Patent Publication Number: US-2006002673-A1

Title: Thermally-shaped optical fiber and a method for forming the optical fiber

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application is a divisional of U.S. patent application Ser. No. 10/167,071, filed on Jun. 11, 2002, entitled “A Thermally-Shaped Optical Fiber and a Method for Forming the Optical Fiber,” which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates to optical waveguides. More particularly, the present invention is directed toward forming optical waveguides from optical fibers, which are suitable for use in data communication.  
      To minimize insertion loss, the loss of optical energy when coupling data links in fiber-optic communication systems, it is important to correctly match the aperture through which optical energy is transmitted with the aperture through which optical energy is detected. As a result, the areas of the apertures must be correctly sized and aligned.  
      The ideal interconnection of one fiber to another would have two fibers that are optically and physically identical and held by a connector that aligns the fibers so that the interconnection does not exhibit any influence on light propagation therethrough. Formation of the ideal interconnect is difficult for several reasons. These include variations in fiber properties, tolerances in the connector, as well as in cost and ease of use.  
      Commercially available interconnection devices have typical insertion losses from between 0.2 dB to 4 dB. This range of insertion loss results from several factors that may be divided into those related to fibers and those related to interconnection devices. Fibers intrinsically contribute loss to an interconnection and any fiber has variations that are produced during manufacture. These variations exist not only among different lots of fibers, but also within a length of a single fiber, as well. The main variations in these cases are in the core and cladding diameters and fiber numerical aperture (NA). The core ellipticity, cladding ellipticity, and core-to-cladding eccentricity exacerbate the problems associated with variations in the core and cladding diameters. Losses caused by diameter variations, NA variations, eccentricity, and ellipticity are intrinsic to the fiber and the total loss contributed by these intrinsic factors can range from less than 0.2 dB to over 2 dB, depending on how well two fibers match.  
      Connector-related losses may also arise even when there are no intrinsic variations in the fibers. These types of losses arise when two fibers are not aligned on their center axes and lateral or axial displacement can be, and usually is, the greatest cause of loss in the connection. For example, a 0.5 dB loss that is due to a displacement, equal to 10% of the core diameter, will require tolerances to be maintained on each connector (fiber) that is within 2.5 μm. Tolerances of this magnitude are difficult to achieve. Add to this, the losses that are also induced due to angular misalignment, and the total tolerances that must be maintained in the termination process, proper fiber and/or connector end preparation becomes problematic.  
      The considerations discussed above with respect to fiber-to-fiber interconnections apply equally to fiber-source and fiber-detector interconnections, as well. The result is that the requirements that should be achieved to provide efficient optical coupling necessitate end-finishing or termination processes that strives to provide lossless propagation of optical energy. To that end, it is desired to provide the end of a fiber that functions as either a transmission or reception aperture with a smooth end finish free of such defects that may change the geometrical propagation patterns of optical energy passing therethrough. These defects include hackles, burrs, fractures, bubbles and other contaminants.  
      Preparation of conventional glass optical fibers employs score-and-break techniques or mechanical polishing techniques. The score-and-break technique provides an optical fiber with an arc that is scored. Tension is applied to that optical fiber so that the score propagates across the width of the optical fiber, segmenting the same. This technique is capable of producing an excellent cleaved end. Repeatability, however, it is difficult, lowering yields and increasing the cost of the finished optical fibers. In addition, a great amount of skill is required to properly control both the depth of the scoring and the amount of tension during breaking. The aforementioned control may be frustrated by intrinsic fiber variations. Finally, the difficulty in controlling both the depth of scoring and breaking tension increases as the length of the optical fiber becomes shorter.  
      Polishing, compared to scoring-and-breaking, has the advantage of consistent results, but is a much more costly technique. Polishing is typically performed after a connector, or ferrule, has been attached to the optical fiber. Polishing a bare optical fiber is impractical. Usually, a polishing fixture is provided that controls the polishing to a fixed dimension, e.g., usually within 0.3 μm.  
      Polymer-based optical fibers may be segmented with a sharp, and preferably hot, blade. As with the polishing technique mentioned above with respect to glass optical fibers, segmenting is performed on polymer-based optical fibers after a connector has been attached. Polymer-based optical fibers may also be polished, but it is very difficult to achieve the performance of a glass or quartz optical fiber.  
