Patent Publication Number: US-7901235-B2

Title: Releasably locking auto-aligning fiber optic connector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The application for claims priority to U.S. patent application Ser. No. 12/049,125, filed Mar. 14, 2008, entitled Releasably Locking Auto-Aligning Fiber Optic Connection and to U.S. Provisional Application No. 60/896,475, filed Mar. 22, 2007 and entitled Releasably Locking Auto-Aligning Fiber Optic Connection, all of which are hereby expressly incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to connectors for fiber optic instruments. More particularly, the invention relates to a module for coupling an optical instrument to an optical measurement device that may be disposed within a catheter. 
     BACKGROUND 
     Optical instruments such as endoscopic imaging devices have been used in medical applications for many years. A common technique for performing minimally invasive imaging involves placement of the imaging device inside a catheter, such as a central venous catheter, which then carries the imaging device to a desired intravenous location. Due to space constraints encountered when inserting these devices into a patient, the size of the imaging transducer is designed to be as small as possible. Thus, electronic components used to process transducer signals are located remotely from the catheter and are typically coupled to the transducer by running cable or optical fiber through the catheter. 
     To ensure a good connection between connecting ends of an optical fiber, connectors are typically designed with cylindrical ferrules suspended within a connector body. A typical fiber optic connector  10  is shown in  FIG. 1 . The ferrule  12  is bored through the center at a diameter that is slightly larger than the diameter of the fiber  14 . The fiber  14  is then fed through the ferrule  12 , so that the end of the fiber  14  coincides spatially with the end of the ferrule  12 . During coupling, the ferrule  12  guides the end of the fiber  14  into an alignment sleeve  16  of a mating receptacle  18 . A locking mechanism  20  may be formed on the outside of the receptacle  18  and the connector body  22  to hold the mated pair securely together. Because the diameter of the fiber  14  may be on the order of 10 μm, very tight dimensional tolerances are required for those components of the connector assembly that are responsible for aligning the fibers. 
     The locking mechanism  20  is typically a bayonet type connection, a threaded sleeve connection, or other locking device that prevents the mated ends from becoming uncoupled in the presence of a pulling force or tension across the connection. The locking mechanism  20  helps to maintain proper alignment of the mating ends of the fiber  14  to minimize insertion loss across the connection. The locking mechanism  20  also helps to ensure the integrity of the optical transmission path when the connection is under tension. Locking connectors may be critical for applications such as telecommunications, security, and other data transmission systems that require very high reliability. 
     In medical applications, however, it may not be desirable to maintain a locked connection, even in the presence of tension across the connection. This is especially true in the case of an imaging device or other measuring device or sensor that is inserted into a patient through an intravenous catheter. For example, when an electronics module or instrument rack connected to the catheter leads is moved or falls over, it can pull the catheter leads with it. Excessive tension placed on the catheter leads or other connective cable may cause considerable discomfort to the patient, displacement of the catheter, or in the worst case, removal of the catheter from the patient access site. 
     SUMMARY 
     The invention discloses a connector assembly for coupling signal lines, such as optical fibers, connected between an optical instrument and an optical sensor installed inside a catheter. The connector assembly provides a releasably locking auto-aligning mechanism for mechanically coupling signal lines and properly aligning them for minimum insertion loss. 
     A plug and receptacle cooperate to create the releasably locking mechanism. The receptacle may include a terminating end for terminating a first signal line and a receiving end for receiving the plug, and the plug may carry a second signal line for coupling to the first signal line. The receptacle may include a housing that defines a channel having a planar surface disposed in the receiving end. A baffle, through which the first signal line extends, may be positioned between the terminating end and the receiving end of the receptacle in a direction normal to the surface of the channel. A rotatable spring-loaded pawl may be mounted on the receptacle above the channel. The rotatable pawl may have a rear end for compressing a spring and a tapered end with a barbed edge. The plug may include a retaining bracket sized and positioned to engage the tapered end of the pawl when the plug slides into the channel. At full engagement, the barbed edge of the pawl may lock against the retaining bracket and impart a retaining force on the plug, the retaining force having a first component normal to the planar surface of the channel, and a second component normal to the baffle, to maintain the first and second signal lines in optimal alignment. The mating end of the plug may be wedge-shaped to help guide the plug into the receptacle channel. The baffle may include an alignment knob that mates with a recess set into the mating end of the plug. The retaining bracket may include a sloped edge to allow for easy release of the barbed edge of the pawl in the presence of a release force. 
