This PDF file contains the front matter associated with SPIE Proceedings Volume 12773, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Dielectric metasurfaces show great potential in light manipulation for applications such as optical filters and semiconductor metasurfaces for generating entangled photons. These applications critically rely on resonant mode properties in micro/nano-structured metasurfaces. Several modes including electric dipole (ED), magnetic dipole (MD), and quasi-bound state in the continuum resonance have been widely explored with the merits of high quality factor and narrow bandwidth. However, these reported metasurface resonances generally do not absorb light due to the transparency of dielectric materials, which limits their usage in some applications such as thermal emission and photon detection etc. In this work, we demonstrate a new class of dielectric metasurfaces, which exhibit the features of both strong light absorption and narrower bandwidth. Our fabricated metasurface consists of a Si cuboid array on top of a SiO₂ spacer layer backed with a metallic Cu film. The cavity mode within the SiO₂ spacer couples with electrical dipole in the Si cuboid, leading to an asymmetric narrow bandwidth Fano resonance within our metasurface structure. Our spectral measurements show that the Fano resonance occurs at the wavelength of 4.19 μm. It has a strong absorption efficiency of 65.8% and a narrow bandwidth of 32.5nm, corresponding to a quality factor as high as 112. As an example to reveal the potentials of our metasurface, the Fano resonance is applied in refractive index sensing with a sensitivity of 518.75nm/RIU and a high figure-of-merit (FoM) of 14.82 RIU^-1. These results indicate that cavity-coupled dielectric metasurface presents an effective way for obtaining both strong light absorption and narrow bandwidth, opening new space for metasurface applications.

Strong and narrow-linewidth circular dichroism (CD) spectroscopy promises potential applications in bio-chemical sensing and detection of the weak chirality in natural molecules. Here we proposed a chiral metasurface formed by the asymmetric metal double split ring resonator (DSRR) arrays, the circular dichroism (CD) of which has been investigated. The maximum CD for absorption response of the metasurface can reach 0.61 with an ultra-narrow spectral linewidth of 9.6 nm in the mid-infrared (MIR) band. Our calculation results show that the chiral metasurface can support two surface lattice resonance modes for the left circularly polarized (LCP) and right circularly polarized (RCP) light. The narrow linewidth of CD is enabled by the spin-selective high-Q resonance modes with a differential absorptivity for LCP and RCP light. Our findings shed light on the potential applications in spin-selective perfect optical absorption, high-sensitive polarization detection, and chirality sensing.

The purpose of this study is to develop an optical inclination angle sensor using a metasurface as a scale. We propose to use the dependence of the reflection or transmission spectrum of the metasurface on the direction of light incident on it to measure the inclination angle. The disadvantages of this approach when using the simplest completely passive metasurfaces are considered. In particular, the use of bulky devices to scan the spectrum of the structure. As an alternative, the possibility of using metasurfaces with parity-time-symmetry properties to measure the inclination angle is proposed and investigated. Then no spectrum scanning of the metasurface is required to perform inclination angle measurements. As an example, a metastructure formed by two optically coupled subwavelength diffraction gratings (one of which is characterized by losses, and the other by gain) with a rectangular stroke profile is considered. The study is based on computer modeling by the finite element method.

The use of metasurfaces as scales of optical rotation angle sensors (encoders) makes it possible to reduce their overall dimensions by several orders of magnitude. The paper briefly discusses one of the possible options for implementing a rotation angle sensor with a scale from a metasurface. As a scale it is proposed to use a metasurface – a dielectric onedimensional subwavelength array designed to operate in the infrared spectral range (at a wavelength of 1.5 microns). By the finite element method, a prototype of an optical angular scale from a metasurface has been developed by computer modeling. The results of an experimental study of a prototype of an optical angular scale from a metasurface are presented. The metasurface was made of tantalum oxide and deposited on a quartz glass substrate. For the convenience of the study, the size of the scales was set to 400 × 400 microns, but if necessary, it can be reduced by more than an order of magnitude. The dependences of the transmission spectra of the prototype scale on its rotation angle are experimentally investigated.

Here we propose a metasurface consisting of asymmetric dielectric tetramer arrays, which can realize a polarization-sensitive light modulation through toroidal dipole resonance (TDR) in the near-infrared (NIR) region. We found, by breaking the C_4v symmetry of the tetramer arrays, two narrow-band TDRs can be created with the linewidth around 1.5 nm. Multipolar decomposition of scattering power and electromagnetic field distribution calculations confirm the excitation of TDRs. Our simulation results show that 100% modulation depth in light absorption and selective field confinement can be achieved by changing the polarization orientation of the incident light. Our findings will prompt versatile applications in optical switching, storage, polarization detection, and light emitting devices.

