发明内容：
[0012]The present invention is predicated on the understanding that a AR display can be made flexible by taking into account the various refractive indexes and material properties of specific materials and determining the optimised internal reflection in order to transmit light from a light source to a user. To this end, it is envisioned that a thin film display fitted with light reflectors as reflective pixels that can reflect images to a user's eye and a flexible waveguide for guiding light from a light source can overcome at least some of the disadvantages. Advantageously, a light guiding apparatus which is flexible and/or curved can improve its installation in a space-limited apparatus as it allows for the image source to be positioned some distance away from a reflector or screen, the image source not in a line of sight to the reflector. Additionally, as each light reflector comprises an array of nanostructures and/or microstructures, with each nanostructures and/or microstructures defining an interface for reflective light, a transparent (or at least a translucent) light reflector is formed. To this end, a see-through effect from a lateral side of the waveguide to another lateral side can be obtained. At the same time the light beam arriving from the image-receiving object can have a high brightness with low consumption of light energy, enhanced field of view, sharpness and can reduce strain to the eyes. This invention can be incorporated as a component in near field applications such as a spectacle or on a helmet or far field applications such as car windscreen and windows. For example, because the electronics can be positioned at a distance away from the display, spectacles are ‘end’ heavy, and thus improve comfort for the user.
[0013]The present invention relates to a light guiding apparatus, comprising:
a) a flexible and/or curved light transmitting polymer guide having a light path extending between a first end and a second end; and
b) at least one light reflector disposed within the polymer guide at an angle relative to the light path;
wherein the at least one light reflector comprises an array of nanostructures and/or microstructures; and
wherein the array of nanostructures and/or microstructures is selected from a metal-polymer boundary, an air-polymer boundary, a material-polymer boundary, or a combination thereof, the material having a lower refractive index than the polymer guide.
[0014]Advantageously, the polymer guide allows an image source to be positioned at a distance away from the user's eyes. Further, the polymer guide allows the light path connecting the image source and light reflector to be in a curved or bent configuration such that the image source and light reflector are not in a line of sight, thereby increasing its adaptability in various augmented reality applications. The image guiding apparatus can carry an image while being bent without distortion and leakage of the image to reach the light reflector such that it is reflect into viewer's eyes while same time being transparent. The array of nanostructures and/or microstructures allows light to be reflected to a viewer's eye and at the same time allows for transparency.
[0015]In some embodiments, the light reflector is fully embedded within the polymer waveguide. In other embodiments, the light reflector is interposed within the polymer guide such that the polymer guide is in contact with both an anterior surface and posterior surface of the light reflector.
[0016]In some embodiments, the light reflector is disposed at an angle of about 5° to about 80° relative to the light path.
[0017]In some embodiments, each of the nanostructures and/or microstructures is disposed at an angle of about 5° to about 80° relative to the light path. Each nanostructure and/or microstructure in the array can have a same angle or different angles with respect to the light path.
[0018]In some embodiments, each of the nanostructures and/or microstructures independently has a thickness of about 4 nm to about 500 μm.
[0019]In some embodiments, each of the nanostructures and/or microstructures independently has a width of about 50 nm to about 1000 μm.
[0020]In some embodiments, each of the nanostructures and/or microstructures independently has a pitch of about 50 nm to about 500 μm.
[0021]In some embodiments, the light guiding apparatus comprises a plurality of light reflectors disposed within the polymer guide and arranged in series at an angle relative to the light path.
[0022]In some embodiments, the polymer guide has a refractive index of about 1.4 to about 1.6.
[0023]In some embodiments, the polymer guide has a transparency of more than 90%.
[0024]In some embodiments, the polymer guide has a flexural modulus of less than about 4 GPa.
[0025]In some embodiments, the polymer guide is made from a material selected from polydimethylsiloxane (PDMS), polycarbonate, polyester, acrylic such as poly(methyl methacrylate), their derivatives and combinations thereof.
[0026]Advantageously, it was found that the use of a flexible polymer can still impart a large viewing angle and high coupling efficiency to the light guiding apparatus.
[0027]In some embodiments, the polymer guide has a cross sectional thickness of about 1 μm to about 10 mm.
