Abstract:
A method and apparatus for securing an optical fiber to a structure and an appropriate strain relief boot to the optical fiber as well as to the structure is disclosed. A channel is formed proximate to an opening in a wall surface of the structure. The fiber is inserted into a passage in a compressible ferrule sized to accommodate the fiber and having a lip around its body and a strain relief boot is slid over one longitudinal end of the fiber to cover the lip. The ferrule and boot are inserted into a channel sized to accommodate the ferrule in a friction fit. The ferrule is cylindrical in shape and has one or more passages through it, aligned along the longitudinal axis of the cylinder. A slot extends the length of the ferrule between its outer surface and a passage proximate thereto. Slots may interconnect passages. The diameter along which the slots extend terminate in notches which narrow the ferrule width along this direction. A key is formed on the outer surface of the ferrule to mate with a keyway in the channel and secure the ferrule to the channel. The channel is U-shaped and has a width greater than the cylinder&#39;s narrow dimension but less than its wide dimension. If the ferrule is inserted so that its narrow dimension extends between the ends of the channel, no compressive force is applied and the fiber is free to move relative to the ferrule. If the ferrule is inserted in a direction normal to this, the channel applies compressive force, shrinking the passage diameter and applying a uniform compressive force to the fiber, securing it to the ferrule. At the same time, the lip on the ferrule cooperates with the channel to clamp the boot to the fiber. The ferrule may be enclosed between the channel and a retaining member to ensure uniform clamping pressure on the boot.

Description:
CROSS-REFERENCE TO PRIOR APPLICATIONS  
       [0001]    This application claims priority from U.S. Provisional Application No. 60/317,130 of the same title filed Sep. 6, 2001 by Trillium Photonics Inc. and naming Lowe et al. as inventors. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to optical communications systems and in particular to an improved strain relief and locking apparatus for attaching optical fibers to a structure.  
         BACKGROUND OF THE INVENTION  
         [0003]    Optical fibers are used as a medium for light transmission in optical communications. The optical characteristics of these fibers are dramatically affected by mechanical stresses imparted by bending, pulling and/or twisting the fibers. Such stresses can be introduced when fibers are not properly retained and strain relieved when entering and exiting a structure, such as a wall of an optical component, module or enclosure, or through a faceplate.  
           [0004]    It is known to apply adhesives over the outer fiber jacket and strain relief boot in order to bond them directly to the wall of the structure. However, the constrained space in which the fiber is situated makes it difficult to properly apply the adhesive. Moreover, in the application process, the fiber is frequently subjected to increased mechanical stresses, such as bending, twisting and stretching of the fiber. Such stresses, introduced during the application and curing of the adhesive, will remain and affect both the short term and long term optical performance of the fiber.  
           [0005]    Additionally, if the adhesive is improperly applied or not permitted to fully cure, the fiber will be inadequately retained. The effectiveness of the adhesive used is reduced by changes in both temperature and humidity. Thus, the use of adhesives may not be conducive to some applications.  
           [0006]    Furthermore, once the adhesive is applied and cured, it is very difficult to remove the fiber and its strain relief boot from the structure. It is common in both the development and manufacturing process and during operation, to remove and re-attach the fibers from time to time. If adhesive has been applied, the fiber must be cut beyond the applied adhesive, re-spliced and then attached to the structure anew. Beyond the inconvenience and effort entailed in removing the adhesive and the discarded portions of the fiber from the structure, it is not trivial to re-splice the fiber, and re-attaching the fiber in this manner reduces the length of the fiber available. This process in turn may introduce additional mechanical stress in the fiber.  
           [0007]    Other approaches have attempted to provide a removable connection mechanism. These approaches typically make use of a threaded connection mechanism which can be tightened to apply pressure on the fiber and thus lock it in place and loosened in order to permit repositioning of the fiber as required. However, such approaches suffer from a number of disadvantages.  
           [0008]    First, as the connection mechanism is being tightened about the fiber, it begins to come into frictional engagement with the fiber. After this point, as the connection mechanism continues to be turned to further tighten the connection, the fiber undergoes torsional stresses in the direction of rotation of the connection mechanism. Torsional stresses are generally to be avoided in optical communications systems because they increase the likelihood of crack formation and introduce unacceptable degradation of the optical performance of the fiber.  
           [0009]    Second, when the connection mechanism is subsequently loosened, by turning the connection mechanism in the opposite direction, the fiber undergoes torsional stresses in the opposite direction. The stresses introduced by the tightening and the loosening of the connection mechanism tend to accumulate rather than cancel out.  
