JPH0545209A - Photoacoustic sensor array system - Google Patents

Abstract

PURPOSE:To reduce influence of the phase noise, and obtain a compact and light-weight system having high reliability, in which corrective action for vibration resistance is facilitated. CONSTITUTION:The continuous light from a light source 41 is divided into two systems by a coupler 42-1, and shifting of frequency and pulse conversion are performed to the divided light of the two systems by Bragg cells 43-1, 43-2. The output light of the Bragg cell 43-2 is delayed by a delay coil 44. The output light of the Bragg cell 43-1 and the output light of the delay coil 44 is combined by a coupler 42-2, and is transmitted to a sensor array 50.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-channel photoacoustic sensor array system using an optical fiber.

[0002]

2. Description of the Related Art Conventionally, as a technique in such a field,
For example, some documents were described in the following documents.

"SP I Volume
586 Fiber Optic Sensors (SPIE Vo
l.586 Fiber Optic Sensors) "(1985) (US) Mic
hael Henning “Improvements in reflectrometric fiber optic
hydrophones) "P.58-64 FIG. 2 is a diagram showing a configuration example of a conventional interferometric photoacoustic sensor array system described in the above document.

In this interferometric photoacoustic sensor array system, when a sound wave is applied to an optical fiber, the refractive index and the fiber length of the optical fiber change, and the phase of propagating light changes, so the phase change is utilized. Then, the sound wave information is detected.

That is, this photoacoustic sensor array system has an optical pulse generating means 10 for generating an optical pulse,
The sensor array 20 and the photodetector 30 are connected to it. The optical pulse generating means 10 has a light source 11 for generating coherent continuous light, and an input end 12a of a Bragg cell 12 is connected to the light source 11. The Bragg cell 12 receives the input end 12a based on the control signal CS.
The frequency of the incident light of is shifted and the pulsed light is sent to the input / output end 12b only for a fixed time by the gate control,
Normally, it has a function of sending light from the input / output terminal 12b to the output terminal 12c.

At the input / output end 12b of the Bragg cell 12,
The sensor array 20 is connected to the output terminal 12c.
Is connected to the photodetector 30. Sensor array 20
Is a sensor for detecting sound waves, and includes a plurality of sensors 21-1, 21-2, ...
A plurality of semi-reflectors 22-1, 22-2, 22- with a small reflection coefficient provided at the front and rear ends of 1, 21, 2 ...
3 and so on.

FIG. 3 is a timing chart of FIG.
The operation of FIG. 2 will be described with reference to this figure.

Continuous light generated from the light source 11 is converted by the Bragg cell 12 and sent out from the input / output terminal 12b to the sensor array 20 as two pulse trains of the frequency f1 and f2 having the time interval T and the pulse width d. In the sensor array 20, the semi-reflector 22-1 causes the first reflection, and similarly, the other semi-reflectors 22-2, 22-3, ...

Each semi-reflector 22-1, 22-2, 22-
Since the round-trip propagation time between 3, ... Is set to be T seconds, the reflected wave of the pulse of the frequency f2 at the semi-reflector 22-1 and the frequency f1 at the semi-reflector 22-2 are compared. The reflected wave of the pulse overlaps and is sent from the input / output end 12b of the Bragg cell 12 to the output end 12c. Then, the photodetector 30 detects the interference component and converts it into an electrical output. In this case, the pulse of the frequency f2 becomes the reference light in the interference action, and the pulse of the frequency f1 is the sensor 21-
It becomes the sensing light of 1.

For example, when a sound wave signal is applied to the sensor 21-1, a phase change occurs, and the interference components of the frequencies f1 and f2 are subjected to processing such as frequency modulation (FM) demodulation to detect sound wave information. become. The other sensors 21-2, ... Are sequentially processed by the same operation, and the sound wave information is detected.

[0011]

However, the system having the above structure has the following problems.

In the conventional system, since the phase change is detected by utilizing the interference between the pulses having the time difference T, the light source 11 needs to have a high coherence. Time difference T is 1μ
Since it is about sec, the spectral width of the light source 11 is several K
Narrow band characteristics below Hz are required. Therefore, the light source 1
1, a gas laser such as He-Ne is used, and the light source itself becomes large. Moreover, in an environment with vibration such as a ship, there is a problem that a vibration isolation table and the like are required, and it is difficult to adapt to an environment where space saving is required, and it is difficult to solve them.

