Wide Tuning Research Articles

Stable single-mode operation of distributed feedback quantum cascade laser under high current via a grating reflector

Abstract We report on an index-coupled distributed feedback (DFB) quantum cascade lasers (QCLs) of high single-mode stability by using of a grating reflector (GR) to reflect effectively light of a specific wavelength. Fabrications of the QCLs were performed with λ∕4 equivalent phase shift (EPS) or sampled Moiré grating (SMG) structure, which regulates the light intensity distribution in the cavity and coupling strength. Both EPS-GR and SMG-GR QCLs demonstrate a high emission wavelength precision and a side-mode-suppression-ratio (SMSR) of 24.5 dB at the injection current of 5 A and the pulse width of 5 μs, offering considerable output power even at the edge of the gain spectrum. Furthermore, we investigated the arrays of EPS-GR and SMG-GR QCLs with lower threshold current and higher output power by introducing semi-insulated InP (Fe) ranging from 8.25 to 8.67 μm and 8.16–8.63 μm, respectively. The present QCLs via a GR are prospective for applications requiring single-mode stability and wide tunability.

Achieving near-infrared-light-mediated switchable friction regulation on MXene-based double network hydrogels

AbstractMXene possesses great potential in enriching the functionalities of hydrogels due to its unique metallic conductivity, high aspect ratio, near-infrared light (NIR light) responsiveness, and wide tunability, however, the poor compatibility of MXene with hydrogels limits further applications. In this work, we report a uniformly dispersed MXene-functionalized poly-N-isopropylacrylamide (PNIPAM)/poly-2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) double network hydrogel (M—DN hydrogel) that can achieve switchable friction regulation by using the NIR light. The dispersity of MXene in hydrogels was significantly improved by incorporating the chitosan (CS) polymer. This M—DN hydrogel showed much low coefficient of friction (COF) at 25 °C due to the presence of hydration layer on hydrogel surface. After illuminating with the NIR light, M—DN hydrogel with good photothermal effect rapidly raised the temperature to above the lower critical solution temperature (LCST), which led to an obvious increase of surface COF owing to the destruction of the hydration layer. In addition, M—DN friction control hydrogel showed good recyclability and controllability by tuning “on-off” of the NIR light. This work highlights the construction of functional MXene hydrogels for intelligent lubrication, which provides insight for interface sensing, controlled transmission, and flexible robotic arms.

Defining the zerogap: cracking along the photolithographically defined Au–Cu–Au lines with sub-nanometer precision

Abstract Cracks are formed along the photolithographically pre-determined lines with extremely high yield and repeatability, when Cu clusters are introduced between planarized Au thin films sequentially deposited on a PET substrate. These clusters act as nanometer-sized spacers preventing the formation of contiguous metallic bond between the adjacent Au layers which will render prepatterned-cracking impossible. While the effective gap width is initially zero in the optical sense from microwaves all the way to the visible, outer-bending the PET substrate allows the gap width tuning into the 100 nm range, with the stability and controllability in the ranges of 100 s and Angstrom-scale, respectively. It is anticipated that our wafer-scale prepatterned crack technology with an unprecedented mixture of macroscopic length and Angstrom-scale controllability will open-up many applications in optoelectronics, quantum photonics and photocatalysis.

Superconducting Resonators with Voltage-Controlled Frequency and Nonlinearity

Voltage-tunable superconductor-semiconductor devices offer a unique platform to realize dynamic tunability in superconducting quantum circuits. By galvanically connecting a gated $\mathrm{In}\mathrm{As}$-$\mathrm{Al}$ Josephson junction to a coplanar waveguide resonator, we demonstrate the use of a superconducting element with wideband gate tunability. We show that the resonant frequency is controlled via a gate-tunable Josephson inductance and that the nonlinearity of the $\mathrm{In}\mathrm{As}$-$\mathrm{Al}$ junction is nondissipative as is the case with conventional ${\mathrm{Al}\mathrm{O}}_{\mathrm{x}}\text{-Al}$ junctions. As the gate voltage is decreased, the inductive participation of the junction increases up to $44\mathrm{%}$, resulting in the resonant frequency being tuned by over $2\phantom{\rule{0.2em}{0ex}}\mathrm{GHz}$. Utilizing the wide tunability of the device, we demonstrate that two resonant modes can be adjusted such that they strongly hybridize, exhibiting an avoided-level crossing with a coupling strength of $51\phantom{\rule{0.2em}{0ex}}\mathrm{MHz}$. Implementing such voltage-tunable resonators is the first step toward realizing wafer-scale continuous voltage control in superconducting circuits for qubit-qubit coupling, quantum limited amplifiers, and quantum memory platforms.

Full C-band wavelength-tunable, 250 MHz repetition rate mode-locked polarization-maintaining fiber laser

We demonstrate a full C-band wavelength-tunable mode-locked fiber laser with a repetition rate of 250 MHz, representing the highest repetition rate for C-band tunable mode-locked lasers thus far to the best of our knowledge. The polarization-maintaining fiber-based Fabry–Perot cavity enables a fundamental repetition rate of 250 MHz with a semiconductor saturable absorber mirror as a mode-locker. We observed a stable and single soliton mode-locking state with wide tunability of the center wavelength from 1505 to 1561 nm by adjusting the incident angle of a bandpass filter inside the cavity. The wavelength-tunable high-repetition-rate mode-locked laser covering the full C-band is expected to be a compelling source for many frequency-comb-based applications, including high-precision optical metrology, broadband absorption spectroscopy, and broadband optical frequency synthesizers.

The Interplay of Organic Spacers and Small Cations for Efficient Dion–Jacobson Perovskite Solar Cells

2D halide perovskites have displayed wide tunability in structure and physicochemical properties through the diversity and versatility of interlayer spacers. However, the interaction between the large spacer and small cation inside the inorganic framework has not been elucidated yet. Herein, the impact of small‐organic cation on the crystallization kinetics, carrier behavior, and the structure distortion of the low‐dimensional Dion–Jacobson (DJ) perovskite materials and solar cells is systematically studied. The formamidium (FA)‐based DJ film exhibits higher crystal orientation and larger crystal domain induced by slower crystallization as compared to methylammonium‐based one, accompanied with lower trap density, more efficient carrier transfer, and higher photovoltaic performance. As a result, the BDAFA2Pb3I10 perovskite solar cell delivers a champion power conversion efficiency up to 15.34%, which is the highest among FA‐based small‐n DJ series. Theoretical simulation results uncover that the smaller tilting and higher rigidity of the octahedra in the FA‐based DJ systems render more outstanding environmental stability, leading to well‐maintained 85% of its efficiency after prolonged storing time of 1020 h at 65 °C.

Suppressing phase disproportionation in quasi-2D perovskite light-emitting diodes

Electroluminescence efficiencies and stabilities of quasi-two-dimensional halide perovskites are restricted by the formation of multiple-quantum-well structures with broad and uncontrollable phase distributions. Here, we report a ligand design strategy to substantially suppress diffusion-limited phase disproportionation, thereby enabling better phase control. We demonstrate that extending the π-conjugation length and increasing the cross-sectional area of the ligand enables perovskite thin films with dramatically suppressed ion transport, narrowed phase distributions, reduced defect densities, and enhanced radiative recombination efficiencies. Consequently, we achieved efficient and stable deep-red light-emitting diodes with a peak external quantum efficiency of 26.3% (average 22.9% among 70 devices and cross-checked) and a half-life of ~220 and 2.8 h under a constant current density of 0.1 and 12 mA/cm2, respectively. Our devices also exhibit wide wavelength tunability and improved spectral and phase stability compared with existing perovskite light-emitting diodes. These discoveries provide critical insights into the molecular design and crystallization kinetics of low-dimensional perovskite semiconductors for light-emitting devices.

High-resolution molecular fingerprinting in the 11.6-15 µm range by a quasi-CW difference-frequency-generation laser source.

We report an approach for high-resolution spectroscopy using a widely tunable laser emitting in the molecular fingerprint region. The laser is based on difference-frequency generation (DFG) in a nonlinear orientation-patterned GaAs crystal. The signal laser, a CO2 gas laser, is operated in a kHz-pulsed mode while the pump laser, an external-cavity quantum cascade laser, is finely mode-hop-free tuned. The idler radiation covers a spectral range of ∼11.6-15 µm with a laser linewidth of ∼ 2.3 MHz. We showcase the versatility and the potential for molecular fingerprinting of the developed DFG laser source by resolving the absorption features of a mixture of several species in the long-wavelength mid-infrared. Furthermore, exploiting the wide tunability and resolution of the spectrometer, we resolve the broadband absorption spectrum of ethylene (C2H4) over ∼13-14.2 µm and quantify the self-broadening coefficients of some selected spectral lines.

Eco-friendly Solvent-Processible and highly luminescent perovskite nanocrystals with polymer zwitterions for Air-Stable optoelectronics

Perovskite quantum dots (QDs) have been studied as building blocks for next-generation optoelectronics owing to the wide tunability of their crystal structure and shape. One of the greatest hurdles for perovskite QDs is material instability when exposed to water, heat and polar solvents. Furthermore, the toxicity of solvents used for perovskite materials can lead to hazardous solution processes, unfavourable for large-area processes. In this paper, we report a perovskite surface engineering technique using zwitterionic polymer ligands, poly(carboxybetaine acrylamide) (PCA), to produce ultrastable perovskite QDs in polar solvents. We demonstrate that PCA polymers have a strong binding energy on the perovskite surface as coordinate bonds, according to experimental data and density functional theory (DFT) calculations. Moreover, the QDs produced with PCA maintained photoluminescence stability for over 50 d and uniform dispersion in alcohol solvents, which shows potential for an eco-friendly processability. Finally, we developed a band-gap-tuned white light-emitting diode (WLED) and produced roll-to-roll-processed thin films using slot-die coating.

Design of Compact Self-Quintuplexing Antenna With High-Isolation for Penta-Band Applications

This article presents a novel compact self-quintuplexing antenna architecture based on a substrate-integrated rectangular cavity (SIRC) for pentaband applications. The proposed self-quintuplexing antenna is constructed by employing an SIRC, one Pi-shaped slot (PSS), one T-shaped slot (TSS), and five 50Ω microstrip feedlines. The PSS and TSS are engraved on the top of the SIRC to create five radiating patches, which are excited by five 50Ω feedlines to achieve pentaband operation with self-quintuplexing characteristics. The resonating frequencies can be tuned independently based on the dimension of the radiator without disturbing other bands. A detailed parametric analysis is carried out to provide a suitable frequency tunable range and high isolation. In addition, an equivalent lumped circuit is developed to analyze the proposed self-quintuplexing antenna. To validate the proposed antenna architecture, an SIRC-based self-quintuplexing antenna operating at 2.29, 2.98, 3.65, 4.37, and 5.08 GHz is fabricated and demonstrated. The fabricated antenna offers competitive performance with a compact size of 0.173λ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , pentaband operation, high isolation of 29.31 dB, and a wide frequency tunability range from 2.29 GHz to 6.03 GHz. Furthermore, the fabricated self-quintuplexing antenna exhibits the measured realized gain of 3.59, 4.55, 3.91, 5.70, and 4.92dBi at 2.29, 2.98, 3.64, 4.37, and 5.08 GHz, respectively.

Investigation of size and barrier dependent efficiency in InAs quantum dot solar cells

Semiconductor Quantum Dots have unique properties, such as the quantum size effect that provide the breakthrough in optoelectronic devices. The small effective mass of electron and hole open-up an avenue of wide bandgap tunability in InAs Quantum Dots (QDs), making them an attractive material for solar cell application. Therein, 4x4 Luttinger Kohn Hamiltonian method is used to calculate the absorption co-efficient of epitaxially grown InAs QDs. Further, we studied the size-dependent absorption co-efficient and the barrier material model of InAs QDs capping with InP and GaAs. Our theoretical simulation predicts the efficiency of InAs/GaAs and InAs/InP system in the intrinsic layer of p-i-n structure solar cells.

Vertical Architecture Solution-Processed Quantum Dot Photodetectors with Amorphous Selenium Hole Transport Layer

Colloidal quantum dots (CQDs) provide wide spectral tunability and high absorption coefficients owing to quantum confinement and large oscillator strengths, which along with solution processability, allow a facile, low-cost, and room-temperature deposition technique for the fabrication of photonic devices. However, many solution-processed CQD photodetector devices demonstrate low specific-detectivity and slow temporal response. To achieve improved photodetector characteristics, limiting carrier recombination and enhancing photogenerated carrier separation are crucial. In this study, we develop and present an alternate vertical-stack photodetector wherein we use a solution-processed quantum dot photoconversion layer coupled to an amorphous selenium (a-Se) wide-bandgap charge transport layer that is capable of exhibiting single-carrier hole impact ionization and is compatible with active-matrix readout circuitry. This a-Se chalcogenide transport layer enables the fabrication of high-performance and reliable solution-processed quantum dot photodetectors, with enhanced charge extraction capabilities, high specific detectivity (D* ∼ 0.5–5 × 1012 Jones), fast 3 dB electrical bandwidth (3 dB BW ∼ 22 MHz), low dark current density (JD ∼ 5–10 pA/cm2), low noise current (in ∼ 20–25 fW/Hz1/2), and high linear dynamic range (LDR ∼ 130–150 dB) across the measured visible electromagnetic spectrum (∼405–656 nm).

Design and Development of Hybrid Halide Perovskites in Laser Devices

Organic-inorganic hybrid halide perovskite is a significant semiconductor material in photonics. Their outstanding optoelectronic characteristics have been reported, increasing energy conversion efficiency of perovskite solar battery by up to 25.5%, which is expected to be major competitors in silicon industry. According to the fundamentals of physics, a viable candidate for a light emitter must really be a superior direct band gap material. Even though there are a lot of papers on perovskite-based light emitting devices in this area, the corresponding laser devices are still lack of research. Here, since the first publication of lasing in hybrid perovskites in the 1990s, great effort has been made especially in 2014. Halide perovskites have the potential to revolutionize the nanophotonics field due to their solution-processed gain medium, almost defect-free semiconductor formation, high luminous efficiency, flexibility of nanostructure, excellent stability, and wide wavelength tunability. This article highlights the important researches on the optical gain from diverse hybrid halide perovskite material and the future challenges of lasing.

Enhanced energy storage performance achieved in Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 ceramics via domain structure and bandgap width tuning

Dielectric capacitors have attracted considerable attention owing to their excellent performance, including high charge-discharge rate as well as good temperature stability and fatigue resistance. Na0.5Bi0.5TiO3(NBT)-based ceramics are considered to be one of the most prospective lead-free dielectric materials because of their unique phase transition and relaxation characteristics. However, the energy storage performance obtained in the currently available materials is not satisfactory. We propose a synergetic optimization strategy through composition design and domain engineering in 0.74Na0.5Bi0.5TiO3-0.26Sr0.7Bi0.2TiO3 (NBSBT) ceramic, i.e., by simultaneously refining the grain size and widening the bandgap width, which facilitates a large breakdown strength and ΔP (Pm–Pr). A high dielectric constant and low remnant polarization is beneficial for obtaining improved energy storage properties. Piezoelectric force microscopy revealed that the introduction of NaNbO3(NN) disrupts the microdomains of the NBSBT ceramics and promotes the generation of polar nano-regions. An excellent energy storage density (Wrec) of 4.83 J/cm3 and a moderate efficiency (η) of 87.4% are obtained at the optimum composition of 0.85NBSBT-0.15NN. These characteristics demonstrate that (1-x)NBSBT-xNN based ceramics are promising candidate materials for high-temperature energy storage devices and provide an effective strategy for the design of next-generation dielectric capacitors.

Versatile full-colour nanopainting enabled by a pixelated plasmonic metasurface.

The growing interest to develop modern digital displays and colour printing has driven the advancement of colouration technologies with remarkable speed. In particular, metasurface-based structural colouration shows a remarkable high colour saturation, wide gamut palette, chiaroscuro presentation and polarization tunability. However, previous approaches cannot simultaneously achieve all these features. Here, we design and experimentally demonstrate a surface-relief plasmonic metasurface consisting of shallow nanoapertures that enable the independent manipulation of colour hue, saturation and brightness by individually varying the geometric dimensions and orientation of the nanoapertures. We fabricate microscale artworks using a reusable template-stripping technique that features photorealistic and stereoscopic impressions. In addition, through the meticulous arrangement of differently oriented nanoapertures, kaleidoscopic information states can be decrypted by particular combinations of incident and reflected polarized light.

Design of Tender X-ray Absorption Spectroscopy Beamline in Taiwan Photon Source

A new tender X-ray absorption spectroscopy beamline for operating over the photon energy range from 1.7 keV to 11 keV is under construction at port 32 of the Taiwan Photon Source (TPS). The TPS 32A beamline uses two back-to-back water-cooled double crystal monochromators (DCMs), InSb(111) and Si(111), for achieving the wide energy tunability. The beamline design takes advantage of the low emittance of the TPS accelerator and a bending magnet (BM) to obtain a high-brightness focussed beam. In order to overcome the issue of poor thermal conductivity of InSb(111) crystals while facing high thermal load, we have implemented the following features : (i) we have controlled the flux and heat load by optimizing the source collection angle of 2 × 0.15 mrad2 (h × v), and (ii) we have installed water cooled double-bounce high harmonic rejection mirrors (HHRMs) with a variable incidence angle upstream of the DCM to reduce the heat load on the first InSb crystal. The DCM is followed by a 2:1 toroidal focusing mirror (TFM) which focuses the beam parallel to the floor of the experimental endstation. The simulated focus beam size is 0.9 × 0.9 mm2 (h × v, FWHM) using the InSb(111) DCM at 1.7 keV, and 0.2 × 0.45 mm2 (h × v, FWHM) using the Si(111) DCM at 4 keV, respectively. The photon flux is 1010 -1012 photons s−1 in the energy range of 1.7 to 11 keV at the sample stage after passing through the Be windows. The design parameters of photon flux and beam spot size will facilitate a tender X-ray source for carrying out high-quality X-ray absorption spectroscopy experiments.

Research Progress of Wide Tunable Bragg Grating External Cavity Semiconductor Lasers.

In this paper, we review the progress of wide tunable Bragg grating external cavity semiconductor lasers (BG-ECSLs). We concentrate on BG-ECSLs based on the wide tunable range for multicomponent detection. Wide tunable BG-ECSLs have many important applications, such as wavelength-division multiplexing (WDM) systems, coherent optical communications, gas detection and atom cooling. Wide tunability, narrow linewidth and a high side-mode suppression ratio BG-ECSLs have attracted much attention for their merits. In this paper, three main structures for achieving widely tunable, narrow linewidth, high side-mode suppression ratio BG-ECSLs are reviewed and compared in detail, such as the volume Bragg grating (VBG) structure, fiber Bragg grating (FBG) structure and waveguide Bragg grating (WBG) structure of ECSLs. The advantages and disadvantages of different structures of BG-ECSLs are analyzed. The results show that WBG-ECSLs are a potential way to realize the integration, small size, wide tuning range, stable spectral output and high side-mode suppression ratio laser output. Therefore, the use of WBG as optical feedback elements is still the mainstream direction of BG-ECSLs, and BG-ECSLs offer a further new option for multicomponent detection and multi-atoms cooling.

Synthesis and Tuning of Gold Nanoparticles Supported on Polymorphic Semicrystalline Nanoporous Polymer for Catalytic Aerobic Oxidation of Alcohols

AbstractThe wide and complex tunability of gold nanoparticles (AuNPs) supported on nanoporous, semicrystalline, and polymorphic polymer matrices consisting of syndiotactic polystyrene (sPS) or multiblock syndiotactic polystyrene‐co‐cis‐1,4 poly(butadiene) (sPSB) is herein described and correlated with the performances in aerobic oxidation of (±)‐1‐phenylethanol. Impregnation or deposition‐impregnation synthetic methods yielded AuNPs of middle size (10–20 nm) on the surface of polymer grains. The co‐precipitation method leads to small AuNPs (4–5 nm) homogenously dispersed in the support with quantitative entrapment of the gold. Thermal or solvent annealing afforded modifications of polymer crystalline phase and AuNPs morphology. The annealing with chloroform/water mixture increases the crystallinity of the nanoporous forms and converts compact γ and β phases into the nanoporous ϵ and δ phases. The thermal treatment of the AuNPs‐sPS(B) catalysts afford defective NPs with enhanced catalytic activity. The solvent‐induced formation of the nanoporous forms improves permeability to solvents and reactants and, in turn, the catalytic properties.

Energy transfer induced color tunable photoluminescence in Tb3+/Sm3+ co-doped Y2O3 nano-phosphor for warm white LEDs

In this work, the Tb3+/Sm3+ doped and co-doped Y2O3 nano-phosphors have been prepared by solution combustion method. The structural and morphological analyses of Y2O3 nano-phosphors confirm its nano-crystalline structure. The EDS spectra reveal the evidence of Y, Sm, Tb and O elements in the co-doped phosphor. The excitation spectrum of the Tb3+/Sm3+ co-doped nano-phosphor contains the excitation bands due to Tb3+ and Sm3+ ions. The Tb3+ doped nano-phosphor gives intense green (541 nm) and slightly weak blue (483 nm) emissions upon 292 nm excitation. The critical distance and PL intensity per activator ion were calculated to identify the factor responsible for quenching the PL intensity. The PL intensity of green and blue emission bands decreases regularly via doping of Sm3+ ion. This occurs due to energy transfer from Tb3+ to Sm3+ ions. The energy transfer leads to improve the PL intensity of the orange red emission band of Sm3+ ion. The energy transfer has been verified by the lifetime measurements and the energy transfer efficiency is found to increase via doping of Sm3+ ion. The CIE diagrams show wide color tunability from the greenish yellow to reddish orange regions and the color purity of Tb3+ doped nano-phosphor also changes accordingly via Sm3+ doping. The CCT analysis of Tb3+/Sm3+ co-doped nano-phosphors indicates a warm nature of the emitted light. Therefore, the Tb3+/Sm3+ co-doped Y2O3 nano-phosphor may be applied in the field of display devices, color tunable devices and warm white LEDs.

Pushing the Emission Envelope for Full-Color Realization of Colloidal Semiconductor Core/Shell Nanoplatelets

Colloidal semiconductor nanoplatelets (NPLs) have been known to exhibit favorable optical characteristics, such as a narrow emission bandwidth, giant oscillator strength, suppressed Auger recombination, and polarized emission, which can merit their use in light-emitting diodes and lasing devices. However, to date, NPLs have shown a relatively limited range of emission energy because of their thickness-dependent discrete band gap and restricted choice of chemical composition (mostly CdSe-based), impeding the realization of R, G, and B full-color display based on NPLs. CdSe-based core/shell NPLs can only cover the emission range from yellowish green (∼550 nm) to red (∼620 nm). In this study, we synthesize CdZnSe/ZnS core/shell NPLs with significantly enhanced spectral tunability over a broad spectral range (425–570 nm). Particularly, to overcome the difficulty in the synthesis of composition-controlled CdZnSe NPLs, we carried out a Cd-to-Zn direct cation exchange reaction on CdSe/ZnS core/shell NPLs using ZnI2 and an oleylamine (or trioctylphosphine oxide) ligand, which allows for the composition change in NPL emitting core while maintaining the original shape of NPLs. With the control of the reaction temperature and time as well as the ligands, the exchange reaction enables us to demonstrate an unprecedentedly wide emission range and spectral tunability of NPLs with the emission wavelength reaching 425 nm. Furthermore, as the core alloying proceeds, NPLs maintain excellent color purity and exhibit linearly polarized emission. Our light-emitting devices using the cation-exchanged CdZnSe/ZnS NPLs hinted at the possibility of using the NPLs in full-color display applications. Based on the elemental mapping analysis and experimental results, we proposed the temperature-dependent cation exchange reaction process in core/shell NPLs.