Abstract:
An apparatus that enables the radiusing and beam profiling of an optical fiber tip protruding from a polishing fixture. When engaged with the polishing fixture, the apparatus positions the fiber tip in a high temperature plasma field generate by an electrode pair. The apparatus is provided with a window that permits the active viewing and monitoring of radiusing procedure. After the radiusing procedure, the same apparatus also permits the analysis of the beam pattern created when light is transmitted through the radiused fiber tip.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to a method and to devices enabling an optical fiber tip to be radiused with subsequent beam profiling, and more particularly to an apparatus that permits these two operations to be performed with a single integrated device that can be engaged with a polishing fixture.  
       BACKGROUND OF THE INVENTION  
       [0002]     Light energy emitted by opto-electrical devices such as lasers and light emitting diodes (LEDs) are often coupled into optical fibers. The optical output and input of other devices such as array wavelength gratings (AWGs), planar waveguides and wave division multiplexers (WDM) are also coupled with fibers. Accurate, sub-micron alignment is required to achieve maximum coupling efficiency.  
         [0003]     The emitted beam pattern of many optical devices is not circular. However the numerical aperture and acceptance angle of optical fibers are typically uniform, optimized to receive a circular beam. Therefore, discreet micro lens systems must be designed into opto-electronic packages to convert the beam pattern and assist with focusing into the fiber. These lens systems are difficult to align, add cost and increase packaging size.  
         [0004]     As an option to lens systems, the tip of a receiving or transmitting fiber can be shaped to create an integrated lens. Holding the bare fiber tip in a polishing fixture at a specific angle, and polishing it into shapes such as cones, chisels, wedges and combinations thereof accomplish this. Once shaped, the pointed fiber tip is then radiused to create a lens. This radiusing procedure is usually accomplished by introducing the fiber tip to a plasma field created by the arcing of a high voltage power source. The heat generated in the plasma field melts the fiber tip forming the lensing radius. Subsequent to creating the lensed tip, the fiber is then tested to analysis its beam pattern. Light is injected into the fiber, and its output pattern is then detected by a charge coupled device (CCD) camera. The video signal from the CCD is analyzed by beam profiling software that computes information such as the aspect ratio of the pattern, numerical aperture and mode field diameter (MFD) of the fiber. If this data corresponds with the output of the opto-electronic device, maximum coupling efficiency can be insured.  
         [0005]     Prior art has demonstrated that machines have been developed to polish bare fibers into shapes such as cones, chisels and wedges. Standard telecommunication fusion splicers are often used to radius fiber tips with their arcing action. CCD cameras, video capture boards and beam profiling software are commercially available for the analysis of lensed fiber light output. While each of these processing systems is capable of performing their own specific task, they are separate and independent equipment.  
         [0006]     The requirement to carry a fiber to and fro between processing equipment is a significant shortcoming in prior art. Fixturing, mounting and alignment of the fiber in each piece of processing equipment are time-consuming, labor intensive and cumbersome. The also exists a high probability of damage to the fragile fiber tip during transfer. Additionally, the fiber is susceptible to potential contamination by dust and debris.  
         [0007]     Prior art also has a significant shortcoming regarding final fiber qualification and rework. An unacceptable fiber is not determined until it has been transfer to the beam analysis step. At this point it must be returned to one of the previous polishing or fusion steps for corrective action. This rework process subjects the fiber to the shortcomings outlined in the preceding paragraph.  
         [0008]     An additional significant shortcoming of prior art is the cumbersome procedures required during the development of fiber radiusing processes. In order to monitor the effects of varying intensities and durations of plasma fields upon the shaped fiber tip, the fiber must constantly be moved back and forth between the fusion splicing station and the beam profiling system. Once again the shortcomings outlined in the previous paragraphs are encountered.  
       SUMMARY OF THE INVENTION  
       [0009]     Therefore, it is the objective of the invention to provide a means for radiusing a shaped fiber tip and analyzing its beam profile with a single probe device, while the fiber is loaded in its polishing fixture.  
         [0010]     An advantage of the present invention is to provide a single probe device that integrates a CCD camera with a fusion module. The fusion module is provided with two electrodes that are capable of being energized to create a plasma field.  
         [0011]     Still another advantage of the present invention is that it is fabricated into a probe that can interface with the polishing fixture of a fiber-shaping machine. This engagement positions the shaped fiber between the electrodes, and above the active surface of the CCD camera.  
         [0012]     A further advantage of the present invention is that it is formed with a viewing window through which the positioning of the shaped fiber in reference to the electrodes can be confirmed. Additionally, the effects of each iterative arc of plasma upon the shaped fiber tip can be monitored without removing the invention from the polishing fixture. The formed radius can therefore be measured with the invention positioned upon the polishing fixture.  
