JPH04151527A - Opto-acoustic sensor system - Google Patents

Abstract

PURPOSE:To make it possible to suppress the attenuation of the power of wave- split light which is inputted into a signal processing means by setting the power splitting ratio with a wave splitting coupler at the approximately constant value, and continuously connecting wave synthesizing couplers from the initial stage to the final stage with one piece of fiber. CONSTITUTION:The power of an input light pulse L is split with a wave-splitting coupler 31-1 at a splitting ratio K into the wave-split lights LS1 and LR1. The light LR1 is received with an optical fiber 34 through a wave synthesizing coupler 33-1. The light is cast into a signal processing means 20 sequentially passing through wave synthesizing couplers 33-2 to 33-(N + 1). The light LS1 is sent into a sensing coil 32-1. The optical characteristic is changed in correspondence with the sound pressure of a sound-wave signal S which is applied on the coil from the outside. The signal is delayed by a delay time T and inputted into a coupler 31-2. In the coupler 31-2, the light LS-2 is split by the same way. With respect to the light LR1 to LR(N + 1) which are cast into the means 20 at the deviation of every time T, each wave-split light is made to be double pulses with a compensator 21. The time overlap is generated between the wave- split lights. The double pulses are mixed, and interference occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a photoacoustic sensor system for detecting sonic information contained in a two-wave signal, which is installed in a sonar system, etc., and particularly relates to its multiplex structure. It is.

(Prior Art) Conventionally, as for technology in this field, for example, the document JOJRNAL OF LIGHTWA
VE TECHNOLOGY, LT-'L7 (19
87-7) P, lCD4-1023, J, L, BR
OOKS, B, Al03LEHIB, Y, KIM, a
nd H, J, SHA%V ”Time-Domai
n Accompanied by Remote
Fiber-Optic Interferometry
There was one described in ``C.

FIG. 2 is a schematic configuration diagram showing one configuration of a conventional photoacoustic sensor system.

This photoacoustic sensor system has a reflective multiplexed structure consisting of photoacoustic sensors using optical fibers, and uses a time division multiplexing method to extract sonic information from external sonic signals. It has a laser 1 that outputs a pulse L, and a photoacoustic sensor section 10 is connected to the output side of the laser 1.

The photoacoustic sensor unit 10 receives an input optical pulse L from the laser 1
It has a function of demultiplexing the light, and for each demultiplexed light, it causes a change in the optical characteristics, for example, a phase change, based on the sound wave signal, and it divides the power of the input optical pulse L from the laser beam 11 and generates each Demultiplexed light Ls1. Lrl, split light Ls2. Multiple stages of cascade-connected duplexer couplers 11 that sequentially demultiplex into Lr2, etc.
1', 11-211-3, etc. Demultiplexer coupler i'r-'.

~ 11-3 etc., respectively, the external sound wave signal S
Due to the sound pressure of the demultiplexing coupler, the demultiplexed light Ls1.
A plurality of sensing coils 12-1.12 = 2 that cause a phase change in Ls2 etc. according to the sound pressure, delay it by a predetermined time T, and send it to the subsequent duplexer coupler.
etc., and each demultiplexing coupler 11-1 to 1
For 1-3 etc., combiner couplers 13-1, 13-
2゜13-3 etc. are connected. This multiplexing coupler 1
3-1.13-2.13-3 etc. are demultiplexed lights Lr1, Lr
The signal processing means 20 is connected to the output side of the final stage multiplexing coupler 13-1. is connected.

The signal processing means 20 outputs the demultiplexed light Lr1. from the photoacoustic sensor section 10. It has a function of detecting changes in the optical characteristics based on Lr2 and the like and extracting the sound wave information of the sound wave signal S, 7), and has a compensator 21 and a photodetector 22.

