Abstract:
A method for polishing a ferrule structure having first and second end faces is disclosed herein. The method includes positioning the ferrule structure within a housing such that the first end face is located outside the housing. The method also includes polishing the first end face while the ferrule structure is positioned within the housing and the first end face is located outside the housing. The method further includes reversing the ferrule structure within the housing such that the second end face is located outside the housing, and polishing the second end face while the ferrule structure is positioned within the housing and the second end face is located outside the housing.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to methods for manufacturing and polishing fiber optic components. More particularly, the present invention relates to methods for polishing fiber optic attenuator ferrules.  
         BACKGROUND OF THE INVENTION  
         [0002]    Fiber optic attenuators are optical components that induce a calibrated loss between two connectors to dampen (i.e., attenuate) an optical signal. Attenuation is desirable if the optical signal has a power level that exceeds the operating range of the equipment to which the signal is being transferred. Excessive signal power can cause saturation at the receiver and induce system errors and failures. Attenuation is typically achieved by passing the signal through an absorption filter or an air gap. Conventional fiber optic attenuators are available in bulkhead, in-line and build-out configurations.  
           [0003]    [0003]FIGS. 1 and 2 illustrate a prior art in-line attenuator  20 . The attenuator  20  includes a ferrule assembly  22  mounted within a housing  24 . The ferrule assembly  22  includes a ferrule structure  26  having a first end face  28  accessible from a first end  29  of the housing  24 , and a second end face  30  accessible from a second end  31  of the housing  24 . The ferrule assembly  22  also includes a hub  32  located at a mid-region of the ferrule structure  26 . The hub  32  nests within a hub receiver  33  defined by the housing  24 . An attenuating structure (e.g., an absorption filter or air gap) is located within the ferrule structure  26 .  
           [0004]    [0004]FIG. 3 shows the attenuator  20  providing an optical coupling between first and second fiber optic connectors  40  and  50 . In FIG. 3, a cover  61  (shown in FIG. 1) at the first end  29  of the housing  24  has been pivoted open to expose the first end face  28 . The first connector  40  is inserted over the first end  29  of the housing  24 , and the second connector  50  is inserted within the second end  31  of the housing  24 . The first connector  40  includes a ferrule  42  having an end face  43  that abuts against the end face  28  of the ferrule structure  26  when the connector  40  is coupled to the attenuator housing  24 . The second connector  50  includes a ferrule  52  having an end face  53  that abuts against the end face  30  of the ferrule structure  26  when the connector  50  is coupled to the attenuator housing  24 . In use, optical signals are transferred between the connectors  40 ,  50  by passing through the ferrule assembly  22 . As the signals pass through the ferrule assembly  22 , the desired attenuation is provided.  
           [0005]    To improve performance parameters such as insertion loss and return loss, it is desirable to polish the end faces  28 ,  30  of the ferrule structure  26 . It is preferred for the end faces  28 ,  30  to be polished at a slight angle (e.g., about 8 degrees relative to a plane perpendicular to a longitudinal axis of the ferrule). To ensure acceptable performance levels, it is preferred for the angled end faces  28 ,  30  of the ferrule/hub assembly  22  to abut angled end faces  43 ,  53  of the connector ferrules  42 ,  52  in a generally parallel relationship as shown in FIG. 3. Slight deviations in the relative orientations of the end faces can result in air gaps between the end faces  28 ,  43  and  30 ,  53  (see FIG. 4 where misalignment is shown between the end faces  28  and  43 ). This type of misalignment can be detrimental to the optical performance of the coupling.  
           [0006]    In the prior art, the end faces  28  and  30  of the ferrule structure  26  are typically polished prior to mounting the ferrule assembly  22  in the housing  24 . One reason for this practice is because the end face  30  of the ferrule structure  26  is not accessible for polishing once the ferrule structure  26  has been mounted within the attenuator housing  24 . However, it has been determined that when the ferrule assembly  22  is mounted within the housing  24  after the end faces  28 ,  30  have already been polished, part tolerances mismatches can cause the end faces  28 ,  30  to be slightly rotationally offset from their intended rotational orientations. With the end faces  28 ,  30  rotationally offset from their intended orientations, the end faces  28 ,  30  may not make parallel contact with the connector end faces  43 ,  53  when the connectors  40 ,  50  are coupled to the attenuator  20 . As indicated above, this type of misalignment can be detrimental to the optical performance of the coupling.  
