Patent Description:
The present invention relates to optical aperture multipliers, and in particular, optical aperture multipliers that include a rectangular optical waveguide optically coupled with thin slab-type optical waveguides.

Optical arrangement for near eye display or head up display require large aperture to cover the area where the eye of the observer is located. Optical devices that provide two-dimensional optical aperture expansion (or multiplication) have been described in various publications by Lumus Ltd (Israel). In one particular set of such optical devices, two-dimensional aperture expansion is achieved by way of two optical waveguides. The first optical waveguide has two pairs of parallel faces that form a rectangular cross-section, and the second optical waveguide, in the form of a thin slab, is optically coupled to the first (rectangular) waveguide and has a pair of parallel major external faces. The two waveguides cooperate to expand the aperture of an injected image in two dimensions, where the first waveguide expands the aperture in a first dimension, and the second waveguide expands the aperture in a second dimension and couples the expanded-aperture image out to be viewed by an eye of a viewer.

In order to maintain image quality, there is a strict requirement for parallelism of the faces of the waveguides and perpendicularity between the two pairs of faces of the rectangular waveguide, as deviations from parallelism and/or perpendicularity can degrade image quality. This requirement for parallelism and perpendicularity can impose strict manufacturing requirements, resulting in higher-cost fabrication processes. <CIT> discloses an optical device that includes a lightguide having a first pair of external surfaces parallel to each other, and at least two sets of facets. Each of the sets including a plurality of partially reflecting facets parallel to each other, and between the first pair of external surfaces. In each of the sets of facets, the respective facets are at an oblique angle relative to the first pair of external surfaces, and at a non-parallel angle relative to another of the sets of facets. The optical device is particularly suited for optical aperture expansion.

Some embodiments of the present invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention.

Attention is now directed to the drawings, where like reference numerals or characters indicate corresponding or like components. In the drawings:.

Embodiments of the present invention provide methods / processes of fabrication of optical aperture multipliers that have rectangular waveguides and optical structures that are intermediate work products in such fabrication methods / processes.

The principles and operation of the methods and intermediate work products according to present invention may be better understood with reference to the drawings accompanying the description. The accompanying drawings are provided with an xyz coordinate system that is arbitrarily labeled but which is consistent between the drawings. This xyz coordinate system is used herein to better explain the disclosed embodiments by providing a common reference frame among the drawings.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the examples. Initially, throughout this document, references are made to directions, such as, for example, top and bottom, upper and lower, front and back, and the like. These directional references are exemplary only, and are used only for ease of presentation and refer to the arbitrary orientations as illustrated in the drawings. The final optical devices may be deployed in any required orientation.

By way of introduction, commonly owned <CIT>, which is incorporated by reference in its entirety herein, describes various embodiments of an optical aperture multiplier <NUM>, shown generally in <FIG>. The optical aperture multiplier <NUM> is particularly suitable for use as part of a near eye display or head up display for augmented reality applications. In general terms, the optical aperture multiplier <NUM> (also referred to as an "optical device") includes a first optical waveguide <NUM> having a direction of elongation (illustrated arbitrarily herein as corresponding to the "x-axis"). The first optical waveguide <NUM> is formed from a light-transmitting material and has first and second pairs of parallel faces <NUM>a, <NUM>b, <NUM>a, <NUM>b forming a rectangular cross-section (i.e., the first and second pairs of faces are perpendicular). The first optical waveguide <NUM> also has an additional pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces). In certain embodiments in which the faces <NUM>a, <NUM>b are parallel faces, the faces <NUM>a, <NUM>b may be perpendicular to the first and second pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b. The first optical waveguide <NUM> has a plurality of mutually parallel partially reflective internal surfaces (also referred to as "facets") <NUM> that at least partially traverse the first optical waveguide <NUM> and are inclined obliquely to the direction of elongation of the first optical waveguide <NUM> (i.e., the facets <NUM> are oblique to the faces <NUM>a, <NUM>b).

Throughout this document, the terms "face", "external face", and "external surface" are used interchangeably. As will become apparent, some of such faces are major faces (also referred to as "major external faces" or "major external surfaces").

The optical aperture multiplier <NUM> also includes a second optical waveguide <NUM>, optically coupled with the first optical waveguide <NUM>, having a third pair of parallel faces <NUM>a, <NUM>b. Here too, a plurality of mutually parallel partially reflective internal surfaces ("facets") <NUM> at least partially traverse the second optical waveguide <NUM> and are inclined obliquely to the faces <NUM>a, <NUM>b. The second optical waveguide <NUM> also has two additional pairs of faces <NUM>a, <NUM>a, <NUM>a, <NUM>b, each of which is non-parallel to faces <NUM>a, <NUM>b, and each of which may or may not be a pair of parallel faces. In certain embodiments, the pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, <NUM>a, <NUM>b are mutually perpendicular. In certain embodiments, the facets <NUM> are also inclined obliquely to one or both of the faces <NUM>a, <NUM>b, however, as will be discussed, in other embodiments the facets <NUM> can be parallel to one or both if the faces <NUM>a, <NUM>b and / or perpendicular to one or both of the faces <NUM>a, <NUM>b.

The second optical waveguide <NUM> is also formed from a light-transmitting material (light-transmitting substrate), and preferably from the same material that is used to form the first optical waveguide <NUM> (such that the two optical waveguides <NUM>, <NUM> have the same refractive index), but forms a thin slab-type waveguide, where the distances between the pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b are at least an order of magnitude greater than the distance between the faces <NUM>a, <NUM>b.

The optical coupling between the optical waveguides <NUM>, <NUM> (at the interface between the faces <NUM>b, <NUM>a), and the deployment and configuration of partially reflective surfaces <NUM>, <NUM> are such that, when image light <NUM> (also referred to as "light beam" or "beam") corresponding to a collimated image (generated by an optical image generator, not shown) is coupled (injected) into the first optical waveguide <NUM> with an initial direction of propagation at a coupling angle oblique to both the first and second pairs of parallel faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, the image advances by four-fold internal reflection (images a<NUM>, a<NUM>, a<NUM>, a<NUM>) along the first optical waveguide <NUM>, with a proportion of intensity of the image reflected at the partially reflective surfaces <NUM> so as to be coupled into the second optical waveguide <NUM>, and then propagates through two-fold internal reflection (images b<NUM>, b<NUM>) within the second optical waveguide <NUM>, with a proportion of intensity of the image reflected (deflected) at the partially reflective surfaces <NUM> so as to be directed outwards from one of the parallel faces <NUM>b as a visible image c, seen by the eye <NUM> of a viewer.

The first optical waveguide <NUM> is also referred to as a two-dimensional (2D) waveguide in the sense that it guides the injected image in two dimensions by reflection between two sets of parallel faces (<NUM>a, <NUM>b, <NUM>a, <NUM>b), while the second optical waveguide <NUM> is also referred to as a one-dimensional (1D) waveguide in the sense that it guides the injected image in only one dimension between one pair of parallel faces (<NUM>a, <NUM>b). The second optical waveguide <NUM> is also referred to interchangeably herein as a light-guide optical element (LOE) or 1D LOE.

<CIT> further describes processes of fabrication of the optical aperture multiplier <NUM>. These processes rely on individually manufacturing the two optical waveguides <NUM>, <NUM> and then coupling together the two individual waveguides <NUM>, <NUM> to produce an individual optical aperture multiplier. However, such fabrication processes make large-scale production of the optical aperture multipliers more challenging.

Embodiments of the present invention provide processes which may be used to fabricate the optical aperture multiplier <NUM>. As will become apparent from the following description, the fabrication processes according to embodiments of the present invention enable large-scale production of optical aperture multipliers, that are particularly suitable for use as part of a near eye display or head up display for augmented reality applications, while maintaining perpendicularity and parallelism over large optical surfaces, thereby enabling tighter manufacturing tolerances.

