Multilayer optical film for solar thermal generation

Abstract

An optical film including a first layer packet and a second layer packet. The first layer packet includes a plurality of first optical repeat units (ORUs), each of the first ORUs including at least two different polymeric layers comprising an A material and a B material arranged in an AB pattern. The second layer packet includes a plurality of second ORUs, each of the second ORUs including at least three different polymeric layers comprising the A material, the B material, and a C material, arranged in an ACBC pattern. For a substantially collimated, substantially normally incident light and each of first and second polarization states, the optical film reflects at least 60% of the incident light in each of a green wavelength range and an infrared wavelength, and the film transmits at least 60% of the incident light in each of a blue wavelength range and a red wavelength range.

Description

PA103181W002MULTILAYER OPTICAL FILM FOR SOLAR THERMAL GENERATIONSummary

[0001] In some aspects of the present description, an optical film is provided, the optical film including a first layer packet and a second layer packet. The first layer packet includes a plurality of first optical repeat units (ORUs) co-extruded and co-stretched with one another. Each of the first ORUs has an average physical thickness of less than about 1000 nm and includes at least two different polymeric layers comprising an A material and a B material arranged in an AB pattern. The second layer packet comprising a plurality of ORUs co-extruded and co-stretched with one another. Each of the second ORUs has an average physical thickness of less than about 1000 nm and includes at least three different polymeric layers comprising the A material, the B material, and a C material, arranged in an ACBC pattern. For a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, the optical film reflects at least 60% of the incident light in each of a green wavelength range extending continuously from about 500 nm to about 600 nm and an infrared wavelength range extending continuously from about 800 nm to about 1600 nm, and transmits at least 60% of the incident light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm, and a red wavelength range extending continuously from about 650 nm to about 700 nm.

[0002] In some aspects of the present description, a multilayer optical film includes a plurality of optical interference layers. The plurality of optical interference layers has a layer thickness profile which include a first section, a second section, and a third section. For a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, the first section of the layer thickness profile is configured such that the multilayer optical film reflects at least 60% of the incident light in a green wavelength range extending continuously from about 500 nm to about 600 nm and transmits at least 60% of the incident light outside the green wavelength range; the second section of the layer thickness profile is configured such that the multilayer optical film reflects at least 60% of the incident light in a first infrared wavelength range extending from about 800 to about 1200 nm and transmits at least 60% of the incident light outside the first infrared wavelength range; and the third section of the layer thickness profile is configured such that the multilayer optical film reflects at least 60% of the incident light in a second infrared wavelength range extending from about 1200 nm to about 1600 nm and transmits at least 60% of the incident light outside the second infrared wavelength range.

[0003] In some aspects of the present description, an optical stack includes a first optical film disposed on a second optical fdm. For a substantially collimated, substantially normally incident light and for each of mutually orthogonal first and second polarization states, the first optical film reflects at least 60% of the incident light in each of a green wavelength range extending continuously from about 500 nm to about 600 nm and a first infrared wavelength range extending continuously from about 800 nm to about 1100 nm; and transmits at least 60% of the incident light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm, a red wavelength range extending continuously from about 650 nm to about 700 nm, and a second infrared wavelength range extending continuously from about 1200 nm to about 1600 nm. For the substantially collimated, substantially normally incident light and each of the mutually orthogonal first and second polarization states, the second optical film transmits at least 60% of the incident light in a first wavelength range extending continuously from about 400 nm to about 1200 nm and reflects at least 60% of the incident light in a third infrared wavelength range extending from about 1200 nm to about 1600 nm.Brief Description of the Drawings

[0004] FIG. 1 is an illustration of an optical system for use in a greenhouse, in accordance with an embodiment of the present description;

[0005] FIG. 2 illustrates the layered structure of an optical film for use in a greenhouse, in accordance with an embodiment of the present description;

[0006] FIGS. 3 A-3B are a transmission curve and layer thickness profile for an optical film known in the art;

[0007] FIGS. 4A-4B are a transmission curve and layer thickness profile for an optical film for use in a greenhouse, in accordance with an embodiment of the present description;

[0008] FIGS. 5A-5B are a transmission curve and layer thickness profile for an optical film for use in a greenhouse with an increased number of optical repeat units, in accordance with an alternate embodiment of the present description;

[0009] FIGS. 6A-6B are a transmission curve and layer thickness profile for an optical film for use in a greenhouse showing improved performance, in accordance with an alternate embodiment of the present description;

[0010] FIGS. 7A-7B are a transmission curve and layer thickness profile for an optical film for use in a greenhouse including improved transmission of ultraviolet wavelengths, in accordance with an alternate embodiment of the present description; and

[0011] FIG. 8 illustrates the layered structure of an optical stack including a first and second optical film for use in a greenhouse, in accordance with an embodiment of the present description.Detailed Description

[0012] In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.

[0013] Greenhouses are essential for controlled-environment agriculture, allowing for the cultivation of plants in regions and seasons where outdoor growing conditions are not favorable. However, the efficiency of greenhouses can be significantly impacted by the management of solar energy. Traditional greenhouse designs often struggle to balance the need for optimal light conditions for plant growth with the need to manage excess heat, which can lead to overheating and increased cooling costs.

[0014] One approach to address this issue involves the use of optical films that can selectively reflect and transmit different wavelengths of light. These fdms can help manage the solar spectrum to enhance plant growth while also capturing or reflecting excess solar energy. However, existing solutions have limitations in their ability to effectively split the solar spectrum in a way that maximizes both plant growth and energy efficiency.

