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Metasurfaces utilize engineered nanostructures to achieve control on all possible dimensions of light, encouraging versatile applications, including beam steering, multifunctional lensing, and multiplexed holograms. Towards the quantum optical regime for metasurfaces, although significant efforts have been put into generating and analyzing specific quantum states, control schemes to further manipulate these quantum states or information are still limited. Here, based on a metasurface, we propose and experimentally demonstrate a continuous heralding scheme to remotely control a vortex beam with high robustness to noise using polarization-entangled photon pairs. Our metasurface entangles polarization and orbital angular momentum (OAM) and the polarization selection on heralding photon erases the which-OAM information on signal photon. It induces an interference of two different OAM states remotely, manifesting a continuous orbital rotation. Our results show that metasurfaces have potential applications in quantum communication and information processing in entangling information with increasing complexity in the content. Heralded detection is widely used in quantum information processing, as it allows real-time tuning the properties of a heralded photon by acting on the heralding photon. With polarization-entangled photon pairs, the authors use a geometric phase metasurface to achieve a remote and continuous control of the vortex states of the heralded photon. [ABSTRACT FROM AUTHOR]

Novel classical wave phenomenon analogs of the quantum spin Hall effect are mostly based on the construction of pseudo-spins. Here we show that the non-trivial topology of a system can also be realized using orbital angular momentum through a coupling between the angular momentum and the wave vector. The idea is illustrated with a tight-binding model and experimentally demonstrated with a transmission line network. We show experimentally that even a very small network cluster exhibits angular momentum-dependent one-way topological edge states, and their properties can be described in terms of local Chern numbers. Our work provides a new mechanism to realize counterparts of the quantum spin Hall effect in classical waves and may offer insights for other systems. Here, the authors show that a system can exhibit angular momentum-dependent topological properties through angular-momentum-orbital coupling and provide a proof-of-principle experimental demonstration using a transmission line network. [ABSTRACT FROM AUTHOR]

We report plasmonic enhanced random lasing from dye-doped polymer with dispersed Au nanoparticles (DP@Au NPs). The Au nanoparticles, fabricated by simple and convenient sputtering and thermal annealing processes, are employed as scatterers in a DCJTB-doped PMMA film. Random-arranged and nearly spherical nano-Au particles are fabricated by optimizing the sputtering time and annealing temperature. Multiple scattering coming from particles plays a fundamental role in random lasing emissions. We demonstrate low-threshold random lasing and also the polarization dependence by observing emission as a function of pump beam power and detection polarization in DP@Au NP system. Our findings provide an effective approach for random lasing and could pave a way for the fabrication of efficient random lasing devices. [ABSTRACT FROM AUTHOR]

Space−time modulated metamaterials support extraordinary rich applications, such as parametric amplification, frequency conversion, and non-reciprocal transmission. The non-Hermitian space−time varying systems combining non-Hermiticity and space−time varying capability, have been proposed to realize wave control like unidirectional amplification, while its experimental realization still remains a challenge. Here, based on metamaterials with software-defined impulse responses, we experimentally demonstrate non-Hermitian space−time varying metamaterials in which the material gain and loss can be dynamically controlled and balanced in the time domain instead of spatial domain, allowing us to suppress scattering at the incident frequency and to increase the efficiency of frequency conversion at the same time. An additional modulation phase delay between different meta-atoms results in unidirectional amplification in frequency conversion. The realization of non-Hermitian space−time varying metamaterials will offer further opportunities in studying non-Hermitian topological physics in dynamic and nonreciprocal systems. Exquisite control of loss and gain in non-Hermitian systems allows waves to propagate in unusual and useful ways. Here, unidirectional amplification is achieved in an acoustic metamaterial by dynamically varying the gain and loss with modulation phase delay between different metaatoms. [ABSTRACT FROM AUTHOR]

Abstract: We report a simple and cost effective method to fabricate regular metallic particle arrays over large areas with good regularity by using holographic lithography interference for the study of localized surface plasmon. Samples of disk-shaped gold nano-particles arranged in square arrays with lattice spacing ranging from 300nm to 600nm were successfully fabricated on glass substrates first by sputtering a thin gold layer onto two-dimensional photoresist templates of hole arrays in square lattice obtained by the holographic method and then removing the photoresist by a lift-off procedure. The plasmonic resonance of the gold nano-particle arrays due to the change of morphology by thermal annealing was studied. The disk-shaped gold nano-particles were found to become more round shaped upon heating and blue shift of the extinction plasmonic band was observed. The results were explained with model calculations using spheroidal particles. [Copyright &y& Elsevier]

