Integrated digital fiber optic hydrophone line array system and time division multiphase demodulation method

Abstract

The application relates to the technical field of optical fiber hydrophone, and provides an integrated digital optical fiber hydrophone line array system and a time division multiphase demodulation method thereof.The system comprises a plurality of digital subarray modules, the digital subarray module comprises an optical emission unit, an optical fiber sensing unit, an optoelectronic demodulation unit and an optoelectronic communication unit, the optoelectronic communication unit is responsible for receiving the digital acoustic signal of the optoelectronic demodulation unit, receiving the digital acoustic signal transmitted by the adjacent downstream digital subarray module of the rear end through the downstream communication optical fiber, collecting the received digital acoustic sensing signal, and sending the digital acoustic sensing signal to the adjacent upstream digital subarray module of the front end through the upstream communication optical fiber, and the digital subarray module at the most front end sends the digital acoustic signals of all the digital subarray modules to an upper computer.The application can complete optical signal emission and optoelectronic signal demodulation in each digital subarray module, output the demodulated digital acoustic signal, and the plurality of digital subarray modules can be flexibly spliced into a larger-scale line array system.

Description

Technical Field

[0001] This invention relates to the field of fiber optic hydrophone technology, and in particular to an integrated digital fiber optic hydrophone linear array system and its time-division multiphase demodulation method. Background Technology

[0002] In the field of fiber optic hydrophone sensing and detection, integrated digital fiber optic hydrophone linear array systems typically consist of two parts: a signal sensing subsystem and an optical transmission demodulation subsystem. The signal sensing part, composed of an array of multiple fiber optic hydrophones, is the underwater section and is usually referred to as the wet end. The optical transmission demodulation part, which transmits optical signals and receives the returned light to demodulate the acoustic signals picked up by the fiber optic hydrophones, is the above-water section and is usually referred to as the dry end. To meet practical application requirements, fiber optic hydrophone linear arrays often need to connect a large number of fiber optic hydrophones into an array. The optical signals from all the wet ends of the fiber optic hydrophones need to be transmitted back to the dry end system for demodulation to obtain the measured underwater acoustic signal.

[0003] In practical engineering, commonly used large-scale hydrophone array technologies include spatial division multiplexing (SDM), time division multiplexing (TDM), and wavelength division multiplexing (WDM). Currently, ordinary-sized fiber optic hydrophone arrays can meet quantity requirements by simultaneously using these multiplexing technologies. For example, the largest common array is 16 SDM × 16 TDM × 16 WDM = 4096 elements. In this type of fiber optic hydrophone, the optical signal between the wet-end array and the dry-end demodulation system is an analog optical signal. The signal quality and signal-to-noise ratio deteriorate with increasing transmission distance. To achieve long-distance detection of tens or even hundreds of kilometers, a large and complex optical amplification system needs to be added at the dry end, making it very difficult and costly to increase the transmission distance. Furthermore, with this dry-end / wet-end separated system design, the scale and complexity of the dry-end system continuously increase with the number of wet-end elements. Dry-end units for different sizes of hydrophone linear array systems all require custom design. Hydrophone linear array systems are large and complex, with significant differences in architecture and interface design between different linear array systems, resulting in poor equipment versatility and scalability. Furthermore, the different sizes of fiber optic hydrophone arrays make it difficult to standardize the manufacturing process and product scale. If the size of the fiber optic hydrophone array is to be increased further, the overall structure needs to be changed, resulting in high production costs. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes an integrated digital fiber optic hydrophone linear array system and its time-division multiphase demodulation method.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: On the one hand, an integrated digital fiber optic hydrophone linear array system is provided, comprising multiple digital subarray modules with identical structures, which are connected in series to form a large-scale integrated digital fiber optic hydrophone linear array system; the digital subarray modules include: The optical emitting unit transmits pulsed optical signals to the fiber optic sensing unit. The fiber optic sensing unit senses acoustic information and converts it into optical signals. The fiber optic sensing unit includes N fiber optic hydrophone probes, where N≥2. The N fiber optic hydrophone probes are connected by time-division multiplexing to form a time-division multiplexed fiber optic hydrophone array. Adjacent fiber optic hydrophone probes are connected by inter-probe delay optical fibers. The photoelectric demodulation unit receives the return optical signal from the fiber optic sensing unit, demodulates the acoustic information sensed by the fiber optic sensing unit, and converts it into a digital acoustic signal. The optoelectronic communication unit is responsible for receiving digital acoustic signals from the optoelectronic demodulation unit. It also receives digital acoustic signals transmitted from the adjacent downstream digital subarray module through the downstream optical communication module and the downstream communication fiber. After summarizing the received digital acoustic sensing signals, it sends them to the adjacent upstream digital subarray module through the upstream optical communication module and the upstream communication fiber. The frontmost digital subarray module sums the digital acoustic signals from all digital subarray modules in the entire linear array system and sends them to the host computer.