[0015] Previous inventions have explored the use of multilayer optical films for photovoltaic (PV) generation in greenhouses. These films are designed to reflect certain wavelengths of light that are not useful for plant growth towards PV cells, thereby generating electricity while allowing the remaining light to pass through to the plants. For example, one system involves a multilayer optical film designed for PV systems in greenhouses, which reflects light up to 1200 nm to match the absorption capabilities of silicon PV cells.

[0016] However, these PV systems are limited by their inability to utilize longer wavelengths of light beyond 1200 nm, which are abundant in the solar spectrum. This limitation reduces the overall efficiency of solar energy capture and utilization in greenhouses. Additionally, the focus on PV generation does not address the need for thermal energy management, which is crucial for maintaining optimal growing conditions in greenhouses.

[0017] Given the limitations of existing PV-based optical films, there is a clear need for a new solution that can more effectively manage the solar spectrum for greenhouse applications. There is a need for a solution that can reflect light in the green and infrared ranges towards a solarthermal absorber, which can convert this light into thermal energy, and transmit light in the blue and red regions, which are essential for plant growth, to the plants in the greenhouse. It may also be useful to provide increased transmission in the ultraviolet (UV) range to further benefit plant growth.

[0018] According to some aspects of the present description, an optical film includes a first layer packet and a second layer packet, wherein each layer packet includes a plurality of optical repeat units, or ORUs. In some embodiments, the first layer packet may include a plurality of first ORUs which are co-extruded and co-stretched with one another. In some embodiments, each of the first ORUs may have an average physical thickness of less than about 1000 nm and may include at least two different polymeric layers comprising an A material and a B material arranged in a repeating, alternating AB pattern.

[0019] In some embodiments, the second layer packet may include a plurality of second ORUs which are co-extruded and co-stretched with one another. In some embodiments, each of the second ORUs may have an average physical thickness of less than about 1000 nm and may include at least three different polymeric layers the A material, the B material, and a third C material, arranged in an ACBC pattern.

[0020]

[0021] In some embodiments, the optical film may be a multilayer optical film structured as a stack or multiple stacks of microlayers, where “microlayers” refer to layers that are sufficiently thin so that light reflected at a plurality of interfaces between such layers undergoes constructive or destructive interference to give the multilayer optical film the desired reflective or transmissive properties. For example, the optical film described herein may include a plurality of microlayers arranged into optical repeat units, or ORUs, where an ORU is the smallest set of layers that recur in a repeating pattern throughout the thickness of the stack. The first layer packet, for example, has ORUs which each include two microlayers, an A microlayer and a B microlayer, where A and B are different polymeric materials that are selected such that the difference in the refractive indices of the two different materials can be configured to change the optical properties of the first layer packet (e.g., to configure it to transmit some wavelengths of light while reflecting others).

[0022] The A and B microlayers have different refractive index characteristics so that some light is reflected at interfaces between adjacent micro layers. For optical films designed to reflect light at ultraviolet, visible, or near-infrared wavelengths, each microlayer typically has an optical thickness (i.e., a physical thickness multiplied by refractive index) of less than about 1 micrometer. Thicker layers can, however, also be included, such as skin layers at the outer surfaces of the film, or protective boundary layers disposed within the film that separate packets of microlayers, as desired.

[0023] Refractive indices of one of the microlayers (e.g., the A layer) may be different depending on the wavelength of light encountering the microlayers, and the refractive indices may be different for light polarized along each of the principal x-, y-, and z-axes (e.g., nx, ny, and nz). The mutually orthogonal x-, y-, and z-axes can, for example, correspond to the principal directions of the dielectric tensor of the material. In many embodiments, and for discussion purposes, the principle directions of the different materials are coincident, but this need not be the case in general. The refractive indices of an adjacent microlayer (e.g., a B layer) may have different refractive indices along the same axes.

[0024] The differences in refractive index between these layers are Anx (=nxa-nxb) along the x-direction, Any (=nya-nyb) along the y-direction, and Anz (=nza-nzb) along the z-direction. The nature of these refractive index differences, in combination with the number of microlayers in the fdm (or in a given stack or layer packet of the film) and their thickness distribution, control the reflective and transmissive characteristics of the film (or of the given stack of the film).

[0025] For example, if adjacent microlayers have a large refractive index mismatch along one in-plane direction (Anx large) and a small refractive index mismatch along the orthogonal in-plane direction (Any~0), the film or packet may behave as a reflective polarizer for normally incident light. A reflective polarizer may be considered to be an optical body that strongly reflects normally incident light that is polarized along one in-plane axis, referred to as the “block axis,” if the wavelength is within the reflection band of the packet, and strongly transmits such light that is polarized along an orthogonal in-plane axis, referred to as the “pass axis.” If desired, the refractive index difference (Anz) between adjacent microlayers for light polarized along the z-axis can also be tailored to achieve desirable reflectivity properties for the p-polarization component of obliquely incident light.

