This PDF file contains the front matter associated with SPIE Proceedings Volume 11903, including the Title Page, Copyright information and Table of Contents

In this paper, localized surface plasmon resonance (LSPR) based tapered multimode optical fiber (TMMF) sensor is developed for the detection of different concentrations of p-cresol solutions. Gold nanoparticles (AuNPs) and molybdenum disulfide nanoparticles (MoS₂-NPs) were immobilized on TMMF probes, respectively. The performance of the designed probe was explored by detecting the response of different concentrations of p-cresol solutions. The combination of AuNPs and MoS₂-NPs enhances the sensitivity and anti-interference ability of the sensing probe. In this work, the enzymatic reaction of p-cresol solution and tyrosinase changes the RI in the vicinity of the probe and records the corresponding spectrum. The probe will also be evaluated in terms of linear range, limit of detection (LoD), reproducibility, reproducibility, stability, selectivity, etc.

In the recent years, lead halide nanocrystals have received extensive research attentions as promising materials in optoelectronics applications due to their excellent light emitting properties including high photoluminescence quantum yield (PLQY), narrow full-width- at- half-maximum, and wide color gamut. However, toxicity is still major concern resulting in the pursuit of harmless lead-free structure development. Among the multifarious structures, copper-based halide nanocrystal is one of the most attractive due to high exciton binding energy leading to high PLQY of this family. In this report, we proposed the protocol for obtaining rubidium copper chloride nanocrystal using ligand- assisted reprecipitation (LARP) together with cooling process. The reprecipitation of cations (Rb+ and Cu+) with anion (Cl- ) were occurred in the presence of oleic acid ligand while the solution was cooled down from temperature at 135ºC to room temperature. We gradually observed cloudy solution within 10 min. The precipitation was purified with isopropanol for several times before further characterization. We found spherical nanoparticles under the transmission electron microscope (TEM), with 6.16 ± 1.2 nm in diameter. Although the X-Ray diffraction reveals two major structures including rubidium copper chloride (Rb2CuCl3) and rubidium copper chloride hydrate (Rb2CuCl4·2H2O), this colloidal nanocrystal still exhibits extremely bright photoluminescence emission peak at 392 and 398 nm under 286 nm excitation. Our finding demonstrates the next-generation light emitting material of rubidium copper chloride in term of low toxicity and bright emission

A Deep Learning (DL) based forward modeling approach has been proposed to accurately characterize the relationship between design parameters and the optical properties of Photonic Crystal (PC) nanocavities. The demonstrated DNN model makes predictions not only for the Q factor but also for the modal volume V for the first time, granting us precise control over both properties in the design process. The experimental results show that the DNN has achieved a state-of-the-art performance in terms of prediction accuracy (up to 99.9999% for Q and 99.9890% for V ) and convergence speed (i.e., orders-of-magnitude speedup). The proposed approach overcomes shortcomings of existing methods and paves the way for DL-based on-demand and data-driven optimization of PC nanocavities applicable to the rapid prototyping of nanoscale lasers and integrated photonic devices of high Q and small V .

Plasmonic nanoresonators exhibiting localized surface plasmon resonance (LSPR) have been extensively investigated for enhancing light-matter interaction and have revolutionized biochemical sensing. However, the high optical absorption in plasmonic materials presents several problems, including the rapid quenching of quantum emitters. Additionally, the incompatibility of common plasmonic materials with the CMOS manufacturing process their incorporation in integrated photonic systems. Although Mie resonant all-dielectric nanostructures could potentially replace plasmonic nanoresonators, higher radiation losses in high refractive-index dielectric nanoparticles prevent high local-field amplification and result in far lower Purcell enhancement. This paper proposes slotted all-dielectric nanodisks and, through systematic numerical study, predicts that high local field enhancement and significantly higher Purcell enhancement can be achieved in such geometries. The following single and arrayed configurations: single asymmetric, chain symmetric, single symmetric with different emitter positions are investigated. In the near IR region, intensity enhancement and the Purcell factor of 1150 and 1800 respectively are predicted for a single slotted nanodisk compared to 30 times near field intensity enhancement and a Purcell enhancement of 20 for a nanodisk. The Purcell factor of a single slotted nanodisk can be further improved to around 2800 by controlling the degree of asymmetry by shifting the slot position. In three symmetric slotted nanodisks, a record high enhancement factor of the Purcell factor of up to 3200 and intensity enhancement exceeding three orders of magnitude was observed. Our findings could lead to novel CMOS-compatible nanoantenna designs for fluorescence signal amplification in biochemical applications and electrical excitation of quantum emitters.