      In addition to providing a smooth end finish, the preparation procedure should provide the optical fiber with a cleaved end, i.e., the end of the optical fiber is typically planar and lies in a plane with the longitudinal axis of the optical fiber extending orthogonally thereto. Otherwise, an angle may exist between the axes of juxtaposed fibers and fiber-devices, referred to as tilting. Tilting can cause additional, and sometimes quite severe, losses in addition to those mentioned previously. While tilting loss can be controlled to some degree by proper end preparation and positioning of adjacent fiber ends, it should not be completely ignored. Often alignment mechanisms are employed to reduce the effects of tilting. Such alignment mechanisms include lenses that may be effectively coupled and aligned, (with minimum loss to the end of the optical fiber).  
      Referring to  FIG. 1 , a fiber-to-fiber arrangement  10  employing lensed optical fibers  12  and  14  is shown. The lenses are shown as  12   a  and  14   a , at the ends of optical fibers  12  and  14 , respectively. Lenses  12   a  and  14   a  are typically spherical and refract optical energy, shown as  12   b  and  14   b , propagating therethrough to facilitate control of the path of light therebetween. In this manner, the lateral and axial alignment between optical fibers  12  and  14  may be relaxed. However, optical fibers  12  and  14  should be accurately placed and aligned behind the lenses in order to actually see any real or significant benefits to the overall loss considerations (e.g., low losses). Moreover, such conditions are most often achieved without the aid of non-integral support elements such as lenses, when the appropriately prepared fiber ends are perpendicular to the fiber axis. One manner in which to form lenses  12   a  and  14   a  is discussed below with respect to a fiber-source arrangement.  
      Referring to  FIG. 2 , shown is a fiber-source arrangement  16  in which a lens  20  is formed on one end of an optical fiber  18 . The source-fiber arrangement  16  includes an optical fiber  18  composed of a core  18   a  and a cladding  18   b . A lens  20  is formed at an end of a fiber core. Were optical fiber  18  formed from silica glass, lens  20  would be formed in the following manner: First, while a portion of the silica glass optical fiber  18  is heated by heating means such as a burner, a tensile force is applied to the fiber in the longitudinal direction thereof, whereby the heated portion extends. When the outer diameter of the heated portion has decreased to a predetermined diameter, optical fiber  18  is cut at the diameter-reduced portion, and then the cut end is again heated for fusion. In the heating step, extreme end  22  of optical fiber  18 , including core  18   a  in the center thereof, becomes spherical in shape due to surface tension, and this spherical end functions as a lens. Thus, lensed optical fiber  18  has a taper portion  24  extending from extreme end  22  to an outer peripheral edge, which is not affected by heat, and having a certain inclination determined by the heating and drawing conditions. Lensed optical fiber  18  produced in this manner is optically connected to a semiconductor laser  26 , and a laser beam  28  is emitted from a light-emitting surface  30  of semiconductor laser  26 . In this case, laser beam  28  radiates in conical form. Laser beam  28  is incident on extreme end  22  at the extremity of core  18   a  and is propagated through core  18   a , as indicated by the arrows in  FIG. 2 , and is used for optical communications. A drawback with the prior art attempt of lens formation is that artifacts are produced by the thermal energy propagating through the optical fiber  18 . These artifacts may lead to increased insertion loss.  
      What is needed, therefore, is a technique to thermally shape an optical fiber while reducing formation of artifacts.  
