Finite-difference Time-domain Research Articles

Design of an on-chip germanium cavity for room-temperature infrared lasing

Germanium (Ge) is one of the most promising material platforms to enable the realization of monolithically integrated laser on silicon because it is a group-IV material with a pseudo-direct-band structure that can be converted into direct-bandgap either through the application of tensile strain or via the tin (Sn) incorporation in Ge. The bandgap modification enhances the light emission efficiency of Ge, where lasing can also be observed if a suitable cavity preserving the strain can be realized. In fact, several different research groups have reported lasing from strained Ge and GeSn optical cavities, however they all report lasing at low temperatures and room-temperature lasing, which is the ultimate goal required for a fully integrated laser, has not been demonstrated yet. In this work, we design an on-chip germanium cavity that has all the ingredients combined to make the room-temperature lasing possible. The design includes a 4.6% uniaxially tensile strained Ge gain medium embedded in a Fabry-Perot like cavity composed of two distributed Bragg reflectors. 3-dimensional (3D) Finite Element Method (FEM) based strain simulations together with a proposed fabrication methodology provides a guideline for the realization of the structure. Furthermore, 3D Finite Difference Time Domain (FDTD) simulations demonstrate that the designed structure is suitable for the room-temperature lasing in a wavelength range of 2410–2570 nm. 3D FEM-based heat transfer simulations performed for the designed cavity verifies the eligibility of the room-temperature operation paving the way for a possible demonstration of on-chip laser that could take part in the fully integrated infrared systems for a variety of applications including biological and chemical sensing, as well as security such as alarm systems and free-space optical communications.

STAR-FDTD: space-time modulated acousto-optic guidestar in disordered media

Abstract We developed a 2D Finite-difference time-domain (FDTD) method for modeling a space-time modulated guidestar targeting wavefront shaping applications in disordered media. Space-time modulation in general (a particular example being the acousto-optic effect) is used here as a guidestar for the transverse confinement of light around the tagged region surrounded by disorder. Together with the guidestar, the iterative optical phase conjugation (IOPC) method is used to overcome the diffusion of light due to multiple scattering. A phase sensitive lock-in detection technique is utilized to estimate the steady-state amplitude and phase of the modulated wavefronts emerging from the guidestar region continuously operating in the Raman-Nath regime. As the IOPC scheme naturally converges to the maximally transmitting eigenchannel profile, one could use the position of the guidestar within the disorder to channelize the maximal transmission through the tagged region. The associated code developed in MATLAB® is provided as an open source (The MIT License) package. The code package is referred by the acronym STAR-FDTD where STAR stands for Space-Time modulated Acousto-optic guidestaR.

Spontaneous Photonic Jammed Packing of Core-Shell Colloids in Conductive Aqueous Inks for Non-Iridescent Structural Coloration.

Integrating structural colors and conductivity into aqueous inks has the potential to revolutionize wearable electronics, providing flexibility, sustainability, and artistic appeal to electronic components. This study aims to introduce bioinspired color engineering to conductive aqueous inks. Our self-assembly approach involves mixing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with sulfonic acid-modified polystyrene (sPS) colloids to generate non-iridescent structural colors in the inks. This spontaneous structural coloration occurs because PEDOT:PSS and sPS colloids can self-assemble into core-shell structures and reversibly cluster into photonic aggregates of maximally random jammed packing within the aqueous environment, as demonstrated by small-angle X-ray scattering. Dissipative particle dynamics simulation confirms that the self-assembly aggregation of PEDOT:PSS chains and sPS colloids can be manipulated by the polymer-colloid interactions. Utilizing the finite-difference time-domain method, we demonstrate that the photonic aggregates of the core-shell colloids achieve close to maximum jammed packing, making them suitable for producing vivid structural colors. These versatile conductive inks offer adjustable color saturation and conductivity, with conductivity levels reaching 36 S cm-1 through the addition of polyethylene glycol oligomer, while enhanced water resistance and mechanical stability are achieved by doping with a cross-linker, poly(ethylene glycol) diglycidyl ether. With these unique features, the inks can create flexible, patterned circuits through processes like coating, writing, and dyeing on large areas, providing eco-friendly, visually appealing colors for customizable, stylish, comfortable, and wearable electronic devices.

