Abstract:
In order to achieve a high brightness optical source with both spatial size and numeric aperture ideal for fiber coupling, an assembly of multiple individually collimated laser diode chips on submount (COS) are mounted onto a common flat surface and redirected through a series of optical components. This is done in such a manner which allows for active reduction of both overall spot size and numeric aperture. This optical stacking technique achieves a high brightness source which is also suitable for directly coupling into an optical fiber, or can achieve enhanced brightness through the use of existing polarization or wavelength combining schemes prior to fiber optic coupling.

Description:
BACKGROUND CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority under 35 C. §119(e) to Provisional Patent Application Ser. No. 61/619,394, titled “Spatial Beam Multiplexing For Multiple Emitters,” filed on Apr. 2, 2012. The subject matter of the foregoing is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of Disclosure 
         [0003]    This disclosure relates to the field of beam multiplexing generally, and specifically to improved spatial beam multiplexing to facilitate coupling optical radiation into a fiber. 
         [0004]    2. Description of the Related Art 
         [0005]    Presently, systems and methods for beam multiplexing generally combine beams in a vertical manner. In order to stack the beam profiles one or more of the laser diodes that generate the beams are placed on mechanical steps such that the height of each laser diode is different from one other. The mechanical steps add additional material between the laser diode and an associated heat sink. Thus, the thermal dissipation of the laser diodes is not uniform, and not as efficient as direct COS soldering to housing. Additionally, the mechanical steps are generally machined to a fixed height and set of mechanical tolerances. The mechanical tolerances of the mechanical steps limit the distances between beam profiles, and accordingly may limit the numerical aperture and/or coupling efficiency of the combined beams with a fiber. 
       SUMMARY 
       [0006]    An assembly includes a first laser diode, a second laser diode, a first collimating assembly, a second collimating assembly, a first redirecting device, and a second redirecting device. In one embodiment, the first laser diode produces a first beam, and the first laser diode is part of a first chip on a submount (COS) that is mounted to a flat surface. The second laser diode produces a second beam, and the second laser diode is part of second COS that is adjacent to the first COS and is mounted to the flat surface. The first collimating assembly collimates the first beam to form a first collimated beam, such that the first collimated beam has a first spatial beam profile. The second collimating assembly collimates the second beam to form a second collimated beam that is parallel to the first collimated beam, such that the second collimated beam has a second spatial beam profile. The first redirecting device adds a vertical offset to the first collimated beam, changes the direction of propagation of the first collimated beam, and rotates the first spatial beam profile of the first collimated output beam by 90 degrees such that the first spatial beam profile has a first vertical elongated side. The second redirecting device is positioned such that the second redirecting device is staggered laterally from the first redirecting device. The second redirecting device adds the vertical offset to the second collimated beam, changes the direction of propagation of the second collimated beam such that the second collimated beam is parallel to the first collimated beam exiting the first redirecting device, and rotates the second spatial beam profile of the second collimated output beam by 90 degrees such that the second spatial beam profile has a second vertical elongated side adjacent to the first vertical elongated side. The second redirecting device allows active translation of the second beam during alignment, thus reducing the unwanted gaps in the beam stacking process. The first and second collimated beams exiting the first and second redirecting devices create a first stacked beam. 
         [0007]    In another embodiment, an assembly includes a first laser diode, a second laser diode, a first collimating assembly, a second collimating assembly, a first redirecting device, and a second redirecting device. The first laser diode produces a first beam, and the first laser diode is part of a first chip on a COS that is mounted to a flat surface. The second laser diode produces a second beam, and the second laser diode is part of a second COS that is adjacent to the first COS and is mounted to the flat surface. The first collimating assembly collimates the first beam to form a first collimated beam, such that the first collimated beam has a first horizontal spatial beam profile with a first horizontal elongated side. The second collimating assembly collimates the second beam to form a second collimated beam that is parallel to the first collimated beam, such that the second collimated beam has a second horizontal spatial beam profile with a second horizontal elongated side. The first redirecting device changes the direction of propagation of the first collimated beam. The second redirecting device adds a vertical offset to the second collimated beam and changes the direction of propagation of the second collimated beam such that the second collimated beam is parallel to the first collimated beam exiting the first redirecting device and the second horizontal elongated side is adjacent to the first horizontal elongated side. The first and second collimated beams exiting the first and second redirecting devices create a first stacked beam. 
