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Fourier Optics and Signal Processing|58 Article(s)
Position Mapping Relationship for Converting Laguerre-Gaussian Beam Array into Hermite-Gaussian Beam Array Based on a Tilted Lens
Guangyun Xiong, Ao Tang, Bin Lan, and Feng Shen
A Laguerre-Gaussian beam can be converted into a Hermite-Gaussian beam using a tilted lens. In this work, a position mapping relationship was derived between the incident Laguerre-Gaussian beam array and the Hermite-Gaussian beam array converted by the tilted lens. When the tilted lens is rotated around an arbitrary axis by a certain angle, the positions of the two beam arrays will be symmetrical about that axis. In the experiments, Laguerre-Gaussian beam arrays of 1×1, 2×2, 3×3, 3×1, and 1×3 were generated using a spatial light modulator and converted into Hermite-Gaussian beam arrays via a tilted lens, and the above theoretical analysis was verified through comparison of the distributions of the two beam arrays. The experimental results are in perfect agreement with the theoretical analysis. Based on the theoretical results and the position distribution of the Hermite-Gaussian beam array, the topological charge of the Laguerre-Gaussian beam array can be detected. This work provides clearer theoretical guidance for the orbital angular momentum detection of Laguerre-Gaussian beam arrays. A Laguerre-Gaussian beam can be converted into a Hermite-Gaussian beam using a tilted lens. In this work, a position mapping relationship was derived between the incident Laguerre-Gaussian beam array and the Hermite-Gaussian beam array converted by the tilted lens. When the tilted lens is rotated around an arbitrary axis by a certain angle, the positions of the two beam arrays will be symmetrical about that axis. In the experiments, Laguerre-Gaussian beam arrays of 1×1, 2×2, 3×3, 3×1, and 1×3 were generated using a spatial light modulator and converted into Hermite-Gaussian beam arrays via a tilted lens, and the above theoretical analysis was verified through comparison of the distributions of the two beam arrays. The experimental results are in perfect agreement with the theoretical analysis. Based on the theoretical results and the position distribution of the Hermite-Gaussian beam array, the topological charge of the Laguerre-Gaussian beam array can be detected. This work provides clearer theoretical guidance for the orbital angular momentum detection of Laguerre-Gaussian beam arrays.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0507001 (2024)
Application of Improved Band-Limited Scaling Angular Spectrum Method in Long-Distance Diffraction Calculation
Xin Zheng, Yuying Zhang, Shenyu Dai, and Shuai Zhao
Angular spectrum method has distortion problem in the long-distance diffraction calculation because of the calculation error caused by the reduction of effective spectrum components and spectrum aliasing. Based on the frequency sampling characteristics of the band-limited angular spectrum method, an improved scaling angular spectrum method is proposed. Then, the method is applied to the diffraction field simulation of large-size square telephoto lenses, circular axicon lenses and diffractive optical elements. The results show that compared with the original band-limited angular spectrum method and the scaling angular spectrum method, the diffraction field obtained by the improved method has higher resolution and no edge distortion. Our research indicates that the improved method has important application potential in the precise calculation of large size, long distance and small diffraction fields. Angular spectrum method has distortion problem in the long-distance diffraction calculation because of the calculation error caused by the reduction of effective spectrum components and spectrum aliasing. Based on the frequency sampling characteristics of the band-limited angular spectrum method, an improved scaling angular spectrum method is proposed. Then, the method is applied to the diffraction field simulation of large-size square telephoto lenses, circular axicon lenses and diffractive optical elements. The results show that compared with the original band-limited angular spectrum method and the scaling angular spectrum method, the diffraction field obtained by the improved method has higher resolution and no edge distortion. Our research indicates that the improved method has important application potential in the precise calculation of large size, long distance and small diffraction fields.
