Multiple non-covalent-interaction-directed supramolecular double helices: the orthogonality of hydrogen, halogen and chalcogen bonding.

In this study, a benzoselenadiazole- and pyridine-bifunctionalized hydrogen-bonded arylamide foldamer was synthesized. A co-crystallization experiment with 1,4-diiodotetrafluorobenzene showed that a new type of supramolecular double helices, which were induced by three orthogonal interactions, namely, three-center hydrogen bonding (O⋯H⋯O), I⋯N halogen bonding and Se⋯N chalcogen bonding, have been constructed in the solid state. This work presents a novel instance of multiple non-covalent interactions that work together to construct supramolecular architectures.

Experimental demonstration of free-space multi-state orbital angular momentum shift keying.

Orbital angular momentum (OAM), a new dimension of photons, has potentials in lots of domains as high-dimensional data coding/decoding. Here we experimentally demonstrate a free-space data transmission system based on 8 bits multi-state OAM shift keying, where multiplexed optical vortices containing 8 various OAM states are employed to constitute 8 bits binary symbols. In the transmitter, the data coding of OAM shift keying is realized by switching a series of special-designed holograms. And in the receiver, the decoding is done by a single Dammann vortex grating along with image processing. We experimentally transmit data, including a gray-scale image, in free-space for 10 meters, showing zero bit-error-rate. The demonstrated results indicate a wide prospect for the future high-dimensional large data rate optical security communications.

Demonstration of free-space one-to-many multicasting link from orbital angular momentum encoding.

Multicasting is necessary when distributing signals between multiple users. In this Letter, we demonstrate an orbital angular momentum (OAM) encoding-based free-space one-to-many multicasting link, where digital signals are encoded into a series of time-varying OAM states and transmitted from one transmitter to multiple receivers with various locations. Moreover, encoding N various signals simultaneously in one transmitter and sending them at the same time to N various receivers separately, is also demonstrated. As a proof-of-concept, four different gray images are coded by one transmitter simultaneously and multicast to four various receivers separately. The favorable decoding results returned by the four receivers show good multicasting performance.

Orbital angular momentum channel monitoring of coaxially multiplexed vortices by diffraction pattern analysis.

We theoretically and experimentally demonstrate a scheme to monitor the weight of a single orbital angular momentum (OAM) channel for coaxial multiplexed optical vortices with large mode spacing. A specially designed holographic grating is illuminated by the incident multiplexed vortices first. Then the weight of each single OAM channel is obtained after analyzing the captured diffraction patterns. This work will find applications in domains where multiplexed optical vortices are of interest, such as the OAM-based data-transmission system, and so on.

Generation of perfect polarization vortices using combined gratings in a single spatial light modulator.

Perfect polarization vortices (PPVs) are a type of vector beam with a diameter independent of the polarization order. In this paper, an experimental method is proposed to generate PPVs with an anisotropic polarization distribution. First, a specially designed hologram is generated on a liquid-crystal spatial light modulator (SLM) to obtain Bessel-Gaussian (BG) beams. Second, the BG beams are transformed into PPVs in the Bessel region by an interferometer, which includes a polarized beam splitter, two reflectors, and several lenses. In our experiment, PPVs with adjustable polarization orders and diameters are obtained by generating various combined holograms on the SLM.

Non-diffractive Bessel-Gauss beams for the detection of rotating object free of obstructions.

Bessel-Gauss beams carrying orbital angular momentum are widely known for their non-diffractive or self-reconstructing performance, and have been applied in lots of domains. Here we demonstrate that, by illuminating a rotating object with high-order Bessel-Gauss beams, a frequency shift proportional to the rotating speed and the topological charge is observed. Moreover, the frequency shift is still present once an obstacle exists in the path, in spite of the decreasing of received signals. Our work indicates the feasibility of detecting rotating objects free of obstructions, and has potential as obstruction-immune rotation sensors in engine monitoring, aerological sounding, and so on.

Simultaneous generation of multiple perfect polarization vortices with selective spatial states in various diffraction orders.

We demonstrate an approach to generate multiple perfect polarization vortices (PPVs) with selective spatial polarization distribution in various diffraction orders. The key is the design of a hologram with an anisotropic polarization diffraction grating. In the experiment, a setup consisting of two spatial light modulators is built. By encoding the specially designed holograms, PPVs with various states are obtained in different diffraction orders simultaneously, for instance, in radial and azimuthal polarized states. These PPVs may have applications in laser processing, optical tweezers, and so on.

