Array type optical fiber ultrasonic imaging system based on multi-path delay parallel detection

Abstract

The invention discloses an array type optical fiber ultrasonic imaging system based on multi-path delay parallel detection, and belongs to the technical field of ultrasonic detection and imaging. The main working process of the system is as follows: continuous laser output by a laser is modulated into pulse laser to be transmitted to an optical fiber ultrasonic detector array, and ultrasonic waves emitted by an ultrasonic wave generating device act on each detection array element to cause the property change of a detection optical signal; through multi-path time delay with the optical fiber as the medium, the detection optical signal forms different transmission time in each channel, is distinguished in a time division mode and is combined into a single path to be output. After photoelectric conversion, electric signals containing multi-channel detection information are collected in parallel, the signals are analyzed at a terminal processor by means of an imaging algorithm with an array parallel architecture, information of a to-be-detected target is obtained, and image reconstruction is completed. The array type optical fiber ultrasonic imaging system has the advantages of being accurate and rapid in scanning detection, simple and compact in system structure and efficient and high-quality in image reconstruction, and large-scale and low-cost array type optical fiber ultrasonic imaging is achieved.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic signal detection and imaging technology, and more specifically, relates to an array-type fiber optic ultrasonic imaging system based on multi-channel time-delay parallel detection. Background Technology

[0002] Ultrasonic waves, with frequencies greater than 20 kHz, are characterized by good directionality, concentrated energy, and strong penetrating power. By detecting changes in the properties of matter before and after the interaction of ultrasonic waves, information about the parameters of the target can be obtained. Optical fiber, as a small, lightweight, and highly resistant to electromagnetic interference light-guiding medium, can sensitively capture changes in external physical quantities. When fiber optic sensing is combined with ultrasonic detection, it becomes fiber optic ultrasonic detection technology, using light as a medium and sound as an ear to decipher the target for researchers.

[0003] The technology of converting detection results into visualization is called imaging technology, which is divided into fiber optic ultrasonic imaging and fiber optic photoacoustic imaging based on the different ultrasonic emission sources. Fiber optic ultrasonic detectors are key components in imaging technology, overcoming the problems of electrical ultrasonic detectors, such as susceptibility to electromagnetic disturbances, narrow bandwidth, and limited application scenarios. Among them, high-precision resonant fiber optic ultrasonic detectors based on optical resonant structures combine small size and high sensitivity. When sound waves act on the resonant cavity, the resonance mechanism is disturbed, and the properties of the beam transmitted in the fiber change. By demodulating the changes in light intensity, wavelength, and phase, sound wave information is obtained, and then image reconstruction algorithms are used to reconstruct the morphology of the target under test. This further safeguards applications such as medical imaging, non-destructive testing, and health monitoring.

[0004] With the increasing demand for high-speed scanning and efficient imaging in practical applications, arrayed line-surface detection has shown remarkable advantages compared to single-point, individual detection. It improves detection efficiency and imaging flexibility while increasing spatial sampling density, helping to capture more detailed information. However, traditional fiber optic ultrasonic detection array demodulation systems are complex in structure and redundant in components, making it difficult to balance large-scale integration with low cost. Time-division multiplexing methods containing optical switches are limited by the time delay of switching between detection channels, making it difficult to synchronize signal transmission and acquisition. Differences in the performance and spacing of detection array elements, as well as the time delay between channel acquisition, cause resolution defects, making it difficult to balance high imaging speed and high quality. These existing problems pose challenges to the detection and imaging of fiber optic ultrasonic and photoacoustic signals, requiring improvements and innovations in system structure design, demodulation and acquisition methods, and image reconstruction quality. Summary of the Invention

[0005] To address the shortcomings and improvement needs of existing technologies, this invention provides an array-type fiber optic ultrasonic imaging system based on multi-channel time-delay parallel detection. The system aims to solve problems such as long scanning time of a single detector leading to low detection efficiency; complex structure of multi-channel integrated systems causing a trade-off between large-scale reuse and low-cost construction; time intervals between channel switching making synchronous signal transmission and reception difficult; and resolution defects in the fabrication and arrangement of detector array elements resulting in insufficient imaging quality.

[0006] To achieve the above objectives, the present invention provides an array-type fiber optic ultrasound imaging system based on multi-path time-delay parallel detection, comprising: The light source module is used to output a rectangular pulse sequence as a probe light signal, which is then transmitted to the fiber optic ultrasonic detector array. The sound source module is used to provide ultrasonic or photoacoustic signals to the target under test, which are reflected, scattered or transmitted to the fiber optic ultrasonic detector array. The fiber optic ultrasonic detector array is used to receive the detection optical signal in multiple channels, and simultaneously receive the ultrasonic or photoacoustic signals reflected, scattered, or transmitted by the target under test in multiple channels. When the ultrasonic or photoacoustic signal acts on the fiber optic ultrasonic detector array with a fiber optic ultrasonic sensing structure, the properties of the detection optical signal will change, carrying the target information, thereby transmitting multiple detection optical signals carrying the target information. The fiber optic delay module is used to delay multiple detection optical signals carrying information about the target under test, forming a multi-channel detection signal and ensuring that the signals of each detection channel are distinguishable. Signal acquisition and imaging is used to acquire multi-channel detection signals in parallel after photoelectric conversion, and to obtain the target information by using imaging algorithms to achieve two-dimensional or three-dimensional imaging.