Strong coupling between plasmonic resonances in metallic nanostructures and molecule vibrations has been reported in structures such as metallic dimers and nanoparticles on mirror, forming new hybrid states called ‘plexcitons’. Strong coupling occurs when the energy exchange rate exceeds the damping rates of both optical mode and the molecular vibration. Sub-radiant plasmonic modes with high quality factor have often been considered as promising candidates for achieving strong coupling with molecules. However, the sub-radiant plasmon mode cannot be directly excited by farfield normal incident plane wave due to destructive interaction among the moments with equal magnitudes but opposite directions, completely cancelling each other out. In this work, we demonstrate a plasmonic metasurface, which exhibits a sub-radiant magnetic quadrupole (MQ) resonance and tunable coupling strength with molecular vibrations. Our fabricated metasurface consists of an asymmetric metallic micro-cross array on top of a dielectric spacer backed with a metallic film. A magnetic quadrupole resonance is excited at 37.8THz at far-field normal incidence condition. Its quality factor reaches 34, which is more than four times of regular radiant magnetic dipole excited in the same structure. Coupling of the MQ resonance with vibration band (Si-CH₃ at 37.8THz) of polydimethylsiloxane (PDMS) leads to Rabi splitting phenomenon in the dispersion curve. As thickness of the spin-coated PDMS film increases from 14 nm to 310 nm, the Rabi splitting gap increases from 0.6THz to 1.13THz, exhibiting a tunable coupling strength. Our demonstrated magnetic quadrupole metasurface presents a versatile scheme for manipulating the light-matter interaction in sensing application.

Chirality is a typical phenomenon in nature that has significant optical research and practical applications. But natural chiral materials typically exhibit a weak chiral response, making it challenging to detect them with great sensitivity. Chiral metasurfaces can greatly increase circular dichroism (CD), efficiently improve the interaction between light and chiral molecules, and enhance chiral sensing. Additionally, combining bound states in the continuum (BIC) to excite numerous high-Q-factor Fano resonances is a useful strategy for enhancing sensing performance in all-dielectric metasurfaces. With its extremely small linewidth and exceptionally high Q value, the Fano resonance created by the quasi-BIC mode can significantly boost the performance of the refractive index sensor. In this study, we combine BIC with chirality, break the structure's mirror and inversion symmetry to construct a chiral all-dielectric metasurface structure based on BIC. Fano resonances with simultaneously high Q value and strong CD are achieved for the chiral optical response. Meanwhile, we investigate its sensing properties to obtain high sensitivity and figure of merit (FOM) for refractive index sensing performance. Our research offers suggestions for applications such as the identification and separation of chiral biological substances.

Vortex beams that carry orbital angular momentum (OAM) have garnered significant attention, as they bring the degree of freedom of OAM to modern optical communication, beyond the traditional degrees of freedom such as amplitude, phase and polarization. Meanwhile, metasurfaces composed of ultra-thin layers of subwavelength structures have also been utilized for light manipulation. Nevertheless, the combination of these two concepts has not been explored in the form of microring resonator-based light emitter. In this work, we demonstrate a Si-based, passive, conjugate symmetrybreaking emitter in numerical simulation. This broken conjugate symmetry enables the emitter to generate OAMs with different topological charges, when it is driven at two opposite input directions.

The current work proposes an optimized design for 2-bit synchronous up counter using silicon nitride on insulator optical microring resonators (MRRs). The research involves exploring the existing designs of up counter structures based on MRRs, and then minimizing the number of rings being used in the proposed model. The proposed design uses four MRRs for Synchronous up counter operation and the model has been validated through the MATLAB simulation result. The main component of the design is the MRR which can act as a switch depending upon the output at the drop port or the through port according to the MRR being in an on-resonance or off-resonance state respectively. The principle of the MRR is that on applying a vertical pump signal over the ring, the non-linear refractive index of the ring undergoes a temporary blue shift resulting due to π- phase shift in the ring, changing the resonant frequency of operation of the ring. The average pump power required for the blue shift can be obtained from the phase shift vs. the average pump power graph simulated in MATLAB. This shift in resonance frequency is employed to switching action for the signal to be output at the drop port or the through port of the MRR and based on the drive signal inputs of the present state and the clock to the rings in the resonator structure which act as pump signal over the ring, the next state of the counter is determined.

