Abstract:
Ferrule for an optical connector, an optical connector containing such a ferrule, and a method for assembling such a ferrule. The ferrule includes a base, at least one cover, at least one fiber section running through a channel between the base and the cover from a cable connection side to an opposite contact face exposing distal ends of the fiber sections. The fibers are adhered to the base and/or to the cover at a bonding section at a distance from the contact face.

Description:
RELATED APPLICATIONS 
     This application is the U.S. National Stage of and claims priority to and the benefit of International Patent Application Number PCT/IB2013/001132, entitled “FERRULE FOR AN OPTICAL CONNECTOR” filed on Apr. 23, 2013, which is herein incorporated by reference in its entirety. 
     FIELD OF INVENTION 
     The present invention relates a to a ferrule for an optical connector, to an optical connector containing such a ferrule, and to a method for assembling such a ferrule. 
     BACKGROUND 
     Optical connectors hold and present terminal ends of cabled optical fibers for optical communication with a complementary receiver connector. For effective fiber optic communication the optical connector should axially align the presented fiber ends with associated optical elements of the receiver connector to which the optical connector is mated. These associated optical receiver element can for example include further optical fibers, or lenses or similar components, such as lenses of a light guide for transferring optical signals to processing units, such as PIN photo diodes, VCEL&#39;s or similar opto-electric or optical components. 
     Optical connectors typically include a ferrule holding and presenting the optical fiber ends for optical contacting the fiber ends with the associated optical components of the receiver connector. Assembling a ferrule typically involves stripping the coating from the fiber ends, advancing the stripped fiber ends through respective openings in the ferrule until the distal fiber ends protrude beyond a contact face of the ferrule. The fibers are secured within the ferrule by gluing. The protruding distal fiber ends are then cleaved and polished to create coplanar convex contact faces. 
     Ferrules are typically bulky and expensive components. The required cleaving and polishing steps are time-consuming and laborious processes and must be performed accurately. Ferrules are generally sensitive for contamination, e.g., by moisture or dirt, and damaging of the optical fiber ends. 
     Therefore, a need exists for a compact and low cost ferrule for an optical cable connector enabling reliable optical communication with a complementary receiver connector. 
     SUMMARY OF THE DISCLOSURE 
     A ferrule is disclosed comprising a base, at least one cover and at least one row of fiber sections extending through channels between the base and the cover from a cable connection side to an opposite contact face exposing distal ends of the fiber sections. The fiber sections are adhered to the base and/or to the cover over a bonding section at a distance from the contact face. This way, no glue or adhesive is present near the distal contact ends of the fibers. The fibers can be cleaved after adhering them to the respective part of the ferrule and no additional polishing is needed. 
     In a specific embodiment, a glue barrier separates the bonding section from an adhesive-free section at the contact face. The glue barrier may for instance include a slot extending parallel to the contact face. 
     Grooves guiding the fibers ends may be present between the contact face and the glue barrier slot. The grooves may form a tight fit with the fiber ends, while the space between the cover and the base part may provide a clearance fit between the glue barrier slot and the bonding section. 
     For accurately positioning the fibers the bonding section may be provided with a series of parallel grooves individually receiving a respective fiber. 
     The glue barrier slot and/or the fiber receiving grooves can for example be positioned in a surface of the cover facing the base part. 
     The fiber sections are stripped at the adhesive-free section but may for instance remain non-stripped and still coated at the bonding section. 
     In a specific embodiment, the ferrule may comprise two covers and two rows of fibers ends sandwiched between the base part and a respective cover. This allows a symmetrical built-up of the ferrule. The two covers can be identical and be made with the same moulds. 
     The ferrule may for example comprise alignment pegs and complementary openings for aligning the one or more covers relative to the base part. 
