Abstract:
An adjustable focus connector with spring action is especially adapted for use with common FC or SMA fiber optic receptacles. The connector includes a ferrule holder which mounts a fiber-carrying ferrule at a distal end thereof. At its proximal end the ferrule holder is threadedly connected to a lead screw member. A thrust collar surrounds the ferrule holder and traps a compression spring in the cavity between the thrust collar and the ferrule holder. Because of appropriate interengagement between the components the ferrule holder cannot rotate relative to the trust collar. A traveler is threadedly connected to the lead screw and abuts against the thrust collar. A connection nut is provided at the distal end of the connector to connect it to the fiber optic receptacle. The spring action of the connector prevents damage to the fiber end during connection of the connector to the fiber optic receptacle

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of Provisional U.S. Patent Application Ser. No. 60/760,406 filed Jan. 20, 2006. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to connectors for connecting optical fibers to receptacles therefor and other related equipment.  
       BACKGROUND OF THE INVENTION  
       [0003]     Existing connectors for optical fibers suffer from several limitations that reduce their effectiveness for precision capture and transfer of light in optical delivery systems, particularly high power laser systems. Fundamental to any such system is the ability to precisely position the fiber at the focus of a laser beam in free space (X, Y and Z planes.).  
         [0004]     Prior Art  FIG. 1  defines the initial application of focusing light into a fiber. A focusing objective lens  100  focuses the light from a laser to a spot  102  closely matching the diameter of the core  104  of fiber  106 . This can be as small as 2 to 3 microns in diameter. The fiber then has to be positioned so the end face of the core is at the precise location of the focused spot.  
         [0005]     Conventional methods use bulky XYZ translation stages to position the fiber and/or the lens in free space to align the fiber core with respect to the focused spot. Such stages are expensive, and are not applicable to systems where the fiber must be aligned, and semi-permanently attached.  
         [0006]     Other methods have been employed where either the fiber is permanently attached to a lens or it is positioned at a fixed distance Z relative to the lens. The fiber/lens assembly is then manipulated and fixed relative to the laser beam in the remaining 5 planes (X, Y, pitch, yaw and roll). U.S. Pat. Nos. 4,753,510 and 4,889,406 of Omur M. Sezerman disclose a tilt-adjustable connector that can be used for such manipulation. The positioning of the fiber in the Z-plane is normally done by terminating the fiber in a conventional fiber connector (see Prior Art  FIG. 2 ). The connector  108  is plugged into a receptacle  110  where it makes contact with a stop  112 . The connector ferrule  114  and sleeve  116  are manufactured to a high degree of precision, restricting the fiber in the X-Y plane. The lens  118  is precisely positioned with respect to the receptacle  110  so that the tip of the fiber is positioned at the focal plane of the lens. Assuming that the laser beam entering the lens is perfectly collimated (ie: the laser beam waist location is well within the Rayleigh distance Z R  from the focusing lens), then the focused spot will be at the same distance Z from the lens as the fiber, and only adjustments in the remaining 5 planes are necessary.  
         [0007]     Note the existence of a key  120  on the connector  108  and keyway  122  on the receptacle  110 . This feature allows one to maintain the angular orientation of the fiber (i.e: to control roll). This is necessary for certain applications, such as working with polarization maintaining fibers or with fibers with angled end faces.  
         [0008]     The limitation of this technique is that if the laser beam is not well collimated the focused spot will not lie at the focal plane of the lens, and thus it will not lie at the tip of the fiber. Therefore for improved alignment, one needs a way to precisely adjust the distance between the fiber and lens during alignment, preferably without affecting the location of the fiber in the other five axes (X, Y, pitch, yaw, and roll).  
         [0009]     One approach to adjust the distance is to move the lens. This suffers from two drawbacks. First the lens is between the fiber and the laser, and is often thus inaccessible. The other is that moving the lens along the Z axis usually causes unwanted motion (play) in the other planes, particularly X and Y.  
         [0010]     Another idea is to simply mount the fiber in a threaded tube, and screw the fiber into a mating threaded receptacle. This has the drawback of being unable to control the roll of the fiber, making it unusable for polarization maintaining fiber applications.  