[0026] As discussed elsewhere herein, two or more layer packets (e.g., the first and second layer packets) may be combined to create a single optical film with the desired optical properties. In the embodiment described here, for example, the first packet may contain ORUs which are arranged in an AB pattern (i.e., each ORU contains a microlayer of an A material paired with a microlayer of a B material) and have a layer thickness profile (a plot of microlayer thickness versus microlayer number) in which the thicknesses of the micro layers may change across the entire layer packet, from one ORU to the next, in order to further configure the optical properties of the first layer packet. In a similar manner, the second layer packet in this embodiment may have ORUs in which each ORU contains 3 microlayers, and A, B, and C microlayer. It is this design of the ORUs and the configuration, number, and thickness profiles of the microlayers which determines the exact optical characteristics of the resulting optical film or optical stack.

[0027] In some embodiments, for a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, the optical film may reflect at least 60% of the incident light in each of a green wavelength range extending continuously from about 500 nm to about 600 nm, and an infrared wavelength range extending continuously from about 800 nm to about 1600 nm (or to about 1700 nm, or to about 1800 nm). For a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, the optical film may further transmit at least 60% of the incident light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm, and a red wavelength range extending continuously from about 650 nm to about 700 nm.

[0028] In some embodiments, for the substantially collimated, substantially normally incident light and each of the mutually orthogonal first and second polarization states, the optical film may further transmit at least 60% of an ultraviolet wavelength range extending from about 320 nm to about 400 nm.

[0029] In some embodiments of the optical film, the A material may include polyethylene naphthalate (PEN), the B material may include polymethyl methacrylate (PMMA), and the C material may include a copolymer of polyethylene naphthalate (CoPEN). In some other embodiments of the optical fdm, the A material may include polyethylene terephthalate (PET), the B material may include a copolymer of poly methyl methacrylate (CoPMMA), and the C material may include polyethylene terephthalate gly col-modified (PETg).

[0030] Other polymeric materials, including variants of those described herein, are possible for an optical film within the scope of the present description, if other combinations of materials collectively create a certain relationship among the refractive indices such that the optical film thus composed substantially meets the optical characteristics defined herein. For example, in some embodiments and for a substantially collimated, substantially normally incident light having a wavelength of about 630 nm, the A material of the first and second layer packets may have a first index of refraction nxa in a first in-plane direction (e.g., the x-axis) of the optical film, the B material may have a corresponding first index of refraction nxb in the same first in-plane direction, and the C material may have a corresponding first index of refraction nxc in the same first in-plane direction, such that an absolute value of nxc - (nxa + nxb) / 2 is less than about 4%, or less than about 3%, or less than about 2%, or less than about 1%. Any appropriate combination of A, B, and C polymeric materials that creates such a relationship of refractive indices, and which meets the optical characteristics (i.e., the transmission and reflection of certain wavelength ranges) as described herein, may be used to create the layer packets.

[0031] In some embodiments, an optical system for use in a greenhouse or a similar environment may include any of the optical films or optical stacks described herein, a thermal receiver, and an optical receiver. In some embodiments, the thermal receiver (e.g., a thermal absorber, such as a black body or a water tank) may be disposed on a first side of the optical fdm and may be configured to receive wavelengths of light in the green and infrared wavelength range (i.e., the light that is reflected by the optical film back toward the thermal receiver). In some embodiments, the optical receiver (e.g., plants in a greenhouse) may be disposed on a second side of the optical film (opposite the first side) and may be configured to receive wavelengths of light in the blue and red wavelength ranges (i.e., the light that is transmitted through the film to the plants or other optical receiver, and which may be useful energy for the optical receiver).

[0032] According to some aspects of the present description, a multilayer optical film includes a plurality of optical interference layers. In some embodiments, the plurality of optical interference layers includes a layer thickness profile that includes a first section, a second section, and a third section.

[0033] In some embodiments, for a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, the first section of the layer thickness profile may be configured such that the multilayer optical film reflects at least 60% of the incident light in a green wavelength range extending continuously from about 500 nm to about 600 nm and transmits at least 60% of the incident light outside the green wavelength range.

[0034] In some embodiments, the second section of the layer thickness profile may be configured such that the multilayer optical film reflects at least 60% of the incident light in a first infrared wavelength range extending from about 800 nm to about 1200 nm and transmits at least 60% of the incident light outside the first infrared wavelength range.

[0035] In some embodiments, the third section of the layer thickness profile may be configured such that the multilayer optical film reflects at least 60% of the incident light in a second infrared wavelength range extending from about 1200 nm to about 1600 nm (or about 1700 nm, or about 1800 nm) and transmits at least 60% of the incident light outside the second infrared wavelength range.

[0036] In some embodiments, the multilayer optical film may further include a first layer packet and a second layer packet. In some embodiments, the first layer packet may include a plurality of first optical repeat units (ORUs) which are co-extruded and co-stretched with one another. In some embodiments, each of the first ORUs may have an average physical thickness of less than about 1000 nm and may include at least two different polymeric layers comprising an A material and a B material arranged in a repeating, alternating AB pattern.

[0037] In some embodiments, the second layer packet may include a plurality of second ORUs which are co-extruded and co-stretched with one another. In some embodiments, each of the second ORUs may have an average physical thickness of less than about 1000 nm and may include at least three different polymeric layers comprising the A material, the B material, and a third C material, arranged in an ACBC pattern.

[0038] In some embodiments of the multilayer optical film, the A material may include polyethylene naphthalate (PEN), the B material may include polymethyl methacrylate (PMMA), and the C material may include a copolymer of polyethylene naphthalate (CoPEN). In some other embodiments of the multilayer optical fdm, the A material may include polyethylene terephthalate (PET), the B material may include a copolymer of polymethyl methacrylate (CoPMMA), and the C material may include polyethylene terephthalate glycol-modified (PETg).

