JP5984111B2 - Wavelength selective filter having retroreflectivity and window material - Google Patents

Description

  The present invention relates to a wavelength selective filter having retroreflectivity, and in particular, retroreflectivity that allows visible light of incident light to pass therethrough and selectively retroreflects light in a specific wavelength range (for example, an infrared wavelength range). The present invention relates to a wavelength selective filter and a window material having

  Sunlight includes, for example, light in the infrared wavelength range (infrared rays) in addition to light in the visible wavelength range. For this reason, when sunlight enters the translucent window glass provided in buildings (office buildings, detached houses, condominiums, etc.) from the outside, visible light and infrared rays (infrared light) out of sunlight enter. This increases the indoor temperature. In order to suppress the indoor temperature rise due to the incident infrared light, it is necessary to operate the cooling equipment. The wavelength range of visible light is about 400 to 800 nm, and the wavelength range of infrared light is about 800 to 1600 nm.

  By the way, in recent years, in order to save energy for the purpose of preventing global warming and reducing consumption of electric energy, it is possible to save energy necessary for cooling to suppress indoor temperature rise due to infrared rays incident on the window glass. It is desired.

  For this reason, the structure which coat | covers the thin film which has a function which permeate | transmits only visible light and reflects infrared rays on the surface of translucent window glass as mentioned above is known conventionally (for example, refer patent document 1). .

JP-A-2005-194169

  In the structure described in Patent Document 1, for example, when sunlight is incident on a flat window glass provided in a building, infrared rays contained in the sunlight are regularly reflected by a thin film layer (infrared shielding film) on the surface of the window glass. For this reason, when sunlight is incident on the flat window glass from above, the infrared rays specularly reflected on the surface illuminate the concrete road surface around the building, thereby raising the temperature of the illuminated area from the surroundings.

  This promotes the heat island phenomenon, especially in urban areas where buildings are densely populated, and increases the amount of energy consumed to cool indoors. Therefore, only visible light in sunlight is transmitted and infrared light is retroreflected. It is hoped that.

  Therefore, an object of the present invention is to provide a wavelength selective filter and a window material having retroreflectivity that allow only visible light of incident light to pass through and select infrared rays to be retroreflected.

In order to achieve the above object, a wavelength selective filter having retroreflectivity according to the present invention includes a first medium having a refractive index n1 having translucency, and a refractive index n2 (n2 ≠ n1) having translucency. and second medium are periodically alternately stacked, and the stacking direction is inclined, the inclination direction Ri same der in the plane, the stacked first, longitudinal side of the second medium the end faces are each located on the same plane and provided with a deflection diffraction grating having a refractive index modulation structure each end faces is Ru parallel der, the normal of the surface where light of the deflecting diffraction grating are incident A light beam is incident from the stacking direction side of the first medium and the second medium with respect to the direction , and is the first- order reflected diffracted light of the incident light beam by the refractive index modulation structure of the deflectable diffraction grating. Select and retroreflect light of one wavelength band, which is different from the first wavelength band It is characterized by transmitting light of the second wavelength band.

  Moreover, the window material which concerns on this invention has arrange | positioned the wavelength selective filter which has the retroreflection property as described in any one of Claims 1 thru | or 9 in the glass outer surface or inner surface which has translucency. It is said.

  According to the wavelength selective filter having retroreflectivity according to the present invention, light is incident from the side of the first and second medium in the stacking direction with respect to the normal direction of the surface on which the light beam of the deflecting diffraction grating is incident. Then, the light of the first wavelength band of the incident light rays is selected and retroreflected by the refractive index modulation structure of the deflecting diffraction grating, and the light of the second wavelength band different from the first wavelength band is transmitted. Therefore, when the light of the first wavelength band is infrared and the light of the second wavelength band is visible light, only visible light of the incident light is transmitted, and the infrared light is selected and retroreflected. Can be made.

  Further, according to the window material according to the present invention, by arranging the wavelength selective filter having the retroreflectivity of the present invention on the glass outer surface or the inner surface, only visible light of sunlight passes through the glass, Infrared rays contained in sunlight can be retroreflected toward the incident direction side of sunlight. Thereby, by applying the window material of the present invention to, for example, a window glass of a building, infrared rays are retroreflected toward the incident direction side of sunlight, thereby suppressing the temperature rise in the room inside the window glass (window material). In addition, since the reflected infrared rays do not go to the ground surface side, the temperature rise around the ground surface can be suppressed.

Schematic which shows the structure of the wavelength selection filter which concerns on embodiment of this invention. The figure which shows an example of the manufacturing method of the wavelength selection filter which concerns on embodiment of this invention. The figure which shows an example of the manufacturing method of the wavelength selection filter which concerns on embodiment of this invention. The figure which showed the reflection characteristic and the transmission characteristic in TE polarized light (30 degree incidence) by the wavelength selection filter of Example 1 of this invention. The figure which showed the reflection characteristic and the transmission characteristic in TM polarized light (30 degree incidence) by the wavelength selection filter of Example 1 of this invention. The figure which showed the reflection characteristic and the transmission characteristic in TE polarized light (-30 degree incidence) by the wavelength selection filter of Example 1 of this invention. The figure which showed the reflection characteristic and transmission characteristic in TM polarized light (-30 degree incidence) by the wavelength selection filter of Example 1 of this invention. The figure which showed the case where incident light injects at -30 degrees with respect to the wavelength selection filter of Example 1 of this invention. The figure which showed the reflection characteristic and the transmission characteristic in TE polarized light (30 degrees incidence) by the wavelength selection filter of Example 2 of this invention. The figure which showed the reflective characteristic and transmission characteristic in TE polarization (30 degree incidence) by the wavelength selection filter of Example 3 of this invention. The figure which showed the reflection characteristic and the transmission characteristic in TE polarized light (30 degrees incidence) by the wavelength selection filter of Example 4 of this invention. Schematic which shows the structure of the wavelength selection filter in Example 5 of this invention. The figure which showed the reflective characteristic and the transmission characteristic in TE polarization (30 degrees incidence) by the wavelength selection filter of Example 5 of this invention. Schematic which shows the structure of the wavelength selection filter in the comparative example 1. FIG. The figure which showed the reflective characteristic and the transmission characteristic in TE polarization (30 degrees incidence) by the wavelength selection filter of the comparative example 1. FIG. Schematic which shows the structure of the wavelength selection filter in the comparative example 2. FIG. The figure which showed the reflection characteristic and the transmission characteristic in TE polarization (30 degrees incidence) by the wavelength selection filter of the comparative example 2. Schematic which shows the window glass by which the wavelength selection filter of this invention is arrange | positioned.

