefringence is oriented in the y-axis direction. In FIG. 4, (a) shows the case where the B member has positive birefringence, and (b) shows the case where the A member has positive birefringence. What is shown with hatching in the figure is a refractive index circle in the xz plane of the A member or the B member. As can be seen from these figures, when the principal axis of birefringence oriented in the y-axis direction, the refractive index is substantially equal to is only n _ay and _{n by, n ax ≠ n bx} , n az ≠ n _bz . Thus, as a typical example of the case where the principal axis of uniaxial anisotropic birefringence is oriented in the y-axis direction, the case where the B member has birefringence as shown in FIG. The condensing optical element 20 will be described.

[Condensing optical element of first configuration]
In the condensing optical element 10 of the first configuration, the p-polarized light (abnormal light) that travels in the y-axis direction out of the light that enters the element from above the condensing optical element and travels through the A member. Since n _ax ≠ n _bx , the B member 12 is identified from the medium (A member 11) and exists as particles. On the other hand, since p-polarized light (ordinary light) traveling in the x-axis direction is n _ay ≈ n _by , the B member 12 is not distinguished from particles, and is the same as a state in which no particles exist (homogeneous medium).

  Therefore, p-polarized light (p-polarized component) that enters from the upper side of the condensing optical element 10 and travels in the y-axis direction causes Mie scattering by the B member 12 that exists as particles in the medium based on the refractive index difference. However, the p-polarized light traveling in the x-axis direction travels in the x-axis direction as it is without being scattered by the B member that is not identified as a particle.

  Since the present invention uses the refractive index difference based on the birefringence as described above, the scattering cross section changes according to the incident angle of the light incident on the B member 12, and the scattering efficiency changes. 5A to 5D are explanatory views schematically showing the relationship between the incident angle of light incident on the B member 12 and scattering. As shown in the figure, when the incident angle to the B member 12 with respect to the y-axis is 0 degree, the refractive index difference is the maximum, the scattering cross section is the maximum, and the scattering is large (a), and the incident angle is 90. When there is no difference in refractive index, the scattering cross section becomes infinitesimal and no scattering occurs (d).

  When the incident angle to the B member is between 0 and 90 degrees, the scattering efficiency becomes a scattering cross section corresponding to the refractive index difference between the A member 11 and the B member 12 at the incident angle (b) ( c). In FIG. 5 (and FIG. 2), the light diffused by scattering is represented by three vectors represented by light traveling straight along the incident optical axis and two lights spreading left and right away from the incident optical axis. This indicates that the scattering efficiency decreases as the incident angle increases and the rate of scattered light spreading to the left and right decreases, and that no scattering occurs when the incident angle is 90 degrees.

  In the condensing optical element 10 having such a configuration, as shown in FIG. 2, B-polarized light in which p-polarized light entering from above the element and traveling in the y-axis direction exists as particles in the A member (medium) 11. For example, 40% of incident light is scattered by the B member 12 near the surface. 40% of the light passing through the side of the B member 12 is scattered by the next B member 12 distributed in the thickness direction, and will eventually be scattered as the stage proceeds. Further, the light scattered by the B member 12 is scattered by the next B member distributed in the thickness direction, and multiple scattered.

  As a result, the ratio of the light vertically incident on the converging optical element 10 decreases in the y-axis direction (vertical direction) as it travels through the element, and the ratio of light inclined obliquely downward in the xy plane. Will increase. The light tilted in the + or − direction of the x-axis has a scattering efficiency that decreases as the incident angle to the B member 12 increases, and the change in the horizontal direction decreases. The ratio of light is increased. Light traveling horizontally along the x axis is not scattered by the B member 12 but travels toward the + or − side edge of the x axis.

At this time, if the inclination angle of the light reaching the lower surface of the condensing optical element in the state inclined in the x-axis direction exceeds the total reflection angle at the interface between the A member 11 and air, the condensing optical element 10 Incident light can be confined in the device. For example, when the refractive index of the A member 11 is n _ax = 1.64, light having an incident angle of 37.6 degrees or more incident on the interface between the A member and the air layer is totally reflected at the interface and condensed. It is confined in the optical element 10. The light totally reflected by the lower surface of the condensing optical element 10 is scattered again by the B member 12 in the process of traveling from the lower surface side to the upper surface side, and the traveling direction is deflected in the x-axis direction.

  For this reason, the light of the p-polarized component incident on the condensing optical element 10 from above is almost entirely directed to either the left or right in the x-axis direction, and the light thus collected has both ends in the x-axis direction. The light is condensed and incident on the photoelectric conversion elements 50 and 50 disposed in the unit.

  According to such a configuration, the light incident from the upper surface of the condensing optical element 10 is scattered in the x-axis direction by the difference in refractive index between the A member 11 and the B member 12, and is scattered in the z-axis direction without a difference in refractive index. The loss associated with can be suppressed. In this case, the light of the s-polarized component (ordinary light) incident from the upper surface of the condensing optical element and traveling in the y-axis direction is transmitted through the condensing optical element 10 as it is, but on the lower surface side of the condensing optical element. The transmitted light can be efficiently condensed by arranging the same condensing optical element 10 rotated 90 degrees around the y axis. A condensing device having such a condensing optical element arrangement will be described in detail later.

[Condensing optical element of second configuration]
The condensing optical element 20 of the second configuration form is a configuration in which a B member 22 having birefringence is oriented and distributed so that the main axis of birefringence is along the y-axis direction (see FIG. 4A). reference). In such a condensing optical element 20, the light that enters the element from above the condensing optical element 20 and travels through the A member is n _ax ≠ n with respect to p-polarized light (ordinary light) traveling in the y-axis direction. _{In addition to bx} , s-polarized light (ordinary light) traveling in the y-axis direction also satisfies n _az ≠ n _bz . For this reason, in the light traveling in the y-axis direction, the B member 22 is identified from the medium (A member 21) for both p-polarized light and s-polarized light, and exists as particles. On the other hand, since p-polarized light (abnormal light) traveling in the x-axis direction is n _ay ≈ n _by , the B member 22 is not distinguished from particles, and is the same as a state where particles are not present (homogeneous medium).

  Therefore, light that enters from the upper side of the condensing optical element 20 and travels in the y-axis direction causes Mie scattering by the B member 22 existing as particles in the medium based on the refractive index difference, but p travels in the x-axis direction. The polarized light travels in the x-axis direction without being scattered by the B member that is not identified as a particle.

