Search

The wavelength tunability of a general transmittance function (GTF) is investigated in a first‐order fibre multiwavelength filter based on a polarisation‐diversified fibre loop, which utilised a composite combination of wave retarders. The filter consists of a polarisation beam splitter, two equal‐length high birefringence fibre (HBF) segments, and two different sets of wave retarders with each set positioned before each HBF segment. Specifically, a combination of a set of dual quarter‐wave retarders (QWRs) and another set of a QWR and a half‐wave retarder is focused upon. By considering the effect of the four wave retarders and two HBF segments on the output polarisation state (OPS) of each element in the filter, the four wave retarder angles (WRAs) are identified that caused all polarisation states on the OPS trace of the second HBF move in the direction of wavelength decrease, resulting in a redshift of the GTF. 360 WRA sets are derived that enabled tuning the GTF by one free spectral range SR. For eight sets chosen from the WRA sets, inducing a wavelength shift of SR/8 for each set order, wavelength‐shifted spectra are calculated. Finally, this theoretical prediction is experimentally verified, confirming the wavelength tunability of the GTF of the filter. [ABSTRACT FROM AUTHOR]

Contrary to local resonances of single nanostructures, collective (or nonlocal) resonances in periodic metasurfaces, such as surface lattice resonances (SLRs), can significantly enhance light–matter interaction, leading to higher spectral selectivity. The dynamic control of such nonlocal response represents an emerging field of research. While tuning of SLRs has been demonstrated in plasmonic metasurfaces, the use of dielectric metasurfaces provides additional conditions to control both reflectance and transmittance, with minimum absorption effects. A close‐to‐homogeneous environment is usually required to guarantee the excitation of SLRs. Here, we propose theoretically and demonstrate experimentally a practical strategy for the tuning of SLRs in dielectric metasurfaces when an arbitrary index mismatch is considered between substrate and superstrate. The approach is based on a generalized lattice sum theory that accounts for the presence of a substrate. Dynamic tuning of the SLRs in silicon metasurfaces placed on a substrate is achieved with a changeable superstrate via an optofluidic process. Two tuning mechanisms are revealed corresponding to shifting and damping of the SLR, depending on the superstrate–substrate refractive index contrast. The demonstrated dynamic manipulation of transmission and reflection may be exploited in dielectric metasurfaces for tunable spectral selectivity, sensing, or novel display technologies. [ABSTRACT FROM AUTHOR]

Abstract The wavelength tunability of a general transmittance function (GTF) is investigated in a first‐order fibre multiwavelength filter based on a polarisation‐diversified fibre loop, which utilised a composite combination of wave retarders. The filter consists of a polarisation beam splitter, two equal‐length high birefringence fibre (HBF) segments, and two different sets of wave retarders with each set positioned before each HBF segment. Specifically, a combination of a set of dual quarter‐wave retarders (QWRs) and another set of a QWR and a half‐wave retarder is focused upon. By considering the effect of the four wave retarders and two HBF segments on the output polarisation state (OPS) of each element in the filter, the four wave retarder angles (WRAs) are identified that caused all polarisation states on the OPS trace of the second HBF move in the direction of wavelength decrease, resulting in a redshift of the GTF. 360 WRA sets are derived that enabled tuning the GTF by one free spectral range SR. For eight sets chosen from the WRA sets, inducing a wavelength shift of SR/8 for each set order, wavelength‐shifted spectra are calculated. Finally, this theoretical prediction is experimentally verified, confirming the wavelength tunability of the GTF of the filter.

Contrary to local resonances of single nanostructures, collective (or nonlocal) resonances in periodic metasurfaces, such as surface lattice resonances (SLRs), can significantly enhance light–matter interaction, leading to higher spectral selectivity. The dynamic control of such nonlocal response represents an emerging field of research. While tuning of SLRs has been demonstrated in plasmonic metasurfaces, the use of dielectric metasurfaces provides additional conditions to control both reflectance and transmittance, with minimum absorption effects. A close‐to‐homogeneous environment is usually required to guarantee the excitation of SLRs. Here, we propose theoretically and demonstrate experimentally a practical strategy for the tuning of SLRs in dielectric metasurfaces when an arbitrary index mismatch is considered between substrate and superstrate. The approach is based on a generalized lattice sum theory that accounts for the presence of a substrate. Dynamic tuning of the SLRs in silicon metasurfaces placed on a substrate is achieved with a changeable superstrate via an optofluidic process. Two tuning mechanisms are revealed corresponding to shifting and damping of the SLR, depending on the superstrate–substrate refractive index contrast. The demonstrated dynamic manipulation of transmission and reflection may be exploited in dielectric metasurfaces for tunable spectral selectivity, sensing, or novel display technologies.