Pulsed laser processing matures as a powerful technique for flexible and high-performing nanostructuration. Rich physics behind the light-matter interaction allows to produce unique surface nanotextures with desired properties, beneficial for various practically-relevant applications such as optical sensing, anti-counterfeiting, realization of nanophotonic platforms and so on. Here we have applied direct femtosecond-laser printing to locally fabricate nanostructures on glass-supported amorphous-silicon thin film for realization of high-resolution (up to 60 000 dots per inch) security labels offering full-optical information encryption in several ways. Since the proposed tag represents array of close-packed amorphous-silicon hemispherical nanoparticles, the first approach for information encryption is to selectively crystallize some of nanoparticles by continuous-wave laser irradiation without morphological changes. Thus, crystalized nanoparticles ordered in a user-defined way indicate encrypted information that can be read using Raman signal intensity mapping at frequency of 519 cm⁻¹, corresponding to the main phonon mode of crystalline silicon. The second way is to hide Mie-resonant nanoparticles between non-resonant ones. Since the latter haven’t proper size to resonantly interact with pump radiation during Raman signal mapping, encrypted information can be revealed via evident variation in Raman yield between resonant and non-resonant nanoparticles. Thereby, we demonstrated facile single step printing of anti-counterfeiting labels at resolution up to 60 000 dots per inch justifying the applicability of the developed approach for optical information encryption.

At the moment, manipulation of liquid microdroplets is required in various microfluidic and lab-on-a-chip devices, as well as advanced sensors. We report a new method for microdroplets manipulation, based on the use non-uniform electrostatic fields. Our platform uses an electrode array embedded in a dielectric planar superhydrophobic substrate produced by direct laser writing. When a voltage is applied to a certain sequence of electrodes, a non-uniform electrostatic field is produced, which acts to attract a droplet on the substrate to the electrodes. This achieves a stepwise movement of the droplet. We realized non-contact, selective and high-speed movement of the individual droplets along specified trajectories and their selective coalescence. In our opinion, this approach has a huge potential for chemical technology applications especially in optical sensors.

We demonstrate the creation of hybrid metal-dielectric nanostructures (NPs) using femtosecond-laser exposure of copper-silicon and gold-silicon films. The formation of arrays of nanoparticles takes place in the process of irradiation of a bilayer film along a circular trajectory. The internal structure of the obtained NPs was studied by means of transmission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The resulting hybrid structures represent a mixture of gold and silicon, and both considered systems demonstrate broadband photoluminescence in the range of 450 - 900 nm with a quantum efficiency of up to 1.1%.

In this work we present a novel technique to fabricate whispering gallery modes microresonators on the regular optical fiber surface. We use a high-resistance wire heated by constant electrical current up to temperatures of 1100 °C. Due to higher temperature stability, high reproducibility of the microcavities shaping is ensured. Our method makes it possible to reduce the cost and simplify the production of WGM microresonators on the optical fiber surface.

The whispering gallery mode (WGM) optical microresonators formed on the optical fiber surface appear as a promising ultraprecise and ultralow loss technological platform (known as Surface Nanoscale Axial Photonics, SNAP) to create miniature optical devices including delay lines, signal processors, photonic sensors, optical frequency comb generators, etc. It is important to note that applications involving high intracavity power may face intense cavity heating and hence unwanted radius changes. Here we the heating effects in SNAP cavities both experimentally and numerically and reveal the changes in the mode structure induced by the heating due to whispering gallery mode energy dissipation.

The absorption of optical power in high-Q microresonators leads to thermal effects, that strongly affect quantum and nonlinear processes. To take these effects into account, rate equations with effective thermal parameters are commonly used. Despite the convenience and simplicity of this approach, its applicability for a certain range of microresonator parameters may not be accurate enough. In our work, we compared various methods for determination of the effective thermal parameters for different resonator structures: the microring and microtorus resonator. As a result, we propose an original and effective method for determining the effective thermal parameters of microresonators based on thermal mode decomposition that considers various thermal relaxation processes. The proposed method agrees better with both direct numerical simulation and well-known theoretical formulas over the entire range of microresonator parameters, in contrast to the classical approach.

