Overlapping facets

Abstract

To reduce non-uniformity in an image out-coupled toward a nominal point of observation on each item by specifically managing a configuration of overlap of facets.SOLUTION: A waveguide including at least two parallel surfaces, first, middle, and last partially reflecting facets are configured such that in a geometrical projection of the facets onto one of the surfaces the facets overlap, preferably, adjacent facets overlap, and non-adjacent facets starts and ends coincide along at least a portion of the waveguide.SELECTED DRAWING: Figure 16B

Description

Technical Field

[0001] This application claims the benefit of Provisional Patent Application (PPA) No. 62 / 474,614, filed on March 22, 2017 by the inventors, and the entire disclosure of which is incorporated herein by reference.

[0002] The present invention generally relates to optical systems, and more particularly, to uniform reflection.

Background Art

[0003] One important application for compact optical elements is a head-mounted display (HMD) in which the optical module functions as both an imaging lens and a combiner, whereby a two-dimensional display is imaged at infinity and reflected into the viewer's eye. The display is obtained directly from a spatial light modulator (SLM) such as a cathode ray tube (CRT), liquid crystal display (LCD), organic light emitting diode array (OLED), scanning source or similar device, or indirectly via relay lenses or fiber optic bundles. The display is imaged at infinity by a collimator lens and includes an array of elements (pixels) transmitted to the viewer's eye by a reflective or partially reflective surface that acts as a combiner for non-see-through or see-through applications, respectively. Typically, conventional free-space optical modules are used for this purpose. As the desired field of view (FOV) of the system increases, such conventional optical modules necessarily become larger, heavier, and bulkier, rendering the device impractical even for moderate performance. These are the major drawbacks of all types of displays, but especially so in head-mounted applications where the system must necessarily be as lightweight and compact as possible.

[0004] Efforts to make the device compact have resulted in several complex optical solutions. All of these are, on the one hand, not yet compact enough for most practical applications, and on the other hand, difficult to manufacture. Furthermore, the eye-motion box (EMB) of the optical viewing angle resulting from these designs is usually very small, typically less than 8mm. Consequently, the performance of the optics is highly sensitive to even small movements of the viewer's eye, and does not allow sufficient pupillary movement to conveniently read the displayed text. [Overview of the Initiative]

[0005] According to the teachings of this embodiment, an optical device including a waveguide is provided, the waveguide having a first surface of at least one pair of surfaces parallel to each other, a first region into which light is connected, and a first array of facets, the facets including a first facet located proximal to the first region and having a first width in the direction between the first pair of surfaces, a last facet located distal to the first array of facets from the first region and having a third width in the direction between the first pair of surfaces, and one or more intermediate facets located between the first and last facets and having a second width in the direction between the first pair of surfaces, each of which has a width in the plane of the facet and is at least partially reflective, oblique to the first pair of surfaces, and the width of the facet The facet has a proximal facet initiation and a distal facet end, and here, the geometric projection is made on one of the first pair of surfaces in the direction of a nominal ray outcoupled from the waveguide, the nominal ray being the central ray of light outcoupled from the waveguide, each geometric projection of the last facet and one or more intermediate facets overlaps with each geometric projection adjacent to one or more intermediate facets and the first facet, and the geometric projection of each facet initiation of the last facet and one or more intermediate facets coincides with each geometric projection of a non-adjacent facet end of one or more intermediate facets and the first facet, the coincidences along at least a portion of the waveguide.

[0006] In any embodiment, the first width of the first facet is less than the second width of one or more intermediate facets. In another arbitrary embodiment, many facets intersect with nominal rays externally connected from the waveguide, and the number of facets is constant for all of the first array. In another arbitrary embodiment, the light corresponds to an image, and the central ray is the central ray from the center of the image. In another arbitrary embodiment, the light corresponds to an image, and the central ray corresponds to the central pixel of the image. In another arbitrary embodiment, the last facet has a reflectance that is substantially 100% of the nominal reflectance, and the nominal reflectance is the total reflection required at a particular location in the waveguide. In another arbitrary embodiment, the third width is less than the second width. In another arbitrary embodiment, the third width is substantially half the second width. In another arbitrary embodiment, one or more intermediate facets are selected from the group consisting of: 1; 2; 3; 4; 5; and a plurality. In another optional embodiment, a certain number of facets overlap in the line of sight toward the nominal observation point of the optical connection from the waveguide by one of the first pair of surfaces. In another optional embodiment, the width of one facet of multiple facets in the first array of facets changes monotonically with respect to the width of one adjacent facet of multiple facets in the first array of facets. In another optional embodiment, the spacing between adjacent facets of a pair in the first array of facets changes monotonically with respect to the spacing between adjacent facets of another pair in the first array of facets. In another optional embodiment, the light from the first region is such that at least a portion of the light strikes the first facet before striking one of one or more intermediate facets. In another optional embodiment, the spacing between adjacent facets is greater than the coherence length of the light connecting to the waveguide.

[0007] In any embodiment, the first width is substantially equal to the second width, and the first facet has a first portion corresponding to the geometric projection of the first facet that does not overlap with the geometric projection of the adjacent intermediate facet. In another arbitrary embodiment, the first portion is transmissive to light. In another arbitrary embodiment, the first portion has a reflectance substantially twice that of the adjacent facet. In yet another arbitrary embodiment, the facet has a uniform partial reflectance across the entire facet.

[0008] In any embodiment, the waveguide further has a second pair of surfaces parallel to each other and not parallel to the first pair of surfaces, and the facets are configured such that when the image is coupled to the waveguide in the first region with its initial direction of propagation at a coupling angle inclined to both the first and second pair of surfaces, the image travels along the waveguide by the amount of four folding reflections. In another arbitrary embodiment, the second pair of surfaces is perpendicular to the first pair of surfaces. In yet another arbitrary embodiment, the facets are oblique to the second pair of surfaces.

[0009] In any embodiment, the first width of the first facet is substantially equal to the second width of the intermediate facet, the first reflectance of the first facet is greater than 50% of the nominal reflectance, the second facet adjacent to the first facet has a second reflectance, the second reflectance and the first reflectance are substantially the nominal reflectance, the third facet adjacent to the second facet has a third reflectance, which is greater than 50% of the nominal reflectance and less than the first reflectance, and the fourth facet adjacent to the third facet has a fourth reflectance, the fourth reflectance and the third reflectance are substantially the nominal reflectance.

[0010] In another optional embodiment, the first width of the first facet is substantially equal to the second width of the intermediate facets, the first array of odd facets includes the first facet and any number of facets every other from the first facet, the first array of even facets includes the second facet adjacent to the first facet and any number of facets every other from the second facet, the first set of facets includes the first odd facet from the first array of odd facets and the corresponding first even facet from the first array of odd facets, the first odd facet is greater than 50% of the nominal reflectance Having a reflectance of 1, the first even facet has a second reflectance, and the second and first reflectances are substantially nominal reflectances; each subsequent set of facets includes the next odd and even facets from the respective sequences of the first odd and even facets; each odd facet from a subsequent set has an odd reflectance greater than 50% of the nominal reflectance and less than the reflectance of the odd facet from the previous set; and each even facet from a subsequent set has an even reflectance such that adding the odd reflectance to the even reflectance of the corresponding even facet results in substantially nominal reflectance. [Brief explanation of the drawing]

[0011] Embodiments are described herein as merely examples with reference to the accompanying drawings.

