JPH02210224A - Acoustic signal detection method and apparatus - Google Patents

Abstract

PURPOSE: To reduce the cost by determining the size of opening for passing a viscous substance depending on the pressure difference of fluid between the space surrounded by a thin film embedded with an optical fiber and an end cap and the space on the outside of thin film. CONSTITUTION: A thin film 7 is formed around a tubular framework 6 and a single mode optical fiber 8 is wound spirally around the thin film 7 thus forming spaces 9, 16 between the thin film 7 and an end cap 17. When this hydrophone is immersed into a fluid, a part of the fluid flows through a hole 15 into the hydrophone to elongate a bladder 12. Consequently, static pressure in the spaces 9, 16 is equalized to the static pressure of fluid on the outside of hydrophone and the fluid stops to flow through the hole 15. The hole 15 and the equalization hole 10 are made small enough to slow down the equalization rate. Variation of acoustic signal measured by the hydrophone causes the thin film 7 to expand or contract radially and to elongate or shrink the fiber 8 longitudinally.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an acoustic signal detection method and an acoustic signal detection apparatus using an optical fiber.

For example, is the prior art in either phase modulation or frequency modulation of light passing through an optical fiber (the signal to be imposed on the light propagating in the optical fiber)? The acousto-optic effect was utilized in that it was used to mechanically or acoustically excite the fibers.

This mechanical or acoustic excitation causes a change in the optical index of the fiber's core. The optical distance of light traveling through the spliced fiber changes.

This light is therefore modulated in phase and frequency by the signal. For glass fiber J3, the change in optical index is extremely small for a given mechanical or acoustic excitation energy. To obtain sufficient modulation, this means that the high level signal energy requires either a long interaction length, which is the length of the fiber that must be acoustically excited at the point where the modulation occurs. It's about that. The sensitivity of optical fibers to direct acoustic excitation is described in J, A.

Applied 0ptics by Bucaro,
Vol. 1B, Nch 6°, March 15, 1979 issue.

A single mode fiber with a thin cladding is constructed for use in a sensor in which phase modulation is caused by stretching the single mode fiber with signal energy according to the present invention. Moreover, the optical fiber of a low order mode is also constructed from the optical fiber with a large diameter used in the present invention.

These two optical fibers are accomplished by etching currently available optical fibers.

Opted by S, 5heel and J, H, Cafe
ics tetters.

Vol.4. No, 10. f' October 1979 issue
Acoustic 5sensitivity of S
ingle Node Optical Power D
In the prior art, single-mode fibers have been used to increase or decrease their optical conductivity without taking into account any changes in their acoustic power or mode structure, as described in J. Etching. It is believed that such an effect, ie, reduced photoconductivity, is undesirable for purposes of the present invention, and the present invention specifically provides an apparatus for minimizing it.

The present invention can be used in limited length distributed wavelength reflectors to reflect light within a single mode optical fiber. Such a reflection is rHethod And A
pparatus For l1adiant Ene
rayModulation In 0ptical
U.S. Patent Application No. 08857 entitled FibresJ
No. 9 and ni, 0. Applied Ph by former 11 et al.
ysics Letters, 32 (10), 1
[Ph0tO3OnSi in the May 15, 978 issue
tiVityin 0ptical fiber
WaV+30LlidQS: App)ica
tion t.

Relectton Fitter Fabrica
tion J.

The present invention can also be used in reflectors that cause reflections within optical fibers in devices similar to Fabry-Bello interferometers. Such devices are P,G.

Applie, September 1, 1979 issue by C1clo
dOptics, Vol. 18, Ha 17 “Fibre Optic 11 Hydrophone:
Improved 5train Conriaura
tionand Environmental No1
se ProtectionJ. A novel detection device is provided that uses this reflector device as one of its multiple components.

The present invention comprises a novel type of fiber optic energy sensor.

The present invention uses an etched single mode fiber as an energy sensor. This energy sensor works as follows.

Signal energy to be sensed or detected is generated and stretches the etched single mode fiber. Etched single mode fiber is a single mode glass-clad fiber whose thickness has been reduced to a certain degree to weaken its strength. When it is necessary to preserve the photoconductive properties of an etched single-mode fiber, the present invention provides a method for removing portions of the glass cladding that have an optical index lower than that of the material of the core of the single-mode fiber. It is also assumed that the plastic material is replaced with a plastic material whose modulus of elasticity is lower than that of the glass crimp to be replaced.

Such etched single mode fibers are weaker and therefore more sensitive to stretching and compression. For a given amount of signal energy, a single mode fiber will stretch a greater amount after it is etched.

The prior art teaches that increasing the length of a single mode fiber changes the optical distance of the electromagnetic radiation propagating through its core.

The prior art further teaches that this change in optical distance increases as the amount that the single mode fiber is stretched increases. Prior art uses this change in optical distance to modulate electromagnetic radiation propagating through the core of the fiber. The prior art also teaches that as the magnitude of the change in optical distance increases, the amount of modulation increases. Therefore, an optical fiber energy sensor constructed of an etched single-mode fiber and operated by longitudinally stretching or compressing the etched single-mode fiber can be used for a given amount of [3] energy. It results in a large modulation and therefore higher sensitivity.

The etching process useful in the present invention is used to produce optical fibers with reduced morphology dispersion from larger diameter optical fibers.

It also provides a manufacturing process for constructing devices using etched optical fibers useful in the present invention. This process allows the mold to be constructed of material that is not affected by the etching process.

These molds are used to hold the fibers to be etched in the same alignment as they should be in the actual device. Various means for allowing the mold to be removed if it is not present in the actual device are also detailed.

An example of an application using the present invention is to make the energy sensor more effective by actually optically detecting the output of the energy sensor, thus substantially reducing the previously extremely large bandwidth required by electronic demodulators. Provides an optical demodulator designed to reduce the amount of light. The provided optical demodulator also allows for multiplexing several energy sensors on the same optical fiber, thus substantially lowering the cost of multiple sensor devices such as Hyde O7-on-arrays.

The optical demodulator disposes each energy sensor between a pair of limited length Bragg reflector members constructed inside an optical fiber.

Each pair of reflectors arranged constitutes a 7 Abry-Perot interferometer that only contains resonances in that portion of the electromagnetic spectrum in which the Bragg reflector operates. Each energy sensor is positioned between a pair of reflectors, so that when signal energy is detected, the resulting change in optical distance of the sensor spectrally shifts the resonance of the Fapley-Perot interferometer. The device then converts this spectral transition into a second
It is partially demodulated using a 77 Briebello interferometer. This resonance of analytical interference J1 has a spectral separation that is proportional to the spectral separation of the interferometer containing the energy sensor so as to provide amplification of the spectral transition. The output of the combined energy sensor interferometer and analytical interferometer is spectrally shifted more than the original spectral shift by an amplification constant times the equation given in the detailed description of the invention. The device also allows the use of one or more analytical interferometers, each performing its own amplification. The resulting amplification can be made to provide an output corresponding to a number of distinct digits, each representing the original spectral shift, thus reducing the bandwidth of the electronic detector and time demodulator.

