Mixed Reality Combiner

Abstract

An optical waveguide combiner having an output coupler including an array of embedded partially reflective dielectric mirrors that expands and combines a virtual arbitrary color image generated by a laser display engine into a user EMB, wherein the dielectric mirrors are configured to have a wavelength band for each lasing band of the laser display engine, the wavelength band including wavelengths of light in the lasing band and a range of wavelengths over which the lasing band is expected to drift, a reflectivity angular range exhibiting a first reflectivity, a transmittance angular range exhibiting a second reflectivity less than the first reflectivity, and a see-through angular transmittance range having high transmittance for natural light incident on the facet.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62 / 980,469, filed on Feb. 24, 2020, and U.S. Provisional Application No. 63 / 001,567, filed on Mar. 30, 2020.

[0002] Embodiments of the present disclosure relate to an optical waveguide system configured to receive an image from a laser display engine with a relatively small input aperture, transmit the image, and output it from a waveguide in an extended output coupling region to fill an enlarged eye motion box for viewing by a user.

Background Art

[0003] Growth head - mounted displays (HMDs) and smart eyewear that provide users with any of various new trends in reality - augmented reality (AR), mixed reality (MR), parallel reality - and are used by users to superimpose a "virtual image" generated by a computer on a "real image" of the real environment in the user's field of view (FOV). The virtual image may, by way of example, provide the user with entertainment and / or information materials related to the real image, tasks performed by the user and / or explicit or implicit user requirements. The image presented to the user, including the real image and the virtual image, may be referred to as an extended reality (XR) image, and any of various hardware configured to provide the user with an XR image may generally be referred to as an XR display.

[0004] In the optical system of an XR display, a computer - controlled display engine, such as a liquid crystal on silicon (LCos), an organic light - emitting diode (OLED), or a laser beam scanning (LBS) microdisplay on a silicon substrate, provides the virtual image. An optical element, called a combiner, is transparent to ambient light, through which the user can see the real environment, but receives the virtual image provided by the display engine and superimposes it on the real image to provide the user with an XR image.

[0005] Generally, the virtual images provided by a display engine are relatively small, having characteristic dimensions of about 5 millimeters or less. The combiner receives the small virtual image at a relatively small input aperture and propagates the image to an output coupler, which outputs the virtual image through the exit aperture of the combiner and into an eye motion box (EMB). When the user's eye is located within the EMB, the virtual image enters through the user's aperture and onto the user's retina and appears as an XR image as a feature of the real image that the user sees through the combiner. To fill the EMB such that the user can comfortably view the virtual image without unduly straining to align their eye with the combiner, the combiner is generally configured to have a relatively large, expanded aperture through which the combiner transmits many replicas of the virtual image into the EMB.

[0006] The optical system of a practical XR display generally needs to satisfy a complex mixture of ergonomic, technical, and economic constraints. It is convenient for the optical system to have a comfortably large EMB, be advantageously small, lightweight, and energy-saving, and be configured to provide a clear virtual image without excessive and obtrusive artifacts such as image ghosts. SUMMARY OF THE INVENTION

[0007] Aspects of one embodiment of the present disclosure relate to an optical waveguide combiner having an output coupler that includes an array of embedded dielectric partial reflectors (hereinafter also referred to as facets) for expanding and combining a virtual arbitrary color image generated by a laser display engine within a user EMB. For light in a wavelength band provided by the laser used by the engine to generate the virtual image, the facets are configured to reflect incident light at an angle of incidence in a first range into the user EMB with a relatively high reflectivity. At an angle of incidence in a second range different from the first range, the facets have a relatively low reflectivity and are configured to transmit light in a substantially identical laser wavelength band with a relatively high transmittance. The transmittance and reflectivity exhibit relatively little variability over a range of wavelengths in the range of the laser wavelength band in the first and second angular ranges. The facets are formed to be substantially colorless and transmissive to visible light, also referred to as natural light from the environment. Optionally, the display engine includes at least one laser that provides light in red, green, and blue (RGB) bandwidths to the display engine and processes the light to generate a virtual RGB color image. In one embodiment, the combiner introduces a color virtual image into the EMB with a relatively high RGB image resolution and relatively low contamination by image artifacts.

[0008] In one embodiment, the waveguide combiner comprises a waveguide having first and second parallel total internal reflection (TIR) surfaces. Light from the display engine is incident on the waveguide, reflected from the TIR surfaces, and bounces back and forth between the TIR surfaces, propagating within a reduced waveguide field of view (wFOV) along the waveguide and reaching and entering the facet. In one embodiment, the facets are equally spaced and parallel, and are tilted at an angle of tilt measured between the normal to the TIR surface and the normal to the facet. The component of the light ray within the wFOV that is parallel to the TIR normal reverses direction each time the light ray bounces back from the first TIR surface and reverses direction each time the light bounces back from the second TIR surface. Light rays within the wFOV that have undergone an even or odd number of bounces (counted from any initial bounce) before entering a given facet enter the given facet at an angle of incidence within a first range or a second range of angles of incidence, respectively. According to one embodiment of the present disclosure, light rays that enter only one of the first and second ranges of angles of incidence are selected, exit the waveguide and are combined to be incident on the EMB, providing the user with a virtual image generated by the display engine.

[0009] For the sake of convenience of presentation, the range of angles of incidence at which light rays within the wFOV are selected to provide a virtual image may be referred to as the "image incidence range". When oriented by TIR reflection within the waveguide to include light rays propagating in the angular direction within the image incidence range, it may be referred to as the "image wFOV". The non-selected range of angles of incidence may be referred to as the "conjugate incidence range", and the wFOV may be referred to as the "conjugate wFOV" when oriented by TIR reflection within the waveguide to include light rays propagating in the angular direction within the conjugate incidence range.

