Abstract:
An apparatus for combining individual light beams to form a coaxial light bundle. The apparatus has a plurality of coupling-in positions, the number of which corresponds to the number of light beams, and also at least one coupling-out position. It is suitable for generating a collimated beam bundle as a multicolour source for use in digital image generation. The apparatus includes an apparatus base body with the coupling-in positions for the light beams and with a coupling-out position for the light bundle and adjusting devices for coaxially orienting the individual light beams relative to the beam direction of the light bundle. The coaxial light bundle can optionally emerge as free beam at the coupling-out position or into an optical waveguide via connecting elements.

Description:
PRIORITY CLAIM 
       [0001]    The present application is a National Phase Entry of PCT Application No. PCT/EP2008/004554, filed Jun. 7, 2008, which claims priority to German Application Number 102007034261.8, filed Jul. 20, 2007, the disclosures of which are hereby incorporated by reference herein in their entirety. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to an apparatus having several coupling-in locations for individual light beams, and at least one coupling-out location for the light beams combined into a coaxial light bundle. The invented apparatus excels by highly precise superposition of the individual light beams and by angular positioning of the coaxial light bundle with angular errors of less than 10 μrad; it is particularly suitable for producing a collimated light bundle as a multicolor source for use in digital image generation. 
       PRIOR ART 
       [0003]    Apparatuses for combining several laser beams of different light wavelengths into a coaxial light bundle are actually known in prior art. A light bundle produced by such apparatuses is employed, e.g., as an RGB multicolor source in microscope imaging, especially in laser scanning microscopes. For such applications, angular positioning of the coaxial light bundle often needs to be made to angular errors of less than 10 μrad. 
         [0004]    The apparatuses known in prior art that satisfy these requirements are made from relatively many components in a complicated process, require complex adjustment for precise coupling of the individual light beams into the light bundle, and are difficult to handle because changing individual optical waveguides used to feed the light beams consume a lot of time and, thus, cost. 
         [0005]    Moreover, they suffer from an essential disadvantage with a negative effect on accuracy, in that fluctuations of ambient temperature impair the adjustment of the beam path. 
       SUMMARY OF THE INVENTION 
       [0006]    On this premise, the invention is based on the problem to create an apparatus for precisely combining individual light beams into a coaxial light bundle, that can be implemented by the simplest possible technical means manufactured at reasonable cost, has the smallest possible volume, and operates accurately and reliably under varying external conditions, especially during temperature fluctuations. 
         [0007]    The problem is solved by an apparatus for precisely combining individual light beams into a coaxial light bundle, comprising
       a body of the apparatus having several coupling-in locations for the light beams and a coupling-out location for the light bundle, and   adjusting devices for coaxially aligning the individual light beams relative to the beam direction of the light bundle.       
 
         [0010]    Preferably, optical waveguides, especially single-mode optical fibers, are provided for guiding the individual light beams, and connecting elements are provided for coupling the optical waveguides to the apparatus in the coupling-in locations. The coaxial light bundle can optionally exit at the coupling-out location as a free (unguided) beam or enter an optical waveguide via connecting elements. 
         [0011]    For producing the light beams, laser radiation sources radiating different light wavelengths may be used to advantage. 
         [0012]    The number of adjusting devices corresponds to the number of coupling-in locations, so that one adjusting device is assigned to each coupling-in location. Each of the adjusting devices is provided with a dichroic mirror that is made to reflect the light wavelength of the light beam to be coupled in at the respective location, and to be transparent to the light wavelengths of the light beams intended to penetrate it. 
         [0013]    Within the body of the apparatus, the dichroic mirrors are arranged in succession, with the direction of this succession corresponding to the direction of the coaxial light bundle. Each dichroic mirror is aligned relative to the direction of the incident light beam so that the light beam is reflected into the center of the light bundle. 
         [0014]    For this purpose, the dichroic mirrors are essentially tilted by 45° relative to the light beam to be coupled in and also by 45° relative to the coaxial light bundle. Each of the dichroic mirrors is connected to a joint to allow adjustment of the reflection direction. These joints may be preferably designed as elastic hinges, with each elastic hinge being coupled to one or several manipulators with which the reflection direction can be altered and, thus, adjusted. 
