Nonlinearity-tailored fiber laser technology for low-noise, ultra-wideband tunable femtosecond light generation

The emission wavelength of a laser is physically predetermined by the gain medium used. Consequently, arbitrary wavelength generation is a fundamental challenge in the science of light. Present solutions include optical parametric generation, requiring complex optical setups and spectrally sliced supercontinuum, taking advantage of a simpler fiber technology: a fixed-wavelength pump laser pulse is converted into a spectrally very broadband output, from which the required resulting wavelength is then optically filtered. Unfortunately, this process is associated with an inherently poor noise figure, which often precludes many realistic applications of such supercontinuum sources. Here, we show that by adding only one passive optical element—a tapered photonic crystal fiber—to a fixed-wavelength femtosecond laser, one can in a very simple manner resonantly convert the laser emission wavelength into an ultra-wide and continuous range of desired wavelengths, with very low inherent noise, and without mechanical realignment of the laser. This is achieved by exploiting the double interplay of nonlinearity and chirp in the laser source and chirp and phase matching in the tapered fiber. As a first demonstration of this simple and inexpensive technology, we present a femtosecond fiber laser continuously tunable across the entire red–green–blue spectral range.

Miniature tunable Airy beam optical meta-device

Tunable Airy beams with controllable propagation trajectories have sparked interest in various fields,such as optical manipulation and laser fabrication.Existing research approaches encounter challenges related to insufficient compactness and integration feasibility,or they require enhanced tunability to enable real-time dynamic manipulation of the propagation trajectory.In this work,we present a novel method that utilizes a dual metasurface system to surpass these limitations,significantly enhancing the practical potential of the Airy beam.Our approach involves encoding a cubic phase profile and two off-axis Fresnel lens phase profiles across the two metasurfaces.The validity of the proposed strategy has been confirmed through simulation and experimental results.The proposed meta-device addresses the existing limitations and lays the foundation for broadening the applicability of Airy beams across diverse domains,encompassing light-sheet microscopy,laser fabrication,optical tweezers,etc.

The Combined Effect of Spin-Transfer Torque and Voltage-Controlled Strain Gradient on Magnetic Domain-Wall Dynamics:Toward Tunable Spintronic Neuron

Magnetic domain wall(DW), as one of the promising information carriers in spintronic devices, have been widely investigated owing to its nonlinear dynamics and tunable properties. Here, we theoretically and numerically demonstrate the DW dynamics driven by the synergistic interaction between current-induced spin-transfer torque(STT) and voltage-controlled strain gradient(VCSG) in multiferroic heterostructures. Through electromechanical and micromagnetic simulations, we show that a desirable strain gradient can be created and it further modulates the equilibrium position and velocity of the current-driven DW motion. Meanwhile, an analytical Thiele's model is developed to describe the steady motion of DW and the analytical results are quite consistent with the simulation data. Finally, we find that this combination effect can be leveraged to design DW-based biological neurons where the synergistic interaction between STT and VCSG-driven DW motion as integrating and leaking motivates mimicking leaky-integrate-and-fire(LIF) and self-reset function. Importantly, the firing response of the LIF neuron can be efficiently modulated, facilitating the exploration of tunable activation function generators, which can further help improve the computational capability of the neuromorphic system.

Tunable superconducting resonators via on-chip control of local magnetic field

Superconducting microwave resonators play a pivotal role in superconducting quantum circuits.The ability to finetune their resonant frequencies provides enhanced control and flexibility.Here,we introduce a frequency-tunable superconducting coplanar waveguide resonator.By applying electrical currents through specifically designed ground wires,we achieve the generation and control of a localized magnetic field on the central line of the resonator,enabling continuous tuning of its resonant frequency.We demonstrate a frequency tuning range of 54.85 MHz in a 6.21-GHz resonator.This integrated and tunable resonator holds great potential as a dynamically tunable filter and as a key component of communication buses and memory elements in superconducting quantum computing.