[0012] [Figure 1] This is a side view of a prior art foldable optical device. [Figure 2] This is a side view of a typical optical guide element. [Figure 3] A and B illustrate the desired reflectivity and transmittance characteristics of the selected reflective surface for two ranges of incident angles. [Figure 4] This diagram illustrates a typical structure of an optical guide element. [Figure 5] This figure illustrates another structure of an optical guide element. [Figure 6]This figure illustrates a detailed cross-sectional view of a one-dimensional waveguide in a symmetrical lateral pupil dilation region. [Figure 7] This diagram illustrates how a beam can be expanded along two axes using a dual LOE structure. [Figure 8] This diagram illustrates another method of expanding a beam along two axes using a dual LOE structure. [Figure 9] A typical embodiment of LOE embedded in a standard eyeglass frame is illustrated. [Figure 10] A is a schematic diagram of a waveguide with non-overlapping facets, illustrating the effect of change on image uniformity. B is a schematic diagram of a waveguide with overlapping facets, illustrating the effect of change on image uniformity. [Figure 11] AC is a typical alternative structure for implementing overlapping facets, possessing propagation structures at various angles. [Figure 12] A and B are schematic side and front views, respectively, of a two-dimensional optical aperture multiplier. CD is a schematic diagram illustrating two possible geometric arrangements of image rays propagating from the optical aperture multipliers A and B to internal facets that partially reflect within the waveguide. [Figure 13] This is a schematic isometric view illustrating a 2D waveguide implementation where the internal partial reflection facets are tilted obliquely to both sets of elongated, parallel outer surfaces. [Figure 14] A and B are schematic side and front views, respectively, of an optical aperture multiplier constructed with overlapping facets. [Figure 15] Figures A and B are schematic side and front views, respectively, of optical aperture multipliers, with the structures of A and B in Figure 14 modified to perform extensions in a free-space optical arrangement. [Figure 16A] This is a schematic diagram of a typical facet implementation. [Figure 16B] This is a schematic diagram of a typical facet implementation. [Figure 16C] This is a schematic diagram of a typical facet implementation. [Figure 17]A is a rough schematic diagram of a double facet. B is a rough schematic diagram with a variable facet interval. C is a rough schematic diagram with a decreasing facet interval from the proximal end to the distal end of the waveguide. D is a rough schematic diagram with a variable facet width. [Figure 18] It is a rough schematic diagram applying duplicate facets to a symmetric structure. [Figure 19A] It is a graph of the total nominal reflectivity in a double duplicate structure. [Figure 19B] It is a typical graph of the total nominal reflectivity in a double duplicate structure using an alternative change in facet reflectivity. [Figure 20] A is a diagram illustrating a process that can be used to generate a waveguide with duplicate facets. B - E are typical procedures for attaching a coupling prism. [Figure 21] A - D are further details of typical procedures for generating a waveguide with duplicate facets.

[0013] <Abbreviations and Definitions> For convenience of reference, this section includes a concise list of abbreviations, initials, and short definitions used in this document. This section should not be considered as limiting. More detailed explanations can be found in the following and applicable standards. 1D - One - dimensional 2D - Two - dimensional CRT - Cathode Ray Tube EMB - Eye Motion Box FOV - Field of View HMD - Head - Mounted Display HUD - Head - Up Display LCD - Liquid Crystal Display LOE - Light - guide Optical Element OLED - Organic Light - Emitting Diode Array SLM - Spatial Light Modulator TIR - Total Internal Reflection [Modes for carrying out the invention]

[0014] The principles and operation of the system according to this embodiment can be better understood by referring to the drawings and accompanying descriptions. The present invention is an optical device that generates uniform reflection to the observer.

[0015] By specifically controlling the configuration of facet overlap, the non-uniformity of the outcoupled image to a nominal point of observation is reduced. A waveguide including at least two surfaces, i.e., the first, intermediate, and last partial reflection facets, is configured such that when the facets are geometrically projected onto one of the surfaces, the facets overlap, preferably adjacent facets, and the start and end of non-adjacent facets coincide along at least a portion of the waveguide.

[0016] <Basic Technology - Figures 1 to 9> Figure 1 illustrates a conventional foldable optical system structure, in which a substrate (2) is illuminated by a display source (4). The display is collimated by a collimating optical system (6), such as a lens. Light from the display source (4) is connected to the substrate (2) by a first reflecting surface (8) such that the principal ray (11) is parallel to the substrate plane. A second reflecting surface (12) connects the light from the substrate to the viewer's (14) eye. Although this configuration is compact, it has a significant drawback. In particular, it can only achieve a very limited field of view (FOV).

[0017] Refer here to Figure 2, a side view of an exemplary optical guide element (LOE). To alleviate the above limitations, this embodiment utilizes an array of selective reflective surfaces fabricated within the optical guide element (LOE). The first reflective surface (16) is illuminated by a collimated display ray (beam) (18) emanating from a light source (not shown) located behind the device. In the present figure, for simplification, generally only one ray is shown, which is the incident ray (38) (also called the “beam” or “incident ray”). Other rays of the incident light, such as beam (18A) and (18B), may be used to specify the edges of the pupil into which the light enters, such as the left and right edges of the pupil into which the light enters. In general, wherever the image is represented here by rays, it should be noted that the beam is a sample beam of the image and is typically formed by multiple beams at slightly different angles, each corresponding to a point or pixel of the image. Unless specifically referred to as the leading edge of the image, the illustrated beam is typically the centroid of the image.

[0018] The reflective surface (16) reflects incident light from the light source so that the light is trapped inside the waveguide (20) by total internal reflection. The waveguide (20) is also called the “planar substrate” and the “light-transmitting substrate”. The waveguide (20) includes at least two (primary) surfaces that are parallel to each other, which are shown in this drawing as the lower (primary) surface (26) and the upper (primary) surface (26A).

[0019] The incident light ray (38) enters the substrate at its proximal end (right side of the figure). The light propagates through the waveguide and one or more facets, usually at least several facets, and typically several facets, toward the distal end of the waveguide (left side of the figure). The light propagates through the waveguide in both the first direction of propagation (28) and the other direction of propagation (30).

[0020] After being reflected several times from the surface of the substrate (20), the captured wave reaches an array of selective reflectors (22), connecting the light from the substrate to the viewer's eye (24). In an alternative configuration, the selective reflectors (22) are present immediately after the light ray (18) enters the substrate (20), without being initially reflected from the surface of the substrate (20).

[0021] Internal partial reflecting surfaces, such as the selective reflecting surface (22), are generally referred to as “facets” in the context of this specification. At its limit, facets can also be completely reflecting (100% reflectivity, or a mirror, e.g., the last facet at the distal end of the substrate) or minimally reflecting. In augmented reality applications, facets are partially reflecting, allowing light from the real world to enter through the upper surface (26A), traverse the substrate containing the facets, and exit the substrate through the lower surface (26) to the viewer’s eye (24). In virtual reality applications, facets may have alternative reflectivity, such as a first internally linked mirror with 100% reflectivity, because light from the image of the real world does not need to traverse this mirror. The internal partial reflecting surface (22) generally traverses the waveguide (20) at least partially at an oblique angle (i.e., neither parallel nor perpendicular) to the extension direction of the waveguide (20).

[0022] References to reflectance generally refer to nominal reflectance. Nominal reflectance is the total internal reflection required at a particular location in the substrate. For example, if the reflectance of a facet is stated as 50%, this generally refers to 50% of its nominal reflectance. If the nominal reflectance is 10%, then 50% reflectance results in a facet reflectance of 5%. Those skilled in the art will understand the use of reflectance percentages in the context of use. Partial reflection can be implemented by various techniques, including, but not limited to, the use of transmission or polarization of a percentage of light.

[0023] Figures 3A and 3B illustrate the desired reflection behavior of a selected reflective surface. In Figure 3A, the ray (32) is partially reflected from the facet (34) and connected to the substrate (20) (38B). In Figure 3B, the ray (36) is transmitted through the facet (34) without any significant reflection.

[0024] Figure 4 is a detailed cross-sectional view of an array of selective reflective surfaces that connect light to the substrate and then outward to the viewer's eye. As can be seen, a ray (38) from the light source (4) strikes the first selective reflective surface. A portion of the ray (41) continues in its original direction and connects outward from the substrate. The rest of the ray (42) is connected to the substrate by total internal reflection. The captured ray is gradually connected outward from the substrate at point (44) by the other two partial reflectors (22). The coating properties of the first reflector (16) do not necessarily have to be similar to those of the other reflectors (22), (46). This coating can be a simpler beam splitter, either metallic, dichroic, or a hybrid of metallic and dichroic. Similarly, in a non-see-through system, the last reflector (46) can be a simple mirror.

[0025] Figure 5 is a detailed cross-sectional view of the apparatus including an array of reflective surfaces, where the last reflective surface (46) is a total reflection mirror. In such a case, the leftmost portion of the last reflective surface (46) cannot be optically active, and peripheral rays (48) cannot be externally connected to the substrate. Therefore, the output aperture of the device will be slightly smaller. However, the optical efficiency will be very high, and the manufacturing process of the LOE can be made very simple.

[0026] Unlike the configuration illustrated in Figure 2, it is important to note that there are constraints on the orientation of the reflective surfaces (16) and (22). In the former configuration, all light is connected inward to the substrate by the reflective surface (16). Therefore, the reflective surface (16) does not need to be parallel to the reflective surface (22). Furthermore, the reflective surfaces may be oriented so that the light is connected outward from the substrate in the direction opposite to the direction of the input wave. However, in the configuration illustrated in Figure 4, some of the input light is not reflected by the reflective surface (16), but continues in the original direction of the input light (38) and is immediately connected outward from the substrate as output light (41). Therefore, in order to ensure that the output direction of all light rays resulting from the same plane wave is the same, it is not sufficient for all the reflective surfaces (22) to be parallel to each other; the reflective surface (16) must also be parallel to these surfaces.

