具体实施方式：
[0022]Embodiments consistent with the present disclosure will be described with reference to the accompanying drawings, which are merely examples for illustrative purposes and are not intended to limit the scope of the present disclosure. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or similar parts, and a detailed description thereof may be omitted.
[0023]Further, in the present disclosure, the disclosed embodiments and the features of the disclosed embodiments may be combined. The described embodiments are some but not all of the embodiments of the present disclosure. Based on the disclosed embodiments, persons of ordinary skill in the art may derive other embodiments consistent with the present disclosure. For example, modifications, adaptations, substitutions, additions, or other variations may be made based on the disclosed embodiments. Such variations of the disclosed embodiments are still within the scope of the present disclosure. Accordingly, the present disclosure is not limited to the disclosed embodiments. Instead, the scope of the present disclosure is defined by the appended claims.
[0024]As used herein, the terms “couple,”“coupled,”“coupling,” or the like may encompass an optical coupling, a mechanical coupling, an electrical coupling, an electromagnetic coupling, or any combination thereof. An “optical coupling” between two optical elements refers to a configuration in which the two optical elements are arranged in an optical series, and a light output from one optical element may be directly or indirectly received by the other optical element. An optical series refers to optical positioning of a plurality of optical elements in a light path, such that a light output from one optical element may be transmitted, reflected, diffracted, converted, modified, or otherwise processed or manipulated by one or more of other optical elements. In some embodiments, the sequence in which the plurality of optical elements are arranged may or may not affect an overall output of the plurality of optical elements. A coupling may be a direct coupling or an indirect coupling (e.g., coupling through an intermediate element).
[0025]The phrase “at least one of A or B” may encompass all combinations of A and B, such as A only, B only, or A and B. Likewise, the phrase “at least one of A, B, or C” may encompass all combinations of A, B, and C, such as A only, B only, C only, A and B, A and C, B and C, or A and B and C. The phrase “A and/or B” may be interpreted in a manner similar to that of the phrase “at least one of A or B.” For example, the phrase “A and/or B” may encompass all combinations of A and B, such as A only, B only, or A and B Likewise, the phrase “A, B, and/or C” has a meaning similar to that of the phrase “at least one of A, B, or C.” For example, the phrase “A, B, and/or C” may encompass all combinations of A, B, and C, such as A only, B only, C only, A and B, A and C, B and C, or A and B and C.
[0026]When a first element is described as “attached,”“provided,”“formed,”“affixed,”“mounted,”“secured,”“connected,”“bonded,”“recorded,” or “disposed,” to, on, at, or at least partially in a second element, the first element may be “attached,”“provided,”“formed,”“affixed,”“mounted,”“secured,”“connected,”“bonded,”“recorded,” or “disposed,” to, on, at, or at least partially in the second element using any suitable mechanical or non-mechanical manner, such as depositing, coating, etching, bonding, gluing, screwing, press-fitting, snap-fitting, clamping, etc. In addition, the first element may be in direct contact with the second element, or there may be an intermediate element between the first element and the second element. The first element may be disposed at any suitable side of the second element, such as left, right, front, back, top, or bottom.
[0027]When the first element is shown or described as being disposed or arranged “on” the second element, term “on” is merely used to indicate an example relative orientation between the first element and the second element. The description may be based on a reference coordinate system shown in a figure, or may be based on a current view or example configuration shown in a figure. For example, when a view shown in a figure is described, the first element may be described as being disposed “on” the second element. It is understood that the term “on” may not necessarily imply that the first element is over the second element in the vertical, gravitational direction. For example, when the assembly of the first element and the second element is turned 180 degrees, the first element may be “under” the second element (or the second element may be “on” the first element). Thus, it is understood that when a figure shows that the first element is “on” the second element, the configuration is merely an illustrative example. The first element may be disposed or arranged at any suitable orientation relative to the second element (e.g., over or above the second element, below or under the second element, left to the second element, right to the second element, behind the second element, in front of the second element, etc.).
[0028]When the first element is described as being disposed “on” the second element, the first element may be directly or indirectly disposed on the second element. The first element being directly disposed on the second element indicates that no additional element is disposed between the first element and the second element. The first element being indirectly disposed on the second element indicates that one or more additional elements are disposed between the first element and the second element.
[0029]The term “processor” used herein may encompass any suitable processor, such as a central processing unit (“CPU”), a graphics processing unit (“GPU”), an application-specific integrated circuit (“ASIC”), a programmable logic device (“PLD”), or any combination thereof. Other processors not listed above may also be used. A processor may be implemented as software, hardware, firmware, or any combination thereof.
