Athermal third harmonic generation in micro-ring resonators
Shaohao Wang, Yuhua Li, Brent E. Little, Leiran Wang, Xiang Wang, Roy R. Davidson, and Sai Tak Chu
Nonlinear high-harmonic generation in micro-resonators is a common technique used to extend the operating range of applications such as self-referencing systems and coherent communications in the visible region. However, the generated high-harmonic emissions are subject to a resonance shift with a change in temperature. We present a comprehensive study of the thermal behavior induced phase mismatch that shows this resonance shift can be compensated by a combination of the linear and nonlinear thermo-optics effects. Using this model, we predict and experimentally demonstrate visible third harmonic modes having temperature dependent wavelength shifts between -2.84 pm/℃ and 2.35 pm/℃ when pumped at the L-band. Besides providing a new way to achieve athermal operation, this also allows one to measure the thermal coefficients and Q-factor of the visible modes. Through steady state analysis, we have also identified the existence of stable athermal third harmonic generation and experimentally demonstrated orthogonally pumped visible third harmonic modes with a temperature dependent wavelength shift of 0.05 pm/℃ over a temperature range of 12 ℃. Our findings promise a configurable and active temperature dependent wavelength shift compensation scheme for highly efficient and precise visible emission generation for potential 2f-3f self-referencing in metrology, biological and chemical sensing applications.Nonlinear high-harmonic generation in micro-resonators is a common technique used to extend the operating range of applications such as self-referencing systems and coherent communications in the visible region. However, the generated high-harmonic emissions are subject to a resonance shift with a change in temperature. We present a comprehensive study of the thermal behavior induced phase mismatch that shows this resonance shift can be compensated by a combination of the linear and nonlinear thermo-optics effects. Using this model, we predict and experimentally demonstrate visible third harmonic modes having temperature dependent wavelength shifts between -2.84 pm/℃ and 2.35 pm/℃ when pumped at the L-band. Besides providing a new way to achieve athermal operation, this also allows one to measure the thermal coefficients and Q-factor of the visible modes. Through steady state analysis, we have also identified the existence of stable athermal third harmonic generation and experimentally demonstrated orthogonally pumped visible third harmonic modes with a temperature dependent wavelength shift of 0.05 pm/℃ over a temperature range of 12 ℃. Our findings promise a configurable and active temperature dependent wavelength shift compensation scheme for highly efficient and precise visible emission generation for potential 2f-3f self-referencing in metrology, biological and chemical sensing applications.
- Jun. 18, 2021
- Opto-Electronic Advances
- Vol.3 Issue, 12 200028-1 (2020)
- DOI：10.29026/oea.2020.200028
Helicity-dependent THz emission induced by ultrafast spin photocurrent in nodal-line semimetal candidate Mg3Bi2
Mingyu Tong, Yuze Hu, Xiangnan Xie, Xiegang Zhu, Zhenyu Wang, Xiang'ai Cheng, and Tian Jiang
Helicity-dependent ultrafast spin current generated by circularly polarized photons in topological materials holds the crux to many technological improvements, such as quantum communications, on-chip communication processing and storage. Here, we present the manipulation of helicity-dependent terahertz emission generated in a nodal line semimetal candidate Mg3Bi2 by using photon polarization states. The terahertz emission is mainly ascribed to the helicity-dependent photocurrent that is originated from circular photogalvanic effects, and the helicity-independent photocurrent that is attributed to linear photogalvanic effect. Our work will inspire more explorations into novel nodal line semimetals and open up new opportunities for developing ultrafast optoelectronics in the topological system.Helicity-dependent ultrafast spin current generated by circularly polarized photons in topological materials holds the crux to many technological improvements, such as quantum communications, on-chip communication processing and storage. Here, we present the manipulation of helicity-dependent terahertz emission generated in a nodal line semimetal candidate Mg3Bi2 by using photon polarization states. The terahertz emission is mainly ascribed to the helicity-dependent photocurrent that is originated from circular photogalvanic effects, and the helicity-independent photocurrent that is attributed to linear photogalvanic effect. Our work will inspire more explorations into novel nodal line semimetals and open up new opportunities for developing ultrafast optoelectronics in the topological system.