     With the connector assembly in a locked state, the first component of the retaining force pushes the mating end of the plug horizontally against the baffle. If a mechanical shock misaligns the connection, the first component provides a restoring force to restore the connection. As the second component of the retaining force pushes the plug downward against the channel, optimal vertical alignment may depend on only a single height dimension. In an optical catheter application, the release force of the locking mechanism may be set to a value less than the force required to pull the catheter out of a patient, to ensure disconnection without affecting catheter installation or causing patient discomfort. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, objects, and advantages of the invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein: 
         FIG. 1  is a typical prior art fiber optic connector assembly with a bayonet-type locking device. 
         FIG. 2  is an exploded top isometric view of a connector assembly according to an embodiment of the invention. 
         FIG. 3  is a transparent side view of a connector assembly showing the assembly in a fully engaged position according to an embodiment of the invention. 
         FIG. 4  is a frontal view of a receptacle of a connector assembly according to an embodiment of the invention. 
         FIG. 5  is a partial top view of a connector assembly showing the assembly in a non-engaged position according to an embodiment of the invention. 
         FIG. 6  a frontal view of a receptacle of a connector assembly according to another embodiment of the invention. 
         FIG. 7  is a partial top view of a connector assembly showing the assembly in a non-engaged position according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention provides a coupling device for medical applications that maintains proper alignment for an optical connection while allowing for easy release from the catheter without disturbing the patient access site.  FIG. 2  shows an isometric drawing of a connector assembly  11  according to an embodiment of the invention. The connector assembly  11  includes a receptacle  13  and a plug  15 . The receptacle  13  and the plug  15  may be made of a rigid dielectric material such as a molded plastic. The receptacle  13  and the plug  15  each terminate a signal line and when mechanically engaged in proper alignment, cooperatively couple the signal lines to ensure signal transmission across the coupling junction with minimal insertion loss. 
     The receptacle  13  includes a terminating end  17  and a receiving end  19 . The terminating end  17  receives and terminates a signal line  21 . In one embodiment, the signal line  21  is a fiber optic line having one or more optical fibers. In other embodiments, the signal line  21  may be a conductive cable, providing one or more conductive paths of single or multistranded wire. The receiving end  19  is configured to receive and engage with the plug  15 . 
     The receptacle  13  includes a housing  23  that defines a channel  25  disposed in the receiving end  19 . The channel  25  includes a planar surface  27  that serves as a contacting plane for receiving the plug  15  and guiding it into engagement with the receptacle  13 . The channel  25  extends in a longitudinal direction, which is the x-direction as indicated in the figure. The receptacle  13  also includes a pawl  29  mounted to the housing  23 . The pawl  29  is positioned above or opposite the channel  25 , as shown. 
     The pawl  29  includes a tapered end  33  and an anchoring end  35  and may be made of a rigid material such as metal or plastic. The tapered end  33  may include a barbed edge  34 . In one embodiment, the pawl  29  is rotatable about an axis  31  oriented transversely to the channel  25 , i.e. in the y-direction. A pin  37  is used to rotatably fasten the pawl  29  to the housing  23  through mounting holes  39  and  41  such that the pin  37  aligns concentrically with the axis  31 . In another embodiment, the pawl  29  may be formed as a flexible component and may be fixed at the anchoring end  35  to the terminating end  17  of the housing  23 , such that a free length of the pawl  29  may flex to allow for displacement of the tapered end  33 . 
