In this work, a dielectric grating/DBR heterostructure has been proposed to create a high-Q hybrid guided mode at nearinfrared (NIR) frequencies. It is found that this nontrivial guided mode can be excited in the dielectric grating/DBR structure, leading to a perfect light transmission with linewidth of about 0.1 nm and Q factor up to 1.3×10⁴. More intriguingly, we show that bound states in the continuum (BIC) can emerge by properly choosing parameters in this resonant regime. The resonant wavelength and Q-factor of this optical mode can be tuned by varying the geometrical parameters, which is polarization-independent under the vertical incident of light. The ultra-narrow linewidth and tunable resonant transmission offered by this simple all-dielectric structure opens new opportunities for developing optical filtering, sensing, and light emitting devices with high-performance.

A cylindrical microresonator based on standard silica optical fibers is a promising platform for nonlinear devices such as low-repetition rate frequency comb generators. Though, enlarged mode volumes lead to higher pump powers and third-order nonlinearity level together with the stricter requirements on low propagation losses in order to achieve effective four-wave nonlinear interactions. We consider sputter deposition of thin films with higher nonlinear refractive index made of silicon and silicon nitride layers to enhance the nonlinearity within the microcavity. We inspect the variations of the cylinder radius that arise during the deposition and determine the quality factors achievable.

We propose using a cylindrical microresonator as a highly dispersive compact delay line for the spectral measurements relying on the dispersive Fourier transformation method. The cylindrical geometry implies a large anomalous dispersion of group velocities for the whispering gallery modes propagating next to the surface of the cylinder. To prove the concept, we demonstrate the frequency-to-time mapping of an optical soliton dispersed by the microcavity made of standard telecom fiber SMF-28.

This research delves into the influence of structural parameters on the performance of bilayer gratings, a critical factor in photonic applications. Employing the finite-difference time-domain (FDTD) method, we scrutinized the impact of duty cycle, period, and thickness on key metrics such as diffraction efficiency and diffraction angle. Our findings indicated that thickness and duty cycle of gratings played crucial roles in optimizing diffraction efficiency while larger gratings’ period decreases diffraction angle. We further simulated a misaligned bilayer gratings and demonstrated diffraction-based overlay measurement, tuning thickness and duty cycle to observe their influence on overlay measurement precision.

Unlike conventional topological edge states confined at a domain wall between two topologically distinct media, the recently proposed large-area topological waveguide states in three-layer heterostructures, which consist of a domain featuring Dirac points sandwiched between two domains of different topologies, have introduced the mode width degree of freedom for more flexible manipulation of electromagnetic waves. Up to now, the experimental realizations of photonic large-area topological waveguide states are exclusively based on quantum Hall and quantum valley-Hall systems. In this work, we propose a new way to create large-area topological waveguide states based on photonic quantum spin-Hall system and observe their unique feature of pseudospin-momentum locking unidirectional propagation for the first time in experiments. Moreover, due to the new effect provided by the mode width degree of freedom, the propagation of these large-area quantum-spin-Hall waveguide states exhibits unusual strong robustness against defects, e.g., large voids with size reaching several unit cells, which has not been reported previously. Our work not only completes the last member of such states in the photonic quantum Hall, quantum valley-Hall and quantum spin-Hall family, but also provides further opportunities for high-capacity energy transport with tunable mode width and exceptional robustness in integrated photonic devices and on-chip communications.

In this paper, the transmission properties of the double-walled carbon nanotube (DWCNT) films in terahertz spectrum are simulated and analyzed using the finite element method. Carbon nanotubes (CNTs) have excellent electromagnetic properties, oxidation resistance and flexibility, so it has become a material that has attracted much attention to replacing metal wire grids. The transmission of the transverse magnetic (TM) gives the power transmission of the polarizer for the component parallel to the grating vector and the transmission of the transverse electric (TE) for the perpendicular component. Our simulation results show that the transmission of the TM mode and the TE mode could be modulated by adjusting the diameter and spacing of the DWCNTs. In the range of 0.3-2.5THz, the transmission of the TM can be modulated from 90.7% to 99.3%, and TE can be modulated from 0.3% to 23%, which offers an alternative way of designing a polarizer with the desired degree of polarization. The simulation results provide numerical results in wide-band THz wave modulation with DWCNTs.

