JPS61284627A - Optical fiber sensor - Google Patents

Abstract

PURPOSE:To easily make a small curve having a small radius of curvature and to speed up a response to variation in the quantity of light by looping an elastic pipe by at least a half - one turn to a specific radius of curvature together with an optical fiber. CONSTITUTION:A sensor 8 consists of the elastic pipe 6 which has superior elasticity and the optical fiber 1 inserted into the pipe 6. Then, when both end parts of the sensor 8 are displaced externally as shown by arrows P1 P2, the internal optical fiber 1 is also displaced together with the elastic pipe 6, so when the quantity of this displacement is set a little bit larger than a critical angle, part of light is transmitted from the core to the clad. Then, the sensor 8 is looped by at least a half - one turn, so the light is transmitted at plural positions and detected as large variation in the quantity of light. Consequently, the sensor reacts to an external load sensitively as variation in the quantity of light and the reaction to the load is speeded up.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to an optical fiber (transparent fiber such as glass or plastic) that transmits light incident from one end to the other end.
Alternatively, they are bundled together to transmit optical images, and have characteristics such as small diameter, light weight, flexibility, non-induction, and non-crosstalk, and are used in large-capacity optical communication systems. ), and in particular, this invention relates to an optical fiber sensor that sensitively reacts to an external load by changing the amount of light, and is capable of responding to this load with sufficient nupede. be.

[Conventional technology]

The fifth country is a cross-sectional view showing a conventional optical fiber cut in the longitudinal direction, FIG. 5(B) is a longitudinal cross-sectional view thereof, and FIG. FIG. 7 is a side view showing a conventional optical fiber sensor composed of an optical fiber and a pair of jigs for bending the optical fiber, and FIG. 8 is an explanatory diagram of the principle of light transmission in the optical fiber. First, in Fig. 5 (A) ω), (1) is the optical refractive index (nt), and a core (1a) with a circular cross section, and a cladding (1b) surrounding this core and having an optical refractive index (n, ). and a protective layer (1c) that protects the surface of this cladding, (3) is the light transmitted in the core (1a), and (6') is the core (1a) and the cladding (1b). ) is the light reflected at the interface (2).

Next, in Fig. 6, (3”) is the light transmitted through the interface (2) between the core (1a) and the cladding (1b), and in Fig. 8, (C1) is the light inside the core (1a). The incident angle formed by the light (3) that transmits , and the interface (2) between the core (1a) and the cladding (1b), (θ) is the light (3”) transmitted through the interface (2) The angle of refraction, (θ.) is the angle of incidence (C1
) is the critical angle when it exceeds a certain value. In Fig. 7, (7) is the critical angle when
b) Form the next pair of jigs (4A).

(4B) is inserted between both jigs, and the uneven part (4m)
, the optical fiber bent into a wave shape by the suppression of (4b) (
1) This is a conventional optical fiber sensor composed of:

Generally, in this fiber, the incident angle (θl) of the light (3) transmitted within one core (1a) is
) is less than the critical angle (θe), as shown in FIG. If the incident angle (θ) of the light (3) transmitted within the core (1a) is greater than or equal to the critical angle (θe), total internal reflection occurs. As a result, the light (3') is transmitted within the core (1a).However, in the case of the straight optical fiber (1) shown in Fig. 5 (4), due to the total internal reflection effect described above, The loss of light (3) is relatively small.

However, when the optical fiber (1) is bent to a predetermined radius as shown in FIG. 6, when the bending is gentle, light transmission occurs in the state of total reflection as described above.
When the bend is steep, the angle at which the light (3) touches the boundary surface (2) must be less than the critical angle (θ), and the cladding (1b
) increases in the amount of light (3'') transmitted through the optical fiber (1), resulting in a significant decrease in light transmission efficiency, and when the optical fiber (1) is extremely bent, no light transmission occurs.

