Abstract:
A method and apparatus are disclosed for aligning the coupling an optical laser fiber using an alignment structure. The disclosed alignment structure accepts an optical fiber having a beam and a detection apparatus. According to one aspect of the teachings, the detection apparatus has a tapered form having a circular cross section at one end to match the laser aperture, and a circular cross section at the other end to match the fiber core.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/821,445, filed on May 9, 2013. The entire disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to the coupling of optical fibers with a laser cutting head and, more particularly, to a method and alignment apparatus for coupling a multimode fiber to the cutting head. 
       BACKGROUND 
       [0003]    The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    A number of coupling techniques have been developed to efficiently couple power between optical fibers and optical devices, especially between a semiconductor laser and an optical fiber, in optical communications and industrial laser systems. For example, proper alignment allows an increase in the coupling efficiency and, thus, a decrease in the coupling loss between the laser and the fiber or receiver, permit an increase in fiber output. However, efficient coupling of semiconductor lasers to optical fibers has been a problem of general concern since the advent of optical fiber laser transmission. Generally, as a result of coupling inefficiencies, a percentage of the laser output is not utilized. Thus, the laser has to be run at a correspondingly higher current to yield the same-coupled power into fiber that a more efficient coupling scheme could provide. In addition, operation of the laser at higher currents results in greater heat to be dissipated and raises questions of long term stability and reliability of the laser itself. As laser-cutting heads can need repair or replacement, realignment of the laser head to the transmission optical fiber with the optical lenses in the laser head is necessary. Typically, power meters are coupled to a laser head optics that attempt to allow maximization of the output of the system caused by proper laser to fiber input coupling. Because of the nature of industrial lasers, power measurement in a working environment may not be the best measure of fiber alignment. 
       SUMMARY 
       [0005]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0006]    Generally, a method and apparatus are disclosed for coupling an optical laser fiber using an alignment structure. The disclosed alignment structure accepts an optical fiber having a beam and provides a detection apparatus. According to one aspect of the teachings, the detection apparatus has a tapered form having a circular cross section at one end to match the laser aperture, and a circular cross section at the other end to match the fiber core. An optical detector is provided which senses the amount of light that does not pass through the aperture, and is thus reflected to the optical detector. 
         [0007]    According to the present teachings, an alignment structure for a laser cutting head is disclosed. The alignment structure has an optical detector that detects misalignment of a beam supplying fiber. The detector defines a reflective cone having a beam accepting through bore. The optical detector provides a signal indicative of light reflected off the reflective cone. 
         [0008]    According to another teaching, a method for improving the alignment of a laser with a fiber is disclosed. The method includes positioning a laser with a first end of a fiber optic cable. An alignment detector is placed at a second end of the fiber optic cable. A first portion of collimated light transmitted through the fiber optic cable is passed through an aperture defined by the detector. A second portion of the collimated light in reflected within the alignment detector. And optical sensor within the alignment detector produces a signal indicative of the second portion of collimated light. The alignment of the laser with the first end of the fiber is then adjusted to minimize the second portion of collimated light. 
         [0009]    Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       DRAWINGS 
         [0010]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0011]      FIG. 1  illustrates an illustrative laser head accordance with the present teachings; 
           [0012]      FIG. 2  illustrates a sectional view of the laser head according to the present teachings; 
           [0013]      FIG. 3  illustrates an exploded view of a fiber alignment feature according to the present teachings; 
           [0014]      FIGS. 4A-4C  illustrate the fiber alignment structure shown in  FIGS. 1-3 ; and 
           [0015]      FIGS. 5A-5C  represent an alignment tool according to alternate teaching. 
       
    
    
       [0016]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0017]    As shown in  FIGS. 1-4C , the fiber coupling alignment system  10 , according to the present teachings, has a fiber coupler  12 , an alignment fixture  14 , and laser head  16 . The laser head  16  contains focusing optics  18  configured to focus a laser beam  20  from the fiber coupler  12  onto a work piece (not shown). The laser head  16  further has an atmospheric control  21  that is configured to supply inert gas into the laser head  16  and beam nozzle  22 , as described in detail below. The laser head  16  can be aligned with the alignment fixture  14  and fiber coupling alignment system  10  to maximize the output of the alignment system  10 . 
         [0018]      FIG. 3  represents an exploded view of the alignment fixture  14  according to the present teachings. The alignment fixture  14  has a fiber interface assembly  24  defining a through bore or aperture  26 , configured to accept the core of a fiber optic transmission line or cable. The alignment fixture  14  is configured to align the fiber so that the fiber optic cable produces a diverging beam. 
