Abstract:
A system and method for creating an anti-reflective surface structure on an optical device includes a shim including a textured pattern, wherein the ship is configured to stamp the optical device with the textured pattern, a connector configured to place the optical device in proximity to the shim and apply a force to the optical device against the shim, and a laser source configured to heat the optical device by generating and applying a laser beam to the optical device when the optical device is placed in proximity to the shim.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/166,802 filed on May 27, 2015, the complete disclosure of which, in its entirety, is herein incorporated by reference. 
     
    
     GOVERNMENT INTEREST 
       [0002]    The embodiments described herein may be manufactured, used, and/or licensed by or for the United States Government without the payment of royalties thereon. 
     
    
     BACKGROUND 
       [0003]    Technical Field 
         [0004]    The embodiments herein relate to optical systems, and more particularly to antireflective surfaces used in optical systems. 
         [0005]    Description of the Related Art 
         [0006]    In optical systems, Fresnel reflections from an optical surface have a variety of undesirable effects. These may include reduced transmittance, feedback into laser systems, stray reflections, and in the case of military applications, potential detection by enemy combatants. In bulk optics, Fresnel reflections are traditionally reduced using thin film dielectric stacks of materials with alternating high and low refractive indices. As a result of thin film interference effects, these stacks may be designed to behave as antireflective (AR) coatings for a range of wavelengths. Such coatings, however, may have several problems associated with them. For example, they may exhibit laser induced damage thresholds (LIDTs) significantly lower than those of the bulk optics, and may be subject to environmental degradations and delamination under thermal cycling, and may perform well only for a limited optical bandwidth and angular range. It is desirable to prevent these issues from occurring in an optical system. 
       SUMMARY 
       [0007]    In view of the foregoing, an embodiment herein provides a system for creating an anti-reflective surface structure on an optical device, the system comprising a shim comprising a textured pattern, wherein the ship is configured to stamp the optical device with the textured pattern; a connector configured to place the optical device in proximity to the shim and apply a force to the optical device against the shim; and a laser source configured to heat the optical device by generating and applying a laser beam to the optical device when the optical device is placed in proximity to the shim. 
         [0008]    The shim may comprise a transparent material, and wherein the laser source is placed on an opposite side of the shim than the optical device. The system may further comprise a pair of lenses configured to focus the laser beam on the optical device. The laser source may be located on the same side of the shim as the optical device. The laser beam may be applied to the optical device from an oblique angle. The shim may comprise a release layer comprising a non-adhesive material. 
         [0009]    The release layer may comprise a thickness less than approximately 20 nm. The laser source may comprise a CO 2  laser source creating a wavelength of approximately 10.6 μm. The optical device may comprise an optical fiber, and wherein the anti-reflective surface structure may be created on a tip of the optical fiber. The optical fiber may comprise any of silicate glass, oxide glass, halide glass, and chalcogenide glass, wherein the oxide glass may comprise any of aluminate, phosphate, germanate, tellurite, bismuthate, and antimonate glasses, wherein the halide glass may comprise any of halogen elements, including fluorine, chlorine, bromine, and iodine, and wherein the chalcogenide glass may comprise any of chalcogen elements including sulfur, selenium, and tellurium. 
         [0010]    The optical fiber may comprise a single crystal comprising any of yttrium aluminum garnet (YAG), sapphire, magnesium aluminate spinel, gadolinium gallium garnet (GGG), and lithium niobate. The optical fiber may be doped with rare earth ions of elements comprising any of cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). The optical fiber may be doped with transition metal ions of elements comprising any of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), and nickel (Ni). 
