JPH09304169A - Optic fiber acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow long term measurement even in liquid by photo-electrically converting interference light generated in an optic fiber region for measuring phase difference and then demodulating to detect vibration acceleration. SOLUTION: A seismic system employing an optic fiber as a spring 14 utilizing its elasticity is constructed, the optic fiber whose part is used as a spring material is made to be a sensing fiber 15, an optic fiber attached to an immobile system is made to be a reference fiber 16, and an O/E(electro-optic) output of an interference light output by phase difference in laser light propagating in these fibers is demodulated by a demodulator 22 via an O/E converter 21, thereby obtaining vibration acceleration α. The optic fiber constituted as a member of an optic fiber acceleration sensor can be utilized also as a light transmission path as it is. In this case, electric components such as a laser light source 18 and the O/E converter 21 are placed on the ground, while the optic fiber acceleration sensor is placed in liquid for operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber acceleration sensor for detecting a change in length of an optical fiber due to vibration acceleration as a phase change of light with an interferometer.

[0002]

2. Description of the Related Art Although there are a large number of vibration measurement devices for measuring vibration acceleration, as a vibration sensor or an acceleration sensor, for example, "Reference: Sensor Handbook, written by Kataoka et al., First edition in 1986, Published by Baifukan, 456-
"Page 462" for each item. In this case, the speed detection and the acceleration detection are performed by the size mode (seism).
It is preferable to apply a vibration sensor based on vibration of an ograph system, that is, it is convenient to use a seismo vibration sensor to form an acceleration sensor.

A conventional general vibration acceleration sensor is
The basic structure is shown in FIG. 4, which is composed of the above-mentioned seismo system composed of "weight-spring-resistance". The "resistor" is also called a "damper" (see Fig. 5.104 of the above-mentioned document). In FIG. 4, the vibration acceleration sensor 1
In the closed box type base 2 which also serves as the case, a combination member which constitutes the seismo system composed of the weight 3, the spring 4 and the resistor 5 is arranged. The basic joining and arranging positions of the respective members are well known, and the explanation thereof will be omitted.

The vibration acceleration sensor 1 is installed on the object 6 to be measured in perfect contact. In the subscripts to the arrows in the figure, x indicates the relative displacement of the weight 3 with respect to the base 2, and α indicates the vibration acceleration that causes a change with respect to the fixed point of the measuring object 6.

In the illustrated state, the vibration acceleration sensor 1
When vibration is applied to the weight 3, a force is generated due to the acceleration α, so that the weight 3 is displaced by x with respect to the base 2. here,
For vibrations below the natural frequency of the system, the displacement x of the weight 3 (spring 4
Change of the weight 3) is proportional to the acceleration α.
The vibration acceleration α can be known by measuring (see above-mentioned document).

One of the methods for detecting the displacement of the weight 3 is a piezoelectric vibration acceleration sensor. In this piezoelectric vibration acceleration sensor, a piezoelectric element (not shown) is sandwiched between a base 2 and a weight 3 to measure a voltage generated by distortion of the piezoelectric element. There are also servo type and strain gauge type vibration acceleration sensors, but the displacement of the weight is detected by electric signals such as current and resistance change amount.

[0007]

In the conventional acceleration sensor as described above, for example, the piezoelectric vibration acceleration sensor, the displacement of the weight due to the vibration acceleration is detected by an electric signal such as a voltage change of the piezoelectric element. Therefore, not only does it require electrical insulation for application in liquids,
There is a problem that it is difficult to obtain long-term reliability such as preventing the sensor from being damaged due to deterioration of insulation and compensating for long-term measurement. In addition, there are problems that long-distance transmission is difficult with electric signals and that, in another aspect, multipoint measurement is relatively expensive.

[0008]

SUMMARY OF THE INVENTION A first optical fiber acceleration sensor according to the present invention comprises a closed casing forming a fixed point, a weight, a base positioned at a predetermined distance from the weight, and an optical unit. It is located at the same fixed point as the housing and a sizing system formed by the elasticity of the optical fiber in the straight line portion formed by a part of the optical fiber wound so as to connect the weight and the base. It has another optical fiber wound around a rigid body, and an acceleration sensor part in which the base part is attached and fixed inside the housing, and the optical fiber and the other optical fiber are connected to the input side and the output side of the acceleration sensor part. Connected to the two optical couplers, the measurement laser beam is branched by the input side optical coupler, one of the branched laser beams is introduced into the optical fiber, and the other is introduced into the other fiber. Combined with an optical coupler and output Introduces the interference light generated in the area of the output optical fiber due to the change in the length of the optical fiber of the straight line part to optical-electric conversion and measures the phase difference, then demodulates and vibrates. The acceleration is detected.

