Patent Publication Number: US-2006018024-A1

Title: Panoramic see-through optical device

Description:
GOVERNMENT INTEREST  
      The invention described herein may be manufactured, used, sold, imported, and/or licensed by or for the Government of the United States of America. 
    
    
     FIELD OF THE INVENTION  
      The present invention applies generally to optical devices. More particularly, the present invention applies to optical devices that incorporate prisms and diffractive lenses made of plastic materials, which further allows for manufacture of panoramic see-through optical devices that are extremely lightweight.  
     BACKGROUND OF THE INVENTION  
      “See-through” display systems are those systems that are partially reflective in order to allow the user to actually see-through the display while at the same time viewing data that is being displayed by the system. Such systems allow for quicker decision-making on the part of the user, and these see-through systems are particularly advantageous for head-mounted systems such as cranials that are used in general aviation and helmets that are used in military applications.  
      For these systems, glass optics has heretofore been used to relay the image of a Cathode Ray Tube (flat) or similar type display panel onto a visor element. The visor element is constructed so that user can see through the visor while at the same time observing the image that is displayed on the visor surface, which is reflected into the user&#39;s eye. Visor approaches, however, limit the user field of view, and visor-type systems also tend to be limited by size and weight constraints.  
      To increase the system field of view (FOV) a panoramic approach is needed, and the advent of available flat panel display technology affords a different technique for display packaging. Specifically, instead of attempting to project a single display image onto the visor of a helmet, it is often more advantageous to use a plurality of display images in a tessellating fashion to yield a panoramic display of data. To do this, a plurality of see-through combiner eyepieces would be needed to provide the panoramic display. If the combiner eyepieces were made of glass, however, the weight of the panoramic display system would be excessive. What is desired is a combiner eyepiece that would take advantage of new panel display technology, in order to improve field of view coverage and simultaneously reduce overall weight.  
      In light of the above, it is an object of the present invention to provide an optical device that provides for panoramic see-through capability. It is another object of the present invention to provide a panoramic see-through optical device that has a reduced size and weight. Yet another object of the present invention is to provide an optical device with plastic lenses that are corrected for chromatic aberration. Still another object of the present invention is to provide a panoramic see-through device that takes advantage of advances in flat panel display by tessellating the output of a plurality of flat panel displays. It is another object of the present invention to provide a panoramic see-through optical device that is relatively easy to manufacture in a cost-effective manner.  
     SUMMARY OF THE INVENTION  
      A panoramic see-through optical device in accordance with the present invention includes at least two combiner prisms with a somewhat cubic shape, with each prism having a partially reflective face plane extending diagonally through the prism. Each prism has one convex surface with a tangent plane thereto. Each prism defines a channel, and the two prisms are positioned next to each other so that the tangent planes are orthogonal to each other, and further so that the reflective face planes are arranged next to each other in a tessellating manner as viewed from the line of sight of a viewer.  
      The device further includes a plurality of image generating means corresponding to the respective combiner prisms. Preferably, the image generating means are flat display panels that are placed about parallel to and spaced-apart from each tangent plane so that the convex surface of the prism faces the panel. Data from each display panel is reflected into the prism and onto the reflective face plane. The reflective face further reflected into the prism and onto the reflective face plane. The reflective face plane further reflects the data into the field of view of the user. At the same time, the operator can see directly through the prism. The result is a field of view with data from the display panel that is superimposed over the field of view.  
      An optical train, which minimally includes a filter and a surface diffractive lens, is located between the display panel and the prism, primarily to correct for chromatic aberration, or color spread. In this regard, the diffractive lens is a plano-convex lens with a flat surface and an opposing curved surface. A plurality of concentric microgrooves are placed in the flat surface, and the diffractive lens is positioned so that the curved surface of the diffractive lens faces the convex surface of the prism. The number of concentric microgrooves and their linear spacing is determined according the materials properties of the diffractive lens. Preferably, the diffractive lens, the combiner prisms and the remainder of the associated optics are made of a plastic material such as Zeonex®, which is manufactured by Zeon Chemicals L.P. This allows for greatly reduced weight of the overall device of the present invention.  