  In order to utilize such a refractive index difference based on birefringence, the scattering cross section changes according to the polarization direction and the incident angle of the light incident on the B member 22, and the scattering efficiency changes. FIGS. 6A to 6D are explanatory views schematically showing the relationship between the incident angle of light incident on the B member 22 and scattering, and in the same manner as FIG. 5, three lights diffused by scattering are shown. This is represented by a vector. In FIG. 6, p-polarized light whose electric field amplitude is parallel to the paper surface is indicated by a double-ended arrow symbol, and s-polarized light whose electric field amplitude is perpendicular to the paper surface is indicated by a circular symbol having dots.

  Of the light that enters the condensing optical element 20 from above and travels in the y-axis direction, p-polarized light (p-polarized component) is when the incident angle to the B member 22 with respect to the y-axis is 0 degree. When the refractive index difference is the maximum and the scattering cross section is the maximum, the scattering is large (a), and when the incident angle is between 0 and 90 degrees, the scattering according to the refractive index difference between the A member and the B member at the incident angle. The scattering efficiency changes with the cross-sectional area (b) and (c), and when the incident angle is 90 degrees, there is no difference in refractive index, and the scattering cross-sectional area becomes infinitely small and is not scattered (d). On the other hand, s-polarized light (s-polarized component) out of light entering the condensing optical element 20 from above and traveling in the y-axis direction is refracted regardless of the incident angle to the B member 22 with respect to the y-axis. The rate difference is constant and the scattering efficiency does not change (a) to (d).

  In the condensing optical element 20 having such a configuration, both p-polarized light and s-polarized light that enter from above the element and travel in the y-axis direction are transmitted by the B member 12 that exists as particles in the medium (A member 21). Multiple scattering due to Mie scattering.

  For this reason, the light vertically incident on the condensing optical element 20 decreases in the proportion of light traveling in the y-axis direction (vertical direction) as it travels downward in the element, and the light inclined obliquely downward in the xy plane. The ratio and the ratio of light inclined obliquely downward in the yz plane increase. The ratio of the inclined light increases toward the lower surface, and the ratio of the light that is greatly inclined (becomes horizontal) increases. In particular, the p-polarized light (abnormal light) traveling along the x axis is not scattered by the B member 22 and travels toward the + or − side edge of the x axis. The light that is greatly inclined obliquely downward on the yz plane travels toward the + or − side edge of the z axis while being scattered by the B member 22.

  At this time, if the tilt angle of the light tilted in the x-axis direction or the z-axis direction exceeds the total reflection angle at the interface between the A member 11 and air, the light incident on the condensing optical element 20 is totally reflected on the lower surface. It is reflected and confined in the condensing optical element 20. The light totally reflected by the lower surface of the condensing optical element 20 is scattered again by the B member 22 in the process of traveling from the lower surface side to the upper surface side, and the traveling direction is deflected in the x-axis direction or the z-axis direction.

  For this reason, in the light incident on the condensing optical element 20 from above, almost the entire p-polarized component goes to the left or right in the x-axis direction, and most of the s-polarized component goes to either the front or back in the z-axis direction. The light condensed in this way is condensed on the photoelectric conversion elements 50 and 50 disposed at both ends in the x-axis direction and the photoelectric conversion elements 50 and 50 disposed at both ends in the x-axis direction. Incident.

  According to such a configuration, the light incident from the upper surface of the condensing optical element 20 is scattered in the x-axis direction and the z-axis direction due to the refractive index difference between the A member 21 and the B member 22, and at the side end portions in each direction. The light is condensed on the photoelectric conversion element 50 provided. In this case, a part of the light of the s-polarized component traveling inside the condensing optical element 20 can be emitted from the upper surface or the lower surface of the condensing optical element 20, but a simple configuration using one condensing optical element. Thus, a condensing device and a photovoltaic device capable of condensing in the x-axis direction and the z-axis direction can be configured.

[Size parameter]
Next, preferred configurations of the A members 11 and 21 and the B members 12 and 22 will be described in more detail based on Mie's scattering theory. The detailed explanation of Mie's scattering theory is omitted in this specification. OF OPTICS ”VolumeI Chapter 6 describes the scattering theory of Mie theory. In the condensing optical elements 10 and 20, the particle diameter d of the B member is set to 0.1λ to 10λ on the order of approximately the same as the wavelength λ of the incident light to cause scattering, and forward scattering is performed in a multiplexed manner. To the side. At this time, it is desired to suppress the backscattering (loss) to make the forward scattering dominant, and to efficiently collect light within a certain thickness. In Mie's scattering theory, the size parameter α is used as the index.

The size parameter α is generally defined by the following equation (1).
α = (π × d) / (λ / n) = (π × d × n) / λ (1)
Here, d is the particle diameter (diameter), and in this specification, the particle diameter of the B member is the equivalent circle diameter by the microscopic method in Japanese Industrial Standard JIS Z 8901 “Test Powder and Test Particles”. The frequency distribution is defined by the most frequent particle diameter (mode diameter). Further, (λ / n) is the wavelength of light traveling through the medium, and n is the refractive index of the medium (A member). In the condensing optical elements 10 and 20 illustrated, the A member 11 does not have birefringence, and the refractive index of the medium is constant at n = n _ax = n _ay = n _az .

FIGS. 7 and 8 are simulation data based on the theory of Mie scattering, in which light incident from the left is scattered by the particles arranged at the center of the circle (distribution of scattered light). It is shown normalized by the size in the 0 degree direction. The semicircle on the right side from the center of the circle is forward and the left side is backward. Common conditions for the particles, medium (medium), and incident light in both figures are as follows.
Particle refractive index n _bx : 1.88
-Refractive index n _{ax of} medium: 1.64
-Incident light wavelength λ: 633 nm

The condition that differs between FIG. 7 and FIG. 8 is the particle diameter d, FIG. 7 is the particle diameter d = 0.15 μm, and FIG. 8 is the particle diameter d = 0.3 μm. Substituting these values into equation (1) to obtain the size parameter α,
Size parameter α in the example of FIG. 7: 1.22
Size parameter α in the example of FIG. 8: 2.44
It becomes. FIG. 9 is a redraw of the scattering distribution of FIG. 7 and the scattering distribution of FIG. 8 with the horizontal axis as an angle of 180 degrees to the left and right where the incident direction is 0 degree, and the vertical axis as the distribution ratio.

  From FIG. 7 to FIG. 9, the distribution form of the scattered light is greatly different between the case where the size parameter α is 1.22 (FIG. 7) and the case of 2.44 (FIG. 8), and the size parameter α = 1.22. In some cases, the scattering angle is widely distributed in the forward and backward directions, and the forward scattering has a large dispersion. On the other hand, in the case of the size parameter α = 2.44, the back scattering is hardly observed and the dispersion of the forward scattering is small. I understand.

