Low Absorption Loss Research Articles

Ultrafast performance of all-optical AND and OR logic operations at 160 Gb/s using photonic crystal semiconductor optical amplifier

The light confined and controlled by photonic crystals (PCs) can be exploited to enhance the performance and reduce the size of semiconductor optical amplifiers (SOAs) in which they are embedded. By incorporating PCSOAs in a Mach-Zehnder interferometer, or using a PCSOA followed by a delayed interferometer, Boolean AND and OR gates are formed, respectively, whose performance when executed all-optically (AO) is thoroughly analyzed at 160 Gb/s. For this purpose, the variation of the quality factor against the critical data signal and PCSOA operating factors is examined and assessed when the effects of amplified spontaneous emission and working temperature are included to make the simulation more realistic. The results obtained from the conducted theoretical study suggest that leveraging the PCSOAs benefits of low absorption loss, suppressed undesirable nonlinear effects, low power consumption, and high power transmission favors realizing the considered AO gates at the target data rate. Compared to conventional SOAs, PCSOAs advanced technology allows to obtain better logic performance, as quantified by the achieved higher metrics values, and to render the practical implementation of the AO gates more feasible, since the requirements for the PCSOAs structural parameters and driving conditions become more relaxed.

Dual-band and ultra-broadband photonic spin-orbit interaction for electromagnetic shaping based on single-layer silicon metasurfaces

Achieving electromagnetic wave scattering manipulation in the multispectral and broad operation band has been a long pursuit in stealth applications. Here, we present an approach by using single-layer metasurfaces composed of space-variant amorphous silicon ridges tiled on a metallic mirror to generate high-efficiency dual-band and ultra-wideband photonic spin-orbit interaction and geometric phase. Two scattering engineered metasurfaces have been designed to reduce specular reflection; the first one can suppress both specular reflectances at 1.05–1.08 μm and 5–12 μm below 10%. The second one is designed for an ultra-broadband of 4.6–14 μm, which is actually implemented by cleverly connecting two bands of 4.6–6.1 μm and 6.1–14 μm. Furthermore, the presented structures exhibit low thermal emission at the same time due to the low absorption loss of silicon in the infrared spectrum, which can be regarded as an achievement of laser–infrared compatible camouflage. We believe the proposed strategy may open a new route to implement multispectral electromagnetic modulation and multiphysical engineering applications.

A high-frequency hydrophone using an optical fiber microknot resonator

We propose a compact fiber-optic hydrophone and use it for acoustic wave measurements. The sensor probe comprises a microresonator formed by simply tying a tapered fiber into a loop structure. When the round-trip phase of light is an integer multiple of 2π, a well-defined resonance spectrum is produced by the resonator, with a quality factor as high as 104. Using spectral filtering technology for power interrogation, the steep linear resonance slope leads to sensitive operation of the sensor for high-frequency acoustic wave detection (of the order of several megahertz). After fabricating the sensor, the knot exhibits low-absorption loss underwater and, thus, the device can possibly be used as a hydrophone. The simple fabrication and small size structure of the sensor make it a good candidate for high-resolution scanning imaging.

Influence of partially-oxidized silver back electrodes on the electrical properties and stability of organic semiconductor diodes

Abstract Silver (Ag) is one of the most suitable metals for electrodes in high-performance organic optoelectronic devices due to its high conductivity and reflectivity, and low parasitic absorption loss at visible wavelengths. However, the electronic work function of Ag is not ideal for use as either the cathode or anode in many organic optoelectronic devices. In this report, we investigate the formation of an ultrathin surface oxide layer on a Ag electrode and its impact on hole injection into an organic conjugated polymer semiconductor. The surface oxide is formed by exposing the Ag electrode to a low-power O2/Ar plasma and which changes the electrical properties of the pure Ag electrode. We study the morphology and the chemical composition of the Ag surfaces after different plasma treatment times through X-ray photoelectron spectroscopy, scanning electron microscopy and dark-field optical microscopy. After plasma exposure the surface oxide is composed of both AgOx and Ag2CO3. As plasma exposure time increases from 1 s to 7 s, the fraction of AgOx increases while Ag2CO3 decreases gradually. Both the turn-on voltages and barrier heights of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-only devices decrease with plasma treated Ag surfaces indicating that the work function of the Ag surface is increased by the surface oxide. F8BT hole-only devices with a thin MoO3 layer and a thicker AgOx layer on the electrode are found to be stable compared to thinner surface oxides and un-treated Ag surfaces.

