Abstract:
An expanded beam optical insert is provided for use in optical data connectors, such as fiber optic connectors or the like. The expanded beam optical insert may be readily assembled, substantially without the use of costly fixturing tools or adhesives, while still allowing the precise positioning of alignment of optical lenses for placement of ferrule assemblies, optical stubs, and the like.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. provisional application Ser. No. 61/532,227, filed Sep. 8, 2011, which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to fiber optic connections and, more particularly, to fiber optic connections utilizing expanded beam lenses. 
     BACKGROUND OF THE INVENTION 
     Typical expanded beam fiber optic connectors, such as those complying with military specification MIL 83526/20 and 83526/21, require very tight dimensional tolerances and use epoxies or other adhesives to hold lenses and various other components in place, so that an optical signal can be reliably transmitted through the connector without being overly susceptible to contaminants and mechanical shock, vibration, etc. However, it is costly to machine components to very tight tolerances, precise and costly fixtures are needed for maintaining dimensional precision while assembling the optical connector components, and adhesives require time to cure, and typically do not allow for subsequent disassembly or servicing of the connector. 
     SUMMARY OF THE INVENTION 
     The present invention provides an expanded beam optical insert for use in fiber optic couplers, which allows for precision alignment of optical lenses and fibers without the use of adhesives, and without need for precise fixtures or tight dimensional tolerances. The optical insert of the present invention accomplishes this with a housing that defines a plurality of tapered passageways, each passageway receiving a respective ball lens and a tapered barrel or sleeve. Each ball lens is centered and secured in one of the tapered passageways by one of the tapered sleeves. The sleeves are press-fit or swaged into the tapered passageways so that the ball lenses are held in compression between the sleeves and the inner surfaces of the tapered passageways, which terminate in respective distal openings that are smaller in diameter than the ball lenses. This centers and holds the lenses in a precise fixed location due to automatic centering caused by the tapered housing passageways. The hollow sleeves receive respective ferrule assemblies or optical stubs, and are typically press-fit to hold these ferrules or stubs in fixed relation relative to the ball lenses, so that the fibers and lenses are maintained in alignment and fixed relation to one another. Because of the tapered surfaces of the housing passageways and hollow sleeves, at least some of the machined or formed components can be manufactured to lower or looser tolerances, without degrading the quality of the optical connection. Moreover, typically no adhesives are needed for holding the lenses and optical fibers and housing in fixed positions relative to one another, due to the press-fit assembly process in which the sleeves and hold the lenses and ferrule assemblies or stubs (containing the optical fibers) in place. 
     According to one form of the present invention, an expanded beam optical insert includes a housing, a lens, and a tapered hollow sleeve. The housing defines a housing passageway with a tapered inner surface for receiving the tapered hollow sleeve and an optical conduit. The housing passageway extends between proximal and distal openings, with the proximal opening being larger than the distal opening. The lens is also positioned in the housing passageway, near the distal opening, and the lens has a larger diameter than does the distal opening of the passageway so that the lens cannot pass through the distal opening. The sleeve has a tapered outer surface that corresponds to the tapered inner surface of the housing passageway. A distal end portion of the sleeve is disposed toward the distal opening of the housing passageway, and further includes a proximal end portion disposed toward the proximal opening of the housing passageway. The lens is securable in a fixed position relative to the housing, between the distal opening of the housing passageway and the distal end portion of the sleeve, with a compressive axial force applied to the proximal end portion of the sleeve in the direction of the distal opening of the housing passageway, to thereby hold the lens, in compression, in its fixed position relative to the housing. 
     In one aspect, the housing includes a substantially planar distal mating surface for engagement with a corresponding mating surface of another optical insert. The distance between the lens and the planar distal mating surface is determined by the diameter of the lens, the diameter the distal opening of the housing passageway, and the taper angle of the inner surface of the housing passageway. 
     In another aspect, the housing passageway has a partial-spherical annular inner surface near the distal opening, and the lens is a spherical lens that seats against the partial-spherical annular inner surface. 