     In the connector assembly  11 , the housing  23  includes a spring  43  disposed in the terminating end  17  and positioned to contact the anchoring end  35  of the pawl  29  as the pawl  29  rotates downward and in a clockwise direction. The spring  43  may be a spring such as a steel helical-wound compression spring, and may include a cap (not shown) for contacting the anchoring end  35  of the pawl  29 . The spring  43  may assume other forms, such as one or more tension, leaf or cantilever springs, mounted appropriately to the housing  23 . 
     The plug  15  includes a terminating end  45  and an insertion end  47 . The terminating end  45  terminates a signal line. The insertion end  47  engages the receptacle  13 . A top side  49  of the plug  15  may be configured with a retaining bracket  51 . A bottom side of the plug  15 , or channel contacting surface (see  FIG. 2 ), may be configured for sliding onto the planar surface  27  of the channel  25 . 
     With the connector assembly  11  so configured, the receptacle  13  and the plug  15  may be coupled together by sliding the insertion end  47  of the plug  15  into the receiving end  19  of the receptacle  13  through the channel  25 . As the plug  15  is drawn into the channel  25 , the tapered end  33  of the pawl  29  engages the retaining bracket  51 , forcing the tapered end  33  to rotate upward while the anchoring end  35  rotates downward to compress the spring  43 , thereby placing a spring load on the pawl  29 . When the barbed edge  34  travels beyond the retaining bracket  51 , the spring  43  releases, forcing the barbed edge  34  downward to snap-lock the pawl  29  to the retaining bracket  51  and urge the plug  15  further into the channel  25 . In this position, also referred to as the fully engaged position, the barbed edge  34  under pressure from the spring  43 , maintains a retaining force on the plug  15  to keep the first and second signal lines in proper alignment and lock the plug  15  to the receptacle  13 . 
       FIG. 3  shows the connector assembly  11  in a fully engaged position. The retaining force on the plug  15  is indicated by force vector F 1 . In one embodiment, the force vector (or retaining force) F 1  has a first component in the z-direction that is normal to the planar surface  27  and a second component in the x-direction that is parallel to the planar surface  27 . Thus, with respect to the coordinate system shown, the retraining force F 1  acts in at least two orthogonal directions. A result of the force vector F 1  acting on the plug  15  is that the plug  15  is forced downward against the planar surface  27  by the first force component, and inward to engage the receptacle  13  by the second force component. 
     Advantageously, by ensuring a downward-acting force that presses a bottom surface of the plug  15  against the planar surface  27 , optimal vertical alignment of the first signal line with the second signal depends on a single height dimension. That is, for manufacturing purposes, proper alignment of the signal lines may be determined by controlling the height of each signal line (i.e. the displacement in the z-direction) above the planar surface  27 . 
     In addition, by ensuring an inward-acting force that urges the insertion end  47  of the plug  15  into the receptacle  13 , optimal positioning along the x-direction may also be achieved. The receptacle  13  further includes a baffle  53  positioned between the terminating end  17  and the receiving end  19 , as shown in the figures. The baffle  53  extends from the planar surface  27  in the z-direction, i.e. in a direction substantially normal to the planar surface  27  of the channel  25 . Thus, the baffle  53  provides a flat or limiting surface facing the receiving end  19  of the receptacle  13  to limit movement of the plug  15  in the x-direction. In the fully engaged position, the insertion end  47  of the plug  15  abuts the baffle  53 . 
     As shown in  FIGS. 4 and 5 , the baffle  53  further includes a hole or throughway  55  for passing an end of the first signal line  21 . In one embodiment, the first signal line  21  extends through the hole  55  until it is flush with the limiting surface of the baffle  53 , forming a planar engagement surface  57  for abutting to the plug  15 . Within the plug  15 , the second signal line similarly passes through a hole  59  to form a planar engagement surface  61  on the insertion end  47 . Thus, in the fully engaged position, the planar engagement surface  57  abuts the planar engagement surface  61 , coupling the end of the first signal line to the end of the second signal line to complete the connection. 
