Patent Application
20080011941
Optical sensors and detectors, including night vision systems, often use multiple imaging channels, each operating at a specified waveband. Standard night vision is enhanced with the addition of an infrared (IR) channel. Typical night vision systems operate in the 0.6 to 0.9 μm spectral waveband. These devices use image intensifier tubes to amplify ambient light not normally visible to the human eye and form an image on a phosphor screen that emits visible (usually green) light.
However, typical IR night vision devices cannot be used by aircraft crew because the canopy and windows of an aircraft are opaque in the thermal infrared wavebands. Furthermore, typical infrared night vision devices do not have sufficient resolution and sensitivity to detect objects hidden under camouflage, to view laser wavelengths commonly used for target designation and for rangefinders or to see through atmospheric obscurants, such as fog.
There is a need for an optical multi-waveband compact and lightweight system that solves the problem of the insufficient sensitivity of conventional IR sensors. There is further a need for a system that is compact, e.g. a common aperture system, and lightweight, e.g. hand-held or head-mounted. There is further a need for a night vision optical system that allows an aircraft crew to see through the canopy and windows, which are opaque in the thermal infrared wavebands.
Accordingly, in one embodiment, the present invention is a multispectral optical device comprising a common aperture objective assembly for image acquisition in the short wave infrared (SWIR) waveband and at least one additional waveband; a SWIR detector for detecting an image in the SWIR waveband; and a beam mixer for fusing an image detected by the SWIR detector and an image acquired in the at least one additional waveband.
In another embodiment, the present invention is a night vision system, comprising means for acquiring a multi-spectral image through a common aperture; means for converting a short wave infrared (SWIR) portion of the acquired image into the visible waveband, thereby generating a converted image; means for fusing the converted image with at least one additional portion of the acquired image.
In another embodiment, the present invention is a method of displaying images, comprising acquiring a multi-spectral image through a common aperture; converting a short wave infrared (SWIR) portion of the acquired image into the visible waveband, thereby generating a converted image; and fusing the converted image with at least one additional portion of the acquired image.
Further facilitating its use in aviation, a system employing short wave IR sensors allows a user to view laser wavelengths commonly used for target designation (1.06 μm) and for rangefinders (1.5 μm). Additionally, the short wave IR band is less sensitive to transmission loss through the atmosphere due to particulate scatter (water droplets, clouds, dust, fog, etc.)
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
A description of preferred embodiments of the invention follows.
The present invention is a common aperture, multi-spectral night vision system that provides a fusion of at least two images: one, originating from an image intensified (I2) optical channel and at least one other image originating in a spectral channel operating in a near infrared band (NIR, approximately 0.9 μm to 1.9 μm) that includes a short wave infrared (SWIR) range of wavelengths from about 1.0 μm to about 1.8 μm. In a preferred embodiment, the night vision (NV) system provides a fused, spatially registered (overlayed on top of each other) imaging. Preferably, one of the spectral channels is a visible image intensifier channel (I2) operating in the range of wavelengths from about 0.6 μm to about 0.9 μm.
In the description below, the terms “NIR” and “SWIR” are used interchangeably as a matter of convenience. It is understood that the present invention can operate in the NIR range. It is further understood that the preferred sensitivity of the NIR detectors is from about 0.9 μm to about 1.8 μm.
As used herein, the term “detector” refers to any one or more elements that receives an image in the visible, infrared or other part of optical spectrum and manipulates and/or transforms this image by amplifying its intensity or converting it to the visible spectrum. As used herein, the term “lens element” refers to one or more elements having optical power, such as lenses, that alone or in combination operate to modify an incident beam of light by changing the curvature of the wavefront of the incident beam of light. A “display” can be any surface used to produce a wavefront encoding an image. Examples of displays include CRT-based, LCD-based or gas-plasma-based flat panel displays. In one embodiment, a display can be a projection screen. As used herein, the term “beam” refers to one or more rays.
