Rail-type device for mechanically splicing optical fibers

A structurally improved rail-type device for mechanically splicing optical fibers while reducing the splicing loss is disclosed. The above splicing device not only has a cladding clamp with a seesaw structure thereby easily splicing the optical fibers, it also separately moves the covers relative to the body to easily perform the tuning operation. Due to coating clamp's protrusions and body's slots engaging with each other, the coating clamp exclusively vertically move relative to the body and prevent the optical fibers from being axially thrust. The splicing device further seperately clamps the coating and cladding parts of the optical fibers, thereby preventing the spliced fibers from breaking due to tensile or torsional force. The sliding motion of the covers relative to the body is achieved by the rails of the covers and rail grooves of the body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to an optical fiber splicing 
device for mechanically splicing optical fibers having a single or 
multi-core structure. More particularly, the present invention relates to 
an optical fiber splicing device of the rail type having a seesaw-type 
cladding clamp suitable for not only tightly clamping the optical fibers 
by a size interference between covers and the clamp of the device but also 
allowing the optical fibers to be easily inserted into the device, thereby 
separately clamping the coating and cladding parts of the optical fibers 
during the optical fiber splicing operation. 
2. Description of the Prior Art 
As well known to those skilled in the art, optical fibers have been spliced 
together through several methods. Representative typical methods for 
splicing optical fibers are fusion splicing and mechanical splicing. In 
the typical fusion splicing method, the optical fibers are melted to be 
spliced. The above fusion splicing method has been generally used for 
permanently splicing the optical fibers. This fusion splicing method has a 
good operational reliability as it results in high optical 
characteristics. However, as the above fusion splicing method has to be 
performed with an expensive precise fusion splicing system while applying 
electric power to the system, the fusion splicing method has a problem in 
that it is scarcely used in a place where it is difficult to obtain 
electric power. 
Meanwhile, the mechanical splicing method has several advantages in that 
the method can be easily performed and doesn't need any additional 
devices. The mechanical splicing method can be thus easily used in any 
place. In addition, the optical characteristics expected by the mechanical 
splicing method is almost equal to those expected by the above fusion 
splicing method. 
However, as the known mechanical splicing method is performed with a 
mechanical splicing device which is operated using several instruments, it 
is somewhat difficult to use the mechanical splicing method in an optical 
fiber laying site. In addition, the above mechanical splicing device used 
in the mechanical splicing method fails to tightly clamp the coating parts 
of the optical fibers during the fiber splicing operation. The mechanical 
splicing device thus occasionally causes the spliced optical fibers to be 
distorted after the lapse of a long time and to break. In order to prevent 
the mechanically spliced optical fibers from breaking due to distortion, 
it is preferable to secondarily clamp the optical fibers at the coating 
parts of the fibers while clamping the cladding parts of the fibers at the 
same time, preventing the torsional force from being directly applied to 
the cladding parts of the fibers. In a known mechanical splicing device 
with a double clamping function, the first and second clamping parts, that 
is, the cladding and coating parts of the optical fibers are clamped at 
the same time. 
The above mechanical splicing device should use specific instruments for 
clamping the optical fibers in order to maintain the arrayed fibers during 
the fiber splicing operation. As the above device uses the specific 
instruments to clamp the optical fibers, the arrayed fibers may be thrust 
axially when the clamping force is axially applied to the fibers during 
the fiber splicing operation. The above mechanical splicing device thus 
often fails to precisely splice the optical fibers and causes a splicing 
loss. In an effort to rectify the above problem, the mechanical splicing 
device may be provided with an additional structure for preventing a 
pressing plate of the clamp unit from being thrust axially during the 
fiber splicing operation. However, the above structure for preventing the 
pressing plate from being axially thrust is small-sized such that it is 
very difficult to form the structure. In addition, the above thrust 
preventing structure has a structural fault requiring careful handling 
during the fiber splicing operation. 
