Method and system for measuring time delay between probes in optical fiber hydrophone array

Abstract

The invention discloses a method and a system for measuring time delay between probes in an optical fiber hydrophone array. The method comprises the following steps: acquiring a time-division sampling interval; time-division probe interference signals are extracted according to time-division sampling intervals; obtaining a reference initial phase corresponding to each time division probe based on the interference signal; and obtaining the actual length corresponding to the time delay between the time division probes, comparing the actual length with the design length corresponding to the time delay between the time division probes, obtaining the difference between the actual length and the design length, and adjusting the length of an optical fiber delay ring between two adjacent probes in the optical fiber hydrophone according to the difference result. The time-division sampling interval is obtained by closing the phase modulation module, the actual length corresponding to the time delay between the time-division probes is obtained after the phase modulation module is started, and the actual length corresponding to the time delay between the time-division probes is compared with the design length corresponding to the time delay between the time-division probes. And the length of the optical fiber delay ring in the optical fiber hydrophone is adjusted according to the difference result.

Description

Technical Field

[0001] This invention relates to the field of fiber optic hydrophone technology, and in particular to a method and system for measuring the time delay between probes in a fiber optic hydrophone array. Background Technology

[0002] Fiber optic hydrophone arrays utilize fiber optic sensors to receive underwater acoustic signals. They feature high sensitivity, wide bandwidth response, and strong resistance to electromagnetic interference and crosstalk. They are widely used in fields such as marine resource exploration, maritime national security, underwater communication, and noise measurement.

[0003] Fiber optic hydrophones can be configured into large-scale arrays through wavelength division multiplexing, space division multiplexing, and time division multiplexing. Among them, time division multiplexing is an efficient and low-cost multiplexing method. Time division multiplexing fiber optic hydrophone arrays can achieve multiplexing of multiple optical signals by allocating time slots through delayed optical fibers. There is no need to manage the optical wavelength, which simplifies the system design and reduces maintenance costs.

[0004] Currently, fiber optic hydrophone time-division multiplexing arrays typically use a light source, an external acousto-optic modulator, a photodetector, an oscilloscope, or a data acquisition board to measure the time delay between probes during the array formation process. This is limited not only by the oscilloscope's sampling rate and storage depth but also by the rise edge width of the acousto-optic modulator. Furthermore, manual calibration and verification are required, resulting in long measurement times. Additionally, the array is separate from the back-end demodulation equipment, requiring subsequent adaptation between the array and the back-end demodulation equipment to test time delay values ​​and component performance. If problems are discovered after the array is manufactured, it will not only increase maintenance costs but also delay the project schedule.

[0005] In view of this, it is necessary to propose a method and system for measuring the time delay between probes in a fiber optic hydrophone array to solve the above-mentioned technical problems. Summary of the Invention

[0006] Based on this, the purpose of the present invention is to provide a method and system for measuring the time delay between probes in a fiber optic hydrophone array. By obtaining the actual length corresponding to the time delay between time-division probes and comparing it with the design length corresponding to the time delay between time-division probes, the length of the fiber delay loop in the fiber optic hydrophone is adjusted according to the difference between the two.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: In a first aspect, a method for measuring the time delay between probes within a fiber optic hydrophone array is provided, comprising the following steps: Step S110: Obtain the time-division sampling interval; Step S120: According to the time-division sampling interval, acquire the interference signal corresponding to each time-division probe; Step S130: Obtain the reference initial phase corresponding to each time-division probe based on the interference signal; Step S140: Obtain the actual length corresponding to the time delay between time-division probes, compare it with the design length corresponding to the time delay between time-division probes, obtain the difference between the two, and adjust the fiber delay loop length between two adjacent probes in the fiber optic hydrophone based on the difference result.

[0008] Secondly, a method for measuring the inter-probe time delay within a fiber optic hydrophone array is also provided, comprising the following steps: Step S110: The demodulation device performs discrete sampling on the returned electrical signal, and obtains the corresponding time-division sampling interval within each repetition frequency within multiple repetition frequencies. ; Step S120: According to the time-division sampling interval Multiple interference signals from each time-division probe are acquired sequentially; Step S130: Within multiple repetition frequencies, acquire multiple reference initial phases corresponding to each time-division probe based on multiple interference signals. This allows us to obtain the reference initial phase corresponding to each time-division probe. average ; Step S140: Obtain the actual length corresponding to the time delay between time-division probes, compare it with the design length corresponding to the time delay between time-division probes, obtain the difference between the two, and adjust the fiber delay loop length between two adjacent probes in the fiber optic hydrophone based on the difference result.

[0009] Thirdly, a measurement system for the time delay between probes in a time-division optical path of a fiber optic hydrophone is also provided. This system includes a laser, a phase modulation module, a pulse modulation module, a demodulation device, a display device, and an array of fiber optic hydrophones under test. The laser emits a narrowband optical signal, which, through the phase modulation module, generates a signal carrying an angular frequency. The signal with a modulation depth of C is then converted into an optical pulse signal by a pulse modulation module, generating a modulated optical pulse signal that enters the fiber optic hydrophone array. The demodulation device includes a photodetector, a digital-to-analog converter, and a signal processing unit. The optical pulse signal emitted by the measurement system is converted into an interference beat frequency signal by an optical fiber hydrophone array. The beat frequency signal is transmitted to the demodulation device, where the photodetector converts the optical signal into an electrical signal. The digital-to-analog converter then converts the optical signal into a discrete electrical signal. Finally, the signal processing unit processes the signal and sends it to the display for waveform display.

