Optical fiber hydrophone based on adaptive differential weak value measurement technology

Abstract

The invention relates to the technical field of quantum precision measurement, in particular to an optical fiber hydrophone based on an adaptive differential weak value measurement technology, which comprises a light-emitting module, a front selection state module, a weak coupling module and a rear selection state module, and is characterized in that the light-emitting module is connected with the front selection state module, and the rear selection state module is connected with the weak coupling module; the output end of the front selection state module is connected with the input end of the weak coupling module through the phase modulation unit and the first partial division unit, the output end of the weak coupling module is connected with the input end of the rear selection state module through the second partial division unit, and the output end of the rear selection state module is connected with the phase modulation unit. Through a push-pull probe structure, differential signal processing and an adaptive modulation process, high-sensitivity and wide-dynamic-range underwater acoustic signal detection is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum precision measurement, and particularly to an optical fiber hydrophone based on an adaptive differential weak value measurement technique, which is applicable to high-precision detection of underwater acoustic signals in fields such as marine geological exploration, seismic detection, and military anti-submarine operations. Background Technique

[0002] Underwater acoustic detection technology, as an important means for exploring the ocean, is mainly used to capture underwater acoustic wave signals and plays an irreplaceable role in civil and military fields such as marine geology and mineral resource exploration, seismic detection and research, and military anti-submarine operations. Currently, underwater acoustic detection technology is mainly divided into two categories: traditional piezoelectric hydrophones and optical fiber hydrophones. Traditional piezoelectric hydrophones are based on the piezoelectric effect and convert acoustic pressure signals into electrical signals. They have the advantages of simple structure and low cost, but their sensitivity is limited by material properties and they are vulnerable to electromagnetic interference in complex marine environments, which restricts their application in high-precision detection. Optical fiber hydrophones, on the other hand, use optical principles to sense acoustic pressure signals by detecting changes in optical signals. They have advantages such as anti-electromagnetic interference, high sensitivity, and excellent environmental adaptability, and have gradually become a research hotspot in the field of underwater acoustic detection.

[0003] However, the complexity and diversity of the marine environment pose severe challenges to underwater acoustic detection technology. Environmental factors such as deep-sea high pressure, sudden temperature changes, and salinity fluctuations will significantly affect the performance of hydrophones, resulting in a decrease in their sensitivity and insufficient stability, thereby affecting the accuracy of detection results. In addition, key acoustic signals in the ocean, such as submarine seismic waves, low-frequency sonars of large marine organisms, and long-distance underwater communication carriers, are mainly concentrated in the low-frequency band below 50 Hz. The sensitivity of traditional hydrophones significantly decreases in the low-frequency band, making it difficult to effectively capture weak signals, which severely restricts their effectiveness in practical applications. With the increasing demands for marine resource development, environmental monitoring, and military anti-submarine operations, there is an urgent need to develop new underwater acoustic detection technologies with higher sensitivity, stronger stability, and a wider detection range.

[0004] In recent years, the rapid development of quantum measurement technology has provided new solutions for high-precision detection. Quantum measurement technology utilizes the characteristics of superposition and entanglement of quantum states to achieve detection accuracy beyond the classical measurement limit. The weak value amplification technology based on quantum measurement can effectively amplify weak signals by coupling weak signals to specific degrees of freedom of quantum states without significantly increasing the system noise, thereby improving detection sensitivity. However, the effective detection range of the standard weak value amplification technology is relatively small, which restricts its popularization in practical applications. Therefore, based on the standard weak measurement technology, the present invention combines differential detection and adaptive modulation to design an optical fiber hydrophone based on an adaptive differential weak value measurement technique, aiming to effectively improve the sensitivity, detection range, and stability of underwater acoustic signal detection. Summary of the Invention