         [0019]    The laser head focusing optics  18  function to focus the diverging beam into an adjustable focal point  28 . The interface assembly  24  has a coupling end  30  which is threaded and configured to be selectively and fixably coupled to the alignment fixture  14 . The alignment fixture  14  has a housing  32  and a beam monitor  34 . The beam monitor  34  is coupled to a housing detection aperture  36  defined in the housing  32 . The housing detection aperture  36  contains a filter  38  which can be held onto the housing  32  using a filter-retaining nut  40 . A panel lens  42  allows for the observation of light reflected within the housing  32  from a non-aligned laser beam from being detected. 
         [0020]    The alignment fixture  14  has a plurality of mechanisms that allow the adjustable coupling of the alignment fixture  14  to the laser head  16 , or as described below a power meter  47  or black body. The mechanism includes an aperture plate  44 , space blocks  46 ,  48 , and an adapter block  50 . It is envisioned dimensional adjustment can occur by adjusting X-Y-Z parameters of the fiber core with respect to the aligned apertures. 
         [0021]      FIGS. 4B and 4C  represent sectional views of the alignment fixture  14  according to the present teachings. As shown, the fiber coupler  12  is mated to the aperture in the housing  32 . This generally aligns the beam from the fiber with the iris  43  of the alignment system  10 . Shown in this particular configuration, the iris  43  can have a fixed through aperture. It is contemplated however that the iris  43  can have a variable sized through aperture. In the fixed iris configuration, the iris  43  can be formed at the apex of a cone  56  and define a cone aperture  54 . 
         [0022]    As best seen in  FIG. 4C , the alignment fixture iris  43  has a conical aperture member  56 . The conical aperture member  56  defines a bore that is aligned with the housing throughbore. The bore can be tapered on a first side so as to have an angle of inclination substantially equal to the divergence angle of the beam or the conical aperture member  56 . The conical aperture member  56  has a tip portion  65  that defines a circular interface between the first concave interior side and an angled exterior convex second side  63 . The angled exterior convex second side,  63  reflects the laser beam when the beam around the interior chamber defined by the alignment tool when the laser is misaligned with the first end of the fiber optic cable. 
         [0023]    The fiber alignment system  10  for coupling the optical fiber  80  to a laser has, a laser producing a collimated beam adjustably coupled to a first end of a fiber optic cable. As described above, should tis alignment be not proper, output of the laser system can be compromised. The alignment fixture is coupled to a second end of the fiber optic cable. As described above, the alignment fixture  14  defines a chamber  81  having a through aperture  83  aligned with the fiber  80 . The alignment fixture  14  has a light detector  60  configured to detect reflected light within the chamber  81  caused by misalignment of a laser beam passing through the aperture  83 . An internal iris  43  within the chamber is aligned with the through aperture  83  of the chamber  81 . 
         [0024]    The iris  43  can be defined within a cone having an exterior convex conical surface. The exteriors conical surface functions as a non-concentrating reflective layer that serves to allow the light detector to measure light being reflected within the chamber. The convex surface need not be highly polished, as the intent of the light detector is to produce a signal indicative of the amount of light in the chamber. Optionally, the iris  43  comprises and an interior concave conical surface. The intent of the interior concave surface is to not interfere or cause reflection of the light properly passing through the iris aperture. It is optional for instance for this interior surface to be cylindrical. The iris  43  can have a tapered surface on a first interior side having an angle of inclination substantially equal to a beam divergence angle. In this regard, the iris  43  can have a tip portion  65  that defines a circular interface between the interior concave surface and the exterior convex surface. The iris  43  the aperture is configured so as that when the beam is properly aligned, iris  43  defines an air gap between the beam and the interior or exterior conical surfaces. 
         [0025]    The aperture is configured so as that when the beam is properly aligned, the conical aperture member will define an air gap between the beam and any internal or external surface. The alignment system  10  is used to align the laser beam with the through aperture of the alignment fixture  14  and laser head  16 . When the originally misaligned beam is turned on, the dispersed beam engages the conical aperture member  56 . Light from the non-aligned beam is reflected around the interior of the housing  32 . The reflected beam passes through the filter  38  and housing detection aperture  36 . At this point an optical detector determines how much of the beam has been misaligned. An operator can use setscrews to adjust the position of the beam with respect to the reflective cone  56  to minimize the amount of light not passing through the reflective cone  56 . 
         [0026]    As shown in  FIGS. 5A-5C , the fiber alignment system  10 , according to the present teachings, has a fiber coupler  12 , an alignment fixture  14 , and black body absorber or power meter  47 . The power meter  47  can contain beam-accepting optics that can for example be configured to accept the non-focused laser beam  20  from the fiber coupler. The power meter  47  further can have a control  61  that is configured to supply inert gas into the power meter  47  as well as water-cooling  52 . The power meter  47  is coupled to the alignment fixture  14  and fiber coupling alignment system  10  to maximize the output of the alignment system  10 . 
