Abstract:
A ferrule for connecting a optical fiber to a mating optical fiber or an item of network gear includes a guide hole having a consistent first dimension in a first region and a larger dimension in a second region. A guide or alignment pin inserted through the guide hole forms a locational or sliding fit with the guide hole in the first region and a loose fit in the second region, allowing the ferrule to rock through the angle formed by the dimension of the second region. Rocking the ferrule through this angle closes the lossy air gap formed by end-face tilt resulting from imperfect polishing of the face of the ferrule and decreases insertion loss.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention is generally directed to a multichannel ferrule for connecting optical fibers to a mating ferrule in which end tilt is corrected.  
       BACKGROUND OF THE INVENTION  
       [0002]     Optical fibers are used to transmit data by transmitting electromagnetic radiation. The optical fibers are generally made of a glass or plastic core and enclosed in a cladding with a lower refractive index. The optical fibers transmit light through their length by internal reflections. The transmitted light can be modulated to transmit a signal, either analog or digital. Optical fibers can therefore be used to carry audio signals or data signals within a network.  
         [0003]     Optical fibers are housed within a connector to mate one or more of the optical fibers to another optical fiber or set of optical fibers, or to a data-generating or data-using item of network gear. The connector may be formed of a ferrule which holds the optical fibers. The end face of the ferrule mates with the end face of a mating ferrule, to align each optical fiber with a corresponding optical fiber in the mating ferrule, to achieve transmission of signal through the optical fibers to the optical fibers of the mating ferrule.  
         [0004]     The termination must protect against light loss, which is caused by a number of factors. In general, the more perfect the alignment between two optical fibers, the less light loss occurs at the connection. Light loss can arise from an air gap between two mating optical fibers or from a lack of alignment between two mating optical fibers. (Light loss can also arise from dirt on the optical fiber ends or from a rough surface on the optical fiber ends. These problems are generally addressed by cleaning the optical fibers during installation and by polishing the optical fibers.)  
         [0005]     An air gap between two optical fibers causes Fresnel reflection, caused by the change in refractive index between the glass optical fiber and the air. The light reflected in this manner is lost in transmission. Improper alignment causes directional loss, when light propagating out of one optical fiber does not all enter the mating optical fiber and therefore does not transmit further. It is desirable to minimize the amount of light lost in transmission, whether by Fresnel reflection or by directional loss. As devices use more and more data, at faster and faster rates, the need to minimize the amount of light lost at an optical fiber termination becomes even more important.  
         [0006]     An MT ferrule is a plastic member carrying multiple optical fibers, usually used for predetermined cable assemblies. The optical fibers are usually positioned in a plane. Two bores or guide holes in the ferrule are aligned parallel to the optical fibers and in the same plane. The bores or guide holes have a consistent dimension along the entire length thereof. Guide or alignment pins extend through the guide holes of the ferrule and into corresponding guide holes of the mating ferrule to keep the ferrule properly aligned. The guide or alignment pins are constructed to form an interference fit into the guide holes of the ferrule and to form an interference fit with the corresponding guide holes of the mating ferrule, to keep the ferrule securely linked to the mating ferrule and to keep each optical fiber aligned to its corresponding optical fiber in the mating ferrule. The secure link also protects against dirt, moisture, vibrations, shock, electromagnetic interference, and radio frequency interference.  
         [0007]     End-face tilt is the angle formed by the imperfect alignment of the facial plane of the ferrule with the facial plane of the mating ferrule. The facial plane of the MT ferrule, perpendicular to the plane in which the optical fibers are arranged, is polished to minimize end-face tilt (as well as to clean the optical fibers and to smooth the surface of the ends of the optical fibers). Polishing is a difficult operation and some end-face tilt will always result, as it is difficult to achieve a perfectly flat facial plane by polishing. End-face tilt is illustrated in  FIGS. 1   a  and  1   b , which show two MT ferrules  2  and  4  mated in, respectively, the x axis (width) and the y axis (depth). The end faces  6  and  8  of the two ferrules  2  and  4  do not align perfectly, leaving a gap  10  in the x axis and  12  in the y axis, between the two end faces  6  and  8 .  
         [0008]     Optical transmission of light through the optical fibers of the MT ferrule is optimized when the end-face tilt is less than 0.03 degrees. Commercial polishers, however, can only achieve end-face tilt of 0.2 degrees. This amount of end-face tilt has a tremendous impact on ferrule performance, as it causes significant insertion losses. An off-square facial plane of an MT ferrule creates an air gap between the mating optical fibers, which leads to Fresnel reflection as described above. This lossy gap between two facial planes, caused by end-face tilt, causes loss of light, and therefore loss of data, at the interface of the MT ferrule and the mating ferrule. Higher end-face tilt causes increasingly higher insertion losses.  