In this work, high resonant reflection of light has been investigated in an atomic thickness resonator consisting of monolayer graphene nanosquare arrays at mid-infrared frequencies. Our numerical results show that more than 90% light reflectivity can be realized due to excitation of dipole resonance in the gap of graphene arrays in this system. Moreover, it is found the high resonant reflection is nearly independent of polarization over a wide-angle range. The resonant wavelength can be dynamically modulated by changing the geometry of the structure or adjusting the graphene chemical potential. Our findings provide new opportunities for the development of optical reflective devices, nano-antenna and highly integrated devices with atomic thickness.

Tunability is a highly desirable feature for nanophotonic devices and metasurfaces that can enable a plethora of exciting applications like dynamic color filtering and displays, motionless beam scanning, and fast focal length tuning compact imagers. Among several alternatives being explored for realizing tunable nanophotonics, phase change materials have been receiving much attention. In particular, chalcogenide glasses like GeSeTe alloys possess several advantages like large refractive index contrast and rapid phase switching properties which enable non-volatile reconfigurable metasurfaces. While previous workers have reported high reflection contrast changes ensuing from laser-induced amorphous-to-crystalline phase changes, detailed studies of the reconfiguration dynamics and optimization of switching processes have not been adequately considered. In this work, we consider simple and dimerized one-dimensional gratings of GST225 and numerically study phase switching as a function of reconfiguration pulse intensity with the objective of minimizing reconfiguration threshold and maximizing the figure of merit (defined as the rate of change of reflection contrast in % to change in pulse intensity beyond the reconfiguration threshold). The numerical study employs coupled electromagnetic and thermal solvers to ascertain the temperature profile and material phase profile for a particular reconfiguration pulse (assumed to be rectangular shaped). This work hopes to provide insights into the reconfiguration dynamics of PCM gratings while scaling down the reconfiguration threshold intensity requirements which can guide experimental activity in PCM based active metasurfaces.

Photonic integrated circuits (PICs) represent a key topic to overpass the frequency limits of the current microelectronics technologies and keep the pace of Moore’s law. Research in the field of PICs is taking a boost, especially because of its compatibility with the modern complementary metal–oxide–semiconductor (CMOS) fabrication techniques utilizing materials such as silicon and silicon dioxide. Silicon-on-insulator slot waveguides are a burgeoning platform for the sophisticated on-chip integration applications. Slot waveguides have been widely used in integrated photonic devices including on-chip optical sensors, lasers, optical amplifiers, optical splitters, optical tweezers, optical phase shifters and so on. The enhancement of electrical fields in slot waveguides is an important topic for improving the performance. In this paper, the structural optimization and parametric analysis of the slot waveguide geometry for optical enhancement and nanoscale confinement are presented at telecom wavelength of 1550 nm. Different designs of the waveguides are studied including photonic crystal slabs with air holes and slot layers made from different dielectric materials such as aluminum nitride, gallium nitride and silicon nitride. The simulation shows that, with the help of periodic air holes in slabs, and by using nitrides in slot regions, the field confinement factor is significantly increased. Our study might be helpful for the design of high efficient subwavelength optical devices which may have great applications in optical computing studies.

We propose an optical beam scanner based on an on-chip 1×100 micro-ring optical switch array. By adopting a combination of optical switch array and lens system, it can achieve beam steering. It uses a simple control circuit to achieve fast beam scanning. The simulation shows that its emission efficiency exceeds 95%, which is conducive to long distance scanning and detection. All the components of this scanner can be fabricated on SOI substrate except for the optical lens, so its cost is low and the overall size of the device can be greatly reduced .In addition, since there are no moving parts in our scanner, it has advantages in performance and service life compared with mechanical optical beam steering devices. These advantages make our scanner is promising in light detection and ranging (LiDAR) field and free space optical communication field.