     SUMMARY OF THE INVENTION  
      Provided are a thermally-shaped optical fiber and a method for forming the same that features creating a flow of thermal energy between two spaced-apart regions of the optical fiber. The flux of thermal energy in the flow is substantially constant to define a graded index of refraction in a portion of the optical fiber located between said two-spaced apart regions. This minimizes formation of unwanted optical artifacts in the portion. For example, a graded index of refraction is formed in the portion, thereby avoiding abrupt changes in the variation of the index of refraction in the portion. Additionally, the formation of a self-focusing lens in the portion is minimized, if not abrogated. Both of the aforementioned optical artifacts, abrupt changes in indices of refraction and the self-focusing lens, leads to insertion loss. By avoiding formation of these optical artifacts, the insertion loss of the optical fiber is greatly reduced, if not completely absent.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view showing coupling of optical energy between two spaced-apart optical fibers, according to the prior art;  
       FIG. 2  is a simplified plan view of a source to fiber coupling arrangement of optical energy in accordance with the prior art;  
       FIG. 3  is a simplified perspective view showing a laser shaping system in accordance with the present invention;  
       FIG. 4  is a perspective view of an optical fiber being exposed to thermal energy of a laser beam shown above in  FIG. 3 , in accordance with the present invention;  
       FIG. 5  is a detailed cross-sectional view of an optical fiber shown bending under force of gravity;  
       FIG. 6  is a cross-sectional view of the optical fiber shown above in  FIG. 5  with sag;  
       FIG. 7  is a detailed perspective view of the fiber shown above in  FIG. 5 ;  
       FIG. 8  is a graph showing the difference in the temperature over the diameter of the optical fiber shown above in  FIGS. 5, 6  and  7 ;  
       FIG. 9  is a perspective view of the optical fiber being segmented with a laser beam in accordance with an alternate embodiment of the present invention;  
       FIG. 10  is a side-sectional view of the optical fiber and laser beam shown above in  FIG. 9  demonstrating a beam focus proximate to the optical fiber rests and spaced apart from a platen;  
       FIG. 11  is a cross-sectional view of the optical fiber and laser beam shown above in  FIG. 10  with a platen having a curved surface, in accordance with an alternate embodiment of the present invention;  
       FIG. 12  is a detailed view showing the mounting arrangement of an optical fiber disposed in a connector to be segmented by the system shown above in  FIG. 3 ;  
       FIG. 13  is a simplified plan view of an optical fiber core segmented in accordance with one embodiment of the present invention;  
       FIG. 14  is a graph showing the change of the index of refraction of the optical fiber shown in  FIG. 13  over the length;  
       FIG. 15  is a simplified plan view of an optical frequency domain reflectometer system used in accordance with one embodiment of the present invention to measure the optical energy reflected in an optical fiber shown in  FIGS. 16 and 17 ;  
       FIG. 16  is a graph showing reflected optical energy vs. length of optical fiber in accordance with an optical fiber segmented in accordance with the prior art;  
       FIG. 17  is a graph showing reflected optical energy vs. length of optical fiber in accordance with an optical fiber segmented in accordance with one embodiment of the present invention; and  
       FIG. 18  is a flow diagram showing a method of thermally-shaping optical fibers in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 3 , an exemplary system  32  that is suitable for shaping optical fibers in accordance with the present invention is shown. The system  32  includes a laser source  34  in optical communication with a platen  36  through a pick-off mirror  38  and beam shaping optics  40 . The platen  36  is attached to a stage  42  that is moveably attached to a frame  44 . Specifically, stage  42  is moveably attached to the frame  44  to reciprocate along at least one axis  46   a . Stage  42  may also be attached to move along an axis orthogonal to axis  46   a , shown as  46   b . To that end, a servo-mechanism  48 , in data communication with a processor  50 , is coupled to the stage  42  to facilitate movement along both axes  46   a  and  46   b  under control of the processor  50 . In this manner, positional control along the axes  46   a  and  46   b  was achieved within 4 μm, with the laser source  34  being able to impinge a beam  52  upon any area of the platen  36 , desired. In the present example, one or more optical fibers  54  are attached to platen  36  using any technique known in the art. The velocity of the stage  42  along either of axes  46   a  and  46   b  may be from stationary to 1 inch/sec or more. Beam  52  impinges upon the optical fibers  54  to segment and/or shape the same.  
      Although any type of laser may be employed, the present exemplary system employed laser manufactured by KERN Electronics and Lasers, Inc. Model # KER6X6-10 to provide basic 10 Watt CO 2  beam. Beam  52 , therefore, comprises of infrared (IR) wavelengths of optical energy of sufficient power to segment optical fibers  54 . The beam profile was adjusted dependent upon the segmentation technique employed, discussed more fully below. With this configuration, the dwell time, period of time in which a single fiber element is exposed to beam  52 , can then be varied from less than a microsecond to more than a millisecond. In addition, manual, single pulse or continuous wave operation of laser source  34  was also made available.  