[0010] According to one embodiment, the tilt angle of the facet is determined to provide a favorable angular separation between the image incident range and the conjugate incident range. The facet is configured to have a reflectance angular range, a transmittance angular range, and a facet wavelength band. For light having a wavelength within the facet wavelength band that is incident on the facet at an incident angle within the reflectance angular range, the facet exhibits a relatively high reflectance and a relatively low dispersion with respect to changes in wavelength and incident angle. Similarly, for light having a wavelength within the facet wavelength band that is incident on the facet at an incident angle within the transmittance angular range, the facet exhibits a relatively low reflectance and a corresponding high transmittance with respect to changes in wavelength and incident angle. The facet wavelength band spans a range of wavelengths that includes the laser oscillation bandwidth of the laser that provides the light processed by the display engine to generate a virtual image, and a range of wavelengths where the laser oscillation bandwidth may vary as a result of drift due to, for example, operating conditions and / or manufacturing tolerances.

[0011] The summary of the invention is provided to introduce a selection of concepts in a simplified form and is further described in the forms for carrying out the following invention. The summary of the invention is not intended to identify the key features or essential features of the subject matter of the claims, nor is it intended to be used to limit the scope of the subject matter of the claims.

Brief Description of the Drawings

[0012] Non-limiting examples of embodiments of the present disclosure are described below with reference to the accompanying drawings listed after this paragraph. Identical features that appear in more than one drawing may be labeled with the same label in the multiple drawings in which they appear. Labels that label an icon representing a given feature of an embodiment of the present disclosure in a drawing may be used to reference the given feature. The dimensions of the features shown in the drawings are selected for the convenience and clarity of presentation and are not necessarily shown to scale.

[0013] [Fig. 1A]A diagram schematically showing a waveguide combiner comprising an output coupler including an array of facets that expands the input aperture of the combiner in one direction and provides an expanded output, the combiner transmitting a virtual image received through the input aperture into the EMB. [Fig. 1B] A cross-section of the combiner shown in FIG. 1A, which reflects light from a laser display engine into a user's EMB, according to an embodiment of the present disclosure, is schematically shown. [Fig. 1C] An enlarged portion of the combiner shown in FIG. 1B, where light from a laser display engine enters the combiner, is schematically shown, according to an embodiment of the present disclosure. [Fig. 1D] An enlarged portion of the combiner shown in FIG. 1B, where light from a laser display engine exits the combiner and enters the EMB, is schematically shown, according to an embodiment of the present disclosure. [Fig. 1E] A schematic graph of reflectance as a function of the angle of incidence of light from a laser display engine on the facets shown in FIGS. 1A and 1C and the reflectance of the facets with respect to natural light is shown, according to an embodiment of the present disclosure. [Fig. 1F] An arbitrary laser oscillation bandwidth for the lasers in the display engine shown in FIGS. 1A and 1B and the corresponding facet wavelength bands of the facets shown in the figure are schematically shown, according to an embodiment of the present disclosure. [Fig. 1G] A graph of reflectance as a function of the wavelength of the facets shown in FIGS. 1A and 1B for the facet wavelength band of blue light is shown, according to an embodiment of the present disclosure. [Fig. 2A] A diagram schematically showing a cross-section of a waveguide combiner similar to the combiner shown in FIG. 1A, including facets tilted at an intermediate tilt angle that reflect light from a laser display engine into a user's EMB. [Fig. 2B] A schematic graph of reflectance as a function of the angle of incidence of light on the facets shown in FIG. 2A is shown, according to an embodiment of the present disclosure. [Fig. 3A]FIG. is a diagram schematically showing a cross section of a waveguide combiner similar to the combiner shown in FIG. 1A according to an embodiment of the present disclosure, including facets inclined at a relatively large inclination angle for reflecting light from a laser display engine into a user EMB. [Fig. 3B] FIG. shows a schematic graph of reflectance as a function of the angle of incidence of light on a facet according to an embodiment of the present disclosure, as shown in FIG. 2A. [Fig. 4] FIG. schematically shows a perspective view of a waveguide combiner including a waveguide system providing two-dimensional aperture expansion according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0014] In this description, unless otherwise stated, adjectives such as "substantially" and "about" that modify the conditions or relative characteristics of one or more features of an embodiment of the present disclosure are understood to mean that the condition or characteristic is defined within an acceptable range acceptable for the operation of the embodiment for its intended use. When general terms of the present disclosure are explained by reference to an instance as an example or a list of instances as examples, the one or more instances referred to are by way of non-limiting examples of the general terms, and the general terms are not intended to be limited to the one or more instances as the specific examples referred to. Unless otherwise indicated, the word "or" in this specification and the claims is to be construed as inclusive "or" rather than exclusive "or", indicating at least one of the items it combines, or any combination of two or more items.

[0015] FIG. 1A schematically shows a waveguide combiner 20 optionally including a waveguide 30 having two relatively large parallel face surfaces 31 and 32, an end face 34, and an output coupler 40 including an array of parallel equally spaced facets 42 embedded in the waveguide. For convenience of presentation, the position of the features of the waveguide combiner 20 may be referenced with respect to the x, y, and z axes of a Cartesian coordinate system 100.

[0016] The face surfaces 31 and 32, also referred to as internal total reflection (TIR) surfaces 31 and 32, are arbitrarily assumed to be parallel to the xy plane of the coordinate system 100. The facet 42 is parallel to the x-axis and is rotated about the x-axis by an inclination angle β in the counterclockwise direction when viewed along the x-axis toward the yz plane. The input aperture, schematically represented by the dashed rectangle 35 of the waveguide 30, is arbitrarily parallel to the xz plane, and the output coupling region of the waveguide, schematically represented by the dashed rectangle 36, is arbitrarily located on the face surface 32. Optionally, the waveguide combiner 20 includes a prism input coupler 50 for coupling light from a virtual image generated by the display engine 70 and entering the waveguide 30 through the input aperture 35. The output coupler 40, according to one embodiment of the present disclosure, operates to expand the input aperture 35 in the y direction, receive light through the input aperture 35, propagate it within the waveguide 30 to the output coupler, and reflect light from a virtual image that enters the EMB 60 through the expanded output coupling region 36 and is viewed by the user 102. In the following drawings, the user 102 may be represented only by the user's eye. As an example, in FIG. 1, a waveguide combiner 20 that generates a virtual image schematically represented by the dashed rectangle 72 is shown. The natural light from the environment that the user 102 views through the waveguide 30 is schematically represented by the block arrow 74.