           [0010]    Third, the connection mechanisms used in such applications tend to provide contact with the fiber only at a localized region along the longitudinal length of the connection mechanism. As pressure is applied at this localized region, the pressure will cause localized deformation of the fiber and consequent performance degradation. Moreover, if there is any bending or twisting of the cable, the fiber may break at the pressure point.  
           [0011]    Thus, it is difficult, if not impossible, to adjust the connection mechanism while the fiber is operational, in order to ensure that the optical performance is not degraded by the use of the connection mechanism.  
           [0012]    In U.S. Pat. No. 6,142,679 entitled “Connection mechanism for Optical Waveguides” issued Nov. 7, 2000 to Bredthauer et al., a removable waveguide connection mechanism is disclosed comprising a complicated structure designed to avoid the introduction of torsional stresses. However, the connection mechanism contains a large number of interlocking parts in order to effect this result. The connection mechanism is accordingly relatively long, which limits its applicability in small footprint applications, and introduces the possibility of fiber breakage where the fiber exits the connection mechanism at either end.  
           [0013]    Furthermore, while technically removable, the Bredthauer connection mechanism requires that the outer jacket and the intermediate insulation be removed from the fiber. The removal of the jacket is irreversible, and does not permit the fiber to be repositioned longitudinally.  
           [0014]    Additionally, the process of removing the outer jacket of the fiber may introduce stress or even breakage in the fiber.  
           [0015]    In U.S. Pat. No. 6,072,931 entitled “Fiber Amplifier Packaging Apparatus” and issued on Jun. 6, 2000 to Yoon et al., there is disclosed a locking apparatus for attaching a fiber to a structure. The structure has a rectangular slot through which the apparatus passes. The external surface of a longitudinal portion of the apparatus is flattened in order to engage the slot and prevent twisting of the fiber. The flat surface of the apparatus is bounded by circular stoppers of a diameter greater than the width of the slot to prevent the fiber from extending too far in either longitudinal direction beyond the structure.  
           [0016]    While the locking apparatus itself is removable from the structure, a portion of the outer jacket of the fiber itself must be removed in order to fit the apparatus onto the fiber, with sufficient friction to grip the fiber.  
           [0017]    In addition to the problems discussed above inherent in the removal of the jacket, when the apparatus is fitted onto the optical fiber, the fiber may be unduly stressed or even break. Of greater concern, positioning the apparatus in a friction fit about the fiber may introduce unpredictable and uneven stresses on the fiber, especially with the jacket removed, that would adversely impact the optical performance of the fiber.  
           [0018]    In U.S. Pat. No. 5,742,719 entitled “Fastening Device for Light Waveguides” issued Apr. 21, 1998 to Birnbaum, there is disclosed a cuboid fastening device capable of fastening and providing strain relief of two fibers. The fibers are introduced into one of two longitudinal bores extending along the length of a base member proximate to the side walls of the base member. A transverse slot is provided for at least a portion of the length of the bore extending to the side wall. A clamp member engages a clamp rail at the side wall to form a frictional lock on the fiber within the bore. A retainer plate is inserted into a retainer slot extending parallel to one of the end faces. Slots in the plate correspond to the fibers within the bores and have a diameter to tightly engage the fibers. The plate is keyed to engage the base member, but, with effort, may be subsequently released.  
           [0019]    However, the Birnbaum device requires, in addition to the base member, two clamps and a retaining plate, all of which are small loose components and prone to be dropped or misplaced. Further, in order to fix the fastening device to a structure, the fastening device must be inserted into a socket plug housing or a pin connection mechanism housing. Moreover, the interaction of the clamp member and the clamp rail, as well as the engagement of the slots in the retainer plate with the fiber apply pressure on the fiber at localized points and not along the length of the bore. Still further, the jacket and the first covering must be removed from the fiber ends in order to engage centering sleeves or projections that extend from the distal end surface and provide an extension for each of the bores.  
           [0020]    In U.S. Pat. No. 5,146,532 entitled “Optical Fiber Retention Device” issued Sep. 8, 1992 to Hodge, there is disclosed a stackable resilient strip member having one or more generally U-shaped channels disposed transversely along one surface of the strip between a pair of keyways. These channels support individual optical fibers in a common plane. The opposing surface of the strip is generally planar, but has resilient keys adapted to engage the keyways of a second identical strip member. The planar surface provides some frictional engagement of the optical fibers.  