The present invention has the problems that the above-mentioned prior art has such as noise (phase noise) generated due to poor coherence of the light source, size increase of the apparatus, special vibration isolation table, etc., and reliability. The present invention provides a photoacoustic sensor array system that solves the problem of low.

[0014]

In order to solve the above-mentioned problems, a first aspect of the present invention provides a sensor array for detecting a sound wave, which is composed of a plurality of optical fibers and a semi-reflector, and an optical pulse to the sensor array. And a light pulse generating means for supplying,
In the photoacoustic sensor array system that detects sound wave information from the phase change of propagating light in the sensor array, the optical pulse generating means is configured as follows.

That is, the optical pulse generating means of the first invention is a light source for generating coherent continuous light, a first coupler for branching the continuous light into two output lights, and
A first Bragg cell for converting one output light of the system into an optical pulse having a constant pulse width and frequency, and another output light of the other system of the two systems into an optical pulse having a constant pulse width and frequency. A second Bragg cell, a delay coil for delaying the output light of the second Bragg cell for a fixed time, and a second coupler for coupling both output lights of the first Bragg cell and the delay coil and supplying the combined light to the sensor array. Is equipped with.

In a second invention, the optical pulse generating means of the first invention is a light source which generates an optical pulse having a constant pulse width by a control signal, and a first optical pulse which branches the optical pulse into two optical pulses. Coupler, a delay coil for delaying one optical pulse of the two systems for a fixed time, and the other optical pulse of the two systems and the output light of the delay coil are combined and supplied to the sensor array. And a second coupler that does.

[0017]

According to the first aspect of the present invention, since the photoacoustic sensor array system is configured as described above, continuous light generated from the light source is split into two systems by the first coupler. The branched lights of these two systems are emitted from the light source at the same time, and the frequency shift and pulse conversion are performed by the first and second Bragg cells. Then, the output light of the second Bragg cell is delayed by the delay coil, and the delayed output light and the output of the first Bragg cell are combined by the second coupler and then sent to the sensor array 50.

According to the second invention, the optical pulse generated from the light source is branched into two optical pulses by the first coupler, one of which is delayed by the delay coil, and the delayed output light and the other branch. The light and the light are coupled by the second coupler and then sent to the sensor array side.

As a result, the structure of the pulse generating means can be simplified, the size and weight can be reduced, the anti-vibration measures can be easily taken, and the phase noise can be suppressed, so that the reliability of the system can be improved. Therefore, the above problem can be solved.

[0020]

First Embodiment FIG. 1 is a block diagram of a multi-channel interference type photoacoustic sensor array system showing a first embodiment of the present invention.

This photoacoustic sensor array system comprises a pulse generating means 40 for generating two pulse trains of frequencies f1 and f2 having a time interval T and a pulse width d. The pulse generating means 40 has a light source 41 that outputs coherent light such as a laser diode, and the first coupler 42-1 is connected to the output side thereof. First coupler 4
Reference numeral 2-1 is for dividing the input light from the light source 41 into two, and at the output side thereof, the first and second Bragg cells 43-
1, 43-2 are connected.

First and second Bragg cells 43-1 and 43-3
-2 is controlled by the control signal CS, has a function of shifting the frequency of each input light, and a function of performing pulse conversion by gate control. The output side of the first Bragg cell 43-1 is connected to the second coupler 42-2, and the second Bragg cell 43-2 is connected to the second coupler 42-2 via the delay coil 44. ing.

The delay coil 44 is a Bragg cell 43-2.
It has a function of delaying the output light of the above for a fixed time T (second). The second coupler 42-2 is for adding and coupling the two outputs of the Bragg cell 43-1 and the delay coil 44, and the sensor array 50 is connected to the output side thereof.

The sensor array 50 is for detecting sound waves, and comprises a plurality of sound wave detecting sensors 51-1, 51-2, ...
A plurality of semi-reflectors 52- having small reflection coefficients (for example, about 1%) provided at the front and rear ends of 1-2 ,.
1, 52-2, 52-3, ...

A photodetector 60 for detecting an interference component and converting the interference component into an electric signal is connected to the output terminal of the second Bragg cell 43-2.