[0010] In summary, the present invention provides a method and system for measuring the inter-probe delay in a fiber optic hydrophone array. By disabling the phase modulation module to obtain the time-division sampling interval and roughly adjusting the time-division optical path, the method ensures that the signals from all time-division probes can return within a repetition frequency. In conjunction with enabling the phase modulation module, the method obtains the actual length corresponding to the inter-probe delay. The method compares the actual length corresponding to the inter-probe delay with the designed length corresponding to the inter-probe delay, and adjusts the length of the fiber delay loop in the fiber optic hydrophone based on the difference between the two. Attached Figure Description

[0011] Figure 1 This is a structural block diagram of a measurement system for inter-probe delay within an optical fiber hydrophone array, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the fiber optic hydrophone array provided in an embodiment of the present invention; Figure 3 This is a waveform diagram of the beat frequency signal returned by the fiber optic hydrophone array provided in an embodiment of the present invention; Figure 4 This is a waveform diagram of the interference signal returned by the fiber optic hydrophone array under test, provided in an embodiment of the present invention. Figure 5 This is a schematic diagram of the waveform acquired after the input signal of the phase modulation module is turned off, as provided in an embodiment of the present invention. Figure 6 This is a rectangular coordinate diagram corresponding to the initial phase calculation results provided in the embodiments of the present invention; Figure 7 A rectangular coordinate graph corresponding to the time delay measurement results provided in the embodiments of the present invention; Figure 8 This is a flowchart illustrating a method for measuring the time delay between probes in a time-division optical path of an optical fiber hydrophone, as provided in an embodiment of the present invention. Detailed Implementation

[0012] To further understand the features, technical means, and specific objectives and functions achieved by the present invention, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0013] Figure 1 This diagram illustrates a measurement system applicable to the method for measuring inter-probe delay within a fiber optic hydrophone array provided by the present invention. Figure 1 and Figure 2As shown, the measurement system is used to distribute optical pulses to several fiber optic hydrophones in the fiber optic hydrophone array at different times through optical fibers and several fiber optic delay coils, thereby realizing time-division multiplexing among several fiber optic hydrophones in the fiber optic hydrophone array; wherein, the number of time divisions of the fiber optic hydrophone array under test can be selected according to the actual situation. In this embodiment, the number of time divisions of the fiber optic hydrophone array under test is 16.

[0014] The input of the measurement system includes a laser, a phase modulation module, and a pulse modulation module. The laser emits a narrowband light signal, which, after passing through the phase modulation module, generates a signal carrying angular frequency. The signal with a modulation depth of C is then converted into an optical pulse signal by a pulse modulation module, generating a modulated optical pulse signal that enters the fiber optic hydrophone array.

[0015] The output of the measurement system includes a demodulation device and a display device. The demodulation device includes a photodetector, a digital-to-analog converter, and a signal processing unit. The optical pulse signal emitted from the output of the measurement system is converted into an interferometric beat frequency signal by an optical fiber hydrophone array. The beat frequency signal is transmitted to the demodulation device, where the photodetector converts the optical signal into an electrical signal. The digital-to-analog converter then converts the optical signal into a discrete electrical signal, which is finally processed by the signal processing unit and sent to the display for waveform display. The signal output of the demodulation device is: ; Where A is the DC amplitude, B is the AC amplitude, and C is the modulation depth. To modulate the angular frequency, For the first i The initial phase of the carrier wave corresponding to each probe The sound signal sensed by the probe of the fiber optic hydrophone array under test.

[0016] The demodulation device is configured with an optical signal pulse width of T, a repetition frequency of Fs, a digital-to-analog converter sampling rate of W, and a discrete sampling point interval of 1 / W. A schematic diagram of the acquired signal is shown below. Figure 3 As shown, the time-division multiplexed fiber optic hydrophone array has N probes, the light propagation speed is c, and the fiber refractive index is n. The design length L corresponding to the time delay between adjacent probes is determined by the optical signal pulse width T, the repetition frequency Fs, and the number of time-division probes N, among other factors. , The design length L consists of the fiber delay loop length, the coupler length, and the probe pigtail length.

[0017] Figure 8 This is a flowchart illustrating a method for measuring inter-probe delay within a fiber optic hydrophone array, as provided in an embodiment of the present invention. Figure 8As shown, the method for measuring the inter-probe time delay within a fiber optic hydrophone array includes the following steps: Step S110: Obtain the time-division sampling interval; within a repetition frequency, when the number of returned optical pulses equals the time-division number of the fiber optic hydrophone array, the number of detected probes conforms to the design result of the fiber optic hydrophone array, based on the fault location. Get the i The sampling interval between the first time-division probe and the second time-division probe , This is used as a reference initial phase for subsequent calculations of each time-division probe; among which, Refers to the first repetition frequency within a certain repetition frequency. i The location of the fault.