In a first set of embodiments, as will be described with reference to <FIG>, a bonded stack of coated transparent plates is obtained. The coated surfaces of the transparent plates form a plurality of mutually parallel partially reflective internal surfaces (which ultimately form the facets <NUM>). The bonded stack is cut along a cutting plane to form an optical structure having a plurality of external surfaces that includes a coupling surface oblique to the major surfaces of the coated transparent plates (i.e., the coupling surface is oblique to the partially reflective internal surfaces <NUM>). A slice (which itself is an optical structure) having a pair of external parallel faces and a plurality of mutually parallel partially reflective internal surfaces (which ultimately form the facets <NUM>) oblique to the pair of parallel faces is optically coupled with the optical structure at the coupling surface to form a second optical structure. This second optical structure is then sliced along two or more parallel cutting planes that are perpendicular to the coupling surface in order to extract one or more optical aperture multipliers <NUM>.

In a second set of embodiments, as will be described with reference to <FIG>, a bonded stack of LOEs <NUM> is obtained. This bonded stack of LOEs constitutes a first optical structure that has a coupling surface that is oblique to the facets <NUM> of the LOEs <NUM> (and is also perpendicular to the faces <NUM>a, <NUM>b of the LOEs <NUM>). Similar to as in the first set of embodiments, a slice having a pair of external parallel faces and a plurality of mutually parallel partially reflective internal surfaces (which ultimately form the facets <NUM>) oblique to the pair of parallel faces is optically coupled with the optical structure at the coupling surface to form a second optical structure. This second optical structure is then sliced along two or more parallel cutting planes that are perpendicular to the coupling surface in order to extract one or more optical aperture multipliers <NUM>. In this case, the cutting planes are parallel to the faces <NUM>a, <NUM>b of the LOEs <NUM>, and in certain cases may be located approximately at the faces <NUM>a, <NUM>b of the LOEs <NUM>. As will be discussed, in certain embodiments the bonded stack of LOEs <NUM> can include a plurality of transparent spacer plates in which the LOEs <NUM> and the spacer plates alternate along the length of the bonded stack perpendicular to the faces <NUM>a, <NUM>b of the LOEs <NUM>. In such embodiments, the consecutive cutting planes are located in consecutive spacer plates having one LOE sandwiched therebetween.

As will become apparent from the ensuing description, both of these sets of embodiments employ steps that generally include: <NUM>) obtaining a slice having a pair of external parallel faces and a plurality of internal surfaces (which ultimately form the facets <NUM>) oblique to the pair of parallel faces; <NUM>) obtaining a first optical structure that has: i) a plurality of external surfaces that includes a coupling surface, and ii) a coupling surface oblique to the coupling surface; <NUM>) forming a second optical structure by optically coupling the slice with the optical structure such that one of the faces of the pair of parallel faces of the slice is in facing relation with the coupling surface of the first optical structure; and <NUM>) cutting the second optical structure through at least two cutting planes that are perpendicular to the coupling surface.

Turning now to <FIG>, there is illustrated steps of preferred methods (processes) which may be used to fabricate an optical aperture multiplier, such as the optical aperture multiplier <NUM>, according to a first set of embodiments of the present invention.

As illustrated in <FIG>, a slice <NUM> having a plurality of external faces that includes a pair of parallel faces <NUM>a, <NUM>b is obtained. The slice <NUM> also has a plurality of mutually parallel partially reflective internal surfaces (facets) <NUM> that are oblique to the faces <NUM>a, <NUM>b. In addition, the slice <NUM> has another pair of faces <NUM>a, <NUM>b, which in certain embodiments is also a pair of parallel faces that together with the faces <NUM>a, <NUM>b forms a rectangular cross-section. The slice <NUM> may further have an additional pair of faces <NUM>a, <NUM>b which may or may not be parallel faces. In certain embodiments, the three pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, <NUM>a, <NUM>b of the slice <NUM> are mutually orthogonal.

Parenthetically, the slice <NUM> is itself an optical structure, and the term "slice" is used herein as a naming convention as a way of referencing preferred methods in which the optical structure <NUM> can be produced. In general, the slice <NUM> can be obtained in various ways, typically whereby the slice is "sliced-out" from an optical structure formed of stacked plates. In one example method, as illustrated in <FIG>, a plurality of coated transparent plates <NUM> having parallel upper and lower surfaces <NUM>a, <NUM>b are obtained. The coatings of the coated transparent plates are selectively reflective coatings that provide the partial reflectivity of the facets <NUM> (i.e., such that the facets <NUM> are partially reflective). The plates <NUM> are aligned and arranged in a staggered stack, and bonded together to form a bonded stack <NUM>, as illustrated in <FIG>. The bonding is such that for each plate <NUM>, the lower surface <NUM>b of the plate is joined with the upper surface <NUM>a of the adjacent plate. Throughout this document, the term "bonded" or "bonding" should be understood to mean attached or attaching with an optical cement or glue, or any other suitable adhesive.

The bonded stack <NUM> is then cut along at least two parallel cutting planes (indicated by dashed lines <NUM> in <FIG>) that are oblique to the surfaces <NUM>a, <NUM>b to produce one or more slices <NUM>. The cutting planes <NUM> are preferably spaced at predetermined and uniform intervals. As a result of the cutting along the cutting planes <NUM>, each slice <NUM> has a pair of parallel faces <NUM>a, <NUM>b and a plurality of mutually parallel partially reflective internal surfaces (facets) <NUM> oblique to the faces <NUM>a, <NUM>b. It is noted that the cutting planes <NUM> define the oblique angle of the facets <NUM> in the final rectangular waveguide <NUM>. In the illustrated embodiment, the planes <NUM> are perpendicular to the side surfaces of the plates <NUM> (which in the figure is in a plane parallel to xy plane). However, in certain embodiments, the cutting planes <NUM> can have an inclination angle relative to the side surfaces (xy plane), such that the facets <NUM> are also oblique to the parallel faces <NUM>a, <NUM>b. The stack <NUM> may be further cut along one or more pairs of cutting planes (preferably but not necessarily pairs of parallel cutting planes), that are preferably but not necessarily orthogonal to the planes <NUM>, to set one or more of the other pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b of the slice <NUM>.

Another exemplary method for obtaining the slice <NUM> is illustrated in <FIG>. Here, the plates <NUM> are aligned and bonded to form a non-staggered bonded stack <NUM> (i.e., a rectangular or approximately rectangular block), which is then cut along parallel cutting planes <NUM>' (that are oblique to the surfaces <NUM>a, <NUM>b) to extract one or more slices <NUM>. In the illustrated embodiment, the planes <NUM>' are perpendicular to the side surfaces of the plates <NUM> (which in the figure is in a plane parallel to xy plane). However, in certain embodiments, the cutting planes <NUM>' can have an inclination angle relative to the side surfaces (xy plane), such that the facets <NUM> are also oblique to the parallel faces <NUM>a, <NUM>b. Also, similar to as with the stack <NUM>, the stack <NUM> may be further cut along one or more pairs of cutting planes (preferably but not necessarily pairs of parallel cutting planes), that are preferably but not necessarily orthogonal to the planes <NUM>', to set one or more of the other pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b of the slice <NUM>.

Returning now to <FIG>, in certain embodiments a plate <NUM>a can be aligned with, and applied to, the face <NUM>a of the slice <NUM>, as illustrated in <FIG>. Alternatively, or in addition, a plate <NUM>b can be aligned with, and applied to, the face <NUM>b of the slice <NUM>, also as illustrated in <FIG>. The application of the plates <NUM>a, <NUM>b to the faces <NUM>a, <NUM>b constitutes an optical coupling between the plates <NUM>a, <NUM>b and the slice <NUM> at the faces <NUM>a, <NUM>b. In certain embodiments, the optical coupling is effectuated by bonding, whereby the plate <NUM>a is bonded to the slice <NUM> such that the plate is joined with the face <NUM>a, and/or the plate <NUM>b is bonded to the slice <NUM> such that the plate <NUM>b is joined with the face <NUM>b.

