Low Absorption Loss Research Articles

Effect of Various Plasticizers in Different Concentrations on Physical, Thermal, Mechanical, and Structural Properties of Wheat Starch-Based Films

Biocomposite materials are essential for environmental protection, as they have the ability of substituting synthetic plastic with natural materials. This work investigated how different plasticizers (Glycerol (G), Fructose (F), Sorbitol (S), and Urea (U)) affect the morphological, mechanical, thermal, and physical characteristics of films made of wheat starch at various concentrations (0%, 15%, 25%, and 35%). Plasticizers were added to improve the flexibility and homogeneity of the wheat starch-based bioplastic. Control film exhibited high tensile strength (38.7 MPa) with low elongation (1.9%). However, films plasticized with 35% sorbitol showed the highest elongation, which was 60.7% at break. At 35% of all plasticizers, fructose showed the highest tensile strength, with 7.6 MPa. The addition of different plasticizers shows improvement in water resistance; films plasticized with glycerol had the lowest water absorption at 35% fructose (187.4%) and also showed coherent surfaces. Glycerol, sorbitol, and urea films showed a higher mass loss compared to fructose films. Fructose showed the highest performance after the analysis of the results, with low water absorption, water content, and mass loss and with high mechanical performance at 35% of fructose. SEM images show that the addition of fructose and glycerol improves the surface homogenate, while sorbitol and urea have a less compact structure with large pores.

Single-mode quantum non-Gaussian light from warm atoms

The distributed quantum information processing and hybridization of quantum platforms raises increasing demands on the quality of light-matter interaction and realization of efficient quantum interfaces. This becomes particularly challenging for needed states possessing fundamental quantum non-Gaussian (QNG) aspects. They correspond to paramount resources in most potent applications of quantum technologies. We demonstrate the generation of light with provably QNG features from a warm atomic ensemble in a single-mode regime. The light is generated in a spontaneous four-wave mixing process in the presence of decoherence effects caused by a large atomic thermal motion. Despite its high sensitivity to any excess noise, direct observability of heralded QNG light could be achieved due to a combination of a fast resonant excitation, large spectral bandwidth, and a low absorption loss of resonant photons guaranteed by the source geometry.

Quasi-monocrystalline silicon for low-noise end mirrors in cryogenic gravitational-wave detectors

Mirrors made of silicon have been proposed for use in future cryogenic gravitational-wave detectors, which will be significantly more sensitive than current room-temperature detectors. These mirrors are planned to have diameters of $\ensuremath{\approx}50$ cm and a mass of $\ensuremath{\approx}200$ kg. While single-crystalline float-zone silicon meets the requirements of low optical absorption and low mechanical loss, the production of this type of material is restricted to sizes much smaller than required. Here we present studies of silicon produced by directional solidification. This material can be grown as quasi-monocrystalline ingots in sizes larger than currently required. We present measurements of a low room-temperature and cryogenic mechanical loss comparable with float-zone silicon. While the optical absorption of our test sample is significantly higher than required, the low mechanical loss motivates research into further absorption reduction in the future. While it is unclear if material pure enough for the transmissive detector input mirrors can be achieved, an absorption level suitable for the highly reflective coated end mirrors seems realistic. Together with the potential to produce samples much larger than $\ensuremath{\approx}50$ cm, this material may be of great benefit for realizing silicon-based gravitational-wave detectors.

