JPH1082717A - Method for measuring microbending - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for estimating a microbending amount easily by comparing the variation in the peak value of transmitted light power ratio of an optical fiber subjected to bending under specific different conditions with the microbending amount of the optical fiber generated intendedly. SOLUTION: A longest wavelength where the ratio between a transmitted light power P1 when an optical fiber 5 of sample length 2m is subjected to bending of 280mmϕ, and a transmitted light power P2 when an optical fiber 5 of identical sample length is subjected to bending of 60mmϕ becomes 0.1dB, is set as a cut-off wavelength. Since the peak value of power ratio measured with the cut-off wavelength is proportional to microbending amount and the sensitivity of variation in the peak value of power ratio is invariant with respect to the microbending amount, the microbending amount can be estimated easily according to a predetermined relationship between the microbending amount and the variation in the peak value of power ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a micro-bending amount, and more particularly to a method for measuring a micro-bending amount of an optical fiber.

[0002]

2. Description of the Related Art Transmission loss, which is important in a single mode optical fiber, increases due to various factors. The causes are roughly classified into two types. One is the intrinsic loss that occurs during the production of the material and the base material, and the other is the additional loss that occurs during the drawing, cable conversion, and laying. The former can be subdivided into structural losses, such as scattering loss, absorption due to impurities, and fluctuations in the refractive index.These technologies, which are currently used in silica-based fibers, require that transmission loss be reduced to near limits using current technology. However, it is said that it is difficult to further reduce transmission loss when using a quartz-based material.

[0003] In the latter case, a loss due to minute bending (microbending loss) generated at the time of drawing or cabling, a bending loss (microbending loss) generated at the time of laying, and a connection loss generated at the time of connecting to another fiber. However, this micro-bending loss mainly occurs when drawing or coating an optical fiber (drawing process), and the cause is known to be the undulation of the optical fiber at the time of drawing and the inclusion of bubbles in the coating. It is said that it can be suppressed during the manufacturing process.

[0004] As for the method of measuring the cut-off wavelength of a single mode optical fiber, the following bending method is currently recommended by ITU-T. The bending method and the transmission light power P ₁ when adding bending φ280mm the optical fiber of sample length 2m, the power ratio of the transmitted light power P ₂ at the time of adding the bending of φ60mm the same optical fiber 0.1 FIG. 1 shows an example of a measurement method of a cut-off wavelength in which the longest wavelength of dB is used as a cut-off wavelength.

[0005] The cut-off wavelength is a mode that propagates up to the longest wavelength called the fundamental mode in the relationship between the wavelength of each mode to be propagated and the propagation constant indicating the easiness of propagation of the mode shown in FIG. Is the shortest wavelength that propagates, and indicates the wavelength at which the propagating light changes from multi-mode to single-mode. In addition, in the relationship shown in FIG. 2, a mode that propagates to a long wavelength next to the fundamental mode is called a first-order mode, and a subsequent mode is called a second-order mode, a third-order mode, and so on.

[0006]

However, when an optical fiber having a high loss is found, the cause of the problem has been discarded without sufficiently investigating the cause. Therefore, this sometimes recurred. Of these losses, microbending is known to occur at the time of drawing, so if the amount of microbending can be measured at the stage of measuring the optical fiber strand, it is easily found that this loss is due to microbending You can change the drawing conditions to prevent recurrence,
Development of a method for easily measuring the microbending amount is required.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances.
Cut transmitted light power P ₁ when added 0mm of bending, the longest wavelength at which the power ratio is 0.1dB of transmitted light power P ₂ at the time of adding the bending of φ60mm in the optical fiber of the same sample length The method for measuring the cutoff wavelength as the off-wavelength is characterized in that the amount of microbending is estimated from the relationship between the amount of change in the peak value of the power ratio obtained by the method and the amount of microbending of the optical fiber intentionally generated. It is assumed that.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention measures the cutoff wavelength by a known bending method, and determines the amount of change in the power ratio obtained from the cutoff wavelength. This is a method of estimating a microbending amount of a target optical fiber as compared with a conventional optical fiber.