- Jun. 18, 2021
- Opto-Electronic Advances
- Vol.3 Issue, 12 200023-1 (2020)
- DOI：10.29026/oea.2020.200023
High-sensitivity distributed dynamic strain sensing by combining Rayleigh and Brillouin scattering
Benzhang Wang, Dexin Ba, Qi Chu, Liqiang Qiu, Dengwang Zhou, and Yongkang Dong
The phase-sensitive optical time-domain reflectometry (φ-OTDR) is a good candidate for distributed dynamic strain sensing, due to its high sensitivity and fast measurement, which has already been widely used in intrusion monitoring, geophysical exploration, etc. For the frequency scanning based φ-OTDR, the phase change manifests itself as a shift of the intensity distribution. The correlation between the reference and measured spectra is employed for relative strain demodulation, which has imposed the continuous measurement for the absolute strain demodulation. Fortunately, the Brillouin optical time domain analysis (BOTDA) allows for the absolute strain demodulation with only one measurement. In this work, the combination of the φ-OTDR and BOTDA has been proposed and demonstrated by using the same set of frequency-scanning optical pulses, and the frequency-agile technique is also introduced for fast measurements. A 9.9 Hz vibration with a strain range of 500 nε has been measured under two different absolute strains (296.7με and 554.8 με) by integrating the Rayleigh and Brillouin information. The sub-micro strain vibration is demonstrated by the φ-OTDR signal with a high sensitivity of 6.8 nε, while the absolute strain is measured by the BOTDA signal with an accuracy of 5.4 με. The proposed sensor allows for dynamic absolute strain measurements with a high sensitivity, thus opening a door for new possibilities which are yet to be explored.The phase-sensitive optical time-domain reflectometry (φ-OTDR) is a good candidate for distributed dynamic strain sensing, due to its high sensitivity and fast measurement, which has already been widely used in intrusion monitoring, geophysical exploration, etc. For the frequency scanning based φ-OTDR, the phase change manifests itself as a shift of the intensity distribution. The correlation between the reference and measured spectra is employed for relative strain demodulation, which has imposed the continuous measurement for the absolute strain demodulation. Fortunately, the Brillouin optical time domain analysis (BOTDA) allows for the absolute strain demodulation with only one measurement. In this work, the combination of the φ-OTDR and BOTDA has been proposed and demonstrated by using the same set of frequency-scanning optical pulses, and the frequency-agile technique is also introduced for fast measurements. A 9.9 Hz vibration with a strain range of 500 nε has been measured under two different absolute strains (296.7με and 554.8 με) by integrating the Rayleigh and Brillouin information. The sub-micro strain vibration is demonstrated by the φ-OTDR signal with a high sensitivity of 6.8 nε, while the absolute strain is measured by the BOTDA signal with an accuracy of 5.4 με. The proposed sensor allows for dynamic absolute strain measurements with a high sensitivity, thus opening a door for new possibilities which are yet to be explored.
- Jun. 18, 2021
- Opto-Electronic Advances
- Vol.3 Issue, 12 200013-1 (2020)
- DOI：10.29026/oea.2020.200013
Multidimensional manipulation of wave fields based on artificial microstructures
Yuebian Zhang, Hui Liu, Hua Cheng, Jianguo Tian, and Shuqi Chen
Artificial microstructures, which allow us to control and change the properties of wave fields through changing the geometrical parameters and the arrangements of microstructures, have attracted plenty of attentions in the past few decades. Some artificial microstructure based research areas, such as metamaterials, metasurfaces and phononic topological insulators, have seen numerous novel applications and phenomena. The manipulation of different dimensions (phase, amplitude, frequency or polarization) of wave fields, particularly, can be easily achieved at subwavelength scales by metasurfaces. In this review, we focus on the recent developments of wave field manipulations based on artificial microstructures and classify some important applications from the viewpoint of different dimensional manipulations of wave fields. The development tendency of wave field manipulation from single-dimension to multidimensions provides a useful guide for researchers to realize miniaturized and integrated optical and acoustic devices.Artificial microstructures, which allow us to control and change the properties of wave fields through changing the geometrical parameters and the arrangements of microstructures, have attracted plenty of attentions in the past few decades. Some artificial microstructure based research areas, such as metamaterials, metasurfaces and phononic topological insulators, have seen numerous novel applications and phenomena. The manipulation of different dimensions (phase, amplitude, frequency or polarization) of wave fields, particularly, can be easily achieved at subwavelength scales by metasurfaces. In this review, we focus on the recent developments of wave field manipulations based on artificial microstructures and classify some important applications from the viewpoint of different dimensional manipulations of wave fields. The development tendency of wave field manipulation from single-dimension to multidimensions provides a useful guide for researchers to realize miniaturized and integrated optical and acoustic devices.