[0039] Other polymeric materials, including variants of those described herein, are possible for a multilayer optical film within the scope of the present description, if other combinations of materials collectively create a certain relationship among the refractive indices such that the multilayer optical film thus composed substantially meets the optical characteristics defined herein. For example, in some embodiments and for a substantially collimated, substantially normally incident light having a wavelength of about 630 nm, the A material of the first and second layer packets may have a first index of refraction nxa in a first in-plane direction (e.g., the x-axis) of the multilayer optical film, the B material may have a corresponding first index of refraction nxb in the same first in-plane direction, and the C material may have a corresponding first index of refraction nxc in the same first in-plane direction, such that an absolute value of nxc - (nxa + nxb) / 2 is less than about 4%, or less than about 3%, or less than about 2%, or less than about 1%.

[0040] Any appropriate combination of A, B, and C polymeric materials that creates such a relationship of refractive indices, and which meets the optical characteristics (i.e., the transmission and reflection of certain wavelength ranges) as described herein, may be used to create the layer packets.

[0041] In some embodiments, an optical system for use in a greenhouse or a similar environment may include any of the multilayer optical films or optical stacks described herein, a thermal receiver, and an optical receiver. In some embodiments, the thermal receiver (e.g., a thermal absorber, such as a black body or a water tank) may be disposed on a first side of the multilayer optical film and may be configured to receive wavelengths of light in the green wavelength range and the first and second infrared wavelength ranges (i.e., the light that is reflected by the multilayer optical film back toward the thermal receiver).

[0042] In some embodiments, the optical receiver (e.g., plants in a greenhouse) may be disposed on a second side of the multilayer optical film (opposite the first side) and may be configured to receive wavelengths of light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm and a red wavelength range extending continuously from about 650 nm to about 700 nm (i.e., the light that is transmitted through the film to the plants or other optical receiver, and which may be useful energy for the optical receiver).

[0043] According to some aspects of the present description, an optical stack includes a first optical film disposed on a second optical film. In some embodiments, the first optical film, for a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, may reflect at least 60% of the incident light in each of a green wavelength range extending continuously from about 500 nm to about 600 nm, and a first infrared wavelength range extending continuously from about 800 nm to about 1100 nm.

[0044] Additionally, the first optical fdm may transmit at least 60% of the incident light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm, a red wavelength range extending continuously from about 650 nm to about 700 nm, and a second infrared wavelength range extending continuously from about 1200 nm to about 1600 nm.

[0045] In some embodiments, the second optical film, for the substantially collimated, substantially normally incident light and each of the mutually orthogonal first and second polarization states, may transmit at least 60% of the incident light in a first wavelength range extending continuously from about 400 nm to about 1200 nm and reflect at least 60% of the incident light in a third infrared wavelength range extending from about 1200 nm to about 1600 nm (or about 1700 nm, or about 1800 nm).

[0046] In some embodiments, the first optical film may include a plurality of first optical repeat units (ORUs) which are co-extruded and co-stretched with one another. In some embodiments, each of the first ORUs may have an average physical thickness of less than about 1000 nm and may include at least two different polymeric layers including an A material and a B material arranged in a repeating, alternating AB pattern.

[0047] In some embodiments, the second optical film may include a plurality of second ORUs which are co-extruded and co-stretched with one another. In some embodiments, each of the second ORUs may have an average physical thickness of less than about 1000 nm and may include at least three different polymeric layers comprising the A material, the B material, and a third C material, arranged in an ACBC pattern.

[0048] In some embodiments of the optical stack, the A material may include polyethylene naphthalate (PEN), the B material may include polymethyl methacrylate (PMMA), and the C material may include a copolymer of polyethylene naphthalate (CoPEN). In some otherembodiments of the optical stack, the A material may include polyethylene terephthalate (PET), the B material may include a copolymer of polymethyl methacrylate (CoPMMA), and the C material may include polyethylene terephthalate glycol-modified (PETg).

[0049] Other polymeric materials, including variants of those described herein, are possible for an optical stack within the scope of the present description, if other combinations of materials collectively create a certain relationship among the refractive indices such that the optical stack thus composed substantially meets the optical characteristics defined herein. For example, in some embodiments and for a substantially collimated, substantially normally incident light having a wavelength of about 630 nm, the A material of the first and second optical films may have a first index of refraction nxa in a first in-plane direction (e.g., the x-axis) of the optical stack, the B material may have a corresponding first index of refraction nxb in the same first in-plane direction, and the C material may have a corresponding first index of refraction nxc in the same first in-plane direction, such that an absolute value of nxc - (nxa + nxb) / 2 is less than about 4%, or less than about 3%, or less than about 2%, or less than about 1%.

[0050] Any appropriate combination of A, B, and C polymeric materials that creates such a relationship of refractive indices, and which meets the optical characteristics (i.e., the transmission and reflection of certain wavelength ranges) as described herein, may be used to create the optical films.