           [0021]    While the strip members are nominally removable, the wedge-shaped keys that connect the strip members do not admit of easy separation. Moreover, the pressure applied by the planar surface of the strip member will not be uniform across all of the connection mechanisms. Further, the pressure is applied only to one side of the connection mechanism, by the planar surface, thus introducing a distortion across the cross-section of the fiber. Finally, a delicate trade-off must be made between the depth of the U-shaped channels and the resiliency of the underlying material in order to provide sufficient pressure to fix the position of the fiber relative to the strip member. Therefore, this approach is not easily adaptable to fibers of differing dimension.  
           [0022]    The introduction of a strain relief boot at the point of exit of a fiber from an optical connection mechanism is also well known. Typically, the strain relief boot is elongated and exteriorly tapered and slips over the rear end portion of the connection mechanism. The prior art in respect of strain relief boots is canvassed in U.S. Pat. No. 5,915,056 entitled “Optical Fiber Strain Relief Device” issued Jun. 22, 1999 to Bradley et al. Typical strain relief boot installations merely provide strain relief in the lateral direction only.  
           [0023]    There are a number of methods of affixing the strain relief boot to the connection mechanism. For instance, the boot may be cemented to the cap. The former approach requires the handling of adhesives with the problems hereinbefore described.  
           [0024]    Alternatively, the boot may be tapered at the end proximal to the connection mechanism and slid under the connection mechanism. The proximal end of the connection mechanism terminates in a series of lips or ridges which engage shoulders within the connection mechanism to fix the boot to the connection mechanism. This approach is relatively permanent as the connection mechanism is not easily removed. Moreover, it requires a degree of customization between the strain relief boot and the connection mechanism to be used, in order that the boot may slide under the connection mechanism already in place.  
         SUMMARY OF THE INVENTION  
         [0025]    Accordingly, it is desirable to provide an improved removable fiber strain relief and locking apparatus.  
           [0026]    It is also desirable to provide a locking apparatus with a minimum of separate parts.  
           [0027]    It is further desirable to provide such an apparatus that does not require removal of any part of the first covering of the optical fiber.  
           [0028]    It is still further desirable to provide a locking apparatus that applies pressure uniformly about both the cross-sectional and longitudinal extent of the fiber so as not to introduce any degradation of the optical performance of the fiber.  
           [0029]    It is also desirable to permit the adjustment of the fiber relative to the structure while the fiber is operational, in order to permit the fiber to be adjusted to suit a designed length without degradation to the fiber.  
           [0030]    Moreover, it is desirable to provide a mechanism for easily and removably affixing a strain relief boot to the structure.  
           [0031]    The present invention accomplishes these aims by providing a method and apparatus for securing an optical fiber to a structure and an appropriate strain relief boot to the optical fiber as well as to the structure. A channel is formed proximate to an opening in a wall surface of the structure. The fiber is inserted into a passage in a compressible ferrule sized to accommodate the fiber and having a lip around its body and a strain relief boot is slid over one longitudinal end of the fiber to cover the lip. The ferrule and boot are inserted into a channel sized to accommodate the ferrule in a friction fit. The ferrule is cylindrical in shape and has one or more passages through it, aligned along the longitudinal axis of the cylinder. A slot extends the length of the ferrule between its outer surface and a passage proximate thereto. Slots may interconnect passages. The diameter along which the slots extend terminate in notches which narrow the ferrule width along this direction. A key is formed on the outer surface of the ferrule to mate with a keyway in the channel and secure the ferrule to the channel. The channel is U-shaped and has a width greater than the cylinder&#39;s narrow dimension but less than its wide dimension. If the ferrule is inserted so that its narrow dimension extends between the ends of the channel, no compressive force is applied and the fiber is free to move relative to the ferrule. If the ferrule is inserted in a direction normal to this, the channel applies compressive force, shrinking the passage diameter and applying a uniform compressive force to the fiber, securing it to the ferrule. At the same time, the lip on the ferrule cooperates with the channel to clamp the boot to the fiber. The ferrule may be enclosed between the channel and a retaining member to ensure uniform clamping pressure on the boot.  
           [0032]    According to a broad aspect of the present invention, there is disclosed a ferrule comprising: a compressible body; and at least one passage through the body sized to accommodate a fiber; whereby when a fiber is placed inside the at least one passage and pressure is exerted on the body, the body is compressed, causing the diameter of the at least one passage to decrease uniformly along its length and consequently friction to be uniformly applied to the fiber.  
           [0033]    According to a second broad aspect of the present invention, there is disclosed a ferrule comprising: a body; and a lip integrally formed around the body and adapted to cooperate with a channel in a friction fit; whereby when a boot is slid longitudinally over one end of the apparatus to cover the lip and the apparatus is inserted into a channel, the channel and the lip secure the boot to the apparatus.  