The cover plates <NUM>a, <NUM>b can provide both mechanical protection to the slice <NUM>, for example by protecting against chips that may form on the slice <NUM> during polishing of either or both of the faces <NUM>a, <NUM>b. In addition to providing mechanical protection, the cover plates <NUM>a, <NUM>b can serve optical functions by having various materials or coatings applied thereto. In one example, the plate <NUM>a (and/or the plate <NUM>b) includes a reflective coating, which prevents light from the external (real-world) scene from entering the waveguide <NUM>, while also preserving conditions of internal reflection at the face <NUM>a (and/or the face <NUM>b) of the waveguide <NUM>. In another example, the optical cement used to bond together the plate <NUM>a (and/or the plate <NUM>b) and the slice <NUM> has a low refractive index (lower than the refractive index of the material from which the slice <NUM> is constructed, i.e., lower than the refractive index of the plates <NUM>) in order to maintain conditions of total internal reflection at the face <NUM>a (and/or the face <NUM>b) of the waveguide <NUM> in spite of accumulation of dirt, debris, or other particulates at the interface between the plate <NUM>a, <NUM>b and the slice <NUM>. Optical cement having, for example, a refractive index of approximately <NUM> can be particularly suitable for bonding the plates <NUM>a, <NUM>b to the slice <NUM>.

In certain embodiments, one of the plates <NUM>a or <NUM>b can have polarization managing properties (i.e., the plate <NUM>b can be a polarization managing plate) to control or modify the polarization of the light that is to be transmitted into the waveguide <NUM> from the waveguide <NUM>. The polarization management plate can be implemented, for example, as a waveplate (such as a halfwave plate) and / or a polarizer.

It is noted that instead of optically coupling plates <NUM>a, <NUM>b that have the aforementioned materials or coatings, the materials or coatings can be applied directly to the either or both of the faces <NUM>a, <NUM>b. For example, a reflective coating can be applied directly to either or both of the faces <NUM>a, <NUM>b to prevent unwanted reflections and preserve conditions of internal reflection at the face <NUM>a and/or face <NUM>b.

Referring now to <FIG>, a plurality of coated transparent plates <NUM> having parallel upper and lower major surfaces <NUM>a, <NUM>b are obtained. The coatings of the coated transparent plates are selectively reflective coatings that provide the partial reflectivity of the facets <NUM> (i.e., such that the facets <NUM> are partially reflective) of the optical waveguide <NUM>.

The plates <NUM> are aligned and arranged in a stack (preferably a non-staggered stack), and bonded together to form a bonded stack <NUM> of parallel plates <NUM>, as illustrated in <FIG>. The bonding is such that for each plate <NUM>, the lower surface <NUM>b of the plate is joined with the upper surface <NUM>a of the adjacent plate. The bonded stack <NUM> has three pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, <NUM>a, <NUM>b, each of which may or may not be a pair of parallel faces. The faces <NUM>a, <NUM>b are preferably parallel faces, and thus are preferably parallel to the surfaces <NUM>a, <NUM>b of the plates <NUM>. In addition, the surface <NUM>a of the top plate in the bonded stack <NUM> forms the face <NUM>a, and the surface <NUM>b of the bottom plate in the bonded stack <NUM> forms the face <NUM>b.

In certain embodiments, the pairs of faces <NUM>a, <NUM>b and <NUM>a, <NUM>b are both pairs of parallel faces and together form a rectangular cross-section. In certain embodiments, each of the pairs of faces of the bonded stack <NUM> is a pair of parallel faces, and the three pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, <NUM>a, <NUM>b are mutually orthogonal. It is noted that in general, if any pair of faces of the bonded stack <NUM> is not initially a pair of parallel faces, either or both of the faces of that pair can be polished to achieve parallelism between the faces of the pair.

It is noted that the exemplary stack <NUM> in the non-limiting embodiment illustrated in <FIG> is a non-staggered stack, whereby the various side surfaces of the plates <NUM> (i.e., the surfaces of the plates <NUM> other than the upper and lower surfaces <NUM>a, <NUM>b) are aligned and coplanar to form generally flat and smooth faces <NUM>a, <NUM>b, <NUM>a, <NUM>b. For example, the frontside surfaces of the plates <NUM> that are in planes that are parallel to the yz plane are aligned to form the face <NUM>a, and the backside surfaces of the plates <NUM> (not shown) that are in planes that are parallel to the yz plane are aligned to form the face <NUM>b, whereby each of the faces <NUM>a, <NUM>b is a generally flat and smooth surface. Similar principles apply to the side surfaces that form the faces <NUM>a, <NUM>b. However, in certain embodiments, for example in embodiments in which the stack <NUM> is formed as a staggered stack, one or more of the faces <NUM>a, <NUM>b, <NUM>a, <NUM>b can include steps or variations in depth (i.e., set down or step up) of the side surfaces of the constituent plates <NUM> that form the stack <NUM>. Therefore, the term "face", as used herein to describe and claim faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, generally refers to the apparent face that is in a plane that is parallel to the surfaces of the plates <NUM> that form that face. For example, the face <NUM>a refers to the apparent face that is in a plane that is parallel to the yz plane, despite variations in depth of the frontside surfaces of the plates <NUM>. In embodiments in which the stack <NUM> is a non-staggered stack and the plates <NUM> are perfectly aligned (for example as illustrated in <FIG>), the apparent faces and the actual faces are one in the same.

Turning now to <FIG>, an optical structure <NUM> (<FIG>) is produced from the bonded stack <NUM>. The optical structure <NUM> has a plurality of external surfaces (faces) that includes a planar coupling surface <NUM> (also referred to as a "coupling face", "interfacing surface", "interface surface", or simply "face" <NUM>) that is oblique to the major surfaces <NUM>a, <NUM>b of the coated transparent plates <NUM> (i.e., the coupling surface <NUM> will be oblique to the internal facets <NUM> formed from the coated transparent plates <NUM>). The face <NUM>a of the second waveguide <NUM> is ultimately formed from the coupling surface <NUM>, and thus a portion of the coupling surface <NUM> forms part of the interface plane between the two waveguides <NUM>, <NUM>.

The external faces of the optical structure <NUM> also includes a major face <NUM>a (formed from the face <NUM>a of the bonded stack <NUM>, as will be discussed below) that adjoins the coupling surface <NUM> at an angle. In certain embodiments, such as the embodiment illustrated in <FIG>, the adjoining angle between the coupling surface <NUM> and the face <NUM>a is <NUM>° (i.e., the coupling surface <NUM> is perpendicular to the face <NUM>a). In other embodiments, the adjoining angle between the coupling surface <NUM> and the face <NUM>a is an oblique angle, preferably an acute angle. Such oblique angle embodiments are particularly suitable for producing a final optical device (optical aperture multiplier product) in which the facets <NUM> of the second optical waveguide <NUM> have a tilt angle relative to the first optical waveguide <NUM> (i.e., tilted relative to faces <NUM>a, <NUM>b). The selection of the particular oblique (and preferably acute) angle may be based on the optical design specification of the final optical aperture multiplier product.

In certain embodiments, the bonded stack <NUM> (whether non-staggered or staggered) is cut along a cutting plane <NUM> (<FIG>) to produce the optical structure <NUM>. In other embodiments, the optical structure <NUM> can be produced by grinding or polishing the bonded stack <NUM> to gradually remove the material in the portion <NUM> of the bonded stack <NUM> until reaching the cutting plane <NUM>.

The cutting plane <NUM> is preferably oblique to the face <NUM>a (and thus oblique to the upper and lower surfaces <NUM>a, <NUM>b of the plates <NUM> that form the stack <NUM> / optical structure <NUM>), and is at an angle relative to the face <NUM>a, such that the cutting plane <NUM> passes through portions of the faces <NUM>a, <NUM>b and such that the resulting coupling surface <NUM> is also oblique to the face <NUM>a and at an angle relative to the face <NUM>a. As discussed above, the angle of the cutting plane <NUM> relative to the face <NUM>a can, in certain embodiments, be <NUM>° (i.e., the cutting plane <NUM> can be perpendicular to the face <NUM>a), and in other embodiments can be an oblique (preferably acute) angle.

