JP2786682B2 - How to search for proper heating conditions when connecting optical fibers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for searching for an appropriate heating condition of an optical fiber when the optical fibers are fusion-spliced to each other.

[Conventional technology]

The fusion splicing of the optical fibers is performed by melting the ends of the optical fibers connected to each other by discharge heating.

At this time, if the discharge heating temperature is not within the predetermined appropriate temperature range, the connection loss between the connected optical fibers increases. For example, when the discharge heating temperature exceeds the appropriate temperature range and is abnormally high, excessive melting occurs due to the amount of heat applied to the end faces of the optical fibers before they come into contact with each other, and as a result, as shown in FIG. As described above, the core 2 of the optical fiber 1 is deformed in the vicinity of the connection portion, and the connection loss increases.

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 to measure this discharge current value as a guide for controlling the discharge heating temperature. (For example, the 1988 IEICE Spring National Convention materials, B-613 "SM" by Takashi Ide et al.
Optimization of fusion conditions in multi-core batch fusion ”).

[Problems to be solved by the invention]

However, as a guide for controlling the discharge heating temperature,
Even when the discharge current value between the discharge electrodes is used, the discharge electrodes are deteriorated by deposits and oxidation during repeated discharge. It has been empirically known that when the discharge electrode deteriorates, the discharge heating temperature increases in spite of the fact that the discharge current value is constant. For this reason, as shown in FIG. 7, the connection loss of the optical fiber gradually increases as the discharge is repeated.

In view of the circumstances, when controlling the discharge heating temperature using the discharge current as a guide, it is necessary to adjust the discharge current value as the number of discharges increases. However, in order to adjust such a discharge current value, strictly, a measuring instrument such as an ammeter or a power meter is used to examine the relationship between the discharge current value and the connection loss, and as shown in FIG. A graph must be prepared and a discharge current value must be determined from the prepared graph so that the discharge heating temperature falls within an appropriate temperature range. Actually, it is difficult to perform such a work at a construction site where fusion splicing of optical fibers is performed, and there is a problem that the work time is lengthened.

In view of the above circumstances, an object of the present invention is to provide a method for searching for an appropriate heating condition when an optical fiber is connected, which can easily determine an appropriate heating condition under which a discharge heating temperature can be within an appropriate temperature range. And

[Means for Solving the Problems] In order to achieve the above-mentioned object, in the automatic adjustment procedure of the proper heating condition at the time of connecting the optical fiber according to the present invention, a pair of discharge electrodes provided apart from each other are arranged between the pair of discharge electrodes. The end face of the optical fiber is positioned, the end face of the optical fiber is discharged and heated by a discharge current to be melted, and a retreat distance of the end face of the optical fiber before and after the melting is determined from the position of the end face of the optical fiber before and after the melting. The procedure is such that it is determined whether or not the value falls within the range of the minimum value ΔL _{min and the} maximum value ΔL _max , which is the proper range. Further, when the discharge current value does not fall within the proper range, the discharge current value is changed, and the above-described procedure is repeated until the discharge current value falls within the proper range. In addition, the minimum value ΔL _min and the maximum value ΔL _max are
By changing the discharge voltage and changing the discharge current, while heating and melting the end face of the optical fiber and changing the retreat distance,
While determining the retreat distance, the procedure of fusion splicing the optical fiber under the same discharge heating conditions corresponding to the retreat distance and measuring the splice loss is repeated, and based on the retreat distance and splice loss determined by this procedure. The minimum value of the retreat distance that does not exceed the allowable connection loss is determined as ΔL _min, and the maximum value of the retreat distance is determined as ΔL _max .

[Operation] By doing so, proper heating conditions are required from which the end of the optical fiber melts so that the discharge heating temperature of the optical fiber falls within an appropriate temperature range.

Also, between the discharge electrodes, the pair of optical fiber end faces are positioned so as to face each other, and by observing the melting of these optical fiber ends, the melting of the pair of optical fiber ends is averaged. Appropriate heating conditions can be determined.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to FIG. 1 to FIG.

FIG. 1 shows the steps for implementing the present invention in order.

First, as shown in FIG. 1 (a), the optical fiber 1 is mounted on the optical fiber fusion splicer. The fusion splicer is provided with a pair of discharge electrodes 3 that are separated from each other, and the end face of the optical fiber 1 is positioned between the discharge electrodes 3. After this positioning, the position (initial position) of the positioned optical fiber end surface is measured. This measurement is performed, for example, based on the brightness distribution of the obtained fiber image in which the end of the optical fiber 1 is imaged by an observation unit such as a microscope, a CCD camera, and an image processing device (not shown) provided in the fusion splicer. This is performed by performing image processing.