  FIGS. 10A to 10D show the distribution of scattered light without normalization when the size parameter α is changed under the above common conditions (that is, when the particle diameter d is changed). (A) α = 1.0, (b) α = 1.5, (c) α = 2.0, and (d) α = 2.5. FIG. 11 is a plot of the scattering rate in the backward 180 degree direction with respect to the scattering rate in the forward 0 degree direction when the size parameter α is changed under the above common conditions.

  10 and 11, when the size parameter α is 1.5 or more, the forward scattering is approximately 90% or more, and the forward scattering becomes dominant. When the size parameter α is 2 or more, the ratio of backscattering to forward scattering becomes almost zero.

  However, as the size parameter α increases, the proportion of forward scattering in the 0 degree direction increases, but the scattering angle becomes smaller (narrower). This is because the orientation accuracy of the birefringent body when the condensing optical elements 10 and 20 are manufactured and the dimension in the thickness direction so that the light reaching the lower surface side of the condensing optical element satisfies the total reflection condition. Affects. That is, the size parameter α is not as good as it is larger than a predetermined value, and needs to be within a certain range from a practical point of view.

  FIG. 12 is a graph showing the relationship between the size parameter α and the scattering angle under the common conditions. The production angle accuracy of the birefringent body (A member or B member) is generally about 1 to 2 degrees, and the scattering angle by the particles needs to exceed this. From FIG. 12, the upper limit of the size parameter α based on the current general manufacturing angle accuracy is around 50.

  Next, the relationship between the size parameter α and the scattering coefficient when the volume of the condensing optical element and the filling rate of the particles occupying the condensing optical element are constant (π / 6) under the above common conditions. As shown in FIG. In the figure, as the scattering coefficient is larger, the thickness of the condensing optical element can be reduced, and the birefringent material can be reduced. From this point, when the particle filling rate is constant, the scattering coefficient becomes maximum at around the size parameter α = 10. The scattering coefficient is preferably 1/5 (20%) or more of the maximum value. In this case, the upper limit of the size parameter α is about α = 40.

  From the viewpoint of manufacturing accuracy, it is preferable that the size parameter capable of securing 5 degrees, which is twice or more of general manufacturing accuracy, is α = 20 or less (FIG. 12). Further, from the viewpoint of the scattering coefficient when the total volume is constant, it is preferable that the scattering parameter has a size parameter α = 20 or less, which is ¼ or more of the peak value (FIG. 13).

  On the other hand, regarding the particle diameter, when the thickness of the condensing optical element is taken into consideration, it is desirable that the thickness be within about 10 mm. In this case, in order for light incident from the upper surface to be scattered 500 times before reaching the lower surface, the particle interval needs to be within 20 μm, and the maximum particle size at this time is 20 μm. When the volume filling factor of the particles is within 5%, the particle diameter is preferably within 10 μm. Note that the size parameter when the particle diameter is d = 10 μm under the common condition is α≈80, and the size parameter when the particle diameter is d = 10 μm and the wavelength λ of incident light is 1.3 μm is α≈. 40.

  In summary, in the condensing optical element composed of the A member and the B member, the size parameter is preferably 1.5 ≦ α ≦ 40, and more preferably 2 ≦ α ≦ 20. The particle diameter d of the B member is preferably 20 μm or less, and more preferably d ≦ 10 μm.

  Specific examples of the condensing optical element 10 having the first configuration and the condensing optical element 20 having the second configuration will be described below. An application example of the condensing optical element 10 is a first example, an application example of the condensing optical element 20 is a second example, and a configuration in which neither the A member nor the B member has birefringence is used as a comparative example. explain.

[First embodiment]
In the first example, the following was applied as the conditions of the A member 11 and the B member 12 in the condensing optical element 10 having the first configuration described above.
_-Refractive index of member A: n _ax = n _ay = n _az = 1.64
_-Refractive index of member B: n _bx = 1.88 (refractive index of extraordinary light)
n _by = n _bz = 1.64 (refractive index of ordinary light)
-Particle size of B member: d = 1.0 μm (particle size after stretching)
・ B member distribution density: 0.1 / μm ³
The size parameter when the wavelength λ of the incident light is 633 nm is α = 8.14.

The above conditions are as follows: A member 11 is a naphthalate 70 / terephthalate 30 copolyester (coPEN) monomer, B member 12 is polyethylene naphthalate (PEN) particles, and B member 12 is uniformly dispersed in A member 11. This corresponds to the case where the light collecting optical element 10 is formed by preparing the sheet and making the sheet uniaxially stretched in the x-axis direction. At this time, the A member 11 (coPEN) does not have birefringence, and the refractive index is constant for light traveling in any direction, so that n _ax = n _ay = n _az = 1.64. On the other hand, the B member 12 has a different refractive index in the stretching direction (x-axis direction) and the other direction, and the polarization plane is about 1.88 with respect to the light along the stretching direction, and about 1.64 in the other direction. Become. In addition, from the scattering theory, the B member may not be spherical, and in this example, the equivalent circle diameter of the B member (particle) after stretching was applied as the above condition.

  Here, since the B member 12 is a uniaxial anisotropic birefringent body in which the main axis of birefringence is oriented in the x-axis direction, the p-polarized light incident on the B member is incident on the xy plane. As a result, the refractive index of the B member 12 changes and the refractive index difference from the A member 11 changes. Therefore, the scattering cross section in Mie's scattering theory changes and the scattering efficiency changes. Specifically, the scattering cross section decreases as the incident angle with respect to the y-axis as a reference (0 degree) increases.

  In FIG. 14, the horizontal axis represents the refractive index of the B member (particle) 12, the vertical axis represents the scattering cross section, and how the scattering cross section changes due to the refractive index change accompanying the change in the incident angle to the B member. It is shown. In the figure, the plot of the black square at the upper left corner is 0 degree (normal incidence) on the B member 12, and the plot of the black square at the lower right corner is 90 degrees (horizontal incidence) on the B member 12. The calculated values for every incident angle of 10 degrees are plotted. From FIG. 14, in the region where the refractive index of the B member 12 is large (the refractive index difference from the A member is large), the scattering cross-section changes almost in proportion to the refractive index change of the B member. It can be seen that in the region where the refractive index is small (the difference in refractive index from the A member is small), the change in the scattering cross section with respect to the change in the refractive index of the B member is small.

