Patent Publication Number: US-2022229300-A1

Title: Optical see through (ost) near eye display (ned) system integrating ophthalmic correction

Description:
FIELD OF THE DISCLOSED TECHNIQUE 
     The disclosed technique relates to optical systems in general, and to wearable optical display systems, in particular. 
     BACKGROUND OF THE DISCLOSED TECHNIQUE 
     U.S. Patent Application Publication No.: US 2015/0168730 A1 to Ashkenazi et al. is directed at a user wearable optical display system that provides information in the form of projected light to a user who wears the system without obstructing the user&#39;s field of regard (FOR). The user wearable optical display system includes a user attachment section, a partially transmissive partially reflective lens, and an electro-optical unit. The user attachment section is for detachably mounting the user wearable optical display system to a head of a user. The partially transmissive partially reflective lens, which is coupled with the user attachment section, is configured to be facing at least one eye of the user. The electro-optical unit is coupled with at least one of the user attachment section and the partially transmissive partially reflective lens. The electro-optical unit includes a processor, and a light projection unit. The processor is coupled with the light projection unit. The light projection unit is configured to transmit light beams onto the partially transmissive partially reflective lens. The electro-optical unit is configured to be positioned with respect to the user attachment section such that when the user wearable optical display system is mounted on the user, the electro-optical unit is located at the glabellar region of the user. 
     SUMMARY OF THE PRESENT DISCLOSED TECHNIQUE 
     It is an object of the disclosed technique to provide a novel optical see-through (OST) near-eye display (NED) system, integrating ophthalmic (vision) correction for an eye of a user. The OST NED system includes a partially transmissive partially reflective lens, and an electro-optical unit. The partially transmissive partially reflective lens includes an inner surface characterized by an inner surface radius of curvature exhibiting a first optical power, and an outer surface characterized by an outer surface radius of curvature exhibiting a second optical power. The partially transmissive partially reflective lens is configured to be facing the eye of the user, and to at least partially transmit incoming light of an outward scene to the eye. The electro-optical unit is configured to be optically coupled with the partially transmissive partially reflective lens. The electro-optical unit includes a light display configured to project a light beam image onto the inner surface, so to enable reflection of the light beam image toward the eye. The electro-optical unit is configured to be located at a glabellar region of the user. The first optical power is configured to provide ophthalmic correction with respect to reflected light beam image for viewing by the eye, wherein the second optical power is configured to provide ophthalmic correction with respect to transmitted incoming light from the outward scene for viewing by the eye. 
     In accordance with another embodiment of the disclosed technique there is provided an optical configuration for an optical see-through (OST) eye-tracking system. The optical configuration includes a partially transmissive partially reflective lens, and an electro-optical unit (sub-system). The partially transmissive partially reflective lens is configured to be facing an eye of a user. The electro-optical unit (sub-system) includes an image sensor, configured to acquire at least one image of an eyeball feature of the eye with reflected light from the eye; a first lens; a second lens; a third lens; a fourth lens; a curved mirror; an optical combiner; and a fifth lens. The optical configuration enables the reflected light to travel along an optical path at least partially reflecting from the partially transmissive partially reflective lens, then refracting through the first lens, the second lens, the third lens, and the fourth lens, then reflecting from the curved mirror and refracting again in reverse order through the fourth lens and then through the third lens, then at least partially passing through the optical combiner, refracting through the fifth lens, and impinging on the image sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
         FIG. 1  is a schematic illustration of an optical see-through (OST) near-eye display (NED) system, integrating ophthalmic correction for an eye of a user, constructed and operative in accordance an embodiment of the disclosed technique; 
         FIG. 2  is a schematic illustration of the OST NED system of  FIG. 1  in an exploded view; 
         FIG. 3A  is a schematic block diagram of a basic configuration of the electro-optical unit of OST NED system, constructed and operative in accordance with the embodiment of the disclosed technique; 
         FIG. 3B  is a schematic block diagram of an accessorized configuration of the electro-optical unit of OST NED system, constructed and operative in accordance with the embodiment of the disclosed technique; 
         FIG. 4  is a schematic illustration showing OST NED system of  FIGS. 1 and 2  in a mounted configuration on a user; 
         FIG. 5  is a schematic diagram of a light path through an optical module of electro-optical unit of OST, constructed and operative in accordance with the embodiment of the disclosed technique; 
         FIG. 6A  is a schematic block diagram of a basic configuration of an electro-optical unit of OST eye-tracking system, constructed and operative in accordance with another embodiment of the disclosed technique; 
         FIG. 6B  is a schematic block diagram of an accessorized configuration of an electro-optical unit of OST eye-tracking system, constructed and operative in accordance with the embodiment of the disclosed technique; 
         FIG. 7  is a schematic diagram of a light path through an optical module of electro-optical unit of OST eye-tracking system, constructed and operative in accordance with the embodiment of the disclosed technique; 
         FIG. 8A  is a schematic illustration showing the principles of the non-pupil forming optical design upon which OST NED system  100  and OST NED eye-tracking system  200  are based, in accordance with the embodiments of the disclosed technique; 
         FIG. 8B  is a schematic illustration showing the a simplified geometric representation of a human eye, looking at a projected image focused at a far distance, and generated by a non-forming exit pupil display system design upon which OST NED system  100  and OST NED eye-tracking system  200  are based, in accordance with the embodiments of the disclosed technique; 
         FIG. 8C  is a schematic illustration showing determination of the distance, d, of the system exit pupil to the eye pupil, according to the disclosed technique; 
         FIG. 9B  is a schematic illustration showing a pantoscopic angle, a wrap angle, and a roll angle, according to the principles of the disclosed technique; 
         FIG. 10A  is a schematic illustration showing a front-facing detailed partial view of characteristic design constraints of the systems of the disclosed technique; and 
