Patent Publication Number: US-6705768-B2

Title: Optical connector, sleeve, and manufacturing method for sleeve

Description:
This is a divisional of application Ser. No. 09/457,009 filed Dec. 8, 1999 U.S. Pat. No. 6,443,630; the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     This invention relates to an optical connector used with a multiplex transmission circuit of a vehicle, such as an automobile, a sleeve placed in a receptacle forming a part of the optical connector, and a manufacturing method for the sleeve. 
     2. Related Art 
     As this type of optical connector and sleeve, an optical connector previously proposed by the applicant (art disclosed in JP-B-6-33443UM) is generally known. 
     The optical connector and sleeve disclosed in the gazette will be discussed with reference to FIGS. 9 to  11 . 
     First, in FIG. 9, reference numeral  1  denotes an optical connector and the optical connector  1  comprises a receptacle  2  as a machine side connector and an optical plug  3  as an optical fiber side connector. 
     As shown in FIGS. 9 and 10, the receptacle  2  has a housing  4  made of a synthetic resin and storage chambers  5  and  5  in the housing  4  stores reception and transmission modules  6  and  6 ′ in a state in which they are supported on back sheets  7  and  7  each made of an elastic member such as rubber. On the rear face, a cap  8  is placed, and reception tubes  10  and  10  extended forward matching the axes of lenses  9  and  9  are placed ahead of the storage chambers  5  and  5  in which the reception and transmission modules  6  and  6 ′ are supported. Sleeves  13  and  13  each comprising a light transmission member  11  consisting of a core and a clad (not shown) (for example, a multimode plastic optical fiber of about Ø1) bonded and fixed to a holder  12  like a metal cylinder and ground on both end faces are inserted into the reception tubes  10  and  10 . 
     The optical fiber  3  is fitted and connected to the receptacle  2  and as shown in FIGS. 9 and 11, comprises ferrule assemblies  15  and  15  for covering optical fibers  14  and  14  (only one is shown throughout the drawings) in a state in which the ends of the optical fibers  14  and  14  are exposed at the tips, a plug housing  17  provided with a tubular partition wall  16  for housing and protecting the ferrule assemblies  15  and  15 , a spring cap  18  fitted and fixed to the plug housing  17 , and a boot  19  fitted to the rear part of the spring cap  18 . 
     The plug housing  17  is formed with shoulder part  17   a  engaging collar-like retention parts  15   a  and  15   a  placed in the latter half parts of the outer peripheries of the ferrule assemblies  15  and  15  and springs  20  and  20  are placed between the retention parts  15   a  and  15   a  and inner tube parts  18   a  and  18   a  of the spring cap  18  so that the ferrule assemblies  15  and  15  are urged forward all the time. 
     The retention parts  15   a  and  15   a  engage the shoulder part  17   a , whereby tip parts A of the ferrule assemblies  15  and  15  (see FIG. 11; corresponding to positions of incidence and emission end faces (light reception face and light emission face) of the optical fibers  14 ) are always retracted inside from front end face B of the plug housing  17  (see FIG.  11 ). 
     In the described configuration, connection of the receptacle  2  and the optical plug  3  will be discussed with reference to FIG.  9 . 
     When the optical plug  3  is fitted to the receptacle  2 , the reception tubes  10  and  10  enter the plug housing  17  and at the same time, the ferrule assemblies  15  and  15  enter the reception tubes  10  and  10 . 
     The ferrule assemblies  15  and  15  abut the tips of the reception tubes  10  and  10  and adequate contact pressure is kept by the elastic force of the springs  20  and  20 . 
     In this state, the tip parts A (see FIG. 11) and the sleeves  13  and  13  and the lenses  9  and  9  and the sleeves  13  and  13  are placed with gaps (not shown) kept to the minimum, whereby the gap loss of the optical connector  1  is minimized, so that a transmission margin when light communication is executed can be widened. 
     [Problem to be Solved by the Invention] 
     By the way, in the described related art, a gap of 6 mm, for example, on the structure exists between the reception and transmission module  6 ,  6 ′ and the optical fiber  14 ,  14 , and the sleeve  13 ,  13  6 mm long, for example, is placed so as to bridge the gap. Preferably, the gap between the reception, transmission module  6 ,  6 ′ and the sleeve  13 ,  13  and the gap between the optical fiber  14 ,  14  and the sleeve  13 ,  13  is made zero from the relation of the described gap loss. 
     However, it is very difficult to make the gaps zero because of the combination of the members; in even the described optical connector  1 , a slight gap occurs in some cases and a light power loss occurs. 
     Taking the gap between the transmission module  6 ′ and the sleeve  13  (not shown) as an example in the description, the transmission module  6 ′ usually uses a light emitting diode and therefore if a gap occurs, a part of light emitted and diverged (emitted like radiation) from the light emitting diode leaks through the gap. A part of the leakage light is not again incident on the light transmission member  11  of the sleeve  13 , of course; thus the light leakage part leads to a light power loss. 
     Since a plastic optical fiber (POF) having the same N.A. (numerical aperture)=0.5 as the optical fiber  14  has been used as the light transmission member  11 , there is a limit on reception of light from the transmission module  6 ′ (light emitting diode). Of course, larger light than the N.A. of the light transmission member  11  exists, thus a light power loss cannot be avoided if the above-mentioned gap is contained. 
     Letting the refractive index of the core be n1 and that of the clad be n2 (n1&gt;n2), the above-mentioned N.A. is defined by a relational expression of N.A.=((n1) 2 −(n1) 2 ) ½ . 
     On the other hand, the above-described light power loss is caused by not only the gap, but also by the assembly state (position) of the sleeve  13 ,  13   
     That is, the receptacle  2  is made of a synthetic resin and a minute protrusion (not shown) for retaining the sleeve  13  is formed in the reception tube  10  molded integrally with the receptacle  2  and the sleeve  13  having the metal holder  12  is inserted into the reception tube  10 . When the sleeve  13  is inserted, the minute protrusion is scraped, for example, by the holder  12  and a longitudinal or lateral shift occurs in the optical axis. Resultantly, a light power loss occurs. 
     Giving a more detailed description, the sleeve  13  is ground on both end faces, thus the possibility that the end face of the holder  12  may be an edge is high and when the sleeve  13  is inserted into the reception tube  10 , it is hard to say that the minute protrusion functions normally. 
     For example, if four minute protrusions are formed at equal intervals in the reception tube  10  and the sleeve  13  is inserted in an insertion axis shift state, at least one of the minute protrusions is scraped by the end face of the holder  12  or is excessively compressed and crashed or broken. 