[0028]In some embodiments, the polymer guide has a cross sectional breadth of about 1 μm to about 30 mm.
[0029]The present invention also relates to an array of light guiding apparatus as disclosed herein.
[0030]In some embodiments, the respective light guiding apparatus in the array are each separated by a cladding layer.
[0031]In some embodiments, the respective light guiding apparatus in the array are each separated by a buffer layer.
[0032]In some embodiments, the respective light guiding apparatus in the array is collectively coated by a buffer layer.
[0033]In some embodiments, the light guiding apparatus or array further comprises a light source disposed adjacent to the first end of the polymer guide of the light guiding apparatus.
[0034]In some embodiments, the light guiding apparatus or array further comprises optical coupling means for coupling light from light source into the polymer guide of the light guiding apparatus.
[0035]The present invention also relates to a method of fabricating a light guiding apparatus, comprising:
a) forming a flexible and/or curved light transmitting polymer guide having a light path extending between a first end and a second end; and
b) disposing at least one light reflector within the polymer guide at an angle relative to the light path;
wherein the at least one light reflector comprises an array of nanostructures and/or microstructures; and
wherein the array of nanostructures and/or microstructures is selected from a metal-polymer boundary, an air-polymer boundary, a material-polymer boundary or a combination thereof, the material having a lower refractive index than the polymer guide.
[0036]The present invention also relates to a method of fabricating an array of light guiding apparatuses, comprising:
a) forming a first flexible and/or curved light transmitting polymer guide having a light path extending between a first end and a second end;
b) stacking a second flexible and/or curved light transmitting polymer guide next to the first light transmitting polymer guide; and
b) disposing at least one light reflector within the first and second polymer guide at an angle relative to the light path;
wherein the at least one light reflector comprises an array of nanostructures and/or microstructures; and
wherein the array of nanostructures and/or microstructures is selected from a metal-polymer boundary, an air-polymer boundary, a material-polymer boundary or a combination thereof, the material having a lower refractive index than the polymer guide.
具体实施方式：
[0052]FIG. 1 shows a side view of an exemplary light guiding apparatus 3 of the present invention. The light guiding apparatus 3 is suitable for transmitting light (as indicated by a dashed arrow) from a light source 1 to a user's eye 5. The light guiding apparatus 3 comprises a light transmitting polymer guide 320 having a first end 31, a second end 32 extending from the first end 31, and a light path 33 extending between the first end 31 and the second end 32. In this embodiment, the second end 32 extends outward from the first end 31; that is, the second end 32 extends from the first end 31, away from the light source 1. The light path 33 is disposed between the first end 31 and the second end 32.
[0053]The polymer guide 320 is capable of transmitting light. The transmittance of a material is the proportion of the incident light that moves all the way through to the other side; i.e. the effectiveness in transmitting light. The polymer guide is light transmitting in that it is capable of transmitting at least 90% of light from the light source, or at least 85%, at least 80%, at least 75%, at least 70%, at least 65% or at least 60%.
[0054]Alternatively, the polymer guide can have a transparency of more than about 90%. Transparency (or transmission of visible light) is characterized by light transmittance, i.e. the measured percentage of incident light transmitted through a material. The higher the transmittance, the higher the transparency. In other embodiments, the transparency is more than about 85%, about 80%, about 75%, about 70%, about 65% or about 60%.
[0055]The polymer guide 320 is capable of transmitting light in the visible light spectrum; i.e. wavelength of about 380 nm to 740 nm. To this end, the polymer guide 320 is capable of transmitting at least the primary colours (red, yellow, blue). The polymer guide 320 can be capable of transmitting monochromatic light (red, orange, yellow, green, cyan, blue, violet). The polymer guide 320 can be also capable of transmitting mixed colours, for example, pink and magenta.
[0056]The light guiding apparatus 3 comprises at least one light reflector 321. The light reflector 321 can be approximate to the second end 32. The light reflector 321 is disposed within the polymer guide. For example, the light reflector can be fully embedded within the polymer guide. Preferably, the light reflector is interposed within the polymer guide. To this end, the light reflector is inserted or placed between two sections of the polymer guide. The light reflector 321 is disposed at an angle relative to the light path 33. In this way, the light reflector 321 reflects the light towards a pre-determined direction, where the user 5 is positioned. The second end 32 can be further surface treated by a coating 322 to form a light-leaving surface, but not limited to this.