The double clamping function of the splicing device is for reducing the 
strain in the spliced junction of the optical fibers. In the fiber 
splicing device with the above double clamping function, the clamping 
motion (first clamping motion) for clamping the cladding parts (splicing 
parts) of the optical fibers and the other clamping motion (second 
clamping motion) for clamping the coating parts of the optical fibers are 
performed at the same time. When clamping the optical fibers while 
inserting one fiber into one insert hole of the above splicing device, 
both the coating and cladding parts (first and second clamping parts) of 
the inserted fiber are pressed down in the splicing section of the device 
at the same time. The splicing section of the splicing device is thus 
closed so that the other optical fiber cannot reach the splicing section 
when inserting the other fiber into the splicing device through the other 
insert hole of the device. It is thus difficult to align the cladding 
parts of the optical fibers in the splicing device during the fiber 
splicing operation. In order to rectify the above problem, the one and 
other optical fibers may be inserted into both insert holes of the 
splicing device while opening the cladding and coating clamps, which clamp 
the cladding and coating parts of the fibers respectively, prior to 
clamping the cladding and coating parts of the fibers at the same time. 
However, as one end portion of the above splicing device is not fixed 
during the splicing operation, it is difficult to perform a tuning step 
for splicing the fibers with low loss. The above tuning step is performed 
to achieve the optimal alignment of the optical fibers. Of course, the 
fiber splicing operation may be performed without any tuning steps. 
However, when the fiber splicing operation is performed without any tuning 
steps, the splicing operation may cause a problem in that the operation 
should be repeated in the event of bad results of a splicing loss 
measurement. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a rail-type 
device for mechanically splicing optical fibers in which the above 
problems can be overcome and which not only has a cladding clamp with a 
seesaw structure thereby easily splicing the optical fibers without using 
any specific instruments, it also separately moves a pair of covers 
thereby easily performing the tuning operation during the fiber splicing 
operation. The above splicing device also includes an axial thrust 
preventing means, comprising coating clamp's protrusions and body's slots 
engaging with each other, whereby the coating clamps are exclusively 
vertically moved relative to the body and a splicing failure of the 
optical fibers due to an axial thrust of the fibers is prevented. The 
above splicing device is further provided with a double clamping function 
for separately clamping the coating and cladding parts of the optical 
fibers, whereby the spliced fibers are prevented from breaking due to 
tensile or torsional force. 
In accordance with an embodiment, the present invention provides a 
rail-type device for mechanically splicing optical fibers of a single or 
multi-core structure, comprising: a body opened upward to form a splicing 
space therein, both bottom side edges of said body being provided with 
axially extending rail grooves; a base panel received in said splicing 
space of the body and having a V-shaped groove, said v-shaped groove being 
axially formed on the top surface of said base panel and adapted for 
laying the optical fibers therein; a cladding clamp and a coating clamp 
placed on said base panel to move up and down, thereby selectively 
clamping the cladding and coating parts of the optical fibers 
respectively; and a cover slidably engaging with said body and adapted for 
selectively pressing said cladding and coating clamps down to fix the 
optical fibers in said splicing device. 
In accordance with another embodiment, the splicing device also includes an 
axial thrust preventing means, comprising protrusions formed on both side 
surfaces of each coating clamp and slots formed on both side walls of the 
body and engaging with the protrusions, thereby preventing the optical 
fibers from being axially thrust during the clamping operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is an exploded perspective view showing the construction of a 
rail-type device for mechanically splicing optical fibers in accordance 
with an embodiment of the present invention. As shown in this drawing, the 
splicing device of this invention includes a longitudinal body 1 which 
receives a longitudinal base panel 12 therein. The body 1 is opened upward 
thereby having a U-shaped cross-section and forming a splicing space 14 
therein. The above splicing space 14 has a predetermined depth and size 
suitable for receiving a pair of optical fibers 13 therein. Both bottom 
side edges of the body 1 are provided with axially extending rail grooves 
6 which will engage with rails 7 of covers 4 as will be described later 
herein. A V-shaped groove 5 is axially formed on the top surface of the 
base panel 12 which is received in the body 1. The optical fibers 13 to be 
spliced together by the device are laid in the above groove 5 to be 
aligned with each other at their cladding parts. 
