Device for retaining wire-like optical wave-guide

A device for retaining a wire-like optical wave-guide for an optical connector includes a cylindrical plug made of an elastic material for gripping the outer peripheral surfaces of a wire-like optical wave-guide with at least one end portion of the plug, having a predetermined length, being divided into a plurality of portions in a circumferential direction. The cylindrical plug has an expanded form in which a distance from an axis of the plug to each of the divided portions gradually increases toward the one end of the plug, with a tightening member pressing a vicinity of a free end of the cylindrical plug, which is in a state where the wire-like optical wave-guide is passed through the plug along the axis of the plug so as to allow the wire-like optical wave-guide to be retained by the cylindrical plug, in a direction substantially perpendicular to the axis of the plug from the outside of the plug. The tightening member deforms the divided portions and causes a retaining force to be applied to the optical fiber in a proximal end of the divided portions spaced from the pressing portion.

BACKGROUND OF THE INVENTION 
The present invention relates to a device for retaining a wire-like optical 
wave-guide of an optical connector or the like. 
Optical connectors are used at many places in optical telecommunication 
systems where detachable optical connection is required, such as 
switch-over of equipment, removal or reception transmission boards or 
adjustment of devices. The optical connector basically includes a sleeve 
or housing coaxially fitted onto the outer periphery of a wire-like 
optical wave-guide (e.g., an optical fiber) consisting of a core and a 
clad to form a first plug having a sufficiently large diameter which 
ensures easy handling, and another plug with a tightening fastener is then 
mounted on the outer periphery of the first plug. A pair of thus-obtained 
assemblies are coupled with each other utilizing the above-described 
another plugs. Alignment and coupling of the two plugs is achieved by 
using a receptacle with a split sleeve or a collet chuck to align a plug. 
Various types of "wire-like optical wave-guide retaining devices" for use 
in an optical connector are known. Examples of such devices include a 
wire-like optical wave-guide fixed by an adhesive, and a wire-like optical 
wave-guide fixed by caulking. 
In such retaining devices which employ the above-described conventional 
fixing techniques, although reliable fixing of the wire-like optical 
wave-guide is provided, a difference in the rate at which the optical 
wave-guide and the retaining member are expanded or contracted when the 
temperature changes, caused by a difference in coefficient of thermal 
expansion between the wire-like optical wave-guide and the optical 
wave-guide retaining member, or variations in the dimensions of the 
components cannot be absorbed. Consequently, an excess stress may be 
generated in the components of the retaining device, particularly, in the 
wire-like optical wave-guide, thus shortening the life of the wave-like 
optical wave-guide. 
Furthermore, in the retaining devices employing the above-described 
conventional fixing techniques, if the retaining device does not conform 
to predetermined standards as determined by an inspection following 
assembly, it is impossible to disassemble the device to replace any 
nonconforming component. Consequently, the output is low, and production 
is very uneconomical. 
In the case of the retaining device which employs an adhesive to fix the 
optical wave-guide, it takes some time for the adhesive to dry thereby 
lowering the productivity. Furthermore, hardening of the adhesive may 
shift the position of the wire-like optical wave-guide. 
If a caulking is employed, when the amount of caulking force exceeds a 
predetermined magnitude, the wire-like optical wave-guide is broken, and, 
consequently, it is necessary to strictly control the application of the 
caulking force. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a device for retaining a 
wire-like optical wave-guide which allows no excess stress to be applied 
to the wire-like optical wave-guide resulting from environmental changes 
such as temperature or dimensional variations in the components. 
Another object of the present invention is to provide a device for 
retaining a wire-like optical wave-guide which provides easy assembly and 
improved productivity, which can be disassembled and reassembled, after an 
inspection test has been conducted on an assembly, and which therefore 
allows production cost to be reduced. 
To this end, the present invention provides a device for retaining a 
wire-like optical wave-guide which comprises a cylindrical plug made of an 
elastic material for gripping the outer peripheral surface of at least one 
wire-like optical wave-guide, with at least one end portion of the plug, 
having a predetermined length, being divided into a plurality of portions 
on the circumference. The divided portions have an expanded form in which 
a distance from an axis of the plug to each of the divided portions 
increases toward the one end, i.e., a free end, of the plug. A tightening 
member presses a vicinity of the free ends of the cylindrical plug, which 
is in a state where the wire-like optical wave-guide is passed through the 
plug along the axis of the plug so as to allow the wire-like optical 
wave-guide to be retained by the cylindrical plug, in a direction 
substantially perpendicular to the axis of the plug from the outside of 
the plug and deforms the divided portions thereby causing a retaining 
force to be applied to the wire-like optical wave-guide in a proximal end 
or a gripping portion of the divided portions having the expanded form, 
which is separated from a pressing portion. 