     In yet another aspect, the tapered inner surface of the housing passageway is a frusto-conical surface, and the outer surface of the tapered hollow sleeve likewise is a frusto-conical surface. 
     In a further aspect, the housing defines a plurality of the housing passageways, each passageway for supporting a respective lens and sleeve. 
     In a still further aspect, the optical insert further includes an inner insert body that engages the proximal end portion of the sleeve, to apply the compressive axial force to the proximal end portion of the sleeve and hold the lens in a fixed position. 
     In another aspect, a lens-mounting end cap in positioned at the housing and defines the distal opening of the housing passageway, with the end cap being engaged by the lens. 
     Optionally, the optical insert includes an alignment pin that projects outwardly from the housing in a distal direction, near the distal opening of the housing passageway, with the alignment pin configured to engage an alignment bore in another optical insert. The housing may further define an alignment bore near the distal opening of the housing passageway, for receiving the alignment pin of another optical insert. 
     According to another form of the present invention, a method is provided for assembling an expanded beam optical insert for use in fiber optic couplers. The method includes providing a housing that defines a housing passageway with proximal and distal passageway openings. The housing passageway has an inner surface that tapers from the proximal opening to the distal opening. A lens is positioned in the housing passageway near the distal opening, with the lens having a larger diameter than the distal opening of the housing passageway, so that the lens cannot pass through the distal opening. A tapered hollow sleeve is positioned in the housing passageway, with a distal end portion of the sleeve disposed towards the distal opening of the housing passageway. The sleeve has a tapered outer surface that corresponds to the tapered inner surface of the housing passageway. A compressive axial force is applied to a proximal end portion of the sleeve, in the direction of the distal opening of the housing passageway, to thereby secure and align the lens in a fixed position with the lens seated in the distal opening of the housing passageway. 
     Accordingly, the expanded beam optical insert of the present invention allows for a faster assembly process by providing a design that is less susceptible to dimensional variations (i.e., its components can be manufactured to lower tolerances), does not require the use of adhesives, and also does not require the use of precise fixturing equipment during assembly. The resulting optical insert can be readily assembled into an optical coupler, which maintains sufficiently precise alignment of the optical components, including lenses and optical fibers, and which is resistant to signal degradation in the presence of contaminants and or mechanical shock. 
     These and other objects, advantages, purposes, and features of the present invention will become more apparent upon review of the following specifications in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an expanded beam optical insert in accordance with the present invention; 
         FIG. 2  is a sectional perspective view of the expanded beam optical insert taken along section line II-II in  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of the outer insert housing, ball lenses, and tapered sleeves of the expanded beam optical insert; 
         FIG. 4  is a sectional perspective view of the outer insert housing portion of the optical insert, including ball lenses in the housing passageways; 
         FIG. 5  is another sectional perspective view of the outer insert housing, including ball lenses and tapered sleeves in the housing passageways; 
         FIG. 6  is a perspective view of a portion of the outer insert housing and inner insert of the optical insert; 
         FIG. 7  is a side sectional elevation of a complete optical coupler assembly including a dust cap with lanyard, and fiber optic lines shown in phantom; 
         FIG. 8  is a sectional prospective view of another outer insert housing; 
         FIG. 9A  is a front perspective view of the housing cap from the outer insert housing of  FIG. 8 ; and 
         FIG. 9B  is a rear perspective view of the housing cap of  FIG. 9A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and the illustrative embodiments depicted therein, an expanded beam optical insert  10  includes an outer insert housing  12 , an inner insert  14 , and a rear insert  16  ( FIGS. 1 and 2 ), for use in an optical coupler assembly  18  ( FIG. 7 ). Outer insert housing  12  defines a plurality of optical channels or housing passageways  20 , each passageway  20  extending between a respective distal opening  22  and proximal opening  24  ( FIGS. 4 and 5 ). Each housing passageway  20  receives a spherical ball lens  26  and a tapered barrel or sleeve  28  for holding the ball lens  26  in position in the passageway  20  at distal opening  22  ( FIGS. 2-5 ). Each tapered sleeve  28  in each housing passageway  20  further receives an end portion of a ferrule assembly  29 , which supports an optical fiber  31  that is in optical communication with lens  26  ( FIG. 2 ), as will be described in greater detail below. 