In general, any deviation from the desired angle between the cutting plane <NUM> and the face <NUM>a, or any deviation from the desired angle between the resulting coupling surface <NUM> and the face <NUM>a, can be corrected by further polishing or slicing/cutting the optical structure <NUM> at the coupling surface <NUM> (i.e., at the location of the cutting plane <NUM>). To avoid wastage, the location of the cutting plane <NUM> in the optical structure <NUM> is preferably selected such that the length of the coupling surface <NUM> (length being measured in the "z" direction in <FIG>) corresponds to length of the slice <NUM> (also measured in the "z" direction in <FIG>).

The portion <NUM> of the bonded stack <NUM> that is removed (either by cutting at the cutting plane <NUM> or grinding or polishing to the cutting plane <NUM>) can, in certain embodiments, generally be a triangular prism portion that includes the following faces: i) a first portion <NUM>a of the face <NUM>a (that can be a minority portion of the face <NUM>a), ii) two approximately triangular portions of the faces <NUM>a, <NUM>b, and iii) a portion (which may be a rectangular portion) <NUM> of the face <NUM>b. In embodiments in which the plane <NUM> is perpendicular to the face <NUM>a, the first portion 231a is a rectangular portion. In embodiments in which the plane <NUM> is oblique to the face <NUM>a, the first portion <NUM>a is a non-parallelogram (and a "trapezoid" in American English). Note that the principles used to define the term "face" in the context of the faces <NUM>a, <NUM>b, <NUM>a, <NUM>b also apply here in the context of the faces <NUM>a, <NUM>b, <NUM>a, <NUM>b.

As a result, in certain embodiments the optical structure <NUM> (formed by removal of the portion <NUM>) can have the following faces: i) a pair of preferably parallel faces <NUM>a, <NUM>b in which the face <NUM>a is a second portion of the face <NUM>a (which is the remaining portion of the face <NUM>a after removal of the first portion <NUM>a) and in which the face <NUM>b is the same as the face <NUM>b, ii) a pair of preferably (but not necessarily) parallel trapezoidal or general quadrilateral shaped faces <NUM>a, <NUM>b that are may be perpendicular to the faces <NUM>a, <NUM>b and that are formed by removal of the triangular portions of the faces <NUM>a, <NUM>b, iii) a face <NUM>a that is the same as the face <NUM>a, and that may be perpendicular to the faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, iv) a face <NUM>b, that may be parallel to the face <NUM>a, and that is the remaining portion of the face <NUM>b after removal of the portion <NUM>, and v) the interfacing face <NUM> that is oblique to the face <NUM>a (i.e., the remaining portion of the face <NUM>a after removal of the portion <NUM>) and is perpendicular (as in <FIG>) or oblique (preferably acute) to the face <NUM>a (i.e., the remaining portion of the face <NUM>a after removal of the portion <NUM>).

In embodiments in which the plane <NUM> is perpendicular to the face <NUM>a, the second portion <NUM>a is a rectangular portion. In embodiments in which the plane <NUM> is oblique to the face <NUM>a, the second portion <NUM>a is a non-parallelogram (and a "trapezoid" in American English).

Note that the plane <NUM> provides (defines) the boundary between the portion <NUM>a and the face <NUM>a, and also provides the boundary between the portion <NUM> and the face <NUM>b.

Again, any deviation from the desired angle between the coupling surface <NUM> and the face <NUM>a can be corrected by polishing the optical structure <NUM> at the location of the cutting plane <NUM>. In fact, since the coupling surface <NUM> ultimately forms part of the interface plane between the two waveguides <NUM>, <NUM>, it is preferable to polish the coupling surface <NUM> even in instances where there are no such angular deviations (or situations in which any such angular deviations are so minor that they do not require correction) in order to ensure that the coupling surface <NUM> is of high optical quality. In embodiments in which the optical structure <NUM> is produced by polishing the bonded stack <NUM> to gradually remove the material in the portion <NUM> of the bonded stack <NUM>, no further polishing step may be necessary.

Turning now to <FIG>, the slice <NUM> is optically coupled with the optical structure <NUM> to form an optical structure <NUM> (which is an intermediate work product of an optical aperture multiplier fabrication process), whereby the faces <NUM>a, <NUM>b are parallel to the coupling surface <NUM> and whereby one of the faces <NUM>a or <NUM>b is brought into facing relation with the coupling surface <NUM>. As an intermediate work product, the optical structure <NUM> includes the slice <NUM> and the optical structure <NUM> as respective first (or second) and second (or first) portions. In embodiments in which the slice <NUM> does not include any cover plate at the coupling face of the slice <NUM> (i.e., face <NUM>a or <NUM>b), the optical coupling is such that one of the faces <NUM>a or <NUM>b is attached to the coupling surface <NUM>.

In the illustrated embodiment, the face <NUM>b is shown as being in facing relation with the coupling surface <NUM>, but the face <NUM>a can alternatively be brought into facing relation with the coupling surface <NUM>. The selection of which of the faces <NUM>a, <NUM>b is to be brought into facing relation with the coupling surface <NUM> can be based on the optical design specification of the final optical aperture multiplier product, including, for example, the deployment location of the optical image generator relative to the waveguide <NUM>. The optical coupling can be effectuated by adhesive bonding such that the face <NUM>b (or <NUM>a) and the coupling surface <NUM> are joined together. Alternatively, the optical coupling can be a mechanical coupling with an air gap of a designed thickness between the face <NUM>b (or <NUM>a) and the coupling surface <NUM>. In embodiments in which the coupling face (<NUM>b or <NUM>a) of the slice <NUM> has a cover plate , the optical coupling between the slice <NUM> and the optical structure <NUM> is such that the cover plate <NUM>b (or <NUM>a) is optically attached to the coupling surface <NUM>, which can be effectuated by bonding the cover plate <NUM>b (or <NUM>a) with the coupling surface <NUM> such that the cover plate <NUM>b (or <NUM>a) and the coupling surface <NUM> are joined together, or via mechanical coupling with an air gap between the cover plate <NUM>b (or <NUM>a) and the coupling surface <NUM>.

The optical structure <NUM> is then cut along at least two parallel cutting planes (indicated by dashed lines <NUM> in <FIG>) that are perpendicular to the coupling surface <NUM> and that pass through the slice <NUM> and the optical structure <NUM> to produce one or more optical aperture multipliers. A single such optical aperture multiplier is shown in <FIG>. It is noted that the waveguide <NUM> has a cover plate <NUM>a at the face <NUM>a, which is produced as a result of cutting the cover plate <NUM>a at the cutting planes <NUM>.

Although only a single optical aperture multiplier is shown as being sliced-out from the optical structure <NUM> in <FIG>, a plurality of optical aperture multipliers can be sliced-out of the optical structure <NUM> by increasing the size and/or number of plates <NUM> used to form the bonded stack <NUM>.

Note that in order to maintain consistent thickness (measured arbitrarily herein along the "z-axis) between the multiple optical aperture multipliers that are sliced out from the optical structure <NUM>, it is preferable that the cutting planes <NUM> be spaced apart at predetermined and uniform intervals.

The perpendicularity between the cutting planes <NUM> and the coupling surface <NUM> simultaneously achieves: i) parallelism between the faces <NUM>a, <NUM>b of the first optical waveguide <NUM>, ii) perpendicularity between first and second pairs of parallel faces <NUM>a, <NUM>b, <NUM>a, <NUM>b (thereby achieving formation of the rectangular cross-section by the faces <NUM>a, <NUM>b, <NUM>a, <NUM>b), and iii) parallelism between the faces <NUM>a, <NUM>b of the second optical waveguide <NUM>.

For increased (optimal) performance, it is also preferable that the cutting planes <NUM> are perpendicular to the face <NUM>a (and hence perpendicular to the face <NUM>a). In certain embodiments, the cutting planes <NUM> can be parallel to the faces <NUM>a, <NUM>b, while in other embodiments the cutting planes <NUM> can be oblique to the faces <NUM>a, <NUM>b.

In certain embodiments, the planes of the internal facets <NUM> of the slice <NUM> are perpendicular to the cutting planes <NUM>. It is noted that in embodiments in which perpendicularity between the facets <NUM> and the cutting planes <NUM> is desired, the slice <NUM> and the optical structure <NUM> should be aligned with high-degree accuracy to ensure minimal deviation from perpendicularity (for example within <NUM> arcseconds).