[0018] In this invention, the delay value between adjacent probes can be calculated by using the waveform characteristics acquired after the phase modulation module is turned off; specifically, the method in step S110 includes the following steps: Step S111: Turn off the modulation input signal of the phase modulation module. The light emitted by the laser is converted into an optical pulse signal by the pulse modulation module.

[0019] Step S112: After the optical pulse signal passes through the fiber optic hydrophone array, it is transmitted to the demodulation device. The demodulation device performs discrete sampling on the returned electrical signal, and obtains the sampled signal set S within one repetition frequency, denoted as S. Where M represents the number of sampled signals within a repetition frequency, Fs represents the repetition frequency, and W represents the sampling rate of the digital-to-analog converter. The sampled signals in the sampled signal set S are arranged sequentially according to the sampling time order. Each sampled signal is labeled to obtain the position information of the sampled signal. The position information of the sampled signal is the arrangement number of the sampled signal in the sampled signal set S. In this embodiment, the position information corresponding to the first sampled signal in the sampled signal set S is 1, and the position information corresponding to other sampled signals in the sampled signal set S is 2, 3, 4...M in sequence. The time interval between adjacent sampled signals is 1 / W. In the following steps of this invention, the position information values ​​of the elements in the set are consistent with the position information values ​​in the sampled signal set S.

[0020] Step S113: Perform differential processing on the sampled signals in the sampled signal set S to obtain a set of differential signals. Arrange the position information of the sampled signals corresponding to the differential signals within the preset detection threshold range to form a position information set P, denoted as P. ; In this embodiment, the preset detection threshold range is set to -0.01V to 0.01V. When the differential signal is within -0.01V to 0.01V, the position information of the corresponding sampled signal is sequentially added to the position information set P. When the differential signal is not within -0.01V to 0.01V, the position information of the corresponding sampled signal is not added to the position information set P. Since the first sampled signal in the sampled signal set S cannot be differentially processed, the number of differential signals obtained by differentially processing the sampled signals in the sampled signal set S is actually M-1.

[0021] Step S114: Compare the position information of adjacent elements in the position information set P sequentially. When the difference between the position information of adjacent elements is greater than 1, that is... , At that time, the fault locations were recorded sequentially. , ... , forming a set of fault locations .

[0022] In this embodiment, the i-th fault location in the fault location set Q The location information values ​​correspond sequentially to the first occurrence of the location information in the location information set P. i Secondary satisfaction hour The location information value; for example, when j When the value is 8, the location information set P experiences its first instance where the difference between adjacent location information is greater than 1, i.e. The location of the first fault Location information values ​​and The location information values ​​are consistent, that is... For example, when j When the value is 28, the location information set P experiences a third instance where the difference between adjacent location information is greater than 1, i.e. The location of the third fault Location information values ​​and The location information values ​​are consistent, that is... .

[0023] Refers to the first repetition frequency within a certain repetition frequency. i The location of the fault, based on the first fault location, i Fault location Get the i The sampling interval between the first time-division probe and the second time-division probe Wherein, the sampling interval between the two time-division probes is the number of sampling points collected between the two time-division probes within a repetition frequency. In this embodiment, when i=1, That is, the sampling interval between the first time-division probes is 0, and the arrangement order of the fault locations is consistent with the probe order in the fiber optic hydrophone array, thus allowing the fault locations to be determined. Arrange the sequence numbers in the fault location set Q. i Knowing the position of the corresponding probe in the fiber optic hydrophone makes it easier to redesign the length of the fiber optic delay loop between the two probes.

[0024] Step S115: Within a repetition frequency, based on the number of fault locations i Obtain the number of returned pulses and determine whether the number of returned optical pulses is equal to the number of time division units in the fiber optic hydrophone array. If the number of returned optical pulses is not equal to the number of time division units in the fiber optic hydrophone array, proceed to step S116. If the number of returned optical pulses is equal to the number of time division units in the fiber optic hydrophone array, proceed to step S117.

[0025] Step S116: When the number of returned optical pulses is not equal to the number of time divisions of the fiber optic hydrophone array, that is, when the number of returned optical pulses is less than the number of time divisions of the fiber optic hydrophone array, the information is reported to the display device, indicating that the fiber optic hydrophone array is unqualified; the test will be repeated after the user adjusts the optical path delay in the fiber optic hydrophone array.

[0026] Alternatively, the method of step S116 is specifically as follows: When the number of returned optical pulses is not equal to the number of time-division multiplexing units in the fiber optic hydrophone array (i.e., the number of returned optical pulses < the number of time-division multiplexing units in the fiber optic hydrophone array), the optical path delay length between the i-th probe and the previous probe is: , The fiber optic delay length between the identified probes and adjacent probes is calculated. Uploaded to the display device, using formula Calculate the length of the fiber delay loop that needs to be trimmed between the i-th probe and the previous probe. The system prompts the user to trim the fiber delay loop length according to the test results and returns to step S111. Here, L refers to the preset length corresponding to the time delay between adjacent probes in the fiber optic hydrophone to be measured. In the initial state, the preset lengths corresponding to the time delay between adjacent probes in the fiber optic hydrophone to be measured are all the same.