Influence of beam polarization on underwater femtosecond laser machining of silicon wafer

This paper investigates the effect of polarization directions on underwater femtosecond laser machining of silicon wafer. Firstly, laser ablation in liquids produces laser-induced periodic surface structures (LIPSS) on both edges of the groove. The direction of LIPSS has direct correlation with the polarization of the laser beam. Secondly, the electric field intensity distribution within the groove is analyzed by numerical simulation employing the finite-difference-time-domain (FDTD) method. The simulation and experimental results reveal that the distribution of the inter electric field intensity within the grooves varies with polarization direction. As the angle between the polarization and scanning directions decreases, the peak electric field strength and groove depth gradually increase. Finally, changing the direction of polarization of the beam affects the symmetry of the groove profile. The groove profile produced by ablation is symmetrical when the beam polarization direction is parallel to the scanning direction. By modulating and optimizing the direction of polarization, grooves with large depth and symmetrical shape can be obtained.

Tunable electrical/thermal output performance of the PV/T system with magnetic nanofluid based spectral beam filter

The photovoltaic/thermal systems with magnetic nanofluid based spectral beam filter would achieve thermal decoupling and utilize the full spectrum to minimize energy loss. The prepared Fe3O4 magnetic nanofluid was introduced into this system as selective absorbing fluid filter. An external magnetic field was added to manipulate the distribution behavior of nanoparticles that affect the optical characteristics of magnetic nanofluids could meet the various application requirements for electrical/thermal output of the photovoltaic/thermal system. The optical properties of magnetic nanofluid with various nanoparticle distribution behaviors under the varying magnetic field were tested by UV–visible spectrophotometric and Finite-Difference Time-Domain simulated respectively. Furthermore, the effect of magnetic nanoparticle concentration and magnetic field strength on the electrical/thermal output performance of the photovoltaic/thermal system was studied. The results show the higher nanoparticle concentration enhances the thermal output of the system but reduces the electrical output, accompanied by a significant reduction in the surface temperature of the cell. Both photothermal and photovoltaic conversion efficiencies are increased below 100mT magnetic field due to the transmission in the response spectrum of monocrystalline silicon cell increase under the formation of chain structure of the nanoparticles. It is concluded that the photothermal, photovoltaic, and total solar energy conversion efficiencies are respectively 59.82%, 13.98%, and 73.75% at 0.0025 wt% concentration under 100 mT magnetic fields, and its function of merit value was increased by 109% compared to the system without spectral beam filter.

Realization of all-optical logic gates using MIM waveguides and a rectangular ring resonator

In this study, all-optical OR, exclusive OR (XOR), NOR, XNOR, AND, NAND, and NOT logic gates using metal-insulator-metal (MIM) waveguides with a rectangular ring resonator are designed and analyzed. The structure has a silver plate with three input waveguides, one output waveguide, and a rectangular ring resonator. One of the input ports is used as a control port. The finite-difference time-domain (FDTD) method is utilized to obtain the optical spectrum of the proposed structures. To realize all-optical logic gate properties of the designed structures, optical signals with the same phase or different phases are passed through the waveguides. Transmission spectrum (T), contrast ratio (CR), and modulation depth (MD) parameters are obtained to determine the performances of all-optical logic gates. To determine the logic 1 (ON) and logic 0 (OFF) states of the output ports, the threshold transmission value is accepted as 0.23 for all-optical logic gates. For the proposed designs, the highest transmission, contrast ratio, and modulation depth values are 217%, 6.75 dB, and 100%, respectively. The structure also supports a data rate of 24 Tb/s. The designed optical logic gates have valuable features for developing high-performance optical devices.

Hot Electrons Induced by Localized Surface Plasmon Resonance in Ag/g-C3N4 Schottky Junction for Photothermal Catalytic CO2 Reduction.