The optical detector finally multiplexes several energy sensors onto the same fiber by having each reflector pair corresponding to each sensor have a different reflection band than all reflector pairs. is being considered.

This device uses a wavelength-scanning laser whose output scans the resonance of one reflector pair at a time.

It can be used in sensitive optical fibers, energy sensors, and photoreducer vA devices that can convert the output of the energy sensor into an electrical analog signal. First, let's explain the energy sensor and then the optical demodulator.

The current technology of optical fiber energy sensors is that if a single mode optical fiber is radially compressed or stretched or longitudinally compressed,
This teaches that the optical distance of electromagnetic radiation propagating through the core of a single mode optical fiber changes. This technique further teaches that as the amount that a single mode fiber is stretched or compressed increases, the change in optical distance also increases. Current technology uses this change in optical distance to cause phase modulation of light propagating through the core. The length of the optical fiber where modulation occurs is called the interaction length.

The present invention provides an etched single mode fiber for use in optical fibers, i.e. energy sensors, useful in the present invention. A single mode fiber is a fiber configured to propagate only the lowest order modes. This lowest order mode in a single mode fiber configuration is 2Fli degenerate. In these cases, the lowest order modes contain two states of propagation that are distinguished by the fact that their polarizations are mutually perpendicular.

Etched single-mode fibers are used in which the thickness of their cladding is reduced by chemical reaction (e.g., etching in a solution of hydrofluoric acid or a solution of hydrofluoric acid buffered with ammonium fluoride), or by ion milling. It is defined as a thin single mode optical fiber.

FIG. 1 is an enlarged cross-sectional view of the fiber before etching. FIG. 2 is an enlarged cross-sectional view of the fiber after edge puffing. FIG. 1 illustrates that the glass cladding, generally designated 2-1, has a thickness designated K. In FIG. 2, the cladding 2-2 is shown to have a reduced thickness indicated by R. In both FIGS. 1 and 2, the cores designated 1-1 and 1-2 have a diameter .largecircle. which remains unchanged due to the nature of the etching process which occurs only at the exposed surface of the fiber.

The usefulness of such fibers will be discussed first in terms of electric shock, and then the ease of manufacturing devices using etched single mode fibers will be discussed. For a given amount of signal energy E to be detected, the fiber of FIG. 1 with a length of 1 and a total cross-sectional area of $1 will be stretched by an amount ΔL1:

Here, YO is the elastic modulus of the fiber material and may be assumed for purposes of explanation to be constant and equal to the elastic modulus of fused silica. Derived as above, however, substituting the thin comb cladding thickness into equation (I) gives the elongation ΔL, which the etched fiber follows for the same given suspension signal energy E.

where $2 is the cross-sectional area of the etched fiber. Since S is larger than S2, formula (I) and formula (II)
Therefore, ΔL > Δ[1. Current technology in optical fiber sensing therefore suggests that for a given amount of signal energy, an etched single-mode fiber will have a larger change in optical distance than a regular single-mode fiber, thus propagating through the core. It is taught that a larger set of phase modulation of the light can be obtained.

Another utility can be appreciated in that fibers with very small overall diameters are difficult to construct using current methods and, even when constructed, are difficult to process. The teachings of the present invention allow devices that may use thin clad combed fibers to be constructed with readily available larger diameter fibers.

Once such a device has been assembled to a point where the larger fiber is in place, the fiber can then be etched, thereby precluding further processing of thin fibers, i.e. fibers with thin cladding. Indulge. A more detailed explanation of this process follows.

Another utility is found when it becomes necessary to construct fibers with small core diameters, and the fibers used in the present invention are constructed from larger diameter fibers. Figure 3 shows a cross section of an optical fiber with a large diameter, 3-3;
This is a core material of diameter F (eg quartz glass). The larger diameter fiber is etched, thus creating a thinner fiber having a reduced diameter G, the cross section of which is shown at 4--4 in FIG. The present invention further provides seven fibers having a diameter G of General Electr.
It is further provided that it can then be coated with a material 5-4 having a lower refractive index than the fiber itself, such as RTV670 silicone rubber manufactured by ICcorp, thus creating an optical fiber with a small core diameter. Such small core diameter fibers are effective in providing a low number of guided optical modes.

As an example of an etching process, the fiber 3-3 of FIG. 3 may have an unetched diameter in the range of 80 .mu.ffl to 100 .mu.m and the etched core 4-4 of FIG. It may have a diameter in the range up to 5 μm.

The present invention provides a particular underwater acoustic energy sensor as illustrated in FIGS. 5 and 6 and, in part, in FIG.

FIG. 5 is an end view of the sensor illustrating its cylindrical shape. FIG. 6 is a sectional view of the sensor. The sensor consists of a rigid cylindrical framework, shown at 6 in FIG. 6, probably made of aluminum.

The outer surface of this cylindrical framework has a reduced diameter between planes H and J. Surrounding this cylindrical framework is a membrane of flexible material, generally designated 7, within which a single mode optical fiber, generally designated 8, is radially wound. Such a flexible material may be, for example, silicone rubber or PvC. This sleeve is joined as at 13 and/or tightened as at 14 to the larger diameter end 13' of the cylindrical framework so that the diameter of the flexible membrane and rigid mold is reduced. A space 9 is provided between the rigid cylindrical frame and the rigid cylindrical frame. The wall of this rigid cylindrical framework, of reduced diameter, is provided with a constant hole 10 extending from the inner wall of the cylindrical framework to the space between the flexible membrane and the rigid framework. On the inner wall of the cylindrical framework there is a protrusion, designated 11 in FIG. Similarly, inside the cylindrical frame, a flexible bladder 12, which serves as a ballast supply, extends and forms a tank 16, which is closed by a constant hole 10 into a space 9.
I am in touch with you. Spaces 16 and 9 are filled with air, helium, or another viscous flexible material, such as silicone oil. End caps 17 are also provided which create an additional space 16', shown in FIG. 6, and include holes 15 extending through the thickness of each end cap.

The Hyde O7 ON shown in FIGS. 5, 6, and 7 operates as follows.