     Horizontal alignment (i.e. in the y-direction) of the signal lines may be accomplished using additional geometric features on both the plug  15  and the receptacle  13 . At the receiving end  19 , the receptacle  13  is formed with angled walls  63  that form a maximum channel width at a position furthest from the baffle  53 . The angled walls  63  lie in the x-y plane and may assist in guiding the plug  15  properly into the receptacle  13 . Similarly, at the insertion end  47 , the plug  15  is formed with the walls  65  angled in the x-y plane for guiding the plug  15  into the receptacle  13 . The angled walls  63  and  65  facilitate engagement, for example, when the connector assembly  11  is connected by hand. 
     The angled walls  63  may be formed such that the maximum distance between them in the y-direction is greater than the maximum width W 1  of the plug  15 . The minimum distance in the y-direction between the angled walls  63  approaches the width W 2  as the angled walls  63  merge into the channel  25 . In the embodiment of  FIGS. 4 and 5 , the horizontal alignment in the y-direction at full engagement is met by providing a width W 2  sized to snugly accommodate width W 1  of the plug  15 . The snug accommodation means that the plug  15  may be fully inserted into the receptacle  13  without excessive friction against the walls of the channel  25  and without allowing any displacement in the y-direction at full engagement. The nominal difference between widths W 1  and W 2  may be established according to desired manufacturing accuracy and tolerances. For aligning electrical cable, for example, the difference may be set between about 0.1 mm and about 0.01 mm. In an embodiment for aligning optical fiber, the nominal difference between W 1  and W 2  may be on the order of about 100 micrometers. In another embodiment, the nominal difference may be on the order of about 10 micrometers. 
     The vertical alignment (i.e. in the z-direction) may also be facilitated by various geometric features. In one embodiment, during engagement of the plug  15  and the receptacle  13 , an angled shelf  67  and an upper stop  69  assist a user by guiding the insertion end  47  into the receiving end  19  at an approximately correct vertical alignment for initial entry of the plug  15  into the channel  25 . 
     In the embodiments of  FIGS. 6 and 7 , the receptacle  13  may be configured with an alignment knob  71  that protrudes from the baffle  53  in a longitudinal direction. The hole  55  may extend all the way through the alignment knob  71  as shown. The alignment knob  71  may be formed as an integral part of the baffle  53 , or it may be separately attached thereto. The alignment knob  71  is further configured with the angled sides  73  to assist in aligning the insertion end  47  of the plug  15  as it approaches full engagement. On the plug  15 , a recess  75  may be configured in the insertion end  47  to receive the alignment knob  71 . In one embodiment, the recess  75  may include sloped sides  81  that form a maximum recess width at an outer edge of the insertion end  47  and a minimum recess width W 4  along an inner wall of the recess  75  nearest the terminating end  45 . At full engagement, when the planar engagement surface  57  abuts the planar engagement surface  61 , the alignment knob  71  extends fully into the recess  75 . In this position, the width W 4  of the alignment knob  71  mates to the width W 4  of the recess  75  such that the hole  55  aligns with the hole  59 . 
     In this embodiment, precision horizontal alignment in the y-direction may be achieved by controlling the width and placement of dimension W 4  on both the plug  15  and the receptacle  13 , and providing that the length of the alignment knob  71  equals or exceeds the receiving depth of the recess  75 . Thus, the plug width W 1  does not need to be very precise for proper horizontal alignment, and its tolerance may be significantly relaxed so long as W 1  is less than the channel width W 3 . Given these constraints, and under a retaining force from the pawl  29  acting in the x-direction against the retaining bracket  51 , the plug  15  may be held firmly in horizontal alignment with the receptacle  13  as the recess  75  is guided into full engagement with the alignment knob  71 . 
