Patent Application
20160139305
1. Field
The embodiments relate generally to granular composite materials. More particularly the embodiments relate to high performance structured granular composite materials, methods for fabrication thereof and applications thereof.
2. Description of the Related Art
The presence and use of optical devices and optical components continues to proliferate within various advanced technology applications, such as but not limited to optical display applications, optical inspection applications, photovoltaic energy conversion applications and biochemical optical marker applications.
Insofar as advanced technology applications continue to proliferate within a variety of optical technology areas, desirable are optical materials and optical components that may lead to optical devices and optical apparatus with enhanced performance.
Macroscopic optical apparatus are generally fabricated from optical materials that are optically adapted with respect to sub-wavelength optical dimensions. For example, in the visible spectrum where optical devices are most useful for military applications such optical adaptation often entails control over complex optical component physical architectures designed and executed at nano-scale optical dimensional limitations.
A critical optical component that may be integrated into a variety of optical systems is an optical display. Recent advances in optoelectronic device fabrication have produced a myriad of optical display architectures, not all of which are practical for field deployment within the context of a military application. Furthermore, most large-area optical displays are heavy, energy consuming and restricted in-practice to a rigid flat geometry. Indeed, such an optical display may block a user's field of view, which is an undesirable feature of most current embodiments. A transparent or opaque optical display that can provide 3D information depiction on a flat or curvilinear surface that is either opaque or transparent is thus clearly desirable. Such an optical display if possibly assembled in a field environment in a short period of time would introduce critical advantages for a range of national defense applications.
Realization of the foregoing optical attributes of optical apparatus often requires precise control over optical scattering from nano-scale features within an optical component. While lithographic strategies are often used to produce conventional display systems, the above described attributes may alternatively more readily be achieved through use of an alternative approach that allows an ordered assembly of nano-particles at macro-scales.
In that light, the embodiments intend to leverage a fabrication methodology that may be used to produce from a nano-scale optical material feedstock a composite optical element in the form of a primary polymeric nano-particle controllably structured and doped with a plurality of secondary optical scattering elements in the form of a plurality of secondary optically active components within a primary optically active component. This composite optical element can be mass-produced from the optical material feedstock using fiber spinning technology combined with thermally controllable fluid dynamic instabilities. Each element of this particular optical material feedstock is rationally designed to provide a specific optical functionality, such as high scattering efficiency with negligible absorption, well-defined polarimetric response and, potentially, wavelength selectivity. The optical material feedstock is maintained until its usage is required in a unique form-factor wherein secondary optically active components are held in isolation from each other in a fiber polymer matrix. The composite optical elements may then be assembled in macroscopic scale optical entities or apparatus by exploiting distinct deployment strategies, such as incorporation into non-woven fabric, spraying the optical material feedstock elements on a surface or painting as a coating on a substrate.
An objective of the embodiments is to provide a passive transparent optical display capable of projecting 3D image information by exploiting the engineered optical behavior of an underlying composite optical element material. One may establish the performance of such a 3D optical display across the visible spectrum and mounted on, for example, a transparent substrate.
A scalable fabrication of multi-component spun fibers is exploited to produce multi-scale composite optical element spherical particles combining amorphous and crystalline nano-scale components that enable tailored optical responses within an optical apparatus into which is included the composite optical element. The embodiments demonstrate a transparent, omni-directional, large-area optical display with a unique set of attributes that stem from underlying nano-structured composite optical elements assembled into a macroscopic optical display apparatus. This optical display is intended as passive, able to provide high-visibility/contrast on a variety of substrates, with appropriate spatial resolution, and also capable of conveying free depth perception (3D information) over the visible spectrum.
Key design elements within the context of the embodiments include:
In comparison with alternative approaches which include, for example, conventional lithographic strategies which produce display systems that are heavy, energy-consuming, opaque, and restricted to rigid flat geometries, the embodiments provide several advantages.
In summary, the embodiments provide the following:
For reference purposes,
Within the specification and the claims, an “optical material feedstock” is intended as at minimum a bi-component optical material prior to thermally activated extrusion cleaving into a plurality of composite optical elements.