[0007] Furthermore, the light source module includes: A signal generating device is used to generate electrical signals of specific frequency, waveform and amplitude to provide a signal source for the entire system and drive the driver to work; A driver is used to drive a modulator to work according to the electrical signals generated by a signal generating device, thereby enhancing the driving capability of the signal. Tunable continuous laser, used to output continuous laser with tunable wavelength; A modulator is used to modulate the continuous laser output from a tunable continuous laser into pulsed laser light using the electrical signal output from the driver, which is then used as a probe light signal.

[0008] Furthermore, the sound source module includes: An ultrasonic generating device used to generate ultrasonic or photoacoustic signals; Trigger controller, used to control the triggering of the ultrasonic generator.

[0009] Furthermore, the ultrasonic generating device is either an ultrasonic transmitter or a photoacoustic excitation source, and has two detection signal output modes: the ultrasonic transmitter is used to generate ultrasonic signals, and the photoacoustic excitation source is used to generate photoacoustic signals. Different sound wave signal output modes are selected according to the ultrasonic or photoacoustic detection requirements.

[0010] Furthermore, the trigger controller is used to synchronously control the transmitter and the digital acquisition card. When an ultrasonic transmitter is used, the trigger controller determines the transmission frequency of the ultrasonic signal to ensure the synchronization of ultrasonic signal transmission and data acquisition. When a photoacoustic excitation source is used, the trigger controller determines the transmission frequency of the excitation laser to ensure that the emission of the excitation laser is synchronized with the acquisition by the digital acquisition card.

[0011] Furthermore, the fiber optic ultrasonic detector array includes N Each of the detection array elements comprises: Transmission optical fibers, used sequentially for transmission N Road detection optical signal; The fiber optic ultrasonic sensing structure is mounted on the transmission optical fiber and is used to sense ultrasonic or photoacoustic signals reflected, scattered, or transmitted by the target under test. After being modulated by sound pressure, the detection light signal inside the fiber optic ultrasonic sensing structure will undergo changes in intensity, wavelength, and phase, carrying the target information. The detection light signal carrying the target information is then transmitted through the transmission optical fiber.

[0012] Based on the characteristics of the acoustic wave detection frequency band and the requirements of the detection scenario, different types of fiber optic ultrasonic sensing structures can be selected to match the optimal detection effect. Fiber optic ultrasonic sensing structures include resonant fiber optic ultrasonic sensing structures or non-resonant fiber optic ultrasonic sensing structures, with resonant fiber optic ultrasonic detectors being preferred. These detectors use optical resonant cavities (such as Fabry-Perot cavities, fiber Bragg gratings, microring resonators, etc.) as the sensing structure. Light waves that meet the resonance conditions will form standing waves or whispering-gallery modes, undergoing multiple reflections or cyclic transmissions within the cavity, enhancing the interaction between sound and light. Under this resonance enhancement effect, high detection sensitivity and signal-to-noise ratio can be achieved.

[0013] The detection principle of a resonant fiber optic ultrasonic detector array is as follows: When external ultrasonic waves act on an optical resonant cavity (such as a Fabry-Perot cavity, fiber Bragg grating, or microring resonator), the resonance mechanism will be disturbed. For example, the length of the Fabry-Perot cavity may change due to sound pressure; the effective refractive index of the grating may change due to acousto-optic or thermal effects; and the propagation characteristics of the microring whispering-gallery mode may change due to ultrasonic modulation boundary vibrations. These disturbances will alter the beam transmission characteristics, manifesting as changes in light intensity, wavelength, and phase. By detecting these changes in the optical properties of the output beam from the cavity, information about the external sound wave can be deduced, thus enabling ultrasonic detection.

[0014] Furthermore, the fiber optic delay module includes: 1× N Fiber optic beam splitters are used to evenly distribute the probe light signal to... N Transmission is performed through each port, forming... N Road detection optical signal; A circulator, comprising a first port, a second port, and a third port, is used to unidirectionally propagate and output the incoming probe optical signal between the three ports in a specific order. The first port... N The path detection optical signal is input to the first N The first port of each circulator receives the light signal carrying the target information. The light signal enters the circulator through the second port and is output from the third port. The first to second... N The path detection optical signal passes through the first to the second in sequence. N After the circulator outputs the first to the... N The path carries the detection light signal containing information about the target being measured; Delay fiber is used to change the transmission time of optical signals in optical fiber. By setting different fiber lengths, the transmission time of light in optical fiber can be changed, so that the signals received by each detection array element are collected sequentially, avoiding signal aliasing and thus achieving the effect of distinguishing detection signals. N ×1 fiber combiner, used to combine the first probe optical signal and the delayed second to third fiber bundles. N The channel detection optical signals are combined into one output to achieve beam combining function.

[0015] The specific delay method is as follows: The probe light signal first passes through 1× N The fiber optic beam splitter is divided into N The optical signal is transmitted along the first branch, with one circulator placed in each branch to ensure sequential unidirectional transmission; secondly, for the first... N Side roads need to be equipped with N -1 delay fiber, for the first N -1 branch road, then needs to be equipped with N -2 delay fibers, and so on recursively; finally... N The detection optical signal of each branch passes through 1 N ×1 fiber combiner coupling output. Based on this, the first... N The delay path of each detection element is N The superposition of -1 delay fiber lengths, the first N The delay path for -1 detector element is N The signal delay between adjacent detector elements is the sum of the lengths of two delay fibers, and so on. The transmission time of the beam in a single delay fiber is the transmission time of the beam. By delaying the return time of signals from different channels, the detection signals of each detector element can be distinguished.

