Abstract:
A night vision device includes an image intensifier tube and a fiber optic screen disposed in operative relationship to each other. The fiber optic screen includes a longitudinal bundle of multiple optical fibers, where the bundle has an outer surface. A groove is formed in the fiber optic screen and extends transversely to the longitudinal bundle. An indicator is positioned adjacent to the outer surface of the bundle and is proximate to the groove, where the groove is configured to redirect light emitted from the indicator for viewing by a user. The groove may be formed circumferentially around a portion of the outer surface of the longitudinal bundle. The groove includes a surface of end portions of multiple cut optical fibers, and the groove is configured to redirect the light emitted from the indicator toward the user by way of the end portions of the multiple cut optical fibers.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates, in general, to the field of night vision devices. More specifically, the present invention relates to the display of indicator lights, such as “low battery”, into the field-of-view of an eyepiece of a night vision device using a fiber optic screen.  
       BACKGROUND OF THE INVENTION  
       [0002]     Image intensifier devices multiply the amount of incident light they receive and provide an increase in light output, which can be supplied either to a camera or directly to the eyes of a viewer. Image intensifiers are constructed for a variety of applications and hence vary in both shape and size. These devices are particularly useful for providing images from dark regions and have both industrial and military applications. For example, image intensifiers are used in night vision goggles for enhancing the night vision of aviators and other military personnel performing covert operations. They are employed in security cameras and in medical instruments to help alleviate conditions such as retinitis pigmentosis (night blindness).  
         [0003]     Image intensifiers include active elements, support elements and supply elements. The active elements include the photo-cathode (commonly called simply “cathode”), microchannel plate (MCP), fiber optic screen (screen), and getter. The cathode detects a light image and changes the light image into an electron image. The MCP amplifies the electron image and the screen changes the electron image back to a light image. The getter absorbs gas which is generated during operation of the tube.  
         [0004]     The support elements comprise the mechanical elements which physically support the active elements of the tube. In a standard tube these support elements are the vacuum envelope (known as the body), input faceplate (sometimes also called “cathode”), and the output faceplate or fiber-optic (also called “screen”).  
         [0005]     The supply elements in the tube include the chrome contact that is deposited on the faceplate to the cathode, the screen aluminum contact which is deposited on the fiber optic or output faceplate, and the metalizing on the MCP glass. In addition the metal parts in the body assembly also provide electrical contact.  
         [0006]     The fiber optics direct the image generated by the screen to a convenient position so that the system optics can properly direct the image to the ocular plane.  
         [0007]     Three major components of image intensifier tubes are the photocathode, fiber optic screen (anode), and MCP disposed between the photocathode and anode. These three components are positioned within the evacuated housing or vacuum envelope, thereby permitting electrons to flow from the photocathode through the MCP and to the anode. In order for the image intensifier tube to operate, the photocathode and anode are normally coupled to an electric source whereby the anode is maintained at a higher positive potential than the photocathode. Similarly, the MCP is biased and operates to increase the density of the electron emission set forth by the photocathode. Furthermore, since the photocathode, MCP and anode are all held at different electrical potentials, all three components are electrically isolated from one another when retained with the vacuum housing.  
         [0008]     Power is provided to the photocathode, MCP and anode by a high voltage power supply, often in the form of an annulus. The power supply is usually axially aligned to surround the image tube.  
         [0009]     It is desirable to display an indication of “low battery” and/or an indication of “IR illuminator ON” to a user of a night vision device. This may be done by use of a low brightness light placed on the exterior of the night vision device to alert the user of the status of the power supply and/or other components. An LED may also be mounted at a convenient location on the exterior housing surface of the night vision device.  
         [0010]     Use of an indicator light on the outside surface of the night vision device, however, has shortcomings. In order to view the indicator light, the user must look away from the field-of-view of the eyepiece, and look at the indicator light. After looking at the indicator light, the user may then resume viewing the field-of-view through the eyepiece, but likely only after a time consuming eye-focusing adjustment. In addition, an indicator light mounted on the exterior surface of the night vision device may potentially give away the user&#39;s position.  
         [0011]     There exists a need for an improved approach to visually informing the user of the status of his night vision device. The present invention addresses such need.  