Converting carbon dioxide (CO2) into high-value-added chemicals using solar energy is a promising approach to reducing carbon dioxide emissions; however, single photocatalysts suffer from quick the recombination of photogenerated electron-hole pairs and poor photoredox ability. Herein, silver (Ag) nanoparticles featuring with localized surface plasmon resonance (LSPR) are combined with g-C3N4 to form a Schottky junction for photothermal catalytic CO2 reduction. The Ag/g-C3N4 exhibits higher photocatalytic CO2 reduction activity under UV-vis light; the CH4 and CO evolution rates are 10.44 and 88.79 µmol·h-1·g-1, respectively. Enhanced photocatalytic CO2 reduction performances are attributed to efficient hot electron transfer in the Ag/g-C3N4 Schottky junction. LSPR-induced hot electrons from Ag nanoparticles improve the local reaction temperature and promote the separation and transfer of photogenerated electron-hole pairs. The charge carrier transfer route was investigated by in situ irradiated X-ray photoelectron spectroscopy (XPS). The three-dimensional finite-difference time-domain (3D-FDTD) method verified the strong electromagnetic field at the interface between Ag and g-C3N4. The photothermal catalytic CO2 reduction pathway of Ag/g-C3N4 was investigated using in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS). This study examines hot electron transfer in the Ag/g-C3N4 Schottky junction and provides a feasible way to design a plasmonic metal/polymer semiconductor Schottky junction for photothermal catalytic CO2 reduction.

Germanium metasurface near-infrared high-q absorber with symmetry-protected bound states in the continuum

The all-dielectric germanium nanohole (GNH) metasurface with a sub-wavelength thickness supports simultaneous excitation of quasi bound state in the continuum (BIC) and super radiant mode. By selecting the different hole depths in a germanium slab, we present a trade-off metasurface between high Q-factor and high absorption in the photonic system. The presented device demonstrated absorption of super-radiant mode ∼98.5% and quasi-BIC ∼93% without back-metal reflector at the telecommunication wavelength. The numerical results, obtained by the finite difference time domain (FDTD) method are explained in the framework of temporal coupled mode theory (TCMT).

VO2-Based Spacecraft Smart Radiator with High Emissivity Tunability and Protective Layer.

In the extreme space environment, spacecraft endure dramatic temperature variations that can impair their functionality. A VO2-based smart radiator device (SRD) offers an effective solution by adaptively adjusting its radiative properties. However, current research on VO2-based thermochromic films mainly focuses on optimizing the emissivity tunability (Δε) of single-cycle sandwich structures. Although multi-cycle structures have shown increased Δε compared to single-cycle sandwich structures, there have been few systematic studies to find the optimal cycle structure. This paper theoretically discusses the influence of material properties and cyclic structure on SRD performance using Finite-Difference Time-Domain (FDTD) software, which is a rigorous and powerful tool for modeling nano-scale optical devices. An optimal structural model with maximum emissivity tunability is proposed. The BaF2 obtained through optimization is used as the dielectric material to further optimize the cyclic resonator. The results indicate that the tunability of emissivity can reach as high as 0.7917 when the BaF2/VO2 structure is arranged in three periods. Furthermore, to ensure a longer lifespan for SRD under harsh space conditions, the effects of HfO2 and TiO2 protective layers on the optical performance of composite films are investigated. The results show that when TiO2 is used as the protective layer with a thickness of 0.1 µm, the maximum emissivity tunability reaches 0.7932. Finally, electric field analysis is conducted to prove that the physical mechanism of the smart radiator device is the combination of stacked Fabry-Perot resonance and multiple solar reflections. This work not only validates the effectiveness of the proposed structure in enhancing spacecraft thermal control performance but also provides theoretical guidance for the design and optimization of SRDs for space applications.

Pearcey Talbot-like plasmon: a plasmonic bottle array generation scheme.

In this Letter, a surface wave, the Pearcey Talbot-like plasmon, which has the properties of self-imaging and multiple autofocusing, is presented as a novel, to the best of our knowledge, plasmonic bottle array generation scheme. With originality, the overall structure and the partial intensity of the plasmonic bottle array can be adjusted through the initial input, and modifying the Pearcey function enables the plasmonic bottle array to exhibit self-bending characteristics, which makes particle capture and manipulation easier and more flexible. A scheme to generate the plasmon is proposed, and we prove it by the finite-difference time-domain numerical simulations.

Liquid microlens compound structure for enhanced sub-micron resolution imaging and accelerated reconfigurable deformation manipulation

