Abstract:
An optical device is disclosed for generating illumination that appears to emanate from a location different from the actual light source. The device includes a waveguide having opposed first and second planar faces. A light source is positioned to direct light into the waveguide. A diffractive optical element (DOE) is formed across the waveguide. The DOE distributes the light entering the waveguide via total internal reflection and couples the light out of the surface of said first face.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/163,724, filed on May 19, 2015, entitled “ILLUMINATOR”, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The subject invention relates to an optical device for generating illumination that appears to emanate from a location different from the actual light source. Such an optical device is useful for a variety of photographic or video capture situations where it is impractical or impossible to place an actual physical light source where needed. 
       BACKGROUND OF THE INVENTION 
       [0003]    Most photographic or video capture situations require some form of illumination. The desired illumination could be supplied, for example, by a flash connected to a camera. However, in many situations, providing the needed illumination can be a challenge. 
         [0004]    One such situation relates to a display system developed by the assignee herein for the creation of an augmented reality for a user. In such a system, the user would be provided with a head mounted device that includes a window for viewing the outside world. The window would have the capability to generate image information and project that image information into the eyes of the user. In such a system, images of simulated objects could be generated and added to the real world scene. A more detailed description of this type of window is provided below. 
         [0005]    There is interest in adding certain functionality to such head mounted displays. For example, there is interest in including a camera for monitoring the gaze direction of the user. Knowing where the user is looking at any moment has many benefits. For example, knowledge of a person&#39;s gaze can be used to control the display system. Knowledge of gaze direction can be used as a selection tool to control a mouse pointer, or its analog. Knowledge of gaze direction can be used to select objects in the field of view. Capturing gaze information with a camera can be improved by providing a source to illuminate the eye. 
         [0006]    Another feature of interest in head mounted displays is the possibility of identifying the user through biometric measurements, such as iris recognition. An iris recognition system will include a camera for capturing an image of the iris. The process of capturing iris information can be improved if a source of illumination is provided. 
         [0007]    The illumination device of the subject invention has some similarities to the structure of the window used by the assignee herein to create augmented reality. Although the embodiment of the subject invention will be discussed in this context, it should be understood that the invention is not limited to augmented reality systems but, in fact, could be used in any situation that requires illumination, particularly where it is desired to create a virtual illumination source. 
         [0008]    The subject device includes a planar waveguide having a structure similar to that proposed for use in augmented reality. A description of a device for creating an augmented reality can be found in U.S. Patent Publication No. 2015/001677, published Jan. 15, 2015, the disclosure of which is incorporated herein by reference. 
         [0009]    As described in the latter publication and illustrated in  FIG. 1  herein, the optical system  100  can include a primary waveguide apparatus  102  that includes a planar waveguide  1 . The planar waveguide is provided with one or more diffractive optical elements (DOEs)  2  for controlling the total internal reflection of the light within the planar waveguide. The optical system further includes an optical coupler system  104  and a control system  106 . 
         [0010]    As best illustrated in  FIG. 2 , the primary planar waveguide  1  has a first end  108   a  and a second end  108   b , the second end  108   b  opposed to the first end  108   a  along a length  110  of the primary planar waveguide  1 . The primary planar waveguide  1  has a first face  112   a  and a second face  112   b , at least the first and the second faces  112   a ,  112   b  (collectively,  112 ) forming a partially internally reflective optical path (illustrated by arrow  114   a  and broken line arrow  114   b , collectively,  114 ) along at least a portion of the length  110  of the primary planar waveguide  1 . The primary planar waveguide  1  may take a variety of forms which provide for substantially total internal reflection (TIR) for light striking the faces  112  at less than a defined critical angle. The planar waveguides  1  may, for example, take the form of a pane or plane of glass, fused silica, acrylic, or polycarbonate. 
         [0011]    The DOE  2  (illustrated in  FIGS. 1 and 2  by dash-dot double line) may take a large variety of forms which interrupt the TIR optical path  114 , providing a plurality of optical paths (illustrated by arrows  116   a  and broken line arrows  116   b , collectively,  116 ) between an interior  118  and an exterior  120  of the planar waveguide  1  extending along at least a portion of the length  110  of the planar waveguide  1 . The DOE  2  may advantageously combine the phase functions of a linear diffraction grating with that of a circular or radial symmetric zone plate, allowing positioning of apparent objects and a focus plane for apparent objects. The DOE may be formed on the surface of the waveguide or in the interior thereof. 