[0051] In some embodiments, an optical system for use in a greenhouse or a similar environment may include any of the optical stacks or optical films described herein, a thermal receiver, and an optical receiver. In some embodiments, the thermal receiver (e.g., a thermal absorber, such as a black body or a water tank) may be disposed on a first side of the optical stack and may be configured to receive wavelengths of light in the green wavelength range and the first and second infrared wavelength ranges (i.e., the light that is reflected by the optical stack back toward the thermal receiver). In some embodiments, the optical receiver (e.g., plants in a greenhouse) may be disposed on a second side of the optical stack (opposite the first side) and may be configured to receive wavelengths of light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm and a red wavelength range extending continuously from about 650 nm to about 700 nm (i.e., the light that is transmitted through the stack to the plants or other optical receiver, and which may be useful energy for the optical receiver).

[0052] Turning now to the figures, FIG. 1 is an illustration of an optical system for use in a greenhouse or a similar application, according to the present description. An optical system 400 includes an optical film 300 (or multiple optical films 300) disposed between an external light source 50 (e.g., the sun) and an optical receiver 20 (e.g., plants in a greenhouse). Light 70 fromexternal light source 50 is incident on optical film 300, and certain wavelengths of light 72 are substantially transmitted through optical film 300 and are incident on optical receiver 20. In some embodiments, transmitted light 72 may include wavelengths of light that may be utilized by optical receiver 20. For example, transmitted light 72 may include light in a blue wavelength range and light in a red wavelength range, as blue and red wavelengths of light can be absorbed and utilized by plants / optical receiver 20 (e.g., for photosynthesis).

[0053] Other wavelengths of light 74, may be reflected by optical film 300, and may be directed toward a thermal receiver 30 (e.g., such as a thermal absorber such as a black body, water tank, etc.). For example, reflected light 74 may include light in a green wavelength range and light in one or more infrared wavelength ranges (as these wavelengths cannot be used by plants / optical receiver 20). The thermal receiver 30 may have the ability to absorb / story heat generated by reflected light 74, which may be used for another purpose (providing heat / energy to another system) or may be redirected / dissipated to keep heat from building up (e.g., redirected out of a greenhouse into space).

[0054] FIG. 2 illustrates the layered structure of an embodiment of an optical film for use in a greenhouse, according to the present description. In some embodiments, optical film 300 may include a first layer packet 300a and a second layer packet 300b.

[0055] First layer packet 300a may include a plurality of first optical repeat units (ORUs) 82ab which are co-extruded and co-stretched with one another. In some embodiments, each first ORU 82ab may have an average physical thickness of less than about 1000 nm. In some embodiments, each first ORU 82ab may include at least two different polymeric layers (microlayers) including an A material 80a and a B material 80b arranged in an AB pattern. In some embodiments, first layer packet 300a may include at least 10, or at least 20, or at least 50, or at least 100 first ORUs 82ab.

[0056] In some embodiments, second layer packet 300b may include a plurality of second ORUs 82acbc co-extruded and co-stretched with one another. In some embodiments, each of the second ORUs 82acbc may also have an average physical thickness of less than about 1000 nm. In some embodiments, each second ORU 82acbc may include at least three different polymeric layers (microlayers) including the same A material 80a, the same B material 80b, and a third C material 80c, arranged in an ACBC pattern. In some embodiments, first layer packet 300b may include at least 10, or at least 20, or at least 50, or at least 100 second ORUs 82acbc.

[0057] In some embodiments, first layer packet 300a may include one or more outer skin layers 85, and second layer packet 300b may include also one or more outer skin layers 85. In some embodiments, one or more outer skin layers 85 may be disposed between first layer packet 300a and second layer packet 300b.

[0058] As described elsewhere herein, the A, B, and C materials used for the microlayers in optical film 300 may be chosen such that the refractive indices of adjacent layers are configured to meet the expected optical characteristics (e.g., transmission and reflection of certain wavelength ranges). The thicknesses (in the z-direction shown in FIG. 2) of the microlayers and the ORUs may also be configured to create the expected optical characteristics of optical film 300 (and first layer packet 300a and second layer packet 300b).

[0059] FIGS. 3 A-3B are a transmission curve and layer thickness profile for an optical film known in the art. The embodiment of this optical film as shown in layer thickness profile of FIG. 3B includes a single layer packet with a first section 95-1 and a second section 95-2. Each of sections 95-1 and 95-2 include ORUs with two polymeric layers arranged in an AB pattern (i.e., the second section 95-2 does not use the ACBC pattern described elsewhere herein). The optical film described by the plots of FIG. 3 A and 3B is designed specifically for photovoltaic (PV) applications (e.g., for use in a greenhouse to split wavelengths into light useful for plants in photosynthesis, which is transmitted, and light that is useful for generating power in a solar cell, which is reflected).

[0060] Looking at FIG. 3 A and plot 90, it can be seen that this optical film has a high transmittance of light in a blue wavelength band 90b, a red wavelength band 90r, and in infrared wavelengths in an infrared range between about 1200 and at least about 1600 nm 90ir2. The blue wavelengths 90b and red wavelengths 90r are transmitted as they represent useful light to the plants (for example) in a greenhouse for photosynthesis. The higher infrared wavelengths 90ir2 are not useful to a solar cell (they generate little electricity and add only additional heat which can damage the solar cell) and so these higher wavelengths are transmitted to keep them away from the solar cell.

[0061] The film of FIG. 3 A also substantially reflects light having green wavelengths 90g and infrared wavelengths between about 800 nm and about 1200 nm 90irl. In this case, the green wavelengths 90g and infrared wavelengths 90irl are considered useful energy for the solar cell, and so they are reflected back toward a solar cell where they can be used.