      For the method of the present invention, the prisms having structure as described above are provided and are arranged so that the tangent planes of the respective convex surfaces are orthogonal. A display image is established at each corresponding display panel, and the display image is projected into the prism for further reflection of the reflective face. After reflection, the operator observes the display image. Simultaneously, because of the material and coatings placed on the prism, the operator can see through the prism and observe the surroundings. The result is a panoramic see-through device wherein display images are superimposed over the operator field of view.  
      If each prism, display panel and optical train defines a channel of approximately thirty-five degrees, the two channels can be placed in front of each eye of the operator. The result is a panoramic field of view of approximately seventy degrees, wherein display data from targeting electronics, etc. is superimposed onto the operator field of view. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The novel features of this invention will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar characters refer to similar parts, and in which:  
       FIG. 1  is a front isometric view of the device of the present invention.  
       FIG. 2  is a front elevational view of the channels of the device of  FIG. 1 , as viewed by the user.  
       FIG. 3  is a rear elevational view of  FIG. 2 .  
       FIG. 4  is an isometric view of the optics for one channel of the device of  FIG. 1 .  
       FIG. 5  is a front elevational view of the optics of  FIG. 4 .  
       FIG. 6  is a top plan view of optics of  FIG. 4 .  
       FIG. 7  is an isometric view of the combiner prisms for the optics of  FIG. 4 .  
       FIG. 8  is an exploded isometric view of the combiner prisms of  FIG. 7 .  
       FIG. 9  is an isometric view a single combiner prism.  
       FIG. 10  is a front elevational view of the combiner prism of  FIG. 9 .  
       FIG. 11  is a side elevational view of the combiner prism of  FIG. 10 . 
    
    
     WRITTEN DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring initially to  FIGS. 1-3 , the panoramic see-through device of the present invention is shown and is generally indicated by character reference  10 . As shown, the device includes two channel assemblies  12   a,    12   b  that are fixed to mounting bar  14 . The mounting bar allows for attachment of the panoramic see-through device  10  to devices such as an aviator&#39;s cranial (not shown), where it is desired that electronic data be superimposed over the viewer field of view (FOV). The channel assemblies define channels corresponding to the eyes of the viewer (not shown) and allow for a panoramic see through capability in a manner described more fully hereinafter.  
      Each channel assembly includes two combiner prisms  16 ,  16  that are fixed within housing  18 . Each channel assembly further comprises two optical trains  20 ,  20  (See  FIGS. 4-6 ) and display panels  22 ,  22  that correspond to a respective combiner prism  16 . The optical trains  18 ,  18  are fixed within the housing, and the display panels are fixed to the outside of the housing so that an associated optical train is located between the display panel and the combiner prism. An image generation means  24 , such as a camera or radar, is electronically attached to generate an image on each respective flat panel. The generated image on the flat panel is in turn reflected into its corresponding combiner prism, onto the internal face plane  26  as hereinafter described.  
      By cross-referencing  FIGS. 1 through 4 , it can be seen how the objects can be combined to provide a panoramic see-through view for the user. For purposes of this application, see-through capability is defined as the ability of the user to see data on a face of a prism while at the same time being able to see-through the prism into the normal field of view (FOV) of the user. The combiner prisms have see-through aspects. The image generations means and display panels are oriented perpendicular to each other and out of the FOV of the user. Each display panel displays data corresponding to the FOV for its respective combiner prism, which is approximately thirty (30) degrees wide. The data is superimposed of the user FOV, and for each channel, combiner prisms are arranged so that their internal face planes lie next to each in a tessellated fashion. The net result is a device having for panoramic see-through capability.  
      Referring now to  FIGS. 4-10 , the optics for the device for the present invention is shown in more detail. As shown, each channel includes the aforementioned combiner prisms. The combiner prisms are roughly cubic in shape have flat surfaces with the exception of one convex surface  26 . The optical train further comprises a plurality of lenses  28  and filters  29  that are chosen according to the intended application of the device and for the manipulation of the image that is generated by image generation means  24 . Importantly, the optical train includes at least one diffractive lens  30  having a convex diffractive surface  32 . The diffractive surface is further formed with a plurality of concentric microgrooves  34  as depicted by  FIG. 7 . When the optical train is positioned between the flat panel and the combiner prism, the diffractive surface of the diffractive lens faces and is immediately proximate to the convex surface of the combiner prism, and the microgrooves formed therein correct for chromatic aberration, or color spread of a generated image within the combiner prism.  
