Method for generating holographic lenses, holographic lenses generated with said method, and system comprising said holographic lenses

Abstract

The invention discloses a method for generating a holographic lens by recording the interference pattern of a coherent reference beam (3) and a coherent object beam (4) on a photosensitive material (2). The photosensitive material (2) is embedded in a medium (8). The generated holographic lens, when arranged on an outer face of a substrate (7), is configured to obtain a diffraction-limited light beam from a reconstruction-limited light beam. The diffraction-limited light beam crosses an outer surface (5, 6) of the holographic lens through a point, forming a limit angle, θlim, inside the substrate (7), said angle being equal to the critical angle of total reflection. The invention also discloses a holographic lens generated with the method, a light guiding system (10) comprising said lens, and an augmented reality viewing device comprising said light guiding system (10).

Description

[0001] DESCRIPTION

[0002] METHOD FOR GENERATING HOLOGRAPHIC LENSES, HOLOGRAPHIC LENSES GENERATED WITH SAID METHOD, AND SYSTEM COMPRISING SAID HOLOGRAPHIC LENSES

[0003] FIELD OF INVENTION

[0004] The present invention relates to a method for generating holographic lenses, to the holographic lenses generated using said method, and to a light-guiding system comprising the holographic lenses generated using said method. Furthermore, the light-guiding systems described in the present invention can preferably be applied in augmented reality (AR) viewing devices.

[0005] BACKGROUND OF THE INVENTION

[0006] Holography is a technique that uses the principles of light diffraction to record and subsequently reconstruct three-dimensional (3D) optical information from objects. Holographic optical elements (HOE) play a key role in this context. These HOE are manufactured from high-resolution photosensitive materials, capable of recording the interference pattern produced by two coherent and spatially superimposed beams (typically laser beams). The first of these beams is often referred to as the reference beam, and the second as the object beam, i.e., a beam reflected or scattered by the object whose optical information is to be recorded in the photosensitive material. Thus, a HOE is generated by causing the reference beam and the object beam to interfere in the photosensitive material, recording the interference pattern inside the photosensitive material, on the surface where the reference beam and the object beam meet.The recorded pattern thus comprises the object's 3D information and creates a photonic structure capable of diffracting light. Consequently, it is possible to obtain a reconstructed image of the object from the diffracted beam resulting from a reconstruction beam incident on the EOH.

[0007] EOHs can be classified as transmission or reflection EOHs, depending on how the beams impinge on the photosensitive material during their generation. In transmission EOH generation, the reference beam and the object beam impinge on the same side of the photosensitive material at the time of recording, while in reflection EOH generation, the beams impinge on opposite sides. Furthermore, EOHs are used in a multitude of devices, such as augmented reality (AR) vision devices. In recent years, AR vision devices have undergone significant development, ranging from the fields of video games and automotive to the generation of new smart devices (e.g., smart glasses or pilot helmets) that allow access to information in real time without having to look away from the screen of an accessory device (e.g., a mobile device).The need to develop this type of device has arisen from two recent technological changes:

[0008] - the widespread consumption of video content accessible via mobile telephone networks or the Internet on mobile devices;

[0009] - the miniaturization of such mobile devices, whose weight and size are essentially determined by the size of their screens.

[0010] Compared to mobile video devices, AR vision devices offer three main advantages: they are hands-free, offer a high level of privacy, and have larger screen sizes. Among the various AR vision devices, those with "see-through" capabilities stand out for their high level of acceptance among the general public. However, combining high-quality image display with clear "through" visibility for different applications remains a challenge for see-through devices.

[0011] In this context, EOHs play an essential role in a multitude of AR vision devices, where EOHs guide light in a light-guiding system, acting as wave couplers that introduce and extract light in the form of an image from wave-guiding substrates. An example of these light-guiding systems is described in US patent 10,877,275 B2, which refers to a system based on three EOHs, specifically, three relief gratings. This system, in addition to being complex and costly, has the main disadvantage that the relief gratings deteriorate much more quickly over time than an EOH based on variations in the refractive index, such as holographic lenses.

[0012] Other AR devices include light-guiding systems based on holographic lenses. An example of such a system is disclosed in US patent application US 2010 / 0157400 A1. However, the recording method that results in the holographic lenses of this system requires the use of high-quality optical prisms, which makes the mass production of these EOHs very costly. Furthermore, the positioning of the prisms for generating the holographic lenses must be so precise that it takes a long time to manufacture each holographic lens in mass production. All of this makes the mass production of holographic lenses, and consequently, of the systems that comprise them, difficult.

[0013] On the other hand, light-guiding systems comprising holographic lenses, such as the one disclosed in US 2010 / 0157400 A1 , present difficulties when it comes to correctly focusing the image guided by said systems. Furthermore, said systems typically comprise an image projector, which generates light in the form of an image that is guided by the light-guiding system. In this way, the light-guiding system forms an image that reproduces the image generated by the image projector, based on the light guided by it. However, these light-guiding systems require image projectors of large dimensions and weight, in order to not negatively affect the size of the image formed.

[0014] BRIEF DESCRIPTION OF THE INVENTION

[0015] The present invention addresses the limitations of the prior art mentioned above by providing a method for generating holographic lenses, holographic lenses generated with said method, and a light guiding system comprising said holographic lenses.

[0016] A first object of the present invention relates to a method of generating a holographic lens configured to guide light into and out of a substrate, wherein said substrate comprises at least one outer face and has a first refractive index n v , and the holographic lens is generated with a photosensitive material configured to record the interference pattern between two coherent light beams, said photosensitive material comprising at least a first outer surface and a second outer surface opposite the first outer surface.

[0017] The method comprises the stages of:

[0018] - incident on the photosensitive material, at least partially, via the first outer surface of the photosensitive material, with a reference beam of wavelength substantially equal to a generation value, X g ;

[0019] - direct an object beam of wavelength substantially equal to the generation value, X g , towards the photosensitive material by means of an analog lens, and incident on the photosensitive material, at least partially, through one of the exterior surfaces of the photosensitive material with said object beam, such that the reference beam and the object beam coincide and interfere inside the photosensitive material;

[0020] - recording inside the photosensitive material the interference pattern between the reference beam and the object beam, where the interference pattern is characterized by a K' lattice vector.

[0021] Furthermore, the method is characterized in that: the photosensitive material is embedded in a medium and at least one of its outer surfaces is in contact with said medium, where the medium has a second refractive index, n a , less than the first refractive index, n v ; before impinging on the photosensitive material, the reference beam propagates in the medium at an angle equal to a first angular value, O1, with respect to the normal to the first exterior surface of the photosensitive material; before impinging on the photosensitive material, the object beam propagates in the medium at an angle equal to a second angular value, O2, with respect to the normal to the first exterior surface of the photosensitive material; at least one of the reference and object beams impinges on the photosensitive material, refracting from the medium towards the interior of the photosensitive material; the photosensitive material has a third refractive index n ggreater than the second refractive index n a , and said third refractive index n g , the value of generation X g , the first angular value 01 and the second angular value 02 fix the grating vector K' of the interference pattern, such that, when the outer surface of the generated holographic lens opposite the outer surface through which the object beam is incident is arranged on the outer face of the substrate, the generated holographic lens is configured to obtain a boundary diffracted light ray from a boundary reconstruction light ray incident on the holographic lens through the first outer surface thereof, where the wavelength of the boundary reconstruction light ray is substantially equal to a boundary value, Xi¡ m , other than the generation value X g. In addition, the limiting diffracted light ray passes through the outer surface arranged on the outer face of the substrate at a point, forming a limiting angle, 0i¡ m , inside the substrate with respect to the perpendicular direction at the point of the outer surface crossed by said limit diffracted light ray, the limit angle being 0i¡ m equal to the arcsine of the quotient between the second refractive index n a and the first refractive index n vThe main advantage of this method is that it generates a holographic lens that guides light, meeting the angular condition of total reflection in the substrate, without using optical prisms to incident the reference beam and the object beam on the photosensitive material. Typically, in methods that employ optical prisms, at least one prism is very precisely bonded to the photosensitive material, and to generate new holographic lenses, said prism is detached from the previously generated holographic lens, cleaned, and then precisely bonded again to another photosensitive material. All of this significantly complicates and slows down the mass production of holographic lenses. In turn, the use of optical prisms increases the cost of mass production of holographic lenses, as such prisms are typically expensive.Therefore, according to the above, the method of the present invention advantageously allows to generate holographic lenses in mass, quickly, easily and economically, in particular, compared to methods using optical prisms.

[0022] In a preferred embodiment of the invention, the object beam strikes the photosensitive material, at least partially, via its first exterior surface. In this way, the lens generated is a transmission holographic lens. Advantageously, to generate an optimally transmitting holographic lens, it is typically sufficient for the resolution of the photosensitive material used to be equal to or less than 0.5 μm, compared to the 0.2 μm typically required to generate an optimally reflecting holographic lens.

[0023] Alternatively, in another embodiment of the method, the object beam is incident on the photosensitive material, at least partially, via its second outer surface. In this way, the lens generated is a reflective holographic lens.

[0024] In a preferred embodiment of the invention, the third refractive index n g , the value of generation X g , the first angular value 01 and the second angular value 02 that fix the grating vector K' of the interference pattern, are such that the generated holographic lens is configured to obtain the boundary diffracted light ray from a boundary reconstruction light ray incident on the first outer surface substantially perpendicularly thereto.

[0025] Furthermore, in another embodiment of the invention, the method additionally comprises the step of stabilizing the interference pattern recorded in the photosensitive material. In this way, the photosensitive material does not change its properties when light subsequently falls on it, after recording the interference pattern. In a further preferred embodiment, the resolution value of the photosensitive material is equal to or less than 0.5 µm.

[0026] In another preferred embodiment, the photosensitive material comprises a geometric center and the analog lens comprises an optical center, the optical center of the analog lens and the geometric center of the photosensitive material being separated by a distance, h, and where the analog lens is a diverging lens; or the analog lens is a converging lens with a focal length equal to a focal value, f, where the distance h between the optical center of the analog lens and the geometric center of the photosensitive material is greater than said focal value f. In this way, the generated holographic lens is a diverging lens.