  Hereinafter, the present invention will be described based on the illustrated embodiments. FIG. 1 is a schematic diagram showing the configuration of a wavelength selective filter having retroreflectivity according to an embodiment of the present invention.

  As shown in FIG. 1, a wavelength selective filter (hereinafter simply referred to as “wavelength selective filter”) 1 having retroreflectivity according to the present embodiment includes a deflecting diffraction grating 2 and an incidence of the deflecting diffraction grating 2 described later. A first translucent substrate 3 provided on the surface side (upper side in FIG. 1) and a second translucent substrate 4 provided on the exit surface side (lower side in FIG. 1) of the deflectable diffraction grating 2. And.

(Configuration of the deflectable diffraction grating 2)
The deflecting diffraction grating 2 includes a first medium 2a made of a material having a refractive index n1 and a second medium 2b made of a material having a refractive index n2 (n2 ≠ n1) alternately inclined and laminated. A refractive index modulation structure having a favorable refractive index distribution is configured. The first medium 2a and the second medium 2b forming the deflectable diffraction grating 2 can be formed of, for example, a light-transmitting resin or an inorganic material such as SiO 2 or TiO 2. In order to adjust the refractive index, these materials may contain fine particles or hollow particles.

  The thickness of the first medium 2a and the second medium 2b in the stacking direction (symbols d1 and d2 in FIG. 1) is set to about 50 to 500 nm.

  The inclined stacking direction A1 of the first medium 2a and the second medium 2b that are inclined and stacked is the normal direction of the surfaces having the same refractive indexes of the first medium 2a and the second medium 2b. Further, an angle formed by the stacking direction A1 and the normal direction A2 of the main surface 2 'on the incident surface side of the deflecting diffraction grating 2 is defined as α. Incident light L such as sunlight is incident on the deflectable diffraction grating 2 from the first translucent substrate 3 side, and the vibration direction of the electric field is the period of the first medium 2a and the second medium 2b. Polarized light parallel to the direction (left-right direction in FIG. 1) is TM polarized light, and polarized light orthogonal to the periodic direction is TE polarized light.

  Moreover, the 1st, 2nd translucent base materials 3 and 4 are formed with the transparent sheet | seat, transparent film, transparent glass, etc. which consist of resin. In addition, the refractive index of the 1st, 2nd translucent base materials 3 and 4 is set to the refractive index n1 same as the 1st inclination layer 2a, or the refractive index close | similar to this refractive index n1.

  In FIG. 1, when incident light L is incident on the principal surface 2 ′ of the deflecting diffraction grating 2 at a predetermined incident angle (θi), a1 is −1st order reflected diffracted light, and a2 is 0th order reflected diffracted light. , A3 are + order reflected diffracted light, b1 is 0th order transmitted light, b2 is −1st order transmitted light, and b3 is + 1st order transmitted light. In the following description, the same definition is used.

  The reflection diffraction efficiency of − (minus) order can be normally set to the diffraction efficiency of the −1st order reflection. When the first medium 2a and the second medium 2b constituting the deflecting diffraction grating 2 have a plurality of periods, reflected light is generated in many orders according to the respective periods and combination periods. Therefore, it is possible to obtain the sum of the diffraction efficiency of the -order. In the case of the -order reflected diffracted light, the incident infrared rays can be recursively reflected in the same manner as the -1st order reflected diffracted light.

  As will be described later, the wavelength selection filter 1 of the present embodiment selects the −1st order reflected diffracted light from the reflected diffracted light and reflects (retroreflects) the incident light L on the incident direction side. The 0th order transmitted light can be selected and transmitted.

  In FIG. 1, when light (incident light L) is incident on the deflectable diffraction grating 2 at a predetermined incident angle (θi) from the first light-transmissive substrate 3 side of the wavelength selective filter 1, a refractive index modulation structure is formed. Reflected diffracted light is generated by the generation of a phase difference in the deflecting diffraction grating 2 (the first medium 2a and the second medium 2b that are inclined and stacked). The diffraction angle of the reflected diffracted light by the deflectable diffraction grating 2 can be obtained from the following equation.

However, in the above formula,
ni: Refractive index of the first medium 2a
nd: refractive index of second medium 2b λ: wavelength of incident light L θi: incident angle of incident light L with respect to normal direction A2 of main surface 2 ′ (normal direction A2 is 0 °) θm: reflection diffraction Mth diffraction angle of light
m: Diffraction order of reflected diffracted light
P: period of the first medium 2a and the second medium 2b that are inclined and stacked (hereinafter referred to as “refractive index modulation period”)
α: angle formed by the inclined stacking direction A1 and the normal direction A2 of the main surface 2 ′ (hereinafter referred to as “stacking angle”)

  The diffraction angle in the tilted refractive index modulation structure as described above is described in detail below, for example.