- Jun. 18, 2021
- Opto-Electronic Advances
- Vol.3 Issue, 11 200002-1 (2020)
- DOI：10.29026/oea.2020.200002
Observation and optimization of 2 μm mode-locked pulses in all-fiber net anomalous dispersion laser cavity
Wanzhuo Ma, Desheng Zhao, Runmin Liu, Tianshu Wang, Quan Yuan, Hao Xiong, Haiying Ji, and Huilin Jiang
We integrally demonstrate 2 μm mode-locked pulses performances in all-fiber net anomalous dispersion cavity. Stable mode-locking operations with the center wavelength around 1950-1980 nm can be achieved by using the nonlinear polarization rotation structure and properly designing the dispersion management component. Conventional soliton is firstly obtained with a total anomalous dispersion cavity. Due to the contribution of commercial ultra-high numerical aperture fibers, net dispersion is reduced to -0.077 ps2. So that stretched pulse with 19.4 nm optical bandwidth is obtained and the de-chirped pulse-width can reach 312 fs using extra-cavity compression. Under pump power greater than 890 mW, stretched pulse can evolve into noise-like pulse with 41.3 nm bandwidth. The envelope and peak of such broadband pulse can be compressed with up to 2.2 ps and 145 fs, respectively. The single pulse energy of largely chirped stretched and noise-like pulse can reach 1.785 nJ and 1.53 nJ, respectively. Furthermore, extra-cavity compression can also contribute to a significant increase of peak power.We integrally demonstrate 2 μm mode-locked pulses performances in all-fiber net anomalous dispersion cavity. Stable mode-locking operations with the center wavelength around 1950-1980 nm can be achieved by using the nonlinear polarization rotation structure and properly designing the dispersion management component. Conventional soliton is firstly obtained with a total anomalous dispersion cavity. Due to the contribution of commercial ultra-high numerical aperture fibers, net dispersion is reduced to -0.077 ps2. So that stretched pulse with 19.4 nm optical bandwidth is obtained and the de-chirped pulse-width can reach 312 fs using extra-cavity compression. Under pump power greater than 890 mW, stretched pulse can evolve into noise-like pulse with 41.3 nm bandwidth. The envelope and peak of such broadband pulse can be compressed with up to 2.2 ps and 145 fs, respectively. The single pulse energy of largely chirped stretched and noise-like pulse can reach 1.785 nJ and 1.53 nJ, respectively. Furthermore, extra-cavity compression can also contribute to a significant increase of peak power.
- Jun. 18, 2021
- Opto-Electronic Advances
- Vol.3 Issue, 11 200001-1 (2020)
- DOI：10.29026/oea.2020.200001
Deep-learning powered whispering gallery mode sensor based on multiplexed imaging at fixed frequency
Anton V. Saetchnikov, Elina A. Tcherniavskaia, Vladimir A. Saetchnikov, and Andreas Ostendorf
During the last decades the whispering gallery mode based sensors have become a prominent solution for label-free sensing of various physical and chemical parameters. At the same time, the widespread utilization of the approach is hindered by the restricted applicability of the known configurations for ambient variations quantification outside the laboratory conditions and their low affordability, where necessity on the spectrally-resolved data collection is among the main limiting factors. In this paper we demonstrate the first realization of an affordable whispering gallery mode sensor powered by deep learning and multi-resonator imaging at a fixed frequency. It has been shown that the approach enables refractive index unit (RIU) prediction with an absolute error at 3×10-6 level for dynamic range of the RIU variations from 0 to 2×10-3 with temporal resolution of several milliseconds and instrument-driven detection limit of 3×10-5. High sensing accuracy together with instrumental affordability and production simplicity places the reported detector among the most cost-effective realizations of the whispering gallery mode approach. The proposed solution is expected to have a great impact on the shift of the whole sensing paradigm away from the model-based and to the flexible self-learning solutions.During the last decades the whispering gallery mode based sensors have become a prominent solution for label-free sensing of various physical and chemical parameters. At the same time, the widespread utilization of the approach is hindered by the restricted applicability of the known configurations for ambient variations quantification outside the laboratory conditions and their low affordability, where necessity on the spectrally-resolved data collection is among the main limiting factors. In this paper we demonstrate the first realization of an affordable whispering gallery mode sensor powered by deep learning and multi-resonator imaging at a fixed frequency. It has been shown that the approach enables refractive index unit (RIU) prediction with an absolute error at 3×10-6 level for dynamic range of the RIU variations from 0 to 2×10-3 with temporal resolution of several milliseconds and instrument-driven detection limit of 3×10-5. High sensing accuracy together with instrumental affordability and production simplicity places the reported detector among the most cost-effective realizations of the whispering gallery mode approach. The proposed solution is expected to have a great impact on the shift of the whole sensing paradigm away from the model-based and to the flexible self-learning solutions.
