Single multiple aperture (“SMART”) lens system

[0002] This invention relates generally to optical systems and, more particularly, to optical devices for determining the position of a source of light incident on the device.

[0003] Optical systems for determining the geographical position of a source of light are used in a variety of applications. For example, conventional laser-guided missiles make use of reflected light from a laser beam pointed toward a potential target. Once a target is selected, information from the laser beam is used to determine the position of the target relative to the missile.

[0004] Such laser-guided missile systems are known in the art. One exemplary system is described in U.S. Pat. 5,784,156, to Nicholson, incorporated herein by reference. The incoming reflected light is detected at apertures located at different points on the exterior of the missile, typically on the nose cone or wing edges. Each aperture is provided with a lens or lens system that focuses the incoming light onto a bundle of fiber optic cables running inside the missile. The fiber bundles then transmit the incoming light onto sensors that convert the incoming light into electrical signals. These electrical signals are then analyzed by computers on board the missile to determine the relative distance, azimuth, and elevation between the missile and the object from which the incoming laser light is reflected.

[0005] Each aperture and its corresponding fiber bundle, or bundles, possesses a field-of-view (“FOV”), i.e., an angle from which it can detect light. All of the individual FOV of the apertures together form the overall FOV of the missile. Since the FOV of a given aperture is limited by the optics involved, to increase the FOV of a missile, one must typically increase the number of apertures and lenses employed by the missile. This problem is illustrated in FIG. 1B.

[0006] FIG. 1B shows a conventional dual lens “telescope” aperture configuration. In this configuration, the aperture is fitted with a primary lens 100 that focuses the incoming light rays, shown by dotted lines 102, onto a secondary lens 104. The secondary lens 104 then focuses incoming light rays onto a bundle of fiber optic cables 106. The fiber bundle 106 then transmits the incoming light onto sensors in the missile that convert the incoming light into electrical signals, which are used to determine the location of the target as discussed earlier. The FOV of the dual lens aperture arrangement shown in FIG. 1B is limited by the optical properties of the primary and secondary lens used. The FOVs are limited by off-axis light rays, and a typical FOV is plus or minus 10 or 15 degrees in conventional missile systems.

[0007] Similarly, another optical laser-guided missile system currently in use employs a plurality of ball lenses at each aperture, with each ball lens associated with a single fiber bundle. This arrangement is shown in FIG. 1 in which a ball lens 108 is used to focus incoming light rays 110 onto a fiber bundle 112. While this system is in some ways more advantageous than the dual lens system shown in FIG. 1B, it, nevertheless, still is limited to the FOV defined by the optical properties of the ball lens 108 and the fiber bundle 112. Increasing the FOV of the missile would still involve providing additional ball lens/fiber bundle arrangements in additional apertures located on the missile. For example, a conventional Hellfire IR seeking missile creates 32 FOVs by using 32 apertures mounted in two circumferential rings in the missile nose.

[0008] In one embodiment, the laser detection system comprises a ball lens and a plurality of fiber optic bundles placed adjacent the ball lens so that incoming light rays are focused onto the bundles by the ball lens. In one version of the invention, a ball lens is one that can provide. an almost infinite number of “principal” axes for off-axis light. Each fiber optic bundle is aimed in a different direction from each other bundle so that each bundle will have a different FOV even though the same ball lens is used to focus the incoming light rays. Because the fields-of-view of all the bundles together form the overall FOV of the ball lens, the more bundles that are incorporated into the system, the larger the FOV of a given ball lens. In one advantageous embodiment, the bundles may be disposed so that their fields-of-view may overlap partially.

[0009] FIG. 1A is a schematic diagram showing a conventional single ball lens aperture configuration.

[0010] FIG. 1B is a schematic diagram showing a conventional dual lens aperture configuration.

[0011] FIG. 2A is a schematic diagram showing an embodiment of the invention in which the FOV of an aperture is increased through the use of multiple ball lenses.

[0012] FIG. 2B is a schematic diagram of an embodiment to the invention which a single ball lens is provided with an increased FOV through the use of multiple fiber bundles.

