WO2019169110A1

WO2019169110A1 - Flexible curved components for providing spectral characteristics for large surfaces

Info

Publication number: WO2019169110A1
Application number: PCT/US2019/020013
Authority: WO
Inventors: Sasaan Alexander SHOWGHI; Robert Andrew NORWOOD
Original assignee: Arizona Board Of Regents On Behalf Of The University Of Arizona
Priority date: 2018-02-28
Filing date: 2019-02-28
Publication date: 2019-09-06

Abstract

Methods, devices and systems for providing optical coatings for large and arbitrary-shaped components are disclosed. One example method includes obtaining a plurality of glass substrates, where each substrate has a flat surface and a predetermined thickness in the range 25 microns to 1 centimeter which allows the glass substrate to deform into a non-flat surface in response to an applied force. A coating is applied onto a flat surface of the glass substrate, each coating having predefined spectral characteristics, and each of the glass substrates is deformed so that conforms to a shape of a corresponding section of the target curved surface. Each of the deformed glass substrates are then attached to the corresponding section of the target curved surface, which can have an area in a range 1 square meter to 1000 square meters.

Description

FLEXIBLE CURVED COMPONENTS FOR PROVIDING SPECTRAL

CHARACTERISTICS FOR LARGE SURFACES

RELATED APPLICATIONS

[0001] This application claims priority to the provisional application with serial number 62/636,783, titled“Flexible Curved Reflector,” filed February 28, 2018. The entire contents of the above noted provisional application are incorporated by reference as part of the disclosure of this document.

TECHNICAL FIELD

[0002] This invention was made with government support under Grant Nos. DE-AR0000465 and DE-AR0000830, awarded by DOE. The government has certain rights in the invention.

BACKGROUND

[0003] Optical coatings play an important role in providing desired spectral transmission and reflection characteristics in a variety of optical systems. An optical coating typically includes one or more thin layers of material deposited on an optical component, such as a lens, a mirror, or a prism, at thicknesses that can be on the order of the wavelength of visible light (about 500 nm). While optical coatings may be feasibly applied to small to medium sized optical components with regular shapes, it is generally difficult, and certainly expensive, to provide complex multilayer coatings onto arbitrary curved surfaces. This problem is further exacerbated when large curved substrates are at issue, such as those used to form reflective optics for collimation and concentration in solar power systems. In such scenarios, the dimensions of the coating are often limited to the size of the equipment that is used for depositing the thin film layers, and additional engineering provisions are required, such as rotating the substrate during deposition. In essence, it becomes more difficult and expensive, and in case of very large optics impossible, to meet the size and optical characteristics requirements of such coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 illustrates a test procedure conducted to characterize a flexible glass positioned on a mirror blank in accordance with some embodiments. [0005] FIG. 2 illustrates transmission characteristics of a first set of test locations associated with the configuration of FIG. 1.

[0006] FIG. 3 illustrates transmission characteristics of a second set of test locations associated with the configuration of FIG. 1. [0007] FIG. 4 illustrates transmission characteristics of a third set of test locations associated with the configuration of FIG. 1.

[0008] FIG. 5(a) illustrates an example solar power generation system that includes flexible dichroic filters that are produced in accordance with the disclosed embodiments.

[0009] FIG. 5(b) illustrates a magnified section of FIG. 5(a). [0010] FIG. 6 illustrates a mirror installation procedure for a portion of the solar power generation system of FIG. 5.

[0011] FIG. 7 illustrates example mirrored sections of a solar power generation system of FIG. 5 after installation of the flexible curved mirrors.

[0012] FIG. 8 illustrates an example plot of the transmission spectrum a section of the solar power generation system of FIG. 5 after installation of the flexible curved mirrors.

[0013] FIG. 9(a) illustrates a part of a process for producing free standing curved reflecting surfaces using a flat coated flexible glass in accordance with some embodiments.

[0014] FIG. 9(b) illustrates another part of the process for producing free standing curved reflecting surfaces using a flat coated flexible glass in accordance with some embodiments. [0015] FIG. 9(c) illustrates a process for changing a shape of a free standing curved reflecting surfaces produced using a flat coated flexible glass in accordance with some embodiments.

[0016] FIG. 9(d) illustrates a process for further changing a shape of free standing curved reflecting surfaces produced using a flat coated flexible glass in accordance with some embodiments. [0017] FIG. 10(a) illustrates a top view of a sample blank that is laminated with a flexible glass layer in accordance with some embodiments.

[0018] FIG. 10(b) illustrates a side view of the configuration shown in FIG. 10(a).

[0019] FIG. 11 illustrates a configuration where an example index-matched fluid is positioned between a flexible glass and a substrate blank in accordance with some embodiments.

[0020] FIG. 12 illustrate a set of operations that can be carried out to provide a flexible optical element in accordance with an example embodiment.

[0021] FIG. 13 illustrate a set of operations that can be carried out to provide a filter on a target curved surface in accordance with an example embodiment. DETAILED DESCRIPTION

[0022] The disclosed technology relates to methods, devices and systems for providing optical coatings for large and arbitrary-shaped components.

