JPH0362005A - Method for retrieving appropriate heating condition at connection of optical fiber - Google Patents

Abstract

PURPOSE:To easily obtain the appropriate heating conditions of optical fibers by regulating a discharge current in accordance with the way how the ends of the optical fibers melt. CONSTITUTION:The end face of the optical fiber 1 is positioned between a pair of discharge electrodes 3. This end part of the optical fiber 1 is melted by electric discharge heating and whether the discharge heating conditions of the end part of the optical fiber are suitable or not is discriminated by the distance DELTAL1 at which this end face retreats. Namely, the fusion splicing of the optical fibers is previously executed and a number of the retreat distances DELTAL1 when the permissible connection loss is obtd. are determined and the max. value among these distances is designated as Lmax and the min. value as Lmin. The end part of the optical fiber is melted and the retreat distance DELTAL1 is determined prior to the fusion splicing of the optical fibers. The discharge current is then so regulated that this retreat distance DELTAL1 is maintained at >=Lmin and <=Lmax. The appropriate heating conditions are easily obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of searching for appropriate heating conditions for optical fibers when fusion splicing optical fibers to each other.

[Conventional technology]

Fusion splicing of optical fibers is performed by melting the ends of the optical fibers to be interconnected by electrical discharge heating.

At this time, if the discharge heating temperature is not within a predetermined appropriate temperature range, connection loss between the connected optical fibers will increase. For example, if the discharge heating temperature exceeds the appropriate temperature range and is consistently high, the amount of heat added to the end faces of the optical fibers before they come into contact causes excessive melting, resulting in the melting of the fibers shown in Figure 6. As a result, the core 2 of the optical fiber 1 is deformed near the splicing portion, resulting in increased splicing loss.

Therefore, it is required to control the discharge heating temperature of the optical fiber within an appropriate temperature range.

Focusing on the fact that there is a predetermined relationship between the discharge current value flowing between the discharge electrodes and the discharge heating temperature, it is known that this discharge current value is measured as a guideline for controlling the discharge heating temperature. (For example, 1986 Institute of Electronics, Information and Communication Engineers spring national conference materials, B-613r by Takashi Ide et al.
(See the paper entitled "Optimization of fusion conditions in SM multi-core-brace fusion").

[Problem to be solved by the invention]

However, even if the discharge current value between the discharge electrodes is used as a guideline for controlling the discharge heating temperature, the discharge electrodes deteriorate due to deposits and oxidation as discharge is repeated. It is empirically known that when a discharge electrode deteriorates, the discharge heating temperature increases even though the discharge current value remains constant.

Therefore, as shown in FIG. 7, the connection loss of the optical fiber gradually increases as the discharge is repeated.

For this reason, when controlling the discharge heating temperature using the discharge current as a guide, it is necessary to make adjustments such as lowering the discharge current value as the number of discharges increases. However, in order to adjust the discharge current value in this way, strictly speaking, the relationship between the discharge current value and the connection loss must be investigated using measuring instruments such as an ammeter and a power meter, as shown in Figure 8. There is no choice but to create a graph and use the created graph to find a discharge current value that will keep the discharge heating temperature within the appropriate temperature range. In fact, it is difficult to perform such work at a construction site where optical fiber fusion splicing is performed, and there is also the problem that the work takes a long time.

Therefore, in view of the above-mentioned circumstances, an object of the present invention is to provide a method for searching for appropriate heating conditions for an optical fiber connection part, which can easily determine appropriate heating conditions under which the discharge heating temperature can be kept within an appropriate temperature range. It is said that

[Means to solve the problem]

In order to achieve the above-mentioned object, in the method of searching for suitable heating conditions when connecting optical fibers according to the present invention, the end face of the optical fiber is positioned between a pair of discharge electrodes provided apart from each other, and the end face of the optical fiber is The end of the optical fiber is melted by electrical discharge heating, and the distance that the end face retreats due to melting is determined from the position of the optical fiber end face before and after melting. Based on this retreating distance, the distance of the optical fiber when the end of the optical fiber is heated by electrical discharge is determined. It is determined whether the discharge heating conditions are suitable as discharge heating conditions for optical fiber fusion splicing.

