A device for compensating for arm length drift of a fiber-optic hydrophone based on deep feedback

Abstract

This invention relates to the field of fiber optic sensing technology, specifically a device for compensating for arm length difference drift in a fiber optic hydrophone based on depth feedback. The device comprises an optical transmitting module, a fiber optic hydrophone, a modulation / demodulation module, and a depth sensor. The modulation / demodulation module is communicatively connected to the optical transmitting module, the fiber optic hydrophone, and the depth sensor, and is also communicatively connected to the fiber optic hydrophone. The modulation / demodulation module includes a photoelectric conversion module for converting the interference optical signal returned from the fiber optic hydrophone into an electrical signal, an analog-to-digital conversion module for converting the analog signal into a digital signal, and an FPGA module for executing a PGC demodulation algorithm to reconstruct the acoustic signal and dynamically adjusting the modulation voltage of the light source based on depth information. The photoelectric conversion module, the analog-to-digital conversion module, and the FPGA module are sequentially communicatively connected. This invention effectively compensates for arm length difference changes caused by deep-sea pressure, thereby reducing the impact of C-value drift on system performance.

Description

Technical Field

[0001] This utility model belongs to the field of fiber optic sensing technology, and in particular relates to a fiber optic hydrophone arm length difference drift compensation device based on depth feedback. Background Technology

[0002] Fiber optic sensing technology plays an irreplaceable role in deep-sea environmental detection as a crucial tool for modern marine monitoring. Among these, fiber optic hydrophones based on the Michelson interferometer structure have become the mainstream technology for deep-sea acoustic detection due to their high sensitivity and wide bandwidth response. These systems typically employ Phase-Generated Carrier (PGC) modulation and demodulation algorithms to accurately detect weak acoustic signals. By converting the optical phase change caused by sound pressure into an electrical signal output, they effectively acquire underwater sound field information. In the PGC demodulation algorithm, the modulation depth parameter C is a key system parameter. Its value depends on both the modulation coefficient of the light source and, more importantly, the arm length difference of the interferometer. The influence of deep-sea hydrostatic pressure causes variations in fiber optic length, which in turn leads to changes in the arm length difference. When the arm length difference changes, the C value parameter experiences a systematic drift. This C-value drift significantly affects the demodulation accuracy and stability of the PGC demodulation algorithm, resulting in significant differences in the performance of fiber optic hydrophones at different depths, severely limiting the reliable application of the system across the entire deep-sea depth range.

[0003] Existing technologies primarily employ algorithm optimization schemes to reduce the impact of C-value drift on system performance. Patent application CN118758345A discloses a real-time modulation depth elimination phase carrier PGC demodulation method and system. This type of method improves the PGC demodulation algorithm, enabling it to tolerate C-value variations within a certain range, thereby reducing performance loss caused by arm length differences. However, such algorithm optimization schemes have high algorithm complexity, significantly increasing the difficulty of system implementation. In particular, when complex operations such as division are introduced, they consume significant amounts of time and space resources of hardware platforms such as Field Programmable Gate Arrays (FPGAs), increasing system implementation costs and power consumption. Furthermore, algorithm optimization is typically only effective within a limited range of C-value variations. When changes in the deep-sea environment cause C-value drift to exceed the preset range, system performance still significantly degrades, failing to achieve truly stable operation across the entire ocean depth.

[0004] Therefore, how to effectively compensate for the arm length difference caused by deep-sea pressure in order to reduce the impact of C-value drift on system performance is a problem that urgently needs to be solved by researchers in this field. Utility Model Content

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a fiber optic hydrophone arm length difference drift compensation device based on depth feedback, in order to solve the problem that existing technologies are unable to compensate for changes in arm length difference caused by deep-sea pressure, resulting in a systematic drift of the C-value parameter and affecting system performance.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a fiber optic hydrophone arm length difference drift compensation device based on depth feedback, comprising:

[0008] The system comprises an optical transmitter module, a fiber optic hydrophone, a modulation / demodulation module, and a depth sensor. The modulation / demodulation module is communicatively connected to the optical transmitter module, the fiber optic hydrophone, and the depth sensor, respectively. The optical transmitter module is also communicatively connected to the fiber optic hydrophone. The modulation / demodulation module includes a photoelectric conversion module for converting the interference optical signal received from the fiber optic hydrophone into an electrical signal, an analog-to-digital conversion module for converting the analog signal into a digital signal, and an FPGA module for executing a PGC demodulation algorithm to restore the sound signal and dynamically adjusting the modulation voltage of the light source based on depth information. The photoelectric conversion module, the analog-to-digital conversion module, and the FPGA module are communicatively connected in sequence. During the calibration phase, the fiber optic hydrophone is placed in a pressure-controlled tank. Starting from atmospheric pressure, the pressure is increased progressively for each n meters of seawater depth. At each pressure node, the modulation / demodulation module runs the standard PGC demodulation algorithm to calculate the actual C value under the current pressure condition. Then, by adjusting the modulation voltage of the light source, the C value is maintained at a preset optimal operating point. The correspondence between the current seawater depth and the required modulation voltage is recorded, forming a depth-modulation voltage calibration table stored in the modulation / demodulation module.