[0006] Furthermore, the digital subarray module includes a head watertight connector, a tail watertight connector, and a main unit between the head watertight connector and the tail watertight connector. The main unit includes a protective sleeve and an optical fiber sensing unit, an optical transmitting unit, an optoelectronic demodulation unit, and an optoelectronic communication unit sealed inside the protective sleeve. Adjacent digital subarray modules are connected in series end to end through the head watertight connector and the tail watertight connector.

[0007] Furthermore, the head watertight connector contains two DC power supply wires and two uplink communication optical fibers, wherein the two uplink communication optical fibers are responsible for bidirectional communication with the adjacent uplink digital subarray module at the front end. The tail watertight connector contains two DC power supply wires and two downlink communication optical fibers, wherein the two downlink communication optical fibers are responsible for bidirectional communication with the adjacent downlink digital subarray module at the rear end.

[0008] Furthermore, the fiber optic sensing unit in the digital subarray module includes multiple fiber optic hydrophone probes, which are optically connected in a time-division multiplexing manner to form a time-division multiplexed fiber optic hydrophone array.

[0009] Furthermore, the fiber optic hydrophone probe adopts a 2×3 interferometer probe structure.

[0010] Furthermore, the fiber optic sensing unit includes N fiber optic hydrophone probes, arranged sequentially from the first to the Nth fiber optic hydrophone probe. The length of the inter-probe delay fiber connecting the i-th and (i+1)-th fiber optic hydrophone probes is: ; in The fiber optic distance between the (i+1)th fiber optic hydrophone probe and the first fiber optic hydrophone probe is 1 to N-1. The width of the pulsed light signal entering the fiber optic hydrophone probe; This represents the propagation speed of the optical signal in the optical fiber.

[0011] Furthermore, the digital subarray module performs unidirectional data transmission according to a set data frame format, with a time interval of T between data frames. f The data frame consists of a frame header and a data segment. The frame header contains the number of fiber optic hydrophone probes, M, and the data segment contains the sensing data of the M fiber optic hydrophone probes.

[0012] A time-division multiphase demodulation method for an integrated digital fiber optic hydrophone linear array system includes: within each digital subarray module, a pulsed optical signal emitted by an optical transmitting unit enters each fiber optic hydrophone probe, wherein the fiber optic hydrophone probe adopts a 2×3 interferometer probe structure; the three interference optical signals of the 2×3 interferometer probe structure have a phase difference of 120° in each interference optical signal. The pulses of the three interference optical signals are combined and output after different delays, which is the interference optical pulse sequence output by the fiber optic hydrophone probe. Each fiber optic hydrophone probe outputs an interference optical pulse sequence containing three pulse sequences that do not overlap in the time domain. Due to the delay effect of the inter-probe delay fiber between adjacent fiber optic hydrophone probes, the interference light pulse sequences output by each fiber optic hydrophone probe are staggered and superimposed, and finally bundled into a return light pulse sequence. The return light pulse sequence is a 3×N staggered superimposed interference light pulse sequence containing N fiber optic hydrophone probes. After the returned optical pulse sequence is converted by photoelectric conversion and collected, the light intensity of 3×N consecutive optical pulses is obtained. Through time-division decomposition, the three-way interference signals of each fiber optic hydrophone probe are obtained. Then, through the multiphase detection method, the interference phase of each fiber optic hydrophone probe at the current moment is calculated. The magnitude of the interference phase is equivalent to the magnitude of the sound pressure intensity sensed by the fiber optic hydrophone probe, thus completing the fiber optic hydrophone demodulation calculation.

