Abstract:
An optically stacked, laser diode array module ( 10 ) includes a mounting block ( 100 ) having a series of stepped, parallel diode mounting surfaces ( 101 ) on one face of the block, each diode mounting surface cooperating with a respective pair of reference surfaces ( 102, 103 ) of the block to form a respective outside block corner, a series of laser diodes ( 300 ) affixed to the block, with facets of the diode aligned with the reference surfaces forming the outside block corner with the mounting surface on which the diode is disposed, such that a corner of each diode is aligned with a respective corner of the block, and a beam reflector ( 200 ) secured to the block and having a series of stepped, parallel surfaces, each positioned to intercept and reflect a respective one of the beams ( 500 ) from the laser diodes, such that the reflected beams are parallel and stacked. The beams ( 500 ) emitted from the laser diodes ( 300 ) can be collimated by microlenses ( 400 ).

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to diode lasers, and more particularly to a module for mounting a plurality of laser diodes in an array. 
       BACKGROUND 
       [0002]    High-power diode lasers are used in many different applications. The usefulness of a laser for a specific application can be characterized by the laser&#39;s output power, the spectral line width of the output light, and the spatial beam quality of the output light. 
         [0003]    The spatial beam quality can be characterized in several ways. For example, a wavelength independent characterization of the spatial beam quality is provided by the beam parameter product (“BPP”), which is defined as the product of the beam waist (i.e., the half diameter of the beam at the so-called “waist” position), w o , and the far-field, half-angle divergence of the beam, Θ O : 
         [0000]        BPP=ω   0 Θ 0    (1) 
         [0004]    As another example, a nondimensional characterization of the spatial beam quality is provided by the beam quality factor, M 2  or Q, where the beam quality factor is given by 
         [0000]        M   2 =1 /Q=πω   o θ o /λ  (2) 
         [0000]    with λ being the wavelength of the output laser light. 
         [0005]    A laser operating in the TEM 00  mode and emitting a Gaussian beam has the lowest possible BPP (M 2 =1). Ridge waveguide and gain-guided laser diodes operating in this mode are called single mode emitters and typically consist of a 3 μm wide stripe (along the lateral axis of the laser). The output power of these emitters is limited to about 1 W due to catastrophic optical damage (“COD”) of the laser facet. To increase the facet area, so called tapered emitters can be used. 
         [0006]    To achieve higher power output from a semiconductor laser diode, a relatively wide effective lateral width of the active material in the laser can be used. Such devices are known as “wide stripe emitters,” broad stripe emitters,” or “multimode devices.” However, when the effective lateral width of the active material is greater than several times the laser output wavelength, gain can occur in higher order spatial modes of the resonant cavity, which can reduce the spatial beam quality of the output laser light. 
         [0007]    Multiple wide stripe emitters and/or single mode emitters can be fabricated side-by-side on a single chip to make an array of single emitters. The output light of multiple individual laser diode emitters in an array can be combined incoherently to increase the overall output power from the chip. However, the beam quality of the combined output beam generally decreases with the number of individual emitters in an array. 
         [0008]    The total output beam of these laser diode arrays is generally strongly asymmetric. For example, a typical beam product parameter (“BPP”) of a 10 mm wide array along the slow axis (i.e., the lateral axis of the laser diode) can be BPP slow =500 mm*mrad, while a typical BPP of an array along the fast axis (i.e., the vertical axis of the laser diode), where the device is typically operating in the TEM 00  mode, can be BPP Fast =0.3 mm*mrad. 
         [0009]    Many laser applications require a symmetric beam. However, it is difficult to symmetrize the strongly asymmetric beam of the array. The output beam of an array can be cut into parts and rearranged (e.g., by step mirrors, tilted plates, or tilted prisms), so that the BPP of the rearranged beam is equal in both axes, but complicated optical systems are necessary to achieve a symmetric beam in such a manner. All these systems have less then 100% transmission efficiency. Therefore, it is desirable to have a light source that produces a symmetric high power output beam without utilizing optical systems that cut the output beam from one or a plurality of arrays into parts. Moreover, it is desirable to have a way of mounting a plurality of laser diode arrays for creating such a high power beam. 
       SUMMARY OF THE INVENTION 
       [0010]    Several aspects of the invention feature an optically stacked, laser diode array module with a common mounting block to which a multiplicity of individual laser diodes are separately secured and positioned in such a way that their individual beams intercept a beam reflector and become optically stacked. 
         [0011]    According to one aspect of the invention, an optically stacked laser diode array module includes a mounting block, a series of laser diodes affixed to the block, and a beam reflector secured to the block. The mounting block has a series of stepped, parallel diode mounting surfaces on one face of the block, each diode mounting surface cooperating with a respective pair of reference surfaces of the block to form a respective outside block corner. Each laser diode is disposed on a respective one of the diode mounting surfaces, with facets of the diode aligned with the reference surfaces forming the outside block corner with the mounting surface on which the diode is disposed, such that a corner of each diode is aligned with a respective corner of the block, one of the aligned facets of each diode defining an output facet from which a beam is emitted, perpendicular to the output facet, when the diode is activated. The beam reflector has a series of stepped, parallel surfaces, each positioned to intercept and reflect a respective one of the beams from the diodes, such that the reflected beams are parallel and stacked. 