Within the specification and the claims, a “composite optical element” is intended as a result of thermally activated extrusion cleaving of an optical material feedstock.
Within the specification and the claims, a “primary optically active component” is a larger component of a composite optical element and is generally but not exclusively in the shape of a first sphere.
Within the specification and the claims, a “secondary optically active component” is a smaller component of a composite optical element and is generally but not exclusively in the shape of a second sphere smaller than the first sphere.
Within the context of the foregoing descriptive summary the embodiments provide a composite optical element, a method for fabricating the composite optical element and an optical apparatus including the composite optical element.
A composite optical element in accordance with the embodiments includes a primary optically active component comprising a backbone material comprising an amorphous material. The composite optical element also includes a plurality of secondary optically active components contained within the primary optically active component and comprising an additive material comprising a nano/micro material, where the backbone material and the additive material are thermally and rheologically mismatched.
A method for fabricating a composite optical element in accordance with the embodiments includes extruding and thermally treating an optical material feedstock comprising an amorphous backbone material and a plurality of additive material components uniformly distributed within the amorphous backbone material to provide a plurality of composite optical elements each comprising a primary optically active component formed from the amorphous backbone material having included therein a sub-plurality of additive material components within the primary optically active component.
An optical apparatus in accordance with the embodiments includes a composite optical element comprising: (1) a primary optically active component comprising a backbone material comprising an amorphous material; and (2) a plurality of secondary optically active components contained within the primary optically active component and comprising an additive material comprising a nano/micro material, where the backbone material and the additive material are thermally and rheologically mismatched. The optical apparatus also includes a substrate upon which is located the composite optical element.
The objects, features and advantages of the embodiments are understood within the context of the Detailed Description of the Non-Limiting Embodiments, as set for the below. The Detailed Description of the Non-Limiting Embodiments is understood within the context of the accompanying drawings, which provide a material part of this disclosure, wherein:
The embodiments provide an optical material feedstock that may be processed to form a plurality of composite optical elements that may be further incorporated into an optical apparatus. The composite optical elements in turn include a primary optically active component (i.e., generally a primary sphere) into which is contained a plurality of secondary optically active components (i.e., generally a plurality of secondary spheres of dimensions smaller than the primary sphere.
The embodiments also provide a method for producing the composite optical element from the optical material feedstock. The embodiments also provide the particular optical apparatus that results from the methods. Such a particular optical apparatus desirably comprises an optical display.
Within the embodiments a particular optical material feedstock includes a bulk carrier material and a plurality of secondary optically active components included within the bulk carrier material. The bulk carrier material typically includes at least one polymer material that possesses optical properties and rheological properties appropriate to provide a functional optical apparatus in accordance with the embodiments. Within the embodiments the secondary optically active components within the bulk carrier material also have specific optical properties and rheological properties to allow for a functional optical apparatus in accordance with the embodiments.
Within the embodiments the at least one polymer material which comprises the bulk polymer material may comprise, but is not necessarily limited to, a thermoplastic polymer material typically having a generally high (i.e., greater than about 90 percent) optical transparency in the visible wavelength region. Within the embodiments the secondary optically active components may comprise any of several optically active materials which may also comprise optically transparent materials. Within the embodiments the bulk carrier material and the secondary optically active components may be mutually selected to provide an optimized optical scattering which may include either a minimum optimized optical scattering or a maximum optimized optical scattering.
Typically and preferably, the optical material feedstock within the context of the embodiments includes approximately 90-95 weight percent bulk base material and about 5-10 weight percent secondary optically active component material which is uniformly mixed within the bulk base material.
A central goal of the embodiments is to demonstrate a transparent large-area optical display with a unique set of optical properties that stem from underlying composite optical element assembled into a macroscopic structure which comprises the large area optical display. Specifically, an optical display in accordance with the embodiments is intended to be passive, to provide a high visibility/contrast on a variety of substrates, and to provide an appropriate spatial resolution. The large area optical display is also capable of conveying depth perception (3D information), provided uniformly over the visible spectrum.