      Referring to  FIGS. 3 and 4 , the type of cut and/or surface finish achieved on each of optical fibers  54  is a function, inter alia, the spatial proximity between beam  52  and optical fiber  54 , as well as the beam energy to which optical fiber  54  is exposed. Specifically, it is shown that the plane in which the segmentation of optical fiber  54  occurs, cutting plane  56 , extends in the {overscore (x )} and {overscore (y )} directions. Beam  152  propagates in the {overscore (z )} direction to impinge upon cutting plane  56 , while relative movement between optical fiber  54  and beam  152  parallel to the {overscore (x )} direction occurs. In this arrangement, the energy distribution in beam  152  is substantially uniform throughout the cross-section thereof. With this beam profile  152 , a two-step technique is employed to segment and polish the end of the core of optical fiber  54 . To that end, beam  152  functions as a straight-edged thermal blade.  
      In the first step, beam  152  is provided with a sufficient amount of energy to propagate through the optical fiber  54  to segment both the cladding and core of the same. The energy of beam  152  to achieve segmentation was found to be in the range of 20% to 30% of total power available from laser source  34 , dependent upon the type of material that beam  152  has to segment. The width “w” of beam  152  is approximately 1.25-1.4 times greater than the core diameter “d”. When exposed to the thermal energy of beam  152 , the core of optical fiber  54  underwent a plurality of phase-changes in which the solid core becomes a viscous liquid and a gas. Specifically, as shown in  FIG. 5 , portion  58  of optical fiber  54  exposed to beam  152  undergoes two phase-changes with some of the material associated therewith vaporizing and the remaining material becoming molten. Regions  54   a  and  54   b  of optical fiber  54  that are in close proximity with beam  152  also become molten.  
      Referring to  FIGS. 3, 5  and  6 , while in the molten state the core material moves under force of gravity, {overscore (g)}, and accumulates proximate to region  54   b , forming a protrusion  62 . The formation of protrusion  62  is typically referred to as sag. The amount of sag may be controlled, in part, by selecting an appropriate dwell time. For a fixed amount of energy in beam  152  the dwell time is set by the velocity of stage  42 . Stage  42  velocity is between 0.2 and 0.5 inch/second, dependent upon the cross-sectional area of optical fiber  54  being segmented. It was found, however, that regulation of the dwell time, alone, was insufficient to substantially reduce, if not eliminate the sag. Rather, the sag that occurs in the molten state is minimized and/or eliminated by stiffening optical fiber  54  so that the same does not bend under force of gravity, {overscore (g)}.  
      As shown in  FIGS. 5 and 7 , it was found that the sag was the result of optical fiber  54  bending upon force of gravity, {overscore (g)}, during segmentation. Specifically, without stiffening optical fiber  54 , longitudinal axis  66  associated with a subportion  68  of optical fiber  54  forms an oblique angle with respect to gravity {overscore (g)}. As a result, when beam  152  segments optical fiber  54 , a temperature gradient develops between opposing regions  54   a  and  54   b  of optical fiber  54 . Region  54   a  heats faster and therefore, reaches a higher temperature, than region  54   b . This results in uneven heat propagation through optical fiber  54 . As a result, for a brief period of time, the end of optical fiber  54  will concurrently have two phase-states present. When beam  152  initially impinges upon optical fiber  54 , region  54   a  becomes molten while region  54   b  maintains a solid state. As heating continues, the end of optical fiber  54  proceeds to a homogenous phase state of a viscous liquid. However, due to a temperature gradient present in optical fiber  54 , a much greater amount of molten material is present in region  54   a  than is present in region  54   b . An exemplary thermal profile of optical fiber  54  is shown by curve  70  in  FIG. 8 . As shown by curve  70 , the temperatures of region  54   a , shown as point  72 , may be 2.5 times greater than the temperature at region  54   b , shown as point  74 . This temperature gradient produces sag.  
      Referring to  FIGS. 3, 5  and  7 , to reduce the sag produced during segmentation, it is ensured that longitudinal axis  66  associated with subportion  68  exposed to the beam  152  extends transversely to gravity {overscore (g)}. To that end, opposing regions  76  and  78  of optical fiber  54  are securely affixed to a rigid surface, such as platen  36 , using any suitable means known in the art. Portion  58  is located between regions  76  and  78 . This has been found to substantially reduce, if not eliminate sag.  