         [0011]     Another issue that one wants to avoid is accidentally extending a fiber too close to a lens or other surface, possibly jamming and damaging the tip of the fiber.  
         [0012]     An alternative to the previously described connecting systems involves the use of a compression spring within the connection device mounting the optical fiber. U.S. Pat. Nos. RE38,205E (being a reissue of U.S. Pat. No. 5,734,778) and 6,250,818 teach connectors that incorporate at least one compression spring that aids in achieving a degree of adjustment of the fiber relative to the receptacle in which it is to be received. However, in these patents the spring action is not such as to permit any compressive movement after the connector Z-position is located. This leaves open the possibility of jamming and damage to the ferrule tip should it be mated to conventional connectors or receptacles, which rely on some compressive spring action being present when mating.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention provides an alternative means for adjusting the position of the fiber along the Z-axis, while enjoying the following features:  
         [0014]     1) The X-Y precision achieved in conventional connector methods;  
         [0015]     2) An optional keyway to control roll;  
         [0016]     3) A spring-loaded mechanism to prevent accidental jamming of the fiber;  
         [0017]     4) Additional features to allow access to the fiber for surface finishing;  
         [0018]     5) Compatibility with existing connector designs.  
         [0019]     The present invention is available in two possible configurations: one that is compatible with an existing FC connector body standard, and another that is compatible with an existing SMA 905 connector body standard. Other designs can be constructed on similar principles.  
         [0020]     The connector of the present invention is very useful in achieving efficient coupling with a laser to fiber coupling system such as that discussed above with reference to U.S. Pat. Nos. 4,753,510 and 4,889,406, permitting for precise adjustment of the focus. It is also very useful in fiber-to-fiber coupling systems using two collimators facing each other. As long as at least one side utilizes the connector of the present invention it is possible to achieve precise positioning in X, Y and Z planes as well as with respect to pitch and yaw, optimizing coupling and minimizing losses. The possibility of avoiding contact between fiber ends also permits the coupler to be used in high power situations where contact between fiber ends can lead to damage of the fibers. In straight fiber-to-fiber coupling systems the spring loading achievable with the invention allows the ferrule ends to mate without damage, while the adjustment feature of the invention allows for the deliberate introduction of a gap between the fiber ends, such that the coupler can function as an attenuator.  
         [0021]     Generally speaking, the present invention may be considered as providing in one embodiment an adjustable focus connector which comprises: a ferrule holder for retaining at a distal end thereof a ferrule mounting an optical fiber therein; a lead screw member threadedly connected to the ferrule holder at a proximal end of the ferrule holder; a thrust collar surrounding the ferrule holder, the thrust collar and the ferrule holder defining a generally annular cavity therebetween; a traveler member theadedly receiving therein the lead screw member and abutting an adjacent end face of a proximal end wall of the thrust collar; a key frame secured to the thrust collar and extending away therefrom to surround the distal end of the ferrule holder; a compression spring retained within the cavity; and a coupling nut surrounding the key frame and retained thereon for connecting said connector to an FC receptacle devoid of any stop member therein.  
         [0022]     The present invention provides in another embodiment an adjustable focus connector which comprises: a ferrule holder for retaining at a distal end thereof a ferrule mounting an optical fiber therein; a lead screw member threadedly connected to the ferrule holder at a proximal end of the ferrule holder; a thrust collar surrounding the ferrule holder, the thrust collar and the ferrule holder defining a generally annular cavity therebetween; a traveler member theadedly receiving therein the lead screw member and abutting an adjacent end face of a proximal end wall of the thrust collar; a compression spring retained within the cavity; and a coupling nut surrounding the ferrule holder for connecting the connector to an SMA receptacle devoid of any stop member therein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  illustrates a prior art arrangement for focusing light into an optical fiber.  
         [0024]      FIG. 2  illustrates another prior art arrangement for connecting an optical fiber to a receptacle.  
         [0025]      FIG. 3  illustrates a connector according to the present invention for use with an FC type of fiber optic connector.  