[0030]The term “controller” may encompass any suitable electrical circuit, software, or processor configured to generate a control signal for controlling a device, a circuit, an optical element, etc. A “controller” may be implemented as software, hardware, firmware, or any combination thereof. For example, a controller may include a processor, or may be included as a part of a processor.
[0031]The term “non-transitory computer-readable medium” may encompass any suitable medium for storing, transferring, communicating, broadcasting, or transmitting data, signal, or information. For example, the non-transitory computer-readable medium may include a memory, a hard disk, a magnetic disk, an optical disk, a tape, etc. The memory may include a read-only memory (“ROM”), a random-access memory (“RAM”), a flash memory, etc.
[0032]The term “film,”“layer,”“coating,” or “plate” may include rigid or flexible, self-supporting or free-standing film, layer, coating, or plate, which may be disposed on a supporting substrate or between substrates. The terms “film,”“layer,”“coating,” and “plate” may be interchangeable.
[0033]The wavelength ranges, spectra, or bands mentioned in the present disclosure are for illustrative purposes. The disclosed optical device, system, element, assembly, and method may be applied to a visible wavelength band, as well as other wavelength bands, such as an ultraviolet (“UV”) wavelength band, an infrared (“IR”) wavelength band, or a combination thereof. The term “substantially” or “primarily” used to modify an optical response action, such as transmit, reflect, diffract, block or the like that describes processing of a light means that a major portion, including all, of a light is transmitted, reflected, diffracted, or blocked, etc. The major portion may be a predetermined percentage (greater than 50%) of the entire light, such as 100%, 98%, 90%, 85%, 80%, etc., which may be determined based on specific application needs.
[0034]It is a desirable feature that an artificial reality device supports custom prescription lenses for the ametropic population. Additional sought-after features may also include an aesthetic appearance, a light weight, and a high power efficiency. To achieve these features in a balanced manner, integration of a waveguide with a custom ophthalmic (or prescription) lens (or lens function) in a scalable and robust fabrication process is desirable for artificial reality applications. The present disclosure provides an integration of a custom prescription lens (or lens function) with a waveguide in artificial reality devices. The disclosed technical solutions may provide simple manufacturing processes for integrating the custom prescription lens with the waveguide.
[0035]FIG. 1 illustrates an x-z sectional view of an optical system 100, according to an embodiment of the present disclosure. As shown in FIG. 1, the optical system 100 may include a light source assembly 105, a waveguide 120, and a prescription (Rx) lens 150 printed (e.g., three-dimensional (“3D”) printed) on the waveguide 120. The light source assembly 105 and the waveguide 120 together may form a waveguide display (or waveguide display system), such as a geometric waveguide display including one or more refractive and/or reflective type couplers, a diffractive waveguide display including one or more diffractive type couplers, a mixed waveguide display including one or more refractive and/or reflective type couplers and one or more diffractive type couplers.
[0036]In the embodiment shown in FIG. 1, the waveguide 120 may include a substrate 110 and a plurality of micro-structures 115 substantially entirely embedded within the substrate 110. The substrate 110 may be referred to as the main body of the waveguide 120. The substrate 110 may be formed based on a suitable material, such as a plastic material having a refractive index of 1.53, which may provide an increased shock resistance and a reduced coefficient of thermal expansion (“CTE”) mismatch. The substrate 110 may be formed via a suitable method, such as injection molding. The substrate 110 may have a first surface or side 110-1 facing an eye-box region 160 of the optical system 100, and a second surface or side 110-2 opposite to the first surface or side 110-1 and facing a real-world environment (e.g., the sun 170). The first surface 110-1 may be referred to as a back surface, and the second surface 110-2 may be referred to as a front surface.
[0037]The substrate 110 may also have a third surface or side 110-3, and a fourth surface or side 110-4 opposite to the third surface or side 110-3. The third surface 110-3 and the fourth surface 110-4 may be located between the first surface 110-1 and the second surface 110-2. In the embodiment shown in FIG. 1, the third surface 110-3 may be an inclined surface located at a longitudinal end of the substrate 110 (or the waveguide 120), connecting the first surface 110-1 and the second surface 110-2. In some embodiments, both the first surface 110-1 and the second surface 110-2 of the substrate 110 may be flat surfaces. In some embodiments, the first surface 110-1 may be a curved surface.