The conventional optical fiber sensor (7) shown in FIG.
, (4B), when the optical fiber (1) is bent into a wave shape by pressing the concavo-convex portion (4m), C4b), the amount of light transmitted changes due to the above-mentioned reasons, and although not shown, the optical fiber By determining the ratio of the amount of light between the light emitting element and the light receiving element provided at both ends of (1), it can be used as a sensor to detect the amount of physical displacement of both jigs (4-A) and (4B) based on changes in the amount of light. can.

[Problem that the invention seeks to solve]

In the conventional optical fiber sensor described above, a change in light intensity is detected by bending the optical fiber (1) into a wave shape by pressing the uneven parts (4m)-(4b) of a pair of jigs (4A) and (4B). Therefore, when both jigs (4A) and (4B) are separated from each other and returned to their original positions, that is, when they are returned to the position where there is no change in the light amount, K indicates that the optical fiber (1) is The fiber must return to its original state by the elastic restoring force of the fiber, but due to its constituent materials, the elastic restoring force is weak, and it is difficult to respond with sufficient speed in response to changes in the load on the AK. There is a drawback that it cannot be done. In addition, in the conventional optical fiber sensor described above, a jig (4A) is used to prevent large bending stress from being applied to the optical fiber (1).

There is a drawback that the radius of curvature of the concavo-convex portion (4m) = (4b) of (4B) must be made large.

Furthermore, in conventional optical fiber sensors, the irregularities with a small radius of curvature (4 m), which can greatly change the amount of light,
, (4b)-1 It is necessary to provide a large number of uneven portions (4m) opposite the jigs (4A) and (4B).

When the optical fiber (1) is repeatedly suppressed and released by
) is easily fatigued and cannot withstand long-term use.

This invention has been made with attention to these points, and it is possible to easily bend an optical fiber with a small radius of curvature, as well as to increase the change in the light amount of an optical fiber sensor. The present invention aims to provide an optical fiber sensor that speeds up the response to changes in light intensity due to target displacement.

[Means for solving problems]

In the optical fiber sensor according to the present invention, an optical fiber sensor is configured by an elastic pipe having excellent elasticity and an optical fiber inserted into the elastic pipe, and the elastic pipe and the optical fiber are arranged at a predetermined radius of curvature. It is formed into a loop shape of at least 1/2 turn to 1 turn.

[Effect]

In this invention, an optical fiber sensor is constituted by an elastic pipe having excellent elasticity and an optical fiber inserted into the elastic pipe, and the elastic pipe and the optical fiber are turned at least 1/2 turn with a predetermined radius of curvature. Since it is formed into a one-turn loop, by applying mutual displacement to both ends of the elastic pipe, displacement can also be given to the internal optical fiber, so that the light that enters the optical fiber is transmitted. The water that permeated from the core to the cladding during the
It is possible to obtain a change in the amount of light according to the displacement by reflecting on the interface between the core and the cladding.

[Embodiments of the invention]

Figures 1 and 2 both show an embodiment of the present invention, with Figure 1 being a front view of an optical fiber antenna, and Figure 2 being an enlarged cross section taken along line (1)-(1) in Figure 1. It is a diagram. (6) has an enlarged optical fiber (1) inside.
: For example, an elastic pipe made of plastic or the like with excellent elasticity, and this elastic pipe (6) and optical fiber (
1) and an optical fiber sensor (8), as shown in FIG.
It is formed into a cI-turn loop shape (6B), or a 1/2-turn loop shape (6B) as in the other embodiment shown in FIG. In addition, on the side wall of the elastic pipe (6),
As shown in the enlarged sectional view of Fig. 2, after inserting the optical fiber (1) in the longitudinal direction inside the elastic pipe, a sulin (61) extending in the longitudinal direction is formed.
If the gap size (6 m) is large, the bending of the elastic pipe (6) will not be accurately transmitted to the internal optical fiber (1), so it must be set to the minimum necessary limit. Since the fiber sensor is configured as described above, when external displacement is applied to both ends of the optical fiber sensor (8) in the direction of arrows (Pl)-(P2) as shown in FIGS. , the internal optical fiber (1) is also displaced along with the elastic pipe (6), but if the amount of displacement is set to be slightly greater than the critical angle (θC) mentioned above, the result will be as shown in Fig. 8. A part of the light (3) comes to be transmitted from the core (1m) into the cladding (1b). And this optical fiber senna (8) is at least 1/
It is formed in a loop shape with 2 turns to 1 turn, so
Light transmission occurs at multiple locations as shown in FIG. 6, and can be detected as a large change in light amount. Note that arrows (Pl)-(Ps) are marked at both ends of the optical fiber sensor (8).
If external displacement is applied in the opposite direction, light transmission will not occur. Needless to say, if the back-and-forth displacement is repeatedly applied, the amount of light will change correspondingly.

