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Fiber Optics and Optical Communications|746 Article(s)
First Arrival Time Pickup Method of Vibration Signals for Distributed Acoustic Sensing Systems
Liang Huang, Lei Liang, Ke Jiang, and Shangming Du
Two-dimensional (2D) spatial position of a vibration source in an optical distributed acoustic sensing (DAS) system can be determined based on a phase-sensitive optical time-domain reflectometer. However, due to interference and noise, this approach may acquire inaccurate arrival time information of the first arrival wave of the vibration source at different positions of the optical cable, resulting in large positioning errors. In this study, we propose a method of estimating the first arrival wave of the vibration source in a DAS system based on bilateral filtered edge detection. First, the spatio-temporal 2D signals collected by the DAS system were converted into a gray-scale map, and then the bilateral filtering method was used to reduce the noise. The edge features in the gray-scale image were extracted using a Canny operator-based edge detection method to obtain the first arrival time of the source. The proposed method can simultaneously consider the overall temporal and spatial characteristics of spatio-temporal 2D data and improve the accuracy of low signal-to-noise ratio signal of first arrival time pickup. Results show that for low signal-to-noise ratio signals affected by interference and system noise, the average error for pickup arrival time does not exceed 3 ms, pickup accuracy is higher than that of the traditional method; the algorithm takes only 0.1 s on average, and pickup time consumption is low. Two-dimensional (2D) spatial position of a vibration source in an optical distributed acoustic sensing (DAS) system can be determined based on a phase-sensitive optical time-domain reflectometer. However, due to interference and noise, this approach may acquire inaccurate arrival time information of the first arrival wave of the vibration source at different positions of the optical cable, resulting in large positioning errors. In this study, we propose a method of estimating the first arrival wave of the vibration source in a DAS system based on bilateral filtered edge detection. First, the spatio-temporal 2D signals collected by the DAS system were converted into a gray-scale map, and then the bilateral filtering method was used to reduce the noise. The edge features in the gray-scale image were extracted using a Canny operator-based edge detection method to obtain the first arrival time of the source. The proposed method can simultaneously consider the overall temporal and spatial characteristics of spatio-temporal 2D data and improve the accuracy of low signal-to-noise ratio signal of first arrival time pickup. Results show that for low signal-to-noise ratio signals affected by interference and system noise, the average error for pickup arrival time does not exceed 3 ms, pickup accuracy is higher than that of the traditional method; the algorithm takes only 0.1 s on average, and pickup time consumption is low.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906009 (2024)
High-Sensitivity Liquid Level Sensor Based on Seven Core Fiber
Min Shao, Hanping Li, Xue Zhao, Dakuan Yu, and Xueguang Qiao
A liquid level sensor based on a single mode-peanut-seven core-peanut-single mode fiber structure is developed. The sensor uses the "peanut structure" as a fiber coupler to improve the coupling efficiency of the single-mode fiber and seven-core fiber. The first fiber "peanut structure" is used to excite the cladding mode, and the second fiber "peanut structure" couples the cladding mode with the core mode to produce interference. Because a phase difference between the cladding and core-based modes appears as they transmit through the seven-core fiber, when the liquid level of the environmental solution changes, the phase difference changes, eventually changing the transmission spectrum. In this study, the liquid level and temperature response characteristics of the sensors with seven-core fiber lengths of 24, 28, and 32 mm were experimentally studied. The experimental results show that with the increase of the liquid level, the transmission spectrum of the sensor shows a blue shift. The liquid level sensitivities of the three sensors are -0.4069, -0.2739, and -0.1653 nm/mm, and their liquid level measurement ranges are 24, 28, and 32 mm, respectively. In the water temperature range of 35?90 ℃, the transmission spectrum of the sensor shows a red shift with an increase in temperature. The temperature sensitivities of the three sensors are 0.0885, 0.0740, and 0.0879 nm/℃. The experiment shows that the sensor has the characteristics of high sensitivity, low cost, and simple fabrication, indicating that it has a good application prospect in the petrochemical industry and other fields. A liquid level sensor based on a single mode-peanut-seven core-peanut-single mode fiber structure is developed. The sensor uses the "peanut structure" as a fiber coupler to improve the coupling efficiency of the single-mode fiber and seven-core fiber. The first fiber "peanut structure" is used to excite the cladding mode, and the second fiber "peanut structure" couples the cladding mode with the core mode to produce interference. Because a phase difference between the cladding and core-based modes appears as they transmit through the seven-core fiber, when the liquid level