         [0011]    An embodiment herein provides a system for creating a random anti-reflective surface structure on an optical fiber, the system comprising a holder, configured to hold the fiber optic, wherein the holder comprises any of a groove and a fiber connector, and wherein the fiber connector comprises any of a SMA, FC, and ST type connector; an adhesive material configured to hold the optical fiber in the holder and fill a gap between the optical fiber and the holder, wherein the adhesive material comprises a temporary adhesive material configured to be removed; glass configured to cover the adhesive material and the optical fiber; and a reactive ion etch device comprising plasma and configured to expose an end face of the optical fiber to the plasma, wherein the plasma is configured to etch the random anti-reflective surface structure on the end face of the optical fiber. 
         [0012]    The plasma may comprise any of fluoride (F − ), chloride (Cl − ), C +4 , oxide (O-2), B +3 , sulfite (S −2 ), and argon (Ar) ions. The plasma may comprise an inductively coupled plasma (ICP). A pressure of the plasma may be maintained between approximately 15 and 100 mT, and wherein a gas flow of the plasma may be maintained between approximately 20 and 150 sccm. The etching may be carried out until a peak-to-valley surface roughness of the random anti-reflective surface structure is between approximately 150 nm and 2 μm. The system may further comprise an etch mask on the tips of the plurality of fibers, wherein the etch mask may comprise a layer of metal comprising a thickness less than approximately 1,000 nm, and wherein the metal may comprise any of gold (Au), silver (Ag), titanium (Ti), aluminum (Al), and chromium (Cr). 
         [0013]    An embodiment herein provides a method for creating a random anti-reflective surface structure on a plurality of optical fibers, the method comprising placing the plurality of optical fibers in a plurality of groves; holding the plurality of optical fibers in place using an adhesive; placing glass on the plurality of optical fibers; coating tips of the plurality of optical fibers with a layer of metal, wherein the metal comprises any of gold (Au), silver (Ag), titanium (Ti), aluminum (Al), and chromium (Cr); and exposing the tips of the plurality of optical fibers to a plasma, wherein the plasma comprises any of fluoride (F − ), chloride (Cl − ), C +4 , oxide (O −2 ), B +3 , sulfite (S −2 ), and argon (Ar) ions. 
         [0014]    These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which: 
           [0016]      FIG. 1A  is a scanning electron microscope (SEM) image of the end faces of fibers in a V-groove holder according to an embodiment herein; 
           [0017]      FIG. 1B  is a schematic diagram illustrating an optical fiber according to an embodiment herein; 
           [0018]      FIG. 1C  is a schematic diagram illustrating a fiber bundle according to an embodiment herein; 
           [0019]      FIG. 1D  is a schematic diagram illustrating a system for etching a surface of an optical fiber according to an embodiment herein; 
           [0020]      FIG. 2  is a SEM image of an etched optical fiber end face surface showing both the core and clad areas according to an embodiment herein; 
           [0021]      FIG. 3A  is a schematic diagram illustrating a first part of a process for stamping antireflective surface structures (ARSSs) used on an optical fiber according to an embodiment herein; 
           [0022]      FIG. 3B  is a schematic diagram illustrating a second part of a process for stamping ARSS on an optical fiber according to an embodiment herein; 
           [0023]      FIG. 3C  is a schematic diagram illustrating a third part of a process for stamping ARSS on an optical fiber according to an embodiment herein; 
           [0024]      FIG. 3D  is a schematic diagram illustrating a fourth part of a process for stamping ARSS on an optical fiber according to an embodiment herein; 
           [0025]      FIG. 4A  is a schematic diagram illustrating an optical fiber with ARSS patterning according to an embodiment herein; 
           [0026]      FIG. 4B  is a schematic diagram illustrating an optical fiber with ARSS patterning according to another embodiment herein; 
           [0027]      FIG. 4C  is a schematic diagram illustrating an optical fiber with ARSS patterning according to still another embodiment herein; 
           [0028]      FIG. 4D  is a schematic diagram illustrating an optical fiber with ARSS patterning according to still another embodiment herein; 
