Patent Abstract:
The invention concerns an illumination apparatus for an optical observation device ( 10 ), in particular a stereomicroscope or a stereo surgical microscope. A multi-armed light guide with coupler ( 2 ) mixes colored light emitted by light-emitting diodes ( 1   a–c ) to yield white mixed light ( 15 ).

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of the German patent application 103 39 618.7 filed Aug. 28, 2003 which is incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention concerns an illumination apparatus for an optical observation device, in particular a stereomicroscope or a stereo surgical microscope. 
     BACKGROUND OF THE INVENTION 
     Light-emitting diodes (LEDs) that emit colored light have now become so bright that they are used, for example, for traffic signal systems and in the rear lights of vehicles. 
     For a microscope illumination system, white light is principally desirable. White-light-emitting LEDs already exist. These are not, however, bright enough for this application. A plurality of light-emitting diodes arranged next to one another and emitting red, green, and blue light can be used to generate white light. 
     DE 37 34 691 C2 presents a solution making possible a variety of illumination types and an intensity control capability with the aid of this type of red-green-blue arrangement of many small LEDs. A bright-field, dark-field, or oblique illumination can be produced by selective local activation of the individual LEDs. The overall intensity of the illumination can be regulated by the fact that either all or fewer LEDs are in operation, or on the other hand only those LEDs that result in a specific configuration. The individual LEDs are not, however, individually controllable; they can only be switched on and off. 
     To achieve uniformly homogeneous coverage of the illumination aperture, a frosted disk must be introduced in the immediate vicinity of the LED light source. 
     A further embodiment according to this existing art provides that white light can be generated with a red, green, and blue planar LED light source and a system of dichroic splitters. This illumination apparatus offers a high light intensity, but is relatively bulky. Because of the long optical paths, the light must be collimated using additional lenses. A further disadvantage is the high alignment accuracy of the dichroic mirrors required to ensure good and constant color accuracy. 
     The disadvantages of tungsten lamps, halogen lamps, etc., as used hitherto for microscopes, are principally high thermal dissipation, high power consumption and short service life, little robustness, large space requirement, and heavy weight (cf. DE 37 34 691 C2, col. 1, lines 7–12). 
     DE 19 13 711 A presents a solution for uniform light distribution and intensity regulation of a single conventional light source (Planck radiator) by means of fiber bundles. For that purpose, a fiber bundle having a single entrance and exit surface is placed after the conventional light source with diaphragm. No positional allocation of the fibers with respect to the entrance and exit surface exists. 
     This offers the advantage that the inhomogeneous intensity distribution of the light source image is homogenized at the end of the fiber, and a continuous intensity regulation is produced at the end of the fiber by way of the diaphragm at the fiber entrance. 
     SUMMARY OF THE INVENTION 
     The basis of the present invention is not primarily the need for a uniform light distribution, but rather the combination and associated increase in intensity of the light from a variety of light sources, with no increase in space requirement and without the aforementioned disadvantages of conventional light sources. 
     It is presently the case in the existing art that a colored-light-emitting LED possesses a higher luminance than a white-light-emitting LED. Combining the light of three color LEDs makes the luminance difference as compared with a single white-light-emitting LED that much greater. 
     According to the present invention, therefore, at least one red-, one green-, and one blue-light-emitting LED are arranged physically next to one another. The light that emerges is fed respectively into a multi-arm light-guiding fiber bundle, each light guide arm being illuminated by one colored-light-emitting LED. The light guide arms are combined into one common light guide, and the individual light fibers are optimally mixed. The result is a light coupler. For effective light yield, it is preferable to use, instead of normal light guides, ones with hot-melted ends. 
     With the aid of these fiber-optic components, the light-emitting diodes can now also be arranged remotely from the microscope. This yields the advantage that the microscope body can be made small and light. A further advantage is the elimination of the need to place a frosted disk immediately in front of the optical system as a diffuser, since the scattering function of the frosted disk is taken over by the light-guiding fibers. 
     The colored light emerges in mixed fashion at the end near the microscope and is usable in toto as white light, and is moreover very much brighter than presently available LED light from white-light-emitting LEDs. 
     The white mixed light need not necessarily be assembled from red, green, and blue LED light; this can also be done using yellow and blue LED light. 
     It is a presently common procedure to mix white light from red, blue, and green light; the invention is, however, expressly not limited to that procedure. It is thus also possible, for example, to assemble white light from blue and yellow light; cf. in this context Siemens Magazin Forschung und Innovation/Leuchtdioden, New World 4/2000, p. 39. 
     The light coupler can also comprise a light-guiding rod system. If the light-guiding rods are correspondingly short, this yields the advantage of a compact design. 
     Numerical aperture adaptation can be achieved by way of a cross-section changer having different entrance and exit areas. 
     The spectrum of the illuminating light can furthermore be freely selected by electrical brightness regulation of the individual light-emitting diodes; no filters are necessary. It would be possible, for example, temporarily to use only the red-light-emitting LED to produce a returned light (red reflection) in ophthalmology, or only the green-light-emitting LED for red-free observation. “Blue light hazard” can be reduced by reducing the emission of the blue-light-emitting LED. 
     Tissue-specific changes can moreover be selectively depicted with this kind of false-color illumination. Better contrast can also thereby be obtained. This is done for diagnostic purposes, but also to ensure an illumination that damages tissue as little as possible. 
     The possibility furthermore exists of generating, with this spectrally selective illumination, only the particular light that contributes to the requisite imaging configuration of the microscope or to the spectral sensitivity of the observer&#39;s eye. If the LEDs cannot be electrically regulated without a change in color, controllable filters that damp the relevant color component as necessary could be selectably placed after them. 