[Effect]

By doing this, appropriate heating conditions can be found that allow the discharge heating temperature of the optical fiber to fall within an appropriate temperature range from the melting of the optical fiber end.

In addition, by positioning the end faces of a pair of optical fibers facing each other between the discharge electrodes and observing the degree of melting at the ends of these optical fibers, the degree of melting at the ends of the pair of fibers can be averaged. Appropriate heating conditions can be determined.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 sequentially shows the steps in implementing the present invention.

As shown in FIG. 1(a), first, the optical fiber 1 is attached to an optical fiber fusion splicer. The fusion splicing device is provided with a pair of discharge electrodes 3 spaced apart from each other,
The end of the tip fiber 1 is positioned between the discharge electrodes 3. After this positioning, a total of 7111 positions (initial positions) of the positioned optical fiber end faces are determined. This measurement is based on the brightness distribution of the obtained fiber image, in which the end of the optical fiber 1 is imaged by an observation means (not shown) provided in the fusion splicer, such as a microscope, a CCD camera, an image processing device, etc. This is done by performing image processing.

After the initial position of the end face of optical fiber 1 is measured, the same figure (
As shown in b), a discharge voltage is applied between the pair of discharge electrodes 3 for a predetermined period of time, and the end of the optical fiber 1 is heated and melted by the discharge. The time during which the optical fiber 1 is heated is sufficient to melt the end of the optical fiber 1, and desirably is such a time that deformation does not occur in any part other than the end of the optical fiber 1. , for example, is appropriately selected within the range of 0.5 seconds or more and 5.0 seconds or less.

Due to this discharge heating, the end of the optical fiber 1 is melted and curled by its surface tension, and its end face recedes, as shown in FIG. 2(c). The end face position (post-melting position) of the optical fiber 1 after this retreat is measured in the same manner as the initial position before melting. As described above, based on the measured initial position and post-melting position of the end face of the optical fiber 1,
The distance ΔL1 that the end face of the optical fiber 1 melted and retreated is determined. This retreat distance ΔL1 has a value depending on the degree of melting of the end of the optical fiber, and has a value depending on the amount of heat given to the optical fiber by discharge heating or the discharge heating temperature. Therefore, the retreat distance ΔL1 changes due to a change in the discharge current value even if the discharge heating time does not change, and changes depending on the degree of deterioration of the discharge electrode even if the discharge current value does not change.

Therefore, by measuring this retreat distance ΔL1, it is possible to evaluate the electrical discharge heating state of the optical fiber based on this distance. That is, the end of the optical fiber is heated and melted under the same discharge heating conditions as when the optical fiber was fusion spliced to obtain an acceptably low splice loss, and the retreat distance ΔL1 at that time was calculated. Ask for it in advance. This operation is repeated, and among the obtained retreat distances ΔL1, the maximum one is set as ΔL1, and the minimum one is set as ΔL.

wax sin Then, before fusion splicing the optical fiber, the end of the optical fiber is melted as described above, the retraction distance ΔL1 of the optical fiber end face is determined, and this retraction distance ΔL1 is within a predetermined appropriate range. The discharge current value ax is relatively adjusted so as to fall within the range (∆L1□ to ∆L). For example, if the retreat distance ΔL found here is smaller than ΔL, then l
ain is a case of insufficient heat, so the discharge current value is increased,
Conversely, if the retreat distance ΔL is greater than ΔL
When wax is too high, the amount of heat is excessive, so the discharge current value is lowered. In this way, the retreat distance ΔL is within the appropriate range (ΔL 0 or more and ΔL or less)1
1111+
The discharge current value is relatively adjusted so as to fall within 1aX.