THOMAS K. GAYLORD and M.M. G. MOHARAM
PROCEEDINGS OF IEEE, Vol. 73, no. 5 (1985)
“Analysis and Applications of Optical
Diffraction by Gratings "

  For light (incident light L) incident on the deflectable diffraction grating 2 from the first translucent base material 3 side, the deflectable diffraction grating 2 (the first medium 2a and the second medium which are inclined and stacked) Since there are a large number of interfaces due to the refractive index modulation according to 2b), it is possible to obtain a high reflectance in a specific wavelength region by interference of reflected light from each interface. For this reason, the specific wavelength range with a high reflectance can be selected by setting the above-described refractive index modulation period (P: see FIG. 1) within an appropriate range.

  According to the experiment by the present inventor, when the light (incident light L) incident on the deflectable diffraction grating 2 from the first light-transmitting substrate 3 side is sunlight, the first medium 2a and the first layer 2 which are inclined and stacked When the refractive index modulation period (P) of the second medium 2b is set in the range of about 100 to 1000 nm, preferably in the range of 200 to 800 nm, more preferably in the range of 300 to 700 nm, the infrared wavelength region of sunlight ( Only light (infrared rays) of about 800 to 1600 nm was selected and reflected.

  Further, according to the experiment by the present inventor, when the refractive index modulation period (P) of the first medium 2a and the second medium 2b that are inclined and stacked is made smaller than about 100 nm, the reflection wavelength region is visible. Visible light was reflected in the light region. Furthermore, when the refractive index modulation period (P) of the first medium 2a and the second medium 2b that are inclined and stacked is made larger than about 1000 nm, diffraction is caused by a wavelength in the visible light region (about 400 to 800 nm). There has occurred.

  Further, as described above, when light (incident light L) is incident on the deflectable diffraction grating 2 from the first translucent substrate 3 side, the deflectable diffraction grating 2 (the first medium stacked with an inclination). The reflection direction (diffraction angle) of the reflected diffracted light (in this embodiment, −1st order reflected diffracted light a1) generated by the generation of the phase difference between 2a and the second medium 2b) is clear from the above equation. It varies depending on the stacking angle α.

  According to the experiments of the present inventors, the stacking angle (α) of the first medium 2a and the second medium 2b that are inclined and stacked is in the range of about 10 to 85 °, preferably in the range of 15 to 80 °, and more preferably. Was set to a range of 20 to 60 °, the −1st-order reflected diffracted light (a1) was reflected toward the incident direction of the incident light L, and retroreflectivity was obtained.

  Further, the refractive index difference (Δn) between the first medium 2a having the refractive index n1 and the second medium 2b having the refractive index n2 forming the deflecting diffraction grating 2 is preferably 0.005 or more. Is set to a range of 0.02 or more, the reflection component at the interface between the first medium 2a and the second medium 2b that are inclined and stacked becomes large. Thereby, the reflectance in a specific wavelength range can be made higher, and the wavelength range to reflect can be expanded.

  If the refractive index difference (Δn) is 0.005 or more, the reflectance can be increased by increasing the thickness t. Moreover, the wavelength range to reflect can be expanded by modulating a period. When the refractive index difference (Δn) is 0.005 or less, the reflection component at the first medium 2a and the second interface cannot be sufficiently increased.

  The thickness of the deflectable diffraction grating 2 (t: see FIG. 1) is set to about 500 nm or more, more preferably about 1000 nm (1 μm) or more, thereby increasing the traveling distance of light into the deflectable diffraction grating 2. can do. Thereby, the reflectance in a specific wavelength range can be made higher, and the reflectance in wavelength ranges other than a specific wavelength range can be reduced effectively, and coloring etc. can be prevented.

  In addition, the first medium 2a and the second medium 2b that are inclinedly stacked in the deflecting diffraction grating 2 are not limited to the configuration in which the same refractive index modulation period (P) is set as shown in FIG. The plurality of the first medium 2a and the second medium 2b may be set so as to have different refractive index modulation periods every predetermined period.

  For example, the first medium 2a and the second medium 2b having the first refractive index modulation period and the first medium 2a and the second medium 2b having the second refractive index modulation period are set to a predetermined period (for example, 5 You may make it carry out the inclination lamination | stacking alternately for every period.

  In this case, the wavelength range reflected by the first medium 2a and the second medium 2b that are inclined and laminated at the first refractive index modulation period, and the first that is inclined and laminated at the second refractive index modulation period. It is possible to simultaneously increase the reflectivities in the wavelength ranges reflected by the medium 2a and the second medium 2b, and the reflection wavelength range can be widened. Moreover, you may pile up the diffraction grating which has a different period.

(Method for manufacturing wavelength selective filter 1)
Next, an example of a manufacturing method of the above-described wavelength selection filter 1 (deflective diffraction grating 2) will be described with reference to FIGS. 2 (a) to 2 (e) and FIGS. 3 (a) to 3 (d). 2 and 3 are shown in a cross-sectional shape.

  In this manufacturing method, first, as shown in FIG. 2A, for example, on a transparent base material 10 (corresponding to the second light-transmitting base material 4), the constituent material of the second medium 2b is used. A resin medium 11 having a certain light transmissivity and a refractive index n2 is applied by spin coating or the like. Then, a photoresist layer 12 is applied on the resin medium 11 by spin coating or the like (FIG. 2B). Then, the photoresist layer 12 is exposed to a lattice pattern and developed to form a photoresist pattern 12a on the resin medium 11 (FIG. 2C).