Laser & Optoelectronics Progress
- Publication Date: Dec. 10, 2023
- Vol. 60, Issue 23, 2307001 (2023)
Fast Acquisition and Processing Method of Optical Frequency Scanning Interferometry Ranging Signal
Yu Wang, Tengfei Wu, Qiang Zhou, Hui Zhao, and Jigui Zhu
The optical frequency scanning interference absolute distance measurement system needs to correct the optical frequency scanning nonlinearity and refine the signal distance spectrum so that it has low data collection and processing efficiency. Therefore, it is difficult to meet the length measurement requirements in large-scale digital manufacturing scenarios. This paper designs a data collection and processing system introducing auxiliary interference signals as the digital signal acquisition system clock, and the nonlinearity of the frequency sweep is corrected meanwhile in the signal collection process, and hence the efficiency of the designed system is high. Sparse fast Fourier transform is used to determine the range of the spectrum refinement interval. Based on the zoom fast Fourier transform, the refinement of the distance spectrum is realized and the efficiency of precise distance calculation is effectively improved. The experimental results show that the data processing speed of the designed system is more than 10 times faster compared with traditional systems using the chirp Z transform. Compared with the commercial interferometer, in the equivalent space distance range of 15.4-16.1 m, the error of the measurement is kept within 10 μm, and the measurement repeatability is better than 6 μm. The optical frequency scanning interference absolute distance measurement system needs to correct the optical frequency scanning nonlinearity and refine the signal distance spectrum so that it has low data collection and processing efficiency. Therefore, it is difficult to meet the length measurement requirements in large-scale digital manufacturing scenarios. This paper designs a data collection and processing system introducing auxiliary interference signals as the digital signal acquisition system clock, and the nonlinearity of the frequency sweep is corrected meanwhile in the signal collection process, and hence the efficiency of the designed system is high. Sparse fast Fourier transform is used to determine the range of the spectrum refinement interval. Based on the zoom fast Fourier transform, the refinement of the distance spectrum is realized and the efficiency of precise distance calculation is effectively improved. The experimental results show that the data processing speed of the designed system is more than 10 times faster compared with traditional systems using the chirp Z transform. Compared with the commercial interferometer, in the equivalent space distance range of 15.4-16.1 m, the error of the measurement is kept within 10 μm, and the measurement repeatability is better than 6 μm.
Laser & Optoelectronics Progress
- Publication Date: Jan. 10, 2023
- Vol. 60, Issue 1, 0107003 (2023)
Transmission Performance of Probabilistic Shaping Orthogonal Frequency Division Multiplexing Radio-over-Fiber Communication System Based on Low Density Parity Check Code
Anliang Liu, and Hongzhi Li
In this study, we propose an orthogonal frequency division multiplexing radio-over-fiber (OFDM-RoF) system based on low density parity check code (LDPC) coded with probabilistic shaping (PS) for optimizing the transmission performance of the OFDM signal. We theoretically analyze the PS technology and the generation and demodulation principle of the PS-OFDM signal. The average power of the modulated OFDM signals for the same transmission power decreased by approximately 20% after PS with a 6.7% extra overhead. Compared with a normal OFDM-RoF system, the proposed PS-OFDM-RoF system can reduce the transmitting power of OFDM signals, and it has a better peak-to-average power ratio (PAPR) performance. Furthermore, a 25 GHz verification RoF system with a data rate of 2.5 Gbps is established for analyzing the transmission characteristics of the PS-OFDM signals. The measured bit error rate curves at different fiber lengths show that a PS-OFDM-RoF system based on LDPC can effectively improve the sensitivity of the receiver and increase the reliable transmission distance of the system. In this study, we propose an orthogonal frequency division multiplexing radio-over-fiber (OFDM-RoF) system based on low density parity check code (LDPC) coded with probabilistic shaping (PS) for optimizing the transmission performance of the OFDM signal. We theoretically analyze the PS technology and the generation and demodulation principle of the PS-OFDM signal. The average power of the modulated OFDM signals for the same transmission power decreased by approximately 20% after PS with a 6.7% extra overhead. Compared with a normal OFDM-RoF system, the proposed PS-OFDM-RoF system can reduce the transmitting power of OFDM signals, and it has a better peak-to-average power ratio (PAPR) performance. Furthermore, a 25 GHz verification RoF system with a data rate of 2.5 Gbps is established for analyzing the transmission characteristics of the PS-OFDM signals. The measured bit error rate curves at different fiber lengths show that a PS-OFDM-RoF system based on LDPC can effectively improve the sensitivity of the receiver and increase the reliable transmission distance of the system.