[0027] Referring again to Figure 4, a system with two reflective surfaces for connecting light to the outside of the substrate is shown, but any number of reflective surfaces can be used depending on the required output aperture of the engineering system and the thickness of the substrate. Naturally, there may be cases where only one external connecting surface is needed. In this case, the output aperture will be substantially twice the size of the system's input aperture. The only reflective surfaces required for the last configuration are a simple beam splitter and mirror.

[0028] As shown in the apparatus in Figure 4, the light from the display source is connected to the substrate at the edge of the substrate; however, there are systems in which a symmetrical system is preferable. That is, the input light should be connected to the substrate at the central part of the substrate.

[0029] Figure 6 illustrates a detailed cross-sectional view of a one-dimensional waveguide with a symmetrical structure of lateral pupil dilation. This drawing illustrates a method of combining two identical substrates to fabricate a symmetrical optical module. As can be seen, some of the light from the light source (4) exits the substrate directly through the partial reflecting surface. The other portion of the light is coupled to the right side (20R) and left side (20L) of the substrate by the partial reflecting surfaces (16R) and (16L), respectively. The captured light is then gradually coupled outward by the reflecting surfaces (22R) and (22L), respectively. Clearly, the output aperture is three times the size of the system's input aperture, the same magnification as shown in Figure 8. However, unlike that system, this system is symmetrical with respect to the junction surface (29) of the right and left substrates.

[0030] Please refer to Figures 7 and 8, which are typical implementations of Figures 5 and 6 on a waveguide. The configurations in Figures 5 and 6 magnify the incident image laterally. The apparatus in Figure 5 may be used to implement the first LOE(20a) in Figure 7, the apparatus in Figure 6 may be used to implement the first LOE(20a') in Figure 8, and the apparatus in Figure 2 may be used to implement the second LOE(20b).

[0031] Figure 7 illustrates an alternative method for expanding a beam along two axes using a dual LOE configuration. The input wave (90) is coupled by a first reflecting surface (16) to a first LOE (20a) having an asymmetrical structure similar to that illustrated in Figure 5, and then propagates along the η-axis. A partial reflecting surface (22a) couples the light outward from the first LOE (20a), and then the light is coupled by a reflecting surface (16b) to a second asymmetrical LOE (20b). The light propagates along the ξ-axis and is then outwardly coupled by a selective reflecting surface (22b). As illustrated, the original beam (90) is expanded along both axes, where the overall expansion is determined by the ratio between the lateral dimensions of elements (16a) and (22b). The configuration provided in Figure 7 is simply an example of how a dual LOE works. Other configurations are possible in which two or more LOEs are combined together to form a complex optical system.

[0032] Refer to Figure 8, which illustrates another method for expanding the beam along two axes using a dual LOE configuration. Typically, the region where light is connected to the second LOE (20b) by the partial reflecting surface (16b) cannot be transparent to ambient light and is not part of the see-through region. Therefore, the first LOE (20a) does not need to be transparent itself. As a result, even in a see-through system, it is usually possible to design the first LOE (20a) to have a symmetrical structure, as seen in this drawing. The second LOE (20b) has an asymmetrical structure that allows the user to see the outside scenery. In this configuration, a portion of the input beam (90) follows the internally connected mirror (16b) of the second LOE (20b) along the original direction (92), while the other portion (94) is connected to the first LOE (20a') by a partial reflecting surface (16a), propagates along the η-axis, and is then connected to the second LOE (20b) by a selective reflecting surface (22a). Next, both portions are connected to the second asymmetric LOE (20b) by a reflecting surface (16b), propagates along the ξ-axis, and is then externally connected by a selective reflecting surface (22b).

[0033] Figure 9 illustrates embodiments of the LOE(20a) / (20a') and (20b) embedded in a standard eyeglass frame (107). The display source (4) and the folding and collimating optical systems (6) are assembled inside the arm portion (112) of the eyeglass frame, located immediately next to the LOE(20a) / (20a') and situated on the edge of the second LOE(20b). If the display source is an electronic device such as a small CRT, LCD, or OLED, the driver electronics (114) for the display source may be assembled inside the rear of the arm (112). The power and data interface (116) can be connected to the arm (112) by lead wires (118) or by other communication devices including wireless communication or optical transmission. Alternatively, the battery and small data link electronics can be integrated into the eyeglass frame. The embodiments shown in Figure 9 are merely examples. Other possible head-mounted display structures can be constructed, including assemblies in which the display source is mounted parallel to the LOE plane or mounted on top of the LOE.

[0034] Further details of this fundamental technology can be found in U.S. Patent No. 7,643,214.

[0035] <First Embodiment - Figures 10A to 21D> Here, please refer to Figure 10A, a schematic diagram of a waveguide with non-overlapping facets, illustrating the effect of change on image uniformity. The source of perceived heterogeneity is related to the angle of overlap of internal facets in different fields of view. In the region of waveguide (10) or (20) illustrated in this diagram (see Figures 12A and 12B), the waveguide contains internal facets (two are shown as the last facet (2515) and the first facet (2517)). Most of the out-connected light is reflected from a single internal facet. However, at the edges of the facet, there is non-uniformity at off-axis angles. For the region of the FOV pointing to the left (marked by the solid arrow), at this angle, there is an effective gap between the light reflected by the last facet (2515) and the first facet (2517), so the conventional gap area (2520) (commonly also called the "underlapping area," "black line" area, or "dark strip" area) does not reflect light, and as a result, a dark strip is perceived. On the other hand, the light out-connected to the right (marked by the dashed line) has a conventional bright area (2525) (commonly also called the "partially overlapping" area or "intense" area), in which there is overlap of light reflected from facets (2515) and (2517), and as a result, the waveguide reflects nearly twice the amount of light. Therefore, the non-uniformity in Figure 10A will vary between approximately 200% and 0% intermediate image intensity across the elongated aperture in various regions of the FOV and eye position.

[0036] Here, refer to Figure 10B, a schematic diagram of a waveguide with overlapping facets, which illustrates the effect of changes on image uniformity. As illustrated in this figure, considerable overlap is introduced between facets. In this case, the spacing between adjacent facets is halved, and as a result, most of the FOV at most eye positions is illuminated from the image via superimposed reflections from two facets. In this typical case, a single intermediate facet (2535) is located between the last facet (2515) and the first facet (2517). Near the angular extremities of the image and the facet endpoints, there will still be variations in the number of overlapping facets contributing to a particular region of the image, as illustrated by the overlapping region (2540) resulting from only one facet (the intermediate facet (2535)) and the bright region (2545) contributed by three adjacent facets (2517), (2535), and (2515). Therefore, the non-uniformity of the output varies between 50% and 150% of the intermediate reflectance.

[0037] Light from the first half of facet (2517) (light propagating from the right) is externally coupled as reduced energy (ray / power beam (2546)) because, at this position, there is no overlap with the next facet (2535), meaning there is only one facet reflecting light back to the observer. The same reduced power occurs in the second half of facet (2515) (ray / power beam (2547)). In these regions, the reflectance is 50% of the intermediate reflectance.

[0038] A key feature of this embodiment is the management of the overlapping facet configuration, specifically optimizing the overlap to obtain a constant number of facets (more than one) that reflect light toward the observer. In other words, at least two facets reflect light toward the observer's field of view (FOV).

[0039] Here, refer to Figures 11A through C, which are typical alternative configurations for the implementation of overlapping facets for different reflection (angle propagation) configurations (these configurations are also described in Figures 12C and 12D). For the sake of simplicity in this figure, only one ray, the incident ray (38) (also called the "beam"), is shown along with its corresponding out-connecting ray (38B). For the sake of simplicity, cross-connecting is not shown. Some of the rays (38B1) pass through the internal facet (2560), and some out-connecting rays (38B2) connect directly to the outside.

[0040] In configuration A of Figure 11, the incident ray (38) intersects internal facet (2560) from both sides. The first intersection is from the rear side of facet (2562), and at this intersection, the coating on this rear side of the facet should be transmissive due to this shallow angle. The beam also intersects facet (2564) from another side, on the front side, opposite the rear side, and at this typical steeper angle, the coating of the facet should be partially reflective so that some of the light is directed out of the waveguide. (A similar single facet is described in U.S. Patent No. 7,391,573 B2.)

