JPS63124921A - Optical fiber hydrophone - Google Patents

Abstract

PURPOSE:To wind an optical fiber in an uniform direction and to improve the sensitivity of an optical fiber hydrophone by constituting the hydrophone so that the optical fiber differ in size from the core to the outer shape of the section in a direction centered on the center of the core. CONSTITUTION:Curved flank parts 5 which are connected slipperily to the external surface of diaphragms 2 fitted to both surfaces are provided at two positions of a support frame 1. The wall of the support frame 1 is much thicker than the diaphragm 2, the optical fiber 3 is wound closely in contact with the flank parts 5 and diaphragms 2, and the parts contacting the diaphragms 2 are fixed with an epoxy adhesive. In this case, the optical fiber 3 is sectioned in an elliptic or long-circle external shape which is symmetrical about a straight line connecting a strain inducing part. Consequently, the optical fiber is wound in the uniform direction, so the high-density hydrophone is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical fiber hydrophone, and more particularly to an optical fiber hydrophone in which the polarization planes of polarization-preserving optical fibers are aligned to increase sensitivity.

[Conventional technology]

An example of a conventional technique for an optical fiber hydrophone will be described with reference to the drawings. FIGS. 4(a) to 4(C) are explanatory diagrams showing the relationship between the external force applied to the optical fiber and the force applied to the core of the optical fiber.

First, as shown in FIG. 4(a), the core 64 is located at the center of the optical fiber, and the surrounding area is filled with a layer of dome 3, which has a lower refractive index than the core 64, and the outer shape of the cross section is generally a circle. ing. In this case, light passing through the core propagates at the same speed no matter which direction it is polarized. However, as shown in FIG. 4(b), nine stress-applying parts 65 made of a material with a larger coefficient of thermal expansion than the materials composing the cladding 63 are installed in the cladding 63. Since the stress-applying part 65 rapidly shrinks when the optical fiber formed by the process is cooled, tension (tensile force) is applied to the periphery of the stress-applying part. Depending on the pressure, the propagation speed of light polarized in that direction changes. Therefore, tension is applied to the core 64 in the direction of the stress-applying part 65, and therefore, the propagation speed of light polarized in the direction connecting the stress-applying parts and light polarized in the direction perpendicular to this is different, and each is independent. It begins to propagate to

On the other hand, we will examine the effect of external force applied to the optical fiber on the core. Here, when the material forming the stress applying portion 65 has a lower elastic modulus (softer) than the material forming the cladding 63, when the same force is applied to both, most of the force is generated by the material having a large elastic modulus (softer) than the material forming the cladding 63. is added to the cladding 63 consisting of a rigid) material. Therefore, in FIG. 4(C), the stress applying part 6
When applying a compressive force (or tensile force) 67 to the original fiber in a direction perpendicular to the line connecting the points 5 to 5, the force will be applied to the narrow part between the stress applying parts, ignoring the propagation of the pressing force in the stress applying parts with a small elastic modulus. It may be considered that most of the pressing force 67 on the optical fiber is applied. Therefore, the pressing force on the core is 67
The person exerts most of the pressure force 67 on the optical fiber. In addition, the pressure force 68 applied to the optical fiber at the point where the stress applying part 65 is connected (this is determined by the size or spread of the optical fiber 9
If the wavelength of the received sound wave is Kana 9 larger than , it will be almost the same as the pressing force 67 mentioned above), and if the propagation of the pressing force in the stress applying part 65 with a small elastic modulus is ignored, the stress applying part A pressing force 68A, which is considerably smaller than the pressing force 68, is applied to the core 64 which is blocked by the pressing force 65.

Therefore, when measuring pressure changes in underwater sound waves using such an optical fiber, light polarized in the direction connecting the two stress-applying parts 65 of the optical fiber and in the direction perpendicular to this is polarized with the same amplitude. into the fiber. Generally, light polarized in the middle of these two directions, that is, at a 45 degree angle from both directions, is input into an optical fiber, passed through a polarizer with the same polarization angle as the input polarization angle, and the change in phase difference is detected, and the light is connected to the optical fiber. Extracts the applied external force or the amount of external force change.

As described above, when the pressing force 68 is applied to the optical fiber in the direction of the line connecting the stress applying parts 65, the pressing force 68A generated on the core 64 is also perpendicular to the line connecting the stress applying parts 65'jt. When a pressing force of 67 gold is applied, the pressing force of 67 A generated in the core is considerably larger. Therefore, when receiving sound pressure from the outside directly or indirectly as a hydrophone, it is found that it is desirable to adopt a method of applying pressurizing force 67.