The optical observation of sub-micron structures encounters significant challenges due to the inadequate spatial shape matching of optical devices and the limitations imposed by diffraction. These factors result in suboptimal imaging resolution and the introduction of defocus distortion. One approach to mitigating these limitations involves utilizing a liquid microlens (LML) assisted microscope, which offers real-time and localized control capabilities. However, the dynamic tuning of LML is subject to volatility and instability, adversely affecting sub-micron resolution imaging. To address this issue, a contour-following coating inspired by the natural cornea is applied to the droplet's surface, resulting in the formation of liquid microlens compound structures (LMLCS). Firstly, photoresist microholes are fabricated on the optical disc. Then, liquid self-assembly technology is used to fill glycerol in the microholes. At last, a conformal spreading method of UV-curable adhesive precursor film is developed to ensure the combination of the microlens bilayer structure. Through the application of optical information transmission theory, finite difference time domain (FDTD) method, and the principle of Abbe microscopic imaging, the imaging magnification process and sub-micron resolution characteristic of the LMLCS are revealed. Remarkably, the obtained focal width at half maximum (FWHM) of 1.54 μm is smaller than the theoretical value, enabling reconfigurable sub-micron resolution observation and 1.63 times imaging magnification of 226 nm grating lines under the optical microscope. Compared with unencapsulated LML, this compound structure exhibits better sub-micron resolution capability, greater imaging magnification, and faster adaptive dynamic response characteristics. Consequently, the LMLCS introduces exciting prospects for exploring optical sub-micron measurement and sensing devices with exceptional performance.

Quantum Interference at the Recombination Junction of Perovskite-Si Tandem Solar Cells Improves Efficiency.

We show quantum interference effects can enhance coherent electron transmission in perovskite tandem solar cells using ultrathin indium tin oxide (ITO) layers. We develop a model for the behavior of the power conversion efficiency based on a finite difference time domain solution of the time-dependent Schrödinger equation. The modeled potential includes an imaginary part to simulate probability loss by incoherent scattering. The results agree with observations of efficiency as a function of ITO thickness, suggesting an optimized design.

Plasmon-mediated photocatalytic conversion in Au or Ag nanorod aggregates by surface-enhanced Raman spectroscopy

Plasmonic nanoparticles (NPs) hold considerable potential as photocatalysts owing to their robust light–matter interactions across diverse electromagnetic wavelengths, which significantly influence the photophysical characteristics of the adjacent molecular entities. Despite the widespread use of noble-metal NPs in surface-enhanced Raman scattering (SERS) applications, little is known about the kinetics of nanoparticle aggregation and how it affects their configurations. This study investigates the plasmon-driven photochemical conversion of 4-nitrobenzenethiol (NBT) to 4,4′-dimercaptoazobenzene (DMAB) on Au and Ag nanorods (NRs) through SERS. Significantly, photoconversion phenomena were observed on Ag NRs but not on Au NRs upon laser excitation at 633 nm. Finite-difference time-domain simulations revealed the presence of stronger electromagnetic fields on Ag NRs than on Au NRs. The aspect ratios and gaps between individual NPs in dimer configurations were determined to elucidate their effects on electromagnetic fields. The Ag NR dimer with an end-to-end configuration, an aspect ratio of 3.3, and a 1-nm gap exhibited the highest enhancement factor of 1.05 × 1012. Our results demonstrate that the primary contribution from diverse configurations in NR aggregates is the end-to-end configuration. The proposed NP design with adjustable parameters is expected to advance research in plasmonics, sensing, and wireless communications. These findings also contribute to the understanding of plasmon-driven photochemical processes in metallic nanostructures.

Chiral 3D structures through multi-dimensional transfer printing of multilayer quantum dot patterns

Three-dimensional optical nanostructures have garnered significant interest in photonics due to their extraordinary capabilities to manipulate the amplitude, phase, and polarization states of light. However, achieving complex three-dimensional optical nanostructures with bottom-up fabrication has remained challenging, despite its nanoscale precision and cost-effectiveness, mainly due to inherent limitations in structural controllability. Here, we report the optical characteristics of intricate two- and three-dimensional nanoarchitectures made of colloidal quantum dots fabricated with multi-dimensional transfer printing. Our customizable fabrication platform, directed by tailored interface polarity, enables flexible geometric control over a variety of one-, two-, and three-dimensional quantum dot architectures, achieving tunable and advanced optical features. For example, we demonstrate a two-dimensional quantum dot nanomesh with tuned subwavelength square perforations designed by finite-difference time-domain calculations, achieving an 8-fold enhanced photoluminescence due to the maximized optical resonance. Furthermore, a three-dimensional quantum dot chiral structure is also created via asymmetric stacking of one-dimensional quantum dot layers, realizing a pronounced circular dichroism intensity exceeding 20°.

