JPS5979137A - Detection for disconnection of optical fiber - Google Patents

Abstract

PURPOSE:To detect immediately the occurrence of disconnection in the light incidence side, by propagating the scattered light, which is reflected at a breaking point when an optical fiber is broken, to the light incidence side while reflecting this light on the boundary face between the first clad layer and the second clad layer and detecting the light. CONSTITUTION:An optical fiber 1 consists of a center core 2 having a refractive index n1, the first clad layer 3 having a refractive index n2, the second clad layer having a refractive index n3, and a protection coating layer 5, and n1> n2>n3 is satisfied. The light from a light source 6 is made incident to the center core 2 of the optical fiber 1 and is propagated to the light exit side. If the optical fiber 1 is broken on the way, the light propagated in the center core 2 is subjected to Fresnel reflection at a breaking point 10, and the scattered light is propagated to the light incidence side while being reflected on the boundary face between clad layer 3 and 4 and is detected in the position of a notched part 9 by a photodetector 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber breakage detection method for detecting a breakage of an optical fiber from the light incident side.

Generally, optical fibers used in optical transmission systems are interposed between the light input side and the light receiving side, and if a failure such as breakage occurs during use of the optical fiber, the propagation of light may be interrupted or significantly interrupted. The light is attenuated and causes an abnormality in the output on the receiving side.
This makes it possible to detect a break in the optical fiber, but this cannot be detected on the light input side, so conventionally a separate line was used to transmit a signal indicating the occurrence of a break to the light input side. There was no other way.

By the way, as a method to detect the break point after a break in the optical fiber is detected, the end of the optical fiber on the light input side is connected to an optical pulse generation circuit such as a laser pulse oscillator, and an optical pulse signal is transmitted into the optical fiber. The pulse reflection method detects the break position by measuring the delay time until it is reflected at the break point and a reflected pulse is obtained. Various backscatter loss measurement methods have been proposed in which the backscattered light reflected from each point in the longitudinal direction of the beam is observed on the time axis and the breaking point is detected from the attenuation curve.

However, these detection methods only detect the position of the break point after it is determined that a break has occurred in the optical fiber, and do not detect the occurrence of the break itself.

Therefore, with the above-mentioned conventional technology, it is possible to automatically detect the occurrence of a disconnection during use in an optical transmission system that does not have a light receiving system, such as a medical optical fiber used in a laser scalpel. First, in order to detect a break, it is necessary to switch the optical transmission circuit to a measurement optical pulse generation circuit, which is a hassle, and it is impossible to constantly monitor the occurrence of a break in the optical fiber.

Therefore, the present invention has developed a new optical fiber that constantly monitors the occurrence of disconnection while using the optical fiber, and can immediately detect the occurrence of disconnection on the light input side, even in an optical transmission system that does not have a light receiving system. The purpose of this invention is to provide a method for detecting fiber breakage.

] - In order to achieve the above object, the present invention covers the core with a first cladding layer having a lower refractive index than this, and coats the first cladding layer with a second cladding layer having an even lower refractive index than this. An optical fiber made of an optical core is used as an optical transmission line, and when the optical core is broken, the scattered light reflected at the breaking point is reflected at the interface between the first cladding layer and the second cladding layer, and light is incident. The occurrence of a break in the optical fiber is detected by transmitting the light to the side and detecting the propagated light from the light incident side.

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

FIG. 1A is a front view showing an example of an optical fiber 1 applicable to the method of the present invention, and FIG. 1B is a sectional view thereof.

In the figure, 2 is a central core with a refractive index ηl, 6 is a first cladding layer with a refractive index η2 concentrically coated around the outer periphery of the central core, and 4
is the refractive index η coated concentrically around the first cladding layer
3 is a second cladding layer, and 5 is a protective coating layer made of a synthetic resin material etc. that is concentrically coated on the outer periphery of the second cladding layer. The refractive index η1 of each of the cladding layers 4. η2 and η
3 is selected such that η1>η2>η3, and the first cladding layer serves as a second core for backscattered light generated when the optical fiber 1 is broken.

Next, an example of an optical transmission system using the optical fiber 1 will be explained with reference to FIG.

6 is a light emitting source such as a laser oscillator, and 7 is a condensing lens. An optical signal from the light emitting source 6 is condensed by the condensing lens 7 and input into the central core 2 of the optical fiber 1.