That is, since the working wavelength of a silica-based single mode optical fiber is usually in the 1.3 μm band, the cutoff wavelength is designed to be 1.2 to 1.3 μm, but most of the cutoff wavelengths are measured. The bending method described above is used. Therefore, when measuring the cutoff wavelength of the optical fiber by this method, the propagated wavelength no longer the primary mode at the time of measurement of the transmitted light power P ₁ when adding bending φ280mm the optical fiber of sample length 2m is 1.2
1.3μm, and the propagated wavelength no longer the primary mode at the time of transmission light power P ₂ measurements when adding bending of φ60mm in the same optical fiber should be 1.0 to 1.2 [mu] m.

The peak at the time of the theoretical cutoff wavelength measurement at this time can be calculated as follows. That is, the mode shown in FIG. 2 described above is further divided into finer modes, two in the fundamental mode, six in the primary mode, and those included in the propagated light. Since the power ratio can be calculated from the ratio of the number of modes,
Theoretical value of the power ratio obtained at the time of cut-off wavelength measurement _{-10 · log (P 2 / P} 1) = - 10 · log { mode number (P ₂₎ / {number of modes _{(P 1)} = -10 ·} log {2 / (2 + 4)} = 4.77 [dB].

On the other hand, as a method of intentionally generating microbending in a pseudo manner, it is known that the method can be performed by sandwiching an optical fiber with sandpaper, placing a weight on the upper part thereof, and applying a load. As shown in FIG. 3, it is well known in the literature that the increase in loss due to micro-bending observed by this method increases as the wavelength becomes longer. Also, for the primary mode,
This is the peak-like loss existing at 1,150 nm. As can be seen from the figure, the tendency that the loss increases as the wavelength becomes longer is the same, but the loss increases more strongly than the fundamental mode. The behavior of increased loss due to such microbending, and if the behavior with respect to the wavelength of the transmitted light power P ₂ at the time of adding the bending of the transmitted light power P ₁ and φ60mm when adding bending φ280mm is normal, different. The change causes an increase in loss near the wavelength at which the first-order mode is not propagated due to the involvement of microbending, as shown in FIG. As for the fundamental mode, as shown in FIG. 5, the increase in loss due to microbending is smaller than that in the primary mode, and the loss does not change when a φ280 mm bend is applied. The peak value of the power ratio obtained is lower than the theoretical value of 4.77 dB as shown in FIG.

From these relationships, it has been found that microbending affects the peak value of the power ratio obtained when measuring the cutoff wavelength in the measurement of the cutoff wavelength of the silica-based optical fiber. As a result of various investigations, it was also found that the amount of change in the peak value of the power ratio with respect to the amount of microbending changes linearly with the amount of microbending and is not affected by the cutoff wavelength. In other words, once the relationship between the amount of change in the peak value of the power ratio with respect to the amount of microbending is examined, the amount of microbending can be easily estimated from the peak value of the power ratio obtained when measuring the cutoff wavelength. Regarding the relationship between the peak value of the power ratio obtained during wavelength measurement and the amount of microbending,
It can be obtained by using an optical fiber in which microbending is intentionally caused.

Therefore, when a high transmission loss is found for an optical fiber, the relationship between the amount of change in the peak value of the power ratio obtained at the time of measuring the cutoff wavelength and the microbending value of the optical fiber intentionally generated. By comparing this, the amount of microbending can be estimated, and if it is determined that the transmission loss is caused by microbending, the condition such as drawing may be changed to prevent recurrence.

[0014]

Next, examples of the present invention will be described. Embodiment A microbending device 1 using a sandpaper (# 320, length 30 mm) 2 and a metal plate 3 as shown in FIG. Is created, and this is shown in FIG.
It is installed in the illustrated portion of the cut-off wavelength measuring device shown in (b), a weight 4 is placed thereon, and the amount of weight added to the micro-bending device is changed to obtain the micro-bending amount and the power obtained at the time of measuring the cut-off wavelength. The change in the peak value of the ratio was observed.