FIG. 15 is a table summarizing how indices such as the scattering cross section and the scattering probability considering the distribution density of the B member change depending on the incident angle to the B member. The incident angle to the particles in the table is an incident angle of light to the B member in the xy plane with the y axis as a reference (0 degree) and the x axis direction as 90 degrees. Scattering efficiency is a value obtained by dividing the scattering cross section obtained by the scattering theory of Mie geometric area B member (πd ^2/4). The scattering coefficient is a value obtained by multiplying the scattering cross section by the density of the B member (the number of particles contained in the unit volume), and the scattering probability is a value obtained by multiplying the scattering cross sectional area by the square of the density of the B member. It is.

In the condensing optical element 10 configured as described above, p-polarized light that is perpendicularly incident from the upper surface of the element and travels in the y-axis direction is scattered by the B member 12 existing as particles in the medium (A member 11). receive. When the particle diameter of the B member 12 is 1 μm and the particle density is 0.1 particles / μm ³ , about 40% of the incident light is scattered at the first stage near the surface, and 60% goes straight without being scattered. 40% of the light that travels straight is scattered by the B member 12 at the next stage, which is distributed in the thickness direction, and will eventually be scattered as the stage proceeds. The scattered light is angled with respect to the y-axis and becomes light inclined obliquely downward.

  In the next stage, the light inclined obliquely downward is bent more obliquely (in the direction in which the incident angle increases), and the other part is bent in the direction to return to the original (the direction in which the incident angle decreases). The remaining light becomes the light traveling as it is without changing the incident angle (see FIG. 2). However, the probability of scattering of light inclined obliquely decreases as the incident angle increases (closer to the horizontal). This is because the refractive index difference between the medium (A member 11) and the particles (B member 12) is reduced, and the scattering cross section is rapidly reduced (see FIGS. 14 and 15). For this reason, the ratio of receiving light with a large incident angle decreases and the ratio of returning to the original vertical direction also decreases.

When the inclination angle (incident angle) of light traveling through the medium is close to 90 degrees, the refractive index n _{bx of the} particles becomes almost the same as the refractive index n _{ax of the} medium, and the scattering probability becomes small enough to be ignored. Therefore, as the number of steps proceeds, the light is confined in the plane direction toward the 90 ° direction, that is, the + side or the − side along the x axis.

  Even if the light reaches the lower surface of the condensing optical element without tilting to the 90 degree direction, the light in the medium is confined in the plane if the tilt angle exceeds the total reflection angle at the interface between the medium and air. It is done. In this embodiment, if the incident angle of light incident on the interface between the A member 11 and the air layer is 37.6 degrees or more, the light is totally reflected at the interface. The totally reflected light is again multiple scattered by the B member 12 in the process of traveling through the medium toward the upper surface, and finally converged in the 90-degree direction, that is, the + side or the − side along the x axis (see FIG. 22, see FIG.

  Therefore, if the A member 11 and the B member 12 are set so that light traveling toward the lower surface through the layer of the B member 12 dispersed on the lowermost surface side is totally reflected on the lower surface, the light enters the condensing optical element 10. All the light of the p-polarized component can be condensed toward the end in the + x direction. According to such a structure, the condensing optical element 10 can be comprised thinly.

Accordingly, FIG. 16 shows simulation data calculated using the index shown in FIG. 15 as to how the angle distribution of light perpendicularly incident on the converging optical element 10 changes due to scattering. In FIG. 16, the horizontal axis represents the light angle (incident angle to the particle) where the angle of light perpendicularly incident on the condensing optical element 10 in the xy plane is 0 degree and the x-axis direction is ± 90 degrees, and the vertical axis. Is the ratio (percentage,%) of light oriented in each angular direction. The parameters indicated by squares, circles, triangles, etc. in the figure are the number of stages of scattering by the particles (B member 12), and are plotted every 2 ⁿ times.

  From this simulation data, it can be clearly understood that the vertically incident light is inclined in the + direction and the − direction of the x-axis as the stage of scattering by the particles proceeds. Looking at this data in detail, it can be seen that the light in the 0 degree direction decreases and the width of the angular distribution increases until the number of stages of scattering by the particles is about 16. However, in this initial process, the light in the 0 degree direction is the most in proportion, and the distribution is a mountain shape with one peak. However, a flat distribution with few peaks is obtained at 32 levels, and a gentle concave distribution with a depressed center is obtained at 64 and 128 levels. After the 256th stage, two symmetrical peaks become clear, and at the 512th stage, light of -20 to 20 degrees is hardly seen. After 1024 steps, the change in the angle at which the peak value is obtained becomes small and has a strong peak in the vicinity of approximately ± 80 degrees, and the light in the angle range of −40 to 40 degrees is substantially zero.

  From this data, when scattering by particles progresses to about 1000 steps, the angle of light propagating in the element is mostly 40 degrees or more and -40 degrees or less, and the total reflection angle at the interface between the A member 11 and the air layer Over. Accordingly, by configuring the condensing optical element 10 so that light vertically incident on the A member 11 is scattered by 1000 or more steps by the B member 12, the incident light is confined in the condensing optical element 10, and the x-axis direction The light can be focused and incident on photoelectric conversion elements 50 and 50 provided at both ends.

[Second Embodiment]
In the second example, the following was applied as the conditions of the A member 21 and the B member 22 in the condensing optical element 20 of the second configuration form described above.
_-Refractive index of member A: n _ax = n _ay = n _az = 1.49
-Refractive index of member B: n _by = 1.49 (refractive index of extraordinary light)
n _bx = n _bz = 1.66 (ordinary refractive index)
-Particle size of B member: d = 1.0 μm
・ B member distribution density: 0.1 / μm ³
The size parameter when the wavelength λ of the incident light is 633 nm is α = 7.40. In this example, in the condensing optical element 20 of the second configuration form, the B member has a negative birefringence (birefringence in which the refractive index of extraordinary light is lower than the refractive index of ordinary light). Illustrate.

The above conditions are as follows: A member 21 is a thermosetting polymer adjusted to have a refractive index after curing of 1.49; B member 22 is a calcite particle having an equivalent circle diameter of 1 μm; This corresponds to the case where the condensing optical element 20 is formed by pouring a solution in which 22 is uniformly dispersed into a flat plate mold and applying heat and curing while applying a voltage of 3 kV / mm above and below the mold. At this time, the A member 21 (cured polymer) does not have birefringence, and the refractive index is constant for light traveling in any direction, so that n _ax = n _ay = n _az = 1.49. On the other hand, the B member 22 has an abnormal axis of dielectric constant aligned with the voltage application direction (y-axis direction) and has a refractive index different from that of the other directions, and the polarization plane is 1.49 with respect to light along the voltage application direction. About 1.66 in other directions.