         [0012]    In, some cases, the beam reflector is secured to two orthogonal surfaces of the block that together locate the reflector with respect to the laser diodes. For greater positioning accuracy, one of the two orthogonal surfaces to which the beam reflector is secured may be parallel to the diode mounting surfaces of the mounting block. 
         [0013]    In some embodiments the reflector is secured to the mounting block through an insulating layer. In some other cases, the reflector is secured directly to the mounting block, in direct contact with a surface of the mounting block. 
         [0014]    Some embodiments also include a series of lenses, each lens disposed between a respective one of the diodes and the beam reflector. Each lens may be affixed to a corresponding one of the reference surfaces of the mounting block, such as with adhesive. In some configurations the lenses each define a cylindrical axis parallel to the output facet of its respective diode. The lenses are preferably adjustable during mounting, to align the output beam of its respective diode. 
         [0015]    In some embodiments an electrically conductive voltage plate is secured to the mounting block and arranged to conduct electrical energy into an n-surface of each laser diode. In some cases the voltage plate is directly connected to each laser diode, such as by wire bonds, to provide power to the diodes in parallel. In some other cases, the voltage plate is directly connected to one of the laser diodes, others of the laser diodes arranged to receive electrical power in series from the diode to which the voltage plate is directly connected. 
         [0016]    The mounting block preferably defines a cooling passage within the block, for circulation of cooling fluid to remove heat generated by operation of the laser diodes. In some configurations, the mounting block includes an upper section and a lower section permanently joined along planar surfaces of the upper and lower sections to define the cooling passage. The upper section may define the diode mounting surfaces and the outer corners to which the diodes are aligned, for example. Preferably, the cooling passage passes directly under at least one of the mounted diodes. 
         [0017]    In some embodiments the laser diodes are secured directly to the diode mounting surfaces of the mounting block, such as by being soldered directly to the diode mounting surfaces. In some other embodiments, the laser diodes are affixed to the mounting block through submounts of a material selected to have a thermal expansion characteristic similar to that of the diodes. The submounts may electrically insulate the diodes from the mounting block, for example. 
         [0018]    Preferably, the diode mounting surfaces of the mounting block have a surface roughness of less than about 0.02 microns. More preferably, the reference surfaces of the mounting block also have a surface roughness of less than about 0.02 microns. 
         [0019]    In a presently preferred construction, each diode mounting surface and its respective pair of reference surfaces are all perpendicular to one another at their mutual corner, such that the corner is square. 
         [0020]    Another aspect of the invention features a solid state laser comprising multiple laser diode modules each constructed as described above, along with optics arranged to combine the beams from the multiple laser diode assemblies into a single beam. 
         [0021]    In some arrangements the multiple laser diode modules are each mounted against a first common mounting surface and arranged such that their output beams are parallel. For example, in one illustrated configuration the laser diode modules are arranged in a series, with alternating ones of the series mounted against a second common mounting surface, such that the beam reflectors of all of the modules of the series are overlapped, alternating ones of the beam reflectors facing in opposite directions. 
         [0022]    In some cases, the first and second common mounting surfaces are perpendicular. 
         [0023]    Some examples also include a fiber coupler with an integrated focusing lens that focuses the single beam into a fiber. 
         [0024]    Another aspect of the invention features a method of assembling an optically stacked laser diode module. The method includes affixing a series of laser diodes to a mounting block having a series of stepped, parallel, diode mounting surfaces on one face of the block, each diode mounting surface cooperating with a respective pair of reference surfaces of the block to form a respective outside block corner, each laser diode disposed on a respective one of the diode mounting surfaces, with facets of the diode aligned with the reference surfaces forming the outside block corner with the mounting surface on which the diode is disposed, such that a corner of each diode is aligned with a respective corner of the block, one of the aligned facets of each diode defining an output facet; securing a beam reflector to the block, the reflector having a series of stepped, parallel surfaces each positioned to intercept and reflect a beam generated by a respective one of the diodes; securing a series of lenses to the mounting block, each lens disposed between a respective one of the diodes and the beam reflector; activating each of the laser diodes to generate a beam emitted perpendicular to the output facet; and adjusting a position of at least one of the lenses to align the beam emitted from its associated diode. 
         [0025]    Preferably, the lenses are each adjusted as they are secured to the mounting block, such as with adhesive. 
         [0026]    Another aspect of the invention features a method of positioning and securing multiple laser diodes on a common mounting block. The method includes providing a mounting block having a series of stepped, parallel, diode mounting surfaces on one face of the block, each diode mounting surface cooperating with a respective pair of reference surfaces of the block to form a respective outside block corner at which the diode mounting surface and respective pair of reference surfaces defining the corner are all perpendicular to one another, such that the corner is square; placing the mounting block in a fixture with surfaces that locate the mounting block with respect to the fixture by contacting each of the reference surfaces of the block, pairs of perpendicular surfaces of the fixture coinciding with pairs of perpendicular surfaces of the block at each of the outside block corners, with the laser diode mounting surfaces exposed; placing a laser diode on each of the laser diode mounting surfaces, with two side surfaces of each laser diode abutting an associated pair of the perpendicular surfaces of the fixture to align the side surfaces of the laser diode with associated reference surfaces of the mounting block; and affixing the laser diodes to the mounting block in their aligned positions. 