[0041] In the configurations shown in Figures 11B and C, the angle of the internal facet (2560) and the direction of light propagation are set so that the beam (incident ray (38)) always passes through the internal facet (2560) from the same side of the facet. Coatings on the facet can be used to set the reflectance and transmittance so that the appropriate beam (38B) is reflected out.

[0042] In Figure 11B, the beam (38) intersects the first internal facet (2560) nearly perpendicularly, as shown at point (2568) where the facet's coating is designed to be transmissive. The second intersection is at a shallow angle, as shown at point (2570) where the coating is designed to be a partial reflector (far from perpendicular) so that some of the light is out-coupled (38B).

[0043] In Figure 11C, the facet coating is set to be a partial reflector at angles that are nearly perpendicular, as shown at point (2574), and far from perpendicular, as shown at point (2576), to be translucent.

[0044] Referring here to the drawings, Figures 12A–12D illustrate overlapping facets in one-dimensional (1D) and two-dimensional (2D) waveguides of an optical aperture multiplier. Generally, in terms of terminology, an optical aperture multiplier according to embodiments of the present invention includes a first optical waveguide (10) having an extension direction arbitrarily illustrated herein as corresponding to the "X-axis". The first optical waveguide (10) has first and second pairs of parallel planes (12a), (12b), (14a), (14b) forming a rectangular cross section. A plurality of internal partial reflecting planes (40) at least partially traverse the first optical waveguide (10) at an oblique angle (not parallel or perpendicular) to the extension direction. The optical aperture multiplier also preferably includes a second optical waveguide (20) optically coupled to a first optical waveguide (10), which has a third pair of parallel planes (22a), (22b) forming a slab-type waveguide, i.e., the other two dimensions of waveguide (20) are at least an order of magnitude greater than the distance between the third pair of parallel planes (22a), (22b). Also herein, a plurality of partial reflecting planes (45) preferably at least partially traverse the second optical waveguide (20) at an oblique angle to the third pair of parallel planes.

[0045] The optical coupling between waveguides, and the arrangement and configuration of the partial reflecting surfaces (40), (45) are such that when the image is coupled to the first optical waveguide (10) in the first direction (28) of propagation (e.g., light rays (38)) at a coupling angle inclined to both the first and second pairs of parallel surfaces (12a), (12b), (14a), (14b), the proportion of the intensity of the image reflected by the partial reflecting surface (40) so as to the second optical waveguide (20) is the ratio of the intensity of the image reflected by the first optical waveguide (10) The optical coupling, arrangement, and configuration proceeds by internal reflections of four folds along (10) (images (a1), (a2), (a3), and (a4)), and then propagates by reflections of two folds in the second optical waveguide (20) (images (b1), (b2)) at a rate equal to the intensity of the image reflected by the partial reflecting surface (45) so as to be oriented outward from one of the parallel planes as a visible image c seen by the user's eye (47).

[0046] Referring more specifically to Figures 12A and 12B, schematic side and front views of a two-dimensional optical aperture multiplier, respectively, illustrate a first example of the implementation described above. The first waveguide (10) is referred to herein as a two-dimensional (2D) waveguide in the sense that it guides an image injected in two dimensions by reflection between two sets of parallel surfaces (in this case, the first and second pairs of parallel surfaces (12a), (12b), (14a), (14b)), while the second waveguide (20) is referred to as a one-dimensional (1D) waveguide, which guides an image injected in only one dimension between a pair of parallel surfaces (in this case, the third pair of parallel surfaces (22a), (22b)).

[0047] As shown in Figure 12B, further improvement in reducing non-uniformity can result from the introduction of a “multipath” image generated by overlapping internal facets. In general, a similar process exists in the implementation of overlapping facets. Light propagating within a 2D waveguide (10) (marked as a solid arrow and designated as “a”) is externally coupled (designated as “b”), but some of the light from b is back-coupled to a’ (marked as a dashed arrow) before being externally coupled as “b’” (marked as a dashed arrow). This back-and-forth coupling between “a’” and “b’” causes an averaging of intensity across the aperture while maintaining parallelism, thereby further improving the uniformity of the light. This improvement can also be implemented in other waveguides using overlapping facets in a similar process, as shown in Figure 12A, etc., for a 1D waveguide (20). Light propagating within the 1D waveguide (20) (marked as solid arrows and indicated as beams "b1" and "b2") is externally coupled (indicated as beam "c"), but some of the light from beam (c) is rear-coupled to (b2') (marked as a dashed arrow) before being externally coupled as beams (c3) and (c4) (marked as dashed arrows).

[0048] A ray (38) from an optical image generator (not shown) is injected into the first waveguide (10) at a certain angle. Finally, the light propagates along the waveguide (10), being reflected from all four outer surfaces of the waveguide as shown in the side view of Figure 12A. In this process, four conjugate beam vectors (a1), (a2), (a3), and (a4) are generated, which represent the same image as the image reflected inward by the surfaces.

[0049] The angle of the beam (38) injected into the waveguide (10) is set so that it reflects from all four outer surfaces of the waveguide. The ray should reflect at a shallow angle (line of sight angle) from the bottom surface (12b) of the first waveguide (10), i.e., the surface adjacent to the second waveguide (20), and preferably propagate from (10) to (20) at a steep angle. This property can be achieved by total internal reflection (TIR) ​​or optical coating. Diffraction patterns can also achieve this optical property by combining diffraction with propagation on the same surface. Reflections from the other three surfaces (12a), (14a), and (14b) of the first waveguide (10) can be achieved in the same manner or by using reflective coatings.

[0050] A portion of the guided rays within the first waveguide (10) (e.g., beam (a1) and beam (a2)) are reflected downward onto the input coupling surface of the second waveguide (20) by internal parallel partial reflectors (facets) (40). In the second waveguide (20), these beams are defined as typical beams (b1) and (b2). In this process, the overlapping configuration causes cross-coupling, thereby improving uniformity without degradation of image quality (as described).

[0051] Beams (b1) and (b2) are reflected by the outer surface and become conjugate; that is, beam (b1) is reflected to become beam (b2) (as shown in Figure 12A), and vice versa. The outer front and back surfaces (14a) and (14b) of the first waveguide (10) should be parallel to each other and to the corresponding outer surfaces (22a) and (22b) of the second waveguide (20) in this implementation. Deviation from parallelism will result in the concatenated image from beams (b1) and (b2) not being an accurate conjugate image, and the image quality will be degraded.

[0052] The internal facets (45) within the second waveguide (20) reflect the beam (b2) out of the waveguide towards the observer's (47) eye. The internal facets (45) can also overlap, thereby further improving image uniformity as described with respect to facet (40).

[0053] The reflection processes by internal facets in waveguides (10) and (20) are further illustrated in Figures 12C and 12D. Two basic configurations are shown, which differ depending on the relative angles of the rays and facets. In this schematic example, beams (a1), (a2), and (b1) are shown as the same vector (only (b1) is referenced) because the same geometric considerations apply to each as observed from a side view of the corresponding waveguide. Beams (a3), (a4), and (b2) are also shown as the same vector (only (b2) is referenced).

[0054] The ray (b2) is actually a beam of light propagating in the same direction, as shown by the two vectors in Figure 12C. In this case, one vector is reflected by the outer surface to become beam (b1) and onto the inner facet (40) (or (45)), where a portion of one vector is reflected as beam (c1). The other beam (b2) vector is reflected directly by the facet as vector beam (c2). The vector beams (c1) and (c2) represent the normal image and the ghost image, though not necessarily in this order. In this configuration, beams (b1) and (b2) strike facet (45) from the same side.

[0055] Figure 12D describes essentially the same process, but the geometric arrangement is such that beams (b1) and (b2) strike facet (40) (or (45)) from the opposite side.

[0056] In both cases, the scale of reflections for images (c1) and (c2) in S and P polarizations is determined by the coatings on these facets. Preferably, one reflection is an image, and the other reflections are suppressed so that the other image corresponds to an unwanted "ghost" image. Coatings suitable for adjusting which ranges of incident beam angles are reflected and which ranges of incident beam angles are transmitted are known in the art and are described in detail in U.S. Patents 7,391,573 and 7,457,040, which were transferred concurrently with the present invention.

[0057] Figure 13 illustrates an alternative implementation in which the partial reflecting surface of the first waveguide (10), designated herein as (155), is oblique to both surfaces (12a) and (14a). (The dashed lines are intended to facilitate visualization of the facet inclination by showing one plane perpendicular to both outer surfaces and another plane inclined to only one surface.)

