Abstract:
The present invention relates to an optical fiber communication component ( 1 ), and particularly a connector receptacle ( 10 ) for connecting to a connector plug ( 20 ) having an optical fiber ( 6 ) mounted within a projecting cylindrical ferrule. The connector receptacle ( 10 ) comprises a housing ( 2 ) that has a passageway ( 3 ) with an entrance for receiving the ferrule ( 7 ). A split sleeve clamp ( 27 ) is seated within the passageway ( 3 ) and has an opening oriented towards the entrance for receiving the projecting ferrule ( 7 ). A hollow sleeve ( 23 ) having a cylindrical outer surface ( 36 ) and an axially extending open channel ( 37 ), is gripped by the split sleeve clamp to define the diameter of the opening to the clamp. The open channel ( 37 ) extends along the longitudinal axis ( 5 ) of the passageway ( 3 ) to allow optical radiation ( 50 ) to be transmitted through the channel ( 37 ) to/from said connector plug ( 20 ).

Description:
FIELD OF THE INVENTION  
     The present invention relates to an optical fibre communication component, and particularly a connector receptacle for connecting to a connector plug having an optical fibre mounted within a cylindrical ferrule. 
     DISCUSSION OF THE BACKGROUND ART 
     Optical communication components, such as optical fibre transmitters and/or receivers, generally referred to hereinafter as optical transceivers, often need to be connected to other such components or optical fibre transmission cables. For example, an optical transceiver may have a connector port into which connector patch cord is plugged. 
     One common type of optical fibre connector, disclosed in U.S. Pat. No. 5,315,680, has an optical port inside of which is a hollow cylindrical split sleeve. The split sleeve is ceramic and has a longitudinal slot and is inwardly sprung so that this clamps over a ceramic ferrule within the port. The ferrule is cylindrical and normally has a diameter of 1.25 mm. An optical fibre is mounted concentrically within the ferrule to form a ferrule fibre assembly. The optical fibre may be a fibre stub that is optically connected to one or more other passive of active optical components, for example a solid state laser or detector device as part of an optical transceiver unit. The split sleeve extends forwards of the ferrule, and forms with a surrounding body a connector receptacle into which a connector plug can be inserted. 
     The connector plug has a cylindrical ceramic ferrule with a concentrically mounted optical fibre. This ferrule is manufactured to the same dimensions and tolerances as the ferrule/fibre assembly within the connector receptacle. The connector plug includes a body portion, with a forwards part of the ferrule/fibre assembly projecting freely from this body portion so that when the connector plug mates with the connector receptacle, the projecting portion of the connector plug fibre/ferrule assembly inserts into the forwards extending portion of the split sleeve. 
     In addition to providing a convenient means for butt-aligning optical fibres, this arrangement provides several advantages. Because both ferrule/fibre assemblies are manufactured to the same tolerance, the fibres are naturally aligned with respect to each other during the connection process to within a sub-micron accuracy. The extending split ferrule and surrounding body portion also provide an effective optical baffle when no connector plug is connected to the connector receptacle by aperturing stray optical radiation. Furthermore, because the output end of the fibre is recessed within the connector receptacle, the arrangement protects the output end of the fibre from mechanical damage as well as preventing a user&#39;s eye from coming closer than a minimum safety from the output end of the fibre. The latter issue is of particular concern as the wavelength of the optical radiation is normally either 1.31 μm or 1.55 μm, and is therefore invisible to the human eye. 
     Although the arrangement described above works effectively, there is a significant amount of cost in manufacturing the various components of the connector receptacle, particularly the ferrule/fibre assembly, which must be formed with an outer diameter toleranced to ±0.5 μm, so that the fibres are axially aligned to within ±1 μm. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a more economical optical fibre connector, and particularly a connector receptacle for connecting to a connector plug having an optical fibre mounted within a cylindrical ferrule. 
     According to a first aspect of the invention, there is provided an optical fibre connector receptacle for connecting to a connector plug having an optical fibre mounted within a projecting cylindrical ferrule, the connector receptacle comprising a housing, a passageway through the housing, the passageway extending along a longitudinal axis between a first entrance for receiving said projecting ferrule and a second entrance, and a clamp seated within the passageway, the clamp extending along the longitudinal axis and presenting radially around the longitudinal axis one or more radially inwards directed clamping surfaces, a first portion of said clamping surface(s) defining an opening to the clamp oriented towards the first entrance and being free for receiving said projecting cylindrical ferrule and a second portion of said clamping surface(s) towards the second entrance, wherein:
         the connector receptacle comprises a hollow sleeve having a cylindrical outer surface and an axially extending open channel;   the second portion of said clamping surface(s) of the seated clamp grips the sleeve outer surface and thereby defines the diameter of the first portion of said clamping surface(s); and   the open channel extends along the longitudinal axis of the passageway to allow optical radiation to be transmitted through the channel to/from said connector plug.       