[0013] Furthermore, the three interference light signals within the fiber optic hydrophone probe are delayed by corresponding delay fibers within the probe. Let the width of the pulse light signal entering the fiber optic hydrophone probe be... The three interference light signals inside the fiber optic hydrophone probe The length of the corresponding delay fiber inside the probe They are respectively: ; in, This represents the propagation speed of the optical signal in the optical fiber.

[0014] The beneficial effects of this invention are: Traditional large-scale fiber optic hydrophone linear arrays are decomposed into a series of structurally identical digital subarray modules. Each digital subarray module's interface consists of only two communication optical fibers and two power supply wires. The connection between digital subarray modules is simple: adjacent modules are connected via watertight connectors, and modules are connected in series end-to-end via simple digital optical communication and power supply interfaces. Multiple digital subarray modules can be flexibly assembled into larger-scale linear array systems, thus simplifying the system structure and design complexity of large-scale fiber optic hydrophone linear arrays. The identical structure of each digital subarray module allows for easy interchangeability, improving system maintainability. The end-to-end series interconnection method allows for the assembly of linear arrays of various sizes, significantly enhancing system scalability.

[0015] The modular digital subarray architecture and streamlined optical system optimize the traditional bulky trunk terminal system of fiber optic hydrophone linear arrays, reduce the difficulty of system deployment, and expand the application scenarios of large-scale linear array systems.

[0016] The subarray design with identical specifications and structure simplifies the types of components required for the system, and allows for mass production of digital subarrays using standardized manufacturing processes, thereby reducing the production cost of large-scale integrated digital fiber optic hydrophone linear array systems.

[0017] Each subarray's optical communication module automatically receives digital acoustic signal data from the downstream subarrays via downlink communication fiber. It then integrates and aggregates the data from all the downstream subarrays before transmitting it to the upstream subarray at the front end via uplink fiber. The frontmost subarray module aggregates the digital acoustic signal data from the entire linear array system and sends it to the host computer. This invention employs digital optical communication technology for data transmission. Compared to the analog optical signal transmission method used in traditional fiber optic hydrophone linear array systems, the digital transmission distance can be significantly improved. Simultaneously, the increased transmission distance does not affect the signal-to-noise ratio and sensitivity of the hydrophone's sensing acoustic signal, thus enhancing the stability of the system performance. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of an integrated digital fiber optic hydrophone linear array system according to one embodiment; Figure 2 This is a schematic diagram of the signal connection of an integrated digital fiber optic hydrophone linear array system in one embodiment; Figure 3 This is a schematic diagram of a time-division multiplexing array scheme based on a 2×3 interferometer in one embodiment; Figure 4 This is a flowchart of an embodiment of an auto-negotiation method for data aggregation and transmission of serial digital subarrays; Figure 5 This is a schematic diagram of a data frame format proposed in one embodiment.