[0058] Refer here to Figures 14A and 14B, which are schematic side and front views, respectively, of optical aperture multipliers constructed with overlapping facets. The general operation of this figure is described above with respect to Figures 12A and 12B. Facet overlapping is applied to the 2D waveguide (10) as well as the 1D waveguide (20). In this example, in Figure 14B, before transmitting light to the observer's (47) eye, the 2D waveguide (10) expands the optical aperture laterally (from right to left in this figure), and the 1D waveguide (20) expands the optical aperture vertically (from top to bottom in this figure).

[0059] In Figure 14A, light (shown as incident ray (38)) is coupled to a 2D waveguide (10). This waveguide includes overlapping facets (40). In this figure, dashed lines are used to indicate the alignment of facet (40), which is shown as double lines. In this implementation, the first facet (40a) and the last facet (40b) have smaller regions than the intermediate facets of the internal facet (40). This makes the externally coupled light ("b") of the 2D waveguide (10) substantially uniform because the externally coupled light "b" is generated by a constant number of facets, including the beginning and end of the 2D waveguide (10). For example, output rays (b10) and (b20), which actually overlap when output from waveguide (10) but are shown slightly separated in the figure for clarity, produce a combined output generated by two facets (the adjacent facets of the first facet (40a) and the internal facet (40)). Similarly, output rays (b30) and (b40) produce outputs from two facets.

[0060] For comparison, see Figure 10B, where the optical output beam (2546) from the first complete facet (2517) and the optical output beam (2547) from the last complete facet are externally coupled as reduced energy. By using partial first and last facets (40a, 40b), this energy reduction is avoided because the partial first facet (40a) and partial last facet (40b) overlap with the adjacent facet (40) due to their shorter length. Note that if the last irradiated facet is designed to have 100% reflectivity (100% nominal reflectivity when used for visibility enhancement), the last facet will perform similarly to a complete facet (2515).

[0061] The configuration of overlapping facets described for the 2D waveguide (10) acts similarly to that of the 1D waveguide (20). The internal facet (45) reflects light to the observer (47). The internal facet (45) of the 1D waveguide overlaps as described for the internal facet (40) of the 2D waveguide. Similar to the partial first and last facets (40a) and (40b), the first and last facets (45a) and (45b) have reduced regions to maintain uniform illumination as described for the 2D waveguide (10).

[0062] Here, refer to Figures 15A and 15B, where the basic structures of Figures 14A and 14B are modified by replacing the 2D waveguide (10) to perform lateral expansion using a free-space optical arrangement (11) (as shown in Figures 5 and 6, for example). The innovative overlapping structure of the 1D waveguide (20) is also used to perform longitudinal expansion.

[0063] Please refer here to Figures 16A to 16C, which show schematic diagrams of typical facet implementations. Facets can be arranged in various overlap configurations, including, but not limited to, the amount of overlap, the angle of the facets relative to the parallel plane of the waveguide substrate (the main edges, such as the pair of lower surfaces (26) and upper surfaces (26A)), and reflectance. Facet overlap can be implemented in what is referred to in the context of this document as single (non-overlapping), double, and triple (overlapping) facets. In general, the overlap of two or more facets (by definition beginning with “double facet”) is referred to as “multiple facets” or “multiple overlaps.” As will be evident from this description and the examples not limited to this, in addition to partial overlaps, additional overlaps beyond triple are also possible. For clarity in this figure, propagation from the incident ray (38) to the out-connecting ray (38B) is not shown.

[0064] As noted above in relation to Figure 2, Figure 16A shows, for reference, a conventional implementation of a single facet, or one without overlap. Waveguide (20) includes facet (22), shown as a double line between the first two surfaces (26, 26A). The first region (54) is the region to which light (shown as a ray (38)) is connected to the substrate. Solid arrows indicate an out-connecting ray (38B) that intersects with only one facet (single facet intersection). Note that references to the number of "intersecting" and "intersected" facets include counting the facet from which the out-connected ray originates. Dashed lines are used to show the alignment of facet (22). In this single-facet configuration, facet (22) does not overlap and is specifically composed of the ends of one facet aligned at the beginning of adjacent facets.

[0065] References to alignment will be obvious to those skilled in the art with respect to the geometric projection of facets onto one surface. For example, the facet start of a typical facet (F1) has a geometric projection onto the lower surface (26) at point (P1). The facet end of a typical facet (F2) also has a geometric projection onto the lower surface (26) at point (P1). The facet start of a typical facet (F2) also has a geometric projection onto the lower surface (26) at point (P2). The facet end of a typical facet (F3) also has a geometric projection onto the lower surface (26) at point (P2).

[0066] Figure 16B is a schematic diagram of a double facet (double facet intersection, double overlap). This is a preferred implementation that minimizes the increase in manufacturing complexity (compared to high-level intersection) while demonstrating that experiments yield superior results. An unspecified example of double facet overlap is typically used in this description. The waveguide (substrate that transmits light, waveguide (20)) contains an overlapping internal facet (40), shown as a double line, between the first (two) surfaces (26, 26A). A solid arrow indicates the incident ray (38). Another solid arrow indicates a nominal ray that intersects the two facets and is then externally connected from the substrate (arrow externally connecting ray (38B)). The intersection of these two facets (facet (F11) and facet (F12)) is a double facet intersection. As in similar figures, dashed lines are used to indicate the alignment of facet (40). In this example, a single initial partial facet (40a) and a single final partial facet (40b) are shown.

[0067] The waveguide includes at least one pair of surfaces parallel to each other (referred to as the "first surface," the lower surface (26) and the upper surface (26A)). The substrate width (52) is the distance between the first surfaces. The first region (54) is the region to which light (indicated as a ray (38)) is connected to the substrate.

[0068] The waveguide includes an array of facets (56). The array of facets (56) includes a first facet (40a), a last facet (40b), and one or more intermediate facets (40c). The first facet (40a) is located adjacent to the first region (54), where proximal is the closest part of the array of facets (56). The first facet has a first width (52a) in the direction between the first surfaces (26, 26a).

[0069] The last facet (40b) is located at the distal end (55) of the facet (56) sequence of the first region (54). The last facet (40b) has a third width (52b) in the direction between the first surfaces (26, 26a).

[0070] One or more intermediate facets (40c) lie between the first facet (40a) and the last facet (40b). Each intermediate facet has a second width (52c) in the direction between the first surfaces (26, 26a). For clarity, only one second width (52c) is shown. In a typical implementation, all widths of intermediate facets are equal. However, this implementation is not limited, and the widths of each facet may differ from one another, as shown below. The number of intermediate facets can vary depending on the application. Typical numbers of one or more intermediate facets include 1, 2, 3, 4, 5, and more.

[0071] Each facet in the array of facets (56) is typically a surface that reflects at least partially, is oblique to the surface (26, 26a), has a facet initiation on the proximal side of the facet width, and a facet termination on the distal side of the facet width. A typical facet initiation is shown as point (57a) for the first facet (40a); as point (57m) for the intermediate facet adjacent to the first facet (40a); as point (57n) for the next intermediate facet; and as point (57b) for the last facet (40b). Similarly, a typical facet termination is shown as point (58a) for the first facet (40a); as point (58m) for the intermediate facet adjacent to the first facet (40a); as point (58n) for the next intermediate facet; and as point (58b) for the last facet (40b).

[0072] The alignment of facet overlaps is described here. First, a geometric projection is defined on one of the surfaces (in this case, the lower surface (26)) in the direction of the nominal ray (38B) that is outwardly connected from the substrate (20). The nominal ray (38B) is typically the central ray of light that is substantially outwardly connected from the substrate (20). Usually, the nominal ray (38B) is the ray that the designer wants to perform optimally in the ray field. The nominal ray (38B) may also be the optimal ray for a particular location on the substrate (20). In certain particularly preferred embodiments, the nominal ray is designed to be perpendicular to the parallel plane of light that guides the optical element, but depending on various design considerations, the nominal ray may be inclined in one or two dimensions relative to perpendicularity to such parallel plane. Note that if the nominal ray (38B) is not perpendicular to the parallel plane (e.g., (26)) of the substrate (20), the nominal ray (38B) is at a certain angle to the surface, and when the nominal ray (38B) is connected to the substrate (20), it refracts and is at a different angle to the substrate (20). In the context of this document, references are usually made to nominal rays (38B) inside the substrate (20). Typically, the nominal ray corresponds to a ray from or near the center of the incident image. In some implementations, the nominal ray is the principal ray of the incident image. Typically, the incident light (38) corresponds to the image, and the central ray is the central ray from the center of the image. Additionally or alternatively, the incident light (38) corresponds to the image, and the central ray corresponds to the central pixel of the image.