     Thus, it is easily understood that the inserted sleeve  13  loses stability, causing a shift to occur in the optical axis. 
     Therefore, also in this case, like the above-described gap problem, it is said that a light power loss cannot be avoided. 
     On the other hand, FIG. 12 graphs the optical axis shift (on horizontal axis, mm units) in a state in which the above-mentioned gap (gap amount, mm units) is contained and the light power loss (on vertical axis, dB units) to relate them to each other. 
     As also seen in the figure, it is said that the gap and the optical axis shift largely cause the light power to be lost. It is preferred that the gap amount and the optical axis shift are extremely small and how to manage them becomes a point for decreasing the light power loss. If the light power loss can be decreased, it is made possible to widen a margin optically downstream from the optical connector  1 . 
     By the way, the sleeve  13  is manufactured through a large number of steps, thus it is preferred that cost reduction is accomplished while the above-mentioned problems are solved. It is also preferred to deal with the yield produced in the manufacturing process of the optical fibers  14 , namely, waste pieces (not shown) left after several optical fibers  14  are cut away from the optical fiber source line wound around a bobbin together with the above-mentioned problems. 
     If the gap is managed more strictly than formerly, it is feared that the productivity of the members and the optical connector  1  will lower because of the dimension accuracy of the members; it does not become a preferred measure. 
     It is therefore an object of the invention to provide an optical connector, a sleeve, and a manufacturing method for the sleeve for making it possible to decrease a light power loss, to widen a transmission margin when light communication is executed, and also to reduce costs. 
     To the end, according to a first aspect of the present invention, there is provided an optical connector comprising sleeves capable of providing optical connection of an optical fiber and reception and transmission modules, the sleeves being placed between the optical fiber and the reception and transmission modules, provided in that 
     N.A. of each of the sleeves is made larger than N.A. of the optical fiber. 
     In the optical connector of a second aspect of the present invention, in the optical connector as the first aspect of the present invention, the N.A. of at least the sleeve corresponding to the transmission module is made larger than the N.A. of the optical fiber. 
     In the optical connector of a third aspect of the present invention, in the optical connector of the first or the second aspect of the present invention, the N.A. of each of the sleeves is 0.5&lt;N.A.&lt;1. 
     In the optical connector of a fourth aspect of the present invention, in the optical connector of the first or the second aspect of the present invention, the N.A. of each of the sleeves is 0.6 or 0.7. 
     In the optical connector of a fifth aspect of the present invention, in the optical connector of the first to the fourth aspect of the present invention, the sleeve is made up of a light transmission member consisting of a core and a clad having a smaller refractive index than the core has and a cylindrical and coat-like holder placed in an outer peripheral margin of the light transmission member, the holder being formed of a synthetic resin material. 
     In the optical connector of a sixth aspect of the present invention, in the optical connector as the fifth aspect of the present invention, the holder is formed of a synthetic resin material which is a material equal to or softer than a member in which the sleeve is placed. 
     In the optical connector of a seventh aspect of the present invention, in the optical connector as the fifth or the sixth aspect of the present invention, the holder is formed of polyethylene. 
     In the optical connector of an eighth aspect of the present invention, in the optical connector as the fifth to seventh aspect of the present invention, the holder can be colored and is colored in a different color from that of the member in which the sleeve is placed. 
     In the optical connector of a ninth aspect of the present invention, in the optical connector as the eighth aspect of the present invention, the color of the holder is a different family color from the color of the member in which the sleeve is placed. 
     In the optical connector a tenth aspect of the present invention, in the optical connector as the eighth or ninth aspect of the present invention, the holder is colored in two distinguishable colors. 
     In the optical connector of an eleventh aspect of the present invention, in the optical connector as the tenth aspect of the present invention, one of the two distinguishable colors is orange if the color of the member in which the sleeve is placed is black. 
     In the optical connector of a twelfth aspect of the present invention, in the optical connector in any of the fifth to eleventh aspect, a collimator lens is formed at least at one end of the light transmission member. 
     In the optical connector of a thirteenth aspect of the present invention, in the optical connector in any of the first to twelfth aspect, the sleeve is formed by cutting an optical fiber source line or a waste tip of the optical fiber source line. 
     To the end, according to a fourteenth aspect of the present invention, there is provided a sleeve being placed between an optical fiber and a reception module or a transmission module placed in an optical connector and capable of providing optical connection of the optical fiber and the reception or transmission module, the sleeve comprising a light transmission member consisting of a core and a clad having a smaller refractive index than the core has and a cylindrical and coat-like holder placed in an outer peripheral margin of the light transmission member, provided in that the sleeve is formed in a larger N.A. than that of the optical fiber and is placed corresponding to at least the transmission module. 
     In the sleeve as a fifteenth aspect of the present invention, in the sleeve as claimed in claim 14, the larger N.A. than that of the optical fiber is 0.5&lt;N.A.&lt;1. 
     In the sleeve as a sixteenth aspect of the present invention, in the sleeve as the fourteenth aspect of the present invention, the larger N.A. than that of the optical fiber is 0.6 or 0.7. 
     In the sleeve as a seventeenth aspect of the present invention, in the sleeve as the fourteenth to the sixteenth aspect of the present invention, the holder is formed of a synthetic resin material which is a material equal to or softer than a receptacle forming a part of the optical connector. 
     In the sleeve of a eighteenth aspect of the present invention in the sleeve as the seventeenth aspect of the present invention, the holder is formed of polyethylene. 
     In the sleeve of a nineteenth aspect of the present invention, in the sleeve as the seventeenth or the eighteenth aspect, the holder can be colored and is colored in a different color from that of the receptacle. 
     In the sleeve of a twentieth aspect of the present invention, in the sleeve as the nineteenth aspect of the present invention, the color of the holder is a different family color from the color of the receptacle. 