[0017] FIG. 1B shows a schematic cross-sectional view of the waveguide combiner 20 along the plane A-A shown in FIG. 1A according to one embodiment of the present disclosure, and the propagation of light from the virtual image 72 within the waveguide 30 for the wFOV supported by the combiner.

[0018] Figure 1B schematically shows light from a virtual image 72 (Figure 1A) within the dFOV of a display engine 70 that irradiates a face surface 51 of an input coupler 50. The input coupler couples the light and directs it into waveguide 30 through input aperture 35. A portion of input coupler 50, input aperture 35, and waveguide 30 located within circle 202 is shown enlarged in Figure 1C for clarity and ease of reference. In plane A-A, the dFOV is defined by positive and negative angles α’ + and α’ - such that the angular range Φ’ of the dFOV = (α’ + − α’ - ) = (|α’ + | + |α’ - |). The angles α’ + and α’ - are the angles that rays 81 and 82 (Figure 1C) that limit the angular range of the dFOV make with the principal ray represented by arrow 83 of the dFOV. Rays 81 and 82 within waveguide combiner 20 and their respective reflections and refractions are represented by solid and dashed lines respectively and may be referred to as positive and negative bounce rays.

[0019] With respect to principal ray 83, the angle of a ray of light from virtual image 72 (Figure 1A) in plane A-A is considered positive if the ray is rotated clockwise with respect to the principal ray in Figure 1B or negative if the ray is rotated counterclockwise. Principal ray 83 is assumed to be perpendicular to the face surface 51 of input coupler 50, and the refractive index of the material from which the input coupler and waveguide 30 are fabricated with respect to air is assumed to be equal to the same refractive index n g .

[0020] Upon entering input coupler 50, as more clearly shown by region 202 of the input coupler enlarged in Figure 1C, the refraction of light reduces the angles α’ g and α’ + and the attendant angular range Φ’ of the dFOV by a factor that is a function of the refractive index n - . In waveguide combiner 20, α’ + and α’ -The corresponding reduced angles are α respectively + and α - represented by, and the reduced angle range characterizing the wFOV of the light from the display engine 70 after entering the waveguide combiner 20 is represented by Φ. The angles α + and α - are the angles formed by the reflected rays 81 and 82 with respect to the principal ray 83 in the waveguide 30 after refracting and entering the input coupler 50. The reflected rays define the range of the wFOV in the waveguide combiner 20, and the angles are such that the angular range of the wFOV is Φ = (|α + | + |α - |). The field of view wFOV is shown shaded in FIGS. 1B and 1C and subsequent drawings.

[0021] α’ + and α’ - are defined as a positive angle and a negative angle respectively, and when entering the input coupler 50, the corresponding angles α + and α - are also noted to be defined as a positive angle and a negative angle respectively. However, due to each reflection from the TIR surface 31 or 32, the reflected rays 81 and 82 reverse their respective rotations with respect to the principal ray 83. As a result, following the convention where clockwise rotation is positive and counterclockwise rotation is negative, the reflected rays 81 and 82 are rotated clockwise by angles α + and α - respectively with respect to the principal ray 83 after reflection from the face surface 31. However, after reflection from the TIR face surface 32, the reflected rays 81 and 82 are rotated counterclockwise by angles -α + and -α - respectively with respect to the principal ray 83.

[0022] In the waveguide 30, as schematically shown in FIG. 1B, the light rays within the wFOV are completely reflected by the TIR face surfaces 31 and 32, bounce back and forth between the TIR face surfaces 31 and 32, and reach and enter the facet 42 of the output coupler 40. With each bounce, the normal to the waveguide "n" wThe components of the light rays (not shown) within the wFOV along 」 are reversed in direction. As a result, the light rays within the wFOV after being reflected and bounced back from the face surface 31 have a z-component in the positive z-direction and may be regarded as "downward" light rays propagating downward from the face surface 31 towards the face surface 32 in the figure. When including downward light rays, the wFOV is oriented downward in the positive z-direction. Similarly, the light rays after being reflected and bounced back from the face surface 32 have a z-component in the negative z-direction and may be regarded as "upward" light rays propagating upward from the face surface 32 towards the face surface 31. In the downward case, the wFOV may be distinguished and referred to as wFOV-Down, and in FIGS. 1B and subsequent figures, it is labeled as wFOV-D. Similarly, in the upward case, the wFOV may be distinguished and referred to as wFOV-Up, and in FIGS. 1B and subsequent figures, it is labeled as wFOV-U. The label "wFOV" generally refers to wFOV-U and wFOV-D.

[0023] When reaching the output coupler 40, the upward light rays within the wFOV-U are incident on the facets 42 within a first range of the incident angle with respect to the normal "n f " to the facet (hereinafter also referred to as the up range), and the downward light rays within the wFOV-D are incident on a second range of the incident angle on the facet (also referred to as the down range). According to an embodiment of the present disclosure, the light rays in one of the wFOV-U or wFOV-D are selected and reflected from the waveguide 30 by the facet 42 through the output coupling region 36 and enter into the EMB60 for user viewing of virtual images such as the virtual image 72 (FIG. 1A) generated by the display engine 70. For the selected light rays within the wFOV-U or wFOV-D, the facet 42 is configured to have a relatively enhanced reflectivity with respect to the incident angles in the corresponding up range or down range. For the light waves within the wFOV that are not selected, the facet 42 is configured to have a relatively enhanced transmittance. The selected wFOV may be referred to as the image wFOV, and the non-selected wFOV may be referred to as the conjugate wFOV.

