Abstract:
An optical fiber connector includes a sleeve having a first end surface, an abutment having a second end surface, the abutment being located within the sleeve and axially movable within the sleeve, and at least three balls located between the first end surface and the second end surface within the sleeve for clamping an optical fiber, the balls having centers disposed in a plane and being axially and radially displaceable in the sleeve and biased radially inwardly toward a central axis of the sleeve. At least one of the first end surface and the second end surface includes a conical surface.

Description:
CLAIM OF PRIORITY 
     This application claims priority under 35 USC § 119(a) to patent application serial number EP 03 012 348.3, filed on May 30, 2003, the entire contents of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to optical fibers and, more particularly to an optical fiber connector arrangement. 
     BACKGROUND 
     Optical fibers, which are used for transmitting high power laser light, include a light-guiding core and at least one cladding that has a lower optical refractive index than the light-guiding core, due to a dopant in the cladding, such that, up to certain angles, total reflection is produced at the interface between the core and the cladding. A protective jacket surrounds the cladding. In optical fiber production, either the core diameter may be produced to have smaller tolerances and the cladding diameter larger tolerances or vice versa. The beam quality of the light guided in the optical fiber is generally better when smaller tolerances of the diameter of the light-guiding core are used. 
     German patent application serial number DE 2853649 C2 discloses two connectors for coupling two optical fibers. Each connector has a sleeve that is disposed to be axially resilient, with three balls that are disposed in one plane and between which the optical fiber is clamped. The balls simultaneously center the optical fiber and define the jacket diameter of the optical fiber relative to the three balls. When two connectors are connected, the balls of each connector are aligned with each other, and the jacket diameters of both optical fibers are concentrically aligned to each other. However, the production of optical fibers entails eccentricities between core and jacket, such that the light-guiding cores may be disposed in a corresponding eccentric relation to each other, with the consequence that a large portion of the light energy is not coupled from one fiber into the other fiber but is absorbed in the connector and converted into waste heat. 
     For solid state lasers, such as, for example, a Nd:YAG laser, the beam quality tends to increase at higher output powers. When the high power solid state laser beam is transported in an optical fiber, to obtain this beam quality also on a work piece to be processed, the cross-section of the light-guiding core of the optical fiber must be reduced. To ensure “plug and play” capability of the optical cable on the laser or on the processing unit with minimum loss, the light-guiding core of the laser optical fiber must be positioned in a very precise manner in a radial direction within the connector. 
     SUMMARY 
     An optical fiber connector arrangement having a least three balls that are simultaneously displaced radially and axially with a sleeve of the connector can be used to fix the location of the core of an optical fiber. 
     In a first general aspect, an optical fiber connector includes a sleeve having a first end surface, an abutment having a second end surface, the abutment being located within the sleeve and axially movable within the sleeve, and at least three balls located between the first end surface and the second end surface within the sleeve for clamping an optical fiber, the balls having centers disposed in a plane and being axially and radially displaceable in the sleeve and biased radially inwardly toward a central axis of the sleeve. At least one of the first end surface and the second end surface includes a conical surface. 
     In another general aspect, an optical fiber connector includes an optical fiber, a sleeve having an first end surface, an abutment having a second end surface, the abutment being located within the sleeve and axially movable within the sleeve, at least three balls located between the first end surface and the second end surface within the sleeve, the balls having centers disposed in a plane and being axially and radially displaceable in the sleeve and biased radially inwardly toward a central axis of the sleeve against the optical fiber and clamping the optical fiber in a fixed position, where at least the first end surface or the second end surface includes a conical surface, and a housing having a central opening larger than an outer diameter of the sleeve, where the sleeve is fixed within the central opening in a position in which a core of the optical fiber is positioned on a central axis of the housing. 