[0009] Furthermore, the optical emission module includes a narrow linewidth laser source and an optical fiber coupler. The narrow linewidth laser source is used to receive the modulation signal sent by the modulation and demodulation module and to sinusoidally modulate the optical frequency generated by the source. The optical fiber coupler is used to receive the modulated optical signal and transmit it to the optical fiber hydrophone.

[0010] Furthermore, the fiber optic hydrophone is based on a Michelson interferometer structure, including a sensing arm and a reference arm with a length difference L between them, and a Faraday rotator is provided at the end of the sensing arm and the reference arm.

[0011] Furthermore, the depth sensor is a pressure-type depth gauge, used to measure the current water depth and convert it into a digital signal, which is then transmitted to the modulation and demodulation module.

[0012] Furthermore, the FPGA module includes a depth acquisition unit, a calibration control unit, a light source modulation unit, and a PGC demodulation unit. The depth acquisition unit is used to acquire the depth sensor data and transmit it to the calibration control unit. The calibration control unit is used to retrieve the optimal modulation voltage corresponding to the current depth and transmit it to the light source modulation unit.

[0013] Compared with the prior art, the fiber optic hydrophone arm length difference drift compensation device based on depth feedback provided by this utility model has at least the following advantages:

[0014] Existing technologies primarily employ algorithm optimization schemes to mitigate the impact of C-value drift on system performance. However, these optimization schemes struggle to compensate for arm length variations caused by deep-sea pressure, resulting in a significant performance degradation and preventing truly stable operation across the entire ocean depth range. This new invention features a simple structure and convenient operation. By integrating a high-precision depth sensor, it acquires real-time water depth information and, combined with a depth-modulation voltage calibration table established during laboratory calibration, achieves dynamic lookup compensation for the modulation depth C-value, a key parameter of the PGC demodulation system. In actual deployment, the demodulation module automatically queries the calibration table based on real-time depth data, accurately loading the optimal modulation parameters matched to the current depth. This ensures the system always operates at its best, effectively improving its stability and reliability across the entire ocean depth range. Attached Figure Description

[0015] To more clearly illustrate the solution of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 A frame diagram of a fiber optic hydrophone arm length difference drift compensation device based on depth feedback provided for an embodiment of this utility model;

[0017] Figure 2 This is a schematic diagram of the signal transmission of the modulation and demodulation module in a fiber optic hydrophone arm length difference drift compensation device based on depth feedback, provided as an embodiment of this utility model. Detailed Implementation

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. For example, terms such as “length,” “width,” “upper,” “lower,” “left,” “right,” “front,” “rear,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” and “outer” indicate orientations or positions based on the orientations or positions shown in the accompanying drawings and are merely for ease of description and should not be construed as limiting the invention.

[0019] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this utility model are intended to cover non-exclusive inclusion; the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this utility model are used to distinguish different objects, not to describe a particular order. In the specification, claims, and accompanying drawings of this utility model, when an element is referred to as "fixed to," "mounted to," "set on," or "connected to" another element, it can be directly or indirectly located on that other element. For example, when an element is referred to as "connected to" another element, it can be directly or indirectly connected to that other element.

[0020] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the present invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] This invention provides a fiber optic hydrophone arm length difference drift compensation device based on depth feedback, applied in the detection process of fiber optic hydrophones in deep-sea environments. The fiber optic hydrophone arm length difference drift compensation device based on depth feedback includes:

[0022] The system comprises an optical transmitter module, an optical fiber hydrophone, a modulation / demodulation module, and a depth sensor. The modulation / demodulation module is communicatively connected to the optical transmitter module, the optical fiber hydrophone, and the depth sensor, respectively. The optical transmitter module is also communicatively connected to the optical fiber hydrophone. The modulation / demodulation module includes a photoelectric conversion module for converting the interference light signal returned from the optical fiber hydrophone into an electrical signal, an analog-to-digital conversion module for converting the analog signal into a digital signal, and an FPGA module for executing the PGC demodulation algorithm to restore the sound signal and dynamically adjusting the modulation voltage of the light source according to the depth information. The photoelectric conversion module, the analog-to-digital conversion module, and the FPGA module are communicatively connected in sequence.