[0062] While the film described in FIGS. 3A and 3B may be useful for PV applications, the wavelengths of light in the higher infrared wavelength range 90ir2 are substantially wasted (not utilized by the solar cell and may add unwanted temperature to the system). This higher infrared energy 90ir2 could be useful, however, if redirected to a thermal receiver (a thermal absorber) which could use the extra energy in the higher infrared range.

[0063] For example, the embodiment of an optical film detailed in FIGS. 4A-4B exhibit a transmission curve and layer thickness profile which could be most useful in a system such as agreenhouse in which the light that is not useful and thus not transmitted to the plants can be collected by a thermal absorber and utilized, rather than sent to a solar cell.

[0064] In the embodiment of an optical film of FIGS. 4A-4B, the film is configured to have two separate layer packets, a first layer packet 96 AB and a second layer packet 96ACBC. First layer packet 96 AB includes ORUs with two polymeric microlayers arranged in a repeating AB pattern, and these are divided into a first section 96-1 and a second section 96-2. Second layer packet 96ACBC has a single section 96-3 where the ORUs have at least three polymeric microlayers arranged in a repeating ACBC pattern. Each section, 96-1, 96-2, and 96-3, has a particular layer thickness profile that contributes to the overall transmission characteristics of the optical film shown in FIG. 4A.

[0065] For example, for a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, first section 96-1 of the layer thickness profile may be configured such that the multilayer optical film reflects at least 60% of the incident light in a green wavelength range (91g in FIG. 4 A) extending continuously from about 500 nm to about 600 nm and transmits at least 60% of the incident light outside the green wavelength range.

[0066] The second section of the layer thickness profile 96-2 may be configured such that the multilayer optical film reflects at least 60% of the incident light in a first infrared wavelength range 9 lirl extending from about 800 to about 1200 nm and transmits at least 60% of the incident light outside the first infrared wavelength range 91ir2.

[0067] In this embodiment, the first 96-1 and second 96-2 sections are part of a first layer packet having ORUs with two different polymeric materials arranged in microlayers having an AB pattern. The first 96-1 and second 96-2 sections are within the same first layer packet but are distinguished from each other by the discontinuity in layer thickness profile shown in FIG. 4B. In this embodiment, as shown in FIG. 4B, the A material is PET and the B material is CoPMMA.

[0068] The third section of the layer thickness profile may be configured such that the multilayer optical film reflects at least 60% of the incident light in a second infrared wavelength range 91ir2 extending from about 1200 nm to at least about 1600 nm and transmits at least 60% of the incident light outside the second infrared wavelength range 91ir2.

[0069] In this embodiment, third section 96-3 is part of a second layer packet having ORUs with three different polymeric materials arranged in microlayers having an ACBC pattern. In this embodiment, as shown in FIG. 4B, the A material is PET, the B material is CoPMMA, and the C material is PETg.

[0070] The three sections of the layer thickness profile, 96-1, 96-2, and 96-3, contribute to the design of the optical film shown in plot 91 of FIG. 4A, which substantially transmits light in a bluewavelength band 91b, and a red wavelength band 91r, and substantially reflects light in a green wavelength band 91g and an infrared wavelength band 9 lir (including first infrared wavelength range 9 lirl and second infrared wavelength range 91ir2).

[0071] In the particular embodiment and plot 91 of FIG. 4 A, it can be seen that some of the light in the infrared band 9 lir is transmitted, although the overall amount of infrared is substantially reduced overall. Other design considerations can be used to increase the amount of infrared reflection in this band. These considerations are discussed elsewhere herein.

[0072] For example, FIGS. 5A-5B are a transmission curve and layer thickness profile for an alternate embodiment of an optical film for use in a greenhouse with an increased number of optical repeat units. Whereas the embodiment shown in FIG. 4B had 325 AB ORUs in first layer packet 96 AB and an additional 325 ACBC ORUs in second layer packet 96ACBC, the embodiment shown in FIG. 5B has 400 AB ORUs in first layer packet 97 AB and an additional 400 ACBC ORUs in second layer packet 97 ACBC. Increasing the total number of ORUs in the optical film has the effect of further reducing the amount of infrared energy that is transmitted in the total infrared range 92ir (including reduced transmissions in 92ir 1 and 92ir2) as shown in plot 92 of FIG. 5A.

[0073] Plot 92 of FIG. 5 A still shows high transmission in blue wavelengths 92b and red wavelengths 92r, and high reflection in green wavelengths 92g and relatively high reflection in infrared wavelength range 92ir. Plot 97 of FIG. 5B is similar to plot 96 of FIG. 4B, having a first layer packet 97 AB having a first section 97-1 and a second section 97-2, and a second layer packet 97 ACBC having a third section of the optical film 97-3. As with the film of FIGS. 4A-4B, the A material for the embodiment of FIGS. 5A-5B is PET, the B material is CoPMMA, and the C material is PETg.

[0074] The shape of the transmission plot can also be modified by changing the materials used in the microlayers of the optical film. For example, FIGS. 6A-6B show a transmission curve and layer thickness profile for another alternate embodiment of an optical film for use in a greenhouse showing improved performance using PEN-based high-index material to increase optical power.

[0075] In the embodiment of an optical film shown in FIGS. 6A-6B, the A material is PEN, the B material is PMMA, and the C material is CoPEN. The embodiment shown in FIG. 6B, using these materials, has 225 AB ORUs in first layer packet 98AB (including sections 98-1 and 98-2) and an additional 325 ACBC ORUs in second layer packet 98ACBC (including section 98-3).