         FIG. 10B  is a schematic illustration showing a detailed side partial view of characteristic design constraints of the systems of the disclosed technique. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The disclosed technique overcomes the disadvantages of the prior art by providing a free-space optical see-through (OST) near-eye display (NED) system integrating ophthalmic correction for an eye of a user of the system. The OST NED system includes a partially transmissive partially reflective lens, and an electro-optical unit. The partially transmissive partially reflective lens includes an inner surface, and an outer surface. The inner surface is characterized by an inner surface radius of curvature exhibiting a first optical power, and an outer surface characterized by an outer surface radius of curvature exhibiting a second optical power. The partially transmissive partially reflective lens is configured to be facing an eye of the user, and further configured to at least partially transmit incoming light of an outward scene to that eye. The electro-optical unit is configured to be optically coupled with the partially transmissive partially reflective lens. The electro-optical unit includes a light display configured to project a light beam image onto the inner surface, so as to enable reflection of the light beam image toward the eye. The electro-optical unit is configured to be located at a glabellar region of the user. The first optical power of the inner surface is configured to provide ophthalmic correction with respect to the reflected light beam image for viewing by the eye, and the second optical power is configured to provide ophthalmic correction with respect to transmitted incoming light from the outward scene for viewing by the eye. 
     According to another aspect of the disclosed technique, there is thus provided a free-space optical configuration for an OST eye-tracking system that includes a partially transmissive partially reflective lens, and an electro-optical sub-system. The electro-optical sub-system includes an images sensor, a first lens, a second lens, a third lens, a fourth lens, a curved mirror, an optical combiner, and a fifth lens. The partially transmissive partially reflective lens is configured to be facing an eye of a user. The image sensor is configured to acquire at least one image of an eyeball feature of the eye with reflective light from the eye. The optical configuration enables reflected the reflected light to travel along an optical path at least partially reflecting from the partially transmissive partially reflective lens, then refracting through the first lens, the second lens, the third lens, the fourth lens, then reflecting from the curved mirror and refracting again in reverse order through the fourth lens and then through the third lens, then at least partially passing through the optical combiner, refracting through the fifth lens, and impinging on the image sensor. 
     Reference is now made to  FIGS. 1 and 2 .  FIG. 1  is a schematic illustration of an optical see-through (OST) near-eye display (NED) system, integrating ophthalmic correction for an eye of a user, generally referenced  100 , constructed and operative in accordance an embodiment of the disclosed technique.  FIG. 2  is a schematic illustration of the OST NED system of  FIG. 1  in an exploded view. OST NED system  100  includes an electro-optical unit  102  and at least one partially transmissive partially reflective lens  108 . Electro-optical unit  102  includes an electronics module  104  ( FIG. 2 ), and an optical module  106 . 
     Optical module  106  is configured to be at least partially housed in an optical housing  110  ( FIG. 2 ). Electro-optical unit  102  is configured to be mechanically and optically coupled such to have fixed position and orientation with respect to at least one partially transmissive partially reflective lens  104  (i.e., and vice-versa). 
       FIGS. 1 and 2  show a user attachment section  112  that enables the detachable coupling of OST NED system  100  to a user (i.e., to be worn by a user). User attachment section  112  is typically embodied in the form of a frame (e.g., resembling eye glasses) and includes two temples  114 R and  114 L (interchangeably “stem portions”), a bridge  114 B (“bridge portion”) that couples between stem portions  114 L and  114 R, and a nosepiece  116 . The terms “user attachment section” and “frame” are herein interchangeable and refer to a device, object or group of objects configured and operative to couple with a wearer of OST NED system  100 .  FIGS. 1 and 2  illustrate two partially transmissive partially reflective lenses, namely, a partially transmissive partially reflective lens  108 R (denoted interchangeably herein simply “lens”, “combiner”, “optical combiner”), and partially transmissive partially reflective lens  108 L, each configured to be facing a different eye of a user wearing OST NED system  100 . 
     Reference is now further made to  FIGS. 3A, 3B, 4, and 5 .  FIG. 3A  is a schematic block diagram of a basic configuration of the electro-optical unit of OST NED system, constructed and operative in accordance with the embodiment of the disclosed technique.  FIG. 3B  is a schematic block diagram of an accessorized configuration of the electro-optical unit of OST NED system, constructed and operative in accordance with the embodiment of the disclosed technique.  FIG. 4  is a schematic illustration showing OST NED system of  FIGS. 1 and 2  in a mounted configuration on a user.  FIG. 5  is a schematic diagram of a light path through an optical module of electro-optical unit of OST, constructed and operative in accordance with the embodiment of the disclosed technique.  FIG. 3A  illustrates a basic configuration of electro-optical unit  102  of OST NED system  100 , denoted by  102   1 . 
     Electro-optical unit  102   1  includes an electronics module  104   1 , and optical module  106 . Electronics module  104   1  includes a light display  130 . Optical module  106  includes optical elements, collectively referenced  132  that are particularized in greater detail in  FIG. 5 . Light display  130  of electronics module  104   1  along with optical elements  132  of optical module  106  form a light projector that is configured and operative to produce, irradiate, and project a light beam image (not shown) onto at least one partially transmissive partially reflective lens  108  (i.e., at least one of  108 R and  108 L). Optical elements  132  are configured and operative to convey and project the image produced by light display  130  onto partially transmissive partially reflective lens  108 , as will be described in greater detail below in conjunction with  FIGS. 4 and 5 . 
       FIG. 3B  illustrates an accessorized configuration of electro-optical unit  102  of OST NED system  100 , denoted by  102   2 , having additional components with respect to the basic configuration of electro-optical unit configuration  102   1 , shown in  FIG. 3A . Electro-optical unit  102  includes an electronics module  104   2 , and optical module  106  (i.e., identical to that in  FIG. 3A ). According to the accessorized configuration, electronics module  104   2  includes light display  130  (i.e., identical to that in  FIG. 3A ), and may optionally include at least one of a processor  134 , a memory device  136 , a user interface  138 , and a communication module  140 . Processor  134  is configured and operative to be communicatively coupled (i.e., wired, wirelessly thereby enabling to at least one of send and receive signals and data) to light display  130 , memory device  136 , user interface  138 , and communication module  140  (interconnections not shown in  FIG. 3B ). Electro-optical unit  102   2  is electrically powered by a power source (not shown). The power source may be embodied in the form of at least one battery that may be housed in user attachment section  112 , such as in stem portions  114 R and  114 L. Alternatively or additionally, solar arrays (not shown) may be integrated with frame  112  and/or with partially transmissive partially reflective lens  108  (e.g., by employing transparent solar arrays, known in the art (e.g., solar window technology)). 