Open-Air Microwave Entanglement Distribution for Quantum Teleportation

Microwave technology plays a central role in current wireless communications, standing among them mobile communication and local area networks (LANs). The microwave range shows relevant advantages with respect to other frequencies in open-air transmission, such as low absorption losses and low energy consumption, and it is additionally the natural working frequency in superconducting quantum technologies. Entanglement distribution between separate parties is at the core of secure quantum communications. Therefore, understanding its limitations in realistic open-air settings, specially in the rather unexplored microwave regime, is crucial for transforming microwave quantum communications into a mainstream technology. Here, we investigate the feasibility of an open-air entanglement distribution scheme with microwave two-mode squeezed states. First, we study the reach of direct entanglement transmission in open-air, obtaining a maximum distance of approximately 500 meters in a realistic setting with state-of-the-art experimental parameters. Afterwards, we adapt entanglement distillation and entanglement swapping protocols to microwave technology in order to reduce environmental entanglement degradation. While entanglement distillation helps to increase quantum correlations in the short-distance low-squeezing regime by up to $46\%$, entanglement swapping increases the reach by $14\%$. Then, we compute the fidelity of a continuous-variable quantum teleportation protocol using open-air-distributed entanglement as a resource. Finally, we adapt the machinery to explore the limitations of quantum communication between satellites, where the thermal noise impact is substantially reduced and diffraction losses are dominant.

A Transparent Electrode Based on Solution-Processed ZnO for Organic Optoelectronic Devices

Achieving high-efficiency indium tin oxide (ITO)-free organic optoelectronic devices requires the development of high-conductivity and high-transparency materials for being used as the front electrode. Herein, sol-gel-grown zinc oxide (ZnO) films with high conductivity (460 S cm−1) and low optical absorption losses in both visible and near-infrared (NIR) spectral regions are realized utilizing the persistent photoinduced doping effect. The origin of the increased conductivity after photo-doping is ascribed to selective trapping of photogenerated holes by oxygen vacancies at the surface of the ZnO film. Then, the conductivity of the sol-gel-grown ZnO is further increased by stacking the ZnO using a newly developed sequential deposition strategy. Finally, the stacked ZnO is used as the cathode to construct ITO-free organic solar cells, photodetectors, and light emitting diodes: The devices based on ZnO outperform those based on ITO, owing to the reduced surface recombination losses at the cathode/active layer interface, and the reduced parasitic absorption losses in the electrodes of the ZnO based devices.

Simulated Performance of Laser-Machined Metamaterial Anti-reflection Coatings

Lenslet-coupled antenna arrays have been used in CMB experiments and are the baseline technology for the next-generation satellite missions such as LiteBIRD and PICO. Lenslets are small hemispherical lenses mounted on the focal plane that couple light to the detectors and are typically made of silicon or alumina due to their high focusing power and low absorption loss. To minimize reflection at the vacuum-dielectric interface, lenslets require anti-reflection (AR) coatings. Metamaterials have been used in large microwave optical components because they avoid any mismatch on the thermal expansion between the lens and its coating, but so far they have only been machined on surfaces of comparatively large radius of curvature. As a first step to understand the feasibility of machining metamaterial AR layers in lenslets through laser-etching for the LiteBIRD mission, a model in ANSYS HFSS was developed. The goal of the simulation was to optimize transmission in three frequency bands while meeting assumed laser machinability constraints and optical requirements. Simulation results from flat silicon show that an AR metamaterial coating made under the assumed conditions is feasible, and the baseline parameters for further curved-surface studies are provided.

Computational Discovery and Experimental Demonstration of Boron Phosphide Ultraviolet Nanoresonators

AbstractControlling ultraviolet light at the nanoscale using optical Mie resonances holds great promise for a diverse set of applications, such as lithography, sterilization, and biospectroscopy. Access to the ultraviolet requires materials with a high refractive index and wide band gap energy. Here, the authors systematically search for such materials by computing the frequency‐dependent optical permittivity of 338 binary semiconductors and insulators from first principles, and evaluate their scattering properties using Mie theory. This analysis reveals several interesting candidate materials among which boron phosphide (BP) appears most promising. Then BP nanoparticles are prepared and it is demonstrated that they support Mie resonances at visible and ultraviolet wavelengths using both far‐field optical measurements and near‐field electron energy‐loss spectroscopy. A laser reshaping method is also presented to realize spherical Mie‐resonant BP nanoparticles. With a refractive index over three and low absorption losses in a broad spectral range spanning from the infrared to the near ultraviolet, BP is an appealing material for a broad range of applications in dielectric nanophotonics.