     According to a refinement, a further fiber bundle can also be provided for feedback purposes. This fiber bundle receives, at the distal end of the fiber bundle (i.e. at the end located opposite the light source), the light reflected from the specimen and conveys it to a sensor that detects the light color and brightness. This information can thus be made available for evaluation, or used for control purposes. For example, any desired spectra can be preselected using a computer, and then compared with the measured ones. Deviations are compensated for by discrete activation and regulation of the respective color LEDs. This allows the generation of any desired illumination spectra deviating from the Planck radiation spectrum. 
     According to a further embodiment of the illumination apparatus according to the present invention, provision is made for acquiring false-color images using a camera, and storing them in the computer. At a later time, as desired, these can be reflected into or overlaid onto the currently active image in one or both stereomicroscope beam paths using a display. 
     Reference is also made to a simultaneously submitted application of the Applicant in which one or more white-light-emitting LEDs are integrated into the surgical microscope or into the illuminating optical system of the microscope. The teachings of the two applications are intended to be combinable. 
     Further embodiments of the invention are described in the Figures and in the dependent claims. The Parts List is a constituent of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail, in symbolic and exemplary fashion, with reference to the Figures. Identical reference characters denote identical components; reference characters with different indices indicate identically functioning or similar components. In the drawings, schematically in each case: 
         FIG. 1  shows an arrangement of three planar LED light sources that, using dichroic mirrors, combine red, green, and blue light into white mixed light in accordance with the existing art; 
         FIG. 2  shows an illumination apparatus according to the present invention for an optical observation device, e.g. a microscope, having three LEDs that blend red, green and blue LED into white mixed light using a light guide with coupler; 
         FIG. 3  shows an arrangement according to  FIG. 2  that has only a yellow- and a blue-light-emitting LED and a corresponding light guide with coupler; 
         FIG. 4  shows the arrangement of  FIG. 2  having an additional light guide arm, a measurement sensor, and a signal processing unit; and 
         FIG. 5  shows the arrangement of a complex LED illumination apparatus according to the present invention having a computer as well as the capability for reflection into the observation beam paths of the optical observation device by means of a display. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , the light of a red, a green, and a blue planar LED light source is mixed into white light, in known fashion, using dichroic splitters. 
     The illumination apparatus depicted in  FIG. 2  encompasses at least one red-light-emitting LED  1   a , one green-light-emitting LED  1   b , and one blue-light-emitting LED  1   c , which respectively emit red light  11   a , green light  11   b , and blue light  11   c . This red-green-blue arrangement constitutes LED arrangement  1 . Each of the light-emitting diodes  1   a ,  1   b ,  1   c  has associated with it one respective input of a total of three light guide arms  2   a ,  2   b ,  2   c . The three light guide arms  2   a ,  2   b ,  2   c  come together and thus constitute a light guide with coupler  2  that has a single output. Here white mixed light  15  travels through an illuminating optical system  3  onto a mirror  4 , by which it is directed through a main objective  5  of an optical observation device  10 . Viewer  7  then sees the illuminated specimen  6  through observation beam path  20   a.    
     The arrangement shown in  FIG. 3  is in principle the same as in  FIG. 2 , but here white illuminating light  15  is assembled from two light-emitting diodes:  1   d  that emits, for example, yellow light  1   d , and  1   e  that emits, for example, blue light  11   c . A three-armed light guide with coupler  2  is no longer necessary for this, a two-armed one instead being sufficient. 
     It is noted that LEDs  1   a  through  1   e  may be laser diodes or other semiconductor light sources. 
       FIG. 4  shows that an additional light guide arm  2   d  conveys specimen light  21 , reflected from specimen  6  and transported by it, via an optical system  9  to a measurement sensor  8 . Measurement sensor  8  in turn forwards its measured data to a signal processing unit  12 . The latter, in a freely preselectable or automatic regulation process, controls light-emitting diodes  1   a ,  1   b ,  1   c  and/or also corresponding filters  14   a ,  14   b ,  14   c  in terms of a desired spectrum. 
       FIG. 5  shows the arrangement of  FIG. 4  supplemented by a computer  13  and a camera  16 . Camera  16 , using a deflection element  18   a , takes from left observation beam path  20   a  of the stereoscopic optical observation device  10  an image that it conveys to computer  13 . Computer  13  can retrieve stored data or images, optionally in false-color depiction, from its memory unit. These data and/or images from computer  13  are reflected via a display  17  and a deflection element  18   b  into right observation beam path  20   b  or right eyepiece  19   b . In principle, stereoscopic reflection into both observation beam paths  20   a ,  20   b  is also possible. 
     Parts List 
     
         
         
           
               1 ,  1 ′ LED arrangement 
               1   a  Red-light-emitting LED 
               1   b  Green-light-emitting LED 
               1   c  Blue-light-emitting LED 
               1   d  Yellow-light-emitting LED 
               1   e  Blue-light-emitting LED 
               2  Light guide with coupler 
               2   a–d  Light guide arms 
               3  Illuminating optical system 
               4  Mirror 
               5  Main objective 
               6  Specimen 
               7  Observer&#39;s eye 
               8  Measurement sensor 
               9  Optical system 
               10  Optical observation device 
               11   a  Red light 
               11   b  Green light 
               11   c  Blue light 
               11   d  Yellow light 
               12  Signal processing unit 
               13  Computer 
               14   a–c  Filter 
               15  White mixed light 
               16  Camera 
               17  Display 
               18   a, b  Deflection elements 
               19   a  Left eyepiece 
               19   b  Right eyepiece 
               20   a, b  Observation beam path 
               21  Specimen light

Technology Classification (CPC): 8