     With reference to  FIG. 4 , frame  112  ( FIGS. 1 and 2 ) enables detachable mounting of OST NED  100  system to a head  12  of user  10 . Particularly,  FIG. 4  shows OST NED system  100  in a mounted configuration on head  12  of user  10  (i.e., being worn). Temples  114 R,  114 L, and nosepiece  116  are constructed and operative to support OST NED system  100 , on the ears  14 R,  14 L and nose  16  (respectively) of user  10  ( FIG. 4 ). Partially transmissive partially reflective lenses  108 R and  108 L are coupled with frame  112 , and each configured to be facing eyes  18 R and  18 L (respectively) of user  10  wearing OST NED system  100 . Specifically, lens  108 R is configured to be facing a right eye  18 R, and lens  108 L is configured to be facing a left eye  18 L of user  10 . When OST NED system  100  is in a mounted configuration on user  10 , user attachment section  112  is configured to enable electro-optical unit  102  including housing  110  to be positioned within a glabellar region  20  of user&#39;s head  12 , as shown in  FIG. 4 . Glabellar region  20  is defined herein as an area covering the glabella (also known as the mesophryon), which, in humans, is an anatomical area between the eyebrows and above the nose  16 . 
     Optical elements (components)  132  ( FIGS. 3A and 3B ) of optical module  106  as shown in  FIG. 4  are further described in greater detail in conjunction with  FIG. 5  that illustrates a schematic diagram of a light path through optical module  106  of electro-optical unit  102  of OST NED  100 . Electro-optical unit  102  (i.e.,  102   1  and  102   2 ) includes light display  130 , and optical elements  132  of optical module  106  that include a first lens  140  ( FIGS. 5 ), a reflector  142 , a second lens  146 , a third lens  148 , a fourth lens  150 , a curved mirror  152 , and a partially transmissive partially reflective element  154 . Further shown in  FIG. 5  is partially transmissive partially reflective lens  108 , and aperture  156  (herein denoted interchangeably as “light display exit pupil”), and an intermediate image (not shown) that forms at an intermediate image plane  144  between first lens  140  and second lens  146 . In general, each partially transmissive partially reflective lens  108  includes an inner surface  160  (herein interchangeably denoted “user-facing surface”), and an outer surface  162  (herein interchangeably denoted “outward-facing surface”). Inner surface  160  is characterized by an inner surface radius of curvature r i  exhibiting a first optical power P i . Outer surface  162  is characterized by an outer surface radius of curvature r o  exhibiting a first optical power P o . In a mounted configuration of OST NED system  100  on user  10 , inner surface  160  is configured to be facing an eye  14 (R,L) of user  10  and outer surface  162  is configured to be facing an outward scene directed away from user  10 . Partially transmissive partially reflective lens  108  is configured to at least partially transmit incoming light of an outward scene, impinging on outer surface  162  and exiting from inner surface  160  toward eye  14 (R,L) of user  10 . 
     Optical elements  132  of optical module  106 , light display  130  of electronics module  104 , and partially transmissive partially reflective lens  108  form an optical arrangement (herein interchangeably “optical configuration”) allowing light rays to propagate as illustrated in  FIGS. 4 and 5 . The optical configuration enables light display  130  to project a light beam image (not shown) onto partially transmissive partially reflective lens  108  (i.e., at least one of  108 R and  108 L) along an optical path represented by light rays  158 . Specifically, light display  130  is configured and operative to produce and irradiate the light beam image (i.e., light encoded data defined as light containing data) that propagates along the optical path described as follows. Light display  130  produces the light beam that impinges onto first main reflector  154 , which in turn is configured to reflect the light beam toward third lens  148 , which in turn is configured to refract the light beam and convey it toward fourth lens  150 , which in turn is configured to refract the light beam and convey it toward curved mirror  152 . Curved mirror  152  is configured to reflect the light beam back toward fourth lens  150 , which in turn is configured to refract the light beam again in reverse order and convey it toward third lens  148 . Third lens  148  is configured to refract the light beam and convey it toward second lens  146 , which in turn is configured to refract the light beam and convey it toward auxiliary reflector  142 . Auxiliary reflector  142  is configured to fold the light beam (not shown) and reflect it toward first lens  140 . First lens  140  is configured to refract the light beam and convey it toward partially transmissive partially reflective lens  108 . Partially transmissive partially reflective lens  108  is configured to reflect the light beam toward at least one eye  18 R,  18 L of user  10 . 
     Inner surface  160  of partially transmissive partially reflective lens  108 , which is characterized by inner surface radius of curvature r i  exhibiting a first optical power P i , is configured to provide ophthalmic correction with respect to the reflected light beam for viewing by at least one eye of the user. Generally, each partially transmissive partially reflective lens  108   1  and  108   2  that is associated with a particular eye (i.e.,  18 R,  18 L) of user  10  (i.e., associated in the sense of configured to be facing that eye in a mounted configuration of OST NED system  100 ), is configured to provide a corresponding ophthalmic correction with respect to its associated eye. The characteristics of each partially transmissive partially reflective lens are tailored to the specific ophthalmic correction required for each associated eye of the user. Accordingly, each partially transmissive partially reflective lens  108   1  and  108   2  is configured to exhibit its corresponding inner surface radius of curvature r i(1)  and r i(2) , respectively, and its corresponding first optical power P i(1) , P i(2) , respectively. Partially transmissive partially reflective lenses  108   1  and  108   2  may have the same characteristics (i.e., inner surface radius of curvature, and optical power), or alternatively, different characteristics with respect to each other. 
     The optical path of the light beams (i.e., exemplified as rays  158  in  FIG. 5 ) originate from light display  130 , reflect off partially transmissive partially reflective element  154 , pass through lenses  148  and  150 , reflect from curved mirror  152 , pass through (i.e., refract by) lenses  150  and  148  again (i.e., and in reverse order), then pass through lenses  146  and  140 , and in due course, reflect from inner surface  160  of partially transmissive partially reflective lens  108  toward an eye ( 18 R,  18 L) of user  10 . Intermediate image forms at intermediate image plane  144  along the optical path between first lens  140  and second lens  146 , and particularly between auxiliary reflector  142  and second lens  146 . Specifically, second lens  146  is configured and operative to be positioned along the optical path and have optical characteristics (e.g., optical power) that allows intermediate image to form at intermediate image plane  144  located perpendicularly along the optical path between itself (second lens  146 ) and first lens  140 . Auxiliary reflector  142  (e.g., fold mirror) facilitates in the minimization of the spatial dimensions of electro-optical unit  102  so that it may substantially meet the spatial constraints of being located substantially at glabellar region  20  of user  10 . 