[0057]Accordingly, the present invention relates to a light guiding apparatus, comprising:
a) a flexible and/or curved light transmitting polymer guide having a light path extending between a first end and a second end; and
b) at least one light reflector embedded within the polymer guide at an angle relative to the light path;
wherein the light reflector is selected from a metal-polymer boundary, an air-polymer boundary, a material-polymer boundary, or a combination thereof, the material having a lower refractive index than the polymer guide.
[0058]By disposing the light reflector within the polymer guide, or preferably interposed within the polymer guide, leakage of the transmitted light beam within the polymer guide is minimised. Further, extension of the polymer guide rearward from the light reflector, such that the polymer guide is in contact with an anterior surface and posterior surface of the light reflector, acts to direct stray light from interfering with the image received at the viewer's eye.
[0059]The light reflector 321 can be a homogenous surface. More advantageously, the light reflector 321 can comprise an array of nanostructures and/or microstructures. For example, FIG. 12 shows a light reflector B and the array of nanostructures and/or microstructures C. FIG. 13 shows the array of nanostructures and/or microstructures as 50 μm square microstructures with 20 μm pitches.
[0060]As used herein, “array” refers to an arrangement of at least two entities.
[0061]It was found that this feature allows for transparency of the light reflector, which allows the light guiding apparatus to be used in augmented reality. In this sense, a virtual image can be reflected to a viewer's eye through reflection at the nanostructures and/or microstructures. The pitch or gaps within the array of structures allows light transmitting from the real world physical object to pass through, thus providing visibility. The viewer can thus see an overlap of the virtual image and the physical object even when the light guiding apparatus is positioned in front of the viewer's eye.
[0062]This is in contrast to the prior art, for example US 2004/0234224, US 2007/0140615 and US 2010/0074579, which are mainly focused in applications in fibre-optics communication and photonic circuits. In such applications, light of a certain wavelength is often used and thus there is no or little need for multiplexing light of various wavelength. Further, much prior focus has been placed on improving transmission of light or reduce noise; through the connection of the polymer guide with the light reflector, and/or the interface of the cladding layer and the light reflector or focusing the light at the light reflector. For example, a concaved light reflector had been suggested to focus the light or the cladding layer can be staggered relative to the light reflector to reduce noise to a detector. The present invention instead uses a light reflector comprising an array of structures, which inadvertently allows some of the transmission light to be lost through the gaps of the structures, in order to at least obtain the benefit of transparency for a viewer to see through the light guiding apparatus.
[0063]Additionally, the thickness, width and size of the nanostructures and/or microstructures can be varied to tune reflectivity and the light transmitted through from outside to enable see through.
[0064]Furthermore, as the transmitted light (dotted line in FIG. 1) may be not travelling directly to the light reflector but can also undergo multiple reflection off the sides of polymer guide 320, the size of the final image received at a user's eye 5 can be varied. This can, for example, be effected using an optics at the first end 31. In this way, a thin waveguide structure can be constructed.
[0065]Further, by multiplexing the light beam transmitting within the polymer guide, a relatively thin light guiding apparatus can be formed. This is in contrast to prior waveguides, in which light from a source is split into a plurality or array of waveguides instead of the light reflector being an array of structures as disclosed herein, with each waveguide independently transmitting light of a different wavelength to a light reflector. A problem with such a setup is that it tends to be bulky and is not suitable for installation in headgear for use in augmented reality.
[0066]When the light reflector 321 is formed as a homogenous surface, it can be selected from a metal-polymer boundary, an air-polymer boundary, a material-polymer boundary or a combination thereof. The boundary is formed from an interface of the polymer guide and a metal, air, material or a combination thereof. The material and air can have a lower refractive index than the polymer guide. The metal can be a dielectric metal. These materials can reflect light travelling in the light path towards the user.