The above central goals with respect to the characteristics of the transparent optical display in accordance with the embodiments may be achieved by leveraging the unique material properties of high-refractive-index transparent dielectrics such as TiO2 in conjunction with polymeric base optical materials. Starting from nano-crystalline TiO2, one may incorporate them into a new geometry: perfect spherical polymer particles with controllable doping densities allocated within the 3D volume of each particle acting as a super-scatterer. This geometric heterogeneity provides unique opportunities for designer optical response from each composite optical element.
Furthermore, the approach used to fabricate these composite optical elements readily provides macroscopic quantities of same using standard processes delivered in a form factor that obviates traditional hurdles and impediments of agglomeration and size and structure uniformity.
The performance of an optical display in accordance with the embodiments will be engineered by leveraging the flexibility afforded by the fabrication technology in accordance with the embodiments. Specifically with respect to an optical display in accordance with the embodiments:
A basic approach for producing nano-particles from a multi-component fiber in accordance with the embodiments is illustrated in
The level of precise structural control over the internal particle structure shown above has profound implications for modifying the fundamental process of optical scattering. This may be confirmed through near-field optical measurements on single composite optical particles. Within the context of the embodiments, modulating the internal particle structure may increase the scattering efficiency above, or decrease it below, that of all the constitutive materials. An example is shown in
The precise structural control over the internal particle structures produced by this technology also allows one to create unique polarization characteristics. As illustrated in
Within the context of the embodiments one may exploit capabilities on both fronts of large-scale computational photonics and highly precise optical characterization.
Although the above structured, multi-material micro- and nano-particle fabrication strategy has demonstrated clear and unique advantages compared to any other competing approach, it nevertheless suffers from two drawbacks to becoming an established methodology for providing composite optical element particle feedstock for controlling optical scattering across the variety of optical apparatus platforms in need of such a capability. Within the embodiments one may address these two drawbacks as follows.
With respect to a lack of scalability to mass-production, while fiber drawing is well-suited for drawing continuous long lengths of fibers, its very nature prevents scaling up to large volumes. Starting from a preform sets an upper limit on the volume that may be produced (basically the volume of the preform itself). Although such an approach is useful for applications that require small quantities of nano-particles (particularly biomedical applications), this is not the case for the applications that will be addressed in this effort, where large volumes—necessitating a clear path towards mass-production—are required.
To address this deficiency, the embodiments may use the scalable fiber fabrication methodology of fiber spinning, which is typically used to produce fibers for non-woven fabrics. To that end, using a single nozzle that already produces fibers with at least two-orders-of-magnitude larger rate (>1 kg/hr) than may be achieved using thermal fiber drawing of the same materials may be desirable. Furthermore, large scale equipment comprises multiple such nozzles operated in parallel may also be desirable. Within the context of the embodiments, one may use fiber drawing as an initial step for determining optimal materials combinations, geometries, and structures, before demonstrating the feasibility of achieving the same parameters in the more scalable fiber-spinning approach.
Within the context of materials that have been used to date to provide high optical refractive indices (i.e., soft glasses with low glass-transition temperatures such as chalcogenides) such materials suffer concomitantly from high optical losses. Thus, while optical scattering from these structured particles is enhanced, optical absorption reduces their utility.
To address this particular deficiency one may use titania (TiO2) nano-particles to provide high optical scattering in the visible while maintaining low optical absorption. Titania is a unique material that has the highest refractive index of a material transparent in the visible, is available at low prices and large volumes, and in a variety of sizes (down to a few 10's nm). One may develop a process for incorporating titania in thermoplastic polymers, thermally drawing the granular composite (polymer+titania) into fibers, and subsequent thermally driven PRI to produce particles. Moreover, one may use this granular composite in fiber-spinning machines with similar results. Preliminary experiments based fiber-spinning technology combined with thermally controllable fluid dynamical instabilities suggest that manufacturing composite structures based on titania nano-particles is feasible. The fabrication of titania-based scattering composite particles is illustrated in
Multi-view 3D systems for display optical information without additional analyzing devices (glasses) rely primarily on holographic techniques. This solution however imposes significant restrictions in terms of real-time operation. Digital holography afforded by large scale diffractive optics elements can operate much faster but the overall efficiency is still seriously affected by the very nature of the display mechanism: diffraction by periodic structures.