           [0029]      FIG. 5  is a flowchart illustrating a method according to an embodiment herein; and 
           [0030]      FIG. 6  is a flowchart illustrating a method according to another embodiment herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein. 
         [0032]    An approach for reducing Fresnel reflections while reducing the problems associated with traditional AR coatings is direct nano-patterning of ARSS on the surface of an optical material. Processing of these structures does not involve a permanent coating on the optic but instead relies on nano-patterning of the surface of the optical material itself. Nano-patterning of the surface may result in antireflective performance of ARSS comparable to that of the traditional AR coatings, while adding significant advantages such as higher laser damage thresholds, wide spectral bandwidths, and large acceptance angles. 
         [0033]    ARSS structures may include providing a gradual transition in refractive index from one medium (medium A) to another (medium B). As light passes from A to B, the effective index in a given plane that is parallel to the interface between A and B increases from that of A to that of B, as more of the area of a given plane is composed of medium B. ARSS structures may include arrays of nanoscale structures in which the period of the pattern is designed to be on a sub-wavelength scale in order to avoid undesired diffraction effects, while the height of the individual features is on the order of one-half the wavelength, in order to simulate a graded index variation between air and the optical substrate. An ARSS may have an ordered, repeating pattern. This is typically the case when an ARSS is created photolithographically or stamped with a patterned shim. Alternately, a random ARSS (rARSS) may be created via an etch process. 
         [0034]    Fiber tips may also be coated with AR dielectric stacks, as is the case with bulk optics. Similar to reflections from bulk optics, reflections from fiber end faces are problematic for a variety of applications due to reduced transmittance and feedback into laser systems. These problems are especially severe in the case of high power laser applications where AR coatings suffer from low LIDT and are subject to adhesion problems. 
         [0035]    ARSS on fiber tips could provide AR performance while increasing LIDT and environmental stability. In an example, ARSS may be implemented on fiber tips in chalcogenide glass. The low softening point of these glasses (typically less than approximately 300° C.) allows them to be heated and stamped with a patterned shim. In contrast, other types of optical fiber have much higher softening points. For example, silica fiber has a softening point greater than approximately 1400° C., making the stamping process provided by conventional techniques difficult. 
         [0036]    An embodiment herein provides a method for patterning rARSS in an optical fiber. In some embodiments herein, the rARSS may be patterned on a fiber through an etch process. In some embodiments herein, a pattern may be stamped on a fiber using a shim and a stamping procedure. Referring now to the drawings, and more particularly to  FIGS. 1A through 6 , where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments. 
         [0037]      FIG. 1A  is a SEM image of the end faces of fibers in a V-groove holder in an assembly  100  according to an embodiment herein. In an embodiment, the tips of fibers  102  are held in a holder. The holder, for example, may be one or more V-grooves  106 , as shown in  FIG. 1 . In an embodiment, V-grooves  106  are grooves with a V-shaped cross section. Alternatively, in embodiments herein, the holder may be a groove having a cross section of any other shape. In an embodiment, the holder may be a glass capillary, which, in turn, is mounted, in a semicircular fixture. The fiber may be held in place with a suitable epoxy or other adhesive  108 , and a cover glass  104  that may slide is placed on top of the assembly  100  to aid in holding the fibers  102  in place. In an embodiment, the adhesive or epoxy may be temporary or removable, to allow removal of the fibers after etching. 
