JP5679286B2 - Condensing optical element, condensing device, and photovoltaic device - Google Patents

Description

  The present invention relates to an apparatus for concentrating light. More specifically, the present invention relates to an apparatus for collecting light emitted from an exit surface having a large aspect ratio by receiving the incident light on an entrance surface facing the exit surface. The present invention relates to a condensing optical element that condenses light in the direction in which the light extends, a condensing device 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 plate-type condensing method such as the fluorescent plate condensing type and the spectroscopic condensing type can reduce the dimension in the optical axis direction of the module and does not necessarily require a tracking device. The light-exiting surface led to has a large aspect ratio of long side / short side, and there is room for improvement in terms of light collection efficiency and matching with solar cells.

  The present invention has been made in view of the above circumstances, and provides a new condensing means that can efficiently use light energy such as sunlight emitted from an emission surface having a large aspect ratio. With the goal.

In order to achieve the above object, a first aspect illustrating the present invention is a condensing optical element. This condensing optical element is provided with wide emission light that is emitted from an emission surface having a large aspect ratio of long side / short side (for example, the emission surface 8a of the light collection panel 8 in the embodiment) facing the emission surface. Is a condensing optical element that condenses light in the direction in which the long side extends (for example, the x-axis direction in the embodiment), the A member having light transmittance, the incident direction of incident light in the A member, and the mutual And a particulate B member having light permeability dispersed in a first direction and a second direction orthogonal to each other. The particle diameter d of the B member has an equivalent circle diameter of 0.1λ to 10λ when the wavelength of incident light is λ. Now, the axis extending in the incident direction includes the y axis, the axis extending in the first direction is the x axis, the axis extending in the second direction is the z axis, the plane including the x axis and the y axis includes the xy plane , the y axis, and the z axis. Let the surface be a zy plane . Then, in the A member, the refractive index of the light whose electric field amplitude proceeds in the y-axis direction in the xy plane is “ naxy”, the refractive index of the light whose electric field amplitude proceeds in the y-axis direction in the zy plane is nazy, and the electric field amplitude is in the xy plane. Where the refractive index of light traveling in the x-axis direction is nayx, the refractive index of light traveling in the y-axis direction in the xy plane is nbxy, and the electric field amplitude is light traveling in the y-axis direction in the zy plane. Nbyx, and the refractive index of the light whose electric field amplitude proceeds in the x-axis direction in the xy plane is nbyx , the difference between nyaxy and nbxy and nazy and nbzy is that nyx and nbyx are substantially equal. It is configured as a feature. 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 addition, when the refractive index of light that the electric field amplitude in the A member advances in the z-axis direction in the zy plane is nayz, and the refractive index of the light that the electric field amplitude in the B member advances in the z-axis direction in the zy plane is nbyz , Nayz and nbyz can be configured to be substantially equal.

  In this case, the relationship between the refractive indexes is as follows: n xy <nbxy and nbxy> nbyx, or nax <nbxy and nax <nyx, or nax> nbxy and nbxy <nbyx, or nax> nbxy and nax> nayx. It can be comprised so that it may become.

  In the A member and the B member, the size parameter α defined by (π × d × naxy) / λ is preferably 1.5 ≦ α ≦ 40, and 2 ≦ α ≦ 20. it can. Moreover, the particle diameter d of B member can also be 20 micrometers or less.

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

The 2nd mode which illustrates the present invention is a condensing device. Condenser of the first example of the configuration included in this embodiment, a focusing optical element according to any one of claims 1 to 12 for emitting light disposed between the exit surface and the incident surface A polarization plane rotation element (for example, the polarization plane rotation element 65 in the embodiment) that rotates the polarization plane by 90 degrees is configured.

Condenser of the second example of the configuration included in the present embodiment, a focusing optical element according to any one of claims 1 to 12 provided along the rear surface on the back side of the converging optical element reflecting A mirror, and a polarization plane rotating element (for example, the polarization plane rotating element 75 in the embodiment) 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. Composed.

Condenser of the third example of the configuration included in the present embodiment, the first focusing optical element according to any one of claims 1 to 12, a second of any of claims 1 to 12 A second condensing optical element, and the second condensing optical element has an x-axis direction of the first condensing optical element on the back side of the first condensing optical element. A polarization plane rotating element (which is arranged so as to be parallel to the axial direction) and rotates the plane of polarization of transmitted light by 90 degrees between the first and second focusing optical elements. For example, a polarization plane rotation element 85) according to the embodiment is provided.

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 12 and light guided in the x-axis direction by the condensing optical element (for example, implementation) And a photoelectric conversion element that photoelectrically converts light guided to at least one of the + x side and the −x side in the embodiment.

The photovoltaic device of the second configuration form included in this aspect includes the light collecting device according to claim 13 or 14 and light guided in the x-axis direction by the light collecting optical element (for example, the + x side in the embodiment) And a photoelectric conversion element that photoelectrically converts light guided to at least one of the −x side).

The photovoltaic device of the third configuration form included in this aspect includes the light collecting device according to claim 15 and light guided in the x-axis direction in the first light collecting optical element (for example, + x in the embodiment) Photoelectric conversion element that photoelectrically converts light guided to at least one of the x-side and the -x side) and second light that photoelectrically converts light guided in the x-axis direction in the second condensing optical element (same as above). The photoelectric conversion element is configured.

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. The A member and the B member have a refractive index of light that travels in the y-axis direction in the xy plane, and the refractive index of light that travels in the y-axis direction in the zy plane, respectively, nazy and nbzy. And the refractive index of light traveling in the x-axis direction within the xy plane is defined as nayx and nbyx, respectively, the light beams traveling in the y-axis direction are different from each other in the n-axis and nbxy , and the nazy and nbzy. Nayx and nbyx are configured to be substantially equal for the light traveling to. At this time , in the light traveling in the y- axis direction, the B member appears as particles because the refractive index “naxy” of the A member is different from the refractive index nbxy of the B member , and nazy and nbzy .