         [0027]    In various embodiments discussed in more detail below, the laser diodes are placed on steps with particularly accurate height displacement enabled, at least in part, by the configuration of the mounting block. Perpendicular to each of these steps two surfaces (perpendicular to each other) are provided. The first of the two surfaces serves as an end stop for the out coupling facet of the laser diode. This ensures that the emission of the laser diode is exactly perpendicular to that surface. The second of the two surfaces serves as an end stop for the side facet of the laser diode. This surface is also accurately displaced from all the other second surfaces that belong to the plurality of steps, that the laser diodes are accurately positioned with the desired lateral distance between them. Together with accurate height displacement, the configurations described herein can ensure that the plurality of laser beams emitted from the laser diodes are accurately spaced in three orthogonal directions and parallel to each other, enabling more ready optical stacking of the individual beams. 
         [0028]    Several examples described below also feature a step mirror attached to an accurately machined surface with two additional end stops (again two surfaces perpendicular to the machined surface) so as to ensure proper alignment of each of the individual steps of the step mirror to each of the parallel beams from the diodes. The step mirror serves the purpose of accurately stacking the parallel laser beams on top of each other. The three surfaces that define the position of the step mirror are accurately machined with respect to the diode mounting and reference surfaces of the mounting block. This ensures that the beams will be very accurately placed on top of each other without major alignment expenditure. 
         [0029]    One set of orthogonal reference surfaces also serves as the attachment base for cylindrical microlenses. Arranging the lenses with their cylindrical axes being substantially perpendicular to the reference surface to which they are secured can greatly facilitate alignment of the microlenses and ensures that the adhesive used to attach the microlens shrinks substantially in such a way that only a displacement of the microlens along the cylindrical axis occurs, so as to have minimal or no optical effect. Because the microlenses can be individually secured and adjusted after the step mirror is attached, adjustment of the lenses can be sufficient as the only alignment step required for the completely assembled module, even accommodating some positioning errors between the block and step mirror. 
         [0030]    A plurality of such fully adjusted, multiple-diode modules or “M-blocks” can be combined in such a way as to multiply the number of laser beams stacked optically on top of each other. An example described below features a center mount with two surfaces that are perpendicular to each other. Each surface holds M-Blocks at different heights such that the step mirrors alternately stack beams from M-Blocks attached to the first and the second surface on the center mount. This ensures that the beams of an unlimited number of laser diodes can accurately be stacked on top of each other without great alignment expenditure, since the surfaces of the M-Blocks that attach to the accurately machined surfaces of the center mount are accurately machined with regards to the diode mounting and reference surfaces of the M-blocks. 
         [0031]    The M-Blocks can be electrically insulated from each other by coating the center mount with an electrical insulator (such as Aluminum oxide). 
         [0032]    The laser diodes on the M-Block can be driven electrically parallel by utilizing a proper n-contact voltage plate which also contains steps of accurate height displacement. Alternatively, the laser diodes on the M-Block can be driven electrically in series by utilizing a proper system of conductive and insulating shims for the n-contact The M-block can be actively water cooled utilizing any laser diode heat sink cooling method, such as simple drilled holes with plugs; milled cooling channels in a part containing a lid and a base, where the lid is hard soldered to the base; a substrate that is made from DCB (direct bonded copper); or a substrate made from micro channel coolers or finned coolers. 
         [0033]    The center mount can be accurately placed on a base plate so that the plurality of stacked laser beams from the plurality of M-Blocks on the center mount can be accurately combined with the plurality of stacked laser beams from the plurality of M-Blocks on another center mount with opposite state of polarization. 
         [0034]    Several center mounts can be accurately placed on a base plate so that the plurality of stacked laser beams having one specific wavelength from the plurality of M-Blocks on one center mount can be accurately combined with the plurality of stacked laser beams having another specific wavelength from the plurality of M-Blocks on another center mount. 
         [0035]    Using the techniques stated above, the emission of the laser diodes on center mounts with any number of specific wavelengths and two states of polarizations can be combined. 
         [0036]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
     
       DESCRIPTION OF DRAWINGS 
         [0037]      FIG. 1  is a perspective view of a partially assembled module with multiple, optically-stacked laser diodes. 
           [0038]      FIG. 2   a  is a front view of the module of  FIG. 1 , with step mirror removed and voltage plate attached. 
           [0039]      FIG. 2   b  is an enlarged front view showing placement of the microlenses. 
           [0040]      FIG. 3  is an exploded view of the module of  FIG. 1 , with voltage plate and insulators. 
           [0041]      FIGS. 4   a  and  4   b  are top and side views of the module of  FIG. 1 , fully assembled. 
           [0042]      FIG. 4   c  and  4   d  are enlarged views of areas  4   c  and  4   d  in  FIGS. 4   b  and  4   a , respectively. 