[0023] An optical coating, in its simplest form, can be formed as a thin metal layer, such as aluminum, silver or even gold, that is deposited on a glass substrate to produce a reflecting surface. To provide better control over the transmission and reflection characteristics, another type optical coating is often implemented by stacking a number of dielectric layers of differing optical materials on top of each other, thereby causing interference of the light waves within the multilayer stack. By selecting the proper number of layers, the proper thicknesses for the layers, the proper sequence of layers and the proper material for each layer, the optical coating becomes a filter that can be designed to provide a desired transmission and/or reflection characteristic. In general, thin film layers can be used to provide optical coatings for different applications including low emissivity panes of glass for houses and cars, anti-reflective coatings on glasses, reflective surfaces for car headlights, precision optical components and the like. A dichroic filter is one example of a thin-film interference filter designed to selectively pass light in a particular range of wavelengths (or colors) while reflecting other wavelengths (or colors). Thin film coatings can also be used to produce spatial filters and phase filters. [0024] In manufacturing, thin film layers are often formed using a physical vapor deposition process, such as evaporation or sputter deposition, or a chemical process such as chemical vapor deposition. It should be noted, however, that the disclosed technology of this patent document is not confined to the above noted thin film deposition techniques, and other processes, such as thermal forming, electroplating techniques, ion implantation, sol gel coating techniques, liquid- based coating techniques, extrusion and others can be used for forming the disclosed coatings.

[0025] Regardless of the particular method that is used to form the thin film layers, it is difficult and expensive to manufacture and apply complex multilayer coatings to large curved surfaces. In many cases, the size of the equipment that is used for deposition of thin films limits the size of the coating and special engineering measures, such as rotating the substrate are required. Moreover, as the size of the substrate for the coating increases, it may become more difficult to achieve a desired uniformity and consistency of the coating. These and other limitations in existing systems make is expensive, and in case of very large curved optics, impossible, to meet the size and optical characteristics requirements for optical coatings. [0026] The disclosed embodiments relate to methods, devices and systems that facilitate provision of coatings and thin film layers on arbitrarily-sized and arbitrarily-shaped curved optical surfaces. The disclosed embodiments overcome the shortcomings of the prior art systems, and provide further benefits and features by, in-part, using a deposition technique to provide a coating on a flat piece of flexible substrate (e.g., glass) that can be subsequently shaped to conform to a particular curved surface. For example, the coated flexible flat sheet can be laminated onto the surface of an arbitrarily-shaped optical component. To provide coatings for large surfaces, multiple smaller-sized coated flat sheets are produced and are placed (e.g., laminated) on the curved surface next to each other in a tiled fashion. As a result, effective, versatile and low-cost solutions for providing optical coatings for curved surfaces are provided that are applicable to arbitrarily large surfaces. The disclosed embodiments find applications in solar power systems (e.g., concentrated photovoltaic systems), telescopes, laser systems, and generally any optical system that requires optical coatings on curved and/or large optical surfaces. [0027] In example embodiments, the coated curved surfaces form curved mirrors (e.g., parabolic or hyperbolic mirrors) that can be laid over a surface and act as a laminating layer. In some example embodiments, the elasticity of the glass substrate allows for the mirrors, with an underlying mechanical constraint, to form free standing contours that act as mirrors. This aspect of the disclosed embodiments is sometimes referred to as pseudo-self-forming. For example, by applying stress to two sides of a thin flexible coating sheet, the sheet can be bent to a desired curvature. In another example, the flexible coating sheet can be pressed or rolled against a blank backing or a mold of a desired shape to transform the flat sheet into a curved format with the desired shape. The flexible glass that is used as a substrate can be coated with metals or stacks of dielectric materials to produce mirrors with various levels of reflectivity and spectral performance. For example, the coated flexible glass can provide a low-cost and improved dichroic filter to replace conventional reflective optics used for collimation and concentration in solar cells. In one example, Coming^® Willow^® glass is used as the flexible glass substrate. In another example, a flexible glass substrate that is optically transparent, is 100-pm thick, and comprises alumino-borosilicate.

[0028] Currently, polymer film and traditional glass represent typical substrates for thin film coatings. Some advantages of the disclosed flexible optical elements over polymer film alternatives include higher optical transparency, improved thermal stability for high temperature applications/processes, reduced coefficient of thermal expansion, improved wear/abrasion resistance, greater mechanical strength, and reduced optical degradation. For example, compared to the traditional polymer films, the disclosed flexible optical elements do not degrade due to exposure to the ultraviolet light. Some advantages over traditional glass mirrors can include scalability for large volume applications (e.g., via tiling), improved thermal/mechanical shock resistance, reduced mass, reduced forming cost (e.g., via pseudo-self-forming), and significant simplification of the thin film coating process.

[0029] The disclosed embodiments further describe methods and devices for affixing curved mirror elements to large substrates through selective lamination processes (e.g., roller, squeegee, etc.), as well as through tongue-in-groove glass constructions that benefit from advanced micromachining processes such as laser cutting and crack propagation. Another aspect of the disclosed embodiments relates to the disposition or placement of an index matching material between the flexible glass element and the underlying glass substrate. This technique is especially advantageous in cases where the flexible mirror element has both reflective and transmissive optical bands. By filling the region between the flexible glass element and the underlying curved glass substrate with index matching liquids, increased transmission, as well as increased mechanical support through strong capillary forces are provided.