A second optical fiber acceleration sensor according to the present invention includes a hermetically sealed casing which constitutes a fixed point, a weight, two bases which are vertically arranged with a predetermined distance from the weight, and two bases. The composite type in which the elasticity of the two pairs of linear portions formed by a part of each one optical fiber wound so as to connect the weight and the two bases is formed as two pairs of springs. It has a seismo system and an acceleration sensor part in which two base parts are attached and fixed inside the housing, and two optical fibers are provided in two optical couplers provided on the input side and the output side of the acceleration sensor part. After connecting, the measurement laser beam is branched by the input side optical coupler, one of the branched laser beams is introduced into the first optical fiber, and the other is introduced into the second optical fiber. Couple it with a coupler and introduce it into the output optical fiber. The interference light generated in the area of the output optical fiber due to a change in the length of expansion and contraction of the parts in opposite directions is optoelectrically converted to measure the phase difference, and then demodulated to perform vibration acceleration in the single axis direction. Is to detect.

A third optical fiber acceleration sensor according to the present invention comprises one cubic weight, six bases of the weight and six bases and six optical fibers which are respectively positioned at predetermined intervals. In this case, the elasticity of the 6 pairs of linear portions formed by a part of each of the 2 optical fibers wound so as to connect the weight to each of the 2 bases is formed as 6 pairs of springs. System and a triaxial acceleration sensor unit in which six bases of this size system are fixed to the inside of the housing, and two optical fibers are provided on each input side and each output side of the acceleration sensor unit. After connecting to each of the two optical couplers provided and introducing the laser light for measurement into the acceleration sensor of the acceleration sensor section for three axes by using the optical coupler and the delay fiber in a time-sharing manner for each axis, The laser light that has passed through the optical fiber of each axis is output by an optical coupler and a delay filter. Generated and multiplexed in the area of the optical fiber for output due to the change in the length that the two pairs of springs out of the six pairs of springs expand and contract in opposite directions The converted interference light is subjected to optical / electrical conversion to measure the phase difference and then demodulated to detect the vibration acceleration for three-axis directions or for multipoint measurement.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the optical fiber acceleration sensor constructed according to the present invention is, in principle, a seismo system acceleration sensor constructed by combining a "weight-spring-resistance" with a base. is there. However, it is very different from conventional accelerometers of the seismo system, and the elasticity of the optical fiber itself (spring property) is obtained by substituting the spring for the optical fiber wound so as to connect the weight and the base installed at intervals. Is used for the spring function of the seismo system. That is, an optical fiber that deforms by utilizing this spring property is used as a sensing fiber, and a fixed optical fiber wound around a rigid structure that constitutes a fixed point independent of this system is adopted as a reference fiber. The interferometer is composed of an optical fiber, and the interference light output from the interferometer is electrically converted to obtain the acceleration of vibration.

[Embodiment 1] FIG. 1 is a schematic explanatory view showing a first embodiment of an optical fiber acceleration sensor according to the present invention. The upper diagram of FIG. It is a perspective view which shows the detail of the seismo system part of embodiment. First, as shown in the upper side of FIG. 1, the optical fiber acceleration sensor 10 includes a weight 13, an optical fiber (a sensing fiber 15 described above; the details will be described later) constituting a spring 14, and a seismo system of a base 12. The acceleration sensor 11 including the housing 22, the rigid structure 17 around which the reference fiber 16 is wound, and the laser light emitted from the laser light source 18 through the optical fiber 20 are detected by the sensing fiber 15 and the reference fiber 16. It is composed of three constituent members, an optical coupler 19 and an optical coupler 19a, which are branched and coupled to each other. The base 12 is attached to the housing 22. The acceleration sensor 11 is fixedly mounted on, for example, the measurement target 6 in the liquid, and the rigid structure 17 is fixedly coupled to the housing 12 forming a relatively immovable system, for example.