Design of modern integrated nanophotonic components requires increasingly sophisticated optical simulation and optimization tools. Modeling and computational challenges arise with the increase in the number of design parameters and the introduction of multiple and often competing performance criteria. In such high dimensional design parameter spaces, it becomes difficult to navigate, explore, and visualize the best candidate designs that satisfy all the requirements. We present our recently developed approach that leverages dimensionality reduction - an area of machine learning – to identify and efficiently investigate only the most relevant portion of the design space. Once this reduced space is found, mapping and optimization can often be achieved several orders of magnitude faster than in the original design space. We showcase our approach on several design scenarios focusing on components such as optical grating couplers and power splitters. We employ principal component analysis for linear dimensionality reduction, achieving impressive performance despite its simplicity. We also demonstrate the use of a non-linear technique, i.e. neural-network based autoencoders, which can improve the effectiveness of dimensionality reduction even further. All components have nontrivial regions of interest in their design space that are identified and explored through the evaluation of various performance metrics. Visualizations of these regions offer a global picture of device behavior. Different component geometries can then be chosen depending on specific performance requirements or fabrication constraints. The proposed framework can be easily integrated into various design toolkits.

A single photonic crystal nanobeam cavity (PCNC) supporting both high-order air and dielectric modes was firstly proposed for on-chip dual-parameter sensing. Due to the different field distributions of the two modes, they have quite different response to ambient refractive index and temperature variations. The geometrical parameters of the PCNC were optimized to achieve a suitable bandgap as well as make the wavelength locate at the commonly used wavelength band. The proposed PCNC shows a refractive index sensitivity of 172.5 nm/RIU (refractive index unit) and a temperature sensitivity of 47.4 pm/K for the air mode, while a refractive index sensitivity of 145.5 nm/RIU and a temperature sensitivity of 54.1 pm/K for the dielectric mode. The footprint of the sensing unit is only 0.8×7.6 μm² .

Programmable random lasing pulses are highly desired due to their promising applications in information security, flexible encoding system, and smart imaging. However, the fixed random scattering configuration hinders their realization. Herein, a programmable random laser is proposed and fabricated based on the external waveguide-assisted random scattering feedback. The various pulse time series of random lasing can be flexibly realized by switching the adhesion/separation state between the gain and the destroyed waveguide structure and further be proposed to built dynamic optical barcodes and flexible information encryption system. The results may widely expand the application prospects of random lasers in the fields of optical data recording, dynamic security labels, smart sensing and flexible imaging.

We theoretically compare two kinds of spin-orbit interaction (SOI) systems in optics, one is that a light beam propagates along the optical axis in a uniaxial crystal, and the other is that it is normally reflected/refracted by a sharp interface. We find that the vortex phases generated by these processes are wavevector-dependent Pancharatnam-Berry phases originating from the topological nature of the beam itself, while the Pancharatnam-Berry phase in an inhomogeneous anisotropic medium (e.g., Q-plates) is coordinate-dependent resulting from the anisotropy of the external materials. We further discuss the SOI efficiency of these systems, and propose several ways to enhance them.

In practical applications, the linear to circular (LTC) polarization conversion of electromagnetic waves is of great significance. In this work, we designed a broadband high-efficiency reflective LTC polarization converter with temperature control in the visible range. Each periodic unit of the LTC polarization converter is composed of a gold mirror, a dielectric layer, a wide L-shaped gold plate and a narrow anti-L-shaped VO₂ strip. The results show that the conversion efficiency can reach 0.9 in the visible range, and the switch of polarization converter can be controlled by VO₂. The linear to circular polarization converter has potential applications in stealth technology, electromagnetic measurement.

High performance absorber is desirable for solar energy, photo detection and optical interconnects. Here an active tunable graphene metamaterials quad-band absorber is theoretically demonstrated. The designed absorber has four higher than 97% absorption peaks in terahertz and infrared range. This absorber consists of a graphene layer, a silica substrate and a metal reflective surface. Simulation demonstrates that absorbance peak can be adjusted by changing geometric parameters of the periodic array structure or the Fermi level of the graphene. Such devices may have potential application in active plasmonic sensor, Light detection, photo thermal conversion and optoelectronic devices.

