Method and means for severing an optical fiber

The method comprises the steps of (a) inflicting a flaw on the glass surface of an optical glass fiber to be severed, (b) contacting an area about the fiber for applying pressure thereto which compresses the fiber, and (c) moving the contacted area along the fiber while applying sufficient pressure to produce frictional force which severs the fiber as the contacted area moves over the flaw. The means of the invention comprises scoring means for inflicting a flaw on the glass surface of an optical glass fiber to provide the fiber with first and second portions which are axially displaced to border the flaw on opposite sides, pressure means which slidably engages and compresses the fiber by applying pressure to a contacted area about the fiber, and displaceable means which applies tension force between the first portion of the fiber and the pressure means to move the fiber with respect to the pressure means so that its contacted area passes over the inflicted flaw on the glass surface as it moves along the fiber from its first portion to its second portion. The pressure means produces frictional force with the motion of the fiber at the contacted area along the surface of the fiber in a direction opposing the motion, which force increases on the second portion of the fiber until it is sufficient to sever the fiber at the inflicted flaw.

BACKGROUND OF THE INVENTION 
The invention relates to a method and means for severing an optical fiber, 
and particularly to a method and means for providing an optical fiber with 
an end having a mirror smooth face normal to the axis of the fiber and 
suitable for mass production or use in the field. 
Heretofore, methods and means have been provided for severing optical 
fibers to produce ends with mirror smooth surfaces for minimizing light 
transmission loss at interfaces. Such means and methods, however, have 
been complex and exacting, and have required that a flaw or defect be 
inflicted on the fiber as by scribing while tension is applied to the 
fiber and/or that different levels of tension be applied during the 
scribing and severing steps of the operation. Previous methods have also 
required that the fiber be scribed while it is positioned about a curved 
mandrel and tensioned to a predetermined extent by being secured at 
opposite sides of the score mark. Since such techniques require that the 
fiber be clamped on opposite sides of the inflicted defect to create the 
breaking stress, the lengths of fiber which can be produced having smooth 
square surfaces at both ends may not be as short as desired. Such 
techniques in addition to requiring extensive hardware can be inadvertent 
twisting of the fiber during fiber crack propogation, produce surface 
irregularities and fail to consistently provided good square breaks. 
SUMMARY OF THE INVENTION 
It is, therefore, a principal object of the invention to provide a new and 
improved method and means for severing an optical fiber which are simple 
in nature and may be easily carried out during the manufacturing process 
as well as in the field for producing a fiber having ends with mirror 
smooth surfaces normal to the axis of the fiber. 
Another object of the invention is to provide a new and improved method and 
means for severing an optical fiber which do not require tensioning of the 
fiber during the inflicting of a flaw on the fiber. 
Another object of the invention is to provide a new and improved method and 
means for severing an optical fiber to produce ends with mirror smooth 
surfaces without requiring that the fiber be tensioned between fixed 
clamps during the severing operation. 
Another object of the invention is to provide a new and improved method and 
means for severing an optical fiber which are highly reliable and 
consistently provides severed fiber ends with mirror smooth surfaces. 
Another object of the invention is to provide a new and improved method and 
means for severing an optical fiber which do not require the removal of 
the outer protective covering over the glass surface of the fiber for the 
severing operation. 
Another object of the invention is to provide a new and improved method and 
means for severing an optical fiber which allow the production of fibers 
of very small length having ends with mirror smooth surfaces normal to the 
axis of the fiber. 
The above as well as many other objects and advantages of the invention are 
achieved by the method of the invention which comprises the steps of (a) 
inflicting a flaw on the glass surface of an optical glass fiber to be 
severed, (b) contacting an area about the fiber for applying pressure 
thereto which compresses the fiber, and (c) moving the contacted area 
along the fiber while applying sufficient pressure to produce frictional 
force which severs the fiber as the contacted area moves over the flaw. 
The term "flaw" as used herein designates a condition on the outer glass 
surface of an optical glass fiber such as a scribe mark, crack, or other 
defect provided for originating a break in the fiber, and as known in the 
prior art and referred to in the article entitled Optical Fiber End 
Preparation for Low-Loss Splices by D. Gloge, P. W. Smith, D. L. Bisbee, 
and E. L. Chinock, published in The Bell System Technical Journal, Vol. 
52, No. 9, November, 1973. 
The apparatus of the invention comprises scoring means for inflicting a 
flaw such as a scribe mark on the glass surface of an optical glass fiber. 