As shown in the lower view of FIG. 1, the seismo system constituted by the sensing fiber 15 as the spring 14 has the outer circumference of the base 12 and the weight 13 positioned with a predetermined spatial interval, The optical fiber used as the sensing fiber 15 is wound (wrapped).
In this case, in the envelope formed by the outside of the base 12 and the weight 13, the outer peripheral portions of both the base 12 and the weight 13 and the portions where the optical fibers are in direct contact are bonded, and the sensing fiber 15 in this portion is fixed. ing. Therefore, the linear portion of the optical fiber to which the sensing fiber 15 is not adhered, that is, the portion of the spring 14 (see the upper diagram of FIG. 1) constitutes a portion corresponding to a spring of the Seismo system.

The optical fiber acceleration sensor 10 according to the present embodiment is constructed as described above, and is installed in a liquid such as water as shown on the right side of the rough dotted line in the upper diagram of FIG. The vibration acceleration of the measuring object 6 is measured. On the other hand, on the land where the measurement is performed, the optical fiber 20 is connected to the laser light source 18, and the optical fiber 20
The laser light propagating in the
Sensing fiber 15 and reference fiber 16
Propagate. Then, the interference light output from the optical fiber acceleration sensor 10 enters the O / E converter (electro-optical converter) 21 through the optical fiber 20a, undergoes optical-electrical conversion, and is then demodulated by the demodulator 22. By performing the above, the acceleration α of the vibration of the measuring object 6 is measured.

The operation or measurement method of the acceleration sensor of the present invention will be described below on the principle of operation. Since the optical fiber is mainly made of glass, the Young's modulus is 70 GPa.
It is an elastic body (spring). That is, as described above, the optical fiber (a part of the sensing fiber 15) between the weight 13 and the base 12 functions as the spring 14, and the sensor is a size-based system composed of "weight-spring (elasticity of fiber) -resistance". Configure. Therefore, when the measurement object 6 vibrates and the housing 23 vibrates accordingly, when the vibration of the natural frequency of the seismo system or less is applied to the seismo system, the spring 14
Is deformed by the force generated in the weight 13, so that the sensing fiber 15 in the spring 14 portion expands and contracts due to the vibration acceleration α.

On the other hand, since the rigid structure 17 is not deformed by vibration, the reference fiber 16 does not expand or contract due to acceleration. Therefore, a difference in length occurs between the sensing fiber 15 and the reference fiber 16 due to acceleration,
Laser light propagating in two fibers has a phase difference φ
(T) occurs. The optical fiber 20 depends on the phase difference φ (t).
Since the O / E output of the interference light output from a also changes,
The vibration acceleration α can be obtained by demodulating the / E output by the demodulator 22 via the O / E converter 21. In this case, the vibration accelerations in all the x, y, and z directions are detected, but the directions cannot be discriminated.

As described above, according to the first embodiment, the elasticity of the optical fiber itself is used to form the seismo system adopted in the spring 14, and the optical fiber using a part of the spring material as the sensing fiber 15 The optical fiber attached to the stationary system is used as the reference fiber 16, and the O / E output of the interference light output by the phase difference φ (t) of the laser light propagating through these fibers is passed through the O / E converter 21. Since the optical fiber acceleration sensor for obtaining the vibration acceleration α is constructed by demodulation processing by the demodulator 22, the excellent effect that the vibration acceleration can be measured is shown without introducing any electric circuit inside or outside the sensor.

The optical fiber configured as one member of the optical fiber acceleration sensor can be used as the optical transmission line as it is. In that case, the laser light source 18 or O
It is also possible to install and operate the electrical components such as the / E converter 21 in the land portion and the optical fiber acceleration sensor 10 in the liquid, so that long-term reliability can be obtained even in the liquid, and a long distance can be obtained. There is also a side effect that it has the flexibility of application such as the advantage that transmission is possible.

[Embodiment 2] FIG. 2 is a schematic explanatory view showing a second embodiment of the present invention. The upper diagram of FIG. 2 is the overall configuration diagram, and the lower diagram is the size model of the present embodiment. It is a perspective view which shows the detail of a system part. Reference numeral 30 is a single-axis optical fiber acceleration sensor according to the present embodiment, and the difference between this and the optical fiber acceleration sensor 10 of the first embodiment will be described below.

First, in the case 31 of the main body, one weight 33
2 is located in the center of the housing 31, and one base 32 and one base 32a are provided inside the walls of the housing 31 above and below the weight 33, respectively, as shown in the lower view of FIG. Base 3
2, the optical fiber 34 and the optical fiber 34a for separately winding the weight 33 and the base 32a are attached as in the case of FIG. That is, the laser light propagating through the optical fiber 20 is branched into two by the optical coupler 19, and one optical fiber 34 is wound so as to connect the weight 33 installed at a distance and the upper base 32, and the other optical fiber. Three
4a is a weight 33 installed at a distance and a lower base 32.
The bases 32 and 32a are attached to the housing 31 by winding so as to tie a.