  Since the B member 22 is a uniaxial anisotropic birefringent body in which the main axis of birefringence is oriented in the y-axis direction, the refractive index of the B member 22 changes depending on the incident angle of light incident on the B member. The difference in refractive index with the member 21 changes. Therefore, the scattering cross section in Mie's scattering theory changes and the scattering efficiency changes. Considering the xy plane, the scattering cross section decreases as the incident angle with the y-axis as a reference (0 degree) increases.

  In FIG. 17, the horizontal axis represents the refractive index of the B member (particle) 22, the vertical axis represents the scattering cross section, and the scattering cross section is determined by the change in the refractive index accompanying the change in the incident angle to the B member in the xy plane. It shows how it changes. In the figure, a black square plot at the upper left corner has an incident angle to the B member 22 of 0 degree (vertical incidence), and a black square plot at the lower right corner has an incident angle to the B member 22 of 90 degrees (horizontal incidence). The calculated values for every incident angle of 10 degrees are plotted. From FIG. 17, in the region where the refractive index of the B member 22 is large (the difference in refractive index from the A member is large), the scattering cross section changes almost in proportion to the refractive index change of the B member. It can be seen that in the region where the refractive index is small (the difference in refractive index from the A member is small), the change in the scattering cross section with respect to the change in the refractive index of the B member is small.

  FIG. 18 is a table summarizing how indicators such as the scattering cross section and the scattering probability considering the distribution density of the B member change depending on the incident angle to the B member. The incident angle to the particles in the table is an incident angle of light to the B member in which the y-axis is 0 degree and the x-axis direction is 90 degrees on the xy plane. Each index of scattering efficiency, scattering coefficient, and scattering probability is the same as in the first embodiment (FIG. 15).

In the condensing optical element 20, p-polarized light that is perpendicularly incident from the upper surface of the element and travels in the y-axis direction is subjected to Mie scattering by the B member 22 that exists as particles in the medium. When the particle size of the B member 22 is 1 μm and the particle density is 0.1 particles / μm ³ , the outline of the scattering process is the same as that in the first embodiment. 40% is scattered at the stage and is scattered as the stage progresses. The scattered light becomes light inclined with respect to the y-axis, and the inclination angle gradually increases.

Similarly to FIG. 16, simulation data calculated as to what angular distribution of light perpendicularly incident on the condensing optical element 20 changes due to scattering is shown in FIG. In FIG. 19, the horizontal axis represents the angle of light (incident angle to the particle) where the angle of light perpendicularly incident on the condensing optical element 20 in the xy plane is 0 degree and the x-axis direction is ± 90 degrees, and the vertical axis. Is the ratio (percentage,%) of light oriented in each angular direction. The parameters indicated by squares, circles, triangles, etc. in the figure are the number of stages of scattering by the particles (B member 22), and are plotted every 2 ⁿ times.

  From the simulation data, it can be seen that the vertically incident light is inclined in the + direction and the − direction of the x-axis as the stage of scattering by the particles proceeds, and this basic tendency is the same as in the first embodiment. is there. Looking at the data in detail, the light in the 0 degree direction decreases and the width of the angular distribution increases until the number of particle scattering stages reaches about 32 stages. In this initial process, the distribution is a peak-shaped distribution of one peak with the largest amount of light in the 0 degree direction. The flat distribution with almost no peaks is in 64 steps, and the distribution changes into a gentle concave distribution in which the center is recessed in 128 and 256 steps. After the 512 stage, two symmetrical peaks become clear, and -20 to 20 degree light is hardly seen in about 1024 stages. And the change of the angle which takes a peak value after 2048 steps becomes small, and has a strong peak in the vicinity of about ± 80 degrees, and light in an angle range of −40 to 40 degrees is substantially zero.

  From this data, when the scattering by the particles proceeds to about 2000 steps, the angle of light propagating in the element is mostly 40 degrees or more and −40 degrees or less, and the total reflection angle at the interface between the A member 21 and the air layer. Over. Accordingly, by configuring the condensing optical element 20 so that light vertically incident on the A member 21 is scattered by 2000 or more stages by the B member 22, the incident light is confined in the condensing optical element 20, and the x-axis direction The light can be focused and incident on photoelectric conversion elements 50 and 50 provided at both ends. Light that is not vertically but obliquely incident is confined with a smaller number of stages than the normal incident in this example.

[Comparative example]
As a comparative example, the same simulation was performed for the case where each of the A member and the B member did not have birefringence. The following was applied as conditions of A member and B member.
_-Refractive index of member A: n _ax = n _ay = n _az = 1.49
_-Refractive index of B member: n _bx = n _by = n _bz = 1.66
-Particle size of B member: d = 1.0 μm
・ B member distribution density: 0.1 / μm ³
The size parameter when the wavelength λ of the incident light is 633 nm is α = 7.40.

  FIG. 20 is a table summarizing how indices such as the scattering cross section and the scattering probability change depending on the incident angle to the B member, as in FIGS. 15 and 18. Further, FIG. 21 shows simulation data calculated as to how the angular distribution of light perpendicularly incident on the condensing optical element changes due to scattering, as in FIGS. 16 and 19.

  From the simulation data shown in FIG. 21, it can be seen that vertically incident light is scattered as the stage of scattering by particles proceeds. Further, by comparing with FIG. 16 and FIG. 19, it is understood that the scattering process is clearly different from the first and second embodiments.

  That is, in Example 1 and Example 2, vertically incident light was tilted in the + and − directions of the x axis due to scattering, and appeared as two distinct peaks through a predetermined stage. However, no such tendency is observed in this comparative example.

  Looking at the data in detail, the tendency of the initial stage where the light in the 0-degree direction decreases due to particle scattering and the width of the angular distribution widens is similar to that in the first and second embodiments. However, in the comparative example, in addition to the fact that this tendency does not change and spreads even if the number of scattering stages increases, the proportion of light that travels in the 90 to 180 degree direction beyond 90 degrees, that is, the ratio of the light that returns to the incident direction. Increasing with increasing scattering stage. This is nothing but a situation where light incident on the element is scattered by particles in the medium and simply diffused. When light reaches the surface opposite to the incident side, all light rays smaller than the total reflection angle escape to the outside. If this is repeated, no light will be trapped inside.

  Therefore, even if the refractive index of the A member and the B member, the particle diameter of the B member, the distribution density of the B member, and the like are the same as those in the example, and the size parameter of Mie scattering is the same, It is easy to understand that it is difficult to condense and enter the photoelectric conversion element provided at the end of the element efficiently.