      It is preferred that the combiner prism and the optical train components be made of the same materials, to minimize the diffractive aspects and further minimize the length and number of components of the optical train. For the materials of the present invention, it is also preferred that the device be as lightweight as possible, particularly in applications where the device is mounted to the aviator&#39;s cranial. Accordingly, although other plastic materials and glass material are also suitable for manufacture thereof, the combiner and optical train are preferably manufactured of a Zeonex® material manufactured by Zeon Chemicals, L.P. This allows for an extremely lightweight device, which can be mounted to the headgear and allows for greater comfort of the user and reduced pilot fatigue.  
      The aforementioned diffractive lens corrects color spread via incorporation of microgrooves in its diffractive surface. The number of microgrooves is varies according the refractive index of the diffractive lens, which further varies according the materials of manufacture thereof. For a combiner prism and optical made of Zeonex® materials, it is preferable that at least 700 micro groups per inch are etched in each plastic surface.  
      Referring now to  FIGS. 8-10  the structure of the combiner prism for the device of the present invention is shown in greater detail. As shown and discussed above, the combiner prism has a polyhedral shape that is substantially cubic, with an opposing front surface  40  and back surface  42  that are substantially flat and that lie in parallel planes. Similarly, opposing side surfaces  43 ,  43  are substantially flat and lie in parallel planes, although it is understood that a portion of the prism could be removed so that the side surfaces are not parallel, in order to save space with the associated optical train.  
      The combiner prism further includes a planar polygonal bottom surface  44  and opposing convex surface  26 , as described above. The bottom surface and convex surface arranged so that the aforementioned tangent plane  45  to the convex surface is parallel to the bottom surface. By cross-referencing  FIGS. 5-7 , it can be seen that when two combiner prisms are arranged within channel  12 , the combiner prisms are arranged so that bottom surface  44  of one combiner prism (shown in phantom in  FIG. 7 ) contacts a side surface  43  of the other combiner prism. This further results in tangent planes  45  that are orthogonal to each other.  
      The combiner prism has a partially reflective internal face plane  36  that extends diagonally through the combiner prism from one edge of the bottom surface to an edge of the convex surface  26 . To establish this face plane, the cubic is cut diagonally along the face plane. A partially reflective coating  38  (depicted in  FIG. 11 ) is then placed on the diagonal surfaces that define the internal face plane in accordance with the guidelines found in Military Standardization Handbook MIL-HDBK-141, Optical Design. Next, the two half cubes are fixed together with a clear adhesive that is commercially available, such as Norland Optical Adhesive 77 (NOA 77) adhesive. Alternatively, the combiner prism can be machined so the two half cubes contact each other and there is no gap therebetween when the half cubes are placed in the housing  18 .  
      The partially reflective coating  38  is what allows the viewer to see through the prism. At the same time, the coating reflects data from the flat panel so that the viewer can observe it. It should be appreciated that although the manner in which the coating is applied is described in the aforementioned MIL-HDBK-141, the type of coating applied is a design choice according to the needs of the user. For example, a fifty/fifty reflective coating (a coating that allows half of the light from the environment to pass through and been seen by the user). In applications where the device is used primarily in daylight, however, a seventy/thirty coating could be used, as less light needs to pass through the combiner prism due to the daylight conditions. Conversely, a thirty/seventy coating can be used where the device is to be used at night or in low light conditions and more light needs to pass through the prism to be seen by the user.  
      As can be seen from the Figures, the combiner prisms can be tessellated to yield a panoramic field of view that is not obstructed by the optical train components. To do this, however, and keeping in mind the optical train is needed to manipulate images from the flat panels and to correct for chromatic aberration, the combiner prism must be arranged in a specific manner. Specifically, the combiner prisms for each channel are preferably arranged so that the planes that are tangent to the convex surfaces are orthogonal. The net result is a relatively lightweight device with panoramic see-through capability.  
      While the panoramic see-through optical device, as herein shown and disclosed in detail, is fully capable of obtaining the objects and providing the advantages above stated, it is to be understood that the presently preferred embodiments are merely illustrative of the invention. As such, no limitations are intended other than as defined in the appended claims.