         [0038]      FIG. 1B , with reference to  FIG. 1A , is a schematic diagram illustrating a fiber  102   a  according to an embodiment herein. The tip  120  of the fiber  102   a  may optionally be coated with a layer  122  of metal, which may be less than approximately 1,000 nm thick. In an embodiment, the metal may comprise any of gold (Au), silver (Ag), titanium (Ti), aluminum (Al), and chromium (Cr). In an embodiment, the assembly  100  is heated and then cooled in order to allow the metal to condense into fine droplets. The metal acts as an etch mask in order to help initiate surface texturing during patterning. 
         [0039]    In an embodiment, the fiber  102   a  may be held by a connector  124 . In an embodiment, the fiber  102   a  may be held by the connector  124  as an alternative to one of the V-grooves  106 . The connector  124  may comprise any of the FC, FC-APC, SMA, ST, and other commercially available or custom-designed optical fiber connectors. 
         [0040]      FIG. 1C , with reference to  FIGS. 1A and 1B , is a schematic diagram illustrating a fiber bundle  130 . In an embodiment, fibers  132 , in the fiber bundle  130 , may be connected by a connector  134 . In an exemplary embodiment, the fibers  132  may comprise a range of approximately 2 to 10,000 fibers in close proximity. In an embodiment, the fibers  132  may be fused or partially fused together. In an embodiment, the fibers  132  may be separate and held in place mechanically or with suitable epoxy. In an embodiment, the end face of the bundle may be polished, and ready to be patterned. 
         [0041]      FIG. 1D , with reference to  FIGS 1A and 1B , is a schematic diagram illustrating a system  150  according to an embodiment herein. In an embodiment, the assembly  100 , including the fibers  102 , may be placed in a reactive ion etch (RIE) system  152  with the fiber tips in the V-groove in a position where it will be exposed to plasma  154 . In an embodiment, the fiber  102   a  may be placed in the RIE. In an embodiment, the fiber bundle  130  may be placed in the RIE. An etch process may then be carried out in the presence of suitable gases which may include any of fluoride (F − ), chloride (Cl − ), C +4 , oxide (O −2 ), B +3 , sulfite (S −2 ), and argon (Ar) ions. In an embodiment, an inductively coupled plasma (ICP) is used. The pressure of the plasma  154  may be maintained between approximately 15 and 100 mT, and the gas flow is maintained between approximately 20 and 150 sccm. Etching may be carried out until peak-to-valley surface roughness is between approximately 150 nm and 2 μm. 
         [0042]      FIG. 2 , with reference to  FIGS. 1A  and  FIG. 1B , shows an SEM image of a surface morphology of the fiber end face after etching, according to an exemplary embodiment herein.  FIG. 2  reveals a similar appearance for a core  202  and clad areas  204  of the fiber  200  (although the two regions are still distinguishable due to differences in the core and clad refractive indices, the dashed circle on  FIG. 2  is added solely for illustration purposes and to generally show the boundary of the core  202 ). 
         [0043]    In an exemplary embodiment, the fiber  200  comprises a single mode silica optical fiber (SMF28). In an exemplary embodiment herein, the fabrication of rARSS on the end faces of the single mode silica optical fiber (SMF28)  102  is achieved using the system  150  of  FIG. 1B . For processing the fiber  200  in the RIE system  152 , an end of the fiber  200  is mounted with epoxy or adhesive  108  in a V-groove of the V-grooves  106  of the assembly  100  as shown  FIGS. 1A and 1B . The end of the fiber  200  is etched as described with reference to  FIGS. 1A and 1B . 
         [0044]    In an exemplary embodiment herein, the measured transmission per end face on a fiber with rARSS is increased to approximately 99.3% at approximately 780 nm wavelength, and approximately 99.4% at approximately 1,550 nm wavelength. This compares favorably to an untreated fiber, which has an end face transmittance of approximately 96.5% at these wavelengths. 
         [0045]    In an exemplary embodiment herein, laser damage testing was performed at 1.06 μm on the end faces of the fiber  200  and untreated silica fibers. The laser parameters are a 20 nsec pulsewidth, a 20 Hz pulse repetition rate, and spot size of 8.7 μm (at 1/e 2 ) which nearly matches the fiber core diameter (8.2 μm). A total of 600 laser shots irradiated the fiber end faces at increasing fluence until damage occurred. The results obtained, as summarized in Table 1, show remarkably high laser damage thresholds, up to 850 J/cm 2  for silica fiber end faces with ARSS, which approaches that of the untreated fiber. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Laser damage threshold values at 1.06 μm for 
               