     The clamp may be a split sleeve and is preferably radially inwardly spring-biased, so that the clamp naturally grips the sleeve and preferably also the projecting ferrule. 
     In one embodiment of the invention, the hollow sleeve extends longitudinally between a first end and a second end and the hollow sleeve is fully open at both ends of the sleeve. 
     In another embodiment of the invention, the sleeve extends longitudinally between a first end and a second end and the hollow sleeve includes at least one optical element which is transparent to optical radiation transmitted through the channel. The element may be a window for example in order to provide sealing or protection against dust or moisture ingress, or sealing, or a lens for example to focus optical radiation passing through the channel. The optical element may be mounted at the end of the sleeve nearest the transceiver device. 
     According to a second aspect of the invention, there is provided an optical fibre connector assembly comprising an optical fibre connector receptacle and a connector plug, the connector receptacle being according to the first aspect of the invention, and the connector plug having an optical fibre mounted within a projecting cylindrical ferrule, the projecting cylindrical ferrule being gripped by the first portion of said clamping surface(s) of the seated clamp when the connector receptacle is joined to the connector plug so that the optical fibre is aligned relative to the longitudinal axis of the passageway. 
     Preferably, both the projecting ferrule and the hollow sleeve are both formed from a ceramic material. 
     According to a third aspect of the invention, there is provided an optical communication component, comprising an optical fibre connector assembly, a focussing element and an optical transceiver device, in which the connector assembly is according to the second aspect of the invention, and the focussing element is arranged to focus optical radiation through the channel between the optical fibre and the transceiver device. 
     The focussing element may be any type of focussing element, for example a lens, a mirror or a holographic element. 
     According to a fourth aspect of the invention, there is provided a method of connecting an optical fibre connector receptacle with a connector plug, the connector plug having an optical fibre mounted within a projecting cylindrical ferrule, the connector receptacle comprising a housing, a passageway through the housing, and seated in the passageway a clamp, the clamp extending along the longitudinal axis and presenting radially around the longitudinal axis one or more radially inwards directed clamping surfaces, the method comprising the steps of:
         (a) inserting a hollow sleeve into a second portion of the clamp in order to define an inner diameter of a first portion of the clamp, the hollow sleeve having an open channel that extends along the longitudinal axis of the passageway; and   (b) inserting the projecting ferrule into the first portion of the clamp so that the clamp grips the projecting ferrule and the optical fibre is aligned axially with the channel.       

     According to a fifth aspect of the invention, there is provided a method of using an optical communication component to send and/or receive optical radiation, the communication component comprising an optical fibre connector receptacle with a connector plug, a focussing element and an optical transceiver device, the connector plug having an optical fibre mounted within a projecting cylindrical ferrule, the connector receptacle comprising a housing, a passageway through the housing, and seated in the passageway a clamp, the clamp extending along the longitudinal axis and presenting radially around the longitudinal axis one or more radially inwards directed clamping surfaces, the method comprising the steps of:
         (a) inserting a hollow sleeve into a second portion of the clamp in order to define an inner diameter of a first portion of the clamp, the hollow sleeve having an open channel that extends along the longitudinal axis of the passageway;   (b) inserting the projecting ferrule into the first portion of the clamp so that the clamp grips the projecting ferrule and the optical fibre is aligned axially with the channel; and   (c) using the focussing element to focus optical radiation through the channel between the optical fibre and the transceiver device.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of an optical fibre connector assembly according to a first embodiment of the invention, comprising an optical fibre connector receptacle and a connector plug; 
         FIG. 2  is a perspective exploded view of some of the internal components of the connector plug of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of an optical fibre connector assembly according to a second embodiment of the invention; and 
         FIG. 4  is a cross-sectional view of an optical fibre connector assembly according to a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows an optical fibre connector assembly  101 , formed from an optical fibre connector receptacle  10  and a connector plug  20 . Both the connector receptacle  10  and connector plug  20  are, for the most part, cylindrically symmetric about a longitudinal axis  5 , which lies in the plane of the drawings. 
     The connector receptacle  10  has an outer housing  2 , which is formed with a passageway in the form of a multiply-stepped axial bore  3 . At one end  32  of the bore  3  is mounted an optical transceiver device, here a transmitter device  8 . The transmitter device  8  is secured to the housing  2  by organic adhesive  4 , which also provides some backfill to the associated open end  32  of the housing  2 . 
     The transmitter device  8  comprises a base plate  12  (also referred to as a “header”), which together with a metal can  13  forms a sealed enclosure  11  housing an infra-red laser diode  14  mounted on a heat sink  15 . The laser preferably operates at either 1.31 μm or 1.55 μm. Also mounted on the heat sink  15  is a monitor photodiode  16 , and on the monitor diode  16  a spherical lens  17  which collimates and focuses the light output of the laser  14 . The lens  17  also serves to scatter light from the laser  14  into the monitoring photodiode  16 . 