[0027] Alternatively, in another preferred embodiment of the invention, the photosensitive material comprises a geometric center and the analog lens comprises an optical center, the optical center of the analog lens and the geometric center of the photosensitive material being separated by a distance, h, and where the analog lens is a converging lens with a focal length equal to a focal value, f, where the distance h between the optical center of the analog lens and the geometric center of the photosensitive material is less than or equal to said focal value f. In this way, the generated holographic lens is a converging lens.

[0028] In another preferred embodiment of the invention, the photosensitive material comprises a geometric center, and the interference pattern recorded in the photosensitive material is centered with respect to said geometric center. Thus, the geometric center of the photosensitive material coincides with the optical center of the holographic lens generated with said material. Thus, in embodiments where a divergent holographic lens is generated with a divergent analog lens, the focal length of the divergent holographic lens is equal to the sum of the focal length of the divergent analog lens and the distance h between the geometric center of the photosensitive material and the optical center of the analog lens.On the other hand, in embodiments where a diverging holographic lens is generated with a converging analog lens, the focal length of the diverging holographic lens is equal to the difference between the distance h between the geometric center of the photosensitive material and the optical center of the analog lens, and the focal value f of the converging analog lens. Likewise, in embodiments where the holographic lens is a converging holographic lens generated with a converging analog lens, the focal length of the converging holographic lens is equal to the difference between the focal value f and the distance h between the optical center of the analog lens and the geometric center of the photosensitive material. Likewise, in another preferred embodiment of the method of the invention, the photosensitive material is one of the following: a phase material, an amplitude material.A photosensitive material is phase-sensitive when light incident on it changes its refractive index or thickness, such that when a wave passes through it, said photosensitive material modifies the phase of the wave. A photosensitive material is called amplitude-sensitive when, when illuminated by light, it changes the light absorption of said photosensitive material, so that when illuminated once the holographic lens is generated, it modifies the amplitude of the wave, that is, its intensity. Preferably, the photosensitive material is a phase-sensitive material. Advantageously, the phase-sensitive material can guide up to 100% of the incident light, while an amplitude-sensitive material fails to guide even 33% of the incident light.

[0029] In another preferred embodiment of the invention, the photosensitive material is composed, at least partially, of at least one of the following: one or more photopolymers, one or more photoresins, one or more dichromated gelatins. Preferably, the photosensitive material is composed of one or more photopolymers. Advantageously, photopolymers require minimal pre- and post-processing compared to other photosensitive materials, such as photoresins or dichromated gelatins.

[0030] On the other hand, in a preferred embodiment, the third refractive index n g is equal to or greater than 0.9 times the first refractive index n v , and less than or equal to 1.1 times the first refractive index n v .

[0031] In another preferred embodiment of the method of the invention, one of the following is used as a means for holding the photosensitive material: the substrate, where one of the exterior surfaces of the photosensitive material is arranged on the exterior face of the substrate; a transparent, low-dispersion neutral block, comprising at least one exterior face, where one of the exterior surfaces of the photosensitive material is arranged on said exterior face. In this context, the expression "low" will be interpreted as meaning that the neutral block disperses less than 10% of the light it receives; or one or more clips that hold the photosensitive material.

[0032] Thus, a holding means prevents the photosensitive material from bending undesirably during interference pattern recording. In another preferred embodiment of the invention, the cross-sectional size of the reference beam and / or the cross-sectional size of the object beam are controlled by at least one diaphragm.

[0033] In another preferred embodiment of the invention, at least one of the outer surfaces of the photosensitive material has adhesive properties.

[0034] In another preferred embodiment of the invention, the thickness of the photosensitive material between the first outer surface and the second outer surface is between 5 .m and 20 .m, and more particularly, between 10 .m and 15 .m.

[0035] On the other hand, a second object of the present invention relates to a holographic lens generated with a method according to the first object of the present invention.

[0036] A third object of the present invention relates to a light guiding system comprising at least one image projector configured to generate light in the form of a first image, a first holographic lens, a second holographic lens, and a waveguiding substrate comprising an input portion, a central portion, and an output portion. The waveguiding substrate further comprises at least one first exterior face and a second exterior face opposite said first exterior face. In addition: the first holographic lens is disposed on one of the exterior faces of the waveguiding substrate at its input portion; the second holographic lens is disposed on one of the exterior faces of the waveguiding substrate at its output portion; the image projector is configured to direct the light it generates toward the first holographic lens;the first holographic lens is configured to guide the light received from the image projector into the input portion of the waveguide substrate; the central portion is configured to guide the light guided by the first holographic lens therein from the input portion to the output portion; the second holographic lens is configured to receive the light guided to the output portion by the central portion and guide said light it receives out of the output portion of the waveguide substrate;and the first holographic lens, the second holographic lens and the waveguide substrate are configured so that the waveguide substrate guides the light generated by the image projector inside it by total reflection, such that, from the light guided by the second holographic lens to the outside of the output portion of the waveguide substrate, the first image generated by the image projector is reproduced with a second image.;

[0037] Furthermore, the light-guiding system is characterized in that the first holographic lens and / or the second holographic lens are holographic lenses according to the second object of the present invention. Advantageously, since said holographic lenses are generated using a method that allows them to be mass-produced quickly, easily, and economically, the systems comprising said holographic lenses are also mass-produced quickly, easily, and economically.

[0038] In a preferred embodiment of the invention, the first holographic lens and / or the second holographic lens comprises at least one of the following: transmission holographic lens, reflection holographic lens, convergent holographic lens, divergent holographic lens.

[0039] In another preferred embodiment of the invention, the second holographic lens is configured to guide the light it receives from within the waveguide substrate toward a screen, such that the second image reproducing the first image generated by the image projector is projected onto said screen. Preferably, the screen is at least partially transparent. Alternatively, the second holographic lens is configured to guide the light it receives from within the waveguide substrate toward the eye of a user, such that the user sees the second image reproducing the first image generated by the image projector.

[0040] In a preferred embodiment of the invention, the first holographic lens comprises an optical center and has a focal length equal to a first focal value h; the second holographic lens comprises an optical center and has a focal length equal to a second focal value Í2; the distance between the optical center of the first holographic lens and the optical center of the second holographic lens is substantially equal to the sum of the first focal value h and the second focal value Í2; the image projector comprises an image plane, wherein said image plane is located at a distance from the optical center of the first holographic lens substantially equal to the first focal value h; and the second image reproducing the first image generated by the image projector is located at a distance from the optical center of the second holographic lens substantially equal to the second focal value Í2.The above embodiment of the light guiding system will be referred to hereinafter as the “4f system”. In the 4f system, the image distance of the first holographic lens is approximately or equal to infinity, while the image distance of the second holographic lens is substantially equal to the second focal value Í2. In a lens with focal length f, the image distance is understood as the distance at which said lens forms an image (real or virtual) of an object from the light reaching it from the object, when the object is located at a given distance from said lens. In this context, advantageously, the 4f system makes it possible to perfectly focus for the human eye the second image reproduced by the first image generated by the image projector.

[0041] Preferably, in the above 4f system, the second focal value Í2 of the second holographic lens is greater than the first focal value h of the first holographic lens. In the 4f system, the final scaling of the second image is directly proportional, with respect to the first image generated by the image projector, to the quotient between the second focal value Í2 and the first focal value fi. Thus, the second image is larger than the first image when the second focal value Í2 is greater than the first focal value fi. Advantageously, this makes it possible to reduce the size and weight of the image projector included in the light guiding system, without the size of the second image being negatively affected.

[0042] On the other hand, in a preferred embodiment of the light guiding system of the present invention, the light directed by the image projector falls on the first holographic lens through the first outer surface thereof, substantially perpendicular to said first outer surface.

[0043] In another preferred embodiment of the invention, the image projector is one of the following: a projector based on one or more spatial light modulators, a laser projector. Preferably, said image projector is one of the following: an LCD projector, a DLP projector.

[0044] In a preferred embodiment of the invention, the image projector is configured to at least one of the following: generate the first image in high definition and / or ultra high definition format, emit light of any combination of colors, and emit monochromatic light. Furthermore, in another preferred embodiment of the invention, the image projector has a spectral width of less than or equal to 40 nm. In another preferred embodiment of the invention, the waveguide substrate is transparent. Thus, the waveguide substrate guides light within itself by total reflection, from the input portion to the output portion, without said light being absorbed or diffused by it.

[0045] Another object of the present invention relates to an augmented reality vision device comprising a light guidance system according to the third object of the present invention. Preferably, the augmented reality vision device comprises one of the following: smart glasses, a smart helmet, or a vehicle windshield.

[0046] DESCRIPTION OF THE DRAWINGS

[0047] To complete the description and to aid in a better understanding of the invention, a set of drawings is provided. These drawings form an integral part of the description and illustrate different embodiments of the present invention, which should not be construed as restricting the scope of the invention, but rather as examples of how it may be carried out. The accompanying drawings specifically comprise the following figures:

[0048] Figure 1 shows a schematic representation of a method of generating holographic lenses, according to an embodiment of the present invention.

[0049] Figure 2 shows a schematic representation of a method of generating holographic lenses, according to another embodiment of the present invention.

[0050] Figure 3 shows a schematic representation of a light guiding system according to an embodiment of the present invention.

[0051] Figure 4 shows a schematic representation of a light guiding system according to another embodiment of the present invention.

[0052] Numerical references used in the figures:

[0053] DETAILED DESCRIPTION OF THE INVENTION

[0054] As mentioned above, an object of the present invention relates to a method of generating holographic lenses.