In other embodiments, the planes of the internal facets <NUM> of the slice <NUM> are oblique to the cutting planes <NUM>. In such embodiments, it is preferable that the angle between the facets <NUM> and the cutting planes <NUM> is far from perpendicular, for example at least <NUM>° and more preferably at least <NUM>° from perpendicular.

In order to achieve the desired angle between the facets <NUM> and the cutting planes <NUM>, the slice <NUM> is aligned with the optical structure <NUM> prior to slicing out the optical aperture multiplier(s). Preferably, the slice <NUM> is aligned with the optical structure <NUM> prior to the step of optically coupling the slice <NUM> with the optical structure <NUM>.

The aligning of the slice <NUM> with the optical structure <NUM> can be performed in various ways. In one example, alignment is performed by maintaining the optical structure <NUM> in a fixed position and orientation and maintaining parallelism between the face <NUM>b or cover plate <NUM>b (or face <NUM>a or cover plate <NUM>a) and the coupling surface <NUM>, and rotating the slice <NUM> (with the face <NUM>b (or <NUM>a) or cover plate <NUM>b (or <NUM>a) on the coupling surface <NUM>) relative to the optical structure <NUM> until the desired angle between the facets <NUM> and the cutting planes <NUM> is achieved (for example <NUM>° within <NUM> arc seconds if perpendicularity is desired, or for example <NUM>° or less if an oblique angle between the facets <NUM> and the cutting planes <NUM> is desired). In another example, the slice <NUM> is maintained in a fixed position and orientation, and the optical structure <NUM> is rotated relative to the slice <NUM> while the face <NUM>b or cover plate <NUM>b (or face <NUM>a or cover plate <NUM>a) is on and parallel to the coupling surface <NUM> until the desired angle between the facets <NUM> and the cutting planes <NUM> is achieved. In yet another example, neither the slice <NUM> nor the optical structure <NUM> are maintained in fixed positions, and the slice <NUM> and the optical structure <NUM> are relatively rotated in opposite directions while the face <NUM>b or cover plate <NUM>b (or face <NUM>a or cover plate <NUM>a) is on and parallel to the coupling surface <NUM> until the desired angle between the facets <NUM> and the cutting planes <NUM> is achieved.

Parenthetically, it is noted that the oblique angle of the coupling surface <NUM> (and thus the oblique angle of the cutting plane <NUM> that forms the coupling surface <NUM>) relative to the upper and lower surfaces <NUM>a, <NUM>b of the plates <NUM> that form the stack <NUM> / optical structure <NUM> defines, in part, the oblique angle of the facets <NUM> of the second optical waveguide <NUM> of the final optical aperture multiplier product. This is primarily due to the interdependency of the orientations of the coupling surface <NUM> and the cutting planes <NUM> (i.e., the cutting planes <NUM> are perpendicular to the coupling surface <NUM>). For example, as the angle between the plane <NUM> / coupling surface <NUM> and the surfaces <NUM>a, <NUM> becomes shallower (i.e., as the coupling surface <NUM> becomes closer to parallel to the face <NUM>b), the cutting planes <NUM> will produce facets <NUM> having a shallower inclination angle relative to the faces <NUM>a, <NUM>b of the second optical waveguide <NUM>. Similarly, as the angle between the plane <NUM> / coupling surface <NUM> and the surfaces <NUM>a, <NUM> becomes steeper (i.e., as the coupling surface <NUM> becomes closer to parallel to the faces <NUM>a, <NUM>b), the cutting planes <NUM> will produce facets <NUM> having a steeper inclination angle relative to the faces <NUM>a, <NUM>b of the second optical waveguide <NUM>.

Referring again to the optical aperture multiplier illustrated in <FIG>, it is noted that the faces <NUM>a, <NUM>a of the optical aperture multiplier form a single continuous external face that is formed as a result of cutting the optical structure <NUM> along one of the cutting planes <NUM>. Similarly, the faces <NUM>b, <NUM>b of the optical aperture multiplier form a single continuous external face that is formed as a result of cutting the optical structure <NUM> along another one of the cutting planes <NUM>. These two continuous faces should be parallel (since parallelism of the faces <NUM>a, <NUM>b and the faces <NUM>a, <NUM>b is critical in order to preserve conditions of internal reflection of light through both of the optical waveguides <NUM>, <NUM>). Parallelism of these two continuous faces can be preserved by ensuring that the cutting planes <NUM> are parallel planes. However, deviation from parallelism of the continuous faces due to deviation from parallelism of the cutting planes <NUM> can be corrected by polishing the continuous faces after cutting the optical structure <NUM> along the cutting planes <NUM>. In addition, preservation of parallelism of the two continuous surfaces also preserves perpendicularity between the two continuous surfaces and the faces <NUM>a, <NUM>b, which ensures perpendicularity between the two pairs of parallel faces <NUM>a, <NUM>b, <NUM>a, <NUM>b (and the formation of the rectangular cross-section) of the first optical waveguide <NUM>. This preservation of parallelism and perpendicularity is critical in order to preserve image uniformity as image light advances along the first optical waveguide <NUM> by four-fold internal reflection.

Although not illustrated in <FIG>, either or both of the faces <NUM>a, <NUM>b can optionally have a transparent cover plate bonded thereto or otherwise optically coupled therewith. Such transparent cover plates can be used to advantage to avoid double reflections within the LOE <NUM>, i.e., situations in which light is reflected twice from the same facet <NUM>. Specifically, the cover plates help to ensure that, after being reflected once by a facet <NUM>, the transmitted portion of the light will propagate over or under that facet, advancing directly to the next facet, thereby resulting in enhanced image uniformity. Examples of optical aperture multipliers having transparent cover plates attached to external faces of the LOE <NUM> are described in commonly owned International Patent Application No. <CIT>.

Turning now to <FIG>, there are illustrated steps of preferred methods (processes) which may be used to fabricate an optical aperture multiplier according to a second set of embodiments of the present invention. In principle, the second set of embodiments are similar to the first set of embodiments in that the second set of embodiments also employ a step of optically coupling the slice <NUM> to an optical structure <NUM> to form a new optical structure from which one or more optical aperture multipliers can be extracted via slicing along two or more cutting planes. However, as mentioned above and as will become further apparent from the discussion below, the primary differences between the two sets of embodiments are with respect to the optical structures <NUM>, <NUM> with which the slice <NUM> is optically coupled.

Referring now particularly to <FIG>, the optical structure <NUM> is formed as a bonded stack <NUM> of LOEs <NUM>, i.e., a stack of LOEs <NUM> which are bonded together. The resulting optical structure <NUM> (i.e., the bonded stack <NUM>) has a plurality of external surfaces including a pair of parallel surfaces <NUM>a, <NUM>b, and a plurality of mutually parallel partially reflective internal surfaces (facets) <NUM> oblique to the surfaces <NUM>a, <NUM>b.

Each of the LOEs of the bonded stack <NUM> is as described above with reference to <FIG>, i.e., each of the LOEs has a plurality of external faces including a pair of parallel faces <NUM>a, <NUM>b (as well as additional faces <NUM>a, <NUM>b, <NUM>a, <NUM>b) and a plurality of internal facets <NUM> oblique to the external faces <NUM>a, <NUM>b. The internal facets <NUM> of each LOE <NUM> constitute a subset of the facets of the optical structure <NUM>. Although the bonded stack <NUM> is illustrated in <FIG> as being formed from only five individual LOEs <NUM>, a larger number of LOEs can typically be used to form the stack, including, for example, ten or more LOEs, and in certain cases twenty or more LOEs.

Methods for fabricating such individual LOEs <NUM> have been described extensively in various publications by Lumus Ltd. (Israel), including, for example, <CIT>, <CIT>, <CIT>, and <CIT>.