ΔL and ΔL are calculated as follows +111
n IuaX. First, the end of the optical fiber is heated and melted to determine ΔL. and,
The discharge heating conditions of the optical fiber when this retraction distance ΔL1 is obtained are fixed, and under the same discharge heating conditions (heating 0 open may be present), the Fi
Make the A connection and calculate the connection loss at that connection.
do. The measurement of the retraction distance ΔL1 and the connection loss is repeated by changing the discharge current value, and the relationship between the retraction distance ΔL1 and the connection loss is determined in advance as a graph shown in FIG. 2. Then, from this graph, find the retraction distance ΔL in a range where the connection loss is sufficiently low to an allowable extent, and set the maximum retraction distance ΔL among the calculated retraction distances ΔL1.
Let the smallest IuaX be ΔL. In addition, ΔL and ΔL1n width +
n
max is stored in the central control unit of the fusion splicer, which includes the CPU, ROM, RAM, and the like. As a result, the retreat distance ΔL determined before fusion splicing of the optical fiber is changed to ΔL
, the display of the fusion splicing device will display "discharge 1 m+n weak" and the retreat distance ΔL will be displayed.
is larger than ΔL, “discharge l
max strong” is displayed, and the retreat distance ΔL1 is within the appropriate range (ΔL
(more than ∆L or less), l1in
In case of aax, "Discharge OKJ" can be displayed.

In the above embodiment, the end of the optical fiber 1 is positioned on one side with respect to the pair of discharge electrodes 3,
The suitability of the discharge heating state is judged from the retreat distance of the optical fiber end face.As shown in Fig. 3, a pair of group 7
The ends of the paired optical fibers 1 are positioned between the discharge electrodes 3 on both sides with respect to the electrode 3, facing each other, and discharge heating is performed, and the suitability of the discharge heating state is determined based on the retreat distance. It is also possible to judge. In this case, in order to prevent the end of the optical fiber from being too far away from the discharge electrode 3, the distance between the end faces of the pair of fibers is 100 μm.
In, the mutual distance (initial distance) Lo between the end faces of the pair of optical fibers before discharge heating is increased by 7 IP + (
Along with Fig. 3(a)), the interval after discharge heating (interval after melting) Lt is measured (Fig. 3(b)), and the initial interval and the interval after melting are 31 in total, forming a pair. ΔL(-L −
Lo) is required.

Then, a graph similar to the graph shown in FIG. 2 was created for the relationship between the sum of the retreat distances ΔL and the connection loss,
Find the range of the sum ΔL of the trailing distances within which the connection loss is allowable (ΔL or more and ΔLffiaxin or less), and relatively adjust the discharge current value so that the sum ΔL of the retreat distances falls within this range. By,
Appropriate discharge heating conditions with low connection loss can be determined without determining the discharge current value.

By the way, when positioning the end of the optical fiber 1 on one side with respect to the discharge electrode 3, even if the discharge heating conditions such as the discharge current value do not change, the tips of the pair of discharge electrodes 3 are connected to each other. When the distance (positioning position) from the virtual line to the end face position of the optical fiber 1 changes, the degree of welding of the end of the optical fiber changes.

Therefore, it is necessary to position accurately so that this distance is constant. If accurate positioning is not possible, the accuracy of searching for appropriate heating conditions will be reduced. Furthermore, the position of discharge sparks may change due to deterioration of the discharge electrode 3, and the accuracy of searching for appropriate heating conditions may decrease as the discharge electrode 3 deteriorates. On the other hand, when the ends of the tip fibers forming a pair are positioned on both sides of the discharge electrode 3, the relative positioning accuracy of the tip fiber 1 with respect to the discharge electrode 3 is such that the optical fiber 1 is positioned on one side of the discharge electrode 3. Even if it is lower than when positioning, as long as the relative positioning of the end faces of the paired optical fibers is done accurately, the melting of the paired optical fiber ends is taken into account, so the pair of light This is similar to averaging the welds at the fiber ends, and it is possible to suppress a decrease in search accuracy. Note that relative positioning between the pair of optical fiber end faces can be performed with high accuracy because both can be recognized by a CCD camera.

