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学者姓名：王大勇
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Abstract ：
For decades, terahertz (THz) microscopic imaging has been limited by the resolution of the system due to the larger wavelength, the power of the source, and the equivalent noise power of the detector, so a lot of research has focused on single-point scanning imaging. With the development of hardware, full-field THz imaging based on high-power continuous-wave THz sources have been developed such as the direct intensity imaging method and lensless coherent imaging. In particular, the THz direct intensity imaging method requires no complicated computational reconstruction, while the high resolution, as a key issue, still needs to be improved. In this paper, the rotating coherent scattering microscopy was applied to THz imaging for the first time. Here, we designed and fabricated a hemisphere lens with high-resistance silicon. The tilted hemisphere lens transformed the incident divergent beam into a plane wave, and the total internal reflection occurred in the planar surface within the hemispherical lens, and generated evanescent waves in the rare medium. At the same time, the sample was placed very close to the plane of the hemispherical lens, so that the sample was illuminated by the evanescent waves. The scattered waves carried high frequency information to the far field, and thus through an objective, the super-resolution imaging was achieved along a single direction. Then, the hemispherical lens was rotated to obtain coherent scattering microscopic images under different evanescent wave illumination angles. Finally, the full-field super-resolution imaging results were obtained through incoherent superposition.
Keyword ：
full-field full-field evanescent wave evanescent wave rotating coherent scattering microscopy rotating coherent scattering microscopy terahertz imaging terahertz imaging super-resolution super-resolution
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| GB/T 7714 | Ma, Duoxuan , Zhao, Jie , Wang, Dayong et al. Full-Field Super-Resolution Terahertz Imaging Based on Rotating Coherent Scattering Microscopy [J]. | APPLIED SCIENCES-BASEL , 2023 , 13 (2) . |
| MLA | Ma, Duoxuan et al. "Full-Field Super-Resolution Terahertz Imaging Based on Rotating Coherent Scattering Microscopy" . | APPLIED SCIENCES-BASEL 13 . 2 (2023) . |
| APA | Ma, Duoxuan , Zhao, Jie , Wang, Dayong , Lin, Hao , Rong, Lu , Wang, Yunxin et al. Full-Field Super-Resolution Terahertz Imaging Based on Rotating Coherent Scattering Microscopy . | APPLIED SCIENCES-BASEL , 2023 , 13 (2) . |
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Abstract ：
In this paper, an iterative denoising phase retrieval method is proposed to solve the twin-image problem in continuous-wave terahertz in-line digital holography. The iterative algorithm is based on the classical error reduction algorithm by adding the positive absorption constraint and a new image denoising for the object field to improve the quality of the reconstructed images. At certain geometrical parameter, the twin-image can be treated as noise superimposed in the object plane. The object field is considered as a complex function affected by the twin-image, and then the denoising process embedded in each iteration is applied to the real and imaginary parts of the object field, respectively. The validity of this approach is demonstrated by the high-quality imaging of samples like the Siemens star and the cicada's wing, which are almost free from the twin-image. Also, the proposed method exhibits good robustness to noises existing in the hologram, and the reconstructed images show better quality compared with other popular phase retrieval methods and denoising algorithm. This work would be helpful to expand the application of continuous-wave terahertz in-line digital holography in biomedical imaging and nondestructive testing.
Keyword ：
Phase retrieval Phase retrieval In-line digital holography In-line digital holography Terahertz imaging Terahertz imaging Image denoising Image denoising Twin-image Twin-image
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| GB/T 7714 | Jin, Xiaoyu , Zhao, Jie , Wang, Dayong et al. Iterative denoising phase retrieval method for twin-image elimination in continuous-wave terahertz in-line digital holography [J]. | OPTICS AND LASERS IN ENGINEERING , 2022 , 152 . |
| MLA | Jin, Xiaoyu et al. "Iterative denoising phase retrieval method for twin-image elimination in continuous-wave terahertz in-line digital holography" . | OPTICS AND LASERS IN ENGINEERING 152 (2022) . |
| APA | Jin, Xiaoyu , Zhao, Jie , Wang, Dayong , Rong, Lu , Wang, Yunxin , Healy, John J. et al. Iterative denoising phase retrieval method for twin-image elimination in continuous-wave terahertz in-line digital holography . | OPTICS AND LASERS IN ENGINEERING , 2022 , 152 . |
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Abstract ：
Fourier ptychographic microscopy (FPM) is an effective computational imaging method that incorporates many advantages such as large field of view, high resolution, label-free, and quantitative phase-contrast imaging. Typically, an LED array is used as the illumination source. Due to the small size and narrow spectral width of the LED unit, FPM is usually treated as a coherent imaging system. However, practically, each LED unit is a spatially-extended light source with a certain emitting area, rather than an ideal point source. The ideal point source approximation will decrease the quality of the reconstructed image, to a certain extent. In this paper, the spatial coherence characteristics of FPM system based on LED illumination is analyzed, and it is found that the optical field on the object plane is partially coherent. Thus, the artifacts exist when the coherent transfer function is used as the frequency domain constraint. To address this problem, a Butterworth-weighted transfer function is proposed as the frequency domain constraint in the iterative reconstruction process. The simulation and experimental results demonstrate that this new constraint approach can not only reduce the ringing effect in low-resolution images, but also improve the reconstruction quality due to its following better the actual physical mechanism inherent in FPM. In addition, it may reduce the requirement of the spatial coherence of the illumination source, which has great significance for promoting the application of FPM.