Here, the compensator 21 converts the input hfS demultiplexed light into one
It has the function of converting 1 to 11 tuple pulses to generate a temporal pattern between the separated light beams and mixing them to cause an interference effect.
a demultiplexer 21-1 that demultiplexes input demultiplexed light into two;
A delay coil 21-2 that delays one output of the duplexer 21-1 by the delay time, and a multiplexer 21 that multiplexes the other output of the duplexer 21-1 and the output of the delay coil 21-2. −
It is composed of 3. Further, the photodetector 22 converts the output of the compensator 21 into an electrical signal.

Furthermore, a sensor output processing section 23 is connected to this photoacoustic sensor system, which calculates the sound pressure of the sound wave signal S based on the output from the signal processing means 20 and performs processing for detecting sound wave information.

Next, the operation of this photoacoustic sensor system will be explained with reference to FIG. Here, FIG. 3 is a diagram for explaining the formation of multiple pulses in the compensator in FIG. The power is divided into split light Lrl
and demultiplexed into demultiplexed light Lsl. One of the demultiplexed lights Lrl is immediately transmitted to the signal processing means 2 via the multiplexing coupler 13-1.
0, and the other demultiplexed light Lsl is sent to the sensing coil 12-1. At this time, sensing coil 12
-1, if the sound wave signal S is applied, then the sound wave signal S
A phase change occurs in the demultiplexed light Lsl. This demultiplexed optical LSI is delayed by a delay time T, and the sensing coil 1
2-1, and is further power-divided by the demultiplexing couplers 11-2 into demultiplexed light Lr2 and demultiplexed light Ls2.6 One of the demultiplexed lights Lr2 is outputted from the demultiplexing couplers 11-2.
2, is delayed by the delay time T by the multiplexing coupler 13-1, is multiplexed with the demultiplexed light Lr1, and is input to the signal processing means 20.

The other demultiplexed light Ls2 is sent to the next stage sensing coil 12-
2 will be sent one after another.

The demultiplexed lights Lrl and Lr2 input to the signal processing means 20
The demultiplexed light Lr2 is delayed by the delay time T with respect to the demultiplexed light Lrl, and is input to the compensator 21, respectively. Then,
The demultiplexed light, rl and Lr2, are each first processed by a compensator 21.
The demultiplexer 21-1 in the splitter 21-1 splits the signal into two, and then a delay coil 21-2 applies a delay time T to one of the split signals, as shown in FIG. Each of the signals is converted into a double pulse to generate a temporal pattern, which is combined by a multiplexer 21-3 to cause interference. The multiplexer 21
-3 optical output is converted into an electrical signal by the photodetector 22,
Thereby, a phase change between the demultiplexed light Lrl and the demultiplexed light Lr2 is detected. The output of the photodetector 22 is sent to the sensor output processing section 23, and the sensor output processing section 23 calculates the sound pressure of the sound wave signal S applied to the sensing coil 12-1 based on the output of the photodetector 22. Then, detection processing of the sound wave information possessed by the sound wave signal S is performed.

In this way, in the conventional photoacoustic sensor system, using the time division multiplexing method, the demultiplexed light Lr1. Lr2
etc. are shifted by delay time T and inputted to the signal processing means 20, thereby detecting the phase change of the demultiplexed light Lr2 etc. caused by the sound wave signal S, and
The sound wave information of the sound wave signal S applied to the second wave can be obtained.

Therefore, this optical 89 sensor system can be configured with a small number of elements, eliminates the need to introduce an electrical system in the photoacoustic sensor section 10, etc., and has advantages such as being less susceptible to the effects of induction and the like.

(Problem M to be solved by the invention) However, in the photoacoustic sensor system with the above configuration,
The following issues were encountered.

A conventional photoacoustic sensor system has a sensing coil 12
-1.If we increase the number of multiplexing by increasing the number of 12-2 etc.
The demultiplexed light received by the signal processing means 20 is accompanied by the division of optical power by the demultiplexer couplers 11-1 to 11-3 and the loss of optical power by the multiplexing couplers 13-1 to 13-3. The power attenuation of Lr1Lr2 etc. becomes large.

In order to minimize the power attenuation i of the demultiplexed lights Lrl, Lr2, etc., it is necessary to appropriately set the optical power division ratio of the demultiplexer couplers 11-1 to ``L1-3'' according to the number of stages. Yes, for example, if the number of sensing coils is N, the power division ratio of the fifth coupler can be set to 1/(Nj÷2), but it is expensive to manufacture a variety of couplers with different power division ratios. It is not a good idea due to its counter-effect.

In addition, if the power division ratio of the demultiplexing couplers 11-1 to 11-3 is set to all stages, signal processing is performed from the demultiplexing coupler at the final stage (and final stage side) through each multiplexing coupler. The power attenuation of the demultiplexed light input to the means 20 may be enormous. Moreover, in this case, the power of each demultiplexed light input to the signal processing means 20 is attenuated, and the signal processing means 20
Differences may occur in the power of the demultiplexed light received at 0, making it impossible to extract sound wave information effectively.

The present invention solves the problem that the prior art had, and when the power division ratio of each demultiplexer coupler is set uniformly, the power attenuation of the demultiplexed light from the final stage (and final stage side) demultiplexer coupler is reduced. The present invention provides an optical Hm sensor system that solves the problem of manufacturing constraints when the number of sensors increases and is set according to each stage.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a plurality of cascade-connected demultiplexers that power-divide input light and sequentially demultiplex it into first and second demultiplexed lights. is provided between the demultiplexer coupler and the demultiplexer coupler of each stage, and changes the optical characteristics of the first demultiplexed light from the demultiplexer coupler of the preceding stage based on the sound wave signal and sends it to the demultiplexer coupler of the latter stage. A plurality of sensing coils to be sent respectively, a multiplexing coupler in multiple stages that sequentially multiplexes the second demultiplexed light from the demultiplexer coupler in each stage, and a multiplexing coupler in the final stage based on the output of the multiplexing coupler in the final stage. The photoacoustic sensor system includes a signal processing means for detecting a change in the optical characteristics and extracting sonic information of the sonic signal, which takes the following measures.

The plurality of stages of demultiplexer couplers have their respective power division ratios set to be approximately the same, and the plurality of stages of multiplexing couplers have the following characteristics:
Multiplexing couplers from the first stage to the final stage which input the second demultiplexed light from the demultiplexer couplers from the first stage to the final stage are connected in cascade through a single fiber, and each
The input second spectral light is sequentially passed through the output from the previous-stage multiplexing coupler and the second-stage multiplexing coupler to the second-stage multiplexing coupler.

(Function) According to the present invention, since the photoacoustic sensor stem is configured as described above, the plurality of stages of demultiplexing collars each separate the first and j-th demultiplexed lights based on the input light. It works to separate the waves with almost the same power division ratio.

In the plurality of stages of multiplexing couplers, the second branch Σ from the multiplexing coupler near the final stage coupler is output from the final stage multiplexing coupler.

The number of multiplexing couplers that the light passes through is reduced, or the paths that each of the second demultiplexed lights passes through before being output from the final stage demultiplexing coupler 2 are made approximately equal to one. For example, each path contains approximately the same number of couplers.

Therefore, the above problem can be solved.

(Example) FIG. 1 is a schematic configuration diagram of a photoacoustic sensor system showing an example of the present invention.

This photoacoustic sensor system has a laser 1 and a signal processing means 20 similar to those in the photoacoustic sensor system shown in FIG. A photoacoustic sensor section 30 is provided.

This photoacoustic sensor unit 30 includes a plurality of cascade-connected demultiplexing couplers that power-divides the input optical pulse L from the laser 1 and demultiplexes it into first demultiplexed light LS and second demultiplexed light LR, respectively. 311, 31-2.3L-3,..., 31(
N+1) etc. Here, each demultiplexing coupler 31
-1 to 3l-(N+1) etc. are input optical pulses or divide the first demultiplexed light LS from the previous stage demultiplexing coupler to the first demultiplexed light LSI, the second demultiplexed light LRI, and the second demultiplexed light LRI, respectively. 1 demultiplexed light LS2 and second demultiplexed light LR2, first demultiplexed light LS3 and second demultiplexed light LR3,..., first demultiplexed light LSN, second demultiplexed light LR (N-1), etc. , and each power division ratio is = demultiplexed light LR/(
The demultiplexed light LST (demultiplexed light LR) is set to, for example, a -ratio. Each branching coupler 31-1 to 3l-(N-i-1
), etc., the sensing coils 32-1, 32-2.
32-3. ..., 32-N, etc. are provided, and multiplexing couplers 33-1.33 2, 33 3.・
..., 3B(N+1), etc. are connected.

The sensing coils 32-1 to 32-N change the optical characteristics, for example, the phase, of the first demultiplexed light LS from the demultiplexing coupler in the previous stage based on the external sound wave signal S, and change the optical characteristics, for example, the phase, according to the cable length, etc. It has a function of delaying the first demultiplexed light LS by a set delay time T and sending it to the subsequent demultiplexing couplers, and is constructed using, for example, a coiled optical fiber.

Multiplexing couplers 33-1 to 33 (N, 1), etc.

The second demultiplexed light LRI to LR(N・1) demultiplexed by the demultiplexing couplers 31 to 1 to 31 (N-, 1) are respectively input, and the second demultiplexed light LRI which is respectively input is
It has the function of combining ~LR (N?1) with the output from the previous-stage multiplexing coupler and sequentially sending it to the subsequent multiplexing coupler, and each multiplexing coupler 33-1 to 33 (NTl), etc. The input side is each multiplexing couple 31-1 to 3l-(N+
1), etc., and each multiplexing coupler 33-
1 to 3B-(NTl), etc. are cascade-connected by - optical fibers 34, respectively. Final stage multiplexing coupler 3
A signal processing means 20 is connected to the output side of 3-(NTl).

Furthermore, a sensor output processing section 23 similar to that shown in FIG. 2 is connected to this photoacoustic sensor system via a single word processing means 20.

Next, the operation will be explained.

The input optical pulse L generated by the laser 1 is power-divided by the demultiplexing coupler 31-1 at a power division ratio and is distributed to the demultiplexing optical LSI and the demultiplexing optical LSI.

One of the demultiplexed lights LR1 is taken into the optical fiber 34 by the multiplexing coupler 33-1, and is sent to the multiplexing couples 33-2 to 33-3.
(N+1) and is input to the signal processing means 20. The other demultiplexed optical LSI is sent to the sensing coil 32-1, causes a change in optical characteristics, for example, a phase change, in accordance with the sound pressure of the sound wave signal S externally applied to this coil, and is delayed by a delay time T. The signal is then input to the demultiplexing coupler 31-2.

The demultiplexing coupler 31-2 that receives the demultiplexed optical LSI divides the power of the demultiplexed optical LSI according to the power division ratio and outputs the demultiplexed optical LSI.
2 and demultiplexed light LR2. One of the demultiplexed lights LR
2 is taken into the optical fiber 34 by the multiplexing coupler 33-2, is multiplexed with a delay time T behind the demultiplexed light LRI, and sequentially passes through the multiplexing couplers 33-3 to 33-(N+1). The signal is input to the signal processing means 20. The other demultiplexed light LS
2 is sent to the sensing coil 32-2 and causes an optical characteristic change, for example, a phase change, in response to the sound pressure of the sound wave signal S applied to this coil from the outside, and is delayed by a delay time T, and is then connected to the demultiplexing coupler. 31-3.

The demultiplexing coupler 31-3 inputting the demultiplexed light LS2 divides the power of the demultiplexed light LS2 at a power division ratio and outputs the demultiplexed light LS2.
3 and demultiplexed light LR3. One of the demultiplexed lights LR
3 is taken into the optical fiber 34 by the multiplexing coupler 33-3, is multiplexed with a delay time T behind the demultiplexed light LR2, and sequentially passes through the multiplexing coupler 33-(N+1) and the like to the signal processing means. 20 is input. The other demultiplexed light LS3 is sent to the sensing coil 32-3 side.

Thereafter, demultiplexing of the demultiplexed light LS3 and the like is performed in the same manner, and the sensing coils 32-3. ..., a phase change of the demultiplexed light LS3 etc. due to 32-H occurs, and the sensing coil 32
-Demultiplexing coupler 31 inputting the demultiplexed light LSN from N
(N+1) is the demultiplexed light LR (
N.1) is input to the signal processing means 20 via the multiplexing coupler 33-(N+1).

The demultiplexed lights LRI to LR(N+1) inputted to the signal processing means 20 after being shifted by the delay time T in this way are processed in the same way as in the photoacoustic sensor system shown in FIG.
First, the compensator 21 separates each demultiplexed light LR1 to LR(N+1
) is converted into double pulses and temporal overlap occurs between the respective demultiplexed lights, and the double pulses are mixed to cause an interference effect.Next, the optical output of the compensator 21 is converted into an electrical signal by the photodetector 22. is converted to As a result, when the demultiplexed light LRI is used as the reference light and the demultiplexed light LR2 is used as the signal light, the demultiplexed light LR
The phase change of the demultiplexed light LR2 with respect to I, and the demultiplexed light LR2
When demultiplexed light LR3 is used as a reference light and demultiplexed light LR3 is used as a signal light, the phase change of demultiplexed light LR3 with respect to demultiplexed light LR2 is detected, and the phase change up to demultiplexed light LR (N+1) is detected in the same way, and the sensor The output processing unit 23
The sound pressure of each sound wave signal S applied to each of the sensing coils 32-1 to 32-N, etc. is calculated, and the sound wave information possessed by each sound wave signal S is detected.

The advantages of this embodiment will be explained with reference to FIG. Here, FIG. 4 is a diagram showing the power division ratio of the coupler in the photoacoustic sensor system of FIG. 1.

In the photoacoustic sensor system shown in FIG. 1, the power division ratio of each demultiplexing coupler 33-1 to 33-(N+1> etc. is uniformly set to K in this embodiment, but as shown in FIG. Generally, the power division ratio of the j-th demultiplexing coupler 33-j is Kj, and the multiplexing couplers 33-1 to 33-j are
33-(N+1) with a power division ratio of Kj, the optical power Pj of the demultiplexed light LRj that becomes the reference light for the signal light output from the j-th sensing coil 32-j is as follows. Letting the optical power of the input optical pulse L from the laser 1 be Pin, it is expressed by the following equation (1).

Kj2 N+1 Pj=Pinx xIT (1-Ki)-(1
)1−Kj ”” As can be seen from equation (1), when Kj=Kj↑1= as in the photoacoustic sensor system of this embodiment, Pj=P
j=1=P. Here, P is expressed by the following equation (2).

-2 P = PlnXk
N is expressed by the following formula (3): PN = plnxK
X (1-K)2(N-''<3.2 Therefore, it can be seen that the following advantages can be obtained in this example.

(A> The power division ratios of the couplers in the photoacoustic sensor system shown in FIG. 1 are all lawful, and restrictions on manufacturing the couplers can be reduced.

(B) Each demultiplexed light LRj serving as a reference light (as well as a signal light) for each sensing coil 32-j passes through the same path before being input to the signal processing means 20, and all have the same power. Since it is input to the signal processing means 20,
Processing in the subsequent signal processing means 20, sensor output processing section 23, etc. becomes easier.

(C> In each case, each branched light LR-i, which becomes the reference light (the same goes for the signal light) of the signal light 32-j, is input to the scale signal processing means 20 where j is large. For example, when comparing the multiplexing structures of this embodiment and a conventional photoacoustic sensor system, the number of multiplexing couplers passing through is reduced. can be reduced to about half, and the amount of power attenuation can be reduced as shown in equation (2).

Here, FIG. 5 shows a comparison result when the attenuation amount by the coupler based on equations (2) and (3) is compared with the power division ratio=0.95. Furthermore, Fig. 5 shows the comparison results of the amount of attenuation caused by the coupler in the photoacoustic sensor systems of Figs. Attenuation due to the coupler ff
1 ldB:li is taken respectively. Further, in the figure, the solid line ■ indicates the case of the embodiment, and the dotted line 2 indicates the case of the conventional example (separated light of the Nth sensing coil).

As can be seen from this figure, as the number of sense sink coils increases and the degree of multiplexing increases, the attenuation value increases and this embodiment is more advantageous. but not limited to.

Various modifications are possible. Examples of such modifications include the following.

(I) In the photoacoustic sensor system shown in FIG. 1, the configurations of the laser 1, signal processing means 20, sensor output processing section 23, and photoacoustic sensor section 30 can be changed, and other configurations can be added as appropriate. . For example, couplers 33-1 to 33 for multiplexing
-(N11) etc., a coupler with even lower loss may be used.

(II) The photoacoustic sensor system of the present invention is widely applicable not only to sonar systems and the like but also to various systems for extracting and detecting sonic information contained in sonic signals.

(Effects of the Invention) As described in detail above, according to the present invention, the power division ratios of the first and second branched lights are set to be almost the same in the plurality of stages of branching couplers. can reduce manufacturing constraints.

The multi-stage multiplexing coupler makes the system a transmission type structure.The demultiplexed light from the downstream multiplexing coupler is input to the signal processing means, and then passes through the multiplexing coupler. The number of couplers can be reduced, and each path through which each demultiplexed light input to the signal processing means can be made almost equal. Therefore, it is possible to suppress the power attenuation of the demultiplexed light input to the signal processing means as small as possible, and the optical power of the demultiplexed light can be made almost uniform, making processing in the signal processing means etc. easier. can be achieved.

Therefore, in the photoacoustic sensor system of the present invention, the attenuation of optical power due to the coupler can be relatively suppressed compared to the conventional one.
Since the power division ratio of the coupler can be made uniform, manufacturing becomes easy, and high effectiveness can be expected especially when applied to a photoacoustic sensor array with a high degree of multiplexing.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a photoacoustic sensor system showing an embodiment of the present invention, and FIG. 2 is a conventional photoacoustic sensor system.
A schematic configuration diagram showing one configuration example; FIG. 3 is a diagram for explaining tuple pulsing in the compensator in FIG. 2; FIG. 4 is a diagram showing the buff-splitting ratio of the coupler in FIG. Figure 5 showing
The figure is a diagram showing a comparison result of the amount of attenuation caused by the coupler in the photoacoustic sensor systems of FIGS. 1 and 2. 1...Laser, 20...Signal processing means, 30...
Photoacoustic sensor section, 31-1 to 3l-(N+1)... Demultiplexing coupler, 32-1 to 32-N... Sensing coil, 33-1 to 33 (N+1>... Multiplexing coupler , L...input optical pulse, LSI~LSN...first demultiplexed light, LRI~LR(N+1)...second demultiplexed light,
S...Sound wave signal.

Claims (1)

[Scope of Claims] Multiple stages of cascade-connected demultiplexing couplers that power-divide input light and demultiplex it into first and second demultiplexed lights in sequence; a plurality of sensing coils provided for changing the optical characteristics of the first demultiplexed light from the preceding stage demultiplexing coupler based on the sound wave signal and sending the same to the subsequent demultiplexing coupler; A multi-stage multiplexing coupler that sequentially multiplexes the second demultiplexed light from the coupler, and a change in the optical characteristics based on the output of the final stage multiplexing coupler, thereby detecting the sound wave information possessed by the sound wave signal. In the photoacoustic sensor system, the plurality of stages of demultiplexing couplers have their respective power division ratios set to be approximately the same, and the plurality of stages of multiplexing couplers have substantially the same power division ratio. , the multiplexing couplers from the first stage to the final stage which respectively input the second demultiplexed light from the demultiplexing couplers from the first stage to the final stage are connected in cascade by one fiber, and A photoacoustic sensor system characterized in that the demultiplexed light is multiplexed with the output from the previous-stage multiplexing coupler and sequentially sent to the second-stage multiplexing coupler.