FIG. 4 is a timing chart of FIG.
The operation of FIG. 1 will be described with reference to this figure.

Continuous light generated from the light source 41 is branched by the first coupler 42-1 and one output light of the continuous light is frequency f1 and pulse width d by the first Bragg cell 43-1.
Is converted into an optical pulse of and transmitted to the second coupler 42-2. The other output light from the first coupler 42-1 is output by the second Bragg cell 43-2 at a frequency f2 and a pulse width d.
Is converted into an optical pulse of
It is delayed by time T seconds and sent to the second coupler 42-2.

In the second coupler 42-2, the output light of the first Bragg cell 43-1 and the output light of the delay coil 44 are combined, and two signals of frequency f1 and pulse width d and frequency f2 and pulse width d are combined. Light pulses are output to the sensor array 50 at time intervals T.

In the sensor array 50, the semi-reflector 52-
The first reflection occurs at 1, and the other semi-reflector 52-
2, 52-3, ..., Reflection occurs sequentially. Sensors 51-1 and 51- are preliminarily set so that the round-trip propagation time between the semi-reflectors 52-1, 52-2, 52-3, ... Is T seconds.
2, ... and the fiber length of the transmission cable are set in advance.
Then, the reflected wave of the pulse of the frequency f2 in the semi-reflector 52-1 and the reflected wave of the pulse of the frequency f1 in the semi-reflector 52-2 are respectively the second coupler 42-2 and the delay coil 44, And to the photodetector 60 via the second Bragg cell 43-2. In the photodetector 60, the frequency f1
The interference component between the pulse of frequency f2 and the pulse of frequency f2
The detected interference signal is electrically output. In this case, the pulse of the frequency f2 becomes the reference light in the interference action, and the pulse of the frequency f1 becomes the sensing signal of the sensor 51-1.

When a sound wave signal is applied to the sensor 51-1, a phase change occurs, and if the output of the photodetector 60 is subjected to processing such as FM demodulation, sound wave information will be detected.
The other sensors 51-2, ... And thereafter are sequentially processed by the same operation, and the sound wave information is detected.

The first embodiment has the following advantages. (A) Since the light source 41 is not required to have high coherence, it is possible to use an ordinary laser diode which is small, lightweight, inexpensive and portable. Therefore, even in a high vibration environment of a ship or the like, it is possible to provide the vibration isolator within the light source 41, and a special vibration isolation table or the like as in the conventional case is not required, so that the antivibration measure becomes easy.

(B) In the present embodiment, since the same pulse of the same light source 41 is used at the time of interference,
Basically, it is possible to suppress the noise (phase noise) generated due to the poor coherence of the light source as in the conventional case as much as possible.

(C) As described in (a) and (b) above, the reliability is improved, and since it is suitable for a multi-channel configuration as an array system, various applications such as an underwater acoustic sensor array such as a sonar are possible. It is possible.

Second Embodiment FIG. 5 is a block diagram of a multi-channel interferometric photoacoustic sensor array system showing a second embodiment of the present invention.
Elements common to the elements inside are given common reference numerals.

In this photoacoustic sensor array system, pulse generating means 40A having a different structure is provided in place of the pulse generating means 40 of FIG. The pulse generating means 40A has a light source 41A for generating an optical pulse having a pulse width d by the control signal CS, and the first coupler 42-1 is connected to the output side thereof. First coupler 42-1
Is for branching the optical pulse from the light source 41A into two systems, one output side of which is connected to the second coupler 42-2, and the other output side of which is connected to the second coupler 42-2 via the delay coil 44. It is connected to the coupler 42-2. Delay coil 4
Reference numeral 4 delays the output light of the first coupler 42-1 by a delay time T seconds and supplies it to the second coupler 42-2.

The second coupler 42-2 is connected to the first coupler 4-2.
The output light of 2-1 and the output light of the delay coil 44 are coupled, and the third coupler 42-3 is connected to the output side thereof. The third coupler 42-3 includes the second coupler 4-3.
While supplying the output light of 2-2 to the sensor array 50,
It has a function of sending the reflected light from the sensor array 50 to the photodetector 60.