[0030] For some applications, it is advantageous to be able to change the optical properties of the system on a temporary basis, for example, for a particular measurement or operation, and/or for a particular duration. These features and benefits are facilitated by the disclosed

embodiments by providing one or more thin optical coating elements than can be removably affixed onto the underlying surface, thereby allowing for the attachment of an alternative flexible component with different optical transmission and reflection bands. For example, when deployed in a hybrid concentrated solar power (CSP)/concentrated photovoltaic (CPV) system, this feature allows the system to be readily reconfigured according to geographic location and seasonal changes. As a result, any one of a plurality of flexible dielectric filters can be attached to support structures and removed to provide easy reconfiguration of the optical system. Such a capability does not exist in traditional optical coatings that are permanently deposited onto optical components.

[0031] FIG. 1 shows a test procedure conducted to characterize Willow^® glass on a mirror blank. In test, a sample was produced by curving the Willow^® glass (without any coatings) 102 to the shape of the mirror blank that was secured using binder clips. The flexible glass conforms practically seamlessly to the curved surface of the mirror blank; note that in the illustration in FIG. 1, the flexible glass is not clearly distinguishable from the blank. A plurality of test locations 104 was identified for optical characterization, arranged in three rows a, b and c, labeled l04a, l04b and lo4c, respectively. To conduct the characterization, a supercontinuum light source 106 was used, along with an integrating sphere 108, and a spectrometer 110. The measured transmittance was used to quantify how well the curved Willow^® glass 102 conforms to the blank backing (e.g., B270 glass). The results indicated good contact having a

transmittance, T, of 92%, with a worse-case scenario of T = 85%. [0032] FIGS. 2 to 4 further illustrate irradiance plots versus wavelength for the test samples shown in FIG. 1. In particular, FIG. 2 illustrates measured irradiance plots for test locations 104 in row a (l04a) of FIG. 1. The plot that is labeled as“Incident” corresponds to the spectrum of the incident radiation put directly into the spectrometer with no Willow^® glass or backing glass in between. FIGS. 3 and 4 show similar plots as in FIG. 2 but for test locations 104 in row b (l04b) and row c (l04c), respectively. As shown in the plots, the test spots across each row exhibit similar behavior. Further, only a small reduction in transmission was observed at each position. This reduction can be attributed at least in-part to the air gap that existed between the Willow^® glass and the blank for this test that were held together using inexpensive means coupling means in the form of binder clips.

[0033] One application of the disclosed technology is in solar power generation systems. These systems often benefit from coatings that allow certain spectral bands (e.g., in the infrared region) of the incident light to be separated and directed elsewhere to generate heat (e.g., for indirect generation of electricity), while allowing other bands to be directed to photovoltaic cells to directly generate electricity. Moreover, a thin film layer can be designed to have special characteristics to improve collection efficiencies in multijunction photovoltaic cells. Due to the large hyperbolic shaped reflecting surfaces, however, it is difficult to provide such coatings in a cost-effective manner using the existing techniques. In contrast, using the disclosed technology, flexible filters with desired reflective and/or transmission characteristics can be provided as smaller tiles and attached to the large reflective surfaces to cover their entire surface.

[0034] FIG. 5(a) and 5(b) illustrate an example solar power system that includes flexible filters that are produced in accordance with the disclosed embodiments. A thin film coating for a dichroic mirror was designed and deposited onto Willow^® glass, a thin flexible glass available from Corning^®. The mirror was then curved to the hyperbolic shape of a previously fabricated mirror blank and secured with standard binder clips 506. One modified section of the solar panels is magnified in the inset as shown in FIG. 5(b), which includes the Willow^® glass mirror. The mirror was installed into the ARPA-E FOCUS hybrid concentrated photovoltaic

(CPV)/concentrated solar power (CSP) system, which generates both direct electricity from photovoltaics and heat (which can be converted to electricity) from the solar thermal section of the system. The Willow^® glass dichroic mirror is designed to distribute some portion of the incident sunlight to the concentrated photovoltaic cells and the remainder to the solar thermal tube.

[0035] FIG. 6 illustrates an actual mirror installation procedure for a portion of the hybrid CPV/CSP system of FIG. 5, in which a technician is affixing the flexible mirror elements onto the mirror blank surface using binder clips. The procedure can simply include placing the tiled (flat) flexible mirrors 602 against the mirror blanks (obfuscated in FIG. 6), and applying the binder clips 604 to secure the flexible mirrors in place. FIG. 7 illustrates the hyperbolic mirrors after the flexible mirror elements have been fastened using the binder clips 704 onto the back surfaces in the hybrid CPV/CSP system of FIG. 5. The plurality of flexible mirrors 702 in FIG. 7, fastened to the backing, collectively form a large hyperbolic surface with the desired reflectivity and transmittance characteristics.

[0036] FIG. 8 illustrates the transmission spectrum (the inverse of the reflection spectrum) of the dichroic Willow^® glass mirror that was installed into the hybrid CSP/CPV system of FIG. 5. Plots that are labeled as Wl and W2 correspond to two different spots on the surface to test the uniformity of the coating. The plot labeled as“incident light” is provided to establish a reference level and corresponds to the transmitted light in the absence of the flexible curved mirrors. As noted earlier, the thin film filters can be designed to produce the desired transmission/reflectance characteristics. The performance of the flexible filter shown in FIG. 8 exhibits a low

transmission levels in a band that starts below 500 nm up to about 900 nm, with a relatively large spike (i.e., high transmission region) between 670-700 nm. This behavior matches well with the design goals for this hybrid CSP/CPV system.