[0016] During operation, the tunable continuous laser outputs probe light with the same operating wavelength as the fiber optic ultrasonic detector array. After being modulated by the modulator, the output probe light is 1× N Fiber optic beam splitters are divided into N Each detection channel enters through a circulator and has a... N A fiber optic ultrasonic detector array with individual detector elements; the probe light generates a resonance enhancement effect within the optical resonant cavity, and undergoes resonant disturbances under the influence of external ultrasonic waves, resulting in changes in its optical properties; the beam modulated by the acoustic waves carries acoustic signal information through a time-delayed optical fiber. N The optical signals detected by each detector element will have different transmission times due to differences in the transmission path; then... N The beam of light passes through N The ×1 fiber combiner couples the beam into a single beam. Since the parallel detection signals have been distinguished, multiple detection information can be transmitted using only a single channel. The multi-channel detection light transmitted in the single channel will be transmitted sequentially to the photodetector, and after signal conversion, it will be output to the digital acquisition card to realize parallel multi-channel signal acquisition.

[0017] Furthermore, the signal acquisition and imaging module includes: A photodetector is used to receive the detection light signal after beam combining and to convert the light signal into an electrical signal using the photoelectric effect, which facilitates subsequent data acquisition. The digital acquisition card acquires electrical signals containing multi-channel detection information in parallel, and performs sampling, quantization, and encoding processing to convert analog electrical signals into digital electrical signals, facilitating signal identification and analysis; the triggering of the digital acquisition card is controlled by a trigger controller. The terminal processor, preferably a computer, receives the digital signal output from the digital acquisition card. Following the basic idea of ​​channel-level parallel operation between multiple detector elements combined with segment-level multi-layer processing within a single detector element, it decomposes the detection signal to obtain modal components using CEEMDAN, calculates the instantaneous energy characteristics of each mode using TEO, identifies and removes trend mode components using threshold conditions, and combines the BM3D denoising algorithm with Wiener filtering as its core to suppress useless noise, enhance useful signals, and improve the system signal-to-noise ratio. Finally, it uses the SAFT image reconstruction algorithm based on DAS to restore the shape of the target under test and displays the reconstructed two-dimensional and three-dimensional images on the host computer.

[0018] Furthermore, the imaging algorithm includes the following operational flow: It utilizes a Graphics Processing Unit (GPU) to accelerate multi-threaded block computation, completing channel-level parallel analysis of multi-channel detection signals; it divides a single-channel detection signal into multiple segments, and uses threads within the thread block to independently execute the three-layer processing stage of each segment, completing segment-level parallel analysis of the single-channel detection signal. The first processing stage uses Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) to adaptively decompose the signal, and combines this with the Teager Energy Operator (TEO) to analyze, identify, and remove modal trend components based on the instantaneous energy features of each mode; the second layer uses a block-matching and 3D filtering (BM3D) denoising algorithm, with Wiener filtering as its core, for efficient noise suppression, improving the signal-to-noise ratio; the third layer employs Synthetic Aperture Focusing (SAFT) technology based on Delay and Sum (DAS). The technique completes the image reconstruction of the target under test and displays the reconstructed two-dimensional or three-dimensional image on the host computer.

[0019] Compared with existing technologies, the array-type fiber optic ultrasound imaging system based on multi-channel time-delay parallel detection provided by this invention combines precise and stable detection performance, a simple and compact system structure, and fast and high-quality imaging advantages. It can achieve large-scale, low-cost parallel detection and imaging of ultrasound or photoacoustic signals, and is applicable to many fields such as medical imaging, industrial inspection, and health monitoring, with broad application prospects. This invention utilizes a fiber optic ultrasound detector array to achieve rapid and efficient multi-point scanning, sets a time-delay fiber gradient to achieve precise and stable signal differentiation, uses multi-channel beam combining and single-channel output to achieve simplified photoelectric direct acquisition, and executes a high-resolution imaging algorithm based on an array parallel architecture to complete multi-level collaborative image reconstruction, ultimately achieving large-scale, low-cost parallel detection and high-quality imaging. Specific beneficial effects include: 1. The array-type fiber optic ultrasonic imaging system based on multi-path delay parallel detection provided by this invention has a simple structural design and precise array unit arrangement, which meets the development needs of high integration and small size of fiber optic ultrasonic detector arrays. The multi-level collaborative image reconstruction algorithm also ensures high-quality imaging.

[0020] 2. This invention integrates optical resonance enhancement effect with array-type acoustic wave detection, giving full play to the advantages of high-sensitivity fiber optic sensing and high-efficiency acoustic wave detection. It not only broadens the application scenarios of acoustic wave detection, but also effectively solves the limitations of single-point detection. By multiplexing fiber optic ultrasonic detectors, it enables simultaneous detection of multi-point acoustic wave signals, which increases the scanning speed by multiple times according to the number of detection array elements, greatly saving time and costs.

[0021] 3. This invention uses optical fiber as the delay medium and achieves the delay requirement by strictly setting the fiber length gradient, which ensures the accuracy and stability of the delay. The longer the delay path, the longer the time for the detection signal to return to the acquisition device. Accordingly, the detection signals of multiple detection array elements are transmitted to the acquisition device in sequence, avoiding the aliasing phenomenon that occurs during signal acquisition, and improving the channel switching rate limitation problem in traditional time division multiplexing technology, thereby improving the acoustic wave detection rate.

