Patent Description:
The present invention relates to light-guide optical elements (LOEs), and in particular, methods for manufacturing compound LOEs for two-dimensional aperture expansion having embedded coupling-in reflectors.

Compound LOEs or "two-dimensional expansion waveguides" have been described in various publications by Lumus Ltd (Israel). One example is <CIT>. In general terms, these compound LOEs employ two regions, each of which is a parallel-faced block of transparent material (i.e., light-transmitting material) for facilitating the propagation of light corresponding to a collimated image by internal reflection at major surfaces, and includes a set of mutually-parallel, internal, partially-reflective surfaces (or "facets"), which redirect the collimated image light while achieving expansion of the optical aperture. By combining two such elements with different facet orientations, it is possible to achieve two-dimensional expansion of the optical aperture within a single compound element, thereby expanding an input image from an image projector and outputting the expanded image over a large area towards the eye of an observer.

Embodiments of the present invention provide methods of fabrication of compound LOEs.

According to the teachings of an embodiment of the present invention, there is provided a method of fabricating a compound light-guide optical element (LOE). The method comprises: obtaining a stack having a first pair of faces and a plurality of LOEs, each of the LOEs having a pair of major parallel surfaces and a first plurality of mutually parallel partially reflective internal surfaces oblique to the pair of major parallel surfaces; obtaining a first optical block having a second pair of faces and a second plurality of mutually parallel partially reflective internal surfaces; bonding together the first optical block and the stack such that one of the faces of the first pair of faces is joined to one of the faces of the second pair of faces and such that the first plurality of partially reflective internal surfaces is non-parallel to the second plurality of partially reflective internal surfaces, thereby forming a second optical block; cutting the second optical block along a cutting plane that passes through the other one of the faces of the second pair of faces, thereby forming a first optical structure having an interfacing surface at the cutting plane; obtaining a third optical block having a third pair of faces and a plurality of mutually parallel reflective internal surfaces; bonding together the third optical block and the first optical structure such that one of the faces of the third pair of faces is joined to the interfacing surface and such that the plurality of reflective internal surfaces is non-parallel to both the first plurality of partially reflective internal surfaces and the second plurality of partially reflective internal surfaces, thereby forming a second optical structure; and slicing out at least one compound LOE from the second optical structure by cutting the second optical structure through at least two cutting planes substantially parallel to the major parallel surfaces of consecutive LOEs.

Optionally, the method further comprises: for each sliced-out compound LOE, polishing external surfaces of the sliced-out compound LOE formed by cutting the optical structure along two consecutive of the cutting planes.

Optionally, the first optical block has a pair of parallel faces, and the second plurality of partially reflective internal surfaces are perpendicular to the pair of parallel faces of the first optical block.

Optionally, the first optical block has a pair of parallel faces, and the second plurality of partially reflective internal surfaces are oblique to the pair of parallel faces of the first optical block.

Optionally, the first optical block has a third plurality of mutually parallel partially reflective internal surfaces non-parallel to the first and second pluralities of partially reflective internal surfaces.

Optionally, the first optical block has a first region that includes the second plurality of partially reflective internal surfaces and a second region that includes the third plurality of partially reflective internal surfaces, the first and second regions of the first optical block are non-overlapping regions.

Optionally, the third plurality of partially reflective internal surfaces are parallel to the major parallel surfaces of the LOEs.

Optionally, each respective one of the third partially reflective internal surfaces is located in a plane that is approximately halfway between the pair of major parallel surfaces of a respective one of the LOEs.

Optionally, the third plurality of partially reflective internal surfaces is located between the first and second pluralities of partially reflective internal surfaces.

Optionally, the second plurality of partially reflective internal surfaces is located between the first and third pluralities of partially reflective internal surfaces.

Optionally, the first optical block is formed by bonding together first and second constituent optical blocks that each have a pair of faces such that one of the faces of the pair of faces of the first constituent optical block is joined to one of the faces of the pair of faces of the second constituent optical block, the first constituent optical block includes the second plurality of partially reflective internal surfaces, and the second constituent optical block includes a third plurality of mutually parallel partially reflective internal surfaces non-parallel to the first plurality of partially reflective internal surfaces and non-parallel to the second plurality of partially reflective internal surfaces.

Optionally, the third optical block and the first optical structure are bonded together such that substantially the entirety of the one of the faces of the third pair of faces is joined to substantially the entirety of the interfacing surface.

Optionally, the third optical block and the first optical structure are bonded together such that the one of the faces of the third pair of faces is joined to a fractional portion of the interfacing surface.

Optionally, the third optical block has an additional pair of faces, the method and the further comprises: obtaining an inert block having first and second pairs of faces; and bonding together the inert block and the third optical block such that one of the faces of the first pair of faces of the inert block is joined to one of the faces of the additional pair of faces of the third optical block, thereby forming a compound block having first and second faces, the first face of the compound block formed from the one of the faces of the third pair of faces and one of the faces of the second pair of faces of the inert block, and the second face of the compound block formed from the other one of the faces of the third pair of faces and the one of the faces of the second pair of faces of the inert block.

Optionally, the method further comprises: obtaining a second inert block having a pair of faces; and bonding together the second inert block and the compound block such that one of the faces of the pair of faces of the second inert block is joined to the second face of the compound block.

Optionally, bonding together the third optical block and the first optical structure includes: bonding together the compound block and the first optical structure such that the first face of the compound block is joined to the interfacing surface.

Optionally, the method further comprises: obtaining an inert block having a pair of faces; and bonding together the inert block and the third optical block such that one of the faces of the pair of faces of the second inert block is joined to the other one of the faces of the third pair of faces of the optical block.

Unless otherwise defined herein, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below.

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:.

The principles and operation of the methods 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.

Referring now to the drawings, <FIG> illustrate various views of a compound LOE <NUM>. The compound LOE <NUM> includes a first LOE <NUM> and a second LOE <NUM> that are bonded together at an interface <NUM>. Typically, the two LOEs <NUM>, <NUM> are manufactured separately and bonded together. 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 first LOE <NUM> is formed from a light-transmitting material and includes a first pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces), a second pair of faces (major external surfaces) <NUM>a, 14b that is a pair of parallel faces, a third pair of faces (major external surfaces) <NUM>a, <NUM>b (that may or may not be parallel faces), and a plurality of mutually parallel partially reflective internal surfaces (also referred to as "facets") <NUM> that at least partially traverse the LOE <NUM> between the faces <NUM>a, <NUM>b. The LOE <NUM> is configured to guide light (image illumination), corresponding to a collimated image injected into the LOE <NUM> by an image projector (not shown), such that the light (represented in <FIG> by light ray <NUM>) is trapped in one dimension by internal reflection (preferably but not exclusively total internal reflection) at the parallel faces <NUM>a, <NUM>b of the LOE <NUM>. The LOE <NUM> is further configured to gradually couple the propagating (trapped) light out of the LOE <NUM> via the facets <NUM>, which are inclined obliquely to the direction of propagation of the light and each reflect a proportion of the intensity of the propagating light, thereby expanding the image illumination in one dimension (which in this case is approximately along the y-axis). In the drawings, the light coupled out of the LOE <NUM> by the facets <NUM> is represented by light rays <NUM> (<FIG>), and the propagation of the collimated image light <NUM> by internal reflection at the faces of the LOE <NUM> is represented by left-going and right-going rays <NUM> (<FIG>).

In general, the facets <NUM> have a first orientation in the compound LOE <NUM>. In certain embodiments, the facets <NUM> are obliquely angled relative to faces <NUM>a, <NUM>b. In other embodiments, the facets <NUM> are orthogonal to the faces <NUM>a, <NUM>b. It is also noted that in certain embodiments the facets <NUM> can be obliquely angled to one or both of the faces <NUM>a, <NUM>b, whereas in other embodiments the facets <NUM> can be orthogonal to one or both of the faces <NUM>a, <NUM>b. In the non-limiting example embodiment illustrated in <FIG>, the faces <NUM>a, <NUM>b are parallel, and the facets <NUM> are inclined obliquely to the faces <NUM>a, <NUM>b.

The reflectivity of the facets <NUM> can be provided via coatings on the internal surfaces prior to forming the LOE <NUM>. The reflectance of each of the facets <NUM> may be the same, or the reflectivity of the facets <NUM> may be different from one another and may increase along a light propagation direction (which in the arbitrarily labeled xyz coordinate system in the drawings is along the y-axis).