         [0008]    In yet another embodiment a modified right angle prism includes a beam entering surface that is triangular in shape, the beam entering surface includes a first edge that is perpendicular to a bottom surface of the modified right angle prism. A collimated beam perpendicular to, and incident on, the beam entering surface is transmitted by the beam entering surface. The modified right angle prism includes a first reflecting surface that is a 45° cut out between a far side surface and a bottom surface of the modified right angle prism, wherein the far side surface is parallel to the beam entering surface. The modified right angle prism includes a second reflecting surface that is the hypotenuse of the modified right angle prism, such that the collimated beam reflects off the first reflecting surface and then the second reflecting surface, adding a vertical offset to the collimating beam and rotating the collimated beam such that a spatial beam profile of the collimated beam is rotated by 90 degrees. The modified right angle prism also includes a beam exiting surface, rectangular in shape, that transmits the collimated beam reflected from the second reflecting surface, the beam exiting surface intersects the beam exiting surface at the first edge. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  example assembly for spatial multiplexing laser diode beams according to an embodiment. 
           [0010]      FIG. 2  shows the laser diode beams spatial beam profile of  FIG. 1 , after spatial transformation by the prisms according to an embodiment. 
           [0011]      FIG. 3  is an illustration of the prism used in  FIG. 1  according to an embodiment. 
           [0012]      FIG. 4  is an illustration of another prism according to an embodiment. 
           [0013]      FIG. 5A  shows an array of the prisms in  FIG. 4  according to an embodiment. 
           [0014]      FIG. 5B  shows a side view of the array of the prisms in  FIG. 5A  according to an embodiment. 
           [0015]      FIG. 6  is an illustration of another prism design according to an embodiment. 
           [0016]      FIGS. 7A  illustrates an exit plane view of the combination of a chip on submount with the prism of  FIG. 6  according to an embodiment. 
           [0017]      FIGS. 7B  illustrates a side view of the combination of a chip on submount with the prism of  FIG. 6  according to an embodiment. 
           [0018]      FIGS. 7C  illustrates a top view of the combination of a chip on submount with the prism of  FIG. 6  according to an embodiment. 
           [0019]      FIGS. 7D  illustrates an isometric view of the combination of a chip on submount with the prism of  FIG. 6  according to an embodiment. 
           [0020]      FIG. 8  illustrates a bank of four chips on a submount, using the prism of  FIG. 6  according to an embodiment. 
           [0021]      FIG. 9  is an example assembly for spatial multiplexing laser diode beams, using the prism of  FIG. 6  according to an embodiment. 
           [0022]      FIG. 10  shows a spatial beam profile of vertically stacked laser diode beams according to an embodiment. 
           [0023]      FIG. 11  is an example assembly for spatial multiplexing laser diode beams, to produce the vertical stacking of  FIG. 10  according to an embodiment. 
           [0024]      FIG. 12A  is an illustration of an Amici roof prism according to an embodiment. 
           [0025]      FIG. 12B  shows an array of the prisms in  FIG. 11  according to an embodiment. 
           [0026]      FIG. 13A  illustrates an exit plane view of the Amici roof prism in  FIG. 12A  according to an embodiment. 
           [0027]      FIG. 13B  illustrates a top view of the Amici roof prism in  FIG. 12A  according to an embodiment. 
           [0028]      FIG. 14  illustrates an example optical system for producing vertically offset laser diode beams, according to an embodiment. 
           [0029]      FIG. 15  illustrates an example optical system for producing vertically offset laser diode beams, according to another embodiment. 
           [0030]      FIG. 16  illustrates an example optical system for producing vertically offset laser diode beams, according to yet another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The Figures (FIGS.) and the following description describe certain embodiments by way of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein. Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. 
         [0032]      FIG. 1  is an example assembly  100  for spatial multiplexing laser diode beams according to an embodiment. The assembly  100  includes a plurality of chip on submounts (COS) 105   a - 105   d , a plurality of fast axis collimators (FACs)  110   a - 110   d , a plurality of slow axis collimators(SACs)  115   a - 115   d , a plurality of prisms  120   a - 120   d , a focusing lens  125 ; and a fiber  140 . The COSs  105   a - 105   d , the FACs  110   a - 110   d , the SACs  115   a - 115   d , and the prisms  120   a - 120   d  are all mounted (e.g., bonded or attached via some other means) to a common surface in the X-Z plane. The diode active area heights at each COS  105   a - 105   d  are the same as the heights of the collimated beams (at beam center) before entering the prisms  120   a - 120   d . In alternate embodiments, the FACs  110   a - 110   d  are bonded directly to their respective COSs  105   a - 105   d , instead of being bonded to the common surface. 
         [0033]    The assembly  100  includes COSs  105   a ,  105   b ,  105   c , and  105   d . Each COS contains a laser diode mounted onto a thermal submount. The submount provides thermal management and stability to the laser diode. Each laser diode produces a beam of radiation with a fast axis (i.e. wide divergence, which is in the Y direction in  FIG. 1 ) and a slow axis (i.e., not as wide divergence, which is in the Z direction in  FIG. 1 ). Each of the COSs  105   a - 105   d are positioned in approximately the same X-Z plane such that beams exiting each COSs  105   a - d  originate at approximately the same height in the Y direction. 
