Abstract:
An optical coupler includes essentially tubular second connecting piece ( 40 ). Second fiber end ( 14 ) inserts completely through second connecting piece ( 40 ) and is held rigidly such second fiber end ( 14 ) is set back from second connecting piece end ( 78 ) by a preselected distance. First essentially tubular connecting piece ( 16 ) is divided axially into first portion ( 30 ) into which first fiber end ( 12 ) is inserted and held rigidly, and second portion ( 32 ) into which second connecting piece ( 40 ) is detachably attached. First and second portions ( 30, 32 ) are arranged such that first fiber end ( 12 ) is coaxial with and in close proximity to second fiber end ( 14 ). Preferably, attachment of second and first connecting pieces ( 40, 16 ) includes an axially symmetric groove ( 46 ) on an outer surface of second connecting piece ( 40 ), and an axially symmetric protrusion ( 24 ) on an inner surface of second portion ( 32 ) which essentially mates with axially symmetric groove ( 40 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Application No. 60/275,058 filed Mar. 12, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the art of illumination devices useful in general lighting applications and, more particularly, relates to an optical commutator useful in specialized fiber optic lighting applications such as, for example, lighting applications which require convenient, efficient, high intensity, small spot size lighting. However, the invention is applicable in any situation where flexible light piping is required, and the incorporated light source may include incandescent, fluorescent, laser, or other light sources. 
     Electrical lamp apparatus have been in existence at least since the invention of the incandescent light bulb. Many modern electric lamps still utilize incandescent sources essentially similar to the original design but incorporating improved filament materials, better electrical current and voltage control, improved vacuum quality, and other improvements. Other modern lamp apparatus employ fluorescent light sources which typically exhibit higher efficiency and longer service life versus incandescent sources. Specialty lamps are also available which use novel sources such as gas discharge tubes using mercury, sodium, or other gas vapors, xenon arc lamps, gas lasers, semiconductor lasers and light emitting diodes (LED&#39;s), and other optical sources. 
     Beyond the light source, the properties of a lamp system are dictated primarily by the optical path design. In the simplest case, there may be no defined optical path, for example, a ceiling fluorescent tube with no associated optical components other than light diffusers, filters, or the like. More commonly, the omni directional light output is conditioned through the use of parabolic reflectors, flat reflectors, lenses or other refractive elements, diffusers such as lamp shades, spectral filters, apertures, and the like. 
     In the case of a fixed, immobile lamp, a great deal of engineering freedom exists in the design of the optical path. Optical path design options are significantly restricted, however, in cases where the point of light emission must be mounted on a flexible arm so that the direction or physical location of the light emission is adjustable. An example is the desktop lamp, which in the conventional commercial design includes a flexible arm such as a “gooseneck” flexible arm, multiple-segment multiple-hinged arm, or the like, and a light emitting head which includes an incandescent or fluorescent light source and associated reflectors or other optical components. Other lamp types which may require flexible mounting and therefore typically incorporate the above-described basic design include surgical operating room lamps and lamps for precision mechanical operations such as semiconductor wire bonding, jewelry work, and other fine mechanical tasks. 
     The requirements for the light emitting head typically include: high brightness, low temperature operation, small spatial size, and low weight. High intensity is required due to the nature of many applications, such as reading and precision jewelry work. Preferably, the lighthead temperature is close to ambient temperature, especially for applications such as desk lighting where the lighthead will be close to a user&#39;s face and hands. A small lighthead size is preferable for flexibility in positioning. Low weight is preferable to reduce the mass and cost of the weight-bearing flexible arm. 
     Conventional lamp designs employing a flexible arm and attached head containing at least the light source require undesirable engineering design compromises between light intensity, thermal temperature, size, and weight. The desired high intensity sources are usually larger and heavier than lower intensity sources. High intensity sources also tend to generate a large amount of heat. The heating problem is especially acute for incandescent sources because these sources tend to be rather inefficient. Replacement of incandescent bulbs by fluorescent tubes may greatly reduce the operating temperature, typically with an accompanying decrease in light intensity which may however be acceptable for certain applications. Improved optics which provide better coupling of the generated light to the area requiring illumination are also beneficial, but the optics may also increase head size and weight. 
