Abstract:
There is provided a mechanical connector for mechanically connecting and optically coupling two optical fiber ends, the connector comprising a longitudinal body, and a fiber conduit in the body for holding the two fiber ends and confining the fibers to be in end to end alignment in the conduit with sufficient inward radial pressure exerted from the conduit on each one of the fiber ends to ensure centering within the fiber conduit to provide the optical coupling without risking damage to a silica core of the fiber ends. The connector is adapted to controllably release the pressure on the fibers to allow for insertion of the fibers in the conduit, and the connector holds the fiber ends in the optical coupling without adhesive. There is further provided a method for mechanically connecting and optically coupling two optical fiber ends.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a connector for optic fibres. 
   BACKGROUND OF THE INVENTION 
   In an optic fibre, an optical signal can be transmitted through the fibre, carrying relatively large amounts of information as compared to a typical copper wire. However, the signal is susceptible to distortion or to a loss of strength if the connection between the ends of two optic fibres is poor. Thus, several different approaches have been proposed for connections that provide good signal conduction. 
   One approach is to fuse the ends of the optic fibres together. This ensures that the ends remain in abutment, however several problems exist with fusion. The optic fibres are often doped with a secondary material that enhances certain desired properties. The act of fusion typically destroys the doping in the ends of the optic fibres, thereby reducing the connection&#39;s capacity to transmit a signal. Furthermore, fusing can usually only be used with pairs of optic fibres that are doped with the same secondary material. 
   Other approaches include a ferrule that receives the two ends of the optic fibres. The ferrule has a conduit that is oversized so that the optic fibres are easily inserted therein. Glue may be placed in the ferrule to help hold the optic fibres together. A problem with this approach is that the ends of the optic fibres are not in certain abutment, because of the oversizing of the aperture in the ferrule and thus, the signals may be comprimised. The ferrule may be mechanically reduced in size by crimping for example, so that it constrains the optic fibres mechanically. This approach however, can easily damage the optic fibres, which are typically fragile. 
   Thus, a continuing need exists for an improved connector for connecting optic fibres that is simple to use and that maintains good signal conduction between the optic fibres. 
   SUMMARY OF THE INVENTION 
   In a first aspect the invention is directed to a connector for connecting optic fibres. The connector includes a body. The body has a first end and a second end, and a fibre conduit extending from the first end to the second end. The body is divided into a plurality of fingers that extend longitudinally at each end. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference will now be made by way of example to the accompanying drawings, showing articles made according to preferred embodiments of the present invention. In the drawings: 
       FIG. 1  is a perspective view of the connector in accordance with a first embodiment of the present invention, with two optic fibres; 
       FIG. 2  is a transparent perspective view of the connector shown in  FIG. 1 ; 
       FIG. 3  is a side sectional view of the connector with both optic fibres inserted therein; 
       FIG. 4  is a perspective view of a connector in accordance with a second embodiment of the present invention; 
       FIG. 5  is a perspective sectional view of a portion of the connector shown in  FIG. 4 ; 
       FIG. 6   a  is a perspective view of one of the fingers of the connector shown in  FIG. 4  in the rest position; 
       FIG. 6   b  is a perspective view of the finger shown in  FIG. 6   a,  in the flexed position; 
       FIG. 7  is a sectional view of a connector assembly incorporating one of the connectors shown in  FIG. 1  or  FIG. 4 ; 
       FIG. 8  is a sectional view of a central sheath of the connector assembly shown in  FIG. 7 ; 
       FIG. 9  is a sectional view of an end member of the connector assembly shown in  FIG. 7 ; and 
       FIG. 10  is a perspective view of stresses and strains incurred by the connector shown in  FIG. 1  after receiving optic fibres. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference is made to  FIGS. 1 ,  2  and  3 , which show a connector  10  in accordance with a first embodiment of the present invention. Connector  10  is used to connect the ends of first and second optic fibres  12  and  13  (see  FIG. 3 ), so that the optic fibres  12  and  13  can transmit optical signals across the connection. The connector  10  has a body  14 , which may be generally cylindrical. The body  14  has a first end  16  and a second end  18 . 