[0037] FIGS. 9(a) to 9(d) illustrate a set of other example implementations in accordance with the disclosed technology. FIG. 9(a) shows an aluminum-coated piece of Willow^® glass 902 acting as a flat mirror that is placed in front of a graph paper 906, with the reflection 908a of the graph paper visible as straight lines through the mirror 902. Brackets 904 (visible on the two sides) are used to support the mirror. In some embodiments, the brackets 904 can be moved manually, or by an electrical/mechanical translation stage. One of the features of the disclosed technology is the ability to tune the focal length by mechanical manipulation of the flexible optical element; this is advantageous for optimizing the solar concentration ratio. In FIG. 9(b), the brackets 904 are moved toward each other to give the mirror 902b some gentle curvature, which is visible from the reflection 908b of the graph paper lines that are bent. As shown in FIG. 9(c), with additional motion of the brackets 904 to increase the curvature, the mirror 904c is further bent to produce a parabolic shape, which is evident from the reflection 908c of graph paper lines that resembles families of hyperbolas. FIG. 9(d) further illustrates the reflection 908d that includes more hyperbola families with tighter curvature that is produced as the brackets 904 are moved even closer to each other to increase the curvature of the mirror 902d.

[0038] In some exemplary embodiments, the thickness of the glass substrate that

accommodates the coating is on the order of 100 microns, which provides sufficient flexibility for the flat pieces of glass. In some example embodiments, flexible glass substrates in the range 25 to 500 microns can be used. In some implementations the thickness can be as high as 1 cm. The glass can be coated with either metals or stacks of dielectric materials to create mirrors with various levels of reflectivity and spectral performance. The glass can then be curved to provide optical focusing power, by achieving classic shapes such as parabolas or hyperbolas. The curvature can be maintained by using an underlying solid substrate with the correct curvature and ancillary properties (transparency, thermomechanical, etc.). In addition, the flexible reflector can be supported by rigid constraints (such as brackets), or as noted earlier, can be conveniently tiled to cover very large underlying substrates (e.g., in the range of 1 to 10 meters on each side). Non limiting example tile sizes include 500 mm x 500 mm tiles, and 800 mm x 350 mm tiles. [0039] In some embodiments, multiple flexible curved surfaces may be combined together to form a single curved surface with a set of predetermined reflectance and transmission

characteristics. This“stacked” flexible filter configuration allows performance requirements of the filter to be satisfied in a cost-effective manner by designing each filter in the stack to contribute only a portion of the final characteristic. For example, with reference to FIG. 8, an additional filter can be designed by providing a thin film on a flexible glass substrate that exhibits low transmittance in the region 670-700 nm, while having high transmittance characteristics across the entire band of 500-900 nm. When this flexible filter is combined with the filter of FIG 8, they collectively form a filter that provides high reflectivity across the band 500-900. Therefore, two or more flexible filters can be combined in accordance with the disclosed embodiments to produce the desired optical characteristics; this can result in an overall manufacturing process that has higher yield and lower cost.

[0040] In general, the disclosed embodiments can reduce the cost of implementation by using multiple lower cost filters (e.g., each having simpler designs) that replace a single (more expensive) filter. Depending on the system requirements, the use of multiple filters can enable feasible implementation of large-scale flexible filters having complicated transmission and/or reflectance characteristics that would be too expensive to produce using a single filter.

Moreover, the disclosed flexible filters can be removably stacked or secured to each other, and/or against a backing, to allow selective addition and/or removal of stacked layers, thereby enabling the transmission characteristics of the system to be modified (e.g., in response to changes in the power generation technology, seasonal variations, geographical location or based on application requirements) without a need for whole-sale replacement of the reflective surfaces.

[0041] The disclosed configurations that utilize multiple flexible filters further exhibit increased mechanical strength due to having multiple layers, and reduced stress on each individual flexible filter that can be caused by forcing the flat filters to conform to a particular curved profile. In some implementations, the backing (e.g., the blank used to mount the flexible filters) can be entirely removed and the flexible stacked filters can be used to form a free- standing curved surface.

[0042] One method for affixing the flexible coated glass onto an optical component is through a lamination process. In an example embodiment, the lamination process includes the following steps. Both the underlying blank and the flexible glass substrates are initially plasma treated, or in the case of removeable/reconfigurable laminates, only the flexible glass is plasma treated. Polydimethylsiloxane (PDMS) prepolymer is then allowed to uniformly coat the curved glass blank and is partially cured. The flexible glass is then curved to cover and conform to the PDMS coated blank and the entire assembly is cured. Alternatively, PDMS is applied to the plasma treated flexible glass, which is then laminated to the blank and fully cured, allowing easy removal for reconfigurability.

[0043] It should be noted that in this document, Willow^® glass substrate and optical blank are used as examples to facilitate the understanding of the underlying techniques. It is, however, understood that the disclosed embodiments can be equally applied to other types of flexible substrates, and other types of optical components (other than blanks). Moreover, the flexible substrate can include any one of a plurality of types of coatings that may be deposited thereon through a variety of coating techniques. Additionally, the term optical (e.g., as is optical filter or optical component) is not meant to limit the scope of the disclosed embodiment to the visible spectral range, but rather the disclosed embodiments can be implemented and used in non-visible spectral ranges, such as in the ultraviolet, the infrared, the microwave and other ranges of the electromagnetic spectrum.