     In the sleeve of a twenty-first aspect of the present invention, in the sleeve as the nineteenth to the twentieth aspect of the present invention, the holder is colored in two distinguishable colors. 
     In the sleeve of a twenty-second aspect of the present invention, in the sleeve in any of the fourteenth to twenty-first aspect, a collimator lens is formed at least at one end of the light transmission member. 
     As the sleeve of a twenty-third aspect of the present, the sleeve in any of the fourteenth to the twenty-second aspect of the present invention, is formed by cutting an optical fiber source line or a waste tip of the optical fiber source line. 
     To the end, according to a twenty-fourth aspect of the present invention, there is provided a sleeve being placed between an optical fiber and a reception module or a transmission module placed in an optical connector and capable of providing optical connection of the optical fiber and the reception or transmission module, the sleeve comprising a light transmission member consisting of a core and a clad having a smaller refractive index than the core has and a cylindrical and coat-like holder placed in an outer peripheral margin of the light transmission member, provided in that the holder is formed of a synthetic resin material which is a material equal to or softer than a receptacle forming a part of the optical connector. 
     In the sleeve of a twenty-fifth aspect of the present invention, in the sleeve in the twenty-fourth aspect of the present invention, the holder can be colored and is colored in a different color from that of the receptacle. 
     In the sleeve of a twenty-sixth aspect of the present invention, in the sleeve in the twenty-fifth aspect of the present invention, the holder is colored in two distinguishable colors. 
     To the end, according to a twenty-seventh aspect of the present invention, there is provided a manufacturing method of a sleeve comprising a light transmission member consisting of a core and a clad having a smaller refractive index than the core has and a cylindrical and coat-like holder placed in an outer peripheral margin of the light transmission member, the manufacturing method comprising the steps of cutting an optical fiber source line or a waste tip of the optical fiber source line and then grinding both end faces. 
     In the manufacturing method of a twenty-eighth aspect of the present invention, in the manufacturing method in the twenty-seventh aspect of the present invention, the holder is colored before or after both end faces are ground. 
     According to the first aspect of the present invention, the N.A. of the sleeve is made larger, whereby the light reception amount of the sleeve, namely, the light reception limit becomes large and the coupling efficiency is improved. The transmission distance of the sleeve is markedly short as compared with that of the optical fiber, thus if the N.A. becomes large, the transmission speed is not affected and the transmission speed similar to that in the related art can be maintained. Further, the limit of light reception becomes markedly large as compared with that in the related art. Thus, if an optical axis shift occurs, the light power loss can be suppressed as much as possible. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin when light communication is executed can be provided. 
     According to the second aspect of the present invention, the N.A. of at least the sleeve corresponding to the transmission module is made large, whereby the reception limit of light emitted from the transmission module becomes markedly large than that in the related art. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided like that described above. 
     According to the third aspect of the present invention as claimed in claim 3, the N.A. of the sleeve can be selected matching the N.A. of the optical fiber used with the optical connector. 
     According to the fourth aspect of the present invention, the N.A. becomes more preferred N.A. considering the productivity and general versatility in the above-mentioned range. Advantages in the optical connector similar to those described above can be provided, of course. 
     According to fifth aspect of the present invention, it is made possible to protect the light transmission member by the holder as in the related art. The holder is a synthetic resin material and thus the holder itself becomes softer than the metal in the related art. When the holder is placed in the optical connector, the trouble as in the related art wherein the holding member of the sleeve is scraped on the end face of the holder is avoided. Thus, it is made possible to suppress an optical axis shift. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided like that described above. 
     According to the sixth aspect of the present invention, the holder is formed of a synthetic resin material which is a material equal to or softer than the member in which the sleeve is placed. Thus, it is made possible to suppress an optical axis shift. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the seventh aspect of the present invention, a synthetic resin material having general versatility is used and it is made possible to contribute to cost reduction, of course. 
     Therefore, the optical connector that can also lead to cost reduction can be provided. 
     According to the eighth aspect of the present invention, the holder is colored, whereby whether or not the sleeve is reliably placed at a predetermined position can be checked easily, and widening a gap can be suppressed. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the ninth aspect of the present invention, visibility is enhanced and it is made possible to determine the sleeve placement position reliably. 
     According to the tenth aspect of the present invention, the holder is colored in two distinguishable colors, so that visibility can be furthermore improved. It is made possible to determine the sleeve placement position reliably. 
     According to the eleventh aspect of the present invention, good visibility as a color combination is provided. Thus, it is hard to put a load on the worker who works for many hours; it is made possible to improve work efficiency. 
     Therefore, it can contribute to cost reduction. 
     According to the twelfth aspect of the present invention, if a collimator lens is provided on the incidence side, such light originally radiated to the clad can also be transmitted. In contrast, if a collimator lens is provided on the emission side, light can be gathered. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided like that described above. 
     According to the thirteenth aspect of the present invention, the sleeve is formed by cutting an optical fiber source line or a waste tip of the optical fiber source line and thus can be provided with general versatility. It contributes to improvement in yield and further the sleeve can be manufactured by recycling an optical fiber. 
     Therefore, the optical connector that can further lead to cost reduction can be provided. 