Laser & Optoelectronics Progress
- Publication Date: Jan. 10, 2023
- Vol. 60, Issue 1, 0107002 (2023)
Non-Dispersive Multi-Wavelength Modulation Absorption Spectrum Measurement Method
Yifan Shi, Ning Li, Xiaolong Huang, Yang Kang, Can Li, and Chunsheng Weng
Aiming at improving the measurement of wavelength modulation via laser absorption spectroscopy, a non-dispersive multi-wavelength second-harmonic measurement method is proposed. By adjusting the relative position between the spectral lines, the demodulation of the multispectral line modulation signal can be achieved without the need for a grating or other spectroscopic devices, and the gas temperature can then be measured online. Based on the 7185.60 cm-1/7444.35 cm-1 H2O absorption spectrum, the influence of the modulation coefficient and the relative position between the spectral lines on the measurement are discussed. Further, the second-harmonic extraction method under different modulation frequency conditions is analyzed using the modulation signal spectrogram. A numerical simulation method is used to establish a complex flow-field change model in the pulse detonation process. The proposed method is used to measure gas temperature during the pulse detonation process, and its correctness is verified in this study. The research results are of great significance to the measurement of wavelength modulation under complex environmental conditions. Aiming at improving the measurement of wavelength modulation via laser absorption spectroscopy, a non-dispersive multi-wavelength second-harmonic measurement method is proposed. By adjusting the relative position between the spectral lines, the demodulation of the multispectral line modulation signal can be achieved without the need for a grating or other spectroscopic devices, and the gas temperature can then be measured online. Based on the 7185.60 cm-1/7444.35 cm-1 H2O absorption spectrum, the influence of the modulation coefficient and the relative position between the spectral lines on the measurement are discussed. Further, the second-harmonic extraction method under different modulation frequency conditions is analyzed using the modulation signal spectrogram. A numerical simulation method is used to establish a complex flow-field change model in the pulse detonation process. The proposed method is used to measure gas temperature during the pulse detonation process, and its correctness is verified in this study. The research results are of great significance to the measurement of wavelength modulation under complex environmental conditions.
Laser & Optoelectronics Progress
- Publication Date: Jan. 10, 2023
- Vol. 60, Issue 1, 0107001 (2023)
Syllable Matching Algorithm with Spectral Peak Point Feature for Chinese Speech
Weikang Tang, Yubin Shao, Hua Long, Qingzhi Du, Yi Peng, and Liang Chen
Based on the spectral peak point characteristics of Chinese speech, this study proposes a syllable matching algorithm to improve the matching effect of Chinese speech syllables in noisy environments. First, a discrete cosine transform is used to extract the speech signal envelope spectrogram, and the human ear masking effect is used for spectral energy judgment to obtain the extreme value points of spectral energy in each frame. Then, the syllable signal is corresponded to a binary sequence by performing binary quantization in the logarithmic frequency range. Finally, the syllable matching result is determined based on the template comparison of the binary sequence. The results show that the proposed algorithm outperforms the conventional methods for matching syllables in the noiseless Chinese speech. Additionally, it has a high matching accuracy at low signal-to-noise ratios. Based on the spectral peak point characteristics of Chinese speech, this study proposes a syllable matching algorithm to improve the matching effect of Chinese speech syllables in noisy environments. First, a discrete cosine transform is used to extract the speech signal envelope spectrogram, and the human ear masking effect is used for spectral energy judgment to obtain the extreme value points of spectral energy in each frame. Then, the syllable signal is corresponded to a binary sequence by performing binary quantization in the logarithmic frequency range. Finally, the syllable matching result is determined based on the template comparison of the binary sequence. The results show that the proposed algorithm outperforms the conventional methods for matching syllables in the noiseless Chinese speech. Additionally, it has a high matching accuracy at low signal-to-noise ratios.