We experimentally demonstrated a stimulated Brillouin laser with hybrid modes, utilizing two coupled silica microtoroid cavities. The first cavity consists of paired modes with a frequency difference close, but not exactly equal, to its Brillouin frequency shift. The second cavity has a resonant mode that is close to one of the modes of the first cavity. The strong coupling between the two similar frequency modes induces mode splitting, resulting in the generation of a hybrid paired mode. This hybrid mode comprises one eigenmode from the first cavity and the super-modes of the coupled microtoroids. By finely tuning the coupling strength to match the frequency difference between the paired modes and the Brillouin shift, we achieve Brillouin lasing. Furthermore, the offset of the frequency shifting in the hybrid modes configuration is much smaller than the Brillouin frequency shift, significantly reducing coupling loss and enabling the realization of a lowthreshold Brillouin laser. We experimentally observed a lasing threshold as low as 0.45 mW, which is two orders of magnitude lower than that of the direct super-modes frequency matching method. This novel approach relaxes the strict requirement of exact frequency matching conditions for Brillouin lasing, making it an excellent platform for compact and ultra-low threshold Brillouin lasers.

The integration of metal-organic frameworks (MOFs) as coordination polymers into the field of nonlinear optics and light conversion has recently attracted significant attention. However, the challenge of achieving high endurance and efficiency for light conversion throughout the entire visible range using a single MOF crystal persists. In this work, we present the design of a non-centrosymmetric MOF based on a 1,3,5-benzenetricarboxylic acid ligand and Erbium (Er) ions, which demonstrates efficient and simultaneous generation of multiple second and third optical harmonics (SHG, THG) across a wavelength range of 400 to 750 nm. Through a combination of optical experiments we have confirmed the effectiveness of SHG and THG in the MOF single crystals. These phenomena are caused by the specific MOF space group and the associated dipole moment. The observation of coherent light conversion throughout the entire visible range by MOF single crystals under ambient conditions enables the realization of multicolor (up to 3) emission, which is essential for modern laser technologies.

The paper investigates the resonances of reflection (transmission) of a structure consisting of two optically coupled subwavelength silicon rectangular diffraction gratings, separated by a layer of optically transparent dielectric. The considered structure combines gain, loss and optical coupling coefficient of the periodic structure to effectively operate in parity-time symmetry mode. The spectral characteristics of the resonant reflection (transmission) of the metastructure are analyzed both in PT-symmetry mode and when switching the system to broken PT-symmetry mode. The advantages and disadvantages of using optical parity-time symmetry to control resonant reflection (transmission) for TM- and TEpolarized light incidence are demonstrated. It is shown that changing the relative arrangement of the gain and loss gratings with respect to the incident signal field significantly affects the ratio of transmission and reflection coefficients. All results are obtained considering the dispersion of the materials used.

The drug resistance of Mycobacterium tuberculosis (MbT) remains a serious challenge to global public health as extensively drug resistant tuberculosis usually leads to a lethal outcome. In the case of diseases with resistant strains, it is extremely important to identify a specific strain as soon as possible in order to start an adequate therapy. We continue investigation of deactivated M. tuberculosis strains of the Beijing family by Raman spectroscopy method. Strains under the study had different drug sensitivity: sensitive, multi and extensively drug resistant. Samples were investigated by Surface-Enhanced Raman spectroscopy using 785 nm diode pumped laser excitation source in fingerprint region. As a result, both glutathione bands and DNA methylation using 5-methylcytosine spectral biomarkers has been investigated. These differences distinguish between drug-sensitive and drug-resistant strains and also between strains. We suppose that the obtained results can be useful for new fast diagnostic tools development for determining various MbT strains in clinical medical practice.

We propose a design for all-dielectric (gallium phosphide, GaP) nanoantenna to enhance single molecule fluorescence. The slotted GaP nanodisk exhibits strong scattering and limited optical loss, resulting in more than 30× excitation enhancement growth at the resonance position. Our proposed scheme also enables precise manipulation of the local density of optical states, leading to a nearly one order of magnitude increments in quantum yield for individual dye (original quantum yield is 0.01) and 12× emission enhancement. We benchmark the overall fluorescent enhancement for the four commercial dye colors (original quantum yield is 0.3) and achieved one-order of enhancement higher than commercialized zero-mode waveguide (ZMW) in the simulation. Our GaP-based design not only provides a solution for next-generation chips for DNA and protein sequencing, but also contributes to single-entity interactions, portable fluorescence detection, and integrated devices with quantum light sources.