High-refractive index, low-loss oxyfluorosilicate glasses for sub-THz and millimeter wave applications

Terahertz (THz) time-domain spectroscopy was used to study the optical properties of two series of oxyfluorosilicate (OFS) glasses. The experimentally measured refractive indices are analyzed by using the Clausius–Mossotti equation to retrieve information about polarizability of the glass. Compared with previously studied oxide-based glasses and chalcogenides, OFS glasses exhibit a balance of relatively low absorption coefficients (6–9 cm−1) and high refractive indices (2.9–3.7) at 0.5 THz. The value of 3.7 is the highest among silicate glasses reported to date and are comparable to those of La3+:chalcogenide glasses. The relatively high values of refractive indices have been attributed to the great increase of the glass polarizability in OFS glasses, which offsets the effect of an increase in molecular volume caused by multicomponent modification of the glass structure. Comparatively low THz absorption of OFS glasses is explained by the structural relaxation effect of fluorine, which effectively suppress the charge fluctuation in the glass structure. The high refractive index and low absorption loss properties of the present OFS glasses should be useful for quasi-optic components such as lens and waveguide devices application in the sub-THz and millimeter wave region.

Square Porous Core Microstructure Fiber for Low Loss Terahertz Applications-=SUP=-*-=/SUP=-

AbstractA new kind of square lattice porous core microstructure fiber is proposed for promising low loss terahertz applications. To analyze the guiding characteristics of proposed fiber Finite Element Method (FEM) based Comsol V4.2 software is used. The proposed fiber structure is very simple and easy to realize. The numerical results ensures that this proposed microstructure fiber exhibits low effective absorption loss of 0.06 cm^–1, low confinement loss of 9.2 × 10^–3 cm^–1, low bending loss of 8.8 × 10^–9 dB/m, and very high power fraction of 47% through the core at 1 THz simultaneously. Moreover, our proposed fiber offers very low dispersion variation of 0.85 ± 0.12 ps/THz/cm over a wide range of frequency from 0.7 to 1.15 THz. The investigated results indicates that this fiber will be a good candidate in terahertz signal transmission as well as different terahertz devices.

Submillisecond-response polymer network liquid crystals for mid-infrared applications.

We formulated a high birefringence, large dielectric anisotropy, UV stable, and low absorption loss nematic liquid crystal mixture, named UCF-15, for mid-wave infrared (MWIR) applications. To achieve fast response time, we fabricated a polymer network liquid crystal (PNLC) using UCF-15 as host. At 40°C operating temperature, our PNLC shows 2π phase change at λ = 4 μm, submillisecond response time, and over 98% transmittance in the 3.8 to 5.1 μm region. Potential applications of this PNLC phase modulator for high speed laser beam steering, adaptive optics, and optical tweezer are foreseeable.

Low-loss ARROW waveguide with rectangular hollow core and rectangular low-density polyethylene/air reflectors for terahertz waves

Designing low-loss waveguides for terahertz waves is challenging as most materials are very lossy in this frequency band. Most scientists simply consider transmitting the waves through low-loss air, which however also has its own difficulties as index-guiding is not possible. In this paper, we report on the design of low-loss waveguides for terahertz waves and associated results by using a finite element leaky mode solver. These results show that waveguides designed using ARROW (anti-resonant reflecting optical waveguide) approach yield a low combined absorption and leakage loss down to only 0.05[Formula: see text]dB/cm for the q-TE[Formula: see text] fundamental mode using realistic values of refractive index at 1 THz operating frequency. The structure employs rectangular hollow-core and low-density polyethylene/air anti-resonant reflecting bilayers, which can be easily fabricated. These results are compared with those of other structures, i.e., a photonic crystal fiber-like structures using the same materials with rectangular holes, which is shown to give a higher loss of 3[Formula: see text]dB/cm and a suspended air-core waveguide with TOPAS vein offering a loss of 1[Formula: see text]dB/cm.