[0044] FIG. 10(a) illustrates a top view and FIG. 10(b) illustrates a side view of a sample blank 1002 that is laminated with a flexible glass layer 1004 in accordance with the above- described lamination process. In one experiment, the laminated blank illustrated in FIGS. 10(a) and 10(b) was cycled 90 times from -10 degrees C to 50 degrees C without failure. Aside from providing durable structures, the disclosed flexible filters provide several improvements over polymer films including an increased thermal performance, an increased chemical resistance, and increased UV resistance.

[0045] As noted earlier, the flexible glass filters can be attached or affixed to the underlying optical components using techniques other than lamination. For example, in some embodiments, clips are used to attach or place the curved flexible mirrors onto the underlying surfaces. In other embodiments, one side of the flexible glass filters can include an adhesive material that allows the flexible glass filter to be pressed on and secured onto the underlying surface. In some embodiments, the flexible filters can be removed and installed multiple times. In one example embodiment, a highly transparent PDMS is used as the adhesive. In some embodiments where mechanical edge retention (e.g. through the use of binder clips) is used to attach the flexible filters, the adhesive can be substituted with a liquid for index matching, as further described below.

[0046] FIG. 11 illustrates another aspect of the disclosed embodiments through an example index-matched fluid that is positioned between the flexible glass (e.g., Willow^® blank) and the substrate blank to improve the efficiency of the performance of the optical component. It should be noted that the configuration of FIG. 11 is provided for illustration purposes, and the depicted dimensions, including the relative thicknesses of the layers, may not be drawn to scale. The index matching material reduces Fresnel reflections at the boundaries and ensures high transmission of the incident light. For example, an index matching fluid can be selected to improve the transmission of light that is directed to the thermal tube of a solar power generation system or, for agricultural applications, to underlying vegetation. Example index matching materials include fluids that comprise ethylene glycol and isopropanol among others. The fluid can be held in place by hydrostatic forces and peelable/removeable polymer (e.g. PDMS, polyvinyl alcohol (PVA)) that is applied to the perimeter to prevent evaporation or leakage of the fluid. The thickness of the index matching layer can be tuned via viscosity selection of the liquid. Typical thicknesses for the index matching layer are in the sub-micron range.

[0047] FIG. 12 illustrate a set of operations that can be carried out to provide a flexible optical element in accordance with an example embodiment. At 1202, an optical glass substrate is provided that includes a flat surface and a predetermined thickness to allow the optical glass substrate to deform into a non-flat surface in response to an applied force. At 1204, a coating onto a first flat surface of the optical glass substrate is provided, and at 1206, the optical glass substrate having the coating thereon is deformed to conform to a shape of a target curved surface.

[0048] In some embodiments, the flexible optical element is one of: an optical filter or a reflector. In another example embodiment, the optical glass substrate comprises a flexible glass material. In yet another example embodiment, the coating is provided using any one of the following: a physical vapor deposition process, an evaporation deposition process, a sputter deposition process, a chemical vapor deposition process, a thermal formation process, an electroplating process, a sol gel coating process, a liquid-based coating process, or an ion implantation process. In still another example embodiment, deforming the optical glass substrate having the coating thereon includes applying pressure to one or more sides of the optical glass substrate having the coating thereon.

[0049] According to one example embodiment, deforming the optical glass substrate having the coating thereon includes providing a support structure to enable the optical glass substrate having the coating thereon to maintain the shape of the target curved surface. In another example embodiment, deforming the optical glass substrate having the coating thereon includes: providing a backing that is shaped to resemble the target curved surface, placing the optical glass substrate having the coating thereon in contact with the backing, and applying pressure to the optical glass substrate having the coating to cause the optical glass substrate having the coating thereon to acquire substantially the same shape as the backing. In another example embodiment, the above noted method for providing a flexible optical element includes attaching or affixing the flexible optical element to an optical component. For example, the optical component can be an optical blank, a lens, a prism, or a mirror. In some embodiments, attaching or affixing the flexible optical element includes one or more of: laminating the flexible optical element onto a surface of the optical component, affixing the flexible optical element onto a surface of the optical component, or attaching the flexible optical element onto a surface of the optical component via an adhesive material.

[0050] In another example embodiment, attaching or affixing the flexible optical element includes removably attaching or affixing the flexible optical element onto a surface of the optical component. In one example embodiment, the above noted method further includes placing a layer comprising an index matching fluid between the flexible optical element and a surface of the optical component. In another example embodiment, the method includes providing a plurality of additional optical glass substrates, each having a flat surface and a predetermined thickness to allow each of the additional optical glass substrates to deform into a corresponding non-flat surface; for each of the additional optical glass substrates, providing a corresponding coating onto a first flat surface of each of the additional optical glass substrates; deforming each of the additional optical glass substrates having the coating thereon to conform to a

corresponding non-flat shape; and attaching or affixing each of the plurality of the additional optical glass substrates having the coating thereon after said deforming onto a corresponding surface of an optical component. In still another example embodiment, the optical component has an area in the range 1 m² to 1000 m². In yet another example embodiment, the flexible optical element is a dichroic filter.