[0005] The object of the present invention is to provide an optical fiber hydrophone based on the adaptive differential weak value measurement technology to solve the problems of insufficient sound pressure sensitivity, high equivalent noise pressure, and limited dynamic range in the prior art. Through a push-pull probe structure, differential signal processing, and an adaptive modulation process, the detection of underwater acoustic signals with high sensitivity and wide dynamic range can be realized.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] An optical fiber hydrophone based on the adaptive differential weak value measurement technology, comprising: a light emitting module, a pre-selection state module, a weak coupling module, and a post-selection state module. Among them, the light emitting module is connected to the pre-selection state module, the output end of the pre-selection state module is connected to the input end of the weak coupling module through a phase modulation unit and a first beam splitting unit, the output end of the weak coupling module is connected to the input end of the post-selection state module through a second beam splitting unit, and the output end of the post-selection state module is connected to the phase modulation unit.

[0008] Optionally, the light emitting module includes a laser, and the laser is used to emit a continuous light beam.

[0009] Optionally, the pre-selection state module includes a first half-wave plate and a first polarizer. Among them, the first half-wave plate is arranged in the output optical path of the light emitting module, the incident end of the first polarizer is butted against the first half-wave plate, and the output end of the first polarizer is connected to the phase modulation unit.

[0010] Optionally, the phase modulation unit includes a Soleil-Babinet compensator SBC, the first beam splitting unit includes a first polarization beam splitter, a second half-wave plate, a third half-wave plate, a first FC type optical fiber interface, and a second FC type optical fiber interface. The Soleil-Babinet compensator SBC is connected to the first polarization beam splitter. The first polarization beam splitter is sequentially connected to the second half-wave plate and the first FC type optical fiber interface as a first beam splitting branch. The first polarization beam splitter is sequentially connected to the third half-wave plate and the second FC type optical fiber interface as a second beam splitting branch;

[0011] The second beam splitting unit includes a second polarization beam splitter, a fifth half-wave plate, a fourth half-wave plate, a fourth FC type optical fiber interface, and a third FC type optical fiber interface. The third FC type optical fiber interface and the fourth half-wave plate are sequentially connected and input to the second polarization beam splitter as a third beam splitting branch. The fourth FC type optical fiber interface and the fifth half-wave plate are sequentially connected and input to the second polarization beam splitter as a fourth beam splitting branch.

[0012] Optionally, the weak coupling module includes a push-pull sensing probe. The input ends of the push-pull sensing probe are respectively connected to the first optical splitting branch and the second optical splitting branch, and the output ends of the push-pull sensing probe are respectively connected to the third optical splitting branch and the fourth optical splitting branch.

[0013] Optionally, the post-selection state module includes a third optical splitting unit, a positive post-selection branch, a negative post-selection branch, and an optical intensity contrast verification unit. Among them, the third optical splitting unit is respectively connected to the positive post-selection branch and the negative post-selection branch. Both the positive post-selection branch and the negative post-selection branch are connected to the optical intensity contrast verification unit, and the optical intensity contrast verification unit is connected to the phase modulation unit.

[0014] Optionally, the third optical splitting unit includes a 50:50 beam splitter. The positive post-selection branch includes a first quarter-wave plate, a second polarizer, a fifth FC-type optical fiber interface, and a first optical intensity detector PD connected in sequence. The negative post-selection branch includes a second quarter-wave plate, a third polarizer, a sixth FC-type optical fiber interface, and a second optical intensity detector PD connected in sequence;

[0015] The input ends of the first quarter-wave plate and the second quarter-wave plate are both connected to the output end of the 50:50 beam splitter, and the output ends of the first optical intensity detector PD and the second optical intensity detector PD are both connected to the optical intensity contrast verification unit.

[0016] Optionally, the transmission axis of the second polarizer forms an angle of +φ with the transmission axis of the first polarizer, and the transmission axis of the third polarizer forms an angle of -φ with the transmission axis of the first polarizer.