   A fibre conduit  20  extends from the first end  16  to the second end  18 . The fibre conduit  20  is used to hold the two ends of the optic fibres  12  and  13  in abutment, so that they can transmit optical signals therebetween. The fibre conduit  20  is sized so that the connector  10  applies a small amount of compressive force on the ends of the optic fibres  12  and  13 , to hold the fibres  12  and  13  in abutment with each other when they are inserted into the connector  10 . It will be appreciated that the compressive force that is applied to the optic fibres  12  and  13  must be suitably small, so as not to damage or break the fibres  12  and  13 . 
   The body  14  is divided into a plurality of first fingers  22 , that extend from the first end  16  towards the second end  18 . The first fingers  22  hold the first optic fibre  12  in place in the connector  10 , when the optic fibre  12  is inserted into the connector  10 . By configuring the first fingers  22  to have a selected length, the compressive force of the connector  10  on the optic fibres  12  and  13  can be controlled and can be varied over the length of the connector body  14 . The connector body  14  may be divided into any suitable number of first fingers  22 , such as, for example, four first fingers  22 . Alternatively, the connector  10  may have more or fewer first fingers  22 , such as, three or five first fingers. The first fingers  22  may occupy any suitable portion of the circumference of the body  14 . For example, the first fingers  22  may each occupy approximately 90° of the circumference. The first fingers  22  may be formed by any suitable method, such as by milling axially-extending slots  24  into the first end  16 , as shown more clearly in  FIG. 2 . 
   Referring again to  FIG. 1 , the body  14  may have a plurality of second fingers  26  that extend from the second end  18  towards the first end  16 . The second fingers  26  hold the second optic fibre  13  in place in the connector  10 , when the second optic fibre  13  is inserted into the connector  10 . The second fingers  26  may be similar in size, length and number to the first fingers  22 . Alternatively, the second fingers  26  may be configured differently than the first fingers  22 , to suit the mechanical properties of the second optic fibre  13 . Thus, the second fingers  26  may be shorter or longer than the first fingers  22 , or may be different in number than the first fingers  22 . The second fingers  26  may be formed by any suitable method, such as by milling axially-extending slots  28  into the second end  18 , as shown more clearly in  FIG. 2 . 
   Referring again to  FIG. 1 , the first and second fingers  22  and  26  may be circumferentially offset from each other, as shown in  FIG. 1 . The offset angle may be any suitable angle, such as, for example, 45°. 
   Furthermore, the fingers  22  and  26  may extend along the connector body  14  far enough from their respective ends so that they overlap with each other along a portion of the connector body  14 . The overlap permits further control over the compressive force exerted by the connector body  14  on the optic fibres  12  and  13 , particularly at the point where the first and second optic fibres  12  and  13  abut each other. 
   The connector  10  may be made from a material that has a shape memory. In other words the material, when deformed from its rest condition by any suitable means, is biased to return to its rest condition when the cause of deformation is removed. An example of such a material is any material that deforms within its elastic limit under mechanical deformation. Another example is any material that expands suitably due to a temperature increase, and then returns to its initial rest condition when the temperature is reduced to the initial temperature. 
   The connector  10  may be made from any of several different materials, depending on the particular environment in which the connector is used, and depending on the particular jurisdictional code that may govern the construction and use of the connector  10 . The connector  10  may, for example, be made from a polymeric material, such as isostatic  1  polybutene, piezoelectric ceramics, copper alloys including binary and ternary alloys, such as Copper—Aluminum alloys, Copper—Zinc alloys, Copper—Aluminum—Beryllium alloys, Copper—Aluminum—Zinc—alloys and Copper—Aluminum—Nickel alloys, Nickel alloys such as Nickel—Titanium—Iron alloys and Nickel—Titanium—Colbalt alloys, Iron alloys such as Iron—Manganese alloys, Iron—Manganese—Silicon alloys, Iron—Chromium—Manganese alloys and Iron—Chromium—Silicon alloys, Aluminum alloys, and high elasticity composites which may optionally have metallic or polymeric reinforcement. 
