Abstract:
An optical system for illuminating and viewing a target ( 15 ) in which an illumination element ( 16 ) and a receiving element ( 13 ) are disposed behind a single optical window ( 14 ), and which obtains data essentially free of backscatter and stray light. The optical window ( 14 ) is configure such that is defines a shape having at least one focal curve, i.e., an ellipsoid shape dome. The illumination element ( 16 ) and the receiving element ( 13 ) are geometrically positioned on the focal curve plane or in proximity of the focal curve plane, such that, when illuminating, rays from the illumination element internally reflected from the optical window ( 14 ) will not incident on the receiving element ( 13 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of PCT Application PCT/IL00/00349, entitled “AN OPTICAL SYSTEM”, filed Jun. 15, 2000, which in turn claims benefit from Israeli Application 130486, entitled “AN OPTICAL SYSTEM”, filed Jun. 15, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an optical system for illuminating and viewing a target. 
     BACKGROUND OF THE INVENTION 
     An optical system for illuminating and viewing a target, which comprises a target, a source of illumination of the target and means for receiving the light remitted from the target, can be defined by an illumination axis and optical axis that converge at the target 
     Such an optical system may be as simple as an operator of an illumination source viewing a target, wherein the operator embodies the means for receiving the light remitted from the target. An example of such an optical system is an operator of a vehicle, that is inside the vehicle and is looking out at an illuminated target such as a road or tunnel walls. 
     More complex optical systems include automated processors as means for receiving the light remitted from a viewed target. Examples of such optical systems can be found in diagnostic apparatuses such as endoscope devices. The endoscopes described in the art comprise an image pickup element and an illuminating element for illuminating an examined target. 
     For these optical systems it is advantageous to have the illuminating element and receiving means contained within a single compartment, namely behind a single optical window. 
     In a vehicle carrying an operator, the illuminating elements are usually situated outside the vehicle, thereby requiring the operator to leave the vehicle for repairs or the like. In vehicles such as submarines or trains traveling in a dark tunnel, this may be a perilous task. 
     In diagnostic apparatuses, especially those meant to be inserted into body orifices, having a single optical window is advisable for hygienic and practical considerations. 
     A frequent problem encountered in having the illumination element and means for receiving remitted light contained behind a single optical window is the “noise” (backscatter and stray light) produced by light remitted from the optical window itself, which is received by the receiving means. 
     Presently used techniques for reducing noise include utilizing light guiding means, or separating the illumination element from the receiving means. 
     For example, U.S. Pat. No. 5,840,014 (Miyano et al.) describes an endoscope having an illumination window and a viewing window having a detachable protective covering and a transparent material for purging air from the space between the front end and the detachable covering, for lowering loss in illumination light quantity. 
     SUMMARY OF THE INVENTION 
     The present invention provides an optical system for illuminating and viewing a target in which an illumination element and a receiving means are disposed behind a single optical window, and which obtains data essentially free of backscatter and stray light. 
     The optical system according to the present invention comprises at least one illumination element and at least one receiving means, both disposed behind a single optical window having a plurality of reflecting surfaces. 
     The optical window is configured such that it defines a shape having at least one focal curve. 
     At least one illumination element and at least one receiving means are geometrically positioned on the focal curve plane or in proximity of the focal curve plane, such that, when illuminating, rays from the illumination elements, that are internally reflected from the optical window surfaces, will not be incident on the is receiving means. 
     It will be appreciated that the term “receiving means” relates to any means suitable for receiving, processing or further transmitting illumination rays remitted from a target or data derived from these rays. 
     In an embodiment of the invention the optical window is an ellipsoid shaped dome. A plurality of illumination elements are positioned on the ellipsoid focal curve and a receiving means is positioned on the axis of symmetry of the ellipsoid at an equal distance from the illumination elements. 
     The components of the system, thus positioned, ensure that when illuminating, all the light internally reflected from the optical window surfaces is received at points on the focal curve and is not incident on the receiving means. 
     The present invention further provides a diagnostic instrument comprising an optical system according to the present invention. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the figures in which: 
     FIGS. 1A and 1B are schematic two and three dimensional illustrations, respectively, of an optical system according to the present invention; and 
     FIGS. 2A and 2B are schematic illustrations of two embodiments comprising the optical system of the present invention; a diagnostic device and a vehicle carrying receiving means, respectively. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to an optical system based on geometrically positioning both illumination elements and means for receiving light behind a single optical window, such that internally reflected light from the optical window will not be incident on the receiving means. 
     The optical window, which is made of any suitable glass or plastic, can be viewed as being assembled from infinitesimal level surfaces, each level surface internally reflecting an illumination ray incident on it at a reflection angle equal to the angle of incidence. The level surfaces are angled to each other such that reflected Illumination rays are always converged at a single known point. 
     This assembly can result in a shape having focal points (for example, an ellipse) and an optical window thus assembled would have the optical property that light rays emitted from one focal point, which are internally reflected will be propagated to the second focal paint in a three dimensional shape (such as an ellipsoid) light rays emitted from a point on a focal curve, which are internally reflected, will be propagated to another point on the focal curve. 
     For example, in the field of arc lamp systems this property is used to collect energy efficiently. For example in Model A-1010 and A-1010B lamp housings provided by Photon Technology International of New Jersey, USA, an are source is located at a foci of an ellipsoid reflector and the radiation is reflected to another foci. Energy is collected efficiently since the light is brought to a focus by reflection rather than by refraction (through a lens) such that there is no loss due to absorption or lens surface back reflection. 