           [0043]      FIG. 5  illustrates a microlens being secured and adjusted in the assembly of the module of  FIG. 1 . 
           [0044]      FIGS. 6   a ,  6   b  and  6   c  are schematic views of the voltage plate of the module of  FIG. 3 . 
           [0045]      FIG. 7   a  is a perspective view of a partially assembled module including a module block formed of two pieces. 
           [0046]      FIG. 7   b  shows a schematic exploded view of the two block components joined to form the block of the assembly of  FIG. 7   a.    
           [0047]      FIG. 8  is a bottom view of the upper component of the mounting block shown in  FIG. 7   a.    
           [0048]      FIG. 9   a  is a top view of the lower component of the mounting block shown in  FIG. 7   a , while  FIG. 9   b  is a cross-sectional view taken along line  9   b - 9   b  in  FIG. 9   a.    
           [0049]      FIG. 10  is a top view of the partially assembled module of  FIG. 7   a , showing internal cooling passages. 
           [0050]      FIGS. 11   a  and  11   b  show cross-sectional views of alternative mounting block constructions comprising laminates. 
           [0051]      FIGS. 12   a  and  12   b  are cross-sectional views of alternative diode mounting arrangements, illustrating submounts. 
           [0052]      FIGS. 13   a  and  13   b  show alternative methods of electrically connecting the laser diodes to a voltage plate. 
           [0053]      FIG. 14   a  is a perspective view of a module with the diodes connected in series to the voltage plate, while  FIG. 14   b  is an enlarged view showing current flow between diodes. 
           [0054]      FIG. 15  is an exploded view of the module assembly shown in  FIGS. 14   a  and  14   b.    
           [0055]      FIG. 16  is a perspective view of the module block of the assembly of  FIG. 3  in an alignment fixture for positioning the laser diodes for mounting. 
           [0056]      FIGS. 17   a - 17   c  are perspective, side and end views, respectively, of multiple laser diode modules mounted to a single mounting block to form a multi-module assembly. 
           [0057]      FIGS. 18 and 19  are top and perspective views, respectively, of a fiber-coupled diode laser system including four multi-module assemblies of the type shown in  FIG. 17   a , combined with other optical components. 
           [0058]      FIGS. 20 and 21  are perspective views of another module construction having a step mirror insulated from the mounting block. 
           [0059]    Like reference symbols in the various drawings indicate like elements. 
       
    
    
     DESCRIPTION 
       [0060]      FIG. 1  shows an M-Block assembly  10  consisting of an M-Block  100  and a step mirror  200 . The M-Block  100  has a plurality of steps (e.g., six steps)  101  that are parallel to each other with an accurately machined heights relative to each other. 
         [0061]    Perpendicular to each of the steps  101  is a first surface  102  and a second surface  103 . Surfaces  102  and  103  are also perpendicular to each other. The design of the plurality of surfaces  101 ,  102  and  103  is such that they can be machined by milling surfaces on the M-Block  100  using only three different orientations between the milling tool and the M-Block. Because each mounting surface  101  is parallel to the other mounting surfaces, each surface  101 , as well as one of the locating surfaces for mounting of step mirror  200 , may be diamond-milled with the M-block fixtured in a single position, minimizing tolerance errors and ensuring parallelism. Similarly, all parallel surfaces  102  may be milled with the M-block held in a single orientation, as can all parallel surfaces  103 . All three sets of surfaces may be milled in orientations in which the M-block is held in locations determined by a common set of surfaces or features, including a surface that locates the M-block in use in a laser assembly. The step mirror  200  is secured to the M-Block after machining, such that the M-Block  100  is machined separately from the step mirror  200 . 
         [0062]    Each of the surfaces  102  provides an end stop against which the out coupling facet of a light emitting device (e.g., a semiconductor diode laser)  300  can be aligned so that the laser beam  500  emitted from any such laser diode  300  is perpendicular to all surfaces  102 . The laser diode  300  can include one or more emitting regions, which can be part of a single chip light emitting device, and, when the chip includes more than one emitting region, the chip may be known as a light emitting array (e.g., a diode laser array). Because each laser diode  300  is aligned so that the laser beam  500  emitted from the laser diode  300  is perpendicular to all surfaces  102 , all laser beams  500  are parallel to each other without any active alignment of the lasers  300  or their output beams  500 . 
         [0063]    Each of the surfaces  101  provides an end stop for a bottom facet of the laser diodes  300 . Since the surfaces  101  are machined in the M-Block  100  at an precisely machined relative heights to each other the vertical displacement of all parallel laser beams  500  emitted from the lasers  300  are aligned with precise relative heights to each other. 
         [0064]    Each of the surfaces  103  provides an end stop for one of the side facets of the laser diodes  300 . Since the surfaces  103  are placed at an accurately machined distance from each other this ensures a precise horizontal distance between all parallel laser beams  500  when they are emitted from the lasers  300  and travel in the direction of the step mirror  200 . 
         [0065]    Surfaces  101 ,  102 , and  103  therefore ensure that the beams of all laser diodes  300  are parallel to each other and precisely spaced horizontally and vertically from each other in all three Cartesian directions. 
