JPH0535639B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a bassive sonar hydrophone using optical fibers, that is, an optical fiber hydrophone.

(Prior art) A bathsive sonar hydrophone is a device that identifies the location of a sound wave source in water by simply receiving sound waves.It emits sound waves toward the source and receives the reflected waves. Compared to active sonar hydrophones, it has the feature of greatly increasing the secrecy of the explorer's presence.

Optical fiber hydrophones are intended to improve various performances such as reception sensitivity and minimum detectable sound pressure by using optical fibers, and research and development are currently being carried out on various forms. Among these, the microbend hydrophone has an extremely simple structure of the sensor section for converting sound pressure into an optical signal, and has a minimum detectable sound wave receiver compared to other methods such as the heterodyne method, grating method, coupler method, etc. This is an extremely practical method because the hydrophone has excellent wave sensitivity and other performance.

A micro-bend hydrophone consists of an optical fiber sandwiched between two waveform surfaces with peaks and valleys facing each other.
J.Acoust.Soc.Am., Volume 67, No. 3, 1980.
Reported on pages 816-819. As shown in Figure 2 a and b, this micro-bend type hydrophone is made by sandwiching an optical fiber between plates with wavy protrusions of a certain pitch on both sides, and the sound pressure applied to the plates is generated by applying pressure. This method is determined by measuring the amount of attenuation of light transmitted through the optical fiber. FIG. 2a is a front view of the sensor section of the microbend type hydrophone. In this sensor section, reference numeral 1 denotes an optical fiber, which is usually coated with plastic to prevent breakage. Further, 2 and 3 are flat plates having liquid protrusions on one side, and the optical fiber 1 is sandwiched therebetween by shifting the convex portions (peak portions) by half a pitch, thereby deforming the optical fiber into a wave shape. As a result, the light incident on the optical fiber 1 from the light source 4 suffers loss due to bending before reaching the detector 5.
When the change in the sound pressure applied to the flat plate is minute, the loss of transmitted light changes approximately in proportion to the sound pressure, so the minute sound pressure can be measured by measuring the change in the amount of attenuation of this transmitted light. FIG. 2b is a perspective view of the sensor section of FIG. 2a with the flat plate 2 removed, in which the optical fiber 1 is arranged along one side with a wavy tooth shape.

(Problems to be Solved by the Invention) Hydrophones are generally devices that search for underwater sound sources, so it is desirable that the receiving sensitivity has as little directivity as possible, that is, it is omnidirectional. However, in the conventional micro-bend type optical fiber hydrophone as shown in Fig. 2a and b, the sensitivity is highest when the sound pressure is perpendicular to the flat plates 2 and 3.
The drawback is that the sensitivity decreases by cos θ for sound pressure incident at an angle θ to the normal to the flat plate.
Therefore, it would be extremely useful if a micro-bend hydrophone could be made omnidirectional.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a micro-bend type optical fiber hydrophone whose receiving sensitivity does not change depending on the direction of arrival of sound pressure.

(Means for Solving the Problems) According to the present invention, in an optical fiber hydrophone in which an optical fiber is sandwiched between two waveform surfaces in which a peak part and a valley part face each other, the top of the peak part and an envelope surface connecting the bottoms of the valleys are both cylindrical surfaces, and the optical fiber is spirally wound between the two cylindrical surfaces. is obtained.

(Function) As described above, in the microbend type optical fiber hydrophone according to the present invention, a cylinder is used in place of the conventional flat plate. That is, the flat plate 3 with the wavy protrusions shown in Fig. 2a is bent into a cylindrical shape so that the protrusions (crests) are on the outside, and the flat plate 2 is also bent into a circular shape so that the protrusions are on the inside. . In such a cylindrical configuration, sound waves that are incident perpendicularly to the central axis of the cylinder are always incident perpendicularly to the outer arc-shaped plate, so the receiving sensitivity is always constant in the circumferential direction of the cylinder, resulting in omnidirectionality. can be realized. Next, it will be explained in detail using the drawings.

(Embodiment) FIGS. 1a and 1b are views showing one embodiment of the present invention, in which FIG. 1a is a plan view and FIG. 1b is a perspective view with arc-shaped plates 7 and 8 removed. Reference numeral 1 denotes an optical fiber, which is usually covered with plastic or the like to prevent breakage. 6 is a cylinder with wavy protrusions on the outer periphery;
7 and 8 are arc-shaped plates with wavy protrusions on the inside. The pitch of the protrusions of the arcuate plates 7 and 8 is the same as that of the cylinder 2.
It is the same as the pitch of the protrusion. Arc-shaped plates 7, 8
By shifting the optical fiber 1 by half a pitch and fitting it into the protrusion of the cylinder 6, the optical fiber 1 wrapped around the cylinder 6 is removed.
will undergo a wave-like deformation. This state is shown in more detail in Figure 1b, which shows the cylinder 6
The optical fiber 1 is shown with the arcuate plates 7 and 8 omitted to show the situation when the optical fiber 1 is wound around the wafer and pressed against the arcuate plates 7 and 8, and the optical fiber 1 is deformed into a wave shape. The cylindrical plate is divided into two pieces 7 and 8 in the figure, but this is done by fitting the wavy protrusion of the arc-shaped plate into the wavy protrusion of the cylinder 6, so if it is more than 2 pieces, the number of divisions is Any amount is fine. In the sensor section of the optical fiber hydrophone having such a configuration, light is made to enter the optical fiber 1 from the light source 4,
Furthermore, by transmitting the wave-like optical fiber and detecting it with the photodetector 5, it is possible to observe changes in the amount of attenuation of the light transmitted through the optical fiber caused by the sound pressure applied to the arc-shaped plates 7 and 8. The minute sound pressure can be determined from the change in .

The micro-bend type optical fiber of the above example
In the hydrophone, the sound pressure that is incident perpendicularly to the central axis 0-0' of the cylinder 6 is also incident on the arcuate plates 7 and 8, so that the receiving sensitivity in the circumferential direction of the cylinder 6 is constant.

(Effects of the Invention) According to the present invention, as described in detail so far, it is possible to realize an optical fiber hydrophone whose receiving sensitivity does not change depending on the arrival direction of the sound pressure, that is, an omnidirectional optical fiber hydrophone. As described above, the optical fiber hydrophone of the present invention has extremely high performance because it is superior in omnidirectionality compared to the conventional type shown in FIGS. 2a and 2b.

[Brief explanation of the drawing]

FIG. 1a is a plan view showing an embodiment of the present invention, FIG. 1b is a perspective view of the embodiment with the arc-shaped plate removed, and FIG. The front view shown in Figure b is the flat plate 2.
FIG. 3 is a perspective view of the hydrophone of FIG. 1... Optical fiber, 2, 3... Flat plate with wavy projections, 4... Light source, 5... Photodetector, 6... Cylinder,
7, 8... Arc-shaped plate.

Claims (1)

[Claims] 1. In an optical fiber hydrophone in which an optical fiber is sandwiched between two waveform surfaces with peaks and valleys facing each other, an envelope connecting the tops of the peaks and an envelope connecting the bottoms of the valleys. An optical fiber characterized in that both surfaces are cylindrical surfaces, and the optical fiber is spirally wound between the two cylindrical surfaces.
Hydrophone.