This hydrowan 4 is immersed in a fluid containing the sound waves to be measured. At any particular depth, according to the invention, a portion of this fluid is admitted through the hole 15 into the Hydro7on and then:
As shown by the dashed line indicated at 12', the protrusion 1
Stretching the bladder 12 around 1 and thus compressing the second viscous flexible material in spaces 16 and 9 makes the static pressure in spaces 9 and 16 equal to the static pressure in the fluid outside of Hydro 7. do. When the pressure in spaces 16 and 9 equals the external pressure plus the additional pressure created between the bladders 12, fluid ceases to flow through the holes 15. Hole 15 and equal stop hole 10
Alternatively, the speed of equalization may be made slow enough to result in a time period much longer than the time period between the sound pressures to be measured.

The acoustic signal to be measured or sensed by the Hydro-7 consists of alternating changes in ambient fluid pressure. Since these changes are not equalized by the bladder mechanism described above, they instead cause the flexible membrane 7 to expand and contract radially, thus longitudinally stretching and compressing the etched single mode fiber 8. I do things.

In those applications that require the underwater acoustic sensor heights of FIGS. 5, 6, and 7 to be in an open position while being used to sense underwater acoustic signals, the present invention It comprises reinforcing strands, such as fibers 8' in FIGS. 6 and 7, attached parallel to the axis of the rigid cylinder. The fibers 8' are bonded to the outer and/or inner surfaces of the flexible iss 17 and extend below each clamping ring 14 around the rigid cylinder 6. The clamping surface is a rigid cylindrical part 13' to which the flexible membrane 7 is attached. Such reinforcing fibers 8' may be made of VIar, tire cord fibers manufactured by Pont, or of glass. Such reinforcing fibers 8' are arranged to increase the strength of the flexible thin film 7 in the longitudinal direction. Therefore, if the underwater acoustic sensor of FIGS. 5, 6 and 7 is accelerated in the axial direction of the rigid cylinder 6, the resulting deformation of the flexible M-membrane 7 will be as shown in FIGS. It is made smaller by the reinforcing fiber 8' in FIG. Furthermore, this reinforcing fiber 8' is connected to a rigid cylinder 6.
flexible WJP against radial contractions such as those caused by an acoustic signal to be substantially sensed when placed parallel to the axis of
Does not increase resistance of IA. Furthermore, the mass of the flexible membrane can be varied as well as the density of the single mode fiber windings 8 which has the effect of shifting the underwater acoustic frequency response.

The present invention also provides underwater sounds as shown in FIGS. 8 and 9! #Give sensor. Figure 8 is underwater sound 111? FIG. 9 is a cross-sectional view of the sensor of FIG. 8 in which 7-9 does not indicate the flexible membrane in which the helix of single mode fiber 8-9 is contained.

The assembly also includes an inner cylinder 202 of a resilient, flexible material, such as silicone rubber, which is comprised of a flexible membrane 7.
-9 is in contact with the inner wall. Reinforcing strands, e.g., fibers 201, are placed parallel to the axis of the flexible thin film 1127-9 and in mechanical contact with the inner cylinder material 202 to increase the longitudinal strength of the inner cylinder without significantly changing its radial flexibility. Try to strengthen it. Reinforced fiber 20
1 may be made of evlar or glass and may extend long beyond the end of the flexible material and may be used to secure the sensor in position. The flexible inner cylinder 202 may also be elongated to position or secure the sensor in position. The present invention also provides that reinforcing fibers 201 are mechanically attached to the outside of the flexible membrane 7-9 parallel to the axis of this membrane 7-9 to increase its longitudinal strength. Increasing the longitudinal strength of the sensor also reduces the durability of the sensor by reducing the amount of radial expansion and contraction caused by longitudinal acceleration of the sensor, but it also reduces the sensor's response to acoustic signals, i.e. radial expansion and contraction;
does not decrease.

The underwater 11 sensors shown in FIGS. 8 and 9 are made as follows. The sensor is immersed in a solution containing the acoustic signal. Thin film 7-9 whose periodic changes in pressure appearing in acoustic signals are flexible
expand or contract. As the thin film 1!7-9 expands or contracts, the etched single mode optical fiber 8-9 is stretched or compressed;
Therefore, as already explained, the electromagnetic radiation propagating in the core of the fiber 8-9 is modulated. moreover,
Since the inner cylinder is also radially flexible, this provides less resistance to the expansion and contraction of the flexible membrane. The present invention provides that the sensors of FIGS.
It is shown that it is advantageous to use a single mode fiber etched as -9.

Etched single mode fibers are useful in all energy sensors, which use a single signal energy to longitudinally stretch or compress the single mode fiber to cause a change in the optical distance of the optical fiber. Some energy sensors may use lower order mode optical fibers if the morphological dispersion of such fibers is low enough to maintain sufficient optical coherence over the interaction length. For these energy sensors, the present invention provides the thin fiber of FIG.

It should be noted that any optical fiber can be etched to increase its sensitivity to longitudinal stretch or contraction, such as multimode step index or hierarchical index fibers.

When the glass cladding of a step index or hierarchical index fiber is etched away to reduce its conductivity for %1 litl radiation, the present invention can be used to remove the resulting fiber from FIG. As shown, it is determined that the fiber core may be coated with a material having a lower optical index than the fiber core, such as RTV670 silicone rubber, to restore its ability to conduct electromagnetic radiation. Therefore, the present invention includes in its object "etched single mode optical fiber" as well as "etched single mode optical fiber" and throughout the detailed description and claims the etched fiber is used in the apparatus. These nomenclatures can be interchanged whenever the etched optical fiber has a low enough morphological dispersion to maintain sufficient optical coherence in proper operation, and the intended use of an etched optical fiber is to When the objective is to increase the sensitivity to shrinkage, or when the objective is to provide a low order mode fiber, i.e. a fiber with low morphology dispersion, or for both of these objectives at the same time. It is.

An optical fiber energy sensor preferably using an etched single mode fiber is manufactured by the following manufacturing method. First, a mold is made that holds the fibers to be etched into the same arrangement or configuration as will be used in the particular sensor being manufactured. In the case of the hydride phons of FIGS. 5, 6, and 7, the fibers are arranged in a helical configuration. A suitable mold for this Hydro7on is a cylinder 18 as shown in FIG. 10, around which is cut a helical groove 19' into which an unetched optical fiber 20' is wound. . If it is desired to remove the mold by etching, the material of the mold must be a material that melts or can be dissolved into a liquid state at a temperature or by a solution that does not damage the material of the substrate or flexible thin film. Must. Such material is beeswax. In general, some mold materials can jeopardize even the etching of the fiber (simply rubbing the wax in the right places on the fiber, thus protecting the fiber from the etching agent). The mold made of the same material is first coated with a thin layer of protective material 21' in FIG. 11 by dipping or spraying the solution. Once this protective material 21' hardens, it does not affect the etching process. A suitable protective material is Type 39 Lo manufactured by Qptclecom.
w Andcx Plastic Cladino 5
olusion, crabynar, i.e. Penn
Vinylidene fluoride manufactured by Walt Chemical Co. If the fiber to be etched does not have enough glass cladding to conduct light, it is determined that the protective material has a lower optical refractive index than the fiber core. TVpel 39 Low Ande
xPlastic Cladding 5otutto
n or Kl/nar has a lower optical index than quartz glass.