Among the envelopes formed by the outside of the base 32 and the weight 33, and among the envelopes formed by the outside of the base 32a and the weight 33, these bases 3
2, 32a and the outer peripheral portions of the weight 33 and the portions where the optical fibers 34 and 34a are in direct contact are adhered to each other, and the optical fibers 34 and 34a in this portion are respectively attached to the base 32,
It is fixed to 32a. Therefore, the optical fibers 34, 34a
The linear portions not bonded to each other constitute the portions corresponding to the two springs of the Seismo system corresponding to two on the same axis. Furthermore, two optical fibers 3
4, 34a are coupled by the optical coupler 19a, and the optical fiber 20
After interfering the laser light with the O / E converter 21,
In addition to optical / electrical conversion by means of, the demodulator 22 performs demodulation processing.

The operation principle of the operation or measurement method of the present single-axis acceleration sensor will be described below. Since the optical fiber is mainly made of glass, the Young's modulus of 70
It is an elastic body (spring) of about GPa. That is, as described above, for example, the non-bonded linear portion of the optical fiber 34 between the weight 33 and one of the bases 32 corresponds to the portion of the spring 14 in FIG. 1, and the acceleration sensor is “weight-spring (elasticity of fiber)”. -Consist a seismo system consisting of resistors. Therefore, when the measurement object 6 vibrates and the housing 31 vibrates accordingly, the spring is deformed by the force generated in the weight 33 when the vibration of the natural frequency of the seismo system or less is applied to the seismo system. The optical fiber 34 in the spring portion expands and contracts due to the vibration acceleration α. The optical fiber 34a also expands and contracts similarly.

Here, as shown in the upper diagram of FIG. 2, x,
Taking the y and z axes, consider the state of vibration in each axis direction. First, when vibration is applied to the z-axis, the optical fibers 34 and 32 are wound around the upper and lower bases 32 and 32a, respectively.
34a expands and contracts in the opposite directions (Push-Pul).
l: push-pull), so two optical fibers 34, 34
A difference in length occurs between a and the laser light propagating through the optical fiber has a phase difference φ (t). Phase difference φ
The O / E output of the interference light also changes depending on (t).
The vibration acceleration α can be obtained by demodulating the E output. On the other hand, in the x- and y-axis accelerations, the two optical fibers 34 and 34a expand and contract in the same direction, so that a difference in length does not occur due to the acceleration, and therefore the phase difference φ in the laser light propagating through the optical fibers. Since (t) does not occur, acceleration cannot be detected. Therefore, if the push-pull structure is formed by locating the bases above and below the weight, it is possible to detect acceleration in only one axis (single axis).

As described above, according to the second embodiment, one weight 33 is used as a common weight, and the bases 32 and 3 are symmetrical to this.
Since the Push-Pull structure is formed by winding the two optical fibers 34, 34a around 2a, it is possible to obtain the effect of being able to detect acceleration in only one axis. Further, as in the case of the first embodiment, the optical fiber configured as one member of the optical fiber acceleration sensor can be used as the optical transmission line with this configuration. In that case, the laser light source 18 or O
It is also possible to install and operate the electrical components such as the / E converter 21 in the land portion and the optical fiber acceleration sensor 10 in the liquid, so that long-term reliability can be obtained even in the liquid, and a long distance can be obtained. It also has a side effect that it has flexibility in application such as an advantage that transmission is possible.

[Third Embodiment] FIG. 13 is a schematic explanatory view showing a third embodiment of the present invention. The upper diagram of FIG. 3 is the overall configuration diagram, and the lower diagram is the size model of the present embodiment. It is a perspective view which shows the detail of a system part. Reference numeral 40 denotes a triaxial optical fiber acceleration sensor according to the present embodiment, which is the same as that of the second embodiment.
The single-axis type optical fiber acceleration sensor 30 is expanded into three axes in the x, y, and z directions with one weight remaining. The structural features will be mainly described below.