Metasurfaces are opening up promising flexibilities to reshape the wavefront of electromagnetic waves, and a notable optical phenomenon is observed with the tailored surface plasmon. However, meta-devices with metallic material face challenges of low transmission efficiency, especially in the visible spectrum. In this work, a multilayer metamaterial strategy is proposed to improve the transmission. By adding dielectric material as space layer is inserted along the propagation direction, vertical cavities are formed to modulate the transmission and reflection. The multilayer structure is numerically studied to discuss the transmission efficiency. A maximum transmission efficiency of 90% is achieved by adding a spin on glass material to the silver layer at the visible spectrum. The transmission efficiency with and without space layer is discussed as a control. Significantly, the surface plasma and the phase could still be modulated by adjusting the geometrical parameters of the multilayer metamaterial for diversified functionalities.

Metasurfaces refers to an artificial sheet material with sub-wavelength periodicity, and had sparked a general interest in their capability to manipulate electromagnetic (EM) fields at high flexibility. One of metasurfaces’ function is performing generalized refraction and reflection, granting it ability similar to of 3D optical instruments such as prism and lens, but executable at a nanoscale level. Using Finite-Difference Time-Domain (FDTD) algorithm, we had designed a metasurface with its unit cell consisting of four TiO₂ rods of same height and different radius to collimate incoming plane wave with 30° incident angle. The refracted wave propagated in direction normal to the metasurface with transmission power of 86% with respect to source.

Particles trapped in optical beams can undergo orbital rotations at the micro/nano-scale and thus find applications in constructing micro-motors/machines, advancing the investigation of micro-rheology, etc. Rather than using the doughnut beams, here we report the orbital rotation of particles in a single Gaussian beam at the wavelength scale. By involving the transverse scattering forces of the light beam in the off-focal plane, the off-axis trapping of nanoparticles is possible and a rotation orbit has been built with small radius even less than the wavelength. Through focusing the incident Gaussian beam with circular polarization, there is the orbital angular momentum converted from the spin angular momentum, and the orbital angular momentum can then drive the particles to undergo orbital rotation. By changing the position of the offfocus plane, the rotation radius and speed can be tuned. The orbital rotation scheme with simple and flexible setup here can find applications in micro-motors and micro-machines.

In this study, we experimentally demonstrate the enhancement of valley contrast through exciton-to-trion conversion at room temperature. Cetyltrimethylammonium bromide (CTAB), a well-known organic molecule commonly used in the intercalation of 2D materials, is shown to facilitate electron transfer to a tungsten disulfide (WS₂) monolayer through chemical doping. Specifically, a 1 mM CTAB solution is drop-casted onto the WS₂ monolayer, inducing the conversion from exciton to trion emission within the material. The introduction of a trion-abundant environment in WS₂ results in a notable increase in valley contrast without the application of external bias. To the best of our knowledge, this study represents the first demonstration of valley contrast enhancement through the chemical doping of CTAB. Consequently, this research provides a detailed exploration of liquid-controlled electron doping from the perspective of valleytronics.

The scattering of polarized plane waves on a rotating spherical particle, especially the far-field characteristics, is studied based on the “instantaneous rest-frame” hypothesis and Minkowski’s theory. The influence of the rotating angular velocity on the scattering is emphasized and is expressed as the dimensionless parameter y. The effects of incident light polarization states and particle size parameter ka are investigated on this basis. Besides, the loss of particles is also introduced. Besides, the influence of material on the scattering characteristic of rotating particles is also a concern, and the particle loss is introduced. Related results have promising applications in the material property research and target detection fields. Furthermore, they can also be extended to planetary research and detection, which plays a vital role in exploring the mysteries of the universe.

