An optical fiber hydrophone array optical path difference testing system and method

Abstract

The application discloses a kind of optical fiber hydrophone array optical path difference test system and method, by wideband light source, tunable laser, isolator, acoustooptic modulator, photoelectric detector, data acquisition system, computer is formed, wideband light source and tunable filter are used to realize wavelength scanning, output wavelength is the continuous light of λ;Acoustooptic modulator enters the continuous light of optical fiber hydrophone array and is modulated into pulsed light;Photoelectric detector converts optical signal into electrical signal;Data acquisition system shows and converts the signal collected by photoelectric detector into digital signal and then transmits to computer, and optical path difference is calculated by computer.The application has the characteristics of simple structure, small mathematical operation amount, wavelength adjustable, high measurement accuracy, strong system reliability and the like, meets the real-time online measurement demand of optical path difference in the process of optical fiber hydrophone array, and has very wide application prospect.

Description

Technical fields:

[0001] This invention belongs to the field of fiber optic sensing, specifically relating to a fiber optic hydrophone array optical path difference testing system and method. Background technology:

[0002] As the strategic importance of the ocean in national development becomes increasingly prominent, the development of high-performance underwater acoustic detection systems plays a vital role in safeguarding national maritime security. Phase interferometric fiber optic hydrophones convert sound field information into light phase change information, and obtaining sound field information by demodulating the phase information is currently the most mature technology.

[0003] In matched interferometric structures, the delay fibers between each element also serve as sensing fibers, simplifying the array's wet-end structure. Furthermore, the near-equal-arm structure of the matched interferometer reduces phase noise caused by system light source frequency jitter and transmission fiber jitter. Clearly, this structure has significant application potential given the trend towards thinner linear arrays in fiber optic hydrophone arrays. Therefore, during array formation, precise measurement and control of the delay fiber lengths between elements in a matched interferometric fiber optic hydrophone array are crucial for reducing phase noise. Consequently, there is an urgent need to design a fiber optic hydrophone array optical path difference testing system and method that offers a large measurement range and high accuracy to meet the requirements for real-time measurement and calibration of optical path difference during the array formation process. Summary of the Invention:

[0004] The technical problem to be solved by the present invention is to provide a fiber optic hydrophone array optical path difference testing system and method. The system has a simple structure, low mathematical computation, adjustable wavelength, large measurement range, and high measurement accuracy. At the same time, the method can meet the needs of real-time measurement and calibration of optical path difference during the arraying process of fiber optic hydrophone array.

[0005] The technical solution of this invention is to provide a fiber optic hydrophone array optical path difference testing system, comprising a broadband light source, a tunable filter, an isolator, an acousto-optic modulator, a circulator, a photodetector, a data acquisition system, and a computer. The broadband light source and tunable filter are used to achieve wavelength scanning, outputting continuous light with wavelength λ; the isolator is used to prevent the light source from being affected by echoes; the output of the acousto-optic modulator is connected to the circulator, and through the circulator, it is connected to the fiber optic hydrophone array, modulating the continuous light entering the array into pulsed light; the photodetector is connected to the circulator, converting the optical signal into an electrical signal; the data acquisition system displays the signal acquired by the photodetector, converts it into a digital signal, and transmits it to the computer, where the computer calculates the optical path difference.

[0006] Preferably, the broadband light source is selected with a wavelength range of 1527nm-1565nm and an output optical power of 13dBm; the tunable filter has a wavelength range of 1520nm-1570nm.

[0007] Preferably, the operating range of the acousto-optic modulator is 1527nm-1565nm.

[0008] Preferably, the photodetector has a detection bandwidth of 10 MHz and the data acquisition system has a sampling rate of 5 GSa / s.