         [0034]    The fast axis and slow axis of the beams of radiation from the laser diodes of COSs  105   a ,  105   b ,  105   c , and  105   d  are collimated by the FACs  110   a ,  110   b ,  110   c , and  110   d , and the SACs  115   a ,  115   b ,  115   c , and  115   d , respectively. A beam existing any of the SACs  115   a - 115   d  is substantially collimated, but it is narrow in the Y direction and elongated in the Z direction. For convenience, the Y direction will be referred to as vertical and the x-z plane as horizontal. Thus, the beam exiting any one of the SACs  115   a - 115   d  has a cross section that is horizontally elongated (horizontal spatial beam profile) as illustrated in plane  130 . Plane  130  is not a physical item, but is merely present to help illustrate each beam&#39;s geometry upon exit from SACs  115   a - 115   d . In alternate embodiments, the beam may not be horizontally elongated. For example, the FACs  110   a - 110   d  and SAC  110   a - 110   d  may be such that the collimated beam has a circular spatial beam profile at plate  130 . 
         [0035]    Exiting the SACs  115   a - 115   d , the four beams in  FIG. 1  are four horizontally elongated beams that are horizontally displaced from each other as shown in plane  130 . The This is a spatial pattern that is difficult to couple efficiently into a fiber as the spatial beam profile for each beam is positioned at the same height and in a manner that makes it difficult to minimize the distance between the spatial beam profiles (e.g., because of the width of each COS). In contrast, the embodiments described herein stack beams in a manner to minimize unwanted optical gaps in the stacking, by the spatial beam profile of the stacked beam, from the optical axis of the element the stacked beam is being coupled to, thus lowering the numerical aperture for item (e.g., fiber) needed for coupling while minimizing power loss. 
         [0036]    The prisms  120   a - 120   d  each rotate the spatial pattern of their respective beam as seen at plane  130  ninety degrees. Additionally, each prism  120  is positioned such that it is staggered laterally with any adjacent prism. For example, the prism  120   b  is positioned such that it is offset from the position of the prism  120   a  in the X direction by Δh. Similarly, each subsequent prism is further offset by Δh in the X direction. Thus,  120   c  is offset from  120   b  an additional Δh in the X direction, and  120   d  is offset from  120   c  an additional Δh in the X direction. The spacing of prisms  120   a - 120   d  stacks the rotated beams to create a stacked beam with the spatial beam profile shown by plane  135  and further illustrated by  FIG. 2 . 
         [0037]      FIG. 2  shows the laser diode beams spatial beam profile of  FIG. 1 , after spatial transformation by prisms  120   a - 120   d  according to an embodiment. Here, the four beams have been rotated by 90 degrees so that they are now elongated in the vertical direction, rather than in the horizontal direction. The spatial beam pattern of each beam having at least one elongated vertical side adjacent to one elongated vertical side of another beam&#39;s spatial beam pattern. The four vertically elongated beams are spaced apart by Δh in the X direction. Typical values of Δh range from, for example, ˜200 to 700 microns. The spatial beam pattern of the stacked beam is more square than the spatial pattern of the beams at plane  130 . Accordingly, the numerical aperture required for efficient coupling is less than, for example, the spatial beam profile at plane  130 . Referring back to  FIG. 1 , the assembly includes the focusing lens  135 . The focusing lens  135  couples the beams into a fiber  140 . 
         [0038]    One advantage of this approach is that the COSs  105   a - 105   d , SACs  115   a - 115   d , and prisms  120   a - 120   d  can be attached on a common flat surface. This simplifies assembly and reduces the component count/cost. Additionally, this helps ensure a common thermal profile across each of the COSs  105   a - 105   d , and better heat dissipation due to reduced thermal path. Moreover, beams from each of the COSs  105   a - 105   d  may be aligned precisely using by positioning the prisms  120   a - 120   d  to minimize Δh, thus reducing the numerical aperture needed for efficient coupling to the fiber  140 . For example, the resulting configuration may result in an average thermal resistance reduction of roughly 10% and an effective N.A. reduction due to active stacking of roughly 10%. 
         [0039]    Another advantage is that the prisms of the same geometry can be used for all four beams, rather than using a slightly different prism for each beam. This reduces the component count and overall cost. 
         [0040]      FIG. 3  is an illustration of the prism  120  used in  FIG. 1 . Functionally, the prism  120  can be divided into three parts: a cube  305 , and two orthogonal right angle prisms  310  and  315 . In some embodiments, one or more of the parts may physically be a single monolithic part. For example, the prism  120  may be a single monolithic structure. In other embodiments, the prism  120  is constructed of separate parts that are bonded together. 
