RU2107282C1 - Fiber-optic interferometer for underwater investigations - Google Patents

Abstract

FIELD: engineering physics; geophysics for measuring hydroacoustic and hydrophysical parameters in natural water reservoir. SUBSTANCE: acoustically sensitive shell is removed from interferometer object coil and the latter is divided into two spatially isolated sections spaced through certain distance apart. Such interferometer makes it possible to discriminate signal proportional to pulse amplitude of investigated medium temperature by means of correlator when it is towed in this medium at known speed and also to measure sound pressure level. Second fiber-optic interferometer, together with main one, provides for additional measurement of pulse amplitude of salinity and sound pressure gradient when its fiber coils are arranged on substrate possessing pressure gradient in flow. EFFECT: enlarged functional capabilities. 6 cl, 3 dwg

Description

 The invention relates to technical physics and can be used in hydrophysics to measure hydroacoustic and hydrological parameters in a natural reservoir.

 At present, the Sagnac fiber-optic interferometer (WIPO), previously used only as a detector of angular velocity in inertial space, has found application in hydroacoustics [1].

 The use of WIPO as a transducer of hydroacoustic parameters is possible under two conditions: 1) the disturbance acts on the fiber ring of the interferometer asymmetrically relative to its middle and 2) the disturbance changes over time. Moreover, in contrast to the traditionally used interferometers, WIPO exhibits an increase in sensitivity with an increase in the frequency of change in the amplitude of the disturbance.

 Known WIPO, made in the form of an optically matched source of coherent light, a fiber ring, a phase modulator (phase shifting device) and a photodetector [2]. A part of the fiber ring of the known WIPO is folded into a support fiber coil, and the other part into an object coil. In this case, an acoustically sensitive sheath is removed from one of the fiber parts and makes it insensitive to the effects of acoustic waves.

 The disadvantage of the analogue [2] is its insufficiently high sensitivity to the useful signal due to the large influence of extraneous interference.

 WIPO has greater sensitivity for marine research of a differential type, made on the basis of a linear 3x3 coupler [3], adopted as a prototype.

 The prototype contains a coherent light source optically matched into a single-ring interferometer, a linear 3x3 coupler, a reference and object fiber coils, and two photodetectors connected by outputs to the inputs of a differential amplifier, as well as a recording system.

 At the output of the differential amplifier of the well-known WIPO, the noise is subtracted, and the useful signals are added, which increases the sensitivity of the device.

 The disadvantage of the prototype is the inability to use it to measure such parameters of the marine environment as temperature pulsations, salinity pulsations and sound pressure gradients.

 The technical result obtained from the implementation of the invention is the expansion of the operational capabilities of WIPO by measuring additional hydroacoustic and hydrological parameters of the marine environment: temperature pulsations, ripples in salinity and sound pressure gradient.

 This technical result is obtained due to the fact that in the well-known WIPO, which contains a coherent light source optically matched into a single-ring interferometer, a linear 3x3 coupler, support and object fiber coils and two photodetectors connected to the inputs of the differential amplifier, as well as a recording system including a recorder sound pressure level, additionally contains two analog-to-digital converters, a correlator, a scaling device and a subtracting device, and register The system also introduced a temperature pulsation recorder, while the output of the differential amplifier is connected through a series-connected first analog-to-digital converter and a scaling device to the first input of the subtractor, and through the series-connected correlator and the second analog-to-digital converter to the second input of the subtractor, the output which is connected to the sound pressure level recorder, and the output of the second analog-to-digital converter is connected to the register an array of temperature pulsations, the object fiber coil being made of fiber with an acoustically sensitive shell removed in the form of two identical spatially separated sections.

 In addition, WIPO may contain a second fiber-optic interferometer, the subject and support fiber coils of which are located coaxially along a substrate having a pressure gradient in the stream, with a voltage amplifier, a third analog-to-digital converter, a second and third subtracting devices, and a differentiating device and a second multiplying device, and a sound velocity gradient recorder and a salinity ripple recorder are additionally introduced into the recording system, and the photopilot output the receiver of the additional fiber-optic interferometer through a series-connected voltage amplifier and a third analog-to-digital converter is connected to the first input of the second subtractor, the second input of which is connected to the output of the second analog-to-digital converter, and the output to the first input of the third subtractor, the output of which is connected to the salinity ripple recorder.

