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Magnetic Skyrmions are topologically protected spin structures with sophisticated swirls of electron spins. In recent times, photonic counterparts of the magnetic Skyrmions have been discovered with new deep-subwavelength characteristics promising for future applications in optical information storage and transfer. While the photonic Skyrmions in real space have been observed in diverse photonic systems, studies on the photonic Skyrmions in momentum space have rarely been done. Here we show different forms of pseudospin Skyrmion around the Dirac point in momentum space of photonic crystals with the Kagome and honeycomb lattice. The pseudospin Skyrmions in momentum space are directly related to the topologically nontrivial states and manipulated by the inter-cell and intra-cell interactions between cylinders of the photonic crystal. The observation of the pseudospin Skyrmion in momentum space is expected to be valuable for manipulation of the flows and polarizations of light in topologically robust ways.

Chiral metasurfaces have recently undergone a dramatic development, due to their important applications in optics, chemistry and biology. However, the tunability and reconfigurability of the chiral metasurfaces remain challenges. Then, we proposed an S-shaped metamirror consisting of a MIM (Au-LiNbO3-Au) structure with a dual-band chiral absorption in the near-infrared range. The proposed structure has two resonant wavelengths with a giant chiro-optical effect. The giant chiro-optical effect originates from the different plasmonic resonances induced by the incident circularly polarized light (CPL) with opposite spin states. By tuning the voltage and thus tuning the refractive index of the lithium niobate (LiNbO3), chiral resonant wavelengths can be dynamically adjusted in a large range as desired. Furthermore, by tuning the refractive index of LiNbO3, we can move the short-wavelength resonance peak to the position of another long-wavelength resonance peak. Therefore, the chiral metamirror can be dynamically reconfigured at the position of the long-wavelength resonance peak. The work offers a further step in developing tunable and reconfigurable chirality for possible applications including reconfigurable chiral hologram, chiral-selective absorber and other chiral components in near-infrared region.

In many previous works, a single-pixel imaging (SPI) system has been constructed as an optical image encryption system. Unauthorized users are not able to reconstruct the plaintext image from the ciphertext intensity sequence without knowing the illumination pattern key. However, the cryptanalysis of encrypted SPI has been seldom investigated in the past. In this work, we propose a known-plaintext attack scheme and a ciphertext-only attack scheme for an encrypted SPI system for the first time. The known-plaintext attack is implemented by interchanging the roles of illumination patterns and object images in the SPI model. The ciphertext-only attack is implemented based on the statistical features of single-pixel intensity values under certain circumstances. The two schemes can crack encrypted SPI systems and successfully recover the key containing correct illumination patterns.

We propose a kind of perfect optical vortex beam (POV) generated via Fourier transformation of Bessel-Gauss (BG) beams through encoding of the amplitude of the optical field with binary amplitude digital micromirrors device. We call them concentric POVs which consist of several POVs and where every POV has the same center and independent characters, and we confirm the correct phase patterns of the concentric POVs with the method of Mach-Zehnder interference and self-interference. This special property could be considered as a potential of implement to increase the orbital angular momentum communication capacity vastly.

The cylindrical vector beams (CVBs) compose two circularly polarized vortex beams carrying orbital angular momentum (OAM) states with the opposite topological charge. We derived the probabilities for OAM of high-order CVB propagation through turbulent atmosphere. The calculated probabilities of OAM are based on the polarization insensitive element detection and phase perturbation coherence function assumption. The numerical calculation results show that the probabilities of OAM state spreading to neighbor states of CVBs through turbulent atmosphere increase with the propagation distance increase. Under the same conditions, the spreading of OAM for CVBs are weaker than Laguerre-Gaussian beam propagation through turbulent atmosphere. The results show that the OAM state of CVBs could improve the performance of optical communications systems in atmospheric turbulence.

Polarization converters that convert incident linearly polarized beams into arbitrary order cylindrical vector beams (CVBs) are derived with the Jones matrix theory. We reveal the existence of an inherent transform mechanism, which links the different order CVB converters. Based on this mechanism, CVB of any desired order can be achieved by the combination of the low-order CVB converters and half waveplates. The order of CVBs can be adjusted flexibly by changing the number of the first- and second-order vortex-waveplates, which are manufactured with the liquid crystal polarization modulation technique. This work facilitates the generation of arbitrary order CVBs, which may find valuable applications in optical trapping, optical communication, etc., as well.

We propose and demonstrate an optical router by selecting data encoded in massive orthogonal orbital angular momentum (OAM) states carried by collinear optical vortex (OV) beams. By switching the OV grating on a digital micromirror device, we achieve information exchange and multicasting in 49 OAM channels with 1.37 Tbit/s aggregated data capacity. The time-domain characterization of the OAM router shows a fast-switching time of 6.9 μs. Both the analytical derivations and experimental demonstrations show that the router has signal-to-noise ratios (SNRs) better than 10.1 dB for all tens of OAM channels. The OAM-based optical interconnect technique is a promising solution for networking multiple users with ultrahigh data capacity density in datacenters.

The spatial confinement of the tip-induced plasmon is a critical factor to determine the resolution of the tip-enhanced Raman spectroscopy (TERS) system. Despite the compressed optical field, only 1 nm is obtained by the self-interaction effect of molecule; however, the deeper physical laws underlying are still under discussion. In addition, due to the gap between the tip and the substrate is only a few nanometers (or less), the quantum effects should be taken into account. For simplicity, we treat the system of the plasmonic dimer with a molecule in the gap as a TERS-like system. In the framework of the newly developed quantum hydrodynamic model, we propose a model to study the light field enhancement and compression affected by the quantum effects in TERS-like system. The results show that the “hot spot” size depends on both the shape and the boundary location of the molecule in the dimer gap. The mechanism of such light field distribution will make us distinguish the boundary of the molecule more clearly. Therefore, our theoretical model offers a new insight into the confinement of the electromagnetic field in the TERS-like system, hence, the physical mechanism of the subnanometer spatial resolution in TERS system.

In lightwave communications, the high-power-efficiency coupling between a laser diode (LD) and a single-mode fiber (SMF) is indispensable. This paper proposes an imaginative two-microlens-array (MLA) coupling scheme whereby two revolved hyperboloid MLAs were used back-to-back between the LD and the SMF, and a coupling efficiency of 83.4% (-0.79 dB) has been achieved. The study also employs a cost-effective fabrication method, with a combination of the sample-inverted reflow technique and the soft lithography replication method, to fabricate revolved hyperboloid MLAs in inorganic-organic hybrid silica-zirconia sol-gel material. As a result, the fabricated MLAs have excellent smooth profiles and negligible discrepancies from the profiles of the ideal hyperboloid MLAs. [ABSTRACT FROM PUBLISHER]

A novel high-corrugation-rate self-processing SiO2--ZrO2 hybrid sol-gel material has been developed and employed in single-step fabrication of refractive microlens array (MLA). In the proposed process, the SiO2--ZrO2 hybrid sol-gel film was exposed to ultraviolet through a binary mask and directly patterned into an MLA, which could be used as an end product with no further development or etching steps. Measurements showed that the surface relief depth could reach 1.32 μm, equivalent to 17.1% of the sol-gel film thickness. As expected, the fabricated refractive MLA had excellent surface smoothness, structural and dimensional conformity. The discrepancy between the designed and actual focal length of the MLA was 5.3%. The self-processing, being a true single-step method, was shown to be a practical, cost-effective, and promising fabrication technique for microoptical elements. [ABSTRACT FROM PUBLISHER]