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 this , the light traveling in the y- axis direction is scattered within a predetermined angle range every time the B member is encountered, and the ratio of the light traveling inclined toward the + x side and the light traveling inclined toward the -x side by repeating this Will increase. In the light whose electric field amplitude travels in the x-axis direction in the xy plane, there is no substantial difference in the refractive index between the refractive index nayx of the A member and the refractive index nbyx of the B member. The light passes through the A member and the B member so as to propagate in the homogeneous medium, and is condensed on the + x side or the −x side in the x-axis direction. Therefore, according to the present invention, it is possible to increase the light collection efficiency by condensing the light emitted from the emission surface having a wide width in the x-axis direction in the x-axis direction, and efficiently radiate light energy such as sunlight. New condensing means that can be used 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 optical energy, such as sunlight efficiently, by simple and compact 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. Therefore, it is possible to provide a photovoltaic device capable of allowing light with high power density to be incident on a small photoelectric conversion element and capable of converting light energy such as sunlight with high efficiency with a small and low-cost configuration. it can.

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 showing the refractive index characteristic in xy plane of A member and B member, and the relationship between both about the case where B member has birefringence. It is explanatory drawing which shows the relationship of the refractive index ellipse in the condensing optical element 10 of a 1st structure form, (a) is B member has positive birefringence in the x-axis direction, (b) is B member This is a case of having negative birefringence in the x-axis direction. It is explanatory drawing which shows the relationship of the refractive index ellipse in the condensing optical element 20 of a 2nd structure form, (a) is B member has negative birefringence in a y-axis direction, (b) is B member This is a case where it has positive birefringence in the y-axis direction. 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 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 apparatus of the 1st structural example. It is a schematic block diagram of the condensing apparatus 60 of the 2nd structural example. It is a schematic block diagram of the condensing apparatus 70 of the 3rd structural example. It is a schematic block diagram of the condensing apparatus 80 of the 4th 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 incident direction of the light incident on the condensing optical element 10 from the condensing panel 8, the x-axis and the z-axis are two axes orthogonal to the incident surface 10a of the condensing optical element 10, and FIG. This corresponds to a schematic cross-sectional view taken along a plane that includes the axis and the y-axis and is perpendicular to the z-axis (xy plane). For convenience of explanation, the posture shown in FIG. 1 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 is provided along a plate-like condensing panel 8 that condenses light incident in the thickness direction (z-axis direction) from the upper surface and emits the light from the emission surface 8a at the side end, and the emission surface 8a. A condensing optical element 10 (20) for condensing the wide outgoing light emitted from the emission surface 8a having a large aspect ratio of the long side / short side in the x-axis direction (or y-axis direction) extending the long side; And a photoelectric conversion element 50 that photoelectrically converts the light condensed by the optical optical element and guided to the end. The illustrated configuration form shows a configuration example in which the condensing optical element 10 (20) is formed in a rod shape or a strip 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 panel]
The condensing panel 8 confines light incident in the thickness direction (z-axis direction) from the upper surface within the plate, condenses it in the y-axis direction (and / or x-axis direction), and exits from the exit surface 8a at the side end. For example, the same scattering theory as that of the above-described fluorescent plate condensing type or spectral condensing type condensing optical element or the condensing optical element 10 (20) described in detail later is applied. Or a waveguide type condensing optical element that condenses a plurality of converged lights primarily condensed by the lens array by guiding them to the exit surface of the side end.

[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 schematically 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 the present specification, in the A member, the refractive index of light that travels in the y-axis direction in the xy plane in the A member is expressed as “naxy”, and the refractive index of light that travels in the x-axis direction in the xy plane. Let nazy be the refractive index of light traveling in the y-axis direction in the zy plane. Similarly, in member B, the refractive index of light traveling in the y-axis direction in the xy plane in the B member is nbxy, the refractive index of light traveling in the x-axis direction in the xy plane is nbyx, and the electric field amplitude is in the zy plane. The refractive index of light traveling in the y-axis direction is nbzy.

  Here, the electric field amplitude is light in the xy plane (light whose electric field amplitude is parallel to the paper surface in FIG. 2), the polarization state is p-polarized light, and the electric field amplitude is in the zy plane (the electric field amplitude is perpendicular to the paper surface in FIG. 2). If the polarization state of the light is s-polarized light, the light whose electric field amplitude travels in the y-axis direction in the xy plane is p-polarized light which travels in the y-axis direction, and the light whose electric field amplitude travels in the x-axis direction in the xy plane is x P-polarized light traveling in the axial direction. In addition, the light whose electric field amplitude travels in the y-axis direction in the zy plane is s-polarized light that travels in the y-axis direction.

  At this time, the A member and the B member are set so that “naxy” and “nbxy” are different and “nayx” and “nbyx” are substantially equal to each other. Note that “nayx” and “nbyx” are substantially equal to each other, a p-polarized light traveling in the x-axis direction means a refractive index relationship that is not significantly scattered or refracted by the B member. A case where the difference is 0.05 or less.

  In such a condensing optical element 10 (20), in the p-polarized light that enters the element from above and proceeds in the y-axis direction, the N member and the nbxy member are different from each other. Recognized as 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 / Naxy) 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 birefringence characteristics and the orientation of the main axis (light rays The state of occurrence of scattering changes depending on the relationship between the direction of the fast axis or the slow axis that becomes abnormal light), the polarization direction of light traveling in the element, and the polarization component.

  For the sake of simplicity, let us consider a case where one of the A member and the B member has birefringence, and the main axis (optical axis) of birefringence is uniaxial. In this case, FIG. 3 shows a straightforward example of a configuration in which “naxy” is different from “nbxy” (naxy ≠ nbxy), and “nayx” is substantially equal to “nbyx” (nayx≈nbyx).

  FIGS. 3A and 3B show the refractive index characteristics of the A member and the B member in the xy plane and the relationship between them when the B member has birefringence. As shown in the figure, the refractive index characteristic 30 of the A member has a refractive index circle having a constant refractive index regardless of the direction (naxy = nayx = nazy), and the refractive index characteristic 40 (41 to 44) of the B member has a refractive index depending on the direction. Are different ellipses of refractive index. The refractive index relationships shown in FIGS. 3A and 3B are both “naxy ≠ nbxy”, so that nyx = nbyx on the y-axis where the refractive index circle 30 of the A member and the refractive index ellipse 40 of the B member intersect. ing.