[0051] According to some example embodiments, a curved optical element includes a flexible glass substrate having a predetermined thickness to allow deformation of the glass substrate in response to an applied pressure, and a coating provided on a first surface of the flexible glass substrate, where the flexible glass substrate which has the coating thereon is adapted to deform and conform to a curved shape of an optical component. In one example embodiment, the curved optical element includes a support structure attached thereto and configured to maintain a shape of the flexible glass substrate having the coating thereon to the curved shape of the optical component. In another example embodiment, the curved optical element further includes an adhesive material positioned on at least a portion of the flexible glass substrate having the coating thereon to allow attachment of the flexible glass substrate having the coating thereon to the optical component. In yet another example embodiment, the curved optical element further includes a layer of index matched material positioned between the optical component and the flexible glass substrate having the coating thereon. In another example embodiment, the curved optical element is a dichroic filter. In still another example embodiment, the curved optical element is configured for use in a hybrid concentrated photovoltaic (CPV)/concentrated solar power (CSP) system. In one example embodiment, the curved optical element is a reflective filter.

[0052] In some example embodiments, a plurality of curved optical elements are provided that are configured to be attached or affixed to an optical component. Each of the plurality of curved optical elements includes: a flexible glass substrate having a corresponding

predetermined thickness to allow deformation of the glass substrate in response to an applied pressure; and a coating provided on a first surface of the flexible glass substrate, where the flexible glass substrate having the coating thereon is adapted to deform and conform to a portion of a curved optical component, and where the plurality of the curved optical elements collectively form a coating surface for the curved optical component when placed next to one another in a tiled fashion.

[0053] FIG. 13 illustrates a set of operations that can be carried out to provide a filter for a target curved surface in accordance with an example embodiment. At 1302, a plurality of glass substrates is obtained that form a first set of glass substrates. Each substrate has a flat surface and a predetermined thickness in the range 25 microns to 1 cm to allow the glass substrate to deform into a non-flat surface in response to an applied force. At 1304, for each of the plurality of glass substrates in the first set, a corresponding coating is applied onto a flat surface of the glass substrate, where each coating has predefined spectral characteristics. At 1306, each of the plurality of glass substrates with the coating thereon is deformed so that each glass substrate with the coating thereon conforms to a shape of a corresponding section of the target curved surface. At 1308, each of the deformed glass substrates with the coating thereon is affixed or attached to the corresponding section of the target curved surface, where the target curved surface has an area in a range 1 square meters to 1000 square meters.

[0054] In one example embodiment, each of the plurality of glass substrates with the coating thereon forms a flexible optical element that is an optical filter or a reflector. In another example embodiment, each of the plurality of glass substrates comprises a flexible glass material. In yet another example embodiment, applying the corresponding coating comprises performing any one of the following processes: a physical vapor deposition process, an evaporation deposition process, a sputter deposition process, a chemical vapor deposition process, a thermal formation process, an electroplating process, a sol gel coating process, a liquid-based coating process, an extrusion process or an ion implantation process.

[0055] According to another example embodiment, deforming each of the glass substrates having the coating thereon includes applying pressure to one or more sides of the glass substrate having the coating thereon to modify the flat surface of the glass substrate to a curved surface.

In one example embodiment, deforming each of the glass substrates having the coating thereon includes providing a support structure to enable the glass substrate having the coating thereon to maintain the shape of the corresponding section of the target curved surface. In another example embodiment, the above noted method for providing a filter for a target curved surface includes providing a plurality of backing elements, where each backing element is shaped to resemble one of the corresponding sections of the target curved surface, and where deforming each of the glass substrates having the coating thereon includes: placing the glass substrate having the coating thereon in contact with a corresponding backing element, and applying pressure to the glass substrate having the coating thereon to cause the glass substrate having the coating thereon to acquire substantially the same shape as the corresponding backing element.

[0056] In one example embodiment, affixing or attaching each of the deformed glass substrates with the coating thereon to the corresponding section of the target curved surface includes attaching or affixing each of the plurality of backing elements including the deformed glass substrates with the coating thereon to the corresponding section of the target curved surface. In another example embodiment, the backing element is an optical blank. In yet another example embodiment, attaching or affixing each of the deformed glass substrates includes laminating each of the deformed glass substrates with the coating thereon onto a surface of the corresponding backing element. In yet another example embodiment, the above noted method further includes placing a layer comprising an index matching fluid between each glass substrate having the coating thereon and the corresponding backing element.

[0057] According to another example embodiment, the target curved surface is the surface of a lens, a prism, or a mirror. In one example embodiment, attaching or affixing each of the deformed glass substrates with the coating thereon includes one or more of: affixing the deformed glass substrate onto the corresponding section of the target curved surface using an edge retention mechanism, or attaching the deformed glass substrate onto the corresponding section of the target curved surface via an adhesive material. In another example embodiment, attaching or affixing each of the deformed glass substrates with the coating thereon allows subsequent removal of one or more of the deformed glass substrates with the coating thereon from the corresponding section or sections of the target curved surface. In yet another example embodiment, the predefined spectral characteristics are associated with a dichroic filter.