In a typical expanded form, according to the present invention, the divided 
portions of the cylindrical plug have the same wall thickness in the axial 
direction of the plug, and the inner and outer surfaces of the divided 
portions are inclined such that they gradually separate from the axis as 
they approach the one end, i.e., a free end thereof. In this form, the 
inner and outer diameters of the divided portions are generally a maximum 
diameter at the free end thereof. In another example of the expanded form, 
the outer diameter of the divided portions remains the same in the axial 
direction of the cylindrical plug while the inner diameter is larger, 
i.e., the wall thickness is smaller, than that of the remaining portion, 
over a predetermined length of the plug from the one end, i.e., from the 
free end thereof. In that case, the inner diameter may be gradually 
increased or may be increased uniformly over the predetermined range from 
the free end, as they approach the free end. In still another example of 
the expanded form, the outer surface of the divided portions is gradually 
separated from the axis toward the one end, i.e., a free end, and the 
inner surface of the divided portions is formed in the same manner as that 
of the second example. In the first example, the inner surface of the 
divided portions is inclined such that it is gradually separated from the 
axis of the plug toward the free end thereof. The angle at which the inner 
surface is inclined is referred to as an expansion angle. In the other two 
examples, the inner surface of the divided portions is not always 
inclined. Thus, a magnitude of the expansion angle is defined by a 
difference between the inner diameter of the portion having a large wall 
thickness which is remote from the free end and the inner diameter of the 
portion having a small wall thickness which is close to the free end. In 
other words, the larger the difference, the larger the expansion angle, 
and the smaller the difference, the smaller the expansion angle. 
The vicinity of the free end of the divided portions of the cylindrical 
plug which are shaped in an expanded form is pressed from the outside 
thereof by the tightening member and is thereby deformed, by which the 
other portion to the divided portions which is separated from the pressing 
portion and which is the proximal end or the gripping portion of the 
divided portions is pressed against the surface of the wire-like optical 
wave-guide so as to allow the wire-like optical wave-guide to be reliably 
retained. According to the present invention, since the point at which the 
pressing force is applied to the divided portions is separated from the 
point at which the retaining force of the divided portion acts on the 
wire-like optical wave-guide in the axial direction of the cylindrical 
plug, the pressing force applied to the divided portion acts on the 
wire-like optical wave-guide in the form of an elastic force of the 
divided portions which serve as cushioning members. The magnitude of the 
retaining force applied to the wire-like optical wave-guide is determined 
by the initial expansion angle of the divided portions because, as the 
initial expansion angle of the divided portions increases, the degree at 
which the free end of the divided portions is deformed by the tightening 
member increases, thereby increasing the pressure exerted on the wire-like 
optical wave-guide by the divided portions, i.e., the retaining force This 
means that the retaining force applied to the wire-like optical wave-guide 
can be adequately determined by suitably selecting the initial expansion 
angle of the divided portions. 
In this invention, even if there exists a difference in the rate at which 
the components of the retaining device and the wire-like optical 
wave-guide are expanded or contracted when the temperature changes, or 
even if there exist variations in the dimensions of the components of the 
retaining device and the optical wave-guide, the difference in the 
expansion or contraction rate or the variations in the dimensions is 
absorbed by the portion of the elastic divided portions which is located 
between the point of application of pressing force and the point of 
action, and generation of excessive stress in the wire-like optical 
wave-guide or damage of the wire-like optical wave-guide can be thereby 
eliminated. 
Furthermore, the retaining device can be easily disassembled by removing 
the pressing force exerted on the cylindrical plug by the tightening 
member, and the separate components can be reassembled to form the 
retaining device. Consequently, the yield can be increased, and the 
production cost can be reduced. 
The cylindrical plug may be formed of any elastic material, such as brass, 
stainless steel (JIS SUS 304), an engineering plastic or a fiber 
reinforced resin. 
The above and further objects and features of the present invention will 
become apparent from the following description taken in connection with 
the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings wherein like reference numerals are used 
throughout the various views to designate like parts and, more 
particularly, to FIG. 1, according to this figure, a device for retaining 
a wire-like optical wave-guide (hereinafter referred to as an optical 
fiber) includes an optical fiber guide tube 1, a cylindrical plug 2 made 
of a relatively soft elastic material, a cylindrical tightening member 3, 
a jacket retaining tube 4, and a pressurizing ring 5. The optical fiber 
guide tube 1 is open at one end and has an end wall 7 at an opposite end 
thereof. An opening 7a having the same diameter as the outer diameter of 
an optical fiber 6 is formed in the end wall 7. The optical fiber guide 
tube 1 may be formed of 18 Cr-8Ni stainless steel (JIS SUS 304), zirconia 
or a resin and have an outer diameter of 1.25 mm, 2.0 mm or 2.5 mm. The 
cylindrical plug 2 is formed of a relatively soft material such as copper 
or a copper alloy. A left half of the cylindrical plug 2 as viewed in FIG. 