       SUMMARY OF THE INVENTION  
       [0012]     To meet this and other needs, and in view of its purposes, the present invention provides a night vision device including an image intensifier tube and a fiber optic screen disposed in operative relationship to each other. The fiber optic screen has a longitudinal bundle of multiple optical fibers and the bundle has an outer surface. A groove is formed in the fiber optic screen and extends transversely to the longitudinal bundle. An indicator is positioned adjacent to the outer surface of the bundle and proximate to the groove, where the groove is configured to redirect light emitted from the indicator for viewing by a user. The groove may be formed circumferentially around a portion of the outer surface of the longitudinal bundle. The groove may also be formed circumferentially around a complete perimeter of the outer surface of the longitudinal bundle. The groove includes a surface of end portions of multiple cut optical fibers, and the groove is configured to redirect the light emitted from the indicator toward the user by way of the end portions of the multiple cut optical fibers. The indicator may be positioned radially away from the outer surface of the fiber optic screen by approximately 1-2 times the value of an outer radial portion of the longitudinal bundle which is disposed outside of the field-of-view of the image.  
         [0013]     Another embodiment of the present invention is a night vision device including a photocathode and an anode configured to provide an image to a user, the anode including a fiber optic screen for channeling light from the image toward an eyepiece of the user. The fiber optic screen includes a longitudinal bundle of multiple optical fibers, the optical fibers providing the channeling of the light. A groove is formed in the fiber optic screen and extends transversely to the longitudinal bundle.  
         [0014]     An indicator is positioned adjacent to the outer surface of the bundle and is proximate to the groove, where the groove is configured to redirect light emitted from the indicator toward the eyepiece for viewing by the user. The groove includes a surface of end portions of multiple cut optical fibers, and the groove is configured to redirect the light emitted from the indicator toward the user by way of the end portions of the multiple cut optical fibers. The indicator may include two or more Is light emitting diodes (LEDs), and the LEDs are spaced circumferentially around the groove, which is formed circumferentially around the fiber optic screen.  
         [0015]     Yet another embodiment of the present invention is a method of providing an alert to a user of a night vision device, where the night vision device includes a fiber optic screen for directing light from an image toward the user, and a power supply for powering the night vision device. The method includes the steps of: (a) configuring the power supply for assembly with the fiber optic screen; (b) placing at least one indicator to provide the alert at a surface of the power supply;  
         [0016]     (c) cutting a groove in the outer surface of the fiber optic screen; and (d) aligning, during assembly, the groove with the indicator so that light emitted from the indicator impinges into the groove; wherein after alignment of the groove with the indicator, the light impinging into the groove is redirected by the fiber optic screen toward the user. Step (c) may include cutting the groove transversely to a longitudinal dimension of the fiber optic screen, and cutting the groove to a radial depth that is smaller than or equal to a radial width of an outer radial portion of the fiber optic screen, the outer radial portion including a bundle of multiple optical fibers that are outside a field-of-view of the night vision device.  
         [0017]     It is understood that the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0018]     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. Included in the drawing are the following figures:  
         [0019]      FIG. 1  is a schematic view of a night vision device, showing a groove cut into a fiber optic screen, in accordance with an embodiment of the present invention;  
         [0020]      FIG. 2  is an exaggerated schematic view of a night vision device, depicting a light emitting diode (LED) emitting light towards the groove in the night vision device, which redirects the emitted light toward an eyepiece used by a viewer, in accordance with an embodiment of the present invention;  
         [0021]      FIG. 3A  is an exaggerated schematic view of the fiber optic screen of  FIG. 1 , showing the groove which is cut into the outer portion of the fiber optic screen, in accordance with an embodiment of the present invention;  
         [0022]      FIG. 3B  is a magnified view of the groove which is cut into the extra fibers of the fiber optic screen shown in  FIG. 3A ; and  
         [0023]      FIG. 4  is a cross section of an exemplary night vision device, showing a transverse groove cut into the fiber optic screen, in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Use of an indicator outside of the field-of-view of the eyepiece prevents continuous viewing of the indicator and may potentially give the user&#39;s position away. Mounting the LED so that it may be in the field-of-view of the eyepiece complicates assembly and repair and limits the space available for other optical components. As will be explained, LEDs are oriented onto an exposed section of the fiber optic screen of an image tube, such that the light is transferred to a viewable portion of the fiber optic screen by use of a shallow groove which is cut into the side of the fiber optic. This approach advantageously provides indicators on the edge of the field-of-view of the image. The portion of the fiber optic screen, which is used for transferring the light from the indicator to the viewer is not used in displaying an image from the screen to the eyepiece. Consequently, no information of the image being viewed is lost. In addition, assembly of the packaged image tube and power supply into a night vision device is simplified, because the indicator is integral to the assembly before installation.  