           [0034]    According to a third broad aspect of the present invention, there is disclosed a channel sized to accommodate a compressible body in a friction fit, whereby when a compressible body having at least one passage sized to accommodate a fiber and containing a fiber is inserted into the channel, the channel compresses the body uniformly along the length of the body and causes friction to be uniformly applied by the body to the fiber.  
           [0035]    According to a fourth broad aspect of the present invention, there is disclosed a channel, adapted to accommodate a body having a lip therearound in a friction fit, whereby when a boot is slid longitudinally over one end of the body to cover the lip and inserted into the channel, the channel and the lip secure the boot to the body.  
           [0036]    According to a fifth broad aspect of the present invention, there is disclosed a retaining member adapted to accommodate a body having a lip therearound, whereby when a boot is slid longitudinally over one end of the body to cover the lip and the retaining member is placed over the body, the retaining member and the lip secure the boot to the body.  
           [0037]    According to a sixth broad aspect of the present invention, there is disclosed a fiber locking apparatus comprising: a ferrule having a compressible body and at least one passage through the body sized to accommodate a fiber; a structure having a wall surface; and a channel adapted for fixation to the wall surface and adapted to accept the ferrule in a friction fit; whereby, when the ferrule is inserted into the channel with a fiber extending through its at least one passage, the channel compresses the body, causing the diameter of the at least one passage to decrease uniformly along the length of the passage and uniformly apply pressure on the fiber, thereby securing it to the structure.  
           [0038]    According to a seventh broad aspect of the present invention, there is disclosed a boot attachment apparatus comprising: a boot; a ferrule having a body and a lip formed around the body; a structure having a wall surface; and a channel adapted for fixation to the wall surface and adapted to accept the ferrule in a friction fit; whereby, when the boot is slid longitudinally over one end of the ferrule and inserted into the channel, the channel and the lip secure the boot to the ferrule and to the structure.  
           [0039]    According to an eighth broad aspect of the present invention, there is disclosed a method of securing a fiber to a structure, comprising the steps of: forming a channel proximate to an opening in a wall surface of the structure; inserting the fiber into a passage in a compressible ferrule sized to accommodate the fiber and adapted to be accepted by the channel in a friction fit; placing the ferrule within the channel; whereby, the channel compresses the body, causing the diameter of the at least one passage to uniformly decrease and apply uniform pressure on the fiber, thereby securing it to the structure.  
           [0040]    According to a ninth broad aspect of the present invention, there is disclosed a method of securing a boot to a fiber, comprising the steps of: inserting the fiber into a passage in a ferrule sized to accommodate the fiber, the ferrule having a lip formed around its body; placing the ferrule within the channel; sliding a boot longitudinally over one end of the ferrule to cover the lip; and inserting the ferrule and boot into a channel adapted to accept the ferrule in a friction fit; whereby the channel and the lip secure the boot to the ferrule. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]    The embodiments of the present invention will now be described by reference to the following figures, in which identical reference numerals in different figures indicate identical elements and in which:  
         [0042]    [0042]FIG. 1 is an exploded isometric view of a removable fiber strain relief and locking apparatus in accordance with an embodiment of the present invention;  
         [0043]    [0043]FIG. 2 is an isometric view of the ferrule of the embodiment of FIG. 1;  
         [0044]    [0044]FIG. 3 is an isometric view of the ferrule and retaining member of the embodiment of FIG. 1;  
         [0045]    [0045]FIG. 4 is an exploded isometric view of an apparatus in accordance with a second embodiment of the present invention;  
         [0046]    [0046]FIG. 5 is an isometric view of the ferrule and the retaining member of the embodiment of FIG. 4;  
         [0047]    [0047]FIG. 6 is a partially exploded isometric view of the apparatus of the embodiment of FIG. 1 when assembled but in the unlocked position;  
         [0048]    [0048]FIG. 7 is a partially exploded isometric view of the apparatus of the embodiment of FIG. 1 when assembled but in the locked position;  
         [0049]    [0049]FIG. 8 is a sectional view of the apparatus of the embodiment of FIG. 1 when assembled; and  
         [0050]    [0050]FIG. 9 is an isometric view of a ferrule in accordance with a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0051]    Referring now to FIG. 1, there is shown a structure  160 , to which a optical fiber  110  is to be attached, by an apparatus, shown generally at  100 .  
         [0052]    In the embodiment of FIG. 1, the structure  160  is the bottom portion of an enclosure for an optical system, module or component (not shown). The enclosure may be completed by a fitted cover  165  which can be fixed to the structure  160 , by means of fasteners in known fashion.  