[0020] Label Explanation: 1. Head watertight connector; 2. Tail watertight connector; 3. Optoelectronic communication unit; 4. Optoelectronic demodulation unit; 5. Optical emission unit; 6. Fiber optic sensing unit; 7. Protective sleeve; 8. Two-core uplink communication fiber; 9. Two-core downlink communication fiber; 10. Two-core DC power supply cable; 601. Bundle splitter; 602. Probe; 603. Internal delay fiber of the probe; 604. Bundle combiner; 605. Inter-probe delay fiber. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Reference Figure 1 and Figure 2 One embodiment of an integrated digital fiber optic hydrophone linear array system includes multiple digital subarray modules. The digital subarray modules have identical structures and are connected in series to form a large-scale integrated digital fiber optic hydrophone linear array system. The digital subarray modules include: The optical emitting unit 5 transmits pulsed optical signals to the optical fiber sensing unit 6; The fiber optic sensing unit 6 senses acoustic information and converts the acoustic information into optical signals. The fiber optic sensing unit includes N fiber optic hydrophone probes, where N≥2. The N fiber optic hydrophone probes are connected by optical paths in a time-division multiplexing manner to form a time-division multiplexed fiber optic hydrophone array. Adjacent fiber optic hydrophone probes are connected by inter-probe delay optical fibers 605. The photoelectric demodulation unit 4 receives the return optical signal from the fiber optic sensing unit, thereby demodulating the acoustic information sensed by the fiber optic sensing unit and converting it into a digital acoustic signal. The optoelectronic communication unit 3 is responsible for receiving digital acoustic signals from the optoelectronic demodulation unit. At the same time, it receives digital acoustic signals transmitted from the adjacent downstream digital subarray module through the downstream optical communication module and the downstream communication fiber. After summarizing the received digital acoustic sensing signals, it sends them to the adjacent upstream digital subarray module through the upstream optical communication module and the upstream communication fiber. The frontmost digital subarray module sums up the digital acoustic signals from all digital subarray modules in the entire linear array system and sends them to the host computer.

[0023] Optical transmitting unit 5 is used to generate transmitted pulsed optical signals and output them to the time-division multiplexed fiber optic hydrophone array. The laser optical path of optical transmitting unit 5 is not limited. For example... Figure 2 As shown, the photoelectric demodulation unit 4 includes a photodetector, an ADC, and a demodulation processor. The photodetector receives the return optical signal from the fiber optic sensing unit and converts it into a digital signal via the ADC (digital-to-analog converter) and transmits it to the demodulation processor. The demodulation processor demodulates the acoustic information sensed by the fiber optic sensing unit and converts it into a digital acoustic signal.

[0024] Furthermore, to implement the aforementioned time-division multiphase demodulation method, a corresponding hardware implementation scheme is proposed. The optical emitting unit 5 consists of a narrow-linewidth laser and a semiconductor optical amplifier. The narrow-linewidth laser outputs narrow-linewidth continuous light, and the semiconductor optical amplifier receives the pulse modulation signal generated by the demodulation processor, generating pulsed signal light. The pulsed signal light passes through a time-division multiplexed fiber optic sensing unit (i.e., Figure 2 After the time-division multiplexing fiber optic hydrophone array is completed, the return light is a staggered multi-pulse optical signal. The return light enters the photodetector of the photoelectric demodulation unit, where it undergoes photoelectric conversion. Then, it is converted from analog to digital signal via an ADC. The converted digital signal enters the demodulation processor to complete de-time-division multiplexing and multi-phase detection demodulation calculations. Compared with traditional fiber optic hydrophone linear array dry-end units, this hardware implementation scheme has a simpler structure and requires fewer components. Therefore, it can be integrated into the protective sleeve of the digital subarray, achieving unified integration of the fiber optic hydrophone's "dry end" and "wet end."

[0025] Reference Figure 2The digital subarray module includes a head watertight connector 1, a tail watertight connector 2, and a main unit between the head watertight connector 1 and the tail watertight connector 2. The main unit includes a protective sleeve 7 and an optical fiber sensing unit 6, an optical emission unit 5, an optoelectronic demodulation unit 4, and an optoelectronic communication unit 3, which are sealed inside the protective sleeve 7. Adjacent digital subarray modules are connected in series end to end through the head watertight connector 1 and the tail watertight connector 2.