Keyword ：
phase retrieval algorithm phase retrieval algorithm Fourier ptychographic microscopy Fourier ptychographic microscopy partially coherent imaging partially coherent imaging Butterworth-weighted transfer function Butterworth-weighted transfer function
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| GB/T 7714 | Zhao, Jie , Wang, Dayong , Han, Yaqian et al. Improved reconstruction with Butterworth-weighted transfer function for Fourier ptychographic microscopy [J]. | HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS XII , 2022 , 12318 . |
| MLA | Zhao, Jie et al. "Improved reconstruction with Butterworth-weighted transfer function for Fourier ptychographic microscopy" . | HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS XII 12318 (2022) . |
| APA | Zhao, Jie , Wang, Dayong , Han, Yaqian , Lin, Shufeng , Wang, Yunxin , Rong, Lu . Improved reconstruction with Butterworth-weighted transfer function for Fourier ptychographic microscopy . | HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS XII , 2022 , 12318 . |
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Abstract ：
In the THz band, the spoof surface plasmon polariton (SSP) can limit the light to the designed specific spatial frequency by constructing a sub-wavelength structure on the metal surface. This ability makes it possible to break through the diffraction limit of THz imaging. In this paper, a one- dimensional metal groove structure is used to generate the SSP, and the frequency shift characteristics of the object's spatial spectrum under the excitation of a 2.52THz beam are analyzed. On this basis, a grating-coupling-based SSP excitation structure is designed, which consists of a combined array of subwavelength metal grooves and subwavelength slits with different periods. This structure is used to generate strong intensity and make full use of the incident beam. It is promising for generating illumination beams for terahertz far-field super-resolution imaging of subwavelength-spacing samples.
Keyword ：
terahertz terahertz Spoof plasmon Spoof plasmon surface waves surface waves
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| GB/T 7714 | Li, Kunlun , Wang, Dayong , Rong, Lu et al. Design and simulation comparison of terahertz surface wave based on grating coupling method [J]. | HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS XII , 2022 , 12318 . |
| MLA | Li, Kunlun et al. "Design and simulation comparison of terahertz surface wave based on grating coupling method" . | HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS XII 12318 (2022) . |
| APA | Li, Kunlun , Wang, Dayong , Rong, Lu , Zhao, Jie , Lin, Shufeng , Wang, Yunxin et al. Design and simulation comparison of terahertz surface wave based on grating coupling method . | HOLOGRAPHY, DIFFRACTIVE OPTICS, AND APPLICATIONS XII , 2022 , 12318 . |
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Abstract ：
In the past few decades, the applications of terahertz (THz) spectroscopy and imaging technology have seen significant developments in the fields of biology, medical diagnosis, food safety, and nondestructive testing. Label-free diagnosis of malignant tumours has been obtained and also achieved significant development in THz biomedical imaging. This review mainly presents the research status and prospects of several common continuous-wave (CW) THz medical imaging systems and applications of THz medical imaging in biological tissues. Here, we first introduce the properties of THz waves and how these properties play a role in biomedical imaging. Then, we analyse both the advantages and disadvantages of the CW THz imaging methods and the progress of these methods in THz biomedical imaging in recent ten years. Finally, we summarise the obstacles in the way of the application of THz bio-imaging application technology in clinical detection, which need to be investigated and overcome in the future.