     In accordance with the disclosed technique, OST NED system  100  is configured and operative to generate and to project light encoded data (i.e., light containing data) in the form of a light representation (e.g., an image, graphical information, symbology, etc.) onto partially transmissive partially reflective lens  108 , the latter of which is configured and operative concurrently, to at least partially reflect the light (i.e., which is encoded with data or that contains information) toward the eyes ( 18 R,  18 L) of user  10  ( FIG. 4 , shown as an example for right eye  18 R) who wears the system, as well as to at least partially transmit incoming light from a scene in the user&#39;s field of regard (i.e., outward-facing environment with respect to the user). Partially transmissive partially reflective lens  108  essentially acts as an optically collimated transparent (or translucent) display enabling the overlay of images and other data projected onto its surfaces (i.e., a combiner), without obstructing a scene viewed by the user. 
     In accordance with the disclosed technique, OST NED system  100  is configured and operative to generate and to project light encoded data (i.e., light containing data) in the form of a light representation (e.g., an image, graphical information). In the basic configuration shown in  FIG. 3A , light display  130  is configured to receive data (e.g., image information from an external source (not shown)) and to generate, irradiate, and project light encoded data in the form of a light representation and to convey the light encoded data toward optical elements  132  of electro-optical unit  102 . Alternatively, light display  130  incorporates an internal memory unit (not shown) configured and operative to store data (e.g., image information), which light display  130  uses to generate the light encoded data. 
     In the accessorized configuration shown in  FIG. 3B , processor  134  ( FIG. 3B ) is configured and operative to produce, process, and modify, data (not shown), for example in the form of electrical signals that convey image data and/or graphical representation data and to provide (communicate) this data to light display  130 . Memory device  136  is configured and operative to store this image data for manipulation (e.g., by processing and modification) and for retrieval (e.g., by processor, by light display  130 ). Memory device  136  is generally embodied in the form of non-volatile memory (e.g., read-only memory (ROM), flash memory, magnetic storage devices (e.g., hard disks), ferroelectric read-only memory (F-RAM), optical memory (e.g., optical discs), etc.) as well as volatile memory (e.g., RAM). 
     Light display  130  is configured and operative to receive data, generate light encoded data based on the data received therefrom, irradiate and project the light encoded data toward partially transmissive partially reflective element  154 . The terms “light encoded data” and “light encoded information” used interchangeably herein, generally refer to light that is encoded with data, and more specifically, to light that contains information that is exhibited in at least one domain, such as in the spectral domain (i.e., wavelengths-colors), in the spatial domain (e.g., in one or multi-dimensions, such as a one-dimensional (1-D) image (e.g., a point, or pixel), a two-dimensional (2-D) image, a three-dimensional (3-D) image), in the temporal domain (e.g., changing-frame rate), in the polarization domain (e.g., by using light polarization encoding techniques), and the like. For example, in case where the encoded data is 2-D color video, the light encoded data that is generated and projected exhibits change in the temporal domain (i.e., as a succession of image frames), in the spatial domain (i.e., as changes in the image space—as in the case of moving objects within the image frames), in the color domain (i.e., representing the different colors of objects in the images), as well in the light intensity domain (i.e., representing, for example the luminance). 
     Particularly, light display  130  receives data (e.g., externally, from an internal memory device, from processor  134 ), and generates a collimated light beam (encoded with data) shown representationally in  FIG. 5  as a plurality of light rays emanating from light display  130  toward partially transmissive partially reflective element  154 . Partially transmissive partially reflective element  154  reflects the light beam toward lens  148 , which is typically a convex-concave (meniscus) lens, which in turn refracts this light beam and relays the refracted light beam toward lens  150 , the latter of which is optically aligned with respect to lens  148 . Lens  150  refracts the refracted light beam relayed from lens  148  and directs the beam toward curved mirror  152 , the latter of which is optically aligned with the former. Lens  150  is typically a concave-convex (meniscus) lens, and curved mirror  152  is typically a concave spherical (front surface or alternatively, a rear surface) mirror. Alternatively, mirror  152  may exhibit curvatures other than spherical, such as aspherical, hyberbolic, elliptical, parabolic, toroidal, and the like. The optical elements group (combination) which includes lens  148 , lens  150 , and curved mirror  152  is constructed and optically arranged to correct aberrations such as astigmatism and distortion that is caused by the optical characteristics such as the curvature of partially transmissive partially reflective lens  108 . The refracted light beam arriving from lens  150  impinges curved mirror  152  such that the consequent reflected light beam is directed to pass (again) through lenses  150  and  148 , thereby forming an angle with respect to the incoming refracted light beam. The combination of curved mirror  152  and lenses  148  and  150  allow the incoming light beam generated and irradiated from light display  130  to pass (refract) twice through lenses  148  and  150 , thereby enabling pre-emptive correction of astigmatism and distortion caused when the light beam reflects off partially transmissive partially reflective lens  108 . Generally, in oblique astigmatism, off-axis rays of light from radial and tangential lines in an object plane focus at different distances in the image space. The utilization of lens  148  with lens  150  in the optical arrangement functions to increase the optical power of the optical system by decreasing the overall focal length of optical elements and in effect, enabling a reduction of the physical dimensions of electro-optical unit  102 , as well as further enabling fine-tuning for minimizing astigmatism and distortion. 