[0009] This invention also provides a method for measuring optical path difference based on the aforementioned optical fiber hydrophone array optical path difference testing system. The output continuous optical signal is modulated by an acousto-optic modulator to generate an optical pulse sequence. A suitable pulse width is manually selected to distort the pulse signal, so that the pulse signal acquired by the data acquisition system is a superposition of positive trigonometric function signals. The optical path difference measurement method includes three steps: array segment data division, peak judgment, and optical path difference calculation. The specific operation is as follows:

[0010] Step 1: Based on the wavelength division multiplexing (WDM) channel λ of the fiber optic hydrophone array under test N ,λ N+1 ,λ N+2 ...,λ M Set the corresponding adjustable voltage value V. N V N+1 V N+2 ...,V M The computer sends voltage value commands to the control circuit sequentially via serial communication.

[0011] Step 2: The computer reads the data acquired by the oscilloscope at each wavelength in a loop through network communication, denoted as Data_l, l = 1, 2, 3...L, and the recording time for each group of data is T1. The acquired data is divided into B segments according to the characteristic data segments, B = floor(T1 / T)-1, and each segment of data is denoted as Data_l_b, b = 1, 2, 3, ..., B;

[0012] Step 3: Find the N+1 reflected signals in the Data_l_b data by setting thresholds and differential thresholds sequentially. Calculate the peaks of each of the N+1 reflected signals using polynomial fitting, with index coordinates labeled x1, x2, x3, x4, ... x N+1 Then the matching optical path differences Δ1, Δ2, Δ3, ..., Δ N The average of the index coordinates of the Data_l_b data in group B was calculated to obtain the results of multiple measurements of the optical path difference at that wavelength.

[0013] Compared with the prior art, the present invention has the following advantages after adopting the above solution:

[0014] This invention can accurately obtain the optical path difference of a fiber optic hydrophone array. It features simple operation, low mathematical computation, large measurement range, and high measurement accuracy. At the same time, it meets the requirements for real-time measurement and calibration of the optical path difference during the arraying process of the fiber optic hydrophone array. The system has high reliability and very broad application prospects. Attached image description:

[0015] Figure 1 This is a schematic diagram of the optical path difference testing system for the fiber optic hydrophone array of the present invention.

[0016] Figure 2 Flowchart of the method for measuring optical path difference of fiber optic hydrophone array;

[0017] Figure 3 This is a schematic diagram of the fiber optic hydrophone array structure under test.

[0018] Figure 4 The optical signal before entering the photodetector;

[0019] Figure 5 This is a schematic diagram of the Fourier transform of a pulse signal;

[0020] Figure 6 This is a schematic diagram of the optical signal actually collected by the photodetector.

[0021] Figure 7 This is a schematic diagram of time-division array data divided by period.

[0022] Figure 8 This is a schematic diagram of the actual time-division data extracted under a certain period;

[0023] Figure 9 This is a schematic diagram of time-division data waveform fitting. Detailed implementation method:

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0025] See Figure 1 and Figure 2 The optical path difference testing system for fiber optic hydrophone arrays of the present invention comprises a broadband light source 1, a tunable filter 2, an isolator 3, an acousto-optic modulator 4, a circulator 5, a photodetector 6, a data acquisition system 7, a computer 8, and the fiber optic hydrophone array under test 9, wherein:

[0026] The wavelength division multiplexing (WDM) channels and time division multiplexing (TDM) channels of the fiber optic hydrophone array 9 under test can be selected, and its structural schematic diagram is shown below. Figure 3 As shown, in this embodiment, the wavelength division multiplexing channels are CH27, CH31, CH35, CH39, CH43, CH47, CH51, and CH55 (ITU standard wavelengths), and the number of time division multiplexing channels is 16.

[0027] Broadband light source 1 is selected with a wavelength range of 1527nm-1565nm and an output optical power of 13dBm; tunable filter 2 is selected with a wavelength range of 1520nm-1570nm to match the wavelength range of the fiber optic hydrophone array 9 under test. The broadband light source emits a continuous optical signal that enters the tunable filter. The tunable filter scans the wavelength division multiplexing (WDM) channel wavelengths of the fiber optic hydrophone array under test, sequentially outputting wavelengths of λ. N ,λ N+1 ,λ N+2 ...,λ M The optical signal.

