JPS5948663A - Arrayed optical type hydrophone system - Google Patents

Abstract

PURPOSE:To make it possible to detect the directionality of sound components through a signaling optical fiber and to enable the detection of said sound components arriving from a sound arriving direction and a desired direction, by winding up the signaling optical fiber so as to be spaced apart at predetermined intervals at every one winding. CONSTITUTION:When the distance (a) between adjacent one windings of a signaling optical fiber 13 is made equal to the wavelength lambda of a sound wave and the numbers (n) of the coils of the fiber 13 are 20, the directional characteristic is changed as shown by the figure 4. That is, it is understood that the directional characteristic of less than + or -20 deg. is possessed. In addition, when n is 100, the directional characteristic becomes shar as shown by the figure 5 and the directional characteristic of + or -10 deg. or less is shown.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical Hyde 90 system that utilizes optical fibers to detect underwater acoustics.

Generally, piezoelectric hydrophones that utilize piezoelectric elements are used to detect underwater acoustics. By the way, in recent years,
With the advancement of optical fibers and optical communication systems, optical sensors have come to be used in various types of sensors, and their use in hydrophones is also being considered. In particular, there are many promising aspects such as the possibility of high sensitivity and the fact that various functions can be added because the optical fiber is transparent to underwater acoustics. That is, FIG. 1 shows a configuration diagram of a conventional optical hide 80 phon system, in which the laser oscillation light L□ output from the laser 1 passes through the half mirror 2 arranged at an angle of 45 degrees with the traveling direction of this light L1. The light is split into horizontal and vertical light, and the horizontal light is guided to the reference optical fiber 3, and the vertical light is guided to the signal optical fiber 4.

The light that has passed through the reference optical fiber 3 is guided directly to the multiplexer 5, while the light that has passed through the signal optical fiber 4 is guided to the multiplexer 5 via the acoustic field 6 made of the medium in which the sound is propagating.
be led to. The multiplexer 5 interferes with the light that has passed through the reference optical fiber 3 and the signal optical fiber 4, respectively, and outputs a combined light L2.

By the way, if the electric field of the reference optical fiber 3 is Er and the electric field of the signal optical fiber 4 is Es, the following equation holds theoretically.

Er=EoeXpCJωt]…(1) Es=Eo exp(jωt+jkp cos ωst
+jφ0]…(2) Here, Eo expcjωt]
is the incident light of optical fibers 3 and 4, p cosωs
t represents an acoustic wave, and kp cosωst represents a phase change of a light wave due to this acoustic wave. Further, φ0 represents the residual optical path difference between the reference light passing through the reference optical fiber 3 and the signal light passing through the signal optical fiber 4 in terms of phase.

Further, the optical interference intensity between the reference light and the signal light, that is, the acoustic component is expressed by the following equation.

Knee 2E 'jC1+cos (kp cosωst+
φo)]...(3) Since kp is actually a sufficiently small value, it can be approximated as follows.

I=2E. (1-kp sin φo sj, n
ωst, :) −(4) In this way, the acoustic component is detected. On the other hand, by shifting the frequency of the reference light by Δω and performing FM (frequency modulation) detection of the interference light intensity factor, it is possible to detect the acoustic component factor ′1□ regardless of the phase φ0 and the electric fields F and o. is also possible. In other words, k' = 2E self [1 + cos (Δω is 10 kp co
sωst+φo)) = (5) ■/ p egg! =F
'ω5-kp cosωSt (6) where F is the sensitivity of the FM receiver.

However, the above-mentioned conventional optical no-hydrophone system has a directivity that is uniquely determined by the optical fiber loop radius and acoustic frequency, and has the disadvantage that it cannot detect any direction in which the sound arrives. . Also,
Since the reference optical fiber 6 and the signal optical fiber 4 are placed in different media, the reference light or signal light is affected by the external environment, and the change in light due to this influence, that is, the output drift increases, and the acoustic component is There was a drawback that the detection was inaccurate.

This invention was made based on the above-mentioned circumstances, and its purpose is to be able to detect arbitrary directivity of acoustic components,
Another object of the present invention is to provide an optical hydrophone system that reduces output drift due to external environmental changes.