         [0013]     An additional advantage of the present invention is that it incorporates a shutter device that can cover the viewing window in order to prevent ambient light from striking the CCD during beam profiling.  
         [0014]     It is still another advantage of the present invention that the beam profile of the newly radiused fiber tip can be analyzed immediately after plasma arcing while the invention is still engaged with the polishing fixture.  
         [0015]     If it is determined that additional radiusing is required, the present invention provides the advantage of immediately inducing additional plasma arcing without removing the invention from the polishing fixture.  
         [0016]     Another advantage of the present invention is if beam profiling determines that the fiber has not been properly shaped, the invention can be removed from the polishing fixture, and the fiber is immediately ready to be re-polished without the need to re-fixture the fiber in the polishing mechanism.  
         [0017]     Other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     For a more complete understanding of this invention, reference should now be had to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention.  
         [0019]      FIG. 1  is an isometric view of the fusion module from the bottom surface.  
         [0020]      FIG. 2  is an isometric view of the fusion module from the top surface.  
         [0021]      FIG. 3  is an isometric, exploded view of the invention illustrating the fusion module and the CCD camera.  
         [0022]      FIG. 4  is a side view of a polishing fixture with a fiber inserted.  
         [0023]      FIG. 5  is the polishing fixture of  FIG. 4  rotated 90 degrees.  
         [0024]      FIG. 6  is a cross sectional view of the invention with a polishing fixture and fiber inserted.  
         [0025]     FIG  7  is a cross sectional view of the invention with a polishing fixture and fiber inserted, rotated 90 degrees. Also illustrated is a microscope positioned to focus inside the viewing window.  
         [0026]      FIG. 8  is a detailed view of a shaped fiber, located between two electrodes, being illuminated by a light source and emitting light upon a CCD camera&#39;s active area.  
         [0027]      FIG. 9  illustrates the light pattern profile projected upon the CCD active area resulting from the configuration of  FIG. 8 .  
         [0028]      FIG. 10  illustrates the plasma field generated between the two electrodes.  
         [0029]      FIG. 1I  illustrates the radiusing effect of the plasma field of  FIG. 10 .  
         [0030]      FIG. 12  is a detailed view of a shaped and radiused fiber, located between two electrodes, being illuminated by a light source and emitting light upon a CCD camera active area.  
         [0031]      FIG. 13  illustrates the light pattern profile projected upon the CCD active area resulting from the configuration of  FIG. 12   
     
    
       [0032]     While the invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the following description.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0033]     Referring to  FIG. 1  and  FIG. 2 , apparatus  1  is provided with a fusion module  20 . A cavity  22  has been formed, opening from the bottom surface of fusion module  20 . The front surface of fusion module  20  is provided with a viewing window  24  that opens into cavity  22 . Suitable materials for fusion module  20  are non-conductive dielectrics such Delrin® and Torlon®. Delrin is preferred.  
         [0034]     Electrodes  26  and  28  are mounted and axially aligned by through holes  30  and  32 . Electrodes  26  and  28  are positioned within cavity  22  and secured by set screws  34  and  36 , respectively. Electrodes  26  and  28  are formed with tips  38  and  40 , respectively. The axial gapping of tips  38  and  40  are controlled by set screws  34  and  36 , respectively. Suitable materials for electrodes  26  and  28  are conductive substances. Tungsten is preferred.  
         [0035]     A bushing  42  is mounted through the top surface of fusion module  20 . The center of bushing  42  opens into cavity  22 . The centerline of bushing  42  is positioned in the same plane created by the axis of electrodes  26  and  28 . Suitable materials for bushing  42  are steel, zirconia, alumina and ceramics. The inside diameter of bushing  42  is large enough to accept the insertion of an industry standard optical ferrule and commercially available bare fiber polishing fixture.  
         [0036]     A shutter means  44  is secured to the top surface of fusion module  20 . Suitable shutter means  44  include conventional piano hinges. Shutter means  44  can be secured to fusion module  20  by either set screws or adhesives. Shutter means  44  has sufficient surface area, and is positioned upon fusion module  20 , such that when closed, shutter means  44  covers and optically seals viewing window  24 .  
         [0037]     Referring next to  FIG. 3 , fusion module  20  is provided with through holes  56 ,  58 ,  60  and  62 . A charge coupled device (CCD) camera  46  is provided with threaded holes  64 ,  66 ,  68  and  70 . Fusion module  20  is preferably attached to camera  46  by inserting mounting screws  48 ,  50 ,  52  and  54  into through holes  56 ,  58 ,  60  and  62  and engaging with threaded holes  64 ,  66 ,  68  and  70 .  