Superiorly low half-wave voltage electro-optic polymer modulator for visible photonics.

Chip-scale optical devices operated at wavelengths shorter than communication wavelengths, such as LiDAR for autonomous driving, bio-sensing, and quantum computation, have been developed in the field of photonics. In data processing involving optical devices, modulators are indispensable for the conversion of electronic signals into optical signals. However, existing modulators have a high half-wave voltage-length product (VπL) which is not sufficient at wavelengths below 1000 nm. Herein, we developed a significantly efficient optical modulator which has low VπL of 0.52 V·cm at λ = 640 nm using an electro-optic (EO) polymer, with a high glass transition temperature (Tg = 164 °C) and low optical absorption loss (2.6 dB/cm) at λ = 640 nm. This modulator is not only more efficient than any EO-polymer modulator reported thus far, but can also enable ultra-high-speed data communication and light manipulation for optical platforms operating in the ranges of visible and below 1000 nm infrared.

Bound states in the continuum in all-van der Waals photonic crystals: a route enabling electromagnetically induced transparency.

Recent studies have demonstrated that multilayer transition metal dichalcogenides can serve as promising building blocks for creating new kinds of resonant optical nanostructures due to their very high refractive indices. However, most of such studies have focused on excitonic regimes of light-material interaction, while there are few on the low-loss region below the bandgap. Here, we conceptually propose all-van der Waals photonic crystals made of electronically bulk MoS2 and h-BN, designed to operate in the telecom wavelengths. And we demonstrate that, due to extremely low absorption loss and destructive interaction between symmetry-protected and resonance-trapped bound states in the continuum, high-quality factor transmission peaks associated with electromagnetically induced transparency (EIT) are observed, thus rendering our proposed structures highly useful for applications like slow light and optical sensing. Furthermore, EIT-like effects are demonstrated in well-engineered MoS2 nanostructures with broken symmetry. We argue that this work is not only of significance for light harvesting in nanostructured van der Waals materials, but provides also a simple path of constructing classical analogues of EIT using dielectric photonic crystals.

Lasing action in a strongly coupled silicon nanowire pair.

High-index dielectric nanostructures are of particular interest for nanoscale lasing due to their low absorption losses. However, the relatively weak near-field restricts the isolated dielectric cavities as low-threshold integrated on-chip laser sources. Here, we demonstrate lasing action in a silicon nanowire pair with 32 nm gap coated with dye-doped shell on the silicon-on-insulator platform. It is found that the quality factor Q is dominated by the coupling of the silicon nanowire pair, which depends on the gap size, the nanowire width, and the dye thickness. A lasing peak at the wavelength of 529 nm with FWHM of 0.6 nm is experimentally realized by the Si nanowire pair width, and the corresponding pumping power threshold is ∼34 µW/cm2. The proposed strategy, based on the well-established Si planar process, lays the groundwork for practical integrated nanolasers that have potential applications in photonic circuits.

Designs for III-nitride edge-emitting laser diodes with tunnel junction contacts for low internal optical absorption loss

The lasing mode and internal optical absorption loss profiles of III-nitride edge-emitting laser diode (LD) designs operating at 440 nm were modeled using the transfer matrix method. These models indicate absorption losses are minimized in LDs utilizing tunnel junction (TJ) contacts that (1) optimize the TJ to be as close to fully depleted as possible; (2) spatially separate the metal contact from the lasing mode using lightly doped n-GaN located above the TJ; (3) in designs with optimized TJs, minimize the total thickness of p-type material. These features reduce absorption losses in the model, relative to comparable LD models with an unoptimized TJ contact or with a transparent conducting oxide p-contact, by up to 15.3% and 12.5%, respectively, while at the same time eliminating most or nearly all p-type material.

Highly birefringent hollow-core anti-resonant terahertz fiber with a thin strut microstructure.

