JP2012072022A - Method for producing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber having a desired optical characteristic with excellent yield, even when drawing a glass preform in which a specific refractive index of a core center part is larger than that of a clad part by ≥0.5%.SOLUTION: This method for producing an optical fiber including a solidification process for producing a solid glass preform by heating a transparent glass tube material is a method for producing the optical fiber by drawing the glass preform in which the specific refractive index of the core center part is larger than that of the clad part by ≥0.5%. In the method, a refractive index distribution of the glass preform is measured from each mutually-different N-direction which is vertical to a center axis of the glass preform by a preform analyzer, to thereby acquire refractive index distribution measurement results to the number of N (where N is an integer of ≥4), and the optical characteristic of the optical fiber after drawing is predicted based on the refractive index distribution measurement results to the number of N, and a succeeding production condition is determined based on an optical characteristic prediction value acquired by the prediction, to thereby produce the optical fiber based on the determined production condition.

Description

  The present invention relates to an optical fiber manufacturing method.

  As an optical fiber manufacturing method, there is known a method of manufacturing an optical fiber by drawing a glass base material, including a solidification step of heating a transparent glass tube material to produce a solid glass base material. The optical fiber manufacturing methods disclosed in Patent Documents 1 and 2 are a deposition process in which glass particulates are deposited on the outer periphery of the starting rod to produce a glass particulate deposit, and the starting rod is pulled out of the glass particulate deposit after the deposition process. A transparent process for producing a transparent glass tube by heating the glass particulate deposit after the process and the drawing process; and a solid pressure by depressurizing the inside of the transparent glass tube and heating the transparent glass tube after the transparent process. An optical fiber preform is manufactured through a solidification process for producing a glass preform, and an optical fiber is manufactured by drawing the preform for the optical fiber.

  Further, in such an optical fiber manufacturing method, as disclosed in Patent Document 3, the refractive index distribution of the glass base material is measured by a preform analyzer, and the light after drawing is drawn based on the measurement result of the refractive index distribution. The optical characteristics of the fiber are predicted, the subsequent manufacturing conditions are determined based on the predicted optical characteristics obtained by the prediction, and the optical fiber is manufactured based on the determined manufacturing conditions. . By doing in this way, it is supposed that the optical fiber which has a desired optical characteristic can be manufactured with a sufficient yield.

US Pat. No. 4,233,052 U.S. Pat. No. 4,204,850 JP-A-6-43068

  By the way, in the glass base material manufactured through the solidification (collapsing) process, the periphery of the collapsed portion after the central hole of the transparent glass tube material is blocked may be non-circular, and the collapsed portion peripheral region It is difficult to make the refractive index distribution of the complete axisymmetric shape. In particular, in a glass base material having a large relative refractive index difference (approximately 0.5% or more) in the surrounding area of the collapsed portion, the axial symmetry of the refractive index distribution in the surrounding area of the collapsed portion is greatly collapsed. In the case of a circular shape, the measurement direction by the preform analyzer has a great influence on the measurement value.

  FIG. 1 is a diagram schematically showing a cross section of a transparent glass tube 1 and cross sections of glass base materials 2A to 2C. This figure shows a cross section perpendicular to the central axis. A transparent glass tube 1 shown in FIG. 1A is obtained by a transparentizing process and has a central hole with a circular cross section in the center. When such a transparent glass tube material 1 is solidified in the solidification step, glass base materials 2A to 2C as shown in FIGS. In the glass base material 2A, the clog of the central hole is linear, in the glass base material 2B, the clog of the central hole is curved, and in the glass base material 2C, the clog of the central hole is Y. It has a letter shape. In the glass base material, the shape of the clog of the central hole is various, and therefore, the refractive index distribution distortion generated in the peripheral region of the collapse portion is also various.

  Therefore, even with the same glass base material, the refractive index distribution measurement result may differ depending on the incident direction of the measurement light of the preform analyzer due to the influence of the non-circularity and the blockage mark described above. Even if the optical properties after drawing are predicted based on the refractive index distribution measurement result of such a glass base material and the subsequent manufacturing conditions are determined and the optical fiber is manufactured, there is an error in the predicted optical properties. Therefore, an optical fiber having desired optical characteristics may not be manufactured with a high yield. That is, the optical fiber after drawing may not meet the predicted value of the optical characteristics. Such a phenomenon is remarkable in a glass base material having a relative refractive index difference of 0.5% or more at the center.