The light that is coupled out of the LOE <NUM> is coupled into the second LOE <NUM>. The LOE <NUM> is also formed from a light-transmitting material and includes a first pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces), a second pair of faces (major external surfaces) <NUM>a, <NUM>b that is a pair of parallel faces, a third pair of faces (major external surfaces) <NUM>a, <NUM>b (that may or may not be parallel faces), and a plurality of mutually parallel partially reflective internal surfaces ("facets") <NUM> that are inclined obliquely relative to faces <NUM>a, <NUM>b. The faces <NUM>a, <NUM>a are generally coincident (coplanar) so as to form a first singular external face of the compound LOE <NUM>. Likewise, the faces <NUM>b, <NUM>b are generally coincident (coplanar) so as to form a second singular external face of the compound LOE <NUM>. The faces <NUM>a, <NUM>a are also preferably generally coincident (coplanar) so as to form a third singular external face of the compound LOE <NUM>, and the faces <NUM>b, <NUM>b are also preferably generally coincident (coplanar) so as to form a fourth singular external face of the compound LOE <NUM>. The remaining two external surfaces of the compound LOE <NUM> are respectively formed from the faces <NUM>a and <NUM>b.

The facets <NUM> have a second orientation in the compound LOE <NUM> that is non-parallel to the first orientation of the facets <NUM>. The reflectivity of the facets <NUM> can be provided via coatings on the internal surfaces prior to forming the LOE <NUM>. The reflectance of each of the facets <NUM> may be the same, or the reflectivity of the facets <NUM> may be different from one another and may increase along a light propagation direction (which in the arbitrarily labeled xyz coordinate system in the drawings is along the x-axis).

The light from LOE <NUM> is coupled into the LOE <NUM> through interface <NUM> (which is coincident with the face <NUM>b and the face <NUM>a). The LOE <NUM> is configured to guide the light by internal reflection (preferably but not exclusively total internal reflection) at the faces <NUM>a, <NUM>b, and to gradually couple the propagating light out of the LOE <NUM> via the facets <NUM>, which each reflect a proportion of the intensity of the propagating light, toward the eye of an observer, thereby expanding the image illumination in a second dimension (which in this case is along the x-axis). In <FIG>, the propagation of image light through the LOE <NUM> by internal reflection at faces <NUM>a, <NUM>b is represented by sets of rays <NUM>, <NUM>. One of the rays <NUM>, <NUM> represents the image and the other of the rays <NUM>, <NUM> represents the image conjugate corresponding to the light <NUM> that coupled into the LOE <NUM> from the LOE <NUM>. The light coupled out of the LOE <NUM> by the facets <NUM> is represented in <FIG> by light rays <NUM>.

The image illumination that is to be coupled into the compound LOE <NUM> for guiding by the LOE <NUM> and the LOE <NUM> is generated by an external image projector (not shown), which is typically implemented as a micro-projector arrangement formed from a microdisplay device (such as an LCoS chip) that generates image illumination, and collimating optics for collimating the image illumination to produce collimated image illumination. The collimated image illumination is coupled into the LOE <NUM> by a coupling-in optical arrangement, in the form of a highly reflective internal surface <NUM> in a coupling-in region of the LOE <NUM>.

In order to fill the LOE <NUM> with the collimated image illumination (whereby both the image and its conjugate propagate through the LOE by internal reflection) while maintaining a small input aperture (small projector), it is preferable to employ at least one additional partially reflective internal surface having a particular orientation relative to the facets <NUM>, <NUM> and the faces of the compound LOE. <FIG> illustrate a compound LOE having such an additional facet <NUM>. The facet <NUM> can be deployed in part of the LOE <NUM>, or as shown in <FIG> as part of a separate light-transmitting substrate <NUM> having three pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, <NUM>a, <NUM>b (where the pair of faces <NUM>a, <NUM>b is a pair of parallel faces). The facet <NUM> is parallel to the faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, and thus has an orientation that is non-parallel to the orientations of the facets <NUM>, <NUM>. When using only a single facet <NUM>, the facet <NUM> is preferably located halfway between faces <NUM>a, <NUM>b (and equivalently halfway between faces <NUM>a, <NUM>b). If using more than one facet <NUM>, the facets <NUM> are preferably evenly spaced between faces <NUM>a, <NUM>b. In the embodiment illustrated in <FIG>, the LOE <NUM> and the substrate <NUM> are bonded together at faces <NUM>b, <NUM>a, and the substrate <NUM> and the LOE <NUM> are bonded together at faces <NUM>a, <NUM>b, such that the facet <NUM> is located between the sets of facets <NUM>, <NUM>. It is noted however that other deployments are also possible, for example in which the facets <NUM> are located between the facet <NUM> and the set of facets <NUM>, depending on the design specification of the specific application for the compound LOE.

In the illustrated embodiment, the light <NUM> (coupled-out by facets <NUM>) is partially reflected by the facet <NUM>. The reflected and transmitted parts of light <NUM> are coupled into the LOE <NUM>, and correspond to rays <NUM> and <NUM>, respectively.

Further details of compound LOEs, including compound LOEs that may be similar to the compound LOEs illustrated in <FIG>, can be found in various publications by Lumus Ltd. (Israel), including, for example, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

Embodiments of the present invention are directed to methods of fabricating compound LOEs. The compound LOEs that are fabricated according to the methods of the present invention may be different in structure from the compound LOEs illustrated in <FIG>, but have similar components, as will become apparent from the ensuing description. The fabrication method steps are described in detail below with reference to <FIG>, and generally include steps of obtaining an optical block <NUM> (<FIG>) having sets of the requisite facets <NUM>, <NUM> (and preferably also a set of facets <NUM>) embedded in regions of the optical block <NUM> and appropriately oriented relative to each other such that the facets <NUM>, <NUM> (and <NUM>) are mutually non-parallel, cutting a portion of the optical block <NUM> at a prescribed cutting plane (<FIG> and <FIG>) that is at a prescribed angle and passes through particular faces of the optical block <NUM> to form an optical structure <NUM>' having an interfacing surface (<FIG> and <FIG>) formed at the cutting plane, obtaining an additional optical block <NUM> (<FIG>) having a set of reflective internal surfaces <NUM> embedded therein, and bonding the optical block <NUM> to the optical structure <NUM>' at the interface surface to form an intermediate optical structure <NUM> (<FIG> and <FIG>) having embedded therein sets of the requisite facets <NUM>, <NUM> (and preferably also a set of facets <NUM>) and a set of the reflective internal surfaces <NUM> that is non-parallel to the facets <NUM>, <NUM>, <NUM>. The intermediate optical structure <NUM> is then cut along two or more cutting planes in order to slice-out one or more compound LOEs (<FIG>), where each compound LOE has facets <NUM> and facets <NUM> (and preferably also at least one facet <NUM>) and an embedded reflective internal surface <NUM>. Each of the sliced-out compound LOEs can then be polished to achieve a final compound LOE having a desired thickness (<FIG>). In certain embodiments, one or more blocks <NUM>, <NUM> of inert material are bonded to the optical block <NUM> to form a compound block <NUM> (<FIG>), which is then bonded to the optical structure <NUM>' (<FIG> and <FIG>) to form the intermediate optical structure <NUM>. As will be discussed, obtaining the optical block <NUM> can include producing the optical block <NUM> by obtaining various other optical blocks <NUM>, <NUM>, <NUM> (<FIG>) and bonding those optical blocks <NUM>, <NUM>, <NUM> together to form the optical block <NUM>. Each of the optical blocks <NUM>, <NUM>, <NUM> has one of the requisite sets of facets <NUM>, <NUM>, <NUM> embedded therein, and can be produced from sets of bonded coated plates that are cut at appropriate angles and thickness.

It is noted that in the drawings, and in accordance with one set of non-limiting embodiments of the present invention, each of the various blocks <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is represented as a rectangular cuboid, i.e., a structure having three pairs of parallel faces that are mutually perpendicular (orthogonal). However, such representation of the blocks as rectangular cuboids is for clarity of presentation only, and parallelism and perpendicularity among all of the faces of the individual blocks is not a strict requirement from an optical standpoint or a manufacturing standpoint. In many embodiments, only one pair of faces of a block need be a pair of parallel faces, and the remaining faces may or may not be parallel. In other embodiments, none of the faces of a block need be a pair of parallel faces.