The external surfaces of the optical structure <NUM> / bonded stack <NUM> also includes a planar coupling surface <NUM> (similar to coupling surface <NUM> of the first set of embodiments) to which the slice <NUM> is to be optically coupled. As will be discussed, the coupling surface <NUM> can be formed from the faces <NUM>a of the constituent LOEs that form the bonded stack <NUM>. The external surfaces of the optical structure <NUM> / bonded stack <NUM> may also include a back surface <NUM>a (formed, for example, by aligning the faces <NUM>a of the LOEs so as to be coplanar), a front surface <NUM>b (formed, for example, by aligning the faces <NUM>b of the LOEs so as to be coplanar) opposite the back surface <NUM>a, and a top (or upper) surface <NUM> (formed, for example, by aligning the faces <NUM>b of the LOEs so as to be coplanar) opposite the coupling surface <NUM>. In certain embodiments, the optical structure <NUM> / bonded stack <NUM> is a rectangular cuboid, whereby the surfaces <NUM>a and <NUM>b, and the surfaces <NUM> and <NUM> are each a pair of parallel surfaces, and whereby the three pairs of parallel surfaces <NUM>a, <NUM>b, <NUM>a, <NUM>b, <NUM>, <NUM> are mutually perpendicular.

In certain embodiments, such as the embodiments illustrated in <FIG>, the bonded stack <NUM> of LOEs <NUM> may also include a plurality of transparent spacer plates <NUM>, and the LOEs <NUM> and the spacer plates <NUM> alternate along a length of the bonded stack <NUM> that is perpendicular to the faces <NUM>a, <NUM>b of the constituent LOEs <NUM>. Portions of these transparent spacer plates <NUM> form transparent cover plates bonded to the faces <NUM>a, <NUM>b of the final optical aperture multiplier product. In such embodiments, a given spacer plate <NUM> is bonded with two adjacent LOEs such that the face <NUM>a of a first adjacent LOE is joined to one side of the spacer plate <NUM> and the face <NUM>b of a second adjacent LOE is joined to the opposing side of the spacer plate <NUM>.

In embodiments in which no transparent spacer plates <NUM> are employed, adjacent LOEs are bonded together such that the face <NUM>a of each LOE is joined to the face <NUM>b of the adjacent LOE.

In order to form the bonded stack <NUM>, the LOEs <NUM> are preferably aligned such that all of the faces <NUM>a, <NUM>b of the LOEs are mutually parallel, and such that all of the internal facets <NUM> of the LOEs are mutually parallel (as shown in <FIG>). In addition, the faces <NUM>a of the LOEs <NUM> may be aligned so as to be coplanar, thereby forming the coupling surface <NUM>. In embodiments having spacer plates <NUM>, alignment of the faces <NUM>a may also include alignment of the minor external surfaces of the spacer plates <NUM>. It is noted that if the faces <NUM>a are not aligned so as to be coplanar, the bonded stack <NUM> can be cut and polished along a plane that is perpendicular to the faces <NUM>a, <NUM>b of the LOEs <NUM> to remove extraneous portions of one or more of the LOEs in order to produce the coupling surface <NUM>.

The pair of parallel surfaces <NUM>a, <NUM>b of the optical structure <NUM> are parallel to the faces <NUM>a, <NUM>b of the individual LOEs <NUM>. Furthermore, in embodiments in which spacer plates <NUM> are provided, the surface <NUM>a is formed from the spacer plate <NUM> at one end of the stack <NUM> (the right end in <FIG>), and the surface <NUM>b is formed from the spacer plate <NUM> at the opposite end of the stack <NUM> (the left end in <FIG>). Parenthetically, the two spacer plates <NUM> at the ends of the stack <NUM> may have an increased thickness relative to the spacer plates <NUM> that are at the interior portions of the stack <NUM>. In addition, the spacer plates <NUM> at the interior portions of the stack preferably have a common (i.e., same) thickness.

In embodiments in which no spacer plates <NUM> are provided, the surface <NUM>a is formed from the face <NUM>a of the LOE at one end of the stack <NUM> (the right end in <FIG>), and the surface <NUM>b is formed from the face <NUM>b of the LOE at the opposite end of the stack <NUM> (the left end in <FIG>).

As illustrated in <FIG>, the slice <NUM> is optically coupled with the optical structure <NUM> / bonded stack <NUM> to form an optical structure <NUM> (which is an intermediate work product of an optical aperture multiplier fabrication process), whereby the faces <NUM>a, <NUM>b are parallel to the coupling surface <NUM> and whereby one of the faces <NUM>a or <NUM>b is brought into facing relation with the coupling surface <NUM>. As an intermediate work product, the optical structure <NUM> includes the slice <NUM> and the optical structure <NUM> (bonded stack <NUM>) as respective first (or second) and second (or first) portions. It is noted that by way of illustrative example only, <FIG> show an optical structure <NUM> that is formed as a bonded stack of <NUM> LOEs (as opposed to the five LOE stack illustrated in <FIG>).

Note that although <FIG> shows the slice <NUM> as having a single cover plate (cover plate <NUM>a attached to the face <NUM>a), it should be understood that the face <NUM>b (which is the coupling face of the slice <NUM>) can also have a cover plate <NUM>b bonded therewith.

In embodiments in which the slice <NUM> does not include any cover plate at the coupling face of the slice <NUM> (i.e., face <NUM>a or <NUM>b), the optical coupling between the slice <NUM> and the optical structure <NUM> is such that one of the faces <NUM>a or <NUM>b is attached to the coupling surface <NUM>. In the illustrated embodiment, the face <NUM>a is shown as being in facing relation with the coupling surface <NUM>, but the face <NUM>b can alternatively be brought into facing relation with the coupling surface <NUM>. The optical coupling can be effectuated by adhesive bonding such that the face <NUM>a (or <NUM>b) and the coupling surface <NUM> are joined together. Alternatively, the optical coupling can be a mechanical coupling with an air gap of a designed thickness between the face <NUM>a (or <NUM>b) and the coupling surface <NUM>.

In embodiments in which the coupling face (<NUM>b or <NUM>a) of the slice <NUM> has a cover plate, the optical coupling between the slice <NUM> and the optical structure <NUM> is such that the cover plate <NUM>a (or <NUM>b) is optically attached to the coupling surface <NUM>, which can be effectuated by bonding the cover plate <NUM>a (or <NUM>b) with the coupling surface <NUM> such that the cover plate <NUM>a (or <NUM>b) and the coupling surface <NUM> are joined together, or via mechanical coupling with an air gap between the cover plate <NUM>a (or <NUM>b) and the coupling surface <NUM>.

The optical structure <NUM> is then cut along at least two preferably parallel cutting planes (indicated by dashed lines <NUM> in <FIG>) that are parallel to the faces <NUM>a, <NUM>b of the LOEs <NUM> and are perpendicular to the coupling surface <NUM>, and that pass through the slice <NUM> and the optical structure <NUM>, to produce one or more optical aperture multipliers. A single such optical aperture multiplier <NUM>' is shown in <FIG>. Similar to the optical aperture multiplier <NUM> of <FIG>, the waveguide <NUM> has cover plate 13a at the face <NUM>a, which is produced as a result of cutting the cover plate <NUM>a at the cutting planes <NUM>. Note that in contrast to the optical aperture multiplier <NUM> of <FIG>, the optical aperture multiplier <NUM>' also has cover plates <NUM>a, <NUM>a (formed by cutting through consecutive spacer plates <NUM>) attached to faces <NUM>a, <NUM>b.

Although only a single optical aperture multiplier is shown as being sliced-out from the optical structure <NUM> in <FIG>, a plurality of optical aperture multipliers can be sliced-out of the optical structure <NUM>.

Any deviation from parallelism of the cutting planes <NUM> relative to the faces <NUM>a, <NUM>b can be corrected by polishing the sliced-out optical aperture multiplier at the sight / location of the cuts along the cutting planes <NUM>.