Hereinafter, one embodiment of the present invention will be explained based on FIGS. 2 to 6. FIG. 2 shows a schematic configuration diagram of the arrayed Hydro 7 ON system of the present invention, in which the laser oscillation light L3 output from the laser 11 is split into two by a half mirror 12, and one of the lights is reflected at right angles for signal use. The other light continues to the optical fiber 16 and is guided to the reference optical fiber 14, respectively. This signal optical fiber 16 is composed of n optical fiber loops 17, and adjacent individual optical fiber coils are separated by a distance a and placed in an acoustic field 15 filled with an acoustic propagation medium.

On the other hand, the reference optical fiber 14 is directly guided to the multiplexer 16. The reference light wave via the reference optical fiber 14 and the signal light wave via the signal optical fiber 16 are transmitted to the multiplexer 1.
5. The multiplexer 15 interferes with the guided reference light and signal light, and as a result outputs a combined light L4.

FIG. 6 shows a detailed configuration diagram of the fiber coil array of the signal optical fiber 13. In this case, it is assumed that each coil of one turn has the same sensitivity, and that this sensitivity is converted into a phase change by kp sinωst. do. Here p
sinωst represents an acoustic wave, and k is a proportionality constant that corresponds to the acoustic detection sensitivity of the fiber. When the one-turn fiber coil 13a of the reference optical fiber 13 is used as a reference and the phase delay of the acoustic wave that interacts with other fiber coils is φ, the electric field Er of the reference light wave and the electric field Es of the signal light wave are expressed by the following equation. It will be done. That is, ... (7) E r = E o exp (jωt + jφo] - (8) φ
= (2πa/λs) cosθ ・−
(9) Here, if the line passing through the center of the fiber coil array - (indicated by the dashed line in FIG. 3) is 2, then θ
is the angle formed by the sound arrival direction or 2.

Further, λS is the wavelength of the acoustic wave. Note that the other explanations are the same as those for equation (2), and will therefore be omitted.

Further, the intensity of the combined light L4 is expressed by the following equation.

1φo)] ...(10) cosα=[1-cosφ+cos(n-1)φ-co
s nφj/2 (1-CO8$) (t-c'os
n chi...αυsinα=(sinφ+5in(
n-1)φ-5innφ]/2F=i==π
... (12) cannot be exceeded, and since kp is actually a sufficiently small value, equation (10) is expanded as shown below. (13) Therefore, a hydrophon with directivity in which the intensity T' of the composite wave light L4 changes depending on the magnitude of θ is constructed as shown in equation (13).

In addition, the frequency of the reference light is changed by Δω, and the above (5) −(
In the same manner as shown in equation 6), the intensity factor FM of the combined light L4 can be determined by FM detection regardless of the residual phase difference φ0 of the electric field EO. □In other words, it becomes.

By such calculation, the directivity characteristic in the array structure can be obtained as shown in the following equation.

φ−(2πa/λs) cosθ
---(+6) It is also known that the optical fiber coil itself has directional characteristics, which is expressed by the following equation.

F(θ)=l Jo((2πr/λs) sinθ
':ll .-(17) where r is the radius of one fiber coil.

In other words, the directivity characteristics of the arrayed nodes 90 configured as described above are expressed as shown below.

D(θ)-A(θ)・F(θ)...(
Country First, calculate A(θ).

Now, the distance a between adjacent strands of the signal optical fibers 16 is made equal to the wavelength of the acoustic wave. That is, in equation 9, a/λs=i. When the number n of coils of the signal optical fiber 16 is set to 20, the directivity characteristic A(θ) due to the array structure changes as shown in FIG. According to FIG. 4, it can be seen that it has a directivity characteristic of a little less than ±20 degrees.

If n=100, the directional characteristic becomes even sharper as shown in FIG. 5, exhibiting a directional characteristic of ±10 degrees or less. Furthermore, as shown in FIG. 6, by changing the detected acoustic frequency or the fiber coil spacing, directivity in any direction can be exhibited. Also, when focusing on the directivity in the 0 degree direction, from equation (151, (16)), when a/λS becomes an integer, directivity repeatedly appears in that direction.

In addition, the directivity F(θ) of the fiber coil always has the maximum sensitivity at θ=0 according to equation (17).As r/λS) increases, the number of sites increases, and the Directivity becomes sharper. As shown in equation (18), the arrayed optical fiber hydrophon is expressed as the product of A(θ) and F(θ), so the fiber coil spacing, the fiber
- Hydrophones with various directivity are constructed by combining coil radius and acoustic frequency.