  Then, a metal layer 13 such as aluminum (Al) or chromium (Cr) is formed on the photoresist pattern 12a and on the resin medium 11 therebetween (see FIG. 2D). Then, the photoresist pattern 12a is removed by elution with an organic solvent, and the photoresist pattern 12a and the metal layer thereon are removed (FIG. 2E). As a result, the metal pattern 13 a remains on the resin medium 11. This metal pattern 13a becomes a mask for subsequent dry etching.

  3A and 3B, the substrate 10 is tilted from the horizontal position by a predetermined angle α (an angle corresponding to the stacking angle α), and the ion beam is applied from above the inclined resin medium 11. By performing etching by irradiating 14, a stripe layer 11 a (corresponding to the second medium 2 b forming the deflecting diffraction grating 2 in FIG. 1) inclined at a constant period is formed on the resin medium 11. Then, as shown in FIG. 3C, the metal pattern 13a on each stripe layer 11a is removed with an acid or the like.

  3A, 3B and 3C, the front and back surface edge regions of the resin medium 11 are not irradiated with an ion beam. A stripe layer is not formed.

  Then, as shown in FIG. 3 (d), for example, an ultraviolet curable resin medium 15 having a translucent refractive index n1, which is a constituent material of the first medium 2a, is formed between the stripe layers 11a. The space is filled and discharged onto the upper part of each stripe layer 11a so as to have a predetermined film thickness. Then, by cutting both sides of the base material 10 and the resin medium 11, the deflectability between the first translucent base material 3 and the second translucent base material 4 as shown in FIG. The wavelength selective filter 1 including the diffraction grating 2 (the first medium 2a and the second medium 2b that are inclined and stacked) is manufactured.

  Next, in order to evaluate the retroreflectivity of light in the infrared wavelength region (infrared light) and the transmittance of visible light by the wavelength selective filter 1 of the present invention described above, it is compared with Examples 1 to 5 shown below. Evaluation was performed using a wavelength selective filter having the configuration of Comparative Examples 1 and 2.

  In addition, in order to evaluate the retroreflectivity and visible light transmission of light in this infrared wavelength range (infrared light), electromagnetic wave analysis simulation software Diffract MOD (R-Soft) by RCWA (strict coupling wave analysis) method The simulation was performed using

<Example 1>
In Example 1, the following conditions were set in the deflectable diffraction grating 2 of the wavelength selective filter 1 shown in FIG.

Refractive index (n1) of the first medium 2a: 1.52
Refractive index (n2) of second medium 2b: 1.72
Refractive index modulation period (P): 300 nm
Thickness (d1) of first medium 2a: 150 nm
Thickness (d2) of second medium 2b: 150 nm
Thickness (t) of the deflectable diffraction grating 2: 1500 nm (1.5 μm)
Lamination angle (α) of first medium 2a and second medium 2b: 30 °

  Further, the following conditions were set for the first and second translucent substrates 3 and 4 provided on both surfaces of the deflectable diffraction grating 2.

Refractive index of the first translucent substrate 3: 1.52
Refractive index of the second translucent substrate 4: 1.52

  4 and 5 show that, as the incident light L, in the wavelength selection filter 1 of the first embodiment, sunlight is the main surface 2 ′ of the deflectable diffraction grating 2 from the first light-transmitting substrate 3 side (see FIG. 1). These are reflection characteristics and transmission characteristics when the polarization directions are TE-polarized light and TM-polarized light when incident at an incident angle θi of 30 ° with respect to the normal line direction (corresponding to an incident angle of 49 ° in air). .

  4A and 4B show the reflection characteristics and transmission characteristics in TE polarization, and FIGS. 5A and 5B show the reflection characteristics and transmission characteristics in TM polarization. In the vertical axis (reflectance) of FIGS. 4 (a) and 5 (a), 1.0 is 100% reflectivity, and in the vertical axis (transmittance) of FIGS. 4 (b) and 5 (b). 1.0 is 100% transmittance. The reflectance includes all orders of diffracted light to be reflected, and the transmittance includes all orders of diffracted light to be transmitted. The same applies to the following examples and comparative examples.

  As shown in FIGS. 4 (a) and 5 (a), in the case of 30 ° incidence, the deflected diffraction grating 2 generates −1st order reflected diffracted light (a1) in the infrared wavelength region for both TE polarized light and TM polarized light. doing. The reflection angle of the generated −1st order reflected diffracted light with respect to the normal direction was 32.8 ° at a wavelength of 950 nm. That is, only light in the infrared wavelength region (infrared rays) is selected and retroreflected.

  In Example 1, generation of + 1st order reflected diffracted light and 0th order reflected diffracted light was almost negligible.

  Further, as shown in FIGS. 4B and 5B, in the case of 30 ° incidence, both the TE-polarized light and the TM-polarized light are transmitted in the visible light wavelength range by the deflecting diffraction grating 2 (0th order transmitted light: b1 ) Passes through and is emitted from the second translucent substrate 4. That is, in the visible light region, since no diffracted light or reflected light is generated in the deflectable diffraction grating 2, the deflectable diffraction grating 2 is transparent and not colored.

  The following table shows the average transmittance of visible light, the maximum reflectance of infrared rays, the -order reflection diffraction efficiency, and the infrared wavelength range in the wavelength selective filters of Example 1 and Examples 2 to 5 and Comparative Examples 1 and 2. 6 is a simulation result showing a ratio (Er / Rmax) between the reflectance Rmax and the -order reflection diffraction efficiency Er at a wavelength at which the maximum reflectance is obtained.