         SUMMARY  
         [0007]    The present disclosure relates to methods for ensuring the proper rotational alignment of a ferrule within a housing. It will be appreciated that the specific method steps disclosed herein are examples of one way the broad concepts of the present invention may be put into practice, and that variations can be made with respect to the described method steps without departing from the broad scope of the inventive concept. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various method steps that are examples of how certain inventions can be put into practice. A brief description of the drawings is as follows:  
         [0009]    [0009]FIG. 1 schematically depicts a prior art in-line attenuator;  
         [0010]    [0010]FIG. 2 is a cross-sectional view taken along section line  2 - 2  of FIG. 1;  
         [0011]    [0011]FIG. 3 shows the ferrule of the attenuator of FIG. 1 coupled to connectors which are schematically depicted;  
         [0012]    [0012]FIG. 4 illustrates an interface mismatch between the end faces of two ferrules;  
         [0013]    [0013]FIG. 5 is an exploded view showing a split sleeve positioned between a fiber optic connecter and a ferrule assembly;  
         [0014]    [0014]FIG. 6 shows the connector and ferrule assembly of FIG. 5 coupled together by the split sleeve;  
         [0015]    [0015]FIG. 7 shows the coupled connector and ferrule assembly of FIG. 6 positioned in alignment with an in-line attenuator housing;  
         [0016]    [0016]FIG. 8 shows the coupled connector and ferrule assembly of FIG. 7 inserted within the attenuator housing;  
         [0017]    [0017]FIG. 9 is a cross-sectional view taken along section line  9 - 9  of FIG. 8;  
         [0018]    [0018]FIG. 9A is a detail view of a portion of FIG. 9;  
         [0019]    [0019]FIG. 10 is a cross-sectional view taken along section line  10 - 10  of FIG. 9;  
         [0020]    [0020]FIG. 10A is a detail view of a portion of FIG. 10;  
         [0021]    [0021]FIG. 11 shows the assembly of FIG. 8 prior to insertion in a polishing fixture;  
         [0022]    [0022]FIG. 12 is a cross-sectional view taken along section line  12 - 12  of FIG. 11;  
         [0023]    [0023]FIG. 13 shows the assembly of FIGS. 8 and 11 after insertion in the polishing fixture;  
         [0024]    [0024]FIG. 14 shows a ferrule end of the assembly of FIG. 8 after polishing;  
         [0025]    [0025]FIG. 15 is an end view of the ferrule end of FIG. 14;  
         [0026]    [0026]FIG. 16 shows the in-line attenuator after final assembly;  
         [0027]    [0027]FIG. 17 is a left end view of the in-line attenuator of FIG. 16 with the end cap removed such that the ferrule end face is visible; and  
         [0028]    [0028]FIG. 18 is a right end view of the in-line attenuator of FIG. 16. 
     
    
     DETAILED DESCRIPTION  
       [0029]    The present disclosure is directed toward methods for ensuring the proper rotational alignment of a ferrule within a housing. The methods disclosed herein are directed specifically toward an in-line attenuator having a ferrule structure with two end faces, only one of which is typically accessible for polishing while the ferrule structure is mounted within the attenuator housing. However, it will be appreciated that the broad inventive concepts of the present disclosure are not limited only to attenuators, but instead are applicable to any type of fiber optic device where it is desirable to mount a ferrule at a particular rotational alignment with respect to a housing. As used herein the term “ferrule structure” means a structure including one or more ferrules.  
         [0030]    [0030]FIG. 5 shows an attenuator ferrule assembly  120  desired to be polished. The assembly  120  includes a ferrule structure  122  and a hub  124 . The hub  124  is mounted at a mid-region of the ferrule structure  122 . The ferrule structure  122  includes first and second end portions  126  and  128 . As shown in FIG. 9, an attenuation structure  130  is located within the hub  124  between the first and second end portions  126 ,  128  of the ferrule structure  122 . The first end portion  126  of the ferrule structure  122  includes an end face  126   a  and the second end portion  128  of the ferrule structure  122  includes an end face  128   a.    
         [0031]    Referring again to FIG. 5, the ferrule assembly  120  is shown in coaxial alignment with a split sleeve  140  and a connector  150 . The connector  150  includes a housing  151  having rotational alignment key  152  and a resilient latch  153 . The connector  150  also includes a ferrule  155  that projects outwardly from the housing  151 .  
         [0032]    The split sleeve  140  is preferably made of a resilient material such as zirconia or phosphorous bronze that allows the split sleeve  140  to be elastically flexed from a reduced diameter configuration to an enlarged diameter configuration. The resilient nature of the split sleeve  140  allows a first end  142  to be pressed over the ferrule  155  of the connector  150  as shown in FIG. 6. Similarly, a second end  144  of the split sleeve  140  can be inserted over the first end portion  126  of the ferrule structure  122 . The split sleeve  140  functions to mechanically couple the ferrule assembly  120  to the connector  150 , and also functions to hold the ferrule structure  122  in coaxial alignment with the ferrule  155  of the connector  150 .  
