JPH0632530B2 - Optical fiber hydrophone - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber hydrophone, and more particularly to an optical fiber hydrophone provided with a light receiving element adjacent to a deformable element that gives a microbend.

(Prior Art) A conventional technology of an optical fiber hydrophone will be described with reference to the drawings. FIG. 2 is an explanatory diagram showing an example of a conventional technique, and FIG. 3 is an explanatory diagram showing microbends and light paths.

When light is guided to the core of an optical fiber consisting of a core and a clad layer, and when the optical fiber is microbend (a slight bending displacement), the light in the core leaks to the clad layer There is a method of detecting a change in intensity or a change in intensity of light leaked from the core to detect the pressure or the amount of change in pressure from the outside that has caused the microbend. The operating principle is shown below.

In FIG. 2, the deformation element 81 acts to deform the optical fiber 83 by receiving a sound wave from the sound source 181 or a surrounding pressure. As shown in FIG. 3, the deformation elements 91A and 91B
The micro-bend is given to the optical fiber 93 by having projections and sandwiching the optical fiber 93 between the projections and holding the deformable elements 91A and 91B from both sides. When light propagates through the core of a straight optical fiber, reflection is repeated at the boundary surface between the core and the cladding layer at an incident angle of a critical angle or more. However, when the microbend is small, looking at the path of the light beam 913, when the incident angle of the point A of the convex portion of the bend of the optical fiber 93 becomes equal to or more than the critical angle, it is totally reflected and propagates, and the concave portion of the optical fiber Even when the light enters the point B, it has the same critical angle as in the above case, so that the light is totally reflected. When the microbend becomes large, a part of the light propagating in the core is incident at an angle smaller than the critical angle and the condition of total reflection is not satisfied. Therefore, the light incident at the point C is reflected and propagates to the core 93A. And a portion leaking to the clad layer 93B. A part of the portion leaked to the clad layer goes out of the optical fiber at a point D outside the clad layer, that is, outside the optical fiber 83, but the rest is reflected on the outer surface of the clad layer 93B and propagates through the clad layer. .

Therefore, there are a method of measuring the intensity of light leaked from the core to the clad layer and a method of measuring the decrease in the intensity of light of the core.

Regarding the method of detecting the decreasing intensity of the light in the core, when the light supplied from the light emitting source to the core of the optical fiber passes through the portion of the optical fiber which is deformed between the deforming elements, it follows the curved curvature. Leaks from the core of the optical fiber to the cladding layer. Therefore, the intensity of light passing through the core is reduced by the amount of light leaking into the cladding layer. However, since the intensity of light leaking to the clad layer is much smaller than the intensity of light supplied to the core, it is difficult to measure the intensity of light passing through the core and accurately calculate the decrease.

In recent years, in order to compensate for this drawback, it has been proposed to measure the intensity of light propagating in the clad layer out of the light leaked from the core to the clad layer. As shown in FIG. 2, according to this method, the light propagating in the clad layer is received by the light receiving element 82 through the index matching liquid, and a photoelectrically converted signal is output. The output or display of an electric signal corresponding to the amount of change exerted on 83 is performed.

However, in the conventional method, the deformation element and the light receiving element are separated from each other, and the coating material (aluminum, nylon) for reinforcing the optical fiber is propagated while the light leaking from the core to the outside of the cladding layer propagates through the cladding layer. However, there is a drawback that it is difficult to maintain the accuracy of measurement because it is attenuated due to the noise) and noise is mixed.

(Problem to be Solved by the Invention) As described above, the problem of the conventional technique to be solved by the present invention is that the distance between the deforming element of the optical fiber and the light receiving element is long, so that the light is propagated through the cladding layer. The light leaks from the clad layer to the outside of the optical fiber is not used at all and is easily affected by noise and the like.

Therefore, it is an object of the present invention to provide an optical fiber hydrophone having a low minimum detected sound pressure level that solves the above-mentioned drawbacks.

(Means for Solving Problems) The optical fiber hydrophone of the present invention provides a microbend to the guided optical fiber to measure the amount of light leaked to the outside of the core of the optical fiber. In an optical fiber hydrophone for measuring an external pressure required for a microbend, a translucent deformation element provided in contact with the optical fiber for transmitting the external pressure to the optical fiber and a translucent deformation element in close contact with the translucent deformation element. And a light receiving element which is formed.

(Example) Next, the present invention will be described in detail with reference to the drawings illustrating an example. FIG. 1 is an explanatory view showing an outline of the present invention, FIG. 4 is a perspective view showing a constitution of a first embodiment of the present invention, and FIG. 5 is a perspective view showing a constitution of a second embodiment of the present invention. Is.

An outline of an embodiment of the present invention will be described.

Referring to FIG. 1, when the light supplied from the light emitting source 4 to the core of the optical fiber 3 passes through a portion of the optical fiber 3 which is deformed between the deformation elements 1, the light is emitted according to the curved curvature. It leaks to the cladding layer of the fiber 3 or to the outside from the cladding layer. The deformable element 1 that is in contact with the optical fiber 3 is made of a material having a light-transmitting property, and takes in light leaked from the optical fiber 3. Next, the deformation element 1 is in contact with the light receiving element 2 (for example, a photodiode, a solar cell, etc.), sends the captured light to the light receiving element 2, and the light receiving element 2 converts the light into an electric signal. At this time, a refractive index matching liquid is generally used between at least two points of the optical fiber 3, the deformation element 1, or the light receiving element 2. The electric signal of the light receiving element 2 is output or displayed by the detector 5 in accordance with the amount of bending deformation of the deformation element 1 exerted on the optical fiber 3 by the detector 5.

