PATENT DOCUMENT

Publication Number: US-10690946-B2
Application Number: US-201615236219-A
Country: US
Kind Code: B2

Title: Flexible photonic crystals with color-changing strain response

Abstract:
Flexible photonic crystal structures capable of changing color in response to strain are described. Methods for forming two-dimensional and three-dimensional flexible photonic crystal structures are described. In some aspects, the flexible photonic crystal structures include an array of holes or voids formed within a flexible material. The flexible material changes dimensions of the array when the flexible photonic crystal structures is stretched, pulled, pushed or bent. In some aspects, the flexible photonic crystal structures include an array of features made of a first material, such as a first type of polymer, embedded within a matrix material made of a second material, such as a second type of polymer. The flexible photonic crystal structures can be used in the manufacture of consumer products, such as electronic products, electronic product accessories, thin films, flexible displays and wearable products.

Claims:
What is claimed is: 
     
       1. A structure that undergoes a change in color when subjected to stress, the structure comprising:
 a region having features comprising intersecting channels that are spaced apart and define voids capable of interfering with visible light incident thereupon, wherein:
 when the region is in an unstressed state, the features are spaced apart by a first distance corresponding to reflecting a first range of wavelengths of the incident visible light, wherein the first range of wavelengths is associated with a first color, and 
 otherwise, when the stress is applied to the region, at least some of the features are spaced apart by a second distance, the second distance associated with at least a portion of the region reflecting a second range of wavelengths of the incident visible light, the second range of wavelengths associated with a second color different from the first color. 
 
 
     
     
       2. The structure of  claim 1 , wherein at least one of the first distance or the second distance is between about 100 to about 800 nanometers. 
     
     
       3. The structure of  claim 1 . wherein the features are disposed in a flexible material, the features comprising a first dielectric material having a first refractive index and the flexible material comprising a second dielectric material having a second refractive index. 
     
     
       4. The structure of  claim 3 , wherein the first dielectric material comprises air and the second dielectric material comprises a polymer. 
     
     
       5. The structure of  claim 3 , wherein the first dielectric material comprises a first polymer and the second dielectric material comprises a second polymer different from the first polymer. 
     
     
       6. The structure of  claim 1 , wherein the features comprise spherically shaped particles and the first distance corresponds to a distance between centers of the spherically shaped particles. 
     
     
       7. The structure of  claim 1 , wherein the structure comprises walls that define a cavity, and the walls are capable of carrying a portable electronic device within the cavity. 
     
     
       8. The structure of  claim 1 , wherein the region of features corresponds to an external surface. 
     
     
       9. The structure of  claim 6 , wherein the spherically shaped particles comprise a polymer. 
     
     
       10. A method of forming a flexible structure having an appearance that changes color when subjected to stress, the method comprising:
 forming the flexible structure comprising an array of features comprising intersecting channels that are spaced apart from each other, wherein the features are capable of causing interference of visible light incident on the array of features, and a region of the flexible structure comprises at least some of the features, the flexible structure being configured to transition between an unstressed state and a stressed state, wherein:
 when the region is in the unstressed state, the features of the region are spaced apart by a first distance, the first distance associated with the region appearing a first color, and 
 when the region is in the stressed state, at least some of the features of the region are spaced apart by a second distance, the second distance associated with at least a portion of the region appearing a second color different from the first color. 
 
 
     
     
       11. The method of  claim 10 , wherein forming the array of features comprises:
 arranging spherically shaped particles within a flexible material, the spherically shaped particles having spherically shaped interior voids. 
 
     
     
       12. The method of  claim 11 , wherein the spherically shaped particles are comprised of a first type of polymer and the flexible material is comprised of a second type of polymer different from the first type of polymer. 
     
     
       13. The method of  claim 11 , wherein the spherically shaped particles comprise a material, and the flexible material comprises the material. 
     
     
       14. The method of  claim 10 , wherein forming the array of features comprises:
 forming intersecting channels within a flexible material, wherein intersections of the channels define voids within the flexible structure. 
 
     
     
       15. The method of  claim 14 , wherein the intersecting channels are formed using a laser ablating process. 
     
     
       16. A pressure sensitive material that undergoes a change in color when subjected to pressure, the pressure sensitive material comprising:
 a structure having a distribution of voids defined by intersecting channels that, wherein a region of the structure comprises a portion of the distribution of voids, the portion configured to interfere with visible light incident on the portion, and to transition between states when the region is subjected to the pressure, wherein: 
 in an absence of pressure applied against the region, the distribution of voids are spaced apart by a first distance such that the region appears as a first color, and 
 in a presence of pressure applied against the region, the distribution of voids are spaced apart by a second distance such that the region appears as a second color different from the first color. 
 