     Electrical connections to the laser are via pins  18   a  and  18   b  of which pin  18   a  is electrically connected to the header  12  and provides electrical connection to the laser diode  14  by way of the heat sink  15 . The other electrical connection is by way of pin  18   b,  which passes through an insulating seal  19  into the interior of the enclosure  11  and is electrically connected via a bond wire  9 . 
     The can  13  has in its top wall  12  an aperture  21 . The aperture is sealed by window  22 , which is transparent to the radiation output of the laser diode  14 . 
     Other arrangements of light source and lenses may, of course, be used instead, such as arrangements employing graded index (GRIN) lenses. 
     The axial bore  3  is open at the end opposite the transmitter  8  to provide a receptacle for the connector plug  20 , only a forward end of which is illustrated in the drawings. The connector plug  20  has a housing  24  with a stepped axial bore  28 , an outer portion of which  28 ″ locates with a matching cylindrical recess  29  in the connector plug housing  2 . The precise external shape of the two housings  2 , 24  and any alignment surfaces will, of course, be determined by the need for matching whichever type of optical fibre connector is employed. 
     An inner portion  28 ′ of the plug housing  24  holds a cylindrical ferrule  7 , held in place with adhesive (not illustrated). The plug ferrule  7  has an axial channel  30 , which holds an optical fibre  6 , bonded in place with an adhesive (not illustrated). The plug ferrule  7  is made from a ceramic material and projects axially from the plug housing  24 . A fibre end  31  is flush with a domed annular end  33  of the plug ferrule  7 . In order to achieve good optical coupling into the optical fibre  6 , the bonded fibre end  31  and the annular end  33  of the plug ferrule  7  are together polished to sub-micron smoothness. 
     The plug ferrule  7  will typically be about 1.25 mm to 3 mm in diameter, with the ferrule channel  30  being about 125 μm in diameter. The optical fibre  6  may be a single mode optical fibre, having a central core (not illustrated) about 8.5 μm in diameter surrounded by index guiding cladding (not illustrated). 
     Reference is now made also to  FIG. 2 . The connector receptacle  10  has a hollow sleeve  23  having cylindrical inner and outer surfaces  35 , 36  both of which are concentric with the longitudinal axis  5  of the assembly  101 . An open channel  37  therefore extends axially through the hollow sleeve  23  between opposite annular ends  40 , 41  that surround corresponding circular openings  42 , 43 . The hollow sleeve  23  is preferably formed from the same ceramic material and in a similar fashion to that for the plug ferrule  7 , so that both the plug ferrule  7  and the hollow sleeve  23  have the same outer diameter. 
     The connector receptacle  10  also has a clamp  27  that extends along the longitudinal axis  5  and which presents radially around the longitudinal axis  5  an inwardly directed clamping surface  34 . In this example, the clamp is in the form of a cylindrical split sleeve  27 , but other forms of clamp having one or more radial clamping surfaces may equivalently be used. 
     As shown in  FIGS. 1 and 2 , the split sleeve  27  has a free first portion  27 ′ for receiving the projecting plug ferrule  7 . A hollow sleeve  23  is partially seated within a second portion  27 ″ of the split sleeve  27 , leaving a first portion  34 ′ of the clamping surface  34  free to receive the plug ferrule  7  when the connector plug  20  is joined with the connector receptacle  10 . 
     The split sleeve  27  may be made from a resiliently deformable metal, for example brass, but is preferably made from the same ceramic material as the hollow sleeve  23  and the plug ferrule  7 , in order to balance coefficients of thermal expansion. Such ceramic materials are stiffer than metals, but will still be resiliently deformable. 
     Prior to insertion of the hollow sleeve  23  into the free first portion  27 ′ of the split sleeve  27 , the split-sleeve  27  has a natural inner diameter slightly less than that of the hollow sleeve  23 , so that when the hollow sleeve  23  is partially inserted, a second portion  34 ″ of the clamping surface  34  is inwardly spring-biased to securely clamp the hollow sleeve  23 . This also has the effect of setting the inner diameter of the first portion  34 ′ of the clamping surface  34 , so that this may accurately locate the plug ferrule  7  with respect to the split sleeve  27 . 
     The connector receptacle  10  also has a second ceramic or metallic split sleeve  26 , which serves as a holder for the cylindrical split sleeve  23 . The second split sleeve  26  has a cylindrical outer surface  38  that makes a push-fit with the associated part  3 ″ of the stepped bore  3  and, in addition, is secured in place by means of adhesive (not illustrated). In this way, the orientation of the optical fibre  6  with respect to the connector receptacle housing is set when the connection plug  20  is joined to the connector receptacle  10 . 