A Transparent Photoresist Made of Titanium Dioxide Nanoparticle-Embedded Acrylic Resin with a Tunable Refractive Index for UV-Imprint Lithography

Transparent photoresists with a high refractive index(RI)and high transmittance in visible wavelengths have promising functionalities in optical fields.This work reports a kind of tunable optical material composed of titanium dioxide nanoparticles embedded in acrylic resin with a high RI for ultraviolet(UV)-imprint lithography.The hybrid film exhibits a tunable RI of up to 1.67(589 nm)after being cured by UV light,while maintaining both a high transparency of over 98%in the visible light range and a low haze of less than 0.05%.The precision machining of optical microstructures can be imprinted easily and efficiently using the hybrid resin,which acts as a light guide plate(LGP)to guide the light from the side to the top in order to conserve the energy of the display device.These preliminary studies based on both laboratory and commercial experiments pave the way for exploiting the unparalleled optical properties of nanocomposite resins and promoting their industrial application.

Defect-induced synthesis of nanoscale hierarchically porous metal-organic frameworks with tunable porosity for enhanced volatile organic compound adsorption

Nanoscale hierarchically porous metal-organic frameworks(NH-MOFs)synergistically combine the advantages of nanoscale MOFs and hierarchically porous MOFs,resulting in remarkable characteristics such as increased specific surface area,greater porosity,and enhanced exposure of active sites.Herein,nanoscale hierarchically porous UIO-66(UIO-66_X)was synthesized using a defect-induced strategy that employed ethylene diamine tetraacetic acid(EDTA)as a modulator.The introduced EDTA occupies the coordination sites of organic ligands,promoting the formation and growth of UIO-66 crystal nuclei and inducing defects during synthesis.The as-synthesized UIO-66_X crystals exhibit a uniform distribution with an average size of approximately 100 nm.In addition,the total pore volume attains a remarkable value of 0.95 cm^(3)g^(-1),with mesopores constituting 36.8% of the structure.Furthermore,the porosities of UIO-66_X can be easily tuned by controlling the molar ratio of EDTA/Zr^(4+).In addition,the as-synthesized UIO-66_X exhibits excellent adsorption capacities for n-hexane(344 mg g^(-1))and pxylene(218 mg g^(-1)),which are 44.5% and 27.5% higher than those of conventional UIO-66,respectively.Finally,the adsorption behavior of n-hexane and p-xylene molecules in UIO-66_X was investigated using density functional theory simulations.

A Dual-polarized Frequency Selective Rasorber with a Tunable Transparent Band

A tunable dual polarization absorption-transmission-absorption(A-T-A)frequency selective absorbers(FSR)to address the issue of high insertion loss in current tunable FSRs is proposed.The lumped resistors are loaded onto the lossy layer to absorb electromagnetic waves within the absorption band.The varactor diodes are loaded onto another lossless layer to control the transmission frequency band of the FSR.Its equivalent circuit model is provided.The proposed tunable FSR can change the passband within the range of 14.5~15.5 GHz by changing the bias voltage applied to the lossless transmission layer,while maintaining insertion loss above-1.67 dB.The series resonant structure of the lossy layer generates bilateral absorption bands between 10.2~13.5 GHz and 17.2~22 GHz,with broadband reflection suppression ranging from 10.3 GHz to 22 GHz(70.7%).The prototype is manufactured,and the measured results have verified the simulation results.

3D Printing of Periodic Porous Metamaterials for Tunable Electromagnetic Shielding Across Broad Frequencies

The new-generation electronic components require a balance between electromagnetic interference shielding efficiency and open structure factors such as ventilation and heat dissipation.In addition,realizing the tunable shielding of porous shields over a wide range of wavelengths is even more challenging.In this study,the well-prepared thermoplastic polyurethane/carbon nanotubes composites were used to fabricate the novel periodic porous flexible metamaterials using fused deposition modeling 3D printing.Particularly,the investigation focuses on optimization of pore geometry,size,dislocation configuration and material thickness,thus establishing a clear correlation between structural parameters and shielding property.Both experimental and simulation results have validated the superior shielding performance of hexagon derived honeycomb structure over other designs,and proposed the failure shielding size(D_(f)≈λ/8-λ/5)and critical inclined angle(θf≈43°-48°),which could be used as new benchmarks for tunable electromagnetic shielding.In addition,the proper regulation of the material thickness could remarkably enhance the maximum shielding capability(85-95 dB)and absorption coefficient A(over 0.83).The final innovative design of the porous shielding box also exhibits good shielding effectiveness across a broad frequency range(over 2.4 GHz),opening up novel pathways for individualized and diversified shielding solutions.