At this time, the sound wave from the sound source 101 or the ambient pressure is first transmitted to the optical fiber 3 through the pressure receiving plate 6 (for example, a metal plate, a rubber plate, etc.), the light receiving element 2 and the deformation element 1. Also, depending on the position of the light receiving element 2, do not pass the pressure receiving plate 6,
It is also possible to apply the pressure of the sound source 101 or the surroundings directly to the deformable element 1 having a light guiding property. When the hydrophone is constructed by this method, since the deformation element 1 and the light receiving element 2 are in close contact with each other, it becomes possible to detect the light leaked to the outside of the optical fiber and propagate it in the upper cladding layer. It is easy to reduce the minimum detected sound pressure level by increasing the measurement accuracy with less propagation attenuation of light and noise mixing.

Here, the configuration and operation of the first embodiment of the present invention will be described. Referring to FIG. 4, the deformation element 2 is used in the first embodiment.
1A * 21B, the light receiving element 22A * 22B, the optical fiber 23, the light emission source 24, the detector 25, and the pressure transmission means 26A * 26B.

The light supplied from the light emission source 24 to the core of the optical fiber 23 is deformable elements 21A and 21B of the optical fiber 23.
When passing through the portion sandwiched between the optical fiber 23 and the optical fiber 23, the light leaks from the core of the optical fiber to the clad layer and further from the clad layer to the outside of the optical fiber according to the bent curvature. Light leaking out of the clad layer out of the clad layers passes through the protrusions of the translucent deformation elements 21A and 21B.
1A / 21B, and further deformable elements 21A / 21
It reaches the light receiving elements 22A and 22B which are in close contact with B.
The light reaching the light receiving elements 22A and 22B is converted into an electric signal and supplied to the detector 25, and the detector 25 outputs an electric signal corresponding to the amount of deformation of the deforming elements 21A and 21B on the optical fiber 23. Or display. In addition, a refractive index matching liquid is generally used between the optical fiber and the deformable element in order to extract light propagating in the clad layer.

On the other hand, the sound wave from the sound source or the surrounding pressure is received by the pressure receiving plate 26A.
.26B receives and is guided to the deformation elements 21A and 21B through the light receiving elements 22A and 22B.
The amount of leakage from the optical fiber to the outside is determined by the curvature of the optical fiber 23, that is, the amount of change exerted on the optical fiber 23 when the protrusion 1B reaches the optical fiber 23 in contact with it. Therefore, the output or display of the detection 25 can output or display an electric signal corresponding to the ambient pressure or sound pressure applied to the pressure receiving plates 26A and 26B.

Next, the configuration and operation of the second embodiment of the present invention will be described. Referring to FIG. 5, the deformation element 4 is used in the second embodiment.
1A to 41N, light receiving elements 22A and 22B, an optical fiber 23, a light emitting source 24, a detector 25, and a pressure receiving plate 26A.
・ 26B is provided.

The second embodiment is different from the first embodiment in the deformable element. That is, in the first embodiment, the deformable elements 21A and 21B having a plurality of protrusions are used, and the protrusions are in contact with the optical fiber 23 and the optical fiber 23 is sandwiched from both side surfaces. Is to give. However, in the second embodiment, a plurality of deformable elements 41A made of a light-transmissive columnar material (for example, a quartz glass rod, an optical fiber cut into short pieces, etc.) is used.
.About.41 N, the optical fibers 23 are arranged so as to be alternately closely contacted from both side surfaces. Therefore, unlike the first embodiment, a deforming element having a special shape is not required, so that it can be easily industrialized even in a relatively small amount of production. The operation of the second embodiment is similar to the operation of the first embodiment except for the operation of the deformable element described above.

(Effects of the Invention) As described in detail above, the optical fiber hydrophone of the present invention is configured such that the deformation element of the optical fiber and the light receiving element are in close contact with each other, and the light propagated in the clad layer up to now is Compared with the method of receiving light, it is possible to eliminate the propagation loss of light and to be less susceptible to the influence of noise. Further, it becomes possible to receive and detect light leaking to the outside of the cladding layer of the optical fiber, which could not be detected up to now, so that the S / N ratio of the light receiving element and the measurement accuracy can be improved. Therefore, it becomes possible to make the minimum detected sound pressure much lower than that of each method.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of the present invention, FIG. 2 is an explanatory diagram showing an example of a conventional technique, FIG. 3 is an explanatory diagram showing microbends and light paths, and FIG. 4 is a diagram showing the present invention. FIG. 5 is a perspective view showing the configuration of one embodiment, and FIG. 5 is a perspective view showing the configuration of the second embodiment of the present invention. 1 ... deformation element, 2 ... light receiving element, 3 ... optical fiber,
4 ... Emission source, 5 ... Detector, 6 ... Pressure receiving plate.

Claims (3)

[Claims] 1. An optical fiber hydrophone for measuring the amount of light leaked to the outside of the core of the optical fiber by applying a microbend to the guided optical fiber to measure the external pressure required for the microbend. , An optical fiber hydrophone comprising a translucent deformation element provided in contact with the optical fiber for transmitting the external pressure to the optical fiber, and a light receiving element in close contact with the translucent deformation element . 2. A refractive index matching liquid is provided between the optical fiber and the translucent deformation element.
The optical fiber hydrophone according to the item (1). 3. The optical fiber hydrophone according to claim 1, further comprising a refractive index matching liquid between the optical fiber, the translucent deformation element and the light receiving element.