The scribe mark divides the fiber into first and second axially displaced 
portions which border the flaw on opposite sides. Pressure means slidably 
engages and compresses the fiber by applying pressure to a contacted area 
about the fiber. Displaceable means applies tension force between the 
first portion of the fiber and the pressure means to move the fiber with 
respect to the pressure means so that its contacted area passes over the 
flaw as it moves along the surface of the fiber from its first portion to 
its second portion. With the motion of the fiber, the pressure means 
produces frictional force at the contacted area along the surface of the 
fiber in a direction opposing the motion. The frictional force applied to 
the first portion of the fiber decreases as the contacted area passes over 
the flaw, while the frictional force applied to the second portion 
correspondingly increases. The frictional force applied to the second 
portion of the fiber which is in opposition to the tension force applied 
to the first portion of the fiber, increases until it is sufficient to 
sever the fiber at the inflicted flaw. 
In the embodiment disclosed, the pressure means comprises a pair of 
oppositely positioned resilient pad elements. The fiber is slidably 
received between the pad elements which apply compressive pressure to the 
contacted area about the fiber. The pressure means includes biasing means 
which urges the pad elements toward each other so that sufficient pressure 
is applied to the fiber by the pad elements to result in the severing of 
the fiber at the inflicted flaw. The displaceable means includes clamping 
means for being secured with the first portion of the fiber and guide 
means for moving the pad elements along the fiber in a direction away from 
the first portion and toward the second portion of the fiber, so that the 
contacted area moves over the flaw for severing the fiber. The fiber 
severing means also includes scoring means comprising blade means for 
engaging the outer glass surface of the fiber to inflict a flaw or lightly 
scribed mark which may be a line which is transverse to the longitudinally 
extending direction of the fiber.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1 and 2, a means 10 for severing an optical glass fiber 
embodying the invention comprises a support member 12 having a horizontal 
base portion 14, and an upstanding intermediate portion 16. A portion 18 
extends horizontally from the top of the portion 16 and overlies the base 
14 of the support member 12. The body 20 of a scoring means 22 has an end 
23 which slidably engages a track 24 mounted on a vertical surface 26 of 
the portion 16 of the support member 12. A blade 28 with its sharpened end 
30 directed downwardly is secured at the free end 32 of the body 20 for 
movement therewith in a vertical direction. A coil spring 34 which extends 
along the track 24 above the body 20 has its bottom end secured with the 
end 23 of the body 20 and its top end attached at the top end 36 of the 
track 24 for urging the body 20 upwardly along the track 24. 
A pressure means 31 comprises resilient upper and lower pad elements 38 and 
40. The lower pad element 40 is secured on an upper surface of the base 
portion 14 of the support member 12 under the end 42 of the horizontal 
portion 18. The upper pad element 38 is movably retained over the pad 
element 40 by being secured with the bottom surface of a plate 44 which is 
attached to the bottom end of a vertical rod 46. The rod 46 is retained 
for vertical movement through an opening 48 in the end 42 of the support 
member 12 as shown by the arrows 49. The rod 46 has an enlarged top 50 
positioned above the end 42 of the member 12, and is provided with a coil 
spring 52 thereabout extending between the plate 44 and the end 42 of the 
member 12. The spring 52 urges the rod 46 in a downward direction for 
moving the outer surface 54 of the pad elememt 38 into engagement with the 
outer surface 56 of the bottom pad element 40. 
The base portion 14 of the support member 12 is provided with a 
horizontally extending opening 58 therethrough. A displaceable means 60 
has an elongated horizontal portion 62 which is slidably received into the 
opening 58 of the base 14, and an upwardly extending end portion 64. The 
opening 58 and horizontal portion 62 of the displaceable means 60 received 
therein preferably are both provided with rectangular cross-sections for 
maintaining the end portion 64 in its upward orientation. The upper end 66 
of the end portion 64 supports a clamp 68 for securing an optical fiber 
therewithin. The end portion 64 has an opening 72 which permits an optical 
fiber 70 to be positioned therethrough into the clamp 68 for being secured 
with the displaceable means 80. 
