Hot Topics

2020-11-25
PIER
Vol. 169, 17-23, 2020
Multi-Laser Scanning Confocal Fluorescent Endoscopy Scheme for Subcellular Imaging (Invited)
Xiaomin Zheng Xiang Li Qiao Lin Jiajie Chen Yueqing Gu Yonghong Shao
Fluorescence confocal laser scanning endomicroscopy is a novel tool combining confocal microscopy and endoscopy for in-vivo subcellular structure imaging with comparable resolution as the traditional microscope. In this paper, we propose a three-channel fluorescence confocal microscopy system based on fiber bundle and two excitation laser lines of 488nm and 650nm. Three fluorescent photomultiplier detecting channels of red, green and blue can record multi-color fluorescence signals from single sample site simultaneously. And its ability for in-vivo multi-channel fluorescence detection at subcellular level is verified. Moreover, the system has achieved an effective field of view of 154μm in diameter with high resolution. With its multi-laser scanning, multi-channel detection, flexible probing, and in-vivo imaging abilities it will become a powerful tool in bio-chemical research and diagnostics, such as the investigation of the transport mechanism of nano-drugs in small animals.
MULTI-LASER SCANNING CONFOCAL FLUORESCENT ENDOSCOPY SCHEME FOR SUBCELLULAR IMAGING (INVITED)
2020-08-22
PIER
Vol. 168, 15-23, 2020
Superscattering of Light in Refractive-Index Near-Zero Environments
Chan Wang Chao Qian Hao Hu Lian Shen Zuo Jia Wang Huaping Wang Zhiwei Xu Baile Zhang Hongsheng Chen Xiao Lin
Enhancing the scattering of light from subwavelength structures is of both fundamental and practical significance. While the scattering cross section from each channel cannot exceed the single-channel limit, it is recently reported that the total cross section can far exceed this limit if one overlaps the contribution from many channels. Such a phenomenon about enhancing the scattering from subwavelength structures in free space is denoted as the superscattering in some literature. However, the scatterer in practical scenarios is not always in free space but may be embedded in environments with non-unity refractive index n. The influence of environments on the superscattering remains elusive. Here the superscattering from subwavelength structures in the isotropic environment with near-zero index are theoretically investigated. Importantly, a smaller n can lead to a larger total cross section for superscattering. The underlying mechanism is that a smaller n can give rise to a larger single-channel limit. Our work thus indicates that the scattering from subwavelength structures can be further enhanced if one simultaneously maximizes the single-channel limit and the contribution from many channels.
SUPERSCATTERING OF LIGHT IN REFRACTIVE-INDEX NEAR-ZERO ENVIRONMENTS
2021-12-20
PIER
Vol. 172, 13-22, 2021
Tunable Topological Refractions in Valley Sonic Crystals with Triple Valley Hall Phase Transitions (Invited Paper)
Ding Jia Yin Wang Yong Ge Shou-Qi Yuan Hong-Xiang Sun
Topological refractions created by valley sonic crystals (VSCs) have attracted great attentions in the communities of physics and engineering owing to the advantage of zero reflection of sound and the potential for designing advanced acoustic devices. In previous works, topological refractions of valley edge states are demonstrated to be determined by the projections of the valleys K and K′, and two types of topological refractions generally exist at opposite terminals or different frequency bands. However, the realization of tunable topological refractions at the fixed frequency band and terminal still poses great challenge. To overcome this, we report the realization of tunable topological refractions by VSCs with triple valley Hall phase transitions. By simply rotating rods, we realize 3 types of topological waveguides (T1, T2 and T3) composed of two VSCs, in which the projections of the observed valley edge states can be modulated between K and K′. Additionally, based on the measured transmittance spectra, we experimentally demonstrate that these valleyedge states are almost immune to backscattering against sharp bends. More importantly, we realize tunable topological refractions at the fixed frequency band and terminal, and experimentally observe the coexistence of positive and negative refractions for T1 and T3, and negative refractions for T2. The proposed tunable topological refractions have potential applications in designing multi-functional sound antennas and advanced communication devices.
TUNABLE TOPOLOGICAL REFRACTIONS IN VALLEY SONIC CRYSTALS WITH TRIPLE VALLEY HALL PHASE TRANSITIONS (INVITED PAPER)
2022-02-28
PIER
Vol. 173, 9-23, 2022
Recent Progress on Achromatic Metalenses (Invited Review)
Qikai Chen Yitian Liu Yaoyuan Lei Sijie Pian Zhuning Wang Yaoguang Ma
As a potential alternative to conventional lenses, metalenses have the advantage of ultrathin volume and light weight. Such miniaturization is expected to apply to compact, nanoscale optical devices such as micro-cameras and high-resolution display. However, chromatic aberration is an important problem in the application of metalenses, which will damage the imaging resolution and color reality for multi-wavelength incident light. Here, we briefly discuss recent development of design methods for achromatic metalenses, containing one or more pieces, and experimental evaluation of their performances.
RECENT PROGRESS ON ACHROMATIC METALENSES (INVITED REVIEW)
2020-08-20
PIER
Vol. 168, 1-13, 2020
Classical and Quantum Electromagnetic Interferences: What Is the Difference?