The following paragraphs describe the structure and production of the optical block <NUM> with reference to <FIG>. Referring first to <FIG>, there is shown the optical block <NUM>, which is formed as a stack of LOEs <NUM> that are bonded together. The optical block <NUM> has at least two pairs of faces (major external surfaces), namely a pair of preferably parallel faces <NUM>a, <NUM>b, and a pair of faces <NUM>a, <NUM>b that is a pair of parallel faces and may be orthogonal (perpendicular) to either or both the faces <NUM>a, <NUM>b. The optical block <NUM> also includes a third pair of faces that may or may not be a pair of parallel faces, and may also be perpendicular to one or more of the faces <NUM>a, <NUM>b, <NUM>a, <NUM>b. The third pair of faces are not shown in <FIG>, but are shown in various other drawings, including <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>. As will become apparent, the faces <NUM>a and <NUM>b can respectively form part of upper and lower face of the optical structure <NUM> (FIGS. 11C and 11D) from which a compound LOE can be sliced-out.

Each of the LOEs <NUM> in the stack of <FIG> is an LOE as illustrated in <FIG>. This LOE <NUM> is also generally similar to the second LOE <NUM> discussed above with reference to <FIG>. As shown in <FIG>, and as discussed above with reference to <FIG>, each LOE <NUM> is formed from a light-transmitting material having parallel faces <NUM>a, <NUM>b and a set (plurality) of internal facets <NUM> inclined obliquely to the faces <NUM>a, <NUM>b. Such an LOE can be used as a standalone LOE (together with appropriate coupling-in optics) in situations in which aperture expansion in only one-dimension is desired. This type of LOE is commonly referred to as a "one-dimensional" LOE, and the structure and methods of manufacturing such one-dimensional LOEs have been described extensively in various publications by Lumus Ltd. (Israel), including, for example, <CIT>, <CIT>, <CIT>, and <CIT>.

<FIG> shows one example method of fabricating a plurality of LOEs <NUM>, which can be used to produce the optical block <NUM>. In <FIG>, a plurality of light-transmitting plates is coated to form coated plates <NUM> which are stacked and bonded together, and then cut along equally spaced parallel cutting planes <NUM> (which in the arbitrarily labeled xyz coordinate system are parallel to the xy plane). Each of the plates <NUM> has a pair of parallel faces (surfaces) <NUM>a, <NUM>b which are appropriately coated with coatings that provide the reflectivity of the facets <NUM> (such that the facets <NUM> are partially reflective). The cutting planes <NUM> are oblique to the faces <NUM>a, <NUM>b and define the oblique angle of the facets <NUM>, and the resulting cuts along the cutting planes <NUM> define the faces <NUM>a, <NUM>b of the LOEs <NUM>. The cutting planes <NUM> are spaced at predetermined intervals. Preferably the predetermined intervals are uniform intervals such that the cutting planes <NUM> are uniformly spaced. The uniform spacing is preferably in the range of <NUM> - <NUM> millimeters, such that the thickness of each LOE <NUM> (measured between faces <NUM>a, <NUM>b) is approximately <NUM> - <NUM> millimeters.

Prior to bonding together the LOEs <NUM> to form the optical block <NUM>, the LOEs <NUM> are first aligned and arranged in a formation <NUM> (<FIG>). The LOEs <NUM> in the formation <NUM> are then bonded together to form the optical block <NUM> (<FIG>) as a bonded stack of LOEs <NUM>, such that the faces <NUM>a and <NUM>b of adjacent (consecutive) LOEs <NUM> are joined together at bonding regions, and such that the sets of internal facets <NUM> of the LOEs <NUM> constitute a plurality of facets <NUM> of the optical block <NUM>. As can be seen from <FIG> and <FIG>, the major surface <NUM>a of the LOE <NUM> at the top end of the stack <NUM> forms the top face <NUM>a of the stack <NUM>, and the major surface <NUM>b of the LOE <NUM> at the bottom end of the stack <NUM> forms the bottom face <NUM>b of the stack <NUM>.

The following paragraphs describe the structure and production of the optical block <NUM> with reference to <FIG>. Referring first to <FIG>, the optical block <NUM> is formed from a light-transmitting material and has an embedded set of the facets <NUM>. The optical block <NUM> includes three pairs of faces (major external surfaces), namely a pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces), a pair of preferably parallel faces <NUM>a, <NUM>b, and a pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces). In certain embodiments, the pairs of faces of the optical block <NUM> are mutually orthogonal (perpendicular), which can simplify the fabrication process.

The optical block <NUM> can be formed from a plurality of bonded, transparent coated plates <NUM> (each plate being formed from a light-transmitting material and coated with a partially reflective coating) to form facets <NUM> that are angled relative to the faces <NUM>a, <NUM> at a predetermined angle, i.e., the facets <NUM> may be inclined obliquely relative to the faces <NUM>a, <NUM>b or may be orthogonal to the faces <NUM>a, <NUM>b. The facets <NUM> may also be inclined obliquely to the faces <NUM>a, <NUM>b at a predetermined angle. Various known methods exist for forming the optical block <NUM>. <FIG> illustrates one such method, in which the coated plates <NUM> are stacked and bonded together (similar to as in <FIG>), and then cut along a first pair of preferably parallel cutting planes <NUM> and along a second pair of preferably parallel cutting planes <NUM> that are preferably perpendicular to the planes <NUM>, in order to extract the optical block <NUM>. In embodiments in which the facets <NUM> are oblique to one or both of the faces <NUM>a, <NUM>b, the angle of the cutting planes <NUM> relative to the faces of the coated plates <NUM> determines the angle at which the facets <NUM> are inclined relative to faces <NUM>a, <NUM>b. In addition, the cuts along the cutting planes <NUM> define the faces <NUM>a, <NUM>b of the optical block <NUM>, and the cuts along cutting planes <NUM> define the faces <NUM>a, <NUM>b of the optical block <NUM>.

In certain embodiments, such as the embodiment illustrated in <FIG>, the cutting planes <NUM>, <NUM> are perpendicular to the thickness dimension of the plates <NUM> such that the resultant facets <NUM> are perpendicular to the faces <NUM>a, <NUM>b of the optical block <NUM>. In the arbitrarily labeled xyz coordinate system used in the drawings, when the cutting planes <NUM>, <NUM> are perpendicular to the thickness dimension of the plates <NUM>, the cutting planes <NUM> are parallel to the yz plane and the cutting planes <NUM> are parallel to the xz plane. The cutting planes <NUM> are perpendicular to the planes <NUM>.

As noted above, other embodiments are possible in which the facets <NUM> are inclined obliquely to the faces <NUM>a, <NUM>b, and as such the cutting planes <NUM> may be inclined at an appropriate oblique angle relative to the xz plane to produce the appropriate facet angle relative to the faces <NUM>a, <NUM>b.

The following paragraphs describe the structure and production of the optical block <NUM> with reference to <FIG>. Referring first to <FIG>, the optical block <NUM> is formed from a light-transmitting material and has an embedded set of the facets <NUM>. The optical block <NUM> includes three pairs of faces (major external surfaces), namely a pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces), a pair of preferably parallel faces <NUM>a, <NUM>b, and a pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces). In certain non-limiting embodiments, the pairs of faces of the optical block <NUM> are mutually orthogonal (perpendicular).

The optical block <NUM> can be formed from a plurality of bonded, transparent coated plates <NUM> (each plate being a formed from a light-transmitting material and coated with a partially reflective coating) to form facets <NUM> that are parallel to faces <NUM>a, <NUM>b and optionally perpendicular to one or both faces <NUM>a, <NUM>b. Various known methods exist for forming the optical block <NUM>. <FIG> illustrates one such method, in which the coated plates <NUM> are stacked and bonded (similar to as in <FIG> and <FIG>), and then cut along a pair of cutting planes <NUM> in order to extract the optical block <NUM>. In certain embodiments, such as the embodiment illustrated in <FIG>, the planes <NUM> are parallel planes (which in the arbitrarily labeled xyz coordinate system are parallel to the yz plane). However, as alluded to above, parallelism between the planes <NUM> is not a strict requirement, and in certain cases it may be advantageous to cut along non-parallel cutting planes, which can improve compactness and overall form factor of the final compound LOE product. In certain embodiments, the planes <NUM> are perpendicular to the major external surfaces (faces) of the plates <NUM>. However, this perpendicularity is also not an optical requirement for producing the final compound LOE product, but is rather a matter of practical convenience when fabricating the compound LOE. The stacked and bonded plates may also be cut along an additional pair of cutting planes <NUM> that pass through two of the plates, and may be parallel to the major external surfaces of the plates <NUM> and perpendicular to planes <NUM>. In the arbitrarily labeled xyz coordinate system used in the drawings, the cutting planes <NUM> are parallel to the xy plane.