Active nanophotonic devices play an important role in optical communication systems. Improving modulation efficiency and reducing the footprint of these devices are crucial for low energy information processing and on chip communication. The Multi Frequency-Domain Finite Difference (MF-FDFD) algorithm was invented to address the inherent the large difference in scale between the modulation frequency and the frequency of optical waves of active nanophotonic devices. However, due to the fact that the MF-FDFD algorithm itself requires solving a large number of unknowns compared to traditional FDFD algorithms, the current MF-FDFD algorithm still stays in two-dimensional and is difficult to calculate in three-dimensional. To solve this problem, we introduced Newton and Born methods to accelerate and complete the the solution of algorithm, and developed a three-dimensional MF-FDFD algorithm. We validated our algorithm by simulating a mode converter. Our algorithm can effectively perform first principles simulations for active nanophotonic devices, laying the foundation for future intelligent inverse design.

Due to the unique sheet structure of two-dimensional (2D) MXene, it is widely used in electromagnetic interference (EMI) shielding. Herein, a transparent and flexible EMI shielding film is proposed by combining MXene with nickel (Ni) mesh fabricated by mask exposure and a selective metal electrodeposited process through a convenient spin-coating method. Covering the MXene sheet with one-dimensional (1D) Ni grid lines improves the conductive network of the structure and its shielding efficiency (SE). The experimentally prepared MXene/Ni/PET film exhibits a visible light transmittance of about 79.46% at 550nm wavelength and a shielding efficiency of about 34.1dB for the X-rays. In addition, the absorption efficiency of the MXene/Ni/PET film increased. This MXene film has excellent EMI shielding performance and transparency. The mass production of this film is relatively simple. It has the potential for many applications, such as transparent display devices, smart windows, aircraft windshields, and other electromagnetic wave shielding-related domains.

The finite difference time domain method (FDTD) is a popular and effective numerical approach for electromagnetic analysis. However, the original explicit FDTD suffers from two primary limitations: the time step is constrained by the Courant-Friedrich-Levy (CFL) condition, and it requires significant amounts of computer memory, particularly when analyzing large objects with fine structures. In this paper, we present a new FDTD algorithm called Reduced-Leapfrog Alternating-Direction-Implicit FDTD (R-Leapfrog ADI-FDTD), which is unconditionally stable and reduces computer memory usage by approximately 23%. The algorithm is based on a conservation formula derived from the conventional electromagnetic divergence. This formula describes the spatial dependence of the field components obtained by the one-step leapfrog ADI-FDTD. By leveraging this spatial dependence, we are able to locally calculate and temporarily store two of the six field components during each iteration, while the remaining four components are stored over the entire 3D spatial grid as usual. Our simulations show that the results are in excellent agreement with those obtained from the original explicit FDTD and one-step leapfrog ADI-FDTD, demonstrating the algorithm’s unconditional stability and accuracy. R-Leapfrog ADI-FDTD is a valuable tool for electromagnetic analysis when computer memory is a critical factor.

High order axially symmetric polarized beams (ASPBs) can create multiple focused spots under tight focusing conditions, and thus have been highly recommended for optical manipulation, but the feasible experiments have never been demonstrated. Cells trapping and manipulation based on optical tweezers using high order ASPBs are presented theoretically and experimentally to verify its feasibility and effectiveness. The focused intensities and corresponding gradient forces for high order ASPBs are first analyzed and calculated if two kinds of particles are trapped respectively based on the electromagnetic theory. Then an optical tweezers based on an inverted microscopy using high order ASPBs is built up, and the yeast cells (~10μm) are trapped and manipulated to shift and rotate using two kinds of ASPBs with P=1 and P=3. One yeast cell is stably trapped and shifted with a speed about 40μm/s and four yeast cells are trapped and rotated simultaneously with a rotation speed about 45°/s, which can also be further modulated and the track of the focusing spot can be programmed by computer. Finally, the optical trap stiffnesses are calculated theoretically using the Boltzmann statistics method and further measured experimentally when the filling factors of the objective lens are 0.50, 0.80 and 1.00 respectively and three microcopy objective lenses with numerical apertures 0.40, 0.65 and 0.85 are used, and the measured results agree well with the calculated results, which shows the trapping performances can be flexibly modulated by setting the system parameters and provides some novel choices for optical manipulations. All these findings benefit the expansion of the practical applications of vector beam OTs in some fields, especially in the field of biomedicine.