         [0041]    The cube  305  includes a mounting surface  307  that provides good registration to a flat mounting surface and rigid attachment. In some embodiments, one or more of the surfaces of the cube (e.g., an entrance plane  320 ) are coated to minimize any reflection over the beam wavelength or range of wavelengths. A collimated beam leaving a collimator assembly (e.g., a FAC and a SAC) enters the cube at the entrance plane  320  and is transmitted to the right angle prism  310 . 
         [0042]    In alternate embodiments, the cube  305  does not have to be a cube-shape, nor does it have to be located in the optical path as shown. Additionally, in some embodiments, the height of the cube  305  in the Y direction may be such that beam passes over the cube and the entrance plane located at the right angle prism  310 . The primary purpose of the cube in  FIG. 3  is to provide good registration and rigid attachment to the flat mounting surface. Other structures can be used to perform this same function. 
         [0043]    After exiting the cube  305 , the beam is reflected, via total internal reflection (TIR), by the hypotenuse  307  (first reflecting surface) the right angle prism  310  and again by the hypotenuse  312  (second reflecting surface) of the right angle prism  315 . The beam then exits the prism  120  at an exit plane  325  in a positive Z direction. In alternate, embodiments, the right angle prism  315  may be rotated such that the beam exits along the negative Z direction, or some other direction. The first reflecting surface (hypotenuse  307 ) and the second reflecting surface (hypotenuse  312 ) are polished in order to maximize total reflection of an incident beam. Additionally or alternatively, in some embodiments, the surfaces may be coated with materials to maximize reflection of the beam. 
         [0044]    The pair of right angle prisms  310  and  315  perform the following functions. They rotate the orientation of the spatial beam profile of the beam exiting from the prism  120  by 90° compared with the spatial beam profile of the entering beam. They elevate the optical axis of the beam. They bend the beam propagation direction by 90°. 
         [0045]    The pair of right angle prisms  310  and  315  preferably is designed so that the exit beam exits close to one of the edges of a second right angle prism (e.g.,  120   b ). The optical axis of the exiting beam preferably is within Δh/2 of the edge. This is because, as shown in  FIG. 1 , the horizontal beam stacking is achieved by shifting each prism  120   a - 120   d  in the X-direction by Δh with respect to each other. If the exiting beam is too far from the edge, then the exiting beam may be obstructed by the other prisms closer to the focusing lens  125 . 
         [0046]    The refractive index of a chosen glass for prism  120  should be high enough so that TIR can happen for all rays of the incoming beam, taking into consideration any residual divergence of the collimated beam and misalignments. For example, the prism  120  may be composed of fused silica, glass, BK7, or any other material that can achieve TIR with low absorption. 
         [0047]      FIG. 4  is an illustration of another suitable prism design  400  according to an embodiment. In this example, the functional aspects of the “cube”  305  and first right angle prism  310  are a single component  405 , and the second right angle prism  315  is a second component  410 . A beam with spatial beam profile  415  entering component  405  is reflected, via TIR, off a back surface  417  (first reflecting surface) of the component  405 . The reflected beam then is then reflected, via TIR, a second time off the hypotenuse  419  (second reflecting surface) of the component  410  before exiting the prism  400 , at an exit plane  420 , along the negative Z direction with a spatial beam profile  425 . The spatial beam profile  425  of the beam is rotated 90 degrees with respect to the spatial beam profile  415 . In alternate, embodiments, the component  410  may be rotated such that the beam exits the prism, via the exit plane  420 , along the positive Z direction, or some other direction. The first reflecting surface (back surface  417 ) and the second reflecting surface (hypotenuse  419 ) are polished in order to maximize total reflection of an incident beam. Additionally, in some embodiments, the surfaces may be coated with materials to maximize reflection of the beam. 
         [0048]    In some embodiments, the components  405  and  410  may physically be a single monolithic part. In other embodiments, the components  405  and  410  are separate parts that are bonded together. 
         [0049]    Additionally, the refractive index of a chosen glass for prism  400  should be high enough so that TIR can happen for all rays of the incoming beam, taking into consideration any residual divergence of the collimated beam and misalignments. For example, the prism  400  may be composed of fused silica, glass, BK7, or any other material that can achieve TIR with low absorption. 
         [0050]      FIG. 5A  shows an array  500  of the prisms in  FIG. 4  according to an embodiment. The array  500  includes prisms  400   a - 400   d . Referring back to  FIG. 4 , each of the prisms  400   a - 400   d  is preferably is designed so that the exit beam exits close to an edge of the component  410  that is above the reflecting surface of the component  405 . For example, for this particular orientation of the component  410 , the exit beam exits close to an edge  430 . 
         [0051]    The optical axis of the exiting beam preferably is within Δh/2 of the edge  430 . This is because the horizontal beam stacking is achieved by shifting each prism  400   a - 400   d  in the X-direction by Ah with respect to each other.  FIG. 5B  shows a side view of the array  500  of the prisms  400   a - 400   d  in  FIG. 5A  according to an embodiment. For example, if the exiting beam of prism  420   a  is too far from the edge  430   a , then the existing beam may be obstructed by an adjacent prism. 
