Abstract:
A sleeve for connecting ferrules supporting optical fibers has a tubular body having a first end surface, a second end surface opposite the first end surface, an inner peripheral surface, and an outer peripheral surface. Convex projections are disposed on the inner peripheral surface of the tubular body and extend continuously from the first end surface to the second end surface of the tubular body.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a sleeve for connecting between ferrules to hold, for example, an optical fiber. 
     Conventionally, split sleeves as shown in FIG. 4 have generally being used to photo-couple to one another to each other, in a simple manner, ferrules for holding an optical fiber. As shown in FIG. 4, the conventional split sleeve  100  is formed with one strip of a penetrating groove  102  in an axial direction of the cylindrical member  101 , which is made of ceramics such as zirconia and usually formed by sintering a cylindrical member, then lapping an inner surface, and then forming a slit by grinding. There has also been used a split sleeve  200  as shown in FIG. 5 that has a plurality of axially-extending concave portions  202  that are spaced at such an interval as to be in parallel with each other on an inner peripheral surface  201   a  of the cylindrical member  201  to have one strip penetrating groove  203  formed in the axial direction. 
     With the shape having the one strip penetrating groove provided in the cylindrical member as shown in FIG. 4, however, the inner peripheral surface is usually formed in a surface without roughening. Accordingly, it becomes difficult to maintain the position in which the ferrule is held constant, and the inner diameter dimension tends to deviate. Therefore, there is a problem that the center of the ferrule may somewhat deviate thereby degrading alignment stability. For example, when the sleeve is used to connect ferrules holding an optical fiber, the coupling loss becomes large. Also, the split sleeve as described above tends to be affected by dusts or ground powders, raising a problem of instability in withdrawal force/coupling loss. 
     Under such circumstances, a split sleeve as shown in FIG. 5 has been used which has the concave portions  202  provided on the inner peripheral surface of the cylindrical member. However, the split sleeve shown in FIG. 5 has to hold a ferrule in a line so that there are disadvantages of high friction and dust occurence. Also, the contact surface between the ferrule and the cylindrical member is small so that the ferrule tends to be removed off, thus keeping the coupling state insufficient. 
     The present invention has been made to overcome the foregoing drawbacks in the conventional art. It is the object of the present invention to provide a sleeve which is excellent in alignment stability and capable of positively supporting a ferrule with less dust occurrence. Another object of the present invention is to provide a manufacturing method for the sleeve. 
     SUMMARY OF THE INVENTION 
     A first form of the present invention lies in a sleeve adapted for fitting rod members therein from respective sides to thereby place the rod members at their tip surfaces in abutment against each other, characterized in that: the sleeve is generally in a cylindrical form to have at least three convex projections or strips provided on an inner peripheral surface that continuously and helically extend at an equal interval from one end to the other end of the sleeve. 
     This can increase the holding force in a ferrule-withdrawal direction to thereby improve alignment stability. 
     Here, the sleeve may have at least one strip of an axially extending penetrating groove. 
     A second form of the present invention lies in a sleeve adapted for fitting rod members therein from respective sides to thereby place the rod members at their tip surfaces in abutment against each other, characterized in that: the sleeve is generally in a cylindrical form to have at least three convex strips provided in an inner peripheral surface that project in a direction inclined from a radial direction to a predetermined circumferential direction so as to extend continuously and at an equal interval from one end to the other end of the sleeve. 
     This enables the convex strip to be elastically deformable by a slight amount in a radial direction so that the ferrule can be given with an urging force and positively held due to the radial elastic deformation. 
     Here, the convex strip may be provided to helically extend between the ends of the sleeve. 
     Also, the sleeve may have at least one strip of a penetrating groove extending in an axial direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are views of a sleeve according to one embodiment of the present invention, wherein FIG. 1A is a perspective view and FIG. 1B is a sectional view. 
     FIGS. 2A and 2B are views of a sleeve according to another embodiment of the present invention, wherein FIG. 2A is a perspective view and FIG. 2B is a side view. 
     FIGS. 3A and 3B are perspective views of a split sleeve according to the present embodiment. 
     FIG. 4 is a perspective view showing one example of a conventional split sleeve. 
     FIG. 5 is a perspective view showing another example of a conventional split sleeve. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Explanations will be made hereinbelow on embodiments of the present invention with reference to the drawings. 