  The present invention has been made to solve the above-described problems, and even when a glass base material having a relative refractive index of 0.5% or more larger at the core central portion than that of the cladding portion is drawn, it is desired. It is an object of the present invention to provide a method capable of producing an optical fiber having the following optical characteristics with high yield.

  The optical fiber manufacturing method of the present invention includes a solidification step in which a transparent glass tube material is heated to produce a solid glass preform, and the relative refractive index of the core center portion is 0.5% or more larger than that of the clad portion. A method of manufacturing an optical fiber by drawing a glass preform, and measuring a refractive index distribution of the glass preform with a preform analyzer from each of N directions which are perpendicular to the central axis of the glass preform and are different from each other. To obtain N refractive index distribution measurement results (where N is an integer of 4 or more), predict optical characteristics of the optical fiber after drawing based on these N refractive index distribution measurement results, A subsequent manufacturing condition is determined based on the predicted optical characteristic value obtained by the prediction, and an optical fiber is manufactured based on the determined manufacturing condition.

  N optical characteristic prediction values are obtained by predicting optical characteristics of the optical fiber after drawing based on the N refractive index distribution measurement results, and the N optical characteristic prediction values are averaged. Subsequent manufacturing conditions may be determined based on the average optical characteristic prediction value obtained by converting to the above.

  Based on the average refractive index distribution measurement result obtained by averaging the N refractive index distribution measurement results, the optical characteristic of the optical fiber after drawing is predicted, and the optical characteristic prediction obtained by this prediction is predicted. Subsequent manufacturing conditions may be determined based on the value.

  When obtaining N refractive index distribution measurement results, it is preferable to vary the measurement direction by the preform analyzer by 360 ° / N.

  A great effect can be obtained when an optical fiber is manufactured by drawing a glass preform having a relative refractive index of 0.9% or more larger than that of the clad at the core center.

  According to the present invention, an optical fiber having a desired optical characteristic can be manufactured with a high yield even when a glass preform having a relative refractive index of 0.5% or more larger than that of a clad portion is drawn. can do.

It is a figure which shows typically the section of transparent glass tube material 1, and each section of glass base materials 2A-2C. It is a figure explaining the refractive index distribution measurement of the glass base material 2 by the preform analyzer in the optical fiber manufacturing method of this embodiment. 4 is a graph showing each of four refractive index distribution measurement results obtained in Example 1 individually. 4 is a graph showing four refractive index distribution measurement results obtained in Example 1 in an overlapping manner. 4 is a table summarizing relative refractive index difference peak values of four refractive index distribution measurement results obtained in Example 1 and wavelength dispersion values at a wavelength of 1550 nm obtained from the respective refractive index distributions. It is a graph which shows the average refractive index distribution measurement result obtained by averaging the four refractive index distribution measurement results obtained in Example 1. It is a graph which shows each of four refractive index distribution measurement results obtained in Example 2 individually. 4 is a graph showing four refractive index distribution measurement results obtained in Example 2 in an overlapping manner. 6 is a table summarizing relative refractive index difference peak values of four refractive index distribution measurement results obtained in Example 2 and wavelength dispersion values at a wavelength of 1550 nm obtained from each refractive index distribution. It is a graph which shows the average refractive index distribution measurement result obtained by averaging the four refractive index distribution measurement results obtained in Example 2.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  The optical fiber manufacturing method of this embodiment is a method of manufacturing an optical fiber by drawing a glass base material, including a solidification step of heating a transparent glass tube material to produce a solid glass base material. The relative refractive index difference at the center of the glass base material is 0.5% or more. A particularly large effect is obtained when the relative refractive index difference at the center of the glass base material is 0.9% or more. The optical fiber manufacturing method of the present embodiment is particularly effective when the outer diameter non-circularity of the glass base material is used as a measure of asymmetry around the collapsed portion and the outer diameter non-circularity is as large as about 0.03% or more. It is.

  FIG. 2 is a diagram for explaining the refractive index distribution measurement of the glass base material 2 by the preform analyzer in the optical fiber manufacturing method of the present embodiment. This figure shows a cross section perpendicular to the central axis. In the present embodiment, when the refractive index distribution measurement of the glass base material 2 is performed by the preform analyzer, measurement light is incident on the glass base material 2 from N directions that are perpendicular to the central axis of the glass base material 2 and are different from each other. Thus, the refractive index distribution is measured, and N refractive index distribution measurement results are obtained. Here, N is an integer of 4 or more. In the figure, the case of N = 4 is shown.