  Thus, when the wavelength selection filter of Example 1 is arranged on the surface of the window glass of a building installed in the vertical direction, the sunlight that is obliquely above corresponds to the above-described 30 ° incidence situation, so infrared rays Light in the wavelength range (infrared light) can be selected and retroreflected to transmit visible light.

  FIGS. 6 and 7 show the main surface of the deflectable diffraction grating 2 from the first translucent substrate 3 side as the incident light L in the wavelength selective filter 1 of the first embodiment, as shown in FIG. Reflection characteristics when the polarization direction is TE polarized light and TM polarized light when incident at an incident angle θi of −30 ° (corresponding to an incident angle of −49 ° in air) with respect to the normal direction of 2 ′ Transmission characteristics. 6A and 6B show the reflection characteristics and transmission characteristics in TE polarized light, and FIGS. 7A and 7B show the reflection characteristics and transmission characteristics in TM polarized light.

  As shown in FIGS. 6A and 7A, in the case of −30 ° incidence, both TE polarized light and TM polarized light are reflected in the deflectable diffraction grating 2 in the visible light wavelength region to the infrared wavelength region ( The −1st order reflected diffracted light a1, the 0th order reflected diffracted light a2, and the + 1st order reflected diffracted light a3) are hardly generated.

  In addition, as shown in FIGS. 6B and 7B, in the case of −30 ° incidence, the 0th-order transmitted light b1 is deflected diffraction in the visible wavelength range to the infrared wavelength range for both TE polarized light and TM polarized light. The light transmitted through the grating 2 and emitted from the second light-transmitting substrate 4. That is, when the incident light L is incident from the first translucent substrate 3 side at a minus (−) incident angle with respect to the normal direction A2 of the main surface 2 ′ of the deflecting diffraction grating 2, the TE polarized light In addition, the TM-polarized light transmits zero-order transmitted light in the visible wavelength range to the infrared wavelength range. In FIG. 7B, b3 is + first order transmitted light.

<Example 2>
In Example 2, the following conditions were set in the deflectable diffraction grating 2 of the wavelength selective filter 1 shown in FIG.

Thickness (t) of the deflectable diffraction grating 2: 2000 nm (20 μm)
Lamination angle (α) of first medium 2a and second medium 2b: 30 °
Other setting conditions are the same as those in the first embodiment.

  FIG. 9 shows the normal line of the principal surface 2 ′ (see FIG. 1) of the deflecting diffraction grating 2 from the first translucent substrate 3 side as the incident light L in the wavelength selective filter 1 of the second embodiment. These are reflection characteristics and transmission characteristics when the polarization direction is TE polarized light when the incident light is incident at an incident angle θi of 30 ° with respect to the direction A2. FIG. 9A shows reflection characteristics in TE polarized light, and FIG. 9B shows transmission characteristics in TE polarized light. Even when the polarization direction was TM polarized light, the reflection characteristics and transmission characteristics were almost the same.

  As shown in FIG. 9A, in the case of 30 ° incidence, −1st order reflected diffracted light a1 is generated in the infrared wavelength region by the deflecting diffraction grating 2, and is particularly high in the range of about 900 to 1050 nm. Next reflection diffracted light is generated. The reflection angle of the generated −1st-order reflected diffracted light with respect to the normal direction A2 was 36.6 ° at a wavelength of 1000 nm. That is, light in the infrared wavelength region (infrared light) is selected and retroreflected.

  In Example 2, the 0th-order reflected diffracted light a2 was slightly generated in a part of the visible light wavelength range (near 460 nm), but the + 1st order reflected diffracted light and the 0th order reflected diffracted light in other wavelength ranges. The generation of light was almost negligible.

  In addition, as shown in FIG. 9B, in the case of 30 ° incidence, light in the visible light wavelength region (0th-order transmitted light b1) is transmitted by the deflecting diffraction grating 2, and the second light-transmitting substrate 4 is emitted. The −1st order transmitted light and the + 1st order transmitted light were almost negligible.

  As described above, when the thickness (t) of the deflectable diffraction grating 2 is made thicker than in the case of the first embodiment, the number of interfaces through which light passes in the deflectable diffraction grating 2 increases, and in the infrared wavelength region. Since reflection becomes larger, light in the infrared wavelength region (infrared rays) can be retroreflected more effectively.

<Example 3>
In Example 3, the following conditions were set in the deflectable diffraction grating 2 of the wavelength selective filter 1 shown in FIG.

Refractive index modulation period (P): 350 nm
The thickness (d1) of the first medium 2a: 175 nm
Thickness (d2) of second medium 2b: 175 nm
Thickness (t) of deflective diffraction case 2: 1500 nm (1.5 μm)
Lamination angle (α) of first medium 2a and second medium 2b: 30 °
Other setting conditions are the same as those in the first embodiment.

  FIG. 10 shows the normal line of the principal surface 2 ′ (see FIG. 1) of the deflecting diffraction grating 2 from the first light-transmitting substrate 3 side as the incident light L in the wavelength selective filter 1 of the third embodiment. These are reflection characteristics and transmission characteristics when the polarization direction is TE polarized light when the incident light is incident at an incident angle θi of 30 ° with respect to the direction A2. FIG. 10A shows reflection characteristics, and FIG. 10B shows transmission characteristics. Even when the polarization direction was TM polarized light, the reflection characteristics and transmission characteristics were almost the same.