     A different solution to the need for a flexible lighting source has become available with the advent of fiber optics. Using fiber optical transmission permits decoupling of the light source from the point of light emission. A design incorporating fiber optics may include a large, hot, heavy, high intensity light source positioned remotely from a light emitting head. The head is movably located at the point of light emission and is connected to the light source by a fiber optical link. The head need only contain those optical components such as reflectors, lenses, and the like which are necessary to shape the fiber optical output appropriately for the application. Certain optical components, such as spectral filters, may be placed near the light source remote from the head. An additional advantage of incorporating fiber optical transmission is that a single light source may provide optical power for a number of flexibly positioned heads. Such a system could be valuable, for example, in a hospital operating room where the surgical area may preferably be illuminated from two or more different angles to reduce shadowing. 
     In spite of the benefits potentially available through the incorporation of fiber optics into flexibly positioned lighting systems, practical difficulties have resulted in limited use of fiber optics in such systems. A critical issue is light transmission efficiency at fiber coupling points. Efficient coupling between adjacent fibers requires similar or preferably identical fiber core sizes, smooth fiber end cleaves preferably including anti-reflection coatings, and extremely precise axial and angular alignment of the two fiber tips. For a flexible lamp, the close axial and angular alignment must be maintained as the lamp arm is moved and rotated about the mechanical joints where the fiber coupling typically is employed. 
     The prior art teaches using standard threaded and snap connectors for connecting fiber optical segments. However, there is a need for a convenient and reliable mechanical configuration for providing a fully rotatable fiber coupling where one fiber end may be rotated freely with respect to the other fiber end while maintaining efficient optical coupling. Such an optical coupling may conveniently be called an “optical commutator” in close analogy to the electrical commutator typically employed in connection of rotor windings in electric motors and generators. An optical commutator having a high light transmission efficiency is a highly desired and critical element for lamp designs in which an arm bearing a fiber-coupled light emitting head is to be freely rotatable about a joint. 
     It is further desired to provide an optical commutator that finds application well beyond lighting systems. Fiber optics are used increasingly in communications and in various medical applications, among others. The optical commutator is applicable to desired areas identified above as well as others where rotatable coupling of fiber segments may be desirable. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a rotatable optical fiber coupler for coupling a first fiber with a second fiber is provided. A first hollow radially symmetric connector has a threaded first end and a second end having a plurality of resilient springy fingers extending therefrom in the axial direction, the fingers having extensions directed radially inward. A second hollow radially symmetric connector has a threaded first end, the second connector also having a circumferential groove on the outer surface. The second connector detachably attaches coaxially to the first connector by spring force pressing the finger extensions of the first connector into the groove of the second connector, whereby the second connector may rotate about the coaxial axis relative to the first connector. 
     A first sleeve is positioned over a length of the first optical fiber and is received into an opening in the threaded end of the first connector, the first sleeve pressing against the first connector and against the first fiber. A second sleeve is positioned over a length of the second optical fiber and is received into the second connector, the second sleeve pressing against the second connector and against the second fiber. 
     A first bushing securely fits into a space in the second end of the first connector and receives an end of the first fiber after the fiber jacket and a portion of the fiber cladding has been stripped from said end. The first bushing has an inner lip against which the first fiber end presses. A second bushing securely fits into a space in a second end of the second connector and receives an end of the second optical fiber after the fiber jacket and a portion of the fiber cladding has been stripped from said end. The second bushing has an inner lip against which the second fiber end presses. 
     A first compression fitting is provided to secure the first fiber end to the first connector. The first compression fitting includes a split ferrule ring which fits onto the first sleeve, and a ferrule nut which accepts the split ferrule ring and threads onto the threaded first end of the first connector, whereby the first sleeve distributively compresses against the first fiber end and secures the first fiber end in the first connector. 
