JPH03210458A - fiber optic sensor - Google Patents

Abstract

PURPOSE:To detect the data of many points by providing a coupling optical fiber and a splitting optical fiber and allowing pulse light to be incident from one end of the coupling optical fiber to observe a change in the quantity of reflection of the splitting optical fiber as the emitted from the incident end of the coupling optical fiber. CONSTITUTION:A plurality of light splitters 3 are connected in series by coupling optical fibers 2 and splitting optical fibers 4 having open ends are connected to one ends of the light splitters and the end surface of each of the fibers 4 is present in oil 5 having a refractive index almost equal to that of the core part of each optical fiber 4 and a reflecting mirror 6 is arranged to the bottom part of the oil 5. The end surfaces of the splitting optical fibers 4 come into contact with the reflecting mirrors 6 or separate therefrom in connection with the movement of the drive parts 7 and the quantities of the reflected lights from the reflecting mirrors change and the movement of the drive parts 7 can be detected on the basis of a change in the quantities of reflection.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical fiber sensor that detects not only information at a single point but also information at multiple points.

(Prior Art) Conventionally, this type of optical fiber sensor includes, for example, a water immersion detection sensor disclosed in Japanese Patent Application Laid-Open No. 83-288333, and a lightning detection sensor disclosed in Japanese Patent Application Laid-Open No. 80-141121. .

The former type of water immersion detection sensor includes a water absorbing member that expands when it absorbs water, a movable member that moves according to the expansion of the water absorbing member, and an optical fiber that is bent by the movable member. It detects flooding by detecting loss.

The latter lightning detection sensor is connected to the optical fiber winding section, the fault current detection section, and the winding and bending section of the optical fiber composite overhead ground wire (OPGW) for each tower of the power transmission line, and changes the degree of winding. A driving section that applies a force in the direction of the detection section is provided, and the driving section is configured to be driven by the output of the detection section.

(Problem to be solved) Conventional sensors of this kind as described above bend optical fibers according to the detected amount, apply stress such as lateral pressure, and reduce the resulting optical transmission loss to 0TDR (Optlcai TimeDo).
The waveform is detected as a step waveform using the Saln Reflectmetry method.

However, in this case, since the optical fiber has a structure that causes optical transmission loss, the optical signal level rapidly decreases as the distance increases, and the effective measurement range of the 0TDRI arrangement is wasted, making it impossible to arrange a large number of sensors. There was a problem.

(Means for Solving the Problems) The present invention solves the above-mentioned problems and provides an optical fiber sensor that makes it possible to detect information at a large number of points. The optical branching devices are connected in series using connecting optical fibers, and a branching optical fiber having an open end is connected to the other terminal of the optical branching device, and the physical quantity to be measured is attached to the end face of the branching optical fiber. The purpose of the present invention is to provide a means for converting the amount of reflection into the amount of reflection, and to input pulsed light from one end of the optical fiber for connection, and observe changes in the amount of reflection of the optical fiber for branching as light emitted from the input end of the optical fiber for connection. .

FIG. 1 is an explanatory diagram of an example of an integrated optical fiber sensor according to the present invention. As shown in the drawing, a plurality of optical splitters (3) are connected in series by a connecting optical fiber (2). One end is connected to 0TDR(+). A branching optical fiber (4) having an open end is connected to the other terminal of the optical splitter (3), and the end face of the branching optical fiber (4) is connected to the other terminal of the optical splitter (3).
It is placed in an oil (5) whose refractive index is approximately the same as that of the core part (4), and a reflecting mirror (6) is installed at the bottom. (
Reference numeral 7) denotes a drive unit, and in conjunction with the movement of the drive unit (7), the end face of the branching optical fiber (4) comes into contact with the reflection mirror (6) or separates from the reflection mirror (6). The amount of reflection changes, and from this the movement of the drive section (7) can be detected. In this case, since the 0TDR (1) is used, it is possible to simultaneously measure information signals from a large number of optical splitters (3) arranged at different positions.