         [0033]    After the ferrule assembly  120  has been secured to the connector  150  by the split sleeve  140 , the connector  150 , the split sleeve  140  and the ferrule assembly  120  are all inserted into a first end  162  of an attenuator housing  160  (see FIGS. 7 and 8). The attenuator housing  160  includes a keyway  163  that receives the key  152  of the connector  150 , and shoulders  165  that interlock with the resilient latch  153  to provide a snap fit connection for holding the connector  150  within the attenuator housing  160 . Preferably, the assembly is pushed into the attenuator housing  160  until the latch  153  snaps into a locked position as shown in FIG. 8. With the connector  150  locked in place, the second end portion  128  of the ferrule structure  122  projects outwardly from a second end  164  of the attenuator housing  160  (see FIG. 8).  
         [0034]    Referring to FIG. 9, the hub  124  of the ferrule assembly  120  preferably nests within the attenuator housing  160  such that the ferrule assembly  120  is positioned at a particular rotational orientation relative to a rotational alignment key  123  (shown in FIGS. 7 and 8) of the attenuator housing  160 . For example, as shown in FIGS. 10 and 10A, the hub  124  has a generally “plus” or “cross” shaped transverse cross-section that preferably fits within a complementary opening  127  defined within the attenuator housing  160 . Additionally, as shown in FIG. 9A, the hub  124  has an end face including angled or ramped surfaces  170  that engage corresponding ramp surfaces  172  defined within the attenuator housing  160 . Contact between the surfaces  170  and  172  prevents relative rotation between the ferrule assembly  120  and the attenuator housing  160 , and also ensures that the ferrule assembly  120  is aligned at a particular rotational alignment relative to the attenuator housing  160 . The ramped surfaces  170  are biased against the ramped surfaces  172  by a spring load provided by spring  158  of the connector  150 . The spring load provided the spring  158  ensures that the angled surfaces  170  seat firmly against the angled surfaces  172  of the attenuator housing  160 .  
         [0035]    The matching “plus” shape of the hub  124  and the opening  127  of the attenuator housing  160  ensures that the ferrule/hub assembly  120  is inserted at approximately the proper rotational alignment relative to the attenuator housing  160 . The exact rotational alignment between the ferrule/hub assembly  120  and the housing  160  is provided by contact between the ramped surfaces  170  and  172 . While one particular configuration for ensuring rotational alignment between the ferrule/hub assembly  120  and the attenuator housing  160  has been shown, it will be appreciated that any number of different types of configurations could be used, and that the broad inventive concepts of the present disclosure are not limited to the particular alignment configuration depicted herein.  
         [0036]    After the connector  150  has been secured within the attenuator housing  160  as shown in FIGS. 8 and 9, the attenuator housing  160  is mounted within a polishing fixture  180  (see FIG. 11). Alternatively, the attenuator housing  160  can be mounted in the fixture  180  prior at receiving the connector  150 . The polishing fixture  180  defines an opening  182  having a shape that complements an outer shape of the second end  164  of the attenuator housing  160 . For example, the opening  182  includes a keyway  184  that receives the rotational alignment key  123  of the attenuator housing  160 . The keyway  184  ensures that the attenuator housing  160  is inserted into the opening  182  in a predetermined rotational orientation.  
         [0037]    In FIGS. 11 and 12, the opening  182  of the fixture  180  is shown bisected by a first reference plane  190 . As best shown in FIG. 12, the opening  182  is skewed within the fixture  180  such that the first reference plane  190  is aligned at an angle θ relative to a second reference plane  192 . The second reference plane  192  is perpendicular to a bottom surface  194  of the polishing fixture  180 . In a preferred embodiment, the angle θ is 8 degrees. In alternative embodiments, other angles such as 9 degrees, 10 degrees or other angles could also be used.  
         [0038]    [0038]FIG. 13 shows the attenuator housing  160  fully inserted in the polishing fixture  180 . As so mounted, the skew of the opening  182  causes the attenuator housing  160  and its corresponding ferrule structure  122  to be skewed at the angle θ relative to the second reference plane  192 . A tip of the ferrule end  128  preferably projects beyond the bottom surface  194  of the polishing fixture. The polishing fixture  180  can also include a clamping mechanism for clamping the ferrule end  128  within the fixture  180  after the attenuator housing  160  has been inserted within the opening  182 .  
         [0039]    After the attenuator housing  160  has been mounted in the fixture  180 , the end face  128  of the ferrule structure  122  is polished. For example, the fixture  180  can be lowered toward a rotating or oscillating polishing mechanism  200 . The polishing mechanism can include a polishing film such as aluminum oxide, silicon carbide, diamond polishing film, etc. Additionally, cushioning pads can be positioned between the polishing film and the drive mechanism. In other embodiments, the fixture  180  can be moved while the polishing film remains stationary. It will be appreciated that any number of conventional polishing techniques can be used for polishing the tip of the ferrule structure  122 .  