     Second lens  146  receives the refracted light beam from third and fourth lenses  148  and  150 , refracts and relays the light beam toward first lens  140  in optical module  106 . Third and fourth lenses  148  and  150  are typically of biconvex type (although other types may be used, e.g., plano-convex). As mentioned, second lens  146  is optically configured and operative to form intermediate image (not shown) at intermediate image plane  144  located at a position along an optical path between first lens  140  and second lens  146 . Further located at a position along this optical path between first and second lenses  140  and  146  is positioned auxiliary reflector  142  (e.g., a planar folding mirror), which is optically configured and operative to reflect light beams from second lens  146  toward first lens  140 , and is employed to bend the optical path into a particular spatial configuration (e.g., required at least for minimizing the spatial dimensions of housing  110  ( FIG. 2 ) of electro-optical unit  102 ). Minimization of spatial dimensions that is at least partially enabled by bending the light beams of the optical path facilitate in meeting the spatial constraints of housing  110  being located substantially at glabellar region  20  of user  10 . The formation of an intermediate image facilitates in the magnification of on outputted generated image, as well as in the widening of the field of view (FOV) that is presented to the user. The formed intermediate image is an aberration-compensated image (or aberration-corrected image) owing to the optical arrangement (and optical characteristics) of curved mirror  152  and lenses  148  and  150 . This aberration-compensated formed intermediate image forestalls aberrations produced, at least partially, by the curvature of partially transmissive partially reflective lens  108 , such that light rays incident upon and reflecting therefrom are aberration-corrected. 
     Partially transmissive partially reflective lens  108  is constructed and operative to partially reflect the light beam impinging thereon from light display  130  (i.e., an image source), and partially transmit incoming light from an outward translucent view in the ambient environment (i.e., a scene). Partially transmissive partially reflective lens  108  effectively functions as a light combiner, such that light from the image source and light from the outward scene are combined to form a combined image (not shown) that is directed and provided to at least one eye of the user. Additionally, partially transmissive partially reflective lens  108  is an ophthalmic lens configured and operative to provide ophthalmic (vision) correction to user  10 . Essentially, each partially transmissive partially reflective lens  108 R and  108 L is a corrective lens used to improve vision of the user (e.g., by correcting for refractive errors of the user&#39;s eye(s)  18 R,  18 L (respectively) such as myopia, hyperopia, presbyopia, and the like). Furthermore, both partially transmissive partially reflective lenses  108 L and  108 R for both the user&#39;s left and right eyes  18 L and  18 R (respectively) are adapted to match the interpupillary distance (IPD) of that user. As such, partially transmissive partially reflective lens  108  is typically constructed from rigid, durable, lens-grade materials such as glass (e.g., optical crown glass), polycarbonate, and the like, as well as at least one reflective optical coating layer whose thickness (at least to some degree) determines its reflective characteristics. The ratio of reflection to transmission, which is typically dependent on the wavelength of light incident on partially transmissive partially reflective lens  108 , may vary. Characteristic reflection percentages typically range between 20-40%; whereas total transmission percentages typically range between 8-70%. Any ratio derived from these percentages is viable. In particular, there may be more than one reflection to transmission ratios of partially transmissive partially reflective lens  108  (which may be different or the same). One reflection to transmission ratio is associated with light impinging on inner surface  160  (produced by light display  130 ), the other associated with light impinging on outer surface  162 . According to one realization, the reflectivity of outer surface  162  may be greater than the reflectivity of inner surface  160 . Other, different realizations may be possible, for example, where outer surface  162  (i.e., and/or at least part of partially transmissive partially reflective lens  108 ) may be embedded with silver halide (silver salts) in microcrystalline form that endow photochromic properties to the lens. The following features and options may apply differently or equally to each partially transmissive partially reflective lens  108 R and  108 L. Optionally, an antireflection coating may also be applied to outer surface  162 . Further optionally, an anti-abrasion coating may also be applied to partially transmissive partially reflective lens  108 . Further optionally, an anti-fog coating may be applied to partially transmissive partially reflective lens  108 . Further optionally, partially transmissive partially reflective lens  108  may be coated and/or incorporate light-polarized material, which generally enhances the contrast of an image viewed through the lens (e.g., especially noticeable in snow covered environments). Partially transmissive partially reflective lens  108  may employ shatter resistant (“shatterproof”) materials (e.g., polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), thermoplastic polyurethane (TPU), polyethylene terephthalate (PET), polycarbonate (PC), combinations thereof, etc.) in its construction and/or manufacture such that it exhibits shatterproof and impact-resistant qualities. Moreover, partially transmissive partially reflective lens  108  complies with known safety standards of eyewear in general, and eyewear (e.g., sunglasses) used for sporting applications, in particular. 
     Partially transmissive partially reflective lens  108  reflects the light beam from first lens  140 , passing through light display pupil  156  and toward the eye of the user, where dotted-line  164  represents a position of a plane that indicates the front eye surface of eye ( 18 R,  18 L) of user. Dotted-line  164  is disposed along the optical path between partially transmissive partially reflective lens  108  and light display pupil  156 . As will be described in greater detail hereinbelow, OST NED system  100  incorporates a non-pupil forming optical design thereby enabling a favorable visual experience for viewing the light image emitted by light display  130  across a wide FOV. 
     According to another embodiment of the disclosed technique, OST NED system  100  is configured and operative with an eye-tracking system. As such there is thus provided an optical configuration for an OST eye-tracking system that includes partially transmissive partially reflective lens (combiner) and an electro-optical unit that includes an image sensor, configured to acquire at least one image of an eyeball feature of an eye of the user, with reflected light from the eye. To further elucidate the particulars of this embodiment of the disclosed technique, reference is now made to  FIGS. 6A, 6B, and 7 .  FIG. 6A  is a schematic block diagram of a basic configuration of an electro-optical unit of OST eye-tracking system, constructed and operative in accordance with another embodiment of the disclosed technique.  FIG. 6B  is a schematic block diagram of an accessorized configuration of an electro-optical unit of OST eye-tracking system, constructed and operative in accordance with the embodiment of the disclosed technique.  FIG. 7  is a schematic diagram of a light path through an optical module of electro-optical unit of OST eye-tracking system, constructed and operative in accordance with the embodiment of the disclosed technique. 