[0013] FIG. 3A is a schematic diagram of an embodiment to the invention showing a single ball lens provided with multiple overlapping FOVs.

[0014] FIG. 3B is a schematic diagram showing the placement of a group of fiber bundles on a ball lens according to an embodiment of the invention.

[0015] FIG. 4 is a cross-sectional view of a drum lens useful with an embodiment of the invention.

[0016] FIG. 5 is a schematic diagram of a laser detection system coupled to a guided vehicle as disclosed herein.

[0017] Referring now to FIG. 2A, there shown an embodiment to the invention using multiple ball lenses. In this case, three lenses, 200, 202, and 204, are arranged at a single aperture at a location on the missile not shown. Each lens is optically coupled to a single fiber bundle, 201, 203, and 205, respectively. Light rays 206 are focused by the ball lenses onto their respective fiber bundle. Fiber bundle 203, connected to ball lens 202, has an elevation of 0 degrees. In practice, this FOV angle would relate to the geometry of the missile or other device on which the fiber bundle 203 was placed. For example, on a guided missile, fiber bundle 203 could be aimed so that the axis of fiber bundle 203 was parallel to the longitudinal axis of the missile. The elevation of the FOV for fiber bundle 205 is increased relative to that of fiber bundle 203. Similarly, the elevation of fiber bundle 201 is decreased with respect to fiber bundle 203. The amount of increase or decrease in the FOV for fiber bundles 201 and 205 is a matter of design choice, and will only be limited by the optical properties of the lenses and fiber bundles used in the construction of the system. By using fiber bundles 201 and 205 in conjunction with fiber bundle 203, the FOV for the entire aperture shown in FIG. 2A is substantially increased in elevation. Of course, similar improvements could be made in azimuth as well.

[0018] According to a further embodiment to the invention, the advantages obtained by the optical system shown in FIG. 2A can be attained using a single ball lens shown in FIG. 2B. In this version of the invention, a single ball lens 208 is used to focus incoming light rays 206 onto a plurality of fiber bundles 209, 210, and 211. Each of these fiber bundles 209, 210, and 211 is positioned with respect to the ball lens 208 so that its FOV differs in elevation from its neighbors. Again, defining somewhat arbitrarily, fiber bundle 210 as having an elevation of zero degrees, then fiber bundle 209 has an elevation of its FOV greater than the elevation of fiber bundle 210 and 211 has an elevation of its FOV somewhat less than fiber bundle 210. In the particular embodiment shown in FIG. 2B, the FOV for each of the fiber bundle overlaps. This is particularly advantageous because the relative contributions of signals from the various fiber bundles allow one to determine angle of arrival information. This in turn produces guidance information for the missile.

[0019] Of course, it is not required that all the field-of-views overlap, and in other embodiments in the invention, the field of views can be non-overlapping, as a matter of design choice. In order to receive signals that can be used for guidance, at least adjacent fiber directions should produce an overlapping field-of-view. The fact that all FOVs do not overlap may be advantageous to systems that combine signals to a single detector. The non-overlapping FOVs in this case would produce less background noise due to a reduced field-of-view.

[0020] Of course, the above embodiments have been described with respect to two dimensional drawings showing differences in the elevation of the field-of-views for the fiber bundles; however, those who are skilled in the art will recognize that it will be useful to arrange fiber bundles to increase the total FOV of the system in azimuth as well as elevational dimensions. FIG. 3 depicts a particularly advantageous arrangement of the fiber bundle placement with respect to the ball lens. Here, the ball lens 212 focuses the incoming light rays 206 onto a plurality of fiber bundles 213A-213G. The fiber bundles 213A-213G are arranged so that each has a unique FOV compared to the rest. The FOV of the total system is increased in a 360 degree pattern compared to the central fiber 213A located at zero degrees elevation and zero degrees azimuth. FIG. 3B is a cross-sectional view through section A—A of FIG. 3A looking in the direction of the arrows shown. It is seen that a central fiber 213A is surrounded by fibers 213B-213G. Each fiber 213B-213G is given a different angle of FOV in either azimuth or elevation, or both with respect to fiber 213A. This creates a larger FOV for the entire ball lens system shown in FIG. 3A, but while still maintaining an overlapping FOV for each individual fiber bundle.