Fundamental dynamic processes at the electronic contact interface, such as carrier injection and transport, become pivotal and significantly affect device performance. Time-resolved photoemission electron microscopy (TR-PEEM) with high spatiotemporal resolution provides unprecedented abilities of imaging the electron dynamics at the interface. Here, we implement TR-PEEM to investigate the electron dynamics at a coplanar metallic 1T′-MoTe2/semiconducting 2H-MoTe2 heterojunction. We find the non-equilibrium electrons in the 1 T′-MoTe2 possess higher energy than those in the 2H-MoTe2. The nonequilibrium photoelectrons collapse and relax to the lower energy levels in the order of picoseconds. The photoexcited electrons transfer from 1 T′-MoTe2 to 2H-MoTe2 with at a rate of ~0.8 × 1012 s−1 (as fast as 1.25 ps). These findings contribute to our understanding of the behavior of photoexcited electrons in heterojunctions and the design of in-plane optoelectronic devices.

Si-based photonic integrated circuit is developing rapidly and has been widely used, such as optical communication, optical neural network, lidar and so on. However, Si has strong optical nonlinear effects, which limits the maximum transmitting optical power. It needs numbers of semiconductor optical amplifiers to expand the scale of the photonic integrated circuit because of the limited input optical power, which increases the complexity and cost of the Si-based photonic integrated circuits. Therefore, with much lower the waveguide loss and optical nonlinear effects than Si, SiN waveguide is able to transmit higher optical power and has received a lot of research. In this paper, a grating coupler based on SiN-Si dual-layer structure is proposed. It is composed of a layer of Si grating above the SiN waveguide layer. In the case of coupling from grating coupler to single-mode fiber, the minimum coupling loss is about -1.07 dB at 1563.5 nm, and the 1 dB bandwidth is over 100 nm. As to coupling from single-mode fiber to grating coupler, the minimum coupling loss is about -2.53 dB at 1553.4 nm, and the 1 dB bandwidth is about 65 nm. With the proposed grating coupler, it is able to effectively reduce the coupling loss between the single-mode fiber and the chip, increase the working bandwidth, and achieve higher input power. It is very helpful to reduce the complexity and cost of Si-based photonic integrated circuits, because of the reduced requirements for the number of semiconductor optical amplifiers. This will be useful in Si-SiN hybrid integration and SiN-based photonic integrated circuits.

Optical metasurfaces are one of the most studied objects in the field of electromagnetism. However, designing optical metasurfaces to meet the desired transfer function is still very challenging. Genetic Algorithm (GA) is an optimization algorithm that simulates the process of inheritance and evolution of organisms in their natural environment. It’s able to perform crossover, mutation, evolution and other operations on many of these gene fragments and ultimately obtain the optimal genetic outcome. In this paper, the structural parameters are optimized by the transfer matrix method in combination with a genetic algorithm to achieve a nonlocal transfer function. As an example, we optimize the multilayer slabs to match the ideal second order differential transfer function and the simulation results confirm the computational capabilities of the device.

As novel planar structures, the metasurfaces exhibit the unprecedented capability to manipulate the amplitude, phase, and polarization of electromagnetic waves. Therefore, metasurface is designed to apply to metalens, holography, nanoprinting display, encryption, and so on. It is very interesting and meaningful work to integrate bifocal metalens and nanoprinting images into a single metasurface. A method is proposed to combine propagation phase and geometric phase, as well as Malus's law to realize the function of the bifocal metalens and clear nanoprinting display in the near field which can be observed at a certain polarization. This original design expands the functional integration of metasurface and improves applications in image displays, optical storage, augmented reality, virtual reality, and many other related fields.

Improving system resolution is an important aspect of developing complex sensors. The theory and method of improving the resolution of imaging system are introduced from the perspective of theory and technology. The high-resolution reconstruction method based on Fresnel field is studied. Then, the multi-resolution method and the computationally efficient algorithms are adopted. The simulation results show that the system can meet the application requirements of MTF and other related indicators.

Fano resonance with high Q-factor based on all-dielectric metasurface is of great significance for the design of optical refractive index sensor. Herein, we proposed an all-dielectric metasurface structure based on silicon, which is composed of two circular holes and one hexagonal hole. The substrate is silica. Two schemes are put forward to achieve asymmetry structure: changing the radius of a circular hole and changing the circular hole into an elliptical hole. Both schemes can generate quasi-BIC mode. The transmission spectrum is calculated by finite difference time domain (FDTD) simulation software, and the maximum Q-factor can exceed 24000. Finally, the extremely narrow linewidth of Fano resonance is utilized to design the optical refractive index sensors, yielding the sensitivity of 273nm / RIU and figure of merit (FOM) of 2730.