Examples 2-6 are described below.

An array structure always has directivity in the θ-90° direction, but by setting r/λS to an appropriate value, CF(θ
)] -0, and the directivity in the θ=900 θ−90° direction can be suppressed.

Furthermore, the directivity in the θ=0° direction of the arrayed optical fiber hide 90 phon becomes sharper as the number n of the coils in the fiber coil arrangement increases, but if it is difficult to increase the number of coils, as mentioned above, the fiber coil radius It is also possible to similarly sharpen the directivity in the OC direction by increasing r. Furthermore, if it is desired to reproduce the directivity due to the coil arrangement, the radius r of the fiber coil can be made small to make the directivity unique to the fiber coil uniform.

Actual applications and examples will be discussed next.

As mentioned above, the arrayed optical fiber hide 80 phon can change the angle of arrival of sound and the sharpness of its directivity, which exhibits high sensitivity, by changing a/λS, r/λS, and n. It can be used not only for detection but also as a radar for underwater exploration using ultrasonic waves.

Further, since the directivity in the θ-0° direction always appears when the detected acoustic frequency changes by an integral multiple, it is also possible to detect harmonic components of underwater sound.

In this way, optical fiber coils are transparent materials with respect to underwater acoustics, and the above-mentioned array arrangement is possible, but with conventional piezoelectric hydrophons, such an arrangement is not possible because they are not transparent with respect to underwater acoustics. be.

The above-mentioned arrayed optical fiber hide 90 unit used only the signal optical fiber for signal detection, but in order to reduce output drift due to changes in the external environment and improve sensitivity, the reference optical fiber was also used for signal detection. A differential fiber optic hide 80 phon system placed in the same acoustic arrival medium as the detection fiber can also be constructed.

A configuration diagram is shown in FIG. The principle is the same as the arrayed optical fiber hydrophone shown in FIG. 2 described above.

The laser oscillation light L5 outputted from the laser 18 is divided into two parts by the half mirror 12, one of the lights is reflected at right angles, the other light goes directly to the signal optical fiber 20, and is guided to the reference optical fiber 21, respectively. This signal optical fiber 20 is composed of n optical fiber loops 24, and adjacent individual optical fiber coils are separated by a distance a and placed in an acoustic field 22 filled with an acoustic propagation medium.

Similarly, the reference optical fiber 21 is made up of n optical fiber loops, each of which is placed in the center of the fiber loop of the signal optical fiber 20, and the last turn is placed at the right end at equal intervals. be done.

As a result, reference optical fiber A-2L signal optical fiber 20
n pairs of coils are constructed, each arranged in the acoustic field 22. Here, the signal light wave electric field Es and the reference light wave electric field Er are expressed by the following equations.

Es=Eo exp[jωt+j2 (kp) sin(
ω5t1=1 +φ(i-1)):] ...a Er,=Eo exp[jωt+j, Z (kp)s
in(ω5t1=1 10φ(i-1)10φ/2)+jφ0] ...(company)
φ: (2πa/λs) cosθ −
(2]) The characters are the same as in the previous calculation.

Here, the optical frequency of the reference light is changed by Δω, and the multiplexing ωs c
It is calculated as os(ωst+φ/4+α) (22).

Here, when compared with formula 04), it can be seen that it has the advantage of doubling the sensitivity.

The angle dependence A' (θ) is expressed as follows and the fourth
．． It is calculated as shown in Figure 8.9.10 in the same way as Figure 5.6. The directivity formula is (17), (Similar to the 1-mark formula, D'(θ)-A' (θ)F(θ) ・
...(23) is expressed. Characteristics of the directivity when using a differential configuration are that there is no directivity in the θ-90' direction, and when there is directivity in the θ-00 direction, the acoustic frequency is an odd harmonic of the fundamental wave. only. Also 1,
Since the reference fiber is placed in the same medium as the signal fiber, it also has the advantage of reducing output fluctuations due to external drift.