     One or more of the following features may be included. For example, the conical surface can have a conical angle of about 60° to about 120°, or a conical angle of about 90°. The optical fiber connector can further include a spring for biasing the first end surface and the second end surface towards each other. The spring can be supported on an axially adjustable spring abutment within the sleeve. The optical fiber connector can further include a housing having a central opening larger than an outer diameter of the sleeve, where the sleeve is fixed within the central opening in a position in which a central core of an optical fiber clamped by the balls can be fixed on the central axis. The sleeve can be fixed within the housing through material-bonding or by an adhesive in a non-positive manner. Each ball can provide a radially inwardly biased fixing point for clamping an optical fiber. The balls can include a material selected from the group consisting of quartz glass, ceramic, and polished metal. The metal material can include a reflecting coating. 
     In another general aspect, an optical fiber connector arrangement includes an optical fiber, a connector, and a sleeve disposed within a central opening of the connector and in which the light guide is clamped by mutually crossing round pins that form a triangular clamping opening that is larger than an outer diameter of the sleeve and that is centered on a central axis of the connector. 
     One or more of the following features may be included. For example, at least one pin can be an adjustable pin that can be adjusted to change the cross-section of the triangular clamping opening. One end of the adjustable pin can be fixed in the sleeve and the other end can be disposed such that it can be deflected. 
     In another general aspect, a method for clamping an optical fiber into a position on a central axis of an optical fiber connector includes, obtaining an optical fiber connector that includes at least three balls, arranging the balls around the optical fiber and between a first end surface of a sleeve that is positioned with the connector and a second end surface of an abutment positioned with the connector, where at least one of the first end surface and the second end surface includes a conical surface, and displacing the first end surface towards the second end surface to cause axial displacement of the balls and radial displacement of the balls towards the central axis and against an outer surface of the optical fiber. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     Other features and advantages of the invention will be apparent from the following detailed description, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal sectional view of an optical fiber connector arrangement with an optical fiber that is held in a sleeve. 
         FIG. 2  is an enlarged view of the sleeve for holding an optical fiber. 
         FIG. 3  is a cross-sectional view of the sleeve through the line III—III of  FIG. 2 . 
         FIG. 4  is an enlarged view of the sleeve for holding an optical fiber. 
         FIG. 5  is a perspective view of a sleeve for holding an optical fiber connector arrangement. 
         FIG. 6  is an end view of the sleeve of  FIG. 5 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     An optical fiber connector arrangement  1 , as shown in  FIG. 1 , includes a sleeve  10 , in which the jacket of an optical fiber  2  is clamped, and a connector housing  3  with a central opening  4 , in which the sleeve  10  is mounted. The diameter of the opening  4  is larger than the outer diameter of the sleeve  10  that is fixed in the opening  4  in that position, in which the light-guiding core of the optical fiber  2 , which is clamped in the sleeve  10 , is centered to the connector axis  5 . The sleeve  10  is aligned in the connector housing  3  through an adjuster that engages with the sleeve  10  and radially displaces the sleeve in the opening  4  in a direction shown by the double arrow  6  until the optical fiber core of the clamped optical fiber  2  is adjusted coaxially to the connector axis  5  or concentrically to its conical connector surface  7 . When this position has been reached, the sleeve  10  is rigidly connected to the connector housing  3  through material-bonding, in a non-positive fashion or by an adhesive (e.g., by welding, soldering, gluing, clamping). 
     As shown in  FIGS. 2 and 3 , the optical fiber  2  is held in the sleeve  10  by three quartz glass balls  11  that are disposed in one plane such that they are mutually offset by 120° and are disposed between a cone  12 , provided in the sleeve  10 , and an abutment  13 . The cone  12  and the abutment  13  each have a central opening  14 ,  15  for the optical fiber  2 . The abutment  13  is formed as a pressure plate and is disposed in the sleeve  10  such that it can be axially displaced in a direction shown by the double arrow  16  and is biased by an axially acting pressure spring  17  in the direction towards the cone  12 . The pressure spring  17  is supported in the sleeve  10  on a spring abutment  18  (e.g., a threaded ring) that can be axially displaced to set the spring force acting on the abutment  13  and thereby of the bias acting on the balls  11 . 