[0076] By using the PEN-based materials, Plot 93 of FIG. 6A still shows relatively high transmission in blue wavelengths 93b and red wavelengths 93r, and high reflection in green wavelengths 93g as well as high reflection in infrared wavelength range 93ir (a significantreduction in transmission of infrared wavelengths in both 93irl and 93ir2 compared to the films shown in FIGS. 4A and 5A).

[0077] In other embodiments, as ultraviolet (UV) light (between about 320 nm and about 400 nm) has potential benefits for plant growth, it is possible to design an optical fdm to achieve higher transmission in the UV band. For the design to have increased transmission in the UV band, the optical film would likely be based on PET rather than PEN, as PEN has high absorption in the UV band.

[0078] For example, FIGS. 7A-7B are a transmission curve and layer thickness profile for an alternate embodiment of an optical film for use in a greenhouse configured to substantially transmit UV wavelengths. The embodiment shown in FIG. 7B has 400 AB ORUs in first layer packet 99AB and an additional 400 ACBC ORUs in second layer packet 99ACBC. For this embodiment, the A material is PET, the B material is CoPMMA, and the C material is PETg.

[0079] Plot 94 of FIG. 7 A still shows high transmission in blue wavelengths 92b and red wavelengths 92r, and now shows high transmission in ultraviolet wavelengths 92u (those wavelengths below about 400 nm). Plot 94 also shows high reflection in green wavelengths 94g and relatively high reflection in infrared wavelength range 94ir (and including 94ir 1 and 94ir2).

[0080] Finally, FIG. 8 illustrates the layered structure of an optical stack including a first and second optical film for use in a greenhouse, according to the present description. Optical stack 305 of FIG. 8 is similar in structure to optical film 300 shown in FIG. 2, except that instead of being a single optical film 300 with a first layer packet 300a and a second layer packet 300b, optical stack 305 comprises two separate films, first optical film 100 and second optical film 200. Other than the physical separation of the AB packet and the ACBC packet into standalone films, the design concepts described for the first 300a and second 300b layer packets, as well as the layer profiles and films of FIGS. 4A-7B, can be applied to the embodiment using two physically separate films. In this embodiment, first optical film 100 can include only ORUs 82ab which include a matched pair of A layer 80a and B layer 80b and any outer skin layers 85 as needed to meet requirements. Second optical film 200 can then include only ORUs 82acbc which include A layer 80a, B layer 80b, and C layer 80c, as well as any outer skin layers 85 as needed to meet requirements. The embodiment using separate films may be done for the purposes of ease of manufacturing, or to add functionality to an existing optical film (such as that used in the PV applications, such as the example shown in FIGS. 3A-3B).

[0081] Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in thepresent description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.

[0082] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially equal” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially equal” will mean about equal where about is as described above. If the use of “substantially parallel” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially parallel” will mean within 30 degrees of parallel. Directions or surfaces described as substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees of parallel, or may be parallel or nominally parallel. If the use of “substantially aligned” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially aligned” will mean aligned to within 20% of a width of the objects being aligned. Objects described as substantially aligned may, in some embodiments, be aligned to within 10% or to within 5% of a width of the objects being aligned.

[0083] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0084] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed:

1. An optical film comprising a first layer packet and a second layer packet, the first layer packet comprising a plurality of first optical repeat units (ORUs) coextruded and co-stretched with one another, each of the first ORUs having an average physical thickness of less than about 1000 nm and comprising at least two different polymeric layers comprising an A material and a B material arranged in an AB pattern; the second layer packet comprising a plurality of second optical repeat units (ORUs) coextruded and co-stretched with one another, each of the second ORUs having an average physical thickness of less than about 1000 nm and comprising at least three different polymeric layers comprising the A material, the B material, and a C material, arranged in an ACBC pattern; such that, for a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, the optical film: reflects at least 60% of the incident light in each of a green wavelength range extending continuously from about 500 nm to about 600 nm, and an infrared wavelength range extending continuously from about 800 nm to about 1600 nm; and transmits at least 60% of the incident light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm, and a red wavelength range extending continuously from about 650 nm to about 700 nm.

2. The optical film of claim 1, wherein, for a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, the optical film transmits at least 60% of an ultraviolet wavelength range extending from about 320 nm to about 400 nm.

3. The optical film of claim 1, wherein the A material comprises polyethylene naphthalate (PEN), the B material comprises polymethyl methacrylate (PMMA), and the C material comprises a copolymer of polyethylene naphthalate (CoPEN).

4. The optical film of claim 1, wherein the A material comprises polyethylene terephthalate (PET), the B material comprises a copolymer of polymethyl methacrylate (CoPMMA), and the C material comprises polyethylene terephthalate glycol-modified (PETg).

5. The optical film of claim 1, wherein, for a substantially collimated, substantially normally incident light having a wavelength of about 630 nm, the A material has a first index of refractionnxa in a first in-plane direction of the optical film, the B material has a corresponding first index of refraction nxb in the first in-plane direction, and the C material has a corresponding first index of refraction nxc in the first in-plane direction, such that an absolute value of nxc - (nxa + nxb) / 2 is less than about 4% (or 3%, or 2%, or 1%)6. An optical system, comprising the optical film of claim 1; a thermal receiver disposed on a first side of the optical film and configured to receive wavelengths of light in the green and infrared wavelength range; and an optical receiver disposed on a second side of the optical film and configured to receive wavelengths of light in the blue and red wavelength ranges.

