scholarly journals Sound vortex diffraction via topological charge in phase gradient metagratings

2020 ◽  
Vol 6 (40) ◽  
pp. eaba9876
Author(s):  
Yangyang Fu ◽  
Chen Shen ◽  
Xiaohui Zhu ◽  
Junfei Li ◽  
Youwen Liu ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Numerical Simulations ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Asymmetric Transmission ◽  
Phase Gradient ◽  
Wave Fields ◽  
Limited Ability ◽  
Helmholtz Resonators ◽  
Powerful Mechanism

Wave fields with orbital angular momentum (OAM) have been widely investigated in metasurfaces. By engineering acoustic metasurfaces with phase gradient elements, phase twisting is commonly used to obtain acoustic OAM. However, it has limited ability to manipulate sound vortices, and a more powerful mechanism for sound vortex manipulation is strongly desired. Here, we propose the diffraction mechanism to manipulate sound vortices in a cylindrical waveguide with phase gradient metagratings (PGMs). A sound vortex diffraction law is theoretically revealed based on the generalized conservation principle of topological charge. This diffraction law can explain and predict the complicated diffraction phenomena of sound vortices, as confirmed by numerical simulations. To exemplify our findings, we designed and experimentally verified a PGM based on Helmholtz resonators that support asymmetric transmission of sound vortices. Our work provides previously unidentified opportunities for manipulating sound vortices, which can advance more versatile design for OAM-based devices.

scholarly journals Photocurrent detection of the orbital angular momentum of light

Science ◽  
2020 ◽  
Vol 368 (6492) ◽  
pp. 763-767 ◽  
Author(s):  
Zhurun Ji ◽  
Wenjing Liu ◽  
Sergiy Krylyuk ◽  
Xiaopeng Fan ◽  
Zhifeng Zhang ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Communication Networks ◽  
Orbital Angular Momentum ◽  
Optical Communication ◽  
Topological Charge ◽  
Optical Intensity ◽  
Phase Gradient ◽  
On Chip ◽  
A Current

Applications that use the orbital angular momentum (OAM) of light show promise for increasing the bandwidth of optical communication networks. However, direct photocurrent detection of different OAM modes has not yet been demonstrated. Most studies of current responses to electromagnetic fields have focused on optical intensity–related effects, but phase information has been lost. In this study, we designed a photodetector based on tungsten ditelluride (WTe2) with carefully fabricated electrode geometries to facilitate direct characterization of the topological charge of OAM of light. This orbital photogalvanic effect, driven by the helical phase gradient, is distinguished by a current winding around the optical beam axis with a magnitude proportional to its quantized OAM mode number. Our study provides a route to develop on-chip detection of optical OAM modes, which can enable the development of next-generation photonic circuits.

scholarly journals High-Efficiency Spin-Related Vortex Metalenses

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1485
Author(s):  
Wei Wang ◽  
Ruikang Zhao ◽  
Shilong Chang ◽  
Jing Li ◽  
Yan Shi ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
High Efficiency ◽  
Infrared Band ◽  
Mid Infrared ◽  
Integrated Devices ◽  
Vortex Beams ◽  
Topological Charges

In this paper, one spin-selected vortex metalens composed of silicon nanobricks is designed and numerically investigated at the mid-infrared band, which can produce vortex beams with different topological charges and achieve different spin lights simultaneously. Another type of spin-independent vortex metalens is also designed, which can focus the vortex beams with the same topological charge at the same position for different spin lights, respectively. Both of the two vortex metalenses can achieve high-efficiency focusing for different spin lights. In addition, the spin-to-orbital angular momentum conversion through the vortex metalens is also discussed in detail. Our work facilitates the establishment of high-efficiency spin-related integrated devices, which is significant for the development of vortex optics and spin optics.

scholarly journals Sectorial perturbation of vortex beams: Shannon entropy, orbital angular momentum and topological charge