1, forms a base portion 8 having a peripheral wall continuous in the 
circumferential direction. A right half of the cylindrical plug 2 has two 
cuts 9 which extend along the axis of the plug 2 from the right end 
thereof through a predetermined length and which thereby divide the 
cylindrical plug 2 into a pair of opposed elastic portions 10 along the 
axial direction thereof. The elastic portions 10 of the cylindrical plug 2 
have an expanded form. Each of the portions 10 has a groove 10a on its 
inner surface at the center thereof and extending over the entire length 
of the portion 10 (FIGS. 4 and 5). In this embodiment, the right half of 
the cylindrical plug 2 has two cuts 9. However, it may have more than two 
cuts. The same thing applies to a cut 11, which will be described later. 
In contrast to the plug 2, the tightening member 3 has two cuts 11 on a 
left half thereof which extend along the axis thereof from its left end 
through a predetermined length and which thereby divide the left half 
portion into a pair of opposed portions 12 in the circumferential 
direction, as shown in FIG. 1. The opposed portions 12 are expanded at the 
open end thereof. The right half of the tightening member 3 forms a base 
portion 13 having a peripheral wall which is continuous in the 
circumferential direction. The tightening member 3 has a protrusion 14 on 
the outer peripheral surface of the portion thereof which is the end 
portions, in the vicinity of the base portion 13, of the divided portions 
12. The protrusion 14 is substantially annular excluding the cuts 11. Each 
of the portions 12 has a groove 12a on its inner surface at the center 
thereof. The groove 12a extends over the entire length of the portion 12 
(FIGS. 4 and 5). 
The jacket retaining tube 4 has a small-diameter center hole 15 having the 
same dimension as the outer diameter of the optical fiber 6, and a 
large-diameter center hole 16 having the same dimension as the outer 
diameter of a jacket 17 which covers the optical fiber 6, as shown in FIG. 
2. The small-diameter center hole 15 and the large-diameter center hole 16 
continue in the longitudinal direction of the jacket retaining tube 4 and 
thereby form a through-hole which passes the tube 4 along the axis 
thereof. The pressurizing ring 5 has an opening 18 at the central portion 
thereof which passes the ring 5 along the axis thereof. The opening 18 has 
an inner diameter which is smaller than the outer diameter of the 
protrusion 14 of the tightening member 3. The pressurizing ring 5 has at 
least one positioning groove 19 on its outer peripheral surface. The 
positioning groove 19 is used to align the optical axis of the optical 
fiber to that of an optical fiber which is retained by an opposite optical 
connector. 
To assemble the retaining device, the divided portions 10 of the plug 2 are 
first inserted into a hollow portion of the tightening member 3 in a state 
where the cuts 9 oppose the corresponding cuts 11, as shown in FIG. 1. 
Next, the forward end portion of the tightening member 3 with the portions 
10 inserted therein is inserted into the hollow portion of the optical 
fiber guide tube 1 until the protrusion 14 contacts the open end of the 
optical fiber guide tube 1. Subsequently, the jacket retaining tube 4 is 
inserted into a central hole formed in the base portion 13 of the 
tightening member 3, and the pressurizing ring 5 is then fitted onto the 
outer periphery of the base portion 13 at a position where the end of the 
pressurizing ring 5 is in contact with the protrusion 14. 
Thus, the optical fiber guide tube 1, the plug 2, the tightening member 3, 
the jacket retaining tube 4 and the pressurizing ring 5 are put together 
to form an assembly. 
Next, in this state, the optical fiber 6 excluding part of the jacket 17 
thereof is passed first through the large-diameter center hole 16 of the 
jacket retaining tube 4, the small diameter center hole 15, a central hole 
20 of the plug 2 then through the opening 7a of the end wall 7 until the 
forward end portion of the optical fiber 6 protrudes from the optical 
fiber guide tube 1 and part of the jacket 17 is placed within the 
large-diameter center hole 16 of the jacket retaining tube 4, as shown in 
FIG. 2. 
Thereafter, the pressurizing ring 5 is forcibly moved in the direction 
indicated by the arrow X in FIG. 2 and fitted onto the protrusion 14. As 
stated above, the portions 12 initially have an expanded form. 