In embodiments in which transparent spacer plates <NUM> are employed, two consecutive cutting planes <NUM> are located in consecutive spacer plates having one of the LOEs <NUM> of the bonded stack <NUM> sandwiched therebetween. Preferably each cutting plane is located at the center of the corresponding spacer plate <NUM> so as to effectively divide the spacer plate <NUM> into two approximately equal portions. It is noted that in situations in which it is desirable to have transparent cover plates bonded to the faces <NUM>a, <NUM>b of the waveguide <NUM>, fabrication of the optical aperture multiplier according to the second set of embodiments may be preferable to fabrication according to the first set of embodiments. This is due to the fact that fabrication of the optical aperture multiplier according to the second set of embodiments results in the cover plates (designated <NUM>a and <NUM>b in <FIG>) being flush with the side surfaces <NUM>a, <NUM>b of the waveguide <NUM>, thereby providing a sleek configuration in which the cover plates do not protrude beyond the surfaces 14a, 14b (which can occur when applying cover plates to waveguide <NUM> fabricated according to the first set of embodiments).

In embodiments in which no transparent spacer plates <NUM> are employed, it is preferable that consecutive cutting planes <NUM> are located between the faces 22a, 22b of consecutive LOEs <NUM> of the bonded stack <NUM>, and more preferably at the bonding regions formed between the faces 22a, 22b of consecutive LOEs <NUM>, such that each sliced-out optical aperture multiplier has only one of the LOEs <NUM> of the bonded stack <NUM>. For example, a first of the cutting planes preferably passes between the bonding region between the face <NUM>b of a first one of the LOEs <NUM> and the face <NUM>a of a second one of the LOEs <NUM> that is adjacent to, and bonded with, the first one of the LOEs <NUM>. A second of the cutting planes that is adjacent to the first of the cutting planes passes between the bonding region between the face <NUM>b of the second one of the LOEs <NUM> and the face <NUM>a of a third one of the LOEs <NUM> that is adjacent to, and bonded with, the second one of the LOEs <NUM>. It is noted herein that the bonding regions (formed between the faces 22a, 22b of consecutive LOEs <NUM>) can provide guides for placement of the cutting planes <NUM>.

Prior to formation of the optical structure <NUM> (with or without spacer plates <NUM>), the slice <NUM> and the optical structure <NUM> are preferably properly aligned in order to achieve increased optical performance in a vein similar to as described above with reference to <FIG>. For example, the slice <NUM> and the optical structure <NUM> are preferably aligned such that the surface <NUM>a and one of the faces <NUM>a or <NUM>b are parallel (and preferably coplanar), and such that the surface <NUM>b and the other of the faces <NUM>b or <NUM>a are parallel (and preferably coplanar). It may also be preferable to align the slice <NUM> and the optical structure <NUM> such that the surface <NUM>a and one of the faces <NUM>a or <NUM>b are parallel (and preferably coplanar), and such that the surface <NUM>b and the other of the faces <NUM>b or <NUM>a are parallel (and preferably coplanar). Such preferred alignment is illustrated in <FIG>.

Alignment may be achieved by rotating the slice <NUM> relative to the optical structure <NUM>, similar to as describe above when discussing alignment of the slice <NUM> and the optical structure <NUM>. It is also noted that the alignment and optical coupling between the slice <NUM> and the optical structure <NUM> necessarily results in the facets <NUM> being non-parallel to the facets <NUM>.

Note that in the embodiments described herein, the slice <NUM> has an initial direction of elongation (illustrated arbitrarily herein as corresponding to the "z-axis") which is perpendicular to the direction of elongation of the waveguide <NUM>, and which is also generally perpendicular to the cutting planes <NUM>, <NUM>. This direction of elongation of the slice <NUM> enables multiple optical aperture multipliers to be extracted from the optical structure (<NUM> or <NUM>) whereby the waveguide <NUM> portion of each extracted optical aperture multiplier is extracted from the slice <NUM> portion of the optical structure (<NUM> or <NUM>).

It is noted that one or more additional optical components can be optically coupled or bonded with the optical aperture multiplier product, produced using the methods described herein, at one or more external faces of the waveguides. Examples of such optical components include, for example, optical coupling-in configurations, polarizers, depolarizers, and lenses. Optical coupling-in configurations, in the form of external coupling prisms or external coupling reflector arrangements, are used to introduce / inject collimated image light from an optical image generator into the first optical waveguide <NUM> such that the injected image advances through the first optical waveguide <NUM> by four-fold internal reflection.

By way of one set of examples, any of the coupling prisms described in <CIT>, for example with reference to FIGS. 8A - 14C of that document, can be bonded or otherwise optically coupled with the first optical waveguide <NUM> in order to provide light injection to the first optical waveguide <NUM>. In certain cases, attachment of such a coupling prism may require application of additional coating to parts of the external waveguide faces <NUM>a, <NUM>b, <NUM>a, <NUM>b and/or cutting or otherwise removing a portion of the first optical waveguide <NUM>.

In another set of examples, a coupling prism (which in certain configurations may also include a coupling reflector on one of the faces of the coupling prism) can be deployed in association with a portion of the front or back face <NUM>a, <NUM>b of the first optical waveguide <NUM>, for example as described in commonly owned International Patent Application No. <CIT>. Such deployment may require dividing the face <NUM>a or <NUM>b into a first region (corresponding to a majority portion of the face <NUM>a or <NUM>b) and a second region (corresponding to the remaining minority of the face <NUM>a or <NUM>b) that have different optical characteristics. The subdivision can be effectuated by a coating or material deployed in association with a majority portion or a minority portion of the face <NUM>a or <NUM>b, which can be accomplished by applying such coating or material to the requisite portions of the face <NUM>a or <NUM>b of the slice <NUM>.

The optical image generator that provides the collimated image to the optical coupling-in configuration is typically a micro projector optical device, that includes at least one light source, typically deployed to illuminate a spatial light modulator, such as a liquid crystal on silicon (LCoS) chip. The spatial light modulator modulates the projected intensity of each pixel of the image, thereby generating an image. Alternatively, the optical image generator may include a scanning arrangement, typically implemented using a fast-scanning mirror, which scans illumination from a laser light source across an image plane of the image generator while the intensity of the beam is varied synchronously with the scanning motion on a pixel-by-pixel basis, thereby projecting a desired intensity for each pixel. In both cases, collimating optics are provided to generate an output projected image which is collimated to infinity. Some or all of the above components of the image generator are typically arranged on surfaces of one or more polarizing beamsplitter cube or other prism arrangement, as is well known in the art.

As mentioned above, it may be desirable to provide one or more additional optical components, in particular optical coupling-in components, to be optically coupled with the optical aperture multiplier. To this end, it may be particularly advantageous to provide an additional optical structure - from which optical coupling-in components can be extracted - that can be optically coupled with the optical structures described above in order to enable mass-production of optical aperture multipliers each having a pair of waveguides and an optical coupling-in configuration attached thereto or otherwise optically coupled therewith. Bearing this in mind, <FIG> illustrate steps of methods (processes) which may be used to fabricate an optical aperture multiplier having waveguides <NUM>, <NUM> and an optical coupling-in configuration bonded to (or otherwise optically coupled with) the waveguide <NUM>, according to embodiments of the present invention. <FIG> illustrates an additional optical structure <NUM> from which multiple optical coupling-in configurations can be extracted, and <FIG> illustrate an optical structure <NUM> formed by the optically coupling of the optical structure <NUM> with the optical structure <NUM> and the extraction of an optical aperture multiplier from the optical structure <NUM>. It is noted that although the examples illustrated in <FIG> are provided within the context of the fabrication process according to the second set of embodiments, similar techniques can also be applied to the fabrication process according to the first set of embodiments.

Turning now to <FIG> in detail, the optical structure <NUM> is formed from a light-transmitting material and has a plurality of external faces including a pair of parallel faces <NUM>a, <NUM>b, and a plurality of mutually parallel internal surfaces <NUM> oblique to the faces 402a, 402b. The external faces of the optical structure <NUM> can also include faces <NUM>a, <NUM>b (which in certain embodiments can be a pair of parallel faces that are perpendicular to faces <NUM>a, <NUM>b) as well as faces <NUM>a, <NUM>b (which in certain embodiments can be a pair of parallel faces, and can also be perpendicular to faces <NUM>a, <NUM>b, <NUM>a, <NUM>b.