Laser & Optoelectronics Progress
- Publication Date: Apr. 10, 2022
- Vol. 59, Issue 7, 0707001 (2022)
Modeling and Analysis of Fine-Grained Interference from International Mobile Communication System Terrestrial Base Stations to Low Earth Orbit Satellites
Yan Shi, Zhuochen Xie, and Huijie Liu
In the context of satellite terrestrial radio frequency/laser wavelength sharing, this paper studies the aggregate interference of International Mobile Telecommunication System (IMT) terrestrial stations that is imposed to the low earth orbit (LEO) satellites equipped with the multi-beam receiving antenna for radio communication with frequencies below 6 GHz and free-space laser communications. For frequencies below 6 GHz, typical kinds of IMT base station deployment scenarios were emulated according to the latest International Telecommunication Union (ITU) Recommendations. By means of Monte Carlo simulation, a statistical clutter loss model was introduced into the interference simulation. The model's applicability was analyzed, and it was used for the random detailed scene simulation. After combining the typical scenarios with the characteristics of the satellite multi-beam antennas, we study the change trends of the different typical base station deployment scenarios with the different satellite antenna beam scanning angels by simulations. The results show that when the height of base station antenna was below rooftop, the clutter loss should not be neglected. On the other hand, we analyze the possible interference of the terrestrial free-space optical communication imposed to the LEO satellite by link calculation. The analysis results have theoretical guiding significance and application value for monitoring the receiving environment of LEO satellites. In the context of satellite terrestrial radio frequency/laser wavelength sharing, this paper studies the aggregate interference of International Mobile Telecommunication System (IMT) terrestrial stations that is imposed to the low earth orbit (LEO) satellites equipped with the multi-beam receiving antenna for radio communication with frequencies below 6 GHz and free-space laser communications. For frequencies below 6 GHz, typical kinds of IMT base station deployment scenarios were emulated according to the latest International Telecommunication Union (ITU) Recommendations. By means of Monte Carlo simulation, a statistical clutter loss model was introduced into the interference simulation. The model's applicability was analyzed, and it was used for the random detailed scene simulation. After combining the typical scenarios with the characteristics of the satellite multi-beam antennas, we study the change trends of the different typical base station deployment scenarios with the different satellite antenna beam scanning angels by simulations. The results show that when the height of base station antenna was below rooftop, the clutter loss should not be neglected. On the other hand, we analyze the possible interference of the terrestrial free-space optical communication imposed to the LEO satellite by link calculation. The analysis results have theoretical guiding significance and application value for monitoring the receiving environment of LEO satellites.
Laser & Optoelectronics Progress
- Publication Date: Feb. 10, 2022
- Vol. 59, Issue 3, 0307002 (2022)
Optical System Error Correction Method for Online Detection of Miniature Spectrometer
Fengbo Zhou, Hongqiu Zhu, and Changgeng Li
Due to its miniaturization, integration, and fast detection speed, the miniature optical fiber spectrometer was suitable for on-line detection of multi-component substances in industrial sites. In view of the problem that the micro spectrometer was affected by the stray light, photometric noise and light source fluctuation, the measurement accuracy of the spectral signal was poor, and an optical system error correction method was proposed for on-line detection of micro spectrometer. Firstly, a micro spectrometer was used to measure the spectral intensity online, and the spectral signal was obtained from the reference solution and the solution to be measured. Secondly, the adaptive wavelet threshold denoising method was used to eliminate the photometric noise of the spectral signal and improve the sensitivity of the spectral signal. Then, a light source stabilization method based on the invariance of the dual wavelength light intensity ratio was proposed to dynamically eliminate the light source error. Finally, the spectral signals of the copper and cobalt were dynamically corrected, and the performance analysis of the correction curve was performed. The results show that the method proposed in this paper is simple and fast, and it was suitable for dynamic correction of spectral signal to meet the needs of online detection of multi metal impurity ions. Due to its miniaturization, integration, and fast detection speed, the miniature optical fiber spectrometer was suitable for on-line detection of multi-component substances in industrial sites. In view of the problem that the micro spectrometer was affected by the stray light, photometric noise and light source fluctuation, the measurement accuracy of the spectral signal was poor, and an optical system error correction method was proposed for on-line detection of micro spectrometer. Firstly, a micro spectrometer was used to measure the spectral intensity online, and the spectral signal was obtained from the reference solution and the solution to be measured. Secondly, the adaptive wavelet threshold denoising method was used to eliminate the photometric noise of the spectral signal and improve the sensitivity of the spectral signal. Then, a light source stabilization method based on the invariance of the dual wavelength light intensity ratio was proposed to dynamically eliminate the light source error. Finally, the spectral signals of the copper and cobalt were dynamically corrected, and the performance analysis of the correction curve was performed. The results show that the method proposed in this paper is simple and fast, and it was suitable for dynamic correction of spectral signal to meet the needs of online detection of multi metal impurity ions.
