GB2356263A

GB2356263A - Optical fibre connector sleeve with larger numerical aperture than fibre

Info

Publication number: GB2356263A
Application number: GB0102588A
Authority: GB
Inventors: Naoshi Serizawa
Original assignee: Yazaki Corp
Current assignee: Yazaki Corp
Priority date: 1998-12-28
Filing date: 1999-12-06
Publication date: 2001-05-16
Anticipated expiration: 2019-12-06
Also published as: GB0102589D0; GB2356264B; GB0102588D0; GB2356264A; GB2356263B

Abstract

A sleeve 25 is placed between an optical fibre 40 and reception and transmission modules 26, 27 located in an optical connector 21. The sleeve 25 has a light transmission member 35, a core 33 and a clad 34 which has a smaller refractive index than the core 33. A cylindrical and coat-like holder 36 is placed in an outer peripheral flange of the light transmission member 35 wherein the sleeve 25 is formed with a numerical aperture (NA) larger than that the numerical aperture (NA) of the optical fibre. The holder 36 can be made from a coloured synthetic resin eg. polyethylene and can be formed by cutting an optic fibre source line (52, figure 7a).

Description

2356263 OPTICAL CONNECTOR SLEEVE 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.

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 61 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 I anu 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 imm diameter) bonded and f ixed to a holder 12 like a metal cylinder and ground on both end f aces are inserted into the reception tubes 10 and 10.

The optical f iber 3 is f itted 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 f ibers 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 f ormed with shoulder part 17a engaging collar-like retention parts 15a and 15a 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 15a and 15a and inner tube parts 18a and i8a of the spring cap 18 so that the ferrule assemblies 15 and are urged forward all the time.

The retention parts 15a and 15a engage the shoulder part 17a, whereby tip parts A of the ferrule assemblies 15 and 15 (see FIG. 11; corresponding to positions of incidence and emission end faces 2 (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 5 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 f errule 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, 61 and the optical fiber 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, 61 and the sleeve 13, 13 and the gap between the optical 3 fiber 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 S 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, (ni > n2), the above-mentioned N.A. is defined by a relational expression of N.A.=[(nl) 2 _ (n2) 2] 1/2.

On the other hand, the above-described light power loss is 4 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 (notshown) 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 f or 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 abovementioned problems are solved. It is also preferred to deal with the yield produced in the manufacturing process of the optical f ibers 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 f eared that the productivity of the members and the optical connector I will lower because of the dimension accuracy of the members; it does not become a preferred measure.

It is th erefore 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 6 wide,., a transmission margin when light communication is 'executed, and also to reduce costs.

To that end, according to a first aspect of the present invention, there is provided a sleeve placed between an optical fiber and one of a reception module and a transmission module placed in an optical connector and capable of providing optical connection of the optical fiber and one of the reception and transmission module, said sleeve comprising: a light transmission member including a core and a clad having a smaller refractive index than the core; and a cylindrical and coat-like holder placed in an outer peripheral flange of t1te light transmission member, wherein said sleeve is formed with a numerical aperture (N.A.) larger than that of the optical fiber and is placed corresponding to at least the transmission module.

As a result of the present invention, the light reception amount of the sleeve, namely, the light reception limit is larger and the coupling efficiency is improved. The transmission distance of the sleeve is markedly short as compared with that of the optical fiber, thus when 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 larger 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.

7 Therefore an optical connector is provided capable of decreasing the light power loss and widening the transmission margin when light communication is executed.

Preferably, the N.A. of at least the sleeve corresponding to the transmission module is larger than the N.A. of the optical fiber. Thereby the reception limit of light emitted from the transmission module is larger than that in the prior art.

The N.A. of each of the sleeves may be given by 0.5 < N.A. < 1. Thus the N.A. of the sleeve can be matched to that of the optical fiber used with the connector.

Preferably, the N.A. of each of the sleeves is 0.6 or 0.7.

Advantageously, 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, 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. This enables the light transmission member to be protected and the holder is softer than the metal used in the prior art. Also scraping the sleeve on the end face of the of the holder is avoided, which helps to reduce optical axis shift.

Preferably, the holder is formed of a synthetic resin material which is equal to or lower in hardness than a member in which the sleeve is placed.

The holder is preferably formed of polyethylene which contributes to cost reduction and is versatile to use.

8 The holder can be colored in a color dif f erent f rom. that of the member in which the sleeve is placed. This helps to ensure that correct positioning is achieved by allowing easy checking and thus avoids problems resulting from a wide gap.

Preferably, the color of the holder is a family color different from the color of the member in which the sleeve is placed.

Additionally, the holder may be colored in two distinguishable colors.

One of the two distinguishable colors may be orange if the color of the member in which the sleeve is placed is black.

This reduces the strain on assembly workers assembling such connectors over a long period and helps to increase efficiency.

Preferably, a collimator lens is formed at least at one end of the light transmission member. If the collimator lens is provided on the incidence side then light originally transmitted to the cladding can also be transmitted and if the collimator lens is provided on the emission side additional light can be gathered.

The sleeve may be formed by cutting at least one of an optical fiber source line and a waste tip of the optical fiber source line. This contributes to improvements in yield and allows the sleeve to be manufactured by recycling an optical fiber.

In the accompanying drawings:

FIG. 1 is an exploded perspective view to show one embodiment of an optical connector according to the invention; 9 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 7D 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.