         [0012]    With reference to  FIG. 1 , the optical coupler subsystem  104  optically couples light to the waveguide apparatus  102 . Alternatively, the light may be coupled directly into the edge of the waveguide  108   b  if the coupler is not used. As illustrated in  FIG. 1 , the optical coupler subsystem may include an optical element  5 , for instance a reflective surface, mirror, dichroic mirror or prism to optically couple light into an edge  122  of the primary planar waveguide  1 . The light can also be coupled into the waveguide apparatus through either the front or back faces  112 . The optical coupler subsystem  104  may additionally or alternatively include a collimation element  6  that collimates light. 
         [0013]    The control subsystem  106  includes one or more light sources and drive electronics that generate image data which may be encoded in the form of light that is spatially and/or temporally varying. As noted above, a collimation element  6  may collimate the light, and the collimated light is optically coupled into one or more primary planar waveguides  1  (only one primary waveguide is illustrated in  FIGS. 1 and 2 ). 
         [0014]    As illustrated in  FIG. 2 , the light propagates along the primary planar waveguide with at least some reflections or “bounces” resulting from the TIR propagation. It is noted that some implementations may employ one or more reflectors in the internal optical path, for instance thin-films, dielectric coatings, metalized coatings, etc., which may facilitate reflection. Light that propagates along the length  110  of the waveguide  1  intersects with the DOE  2  at various positions along the length  110 . The DOE  2  may be incorporated within the primary planar waveguide  1  or abutting or adjacent one or more of the faces  112  of the primary planar waveguide  1 . The DOE  2  accomplishes at least two functions. The DOE  2  shifts an angle of the light, causing a portion of the light to escape TIR, and emerge from the interior  118  to the exterior  120  via one or more faces  112  of the primary planar waveguide  1 . The DOE  2  can also be configured to direct the out-coupled light rays to control the virtual location of an object at the desired apparent viewing distance. Thus, someone looking through a face  112   a  of the primary planar waveguide  1  can see the virtual light source as if from a specific viewing distance. 
         [0015]    As will be discussed below, the subject illuminator can be configured using the DOE and waveguide technology discussed above. 
       BRIEF SUMMARY OF THE INVENTION 
       [0016]    An optical device is disclosed for generating illumination that appears to emanate from a location different from the actual light source. The device includes a waveguide having opposed first and second planar faces. A light source is positioned to direct light into the waveguide. A diffractive optical element (DOE) is formed across the waveguide. The DOE distributes the light entering the waveguide via total internal reflection and couples the light out of the surface of said first face. 
         [0017]    In one embodiment, the DOE is configured to collimate the outgoing light, so as to emulate the light field of a source positioned at an infinite distance from the waveguide. In another embodiment, the DOE is configured to diverge the outgoing light, so as to emulate a light field of a source that is a predetermined distance from the waveguide. In a preferred embodiment, the light source generates a narrow bandwidth of radiation in the infrared region of the spectrum. 
         [0018]    For instance, the DOE may be configured such that light rays exit said first face perpendicular thereto, or such that light rays exit said first face in a manner to create a virtual source in space opposite the second face; or such that light rays exit said first face in a manner to create at least two virtual sources in space opposite the second face. 
         [0019]    Additionally, the light source may generate infrared radiation. The second face may be provided with a coating reflective for infrared radiation. 
         [0020]    The light from the light source may be directed into the waveguide via the first face thereof and/or via the second face thereof. In another embodiment, the light source from the light source may be directed into the waveguide via an edge of the waveguide. In such an embodiment, the illuminator may include a second waveguide extending along the edge of the first waveguide. The second waveguide may receive the radiation from the light source and distribute the light along an axis of the first waveguide parallel to the edge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic diagram showing an optical system including a waveguide apparatus, a subsystem to couple light to or from the waveguide apparatus, and a control subsystem, according to one illustrated embodiment. 
           [0022]      FIG. 2  is an elevational view showing a waveguide apparatus including a planar waveguide and at least one diffractive optical element positioned within the planar waveguide, illustrating a number of optical paths including totally internally reflective optical paths and optical paths between an exterior and an interior of the planar waveguide, according to one illustrated embodiment. 
           [0023]      FIG. 3  is a schematic diagram showing an illuminator formed in accordance with a first embodiment of the subject invention where the virtual light source is at infinity. 