     The retaining bracket  51  also includes a leading edge  77  and a trailing edge  79 . One or both of these edges may be sloped in the x-z plane. The height of the retaining bracket  51  above the plug  15  may be configured such that during insertion of the plug, the leading edge  77  initially contacts the tapered end  33  of the pawl  29  when the pawl  29  is unloaded. As the plug  15  is inserted further into the receptacle  13 , the tapered end  33  slides up the leading edge  77 , spring-loading the pawl  29 , until the barbed edge  34  passes over the top of the bracket  51 . At this point, the barbed edge  34  slides down the trailing edge  79 , transmitting the retaining force through the retaining bracket  51  in the x-direction for horizontal alignment, and through the retaining bracket  51  and/or the plug  15  in the z-direction for vertical alignment. 
     Referring now to  FIGS. 2 and 3 , the plug  15  is shown in a fully engaged position within the receptacle  13 , with the barbed edge  34  of the pawl  29  spring-locked against the trailing edge  29  of the retaining bracket  51 . The vertical component of the retaining force F 1  allows a channel contacting surface  52  of the plug  15  to engage the planar surface  27  of the channel  25 . In this example, the channel contacting surface  52  may be a foot or rail extending downward from the bottom planar surface  50 . The foot or rail  52  may be formed with a bottom edge or bottom surface designed to slide smoothly along the channel  25 . 
     In the fully engaged position, the channel contacting surface  52  is pressed flush against the channel  25  to reduce the number of dimensional controls needed for vertical alignment, down to a single vertical dimension on the plug  15  or the receptacle  13 . For example, provided that height H between a centerline  80  and the bottom of the channel contacting surface  52  is controlled to a desired accuracy, force F 1  provides that at full engagement, the plug  15  vertically aligns to a properly dimensioned receptacle. Concurrently, provided that height H between a centerline  80  and the planar surface  27  is controlled to a desired accuracy, force F 1  provides that the receptacle  13  vertically aligns to a properly dimensioned plug. Alternatively, the plug  15  may be formed without the foot or rail  52 , in which case the bottom planar surface  50  becomes the channel contacting surface. A foot or rail may be preferred, however, to minimize frictional forces. 
     With a connector assembly  11  configured as in any of the disclosed embodiments, alignment of a first signal line running through the receptacle to a second signal line running through the plug may be accomplished with high precision in the x, y and z dimensions. Moreover, this precision may be achieved by reducing control dimensions in the y-direction to a single height dimension. This significantly simplifies manufacturing as compared to typical prior art methods that require control of up to four vertical dimensions (i.e. spatial placement of the four corners of a trapezoid) to ensure proper configuration. Thus, the invention is advantageous for fiber optic connectors needing very high precision, for example, on the order of about 10 μm to about 100 μm. In another embodiment, acceptable alignment of the optical fibers may be ensured by maintaining a spacing tolerance of each fiber end within the plug or receptacle at about +/−0.001 inch for the spatial dimensions under control. 
     A further advantage of a fiber optic connector configured according to the invention is excellent coupling with minimal insertion loss. In one embodiment, as shown in  FIGS. 2-6 , the assembly may be equipped with signal lines that are optical fibers routed through holes  55  and  59 . The connector assembly  11  includes a first fiber optic line extending through an alignment knob in the baffle  53  until the end of the optical fiber is flush with the end of the alignment knob furthest from the baffle  53 . A second fiber optic line extends through the plug  15  until flush with the inner wall of a recess  75 . When the alignment knob and the recess engage under the retaining force, the optical lines are coupled and aligned with high precision. This may be achieved without the use of a coupling fluid or gel that can cause additional problems such as end gaps or concentric offset. Coupling optical fibers according to the invention is therefore less susceptible to insertion loss from various forms of misalignment. 
