Electric heating – Heating devices – Electric arc-type devices
Reexamination Certificate
2000-03-21
2001-09-25
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
Electric arc-type devices
C385S097000, C065S407000
Reexamination Certificate
active
06294760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for calibrating the discharge heat energy used in an optical fiber fusion splicing device which fuses and joins two optical fibers by heating due to electric discharge.
2. Description of the Related Art
In an optical fiber fusion splicing device, optical fibers ends are fused and joined by using high frequency discharge. When the optical fibers are fusion spliced using high frequency discharge, the minimum splice loss occurs at a particular discharge heat energy, as indicated in a graph shown in
FIG. 1
, which relates splice loss to discharge heat energy. Therefore, it is important to apply adequate discharge heat energy to minimize the splice loss.
In general, in a fusion splicing device of optical fibers, the discharge current is maintained at a given value while discharging, by a feed back control. The quantity of heat applied to the optical fibers can be controlled by adjusting a reference value of this feedback control current. The relation between the discharge current x and the discharge beat energy y can generally be represented by a relational expression y=f(x), which produces curves such as the ones shown in
FIG. 2
, where the discharge current is shown on x-axis and the discharge heat energy is shown in y-axis.
However, it has been observed that even though the discharge current may be maintained at a constant, the quantity of heat applied to the optical fibers changes gradually with usage of the discharge electrode. This is because the relationship between the discharge current and the discharge heat energy is affected by the changes in the fusion parameters caused by such factors as glass deposition on the discharge electrode, wear of the discharge electrodes and changes in discharge paths. Because the changes in the condition of the discharge electrodes often causes a change of the electrical resistance between the electrodes, the heat energy changes with usage of the electrodes. In other words, the relationship between the discharge heat energy and discharge current changes as illustrated by a curve y=f(x) in FIG.
2
.
For this reason, although fusion splicing operation is carried out under a constant discharge current, actual heat applied to the optical fibers changes in practice, and splice loss often deviates from the initial splicing conditions aimed for minimum splice loss. That is, in the curve shown in
FIG. 1
, actual discharge heat energy applied optical fibers shifts from the minimum point.
To avoid such problems in producing a low-loss splice by fusion splicing, it is necessary to establish a constant discharge heat energy applied to the optical fibers. In order to maintain a constant discharge heat energy, it is necessary to calibrate the discharge heat energy by altering either the reference discharge current for feedback control or discharging duration.
This method of measuring the discharge heat energy is disclosed in a Japanese Patent Application, First Publication, Hei 5-150132, which is based on using dummy optical fibers before starting to weld the actual optical fibers to calibrate discharge heat energy by observing the state of fusion of the optical fiber ends.
The method of measuring the discharge heat energy will be explained with reference to
FIGS. 5A-5C
. First, the two optical fibers
10
are placed with a known gap L
1
, as shown in FIG.
5
A. Next, as shown in
FIG. 5B
, discharge electrodes
21
are activated to generate a high frequency discharge to melt the ends of the optical fibers
10
while maintaining the relative positions of the optical fibers
10
. The result is a fusion of the ends of the optical fibers
10
to cause them to retract to result in a gap of L
2
. The change of the gap (L
2
−L
1
), that is, retracting amount, is used to measure and calibrate the discharge heat energy generated during fusion splicing.
However, the extent of end retraction is affected by the degree of spreading of the discharge field. Therefore, the discharge heat energy measured according to the method described above, which is based on measuring the discharge heat energy according to the change of the ends gap of two optical fibers, does not give an accurate estimate of the discharge heat energy. For this reason, discharge heat energy data calibrated by the distance of end retraction do not coincide with the adequate discharge heat energy to achieve the minimum splice loss.
There is also a related patent that is an ECF function. To splice fibers having eccentric cores, if fusion splicing is carried out by aligning the central axes of the cores
11
(referred to as the core axes), as shown in
FIG. 3A
, the surface tension forces act on the end portions of the optical fiber to reduce the cladding axes offset of the opposing fibers
10
. The resulting splice has a straight cladding axis, but the core axis has offset, as shown in
FIG. 3B
, and a higher splice loss is experienced by the core axes offset.
Therefore, there is a method of splicing, called eccentricity correct function (ECF) in which the self-aligning effects of the cladding axes caused by the surface tension forces on fused optical fiber are into account. In the ECF method, optical fibers
10
are aligned with intentional core axes offset of the optical fibers
10
, as shown in FIG.
4
A. The amount of the core axes offset of the optical fibers
10
caused by the self-aligning effect is calculated from the core eccentricities. Then, the optical fibers
10
are fusion spliced while maintaining this relative position of the optical fibers
10
. Optical fibers
10
thus joined exhibits a cladding axes offset but the cores are straight as shown in
FIG. 4B
, thereby producing an optical fiber with good core alignment, and reducing the splice loss. The details of this technology are disclosed in a Japanese Patent Application, First Publication, Sho 60-195504.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of calibrating the discharge heat energy generated during the actual fusion splicing operation with high
According to a first aspect of the present invention, a method of calibrating discharge heat energy used in the optical fiber fusion splicing device in which the discharge heating energy is measured and calibrated based on a change of the fiber cladding axes offset.
In the first method of the present invention, the fiber cladding axes offset is intentionally produced, the discharge heat energy is measured and calibrated. A change of the fiber cladding axes offset is not affected by the degree of spreading of the discharge field, as in the conventional methods. Therefore, it is possible to exactly measure the discharge heat energy.
According to a second aspect of the present invention, a method of calibrating heat energy used in the optical fiber fusion splicing device comprises the steps of:
abutting the two optical fibers with fiber cladding axes are offset;
performing discharge heating so as to produce a first fused joint exhibiting a residual axes offset;
subjecting the first fused joint to a series of successive additional discharge heating while the each discharge heat energy is measured at additional discharge heating process from on a change of the fiber cladding axes offset due to additional discharge heating.
According to the second method, the ends of the optical fibers are joined, and the fused joint is subjected to a series of additional heating steps. The change of the factors of the fiber cladding axes offset are measured and calibrated from due to a series of successive additional discharge heating. Therefore, when the change of the fiber cladding axes offset is concerned, the discharge heat energy can be measured on the same fused joint produced without being affected by the conditions of the optical fiber ends. Measured results are affected by the response of the optical fibers to the heat energy being applied presently, therefore, the results are more pertinent and precise. Also by repeating post-discharge hea
Inoue Koichi
Kawanishi Noriyuki
Sasaki Katsumi
Suzuki Yosuke
Tsutsumi Yukinari
Burns Doane Swecker & Mathis
Fujikura Ltd.
Jeffery John A.
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