Abstract:
A diode laser having a beam-forming device and a method for producing it are described. The diode laser includes at least one diode laser bar, the diode laser bar having a multitude of emitters, the emitters being disposed next to each other in the direction of their longitudinal axes. The diode laser includes a beam-forming device assigned to the diode laser bar, for the laser beam emerging from the diode laser bar, the beam-forming device having a light-guide device having a plurality of fibers, into which the laser beam is coupled. The maximum thickness of the optical fibers at their end facing the diode laser bar is considerably smaller than their width.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a diode laser having a device for beam forming, in which the in-coupling of the laser light emitted by the diode laser is improved further, and further relates to a method for producing a beam-forming device of such a diode laser. 
       BACKGROUND INFORMATION 
       [0002]    German patent document DE 10 2004 006 92 B2 discusses a diode laser having a device for beam forming. In this diode laser the ends of the optical fibers are deformed on the coupling side such they fuse with the neighboring optical fibers and take on a rectangular cross-section. This is meant to achieve optimal in-coupling of the laser light emitted by the emitters of the diode laser, into the optical fibers. 
       SUMMARY OF THE INVENTION 
       [0003]    According to the exemplary embodiments and/or exemplary methods of the present invention, in a diode laser having at least one diode laser bar, the diode laser bar having a multitude of emitters, the emitters being disposed next to each other in the direction of their longitudinal axes, and having a beam-forming device assigned to the diode laser bar for the laser beam emerging from the diode laser bar, the beam-forming device including a light-guide device having a plurality of fibers into which the laser beam is coupled, the object is achieved in that the fibers have an elliptical cross-section at their ends facing the diode laser bar. 
         [0004]    The deformation of the cross-section of the fibers at their ends facing the diode laser bar makes it possible to approximate the cross-section of the fibers to the outlet cross-section of the emitters of the diode laser bar, so that the diameter of the fibers is able to be reduced without changing the in-coupled light capacity. For example, by beveling the originally circular cross-section of the fibers to one half of its size, the width of the fiber being enlarged correspondingly, it is possible to achieve a light output (brightness) per area and solid angle that is increased by a factor of four. 
         [0005]    It is therefore possible to use thinner and thus more cost-effective optical fibers, and the shaping of the light at the exit of the light guide is able to be improved in its optical quality. 
         [0006]    In one further advantageous development of the present invention, the beam-forming device includes at least one optical element, which is integrally joined to the optical fibers. The sheathing of the optical fibers in the region of the optical element may be removed prior to joining the optical element to the optical fibers in an integral manner. The optical element may be made from glass. In this way the light conduction characteristic of the fibers on the in-coupling side of the light guide is not defined by the difference in the refractive index between fiber core and the sheath of the fibers, but between the fiber core and the optical element. 
         [0007]    This results in additional degrees of freedom in the optical configuration of the beam-forming device. In particular, the angle of divergence of the radiation coupled into the fiber is able to be enlarged by suitable selection of the glass and suitable shaping of the optical element, so that a further optimization of the in-coupling of the laser light into the light guide is made possible. Here, considerable optimization potential exists by way of appropriate selection of the combination of the glass qualities of optical element and fibers. 
         [0008]    The object mentioned in the introduction is also achieved by a method for producing a beam-forming device of a diode laser, in which the fibers of a light guide are initially aligned in a center section in such a way that a plurality of fibers runs in one plane and parallel to one another. Then, the fibers in the center section are heated to their softening point. In this state the fibers in the center section are compressed with the aid of one or a plurality of molded parts until they have obtained the desired cross-section; at the same time they are integrally joined to the molded parts. The integral connection may also be implemented by subsequent addition of a suitable adhesive agent. The fibers are then separated in a separation plane that runs through the center section and orthogonally to the fibers. 
         [0009]    The separation of the fibers produces two ends of light guides having deformed cross-sections of the fibers according to the present invention. This means that two light guides according to the present invention are able to be produced by implementing the method according to the present invention a single time, all methods steps having to be executing only once. Therefore, the method of the present invention is characterized by high efficiency and economy. 