         [0066]    Step mirror  200  is accurately aligned to three surfaces on the M-Block not shown in  FIG. 1 , so that each mirror surface on the step mirror has a precisely defined orientation to the laser beam  500  it reflects and a precise distance to the laser diode  400  that emits the beam  500 . The mirrors of the step mirror  200  deflect the laser beams  500  by 90 degrees and stack them on top of each other as shown in  FIG. 1 . After reflection from the step mirror  200 , the optical path length of all laser beams  500  is identical. This is ensured by the proper placing of the step mirror surfaces and the surfaces  102 . 
         [0067]    Surfaces  103  also serve the purpose of allowing accurate placement of a plurality of microlenses  400  for focusing or collimating the beams  500  in the fast axis direction of the laser diodes  300 . Surfaces  102  also serve the purpose of reference plane for the microlenses, ensuring the proper distance from the out coupling facets of the laser diode  300 . 
         [0068]    All laser diodes  300  can be electrically connected using wire bonds  305  or other appropriate means, such as, for example, n-contact shims. Also shown are water inlet and outlet fittings  110  and a plug  111 , which can be used to achieve a specific active cooling of the M-Block  100  and the mounted laser diodes  300 . Not shown in  FIG. 1  are internal bores that transport the cooling fluid close to the laser diodes  300 . 
         [0069]      FIG. 2   a  shows the M-Block  100  in a plane parallel to surfaces  102 . Clearly visible are the accurately placed microlenses  400 , which have an accurate lateral and vertical distance from each other. Not visible is the accurate distance that microlenses  400  have in the direction perpendicular to surfaces  102 . Visible is surface  106 , which is manufactured accurately with respect to all surfaces  101 ,  102 , and  103 , such that it allows accurate attachment of the M-block to a center mount  20 , as shown in  FIG. 19   a  and described below. Surface  106  is perpendicular to surfaces  101  and is oriented at a 45 degree angle with respect to surfaces  102  and surfaces  103 . 
         [0070]    Visible is also the n-contact  600  that is attached to the M-Block using two non-conductive screws  610 . 
         [0071]    Microlenses  400  are placed at precise distances in lateral and vertical directions relative to each other to ensure optimum stacking of the beams  500  with maximum fill factor of the combined beam after reflection by the surfaces of the step mirror  200 . Surfaces  104  and  107  ensure accurate placement of the step mirror  200 , and surface  106  ensures accurate placement of a plurality of M-Blocks  100  on a center mount and therefore with respect to each other, as described in more detail below. Adhesive reservoir  105  is used to hold adhesive to glue the step mirror  200  to the M-Block  100 . The surfaces  102  are parallel to each other at an precisely machined distances from each other in order to ensure an identical optical path length of the individual beams after reflection from the step mirror  200 . 
         [0072]      FIG. 2   b  shows the accurate placement of microlenses  400 . The microlenses  400  are cylindrical lenses having an axis that is perpendicular to the surface  103 . Between surface  103  and microlens  400  a gap  420  exists that holds adhesive for fixing the lens  400  in its proper location. During the curing process, the adhesive shrinks and results in movement of the microlens  400 . The particular setup ensures that this shrinkage moves the microlens substantially along the cylindrical axis, which has no optical effect on the collimated beam  500 . 
         [0073]      FIG. 3  is an exploded view of the entire M-Block assembly  100 . Shown is the M-Block  100  with the plurality of surfaces  101 ,  102 , and  103 . The M-Block  100  contains perpendicular surfaces  104  and  107  ( FIG. 2   a ) that allow accurate attachment of step mirror  200  and that ensures proper positioning of the step mirror  200  with respect to the laser beams  500 . Surface  104  also contains a pocket  105  that serves as an adhesive reservoir in case the step mirror  200  is to be glued to the M-Block  100 . 
         [0074]    Fittings  110  and plug  111  are used to flow a cooling fluid through the M-Block  100  and route the fluid through simple bores to transport cooling fluid close to the plurality of laser diodes  300 . Electrically insulating sheets  620  are placed on the surfaces  101  to insulate n-contact sheet  600  from the base of the M-Block  100  and two insulated screws  610  attach the n-contact sheet  600  to the M-Block  100 . Electrical contact between the n-contact sheet and the diodes can be established by utilizing wirebonds  305  or other appropriate means. 
         [0075]    To collimate the light emitted from the laser diodes  300  cylindrical microlenses  400  are used. 
         [0076]      FIG. 4   a  shows a top view of a portion of the M-Block  100  that is parallel to surfaces  101 . The n-contact sheet  600  and the screws  610  are visible as well as the insulating sheets  620 . Wirebonds  305  connect the laser diodes  300  to the n-contact sheet  600 . Microlenses  400  collimate the light emission of the laser diodes  300  in the fast axis direction. Facing each laser diode  300  is a mirror on the step mirror  200 , which deflects the beam by 90 degrees and is located with respect to the laser diode  300  so as to ensure that the optical path length of all laser beams  500  is identical when the beams are combined. 