With continued reference to <FIG>, refer now to <FIG> which show the three optical blocks <NUM>, <NUM>, <NUM> prior to being bonded together to form the optical block <NUM> (<FIG>). Prior to bonding, it is important that the optical blocks <NUM>, <NUM>, <NUM> are appropriately aligned such that the orientation of the facets <NUM> is non-parallel to the orientation of the facets <NUM>, and such that the orientation of the facets <NUM> is non-parallel to the orientations of the facets <NUM>, <NUM>. In other words, the blocks <NUM>, <NUM>, <NUM> are aligned such that the facets <NUM>, <NUM>, <NUM> are mutually non-parallel.

It also preferable that the optical block <NUM> is aligned with the optical block <NUM> such that the facets <NUM> of optical block <NUM> are in planes that are parallel to the planes of faces <NUM>a, <NUM>b of the optical block <NUM>. In embodiments in which each compound LOE is to have only a single facet <NUM>, the optical blocks <NUM> and <NUM> are preferably aligned such that each respective facet <NUM> is located in a plane that is approximately halfway between the major external surfaces <NUM>a, <NUM>b of a respective one of the LOEs <NUM> that forms the optical block <NUM>. In embodiments in which each compound LOE is to have multiple facets <NUM> (say N facets <NUM>), the optical blocks <NUM> and <NUM> are preferably aligned such for each set of N facets <NUM>, the N facets <NUM> are evenly spaced between the major external surfaces <NUM>a, <NUM>b of a respective one of the LOEs <NUM> that forms the optical block <NUM>. It is noted, however, that the block <NUM> can be positioned relative to the block <NUM> without applying too much scrutiny with respect to the positioning of the facets <NUM> relative to the major external surfaces <NUM>a, <NUM>b, and that any mispositioning of the facets <NUM> relative to the major external surfaces <NUM>a, <NUM>b in a sliced-out compound LOE can be corrected (typically by polishing or grinding) at the final stages of fabrication if there are enough spare regions in the sliced-out compound LOE.

With reference to the coordinate system shown in <FIG>, the alignment of the optical blocks <NUM>, <NUM>, <NUM> (when each such optical block is constructed as a rectangular cuboid) can be understood as follows: each of the faces <NUM>a, <NUM>a, <NUM>a is in a plane parallel to the yz plane, each of the faces <NUM>b, <NUM>b, <NUM>b is in a plane parallel to the yz plane, each of the faces <NUM>a, <NUM>a, <NUM>a is in a plane parallel to the xy plane, each of the faces <NUM>b, <NUM>b, <NUM>b is in a plane parallel to the xy plane, each of the faces <NUM>a, <NUM>a, <NUM>a is in a plane parallel to the xz plane, and each of the faces <NUM>b, <NUM>b, <NUM>b is in a plane parallel to the xz plane. The alignment of the optical blocks <NUM>, <NUM>, <NUM> is also such that each of the facets <NUM> is in a plane that is parallel to the xy plane.

In order to reduce wastage, the optical blocks <NUM>, <NUM>, <NUM> are preferably designed to have the same or very close to the same dimensions i.e., length, width, and thickness. In the arbitrarily labeled xyz coordinate system in the drawings, the length is measured along the y-axis, i.e., measured between faces <NUM>a, <NUM>b, faces <NUM>a, <NUM>b, and faces <NUM>a, <NUM>b. In the arbitrarily labeled xyz coordinate system in the drawings, the width is measured along the x-axis, i.e., measured between faces <NUM>a, <NUM>b, faces <NUM>a, <NUM>b, and faces <NUM>a, <NUM>b. In the arbitrarily labeled xyz coordinate system in the drawings, the thickness is measured along the z-axis, i.e., measured between faces <NUM>a, <NUM>b, faces <NUM>a, <NUM>b, and faces <NUM>a, <NUM>b.

Employing optical blocks <NUM>, <NUM>, <NUM> having the same thickness (or very close to the same thickness) is critical to minimizing wastage from the final cutting step to slice-out compound LOEs. Therefore, in particularly preferred embodiments, the alignment of the optical blocks <NUM>, <NUM>, <NUM> is such that the faces <NUM>a, <NUM>a, <NUM>a are coplanar (i.e., lie in a common plane), the faces <NUM>b, <NUM>b, <NUM>b are coplanar, the faces <NUM>a, <NUM>a, <NUM>a are coplanar, the faces <NUM>b, <NUM>b, 312b are coplanar, the faces <NUM>a, <NUM>a, <NUM>a are coplanar, and the faces <NUM>b, <NUM>b, <NUM>b are coplanar.

Once properly aligned, the optical blocks <NUM>, <NUM>, <NUM> are bonded together as illustrated in <FIG> to form the optical block <NUM> (which is a compound optical block composed of multiple sub-blocks), while maintaining the alignment described with reference to <FIG>. In the illustrated embodiment, the optical block <NUM> is a rectangular cuboid and has three regions, namely one region having the optical block (stack) <NUM> which carries the bonded LOEs <NUM> with facets <NUM>, another region having the optical block <NUM> which carries the facets <NUM>, and another region having the optical block <NUM> which carries the facets <NUM>. In the illustrated embodiment, the three regions are non-overlapping, and the three optical blocks <NUM>, <NUM>, <NUM> have the same thickness. In such embodiments, the faces <NUM>a, <NUM>b form a first pair of parallel faces <NUM>a, <NUM>b of the optical block <NUM>, the face <NUM>a (formed from coplanar faces <NUM>a, <NUM>a, <NUM>a) and the face <NUM>b (formed from coplanar faces <NUM>b, <NUM>b, <NUM>b) form a second pair of parallel faces of the optical block <NUM>, and the face <NUM>a (formed from coplanar faces <NUM>a, <NUM>a, <NUM>a) and the face <NUM>b (formed from coplanar faces <NUM>b, <NUM>b, <NUM>b) form a third pair of parallel faces of the optical block <NUM>. It is noted that in embodiments in which the block <NUM> is not a rectangular cuboid, neither one of the three pairs of faces <NUM>a, <NUM>b, <NUM>a, <NUM>b, <NUM>a, <NUM>b necessarily needs to be a pair of parallel faces.

As can be seen from <FIG>, <FIG>, <FIG> and 7D, the major surface 24a of the LOE <NUM> at the top end of the stack <NUM> forms part of the top face <NUM>a of the optical block <NUM>, and the major surface 24b of the LOE <NUM> at the bottom end of the stack <NUM> forms part of the bottom face <NUM>b of the optical block <NUM>.

In certain embodiments, the optical blocks <NUM>, <NUM>, <NUM> can be bonded together in stages. For example, the optical blocks <NUM>, <NUM> can be bonded together, and then the optical blocks <NUM>, <NUM> can be bonded together. Alternatively, the optical blocks <NUM>, <NUM> can be bonded together, and then the optical blocks <NUM>, <NUM> can be bonded together. The optical blocks <NUM>, <NUM> are bonded together such that the face <NUM>b is joined to the face <NUM>a. The optical blocks <NUM>, <NUM> are bonded together such that the face <NUM>b is joined to the face <NUM>a. As a result of the bonding (and proper aligning) of the optical blocks <NUM>, <NUM>, <NUM>, the facets <NUM> are non-parallel to the facets <NUM>.

In certain embodiments, such as the embodiments illustrated in the drawings, the optical blocks <NUM>, <NUM>, <NUM> are arranged such that the optical block <NUM> is positioned between the optical block <NUM>, <NUM>, resulting in the facets <NUM> being located between the facets <NUM>, <NUM>. However, other embodiments are possible in which the order of the optical blocks is different from that shown in the drawings, for example in which the optical block <NUM> is positioned between the optical block <NUM>, <NUM>, resulting in the facets <NUM> being located between the facets <NUM>, <NUM>. In such embodiments, the face <NUM>a of the optical block <NUM> forms the face <NUM>a of the optical block <NUM>.

The embodiments described thus far have pertained to employing three optical blocks to form compound optical block <NUM>. However, in certain embodiments the optical block <NUM> can be omitted or replaced with one or more optical blocks carrying facets at different orientations from the facets <NUM>. Therefore, the optical block <NUM> can generally be considered as being formed from two optical sub-blocks and having two regions, where the optical block <NUM> with facets <NUM> forms a first of the sub-blocks (a first region), and the optical block <NUM> with facets <NUM> forms a second of the sub-blocks (a second region). In the embodiments illustrated in the drawings, the second sub-block includes two sub-sub-blocks (two sub-regions), where the facets <NUM> are located in the first sub-sub-block (first sub-region), which in this case is optical block <NUM>, and the facets <NUM> are located in the second sub-sub-block (second sub-region), which in this case is optical block <NUM>.