A low-frequency pure metal metamaterial absorber with continuously tunable stiffness

To address the incompatibility between high environmental adaptability and deep subwavelength characteristics in conventional local resonance metamaterials,and overcome the deficiencies in the stability of existing active control techniques for band gaps,this paper proposes a design method of pure metal vibration damping metamaterial with continuously tunable stiffness for wideband elastic wave absorption.We design a dual-helix narrow-slit pure metal metamaterial unit,which possesses the triple advantage of high spatial compactness,low stiffness characteristics,and high structural stability,enabling the opening of elastic flexural band gaps in the low-frequency range.Similar to the principle of a sliding rheostat,the introduction of continuously sliding plug-ins into the helical slits enables the continuous variation of the stiffness of the metamaterial unit,achieving a continuously tunable band gap effect.This successfully extends the effective band gap by more than ten times.The experimental results indicate that this metamaterial unit can be used as an additional vibration absorber to absorb the low-frequency vibration energy effectively.Furthermore,it advances the metamaterial absorbers from a purely passive narrowband design to a wideband tunable one.The pure metal double-helix metamaterials retain the subwavelength properties of metamaterials and are suitable for deployment in harsh environments.Simultaneously,by adjusting its stiffness,it substantially broadens the effective band gap range,presenting promising potential applications in various mechanical equipment operating under adverse conditions.

Liquid Metal Grid Patterned Thin Film Devices Toward Absorption‑Dominant and Strain‑Tunable Electromagnetic Interference Shielding

The demand of high-performance thin-film-shaped deformable electromagnetic interference(EMI)shielding devices is increasing for the next generation of wearable and miniaturized soft electronics.Although highly reflective conductive materials can effectively shield EMI,they prevent deformation of the devices owing to rigidity and generate secondary electromagnetic pollution simultaneously.Herein,soft and stretchable EMI shielding thin film devices with absorption-dominant EMI shielding behavior is presented.The devices consist of liquid metal(LM)layer and LM grid-patterned layer separated by a thin elastomeric film,fabricated by leveraging superior adhesion of aerosol-deposited LM on elastomer.The devices demonstrate high electromagnetic shielding effectiveness(SE)(SE_(T) of up to 75 dB)with low reflectance(SER of 1.5 dB at the resonant frequency)owing to EMI absorption induced by multiple internal reflection generated in the LM grid architectures.Remarkably,the excellent stretchability of the LM-based devices facilitates tunable EMI shielding abilities through grid space adjustment upon strain(resonant frequency shift from 81.3 to 71.3 GHz@33%strain)and is also capable of retaining shielding effectiveness even after multiple strain cycles.This newly explored device presents an advanced paradigm for powerful EMI shielding performance for next-generation smart electronics.

Review of the State of Art of Tunable Impulse Ultra-Wideband Technology as Integrator for Wireless Sensing and Identifications Short-Range Networks

Impulse based Ultra wideband technology has been the motivation of many recent researches with the potential of many applications to be researched. The uniqueness of the physical characteristics of the generated signal combined with the high flexibility of for different data rates at the physical layer design level have been addressed in considerable number of researches recently. This paper presents in depth reviews of the different concepts of tunable impulse based ultra wideband from the different researchers views. Research proposals of Cross layer architectures as PHY-MAC aware Impulse based ultra wideband solutions, link-budget communication design with performance evaluations in different test beds implementations are investigated in this paper. Such in-depth review can help researchers in this field to have better understanding of the different possibilities of designing new impulse-based ultra wideband solutions for future potential communication scenarios. Special focus on utilizing the advantage of impulse-based ultra wideband signal design flexibility as integrator for different short to medium wireless infrastructures mainly sharing common design constraints and requirements. Finding remarks from reviewing nearest-field literature combined with researches benchmarking to inspire researches proposal for this topic.

Micromechanical Tunable Optical Filter

A micromachined vertical cavity tunable filter with AlGaAs/GaAs distributed Bragg reflector is presented.This filter can be electrostatic tuning over a range of 28nm with an applied voltage of 7V.

1.55μm Fabry-Perot Thermo-Optical Tunable Filter with Amorphous-Si as Cavity

A 1.55μm Fabry-Perot (F-P) thermo-optical t unable filter is fabricated.The cavity is made of amorphous silicon (a-Si) layer grown by electron-beam evaporation technique.Due to the excellent thermo-optical property of a-Si,the refractive index of the F-P cavity will be changed by heating;the transmittance resonant peak will therefore shift substantially.The measured tuning rang is 12nm, FWHM (full-width-at-half-maximum) of the transmissi on peak is 9nm,and heating efficiency is 0.1K/mW.The large FWHM is mainly due to th e non-ideal coating deposition and mirror undulation.Possible improvements to increase the efficiency of heating are suggested.