[0017] The beneficial effects of the present invention are as follows:

[0018] The fiber optic hydrophone based on the adaptive differential weak value measurement technology provided by the present invention improves the acoustic pressure sensitivity by designing a push-pull probe structure and utilizing the opposite deformation of the double cylinders; combined with the differential weak value measurement scheme, through the differential processing of the positive and negative post-selection optical intensities, the equivalent noise pressure is significantly reduced, and the detection ability for weak acoustic wave signals is enhanced; at the same time, an adaptive modulation process is introduced, and the post-selection angle and modulation phase are adjusted in real-time feedback according to the optical intensity contrast, solving the problem that it is difficult to balance the high measurement sensitivity and wide dynamic range of traditional hydrophones. The fiber optic hydrophone based on the adaptive differential weak value measurement technology provided by the present invention is applicable to high-precision detection of underwater acoustic signals in the fields of marine geological exploration, seismic detection, military anti-submarine, etc. Description of the Drawings

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for use in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0020] Figure 1 Schematic diagram of a fiber optic hydrophone structure based on the adaptive differential weak value measurement technology according to an embodiment of the present invention;

[0021] Figure 2 Principle diagram of weak value measurement and signal processing according to an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of the weak coupling module structure according to an embodiment of the present invention;

[0023] Among them, 1 is a laser, 2 is a first half-wave plate, 3 is a first polarizer, 4 is a Soleil-Babinet compensator SBC, 5 is a first polarization beam splitter, 6 is a second half-wave plate, 7 is a third half-wave plate, 8 is a first FC type fiber optic interface, 9 is a second FC type fiber optic interface, 10 is a push-pull probe, 11 is a third FC type fiber optic interface, 12 is a fourth FC type fiber optic interface, 13 is a fourth half-wave plate, 14 is a fifth half-wave plate, 15 is a second polarization beam splitter, 16 is a 50:50 beam splitter, 17 is a first quarter-wave plate, 18 is a second quarter-wave plate, 19 is a second polarizer, 20 is a third polarizer, 21 is a fifth FC type fiber optic interface, 22 is a sixth FC type fiber optic interface, 23 is a first photodetector PD, 24 is a second photodetector PD, and 25 is a computer. Specific implementation manner

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0025] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0026] This embodiment provides a fiber optic hydrophone based on the adaptive differential weak value measurement technology, as Figure 1As shown in the figure, it includes: a light-emitting module, a pre-selection state module, a weak coupling module, and a post-selection state module. Among them, the light-emitting module is connected to the pre-selection state module. The output end of the pre-selection state module is connected to the input end of the weak coupling module through a phase modulation unit and a first beam splitting unit. The output end of the weak coupling module is connected to the input end of the post-selection state module through a second beam splitting unit. The output end of the post-selection state module is connected to the phase modulation unit.

[0027] Specifically, in this embodiment, by designing a push-pull probe structure, the acoustic pressure sensitivity is improved by using the opposite deformation of the double cylinders; combined with the differential weak value measurement scheme, through the differential processing of the positive and negative post-selection light intensities, the equivalent noise pressure is significantly reduced, and the detection ability of weak acoustic wave signals is enhanced; at the same time, an adaptive modulation process is introduced, and the post-selection angle and modulation phase are adjusted in real-time according to the light intensity contrast, solving the problem that it is difficult to balance the high measurement sensitivity and wide dynamic range of traditional hydrophones.

[0028] The fiber optic hydrophone in this embodiment is based on the weak measurement theory. The weak measurement theory includes three processes: pre-selection, the coupling of the system and the pointer, and post-selection. In the weak measurement theory, the coupling strength between the system and the pointer is weak, which is represented by the unitary operator as where U represents the unitary transformation operator, is the observable of the system, is the operator acting on the pointer, g represents the coupling strength, exp(·) represents the exponential function of e, and i represents the imaginary unit. Assume that the pre-selection state of the system is |ψ i >, and the post-selection is performed on the measurement result. The post-selection state is |ψ f >, which is almost orthogonal to the pre-selection state |ψ i >. Therefore, a certain physical quantity to be measured is related to the weak value, and the weak value can be expressed as:

[0029]