Next, the operation will be described. The light source 41A is controlled by the control signal CS and generates an optical pulse having a pulse width d. This optical pulse is output by the first coupler 42-1 to 2
To the system, one of which is directly connected to the second coupler 42-
2 is sent to the second coupler 42-2 after being delayed by the delay coil 44 for the delay time T seconds. The second coupler 42-2 couples the output light of the first coupler 42-1 and the output light of the delay coil 44, and outputs optical pulses of the same frequency to the sensor array 50 at time intervals T.

In the sensor array 50, the reflected wave from the semi-reflector 52-1 and the semi-reflector 52 are the same as in the first embodiment.
The reflected wave at -2 is sent to the photodetector 60 via the third coupler 42-3. In the photodetector 60, the reflector 52
The interference signals of the reflected waves from -1, 52-2 are electrically output. Here, since the interference of the optical pulses is used at the same frequency, the output of the photodetector 60 is not subjected to FM modulation or the like as in the first embodiment, but homodyne demodulation is performed to detect the sound wave information. Will be done. Even after the sensor 51-2, the same operation is sequentially performed and the sound wave information is detected.

In the second embodiment, since the light pulse is generated from the light source 41A by using the control signal CS, the structure becomes more complicated than that of the light source 41 in FIG. Simple first and second couplers 42-1 and 42-in place of the first and second Bragg cells 43-1 and 43-2
Since 2 is provided, almost the same advantages as those of the first embodiment can be obtained with a circuit scale similar to that of FIG.

The present invention is not limited to the above embodiment,
Various modifications can be made, for example, by providing another optical circuit for improving the function in the pulse generating means 40, 40A shown in FIGS.

[0041]

As described in detail above, according to the first aspect of the invention, the optical pulse generating means includes the light source, the first and second couplers, the first and second Bragg cells, and the delay coil. Therefore, it is possible to reduce the influence of the phase noise generated due to the poor coherence of the light source as in the related art. Further, since the light source itself is not required to have high coherence, a usual laser diode or the like can be used. Therefore, the entire system can be made smaller and lighter, and since the light source itself can take anti-vibration measures, it is possible to provide a highly reliable system without requiring a special anti-vibration table or the like.

According to the second invention, the optical pulse generating means includes the light source, the first and second couplers, and the delay coil. Therefore, the structure of the light source itself becomes more complicated than that of the first invention. However, since the first and second couplers having a simple structure are provided in place of the first and second Bragg cells of the first invention, the pulse generating means has a circuit scale substantially similar to that of the first invention. realizable. Therefore, the same effect as the first invention can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a multi-channel interferometric photoacoustic sensor array system showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional multi-channel interferometric photoacoustic sensor array system.

FIG. 3 is a timing chart of FIG.

FIG. 4 is a timing chart of FIG.

FIG. 5 is a configuration diagram of a multi-channel interferometric photoacoustic sensor array system showing a second embodiment of the present invention.

[Explanation of symbols]

40, 40A pulse generation means 41, 41A light source 42-1, 42-2, 42-3 1st, 2nd, 3rd
43-1, 43-2 first and second Bragg cells 44 delay coil 50 sensor array 51-1, 51-2 sensor 52-1, 52-2, 52-3 semi-reflector 60 photodetector

Claims (2)

[Claims] 1. A sensor array for detecting a sound wave, which comprises a plurality of optical fibers and a semi-reflector, and an optical pulse generating means for supplying an optical pulse to the sensor array. In the photoacoustic sensor array system for detecting acoustic wave information from a phase change, the optical pulse generation means includes a light source that generates coherent continuous light, and a first coupler that branches the continuous light into two output light beams. A first Bragg cell for converting one output light of the two systems into a light pulse having a constant pulse width and frequency, and the other output light of the two systems into a light pulse having a constant pulse width and frequency. A second Bragg cell to be converted, a delay coil for delaying the output light of the second Bragg cell for a predetermined time, and a combination of the output lights of the first Bragg cell and the delay coil Photoacoustic sensor array system characterized by the second coupler to be supplied to the sensor array, comprising a Te. 2. The photoacoustic sensor array system according to claim 1, wherein the light pulse generating means generates a light pulse having a constant pulse width by a control signal, and the light pulse is divided into two systems of light pulses. A first coupler that branches, a delay coil that delays one optical pulse of the two systems for a certain period of time, and the other optical pulse of the two systems and the output light of the delay coil are coupled to each other. A photoacoustic sensor array system comprising: a second coupler that supplies the sensor array.