         [0010]    In addition, it is easier to align, or guide, the fibers parallel to each other in a center section, i.e., not at an end of the light guide, compared to fibers that would need to be aligned at an end of the light guide. 
         [0011]    In one further advantageous development of the method according to the present invention, the fibers are cooled below their softening temperature following the pressing operation, so that no further deformation takes place. 
         [0012]    It is especially advantageous if the fibers are aligned in such a way that their lateral spacing corresponds to the spacing of the emitters of a diode laser bar in the direction of the slow-axis. In this way, the subsequent assignment of a fiber to an emitter of the diode laser bar is achieved with the necessary precision while implementing the method according to the present invention. This is particularly advantageous from an economical standpoint in a series production. In addition, the in-coupling of the light emitted by the diode laser bar into the light guide is improved and simplified. 
         [0013]    Another particularly advantageous development of the present invention provides for the molded parts to enter into an integral connection with the fibers in the region of the center section during the pressing process. These molded parts may be made from glass, the sides of the molded parts facing the fibers possibly having the desired form of the fibers of the light guide, so that the molded parts first of all bring about the desired deformation of the optical fibers and, having fused with the fibers, then serve as optical element. 
         [0014]    These molded parts therefore permit additional degrees of freedom in the design of the coupling device and, due to their larger dimensions and their robustness, allow simpler processing of the light guide on the coupling side. The optical element may be made from an opaque material, such as metal, or from a material transmissive for laser radiation, such as glass. If the optical element is made of glass, then it may be ground and polished and designed in the form of a cylindrical lens or a prism. 
         [0015]    If a separate insert is placed in the form tool above and below the fibers, then it is recommended to cut the inserts together with the fibers. This may be done by sawing or grinding, for example. As an alternative, it is also possible to insert two inserts above the fibers and below the aligned fibers, the inserts being in contact in the region of a separation surface (C-C). In this way, the fibers simultaneously may be integrally connected to the inserts during the pressing operation, so that it will not be necessary later on to cut the entire optical element again. In this case the only task that remains to be carried out is to separate the fibers in the region of the separation surface. 
         [0016]    It has shown to be advantageous if the lateral distance of the fibers relative to each other is able to be set by v-grooves, recessed v-grooves or semi-circular grooves. As an alternative, this may be accomplished by corresponding grooves in one of the molded parts or a frame surrounding the molded parts. This prevents “twisting” or “crossing” of the fibers in the region of the center section in a reliable and simple manner. 
         [0017]    Additional advantages and advantageous embodiments of the present invention may be found in the following drawing, and its description. In this context, all the features described in the drawing, their description, and the claims may be essential to the present invention, both individually and in any combination with one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1   a  shows a schematic illustration of an internal combustion engine having a laser-based ignition device. 
           [0019]      FIG. 1   b  shows a schematic representation of the ignition device in  FIG. 1   a.    
           [0020]      FIG. 2  shows a schematic plan view of a laser light source according to the present invention of the ignition device from  FIG. 1   b.    
           [0021]      FIGS. 3 ,  4 , and  5  show a first exemplary embodiment of the method according to the present invention, in various stages. 
           [0022]      FIGS. 6 ,  7 ,  8 ,  9 ,  10 ,  11  and  12  show a second exemplary embodiment of the method according to the present invention, in various stages. 
           [0023]      FIG. 13  show various exemplary embodiments of grooves for aligning the fibers. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    In  FIG. 1   a , an entire internal combustion engine is denoted by reference numeral  10 . It may be used for driving a motor vehicle that is not shown. Internal combustion engine  10  includes a plurality of cylinders, of which only one, having a reference numeral  12 , is shown in  FIG. 1 . A combustion chamber  14  of cylinder  12  is bounded by a piston  16 . Fuel reaches combustion chamber  14  directly through an injector  18 , which is connected to a fuel pressure reservoir  20  which is also referred to as a rail. 
         [0025]    Fuel  22  injected into combustion chamber  14  is ignited using a laser pulse  24 , which is eradiated into combustion chamber  14  by an ignition device  27  which includes a laser device  26 . For this purpose, laser device  26  is fed, via a light-guide device  28 , with pumped light which is provided by a pumped light source  30 . Pumped light source  30  is controlled by a control unit  32 , which also triggers injector  18 . 