[0030] The larger the weak value, the higher the magnification of the physical quantity to be measured. It can be seen from Equation (1) that the more orthogonal the pre-selection state and the post-selection state are, the smaller the denominator is, and the larger the weak value is. Based on the differential weak measurement theory, the present invention realizes maintaining high sensitivity while expanding the dynamic range of the fiber optic hydrophone by introducing an adaptive feedback modulation process and using the total post-selection light intensity as the pointer. The weak value measurement and signal processing principle in this embodiment is as Figure 2 shown. The initial state of the pointer is expressed as |ψ pi >, the pre-selection state of the system is expressed as |ψ si >. Through the weak coupling effect, the initial joint state of the pointer and the system evolves under the action of the evolution operator U. Positive and negative post-selections are performed on the system, and the total system evolution state is projected onto the post-selection state |ψ sf± >, the post - selected light intensity I can be obtained through the pointer final state f ± , and finally the light intensity contrast η is calculated.

[0031] Furthermore, the light - emitting module includes a laser 1, and the laser 1 is used to emit a continuous light beam.

[0032] Taking the continuous light with a central wavelength λ0 = 1550nm emitted by the laser 1 as the light source, the initial state of the incident light is:

[0033] |ψ pi > = ∫dωf(ω)|ω> (2);

[0034] where, |ψ pi > represents the initial state vector of the incident light, that is, the pointer state, |ω> represents the frequency state vector, f(ω) is a Gaussian - type wave function in the frequency domain, expressed as f(ω)=(2πσ 2 ) -1 / 4 exp[-(ω - ω0) 2 / 4σ 2 , ω represents the initial light frequency, ω0 represents the central frequency corresponding to the central wavelength of the initial light, σ represents the spectral width of the initial light, and exp[·] represents the natural logarithm.

[0035] Furthermore, the pre - selected state module includes a first half - wave plate 2 and a first polarizer 3. Among them, the first half - wave plate 2 is arranged in the output optical path of the light - emitting module, the incident end of the first polarizer 3 is docked with the first half - wave plate 2, and the output end of the first polarizer 3 is connected to the phase modulation unit.

[0036] Specifically, in this embodiment, the pre - selected state module is used to obtain the pre - selected state of the incident light. The light beam enters the input end of the first polarizer 3 through the first half - wave plate 2. The output end of the first polarizer 3 is connected to the phase modulation unit. The transmission axis of the first polarizer 3 is placed in the 45° direction to generate 45° linearly polarized light. In order to obtain higher precision, the incident light first passes through the first half - wave plate 2, and the intensity of the incident light can be adjusted by adjusting the placement angle of the first half - wave plate 2, and then passes through the first polarizer 3 for pre - selection. The pre - selected state |ψ si > is:

[0037]

[0038] where, |H> represents the horizontal polarization state of the photon, and |V> represents the vertical polarization state of the photon.

[0039] Therefore, the initial system - pointer joint state |ψ spi > is:

[0040]

[0041] Among them, |ψ pi > represents the initial state vector of the incident light, represents the direct product.

[0042] Further, the phase modulation unit includes a Soleil - Babinet compensator SBC4, and the first beam splitting unit includes a first polarization beam splitter 5, a second half - wave plate 6, a third half - wave plate 7, a first FC - type optical fiber interface 8, and a second FC - type optical fiber interface 9. The Soleil - Babinet compensator SBC4 is connected to the first polarization beam splitter 5. The first polarization beam splitter 5 is sequentially connected to the second half - wave plate 6 and the first FC - type optical fiber interface 8 as the first beam splitting branch, and the first polarization beam splitter 5 is sequentially connected to the third half - wave plate 7 and the second FC - type optical fiber interface 9 as the second beam splitting branch;

[0043] The second beam splitting unit includes a second polarization beam splitter 15, a fifth half - wave plate 14, a fourth half - wave plate 13, a fourth FC - type optical fiber interface 12, and a third FC - type optical fiber interface 11. The third FC - type optical fiber interface 11 and the fourth half - wave plate 13 are sequentially connected and input to the second polarization beam splitter 15 as the third beam splitting branch, and the fourth FC - type optical fiber interface 12 and the fifth half - wave plate 14 are sequentially connected and input to the second polarization beam splitter 15 as the fourth beam splitting branch.

