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Photonic crystals

Tenghao Yin, Danming Zhong, Junjie Liu, Xiangjiang Liu, Honghui Yu, Shaoxing Qu
The tunable diffracted pattern (Debye ring) of the well-ordered close-packed 2D photonic crystal (PC) is achieved via large deformation of the dielectric elastomer (DE) membrane for the first time. Two deformation models are proposed, the in-plane deformation driven by voltage and the out-of-plane deformation actuated by pressure. Both experimental and theoretical analyses are conducted to explore the tunability of the DE stretch on the Debye ring of the 2D PC, by voltage and pressure. An excellent agreement is found between the experimental and analytical results...
January 17, 2018: Soft Matter
Xiaogang Yang, Xianqing Lin, Yong Sheng Zhao, Dongpeng Yan
Micro- and nanometer-sized metal-organic frameworks (MOFs) materials have attracted great attention due to their unique properties and various potential applications in photonics, electronics, high-density storage, chemo-, and biosensors. The study of these materials supplies insight into how the crystal structure, molecular components, and micro-/nanoscale effects can influence the performance of inorganic-organic hybrid materials. In this Minireview article, we introduce recent breakthroughs in the controlled synthesis of MOF micro-/nanomaterials with specific structures and compositions, the tunable photonic and electronic properties of which would provide a novel platform for multifunctional applications...
January 16, 2018: Chemistry: a European Journal
Marc Serra-Garcia, Valerio Peri, Roman Süsstrunk, Osama R Bilal, Tom Larsen, Luis Guillermo Villanueva, Sebastian D Huber
The modern theory of charge polarization in solids is based on a generalization of Berry's phase. The possibility of the quantization of this phase arising from parallel transport in momentum space is essential to our understanding of systems with topological band structures. Although based on the concept of charge polarization, this same theory can also be used to characterize the Bloch bands of neutral bosonic systems such as photonic or phononic crystals. The theory of this quantized polarization has recently been extended from the dipole moment to higher multipole moments...
January 15, 2018: Nature
Wenwen Lin, Constantinos C Stoumpos, Oleg Y Kontsevoi, Zhifu Liu, Yihui He, Sanjib Das, Yadong Xu, Kyle M McCall, Bruce W Wessels, Mercouri G Kanatzidis
Cu2I2Se6 is a new wide-bandgap semiconductor with high stability and great potential towards hard radiation and photon detection. Cu2I2Se6 crystallizes in the rhombohedral R3 ̅m space group with a density of d = 5.287 g·cm-3 and a wide bandgap Eg of 1.95 eV. First-principles electronic band structure calculations at the density functional theory level indicate an indirect bandgap and a low electron effective mass me* of 0.32. The congruently melting compound was grown in centimeter-size Cu2I2Se6 single crystals using a vertical Bridgman method...
January 14, 2018: Journal of the American Chemical Society
Davide Raffaele Ceratti, Yevgeny Rakita, Lorenzo Cremonesi, Ron Tenne, Vyacheslav Kalchenko, Michael Elbaum, Dan Oron, Marco Alberto Carlo Potenza, Gary Hodes, David Cahen
Self-healing, where a modification in some parameter is reversed with time without any external intervention, is one of the particularly interesting properties of halide perovskites. While there are a number of studies showing such self-healing in perovskites, they all are carried out on thin films, where the interface between the perovskite and another phase (including the ambient) is often a dominating and interfering factor in the process. Here, self-healing in perovskite (methylammonium, formamidinium, and cesium lead bromide (MAPbBr3 , FAPbBr3 , and CsPbBr3 )) single crystals is reported, using two-photon microscopy to create damage (photobleaching) ≈110 µm inside the crystals and to monitor the recovery of photoluminescence after the damage...
January 12, 2018: Advanced Materials
Andrzej Miniewicz, Hanna Orlikowska, Anna Sobolewska, Stanislaw Bartkiewicz
Single-component azobenzene-based phototropic liquid crystals (PtLC) are promising materials that have started to be explored for photonic applications. One of the essential factors determining the applicability of these materials is the rate of the thermally driven cis-trans isomerization. In this paper, the kinetics of the thermal back cis-to-trans reaction in a pure 4-hexyl-4'-methoxyazobenzene (6-AB-O1) compound in its isotropic liquid and nematic phases is studied (the undoped LC). The reaction rate constants, activation energies and thermal activation parameters were determined based on spectroscopic studies...