         [0009]     The guide or alignment pins must fit tightly in order to prevent offset of the lateral optical fiber-to-optical fiber alignment, and the tight fit of the guide or alignmentpins in the guide holes prohibits any rotation of the ferrule to accommodate end-face tilt.  
         [0010]     Accordingly, a need exists for a way to connect an MT ferrule to another ferrule that minimizes the air gap caused by end-face tilt, but preserves alignment of the optical fibers.  
       SUMMARY OF THE INVENTION  
       [0011]     A ferrule that compensates for end-face tilt by changing the geometry of the guide or alignment pins in the guide holes is provided. The ferrule of the preferred embodiment includes guide holes that are of consistent dimension in a first region proximal to the facial plane, and tapered radially outward in a second region distal to the first region. In another embodiment, the second region has a consistent, second dimension which is larger than the dimension of the first region. In the preferred embodiment, the first region is approximately one-fourth of the total length of the guide hole. The guide or alignment pins form sliding or locational fits with the guide holes in the first region, keeping the ferrule tightly connected to the mating ferrule and restricting lateral movement. The ferrule can rock rotationally in the second region and thereby decrease the lossy air gap formed by end-face tilt.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which:  
         [0013]      FIG. 1   a  is a plan view of two mated prior art MT ferrules, showing the gap resulting from end-face tilt in the x direction;  
         [0014]      FIG. 1   b  is a side view of two prior art mated MT ferrules, showing the gap resulting from end-face tilt in the y dimension;  
         [0015]      FIG. 2  is a perspective view of an MT ferrule which incorporates the features of the present invention with a cutaway illustrating a guide pin hole;  
         [0016]      FIG. 3   a  is a cross-sectional view of one embodiment of an MT ferrule of the present invention;  
         [0017]      FIG. 3   b  is a cross-sectional view of another embodiment of an MT ferrule of the present invention;  
         [0018]      FIG. 4   a  is a cross-sectional view of a ferrule and a guide or alignment pin of an MT ferrule of an embodiment of the present invention; and  
         [0019]      FIG. 4   b  is a cross-sectional view of the ferrule and a side view of one guide or alignment pin of an MT ferrule of an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, specific embodiments with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein.  
         [0021]      FIG. 2  shows an MT ferrule  22  of the preferred embodiment of the present invention. The ferrule  22  includes a body  24  which has a width x, a depth y, and a length z. The body  24  is preferably formed of plastic. The body  24  has a top  26  and a bottom  28 , both in the x-z plane, and two sides  30  and  32 , both in the y-z plane. The body has a distal end  34  and a proximal end  36 , both in the x-y plane. The proximal end  36  is formed of a planar end face  38 . The body  24  has a shoulder  25  extending outwards from the top  26 , bottom  28 , and sides  30  and  32 , at the distal end  34 .  
         [0022]     A plurality of spaced-apart passageways  52  extend through the body  24  from the distal end  34  to the proximal end  36  of body  24 . An optical fiber  50  is carried in each respective passageway  52  and terminates at the end face  38 . Preferably, twelve (12) optical fibers are provided. The optical fibers  50  are preferably glass or plastic used to transmit light. The body  24  is illustrated in  FIG. 2  with an aperture  40  to show the placement of the optical fibers  50  within passageway  52 . In use, the aperture  40  would be filled with epoxy or any adhesive.  
         [0023]     Two guide holes  60  and  62  extend through the body  24  from the distal end  34  to the proximal end  36  and are used to align the ferrule  22  with a mating ferrule. The passageways  52  extend between the guide holes  60  and  62 , and in the same plane as the guide holes  60  and  62 . Guide hole  62  is shown cut away in  FIGS. 2, 3   a , and  3   b  to reveal its internal geometry. The guide hole  62  has a longitudinal first region  64  with a first dimension  66 , consistent throughout the extent of the first region  64 . The first region  64  extends from the end face  38  into body  24 , where first region  64  meets with a longitudinal second region  68  which extends from first region  64 , through body  24 , to the distal end  34 . The dimension of the guide hole  62  in the second region  68  is greater than the first dimension  66 . In the preferred embodiment, the second region  68  gradually tapers radially outward from the first dimension  66  to the distal end of the body  24 . In the preferred embodiment, the first region  64  is approximately one-fourth of the total length of the guide hole  62 . The guide hole  62  is identical to the guide hole  60  in the preferred embodiment.  