         [0053]    Alternatively, the structure  160  may comprise a faceplate through which the optical fiber  110  is to pass and to which it is to be attached as shown in FIG. 4.  
         [0054]    The apparatus  100  comprises a ferrule  120 , a channel  130 , a strain relief boot  140  and a retaining member  150 .  
         [0055]    The optical fiber  110  typically comprises successive cylindrical layers commencing at the interior with a glass or plastic fiber and terminating at the exterior with an outer jacket, typically of a polymer material. Between the jacket and the central glass fiber may be disposed one or more layers of covering, cladding, and/or insulation. The intermediate layers of covering, cladding and/or insulation are selected for their protective and/or optical properties and may comprise any number of materials, including Kevlar™. The intermediate layers may be designed to compress slightly and absorb stresses that would otherwise be imposed upon the central fiber. The jacket is intended to contain the intermediate layers and to protect the central glass fiber from injury. The outer diameter of the optical fiber  110  in this embodiment is 900 μm. However, those skilled in this art will recognize that the optical fiber  110  may generally be of any diameter.  
         [0056]    As best viewed in FIG. 2, the ferrule  120  is substantially cylindrical in shape. In the embodiment of FIG. 1, the ferrule  120  comprises first and second coaxial cylindrical portions  210 ,  220 , having different diameters, disposed end to end. The second portion  220  is shown as having a larger cross-section than the first cylindrical portion  210 . However, those skilled in this art will recognize that the ferrule  120  could equally comprise a single cylindrical portion.  
         [0057]    The ferrule  120  is composed of a resilient material that has excellent flexural properties and is preferably composed of a non-flammable material, such as PEEK. It will be recognized that other suitable materials may include machined aluminum and other plastics.  
         [0058]    In the present embodiment, for use with a single 900 μm (0.0354″) outer diameter jacketed optical fiber, a suitable diameter of the first cylindrical section  210  is 0.150″. A suitable diameter of the second cylindrical section  220  is 0.200″.  
         [0059]    A central bore  240  or passage extends coaxially through the first and second cylindrical portions  210 ,  220 . The bore  240  is of sufficient diameter to accept the optical fiber  110  without frictional contact. In the present embodiment, a bore diameter of 0.036″ is suitable.  
         [0060]    A first rectangularly shaped notch  260  extends along the length of the ferrule  120  and radially inward from the surface of the ferrule  120 . The depth of the first notch  260  varies along the length of the ferrule  120  such that the depth of the material  265  remaining between the first notch  260  and the bore  240  remains constant along the length of the ferrule  120 . A suitable depth of the material  265  remaining between the first notch  260  and the bore  240 , at its narrowest, is 0.020″. A suitable width of the first notch  260  may be 0.063″.  
         [0061]    A slot  250  extends radially outward from the bore  240  along the length of the ferrule  120  to the surface of the ferrule  120  where it terminates in a second notch  270 . The width of the slot  250  is sufficient so that when the extremities  251 ,  252  of the slot  250  are pinched together, the diameter of the bore  240  will be sufficiently reduced to firmly grip the optical fiber  110 . In the present embodiment, a suitable width of the slot  250  is 0.024″. A suitable width of the second notch may also be 0.063″. When the extremities  251 ,  252  are pinched together, the bore  240  is reduced in diameter to 0.023″.  
         [0062]    As a result of the removal of the material in the notches  260 ,  270 , the width of the ferrule, measured across diameter b is slightly less than the width of the ferrule measured along diameter a. In the present embodiment, the difference in width, measured at the end of the second cylindrical portion  220 , amounts to 0.020″.  
         [0063]    The material  265  remaining between the bore  240  and the first notch  260  is sufficiently thin that the extremities  251 ,  252  of the slot  250  may be pinched together with a minimum of force. At the same time, the remaining material  265  is sufficiently thick so as to permit the ferrule  120  to return to its original shape once the applied force is removed.  
         [0064]    A cylindrical key  230  extends transversely about the outer surface of the second cylindrical portion  220  at an intermediate point along its length, without overlapping either of the two notches  260 ,  270 . Suitable dimensions for the key  230  may be a diameter of 0.229″ and a depth of 0.045″.  
         [0065]    A cylindrical lip  280  extends transversely about the outer surface of the first cylindrical portion  210  at an intermediate point along its length, without overlapping either of the two notches  260 ,  270 . The lip  280  is of such a diameter as to readily accept the larger end of the strain relief boot  140  discussed below. A suitable diameter is 0.166″.  