[0023] This invention effectively compensates for the arm length difference caused by deep-sea pressure, thereby reducing the impact of C-value drift on system performance.

[0024] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0025] This invention provides a depth-feedback-based fiber optic hydrophone arm length difference drift compensation device, applied in the detection process of fiber optic hydrophones in deep-sea environments, combined with... Figure 1 and Figure 2 In this embodiment, the fiber optic hydrophone arm length difference drift compensation device based on depth feedback includes:

[0026] The system comprises an optical transmitter module, an optical fiber hydrophone, a modulation / demodulation module, and a depth sensor. The modulation / demodulation module is communicatively connected to the optical transmitter module, the optical fiber hydrophone, and the depth sensor, respectively. The optical transmitter module is also communicatively connected to the optical fiber hydrophone. The modulation / demodulation module includes a photoelectric conversion module for converting the interference light signal returned from the optical fiber hydrophone into an electrical signal, an analog-to-digital conversion module for converting the analog signal into a digital signal, and an FPGA module for executing the PGC demodulation algorithm to restore the sound signal and dynamically adjusting the modulation voltage of the light source according to the depth information. The photoelectric conversion module, the analog-to-digital conversion module, and the FPGA module are communicatively connected in sequence.

[0027] Specifically, in this embodiment, the optical emission module includes a narrow linewidth laser source and an optical fiber coupler. It receives the modulation signal sent by the modulation and demodulation module, performs sinusoidal modulation on the optical frequency generated by the light source, and generates a modulated optical signal that is transmitted to the optical fiber hydrophone via the optical fiber after passing through the optical fiber coupler. The larger the amplitude of the modulation signal, the larger the offset of the optical frequency. The ratio k is called the modulation coefficient.

[0028] Preferably, after the output optical signal is passed through a series of optical devices such as an optical amplifier and a pulsed light modulator, the optical signal emitted by the light source can be modulated in other ways.

[0029] Specifically, in this embodiment, the fiber optic hydrophone is based on a Michelson interferometer structure, including a sensing arm and a reference arm with a length difference L between them. The sensing arm is strongly coupled to the seawater for picking up acoustic signals, while the reference arm is sealed in a pressure-resistant chamber as a reference. Both the sensing arm and the reference arm are equipped with Faraday rotators at their ends to reflect the light emitted by the light source back. Due to the length difference L, interference will occur at the interferometer.

[0030] Specifically, in this embodiment, the modulation and demodulation module includes a photoelectric conversion module, an analog-to-digital conversion module, and an FPGA module. The photoelectric conversion module is used to convert the interference light signal returned by the fiber optic hydrophone into an electrical signal. The analog-to-digital conversion module is used to convert the analog signal into a digital signal. The FPGA module executes the PGC demodulation algorithm to restore the sound signal and dynamically adjusts the modulation voltage of the light source according to the depth information, thereby changing the modulation depth C value and ensuring the stability of the sound signal.

[0031] Furthermore, in this embodiment, the FPGA module includes multiple sub-units such as a depth acquisition unit, a calibration control unit, a light source modulation unit, and a PGC demodulation unit. The depth acquisition unit continuously acquires depth sensor data and transmits it to the calibration control unit. The calibration control unit then retrieves the optimal modulation voltage corresponding to the current depth in real time based on the depth-modulation voltage calibration table formed during calibration, and transmits the modulation voltage to the light source modulation unit. After receiving the modulation voltage, the light source modulation unit forms a new modulation signal and sends it to the light source, thereby ensuring that the system always operates at the optimal modulation depth C value. The PGC demodulation unit still runs the traditional demodulation algorithm. The entire process does not require complex algorithm calculations, but only simple table lookup operations, which greatly reduces the system complexity.

[0032] Specifically, in this embodiment, the depth sensor is a pressure-type depth gauge, which measures the current water depth in real time and converts it into a digital signal, which is then transmitted to the modulation and demodulation module.

[0033] The following describes the working process of a fiber optic hydrophone arm length difference drift compensation device based on depth feedback provided in this embodiment of the present invention:

[0034] During the calibration phase, the fiber optic hydrophone is placed in a pressure-controlled tank. Starting from atmospheric pressure, the pressure is increased progressively at each pressure increment equivalent to n meters of seawater depth. At each pressure node, the modulation and demodulation module runs the standard PGC demodulation algorithm to calculate the actual C value under the current pressure condition. Then, by adjusting the modulation voltage of the light source, the C value is kept at the preset optimal operating point. The correspondence between the current seawater depth and the required modulation voltage is recorded, forming a depth-modulation voltage calibration table stored in the modulation and demodulation module.