         [0077]    Fittings  110  and Plug  111  allow a cooling fluid to flow through the M-Block  100  to cooling the block. 
         [0078]      FIG. 4   b  shows a side view of a portion of the M-Block  100  that is parallel to surfaces  103 . The mirrors of the step mirror  200  are oriented at an angle of 45 degrees to this plane. The cylindrical axis of the microlenses  400  is perpendicular to this plane. Surfaces  103  are parallel to each other and placed at precise distances relative to each other in order to ensure proper optical stacking of the beams. 
         [0079]      FIG. 4   c  is a detailed view of a portion of  FIG. 4   b  and shows a side view of M-Block  100  that is parallel to surfaces  103 . The accurate placement of the cylindrical microlenses  400  with respect to the laser diodes  300  can be seen in  FIG. 4   d , which ensures proper collimation of the laser beams  500 . The accurate positioning of the laser diodes  300  with respect to each other is also visible. In the case shown, the laser diodes  300  are electrically connected to the n-contact sheet  600  by wirebonds  305 . The microlenses  400  and the laser diodes  300  are placed such that the radiation of the laser diodes  300  is reflected from the step mirror  200  with minimum loss. In case of a symmetrical intensity distribution in the fast axis of the collimated beam this means that the optical axis of each of the laser beams lies in the center of the corresponding step of the step mirror  200 . 
         [0080]    The groove  105  is part of the adhesive reservoir for attachment of the step mirror  200 . 
         [0081]      FIG. 4   d  is a detailed view of a portion of  FIG. 4   a  and shows a top view of a portion of the M-Block  100 , which is parallel to surfaces  101 . From  FIG. 4   e  it can be seen how the surfaces  103  and  102  serve as end stops for the accurate placement of the laser diodes  300 . Also visible is the gap  420  that contains the adhesive for attachment of the microlens  400 . The precise machining of surfaces  103  allows for extremely small gap width  420  (on the order of 10 μm or less) and therefore ensures a very controlled shrinking process during curing of the adhesive. In addition the specific choice of geometry will ensure that the shrinkage occurs substantially along the cylindrical axis of the microlens  400  and, therefore, that the shrinkage has no optical effect on the collimated beams  500 . From  FIG. 4   e , it can be seen how the individual steps of the step mirror  200  are placed at an angle of 45 degrees with respect to surfaces  102  and  103  and therefore ensure accurate 90 degree deflection of the beams  500 . 
         [0082]      FIG. 5  shows how microlenses  400  can be aligned with respect to laser diodes  300  and with respect to each other and how the microlens alignment can occur after the attachment of the step mirror  200  to the M-Block  100 . While the step mirror  200  can be very accurately placed with respect to surfaces  101 ,  102 , and  103 , a tolerance chain between the steps of the step mirror  200  and the out coupling facets of the laser diodes  300  exists that contains at least two interfaces. Therefore the active alignment of the microlenses  400  after attachment of the step mirror  200  can be utilized to compensate for any inaccuracy between the placement of the outcoupling facets of the laser diodes  300  and the steps of the step mirror  200 . The microlenses  400  are placed in front of the laser diodes  300  using a vacuum collet  490  that is attached to a six axis alignment stage. During the active alignment, the position and the size of the deflected laser beam  500  at a large distance from step mirror  200  is adjusted until the beam  500  is perfectly collimated and is accurately placed in the proper vertical distance from the other laser beams (unless it is the first beam that is aligned) and in line with the other beams in horizontal direction. This approach advantageously allows the module to be completely assembled and adjusted as a replaceable unit. 
         [0083]    If the laser beams  500  of multiple M-blocks  100  are to be aligned properly with respect to each other, an alignment fixture with a reference surface to which the M-Block surface  106  is accurately attached, and a template is placed at a large distance from the fixture the indicates the desired size and placement of the individual laser beams of each M-Block. That way the first of laser beams  500  of any M-Block is repeatably referenced to surface  106  and two perpendicular edges of surface  106  such that the laser beams  500  not only of one particular M-Block  100  are aligned accurately to each other, but that the laser beams  500  of multiple M-Blocks  100  are also aligned to each other, which can be useful if multiple M-Blocks  100  are placed on a center mount. 
         [0084]    If the attachment of the microlens  400  to surface  103  of M-Block  100  at only one side of the microlens  400  is not reliable enough, a lens plate  410  can be attached to the other side of the microlens  400  and the neighboring surface  103  to hold the microlens  400  from both sides. 
         [0085]      FIG. 6   a  shows a top view of the n-contact  600 . A plurality of thinned regions  601  that allow attachment of wire bonds  305  are shown. The regions  601  are thinned, because the wire bond  305  typically does not allow for bridging a substantial height difference between the laser diode and the n-contact  600 . On the other hand, the n-contact  600  should have a certain thickness to ensure stiffness and some heat removal capacity. Because of the limited ability to bridge height differences between surfaces  101  with a wire bond  305 , the n-contact sheet  600  contains similarly spaced steps as the M-Block, parallel to surfaces  101 . These steps in the n-contact sheet  600  can be very accurately and inexpensively fabricated using a coining operation. 