     
     
       17. The pressure sensitive material of  claim 16 , wherein the distribution of voids are in a three-dimensional array. 
     
     
       18. The pressure sensitive material of  claim 16 , wherein the pressure sensitive material is a film capable of covering a display of a portable electronic device. 
     
     
       19. The pressure sensitive material of  claim 16 , wherein the structure includes walls that define a cavity, and the walls are capable of carrying a portable electronic device within the cavity. 
     
     
       20. The pressure sensitive material of  claim 16 , wherein the pressure sensitive material is composed of a polymer.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/210,384, entitled “FLEXIBLE PHOTONIC CRYSTALS WITH COLOR-CHANGING STRAIN RESPONSE,” filed on Aug. 26, 2015, which is incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This disclosure relates generally to photonic crystal structures and methods for forming the same. In particular embodiments, the photonic crystals include flexible material that causes the photonic crystals to change color in response to pressure, bending or other types of strain. 
     BACKGROUND 
     Photonic crystals are periodic microstructures that affect the motion of photons that are incident upon the photonic crystals in a way that causes visual effects. These structures manipulate specific wavelengths of light, resulting in a visually varied or patterns of color. Unlike colored objects that contain chemical substances that reflect and absorb certain wavelengths of light to give the object a particular color, photonic crystals reflect color by its physical microstructures, and are therefore said to reflect color by “structural coloration.” 
     Examples of photonic crystal structures in nature include some butterfly wings that are brilliant iridescent blue due to microstructures within the butterfly wing. Photonic crystals can also be fabricated using stacks of dielectric layers of material or by forming two-dimensional patterns within a substrate. For example, two materials having different refractive indices arranged in very closely packed array patterns can create such photonic crystal effects. However, fabricated photonic crystals have fixed microstructures, and therefore have fixed responses to incident light and therefore have corresponding fixed colors. 
     SUMMARY 
     This paper describes various embodiments that relate to photonic crystal structures capable of changing color in response to strain or stress. The systems and methods described can be used in the manufacture of consumer products, such as electronic products and electronic product accessories. 
     According to one embodiment, a flexible structure having an appearance that changes color when subjected to stress is described. The flexible structure includes an array of features within a flexible material. The flexible structure is configured to transition between a stressed state and an unstressed state. When in the unstressed state, the features are uniformly spaced a first distance apart. The first distance is associated with the flexible structure reflecting a first range of wavelengths of visible light associated with a first color. When in the stressed state, at least some of the features are spaced a second distance apart. The second distance is associated with at least a portion of the flexible structure reflecting a second range of wavelengths of visible light associated with a second color different from the first color. 
     According to another embodiment, a method of forming a flexible structure having an appearance that changes color when subjected to stress. The method includes forming an array of features. Distances between the features cause interference of visible light incident on the array of features. The flexible structure is configured to transition between a stressed state and an unstressed state. When in the unstressed state, the distances between the features is a first distance associated with the flexible structure appearing a first color. When in the stressed state, a distance between at least some of the features changes to a second distance associated with at least a portion of the flexible structure appearing a second color different from the first color. 
     According to an additional embodiment, a pressure sensitive material having an appearance that changes color in response to an applied pressure is described. The pressure sensitive material includes a distribution of voids that are spaced apart such the voids interfere with visible light incident on the pressure sensitive material. In the absence of the applied pressure, spacing between the voids is such that the pressure sensitive material appears as a first color. When the pressure is applied to a region of the pressure sensitive material, the spacing between the voids changes within the region causing the region to appear a second color different from the first color. 
     These and other embodiments will be described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIG. 1  shows a portion of a flexible photonic crystal structure. 
         FIGS. 2A and 2B  show portions of the photonic crystal structure of  FIG. 1  being bent along a reference line. 
         FIG. 3  shows a portion of the photonic crystal structure of  FIG. 1  after a force was applied to its surface. 
         FIG. 4  shows a portion of a flexible photonic crystal structure that includes spherically shaped particles within matrix material. 
         FIG. 5  shows a flowchart indicating a process for forming the flexible photonic crystal structure of  FIG. 4 . 
         FIG. 6  shows a flexible photonic crystal structure having regularly spaced channels and voids. 
         FIG. 7  shows a flowchart indicating a process for forming the flexible photonic crystal structure of  FIG. 6 . 
         FIGS. 8A and 8B  show portions of layered flexible photonic crystal structures, each having multiple layers of photonic crystal structures. 