[0055] Figure 1 shows a schematic representation of the method for generating a holographic lens from an analog lens (1), according to a preferred embodiment of the present invention. In this context, the analog lens (1) is understood as any optical element configured to focus or disperse light by means of refraction. Thus, the holographic lens is generated by recording in a photosensitive material (2) the interference pattern between two light beams (3, 4) coherent in time and space. The first light beam is a reference beam (3), while the second light beam is an object beam (4) coming from the analog lens (1) whose three-dimensional information is to be reconstructed by means of the recorded interference pattern. In this sense, the interference pattern recorded in the photosensitive material (2) is such that the generated holographic lens is capable of focusing or dispersing light as if it were an analog lens.

[0056] In the above context, the wavelength of the reference beam (3) and the wavelength of the object beam (4) are substantially equal to a generation value X g . Here, the expression “substantially” will be interpreted as equal to or within a range of variation of ± 0.02%, so that the well-known beating phenomenon is avoided and the beams (3, 4) are coherent in time and space.

[0057] The photosensitive material (2) comprises a first outer surface (5) and a second outer surface (6), opposite the first outer surface (6). In this context, the reference beam (3) and the object beam (4) impinge on the photosensitive material (2), at least partially, via its first outer surface (5), such that the reference beam (3) and the object beam (4) coincide and interfere inside the photosensitive material (2). Furthermore, the analog lens (1) of Figure 1 is a convergent analog lens. Thus, the generated holographic lens is a transmission convergent holographic lens.

[0058] On the other hand, in the embodiment of Figure 1 , the second outer surface (6) of the photosensitive material (2) is arranged on an outer face of a substrate (7). In this context, substrate (7) is understood to be any waveguiding substrate that will form part of a light guiding system. Typically, a light guiding system comprises at least a first holographic lens, a waveguiding substrate, a second holographic lens and an image projector. In this context, the light guided by the light guiding system is that generated in the form of a first image by the image projector. Said light is first introduced into the waveguiding substrate by means of the first holographic lens, subsequently guided through the interior of the waveguiding substrate, and finally directed towards the exterior of said substrate by means of the second holographic lens.

[0059] Light-guiding systems are typically applied in augmented reality (AR) viewing devices. Non-limiting examples of these AR viewing devices are smart glasses or helmets, where the wave-guiding substrate is typically a transparent element through which a user of the AR viewing device sees the world. Generally, this type of wave-guiding substrate is composed of glass, plastic, or other materials known in the state of the art. In this context, the light from the light-guiding system is guided out of the wave-guiding substrate by means of the second holographic lens, such that the user sees, through said wave-guiding substrate, a second image that reproduces the first image generated by the image projector. Said second image is superimposed on the real world that the user sees through the wave-guiding substrate.In this sense, the light has to propagate by total reflection inside the waveguide substrate, so as not to lose information from the first image during light propagation in the light guiding system.

[0060] Therefore, according to the above, the holographic lens generated in Figure 1 and the substrate (7) will be part of a light guiding system, where the generated holographic lens will be one of the holographic lenses included in said light guiding system. In this way, the photosensitive material (2) does not bend undesirably during the implementation of the method and, advantageously, it is not necessary to remove the holographic lens from the substrate (7) after generating it and then place it in a light guiding system. This avoids subjecting said holographic lens to stresses that may deform it.

[0061] On the other hand, the substrate (7) has a first refractive index n v, and is embedded in a medium (8) having a second refractive index n a less than the first refractive index n v . Thus, if light propagates inside said substrate (7) by total reflection, said light is not refracted from the interior of the substrate (7) towards the medium (8) in which it is embedded. Non-limiting examples of the medium (8) are air, water, among others.

[0062] In this context, unlike methods for generating holographic lenses that use optical prisms, the photosensitive material (2) is embedded in the medium (8). In addition, the first outer surface (5) of the photosensitive material (2) is in contact with said medium (8).

[0063] Likewise, before striking the photosensitive material (2), the reference beam (3) propagates in the medium (8) at an angle equal to a first angular value, 0i, with respect to the normal to the first exterior surface (5) of the photosensitive material (2). Preferably, the reference beam (3) is a collimated beam, that is, a light beam comprising a plurality of light rays parallel to each other. Likewise, before striking the photosensitive material (2), the object beam (4) propagates in the medium (8) at an angle equal to a second angular value, 02, with respect to the normal to the first exterior surface (5) of the photosensitive material (2). Moreover, the incidence on the first exterior surface (5) of both beams (3, 4) is such that they pass through said surface (5) refracting from the medium (8) towards the interior of the photosensitive material (2).In the embodiment of Figure 1 , and further in the embodiment of Figure 2 , the normal direction to the first outer surface (5) is shown with a dashed arrow. In this context, the normal direction to the first outer surface (5) is typically taken to be the direction which, after recording, will define the axis with respect to which the recorded interference pattern will be centered within the photosensitive material (2). In the embodiments of Figures 1 and 2, the normal to the first outer surface (5) is the direction normal to the first outer surface (5) at the point located at the center of said outer surface (5), and the reference and object beams (3, 4) are caused to interfere such that the recorded interference pattern is centered with respect to the first outer surface (5).In other embodiments, the normal direction to the first outer surface (5) is the normal direction of another point on the first outer surface (5), and the reference and object beams (3, 4) are made to interfere so that the recorded interference pattern is not centered relative to the first outer surface (5).

[0064] According to the previous description, the first angular value 01 and the second angular value 02 are defined with respect to the normal to the first exterior surface (5) of the photosensitive material (2). Said normal direction can be taken, for example, as the direction of a Cartesian axis. In this context, when the direction and sense of each of the two reference and object beams (3, 4) are such that said direction passes through the first exterior surface (5), and said sense goes from outside to inside of the photosensitive material (2), the corresponding angular value 0i,2 is taken, with respect to the Cartesian axis, in a counterclockwise direction and with a positive value. On the other hand, when the direction and sense of each beam (3, 4) are such that said direction passes through the first exterior surface (5), and said sense goes from inside to outside of the photosensitive material (2), the corresponding angular value 0i,2 is taken, with respect to the Cartesian axis, in a clockwise direction and with a negative value.Thus, in Figure 1 and Figure 2, the arcs of the first angular value 01 and the second angular value 02 are represented by dotted lines. The corresponding direction (clockwise or counterclockwise) is also indicated on these lines, as explained above.

[0065] On the other hand, where necessary, the directions of the reference and object beams (3, 4) are represented by dotted straight lines in Figures 1 and 2, in order to better visualize how the corresponding angular values ​​0i,2 are taken. The propagation direction of a beam (3, 4) is given by the direction of the least inclined light ray included in said beam (3, 4), with respect to the normal to the first outer surface (5) of the photosensitive material (2). If the light beam is a collimated beam (like the reference beam (3) of Figures 1 and 2), all the rays included therein are parallel and have the same inclination with respect to said normal. If the beam is directed towards the photosensitive material (2) by means of a converging analogue lens (1) (like the object beam (4) of Figures 1 and 2), the direction of the beam corresponds to that of the outermost ray of the same after being focused by said analogue lens (1).On the other hand, if the beam is directed towards the photosensitive material (2) by means of a divergent analog lens (1), the direction of the beam corresponds to that of the innermost ray of the same after being dispersed by said analog lens (1).

[0066] Likewise, the photosensitive material (2) has a third refractive index n g In this sense, the refractive index n g of the photosensitive material (2) is the one it has when light falls on it. For example, as is known, if the photosensitive material (2) is a phase material, its refractive index is sometimes different when light falls on said photosensitive material (2) to when no light falls on it, while if the photosensitive material (2) is an amplitude material, the index is the same whether or not light falls on the photosensitive material (2). On the other hand, preferably, the third refractive index n g is greater than the second refractive index n a .

[0067] In this context, the third refractive index n g , the first angular value 0i, the second angular value 02 and the generation value X gare such that the holographic lens generated with the method is configured to diffract a boundary reconstruction light ray into the substrate (7). The boundary diffracted light ray is the light ray diffracted by the holographic lens, from a boundary reconstruction ray. In the context of the present invention, the boundary reconstruction light ray is a ray incident on the first outer surface (5) of the holographic lens generated with the method, such that it meets the following conditions: a) its respective reconstruction lattice vector K is equal to the lattice vector K' characterizing the interference pattern; and b) its respective boundary diffracted light ray passes through one of the outer surfaces (5, 6) of the holographic lens at a point, forming a limit angle 0i¡ minside the substrate (7) with respect to the direction perpendicular to said crossed point. The outer surface (5, 6) crossed by the limit diffracted light ray, is the outer surface (5, 6) opposite to the outer surface (5, 6) through which the object beam (4) falls in the generation of the holographic lens. Thus, in the lens generated in Figure 1 , the outer surface (5, 6) crossed by the limit diffracted light ray is the second outer surface (6) of the generated holographic lens. The limit angle 0i¡ m is equal to the critical angle of total reflection, that is, it is equal to the arcsine of the quotient between the second refractive index n a and the first refractive index n v , 0i¡ m = arcsin(n a / n v ).

[0068] Furthermore, unlike methods using optical prisms, the value of the wavelength of the boundary reconstruction light ray is distinct from the generation value X g , and is substantially equal to a limiting value Xi¡ m In this context, the expression “substantially” shall be interpreted as equal to or falling within a range of variation of ± 0.02%.

[0069] In the above context, the lattice vector K' that characterizes the interference pattern is given by

[0070] ~K' = - 1T2, that is, the difference between the characteristic vector of the reference beam (3) and the characteristic vector of the object beam (4). Both characteristic vectors have the same module |^i| = |^21> q ue is given by |^| = |^| = 2 TT n g / X g , where n g is the third index of refraction and X gis the generation value. Furthermore, the direction of the characteristic vector of each beam (3, 4) is given by the angle formed by said beam (3, 4) inside the photosensitive material (2), and which is related to the first / second angular value ©i ,2 by means of Snell's law. Thus, based on the above, the third refractive index n g , the first angular value 0i, the second angular value 02 and the generation value X g They set the K' lattice vector that characterizes the interference pattern recorded in the photosensitive material (2).