  Therefore, p-polarized light traveling in the y-axis direction through the condensing optical element is recognized as a particle by the B member as follows: On the other hand, in the p-polarized light traveling in the x-axis direction in the element, since Nayx = nbyx, the B member is not recognized as a particle.

  The above has been described with respect to the refractive index on the xy plane for the sake of simplicity. The conceptual diagram which expressed this three-dimensionally is shown in FIG. 4, FIG. FIG. 4A shows a case where the B member has positive birefringence (birefringence in which the refractive index of extraordinary light is higher than the refractive index of ordinary light) 41 in the x-axis direction. This is an example in which the B member has negative birefringence (birefringence in which the refractive index of extraordinary light is lower than the refractive index of ordinary light) 42 in the x-axis direction. 5A shows an example in which the B member has negative birefringence 43 in the y-axis direction, and FIG. 5B shows an example in which the B member has positive birefringence 44 in the y-axis direction. is there.

  What is shown with hatching in FIG. 4 is a refractive index circle in the zy plane of the A member and the B member. As can be seen from both figures, when the main axis of birefringence is oriented in the x-axis direction, not only nayx and nbyx, but also nazy and nbzy are substantially equal, so that nayx = nazy≈nbyx = nbzy. This is the same even if the refractive index relationship between the A member and the B member is reversed (even when the A member has birefringence). A case where the principal axis of birefringence having uniaxial anisotropy is oriented in the x-axis direction will be described as the condensing optical element 10 of the first configuration form.

  Also, in FIG. 5, hatching indicates the refractive index circles in the xz plane of the A member and B member, respectively. As can be seen from both figures, when the main axis of birefringence is oriented in the y-axis direction, the refractive indices are substantially equal only to nayx and nbyx, and thus, n ≠ nbxy, nazy ≠ nbzy. The same applies if the relationship between the refractive indexes of the A member and the B member is reversed. The case where the principal axis of biaxial refraction having uniaxial anisotropy is oriented in the y-axis direction will be described as the condensing optical element 20 of the second configuration form.

[Condensing optical element of first configuration]
In the condensing optical element 10 of the first configuration, the p-polarized light traveling in the y-axis direction out of the light that is emitted from the condensing panel 8, enters the condensing optical element 10, and travels through the A member, Since ≠ nbxy, the B member 12 is identified from the medium (A member 11) and exists as particles. On the other hand, for p-polarized light traveling in the x-axis direction, since nyx≈nbyx, the B member 12 is not identified as a particle, and is the same as a state where there is no particle (homogeneous medium).

  Therefore, the 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 is scattered by the B member 12 that exists as particles in the medium based on the refractive index difference. 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. 6A to 6D 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 θ 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 a large scattering occurs (a), and the incident angle is When θ = 90 degrees, there is no difference in refractive index, and the scattering cross section becomes infinitesimal and no scattering occurs (d).

  When the incident angle [theta] to the B member is between 0 and 90 degrees, the scattering efficiency varies with the 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. 6 (and FIG. 2), the light diffused by scattering is represented by three vectors represented by light that travels straight along the incident optical axis and two light that spreads left and right away from the incident optical axis. This shows that the scattering efficiency decreases as the incident angle θ increases, and the rate of scattered light spreading left and right decreases, and that scattering does not occur when the incident angle θ is 90 degrees.

  In the condensing optical element 10 having such a configuration, as shown in FIG. 2, p-polarized light that enters from the incident surface 10 a of the condensing optical element and travels in the y-axis direction enters 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 light incident on the condensing optical element 10 along the y-axis decreases in the ratio of light traveling parallel to the y-axis as it travels through the element, and increases in the ratio of light inclined obliquely on the xy plane. To do. The light inclined in the + direction or the − direction of the x-axis has a lower scattering efficiency and a smaller change in the inclination angle as the incident angle to the B member 12 increases, but the light inclined greatly in the x-axis direction (FIG. 2). And the ratio of the light that is nearly horizontal in FIG. 6 increases. The light traveling 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 back surface 10b of the condensing optical element in the state inclined in the x-axis direction is equal to or larger than the total reflection angle at the interface between the A member 11 and air, the condensing optical element 10 can be confined in the device. For example, when the refractive index of the A member 11 is 1.64, light having an incident angle of 37.6 degrees or more incident on the interface between the A member 11 and the air layer is totally reflected at the interface, and the condensing optical element 10 to be trapped. The light totally reflected by the back surface 10b of the condensing optical element is scattered again by the B member 12 in the process of traveling from the back surface side to the incident surface side, and the traveling direction is deflected in the x-axis direction.

  When a protective film having a refractive index different from that of the A member 11 is formed on the back surface 10b of the condensing optical element, light is refracted according to the refractive index of the film at the interface between the A member 11 and the film. . However, since Snell's law is established at the interface between the A member 11 and the film and the interface between the film and the air, the inclination angle of the light reaching the back surface is greater than the total reflection angle at the interface between the A member and the air. Then, the total reflection condition is satisfied at least at the interface between the film and air, and is confined in the condensing optical element 10.

  Further, in the configuration having the protective film or the like, when the inclination angle of the light reaching the back surface is greater than or equal to the total reflection angle at the interface between the A member and the film, total reflection is performed at the interface between the A member and the film. The light that reaches the back surface when the condition is satisfied is totally reflected into the A member without entering the film. Therefore, even when the total reflection condition cannot be maintained at the interface between the film and air because the outer surface of the film is not smooth, the light of the p-polarized component incident on the condensing optical element 10 is confined in the condensing optical element 10. And deflected in the x-axis direction.