In embodiments in which optical block <NUM> is omitted, the optical blocks <NUM>, <NUM> are bonded together to form the optical block <NUM> such that the face <NUM>b is joined to the face 212a. As a result of the bonding (and proper aligning) of the optical blocks <NUM>, <NUM>, the facets <NUM> are non-parallel to the facets <NUM>.

With continued reference to <FIG>, refer now to <FIG>, which illustrate steps for cutting the optical block <NUM> (<FIG> and <FIG>) and the result of cutting the optical block <NUM> (<FIG> and <FIG>). Generally speaking, and as shown in <FIG> and <FIG>, the optical block <NUM> is cut along a cutting plane <NUM> that passes through the face 412a (which in the illustrated embodiment is face <NUM>a, but may be face 312a in embodiments in which the positions of the optical blocks <NUM>, <NUM> are exchanged) and at least one of the faces <NUM>a, <NUM>a, <NUM>a. In embodiments in which the faces <NUM>a, <NUM>a, <NUM>a are coplanar and form the face 416a, the cutting plane <NUM> passes through the face <NUM>a. The location of the cutting plane <NUM> is such that the cutting plane <NUM> at least passes through a portion of the optical sub-block having the facets <NUM> or facets <NUM>. In the illustrated embodiment, the cutting plane <NUM> passes through a portion of the optical sub-block having the facets <NUM>, which in the illustrated embodiment is the optical block <NUM>. However, in some practical implementations, the cutting plane <NUM> may pass through all three regions of the optical block <NUM> (i.e., pass through regions which in combination contain facets <NUM>, <NUM>, <NUM>).

In certain embodiments, the cutting plane <NUM> is oblique to the face <NUM>a (<NUM>a or <NUM>a), and may also be oblique to one or more of the faces <NUM>a, <NUM>a, <NUM>b, <NUM>b, <NUM>a, <NUM>b, <NUM>a, depending on the construction of the optical block <NUM>. The cutting plane <NUM> is preferably perpendicular to the face 114a (and therefore also perpendicular to faces <NUM>a, <NUM>a in embodiments in which the faces <NUM>a, <NUM>a, <NUM>a are parallel). The cutting of the optical block <NUM> along cutting plane <NUM> results in the formation of an optical structure <NUM>' having an interfacing surface <NUM> (or "face" <NUM>) at the location of the cutting plane <NUM>, as illustrated in <FIG> and <FIG>.

In some of the embodiments in which the optical block <NUM> comprises the three optical blocks <NUM>, <NUM>, <NUM> as illustrated in <FIG>, the location of the cutting plane <NUM> can be restricted such that the cutting plane <NUM> only passes through a portion of the optical block <NUM> and does not pass through any of the other optical blocks <NUM>, <NUM> such that the portion to be cut is exclusively part of the optical block <NUM>. However, in other embodiments, the location of the cutting plane <NUM> may be such that the cutting plane <NUM> passes through a portion of the optical block <NUM> and may also pass through a portion of the optical block <NUM>.

In embodiments in which the faces <NUM>a, <NUM>a, <NUM>a are coplanar and combine to form the face <NUM>a, the portion of the optical block <NUM> that is cut-off (i.e., removed) is a triangular prism (typically a right triangular prism) portion (represented in <FIG> and <FIG> by <NUM>). In embodiments in which the optical block <NUM> is sandwiched between the optical blocks <NUM>, <NUM>, the portion <NUM> includes a portion (typically the entirety) of the face 116a and a portion (which may be a minority portion, for example roughly <NUM>% - <NUM>%) of the face <NUM>a.

In some of the embodiments in which the positions of the optical blocks <NUM>, <NUM> is exchanged such that the optical block <NUM> is sandwiched between the optical blocks <NUM> and <NUM>, the location of the cutting plane can be restricted such that the cutting plane <NUM> only passes through a portion of the optical block <NUM> and does not pass through any of the other optical blocks <NUM>, <NUM>, such that the portion to be cut is exclusively part of the optical block <NUM>. However, similar to as mentioned above, in certain embodiments the cutting plane <NUM> may pass through a portion of the optical block <NUM> and may also pass through a portion of the optical block <NUM>.

<FIG> and <FIG> illustrate the optical structure <NUM>', having the interfacing surface <NUM>, that is formed as result of cutting the optical block <NUM> along the cutting plane <NUM> and removing triangular prims portion <NUM>. The optical block <NUM>, having coupling-in reflectors, is bonded to the optical structure <NUM>' at the interfacing surface <NUM>.

The following paragraphs describe the structure and production of the optical block <NUM> with reference to <FIG>. Referring first to <FIG>, the optical block <NUM> is formed from a light-transmitting material and has a set of reflective internal surfaces <NUM> (highly reflective mirrors), each of which is used as a coupling-in configuration for the final compound LOE. The optical block <NUM> includes three pairs of faces (major external surfaces), namely a pair of preferably parallel faces <NUM>a, <NUM>b, a pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces), and a pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces). In certain embodiments, the three pairs of faces of the optical block <NUM> are mutually orthogonal (perpendicular), however, other embodiments may be preferred in which the pairs of faces are not mutually orthogonal.

The optical block <NUM> can be formed from a plurality of bonded, transparent coated plates <NUM> (each plate being formed from a light-transmitting material and coated with a partially reflective coating) to form reflective internal surfaces <NUM> that are inclined obliquely to either or both of the faces <NUM>a, <NUM>b at a predetermined angle. Various known methods exist for forming the optical block <NUM>. <FIG> illustrates one such method, in which the coated plates <NUM> are stacked and bonded (similar to as in <FIG>, <FIG>, and <FIG>), and then cut along equally spaced parallel cutting planes <NUM> (which in the arbitrarily labeled xyz coordinate system are parallel to the yz plane) to produce sliced-out optical structures <NUM>. One of the optical structures <NUM> is used to form the optical block <NUM>. Unlike the coatings used to produce the facets <NUM>, <NUM>, <NUM>, the coatings used to form coated plates <NUM> are not partially reflective but rather are fully (and preferably highly) reflective, such that the resultant internal surfaces <NUM> act as fully reflective mirrors. Dielectric coatings are one example of suitable coatings that can be used to form the reflective internal surfaces <NUM>. The cutting planes <NUM> are obliquely angled relative to the coated faces the plates <NUM>, where the oblique angle of the planes <NUM> determines the oblique angle at which the internal surfaces <NUM> are inclined relative to faces <NUM>a, <NUM>b.

In certain embodiments, each of the optical structures <NUM> can be cut along two additional parallel planes <NUM>, <NUM> that are perpendicular to planes <NUM> in order to form surfaces <NUM>a, <NUM>b such that the optical block <NUM> has a rectangular cross-section. In the arbitrarily labeled xyz coordinate system, the planes <NUM>, <NUM> are parallel to the xy plane.

With continued reference to <FIG>, attention is also directed to <FIG> and <FIG> which show the optical block <NUM> and the optical structure <NUM>' prior to being bonded together to form optical structure <NUM> (<FIG> and <FIG>). Prior to bonding, it is important that the optical block <NUM> and the optical structure <NUM>' are appropriately aligned such that the orientation of the internal surfaces <NUM> is non-parallel to the orientations of the facets <NUM>, <NUM>, <NUM> (i.e., such that the internal surfaces <NUM> are non-parallel to the facets <NUM>, <NUM>, <NUM>), and such that each internal surface <NUM> is associated with a respective one of the LOEs <NUM> in the optical block <NUM> such that the projection of the internal surface in the thickness dimension of the respective LOE (which in the arbitrarily labeled xyz coordinate system in the drawings is the yz plane) is bounded by the major surfaces <NUM>a, <NUM>b of the LOE <NUM>.

In certain embodiments, it may also be preferable that each of the faces <NUM>a, <NUM>a is in a plane parallel to the xy plane, and that each of the faces <NUM>b, <NUM>b is in a plane parallel to the xy plane.

In order to avoid wastage at the final cutting step for slicing-out the compound LOE, the optical block <NUM> preferably has the same thickness (measured along the z-axis, i.e., between faces <NUM>a, <NUM>b) as the constituent optical blocks <NUM>, <NUM>, <NUM>, and thus the same thickness as the optical structure <NUM>'. In such embodiments, the alignment of the optical block <NUM> with the optical structure <NUM>' is preferably such that the faces <NUM>a, <NUM>a are coplanar, as are the faces <NUM>b, <NUM>b. In such embodiments, the alignment of the optical block <NUM> with the optical structure <NUM>' is also such that the faces <NUM>b, <NUM> are aligned and practically coincident.