As shown in FIG. 3, the weight 43 is formed of a cube, and a total of six bases are provided at predetermined intervals so as to face each surface of the cube, and the second embodiment is adopted.
Similarly, each base is attached to the housing 41. As shown in the lower view of FIG. 3, with respect to the weight 43, the x-axis bases are the bases 42 and 42a, and the y-axis base is the base 42.
b, 42c, z-axis bases 42d, 42e, and optical fibers 44, 42e for connecting the bases to the respective surfaces of the weight 43.
44a (x axis), 44b, 44c (y axis), 44d, 4
By winding 4e (z axis), the triaxial acceleration sensor 52 according to the present embodiment is formed.

Therefore, the three sensor portions arranged and illustrated separately from the center to the right side of the upper part of FIG. 3 are apparently separated sensor elements sharing one weight 43. Actually, FIG. 3 shows a state in which one composite x, y, z triaxial composite acceleration sensor 52 shown in the lower view of FIG. 3 is viewed from three directions. And
For convenience of explanation in the upper diagram of FIG. 3, the x-axis sensor is the acceleration sensor 52x, the y-axis sensor is the acceleration sensor 52y, and the z-axis sensor is the acceleration sensor 52z. In addition, the optical fibers 44, 44 of the acceleration sensor 52x
The optical couplers 45 and 45a are provided on the input and output sides of a, respectively.
However, optical couplers 45b and 45c are provided on the input and output sides of the optical fibers 44b and 44c of the acceleration sensor 52y,
Optical couplers 45d and 45e are connected to the input and output sides of the optical fibers 44d and 44e of the acceleration sensor 52z, respectively.

In the upper view of FIG. 3, first, the pulsed light obtained by pulsing the laser light from the laser light source 18 by the pulse gate 51 is branched into two via the optical coupler 53, and one branched pulsed light is The light is branched by the optical coupler 45 and input to the optical fibers 44 and 44a of the acceleration sensor 52x. Then, one pulsed light coupled by the optical coupler 45a connected to the output side optical fibers 44, 44a is the optical coupler 53c.
It is input to the O / E converter 21 via.

On the other hand, the other pulsed light branched into two via the optical coupler 53 propagates through the delay fiber 54 and is branched by the optical coupler 53a, and the branched one pulsed light is fed into the optical coupler 45b. The light is branched and input to the optical fibers 44b and 44c of the acceleration sensor 52y. Then, one pulsed light coupled by the optical coupler 45c connected to the output side optical fibers 44b, 44c propagates through the optical coupler 53b through the delay fiber 54a and is input to the optical coupler 53c. Then, one pulsed light coupled by the optical coupler 53c is O
It is input to the / E converter 21.

Similarly, the other one pulse light branched into two via the optical coupler 53a propagates through the delay fiber 54b and is branched by the optical coupler 45d, and the two branched pulse lights are acceleration sensors. 52z optical fibers 44d and 44
Enter e. Then, the optical fibers 44d, 4 on the output side
One pulse light coupled by the optical coupler 45e connected to 4e propagates through the delay fiber 54c, propagates through the optical coupler 53b and the delay fiber 54a, and is input to the optical coupler 53c. Then, one pulsed light coupled by the optical coupler 53c is input to the O / E converter 21.

As described above, the system of the acceleration sensor configured by using the single composite x, y, z triaxial composite acceleration sensor 52 as shown in the lower view of FIG. The pulsed light pulsed by the pulse gate 51 and the delay fibers 54, 54a, 54b, 54c constitute a triaxial interferometer. That is, the pulsed light is transmitted to the delay fiber 5
4, 54a, 54b, 54c are time-divided into x, y,
A z-axis interferometer capable of performing multiplexing processing is configured by inputting it to the z-axis acceleration sensor 52. And O / E
The pulsed light input to the converter 21 is optically / electrically converted, and the pulsed light on each axis is separated, and then demodulated by the demodulator 22.

The principle of operation of the operation or measuring method of the present triaxial acceleration sensor will be described below. As described above, since the optical fiber is mainly made of glass, it is an elastic body (spring) having a Young's modulus of about 70 GPa.
That is, as described above, for example, the weight 43 and the three-sided base 4
The non-bonded straight line portion of the optical fibers 44, ... Between 2, ... corresponds to the portion of the spring 14 of FIG. 1, and each triaxial acceleration sensor has a separate "weight-spring (elasticity of fiber) -resistance". It is composed of the "Saimo" system.