The above splicing device also includes two types of clamps, that is, one 
cladding clamp 2 for clamping the cladding parts (splicing parts) of the 
optical fibers 13 and a pair of coating clamps 3 for clamping the coating 
parts of the fibers 13. The above cladding and coating clamps 2 and 3 are 
placed on the base panel 12 in the body 1 to move up and down, thereby 
clamping the cladding and coating parts of the fibers 13 respectively. The 
opened space 14 of the body 1 is covered with the pair of covers 4 which 
slidably engage with the body 1. Each cover 4 has the pair of rails 7 
which are formed on both side walls of each cover 4 and slidably engage 
with the rail grooves 6 of the body 1, thereby forming a rail means. With 
the slidable engagement of the grooves and rails 6 and 7, the covers 4 
horizontally move relative to the body 1. That is, each cover 4 slidably 
moves between the center and an associated end of the body 1. In the above 
splicing device, each coating clamp 3 has a top embossment 15, while the 
cladding clamp 2 has a pair of top side embossments 20 for generating a 
size interference. The above covers 4 press the cladding and coating 
clamps 2 and 3 down due to the size interference between the covers 4 and 
the embossments 15 and 20 of the clamps 3 and 2, thereby tightly clamping 
or fixing the optical fibers 13 arrayed in the V-shaped groove 5 of the 
panel 12. 
FIGS. 2A to 2C are sectional views of the coating clamp 3, cover 4 and 
cladding clamp 2 of the splicing device of FIG. 1 respectively. 
Particularly, FIGS. 2A to 2C show stepped configurations of the cover 4 
and clamps 2 and 3 for generating the size interference. 
As shown in FIG. 2A, each coating clamp 3 used for clamping the coating 
part of an associated optical fiber is stepped on its top surface 16 to 
form the embossment 15 on the top center of the surface 16. The height of 
the above embossment 15 is represented as .alpha. (height difference 
between the portions 15 and 16) in FIG. 2A. As shown in FIG. 2B, the top 
plate of each cover 4 which is placed over an associated coating clamp 3 
is stepped on its internal surface to form a pair of thick side portions 
18 and 18' with a thin center portion 17. The two thick side portions 18 
and 18' have different thicknesses. That is, the first thick portion 18 
which has a height difference .beta. between the portions 17 and 18 is 
thicker than the second thick portion 18' which has a height difference 
.tau. between the portions 17 and 18'. Due to the stepped top plate of 
each cover 4, a size interference is selectively generated between each 
cover 4 and an associated coating clamp 3 thereby selectively pressing the 
coating clamp 3 down and causing the clamp 3 to generate a downward 
clamping force for clamping the coating part of the fiber 13. FIG. 2C 
shows the configuration of the cladding clamp 2 used for commonly clamping 
the cladding parts (splicing part) of the optical fibers 13. As shown in 
FIG. 2C, the cladding clamp 2 is symmetrically stepped on its top surface 
to form a top center embossment 19 and the pair of top side embossments 
20. The center embossment 19 is further embossed than the side embossments 
20. A groove is formed between the center embossment 19 and each side 
embossment 20. The top surface of the clamp 2 is also stepped on both its 
edges to form a pair of depressed edges 21 which extend from the side 
embossments 20 outward, respectively. The height of each side embossment 
20 is represented as .delta. (height difference between the portions 20 
and 21) in FIG. 2C. On the other hand, the bottom surface 23 of the above 
cladding clamp 2 is stepped to form a bottom center embossment 22. 
FIGS. 3 and 4 are sectional views of the splicing device of this invention 
to represent the size interference selectively generated between the 
covers 4 and clamps 2 and 3 in accordance with positions of the covers 4. 
FIG. 3 shows the covers 4 placed in their opened positions, while FIG. 4 
shows the covers 4 placed in their closed positions. When the covers 4 are 
in their opened positions as shown in FIG. 3, the top embossments 15 of 
the coating clamps 3 meet with the thin center portions 17 of the covers 4 
respectively. In this state, the size interference is not generated 
between the coating clamps 3 and covers 4 so that the clamps 3 do not 
generate any clamping force. 
However, when the covers 4 are in their closed positions as shown in FIG. 
4, the size interference is generated between the clamps 3 and covers 4, 
thereby generating the clamping force of the clamps 3 for maintaining the 
arrayed optical fibers 13 in the V-shaped groove 5 of the base panel 12. 