In using the apparatus 10 for carrying out the method of the invention, an 
optical glass fiber 70 which is to be severed has a length of its 
outermost plastic cover 74 removed to uncover a region 76. However, the 
thin protective coating which may be provided over the glass surface of 
the fiber shielding the uncovered region 76 can be retained, if desired, 
for enhancing the strength of the fiber 70. The uncovered region 76 of the 
optical fiber 70 is positioned under the edge 30 of the blade 28 as 
illustrated, and the body 20 of the scoring means 22 is moved downwardly 
along the track 24 in opposition to the tension of the spring 34, until 
the blade edge 30 as shown at 30' strikes the uncovered region 76 and 
penetrates the protective coating to inflict a flaw on the glass surface 
of the optical fiber 70. The flaw may be in the form of a scribe mark 82 
(FIG. 3) which may be a line transverse to the longitudinal extension or 
axis 97 of the optical fiber. Upon the release of the body 20 of the 
scoring means 22, the spring 34 moves it upwardly and away from the fiber 
70, allowing the fiber 70 to be removed. The scribing of the fiber 70, 
thus, is accomplished in a simple and efficient manner without the need to 
placing the fiber under tension or subject it to any other conditions such 
as curving or stressing. 
With the flaw or scribe mark 82 preferably facing upwardly, the fiber 70 is 
positioned so that its uncovered region 76 extends through the opening 72 
and clamp 68 of the displaceable means 60. The end 50 of the rod 46 is 
lifted to allow the fiber 70 with its scribe mark 82 to pass between and 
beyond the pair of pads 38, 40. The end 50 of the rod 46 is then released 
to permit the pads 38 and 40 to approach each other and engage the 
uncovered portion 76 of the fiber 70 between the pad outer surfaces 54, 
56, and the clamp 68 is engaged to secure the fiber therewithin. The 
spring 52 exerts pressure on the pads 38 and 40, so that they subject the 
contacted areas 81 of the fiber 70 therebetween to compressive force as 
shown in FIG. 3. To provide a mirror smooth end at the scribe mark 82 on 
the fiber 70, the displaceable means 60 is actuated in the direction 
indicated by the arrow 80 of FIG. 1 so that its horizontal portion 62 
moves to the right out of the opening 58 of the base 14 as shown by the 
dashed lines at 64'. The fiber 70 retained by the clamp 68 is also 
displaced to the right, so that the scribe mark 82 moves between the pads 
38 and 40, is subjected to pressure therebetween, and is severed at the 
scribe mark 82. 
Refer to FIGS. 3 to 6 for a description in greater detail of the manner in 
which the method and apparatus severs the optical fiber 70 when the 
displaceable means 62 is moved from its retracted position shown by solid 
lines in FIGS. 1 and 2 to its extended position shown at 64' by the dashed 
lines. FIG. 3 illustrates the uncovered portion 76 of the optical fiber 70 
positioned between lower and upper pads 38 and 40 with the scribe mark 82 
facing upwardly and to the left and out of contact with the pads 38 and 
40. The outer surfaces 54 and 56 of the pad elements 38 and 40, contact 
and envelope the optical fiber portion 76 within a region 81 therebetween. 
Since the relative size of the fiber 76 with respect to the pad elements 
38 and 40 are exaggerated, the fiber 76 being much smaller in comparison, 
the resilient pad elements 38 and 40 contact and engage a substantial 
peripheral surface area 84 of the portion 76 of the fiber 70. The scribe 
mark 82 is also shown in exaggerated form for purpose of illustration. 
With the movement of the displaceable means 62 to the right, a tension 
force F.sub.T is exerted on the forward end 86 of the fiber portion 76 as 
illustrated in FIG. 3. This results in the relative movement of the fiber 
portion 76 between the pad elements 38 and 40. Since a pressure P is 
exerted by the pad elements 38 and 40 on the contacted area 81 of the 
fiber in the region 84 therebetween, a frictional force F.sub.F is 
produced opposing the tension force F.sub.T as illustrated. As the fiber 
76 moves to the right, the scribe mark 82 enters into the region 84 
between the pads 38 and 40. Since the frictional force F.sub.F is produced 
within the region 84 by contact with the pad elements 38 and 40, a portion 
of the total frictional force F.sub.F is produced on a portion 88 of the 
fiber axially displaced to the left of the scribe mark 82, while the 
remaining frictional force is produced on the portion 90 axially displaced 
to the right of the scribe mark 82 within the contacted region 84. 