     According to the fourteenth aspect of the present invention, the reception amount of incident light, namely, the light reception limit becomes large and the coupling efficiency is improved. The transmission distance is markedly short as compared with that of the optical fiber, thus if the N.A. becomes large, the transmission speed involved in the whole of the optical fiber is not affected and the transmission speed similar to that in the related art can be maintained. Further, the limit of light reception becomes markedly large as compared with that in the related art. Thus, if an optical axis shift occurs, the light power loss can be suppressed as much as possible. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin when light communication is executed can be provided. 
     According to the fifteenth aspect of the invention, the N.A. of the sleeve can be selected matching the N.A. of the optical fiber placed in the optical connector. 
     According to the sixteenth aspect of the present invention, the N.A. becomes more preferred N.A. considering the productivity and general versatility in the above-mentioned range. Advantages in the sleeve similar to those described above can be provided, of course. 
     According to the seventeenth aspect of the present invention, the holder is formed of a synthetic resin material which is a material equal to or softer than the receptacle forming a part of the optical connector is placed. Thus, it is made possible to suppress an optical axis shift. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the eighteenth aspect of the present invention, a synthetic resin material having general versatility is used and it is made possible to contribute to cost reduction, of course. 
     Therefore, the connector that can also lead to cost reduction can be provided. 
     According to the nineteenth aspect of the invention, the holder is colored, whereby whether or not the sleeve is reliably placed at a predetermined position can be checked easily, and widening a gap when the sleeve is placed in the optical connector can be suppressed. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the twentieth aspect of the present invention as claimed in claim 20, when the sleeve is placed at the assembling time of the optical connector or the sleeve placement position is checked, visibility is enhanced. It is made possible for the worker to make an accurate determination as to placement of the sleeve. 
     According to the twenty-first aspect of the present invention, the holder is colored in two distinguishable colors, so that visibility can be furthermore improved. It is made possible to determine the sleeve placement position reliably. 
     According to the twenty-second aspect of the present invention, if a collimator lens is provided on the incidence side in the optical connector, such light originally radiated to the clad can also be transmitted. In contrast, if a collimator lens is provided on the emission side in the optical connector, light can be gathered. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin can be provided like that described above. 
     According to the twenty-third aspect of the present invention, the sleeve is formed by cutting an optical fiber source line or a waste tip of the optical fiber source line and thus the optical fiber can be provided with general versatility. It contributes to improvement in yield and further the sleeve can be manufactured by recycling an optical fiber. 
     Therefore, the sleeve that can further lead to cost reduction can be provided. 
     According to the twenty-fourth aspect of the present invention, it is made possible to protect the light transmission member by the holder as in the related art. The holder is a synthetic resin material and thus the holder itself becomes softer than the metal in the related art. When the holder is placed in the optical connector, the trouble as in the related art wherein the holding member of the sleeve is scraped on the end face of the holder is avoided. Thus, it is made possible to suppress an optical axis shift. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the twenty-fifth aspect of the present invention, the holder is colored, whereby whether or not the sleeve is reliably placed at a predetermined position can be checked easily, and widening a gap when the sleeve is placed in the optical connector can be suppressed. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the twenty-sixth aspect of the present invention as claimed in claim 26, the holder is colored in two distinguishable colors, so that visibility can be furthermore improved. It is made possible to determine the sleeve placement position reliably. 
     According to the twenty-seventh aspect of the present invention, such a manufacturing method is adopted, whereby the optical fiber placed in the optical connector can be provided with general versatility. It contributes to improvement in yield and further the sleeve can be manufactured by recycling an optical fiber. 
     Therefore, the sleeve manufacturing method that can lead to cost reduction can be provided. 
     According to the twenty-eighth aspect of the present invention, it is made possible to manufacture the sleeve independently of the coat color of the optical fiber source line that the holder is made of. 
     Therefore, it can further contribute to cost reduction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is an exploded perspective view to show one embodiment of an optical connector according to the invention; 
     FIG. 2 is an exploded perspective view of a receptacle in FIG. 1; 
     FIG. 3 is a transverse sectional view of the receptacle in FIG. 1; 
     FIG. 4 is a longitudinal sectional view of the receptacle in FIG. 1; 
     FIG. 5 is a longitudinal sectional view of a sleeve in FIG. 2; 
     FIG. 6 is a longitudinal sectional view of an optical plug in FIG. 1; 
     FIGS. 7A to  7 D are schematic representations of a manufacturing process of the sleeve in FIG. 2; FIG. 7A is a schematic representation of a cutting step, FIG. 7B is a schematic representation of a coarse grinding step, FIG. 7C is a schematic representation of a grinding step with a buff, and FIG. 7D is a schematic representation of a dirt removing step; 
     FIG. 8 is a schematic representation of a coloring state of the sleeve in FIG. 2; 
     FIG. 9 is a transverse sectional view of an optical connector in a related art; 
     FIG. 10 is transverse sectional view of a receptacle in FIG. 9; 
     FIG. 11 is transverse sectional view of an optical plug in FIG. 9; and 
     FIG. 12 is a graph to represent the relationship between optical axis shift and light power loss. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the accompanying drawings, there is shown one preferred embodiment of the invention. 
     FIG. 1 is an exploded perspective view to show one embodiment of an optical connector according to the invention. FIG. 2 is an exploded perspective view of a receptacle in FIG. 1, FIG. 3 is a transverse sectional view of the receptacle in FIG. 1, FIG. 4 is a longitudinal sectional view of the receptacle in FIG. 1, FIG. 5 is a longitudinal sectional view of a sleeve in FIG. 2, and FIG. 6 is a longitudinal sectional view of an optical plug in FIG.  1 . In FIG. 1, reference numeral  21  denotes an optical connector used with a multiplex transmission circuit of a vehicle, such as an automobile, and the optical connector  21  comprises a receptacle  22  made of a synthetic resin and an optical plug  23 . 