  For this reason, the light of the p-polarized component emitted from the light collecting panel 8 and entering the light collecting optical element 10 is almost entirely directed toward either the positive or negative end face in the x-axis direction, and is thus collected. The collected light is condensed and incident on the photoelectric conversion element 50 disposed at the end in the x-axis direction. In this case, the light of the s-polarized component that is incident on the condensing optical element and travels in the y-axis direction is transmitted through the condensing optical element 10 as it is. Light can be collected efficiently.

  According to such a configuration, the light emitted from the exit surface that is wide in the x-axis direction and has a large aspect ratio (for example, the exit surface having an aspect ratio of about 50 to 500) exiting from the collector panel 8 10 is condensed in the x-axis direction and the aspect ratio is reduced (for example, the aspect ratio on the exit surface of the condensing optical element 10 is reduced to about 1 to 10), and the light collection efficiency can be greatly improved. In addition, according to the condensing optical element having such a configuration, since no scattering occurs in the z-axis direction without a difference in refractive index, scattering loss in this direction can be suppressed.

[Condensing optical element of second configuration]
The condensing optical element 20 of the second configuration form has a configuration in which the principal axis of uniaxial anisotropic birefringence is oriented and distributed along the y-axis direction (see FIG. 5). In such a condensing optical element 20, the p-polarized light out of the light that enters the condensing optical element 20 and travels through the A member is the same as the condensing optical element 10 of the first configuration described above. is there.

  That is, of the light that enters the condensing optical element 20 and travels through the A member 21, the p-polarized light traveling in the y-axis direction satisfies the relationship of n ≠ nbxy, so that the B member 22 is identified from the medium as particles. Exists. Further, in the p-polarized light traveling in the A-axis direction in the x-axis direction, since nayx≈nbyx, the B-member 22 is not recognized as a particle, which is the same as a state where no particle exists.

  In the condensing optical element 20, the s-polarized light that enters the condensing optical element 20 and travels in the A member in the y-axis direction has the same action as described above. In the condensing optical element 20, the principal axis of uniaxially anisotropic birefringence is oriented along the y-axis direction, and the refractive index relationship between the A member 21 and the B member 22 is axisymmetric about the y axis. It has become. Therefore, the same action as described above occurs on the zy plane orthogonal to the xy plane.

  That is, of the light that enters the condensing optical element 20 and travels through the A member, the light whose field amplitude travels in the y-axis direction in the zy plane (p-polarized light that travels in the y-axis direction on the zy plane) Since it is not nbzy, the B member 22 is identified from the medium (A member 21) and exists as particles. Further, among the light traveling through the A member, the light whose amplitude of the electric field travels in the z-axis direction in the zy plane (p-polarized light traveling in the z-axis direction in the zy plane) is nayz≈nbyz. 22 is not recognized as a particle, which is the same as a state in which no particle exists.

  Therefore, the light traveling in the y-axis direction in the A member 21 is scattered by the B member 22 existing as particles in the medium based on the difference in refractive index between the A member and the B member for both p-polarized light and s-polarized light. Further, the light traveling in the A member in the x-axis direction or the z-axis direction travels in the x-axis direction or the z-axis direction as it is without being scattered by the B member 22 that is not identified as a particle. The scattering cross section of the B member 22 changes according to the incident angle of light, and is the same as the situation described with reference to FIGS. 6A to 6D except that the change is axisymmetric. .

  Specifically, when the incident angle θ to the B member 22 with respect to the y-axis is 0 degree, the refractive index difference is maximum and the scattering cross-section is maximum, resulting in large scattering (see FIG. 6A). When the incident angle is θ = 90 degrees, there is no difference in refractive index, the scattering cross section becomes infinitely small, and no scattering occurs (see FIG. 6D). When the incident angle θ to the B member is between 0 and 90 degrees, the scattering cross section 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, and the scattering efficiency changes (FIG. 6). (See (b) and (c)).

  For this reason, in the condensing optical element 20, the light incident from the incident surface and traveling in the y-axis direction is scattered by the B member 22 existing as particles in the A member 21, and is distributed in the thickness direction. Multiple scattering is caused by the B member 22. Among these, the p-polarized light (p-polarized component) in FIG. 2 decreases in the proportion of light traveling parallel to the y-axis as it travels through the device, and the proportion of light tilted to the + x side or −x side on the xy plane. Will increase. In addition, in FIG. 2, s-polarized light (s-polarized component) light decreases in the proportion of light traveling parallel to the y-axis as it travels through the element, and the proportion of light tilted to the + z side or the −z side on the zy plane. To increase.

  The ratio of the inclined light increases as the distance toward the back surface increases. The p-polarized light traveling along the x-axis is not scattered by the B member 22 and travels toward the + -side or −-side end surface of the x-axis. The s-polarized light traveling along the z-axis is not scattered by the B member 22 but travels toward the + -side or −-side end surface of the z-axis.

  At this time, if the inclination angle of the light inclined in the x-axis direction or the z-axis direction exceeds the total reflection angle at the interface between the A member 11 and the air, the light incident on the condensing optical element 20 is on the back surface (s In the case of polarized light, the light is totally reflected by the upper surface or the lower surface) and confined in the condensing optical element 20. The light totally reflected on the back surface of the condensing optical element 20 is scattered again by the B member 22 in the process of traveling from the back surface side to the incident surface side, and the traveling direction is deflected in the x-axis direction or the z-axis direction. The case where a protective film having a refractive index different from that of the A member 21 is formed on the lower surface of the condensing optical element is the same as that of the condensing optical element 10 of the first configuration form.

  For this reason, the light incident on the condensing optical element 20 from the condensing panel 8 has almost all of the p-polarized light component directed to one of the front and rear end faces in the x-axis direction. The light is focused and incident on the photoelectric conversion element 50 disposed at the end in the x-axis direction. On the other hand, the light of the s-polarized component that enters the condensing optical element and travels in the y-axis direction is almost entirely directed to either the upper or lower end surface in the z-axis direction. These can be efficiently condensed by guiding them in the x-axis direction in the same manner as the p-polarized light component.

  According to such a configuration, light exiting from the exit surface that is wide in the x-axis direction and has a large aspect ratio exiting from the light collecting panel 8 is condensed in the x-axis direction by the condensing optical element 20 and the aspect ratio is reduced. Thus, the light collection efficiency can be greatly improved.