         [0026]      FIG. 4  is a cross-sectional view taken on the line  4 - 4  of  FIG. 3 .  
         [0027]      FIG. 5  is an enlarged view of the distal end of the ferrule used in the embodiment of  FIG. 3 .  
         [0028]      FIG. 6  is a perspective view showing the components of the connector of  FIG. 3 .  
         [0029]      FIG. 7  illustrates a connector according to the present invention for use with an SMA type of fiber optic connector.  
         [0030]      FIG. 8  is a cross-sectional view taken on the line  8 - 8  of  FIG. 7 .  
         [0031]      FIG. 9  is a perspective view showing the components of the connector of  FIG. 7 .  
         [0032]      FIG. 10  illustrates a laser-to-fiber coupler system designed for use with an adjustable focus connector of the present invention.  
         [0033]      FIG. 11  illustrates a fiber-to-fiber coupler system designed for use with an adjustable focus connector of the present invention.  
         [0034]      FIG. 12  illustrates a fiber having an end cap thereon with which an adjustable focus connector of the present invention is particularly useful. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0000]     FC Type Fiber Optic Connector  
         [0035]     FIGS.  3  to  6  illustrate an adjustable fiber optic connector  10  according to the present invention especially adapted for use with an FC type of connector or receptacle.  
         [0036]     A ferrule holder  12  presents a counterbore in a distal end section thereof (right hand side in  FIG. 4 ) for the mounting of any type of FC ferrule  14 . The ferrule (high power version shown) may be of any type suitable to the end user&#39;s purpose.  
         [0037]     The high power ferrule concept is presented here as it is often seen in use with adjustable focus connector. Note that the fiber  16  is suspended in free space with a protective ring around it to prevent accidental damage to the exposed fiber. This design has two features that are advantageous. With reference to  FIG. 5  it is first of all seen that the fiber tip is recessed by a distance x, only a few microns, preventing any damage to the fiber should the tip come in contact with a flat surface. The second is the presence of a notch  18  in the ring. This notch permits side inspection of the fiber, and possible access to the fiber for processes like cleaning, or surface treatment of the fiber.  
         [0038]     The proximal end of the ferrule holder  12  (left hand side in  FIG. 4 ) presents a threaded section  20  so it may be threaded into and glued permanently to the lead screw  22 .  
         [0039]     The outside surfaces of the distal section of ferrule holder  12  define a polygonal cross-section, preferably a square section  24  ( FIG. 6 ), which passes through a mating hole in the key frame  26 .  
         [0040]     A thrust collar  28  surrounds the ferrule holder  12 , the thrust collar having a bottom end wall  30  and, with the outer surface of the ferrule holder  12 , defining a generally annular cavity  32 . A radially outwardly directed flange  34  intermediate the length of the ferrule holder  12  is located adjacent the distal end of the cavity  32 .  
         [0041]     A compression spring  36  is trapped in the generally annular cavity  32  defined between the bottom end wall  30  of the thrust collar  28 . This spring serves to continuously provide force on the ferrule holder/lead screw combination, acting toward the right in  FIG. 4 .  
         [0042]     A traveler member  38 , which is basically a nut with an internal thread of fine pitch (80 t.p.i.), is engaged with an external thread on the lead screw  22 . It makes contact with the external (left hand side) surface of the thrust collar bottom end wall  30 .  
         [0043]     A spring guard  40  fits over the traveler  38  and is threaded and permanently affixed onto the thrust collar  28 .  
         [0044]     The key frame  26  and the thrust collar  28  are glued together, confining the compression spring  34  and ferrule holder  12  inside, and confining an installation or coupling nut  42  outside.  
         [0045]     A setscrew  44  is provided for threaded engagement with a threaded bore  46  in the traveler  38  to lock the traveler  38  and lead screw  22  together when required.  
         [0046]     A crimp sleeve  48  is for cable jacket attachment, and is not considered part of this device.  