Note that the cross-sectional shape of the elastic pipe (6) described above is not necessarily limited to a circular shape as shown in FIG.
As shown in the figure, the same effect can be obtained even if the elastic pipe (6) is square or rectangular, and the cross-sectional thickness of the elastic pipe (6) can be the same throughout as shown in Figure 2. As shown in FIG.
It goes without saying that the characteristics of the senna can be adjusted by appropriately selecting the overall cross-sectional thickness of the elastic pipe (6) and changing the elastic force of the elastic pipe (6).

〔Effect of the invention〕

As described above, the present invention constitutes an optical fiber sensor by an elastic pipe having excellent elasticity and an optical fiber inserted into the elastic pipe, and also allows the elastic pipe and the optical fiber to have a predetermined radius of curvature. Since it is formed in a loop shape of at least 1/2 turn to 1 line, it responds sensitively to external loads by changing the amount of light, and responds to these loads with sufficient speed. Not only can it have excellent effects, but also
Since the optical fiber is inserted into the elastic pipe having excellent elasticity, the optical fiber can be protected by the elastic pipe, and the optical fiber can be used for a long time.

[Brief explanation of the drawing]

Figures 1 and 2 show an embodiment of the present invention, with Figure 1 being a front view and Figure 2 being (If) - (summer) in Figure 1.
FIG. FIG. 3 is a front view showing another embodiment of the invention, and FIG. 4 is an enlarged sectional view showing still another embodiment of the invention. Figure 5 (4) (B) - 8th
The figures show a conventional optical fiber sensor and an optical fiber. FIG. 5 (4) is a cross-sectional view of a conventional optical fiber cut in the longitudinal direction, FIG. 5 (B) is a longitudinal cross-sectional view thereof, and FIG. 6
The figure is a sectional view of an optical fiber bent to a predetermined radius of curvature, FIG. 7 is a side view showing an optical fiber sensor, and FIG. 8 is an explanatory diagram of the principle of light transmission in the optical fiber. In the figure, (1) is an optical fiber, (6) is an elastic pipe, (6A) is a 1-turn loop, (6B) is a 1/2-turn loop, (6a) is a slit of an elastic pipe, (
6b) is a part of the elastic pipe, and (8) is an optical fiber sensor. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Patent Attorney Tadashi Sato Figure 1 Figure 2 Figure 3 B Figure 4 Figure 5 Figure 7 Figure 9 $8

Claims (5)

[Claims] (1) Consisting of an elastic pipe with excellent elasticity and an optical fiber inserted into the elastic pipe, the elastic pipe is turned along with the optical fiber at least 1/2 turn to 1 turn at a predetermined radius of curvature. An optical fiber sensor characterized by being formed into a loop shape. (2) The optical fiber sensor according to claim 1, wherein the elastic pipe is made of plastic or the like. (3) The optical fiber sensor according to claim 1, wherein a slit is formed in the side wall of the elastic pipe for inserting an optical fiber in the longitudinal direction of the elastic pipe. (4) The optical fiber sensor according to claim 1, wherein the cross-sectional shape of the elastic pipe is circular or square. (5) Is the cross-sectional thickness of the elastic pipe the same throughout?
The optical fiber sensor according to claim 1, wherein the optical fiber sensor has different thicknesses.