After the initial position of the end face of the optical fiber 1 is measured, a discharge voltage is applied for a predetermined time between the pair of discharge electrodes 3 as shown in FIG. Is heated and melted. The time during which the optical fiber 1 is heated needs to be long enough to melt the end of the optical fiber 1, and it is desirable that the time be such that no deformation occurs at any portion other than the end of the optical fiber 1. For example, it is appropriately selected from 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, rounded by its surface tension, and its end face recedes as shown in FIG. Then, the end face position (post-fusion position) of the optical fiber 1 after the retreat is measured in the same manner as the initial position before the fusion. As described above, the distance ΔL ₁ at which the end surface of the optical fiber 1 is melted and retracted is obtained based on the measured initial position of the end surface of the optical fiber 1 and the position after melting. The receding distance ΔL ₁ is a value corresponding to the melting of the end of the optical fiber, and is a value corresponding to the amount of heat given to the optical fiber by the discharge heating or the discharge heating temperature. Therefore, the retreat distance ΔL ₁ changes due to a change in the discharge current value even if the discharge heating time does not change,
Even if the discharge current value does not change, it changes according to the degree of deterioration of the discharge electrode.

Thus, by measuring the reverse distance [Delta] L _1, based on this, it is possible to evaluate the discharge heating state of the optical fiber. That is, the fusion splicing of the optical fiber is performed, and the optical fiber end is heated and melted under the same discharge heating condition as when a splicing loss sufficiently low is obtained, at which time the retreat distance ΔL ₁ Is obtained in advance. This operation is repeatedly performed, and the maximum _one of the determined retreat distances ΔL1 is ΔL _max , and the minimum one is ΔL _min .

Then, prior to the fusing of the optical fiber connection, an optical fiber end portion to melt in the manner described above, determine the reverse distance [Delta] L ₁ of the optical fiber end face, in the proper range the reverse distance [Delta] L ₁ is obtained in advance (Less than or equal to ΔL _{min and} equal to or less than ΔL _max ), the discharge current value is relatively adjusted. For example, if the retreat distance ΔL ₁ obtained here is smaller than ΔL _min, it is a case of insufficient heat, so that the discharge current value is increased,
Conversely, retraction distance [Delta] L ₁ is, the larger than [Delta] L _max are the case of heat excess, to lower the discharge current value. In this way, the retreat distance ΔL ₁ is within an appropriate range (ΔL _min or more Δ
Discharge current value to fit L _max or less) is adjusted relative.

ΔL _min and ΔL _max are obtained as follows. First, the end of the optical fiber is heated and melted to obtain ΔL ₁ . Then, the discharge heating condition of the optical fiber when the retreat distance ΔL ₁ is obtained is fixed, and under the same discharge heating condition (the heating time may be different), the fusion splicing of the optical fibers is performed. And measure the connection loss at the connection. The measurement of the connection loss between the retraction distance [Delta] L _1, performed repeatedly by changing the discharge current value, the relationship between the connection loss and the reverse distance [Delta] L _1, determined in advance as a graph shown in Figure 2. Then, from this graph, a retreat distance ΔL _{1 in a} range where the connection loss is sufficiently low to an acceptable level is obtained, and among the obtained retreat distances ΔL ₁ , a maximum retreat distance ΔL _max , and a minimum one is ΔL _min . I do. Note that ΔL _max and ΔL _min are stored in a central control unit including a CPU, a ROM, a RAM, and the like of the fusion splicing apparatus. Thereby, when the retreat distance ΔL ₁ obtained before the fusion splicing of the optical fiber is smaller than ΔL _min , “weak discharge” is displayed on the display unit of the fusion splicer, and the retreat distance ΔL ₁ is ΔL ₁ If the discharge distance is larger than _max , “Discharge strong” is displayed, and if the retreat distance ΔL ₁ is within an appropriate range (from ΔL _{min to} ΔL _max ), “discharge OK” can be displayed. It has become.