[0067]The presently disclosed light guiding apparatus is flexible. To this end, the polymer guide can be made from a flexible polymer. Accordingly, while this embodiments shows the light guiding apparatus 3 as a straight bar structure, it is not limited to this. In other embodiments, the light guiding apparatus 3 can be a curved structure or can be bent accordingly to conform to a surface.
[0068]The presently disclosed light guiding apparatus can also be curved. To this end, the polymer guide can be of a curved configuration. When the polymer guide is curved, there is no line of sight along the light path between the first end and the second end.
[0069]Stiffness (or rigidity) is a property of a polymers that can be described by flexural modulus or bending modulus of elasticity. Flexural modulus denotes the ability of a material to bend. It is a measure of a materials stiffness/resistance to bend when a force is applied perpendicular to the long edge of a sample—known as the three point bend test. The flexural modulus is represented by the slope of the initial straight line portion of the stress-strain curve and is calculated by dividing the change in stress by the corresponding change in strain. Hence, the ratio of stress to strain is a measure of the flexural modulus. Flexural Modulus can be measured by test methods such as ASTM D790 and ISO 178. Flexural or bending modulus of elasticity can be equivalent to the tensile modulus (Young's modulus) or compressive modulus of elasticity.
[0070]By bending the light via the light guiding apparatus 3, the installation flexibility in a space-limited apparatus can be improved.
[0071]The polymer guide can have a flexural modulus of less than about 4 GPa. This provides the light guiding apparatus with an acceptable flexibility for conforming to a morphology of a surface. For example, the surface can have a curved morphology. To this end, the light guiding apparatus can be flexible to conform to the curved morphology of the surface, or the light guiding apparatus can be curved (moulded in a mould) which can be positioned in close contact with the surface having a curved morphology.
[0072]The flexibility of the polymer guide can be characterised by a stiffness value and/or a hardness value. The stiffness can be a bending stiffness. For example, when polydimethylsiloxane (PDMS) is used, the stiffness can be from about 0.5 MPa to about 8 MPa.
[0073]The polymer guide can have a refractive index of about 1.4 to about 1.6. For example, if PDMS is used to form the polymer guide, the polymer guide can have a refractive index of about 1.4.
[0074]The refractive index (n) of a material is a dimensionless number that describes how fast light travels through the material. It is defined as
n=cv
where c is the speed of light in vacuum and v is the phase velocity of light in the medium. The refractive index determines how much the path of light is bent, or refracted, when entering a material.
[0075]The polymer guide can be made from a material selected from polydimethylsiloxane (PDMS), polycarbonate, polyester, acrylic such as poly(methyl methacrylate), their derivatives and combinations thereof.
[0076]The polymer guide can have a cylindrical structure, or a rectangular structure, or a polygonal structure along the light path. The polymer guide can have a circular cross section, or a squarish, rectangular or polygonal cross section. The polymer guide can have a cross sectional thickness of about 1 μm to about 10 mm.
[0077]The polymer guide can have a cross sectional breadth of about 1 μm to about 30 mm.
[0078]The end surface of the first end 31 and the second end 32 of the light guiding apparatus 3 can be a flat, sloped, convex, or concave surface. For convenient expression, the end surface of the second end 32 of the light guiding apparatus 3 is shown and is represented by a flat surface in the current embodiment, but not limited to this.
[0079]A groove can be further formed on the light path 33 of the light guiding apparatus 3. In other embodiments, a plurality of grooves can be formed on the light path 33 of the light guiding apparatus 3 and can be disposed in a parallel or in an array form. The grooves can be disposed close to both or either of the first end 31 and the second end 32. Advantageously, the grooves can be used to alter light travelling in the light path 33 as it refract or reflects through different optical structures. The shape, size of the image formed by the light can thus be adjusted and which functions to modify the image achieved by the user.
[0080]The light reflector 321 is disposed within the polymer guide 320. Alternatively, the light reflector 321 can be disposed within the polymer guide 320 adjacent to the second end 32, as shown in FIG. 2. Alternatively, the light reflector 321 can be disposed within the polymer guide 320 adjacent to the first end 31. Preferably, the light reflector is interposed within the polymer guide.