Field enhancement and spectral features of hexagonal necklaces of silver nanoparticles for enhanced nonlinear optical processes.

The nonlinear properties of hybrid metallic-dielectric systems are attracting great interest due to their potential for the enhancement of frequency conversion processes at nanoscale dimensions. In this work, we theoretically and experimentally address the correlation between the near field distribution of hexagonal plasmonic necklaces of silver nanoparticles formed on the surface of a LiNbO3 crystal and the second harmonic generation (SHG) produced by this nonlinear crystal in the vicinities of the necklaces. The spectral response of the hexagonal necklaces does not depend on the polarization direction and is characterized by two main modes, the absorptive high-energy mode located in the UV spectral region and the lower energy mode, which is strongly radiant and extends from the visible to the near infrared region. We show that the spatial distribution of the enhanced SHG is consistent with the local field related to the low energy plasmon mode, which spectrally overlaps the fundamental beam. The results are in agreement with the low absorption losses of this mode and the two-photon character of the nonlinear process and provide deeper insight in the connection between the linear and nonlinear optical properties of the hybrid plasmonic-ferroelectric system. The study also highlights the potential of hexagonal necklaces as useful plasmonic platforms for enhanced optical processes at the nanoscale.

Efficient terahertz and infrared Smith-Purcell radiation from metal-slot metasurfaces.

We demonstrate that when a charged particle moves on top of a metal-slot metasurface consisting of metallic slot resonators, strong Smith-Purcell electromagnetic (EM) radiation can be produced at resonant frequency. By adjusting the period of the metasurface, the resonant (or working) frequency can be tuned from gigahertz to terahertz and infrared regions. Since the EM field is localized in the slots rather than at the metal surface, the metasurfaces are found to exhibit a very low absorption loss ratio (<1%) in low working frequencies (<1 THz). Although it becomes larger in high frequencies (>1 THz), the loss ratio remains relatively low (<12%). In addition, a nonlinear relationship is also uncovered between the resonant frequency and the reciprocal of the period. Our results could benefit the construction of efficient, compact terahertz, and infrared free-electron light sources.

Effects of oxygen flows on optical properties, micro-structure and residual stress of Ta2O5 films deposited by DIBS

High precision optical components, such as ultra-high reflectors, severely suffer from absorption losses. In order to get optical films with low absorption losses, many techniques, such as annealing and laser conditioning, have been widely employed as a post-deposition treatment process to deal with as-deposited films. However, the success of these processes starts with the correct choice of the deposition parameters. In this paper, Ta2O5 films are deposited by dual ion beam sputtering (DIBS) method and the effects of target oxygen flows on optical properties, microstructure and residual stress are systematically investigated. The results show that target oxygen flows can significantly affect the absorption losses and residual stress of Ta2O5 film. The XRD patterns reveal that Ta2O5 films deposited at different parameters are all amorphous. Finally, based on the results of Ta2O5 films, broadband dielectric mirror with high reflection and low absorption losses in the range from 380 nm to 750 nm is successfully fabricated.