     A second compression fitting is provided to secure the second fiber end to the second connector. The second compression fitting includes an insert with a flange which presses against the second sleeve. A nut accepts the flange of the insert and threads onto the threaded first end of the second connector, whereby the flange compresses against the second sleeve and compressively secures the second fiber end in the second connector 
     In accordance with another aspect of the present invention, an optical commutator for coupling a second fiber end to a first fiber end in a detachable rotatable manner is disclosed. A second connecting piece is essentially tubular in shape. The second fiber end is inserted completely through the second connecting piece and held rigidly therein such that the second fiber end is set back a preselected distance. A first connecting piece is essentially tubular in shape and essentially divided along the axial direction into a first portion into which the first fiber end is inserted and held rigidly, and a second portion into which a portion of the second connecting piece is coaxially detachably inserted and rotatably attached therein. The first portion and the second portion are apportioned such that the first fiber end is coaxial with and in close proximity to the second fiber end whereby light coupling across the fiber ends is obtained. 
     Preferably, the detachable attachment of the second connecting piece to the first connecting piece second portion includes an axially symmetric groove on an outer surface of the second connecting piece, and an axially symmetric protrusion on an inner surface of the second portion of the first connecting piece which essentially mates with the axially symmetric groove of the second connecting piece. 
     One advantage of the present invention is that a fully rotatable light-emitting head may remain cool during operation independent of the temperature of the light source. 
     Another advantage of the present invention is that it decouples the light-emitting head from the light source of a flexibly positioned lighting source. 
     Another advantage of the present invention is that it permits full rotation of an arm bearing a light-emitting head about any angle, even including angles beyond 0°-360°, i.e. multiple turn rotation. 
     Another advantage of the present invention is that it provides a rotatable fiber coupling which is easily detachable. 
     Another advantage of the present invention is that it facilitates a modular lighting system wherein multiple detachable lighting fixtures are available for different applications. 
     Yet another advantage of the present invention is that it efficiently couples light via fiber optical connection from a light source through a fully, continuously rotatable joint in a lamp arm. 
     Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for the purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
     FIG. 1 is an exploded view of the preferred embodiment of the subject optical commutator; 
     FIG. 2 is a cross-sectional view of the optical commutator of FIG. 1 taken along line  2 — 2 ; 
     FIG. 3 is a cross-sectional view of the first connector portion of the commutator shown in FIG. 1 taken along line  3 — 3 ; 
     FIG. 4 is a cross-sectional view of the second connector portion of the commutator shown in FIG. 1 taken along line  4 — 4 ; and 
     FIG. 5 is a side view of the bushings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1-5, a preferred embodiment of the invention will be described. The subject rotatable fiber coupler or optical commutator  10  is provided to couple a pair of associated optical fiber ends  12  and  14  in a rotatable manner. A first connector body member  16  has a generally cylindrical shape and is preferably radially symmetric about an axis  17  and hollow. First connector  16  has a threaded end  18 , and a second end  20  which includes a plurality of springy fingers  22  extending axially therefrom in a direction opposite from the threaded end. The fingers each have an extension or protrusion  24  directed radially inward. Preferably, a mounting bracket  26  is integrally formed into the first connector body member  16  whereby the first connector may be secured to an associated fixture by mounting holes  28  or the like. It will be recognized that first connector  16  defines a first portion  30  into which the first fiber end is selectively inserted, and a second portion  32  adopted to relatively receive a second connector  40  in a manner to be described below. 
     The second connector body member  40  has a generally cylindrical shape and is also preferably hollow and radially symmetric about an axis  42 . Second connector  40  includes a threaded end  44  and a radially symmetric circumferential groove  46 . Second connector  40  is sized to fit inside the fingers  22  of first connector  16  so that a circumferential groove  46  aligns with finger protrusions  24  whereby the first connector  16  and the second connector  40  are detachably coupled, being held together by spring force pressing the finger extensions or protrusions  24  retained in groove  46 . The detachable coupling essentially coaxially aligns the symmetry axes  17  and  42  of the first and second connectors  16 ,  40  but permits unfettered relative rotational movement of connectors  16 ,  40  about the coincident axes  17 ,  42 . It will be recognized that although the preferred springy finger-and-groove configuration is illustrated herein for holding the connectors in the coupled relative orientation, many other rotatable interconnects are also contemplated such as replacing the springy fingers  22  with a continuous opening having radially inwardly protruding semi-flexible elements, and other suitable variations or equivalent constructions. 