   To connect the two optic fibres  12  and  13 , the fibre conduit  20  is enlarged by deforming the connector  10  in any suitable way. For example, the connector  10  may be heated to a sufficient temperature so that the connector  10  undergoes sufficient thermal expansion for the optic fibres  12  and  13  to be inserted into the fibre conduit  20 . The amount of heating required and the final require temperature for the connector  10  is dependent on the material of manufacture for the connector  10 . 
   A gel that has substantially the same index of refraction as the optic fibres  12  and  13  may be inserted into the fibre conduit  20 . The gel provides uniform optical properties across the connection between the optic fibres  12  and  13 , to reduce a loss of the signal due to internal reflection and refraction of the optical signals at the ends of the optic fibres  12  and  13 . 
   The optic fibres  12  and  13  are typically covered in a sheath  30 , which, among other things, protects the optic fibres  12  and  13  from mechanical damage during installation and use. The combination of the sheath  30  and the optic fibre  12  or  13  makes up a cable  32  or  34  respectively. The sheath  30  on the ends of the optic fibres  12  and  13  is removed, exposing the optic fibres  12  and  13 . 
   The optic fibres  12  and  13  are inserted into the heated connector  10 . As they are inserted, the optic fibres  12  and  13  displace excess gel that is in the fibre conduit  20 . The displaced gel can escape from the connector  10  through the slots  24  and  28 . 
   Once the optic fibres  12  and  13  are fully inserted into the heated connector  10 , their respective ends abut each other. The connector  10  may then be cooled, so that it returns to its initial size. Once the connector  10  returns to its original size, the fingers  22  and  26 , and the body  14  in general exerts a controlled compressive force on the optic fibres  12  and  13 , that is large enough to retain the optic fibres  12  and  13  in abutment with each other, but is small enough so that the optic fibres  12  and  13  are not damaged by the compression. 
   During the step wherein the connector  10  returns to its rest condition, there may be a tendency for the connector  10  to push the ends of the optic fibres  12  and  13  apart slightly. Thus, it may be necessary to hold the fibres  12  and  13  in a fixed position during the step where the connector returns to its original size to prevent the optic fibres  12  and  13  from being moved apart. For example, the sheath  30  covering each optic fibre  12  and  13  may be fixedly clamped by fixedly positioned clamps  36 , as shown in  FIG. 3 , so that axial movement of the optic fibres  12  and  13  is not permitted. By clamping the sheath  30 , the risk is reduced of damaging the optic fibres  12  and  13 . 
   Reference is made to  FIG. 4 , which shows a connector  40 , in accordance with a second embodiment of the present invention. The connector  40  is similar to connector  10  except that connector  40  includes an accordion portion  42  that extends along some or all of the length of each finger  22 ,  26 . The accordion portion  42  may extend from the free end of each finger  22 ,  26  as shown in  FIG. 4 . The accordion portion  42  causes optic fibres  12  and  13  to be retained in abutment with each other while the connector  40  returns to its initial rest condition from a deformed condition. 
   For each first finger  22 , the accordion portion  42  may be created by milling a plurality of transverse slots  44  into each finger  22 . The slots  44  may be milled into each finger  22  so that they extend transversely alternately from each circumferential edge of each finger  22 . Referring to  FIG. 6   a,  the slots  44  each have a thickness T 1  and they define a plurality of transverse accordion fingers  46 , each of which has a thickness T 2 . The thickness T 1  of the slots  44  and the thickness T 2  of the accordion fingers, along with the material of manufacture of the connector  40 , may be selected to provide a desired elasticity and deformability to the fingers  22 , for a given mechanical load. The slots  44  define accordion fingers  46 . 
   The slots  44  are shown more clearly in  FIG. 5 . Each slot  44  is milled only partially through the fingers  22 , so that a portion  48  is left unmilled. The portion  48  is a joining portion, which joins adjacent accordion fingers  46 . The joining portion  48  may have any suitable shape. For example, the joining portion  48  may be generally wedge-shaped, and may extend only partially through the radial depth of its associated finger  22 . This wedge shape has been found to be advantageous during the deformation and reformation of the accordion portions  42 . 