In conventional technology, a single optical fiber receives sound waves from all directions, and either utilizes the anisotropy of stress on the core generated by the internal structure described above, or, as shown in Figure 3, receives sound waves from all directions. By closely winding the optical fibers 52t on the diaphragm 51, which has been converted into flexural vibration (also called bending vibration) by an appropriate method, and fixing it with adhesive 53, the compression or tension received in the direction of the acting force 56 is applied. It uses power. However, since the optical fiber 52 has a circular cross-sectional outline, when it is fixed to the diaphragm 51, it is extremely difficult to align the direction of the stress-applying portion with respect to the cross-section. Therefore, if the optical fibers are arranged in this way, even if the optical fibers are connected in series, only the average sensitivity of the optical fibers facing different directions will be lost, and the diaphragm will be distorted. The effect of increasing the sensitivity by amplifying the stress in one direction and adding it to the optical fiber is reduced.

[Problem that the invention seeks to solve]

The problem of the prior art that the present invention aims to solve is, as mentioned above, that when all the optical fibers are tightly wound and fixed around a vibrating body, the cross-sectional directions of the optical fibers are not aligned, so a large number of optical fibers are attached to the vibrating body. The problem is that the sensitivity does not increase even if the winding is repeated.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a highly sensitive optical fiber hydrophone that overcomes the above-mentioned drawbacks.

[Means for solving problems]

The optical fiber hydrophone of the present invention includes a core, a cladding surrounding the layers thereof, and two stress-applying parts at symmetrical positions with the core as the center, and the cross-sectional outline and the stress-applying parts are different from each other. In a noidrophone comprising an optical fiber having the same relative relationship in the longitudinal direction, closely wound around a vibrating body and fixed to the vibrating body, the dimension from the core of the optical fiber to the outer diameter of the cross section is centered on the core. It is configured differently depending on the direction in which it is viewed.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings. Figures 1 (a) to (b) are perspective views showing the first to second embodiments of the present invention, and Figures 2 (a) to (C) are the structure of the original fiber used in the present invention and the optical fiber. FIG. 3 is a perspective view showing a structure in which a vibrator is tightly wound around a vibrating body.

First, an overview of the present invention will be explained.

As mentioned earlier, the direction of maximum sensitivity of the original fiber when pressure is applied from the outside is closely related to the position of the stress-applying part within it, and it is located at a symmetrical position with respect to the core of the optical fiber. It is determined by the magnitude of the elastic modulus of the stress-applying portion and the cladding surrounding them. In other words, when the elastic modulus of the stress-applying part is small (soft), it is necessary to receive stress from a direction perpendicular to the straight line connecting the two stress-applying parts to increase the sensitivity of the optical fiber hydrophone. .

Therefore, in the cross section of the optical fiber, it is possible to have an outer shape that is parallel to both sides of a straight line connecting the two stress applying parts or a straight line perpendicular to this, or an ellipse or an ellipse that is symmetrical with respect to the straight line connecting the two stress applying parts. By configuring it with an oval outer shape, it is convenient for winding it closely around a vibrating body to construct a Hikari 7 Aipah hydrophone.

That is, looking at FIGS. 2(a) to (C), the diaphragms 31 to
The optical fibers 21C to 23c are arranged in close proximity to each other around the diaphragms 31 to 33, and are generally wound as shown in FIG. An external force such as acting force 56 in FIG. 3 is applied to the fibers 210-23c.

Therefore, in the configurations shown in FIGS. 2(a) to (C) that receive external force in a direction perpendicular to the straight line connecting the stress applying parts of the optical fiber, the elastic modulus of the stress applying parts 21B to 23B is smaller than the elastic modulus of the cladding. (soft) for maximum sensitivity.

Figure 2 (a) shows an optical fiber whose cross-sectional shape is symmetrical with respect to the straight line connecting the stress-applying parts.
), and the outer shape is parallel to the straight line connecting the stress-applying parts on both sides, as shown in Figure 2(b).
The structure shown in FIG. 3(C) is a structure in which a plane perpendicular to the straight line connecting the stress applying parts is provided on the outside of the stress applying parts.

Therefore, by adopting the above-mentioned structure, when the optical fiber is tightly wound and fixed around the diaphragm, the external force from the diaphragm is applied to the optical fiber in the direction of the highest sensitivity. .