Keyword ：
biomedical imaging biomedical imaging terahertz imaging terahertz imaging ptychography ptychography digital holography digital holography terahertz computed tomography terahertz computed tomography
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| GB/T 7714 | Zhang, Yaya , Wang, Chuting , Huai, Bingxin et al. Continuous-Wave THz Imaging for Biomedical Samples [J]. | APPLIED SCIENCES-BASEL , 2021 , 11 (1) . |
| MLA | Zhang, Yaya et al. "Continuous-Wave THz Imaging for Biomedical Samples" . | APPLIED SCIENCES-BASEL 11 . 1 (2021) . |
| APA | Zhang, Yaya , Wang, Chuting , Huai, Bingxin , Wang, Shiyu , Zhang, Yating , Wang, Dayong et al. Continuous-Wave THz Imaging for Biomedical Samples . | APPLIED SCIENCES-BASEL , 2021 , 11 (1) . |
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Abstract ：
基于微波频差转换的光学拍频研究
Keyword ：
频率变换 频率变换 光学拍频 光学拍频 实验教学 实验教学
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| GB/T 7714 | 王云新 , 王大勇 , 杨登才 et al. 基于微波频差转换的光学拍频研究 [J]. | 王云新 , 2021 , 40 (3) : 43-47 . |
| MLA | 王云新 et al. "基于微波频差转换的光学拍频研究" . | 王云新 40 . 3 (2021) : 43-47 . |
| APA | 王云新 , 王大勇 , 杨登才 , 李平雪 , 戎路 , 赵洁 et al. 基于微波频差转换的光学拍频研究 . | 王云新 , 2021 , 40 (3) , 43-47 . |
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Abstract ：
Photonics-Assisted frequency conversion based on cascaded modulators is an effective way to satisfy the requirements of distributed antenna array applications. A filter-free photonic image-rejection down-converter with immunity to dispersion-induced power fading is proposed and demonstrated. The radio frequency (RF) signal from the distributed antenna unit is injected into a dual-drive Mach-Zehnder modulator (DDMZM) through an electrical 90° hybrid coupler (HC), and a single-sideband (SSB) signal is realized. It is then transmitted to the center office by an optical fiber link. At the center office, the modulated RF signal is injected into a dual-polarization dual-parallel MZM (DP-DPMZM) after a polarization controller (PC). Afterwards, an LO signal remodulates it through the Y-DPMZM, and carrier-suppressed SSB modulation is fulfilled via another electrical 90° HC. After the power splitting, quadrature I and Q IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Through a combination of the I/Q IF signals with a low-frequency electrical 90° HC, a photonics image-rejection down-converter based on phase cancellation is realized. Moreover, no optical filter is required; thus, the image-rejection down-converter can work with a large bandwidth. The proposed filter-free photonic image-rejection down-converter is theoretically analyzed and experimentally verified. © 2009-2012 IEEE.
Keyword ：
Fading (radio) Fading (radio) Polarization Polarization Modulators Modulators Photonics Photonics Optical fibers Optical fibers Electric connectors Electric connectors Antenna arrays Antenna arrays Image converters Image converters
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| GB/T 7714 | Wang, Dayong , Yang, Feng , Wang, Yunxin et al. Filter-Free Photonic Image-Rejection Down-Conversion for Distributed Antenna Applications [J]. | IEEE Photonics Journal , 2021 , 13 (2) . |
| MLA | Wang, Dayong et al. "Filter-Free Photonic Image-Rejection Down-Conversion for Distributed Antenna Applications" . | IEEE Photonics Journal 13 . 2 (2021) . |
| APA | Wang, Dayong , Yang, Feng , Wang, Yunxin , Chen, Zhiyu , Yang, Dengcai , Wu, Fuzheng . Filter-Free Photonic Image-Rejection Down-Conversion for Distributed Antenna Applications . | IEEE Photonics Journal , 2021 , 13 (2) . |
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Abstract ：
Terahertz (THz) phase imaging is widely spreading in various scenarios, among which full-field phase distributions are commonly retrieved by digital holography or ptychography. In this Letter, the transport of the intensity equation reconstruction method is applied into the THz band. An algorithm named the lensless US-transport of intensity equation (TIE) is proposed to accommodate to an in-line configuration. The object phase is retrieved by primarily conducting iterations between the axial intensity derivative and the phase distribution at the recording plane and sub-sequent backward diffraction propagation. This method is applicable to both isolated and extended weakly absorbing samples with higher reconstruction quality and remarkably less time cost than holographic phase retrieval algorithms. It can also be attempted in other non-interferometric geometries or using low-cost partially coherent THz sources, which significantly broaden the application scope of THz phase imaging. (C) 2021 Optical Society of America
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| GB/T 7714 | Rong, Lu , Wang, Shiyu , Wang, Dayong et al. Transport of intensity equation-based terahertz lensless full-field phase imaging [J]. | OPTICS LETTERS , 2021 , 46 (23) : 5846-5849 . |