[0027] Step S117: When the number of returned optical pulses equals the time-division multiplexing of the fiber optic hydrophone array, the number of detected probes matches the design result of the fiber optic hydrophone array, based on the fault location. Get the i The sampling interval between the first time-division probe and the second time-division probe , This is used as a reference initial phase for subsequent calculations of each time-division probe.

[0028] Step S120: According to the time-division sampling interval Sequentially acquire the interference signals corresponding to each time-division probe. Where A is the DC amplitude, B is the AC amplitude, and C is the modulation depth. To modulate the angular frequency, For the first i The initial phase of the carrier wave corresponding to each probe The acoustic signal sensed by the fiber optic hydrophone array probe under test; the input signal of the phase modulation module is turned on and sampled according to the time-division sampling interval. The interference signals corresponding to each time-division probe are obtained.

[0029] Step S130: Obtain the reference initial phase corresponding to each time-division probe based on the interference signal. , .

[0030] Specifically, the method of step S130 includes the following steps: Step S131: Generate two reference signals , The interference signal is mixed with two reference signals respectively, and then low-pass filtered to obtain two signals L1 and L2: ; Where J1 represents the first-order Bessel function; Step S132: Perform arctangent calculation on the two signals L1 and L2 to obtain the reference initial phase of each time-division probe. , .

[0031] Furthermore, to ensure the reference initial phase corresponding to each time-division probe... To ensure the accuracy of the obtained data, the method in step S132 of this invention is specifically implemented as follows: The arctangent operation is performed on the two signals L1 and L2. Quadrant detection is then performed on the arctangent operation result to obtain the reference initial phase corresponding to each time-division probe. , To reference the initial phase after arctangent operation The calculation results are expanded from the range of -π / 2 to π / 2 to the range of -π to π, improving the reference initial phase. The accuracy of the data obtained.

[0032] Step S140: Obtain the actual length corresponding to the time delay between time-division probes, compare it with the design length corresponding to the time delay between time-division probes, obtain the difference between the two, and adjust the fiber delay loop length between two adjacent probes in the fiber optic hydrophone based on the difference result.

[0033] Specifically, the method of step S140 includes the following steps: Step S141: Obtain the initial phase difference between the i-th probe and its preceding probe. , Thus, the time delay between the i-th probe and the previous probe is obtained as follows: This allows us to obtain the actual delay length between time-division probes. Where W is the sampling frequency of the digital-to-analog converter in the demodulation device. The modulation angular frequency applied to the phase modulation module in the demodulation device is denoted by c, where c is the speed of light and n is the refractive index of the fiber, typically 1.476. The demodulation device discretely samples the returned electrical signal, acquiring multiple sets of sampled signals within multiple repetition frequencies. Multiple measurements are then performed to determine the reference initial phase corresponding to each time-division probe. average hour, ; Step S142: Calculate the actual length corresponding to the time delay between time-division probes. Design length corresponding to the time delay between time-division probes Compare the two and obtain the difference. Based on the difference results Adjust the fiber delay loop length between the i-th probe and the previous probe in the fiber optic hydrophone; in this embodiment, the calculation result is as follows: Figure 7 As shown; when When the value is positive, the length of the fiber delay loop between the two corresponding probes needs to be increased to ensure the actual performance quality of the fiber optic hydrophone array product; when... When the value is negative, the length of the fiber delay loop between the two corresponding probes needs to be reduced to ensure the actual quality of the fiber optic hydrophone array product.

[0034] This invention discloses a method for measuring the inter-probe delay within a fiber optic hydrophone array. By disabling the phase modulation module, the sampling interval between time-division probes is obtained, and the time-division optical path is roughly adjusted to ensure that signals from all time-division probes return within a single repetition frequency. Conversely, by enabling the phase modulation module, the actual length corresponding to the inter-probe delay is obtained. This actual length is compared with the designed length corresponding to the inter-probe delay, and the length of the fiber delay loop between probes in the fiber optic hydrophone is adjusted accordingly based on the difference. This prevents signal aliasing in the array elements, thereby achieving a strict match with the digital sampling interval.

[0035] Example 2 The difference between Example 2 and Example 1 is that, to ensure the accuracy of the initial reference phase acquisition for each probe, the initial reference phase for each probe can be obtained by averaging multiple samples. Specifically, the method for measuring the time delay between probes in the fiber optic hydrophone array includes the following steps: Step S110: The demodulation device performs discrete sampling on the returned electrical signal, and obtains the corresponding time-division sampling interval within each repetition frequency within multiple repetition frequencies. ; Step S120: According to the time-division sampling interval Multiple interference signals from each time-division probe are acquired sequentially; Step S130: Within multiple repetition frequencies, acquire multiple reference initial phases corresponding to each time-division probe based on multiple interference signals. This allows us to obtain the reference initial phase corresponding to each time-division probe. average In this embodiment, the calculation result is as follows: Figure 6 As shown; Step S140: Obtain the actual length corresponding to the time delay between time-division probes, compare it with the design length corresponding to the time delay between time-division probes, obtain the difference between the two, and adjust the fiber delay loop length between two adjacent probes in the fiber optic hydrophone based on the difference result.