In certain embodiments, the internal surfaces <NUM> are reflective surfaces, whereas in other embodiments the internal surfaces <NUM> are partially reflective surfaces (such as beam splitting surfaces). The optical structure <NUM> can be obtained in various ways, including producing the optical structure <NUM> by stacking and bonding together transparent plates (which can be coated with reflective or partially reflective coatings) and then slicing the bonded plates, in a manner similar to that used to produce the slice <NUM>, as described above.

As illustrated in <FIG>, the optical structure <NUM> is optically coupled with the slice <NUM> portion of the optical structure <NUM> such that a coupling face of the optical structure <NUM> (which can be one of the faces <NUM>a, <NUM>b) is brought into facing relation with one of the external faces of the slice <NUM>. The optically coupling between the optical structures <NUM>, <NUM> produces a new optical structure <NUM> that is an intermediate work product having three portions: <NUM>) the bonded stack of LOEs portion (i.e., optical structure <NUM>), <NUM>) the slice <NUM> portion, and <NUM>) the optical structure <NUM> portion.

In the illustrated embodiments, the coupling face of the optical structure <NUM> is the face <NUM>a, which is deployed in facing relation to the face <NUM>b of the slice <NUM>. In certain embodiments, the optical structure <NUM> is bonded with the slice <NUM> such that the coupling face (e.g., face <NUM>a) is joined to the face <NUM>b (or face <NUM>a). Note that the selection of which of the external faces of the slice <NUM> is to be brought into facing relation with the coupling face of the optical structure <NUM> can be based on the optical design specification of the final optical aperture multiplier product, including, for example, the deployment location of the optical image generator relative to the optical coupling-in configuration and the waveguide <NUM>.

Prior to optically coupling the optical structure <NUM> with the slice <NUM>, the optical structure <NUM> and the slice <NUM> are preferably aligned. In the illustrated embodiment, the alignment is preferably such that each internal surface <NUM> corresponds to, and is preferably located between the faces 22a, 22b of, a corresponding one of the LOEs of the bonded stack <NUM>. In certain embodiments, the alignment is such that each internal surface <NUM> extends between the faces <NUM>a, 22b of the corresponding LOE. The alignment is further such that the internal surfaces <NUM> are non-parallel to the facets <NUM> and <NUM>.

In certain embodiments, the alignment of the optical structure <NUM> with the slice <NUM> is also such that the faces <NUM>a and <NUM>a are parallel (and preferably coplanar), and such that the faces <NUM>b and <NUM>b are parallel (and preferably coplanar).

<FIG> shows the optical structure <NUM> with example cutting planes <NUM> (same as illustrated in <FIG>). The optical structure <NUM> is cut along the two or more cutting planes <NUM> to produce (extract / slice-out) one or more optical aperture multipliers. A single such sliced-out optical aperture multiplier <NUM>", having a pair of waveguides (<NUM>, <NUM>) and a coupling-in configuration <NUM> attached thereto, is illustrated in <FIG>. The optical coupling-in configuration <NUM> is produced from the optical structure <NUM> and includes a single internal surface <NUM>.

Note that although the slice <NUM> is illustrated without cover plates <NUM>a, <NUM>b in the embodiments of <FIG>, it should be understood that one or both of the cover plates <NUM>a, 120b can be applied to the respective faces <NUM>a, <NUM>b.

As mentioned above, similar techniques for producing optical aperture multipliers with attached optical coupling-in configurations can be used with the fabrication process according to the first set of embodiments. For example, the optical structure <NUM> can be optically coupled with the optical structure <NUM> of <FIG>, for example at the face <NUM>b, in order to produce an optical aperture multiplier having a pair of waveguides <NUM>, <NUM> and an optical coupling-in configuration <NUM> attached thereto.

It is noted that the optical structure <NUM> illustrated in the drawings is just one non-limiting example of an optical structure from which optical coupling-in configurations can be extracted. In general, any optical structure having a coupling surface (e.g., face <NUM>a) and a plurality of optical coupling-in surfaces (e.g., internal surfaces <NUM>) or elements or surface sections geometrically associated with the coupling surface can be optically coupled with the optical structure <NUM> or <NUM>. An elongated prism is another non-limiting example of an optical structure from which optical coupling-in configurations can be extracted. Such an elongated prism may have a plurality of external surfaces that includes a coupling surface (for optically coupling with the slice <NUM>) and an optical coupling-in surface that can be subdivided into a plurality of non-overlapping sections. Each section can correspond, for example, to a different respective LOE <NUM> of the optical structure <NUM>, such that when sliced along cutting planes <NUM> each section becomes the optical coupling-in surface for the optical aperture multiplier.

The alignment of the various optical structures described herein can be performed using any suitable optical alignment apparatus / device(s) / tool(s) that perform suitable optical alignment techniques / methods. Such suitable optical alignment apparatus / device(s) / tool(s) can include, for example, one or more computerized control device, one or more computerized processing device, one or more optical subsystem having, for example, one or more light source, one or more light detector / sensor (including optical sensors), one or more optical component (e.g., one or more lens, one or more folding optic, one or more prism, etc.), autocollimators, and the like. Details of non-limiting examples of suitable optical alignment apparatus / device(s) / tool(s) / method(s) that can be used for aligning the various optical structures described herein can be found in various publications by Lumus Ltd. (Israel), including, for example, International Patent Application No. <CIT> and International Patent Application No. <CIT>.

The present disclosure has described various cutting steps in which optical structures or materials are cut along cutting planes in order to produce various other optical structures or optical products. It is noted that in certain embodiments, some or all of the surfaces of these optical structures and materials, including and in particular those surfaces that result from these cutting steps, can be polished to, for example, increase optical quality. In certain embodiments, polishing can be performed as part of, or subsequent to, these cutting steps, and prior to subsequent optical coupling (e.g., bonding) steps. In the above-described fabrication methods, the cutting or slicing of the various optical structures described herein can be performed by any suitable cutting apparatus / device / tool, as should be understood by those of ordinary skill in the art. The polishing of the faces and surfaces of the various optical structures described herein can be performed by any suitable polishing apparatus / device / tool, as should be understood by those of ordinary skill in the art.

As used herein, the singular form, "a", "an" and "the" include plural references unless the context clearly dictates otherwise.

Claim 1:
A method of fabricating an optical aperture multiplier (<NUM>, G, <NUM>") comprising:
obtaining a slice (<NUM>) having a plurality of external faces including a pair of parallel faces (112a, 112b), and a first plurality of mutually parallel partially reflective internal surfaces (<NUM>) oblique to the pair of parallel faces (112a, 112b);
obtaining a first optical structure (<NUM>, <NUM>) having a plurality of external surfaces including a planar coupling surface (<NUM>, <NUM>), and a second plurality of mutually parallel partially reflective internal surfaces (203a, <NUM>) oblique to the coupling surface (<NUM>, <NUM>); bonding the slice (<NUM>) with the first optical structure such that one of the faces of the pair of parallel faces (112a, 112b) is brought into facing relation with the coupling surface (<NUM>, <NUM>), thereby forming a second optical structure (<NUM>, <NUM>); and slicing out at least one optical aperture multiplier (<NUM>, G, <NUM>") from the second optical structure (<NUM>, <NUM>) by cutting the second optical structure (<NUM>, <NUM>) through at least two cutting planes (<NUM>, <NUM>) that are perpendicular to the coupling surface (<NUM>, <NUM>);
wherein the first optical structure (<NUM>) is formed as a bonded stack (<NUM>) of light-guide optical elements LOEs (<NUM>), each LOE (<NUM>) of the bonded stack (<NUM>) having a pair of major parallel surfaces (22a, 22b) and a subset of the second plurality of mutually parallel partially reflective internal surfaces (<NUM>) oblique to the pair of major parallel surfaces (22a, 22b);
characterized in that
the bonded stack (<NUM>) includes a plurality of transparent spacer plates (<NUM>), wherein the LOEs (<NUM>) and the transparent spacer plates (<NUM>) alternate along a length of the bonded stack (<NUM>) perpendicular to the major parallel surfaces (22a, 22b) of the LOEs (<NUM>) and wherein the at least two cutting planes (<NUM>) are located in consecutive spacer plates (<NUM>) having one of the LOEs (<NUM>) sandwiched therebetween.