         [0026]    As may be seen in  FIG. 1   b , pumped light source  30  feeds a plurality of light-guide devices  28  for different laser devices  26 , which are allocated to a particular cylinder  12  of internal combustion engine  10  in each case. Toward this end, pumped light source  30  includes a plurality of single laser light sources  340 , which are connected to a pulsed current supply  36 . The presence of the plurality of individual laser light sources  340  provides a virtually “stationary” distribution of pumped light to the various laser devices  26 , so that no optical distributors or the like are required between pumped light source  30  and laser devices  26 . 
         [0027]    For example, laser device  26  has a laser-active solid-state body  44  having a passive Q-switch  46 , which in conjunction with a coupling mirror  42  and an output coupler  48  forms an optical resonator. When pumped light generated by pumped light source  30  is applied, laser device  26  generates a laser pulse  24  in a manner known per se, which a focusing optics  52  focuses on an ignition point ZP situated in combustion chamber  14  ( FIG. 1   a ). The components located inside housing  38  of laser device  26  are separated from combustion chamber  14  by combustion chamber window  58 . 
         [0028]      FIG. 2  shows a schematic plan view of a first specific embodiment of laser light source  340  according to the present invention. As can be gathered from  FIG. 2 , laser light source  340  includes a plurality of emitters  342  emitting laser light, whose laser light is used as pumped light  60  for the optical pumping of laser device  26  ( FIG. 1   b ) or laser-active solid-state body  44  situated therein, and which is coupled into light-guide device  28  accordingly. The lateral distance between emitters  342  has been denoted by reference numeral  74 . Light-guide device  28  includes a multitude of optical fibers  68 , which hereinafter are also referred to as fibers  68 . In the exemplary embodiment shown in  FIG. 2 , an individual emitter  342  is allocated an individual optical fiber  68  in order to minimize the losses in the in-coupling of the pumped light, emitted by emitters  342 , into light-guide device  28 . Using the method according to the present invention, the allocation of fibers  68  to emitters  342  is able to be improved; simultaneously, by deforming the cross-section of fibers  68  at their ends facing emitters  342 , it is possible to reduce the diameters of the fibers without changing the in-coupled light capacity. This saves space and expense. 
         [0029]    Using  FIGS. 3 through 5 , a first exemplary embodiment of the method according to the present invention will be described in the following text. 
         [0030]    An aspect of the method according to the present invention is that fibers  68  are not brought into the desired shape and position at their ends, but that fibers  68  are brought into the desired shape and position in a center section  70  and are subsequently separated in this center section  70 . This always creates two ends of a light-guide device  28  produced according to the present invention at one time, and the handling of fibers  68  is simplified at the same time. 
         [0031]    The placement of fibers  68  at the desired lateral distance, which corresponds to lateral distance  74  between emitters  342 , and the deformation of the cross-section of fibers  68  are accomplished with the aid of a lower molded part  64  and an upper molded part  66 . Both molded parts  64  and  66  are integrally joined to fibers  68  using the method according to the present invention, and they then form an optical element, which enables or improves the in-coupling of the pumped light into light-guide device  28 . 
         [0032]      FIG. 3   a  shows a lateral view of lower molded part  64  and upper molded part  66 . Molded parts  64 ,  66  have a symmetrical design in the longitudinal direction of fibers  68 . The plane of symmetry C-C usually coincides with a separation plane whose meaning will be explained in the following text. 
         [0033]    Disposed to the right and left of separation plane C-C is what is referred to as center section  70  of molded parts  64  and  66 . The desired deformation of fibers  68  takes place in the region of center section  70 , and molded parts  64  and  66  enter into an integral connection with fibers  68 . For this reason, molded parts  64  and  66  have a “semi-elliptical” design in the region of the center section (cf.  FIG. 3   d , in particular). 