     As shown in FIGS. 1 and 2, the receptacle  22  has a connector housing  24  like a rectangle opened back and forth and the optical plug  23  is fitted into the front open portion of the connector housing  24 . As shown in FIG. 2, sleeves  25  and  25 , reception and transmission modules  26  and  27 , and a cap  28  are fitted into the rear open portion in order. 
     As shown in FIG. 1, the connector housing  24  is formed in the front open portion with a fit part  29  to the optical plug  23  and is formed on a front top wall with an optical plug retention part  30  that a rocking arm  44  (described later) of the optical plug  23  engages. 
     The optical plug retention part  30  is formed in such a manner that a part of the fit part  29  is projected from the inside of the connector housing  24  to the outside thereof, and is formed on the top face with a rectangular engagement hole  30   a  corresponding to a retention protrusion  44   a  of the rocking arm  44 . 
     As shown in FIG. 2, the connector housing  24  is formed in the rear open portion with storage chambers  31  and  31  corresponding to the reception and transmission modules  26  and  27 . Each of the storage chambers  31  and  31  is formed with two openings  24   a  and  24   b  piercing top and bottom walls (see FIG.  4 . Four (two because the lower margin side is not shown) engagement protrusions  28   a  formed on upper and lower margins of the cap  28  engage the openings  24   a  and  24   b , and connection parts (electrodes)  26   a  and  27   a  of the reception and transmission modules  26  and  27  are derived to the outside through the openings  24   b  (see FIG.  4 ). 
     Further, as shown in FIGS. 3 and 4, in intermediate portions in the connector housing  24 , reception tubes  32  and  32  communicating with the storage chambers  31  and  31  from the fit part  29  are extended in the direction corresponding to the above-mentioned front and rear and are formed integrally so as to project into the fit part  29 . The reception tube  32 ,  32  is stepped both inside and outside and with the inner step as a boundary, the front side becomes a tube portion for placing a ferrule assembly  37  (described later; see FIG. 6) of the optical plug  23 . In contrast, the sleeve  25 ,  25  is inserted into the rear of the step through the storage chamber  31 ,  31  and when the sleeve  25 ,  25  abuts the step, it is positioned. 
     For example, four minute protrusions (not shown) for retaining the sleeve  25 ,  25  are formed at equal intervals in the reception tube  32 ,  32  into which the sleeve  25 ,  25  is inserted. 
     As shown in FIG. 5, the sleeve  25  is made up of a light transmission member  35  consisting of a core  33  (refractive index: n1) and a clad  34  having a refractive index larger than that of the core (refractive index: n2 (n1&gt;n2)) and a cylindrical and coat-like holder  36  placed in the outer peripheral margin of the light transmission member  35 ; the sleeve  25  of the embodiment is manufactured of a plastic optical fiber  52  (POF, see FIG. 7A) described later. 
     Since the sleeve  25  is formed having N.A. (numerical aperture)=0.6 and N.A. is defined as sin θmax (=[(n1)2−(n2)2]½), the maximum light reception angle θmax is nearly equal to 36.9 degrees. 
     Therefore, the maximum light reception angle θmax becomes large by about 6.9 degrees as compared with the sleeve in the related art (in which the sleeve having N.A.=0.5 is used) and more light can be received, of course; thus the sleeve  25  contributes to a decrease in a light power loss. 
     That is, for example, giving a description on optical connection to the transmission module  27 , if a distance exists between the element of the transmission module  27  (not shown) and the sleeve  25  (the element of the transmission module  27  (not shown) is buried and in fact, a distance occurs), more light than before can be received because the maximum light reception angle θmax becomes large. 
     The holder  36  corresponds to the coat portion of a plastic optical fiber  54  (POF, see FIG. 7A) described later, and is made of a synthetic resin (PE: Polyethylene). It is made of a material softer than the connector housing  24  of the receptacle molded of PPS (polyphenylene sulfide); however, it is not limited to the material and may be an equivalent or soft material and preferably, a general-purpose synthetic resin is used to decrease the costs. 
     The reception and transmission modules  26  and  27  shown in FIG. 2 use modules of known configurations and therefore will not be discussed in detail. The cap  28  is formed with two protrusions  28   b  and  28   b  which are roughly triangular in cross section for pressing the reception and transmission modules  26  and  27 . 
     On the other hand, as shown in FIG. 6, the optical plug  23  comprises the ferrule assemblies  37  and  37  (see FIG. 6, only one is shown), a plug housing  38  made of a synthetic resin (for example, the above-mentioned PPS), and a spring cap  39 . 
     The ferrule assembly  37  is made up of an optical fiber  40 , a ferrule  41  attached to the tip of the optical fiber  40 , and a spring  42 . 
     The optical fiber  40 , which is already known, is made up of a light transmission member (not shown) consisting of a core (not shown) and a clad (not shown) having a refractive index smaller than the core has and a primary sheath (not shown) and a secondary sheath  40   a  for coating the light transmission member (not shown); the primary sheath (not shown) and the secondary sheath  40   a  on the tip side are stripped off and are attached to the ferrule  41  although not shown. The N.A. of the optical fiber  40  is 0.5 as in the related art. 
     The ferrule  41  is made of a synthetic resin and has a small diameter part  41   a  and a large diameter part  41   b  each roughly like a cylinder; the light transmission member (not shown) of the optical fiber  40  is housed in the small-diameter part  41   a  and the primary sheath (not shown) is housed in the large-diameter part  41   b . The ferrule  41  and the optical fiber  40  are fixed strongly with an adhesive, etc., so as to prevent the optical fiber  40  from being left out of the ferrule  41 . 
     The large-diameter part  41   b  is formed on the periphery with two flange parts  41   c  and  41   c  and a spring  42  is placed between the rear flange part  41   c  and the spring cap  39 . 
     The plug housing  38  is a rectangular box having hollow housing chambers  43  and  43  (only one is shown) for housing the ferrule assemblies  37  and  37  and is formed at the front end of the top wall with a rocking arm  44  extending backward at a position partitioning the housing chambers  43  and  43  (see FIG.  1 ). The rocking arm  44  has a retention protrusion  44   a  engaging the engagement hole  30   a  (see FIGS. 1 and 2) in the optical plug retention part  30  and the tip part of the rocking arm  44  is pressed, whereby the fit operation into the receptacle  22  of the optical plug  23  is enabled (see FIG.  1 ). 
     As shown in FIG. 1, the plug housing  38  is formed on the rears of both side walls with slit covers  45  and  45  each roughly like a strip projecting backward from the rear end face of the plug housing  38  for closing plug introduction slits  46  and  46  (described later) of the spring cap  39 . 