If necessary, it is also provided that the fiber is bonded to the mold, perhaps at both ends of the etched core, as shown at 22' in FIG.

As the protective material explained above, a bonding agent is sufficient.

If it is necessary to protect sections of the fiber from etching agents, these sections should also be protected as shown in FIG.
As shown in 3', it may be covered with the protective material already described.

If the optical fiber energy sensor is to use an etched single mode fiber, then place the fiber 20 in the appropriate position as illustrated in FIG.
' in a solution of either hydrofluoric acid or hydrofluoric acid buffered with ammonium bifluoride, or any other chemical capable of dissolving or removing the glass cladding of the fiber. put. Typically, the etching solution is ultrasonically agitated, if necessary, to promote entrainment of the etching agent around all portions of the fiber that are to be etched.

After the etching period (which can be determined empirically) the mold with the gold-etched fibers in place is removed from the solution, rinsed with water, dried and then coated with the dissolved or melted coating. It can be soaked in a solution and removed, or sprayed with or otherwise coated with a solution of a substance that, when cured, dried, or cooled, becomes a flexible *a material. Ultrasonic agitation of the solution is performed when necessary to promote coating liquid around all parts of the fiber. The invention also provides that the application of the coating material may be carried out in a vacuum for the purpose of coating uniformity and eliminating air pockets.

When using such a fiber that does not have a cladding thickness sufficient to conduct electromagnetic radiation into the core after etching, the present invention provides that the cladding has a lower index of refraction than the material of the core. stipulate that Such a coating solution may be the protective material already described or the General El
Any silicone rubber such as RTV670 from Electric Company may be used. The viscosity of the coating solution can be varied as a means of increasing the thickness of the coating remaining on the mold to 14 m upon removal from the solution. A lower viscosity of the coating solution provides a thinner coating. The mold, removed from the coating solution, is then rotated until the coating hardens to achieve a uniform coating where the grooves are. FIG. 12 shows the completed mold and fiber of FIG. 10 after the etching and immersion process. Etched fiber is 20-E
The flexible thin film material is indicated by 124.

After the coating in FIG. 12 has solidified, holes are drilled extending through the coating and protector into the mold material. The location of such holes must be selected so that the material of the mold can be removed by melting or melting without damaging the fibers in the coating. Such a hole 125 is the 12th
It is shown in the figure.

The mold is contracted to #i out of the flexible wJIlm and protective material, thus facilitating removal of the mold through the much larger opening 126 in FIG. 12 formed by cutting the membrane in the plane marked P in FIG. It is best if the mold is made of a material such as Teflon that can be cooled with liquid nitrogen. Additionally, it would be advantageous for the mold to disintegrate to aid its removal. Figures 5 and 6
In the Hydro 7-on of FIG. 7 and FIG. 7, a suitable mold for collapsing is shown in FIG. 13, an end view.

FIG. 13 is an end view of cylinder 257. The removed portion of this cylinder, called the key, is indicated at 256. key 25
6 extends parallel to the axis of the cylinder and over the entire length of the cylinder. The arrow marked Zz illustrates the movement of the key to aid in its removal. By removing the key, cylinder 2
57 collapses radially so that it can be removed from the flexible thin film material after etching and immersion.

If it is desired to manufacture a fiber optic energy sensor that uses a flexible sleeve or shroud to provide the unetched optical fiber, the present invention can also eliminate the etching and cleaning steps from the manufacturing process described above. .

FIG. 14 shows an optical demodulator as an application example using the present invention. Referring to FIG. 14, 24 designates an optical fiber onto which are mounted several pairs of distributed Bragg reflectors 25 of length ti1. A distributed Bragg reflector t of length υ1, as used in the present invention, partially reflects a specific wavelength band of electromagnetic radiation propagating in an optical fiber and returns it to the source. The device is such that light that is spectrally outside these particular wavelength bands is transmitted first and passed through an optical fiber where it is largely unaffected.

Such a reflector causes a spatial periodic perturbation of the optical index of the cladding surrounding the core of the optical fiber so that the spatial periodicity exists in a direction parallel to the axis of the core and there is no interference of light in the optical fiber. The spatial period may be configured by ensuring that the spatial period does not exceed a length such that the property is maintained. The spatial periodic perturbation involves partially removing the cladding from the length of the fiber and then orienting the fiber toward the optical grating so that the teeth of the grating are perpendicular to the axis of the core. This can be caused by The magnitude of the reflectance can be increased or decreased by removing more or less of the cladding and thus moving the optical grating closer or further away from the core, as described in U.S. Pat. Application No. 08857
It is disclosed in No. 9. Such a reflector is II i
rPhoLosensitiv developed by l l et al.
ity in 0f)tical FiberWaVe
(luides:ADI)licatiOn tORe
r+ect+on FilterFdbrication
n J^pplied Physics Lettrs
#32(10), May 15, 1978, where it is shown that the reflected wavelength band occurs when:

λ, H”' 2 n d M
(III) where λCH is the center of the reflected wavelength band for a particular value of M, n is the effective optical index in the optical fiber core, d is the spatial period of the perturbation that creates the Bragg reflector, and M is less than zero. It is a large integer and is called the order of the reflection band.

The width, Δλ, is the total spectral width of a particular reflection band measured at the half point of the total H1 reflection intensity captured by a particular Bragg reflector. This has been shown in the prior art to be the case.

Here 1 is the length of the length-limited Bragg reflector.

Referring again to FIG. 14, reflector pair 25 includes A and B.
, C, . . . are attached. The reflectors in each pair both spatially reflect the same wavelength band and e.g.
By adjusting and 1, they are made to have the same transmission spectrum. However, each pair can again be made to reflect a particular wavelength band that is spectrally different from that of any other pair by adjusting d and 1 according to equations (III) and (IV). , so that the wavelength interval w,i includes at least one of only these specific wavelength bands in each reflector to be used.

exists.

Each pair 25 constitutes a Fapley-Bello interferometer inside the single mode fiber 24. This Fapley-Perot interferometer is sensitive only to electromagnetic radiation that lies spectrally within the reflection wavelength band of a particular pair of distributed Bragg reflectors.

FIG. 15 is an explanatory diagram of the transmission of a particular anti-ca pair.