         [0000]     Operation:  
         [0047]     This male FC connector  10  is installed in the matching female receptacle by inserting the ferrule  14  into the receptacle “hole”, and engaging and tightening the installation nut  42  onto the external thread present on the receptacle. The “hole” in the receptacle, manufactured to suitable tolerances, is a close match to the diameter of the ferrule  14 , and is depended upon to prevent lateral movement of the ferrule  14 . This action is similar to all available FC connector/receptacle matchings. A key required difference is that there must not be any stop inside the receptacle. The existence of a stop would prevent forward motion of the ferrule.  
         [0048]     With conventional fixed-length ferrule designs, no further actions to facilitate axial (in-out) movement of the ferrule are available to the user. Since the end plane of the fiber is at the outside end of the ferrule, the position of the fiber&#39;s end is fixed. The optical coupling obtained between the fiber end and the intended optical mate (lens, other fiber end, etc.) inside the receptacle depends on the manufacturing control of the ferrule length. Also, no ability to influence the accuracy of placement of the optical mate within the receptacle is available to the user of the connector, and this positioning also affects coupling efficiency.  
         [0049]     In order to effect user control of coupling efficiency, the connector in question is able to vary the projection of the ferrule as follows:  
         [0050]     Before installation of the connector into the receptacle, the user rotates the traveler  38  clockwise, which, by virtue of it&#39;s thrust upon the thrust collar  28 , will cause the lead screw  22 , ferrule holder  12 , ferrule  14 , and fiber end to move as a unit to the left, compressing the spring  36 . The moving items will not rotate, because of the action of the square section of the ferrule holder in the square hole in the key frame  26 . The spring  36  will eventually reach the limit of it&#39;s compression (go “solid”). This condition represents the minimum ferrule projection (fully retracted).  
         [0051]     The connector  10  is installed to the receptacle in the conventional manner as described at the beginning of this section.  
         [0052]     The traveler  38  is then rotated counterclockwise by the user, causing the ferrule and other associated parts to move to the right. Thus, by turning the traveler one way or the other, the user can make the ferrule move in and out, i.e. change its projection. By conducting light through the system from receptacle to connector during the adjustment, the user can measure coupling efficiency with an optical power meter, and stop the adjustment when the best coupling is achieved.  
         [0053]     Should the user cause a collision to occur between the ferrule end and the optical mate inside the receptacle, the force transmitted by the collision is limited by the compressibility of the spring  36 , preventing damage. Also, in the case of a collision, the user will be notified by an abrupt decrease in the turning force required, since the traveler  38  will no longer be contacting the thrust collar  28 . In certain cases, causing a collision is actually desirable, since this is the position at which best coupling efficiency is obtained.  
         [0054]     The connector can be locked against further adjustment by tightening the setscrew  44  installed in the traveler  38 , locking it against the lead screw  22 .  
         [0055]     When this adjustment procedure has been completed, further adjustment is not possible without loosening the setscrew. Accidental adjustment is not possible.  
         [0056]     Although the ferrule projection has been set and locked, a further safety factor exists in the form of residual spring action availability. If the connector were to be carelessly installed into any new situation whereby the existing ferrule projection was too great, and a collision with the optical mate was assured, the spring  36  can still limit the collision force, because of the ability of the traveler  38  to lift clear of the thrust collar  28 .  
         [0057]     The subject connector thus allows for adjustable ferrule length and hence the ability to maximize optical coupling, and it retains the inherent safety feature of spring “cushioning” regardless of the length to which it has been adjusted.  
         [0000]     SMA Style Fibre Optic Connector  
         [0058]     Referring now to FIGS.  7  to  9  a connector  50  especially adapted to work with an SMA type of connector is illustrated  
         [0059]     A ferrule holder  52  presents a counterbore at a distal end thereof (right hand side in  FIG. 8 ) for the mounting of any type of SMA ferrule  54 . The ferrule (high power version shown) may be of any type suitable to the end user&#39;s purpose.  
         [0060]     At the proximal end of the ferrule holder  52  there is a threaded section  56  so that it may be threaded into and glued permanently to a lead screw  58 .  