In Figure 4, the ends of a pair of optical fibers are positioned so that the distance between their end faces is 10 μm, the discharge current value is constant, the discharge time is 3.0 seconds, and the end of the first fiber is discharged. The relationship between the number of discharges and the spread of the end face spacing (sum of retreat distances ΔL) in the case of heating is shown as a graph. From this graph, even if the discharge current value is constant, as the number of discharges increases, the sum of retreat distances ΔL increases, and the number of discharges reaches the predetermined number n. It has been found that ΔL exceeds the allowable appropriate range of connection loss (ΔL 0 or more and 11n ΔL or less) when the value exceeds ΔL. The discharge amount ax is a predetermined number of times n. FIG. 5 shows the relationship between the connection loss and the frequency of occurrence when the connection loss exceeds . Figure (a) shows the discharge current value i
This figure shows the case where fusion splicing is performed while keeping constant (i-io), and in the same figure (b), ΔL is within the appropriate range (ΔL or more Δ
(L or less) 1in a+
This shows the case where the discharge current value i was lowered to 11 so that fusion splicing was performed. As is clear from this result,
Adjust the discharge current fUi so that ΔL falls within the appropriate range;
By adjusting J, good connection performance was obtained.

〔Effect of the invention〕

As explained above, according to the method of searching for suitable 1E heating conditions when connecting optical fibers according to the present invention, it is possible to find the appropriate heating conditions for optical fibers by adjusting the discharge current in the opposite direction based on the melting condition of the optical fiber end. Heating conditions can be easily determined. Therefore, since there is no need to determine the N discharge current value or to take into account the deterioration of the discharge electrode, appropriate heating conditions can be easily determined even when connecting fibers in the field. Particularly in optical fiber fusion splicing work in high altitude areas, the electrical resistance between the discharge electrodes decreases due to the decrease in atmospheric pressure, which causes the discharge heating temperature to decrease. Appropriate heating conditions can be found.

In addition, since the appropriate heating conditions are determined based on the melting state of the optical fiber, even if the type of target fiber to be worked on changes and its melting temperature changes, the appropriate heating conditions for the target fiber can be easily determined. I can do it.

Furthermore, between the discharge electrodes! By positioning the end faces of the optical fibers forming I4 so as to face each other and observing the degree of welding of these optical fiber ends, the result is the same as that of averaging the degree of welding of the ends of the pair of tip fibers. Errors in searching for appropriate heating conditions due to positioning errors are suppressed.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a graph showing the relationship between retreat distance and connection loss, and Fig. 3 is a diagram showing an embodiment of the present invention different from the embodiment shown in Fig. 1. Figure 4 is a graph showing the relationship between the number of discharges and the sum of trailing distances, Figure 5 is a graph showing the distribution of connection loss, and Figure 6 is an example of an optical fiber connection failure. 7 is a graph showing the relationship between the number of discharges and connection loss, and FIG. 8 is a graph showing the relationship between discharge current and connection loss. 1... Optical fiber, 2... Core, 3... Discharge electrode.

Claims (1)

[Claims] 1. A step of positioning an end face of an optical fiber between a pair of discharge electrodes provided apart from each other, and measuring an initial position of the positioned end face of the optical fiber; a heating step in which a discharge voltage is applied between the discharge electrodes and the end of the optical fiber is heated and melted; a step in which the position of the end face of the optical fiber after melting is measured; Based on this, the distance that the optical fiber end face has retreated from the initial position is determined,
and a step of determining whether or not the discharge heating conditions for the optical fiber in the heating step are suitable as the discharge heating conditions for optical fiber fusion splicing based on the retreat distance. How to search for appropriate heating conditions when connecting. 2. The step of positioning the end faces of the pair of optical fibers facing each other between a pair of discharge electrodes provided apart from each other, and measuring the initial distance between the positioned end faces of the optical fibers. , a heating step in which a discharge voltage is applied between the pair of discharge electrodes and the end portions of the optical fiber are heated and melted; a step in which a distance between the end surfaces of the optical fibers after melting is measured; and the initial distance. Based on the post-melting interval, the sum of the distances that the optical fiber end faces have melted and retreated is calculated, and based on the sum of the retreat distances, the discharge heating conditions for the optical fiber in the heating step are determined to be suitable for optical fiber fusion splicing. 1. A method for searching for appropriate heating conditions for optical fiber connection, the method comprising the step of determining whether or not the conditions are suitable as discharge heating conditions for an optical fiber connection.