Study of Absorption Loss Effects on Acoustic Wave Propagation in Shallow Water Using Different Empirical Models

&lt;p&gt;&lt;span lang="EN-US"&gt;Efficient underwater acoustic communication and target locating systems require detailed study of acoustic wave propagation in the sea. Many investigators have studied the absorption of acoustic waves in ocean water and formulated empirical equations such as Thorp’s formula, Schulkin and Marsh model and Fisher and Simmons formula. The Fisher and Simmons formula found the effect associated with the relaxation of boric acid on absorption and provided a more detailed form of absorption coefficient which varies with frequency. However, no simulation model has made for the underwater acoustic propagation using these models. This paper reports the comparative study of acoustic wave absorption carried out by means of modeling in MATLAB. The results of simulation have been evaluated using measured data collected at Desaru beach on the eastern shore of Johor in Malaysia. The model has been used to determine sound absorption for given values of depth (D), salinity (S), temperature (T), pH, and acoustic wave transmitter frequency (f). From the results a suitable range, depth and frequency can be found to obtain best propagation link with low absorption loss.&lt;/span&gt;&lt;/p&gt;

Enhanced Solar Light Absorption and Photoelectrochemical Conversion Using TiN Nanoparticle-Incorporated C3N4-C Dot Sheets.

In this work, a promising strategy to increase the broadband solar light absorption was developed by synthesizing a composite of metal-free carbon nitride-carbon dots (C3N4-C dots) and plasmonic titanium nitride (TiN) nanoparticles (NPs) to improve the photoelectrochemical water-splitting performance under simulated solar radiation. Hot-electron injection from plasmonic TiN NPs to C3N4 played a role in photocatalysis, whereas C dots acted as catalysts for the decomposition of H2O2 to O2. The use of C dots also eliminated the need for a sacrificial reagent and prevented catalytic poisoning. By incorporating the TiN NPs and C dots, a sixfold improvement in the catalytic performance of C3N4 was observed. The proposed approach of combining TiN NPs and C dots with C3N4 proved effective in overcoming low optical absorption and charge recombination losses and also widens the spectral window, leading to improved photocatalytic activity.

Studyof Silver Sulphide Nanoparticle Decorated SiNW Array on Multi-c-Si Wafer

Silver sulphide (Ag2S) nanoparticle decorated silicon nanowire (SiNW) arrays were synthesized by metal assisted chemical etching (MACE) technique on p-type multicrystalline (multi-c-Si) wafers with resistivity 1-5Ω-cm. The structural and optical properties were characterized using FESEM and UV-VIS-NIR spectroscopy. Substantial low broadband reflection is visible for the prepared nanostructure with weighted average reflection 1.82% over the range of 300 to 1100 nm;where as bare SiNW array show an average reflectance of 2.62%. The advantage of Ag2S NPs over various metal nanoparticles is the low absorption loss over a broad wavelength (300 to 1100 nm) range.

Highly Birefringent Terahertz Waveguide Formed With Dual-Subwavelength Polymer Wires

We propose a highly birefringent terahertz (THz) waveguide, which is formed with two touching subwavelength polymer wires. The waveguide can provide a high modal birefringence larger than 0.01 over a wide frequency range, and a maximum birefringence up to 0.0525 is achieved when the waveguide is made of Topas. Different from other THz birefringent waveguides, a simple scaling rule exists for the proposed birefringent waveguide so that the waveguide can be designed easily for any desired operation frequency to obtain the maximum birefringence. Moreover, when the maximum birefringence takes place, a high coupling efficiency of 93%, a low absorption loss of 0.04 and 0.03 cm−1 for x - and y -polarizations, and a negligible bending loss are demonstrated in our simulations. Finally, the influence of material index is further examined. It is found that as the refractive index of the waveguide material increases, the magnitude of birefringence increases as well, while the frequency at which the maximum birefringence occurs will shift toward the lower region.

Generation of broadband terahertz pulses via optical rectification in a chalcopyrite CdSiP2 crystal.

We report on the generation of broadband (0.07-6THz) terahertz (THz) radiation via optical rectification in a ⟨110⟩ CdSiP2 (CSP) crystal pumped by a 50fs, 780nm central wavelength optical pulse. By measuring the THz phase refractive index and the optical pump group refractive index, good phase matching can be achieved for a crystal thickness ≲200 μm. Due to this crystal's high second order nonlinearity and low absorption losses, it is envisioned that THz generation from CSP could be further enhanced by confining the optical pump pulse to sub-wavelength waveguides.