[0024] As an example, in waveguide 30, facets 42 are oriented at a relatively small tilt angle β, and the rays of wFOV-U and wFOV-D are incident on the facets from the opposite side of the facets. According to one embodiment of the present disclosure, wFOV-U is selected as the image wFOV, and the rays within wFOV-U are selected and reflected from waveguide 30 through output coupling region 36 to provide an output viewing field O-FOV within EMB60 for viewing a virtual image generated by display engine 70. For purposes of presentation and reference, the region of FIG. 1B shown by circle 204 is enlarged and shown in FIG. 1D.

[0025] The enlarged region 204 of FIG. 1D shows an enlarged portion of the virtual image including waveguide 30 including facets 42, EMB60, and O-FOV, the angles associated with the embodiment of the present disclosure, and virtual images such as virtual image 72 provided by display engine 70 as seen by user 102. The figure schematically shows the light from upward bounce rays 81 and 82 that are reflected as positive and negative bounce output rays 91 and 92 and enter EMB60 by a given facet 42 within output coupler 40 (FIG. 2A). Rays 91 and 92 define the range of the output viewing field O-FOV as seen by user 102. As an example, it is assumed that O-FOV has a range Φ' of the same angle as viewing field dFOV (FIG. 1C) and includes light received by prism input coupler 50 that is introduced into waveguide 30 through input aperture 35 by the input coupler. The bounce output lines 91 and 92 in waveguide 30 each form an angle α + and α - with respect to output principal ray 93 of O-FOV that is reflected by facet 42 from principal ray 83. Optionally, output lines 91 and 92 also form an angle α w with respect to normal n + and α - with respect to the faces 31 and 32. The bounce output lines 91 and 92 are refracted when entering EMB60 and each form an angle α' + and α' - with respect to the light of output principal line 93.

[0026] The negative bounce ray 82 that is incident on the facet 42 and the facet reflects the light to form the negative bounce output ray 92 forms an angle γ w with respect to the normal n - . Similarly, the positive bounce ray 81 that is incident on the facet 42 and the facet reflects the light to form the positive bounce output ray 91 forms an angle γ w with respect to the normal n + . The angles γ - and γ + are functions of the tilt angle β and the angles α - and the angle α + respectively, and may be described as follows. 1) γ - = (2β - α - ) and 2) γ + = (2β - α + ) Here, by definition, note that the "counterclockwise" angle α - has a negative value, and the "clockwise" angle α + has a positive value. The relationships provided by equations 1) and 2) are valid for any ray within the wFOV. When α represents the angle that any ray within the wFOV makes with respect to the chief ray 83, for any α, the angle γ may be described as follows. 3) γ = (2β - α) Therefore, the rays in the wFOV-U are incident on the facet 42 at an incident angle φ f with respect to the normal n u to the facet, and may be given by the following equation. 4) φ u = (γ - β) = (β - α) The associated up-range of the incident angle selected as the incident range of the image includes all incident angles between (β - α + ) and (β - α - ), and may be given by the following equation. 5) Up-range = {∀φ u |(β - α + ) ≤ φ u ≤ (β - α - )} Similarly, the rays in the wFOV-D are the normal nf incident angle φ with respect to d incident on the facet at, and may be given by the following equation. 6) φ d = (γ + β) = (3β - α) The associated downrange, selected as the conjugate incidence range, may be described as follows. 7) Downrange = {∀φ d |(3β - α + ) ≤ φ d ≤ (3β - α - )}

[0027] According to an embodiment of the present disclosure for rendering the appearance of the artifacts associated with the virtual image in EMB60 appropriate, it is advantageous for all rays in wFOV-U to be incident on the same side of the facet 42 and for all rays in wFOV-D to be incident on the same side of the facet 42. The side on which the rays in wFOV-U are incident on the facet 42 may be the same side or a different side of the facet on which the rays in wFOV-D are incident on the facet, according to one embodiment.

[0028] As an example, the waveguide combiner 20 and the field of view wFOV are configured such that all rays in wFOV-U are incident on the side of the facet 42 facing in the direction of the face plane 32, and all rays in wFOV-D are incident on the opposite side of the facet, i.e., the side facing the face plane 31. To provide for opposite-side incidence, the waveguide combiner 20 is configured such that, for any ray within the wFOV supported by the waveguide combiner, the complementary angle of γ is greater than the tilt angle β of the facet 42. In symbols, it is as follows. 8) (90 - γ) > β When substituting γ with α + > α - Note that the tilt angle β within the combiner 20 needs to satisfy a first constraint according to an embodiment of the present disclosure given by the following equation. 9) β < (30° + α - / 3) To provide total internal reflection of light within the wFOV from the face surfaces 31 and 32, for any ray of light within the wFOV, the angle γ must be greater than the critical angle θ of the waveguide 30, which becomes the second constraint that the tilt angle β within the combiner 20 must satisfy. c This results in the second constraint that the tilt angle β within the combiner 20 must satisfy the following. 10) γ + =(2β - α + ) > θ c ⇒ β > (θ c + α + ) / 2 The constraints given by equations 9) and 10) may be combined into the following single equation that provides a limit on the tilt angle β of the combiner 20. 11) (θ c + α + ) / 2 < β < (30° + α - ) / 3 As an example, assuming |α + | = |α - | = Φ / 2, the constraints on the tilt angle β within the combiner 20 may be expressed as a function of the field of view wFOV as follows. 12) (θ c + Φ / 2) / 2 < β < (30° + Φ / 6) Regarding the angular range Φ' of the output field of view O - FOV that the user 102 sees within the EMB60, the constraints on β may be approximated as follows by equation 11). 13) (θ c + Φ' / 2n g ) / 2 < β < (30° + Φ' / 6n g ) Here, n g is the refractive index of the material in which the waveguide combiner 20 is formed.