A novel highly birefringent and low transmission loss hollow-core anti-resonant (HC-AR) fiber with a central strut is proposed for terahertz waveguiding. To the best of our knowledge, it is the first time that a design of a highly birefringent terahertz fiber based on the hybrid guidance mechanism of the anti-resonant mechanism and the total internal reflection mechanism is provided. Several HC-AR fibers with both ultra-low transmission loss and ultra-low birefringence have been achieved in the near-infrared optical communication band. We propose a HC-AR fiber design in terahertz band by introducing a microstructure in the fiber core which leads to tremendous improvement in birefringence. Calculated results indicate that the proposed HC-AR fiber achieves a birefringence higher than 10-2 in a wide wavelength range. In addition, low relative absorption loss of 0.8% (8.6%) and negligible confinement loss of 1.69×10-4 dB/cm (9.14×10-3 dB/cm) for x-polarization (y-polarization) mode at 1THz are obtained. Furthermore, the main parameters of the fiber structure are evaluated and discussed, proving that the HC-AR fiber possesses great design and fabrication tolerance. Further investigation of the proposed HC-AR fiber also suggests a good balance between birefringence and transmission loss which can be achieved by changing strut thickness to cater numerous applications ideally.

Manipulating the directional emission of monolayer semiconductors by dielectric nanoantenna arrays

Collective Mie resonances in silicon (Si) nanoparticle arrays (NPAs) feature low absorption losses and strong field enhancement extending to a large area. They provide a high-efficient scheme to manipulate the emission properties of monolayer semiconductors. However, the poor quality factor of the current reported Si NPA limits the performance of light-emitting devices. It is mainly due to the constituent materials of nanoparticles being amorphous or polycrystalline Si, which have higher absorption coefficients in comparison with monocrystalline silicon (c-Si) among the visible band. This invited paper demonstrates a versatile technique to integrate the atomic layers onto the c-Si NPA. We show that our method can fully preserve the monolayer sample. We further investigate the directional emission tailored by the NPA with different diameters by combining back-focal-plane imaging and reciprocity simulations. The flexible tune of the geometry parameters of NPAs can offer many possibilities to control and manipulate the emission from monolayer semiconductors by engineering their photonic environments.

Terahertz Refractive Index Sensing Based on Gradient Metasurface Coupled Confined Spoof Surface Plasmon Polaritons Mode

We have investigated the sensing performance of the terahertz (THz) spoof surface plasmon polaritons (SSPs) on a metal groove array excited by a one-dimensional (1D) dielectric gradient metasurface (GMS) coupler. Such a compact SSPs coupler overcomes the disadvantages of their metal counterparts consisted of subwavelength metal antennas such as low efficiency and absorption loss. The normal incident terahertz wave is deflected by the dielectric GMS to the predetermined angles in the dielectric substrate which excites the SSPs modes on the metal groove array. Treating the 1D all-dielectric GMS as the excitation coupler, the confined SSPs modes can be generated in a small resonant cavity, leading to the strong light-matter interaction. The designed SSPs dielectric meta-couplers can be used to construct ultra-thin and compact sensing devices. Detailed investigation shows that the reflected amplitudes and phases of terahertz wave exhibit resonant responses to the change of the sample refractive index filled in the gap between the coupler and the metal groove array. The SSPs sensing by GMS coupling with the resonant frequency around 0.46 THz exhibits a high sensitivity of about 517.9 GHz/RIU with the resolution of 0.0001 RIU. A high Q-factor of 262 can also be achieved. In addition, the sensitivity of 410 GHz/RIU can be achieved with the resolution of 0.05 RIU, which can be used to detect large changes in refractive index. The study paves the ways for practical applications of terahertz trace-amount detection of chemical, organic or biomedical materials.