     Housing passageways  20  are defined by tapered frusto-conical inner surfaces  30  of inner insert  14  ( FIGS. 4 and 5 ). Each passageway  20  has a relatively larger inner diameter at proximal openings  24 , and a relatively smaller inner diameter at distal openings  22 . Housing passageways  20  are dimensioned with the inner diameter at distal opening  22  sized at least somewhat smaller than the outer diameter of ball lens  26 , so that ball lenses  26  cannot be pushed fully through the distal openings  22  ( FIGS. 4 and 5 ). Ball lenses  26  can thus be wedged in the housing passageways  20  where the inner diameter of the respective tapered inner surfaces  30  is equal to the outer diameter of the ball lenses  26 . 
     It will be understood that ball lenses  26  contact the tapered frusto-conical inner surface  30  of passageway  20  along an annular contact patch where the inner diameter of housing passageway  20  is slightly less than the outer diameter ball lens  26 . This is because of the tapered shape of inner surface  30 , which dictates that the surface  30  will contact lens  26  along an annular surface tangent of the lens, the annular surface tangent located slightly forward of a great circle along the outer surface of the ball lens, and oriented perpendicularly to the longitudinal axis of housing passageway  28 . 
     Each tapered sleeve  28  includes a forward or distal portion  28   a  and a rearward or proximal portion  28   b . Tapered sleeves  28  have tapered frusto-conical outer surfaces  32  so that the outer diameter of tapered sleeve  28  is smaller at distal end portion  28   a  than at proximal end portion  28   b . The angle of taper of frusto-conical outer surface  32  generally corresponds to the angle of taper of frusto-conical inner surface  30  of housing passageway  20 , so that the surfaces  30 ,  32  engage one another as shown in  FIG. 5 . Tapered sleeve  28  includes a substantially constant-diameter inner cylindrical surface  34  and, in the illustrated embodiment of  FIG. 5 , has a bevel region  34   a  at distal end portion  28   a , and a shoulder region  34   b  at proximal end portion  28   b . Bevel region  34   a  is an annular surface that is concave to generally conform to a ring-shaped portion of the outer surface of ball lens  26 . The concave surface of bevel region  34   a  increases the surface area over which tapered sleeve  28  engages ball lens  26 . Shoulder region  34   b  facilitates inserting the forward end portion of ferrule assembly  29  into tapered sleeve  28  and also facilitates a press-fit operation to secure sleeve  28  and ferrule assembly  29  in housing passageway  20 . A lip  36  ( FIG. 5 ) defines the distal end of shoulder region  34   b.    
     Tapered sleeve  28  is typically made from a softer material than outer insert housing  12  so that tapered sleeve  28  may plastically deform, such as during the installation of the tapered sleeve into housing passageway  20 . For example, tapered sleeve  28  may be made from stainless steel and outer insert housing  12  may be made from ARCAP® brand non-ferrous alloy. The material of the outer insert housing  12  should be sufficiently hard so that ball lens  26  cannot deform inner surface  30  of housing passageway  20 , so that ball lens  26  will only travel along the housing passageway. 
     Thus, distal end portion  28   a  of tapered sleeve  28  may deform at least partly into the annular space define between ball lens  26 , inner surface  30  of housing passageway  20 , and distal end portion  28   a  of tapered sleeve  28 . In addition, outer surface  32  of tapered sleeve  28  may expand outwardly into tight contact with inner surface  30  of housing passageway  20  during the installation of tapered sleeve  28 , and may further expand inwardly into tight contact with the outer surface of ferrule assembly  29 , particularly in the vicinity of shoulder region  34   b  and lip  36  along inner surface  34 . The expansion and/or deformation of tapered sleeve  28  during the installation process may result in a swage or swage-like permanent or semi-permanent coupling between tapered sleeve  28 , outer insert housing  12 , and ferrule assembly  29 . 