         [0066]    Referring once again to FIG. 1, the channel  130  is a U-shaped channel that is integral to or is fixed to the structure  160  to which the fiber  110  is to be connected.  
         [0067]    The width of the channel  130  is greater than the width of the second cylindrical portion  220  along direction b but less than the width of the second cylindrical portion  220  along direction a. The channel  130  is sufficiently deep to accept substantially all of the ferrule  120 . In the present embodiment, a channel width of 0.202″ and a depth at its deepest of 0.301″ are suitable.  
         [0068]    The channel  130  has a semicylindrical keyway  135  disposed transversely of its length and adapted to accept the key  230  of the ferrule  120 .  
         [0069]    Accordingly, the channel  130  is adapted so that the ferrule  120  may be seated within it without the application of force when oriented so that the notches  260 ,  270  are roughly perpendicular to the axis  600  bisecting the channel  130 , as shown in FIG. 6.  
         [0070]    On the other hand, if the ferrule  120  is oriented so that the notches  260 ,  270  are bisected by the axis  600  bisecting the channel  130 , as shown in greater detail in FIGS. 1 and 7, the ferrule  120  will engage the channel  130  in a tight friction fit.  
         [0071]    The channel  130  may be oriented in any direction transverse to the surface of the structure  160 , however preferably the channel  130  is positioned obliquely with respect to the surface of the structure  160  as shown in FIG. 1 as angle α. A suitable value for angle α is 30°.  
         [0072]    Additionally, the channel  130  is positioned relative to the structure  160 , such that the cylindrical lip  280  of the ferrule  120 , when inserted into the channel  130 , lies proximate to but does not extend beyond the surface  161  of the structure  160  from which the first cylindrical portion  210  protrudes. Where the structure  160  forms part of an enclosure, the surface  161  is the outer surface of the enclosure.  
         [0073]    The strain relief boot  140  is roughly funnel-shaped. It has a bore of varying diameter passing entirely through its centre and is adapted to loosely fit over the first cylindrical portion  210  and the cylindrical lip  280 . The boot  140  is composed of a resilient material, for example, a thermoplastic elastomer, and which also has a V-0 (UL94) flammability rating.  
         [0074]    Suitable strain relief boots, such as model no. HW-20013-02 manufactured by Fotelco are also suitable for use in the present invention.  
         [0075]    The retaining member  150  comprises a shaped member  155  which is integral to or fixed to the structure  160  to which the fiber  110  is to be connected.  
         [0076]    As shown in FIG. 1, the structure  160  is the bottom portion of an enclosure for an optical communications component or module and the channel  130  lies immediately below the edge of the structure  160  against which the cover  165  will be positioned and fixed. In this embodiment, the retaining member  150  may be integral to the enclosure cover  165 , as also shown in FIG. 1 and shown in detail in FIG. 3.  
         [0077]    The retaining device  150  is oriented in the same direction a as the channel  130 . The profile of the retaining device  150  is adapted to mate with the channel  130  and key  230  on ferrule  120 . The profile of the retaining device  150  includes a curved surface that is adapted to tightly mate with the compliant strain relief boot  140  that is inserted over the cylindrical lip  280  of the ferrule  120 .  
         [0078]    In operation, the optical fiber  110  is inserted into the bore  240  of the ferrule  120 . The ferrule  120  is oriented with respect to the fiber  110  such that the first cylindrical portion  210  of the ferrule  120  is facing that portion of the fiber  110  that will protrude beyond the surface  161  of the structure  160  when the apparatus is attached to the structure.  
         [0079]    The strain relief boot  140  is thereafter fitted over the cylindrical lip  280  and the first cylindrical portion  210  of the ferrule  120 . The strain relief boot  140  may only protrude over the ferrule  120  to a limited extent, stopped by the wall of the key  230 , as shown in cross-section in FIG. 8.  
         [0080]    The ferrule  120  and the strain relief boot  140  are then inserted into the channel  130  so that direction a is parallel to the axis  600  bisecting the channel  130 , and with the key  230  lying within the keyway  135  of the channel  130 .  
         [0081]    In this position, shown in FIG. 6, the ferrule  120  lies loosely within the channel  130 , so that the channel  130  applies no compressive force on the ferrule  120 . The ferrule  120  is prevented from movement longitudinally with respect to the channel  130  because of the interlocking of the ferrule&#39;s key  230  and the channel&#39;s keyway  135 . Nevertheless, the fiber  110  remains relatively free within the ferrule  120  to move longitudinally in either direction. Thus, the position of the apparatus as shown in FIG. 6 is considered to be unlocked.  