         [0015]    Varying with the embodiment of the invented apparatus, the manipulators for manual operation are designed, e.g., in the form of adjusting screws or rotatable wedge plates, or the manipulators may be coupled to controllable electromechanical drive units connected to a control unit designed to generate control commands. 
         [0016]    The body of the apparatus may be made as a monolithic body of glass, vitroceram, ceramics, plastic or metal, preferably stainless steel or anodized aluminum. It is recommendable to make the adjusting devices including the elastic hinges of the same material of which the body of the apparatus is made. 
         [0017]    In a further development of the invented apparatus, the individual light beams are provided with collimating optics or one- or multilens telescope arrangements for influencing the beam, which may be arranged at the coupling-in locations. 
         [0018]    For connecting the optical waveguides with the body of the apparatus at the coupling-in locations, special, highly precise fiber connectors can be provided. These fiber connectors are provided with connecting elements that have, on the side of the optical waveguide and on the side of the body of the apparatus, reference surfaces that correspond to each other and ensure accurate and reproducible alignment of the optical waveguide relative to the body of the apparatus and, thus, to the respective dichroic mirror. 
         [0019]    In this connection, in one embodiment of the invented apparatus, the body of the apparatus has a polished outer surface with areas that serve as reference faces for receiving the fiber connectors. Centering collars serve as auxiliary means for aligning the fiber connectors and, thus, the optical waveguides relative to the respective dichroic mirror in the body of the apparatus, with one centering collar seated on each of the areas and being fixed to it. Attached to each centering collar is a spring ring fitting the form of the centering collars. 
         [0020]    This enables fast and problem-free alignment of the optical waveguides relative to the apparatus when they are changed or re-plugged. 
         [0021]    In one embodiment, the material in the said areas is harder than the rest of the material of which the body of the apparatus consists. For this purpose, the material of the body of the apparatus (depending on its kind) is either hardened, or the body of the apparatus is provided with a hard coating in these areas, or a layer of harder material is embedded into the material of the body of the apparatus. 
         [0022]    Furthermore it is within the scope of the invention to provide, in the coaxial light bundle at the coupling-out location, means for beam shaping, such as, e.g., for beam expansion or for focusing the light bundle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Below, the invention will be explained in more detail in an exemplary embodiment, with reference to the accompanying drawings in which: 
           [0024]      FIG. 1  depicts the principle of the invented apparatus by a section through the optical axes of the light beams to be combined and of the coaxial light bundle, 
           [0025]      FIG. 2  depicts the invented apparatus in a bottom view of the arrangement shown in  FIG. 1 , looking at the adjusting devices embedded in the body of the apparatus, 
           [0026]      FIG. 3  depicts, as an excerpt from  FIG. 1 , one of the adjusting devices in a section through the beam guiding orifices for the light beam to be coupled in, and for the coaxial light bundle, and 
           [0027]      FIG. 4  depicts a perspective view of the invented apparatus, looking at the coupling-in locations for the light beams to be combined. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  depicts a section of the invented apparatus  1 . It can be seen that the apparatus  1  includes a body  2 , which is provided with coupling-in locations  3 ,  4 ,  5  and  6  for individual light beams  7 ,  8 ,  9  and  10 , and one coupling-out location  11 , at which a coaxial light bundle  12  exits, in which the light beams  7 ,  8 ,  9 ,  10  are combined. 
         [0029]    In one embodiment, the light beams  7 ,  8 ,  9 ,  10  are laser beams of different light wavelengths, which are fed to the apparatus  1  by optical waveguides (not shown in the drawing). For example, light of the “red” wavelength range is coupled into the apparatus  1  by light beam  7 . Let the other light beams  8 ,  9 ,  10  be intended for light wavelengths in the “green”, “blue” and “ultraviolet” ranges. 
         [0030]    Fiber connectors  13  are provided for connecting the optical waveguides with the body of the apparatus  2 , i.e. for coupling the light beams  7 ,  8 ,  9 ,  10  into the apparatus  1 . 
         [0031]    In the example embodiment chosen here, the coaxial light bundle  11  exits as a free light beam. Alternatively, though, it is also feasible to arrange a fiber connector  13  also at the coupling-out location  11 , and to conduct the coaxial light bundle  12  within an optical waveguide from the apparatus  1  to an imaging instrument. 