     The covers of the ferrule can be recessed relative to the base part at the contact face. This way, a ferrule is obtained holding at least one row of fiber sections extending from a cable connection side to a contact face with at least one recessed section exposing sunk distal ends of the fiber sections. Since the fiber ends are in a recessed part of the contact face, they do not physically contact the signal receiving components of the complementary connector. The optical signals are transferred via an air gap of an accurately dimensioned width. In this configuration the fiber ends do not need to be polished. Moreover, positioning the distal fiber ends in a recessed part of the contact face protects the cleaved fiber ends against mechanical damage. 
     In a further aspect, a method is disclosed for assembling the disclosed ferrule. In a first step, the fibers ends of an optical cable are arranged in a line and distal ends of the fiber ends are stripped, while the rest of the fibers remains coated. The coated sections are glued onto a bonding section of a cover. The stripped sections are arranged at an adhesive free section of the cover and cleaved to become coplanar with the contact face of the cover. The fiber ends are then sandwiched between the cover and the base part. 
     Optionally, the fiber ends are first arranged in a line by a gauge having alignment grooves for positioning the fiber ends. The gauge may be removed after curing of the glue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the connector will be further explained under reference to the accompanying drawing. 
         FIG. 1 : shows in perspective view an exemplary embodiment of a ferrule; 
         FIG. 2 : shows the ferrule of  FIG. 1  in exploded view; 
         FIG. 3 : shows a cover of the ferrule of  FIG. 1 ; 
         FIG. 4 : shows a distal end of an optical cable; 
         FIG. 5 : shows the cable of  FIG. 4  in a first step of a method for assembling the ferrule of  FIG. 1 ; 
         FIG. 6 : shows a first step of a method for assembling the ferrule of  FIG. 1 ; 
         FIG. 7 : shows a second step of a method for assembling the ferrule of  FIG. 1 ; 
         FIG. 8 : shows a third step of a method for assembling the ferrule of  FIG. 1 ; 
         FIG. 9 : shows a cleaving step of a method for assembling the ferrule of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIGS. 1 and 2  show a ferrule  1  comprising a base  2  between two covers  3 . The ferrule  1  has a contact face  4  presenting two rows  6  of unpolished distal ends  7  of fibers  8  from two optical cables  9  at a cable connection side  11  of the ferrule  1 . The fibers  8  are sandwiched between the base  2  and a respective cover  3 . 
     In the shown exemplary embodiment, the fibers are held by a round cable with a sheath which is removed at the outer end to expose the fiber ends. The fibers have a cylindrical core in a cylindrical coating. The distal ends of the fibers are stripped, such that the coating has been removed to expose the bare core. In other embodiments, other types of cable can be used, such as ribbon cables. 
       FIG. 3  shows a cover  3  with the surface  10  facing the base  2  when the ferrule  1  is assembled, turned upwardly. The surface  10  comprises a bonding section  12 , extending from the cable connection side  11  to an adhesive-free section  13  of the surface  10 . The bonding section  12  is formed by a series of parallel equidistantly arranged grooves  14 , dimensioned to individually receive and align a coated (not stripped) section  16  of a respective fiber  8  (see  FIG. 2 ). At the contact face  4 , the adhesive free section  13  comprises a ridge  17  (see also  FIG. 9 ) supporting stripped distal ends  18  of the fibers  8 . Opposite to the ridge  17  the opposite section of the base  2  comprises parallel grooves  19  the stripped ends  18  of the fibers  8  with a tight fit. At the side opposite to the contact face  4  the ridge  17  is bordered by a glue barrier slot  21 . Between the glue barrier slot  21  and the bonding section  12  a clearance  22  contributes to further separation of the bonding section  12  and the ridge  17 . 
     At two opposite sides parallel to the grooves  14  the cover  3  comprises a strip  23  with a circular alignment hole  24  near the contact face  4 , and an alignment slot  25  near the cable connection side  11 . At the cable connection side  11  the strips  23  are flush with the bonding section  12 . In the direction of the contact face  4 , the strips  23  have a recessed and chamfered side  26 . The thickness of the strips  23  is less than the thickness of the bonding section  12 , which is flush with the strips  23  at the face opposite to the surface  10  with the fiber alignment grooves  14 . 