     Outer insert housing  12  includes an annular planar mating surface  38  at the end of an annular wall  39  ( FIGS. 1-5 ), the planar mating surface  38  for engaging a corresponding mating surface of another outer insert housing when two optical coupler assemblies  18  are assembled together. Mating surface  38  is spaced distally from the distal openings  22  of housing passageways  20  a desired distance so that ball lenses  26  are spaced a desired distance from the ball lenses  26  of another expanded beam optical insert  10  in an optical coupler assembly  18 , according to lens focal length. Optionally, annular wall  39  includes notches  39   a  along an inner surface thereof, in proximity to each distal opening  22  and ball lens  26 . By forming notches  39   a  along the inner surface of annular wall  39  in these locations, the chance of optical signal degradation (e.g., due to light signals passing through a ball lens and being absorbed or reflected by annular wall  39 , rather than received by a corresponding ball lens) is reduced. 
     In the illustrated embodiment, outer insert housing  12  includes an alignment pin  40  that projects distally outwardly from a generally planar end surface  42  in which distal openings  22  are formed. A pin-receiving bore  44  is formed in planar end surface  42 , directly across from alignment pin  40 , so that two substantially identical outer insert housings  12  may be assembled together with their respective ball lenses  26  in proper alignment, with the alignment pin  40  of one housing engaging the corresponding bore  44  of the other housing, and vice versa. Optionally, alignment pin  40  may have a tapered tip portion  40   a  that facilitates the insertion of pin  40  into the pin-receiving bore  44  of another insert housing  12 . 
     As best shown in  FIG. 2 , once inner insert  14  is assembled to outer insert housing  12 , inner insert  14  blocks or contacts the proximal ends  28   b  of taper sleeves  28  to prevent possible dislocation or movement of the sleeves  28  and ferrule assemblies  29  during vibration or environmental changes around the optical insert  10 . Ferrules  29  are further supported in respective tubular sleeves  46  positioned in respective inner chambers  48  of rear insert  16 . Tubular sleeves are inserted into inner chambers  48  through a forward or distal end of rear insert  16 , and held in place by inner insert  14 . The rear or proximal end portion of ferrule assembly  29  is received in a ferrule holder  50 , through which optical fiber  31  exits the optical insert  10 . A forward portion of ferrule holder  50  is received in a rear inner chamber  52  of rear insert  16 , and an end cap  54  is attached to the rear or proximal end of rear insert  16  to secure ferrule holder  50  in place. An O-ring seal  56  substantially limits or prevents contaminants from entering ferrule assembly  29  through an opening  58  in end cap  54 , through which a rear or proximal end portion of ferrule holder  50  and optical fiber  31  exit the optical insert  10 . 
     As noted above, outer insert housing  12  is typically made of ARCAP® or the like, which is a harder material than that of tapered sleeves  28 , which are typically made of stainless steel or the like. Ferrule assemblies  29  include cylindrical bodies made of ceramic or the like, while ferrule holders  50  are typically made of any sufficiently durable and strong metal or resinous plastic material. Tubular sleeve  46 , which supports the ceramic cylindrical body of ferrule assembly  29 , is typically also made of ceramic material. 
     Optionally, an annular spacer  60  may be positioned between ball lens  26  and the distal ends of tapered sleeve  28  and ferrule assembly  29 . Spacer  60  may be particularly useful such as when longer focal lengths are desired to improve transmission of multi-mode light signals, and can be made of stainless steel, for example. Optical fiber  31  typically has a polished distal end  31   a  where it exits or is exposed in the distal end of ferrule assembly  29  ( FIG. 2 ), also for improved light signal transmission. 