[0071] On the other hand, the reconstruction network vector K is given by

[0072] K = -K, that is, the difference between the characteristic vector of the boundary reconstruction light ray and the characteristic vector / of the boundary diffracted light ray. Both characteristic vectors have the same modulus |^| = |^|, which is given by |^| = |^| = 2 TT n g / Xi¡ m, where n g is the third refractive index, and Xi¡ m is the limiting value. The direction of the characteristic vector / of the limiting diffracted light ray is given by the angle formed by said ray inside the photosensitive material (2). This angle is related, by means of Snell's law, to the limiting angle 0i¡ m - Also, the direction of the characteristic vector of the limit reconstruction light ray is given by the angle formed by said ray inside the photosensitive material (2). This angle is related, by means of Snell's law, with the angle formed by the limit reconstruction light ray in the medium (8) before hitting the first exterior surface (5).

[0073] In this context, the transmission holographic lens generated in Figure 1 is configured to guide a test ray incident on the first outer surface (5) thereof towards the interior of the substrate (7), where the angle of incidence with respect to the normal to the first outer surface (5) is greater than or equal to the limit reconstruction ray. The resulting diffracted ray passes through the second outer surface (6) at a point thereof, and forms an angle inside the substrate (7) with respect to the perpendicular direction at that point greater than the limit angle 0i¡. m - For this to happen, the value of the wavelength of the test ray must be greater than the value of the wavelength of the limit reconstruction ray. In this sense, the test ray is a ray whose respective grating vector Kp is equal to the grating vector K' that characterizes the interference pattern. The grating vector of the test beam is given by Kp = Kp - K pd , that is, the difference between the characteristic vector Kp of the test ray and the characteristic vector of the ray diffracted by the holographic lens from the test ray. These characteristic vectors are defined in a manner analogous to those described above. On the other hand, the diffracted ray forms an angle inside the substrate (7) that satisfies the angular condition required for total reflection (i.e., it is greater than or equal to the critical angle of total reflection).

[0074] Likewise, the holographic lens generated in Figure 1 is also configured to guide light towards the outside of the substrate (7). And, more specifically, the holographic lens diffracts another test ray of wavelength greater than or equal to that of the limit reconstruction ray, when said test ray hits, from the inside of the substrate (7), the second exterior surface (6) at a point thereof. The resulting diffracted ray forms an angle with respect to the normal to the first exterior surface (5), greater than or equal to that formed by the limit reconstruction ray. For this to happen, the test ray forms an angle of incidence inside the substrate (7) greater than or equal to the limit angle 0i¡ m, with respect to the perpendicular direction at the point on the second outer surface (6) which it passes through. Thus, the test ray is again a ray whose respective grating vector Kp is equal to the grating vector K' which characterizes the recorded interference pattern. The grating vector of the test beam is defined analogously to the previous cases. On the other hand, the test beam forms an angle inside the substrate (7) that satisfies the angular condition required for total reflection (that is, it is greater than or equal to the critical angle of total reflection). Based on the above, the holographic lens generated in the method of the present invention is configured to guide light into and out of the substrate (7), where the light guided by the holographic lens can propagate inside said substrate (7) by means of the phenomenon of total reflection and, consequently, not be refracted towards the medium (8) in which the substrate (7) is embedded. This occurs not only in embodiments where the holographic lens is arranged on one of the two opposite faces of a substrate (7), where said opposite faces are flat and parallel (as in Figures 1 and 2).In other non-limiting examples, said opposite faces of the substrate (7) are curved (for example, a convex or concave substrate (7). The conditions necessary for a ray of light to propagate by total reflection inside a substrate (7) of any geometric shape are known to those skilled in the art. For example, consider that the substrate (7) has opposite curved faces, is made of glass with the first refractive index n. v equal to 1.5, and the medium (8) in which said substrate (7) is embedded is air with the second refractive index n aequal to 1. In such a case, a ray of light propagates inside said substrate (7) by total reflection, when between a first internal reflection at a first point of one face of the substrate (7) and the immediately subsequent internal reflection at a second point of the opposite face of said substrate (7), the angle formed by the normal direction at the first point and the normal direction at the second point is preferably equal to or less than about 20°.

[0075] However, in the method of the present invention, holographic lenses are generated such that the light they guide meets the angular condition of total reflection in the substrate (7), without using optical prisms to incident the reference beam (3) and the object beam (4) on the photosensitive material (2). Generally, in the methods that use optical prisms, at least one optical prism is glued to the photosensitive material (2) by its first outer surface (5). Subsequently, at least one of the reference and object beams (3, 4) is made to pass through the faces of the prism, such that, by means of internal reflections and refractions in the prism, at least one of said beams (3, 4) hits the photosensitive material (2), refracting from the prism towards said photosensitive material (2).Typically, the prism is configured so that the angles of incidence of the beams (3, 4) on the photosensitive material (2) are such that the limit reconstruction ray that meets the conditions a) and b) described above is the one whose limit value Xi¡. m matches the value of generation X g of the reference and object beams (3, 4). On the other hand, the bonding of the optical prism to the photosensitive material (2) must be very precise, avoiding the formation of bubbles between the photosensitive material (2) and the prism. Furthermore, even if this were achieved, in order to generate new holographic lenses it is necessary to detach the prism from the lens already generated, clean it, and glue it again precisely onto another photosensitive material (2). All of this makes mass production of holographic lenses difficult and slows down considerably. Furthermore, optical prisms are relatively expensive, which makes mass production more expensive.

[0076] As described above, since the method of the present invention generates a holographic lens without the use of optical prisms, it advantageously allows for mass production of holographic lenses, quickly, easily and economically.

[0077] In a preferred embodiment of the method of the invention, the third refractive index n g , the value of generation X g, the first angular value 0i, and the second angular value 02 are such that the previously defined limit reconstruction light ray is the one that falls on the holographic lens generated by its first outer surface (5), substantially perpendicular to it. The holographic lens thus generated is suitable, for example, for AR vision devices comprising a light guiding system, where an image projector generates the light guided by said system, and where said light falls substantially perpendicular to the holographic lens that guides the light into a waveguide substrate. In this sense, the expression "substantially" will depend on the thickness of the holographic lens. As is known to those skilled in the art, the angular selectivity of a holographic lens depends on its thickness, the angular selectivity being more restrictive the greater said thickness.Thus, for example, when a holographic lens has a thickness of 20 µm, and a ray of light strikes a point on the first outer surface (5) thereof in a substantially perpendicular manner, the expression “substantially” is interpreted as the direction of said ray being parallel to the normal to said first outer surface (5), with a range of variation with respect to said direction of ± 5. o . When, in another example, the thickness is 5 m, the expression “substantially” is interpreted as the direction of said ray being parallel to the normal to said first exterior surface (5), with a range of variation with respect to said direction of ± 10°.

[0078] An example with numerical values ​​is shown below, where the holographic lens generated in Figure 1 guides rays of wavelength greater than or equal to 633 nm (i.e., wavelength of the color red) towards the interior / exterior of the substrate (7). The directions of said rays comply with the angular condition required for total reflection inside the substrate (7). Likewise, said rays perpendicularly pass through the first outer surface (5) of the holographic lens. For this purpose, the holographic lens is generated with a reference beam (3) and an object beam (4), where the generation value X g of its wavelength is equal to 532 nm. For example, the reference beam (3) and the object beam (4) can be green laser beams, commonly used in the generation of holographic optical elements. Likewise, the second refractive index n a(that is, the middle one (8)) is equal to 1 (that is, the medium (8) is air), and the third refractive index n g (i.e., that of the photosensitive material (2)) is equal to 1.478. In addition, the reference beam (3) strikes the photosensitive material (2) with a first angular value 01 equal to 5.2°, and the object beam (4) strikes the photosensitive material (2) with a second angular value 02 equal to 68.5°. Thus, the limit value i¡ m of the limit reconstruction ray incident on photosensitive material (2) perpendicular to the first outer surface (5), and which meets conditions a) and b) described above, is equal to 633 nm. On the other hand, if the value of the first refractive index n v (that is, that of the substrate (7)) is equal to 1.5 (as, for example, when the substrate (7) is composed of glass) the limiting angular value 0i¡ m is equal to 41.8 o .

[0079] Other numerical examples of the embodiment of Figure 1 are easily deducible by a person skilled in the art, from the information contained herein. For example, the holographic lens generated in Figure 1 can be configured to guide white light towards the interior / exterior of the substrate (7), where said light meets the angular condition required for total reflection inside it. In the present invention, white light is defined as a light beam formed by rays with three wavelengths (red wavelength Xi, green wavelength Xa, and blue wavelength X3), where said rays have the same luminous intensity. In addition, the wavelength of red i is substantially equal to 700.0 nm, the wavelength of green Xa is substantially equal to 546.1 nm, and the wavelength of blue s is substantially equal to 435.8 nm.Here the expression “substantially” shall be interpreted as equal to or falling within a range of variation of ± 1 %. In this context, the generation value X. g the length of the reference beam (3) and the object beam (4) is between an upper limit and a lower limit, where the upper limit is equal to 470 nm and the lower limit is equal to 400 nm.

[0080] On the other hand, in Figure 1 the size of the cross section of the reference beam (3) is controlled by means of a diaphragm (9), whilst the size of the cross section of the object beam (4), before passing through the analog lens (1), is controlled by means of another diaphragm (9'). For example, the diaphragms (9, 9') can fix the size of said cross sections, so that their diameter is equal to 1.5 cm. Advantageously, when the generated holographic lens is subsequently used in a light guiding system, the diaphragms (9, 9') make it possible to pre-adjust the cross section of the beams (3, 4) to the size of the image generated by the image projector included in said light guiding system.

[0081] In other embodiments of the method of the present invention, the generated holographic lens is a reflective holographic lens. Again, the method advantageously generates a holographic lens without the use of optical prisms.

[0082] Figure 2 shows a schematic representation of the method for generating a reflective convergent holographic lens, according to a preferred embodiment of the present invention. Indeed, Figure 2 presents the same elements as Figure 1 , but arranged to generate a reflective convergent holographic lens, instead of a transmission convergent holographic lens. Thus, in Figure 2, the reference beam (3) strikes the photosensitive material (2), at least partially, via its first outer surface (5), while the object beam (4) strikes the photosensitive material (2), at least partially, via its second outer surface (6).