Plasmon-Induced Transparency (PIT) is extended from the classical electromagnetically induced transparency (EIT), which has been a hotspot in recent years because of its potential applications in optical integrated devices. In this letter, multiple Plasmon-Induced Transparency (PIT) effects are achieved by periodically arranged rectangular resonators (RRs). The proposed structure is composed of metal-dielectric-mental (MDM) waveguide with a connected stub cavity and coupled RRs. Two RRs with the same parameters are placed vertically and seen as a periodic unit. New PITs arise one by one as new RRs are etched continually. The interesting phenomenon can be applied in optical devices.

During the preparation of optical films, each interface of the film system will deviate from the ideal shape of the smooth surface, and micro-roughness optical surface formed by random fluctuation of film thickness. With the rapid development of thin-film/semiconductor chip micro-nano periodic structures, periodic units and defect sizes are gradually approaching the nano-level, the influence of the roughness of the optical surface on the overall performance of the system cannot be ignored. Based on the three dimensional FDTD/MRTD algorithm, the system studies the light field distribution characteristics of the surface of complex optical structures at the micro-nano scale. Numerically analyze the optical field characteristics of the film surface with a multilayer periodic structure, and obtain the key parameters that affect the optical field of the film surface by analyzing the changes of the structure parameters. In view of the special structure of the multilayer periodic structure film, the concept of roughness is introduced to analyze the surface field changes on the surface of the multilayer film when the roughness exists, discuss the influence of the change of roughness parameters on the light field distribution, and give the influence law a detailed physical explanation.

Microdisplays based on an array of micro-sized GaN-based light emitting diodes (μLEDs) are very promising for high brightness applications. As the size of Micro-LED decreases, the sidewall damage caused by plasma etching becomes an important factor in reducing the luminescence efficiency. Here, the photoluminescence, scanning electron microscope (SEM) and high‑resolution transmission electron microscopy (HR‑TEM) were combined to reveal physical defects on the sidewall surface, such as plasma-induced lattice disorder, the enrichment of impurity atoms such as oxygen, and the destruction of the exposed part of the quantum well during etching. The structure of the 20 um mesa after inductively coupled plasma (ICP) dry etching was characterized optically, and the luminescence intensity begins to decrease gradually at 5 um from the sidewall, which was caused by the surface non-radiative recombination. Finally, through the combination of tetramethylammonium hydroxide (TMAH) treatment and SiO2 passivation, the sidewall passivation process is optimized, and the luminous efficiency of Micro-LED edge is effectively improved 4.5 times. These results have reference significance for reducing sidewall defects to improve Micro-LEDs luminescence efficiency in the future.

Integration of photon number resolving superconducting nanowire single-photon detectors (PNR-SNSPDs) with nanophotonic waveguides is a key technology that enables a broad range of quantum technologies on chip-scale platforms. However, all on-chip integrated SNSPDs are fabricated above the waveguide layer, which makes the characteristics of the detector’s photoresponsive film material only depend on the waveguide material, thus lowering the waveguide selectivity. Here, we report an on-chip integrated SNSPD based on optimized topology that the nanowire is sandwiched between the waveguide and the substrate. This device maintains the film characteristics with different waveguides and the light transmitted from the upper waveguide to the substrate is absorbed by the film, which not only increases the selectivity of the waveguide, but also improves light absorption of SNSPD. As an example, SiO2 waveguide with the lower optical transmission loss was fabricated in an integrated PNR-SNSPD. We proposed a multi-channel photon response amplitude superposition multiplexing scheme, which realized photon detection by integrating SNSPD on the optical transmission waveguide in the photonic integrated circuit. The solution not only can effectively read the photon responses of multiple SNSPDs through a readout port, but also can distinguish the number of photons and the corresponding response channels through the amplitude of the readout circuit, thereby realizing a photonic integrated circuit with multiple modes. Finally, we prepared a 4-channel integrated PNR-SNSPD, which resolved the number of photons and corresponding photon response positions through 16 different signal amplitudes. This result is compatible of a wide range of waveguide materials, overcoming the limitation of single photon detector integrated on waveguide for quantum photonic integrated circuit.