Referring to FIG. 15, the ordinate represents the transmission of electromagnetic radiation through a particular reflector pair and the abscissa represents the wavelength of the electromagnetic radiation propagating through the fiber 24 and incident on the reflector pair. ing. Electromagnetic radiation that lies spectrally outside a particular pair of reflected wavelength bands is transmitted virtually unaffected. Such radiation is shown in FIG. 15 as area a.

The largest beam of radiation propagating in the fiber and spectrally within the reflection band of a particular reflector pair is transmitted forward through the reflector pair, where the wavelength is OPL. N is a positive integer. A minimum amount of electromagnetic radiation, if any, is transmitted forward through the reflector pair.

As a result, spectrally periodic transmission occurs as shown in the region of FIG.

As taught in the field of interferometry, the spectral width of the transmission peak, marked J3 and 300 in Figure 15, is limited by the length of the reflector pair responsible for the transmission peak. By varying the magnitude of the reflectance of the Bragg reflector, the spectral separation Δλ of the transmission peaks can be varied. This can be achieved as already explained.

The number of peaks 300 in the wavelength fIA range of FIG. 15 is given as follows.

X~□ (■) where 7 is the geometric length between the reflectors as measured along the axis of the single mode fiber and 1 is the distribution Bragg as measured along the axis of the fiber is the length of the reflector.

As the optical distance between the gates of the pair of two reflectors changes, the transmission peak in the wavelength region 1i1b shown in FIG.
Spectrally shifts within this region, as shown in equation (V).

In this application using the present invention, a portion or all of the length of optical fiber 24 disposed between a pair of two reflectors may be used as an optical fiber energy sensor, e.g. Let's use the interaction length of the acoustic energy sensor in Figure 7. As previously discussed, such sensors operate by changing the optical distance of an optical fiber by elongating or contracting the length of the optical fiber with the detected signal energy. Therefore, for example, in a pair B of reflectors, within which the interaction length of the optical fiber energy sensor detecting the signal is located, the region of FIG. The transmission peak of b shifts spectrally as caused by the signal energy being detected.

Referring again to FIG. 14, a wavelength-scanning laser 26 is used to provide electromagnetic radiation which is then directed to a pair of reflectors 25.
is incident by a suitable condenser lens 27 into a single-mode fiber 24 in which a single mode fiber 24 is arranged. The output of laser 26 is scanned or dipped for a particular wavelength range.

FIG. 16 is a graph of laser power suitable for the present invention.

The scanning range is Δλ, and is marked as such in FIG.

The wavelength spacing w,i, as described above, is chosen so that the reflector wavelength band region of FIG. 15 of each pair 25 of FIG. 14 is spectrally within the scanning range.

Referring to FIG. 14, the assembly includes a beam splitter 127 for directing a portion of the laser output beam to a seven-Brievero interferometer 28 (hereinafter referred to as the reference Fabry-Bello interferometer). Laser output wavelength λ
, where Q is a positive integer and 1] is the Fapley-Bello interferometer 28
The optical distance between each of the anti(l14) that constitutes.

A reference Fapley-Bello interferometer 28 directs a portion of this radiation to the first
4 to a photodetector 29, which then generates an electrical reference signal. Photodetector 29 is a commercially available device, for example Iexas In5tru
l (! IJ built by ntS Inc.
T[XL, whose output is an electrical signal whose amplitude is a well-known function of the amplitude of the incident radiation.

If the laser is scanning as in Figure 16,
Standard) The transmitted output of 7Brievero interference effect 128 is M
This results in a series of temporally separated peaks corresponding to the resonance of the quasi-Fapley-Perot interferometer 28.

The present invention determines the optical length 10 of the reference Fapley-Bello interferometer 28 and adjusts the spatial period of the reflectors in each reflector pair 25 to the laser scanning range Δλ.

The transmission peak of the reference Fabry-Perot interferometer 28 is selected to occur at a wavelength very close to the reflector wavelength band of each reflector of the pair 25.

Referring again to FIG. 14, the output end of the single mode fiber 24, ie, the end opposite to where the laser beam is incident, is focused into a Fapley-Bello interferometer 30 as illustrated in FIG. and a suitable focusing mechanism 32. The output of this interferometer 30 is directed to a photodetector 31.

Interferometric prior art and reflector pairs 25
From the above explanation of the spectral transmission of , the following can be seen. If a scanning laser is injecting into the fiber at a particular time a particular wavelength λ1 of electromagnetic radiation falling within the wavelength range shown in FIG. 15 of a particular reflector pair A, then
This 11 radiation then passes through a particular reflector pair A, passes through the remaining fibers, and passes through all other reflector pairs, so that the present invention provides additional reflector pairs B, C, etc. (so that all the different reflected wavelength bands of
5 is spectrally centered on a particular transmission peak, and this particular transmission peak is also spectrally centered on the transmission peak of the Fapley-Bello interferometer 30, hereafter referred to as the analytical Fapley-Bello interferometer. When they match,
Transmitted at maximum strength.

For example, for reflector pair B, the optical distance between the reflectors is 11iT
R~(n>(Z) is determined such that in a particular wavelength region between λ1o and λ2D the reflector pair B produces a transmission peak of SI (if this happens).

λ1. and 22. In the same wavelength region between, if the following equation holds true, the following formula holds true: analysis) 7 Briebello interferometer 30 where TA is the optical distance between the reflectors of analysis Fabry-Bello interferometer 30.

As previously explained, if a signal is detected by an optical fiber energy sensor placed, for example, between the length-limited Bragg reflectors of pair B, then all of the regions of FIG. The transmission peak of R indicates the spectral shift within the region, Δλ. By adjusting the reciprocal values of S and SR using equations (IX) and (X), the present invention results in the pair B and the analytical interferometer 30, which are combined in FIG.
This spectral shift, Δλ3R, is actually amplified by using the transmission spectral shift, ΔλSA@, as shown in the following equation.

ΔλSA〜UΔλsR(XI) Here, U is the amplification coefficient, for example, given by the following equation: However, S - (f) (SR) ±1 ^ where SA and SR are greater than 2 and f is a positive integer.

In order to better explain the demodulation device and to show fewer obvious limitations to consider in its completion, one of the devices of FIG. Let us walk through the example in detail through two laser scanning intervals. Laser scanning does not fall within any of the 25 reflection wavelength bands.
Start with 1. As the laser output wavelength eventually scans,
Eventually a scan over a particular pair of A transmission peaks is initiated. Reference interferometer 28 then transmits pulses of the laser beam to photodetector 29, which in turn provides electrical pulses to time demodulator 33. This electrical reference pulse is used in the time demodulator 33 to reset or start the electrical clock. The time demodulator 33 is also 1
Count the reference pulses in one scan interval and, depending on this number of pulses, direct the last output of the electrical clock to one of the electrical outputs corresponding to the particular reflector pair whose transmission peak is being scanned at that time. Transmit. Such electronic circuits are readily available from products currently on the market.