Small perforations in corrugated sandwich panel significantly enhance low frequency sound absorption and transmission loss

Numerical and experimental investigations are performed to evaluate the low frequency sound absorption coefficient (SAC) and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations, including perforations in one of the face plates, in the corrugated core, and in both the face plate and the corrugated core. Finite element (FE) models are constructed with considerations of acoustic-structure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich without perforation, the corrugated sandwich with perforated pores in one of its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The influences of perforation diameter and perforation ratio on the vibroacoustic performance of the sandwich are also explored. For a corrugated sandwich with uniform perforations, the acoustical resonance frequencies and bandwidth in its SAC and STL curves decrease with increasing pore diameter and decreasing perforation ratio. Non-uniform perforation diameters and perforation ratios result in larger bandwidth and lower acoustical resonance frequencies relative to the case of uniform perforations. The proposed perforated sandwich panels with corrugated cores are attractive ultralightweight structures for multifunctional applications such as simultaneous load-bearing, energy absorption, sound proofing and sound absorption.

Ultra-low Loss with Single Mode Polymer-Based Photonic Crystal Fiber for THz Waveguide

Abstract In this article, a low loss circular photonic crystal fiber (C-PCF) has been suggested as Terahertz (THz) waveguide. Both the core and cladding vicinity of the suggested PCF are constituted by circular-shaped air holes. The optical properties such as effective material loss, effective area, core power fraction and V-parameter have numerically been probed by utilizing full vectorial finite element method (FEM) with perfectly matched layers (FMLs) boundary condition. The reported PCF reveals low absorption loss and large effective area of 0.04 cm−1 and 2.80×10−07 m2 respectively at 1 THz operating frequency. In addition, the core power fraction of the fiber is about 50.83 % at the same activation frequency. The V-parameter shows that the proposed PCF acts as a single mode over 0.70 to 1.15 THz frequency. So, the reported PCF offers the best performance in long distance communication applications.

Measurement of ultrafast optical Kerr effect of Ge–Sb–Se chalcogenide slab waveguides by the beam self-trapping technique

We present a reliable and original experimental technique based on the analysis of beam self-trapping to measure ultrafast optical nonlinearities in planar waveguides. The technique is applied to the characterization of Ge–Sb–Se chalcogenide films that allow Kerr induced self-focusing and soliton formation. Linear and nonlinear optical constants of three different chalcogenide waveguides are studied at 1200 and 1550 nm in femtosecond regime. Waveguide propagation loss and two photon absorption coefficients are determined by transmission analysis. Beam broadening and narrowing results are compared with simulations of the nonlinear Schrödinger equation solved by BPM method to deduce the Kerr n2 coefficients. Kerr optical nonlinearities obtained by our original technique compare favorably with the values obtained by Z-scan technique. Nonlinear refractive index as high as (69±11)×10−18m2∕W is measured in Ge12.5Sb25Se62.5 at 1200 nm with low nonlinear absorption and low propagation losses which reveals the great characteristics of our waveguides for ultrafast all optical switching and integrated photonic devices.

Silicon Nanostructures for Bright Field Full Color Prints

Nanoscale color printing has recently emerged as a unique alternative to traditional pigments by providing record spatial resolution, angular independent, durable and single material colors. Widely based on plasmonic nanostructures, numerous efforts in the field have aimed at extending color range and saturation relying on a variety of designs and metals. Alternatively, silicon nanostructures support finely tunable electric and magnetic multipolar resonances, afford low absorption losses and benefit from well-established industrial fabrication processes, all features ideally suited to nanoscale color printing. Here we compare the properties of silicon nanodiscs with those of aluminum and silver plasmonic elements for the specific purpose of nanoscale color reproduction targeting the coverage of a broad and vivid color palette. We highlight the different properties of such metallic and dielectric resonators in various geometric and illumination conditions leading to the optimization of silicon nanodisc arr...