[0073] Next, the geometric projection of the last facet (40b) and one or more intermediate facets (40c) overlaps with the geometric projection of one or more adjacent intermediate facets (40c) and the first facet (40a). In short, adjacent facets overlap. For example, the last facet (40b) at the distal end overlaps with the adjacent leftmost intermediate facet (in the figure), each intermediate facet (40c) overlaps with an adjacent intermediate facet, and the rightmost intermediate facet at the proximal end overlaps with the first facet (40a).

[0074] In addition, the geometric projections of the facet start of the last facet (57b) and one or more intermediate facets ((57n), (57m), etc.) preferably substantially coincide with the geometric projections of one or more intermediate facets ((58n), (58m), etc.) and the non-adjacent facet end of the first facet (58a). In short, each facet start aligns with, or preferably is close to, the non-adjacent facet end in the direction of the nominal outward connection of the rays (with the first facet (40a) being an obvious exception, as there is no facet end to align with). The coincidence is along at least a portion of the substrate.

[0075] Alternatively, facet overlap can be described as a constant of overlapping facets in the line of sight to the nominal point of observation of light connected externally from the substrate via one of the surfaces. In short, the nominal point is the typical position of the user's eye (47), most likely the position of the pupil of the observer's eye. In some applications, the nominal point is the center of the observer's eyeball. The internal facets are optimized to produce uniform reflection to the observer by having a constant of overlapping facets in the line of sight to the nominal point of observation.

[0076] A feature of this embodiment is the specific management of the overlapping facet configuration. In this case, of the intersections of double facets, the end points of the first facet and all intermediate facets lie on the same line as the center of the adjacent intermediate facet or the last facet. Similarly, the start points of the last facet and all intermediate facets lie on the same line as the center of the adjacent intermediate facet or the last facet. In this case, the following typical facets have the following geometric projection onto the lower surface (26): The end of the facet (F11) at point (P11); The midpoint of facet (F11) at point (P12); The facet start point of facet (F11) at point (P14); The end of the facet (F12) at point (P12); The midpoint of facet (F12) at point (P14); The end of the facet of facet (F13) at point (P14); and The ray (38B) intersects facets (F11) and (F12) at point (P13).

[0077] Therefore, the proximal end of the intermediate facet (F11) overlaps with the distal end of the adjacent intermediate facet (F12), and the facet start of the intermediate facet (F11) aligns with the facet end of the non-adjacent intermediate facet (F13).

[0078] Facets are typically parallel to each other and spaced at regular intervals; that is, the spacing between one pair of adjacent facets in a facet array is the same as the spacing between another pair of adjacent facets in a facet array. For example, the spacing (59a) between facet (F11) and facet (F12) is substantially the same as the spacing (59b) between facet (F12) and facet (F13). The spacing between adjacent facets is typically greater than the coherence length of the light coupled to the substrate. The coherence length is the propagation distance over which a coherent wave (e.g., an electromagnetic wave) maintains a given degree of coherence. Typically, the coherence length is the wavelength, which is squared and divided by the spectral width. If the facet spacing varies along the waveguide, the overlap condition must be preserved.

[0079] In a preferred embodiment, the first width of the initial facet is less than the second width of one or more intermediate facets. In short, the initial facet is a partial facet. In a typical implementation, the first width is approximately half the width of the second facet.

[0080] In another option, the third width is less than the second width. In short, the last facet is a partial facet, preferably half the width of the intermediate facets (the third width is approximately half the width of the second). In another option, half of the last facet has reflectivity, which is substantially 100% nominal reflectivity. For example, if the nominal reflectivity is 50% (as in the case of double overlap), then half of the distal end of the waveguide will have 50% reflectivity in the last facet. For example, in Figure 10B, if half of facet (2517) has 100% nominal reflectivity, then ray (2546) will have the same intensity as the rest of the externally coupled light. Similarly, if half of facet (2515) has 100% reflectivity, then ray (2547) will also have the same intensity as the rest of the externally coupled light.

[0081] Light propagation from the first region is propagation such that at least a portion of the light encounters the first facet before encountering one or more intermediate facets.

[0082] Referring here to Figure 16C, there is a schematic diagram of a triple facet (intersection of triple facets, triple overlap). As in other examples, the waveguide (waveguide (20)) contains an overlapping internal facet (40), shown as a double line, between the first surfaces (26, 26A). The solid arrow indicates a nominal ray that intersects the three facets and is then externally connected from the substrate (arrow externally connecting ray (38B)). As in similar figures, the dashed line is used to indicate the alignment of facet (40). In this example, multiple (specifically two) initial subfacets and multiple (two) final subfacets are shown.

[0083] Typically, many facets are intersected by nominal rays externally connected from the waveguide substrate. In the example of double-facet intersection, the number of intersecting facets is 2. Similarly, in the example of triple-facet intersection, the number of intersecting facets is 3. Typically, the number of intersecting facets is constant for the entire array of facets. The construction of waveguides with a constant number of intersecting facets can be carried out in various configurations. For example, as described with respect to Figure 16B, the first width (52a) of the first facet (40a) may be approximately half the second width (52c) of the adjacent intermediate facet (one facet of the intermediate facet (40c)). In another example, 1 / 4 of the first facet and 3 / 4 of the adjacent facet may be used. In another example, referring to Figure 16C, both the first facet (40a) and the first adjacent facet (F14) are portions of the width of the next adjacent facet (F15).

[0084] Based on the current description that a typical 1D waveguide (e.g., 1D waveguide (20)) is used for the implementation of overlapping facets, a person skilled in the art can implement overlapping facets for 2D waveguides (e.g., in 2D waveguide (10)) and other waveguide configurations.

[0085] Return to the references in Figure 14A, Figure 14B, and Figure 13. Typically, in a 2D waveguide, the waveguide includes a first surface (26, 26a, or 12b, 12a) and a second pair of surfaces (14a, 14b). The second surfaces (14a, 14b) are parallel to each other and not parallel to the first surface (12b, 12a). Similar to the width of the facets relative to the first surface, the first facet has a fourth width in the direction between the second surfaces, the last facet has a sixth width in the direction between the second surfaces, and one or more intermediate facets have a fifth width in the direction between the second surfaces. A characteristic feature of a 2D waveguide is that the facets are configured such that when the image is coupled to the waveguide in the first region in the first direction of propagation at a coupling angle inclined with respect to both the first and second surfaces, the image propagates by four folding in-reflections along the waveguide.

[0086] In an alternative embodiment, the second surface is perpendicular to the first surface. In another alternative embodiment, each facet is oblique to the second surface.

[0087] Referring to Figures 17A-D, we can see a rough schematic of an alternative facet configuration. In this diagram, the facets are parallel.

[0088] Referring here to Figure 17A, for comparison, there is a rough schematic of a dual-faceted configuration, as detailed in Figure 16B. As the waveguide projects an image to the user's eye (47), different rays propagate at different angles, thereby generating overlap and underlap that reduce uniformity (introduce non-uniformity), as described above with respect to Figure 10A. The overlapping configuration in Figure 17A (similarly in Figure 16B and Figure 10B) reduces the effect of this non-uniformity compared to the non-overlapping configuration in Figure 10A (similarly in Figure 16A). For many applications, this dual-faceted configuration is sufficient, as the overlap adequately suppresses non-uniformity.

[0089] Referring here to Figure 17B, there is a rough schematic of different facet spacings. A further reduction in non-uniformity from the double-facet configuration of Figure 17A is shown in Figure 17B, where the spacing between one pair of adjacent facets in the facet array is different from the spacing between adjacent pairs of adjacent facets in the facet array. In a preferred embodiment, the change in spacing is monotonic between one pair of adjacent facets and another pair of adjacent facets. For example, spacing (59d) is greater than spacing (59c), and spacing (59e) is greater than spacing (59d). Note that the change in facet spacing can be reduced by the refraction of the output ray (38B) as it bends perpendicularly as it leaves the substrate (not depicted for brevity). In this configuration, different angles of nominal waves are dealt with, and the overlap is constant with respect to the observer (user's eye (47)). In this unspecified example, the nominal output ray will always pass through two facets. Note that in this figure, the nominal ray (38B) at the center of the substrate (20) is at a different angle than the nominal rays at the edges of the substrate (20), such as the proximal and distal ends.