     As shown in FIG. 1, the spring cap  39  is formed over both side walls and a part of the rear end face with the plug introduction slits  46  and  46  as notches and a support wall  47  is placed integrally so as to project in the proximity of the margins of the plug introduction slits  46  and  46  (only one is shown) on the rear end face. The spring cap  39  is formed at the center of the top wall with a concave part  48  corresponding to the rocking arm  44  and protection walls  49  and  49  are placed upright on both sides with the concave part  48  between 
     The spring  42  abuts the inside of the rear end face of the spring cap  39  (see FIG.  6 ). The spring cap  39  is formed at the internal center with a retention protrusion (not shown) corresponding to the plug housing  38 . 
     After the ferrule assemblies  37  and  37  are placed through the plug introduction slits  46  and  46  of the spring cap  39 , the spring cap  39  is engaged with the plug housing  38 , whereby the optical plug  23  is assembled. When the ferrule assemblies  37  and  37  are housed in the housing chambers  43  and  43 , retention protrusions  50  and  50  (see FIG. 6, only one is shown) placed on the plug housing  38  are fitted to space between the two flange parts  41   c  and  41   c  of the ferrule  41 , regulating the positions of the ferrule assemblies  37  and  37 . The ferrule assemblies  37  and  37  are urged forward by the springs  42  and  42  and stoppers  51  and  51  (see FIG. 6, only one is shown) formed in the housing chambers  43  and  43  suppress projection of the ferrule assemblies  37  and  37 . 
     In the described configuration, if the optical plug  23  is fitted into the receptacle  22 , the reception tube  32  enters the plug housing  38  and at the same time, the small-diameter part  41   a  of the ferrule assembly  37  enters the reception tube  32 . The large-diameter part  41   b  of the ferrule assembly  37  abuts the tip of the reception tube  32  and adequate contact pressure is kept by the elastic force of the spring  42 . 
     In this state, the tip part of the ferrule assembly  37  and the sleeve  25  and the reception, transmission module  26 ,  27  and each sleeve  25  are placed with gaps (not shown) kept to the minimum. 
     Next, a manufacturing method for the sleeve  25  will be discussed. 
     First, as shown in FIG. 7A, an optical fiber source line, for example, a plastic optical fiber  52  (POF) is cut with appropriate cut means such as scissors or a cutter (not shown) (it can be cut not only manually, but also by an automatic machine). 
     The cut POF piece is denoted by reference numeral  54  (see FIG. 7B, at the time, the POF  54  has length L 1 ). The optical fiber source line refers to an optical fiber wound around the same bobbin as that when the optical fiber  40  is manufactured, for example. Further, the optical fiber source line is not limited to it and waste pieces of the optical fiber source line or unnecessary optical fibers can also be used if they can be recycled. 
     Subsequently, the POF  54  is fixed in a first grinding jig  55  roughly like a cylinder shown in FIG.  7 B. The first grinding jig  55  has an upper grinding part  55   a  and a lower grinding part  55   b  and an intermediate plate  55   c  is placed therebetween. 
     Subsequently, the POF  54  is coarsely ground with waterproof grinding paper (#1500). After the intermediate plate  55   c  is removed, the POF  54  is ground with a buff (#2000) as shown in FIG.  7 C. At the time, the POF  54  has length L 2 . 
     Subsequently, the POF  54  is fixed in a second grinding jig  56  roughly like a cylinder shown in FIG.  7 B. Like the first grinding jig  55 , the second grinding jig  56  has an upper grinding part  56   a  and a lower grinding part  56   b  and an intermediate plate  56   c  is placed therebetween. The length L 3  of the POF  54  is the same as L 2 . 
     Subsequently, the POF  54  is coarsely ground with waterproof grinding paper (#1500). After the intermediate plate  56   c  is removed, the POF  54  is ground with a buff (#2000) as shown in FIG.  7 C. At the time, the POF  54  has length L 4 . 
     Subsequently, the POF  54  is removed from the second grinding jig  56  and as shown in FIG. 7D, the POF  54  is cleaned with a dedicated cloth  57 , thereby removing dirt on both end faces of the POF  54 . 
     Last, the dimension between both end faces of the POF  54  is checked (not shown). It is also possible that manufacturing the sleeve  25  (see FIG. 5) is now complete. In the embodiment, however, to enable reliable placement in the reception tube  32  (see FIGS.  3  and  4 ), the sleeve is colored for suppressing optical axis shift and gap occurrence; preferably, the sleeve is colored in a different color from that of the receptacle  22  because of visibility. 
     That is, as shown in FIG. 8, the holder  36  is colored on the surface in two distinguishable colors  58  and  59 . The purpose of adopting two colors  58  and  59  is to rapidly determine the projection amount of a part of the sleeve  25  to the storage chamber  31  (see FIGS.  3  and  4 ). 
     By the way, the receptacle  22  of the embodiment (see FIGS. 1 and 2) is molded of a black synthetic resin and the color  58  on the projection side of the sleeve  25  is orange, which is color providing good visibility, determined by worker inspection, and is hard to put a load on the worker who works for many hours; work efficiency can be improved. 
     The holder  36  can also be colored on the surface in a single color, of course. At the time, the effect on work for many hours can be produced. 
     As described so far with reference to FIGS. 1 to  8 , the N.A. of the sleeve  25  is larger than that of the optical fiber  40 , so that the light reception amount of the sleeve  25 , namely, the light reception limit becomes large and the total efficiency is improved. 
     If the N.A. of the sleeve  25  is set to 0.5&lt;N.A.&lt;1, the light reception limit becomes larger than that in the related art, of course; in addition, it is also made possible to properly use (select) the sleeve  25  matching the N.A. of the corresponding optical fiber  40 . 
     Further, if the N.A. of the sleeve  25  is set to 0.6 or 0.7, the productivity and general versatility are not adversely affected That is, if the N.A. is 0.6 or 0.7, the POF  52  itself from which the sleeve  25  is manufactured can be used with other products, etc., as an optical fiber of a comparatively short distance, for example. (The sleeve  25  is not customized.) 
     The relationship between the N.A. of the sleeve  25  and light power is as listed in Table 1 given below. (Light from the transmission module  27  is received at the sleeve  25  and then is transmitted 1 m in the optical fiber  40 . At the time, the light power is measured.) 
     Comparing the light power with the sleeve  25  with that with the sleeve in the related art (N.A.=0.5), the difference therebetween becomes 0.9 dBm, 1.6 dBm, meaning a decrease in the light power loss as much as the value. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 N.A. of sleeve 
                 Power (dBm) 
               