         [0061]     A longitudinally extending intermediate section  60  of the ferrule holder  52  presents a polygonal cross-section, preferably a square section, which passes through a mating polygonal hole in a proximal end wall  62  of a thrust collar  64  that generally surrounds the ferrule holder  52 . The intermediate section  60  of the ferrule holder  52  and the surrounding thrust collar  64  define therebetween a generally annular cavity  66 .  
         [0062]     A compression spring  68  is trapped in the cavity  66  between the inner surface or shoulder of the proximal end wall  62  of the thrust collar  64  and a radially outwardly directed flange  70  intermediate the length of the ferrule holder  52  and located generally towards the distal end of the cavity  66 . This spring serves to continuously provide force on the ferrule holder/lead screw combination, acting toward the right in  FIG. 8 .  
         [0063]     A traveler  72 , which is basically a nut with an internal thread of fine pitch (80 t.p.i.), is engaged with an external thread on the lead screw  58 . It makes contact with the external (left hand side) surface proximal end wall  62  of the thrust collar  64 .  
         [0064]     A spring guard  74  fits over the traveler  70  and is threaded and permanently affixed onto the thrust collar  64 .  
         [0065]     A nut retainer  76  and stop frame  78  are glued together as at  86  and are glued to the thrust collar  64 , and serve to hold captive the coupling or installation nut  80 .  
         [0066]     A setscrew  82  is provided for threaded engagement with a threaded bore  84  in the traveler  72  to lock the traveler and lead screw together when required.  
         [0000]     Operation:  
         [0067]     This male SMA connector is installed in the matching female receptacle by inserting the ferrule  54  into the receptacle “hole”, and engaging and tightening the installation nut  80  onto the external thread present on the receptacle. The “hole” in the receptacle, machined to suitable tolerances, is a close match to the diameter of the ferrule, and is depended upon to prevent lateral movement of the ferrule. This action is similar to all available SMA connector/receptacle matchings. A key required difference is that there must not be any stop inside the receptacle. The existence of a stop would prevent forward motion of the ferrule.  
         [0068]     With conventional fixed-length ferrule designs, no further actions to facilitate axial (in-out) movement of the ferrule are available to the user. Since the end plane of the fiber  88  is at the outside end of the ferrule, the position of the fiber&#39;s end is fixed. The optical coupling obtained between the fiber end and the intended optical mate (lens, other fiber end, etc.) inside the receptacle depends on the manufacturing control of the ferrule length. Also, no ability to influence the accuracy of placement of the optical mate within the receptacle is available to the user of the connector, and this positioning also affects coupling efficiency.  
         [0069]     In order to effect user control of coupling efficiency, the connector in question is able to vary the projection of the ferrule as follows:  
         [0070]     Before installation of the connector into the receptacle, the user rotates the traveler  72  clockwise, which, by virtue of its thrust upon the thrust collar  64 , will cause the lead screw  58 , ferrule holder  52 , ferrule  54 , and fiber end to move as a unit to the left, compressing the spring  68 . The moving items will not rotate, because of the action of the square section  60  of the ferrule holder  52  in the square hole in the proximal end wall  62  of the thrust collar  64 . The spring  68  will eventually reach the limit of its compression (go “solid”). This condition represents the minimum ferrule projection (fully retracted).  
         [0071]     The connector is installed to the receptacle in the conventional manner as described at the beginning of this section.  
         [0072]     The traveler  72  is then rotated counterclockwise by the user, causing the ferrule and other associated parts to move to the right. Thus, by turning the traveler  72  one way or the other, the user can make the ferrule  54  move in and out, i.e. change its projection. By conducting light through the system from receptacle to connector during the adjustment, the user can measure coupling efficiency with an optical power meter, and stop the adjustment when the best coupling is achieved.  
         [0073]     Should the user cause a collision to occur between the ferrule end and the optical mate inside the receptacle, the force transmitted by the collision is limited by the compressibility of the spring  68 , preventing damage. Also, in the case of a collision, the user will be notified by an abrupt decrease in the turning force required, since the traveler  72  will no longer be contacting the thrust collar  64 . In certain cases, causing a collision is actually desirable, since this is the position at which best coupling efficiency is obtained.  