[0044] The weak coupling module includes a push - pull sensing probe 10. The input ends of the push - pull sensing probe 10 are respectively connected to the first beam splitting branch and the second beam splitting branch, and the output ends of the push - pull sensing probe 10 are respectively connected to the third beam splitting branch and the fourth beam splitting branch.

[0045] Specifically, in this embodiment, after the incident light is pre - selected, it enters the weak coupling module through reflection by the first beam splitting unit, that is, it enters the weak coupling module through the first polarization beam splitter 5, the second half - wave plate 6, the third half - wave plate 7, the first FC - type optical fiber interface 8, and the second FC - type optical fiber interface 9. The weak coupling module includes a push - pull probe 10. As Figure 3As shown, the light prepared by the pre-selection state module is split into two beams of horizontally polarized and vertically polarized light by the first polarization beam splitter 5. Among them, the horizontally polarized light passes through the second half-wave plate 6 and is then coupled into the polarization-maintaining fiber by the first FC fiber optic interface 8, wound around the inner tube of the probe. After fiber optic transmission, it exits from the third FC fiber optic interface 11, passes through the fourth half-wave plate 13 and reaches the second polarization beam splitter 15. The combination of the second half-wave plate 6 and the fourth half-wave plate 13 realizes the polarization-maintaining effect; the vertically polarized light passes through the third half-wave plate 7 and is then coupled into another polarization-maintaining fiber by the second FC fiber optic interface 9, wound around the outer tube of the probe. After fiber optic transmission, it exits from the fourth FC fiber optic interface 12, passes through the fifth half-wave plate 14 and reaches the second polarization beam splitter 15. The combination of the third half-wave plate 7 and the fifth half-wave plate 14 realizes the polarization-maintaining effect; the two beams of orthogonally polarized light are combined and then enter the post-selection state module.

[0046] When the probe is placed in water to measure the sound pressure signal, the inner wall of the inner tube contacts water and the outer wall contacts air; conversely, the inner wall of the outer tube contacts air and the outside is filled with water. When the sound pressure p changes, the inner tube is subjected to a radially outward pressure and expands outward; at the same time, the outer tube is subjected to a radially inward pressure and contracts inward. The opposite deformations of the two tubes constitute a push-pull structure. At this time, the length of the optical fiber wound around the tube will change slightly, and a small phase shift will be generated between the horizontal and vertical polarizations. This phase shift has a linear relationship with the applied sound pressure p, that is:

[0047]

[0048] where S is the sound pressure sensitivity of the fiber optic hydrophone. Therefore, by measuring the phase shift the underwater sound pressure p can be indirectly obtained.

[0049] The sound pressure sensitivity S of the fiber optic hydrophone is an important indicator to measure its response degree to the sound pressure signal, and is defined as the amount of change in the optical phase caused by the action of the underwater sound pressure p signal on the probe of the fiber optic hydrophone When it occurs, under the condition of unit sound pressure, the change amount of the fiber optic phase. The traditional fiber optic hydrophone probe usually directly winds the sensing fiber on a single-layer elastic cylinder to realize sound field detection. Due to the opposite deformations of the two tubes of the push-pull type probe 10 in this embodiment, under the same sound pressure p, the phase shift is twice that in the case of a single tube. Therefore, it can be seen from Equation (5) that theoretically its sound pressure sensitivity is twice that of the single-tube structure.

[0050] The Hamiltonian H of the interaction between the target system and the measurement pointer can be expressed as:

[0051]

[0052] where g(t) is the coupling coefficient, is the measurement operator of the system. Here, let After weak coupling, the state of the whole system evolves into:

[0053]

[0054] where is the small phase difference generated by the sound pressure change in the horizontal and vertical polarization directions, which is the phase shift to be measured. Equation (7) is obtained by performing a first-order Taylor approximation under the condition of Further, the post-selection state module includes a third beam splitting unit, a positive post-selection branch, a negative post-selection branch, and an optical intensity contrast verification unit. Among them, the third beam splitting unit is respectively connected to the positive post-selection branch and the negative post-selection branch, both the positive post-selection branch and the negative post-selection branch are connected to the optical intensity contrast verification unit, and the optical intensity contrast verification unit is connected to the phase modulation unit.