of the environmental solution changes, the phase difference changes, eventually changing the transmission spectrum. In this study, the liquid level and temperature response characteristics of the sensors with seven-core fiber lengths of 24, 28, and 32 mm were experimentally studied. The experimental results show that with the increase of the liquid level, the transmission spectrum of the sensor shows a blue shift. The liquid level sensitivities of the three sensors are -0.4069, -0.2739, and -0.1653 nm/mm, and their liquid level measurement ranges are 24, 28, and 32 mm, respectively. In the water temperature range of 35?90 ℃, the transmission spectrum of the sensor shows a red shift with an increase in temperature. The temperature sensitivities of the three sensors are 0.0885, 0.0740, and 0.0879 nm/℃. The experiment shows that the sensor has the characteristics of high sensitivity, low cost, and simple fabrication, indicating that it has a good application prospect in the petrochemical industry and other fields.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906008 (2024)
Structural Design and Investigation of Micro-Broadband Fiber Bragg Grating Vibration Sensor
Huizhi Zhao, Mingli Dong, Jingtao Xin, Yanming Song, Xu Zhang, and Jun Wu
A miniaturized, wide-band, high-sensitivity fiber Bragg grating (FBG) vibration sensor is proposed. The millimeter-scale FBG is used to design the sensor structure. The "lever hinge" structure is used as the strain transfer beam, and the center of gravity of the entire mass block is adjusted by hollowing out the end of the mass block, which improved the natural frequency of the sensor. This structure increases the natural frequency of the sensor with a slight decrease in sensitivity. In this study, a vibration sensor with a volume of 15 mm × 15 mm × 15 mm is designed to satisfy the miniaturization requirements of sensors on space cameras, and structural design and finite element simulation analysis were performed. The structural optimization of the sensor is completed, considering the working frequency band and sensitivity. The sensor is fabricated by millimeter FBG writing and sensor packaging. A vibration test system is built to test and analyze the characteristics of the sensor. The results show that the natural frequency of the sensor is approximately 1250 Hz, the sensitivity exceeds 83.3 pm·g-1 when the excitation frequency is 750 Hz, the lateral anti-interference ability of the sensor is excellent, and the cross-sensitivity is lower than 4%. A miniaturized, wide-band, high-sensitivity fiber Bragg grating (FBG) vibration sensor is proposed. The millimeter-scale FBG is used to design the sensor structure. The "lever hinge" structure is used as the strain transfer beam, and the center of gravity of the entire mass block is adjusted by hollowing out the end of the mass block, which improved the natural frequency of the sensor. This structure increases the natural frequency of the sensor with a slight decrease in sensitivity. In this study, a vibration sensor with a volume of 15 mm × 15 mm × 15 mm is designed to satisfy the miniaturization requirements of sensors on space cameras, and structural design and finite element simulation analysis were performed. The structural optimization of the sensor is completed, considering the working frequency band and sensitivity. The sensor is fabricated by millimeter FBG writing and sensor packaging. A vibration test system is built to test and analyze the characteristics of the sensor. The results show that the natural frequency of the sensor is approximately 1250 Hz, the sensitivity exceeds 83.3 pm·g-1 when the excitation frequency is 750 Hz, the lateral anti-interference ability of the sensor is excellent, and the cross-sensitivity is lower than 4%.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906007 (2024)
Photonics-Aided Quadruple Frequency W-Band Linear Frequency Modulated Signal Sensing and Ranging
Longwei Pan, Yanyi Wang, Yuxuan Tan, Yuangang Wang, Kaihui Wang, and Wen Zhou
A new system based on optical external modulator frequency multiplication is proposed to generate W-band linear frequency modulated (LFM) signals for high-resolution ranging. The LFM signals from the arbitrary waveform generator (AWG) are modulated to the sideband of the optical carrier through the optical modulator. The photoelectric conversion is completed in the photodetector (PD) to generate quadruple frequency W-band LFM signals, whose center frequency and bandwidth are four times the original LFM signal. This broadband LFM signal is emitted to free space for target detection. For distance measurements, the two targets are separated by 50 cm, and the measured value is 48.8 cm with an error of 1.2 cm. The distance between the two objects is set to 40 cm to demonstrate the reliability of the experiment. The measured value is 38.9 cm, and the error is 1.1 cm. The system overcomes the “electronic bottleneck” that is difficult to directly generate high-frequency signals in the electrical domain and achieves high-resolution ranging via photonics-aided generation of the broadband LFM signal. Thus, the proposed method provides a solution for future ultrahigh-resolution LFM continuous-wave radar systems. A new system based on optical external modulator frequency multiplication is proposed to generate W-band linear frequency modulated (LFM) signals for high-resolution ranging. The LFM signals from the arbitrary waveform generator (AWG) are modulated