[0036] In this embodiment, the method of step S110 includes the following steps: Step S111: Turn off the modulation input signal of the phase modulation module, and the light emitted by the laser is converted into an optical pulse signal by the pulse modulation module; Step S112: After the optical pulse signal passes through the fiber optic hydrophone array, it is transmitted to the demodulation device. The demodulation device performs discrete sampling on the returned electrical signal, acquiring multiple sample signal sets S within multiple repetition frequencies, denoted as... Where M represents the number of sampled signals within a repetition frequency, Fs represents the repetition frequency, W represents the sampling rate of the digital-to-analog converter, the sampled signals in the sampled signal set S are arranged sequentially according to the sampling time order, each sampled signal is labeled to obtain the position information of the sampled signal, the position information of the sampled signal is the arrangement number of the sampled signal in the sampled signal set S; wherein, in the following steps of this invention, the position information values ​​of the elements in the set are consistent with the position information values ​​in the sampled signal set S; Step S113: Perform differential processing on the sampled signals in the sampled signal set S to obtain a set of differential signals. Arrange the position information of the sampled signals corresponding to the differential signals within the preset detection threshold range in sequence to form a position information set P, denoted as P. ; Step S114: Compare the position information of adjacent elements in the position information set P sequentially. When the difference between the position information of adjacent elements is greater than 1, that is... , At that time, the fault locations were recorded sequentially. , ... , forming a set of fault locations ; Step S115: Within a repetition frequency, based on the number of fault locations i Obtain the number of returned pulses and determine whether the number of returned optical pulses is equal to the number of time division arrays of the fiber optic hydrophone array; if the number of returned optical pulses is not equal to the number of time division arrays of the fiber optic hydrophone array, proceed to step S116; if the number of returned optical pulses is equal to the number of time division arrays of the fiber optic hydrophone array, proceed to step S117. Step S116: When the number of returned optical pulses is not equal to the number of time divisions of the fiber optic hydrophone array, that is, when the number of returned optical pulses is less than the number of time divisions of the fiber optic hydrophone array, the information is reported to the display device, indicating that the fiber optic hydrophone array is unqualified. Step S117: When the number of returned optical pulses equals the time-division multiplexing of the fiber optic hydrophone array, the number of detected probes matches the design result of the fiber optic hydrophone array, based on the fault location. Get the i The sampling interval between the first time-division probe and the second time-division probe , ; Step S118: Repeat steps S113 to S117 to obtain the time-division sampling interval corresponding to each repetition frequency within multiple repetition frequencies.

[0037] In this embodiment, the method of step S130 includes the following steps: Step S131: Generate two reference signals , One of the interference signals is mixed with the two reference signals respectively, and then low-pass filtered to obtain two signals L1 and L2: ; Where J1 represents the first-order Bessel function; Step S132: Perform arctangent calculation on the two signals L1 and L2 to obtain one of the reference initial phases corresponding to each time-division probe. , .

[0038] In this embodiment, the demodulation device performs discrete sampling on the returned electrical signal, and after obtaining the time-division sampling interval corresponding to each repetition frequency within multiple repetition frequencies, the method of step S140 includes the following steps: Step S141: Obtain the initial phase difference between the i-th probe and its preceding probe. , Thus, the time delay between the i-th probe and the previous probe is obtained as follows: This allows us to obtain the actual delay length between the time-division probes; where W is the sampling frequency of the digital-to-analog converter unit in the demodulation device. The modulation angular frequency of the signal applied to the phase modulation module in the demodulation device, where c is the speed of light and n is the refractive index of the optical fiber; Step S142: Calculate the actual length corresponding to the time delay between time-division probes. Design length corresponding to the time delay between time-division probes Compare the two and obtain the difference. Based on the difference results Adjust the length of the fiber delay loop between the i-th probe and the previous probe in the fiber optic hydrophone.

[0039] This invention discloses a method for measuring the inter-probe delay within a fiber optic hydrophone array. By disabling the phase modulation module, the sampling interval between time-division probes is obtained, and the time-division optical path is roughly adjusted to ensure that signals from all time-division probes return within a single repetition frequency. Conversely, by enabling the phase modulation module, the actual length corresponding to the inter-probe delay is obtained. This actual length is compared with the designed length corresponding to the inter-probe delay, and the length of the fiber delay loop between probes in the fiber optic hydrophone is adjusted accordingly based on the difference. This prevents signal aliasing in the array elements, thereby achieving a strict match with the digital sampling interval.

[0040] Example 3 To make the technical solution of the present invention clearer, preferred embodiments are described below, taking a 16-element array as an example, as detailed below.

[0041] like Figures 1 to 8 As shown, the measurement system for inter-probe time delay within an optical fiber hydrophone array of the present invention includes a laser, a phase modulation module, a pulse modulation module, a demodulation device, a display device, and an optical fiber hydrophone array under test. The number of time divisions in the optical fiber hydrophone array under test can be selected according to actual conditions; in this embodiment, the number of time divisions in the optical fiber hydrophone array is 16.

[0042] The wavelength of the narrowband light source emitted by the laser needs to be selected according to the wavelength of the fiber optic hydrophone array under test; in this embodiment, the laser is selected as a C30 laser with an output optical power of 10dBm.