               
                 fused silica SMF28 optical fibers 
               
             
          
           
               
                 Fiber Array I.D. 
                 Fiber Type 
                 Threshold (J · cm −2 ) 
                 Type of Damage 
               
               
                   
               
             
          
           
               
                 #00 
                 uncoated #1 
                 650 
                 end-face 
               
               
                 #00 
                 uncoated #2 
                 1000 
                 end-face 
               
               
                 #13 
                 ARSS #1 
                 700 
                 end-face 
               
               
                 #13 
                 ARSS #2 
                 750 
                 end-face 
               
               
                 #17 
                 ARSS #3 
                 750 
                 end-face 
               
               
                 #17 
                 ARSS #4 
                 850 
                 end-face 
               
               
                   
               
             
          
         
       
     
         [0046]      FIGS. 3A through 3D , with reference to  FIGS. 1A through 2 , are schematic diagrams illustrating systems for creating an ARSS pattern according to some embodiments herein.  FIG. 3A  illustrates an embodiment where the tip of a fiber  306  is placed in close proximity or contact with a patterned shim  302  with the fiber optionally held in a fiber connector  304 . The textured shim  302  may be made from silicon or another metal or ceramic with a melting temperature higher than that of silica. The textured shim  302  may be coated with a release layer  308 . The release layer  308  may comprise a material that does not adhere strongly to either the fiber  306  or the shim  302 . In an exemplary embodiment, the release layer comprises any of boron nitrite and molybdenum disulfide. In an embodiment, the release layer  308  comprises a thickness less than approximately 20 nm. In an embodiment, a force may be applied to the fiber  306  against the shim  302  using the fiber connector  304  when placed in close proximity or contact with the patterned shim  302 . 
         [0047]      FIG. 3B , with reference to  FIG. 3A , is a schematic diagram illustrating a system  330  for creating an ARSS pattern according to some embodiments herein. In an embodiment, the tip of the fiber  306  may be heated with a laser beam  332 . The fiber  306  may then be pressed against the shim  302  so that the pattern of the shim  302  is imprinted on the tip of the fiber  306 . 
         [0048]    The laser beam  332  is created by a laser source  334 . In an embodiment, the laser source  302  comprises a CO 2  laser source that creates an emission at a wavelength of approximately 10.6 μm. In another embodiment, other laser sources with a wavelength readily absorbed by the optical fiber  306  may be used. If the shim  302  is completely or partially transparent to the laser radiation  332  (e.g., 10.6 μm radiation passing through a silicon shim), it may be focused on the fiber tip through the shim  302  using a pair of lenses  336 . 
         [0049]      FIG. 3C , with reference to  FIGS. 3A and 3B , is a schematic diagram illustrating a system  360  for creating an ARSS pattern according to some embodiments herein. In the system  360 , a laser source  362  is located on the same side of the shim  302  as the fiber  306 , and it produces a laser beam  364  that may be focused on the tip of the fiber  306  from an oblique angle. In an embodiment, the tip of the fiber  306  is heated for a sufficiently long enough period of time that the glass softens and conforms to the surface structure of the shim  302 , thereby transferring the pattern from the shim  302  to the fiber  306 .  FIG. 3D , with reference to  FIGS. 3A through 3C , is a schematic diagram illustrating the fiber  306  and the fiber connector  304  removed from the shim  302 , resulting in a fiber face stamped with an ARSS pattern. 
         [0050]    Embodiments provided herein may dramatically reduce surface reflections from a fiber end face. For example, using the embodiments herein, the reflection from a silica fiber end face is reduced from approximately 3.5% to less than approximately 0.1%. Using embodiments herein, the anti-reflective property of the component remains optically broadband, with low reflection over a spectral range that is typically greater than approximately 500 nm. 
         [0051]    The embodiments herein provide reduced surface reflection that serves to increase fiber throughput and prevent back reflections that can be detrimental to the performance of lasers and other optical components. The embodiments herein further result in a significantly higher LIDT in comparison to an AR-coated fiber. 