As shown in FIG. 5, the continued movement of the fiber portion 76 to the 
right results in the translation of the scribe mark 82 towards the center 
of the region 84 of the pads 38 and 40, so that the frictional force 
produced and exerted on the contacted portion 88 of the fiber 70 to the 
left of the scribe mark 82 is equal to the frictional force on the 
contacted portion 90 to the right of the scribe mark 82. As seen from the 
FIGS. 3 to 5, as the scribe mark 82 moves to the right through the 
contacted region 84, the pad elements 38 and 40 contact a larger portion 
88 to the left of the scribe mark 82, producing increased frictional force 
thereon. As the frictional force on the portion 88 of the fiber 70 
increases, it reaches a critical value resulting in crack propagation at 
the scribe mark 82, severing the fiber at the scribe mark 82 to produce 
end faces 92 and 94, respectively, on the portions 88 and 90 of the fiber 
76 which are mirror surfaces normal to the axis 97 of the fiber 70 as 
illustrated in FIG. 6. 
The method and apparatus of the invention, thus, does not require that the 
optical fiber be subjected to tension during scribing or that it be 
fixedly secured at opposite ends for tensioning to produce the severed 
ends with the desired optical properties. Since both ends need not be 
clamped or fixed, the optical fiber is not subjected to torsional or 
twisting stresses which could otherwise be present. Such twisting and 
misaligning is undesirable because it results in end surfaces which are 
distorted and/or not normal to the direction of the longitudinal axis 97 
of the fiber 70. The process and apparatus of the invention provides 
opposing forces on opposite sides of the scribe mark 82 which gradually 
increase as the scribe mark 82 moves through the contacted region 84 
between the pad elements 38 and 40 with the movement of the displaceable 
means 82. The forces which are, thus, applied for causing the severing of 
the fiber, need not be adjusted to any particular values since they 
increase until they cause the severing action, and are removed as the left 
and right portions 88 and 90 of the optical fiber are severed as shown in 
FIG. 6. The frictional force produced by the pressure applied to the fiber 
may be controlled by varying the contour of the resilient surfaces 54 and 
56 of the pads 40 and 38. Thus, by providing the contacting surfaces 54 
and 56 with a curved contour increased pressure and greater compression 
are provided at their center regions 96, 98. Since the frictional force 
applied to the fiber 70 varies within the contacted region 84 with the 
applied pressure being greatest at the center contact regions 96, 98, this 
results in a non linear increase of frictional force applied to the 
portion 88 of the fiber as the scribe mark 82 moves between the pad 
elements 38 and 40 toward the center regions 96, 98. Movement of the 
scribe mark 82 passed the center regions 96, 98, while continuing to 
increase the frictional force applied to the portion 88 for severing the 
fiber, provides a reduced rate of increase. By such contouring of the 
surfaces of the pad elements 38 and 40, the range of frictional forces 
applied, may be controlled and selected so that the apparatus may be 
effective for severing fibers of different diameters without adjustment of 
the force provided by the spring 52. If desired, the force of the spring 
52 may also be adjusted by compressing it or by other known means, for 
controlling the force P exerted between the pad elements 38 and 40 and the 
resulting frictional forces. 
For the purpose of producing extremely short length of optical fiber having 
a second mirror smooth end face 100 represented by the dashed line in FIG. 
6, the portion 90 of the fiber 70 having the mirror end face 94 may be 
provided with a scribe mark 82' by use of the scoring means 22, and then 
subjected to the severing action of the pad elements 38 and 40 as just 
described. This will sever the portion 90 of the optical fiber 70 to 
provide the end face 100 shown by the dashed line and produce a very short 
portion 102 of optical fiber with mirror smooth ends 92 and 100. Of 
course, scribe marks 82' may be positioned at selected locations for 
providing optical fibers of any desired length, and by the process and 
techniques disclosed may provide fibers as short as 0.060 inch and perhaps 
shorter. This can be achieved by the invention, since only one end of 
optical fiber need be secured at a distal end 86 for severing the fiber 
and producing the mirror optical surfaces. 
The method and apparatus of the invention operates with great reliability 
to consistently provide mirror smooth end surfaces normal to the fiber 
axis. The invention may be utilized in manufacturing and in the field and 
is so simple and effective that it can be carried out by hand by scribing 
a transverse line on the glass surface of the optical fiber to be severed, 
after which the optical fiber is drawn between two fingers of one hand 
while sufficient pressure is applied by the fingers to the fiber to 
produce the frictional force which severs the fiber as the contacted area 
moves over the scribed line. Although only one embodiment of the device 
for carrying out the method of the invention is described in detail, it is 
apparent that many other embodiments may also be utilized for providing 
the advantages of the invention. 
It will thus be seen that the objects set forth above, among those made 
apparent from the preceding description, are efficiently attained and, 
since certain changes may be made in the above method and apparatus 
without departing from the scope of the invention, it is intended that all 
matter contained in the above description shall be interpreted as 
illustrative and not in a limiting sense.