  As shown in FIG. 10A, in the case of 30 ° incidence, −1st order reflected diffracted light a1 is generated in the infrared wavelength region by the deflecting diffraction grating 2. The reflection angle of the generated −1st order reflected diffracted light with respect to the normal direction A2 was 32.3 ° at a wavelength of 1100 nm. That is, light in the infrared wavelength region (infrared rays) is selected and retroreflected.

  In Example 3, the 0th-order reflected diffracted light a2 is slightly generated in a part of the visible light wavelength range. However, the + 1st-order reflected diffracted light and the 0th-order reflected diffracted light are generated in other wavelength ranges. It was almost negligible.

  As shown in FIG. 10B, in the case of 30 ° incidence, light in the visible light wavelength region (0th-order transmitted light b1) is transmitted by the deflecting diffraction grating 2, and the second light-transmitting substrate 4 is emitted. The −1st order transmitted light and the + 1st order transmitted light were almost negligible.

  In this way, the refractive index modulation period (P) of the first medium 2a and the second medium 2b that are inclined and stacked is changed (in Example 3, the 300 nm of Example 1 is changed to 350 nm) to reflect the refractive index. It is possible to control the wavelength range (infrared wavelength range) for (retroreflection). That is, when the refractive index modulation period (P) is changed so as to increase, the wavelength range (infrared wavelength range) for reflection (retroreflection) can be shifted to the longer wavelength side.

<Example 4>
In Example 4, the following conditions were set in the deflectable diffraction grating 2 of the wavelength selective filter 1 shown in FIG.

Refractive index modulation period (P): 460 nm
Thickness (d1) of first medium 2a: 230 nm
Thickness (d2) of second medium 2b: 230 nm
Lamination angle (α) of first medium 2a and second medium 2b: 50 °
Other setting conditions are the same as those in the first embodiment.

  FIG. 11 shows the normal line of the principal surface 2 ′ (see FIG. 1) of the deflecting diffraction grating 2 from the first translucent substrate 3 side as the incident light L in the wavelength selective filter 1 of the fourth embodiment. These are reflection characteristics and transmission characteristics when the polarization direction is TE polarized light when the incident light is incident at an incident angle θi of 30 ° with respect to the direction A2. FIG. 11A shows reflection characteristics, and FIG. 11B shows transmission characteristics. Even when the polarization direction was TM polarized light, the reflection characteristics and transmission characteristics were almost the same.

  As shown in FIG. 11A, in the case of 30 ° incidence, −1st order reflected diffracted light a1 is generated in the infrared wavelength region by the deflecting diffraction grating 2. The reflection angle of the generated −1st order reflected diffracted light with respect to the normal direction A2 was 54.7 ° at a wavelength of 1200 nm. That is, light in the infrared wavelength region (infrared rays) is selected and retroreflected.

  In Example 4, the generation of + 1st order reflected diffracted light and 0th order reflected diffracted light in other wavelength regions was almost negligible.

  In addition, as shown in FIG. 11B, in the case of 30 ° incidence, light in the visible light wavelength region (0th-order transmitted light b1) is transmitted by the deflecting diffraction grating 2, and the second light-transmitting substrate 4 is emitted. The −1st order transmitted light and the + 1st order transmitted light were almost negligible.

  In this way, by changing the refractive index modulation period (P), the thicknesses (d1, d2) of the first medium 2a and the second medium 2b, and the stacking angle (α), the wavelength range of the infrared rays to be retroreflected is changed. Range and reflection angle can be controlled.

<Example 5>
FIG. 12 is a schematic configuration diagram illustrating the wavelength selective filter 1 having the deflecting diffraction grating 2 ′ according to the fifth embodiment.

  As shown in FIG. 12, the deflecting diffraction grating 2 ′ of Example 5 includes a first medium 2a and a second medium 2b having a refractive index modulation period (P1) of 300 nm, and a refractive index modulation period (P2). The first medium 2a and the second medium 2b, each having a thickness of 350 nm, are alternately laminated at every five cycles.

  In Example 5, the following conditions were set for the deflectable diffraction grating 2 'of the wavelength selective filter 1 shown in FIG.

Refractive index (n1) of the first medium 2a: 1.52
Refractive index (n2) of second medium 2b: 1.72
Refractive index modulation period (P1): 300 nm
Refractive index modulation period (P2): 350 nm
The thickness (d1) of the first medium 2a in the refractive index modulation period (P1): 150 nm
Thickness (d2) of second medium 2b at refractive index modulation period (P1): 150 nm
Thickness (d′ 1) of first medium 2a at refractive index modulation period (P2): 350 nm
Thickness (d′ 2) of second medium 2b at refractive index modulation period (P2): 350 nm
Thickness (t) of the deflectable diffraction grating 2 ′: 6000 nm (6 μm)
Lamination angle (α) of first medium 2a and second medium 2b: 30 °

  The conditions of the first and second translucent substrates 3 and 4 provided on both surfaces of the deflectable diffraction grating 2 'are the same as those in the first embodiment.

  In the deflectable diffraction grating 2 ′ of the fifth embodiment, one calculated period (= 300 nm × 5 periods + 350 nm × 5 periods) of the first medium 2a and the second medium 2b that are inclined and stacked is 3250 nm. Reflected diffracted light and transmitted light of the order matching the period can be obtained. In addition, diffraction by a refractive index modulation period (P1) of 300 nm, diffraction by a refractive index modulation period (P2) of 350 nm, and the like are mixed, and diffracted light is generated over many orders. In this example, -8th order, -9th order, -10th order, -11th order, and -12th order diffracted light were obtained. In this embodiment, these are collectively referred to as -side reflected diffracted light (a'1).