2019 ◽  
Vol 43 (5) ◽  
pp. 723-734 ◽  
Author(s):  
A.V. Volyar ◽  
M.V. Bretsko ◽  
Ya.E. Akimova ◽  
Yu.A. Egorov ◽  
V.V. Milyukov
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Shannon Entropy ◽  
Topological Charge ◽  
External Perturbation ◽  
Informational Entropy ◽  
Large Perturbation ◽  
Wide Range ◽  
Vortex Beams ◽  
Computing Measuring

Transformations of the vortex beams structure subjected to sectorial perturbation were theoretically and experimentally studied. The analysis was based on computing (measuring) the vortex spectrum that enables us to find the orbital angular momentum (OAM) and Shannon entropy (informational entropy). We have revealed that, in the general case, the number of vortices caused by an external perturbation is not related to the topological charge. For arbitrary perturbation, the topological charge remains equal to the initial topological charge of the unperturbed vortex beam. Growth of the vortex number induced by perturbations is associated with the optical uncertainty principle between the sectorial angle and the OAM. The computer simulation has shown that OAM does not depend on the number of vortices induced by perturbations. Moreover, two maxima are formed both in the positive and negative regions of the vortex spectrum. As a result, the OAM does not practically change in a wide range of perturbation angles from 0 to 90 °. However, at large perturbation angles, when the energy is almost equally redistributed between the vortex modes with opposite signs of the topological charge, the OAM rapidly decreases. At the same time, the Shannon entropy monotonically increases with growing perturbation angle. This is due to the fact that the entropy depends only on the number of vortex states caused by external perturbations.

scholarly journals A Small-Divergence-Angle Orbital Angular Momentum Metasurface Antenna

Research ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-8 ◽  
Author(s):  
Jianchun Xu ◽  
Ke Bi ◽  
Ru Zhang ◽  
Yanan Hao ◽  
Chuwen Lan ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Electromagnetic Waves ◽  
Divergence Angle ◽  
Compact Structure ◽  
Phase Gradient ◽  
Practical Applications ◽  
Circular Arrangement ◽  
Low Efficiency ◽  
Theoretical Analyses

Electromagnetic waves carrying an orbital angular momentum (OAM) are of great interest. However, most OAM antennas present disadvantages such as a complicated structure, low efficiency, and large divergence angle, which prevents their practical applications. So far, there are few papers and research focuses on the problem of the divergence angle. Herein, a metasurface antenna is proposed to obtain the OAM beams with a small divergence angle. The circular arrangement and phase gradient were used to simplify the structure of the metasurface and obtain the small divergence angle, respectively. The proposed metasurface antenna presents a high transmission coefficient and effectively decreases the divergence angle of the OAM beam. All the theoretical analyses and derivation calculations were validated by both simulations and experiments. This compact structure paves the way to generate OAM beams with a small divergence angle.

scholarly journals Measuring the Topological Charge of Orbital Angular Momentum Beams by Utilizing Weak Measurement Principle

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jing Zhu ◽  
Pei Zhang ◽  
Qichang Li ◽  
Feiran Wang ◽  
Chenhui Wang ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Weak Measurement ◽  
Measurement Principle

scholarly journals Effects of the Coupling between the Orbital Angular Momentum and the Temporal Degrees of Freedom in the Most Intense Ring of Ultrafast Vortices

2020 ◽  
Vol 10 (6) ◽  
pp. 1957 ◽  
Author(s):  
Miguel A. Porras
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Pulse Energy ◽  
Topological Charge ◽  
Degrees Of Freedom ◽  
Maximum Energy ◽  
Laser Source ◽  
Source Spectrum ◽  
Vortex Center ◽  
Peak Intensity