[0038]In some embodiment, the light source assembly 105 may include a light source (e.g., a display element, not shown) and a collimating lens (not shown). In the embodiment shown in FIG. 1, the light source assembly 105 may be disposed at the third surface 110-3 of the substrate 110, and may output an image light 130 representing a virtual image toward the third surface 110-3. The image light 130 may be a divergent image light including a plurality of bundles of parallel rays having different incidence angles at the third surface 110-3. For discussion purposes, FIG. 1 shows a single ray in a bundle of parallel rays included in the image light 130.
[0039]The third surface 110-3 may also be referred to as a light inputting surface where the image light 130 is input into the waveguide 120. The inclination of the third surface 110-3 may be configured to the couple the image light 130 output from the light source assembly 105 into a total internal reflection (“TIR”) path inside the substrate 110. In some embodiments, with the inclined surface 110-3, a separate in-coupling element may not be needed. Although the light source assembly 105 is shown as being disposed in direct contact with the third surface 110-3 in FIG. 1, in some embodiments, the light source assembly 105 may be disposed adjacent the third surface 110-3 and spaced apart from the third surface 110-3. In some embodiments, although not shown, a separate in-coupling element may be coupled to the waveguide 120, such as adjacent the third surface 110-3, to couple the image light 130 output from the light source assembly 105 into a TIR path inside the substrate 110.
[0040]The micro-structures 115 may be substantially entirely embedded within the substrate 110 between the first surface 110-1 and the second surface 110-2. The micro-structures 115 may include one or more folding or redirecting structures 115-1 configured to redirect the image light 130 to propagate inside the substrate 110, and one or more out-coupling structures 115-2 configured to couple the image light 130 out of the substrate 110. For discussion purposes, the term “micro-structure” as used herein may encompass a structure having micrometer (μm) scale dimensions and/or a structure having millimeter (mm) scale dimensions (e.g., a few millimeters). The micro-structures 115 may include reflectors, mirrors, prisms, or gratings, etc.
[0041]For illustrative and discussion purposes, reflectors (also referred to as 115) are used in the embodiment shown in FIG. 1 as examples of micro-structures (out-coupling structures and folding structures). The reflectors 115 may include one or more flat reflectors, and one or more curved reflectors (e.g., concave reflectors) disposed at suitable locations within the substrate 110. For example, as shown in FIG. 1, each folding structure 115-1 may include a curved reflector (also referred to as 115-1), and each folding structure 115-2 may include a flat reflector (also referred to as 115-2). For discussion purposes, FIG. 1 shows one curved reflector 115-1, and three flat reflectors 115-2 arranged in parallel. Any suitable number of curved reflectors and flat reflectors may be included, depending on application needs.
[0042]The flat reflectors 115-2 may be located between the curved reflector (e.g., concave reflector) 115-1 and the third surface 110-3. For example, the flat reflectors 115-2 may be substantially entirely embedded within a relatively central portion of the substrate 110, and the curved reflector (e.g., concave reflector) 115-1 may be substantially entirely embedded at a side of the flat reflectors 115-2 in the longitudinal direction of the substrate 110. The reflectors 115 may provide a substantially high reflection for the image light incident onto the reflectors 115, thereby providing a high light efficiency (e.g., 10-15%). The reflectors 115 may also provide a high color uniformity to the image light incident onto the reflectors 115.
[0043]It is understood that the curved reflector 115-1 is an example of the folding structure. In some embodiments, other types of folding structure (e.g., prism, grating) may replace the curved reflector 115-1. Although one curved reflector is shown in FIG. 1, in some embodiments, multiple curved reflectors 115-1 may be substantially entirely embedded at multiple locations within the substrate 110. It is understood that the flat reflectors 115-2 are examples of the out-coupling structures that may be substantially entirely embedded within the substrate 110. Other types of out-coupling structures may replace the flat reflectors 115-2.
[0044]The waveguide 120 may guide the image light 130 to propagate from the third surface 110-3 toward the first surface 110-1 where the prescription (Rx) lens 150 is disposed. As shown in FIG. 1, the image light 130 may first propagate inside the substrate 110 toward the curved reflector 115-1 via TIR at the second surface 110-2. Thus, the second surface 110-2 may also be referred to as a TIR light reflecting surface. The curved reflector 115-1 may reflect the image light 130 back to the second surface 110-2 as an image light 131, which may be totally internally reflected at the second surface 110-2 toward to the flat reflectors 115-2. The flat reflectors 115-2 may be configured to couple the image light 131 received from the second surface 110-2 out of the substrate 110 as a plurality of output image lights 132 propagating toward the prescription (Rx) lens 150. Thus, the first surface 110-1 of the substrate 110 may also be referred to as a light outputting surface of the waveguide 120.