         [0025]     Referring to  FIG. 1 , there is shown a schematic view of night vision device  10 . It will be appreciated, that night vision device  10  is of the type currently manufactured by ITT Night Vision of Roanoke, Virginia. At the entrance side of night vision device  10 , objective lens  12  collects low intensity light from a scene and transmits it to image intensifier tube  14 . Image intensifier tube  14  amplifies the light received from objective lens assembly  12  and transmits the intensified light to fiber optic screen  20 , which provides an image conduit for the light to be injected from the side of image intensifier tube  14  into a direction at the other end of the fiber optic screen. It will be appreciated that fiber optic screen  20  includes multiple fibers that are fused together to form the conduit channel for the light. Although not shown, it will be appreciated that fiber optic screen  20  may be twisted or bent so that it can provide almost any desired path between the image intensifier tube and the eyepiece  22 .  
         [0026]     As shown, the output side of fiber optic screen  20  is coupled to eyepiece  22  which provides a focused image to the user. The user thus may view an intensified image which is channeled from the input side of the night vision device, at objective lens  12  to the output at eyepiece  22 . As known, the image may be inverted or may be of a different size then the image having entered the night vision device.  
         [0027]     Also shown in  FIG. 1  is power supply  15  which in the figuration shown in  FIG. 1  is of a ring type that surrounds image intensifier tube  14  and fiber optic screen  20 . In the exemplary embodiment shown power supply  15  includes two indicators  16  and  18  positioned at the surface of annular power supply  15  and positioned to be adjacent to the outer cylindrical surface of fiber optic screen  20 . It will be appreciated that more than two indicator lights may be positioned around the inner surface of annular power supply  15 , as may be necessary.  
         [0028]     A shallow groove is cut into the outer portion of fiber optic screen, designated as groove  24 . Groove  24  completely encompasses the outer portion of fiber optic screen  20 . By cutting a shallow groove in the outer portion of fiber optic screen  20  light radiating from indicators  16  and  18 , which are integral to power supply  15  may then be transferred to the user&#39;s end by way of the fiber optic channels provided within fiber optic screen  20 . It will be appreciated that groove  24  does not interfere with the portion of the fiber optic screen which is used for displaying the viewed scene in the user&#39;s field-of-view. As will be explained, the outer portion of fiber optic screen  20  denoted by a width of D 1 , is defined as the unused portion of fiber optic screen  20 . The portion of fiber optic screen  20  which is exterior to links D 1  is defined as the useful portion of fiber optic screen  20 .  
         [0029]     Referring next to  FIG. 2 , there is shown the same night vision device  10 . As shown, the front end of night vision device  10  includes objective lens  12  and the back end of the night vision device includes eyepiece  22 . Positioned between objective lens  12  and eyepiece  22  are image intensifier tube  12  and fiber optic screen  20  the input side of fiber optic screen  20  includes a layer of phosphor, which provides an image screen for the field-of-view being imaged by objective lens  12 . Phosphor screen is generally designated as element  26 .  
         [0030]     It will be understood that for the sake of explanation, fiber optic screen  20  has been exaggerated in showing its fiber optic having been bundled to form fiber optic screen  20 . A groove is shown in fiber optic screen  20 , generally designated by element  24 . The groove has a depth of D 1 , as shown. An indicator, for example LED  16 , which is part of power supply  15  (shown in  FIG. 1 ) is positioned adjacent to groove  24 . For the sake of clarity the groove as shown in  FIG. 1  which is of annular shape, has been omitted from  FIG. 2 .  