[0081]As shown in FIG. 1, the light reflector 321 is positioned at an angle relative to the light path 33. This allows the light to be reflected out of the light path 33 towards a user 5. Preferentially, the light reflector is positioned or disposed such that it is not parallel to the light path, or not parallel to a longitudinal dimension or curvature of the light path. The light reflector is also positioned or disposed such that it is not perpendicular to the light path, or not perpendicular to a longitudinal dimension or curvature of the light path. For example, the light reflector can be disposed at an angle of about 5° to about 80° relative to the light path. Preferably, the angle of about 5° to about 60° relative to the light path.
[0082]For the light reflector to sufficiently be able to reflect light, the light reflector can be of a certain thickness. For example, the light reflector can have a thickness of about 3 nm to about 800 μm. In other embodiments, the light reflector has a thickness of about 3 nm to about 250 nm.
[0083]Without wanting to be bound by theory, based on Snell's law and total internal reflection (nPDMS sin (Qc)=nair sin (90)), when the light enters from the polymer guide (PDMS refractive index=1.43) to light reflector (air gap structure), the light reflects due to the total internal reflection provided the angle of the air-gap structure (boundary between the PDMS and air-filled pixel) is optimised. Here, by controlling the thickness of the air-filled structures from a few microns to tens of microns, it is possible to control the reflected light intensity to make the sample transparent to the viewer. Hence the total reflection TF=f(s)*f(d), in which f(s) is total internal reflection and f(d) is the depth or thickness of the air-filled structures.
[0084]At least one light reflector can be disposed within the light path. For example, a plurality of light reflectors can be positioned in parallel or in series or in an array within the light path. The plurality of light reflectors can be positioned at various angles independent of each other. This allows more light to be reflected to the user, and can thus provide for a more efficient light guiding apparatus. Further, a plurality of light reflectors advantageously allows for the light reflectors to be each smaller in size, and can improve the transparency of the light guiding apparatus as a whole. Since each light reflector can be partially reflecting, it is possible for a viewer to see through the real world and overlay with images from the micro-display. The light leakage and image distortion, especially while bending along the frame is reduced (increased sharpness) when a plurality of light reflectors are used. Here, the eyestrain is reduced due to the thin planar structure and field of view/eye box has increased due to the multiple reflector structures.
[0085]FIG. 3a shows an example of a light guiding apparatus 3 having a plurality of light reflectors 321a, 321b, 321c. In this embodiment, the light reflectors are arranged in series, such that light not reflected by a preceding light reflector (or by the array of nanostructures and/or microstructures in a preceding light reflector) is reflected by the following light reflector (or the array of nanostructures and/or microstructures in the following light reflector). The light reflector and/or each of the nanostructures and/or microstructures are made from a metal such as gold. The light guiding apparatus 3 is also shown in a non-linear configuration. As the light is internally reflected within the light path 33, the light is able to reach the light reflectors 321a, 321b, 321c when the polymer guide 320 is bent or curved.
[0086]FIGS. 3b and 3c shows other embodiments of the light guiding apparatus 3. The non-linear configuration of the light guiding apparatus 3 can be of an angular configuration, for example a prism cut 326a on the outer curvature or prism cut 326a and 326b in both outer and inner curvature. Alternatively, the light guiding apparatus 3 can have multiple angles 328 as shown in FIG. 3C. The light guiding apparatus 3 can have a cladding layer deposited on one side 322a (partially covering) or both sides 322a and 322b (fully covering) of the light guiding apparatus 3. The cladding layer can be made of nanoscale metallic film or metal dielectric film or dielectric mirror.
[0087]FIG. 4 shows the image formed using the light guiding apparatus of FIG. 3a.
[0088]A layer of metal such as aluminium or silver is a good reflector for light the visible spectrum. The reflectance of a metal layer can be calculated from the index of refraction n and the extinction coefficient k of the metal. The reflectance (R) of a metal surface in air is given by:
R (%)=(n-1)2+k2(n+1)2+k2×100.
[0089]In some embodiments, when the light reflector and/or each of the nanostructures and/or microstructures is a metal, the metal selected from gold, silver, aluminium, chromium, copper, nickel, platinum or their combination thereof.