[0083] On the other hand, the first exterior surface (5) of the photosensitive material (2) is arranged on an exterior face of the substrate (7). In particular, said exterior face is the opposite of the exterior face on which the second exterior surface (6) of the photosensitive material (2) is arranged in Figure 1. Furthermore, unlike the methods for generating reflective holographic lenses that use optical prisms, the photosensitive material (2) is embedded in the medium (8), and the second exterior surface (6) thereof is in contact with said medium (8). In addition, the reference beam (3), before striking the photosensitive material (2), propagates through the medium (8) at an angle equal to a first angular value, 0i, with respect to the normal to the first exterior surface (5). Subsequently, said reference beam (3) passes through the substrate (7) towards the first exterior surface (5) of the photosensitive material (2).On the other hand, before hitting the photosensitive material (2), the object beam (4) propagates in the medium (8) at an angle equal to a second angular value, 02, with respect to the normal to the first exterior surface (5) of the photosensitive material (2). Moreover, the incidence on the second exterior surface (6) of the object beam (4) is such that it passes through said second exterior surface (6) refracting from the medium (8) towards the interior of the photosensitive material (2).

[0084] Analogously to the generation of a transmission holographic lens, the third refractive index n g , the value of generation X g, the first angular value 01, and the second angular value 02 fix the grating vector K' that characterizes the interference pattern, such that the reflection holographic lens generated in Figure 2 is configured to diffract, towards the interior of the substrate (7), a boundary reconstruction light ray. Said boundary reconstruction ray is incident on the first exterior surface (5) of the holographic lens. However, since the holographic lens generated in Figure 2 is a reflection holographic lens, the resulting boundary diffracted light ray passes through the first exterior surface (5) thereof, instead of the second exterior surface (6). Thus, the boundary diffracted light ray passes through said first exterior surface (5) at a point thereof, forming a limit angle 0i¡ mequal to the critical angle of total reflection, with respect to the perpendicular direction at the point crossed. Again, unlike methods using optical prisms, the limiting value Xi¡m is distinct from the generation value X g .

[0085] In the above context, the reflection holographic lens generated in Figure 2 is configured to guide, towards the interior of the substrate (7), a test ray that strikes the first outer surface (5) thereof, in a manner analogous to the holographic lens generated in Figure 1. Said test ray strikes at an angle with respect to the normal to the first outer surface (5) greater than or equal to that of the limit reconstruction ray, and its respective grating vector lí^ is equal to the grating vector K' that characterizes the interference pattern. The angle formed by the resulting diffracted light ray, inside the substrate (7) and with respect to the perpendicular direction at the point that it passes through the outer surface of the holographic lens, is greater than the limit angle 0i¡. m- However, unlike the embodiment of Figure 1 , the point through which said diffracted light ray passes is a point on the first outer surface (5). Furthermore, also unlike the embodiment of Figure 1 , the value of the wavelength of the test ray is smaller than the value of the wavelength of the limit reconstruction ray.

[0086] Likewise, the holographic reflection lens generated in Figure 2 is also configured to guide another test ray towards the outside of the substrate (7). Said test ray hits the holographic lens from the inside of the substrate (7), forming an angle of incidence inside the same greater than or equal to the limit angle 0i¡ m , relative to the perpendicular direction at the point traversed by the test ray on the outer surface of the holographic lens. The grating vector of said test ray is equal to the grating vector K' that characterizes the interference pattern, and the resulting diffracted ray forms an angle greater than or equal to that formed by the limit reconstruction ray, with respect to the normal to the first exterior surface (5). However, unlike the embodiment of Figure 1 , the test ray strikes the holographic lens through the first exterior surface (5) thereof, and its wavelength is equal to or less than that of the limit reconstruction ray. Thus, the resulting diffracted ray, after passing through the first exterior surface (5) of the holographic lens, propagates through the interior of the substrate (7) and exits towards the medium (8) in which said substrate (7) is embedded.

[0087] In a preferred embodiment of the method of Figure 2, the third refractive index n g , the value of generation X g, the first angular value 0i, and the second angular value 02 are such that the limit reconstruction light ray is incident on the reflection holographic lens generated by its first outer surface (5), substantially perpendicularly thereto. The expression “substantially” will depend on the thickness of the holographic lens, in the same way as in the embodiments in which a transmission holographic lens is generated.

[0088] An example with numerical values ​​is shown below, where the holographic reflection lens generated in Figure 2 guides rays of wavelength less than or equal to 482 nm (i.e., wavelength of the color blue) towards the interior / exterior of the substrate (7). The directions of said rays satisfy the angular condition required for total reflection inside the substrate (7). Likewise, said rays pass perpendicularly through the first outer surface (5) of the holographic lens. The same numerical values ​​are taken from the generation value X g , the second refractive index n a , and the third refractive index n g as in the example in Figure 1 (i.e., 532 nm, 1 and 1,478 respectively). Furthermore, the first angular value O1 and the second angular value O2 are respectively equal to 60° and -30°. Thus, the limiting value Xi¡ mof the limit reconstruction light ray incident on the generated holographic lens, perpendicular to its first outer surface (5), is equal to 482 nm. On the other hand, if we again take the value of the first refractive index n v (that is, that of the substrate (7)) is equal to 1.5, the limiting angular value 0i¡ m is again equal to 41.8°.

[0089] The holographic lenses generated in Figures 1 and 2 are converging holographic lenses with a focal length. In this context, the converging analog lens (1) comprises an optical center and has a focal length equal to a focal value f. Furthermore, the optical center of the analog lens (1) is located at a distance, h, from the geometric center of the photosensitive material (2). When the reference and object beams (3, 4) interfere in the photosensitive material (2), such that the interference pattern recorded in said photosensitive material (2) is centered with respect to the geometric center thereof, the geometric center of the photosensitive material (2) coincides with the optical center of the holographic lens generated with said photosensitive material (2).Thus, the focal length of the generated convergent holographic lens is given by the difference between the focal value f of the analog lens (1), and the separation distance h between the optical center of the analog lens (1) and the geometric center of the photosensitive material (2). For example, if the analog lens (1) has a focal value f equal to 15 cm, and the separation distance h between the optical center of the analog lens (1) and the geometric center of the photosensitive material (2) is equal to 5 cm, the focal length of the generated convergent holographic lens is equal to 10 cm. In other embodiments of the invention, the generated holographic lens is a divergent holographic lens. To do this, one option is to replace the convergent analog lens (1) with a divergent one.In such a case, the focal length of the generated divergent holographic lens is equal to the sum of the focal length of the divergent analog lens (1), and the distance h between the optical center of the analog lens (1) and the geometric center of the photosensitive material (2).

[0090] On the other hand, in embodiments of the invention, the interference pattern recorded in the photosensitive material (2) of Figures 1 and 2 is stabilized after the generation of the holographic lens. In this way, the photosensitive material (2) does not change its properties when light subsequently falls on it, after recording the interference pattern. For example, in embodiments where the photosensitive material (2) is composed, at least partially, of photopolymers, the stabilization of the interference pattern comprises curing the photosensitive material (2) with white and / or ultraviolet light. This makes it possible to eliminate monomers that do not record an interference pattern. Other ways of stabilizing the interference pattern applicable to photopolymers or other types of photosensitive materials (2) are known to those skilled in the art.

[0091] In a preferred embodiment of the method, the photosensitive material (2) is composed, at least partially, of one or more photopolymers, such as the commercial photopolymer Bayfol hx 200. In other embodiments, the photosensitive material (2) is composed, at least partially, of photoresins, dichromated gelatins, and / or other materials known to those skilled in the art.

[0092] In non-limiting embodiments of the present invention, the photosensitive material (2) employed in the method is a phase material. In other non-limiting embodiments, the photosensitive material (2) is an amplitude material.

[0093] In a preferred embodiment, the third refractive index n g is equal to or greater than 0.9 times the first refractive index n v , and less than or equal to 1.1 times the first refractive index n v . When the deviation of the refractive index n gof the photosensitive material (2) with respect to the refractive index n vof the substrate (7) is not greater than ±10%, the generated holographic lens is more effective in guiding light into / out of the substrate (7). In a preferred embodiment, the resolution value of the photosensitive material is equal to or less than 0.5 µm. Preferably, in generating a reflection holographic lens, the photosensitive material (2) has a resolution value equal to or less than 0.2 µm. A resolution value equal to 0.5 µm is equivalent to being able to record an interference fringe density approximately equal to two thousand fringes per millimeter of photosensitive material (2). On the other hand, a resolution value equal to 0.2 µm is equivalent to being able to record an interference fringe density approximately equal to five thousand fringes per millimeter of photosensitive material (2). In the context of the present invention, fringes are the maxima and minima of the interference pattern recorded on the photosensitive material (2).

[0094] On the other hand, in preferred embodiments of the invention, the thickness of the photosensitive material (2) between the first outer surface (5) and the second outer surface (6) is between 5 m and 20 m, and more preferably, between 10 m and 15 m. In the context of the present invention, the thickness of the photosensitive material (2) is the thickness it has when light falls on it. For example, as is known, if the photosensitive material (2) is a phase material, its thickness is sometimes different when light falls on said photosensitive material (2) to when no light falls on it. Said difference can amount to a reduction in thickness of less than 5%. On the other hand, if the photosensitive material (2) is an amplitude material, the thickness is the same whether or not light falls on the photosensitive material (2).Furthermore, in embodiments where the method includes the step of stabilizing the interference pattern, the thickness of the photosensitive material (2) of the generated holographic lens barely differs from the thickness prior to performing said step. For example, when stabilization involves curing the photosensitive material (2), the thickness can be reduced by less than 1%. However, within the above ranges of thicknesses of the photosensitive material (2), the holographic lens generated by the method of the invention is typically a volume EOH. A volume EOH is one such that, when a beam is incident thereon, said EOH does not split the incident beam into more than two beams.