Consequently, the forced movement of the pressurizing ring 5 presses the 
portions 12 inwardly. As shown in FIG. 6, when the pressing force F is 
applied perpendicular to the axis of the plug 2, the free end portions of 
the divided portions 10 are pressed toward the axis of the plug 2. This 
causes the gripping portion 21 of the divided portions 10 which is close 
to the base portion to elastically grip the periphery of the optical fiber 
6. FIG. 5 shows a state in which the substantially overall periphery of 
the optical fiber 6 is firmly gripped by the elastic portions 10. The free 
end portions of the divided portions 10 are not in contact with the 
optical fiber 6, as shown in FIG. 4. They are separated from the optical 
fiber 6 by a gap 22. Thus, the gripping portion 21 of the divided portions 
10 (a point of gripping action) and a pressing portion 23 (a point of 
application of force) are separated by a predetermined distance in the 
axial direction of the optical fiber 6, that is, the pressing portion 23 
is not equal to the gripping portion 21. 
FIG. 5A shows another examples of the divided portions 10 and 10A. In this 
example, only one divided portion 10 in the pair of divided portions has a 
groove 10a. 
After the optical fiber 6 has been retained in the above-described manner, 
the forward end portion (shown by the dot-dashed line in FIG. 3) of the 
optical fiber 6 protruding from the optical fiber guide tube 1 is cut or 
polished to align the optical fiber 5 to the forward end surface of the 
optical fiber guide tube 1, thereby completing assembly of a ferrule type 
optical connector. 
In this embodiment, the pressurizing ring 5 is forcibly fitted onto the 
outer periphery of the tightening member 3 to impart a pressing force to 
the plug 2 through the tightening member 3. However, the optical fiber 
guide tube 1 may be arranged such that it has the function of the 
pressuring ring 5. 
In the embodiment of FIG. 7, the cylindrical plug 2, made of an elastic 
material, has a base portion 8 at a center thereof, and a plurality of 
divided portions 10 on the two sides of the base portion 8. When the 
cylindrical tightening member 3 is forcibly fitted onto the outer 
periphery of the plug 2, the pressing force is received by the pressing 
portion 23, by which the optical fiber 6 is elastically gripped by the 
gripping portion 21. In the embodiment of FIG. 7, the gripping portion 21 
and the pressing portion 23 are separated from each other along the axis 
of the optical fiber 6, as in the case of the embodiment of FIGS. 1-6. It 
will be also understood that a modified plug, being divided into a 
plurality of portions over the entire length thereof without base 
ring-like portion such as the portion 8, can be adopted by those skilled 
in the art, maintaining the same function as the plug 2. 
In the embodiment of FIG. 8, the tightening member 3 has no cuts and thus 
has a cylindrical shape. The tightening member 3 has a shoulder 25 on its 
inner peripheral surface at the substantially central position thereof in 
the longitudinal direction, with the shoulder 25 being inclined inwardly 
in the radial direction. 
A cylindrical holder 26 is interposed between the optical fiber guide tube 
1 and the plug 2. The cylindrical holder 26 has a collar 27 on its outer 
periphery at a substantially central position. A washer 28 is fitted onto 
the outer periphery of the tightening member 3 at a position in contact 
with a stopper shoulder formed on the outer periphery of the tightening 
member 3. Between the washer 28 and the collar 27 is interposed a 
compression coil spring 29. 
FIG. 8 shows a state in which the wire-like optical wave-guide retaining 
device is being assembled. The spring 29 is not yet compressed, and the 
bifurcated forward end portion 30 of the plug 2 is opposed to the inclined 
shoulder 25 of the tightening member 3. 
In this state, the optical fiber 6 is inserted into the central hole 20 of 
the plug 2, and the tightening member 3 is then forcibly moved toward the 
holder 26 against the elastic force of the spring 29. This causes the 
forward end portions 30 of the plug 3 to ride on the inclined shoulder 25 
of the tightening member 3. As a result, a strong gripping force is 
generated in the pair of portions 10 which are expanded toward the open 
ends thereof, and reliable retaining of the optical fiber 6 is thereby 
ensured. 
As will be understood from the foregoing description, since the gripping 
portion (the point of gripping action) of the divided portions which 
retain the wire-like optical wave-guide and the pressing portion (the 
point of application of force) are separated from each other in the axial 
direction of the plug, a difference in the coefficient of thermal 
expansion between the wire-like optical wave-guide and the plug or 
variations in the dimensions in the radial direction can be absorbed, and 
no undesired stress is generated. 
When an inspection test reveals that the completed retaining assembly does 
not conform to the desired standard, the retaining assembly can be 
disassembled into components without damage by removing the tightening 
member or the like and thereby removing the pressing or tightening force, 
with the disassembled components then being reassembled. Consequently, the 
yield is increased, and production cost is reduced.