     Preferably, the first fiber end  12  is rigidly attached to the first connector  16  and the second fiber end  14  is rigidly attached to the second connector  40 . The pair of fiber ends are coaxially oriented and located in precise close proximity when the first and second connectors are brought together and coupled. As a consequence, the relative rotational freedom of connectors  16 ,  40  provides equivalent relative rotational freedom of the fiber ends  12 ,  14  in accordance with the desired mechanical operation of the subject optical commutator  10 . The connectors  16 ,  40  are selectively mechanically coupled by cooperative interaction between the resilient springy fingers  22  of first connector  16  and the groove  46  of second connector  40  as described previously. In that way, the fiber ends are selectively optically coupled by the subject optical commutator  10 . 
     The rigid attachment of first fiber end  12  with first connector  16  is now described with reference to FIGS. 2 and 3. A first sleeve  50  is inserted into an opening  52  at the threaded end  18  of first connector  16 . First sleeve  50  does not completely insert, but rather extends slightly beyond the threaded end  18  of first connector  16  when maximally inserted. 
     A first bushing  54  is tightly inserted into an opening  56  accessed through second end  20  of first connector  16  and is held in place preferably by friction. As seen in FIG. 5, bushing  54  has an inner opening  100  defining an inside diameter that is preferably essentially the same as the inside diameter of a portion  57  of first connector  16  formed between sleeve opening  52  and bushing opening  56 . As shown in FIG. 5, bushing  54  also has an inner lip  110  on one end. 
     The fiber jacket  51  and a portion of the optical fiber cladding (not shown) is stripped off a portion  53  of first fiber end  12 . The stripping preferably removes a portion of the fiber cladding because closer tolerances are realized when the cladding is removed compared with jacket removal. The outer diameter of the stripped section  53  of first fiber end  12  preferably matches the inner diameter of bushing  54 , or equivalently matches the inner diameter of portion  57  of first connector  16 , so that as first fiber end  12  is slidably inserted into the first connector assembly the stripped portion  53  of first fiber end  12  fits closely within bushing  54  and portion  57  of first connector  16  to obtain precise coaxial alignment of first fiber end  12  relative to first connector axis  17 , and also to prevent torsional motion of first fiber end  12 . First fiber end  12  preferably presses against inner lip  110  of bushing  54  to precisely define the axial position of the first fiber end  12 . 
     A first compression fitting  60  is provided for locking first fiber end  12  in place within first connector  16 . First compression fitting  60  includes a split ferrule ring  62  which fits onto the first sleeve  50 , and a ferrule nut  64  which accepts split ferrule ring  62  and threads onto threaded first end  18  of first connector  16 . As ferrule nut  64  is tightened, split ferrule ring  62  compresses first sleeve  50  against first fiber end  12 . First sleeve  50  thereby distributes the compressive force along an extended length of first fiber end  12 . Of course, other suitable fittings may alternatively be employed, such as replacing the split ferrule ring with an insert including a flange which compresses against first sleeve  50 . 
     Turning now to the second connector  40  shown in FIGS. 2 and 4, a second sleeve  70  is inserted into an opening  72  at the threaded end  44  of second connector  40 . Second sleeve  70  does not completely insert, but rather extends slightly beyond the threaded end  44  of second connector  40  when maximally inserted. 
     A second bushing  74  is tightly inserted into an opening  76  at second end  78  of second connector  40  and is preferably held in place by friction. Bushing  74  has essentially the same conformation as bushing  54  used in conjunction with first connector  16 , and has an inner opening  100  defining an inside diameter preferably essentially the same as the inside diameter of a portion  77  of second connector  40  lying between sleeve opening  72  and bushing opening  76 . As shown in FIG. 5, bushing  74  also has an inner lip  110  on one end. 
     The fiber jacket  71  and a portion of the optical fiber cladding (not shown) is stripped off a portion  73  of second fiber end  14 . The stripping preferably removes a portion of the fiber cladding because closer tolerances are obtainable for cladding removal compared with jacket removal. The outer diameter of the stripped section  73  of second fiber end  14  preferably matches the inner diameter of bushing  74 , or equivalently matches the inner diameter of portion  77  of second connector  40 , so that as second fiber end  14  is slidably inserted into the second connector assembly the stripped section  73  of second fiber end  14  fits closely within bushing  74  and portion  77  of second connector  40  to obtain precise coaxial alignment of second fiber end  14  with second connector axis  42 , and also to prevent torsional motion of second fiber end  14 . Second fiber end  14  preferably presses against inner lip  110  of bushing  74  to precisely define the axial position of second fiber end  14  relative to the connector body  40 . 