         [0040]    Once the polishing process has been completed, the end face  128   a  of the ferrule structure  122  is preferably aligned parallel with the bottom surface  194  of the fixture and thus perpendicular with respect to the second reference plane  192 . In some embodiments, the end face  128   a  is flush with the bottom surface  194 . Referring to FIG. 14, the end face  128   a  is aligned at the angle θ relative to a plane  197  oriented perpendicular to a central axis  198  of the ferrule structure  122 . Because the end face  128   a  is polished at an angle, the end face  128   a  has an elliptical configuration after polishing as shown in FIG. 15. Referring to FIGS. 14 and 15, the elliptical configuration of the end face  128   a  defines a major axis  202 , and outermost and innermost apexes  230 ,  232 .  
         [0041]    In the depicted embodiment, the fixture  180  was shown including only one opening  182 . It will be appreciated that in a preferred embodiment, the fixture includes multiple openings for allowing a plurality of ferrules to be polished simultaneously.  
         [0042]    After the end face  128   a  of the ferrule structure  122  has been polished, the attenuator housing  160  can be removed from the opening  180  in the fixture, and the connector  150  can be disconnected from the attenuator housing  160 . Thereafter, the first end portion  126  of the ferrule structure  122  is pulled from the split sleeve  140  and the ferrule assembly  120  is reversed. To reverse the ferrule assembly  120 , the assembly  120  is rotated  180  degrees and the previously polished end portion  128  of the ferrule structure  122  is inserted into the split sleeve  140  mounted on the connector  150 . The connector is then inserted into and locked within the first end  162  of the attenuator housing  160 . As so positioned, the first end portion  126  of the ferrule structure  122  projects beyond the second end  164  of the attenuator housing  160 . Subsequently, the attenuator housing  160  can be reinserted into the polishing fixture  180 , and the end face  126   a  of the ferrule structure  122  can be polished in the same manner previously described with respect to the end face  128   a . The end of the hub  124  positioned adjacent to the first end portion  126  has the same ramped surfaces  170  provided at the opposite end of the hub  124 . Thus, the end of the hub adjacent the first end portion  126  of the ferrule structure  122  nests within the attenuator housing  160  in the same manner previously described with respect to the opposite end of the hub.  
         [0043]    Once the end face  126   a  of the ferrule structure  122  has been polished, the housing  160  is again removed from the polishing fixture  180 , and the connector  150  is removed from the first end  162  of the attenuator housing  160 . The ferrule assembly  120  can then be final mounted within the housing  160 . When the ferrule assembly  120  is final mounted within the housing  160 , the ferrule assembly is not readily removable from the housing, and the assembly is essentially ready for use/sale as an in-line attenuator. FIG. 16 shows one example of how the ferrule assembly  120  can be final mounted within the housing  160 . It will be appreciated that the configuration for holding the ferrule assembly within the housing is the same as the one depicted in the prior art arrangement of FIG. 2. As shown in FIG. 16, a retaining assembly  210  is mounted (e.g., by means such as a threaded, press fit or adhesive connection) at the second end  164  of the attenuator housing  160  to capture the ferrule assembly  120  within the housing  160 . The retaining assembly  210  includes a spring  212  that biases the ferrule assembly against the ramp surfaces  170  of the housing  160 . A pivoting cover  220  can also be mounted at the first end  162  of the housing  160 .  
         [0044]    When the ferrule assembly  120  is mounted within the housing  160 , rotational alignment of the angled end faces  126   a ,  128   a  and the keying structures of the attenuator housing  160  are ensured because both of the end faces  126   a ,  128   a  were polished while the ferrule assembly  120  was mounted within the housing  160 . For example, the alignment of the attenuator housing  160  within the polishing fixture  180  ensures that major axes  201 ,  202  (shown in FIGS. 17 and 18) of the elliptical end faces  126   a ,  128   a  are aligned perpendicular relative to a reference plane  204  that bisects the alignment key  123  and the alignment keyway  163  of the attenuator housing  160 . In the depicted embodiment, outermost apexes  229 ,  230  of the end faces  126   a ,  128   a  are aligned at a 3 o&#39;clock position relative to the key  123  and keyway  163 , respectively. Thus, the end faces  126   a ,  128   a  are adapted to make gap-free connections with connector ferrules that are similarly oriented in the 3 o&#39;clock position. It will be appreciated that the orientation of the angled end faces can be varied to correspond to connectors having angled end faces oriented in different rotational positions.  
         [0045]    It is preferred for the attenuator housing  160  used during the polishing process to be the actual attenuator housing in which the ferrule/hub assembly  120  is ultimately mounted to manufacture a finalized in-line attenuator. However, in certain embodiments, a housing that replicates the actual end use housing may be used.  
         [0046]    The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.