[0058] According to another example embodiment, the above noted method further includes obtaining an additional set of glass substrates, each having a flat surface and a predetermined thickness in the range 25 microns to 1 cm; for each glass substrate in the additional set, providing a corresponding coating on a flat surface the glass substrate, the coating having different spectral characteristics than the coating provided for the plurality of glass substrates in the first set; and stacking each of the plurality of glass substrates with the coating thereon in the first set with another glass substrate having the coating thereon from the additional set to form a stacked multi-layer structure. In this embodiment, deforming each of the plurality of glass substrates with the coating thereon comprises deforming each of the stacked multi-layer structures to conform to the shape of the corresponding section of the target curved surface.

[0059] Another aspect of the disclosed embodiments relates to a multi-element flexible optical structure for covering a curved surface of an optical component that includes a plurality of flexible glass substrates, each having a predetermined thickness in the range 25 microns to 1 cm to allow deformation of the glass substrate in response to an applied pressure. The multi- element flexible optical structure further includes a coating having predesigned spectral characteristics on a first surface of each of the plurality of flexible glass substrates, where each of the flexible glass substrates having the coating thereon is adapted to conform to a curved shape of a section of the optical component, and the plurality of flexible glass substrates having the coating thereon when placed side-by-side cover a contiguous area of the curved surface of the optical component that exhibit the predesigned spectral characteristics.

[0060] In one example embodiment, the multi-element flexible optical structure further includes a plurality of support structures attached to two or more of the flexible glass substrates and configured to maintain a shape of the flexible glass substrate having the coating thereon to the curved shape of the section of the optical component. In another example embodiment, the multi-element flexible optical structure further includes an adhesive material positioned on at least a portion of two or more of the flexible glass substrates having the coating thereon to allow attachment of the flexible glass substrate having the coating thereon to the section of the optical component. In yet another example embodiment, the multi-element flexible optical structure further includes a plurality of backing elements, where each backing element is shaped to resemble one of the sections of the optical component, and where each of the plurality of the flexible glass substrates is affixed or attached to a corresponding backing element. [0061] In another example embodiment, the multi-element flexible optical structure further includes a layer of refractive index matched material positioned between each of the backing elements and the flexible glass substrates. In yet another example embodiment, the predesigned spectral characteristics correspond to a dichroic filter or a reflective filter. In still another example embodiment, the multi-element flexible optical structure is configured to cover the curved surface of the optical component in a hybrid concentrated photovoltaic

(CPV)/concentrated solar power (CSP) system. In one example embodiment, the optical component has an area in the range 1 m² to 1000 m².

[0062] Another aspect of the disclosed embodiments relates to a multi-element flexible optical structure for covering a curved surface of an optical component that includes two or more sets of flexible glass substrates, where each set includes a plurality of flexible glass substrates each having a predetermined thickness in the range 50 microns to 500 microns to allow deformation of the glass substrate in response to an applied pressure. The multi-element flexible optical structure further includes a first coating having a first predesigned spectral characteristic applied to a first surface of each of the plurality of flexible glass substrates in the first set flexible glass substrates, and at least a second coating having a second predesigned spectral characteristic applied to a first surface of each of the plurality of flexible glass substrates in the second set flexible glass substrates. Each of the flexible glass substrates having the first coating thereon is stacked on top of a flexible glass substrates having the second coating thereon to form a stacked structure that is adapted to conform to a curved shape of a section of the optical component. The stacked structures when placed side-by-side cover a contiguous area of the curved surface of the optical component and provide a coating that exhibits a third spectral characteristic that is a combination of the first and the second predesigned spectral characteristics.

[0063] The foregoing description of embodiments has been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit embodiments of the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments. The embodiments discussed herein were chosen and described in order to explain the principles and the nature of various embodiments and its practical application to enable one skilled in the art to utilize the present invention in various embodiments and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products.

Claims

WHAT IS CLAIMED IS:

1. A method for providing a filter on a target curved surface, the method comprising:

obtaining a plurality of glass substrates forming a first set of glass substrates, each substrate having a flat surface and a predetermined thickness in the range 25 microns to 1 centimeter to allow the glass substrate to deform into a non-flat surface in response to an applied force;

for each of the plurality of glass substrates in the first set, applying a corresponding coating onto the flat surface of the glass substrate, each coating having predefined spectral characteristics;

deforming each of the plurality of glass substrates with the coating thereon so that each glass substrate with the coating thereon conforms to a shape of a corresponding section of the target curved surface; and

affixing or attaching each of the deformed glass substrates with the coating thereon to the corresponding section of the target curved surface, wherein the target curved surface has an area in a range 1 square meter to 1000 square meters.

2. The method of claim 1, wherein each of the plurality of glass substrates with the coating thereon forms a flexible optical element that is an optical filter or a reflector.

3. The method of claim 1, wherein each of the plurality of glass substrates comprises a flexible glass material.

4. The method of claim 1, wherein applying the corresponding coating comprises performing any one of the following processes:

a physical vapor deposition process,

an evaporation deposition process,

a sputter deposition process,

a chemical vapor deposition process,

a thermal formation process,

an electroplating process,

a sol gel coating process, a liquid-based coating process,

an extrusion process, or

an ion implantation process.

5. The method of claim 1, wherein deforming each of the glass substrates having the coating thereon includes applying pressure to one or more sides of the glass substrate having the coating thereon to modify the flat surface of the glass substrate to a curved surface.

6. The method of claim 1, wherein deforming each of the glass substrates having the coating thereon includes providing a support structure to enable the glass substrate having the coating thereon to maintain the shape of the corresponding section of the target curved surface.