[0045]It is noted that as the TIR of the image lights 130 and 131 may only occur at the second surface (or the TIR light reflecting surface) 110-2, and may not occur at the first surface (or the light outputting surface) 110-1. The second surface 110-2 may be exposed to an external environment (e.g., a real-world environment). The air is used as an example of the external environment. In some embodiments, instead of being exposed to the air, the second surface 110-2 may be exposed to a medium or material layer that has a lower refractive index than the substrate 110, thereby facilitating the TIR of the image lights 130 and 131 at the second surface 110-2. Further, as the TIR of the image lights 130 and 131 may not occur at the first surface (or the light outputting surface) 110-1, an air gap (or a low refractive index material layer) may be omitted between the first surface (or the light outputting surface) 110-1 and the prescription lens 150. In other words, the first surface 110-1 may be in direct contact with the prescription lens 150, or that the prescription lens 150 may be directly printed onto the first surface 110-1 of the substrate 110 through 3D printing. Thus, the undesirable surface reflection at the first surface 110-1 may be reduced, and the image quality may be improved.
[0046]The prescription lens 150 may focus (or converge) or defocus (or diverge) each output image light 132 as an image light 134 propagating toward the eye-box region 160. A plurality of exit pupils 157 may be located within the eye-box region 160 of the optical system 100. An exit pupil 157 is a region in space where an eye-pupil 158 of an eye 159 of a user is positioned in the eye-box region 160 to receive the image lights 134 representing content of a virtual image output from the light source assembly 105. The prescription lens 150 may provide a suitable optical power for vision correction, e.g., astigmatism, myopia, and/or hyperopia of the eye 159 of the user. The prescription lens 150 may be 3D printed over the first surface 110-1 of the waveguide 120. In some embodiments, the prescription lens 150 may be in direct contact with the substrate 110. For example, as shown in FIG. 1, the prescription lens 150 may have a flat front surface that is in direct contact with the first surface 110-1 of the substrate 110, and a curved back surface that provides the suitable optical power to the output image lights 132. Although the prescription lens 150 in FIG. 1 is shown as a concave lens, the prescription lens 150 may be a convex lens or any other suitable lens. It is noted that in some embodiments, the prescription lens 150 may be replaced by a non-prescription lens that is 3D printed over the first surface 110-1 of the substrate 110.
[0047]In some embodiments, the substrate 110 and the prescription lens 150 may be fabricated based on two different materials having substantially close refractive indices. For example, the two different materials may be a first material having a first refractive index of 1.52 and a second material having a second refractive index of 1.53, a first material having a first refractive index of 1.52 and a second material having a second refractive index of 1.54, a first material having a first refractive index of 1.525 and a second material having a second refractive index of 1.53, a first material having a first refractive index of 1.525 and a second material having a second refractive index of 1.535, a first material having a first refractive index of 1.53 and a second material having a second refractive index of 1.535, etc. The difference between the first refractive index and the second refractive index may be less than or equal to 0.05, 0.1, 0.15, or 0.2, which may be regarded as “substantially close.” In some embodiments, each of the first refractive index and the second refractive index may be any suitable value within a range of [1.52, 1.53], [1.525, 1.535], [1.52, 1.54], [1.53, 1.54], etc.
[0048]In some embodiments, the substrate 110 and the prescription lens 150 may be fabricated based on the same material, such as a plastic material having a refractive index of 1.53. Accordingly, the undesirable surface reflection at the first surface 110-1 of the substrate 110 may be further reduced, and the image quality perceived by the eye 159 may be further improved. In some embodiments, although not shown, a coating layer configured to facilitate the 3D printing of the prescription lens 150 may be disposed on the first surface 110-1 of the substrate 110 before the prescription lens 150 is 3D printed. For example, the coating layer may enhance the adhesion between the prescription lens 150 and the substrate 110, and/or improve the optical quality of the prescription lens 150, etc. In some embodiments, the substrate 110 and the prescription lens 150 may be fabricated based on different materials, and the coating layer disposed therebetween may also function as a refractive index matching layer configured to match the refractive indices of the substrate 110 and the prescription lens 150. For example, the coating layer may be configured to have a first refractive index substantially matching with the refractive index of the substrate 110 at a first interface, a second refractive index substantially matching with the refractive index of the prescription lens 150 at a second interface, and a gradient transition between the first refractive index and the second refractive index within the coating layer between the first interface and the second interface.