[0095] Likewise, in preferred embodiments of the method of the invention, at least one of the outer surfaces (5, 6) of the photosensitive material (2) has adhesive properties. For example, in the embodiments of Figures 1 and 2, the surfaces of the photosensitive material (2) that are arranged on the substrate (7) (the second outer surface (6) in Figure 1, and the first outer surface (5) in Figure 2), preferably have adhesive properties, to remain in such arrangement. In other embodiments of the invention, alternative fastening means to the substrate are used.

[0096] (7) (e.g., a neutral block, tweezers, etc.), to prevent the photosensitive material (2) from bending undesirably during generation of the holographic lens. Typically, after generating the holographic lens with the method, it is released from said holding means, and is arranged on an outer face of the substrate (7) to form a light guiding system.

[0097] Thus, in an alternative embodiment of the method, a neutral block is used as a holding means, with at least one exterior face, on which one of the exterior faces (5, 6) of the photosensitive material (2) is arranged. In addition, said neutral block is transparent and has low dispersion, that is, it disperses less than 10% of the light it receives. In this way, during the generation of the holographic lens, there is no loss of coherence of the reference and object beams (3, 4), nor of quality in the interference pattern recorded in the photosensitive material (2). In a non-limiting example, the neutral block has the same geometric shape as the substrate (7) of Figure 1 and Figure 2, and the photosensitive material (2) is arranged on said neutral block in an equivalent manner on the faces of the neutral block.

[0098] In alternative embodiments of the method, one or more tweezers holding the photosensitive material (2) are employed as a holding means. Generally, in such embodiments both outer surfaces (5, 6) of the photosensitive material (2) are in contact with the medium.

[0099] (8) in which the photosensitive material (2) is embedded, and the two reference and object beams (3, 4) hit the photosensitive material (2) refracting from the medium (8) towards the interior of the photosensitive material (2).

[0100] Another object of the present invention relates to a light guiding system comprising holographic lenses, where at least one of them is generated with a method according to the present invention.

[0101] Figure 3 shows a schematic representation of a light guiding system (10) according to a preferred embodiment of the invention. Said light guiding system (10) comprises an image projector (11), a first holographic lens (12), a wave guiding substrate (13) and a second holographic lens (14).

[0102] In the present invention, the image projector (11) is configured to generate light in the form of a first image (15). In particular, in Figure 3, the image projector (11) generates the image (15) of the number three. Non-limiting examples of image projectors (11) are projectors based on one or more spatial light modulators (SLMs). There are various types of SLM-based projectors. For example, LCD projectors (Liquid Crystal Displays), such as those based on liquid crystal displays on silicon (LCoS). Another example is DLP projectors (Digital Light Processing), such as those based on micromirrors on a DMD (Digital Micromirror Device).The light source of the SLM-based image projectors (11) may be one or more halogen lamps, LEDs, lasers, among others. Other non-limiting examples of image projectors (11) are laser projectors, where several beams are deflected by one or more mirrors at very high speeds to give the sensation of a continuous image.

[0103] The first holographic lens (12) has a focal length equal to a first focal value fi. Likewise, the second holographic lens (14) has a focal length equal to a second focal value Í2. In particular, said first and second lenses (12, 14) of Figure 3 are transmission holographic lenses.

[0104] Furthermore, the waveguide substrate (13) comprises an input portion (16), a central portion (17) and an output portion (18). In turn, the waveguide substrate (13) comprises a first outer face (19) and a second outer face (20) opposite said first outer face (19). The first holographic lens (12) is arranged on the first outer face (19) of the waveguide substrate (13) at its input portion (15), while the second holographic lens (14) is arranged on the first outer face (19) of the waveguide substrate (13) at its output portion (18). On the other hand, the waveguide substrate (13) is preferably composed of one or more materials such as glass, plastic, among others, such that said waveguide substrate (13) is transparent.

[0105] In this context, the image projector (11) is configured to direct the light it generates towards the first holographic lens (12). Said light strikes the first holographic lens (12) via its first outer surface, that is, the outer surface via which the reference beam strikes the photosensitive material during the generation of said first holographic lens (12). The first holographic lens (12) is configured to guide the light it receives from the image projector (11) towards the interior of the input portion (16) of the waveguide substrate (13). Likewise, the central portion (17) is configured to guide the light guided by the first holographic lens (12) inside it, from the input portion (16) to the output portion (18). The second holographic lens (14) is configured to receive the light guided to the output portion (18) by the central portion (17).Furthermore, the second holographic lens (14) is configured to guide said light that it receives towards the outside of the output portion (18) of the waveguide substrate (13). Thus, the light guided by the second holographic lens (14) towards the outside of the output portion (18) of the waveguide substrate (13), contains information of the first image (15) generated by the image projector (11).

[0106] On the other hand, the first holographic lens (12), the second holographic lens (14) and the waveguide substrate (13) are configured so that said waveguide substrate (13) guides the light generated by the image projector (11) inside it by total reflection. In this sense, the light guiding system (10) is embedded in a medium (for example, air, water, among others) with a refraction index lower than that of the waveguide substrate (13), such that said total reflection takes place inside the waveguide substrate (13). Thus, each ray of the light guided inside the waveguide substrate (13) strikes a point on the separation surface between said waveguide substrate (13) and the medium in which it is embedded, with an angle of incidence with respect to the perpendicular direction at said point greater than the critical angle of total reflection.The critical angle of total reflection is equal to the arcsine of the quotient between the refractive index of the medium in which the waveguide substrate (13) is embedded and the refractive index of the waveguide substrate (13). In Figure 3 (and in the subsequent Figure 4) a ray of light guided by total reflection has been represented inside the waveguide substrate (13), to illustrate what was described above.

[0107] Since the light generated by the image projector (11) propagates by total reflection inside the waveguide substrate (13), no information from the first image (15) is lost in said propagation. Thus, from the light guided by the second holographic lens (14) towards the outside of the output portion (18) of the waveguide substrate (13), the first image (15) generated by the image projector (11) is correctly reproduced with a second image (21).

[0108] Thus, the first holographic lens (12) and / or the second holographic lens (14) of the light guiding system (10) are advantageously generated by a method according to the first subject matter of the invention. This makes it possible to reduce the costs and times of mass production of the light guiding system (10), compared to light guiding systems comprising holographic lenses generated by methods using optical prisms. Preferably, both holographic lenses (12, 14) are generated in a method according to the present invention. For example, said holographic lenses (12, 14) can be generated such that the wave guiding substrate (13) guides by total reflection inside it the light from the image projector (11) for wavelengths greater than a particular limiting value Xi¡m.

[0109] The first holographic lens (12) of Figure 3 is a convergent holographic lens, which facilitates that all the rays of the light guided by said first holographic lens (12) arrive by total reflection from the input portion (16) to the output portion (18). In other embodiments of the invention, said first holographic lens (12) is divergent. On the other hand, the second holographic lens (14) of Figure 3 is a convergent holographic lens. In this sense, the two outermost light rays of the light guided by the second holographic lens (14) towards the outside of the output portion (18) of the waveguide substrate (13) have been represented in Figure 3.

[0110] As described above, in the embodiment of Figure 3, the light guiding system (10) additionally comprises a screen (22). In particular, said screen (22) is located in front of the first outer face (19) of the wave guiding substrate (13), opposite the second holographic lens (14). The second holographic lens (14) is configured to guide the light that it receives from the interior of the wave guiding substrate (13) towards the screen (22), such that the second image (21) is projected on said screen (22). Said second image (21) is a reproduction of the first image (15) generated by the image projector (11). In a preferred embodiment, the screen (22) is at least partially transparent. This allows the second image (21) to be seen on the screen (22), while at least partially seeing everything that exists behind the screen (22).In non-limiting examples, the screen (22) is the windshield of a vehicle (car, train, airplane, boat, rocket, among others) of an AR vision device that comprises the light guidance system (10) of Figure 3.

[0111] On the other hand, the light guiding system (10) of Figure 3 is advantageously a 4f system. In this way, the second image (21) is perfectly focused on the screen (22). Thus, the first holographic lens (12) comprises an optical center, the second holographic lens (14) comprises another optical center, and the distance between the optical center of the first holographic lens (12) and the optical center of the second holographic lens (14) is substantially equal to the sum of the first focal value h of the first holographic lens (12) and the second focal value Í2 of the second holographic lens (14). Likewise, the image projector (11) comprises an image plane, where said image plane is located at a distance from the optical center of the first holographic lens (12) substantially equal to the first focal value fi.Furthermore, the screen (22) and, consequently, the second image (21) projected thereon are located at a distance from the optical center of the second holographic lens (14) substantially equal to the second focal value Í2. In this context, the expression “substantially” will be interpreted as equal to or within a range of variation of ± 0.5%. Said range of variation in one or more of the distances between the elements defining the 4f system, supposes a blurring in the second image (21) that is imperceptible to the human eye.

[0112] The image plane of the image projector (11) is the plane where the image projector (11) generates the first image (15). Preferably, the distance from the image plane of the image projector (11) to the geometric center of the first holographic lens (12) is measured from the center of the first image (15) formed in said image plane. For example, in a non-limiting embodiment, the image projector (11) is based on a single liquid crystal on silicon (LCoS) display, where the image plane is the one containing the LCoS itself within the image projector (11). In said embodiment, generally, the center of the first image (15) coincides with the geometric center of the LCoS itself.

[0113] In other embodiments of the invention, the light guiding system (10) is not a 4f system, such that at least one of the above distances between the elements of the light guiding system (10) is different from the values ​​described above.

[0114] Figure 4 shows a schematic representation of a light guiding system (10) according to another preferred embodiment of the invention. Said light guiding system (10) also comprises an image projector (11), a first transmission holographic lens (12), a wave guiding substrate (13) and a second transmission holographic lens (14).