Electromagnetic tomography measuring bench for estimating the density of materials

In the laboratory, the density of pavement cores (cylindrical samples of hot mix asphalt (HMA) material taken from roads) is assessed using an electromagnetic (EM) bench consisting of two ultra-wideband (UWB) Vivaldi antennas and a vector network analyser (VNA). The main objective is to replace the nuclear gauge system currently used in the laboratory as the standard method for this purpose. Firstly, specific antipodal Vivaldi antennas have been adapted from the literature. Their dimensions are 7 × 7 cm with a bandwidth [1.5–15 GHz]. Secondly, a tomographic approach is compared with an analytical solution and a Finite-Difference Time Domain (FDTD) simulation, based on a time-domain estimation of the dielectric under test (DUT) with a single transmitter/receiver configuration. A laboratory validation is presented and the adapted antennas as well as the time domain approach show acceptable results for assessing the dielectric constant on known materials. Finally, to show that the proposed EM bench is a promising non-ionizing solution, the density or equivalent compactness of HMA cylindrical samples is estimated and compared with nuclear gauge results.

Ultrasensitive detection of contaminants in milk using a novel NMS-Ag modified water-resistant paper substrate

Rapid and precise detection of harmful substances in food products is essential for ensuring public health and safety. This study introduces a novel surface-enhanced Raman spectroscopy (SERS) substrate, composed of a molybdenum disulfide‑silver nanocomposite, applied to flexible, water-resistant filter paper for detecting melamine and bisphenol A (BPA) in milk. Optimized molybdenum disulfide (NMS) nanoflowers (NFs) were synthesized through hydrothermal methods and high-temperature annealing, then modified with silver (Ag) nanoparticles to form the NMS-Ag nanocomposite (NMSA6). This substrate greatly enhances the Raman signal, achieving an enhancement factor of approximately 1.49 × 107 and a detection limit as low as 10−11 M for simultaneous multi-component analysis. Finite-difference time-domain (FDTD) simulations confirm the enhancement mechanism. The NMSA6 substrate demonstrates remarkably low detection limits for BPA and melamine, facilitating the analysis of various hazardous substances. These findings highlight the substrate's potential for highly sensitive, label-free detection, presenting a viable tool for food safety monitoring.

Impact of Graphene Oxide on SERS Enhancement of Arylated Gold Nanospheres: Mechanistic Insight.

The performance of gold nanospheres as substrates for surface-enhanced Raman spectroscopy (SERS) investigation has been compromised by their low adsorption efficiency, high colloidal dispersibility, and diminishing hot spots. However, gold nanosphere substrates modified using aryldiazonium gold(III) chemistry via durable gold-carbon bonds are promising for SERS enhancement due to their controlled organic layer density. In this study, arylated gold nanospheres AuNSs-COOH have shown SERS enhancement when incorporated into graphene oxide (GO) to form nanocomposites (NCs) labeled AuNSs-COOH/GO (AuNCs). Our investigation using X-ray photoelectron spectroscopy (XPS) surface analysis showed that the gold-aryl nanospheres reached their maximum SERS enhancement with an optimal coating. The evaluation included the Au 4f chemical environment and compact graphitic layers for the SERS substrate optimization. The fabricated AuNC substrates demonstrated superior efficiency and reproducibility. A broad linear range of 10-3-10-7 M 4-nitrophenol detection was obtained with exceptional repeatability, as evidenced by the relative standard deviation (RSD) of 9.32%. A detailed investigation of the energy profiles, particularly the valence band maximum (VBM) and band gap values of the substrate and analyte, depicted the electromagnetic (EM) and charge-transfer-induced enhancement and the role of GO inclusion in substrate efficiency in SERS enhancement mechanisms. The finite-difference time domain (FDTD) simulation results revealed that AuNCs incorporated with graphitic nanostructures exhibited the most substantial SERS effect through an EM field enhancement mechanism. This study demonstrated significant SERS enhancement using gold-aryl nanospheres when modified with GO, in contrast to the typical reliance on anisotropic nanostructures.