         FIGS. 9A and 9B  show a case that includes a photonic crystal structure. 
         FIG. 10  shows a display assembly that includes a flexible photonic crystal structure. 
         FIGS. 11A and 11B  show a flexible screen that includes a flexible photonic crystal structure. 
         FIG. 12  shows a flexible sheet of material that includes a flexible photonic crystal structure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, they are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     Described herein are photonic crystal structures capable of changing color in response to pressure, bending or other types of strain. The photonic crystals include periodic microstructures formed within a deformable material such that when a compressive or tensile stress is applied to the photonic crystals, dimensional changes in the microstructures cause an apparent color shift. As used herein, the term “microstructure” is used to describe a structure of very small size, such as structures having dimensions on the scale of nanometers or micrometers. The photonic crystals can be incorporated into base materials for a number of applications, such as casings and enclosures for consumer products, fabrics for clothing, and thin films for application onto windows or display screens. The photonic crystals can be used for purely cosmetic purposes with dynamic color changes providing unusual visual effects, or they can provide a functional purpose, such as acting as visual sensors. 
     In some embodiments, the photonic crystals include particles of a first material embedded within a matrix of a second material, where the first material has a different index of refraction than the second material. For example, the particles can be composed of polymer, glass or ceramic, which are embedded within a matrix of polymer. Any suitable polymer material can be used. For example, polymer can be an organic polymer, a non-organic polymer or a combination thereof. In some embodiments, the polymer is a silicone or silicon-based polymer. The particles can have substantially the same diameter such that when the particles are closely packed within the second material, a periodic structure capable of producing photonic crystal colorization arises. 
     In some embodiments, the microstructures are voids formed within a flexible material using, for example, a laser. The voids can have any suitable shape and arrangement capable of forming the periodic microstructures of a photonic crystal. In some cases, the voids are in the shape of holes or channels within the flexible material. In some embodiments, the voids are filled with air, while in other embodiments the voids are filled with a liquid. In some embodiments, a composite material that includes multiple layers of photonic crystal structures is formed. 
     The flexible photonic crystal structures described herein are well suited for incorporation into consumer products. For example, the flexible photonic crystal structures described herein can be used to form aesthetically appealing products for computers, portable electronic devices, wearable devices, and device accessories, such as those manufactured by Apple Inc., based in Cupertino, Calif. 
     These and other embodiments are discussed below with reference to  FIGS. 1-12 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
     The flexible photonic crystal structures described herein can have any of a number of suitable characteristics and be manufactured using any of a number of suitable techniques.  FIGS. 1-3  show different views of flexible photonic crystal structure  100 , in accordance with some embodiments. 
       FIG. 1  shows a plan view of a portion of flexible photonic crystal structure  100 . Flexible photonic crystal structure  100  includes first material  102  of distinctly defined features  108  surrounded by second material  104 . Distance d refers to distances between adjacent features  108  as measured from the centers of features  108 . In some embodiments, distance d between adjacent features  108  is substantially the same—that is features  108  are substantially uniformly spaced apart by distance d. In other embodiments, features  108  of one portion of flexible photonic crystal structure  100  are spaced substantially the same distance apart from each other while other features  108  of another portion of flexible photonic crystal structure  100  are spaced a different distance apart, such that flexible photonic crystal structure  100  appears to have different colors. First material  102  has a different refractive index (RI) than second material  104 . For example, first material  102  and second material  104  can be made if different dielectric materials (e.g., polymer, glass and/or ceramic). In some embodiments, first material  102  is air (RI is about 1) where features  108  correspond to holes or voids (e.g., spherically shaped voids or cylindrically shaped voids) within second material  104 . If filled with air, features  108  can be formed, for example, using a laser ablation process, whereby selected portions of second material  104  are removed by laser ablation. First material  102  can be in solid, semi-solid, liquid or gaseous form. In some embodiments, first material  102  and second material  104  are individually substantially transparent or clear, i.e., do not appear to have significant color, thus allow most or all incident light to pass through when not arranged in photonic crystal structure  100 . 