Once properly aligned, the optical block <NUM> and the optical structure <NUM>' are bonded together as illustrated in <FIG> and <FIG> to form optical structure <NUM> (which is an intermediate work product of a compound LOE fabrication process). The bonding of the optical block <NUM> and the optical structure <NUM>' is such that the face 512b is joined to the face (interfacing surface) <NUM>, while maintained the alignment described above. Preferably, the faces <NUM>b, <NUM> are equally dimensioned, or very close to equally dimensioned. In certain embodiments, alignment of the optical block <NUM> with the optical structure <NUM>' can also include twisting or rotating the face <NUM>b relative to the interfacing surface <NUM>, such that the internal surfaces <NUM> are tilted at angle relative to the optical structure <NUM>' in addition to being inclined relative to either or both of the faces <NUM>a, <NUM>b. In the drawings, such a tilt angle and inclination angle correspond to the internal surfaces <NUM> being inclined at two angles relative to the xy plane.

As illustrated in <FIG>, after forming the optical structure <NUM>, the optical structure <NUM> is cut (sliced) along two or more preferably parallel cutting planes <NUM> at predetermined intervals in order to extract one or more compound LOEs. The cutting planes <NUM> are preferably parallel to the major external surfaces <NUM>a, <NUM>b of the LOEs <NUM> that form the optical block <NUM>. Most preferably, consecutive cutting planes <NUM> are located between the surfaces <NUM>a, <NUM>b of consecutive LOEs <NUM>, in particular the bonding regions formed between the surfaces <NUM>a, <NUM>b of consecutive LOEs <NUM>. For example, a first <NUM>-<NUM> of the cutting planes <NUM> passes between the bonding region between the second surface <NUM>b-<NUM> of a first one <NUM>-<NUM> of the LOEs <NUM> and the first surface <NUM>a-<NUM> of a second one <NUM>-<NUM> of the LOEs <NUM> that is adjacent to the first LOE <NUM>-<NUM> and bonded to the first LOE <NUM>-<NUM>, and a second <NUM>-<NUM> of the cutting planes <NUM> that is adjacent to the first cutting plane <NUM>-<NUM> passes between the bonding region between second surface <NUM>b-<NUM> of the second LOE <NUM>-<NUM> and the first surface <NUM>a-<NUM> of a third one <NUM>-<NUM> of the LOEs <NUM> that is adjacent to the second LOE <NUM>-<NUM> and bonded to the second LOE <NUM>-<NUM>. It is noted herein that the bonding regions (formed between the surfaces <NUM>a, <NUM>b of consecutive LOEs <NUM>) can provide guides for placement of the cutting planes <NUM>. It is further noted that minor deviations from parallelism of the cutting planes which result in the two major surfaces, formed by cutting along consecutive cutting planes <NUM>, of a sliced-out compound LOE being approximately parallel but not perfectly parallel can be corrected by polishing the compound LOEs along the two major surfaces.

With additional reference to <FIG>, there is shown one compound LOE <NUM> that is sliced-out from the optical structure <NUM> after cutting along cutting planes <NUM>. The compound LOE <NUM> includes a first pair of faces <NUM>a, <NUM>b (that include parts of faces <NUM>a, <NUM>b, and which may or may not be parallel faces), a second pair of parallel faces <NUM>a, <NUM>b (major surfaces) formed by cutting the optical structure <NUM> along consecutive cutting planes <NUM> (and preferably formed in part by surfaces <NUM>a, <NUM>b of one of the LOEs <NUM>), and a third pair of faces <NUM>a, <NUM>b (that include parts of faces <NUM>a, <NUM>b, and which may or may not be parallel faces). Most notably, the compound LOE <NUM> has a first plurality of facets <NUM> (in a first LOE region <NUM>) having a first orientation and which also may be inclined obliquely to the faces <NUM>a, <NUM>b or orthogonal to the faces <NUM>a, <NUM>b, a second plurality of facets <NUM> (in a second LOE region <NUM>) inclined obliquely to the faces <NUM>a, <NUM>b and having an orientation non-parallel to the orientation of the facets <NUM>, and at least one facet <NUM> located in a region <NUM> between the first and second LOE regions and having an orientation parallel to the faces <NUM>a, <NUM>b and non-parallel to the orientations of the facets <NUM>, <NUM>. The compound LOE <NUM> also includes a (highly) reflective internal surface <NUM> (also referred to as a coupling-in reflector) located in a coupling-in region <NUM> bounded by faces <NUM>a, <NUM>a', <NUM>b' <NUM>a, <NUM>b, and having an orientation that is non-parallel to the orientations of the facets <NUM>, <NUM>, <NUM> (i.e., reflective internal surface <NUM> is non-parallel to the facets <NUM>, <NUM>, <NUM>). Faces 514a', 514b' are mutually parallel faces and form part of faces <NUM>a, <NUM>b. In embodiments in which the face <NUM>b of the optical block <NUM> (or face <NUM>b' of block <NUM>' or face <NUM> of block <NUM>/<NUM>) is twisted or rotated relative to the interfacing surface <NUM>, the reflective surface <NUM> is tilted about two axes relative to the waveguide axes (which can be a tilt angle measured relative to the x-axis and the y-axis in the arbitrarily labeled xyz coordinate system in the drawings).

As should be apparent, unlike the compound LOEs illustrated in <FIG>, the compound LOE <NUM> does not have a rectangular cross-section in the two-dimensional planes (mostly noticeable in the xy plane shown in <FIG>), due to the cutting and bonding steps described above with reference to <FIG>.

After slicing-out the compound LOEs <NUM>, each of the compound LOEs can be polished on the external surfaces <NUM>a, <NUM>b in order to form a final compound LOE having a desired thickness (measured along the z-axis in the arbitrarily labeled xyz coordinate system in the drawings), and to ensure parallelism between the surfaces <NUM>a, <NUM>b (and the optional facet <NUM>). <FIG> shows one view of the resulting polished compound LOE, with parallel surfaces <NUM>a', <NUM>b' corresponding to the surfaces <NUM>a, <NUM>b after being polished.

The compound LOE produced using the fabrication process according to the embodiments disclosed herein provide several advantages over compound LOEs produced using conventional fabrication methods. First, the location of the cutting plane <NUM> at the specified region of the optical block <NUM> (<FIG> and <FIG>) accommodates placement of the coupling-in reflector <NUM> in a region that presents a more aesthetic overall design of the compound LOE <NUM>. In addition, the spatial positioning of the coupling-in reflector <NUM>, which is determined by the oblique angle of the cutting plane <NUM> and the oblique angle of the cutting planes <NUM> (<FIG>), determines the spatial orientation of the image projector that produces collimated image light. In the disclosed embodiments, the spatial orientation of the coupling-in reflector <NUM> can be designed to accommodate spatial positioning of the image projector below the compound LOE in association with a portion of the face <NUM>b' at or near the coupling-in region <NUM>, thereby providing aesthetic placement of the image projector and reducing the overall formfactor of the optical system formed from the compound LOE and image projector, which can be implemented as part of a head-mounted display and in certain non-limiting implementations as part of an eyeglasses formfactor. Furthermore, the reduced wastage of raw materials and the fact that a large number of compound LOEs can be sliced-out from a single optical structure <NUM> as enabled by the disclosed fabrication processes, facilitates large-scale production of the compound LOEs while maintaining lower manufacturing cost compared to conventional fabrication methods used to produce compound LOEs.

As mentioned, the compound LOE according to the disclosed embodiments can be attached or otherwise coupled to an image projector that produces collimated image light that can be coupled into the compound LOE by the reflective internal surface <NUM>. In preferred embodiments, the coupling-in reflector is designed to accommodate spatial positioning of the image projector below the compound LOE. For both functional and aesthetic reasons, it is typically desired that the collimated image rays corresponding to the central field of view chief ray should generate an approximately perpendicular angle (up to approximately <NUM>°) with relation to the compound LOE both at the input to the compound LOE from the image projector (i.e., input to the first LOE region via coupling-in from the reflective internal surface <NUM>) and at the output of compound LOE to the eye of the observer (i.e., output from the second LOE region via facets <NUM>). Accordingly, it is preferable that the reflective internal surface <NUM> and the facets <NUM> have similar elevation angle. In other words, the oblique angle of the reflective internal surface <NUM> measured relative to the faces <NUM>a, <NUM>b is often approximately equal to the oblique angle of the facets <NUM> measured relative to the faces <NUM>a', <NUM>b' (or equivalently measured relative to surfaces 24a, 24b of the constituent LOE <NUM> that forms the compound LOE).