[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. Detailed explanation of Mie's scattering theory itself is omitted, but for example, “HANDBOOK OF OPTICS” Volume I Chapter 6 supervised by the American Optical Society OSA (OPTICAL SOCIETY OF AMERICA) released in 1995 (McGRAW-HILL, INC) It describes the scattering theory of Mie theory. In the condensing optical elements 10 and 20, scattering is caused by setting the particle diameter d of the B member to 0.1λ to 10λ which is approximately the same order as the wavelength λ of incident light, 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 illustrated condensing optical elements 10 and 20, the A member 11 does not have birefringence, and the refractive index of the medium is constant such that n = naxy = nayx = nazy.

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 the front and the left side is the rear, and the dotted line indicates the azimuth angle every 30 degrees. Common conditions for the particles, medium (medium), and incident light in both figures are as follows.
-Particle refractive index nbxy: 1.88
-Refractive index of the medium, sodium: 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 thickness direction for satisfying the total reflection condition for the light reaching the back surface side of the condensing optical element ( (y-axis direction) affects the dimensions. 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 that the light incident from the incident surface is scattered 500 times before reaching the back surface side, 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 A member: n ay = nayx = nazy = 1.64
-Refractive index of B member: nbxy = 1.88
nbyx = nbzy = 1.64
-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. In this example, in the condensing optical element 20 of the first configuration, the B member has positive birefringence (birefringence in which the refractive index of extraordinary light is higher than the refractive index of ordinary light) in the x-axis direction. Corresponds to the case.

  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 the value of about n xy = nayx = nazy = 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 depends on the incident angle in the xy plane. The refractive index of the member 12 changes, and the refractive index difference with 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 θ increases with the y-axis as a reference (0 degree).

  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 has an incident angle to the B member 12 of θ = 0 degrees (perpendicular incidence to the incident surface), and the plot of the black square at the lower right corner has an incident angle to the B member 12 of θ = 90 degrees (horizontal incidence), and the calculated values for every 10 degrees of incidence angle 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 the incident angle θ of light on the B member with the y axis as the reference (0 degree) and the x axis direction as 90 degrees on the xy plane. 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, the p-polarized light that is incident from the incident surface 10a and proceeds in the thickness direction is subjected to Mie scattering by the B member 12 that exists 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 progresses. The scattered light is angled with respect to the y-axis and becomes light inclined obliquely.

  In the next stage, the light that is tilted obliquely is bent more obliquely (in the direction in which the incident angle θ increases), and the other part is bent in the return direction (in the direction in which the incident angle θ 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 in FIG. 2). 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 tilt angle (incidence angle θ) of light traveling in the medium is close to 90 degrees, the refractive index nbyx of the particles becomes almost the same as the refractive index nayx of the medium, and the scattering probability becomes so small that it can 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 back surface 10b of the condensing optical element without tilting to the 90 degree direction, the light in the medium is in-plane if the tilt angle is equal to or greater than the total reflection angle at the interface between the medium and air. Trapped in. 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 incident surface 10a, and finally collected in the 90-degree direction, that is, the + side or the − side along the x axis ( See FIGS. 22-25.

  Therefore, if the A member 11 and the B member 12 are set so that the light traveling toward the back surface through the layer of the B member 12 dispersed most on the back surface side is totally reflected on the back surface 10b, the condensing optical element 10 All incident p-polarized light components 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 what angle distribution the light incident on the condensing optical element 10 changes due to scattering. In FIG. 16, the horizontal axis represents the angle of light (incident angle to the particle) with the angle of light perpendicularly incident on the incident surface 10 a of the condensing optical element on the xy plane being 0 degrees and the x-axis direction being ± 90 degrees, and the vertical axis. The axis is the percentage of light oriented in each angular direction (percentage,%). 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 seen how the light perpendicularly incident on the incident surface 10a is inclined in the + and − directions 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 the photoelectric conversion element 50 provided at the end of the light source.

[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 the A member: n ay = nayx = nazy = 1.49
-Refractive index of B member: nbxy = 1.49
nbyx = nbzy = 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. In this embodiment, in the condensing optical element 20 of the second configuration form, the B member has negative birefringence (birefringence in which the refractive index of extraordinary light is lower than the refractive index of ordinary light) in the y-axis direction. Corresponds to the case.

  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, and is approximately equal to: n a y = n a y x = na z = 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 θ increases with the y-axis as a reference (0 degree).

  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 how the scattering cross section is represented by the change in the refractive index accompanying the change in the incident angle to the B member in the xy plane. It shows what will change. In the figure, the black square plot at the upper left corner indicates that the incident angle to the B member 22 is θ = 0 degrees (perpendicularly incident on the incident surface), and the black square plot at the lower right corner indicates the incident angle to the B member 22 is θ. = 90 degrees (horizontal incidence), and the calculated values for every 10 degrees of incidence angle 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 the incident angle θ of light on the B member with the y-axis being 0 degree and the x-axis direction being 90 degrees on the xy plane. Each index of scattering efficiency, scattering coefficient, and scattering probability is the same as that of FIG. 15 of the first embodiment.

In the condensing optical element 20, p-polarized light incident from the incident surface and traveling in the y-axis direction is subjected to Mie scattering by the B member 22 existing 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 angle distribution the light incident on the condensing optical element 20 changes due to scattering is shown in FIG. In FIG. 19, the horizontal axis represents the light angle (incident angle to the particle), the vertical angle of the light incident perpendicularly to the incident surface of the condensing optical element 20 on the xy plane, and the x-axis direction ± 90 degrees. The axis is the percentage of light oriented in each angular direction (percentage,%). 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 light perpendicularly incident on the incident surface is inclined in the + direction and the − direction of the x-axis as the stage of scattering by the particles proceeds. This basic tendency is the first example. It is the same. 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 the photoelectric conversion element 50 provided at the end of the light source. 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 the A member: n ay = nayx = nazy = 1.49
-Refractive index of B member: nbxy = nbyx = nbzy = 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 average 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 the Mie scattering is the same, the incident in the comparative example It is easily understood that light cannot be confined in the element and it is difficult to efficiently collect and enter the photoelectric conversion element provided at the end of the element.