[0021] In another embodiment of the invention, it is useful if the ball lenses are manufactured from different types of materials or glass. This allows one to modify the field-of-view of the lens and to affect the amount of coupling of light to the adjacent fiber bundles. One also has the flexibility to use different sizes of ball lenses. This also affects the overall FOV when used in conjunction with fiber bundles of different diameters and different numerical apertures (“NA”).

[0022] In still a further embodiment to the invention, it is possible to substitute a drum lens in place of the ball lens shown in FIGS. 2A-3B. Although technically not a “ball” lens, the drum lens shares some of the properties of a ball lens. FIG. 4 shows a comparison of a Ball Lens 400 and a Drum Lens 402. The length of both lenses is D as shown in FIG. 4. The height of the Drum Lens is H. As long as incident rays stay within the drum lens volume, the two lenses are functionally identical.

[0023] In still a further embodiment to the invention, it is useful that the effective FOV of the lens/fiber system be varied as follows. All fiber bundles point toward the center of the ball lens. The field-of-view is changed by varying the angle of each fiber bundle relative to the central or principal axis. The amount of overlapping signal depends upon the size of the fiber bundle at a particular angle. By pushing the fiber bundles closer to the ball lens, the amount of overlap between adjacent fiber bundles increases. The FOV can also be changed by varying the NA of each fiber. Therefore, the overall FOV can be controlled by changing the ball lens diameter or material composition, by changing the fiber numerical aperture, by changing the fiber bundle size, and/or by changing the fiber displacement from the ball lens. All of these factors are related to the required guidance precision.

[0024] There are many ways information from the reflected light energy may be used to determine the direction to the target. In one embodiment of the invention, each fiber bundle is coupled to a detector that converts the reflected light into electrical signals. The amplitudes of these electrical signals are related to the amount of light energy received from its corresponding fiber bundle. Because each fiber bundle has a unique FOV, those of skill in the art will recognize that the amount of energy received at the various FOVs can be interpolated to calculate the direction to the target.

[0025] FIG. 5 is a schematic diagram of a laser detection system 500 coupled to a guided vehicle 502 as disclosed herein. The guided vehicle 502, for example, can be a missile. A ball lens 504 is coupled to the guided vehicle. The balls lens 504 has an interior that is formed from a solid, that is, is a single element ball lens. A plurality of fiber bundles 506, 508, 510 are disposed adjacent the ball lens 504. At least some of the fiber optic bundles are pointed toward a center of the ball lens 504 and have overlapping fields-of-view with other fiber optic bundles. A sensor system 512 can include a plurality of detectors 514, 516, 518 and associated hardware that converts light from the fiber bundles into electrical signals. A computer system 520 can use the electrical signals from the detectors to compare an amount of energy contained in the light from various fiber optic bundles to calculate the direction of the guided vehicle to a target 522. A laser 524 can be used to direct a beam of light 526 toward the target 522 that is reflected and to the ball lens 504. Naturally, the guided vehicle can have one or more of the ball lens and fiber optic bundle arrangements coupled to the computer system to provide other information as desired.

[0026] Although the present invention has been described with respect to its application in guided missile systems, those who are skilled in the art will recognize that the invention also pertains to increased field-of-views in optical systems employing fiber optic cables in connection with optical lenses. For example, the invention is easily adapted to any system that uses reflected laser energy for guidance. For example, any robotic system could use reflected laser light in conjunction with the ball lens for increased precision in navigating toward the target. This could include mobile robots, such as cars, androids, etc. that have a task to move from point A (their present location) to point B where the item of interest is located. Similarly, a robotic arm could be guided to a laser illuminated “part of interest” located on a moving platform, such as a conveyor belt. Still other applications within the scope and spirit of the present invention will occur to those of skill in the art in view of the foregoing disclosure.