     In the optical system of the present invention the illumination elements are positioned on focal points and the receiving means&#39; position does not coincide with the focal points, thus ensuring that internally reflected light is propagated to focal points and not received by the receiving means. 
     Reference is now made to FIG. 1A which is a schematic two dimensional presentation of an optical system according to the present invention. 
     FIG. 1A is a two dimensional illustration of an optical system generally referenced  10 . The optical system  10  comprises an illumination element  11  and receiving means  13 , both disposed behind an optical window  14 , for viewing target  15 . Optical window  14  has a surface configured such that a shape defined by it and by broken line A has an axis of symmetry B and two focal points  19  and  12 . Illumination element  11  is positioned on focal point  19  and receiving means  13  is positioned on the axis of symmetry B not coinciding with either focal point  19  or  12 . 
     The course of light rays emitted from illumination element  11  will be followed as an example of the behavior of illumination rays in the optical system of the invention. Light  16  is emitted from illumination element  11  (which elements position coincides with focal point  19 ) for illuminating target  15 . A certain percent of the light (represented by ray  17 ) is internally reflected from the optical window  14  surfaces  14 ′ and  14 ″ and is propagated to the second focal point  12 . A percent of the light  16  (represented by ray  18 ) is incident on target  15 , is reflected from target  15  and received by receiving means  13 . 
     Thus, internally reflected light rays (such as ray  17 ) are propagated to areas outside the receiving means  13  area. 
     Receiving means  13  is also unexposed to direct illumination from illumination element  11 . Illumination element  11  may illuminate light  16  in a circular band that is tangent to line B. In this case, if receiving means  13  is positioned on line B it will not receive any direct illumination rays from illumination element  11 . Alternatively, receiving element  13  can be concealed in a niche  13 ′ to avoid receiving direct illumination rays from illumination element  11 . 
     Thus, geometric positioning of the components of the system ensures that no backscatter, such as ray  17 , and no direct light, only incident light, such as ray  18 , is received by receiving means  13 . 
     In actuality, the optical window  14  is a three dimensional shape. A three dimensional representation of the optical system  10  of FIG. 1A, is shown in FIG.  1 B. 
     In the optical system  10  shown in FIG. 1B plane B, formed along line B from FIG. 1A, is shown. Axis C is perpendicular to plane B. The shape on plane B which is defined by optical window  14 , encompasses focal curve D. 
     A plurality of illumination elements, such as  11  and  11 ′, may be positioned on focal curve D to enable a uniform spatial illumination, though it should be appreciated that any number of illuminating elements can be used according to specific requirements of the system. 
     Receiving means  13  is positioned at a point which is on, or in the vicinity of, axis C, essentially at an equal distance from both illuminating elements  11  and  11 ′, and on, or in the vicinity of plane B, such that it receives incident light remitted from target  15 . All the light radiated from illuminating elements  11  and  11 ′ that is internally reflected from the optical window surfaces is received at points on focal curve D and is not incident on receiving means  13 . 
     Thus data obtained by receiving moans  13  is essentially free of backscatter and stray light. 
     Two of the possible applications for the optical system of the present invention are provided as two different embodiments, illustrated in FIGS. 2A and 2B. 
     FIG. 2A illustrates a swallowable capsule which includes a) a camera system, b) an optical system for imaging an area of interest onto the camera system and c) a transmitter which transmits the video output of the camera system. Such a swallowable capsule is disclosed in U.S. Pat. No. 5,604,531, assigned to the common assignees of the present application, which is hereby incorporated by reference. The swallowable capsule can pass through the entire digestive tract and thus, operates as an autonomous video endoscope. 
     The capsule, generally referenced  20  is shaped as an ellipsoid. The capsule  20  comprises a housing unit  21  and a viewing unit  23 , for viewing a target point  29  on the digestive tract wall. The viewing unit  23  comprises an optical system according to the invention. 
     The optical system comprises a protective optical window  24 , preferably made of isoplast, two illumination elements  25  and  27  and an imaging device  28 . 
     Illumination elements  25  and  27  are positioned on a focal plane perpendicular to the axis of symmetry of the ellipsoid defined by the body of the capsule  20 . The imaging device  28 , such as a camera, is positioned on the axis of symmetry of the capsule  20 . 
     Light rays emitted from illumination elements  25  and  27 , that reach a target point  29  on the digestive tract wall are reflected to imaging device  28 , whereas light rays internally reflected from protective optical window  24  are propagated to points on the focal curve and not to Imaging device  28 . 
     It will be appreciated that protective optical window  24 , being a single and complete unit, is easily disposable, and can be smoothly replaced between different passes through the digestive tract. This fact, which is not affordable by endoscopes described in the art, contributes to the sterile and facile use of a diagnostic device comprising the optical system of the invention. 
     Thus, the present invention provides a simply assembled diagnostic device which can obtain data, essentially free of noise such as backscatter and stray light. 
     FIG. 2B illustrates a vehicle, such as a submarine, generally referenced  30 . Submarine  30  is shaped such that its eccentricity is equal to or larger than zero and smaller than  1 . 
     The submarine  30  comprises a propulsion unit  31  and a viewing cell  33 , encased by window  34 , in which an operator or a monitoring device  38  are positioned on the axis of symmetry of the shape of submarine  30 . A target of interest  39 , in the deep waters, is being viewed. The target of interest  39  is illuminated by illumination elements  35  and  37  that are positioned on a focal plane of the shape defined by the body of the submarine  30 , such that light rays internally reflected from window  34  do not blind the operator and/or are not received by monitoring device  38 .