Chirality is a common phenomenon in nature, mainly manifested in the symmetry of matter, which means that matter and its mirror image cannot overlap through rotation or translation. Chirality has significant research and application value in the field of optics. Circularly polarized light itself has chirality, that is, left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light. When a chiral circularly polarized light interacts with different chiral optical metasurface, it will show different optical properties. As a result, the chiral electromagnetic response can be adjusted through the construction of an optical metasurface through material choice and structural design, and the strong chiral field limited near the structure of chiral metasurface can also enhance the circular dichroism (CD) signal of the chiral molecules located therein, which has important application value in the fields of optical chiral sensing, chiral particle separation, and chiral regulation. Here, we calculate the CD value using the transmission spectra of LCP and RCP incident light. In this paper, we present the design of an innovative chiral metasurface predicated upon silicon nanostructures, which incorporates two distinct open-ring resonators. Through meticulous parameter optimization, we attain a maximum CD value of 0.94432 upon exciting the metasurface's inherent chirality. Furthermore, we employ the electromagnetic multipole decomposition technique to elucidate the preeminent electromagnetic modes. This study holds paramount significance in advancing our comprehension of optical-matter interactions and in augmenting our chiral sensing capabilities. Subsequent to an exhaustive analysis of the sensing characteristics, the calculated sensitivity is determined to be 287 nm/RIU.

The finite-difference frequency-domain (FDFD) method is an effective method for numerical simulation of electromagnetic fields. It has great advantages in dealing with electromagnetic scattering problems of complex structures and complex media. This method can transform the frequency-domain Maxwell equations into a linear system for solution by difference operation on the spatial grid. However, high-precision differential calculations can result in more memory consumption and a decrease in computational speed. In previous reports, subgridding technique is often used to solve such problems, where mesh refinement is only performed in local areas, while coarse mesh partitioning is still used in other areas. However, the refinement area can only be manually set, lacking flexibility and accuracy. Therefore, we propose a novel FDFD method based on adaptive grids, which uses the cartesian tree-based hierarchical grids to discrete the spatial domain. It can automatically refine the local grids according to the geometrical characteristic of the model to improve the accuracy of specific areas, without significantly increasing the number of unknowns, and has strong flexibility while improving the calculation efficiency. In this study, we use two levels of grids for adaptive grids construction, with a mesh size ratio of 3:1. Using second-order interpolation to handle the transmission problem of electromagnetic field components at different grid boundaries. The simulation results show that the computation speed of the adaptive grids FDFD system is faster than that of structured grids.

Chiral nanohole arrays (NAs) are of significant research interest for their label-free enantiodiscrimination of biomolecules and drug compounds, even at the picogram level. This study systematically explored the impact of various parameters on chiral optical responses of NAs, enhancing our understanding of underlying mechanisms and optimization strategies. We designed dual-layer nanohole arrays with 3600 elements each, alternating Ag and Au layers. We manipulated incident angles (Δθ, θ₁) and azimuthal angles (Δφ, φ₁) using shadow sphere lithography (SSL) and introduced SiO₂ between the Au and Ag layers to enhance the response. MATLAB generated the NAs, subsequently simulated using the finite-difference time-domain (FDTD) program. Findings revealed central symmetry in circular dichroism (CD) value changes concerning Δθ and Δφ, with a more pronounced effect than variations in θ₁ and φ₁. The inclusion of SiO₂ led to a notable 118% increase in the maximum |CD|_max value, reaching 6.50° for the 100 nm sandwiched NA (SNA150) with a radius of r = 150 nm. The maximum |g-factor| of the Ag-Au SNA150 increased with the r. An efficient model categorized NAs with similar CD responses, reducing simulations to 498 based on mirror, symmetry and a 60° differential rotation property. This research provides a valuable resource for future machine learning analyses and predictions across diverse structural configurations, significantly advancing applications such as the detection of weak chiral optical molecules or proteins, compact polarization converters, and label-free chiral sensors, fostering innovation in nanohole array technology, particularly in biomedicine and optoelectronics.

Hydrogen has become as a significant energy source. Nonetheless, its threat of explosion poses a challenge to the production and use of hydrogen. This study employs electron beam evaporation technology to produce the Ag-Pd multilayer composite plasmonic hydrogen sensors (PHS), which fulfills the requirement for hydrogen safety detection. The sensing characteristics of monolayer, double-layer and multilayer metal film arrays are systematically compared. The excited local surface plasmon resonance (LSPR) on the multilayer composite films enhance the signal intensity effectively. At the same time, the hot spots area excited by the electric field provide energy for hydrogen adsorption, which synergically promotes the fast response of hydrogen. The PHS based on the Ag-Pd multilayer composite films array has the advantages of fast response, high sensitivity and low detection limit. The multilayer composite plasmonic hydrogen sensing platform developed provides an important theoretical basis and technical support for the development of high-performance hydrogen sensors.