Ultra‐thin electron collectors based on nc‐Si:H for high‐efficiency silicon heterojunction solar cells

AbstractLow parasitic absorption and high conductivity enable (n)‐type hydrogenated nanocrystalline silicon [(n)nc‐Si:H], eventually alloyed with oxygen [(n)nc‐SiOx:H], to be deployed as window layer in high‐efficiency silicon heterojunction (SHJ) solar cells. Besides the appropriate opto‐electrical properties of these nanocrystalline films, reduction of their thickness is sought for minimizing parasitic absorption losses. Many strategies proposed so far reveal practical limits of the minimum (n)‐layer thickness that we address and overcome in this manuscript. We demonstrated the successful application of an ultra‐thin layer of only 3‐nm‐thick based on (n)nc‐Si:H PECVD plasma growth conditions without the use of additional contact or buffer layers. For simplicity, we still name (n)nc‐Si:H this ultra‐thin layer and the solar cell endowed with it delivers a certified efficiency η of 22.20%. This cell shows a 0.61 mA/cm2 overall JSC gain over the (n)a‐Si:H counterpart mainly owing to the higher transparency of (n)nc‐Si:H, while maintaining comparable VOC > 714 mV and FF > 80%. Our optimized (n)nc‐Si:H layer yields low absorption losses that are commonly measured for (n)nc‐SiOx:H films. In this way, we are able to avoid the detrimental effect that oxygen incorporation has on the electrical parameters of these functional layers. Further, by applying a MgF2/ITO double‐layer anti‐reflection coating, a cell with 3‐nm‐thick (n)nc‐Si:H exhibits a JSC,EQE up to 40.0 mA/cm2. By means of EDX elemental mapping, we additionally identified the (n)nc‐Si:H/ITO interface as critical for electron transport due to unexpected oxidation. To avoid this interfacial oxidation, insertion of a 2‐nm‐thick (n)a‐Si:H on the 3‐nm‐thick (n)nc‐Si:H contributes to FF gains of 1.4%abs. (FF increased from 78.6% to 80.0%), and showing further room for improvements.

High-efficiency hybrid solar cell with a nano-crystalline silicon oxide layer as an electron-selective contact

The efficiency of silicon heterojunction solar cells is limited by various factors including low surface passivation, parasitic absorption, and recombination losses. Herein, the surface passivation quality of crystalline silicon solar cells is improved by a hybrid passivation structure including a silicon heterojunction contact at the front side and a stack of tunneling oxide with n-type nano-crystalline silicon oxide (nc-SiOx(n)) passivating contact at the rear side. A passivation contact with thin silicon oxide (SiO2) and poly-silicon was previously proposed to enhance the rear surface passivation. In our study, the poly-silicon layer is swapped with the nc-SiOx(n) layer to improve the effective surface passivation, electrical properties, recombination losses, and carrier selectivity. The hybrid passivation structure shows significant passivation improvement with lifetime (τeff) of 2696 μs and implied open-circuit voltage (i-Voc) of 735 mV as compared with both-sides traditional silicon heterojunction (1650 μs, 719 mV) and tunneling passivation contact (2146 μs, 725 mV). The hybrid solar cell shows a potential performance as; open circuit voltage (Voc) = 724 mV, short circuit current (Jsc) = 38.95 mA/cm2, fill factor (FF) of 75.9%, efficiency (η) = 21.4%. However, there is room to further improve the overall cell performance.

Tunable Terahertz Wavelength Conversion Based on Optofluidic Infiltrated Rib Silicon Waveguides

Terahertz (THz) sources have attracted special attention for various applications. Compared to the standard silica-based optical fibers, silicon waveguides have more advantages such as higher refractive index and lower absorption loss over the THz region. In this paper, for the first time, a rib silicon waveguide based on the photonic crystal (PC) idea is designed and by using the scalar modulation instability (SMI) phenomenon, tunable wavelength conversion for THz wave generation is simulated. By changing the structural parameters such as the air-hole diameter of the PC and infiltration of optical fluids into the air holes, linear and nonlinear characteristics of the waveguide are controlled and hence the generated THz radiation is considered as a tunable source. Simulation presents that the maximum converted wavelength, 326.17 μm, is obtained when the air-hole diameter is set at d = 0.86 μm and the pump wavelength is in the normal dispersion regime. Also, we have infiltrated optical fluids into PC air holes in order to change the dispersion properties of the waveguide while keeping the geometrical parameters unchanged. This led to converted wavelengths of 70.5, 76.8 and 107.5 μm, all located in the THz region. The loss of this waveguide is less than 0.8\( \raisebox{1ex}{$ dB$}\!\left/ \!\raisebox{-1ex}{$ cm$}\right. \), which is less than that of previously reported in similar silicon waveguides.