7. The optical system of claim 6, wherein the thermal receiver comprises a thermal absorber.

8. The optical system of claim 6, wherein the optical receiver comprises one or more plants.

9. A multilayer optical film comprising a plurality of optical interference layers, the plurality of optical interference layers comprising a layer thickness profile comprising a first section, a second section, and a third section; such that, for a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states: the first section of the layer thickness profile is configured such that the multilayer optical film reflects at least 60% of the incident light in a green wavelength range extending continuously from about 500 nm to about 600 nm and transmits at least 60% of the incident light outside the green wavelength range; the second section of the layer thickness profile is configured such that the multilayer optical film reflects at least 60% of the incident light in a first infrared wavelength range extending from about 800 to about 1200 nm and transmits at least 60% of the incident light outside the first infrared wavelength range; and the third section of the layer thickness profile is configured such that the multilayer optical film reflects at least 60% of the incident light in a second infrared wavelength range extending from about 1200 nm to about 1600 nm and transmits at least 60% of the incident light outside the second infrared wavelength range.

10. The multilayer optical film of claim 9, further comprising a first layer packet and a second layer packet, wherein the first layer packet comprises a plurality of first optical repeat units (ORUs) co-extruded and co-stretched with one another, each of the first ORUs having an average physical thickness of less than about 1000 nm and comprising at least two different polymeric layers comprising an A material and a B material, arranged in an AB pattern; and the second layer packet comprises a plurality of second optical repeat units (ORUs) coextruded and co-stretched with one another, each of the second ORUs having an average physical thickness of less than about 1000 nm and comprising at least three different polymeric layers comprising the A material, the B material, and a C material, arranged in an ACBC pattern.

11. The multilayer optical film of claim 10, wherein the A material comprises polyethylene naphthalate (PEN), the B material comprises polymethyl methacrylate (PMMA), and the C material comprises a copolymer of polyethylene naphthalate (CoPEN).

12. The multilayer optical film of claim 10, wherein the A material comprises polyethylene terephthalate (PET), the B material comprises a copolymer of polymethyl methacrylate (CoPMMA), and the C material comprises polyethylene terephthalate gly col-modified (PETg).

13. The multilayer optical film of claim 9, wherein, for a substantially collimated, substantially normally incident light having a wavelength of about 630 nm, the A material has a first index of refraction nxa in a first in-plane direction of the multilayer optical film, the B material has a corresponding first index of refraction nxb in the first in-plane direction, and the C material has a corresponding first index of refraction nxc in the first in-plane direction, such that an absolute value of nxc - (nxa + nxb) / 2 is less than about 4% (or 3%, or 2%, or 1%)14. An optical system, comprising the multilayer optical film of claim 9; a thermal receiver disposed on a first side of the multilayer optical film and configured to receive wavelengths of light in the green wavelength range and the first and second infrared wavelength ranges; and an optical receiver disposed on a second side of the multilayer optical film and configured to receive wavelengths of light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm and a red wavelength range extending continuously from about 650 nm to about 700 nm.

15. The optical system of claim 14, wherein the thermal receiver comprises a thermal absorber.

16. The optical system of claim 14, wherein the optical receiver comprises one or more plants.

17. An optical stack comprising a first optical film disposed on a second optical film; wherein the first optical film, for a substantially collimated, substantially normally incident light and each of mutually orthogonal first and second polarization states, reflects at least 60% of the incident light in each of a green wavelength range extending continuously from about 500 nm to about 600 nm, and a first infrared wavelength range extending continuously from about 800 nm to about 1100 nm; and transmits at least 60% of the incident light in each of a blue wavelength range extending continuously from about 400 nm to about 450 nm, a red wavelength range extending continuously from about 650 nm to about 700 nm, and a second infrared wavelength range extending continuously from about 1200 nm to about 1600 nm; and wherein the second optical film, for the substantially collimated, substantially normally incident light and each of the mutually orthogonal first and second polarization states, transmits at least 60% of the incident light in a first wavelength range extending continuously from about 400 nm to about 1200 nm and reflects at least 60% of the incident light in a third infrared wavelength range extending from about 1200 nm to about 1600 nm.

18. The optical stack of claim 17, wherein the first optical film comprises a plurality of first optical repeat units (ORUs) co-extruded and co-stretched with one another, each of the first ORUs having an average physical thickness of less than about 1000 nm and comprising at least two different polymeric layers comprising an A material and a B material, arranged in an AB pattern; and the second optical film comprises a plurality of second optical repeat units (ORUs) coextruded and co-stretched with one another, each of the second ORUs having an average physical thickness of less than about 1000 nm and comprising at least three different polymeric layers comprising the A material, the B material, and a C material, arranged in an ACBC pattern.

19. The optical stack of claim 18, wherein the A material comprises polyethylene naphthalate (PEN), the B material comprises polymethyl methacrylate (PMMA), and the C material comprises a copolymer of polyethylene naphthalate (CoPEN).

20. The optical stack of claim 18, wherein the A material comprises polyethylene terephthalate (PET), the B material comprises a copolymer of polymethyl methacrylate (CoPMMA), and the C material comprises polyethylene terephthalate gly col-modified (PETg).

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