(Invited) Quantitative Photonic Characterization and Modelling of Light Emission, Confinement, and Enhancement in Nanostructured Materials

Optical spectroscopy and imaging provide non-destructive, contactless, and fast strategies to study the nature and technological aspects of thin films and nanostructured materials for photonic and optoelectronic applications. Furthermore, the design, engineering, and optimization of such devices requires quantitative information with high-precision standards in measuring and modelling as is the case, for example, in the determination of the optical critical dimension (OCD) in the semiconductor industry. Our application of these strategies to the study of tunable self-assembled nanolasers, hybrid photonic-plasmonic sensors, and photovoltaic devices, among many other materials and devices has led us to the development of i) new modelling strategies based on the Finite-Difference Time-Domain (FDTD) method, and ii) home-made customizable characterization strategies based on spectroscopic ellipsometry (SE). The advantages of the FDTD method include its ability to i) obtain a wide spectral response from one time-domain simulation, ii) model single non-periodic structures, and iii) flexibility and generality to include, for example, non-linear and thermal effects. On its part, SE stands out from other optical techniques because, as a self-referenced and phase sensitive strategy, it can deliver extreme precision and sensitivity and has demonstrated flexibility that has been implemented in multiple spectral ranges and operation conditions. With this in mind, our group has systematically demonstrated the synergic use of FDTD-SE strategy, with complementary strengths and close-matched precision, in a range of materials and devices. We will report the fundamentals, status of our on-going efforts, and a critical review of the perceived limitations and expected outcomes of the FDTD-SE strategy as a quantitative tool for photonic and plasmonic subwavelength structures of interest in optoelectronic, sensing, and energy applications.We gratefully acknowledge the financial support from the RGC (Projects CityU - 11210218, 11219919, 11215121 and 11310122) and ITC (Project ITS/461/18) of HKSAR, China.

Bioinspired Diffuse Reflectance Coatings for Fabric-Based Radiative Coolers

As global temperatures rise due to anthropogenic climate change, thermal comfort becomes an increasingly critical area of research. While most buildings are equipped to cool and heat their interiors, this process is very energy intensive; a smarter approach is to enable personal thermal management using clothing and textiles. In particular, we are interested in the ability to use textiles and clothing to cool bodies in extreme heat, both to maintain comfort and prevent deaths in urban deserts due to heat stroke. One innovative category in this realm is radiative coolers—surfaces adept at manipulating light to passively regulate temperature. These coolers achieve sub-ambient surface temperatures by selectively reflecting or refracting sunlight wavelengths (200nm-2.5µm) while emitting infrared light (8-13µm). This unique capability allows them to maintain cooler temperatures, even when exposed to direct sunlight and the open sky. Coatings facilitating this cooling action typically consist of a porous media filled with refractive gaps, requiring specific substrates and custom production processes, thereby limiting their applications. Furthermore, the necessity of low light transmission presents issues in creating fabrics that radiatively cool while still retaining high breathability and durability. In this study we present a method whereby an optically active coating comprised of a mixture of CaCO3 and BaSO4 microcrystals was applied to multiple fabric substrates to create a radiative cooler. Through the use of photoinitiated chemical vapor deposition (pICVD), a 5 µm thick layer of a hydrophilic polymer polyhydroxyethyleneacrylate (pHEA) was deposited on the fabric substrate. Subsequently, through serial immersion in solutions containing Ca and Ba ions and solutions containing CO3 and SO4 ions, inorganic microcrystals were grown directly on the surface of the fabric. These microcrystals formed with a large polydispersity, endowing the coating with excellent reflective properties in the solar spectrum. Mie scattering calculations confirmed that the CaCO3 and BaSO4 microcrystals were primarily responsible for scattering. Further simulations using finite difference time domain software revealed, surprisingly, that surface-immobilized crystals provided the highest reflection efficiency, indicating that composite fibers with embedded particles are not as efficient. Upon outdoor testing, the device showed a cooling ability of 8°C compared to an uncoated fabric, achieving a maximum cooling of 4°C below ambient temperature. Washing and durability testing of the coating found no degradation in the material's performance, affirming its resilience and long-term effectiveness.

Simulation of a SiN 2 × 2 adiabatic 3-dB coupler for 800-nm to 1000-nm wavelength range

We conducted numerical simulations on a 2×2 adiabatic 3-dB coupler tailored for the 800-nm to 1000-nm range, operating on a silicon-nitride (SiN) platform. Through the finite difference time domain method, we achieved a power splitting ratio close to 3 dB with a tight tolerance of ±0.27dB and an insertion loss below 0.19 dB across the wavelength range of 800 nm to 1000 nm. Additionally, we simulated a 2×2 switch utilizing two 2×2 adiabatic 3-dB couplers, revealing a theoretical extinction loss of approximately −14dB, particularly prominent around 900 nm.