[0055] Among them, the third beam splitting unit includes a 50:50 beam splitter 16. The positive post-selection branch includes a first quarter-wave plate 17, a second polarizer 19, a fifth FC-type optical fiber interface 21, and a first optical intensity detector PD23 connected in sequence. The negative post-selection branch includes a second quarter-wave plate 18, a third polarizer 20, a sixth FC-type optical fiber interface 22, and a second optical intensity detector PD24 connected in sequence;

[0056] The input ends of the first quarter-wave plate 17 and the second quarter-wave plate 18 are both connected to the output end of the 50:50 beam splitter 16. The output ends of the first optical intensity detector PD23 and the second optical intensity detector PD24 are both connected to the optical intensity contrast verification unit.

[0057] The transmission axis of the second polarizer 19 forms an angle of +φ with the transmission axis of the first polarizer 3, and the transmission axis of the third polarizer 20 forms an angle of -φ with the transmission axis of the first polarizer 3.

[0058]

[0059] ​Specifically, in this embodiment, the transmitted light beam is split into two light beams by a 50:50 beam splitter 16. One beam enters the positive post-selection branch, and the other beam enters the negative post-selection branch. The positive post-selection branch includes a first quarter-wave plate 17, a second polarizer 19, a fifth FC-type fiber optic interface 21, and a first optical intensity detector PD23. The first quarter-wave plate 17 is placed at a 45° angle to make the post-selection state almost orthogonal to the pre-selection state, thereby obtaining a larger weak value. The angle between the transmission axis of the second polarizer 19 and the transmission axis of the first polarizer 3 is +φ, introducing a very small phase offset +φ. The light beam entering the positive post-selection branch passes through the first quarter-wave plate 17 and the second polarizer 19 in sequence to achieve positive post-selection and obtain the positive post-selection state |ψ sf + >, and the positive post-selection state |ψ sf + > is:

[0060]

[0061] where φ represents the post-selection angle, that is, the offset phase, and i represents the imaginary unit.

[0062] Project the evolved joint state onto the positive post-selection state, and the output optical intensity I is detected by the first optical intensity detector PD23 f + , I f + can be expressed as:

[0063] I f + = I0|<ψ sf + |Ψ(t)>| 2 ≈ I0(sin 2 φ)[1 - Im(A w )pS] (9);

[0064] where I0 is the optical intensity value without post-selection, represents the weak value of the observable, and Im(A w ) represents the imaginary part of the weak value. When , the approximation in equation (9) is feasible. It can be seen that after post-selection, the optical intensity is linearly related to Im(A w ).

[0065] The negative post-selection branch includes a second quarter-wave plate 18, a third polarizer 20, a sixth FC-type fiber optic interface 22, and a second optical intensity detector PD24. The second quarter-wave plate 18 is set at a 45° direction. Similarly, in this case, the post-selected state and the pre-selected state are almost orthogonal, and a larger weak value can be obtained. The angle between the transmission axis of the third polarizer 20 and the transmission axis of the first polarizer 3 is -φ, introducing a very small phase shift -φ. A beam of light entering the negative post-selection branch passes through the second quarter-wave plate 18 and the third polarizer 20 in sequence to achieve negative post-selection and obtain the negative post-selected state |ψ sf - >, and the negative post-selected state |ψ sf - > is:

[0066]

[0067] Project the evolved joint state onto the negative post-selected state, and the second optical intensity detector PD24 detects the output optical intensity I f - , I f - The expression of is:

[0068] I f - =I0|<ψ sf - |Ψ(t)>| 2 ≈I0(sin 2 φ)[1+Im(A w )pS] (11);

