JPH0727871A - Landslide detecting sensor using optical fiber - Google Patents

Abstract

PURPOSE:To improve the economy of a landslide detecting sensor using optical fiber. CONSTITUTION:The light from a light source 4 is made incident on the near end 3b of an optical fiber 2 (laid along the location to be inspected) through a photocoupler 5. The incident light is returned to the near end 2b after it is totally reflected at the far end of the fiber 2 or returned by a photocoupler 5, branched by the photocoupler 5, and made incident on a photodetector 6 which detects the quantity of the light. When a landslide occurs, the landslide is detected, because the fiber 2 is bent or twisted and a lateral pressure or tension is applied to the fiber 2 and, as a result, the light transmission loss of the fiber 2 increases. In the case where the fiber 2 is disconnected due to the landslide, the light receiving level of the photodetector 6 drops and the landslide can be detected, because the light reflectivity at the disconnected point becomes extremely small in addition to an increase in transmission loss due to the bending, twisting, lateral pressure, tension, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a landslide detection sensor using an optical fiber, and more particularly to its economic efficiency.

[0002]

2. Description of the Related Art A landslide detection sensor is provided at a place where a landslide may occur when there is a risk that the landslide will destroy houses, roads, railways, etc., or interfere with safe operation of people, vehicles, trains, etc. Is desirable. In the conventional sensor, the optical fiber is laid back and forth along the place where the landslide should be detected, and the light is turned back at the far end. The intensity of the returned light was detected by a photodetector.

When the landslide causes bending or twisting of the optical fiber or lateral pressure or tension, the optical transmission loss of the optical fiber increases. As an example, FIG. 2 shows changes in optical loss with respect to the radius of curvature when the optical fiber is bent. A photodetector can detect changes in the amount of light and can detect landslides.

[0004]

Recently, in order to popularize a landslide detection sensor, there has recently been a strong demand for economic efficiency. This invention was made in order to meet the demand for economic efficiency.

[0005]

[Means for Solving the Problems]

(1) The landslide detection sensor according to claim 1 is a light source, an optical fiber that is laid at a place where landslide should be detected, and has its far end subjected to total reflection processing, and the light from the light source near the optical fiber. An optical coupler that is incident on the end of the optical fiber, is totally reflected at the far end of the optical fiber, and branches the reflected light returned to the near end, and light that detects the amount of the reflected light branched by the optical coupler. It is composed of a detector.

The landslide can bend or twist the optical fiber and generate lateral pressure or tension, which increases the transmission loss of light and can detect the landslide. Since it is not necessary to lay the optical fiber back and forth, the economy can be increased accordingly. (2) The landslide detection sensor according to claim 2 includes a light source, an optical fiber laid at a location where landslide should be detected, and a first light provided at the far end of the optical fiber and connected so as to return light. A coupler and second light that causes light from the light source to enter the near end of the optical fiber, is reflected by the first optical coupler at the far end of the optical fiber, and branches the light returned to the near end. It is composed of a coupler and a photodetector that detects the amount of light branched by the second optical coupler.

With this configuration, the same operational effect as the item (1) can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG. In the present invention, in order to make the sensor economical, the optical fiber 2 to be laid is only the outward path, and in the invention of claim 1, the far end 2a is subjected to total reflection processing. That is,
After polishing the end faces, a reflective film such as gold or arni is deposited (FIG. 1A).

According to the second aspect of the invention, instead of totally reflecting the far end of the optical fiber, the optical coupler 3 is provided at the far end 2a.
One optical fiber is connected and the other pair of optical fibers is fusion-spliced so that the light is returned to the near end side (FIG. 1B). The light from the light source 4 is incident on the near end 2b of the optical fiber 2 through the optical coupler 5, and the light totally reflected or folded at the far end 2a is returned to the near end 2b and branched by the optical coupler 5 to be a photodetector. It is incident on 6, and the amount of light is detected. In addition, operating power is supplied from the power supply unit 7 to the light source 4 and the photodetector 6.

When the optical fiber 2 is broken due to a landslide, the bending, twisting,
In addition to lateral pressure, tension, and the like, the reflectance of light at the disconnection point is considerably reduced, so that the light receiving level of the photodetector 6 is lowered and detection is possible in the same manner. As the optical fiber 2,
A 1.3 μm band single-core optical code can be used, and the light source 4 can be a laser light source with a wavelength of 1.55 μm so that the change in the light amount is large. However, as the optical fiber 2, another optical fiber that becomes multimode or single mode with respect to the light source is used, and as the light source, a laser diode (LD) or a light emitting diode having one or a plurality of generated wavelengths
Alternatively, a white light source including innumerable wavelengths can be used.

[0011]

According to the present invention, since the optical fiber is reciprocated by totally reflecting or folding the light at the far end of the optical fiber, it is only necessary to lay the outward path. It will be 1/2 of that, and that will be economical.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing changes in optical transmission loss with respect to a radius of curvature when an optical fiber is curved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuzo Kosaka 1-21-6, Dogenzaka, Shibuya-ku, Tokyo Japan Aviation Electronics Industry Limited

Claims (2)

[Claims] 1. A light source, an optical fiber laid at a place where a landslide should be detected, and having a far end subjected to total reflection treatment; and light from the light source is incident on the near end of the optical fiber, An optical coupler for branching the reflected light that is totally reflected at the far end of the optical fiber and returned to the near end, and a photodetector for detecting the amount of the reflected light branched by the optical coupler. A landslide detection sensor using an optical fiber. 2. A light source, an optical fiber laid at a place where a landslide should be detected, a first optical coupler provided at the far end of the optical fiber and connected to fold back the light, and the light from the light source. To the near end of the optical fiber, the light is returned by the first optical coupler at the far end of the optical fiber, and a second optical coupler for branching the light returned to the near end; A landslide detection sensor using an optical fiber, comprising: a photodetector that detects the amount of light branched by a coupler.