- Jun. 18, 2021
- Opto-Electronic Advances
- Vol.3 Issue, 11 200048-1 (2020)
- DOI：10.29026/oea.2020.200048
Phase Unwrapping Correction Method for Dual-Frequency Fringe Projection Profilometry
Cheng Lei, Pan Yanjuan, Xi Dongdong, Wang Yuwei, and Liu Lu
Dual-frequency fringe projection method is a common phase unwrapping algorithm. Due to the influence of factors such as random noise and camera defocusing, the fringe order calculation results of the dual-frequency phase unwrapping algorithm often have errors, leading to phase errors. In order to solve this problem, this paper proposes a phase unwrapping correction algorithm to correct the high-frequency fringe orders. First, the entire fringe region is divided into two masks according to the value range of high-frequency truncated phase. Then, the connected components of these two masks are marked, respectively. In addition, the fringe orders that appear most frequently in each marked region are counted, whose values are assigned to all pixels in the current marked region. Finally, the absolute phase is obtained by unwrapping the corrected fringe orders. The simulation and actual experimental results show that the proposed method can be used to effectively eliminate the phase unwrapping errors in the dual-frequency fringe projection method.Dual-frequency fringe projection method is a common phase unwrapping algorithm. Due to the influence of factors such as random noise and camera defocusing, the fringe order calculation results of the dual-frequency phase unwrapping algorithm often have errors, leading to phase errors. In order to solve this problem, this paper proposes a phase unwrapping correction algorithm to correct the high-frequency fringe orders. First, the entire fringe region is divided into two masks according to the value range of high-frequency truncated phase. Then, the connected components of these two masks are marked, respectively. In addition, the fringe orders that appear most frequently in each marked region are counted, whose values are assigned to all pixels in the current marked region. Finally, the absolute phase is obtained by unwrapping the corrected fringe orders. The simulation and actual experimental results show that the proposed method can be used to effectively eliminate the phase unwrapping errors in the dual-frequency fringe projection method.
- Jun. 18, 2021
- Laser & Optoelectronics Progress
- Vol.58 Issue, 12 1210017 (2021)
- DOI：10.3788/LOP202158.1210017
Deep Graph Attention Convolution Network for Point Cloud Semantic Segmentation
Chai Yujing, Ma Jie, and Liu Hong
Compared with convolutional neural networks, graph convolution network is more suitable for processing irregular point cloud data. However, it has the problem that the number of network layers is limited and the fixed and standardized aggregation method affects the result of point cloud semantic segmentation. To solve these problems, a depth graph attention convolutional network for point cloud semantic segmentation is proposed herein. The network uses residual connections to deepen the number of layers of the graph convolutional network, which can effectively solve the problems of gradient disappearance and network degradation caused by the network being too deep. The attention mechanism is used to make the network selectively focus on the most relevant neighborhood points, and it assigns different attention weights to it. Simultaneously, the graph is reconstructed after each layer of graph convolution to better characterize the graph structure. Experimental results show that the average intersection ratio of the network on Stanford large-scale three-dimensional indoor spatial dataset reaches 64.5%.Compared with convolutional neural networks, graph convolution network is more suitable for processing irregular point cloud data. However, it has the problem that the number of network layers is limited and the fixed and standardized aggregation method affects the result of point cloud semantic segmentation. To solve these problems, a depth graph attention convolutional network for point cloud semantic segmentation is proposed herein. The network uses residual connections to deepen the number of layers of the graph convolutional network, which can effectively solve the problems of gradient disappearance and network degradation caused by the network being too deep. The attention mechanism is used to make the network selectively focus on the most relevant neighborhood points, and it assigns different attention weights to it. Simultaneously, the graph is reconstructed after each layer of graph convolution to better characterize the graph structure. Experimental results show that the average intersection ratio of the network on Stanford large-scale three-dimensional indoor spatial dataset reaches 64.5%.