     With reference again to  FIG. 3 , a release force F 2  and a restoring force F 3  of the present invention are now described. In one embodiment, the retaining bracket  51  is configured with a trailing edge  79  that slopes upward in the x and z directions from the top side  49  of the plug  15 . The degree of this slope may be varied from between about 0 and 90 degrees, preferably between about 20 and 60 degrees, to allow the barbed edge  34  of the pawl  29  to slide up the slope in the presence of a shock or pulling force tending to separate a fully engaged plug  15  and receptacle  13 . The minimum force needed to completely separate a fully engaged connection is the release force F 2 , which acts in the x-direction. Complete separation means that the barbed edge  34  has been unlocked from the retaining bracket  51 , i.e. displaced to a point on the leading edge  77  or further away from the retaining bracket  51  where the spring force has been removed from the pawl  29  and the connector is no longer fully engaged. 
     The degree of the slope, the contacting angle of the barbed edge  34 , the materials of construction, and the spring force are all determining factors for establishing a release force for the connector assembly  11 . In one embodiment, the spring-loaded pawl  29  of the receptacle  13  may be releasably lockable to the retaining bracket  51 . This means that release force F 2  may be established to allow the connector assembly to be pulled apart by hand without undue difficulty, and yet provide a reliable long-term connection that maintains the pawl  29  locked to the retaining bracket  51  in the absence of a separating force. In one embodiment, the release force may be set to be between about 0.5 pounds and about 10.0 pounds. In another embodiment, the release force may be set to be between about 3.0 pounds and about 8.0 pounds. In another embodiment, the release force may be set at about 1.0 pound. 
     A connector provides a restoring force F 3  acting in the x-direction that tends to reconnect and realign the plug  15  within the receptacle  13  in the event of a partial separation. A partial separation may occur if a shock or pulling force tending to separate the plug  15  from the receptacle  13  is less than the release force. During a partial separation event, the barbed edge  34  may slide part way up the slope of the trailing edge  79  or even to the top surface of the retaining bracket  51 , without complete separation. In this case, the anchoring end  35  of the pawl  29  rotates downward to compress the spring  43 , causing a reaction force from the spring  43  that pushes back against the anchoring end. When the shock or pulling force is removed, the reaction force F 3  causes the tapered end  33  of the pawl  29  to rotate downward against the trailing edge  79  of the retaining bracket  51 , thereby reestablishing force vector F 1  to realign and reconnect the plug  15  to the receptacle  13 . Thus, a connector assembly  11  advantageously provides a mass-spring suspension system for automatically restoring proper alignment in response to shock. 
     The invention provides particular advantages in medical instrument applications. For example, when coupling electronic instruments to catheters equipped with electronic or optical sensors, it is important to make and break the coupling without placing undue tension on the catheter installation to prevent displacement of the installation or patient discomfort. In an accident scenario, where the instrument coupled to the catheter gets moved or falls from a bench or hospital bed causing tension on the catheter, the release force allows the electrical or optical connection to break first to preserve the integrity of the catheter installation. With the connector assembly in a latched state, a component of the spring force may resiliently push the proximal end of the catheter plug horizontally against the distal end of the instrument receptacle, thereby coupling the optical fibers in optimal alignment under static conditions, and providing a restoring force to restore the optimal alignment after mechanical shock. To allow for the integrity of the catheter installation, the release force of the locking mechanism may be established between about one and about twenty times less than a target force, where the target force may represent an approximate force needed to pull the catheter out of the patient, displace the catheter, or cause undue patient discomfort. In another embodiment, the release force may be set in the range of about five and about ten times less than the target. In another embodiment, the release force may be set to about eight times less than the target force. 
     The invention has been disclosed in an illustrative manner. Accordingly, the terminology employed throughout should be read in an exemplary rather than a limiting manner. Although minor modifications of the invention will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted, except in light of the appended claims and their equivalents.