In many cases, only a portion of the reflective internal surface <NUM> provides a useful active area that couples light from the image projector into the compound LOE, while the remaining portions of the reflective internal surface <NUM> either do not couple any light into the compound LOE, or couple in light at angles which result in unwanted reflections at major surfaces of the compound LOE that give rise to ghost images. In addition, the reflective coatings used to form coated plates <NUM> (<FIG>) for producing reflective internal surface <NUM> typically have a high cost, and therefore reduction of any unused (i.e., "inactive" ) area of the internal surfaces <NUM> can reduce manufacturing costs. Therefore, in order to reduce manufacturing costs and mitigate ghost images by preventing or reducing unwanted reflections, it may be advantageous to limit the size of the reflective internal surfaces <NUM> to the active area, and to fill the remaining area with a less expensive inert material (such as glass, plastic, or even metal).

With additional reference to <FIG>, the following paragraphs describe embodiments in which a reduced-sized reflective internal surface <NUM> is produced from a reduced-sized optical block <NUM>' that is bonded together with one or more blocks <NUM>, <NUM> of inert material such as, for example, glass, plastic, or metal. The material used to form blocks <NUM>, <NUM> (referred to interchangeably herein as "inert blocks") can be the same or different. For example, both blocks <NUM>, <NUM> can be formed from glass, or one of the blocks can be formed from glass and the other formed from plastic. The optical block <NUM>' is similar in structure to the optical block <NUM>, with the noted exception being that the length of the optical block <NUM>' (which in the arbitrarily labeled xyz coordinate system in the drawings is measured along the y-axis) is reduced compared to the length of the optical block <NUM>, thereby limiting the size of the internal surfaces <NUM> to only the useful active area. Due to the similarity of the structure of the optical blocks <NUM>', <NUM>, like reference numerals will be used to identify like components, with an apostrophe (" ' ") appended to the reference numerals of the optical block <NUM>'.

The inert block <NUM> has three pairs of faces (major external surfaces), namely a first pair of preferably parallel faces <NUM>a, <NUM>b, a second pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces), and a third pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces). The optical block <NUM>' is limited in size by the inert block <NUM>, and therefore the inert block <NUM> can be understood to function as a ghost-reducing element, which limits the size of the internal surfaces <NUM> to only the useful active area. In certain embodiments, the block <NUM> is a rectangular cuboid.

The inert block <NUM> also has three pairs of parallel faces (major external surfaces), namely a first pair of preferably parallel faces <NUM>a, <NUM>b, a second pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces), and a third pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces). In certain embodiments, the block <NUM> is a rectangular cuboid. As will be discussed, the block <NUM> is optional, but can be used to advantage to provide structural reinforcement and support to the optical block <NUM>'.

The bonding is preferably performed in stages, where the optical block <NUM>' and the block <NUM> are first bonded together to form compound block <NUM>. The blocks <NUM>', <NUM> are appropriately aligned prior to being bonded together. With reference to the coordinate system shown in <FIG>, the alignment of the blocks <NUM>', <NUM> (when each of the blocks <NUM>', <NUM> is constructed as a rectangular cuboid) can be understood as follows: the faces <NUM>a', <NUM>a are in a plane parallel to the yz plane and are preferably coplanar, the faces <NUM>b', <NUM>b are in a plane parallel to the yz plane and are preferably coplanar, the faces <NUM>a', <NUM>a are in a plane parallel to the xy plane and are preferably coplanar, the faces <NUM>b', <NUM>b are in a plane parallel to the xy plane and are preferably coplanar, and the faces <NUM>b', <NUM>a are aligned in a plane parallel to the xz plane and are coincident.

The blocks <NUM>', <NUM> are bonded together to form compound block <NUM> such that the face <NUM>b' is joined to the face <NUM>a, while maintaining the alignment described with reference to <FIG>. Block <NUM> is shown in <FIG>, and has a first pair of preferably parallel faces <NUM>a, <NUM>b respectively formed from faces <NUM>a', <NUM>a and <NUM>b', <NUM>b, a second pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces) respectively formed from faces <NUM>a', <NUM>a and <NUM>b', <NUM>b, and a third pair of faces <NUM>a', <NUM>b (which may or may not be parallel faces). The internal surfaces <NUM> are in a first region of the block <NUM> and are inclined obliquely to the faces <NUM>a, <NUM>b.

In certain embodiments, the blocks <NUM>, <NUM> can then be bonded together to form compound block <NUM>, as illustrated in <FIG>. The blocks <NUM>, <NUM> are appropriately aligned prior to being bonding together. With reference to the coordinate system shown in <FIG>, the alignment of the blocks <NUM>, <NUM> (when each of the blocks <NUM>, <NUM> is constructed as a rectangular cuboid) can be understood as follows: the faces <NUM>a', <NUM>a are in a plane parallel to the xz plane and are preferably coplanar, the faces <NUM>b', <NUM>b are in a plane parallel to the xz plane and are preferably coplanar, the faces <NUM>a, <NUM>a are in a plane parallel to the xy plane and are preferably coplanar, the faces <NUM>b, <NUM>b are in a plane parallel to the xy plane and are preferably coplanar, and the faces <NUM>a, <NUM>b are aligned in a plane parallel to the yz plane and are coincident.

The blocks <NUM>, <NUM> are bonded together to form compound block <NUM> such that the face <NUM>b is joined to the face <NUM>a, while maintaining the alignment described with reference to <FIG>. Block <NUM> is shown in <FIG> and has a first pair of parallel faces <NUM>a, <NUM>b, a second pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces) respectively formed from faces <NUM>a, <NUM>a and <NUM>b, <NUM>b, and a third pair of faces <NUM>a, <NUM>b (which may or may not be parallel faces) respectively formed from faces <NUM>a, <NUM>a and <NUM>b, <NUM>b.

Block <NUM> can then be aligned and bonded together with the optical structure <NUM>' in place of optical block <NUM>, similar to as described with reference to <FIG>. When using block <NUM> instead of block <NUM>, the bonding of block <NUM> together with the optical structure <NUM>' is such that the face <NUM>b is joined to interfacing surface <NUM>, as shown in <FIG> and <FIG>. As a result, only a fractional portion of the interfacing surface <NUM> is joined to the face <NUM>b' (which forms part of face <NUM>b). This is in contrast to the embodiment illustrated in <FIG> and <FIG>, in which the entirety of the face <NUM>b is joined to the entirety of the interfacing surface <NUM>. The optical structure formed as a result of bonding together block <NUM> and optical structure <NUM>' can then be sliced at predetermined intervals demarcated by parallel cutting planes in order to extract one or more compound LOEs, similar to as described with reference to <FIG>.

In certain embodiments, the inert block <NUM> can be bonded without the inert block <NUM> in order to provide structural reinforcement and support to the optical block <NUM>. For example, in one embodiment, the inert block <NUM> and the optical block <NUM> are bonded together to form an intermediate block such that the face <NUM>b is joined to the face <NUM>a of the optical block <NUM>. In such an embodiment, the inert block <NUM> and the optical block <NUM> are appropriately aligned prior to being bonding together.

In another similar embodiment, the inert block <NUM> and the optical block <NUM>' are bonded together without the presence block <NUM>. In such an embodiment, the bonding is such that that the face <NUM>b is joined to the face <NUM>a' of the optical block <NUM>'. In such an embodiment, the inert block <NUM> and the optical block <NUM>' are appropriately aligned prior to being bonding together. Optionally, the size of the inert block <NUM> can be reduced to match the size of the optical block <NUM>'.

In certain embodiments, it may be advantageous to provide a transparent cover plate on either or both of the polished surfaces <NUM>a', <NUM>b' of the sliced-out compound LOE, such as the compound LOE illustrated in <FIG>. In certain embodiments, such transparent cover plates can be provided directly to the surfaces <NUM>a', <NUM>b' (i.e., after the sliced-out compound LOE is polished).

