US 20040196566 A1
A system (S) for combining multi-spectral images of a scene includes a first detector (18) for transmitting a scene image in a first spectral band. A separate, second detector (22) senses the scene in a second spectral band. The second detector (22) has an image output that is representative of the scene. A transparent display (26) mounted in the output viewing path (30) of the first detector (18) and displays a displayed image in the second spectral band. The image of the transparent display is aligned such that the image (12) of the scene in the second spectral band combines with the image output (10) in the first spectral band. The combined multi-spectral images (54) are conveyed to an output (32) for a user (U).
1. A system for combining multi-spectral images of a scene, the system comprising:
a channel for transmitting a scene image in a first spectral band;
a separate second detector for sensing the scene in a second spectral band, the second detector having an image output representative of the scene;
a transparent display for receiving the image output of the second detector, and displaying a displayed image from the second spectral band; and
the transparent display being positioned in an output path of the transmitted scene in the first spectral band.
2. The invention of claim [Claim Reference] wherein the transparent display is self luminous.
3. The invention of claim [Claim Reference] wherein the transparent display is a transparent Organic Light Emitting Diode (OLED).
4. A method for combining multi-spectral images of a scene, which comprises:
transmitting a scene image in a first spectral band through a first channel;
sensing the scene with a second separate detector responding to a second spectral band, the second detector having an image output representative of the scene; and
combining the scene image in the first spectral band with an image displayed by a transparent display adapted for receiving the image output of the second detector; the transparent display being positioned in an output path of the transmitted scene in the first spectral band.
5. The method of claim [Claim Reference] wherein the transparent display is self luminous.
6. The method of claim [Claim Reference] wherein the transparent display is a transparent Organic Light Emitting Diode (OLED).
 This application claims the benefit of U.S. Provisional Application Serial No. 60/319,299, filed Jun. 6, 2002, entitled INTEGRATED DISPLAY IMAGE INTENSIFIER ASSEMBLY.
 1. Technical Field
 The invention relates to the field of night vision devices, and particularly to a system for combining images from an image intensifier and an infrared camera system.
 2. Background Art
 Standard night vision is enhanced with the addition of IR information. Whereas typical night vision devices (image intensifiers) can only see visible wavelengths of radiation, the fused system provides additional situational awareness by providing infrared (heat) information to the image. A typical scenario where this might be important is in a situation where a person is camouflaged and cannot be seen with image intensification. However, with the addition of infrared information to the same image, the camouflaged person's heat signature is seen. Typical infrared night vision devices do not have sufficient resolution and sensitivity to provide good imagery of the full environment being looked at. Use of overlay image intensification (II) and infrared radiation (IR) fusion provides benefit of II resolution and environment awareness with benefit of infrared signatures, smoke penetration, etc.
 Generally, there are two alternative methods of fusion: digital fusion and analog fusion.
 Previous designs for combining images have used a dichroic beam splitter. The image intensifier image would pass directly through the beam splitter while the infrared image projected by a display would reflect off the beam splitter and merge onto the image intensifier image.
 One technique known for combining an infrared image with an image displayed at visible wavelengths is described in U.S. Pat. No. 4,751,571 to Lillquist. The system disclosed in this patent has two separate image paths. One path transmits visible light to an image intensifier while a second path transmits thermal IR to an IR detector. Both the intensified image and the IR image are converted to electronic video signals. The two electronic signals are then mixed at a video mixer and then displayed on a color monitor. The technique described in the Lillquist patent has the disadvantage of requiring that both signals be electronically converted and electronically combined before being displayed to a user. Such electronic conversion will lose the very high resolution of the image intensified night vision device. Additionally, the Liliquist approach requires a dedicated system not usable with the vast population of existing night vision devices.
 Another image fusion system is described in U.S. Pat. No. 5,035,472 to Hansen. This patent describes a device that conveys the image along two separate paths. One path directs the image to an IR detector which produces an IR image. The IR image is then transmitted to a CRT which displays the image. A second path directs the image of the scene to an image intensifier tube which generates an intensified image which also produces a visual display of the image. The displayed IR and intensified images are optically combined for display to a user. The technique described in the Hansen patent requires both images to be visibly generated before they are optically combined behind the image intensifier. This approach has the disadvantage of requiring a dedicated system not usable with the vast population of existing night vision devices.
