JPS6086437A - Method and apparatus for detecting defective position of optical fiber - Google Patents

Abstract

PURPOSE:To detect a defective position of an optical fiber by moving the optical fiber while bending a part of the optical fiber continuously, and measuring the variation of transmitted light at the bent part continuously. CONSTITUTION:Light emitted from a light source device 1 is made incident on one end of an optical fiber 2, transmitted to a bending device 6 provided with a vertical roller 4 and a horizontal roller 5 through the optical fiber 2 and then measured by a photodetecting device 8 fitted to the other end of the optical fiber 2. A photodiode or the like is used as the photodetecting device 8 and an output from the device 8 is recorded by a recorder 9. If a defect exists in the optical fiber 2, the defective position can be detected on the basis of the variation of the transmitted light quantity of the optical fiber by recording the position of the bending device 6 on the fiber and the quantity of photodetection.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting defect positions in optical fibers.

Conventionally, the method for detecting the position of a defect in an optical fiber is to input pulsed light from one end of the optical fiber through a directional coupler, and then to cause the pulsed light to enter the optical fiber again due to Rayleigh scattering within the optical fiber, reflection at the defective part, the exit end face, etc. A method is used to measure the light that returns to the end face, and devices are already commercially available as failure point detection devices.

However, with this device, the transmission loss of the optical fiber is several dB.
This is effective when the distance is as small as /km, but it is effective when the distance is as small as several tens of dB, such as plastic optical fiber or multi-component glass fiber.
In optical fibers that have a large transmission loss of several hundred dB/km from /krt+, Rayleigh scattering, defects, and reflected light from the output end face are greatly attenuated, so the level of light that returns to the input end face is extremely small, making it difficult to measure. Moreover, since it handles weak signals, the electric circuit becomes complicated and the device becomes expensive.

The present invention improves these drawbacks of conventional optical fiber defect position detection devices, and makes it easy to search for defect positions even in optical fibers with transmission losses of about 300 dB/+s. A detection method and apparatus are provided.

In other words, the gist of the present invention is to move a part of the optical fiber in one direction while continuously forming a bent part, continuously measure the variation in the amount of transmitted light at the bent part, and measure the variation in the amount of light transmitted at the defective part. The first invention is a method for detecting the position of a defect in an optical fiber, which is characterized by detecting the position of a defect, and further includes a light source input section device that allows light to enter one end of the optical fiber and detects the emitted light at the other end. A second invention is an optical fiber defect position detecting device having a light emitting/receiving unit device and a bending portion forming device consisting of a guide or roller for bending the optical fiber and passing the optical fiber.

It is known that higher-order mode light of light propagating within an optical fiber is radiated into the fiber due to bending if the bending curvature is small. Further, when an optical fiber has a flaw on its side surface due to some manufacturing reason, the light emitted from the flawed portion is enhanced by the formation of a bent portion of the fiber. That is, when the position of the flaw is on the outside of the bend, it increases, and conversely, when it is on the inside, it decreases.

The present invention utilizes the above-mentioned characteristics to provide an extremely effective means for quality control of optical fibers with relatively large transmission losses.

Furthermore, the ability to non-destructively detect Kuki positions during optical fiber installation work, coupled with the low cost of the equipment and good handling, is of practical significance.

In the present invention, the term "optical fiber" includes not only uncoated fibers but also optical fiber cords and cables.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a perspective view of an example of an optical fiber defect position detection device of the present invention, in which light emitted from a light source device (1) is incident on one end of an optical fiber (2), and a bobbin (3) is
The vertical roller (
4), passes through a bending device (6) equipped with a horizontal roller (5), is wound around a bobbin (7) on the receiving side, and the light at the other end of the optical fiber is transferred to a light receiving device (
8).

A photodiode, a photoelectron multiplier, or the like is used for the light receiving device (8), and the output from this light receiving device (8) is recorded by a recorder (9). By recording the position on the fiber of the bending device and the amount of light received, if there is a defect in the optical fiber /<- (2), the location of the defect in the optical fiber (2) can be determined by an increase or decrease in the amount of light transmitted through the optical fiber. can do. (lO) drives the bobbin (3) with a motor. The vertical roller (4) is a 3-wooden metal roller (
4-1), (4-2), and (4-3) to bend the optical fiber. In FIG. 1, a horizontal roller (5) is installed following the vertical roller (4) to improve detection accuracy, but this is not always necessary.

Alternatively, the optical fiber may be bent using a fixed body having a suitably curved contact surface, or may be wound around four wooden rollers each having a different bending direction.

According to the experiments of the wood inventors, the angle of bending is from lOo to 36
As the angle increases up to 0°, the power to detect defects improves, but the amount of transmitted light decreases, so selecting the angle according to the length of the optical fiber to be measured and the optical loss level will yield preferable results.

As the light source device (1), continuous light or chopping light from tungsten, a laser, a semiconductor light emitting device, etc. can be used, and an optical fiber (2
) to allow light to enter the end face. Bending device (6)
It is possible to have vertical rollers (4) or horizontal rollers (5) on which the optical fiber runs, or the bending device itself can run over the optical fiber.

Example Diameter: 10 mm with polymethyl methacrylate as the core.
A planutic optical fiber cord with a numerical aperture of 0.5 (polyethylene coated outer diameter 2.2 mm, Eska manufactured by Mitsubishi Rayon Co., Ltd.) A 250 mm lamp is used as a light source for every 500 m, and the optical fiber is connected through a heat ray absorption filter and a collimator lens. Three metal rollers (4-1) and (4-2) each having a diameter of 25+am and allowing light to enter from one end surface.

(4-3) was passed through a bending device arranged as shown in Figure 2, and the amount of light at the output end of the optical fiber was measured.
Obvious changes in the amount of light were measured at the positions of minute scratches previously applied to the optical fiber.

As a result, the defect position could be detected without destroying the test object.A similar effect was confirmed even when the test piece was wound around a roller of other diameters or a single roller.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an example of the optical fiber defect position detecting device of the present invention, and FIG. 2 is a drawing showing the arrangement of the bending roller of the bending device and the optical fiber. (1) Light source device (2) Optical fiber (4), (5) Bending roller (6) Bending device (8) Light receiving device (9) Recorder

Claims (1)

[Claims] 1. A part of the optical fiber is moved in one direction while continuously forming a bent part, and the fluctuation in the amount of transmitted light at the bent part is continuously measured, and the fluctuation in the amount of light at the defective part is measured. A method for detecting the position of a defect in an optical fiber, characterized by detecting the position of the defect. 2. It has a light source input unit device that allows light to enter one end of the optical fiber, an output light receiving unit device that detects the emitted light at the other end, and a bending part forming device that consists of a guide or roller for bending and passing the optical fiber. Optical fiber defect position detection device.