     OST eye-tracking system  200  (not number-referenced in Figures) (herein denoted interchangeably as “OST NED eye-tracking system”) generally incorporates similar features and components of OST NED system  100 , however, OST NED eye-tracking system  200  includes an electro-optical unit that employs an eye-tracker as detailed below.  FIG. 6A  illustrates a basic configuration of an electro-optical unit of OST NED eye-tracking system  200 , denoted by  202   1 . Electro-optical unit  202   1  includes an electronics module  204   1 , and an optical module  206 . Particularly, electronics module  204   1  includes a light display  130 , and eye-tracker  230 . Note that identically referenced numbers in the embodiments OST NED system  100  and OST NED eye-tracking system  200  relate to the same components (i.e., same type and function). (For example, light display  130  in OST NED system  100  shown in  FIG. 3A  is identical to light display  130  in OST NED eye-tracking system  200 , shown in  FIG. 6A .) Optical module  206  includes optical elements, collectively referenced  232  that are particularized in greater detail in  FIG. 7 . Light display  130  of electronics module  204   1  along with optical elements  232  of optical module  206  form a light projector that is configured and operative to produce, irradiate, and project a light beam image (not shown) onto at least one partially transmissive partially reflective lens  108  (i.e., at least one of  108 R and  108 L), in a similar manner described hereinabove with respect to OST NED system  100 . Optical elements  232  are configured and operative to convey and project the image produced by light display  130  onto partially transmissive partially reflective lens  108 . 
       FIG. 6B  illustrates an accessorized configuration of electro-optical unit  102  of OST NED eye-tracking system  200 , denoted by  202   2 , having additional components with respect to the basic configuration of electro-optical unit configuration  202   1 , shown in  FIG. 6A . Electro-optical unit  202   2  includes an electronics module  204   2  and optical module  206  (i.e., identical to that in  FIG. 6A ). According to the accessorized configuration, electronics module  204   2  includes light display  130 , an eye-tracker  230  (i.e., identical to that in  FIG. 6A ), and may optionally include at least one of a processor  134 , a memory device  136 , a user interface  138 , and a communication module  140 . Processor  134 , memory device  136 , user interface  138 , and communication module  140  are identical to those shown in  FIG. 3B , except for added configuration, functionality, and features (e.g., software) associated with eye-tracker  230 . Optical elements (components)  232  ( FIGS. 6A and 6B ) of optical module  206  are further described in greater detail in conjunction with  FIG. 7 . 
     With particular reference now to  FIG. 7 , which is an illustration showing a schematic diagram of two light paths through optical module  206  of electro-optical units  202   1  and  202   2  of OST NED eye-tracking system  200 . Eye tracker  230  typically includes several components of an image sensor  230   1  and two lenses  230   2 ,  230   3 , as shown in  FIG. 7 . Image sensor  230   1  is part of electronics module  204   1  of electro-optical units  202   1  and  202   2 , and lenses  230   2  and  230   3  are part of optical elements  232  of optical module  206  of electro-optical units  202   1  and  202   2  (with reference to  FIGS. 6A and 6B ). For both basic and accessorized configurations, eye-tracker  230  may further optionally include at least one light source (e.g., visible and/or infrared light emitter(s)—not shown) that is configured and operative to illuminate at least one eye of the user, thereby facilitating in tracking the eye position (e.g., gazing direction, from eyeball features such as the pupil, as known in the art). All other components shown in  FIG. 7  having the same reference numbers as those shown in  FIG. 5  are identical to each other. In that respect OST NED eye-tracking system  200  is similar to OST NED system  100 .  FIG. 7  illustrates two light ray bundles (beams)  158  and  168  propagating along two different light paths. Light rays  158  represent an optical path of light display  130 , while light rays  168  represent an optical path associated with eye-tracker  230 . 
     Specifically, electro-optical unit  202  (i.e.,  202   1  and  202   2 ) includes light display  130 , and optical elements  232  of optical module  206  that include first lens  140 , reflector  142 , second lens  146 , third lens  148 , fourth lens  150 , curved mirror  152 , partially transmissive partially reflective element  154 , and lenses  230   2  and  230   3  of eye-tracker  230 .  FIG. 7  further shows partially transmissive partially reflective lens  108 , aperture  156  (herein denoted interchangeably as “light display exit pupil”), an intermediate image plane  144  where an intermediate image of light display (not shown) forms between first lens  140  and second lens  146 , as well an intermediate image plane  166  where an intermediate image of eye-tracker (not shown) forms at between third lens  148  and second lens  146 . Partially transmissive partially reflective lens  108  is the same as described in conjunction with  FIG. 5  (i.e., it includes inner surface  160  and outer surface  162 , whereby inner surface  160  is characterized by an inner surface radius of curvature r i  exhibiting a first optical power P i  and outer surface  162  is characterized by an outer surface radius of curvature r o  exhibiting a first optical power P o ). 
     Optical elements  232  of optical module  206 , light display  130  of electronics modules  204   1  and  204   2 , and partially transmissive partially reflective lens  108  form an optical arrangement (herein interchangeably “optical configuration”) allowing light rays to propagate along two light beams  158  and  168 , as illustrated in  FIG. 7 . Reflected light from the eye (i.e., front eye surface (dotted-line  164 ) of the user (i.e., natural (ambient) light, or artificial light (from a dedicated light source), or both) reflects off the eyeball of the user and that light is made to traverse an optical path that travels such that at least partially reflects from partially transmissive partially reflective lens  108 ; then refracts through first lens  140 , second lens  146 , third lens  148 , and fourth lens  150 , then reflects from curved mirror  152  and refracts again in reverse order through fourth lens  150  and then through third lens  148 , then at least partially passing through partially transmissive partially reflective element (optical combiner)  154 , refracts through lenses  230   2  and  230   3 , and impinges on image sensor  230   1 . Image sensor  230   1  is configured and operative to acquire an image (not shown) of the eyeball (i.e., having at least one eyeball feature such as the pupil), to produce image data corresponding the acquired image, and to enable the communication of the image data to processor  134  for processing. 