 The WIPO substrate can be made cylindrical in shape with a poorly streamlined nose, with both fiber coils of the main interferometer located at a distance of more than eight diameters from the nose of the substrate.

 The interferometer fiber coils may be flush with the surface of the substrate.

 WIPO in a support or subject coil may comprise a phase shifting device.

 WIPO in the support coil may include a frequency-shifting device.

 In FIG. 1 is an optical diagram of WIPO; figure 2 - the structural part of the optical part of the device; figure 3 is an electronic functional diagram of the device.

 WIPO for underwater research contains (Fig. 1) a coherent light source 1 optically matched into a single-ring interferometer, a linear 3x3 coupler 2, support and object fiber coils 3 and 4. Moreover, the object fiber coil 4 is made of fiber with an acoustically sensitive shell removed (as in analogue [2]) in the form of two identical spatially spaced sections 5 and 6. There are also two photodetectors 7 and 8 located at the output of WIPO.

 In one of the arms of the interferometer (for example, in the object fiber coil 4), a phase-shifting device 9 can be installed. In an alternative embodiment, a frequency-shifting device (not shown) can be installed in the reference arm of the interferometer (reference fiber coil 3). In the first case, WIPO operates on a homodyne principle, and secondly, on a heterodyne principle.

 Fiber coils 3, ..., 6 can be mounted coaxially along a cylindrical substrate 10 (Fig. 2) with a poorly streamlined nose 11.

 On the nose 11 of the substrate 10 are installed support and subject fiber coils 12 and 13 of the second interferometer assembled according to any known scheme [1]. In this case, the fiber coils 3, ..., 6 of the main interferometer are located on that part of the substrate 10, in which there is no velocity gradient in the flow along the substrate. All fiber spools are flush with the surface of the substrate.

In FIG. Figure 2 shows an embodiment of the device in which all fiber coils are coaxial and flush with the surface of the substrate. Moreover, parts 5 and 6 of the object fiber coil 4 of the first interferometer are located at a distance ΔX ₁ and the fiber coils 12 and 13 of the second interferometer are at a distance ΔX ₂ along the substrate.

 The substrate 10 is attached to the carrier (not shown in the drawing).

 The WIPO electronic circuit (Fig. 3) includes a differential amplifier 14, the inputs of which are connected to the outputs of the photodetectors 7 and 8 (Fig. 1) and a voltage amplifier 15 connected to the output of the photodetector of the second interferometer (this photodetector is not shown in the drawing). There are also analog-to-digital converters (ADCs) 16-18, correlator 19, two multiplying devices 20 and 21, three subtracting devices 22-24, a differentiating device 25 and a recording system 26, including recorders 27-30, respectively, of temperature pulsations, sound pressure level, salinity pulsations and sound pressure gradient.

 The electrical connection diagram is shown in FIG. 3 and is described in the description of the invention. All electrical units are located inside or on board the carrier.

 WIPO works as follows.

 Place the underwater part of the device (Fig. 2) at a given depth of the natural reservoir.

 The source of coherent light 1 (as well as the light source of the second interferometer, not shown in the drawing) is turned on. The initial phase difference of the interfering rays is adjusted using the phase shifting device 9 by an amount equal to π / 2. A similar preparation for measurements is carried out with an auxiliary interferometer.

The device is towed at a known speed using a carrier (not shown in the drawing) at a given course. Since the reference fiber coil 3 is sensitive to temperature pulsations and sound pressure at the same time, and the object 4 coil is sensitive only to temperature pulsations, signals proportional to sound pressure level ΔP and temperature pulsation amplitude ΔT will be present at the output of photodetectors 7 and 8. Moreover, the latter appear at the outputs of the photodetectors 7 and 8 after a time t = ΔX ₁ where ΔX ₁ is the distance between the spatially spaced sections 5 and 6 of the object fiber coil. This makes it possible to filter this signal with the help of a correlator. At the output of the differential amplifier 14 there is a signal filtered out from interference. This signal is supplied to the correlator 19, tuned to the delay time t, to select a signal proportional to ΔT at its output. . The same signal is also sent to the ADC 16, then adjusted in the scaling device 20 to the desired value. Then it is fed to the first input of the subtracting device 22, the second input of which is sent after the ADC 18, a signal proportional to the temperature fluctuations ΔT. . The same signal is recorded by the temperature pulsation recorder 27.