   The accordion portions  42  on the fingers  26  may be similar to those on the fingers  22 . The accordion portions  42  on the fingers  26  may be created by milled slots  44  which alternately extend from each circumferential side of each finger  26 . The thickness T 1  of the slots  44  and the thickness T 2  of the transverse accordion fingers  46  on the fingers  26  may be the same or different from those on the fingers  22 , depending on the mechanical properties of the optic fibre  13 . 
   Reference is made to  FIG. 6   b,  which shows one of the fingers  22 ,  26  in a deformed condition. In the deformed condition, the accordion portion  42  is compressed. As shown, in the deformed condition the normally parallel accordion fingers  46  contact each other, and the normally parallel side edges of the slots  44  form an angle Θ 1 . The thickness T 1  of the slots  44  determines the maximum angle Θ 1  for the accordion fingers  46 . These parameters are set based on the elastic stress limit of the material of manufacture for the connector  40  and based on the requirements of the particular installation, such as the environment in which the connector will be used. 
   In the deformed condition, the accordion portion  42  distorts the fibre conduit  20 , so that the fibre conduit  20  is divided into a plurality of segments  50  that are each at an angle Θ 2  with the longitudinal axis of the connector  40 . Because the segments  50  are kinked with respect to one another in the deformed condition, an optic fibre that is inserted into the fibre conduit  20  is gripped firmly therein by the kinked segments  50 . The configuration of the accordion portion  42  may be selected to provide any suitable angle Θ 2  so that the optic fibre  12  or  13  is gripped firmly without being damaged. The gripping action of the accordion portion  42  prevents the optic fibres  12  and  13  from being pulled apart slightly when the connector returns from a thermally expanded condition, for example, to its original rest condition, as shown in  FIG. 6   a.  By gripping the optic fibre  12  or  13  with the accordion portion when the connector  40  is in the deformed condition, it is therefore unnecessary to clamp the sheath  30  of the cable  32  or  34 , as may be required using connector  10 . 
   Reference is made to  FIG. 7 , which shows a connector assembly  60 , which is used to connect the optic fibres  12  and  13  and which incorporates connector  10  or connector  40 . The connector assembly  60  also includes a central sheath  62 , first and second end members  64  and  66 , and may include a signal transmitter  68 , and a signal receiver  70 . 
   The central sheath  62  is shown more clearly in  FIG. 8 . The central sheath  62  may be generally tubular and may have an aperture  72  at each end. Each aperture  72  is sized for receiving and holding a portion of one of the end members  64  and  66  (see  FIG. 7 ). Each aperture  72  may end at an internal shoulder  74 , which provides an abutment surface for the ends of one of the end members  64  and  66 . Each aperture  72  may include a circumferential channel  76 , which mates with a circumferential boss  78  on each of the end members  64  and  66 . 
   A pass-through  80  extends between the shoulders  74  to connect the two apertures  72 . The pass-through  80  is sized to fixedly retain one of the connectors  10  or  40  in place therein, so that one of the ends  16  and  18  of the connector  10 ,  40  extends into each of the apertures  72  (see  FIG. 7 ). 
   A pair of radial apertures  82  may extend through the central sheath  62  on a line that is at the longitudinal center of the central sheath  62 . The radial apertures  82  extend from the outer surface of the central sheath  62  to the pass-through  80 , on opposing points on the circumference of the central sheath  62 . The signal transmitter  68  and the signal receiver  70  may extend into the radial apertures  82  (see  FIG. 7 ). The signal transmitter  68  may be, for example an optic fibre that transmits a light beam. The signal receiver  70  may be any suitable type of receiver, such as another optic fibre, which is adapted to receive signals from the transmitter  68 . The receiver  70  may be connectable to amplification means or a suitable processing means (not shown), for determining whether the signal is being received. 