Water droplets are a highly abundant phase-change material to realize tunable optical lenses. We demonstrated for the first time that freezing mesoscale water droplets could be used as a tunable optical lens, such that freezing becomes an asset despite the low absolute values of the refractive indices of the shell and core materials and their optical contrast. It is shown that the dielectric shell of mesoscale water droplets in solid ice allows controlling both the maximum field intensity and the focus position of the formed photonic nanojet. The ice formation with air bubbles during the freezing of a water droplet is appropriate for a dynamic increase in the range of change of the focal position compared to solid ice. The proposed concept of a tunable spherical lens based on a freezing water drop can be used for microscopy and optical trapping in "green" mesotronics.

Due to the unique optical control ability and nanoscale structural characteristics of metasurfaces, they can achieve precise control and customized design of light, showing obvious advantages in many practical applications. However, since the structural design and electromagnetic simulation of most metasurfaces need to be manually adjusted step by step and are highly dependent on experience, once the optimization target changes, the unit structure needs to be re-optimized, resulting in excessive design costs and time. In this paper, a shape topology optimization method based on adjointness is used to reverse design the shape of the metasurface structure, and a free shape continuous metasurface with a deflection angle of the 30 degree is proposed. Compared with the discrete metasurface used in traditional design methods, the free shape continuous metasurface optimized by topology has higher light transmittance. The free shape metasurface lens designed in this paper has the advantages of high transmission efficiency, fast design speed, and has potential application prospects in optical communications, micro-nano light field control and other fields.

Dielectric laser accelerators (DLAs) can achieve acceleration gradients that are 1 to 2 orders of magnitude higher than traditional radiofrequency (RF) accelerators. Due to the micrometer-scale dimensions of the DLA acceleration structure, on the one hand, high requirements are imposed on the quality of the electron beam and the alignment among the electron beam, driving laser, and DLA in experiments. On the other hand, although the DLA acceleration gradient is very high, the acceleration distance is insufficient, resulting in relatively small absolute energy gain for sub-relativistic electrons after DLA acceleration. These electrons are susceptible to interference from stray electromagnetic fields during propagation, posing significant challenges to the resolution and accuracy of sub-relativistic electron energy spectrum testing. Based on the principle of laser-driven grating-structure DLA for accelerating electron beams, this paper designs a complete test system, constructs electronic dynamics simulation models and magnetic field measurement electron energy spectrum simulation models for verification, designs a double-layer magnetic shunt to shield the interference of leakage magnetic fields on electrons in the simulation, considers factors such as the beam spot radius, divergence angle, and geomagnetic field intensity of the electron beam that conform to experimental conditions, and finally obtains simulated images of electron spots on the fluorescent screen after the electron beam is deflected by the magnetic field. The electron dynamics simulation results show that the electron beam achieves a maximum energy gain of 14.4401 keV over an acceleration length of 36 μm, with an acceleration gradient reaching 401.114 MeV/m. Based on the acceleration effect, a magnetic field of 𝐵𝐵 = 170 Gs is set, and an electron spot after deflection is obtained. The edges of the spots before and after acceleration are separated by Δ𝑑 = 4.2889 mm, and the maximum energy gain measurement error is ε_ΔΕ' = 4.45%, realizing precise measurement of the energy gain of sub-relativistic electrons.

Reconfigurable, programmable and compact devices hold immense importance in high-density programmable photonic-integrated circuits (PICs) used in optical communications and signal processing. Compared with traditional methods of designing devices, the inverse design approach provides a new avenue for achieving high-density PICs. However, the majority of programmable photonic systems result in large footprints and high energy consumption due to the relatively weak modulation capability. This severely limits high-density integration of on-chip photonic systems. In recent years, chalcogenide phase-change materials (PCMs) have emerged as a promising alternative for achieving reconfigurable photonic devices by utilizing their high refractive index contrast and reversible phase transition between amorphous and crystalline states. In this work, we demonstrate a 1 × 2 multifunctional and compact photonic device based on phase-change material Sb2Se3 with footprints of only 4.8 × 4.8 μm2. We adopt the adjoint optimization approach to design the Sb₂Se₃ film on the silicon 3dB power splitter designed in advance. Subsequently, we can use laser heating technique to change the phase patterns on the Sb₂Se₃ film to achieve the designed device function. This enables the device to be reconfigurable from an optical switch to an arbitrary ratio power splitter. Remarkably, the functionality of our photonic device is rewritable, allowing for the erasure and reconfiguration of the Sb₂Se₃phase pattern. The demonstrated programmable phase-change photonic devices will significantly enhance the flexibility of photonic devices and promote the development of high-density programmable PICs.