Organic non-linear waveguides based on 4-N,N-Dimethylamino-4’-N’-methyl-stilbazolium tosylate (DAST) were directly grown by a cooling soft template method. Results revealed that as-yielded DAST hydrate waveguides (HWs) exhibit excellent waveguide performance, exciton polariton, and fluorescence properties, which can be rationally controlled by the annealing temperature. The red shift fluorescence excitation and emission spectra in the annealed DAST HWs are attributed to the recrystallization and J-aggregation of the chromophore cations in a head-to-tail stacking mode, which increase the charge transfer efficiency from one chromophore to another. Particularly, the fluorescence can propagate along the DAST HWs axis due to the produced exciton polaritons. Moreover, the annealed DAST HWs exhibit strong second harmonic generation (SHG) intensity, but no SHG activity was observed in DAST HWs. These findings further extend the applications of DAST HWs into a wide range of fields, such as integrated optical modulation, micro lasers, and fluorescent

Resolution is one of the key performances of the lithography tool. Decreasing the exposure wavelength and increasing the numerical aperture (NA) of the objective lens can enhance the lithography tool resolution. Therefore, the exposure wavelength is reduced to deep ultraviolet (DUV), and a polarized illumination is adopted. The polarization effect of the exposure system seriously affects the imaging quality. The polarization parameters must be measured accurately. Due to the grating polarizer's compactness and wide acceptance angle, it is introduced to the polarization measurement. It could simplify the measurement system and achieve high-accuracy real-time measurement. A bilayer metallic grating polarizer with tapered slits is designed based on the inverse polarizing effect and transmission enhancement effect of TE-polarized light. The physical mechanism of transmission enhancement on TE-polarized light and transmission suppression on TM polarized light have been analyzed. The simulation results show that the enhancement of TE-polarized light transmission and the extinction ratio is mainly modulated by the middle dielectric layer height and the metal width and height of the top layer grating. For the designed grating polarizer with tapered slits, the transmission of TE-polarized light is 59.4%, and the extinction ratio is 75dB at normal incidence. Compared with the previous bilayer metal grating polarizer, both the TE transmission and extinction ratio are enhanced simultaneously. The designed grating polarizer can meet the performance requirements of the polarization measurement device in immersion lithography tools within a large process tolerance range.

We designed ab all-dielectric device based on permittivity-asymmetric rectangular holes, yielding multiple Fano resonances with high Q-factor in the near-infrared regime. there is a newly-generated sharp Fano peak with arising from the interference between sub-radiant modes and the electric and magnetic dipole resonance modes. Combining the multipole decomposition based on cartesian system and the field distribution, the resonance modes are analyzed to be toroidal dipole (TD) and magnetic dipole (MD). Furthermore, the dependence on materials and geometric parameters has been studied and the maximal quality (Q)-factor reaches 28503. This structure may be used for optical switching, nonlinear optical devices, and laser

An all-dielectric metasurface structure, composed of triple silicon strip arrayed on silica substrate, is proposed in this letter. Simulation results show that multiple Fano resonances arise in the transmission spectrum, performing high-quality (Q)- factor and nearly 100% modulation depth. The highest Q-factor of ~2000. In addition, the Cartesian multipole decomposition technique (CMDT) is adopted to verify the excitation mode of the Fano resonances. The sensing performances of the proposed structure are investigated as well, yielding the refractive index sensitivity (S) of ~ 350 nm/RIU and maximum figure of merit (FOM) of ~ 56.7 RIU^-1 . It is believed that the designed structure can provide some inspirations for the applications in nonlinear optics, optical modulations, lasing and biochemical sensing.

Research on mid-IR silicon-based waveguides has recently received strong interest. This paper focuses on optical integration between a broadband LED mid-infrared light source and micro-scale optical waveguide. The optical coupling scheme is crucial for the exploitation of LED light sources in waveguide-based spectroscopic sensing applications. Optical simulations based on Eigen Mode Expansion (EME) and FDTD methods is used to obtain approximate and optimized parameters. The sensitivity of the optical sensors will be evaluated with respected to the required optical power at the optical sources. The ability to efficiently couple light from a LED light source into a micron-scale waveguide could be beneficial for a wide range of application that is cost-sensitive.