   Referring to  FIG. 7 , the connector  10 ,  40  may be positioned in the pass-through  80  so that the longitudinal center of the connector  10 ,  40 , which is shown at C is aligned with the apertures  82 . Furthermore, the connector  10 ,  40  may be oriented so that slots  24  or  28  align with the radial apertures  82 , so that the receiver  70  can receive signals from the transmitter  68  through the connector  10 ,  40 . At least one pair of slots  24 ,  28  may extend from its respective end  16 ,  18  past the longitudinal center of the connector  10 ,  40 , so that the receiver  70  can ‘see’ the transmitter  68 . Alternatively, the connector  10 ,  40  may have a transverse pass-through that extends transversely through the connector, along a line at the longitudinal center of the connector  10 ,  40 . 
   The end members  64  and  66  are positioned in the apertures  72  and extend outward therefrom. The end members  64  and  66  receive the ends of the cables  32  and  34  respectively. 
   The end members  64  or  66  is shown more clearly in  FIG. 9 . The end member  64  has a sheath-receiving aperture  84  at its outer end. The sheath-receiving aperture  84  receives and retains the sheath  30  of the cable  32 . The sheath-receiving aperture  84  has an internal shoulder  86 , against which the sheath  30  can abut during the connection process. The outer end of the sheath-receiving aperture  84  may be flared to reduce stresses imparted to the optic fibre  12  during bending of the cable  32  in the portion that extends outward from the end member  64 . 
   The end members  64  each have a connector-receiving aperture  88  in their respective inner ends. The connector-receiving aperture  88  is sized to receive and retain connector  10 ,  40 , and to align the connector  10 ,  40  and the end member  64  with respect to each other (see  FIG. 7 ). 
   A pass-through  90  extends between the radial center of the connector-receiving aperture  88  and the radial center of the sheath-receiving aperture  84 , permitting the optic fibre  12  to pass-through from the end of the sheath  30  to the connector  10 ,  40 . 
   End member  66  is similar to end member  64  and is for receiving and retaining the end of cable  34  in the same way that end member  64  receives and retains the end of cable  32 . 
   To connect cables  32  and  34 , or more specifically, optic fibres  12  and  13 , using the connector assembly  60 , the following steps are carried out. The connector assembly  60  may be assembled as one complete unit by any suitable means. 
   Before using the connector assembly  60 , a portion of the sheath  42  surrounding the optic fibres  12  and  13  is removed, exposing a selected length of each of the fibres  12  and  13 . The tips of the fibres  12  and  13  are cleaved by any suitable cleaving means, such as a laser, so that the same length of optic fibre is exposed on each cable  12  and  13 . Cleaving also ensures that the end faces are generally perpendicular to the longitudinal axis of the optic fibres  12  and  13 , so that they mate well together. 
   The connector assembly  60  may be heated so that the connector  10 ,  40  expands sufficiently to permit the easy insertion of the optic fibres  12  and  13  therein. The transmitter  68  and receiver  70  are activated, so that a light beam or other suitable signal, for example, is transmitted through the connector and is received at the receiver  70 . Gel may be inserted into the fibre conduit  20  of the connector, so that when the optic fibres  12  and  13  are inserted, the gel fills in any gaps at the abutment between them to prevent loss of or distortion of an optical signal being transmitted through the optic fibres. As before, the gel has substantially the same index of refraction as the optic fibres  12  and  13 . 
   The ends of the cables  32  and  34  are then inserted into the sheath receiving apertures  84  in the connector assembly  60 , until the ends of the sheaths  30  approach the internal shoulders  86 . The pass-throughs  90  guide the ends of the optic fibres  12  and  13  into the fibre conduit  20  of the connector  10 ,  40 . The optic fibres  12  and  13  are micro-advanced in the fibre conduit  20 , while verification takes place that the light beam from the transmitter  68  is not broken, and is received by the receiver  70 . Any excess gel that is in the fibre conduit  20  is gradually displaced by the advancement of the optic fibres  12  and  13 , and can seep out through the slots  24 ,  28  and possibly through slots  44 . 