     Flexible photonic crystal structure  100 , like photonic crystal structures in general, includes an array  110  of features  108  where the array  110  interferes with visible light incident on flexible photonic crystal structure  100  and causes optical effects. Array  110  can also be referred to as an arrangement or periodic arrangement or series of features  108 . In particular, features  108  act together to give flexible photonic crystal structure  100  a perceived color, referred to as structural coloration. Array  110  can be a two-dimensional or three-dimensional arrangement of features  108 . If distance d between features  108  is in the order of wavelengths of light, flexible photonic crystal structure  100  will reflect incident light in a particular wavelength. Specifically, incident light with a wavelength about 2 times distance d between features  108  will be reflected, in accordance with solution to Maxwell&#39;s Equations for light diffraction. That is, the periodicity of features  108 , corresponding to distance d between features  108 , is around half the wavelength of the incident light in order to be reflected. Therefore, distance d of about 200 nanometers can correspond to photonic crystal structure  100  appearing a blue color, and distance d of about 350 nanometers can correspond to photonic crystal structure  100  appearing a red color. In addition, disallowed bands of wavelengths (band gaps) and groups of allowed bands of wavelengths (modes) result is a distinct optical appearance, such as high efficiency light reflection of specific wavelength corresponding to specific visible colors. In some embodiments, distance d is between about 200 to about 350 nanometers. In some embodiments, distance d is between about 400 to about 700 nanometers. In some embodiments, distance d is between about 100 to about 800 nanometers. 
     It should be noted that features  108  can have any suitable shapes and are not limited to dot/circular shapes shown in  FIG. 1 . For example, features  108  can have square, triangular, rectangular, oval, oblong, irregular, or linear shapes. In some embodiments, features  108  have different shapes within a single array  110 . 
     Flexible photonic crystal structure  100  is flexible in that it can be deformed without breaking. To provide flexibility to flexible photonic crystal structure  100 , one or both of first material  102  and second material  104  are made of a flexible material that can be physically bent, expanded or compressed.  FIGS. 2A and 2B  show portions of photonic crystal structure  100  being locally bent or creased along reference line  202 . 
       FIG. 2A  shows photonic crystal structure  100  bent along reference line  202  in a first direction with ends  201  and  203  “going into the page” such that region  204  of photonic crystal structure  100  is locally expanded. This causes features  108  within region  204  to be spaced wider apart from each other. In particular, features  108  in region  204  are spaced an expanded distance d a  from each other, compared to features  108  in unexpanded regions that are space the original distance d apart from each other. Since the distance between features  108 , in part, define the color of photonic crystal structure  100 , widening this distance will change the color of photonic crystal structure  100  at region  202 . In particular, widening the distance to d a  will cause light having longer wavelengths to reflect off region  204  compared to surrounding unbent regions of photonic crystal structure  100 . For example, distance d can be chosen such that unbent regions of photonic crystal structure  100  have a green color, while expanded distance d a  causes region  204  to have a red color. In some embodiments, distance d a  is expanded to a distance too large to cause in structural coloration of visible wavelengths of reflective light—in some cases resulting in region  204  appearing substantially transparent or colorless. 
       FIG. 2B  shows photonic crystal structure  100  bent or creased along reference line  202  in a second direction with ends  201  and  203  “coming out of the page” such that region  204  of photonic crystal structure  100  is locally compressed. This causes features  108  within region  204  to be spaced closer together. In particular, features  108  in region  204  are spaced a compressed distance d b  with respect to each other, compared to features  108  in uncompressed regions that are space the original distance d apart from each other. Compressed distance to d b  will cause light having shorter wavelengths to reflect off region  204  compared to surrounding unbent regions of photonic crystal structure  100 . For example, distance d can be chosen such that unbent regions of photonic crystal structure  100  have a green color, while compressed distance d b  is smaller than distance d, resulting in region  204  appearing a blue color. In some embodiments, distance d b  is compressed to a distance too small to cause in structural coloration of visible wavelengths of reflective light—in some cases resulting in region  204  appearing substantially transparent or colorless. 
     Photonic crystal structure  100  can also be responsive to other deformation forces other than bending or creasing. For example, opposing ends  201  and  203  can be pulled apart, thereby expanding portions of photonic crystal structure  100  and causing a corresponding color change in these expanded portions. Likewise, opposing ends  201  and  203  can be pushed together, thereby compressing portions of photonic crystal structure  100  and causing a corresponding color change in these compressed portions. In some embodiments, photonic crystal structure  100  deforms in response to heating or cooling such that photonic crystal structure  100  changes color in response to an applied heat or cooling. 
     In some embodiments, photonic crystal structure  100  flexes in response to a force that is exerted on its surface, such as a pressing force from a person&#39;s finger.  FIG. 3  shows a perspective view of a portion of photonic crystal structure  100  after a force was applied to its surface  302 . In particular, a pressing force was applied to surface  302  locally deforming region  304  of photonic crystal structure  100 . Some of features  108  within deformed region  304  become positioned farther apart than distance d, while other features  108  within deformed region  304  become positioned closer to each other than distance d. This results in deformed region  304  appearing different colors than flat regions of photonic crystal structure  100 . In this way, flexible photonic crystal structure  100  can act as a type of visible pressure sensor. 