Orbital angular momentum (OAM) beams are special beams with helical phase distribution. The conventional methods for generating OAM beams primarily rely on devices such as spiral phase plates, cascaded lens, and spatial light modulators. However, these methods incur high costs and face challenges in meeting the demands for optical system miniaturization and integration. The appearance of metasurface provides a new platform for the generation of integrated OAM beams. In order to achieve low crosstalk multi-channel OAM multiplexing on a single-layer metasurface, this work researches the phase and amplitude characteristics of co-polarization and cross-polarization in the transmission phase generation process. In addition, under the normal irradiation of circularly polarized light, three OAM beams carrying different topological charges are successfully generated by adjusting the structural parameters and rotation angles of the unit. The proposed terahertz metasurface demonstrates the ability to control complex wavefronts and offers a new avenue for developing multi-channel terahertz metasurfaces.

In this work, transverse optical vortices with phase singularities and orbital angular momentum are generated by the interference of three linearly polarized lights. The positions of the transverse optical vortices can be regulated by the relative amplitude and initial phase of the three incident lights. An analytical model is built for control the positions of the generated vortices and its correctness is proved by FDTD simulation, and a method for judging the positive or negative topological charge of the transverse vortices is derived. Based on the Poynting vector distribution of the transverse vortex field, it is found that there is an inverse energy flow near the phase singularity, that is, Poynting vector points to the light source rather than the propagation direction. It is further found that the controllable singularities and the backward energy flow region of the vortex field are very sensitive to the scattering of nanoparticles. When a single metal nanoparticle is placed in the region, several singularity lines with specific directions can be found in the scattering field. By changing the relative position of the single metal nanoparticle to the singularity in nanoscale, the directions of the singularity lines can be modulated. This work realizes the generation and manipulation of transverse optical vortices, and reveals the interaction between the transverse phase singularity and the scattering of metal nanoparticles, which is expected to be applied to nanoscale displacement sensing for nanoparticles.

Bismuth has attracted much attention because of its broadband near-infrared luminescence and it has also exhibited great potentials in optical communication and system laser technology. Bismuth element exhibits excellent properties in Bismuth element exhibits excellent properties in porous glass based on phase separation technology glass based on phase separation technology. In this paper, we investigate the dependence of Bismuth Active Center (BAC) on Na element in nanoporous glass. Based on phase separation technology, we prepared Bi doped nanoporous glass with different acid leaching times. An increase in the number of acid leaching cycles can reduce the content of Na elements in the glass by 96 wt%, effectively enhancing the luminescence intensity of BAC-Si and BAC-Ge, and causing their peak to blue-shift. Na ions are more likely to capture the electrons of oxygen ions in the glass, thereby weakening the electron supply of oxygen ions to Bi ions. This article lays a solid foundation for the study of Bi-doped nanoporous glass.

In this work, a novel spiral Airy beam with ultra-long anti-diffraction propagation distance and spiral intensity distribution is generated and studied. Changing the vortex topology charges and circular Airy phase parameters can flexibly modulate the properties of the beam, such as beam size, spiral intensity shape, propagation direction, and anti-diffraction propagation distance. Such beam has the property of self-healing and can restore to the spiral pattern. An array of spiral Airy beams can also be generated, and the spiral patterns and propagation directions of each beam of the array can be manipulated. This beam can be utilized in various applications such as optical tweezers and laser processing for chiral structures.