Reference numeral 8 denotes a photodetector such as a photodiode, which is disposed in a notch 9 formed by partially removing the second cladding layer 4 and the protective coating layer 5 near the light incident end face of the optical fiber 1. Then, the detection output from the photodetector 8 is supplied to, for example, the light emitting source 6, and the generation of the optical signal from the light emitting source 6 is stopped.

In the optical transmission system configured as described above, an optical signal from the light emitting source 6 is normally input into the central core 2 of the optical fiber 1, and the core and first cladding are connected within the core as shown by the broken line. The light is propagated to the light output side while being totally reflected at the interface with the layer 6, so that the light is not irradiated onto the photodetector 8 and no detection output is obtained.

However, if the optical fiber 1 breaks midway during transmission as shown in FIG. 2, the light that was propagating within the central core 2 toward the light output side is Fresnel-reflected at the break point 10 and becomes scattered light. The light is in a higher order mode than a normal optical signal.

As a result, the first cladding layer 6 with a refractive index η2 becomes a second core for the scattered light, and the scattered light is transmitted as shown in FIGS.
As shown in the figure, the light is propagated within the first cladding layer 6 toward the light incident side while being reflected at the interface between the cladding layer and the second cladding layer 4.

When the propagated light reaches the vicinity of the light incident end face, since the second cladding layer 4 has been removed at the position of the notch 9, it is radiated to the outside from the notch 9, and is emitted to the photodetector 8. Accordingly, the occurrence of a break in the optical fiber 1 is detected, and furthermore, the generation of an optical signal from the light emitting source B is stopped based on the detection output of the photodetector 8.

In this example, a case has been described in which the light emission of the light source 6 is stopped by the output of the photodetector 8, but instead of this, an alarm may be generated.

As described above, according to the present invention, the backscattered light generated at the break point of the optical fiber is propagated through the cladding layer to the light incident side, and the occurrence of a break in the optical fiber is detected by detecting this with a photodetector. Because of this, it has the excellent effect of allowing signal light to propagate within the optical fiber without causing any damage to the signal light, and constantly monitoring the occurrence of breakage in the optical fiber in use from the light input side. have

In addition, the detection output of the photodetector makes it possible to immediately stop the emission of light from the light source, and therefore, it is possible to immediately stop the light emission from the light source, and therefore, it is possible to use a laser scalpel used as a medical instrument, in particular, when an optical fiber is broken during surgery and the light is scattered from the broken point. The fear that the laser beam may damage healthy living organisms is also eliminated, and surgery can be performed safely.

Furthermore, in the case of the present invention, there is no need to provide a special member for detecting light leakage within the optical fiber or its connector, so the diameter of the optical fiber can be made extremely thin, and there is no need for a light receiving system. Since disconnection can be detected even in optical transmission systems, it is extremely useful for application to various medical optical fiber products, including medical laser scalpels used in surgeries.

It goes without saying that the method of the present invention is not limited to the above, but can be applied to any other optical transmission system.

[Brief explanation of drawings]

Figures 1A and B are a front view and a cross-sectional view showing an example of an optical fiber that can be applied to the method of the present invention, Figure 2 is an explanatory diagram of the method of the present invention, and Figure 3 is a reflection at the breaking point when the optical fiber is broken. FIG. 2 is a longitudinal cross-sectional view of an optical fiber showing the propagation state of scattered light. Explanation of symbols 1... Optical fiber, 2... Central core, 6... First
Cladding layer, 4... Second cladding layer, 6... Light emitting source, 7... Condensing lens, 8... Photodetector, 9... Notch, 10... Breaking point. Patent applicant: Director of the Agency of Industrial Science and Technology (1) Daiichi Denko Co., Ltd.

Claims (1)

[Claims] A first cladding layer having a lower refractive index than this is coated on the fiber, and a second cladding layer having a lower refractive index than this is coated on the first cladding layer.
Clad layer? A coated optical fiber is used as an optical transmission line, and when the optical fiber is broken, light is incident while the scattered light reflected at the break point is reflected at the interface between the first cladding layer and the second cladding layer. 1. A method for detecting a break in an optical fiber, characterized in that the occurrence of a break in an optical fiber is detected by propagating the light to the side and detecting the propagated light from the light incident side.