     In some applications, flexible photonic crystal structure  100  is used as film or layer that is adhered to a surface of a larger structure, such as a display screen for an electronic device. In some applications, flexible photonic crystal structure  100  is cut into structures, much like a fabric. Note that  FIG. 3  shows flexible photonic crystal structure  100  as having a layer or film shape. However, it should be noted the flexible photonic crystal structures described herein are not limited to those having layer or film shapes. For example, the flexible photonic structures can have a more substantial thickness, suitable being sculpted or machined into a larger structure. These and other embodiments are described below. 
     In some embodiments, the flexible photonic crystal structures include particles made of one material that are packed within another material.  FIG. 4  shows a plan view of a portion of flexible photonic crystal structure  400 , which includes spherically shaped particles  402  arranged in a close-packed arrangement  405  within matrix material  404 . Spherically shaped particles  402  are made of a first material  406  and have corresponding spherically shaped interior volumes  408 , which can be filled with a second material. In some embodiments, spherically shaped particles  402  are hollow such that spherically shaped interior volumes  408  are filled with air. In this way, spherically shaped interior volumes  408  can correspond to an array of voids. This can be accomplished, for example, by coating carrier particles with first material  406 , then removing the material of the carrier particles such that first material  406  have spherical shapes with voids. In other embodiments, spherically shaped interior volumes  408  are filled with liquid or solid material. 
     Spherically shaped particles  402  are in a close-packed arrangement such that a highly regular three-dimensional arrangement of spherically shaped particles  402  and spherically shaped interior volumes  408  is achieved. Spherically shaped particles  402  also have substantially the same outer diameter OD and inner diameter ID, which are in the scale of nanometers. In this way, flexible photonic crystal structure  400  includes an array of microstructures capable of providing photonic crystal structural coloration. That is, intra-particle distance d between adjacent spherically shaped particles  402  is about half the wavelength of a wavelength of reflected light. For example, intra-particle distance d of about 200 nanometers can result in photonic crystal structure  400  having a blue color, and intra-particle distance d of about 350 nanometers can correspond to photonic crystal structure  100  appearing a red color. 
     In some embodiments, matrix material  404  has substantially the same RI as first material  406 , such that the photonic crystal optical affects are dependent upon the difference in RI of second material  408  and matrix material  404 /first material  406 . In other embodiments, first material  406  has substantially the same RI as second material  408 , such that the photonic crystal optical affects are dependent upon the difference in RI of matrix material  404  and first material  406 /second material  408 . In other embodiments, matrix material  404 , first material  406  and second material  408  are each has a different RI. In one embodiment, matrix material  404  and first material  406  are polymer materials. In a particular embodiment, first material  406  of spherically shaped particles  402  is a first type of polymer material and matrix material  404  is a second type of polymer material that has a different RI than the first type of material. In another embodiment, matrix material  404  and spherically shaped particles  402  are made of substantially the same material. In another embodiment, matrix material  404  is a polymer material, and first material  406  is glass or ceramic. 
     Matrix material  404 , first material  406  and/or second material  408  can be flexible such that intra-particle distance d within certain regions of photonic crystal structure  400  are compressible or expandable, corresponding to a change in reflected wavelengths of light in these regions, similar to described above with reference to  FIGS. 1-3 . In this way, flexible photonic crystal structure  400  will be an original color when intra-particle distance d is unchanged, and have a different color at portions where flexible photonic crystal structure  400  is deformed, such as by bending, flexing, pulling apart, pushing together, pressing (e.g., by a finger), or heating/cooling. In some embodiments, flexible photonic crystal structure  400  becomes substantially transparent in those regions that undergo deformation, as described above. 
     Flexible photonic crystal structure  400  can be fabricated using any suitable technique.  FIG. 5  shows flowchart  500  indicating a process for forming flexible photonic crystal structure  400 , in accordance with some embodiments. At  502 , a mixture is formed by mixing spherically shaped particles in a matrix material while the matrix material is in a liquid form. In one embodiment, the spherically shaped particles are made of a first type of polymer material and the matrix material is made of a second type of polymer material that has a lower melting point than the first type of polymer material. The matrix material can be liquefied by heated the matrix material to at least a melting point temperature of the second material, but not as high as the melting point of the first material. This way, the spherically shaped particles can remain intact during the mixing process. 