(Function) In conventional sensors of this kind, as mentioned above, the optical fiber is bent and stress such as lateral pressure is applied, and the resulting Rayleigh scattering loss is detected as a step waveform using the 0TDR method. . Since the intensity of Rayleigh scattering is very weak, the range in which it can be detected accurately is limited. However, since the sensor of the present invention detects the intensity of reflected light that is much stronger than Rayleigh scattering, the loss that occurs in the sensor section is small, and it is possible to arrange a large number of sensors.

In addition, with conventional stress-applying type sensors, the waveform obtained by the 0TDR method is sagged due to the influence of higher-order modes that occur after the stress-applied area, so it is not possible to place a second sensor in this area. . However, since the optical fiber sensor of the present invention detects reflected light, the sensor can be placed close to the sensor without being affected by higher-order modes.

Furthermore, it is conceivable to use the reflection (Fresnel reflection) of about 3% at the end face of an optical fiber that occurs when the end face is left in the air, but the optical fiber sensor of the present invention, which is brought into contact with a reflective mirror, is more effective than this. Since the amount of reflection increases, there is no need to branch a large amount of light to the sensor section, and light loss due to branching can be further reduced, making it possible to arrange a larger number of sensors.

(Example) FIG. 2 is an explanatory diagram of an example of the optical fiber sensor of the present invention.

(1) is 0T with an optical pulse width of 10 ns and a measurement interval of 10 ns.
It is a DR device. A multimode optical fiber is used as the coupling optical fiber (2), the core is made of 5102-Ge03 glass with a refractive index of 1.473, and the cladding is made of 5102-Ge03 glass with a refractive index of 1.45.
8 pure 5102 glass, the outer diameters of which are 50 μm and 125 μm, respectively. As the optical splitter (3), an optical coupler is used with a branching ratio of 1:1500, a branching optical fiber with an open end is connected to one terminal, and a subsequent optical coupler (3) is connected to the other terminal. ) is connected to the connecting optical fiber (2) to form five sensor units (M to E) in succession. The open end of the branching optical fiber (4) is in oil (5) whose refractive index is approximately the same as that of the core of the optical fiber (4), and when the sensor detecting section is driven, the refractive index is approximately 80%.
It has a structure in which it contacts a reflecting mirror (8) with a reflectance of .

In this embodiment, the sensor sections B and D operate and come into contact with the reflecting mirror (6), and the end surfaces of the branching optical fibers (4) of the other sensor sections C and E are coated with oil (5). ) inside.

The waveform of 0TDR (1'') observed at this time is as shown in FIG.

In this embodiment, an optical coupler is used as the optical splitter, but similar effects can be obtained by using other optical splitters such as dielectric waveguides.

(Effects of the Invention) As explained above, according to the optical fiber sensor of the present invention, reflected light is generated at the end face of the optical fiber, so compared to conventional optical fiber sensors, a large number of sensors can be placed close together. It is possible to place the

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a specific example of the optical fiber sensor of the present invention. FIG. 2 is an explanatory diagram of an embodiment of the optical fiber sensor of the present invention,
FIG. 3 is an explanatory diagram of an example of the 0TDR waveform observed in the above embodiment. 1...0TDRI placement, 2...optical fiber for connection, 3
. . . Optical splitter, 4. Optical fiber for branching having an open end, 5. Oil having approximately the same refractive index as the core portion of the optical fiber, 6. Reflection mirror, 7. Drive unit.

Claims (2)

[Claims] (1) Connect one or more optical splitters in series with a coupling optical fiber, connect a branching optical fiber with an open end to the other terminal of the optical splitter, and connect the branching optical fiber to the other terminal of the optical splitter. A means for converting the physical quantity to be measured into the reflection amount of the end surface is provided on the end face of the fiber, and a pulsed light is input from one end of the connecting optical fiber, and the change in the reflection amount of the branching optical fiber is measured from the input end of the connecting optical fiber. An optical fiber sensor characterized by observing as emitted light. (2) The optical fiber sensor according to claim 1, wherein the means for converting the physical quantity to be measured into the amount of reflection on the end face is constituted by means for attaching and detaching a reflecting mirror from the end face of the optical fiber.