Referring to one embodiment of this device, the laser output is now
We are beginning to scan the transmission peak of . The laser output wavelength is
At λ2, when within the first peak of the pair Δ,
The laser beam passes through pair A and all other pairs and finally propagates to the analytical interferometer 30. For illustrative purposes, the apparatus of FIG.
Assume that the design is designed to give . For simplicity, equation X and equation XI's λ1o, λ2 . The spacing between them is assumed to spectrally match the area of FIG. 15 in each reflector pair. Therefore, U-100, S-1
For 0, 5A=99.

Similarly, assume that analytical interferometer 30 has a peak that spectrally matches the first peak of pair A. Therefore, when the laser beam is transmitted to the photodetector 31, the photodetector 31 generates an electrical output which is transmitted over time m:I to the photodetector 33.
, which pauses the electrical clock and its final output is an electrical signal corresponding to the time in the clock, which is applied to the conductor or lead marked A. As the laser continues to scan, the wavelength of its output finally approaches the peak of its transmission to the sun. Again, the reference interferometer 28 transmits pulses of light that cause the photodetector 29 to generate pulses that reset or start the clock and provide a straight lead to the last output of the clock. Prepare line B.

As the signal being detected by the energy sensor of pair A changes, the transmission peak of pair A shifts spectrally. Assume that the signal has already shifted its peak by = (Δλ) at some time before the second laser scan. When the second laser scan begins,
The output wavelength becomes λ1 again. Shortly after the start of the scan, the laser power is again at the first Δλ into the pair. However, since this wavelength does not coincide with the peak of analytical interferometer 30, no light is transmitted to photodetector 31 and the clock is not paused.

However, as the laser continues to scan, its output is the spectral position of the second transmission peak of A.

The above equation regarding the amplification factor U of the device of this embodiment -1 A2 + TAj + A, 1 is also the spectral position of the transmission peak of the 1 analysis interferometer 30, which is next to the peak located at λ2 spectrally. . Transmission is therefore made through analytical interferometer 30 and photodetector 31 generates a signal that pauses the clock. Even if the transmission peak of pair A shifts by only □(Δλ), the output of the combination of pair A and interferometer 30 will be such that the wavelength of the laser output is 12
+ -; a)'+aac 5 so 0 would not have occurred until the vector amplification was 100. The remainder of the second scan interval continues as described for the first RADE scan interval.

Re: Completion of the GL device requires special attention to the width of the band t4 of the optical fiber 24. The bandwidth must be high enough to preserve the narrowness of the transmission peak of the returning reflector pair. It should be noted that the optical demodulator can be used whenever it is desired to measure the spectral movement of the Fabry-Bello interferometer fringes, with or without the use of optical fibers. It is also recognized that the laser beam can first pass through the analytical Fabry-Perot interferometer and then be transmitted to the Fabry-Perot interferometer, one of whose intervals is to be measured. However, if an optical fiber is used to transmit the laser beam to the Fapley-Bello interferometer being measured, then if the laser beam is first passed to the analytical interferometer, then the beam is transferred from the analytical interferometer to the Fapley-Bello interferometer. It is necessary to select an optical fiber with low dispersion for transmission. This is because this beam has an additional amplitude time dependence as caused by the spectrally circular transmission of the analytical interferometer. Furthermore, the features of both the analytical interferometer 21 and the sensor interferometer are chosen such that even if there are no spectrally exactly matched transmission peaks, there is still only enough overlap to produce a significant combined output. Must. Finally, the example device produces an ambiguous output if the spectral shift of the transmission peak of the reflector pair is allowed to be greater than 1 Δλ or less than □Δλ.

Finally, it is specified that the electrical reference signal may be derived from the same signal that causes the laser to scan. The reference in the reference signal is that it must have a known position in time with respect to the position in time of any particular wavelength of the laser scan. In general, one criterion for proper laser scanning is that the scan interval must first be adjusted in time period to detect the highest frequency of oscillation of the temporal position of the output of the reflector pair and analytical interferometer combination. It must occur often enough and, secondly, the output wavelength of the scanning laser must be a known function of time.

To eliminate obscurity in excessive peak migration, the present invention employs an alternative analytical interferometer 308, illustrated in FIG.
Add. FIG. 17 is a schematic diagram of a subsystem that is replaced by the subsystem W surrounded by a broken line in FIG. 14. This additional analyzer 30B is configured to provide a lower magnification when used with the same protrusion of the reflector pair, for example, by a method. From the foregoing discussion, it can be seen that coupling lower amplification can give the transmission peak shift a higher threshold at which obscurity initially occurs. Using the formula °C to determine the amplification factor U, an apparatus using two analytical interferometers, each with a different amplification of the threshold value, is given by:

The first interferometer 30 may have a transmission peak of 5A=99 between λ1o and λ2 as in the previous embodiment of the detection device. The reflector pair may have the SRD -10 peak between λ1o and λ2o and the additional interferometer 30B may have the 5A-9 peak between λ1.
and λ2. It may be between. If, for example, time! If regulators 33 and 33B give analog outputs, then at a particular transition Δλ8R corresponding to pair A, the electrical output of regulator 33B at a time corresponding to pair A will be such that the voltage e
It will be.

e1=Δλ8RU1 (X■) where K is a constant (), is 5R=10 and 5A-91,: 101.
: Equal amplification factor or Δλ8Il) is the spectral shift of the peak in the region S of FIG. 15 corresponding to the 4th line A.

The output e of the demodulator 33 is as follows.

02- to Δλ5RU2 (XIv)-1
00KΔλ8R Here, 100 is 5R-10,! :5A-991. :j5
is the amplification coefficient U21).

Such a device can of course be expanded to include a large number of such analyzers with different amplifications, and can easily be expanded to include more beam splitters such as 127'.
may be added to split the output of the reflector pair between the analytical and interfering sides.

Note from the foregoing discussion that analytical interferometer 308 can begin to exhibit obscurity at spectral transitions smaller than 1Δλ. However, analyzer 30 produces significant output at spectral transitions of 1 Δλ or less, as previously discussed. One may therefore wish to add analytical interferometers that will provide either lower or higher amplification than the analytical interferometers already provided in one device.

A timer is an electrical device that performs two functions: First, it is a pulse from a photodetector that receives and analyzes electromagnetic radiation from a Fapley-Bello interferometer, referred to as an ANAL pulse, for example by its amplitude, frequency of vibration, or phase of vibration. Receiving additional pulses
The second step is to generate an electrical signal that includes, or conveys, the time taken by the user to take the signal.
It is to transmit to a specific output line or a specific group of output lines of the book. There are a number of electrical circuits that can accomplish this, one of which is schematically illustrated in FIG. Referring to FIG. 18, Ul and U2 are voltage comparators, e.g.
, U4 and U5 are counters, such as TexasInStrt++ component #74161, and U3 is a clock generator,
For example, part #74LS124 manufactured by Texas InS[rlJ110ntS, 1.16 is de+eux
, for example, Texas Instruments part #74155, LJ7. tJ8 and U9 are latches, e.g.
It is part #74175 manufactured by TS.