     The two covers  3  are identically shaped and sized and can be made with the same moulds. The base  2  comprises two identical cover receiving surfaces  27  having a recessed middle part  28  for receiving the respective bonding sections  12  and the fiber sections  8 . At the contact face  4 , the middle part  28  of the base  2  comprises the alignment grooves  19  for accurately aligning the stripped distal fiber ends  18 . The middle part  28  of the base  2  is flanked by a pair of side edges  29  which are thicker than the middle part  28 . The side edges  29  are provided with alignment pegs  31  dimensioned to cooperate with the alignment holes and slots  24 ,  25  of the covers  3  to align the covers  3  when they are attached to the base  2 . The opposed surfaces of the cover  3  and the base  2  are complementary and form a matching fit enabling accurate alignment of the distal fiber ends  18  at the contact face  4  of the ferrule  1 . 
     At the contact face  4  of the ferrule  1  the covers  3  are recessed relative to the base part  2 . This creates a recessed part  5  of the contact face  4  the extending part of the base  2  protects the exposed fiber ends  7 . 
     The ferrule  1  can be used with any type of cable, including ribbon cables or round cables.  FIG. 4  shows an example of such a cable  9 , comprising a bundle of optical fibers  8  sheathed in an inner sleeve  32 , for instance a polyaramid sleeve, and an outer jacket  33 . To assemble the ferrule  1  using a round optical cable  9 , the outer jacket  33  is first stripped from the terminal end of the cable  9 . Subsequently, the inner sleeve  32  is folded backwards to expose the individual fibers  8 , as shown in  FIG. 5 . 
     For the subsequent steps, a gauge or jig  36  is used comprising an upper clamp  34 , a lower clamp  35  and a T-shaped front support  40  next to but separate from the lower clamp  35 . The exposed fiber ends are first positioned between the upper clamp  34  and a lower clamp  35  of the gauge  36 , as shown in  FIG. 6 . Subsequently, the fiber ends are stripped and cleaned. In a next step, the support  40  is positioned below the planned position of the cover, as shown in  FIG. 7 . The support  40  comprises a distal end  37  with alignment pegs  38  flanking the fiber ends  8 , and an alignment end with an alignment block  39  having a height corresponding to the thickness of the bonding section  12  of the cover  3 . The upper part  34  of the gauge  36  only faces the alignment block  39  of the lower part  35 . The opposed faces of the upper part  34  and the alignment block  39  comprise alignment grooves (not shown) spreading the fibers  8  equidistantly in a row. 
     During stripping the upper and lower parts  34 ,  35  of the gauge are clamped onto each other, e.g., by means of magnets (not shown). The stripped fiber ends  18  may for example have a diameter of 120-130 μm, while the coated fiber sections  16 , which are not stripped, have a diameter which is about twice the diameter of the stripped sections  18 . The fiber sections  16  between the cable sheath  32  and the stripped distal ends  18  are not stripped and remain coated. 
     In a next step, shown in  FIG. 8 , a cover  3  is positioned between the aligned fibers  8  and the lower part  35  of the gauge  36  in such a way that the alignment pegs  38  of the lower gauge part  35  are received in the circular alignment openings  24  in the cover  3 . The coated fiber sections  16  which are not stripped rest in the alignment grooves  14  of the bonding section  12  of the cover  3 . The fibers  8  are now accurately aligned and a glue, such as a heat curable or UV curable epoxy adhesive, can be applied over the coated, not stripped sections  16  of the fibers  8 . After curing, the gauge  36  can be removed. 
     The stripped distal fiber ends  18  protrude from the contact face  4  of the cover  3 . The protruding parts of the distal fiber ends  18  are removed by cleaving. To obtain a flat and smooth cleavage surface, first a scratch is made at one side of the fiber. Subsequently a shear force is exerted to the opposite side of the fiber until the distal end breaks off. The stripped distal fiber ends are now coplanar with the contact face  4  of the cover  3 , as shown in  FIG. 9 .