[0028] Isolator 3 is used to connect tunable filter 2 and acousto-optic modulator 4 to prevent the light source from being affected by echoes.

[0029] The modulation pulse width and modulation period of the acousto-optic modulator 4 and the bandwidth of the photodetector have certain requirements. In this embodiment, the operating range of the acousto-optic modulator 4 is 1527nm-1565nm, the modulation period is 10µs, the modulation pulse width is 100ns, the modulation bandwidth is 10MHz, and the detection bandwidth of the photodetector 6 is 20MHz. The optical signal enters the acousto-optic modulator 4 after passing through the isolator 3. The output of the acousto-optic modulator 4 is connected to the first port 11 of the circulator 5, and is connected to the fiber optic hydrophone array 9 under test through the second port 12 of the circulator 5. The continuous light entering the fiber optic hydrophone array 9 under test is modulated into a pulse light with a period of T and a pulse width of τ. The optical pulse signal returned by the fiber optic hydrophone array 9 under test is output from the third port 13 of the circulator 5 and enters the photodetector 6.

[0030] The continuous optical signal output from the tunable filter is modulated by the acousto-optic modulator 4 to generate, theoretically, as... Figure 4 The light pulse sequence shown has a spectrum consisting of a series of discrete spectral lines enveloped by the sinc function, which can be expressed as:

[0031]

[0032] in,

[0033]

[0034] When n is large enough, f(x) can be approximated as a light pulse signal, such as Figure 5 As shown.

[0035] With a fixed bandwidth for photodetector 6, the pulse width τ is gradually reduced, and the pulse signal can be considered as a superposition of low-order trigonometric functions. To distinguish pulse signals from adjacent periods of the array, the characteristic region between the pulse signals should be as large as possible. In this embodiment, the bandwidth of photodetector 6 is selected as 20MHz, and the pulse width as 100ns. The pulse signal becomes distorted, and the data acquisition system 7 acquires a pulse signal that is a superposition of positive trigonometric function signals, such as... Figure 6 As shown, the corresponding theoretical and actual extracted time-division data are as follows: Figure 7 and Figure 8 As shown, the optical pulse signal is converted into an electrical signal by the photodetector 6 and input into the data acquisition system 7.

[0036] The data acquisition system 7 can be a high-speed acquisition system, typically a high-speed acquisition card, or it can be replaced by an oscilloscope. In this embodiment, the data acquisition system 7 is replaced by a Tektronix oscilloscope with a sampling rate of 5 GSa / s. The data acquisition system 7 displays the signal acquired by the photodetector 6, converts it into a digital signal, and then transmits it to the computer 8. The computer 8 uses general signal processing software to write the processing procedure to realize the real-time calculation of the optical path difference.

[0037] In this embodiment, the optical path difference measurement method based on the above-mentioned optical fiber hydrophone array optical path difference testing system includes three steps: array segment data division, peak judgment, and optical path difference calculation. The specific operation is as follows:

[0038] Step 1: Based on the wavelength division multiplexing (WDM) channel λ of the fiber optic hydrophone array under test N ,λ N+1 ,λ N+2 ...,λ M Set the corresponding adjustable voltage value V. N V N+1 V N+2 ...,V M The computer sends voltage value commands to the control circuit sequentially via serial communication.

[0039] Step 2: The computer reads the data collected by the oscilloscope at each wavelength in a loop through network communication, denoted as Data_l, l = 1, 2, 3...L, and the recording time for each group of data is T1. The collected data is divided into B segments according to the characteristic data segments, B = floor(T1 / T)-1, and each segment of data is denoted as Data_l_b, b = 1, 2, 3, ..., B.