 Another technique calls for detecting a scene using multiple sensors which convert the images to digital data and then algorithmically combine the data using microelectronic processors. The disadvantages of this approach are that it is time consuming, requires substantial processing power, and the high resolution of a night vision channel cannot be captured electronically.
 Prior designs typically use a dichroic beam splitter. The image intensifier image passes directly through the beam splitter while the infrared image projected by a display would reflect off the beam splitter and merge onto the image intensifier image. Use of the beam splitter in such prior designs adds weight, size, forward projection as well as requiring additional parts to hold the beam splitter assembly.
 While the above cited references introduce and disclose a number of noteworthy advances and technological improvements within the art, none completely fulfills the specific objectives achieved by this invention.
 In accordance with the present invention, a system for combining multi-spectral images of a scene includes a first channel or detector for transmitting a scene image in a first spectral band. A separate, second detector senses the scene in a second spectral band. The second detector has an image output that is representative of the scene. A transparent display mounted in the output viewing path of the first detector and displays a displayed image in the second spectral band. The image of the transparent display is aligned such that the image of the scene in the second spectral band combines with the image output in the first spectral band. The combined multi-spectral images are conveyed to an output for a user.
 An object of the present invention is to provide a means to fuse an image intensifier and an IR camera image using optical overlay methods while minimizing the weight, size, form factor, goggle forward projection of the night vision goggle assembly.
 These and other objects, advantages and features of this invention will be apparent from the following description taken with reference to the accompanying drawings, wherein is shown the preferred embodiments of the invention.
 A more particular description of the invention briefly summarized above is available from the exemplary embodiments illustrated in the drawings and discussed in further detail below. Through this reference, it can be seen how the above cited features, as well as others that will become apparent, are obtained and can be understood in detail. The drawings nevertheless illustrate only typical, preferred embodiments of the invention and are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.
FIG. 1 is a block diagram for the system of the present invention.
FIG. 2 is an exploded view of one embodiment of the present goggle design.
 So that the manner in which the above recited features, advantages, and objects of the present invention are attained can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to the embodiment thereof that is illustrated in the appended drawings. In all the drawings, identical numbers represent the same elements.
 This invention relates generally to the subject matter of the Provisional Patent Application No. 60/319,296, filed Jun. 5, 2002, entitled “Enhanced Night Vision Goggle Assembly” and its description is incorporated by reference as if fully set forth herein.
 The present invention describes a night vision system or device S that provides fusion of two images 10, 12 originating from an image intensifier 14 and an infrared camera 16.
 The system S for combining multi-spectral images of a scene includes a first channel or detector 18 for transmitting a scene image 20 in a first spectral band. A separate, second detector 22 senses the scene 22 in a second spectral band. The second detector 22 has an electronic signal image output 26 that is representative of the scene 22. A transparent display 28 mounted in the output viewing path 30 of the first detector 18 and displays a displayed image 12 in the second spectral band. The image 12 of the transparent display 28 is aligned such that the image 12 of the scene in the second spectral band combines with the image output 10 in the first spectral band. The combined multi-spectral images are conveyed to an output 32 for a user U.
 The image intensifier 14 provides an imager using known photo-cathode, microchannel plate, and phosphor screen technology. Visible and near infrared light is collected by an optical element (objective) 34 and is focused onto the photo-cathode 36, where photons are converted to electrons. The electrons are accelerated through the microchannel plate 38, creating new electrons. The resultant multiplication of electrons land on a phosphor screen 40 where luminescence occurs. The image created is passed through a fiber optic bundle 42 creating an optical imaging focal plane.
 A known infrared camera 16 is used to convert infrared imagery into a visible image. Since the present invention can utilize any type of infrared camera, the description of converting infrared imagery into a visible image is not set out here. However, it is important that the output 26 of the infrared camera is provided in a form that can be formatted for presentation by a display.
 The display 28 of the present invention is preferably located at the image intensifier image plane 44. It must be a transparent, self luminous, display that allows the light emitting from the first detector 18, or image intensifier 14, to pass through. The display 28 provides the image 12 of the output 26 from the second detector 16, or IR camera.