[0026] Furthermore, the head watertight connector 1 includes a two-core DC power supply wire 10 and a two-core uplink communication optical fiber 8, wherein the two-core uplink communication optical fiber 8 is responsible for bidirectional communication with the adjacent uplink digital subarray module at the front end. The tail watertight connector 2 contains a two-core DC power supply wire 10 and a two-core downlink communication optical fiber 9, wherein the two-core downlink communication optical fiber 9 is responsible for bidirectional communication with the adjacent downlink digital subarray module at the rear end.

[0027] Furthermore, the fiber optic sensing unit 6 in the digital subarray module includes multiple fiber optic hydrophone probes, which are optically connected via time-division multiplexing to form a time-division multiplexed fiber optic hydrophone array. Furthermore, the fiber optic hydrophone probe employs a 2×3 interferometer probe structure to sense acoustic information and convert it into optical signals. (See reference...) Figure 3 The fiber optic sensing unit includes N fiber optic hydrophone probes, arranged sequentially from the first to the Nth fiber optic hydrophone probe. Each fiber optic hydrophone probe includes a beam splitter 601, a probe 602, an internal delay fiber 603, and a combiner 604, all connected in sequence. The pulsed light signal input to the fiber optic hydrophone probe is split into two paths by the beam splitter 601. One path enters the next fiber optic hydrophone probe, and the other path enters the probe 602. The probe 602 is a 2×3 interferometer probe, which is existing technology in the field. It includes an internal beam splitter and a 2×3 interferometer. The pulsed light signal input to the probe is split into two paths by the internal beam splitter, and each path is input through one of the two ports on the input side of the 2×3 interferometer. The three ports on the output side of the 2×3 interferometer are respectively connected to one end of three internal delay fibers 603 of different lengths. The other ends of the three internal delay fibers 603 of different lengths are connected to the combiner 604. The return light from each fiber optic hydrophone probe is transmitted to the optoelectronic demodulation unit via the inter-probe delay fiber 605 between the fiber optic hydrophone probes in a time-division multiplexing manner.

[0028] The same pulsed optical signal is split into three paths and passed through three delay optical fibers 603 of different lengths within the probe, resulting in different propagation times for each path. In one embodiment, the width of the pulsed optical signal entering the fiber optic hydrophone probe is assumed to be... Then the lengths of the delay fibers inside the probe corresponding to the three ports of the 2×3 interferometer are... , , They are respectively: ; in, The speed at which light signals propagate in an optical fiber; In one embodiment, the length of the inter-probe delay fiber 605 connecting the i-th fiber optic hydrophone probe and the (i+1)-th fiber optic hydrophone probe is: ; in The fiber optic distance between the (i+1)th fiber optic hydrophone probe and the first fiber optic hydrophone probe is 1 to N-1. The width of the pulsed light signal entering the fiber optic hydrophone probe; This represents the propagation speed of the optical signal in the optical fiber.

[0029] In another embodiment, the digital subarray module performs unidirectional data transmission according to a set data frame format, with a time interval of T between data frames. f , refer to Figure 5 The data frame consists of a frame header and a data segment. The frame header contains the number of fiber optic hydrophone probes, M, and the data segment contains the sensing data of the M fiber optic hydrophone probes.

[0030] In one embodiment, reference is made to Figure 4 This paper proposes an auto-negotiation method for data aggregation and transmission of serial digital subarrays. The digital subarray modules achieve unidirectional data transmission of data frames through this method, including: (1) Beginning; (2) The digital subarray module performs a self-test to confirm the number of elements n (i.e. the number of fiber optic hydrophone probes n) contained in its time-division multiplexed fiber optic hydrophone array. (3) Try to connect the uplink communication link and establish an uplink communication link with the uplink digital subarray module adjacent to the front end. If the uplink communication link is not connected, return to step (3) until the uplink communication link is connected, and then proceed to step (4). (4) Try to connect the downlink communication link and confirm whether the downlink communication link is connected. If the downlink communication link is not connected, it means that the current digital subarray module is the last digital subarray module. Proceed to step (5). If the downlink communication link is successfully connected, proceed to step (7). (5) Create a new blank data frame and set it as the current data frame. Set the M field of the frame header of the current data frame to n. (6) Obtain the current time interval T of the n primitives (i.e., fiber optic hydrophone probes) in the time-division multiplexed fiber optic hydrophone array of the current digital subarray module.f The sensing data within the frame is the digital acoustic signal obtained after photoelectric conversion and photoelectric demodulation of the acoustic information sensed by each fiber optic hydrophone probe. The data of the current n primitives are added to the end of the current data frame (i.e., the data segment of the current data frame) to obtain the converged data frame. The convergence of the current data frame is completed. The current data frame is sent to the adjacent uplink digital subarray module at the front end through the uplink communication link, and then proceed to step (4). (7) Receive the data frame sent by the downlink digital subarray module and copy it as the current data frame. Parse the M field of the frame header of the data frame sent by the downlink digital subarray module. L Obtain the number M of primitives contained in the downlink digital subarray module. L Update field M in the frame header of the current data frame to M. L +n, proceed to step (6).