[0040] Step 3: By sequentially setting thresholds and differential thresholds, find the N+1 reflection signals in the Data_l_b data. Then, use polynomial fitting to calculate the peaks of each of the N+1 reflection signals. The fitting result is as follows: Figure 9 As shown, the index coordinates are x1, x2, x3, x4, ... xN+1 Then the matching optical path differences Δ1, Δ2, Δ3, ..., Δ N The average of the index coordinates of the Data_l_b data in group B was calculated to obtain the results of multiple measurements of the optical path difference at that wavelength.

[0041] In practical applications, this fiber optic hydrophone array testing system and method exhibits high accuracy in optical path difference measurement: the maximum deviation compared to OBR is 0.3 nm. Furthermore, in practical applications, different wavelength outputs can be set according to different project requirements to achieve the versatility of the testing equipment. In addition, with a fixed wavelength output, this invention can measure up to 16-time-division fiber optic hydrophone arrays in practical applications. At the same time, this invention offers fast testing speed: taking 16-time-division 8-wavelength as an example, the testing speed is approximately 60 seconds.

[0042] The above description only illustrates preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. Any equivalent structural or procedural modifications made using this specification are included within the patent protection scope of the present invention.

Claims

1. A fiber optic hydrophone array optical path difference testing system, characterized in that: include Broadband light source, used to emit continuous light signals; A tunable filter is used to achieve wavelength scanning and output continuous light with wavelength λ. An acousto-optic modulator and a circulator are provided. The output of the acousto-optic modulator is connected to the circulator and is connected to the fiber optic hydrophone array under test through the circulator. The continuous light entering the fiber optic hydrophone array under test is modulated into pulsed light. An isolator is used to connect the tunable filter and the acousto-optic modulator to prevent the broadband light source from being affected by echoes. A photodetector is used to convert optical signals into electrical signals, and the photodetector is connected to the circulator. The data acquisition system is used to display the signals acquired by the photodetector and convert them into digital signals; The computer receives the digital signals from the data acquisition system and performs optical path difference calculation; The optical path difference measurement method of the fiber optic hydrophone array optical path difference testing system includes three steps: array segment data division, peak judgment, and optical path difference calculation. The specific operation is as follows: Step 1: Based on the wavelength division multiplexing (WDM) channel λ of the fiber optic hydrophone array under test N ,λ N+1 ,λ N+2 ...,λ M Set the corresponding adjustable voltage value V. N V N+1 V N+2 ...,V M The computer sends voltage value commands to the control circuit sequentially via serial communication. Step 2: The computer reads the data acquired by the oscilloscope at each wavelength in a loop through network communication, denoted as Data_l, l = 1, 2, 3...L, and the recording time for each group of data is T1. The acquired data is divided into B segments according to the characteristic data segments, B = floor(T1 / T)-1, and each segment of data is denoted as Data_l_b, b = 1, 2, 3, ..., B; Step 3: Find the N+1 reflected signals in the Data_l_b data by setting thresholds and differential thresholds sequentially. Calculate the peaks of each of the N+1 reflected signals using polynomial fitting, with index coordinates labeled x1, x2, x3, x4, ... x N+1 Then the matching optical path differences Δ1, Δ2, Δ3, ..., Δ N The average of the index coordinates of the Data_l_b data in group B was calculated to obtain the results of multiple measurements of the optical path difference at that wavelength.

2. The optical path difference testing system for fiber optic hydrophone arrays according to claim 1, characterized in that: The broadband light source is selected with a wavelength range of 1527nm-1565nm and an output optical power of 13dBm; the tunable filter has a wavelength range of 1520nm-1570nm.

3. The optical path difference testing system for fiber optic hydrophone arrays according to claim 1, characterized in that: The operating range of the acousto-optic modulator is 1527nm-1565nm.

4. The optical path difference testing system for fiber optic hydrophone arrays according to claim 1, characterized in that: The photodetector has a detection bandwidth of 10 MHz; the data acquisition system has a sampling rate of 5 GSa / s.

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