  In the above description, the case where the A member has no birefringence and the B member has a positive or negative birefringence has been described. However, the opposite may be possible, and both the A member and the B member are birefringent. May have the property. 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 or the center of gravity of the wavelength band, and the particle diameters d1, d2, and d3 are divided into a plurality of wavelength bands and matched to the divided bands. It is also possible to set (as a mixture of a plurality of B members having different particle diameters).

  Next, a condensing device using the condensing optical element as described above will be described with reference to FIGS. 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.

[Configuration example 1 of condensing device and photovoltaic device]
As described above, the condensing optical element 10 of the first configuration form is different in the refractive index of the A member 11 and the B member 12 with respect to p-polarized light traveling in the y-axis direction, and is s-polarized light traveling in the y-axis direction. And light traveling in the x-axis direction are configured to be substantially equal.

  Therefore, when the light emitted from the exit surface 8a of the condensing panel is p-polarized linearly polarized light, the light incident on the condensing optical element 10 is scattered by the B member as shown in FIG. The traveling direction (light vector) is oriented to the + x side or the -x side and is collected at the end in the x-axis direction. Therefore, a condensing device that condenses all the incident light emitted from the exit surface 8a of the condensing panel in the x-axis direction can be configured by the condensing optical element 10 alone. And the photovoltaic device 1 shown in FIG. 1 can be comprised by a very simple and low-cost structure by providing the photoelectric conversion element 50 in the edge part of a x-axis direction.

[Configuration example 2 of condensing device and photovoltaic device]
Further, when the light emitted from the exit surface 8a of the condensing panel is s-polarized linearly polarized light (for example, when the condensing panel 8 is configured by the A member and the B member similar to the condensing optical elements 10 and 20) ) Is applicable to the light collecting device 60 shown in FIG.

  The condensing device 60 includes the condensing optical element 10, and a polarization plane rotating element 65 disposed between the exit surface 8a of the condensing panel and the incident surface 10a of the condensing optical element. The polarization plane rotating element 65 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 60 having such a configuration, the s-polarized light emitted from the exit surface 8 a of the condensing panel is converted to p-polarized light by passing through the polarization plane rotating element 65 and is incident on the condensing optical element 10. . Therefore, all the light incident on the condensing optical element 10 is scattered by the B member, the traveling direction is oriented to the + x side or the −x side, and is condensed at the end in the x-axis direction. As a result, a condensing device that condenses all the incident light emitted from the exit surface 8a of the condensing panel in the x-axis direction with a simple configuration including the pair of condensing optical elements 10 and the polarization plane rotating element 65. Can be configured. And the photovoltaic device 2 can be comprised by a simple and low-cost structure by providing the photoelectric conversion element 50 in the edge part of a x-axis direction.

[Configuration Example 3 of Condensing Device and Photovoltaic Power Generation Device]
When light emitted from the exit surface 8a of the light collecting panel is composed of both p-polarized light and s-polarized light (for example, in addition to light composed of polarized components in two orthogonal directions, random polarized light composed of p-polarized components and s-polarized components and elliptical (In the case of polarized light, circularly polarized light, etc.), in the condensing devices of the first configuration example and the second configuration example, the light of the s-polarized component incident on the condensing optical element 10 is not condensed in the x-axis direction. The light is emitted to the back side of the element 10. The condensing devices 70 and 80 of the third and fourth configuration examples are configured to collect all the light incident on the condensing optical element 10 regardless of the polarization composition of the incident light.

  As shown in FIG. 24, the condensing device 70 of the third configuration example includes the condensing optical element 10, a reflecting mirror 72 provided along the back surface 10 a on the back surface side of the condensing optical element 10, A polarization plane rotating element 75 provided between the optical element 10 and the reflecting mirror 72 is provided. The polarization plane rotation element 75 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 70 having such a configuration, of the light incident from the incident surface 10a, the light of the p-polarized component is scattered by the B member, and the traveling direction is oriented to the + x side or the −x side of the x axis direction. It is condensed at the end in the axial direction. On the other hand, of the light incident in the thickness direction from the incident surface 10a, the light of the s-polarized component passes through the condensing optical element 10 and is emitted from the back surface 10b without being scattered by the B member.

  The light of the s-polarized component emitted to the back surface side of the condensing optical element 10 is transmitted through the polarization plane rotating element 75 and reflected by the reflecting mirror 72, and is again transmitted through the polarization plane rotating element 75 to The light enters the condensing optical element 10 again from the back surface 10b. At this time, the light re-entering the condensing optical element 10 is transmitted through the polarization plane rotating element 75 twice, so that the polarization plane is rotated by 90 degrees to become p-polarized component light. Therefore, the p-polarized component light re-entering from the back surface 10b and proceeding in the thickness direction is directed from the back surface side to the incident surface side in the same manner as the p-polarized component light totally reflected on the back surface of the condensing optical element 10. In the process of moving forward, the light is scattered by the B member and condensed on the side end portion on the + x side or the −x side in the x-axis direction.

  Therefore, according to the condensing device 70 having such a configuration, the light is emitted from the light exiting surface 8a of the light condensing panel with a simple structure including the pair of condensing optical elements 10, the polarization plane rotating element 75, and the reflecting mirror 72. A condensing device that condenses all of the incident light in the x-axis direction can be configured. And the photovoltaic device 3 can be comprised by a comparatively simple and low-cost structure by providing the photoelectric conversion element 50 in the edge part of a x-axis direction.

[Configuration example 4 of condensing device and photovoltaic device]
Condenser 80 of the fourth configuration example, as shown in FIG. 25, a first focusing optical element 10 _1, and the second focusing optical element 10 ₂ provided on the back side, these collector It comprises a polarization plane rotating element 85 provided between the optical optical elements 10 ₁ and 10 ₂ , and the x-axis direction of the _first condensing optical element 10 _{1 and} the x-axis direction of the second condensing optical element 10 _2. Are arranged in parallel with each other. The polarization plane rotation element 85 is an optical element that rotates the polarization plane of the transmitted light by 90 degrees in the same manner as the polarization plane rotation element 65 described above. For example, the light in the wavelength band of sunlight can be transmitted once. A broadband half-wave plate that converts s-polarized light into p-polarized light is preferably used.