         [0082]    While in this position, the fiber  110  can be longitudinally adjusted with the apparatus  100  in place to ensure that there is a sufficient length of fiber  110  on either side of the structure  160  to meet the requirements of the application for which the fiber  110  is used.  
         [0083]    The loose fit of the ferrule  120  in the channel  130  while unlocked permits adjustments to be conveniently made without having to hold the fiber  110  in position.  
         [0084]    Once such longitudinal adjustments to the position of the fiber  110  have been made, the ferrule  120  and the strain relief boot  140 , if in place, are removed from the channel  130 . The ferrule  120  is rotated 90° so that the slot  250  is positioned parallel to the axis of the channel  130  and facing the closed end of the channel  130 . While the ferrule  120  is being rotated, the fiber  110  typically is not rotated, so as to avoid a torsional stress being imposed on the fiber  110 .  
         [0085]    The ferrule  120 , while in this rotated or locked position, together with the fiber  110  and the strain relief boot  140 , are reinserted into the channel  130 , as shown in FIG. 7. In this orientation, the width of the ferrule  120  is slightly greater than the width of the channel  130 . Accordingly, a slight force is required to push the ferrule  120  completely into the channel  130 .  
         [0086]    The amount of force required to insert the ferrule  120  into the channel  130  in the locked position is minimized by a suitable choice of material for the ferrule  120  and by the presence of the notches  260 ,  270 . The notch  260  serves to remove material from the ferrule  120  on the side of the bore  240  opposite the slot  250 , so that less force is required to insert the ferrule  120  into the channel  130 .  
         [0087]    The curved profile of the ferrule  120  and the second notch  270  also serve to minimize the required insertion force.  
         [0088]    This insertion force imposes a slight compressive force on the ferrule  120  where it comes into contact with the channel, forcing the ends  251 ,  252  of the slot  250  to approach each other and the slot  250  to narrow in width substantially uniformly along its length. Accordingly, the ferrule  120  is placed in a friction fit with the channel  130  and cannot be easily removed.  
         [0089]    Indeed, in order to permit the ferrule  120  to be more easily removed from the channel  130  when in the locked position, a small removal bore  162  may extend from the surface  161  of the structure  160  to the bottom of the channel  130 . The removal bore  162  may be conveniently situated in the bottom of the keyway  135 . When the ferrule  120  must be removed, a tool  163  may be inserted into the removal bore  162  to push the ferrule  120  out of the channel  130 .  
         [0090]    Furthermore, the compression of the slot  250  causes the diameter of the bore  240  to reduce slightly and to grip the fiber  110  with a uniform pressure longitudinally along the length of the ferrule  120  and axially about the fiber  110  in a friction fit. The friction fit prevents the fiber  110  from thereafter being moved longitudinally with respect to the ferrule  120 , and by extension, the structure  160 .  
         [0091]    The uniformity of the pressure applied by the ferrule  120  on the fiber  110  minimizes the possibility of breakage of the fiber  110 . It also reduces the likelihood degradation in optical performance of the fiber  110 .  
         [0092]    The removability of the ferrule  120  means that, if the optical performance of the fiber  110  is monitored during the installation process and if any degradation is observed, the ferrule  120  can be removed, as discussed above, the fiber  110  adjusted and the ferrule  120  reinserted.  
         [0093]    The interaction of the channel  130  with the ferrule  120 , whether in the locked or unlocked position, also serves to pinch a portion of the strain relief boot  140  between the cylindrical lip  280  of the ferrule  120  and the channel  130 . Thus, the strain relief boot  140  is temporarily fixed in place to varying degrees. However, the strain relief boot  140  is easily removed from between the cylindrical lip  280  of the ferrule  120  and the channel  130 , whether or not the ferrule  120  is lifted from the channel  130 . Thus the adjustment of the strain relief boot  140  may be performed independently from adjustment of the fiber  110 .  
         [0094]    When the fiber  110  is satisfactorily attached to the structure  160  by means of the interaction of the ferrule  120  in the locked position and the channel  130 , the retaining member  150  is applied to the channel  130 . Where, as shown in FIG. 3, the retaining member  150  is integral with the cover  165  of the structure  160 , this is accomplished merely by fastening the cover  165  to the enclosure by known means.  