Programmable integrated photonics is one of the most promising hardware acceleration schemes for deep learning. The programing method based on phase change materials makes the device non-volatile but reduces the resolution, which may result in a loss of performance. Here we propose an on-chip optical neural network implemented with a cascaded array of 1:1 couplers and waveguides with a digital non-volatile phase shifter. The Sb₂Se₃-assisted phase shifters can achieve a phase shift from 0 to 2π in steps of π/16 through 5 independent non-volatile reconfigurable units. We also proposed a Digital-Aware-Training regime to train this digital model. The network achieves 100% and 83.7% accuracy in the recognition of 4 Latin letters and iris project, respectively. Compared with conventional reconfigurable schemes, this computing platform has the characteristics of non-volatile, low power consumption, and high modulation robustness.

Resonant modes with BIC effects can be produced and isolated from other radiation modes in the spectrum by using particular geometrical forms and material properties, as well as by breaking inversion and rotational symmetries in metasurfaces. The Q-factor of metasurfaces is considerably increased by this decoupling process, permitting effective optical responses over a limited frequency range. Optical chirality is the asymmetry that optical systems or materials exhibit when interacting with circularly polarized light. As light travels through chiral materials or structures, its rotation direction may change or it may encounter selective transmission, reflection, or absorption, resulting in differences between lefthanded and right-handed circularly polarized light. In our research, we developed all-dielectric metasurfaces that concurrently violate rotational and planar mirror symmetry, resulting in strong chirality and high-Q quasi-BIC resonances, which shows high circular dichroism (CD) of 0.954. Through numerical simulations, the effectiveness of this design was confirmed, highlighting the major benefits of chiral metasurfaces in selective transmission and polarization conversion. The outcomes of our work, in contrast to methods based on accidental BICs, have engineering tunability, making them useful for chiral biosensing, circular dichroism nonlinear optical systems, and other applications.

Nanophotonics employ chiro-optical effects for a variety of applications, including advanced imaging and molecular detection and separation. Due to their outstanding qualities in light-matter interactions, planar metasurfaces comprised of subwavelength meta-atoms have attracted a lot of attention. Despite of the vast potential of metasurfaces, achievement of large chiro-optical effects compactly on-chip at the visible wavelengths is still hindered by its complex design and optimization procedure. Deep-learning (DL) based modelling techniques have been put out as an alternative to the time-consuming and computationally demanding traditional design and optimization procedure of metasurfaces during the past few years. In this work, we have employed deep-learning based forward and inverse models to design and optimize achiral nano-fins to achieve giant chiro-optical affects at the visible wavelengths. A regression based forward neural network is proposed, that takes all the structural dimensions of the achiral nano-fins as input and trained separately to predict three different types of asymmetric transmissions i.e., TLL, TLR and TRL and circular dichroism. An inverse design model is also demonstrated that simultaneously considers all the three target transmissions and optimizes the dimensions of the achiral nano-fins in such a way that they experience constructive and destructive interference, resulting in an average circular dichroism of more than 60% and 70% asymmetric transmission. With potential applications in chiral polarizers for optical displays, flat integrated polarization shifter’s exhibiting high efficiency, chiral-metasurface sensors and chiral beam splitters, the suggested DL-enabled design techniques ease the realization of op-chip giant chiro-optical response through planar metasurface.

Deep Neural Networks (DNNs) have emerged as a powerful tool for predicting the structure and composition of diverse nanophotonic devices based on their desired response. These techniques have played a pivotal role in driving advancements across a spectrum of fields within optics and photonics. Notably, they have significantly contributed to the progress and innovation observed in the domains of plasmonics, holography, chirality, topological photonics, airy beams, color filters, vortex beams, and absorbers. This paper reviews the most recent advances in using Machine Learning (ML) and Deep Learning (DL) for inverse design of nanophotonic devices. In the past, conventional optimization techniques have been used as a design tool to optimize the metasurface and nanodevice structures but in recent years ML and DL based techniques have revolutionized this process. These techniques are more time efficient and accurate.