[0090]When the light reflector and/or each of the nanostructures and/or microstructures is a metal-polymer boundary, at least one metal pixel is formed within the polymer guide. The metal can have a thickness of about 3 nm to about 80 nm. Preferably, the thickness is about 4 nm to about 60 nm. Depending on the thickness of the metal layer, the amount of light that is reflected can be varied, and at the same time the transparency of the image guiding apparatus can be varied.
[0091]A material or air having a lower refractive index than the polymer guide can be used as a light reflector. This is based on the understanding of Snell's law and total internal reflection that light in an optically denser medium can be reflected off an interface with a optically less dense medium if the angle at which the light makes with the normal of the interface is more than the critical angle. The critical angle is the angle of incident in an optically denser medium for which the angle of refraction is 90°.
[0092]Accordingly, the light reflector and/or each of the nanostructures and/or microstructures can be an air-polymer boundary or a material-polymer boundary. The material can have a refractive index of less than about 1.4. In other embodiments, the material is polytetrafluoroethylene (PTFE). Alternatively, when air is used, at least one air filled gap (air pixel, air filled nanostructure and/or microstructure) is formed within the polymer guide.
[0093]When the light reflector and/or each of the nanostructures and/or microstructures is a material having a refractive index of less than about 1.4, the material can have a thickness of about 10 nm to about 200 μm. Preferably, the thickness is about 20 nm to about 10 μm. Depending on the thickness of the material, the amount of light that is reflected can be varied, and at the same time the transparency of the image guiding apparatus can be varied.
[0094]Such nanostructures and/or microstructures can efficiently couple the light and provide an effect of focusing light towards the user 5, thus provides for a brighter and clearer image.
[0095]For example, the light reflectors 321a, 321b, 321c of FIG. 3 can be pixelated in the sense that the light reflectors comprises an array of structures, the structures separated from each other by a pitch. To this end, the reflection or transmission is controlled by varying the pitch of nanostructures and/or microstructures (pixels), size and thickness. This gives more degree of freedom for reflection and see through transmission.
[0096]The nanostructures and/or microstructures each independently can have a thickness of about 4 nm to about 500 μm, about 4 nm to about 300 μm, about 4 nm to about 100 μm, about 4 nm to about 50 μm, or about 4 nm to about 10 μm. The nanostructures and/or microstructures can be made of a metal and have a thickness of about 4 nm to about 50 nm. The nanostructures and/or microstructures can be made of a material of lower refractive index compared to the polymer guide and have a thickness of about 4 nm to about 20 μm.
[0097]The nanostructures and/or microstructures can each independently have a size or width of about 50 nm to about 1000 μm, about 50 nm to about 700 μm, about 50 nm to about 500 μm, about 50 nm to about 300 μm, about 50 nm to about 100 μm, about 50 nm to about 70 μm, about 50 nm to about 50 μm, or about 50 nm to about 10 μm. For example, nanostructures and/or microstructures can made of gold and have a size of about 50 μm.
[0098]The pitch between the nanostructures and/or microstructures can each independently be about 50 nm to about 500 μm, about 50 nm to about 400 μm, about 50 nm to about 300 μm, about 50 nm to about 200 μm, about 50 nm to about 100 μm, about 50 nm to about 70 μm, about 50 nm to about 50 μm, or about 50 nm to about 10 μm. For example, pitch can be about 20 μm.
[0099]The nanostructures and/or microstructures can have each independently have a different shape. For example, the shape can be square, rectangle, triangle, circular, hexagonal or polygonal. The above array of nanostructures and/or microstructures can be arranged in different configurations. For example, the array can be a square array, hexagonal array, triangular array, rectangular array. The boundaries of the array can be undefined or not straight such that a random array is arranged.
[0100]When the light reflectors comprises of nanostructures and/or microstructures (pixilation), the reflectance (R) of a metal surface in air is given by:
R (%)=(n-1)2+k2(n+1)2+k2×fpitch×fstructure size×fstructure thickness×100
wherein ‘f’ denotes ‘function of’.
[0101]Similarly for air-filled pixels, the reflectance (T) is given by
T(%)=fs×fpitch×fstructure size×fstructure thickness×100
[0102]Wherein fs is a function of the total internal reflection.