         [0052]      FIG. 6  is an illustration of yet another prism  600 . Prism  600  has a beam entering surface  605 , a far side surface  610 , a bottom surface  615 , a first reflecting surface  620 , a second reflecting surface  625 , and a beam exiting surface  630 . Prism  600  is a monolithic structure. In alternate embodiments, the prism  600  is composed of one or more parts. Additionally, in some embodiments, one or more of the surfaces  605  and  630  may be coated with materials to maximize transmission of a beam. 
         [0053]    The beam entering surface  605  is triangular in shape. The beam entering surface  605  includes an edge  640  that is perpendicular to the bottom surface  615 . The beam exiting surface  630  intersects the edge  640 . The far side surface  610  is parallel to the beam entering surface  605  and is also triangular in shape. 
         [0054]    Prism  600  is a modified right angle prism. The modification is the first reflecting surface  620  which is a 45° cut out between the far side surface  610  and the bottom surface  615  of the prism  600 . The first reflecting surface  620  and the second reflecting surface  625  are polished in order to maximize total reflection of an incident beam. In alternate embodiments, the angle of the first reflecting surface  620  and/or the second reflecting surface with respect to the bottom surface  615  may be angles other than 45 degrees. Additionally or alternatively, in some embodiments, one or more of the surfaces  620  and  625  may be coated with materials to maximize reflection of the beam. 
         [0055]    Functionally, the first reflecting surface  620  acts as the first right angle prism  310  in  FIG. 3 . Similarly, the second reflecting surface  625  (i.e., the hypotenuse of the prism  600 ) acts as the second right angle prism  315 . For example, a collimated beam perpendicular to, and incident on, the beam entering surface  605  is transmitted by the beam entering surface  605 . The collimated beam is reflected by the first reflecting surface  620  and the second reflecting surface  625  resulting in a vertical offset to the collimated beam and rotating the collimated beam such that a spatial beam profile of the collimated beam is rotated by  90  degrees. The collimated beam then exits the prism  600  via the exiting surface  630 . 
         [0056]    In alternate embodiments, the prism  600  may be modified such that the beam exits in the positive Z direction. The bottom surface  615  provides registration and attachment to a flat surface. 
         [0057]    The prism  600  provides a pair of opposing surfaces, the beam entering surface  605  and the far side surface  610 , that are easily gripped without interfering with the collimated beam (or some other laser light used for alignment) entering or exiting the prism  600 . This is extremely useful while aligning the prism  600  when it is part of a larger assembly (e.g., assembly  800  discussed below). For example, the prism  600  may be gripped via the opposing surfaces using a tool. The position of the prism  600  may then be adjusted with the tool such that the collimated beam is properly aligned. Thus, facilitating precise alignment of the prism  600  within a larger assembly (e.g., as shown in  FIG. 8 ) without interfering with the collimate beam. 
         [0058]      FIGS. 7A-7D  illustrate different views of the prism  600  in combination with a COS  105 .  FIGS. 7A  illustrates an exit plane view of the combination of a COS  105  with the prism  600 .  FIG. 7B  illustrates a side view of the combination of a COS  105  with the prism  600 .  FIG. 7C  illustrates a top view of the combination of a COS  105  with the prism  600 . In each of  FIGS. 7A-7C  the prism  600  and the COS  105  are mounted on a flat surface  715 .  FIGS. 7D  illustrates an isometric view of the combination of a chip on submount with the prism of  FIG. 6  according to an embodiment. 
         [0059]      FIG. 8  illustrates a bank of four COS using the prism of  FIG. 6 . In  FIG. 8 , each prism  600  is positioned such that it is staggered laterally with respect to adjacent prism. Note one difference between  FIG. 8  and  FIG. 1  is the following. In  FIG. 8  the beams exit from the righthand side of the prisms&#39; beam exiting surfaces ( beam exiting surface  630 ), whereas in  FIG. 1  the beams exit from the lefthand side of prisms&#39; beam exiting surfaces (i.e., exit plane  325 ) (where right is defined as the −x direction and left is defined as the +x direction). As a result, travelling from the prism farthest (i.e., prism  600   d ) from the focusing lens  125  to the one nearest (i.e., prism  600   a ) to the focusing lens  125 , in  FIG. 8  each successive prism is shifted to the left whereas in  FIG. 1  each successive prism is shifted to the right. The COSs  105   a - 105   d , the FACs  110   a - 110   d , the SACs  115   a - 115   d , and the prisms  600   a - 600   d  are all mounted (e.g., bonded or attached via some other means) to a common surface in the X-Z plane. The diode active area heights at each of the COSs  105   a - 105   d  are the same as the heights of the collimated beams (at beam center) before entering the prisms  600   a - 600   d . In alternate embodiments, the FACs  110   a - 110   d  are bonded directly to their respective COSs  105   a - 105   d , instead of being bonded to the common surface. 