   The advancement continues until the light beam is broken, indicating that the optic fibres  12  and  13  are in abutment at the longitudinal center of the connector  10 ,  40 . It will be noted that the slots  24 ,  28  or any pass-through aperture on the connector  10 ,  40  for the light beam may be sized large enough to accommodate some degree of off-centeredness in the abutment of the ends of the optic fibres  12  and  13 . 
   Once the abutment is achieved, the connector assembly  60  is cooled, to return the connector  10 ,  40  to its original size. If connector  10  is used in the assembly  60 , then the sheaths  30  of the cables  32  and  34  are clamped to ensure that the optic fibres  12  and  13  are not pushed away from each other during the cooling of the connector assembly  60 . 
   If the connector  40  is used in the assembly  60 , then clamping of the sheaths  30  is not required. The connector  40  can be compressed slightly by mechanical or other suitable means, so that the accordion portions  42  grip the optic fibres  12  and  13 , while ensuring that the ends of the optic fibres  12  and  13  remain abutted against one another. 
   Once the connector assembly  60  is cooled, the end members  64  and  66  are fixedly joined to the cables  32  and  34  respectively, for example, by a crimping tool, to crimp a sleeve portion  92  of the end members  62  and  64  to the sheath  30  of the cables  32  and  34 . 
   The connectors  10 ,  40  in accordance with the present invention, may offer one or more of the following advantages, when used to connect optic fibres. For example, one optional advantage is that the connectors  10 ,  40  facilitate achieving a tight alignment of two optic fibres, whereby the ends of the fibres are aligned with each other and are held in centred, face-to-face abutment with each other. Another optional advantage is that the connectors  10 ,  40  of the present invention maintain a compressive force pushing the optic fibres towards each other. This reduces the air gap between the ends of the fibres, which can occur with other joining means of the prior art. Yet another optional advantage of the connectors  10 ,  40  is that they exert a clamping force at each end to firmly hold the fibres together. In particular, the connector  40  can produce a greater clamping force than the connector  10 . 
   Reference is made to  FIG. 10 , which illustrates the stress distribution that exists in the connector  10  upon receiving a pair of optic fibres therein (not shown). While the stress distribution in the connector  10  is, in fact, non-discrete,  FIG. 10  shows discrete regions having ranges of stresses, to illustrate generally the stress distribution. Areas of relatively lower stresses are shown at  94 . Regions of relatively greater stress are shown at  96 . Regions of greatest stress are shown at  98 . It can be seen from  FIG. 10  that the the stress varies along the length of the connector  10 . The stress that occurs in the connector  10  when fibres are inserted therein, depends on the number and position of the slots  24  and  28 . 
   The variable progression of stress along the length of the connector  10  allows a sequence of alignment, compression and clamping to be exerted on the optic fibres. When the fibres are first inserted into the connector  10 , the ends of the fibres are maintained in alignment with each other by virtue of the size of the fibre conduit  20  in the region of the connector  10  where the ends of the fibres meet. Once the external forces that hold the connector  10  in the open position are removed, the connector  10  is permitted to relax around the fibres. As the connector relaxes, the connector  10  imparts a longitudinally compressive force on the fibres, pushing the ends of the fibres together. Furthermore, during the relaxing of the connector  10 , the ends  16  and  18  of the connector  10  apply a clamping force to the fibres to retain the fibres in position and in compression against each other. The compression and the clamping forces on the fibres will be at least in part controlled by the size, the number and the position of the slots  24  and  28 . The connector  10  is configured so that these forces are low enough to prevent damage to the fibres. 
   It will be appreciated that the above description regarding the stress distribution and the sequence of operations whereby the optic fibres are aligned, compressed and clamped applies generally to the connector  40  ( FIG. 4 ). In other words, the connector  40  incurs increased stresses proximate its ends when holding fibres. The compression and clamping that occurs on the fibres however, is enhanced with the connector  40 , relative to the connector  10 , because of the presence of the accordion portions  42 . 
   While the above description constitutes the preferred embodiments, it will be appreciated that the present invention is susceptible to modification and change without departing from the fair meaning of the accompanying claims.