[0115] As in Figure 3, the light guiding system (10) of Figure 4 guides the light generated by the image projector (11) so that, after being guided first by the first holographic lens (12) towards the interior of the wave guiding substrate (13), and subsequently by total reflection inside the wave guiding substrate (13), said light is guided towards the exterior of the wave guiding substrate (13) by means of the second holographic lens (14).

[0116] However, unlike the embodiment of Figure 3, the second transmission holographic lens (14) is a diverging holographic lens, and the light guiding system (10) lacks a screen (22). Indeed, in the light guiding system (10) of Figure 4, the light generated by the image projector (11) is guided toward the eye (23) of a user, instead of toward a screen (22). Thus, the second holographic lens (14) is configured to receive the light guided to the exit portion (18) by the central portion (17), and to guide said received light toward the eye (23) of the user located outside the waveguide substrate (13). The two outermost rays of the light guided by the second holographic lens (14) toward the eye (23) of the user are shown in Figure 4. Said user sees the second image (21) that reproduces the first image (15) generated by the image projector (11).Specifically, in Figure 4 the second image (21) is a virtual image that the user sees through the waveguide substrate (13), located on the outside of the same and in front of its second outer face (20). In non-limiting examples, the light guiding system (10) of Figure 4 is included in smart AR glasses or helmet, where the user of said glasses or helmet sees, through the waveguide substrate (13), the outside world and the second image (21) superimposed on it.

[0117] The embodiment of Figure 4 is advantageously a 4f system, such that the user's eye (23) perfectly focuses the second image (21). Thus, in a manner analogous to the embodiment of Figure 3, the distance between the optical center of the first holographic lens (12) and the optical center of the second holographic lens (14) is substantially equal to the sum of the first focal value h of the first holographic lens (12) and the second focal value Í2 of the second holographic lens (14), the image plane of the image projector (11) is located at a distance from the optical center of the first holographic lens (12) substantially equal to the first focal value fi, and, thanks to the crystalline lens of the user's eye (14) acting as a converging lens, the user sees the second image (21) at a distance from the optical center of the second holographic lens (14) substantially equal to the second focal value Í2.Again, the expression “substantially” shall be interpreted in this context as equal to or within a range of variation of ± 0.5%.

[0118] In alternative embodiments to that of Figure 4, the second holographic lens (14) that guides the light towards a user's eye (23) is a converging holographic lens. Thus, in order for the user to see the second virtual image (21), the user's near point must be located in the space between the waveguide substrate (13) and the user's eye (23). As is known, a user's near point is a point located at the closest distance to the user's eye (23) where said user sees an object clearly and with perfect accommodation. For example, for a person under 40 years of age said distance is typically equal to 10 cm. Under these conditions, the user sees the second image (21) at a distance substantially equal to the second focal value Í2, on the outside of the waveguide substrate (13) and in front of the first outer face (19) thereof.Again, the expression “substantially” shall be interpreted here as equal to or within a range of variation of ± 0.5%.

[0119] On the other hand, in 4f systems the final scaling of the second image (21) is directly proportional, with respect to the first image (15), to the quotient between the second focal value Í2 of the second holographic lens (14) and the first focal value fi of the first holographic lens (12). Thus, in the embodiments of Figures 3 and 4, the second focal value Í2 of the second holographic lens (14) is smaller than the first focal value h of the first holographic lens (12), such that the size of the second image (21) is smaller than the size of the first image (15).

[0120] As described above, in preferred embodiments of the invention, the second focal value Í2 of the second holographic lens (14) is greater than the first focal value h of the first holographic lens (12), such that the size of the second image (21) is greater than the size of the first image (15). This makes it possible to reduce the dimensions and weight of the image projector (11), without negatively affecting the size of the second image (21) reproducing the first image (15) generated by said image projector (11).

[0121] Other embodiments of the light guiding system (10) according to the present invention can be deduced by a person skilled in the art from the content of this document. In non-limiting examples, the light guiding systems (10) comprise two reflection holographic lenses (12, 14) instead of two transmission holographic lenses (12, 14), where said holographic lenses (12, 14) are arranged on the second outer face (20) of the wave guiding substrate (13) instead of on the first outer face (19) thereof. In these examples, when the image projector (11) directs the light it generates towards the first holographic lens (12), said light typically hits the first holographic lens (12) through the first outer surface thereof, after passing through the interior of the wave guiding substrate (13) through the input portion (16) thereof.Thus, the first holographic lens (12) receives the light generated by the image projector (11) and introduces it again into the interior of the waveguide substrate (13) in the input portion (16) thereof. Likewise, the second holographic lens (14) receives the light guided to the output portion (18) by the central portion (17), and guides said light that it receives towards the outside of the output portion (18), such that, before leaving the interior of the waveguide substrate (13), it passes through the interior of said waveguide substrate (13) through the output portion (18) thereof. In other non-limiting embodiments of the invention, the light guiding system (10) comprises holographic lenses (12, 14), where one is a transmission holographic lens and the other is a reflection holographic lens.Likewise, in other embodiments of the invention, the first holographic lens (12) is arranged on an outer face (19, 20) of the waveguide substrate (13) different from the outer face (19, 20) on which the second holographic lens (14) is arranged, and the image projector (11) and the screen (22) or the eye (23) of the user are located on opposite sides with respect to the waveguide substrate (13).

[0122] On the other hand, preferably the arrangement of the first holographic lens (12) and the second holographic lens (14) is such that there is no air between said holographic lenses (12, 14) and the waveguide substrate (13). In embodiments of the invention, the photosensitive material of the first and / or second holographic lenses (12, 14) is such that the surfaces of said holographic lenses (12, 14) that are in contact with the waveguide substrate (13) have adhesive properties. This allows them to remain arranged on the outer faces (19, 20) of the waveguide substrate (13). Other ways of arranging the holographic lenses (12, 14) on the outer faces (19, 20) of the waveguide substrate (13) are known to those skilled in the art. For example, a transparent glue or silicone can be used, with a refractive index substantially equal to that of the waveguide substrate (13).In this context, the expression “substantially” shall be interpreted here as equal to or within a range of variation of ± 2%.

[0123] Furthermore, in preferred embodiments of the invention, the image projector (11) has a spectral width of less than or equal to 40 nm. Generally, 40 nm is the spectral width of image projectors (11) comprising LEDs.

[0124] On the other hand, in other embodiments of the invention, the image projector (11) has a resolution sufficient to preferably generate the first image (15) in high definition (HD) and / or ultra high definition (UHD) format. In this context, the UHD format refers to 4K, 8K, and / or 16K resolutions.

[0125] In embodiments of the invention, the image projector (11) is configured to emit light of any combination of colors in the chromatic palette (for example, an RGB projector). In other embodiments, the image projector (11) is configured to emit monochromatic light, that is, to emit light of a single color. Likewise, in other embodiments of the invention, the light directed by the image projector (11) falls on the first holographic lens (12) through its first outer surface, substantially perpendicular to it. In accordance with what was explained above, the angular selectivity of the first holographic lens (12) depends on its thickness, the angular selectivity being more restrictive the greater said thickness. Therefore, the expression "substantially" will depend on the thickness of said first holographic lens (12).Thus, in non-limiting examples, if a ray of light strikes a point on the first outer surface of the first holographic lens (12), the expression “substantially” is interpreted as the direction of said ray being parallel to the normal to said first outer surface, with a range of variation with respect to said direction of ± 5. oif the thickness of the first holographic lens (12) is 20 .m, or ± 10° if said thickness is 5 .m. The normal direction to the first outer surface of the first holographic lens (12) is taken as the direction that defines the axis with respect to which the interference pattern recorded inside the photosensitive material of said first holographic lens (12) is centered. In Figures 3 and 4, a ray of light directed by the image projector (11) that falls on the first holographic lens (12) through its first outer surface, perpendicular to it, in accordance with what is described above, has been represented by a straight line.

[0126] However, the thickness of the waveguide substrate (13) of the light guiding system (10) is not particularly relevant. Said thickness only determines the number of internal reflections that take place within the waveguide substrate (13) when the light propagates by total reflection inside it. Advantageously, this makes it possible to easily adapt the light guiding system (10) to the particular dimensions of AR vision devices such as smart glasses, smart helmets, etc.

[0127] On the other hand, the waveguide substrate (13) is not limited to a waveguide substrate (13) with flat and parallel outer faces (19, 20) like those in Figures 3 and 4. In non-limiting examples, said opposite outer faces (19, 20) of the waveguide substrate (13) are curved (for example, a convex or concave waveguide substrate (13). As described above, the conditions necessary for a light ray to propagate by total reflection inside a waveguide substrate (13) of any geometric shape are known to a person skilled in the art. Likewise, the curvature of the outer faces (19, 20) of the waveguide substrate (13) does not influence the values ​​of the distances between the image projector (11), the holographic lenses (12, 14) and the second image (21) that define the 4f embodiment of the light guiding system (10).In this sense, in the 4f system, the optical path of a light ray propagating inside the waveguiding substrate (13) by total reflection, from the moment it is introduced by the first holographic lens (12) until it is extracted by the second holographic lens (14), is substantially equal to the quotient between the sum of the first focal value hy and the second focal value Í2, and the refractive index of the waveguiding substrate (13), independently of the curvature of the outer faces (19, 20) of the waveguiding substrate (13). Again, the expression “substantially” is interpreted here as equal to or within a variation range of ± 0.5%.