Laser & Optoelectronics Progress
- Publication Date: Feb. 10, 2022
- Vol. 59, Issue 3, 0307001 (2022)
Optimal Design of Sparse Arrays for Spatial Expansion Communication Model
Yaming Wei, Bin Xue, Wang Cai, Dongliang Wang, and Fanpeng Dong
Developing improved communication models for expanding wireless communication capacity in spatial dimensions is an important research goal. However, there are two main theoretical concerns with the construction of orthogonal channels in spatial dimensions: one is ill-conditioned problem, and the other is sparseness. Addressing these two issues, we propose a new communication model for spatial-dimension expansion. Considering the acousto-optic effect, a laser is used to expand the spatial dimension; a sparse array layout is designed by an optimization algorithm; and the optimal distribution is determined by a clustering algorithm to complete the model layout design. Through the simulation calculation model example, it can be obtained that its condition number is 25. After cluster analysis, only 4 laser receivers can replace the original 88 unit antennas to form a receiving array. This model plays an important role in improving wireless communication capacity, provides a new concept for building underwater lightweight long-distance and high-capacity integrated communication systems, and contributes basic research for the theoretical development of future wireless communication models. Developing improved communication models for expanding wireless communication capacity in spatial dimensions is an important research goal. However, there are two main theoretical concerns with the construction of orthogonal channels in spatial dimensions: one is ill-conditioned problem, and the other is sparseness. Addressing these two issues, we propose a new communication model for spatial-dimension expansion. Considering the acousto-optic effect, a laser is used to expand the spatial dimension; a sparse array layout is designed by an optimization algorithm; and the optimal distribution is determined by a clustering algorithm to complete the model layout design. Through the simulation calculation model example, it can be obtained that its condition number is 25. After cluster analysis, only 4 laser receivers can replace the original 88 unit antennas to form a receiving array. This model plays an important role in improving wireless communication capacity, provides a new concept for building underwater lightweight long-distance and high-capacity integrated communication systems, and contributes basic research for the theoretical development of future wireless communication models.
Laser & Optoelectronics Progress
- Publication Date: Dec. 10, 2022
- Vol. 59, Issue 23, 2307001 (2022)
Feature Extraction of Bearing Faults Under Nonlinear Equalization of Variance Based on Wavelet Packet Decomposition
Zhiqing Zheng, Haiyan Quan, and Junbing Qian
When the bearing has various faults, the vibration signal's variance distribution in various frequency bands is not balanced. In order to extract the features of various fault signals efficiently and for the frequency components generated from the bearing fault signal's wavelet packet decomposition, this study proposed a variance equalization method of nonlinear equalization. The higher discrimination degree of fault characteristics can In order to extract the features of various fault signals efficiently and for the frequency components generated from the bearing fault signal's wavelet packet decomposition, this study proposes a variance equalization method of nonlinear equalization. The higher discrimination degree of fault characteristics can be achieved. Based on the data from Case Western Reserve University's bearing data center's collected bearing vibration in the experiment, the variance parameters extracted from a normal, inner ring fault, outer ring fault, and rolling element fault bearing signal under four speeds are investigated using this approach. The results reveal that the variance parameters of various fault signals after equalization have better discrimination. It can efficiently differentiate the types of bearing faults. When the bearing has various faults, the vibration signal's variance distribution in various frequency bands is not balanced. In order to extract the features of various fault signals efficiently and for the frequency components generated from the bearing fault signal's wavelet packet decomposition, this study proposed a variance equalization method of nonlinear equalization. The higher discrimination degree of fault characteristics can In order to extract the features of various fault signals efficiently and for the frequency components generated from the bearing fault signal's wavelet packet decomposition, this study proposes a variance equalization method of nonlinear equalization. The higher discrimination degree of fault characteristics can be achieved. Based on the data from Case Western Reserve University's bearing data center's collected bearing vibration in the experiment, the variance parameters extracted from a normal, inner ring fault, outer ring fault, and rolling element fault bearing signal under four speeds are investigated using this approach. The results reveal that the variance parameters of various fault signals after equalization have better discrimination. It can efficiently differentiate the types of bearing faults.
Laser & Optoelectronics Progress
- Publication Date: Nov. 10, 2022
- Vol. 59, Issue 21, 2107001 (2022)
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