This circuit operates as follows. U1 and U21), the voltage comparators, operate to convert the reference pulse and the additional pulses to standard TTL-logic voltage levels for use in rectification. The spaced reference pulses are arranged such that the reference pulses, as driven by the clock generator U3, reset the counter U4, which is counting continuously at approximately 16 times the rate of the reference pulse repetition rate. to work. The output of the resulting counter (4) is a number that starts at vlo, where the reference pulse is taken, counts upwards, resets again with another reference pulse, and starts its counting anew when it reaches O. Meanwhile, Counter U5 is incremented each time a reference pulse is received. It is set to automatically return to O after counting the appropriate number of channels (3 in this case). ANAL
When a pulse is sent, it is sent via demux U 6 to the appropriate latch (U7.tJ8.or U9). The number at the output of the counter is latched into the appropriate channel latch and represents the time between the zeroing pulse and the ANΔ[pulse. The next ANAL pulse causes the next channel latch to store a number representing the time between these reference pulses and the ANAL pulse, and so on. Each time a new time count is latched, the trailing edge of the latch pulse signals the user that new data is available.

An improved optical fiber energy sensor and method of making the sensor is provided, as well as an improved optical fiber neck, which is particularly sensitive to stretch and compression due to the signal energy to be sensed.

[Brief explanation of the drawing]

1 is a greatly enlarged cross-sectional view of the single mode optical fiber; FIG. 2 is a greatly enlarged cross-sectional view of the etched single mode optical fiber of FIG. 1; and FIG. 3 is a greatly enlarged cross-sectional view of the single mode optical fiber of FIG. 4 is a greatly enlarged cross-sectional view of the large diameter fiber of FIG. 3 after being etched and coated, and FIG. 5 is a greatly enlarged cross-sectional view of the large diameter fiber of FIG. 6 is an end view of the illustrated acoustic energy sensor; FIG. 6 is a cross-sectional view taken along line 6-6 of the hemorrhoidal energy sensor of FIG. 5; and FIG. Figure 6? 8 is an enlarged illustration of a portion of an IW energy sensor, FIG. 8 is an end view of another acoustic energy sensor provided by the present invention, and FIG. 9 is an enlarged illustration of a portion of the acoustic sensor of FIG. 10 is an explanatory diagram of a mold and single mode optical fiber for manufacturing an optical fiber energy sensor, and FIG. 11 is a diagram of only the mold of FIG. 10 after being coated with a protective material. 12 is an illustration of the mold and single mode optical fiber of FIG. 10 after etching and coating, and FIG. 13 is an end view of a collapsible mold that can be used in the etching process. , 14th
The figure is a schematic diagram of an optical demodulator which is an application example using the present invention, FIG. 15 is an explanatory diagram of typical transmission of the pair 25 of reflectors in FIG. 14, and FIG. FIG. 17 is a graph of the laser output suitable for use in the optical demodulator of FIG. 14, and FIG. FIG. 18 is a schematic diagram of the time demodulation circuit of one embodiment exemplarily shown in FIGS. 14 and 17. Explanation of symbols 1-1...Core, 2-1...Glass clad, 6.
...Skeleton, 7.7-9...Flexible thin film, 8.8-9
．． 24...Single mode optical fiber, 8', 201
-9... Reinforced strut, 9.16'... Space, 1
6...Storage, 10.15...Opening, 11...Protrusion, 12...Bladder 14...Tightening with ring, 17.
...End cap, 202-9...Inner cylinder, 257
...Cylinder, 18'18-12...Type, 19'...
Spiral groove, 125...hole, 126...opening, 25.
...Pair of Bragg reflectors of limited length, 26...
Wavelength scanning laser, 127°127'...Beam splitter-28...Reference Fabry-Perot interferometer, 29.
31,318...Photodetector, 30.30B...Analytical Fapley-Perot interferometer, 33.33B...Time demodulator. Agent Asamura Akira F
IG/. FIG 2゜FIG 3゜FIG, 4゜FIG, 5 2゜FIG, 10゜FIG, 12゜F/to, /J. FIG/? FIG, /6゜Shoulder

Claims (38)