         [0052]    In an embodiment herein, the fiber used, for example the fiber  102 ,  200 ,  306  may comprise any of a silicate glass. In some embodiments, the fiber may comprise any of an oxide glass other than a silicate glass. The oxide glass may comprise any of aluminate, phosphate, germanate, tellurite, bismuthate, and antimonate glasses. In an embodiment herein, the fiber may comprise a halide glass. Halide glasses comprise any of halogen elements, including fluorine, chlorine, bromine, and iodine, or combinations thereof. In an embodiment herein, the fiber may comprise a chalcogenide glass. Chalcogenide glasses comprise any of chalcogen elements including sulfur, selenium, and tellurium, or combinations thereof. 
         [0053]    In an embodiment herein, the fiber may comprise a single crystal rather than glass. The single crystal may be any optically transmissive crystalline material that is readily drawn into a fiber form. The crystalline material may comprise any of yttrium aluminum garnet (YAG), sapphire, magnesium aluminate spinel, gadolinium gallium garnet (GGG), and lithium niobate. In an embodiment, the ARSS as described herein may be fabricated on a fiber doped with rare earth ions of elements comprising any of cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). In an embodiment herein, the ARSS may be fabricated on a fiber doped with transition metal ions of elements comprising titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), and nickel (Ni). 
         [0054]    In embodiments herein, the fiber  102 ,  200 ,  306  used may comprise an active or a passive optical fiber. In an embodiment, the fiber  102 ,  200 ,  306  may be removed from its holder, for example V-grooves  106  in  FIG. 1A  or fiber connector  304  in  FIGS. 3A through 3D , after the ARSS patterning. The fiber  102 ,  200 ,  306  may then be connected or mounted in another holder. 
         [0055]      FIG. 4A , with reference to  FIGS. 1A through 3D , illustrates a fiber  400  with ARSS according to an embodiment herein. The fiber  400  comprises undoped sections  402  and  406 , and a doped section  404 . In an embodiment, the ARSS may be fabricated on the surface  408  of the undoped section  402 . In an embodiment, the section  402  may be spliced or bonded onto the doped section  404 . 
         [0056]      FIG. 4B , with reference to  FIGS. 1A through 4A , illustrates a fiber  420  with ARSS according to an embodiment herein. In an embodiment herein, the ARSS  424  may be patterned on a thin glass endcap  426 . The endcap  426  may be attached to an untreated fiber  422  via fusion splicing or optical cement. 
         [0057]      FIG. 4C , with reference to  FIGS. 1A through 4B , illustrates a fiber  430  with ARSS according to an embodiment herein. In an embodiment, the fiber  430  may be tapered to reduce its diameter, and an ARSS pattern  432  may be applied to the side rather than the end face of the fiber  430 . This structure may couple light out of the fiber, serving to reduce cladding-coupled light, reduce transmission in higher order modes, or dump unabsorbed pump light.  FIG. 4D , with reference to  FIGS. 1A through 4C , illustrates a fiber  440  with ARSS according to an embodiment herein. In an embodiment, the fiber  440  may be tapered in the middle to reduce its diameter, and an ARSS pattern  442  may be applied to the tapered surface of the fiber  440 . 
         [0058]    In an embodiment, a fiber tip that is composed of either a silicate glass or non-silicate material could be coated with a film of silica, with a thickness greater than approximately 500 nm, and this film may subsequently be patterned according to any of the embodiments provided herein. 
         [0059]      FIG. 5 , with reference to  FIGS. 1A through 1D , is a flowchart illustrating a method  500  for creating a rARSS pattern on optical fibers  102 , according to an embodiment herein. At step  502 , optical fibers  102  may be placed in one or more grooves  106 . At step  504 , the optical fibers  102  and held with adhesive  108 . At step  506 , the cover glass  104  may be placed on the optical fibers  102 . At step  508 , a tip  120  of the optical fiber  102   a  may be coated with the metal layer  122 . The metal may comprise any of gold (Au), silver (Ag), titanium (Ti), aluminum (Al), and chromium (Cr). At step  510 , the tips of the optical fibers may be exposed to plasma  154 . The plasma may comprise any of fluoride (F − ), chloride (Cl − ), C +4 , oxide (O −2 ), B +3 , sulfite (S −2 ), and argon (Ar) ions. 
         [0060]      FIG. 6 , with reference to  FIGS. 3A through 3D , is a flowchart illustrating a method  600  for creating an ARSS pattern on an optical fiber. At step  602 , the optical fiber  306  is held against the patterned shim  302 . At step  604 , the optical fiber  306  is heated using the laser  334 . The laser  334  may be a CO 2  laser. At step  606 , the pattered shim  308  is pressed against the optical fiber  306  to create the ARSS pattern. In an embodiment, methods  500  or  600  may be used to create the ARSS pattern using any of the assembly  100  in  FIG. 1A  and the fiber bundle  130  in  FIG. 1C . 
         [0061]    The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.