Gallium arsenide (GaAs) semiconductor wires have emerged as potent candidates for nonlinear optical devices, necessitating bandgap engineering for an expanded operational wavelength range. We report the successful growth of strain-mediated GaAs microwires (MWs) with an average diameter of 1.1 μm. The axial tensile strain in these wires, as measured by X-ray diffraction and Raman scattering, ranges from 1.61 % to 1.95 % and from 1.44 % to 2.03 %, respectively. This strain condition significantly reduces the bandgap of GaAs MWs compared to bulk GaAs, enabling a response wavelength extension up to 1.1 μm. Open aperture Z-scan measurements reveal a nonlinear absorption coefficient of -15.9 cm/MW and a third-order magnetic susceptibility of -2.8 × 10 -8  esu at 800 nm for these MWs. I-scan measurements further show that the GaAs saturable absorber has a modulation depth of 7.9 % and a nonsaturation loss of 3.3 % at 1050 nm. In laser applications, GaAs MWs have been effectively used as saturable absorbers for achieving Q-switched and dual-wavelength synchronous mode-locking operations in Yb-bulk lasers. These results not only offer new insights into the use of large diameter semiconductor wires but also expand the potential for applications requiring bandgap tuning., Competing Interests: Conflict of interest: Authors state no conflicts of interest., (© 2024 the author(s), published by De Gruyter, Berlin/Boston.)

Metasurfaces have recently opened up applications in the quantum regime, including quantum tomography and the generation of quantum entangled states. With their capability to store a vast amount of information by utilizing the various geometric degrees of freedom of nanostructures, metasurfaces are expected to be useful for processing quantum information. Here, we propose and experimentally demonstrate a programmable metasurface capable of performing quantum algorithms using both classical and quantum light with single photons. Our approach encodes multiple programmable quantum algorithms and operations, such as Grover's search algorithm and the quantum Fourier transform, onto the same metalens array on a metasurface. A spatial light modulator selectively excites different sets of metalenses to carry out the quantum algorithms, while the interference patterns captured by a single-photon camera are used to extract information about the output state at the selected output directions. Our programmable quantum metasurface approach holds promising potential as a cost-effective means of miniaturizing components for quantum computing and information processing., Competing Interests: Conflict of interest: Authors state no conflicts of interest., (© 2024 the author(s), published by De Gruyter, Berlin/Boston.)

Photothermal phenomenon is one of the natural responses in light-matter interactions in which the energy of the incident light is converted into heat, resulting in a temperature increase in the illuminated material. This effect has a direct influence on the refractive index of the material such that its change of spectral dependency with temperature can be exploited for different applications. However, it is also important to separate/identify the thermal effect from the optical/electronic resonance effect to expand potential applications of light-matter interactions. In this work, we demonstrate the use of a white-light interferometry approach combined with a windowed Fourier transform method and a consistency-checking peak-fitting method to obtain the refractive index of an Rh6G-ethanol dye solution with a sensitivity of about ∼10 -6 (RIU) for the visible range. Moreover, we also perform both static and dynamic measurements to study the photothermal effect of the Rh6G solution under external excitation. Importantly, we separate the optical and thermal effects due to the external excitation and obtain very good agreement with the experimental results by modeling the relative refractive index of the Rh6G solution with an expression consisting of spectrally a Fano-like resonance term and a linear dependent thermal term. We find that the response due to the optical effect is about ∼0.2 × 10 -3 of that due to the thermal effect in the low-light regime. Our approach to separating the optical and thermal effects could shed light on other fields for potential applications through precision measurements of the transmission phase or refractive index.