It is challenging to construct nano-scaled meta-structures enabling efficient and versatile electro-optic modulations, especially those related to circular dichroism (CD), which is useful in detection of chiral molecules and optical manipulation. In this study, we have modeled chiral metasurfaces based on single-crystal LiNbO3 using finite element method. The numerical calculation and characterization indicate that a quasi-BIC(q-BIC) resonance with a high Q-factor optical signal of 9.3 × 10⁴ and a peak CD signal of 0.89 at 972.76 nm could be obtained by breaking the structural symmetry of the chiral metasurface. The pockels effect of LiNbO₃ is enhanced via q-BIC resonance, resulting in a highly efficient electro-optic modulation of the CD signal. The modulation efficiency was found to be 1 nm/1.25×10⁵ V/m at 972.76 nm. Furthermore, we have investigated in detail the polarization-dependent electro-optic properties of the LiNbO₃ metasurface. The polarization states of the output far-field radiation can be actively tuned by electro-optic modulation efficiently. The modulation ranges of polarized rotary angle were found to be 55° and 48° for right-handed and left-handed polarization, respectively. The ellipticity can be tuned in a range of 62° and 3.3° for right-handed and left-handed polarization, respectively. Benefiting from the high Q-factor, this metasurface shows a high sensitivity to environmental refractive index of 590nm/RIU and a high figure of merit of 5.9×10⁴. These results show that the studied metasurface is promising as an electro-optic modulator and for applications in sensing of chiral responses.

Quantum effects, which become dominant at the nano- and molecular scales, are critically important for optical fiber connections and optical devices and systems, which are immune to electromagnetic interference. Optical nanodevices such as nanorobots, nanomotors and plane parallel elements of optical nanosystems subject to the Casimir force which may lead to uncontrolled changes in the optical properties and data transmission errors. In this work, we investigate the impact of the Casimir force on individual components of optical systems and determine the extent at which it affects charge distributions and orbital energies and leads to excited states causing considerable variations in the optical properties. Numerical simulations were carried out using a mathematical model, which based on LCAO and a numerical solution of the Schrödinger equation using the Hartree-Fock method, with the Casimir force being included in the operators of exchange interactions for the nuclei and electrons. Computational experiments were performed for the main components of glass surfaces, such as SiO₂, Na₂CO₃ and CaO. We found that the strongest effect of Casimir force in the case of SiO₂ and the foil surface, while Na₂CO₃ is the least sensitive to the Casimir force, with CaO being in between the former two. Acrylic and polystyrene surfaces showed a similar smaller effect on the system energy compared to foil Cases, in which the Casimir force can lead to significant variations in optical properties and data transmission errors, were studied and its use in the design and calibration of optical devices with controlled properties was explored.

Photonic crystals are widely used to control the electromagnetic radiation using local field enhancement properties and photonic bandgap properties allowing for significantly increasing efficiency of nonlinear optical interactions of various types. In our experimental study, we investigated excitation and emission of electromagnetic radiation in synthetic opal matrices. A long afterglow of the samples in the anti-Stokes region of the spectrum, reaching several seconds, was detected. The generation of directed X-ray radiation in the samples was discovered, its temperature and energy thresholds were determined, and the possible physical mechanisms explaining the phenomena observed were explored. The threshold for the occurrence of stimulated low-frequency Raman scattering was on the order of 0.01 GW/cm² and was determined by the morphology of the sample used. All experiments were carried out in a vacuum, with various liquids such as ethanol, acetone, water and others being used as infiltrates. After using high-speed photography of the electromagnetic glow dynamics of the sample in the optical range, wave-like gigahertz fluctuations in the glow intensity that may be an indication of the relaxational nature of radiation generation in the gigahertz range, were observed.

When exoplanets pass their host stars, an absorption spectrum, the transmission spectrum, can be observed. From the transmission spectrum, the presence of different molecules can be implied. The detection of water has been a crucial area of research. This paper uses the Transfer Matrix Method and Matlab to design 1D photonic crystals that produce a photonic band gap with single or double defects. The designed structure of Air/(AB)³/C/AB³/Air where layer A is SiO₂, layer B is WTe₂, and layer C is Y bF₃ is applied to three filters. Considering the light curve obtained by the filtered light, the presence of water in an exoplanet’s atmosphere can be obtained. The defect modes centered at the wavelengths of 1.4μm and 1.9μm correspond to the two ranges of water absorption. The photonic filter can potentially be used to search for life-carrying planets.