               
                   
                   
               
             
            
               
                   
                 0.5 (in related art) 
                 −8.5 
               
               
                   
                 0.6 
                 −7.6 
               
               
                   
                 0.7 
                 −6.9 
               
               
                   
                   
               
            
           
         
       
     
     On one hand, if the N.A. of the sleeve  25  becomes large, the transmission distance is markedly short as compared with that of the optical fiber  40 , thus the transmission speed involved in light communication is not affected and the transmission speed similar to that in the related art can be maintained. 
     The limit of light reception becomes markedly large as compared with that in the related art. Thus, if an optical axis shift occurs, it is absorbed and the light power loss can be suppressed as much as possible. 
     Further, a transmission margin can be widened downstream from the optical connector  21  as much as the light power loss is suppressed. 
     On the other hand, the holder  36  forming a part of the sleeve  25  is a synthetic resin material and thus the holder  36  itself becomes softer than the metal in the related art. Therefore, when the holder  36  is placed in the optical connector  25 , the trouble as in the related art wherein the holding member of the sleeve  25  (minute protrusion not shown) is scraped on the end face of the holder  36  is avoided. The light reception face of the sleeve  25  becomes perpendicular to the optical axis, so that an optical axis shift can be suppressed. 
     Since the holder  36  is colored, whether or not the sleeve  25  is reliably placed at a predetermined position can be checked easily, and widening a gap can be suppressed. If the holder  36  is colored in two distinguishable colors  58  and  59  as described above, visibility is further enhanced. Of course, if the work area is dark, it is effective to color the holder  36  in two distinguishable colors. 
     Further, the sleeve  25 , which is formed from the POF  52  such as an optical fiber source line, can contribute to improvement in yield and recycling, and since the sleeve can be provided more easily than a new sleeve is designed and manufactured, cost reduction can be accomplished. 
     Various modified embodiments of the invention are possible without departing from the spirit and the scope of the invention, needless to say. 
     That is, the sleeve  25  can be disposed at least only in the transmission module  27 . In this case, the advantages similar to those described above can also be provided. 
     A collimator lens can be formed at least at one end of the light transmission member  35 . If the collimator lens is provided on the incidence side, such light originally radiated to the clad  34  can also be transmitted. In contrast, if the collimator lens is provided on the emission side, light can be gathered. 
     Further, it is also possible to decrease the light power loss simply by changing the material of the holder  36  or coloring the holder  36  with the N.A. of the sleeve  25  set as in the related art. 
     As listed in Table 2 given below, the light power loss can also be decreased if the N.A.s of the sleeve  25  and the optical fiber  40  are set to 0.6. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 N.A. of optical fiber 
                   
               
            
           
           
               
               
               
            
               
                   
                 0.5 
                 0.6 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 N.A. of sleeve 
                 0.5 
                 −8.5 dBm 
                 −8.3 dBm 
               
               
                   
                   
                 0.6 
                 −7.6 dBm 
                 −7.5 dBm 
               
               
                   
                   
               
            
           
         
       