7. The method of claim 1, further comprising:

providing a plurality of backing elements, each backing element shaped to resemble one of the corresponding sections of the target curved surface, wherein deforming each of the glass substrates having the coating thereon includes:

placing the glass substrate having the coating thereon in contact with a corresponding backing element, and

applying pressure to the glass substrate having the coating thereon to cause the glass substrate having the coating thereon to acquire substantially the same shape as the corresponding backing element.

8. The method of claim 7, wherein affixing or attaching each of the deformed glass substrates with the coating thereon to the corresponding section of the target curved surface includes attaching or affixing each of the plurality of backing elements including the deformed glass substrates with the coating thereon to the corresponding section of the target curved surface.

9. The method of claim 7, wherein the backing element is an optical blank.

10. The method of claim 7, wherein attaching or affixing each of the deformed glass substrates includes laminating each of the deformed glass substrates with the coating thereon onto a surface of the corresponding backing element.

11. The method of claim 7, further including placing a layer comprising an index matching fluid between each glass substrate having the coating thereon and the corresponding backing element.

12. The method of claim 1, wherein the target curved surface is the surface of a lens, a prism, or a mirror.

13. The method of claim 1, wherein attaching or affixing each of the deformed glass substrates with the coating thereon includes one or more of:

affixing the deformed glass substrate onto the corresponding section of the target curved surface using an edge retention mechanism, or

attaching the deformed glass substrate onto the corresponding section of the target curved surface via an adhesive material.

14. The method of claim 1, wherein attaching or affixing each of the deformed glass substrates with the coating thereon allows subsequent removal of one or more of the deformed glass substrates with the coating thereon from the corresponding section or sections of the target curved surface.

15. The method of claim 1, wherein the predefined spectral characteristics are associated with a dichroic filter.

16. The method of claim 1, further comprising:

obtaining an additional set of glass substrates, each having a flat surface and a predetermined thickness in the range 25 microns to 1 centimeter; for each glass substrate in the additional set, providing a corresponding coating onto the flat surface of the glass substrate, the coating having different spectral characteristics than the coating provided for the plurality of glass substrates in the first set; and

stacking each of the plurality of glass substrates with the coating thereon in the first set with another glass substrate having the coating thereon from the additional set to form a stacked multi-layer structure; wherein

deforming each of the plurality of glass substrates with the coating thereon comprises deforming each of the stacked multi-layer structures to conform to the shape of the

corresponding section of the target curved surface.

17. A multi-element flexible optical structure for covering a curved surface of an optical component, comprising:

a plurality of flexible glass substrates, each having a predetermined thickness in the range 25 microns to 1 centimeter to allow deformation of the glass substrate in response to an applied pressure; and

a coating having predesigned spectral characteristics on a first surface of each of the plurality of flexible glass substrates, wherein

each of the flexible glass substrates having the coating thereon is adapted to conform to a curved shape of a section of the optical component, and

the plurality of flexible glass substrates having the coating thereon when placed side- by-side cover a contiguous area of the curved surface of the optical component that exhibit the predesigned spectral characteristics.

18. The multi-element flexible optical structure of claim 17, further including a plurality of support structures attached to two or more of the flexible glass substrates and configured to maintain a shape of the flexible glass substrate having the coating thereon to the curved shape of the section of the optical component.

19. The multi-element flexible optical structure of claim 17, further including an adhesive material positioned on at least a portion of two or more of the flexible glass substrates having the coating thereon to allow attachment of the flexible glass substrate having the coating thereon to the section of the optical component.

20. The multi-element flexible optical structure of claim 17, further including:

a plurality of backing elements, each backing element shaped to resemble one of the sections of the optical component, wherein each of the plurality of the flexible glass substrates is affixed or attached to a corresponding backing element.

21. The multi-element flexible optical structure of claim 18, further comprising:

a layer of refractive index matched material positioned between each of the backing elements and the flexible glass substrates.

22. The multi-element flexible optical structure of claim 17, wherein the predesigned spectral characteristics correspond to a dichroic filter or a reflective filter.

23. The multi-element flexible optical structure of claim 17, configured to cover the curved surface of the optical component in a hybrid concentrated photovoltaic

(CPV)/concentrated solar power (CSP) system.

24. The multi-element flexible optical structure of claim 17, wherein the optical component has an area in the range 1 m² to 1000 m².

25. A multi-element flexible optical structure for covering a curved surface of an optical component, comprising:

two or more sets of flexible glass substrates, each set including a plurality of flexible glass substrates each having a predetermined thickness in the range 25 microns to 1 centimeter to allow deformation of the glass substrate in response to an applied pressure; and

a first coating having a first predesigned spectral characteristic applied to a first surface of each of the plurality of flexible glass substrates in the first set of flexible glass substrates; at least a second coating having a second predesigned spectral characteristic applied to a first surface of each of the plurality of flexible glass substrates in the second set of flexible glass substrates; wherein

each of the flexible glass substrates having the first coating thereon is stacked on top of a flexible glass substrate having the second coating thereon to form a stacked structure that conforms to a curved shape of a section of the optical component, and

the stacked structures when placed side-by-side cover a contiguous area of the curved surface of the optical component and provide a coating that exhibits a third spectral characteristic that is a combination of the first and the second predesigned spectral characteristics.