[0029] As a numerical example, for green light having a wavelength of approximately 550 nanometers, n g is equal to 1.51, and the absolute values |α + | and |α -Assume that both | are equal to approximately 13°, and Φ’ has an angular range of approximately 30° and an aspect ratio of 16:9. For β equal to approximately 26°, the up-range, reflectance angle range of the incident angle advantageously extends from approximately 17° to 35°, and the down-range transmittance angle range advantageously extends from approximately 66° to approximately 84°. Advantageously, the reflectance of the light rays within the up-range is from approximately 9% to approximately 11%, optionally greater than approximately 10%, and the reflectance of the light rays within the down-range is less than approximately 1.5%, optionally less than approximately 1%. The angular “see-through” range for the ambient natural light 74 (FIG. 1A) incident on the facet advantageously extends from approximately 5° to approximately 45° and exhibits a substantially colorless transmittance of 85% or more.

[0030] FIG. 1E shows a graph 210 of the reflectance of a facet 42 that may be manufactured to substantially match the numerical specifications described above. The graph includes a reflectance curve 212 that gives the reflectance of the facet 42 within the waveguide 30 as a function of the incident angle of the light on the facet. The reflectance (percent) is shown along the vertical axis of the graph 210, and the incident angle of the light on the facet 42 is shown along the horizontal axis. The up-range of the incident angle and the reflectance angle range selected to be the image wFOV are schematically represented by the shaded region 218. The down-range of the incident angle selected to be the transmittance angle range and the conjugate wFOV are schematically represented by the shaded region 216. The dashed hat function 214 shows the “see-through” angle range of the facet for the natural light 74 (FIG. 1A) according to an embodiment of the present disclosure.

[0031] Assume that the display engine 70 includes a laser diode (LD) that provides the R, G, and B light that the display engine processes to generate a virtual image. Then, the facet 42 is designed such that the reflectance of the facet is relatively constant as a function of the wavelengths in the up-range and down-range of the incident angle for each of the R, G, B laser oscillation bandwidths for which the LD is expected to laser oscillate. Optionally, the dispersion of the reflectance of the facet with respect to the wavelength within each of the R, G, and B facet wavelength bands is less than 5%. In one embodiment, the dispersion is less than 2%.

[0032] The LD typically laser oscillates at a wavelength with a relatively narrow wavelength bandwidth between 1 to 2 nm (nanometers) FWHM (Full Width at Half Maximum). However, the LD laser oscillation bandwidth can shift, for example, 0.1 nanometer to 0.35 nanometer for each degree Celsius (°C) change in the LD operating temperature, and the operating temperature can easily change by 20°C. Furthermore, manufacturing tolerances can allow a variation of up to 5 nanometers in the central laser oscillation wavelength at which the same type of LD laser oscillates. According to one embodiment, the facet 42 is advantageously configured to have a facet wavelength band for each of the R, G, and B lights generated by the LD for incident angles in an uprange and downrange of about 20 nanometers or more. Advantageously, for each facet wavelength band, the change in reflectivity with respect to the wavelength within the band is less than 3% of the average reflectivity, providing a gamut chromaticity difference radius “ΔCG” in the CIE 1931 xy chromaticity space of about 0.02 or less.

[0033] As an example, FIG. 1F schematically shows the laser oscillation bandwidths 120R, 120G, and 120B of the R, G, and B laser oscillations of the LD in the display engine 70, and the corresponding facet wavelength bands 121RW, 121GW, and 121BW of the facet 42, according to one embodiment of the present disclosure. FIG. 1G shows a graph 230 of a curve 232 giving the reflectivity of the facet 42 as a function of wavelength for the range of blue wavelengths in the visible spectrum. In the inset 234, a portion of the curve 232 is enlarged and marked to show the region of the curve centered on a blue wavelength of about 450 nanometers between about 445 nanometers and about 455 nanometers, which graphs the reflectivity as a function of wavelength in the facet wavelength band 121BW. The reflectivity of the facet 42 with respect to the wavelength of the facet wavelength band 121BW is equal to about 4.8%, and the change with respect to the wavelength of this wavelength band is less than about 5%.

[0034] The facets 42 having reflectivities in the incident angle sheath-through range, up range, and down range shown in FIG. 1E, and the R, G, B facet wavelength bands shown in FIG. 1F may include a partially reflective dielectric mirror. The partially reflective dielectric mirror may be manufactured by depositing a partially reflective film on the surface of a prism with a pre-formed partially reflective film and bonding the prisms together. The prism may be manufactured by grinding and polishing a silicate material such as BK-7 into a desired shape, or by injection molding a suitable polymer or sol-gel. The film may be formed from any of various suitable materials such as, for example, hafnium dioxide (HfO2), magnesium fluoride (MgF2), and / or tantalum pentoxide (Ta2O5).

[0035] FIG. 2A schematically shows another waveguide combiner 320 according to an embodiment of the present disclosure. The waveguide combiner 320 is similar to the waveguide combiner 20 and has wFOV-U and wFOV-D respectively selected for the image wFOV and the conjugate wFOV. However, the waveguide combiner 320 includes a waveguide 330 having a facet 342 that is inclined at an inclination angle β greater than the inclination angle of the facet 42 in the waveguide combiner 20. Further, unlike the waveguide combiner 20, the waveguide combiner 320 is configured such that the light rays of both wFOV-D and wFOV-U are incident on the same side of the facet 242, that is, the side facing the TIR face 32.

[0036] To provide the same-side incidence shown by the waveguide combiner 320, as a result of calculations similar to those performed to form the waveguide combiner 20, the following constraints for the waveguide combiner 320 are obtained. For all γ, 14) β > 90 - γ ⇒ β > 30° + α + / 3 15) γ = (2β - α - ) < 90° ⇒ β < (90° + α - ) / 2 16) (30° + α + / 3) < β < (45° + α - / 2) or (30°+Φ / 6)<β<(45°-Φ / 4) The angular up-range and down-range for the waveguide combiner 32 are as follows: 17) Uprange = {∀φ u |(β-α + )≦φ u ≦(β-α - )} and 18) Downrange = {∀φ d |(180°-3β+α - )≦φ d ≦(180°-3β+α + )} Here, φ u and φ d are the angles of incidence of the light waves at wFOV-U and wFOV-D, respectively.