Two-photon interference is an important effect that is tightly related to the quantum nature of light. Recently, it has been shown that the photon bunching from the Hong-Ou-Mandel (HOM) effect can be used for quantum imaging in which sample properties (reflection/transmission amplitude, phase delay, or polarization) can be characterized at the pixel-by-pixel level. In this work, we perform Jones matrix imaging for an unknown object based on two-photon interference. By using a reference metasurface with panels of known polarization responses in pairwise coincidence measurements, the object's polarization responses at each pixel can be retrieved from the dependence of the coincidence visibility as a function of the reference polarization. The post-selection of coincidence images with specific reference polarization in our approach eliminates the need in switching the incident polarization and thus parallelized optical measurements for Jones matrix characterization. The parallelization in preparing input states, prevalent in any quantum algorithms, is an advantage of adopting two-photon interference in Jones matrix imaging. We believe our work points to the usage of metasurfaces in biological and medical imaging in the quantum optical regime., (© 2022 the author(s), published by De Gruyter, Berlin/Boston.)

Metasurfaces provide a promising route for structuring light and generating holograms with designed amplitude, phase, and polarization profiles, leading to a versatile platform for integrating and constructing optical components beyond the conventional ones. At the same time, incorporating coincidence in imaging allows a high signal-to-noise ratio for imaging in very low light levels. As beneficial from the recent development in both metasurfaces and single-photon avalanche diode (SPAD) cameras, we combine the polarization-sensitive capability of metasurfaces with Hong-Ou-Mandel (HOM)-type interference in generating images with tailor-made two-photon interference and polarization coincidence signatures. By using orthogonal linear-polarized photons as incidence, correlated, anticorrelated, and uncorrelated polarization coincidence features can be observed within the same image from the pairwise second-order coherence statistics across different pixels of the image. Our work adds polarization to the demonstrated amplitude and phase sensitivity in the domain of "HOM microscopy" and can be useful for biological and security applications., Competing Interests: The authors declare no competing interests., (© 2022 The Authors.)

Metasurfaces with ultrathin artificial structures have attracted much attention because of their unprecedented capability in light manipulations. The recent development of metasurfaces with controllable responses opens up new opportunities in various applications. Moreover, metasurfaces composed of twisted chiral structures can generate asymmetric responses for opposite incidence, leading to more degrees of freedom in wave detections and controls. However, most past studies had focused on the amplitude responses, not to mention using bi-directional phase responses, in the characterization and light manipulation of chiral metasurfaces. Here, we report a birefringent interference approach to achieve a controllable asymmetric bi-directional transmission phase from planar chiral metasurface by tuning the orientation of the metasurface with respect to the optical axis of an add-on birefringent substrate. To demonstrate our approach, we fabricate planar Au sawtooth nanoarray metasurface and measure the asymmetric transmission phase of the metasurface placed on a birefringent sapphire crystal slab. The Au sawtooth metasurface-sapphire system exhibits large oscillatory behavior for the asymmetric transmission phase with the tuning parameter. We confirm our experimental results by Jones matrix calculations using data obtained from full-wave simulations for the metasurface. Our approach in the characterization and light manipulation of metasurfaces with controllable responses is simple and nondestructive, enabling new functionalities and potential applications in optical communication, imaging, and remote sensing., (© 2021 Ranran Zhang et al., published by De Gruyter, Berlin/Boston.)

Qubit operation belonging to unitary transformation is the fundamental operation to realize quantum computing and information processing. Here, we show that the complex and flexible light-matter interaction between dielectric metasurfaces and incident light can be used to perform arbitrary U(2) operations. By incorporating both coherent spatial-mode operation together with two polarizations on a single metasurface, we further extend the discussion to single-photon two-qubit U(4) operations. We believe the efficient usage of metasurfaces as a potential compact platform can simplify optical qubit operation from bulky systems into conceptually subwavelength elements.

Laser propulsion of a graphene sponge shows tremendous potential in propellant-free flight, photoresponsive actuators and micro opto-electro mechanical systems. However, the mechanism is still in dispute and the propulsion force hasn't been accurately measured, seriously hindering its development. This work develops a quantitative method to measure the propulsion force. It is found that the characteristics of the force agree qualitatively with the Knudsen force due to laser-induced thermal nonequilibrium in rarefied gas, which might be another possible mechanism of laser propulsion of a graphene sponge. Also, this kind of laser propulsion is highly efficient, stable and sustainable.