     At  504 , a close-packed geometry the spherically shaped particles is formed. This forms a periodic optical nanostructure corresponding to a photonic crystal structure. The close-packed geometry can be accomplished by compressing the mixture under pressure and/or by allowing the spherically shaped particles to settle within the liquefied matrix material. In some embodiments, the spherically shaped particles are coated with an adhesion-promoting coating that promotes the adhesion of the spherically shaped particles to each other. 
     At  506 , the matrix material is hardened, thereby fixing the relative positions of the spherically shaped particles in the close-packed geometry. The hardening process can include allowing the matrix material to cool to below its melting point. In some embodiments, the matrix material is made of an ultraviolet (UV) light curable material such that it can be hardened by exposure to UV light. The matrix material can be chosen based on its flexibility once cured (i.e., low Young&#39;s modulus). The resultant structure is a three-dimensional flexible photonic crystal structure. 
       FIG. 6  shows a plan view of flexible photonic crystal structure  600  formed using a laser process, in accordance with some embodiments. Flexible photonic crystal structure  600  includes channels  602  formed within matrix material  604 . Channels  602  correspond to linear shaped voids cut within matrix material  604  using, for example, a laser from a laser. Channels  602  are oriented in a crisscross pattern in three-dimensions within matrix material  604  such that intersections of channels  602  form voids  606  spaced a consistent distance d apart from one another. In addition, voids  606  have substantially the same size (e.g., diameter D) and shape. In this way, channels  602  are formed such that matrix material  604  defines an array of substantially the same voids  606 . The shape and size of voids  606  will depend, in part, on the size and number of crisscrossing channels  602  formed within matrix material  604 . In some embodiments, three-sets of parallel channels  602  (e.g., formed in x, y, z directions) are used to form voids  606  having cubic shapes. The number, size and distance between channels  602  can be chosen such that distance d causes coloration by photonic crystal effects, as described above. That is, distance d can be chosen to result in photonic crystal structure  600  to reflect any of a number of visible wavelengths of light and appear a corresponding color. 
     Matrix material  604  is a flexible material, such as a polymer material, that can be deformed (e.g., compressed or expanded) so as to change the distance d, similar to as described above with reference to flexible photonic crystal structures  100  and  400 . For example, a compressive force can be applied to regions of photonic crystal structure  600  to locally reduce distance din those compressed regions, resulting in shorter wavelengths of light being reflected off of those compressed regions of photonic crystal structure  600 . Likewise, an pulling or expanding force can be applied to regions of photonic crystal structure  600  to locally increase distance din those expanded regions, resulting in longer wavelengths of light being reflected off of those expanded regions of photonic crystal structure  600 . The compressing and expanding forces can be applied by bending, pulling, pressing, pushing, or heating/cooling photonic crystal structure  600 . 
       FIG. 7  shows flowchart  700  indicating a process for forming flexible photonic crystal structure  600 , in accordance with some embodiments. At  702 , a first set of regularly spaced channels is formed within a flexible material in accordance with a first plane. The flexible material can include any suitable compressible material, such as polymer material. The channels can have a linear shape and can be formed using a laser beam that is produced by laser. Any suitable type of laser can be used—which can depend, in part, on the type of flexible material. In some embodiments, the laser beam ablates portions of the flexible material, thereby forming the channels. Lasers can provide a precision cutting and material removal mechanism for create channels having very small dimensions (e.g., widths) with precise spacings between the channels. 
     At  704  a second set of regularly spaced channels is formed within the flexible material in accordance with a second plane that is non-parallel to the first plane such that the second set of channels intersect with the first set of channels. The points of intersection correspond to voids having substantially the same shape and that are substantially the same distance apart from one another, with the surrounding flexible material defining the size and shape of the voids. In this way, a two-dimensional array is formed within the flexible material. The size and distance between the voids can be chosen such that the light incident on the array reflects light in accordance with a photonic crystal. In some embodiments, the resultant photonic crystal is periodic in two dimensions. 
     At  706 , a third set of regularly spaced channels is optionally formed within the flexible material in accordance with a third plane that is non-parallel to the first plane and the second plane. The third set of channels allows for more dimension freedom. In particular, a photonic crystal that is periodic in three dimensions can be formed. It should be noted that flowchart  700  does not necessarily indicate a temporal sequence of  702 ,  704  and  706 . For example, forming the first and second sets of channels ( 702  and  704 ) can be done in a single laser procedure. Likewise, forming the first, second and third sets of channels ( 702 ,  704  and  706 ) can be done in a single laser procedure. 