      Subsequent to segmenting optical fiber  54 , the energy in beam  152  is reduced to be 30% or less of the energy employed to segment optical fiber  54 , while maintaining the same beam width. Optical fiber  54  is then exposed to the thermal energy of beam  152  so as to minimize the dwell time. This may be achieved by first having optical fiber  54  thermally insulated from beam  152 . Then movement between optical fiber  54  and beam  152  in a direction parallel to the {overscore (x )} axis is undertaken. In this manner, the dwell time is on the order of a few microseconds. During the dwell time, end  59  of optical fiber  54  rapidly undergoes two phase-changes before any sag occurs: solid to a viscous liquid and viscous liquid to a solid. This allows the end  59  of optical fiber  54  to reflow, thereby providing a smooth surface, while avoiding the effects of gravity when optical fiber  54  is placed in the molten state for too long a period of time. This results in a fire polish of end  59  with surface anomalies of 50 nm or less, while minimizing curvature. The depth of refractive action within optical fiber  54  itself due to the curvature itself is minimal at less than 1 μm, which is considered as a perpendicular cut and polish.  
      It should be understood, that the polishing step may be achieved by movement between optical fiber  54  and beam  152  along a direction parallel to the {overscore (y )} axis. In this manner, beam  12  is initially collinear with optical fiber  54 , but spaced-apart a sufficient distance to be thermally insulated from the optical fiber  54 . After, beam  152  and optical fiber  54  are positioned collinearly, rapid movement along the {overscore (y )} axis is facilitated to expose optical fiber  54  to the thermal energy of beam  152 , while minimizing dwell time for the reasons discussed above.  
      Referring to  FIG. 9  in another embodiment, a single step may be employed to segment optical fiber  54  and polish the resulting end  59  thereof. To that end, beam  252  includes a narrow waist  252   a  that is disposed proximate to optical fiber  54 . In this fashion, beam  252  functions as a thermal scalpel, with waist  252   a  having a greater energy per unit area than the remaining regions of beam  252 . This beam profile presents, to optical fiber  54 , a thermal wavefront having a high temperature gradient, which exacerbates control of sag. This thermal wavefront results in uneven heat propagation through optical fiber  54 . The uneven heat propagation produces a temperature gradient in optical fiber  54 , whereby one region of optical fiber  54   a  is heated to a greater temperature than an opposing region  54   b . As a result, for a brief period of time, the end of optical fiber  54  will concurrently have two phase-states present. Specifically, when beam  252  initially impinges upon optical fiber  54 , the region  54   a  becomes molten while the region  54   b  maintains a solid state. As heating continues, the end of optical fiber  54  proceeds to a homogenous phase state of a viscous liquid. However, due to the temperature gradient present in optical fiber  54 , a much greater amount of molten material is present in region  54   a  than is present in region  54   b . This temperature gradient present in optical fiber  54  frustrates control of the shaping of the end due to the presence of sag.  
      Referring to  FIGS. 9 and 10 , to reduce, if not eliminate, the temperature gradient between regions  54   a  and  54   b , platen  36  is selected to be thermally reflective. In this manner, thermal energy E 1  and E 2  propagates along a direction parallel to the {overscore (z )} axis to impinge upon optical fiber  54  from opposite directions. In one direction, thermal energy E 1  from beam  252  impinges upon region  54   a . A portion of-thermal energy E 1  is reflected from platen  36  in the form of reflected thermal energy E 2  to impinge upon region  54   b . To that end, a spacing, “s” between waist  252   a  and platen  36  is chosen to ensure that the flux of reflected energy E 2  impinging upon region  54   b  results in a temperature difference between regions  54   a  and  54   b , t, that is approximately zero. The exact spacing, s, is dependent upon the reflecting surface, the diameter of optical fiber  54  and the temperature gradient presented by beam  252 . As a result, waist  252   a  may be positioned above or below the cutting plane.  
      Referring to  FIG. 11 , in an alternative embodiment, a parabolic reflective surface  137  may be employed that may be formed integrally with platen  136 . Alternatively, an additional body (not shown) may be disposed between platen  136  and optical fiber  54  that is thermally reflective and defines a parabolic surface. Parabolic reflective surface  137  defines a focus  138  and optical fiber  54  would be positioned proximate to focus  138 . In this manner greater control of the flux of thermal energy E 2  that impinges upon optical fiber  54  may be obtained.  