[0022] 4. This invention reduces structural design complexity, significantly decreasing the redundant deployment of electronic components such as photodetectors and digital acquisition cards. Only a single signal conversion device and data acquisition equipment are needed to meet the reuse requirements of a multi-channel detection system. This means that when the number of reused components is... N In the array demodulation system, compared with the traditional multi-channel multiplexing design, the number of photodetectors and digital acquisition cards is reduced by [number missing]. N -1, which realizes the function of multi-channel parallel demodulation, is suitable for large-scale array multiplexing scenarios, and significantly reduces manufacturing costs.

[0023] 5. The high-resolution imaging algorithm based on array parallel architecture provided by this invention compensates for the resolution defects caused by minor differences in array processing and arrangement. By combining parallel processing among multiple detector array elements with collaborative analysis within a single detector array element, and with CEEMDAN decomposition and the introduction of TEO to extract features, the trend mode components of the detection signal are identified and removed. The BM3D denoising algorithm with Wiener filtering as its core is used to achieve noise suppression and signal enhancement, thereby improving the system signal-to-noise ratio. Finally, the high-resolution two-dimensional and three-dimensional image reconstruction is completed with the help of the SAFT imaging algorithm based on DAS. Attached Figure Description

[0024] Figure 1 A schematic diagram of an array-type fiber optic ultrasonic imaging system based on multi-path delay parallel detection provided by the present invention.

[0025] Figure 2 This is a schematic diagram of the fiber optic ultrasonic detector array structure provided by the present invention.

[0026] Figure 3 The signal transmission and reception synchronization timing diagram provided for this invention.

[0027] Figure 4The flowchart of the array-type fiber optic ultrasound imaging algorithm provided by this invention is shown.

[0028] Figure 5 This is an imaging result diagram of the present invention under 10 MHz pulsed ultrasound.

[0029] Reference numerals: 1. Signal generating device; 2. Driver; 3. Tunable continuous laser; 4. Modulator; 5. 1× N 6. Fiber optic beam splitter; 7. Ultrasonic wave generator; 8. Trigger controller; 9. Fiber optic ultrasonic detector array; 10. Circulator; 11. Time-delay fiber; N ×1 Fiber optic combiner, 12. Photodetector, 13. Digital acquisition card, 14. Terminal processor, 8-1. Transmission fiber, 8-2. First reflective film, 8-3. Sensing film, 8-4. Second reflective film, 8-5. Waterproof film, a. First port, b. Second port, c. Third port. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] This invention consists of Ch 1 (i.e., Channel 1, referring to the branch where the first detection element is located; hereinafter, all detection branches are abbreviated as Ch), Ch 2, Ch 3, etc. N An array of fiber optic ultrasonic detectors, composed of detector elements, enables the detection of multi-point acoustic information. Fiber optic ultrasonic sensor structures are diverse; in practical applications, a suitable sensor structure can be selected based on the required acoustic frequency band to achieve optimal detection performance. Taking a polymer fiber optic Fabry-Perot ultrasonic detector with a multi-layer thin-film stacked structure (reflective layer-sensing layer-reflective layer) as an example, the lateral dimension of a single detector element does not exceed 130 μm, and the spacing between detector elements does not exceed 200 μm. Thanks to its small size and regular arrangement, this array supports high-density integration and is suitable for large-scale reuse.

[0032] Combination Figure 1 and Figure 2 The technical solution adopted in this invention is a fiber optic ultrasonic detector based on a Fabry-Perot resonator. It includes: a transmission optical fiber 8-1, a first reflective film 8-2, a sensing film 8-3, a second reflective film 8-4, and a waterproof film 8-5.

[0033] Specifically, the first reflective film 8-2 and the second reflective film 8-4 together constitute a Fabry-Perot double-reflection cavity, with the sensing film 8-3 in the middle serving as the transmission medium. The ultrasonic waves transmitted to the fiber optic ultrasonic detector exert a certain pressure, causing a slight deformation of the cavity. This change in cavity length alters the optical path of the beam propagating within the cavity, thereby causing a change in the intensity of the interference beam. By detecting the change in the intensity of the light output from the cavity, external sound wave information can be deduced, thus achieving sound wave detection.

[0034] The first reflective film 8-2 and the second reflective film 8-4 can be made of high reflectivity materials, such as films composed of zinc sulfide and sodium hexafluoroaluminate, silicon dioxide and titanium dioxide, silicon dioxide and zirconium dioxide in alternating layers, or metal reflectors such as gold, silver and aluminum foil.

[0035] The sensing film 8-3 can be made of materials with low Young's modulus and good wear resistance, such as terephthalic acid, epoxy resin, and polyethylene terephthalate, and is suitable for ultrasonic detection in water.

[0036] The waterproof film 8-5 is applied to the surface of the second reflective film 8-4. It can be made of materials such as polyurethane, silicone, or fluorinated polymers, which are resistant to environmental corrosion and have good waterproof performance. It is used to isolate external air and moisture, prevent the surface material of the detection array from falling off, and thus protect the sensing structure.