     A second compression fitting  80  locks second fiber end  14  in place within second connector  40 . Second compression fitting  80  includes an insert  82  with a flange  83  which presses against second sleeve  70 , and a nut  84  which accepts flange  83  of insert  82  and threads onto threaded first end  44  of second connector  40 . Nut  84  drives insert flange  83  against second sleeve  70  as nut  84  threads onto threaded end  44  of second connector  40 , and second sleeve  70  is compressively collapsed against second fiber end  14 . Second sleeve  70  thereby distributes the compressive force along second fiber end  14 . Of course, other suitable fittings may alternatively be employed, such as replacing the insert with a split ferrule ring similar to that used for securing first fiber end  12  within first connector  16 . 
     Preferably, the rigid attachment of second fiber end  14  to second connector  40  includes a third sleeve  90  positioned over a length of the second fiber jacket  91  and extending over a portion of insert  82  to reduce the possibility of fiber damage due to excessive mechanical bending. Although not illustrated here, a similar sleeve may be included for sealing the connection of first fiber end  12  to first connector  16  if the split ferrule ring  62  is replaced by an insert similar to the insert  82  shown for second compression fitting  80 . 
     The subject rotatable optical fiber coupler  10  is preferably manufactured from a lightweight, sturdy material such as a plastic material. In order to provide a precise gap between the fiber ends required for good light coupling across the gap, it was found preferable to use separately manufactured bushings as described above, and these bushings are preferably made from aluminum. However, bushings  54 ,  74  are contemplated to be manufactured from other materials as well, including plastic. In that regard, bushing  54  may be integrally formed with the first connector  16  and manufactured as a single unitary piece with a sufficiently thin inner lip. Similarly, bushing  74  may be integrally formed with the second connector  40 . Inner surfaces of bushings  54 ,  74  are preferably polished to be highly reflective, especially in the vicinity of the extreme fiber tips where the light coupling across the fiber tips  12 ,  14  occurs. 
     Having described the preferred structure of the subject optical commutator  10 , the operation of the commutator is now described. For exemplary purposes only, it will be assumed that first fiber end  12  is connected by optical fiber to a stationary light source (not shown) and first connector  16  is rigidly attached by mounting bracket  26  to a wall, ceiling, or other fixed location (not shown). Second connector  40  may then be inserted into first connector  16  by simply pressing second end  78  of second connector  40  into the springy fingers  22  of first connector  16  until the finger extensions  24  engage with groove  46  of the second connector  40 . Preferably, fingers  22  are sufficiently stiff to hold second connector  40  in a fixed position in the absence of manual manipulation. By applying manual force, second connector  40  may be rotated about axis  42  without any angular limitations. For all relative rotational angles between first connector  16  and second connector  40 , fiber ends  12 ,  14  remain in precise coaxial alignment defined by the engagement between the connector bodies  16 ,  40 , and in close axial proximity defined essentially by the thicknesses of inner lips  110  of bushings  54 ,  74 . In the present embodiment, inner lip  110  thicknesses are approximately 15 thousandths of an inch for each lip  110 . A thicker inner lip  110  typically improves manufacturability but reduces light coupling efficiency due to a correspondingly larger gap. If desired, second connector  40  and its associated arm may be removed by applying a moderate manual force in opposite axial directions to the first and second connectors  16 ,  40  respectively. 
     One major advantage of the present invention is that it facilitates a modular lighting system wherein multiple detachable lighting fixtures are available for different applications, each including a fiber coupler terminating in first connector  40 . Additionally, a single light source may include several fiber connections each terminating in a first connector  16 , and possibly each terminating in a different area of a room or even in different rooms. Any of the detachable lighting fixtures of the modular lighting system may then be attached to any of the several fiber connections of the light source. 
     Other applications, including applications outside of lighting, are contemplated for the subject commutator. The detachable rotatable optical commutator finds application in laser surgery systems, fiber optical communication systems, and other applications where a versatile and detachable fiber coupling may be desirable. 
     The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.