  In the above description, the case where the A member does not have birefringence and the B member has positive or negative birefringence has been described, but the opposite may be possible (FIGS. 3B and 4B). )), Both the A member and the B member may have birefringence. In addition, for simplicity of explanation, the case where the wavelength λ is constant has been illustrated, but when the wavelength λ has a width, the particle diameter d of the B member should be appropriately set according to the wavelength band of the collected light. Can do. Specifically, the conversion efficiency of the photoelectric conversion element 50 in the photovoltaic device described below is set in a range of 400 to 1800 nm according to the emission spectrum of sunlight, or in a range of 400 to 800 nm where the intensity of the emission spectrum is high. It can be a high range. In this case, the particle diameter d of the B member can be set in accordance with the center, the center of gravity, etc. of the wavelength band, and the particle diameters d1, d2, and d3 are divided into a plurality of wavelength bands and matched to the respective divided bands. It is also possible to set (as a mixture of a plurality of B members having different particle diameters).

[Configuration example 1 of condensing device and photovoltaic device]
Next, a condensing apparatus using the condensing optical element as described above will be described as a representative example using the condensing optical element 10. As described above, the condensing optical element 10 has different refractive indexes of the A member 11 and the B member 12 with respect to the p-polarized light with respect to the light traveling in the y-axis direction, and substantially with respect to the light traveling in the x-axis direction. By setting to be equal, the light of the p-polarized component incident in the thickness direction is guided in the x-axis direction and condensed.

  In the condensing optical element 10, the light of the s-polarized component out of the light incident from above the element is not condensed in the x-axis direction and is emitted from the lower surface side of the condensing optical element 10. Therefore, the condensing devices 60, 70, and 80 according to the aspect of the present invention are configured to collect all the light incident from above the condensing optical element, including the light of the s-polarized component. Hereinafter, a typical configuration example of the light collecting device will be described with reference to the drawings. In each figure, p-polarized light whose electric field amplitude is parallel to the paper surface is indicated by a double-ended arrow symbol, and s-polarized light whose electric field amplitude is perpendicular to the paper surface is indicated by a circular symbol having dots.

  A schematic configuration of the condensing device 60 of the first configuration example is shown in FIG. The condensing device 60 shown in the figure includes the condensing optical element 10, a reflecting mirror 62 provided on the lower surface side of the condensing optical element 10 along the lower surface, and between the condensing optical element 10 and the reflecting mirror 62. The polarization plane rotation element 65 is provided. Note that the condensing optical element 20 of the second configuration example may be used as the condensing optical element.

  The polarization plane rotation element 65 is an optical element that rotates the polarization plane of light transmitted twice, by 90 degrees. As a polarization plane rotation element having such a function, for example, for light in the wavelength band of sunlight, s-polarized light is converted to circularly polarized light by the first transmission, and circularly polarized light is converted to p-polarized light by the second transmission. A broadband quarter-wave plate is preferably used.

  In the condensing device 60 having such a configuration, among the light incident in the thickness direction from the upper surface side of the condensing optical element 10, the p-polarized component light is a large number of B members uniformly dispersed in the A member 11. 12, the traveling direction (light vector) is oriented to the + x side or the -x side in the x-axis direction and is collected at both ends. On the other hand, of the light incident in the thickness direction from the upper surface side of the condensing optical element 10, the light of the s-polarized component is emitted from the lower surface side of the condensing optical element 10 without being scattered by the B member 12.

  The light of the s-polarized component emitted from the lower surface side of the condensing optical element 10 is transmitted through the polarization plane rotating element 65, reflected by the reflecting mirror 62, and again transmitted through the polarization plane rotating element 65, and the condensing optical element 10 Is incident on the condensing optical element 10 again from the lower surface side.

  At this time, the light re-entering the condensing optical element 10 is transmitted through the polarization plane rotating element 65 twice, so that the polarization plane is rotated by 90 degrees to become p-polarized component light. Therefore, the light of the p-polarized component that re-enters from the lower surface side of the condensing optical element 10 and proceeds in the thickness direction is totally reflected on the lower surface of the condensing optical element 10 (interface between the A member 11 and the air layer). Similar to the light of the p-polarized component, the light is scattered by the B member 12 in the process of traveling from the lower surface side toward the upper surface side, and is collected on the side end portion on the + x side or the −x side in the x-axis direction.

  Therefore, according to the condensing device 60 having such a configuration, a single condensing optical element 10 can condense all the light incident from above onto both ends in the x-axis direction. Further, by providing the photoelectric conversion element 50 that photoelectrically converts the light condensed at the end of the condensing optical element 10, the condensing optical element 10 and the photoelectric conversion element 50 have a simple and low-cost configuration. The photovoltaic device 2 that photoelectrically converts all the light incident on the condensing optical element 10 can be configured.

[Configuration example 2 of condensing device and photovoltaic device]
Next, the condensing device of the second configuration example will be briefly described. The condensing device of this configuration example (not shown, but for convenience of explanation, referred to as the condensing device 70) is configured using the two condensing optical elements described above. Here, the case where two (10 ₁ and 10 ₂ ) condensing optical elements 10 are used will be described as an example.

Condenser 70, ₁ and the first condensing optical element 10 consists of a second focusing optical element 10 ₂ which provided on the lower surface side, a second x-axis direction of the condensing optical element 10 ₂ Are arranged so as to be parallel to the z-axis direction of the _first condensing optical element 101. In short, the second condensing optical element 10 ₂ located on the first lower focusing optics 10 _1, the light collector 70 by arranging rotated 90 degrees around the y-axis configuration Is done.

Therefore, the s-polarized light in the coordinate system of the _first condensing optical element 101 becomes p-polarized light in the coordinate system of the _second condensing optical element 102. As a result, the light incident on the _first condensing optical element 10 ₁ from above the condensing device 70 is scattered by the p-polarized component light in the _first condensing optical element 10 ₁ . The light condensed at both ends of the element 10 _{1 in} the x-axis direction and transmitted through the condensing optical element 10 ₁ becomes light of the p-polarized component in the _second condensing optical element 10 ₂ , and the second condensing element It is focused on both ends of the x-axis direction of the light optical elements 10 _2.