First, when vibration is applied to the housing 41 in the z-axis direction, the weight 43 is displaced in the housing 41 due to the acceleration, so that the optical fibers 44d and 44e in the z direction expand and contract in opposite directions. , X, y optical fibers 44 ..., 4
4b ... extends in the same direction. Therefore, only the interferometer in the z-axis direction of each interferometer has a difference in length between the two optical fibers 44d and 44e, and the interference light changes according to the phase difference φ (t). The O / E output of the changed interference light is demodulated by the demodulator 22.
By performing the demodulation processing with, the vibration acceleration in the z-axis direction can be detected. Similarly, in the vibration in the x-axis direction, only the x-axis interferometer can detect the vibration acceleration, and in the vibration in the y-axis direction, only the y-axis interferometer can detect the vibration acceleration. Therefore, if the optical fibers are wound around the 6 surfaces of the weight and three sets of Push-Pull interferometers are configured by one weight so as to be orthogonal to each other as in the present embodiment, the three-axis acceleration is obtained. Can be detected.

In the triaxial optical fiber acceleration sensor 40 of this embodiment, the delay line fibers 54, 54a, 5 are used.
Since the interferometers of the respective axes are connected via 4b and 54d, a propagation time difference occurs in the pulsed light that reaches the O / E converter 21 through the interferometers of the respective axes. Therefore, after O / E conversion, if the pulsed light of each axis is separated and demodulated, the acceleration of three axes can be obtained with one laser light. The time-division multiplexing method of such an optical fiber type acceleration sensor is not limited to application to one 3-axis type optical fiber acceleration sensor, but a plurality of single-axis type or 3-axis type optical fiber acceleration sensors. It can also be multiplexed using sensors. In that case, it is possible to measure acceleration at multiple points.

As described above, according to the third embodiment, three interferometers are formed by winding optical fibers around the six faces of one cubic weight 43 and making them orthogonal to each other.
The axial optical fiber acceleration sensor 40 can easily detect vibration acceleration in three axes. Also, with this configuration, it is possible to perform time division multiplexing using optical pulses and delay fibers. In this case, there is no need to prepare a laser device or O / E converter for each axis, and the system can be manufactured at low cost. Can be configured. Further, the time division multiplexing of the optical fiber acceleration sensor is not limited to the three axes as in the present embodiment, and has an effect that it can be applied to multipoint measurement at low cost.

Further, as in the case of the first and second embodiments,
The optical fiber configured as one member of the optical fiber acceleration sensor can be used as the optical transmission line as it is.
In that case, electrical components such as the laser light source 18 and the O / E converter 21 can be installed on the land portion, and the optical fiber acceleration sensor 40 can be installed and operated in the liquid. In addition, it is possible to obtain the advantage that it has flexibility in application such as the advantage that long distance transmission is possible.

[0037]

As described above, according to the present invention, the elasticity of the optical fiber itself is utilized to form a seismo system adopted for a spring, and a part of the system is used as an optical fiber and a fixed point body. By using another attached optical fiber and demodulating the O / E output of the interference light output by the phase difference φ (t) of the laser light propagating through these fibers through the O / E converter. Since the optical fiber acceleration sensor for obtaining the vibration acceleration is constructed, it has an excellent effect that the vibration acceleration can be measured without introducing any electric circuit inside or outside the sensor.

Further, the optical fiber constructed as one member of the optical fiber acceleration sensor can be used as the optical transmission line as it is. In that case, it is possible to install and operate electrical components such as a laser light source and an O / E converter on the land, and to operate the optical fiber acceleration sensor in a liquid, so long-term reliability can be obtained even in a liquid. In addition, there is also a large secondary effect that it has flexibility in application such that long-distance transmission is possible. Further, with the configuration according to the second embodiment of the present invention, it is possible to obtain the effect of being able to detect acceleration in only one axis (single axis).

Furthermore, a three-axis optical fiber acceleration sensor having three interferometers can be obtained by the configuration of the third embodiment of the present invention in which one axis is expanded to three axes, and vibration acceleration of three axes is obtained. Can be easily detected. Also, with this configuration, it is possible to perform time division multiplexing using optical pulses and delay fibers. In this case, there is no need to prepare a laser device or O / E converter for each axis, and the system can be manufactured at low cost. Can be configured. Further, the time division multiplexing of the optical fiber acceleration sensor is not limited to three axes, and has an effect of being applicable to multipoint measurement at low cost.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a first embodiment of the present invention.

FIG. 2 is a schematic explanatory view showing a second embodiment of the present invention.