January 12, 2018: Physical Chemistry Chemical Physics: PCCP
Xian Zhang, Xiao-Song Zhu, Yi-Wei Shi
A high performance hollow fiber (HF) surface plasmon resonance (SPR) sensor utilizing one-dimensional photonic crystal (1DPC) is proposed. The performance of the designed sensor is analyzed theoretically with respect to the center wavelength and the bilayer period. Because the light transmitted in the sensor mostly have large incident angles, the center wavelength of the 1DPC should shift to longer wavelength to ensure the band gap covers the spectrum range of the incident light. The sensor exhibits better performance when the detection spectral range is located in the band gap of 1DPC for incident angle larger than 80°...
January 8, 2018: Optics Express
Joshua R Hendrickson, Richard Soref, Ricky Gibson
Design and simulation results are presented for an on-chip 2×2 Mach-Zehnder-based optical switch where each arm of the interferometer is composed of a coupled-resonator optical waveguide. The individual resonators are one-dimensional photonic crystal nanobeam cavities, and switching occurs through thermally induced changes in the refractive index of the silicon structure using integrated heating pads. The performance of the coupled-resonator device is directly compared to its single resonator counterpart, and significant improvement is found in the bar-state CT metric...
January 15, 2018: Optics Letters
Maximilian Hoffmann, Ioannis N Papadopoulos, Benjamin Judkewitz
The controlled modulation of an optical wavefront is required for aberration correction, digital phase conjugation, or patterned photostimulation. For most of these applications, it is desirable to control the wavefront modulation at the highest rates possible. The digital micromirror device (DMD) presents a cost-effective solution to achieve high-speed modulation and often exceeds the speed of the more conventional liquid crystal spatial light modulator but is inherently an amplitude modulator. Furthermore, spatial dispersion caused by DMD diffraction complicates its use with pulsed laser sources, such as those used in nonlinear microscopy...
January 1, 2018: Optics Letters
Smriti Sahu, Rituraj Sharma, K V Adarsh, Anbarasu Manivannan
Rapid and reversible switching between amorphous and crystalline phases of phase-change material promises to revolutionize the field of information processing with a wide range of applications including electronic, optoelectronics, and photonic memory devices. However, achieving faster crystallization is a key challenge. Here, we demonstrate femtosecond-driven transient inspection of ultrafast crystallization of as-deposited amorphous Ge1Sb2Te4 and Ge1Sb4Te7 thin films induced by a series of 120 fs laser pulses...
January 10, 2018: Applied Optics
Fengji Gui, Ping Jiang, Huajun Yang, Yan Qin, Weinan Caiyang
In this work, a novel design of a high birefringence photonic crystal fiber (HB-PCF) with multimode and low confinement loss is proposed. To achieve high birefringence, the core is designed as an elliptical region, which is enclosed by twelve small holes. Based on this design, replacing the two circular holes at the top and bottom of the core region with two elliptical holes can further improve the birefringence. At the wavelength of 1.55 μm, the birefringence of the fundamental mode (LP01) and the second-order mode (LP11) are 1...
January 1, 2018: Applied Optics
Pau Molet, Juan Luis Garcia-Pomar, Cristiano Matricardi, Miquel Garriga, Maria Isabel Alonso, Agustín Mihi
The design of ultrathin semiconducting materials that achieve broadband absorption is a long-sought-after goal of crucial importance for optoelectronic applications. To date, attempts to tackle this problem consisted either of the use of strong-but narrowband-or broader-but moderate-light-trapping mechanisms. Here, a strategy that achieves broadband optimal absorption in arbitrarily thin semiconductor materials for all energies above their bandgap is presented. This stems from the strong interplay between Brewster modes, sustained by judiciously nanostructured thin semiconductors on metal films, and photonic crystal modes...
January 12, 2018: Advanced Materials
Hengyun Zhou, Chao Peng, Yoseob Yoon, Chia Wei Hsu, Keith A Nelson, Liang Fu, John D Joannopoulos, Marin Soljačić, Bo Zhen
The ideas of topology have found tremendous success in closed physical systems, but even richer properties exist in the more general open or dissipative framework. We theoretically propose and experimentally demonstrate a bulk Fermi arc that develops from non-Hermitian radiative losses in an open system of photonic crystal slabs. Moreover, we discover half-integer topological charges in the polarization of far-field radiation around the bulk Fermi arc. Both phenomena are shown to be direct consequences of the non-Hermitian topological properties of exceptional points, where resonances coincide in their frequencies and linewidths...