         [0060]      FIG. 9  is an example assembly  900  for spatial multiplexing laser diode beams using the prism  600  shown in  FIG. 6 . The assembly  900  includes a subassembly  905 , a subassembly  910 , an overlay mirror  915 , a half-wave plate  920 , a polarization beam combiner  925 , a focusing lens  125 , and a fiber  140 . In this example, each subassembly  905  and  910  contains a bank of four laser diodes. For each laser diode there is a corresponding SAC, a FAC, and a prism. Within each bank, the four laser diode beams are combined using the approach described with reference to  FIGS. 6-8 . In subassembly  905 , the prism corresponding to each laser diode is a prism  600 . In subassembly  910 , the prism corresponding to each laser diode is a prism  600  that has been modified such that the beam exits in the positive Z direction. The components for each subassembly  905  and  910  are all mounted to a common surface in the X-Z plane. The diode active area heights at each of the COSs are the same as the heights of the collimated beams (at beam center) before entering the prisms  600 . In alternate embodiments, the FACs are bonded directly to their respective COSs, instead of being bonded to the common surface. 
         [0061]    The overlay mirror  915  directs the beams from the subassembly  905  to the half-wave plate  920 . The half-wave plate  920  rotates the polarization of the beams 90 degrees. The beams from the two subassemblies are then combined using the polarization beam combiner  925 . Although the beam orientation is rotated by 90° on the exit plane of the prisms described in previous embodiments, the polarization is still maintained in the slow-axis direction. Therefore, a polarization combination technique can be used to enhance brightness. Two different prism designs (left-to-right inverted prisms) may be used, one for each bank, in order to reduce the overall area required. 
         [0062]      FIGS. 1-9  spatially multiplex laser diode beams by transforming the beams from horizontally elongated to vertically elongated cross sections, and then horizontally stacking the vertically elongated beams as shown in  FIG. 2 . This approach was illustrated using a pair of 45°-angled reflecting surfaces. In the specific embodiments shown, the pair of angled surfaces were implemented as TIR in right angle prisms. However, the approach is not limited to these specific examples. For example, other angles for reflecting surfaces may be used which may be coated to maximize reflection. 
         [0063]      FIGS. 10-13  illustrate a different approach based on vertically stacking the originally horizontally elongated beams.  FIG. 10  shows a spatial beam profile of vertically stacked laser diode beams according to an embodiment. The spatial beam pattern of each beam having at least one elongated horizontal side adjacent to one elongated horizontal side of another beam&#39;s spatial beam pattern. The four horizontally elongated beams are spaced apart by Ah in the Y direction. Typical values of Ah range from, for example, ˜200 to 700 microns. 
         [0064]      FIG. 11  is an example assembly  1100  for spatial multiplexing laser diode beams, to produce the vertical stacking shown in  FIG. 10  according to an embodiment. The assembly  1100  includes a subassembly  1105  and subassembly  1110 , an overlay mirror  915 , a half wave plate  920 , a polarization beam combiner  925 , a feedback isolation filter  1115 , a focusing lens  125 , a fiber shim  1120 , and a fiber  140 . 
         [0065]    Each subassembly  1105  and  1110  produces a vertically stacked beam with a spatial beam profile similar to that of  FIG. 10 . The beams from each subassembly  1105  and  1110  are combined using the overlay mirror  915 , the half wave plate  920 , and the polarization beam combiner  925  in a manner similar to that described above with reference to  FIG. 9 . 
         [0066]    The combined beams then pass through the feedback isolation filter  1115 . The feedback isolation filter  1115  is a filter that attenuates any feedback signal from the fiber  140 . For example, the fiber  140  may be part of a fiber laser (e.g., gain medium) that produces a feedback beam (e.g., at 1300 nm). The feedback isolation filter  1115  attenuates the feedback beam to prevent possible damage to components (e.g., laser diodes) of the assembly  1100 . In alternate embodiments, the assembly  1100  does not include the feedback isolation filter  1115 . 
         [0067]    The combined beams are then coupled to the fiber  140  via the focusing lens  125 . In this embodiment, the fiber  140  is attached to a fiber shim  1120  which holds the fiber  140  in position. 
         [0068]    Each subassembly  1105  and  1110  includes a bank of four COS  105 , four FACs  110 , four SACs  114 , three prisms  1125   a - 1125   c , and a reflector  1130  that are mounted (e.g., bonded or attached via some other means) to a common flat surface  1135 . The diode active area heights at each of the COSs  105  are the same as the heights of the collimated beams (at beam center) before entering the prisms  1125   a - 1125   c  and the reflectors  1130 . In alternate embodiments, the FACs are bonded directly to their respective COSs, instead of being bonded to the common surface  1135 . 
