Abstract:
A fusion night vision system has an optical element coupled to a display for improving the performance and viewability of images through a fusion night vision device while reducing overall system cost. The display producing a scene image from an image detector. The optical element has a flat input surface and a curved output surface. The curved output surface shaped to match an output surface of an image intensifier tube. The output from the display and the image intensifier being combined in an image combiner before entering an eyepiece for presentation to an operator as a fused image.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit under 35 U.S.C. 120 to U.S. patent application Ser. No. 11/928,328, filed Oct. 30, 2007, which is a continuation application of U.S. patent application Ser. No. 11/173,234, filed Jul. 1, 2005, now U.S. Pat. No. 7,307,793, the entire disclosures of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The invention is generally related to night vision devices and, more particularly, to systems and methods for improving the performance and viewability of images through a fusion night vision device. 
     BACKGROUND OF THE INVENTION 
     Night vision systems include image intensification, thermal imaging, and fusion monoculars, binoculars, and goggles, whether hand-held, weapon mounted, or helmet mounted. Standard night vision systems are typically equipped with one or more image intensifier tubes to allow an operator to see visible wavelengths of radiation (approximately 400 nm to approximately 900 nm). They work by collecting the tiny amounts of light, including the lower portion of the infrared light spectrum, that are present but may be imperceptible to our eyes, and amplifying it to the point that an operator can easily observe the image. These devices have been used by soldier and law enforcement personnel to see in low light conditions, for example at night or in caves and darkened buildings. These devices take ambient light and magnify the light up to and in excess of 50,000 times and display the image for viewing through an eyepiece. A drawback to night vision goggles is that they cannot see through smoke and heavy sand storms and cannot see a person hidden under camouflage. 
     Infrared thermal sensors allow an operator to see people and objects because they emit thermal energy. These devices operate by capturing the upper portion of the infrared light spectrum, which is emitted as heat by objects instead of simply reflected as light. Hotter objects, such as warm bodies, emit more of this wavelength than cooler objects like trees or buildings. Since the primary source of infrared radiation is heat or thermal radiation, any object that has a temperature radiates in the infrared spectrum. One advantage of infrared sensors is that they are less attenuated by smoke and dust and a drawback is that they typically do not have sufficient resolution and sensitivity to provide acceptable imagery of the scene and cannot be used to read road signs. 
     Fusion systems have been developed that combine image intensification with thermal image sensing. The image intensification information and the infrared information is optically combined to provide a fused image that provides benefits over just image intensification or just thermal sensing. Whereas typical night vision devices with image intensification can only see visible wavelengths of radiation, the fused system provides additional information by providing heat information to the operator. 
     According to one aspect of the invention, there is provided a fusion night vision system including a housing, an image intensifier for processing information in a first range of wavelengths, the image intensifier having a first curved output image surface, an image detector for processing information in a second range of wavelengths, a display for displaying processed information from the image detector, an image combiner for combining the output from the image intensifier with the output of the image detector, and an optical element aligned with the display and an input to the image combiner, the optical element having a generally flat input surface and a curved output surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention, together with other objects, features and advantages, reference should be made to the following detailed description which should be read in conjunction with the following figures wherein like numerals represent like parts: 
         FIG. 1  is a ray trace of a portion of an optically fused night vision system. 
         FIG. 2  is a ray trace of a portion of an optically fused night vision system consistent with the current disclosure. 
         FIG. 3  is a block diagram of an optically fused night vision monocular. 
         FIG. 4  is a block diagram of an optically fused night vision binocular. 
         FIG. 5  is a block diagram detailing interconnections between blocks shown in the optically fused night vision monocular of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 3  is a block diagram of a first optically fused night vision system configured as a monocular  400 ;  FIG. 4  is a block diagram of a second optically fused night vision system configured as a binocular  400 ′; and  FIG. 5  is a block diagram detailing interconnections between blocks shown in the optically fused night vision monocular of  FIG. 3  consistent with the current disclosure. The system electronics and optics may be housed in a housing  402 , which can be mounted to a military helmet. 
     An operator  404  looking through an eyepiece  406  within the housing  402  may be able to see a fused image  490  of a target  408 . Enclosed at least partially within the housing  402  may be an image intensifier (I 2 ) tube  422 , an infrared (IR) image detector  428 , for example a focal plane array (FPA), a combiner optics  432 , a display  434 , an illumination LED  436 , an analog circuit card assembly  438 , a digital circuit card assembly  440 , and a power circuit card assembly  442 . Suitable I 2  tubes  422  may be Generation HI tubes and are available from L-3 Communication Corporation and ITT. 