     
     However, it is feared that the transmission speed of the optical fiber  40  may be affected; thus, preferably the forms described above are adopted. 
     As described above, according to the first aspect of the present invention, the optical connector comprises sleeves placed between an optical fiber and reception and transmission modules, wherein the N.A. of each of the sleeves is made larger than the N.A. of the optical fiber. 
     The N.A. of the sleeve is thus made larger, whereby the light reception amount of the sleeve, namely, the light reception limit becomes large and the coupling efficiency is improved. The transmission distance of the sleeve is markedly short as compared with that of the optical fiber, thus if the N.A. becomes large, the transmission speed is not affected and the transmission speed similar to that in the related art can be maintained. Further, the limit of light reception becomes markedly large as compared with that in the related art. Thus, if an optical axis shift occurs, the light power loss can be suppressed as much as possible. 
     According to the second aspect of the present invention, the N.A. of at least the sleeve corresponding to the transmission module is larger than the N.A. of the optical fiber used with the optical connector. 
     Thus the N.A. of at least the sleeve corresponding to the transmission module is made large, whereby the reception limit of light emitted from the transmission module becomes markedly large than that in the related art. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided like that described above. 
     According to the third aspect of the present invention, the N.A. of each of the sleeves is 0.5&lt;N.A.&lt;1, so that the N.A. of the sleeve can be selected matching the N.A. of the optical fiber used with the optical connector. 
     According to the fourth aspect of the invention, the N.A. of each of the sleeves is 0.6 or 0.7 and becomes more preferred N.A. considering the productivity and general versatility in the above-mentioned range. Advantages in the optical connector similar to those described above can be provided, of course. 
     According to the fifth aspect of the present invention, the sleeve is made up of a light transmission member consisting of a core and a clad and a cylindrical and coat-like holder, and the holder is formed of a synthetic resin material. 
     The sleeve is thus formed, whereby it is made possible to protect the light transmission member by the holder as in the related art. The holder is a synthetic resin material and thus the holder itself becomes softer than the metal in the related art. When the holder is placed in the optical connector, the trouble as in the related art wherein the holding member of the sleeve is scraped on the end face of the holder is avoided. Thus, it is made possible to suppress an optical axis shift. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided like that described above. 
     According to the sixth aspect of the present invention, the holder is formed of a synthetic resin material which is a material equal to or softer than the member in which the sleeve is placed. Thus, it is made possible to suppress an optical axis shift. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the seventh aspect of the present invention, the holder is formed of polyethylene, thus a synthetic resin material having general versatility is used and it is made possible to contribute to cost reduction, of course. 
     Therefore, the optical connector that can also lead to cost reduction can be provided. 
     According to the eighth of the present invention, the holder is colored in a different color from that of the member in which the sleeve is placed. 
     Thus, the holder is colored, whereby whether or not the sleeve is reliably placed at a predetermined position can be checked easily, and widening a gap can be suppressed. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the ninth aspect of the present invention, the color of the holder is a different family color from the color of the member in which the sleeve is placed, so that visibility is enhanced and the sleeve placement position can be determined reliably. 
     According to the tenth aspect of the present invention, the holder is colored in two distinguishable colors, so that visibility can be furthermore improved. The sleeve placement position can be determined reliably. 
     According to the eleventh aspect of the present invention, one of the two distinguishable colors is orange if the color of the member in which the sleeve is placed is black, so that good visibility as a color combination is provided. Thus, it is hard to put a load on the worker who works for many hours; it is made possible to improve work efficiency. 
     Therefore, it can contribute to cost reduction. 
     According to the twelfth aspect of the present invention, a collimator lens is formed at least at one end of the light transmission member. Thus, if the collimator lens is provided on the incidence side, such light originally radiated to the clad can also be transmitted. In contrast, if the collimator lens is provided on the emission side, light can be gathered. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided like that described above. 
     According to the thirteenth aspect of the present invention, the sleeve is formed by cutting an optical fiber source line or a waste tip of the optical fiber source line and thus can be provided with general versatility. It contributes to improvement in yield and further the sleeve can be manufactured by recycling an optical fiber. 
     Therefore, the optical connector that can further lead to cost reduction can be provided. 
     According to the fourteenth aspect of the present invention, the sleeve is placed between an optical fiber and a reception module or a transmission module placed in an optical connector and capable of providing optical connection of the optical fiber and the reception or transmission module, and comprises a light transmission member consisting of a core and a clad and a cylindrical and coat-like holder; the sleeve is formed in a larger N.A. than that of the optical fiber and is placed corresponding to at least the transmission module. 
     Thus, the reception amount of incident light, namely, the light reception limit becomes large and the coupling efficiency is improved. The transmission distance is markedly short as compared with that of the optical fiber, thus if the N.A. becomes large, the transmission speed involved in the whole of the optical fiber is not affected and the transmission speed similar to that in the related art can be maintained. Further, the limit of light reception becomes markedly large as compared with that in the related art. Thus, if an optical axis shift occurs, the light power loss can be suppressed as much as possible. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin when light communication is executed can be provided. 
     According to the fifteenth aspect of the present invention, the larger N.A. than that of the optical fiber is 0.5&lt;N.A.&lt;1, thus the N.A. of the sleeve can be selected matching the N.A. of the optical fiber placed in the optical connector. 
     According to the sixteenth aspect of the present invention, the larger N.A. than that of the optical fiber is 0.6 or 0.7; it becomes more preferred N.A. considering the productivity and general versatility in the above-mentioned range. Advantages in the sleeve similar to those described above can be provided, of course. 
     According to the seventeenth aspect of the present invention, the holder is formed of a synthetic resin material which is a material equal to or softer than the receptacle forming a part of the optical connector is placed. Thus, it is made possible to suppress an optical axis shift. 
     Therefore, the optical connector intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the eighteenth aspect of the present invention, the holder is formed of polyethylene, thus a synthetic resin material having general versatility is used and it is made possible to contribute to cost reduction, of course. 
     Therefore, the connector that can also lead to cost reduction can be provided. 
     According to the nineteenth aspect of the present invention, the holder is colored in a different color from that of the receptacle. 
     The holder is thus colored, whereby whether or not the sleeve is reliably placed at a predetermined position can be checked easily, and widening a gap when the sleeve is placed in the optical connector can be suppressed. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the twentieth aspect of the present invention, the color of the holder is a different family color from the color of the receptacle. Thus, when the sleeve is placed at the assembling time of the optical connector or the sleeve placement position is checked, visibility is enhanced. The worker can make an accurate determination as to placement of the sleeve. 
     According to the twenty-first aspect of the present invention, the holder is colored in two distinguishable colors, so that visibility can be furthermore improved. The sleeve placement position can be determined reliably. 
     According to the twenty-second aspect of the present invention, a collimator lens is formed at least at one end of the light transmission member. Thus, if the collimator lens is provided on the incidence side in the optical connector, such light originally radiated to the clad can also be transmitted. In contrast, if the collimator lens is provided on the emission side in the optical connector, light can be gathered. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin can be provided like that described above. 
     According to the twenty-third aspect of the present invention, the sleeve is formed by cutting an optical fiber source line or a waste tip of the optical fiber source line and thus the optical fiber can be provided with general versatility. It contributes to improvement in yield and further the sleeve can be manufactured by recycling an optical fiber. 
     Therefore, the sleeve that can further lead to cost reduction can be provided. 
     According to the twenty-fourth aspect of the present invention, the sleeve is placed between an optical fiber and a reception module or a transmission module placed in an optical connector and capable of providing optical connection of the optical fiber and the reception or transmission module, and comprises a light transmission member consisting of a core and a clad and a cylindrical and coat-like holder; the holder is formed of a synthetic resin material which is a material equal to or softer than a receptacle forming a part of the optical connector. 
     The sleeve is thus formed, whereby it is made possible to protect the light transmission member by the holder as in the related art. The holder is a synthetic resin material and thus the holder itself becomes softer than the metal in the related art. When the holder is placed in the optical connector, the trouble as in the related art wherein the holding member of the sleeve is scraped on the end face of the holder is avoided. Thus, it is made possible to suppress an optical axis shift. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the twenty-fifth aspect of the present invention, the holder is colored in a different color from that of the receptacle. 
     The holder is thus colored, whereby whether or not the sleeve is reliably placed at a predetermined position can be checked easily, and widening a gap when the sleeve is placed in the optical connector can be suppressed. 
     Therefore, the sleeve intended for decreasing the light power loss and widening a transmission margin can be provided. 
     According to the twenty-sixth aspect of the present invention, the holder is colored in two distinguishable colors, so that visibility can be furthermore improved. It is made possible to determine the sleeve placement position reliably. 
     According to the twenty-seventh aspect of the present invention, the manufacturing method of a sleeve comprising a light transmission member consisting of a core and a clad and a cylindrical and coat-like holder comprises the steps of cutting an optical fiber source line or a waste tip of the optical fiber source line and then grinding both end faces. 
     Such a manufacturing method is adopted, whereby the optical fiber placed in the optical connector can be provided with general versatility. It contributes to improvement in yield and further the sleeve can be manufactured by recycling an optical fiber. 
     Therefore, the sleeve manufacturing method that can lead to cost reduction can be provided. 
     According to the twenty-eighth aspect of the present invention, the holder is colored before or after both end faces of the sleeve are ground. Thus, it is made possible to manufacture the sleeve independently of the coat color of the optical fiber source line that the holder is made of. 
     Therefore, it can further contribute to cost reduction.