[0037] More specifically, the number of parallel detectors in the fiber optic ultrasonic detector, i.e., the number of reusable detector elements, is mainly determined by the repetition frequency of the trigger controller 7 and the imaging depth of the system, involving the following formula: (1) (2) (3) in, N To detect the number of array elements, N Take a positive integer. t acq The single acquisition time of digital acquisition card 13. T This refers to the duration of the pulsed optical signal modulated by modulator 4, which is also the acquisition time of a single-channel probe optical signal. RF The repetition frequency of the trigger controller 7 is as shown in formula (1), and its value is the reciprocal of the single acquisition time of the digital acquisition card 13. S is the transmission speed of ultrasound in water, which is taken as 1500 m / s. D The system's imaging depth is the vertical distance between the fiber optic ultrasonic detector and the target. Depending on the imaging method, in formula (2)... D and TThe values ​​must correspond. Taking reflective imaging as an example, for reflective ultrasound imaging, after the ultrasound signal output by the ultrasound transmitter is transmitted to the surface of the target, it needs to return to the fiber optic ultrasound detector array 8 for signal reception. Therefore, the actual transmission distance of the ultrasound signal is a two-way trip. D In formula (2) T It needs to be doubled; for reflective ultrasound imaging, the actual transmission distance of the photoacoustic signal output from the photoacoustic excitation source is also two-way. D However, since the speed of light in water is much greater than the speed of sound in water, the time it takes for the excitation laser to reach the target can be ignored. Therefore, in formula (2) T This is the actual transmission time of the photoacoustic signal. From formula (3), we can see that the repetition frequency of the trigger controller 7... RF Smaller, system imaging depth D The smaller the value, the more reusable the detection system becomes. N The more repetition frequency, the longer the acquisition interval and the lower the detection rate. Furthermore, medical imaging also has certain requirements for imaging depth; insufficient depth makes it difficult to meet application needs. Therefore, the actual number of reusable detection array elements is limited. N A specific analysis based on the requirements is needed. Furthermore, constraints such as the dispersion characteristics of the optical fiber, the spatial volume of the delay fiber, the insertion loss of the multiplexing devices, and the power limit of the light source output must be comprehensively considered to ultimately determine the number of parallel detectors required for the fiber optic ultrasonic detector. N .

[0038] To further explain, the first aspect of this invention... N Branch routes N -1 delay fiber is used as the delay medium in the transmission path of the detector array element, the first... N -1 branch route N Two delay fibers are used as the delay medium in the transmission path of the detection array element, and so on, thus achieving the differentiation of the detection optical signal at the optical path transmission level. By using the fiber itself for signal delay, the shortcomings of insufficient stability and low delay accuracy of electrical components are cleverly avoided, thereby improving system performance.

[0039] Combination Figure 1 The technical solution adopted in this invention is based on fiber length gradient. N Branch differential delay. Includes: 1× N Fiber optic bundle splitter 5, circulator 9, delay fiber 10, N ×1 Fiber optic combiner 11.

[0040] Specifically, for N Each detector element, the laser first passes through 1× N Fiber optic beam splitter 5 is divided into NThe optical signal is transmitted through a circulator, with one circulator 9 placed in each branch to ensure unidirectional transmission in a specific order. Meanwhile, for the first... N Branch roads need to be equipped with N -1 delay fiber 10, for the first N -1 branch road needs to be equipped with N - Two delay fibers 10 are required, meaning that no delay fiber 10 needs to be set in the transmission path of the first detector element, and the rest... N Each detector element is equipped with a 10-meter delay fiber. In addition, the entire system requires one... N ×1 fiber optic combiner 11, N The detection light is coupled and output from the detection array element. Therefore, the first... N The delay path of each detection element is N -1 delay fiber, 10 lengths superimposed, the first N The delay path for -1 detector element is N The signal delay between adjacent detector elements is the sum of the lengths of two delay fibers 10, and so on. This is the transmission time of the light beam in a single delay fiber 10. Based on this, the detection optical signals of each detector element can be distinguished.

[0041] The 1× N Fiber optic beam splitter 5 selected N A beam splitter that distributes optical power evenly across all branches ensures that each branch has the same splitting ratio.

[0042] The circulator 9 is a three-port circulator, with the first port a connected to 1× N The fiber optic beam splitter 5 has its second port b connected to the fiber optic ultrasonic detector array 8, and its third port c connected to the delay fiber 10. The light split by the beam splitter is coupled into the first port a of the circulator 9, and injected into the fiber optic ultrasonic detector array 8 from the second port b. The probe light signal, modulated by the external ultrasonic waves, is reflected from the fiber optic ultrasonic detector array 8, enters again through the second port b of the circulator 9, and is output from the third port c of the circulator 9.

[0043] The delay fiber 10 is selected as a single-mode fiber, based on the formula for the propagation delay of light per unit length of fiber: (4) (5) (6) in, For optical path, n 0 represents the effective refractive index of the fiber core. L Let c be the length of the optical fiber, and c be the speed of light in a vacuum, with a value of 3 × 10⁻⁶. 8 m / s, v The speed at which light travels in an optical fiber. This represents the transmission time of an optical signal per unit length of optical fiber.

[0044] The N ×1 fiber optic combiner 11, N The detection light from each branch is coupled together and output to the photodetector 12.

[0045] To further illustrate, this invention can be implemented using only one photoelectric conversion device. N The photoelectric signal conversion of each detector element can be performed through only one acquisition channel. N Signal acquisition from each detection branch. Unlike traditional signal acquisition methods that configure an independent photodetector for each circulator, this invention significantly reduces the number of electrical components used, saving energy. N -1 photodetector and N One digital acquisition card simplifies the system structure and saves production costs.

[0046] Combination Figure 1 The technical solution adopted in this invention is a multi-channel parallel acquisition based on a minimalist component deployment. It includes: a photodetector 12 and a digital acquisition card 13.