[Claims] (1) A method for detecting acoustic signals in a viscous medium, comprising: placing a flexible thin film in contact with the viscous medium; burying an optical fiber in the flexible thin film; and connecting an end to the thin film. attaching a cap to create a physically enclosed space within the flexible membrane and the end cap; and providing an opening coupling the enclosed space to a space outside the flexible membrane; sizing and shaping said aperture to adjust the rate at which a viscous substance can flow through said aperture in response to a fluid pressure difference between an enclosed space and a space external to said flexible membrane; The acoustic signal detection method characterized in that it includes the following steps. (2) Claim (1) further includes adding a flexible bladder to isolate the viscous material outside the flexible sleeve from the viscous material inside the portion of the enclosed space. The acoustic signal detection method, further comprising: (3) The acoustic device according to claim 1, further comprising attaching reinforcing strands parallel to the axis of the flexible membrane to increase the longitudinal strength of the flexible membrane. Signal detection method. (4) In claim (1), the amount of phase modulation of the acoustic signal is increased by etching an optical fiber in place of at least a portion of the optical fiber embedded in the flexible thin film. The acoustic signal detection method characterized in that the method includes: (5) The acoustic signal detection method according to claim (4), wherein the etched optical fiber is an etched single mode optical fiber. (6) In claim (2), resisting radial expansion or compression of the flexible thin film by a material in the surrounding space, including filling a portion of the surrounding space with a viscous flexible material. The method for detecting an acoustic signal, comprising: reducing the (7) A method of sensing an acoustic signal, comprising: forming a flexible thin film; burying an optical fiber in the thin film; placing the thin film in a viscous medium to which an acoustic signal is applied; fixing a flexible membrane to a rigid cylinder, reducing its diameter at its external surface, and radially compressing or stretching said flexible membrane around a portion of the cylinder having the reduced diameter. The method for detecting an acoustic signal, comprising: stretching or compressing the optical fiber in a longitudinal direction using an acoustic signal. (8) Claim (7) further includes increasing the longitudinal strength of the flexible membrane by securing reinforcing strands generally parallel to the axis of the flexible membrane. The acoustic signal detection method is characterized by: (9) Claim (7), including etching at least a portion of the optical fiber embedded in the flexible thin film to increase the amount by which the optical fiber stretches or contracts in response to an acoustic signal. The acoustic signal detection method is characterized in that: (10) The acoustic signal detection method according to claim (9), wherein the etched optical fiber is an etched single mode fiber. (11) In claim (7), an enclosed space between the inner surface of the flexible thin film and the outer surface of the skeleton where the diameter is reduced is filled with a viscous flexible substance. The method of detecting an acoustic signal further comprising increasing the amount of radial compression or expansion of the flexible membrane in response to the acoustic signal. (12) In claim (11), the flexible thin film responds to changes in low frequency pressure by isolating a tank of viscous flexible material from a viscous material outside the flexible sleeve. further comprising reducing radial expansion or contraction and causing material in the tank to flow through an equalization aperture into the enclosed space, the size and shape of the equalization aperture being selected to adjust the flow rate of the tank material; The acoustic signal detection method, characterized in that: (13) Claim (12) includes maintaining the position of the flexible bladder with respect to the cylinder by forming a protrusion inside the cylinder and expanding the flexible bladder around the protrusion. The acoustic signal detection method is characterized in that: (14) In claim (12), the amount of radial expansion or contraction of the flexible sleeve in response to low frequencies of changes in pressure of the fluid in the medium containing the acoustic signal being sensed; viscous material external to the viscous sleeve is further reduced through an opening in the end cap and into an additional space on a side of the bladder opposite to the side surrounding the reservoir of viscous flexible material; The acoustic signal detection method is characterized in that the additional space is physically surrounded, and the flow rate of the viscous substance inside and outside the additional space is adjusted by the size and shape of the opening. . (15) A method for detecting acoustic signals in a medium, the method comprising: forming a flexible thin film in which an optical fiber is embedded; and forming an inner surface of the flexible thin film from an elastic flexible substance. and radially expanding or compressing the flexible membrane with an acoustic signal to longitudinally stretch or compress the optical fiber. A method for detecting acoustic signals in the medium. (16) In claim (15), the longitudinal strength of the elastic flexible inner cylinder is increased by attaching reinforcing strands within and generally parallel to the elastic flexible inner cylinder. A method for detecting acoustic signals in the medium, characterized in that the method comprises increasing the number of acoustic signals in the medium. (17) Claim (15) further includes increasing the longitudinal strength of the flexible membrane by attaching the membrane reinforcing strands generally parallel to the axis of the flexible membrane. A method for detecting an acoustic signal in the medium as described above. (18) In claim (15), the amount of elongation or compression of the optical fiber is controlled by embedding an etched optical fiber in the thin film as at least a portion of the optical fiber embedded in the flexible thin film. A method for detecting acoustic signals in the medium, characterized in that the method comprises increasing the number of acoustic signals in the medium. (19) The method for detecting an acoustic signal in the medium according to claim (18), wherein the etched optical fiber is an etched single mode optical fiber. (20) A device for sensing an acoustic signal, the device comprising: a flexible thin film in which an optical fiber is embedded; an end cap providing an enclosed space; and an opening in the end cap connecting the enclosed space to a space outside the flexible membrane, the dimensions of the opening allowing viscous flow through the opening. The acoustic signal sensing device is characterized in that the velocity of the substance is adjusted according to the difference in fluid pressure between the surrounding space and the space outside the flexible thin film. (21) The acoustic signal sensing device according to claim (20), further comprising a flexible bladder that separates the substance outside the flexible thin film from a part of the surrounding space. . (22) Claim (20), further comprising reinforcing strands attached parallel to the axis of the flexible thin film, thereby increasing the longitudinal strength of the flexible thin film. The acoustic signal sensing device. (23) The acoustic signal sensing device according to claim (20), wherein at least a portion of the optical fiber embedded in the flexible thin film wall is an etched optical fiber. (24) The acoustic signal sensing device according to claim 23, wherein at least a portion of the etched optical fiber comprises an etched single mode fiber. (25) The acoustic signal sensing device according to claim (21), wherein a portion of the surrounding space is filled with a viscous and flexible substance. (26) A device for sensing acoustic signals comprising: a rigid cylindrical skeleton with a portion having a reduced diameter; and a flexible cylindrical skeleton embedded with an optical fiber surrounding the portion of the skeleton having a reduced diameter. a membrane; and means for securing the flexible membrane to the framework to physically enclose the space between the interior surface of the flexible membrane and the exterior surface of the framework. The acoustic signal sensing device. 27. The acoustic signal sensing device of claim 26, further comprising a reinforcing strand fixed generally parallel to the axis of the flexible membrane. (28) The acoustic signal sensing device according to claim 26, wherein at least a portion of the optical fiber embedded in the flexible thin film is an etched optical fiber. (29) The acoustic signal sensing device according to claim 28, wherein at least a portion of the etched optical fiber comprises an etched single mode optical fiber. (30) The acoustic signal according to claim (26), characterized in that an enclosed space between the inner surface of the flexible thin film and the outer surface of the skeleton is filled with a viscous and flexible substance. Sensing device. (31) Claim 30, further comprising: a flexible bladder that physically separates a reservoir of said viscous flexible material from a material external to said flexible thin film; and said viscous flexible material. The acoustic signal sensing device further comprises a pressure equalization hole that allows a substance to flow between the enclosure containing the additional viscous flexible substance and the reservoir. (32) The acoustic signal detection device according to claim (31), characterized in that the framework is provided with a protrusion that can hold the flexible bladder and spread the bladder around it. (33) Claim 31, further comprising: at least one end cap forming an additional space on a side of the bladder opposite to a side surrounding the tank of viscous flexible material; a hole in the end cap that joins a space outside the flexible membrane, the diameter of the hole being sized to connect the space between the additional space and the space outside the flexible membrane. The acoustic signal detection device is defined to adjust the flow rate of the acoustic signal. (34) A device for detecting an acoustic signal, comprising: a flexible thin film; an optical fiber embedded in the flexible thin film; and an elastic flexible wire in contact with an inner surface of the flexible thin film. The acoustic signal sensing device comprising: an inner cylinder; (35) According to claim (34), reinforcing strands are arranged generally parallel to and placed inside the flexible cylinder so as to increase longitudinal strength of the elastic flexible inner cylinder. The acoustic signal detection device further comprises: (36) In claim (34), reinforcing strands and reinforcing fibers arranged generally parallel to the axis of the flexible thin film are fixed to the flexible thin film to increase its longitudinal strength. The acoustic signal detection device further comprises means for making the above sound signal detecting device. (37) The acoustic signal detection device according to claim 34, wherein at least a portion of the optical fiber embedded within the flexible sleeve is an etched optical fiber. (38) The acoustic signal detection device according to claim (37), wherein at least a portion of the etched optical fiber is an etched single mode fiber.