FIG. 3 is a schematic explanatory view showing a third embodiment of the present invention.

FIG. 4 is a schematic explanatory view showing a basic configuration of a conventional general vibration acceleration sensor.

[Explanation of symbols]

1, 11 Acceleration sensor 2, 12, 32, 32a Base 3, 13, 33 Weight 4, 14 Spring 5 Resistance 6 Measurement object 10 Optical fiber acceleration sensor 15 Sensing fiber 16 Reference fiber 17 Rigid structure 18 Laser light source 19, 19a Optical coupler 20, 20a, 34, 34a Optical fiber 21 O / E modulator 22 Demodulator 23, 31 Housing 30 Single axis type optical fiber acceleration sensor 40 Three axis type optical fiber acceleration sensor 42, 42a, 42b, 42c, 42d , 42e Base 44, 44a, 44b, 44c, 44d, 44e Optical fiber 45, 45a, 45b, 45c, 45d, 45e Optical coupler 51 Pulse gate 52, 52x, 52y, 52z Accelerometer 53, 53a, 53b, 53c Optical coupler 54, 54a, 54b, 54c Delay Aiba

Claims (4)

[Claims] 1. A hermetically sealed case forming a fixed point, a weight, a base positioned at a predetermined distance from the weight, and an optical fiber, and wound so as to connect the weight to the base. A seismo system in which the elasticity of the optical fiber of the straight line portion that constitutes a part of the optical fiber is formed as a spring, and another optical fiber wound around a rigid object located at the fixed point similar to the case, Two optical couplers having an acceleration sensor unit in which the base portion is attached and fixed to the inside of the housing, and the optical fiber and the other optical fiber are provided on an input side and an output side of the acceleration sensor unit. The measuring laser beam is branched by the optical coupler on the input side, one of the branched laser beams is introduced into the optical fiber, and the other is introduced into the other fiber. Combine and output Introduced into the optical fiber of the, the interference light generated in the area of the optical fiber for output due to the change in the length of the optical fiber of the linear portion is optically-electrically converted to measure the phase difference, and then demodulated. An optical fiber acceleration sensor characterized by detecting vibration acceleration. 2. A closed casing that constitutes a fixed point, a weight, two bases located vertically above and below the weight and a predetermined distance, and two optical fibers, and the weight and the weight. A composite type seismic system in which the elasticity of two pairs of linear portions formed by a part of each one optical fiber wound so as to connect two bases is formed as two pairs of springs, and the two bases. And an acceleration sensor part fixed to the inside of the housing, and the two optical fibers are connected to two optical couplers provided on the input side and the output side of the acceleration sensor part for measurement. Laser beam is branched by the optical coupler on the input side, one of the branched laser beams is introduced into the first optical fiber and the other optical fiber is introduced into the second optical fiber, and then coupled by the optical coupler on the output side. And introduce it into the output optical fiber, and the two pairs of spring parts Of the interference light generated in the area of the optical fiber for output due to the change in the length that expands and contracts in the opposite direction is measured, and the phase difference is measured after demodulating and the vibration acceleration in the uniaxial direction is obtained. A single-axis type optical fiber acceleration sensor, which is characterized by detecting. 3. A cube weight, six bases of the weight and six bases respectively located at predetermined intervals, and six optical fibers, the weight and the two bases each. A triaxial composite type seismo system in which elasticity of 6 pairs of linear portions formed by a part of each of two optical fibers wound so as to connect to each other is formed as 6 pairs of springs, and A plurality of bases fixed to the inside of the housing for three-axis acceleration sensors, and each two optical fibers provided on each input side and each output side of the acceleration sensor section. After being connected to the optical coupler of FIG. 3 and introducing the measurement laser light into the acceleration sensor of the acceleration sensor unit for the three axes by time division with respect to each axis using the optical coupler and the delay fiber, Laser light that has passed through the fiber is combined with an output optical coupler and a delay fiber for multiplexing. And output from the output optical fiber, and generated / multiplexed in the area of the output optical fiber due to a change in length in which two pairs of springs of the six pairs of spring portions expand and contract in opposite directions. A three-axis optical fiber acceleration sensor, which detects the vibration acceleration in the three-axis directions by performing demodulation processing after performing optical-electric conversion of interference light to measure a phase difference. 4. The optical fiber acceleration sensor according to claim 3, wherein a plurality of acceleration sensor units for detecting vibration acceleration in the three-axis directions are combined to configure for multipoint measurement.