  In this embodiment, the optical characteristics of the optical fiber after drawing are predicted based on these N refractive index distribution measurement results, and the subsequent manufacturing is performed based on the predicted optical characteristics obtained by this prediction. Conditions are determined, and an optical fiber is manufactured based on the determined manufacturing conditions. By doing so, even when a glass base material having a relative refractive index of 0.5% or more larger than that of the clad portion is drawn, the accuracy of prediction of optical characteristics is improved. An optical fiber having desired optical characteristics can be manufactured with a high yield.

  At this time, N optical characteristic prediction values are obtained by predicting the optical characteristics of the optical fiber after drawing based on each of the N refractive index distribution measurement results, and these N optical characteristic prediction values are obtained. Subsequent manufacturing conditions may be determined based on the average optical property prediction value obtained by averaging the values. Alternatively, based on the average refractive index distribution measurement result obtained by averaging the N refractive index distribution measurement results, the optical characteristics of the optical fiber after drawing are predicted, and the optical characteristics obtained by this prediction are calculated. Subsequent manufacturing conditions may be determined based on the characteristic prediction value.

  In the case where the clogging of the central hole has a complicated shape as shown in FIGS. 1C and 1D, or when the noncircular shape is irregular, as shown in FIG. When obtaining the distribution measurement result, it is preferable to change the measurement direction by the preform analyzer by 360 ° / N. In addition, as shown in FIG.1 (b), when the obstruction | occlusion trace of a center hole is a simple shape, an effect can be anticipated also by implementing a measurement of a preform analyzer over 180 degree half circles.

  Next, Embodiments 1 and 2 will be described with reference to FIGS. In Examples 1 and 2, N = 4. In Example 1, the refractive index distribution of a glass base material manufactured so that the peak of the relative refractive index difference at the center was 0.58% was measured with a preform analyzer. In Example 2, the refractive index distribution of the glass base material produced so that the peak of the relative refractive index difference at the center was 0.93% was measured with a preform analyzer.

  3 to 6 show the measurement results in the case of Example 1. FIG. FIG. 3 is a graph showing each of the four refractive index distribution measurement results obtained in Example 1 individually. FIG. 6A shows the refractive index distribution measurement result from the angle 0 ° direction, FIG. 10B shows the refractive index distribution measurement result from the angle 90 ° direction, and FIG. 10C shows the angle 180 ° direction. (D) shows the refractive index distribution measurement result from the angle 270 ° direction. FIG. 4 is a graph in which the four refractive index distribution measurement results obtained in Example 1 are superimposed. In the figure, “a.u.” used for the horizontal axis of the graph is an abbreviation for “arbitrary unit (arbitrary scale)”.

  FIG. 5 shows the relative refractive index difference peak values of the four refractive index distribution measurement results obtained in Example 1, and the predicted value of the chromatic dispersion value at a wavelength of 1550 nm, which is one of the optical characteristics from each refractive index distribution. Is a chart summarizing these. The average value of the relative refractive index difference peak values of the four refractive index distribution measurement results was 0.577%, and the standard deviation (variation) was 0.009%. Moreover, the difference between the maximum value and the minimum value among the relative refractive index difference peak values of the four refractive index distribution measurement results was 0.20%, and the relative refractive index difference peak value was greatly different depending on the measurement direction. . The predicted values of chromatic dispersion values at a wavelength of 1550 nm obtained from these refractive index distributions are as shown in the chart, the average value is 14.23 ps / nm / km, and the standard deviation is 0.11 ps / nm / km. Met. That is, this means that an error of about 2% at maximum is generated in the predicted value obtained from the measurement result of the refractive index distribution from one direction.

  FIG. 6 is a graph showing an average refractive index distribution measurement result obtained by averaging the four refractive index distribution measurement results obtained in Example 1. The relative refractive index difference peak value in the average refractive index distribution measurement result is 0.577%, which coincides with the average value of the relative refractive index difference peak values of the four refractive index distribution measurement results. Further, when the predicted value of the chromatic dispersion value at the wavelength of 1550 nm, which is one of the optical characteristics, is obtained from the refractive index distribution of FIG. 6, it is 14.22 ps / nm / km, which is almost the same as the average value of FIG. Further, the chromatic dispersion at the wavelength of 1550 nm of the optical fiber after drawing at this time was 14.24 ps / nm / km, which substantially coincided with the average value of FIG. 5 and the predicted value obtained from FIG.