[0047] Specifically, when the tunable continuous laser 3 outputs probe light with the same operating wavelength as the fiber optic ultrasonic detector array 8, after being modulated by the modulator 4, the output probe light enters the fiber optic ultrasonic detector array 8 through the circulator 9. At this time, the probe light will reflect back and forth within the sensing cavity with a Fabry-Perot structure, forming interference, and will be modulated by external ultrasonic waves. Afterwards, the ultrasonically modulated beam carries ultrasonic signal information back to the circulator 9 and exits from the third port c, passing through a delay fiber 10 before being... N The ×1 fiber optic combiner 11 couples the optical signal into a single beam, which is then output to the photodetector 12. The photodetector 12 converts the received optical signal into an electrical signal and outputs it to the digital acquisition card 13 for further signal processing.

[0048] The photodetector 12 is connected at one end to N The ×1 fiber optic combiner 11 performs photoelectric conversion processing on the optical signal received from the combiner, converting it into an electrical signal output for subsequent signal analysis.

[0049] The digital acquisition card 13 receives the signal converted by the photodetector 12. By combining the acquisition rate, the transmission delay of light within a unit length of optical fiber, and the return time of the detection signal of each detection element, the time requirement of the delay signal of the detection element can be determined, thereby reasonably setting the length of the delay optical fiber 10, so as to achieve the purpose of different detection signals arriving at the same photodetector 12 in sequence.

[0050] More specifically, the digital acquisition card 13 is controlled by the trigger controller 7, and the acquisition start time is synchronized with the ultrasonic or photoacoustic signal emission start time of the ultrasonic generating device 6. For example... Figure 3 As shown, firstly, the signal generating device 1 sends a pulse trigger signal to the modulator 4 at time t0 via the driver 2, modulating the continuous light emitted by the tunable continuous laser 3 into a duration from t0 to t... m The pulsed light output. Simultaneously, the trigger controller 7 controls the ultrasonic generator 6 to generate ultrasonic or photoacoustic signals, and synchronously controls the digital acquisition card 13 to acquire the signals. For devices with... N A fiber optic ultrasonic detector array with 8 detector elements, at time t0. N Several fiber optic ultrasonic detectors simultaneously detect ultrasonic or photoacoustic signals and return at time t1. However, the lengths of the delay fibers 10 in each branch differ. N The different transmission paths of the branch detection signals returning to photodetector 12 result in different arrival times for each branch detection signal to reach digital acquisition card 13. The length of the transmission path determines the order in which the acquisition card receives the branch detection signals. In branch Ch1, where the first detection element is located, no delay fiber 10 is provided, so the detection signal arrives at the acquisition card first at time t1. In branch Ch2, where the second detection element is located, one delay fiber 10 is provided, so the detection signal arrives at the acquisition card at time t2, and so on. N The branch where each detection element is located (Ch) N set up N -1 delay fiber 10, the detection signal at t N The data finally arrives at the acquisition card. Thus, the first complete acquisition is finished. N The channel detection signals are acquired in parallel, avoiding signal aliasing. Then, the signal generation device 1... The pulse trigger signal is sent for the second time at time 1, and the second complete pulse trigger is performed. N The channel detection signals are acquired in parallel, and so on, repeating the above steps until the end.

[0051] To further explain, this invention follows the basic idea of ​​combining channel-level parallel operation between multiple detector array elements with segment-level multi-layer processing within a single detector array element. It further processes the digital signals received by the digital acquisition card, solving the problem of performance differences caused by manufacturing errors and resolution degradation caused by arrangement errors in the detector array, and optimizing the image reconstruction quality.

[0052] Combination Figure 4 The technical solution adopted in this invention is image reconstruction based on an array parallel architecture. It includes a terminal processor 14.

[0053] Specifically, when the digital acquisition card 13 transmits the converted digital signal to the terminal processor 14, the detection signal is received and stored, such as... Figure 4 As shown, GPU-accelerated N Thread-block parallel computing ensures high-speed parallel processing of multi-channel signals, thereby improving data processing efficiency. At the same time, each detection channel signal is divided into different segments, and corresponding threads are allocated to independently execute three layers of processing, maximizing the parallel execution efficiency of the GPU and efficiently completing various preprocessing of the detection signals. This improves the system signal-to-noise ratio and compensates for the degradation of imaging resolution caused by minor errors in fiber processing technology and packaging arrangement.

[0054] The three processing levels executed independently by the allocated thread are the detrending processing level, the denoising and enhancement processing level, and the image reconstruction processing level. This invention will use... N The first randomly selected element from the detection array signal R Taking a single detection array element as an example, combined with its division into... r Each independent segment explains the operational steps of these three processing levels.

[0055] More specifically, the first-level processing stage, "CEEMDAN decomposition + TEO feature extraction," aims to identify and remove signal trend components, solving the problem of effective signal overwhelmed by trend masking, and providing high-purity useful signal input for subsequent denoising and imaging. For example... Figure 4 As shown in (a), for a certain sampling time point p First, Ch R The detected signals are divided into r Each non-overlapping time segment is assigned a corresponding thread for task processing. Signals for each segment are transmitted via... M The next iteration injects zero-mean white noise, and the resulting CEEMDAN decomposition yields multiple Intrinsic Mode Function (IMF) components. and a residual This is expressed by equation (7). Secondly, splicing in the time domain... r The IMF components of each signal segment are then analyzed. Subsequently, a Fast Fourier Transform is performed on each IMF component to extract frequency features, and the maximum frequency corresponding to the amplitude spectrum is taken as the dominant frequency. f k Simultaneously, the transient similarity between the IMF and the original signal was calculated using TEO, and the Pearson correlation coefficient was used. ρ k This indicates. Finally, through ρ k > α and f k < f thres The threshold condition filters out low-frequency signals that are highly correlated with the original signal, treats them as trend mode components, and removes them, while the remaining signals are retained.