         [0069]    Each subassembly  1105  and  1110  produces a beam cross section similar to the one shown in  FIG. 10 . In  FIG. 11 , the offset in the vertical direction is produced by prisms  1125   a - 1125   c . For example, in subassembly  1110 , the beam produced by the laser diode closest to the focusing lens  125  is turned by a mirror  1130  (i.e., no vertical offset). The beam produced by the next laser diode is turned by the prism  1125   a , which both turns the beam and vertically offsets it. The beam produced by the next laser diode is turned by the prism  1125   b , but with a greater vertical offset, and so on. 
         [0070]    The dimensions of each prism  1125   a - 1125   c  within a subassembly are chosen such that the beam exiting each of the prisms  1125   a - 1125   c  and the reflector  1130  are vertically stacked in the manner shown in  FIG. 10 . Each prism  1125  is an Amici roof prism, with slightly different dimensions. The dimensions of the prism  1125   c  are such that the beam exiting prism  1125   c  passes above (in the Y direction) the reflector  1130 . Likewise, the dimensions of the prism  1125   b  are such that the beam exiting prism  1125   b  passes above the prism  1125   a , and the dimensions of the prism  1125   c  are such that the beam exiting prism  1125   c  passes above the prism  1125   b . Accordingly, the width and height of prisms  1125   a ,  1125   b , and  1125   c  are different from each other, as discussed below with reference to  FIG. 12B . 
         [0071]    The reflector  1130  is a mirror that has high reflectance at the wavelength or band of wavelengths of the beams produced by the COS  105 . In alternate embodiments, the reflector  1130  may be replaced with, for example, a right angle prism. 
         [0072]      FIG. 12A  is an illustration of a prism  1125  and its operation. Prism  1125  is a monolithic structure. Prism  1125  has a beam entering surface  1205 , a first reflecting surface  1210 , a second reflecting surface  1215 , a beam exiting surface  1220 , and a mounting surface  1225 . The prism  1125  is generally shaped like a standard right-angled prism with an additional “roof” section (consisting of the first reflecting surface  1210  and the second reflecting surface  1215  meeting at a 90° angle) on the longest side. Total internal reflection from the roof section flips the image laterally. Additionally, in some embodiments, the first reflecting surface  1210  and the second reflecting surface  1215  of the prism  1125  are coated with materials to maximize reflection of the beam. 
         [0073]      FIG. 12B  shows an array  1250  of the prisms in  FIG. 11  according to an embodiment. The array  1250  includes prisms  1125   a  and  1125   b  from subassembly  1105 . The dimensions of the prisms  1125   a  and  1125   b  are different from one another. Specifically, prism  1125   a  is larger than prism  1125   b . Prism  1125   a  is simply prism  1125   b  scaled to larger dimensions. The size differential is such that the beam exiting prism  1125  a passes over prism  1125   b . Likewise, the prism  1125   b  would be larger than prism  1125   c  (not shown), such that the beam exiting prism  1125   b  exits over the prism  1125   c . The collimated beams entering the array  1250  are at the same height in the Y direction with a spatial beam profile as shown in plane  1255 . Additionally, each of the prisms  1125  are aligned such that the beams exiting the prisms are vertically stacked as shown in plane  1260 . 
         [0074]      FIGS. 13A-13B  illustrate different views of the prism  1125 .  FIG. 13A  illustrates an exit plane view of the Amici roof prism  1125  in  FIG. 12A  according to an embodiment.  FIG. 13B  illustrates a top view of the Amici roof prism  1125  in  FIG. 12A  according to an embodiment. 
         [0075]    One advantage of this approach is that the COSs  105 , SACs  105  and prisms can be attached on a common flat surface. As with  FIGS. 1-9 ,  FIGS. 10-13  are examples and the disclosure is not limited to these examples. Other arrangements and variations of Amici roof prisms can be used. In addition, devices other than Amici roof prisms can be used to produce the vertical offset. 
         [0076]      FIGS. 14-16  illustrate yet other approaches where vertical offset is produced by inclining the direction of beam propagation and allowing the beam to propagate along the inclined direction to achieve a certain vertical offset. The amount of vertical offset, ΔV, can be changed by changing the angle of inclination and/or the distance over which the inclined beam propagates. 
         [0077]      FIG. 14  illustrates an example optical system  1400  for producing vertically offset laser diode beams, according to an embodiment. The system  1400  includes a COS  105 , a FAC with wedge  1410 , and a SAC with wedge  1420 . The FAC with wedge  1410  collimates the fast axis of the beam generated by the COS  105  and deflects the beam by a fixed angle, θ A . The SAC with wedge  1420  collimates the slow axis of the beam and deflects the beam by a fixed angle, −θ A . The beam exiting the SAC with wedge  1420  is vertically offset from the beam generated by the COS  105  by a distance of ΔV A . The double line on the SAC with wedge  1420  represents that the optical element has a curved face from which the beam exits. The FAC with wedge  1410  and the SAC with wedge  1420  may be composed of fused silica, glass, BK7, or some other material. Additionally, the material may have a low or high index of refraction, however, a high index of refraction is preferred. 