           [0024]      FIG. 4  is a schematic diagram showing an illuminator formed in accordance with a second embodiment of the subject invention where the virtual light source is a point in space some finite distance from the waveguide. 
           [0025]      FIG. 5  is a schematic diagram showing an illuminator formed in accordance with a third embodiment of the subject invention which includes a distribution waveguide. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 3  illustrates a first embodiment of an illumination device  10  made in accordance with the subject invention. The device may be used in a wide variety of applications that require illumination. The device may be particularly useful with head mounted displays for implementing features such as gaze tracking or iris identification. 
         [0027]    Device  10  includes a planar waveguide  20 . One or more diffractive optical elements (DOEs)  22  are formed in the waveguide. The DOE can be formed on a surface of the waveguide or be embedded within the waveguide. 
         [0028]    A light source  24  is provided for generating optical radiation for illumination. A wide variety of light sources could be used. In the preferred embodiment, the light source generates a single wavelength or a narrow band of wavelengths. In one example, the light source  24  is a light emitting diode (LED). The light output of the LED is directed into the waveguide. The light can be directed into either side of the waveguide or along the edge thereof. The light then propagates throughout the waveguide by total internal reflections. 
         [0029]    The DOE is arranged to out couple the light at various points along the surface of the waveguide. In the embodiment of  FIG. 3 , the light rays coupled out are substantially perpendicular to the surface of the waveguide. This approach emulates the situation where the light source would be located at an infinite distance from the waveguide and the light is substantially collimated. 
         [0030]      FIG. 4  illustrates a device  10   b  in accordance with a second embodiment of the invention. In the  FIG. 4  embodiment, the DOE  22   a  of waveguide  20   a  is arranged to create diverging rays to emulate the effect of a point source  30  located a particular distance from the opposite side of the waveguide. The particular location of the virtual light source is controlled by configuring the DOE. 
         [0031]    The DOE can be arranged to place the virtual light source in any location, from quite close to the waveguide to quite far away. The choice will depend on providing the best illumination for the particular application. For example, if the illumination of the eye is used to capture images of the iris, it may be better to move the virtual source farther away from the waveguide to create a more uniform illumination. 
         [0032]    For augmented reality applications, it is preferable that the light source emits illumination in the infrared spectrum so that the radiation is not visible to the user. In this way, the illuminator would not interfere with the real world or computer generated images reaching the user. Using infrared illumination is particular useful for iris recognition as a much higher level of detail of the iris is available in this wavelength range. 
         [0033]    In a system using an infrared source, it may be preferable to provide a coating that reflects infrared radiation on the side  32  ( 32   a ) of the waveguide (opposite the transmission side). An infrared coating would minimize any losses due to light leakage on that side. The infrared coating would not interfere with the transmission of visible light from the real world, through the waveguide and into the eyes of the user. 
         [0034]    The embodiment of  FIG. 4  shows how the DOE can be configured to emulate light coming from a single point source. It is within the scope of the subject invention to configure the DOE to create diverging light rays that emulate light emanating from two or more virtual light sources. This could be achieved by allocating some fraction of the pixels of the DOE to one virtual source and another fraction of the DOE pixels to another virtual source. Of course, one could achieve a similar result by using two waveguides  30   a . The two waveguides would be aligned parallel to each other. Each waveguide  30   a  would be configured to emulate a point light source at a different location. 
         [0035]    Various pupil tracking systems are configured to require multiple light sources to generate multiple reflections from the eye. It is envisioned that an embodiment of the subject invention which can generate multiple virtual point source could be used to implement these type of pupil tracking systems. 
         [0036]      FIG. 5  is a diagram of a system  10   c  that includes a planar waveguide  50  having a DOE  52 . System  10   c  further includes a second waveguide  56  aligned with an edge of waveguide  50 . Second waveguide  56  includes a DOE  58 . Light source  54  directs light into the second waveguide. The light spreads across the second waveguide  56  via total internal reflection. The light exits second waveguide  56  and enters waveguide  50 . In this embodiment, waveguide  56  acts to distribute light along the axis thereof (vertical axis of  FIG. 5 ). Waveguide  50  then distributes the light along the horizontal axis of  FIG. 5 . The use of the second waveguide may improve coupling efficiency. 
         [0037]    While the subject invention has been described with reference to some preferred embodiments, various changes and modifications could be made therein by one skilled in the art, without varying from the scope and spirit of the subject invention as defined by the appended claims.