Perfect optical vortex array with controllable diffraction order and topological charge: erratum.

A correction is given for the statement after Eq. (7) [J. Opt. Soc. Am. A33, 1836 (2016)JOAOD60740-323210.1364/JOSAA.33.001836].

Perfect optical vortex array with controllable diffraction order and topological charge.

We have demonstrated a holographic grating, the far-field diffraction pattern of which is a perfect optical vortex (POV) array. The diffraction order, as well as the topological charge of each spot in the array, is controllable. By setting different parameters when designing the hologram, the spot in different diffraction orders will be changed, resulting in the variance of the POV array. During the experiment, we uploaded holograms of different design on a phase-only spatial light modulator. We then observed POV arrays with different dimensions and topological charges using a CCD camera, which fit well with the simulation. This technique provides the possibility to generate multiple POVs simultaneously, and can be used in domains where multiple POVs are of high interest such as orbital angular momentum multiplexed fiber data transmission systems.

Rectilinear lattices of polarization vortices with various spatial polarization distributions.

In this paper, we propose a type of rectilinear lattices of polarization vortices, each spot in which has mutually independent, and controllable spatial polarization distributions. The lattices are generated by two holograms under special design. In the experiment, the holograms are encoded on two spatial light modulators, and the results fit very well with theory. Our scheme makes it possible to generate multiple polarization vortices with various polarization distributions simultaneously, for instance, radially and azimuthally polarized beams, and can be used in the domains as polarization-based data transmission system, optical manufacture, polarization detection and so on.

Generating perfect polarization vortices through encoding liquid-crystal display devices.

Perfect polarization vortices (PPVs) are a new kind of vector beams with identical diameters. In this paper, we propose an approach that uses encoded liquid-crystal display devices to generate PPVs and is based on the Fourier transformation of high-order Bessel-Gaussian (BG) beams. The liquid-crystal display device used here is a phase-only liquid-crystal spatial light modulator (SLM). In the experiment, a hologram consists of a holographic axicon, and a spiral phase plate is encoded on a SLM to generate high-order BG beams. Then, another SLM and a convex lens can realize the transformation from BG beams into PPVs. We analyze the diameter of the PPV obtained by our approach, and find it is impacted by the focal length of the lens as well as the period of the holographic axicon, but is little influenced by polarization order.

Pre-turbulence compensation of orbital angular momentum beams based on a probe and the Gerchberg-Saxton algorithm.

We propose a scheme that uses a probe Gaussian beam and the Gerchberg-Saxton (GS) algorithm to realize the pre-turbulence compensation of beams carrying orbital angular momentum (OAM). In the experiment, spatial light modulators are utilized to simulate the turbulent atmosphere and upload the retrieval holograms. A probe Gaussian beam is used to detect the turbulence. Then, the retrieval holograms, which can correct the phase distortion of the OAM beams, are obtained by the GS algorithm. The experimental results show that single or multiplexed OAM beams can be compensated well. The compensation performances under different iterations are also analyzed.

Measurement of orbital angular momentum spectra of multiplexing optical vortices.

Optical vortex beams carrying orbital angular momentum (OAM) are widely investigated for their unique performance in recent years. They can be used to extend the capacity of optical communications system due to the orthogonality of different channels. In the receiver side of a multiplexing optical vortices system, verifying the OAM spectrum is of great importance. A new kind of diffraction element called Dammann vortex grating can distribute energies among different diffraction orders equally. Based on this unique characteristic, we reported a new algorithm to analyze the spot of each diffraction order. The OAM spectrum in the receiver side can then be obtained. In the experiment, the OAM spectrum measurement of at most six-channel multiplexing optical vortices is realized. The experimental results illustrate that the OAM spectrum gained by this approach is highly consistent with the theoretical value.

Integrating 5 × 5 Dammann gratings to detect orbital angular momentum states of beams with the range of -24 to +24.

The 5×5 2D binary Dammann vortex grating can distribute energy among different diffraction orders equally and can realize measurement of orbital angular momentum (OAM) states from -12 to +12. Here we combine a 5×5 Dammann vortex grating and a spiral phase plate with the order +12 or -12, which makes the topological charge of beams in the array increase or decrease by 12; thus, the range of measuring OAM states can be extended to a range from -24 to +24. We upload the holograms of such gratings on a liquid crystal spatial light modulator to do the experiment. The experimental results fit well with the simulation results. This method is also effective for multiplexed OAM beams and can be used in optical communications in the future.