| MLA | Rong, Lu et al. "Transport of intensity equation-based terahertz lensless full-field phase imaging" . | OPTICS LETTERS 46 . 23 (2021) : 5846-5849 . |
| APA | Rong, Lu , Wang, Shiyu , Wang, Dayong , Tan, Fangrui , Zhang, Yaya , Zhao, Jie et al. Transport of intensity equation-based terahertz lensless full-field phase imaging . | OPTICS LETTERS , 2021 , 46 (23) , 5846-5849 . |
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Abstract ：
By virtue of its versatile recording geometries, ptychography is a promising full-field lensless phase imaging approach in the prosperous research area of terahertz imaging. In this paper, we propose an extrapolation extended ptychographical iterative engine, named as the EE-PIE reconstruction algorithm, to increase the lateral resolution of terahertz ptychography. A divergent spherical beam is applied to illuminate the object, while diffraction patterns are recorded in the Fresnel region. The signal-to-noise ratio of the diffraction patterns is enhanced under divergent probe illumination, while the size of the diffraction patterns is numerically enlarged by the proposed algorithm. Both the reconstruction quality and the resolution are enhanced without adding to the complexity of the setup or increasing the data acquisition time. The proposed method is experimentally demonstrated using a cluster of phylloclades, a patterned polypropylene plate and a Siemens star target. Compared with the planar illumination, the resolution of the divergent spherical illumination is improved by 2.14 times. On this basis, the extrapolation algorithm further improves the experimental resolution by 1.26 times.
Keyword ：
Phase imaging Phase imaging Ptychography Ptychography Terahertz imaging Terahertz imaging Divergent illumination Divergent illumination Extrapolation algorithm Extrapolation algorithm
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| GB/T 7714 | Rong, Lu , Tan, Fangrui , Wang, Dayong et al. High-resolution terahertz ptychography using divergent illumination and extrapolation algorithm [J]. | OPTICS AND LASERS IN ENGINEERING , 2021 , 147 . |
| MLA | Rong, Lu et al. "High-resolution terahertz ptychography using divergent illumination and extrapolation algorithm" . | OPTICS AND LASERS IN ENGINEERING 147 (2021) . |
| APA | Rong, Lu , Tan, Fangrui , Wang, Dayong , Zhang, Yaya , Li, Kunlun , Zhao, Jie et al. High-resolution terahertz ptychography using divergent illumination and extrapolation algorithm . | OPTICS AND LASERS IN ENGINEERING , 2021 , 147 . |
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Abstract ：
For a noncooperative target, multiple-dimension detection is required to determine its spatial location. A microwave photonic radar is proposed for simultaneous detection of the distance and direction of targets. At the transmitter, a linear frequency modulation (LFM) signal with a large instantaneous bandwidth was obtained by frequency doubling. Meanwhile, the optical reference signal was supplied. At the receiver, two antennas with a certain baseline length were used to receive the echo signal. The dechirp process and fixed-length cable are combined to decouple the distance and direction and distinguish between the positive and negative directions of a target. Theoretical derivation has already verified that the distance and direction can be resolved simultaneously by dechirping of the echo modulation signal and reference signal. In experiments, an LFM signal with an instantaneous bandwidth of 2 GHz (2-4 GHz) was generated and launched as the detection signal. Targets at different distances with positive and negative angles were detected. The results show that the directional measurement ranges from -72.5 0 to 72.5 degrees, and the error is less than 1.6 degrees. The measured distance was found to be quite similar to the actual distance. The proposed approach can confirm the spatial location of a noncooperative target by combining the detection of both distance and direction. Furthermore, the baseline length need not be less than half the wavelength of the echo signal, and large antennas can be chosen to improve the detection distance and range accuracy. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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| GB/T 7714 | Wang, Yunxin , Hou, Xueyuan , Li, Tao et al. Simultaneous detection of the distance and direction for a noncooperative target based on the microwave photonic radar [J]. | OPTICS EXPRESS , 2021 , 29 (20) : 31561-31573 . |
| MLA | Wang, Yunxin et al. "Simultaneous detection of the distance and direction for a noncooperative target based on the microwave photonic radar" . | OPTICS EXPRESS 29 . 20 (2021) : 31561-31573 . |
| APA | Wang, Yunxin , Hou, Xueyuan , Li, Tao , He, Ziang , Wang, Dayong , Yang, Feng et al. Simultaneous detection of the distance and direction for a noncooperative target based on the microwave photonic radar . | OPTICS EXPRESS , 2021 , 29 (20) , 31561-31573 . |
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