     The focal plane array may be a U7000J from DRS. Other image detectors including near infrared electron bombarded active pixel sensors and short wave InGaAs arrays operating in other wavelengths, may be used without departing from this disclosure. Image detectors operating in the same wavelength may be used together. Information from the I 2  tube  422  and the IR image detector  428  may be fused together for viewing by an operator through the one or more eyepieces  406 . The eyepiece(s)  406  have one or more ocular lenses for magnifying and/or focusing the fused image. The I 2  tube  422  may be configured to process information in a first range of wavelengths (the visible portion of the electromagnetic spectrum from 400 nm to 900 nm) and the IR image detector  428  may be configured to process information in a second range of wavelengths (7,000 nm-14,000 nm). The I 2  tube  422  may have an objective focus  424  and the IR image detector  428  may have an objective focus  426 . 
     The analog circuit card assembly  438 , the digital circuit card assembly  440 , and the power circuit card assembly  442  may be combined on a single flexible circuit assembly  446 . The display  434  may be a yellow monochrome organic light emitting diode (OLED) microdisplay available from eMagin Corp. as part no. EMA-100116. The fusion night vision system  400 ,  400 ′ may be powered by a separate and removably disconnectable battery pack  444 . 
     Scene information  450  from the image intensifier tube  422  may be directed into optics  432 , for example a partially reflective beam combiner and information  452  from the image detector  428  may be directed into the system electronics on the analog circuit card assembly  438 . An analog video out signal  454  from the analog circuit card assembly  438  may be inputted into the display  434 . A serial bus  458  coupled to the digital circuit card assembly  440  may control the size, resolution, and offset of the display  434 . An output  456  from the display  434  may be directed through a first optical element  108  (see  FIG. 1 ), for example a lens having a curved input and curved output surface, towards the image combiner  432  and then the fused image  490  is directed towards the operator  404 . The first optical element  108  may be aligned with the display  492 . A second optical element  106  may be disposed between an output image plane  202  of the image intensifier tube  422  and the image combiner  432 . 
     Alternatively, as shown in  FIG. 2 , an optical element  208 , for example a glass or fiber optic bundle may be disposed between the display  434  and the image combiner  432 . The optical element  208  may be aligned with the display  492  and then coupled to the display with an adhesive. The optical element  208  may be have a generally flat input surface  208 ′ and a curved output surface  208 ″. The curved output surface  208 ″ may have a concave shape that cooperates with the curved output image plane  202  of the image intensifier tube  422  to improve viewability of the fused image as the eyepiece  406  is moved relative to the optic  432 . The output surface  208 ″ may have a radius of curvature similar to the output surface  202  of the image intensifier tube  422 . The eyepiece  406  may be moved relative to the optic  432  in fusion night vision system  400 ,  400 ′ to provide diopter adjustment to accommodate vision corrections unique to each user without compromising precision registration between the two images (from the display  434  and the output of the image intensifier tube  422 ). If both the image from the image intensifier tube and the image detector are to be affected identically by diopter adjustment, they must have identical effective focal length and identical distortion curves. By properly shaping the output surface of the optical element  208  to match the output image plane of the image intensifier tube, the system can achieve similarly shaped image planes and improve viewability of the fused image as diopter adjustments are made. Although the fiber bundle is shown with a flat display and an image intensifier tube having a curved output image plane, the bundle can be used with any system having two or more image planes having differing physical geometries. The bundle may be used even if the two image planes do not need to be the exact same shape, rather it can be used with any image plane that needs to be modified from its original geometry. No additional ( 106  and  108 ) optical elements may be required in this embodiment. 
     In an alternative embodiment, the optical element may be used in a system with an image intensifier and a display for displaying received digital information, for example digital map or target location information, instead of scene information from a detector and the combined image is the digital information overlayed on the scene information. 