Circular phase-dichroism (CPD) has been suggested for the characterization of chiral metasurfaces in supplementing the conventional circular dichroism (CD). Conventional CD probes the bulk properties while the CPD, reported recently in 2D chiral metasurfaces using an air-gap Fabry-Perot setup, is based on the surface properties. Here we propose and demonstrate a robust birefringent interference approach to obtain the CPD by replacing the air-gap with a uniaxial birefringent material in which interference is realized by the difference in the refractive indexes for the ordinary and extraordinary components of the material. We measure the transmission phases of metasurfaces fabricated on birefringent sapphire substrates and obtain clear CPDs for chiral metasurfaces but vanishing for achiral metasurfaces. Importantly, our approach can be applied to metasurfaces fabricated on nonbirefringent substrates by add-on birefringent materials. We confirm our results by a Jones matrix method using data obtained from full-wave simulations, and good agreements with experiments are obtained.

An exceptional point occurring in a tailor-made lossy optical system has been recently found to alter optical properties in counter-intuitive ways. In the context of tunable plasmonic devices, exceptional points can be useful as a driving mechanism to enhance tunability. Here, we experimentally demonstrate how a plasmonic exceptional point can be incorporated in metasurface Q-plates to have the generated vortex beam tuned through a change of structural parameter. We have observed an orbital rotation in the far-field by 45 degrees in crossing the exceptional point. We expect a new generation of tunable plasmonic devices in polarization control, beam structuring and holograms, which can take advantage of the huge sensitivity from exceptional points.

Photonic crystals (PCs) are usually fabricated on bulk substrates which break the symmetry of the PC system for incidence from either side of the PCs. Here we report the fabrication of a free-standing 1D layered dielectric PC by using a two-beam holographic interference method. The free-standing PC exhibits distinct photonic bandgaps as well as Fabry-Perot oscillations in the photonic bands. Furthermore, we show that the PC can be modeled by an effective medium approach and obtain the reflection phase for the photonic bands of the PC. We have also performed full-wave simulations for the PC and obtained very good agreement with the experiment. The free-standing PC enables a better comparison between experiment and simulation, and importantly, it is flexible enabling new applications for PCs.

Surface plasmon resonance (SPR) has found wide applications in sensing down to molecular level due to its extreme sensitivity to change of dielectric properties. An unavoidable effect in SPR is surface deformation (thermal bump) due to local heating by incident laser light used in SPR. In addition, changes in the reflection phase from the metal film used in SPR could also contribute to the SPR signal, and thus proper handling of the SPR signal is very important in order to broaden the potential applications of SPR. Here we report a simple Fabry Perot (FP) interference technique for measuring, simultaneously, the thermal bump height as well as the reflection phase shift of gold film used in SPR. We find that the shift of the FP signal is dominated by the effect of the thermal bump while it is small for the effect of the reflection phase shift due to change of dielectric property of the metal. To support our experimental results, we have also performed model simulation for the SPR system and obtain good agreement with the experiment. As both amplitude and phase can be measured, our method could lead to better characterization of SPR and can also be applied to the study of active metasurfaces under external excitation.

Micro-nano photonic structures are developing vigorously based on the progress of photonics, semiconductor physics and microfabrication technology. A series of results are achieved in structure characterization, theory, and fabrication of them. Most high quality photonic structures are man-made ones; however, there are still some challenges in fabricating artificial large-area and high-quality photon materials. With the advantages of photonic structure processing technology, holographic lithography, a low-cost, time-saving and high-efficiency microfabrication method, performs superior application potentials in making metamaterials as well as photonic crystal templates. In this article, we introduced the principles of holographic lithography and described the applications in fabricating various micro-nano photonic structures, such as three dimensional face-center-cubic, wood-pile, diamond-like photonic crystals, as well as quasi-crystalline structure, chiral metamaterials and periodic defect-mode structures. Moreover, the applications of some structures in solar cell and optical fiber sensing are discussed. The success of fabricating micro-nano photonic structures by holographic lithography would pave the way for more applications of these structures in wide fields.

We report measurements of the static shear modulus of electrorheological (ER) fluids consisting of water-wetted silica microspheres in silicone oil. A shear-annealing method, using creep-recovery (CR) cycles under an external electric field, is used to enhance ER properties of the fluid. The shear-annealing method enables the silica spheres in the ER fluid to form better aligned and denser column microstructures. A stable state with elastic shear deformation is obtained after a sufficient number of CR cycles, with an optimal combination of stress duration and shear strength. Static shear modulus is obtained by measuring the elastic deformations at different shear stresses for an electric field frequency from 10 to 1000 Hz. A water-bridge model is proposed to explain the enhanced shear modulus.