      Referring to  FIG. 12 , optical fiber  354  that is to be segmented is typically mounted in a connector  302  that includes a ferrule  304  and has had the cladding (not shown) removed. Ferrule  304  may be made from any suitable material to dissipate thermal energy propagating along optical fiber  354 , such as ceramic and polymer. Optical fiber  354  is typically fixed to ferrule  304  using any suitable adhesive, such as epoxy. Section  306  of optical fiber  354  that is to be segmented extends from ferrule  304 , proximate to region  304   a  terminating in an end  308 . End  308  is mounted to a first mechanical support  310 , and connector  302  is mounted to a second mechanical support  312 . First  310  and second  312  mechanical supports rest against platen  336 , with section  306  being spaced-apart therefrom. Extending beneath section  306  is a thermally reflective body  314  that includes a recess defining a curved surface, the nadir of which is shown by dotted line  316 .  
      In this arrangement, typically a beam having a narrow waist  352   a  is employed, as discussed above, with waist  352   a  of beam  352  being focused proximate to optical fiber  354 , shown in  FIG. 12 . Considerations when segmenting optical fiber  354  concern providing a sufficient length, l, between region  358  to be vaporized by beam  352  and region  304   a . Specifically, the length, l, should be sufficient to ensure dissipation of thermal energy propagating through optical fiber  354  does not damage ferrule  304 . In addition, the length, l, should be sufficiently short to facilitate efficient coupling of the connector/fiber combination with another connector/fiber combination while providing a fiber-to-fiber interface.  
      Length, l, was found to be determined on numerous factors, such as the material from which optical fiber  354  was formed, the heat dissipation characteristics of ferrule  304  and the thermal flux transferred to optical fiber  354  from beam  352 . Specifically, it was found that by creating a flow of thermal energy between two spaced-apart regions, such as region  358  and region  304   a , the flux of which is substantially constant, abrupt changes in the index of refraction over the length, l, of optical fiber  354  may be reduced, if not avoided. The constant flux of thermal energy in the flow results in the formation of a graded index of refraction over length, l, between spaced apart regions  358  and  304   a , i.e., the index of refraction changes linearly over length, l. In addition to minimizing formation of abrupt changes in the index of refraction, a self-focusing lens formation is also reduced. Both of the aforementioned optical artifacts exacerbate insertion loss.  
      Referring to  FIG. 13 , formation of optical fiber  354  in accordance with one embodiment of the present invention provides optical fiber  354  having three regions  360   a ,  360   b  and  360   c  with differing indices of refraction. Assuming in the present example that optical fiber  354  is formed from glass, region  360   a  may have an index of refraction measuring approximately 1.502. At region  360   b , a lens is formed having a differing index of refraction, measuring approximately 1.550. To minimize reflection of optical energy propagating along region  360   a  into region  360   b , region  360   c  is formed to have a graded index of refraction that changes linearly between region  360   a  and  360   b . This is shown by the linear slope of region  380   a  of curve  380  of  FIG. 14 . The benefit of providing a linear change in the index of refraction in region  360   c  is that insertion loss of optical energy propagating from region  360   a  to region  360   b  is minimized.  
      The manner in which it was determined that a graded index of refraction was produced and, therefore, that the flux of thermal energy between spaced-apart regions  358  and  304   a  occurred, was by use of Optical Frequency Domain Reflectometry (OFDR). Specifically, an Optical Frequency Domain Reflectometer of the type available from the Group of Applied Physics University of Geneva, Geneva, Switzerland [hereinafter referred to as GAP-Optique] was employed to measure the optical power propagating along optical fiber  354 . Optical Frequency Domain Reflectometry measures back reflections from optical fibers and provides the advantages in that greater spatial resolution and sensitivity is provided than that provided by the standard Optical Time Domain Reflectometry (OTDR).  
      Referring to  FIG. 15 , OFDR, in accordance with the present invention, included the prototype Optical Frequency Domain Reflectometer available from GAP-Optique. The GAP-Optique Reflectometer system  400 , used in accordance with one embodiment of the present invention, includes a laser source  402 , a fast Fourier transform spectrum analyzer  404  having a photo detector  404   a  in data communication therewith, a local oscillator (LO)  406  all in optical communication with optical fiber  354  through an interferometer  408 . Laser source  402  produces optical energy that propagates through interferometer  408  to impinge upon both LO  406  and optical fiber  354 . LO  406  beats the optical energy impinging thereupon with a suitable frequency to produce a fixed Fresnel reflection. Back reflections from optical fiber  354  propagates through interferometer  408 , producing back reflections beat with the fixed Fresnel reflection that are sensed by detector  404   a . Laser source  402  is swept to produce a light over a range of optical frequencies so that reflections from points at different distances along optical fiber  354  correspond to different beat frequencies on detector  404   a . Detector  404   a  produces signals in response to the optical frequency sense that are Fourier transformed, and analyzed in the frequency domain by spectrum analyzer  404 . As a result, each frequency corresponds to a particular distance in optical fiber  354 .  