[0035] Once the fiber optic hydrophone system is deployed in the deep sea, multiple sub-units, including a depth acquisition unit, a calibration control unit, a light source modulation unit, and a PGC demodulation unit, run within the FPGA module. The depth acquisition unit continuously measures depth sensor data and transmits it to the calibration control unit. The calibration control unit then uses the depth-modulation voltage calibration table generated during calibration to retrieve the optimal modulation voltage corresponding to the current depth in real time and transmits this modulation voltage to the light source modulation unit. Upon receiving the modulation voltage, the light source modulation unit generates a new modulation signal and sends it to the light source, thus ensuring that the system always operates at the optimal modulation depth C value. The PGC demodulation unit still runs the traditional demodulation algorithm. The entire process does not require complex algorithm calculations, only simple table lookup operations, greatly reducing system complexity.

[0036] The fiber optic hydrophone arm length drift compensation device based on depth feedback described in the above embodiments differs from existing technologies. Existing technologies primarily employ algorithm optimization schemes to reduce the impact of C-value drift on system performance. However, these algorithm optimization schemes struggle to compensate for arm length differences caused by deep-sea pressure, resulting in a significant decrease in system performance and preventing truly stable operation across the entire ocean depth range. This invention features a simple structure and convenient operation. By integrating a high-precision depth sensor, it acquires real-time water depth information and, combined with a depth-modulation voltage calibration relationship table established during laboratory calibration, achieves dynamic lookup compensation for the modulation depth C-value, a key parameter of the PGC demodulation system. In actual deployment, the demodulation module automatically queries the calibration table based on real-time depth data, accurately loading the optimal modulation parameters matched to the current depth, ensuring the system always operates at its best and effectively improving the system's stability and reliability across the entire ocean depth range.

[0037] Obviously, the embodiments described above are merely preferred embodiments of this utility model, and not all embodiments. The accompanying drawings show preferred embodiments of this utility model, but do not limit the patent scope of this utility model. This utility model can be implemented in many different forms; rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of this utility model. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this utility model specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this utility model.

Claims

1. A fiber optic hydrophone arm length difference drift compensation device based on depth feedback, characterized in that, include: The system includes an optical transmitting module, an optical fiber hydrophone, a modulation and demodulation module, and a depth sensor. The modulation and demodulation module is communicatively connected to the optical transmitting module, the optical fiber hydrophone, and the depth sensor, respectively. The optical transmitting module is also communicatively connected to the optical fiber hydrophone. The modulation and demodulation module includes a photoelectric conversion module for converting the interference optical signal received from the fiber optic hydrophone into an electrical signal, an analog-to-digital conversion module for converting the analog signal into a digital signal, and an FPGA module for executing the PGC demodulation algorithm to restore the sound signal and dynamically adjusting the modulation voltage of the light source according to the depth information. The photoelectric conversion module, the analog-to-digital conversion module, and the FPGA module are connected in sequence.

2. The fiber optic hydrophone arm length difference drift compensation device based on depth feedback according to claim 1, characterized in that, The optical emission module includes a narrow linewidth laser source and an optical fiber coupler. The narrow linewidth laser source is used to receive the modulation signal sent by the modulation and demodulation module and to sinusoidally modulate the optical frequency generated by the source. The optical fiber coupler is used to receive the modulated optical signal and transmit it to the optical fiber hydrophone.

3. The fiber optic hydrophone arm length difference drift compensation device based on depth feedback according to claim 2, characterized in that, The fiber optic hydrophone is based on a Michelson interferometer structure and includes a sensing arm and a reference arm with a length difference L between them. The ends of the sensing arm and the reference arm are equipped with Faraday rotators.

4. The fiber optic hydrophone arm length difference drift compensation device based on depth feedback according to claim 3, characterized in that, The depth sensor is a pressure-type depth gauge, used to measure the current water depth and convert it into a digital signal, which is then transmitted to the modulation and demodulation module.

5. The fiber optic hydrophone arm length difference drift compensation device based on depth feedback according to claim 1, characterized in that, The FPGA module includes a depth acquisition unit, a calibration control unit, a light source modulation unit, and a PGC demodulation unit. The depth acquisition unit is used to acquire the depth sensor data and transmit it to the calibration control unit. The calibration control unit is used to retrieve the optimal modulation voltage corresponding to the current depth and transmit it to the light source modulation unit.

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