         [0027]    As described above, the alignment fixture  14  can define a cone defining a through aperture that accepts a first portion of a collimated beam. The cone can have a first concave conical surface annularly disposed at a first angle about the aperture and a second inner convex conical surface disposed at a second angle. Optionally, the aperture can be defined by a third conical convex surface having an angle that generally corresponds to a desired beam radius for a given position along the beam axis. 
         [0028]    In practice, a laser is adjustably coupled with a first end  62  of a fiber optic  80 . An alignment detector  60  is placed at a second end of the fiber optic cable  82 . A first portion of collimated light transmitted through the fiber optic cable is passed through an aperture defined by the alignment detector and into the power meter  47 . A second portion of the collimated light in reflected off of the first conical surface and is reflected within the alignment detector  60 . At least a portion of this second portion of collimated light is accepted by the optical detector positioned within the alignment detector. This second portion of reflected light corresponds to light caused by misalignment of the laser with the first end  62 . The optical sensor  61  within the alignment detector  60  produces a signal indicative of the second portion of collimated light. The alignment of the laser with the first end of the fiber  62  is then adjusted to minimize the second portion of collimated light by minimizing the output signal from the optical detector. 
         [0029]    The power meter can have focusing optics  18  that function to safely accept the output of the fiber and to measure to potential output of the aligned system. Once the fiber has been aligned with the laser, further alignment is not required to for instance service the laser processing head. The fiber to laser alignment can, for instance during routine system maintenance be accomplished using the alignment detector  60 . The alignment tool can as shown in  FIG. 1-4C  be incorporated between the laser processing head and the fiber, of can simply removed prior to coupling the head to the tool (see  FIGS. 5A-5C ). 
         [0030]    The alignment fixture  14  has a plurality of mechanisms that allow the adjustable coupling of the alignment fixture  14  to the power meter  16 . The mechanism includes an aperture plate  44 , space blocks  46 ,  48 , and an adapter block  50 . It is envisioned dimensional adjustment can occur by adjusting X-Y-Z parameters of the fiber core with respect to the aligned apertures. 
         [0031]    Although not shown in this view, the alignment fixture  14  has a conical aperture member  56 . The conical aperture member  56  defines a bore therethrough. The bore can be tapered on a first side so as to have an angle of inclination substantially equal to the divergence angle of the conical aperture member  56 . The conical aperture member  56  has a tip portion  65  that defines a circular interface between the first side and an angled second side,  63  that reflects the laser beam when the beam is misaligned. 
         [0032]    The aperture is configured so as that when the beam is properly aligned, the conical aperture member will define an air gap between the beam and any internal or external surface. The alignment system  10  is used to align the laser beam with the through aperture of the alignment fixture  14  and power meter  47 . When the originally misaligned beam is turned on, the dispersed beam engages the conical aperture member  56 . Light from the non-aligned beam is reflected around the interior of the housing  32 . The reflected beam passes through the filter  38  and housing detection aperture  36 . At this point an optical detector determines how much of the beam has been misaligned. An operator can use setscrews to adjust the position of the laser with respect to the input of the fiber so as to adjust the position of the laser beam with respect to the reflective cone  56  to minimize the amount of light not passing through the reflective cone  56 . 
         [0033]    It is envisioned the adjustment of the beam location can be done automatically using actuators such as stepper motors, or manually controlled by a controller (not shown). Once the beam is aligned, the laser head  16  can be removed, repaired and replaced without realignment of the beam. 
         [0034]    The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. 
         [0035]    In this application, including the definitions below, the term module may be replaced with the term controller. The term module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; memory (shared, dedicated, or group) that stores code executed by a processor; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. 
         [0036]    Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
         [0037]    The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0038]    When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0039]    Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
         [0040]    Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated  90  degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
         [0041]    The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term-shared processor encompasses a single processor that executes some or all code from multiple modules. The term group processor encompasses a processor that, in combination with additional processors, executes some or all code from one or more modules. The term-shared memory encompasses a single memory that stores some or all code from multiple modules. The term group memory encompasses a memory that, in combination with additional memories, stores some or all code from one or more modules. The term memory may be a subset of the term computer-readable medium. The term computer-readable medium does not encompass transitory electrical and electromagnetic signals propagating through a medium, and may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory tangible computer readable medium include nonvolatile memory, volatile memory, magnetic storage, and optical storage. 
         [0042]    The apparatuses and methods described in this application may be partially or fully implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on at least one non-transitory tangible computer readable medium. The computer programs may also include and/or rely on stored data.