FIG. 9 shows that the cutoff wavelength under normal conditions is
The figure shows the variation of the power ratio due to the weight of the optical fiber with a wavelength of 1,240 nm.According to this, the peak value of the power ratio decreases as the weight of the weight as the microbending amount increases. However, when this was separated into the transmitted light powers P ₁ and P ₂ , it was confirmed that FIGS. 10 and 11 were obtained.

Further, in order to see the difference in the sensitivity of the change in the power value to the microbending due to the difference in the cutoff wavelength, two cutoff wavelengths of 1,240 nm and 1,340 nm were used.
When the same experiment was performed on the book, the result as shown in FIG. 12 was obtained. This relationship indicates that the peak value of the power ratio obtained when measuring the cutoff wavelength is proportional to the microbending amount, and that the sensitivity of the fluctuation of the power ratio peak value to the microbending amount does not change even if the cutoff wavelength differs. Therefore, if the relation of the peak value of the power ratio to the microbending amount is separately examined, the microbending amount can be easily estimated from the peak value variation of the power ratio obtained at the time of the cutoff wavelength measurement. I understand.

[0017]

According to the present invention, when a high transmission loss is found for an optical fiber, the peak value of the power ratio between the transmitted light powers P ₁ and P ₂ obtained by measuring the cutoff wavelength is determined. The microbending amount can be easily estimated from the fluctuation ratio and the known data, and if it is determined that the transmission loss is caused by the microbending, there is an advantage that recurrence can be prevented by changing the drawing condition.

[Brief description of the drawings]

FIG. 1 shows a chart of a power ratio of a normal optical fiber.

FIG. 2 is a diagram showing the relationship between the wavelength of each mode included in the propagated light and the propagation constant.

FIG. 3 shows a behavior diagram of a loss increase caused by microbending.

FIG. 4 shows an optical fiber in which microbending has occurred.
FIG. 4 shows a change diagram of transmitted light power when a φ280 mm bending is applied.

FIG. 5 shows an optical fiber in which microbending has occurred.
FIG. 4 is a diagram showing a change in transmitted light power when a φ60 mm bend is applied.

FIG. 6 shows a chart of a power ratio of an optical fiber in which microbending has occurred.

FIG. 7 is a longitudinal sectional view of a microbending device for an optical fiber.

FIG. 8 is a schematic longitudinal sectional view of a cut-off wavelength measuring device provided with a microbending device, and (a).
3B shows a state in which a bend of φ280 mm is applied to the optical fiber, and FIG. 3B shows a state in which a bend of φ60 mm is applied.

FIG. 9 is a chart showing a power ratio chart of an optical fiber in which microbending is artificially generated.

FIG. 10 is a diagram showing a change in transmitted light power when a φ280 mm bend is applied to an optical fiber in which microbending is artificially generated.

FIG. 11 is a diagram showing a change in transmitted light power when a φ60 mm bend is applied to an optical fiber in which micro-bending has been artificially generated.

FIG. 12 is a diagram showing the relationship between the pseudo bending amount and the peak value of the power ratio obtained at that time in optical fibers having different cutoff wavelengths.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Micro-bending application tool 2 ... Sandpaper 3 ... Metal plate 4 ... Weight 5 ... Optical fiber wire 6 ... Holding part 7 ... Light source 8 ... Light receiving part

Claims (1)

[Claims] And 1. A transmission light power P ₁ when adding bending φ280mm the optical fiber of sample length 2m, of φ60mm the optical fiber of the same sample length bending of the transmission light power P ₂ at the time of addition In the method of measuring the cutoff wavelength with the longest wavelength at which the power ratio becomes 0.1 dB as the cutoff wavelength, the amount of change in the peak value of the power ratio and the amount of intentionally generated optical fiber microbending are calculated. A method for estimating the amount of microbending from the relationship: