Broadband Spectral Range Research Articles

Design and Simulation of a Broadband Plasmonic Optical Isolator

In this paper, a new approach for optical isolator based on the Plasmonic effect is proposed. Metallic nanoparticles of different sizes are used to realize the proposed idea. Metallic nanoparticles spin-coated on alumina thin layer that is coated on Silicon waveguide. We demonstrated that the proposed idea operates in a broadband spectral range (more than 800nm) as well as back-propagating wave attenuated more than 120dB. The proposed idea can enhance the isolation ratio and also can provide wider bandwidth for isolation. The proposed idea is based on solution process nanotechnology that is simple, low cost, and available.

Ultrafast and Highly Stable Photodetectors Based on p-GeSe/n-ReSe2 Heterostructures.

Two-dimensional transition-metal dichalcogenide (2D-TMD) semiconductors and their van der Waals heterostructures (vdWHs) have attracted great attention because of their tailorable band-engineering properties and provide a propitious platform for next-generation extraordinary performance energy-harvesting devices. Herein, we reported unique and unreported germanium selenide/rhenium diselenide (p-GeSe/n-ReSe2) 2D-TMD vdWH photodetectors for extremely sensitive and high-performance photodetection in the broadband spectral range (visible and near-infrared range). A high and gate-tunable rectification ratio (RR) of 7.34 × 105 is achieved, stemming from the low Schottky barrier contacts and sharp interfaces of the p-GeSe/n-ReSe2 2D-TMD vdWHs. In addition, a noticeably high responsivity (R = 2.89 × 105 A/W) and specific detectivity (D* = 4.91 × 1013 Jones), with good external quantum efficiency (EQE = 6.1 × 105) are obtained because of intralayer and interlayer transition of excitations, enabling the broadband photoresponse (λ = 532-1550 nm) at room temperature. Furthermore, fast response times of 16-20 μs are estimated under the irradiated laser of λ = 1550 nm because of interlayer exciton transition. Such a TMD-based compact system offers an opportunity for the realization of high-performance broadband infrared photodetectors.

Mechanochromic Detection for Soft Opto-Magnetic Actuators

New multi-stimuli responsive materials are required in smart systems applications to overcome current limitations in remote actuation and to achieve versatile operation in inaccessible environments. The incorporation of detection mechanisms to quantify in real time the response to external stimuli is crucial for the development of automated systems. Here, we present the first wireless opto-magnetic actuator with mechanochromic response. The device, based on a nanostructured-iron (Fe) layer transferred onto suspended elastomer structures with a periodically corrugated backside, can be actuated both optically (in a broadband spectral range) and magnetically. The combined opto-magnetic stimulus can accurately modulate the mechanical response (strength and direction) of the device. The structural coloration generated at the corrugated back surface enables to easily map and quantify, in 2D, the mechanical deflections by analyzing in real time the hue changes of images taken using a conventional RGB smartphone camera, with a precision of 0.05°. We demonstrate the independent and synergetic optical and magnetic actuation and detection with a detection limit of 1.8 mW·cm–2 and 0.34 mT, respectively. The simple operation, versatility, and cost-effectiveness of the wireless multiactuated device with highly sensitive mechanochromic mapping paves the way to a new generation of wirelessly controlled smart systems.

Robust broadband athermal 2 × 2 Mach-Zehnder interferometer with sub-wavelength grating adiabatic couplers.

We report an all-silicon thermally insensitive (-1.5pm/∘C) 2×2 Mach-Zehnder interferometer (MZI) over a spectral range from 1540 to 1620 nm. Additionally, the proposed MZI exhibits no imbalance in its extinction ratio with temperature. The broadband spectral range with minimal temperature sensitivity is achieved by slightly overcompensating the MZI design for temperature variations. At the same time, the uniformity in the extinction ratio is controlled using sub-wavelength grating adiabatic couplers for splitting and combining.

Broadband Metallic Carbon Nanotube Saturable Absorber for Ultrashort Pulse Generation in the 1500–2100 nm Spectral Range

Herein, we report on the possibility of ultrashort laser pulse generation in the broadband spectral range using a saturable absorber based on free-standing metallic carbon nanotube thin film. Erbium, thulium, and holmium-doped all-fiber lasers were mode-locked with a single saturable absorber containing a 300 nm thick material layer. Subpicosecond pulses were generated at 1559, 1938, and 2082 nm. Our work validates the broadband operation of metallic carbon nanotube-based saturable absorbers and highlights the suitable performance of nanomatematerial for ultrafast photonic applications.

Use of Dielectric Metasurfaces to Generate Deep‐Subwavelength Nondiffractive Bessel‐Like Beams with Arbitrary Trajectories and Ultralarge Deflection

AbstractFor decades, accelerating beams have attracted considerable interest in fundamental physics and in various emerging applications. However, not only are conventional accelerating beam generators (such as spatial light modulators) bulky and diffraction‐inefficient, they also have a poorly resolved ability of phase manipulation that limits the accelerating beam's minimum size and maximum degree of curvature. In this study, a dielectric metasurface is used to generate highly focused nondiffractive Bessel‐like accelerating beams with predefined arbitrary trajectories within a broadband spectral range of 550–710 nm. In particular, a similar metasurface with a combined phase profile allows the generation of a Bessel‐like vortex beam with an ultrahigh numerical aperture of 0.79, resulting in a subwavelength beamwidth of 234 nm (≈0.43λ) down to the diffraction limit. In addition, various accelerating Bessel‐like beams and beam arrays with different predefined trajectories and characteristic beam parameters that are not otherwise achievable with conventional spatial light modulators are demonstrated with synthetic‐phase metasurfaces. This study promotes the diversity of Bessel‐like accelerating beams for practical applications in fields such as optical manipulation, optical storage, biomedical imaging, and material processing.

Giant enhancements of high-order upconversion luminescence enabled by multiresonant hyperbolic metamaterials

Photonic nanostructures with resonant modes that can generate large electric field (EF) enhancements are applied to enhance light-matter interactions in nanoscale, bringing about great advances in both fundamental and applied science. However, a small hot spot (i.e., the regions with strong EF enhancements) and highly inhomogeneous EF distribution of the resonant modes usually hinder the enhancements of light-matter interactions in a large spatial scale. Additionally, it is a severe challenge to simultaneously generate multiple resonant modes with strong EF enhancements in a broadband spectral range, which greatly limits the capacity of a photonic nanostructure in boosting optical responses including nonlinear conversion, photoluminescence, etc. In order to overcome these challenges, we presented an arrayed hyperbolic metamaterial (AHMM). This AHMM structure is applied to simultaneously enhance the three-photon and four-photon luminescence of upconversion nanoparticles. Excitingly, the enhancement of the three-photon process is 1 order of magnitude larger than previous records, and for the enhancing four-photon process, we achieve an enhancement of 3350 times, greatly beneficial for overcoming the crucial problem of low efficiency in near infrared light upconversion. Our results demonstrated a promising platform for realizing giant enhancements of light-matter interactions, holding potential in constructing various photonics applications such as the nonlinear light sources.

Passive silicon ring-assisted Mach-Zehnder interleavers operating in the broadband spectral range.

We propose and experimentally demonstrate a passive and compact interleaver on a silicon on insulator (SOI) platform using a ring-assisted asymmetrical Mach-Zehnder interferometer configuration. The wavelength-insensitive couplers, i.e., multimode interference couplers and adiabatic 3-dB couplers, are introduced to eliminate the effect of an unequal splitting ratio and wavelength on crosstalk and the operating spectral range. In addition, there exists an inherent phase shift between the two couplers; the device can be fully passive and works well without additional thermal tuning. In the calculation, the influence of wavelength sensitivity of self-coupling coefficients and couplers on the performance of the interleaver is considered. The experiment shows that, by employing wavelength-insensitive couplers, the operating spectral range of the proposed interleavers was extended to be >140nm for all sorts of channel spacing and channel count. The measured free spectral range is 4.6 nm, and the crosstalk is as low as -46.6dB for the best case.

Structured metal double-blazed dispersion grating for broadband spectral efficiency achromatization.

The majority of spectrometers use reflective dispersion gratings with a metal-coated blazed grating profile for spectral decomposition. They achieve high diffraction efficiency at the design wavelength, which decays considerably in the adjacent longer and shorter wavelength ranges. We introduce a structured metal double-blazed grating with a high diffraction efficiency for a broadband spectral range, consisting of a sawtooth-like structured metal surface filled with a first dielectric transparent material. The planarized upper surface is covered with a second blazed profile of a different transparent material. We present a systematical theoretical analysis of the diffraction efficiency in reflection geometry, based on a scalar approach involving fundamental dispersion parameters such as Abbe numbers and relative partial dispersions of the materials. We find material combinations reducing the profile heights down to 1-2 µm.

Optimization and characterization of silicon nano-grass antireflection layer on textured silicon wafer

We propose in this paper silicon nano-grass layer as an alternative of conventional black silicon nanowire structure. Conventional metal-assisted chemical etching process by HF produces porous silicon nanowire structure. This is due to uncontrollable chemical reaction making long-heighted nanowires which causes detrimental effect on further solar cell processing. The shape and height of silicon nanostructure was reduced by new chemical solution to minimize the porosity. Silicon nano-grass layer was grown on textured silicon surface and investigated in detail. The structure was formed by NH4F/H2SO4/H2O2 solution at room temperature. Substantial reflectance reduction with broadband spectral range was observed. The etching mechanism and the effect of etch constituents of the etching solution on the structure of nano-grass were studied elaborately. Reflectance and photoluminescence were studied accordingly, and the variations in the surface porosity and light absorbance property have been monitored. At the very end, a comparative study of conventional black silicon etching process by HF/H2O2 and nano-grass on textured silicon by NH4F solution has been investigated. The etch rate and the optical superiority of nanostructures formed by both the solutions have been manifested and explained. For the commercial production level, silicon nano-grass structure is much persistent than silicon nanowire.

High performance terahertz emitter based on inverse spin Hall effect in metallic Fe/Au heterostructure

Since many applications of terahertz spectroscopy depend on spectral bandwidth, the generation of ultra-broadband terahertz radiation is one of the most important challenges faced by terahertz scientists. Spintronic terahertz emitters (STEs) are promising sources to produce very compact terahertz pulses and broadband spectra. Here we optimized the iron/gold heterostructure based on the metal layer thicknesses for the first time. The optimization was performed experimentally based on the obtained theoretical results. The optimized thicknesses were obtained as 2 and 5 nm for Fe and Au layers, respectively. The experimental results were in very good agreement with corresponding theoretical results. The optimized STE generates terahertz bandwidth up to 4 THz which is limited by the frequency response of the used detector. The dynamic range is well above 60 dB with the maximum around 0.5 THz. The results show that the presented STE is capable of producing large amplitude terahertz pulses and broadband spectral range. Based on our knowledge, this is the first time that the Fe/Au spintronic terahertz emitter has been optimized.

Optical gain and stimulated emission in optically pumped heavily doped Al0.74Ga0.26N:Si structures with external cavity

The pulse lasing in the broadband spectral range 420–590 nm was obtained from two squeezed together heavily Si doped Al0.74Ga0.26N/AlN/Al2O3 structures with external cavity under pump radiation with λp = 266 nm wavelength. These structures were grown by molecular beam epitaxy on (0001) oriented thick sapphire substrates. Stimulated emission at room temperature was observed with optical pumping thresholds 50 kW/cm2 in the semiconfocal cavity. The linear transverse-electric polarization dominates in the output emission. The optical gain coefficients values of (0.12–6) × 103 cm−1 for Al0.74Ga0.26N:Si films with inhomogeneous luminescence broadening were measured at 10–600 kW/cm2 pump power density radiation with 266 nm wavelength, 8 ns pulse duration and 10 Hz repetition rate.

Multifunctional Sulfur‐Hyperdoped Silicon Nanoparticles with Engineered Mid‐Infrared Sulfur‐Impurity and Free‐Carrier Absorption

AbstractSi nanoparticles (NPs), which are innovative promising light‐harvesting components of thin‐film solar cells and key‐enabling biocompatible theranostic elements of infrared‐laser and radiofrequency hyperthermia‐based therapies of cancer cells in tumors and metastases, are significantly advanced in their near/mid‐infrared band‐to‐band and free‐carrier absorption via donor sulfur‐hyperdoping during high‐throughput facile femtosecond‐laser ablative production in liquid carbon disulfide. High‐resolution transmission electron microscopy and Raman microscopy reveal their mixed nanocrystalline/amorphous structure, enabling the extraordinary sulfur content of a few atomic percents and very minor surface oxidation/carbonization characterized by energy‐dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy. A 200‐nm thick layer of the nanoparticles exhibits near−mid‐infrared absorbance, comparable to that of the initial 380‐micron thick n‐doped Si wafer (phosphor‐dopant concentration ≈1015 cm−3), with the corresponding extinction coefficient for the hyperdoped NPs being 4–7 orders higher over the broadband spectral range of 1–25 micrometers. Such ultimate, but potentially tunable mid‐IR structured, multi‐band absorption of various sulfur‐impurity clusters and smooth free‐carrier absorption are break through advances in mid‐infrared (mid‐IR) laser and radiofrequency (RF) hyperthermia‐based therapies, as envisioned in the RF‐heating tests, and in fabrication of higher‐efficiency thin‐film and bulk photovoltaic devices with ultra‐broad (UV−mid‐IR) spectral response.

Second-harmonic generation with metal/dielectric/metal hybridized nanoantennas: enhanced efficiency, reduced mode volume and ideal magnetic/electric dipole scattering

Although nonlinear optical responses with high refractive index dielectric nanostructures benefit from the large mode volume of the Mie resonances, it is an obstacle to achieve ultra-compact devices compared with plasmonic nanostructures. Besides that, the nonlinear emissions for dielectric nanoparticles often possess complex multipolar contributions, which is not favorable for nonlinear far-field manipulating such as beam steering. This study numerically demonstrates that with the formation of mode-matching condition, the efficiency of second-harmonic generation with an Au/AlGaAs/Au hybridized sandwich nanodisk can be enhanced by two orders compared with a same size AlGaAs nanoparticle, and the mode volume is reduced by about two orders at the same time. What is more interesting is that the nonlinear sources and far-field scattering are tailored by the hybridized resonances, where an ideal magnetic (or electric) dipole scattering around a broadband spectral range is observed for the second-harmonic generation, which provides a reliable way to generate pure magnetic light and to manipulate the nonlinear far-field emissions. The realization of enhanced nonlinear efficiency, the reduced mode volume, the background-free responses, and the ideal magnetic/electric dipole scattering make the sandwich hybridized nanoparticle a promising platform for nonlinear nanophotonics.

Acid etching followed by hydrothermal preparation of nanosized Bi2O4/Bi2O3 p-n junction as highly efficient visible-light photocatalyst for organic pollutants removal

As a promising visible-light photocatalyst, Bi2O4 has the advantage of broadband spectral response range. However, the high recombination rate of photoexcited charge carriers induced by the submicrorod morphology of pure Bi2O4 greatly restricts its visible-light photocatalytic performance. Herein, a novel nanosized Bi2O4/Bi2O3 p-n junction was developed by a dilute HCl acid etching and subsequent hydrothermal method, using NaBiO3·2H2O as the sole bismuth precursor. A product of NaBiO3·2H2O@BiOCl was formed firstly when NaBiO3·2H2O was partially reduced by insufficient dilute HCl aqueous solution. Then, BiOCl reacted with NaBiO3·2H2O during the following hydrothermal reaction process, resulting in the formation of Bi2O4 nanoparticles (NPs) anchored on the surface of plate-like Bi2O3. The content of Bi2O3 in the junction can be easily controlled by changing the added amount of dilute HCl acid. This strategy could not only realize the NPs-sized Bi2O4 but also construct nanometered Bi2O4/Bi2O3 p-n junction simultaneously, which remarkably improves the separation efficiency of charge carriers. Furthermore, the obtained Bi2O4/Bi2O3 heterojunctions have larger specific surface areas than Bi2O4 alone. Due to these advantages, the photocatalytic removal rate of methyl orange (MO) and phenol for the optimal Bi2O4/Bi2O3 heterostructure increased respectively by 5.06 and 2.16 times under visible light, when compared with single Bi2O4. The results of active species trapping experiment and electron spin resonance (ESR) spectra indicate that holes (h+) and superoxide radicals (O2−) are the primary and secondary reactive active species during the photocatalytic degradation process, respectively. This work provides a novel perspective for the design and preparation of high performance Bi2O4-based photocatalyst.