[0056] (7) in, k The order of the decomposition is... E 1. Represents the operator for extracting the first-order IMF. For the injected adaptive noise amplitude, For the first m Zero-mean white noise injected in the second phase, α The correlation threshold, f thres This is an adaptive frequency threshold.

[0057] More specifically, the second processing stage, "BM3D denoising based on Wiener filtering," aims to suppress unwanted noise, enhance useful signals, solve noise interference problems, and provide high-fidelity signal input for subsequent imaging. For example... Figure 4 As shown in (b), firstly, the reconstructed signal after detrending processing is divided into... i Each of the 1D (One-Dimensional) overlapping blocks is found within the search window based on Euclidean distance. K The most similar blocks b i,0 , b i,1 、 … 、b i,K-1 Form a set of similar blocks Secondly, they are stacked into a 3D (Three-Dimensional) array along the similarity dimension. i The 3D arrays converted from the set of similar blocks are denoted as follows: , … As shown in equation (8). Then, 3D Discrete Cosine Transform (DCT) is performed on these arrays respectively to achieve signal conversion from the spatial domain to the transform domain. The energy of the effective ultrasonic signal will be concentrated in the transform domain coefficients at the corresponding frequencies, while noise will be dispersed. Next, the transform domain coefficients are calculated by estimating the ratio of signal power to total power in the transform domain. Wiener gain at various locations The result is expressed by equation (9). When the Wiener gain is close to 1, it indicates that the energy at that location is concentrated and represents a useful ultrasonic signal, so the coefficient is retained; when it is close to 0, it indicates that the energy at that location is dispersed and represents useless noise, so the coefficient is suppressed. Finally, the filtered coefficients are subjected to inverse DCT, transforming from the transform domain back to the spatial domain, to obtain the denoised 3D array as follows: , … Then, based on similarity, a weighted merging process is performed to eliminate block boundary effects and recover a continuous and complete signal.

[0058] (8) (9) in, Q The length of each 1D block, For the first Q- At the first sampling location, the first i The first 1D block K -1 similar blocks, This is the transformation index along the length of the 1D block, with a value range of [0, ...]. Q -1], This is the transformation index in the direction of the number of similar blocks, with a value range of [0, ...]. K -1], This is the index of the third-dimensional transform of the 1D signal, and is always 0. The estimated values ​​of the effective signal power at each coefficient position in the transform domain. This is an estimate of the global noise power in the transform domain.

[0059] More specifically, the third processing layer, "DAS-based SAFT image reconstruction," aims to focus the denoised signals of each detector element onto the imaging point, achieving high-resolution two-dimensional or three-dimensional image reconstruction. For example... Figure 4 As shown in (c), firstly, the XY plane is taken as the detection scanning plane, and the Z-axis is the imaging depth direction, thus constructing an XYZ three-dimensional imaging space. For the randomly selected... R Location of each detection element Its distance from any imaging point straight-line distance This is expressed by equation (10). Secondly, the time delay required for the signal from each detector element to reach the imaging point is obtained to ensure that each detector element arrives at the same imaging point in phase and is superimposed. Finally, the denoised signals from each detector element are superimposed after a delay and focused to obtain the imaging point. Total signal strength It is represented by equation (11).

[0060] (10) (11) in, To detect array elements R The signal after noise reduction Delay The signal obtained afterward.

[0061] According to some embodiments of the present invention, Figure 5This is an imaging result diagram of an embodiment of the present invention under 10 MHz pulsed ultrasound. The number of detector elements in the fiber optic ultrasonic detector array... N The fiber optic beam splitter is 1×3, ensuring uniform beam splitting in each branch. After passing through a 2500 m length-gradient delay fiber, the three probe optical signals are coupled into a single signal via a 3×1 fiber combiner and output to the photodetector. The fiber optic ultrasonic detector array is perpendicular to the scanning direction, with the three detector elements arranged linearly and uniformly. It performs a transmission scan on a solid metal plate with a 4 mm diameter circular through-hole at its center within a 10 mm × 10 mm XY plane. The fiber optic ultrasonic detector array experiences three detection states: "without obstruction - with obstruction - without obstruction". Figure 5 As shown in the two-dimensional reconstruction diagram (a) in the image, when the signal is in the state of "with obstruction" (scanning to the solid metal plate), the signal strength is significantly lower than that when it is in the state of "without obstruction" (scanning to the through hole). This is because sound waves undergo attenuation and diffraction when passing through obstacles, which is visually manifested as a decrease in the amplitude of the detected signal. Based on this, Figure 5 As shown in (b) of the 3D reconstruction effect diagram, this embodiment has achieved accurate identification of the shape of the target under test. Therefore, the embodiment provided by the present invention corresponds the reconstructed image to the actual scanning range, presenting excellent imaging effect. Moreover, the array scanning speed is increased exponentially with the number of detector elements compared to the single-point scanning speed, improving time utilization while ensuring high-quality imaging.

[0062] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. It should be noted that the terms "in one embodiment," "for example," and "again" in this invention are intended to illustrate the invention and are not intended to limit the invention.

[0063] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. 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.