     The optical configuration enables light display  130  to project a light beam image (not shown) onto partially transmissive partially reflective lens  108  (i.e., at least one of  108 R and  108 L) along the optical path represented by light rays  158  (as described in hereinabove in conjunction with  FIG. 5 ) simultaneously while eye-tracker  230  tracks the eye of the user along the optical path represented by light rays  168 . Partially transmissive partially reflective element  154  (combiner) functions both as a fold mirror as well as a cold mirror that is configured and operative to reflect at least one range of wavelengths of light in electro-magnetic (EM) spectrum (i.e., typically visible light from produced by light display  130 ), while transmitting at least another range of wavelengths of light in the EM spectrum (i.e., typically infrared (IR) light captured by image sensor  230   1 ). Combiner  154  exhibits optical characteristics that include being 90% transmissive at a wavelength of 850 nm (nanometers), as well as being 90% reflective between the wavelength range of 450-650 nm. Optional flood lights (e.g., IR light-emitting diodes (LEDs)) may be used to illuminate the eye of the user thus enabling image sensor  230   1  to detect IR light reflecting off the eye. When illuminating the eye of user with IR light the user&#39;s pupil appears as a “dark pupil” facilitates detection and determination of eye pupil position (e.g., gaze direction) of the user. Image sensor  230   1  may be optimized to detect IR light at 850 nm, and may typically be based on a complementary metal-oxide-semiconductor (CMOS) technology, charge-coupled device (CCD) technology, and the like. Additional characteristics of image sensor  230   1  include it being of small size on the order of a few millimeters, incorporating a global shutter, and a sampling rate of 120 Hz, and a typical FOV of 50 degrees. Lenses  230   2  and  230   3  are typically embodied as aspheric lenses and configured and operative to focus light from eye front surface (represented by dotted line  164 ) to image sensor  230   1 . 
     OST NED eye-tracking system  200  enables an eye coverage area of approximately, 20×20 mm, and gaze coverage of ±35 degrees (left and right), an eye box of 7×3 mm that is adapted to different IPDs. OST NED eye-tracking system  200 , and particularly processor  134 , based on image data acquired from image sensor  230   1 , are configured and operative to detect blinking of the eye of the user, as well as for gaze orientation tracking, user-interface interaction, IPD adjustment, line-of-sight (LOS) stabilization, focus distance estimation, near field AR auto-correction for parallax (i.e., eye-camera-LOS), as well as fatigue detection. 
     Reference is now made to  FIGS. 8A, 8B, and 8C .  FIG. 8A  is a schematic illustration showing the principles of the non-pupil forming optical design upon which OST NED system  100  and OST NED eye-tracking system  200  are based, in accordance with the embodiments of the disclosed technique.  FIG. 8B  is a schematic illustration showing the a simplified geometric representation of a human eye, looking at a projected image focused at a far distance, and generated by a non-forming exit pupil display system design upon which OST NED system  100  and OST NED eye-tracking system  200  are based, in accordance with the embodiments of the disclosed technique.  FIG. 8C  is a schematic illustration showing determination of the distance, d, of the system exit pupil to the eye pupil, according to the disclosed technique. 
       FIG. 8A  shows a simplified geometric representation of a human eye ( 18 R,  18 L, also denoted interchangeably herein “ 18  (R,L)”, and simply “ 18 ”) that is gazing at a projected image (not shown) focused at a far distance therefrom, and generated by a non-pupil forming exit display system, in accordance with the principles of the disclosed technique. As eye  18 R,L of user looks to one side of the FOV at an angle (±) a (degrees), a portion of a ray bundle penetrates the eye&#39;s pupil  24 . At the center of the FOV near an eye projection system, the user will be expected to see the whole image of the display (e.g. the center of the field using central vision, as well as the sides of the field using peripheral vision). Further, while looking to the sides of the FOV of a near-eye projection system, the user is expected to clearly see the side of the field using central vision, and the remaining field using peripheral vision. From  FIG. 8A  it is clear that achieving that expectation for visual experience requires consideration and specific design to optimize the configuration of the eye projection system, such that the design position of the exit pupil of the eye projection system is taken into account with respect to the eye pupil position, as well as with respect to the size of the pupil, the size of the bundle of rays arriving from the projection unit (from each direction across the field of view), as well as the total size of the field of view of the projection unit. 
     Referring now to  FIG. 8B ,  FIG. 8B  is a schematic illustration showing a simplified geometric representation of human eye  18 R,  18 L, looking at a projected image (not shown) that is focused at a far distance from a user. A user of the OST NED system  100  and OST NED eye-tracking system  200  gazes at the projected image focused at a far distance, and that is generated by a non-pupil forming exit display system, in accordance with the embodiments of the disclosed technique.  FIG. 8B  shows a representation of three bundles of light rays arriving at angles 0, and ±α, which are to be considered as arriving from the projection display system, which is interchangeably denotes light display  130 . The light ray bundle represents portions of the FOV of the display (e.g. the bundle of light rays arriving at an angle of zero degrees originate at the center of the FOV of light display  130 ). Similarly, assuming a represents the maximal angle of view of the projection display system, the bundle of light rays arriving at angle of +α degrees originate at one side of light display  130 . Furthermore,  FIG. 8B  includes annotations, were R represents the eye&#39;s  18  (R, L) radius of rotation, r represents the distance of eye&#39;s pupil  24  from eye&#39;s  18  (R, L) center of rotation, d represents the distance of eye&#39;s pupil  24  to the eye projection system exit pupil, and x represents a diameter of the bundle of light rays. When the user&#39;s eye looks straight ahead at an angle of 0 degrees, a portion of the light ray bundle penetrates pupil  24 . In addition, at least a portion of the light ray bundles arriving from the range of angles +α to 0° and −α to 0° also penetrate pupil  24 . This situation represents a case were eye  18  (R, L) is able to see both the center of the FOV of light display  130  (known as “central vision”, imaged by the eye&#39;s fovea), as well as the sides of the FOV of the light display  130  (known as “peripheral vision”). 
     Referring now to  FIG. 8C , which shows a schematic illustration for facilitating the determination of the distance, d, of the system exit pupil to the eye pupil, according to the disclosed technique, where x represents a (projected) light ray bundle diameter (“light ray bundle fan size”), r represents the distance of the eye&#39;s pupil from the eye&#39;s center of rotation, p represents the pupil diameter, A represents the projected distance between the center of the pupil and the center of the optical exit pupil. The schematic illustrates two poses (positions and orientations) of the eye: (1) looking forward, and (2) looking to the side at an angle of a, which is half the FOV as shown in  FIGS. 8A-C  (i.e., at the direction of light rays arriving from light display  130 ). From  FIG. 8C  it is determined that the optimal position for the exit pupil of the eye projection system is according to the following formula: 
     