 Optionally, the incoming path 46 for collecting incoming radiant energy for the image intensifier 14 is separate from, but essentially parallel, to the incoming path 48 for the infrared camera.
 An optical lens (eyepiece) 50 provides the ability to focus on the focal plane/display image plane 52 of the transparent display 28 providing the combined image 54 to a users eye 55.
 The final product of the present assembly results in a fused multi-spectral optical overlay image 32.
 It is preferred that a transparent Organic Light Emitting Diode (OLED) is used to display the digitized IR camera data 26. The OLED device provides a robust, integrated design that requires minimal power, and does so under a full military type temperature range. Other known types of displays require external illumination often either lose performance as the ambient temperature is lowered or require a heating element to keep its temperature at acceptable levels to meet performance requirements. The use of the OLED in the Night Vision Goggle (“NVG”) S is ideal for minimizing power, which is critical and rationed for extended battery life, across the full NVG operational temperature ranges.
 The transparent OLED's format and size is designed so that when the scene from the first detector 18, such as the image intensifier 14, is projected through the display 28, the image intensifier's output circumscribes the display's format. This allows the fused image to reside in the central portion of the user's field of view. An alternative is considered whereas the image intensifier's output is inscribed in the display.
 Alternative designs for the eyepiece design may be used whereas the display 28 has a format that is either larger or smaller than that required for the direct overlay fusion onto the image intensifier's output. In this case, a fiber optic bundle with taper or enlarger, a field flattener or magnifier, or other optical device that would magnify or shrink the display's format so that it would fit within the required image intensifier's output would be used. Again, the projected display image may either be inscribed or circumscribed by the image intensifier's (II) 14 output.
 The present invention further optionally uses a push button control 56 and associated micro-electronic function 58 for operation of image intensifier and IR display brightness. A micro-controller 58 may be packaged within the NVG to provide a broad spectrum of features to the user. First, the micro-controller 58 may control the brightness of both the image intensifier 14 and the display 28. In changing the brightness of the two separate images, the user U is able to determine the best mix within the fused image for optimal viewing. With the micro-controller's programmable feature, the user U is able to determine which method of mixing the user would like to use.
 Alternatively, the display 28 may be fabricated directly on the fiber optic output the same surface as the image intensifier's image or by fabricating the display on a transparent glass or plastic substrate. The display 28 is a passive display utilizing transparent polymers and line drivers for operation. The size, shape, and spacing of the line drivers are considered to ensure that the transmission through the display is sufficient to allow the image from the image intensifier to pass.
 Several variations in the type of image fusion mixing may be used. One such method is where the display brightness and the image intensifier brightness are controlled in a double ramp fashion. Starting in the middle, both components' brightness is set at 50% of their full brightness. As the user pushes on one button, the display's brightness ramps to 100% (full on) while the II's brightness ramps to 0% (off). From this point, if the user pushes another button, the brightness of the display ramps back down while the II's brightness ramps up. Ramping continues back to the 50/50 point and continues until the displays brightness is at 0% (off) and the II's brightness is full on.
 The micro-controller 58 may also monitor the voltages from the batteries 60 and provides warning lights to the user when batteries are low. Since the IR camera is the biggest power load on the batteries, the micro-controller 58 provides the user a few minutes of operation after the low light indicator is turned on. After that point, the IR camera may be turned off and the image intensifier may be left on allowing the user to continue with just image intensifier operation for another two hours. This feature provides the user to “limp home” to retrieve new battery resource or replacement.
 A method for combining multi-spectral images of a scene comprises transmitting a scene image in a first spectral band through a first channel 18. Essentially simultaneously the scene is sensed with a second separate detector channel 22 responding to a second spectral band. The second detector 22 has an image output that is also representative of the scene. The scene image in the first spectral band is combined with an image displayed by a transparent display 26 adapted for receiving and displaying the image output of the second detector 22. The transparent display 28 is positioned in an output path 30 of the transmitted scene in the first spectral band.
 Referring to FIG. 2 one embodiment of the NVG S of the present invention is shown mounted within a housing assembly including a first or frontal section 62 that mates with a rear housing segment 64 The scene to be observed P is represented within the general optical alignment of the first channel 18 and the second channel 22.
 The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.