  FIG. 13 shows that in the wavelength selective filter 1 of Example 5, sunlight as incident light L from the first translucent substrate 3 side to the normal direction A2 of the main surface 2 ′ of the deflectable diffraction grating 2 ′. These are reflection characteristics and transmission characteristics when the polarization direction is TE polarized light when incident at an incident angle θi of 30 °. FIG. 13A shows reflection characteristics, and FIG. 13B shows transmission characteristics. Even when the polarization direction was TM polarized light, the reflection characteristics and transmission characteristics were almost the same.

  As shown in FIG. 13A, the deflectable diffraction grating 2 'generates -side reflected diffracted light (reflected diffracted light including a number of -orders) a'1 in the infrared wavelength region. The reflection angle of the generated -side reflected diffracted light with respect to the normal direction A2 is 33.8 ° at a wavelength of 870 nm, 34.7 ° at a wavelength of 960 nm, 35.0 ° at a wavelength of 1060 nm, and 34.5 at a wavelength of 1170 nm. And 34.7 ° at a wavelength of 1320 nm. That is, light in the infrared wavelength region (infrared rays) is selected and retroreflected.

  In Example 5, the generation of 0th-order reflected diffracted light and + order reflected diffracted light (+ side reflected diffracted light) in other wavelength regions was almost negligible.

  Further, as shown in FIG. 13B, light (0th order transmitted light b <b> 1) in the visible light wavelength region is transmitted by the deflectable diffraction grating 2 ′ and emitted from the second light transmissive substrate 4. Note that the -order transmitted light (-side transmitted light) and the + order transmitted light (+ side transmitted light) were almost negligible.

  As described above, the first medium 2a and the second medium 2b having different refractive index modulation periods are alternately inclined and laminated every predetermined period (5 periods in the present embodiment), so that a wide wavelength range can be obtained. A high reflectance can be realized, and the wavelength range of infrared light that is retroreflected and the overlapping degree of each reflection peak can be controlled.

<Comparative example 1>
FIG. 14 is a schematic configuration diagram illustrating a wavelength selection filter in the first comparative example.

  As illustrated in FIG. 14, the wavelength selection filter in Comparative Example 1 has a first layer 20 having a light-transmitting refractive index of 1.52 and a thickness d1 of 150 nm, and a light-transmitting refractive index of 1.72. And the second layer 21 having a thickness d2 of 150 nm alternately stacked (16 layers in this comparative example 1), and a refractive index of 1.52 provided on both surfaces of the stacked body 22, respectively. The first and second light-transmitting substrates 23 and 24 such as a transparent resin sheet having a thickness of 2000 nm (2 μm) are used.

  FIG. 15 shows that in the wavelength selective filter of Comparative Example 1, sunlight is incident as incident light L at an incident angle θi of 30 ° with respect to the normal direction of the laminate 12 from the second translucent substrate 24 side. The reflection characteristics and the transmission characteristics when the polarization direction is TE polarized light. FIG. 15A shows reflection characteristics, and FIG. 15B shows transmission characteristics.

  As shown in FIG. 15A, a part of the light in the infrared wavelength region (infrared rays) is selected and regularly reflected (0th-order reflection a) by the laminate 12. Note that some of the light in the visible light region is also slightly specularly reflected (0th-order reflection). Further, in the wavelength selective filter of Comparative Example 1, the generation of −1st order reflected light and + 1st order reflected light was almost negligible.

  Further, as shown in FIG. 15B, light (0th-order transmitted light b) in the visible light wavelength region is transmitted by the laminate 12 and is emitted from the second light-transmitting substrate 14. The −1st order transmitted light and the + 1st order transmitted light were almost negligible.

  Thus, in the wavelength selective filter of Comparative Example 1, only a part of the light in the infrared wavelength range (infrared) is selected and specularly reflected (zero-order reflection), and no retroreflectivity is obtained. .

<Comparative example 2>
FIG. 16 is a schematic configuration diagram illustrating a wavelength selection filter in the second comparative example.

  As shown in FIG. 16, the wavelength selection filter in Comparative Example 2 has a first medium 30 having a light-transmitting refractive index of 1.52 and a width d1 of 300 nm, and a light-transmitting refractive index of 1.72. A diffraction grating 32 having a configuration in which second media 31 having a width d2 of 300 nm are alternately arranged with a period of 600 nm, and a refractive index of 1.72 and a thickness of 2000 nm (2 μm) provided on both surfaces of the diffraction grating 32, respectively. It is comprised with 1st, 2nd translucent base materials 33 and 34, such as a transparent resin sheet. The height h of the diffraction grating 22 is 4000 nm (4 μm).

  FIG. 17 shows that in the wavelength selective filter of Comparative Example 2, sunlight is incident as incident light L at an incident angle θi of 30 ° with respect to the normal direction of the diffraction grating 32 from the first translucent substrate 13 side. The reflection characteristics and the transmission characteristics when the polarization direction is TE polarized light. Note that FIG. 17A shows reflection characteristics, and FIG. 17B shows transmission characteristics.

  As shown in FIG. 17A, only a part of the light in the infrared wavelength region (infrared) is specularly reflected (0th-order reflection a) by the diffraction grating 32, and almost no reflection occurs in other wavelength regions. There wasn't.

  Further, as shown in FIG. 17B, light (0th order transmitted light b1 and −1st order transmitted light b2) from the visible wavelength range to the infrared wavelength range that has passed through the diffraction grating 2 is diffracted. The + 1st order transmitted light was almost negligible.