[0031] By using the serial digital subarray data aggregation and transmission method, each digital subarray module can adaptively aggregate the data from the downlink digital subarray module and its own digital subarray module to obtain the total number of elements in the current linear array system (i.e., the total number of fiber optic hydrophone probes). At the same time, adding or removing a digital subarray module at any position in the linear array system does not require modification of the settings, and the digital subarray module automatically completes the data aggregation and communication. This method has strong scalability and adaptability.

[0032] On the other hand, the present invention provides a time-division multiphase demodulation method for an integrated digital fiber optic hydrophone linear array system, comprising: within each digital subarray module, a pulsed optical signal emitted by an optical emitting unit enters each fiber optic hydrophone probe, wherein the fiber optic hydrophone probe adopts a 2×3 interferometer probe structure; the three interference optical signals of the 2×3 interferometer probe structure have a phase difference of 120° in each interference optical signal. The pulses of the three interference optical signals are combined and output after different delays, which is the interference optical pulse sequence output by the fiber optic hydrophone probe. Each fiber optic hydrophone probe outputs an interference optical pulse sequence containing three pulse sequences that do not overlap in the time domain. Due to the delay effect of the inter-probe delay fiber between adjacent fiber optic hydrophone probes, the interference light pulse sequences output by each fiber optic hydrophone probe are staggered and superimposed, and finally bundled into a return light pulse sequence. The return light pulse sequence is a 3×N staggered superimposed interference light pulse sequence containing N fiber optic hydrophone probes. After the returned optical pulse sequence is converted by photoelectric conversion and collected, the light intensity of 3×N consecutive optical pulses is obtained. Through time-division decomposition, the three-way interference signals of each fiber optic hydrophone probe are obtained. Then, through the multiphase detection method, the interference phase of each fiber optic hydrophone probe at the current moment is calculated. The magnitude of the interference phase is equivalent to the magnitude of the sound pressure intensity sensed by the fiber optic hydrophone probe, thus completing the fiber optic hydrophone demodulation calculation.

[0033] Among them, the three interference optical signals of each fiber optic hydrophone probe The expression is as follows: ; in, The phase of the interference to be measured, A Output DC current to the light source. B The amplitude value of the interference signal; The three interference light signals inside the fiber optic hydrophone probe are delayed by the corresponding delay fibers inside the probe. Let the width of the pulse light signal entering the fiber optic hydrophone probe be... The three interference light signals inside the fiber optic hydrophone probe The length of the corresponding delay fiber inside the probe They are respectively: ; in, This represents the propagation speed of the optical signal in the optical fiber.