In the above-described embodiment, the end of the optical fiber 1 is positioned on one side with respect to the pair of discharge electrodes 3, and the appropriateness of the discharge heating state is determined based on the retreat distance of the end face of the optical fiber. However, as shown in FIG. 3, on both sides of the pair of discharge electrodes 3, the ends of the optical fibers 1 forming a pair face each other and are positioned between the discharge electrodes 3 to perform discharge heating. It is also possible to judge the suitability of the discharge heating state based on these retreat distances. In this case, the distance between the end faces of the pair of optical fibers is 100 μm so that the ends of the optical fibers are not too far from the discharge electrode 3.
Is less, the spacing between the pair of optical fiber end faces before discharge heating (initial gap) L ₀ is measured (FIG. 3 (a)), the interval after discharge heating (after melting interval) L ₁ is measured Then, based on the measured initial interval and the post-melting interval, ΔL (= L ₁ −L ₀ ) is obtained as the sum of the distances at which the end faces of the pair of optical fibers have receded, respectively (FIG. 3B). .

A graph similar to the graph shown in FIG. 2 is prepared for the relationship between the sum of the receding distances ΔL and the connection loss, and the sum of the receding distances ΔL in which the connection loss is within an allowable range.
(ΔL _min or more and ΔL _max or less) is obtained, and the discharge current value is relatively adjusted so that the sum of the receding distances ΔL falls within this range.
Appropriate discharge heating conditions with low connection loss are required.

By the way, when the end of the optical fiber 1 is positioned on one side with respect to the discharge electrode 3, the tips of the pair of discharge electrodes 3 are connected to each other even if the discharge heating condition such as the discharge current value does not change. When the distance (positioning position) from the imaginary line to the end face position of the optical fiber 1 changes, the melting of the end of the optical fiber changes. Therefore, it is necessary to accurately position the distance so as to be constant. If accurate positioning is not possible, the accuracy of searching for appropriate heating conditions will decrease. In addition, the position where the discharge spark flies may change due to the deterioration of the discharge electrode 3, and the search accuracy of the appropriate heating condition may decrease with the deterioration of the discharge electrode 3. In contrast,
When the pair of optical fiber ends is positioned on both sides of the discharge electrode 3, the relative positioning accuracy of the optical fiber 1 with respect to the discharge electrode 3 is high when the optical fiber 1 is positioned on one side of the discharge electrode 3. Even if it is lower, if the relative positioning between the end faces of the pair of optical fibers is accurately performed, both melting of the ends of the pair of optical fibers are considered, so that the ends of the pair of optical fibers are considered. This is the same as averaging the melting, and it is possible to suppress a decrease in search accuracy. The relative positioning between the pair of optical fiber end faces can be recognized with a CCD camera, so that the positioning can be performed with high accuracy.

In FIG. 4, the ends of the pair of optical fibers were positioned so that the distance between the end faces was 10 μm, the discharge current value was constant, the discharge time was 3.0 seconds, and the end of the optical fiber was heated by discharge. The graph shows the relationship between the number of discharges in the case and the spread of the end face interval (the sum of retreat distances ΔL). From this graph, even if the discharge current value is constant, as the number of discharges increases, the sum ΔL of the receding distance increases, and when the number of discharges exceeds a predetermined number n ₀ , ΔL becomes the allowable connection loss. It was found that the allowable range (ΔL _min or more and ΔL _max or less) was exceeded. FIG. 5 shows the relationship between the connection loss and the occurrence frequency when the number of discharges exceeds a predetermined number n ₀ . FIG. 3A shows a case where the fusion splicing is performed with the discharge current value i kept constant (i = i ₀ ), and FIG. 4B shows a case where ΔL is within an appropriate range (ΔL _min or more and ΔL _max or less). 2 shows a case where the fusion splicing is performed by lowering the discharge current value i to i ₁ so as to be within the range. As is apparent from this result, by adjusting the discharge current value i so that ΔL falls within an appropriate range,
Good connection characteristics were obtained.

〔The invention's effect〕

As described above, according to the method for retrieving the proper heating condition when connecting the optical fiber according to the present invention, the proper heating of the optical fiber is performed by relatively adjusting the discharge current based on the melting of the end of the optical fiber. Conditions can be easily obtained. Therefore, there is no need to determine the discharge current value and no need to consider the deterioration of the discharge electrode, so that an appropriate heating condition can be easily obtained even in an optical fiber connection operation outdoors or the like. In particular, in the fusion splicing of optical fibers in an area at high altitude, the discharge heating temperature decreases due to a decrease in the electric resistance between the discharge electrodes due to a decrease in the atmospheric pressure. Conditions can be determined.