         [0034]    To the right and left of center section  70 , at the location of sectional lines A-A and B-B, no permanent deformation of fibers  68  takes place. In the region of sectional lines A-A, fibers  68  are mutually aligned at the desired distance. This may be accomplished with the aid of V-shaped grooves  72  (cf. section A-A in  FIG. 3   b ). The distance between grooves  72  corresponds to distance  74  between emitters  342  (cf.  FIG. 2 ). Then upper molded part  66  is lowered onto lower molded part  64 , as shown in  FIG. 4   a . This causes upper molded part  66  to come closer to lower molded part  64  in the region of sectional planes A-A (cf.  FIG. 4   b ), such that fibers  68  are fixed inside grooves  72 . In the area of section B-B (cf.  FIG. 4   c ), fibers  68  are not clamped between upper molded part  66  and lower molded part  64  even when upper molded part  66  has been lowered. 
         [0035]    If fibers  68  are then subjected to slight tensile stressing, it is ensured that fibers  68  exhibit the desired mutual distance in center region  70  as well. At the same time, fibers  68  are heated up to their softening temperature in the center section. The fiber alignment may also be achieved by suitable design of grooves  72 . Especially suitable shapes of grooves  72  are illustrated in  FIG. 13 . 
         [0036]    In the region of center section  70  (section C-C), molded parts  64 ,  66  deform fibers  68  in such a way that they take on an essentially elliptical cross-section. This cross-section is illustrated in the sectional view in  FIG. 4   d . Simultaneously with the deformation of fibers  68 , molded parts  64  and  66  are integrally joined with fibers  68  and form an optical element. In addition, the connection may also be bonded subsequently. If, for example, a UV adhesive for fiber applications is used, then the adhesive penetrates the fibers due to the capillary effect of the fibers, so that a stable adhesive bond will be formed. Molded parts  64  and  66  may be made from glass, it being possible to use a different type of glass than for fibers  68 . 
         [0037]    A lateral distance S I  between fibers  68  is shown in sectional view C-C of  FIG. 3   d . This lateral distance S 1  corresponds to distance  74  between emitters  342  (cf.  FIG. 2 ). This permanently fixes the fibers in place with regard to their lateral distance S 1 , and the desired allocation of fibers  68  to individual emitters of the diode laser takes place. 
         [0038]      FIG. 5   a  shows the placement of molded parts  64  and  66  in an open compression molding die  62 . 1  and  62 . 2  in separation plane C-C, in an enlarged view. As can be gathered from  FIG. 5   a , molded parts  64  and  66  have semi-elliptical recesses (without reference numerals) on their sides facing fibers  68 , which are utilized for deforming and accommodating fibers  68 . 
         [0039]    If compression molding die  62  is then closed, and at least fibers  68  have been brought to their softening temperature, molded parts  64  and  66  plastically deform fibers  68 . At the same time, upper molded part  66 , lower molded part  64 , and fibers  68  are joined, so that a monolithic glass body is obtained. Optical element  80  is worked out of this glass body. 
         [0040]    In  FIG. 5   b  such an optical element  80  is shown in a sectional view, the solid lines indicating the former separation lines between fibers  68 , a first insert  76  and a second insert  78 . 
         [0041]    In summary, the first exemplary embodiment of a method according to the present invention may be described here in greater detail with reference to  FIGS. 3 through 5 . 
         [0042]    In a first step, a plurality of fibers  68  is aligned next to each other and inserted in grooves  72  of lower molded part  64 . This is done on both sides of the center section (cf. sectional planes A-A in  FIGS. 3   b  and  4   b ). 
         [0043]    In an intermediate region (cf. sectional planes B-B in  FIGS. 3   c  and  4   c ), molded parts  64  and  66  do not touch the fibers; instead, fibers  68  are situated in the gap between upper molded part  66  and lower molded part  64 . It may be useful and advantageous if fibers  68  are kept under slight tensile stress following the alignment, so that fibers  68  do not droop in the region of center section  70  and have a straight characteristic. 
         [0044]    In a next step, fibers  68  are heated, especially in the region of center section  70 . This may be accomplished by infrared radiation, for example. As an alternative, upper molded part  66  and/or lower molded part  64  may be heated locally and the required heat provided in this manner. In so doing, fibers  68  attain at least their softening temperature, so that they are able to be deformed easily without breaking. 