Multi-projector approaches are another alternative. A myriad of solutions has been suggested to discretize a 3D viewing space and create a stereoscopic effect. However, so far only large scales and static applications have been demonstrated.
A solution one may pursue is fully passive and relies on the unique scattering properties afforded by non-resonant, all-dielectric particles composites. They can be incorporated in a variety of substrates to create display with various form factors.
The visibility of a scattering-based display depends on the efficiency of scattering centers and the directionality of the outgoing flow of energy. These characteristics are determined, in general, by the material properties and the length scales involved in the interaction with light. In common cases, the size of the particle determines in great degree the way in which the light is scattered or redirected. Small particles scatter light isotropically, which is highly desired for a display, but their scattering efficiency is strictly limited. Thus, it would be highly desirable to use larger particles that scatter more but, unfortunately, their efficiency is highly anisotropic. Ideally, one would require particles that are both isotropic and very efficient scatterers. In addition, one would desire the natural isotropy of spherically symmetric structures which do not require any alignment as well as lossless materials to minimize other dissipative processes. No homogeneous materials can provide all these features.
The unique approach in accordance with the embodiments relies on modifying the internal structure of large particles to permit significantly control of their scattering directivity. This task can be achieved using appropriately designed lossless composites based on nano-size TiO2 pigments and a variety of polymeric hosts. The distinctive properties that can be achieved are illustrated in
There are several optical characteristics that should be optimized for use in scattering-based displays. Aside from the choice of materials and the nano-size dimensions of the primary components, both the scattering efficiency and scattering directivity depend on the internal structure, adjustable from nano to micro scales, and the environment in which the particles are placed. Ultimately, an optical display substrate will also influence the performance. The spatial resolution is determined by the extent of embedded microstructure as well as the overall density. A uniform spectral response is anticipated due to both the non-resonant all dielectric scattering and the multiple scattering spectral homogenization generated by their internal structure.
In addition, these all-dielectric composites can also be structured such that their optical responses are strongly polarization dependent. This feature makes them capable of conveying depth perception (3D) without additional analyzing device (glasses). As illustrated in
The fabrication technology permits to conveniently add other functionalities. Different nano feedstock could be incorporated into the composite structures described here. For instance, a magnetic response can be integrated, which would allow modulating of optical response and provide unique possibilities for applications such as tagging.
Structural, mechanical, thermal and electric functionalities can be integrated with optical interface provided by super-scattering structures. One may emphasize that unique optical properties will be provided by all-dielectric materials at low optical powers where the response is linear. The functionality can be obtained without appealing to high-power or pulsed laser sources.
The following outline summarizes the embodiments. In particular, structured granular composite materials may be described as follows:
Paints and coatings for their optical properties; as reflective, transmissive or scattering elements in optical displays; whitening agents in dental applications; thermal management of optical and infrared radiation; components in other composite materials; components for thermo-mechanical control and management; optical or magnetic tags; optical microtags for authentication and security.
All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference in their entireties to the same extent as if each reference was individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening.
The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it was individually recited herein.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed.
No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. There is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
This application derives from, and is related to, U.S. Provisional Patent Application Ser. No. 62/079,907, filed 14 Nov. 2014 and titled “Structural Granular Composite Materials, Methods of Fabrication Thereof and Applications Thereof,” the contents of which are incorporated herein fully by reference.
Research that lead to the embodiments as described herein, and the invention as claimed herein, was funded by the United States Defense Advanced Research Projects Agency (DARPA) under contract DARPA-BAA-14-56. The United States Government has rights in the invention as claimed herein.
| Number | Date | Country | |
|---|---|---|---|
| 62079907 | Nov 2014 | US |