[0037] n equals approximately 1.5 at a wavelength of approximately 550 nanometers g , with absolute value |α equal to approximately 13° + | and |α - As a numerical example for a waveguide 330 of Φ′ having a diagonal extent of about 30° and an aspect ratio of 16:9, β may be equal to about 35°. The up-range of incidence angles selected for the image wFOV, the reflectance angular range, advantageously extends from about 26° to about 44°, and is optionally characterized by an average reflectance between about 9% and 11%, optionally 10% or more. The down-range, the transmittance angular range selected for the conjugate wFOV, advantageously extends from about 66° to about 84°, and is characterized by an average reflectance that is about 5% or less, optionally 2% or less. The see-through range, advantageously extends from about 15° to about 55°, and is characterized by a transmittance of about 85% or more.

[0038] Figure 2B shows a graph 350 of the reflectance of facet 242, which may optionally be fabricated in a similar manner to the method of fabricating facet 42, to substantially match the numerical specifications described above. The graph includes a reflectance curve 312 that gives the reflectance of facet 242 within waveguide 330 as a function of the angle of incidence of light on the facet. Reflectance (percent) is shown along the vertical axis of graph 351, and the angle of incidence of light on facet 242 is shown along the horizontal axis. The upper range of angles of incidence and the range of reflectance angles selected to be like the image wFOV are schematically represented by the shaded region 351. The lower range of angles of incidence and the range of transmittance angles selected to be like the conjugate wFOV are schematically represented by the shaded region 352. The dashed hat function 353 indicates the "see-through" angular range of the facets for natural light 74 (FIG. 1A) according to embodiments of the present disclosure.

[0039] FIG. 3A schematically shows another waveguide combiner 420 according to an embodiment of the present disclosure. Waveguide combiner 420 is similar to waveguide combiner 320 shown in FIG. 2A, but includes a waveguide 430 having a facet 442 that is tilted at an angle β greater than the tilt angle of facet 342 within waveguide 330. Further, waveguide combiner 420 is configured such that, similar to waveguide combiner 320, light rays in both wFOV-D and wFOV-U are incident on the same side of facet 342 (the side facing face 32), but in waveguide combiner 420, unlike waveguide combiner 320, wFOV-D is the image wFOV and wFOV-U is the conjugate wFOV.

[0040] Regarding waveguide combiner 420, 19) γ ± = 180° - 2β - α ± or γ = 180° - 2β - α, and for combiner 420, γ - > γ + It should be noted that the following constraints are satisfied to provide the configuration of waveguide combiner 420 where wFOV-D, rather than wFOV-U, is the image wFOV. 20) (90° - γ - ) > 0 ⇒ 21) β > 45° - α - / 2 and 22) γ +> θ c ⇒ 23) β < 90° - (α + + θ c ) / 2 Combining equations 21 and 23 gives the following equation for the constraint on β. 24) 45° - α - / 2 < β < 90° - (α + + θ c ) / 2 The up - range of angles, which is the transmittance range, and the down - range, which is the reflectance range of the waveguide combiner 420, may be described as follows. 25) Up - range = {∀φ u | (180° - 3β - α + ) ≤ φ u ≤ (180° - 3β - α - )} and 26) Down - range = {∀φ d | (β + α - ) ≤ φ d ≤ (β + α + )}

[0041] Figure 3B provides a graph 450 showing the angular positions and ranges of the up - range (transmittance range) 451, down - range (reflectance range) 452, and through - range 453 for the facet 442 within the waveguide combiner 430.

[0042] As a numerical example for the waveguide 430, for a wavelength of 550 nanometers, n g is approximately equal to 1.51, and the absolute values |α + | and |α -Assuming that | is equal to approximately 13° and Φ’ has a diagonal range of approximately 30° and an aspect ratio of 16:9, β may be equal to 63.5°. The up-range of the incident angle and the transmittance angle range advantageously extend from approximately 2° to approximately 20°, and advantageously have a relatively low average reflectance of less than approximately 5%, and optionally less than approximately 2.0%. The down-range selected for the reflection angle range and the image wFOV advantageously extends from approximately 55° to approximately 75° and has a relatively high average reflectance between approximately 9% and approximately 11%, optionally greater than or equal to 10%. The see-through range advantageously extends from approximately 40° to approximately 80° and is characterized by a transmittance of greater than or equal to approximately 85%.

[0043] Figure 3B shows a graph 450 of the reflectance of facet 342, which may optionally be manufactured in the same manner as the manufacturing method of facet 42, to substantially match the numerical specifications described above. The graph includes a reflectance curve 412 that gives the reflectance of facet 342 in waveguide 430 as a function of the angle of incidence of light on the facet. The reflectance (percent) is shown along the vertical axis of graph 351, and the angle of incidence of light on facet 342 is shown along the horizontal axis. The up-range of the angle of incidence and the transmittance angle range selected to be the conjugate wFOV are schematically represented by the shaded region 451. The down-range of the angle of incidence selected to be the reflection angle range and the image wFOV are schematically represented by the shaded region 452. The dashed hat function 453 shows the see-through angle range of the facet with respect to natural light 74 (Figure 1A) according to an embodiment of the present disclosure.