to the sideband of the optical carrier through the optical modulator. The photoelectric conversion is completed in the photodetector (PD) to generate quadruple frequency W-band LFM signals, whose center frequency and bandwidth are four times the original LFM signal. This broadband LFM signal is emitted to free space for target detection. For distance measurements, the two targets are separated by 50 cm, and the measured value is 48.8 cm with an error of 1.2 cm. The distance between the two objects is set to 40 cm to demonstrate the reliability of the experiment. The measured value is 38.9 cm, and the error is 1.1 cm. The system overcomes the “electronic bottleneck” that is difficult to directly generate high-frequency signals in the electrical domain and achieves high-resolution ranging via photonics-aided generation of the broadband LFM signal. Thus, the proposed method provides a solution for future ultrahigh-resolution LFM continuous-wave radar systems.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906006 (2024)
Research on Φ-OTDR Perimeter Security Monitoring Based on GAF-HorNet
Sheng Hu, Xinmin Hu, Shasha Li, Lü Puchu, Haixin Qin, Can Zhao, Minghu Wu, and Cong Liu
Phase-sensitive optical time-domain reflection (Φ-OTDR) technology is a distributed fiber-optic sensing technique with the advantage of high-precision vibration monitoring. It can be used to detect disturbance events in the field of perimeter security. Traditional recognition methods require the manual extraction of vibration signal features and cannot retain a time correlation, leading to information loss. To solve this problem, a disturbance event recognition method based on GAF-HorNet, which does not require a feature extraction step, is developed. A one-dimensional vibration signal is converted into a two-dimensional image through a Gramian angular field (GAF), and HorNet is used to train the model and perform recognition and classification. To verify the performance of the algorithm, four classical algorithms are selected to train the model for comparative experiments. The experimental results demonstrate that the average accuracy of the proposed algorithm is 93.56% for six types of signal: background noise, stone knocking, stone stroking, branch stroking, pulling, and climbing. Compared with previous methods, the method proposed has better recognition rate and false alarm rate performances. Phase-sensitive optical time-domain reflection (Φ-OTDR) technology is a distributed fiber-optic sensing technique with the advantage of high-precision vibration monitoring. It can be used to detect disturbance events in the field of perimeter security. Traditional recognition methods require the manual extraction of vibration signal features and cannot retain a time correlation, leading to information loss. To solve this problem, a disturbance event recognition method based on GAF-HorNet, which does not require a feature extraction step, is developed. A one-dimensional vibration signal is converted into a two-dimensional image through a Gramian angular field (GAF), and HorNet is used to train the model and perform recognition and classification. To verify the performance of the algorithm, four classical algorithms are selected to train the model for comparative experiments. The experimental results demonstrate that the average accuracy of the proposed algorithm is 93.56% for six types of signal: background noise, stone knocking, stone stroking, branch stroking, pulling, and climbing. Compared with previous methods, the method proposed has better recognition rate and false alarm rate performances.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906005 (2024)
Damage Detection Method for Wind Turbine Blade Based on Optical Frequency Domain Reflectometry
Junchao Dong, Mingming Luo, Jianfei Liu, and Wenrong Yang
A new wind turbine blade damage detection method is proposed to address the challenges surrounding imprecise positioning and the inability to monitor the turbine under operating conditions, which is a shortcoming of traditional wind turbine blade damage detection. The proposed method uses optical frequency domain reflectometry(OFDR) to measure the surface strain of the wind turbine blade. Subsequently, fast Fourier transform is taken for the strain value and its fundamental frequency amplitude is taken to obtain the blade surface strain distribution. On this basis, the position, length and width of the blade damage are calculated. According to the relationship between the strain and damage degree, the damage degree judgment formula is fitted, and the blade damage degree is identified. Based on OFDR, a cantilever beam damage detection experiment is designed to simulate the instantaneous state of the cantilever beam vibration, and the damage location is identified according to the strain distribution, which verifies the feasibility of the proposed damage identification method. A new wind turbine blade damage detection method is proposed to address the challenges surrounding imprecise positioning and the inability to monitor the turbine under operating conditions, which is a shortcoming of traditional wind turbine blade damage detection. The proposed method uses optical frequency domain reflectometry(OFDR) to measure the surface strain of the wind turbine blade. Subsequently, fast Fourier transform is taken for the strain value and its fundamental frequency amplitude is taken to obtain the blade surface strain distribution. On this basis, the position, length and width of the blade damage are calculated. According to the relationship between the strain and damage degree, the damage degree judgment formula is fitted, and the blade damage degree is identified. Based on OFDR, a cantilever beam damage detection experiment is designed to simulate the instantaneous state of the cantilever beam vibration, and the damage location is identified according to the strain distribution, which verifies the feasibility of the proposed damage identification method.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906004 (2024)