Metasurfaces offer novel design capability of optical wavefront shaping to realize ultra-compact flat optical components which have remarkable potential to mitigate the constraints of size and design complexities in imaging systems. However, aberration correction and diffraction-limited response over the broad spectrum greatly hindered their applicability because of simultaneous phase engineering at multiple wavelengths on a single metasurface interface. Conventionally reported design methodologies overcome the challenges mentioned earlier by exploiting resonance tuning, layer stacking, and phase mergence strategies. They suppressed the aberration effect with high efficiency but have complex design and meta-atom geometry with limited functionalities. Here in this research script, we have introduced broadband achromatic bifocal metalens based on a single-layer array of nano-rectangular bars in transmission mode. In order to have wavelength-independent focusing, we developed a library of meta-atoms to provide required phase compensations. In addition to this, a novel material zinc selenide (ZnSe) is introduced as a constituent which is a large transparent window in the optical regime. The high efficiency and unprecedented capability of aberration correction along with multi-functionality make the proposed metalens a potential candidate for next-generation advanced imaging technology.

Vortex beams offer a novel avenue for advancing information transmission, storage, and processing within the optical domain. However, conventional optical apparatus and systems depend on the phase accumulation technique to create vortex beams. These methods frequently lead to the development of cumbersome and expensive configurations, hindering the integration with on-chip photonic systems. Metasurfaces, planar structures composed of nano-elements, hold immense promise for extensive adoption in optics and photonics. Their remarkable capacity to manipulate light at the nano-level has led to widespread utilization, particularly in generating optical vortices. In this work, we proposed an all-dielectric transmissive metasurface platform that generates a perfect vortex beam with a trigonometric function embedded in it to achieve an infinite topological charge. We selected silicon nitride (Si3N4) as the material of choice. It exhibits transparency in the ultraviolet (UV) region and across the visible spectrum. It also exhibits best-suited optical properties to ensure exceptional response in the targeted dual bands. We selected a numerical aperture of NA = 0.7 for verification of the concept, and two trigonometric functions are θ. cos⁡(θ) and ½ sin⁡(θ). The presented design technique and material may find potential applications in biomedicine, free-space optical data communications, and optical data modulation.

In this manuscript, a dielectric nanoparticle-assisted excitation of optical Tamm mode (OTM) is proposed using a 1DPhotonic Crystal configuration. The structure comprises a bilayer photonic crystal structure having silicon nanoparticles placed at the top interface of the structure. The structural parameters and nanoparticle sizes are optimized to break the translational symmetry. The reflectance spectrum and field distribution map are analytically studied by the finite element method. The analytical results exhibit the excitation and confinement of OTM. The excited OTM modes show a strong dependency on the angle of incidence and the nanoparticle size. The obtained results exhibit that dielectric nanoparticles can be utilized as compact surface mode exciters and scatterers. This further facilitates the development of OTM devices for integrated photonic applications.

Free space optical (FSO) communication is an evolving technology that opens up the doors to use huge unlicensed bandwidth and can manifest high-speed communication. As the radio frequency spectrum is getting overburdened and unable to meet the ever-increasing demands of the internet, the optical spectrum can prove to be a paradigm shift to achieve the KPIs of communication including high data-rates, low latency and efficiency. In our study, a fluid-infiltrated reconfigurable intelligent surface (RIS) has been proposed that is proficient in directing the light on the concerned user. We proposed the integration of RIS in FSO communication to simultaneously enhance the data transmission range and acquire reconfigurability on run-time. Our proposed design can provide the communication link to the legitimate user while blocking the eavesdropper’s reception. The proposed miniature-sized surface is envisaged to be an efficient meta-device for dynamic applications in FSO Communication.

Effective dispersion management is critical in constructing super prism, spectrometers, and achromatic lens-based optical systems. Metasurfaces, the artificially engineered structures, promise the miniaturization of such dispersive devices to enable compactness and integration with on-chip devices. The miniaturization is due to the planar nature of the fundamental building blocks that offer unprecedented control of optical properties of light, such as phase, amplitude, and polarization. These building blocks abruptly vary the light characteristics to engineer the output behavior. The response of the metasurface depends upon geometry and material, which, in turn, is dependent on the wavelength of the incident light, amongst other factors. Conventional ways of dispersion management are not only complex but also give rise to aberration-related challenges. Metasurfaces provide alternatives to combat the above-said limitation. A single-layered, single-cell driven all-dielectric super dispersive metalens is not reported for the visible regime. Here, we proposed a zinc sulfide (ZnS) based highly dispersive metalens with a parabolic phase profile that operates in the visible spectrum and resolves the spectrum of the incident wave by dispersing different wavelengths to different positions at the edge of the metasurface for easy instrumentation integration. Simulations are carried out to verify the proposed design's theoretical dispersion characteristics. The proposed element's high transmission and polarization conversion efficiency ensure broad practical usage. The proposed metasurface can potentially be used in spectrometers, tomography, microscopy, etc.