Next, an embodiment of the optical hydrophone of the present invention will be described with reference to FIGS. 1(a) and 1(b).

First, the configuration and operation of the first embodiment will be explained. Referring to FIG. 1(a), the first embodiment is composed of a support framework 1, a diaphragm 2, and an optical fiber 3.
A diaphragm 2 is formed on both sides by adhesive or the like. Further, the support framework l has two curved side surfaces 5 that are smoothly connected to the outer surfaces of the diaphragm 2 attached to both sides. The wall thickness of the support framework l is configured to be sufficiently thicker than the thickness of the diaphragm 2, and the optical fiber 3 is wound closely while in contact with the side surface portion 5 and the diaphragm 2 mentioned above, so that it is in contact with at least the diaphragm 2. The parts are fixed with epoxy adhesive. Therefore, here, any of the types shown in FIGS. 2(a) to 2(C) may be wound as the polarization-maintaining optical fiber 3 described above.

Next, the configuration and operation of the second embodiment will be explained. Referring to FIG. 1(b), the second embodiment has a support framework 11.
It consists of a vibrating cylinder 12, and an optical fiber 3, and both ends of the vibrating cylinder 12 are fixed with a support framework 11 (generally, the support framework is integrated inside the vibrating cylinder 12), and receives sound waves. Sometimes, when the surrounding pressure of the vibrating cylinder 12 decreases due to the pressure of sound waves, the vibrating cylinder 12 becomes thicker like a drum, and when the surrounding pressure increases, the vibrating cylinder 12 becomes thicker.
It becomes thin like a drum. Therefore, even in this case, the optical 7 eyeper 13 is tightly wound while being in contact with the vibrating cylinder 12.
If at least the part in contact with the vibrating cylinder 12 is fixed with an adhesive such as epoxy synthetic resin, the cross section of the optical fiber wound part of the vibrating cylinder 12 can be considered to move in the same way as the diaphragm 51 in FIG. 3. be able to. Therefore, here:
All types of optical fibers shown in FIGS. 2(a) to 2(C) can be used as the polarization-maintaining optical fiber 13 mentioned above, and any one of them can be wound around the vibrating cylinder 12. do it.

By the method described above, it has become extremely easy to increase the sensitivity of an optical fiber hydrophone.

〔Effect of the invention〕

As explained in detail above, the optical fiber hydrophone of the present invention has a vibration shape of the optical fiber hydrophone in a cross section of an ellipse, an oblong, or a parallel line with respect to a straight line connecting stress applying parts or a straight line orthogonal to this. By forming a part of the optical fiber into a shape, the optical fiber can be wound in the same direction, resulting in an extremely sensitive hydrophone.

[Brief explanation of the drawing]

FIGS. 1(a) to (b) are perspective views showing the structures of the first to second embodiments of the present invention, and FIGS. 2(a) to (C) are the structures of the optical fibers used in the present invention. A perspective view showing a structure in which an optical fiber is tightly wound around a vibrating body. FIG. 3 is a perspective view showing an example of a conventional optical fiber structure and a structure in which an optical fiber is tightly wound around a vibrating body. , Figures 4(a) to (C)
FIG. 2 is an explanatory diagram showing the relationship between the force applied to the optical fiber and the force applied to the core of the optical fiber. 1.11... Support framework, 2... Vibration plate, 3, 13... Optical fiber, 5... Side part, 12...・Cross section of an optical fiber that is tightly wound and fixed on a vibrating disk. 21!r (Nio Z f! IJCC)

Claims (4)

[Claims] (1) Comprising a core, a cladding surrounding the core, and two stress applying parts at symmetrical positions around the core,
In a hydrophone in which an optical fiber whose cross-sectional outline and the relative relationship with the stress-applying portion are the same in the longitudinal direction is tightly wound and fixed around a vibrating body, the dimension from the core to the outside of the optical fiber is the same as the core. An optical fiber hydrophone that differs depending on the direction of its center. (2) The optical fiber hydrophone according to claim 1, wherein a part of the fiber hydrophone has a cross-sectional outline parallel to the straight line on both sides of the straight line connecting the two stress applying parts. (3) The optical fiber hydrophone according to claim 1, characterized in that the optical fiber hydrophone has an elliptical or oblong cross-sectional outline that is symmetrical with respect to a straight line connecting the two stress-applying parts. (4) The optical fiber hydrophone as set forth in claim 1, wherein at least one of the stress applying portions as set forth in claim 2 has a flat portion on the outside thereof that is orthogonal to a straight line connecting the stress applying portions.