Coherent Optical Communication Speed Measurement Method Based on Modulated Code Element Doppler Frequency Measurement
Quan Zhang, Qingchen Xu, Xiong Hu, Xiaocheng Wu, and Junfeng Yang
High precision inter-satellite velocity measurement technology is one of the key technologies for realizing integration of satellite laser communication measurements and autonomous navigation. We propose an inter-satellite coherent optical communication link velocity measurement method based on modulated code element Doppler measurement. The method adopts a one-way unidirectional approach to obtain phase-continuous code element Doppler signals by using the phase and symbol information of code element symbol synchronization and verdict at the receiver side and by removing the phase modulation information in the baseband sampling data. This can aid in realizing the real-time high accuracy of satellite relative motion velocity while completing inter-satellite communication. The simulation results verify that this method can achieve the relative velocity measurement from 0 to 11.625 km/s at a communication rate of 1 Gbit/s and bit error rate (BER) of 10-9. Furthermore, the velocity measurement uncertainty exceeds 10.00 mm/s. High precision inter-satellite velocity measurement technology is one of the key technologies for realizing integration of satellite laser communication measurements and autonomous navigation. We propose an inter-satellite coherent optical communication link velocity measurement method based on modulated code element Doppler measurement. The method adopts a one-way unidirectional approach to obtain phase-continuous code element Doppler signals by using the phase and symbol information of code element symbol synchronization and verdict at the receiver side and by removing the phase modulation information in the baseband sampling data. This can aid in realizing the real-time high accuracy of satellite relative motion velocity while completing inter-satellite communication. The simulation results verify that this method can achieve the relative velocity measurement from 0 to 11.625 km/s at a communication rate of 1 Gbit/s and bit error rate (BER) of 10-9. Furthermore, the velocity measurement uncertainty exceeds 10.00 mm/s.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906003 (2024)
Design of Pattern Reconfigurable Microstrip Array Antenna in Terahertz Band
Ying Wang, Chunshu Li, and Xiang Yan
A graphene-based reconfigurable microstrip array antenna suitable for the terahertz band was designed in this study. The design combined the unique advantages of grapheme for impedance matching and electrical controllability in the terahertz band and the characteristics of high radiation efficiency of the reconfigurable microstrip array antenna. The array antenna unit embedded a graphene patch in the radiant patch as a switch and changed the switch's on-off and off-off states by adjusting the applied bias voltage of graphene. The antenna unit and the array antenna have an operating frequency of 5.012 THz. The antenna unit exhibits strong gain characteristics and anti-interference performance, and can realize the pattern of adjustment to 12°?24° at the working frequency. The 2×2 microstrip array antenna composed of the antenna unit can realize the pattern reconfiguration function of 0°?13°. The simulation results show that the maximum gain of the array antenna is 12.5 dBi and the maximum beam width is 51.4°. In addition, the array antenna exhibits good directivity and anti-interference ability. A graphene-based reconfigurable microstrip array antenna suitable for the terahertz band was designed in this study. The design combined the unique advantages of grapheme for impedance matching and electrical controllability in the terahertz band and the characteristics of high radiation efficiency of the reconfigurable microstrip array antenna. The array antenna unit embedded a graphene patch in the radiant patch as a switch and changed the switch's on-off and off-off states by adjusting the applied bias voltage of graphene. The antenna unit and the array antenna have an operating frequency of 5.012 THz. The antenna unit exhibits strong gain characteristics and anti-interference performance, and can realize the pattern of adjustment to 12°?24° at the working frequency. The 2×2 microstrip array antenna composed of the antenna unit can realize the pattern reconfiguration function of 0°?13°. The simulation results show that the maximum gain of the array antenna is 12.5 dBi and the maximum beam width is 51.4°. In addition, the array antenna exhibits good directivity and anti-interference ability.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906002 (2024)
Vortex Mode Amplification Based on Ring-Core Fiber Doped with PbSe Quantum Dots
Hengfei Guo, Huimei Wei, Na Chen, Yanhua Dong, Jianxiang Wen, Yana Shang, Zhenyi Chen, and Fufei Pang