      Referring to  FIGS. 13, 15  and  16 , using system  400 , the reflection characteristics of optical fiber  354  are measured to ensure that a graded index is provided in region  360   c , shown by curve  420 . Curve  420  shows the reflection of optical energy along a length of a fiber not formed in accordance with the present invention. Curve  420  includes two peaks  422  and  424 . Peak  424  corresponds to lens-air interface where the index of refraction undergoes an abrupt change. Peak  422  corresponds to lens-fiber interface, located proximate to region  360   c , which is an undesirable characteristic that the present invention overcomes. This is shown with respect to  FIG. 17  in which curve  520  includes only one peak  524 .  
      Referring to  FIGS. 15 and 17 , curve  520  corresponds to the reflection loss of a fiber formed in accordance with the present invention. Peak  524  corresponds to the lens-air interface. Region  522  corresponds to the fiber-lens interface. As seen, the reflectivity in region  522 , compared to the reflectivity of regions adjacent thereto, does not demonstrate an abrupt change. Rather, the reflectivity in this region of optical fiber  354  does not show a substantial loss in signal strength due to reflectivity. This corresponds to the presence of a graded index of refraction in this region of fiber, thereby result in deminimus insertion loss of optical energy propagating from the fiber and into the lens.  
      Referring to  FIGS. 12 and 18 , to avoid formation of these optical artifacts, a method for thermally shaping optical fiber  354  includes, at step  600 , exposing a first region, such as region  358 , of the optical fiber  352  to thermal energy, such as beam  352 . A portion of the thermal energy in beam  354  propagates along a longitudinal axis  354   a  of optical fiber  354 , defining transferred energy. At step  602 , the transferred energy is dissipated at a second region of optical fiber  354 , such as region  304   a , which is spaced-apart from region  358 . Thermal energy passing between regions  358  and  304   a  form a flow. At step  604 , thermal transfer between regions  358  and  304   a  is maintained to be a constant flux of thermal energy. To that end, beam  352  is established to have a constant thermal profile while impinging upon optical fiber  354 , i.e., the variances in thermal energy provided by beam  352  is minimized. Additionally, dissipation of optical energy at region  304   a  occurs in two orthogonal directions, parallel to longitudinal axis  354   a  and radially away therefrom in direction  354   b . In the present embodiment, the transferred thermal energy is removed from optical fiber  354  at region  304   a  radially symmetrically about the longitudinal axis  354   a , as well as longitudinally. The advantage of removing thermal energy from optical fiber  354  in this fashion is manifold. Firstly, it provides the graded index of refraction, as mentioned above. This is useful when lensing an end of optical fiber  354 , proximate to region  358  as discussed above. The index of refraction may be adjusted so that it varies, linearly over length, l, merely 4%, with the aforementioned lens having a maximum value of the index of refraction and the optical fiber  354  located proximate to region  304   a  having a minimum value. In one example, optical fiber  354  was manufactured from glass and had an index of refraction of approximately 1.502 at region  304   a . At region  358  optical fiber  354  has an index of refraction of approximately 1.550. A second benefit of removing thermal energy from optical fiber  354  in two differing orthogonal directions is that it affords removing thermal energy at a sufficient rate to reduce, if not prevent, formation of a self-focusing lens in optical fiber  354 . As a result, the insertion loss of optical fiber  354  is substantially reduced.  
      It is seen that shaping of optical fibers in accordance with the present invention, facilitates concurrently segmenting, polishing and lensing of the optical fiber while avoiding unwanted optical artifacts. Thus, the optical fibers may be quickly and easily shaped to minimize insertion loss.  
      Moreover, there are other arrangements that may be employed that would fall within the scope of the present invention. As stated above, virtually any type of thermal beam source may be employed, e.g., an Ultra Violet laser such as an Excimer may be employed. Therefore, the scope of the invention should not be based upon the foregoing description. Rather, the scope of the invention should be determined based upon the claims recited herein, including the full scope of equivalents thereof.