 The output of the subtractor 22 is allocated a signal proportional to the sound pressure level ΔP recorded by the recorder 28.

 The implementation of the second claim makes it possible to measure two more hydrophysical parameters of the marine environment: ripples of salinity and the gradient of sound pressure.

 Moreover, since the fiber coils 12 and 13 of the auxiliary interferometer are located along the surface of the substrate 10, which has a velocity gradient in the flow, a signal proportional to the pressure fluctuations Δρv will be present at the output of the interferometer, where Δρ is the amplitude of fluctuations in the density of the marine environment. And the magnitude of the latter is proportional to the amplitude of the pulsations of the temperature ΔT and salinity ΔS.

In addition, the fiber coils of the auxiliary interferometer are sensitive to the sound pressure gradient ΔP / ΔX ₂ .

 From the output of the photodetector of the auxiliary interferometer, the signal is directed through the voltage amplifier 15 and the ADC 18 to the first input of the subtractor 23, the second input of which receives a signal from the ADC 17 proportional to ΔT.

 The signal from the output of the subtractor 22, proportional to ΔP, is sent to a differentiating device 25, and then to a multiplying device 21, where the derivative of the sound pressure level is adjusted (taking into account the speed of sound and towing speed) to the value of the sound pressure gradient recorded by the recorder 30. In addition , the magnitude of the sound pressure gradient is directed to the second input of the subtractor 24, the first input of which from the subtractor 23 is supplied with a signal proportional to the amplitude of the pulsations with laziness gradient ΔS and sound pressure. The output of the subtractor 24 is allocated a signal proportional to ΔS, registered by the registrar 29.

 Thus, the proposed interferometer allows you to simultaneously measure four hydrophysical parameters of the marine environment: ripple, temperature, ripple salinity, sound pressure level and gradient of sound pressure. What confirms the achievement of the technical result.

Claims (6)

 1. Fiber-optic Sagnac interferometer for underwater research, containing a coherent light source optically matched to a single-ring interferometer, a linear 3 x 3 coupler, a reference and object fiber coils and two photodetectors connected to the inputs of the differential amplifier, as well as a recording system including a recorder sound pressure level, characterized in that it further comprises two analog-to-digital converters, a correlator, a scaling device and a subtracting device property, and a temperature pulsation recorder is additionally introduced into the recording system, while the output of the differential amplifier is connected through a series-connected first analog-to-digital converter and a scaling device to the first input of the subtractor, and through a series-connected correlator and a second analog-to-digital converter to the second input a subtracting device, the output of which is connected to the sound pressure level recorder, and the output of the second analog-to-digital converter connected to a recorder of temperature fluctuations, the objective optic coil made of fibers with removed acoustically sensitive sheath in the form of two identical spatially separated portions.  2. The interferometer according to claim 1, characterized in that it further comprises a second fiber-optic interferometer, the subject and reference fiber coils of which are located coaxially along a substrate having a pressure gradient in the stream, while a voltage amplifier and a third analog-to-digital converter are additionally introduced, the second and third subtracting devices, a differentiating device and a second scaling device, and a sound velocity gradient recorder and a recorder are additionally introduced into the recording system salinity, and the output of the photodetector of an additional fiber-optic interferometer through a series-connected voltage amplifier and a third analog-to-digital converter is connected to the first input of the second subtractor, the second input of which is connected to the output of the second analog-to-digital converter, and the output to the first input of the third subtractor a device whose output is connected to a salinity ripple recorder, and the output of the first subtracting device is additionally connected through the serial a differentiating device and a second scaling device are connected to the sound velocity gradient recorder.  3. The interferometer according to claims 1 and 2, characterized in that the substrate having a pressure gradient in the flow is made in the form of a cylinder with a nozzle fixed to the end face, while both fiber coils of the main interferometer are located at a distance exceeding eight of its diameters .  4. The interferometer according to claims 1 and 2, characterized in that all the fiber coils are flush with the surface of the substrate.  5. The interferometer according to claim 1, characterized in that a phase-shifting device is introduced into the support or object coil.  6. The interferometer according to claim 1, characterized in that a frequency-shifting device is introduced into the support coil.

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