As explained above, according to the present invention, since the signal optical fiber is wound with a predetermined spacing between each turn, the directivity of the acoustic component can be detected through the signal optical fiber. Various features can be added to the directivity by changing the fiber coil radius, coil spacing, and number of coils. Therefore, by detecting a sound component, it is also possible to know the direction of arrival of the sound or the sound component arriving from a desired direction.

It also becomes possible to measure harmonics. Further, each turn of the reference optical fiber is wound with a predetermined spacing between each turn, and one turn of the reference optical fiber and one turn of the signal optical fiber are alternately arranged in the acoustic propagation medium at a constant interval. Therefore, the sensitivity is twice as high as that of the sound detection method described above, and the output drift caused by changes in the external environment can be reduced to improve the accuracy of sound component detection. Furthermore, directivity in the θ-90° direction can be eliminated, making it possible to measure only odd harmonics. Furthermore, the directivity can be changed by changing the predetermined interval between each winding of the signal optical fiber or the fixed interval between the signal optical fiber and the reference optical fiber, and it is also possible to detect the sound propagating in the acoustic propagation medium. Since the directivity can also be changed by varying the acoustic frequency, it can be used not only as a simple underwater acoustic measuring device but also for a wide range of applications such as radars for seabed exploration using ultrasonic waves. A structure with such advantages is not possible with the current piezoelectric hydrophon, which is opaque to underwater acoustics, and was made possible only by using optical fibers.

4, , [: Brief description of the drawings] Fig. 1 is a schematic configuration diagram of a conventional optical hydro-on system, and Fig. 2 is a schematic configuration diagram showing an embodiment of the arrayed optical hydro-on system of the present invention. Figures 3 and 3 are arrangement diagrams of each fiber for signal, Figures 4 and 5 are
In the case shown in the figure, the directional characteristics are shown when a/λs = 1 and the number of signal fine coils is 20 and 100, respectively. Figure 6 shows the directional characteristic diagram when the acoustic wavelength λS or the fiber pair spacing a is changed in the case of Figure 2. Fig. 7 is a configuration diagram of a differential array-like optical fiber part idrophon, and Fig. 8 and Fig. 9 show a directivity characteristic diagram when a/λs = 1 in Fig. 7, and a fiber coil The logarithm is 20.
The directivity diagram in the case of 10'0, Fig. 10, shows a/
It is a directional characteristic diagram when changing λS.

11...L/-f-112...No1-fmirror, 1
4... Reference optical fiber, 16... Signal optical fiber, 15... Acoustic field, 16... Multiplexer, 17...
...Fiber coil, 18...Laser, 19...
・Half mirror 120...Signal optical fiber, 21
...Reference optical fiber, 22...Acoustic field, 26.
...Multiplexer.

Patent applicant: Sumitomo Electric Industries, Ltd. (4 others) 9o Ri 60″ 3F D
, 5Q"6F" 40-Leather,
10 sound 1) j sun power food 1 yu (θ) kutsu v

Claims (5)

[Claims] (1) The light output from the light source is split, one light is guided through a reference optical fiber, and the other light is guided through a signal optical fiber provided in an acoustic propagation medium to a multiplexer. In an optical hydrophone system that detects sound propagating in the acoustic propagation medium by interfering both lights, the signal optical fiber is wound with a predetermined distance between each turn, and the directivity of the optical fiber loop is adjusted. In addition to this, the arrayed optical Hydro 7-on system is characterized by having sharp directivity due to the array structure. (2) Each turn of the reference optical fiber is wound with a predetermined spacing between each turn, and each turn of the reference optical fiber and one turn of the signal optical fiber are alternately arranged at a constant interval in the acoustic propagation medium. , the differential array type according to claim 1, characterized in that the output lift due to changes in the external environment is reduced, the detection of the sound is made directional, and the sensitivity is multiplied. Optical hide 80 phon system. (3) The directivity is varied by changing the predetermined interval between the signal optical fibers or the constant interval between the signal optical fiber and the reference optical fiber. Second
Arrayed optical hide 80 phon system as described in . (4) The arrayed optical hydrometer according to claim 1 or 2, wherein the directivity is varied by varying the detection acoustic frequency of the sound propagating in the acoustic propagation medium. 7 on system. (5) The axial directivity of the array is reproduced by multiplying the detected acoustic frequency by an integer, thereby making it possible to detect harmonic components as well.
The arrayed optical hide 90 phon system according to item 1 or 2.