       FIGS. 8A and 8B  show cross section views portions of layered flexible photonic crystal structures  800  and  810 , respectively, in accordance with some embodiments. Layered flexible photonic crystal structures  800  and  810  each include multiple layers of photonic crystals. Layered flexible photonic crystal structure  800  of  FIG. 8A  includes first layer  802  and second layer  804 , each of which is a photonic crystal structure in itself. That is, each of first layer  802  and second layer  804  has an array of a first material (e.g., air within voids) within a second material, where the first material has a first RI that is different from a second RI of the second material and where the array produces structural coloration in accordance with a photonic crystal. First layer  802  and second layer  804  can be coupled together using, for example, adhesive or by melting/molding first  802  and second  804  layers together. 
     In some embodiments, first layer  802  and second layer  804  have different periodic structures and therefore reflect different visible wavelengths of light. For example, first layer  802  can have a photonic crystal structure suitable for reflecting wavelengths associated with a blue color and second layer  804  can have a photonic crystal structure suitable for reflecting wavelengths associated with a red color. This can give layered flexible photonic crystal structure  800 , when viewing surface  808 , a combined blue and red appearance color, perhaps a purple color. Likewise, if first layer  802  reflects wavelengths associated with a blue color and second layer  804  reflects wavelengths associated with a green color, layered flexible photonic crystal structure  800  at surface  808  can appear to have a combined blue and green color, perhaps a bluish-green or aqua color when viewing surface  808 . In this way, the multiple layered configuration of layered flexible photonic crystal structure  800  can provide a variety of colors that may be difficult to achieve using only a single layer of photonic crystal. In addition, one or both of first layer  802  and second layer  804  can be flexible so as to change color in response to stress or strain, such as bending, flexing, pulling apart, pushing together, pressing or heating/cooling—thereby providing even more color variations and possible combinations. 
       FIG. 8B  shows flexible photonic crystal structure  810 , which includes three layers: first layer  812 , second layer  814  and third layer  816 —each of which is a photonic crystal structure. This configuration allows for even more possible color variations for flexible photonic crystal structure  810  when viewing surface  818 . For example, first layer  812 , second layer  814  and third layer  816  can each have different periodic structures and reflect different visible wavelengths of light. Alternatively, first layer  812  and third layer  816  can reflect the a first set of visible wavelengths of light, while second layer  814  reflects a second set of visible wavelengths of light different from the first set. Note that flexible photonic crystal structures having any suitable number of layers and combinations can be used, and are limited by two or three layers shown in  FIGS. 8A and 8B . 
     There are numerous applications for the flexible photonic crystal structures described herein, such flexible photonic crystal structures  100 ,  400 ,  600 ,  800  and  810  described above. Some such applications are described below with reference to  FIGS. 9A-12 . 
       FIGS. 9A and 9B  show perspective views of case  900  that includes a photonic crystal structure, in accordance with some embodiments.  FIG. 9A  shows a back view and  FIG. 9B  shows a front view of case  900 . Case  900  is designed to cover and protect part of an electronic device, such as a mobile phone, tablet device or other portable electronic device. Cavity  902  is shaped and sized to accommodate the electronic device therein, such that the back and sides of the electronic device are covered. In some embodiments, case  900  is flexible so that portions of case can be bent or twisted to position the electronic device within cavity  902 . 
     Portions of case  900 , such as exterior surfaces  904 , include a flexible photonic crystal structure such as described above. In some embodiments, the flexible photonic crystal structure in the form of a film or layer that is applied onto a larger support structure that defines an overall shape of case  900 . In other embodiments, the flexible photonic crystal structure includes the support structure of case  900 —that is, the flexible photonic crystal structure is a bulk flexible material that is shaped in accordance with the shape of case  900 . 
     The photonic crystal structure of case  900  can change color in response to stress or strain, such as a pressure applied to back surface  903  and side surfaces  905 . For example, pressed regions  906  and  908  of can visually change color in response to a pressing force from a user&#39;s finger. That is, the applied pressure deforms the periodic photonic crystal structure pressed regions  906  and  908  such that these regions reflect a different color than un-pressed regions of case  900 . For example, pressed regions  906  and  908  can appear blue while un-pressed regions surrounding pressed regions  906  and  908  appear green or red. In some embodiments, pressed regions  906  and  908  appear multi-colored. In some embodiments, pressed regions  906  and  908  can change to a substantially colorless or translucent appearance. 
     The shapes of first region  906  and second region  908  correspond to the deformed areas of the photonic crystal structure. In some embodiments, flexible photonic crystal structure is made of a flexible material that is formulated to have a particular timescale for re-expansion after compression, such that pressed regions  906  and  908  take time to re-expand and return to an original color, thereby appearing to fade away. 