         [0032]    Assigned to the coupling-in location  3  is an adjusting device  14 , which bears a dichroic mirror  15 . In an analogous manner, an adjusting device  16  with a dichroic mirror  17  is assigned to coupling-in location  4 , an adjusting device  18  with a dichroic mirror  19  to coupling-in location  5 , and an adjusting device  20  with a dichroic mirror  21  to coupling-in location  6 . 
         [0033]    The dichroic mirrors  15 ,  17 ,  19 ,  21  are aligned essentially at an angle of 45° relative to the respective light beam to be coupled in, i.e.  7 ,  8 ,  9 ,  10 , and also at an angle of 45° relative to the coaxial light bundle  12  run within the body of the apparatus  2 . The word “essentially” in this connection means that the decisive criterion is not an inclination of exactly 45°, but rather the direction in which the respective light beam  7 ,  8 ,  9 ,  10  is reflected when it hits the dichroic mirror  15 ,  17 ,  19 ,  21  assigned to it. This direction should correspond, with the least possible deviation, to the direction of the center of the coaxial light bundle  12  within the body of the apparatus  2 . 
         [0034]    To achieve this, each of the adjusting devices  14 ,  16 ,  18 ,  20  is provided with an elastic hinge  23 . By means of the elastic hinges  23 , the inclinations of the dichroic mirrors  15 ,  15 ,  19 ,  21  can be adjusted by the amount needed to satisfy the requirement mentioned. This adjustment facility is explained in more detail below in connection with  FIG. 3 . 
         [0035]    It is to be understood that it is also within the scope of the invention if the said adjustment is used deliberately to set slight differences in beam direction between the individual light beams. 
         [0036]    The dichroic mirror  15  is designed so as to reflect the light wavelength of light beam  7 , while being transparent to the light wavelengths of light beams  8 ,  9  and  10 . In an analogous manner, the dichroic mirror  17  is made to reflect light beam  8  and to be transparent to light beams  9  and  10 , and the dichroic mirror  19  is made to reflect light beam  9  and to be transparent to light beam  10 , whereas the dichroic mirror  21  is made to reflect light beam  10 . 
         [0037]    So that the coaxial light bundle  12  can be coupled out in the direction as shown in  FIG. 1 , a mirror  24  is provided within the body of the apparatus  2 , this mirror being made to reflect the wavelengths of all light beams  7 ,  8 ,  9 ,  10  coupled in, so that the light beams  7 ,  8 ,  9 ,  10  combined in the coaxial light bundle  12  are, within the body of the apparatus  2 , are deflected by mirror  24  to the coupling-out location  11 . 
         [0038]    Alternatively it is possible, within the scope of the invention, to do without mirror  24  and thus to shift the coupling-out location  11  to location  25 . There, too, it is alternatively possible to have the light bundle  12  exit as a free beam or to couple it into an optical waveguide by means of another fiber connector  13 . 
         [0039]    It is further feasible to replace the mirror  24  with a polarizing beam splitter and thus to combine the coaxial light bundle  12  with another light beam that is perpendicular to it and may, in itself, be a bundle of light of different wavelengths. 
         [0040]    As can be seen in  FIG. 1 , the adjusting device  14 ,  16 ,  18 ,  20  are fastened to the body of the apparatus  2  by means of screw connections, for example, by the screws  22 . 
         [0041]    In the light beams  7 ,  8 ,  9 ,  10  (for example at the coupling-in locations  3 ,  4 ,  5 ,  6 ), collimating lenses may be arranged which have a focal length of, e.g., f=4 mm and which cause the light beams  7 ,  8 ,  9 ,  10  to hit the dichroic mirrors  15 ,  17 ,  19 ,  21  with beam diameters of about 1 mm if these light beams are guided there by optical fibers of NA≈0.1. 
         [0042]    Comparably, optical elements may be arranged in the coaxial light bundle  12  at the coupling-out location  11 , which cause an expansion of the light bundle  12  to a beam diameter that corresponds to the intended purpose of the light bundle  12 . 
         [0043]    The body of the apparatus  2  may, for example, made of stainless steel of a low expansion coefficient. To minimize the external influence of temperature fluctuations on the apparatus  1  and, thus, accuracy deviations in beam guiding, the adjusting devices  14 ,  16 ,  18 ,  20  including the elastic hinges  23  should be made of the same stainless steel. 