- Jun. 18, 2021
- Laser & Optoelectronics Progress
- Vol.58 Issue, 12 1210016 (2021)
- DOI：10.3788/LOP202158.1210016
Design and Identification of Cooperative Coded Targets
Liu Huijie, Mamtimin Geni, Gulbahar Tohti, Yakup Ahmat, and Zhang Quanzhong
To improve the encoding capacity and decoding accuracy of encoded marker points in close-range photogrammetry, a method of cooperative encoding and positioning corresponding circular markers comprising positioning crosses, initial numbers, and encoded characters is proposed. Gaussian filtering is used to smoothly preprocess the collected images to eliminate noise. The adaptive local threshold method is employed to segment the target to obtain the character area and cross mark area. TensorFlow-MLP (Multilayer Perceptron) neural network is trained using the character sample library to classify and recognize characters. Finally, the cross mark area is filled and repaired. Sub-pixel positioning is achieved through the gray square weighted centroid method. This type of cooperative coding sign is uniquely identifiable in practical applications with high positioning accuracy and accurate and efficient decoding.To improve the encoding capacity and decoding accuracy of encoded marker points in close-range photogrammetry, a method of cooperative encoding and positioning corresponding circular markers comprising positioning crosses, initial numbers, and encoded characters is proposed. Gaussian filtering is used to smoothly preprocess the collected images to eliminate noise. The adaptive local threshold method is employed to segment the target to obtain the character area and cross mark area. TensorFlow-MLP (Multilayer Perceptron) neural network is trained using the character sample library to classify and recognize characters. Finally, the cross mark area is filled and repaired. Sub-pixel positioning is achieved through the gray square weighted centroid method. This type of cooperative coding sign is uniquely identifiable in practical applications with high positioning accuracy and accurate and efficient decoding.
- Jun. 18, 2021
- Laser & Optoelectronics Progress
- Vol.58 Issue, 12 1210015 (2021)
- DOI：10.3788/LOP202158.1210015
Matching Multi-Scale Features and Prediction Tasks for Real-Time Object Detection
Du Hongjie, Sun Hanqing, Cao Jiale, and Pang Yanwei
In object detection algorithms based on convolutional neural networks, high-resolution features from lower levels contain more detailed information, which can help the abstract features complete the accurate positioning task; deep-level features contain abstract semantic information, which is more suitable for target existence prediction task. When the most existing anchor-free detection method directly predicts all tasks on the same feature map, it does not match the above features and prediction tasks, which limits the detection accuracy. To this end, the MFT detector, a real-time object detection algorithm, is proposed to match multi-scale features and prediction tasks of targets. MFT detector is based on CenterNet detector, which can match shallow detail features with accurate positioning task, and match multi-scale, multi receptive field abstract features with target existence prediction task. Experimental results show that the proposed MFT detector alleviates the mismatch between features and prediction tasks, and significantly improves the detection precision while maintaining a high speed of 94.5 frame/s, which meets the requirement of a real-time vision system.In object detection algorithms based on convolutional neural networks, high-resolution features from lower levels contain more detailed information, which can help the abstract features complete the accurate positioning task; deep-level features contain abstract semantic information, which is more suitable for target existence prediction task. When the most existing anchor-free detection method directly predicts all tasks on the same feature map, it does not match the above features and prediction tasks, which limits the detection accuracy. To this end, the MFT detector, a real-time object detection algorithm, is proposed to match multi-scale features and prediction tasks of targets. MFT detector is based on CenterNet detector, which can match shallow detail features with accurate positioning task, and match multi-scale, multi receptive field abstract features with target existence prediction task. Experimental results show that the proposed MFT detector alleviates the mismatch between features and prediction tasks, and significantly improves the detection precision while maintaining a high speed of 94.5 frame/s, which meets the requirement of a real-time vision system.
- Jun. 18, 2021
- Laser & Optoelectronics Progress
- Vol.58 Issue, 12 1210014 (2021)
- DOI：10.3788/LOP202158.1210014
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Special Issue on High Power Laser Science and Engineering 2021 (2021)
Submission Open:25 February 2021; Submission Deadline: 31 July 2021
Editor (s): Colin Danson, Jianqiang Zhu
Submission Open:1 January 2021; Submission Deadline: 1 July 2021
Editor (s): Max Lederer, Haixiao Deng, Sergio Carbajo
Special Issue on 60th Celebration of First Laser (2020)
Submission Open:1 January 2020; Submission Deadline: 31 December 2020
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