[0069] Input I f + and I f - into the light intensity contrast verification unit, that is, the computer 25, and perform differential processing to obtain the light intensity contrast, which is represented by η as:

[0070]

[0071] The light intensity contrast can directly reflect the normalized light intensity change caused by the amplification of the underwater acoustic signal by the weak value. The sound pressure p can only be amplified within the range that satisfies the approximate conditions of weak value measurement. The approximation in Equation (12) still ensures that the linear weak value amplification region is satisfied. When the post-selection angle is larger, the effective measurement range of the sound pressure is larger, but the measurement sensitivity is lower. Therefore, in order to increase the dynamic measurement range of the fiber optic hydrophone, a certain measurement sensitivity may be sacrificed, which cannot meet the requirements of practical applications.

[0072] During measurement, it is necessary to ensure that the change range of underwater sound pressure is within the effective linear region, and this region corresponds to the threshold range of light intensity contrast. In this embodiment, it is considered that when the measured light intensity contrast is within the specified threshold range, the measurement result is valid; if the measured light intensity contrast is not within this range, a modulation phase needs to be added.

[0073] In this embodiment, the phase modulation unit adopts a Soleil - Babinet compensator SBC4, and feeds back the measurement result of the light intensity contrast of the post - selection state module to the Soleil - Babinet compensator SBC4. At this time, after positive and negative post - selections, the corresponding light intensity can be rewritten as:

[0074]

[0075] where φ M is the post - selection angle after adding modulation. When |pS + β| / 2 << |φ M |, the approximation is feasible, and at this time it is in the linear modulation region. Correspondingly, the light intensity contrast η M is:

[0076]

[0077] Therefore, as long as an appropriate modulation phase β is introduced, linear weak - value amplification of the acoustic signal can always be achieved, so as to ensure that when the underwater sound pressure is large, a high measurement sensitivity is still maintained, and the dynamic measurement range of the fiber optic hydrophone is broadened.

[0078] In this embodiment, a first light intensity detector PD23 and a second light intensity detector PD24 are respectively connected after positive and negative post - selections to detect the output electrical signal. When measuring at the positive post - selection angle +φ, the voltage value output by the fiber optic hydrophone can be expressed as:

[0079] V1 = KΔI1 = K(I f + -I f ') (15);

[0080] where K is the photoelectric conversion efficiency, I f ' = I0sin 2 φ is the light intensity value after post - selection when there is no acoustic pressure effect (i.e., ), and I f + is the output light intensity value when there is an acoustic pressure effect. When measuring at the negative post - selection angle -φ, similarly, we can get:

[0081] V2 = KΔI2 = K(I f - -I f ') (16);

[0082] Taking the difference between V1 and V2 gives

[0083] ΔV = V1 - V2 = K(I f + -I f - ) (17);

[0084] In the standard weak value measurement scheme, that is, measuring only under +φ or -φ, only V1 or V2 can be measured. Due to the limitation of the noise of the fiber optic hydrophone system, if the underwater sound pressure is less than the equivalent noise pressure at this time, the amplitude of the effective electrical signal is very small, that is, V1 or V2 will be submerged by the noise. In order to reduce the equivalent noise pressure, the differential weak value measurement method is adopted in this embodiment. After taking the difference between V1 and V2, part of the noise can be cancelled, which is equivalent to doubling the amplitude of the effective electrical signal. Therefore, the ΔV at this time can exceed the noise threshold limit, so as to achieve detection and can significantly reduce the equivalent noise pressure.

[0085] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. An optical fiber hydrophone based on the adaptive differential weak value measurement technique, characterized in that Including: A light-emitting module, a front selection state module, a weak coupling module, and a rear selection state module. Among them, the light-emitting module is connected to the front selection state module. The output end of the front selection state module is connected to the input end of the weak coupling module through a phase modulation unit and a first beam splitting unit. The output end of the weak coupling module is connected to the input end of the rear selection state module through a second beam splitting unit. The output end of the rear selection state module is connected to the phase modulation unit.