     The fusion night vision system  400 ,  400 ′ may have a plurality of user actuatable actuators including illumination LED actuator  460 , power on/off actuator  462 , stand-by actuator  464 , increase perceived mix of thermal to I 2  information actuator  466 , increase perceived mix of I 2  to thermal information actuator  468 , brightness down actuator  470 , brightness up actuator  472 , and thermal mode select actuator  480 . The actuators may employ a silicone overlay over tactile dome switches. The overlay may be coupled to the housing  402  to seal out moisture and particulates and the dome switches may be coupled to a processor. The increase perceived mix of thermal to I 2  information actuator  466  and the increase perceived mix of I 2  to thermal information actuator  468  may be fixed together and rotatable about a pivot. Rotation of the combined actuator in a first rotational direction increases the perceived mix of information in the eyepiece from the I 2  channel and rotation of the actuator in a second rotational direction increases the perceived mix of information in the eyepiece from the thermal channel. The increase or decrease in the perceived mix of information in the eyepiece from the I 2  channel can be changed continuously (ramp) or in discrete steps by the processor. 
     The illumination LED actuator  460  may turn illumination LED  436  on and off. A single actuation of the illumination LED actuator  460  may turn the illuminating LED  436  on as long as the actuator  460  is actuated and a double tap (two actuations within a short period of time, for example 500 msec, may cause the illuminating LED  436  to latch on. A subsequent actuation of illumination LED actuator  460  may turn the illuminating LED  436  off. Stand-by actuator  464  may switch the system  400  to a lower power usage state without turning the system  400 ,  400 ′ off. The thermal mode select actuator  480  allows the user to reverse the polarity of the image i.e. change the light pixels to dark and the dark pixels to light, enable or disable the edge detection filter circuit (to be discussed below), and calibrate the system. The fusion night vision systems  400 ,  400 ′ may also have a low battery signal generator  482 . The low battery signal generator  482  may generate a visible or an audible signal to the operator to signal that the batteries in the battery pack  444  are low. Alternatively, the low battery signal may be displayed in the display  434 . The fusion night vision systems  400 ,  400 ′ may also have a programming port  484  and a digital data port  486  for transferring data. Alternatively, the system  400  may utilize scroll actuators as discussed in relation to  FIG. 3 . 
     The fusion night vision systems  400 ,  400 ′ may be called upon by the operator  404  to view the target  408  in a variety of adverse conditions, for example in very low light conditions, through smoke or heavy fog, and sand storms. In each of these conditions the operator may wish to rely more heavily on the image intensifier  422  than the image detector  428  and in other conditions the user may wish to rely more heavily on the image detector  428  than the image intensifier  422 . The increase perceived mix of thermal to I 2  information actuator  466  and the increase perceived mix of I 2  to thermal information I 2  image actuator  468  may be actuated to adjust the perceived mix of information from the image intensifier  422  and the image detector  428  viewable through the eyepiece(s)  406 , while generally maintaining the brightness of the display  434 . At one extreme the viewable image contains generally 100% image intensification information, at the other extreme the viewable image contains generally 100% thermal information, and in between the two extremes, the power circuit card assembly  442  controls the mix of I 2  and thermal information to the eyepiece  406 . The actuators  466 ,  468  may be coupled to a microcontroller on the power circuit card assembly  442  that controls the gain of the I 2  tube  428  and the contrast and brightness of the thermal image presented in display  434 . The microcontroller may control a digital potentiometer coupled to the gain control input of the I 2  tube. As noted above, the increase or decrease may be ramped or stepped. The increase perceived mix of IR to I 2  information actuator  466  and the increase perceived mix of I 2  to IR information actuator  468  may be positioned on opposite ends of a rocker mechanism to prevent simultaneous actuation. 
     Certain embodiments of the invention can be implemented in hardware, software, firmware, or a combination thereof. In one embodiment, the filter circuit and/or the threshold comparator and clamp circuit are/is implemented in software or firmware that is stored in a memory and that is executable by a suitable instruction execution system. If implemented in hardware, as in an alternative embodiment, the circuits can be implemented with any or a combination of the following technologies, which are well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. 
     The display  434  may be a miniature flat panel display, more particularly; it may be a monochrome organic light emitting diode (OLED) microdisplay or a liquid crystal display (LCD). The focal plane array and imaging electronics may be a micro bolometer imager currently available from L-3 or DRS. Other detectors capable of processing scene information, including a digital image intensification tube, a near infrared electron bombarded active pixel sensor, a short wave InGaAs array, a charged couple device, and a CMOS detector, may be used without departing from the invention. 
     Although several embodiments of the invention have been described in detail herein, the invention is not limited hereto. It will be appreciated by those having ordinary skill in the art that various modifications can be made without materially departing from the novel and advantageous teachings of the invention. Accordingly, the embodiments disclosed herein are by way of example. It is to be understood that the scope of the invention is not to be limited thereby.