     Additional alignment pins  40 ′ project or extend rearwardly from inner insert  14  for engagement with pin-receiving bores  44 ′ in the forward or distal end of rear insert  16 , such as shown in  FIGS. 2 and 6 . A forward or distal end portion of each alignment pin  40 ′ is received in pin-receiving bore  44 , which passes entirely through outer insert housing  12  as shown in  FIG. 2 . Thus, alignment pins  40 ′ ensure proper alignment of outer insert housing  12  with inner insert  14  and rear insert  16 . Additional alignment pins  40 ″ are received in pin-receiving bores  44 ″ at the rear or proximal end of rear insert  16 , and project rearwardly through end cap  54  to maintain proper alignment of end cap  54  with rear insert  16  ( FIG. 2 ). 
     Referring now to  FIG. 7 , expanded beam optical insert  10  is shown incorporated into an optical connector assembly  62 , which terminates a fiber optic line  64 . A flexible dust boot and strain relief  66  secures fiber optic line  64  to connector assembly  62 , which includes several concentric housings  68 ,  70 ,  72 ,  74 , seals, and typically a soft rubber or rubberized outer casing  76  to improve the connector assembly&#39;s resistance to mechanical shock, vibration, and contamination. In the illustrated embodiment of  FIG. 7 , connector assembly  62  includes a dust cap  78  that substantially limits or prevents contaminants from reaching outer insert housing  12 , including lenses  26 , distal openings  22 , and annular wall  39  and distal mating surface  38  when the connector assembly  62  is not in use. When the connector assembly  62  is to be put into use, dust cap  78  is removed (and may remain tethered to connector assembly  62  via a lanyard  80 ) and the connector assembly  62  may be coupled to a substantially identical connector assembly (not shown) with their respective alignment pins  40  engaging corresponding pin-receiving bores  44 , and with mating surfaces  38  engaging one another so that the coupled connector assemblies are arranged substantially as a mirror image to one another. 
     Optionally, and with reference to  FIGS. 8-9B , an alternative outer insert housing  112  defines a plurality of housing passageways  120  for receiving sleeves  128  and ball lenses  126  in a somewhat similar arrangement as with outer insert housing  12 , described above. Unlike housing passageways  20  and tapered sleeves  28 , however, housing passageways  120  have a substantially constant inner diameter and sleeves  128  have a substantially constant outer diameter. Outer insert housing  112  has a forward housing cap  130  that attaches (such as via an adhesive or other mechanical fastener or the like) to a main body  132  of insert housing  112 . Housing cap  130  includes an annular wall  139  defining a forward planar mounting surface  138  spaced distally outwardly from a generally planar end surface  142 . Distal openings  122  in end surface  142  have smaller diameters than ball lenses  126 , so that the ball lenses can extend partially (but not entirely) through the distal openings  122 . 
     Forward housing cap  130  defines a concave annular seat portion  146  ( FIGS. 8 and 9B ) between each housing passageway  120  and corresponding distal opening  122 . Annular seat portions  146  are concave surfaces that generally conform or correspond to the curvature of the outer surface of each spherical ball lens  126 , and are spaced a desired distance from annular mating surface  138  so that each optical lens  126  is positioned at a precise distance (focal length) for optical data transmission through the lenses of expanded beam optical insert. With ball lenses  126  installed in housing passageways  120 , sleeves  128  are inserted and pressed or urged into place, which secures each ball lens  126  against a respective annular seat portion  146 . Seat portions  146  are formed so that each ball lens  126  is at a precise desired location and held or fixed in that location by a respective sleeve  128 . 
     Thus, the expanded beam optical inserts of the present invention facilitate secure connection of optical data transmission conduits with precise alignment of optical lenses. The resulting connector is resistant to contaminants, vibration, mechanical shock, and other hazards. The expanded beam optical insert does not require epoxy or other adhesives for holding the various components together, and nor does it require precise fixturing tools or other expensive equipment for achieving a desired level of precision in the optical connectors, since the ball lenses are self-aligning in the optical inserts. 
     Changes and modifications in the specifically-described embodiments can be carried out without departing from the principles of the present invention, which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents.