JPH01297515A - Photo-acoustic sensor - Google Patents

Abstract

PURPOSE:To reduce the mounting space by providing a reflecting mirror so as to be opposed to an optical lattice which is fixed to the end face of an optical fiber and providing a movable optical lattice for interlocking with a displacing means between both of them. CONSTITUTION:An optical fiber 1 is fixed with a screw to an optical guide which has been attached to a containing vessel 2. On the end face of this optical guide 3, a fixed optical lattice 4 is installed, and also, so as to be opposed thereto, a movable optical lattice of the same type is installed in a supporting column which has been connected to a diaphragm 6. On the rear face of these lattice 4, 5, a mirror 7 is provided. In such a state, when the diaphragm 6 vibrates in accordance with an acoustic wave which is propagated in the water or in the air, the lattice 5 is displaced by interlocking therewith. In its state, a light beam which is made incident from the optical fiber 1 passes through each light transmitting part of the lattices 4, 5. Subsequently, the light beam which has transmitted through is reflected by the mirror 7, turned back from the light transmitting part of the lattices 4, 5, and returned to the optical fiber 1. In such a way, the variation quantity of the light beam which has been returned is proportional to pressure of the acoustic wave which is propagated, and acoustic pressure is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an acoustic system using optical fibers.

(Prior Art) FIG. 4 is a principle diagram showing an example of the configuration of a conventional photoacoustic sensor (see Japanese Patent Laid-Open No. 60-238725). The propagated sound waves reach the diaphragm 6, and the diaphragm 6 is deflected by the pressure of the sound waves, and the deflection displaces the movable optical grating 5. As a result, a positional deviation occurs from the fixed optical grating 4, and the amount of transmitted light is modulated. be done. Sonic pressure can be measured by detecting this modulated light intensity.

The optical transmission fibers are arranged so as to sandwich the optical grating from both sides, and are composed of an input optical fiber 1a and an output optical fiber 1b.

(Problems to be Solved by the Invention) This photoacoustic sensor is of a type that uses optical fibers as a transmission path, but in order to transmit light back and forth, a total of two optical fibers are used, one for the outward path and one for the return path. I need. Two fibers come out in a straight line facing each other from the sensor nozzle, making it difficult to separate the cables.
In addition to taking up extra space for mounting, it also requires twice as many holding mechanisms, including cable vibration isolation, compared to a single cable. An increase in the number of parts is also disadvantageous in terms of reliability and price.

Therefore, an object of the present invention is to
- The object of the present invention is to reduce space, facilitate the handling of sensors and fibers, and reduce the number of work steps for aligning optical fibers, thereby making it easier to adapt to array systems.

(Means for Solving the Problems) This invention provides a reflecting mirror opposite to an optical grating fixed to an end face of an optical fiber, and between the two, another optical grating that is interlocked with a displacement means (such as a diamond slam). This is what was installed.

(Operation) Light for measurement is introduced from an optical fiber, passes through two optical gratings, is reflected by a reflecting mirror, passes through two optical gratings again, and is led out of the optical fiber toward the detector. .

On the other hand, via a diaphragm or the like, one of the optical gratings is displaced in response to the acoustic pressure, changing the amount of light transmitted.

(Example) FIG. 1 is a structural diagram of a photoacoustic sensor showing an example of the present invention. The optical fiber 1 is screwed and fixed to a light guide 3 attached to a storage container 2. A fixed optical grating 4 is installed on the end face of the light guide 3, and a movable optical grating 5 of the same type opposite thereto is installed on a support column connected to a diaphragm 6. A reflecting mirror 7 is provided on the rear surface of this grating pair. Optical fiber 1, fixed optical grating 4. The movable optical grating 5 and the mirror 2 are placed facing each other so that their optical axes coincide. The optical gratings 4.5 are each 3
It has a light-transmitting part and a light-blocking part at regular intervals of 0 to 200 μm.

Next, the operation of the photoacoustic sensor shown in FIG. 1 will be explained.

In response to sound waves propagating through water or air.

When the diaphragm 6 vibrates, the movable optical grating 5 is displaced in conjunction with the vibration. In this state, the light incident from the optical fiber 1 passes through each transparent portion of the fixed optical grating 4 and the movable optical grating 5. The passed light is reflected by the mirror 7, and is returned to the optical fiber 1 by folding back the light-transmitting portions of both optical gratings.

As a result, the original transducer returned to the optical fiber 1 is proportional to the pressure of the propagated sound wave, making it possible to detect the sound pressure.

FIG. 2 is a configuration diagram showing an example of an array system using the photoacoustic sensor described above. A number of photoacoustic sensors (hereinafter referred to as sensors) are connected in parallel to the light source. The LED light source 11 generates a light noculus, which is controlled by a light source generator 2. The light pulse is
The light enters the first sensor 16 via the optical coupler 131 source fiber 14 and the optical coupler 15, is intensity-modulated by sound pressure, and is returned. The return light is again optical power graph 15. optical fiber 1
4 and an optical coupler 13 to a photodetector 17, where it is converted into an electrical signal and sent to a processor 18.

The processor 18 extracts a signal at a time corresponding to the round trip propagation time between the laser light source 1 and the first sensor, based on the transmission trigger time of the pulse generator 12, and calculates a detection output proportional to the sound pressure. do. The optical pulse signals from the second sensor onwards are inputted to the processor 18 with a propagation delay and sequentially processed in a similar manner. The period of pulses sent out from the radar light source 1 is set to be larger than the maximum value of the round-trip propagation time between the sensors. Optical Cazola basically has a one-manpower/two-output configuration, and the coupling ratio of one output to one input is about 50%. or.

There is reversibility between input and output. In this example, a difference of Q6 dB occurs in the light intensity between adjacent sensors due to optical cazola insertion, so it is necessary to correct it in the processor 18.

FIG. 3 is a configuration diagram showing another example of the array system. A star coupler 19 is used to optically couple each cell and the other components are the same as in the previous example. Therefore, no difference in light intensity level occurs between the sensors.

(Effects) As explained above, in this invention, the round-trip transmission of light can be
Because it was realized with optical fiber.

(-) When mounting the sensor, it is easier to handle the fiber and the mounting space is also much smaller.

(b) The process of aligning optical fibers during manufacturing is reduced. (c) When configuring an array system, the number of parts and mounting space are reduced by a fraction of the cost, making it lightweight and compact. This has the advantage of being a highly reliable and low-cost system.

Additionally, photoacoustic sensors are essentially small, lightweight, and highly sensitive.
! It has the advantage of not being subjected to magnetic induction.

In addition, it is effective for safe remote measurement with strong resistance to noise under adverse environments such as high voltage, high electromagnetic field, and flammable and explosive atmospheres. It is also effective in devices for detecting the direction of underwater objects using sound waves, which requires an array system in underwater acoustics.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the photoacoustic sensor of the present invention, FIGS. 2 and 3 are block diagrams of an array system using the photoacoustic sensor shown in FIG. 1, and FIG. FIG. 2 is an explanatory diagram of a prior art. I... Optical fiber, 2... Storage container, 3... Light guide, 4... Fixed optical grating, 5... Movable optical grating,
6...Diaphragm, 11...Rede light source, 13.
...Hikari Gura. 4...Optical fiber, 15... Original coupler, 16...
- Sensor, 17... Photodetector, 18... Processor. The light of the present invention @Kyotonsa StructureArchime 2 Fig.1

Claims (1)

[Claims] An optical fiber having a fixed end, an optical grating fixed to the end face of the optical fiber, a reflecting mirror placed opposite the end face, and means for displacing in response to acoustic pressure. A photoacoustic sensor comprising: and another optical grating that is attached so as to be interlocked with the displacement means and inserted between the optical grating and the reflecting mirror.