         [0024]      FIGS. 4   a  and  4   b  show the MT ferrule  22  with a guide or alignment pin  80  inserted in guide hole  62 . In use, an identical guide or alignmentpin  80  is inserted in guide hole  60 . The guide or alignment pin  80  of the preferred embodiment, as depicted, is cylindrical and preferably includes a grooved rear portion  82  at a second end  84  for ease of holding the pin inside the connector, and a rounded point  86  at a first end  88  for ease of insertion into a guide hole  60  or  62 . The alignment pin  80  is constructed to extend into and form a sliding or locational fit in the guide holes  60  and  62 , as hereinafter described, and through the body  24  into a corresponding guide hole of a mating ferrule, where it forms a fit with the corresponding guide hole, to keep the MT ferrule  22  securely linked to the mating ferrule and to keep each optical fiber  50  aligned to its corresponding optical fiber in the mating ferrule.  
         [0025]     Also depicted in  FIGS. 4   a  and  4   b  is the angle β, caused by the imperfect polishing of the end face  38 . The dimension of and orientation of the angle β depends on the imperfection in the polishing of the end face  38 . In  FIG. 4   a , the angle α is formed around the z-axis thereby forming a conical surface. In  FIG. 4   b , the angle α is formed around the z-axis.  
         [0026]     The guide holes  60  and  62  of the preferred embodiment are circular in cross-section and the guide or alignment pin  80  of the preferred embodiment is a cylinder. In another embodiment, the guide holes  60  and  62  are passageways through body  24  and have circular cross-sections. However, the cross-sections of the guide holes  60  and  62  and the guide or alignment pin  80  could be square, oval, star-shaped, or any other shape that a skilled user chooses to achieve the same object of the invention.  
         [0027]     The outer dimension  90  of the guide or alignment pin  80  of the preferred embodiment is selected to form a sliding or locational fit with the first region  64  of the guide hole  62 .  
         [0028]     Because of the gradual taper in the preferred embodiment of guide hole  62  from the first dimension  66  to the second dimension  70  in the second region  68 , as depicted in  FIG. 3   a , an angle α is created between the guide or alignment pin  80  and the guide hole  62 . Preferably, the degree of taper in the second region is selected so that preferably the angle α equals or exceeds the angle β. It is to be noted that although not optimal, the angle β could also be greater than the angle α, and would still improve overall performance.  
         [0029]     In an alternative embodiment, as depicted in  FIG. 3   b , the second region  68  has second dimension  70  throughout the extent of its length from the first region  64  to the distal end  34 . In this embodiment, instead of a gradual taper, there is an abrupt transition from the first dimension  66  in the first region  64  to the second, larger dimension  70  in the second region  68 .  
         [0030]     Because the guide or alignment pin  80  is loose within the guide hole  62  during the three-quarters of its length because of the second region  68 , the ferrule  22  can rock through angle α in either of the illustrated embodiments. By pressing the ferrule  22  against the mating ferrule, the MT ferrule  22  can be rocked through the angle α, thereby closing the lossy air gap  10  or  12  or both between the end face  38  of the MT ferrule  22  and the mating ferrule. As a result, insertion loss is substantially decreased.  
         [0031]     Since the angle α can exist 360 degrees around the guide or alignment pin  80 , the ferrule  22  can be rocked along its conical axis to close the angle β wherever it exists. In  FIG. 4   a , line  92  illustrates how the guide or alignment pin  80  can rock through the angle α in either direction in the x-z plane. In  FIG. 4   b , line  94  illustrates how the guide or alignment pin  80  can rock through the angle a in either direction in the y-z plane. It should be noted that since the hole is conical, the pin  80  can rock in an an almost unlimited number of directions.  
         [0032]     Once the ferrule  22  has been rocked through the angle α to close the lossy air gap  10  or  12 , the connector spring keeps the ferrule  22  in that closed position. Additionally, the same fit prevents the end face  38  of the ferrule  22  from moving outside its tolerance, thereby preserving alignment of the optical fibers  50  with the mating optical fibers and preventing directional losses.  
         [0033]     It is to be understood that the above description applies to female ferrules as well. In particular, the female ferrule has the same geometry as the male ferrule (described above) but lacks the pins. As such, the rocking motion may happen in either of the ferrules.  
         [0034]     While a preferred embodiment of the present invention is shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.