[0049]FIGS. 2A and 2B illustrate processes for integrating the prescription lens 105 with the waveguide 120 shown in FIG. 1, according to an embodiment of the present disclosure. As shown in FIG. 2A, the waveguide 120 may be provided. The waveguide 120 may include the substrate 110 and the micro-structures 115 substantially entirely embedded within the substrate 110. As shown in FIG. 2B, after the waveguide 120 is provided, the prescription lens 150 may be 3D printed over the first surface 110-1 of the substrate 110. In some embodiments, the prescription lens 150 may be directly printed (e.g., through 3D printing) over, and may be in direct contact with, the first surface 110-1, without a gap therebetween. As the out-coupling structures (e.g., flat reflectors) 115-2 may be substantially entirely embedded within the substrate 110, the prescription lens 150 may not be in direct contact with the out-coupling structures 115-2.
[0050]In some embodiments, the substrate 110 and the prescription lens 150 may be fabricated based on two different materials having substantially close refractive indices, e.g., substantially close to 1.53. For example, the two different materials may be a first material having a first refractive index of 1.52 and a second material having a second refractive index of 1.53, a first material having a first refractive index of 1.52 and a second material having a second refractive index of 1.54, a first material having a first refractive index of 1.525 and a second material having a second refractive index of 1.53, a first material having a first refractive index of 1.525 and a second material having a second refractive index of 1.535, a first material having a first refractive index of 1.53 and a second material having a second refractive index of 1.535, etc. The difference between the first refractive index and the second refractive index may be less than or equal to 0.05, 0.1, 0.15, or 0.2, which may be regarded as “substantially close.” In some embodiments, each of the first refractive index and the second refractive index may be any suitable value within a range of [1.52, 1.53], [1.525, 1.535], [1.52, 1.54], [1.53, 1.54], etc.
[0051]In some embodiments, the substrate 110 and the prescription lens 150 may be fabricated based on the same material, such as a plastic material having a refractive index of 1.53. In some embodiments, although not shown, a coating layer may be formed over the first surface 110-1, and the prescription lens 150 may be 3D printed over the coating layer.
[0052]In some embodiments, as shown in FIG. 2C, after the prescription lens 150 is 3D printed over the first surface 110-1 of the substrate 110, the light source assembly105 may be assembled with the waveguide 120. In some embodiments, the light source assembly 105 may be disposed at the third surface (or the inclined surface) 110-3 of the substrate 110, where the image light output from the light source assembly 105 is coupled into the waveguide 120. Although the light source assembly 105 is shown as being directly disposed on the third surface (or inclined surface) 110-3, in some embodiments, the light source assembly 105 may be disposed at a distance from the third surface (or inclined surface) 110-3. In some embodiments, the light source assembly 105 may be disposed at any other suitable locations relative to the waveguide 120. In some embodiments, although not shown, after the waveguide 120 is provided, the light source assembly 105 may be assembled with the waveguide 120 before the prescription lens 150 is 3D printed over the first surface 110-1 of the substrate 110.
[0053]FIG. 3 illustrates an x-z sectional view of an optical system 300 including a waveguide 320 integrated with a prescription lens 350, according to an embodiment of the present disclosure. FIGS. 4A-4C illustrate processes for integrating the prescription lens 350 with the waveguide 320 shown in FIG. 3, according to an embodiment of the present disclosure. The optical system 300 shown in FIG. 3 may include structures or elements that are the same as or similar to those included in the optical system 100 shown in FIG. 1. Descriptions of the same or similar structures or elements included in the embodiments shown in FIG. 3 can refer to the above descriptions, including those rendered in connection with the embodiment shown in FIG. 1.
[0054]As shown in FIG. 3, the optical system 300 may include the waveguide 320, and the prescription (Rx) lens 350 printed (e.g., 3D printed) over the waveguide 320. The optical system 300 may also include a light source assembly (not shown, e.g., similar to the light source assembly 105 shown in FIG. 1) coupled with the waveguide 320. The waveguide 320 may include a substrate 310 and a plurality of micro-structures 115. The substrate 310 may be formed based on a suitable material, such as a plastic material having a refractive index of around 1.53. The substrate 310 may have a first surface (or back surface) 310-1 facing the eye-box region 160 of the optical system 300, and a second surface (or front surface) 310-2 opposite to the first surface 310-1. The second surface 310-2 may face the real-world environment (e.g., the sun 170). In some embodiments, the second surface 310-2 of the substrate 310 may be a flat surface. The substance 310 may also have a third surface 310-3, and a fourth surface 310-4 opposite to the third surface 310-3. The third surface 310-3 and the fourth surface 310-4 may be located at the longitudinal direction of the substrate 110, between and connecting the first surface 310-1 and the second surface 310-2.