1.3μm Si-Based MOEMS Optical Tunable Filter with a Tuning Range of 90nm

Optical filters capable of single control parameter based wide tuning are implemented and studied.A prototype surface micromachined 1 3μm Si based MOEMS (micro opto electro mechanical systems) tunable filter exhibits a continuous and large tuning range of 90nm at 50V tuning voltage.The filter can be integrated with Si based photodetector in a low cost component for coarse wavelength division multiplexing systems operating in the 1 3μm band.

Monolithic Integration of a Widely Tunable Laser with SOA Using Quantum-Well Intermixing

This paper presents an SG-DBR with a monolithically integrated SOA fabricated using quantum-well intermixing （QWI） for the first time in China's Mainland. The wavelength tuning range covers 33nm and the output power reaches 10mW with an SOA current of 50mA. The device can work at available channels with SMSR over 35dB.

A Wavelength Tunable DBR Laser Integrated with an Electro-Absorption Modulator by a Combined Method of SAG and QWI

We report a wavelength tunable electro-absorption modulated DBR laser based on a combined method of SAG and QWI. The threshold current is 37mA and the output power at 100mA gain current is 3.5mW. When coupled to a single-mode fiber with a coupling efficiency of 15% ,more than a 20dB extinction ratio is observed over the change of EAM bias from 0 to -2V. The 4.4nm continuous wavelength tuning range covers 6 channels on a 100GHz grid for WDM telecommunications.

Tunable Distributed Bragg Reflector Laser Fabricated by Bundle Integrated Guide

The tunable BIG RW distributed Bragg reflector lasers with two different coupling coefficient gratings are proposed and fabricated.The threshold current of the laser is 38mA and the output power is more than 8mW.The tunable range of the laser is 3 2nm and the side mode suppression ratio is more than 30dB.The variation of the output power within the tunable wavelength range is less than 0 3dB.

Computer aided design and analysis of a tunable muzzle brake

This research work deals with the design of a tunable muzzle brake [10] for a rifle chambered in 5.56 x 45 NATO ammunition. It proposes to solve the problem of handling differences from shooter to shooter by incorporating the feature of tunability. Beside this, it also solves the problem of requirement of optimum recoil in short recoil weapons. This innovation gives this design an edge over its already existing counterparts in the market. The product is designed using the internal ballistics calculations and the investigations been performed using solidworks flow simulation tool and ANSYS static structural to check the parameters like velocity distribution, pressure growth, and muzzle brake force along the series of ports and comparison of the so found results with those devised by the authors of the documents mentioned in references. This assures the market adaptability of the product for satisfactory performance, when brought among its already existing counterpart, though with a slight edge over them due to tunability. The results so found shall be concluded satisfactory regarding the performance of muzzle brake.

Influence of laser intensity in second-harmonic detection with tunable diode laser multi-pass absorption spectroscopy

Tunable diode laser absorption spectroscopy （TDLAS） has been widely employed in atmospheric trace gases detection. The ratio of the second-harmonic signal to the intensity of laser beam incident to the multi-pass cell is proved to be proportional to the product of the path length and the gas concentration under any condition. A new calibration method based on this relation in TDLAS system for the measurement of trace gas concentration is proposed for the first time. The detection limit and the sensitivity of the system are below 110 and 31ppbv （parts-per-billion in volume）, respectively.

Research of an Active Tunable Vibration Absorber for Helicopter Vibration Control

Significant structural vibration is an undesirable characteristic in helicopter flight that leads to structural fatigue, poor ride quality for passengers and high acoustic signature. Previous Individual Blade Control (IBC) techniques to reduce these effects have been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an active tunable vibration absorber using IBC approach to adaptively alter the 'structural impedance' at the blade root. In this paper, a mathematical model was developed to predict the response under harmonic excitations. An adaptive notch algorithm was designed and implemented on a TMS320c40 DSP platform. Reference signal synthesis techniques were used to automatically track the shifts in the fundamental vibratory frequency due to variations in flight conditions. Closed-loop tests performed on the proof-of-concept hardware achieved significant vibration suppression at harmonic peaks as well as the broadband reduction in vibration. The investigation verified the capability of the Smart Spring to suppress multiple harmonic components in blade vibration through active impedance control.