[0043] The pulse modulation module needs to be configured according to the design time delay value between the time-division probes of the fiber optic hydrophone array under test. In this embodiment, the pulse width of the pulse modulation module is set to 300ns. The output signal frequency of the phase modulation module is 10MHz, the sampling frequency of the demodulation device is 200MHz, and the repetition frequency is 200kHz.

[0044] After the laser emits a continuous light signal, it passes through a phase modulation module to generate a signal carrying an angular frequency. The signal with a modulation depth of C is then converted into an optical pulse signal by a pulse modulation module, generating a modulated pulse signal. After passing through the fiber optic hydrophone array under test, it becomes an interferometric beat frequency signal, which is then transmitted to the demodulation device.

[0045] The demodulation device consists of a signal processing unit, a photodetector, and an analog-to-digital converter. It converts the interferometric optical signal into a discrete electrical signal, which can be represented as: Where A is the DC amplitude, B is the AC amplitude, and C is the modulation depth. To modulate the angular frequency, For the first i The initial phase of the carrier wave corresponding to each probe This represents the acoustic signal sensed by the fiber optic hydrophone array probe under test. In this embodiment, after passing through a photodetector and a digital-to-analog converter, the interference signal waveform is as follows: Figure 4 As shown.

[0046] Based on the above-mentioned measurement system for inter-probe delay within a fiber optic hydrophone array, this invention also provides a method for measuring inter-probe delay within a fiber optic hydrophone array, comprising the following steps: When the phase modulation module is turned off, the light wave emitted by the laser is converted into an optical pulse signal by the pulse modulation module, generating a modulated optical pulse signal. The optical pulse signal passes through an optical fiber hydrophone array and is transmitted to a demodulation device. After being acquired and discretely sampled by the demodulation device, a set of discrete sampling points is obtained, denoted as the sampled signal set. M represents the number of sampled signals within a repetition frequency. The sampled signals in the sampled signal set S are arranged sequentially according to their sampling time. Each sampled signal is labeled to obtain its position information, which is the sequence number of the sampled signal in the sampled signal set S. In this embodiment, the position information corresponding to the first sampled signal in the sampled signal set S is 1, and the position information corresponding to other sampled signals in the sampled signal set S is 2, 3, 4...M. The time interval between adjacent sampled signals is 1 / W. The acquired electrical signal waveform is as follows: Figure 5 As shown; Differential processing is performed on the sampled signals in the sampled signal set S to obtain a set of differential signals. The sampled signals corresponding to the differential signals within the preset detection threshold range are then arranged sequentially to obtain the position information set P, denoted as P. ; Compare the position information of adjacent elements in the position information set P one by one. When the difference between the position information of adjacent elements is greater than 1, that is... , At that time, the fault locations were recorded sequentially. , ... , forming a set of fault locations ; Within a repetition frequency, the number based on fault location i The number of returned pulses is obtained. When the number of returned optical pulses equals the number of time-division multiplexing units in the fiber optic hydrophone array, the number of probes is detected to be consistent with the design results of the fiber optic hydrophone array. Based on the first... i Fault location Get the i The sampling interval between the first time-division probe and the second time-division probe , This is to provide a reference initial phase for subsequent calculations of each time-division probe; Turn on the input signal of the phase modulation module and sample it according to the time-division sampling interval. Acquire the interference signals corresponding to each time-division probe; Generate two reference signals , The interference signal is mixed with two reference signals respectively, and then low-pass filtered to obtain two signals L1 and L2: ; Where J1 represents the first-order Bessel function; The arctangent of the two signals L1 and L2 is performed to obtain the reference initial phase of each time-division probe. , ; Obtain the reference initial phase corresponding to each time-division probe. , recorded as The reference initial phase for each time-division probe can also be determined through multiple measurements. average ,at this time, = In this embodiment, the calculation result is as follows: Figure 6 As shown.

[0047] Obtain the initial phase difference between the i-th probe and its preceding probe. , Thus, the time delay between the i-th probe and the previous probe is obtained as follows: This allows us to obtain the actual delay length between time-division probes. Where W is the sampling frequency of the digital-to-analog converter in the demodulation device. The modulation angular frequency of the signal applied to the phase modulation module in the demodulation device, where c is the speed of light and n is the refractive index of the optical fiber; The actual length corresponding to the time delay between time-division probes Design length corresponding to the time delay between time-division probes Compare the two and obtain the difference. Based on the difference results Adjust the fiber delay loop length between the i-th probe and the previous probe in the fiber optic hydrophone. In this embodiment, the calculation result is as follows: Figure 7 As shown.

[0048] In summary, the present invention provides a method and system for measuring the inter-probe delay in a fiber optic hydrophone array. By disabling the phase modulation module to obtain the time-division sampling interval and roughly adjusting the time-division optical path, the method ensures that the signals from all time-division probes can return within a repetition frequency. In conjunction with enabling the phase modulation module, the method obtains the actual length corresponding to the inter-probe delay. The method compares the actual length corresponding to the inter-probe delay with the designed length corresponding to the inter-probe delay, and adjusts the length of the fiber delay loop in the fiber optic hydrophone based on the difference between the two.