[0034] After passing through the internal delay fiber and the combiner, the three interference optical signals form three non-overlapping pulse sequences in the combined fiber. Due to the inter-probe delay fiber of a certain length between adjacent fiber optic hydrophone probes, the delay effect ensures that the interference pulses from each probe are staggered and superimposed, ultimately resulting in a single return optical pulse sequence. This return sequence consists of 3×N staggered superimposed optical pulses from N fiber optic hydrophone probes. The return pulse sequence then enters the photodetector in the photoelectric demodulation unit. After the ADC acquires the optical signal, the demodulation processor obtains the light intensity of 3×N consecutive optical pulses. Time-division multiplexing is then used to obtain the three interference optical signals from the N fiber optic hydrophone probes. Finally, a multiphase detection method is used to calculate the interference phase of each probe at the current moment. The magnitude of the interference phase is equivalent to the sound pressure level sensed by the probe, completing the fiber optic hydrophone demodulation calculation as follows:

[0035] The time-division multiplexing array scheme and multiphase interference modulation and demodulation scheme based on the 2×3 interferometer have the characteristics of simple structure and reduced number of components. The optical emission unit and photoelectric demodulation unit are directly integrated into the array cable protective sleeve, which can complete the optical signal transmission and photoelectric signal demodulation inside the digital subarray and output the demodulated digital acoustic signal to the outside.

[0036] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. An integrated digital fiber optic hydrophone linear array system, characterized in that, It includes multiple digital subarray modules, which have the same structure and are connected in series to form a large-scale integrated digital fiber optic hydrophone linear array system. The digital subarray module includes: The optical emitting unit transmits pulsed optical signals to the fiber optic sensing unit. The fiber optic sensing unit senses acoustic information and converts it into optical signals. The fiber optic sensing unit includes N fiber optic hydrophone probes, where N≥2. The N fiber optic hydrophone probes are connected by time-division multiplexing to form a time-division multiplexed fiber optic hydrophone array. Adjacent fiber optic hydrophone probes are connected by inter-probe delay optical fibers. The photoelectric demodulation unit receives the return optical signal from the fiber optic sensing unit, demodulates the acoustic information sensed by the fiber optic sensing unit, and converts it into a digital acoustic signal. The optoelectronic communication unit is responsible for receiving digital acoustic signals from the optoelectronic demodulation unit. At the same time, it receives digital acoustic signals transmitted from the adjacent downstream digital subarray module through the downstream optical communication module and the downstream communication fiber. After summarizing the received digital acoustic sensing signals, it sends them to the adjacent upstream digital subarray module through the upstream optical communication module and the upstream communication fiber. The frontmost digital subarray module sums up the digital acoustic signals of all digital subarray modules in the entire linear array system and sends them to the host computer. Inside each digital subarray module, the pulsed light signal emitted by the optical emitting unit enters each fiber optic hydrophone probe, which adopts a 2×3 interferometer probe structure; the three interference light signals of the 2×3 interferometer probe structure have a 120° phase difference in each interference light signal. The pulses of the three interference optical signals are combined and output after different delays, which is the interference optical pulse sequence output by the fiber optic hydrophone probe. Each fiber optic hydrophone probe outputs an interference optical pulse sequence containing three pulse sequences that do not overlap in the time domain. Due to the delay effect of the inter-probe delay fiber between adjacent fiber optic hydrophone probes, the interference light pulse sequences output by each fiber optic hydrophone probe are staggered and superimposed, and finally bundled into a return light pulse sequence. The return light pulse sequence is a 3×N staggered superimposed interference light pulse sequence containing N fiber optic hydrophone probes. After the returned optical pulse sequence is converted by photoelectric conversion and collected, the light intensity of 3×N consecutive optical pulses is obtained. Through time-division decomposition, the three-way interference signals of each fiber optic hydrophone probe are obtained. Then, through the multiphase detection method, the interference phase of each fiber optic hydrophone probe at the current moment is calculated. The magnitude of the interference phase is equivalent to the magnitude of the sound pressure intensity sensed by the fiber optic hydrophone probe, thus completing the fiber optic hydrophone demodulation calculation.

2. The integrated digital fiber optic hydrophone linear array system according to claim 1, characterized in that, The digital subarray module includes a head watertight connector, a tail watertight connector, and a main unit between the head watertight connector and the tail watertight connector. The main unit includes a protective sleeve and an optical fiber sensing unit, an optical transmitting unit, an optoelectronic demodulation unit, and an optoelectronic communication unit sealed inside the protective sleeve. Adjacent digital subarray modules are connected in series end to end through the head watertight connector and the tail watertight connector.