         [0086]      FIG. 6   b  shows a side view of the n-contact  600 , which shows the thinned regions  601  used for wire bonding. 
         [0087]      FIG. 6   c  shows a side view of the n-contact  600 , including the steps in the n-contact sheet  600 . 
         [0088]      FIG. 7   a  shows an M-Block with a structure for an alternative cooling scheme. As shown, the M-block  100  includes a lid  120  and a base  130  that are brazed using hard solder. After brazing the surfaces  101 ,  102 ,  103 ,  114  and  106  are accurately machined. Step mirror  200  is attached to the finished M-Block  100 , as describe above. 
         [0089]      FIG. 7   b  shows an exploded view of this alternate cooling scheme. The lid  120  contains machined cooling channels  121  that ensure very homogenous cooling of the laser diodes  300 . The cooling fluid is supplied to the cooling channels  121  in lid  120  through the base  130 . 
         [0090]      FIG. 8   a  shows a bottom view of the lid  120  in which the plurality of cooling channels  121  is clearly visible. The surface  122  is preferably flat to ensure very good hard soldering to the base  130 . 
         [0091]      FIG. 9   a  shows a top view of the base  130 , which contains a plurality of cooling fluid inlet bores  131  to feed the plurality of cooling channels  121  in the lid and a plurality of cooling fluid outlet bores  132  to remove the fluid from the cooling channels  121  in the lid. Surface  134  is the flat surface to which surface  122  of the lid can be soldered. A flat surface can be used to allow for very good solder joints. 
         [0092]      FIG. 9   b  shows a side view of the base  130 , which contains two cooling fluid manifold bores  133  (one of which is shown) to supply and remove the fluid from the plurality of fluid input bores  131  and water output bores  132 . 
         [0093]      FIG. 10  shows a top view of ah entire M-Block assembly  10  that is built utilizing the alternative cooling scheme describe above. The plurality of cooling channels  121  beneath the plurality of laser diodes  300  is seen as a dashed line. Also visible are the step mirror  200 , is the microlenses  400 , and the wire bonds  305 . 
         [0094]      FIG. 11   a  shows another cooling alternative for the M-block  100  in which a direct copper bonded (DCB) substrate is used from which the M-Block  100  is machined. The direct copper bonded substrate includes two ceramic layers  142  and multiple cooling channels  141  that are formed by directly bonding sheets of metal. On top of the top most ceramic layer  142  a heat sink  143  is bonded, which is precisely machined as described above and on which the laser diodes  300  are directly placed. 
         [0095]      FIG. 11   b  shows the same structure as  FIG. 11   a , except that a submount  310  is placed between the laser diode  300  and the heat sink  143 . The submount  310  can be expansion matched to the crystalline material of the laser diode  300  to allow hard soldering of the laser diode  300 . Such an expansion-matched submount  310  can be used with the other cooling schemes also. 
         [0096]      FIG. 12   a  shows one alternative mounting arrangement including an expansion matched submount  311  for hard soldering to the laser diode  300 . The M-Block  100  contains cooling channels  121  formed by any of the mentioned cooling methods. The submount  311  is electrically insulating and the p-side of the laser diode  300  is hard soldered to the insulating submount  311 . The n-side of the laser diode  300  is contacted to the n-contact sheet  600  by wire bonds  305  or any other appropriate method. The insulator  620  is optional. 
         [0097]      FIG. 12   b  shows another mounting arrangement including an expansion-matched submount  313  for hard soldering to place the laser diode  300 . The M-Block  100  contains cooling channels  121  formed by any of the mentioned cooling methods. The submount  313  is conductive, and the p-side of the laser diode  300  is hard soldered to a conductive submount  313 . The n-side of the laser diode  300  is contacted to the n-contact sheet  600  by wire bonds  305  or any other appropriate method. The n-contact sheet  600  is isolated from the conductive submount  313  using an insulator  620 , and the conductive submount  313  and the insulator  620  are placed on an insulator  312 . 
         [0098]      FIG. 13   a  shows generally how an electrical contact is made between the laser diodes  300  and the n-contact sheet  600  using wire bonds  305 . The n-contact sheet  600  is insulated from the M-Block  100  using an insulator  620 . 
         [0099]      FIG. 13   b  shows, alternatively, how an electrical contact is made between laser diodes  300  and an n-contact sheet  600  using an n-contact shim  315 . The n-contact sheet  600  is insulated from the M-Block using an insulator  620 . 
         [0100]      FIGS. 14   a  and  14   b  show how an M-Block  100  can be configured in order to drive all laser diodes  300  on the M-Block  100  in series. A series n-contact sheet  700  allows current flow  701  to the first laser diode  300 .  FIG. 14   b  shows a detail of  FIG. 14   a  and shows how the current  702  flowing to the n-contact of the first laser diode  300 , passes through the laser diode  300 , and then the current  703  continues along a small n-contact shim  710  to the n-side of the second diode. It passes the second diode to its p-side, and form there the current  704  flows to the n-side of the next diode, and so on.  FIG. 14  a shows how the current  705  flows from the p-side of the last diode through some end wire bonds to the M-block  100 , which serves as the p-contact of the system of a plurality of laser diodes  300  in series with each other. 