[0049] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0050] In the embodiments provided by this invention, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the system embodiments described above are merely illustrative. For example, the division of each unit is only a logical functional division, and there may be other division methods in actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed.

[0051] The steps in the method of the embodiments of the present invention can be adjusted, merged, and deleted according to actual needs. The units in the device of the embodiments of the present invention can be merged, divided, and deleted according to actual needs. Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a device (which can be a personal computer, a terminal, or a network device, etc.) to execute all or part of the steps of the method described in the various embodiments of the present invention.

[0052] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method of measuring inter-probe time delays in an optical fiber hydrophone array, comprising: The method comprises the following steps: Step S110, acquiring a time division sampling interval; Step S120, acquiring an interference signal corresponding to each time division probe according to the time division sampling interval; Step S130, acquiring a reference initial phase corresponding to each time division probe based on the interference signal; Step S140, acquiring an actual length corresponding to a time delay between time division probes, and comparing the actual length with a designed length corresponding to the time delay between time division probes to acquire a difference value, and adjusting a length of a fiber delay loop between two adjacent probes in the fiber hydrophone according to the difference value.

2. The method of claim 1, wherein, The method of step S110 comprises the following steps: Step S111, closing a modulation input signal of a phase modulation module, and converting light emitted by a laser into an optical pulse signal through a pulse modulation module; Step S112, transmitting the optical pulse signal to a demodulation device after the optical pulse signal passes through the fiber hydrophone array, and performing discrete sampling on a returned electrical signal by the demodulation device, and acquiring a sample signal set S in one repetition frequency, denoted as ; wherein M refers to the number of sampling signals within a repetition frequency, Fs refers to the repetition frequency, W refers to the sampling rate of the digital-to-analog conversion unit, the sampling signals in the sampling signal set S are arranged in turn according to the sampling time sequence, each sampling signal is labeled to obtain the position information of the sampling signal, and the position information of the sampling signal is the arrangement serial number of the sampling signal in the sampling signal set S; Step S113, performing differential processing on sample signals in the sample signal set S to obtain a group of differential signals, and sequentially arranging position information of sample signals corresponding to the differential signals within a preset detection threshold range to form a position information set P, denoted as ； Step S114, the position information of adjacent elements in the position information set P is compared in turn, and when the difference between the position information of adjacent elements is greater than 1, the position information of adjacent elements is recorded in turn as fault position , , , , , and the fault position set is composed ； Step S115, based on the number of fault positions within one repetition frequency i The number of returned pulses is obtained, and it is judged whether the number of returned light pulses is equal to the number of time divisions of the fiber hydrophone array; when the number of returned light pulses is not equal to the number of time divisions of the fiber hydrophone array, step S116 is executed; when the number of returned light pulses is equal to the number of time divisions of the fiber hydrophone array, step S117 is executed; Step S116, when the number of returned optical pulses is not equal to the number of time divisions of the fiber hydrophone array, i.e., the number of returned optical pulses < the number of time divisions of the fiber hydrophone array, reporting to a display device to prompt that the fiber hydrophone array is unqualified; Step S117, when the number of returned light pulses equals the time division number of the fiber hydrophone array, it is detected that the number of probes conforms to the design result of the fiber hydrophone array, and the fault position is determined based on the time division number acquiring the sampling interval between the first time division probe and the first time division probe i , .​ 3. The method of claim 1, wherein, The method of step S130 comprises the following steps: Step S131, generating two reference signals , The interference signal is mixed with the two reference signals respectively, and then two signals L1 and L2 are obtained through low-pass filtering. ； Wherein, J1 represents a first-order Bessel function; Step S132, the two-way signal L1, L2 is inverse tangent operation, obtain each time division probe reference initial phase , denoted as , .

4. The method of claim 3, wherein, The method of step S132 comprises the following specific operations: The arctangent operation is performed on the two signals L1 and L2. Quadrant detection is then performed on the arctangent operation result to obtain the reference initial phase corresponding to each time-division probe. , To reference the initial phase after arctangent operation The calculation results are expanded from the range of -π / 2 to π / 2 to the range of -π to π.

5. The method of claim 3, wherein, The method of step S140 comprises the following steps: Step S141, obtaining the initial phase difference between the ith probe and its previous probe , , thereby obtaining the time delay between the ith probe and its previous probe , and further obtaining the actual time delay length corresponding to the time division probes ; wherein W is the sampling frequency of the digital-to-analog conversion unit in the demodulation device, is the modulation angular frequency of the signal applied by the phase modulation module in the demodulation device, c is the speed of light, and n is the refractive index of the optical fiber. Step S142, obtaining actual length corresponding to time division inter-probe time delay design length corresponding to time division inter-probe time delay comparing, and obtaining difference value between them , according to difference value adjusting fiber delay loop length between the i th probe and the previous probe in the fiber hydrophone.