         [0044]      FIG. 2 , a bottom view of the arrangement shown in  FIG. 1 , depicts the adjusting devices embedded in the body of the apparatus. One can see the adjusting devices  14 ,  16 ,  18 ,  20  inserted in the body of the apparatus  2  at the coupling-in locations  3 ,  4 ,  5 ,  6 , as well as the cheese-head screws  22  with which the adjusting devices  14 ,  16 ,  18 ,  20  are fastened to the body of the apparatus  2 . 
         [0045]    At the coupling-out location  11 , a holder  31  for the mirror  24  is shown which is fastened to body of the apparatus  2  with three cheese-head screws  26 . 
         [0046]      FIG. 3  shows the adjusting device  14  as an exemplary detail from  FIG. 1 . Here one can see the dichroic mirror  15  and an orifice  28  for the coaxial light bundle  12 . 
         [0047]    Also to be seen are the holes  29  for the cheese-head screws  22  with which the adjusting device  14  is fastened to the body of the apparatus  2 , the reduction of the material cross section that acts as an elastic hinge  23 , and the adjusting screws  30  passing through threaded holes in the adjusting device  14 . 
         [0048]    Four each of the said adjusting screws  30 , the locations of which can be seen from  FIG. 3  in connection with  FIG. 2 , are assigned to the adjusting device  14  as well as to each of the other adjusting devices  16 ,  18  and  20 . By manipulation of the adjusting screws  30  and the ensuing influencing of the respective elastic hinge  23 , the alignment of the dichroic mirror  15  can be varied until it is sure that the coupled-in light beam  7  is precisely aligned with the desired direction, viz. that of the coaxial light bundle  12 . 
         [0049]    Depending on the properties of the material of which consist the elastic hinges  23  or, in case of a monolithic design, the body of the apparatus  2  including the elastic hinges  23 , aligning the dichroic mirror  15  is effected by the plastic or elastic deformation brought about by the said manipulation. 
         [0050]    A more developed embodiment of the invented apparatus features not only means—in the form of the adjusting devices  14 ,  16 ,  18 ,  20 —provided for the angular alignment of the light beams  7 ,  8 ,  9 ,  10  to be coupled in, but also means by which the light beams  7 ,  8 ,  9 ,  10  to be coupled in can be shifted perpendicularly to the beam direction, as explained below. 
         [0051]    As  FIG. 4  shows, the body of the apparatus  2  is provided with a polished outer surface  31  of high planarity, which has four areas  32 ,  33 ,  34  and  35 . The areas  32 ,  33 ,  34 ,  35  serve as reference faces for seating the fiber connectors  13  and for their accurate and reproducible aligning. 
         [0052]    According to the invention, centering collars  36  are provided for the purpose of aligning the fiber connectors  13  as they are coupled to the body of the apparatus  2 , with one centering collar  36  seated on, and fastened to, one of the areas  32 ,  33 ,  34 ,  35  each. As  FIG. 4  shows for the coupling-in location  6  as an example, the centering collars  36  are fastened to the body of the apparatus  2  by means of cheese-head screws  37 . 
         [0053]    Attached to each centering collar  36  and matching its shape is a spring ring  38 , which is fastened by, e.g., eight cheese-head screws  39 . 
         [0054]    The material of the four areas  32 ,  33 ,  34 ,  35  is preferably harder than the rest of the material of which the body of the apparatus  2  consists. For this purpose, depending on the kind of material of the body of the apparatus  2 , either the material is hardened at the surface or provided with a hard coating, or a layer of harder material is embedded in the material of the body of the apparatus  2 . 
       LIST OF REFERENCES 
       [0000]    
       
         
           
               1  apparatus 
               2  body of the apparatus 
               3 ,  4 ,  5 ,  6  coupling-in locations 
               7 ,  8 ,  9 ,  10  light beams 
               11  coupling-out location 
               12  coaxial light bundle 
               13  fiber connector 
               14 ,  16 ,  18 ,  20  adjusting devices 
               15 ,  17 ,  19 ,  21  dichroic mirrors 
               22  cheese-head screw 
               23  elastic hinge 
               24  mirror 
               25  location 
               26  cheese-head screw 
               27  seating face 
               28  orifice 
               29  hole 
               30  adjusting screws 
               31  outer surface 
               32 ,  33 ,  34 ,  35  areas 
               36  centering collar 
               37  cheese-head screw 
               38  spring ring 
               39  cheese-head screw