In such a configuration of the condenser 80, of the light incident in the thickness direction from the first incident surface side of the converging optical element 10 _1, the light of p-polarized light component, first collection optics 10 Scattered by the B member 12 uniformly dispersed in ₁ , the traveling direction is oriented to the + x side or the -x side, and is condensed at the end in the x-axis direction. On the other hand, the light of the transmitted s-polarized component of the first focusing optical element 10 ₁ is incident on the polarization plane rotating element 85 is emitted from the first light-converging optical element 10 ₁ of the rear surface side.

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 by the second focusing B member 12 are uniformly dispersed in the optical element 10 ₂ Scattered and collected at the end in the x-axis direction.

Therefore, according to the condensing device 80 having such a configuration, the light emitted from the condensing panel 8 can be configured with a relatively simple structure in which the two condensing optical elements 10 and the polarization plane rotating element 85 are arranged to overlap each other. A condensing device that condenses everything in the x-axis direction can be configured. Moreover, the photovoltaic device 4 can be configured with a relatively simple configuration by providing the photoelectric conversion element 50 that photoelectrically converts the light collected at each end of the condensing optical elements 10 ₁ and 10 _2. it can.

  Although the case where the condensing optical element 10 is used has been described as an example of the condensing device using the condensing optical element, the same method is used for condensing light when the condensing optical element 20 is used. A device can be configured. First, when the light exiting from the exit surface 8a of the condensing panel is p-polarized linearly polarized light, or when the light exiting from the exit surface 8a of the condensing panel is s-polarized linearly polarized light, FIG. This is the same as the condensing device of the first and second configuration examples described with reference to FIG.

  On the other hand, when the light emitted from the exit surface 8a of the condensing panel is composed of both p-polarized light and s-polarized light, the s-polarized component incident in the thickness direction from the incident surface in the condensing optical element 20 of the second configuration form. Is emitted from the + z-direction surface (upper surface) or the −z-direction surface (lower surface) of the condensing optical element 20. The light emitted from the upper surface or the lower surface of the condensing optical element 20 is light whose electric field amplitude travels in the z-axis direction in the zy plane, and the traveling direction of the light cannot be deflected in the x-axis direction as it is.

  In this case, for example, similarly to the condensing device 70 of the third configuration example, the polarization plane rotating element (75) and the reflecting mirror (72) are provided along the emission surface (for example, the upper surface) of the s-polarized component light to collect the light. By rotating the polarization plane of light emitted from the upper surface of the optical optical element 20 by 90 degrees and re-entering the condensing optical element 20, the light can be condensed on the + x side or the −x side end of the x-axis direction. it can.

  Similarly to the condensing device 80 of the third configuration example, the polarization plane rotating element (85) and the second condensing optical element 10 (or 20) are arranged along the emission surface (for example, the upper surface) of the s-polarized component light. The polarization plane of the light emitted from the upper surface of the condensing optical element 20 is rotated by 90 degrees and is incident on the second condensing optical element 10, so that the + x side or −x side side end in the x-axis direction It can be condensed.

[Method of extracting light energy at the end of the condensing optical element]
Next, in the condensing optical elements 10 and 20 described above, FIGS. 26A to 26E illustrating some typical concepts regarding the energy extraction method of the light condensed in the x-axis direction. It will be explained briefly with reference.

  (a) and (b), in the condensing optical elements 10 and 20, a reflecting means for reflecting light is provided at either one of the + x side and the −x side (for example, the −x side), A configuration example is shown in which incident light is collected at the other end in the x-axis direction (for example, the + x side end). Among these, (a) provides a mirror 91 on the −x side end face of the condensing optical elements 10 and 20 or forms a reflection film, and condenses light propagating in the −x direction by folding it back in the + x direction. It is the example of a structure to do. In (b), a prism-like folded portion 92 is formed at the end of the condensing optical elements 10 and 20 on the −x side, or a right-angle prism is provided facing the end surface on the −x side, and in the −x direction. This is a configuration example in which propagating light is folded in the + x direction and collected. According to such a configuration, the light collection rate (power density of extracted light) by the light collection optical elements 10 and 20 can be doubled.

  (c) is a structural example in the case of using the light condensed on the end portion by converting it into electric energy or heat energy. This structure shows the structural example which couple | bonds the photoelectric conversion element 50 with the condensing end of the condensing optical elements 10 and 20, and takes out as an electrical energy. In addition, when taking out the condensed light as a thermal energy, the heat pipe with a light absorber etc. are illustrated as a photothermal conversion means.

  (d) is an example of a structure in the case of taking out the light condensed on the end part by further increasing the light collection rate. The condensing optical elements 10 and 20 of this configuration are such that at least one of the dimension in the x-axis direction and the dimension in the y-axis direction gradually decreases in the region near the end on the condensing side (that is, the opening area of the end is small). The light collected in the x-axis direction has a higher light collection rate at the exit end. Thereby, the power density in the case of making the condensed light enter into the photoelectric conversion element 50 and a heat pipe can further be raised.

  (E) shows a configuration example in which an optical fiber 96 is connected to the end portions of the condensing optical elements 10 and 20 via a coupler 95. The coupler 95 is made of, for example, a truncated cone-shaped optical member. Thereby, the light condensed by the condensing optical elements 10 and 20 can be used at an appropriate place away from the condensing panel 8. For example, the photoelectric conversion element 50 is installed in a unit box provided with a cooling device that prevents overheating of the photoelectric conversion element, and is condensed by the condensing optical elements 10 and 20 through the optical fiber 96 in the unit box. It can be configured to transmit light. Similarly, the light condensed by the condensing optical elements 10 and 20 can be transmitted through the optical fiber 96 and used in a vegetable factory or the like that is geographically separated from the condensing device.