Therefore, according to the condensing device 70 having such a configuration, all the light incident from above can be obtained with a simple configuration in which the two condensing optical elements are arranged so as to be rotated at a relative angle of 90 degrees around the y axis. Can be condensed. Further, by providing the photoelectric conversion element 50 that photoelectrically converts the condensed light at each end portion, a photovoltaic device 3 (not shown) that photoelectrically converts all light incident from above with a simple configuration is configured. be able to. Furthermore, a photoelectric conversion element provided in the first collection optics 10 _1, since the photoelectric conversion element provided in a second condensing optical element 10 ₂ do not overlap vertically, the construction and the arrangement of the photoelectric conversion element A degree of freedom can be secured.

  The first condensing optical element and the second condensing optical element use two condensing optical elements of the same type (for example, two condensing optical elements 10 or two condensing optical elements 20). Alternatively, different types of condensing optical elements may be used in combination. When combining different types of condensing optical elements, any of them may be arranged above.

[Configuration Example 3 of Condensing Device and Photovoltaic Power Generation Device]
Next, the condensing device 80 of the third configuration example will be described with reference to FIG. The condensing device 80 of this configuration example includes the two condensing optical elements and the polarization plane rotating element 85 described above. FIG. 23 illustrates a case where two condensing optical elements 10 (10 ₁ , 10 ₂ ) are used.

The condensing device 80 is provided between the first condensing optical element 10 ₁ , the second condensing optical element 10 ₂ provided on the lower surface side thereof, and these condensing optical elements 10 ₁ and 10 _2. consist obtained polarizing plane rotating element 85., a first x-axis direction of the condensing optical element 10 ₁ and the second focusing optical element 10 ₂ of the x-axis direction are disposed in parallel.

  The polarization plane rotation element 85 is an optical element that rotates the polarization plane of transmitted light by 90 degrees. As a polarization plane rotating element having such a function, for example, a broadband half-wave plate that converts s-polarized light into p-polarized light with a single transmission is preferably used.

In the condensing device 80 having such a configuration, of the light incident in the thickness direction from the upper surface side of the _first condensing optical element 10 ₁ , the p-polarized component light is the first condensing optical element 10 _1. Scattered by a large number of B members 12 uniformly dispersed in the A member 11, the traveling direction (light vector) is oriented to the + x side or −x side in the x-axis direction, and is condensed at both ends. On the other hand, s-polarized light component transmitted through the first focusing optical element 10 ₁ is incident on the polarization plane rotating element 85 is emitted from the lower surface side of the first focusing optical element 10.

The light of the s-polarized component incident on the polarization plane rotating element 85 is rotated by 90 degrees in the process of passing through the polarization plane rotating element 85, and is emitted from the polarization plane rotating element 85 as p-polarized component light. . Therefore, the second focusing optical element 10 _2, the plane of polarization is rotated is incident light becomes p-polarized light component is uniformly dispersed in the A member 11 of the second focusing optical element 10 ₂ Further, the light is scattered by a large number of B members 12 and collected at both ends in the x-axis direction.

Therefore, according to the condensing device 80 having such a configuration, it is possible to condense all the light incident from above with a simple configuration in which the two condensing optical elements are arranged in an overlapping manner. In addition, by providing a photoelectric conversion element 50 that photoelectrically converts the light collected at each end of the condensing optical elements 10 ₁ and 10 ₂ , light that photoelectrically converts all light incident from above with a simple configuration. The power generation device 4 can be configured.

In this case, the + x-side end portions and the −x-side end portions of the first condensing optical element 10 ₁ and the second condensing optical element 10 ₂ are arranged vertically. Therefore, a light guide that connects the respective + x side ends to each photoelectric conversion element 50 and a light guide that connects each −x side end to each photoelectric conversion element 50 are provided. You can also. According to such a configuration, the number of relatively expensive photoelectric conversion elements can be reduced. In addition, the 1st condensing optical element and the 2nd condensing optical element may use the two condensing optical elements 20, and may use it combining the condensing optical element 10 and the condensing optical element 20. FIG. good.

[Method of extracting light energy at the end of the condensing optical element]
Next, in the condensing optical elements 10 and 20 described above, some typical concepts are illustrated with respect to an energy extraction method of the light condensed at the + x side and −x side ends in the x-axis direction. A brief description will be given with reference to FIGS.

  (a) is the conceptual diagram of the structural example which takes out the light condensed on the edge part as it is, and uses it as light. In this case, the light emitted from the end of the condensing optical element is condensed in the z-axis direction via the cylindrical lens 91, the condensing rod 92, etc., and the condensed light is guided to a desired position by the optical fiber 93. Such a configuration is exemplified.

  (b) is a conceptual diagram of the 1st structural example in the case of using the light condensed on the edge part, converting into electric energy or thermal energy. This figure shows a configuration example in which the photoelectric conversion element 50 is coupled to the condensing side ends of the condensing optical elements 10 and 20 and taken out as electric energy. In addition, when taking out the condensed light as a thermal energy, the heat pipe with the light absorber etc. which carry out photothermal conversion are used suitably.

  (c) is a conceptual diagram of the 2nd structural example in the case of converting and using the light condensed on the edge part as an electrical energy or a thermal energy. In this configuration example, the end portions of the condensing optical elements 10 and 20 are cut obliquely to dispose the mirror 94 (or a reflection film is formed on the inclined surface), and the upper surface side of the condensing optical elements 10 and 20 ( Or it is the structural example condensed on the photoelectric conversion element 50 provided in the lower surface side. Thereby, even if the condensing optical elements 10 and 20 are thin sheet-like, the photoelectric conversion element 50 of a predetermined area can be attached stably. In addition, when taking out the condensed light as heat energy, the heat pipe with a light absorber like the above is used suitably.

  (d) is a conceptual diagram of a third configuration example in the case where light collected at the end is used after being converted into electric energy or heat energy. In this configuration example, the end portions of the condensing optical elements 10 and 20 are cut obliquely to dispose the dichroic mirror 95 (or a reflective film having wavelength selectivity is formed on the inclined surface). , 20 is divided into photoelectric conversion elements 50 and 50 ′ provided on the upper surface side (or lower surface side) of the light collecting optical elements 10 and 20 and on the side of the condensing optical elements 10 and 20. According to such a configuration, since a highly efficient photoelectric conversion element can be used for each divided wavelength band, a photovoltaic device with high conversion efficiency can be configured at a relatively low cost.

  One of the divided lights (for example, light in the infrared region) is incident on a heat pipe with a light absorber and used as thermal energy, and the other (for example, light in the visible region and ultraviolet region) is used as a photoelectric conversion element. A configuration in which the light is incident on 50 and used as electric energy is also a preferable application example.