[0044] More generally, v u shall represent the normalized vector in the propagation direction of the upward light rays included in wFOV-U in waveguide 30, 330, or 430 of waveguide combiners 20, 320, or 420, but is not necessarily included in plane A-A shown respectively for the waveguide combiners of Figures 1B, 2B, or 3B. Next, the angle of incidence φ of the upward light rays on the facet of the waveguide with respect to the normal to the facet u may be given by the following equation. 27) φ u = cos-1 (v u .n f ) Here, n f is a vector perpendicular to the facet. Similarly, although v d represents the propagation direction of the downward light ray included in the wFOV-D and is not necessarily included in the plane A-A, the incident angle φ d of the light ray to the facet of the waveguide may be described as follows. 28) φ d = cos -1 (v d .n f ) = cos -1 ((v u - 2v u .n w ).n f ) Here, n w is a vector perpendicular to the TIR face of the waveguide.

[0045] The constraints described above with reference to the plane A-A on the waveguide combiner according to an embodiment of the present disclosure may be generalized as a function of v u and / or v d . For example, for the waveguide combiner 420, equations 24) and 25) may be rewritten as follows. 29) Uprange = {∀φ u | (-180° + 3β + α - ) ≤ cos -1 (v u .n f ) ≤ (-180° + 3β + α + )} and 30) Downrange = {∀φ u | (β + α - ) ≤ cos -1 ((v u - 2v u .n w ).n f ) ≤ (β + α + )}

[0046] In the above description, it should be noted that each facet in the combiner waveguide according to one embodiment is designed to have reflectance and transmittance angular ranges for each of R, G, and B lights. However, the practice of one embodiment of the present disclosure is not limited to facets having angular ranges for each of R, G, and B lights. A facet according to one embodiment may be designed to function for colors different from R, G, and B, and may be configured to function for four or more or two or fewer colors. For example, each facet may be designed to function for only one or only two of R, G, or B.

[0047] Furthermore, the spacing between facets, referred to as the facet pitch “P”, may be defined by the formula P = ηLcosβ, where L is the length of the facet between the TIR face surfaces, η is a coefficient, typically less than 1, and it should be noted that, for example, advantageously, it may be different from that shown in FIGS. 1B, 2A, or 3A. In FIGS. 1B and 2A, η is substantially equal to 1, and the pitch P is shown to be substantially equal to P = Lcosβ. In FIG. 3A, η is substantially equal to 0.7, and P = 0.7Lcosβ. A smaller pitch P may be advantageous for providing spatial coherence to the virtual image provided by the waveguide combiner according to one embodiment.

[0048] The waveguide combiner described by way of example above expands the input aperture 35 in one direction along the y-axis (as shown in FIG. 1A, for example) according to an embodiment of the present disclosure. A waveguide combiner that expands the input aperture along two directions, for example, the x and y directions, according to one embodiment of the present disclosure may be provided by replacing the input coupler 50 in the waveguide combiner shown in FIG. 1A with a waveguide combiner that expands the input aperture in the x direction.

[0049] FIG. 4 schematically shows a waveguide combiner 500 that, according to an embodiment of the present disclosure, extends the input aperture 535 in two arbitrarily orthogonal directions to provide an extended output coupling region 536 where the waveguide combiner guides light into the EMB 560.

[0050] According to an embodiment of the present disclosure, the waveguide combiner 500 optionally includes a prism input coupler 550, a first waveguide 530, and a second waveguide 630. The input coupler 550 receives light from a virtual image generated by the laser display engine 570 through the input aperture 535 and inputs the light into the waveguide 530. The waveguide 530 includes a first TIR face 531 and a second TIR face 532 that are each arbitrarily parallel to the xy plane of the coordinate system 100, as well as a top surface and a bottom surface 532 and 534. The waveguide has an output coupler 540 that includes a plurality of parallel facets 542 according to an embodiment of the present disclosure. Optionally, the facets are perpendicular to the face surfaces 531 and 532 and are rotated by an angle β * only about the z-axis. Optionally, the facets are evenly spaced. The light rays in the light received from the input coupler 550 are repeatedly totally reflected between the TIR face surfaces 531 and 532, bouncing back and forth, and reach and enter the facets 542 of the output coupler 540. The facets 542 are arranged over a relatively extended distance in the x-axis direction, reflect the light rays from the waveguide 530 in the general direction of the minus y-axis, and cause the light to enter the waveguide 630 through an extended output aperture 545 that extends the input aperture 535 in the x direction. The waveguide 630 may be any waveguide configured to receive light from an image generated by the display engine through an input aperture such as the input aperture 535 and project the light received from the waveguide through an output coupling region such as the output coupling region 545 that is substantially extended in a single direction.

[0051] The waveguide 630 is assumed, by way of example, to be similar to the waveguide 30, parallel to the xy plane, and optionally comprises facets 42 and TIR facet surfaces 31 and 32 that are continuous with the face surfaces 531 and 532, respectively. The waveguide 630 expands the image within 545 of the waveguide 530 in the minus y direction and reflects the light received from the waveguide 530 through an output coupling region 536 that extends in both the x and y directions into the EMB 560. The waveguide 630 is assumed to be similar to the waveguide 30 shown in FIG. 1A, but it should be noted that the waveguide 630 may be similar to any of various waveguides, for example, a waveguide 330 (FIG. 2A) or a waveguide 430 (FIG. 3A) that includes facets and is configured according to an embodiment of the present disclosure.

[0052] Equations (25) and (26) may be chained so as to relate to the desired constraints on the output field of view provided by the waveguide combiner 500 to the EMB 560. The upward and downward light rays propagating within the waveguide 530 with respect to the face surfaces 531 and 532 are represented by vectors v u (530) and v d (530), respectively, as follows. 31) v d (630) = (v u (630) - (2v u (630).n w )n w , where n w is the normal to the face surfaces 531, 532, 31, and 32 within the waveguide combiner 500, and the upward and downward light rays are optionally considered to be moving in the minus and plus z directions, respectively. One of the upward and downward groups of light rays propagating within the waveguide 530 is reflected into the waveguide 630 by the facet 542. By way of example, assume that the v u (530) light ray is reflected into the waveguide 630. Next, since the reflection by the facet 542 does not change the component of the light ray propagation in the z direction, the v u(530) The light enters the waveguide 630 as upward light rays with respect to the face surfaces 31 and 32. Let the upward light ray after entering the waveguide 630 be represented as v u (630). Next, as a result of the reflection of the waveguide 530 by the facet 542 into the waveguide 630, when the light ray is incident on the waveguide 630, the light ray v u (630) has a direction given by the following equation. 32) v u (630) = v u (530) - 2(v u (530).n f (542) n f After reflection by the face surface 32, the upward v u (630) "becomes" the downward light ray v d (630). Here, 33) v d (630) = v u (630) - 2(v u (630).n w ) n w