         [0074]     The connector can be locked against further adjustment by tightening the setscrew  84  installed in the traveler  72 , locking it against the lead screw  58 .  
         [0075]     When this adjustment procedure has been completed, further adjustment is not possible without loosening the setscrew. Accidental adjustment is not possible.  
         [0076]     Although the ferrule projection has been set and locked, a further safety factor exists in the form of residual spring action availability. If the connector were to be carelessly installed into any new situation whereby the existing ferrule projection was too great, and a collision with the optical mate was assured, the spring  68  can still limit the collision force, because of the ability of the traveler  72  to lift clear of the thrust collar  64 .  
         [0077]     The subject connector thus allows for adjustable ferrule length and hence the ability to maximize optical coupling, and it retains the inherent safety feature of spring “cushioning” regardless of the length to which it has been adjusted.  
         [0000]     Other Applications of the Connector:  
         [0078]     Another use of the adjustable connector is for launching light out of a fiber through a lens to focus the light. Again the position of the fiber relative to the lens needs precise adjustment while minimizing unwanted movement in the other planes. Conventional methods of moving the lens to focus the light introduce play, again mainly in the X-Y planes. By using the adjustable focus connector, with its precision sleeve, one is able to move the fiber along the Z-axis only, thus allowing one to change the position and magnification of the focused spot, while tightly constraining its position along a single axis.  
         [0079]      FIG. 10  illustrates a coupler system for effecting laser-to-fiber coupling utilizing an adjustable focus connector of the present invention. The system provides a base member  100  having a central opening or bore  102  in which a lens  104  is mounted. The base member can be adjusted relative to the substrate to which it is secured by way of tilt adjustment screws  106  as described in the aforementioned US patents of Omur M. Sezerman. A resilient sealing member  108  is positioned between the base member and substrate to provide resistance to the adjusting screws and to hermetically seal the assembly. A receptacle  110  is secured to the base member  100  and is provided with a threaded boss  112  projecting from an outer surface thereof. A bore  114  extends through the boss and receptacle  110  and is axially aligned with the bore  102 . The receptacle  110  does not include any stop against which the ferrule of the present connector could abut; however, the receptacle may include a stop face  116  against which the end face of key frame  26  can abut to assure repeatability in the Z direction. When the connector of the present invention has been secured to the receptacle  110  the adjustment operation previously described will control the distance between the fiber end and the lens  104  in the Z direction, while adjustment of the tilt screw  106  will effect any desired adjustment of the fiber in X, Y, pitch and yaw.  
         [0080]      FIG. 11  illustrates a system similar to that shown in  FIG. 10  for a fiber-to-fiber coupling system. The assemblies  120  and  122  are similar to that shown in  FIG. 10 , with each mounting a lens  124 . The base members  126 ,  128  are adjustable relative to each other by adjusting screws  130 , it being noted that there is a resilient sealing member  132  positioned between the base members to provide resistance to the adjusting screws and to hermetically seal the assembly. At least one of the optical fibers secured to the coupling system is adjustably mounted to one of the receptacles  134  of the base members as described above with respect to  FIG. 10 . Light from one of the fibers is collimated by its lens  124  and then focused into the other fiber by the other lens  124 . The position of the focus spot is adjusted in the XY plane by the tilt adjustment mechanism of the assembly, using the screws  130 . The position of the focus spot in the Z direction relative to the fiber pair is achieved through adjustment of the adjustable connector as described hereinabove.  
         [0081]      FIG. 12  shows an optical fiber  140  having a piece of silica  142  fused to the end thereof, forming a window or endcap. This allows for high power handling. Light from the fiber core  144  can then expand so that when such light reaches the fused silica/air interface  146  the energy density (W/m 2 ) is greatly reduced, minimizing the risk of damage to the fiber. However, the use of an endcap prevents utilization of a conventional stop in couplers such as those of the Sezerman patents, as the location of the minimum waist no longer coincides with the end of the device. This problem is rectified when a fiber with endcap is mounted in an adjustable focus connector of the present invention since the adjustability compensates for the different light pattern resulting from the use of an endcap.