     The pressure spring  17  applies a force to the balls  11  through the abutment  13  and causes the balls  11  to contact the cone  12 , where the axial force is divided also into a force component that acts radially on the balls  11  such that the balls  11  exert a radial force on the laser optical fiber  2 , thereby keeping the optical fiber free from play. The pressing force acting on the optical fiber  2  is defined by the conical angle (e.g., 90°) and the spring force of the pressure spring  17 . The conical angle need not be 90° and can vary (e.g., from 60° to about 120°). 
     In case of a temperature change, the balls  11  permit radial expansion of the optical fiber  2  against the force of the pressure spring  17  as well as change of the axial length between the optical fiber  2  and the sleeve  10  due to different longitudinal expansion coefficients of the various components. The ability of the connector arrangement  1  to adapt to temperature changes allows the position of the optical fiber  2  in the connector housing  3  to remain fixed and to maintain stability over the entire working temperature range of the connector arrangement  1 , thereby preventing play in the position of the optical fiber  2  or deformation forces acting on the optical fiber  2  due to temperature changes. Also, diameter changes and changes of the axial length of the optical fiber  2  or of the connector housing  3  due to temperature changes are possible without producing play in position of the optical fiber  2  or external forces on the optical fiber  2 , which would cause tension in, and deformation of, the optical fiber  2 . The tolerance of the optical fiber&#39;s jacket diameter has little or no effect on centering of the optical fiber  2 , thus permitting production of optical fibers with very narrow core diameter tolerances, which has a positive effect on the beam quality of the laser system. 
     Compared to the sleeve  10 , a sleeve  10 ′ shown in  FIG. 4  differs in that the cone  12 ′ is provided on a pressure plate  19  that is disposed such that it can be axially displaced in a direction shown by the double arrow  16 , and an abutment  13 ′ is mounted to the bottom of the sleeve  10 ′. The pressure plate  19  is loaded by the pressure spring  17  and forces the balls  11  against the abutment  13 ′ and, due to the cone  12 ′, also against the optical fiber  2 . 
     In another embodiment, a sleeve  20 , as shown in  FIGS. 5 and 6 , includes three mutually crossing round pins  21 ,  22 , and  23  of quartz glass. The pins, which are disposed at angles of 120°, form a triangular, equally-sided clamping opening  24  within the sleeve  20 , in which the optical fiber  2  is clamped. Two pins  21  and  22  are tightly fixed in the sleeve  20 , while the third pin  23  can be disposed in the sleeve  20 , such that the third pin  23  can be adjusted along the direction of the double arrow  25 . One end of the third pin  23  is therefore fixed in the sleeve  20  and the other end is fixed in a ring  26 , which can be rotatably disposed outside on the sleeve  20 . When the optical fiber  2  has been inserted into the clamping opening  24 , the ring  26  can be rotated until the third pin  23  positions the optical fiber  2 , such that the optical fiber  2  tangentially abuts all three pins in one plane. The ring  26  can be fixed to the sleeve  20  in this position. In case of temperature changes, the pins  21 ,  22 , and  23  permit radial extension of the optical fiber  2  either due to their elasticity or against the action of a torsion spring (not shown) acting on the third pin  23  as well as change of the axial length between the optical fiber  2  and sleeve  20  due to different longitudinal expansion coefficients of the various components. 
     The balls  11  and pins  21 ,  22 , and  23  can be produced from quartz glass that has a high transmission factor for laser light of the corresponding wavelength of a solid state laser, or from ceramics that have a high temperature stability. Alternatively, the balls  11  and pins  21 ,  22 , and  23  can be produced from a metallic material, which can be polished or provided with a highly-reflecting coating (e.g., of gold) and therefore mainly reflect the laser radiation. This can reduces the detrimental influence of the laser radiation on the optical fiber holder due to scattered radiation and radiation that is not coupled into the optical fiber  2  during adjustment or in case of imperfect radial orientation. 
     The optical fiber connector arrangement  1  can be used to accurately position an optical fibers  2 , for example, when light from one optical fiber  2  is coupled to another optical fiber. 
     Other Embodiments 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other embodiments are within the scope of the following claims.