[0103]Accordingly, in some embodiments, the at least one light reflector is provided by a single air filled gap, an array of micro or nano-size air filled gaps or an array of metal micro or nano-sized structures. The metal can be gold or silver.
[0104]When the light reflector 321 is positioned at an angle relative to the light path 33, each of the nanostructures and/or microstructures can be independently positioned at an angle relative to the light reflector. In this sense, each of the nanostructures and/or microstructures is positioned at various angles relative to the light path. For example, when the light reflector is positioned at 45° relative to the light path, each of the nanostructures and/or microstructures can be independently positioned at an angle of 0° to about 40° offset from the plane of the light reflector. Accordingly, each nanostructures and/or microstructures can independently be about 5° to about 85° relative to the light path. Preferably, the angle is of about 5° to about 80°, or about 15° to about 60° relative to the light path.
[0105]It was found that this is further advantageous as it provides for a wider field of view to the viewer. Accordingly, the viewer's eye does not have to be positioned at a specific location to receive the output light, but can be adjusted about a 3D volume. This is particularly advantageous for applications in headgear, as it accommodates for different head sizes and a perceived depth of field by the viewer.
[0106]Further, as the array of nanostructures and microstructures allows for multiple reflections at various angles, by tuning the angles of these structures, an image at a light source can be expanded to an appropriate size for viewing by a viewer. This allows for miniaturization of other components that are used together with the light guiding apparatus.
[0107]The expansion of an image from a source to the eye can be dependent on width and thickness (depth) of the nanostructures and/or microstructures. In some embodiments, the thickness (depth) of the structures is about 5 nm to about 500 μm and the width is about 50 nm to about 500 μm.
[0108]In some embodiments, an expansion ratio (of the image at a light source to the image at an eye) is about 2 to about 100.
[0109]Further advantageously, by having an array of nanostructures and/or microstructures each independently at various angles, the light beam transmitted within the polymer guide can be scrambled. In this regard, a spectral image can be obtained (imaging that uses multiple bands across the electromagnetic spectrum). Accordingly, more information can be relayed to a viewer's eye as the image can be coloured. Further, as a more of the light beam in the polymer guide is reflected towards the eye, a better image quality can be received at the viewer's eye which is suitable for outdoor use where there is a high background noise. This is in contrast to prior waveguides which uses laser beams as a light source, which only allows for a monotonous colour, is excessively bright and has a large light loss.
[0110]The light guiding apparatus 3 can further comprise a cladding layer, or a coating 322. The cladding layer envelopes or encapsulates the polymer guide 320 and/or light path 33. The cladding layer can be in contact with the polymer guide 320 and/or light path 33. The cladding layer can comprise one or more layers of materials of lower refractive index than the polymer guide 320 and/or light path 33 which has a higher refractive index. The cladding layer is preferentially advantageous as it allows light to be confined to the polymer guide 320 and/or light path 33 by total internal reflection (instead of just internal reflection) at the boundary between the two. To this end, light propagation in the cladding layer is suppressed and light leakage can be eliminated or at least reduced.
[0111]The cladding layer or coating 322 can be applied adjacent to the second end 32. When applied as such, the coating serves to remove stray light such that a focused image is formed at the user 5. Alternatively, the coating 322 can be applied throughout a surface of the polymer guide 33. When applied as such, the coating serves to improve the internal reflection such that a brighter image is formed at the user 5.
[0112]The cladding layer can be selected from a metal, a material having a lower refractive index than the polymer guide, or a combination thereof. When the cladding layer is a metal, the metal can be selected from gold, silver, aluminium, chromium, copper, nickel, or platinum. When the cladding layer is a material having a lower refractive index than the polymer guide, the material can be selected from air, or polytetrafluoroethylene (PTFE). In some embodiments, the cladding layer comprises a dielectric material or a dielectric mirror (a dielectric stack). A dielectric mirror, also known as a Bragg mirror, is a type of mirror composed of multiple thin layers of dielectric material. Some dielectric materials, but are not limited to, are magnesium fluoride, silicon dioxide, tantalum pentoxide, zinc sulfide, and titanium dioxide.