Claims

CLAIMS 1 Method for generating a holographic lens configured to guide light into and out of a substrate (7), wherein said substrate (7) comprises at least one outer face and has a first refractive index n v , and the holographic lens is generated with a photosensitive material (2) configured to record the interference pattern between two coherent light beams (3, 4), said photosensitive material (2) comprising at least a first outer surface (5) and a second outer surface (6) opposite the first outer surface (5); where the method comprises the steps of - incident on the photosensitive material (2), at least partially, via the first outer surface (5) of the photosensitive material (2), with a reference beam (3) of wavelength substantially equal to a generation value, X g ; - directing an object beam (4) of wavelength substantially equal to the generation value, X g , towards the photosensitive material (2) by means of an analog lens (1), and impact the photosensitive material (2), at least partially, through one of the exterior surfaces (5, 6) of the photosensitive material (2) with said object beam (4), such that the reference beam (3) and the object beam (4) coincide and interfere inside the photosensitive material (2); - recording inside the photosensitive material (2) the interference pattern between the reference beam (3) and the object beam (4), where the interference pattern is characterized by a lattice vector K'-, where the method is characterized in that the photosensitive material (2) is embedded in a medium (8) and at least one of its outer surfaces (5, 6) is in contact with said medium (8), where the medium (8) has a second refractive index, n a, less than the first refractive index, n v ; before striking the photosensitive material (2), the reference beam (3) propagates in the medium (8) at an angle equal to a first angular value, 0i, with respect to the normal to the first exterior surface (5) of the photosensitive material (2); before striking the photosensitive material (2), the object beam (4) propagates in the medium (8) at an angle equal to a second angular value, 02, with respect to the normal to the first exterior surface (5) of the photosensitive material (2); at least one of the reference and object beams (3, 4) strikes the photosensitive material (2) by refracting from the medium (8) towards the interior of the photosensitive material (2); The photosensitive material (2) has a third refractive index n g greater than the second refractive index n a , and said third refractive index n g , the value of generation X g, the first angular value 01 and the second angular value 02 fix the grating vector K' of the interference pattern, such that, when the outer surface (5, 6) of the generated holographic lens opposite the outer surface (5, 6) through which the object beam (4) is incident is arranged on the outer face of the substrate (7), the generated holographic lens is configured to obtain a boundary diffracted light ray from a boundary reconstruction light ray incident on the holographic lens through the first outer surface (5) thereof, where the wavelength of the boundary reconstruction light ray is substantially equal to a boundary value, Xi¡ m , other than the generation value X g , the limit diffracted light ray passes through the outer surface (5, 6) arranged on the outer face of the substrate (7) at a point, forming a limit angle, 0i¡ m, inside the substrate (7), with respect to the perpendicular direction at the point of the outer surface (5, 6) crossed by said limit diffracted light ray, the limit angle being 0i¡ m equal to the arcsine of the quotient between the second refractive index n a and the first refractive index n v . 2.- Method according to claim 1, wherein the object beam (4) affects the photosensitive material (2), at least partially, through the first outer surface (5) thereof. 3.- Method according to claim 1, wherein the object beam (4) affects the photosensitive material (2), at least partially, through the second outer surface (6) thereof. 4.- Method according to any of claims 1-3, wherein the third refractive index n g , the value of generation X g, the first angular value 01 and the second angular value 02 that fix the grating vector K' of the interference pattern, are such that the generated holographic lens is configured to obtain the boundary diffracted light ray from a boundary reconstruction light ray that strikes the first outer surface (5) substantially perpendicularly thereto. 5.- Method according to any of claims 1-4, wherein the method additionally comprises the step of stabilizing the interference pattern recorded in the photosensitive material (2). 6.- Method according to any of claims 1-5, wherein the value of the resolution of the photosensitive material (2) is equal to or less than 0.5 .m.

7. Method according to any of claims 1-6, wherein the photosensitive material (2) comprises a geometric center and the analog lens (1) comprises an optical center, the optical center of the analog lens (1) and the geometric center of the photosensitive material (2) being separated by a distance, h, and where the analog lens (1) is a diverging lens; or the analog lens (1) is a converging lens with a focal length equal to a focal value, f, where the distance h between the optical center of the analog lens (1) and the geometric center of the photosensitive material (2) is greater than said focal value f.

8. Method according to any of claims 1-6, wherein the photosensitive material (2) comprises a geometric center and the analog lens (1) comprises an optical center, the optical center of the analog lens (1) and the geometric center of the photosensitive material (2) being separated by a distance, h, and where the analog lens (1) is a converging lens with a focal length equal to a focal value, f, where the distance h between the optical center of the analog lens (1) and the geometric center of the photosensitive material (2) is less than or equal to said focal value f. 9.- Method according to any of claims 1-8, wherein the photosensitive material (2) comprises a geometric center and the interference pattern recorded in the photosensitive material (2) is centered with respect to said geometric center. 10.- Method according to any of claims 1-9, wherein the photosensitive material (2) is one of the following: a phase material, an amplitude material. 11.- Method according to any of claims 1-10, wherein the photosensitive material (2) is composed, at least partially, of at least one of the following: one or more photopolymers, one or more photoresins, one or more dichromated gelatins. 12.- Method according to any of claims 1-11, wherein the third refractive index n g is equal to or greater than 0.9 times the first refractive index n v , and less than or equal to 1.1 times the first refractive index n v . 13.- Method according to any of claims 1-12, wherein one of the following is used as a means of holding the photosensitive material (2): the substrate (7), where one of the outer surfaces (5, 6) of the photosensitive material (2) is arranged on the outer face of the substrate (7); a transparent and low-dispersion neutral block, comprising at least one outer face, where one of the outer surfaces (5, 6) of the photosensitive material (2) is arranged on said outer face; or one or more tweezers holding the photosensitive material (2).

14. Method according to any of claims 1-13, wherein the size of the cross section of the reference beam (3) and / or the size of the cross section of the object beam (4) are controlled by means of at least one diaphragm (9,9'). 15.- Method according to any of claims 1-14, wherein at least one of the outer surfaces (5, 6) of the photosensitive material (2) has adhesive properties. 16.- Method according to any of claims 1-15, wherein the thickness of the photosensitive material (2) between the first outer surface (5) and the second outer surface (6) is between 5 .m and 20 .m, and more particularly, between 10 .m and 15 .m. 17.- Holographic lens generated with a method according to any of claims 1-16.

18. Light guiding system (10) comprising at least one image projector (11) configured to generate light in the form of a first image (15), a first holographic lens (12), a second holographic lens (14), and a wave guiding substrate (13) comprising an input portion (16), a central portion (17) and an output portion (18), wherein the wave guiding substrate (13) comprises at least a first outer face (19) and a second outer face (20) opposite said first outer face (19); the first holographic lens (12) is arranged on one of the outer faces (19, 20) of the wave guiding substrate (13) at its input portion (16); the second holographic lens (14) is arranged on one of the outer faces (19, 20) of the wave guiding substrate (13) at its output portion (18); the image projector (11) is configured to direct the light it generates towards the first holographic lens (12); the first holographic lens (12) is configured to guide the light received from the image projector (11) into the input portion (16) of the waveguide substrate (13); the central portion (17) is configured to guide the light guided by the first holographic lens (12) inside, from the input portion (16) to the output portion (18); the second holographic lens (14) is configured to receive the light guided to the output portion (18) by the central portion (17), and guide said light it receives towards the outside of the output portion (18) of the waveguide substrate (13);and the first holographic lens (12), the second holographic lens (14) and the waveguide substrate (13) are configured so that the waveguide substrate (13) guides the light generated by the image projector (11) therein by total reflection, such that, from the light guided by the second holographic lens (14) to the outside of the output portion (18) of the waveguide substrate (13), the first image (15) generated by the image projector (11) is reproduced with a second image (21); the light guiding system (10) being characterized in that the first holographic lens (12) and / or the second holographic lens (14) are holographic lenses according to claim 17; 19.- Light guiding system (10) according to claim 18, wherein the first holographic lens (12) and / or the second holographic lens (14) comprises at least one of the following: transmission holographic lens, reflection holographic lens, convergent holographic lens, divergent holographic lens.

20. Light guiding system (10) according to any of claims 18-19, wherein the second holographic lens (14) is configured to guide the light it receives from the inside of the wave guiding substrate (13) towards a screen (22), such that the second image (21) reproducing the first image (15) generated by the image projector (11) is projected on said screen (22); alternatively, the second holographic lens (14) is configured to guide the light it receives from the inside of the wave guiding substrate (13) towards the eye (23) of a user, such that the user sees the second image (21) reproducing the first image (15) generated by the image projector (11). 21.- Light guidance system (10) according to claim 20, wherein the screen (22) is at least partially transparent.

22. Light guiding system (10) according to any of claims 18-21, wherein the first holographic lens (12) comprises an optical center and has a focal length equal to a first focal value fi; the second holographic lens (14) comprises an optical center and has a focal length equal to a second focal value Í2; the distance between the optical center of the first holographic lens (12) and the optical center of the second holographic lens (14) is substantially equal to the sum of the first focal value h and the second focal value Í2; the image projector (11) comprises an image plane, where said image plane is located at a distance from the optical center of the first holographic lens (12) substantially equal to the first focal value h; the second image (21) reproducing the first image (15) generated by the image projector (11) is located at a distance from the optical center of the second holographic lens (14) substantially equal to the second focal value Í2. 23.- Light guiding system (10) according to claim 22, wherein the second focal value Í2 of the second holographic lens (14) is greater than the first focal value h of the first holographic lens (12). 24.- Light guidance system (10) according to any of claims 18-23, wherein the light directed by the image projector (11) falls on the first holographic lens (12) through the first outer surface thereof, substantially perpendicular to said first outer surface. 25.- Light guidance system (10) according to any of claims 18-24, wherein the image projector (11) is one of the following: a projector based on one or more spatial light modulators, a laser projector. 26.- Light guiding system (10) according to claim 25, wherein the image projector (11) is one of the following: an LCD projector, a DLP projector. 27.- Light guidance system (10) according to any of claims 18-26, wherein the image projector (11) is configured for at least one of the following: generating the first image (15) in high definition and / or ultra high definition format, emitting light of any combination of colors, emitting monochromatic light. 28.- Light guidance system (10) according to any of claims 18-27, wherein the image projector (11) has a spectral width less than or equal to 40 nm. 29.- Light guiding system (10) according to any of claims 18-28, wherein the wave guiding substrate (13) is transparent. 30.- Augmented reality vision device comprising a light guidance system (10) according to any of claims 18-29. 31.- Augmented reality vision device according to claim 30, wherein the augmented reality vision device comprises one of the following: smart glasses, a smart helmet, or a windshield of a vehicle.

Images