     (Embodiment 1) 
     FIG. 1 is a perspective view of a sleeve according to a present embodiment. 
     As shown in FIG. 1, the sleeve  10  of the present embodiment comprises a generally cylindrical tubular body or member  11  having a first end surface  11   b , a second end surface  11   c , an inner peripheral surface  11   a , an outer peripheral surface  11   d , and projections three convex projections or strips  12 A,  12 B and  12 C (hereinafter represented by  12 ) provided on the inner peripheral surface  11   a  so as to helically and continuously extend at an equal interval from one end to the other end of the generally cylindrical member  11 . These convex strips  12  are sectionally in an arcuate form so that these arcuate convex strips  12  holds a ferrule in linear contact therewith in a manner surrounding an outer periphery of the ferrule. 
     The sleeve  10  employs for example, as a material, yttria-added partially-stabilized zirconia (ZrO 2 . Y 2 O 3  (Y 2 O 3 : contained 3% by mol), which is formed by heating, for example, at 150° C. and further sintering at a high temperature of approximately 1500° C. 
     The sleeve  10  has an increased holding force in a ferrule-removal direction by helically providing the convex strips, as compared to the one provided with convex strips in parallel with the afore-said axis, making possible to improve alignment stability. Also, since the ferrule is held in linear contact, it is possible to reduce the occurrence of dusts and decrease the coupling loss. 
     Incidentally, the sleeve of the present embodiment having the convex strips  12  can be manufactured by forming during the formation and sintering. 
     (Embodiment 2) 
     FIG. 2A is a perspective view of a sleeve according to a second embodiment, while FIG. 2B is a side view of a sleeve of the second embodiment. As shown in FIG.  2 A and FIG. 2B, the sleeve  20  of this embodiment comprises a generally cylindrical tubular body or member  21  having a first end surface  21   b , a second end surface  21   c , an inner peripheral surface  21   a , an outer peripheral surface  21   d , and three convex projections or strips  22 A,  22 B and  22 C (hereinafter represented by  22 ) provided projecting at a predetermined inclined angle θ from a radial direction to a predetermined circumferential direction on the inner peripheral surface  21   a  so as to extend continuously and at an equal interval from one end to the other end of the generally cylindrical member  21 . Each convex strip  22  has a convex tip portion  23  having a radius R, and connecting portions  24  and  25  connecting the convex strip  22  to the inner peripheral surface  21   a  of the generally cylindrical member  21  and having respective radiuses R. These convex strips  22  and the inner peripheral surface  21   a  have a space  26  existing therebetween so that the convex strips are somewhat elastically deformable in the radial direction. 
     According to the sleeve of the present embodiment, although the ferrule can be held in linear contact in a line form, it is positively supported because an urging force due to radial deformation of the convex strip is available. Also, the convex strip  22  of the present embodiment may be helically provided similarly to the embodiment 1. This can increase the holding strength in a ferrule-withdrawal direction. 
     (Embodiment 3) 
     Further, each sleeve of the above-stated embodiments may have a penetrating groove ex tending in the axial direction. FIG. 3 shows one example of a split sleeve of a present embodiment. 
     As shown in FIG. 3A, the split sleeve  30  is the same as the sleeve  10  of the embodiment  1  except for having a longitudinal slot or penetrating groove  33  extending in the axial direction in the generally cylindrical member  31 , so that it has convex strips  32 A- 32 C on the inner peripheral surface  31   a.    
     This split sleeve  30  is formed from a split sleeve material  30 A shown in FIG.  3 B. The split sleeve material  30 A shown in FIG. 3B has, at respective ends, annular end portions  34  and  35  at which no penetrating groove  33  is formed. This split sleeve material  30 A is formed into a split sleeve  30  as shown FIG. 3A, by cutting the annular end portions at the respective ends to open the both ends of the penetrating groove  33 . 
     This split sleeve  30  is very easy to manufacture because the penetrating groove is formed in a different manufacturing method from the conventional. 
     Incidentally, the shape of the penetrating groove is not limited to the above. For example, a plurality strips of penetrating grooves may be provided that do not continue up to the respective end portions. 
     As explained above, according to the present invention, the ferrule can be held more positively by providing the convex strips helically or elastically deformably on the inner peripheral surface of the generally cylindrical member. Also, the convex strips and the ferrule are in linear contact so that occurrence of dusts can be reduced to a remarkable extent.