         [0045]    As soon as fibers  68  in the region of center section  70  have reached the softening temperature, compression molding die  62  is closed and upper molded part  66  thereby lowered onto lower molded part  64 . In the process, force as well as heat may be transmitted to optical fibers  68  simultaneously. In addition, molded parts  64  and  66  enter into an integral connection with optical fibers  68 . As an alternative or in addition, molded parts  64  and  66  and optical fibers  68  may also be adhesively bonded to one another. 
         [0046]    Subsequently, optical fibers  68  are cooled until they are no longer able to be plastically deformed. Fibers  68  together with molded parts  64  and  66  are then separated in the region of the plane of symmetry and separation plane C-C, so that two pieces of a light-guide  28  are subsequently obtained, in which one end of fibers  68  is elliptically deformed according to the method of the present invention. The separation plane produced in the separation is then brought into the desired form, polished and coated, if necessary. It has shown to be especially suitable if molded parts  64  and/or  66  are produced from glass, the melting point of molded parts  64  and  66  being higher than the melting point of optical fibers  68 . 
         [0047]    With the aid of  FIGS. 6 through 12 , an additional exemplary embodiment of a method according to the present invention will now be explained. Identical components are provided with identical reference numerals, and the statements made with regard to  FIGS. 1 through 5  apply accordingly. 
         [0048]    In the exemplary embodiments according to  FIG. 6  ff, the alignment of fibers  68  is accomplished with the aid of combs  82 . These combs  82  are made up of a multitude of grooves  72  running parallel with each other. Combs  82  are disposed in a frame  84  along both sides of a rectangular recess  86 . In the plan view of frame  84 , recess  86  and fibers  68 , aligned in parallel with one another by combs  82 , can be seen quite clearly. 
         [0049]      FIG. 6   a  shows combs  82  without fibers  68 , while a fiber  68  and lateral distance S 1  has been plotted in the associated detail X (cf.  FIG. 6   b ) for better understanding. 
         [0050]    In a further step, a first glass wafer  88  is placed on frame  84  and fibers  68  lying on frame  84  (cf.  FIG. 7 ). First glass wafer  88  extends across frame  84  in the direction of fibers  68  and retains fibers  68  inside grooves  72 . 
         [0051]    In a further step, which is illustrated in  FIG. 8 , frame  84 , fibers  68  and first glass wafer  88  are fixed in place relative to each other by a plurality of holders  90 , and the top side is rotated to point down (cf.  FIG. 9 ). 
         [0052]    As can be gathered from  FIG. 10 , a total of four washers  92  are then placed on first glass wafer  88  to the right and left of fibers  68  and at a certain distance relative to separation plane C-C. In the subsequent step, a second glass wafer  94  is then placed on washers  92  and first glass wafer  88 , to the left and right of separation plane C-C. This constellation is shown in a side view in  FIG. 11  at the bottom left. Washers  92  are used for achieving an inclined position of second glass wafer  94  relative to first glass wafer  88 . 
         [0053]    First glass wafer  88 , fibers  68  and second glass wafer  94  are then compression-molded with the aid of stamps  96  and under the action of heat. In the process, the desired deformation of fibers  68  and the integral connection of first glass wafer  88 , fibers  68  and second glass wafer  94  take place, primarily in the region of separation plane C-C. Due to the inclined position of second glass wafer  94 , fibers  68  take on a circular cross-section again as the distance to separation plane C-C increases. 
         [0054]    Finally, once cooling has occurred, fibers  68  and first glass wafer  88  are separated along separation plane C-C, and the cut surfaces are ground and polished, so that an optical element  80  is produced. 
         [0055]    The advantage of the second exemplary embodiment of the method according to the present invention is that the required structured components, which are produced with great precision, are used only as tool and thus may be used multiple times. 
         [0056]      FIG. 13  shows various exemplary embodiments of grooves  72 . In  FIG. 13   a , a plurality of V-grooves is illustrated in a sectional view.  FIG. 13   b  shows “recessed” V-grooves  72 , and in the exemplary embodiment according to  FIG. 13   c , the bottom of grooves  72  has a semicircular design.