Improve the Effective Resonance Light Scattering of Three-Layered Plasmonic Au@Dielectric@Ag Bimetallic Nanoshells

The strong light scattering from SPR has received an extraordinary attention due to the useful applications in photodetectors and cell and biomedical imaging. However, the applications using light scattering require a high scattering cross-section along with low absorption losses near the resonance wavelength. In this paper, effective plasmonic scattering of three-layered Au–Ag bimetallic nanoshells with a dielectric separate layer has been studied using the quasi-static approximation of classical electrodynamics. Because of the surface plasmon resonance (SPR)-induced intense light absorption, the effective scattering intensity is much weaker than that of scattering cross-section. However, the effective scattering intensity could be improved by tuning the geometric dimension and local dielectric environment of the nanostructure. It has been found that the greatest effective scattering takes place when the outer Ag nanoshell has a thick thickness or the dielectric separate layer has a small dielectric constant. The effective scattering also depends on the inner Au sphere radius and outer surrounding dielectric constant. Because of the mode transformation of the SPR, the effective scattering could also be greatly improved when the inner Au sphere has a very small or large size. However, the effective scattering intensity changes non-monotonously as the surrounding dielectric constant increases. The greatest effective scattering could be obtained when the surrounding dielectric constant has an intermediate value. This tunable effective plasmonic scattering of Au@Ag three-layered nanoshells presents a potential for design and fabrication of plasmonic optical nanodevice based on resonance light scattering.

Hollow Core Photonic Crystal Fiber (PCF)–Based Optical Sensor for Blood Component Detection in Terahertz Spectrum

Hollow core photonic crystal fiber is suggested and analyzed in this article for the identification of different blood components present in human blood. In order to visualize the fiber and investigate the performance of that sensor based on COMSOL simulation software, the suggested fiber is numerically analyze in terahertz frequency spectrum from 1.5 to 3 THz to obtain higher relative sensitivity (RS) and NA as well as lower absorption loss and confinement loss (CL) for better sensing applications. The reported hollow core fiber provides better interaction of light and the analytes, so that extremely high RS is achieved at a particular geometric condition. Furthermore, extremely low CL and effective material loss (EML) with high numerical aperture (NA) can be achieved from the suggested sensor which paves the way to apply the fiber in numerous biomedical applications.

Designs of Silicon Nitride Slot Waveguide Modulators With Electro-Optic Polymer and the Effect of Induced Charges in Si-Substrate on Their Performance

Dimensional parameters are optimized comparing stoichiometric and Si-rich silicon nitride-based push-pull modulators using a slot waveguide structure, electro-optic polymer cladding, and in-plane ground-signal-ground electrode. An optical power confinement in slot spacing is examined for choosing the optimal device parameters for wavelength of 1550 nm. The electrical simulations are set to calculate an asymmetric spatial distribution of poling efficiency and modulating refractive index change in polymer. The influence of carrier charge in Si-substrate is also considered. The voltage-length products as well as the poling efficiency of Si-rich SiN are calculated as 1.47 V·cm and 0.74 respectively for a polymer with a γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33,bulk</sub> of 100 pm/V. For the selected polymer the calculated efficiency comparable to standard silicon based plasma dispersion depletion modulators. The efficiency can be increased more than two times for demonstrated polymers with a γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33,bulk</sub> of ~230. Low metal absorption loss of ~ 1dB/cm can be achieved from the optimal designed device. Comparing to the conventional simulation method without Si-substrate effect, a more accurate simulation method is also presented in this work.