2. The fiber optic hydrophone based on the adaptive differential weak value measurement technique according to claim 1, characterized in that The light-emitting module includes a laser (1), and the laser (1) is used to emit a continuous light beam.

3. The fiber optic hydrophone based on the adaptive differential weak value measurement technique according to claim 1, wherein The front selection state module includes a first half-wave plate (2) and a first polarizer (3). Among them, the first half-wave plate (2) is arranged in the output optical path of the light-emitting module. The incident end of the first polarizer (3) is butted against the first half-wave plate (2), and the output end of the first polarizer (3) is connected to the phase modulation unit.

4. The fiber optic hydrophone based on the adaptive differential weak value measurement technique according to claim 1, wherein The phase modulation unit includes a Soleil-Babinet compensator SBC (4). The first beam splitting unit includes a first polarization beam splitter (5), a second half-wave plate (6), a third half-wave plate (7), a first FC-type optical fiber interface (8), and a second FC-type optical fiber interface (9). The Soleil-Babinet compensator SBC (4) is connected to the first polarization beam splitter (5). The first polarization beam splitter (5) is sequentially connected to the second half-wave plate (6) and the first FC-type optical fiber interface (8) as a first beam splitting branch. The first polarization beam splitter (5) is sequentially connected to the third half-wave plate (7) and the second FC-type optical fiber interface (9) as a second beam splitting branch; The second beam splitting unit includes a second polarization beam splitter (15), a fifth half-wave plate (14), a fourth half-wave plate (13), a fourth FC-type optical fiber interface (12), and a third FC-type optical fiber interface (11). The third FC-type optical fiber interface (11) and the fourth half-wave plate (13) are sequentially connected and input to the second polarization beam splitter (15) as a third beam splitting branch. The fourth FC-type optical fiber interface (12) and the fifth half-wave plate (14) are sequentially connected and input to the second polarization beam splitter (15) as a fourth beam splitting branch.

5. The fiber optic hydrophone based on the adaptive differential weak value measurement technique according to claim 4, wherein The weak coupling module includes a push-pull sensing probe (10). The input ends of the push-pull sensing probe (10) are respectively connected to the first beam splitting branch and the second beam splitting branch. The output ends of the push-pull sensing probe (10) are respectively connected to the third beam splitting branch and the fourth beam splitting branch.

6. The fiber optic hydrophone based on the adaptive differential weak value measurement technique according to claim 1, wherein The rear selection state module includes a third beam splitting unit, a positive rear selection branch, a negative rear selection branch, and a light intensity contrast verification unit. Among them, the third beam splitting unit is respectively connected to the positive rear selection branch and the negative rear selection branch. Both the positive rear selection branch and the negative rear selection branch are connected to the light intensity contrast verification unit. The light intensity contrast verification unit is connected to the phase modulation unit.

7. The fiber optic hydrophone based on the adaptive differential weak value measurement technique according to claim 6, characterized in that The third beam splitting unit includes a 50:50 beam splitter (16), the positive post-selection branch includes a first quarter-wave plate (17), a second polarizer (19), a fifth FC-type optical fiber interface (21), and a first optical intensity detector PD (23) connected in sequence, and the negative post-selection branch includes a second quarter-wave plate (18), a third polarizer (20), a sixth FC-type optical fiber interface (22), and a second optical intensity detector PD (24) connected in sequence; The input ends of the first quarter-wave plate (17) and the second quarter-wave plate (18) are both connected to the output end of the 50:50 beam splitter (16), and the output ends of the first optical intensity detector PD (23) and the second optical intensity detector PD (24) are both connected to the optical intensity contrast verification unit.

8. The fiber optic hydrophone based on the adaptive differential weak value measurement technique according to any one of claims 1-7, characterized in that, The angle between the transmission axis of the second polarizer (19) and the transmission axis of the first polarizer (3) is +φ, and the angle between the transmission axis of the third polarizer (20) and the transmission axis of the first polarizer (3) is -φ.

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