All-reflective self-referenced spectral interferometry for single-shot measurement of few-cycle femtosecond pulses in a broadband spectral range

An all-reflective self-referenced spectral interferometry based on the transient grating (TG) effect is proposed for single-shot measuring of the amplitude and phase of ultrashort pulses in a broadband spectral range. Except for a thin third-order nonlinear medium, which was used to generate the TG signal, no transmitted optics were used in the proposed device, and few-cycle pulses in a broad spectral range from deep UV to mid-IR can be characterized. With a homemade compact and alignment-free device, a 5.0 fs pulse at 800 nm corresponding to about two cycles and a 14.3 fs pulse at 1800 nm corresponding to less than three cycles were successfully characterized.

Ultra-broadband photon harvesting in large-area few-layer MoS2 nanostripe gratings.

Flat optics nanoarrays based on few-layer MoS2 are homogeneously fabricated over large-area (cm2) transparent templates, demonstrating effective tailoring of the photon absorption in two-dimensional (2D) transition-metal dichalcogenide (TMD) layers. The subwavelength subtractive re-shaping of the few-layer MoS2 film into a one-dimensional (1D) nanostripe array results in a pronounced photonic anomaly, tunable in a broadband spectral range by simply changing the illumination conditions (or the lattice periodicity). This scheme promotes efficient coupling of light to the 2D TMD layers via resonant interaction between the MoS2 excitons and the photonic lattice, with subsequent enhancement of absorption exceeding 400% relative to the flat layer. In parallel, an ultra-broadband absorption amplification in the whole visible spectrum is achieved, thanks to the non-resonant excitation of substrate guided modes promoted by MoS2 nanoarrays. These results highlight the potential of nanoscale re-shaped 2D TMD layers for large-area photon harvesting in layered nanophotonics, quantum technologies and new-generation photovoltaics.

Hybrid metal-graphene plasmonic sensor for multi-spectral sensing in both near- and mid-infrared ranges.

This paper proposes a hybrid metal-graphene plasmonic sensor which can simultaneously perform multi-spectral sensing in near- and mid-IR ranges. The proposed sensor consists of an array of asymmetric gold nano-antennas integrated with an unpatterned graphene sheet. The gold antennas support sharp Fano-resonances for near-IR sensing while the excitation of graphene plasmonic resonances extend the sensing spectra to the mid-IR range. Such a broadband spectral range goes far beyond previously demonstrated multi-spectral plasmonic sensors. The sensitivity and figure of merit (FOM) as well as their dependence on the thickness of the sensing layer and Fermi energy of graphene are studied systematically. This new type of sensor combines the advantages of conventional metallic plasmonic sensors and graphene plasmonic sensors and may open a new door for high-performance, multi-functional plasmonic sensing.

Spectral-Topological Superefficient Quantum Memory

In this work, we propose a universal (spectral-topological) approach towards the realization of the quantum memory, consisting of a small number of controlled absorbers, providing a super-high quantum efficiency of more than 99.9% required for practical quantum information science. In this way, we have found a series of spectral-topological matching conditions for the spectroscopic parameters of the absorbers which ensure the maximal efficiency in the broadband spectral range due to controlling the relative position (topology) of the eigenfrequencies in the absorbers spectrum. We also discuss the implementation of the proposed approach using the modern microwave and optical technologies.

Three-area-array coherent-dispersion stereo-imaging spectrometer.

A coherent-dispersion stereo-imaging spectrometer is presented, which combines three-view stereo imaging, interferometric spectroscopy and dispersive spectroscopy. Three area-array detectors record three spectral images of each scene unit from three views. For each of the three views, each scene unit is imaged on a given column of one area-array detector, and different wavelengths are dispersed across different rows of that column. For each scene unit, multiple interferograms are simultaneously generated at each view, each interferogram covering a separate wavelength range and located in a separate pixel. The orthographic view image is used to create a two-dimensional orthophoto image. The front view and back view images are used to reconstruct the three-dimensional stereoscopic image. Preliminary theoretical calculations are given. The instrument is a unique concept to obtain three-dimensional spatial information and one-dimensional spectral information while achieving high spectral resolution measurement of an ultraviolet-visible broadband spectral range (e.g., 0.05 nm at 450 nm together with 0.1 nm at 700 nm). It will be suitable for ultraviolet-visible hyperspectral remote sensing.