It has recently been shown that the temporal and the orbital angular momentum (OAM) degrees of freedom in ultrafast (few-cycle) vortices are coupled. This coupling manifests itself with different effects in different parts of the vortex, as has been shown for the ring surrounding the vortex where the pulse energy is maximum, and also in the immediate vicinity of the vortex center. However, in many applications, the ring of maximum energy is not of primary interest, but the one where the peak intensity of the pulse is maximum, which is particularly true in nonlinear optics applications such as experiments with ultrafast vortices that excite high harmonics and attosecond pulses that also carry OAM. In this paper, the effects of the OAM-temporal coupling on the ring of maximum pulse peak intensity, which do not always coincide with the ring of maximum pulse energy, are described. We find that there is an upper limit to the magnitude of the topological charge that an ultrafast vortex with a prescribed pulse shape in its most intense ring can carry, and vice versa, a lower limit to the pulse duration in the most intense ring for a given magnitude of the topological charge. These limits imply that, with a given laser source spectrum, the duration of the synthesized ultrafast vortex increases with the magnitude of the topological charge. Explicit analytical expressions are given for the ultrafast vortices that contain these OAM-temporal couplings effects, which may be of interest in various applications, in particular in the study of their propagation and interaction with matter.

Topological charge transfer in frequency doubling of fractional orbital angular momentum state

2016 ◽  
Vol 109 (15) ◽  
pp. 151103 ◽  
Author(s):  
R. Ni ◽  
Y. F. Niu ◽  
L. Du ◽  
X. P. Hu ◽  
Y. Zhang ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Charge Transfer ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Frequency Doubling ◽  
Momentum State ◽  
Angular Momentum State

Detecting the topological charge of a vortex beam by an arc slit diffraction

2017 ◽  
Vol 31 (23) ◽  
pp. 1750172 ◽  
Author(s):  
Dongzhi Fu ◽  
Hailong Zhou ◽  
Kaiwei Wang ◽  
Pei Zhang ◽  
Jianji Dong ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Diffraction Pattern ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Light Spot ◽  
Far Field ◽  
Vortex Beam ◽  
Efficient Measurement ◽  
Vortex Beams

The simple and efficient measurement of the light orbital angular momentum (OAM) is essential to both the classical and quantum applications with vortex beams. Here, we study the diffraction pattern in the far field when a vortex beam passes through an arc slit and demonstrate experimentally that a light spot of the diffraction pattern has a displacement which is linear to the topological charge (TC) of the incident vortex beam. Based on this property, this method is capable of measuring both modulus and sign of TC of the vortex beam. Furthermore, this scheme allows identifying multiple OAM states simultaneously.

scholarly journals Second-harmonic generation and the conservation of spatiotemporal orbital angular momentum of light

2020 ◽  
Author(s):  
Guan Gui ◽  
Nathan Brooks ◽  
Henry Kapteyn ◽  
Margaret Murnane ◽  
Chen-Ting Liao
Keyword(s):  
Angular Momentum ◽  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Second Harmonic ◽  
Space Time ◽  
Generation Process ◽  
Space And Time ◽  
Phase Singularities

Abstract Light with spatiotemporal orbital angular momentum (ST-OAM) is a recently discovered type of structured electromagnetic field with characteristic space-time spiral phase structure and transverse OAM. In this work, we present the first generation and characterization of the second-harmonic of ST-OAM pulses. By uncovering the conservation of transverse OAM in a second-harmonic generation process, where the space-time topological charge of the fundamental field is doubled along with the optical frequency, we establish a general nonlinear scaling rule— analogous to that describing the spatial topological charges associated with the conventional longitudinal OAM of light. Furthermore, we observe that the topology of a second-harmonic ST-OAM pulse can be modified by complex spatiotemporal astigmatism, giving rise to multiple phase singularities separated in space and time. Our finding thus confirms that a spatiotemporal phase winding, surrounding one or many phase singularities in space and time, can be interpreted as a new class of topological charge. Our study opens a new route for nonlinear conversion and scaling of light carrying ST-OAM with the potential for driving other secondary ST-OAM sources of electromagnetic fields, electron pulses, and beyond.

Sign in / Sign up

Export Citation Format

Share Document