         [0095]    It is not until the retaining member  150  is attached to the channel  130 , that the strain relief boot  140  is firmly attached to the ferrule  120 , and thus, the structure  160 . When the retaining member  150  is attached, it pinches the rest of the strain relief boot  140  that is in contact with the cylindrical lip  280  of the ferrule and applies uniform pressure around the circumference of the strain relief boot  140  where it comes into contact with the cylindrical lip  280  of the ferrule. As shown in FIG. 8, the tight engagement between the retaining member  150 , the strain relief boot  140 , the cylindrical lip  280  and the channel  130  fixes the strain relief boot  140  in relation to the ferrule  120 , and by extension, to the fiber  110  and to the structure  160 .  
         [0096]    In conjunction with the oblique orientation of the channel  130  relative to the surface  161  of the structure, the strain relief boot  140  thereafter acts to protect the fiber  110  from severe bending.  
         [0097]    As shown in FIG. 1, the channel  130  lies immediately below the edge of the structure  160  against which the cover  165  will be positioned. Alternatively, as shown in FIG. 4, the channel  410  may constitute an opening in the structure  160  that is sufficiently large to accept the cross-section of the first cylindrical portion  210  but smaller than the cross-section of the key  230 . The channel  410  may be integral with or attached to the structure  160  by machine screws or other known fastening means.  
         [0098]    The channel  410  will not have a keyway  135 . Rather, the channel  410  and the key  230  will cooperate to prevent the ferrule  120  from moving forward through the opening  400  in the structure  160 . The interaction of the channel  410  and the retaining member  500 , discussed below, will prevent the ferrule  120  from moving backward away from the structure  160 .  
         [0099]    In this alternative embodiment, the retaining member  500  will be a discrete component for attachment to the structure  160  immediately above the channel  410 , as shown in FIG. 5. The retaining member  500  may also be used in conjunction with the channel  130  of the first embodiment as an alternative to integrally molding the retaining member  150  into the cover  165 , although of slightly different configuration.  
         [0100]    Those having ordinary skill in this art will also readily appreciate that the apparatus  100  can accept a plurality (two or more) of fibers  110 . As shown in FIG. 9, the ferrule  800  may have a plurality of bores or passages  240 ,  810 ,  820 . These bores are disposed longitudinally through the ferrule  800 , between the first and second notches  260 ,  270 . The bores  240 ,  810 ,  820  are separated by slots  830 ,  840 . The slots extend along the diameter extending in direction b of the ferrule  800 .  
         [0101]    Additionally, a partial slit  850  extends between the bore  810  approximate to the second notch  270 , but only along a portion of the length of the ferrule  800 , starting from the extremity of the second cylindrical portion  220 . The partial slit  850 , the slots between the bores  240 ,  810 ,  820  are chosen to ensure relative uniformity of gripping pressure on the fibers  110  passing through the bores  240 ,  810 ,  820 .  
         [0102]    The use of a single ferrule  800  to attach a plurality of fibers  110  is advantageous as an objective of many optical components is to minimize the footprint of the device. Using a multi-fiber ferrule  800  permits the structure  160  to be smaller, because fewer channels  130  must be provided in the structure  160 . Additionally, the device can be manufactured at a lower cost because the cost of preparing the channels  130  and the retaining devices will be correspondingly reduced, without increasing the cost of the ferrule  800  appreciably or at all. As well, fewer strain relief boots  140  will be required. A slight saving on installation of the fibers  110  may also be realized in such an application.  
         [0103]    The number of bores  240 ,  810 ,  820  that may be added to a ferrule  800  will be limited by a number of factors. First, the overall dimensions of the ferrule  800 , and the corresponding dimensions of the channel  130  and the retaining member  150  will only permit a limited number of bores  240 ,  810 ,  820 . Second, the ability of the ferrule  800  to apply sufficient gripping force on the fibers  110  and the strain relief boot  140 , will be affected by the number of bores  240 ,  810 ,  820 . Third, the smaller footprint may restrict an installer&#39;s ability to position fibers  110  in a confined space within the structure without risk of fiber breakage or degradation in optical performance.  
         [0104]    Experimentation has demonstrated that a ferrule  800  with two or three bores  240 ,  810 ,  820  (i.e. two or three fibers  110  per ferrule  800 ) can be easily implemented. Nevertheless, the upper limit on the number of bores  240 ,  810 ,  820  has not been determined to date.  
         [0105]    It will be apparent to those skilled in this art that various modifications and variations may be made to the embodiments disclosed herein, consistent with the present invention, without departing from the spirit and scope of the present invention.  
         [0106]    Other embodiments consistent with the present invention will become apparent from consideration of the specification and the practice of the invention disclosed therein.  
         [0107]    Accordingly, the specification and the embodiments are to be considered exemplary only, with a true scope and spirit of the invention being disclosed by the following claims.