     The split sleeve  27 , therefore centres and lightly clamps the projecting end of the plug ferrule  7 , thus aligning and supporting the optical fibre  6  in directions transverse to the longitudinal axis  5 . When the connector plug  20  is joined to the connector receptacle  10 , the annular end  33  of the plug ferrule  7  preferably comes into abutting contact with the annular end  41  of the hollow sleeve  23 , thereby also setting the longitudinal spacing between the transmitter device  8  and the exposed end  31  of the optical fibre  6 . 
     It should be noted that in order to allow a small amount of radical expansion of the split sleeve  27 , to accommodate variation in diameter of the plug ferrule  7 , the external surface of the split sleeve  27  makes a loose fit within the corresponding section  3 ′ of the axial bore  3 . 
     The open channel  37  through the hollow sleeve  23  then extends along the longitudinal axis  5  of the passageway  3  between the transmitter device  8  and the end  31  of the optical fibre  6 . Radiation  50  from the laser diode  14  is coupled via the spherical lens  17  and the window  22  directly into the optical fibre  6 . 
     This arrangement provides several advantages. First, unlike the channel  30  supporting the optical fibre, the open channel  37  of the hollow sleeve  36  does not need to be precisely formed, and is therefore considerably less expensive to manufacture. The open channel  37  only needs to be wide enough to allow optical radiation to pass from the lens  17  to the optical fibre  6 . For example, if the hollow sleeve is 1.25 mm in diameter, then the diameter of the open channel  37  may be about 0.8 mm. 
     Another advantage stems from the fact that the annular ends  40 ,  41  of the hollow sleeve  36  do not need to be polished to the same degree of accuracy as the projecting annular end  33  of the plug ferrule  7 . The annular end  41  of the hollow sleeve  23  is more simply prepared to remove any rough edges and so provide a reliable abutting contact with the domed end  33  of the plug ferrule  7 . 
     The assembled connector receptacle  10  also provides a minimum eye-safety distance when no connector plug  20  is joined to the receptacle  10 , owing to the distance between the focus point at which radiation would otherwise be coupled into the optical fibre end  31  and the external opening to the passageway  3 . The connector receptacle  10  therefore provides an effective optical baffle. 
     Finally, there is no contact with the exposed end  33  of the optical fibre  6  when the plug ferrule  7  and hollow sleeve  23  come into contact, thus sparing the optical fibre  6  from any damage or wear. 
     The length of the hollow sleeve may be between 2 mm and 5 mm. The minimum spot size will depend on this distance, and the effective numerical aperture of the focussing lens  17 , but will typically be between about 7 μm and 20 μm in diameter, which is comparable with the diameter of the core of the optical fibre  6 . Although the spot size will be larger than with the prior art arrangement using an abutting optical fibre stub, there are inevitable coupling losses with such stubs, and so the overall coupling efficiency of this arrangement is adequate for many applications. 
       FIG. 3  shows a second embodiment of an optical fibre connector assembly  1 , in which components the same as those of the first embodiment 101 are indicated with the same reference numerals. The assembly  1  differs from that of the first embodiment 101 in that the circular opening  42  of the hollow sleeve  23  holds a circular window  122 , which may be either tilted or antireflection coated to prevent stray reflections back into the laser diode  14 . The advantage of this arrangement is that the window  122  provides protection against dust or moisture ingress into the vicinity of the transmitter device  8 . 
       FIG. 4  shows a third embodiment of an optical fibre connector assembly  201 , in which components the same as those of the first and second embodiments 101 ,1 are indicated with the same reference numerals. The assembly  201  differs from that of the first embodiment 101 mainly in that the transmitter device  208  does not have a collimating lens  17 . Instead, a collimating lens  117  is mounted inside the circular opening  42 , and arranged to focus optical radiation  250  onto the free end  31  of the optical fibre  6 . The lens  117  may be held in place by an adhesive, for example a uv-curable adhesive (not illustrated). 
     The transmitter device  208  has a monitor photodiode  116  arranged to collect optical radiation from a back facet of the laser diode  14 . An advantage of this arrangement is that the collimating lens  117  is of larger diameter and closer to the end  31  of the optical fibre  6 , thereby increasing the numerical aperture of the system, reducing the resulting focus spot and increasing the coupling efficiency between the laser diode  14  and the optical fibre  6 . In addition, the lens  117  provides similar protection to that of the circular window  122  described above against dust or moisture ingress into the vicinity of the transmitter device  208 . 
     The invention described above is also applicable to other types of optical communication component, in particular an optical receiver or relay component, having instead of the transmitter device  8  an optical receiver device, such as a photodiode or an optical amplifier. The invention allows economies to be made in the manufacture of a wide range of optical fibre connector receptacles.