[0053] The upward and downward light rays in the waveguide 630 are respectively included in the upward field of view wFOV-U and the downward field of view wFOV-D, as schematically shown in FIGS. 1A, 2A, and 3A. Further, according to one embodiment, the light ray in one of wFOV-U and wFOV-D in the waveguide 630 is selected for reflection into the EMB 560 by the facet 42 passing through the output coupling region 536 in the output field of view O-FOV. The desired constraints on the light rays in the O-FOV may be propagated backward to match the tilt angles β and β * characterizing the facets 42 and 542 in the waveguides 30 and 530.

[0054] In the description and claims of this application, each of the verbs "comprise", "include", and "have", and their conjugates, is used to indicate that one or more of the verb's objects are not necessarily a complete list of the components, elements, or parts of one or more of the verb's subjects.

[0055] The description of the embodiments of the present disclosure in this application is provided by way of example and is not intended to limit the scope of the present disclosure. The described embodiments include different features, and not all of them are required in all embodiments. Some embodiments utilize only some of the features or possible combinations of features. Variations of the described embodiments of the present disclosure and embodiments including different combinations of the features mentioned in the described embodiments will be contemplated by those skilled in the art. The scope of the present invention is limited only by the claims.

Claims

1. An optical waveguide combiner, Normal "n" w A first waveguide including first and second parallel internal total reflection face surfaces having the same, an input aperture through which light enters the first optical waveguide, an output coupling configuration associated with an output coupling region, extending the input aperture in at least one direction, and through which light entering the first optical waveguide exits the first optical waveguide, Embedded in the first waveguide, n w And a plurality of parallel facets having a facet tilt angle β between the normal "n f " with respect to the facet, and an output coupler including the plurality of parallel facets, wherein the facet propagates along the first waveguide and reflects the light incident on the facet to the outside through the output coupling region. An output coupler, wherein the facet has, a facet wavelength band for each laser oscillation band of at least one laser oscillation band of light provided by a laser including a laser oscillation band and wavelengths of light in a wavelength range where the laser oscillation band is expected to change, a reflectance angle range that propagates in the first optical waveguide and exhibits a first reflectance with respect to light having a wavelength in the facet wavelength band that is incident on the facet at an incident angle in a first range, a transmittance angle range that propagates in the first optical waveguide and exhibits a second reflectance lower than the first reflectance with respect to light having a wavelength in the facet wavelength band that is incident on the facet at an incident angle in a second range, and a through-angle transmittance range having a high transmittance with respect to natural light incident on the facet at an incident angle in a third range, where the third range overlaps the first range and is wider than the first range, (90° - γ) > β, γ > θ c where γ is n w and represents the angle between the light ray that propagates through the first waveguide and the output coupler reflects light outward from the first waveguide through the output coupling region and the incident direction of the light ray on the face surface, and θ c represents the critical angle of the first waveguide with respect to light having a wavelength within the facet wavelength band. The tilt angle β satisfies the constraint (θ c + α + ) / 2 < β < (30° + α - / 3), where α + and α - are angles in a plane perpendicular to the face plane and the facet, and the normal to the face plane coincides with the direction in which the facet reflects incident light outward from the first waveguide, α + is larger than α - and is positive when rotated clockwise with respect to the normal and negative when rotated counterclockwise, α + and α - respectively determine the minimum and maximum values of γ that define the field of view wFOV of the light propagating in the first waveguide. wherein the reflectance angle range is over the range of the incident angle φ of (β - α + ) ≤ φ ≤ (β - α - ); wherein the transmittance angle range is (3β - α + ) ≤ φ ≤ (3β - α - ), and the waveguide combiner is over the range of the incident angle φ.

2. The optical waveguide combiner according to claim 1, wherein an average reflectance with respect to the incident angle in the reflectance angle range and the wavelength in the facet wavelength band is between 9% and 11%.

3. The optical waveguide combiner according to claim 1 or 2, wherein an angular width of the reflectance angle range is equal to 18°.

4. The optical waveguide combiner according to any one of claims 1 to 3, wherein the reflectance angle range has a lower limit of 26°.

5. The optical waveguide combiner according to any one of claims 1 to 4, wherein an average reflectance with respect to the incident angle in the transmittance angle range and the wavelength in the facet wavelength band is 5% or less.

6. The optical waveguide combiner according to any one of claims 1 to 5, wherein an angular width of the transmittance angle range is equal to 18°.

7. The optical waveguide combiner according to any one of claims 1 to 6, wherein the transmittance angle range has a lower limit of 66°.

8. The optical waveguide combiner according to any one of claims 1 to 7, wherein the at least one laser oscillation band includes at least one or any combination of laser oscillation bands of red, green, and blue.

9. The waveguide combiner according to any one of claims 1 to 8, wherein the maximum value of the transmittance in the through-angle transmittance range is 85% or more.

10. The waveguide combiner according to any one of claims 1 to 9, wherein the angular width of the through-angle transmittance range is equal to 40°.

11. The waveguide combiner according to any one of claims 1 to 10, wherein the through-angle transmittance range has a lower limit of 15°.

12. A second waveguide having a second input aperture, and a second output coupling region through which light received through the second input aperture exits the second waveguide and enters the first waveguide, the second output coupling region being expanded with respect to the second input aperture in a direction different from at least one direction in which the output aperture of the first waveguide is expanded. The waveguide combiner according to any one of claims 1 to 11.

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