Dong-Yeop Na Weng Cho Chew
The zeroing of second order correlation functions between output fields after interferences in a 50/50 beam splitter has been accepted decades-long in the quantum optics community as an indicator of the quantum nature of lights. But, a recent work [1] presented some notable discussions and experiments that classical electromagnetic fields can still exhibit the zero correlation under specific conditions. Here, we examine analytically classical and quantum electromagnetic field interferences in a 50/50 beam splitter in the context of the second order correlation function for various input conditions. Adopting the Heisenberg picture in quantum electromagnetics, we examine components of four-term interference terms in the numerator of second order correlation functions and elucidate their physical significance. As such, we reveal the fundamental difference between the classical and quantum interference as illustrated by the Hong-Ou-Mandel (HOM) effect. The quantum HOM effect is strongly associated with: (1) the commutator relation that does not have a classical analogue; (2) the property of Fock states needed to stipulate the one-photon quantum state of the system; and (3) a destructive wave interference effect. Here, (1) and (2) imply the indivisibility of a photon. On the contrary, the classical HOM effect requires the presence of two destructive wave interferences without the need to stipulate a quantum state.
CLASSICAL AND QUANTUM ELECTROMAGNETIC INTERFERENCES: WHAT IS THE DIFFERENCE?
2022-02-08
PIER
Vol. 173, 1-8, 2022
An Ultra-Thin Wideband Reflection Reduction Metasurface Based on Polarization Conversion
Tiancheng Han Kaihuai Wen Zixuan Xie Xiuli Yue
Reflection reduction metasurface is capable of suppressing the radar cross section of a target, which is of great importance in stealth technology. However, it is still a challenge to realize broadband and low-profile simultaneously within a simple design. Here, we experimentally demonstrate an ultra-thin wideband reflection reduction metasurface, which is achieved by utilizing polarization conversion instead of resonant absorption. The simple cut-wire unit cell is adopted to perform efficient cross polarization conversion, which leads to a polarization conversion ratio above 90% ranging from 8.4 to 14.7 GHz. By arranging the 0/1 units in chessboard layout, the reflection reduction reaches 10\,dB from 8.1 GHz to 14.6 GHz. Measured results agree well with simulated ones, which validates the effectiveness of the proposed structure. The ratio of thickness to maximum wavelength reaches 0.56 while the relative bandwidth reaches 57.3%, demonstrating an excellent comprehensive performance. Since our structure consists of refractory ceramic materials, it is promising for radar cross section reduction in high temperature environment.
AN ULTRA-THIN WIDEBAND REFLECTION REDUCTION METASURFACE BASED ON POLARIZATION CONVERSION
2022-04-27
PIER
Vol. 174, 1-22, 2022
On the Low Speed Limits of Lorentz's Transformation - How Relativistic Effects Retain OR Vanish in Electromagnetism
Hao Chen Wei E. I. Sha Xi Dai Yue Yu
This article contains a digest of the theory of electromagnetism and a review of the transformation between inertial frames, especially under low speed limits. The covariant nature of the Maxwell's equations is explained using the conventional language. We show that even under low speed limits, the relativistic effects should not be neglected to get a self-consistent theory of the electromagnetic fields, unless the intrinsic dynamics of these fields has been omitted completely. The quasi-static limits, where the relativistic effects can be partly neglected are also reviewed, to clarify some common misunderstandings and imprecise use of the theory in presence of moving media and other related situations. The discussions presented in this paper provide a clear view of why classical electromagnetic theory is relativistic in its essence.
On the Low Speed Limits of Lorentz's Transformation - How Relativistic Effects Retain OR Vanish in Electromagnetism
2020-11-06
PIER
Vol. 169, 1-15, 2020
The Multilevel Fast Physical Optics Method for Calculating High Frequency Scattered Fields
Zhiyang Xue Yu Mao Wu Weng Cho Chew Ya-Qiu Jin Amir Boag
The multilevel fast physical optics (MLFPO) is proposed to accelerate the computation of the fields scattered from electrically large coated scatterers. This method is based on the quadratic patch subdivision and the multilevel technology. First, the quadratic patches are employed rather than the planar patches to discretize the considered scatterer. Hence, the number of the contributing patches is cut dramatically, thus making the workload of the MLFPO method much lower than that of the traditional Gordon's method. Next, the multilevel technology is introduced in this work to avoid calculating the physical optics scattered fields from the considered scatterer directly, so that the proposed algorithm can significantly reduce the computational complexity. Finally, numerical results have demonstrated the accuracy and efficiency of the MLFPO method based on the quadratic patches.
THE MULTILEVEL FAST PHYSICAL OPTICS METHOD FOR CALCULATING HIGH FREQUENCY SCATTERED FIELDS
2022-07-14
PIER
Vol. 175, 1-11, 2022
Machine-Learning-Enabled Recovery of Prior Information from Experimental Breast Microwave Imaging Data
Keeley Edwards Joe LoVetri Colin Gilmore Ian Jeffrey
We demonstrate the recovery of simple geometric and permittivity information of breast models in an experimental microwave breast imaging system using a synthetically trained machine learning workflow. The recovered information consists of simple models of adipose and fibroglandular regions. The machine learning model is trained on a labelled synthetic dataset constructed over a range of possible adipose and fibroglandular regions and the trained neural network predicts the geometry and average permittivty of the adipose and fibroglandular regions from calibrated experimental data. The proposed workflow is tested on two different experimental models of the human breast. The first model is comprised of two simple, symmetric phantoms representing the adipose and fibroglandular regions of the breast that match the model used to train the neural network. The second, more realistic model replaces the symmetric fibroglandular phantom with an irregularly shaped, MRI-derived fibroglandular phantom. We demonstrate the ability of the machine learning workflow to accurately recover geometry and complex valued average permittivity of the fibroglandular region for the simple case, and to predict a symmetric convex hull that is a reasonable approximation to the proportions of the MRI-derived fibroglandular phantom.
MACHINE-LEARNING-ENABLED RECOVERY OF PRIOR INFORMATION FROM EXPERIMENTAL BREAST MICROWAVE IMAGING DATA