The PbSe quantum dot-doped ring-core fiber is successfully prepared using a modified chemical vapor deposition method. The fiber has a double-clad structure, with a refractive index difference of approximately 2.2% between the ring core and the inner cladding. The types and contents of elements in the fiber are verified via electron probe microanalysis. The crystal structure of PbSe quantum dots is examined using a high-resolution transmission electron microscope, and the Raman spectrum is measured. The results proved that PbSe quantum dots were doped successfully into the ring-core fiber. This provides an important reference value for preparing semiconductor quantum dot-doped fiber. The PbSe quantum dot-doped ring-core fiber is the foundation for the vortex mode amplification system. The first- to third-order vortex amplifying modes are realized at 1550 nm. When the pump power is 634 mW, the on-off gains of all modes are greater than 13 dB, and the differential mode gains are less than 2.45 dB. This experimental system is expected to promote further research on vortex mode broadband amplification. The PbSe quantum dot-doped ring-core fiber is successfully prepared using a modified chemical vapor deposition method. The fiber has a double-clad structure, with a refractive index difference of approximately 2.2% between the ring core and the inner cladding. The types and contents of elements in the fiber are verified via electron probe microanalysis. The crystal structure of PbSe quantum dots is examined using a high-resolution transmission electron microscope, and the Raman spectrum is measured. The results proved that PbSe quantum dots were doped successfully into the ring-core fiber. This provides an important reference value for preparing semiconductor quantum dot-doped fiber. The PbSe quantum dot-doped ring-core fiber is the foundation for the vortex mode amplification system. The first- to third-order vortex amplifying modes are realized at 1550 nm. When the pump power is 634 mW, the on-off gains of all modes are greater than 13 dB, and the differential mode gains are less than 2.45 dB. This experimental system is expected to promote further research on vortex mode broadband amplification.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0906001 (2024)
Design of Ground Receiver System For 500 mm Aperture Satellite-Ground Laser Communication
Cong Li, Xiaolong Ni, Xin Yu, Jun Liu, Suping Bai, and Lixia Shi
In order to enhance the sensitivity and resolution of the ground receiver for satellite-based laser communication, as well as simplify the acquisition process for beacon light, a 500 mm aperture ground receiver system is developed. This system is designed based on the link and design scheme of satellite-based laser communication, incorporating adaptive optics (AO) technology. It consists of four units: Cassegrain antenna with common aperture spectral detection, precision tracking tilt mirror, ultra-precision tracking AO, and AO wavefront detection. The antenna objective utilizes a coaxial Cassegrain structure combined with a refractor group to form a Kepler telescopic structure that considers volume and pupil distance requirements. To address optical axis correction issues causing pupil plane drift, a 4f system is implemented between the precise tracking tilt mirror and AO tilt mirror. Additionally, a double telecentric system is employed between the wavefront detector and deformable mirror to establish conjugate relationship and minimize axial error in wavefront detection. Optical passive methods are utilized in designing these four units to improve temperature adaptability of the system. Experimental results demonstrate that each element's wave aberration falls within 1/10λ (λ=632.8 nm) range at temperatures ranging from 10 ℃ to 30 ℃, meeting design specifications while offering valuable references for engineering applications. In order to enhance the sensitivity and resolution of the ground receiver for satellite-based laser communication, as well as simplify the acquisition process for beacon light, a 500 mm aperture ground receiver system is developed. This system is designed based on the link and design scheme of satellite-based laser communication, incorporating adaptive optics (AO) technology. It consists of four units: Cassegrain antenna with common aperture spectral detection, precision tracking tilt mirror, ultra-precision tracking AO, and AO wavefront detection. The antenna objective utilizes a coaxial Cassegrain structure combined with a refractor group to form a Kepler telescopic structure that considers volume and pupil distance requirements. To address optical axis correction issues causing pupil plane drift, a 4f system is implemented between the precise tracking tilt mirror and AO tilt mirror. Additionally, a double telecentric system is employed between the wavefront detector and deformable mirror to establish conjugate relationship and minimize axial error in wavefront detection. Optical passive methods are utilized in designing these four units to improve temperature adaptability of the system. Experimental results demonstrate that each element's wave aberration falls within 1/10λ (λ=632.8 nm) range at temperatures ranging from 10 ℃ to 30 ℃, meeting design specifications while offering valuable references for engineering applications.
Laser & Optoelectronics Progress
- Publication Date: Apr. 10, 2024
- Vol. 61, Issue 7, 0706021 (2024)
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