Also, since the appropriate heating conditions are determined from the melting point of the optical fiber, it is easy to determine the appropriate heating conditions for the optical fiber even when the type of the optical fiber to be worked on changes and its melting temperature changes. Can be.

Furthermore, between the discharge electrodes, the end faces of the pair of optical fibers were positioned so as to face each other, and by observing the melting of the ends of these optical fibers, the melting of the ends of the pair of optical fibers was averaged. As a result, the search error of the proper heating condition due to the positioning error of the optical fiber is suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a graph showing the relationship between the 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. FIG. 4, FIG. 4 is a graph showing the relationship between the number of discharges and the sum of the retreat distance, FIG. 5 is a graph showing the distribution of connection loss, and FIG. 6 is a diagram showing an example of an optical fiber connection failure. FIG. 7 is a graph showing the relationship between the number of discharges and the connection loss, and FIG. 8 is a graph showing the relationship between the discharge current and the connection loss. 1 ... optical fiber, 2 ... core, 3 ... discharge electrode.

Continued on the front page (72) Inventor Hideji Furuya 1-chome, Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Michito Matsumoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Within Telephone Co., Ltd. (72) Inventor Nobuo Hirano 1-1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-1-169331 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) G02B 6/24 301

Claims (2)

(57) [Claims] 1. An initial position measuring step in which an end surface of an optical fiber is positioned between a pair of discharge electrodes provided apart from each other, and an initial position of the positioned optical fiber end surface is measured. A discharge voltage is applied between the discharge electrodes, a heating step in which the end of the optical fiber is heated and melted, a retreat position measuring step in which a post-melting position of the optical fiber end face is measured, and the initial position and the melting. Based on the rear position, a retreat distance in which the optical fiber end face retreats from the initial position is determined, and the discharge heating condition of the optical fiber in the heating step is determined in advance as the retreat distance suitable as the discharge heating condition at the time of optical fiber fusion splicing. the following [Delta] L _min or more [Delta] L _max in the proper range has been determined, a determination process of whether or not include the retreat distance is determined, the discharge current in the heating step Further to the to the retracted distance falls within the proper range, the initial position measuring step, the heating step, and a step of repeating said retracted position measuring step and the determination step, the [Delta] L _min and the [Delta] L _max While changing the retreat distance by changing the discharge current, the initial position measuring step, the heating step, the retreat position measuring step, and the retreat distance are obtained, and the same corresponding to the retreat distance. The connection step of measuring the connection loss by fusion splicing the optical fibers according to the discharge heating conditions, is repeated.Based on the receding distance and the connection loss determined in the connecting step, the retreat distance not exceeding an allowable connection loss. the minimum value with the said [Delta] L _min, the determined maximum value of the reverse distance as the [Delta] L _max, the optical fiber connection, characterized in that How to search for proper heating conditions at the time. 2. An end face of a pair of optical fibers is positioned opposite to each other between a pair of discharge electrodes provided apart from each other, and an initial distance between the positioned optical fiber end faces is measured. An initial position measuring step, a discharge voltage is applied between the pair of discharge electrodes, and a heating step in which the end of the optical fiber is heated and melted; and a post-fusion interval between the optical fiber end faces is measured. The retreat distance step, based on the initial interval and the post-melting interval, the sum of the retreat distances at which the optical fiber end faces are respectively melted and receded is determined, and the discharge heating condition of the optical fiber in the heating step is an optical fiber fusion condition the below [Delta] L _min or more [Delta] L _max is a proper range determined in advance of the sum of the recess distance suitable as a discharge heating condition at the time of connection, whether includes the sum of the retraction distance is determined Determining the discharge current in the heating step and repeating the initial position measurement step, the heating step, the retreat position measurement step and the determination step until the sum of the retreat distances falls within the appropriate range. And wherein the ΔL _min and ΔL _max are the initial position measurement step, the heating step, the retreat position measurement step, while changing the sum of the retreat distances by changing the discharge current. The connection step of measuring the connection loss by fusion splicing the optical fibers under the same discharge heating conditions corresponding to the sum of the retreat distances and obtaining the retreat distance is repeated. based on the sum and the connection loss of the distance, the minimum value of the sum of the recess distance not exceeding the connection loss acceptable while with the [Delta] L _min, the retraction distance Of the maximum value of the sum is determined as the [Delta] L _max, proper heating condition searching method during the optical fiber connection, characterized in that.