  7 to 10 show measurement results in the case of Example 2. FIG. FIG. 7 is a graph showing each of the four refractive index distribution measurement results obtained in Example 2 individually. FIG. 6A shows the refractive index distribution measurement result from the angle 0 ° direction, FIG. 10B shows the refractive index distribution measurement result from the angle 90 ° direction, and FIG. 10C shows the angle 180 ° direction. (D) shows the refractive index distribution measurement result from the angle 270 ° direction. FIG. 8 is a graph showing four refractive index distribution measurement results obtained in Example 2 in an overlapping manner.

  9 shows the relative refractive index difference peak values of the four refractive index distribution measurement results obtained in Example 2, and the predicted value of the chromatic dispersion value at a wavelength of 1550 nm, which is one of the optical characteristics from each refractive index distribution. Is a chart summarizing these. The average value of the relative refractive index difference peak values of each of the four refractive index distribution measurement results was 0.929%, and the standard deviation (variation) was 0.019%. Moreover, the difference between the maximum value and the minimum value among the relative refractive index difference peak values of the four refractive index distribution measurement results was 0.44%, and the relative refractive index difference peak value was greatly different depending on the measurement direction. . The variation of the relative refractive index difference peak value of each of the four refractive index distribution measurement results was larger in the case of Example 2 than in the case of Example 1. Predicted values of chromatic dispersion values at a wavelength of 1550 nm obtained from these refractive index distributions are as shown in the chart, the average value is 16.07 ps / nm / km, and the standard deviation is 0.24 ps / nm / km. Met.

  FIG. 10 is a graph showing an average refractive index distribution measurement result obtained by averaging the four refractive index distribution measurement results obtained in Example 2. The relative refractive index difference peak value in the average refractive index distribution measurement result is 0.929%, which matches the average value of the relative refractive index difference peak values of the four refractive index distribution measurement results. Further, when the predicted value of the chromatic dispersion value at the wavelength of 1550 nm, which is one of the optical characteristics, is obtained from the refractive index distribution of FIG. 10, it is 16.07 ps / nm / km, which is almost the same as the average value of FIG. Further, the chromatic dispersion at the wavelength of 1550 nm of the optical fiber after drawing at this time was 16.09 ps / nm / km, which substantially coincided with the average value of FIG. 9 and the predicted value obtained from FIG.

  DESCRIPTION OF SYMBOLS 1 ... Transparent glass tube material, 2, 2A-2C ... Glass base material.

Claims (5)

It includes a solidification process in which a transparent glass tube is heated to produce a solid glass preform, and a glass preform having a relative refractive index of 0.5% or more larger at the core central portion than that of the cladding portion is drawn to produce light. A method of manufacturing a fiber comprising:
N refractive index distribution measurement results are obtained by measuring the refractive index distribution of the glass base material with a preform analyzer from different N directions perpendicular to the central axis of the glass base material. Is an integer of 4 or more),
The optical characteristics of the optical fiber after drawing are predicted based on these N refractive index distribution measurement results, and subsequent manufacturing conditions are determined based on the predicted optical characteristic values obtained by this prediction. Manufacturing optical fiber based on the manufacturing conditions
An optical fiber manufacturing method.   N optical characteristic prediction values are obtained by predicting optical characteristics of the optical fiber after drawing based on each of the N refractive index distribution measurement results, and these N optical characteristic prediction values are obtained. 2. The optical fiber manufacturing method according to claim 1, wherein subsequent manufacturing conditions are determined based on an average optical characteristic prediction value obtained by averaging.   Based on the average refractive index distribution measurement result obtained by averaging the N refractive index distribution measurement results, the optical characteristics of the optical fiber after drawing are predicted, and the optical characteristics obtained by this prediction are calculated. 2. The optical fiber manufacturing method according to claim 1, wherein subsequent manufacturing conditions are determined based on the predicted value.   The optical fiber manufacturing according to any one of claims 1 to 3, wherein when the N refractive index distribution measurement results are acquired, a measurement direction by the preform analyzer is varied by 360 ° / N. Method.   5. The optical fiber is manufactured by drawing a glass base material having a relative refractive index of 0.9% or more larger than that of the clad portion in the core center portion. 6. Optical fiber manufacturing method.

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