         [0031]     The light emanating from LED  16 , indicated by light rays  28  impinge on groove  24  and enter a portion of the fiber optics that are in the fiber optic bundle comprising fiber optic element  20 . The fiber optics within the outer portion of fiber optic screen  20 , having a width of D 1 , channel the impinging light rays  28  towards both ends of fiber optic screen  20 . As shown, some of the light rays  28  are channeled toward the front end of fiber optic screen  20  and are stopped by phosphor screen  26 . On the other hand, some of light rays  28  are channeled towards the back end of fiber optic screen  20  for eventual exit from fiber optic screen  20  and for transmission onto eyepiece  22 . A user viewing an image through eyepiece  22  would easily see the indication provided by LED  16 .  
         [0032]     Referring next to  FIG. 3A  and  FIG. 3B  there is shown groove  24  in relations to fiber optic bundle  20 . As shown, fiber optic screen  20  includes an inner portion having active imaging fibers and a portion, denoted as extra fibers which are outside of the active imaging portion viewed by a user.  
         [0033]     The outer portion of fiber optic screen  20 , denoted by extra fibers, has a width of D 2 . The groove portion designated  24  which is cut into the extra fibers has a depth of D 1 . It will be appreciated that the groove may have a depth of D 1  which may be almost as width D 2 , as shown in  FIG. 3B . The shape and depth of groove  24  is not critical.  
         [0034]     As discussed above, the shape of the cut of groove  24  is not critical. In an exemplary embodiment, the depth of groove  24  may be approximately 0.5 mm (D 1 ). The width of the extra fibers portion may be of approximately 1 mm (D 2 ).  
         [0035]     It will be understood that groove  24  need not be annular in shape and completely envelope fiber optic element  20 . If, for example, only one LED is required for indication to the user then the groove may just be a smaller groove and need not completely surround fiber optic element  20 . If, on the other hand, it is desirable to have two or three or more indicators, then it is probably faster and less expensive to provide an annular groove  24  that completely surrounds the fiber optic screen  20 . The indicators may then be positioned around the fiber optic screen and be housed in the power supply at a location or locations that are adjacent to groove  24 . Indicators  4  providing an alert to the user, may be of a type other then LEDs. As shown in  FIG. 1 , for example, indicator  16  may be an IR illuminator indicator and indicator  18  may be a low battery indicator.  
         [0036]     Referring to  FIG. 2 , in an exemplary embodiment, LED  16  may be positioned approximately 1-2 mm away from the outer surface of fiber optic screen  20 . Such positioning, is adequate for allowing the light that is emitted from LED  16  to be channeled into the extra fibers and be transmitted to the user.  
         [0037]     In another exemplary embodiment LED  16  may be red in color, while LED  18  may be yellow in color.  
         [0038]     In an alternate embodiment, although it is not a preferred approach, groove  24  may extend deeper than the width of the width of extra fibers of fiber optic screen  20 . This embodiment would be functional and provide re-channeling of the LED indicators to the user. Of course, such embodiment would interfere with the field-of-view that is being imaged by objective lens  42  and being amplified by image intensifier tube  14 .  
         [0039]     Referring next to  FIG. 4 , there is shown a cross section of an exemplary night vision device  40 . As shown, on the entrance side of night vision device  40  there are several objective lenses, generally indicated as  42 . At the exit side of night vision device  40  there are several lenses used as an eyepiece for viewing by a viewer, the eyepiece generally designated by  48 . Objective lens  42  collects low intensity light from a scene and transmits it to image intensifier tube  44 . The image intensifier tube intensifies the light received from objective lens  42  and transmits the intensified light onto beam combiner  46 . Parallel light entering objective lens  42  at the top portion of night vision device  40  is collimated and transmitted to beam combiner  46 . Beam combiner  46  combines both rays from top of objective lens  42  and the bottom objective lens  42  and forwards it to the viewer by way of eyepiece  48 .  
         [0040]     A groove has been cut in fiber optic screen  52 , the groove generally being designated by element  50 . Although not shown in  FIG. 4 , an indicator, for example, such as LED  16  or LED  18  ( FIG. 1 ) which may be part of the outer surface of power supply  15 , may be positioned to be adjacent to groove  50 , as shown in  FIG. 2  by LED  16  being adjacent to groove  24  ( FIG. 2 ).  
         [0041]     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.