         [0078]      FIG. 15  illustrates an example optical system  1500  for producing vertically offset laser diode beams, according to another embodiment. The system  1500  includes a COS  105 , a FAC  110 , a SAC with wedge  1505 , and a wedge  1510 . The SAC with wedge  1505  collimates the slow axis of the beam and deflects the beam by a fixed angle, θ B . The wedge  1510  deflects the beam by a fixed angle, −θ B . The beam exiting the wedge  1510  is vertically offset from the beam generated by the COS  105  by a distance of ΔV B . The double line on the SAC with wedge  1505  represents that the optical element has a curved face from which the beam exits. The SAC with wedge  1505  and the wedge  1510  may be composed of fused silica, glass, BK7, or some other material. Additionally, the material may have a low or high index of refraction, however, a high index of refraction is preferred. 
         [0079]      FIG. 16  illustrates an example optical system  1600  for producing vertically offset laser diode beams, according to yet another embodiment. The system  1600  includes a COS  105 , a FAC  110 , a SAC with wedge  1505 , and a reflecting wedge  1605 . The SAC with wedge  1505  collimates the slow axis of the beam and deflects the beam by a fixed angle, θ C . The reflecting wedge  1605  deflects the beam by a fixed angle, −θ C , and reflects the beam 90 degrees. For example, the reflecting wedge  1605  may contain a 45 degree polished surface (or mirrored surface) such that the beam undergoes TIR and is reflected toward the positive Z direction. The beam exiting the reflecting wedge  1605  is vertically offset from the beam generated by the COS  105  by a distance of ΔV C , and is bent to propagate in the positive Z direction. In alternate embodiments, the reflecting wedge  1605  may be modified such that the exiting beam propagates in the negative Z direction, or some other direction. The reflecting wedge  1605  may be composed of fused silica, glass, BK7, or some other material. Additionally, the material may have a low or high index of refraction, however, a high index of refraction is preferred. 
         [0080]    Additionally, pluralities of assemblies described by  FIGS. 14-16  may be used to create a stacked beam. In some embodiments, the same assembly is used to the stacked beam (e.g.,  FIG. 14 ), in alternate embodiments combinations of different assemblies are used to create the stacked beam (e.g.,  FIG. 14  and  FIG. 15 ). In some embodiments, the stacked beam may be combined with a second stacked beam using, for example, the methods described above with reference to  FIG. 9 . 
         [0081]    The combination of components uses to create a collimated beam may be referred to as a collimating assembly. For example, a FAC and its respective SAC embody a collimating assembly. Additionally, in some embodiments, the collimating assembly may include one or more wedges or other components which add a vertical offset to the collimated beam. 
         [0082]    A redirecting device is used to re-direct the collimated beam exiting a collimating assembly toward, for example, a focusing lens or some other optical element. Examples of redirecting devices are the prisms  120 ,  400 ,  600 , and  1125 , the reflector  130 , etc. 
         [0083]    Alignment of the optical elements in one or more of the assemblies described above may be automatic or manual. In some embodiments, the optical elements are actively aligned using, e.g., a far field and near field camera and a  6  axis manipulator. Once the components are properly aligned they are mounted to a common surface. For example, prisms  120   a - 120   d  may be glued to a common surface. Additionally, in some embodiments, the common surface may include guide lines as a starting point for one or more optical elements to help facilitate active alignment. 
         [0084]    The assemblies (e.g.,  100 ,  800 ,  900 , and  1100 ) described above have a dedicated COS  105  and dedicated optics (e.g., FAC, SAC, and prism) for each laser diode. Separate COSs for each laser diode have thermal advantages over systems that have multiple laser diodes mounted on the same COS. For example, separate COSs for each laser diode are able to dissipate heat faster and evenly when compared to systems that include multiple laser diodes on a single COS. Additionally, systems that include multiple laser diodes on a single COS generally require larger optics area, and the cost of optical elements generally scales with area. Accordingly, there is a cost advantage in having separate optics for each COS. 
         [0085]    Although the detailed description contains many specifics, these should not be construed as limiting the scope of the disclosure but merely as illustrating different examples and aspects of the disclosure. It should be appreciated that the scope of the disclosure includes other embodiments not discussed in detail above. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. 
         [0086]    In the claims, reference to an element in the singular is not intended to mean “one and only one” unless explicitly stated, but rather is meant to mean “one or more.” In addition, it is not necessary for a device or method to address every problem that is solvable by different embodiments of the invention in order to be encompassed by the claims.