         [0038]     Camera  46  is provided with a CCD active area  72 . Upon attachment of fusion module  20  with camera  46 , the center of active area  72  is aligned with the centerline of bushing  42 . Camera  46  has an output video signal lead  74  and power lead  76 . Output video signal lead  74  interfaces with a PC video capture board (not shown). Power lead  76  is energized by conventional power supplies (not shown).  
         [0039]     The operation of apparatus  1  will now be described. Referring to  FIG. 4  and  FIG. 5 , a polishing fixture  86  is presented. Polishing fixture  86  is a mechanism for holding an optical fiber  84  during polishing and shaping processes. Suitable polishing fixtures include those used with the FiberSmith™ Bare Fiber Processing System (Model FS200) manufactured by Krell Technologies Inc. (Morganville, N.J.) and referred to as ferrule assemblies. Polishing fixture  86  is comprised of an optical ferrule  78  mounted in a stem fixture  80 . Ferrule  78  is press fit into stem fixture  80 . The outer diameter of ferrule  78  permits a slip fitting into bushing  42 .  
         [0040]     An optical fiber  84  has been shaped. Shapes include chiseled, conical, wedge, cleaved and angled. A chiseled shape is illustrated in  FIG. 4  and  FIG. 5 . Optical fiber  84  is located within, and protruding from ferrule  78 .  
         [0041]     Referring now to  FIG. 6  and  FIG. 7 , apparatus  1  is positioned upon polishing fixture  86  by means of inserting ferrule  78  into bushing  42 . Upon contact between bushing  42  and stem fixture  80 , the shaped tip of optical fiber  84  is positioned approximately between electrode tips  38  and  40 . With shutter  44  in its open position, a microscope  88  is used to monitor the position of optical fiber  84  relative to electrode tips  38  and  40  through viewing window  24 . The shaped tip of optical fiber  84  is positioned in line with electrode tips  38  and  40  by moving optical fiber  84  within polishing fixture  86 .  
         [0042]     After alignment of the shaped tip of optical fiber  84  with electrode tips  38  and  40 , shutter  44  is closed over window  24 . Shutter  44  optically seals cavity  22  and prevents ambient light from striking CCD active area  72 .  
         [0043]     Referring to  FIG. 8 , light is injected into the far, un-shaped end of optical fiber  84 . As the light exits the shaped tip of optical fiber  84 , it strikes CCD active area  72  and energizes its surface.  
         [0044]     Referring to  FIG. 9 , the projected light from optical fiber  84  creates a beam pattern  90  upon CCD active area  72 . The characteristics of projected beam pattern  90  are determined by the geometry of the shaped fiber tip of optical fiber  84 . Beam pattern  90  is converted into a video signal by camera  46  that is transmitted to a video capture board for analysis by commercially available beam profiling software. Suitable beam profiling software include the LBA300PC Laser Beam Analyzer manufactured by Spiricon Inc. (Logan, Utah). Analysis of the beam profile can be use to qualify the geometry of the tip of optical fiber  84  and determine if additional polishing processing is required. If it is determined that optical fiber  84  requires additional polishing and shaping, apparatus  1  can be disengaged from polishing fixture  86 .  
         [0045]     Referring to  FIG. 10 , voltage is applied to electrodes  26  and  28  by means of a conventional and commercially available power supply. Once a breakdown voltage is achieved, arcing will occur, creating a plasma field  92  between electrodes  26  and  28 . The shaped tip of optical fiber  84  is positioned within plasma field  92 .  
         [0046]     Referring to  FIG. 11 , the elevated temperature within plasma field  92  melts the shaped tip of optical fiber  84 , creating a radiused tip  94 . The resulting radiused tip  94  can be visually viewed with microscope  88  by opening shutter  44 .  
         [0047]     Referring now to  FIG. 12 , shutter  44  is once again closed to optically seal cavity  22  and prevent ambient light from striking CCD active area  72 . Light is injected into the far, un-shaped end of optical fiber  84 . As the light exits radiused tip  94 , it focuses upon CCD active area  72  and energizes its surface.  
         [0048]     Referring to  FIG. 13 , the projected light from optical fiber  84  creates a beam pattern  96  upon CCD active area  72 . The characteristics of projected beam pattern  96  are determined by the new geometry of radiused tip  94 . Beam pattern  96  is converted into a video signal by camera  46  that is transmitted to a video capture board for analysis by commercially available beam profiling software. Analysis of the beam profile can be use to qualify the fiber tip geometry and determine if additional processing is required. If additional radiusing is required, the tip of optical fiber  84  is correctly positioned for the generation of another plasma field  92 . If the tip of optical fiber  84  has been over-radiused, apparatus  1  can be disengaged from polishing fixture  86  for additional optical fiber  84  polishing and shaping.