In order to reach the closed positions of FIG. 4, the covers 4 move inward 
relative to the body 1 by the sliding motion of the rails 7 of the covers 
4 along the rail grooves 6 of the body 1. In this state, the size 
interferences are generated between the covers 4 and clamps 2 and 3 as the 
embossments of the covers 4 and clamps 2 and 3 meet together. That is, the 
interference between the coating clamps 3 and covers 4 is generated at 
portions 8 due to the height differences .alpha. and .tau.. Meanwhile, the 
interference between the cladding clamp 2 and covers 4 is generated at 
portions 9 due to the height differences .beta. 15 and .delta.. Due to the 
above size interferences generated at portions 8 and 9, the coating clamps 
3 and cladding clamp 2 are pressed down by the covers 4 in proportion to 
the interference amounts, thereby clamping the coating and cladding parts 
of the optical fibers 13 and fixing the arrayed fibers 13 in the splicing 
device. 
FIGS. BA and 5B are perspective views of the splicing device of this 
invention with the closed and opened covers 4 respectively. These drawings 
particularly show the sliding motion of the covers 4 relative to the body 
1 for generating the clamping force due to the size interferences between 
the covers 4 and clamps 2 and 3. The sliding motion of the covers 4 
relative to the body 1 is achieved by the sail means. The above rail means 
is the base for generating the clamping force of the splicing device and 
guides the sliding motion of the covers 4 relative to the body 1. 
FIG. 6 shows in detail the rail means of the optical fiber splicing device 
of this invention. As shown in this drawing, the rail means comprises the 
rails. 7 and grooves 6 which slidably engage with each other. In the 
embodiment of this invention, the rails 7 are formed in each cover 4, 
while the grooves 6 are formed in the body 1. Of course, it should be 
understood that the grooves 6 and rails 7 may be formed in the covers 4 
and body 1, respectively. 
In accordance with another embodiment of this invention, the optical fiber 
splicing device may be provided with means for preventing the covers 4 
from axially thrusting the optical fibers 13 during the sliding motion of 
the covers 4 relative to the body 1. As shown in FIG. 7, the axial thrust 
preventing means comprises protrusions 10 and slots 11. The protrusions 10 
are formed on both side surfaces of each coating clamp 3, while the slots 
11 for receiving the protrusions 10 are formed on the internal surfaces of 
both side walls of the body 1. In the above embodiment, the axial thrust 
preventing means achieves a structural balance as both the protrusions 10 
and slots 11 are formed on both sides of each clamp 3 and body 1. With the 
above axial thrust preventing means, the splicing device prevents fiber 
splicing loss, partial stress application and optical fiber's breakage 
caused by the axial thrust generated during the clamping operation. 
In the present invention, each protrusion 10 of the coating clamps 3 has a 
balled portion. In the same manner, each slot 11 of the body 1 has a 
balled socket for receiving the balled portion of the protrusion 10 
thereby forming a ball-and-socket joint. With the ball-and-socket joint, 
each coating clamp 3 has a seesaw structure having the balled protrusions 
10 as the seesawing shaft. Due to the seesaw structure, each coating clamp 
3 performs a seesawing motion thereby being easily lifted to allow the 
optical fiber 13 to be easily inserted into the splicing device when the 
optical fiber 13 is initially inserted into the device. 
The operational effect of the above optical fiber splicing device will be 
described in detail hereinbelow. 
When one optical fiber or a first fiber 13 is inserted into the splicing 
device through one insert hole while placing one cover 4 in its closed 
position, the first fiber 13 can be easily inserted into the device due to 
the seesawing motion of one coating clamp 3. In this case, the splicing or 
cladding part of the first fiber 13 will naturally and smoothly reach the 
bottom center of the cladding clamp 2 by simply inserting the first fiber 
13 into the device until the cladding part of the fiber 13 reaches the 
bottom of the cladding clamp 2. After the cladding part of the first fiber 
13 reaches the bottom center of the cladding clamp 2, the other cover 4 
which has been opened is moved to its closed position to fix the first 
fiber 13 in the device. Thereafter, the one cover 4 is moved from the 
closed position to the opened position prior to inserting the other 
optical fiber or a second fiber 13 into the device through the other 
insert hole. The second fiber 13 is thus smoothly inserted into the device 
due to the seesawing motion of the other coating clamp 3 until the 
cladding part of the second fiber 13 comes into contact with that of the 
first fiber 13. Thereafter, the one cover 4 is closed to finish the 
optical fiber splicing operation. In the present invention, the cladding 
clamp 2 is preferably formed of a transparent material into a convex lens 
configuration thereby easily checking the contact alignment of the 
cladding parts of the first and second fibers 13 from the outside of the 
device. 