Claims

1. An array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection, characterized in that, include: The light source module is used to output a rectangular pulse sequence as a probe light signal, which is then transmitted to the fiber optic ultrasonic detector array. The sound source module is used to provide ultrasonic or photoacoustic signals to the target under test, which are reflected, scattered or transmitted to the fiber optic ultrasonic detector array. The fiber optic ultrasonic detector array is used to receive the detection optical signal in multiple channels, and simultaneously receive the ultrasonic or photoacoustic signals reflected, scattered or transmitted by the target under test in multiple channels. The ultrasonic or photoacoustic signals act on the fiber optic ultrasonic detector array with a fiber optic ultrasonic sensing structure, causing the properties of the detection optical signal to change and carry the target information, thereby transmitting multiple detection optical signals carrying the target information. The fiber optic delay module is used to delay multiple probe optical signals carrying information about the target to be tested, forming a multi-channel probe signal. The signal acquisition and imaging module is used to acquire data by photoelectric conversion of multi-channel probe light signals, and to obtain the target information by using imaging algorithms to achieve two-dimensional or three-dimensional imaging.

2. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 1, characterized in that, The light source module includes: The signal generating device (1) is used to generate an electrical signal with a preset frequency, waveform and amplitude; the driver (2) is used to drive the modulator (4) to work according to the electrical signal generated by the signal generating device (1); the tunable continuous laser (3) is used to output a continuous laser with a tunable wavelength; the modulator (4) is used to modulate the continuous laser into a rectangular pulse sequence for output as a probe light signal.

3. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 1, characterized in that, The sound source module includes: An ultrasonic generating device (6) is used to generate ultrasonic or photoacoustic signals; a trigger controller (7) is used to control the triggering of the ultrasonic generating device (6).

4. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 1, characterized in that, The fiber optic ultrasonic detector array (8) includes N Each of the detection array elements comprises: Transmission fiber (8-1), used sequentially for transmission N The optical fiber detector is used to detect the ultrasonic or photoacoustic signals reflected, scattered, or transmitted by the target. After being modulated by sound pressure, the internal detector optical signal will undergo changes in intensity, wavelength, and phase, carrying the target information. The detector optical signal carrying the target information is then transmitted through the transmission optical fiber.

5. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 1, characterized in that, The fiber optic ultrasonic sensing structure includes a resonant fiber optic ultrasonic sensing structure or a non-resonant fiber optic ultrasonic sensing structure. The resonant fiber optic ultrasonic sensing structure includes a Fabry-Perot cavity, a fiber Bragg grating, and a microring resonator.

6. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 1, characterized in that, The fiber delay module includes: 1× N Fiber optic beam splitter (5) is used to evenly distribute the probe optical signal to N Transmission is performed through each port, forming... N The path detection optical signal; circulator (9), each circulator (9) includes a first port, a second port and a third port, the third port... N The path detection optical signal is input to the first N The first port of each circulator (9) leads to the second port, and the detection light signal carrying the target information enters the circulator (9) through the second port and is output from the third port. N The path detection optical signal passes through the first to the second in sequence. N The output of each circulator (9) is the first to the second. N The path carries the detection optical signal of the target to be tested; the delay fiber (10) is used to sequentially increase the transmission time of each detection optical signal in the fiber, so that the signals received by each detection array element are distinguished and the phenomenon of signal aliasing is avoided. N ×1 fiber combiner (11) is used to combine the first probe optical signal and the delayed second to third fiber bundles. N The channel detection optical signals are combined into one output.

7. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 3, characterized in that, The signal acquisition and imaging module includes: A photodetector (12) is used to receive the detection light signal after beam combining and convert the light signal into an electrical signal; a digital acquisition card (13) is used to acquire electrical signals containing multi-channel detection information in parallel and to perform sampling, quantization, and encoding processing to convert analog electrical signals into digital electrical signals. The triggering of the digital acquisition card (13) is controlled by the trigger controller (7); a terminal processor (14) is used to execute an imaging algorithm based on an array parallel architecture, which combines channel-level parallel operation between each detection array element with segment-level multi-layer processing within a single detection array element to complete detrending processing, noise reduction enhancement, and image reconstruction of multiple signals.

8. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 3, characterized in that, The ultrasonic generating device (6) is an ultrasonic transmitter or a photoacoustic excitation source.

9. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 1, characterized in that, The delay fiber (10) is used to sequentially increase the transmission time of each probe optical signal in the fiber, including: The second to the third N The detection light signal carrying the information of the target to be measured passes through one to one in sequence. N -1 delay fiber (10) to form the second to the third N Channel detection signal, number N The channel's delay path is N The superposition of -1 delay fiber (10) lengths, the first N The delay path for -1 detector element is N The signal delay between adjacent channels is the transmission time of the probe optical signal in a single delay fiber (10) by superimposing the lengths of the two delay fibers (10). By delaying the return time of signals from different channels, the detection signals of each detection element are distinguished.

10. The array-type fiber optic ultrasonic imaging system based on multi-path time-delay parallel detection according to claim 3, characterized in that, The imaging algorithm includes the following operation flow: The system utilizes a GPU to accelerate multi-threaded block computation, enabling channel-level parallel analysis of multi-channel probe signals. A single-channel probe signal is divided into multiple segments, and threads within each segment independently execute a three-layer processing stage to achieve segment-level parallel analysis. The first processing layer uses the fully integrated empirical mode CEEMDAN to adaptively decompose the signal, and, in conjunction with the Teager energy operator TEO, calculates the instantaneous energy characteristics of each mode to analyze, identify, and remove modal trend components. The second layer uses a block-matching 3D filtering algorithm (BM3D) based on Wiener filtering for noise suppression. The third layer employs the synthetic aperture focusing technique SAFT based on time-delay superposition DAS to reconstruct the image of the target, displaying the reconstructed 2D or 3D image on a host computer.

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