  In the embodiment, for the purpose of simplifying the explanation, the condensing optical element is exemplified as a band plate shape or a square bar shape, and in order to explain the operation of the condensing optical element, the A member and the B member are specifically described. Although the structural example which applied the refractive index of the typical substance was demonstrated, this invention is not limited to these structural forms and structural examples. For example, the shape of the condensing optical element may be a columnar shape or a linear shape, and the material of the A member and the B member can be configured by appropriately selecting various resin materials, inorganic materials, and the like. 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, the condensing optical elements 10 and 20 condense the wide emission light emitted from the emission surface of the light collection panel 8 having a large aspect ratio of the long side / short side in the direction in which the long side extends. . Therefore, according to the present invention, it is possible to increase the light collection efficiency of light emitted from the emission surface having a wide width in the x-axis direction, and a new light collecting means that can efficiently use light energy such as sunlight. Can be provided. The condensing devices 60, 70, 80 and the photovoltaic power generation devices 1 to 4 are configured using such condensing optical elements, and efficiently use light energy such as sunlight with a simple, small, and low-cost configuration. It is possible to provide a condensing device and a photovoltaic device that can be used for the above.

1-4 Photovoltaic generator 8 Condensing panel (8a outgoing surface)
10 (10 ₁ , 10 ₂ ) Condensing optical element of the first configuration form (10a incident surface)
11 A member 12 B member 20 Condensing optical element 21 of 2nd structure form A member 22 B member 30 Refractive index characteristic 40 (41-44) of A member B Refractive index characteristic 50 of B member Photoelectric conversion element 60 2nd structural example Condensing device 65 Polarizing surface rotating element 70 Condensing device 72 of the third configuration example Reflecting mirror 75 Polarizing surface rotating element 80 Condensing device 85 of the fourth configuration example Polarizing surface rotating element 91 Mirror (reflecting means)
92 Prism-shaped folding part (reflection means)
95 coupler 96 optical fiber

Claims (18)

Condensing light emitted from an exit surface having a large aspect ratio of long side / short side received by an entrance surface provided opposite to the exit surface and collecting the incident light in a direction in which the long side extends. An optical element,
A member having light transmittance, and a particulate B member having light transmittance dispersed in the incident direction of the incident light and the first direction and the second direction orthogonal to each other in the A member. Configured with
The particle diameter d of the B member has an equivalent circle diameter of 0.1λ to 10λ when the wavelength of the incident light is λ.
The axis extending in the incident direction is the y axis, the axis extending in the first direction is the x axis, the axis extending in the second direction is the z axis, the plane including the x axis and the y axis is the xy plane , the y axis, A plane including the z-axis is a zy plane ;
In the member A, the refractive index of light that travels in the y-axis direction in the xy plane is expressed as “naxy”, the refractive index of light that travels in the y-axis direction in the zy plane is nazy, and the electric field amplitude is The refractive index of light traveling in the x-axis direction in the xy plane is defined as nayx,
In the member B, the electric field amplitude is nbxy as the refractive index of light traveling in the y-axis direction in the xy plane, the electric field amplitude is nbzy as the refractive index of light traveling in the y-axis direction in the zy plane, and the electric field amplitude is When the refractive index of light traveling in the x-axis direction in the xy plane is nbyx,
naxy and Nbxy, and is different from the nazy and Nbzy, converging optical element and nayx and nbyx is equal to or substantially equal. In the A member, the refractive index of light whose electric field amplitude proceeds in the z-axis direction in the zy plane is defined as nayz,
When the refractive index of light traveling in the z-axis direction in the zy plane in the B member is nbyz,
  The condensing optical element according to claim 1, wherein nayz and nbyz are substantially equal. 3. The condensing optical element according to claim 1, wherein the relationship between the refractive indexes is: n a y <nb x y and n b x y> n b yx. 3. The condensing optical element according to claim 1, wherein the relationship between the refractive indexes is: n y <nb x y and n y <n y x. 3. The condensing optical element according to claim 1, wherein the relationship between the refractive indexes is: n a y> nb b y and n b x y <n b yx. 3. The condensing optical element according to claim 1, wherein the relationship between the refractive indexes is: n y> nb y and n y> n yx. The A member and the B member have a size parameter α defined by (π × d × naxy) / λ, wherein 1.5 ≦ α ≦ 40. The condensing optical element described in 1. 8. The size parameter α defined by (π × d × naxy) / λ of the A member and the B member is 2 ≦ α ≦ 20, according to claim 1. Condensing optical element. 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 on the y-axis direction from the incident surface, and the light scattered by the plurality of B members toward the back surface of the condensing optical element is The condensing optical element according to claim 1, wherein the condensing optical element is set so as to be totally reflected on the back surface. The size in the y-axis direction and the z-axis direction is sufficiently small with respect to the size in the x-axis direction, and is formed in a rod shape or a line shape. The condensing optical element described in 1. The condensing optical element according to claim 1, further comprising a reflection unit configured to reflect light at one end in the x-axis direction. The condensing optical element according to any one of claims 1 to 12,
  A condensing device provided with a polarization plane rotating element that is provided between the exit surface and the entrance surface and rotates the polarization plane of the exit light by 90 degrees. The condensing optical element according to any one of claims 1 to 12,
  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 12,
  The second condensing optical element according to any one of claims 1 to 12,
  The second condensing optical element has a back surface side of the first condensing optical element, and the x-axis direction of the second condensing optical element is the x-axis 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 12,
  A photovoltaic device comprising: a photoelectric conversion element that photoelectrically converts light guided in the x-axis direction by the condensing optical element. The light collecting device according to claim 13 or 14,
  A photovoltaic device comprising: a photoelectric conversion element that photoelectrically converts light guided in the x-axis direction by the condensing optical element. The light collecting device according to claim 15;
  A photoelectric conversion element that photoelectrically converts light guided in the x-axis direction in the first condensing optical element;
  A photovoltaic device comprising: a photoelectric conversion element that photoelectrically converts light guided in the x-axis direction in the second condensing optical element.

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