  (e) is a conceptual diagram of a configuration example in which the light condensed at the end is further condensed and extracted in the thickness direction. The condensing optical elements 10 and 20 of this configuration are configured so that the thickness gradually decreases in a region near the end on the condensing side, and light traveling in the x-axis direction inside the element is reflected on the upper surface or the lower surface. It is totally reflected and condensed in the thickness direction. Thereby, for example, when using light as it is, it can be configured without using a cylindrical lens or the like, and when entering the photoelectric conversion element 50 or the heat pipe, the power density of incident light is increased with a simple configuration. Can do.

  In the embodiment, for the sake of simplification of explanation, the condensing optical element is illustrated as a plate-like form, and in order to explain the operation of the condensing optical element, specific materials are applied to the A member and the B member. Although the structural example which applied the refractive index was demonstrated, this invention is not limited to these structural forms and structural examples. For example, the condensing optical element may have a thin sheet shape or a rod shape such as a prism or a cylinder, and the material of the A member and the B member may be appropriately selected from various resin materials and inorganic materials. can do. Further, other members than the A member and the B member may be included without departing from the gist of the present invention.

  As described above, in the condensing optical elements 10 and 20, the particulate B member whose particle diameter is approximately the same as the wavelength of the light to be condensed is dispersed in the A member serving as the base material or the base material. The relationship between the refractive indexes of the two is different for p-polarized light traveling in the y-axis direction, which is the thickness direction, and is configured to be substantially equal in the x-axis direction. The condensing devices 60, 70, 80 and the photovoltaic power generation devices 1 to 4 are configured using such condensing optical elements.

  Therefore, according to the concentrating optical elements 10 and 20 and the concentrating devices 60, 70, and 80 described above, a new condensing that can efficiently use light energy such as sunlight with a thin and simple configuration. Means can be provided. In addition, the photovoltaic power generators 1 to 4 to which the condensing optical elements 10 and 20 and the condensing devices 60, 70, and 80 are applied are thin, small, and lightweight in the optical axis direction of the condensing unit. It can be suitably applied as a new solar power generation means that does not necessarily require a tracking device.

1-4 Photovoltaic power generation device 10 (10 ₁ , 10 ₂ ) Condensing optical element 11 in the first configuration form A member 12 B member 20 Condensing optical element 21 in the second configuration form A member 22 B members 50, 50 ′ Photoelectric Conversion element 60 Condensing device 62 of the first configuration example Reflecting mirror 65 Polarization plane rotation element 80 Condensing device 85 of the third configuration example Polarization plane rotation element

Claims (18)

A member having light permeability, and a particulate B member having light transmittance dispersed in the thickness direction and the first direction and the second direction orthogonal to each other in the A member. Configured,
The particle diameter d of the B member has an equivalent circle diameter of 0.1λ to 10λ, where λ is the wavelength of light incident in the thickness direction,
In the A member, the refractive index of light along which the electric field amplitude is along the first direction is _nax , and the refractive index of light along which the electric field amplitude is along the thickness direction is _nay ,
In the B member, when the electric field amplitude is n _{bx as} the refractive index of light along the first direction and the electric field amplitude is as n _by the refractive index of light along the thickness direction,
n _ax and n is different from the _bx, converging optical element n _ay and the n _By is equal to or substantially equal. 2. The condensing optical element according to claim 1, wherein the refractive index relationship is n _ax <n _bx and n _bx > n _by . 2. The condensing optical element according to claim 1, wherein the relationship between the refractive indexes is n _ax <n _bx and n _ax <n _ay . 2. The condensing optical element according to claim 1, wherein the refractive index relationship is n _ax > n _bx and n _bx <n _by . The condensing optical element according to claim 1, wherein the relationship between the refractive indexes is n _ax > n _bx and n _ax > n _ay . In the A member, the refractive index of light whose electric field amplitude is along the second direction is _naz ,
When the electric field amplitude in the B member is _{nbz as} the refractive index of light along the second direction,
_{6. The} condensing optical element according to claim 1, wherein n _az and n _bz are substantially equal. The A member and the B member have a size parameter α defined by (π × d × n _ax ) / λ _satisfying 1.5 ≦ α ≦ 40. The condensing optical element according to item. The A member and the B member have a size parameter α defined by (π × d × n _ax ) / λ _satisfying 2 ≦ α ≦ 20, according to claim 1. The condensing optical element as described.   The condensing optical element according to claim 1, wherein a particle diameter d of the B member is 20 μm or less.   The density of the B member dispersed in the A member is incident in the thickness direction from the surface of the condensing optical element, and multiple scattered by the plurality of B members toward the back surface of the condensing optical element. The condensing optical element according to claim 1, wherein light is set so as to be totally reflected on the back surface.   The size in the first direction and the second direction is sufficiently larger than the size in the thickness direction, and is formed in a plate shape or a sheet shape. The condensing optical element according to item. The condensing optical element according to any one of claims 1 to 11,
A reflecting mirror provided on the back side of the condensing optical element along the back side;
A condensing device comprising: a polarization plane rotating element that is provided between the condensing optical element and the reflecting mirror and rotates a polarization plane of light that has been transmitted twice by 90 degrees. The first condensing optical element according to any one of claims 1 to 11,
A second condensing optical element according to any one of claims 1 to 11,
The second condensing optical element has a back surface side of the first condensing optical element, and the first direction of the second condensing optical element is the second direction of the first condensing optical element. It is arrange | positioned so that it may become parallel with. The first condensing optical element according to any one of claims 1 to 11,
A second condensing optical element according to any one of claims 1 to 11,
The second condensing optical element has a back surface side of the first condensing optical element, and the first direction of the second condensing optical element is the first direction of the first condensing optical element. And a polarization plane rotation element that rotates the plane of polarization of the transmitted light by 90 degrees between the first light collection optical element and the second light collection optical element. A condensing device provided. The condensing optical element according to any one of claims 1 to 11,
A photovoltaic device comprising: a photoelectric conversion element that photoelectrically converts light guided in the first direction by the condensing optical element. The condensing optical element according to any one of claims 1 to 11,
A photoelectric conversion element that photoelectrically converts light guided in the first direction by the condensing optical element;
A photovoltaic device comprising: a photoelectric conversion element that photoelectrically converts light guided in the second direction by the condensing optical element. The light collecting device according to claim 12,
A photovoltaic device comprising: a photoelectric conversion element that photoelectrically converts light guided in the first direction by the condensing optical element. The light collecting device according to claim 13 or 14,
A photoelectric conversion element that photoelectrically converts light guided in the first direction in the first condensing optical element;
A photovoltaic device comprising: a photoelectric conversion element that photoelectrically converts light guided in the first direction in the second condensing optical element.

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