January 11, 2018: Science
Biao Yang, Qinghua Guo, Ben Tremain, Rongjuan Liu, Lauren E Barr, Qinghui Yan, Wenlong Gao, Hongchao Liu, Yuanjiang Xiang, Jing Chen, Chen Fang, Alastair Hibbins, Ling Lu, Shuang Zhang
Weyl points are the crossings of linearly dispersing energy bands of three-dimensional crystals, providing the opportunity to explore a variety of intriguing phenomena such as topologically protected surface states and chiral anomalies. However, the lack of an ideal Weyl system in which the Weyl points all exist at the same energy and are separated from any other bands, poses a serious limitation to the further development of Weyl physics and potential applications. By experimentally characterizing a microwave photonic crystal of saddle-shaped metallic coils, we observe ideal Weyl points that are related to each other through symmetry operations...
January 11, 2018: Science
Wei Luo, Qian Cui, Kai Fang, Ke Chen, Huiru Ma, Jianguo Guan
Microenvironment sensing and imaging are of importance in microscale zones like microreactors, microfluidic systems, and biological cells. But they are so far implemented only based on chemical colors from dyes or quantum dots, which suffered either from photobleaching, quenching, or photoblinking behaviors, or from limited color gamut. In contrast, structural colors from hydrogel-based photonic crystals (PCs) may be stable and tunable in the whole visible spectrum by diffraction peak shift, facilitating the visual detection with high accuracy...
January 17, 2018: Nano Letters
Myungjae Lee, Jeongkug Lee, Sunghwan Kim, Ségolène Callard, Christian Seassal, Heonsu Jeon
Anderson localization in random structures is an intriguing physical phenomenon, for which experimental verifications are far behind theoretical predictions. We report the first experimental confirmations of photonic band-tail states and a complete transition of Anderson localization. An optically activated photonic crystal alloy platform enables the acquisition of extensive experimental data exclusively on pure eigenstates, revealing direct evidence of band-tail states and Anderson localization transition within the band-tail states...
January 2018: Science Advances
Tao Cao, Mingchen Liu, Chang Xu, Jikun Yan, Chaochao Shen, Shaozhen Liu, Hao Peng, Jiahui Peng, Alexei V Sokolov
Optimization of laser output parameters vs. f-to-2f beating signals can be mutually contradicting, when an octave-spanning supercontinuum is employed for f-to-2f measurements. We show that resonant dispersive waves will solve this issue, thanks to their frequency stability against changes in laser power and chirping.
January 9, 2018: Scientific Reports
Qichun Zhang, Huanqing Ye, Guangfeng Liu, Sheng Liu, David Casanova Casanova, Xin Ye, Xutang Tao, Qihua Xiong
Singlet-triplet conversion in organic light-emitting materials introduces non-emissive (dark) and long-lived triplet states, which represents a significant challenge in constraining the optical properties. There have been considerable attempts in separating singlets and triplets in polymers, scavenging or quenching triplets by heavy metals. Such triplet-induced loss cannot be fully eliminated. Herein, we report a new strategy of crafting periodic molecular barrier into the π-conjugated matrices of organic aromatic fluorophores...
January 6, 2018: Angewandte Chemie
Jing-Yuan Wu, Young Tea Chun, Shunpu Li, Tong Zhang, Junzhan Wang, Pawan Kumar Shrestha, Daping Chu
Inverse photoresponse is discovered from phototransistors based on molybdenum disulfide (MoS2 ). The devices are capable of detecting photons with energy below the bandgap of MoS2 . Under the illumination of near-infrared (NIR) light at 980 and 1550 nm, negative photoresponses with short response time (50 ms) are observed for the first time. Upon visible-light illumination, the phototransistors exhibit positive photoresponse with ultrahigh responsivity on the order of 104 -105 A W-1 owing to the photogating effect and charge trapping mechanism...
January 8, 2018: Advanced Materials
A Schori, C Bömer, D Borodin, S P Collins, B Detlefs, M Moretti Sala, S Yudovich, S Shwartz
We report the observation of parametrically down-converted x-ray signal photons at photon energies that correspond to idler photons at optical wavelengths. The count-rate dependence on the angles of the input beam and of the detector and on the slit sizes agrees with theory within the experimental uncertainties. The nonlinear susceptibility, which we calculated from the measured efficiencies, is comparable to the nonlinear susceptibility evaluated from the measurements of x-ray and optical wave mixing. The results of the present Letter advance the development of a spectroscopy method for probing valence-electron charges and the microscopic optical response of crystals with atomic-scale resolution...
December 22, 2017: Physical Review Letters
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