       
         
           
             
               
                 
                   
                     d 
                     &gt; 
                     
                       r 
                       - 
                       
                         ( 
                         
                           
                             x 
                             + 
                             p 
                           
                           
                             
                               2 
                               ⁢ 
                               sin 
                             
                             ∝ 
                           
                         
                         ) 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where d represents the distance between the exit pupil to a position located behind the eye&#39;s pupil (i.e., inside the eye). At positions d satisfying formula (1), the whole aperture is configured to be covered or illuminated with light rays. Similarly, from  FIG. 8C  it is determined that while the user gazes forward, the optimal position for the exit pupil of the eye projection system (light display  130 ) is dictated according to the following formula: 
     
       
         
           
             
               
                 
                   
                     d 
                     &lt; 
                     
                       
                         x 
                         + 
                         
                           p 
                           ⁡ 
                           
                             ( 
                             
                               cos 
                               ∝ 
                             
                             ) 
                           
                         
                       
                       
                         
                           2 
                           ⁢ 
                           sin 
                         
                         ∝ 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where d represents the distance between the exit pupil to a position located in-front of the pupil (i.e., facing forward the eye). OST NED system  100  and OST NED eye-tracking system  200  with a non-pupil forming exit abiding according to equations (1) and (2) enable an optimal visual experience for viewing light display  130  across its entire FOV. 
     In accordance with the disclosed technique, OST NED system  100  and OST NED eye-tracking system  200  are characterized by several important features which will be described hereinbelow in greater detail. Reference is now made to  FIG. 9A , which is a schematic illustration of illustrating optical design features of the systems of the disclosed technique with respect to an eye motion box in relation to an exit aperture. The center portion of  FIG. 9A  illustrates a simplified schematic illustration showing user  10 , partially transmissive partially reflective lens  108  (interchangeably “visor”, and “combiner”), an exit aperture  240 , and a system pupil  242 . The top right portion of  FIG. 9A  illustrates a coordinate system whose origin is located at the user&#39;s eye pupil position. An eye motion box is determined by exit aperture  240  (and eye position). The position and orientation (P&amp;O) of light display  130  is determined by the combiner (visor) rake angle. The image angle with respect to the real-world outward scene horizon is dictated by the angle of attack and the P&amp;O of light display  130 . The position of the eye and the eye box in conjunction with the conferred FOV to the user is dependent upon the “visor distance” (i.e., the distance between system pupil  242  and partially transmissive partially reflective lens  108 ), which in turn is determines the size of exit aperture  240 .  FIG. 9A  further shows the visor rake angle (also referred as the “pantoscopic angle”). 
     To further explain the pantoscopic angle&#39;s relation to the disclosed technique, reference is now further made to  FIG. 9B , which is a schematic illustration showing a pantoscopic angle, a wrap angle, and a roll angle, according to the principles of the disclosed technique. The pantoscopic angle is defined as an angle between a plane of partially transmissive partially reflective lens (combiner)  108  and the vertical y-axis, as indicated in  FIG. 9A . Mathematically, the pantoscopic angle is defined as: cos(Roll)*Tilt.  FIG. 9B  shows a side partial view of user  10 , and combiner  108 , where the vertical dotted line indicates the vertical axis (y-axis), and a pantoscopic angle from a plane of combiner  108  to the vertical axis.  FIG. 9B  further shows a wrap angle (also denoted as total wrap angle of frame  112 ), which is a measure of how frame  112  wraps around user&#39;s  10  face, and defined mathematically as sin(Roll)*Tilt. The roll angle as shown in  FIG. 9B  is defined as the projected exit aperture angle, as illustrated. 
     The characteristics described hereinabove in conjunction with  FIGS. 8A, 8B, 9A and 9B  enable to characterize the OST NED system (and product) according to the disclosed technique exhibiting the following features, characteristics, optical design data, and tolerances:
         OST NED system  100  and OST NED eye-tracking system  200  embodied as a product (apparatus) having the form of eyewear (e.g., eye glasses with ophthalmic correction) is based on free-space optical design having a partially transmissive partially reflective lens  108  (i.e., combiner, visor), and an electro-optical unit (that includes light display  130 );   Partially transmissive partially reflective lens  108  (combiner, visor) exhibits a pantoscopic tilt of 22 degrees (herein abbreviated “deg.” or °)±4 deg., and a wrap angle of 22 deg. ±4 deg. and curvature radii of 100 mm±34 mm;   Partially transmissive partially reflective lens  108  maximal distance from the eye cornea location is 15 mm±2 mm;   Light display  130  (i.e., image projection unit) has an exit aperture exhibiting a projection angle of 45 deg.±5 deg. roll angle around the Z-axis, and 31 deg.±4 deg. tilt relative to the normal of the visor, and a distance of 6 mm±2 mm from the visor;   Light display  130  (i.e., image projection unit) exit aperture is positioned relative to the eye pupil location at a minimal distance defined with a borderline at roll angle of 45 deg.±5 deg. around Z axis positioned 14 mm±3m from the eye pupil center along Z axis , and a projected distance of at least 8 mm±2 mm from the eye pupil center;   Light display  130  (i.e., image projection unit) exit aperture has a field of projection 24×13±2 deg. that creates an eye box of 6×3±1 mm; and   The center of the virtual image is placed at an elevation angle of 2 degrees max.±3 deg. relative to the horizon.       

     Reference is now made to  FIGS. 10A and 10B .  FIG. 10A  is a schematic illustration showing a front-facing detailed partial view of characteristic design constraints of the systems of the disclosed technique.  FIG. 10B  is a schematic illustration showing a detailed side partial view of characteristic design constraints of the systems of the disclosed technique. As shown in  FIG. 10A  a dotted line denoted “borderline” represents a borderline of first lens  140  ( FIGS. 5 and 7 ) with respect to eye  18 R of user  10 . The projected distance from the borderline to the pupil of eye  18 R is 8±2 mm. As shown in  FIG. 10B  a dotted line denoted “borderline” represents a borderline of several optical elements  132  ( FIGS. 5 ) and  232  ( FIG. 7 ) with respect to a distance to pupil of the eye along the Z-axis ( FIG. 9A ). 
     It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.