When the cladding parts of the optical fibers 13 have a bad contact 
alignment, one of the covers 4 is opened prior to tuning the optical 
fibers. After tuning, the opened cover 4 is closed to fix the fiber 13 in 
the splicing device. In addition, it is preferable to use refractive index 
regulating liquid in the cladding junction between the optical fibers 13. 
In this case, the device reduces the insertion and reflection loss and 
thereby reduces the fiber splicing loss. 
Hereinbelow, the seesaw structure of the cladding clamp 2 will be described 
in detail. 
FIG. 8 is a view representing the seesaw structure of the cladding clamp 2 
of the splicing device of the present invention. As shown in FIG. 8, the 
bottom surface 23 of the above cladding clamp 2 is stepped at portions 24 
to form the bottom center embossment 22. The cladding clamp 2 selectively 
comes into contact with the covers 4 at the side embossments 20 thereby 
being pressed down to generate the clamping force. The center of each side 
embossment 20 is positioned outside a seesawing axis "i" vertically 
extending from each step 24. When one of the covers 4 is in its closed 
position, the closed cover 4 thus presses a corresponding half portion of 
the clamp 2 down while lifting the other half portion of the clamp 2. In 
this case, the lifting height Y.sub.1 of the clamp 2 is preset as the 
result of subtracting the thickness of a part of the fiber 13 received in 
the V-shaped groove 5 of the panel 12 from the diameter of the fiber 13. 
The above lifting height Y.sub.1 can be designed using variables X and 
L.sub.1. In this case, the variable X is the distance between a step 24 
and an opposite end of the clamp 2, while the variable L.sub.1 is the 
distance between the step 24 and the center of the clamp 2. 
In addition, the space height Y.sub.2 between each depressed edge 21 of the 
cladding clamp 2 and the first thick portion 18 of an associated cover 4 
will be represented by the following equation 
EQU Y.sub.2 =X.multidot.Y.sub.1 /L.sub.1 
wherein 
X is the distance between the seesawing axis "i" and one end of the 
cladding clamp; 
L.sub.1 is the distance between the seesawing axis "i" and the center of 
the cladding clamp; and 
i is the seesawing axis vertically extending from each step of the cladding 
clamp 2. 
The seesaw structure of the cladding clamp 2 of the splicing device of this 
invention is designed by the above equation. When one cover 4 is closed to 
press one half portion of the cladding clamp 2, the other half portion of 
the clamp 2 is lifted due to the above seesaw structure, thereby allowing 
the cladding part of an optical fiber 13 to smoothly reach the bottom 
center of the clamp 2. In addition, as the cladding clamp 2 is formed of a 
transparent material into a convex lens configuration as described above, 
the contact alignment of the cladding parts of the optical fibers 13 can 
be checked from the outside of the device. Therefore, it is possible to 
determine whether the contact alignment of the fibers 13 needs to perform 
the tuning step. The operational effect of the splicing operation is thus 
further improved. 
As described above, the present invention provides a structurally improved 
mechanical splicing device for optical fibers. As the device of this 
invention is provided with a cladding clamp having a seesaw structure, the 
device easily splices the optical fibers having single or multi-core 
structure without using any specific instruments. The splicing device 
separately clamps the coating and cladding parts of the optical fibers 
through double clamping motions during the fiber splicing operation. The 
device thus reduces strain of the optical fibers and prevents breaking of 
the spliced fibers due to distortion. The above splicing device also 
vertically applies the clamping force to the optical fibers during the 
clamp operation, thereby preventing alignment failure of the optical 
fibers without using any instruments. Another advantage of the fiber 
splicing device resides in that the device reduces the number of elements 
and simplifies the structure while compositely performing various 
functions and easily splicing the optical fibers. 
Although the preferred embodiments of the present invention have been 
disclosed for illustrative purposes, those skilled in the art will 
appreciate that various modifications, additions and substitutions are 
possible, without departing from the scope and spirit of the invention as 
disclosed in the accompanying claims.