         [0101]      FIG. 14   b  also shows the conductive submount (or metal plated insulating submount)  314  and a small insulator  720  that insulates the small n-contact shims  710  from the submounts  314 . 
         [0102]    The insulator  720  between the small n-contact shims  710 , the n-contact sheet  700  and the conductive or metal coated insulating submounts  314  are better visible. It is also clear how the current  702  flows into the n-side of a diode  300  and the current  703  flows out of the p-side to the next diode. 
         [0103]      FIG. 15  shows an exploded view of an M-block  100  with all diodes in series. Visible are the step mirror  200 , the microlenses  400 , the M-Block  100 , the conductive or metal-coated insulating submounts  314 , the laser diodes  300 , the insulators  720 , the small n-contact shims  710 , the n-contact sheet  700 , and the insulating screws  610  that attach the n-contact sheet  700  to the M-block  100 . 
         [0104]      FIG. 16  shows how the laser diodes  300  can be aligned accurately to the surfaces  102  and  103  during the bonding processes. The M-block  100  is placed inside a holder  840 . An accurately machined template  800  contains precisely machined surfaces  810  and  820 . All surfaces  810  are parallel to each other, and all surfaces  820  are parallel to each other. Surfaces  810  are perpendicular to surfaces  820 , and surfaces  810  are separated from surfaces  820  by an undercut  830 . All surfaces  810  are brought into direct contact with all surfaces  102 , and all surfaces  820  are brought into direct contact with surfaces  103 . Such tolerances are possible because of the 1.0 μm accuracy of modern diamond machining tools. 
         [0105]    The outcoupling facets of the laser diodes  300  are pushed against surfaces  810 , with their side facets against surfaces  820  during the bonding process to ensure accurate placement of the laser diodes  300 . The laser diodes then are bonded onto surfaces  101 . In some cases, surfaces  810  of the alignment fixture are each slightly stepped, such that as aligned, the outcoupling facets of the laser diodes slightly overhang the diode mounting surfaces  101  of the mounting block, such as with an overhang of about 10 μm. This can help to ensure than no solder creeps up the output facet. 
         [0106]      FIG. 17  shows a plurality of M-blocks  10  attached to a center mount  20 . Because the center mount and the M-block surface  106  are accurately machined highly accurate placement of all laser diode beams on all M-blocks  10  can be achieved. The M-blocks  10  have a set distance from each other and are alternately placed on the two attachment surfaces of the center mount  20 . On one of the attachment surfaces the M-blocks  10  are attached upside down to ensure a maximum number of total beams  500  in a minimum height, which corresponds to an optimum fill factor of the combined beam. 
         [0107]      FIGS. 17   b  and  17   c  show end and side views of the center mount  20  including the M-block assemblies  10 . Features  30  along common mounting surface  31  accurately position each M-block assembly on the center mount. 
         [0108]      FIG. 18  shows a fiber coupled diode laser system based on two center mounted M-block stacks  1100  that emit light at a first wavelength and two center mounted M-block stacks  1150  that emit light at a second wavelength. All four center mounted M-block stacks  1100  and  1150  emit a stack of individual beams that are shaped using beam shaping optics  1200 . After passing bending mirrors  1220 , the radiation of the first wavelength is combined with the radiation of the second wavelength using dichroic mirrors  1230  that are transparent for the second wavelength and reflective for the first wavelength. This happens twice—once for the two stacks on the left side and once the two stacks on the right side. 
         [0109]    One of the two remaining beams of the combined first and second wavelengths changes its state of polarization perpendicular to the other beams of the combined first and second wavelengths by passing a half-lambda plate  1240 . 
         [0110]    Then, the two remaining beams of the combined first and second wavelengths are polarization combined in a polarization combining prism  1250 . The beam continues along a set of backscattering filters  1300  into a beam switch  1400 . The beam can either leave the beam switch and propagate into a beam dump  1500  (laser on standby) or can propagate into a fiber coupler  1600  with an integrated focusing lens, which focuses the beam into a fiber  1640  that is fixed using a fiber plug  1620 . The entire system is mounted on a base plate  1700 . 
         [0111]      FIG. 19  shows a three dimensional view and details of the system described in  FIG. 20 . 
         [0112]      FIG. 20  shows an alternative design of the M-block  3100 . In this case, the alternative step mirror  3200  is isolated from the M-block utilizing an insulator  3300 . 
         [0113]      FIG. 21  shows another such alternative. In this case, each step surface  101  of the M-Block  100  includes a plurality of laser diodes  300 , which can provide stress relief to the laser diodes  300  if they are hard soldered to a submount that is not perfectly expansion matched. Additionally, this configuration might also be beneficial for heat removal. 
         [0114]    Other details regarding particular embodiments may be found in pending U.S. Provisional Patent Application Ser. No. 60/575,390, filed on Jun. 1, 2004, or in a U.S. Patent Application filed concurrently herewith by us and entitled DIODE LASER ARRAY STACK. The entire contents of both of these mentioned applications are hereby incorporated by reference. 
         [0115]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.