  Thus, the wavelength selective filter of Comparative Example 2 does not provide retroreflectivity of light in the infrared wavelength region (infrared rays).

  As shown in the table above, in the wavelength selective filters of Examples 1 to 5, the -order reflection diffraction efficiency was 29 to 100%. However, in the wavelength selective filters of Comparative Examples 1 and 2, the -order reflection was performed. The diffraction efficiency was 0%. In the wavelength selective filters of Examples 1 to 5, the ratio (Er / Rmax) between the reflectance (Rmax) at the wavelength having the maximum reflectance in the infrared wavelength region and the -order reflection diffraction efficiency (Er) is 0. In the wavelength selective filters of Comparative Examples 1 and 2, Er / Rmax was 0.00.

(Window glass provided with the wavelength selective filter 1 of the present invention)
As shown in FIG. 18, when the wavelength selective filter 1 having the above-described deflecting diffraction grating 2 is arranged on the outer surface (or the inner surface) of a window glass 40 as a window material of a building such as a building, it is obliquely upward. When the sunlight L is incident from the light, only the first-order reflected diffracted light a1 that is light in the infrared wavelength range (infrared rays) is selected and retroreflected as described above, and the light is in the visible wavelength range (visible light). Only the 0th-order transmitted light b1 is transmitted.

  As this deflectable diffraction grating 2, for example, the one having the configuration of the first embodiment can be used.

  Thus, by arranging the deflectable diffraction grating 2 on the window glass 40, only visible light in the sunlight is transmitted through the window glass 40, and infrared rays contained in the sunlight are recursed toward the incident direction side of the sunlight. Can be reflected.

  Thereby, since infrared rays are retroreflected toward the incident direction side of sunlight, the temperature rise in the room inside the window glass 40 can be suppressed, and the reflected infrared rays do not go to the ground surface side. Temperature rise can also be suppressed. Therefore, it is possible to suppress a temperature rise due to a heat island phenomenon particularly in an urban area where buildings are densely packed, so that it is possible to reduce energy consumption for indoor cooling.

  In addition to installing the wavelength selection filter 1 on a window glass of a building, infrared rays included in sunlight by installing the wavelength selection filter 1 on a window glass (front window, side window, rear window, etc.) of a vehicle such as an automobile, for example. Can be retroreflected toward the incident direction of sunlight, so that the reflected infrared rays can be significantly suppressed from illuminating the road surface of the road.

DESCRIPTION OF SYMBOLS 1 Wavelength selection filter 2, 2 'Deflection diffraction grating 2a 1st medium 2b 2nd medium 3 1st translucent base material 4 2nd translucent base material 40 Window glass a1-1st-order reflection diffraction light

Claims (10)

A first medium having a light-transmitting refractive index n1 and a second medium having a light-transmitting refractive index n2 (n2 ≠ n1) are alternately and periodically stacked, and the stacking direction is inclined. , the inclination direction Ri same der in the plane, the stacked first, the end faces of the longitudinal side of the second medium is in the respective coplanar, and wherein the Ru respective end faces parallel der Comprising a deflectable diffraction grating having a refractive index modulation structure;
The refractive index modulation structure of the deflecting diffraction grating by allowing the light to enter from the stacking direction side of the first and second media with respect to the normal direction of the surface on the light incident side of the deflecting diffraction grating. To select and retroreflect light of the first wavelength band that is the −1st order reflected diffracted light of the incident light, and transmit light of the second wavelength band different from the first wavelength band. A wavelength selective filter having a retroreflective characteristic.   The angle α is 10 to 80 °, where α is an angle formed by the normal direction of the surface on the light incident side of the deflecting diffraction grating and the stacking direction of the first and second media. The wavelength selective filter having retroreflectivity according to claim 1.   3. The retroreflective property according to claim 1, wherein a period p in the stacking direction of the first medium and the second medium stacked in an inclined manner is p, and a width of the period p is 100 to 1000 nm. A wavelength selective filter having:   The wavelength selective filter according to claim 3, wherein the periods p are set to have the same width.   4. The wavelength selective filter having retroreflectivity according to claim 3, wherein the period p is set to at least a first width and a second width different from the first width.   6. The wavelength selective filter having retroreflectivity according to claim 1, wherein the thickness t of the deflectable diffraction grating is set to at least 500 nm, where t is a thickness.   A first translucent substrate is disposed on the surface of the deflecting diffraction grating on which the light beam is incident, and a second translucent substrate is disposed on the surface of the deflecting diffraction grating opposite to the surface on which the light beam is incident. The refractive index of the said 1st, 2nd translucent base material is substantially the same as the refractive index of the said 1st medium or the said 2nd medium, The 1st thru | or 6 characterized by the above-mentioned. The wavelength selective filter which has the retroreflective property as described in any one of these.   The light in the first wavelength band is light in an infrared wavelength band, and the light in the second wavelength band is light in a visible light wavelength band. The wavelength selective filter which has the retroreflective property of description.   When the incident angle of the light beam incident on the deflecting diffraction grating is 30 °, the average transmittance in the wavelength range of visible light transmitted through the deflecting diffraction grating is 80% or more, and the maximum reflection in the infrared wavelength range. 9. The recursion according to claim 8, wherein the ratio is 20%, and the ratio of the reflectance at the wavelength having the maximum reflectance in the infrared wavelength region to the negative-order reflection diffraction efficiency is 0.8 or more. A wavelength selective filter having reflectivity.   A window material comprising the wavelength selective filter having retroreflectivity according to any one of claims 1 to 9 disposed on a glass outer surface or inner surface having translucency.