[0055]As shown in FIG. 3 and FIG. 4A, the substrate 310 may include a plurality of supporting structures 330 formed at a predetermined portion of the first surface 310-1 of the substrate 310. The supporting structures 330 may be protrusions from the first surface (or back surface) 310-1 of the substrate 310, and may have a suitable shape. For example, as shown in FIG. 3 and FIG. 4A, the supporting structures 330 may have a saw teeth shape, and each supporting structure 330 may have a triangle cross section. The remaining first surface 310-1 of the substrate 310 where the supporting structures 330 are not formed may be flat. In some embodiments, the supporting structures 330 may be integrally formed as a part of the substrate 310 at the first surface (or back surface) 310-1 of the substrate 310. For example, the supporting structures 330 and rest of the substrate 310 may be made of the same plastic material with a refractive index of, e.g., around 1.53. In some embodiments, the supporting structures 330 may be separately formed, and may be disposed at (e.g., affixed to) the first surface (or back surface) 310-1 of the substrate 310.
[0056]The micro-structures 115 may include one or more folding or redirecting structures (e.g., curved reflector) 115-1 substantially entirely embedded inside the substrate 310, and one or more out-coupling structures (e.g., flat reflectors) 115-2 disposed at predetermined surfaces of the supporting structures 330 facing the prescription (Rx) lens 350. The predetermined surfaces of the supporting structures 330 facing the prescription (Rx) lens 350 may be parallel surfaces, and the out-coupling structures (e.g., flat reflectors) 115-2 disposed at predetermined surfaces of the supporting structures 330 facing the prescription (Rx) lens 350 may be arranged in parallel. The supporting structures 330 may provide support for the out-coupling structures 115-2 to be formed thereon. In the waveguide 320 shown in FIG. 3, the out-coupling structures 115-2 disposed at predetermined surfaces of the supporting structures 330 are exposed to the air before the prescription (Rx) lens 350 is 3D printed on the waveguide 320, whereas in the waveguide 120 shown FIG. 1, the out-coupling structures 115-2 are substantially entirely embedded in the substrate 110.
[0057]The light source assembly (not shown in FIG. 3) may be disposed at the third surface 310-3 or the fourth surface 310-4 of the substrate 310, and may output the image light 130 toward a light inputting surface of the substrate 310 (or the waveguide 320), similar to the configuration shown in FIG. 1. For discussion purposes, FIG. 3 shows that the third surface 310-3 of the substrate 310 is the light inputting surface of the substrate 310 (or the waveguide 320). The waveguide 320 may guide the image light 130 to propagate from the third surface 310-3 toward the first surface 310-1 where the prescription (Rx) lens 350 is disposed. As shown in FIG. 3, the image light 130 may first propagate inside the substrate 310 toward the curved reflector 115-1 via TIR at the second surface 310-2. Thus, the second surface 310-2 may also be referred to as a TIR light reflecting surface of the waveguide 320 (or the substrate 310). The second surface 310-2 may be exposed to an external environment (e.g., a real-world environment), where the air is used as an example of the external environment. In some embodiments, instead of being exposed to the air, the second surface 310-2 may be exposed to another medium or material layer that has a lower refractive index than the substrate 310 to facilitate the TIR of the image light 130 at the second surface 310-2.
[0058]The curved reflector 115-1 may reflect the image light 130 back to the second surface 310-2 as the image light 131, which may be totally internally reflected at the second surface 310-2 toward to the flat reflectors (out-coupling structures) 115-2. The flat reflectors 115-2 may be configured to couple, via reflection, the image light 131 received from the second surface 310-2 out of the substrate 310 as a plurality of output image lights 332 propagating toward the prescription (Rx) lens 350. Thus, the first surface 310-1 of the substrate 310 may also be referred to as a light outputting surface of the of the waveguide 320 (or the substrate 310). The prescription lens 350 may focus (or converge) or defocus (or diverge) each output image light 332 into an image light 334, which may propagate toward the eye-