6. A method of measuring inter-probe time delays in an optical fiber hydrophone array, comprising: The method comprises the following steps: Step S110, the demodulation device performs discrete sampling on the returned electric signal, and obtains a corresponding time division sampling interval in each repetition frequency within a plurality of repetition frequencies ; Step S120, sampling according to time division obtaining a plurality of interference signals corresponding to each time division probe in sequence; In step S130, a plurality of reference initial phases corresponding to each time-division probe are obtained based on the plurality of interference signals in a plurality of repetition frequencies , and then an average value of the reference initial phases corresponding to each time-division probe is obtained . ​ Step S140, acquiring an actual length corresponding to a time delay between time division probes, and comparing the actual length with a designed length corresponding to the time delay between time division probes to acquire a difference value, and adjusting a length of a fiber delay loop between two adjacent probes in the fiber hydrophone according to the difference value.

7. The method of claim 6, wherein, The method of step S110 comprises the following steps: Step S111, closing a modulation input signal of a phase modulation module, and converting light emitted by a laser into an optical pulse signal through a pulse modulation module; Step S112, transmitting the optical pulse signal to a demodulation device after the optical pulse signal passes through the fiber hydrophone array, and performing discrete sampling on a returned electrical signal by the demodulation device, and acquiring a sample signal set S in one repetition frequency, denoted as ; wherein M refers to the number of sampling signals within a repetition frequency, Fs refers to the repetition frequency, W refers to the sampling rate of the digital-to-analog conversion unit, the sampling signals in the sampling signal set S are arranged in turn according to the sampling time sequence, each sampling signal is labeled to obtain the position information of the sampling signal, and the position information of the sampling signal is the arrangement serial number of the sampling signal in the sampling signal set S; Step S113, performing differential processing on sample signals in the sample signal set S to obtain a group of differential signals, and sequentially arranging position information of sample signals corresponding to the differential signals within a preset detection threshold range to form a position information set P, denoted as ； Step S114: Compare the position information of adjacent elements in the position information set P sequentially. When the difference between the position information of adjacent elements is greater than 1, that is... , At that time, the fault locations were recorded sequentially. , ... , forming a set of fault locations ； Step S115, based on the number of fault positions within one repetition frequency i The number of returned pulses is obtained, and it is judged whether the number of returned light pulses is equal to the number of time divisions of the fiber hydrophone array; when the number of returned light pulses is not equal to the number of time divisions of the fiber hydrophone array, step S116 is executed; when the number of returned light pulses is equal to the number of time divisions of the fiber hydrophone array, step S117 is executed; Step S116, when the number of returned optical pulses is not equal to the number of time divisions of the fiber hydrophone array, i.e., the number of returned optical pulses < the number of time divisions of the fiber hydrophone array, reporting to a display device to prompt that the fiber hydrophone array is unqualified; Step S117, when the number of returned light pulses equals the time division number of the fiber hydrophone array, it is detected that the number of probes conforms to the design result of the fiber hydrophone array, and the fault position is determined based on the time division number acquiring the sampling interval between the first time division probe and the first time division probe i , ;​ Step S118, repeating steps S113 to S117 to acquire a time division sampling interval corresponding to each repetition frequency in multiple repetition frequencies.

8. The method of claim 6, wherein, The method of the step S130 comprises the following steps: Step S131, generating two reference signals , One of the interference signals is mixed with the two reference signals respectively, and then two signals L1 and L2 are obtained through low-pass filtering. ； Wherein, J1 represents a first Bessel function; Step S132, the two-way signal L1, L2 is carried out inverse tangent operation, obtain each time division probe corresponding to one of the reference initial phase , .

9. The method of claim 6, wherein, The method of the step S140 comprises the following steps: Step S141, obtaining the initial phase difference between the ith probe and its previous probe , , thereby obtaining the time delay between the ith probe and its previous probe , and further obtaining the actual time delay length corresponding to the time division probes ; wherein W is the sampling frequency of the digital-to-analog conversion unit in the demodulation device, is the modulation angular frequency of the signal applied by the phase modulation module in the demodulation device, c is the speed of light, and n is the refractive index of the optical fiber. Step S142, comparing the actual length corresponding to the time division inter-probe time delay with the designed length the designed length corresponding to the time division inter-probe time delay to obtain a difference value According to the difference value adjust the fiber delay loop length between the i th probe and the previous probe in the fiber hydrophone.

10. A system for measuring the time delay between the optical paths of a time-division optical fiber hydrophone probe, characterized by, The application relates to a fiber-optic hydrophone array test system, which comprises a laser, a phase modulation module, a pulse modulation module, a demodulation device, a display device and a fiber-optic hydrophone array. The laser emits a narrow-band light signal, the phase modulation module generates a signal carrying an angular frequency of 2pi f0 and a modulation depth of C, then the signal passes through the pulse modulation module and becomes an optical pulse signal, a modulated optical pulse signal is generated and enters the fiber-optic hydrophone array. The demodulation device comprises a photoelectric detector, a digital-analog conversion unit and a signal processing unit. The light pulse signal emitted by the measurement system passes through the fiber hydrophone array and becomes an interference beat frequency signal. The beat frequency signal is transmitted to the demodulation device. The photoelectric detector in the demodulation device converts the optical signal into an electrical signal, and the digital-analog conversion unit converts the optical signal into a discrete electrical signal. Finally, the signal processing unit processes and sends the signal to the display, and the waveform is displayed on the display.

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