     The flexible photonic crystal structures described herein can also be used with display screen for an electronic device.  FIG. 10  shows display assembly  1000 , which includes housing  1002  and display screen  1004 . In some embodiments, display screen  1004  is a touch screen. Display assembly  1000  can correspond to a portion of a display monitor as part of a computing device. Flexible photonic crystal structure  1006  is positioned on display screen  1004  such that a user touches flexible photonic crystal structure  1006  when attempting to touch display screen  1004 . In some embodiments, flexible photonic crystal structure  1006  is an integral part of the display screen assembly of the computing device. In other embodiments, flexible photonic crystal structure  1006  is in the form of a film that is applied onto display screen  1004  using, for example, an adhesive. 
     Pressed region  1008  corresponds to a region of flexible photonic crystal structure  1006  that has been pressed, such as by a user&#39;s finger. This locally deforms the periodic structure of flexible photonic crystal structure  1006 , thereby causing pressed region  1008  to change color. In this way, flexible photonic crystal structure  1006  can act as a sensor that shows visible evidence of display screen  1004  being touched. In some embodiments, pressed region  1008  changes to a substantially colorless or translucent appearance. As described above, the flexible material of flexible photonic crystal structure  1006  is chosen to have a particular timescale for re-expansion and return to an original color. 
     In some embodiments, the flexible photonic crystal structures are used to form flexible screen.  FIGS. 11A and 11B  show perspective views of flexible screen  1100 , which can be used incorporated in a consumer product, such as a flexible display for an electronic device or a flexible electronic paper display. Flexible screen  1100  includes flexible photonic crystal structure  1102 . In some embodiments, flexible photonic crystal structure  1102  comprises one or more layers as part of flexible sheet  1100 —while in other embodiments, flexible photonic crystal structure  1102  and flexible screen  1100  are one in the same.  FIG. 11A  shows flexible screen  1100  in a flat configuration such that the periodic structure of flexible photonic crystal  1102  is substantially consistent. This flat configuration causes flexible photonic crystal structure  1102  to appear as a single consistent color. In some embodiments, flexible screen  1100  appears substantially colorless in the flat configuration shown in  FIG. 11A . 
       FIG. 11B  shows flexible screen  1100  in a flexed configuration where different portions of flexible photonic crystal structure  1102  are flexed at varying degrees, resulting in flexible screen  1100  taking on a corresponding pattern of colors. For example, first region  1104  can be flexed a first amount such that first region  1104  appears a first color, second region  1106  can be flexed a second amount such that second region  1106  appears a second color, and third region  1108  can be flexed a third amount such that third region  1106  appears a third color. The result is flexible screen  1100  takes on a multicolored pattern appearance in response to bending. Flexible screen  1100  can also respond to stretching, compressing, bending, pressing and twisting forces to achieve correspondingly different color patterns. This gives flexible screen  1100  the ability to dynamically change color in accordance with its change in shape. In some embodiments, flexible screen  1100  is substantially colorless in the flat configuration of  FIG. 11A  and becomes colored in the flexed configuration of  FIG. 11B . In other embodiments, flexible screen  1100  appears colored in the flat configuration of  FIG. 11A  and becomes substantially colorless in the flexed configuration of  FIG. 11B   
     In some embodiments, the flexible photonic crystal structures are used as soft-good material.  FIG. 12  shows a perspective view of a roll  1200  of flexible sheet  1202 . Flexible sheet  1202  includes one or more layers of a flexible photonic crystal structure such that stresses placed on flexible sheet  1202 , such as stretching, compressing, bending, pressing and twisting forces, can result in a corresponding color change. For example, creases  1204  within flexible sheet  1202  can have a different color than surrounding portions of flexible sheet  1202 . Flexible sheet  1200  can be used to fabricate any of a number of consumer products, such as bags and backpacks that change color along creases and folds and that change color based on whether a compressive or tensile force is applied. Other products include wearable items, such as clothing (e.g., shirts or portions of shirts) and accessories such as wristbands, headbands, jewelry, gloves, belts, watches, ties, scarves, etc. 
     The flexible photonic crystal structures described herein can be used for any of a number of applications other than those described above. For example, the flexible photonic crystal structures can be used to form a track pad or mouse that changes color in locations where it is pressed. The flexible photonic crystal structures can be used to form toys, such as balls that change color when bounced off the floor. Other applications include stress balls or exercise equipment that change color in locations that are squeezed. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20160812
Publication Date: 20200623
Grant Date: 20200623
Priority Date: 20150826
Inventors: WILSON, JAMES R.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B1/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/0131", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/0131", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B1/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/0131", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01L1/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/005", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 58103600