In other embodiments, the transparent cover plates can be provided as spacer plates between the LOEs <NUM> during production of the optical block <NUM>, as shown in <FIG> and <FIG>. Looking first at <FIG>, there is illustrated an aligned arrangement <NUM> of LOEs <NUM> and transparent cover plates <NUM>, in which the LOEs <NUM> and the cover plates <NUM> alternate along a length of the arrangement <NUM> perpendicular to the parallel faces <NUM>a, <NUM>b of the LOEs <NUM> (here the length is along the z-axis). Each cover plate <NUM> has a pair of parallel external faces <NUM>a, <NUM>b. The cover plates <NUM> and the LOEs <NUM> are bonded together to form a bonded stack <NUM>' (also referred to as optical block <NUM>'), as shown in <FIG>. The bonding is such that the faces <NUM>b, <NUM>a of adjacent cover plates <NUM> and LOEs <NUM> are joined, and such that the faces <NUM>a, <NUM>b of adjacent cover plates <NUM> and LOEs <NUM> are joined.

The stack <NUM>' is generally similar in structure to the stack <NUM> of <FIG> (i.e., the stack <NUM>' has three pairs of parallel faces and is formed from a plurality of bonded LOEs) and the like reference numerals will be used to denote like elements. One notable difference between stacks <NUM> and <NUM>' is that the stack <NUM>' is a bonded stack of LOEs <NUM> and cover plates <NUM> in which the LOEs <NUM> and the cover plates <NUM> alternate along a length of the stack <NUM>' that is perpendicular to the faces <NUM>a, <NUM>b (and parallel to faces <NUM>a, <NUM>b). These transparent cover plates <NUM> are also referred to as transparent spacer plates, as they provide spacing between consecutive LOEs.

In embodiments in which optical block <NUM>' is provided, having LOEs <NUM> provided with spacer plates <NUM> therebetween, the thickness of the coated plates <NUM> used in forming optical block <NUM> should be adjusted to account for the overall thickness of the optical block <NUM>' and to ensure that alignment of the optical blocks <NUM>', <NUM> results in each facet <NUM> being located in a plane that is halfway between the major surfaces <NUM>a, <NUM>b of the associated LOE <NUM> such that the optical blocks <NUM>', <NUM> are bonded together at the proper alignment. In addition, when performing the cutting step to slice-out compound LOEs when employing optical block <NUM>' instead of optical block <NUM>, the consecutive cutting planes should pass through consecutive spacer plates <NUM> having one of the LOEs <NUM> therebetween, as illustrated in <FIG>, and preferably pass approximately through the center of the spacer plates <NUM>.

An example of a sliced-out compound LOE <NUM> having two transparent cover plates <NUM>, <NUM> is illustrated in <FIG>. The cover plates <NUM>, <NUM> are formed from two of the cover plates <NUM> in the stack <NUM>' that are sliced along two of the cutting planes <NUM>. The cover plates <NUM>, <NUM> are bonded to the LOE <NUM> such that the face <NUM>b of cover plate <NUM> is joined to the face <NUM>a of LOE <NUM>, and the face <NUM>a of cover plate <NUM> is joined to the face <NUM>b of LOE <NUM>. The face <NUM>a of the cover plate <NUM> (which is opposite face from face <NUM>b of cover plate <NUM>), and the face <NUM>b of the cover plate <NUM> (which is opposite from face <NUM>a of cover plate <NUM>) respectively form part of the major external surfaces <NUM>a, <NUM>b of the compound LOE <NUM>. The surfaces <NUM>a, <NUM>b of the compound LOE of <FIG> can then polished, similar to as described above with reference to <FIG> to achieve a final compound LOE having a desired thickness and to ensure parallelism between the faces <NUM>a, <NUM>b.

Although the embodiments described herein have pertained to bonding the optical block <NUM> (or <NUM>') to the optical structure <NUM>' such that the coupling-in reflector <NUM> accommodates spatial positioning of the image projector below the final compound LOE product, other embodiments are possible which accommodate different spatial positioning of the image projector. For example, the optical block <NUM> can be inverted (for example by exchanging the positions of the faces <NUM>a, <NUM>b) such that the internal surfaces <NUM> are inclined upward, rather than downward as shown in <FIG>, <FIG>, and <FIG>. Such a configuration allows deployment of the image projector above the final compound LOE product.

Although not illustrated in the drawings, additional optical components, such as prisms, can be optically coupled or bonded with the optical block <NUM> (or <NUM>'), with or without inert blocks <NUM> and/or <NUM>, prior to slicing-out the compound LOE in order to provide additional coupling-in geometries of the final compound LOE product. Alternatively, in addition, one or more additional optical components, such as a prism, can be optically coupled or bonded with the coupling-in reflector <NUM> at the coupling-in region <NUM>.

The present disclosure has described various cutting steps in which optical materials are cut along cutting planes in order to produce various optical blocks and sub-components of optical blocks. It is noted that in certain embodiments, some or all of the surfaces that result from these cutting steps can be polished prior to bonding steps. For example, the joined faces of the optical blocks <NUM>, <NUM>, <NUM> can be polished prior to bonding together the optical blocks <NUM>, <NUM>, <NUM>. In addition, the major surfaces of the LOEs used to form the optical block <NUM> can be polished prior to forming the bonded stack of LOEs (optical block <NUM>). Furthermore, the interfacing surface <NUM> and the joining face of the optical block <NUM> can be polished prior to bonding together the optical blocks <NUM>, <NUM>.

The alignment of the various blocks and 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, one or more optics (e.g., one or more lens, folding optics, 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 blocks and 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>, which are unpublished as of the filing date of this application and do not constitute prior art.

The cutting or slicing of the optical blocks and the 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 optical blocks and optical structures (including the compound LOEs) described herein can be performed by any suitable polishing apparatus / device / tool, as should be understood by those of ordinary skill in the art.

Although the embodiments described thus far have pertained to bonding together two or three optical blocks respectively carrying two or three set of facets at prescribed orientations to accommodate deflection of light in prescribed directions, other embodiments are contemplated herein in which one or more additional optical blocks carrying one or more additional sets of facets or an optical retarder (such as one or more waveplates) at prescribed orientations are bonded to the aforementioned optical blocks. The scope of the present invention should not be limited to any particular number of the aforementioned optical blocks.

The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

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

To the extent that the appended claims have been drafted without multiple dependencies, this has been done only to accommodate formal requirements in jurisdictions which do not allow such multiple dependencies. It should be noted that all possible combinations of features which would be implied by rendering the claims multiply dependent are explicitly envisaged and should be considered part of the invention.

Claim 1:
A method of fabricating a compound light-guide optical element (LOE), comprising:
obtaining a stack (<NUM>) having a first pair of faces (212a, 212b) and a plurality of LOEs (<NUM>), each of the LOEs (<NUM>) having a pair of major parallel surfaces (24a, 24b) and a first plurality of mutually parallel partially reflective internal surfaces (<NUM>) oblique to the pair of major parallel surfaces (24a, 24b);
obtaining a first optical block (<NUM>, <NUM>) having a second pair of faces (112a, 112b, 312a, 312b) and a second plurality of mutually parallel partially reflective internal surfaces (<NUM>, <NUM>);
bonding together the first optical block (<NUM>, <NUM>) and the stack (<NUM>) such that one of the faces (212a) of the first pair of faces is joined to one of the faces (112b, 312b) of the second pair of faces and such that the first plurality of partially reflective internal surfaces (<NUM>) is non-parallel to the second plurality of partially reflective internal surfaces (<NUM>, <NUM>), thereby forming a second optical block (<NUM>);
cutting the second optical block (<NUM>) along a cutting plane (<NUM>) that passes through the other one of the faces (112a, 312a) of the second pair of faces, thereby forming a first optical structure (<NUM>') having an interfacing surface (<NUM>) at the cutting plane (<NUM>);
obtaining a third optical block (<NUM>) having a third pair of faces (512a, 512b, 512a', 512b') and a plurality of mutually parallel reflective internal surfaces (<NUM>);
bonding together the third optical block (<NUM>) and the first optical structure (<NUM>') such that one of the faces (512b, 512b') of the third pair of faces is joined to the interfacing surface (<NUM>) and such that the plurality of reflective internal surfaces (<NUM>) is non-parallel to both the first plurality of partially reflective internal surfaces (<NUM>) and the second plurality of partially reflective internal surfaces (<NUM>, <NUM>), thereby forming a second optical structure (<NUM>'); and
slicing out at least one compound LOE (<NUM>) from the second optical structure (<NUM>) by cutting the second optical structure (<NUM>) through at least two cutting planes (<NUM>) substantially parallel to the major parallel surfaces (24a, 24b) of consecutive LOEs (<NUM>).