[0090] Referring here to Figure 17C, there is a rough schematic diagram of the decrease in facet spacing from the proximal end to the distal end of the waveguide. Waveguide (20) includes a first spacing in a first portion of waveguide (20) and at least a second spacing in a second portion of waveguide (20). In this non-limiting example, the first portion (61a) includes non-overlapping facets. The second portion (61c) includes double overlapping facets, and another portion (61e) includes triple overlapping facets. Portions (61b) and (61d) are transitional portions, or regions of transition from one distinct overlap to another distinct overlap. In alternative embodiments, the overlap of portions may be non-distinct, continuously changing, or different spacing configurations designed to manage the effective output intensity from the waveguide.

[0091] To maintain a constant reflected intensity along the waveguide, all facets must have a higher reflectivity, starting from the proximal end and increasing towards the distal end. This control of reflected intensity improves the uniformity of the output (intensity uniformity) to the observer. In the current diagram, the reflectivity of all facets can be kept constant, while the spacing between facets varies according to the required reflectivity. The light is introduced into the waveguide from the proximal end (right side of the current diagram) and therefore has the highest intensity at the proximal end. At the proximal end, the spacing between facets is maximum, and the overlap between facets is minimum. As the light propagates along the waveguide (not shown), the power of the light decreases, and the higher overlap of facets compensates for this decrease in power. Therefore, the overall power output is maintained along the waveguide.

[0092] If no discontinuity of overlap is observed, continuity can be maintained along the waveguide at narrow intervals between facets by discontinuous or continuous (non-integer) changes of overlapping integers.

[0093] If the spacing and height of the facets are kept constant across the waveguide, the optimization procedure should consider the effects of facet overlap versus underlap. Overlapping facets result in non-uniformity, more output power, and more mixing. Furthermore, overlap results in intensity changes of 100% to 150% (or 100% ± 20%), while underlap results in intensity changes of 50% to 100% (or 100% ± 33%). In overlap, the change in relative intensity is lower. Therefore, the reflectance of one or more facets varies from the reflectance of another or more facets in the facet array.

[0094] Furthermore, it should be noted that the observer's eye does not respond linearly to changes in intensity, but rather exhibits a logarithmic response. This suggests that underlap has a greater impact on the observer's perception. Therefore, the reduction of underlap should be further considered at the cost of increasing overlap.

[0095] Refer here to Figure 17D, a rough schematic of fluctuating facet widths. A further reduction in non-uniformity from the dual facet configuration of Figure 17A is shown in the current figure, where the width of one facet in the facet array varies proportionally to the width of an adjacent facet in the facet array. In a preferred embodiment, the width change is monotonic between one facet and an adjacent facet for the entire facet array. In the current figure, as the facet array traverses from the proximal end to the distal end, the width narrows from the bottom to the top of the waveguide. An alternative implementation is to reduce the facet width from both sides (from the top and bottom of each facet, towards the center). In the current example, width (59e) is greater than width (59d), and width (59f) is greater than width (59e).

[0096] In both implementations of Figure 17B, where the spacing between facets is varied, and Figure 17D, where the width of the facets is varied, the observer (user's eye 47) will not see any overlap or underlap in the nominal convergence of the rays (output rays (38B)). However, any change in eye position will cause some overlap / underlap, which is suppressed by the dual facet configuration.

[0097] Here, we refer to Figure 18, a rough schematic diagram of applying overlapping facets to a symmetrical structure as described in Figures 6 and 8. In the current diagram, only the upper lateral waveguide is shown, which is similar to the overlapping configuration in Figure 17B. In this symmetrical configuration, the first region (similar to the first region (54) in Figure 16B) is the region to which light (shown as a ray (38)) is connected to the substrate, and in this case, it is the region in the middle of the waveguide. Each of the symmetrical left and right sides of the waveguide has a region to which light is connected to the respective side of the substrate (alternatively called the adjacent first and second regions), and the left and right facets are equal, oppositely sloped sides. This symmetrical structure can also be implemented along with the parallel configuration of facets in Figure 17A and the variable width configuration in Figure 17D.

[0098] Refer again to Figure 10B, where in the overlapping configuration, the (first complete) facet (2517) and the (last complete) facet (2515) do not partially overlap. Clearly, as stated above, the beginning of facet (2517) does not overlap with facet (2535), and the end of facet (2515) does not overlap with facet (2535). Therefore, the intensity of the out-connected light ((2546) and (2547)) is not very strong in these non-overlapping portions. For example, in a double overlapping configuration, half of the first complete facet is non-overlapping, and half of its power will be out-connected from the non-overlapping portion.

[0099] Several techniques can be used to overcome the problem of lower intensity in non-overlapping start and end sections.

[0100] 1. Use shorter facets at the beginning and end, as described above with respect to Figure 14B, elements (40a) and (40b), and Figure 16B.

[0101] 2. Coat the non-overlapping portions with a high-reflectivity coating that increases the reflectivity of the non-overlapping portions in proportion to the nominal reflectivity of the other (intermediate) facets.

[0102] 3. Gradually change the characteristic reflectivity of the facets from the non-overlapping portion to the overlapping portion, as shown below.

[0103] Here, the technique for gradually changing characteristic reflectivity is described using a double overlapping configuration for simplicity, but this technique can be applied to more advanced overlapping configurations.

[0104] Here, we refer to Figure 19A, a graph of all nominal reflectances in a double overlapping configuration. The x-axis shows the facets starting with the facet numbered "1" (one), which is the first facet near the first region 54, in which light is coupled to the waveguide (substrate). The increasingly numbered facets are the facets that follow facet "1" toward the distal end (55) of the waveguide. The y-axis shows the reflectance as a percentage of nominal reflectance. The thin black boxes represent the reflectance of each individual facet (percentage of nominal reflectance), and the thick black lines represent the characteristic reflectance—the effective reflectance received by the out-coupled rays. It is shown that each facet has a certain nominal reflectance, e.g., 50% nominal required reflectance.

[0105] The characteristic reflectance is the sum of the individual reflectances for the portion of the waveguide to which the ray is externally connected. As described above, the characteristic reflectance externally connected from the non-overlapping portion from facet "1" in the current example is 50% (nominal reflectance), as can be shown as ray (2546) (or ray (2547)) in Figure 10B. The characteristic reflectance externally connected from the overlap between facet "1" and facet "2" (overlapping of two adjacent facets) achieves 100% (nominal reflectance). Thus, there is a discontinuity between the beginning and the next portion of the waveguide (50% vs. 100%).

[0106] Here, we refer to Figure 19B, a model graph of the total nominal reflectance in a double overlapping configuration using alternating changes in facet reflectance. In the current figure, facet "1" (the first facet) is designed to approach a state of no overlap (i.e., having approximately 100% nominal reflectance), and facet "2" (the second facet) is designed to have the minimum reflected light. Therefore, when combined, the first and second facets have approximately non-overlapping characteristic reflectances. Similarly, facet "3" (the third facet) has a reflectance that is almost the same as facet "1" but decreased, and facet "4" has a reflectance that is almost the same as facet "2" but increased. In the current figure, facets "7" and "8" have a (nominal) reflectance of 50%, resulting in characteristic reflectances as described in Figure 19A in the double overlapping configuration. The dashed lines represent the reflectance of odd-numbered facets (starting with the non-overlapping coating parameter), while the dashed lines represent the reflectance of even-numbered facets (representing increasing overlapping characteristics). The thick black lines (solid lines) represent the characteristic reflectance of the sum of the reflectances of two adjacent facets (such as those caused by the double overlap and non-overlapping first facets), showing that the first half of the facets does not even have half the reflectance compared to the 50% characteristic reflectance of facet "1" in Figure 19A.

[0107] The configuration in Figure 19A has a discontinuity between the beginning and the next section of the waveguide (50% vs. 100%), while the innovative configuration in Figure 19B reduces this discontinuity. The remaining discontinuity depends on the convergence rate; for example, with respect to convergence, after six facets, the discontinuity will be approximately 10%. Thus, the problem of less intensity in the non-overlapping beginning and ending sections is overcome. The current configuration can be repeated on the opposite side at the distal end of the waveguide. The slope of the reflectance change (dotted and dashed lines) can be modified to change the resulting effect and characteristic reflectance of the facet arrangement. The waveguide can have various combinations of overlapping and non-overlapping characteristic reflectances over the length of the waveguide. For example, facets "4" and "5" in the current figure may be repeated over at least part of the facet arrangement without converging to the configuration of facets "7" and "8".

[0108] Figure 20A illustrates a non-restrictive but preferred process, which may be used to first generate a 1D waveguide (10). For clarity, internal facets are not shown in scale or density in the drawing.