3. The integrated digital fiber optic hydrophone linear array system according to claim 2, characterized in that, The head watertight connector contains two DC power supply wires and two uplink communication optical fibers, wherein the two uplink communication optical fibers are responsible for bidirectional communication with the adjacent uplink digital subarray module at the front end. The tail watertight connector contains two DC power supply wires and two downlink communication optical fibers, wherein the two downlink communication optical fibers are responsible for bidirectional communication with the adjacent downlink digital subarray module at the rear end.

4. The integrated digital fiber optic hydrophone linear array system according to any one of claims 1 to 3, characterized in that, The fiber optic sensing unit in the digital subarray module includes multiple fiber optic hydrophone probes, which are connected by time-division multiplexing to form a time-division multiplexed fiber optic hydrophone array.

5. The integrated digital fiber optic hydrophone linear array system according to claim 4, characterized in that, The fiber optic sensing unit includes N fiber optic hydrophone probes, arranged in the order of connection from the first to the Nth fiber optic hydrophone probe. The length of the inter-probe delay fiber connecting the i-th and (i+1)-th fiber optic hydrophone probes is: in The fiber optic distance between the (i+1)th fiber optic hydrophone probe and the first fiber optic hydrophone probe is 1 to N-1. The width of the pulsed light signal entering the fiber optic hydrophone probe; This represents the propagation speed of the optical signal in the optical fiber.

6. The integrated digital fiber optic hydrophone linear array system according to claim 1, 2, 3, or 5, characterized in that, The digital subarray module transmits data unidirectionally according to a set data frame format, with a time interval of T between data frames. f The data frame consists of a frame header and a data segment. The frame header contains the number of fiber optic hydrophone probes, M, and the data segment contains the sensing data of the M fiber optic hydrophone probes.

7. The integrated digital fiber optic hydrophone linear array system according to claim 6, characterized in that, The digital subarray modules achieve unidirectional data frame transmission through a serial digital subarray data aggregation and transmission method, including: (1) Beginning; (2) The digital subarray module performs a self-test to confirm the number n of fiber optic hydrophone probes contained in its time-division multiplexed fiber optic hydrophone array. (3) Try to connect the uplink communication link and establish an uplink communication link with the uplink digital subarray module adjacent to the front end. If the uplink communication link is not connected, return to step (3) until the uplink communication link is connected, and then proceed to step (4). (4) Try to connect the downlink communication link and confirm whether the downlink communication link is connected. If the downlink communication link is not connected, it means that the current digital subarray module is the last digital subarray module. Proceed to step (5). If the downlink communication link is successfully connected, proceed to step (7). (5) Create a new blank data frame and set it as the current data frame. Set the M field of the frame header of the current data frame to n. (6) Obtain the current time interval T of the n fiber optic hydrophone probes in the time-division multiplexed fiber optic hydrophone array of the current digital subarray module. f The sensor data within is collected and added to the data segment of the current data frame to complete the aggregation of the current data frame. The current data frame is then sent to the adjacent uplink digital subarray module at the front end via the uplink communication link, and then proceeds to step (4). (7) Receive the data frame sent by the downlink digital subarray module and copy it as the current data frame. Parse the M field of the frame header of the data frame sent by the downlink digital subarray module. L Update field M in the frame header of the current data frame to M. L +n, proceed to step (6).

8. The integrated digital fiber optic hydrophone linear array system according to claim 1, characterized in that, The three interference light signals inside the fiber optic hydrophone probe are delayed by the corresponding delay fibers inside the probe. Let the width of the pulse light signal entering the fiber optic hydrophone probe be... The three interference light signals inside the fiber optic hydrophone probe The length of the corresponding delay fiber inside the probe They are respectively: in, This represents the propagation speed of the optical signal in the optical fiber.

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