A conceptual diagram of the invention is illustrated in
Beamsplitter 104 causes beam 103 to be separated into a short wave infrared (SWIR) waveband portion 110 and at least one beam 106. In the embodiment shown in
Following beamsplitter 104, beam 106 is incident on image intensifier tube 108, where the signal is amplified (spectral waveband 0.6-0.91 μm, in general).
Similarly, beam 110 is reflected by beamsplitter 104 to focal plane array 112. One skilled in the art understands that FPA detectors include standard electronic components required for processing the detected images.
Focal plane arrays capable of detecting the NIR waveband, including SWIR, can be any commercially available SWIR detector. Preferably, focal plane array 112 includes InGaAs semiconducting material. Examples of commercially available SWIR detectors are the SUI™, sold by Sensors Unlimited, Inc. of Princeton, N.J.
The signal detected by focal plane array 112 is processed, if required, by optional programmable CPU 114 and then displayed on display 116. Display 116 is preferably a visible organic light emitting diode (OLED) microdisplay. Beam 118 from display 116 and beam 120 from the phosphor surface of image intensifier tube 108 are combined into a single image in eyepiece assembly 122. Eyepiece assembly 122 includes beam mixer 124 and lens 126 in an arrangement similar to that used in the objective assembly 101. Preferably, beam mixer 124 is a beamsplitter. Other embodiments of beam mixers can be used, as will be described below with reference to
In an alternative embodiment, image intensifier tube 108 can be replaced by an additional FPA detector (not shown). In this embodiment, an additional display, driven by an electrical signal generated by the additional FPA detector can be placed adjacent to beam mixer 124. Beam splitter 124 will fuse the beams generated by display 116 and the additional display.
An alternative embodiment of the invention is device 200 shown in
A preferred embodiment of a device of the present invention is shown in
Device 300 includes objective focusing cell 301, housing 336, eyepiece housing 346 and eyepiece diopter cell 348. Objective focusing cell 301 includes focus ring 332 for adjusting the focal length of cell 301. Similarly to device 100, shown in
The image-intensified beam continues through additional lens 344 toward second beamsplitter 324, which fuses the image carried by the image-intensified beam and the image produced by display 316, which is driven by an electrical signal generated by SWIR detector 340. The fused image is viewed by an observer through eyepiece diopter cell 348. Second beamsplitter 324 and display 316 are disposed within eyepiece housing 346.
A preferred use of device 300 is shown in
Field 502 represents the field of view (FOV) of image intensifier tube 308 (I2 channel). In this example, the FOV for the I2 channel is 36-40 degree at greater than 1.4 cycles per mrad.
Field 504 represents the FOV for commercially available SWIR detectors, which typically have 320×240 pixels and a 25 micron pitch (the distance between adjacent pixels). The FOV for this type of a SWIR detector is 22.5-25 degrees at 0.5 cycles per mrad. (Instantaneous FOV=1 mrad for 25 μm pitch).
Field 506 represents the FOV for SWIR detectors, which typically have 320×240 pixels at 40 micron pitch. The FOV for this type of a SWIR detector is 36 degree for 0.315 cycles per mradian. (IFOV=0.63 mrad; 40 μm pitch).
A device of the present invention, such as device 300 shown in
Device 300 provides a reliably sufficient output under very low ambient light, such as, for example, star light. The plots presented in
While image intensifiers of device 300 amplify ambient light, the longer wavelengths of the SWIR spectrum enable significant gain in starlight conditions as well as detection of thermal emission of hot objects.
Due to the inherent change in reflectance of many natural materials, device 300 is very effective for detection of objects hidden under camouflage.
Yet another advantage of device 300 is its ability to see through fog and other atmospheric obscurants, as illustrated by
Furthermore, device 300 is capable of detecting laser waveband used for target designation and operates at the range of wavelength for which an aircraft canopy is transparent.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
This application is related to U.S. application Ser. No. 11/176,690, filed Jul. 7, 2005. This application claims the benefit of U.S. Provisional application No. 60/627,116, filed Nov. 12, 2004. The entire teachings of the above applications are incorporated herein by reference.
The invention was supported, in whole or in part, by a grant FA8650-05-C-6507 from the U.S. Air Force. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60627116 | Nov 2004 | US |