[0113]The cladding layer can be about 50 nm to about 200 nm thick. Alternatively, it can be less than about 150 nm, about 120 nm, about 100 nm, about 80 nm, about 50 nm, about 40 nm, about 30 nm, about 20 nm or about 10 nm.
[0114]The light guiding apparatus 3 can further comprise a buffer layer. A buffer layer can be used to envelope or encapsulate the light guiding apparatus for the purpose of providing mechanical isolation, protection from physical damage and ease of identification. The buffer layer may take the form of a miniature conduit, containing but not connected to the light guiding apparatus (loose buffer). Alternatively, the buffer layer can be in intimate contact with the light guiding apparatus (tight buffer).
[0115]The buffer layer can be applied to the light guiding apparatus by methods such as spraying, dipping, extrusion and electrostatic methods. Materials used to create buffers can include fluoropolymers such as polyvinylidene fluoride (Kynar), polytetrafluoroethylene (Teflon), silicon dioxide or polyurethane.
[0116]Advantageously, as the light guiding apparatus is transparent and flexible, it can be integrated into a transparent surface and not restrict the viewing angle or view of a user.
[0117]The light guiding apparatus 3 can be disposed adjacent to a light source 1.
[0118]The light source 1 is used to project a visible light beam which is indicated by a dashed arrow. In some embodiment, the light source 1 is an organic light-emitting diode display. In other embodiments, the light source 1 is a light-emitting diode display, a micro light-emitting diode display, a MEMS controlled laser projector, a liquid crystal on silicon projector, a thin film transistor liquid crystal display, or a digital light processing projector. In some embodiments, the light source can be from a screen of a mobile phone. For example, the micro-display unit can be integrated with processors, electronics and rechargeable mini-batteries for feeding images.
[0119]FIG. 3 shows an example of the light guiding apparatus 3 coupled to a light source 1. FIG. 3d shows an example of the light guiding apparatus being bent but still able to transmit light from the source to the light reflector.
[0120]The visible light beam can have a wavelength ranging from about 380 nm to about 750 nm, which can be observed by human eyes.
[0121]The visible light beam projected correspondingly by the light source 1 is received at the first end 31 and guided to an image-receiving object 5 out of the second end 32 through the light path 33 to form an image. The visible light beam projected by the light source 1 can travel in a straight path or a non-direct path (internal reflection).
[0122]FIG. 5 shows an embodiment of the light guiding apparatus 3. The light source 1 is a micro display. A Micro display is a display too small for direct viewing and can be also called “spatial light modulator”. Light from the light source 1 at the first end 31 is at least internally reflected via the light path 33 towards the second end 32. The polymer guide 320 is bent at a position adjacent to the first end 31. For transmitting light and retaining information from the micro display (micro optics) to the user 5, a coupling means 7 such as a micro optics coupling technology can be included. A micro lens array 9, which contains multiple micro lenses in a square or hexagonal packing, can be further included. Such arrays can be used for homogenization, beam shaping and coupling into the light path 33.
[0123]FIG. 6 shows a magnified view of the embodiment in FIG. 5 at the second end 32. Light reflectors 321 are incorporated proximate to the second end 32. The light reflectors 321 are air filled micro/nano structures, arranged in a fashion to efficiently couple light from different angles to a user 5.
[0124]FIG. 7 shows that the light guiding apparatus 3 can be flexible. FIG. 8 shows that the light guiding apparatus 3 is capable of enabling a light from a light source arriving at the image-receiving object to have high brightness.
[0125]The light guiding apparatus 3 can further comprise a lens. The lens can be a single lens or an array or lenses. The lens can be positioned within the polymer guide, or between the first end of the polymer guide and the light reflector. In this way, the image from, for example, a micro-display can be be coupled into the first end of the polymer guide (waveguide) using suitable coupling optics. The images in the waveguide can undergo multiple reflection. After each reflection, the image can increase in size or will remain same size depending on the magnification of the lens or lenses. The magnified image can thus be reflected out to the user.
[0126]The light guiding apparatus can be installed as a one dimensional thin film comprising light reflectors having a line of pixels. The length and width of each reflecting pixel can be optimised to increase the light reflection