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 thereceptacle 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..

11 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 30a corresponding to a retention protrusion 44a 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 24a and 24b piercing top and bottom walls (see FIG. 4. Four (two because the lower margin side is not shown) engagement protrusions 28a formed on upper and lower margins of the cap 28 engage the openings 24a and 24b, and connection parts (electrodes) 26a and 27a of the reception and transmission modules 26 and 27 are derived to the 12 outside through the openings 24b (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 f it part 2 9 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, 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. 5,1 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 (ni>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 def ined as sin0max (=[ (nl) 2 - (n2).2] 1/2), the 13 maximum light reception angle Omax is nearly equal to 36.9 degrees. Therefore, the maximum light reception angle Omax 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 Omax 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 28b and 28b which are roughly triangular in cross section for pressing the reception and transmission modules 26 and 27.

14 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 f iber 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 40a for coating the light transmission member (not shown); the primary sheath (not shown) and the secondary sheath 40a on the tip side are stripped of f and are attached to the f errule 41 although not shown. The N.A. of the optical fiber 40 is 0.5 as in the related art.

The f errule 41 is made of a synthetic resin and has a small diameter part 41a and a large diameter part 41b each roughly like a cylinder; the light transmission member (not shown) of the optical fiber 40 is housed in the small.-diameter part 4 la and the primary sheath (not shown) is housed in the large-diameter part 41b. 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 41b is formed on the periphery with two flange parts 41c and 41c and a spring 42 is placed between the rear flange part 41c 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 3 7 and 3 7 and is f ormed at the f ront 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 44a engaging the engagement hole 30a (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 f ace 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 16 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) 5 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 3 8 are f itted to space between the two f lange parts 41c and 41c 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 41a of the ferrule assembly 37 enters the reception tube.32. The large-diameter part 41b 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 17 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, f or example, a plastic optical f iber 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 Ll). 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 f iber 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 roughly like a cylinder shown in FIG. 7B. The first grinding jig 55 has an upper grinding part 55a and a lower grinding part 55b and an intermediate plate 55c is.placed therebetween.

Subsequently, the POF 54 is coarsely ground with waterproof grinding paper (#1500). After the intermediate plate 55c is removed, the POF 54 is ground with a buff (#2000) as shown in FIG.

7C. At the time, the POF 54 has length L2.

Subsequently, the POF 54 is fixed in a second grinding jig 56 roughly like a cylinder shown in FIG. 7B. Like the first grinding 18 jig 5-5, the second grinding jig 56 has an upper grinding part 56a and a lower grinding part 5 6b and an intermediate plate 5 6c is placed therebetween. The length L3 of the POF 54 is the same as L2. - Subsequently, the POF 54 is coarsely ground with waterproof grinding paper (#1500). After the intermediate plate 56c is removed, the POF 54 is ground with a buff (#2000) as shown in FIG.

7C. At the time, the POF 54 has length L4-.

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 f aces of the POF 54 is checked (not shown). It is also possible that manufacturing the sleeve 2 5 (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 19 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 < N.A. <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 manuf actured can be used with other products,. etc., as an optical f iber of a comparatively short distance, for example. (The sleeve 25 is notcustomized.) 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 I 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 f iber 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 f rom. th e 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 21 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 ef f ective to color the holder 3 6 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 f rom 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.

22 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 10 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 both set to 0.6, although this is outside the scope of the present invention.

Table 2

N.A. of optical fiber 0.5 0.6 0.5 - 8.5 dBm - 8.3 dBm N.A. of sleeve 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.

23

Claims

1. A sleeve placed between an optical f iber and one of a reception module and a transmission module placed in an optical connector and capable of providing optical connection of the optical fiber and one of the reception and transmission module, said sleeve comprising:

a light transmission member including a core and a clad having a smaller refractive index than the core; and a cylindrical and coat-like holder placed in an outer peripheral flange of the light transmission member, wherein said sleeve is formed with a numerical aperture (N.A.) larger than that of the optical fiber and is placed corresponding to at least the transmission module.

2. The sleeve as claimed in claim 1, wherein the N.A. of the sleeve is 0. 5 < N.A. < 1.

3. The sleeve as claimed in claim 1 or claim 2, wherein the N.A. of the sleeve is 0.6 or 0.7.

4. The sleeve as claimed in any of claims 1 to 3, wherein the holder is formed of a synthetic resin material equal to or lower in hardness than a receptacle forming a part of the optical connector.

5. The sleeve as claimed in claim 4, wherein the holder is formed of polyethylene.

24

6. The sleeve as claimed in claim 4 or 5, wherein the holder can be colored and is colored in a different color from that of the receptacle.

7. The sleeve as claimed in claim 6, wherein the color of the holder is a different family color from the color of the receptacle.

8. The sleeve as claimed in claim 6 or 7, wherein the holder 10 is colored in two distinguishable colors.

9. The sleeve as claimed in any of claims 1 to 8, wherein a collimator lens is formed at least at one end of the light transmission member.

is

10. The sleeve as claimed in any of claims 1 to 9, the sleeve is formed by cutting an optical fiber source line or a waste tip of the optical fiber source line.

11. A sleeve according to claim 1, substantially as described with reference to any one of the examples illustrated in Figures I to 8 of the accompanying drawings.