[0109] A set of covered transparent parallel plates are mounted together as a stack (400). The stack is cut diagonally (402) to produce a slice (404). If necessary, a cover transparent plate (405) can be mounted on the top and / or bottom (not shown) of the slice (404). The slice (404) is then cut perpendicular to the edge of the facets if a 1D facet bevel is required (dashed line on (404)) or diagonally if a 2D facet bevel is required to produce a 2D waveguide (406) (dotted line on (404)).

[0110] Figures 20B-20E show a typical procedure for mounting a linked prism. The sliced ​​2D waveguide (406) is shown in Figure 20B with overlapping facets (two reflective facets per line of sight). This is only a non-restrictive example, and non-overlapping facets are also possible.

[0111] As illustrated in Figure 20B, the 2D waveguide (406) (shown opaquely for clarity) is cut along, for example, the dotted line (420A) shown. This cut may be in any orientation, but a perpendicular cut relaxes the strict refractive index matching requirement. If overlapping facets exist to maintain illuminance uniformity (see the cut end in Figure 20C), the cut is preferably performed as seen in Figure 20C. Otherwise, the first facets would reflect without overlap, resulting in reduced illuminance. If necessary, a transparent extension (413) can be added, and a prism (414) can be attached to the waveguide (406) to create the 2D waveguide (416) with the extension and connecting prism (as shown in Figure 20D). If the extension is not necessary, it may be attached directly to the waveguide (406) to create an assembled waveguide (417) (as shown in Figure 20D). The distal end of the waveguide (406) may be left exposed, causing afterglow to be scattered from there, or it may be optionally painted with a light-absorbing material (e.g., black paint) to minimize the deflection of reflections.

[0112] Figures 21A-21D show a typical procedure for creating a waveguide using overlapping facets. In Figure 21A, the sliced ​​2D waveguide (406) will be cut perpendicularly along both sides, for example, i.e., along the dotted line (420A) to become the proximal end of the waveguide and along the dotted line (420B) to become the distal end of the waveguide. This results in waveguide (420) with partial facets (40a) and (40b) at the respective proximal and distal ends. In Figure 21B in this example, waveguides (426) and (424) are attached to the proximal and distal ends of waveguide (420), respectively, and the combination of ((420), (424), and (426)) is polished to produce the smooth outer surface of the combined waveguide (428) in Figure 21C. In this combined waveguide (428), the attached waveguides (426) and (424) do not need to have as precise a refractive index as waveguide (406).

[0113] This manufacturing method can also be applied to waveguides without overlapping facets, eliminating the need for precise refractive index matching.

[0114] In Figure 21D, optionally, the smoothness and optical properties of the external facets of the combined waveguide (428) can be improved by attaching an outer surface (427) with refractive index matching to obtain a waveguide (429).

[0115] Figures 21C and 21D illustrate separate component margins, but note that for light (incoming light, rays (38), etc.), the margins are transmissive, and only the outer surface and the inclined covered inner facets reflect light.

[0116] The current method (Figures 20A-21D) can be applied to 1D waveguides as well as 2D waveguides.

[0117] Various embodiments in this description, such as the spacing, width, and reflectance of the varying facets, have been described individually for clarity. Those skilled in the art will understand that these embodiments can be combined. For example, the spacing of the varying facets could be narrowed while the width of the facets from the proximal to the distal end of the waveguide could be varied.

[0118] It should be noted that the above examples, numbers used, and typical calculations are for the purpose of illustrating this embodiment. Unintentional typographical errors, mathematical inaccuracies, and / or the use of simplified calculations will not impair the usefulness and fundamental interests of the present invention.

[0119] To the extent to which the attached claims have been formulated without multiple dependencies, the present invention is implemented solely to comply with formal requirements in jurisdictions that do not permit such multiple dependencies. It should be noted that all possible combinations of features that may be suggested by the compound dependencies of the claims should be clearly assumed and considered to be part of the present invention.

[0120] The above description is intended to serve as an example only, and it will be understood that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. An optical device, (a) A waveguide having at least a first pair of outer surfaces parallel to each other, (b) A collimated image source optically coupled to the waveguide to introduce the collimated image light into the waveguide so that the collimated image light propagates in the waveguide by internal reflection from the first pair of outer surfaces, wherein the collimated image light includes a nominal ray at the center of the collimated image light, The waveguide further includes an array of facets, Each of the aforementioned facets is (A) A partial reflective surface that partially reflects the collimated image light internally reflected from the first pair of outer surfaces so as to coupled output the collimated image light from the waveguide, (B) at an oblique angle with respect to the first pair of outer surfaces, (C) Located inside the waveguide, The geometric projection of one of the facets onto one of the first pair of outer surfaces in the direction of the nominal ray coupled out from the waveguide overlaps with the geometric projection of each of the adjacent facets, and the overlap is along at least a portion of the waveguide. The waveguide further includes a first region in which the collimated image light is coupled to the waveguide. The waveguide is, (a) further having a second pair of outer surfaces that are parallel to each other and non-parallel to the first pair of outer surfaces, (b) The facet is configured such that when the image is coupled to the waveguide in the first region in the initial direction of propagation at an oblique coupling angle with respect to both the first and second pairs of outer surfaces, the image propagates along the waveguide by four folding internal reflections. Optical devices.

2. (c) The optical device according to claim 1, further comprising a second waveguide, the second waveguide being positioned relative to the waveguide such that the collimated image light coupled out from the waveguide is coupled into the second waveguide.

3. Each of the facets has a front side in the direction of the first region and a rear side opposite to the front side, The optical device according to claim 1, wherein the oblique angle and the combined input of the collimated image light are such that the collimated image light always passes through the facet from the front to the rear.

4. The waveguide is, The first region further includes where light is coupled to the waveguide, The arrangement of the aforementioned facets is (A) The first facet, (I) Located proximal to the first region, (II) A first facet having a first width in a direction between the first pair of outer surfaces, (B) The last facet, (I) Located at the distal end of the arrangement of facets from the first region, (II) The last facet having a third width in a direction between the first pair of outer surfaces, (C) One or more intermediate facets, (I) between the first facet and the last facet, (II) comprising one or more intermediate facets having a second width (52c) in a direction between the first pair of outer surfaces, Each of the aforementioned facets is (i) The width lies within the plane of the facet, (ii) Having a facet initiation portion on the proximal side of the facet width, (iii) Having a facet end portion on the distal side of the facet width, The optical device according to claim 1, wherein the geometric projection of each of the last facet and the one or more intermediate facets overlaps with the geometric projection of each of the adjacent one or more intermediate facets and the first facet.

5. The optical device according to claim 4, wherein the first width of the first facet is less than the second width of the one or more intermediate facets.

6. The optical device according to claim 1, wherein a certain number of the facets are traversed by the nominal ray coupled out from the waveguide, and the certain number of facets is constant for all of the facet arrangement.

7. The optical device according to claim 4, wherein the last facet has a reflectance that is substantially 100% of the nominal reflectance, and the nominal reflectance is the total reflection required at a particular location in the waveguide.

8. The optical device according to claim 4, wherein the third width is substantially half the second width.

9. The optical device according to claim 1, wherein a certain number of facets overlap in a line of sight toward a nominal observation point of light coupled out from the waveguide via one of the first pair of outer surfaces.

10. The optical device according to claim 4, wherein the width of one of the facets in the facet array changes monotonically with respect to the width of one adjacent facet in the facet array.

11. The optical device according to claim 1, wherein the spacing between a pair of adjacent facets in the facet array varies with respect to the spacing between adjacent facets in another pair of adjacent facets in the facet array.

12. The optical device according to claim 4, wherein the propagation of light from the first region is such that at least a portion of the light encounters the first facet before encountering one of the one or more intermediate facets.

13. (a) The first width is substantially equal to the second width, (b) The optical device according to claim 4, wherein the first facet has a first portion corresponding to the geometric projection of the first facet, which does not overlap with the geometric projection of an adjacent intermediate facet.

14. The optical device according to claim 1, wherein each of the facets has a uniform partial reflectance across the facet.

15. The optical device according to claim 1, wherein the second pair of outer surfaces is perpendicular to the first pair of outer surfaces.

16. The optical device according to claim 1, wherein each of the facets forms an oblique angle with respect to the second pair of outer surfaces.

17. The optical device according to claim 4, wherein the geometric projection of the facet start portion of each of the last facet and the one or more intermediate facets coincides with the geometric projection of the non-adjacent facet end portions of the one or more intermediate facets and the first facet.

18. The waveguide is, The optical device according to claim 1, further comprising one or more external sheets, each of which external sheets is attached to one of the first pair of external surfaces, and which external sheets have a refractive index that matches that of the first pair of external surfaces.

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