Semiconductor–metal nanocomposites have been widely investigated to modify the intrinsic properties of materials used for optoelectronic devices and sensing applications. In this study, a method for rapid synthesis of MoS2–Ag nanocomposites via laser-assisted photoreduction was proposed. For the photoreduction process, we used AgNO3 solution as a metal source. Under laser irradiation, Ag ions were easily reduced on MoS2 by photo-generated electrons from MoS2. The optical properties of MoS2–Ag nanocomposites were easily controlled by simple adjustment of the photoreduction time. To investigate the surface-enhanced Raman scattering (SERS) effect of the MoS2–Ag nanocomposites, the SERS spectra of methylene blue (MB) on MoS2–Ag nanocomposites were measured, and the nanocomposites were found to enhance the Raman scattering intensity of MB up to ∼106. Therefore, the laser-assisted photoreduction method has great potential for rapid synthesis and optical tuning of semiconductor–metal nanocomposites.

Metasurfaces can be opportunely and specifically designed to manipulate electromagnetic wavefronts. In recent years, a large variety of metasurface-based optical devices such as planar lenses, beam deflectors, polarization converters, and so on have been designed and fabricated. Of particular interest are tunable metasurfaces, which allow the modulation of the optical response of a metasurface; for instance, the variation in the focal length of a converging metalens. Response tunability can be achieved through external sources that modify the permittivity of the materials constituting the nanoatoms, the substrate, or both. The modulation sources can be classified into electromagnetic fields, thermal sources, mechanical stressors, and electrical bias. Beside this, we will consider optical modulation and multiple approach tuning strategies. A great variety of tunable materials have been used in metasurface engineering, such as transparent conductive oxides, ferroelectrics, phase change materials, liquid crystals, and semiconductors. The possibility of tuning the optical properties of these metamaterials is very important for several applications spanning from basic optics to applied optics for communications, depth sensing, holographic displays, and biochemical sensors. In this review, we summarize the recent progress on electro-optical magnetic, mechanical, and thermal tuning of metasurfaces actually fabricated and experimentally tested in recent years. At the end of the review, a short section on possible future perspectives and applications is included. [ABSTRACT FROM AUTHOR]

[Display omitted] Ligand-assisted re-precipitation (LARP) is one of the most practicing techniques for synthesizing colloidal nanocrystals (NCs). But due to its fast reaction kinetics, it offers limited synthesis control. In the present study, we report a novel, precursor silanization-based room temperature technique unveiling slow crystallization of Cs 4 PbBr 6 /CsPbBr 3 dual-phase nanocrystals (DPNCs) protected with a dense silica cloud-like matrix. Unlike conventional LARP, we can observe the tuneable optical bandgap of the DPNCs as a function of reaction time because of the slow reaction kinetics. The as-synthesized DPNCs exhibit a high photoluminescence quantum yield (PLQY) of 76% with ultrahigh stability while retaining ∼ 100% of their initial PLQY in an ambient environment with a relative humidity of 55% for more than 1 year. DPNCs demonstrates ambient photostability of 560 h, and water stability of 25 days. This interesting precursor silanization technique developed here can be extended for the synthesis of other nanomaterials. [ABSTRACT FROM AUTHOR]

Pure Q-switching (self-pulsating) behaviour is shown for the first time in an optically injected two-section quantum-dot laser. Upon CW optical injection, it was possible to switch the operation regime from free-running mode-locking to locked Q-switching. Under this regime, the pulse repetition rate of around 1 GHz was tunable with injection power (by more than 100 MHz) and absorber reverse bias. Moreover, through injection-locking, the Q-switched output was spectrally tunable by around 7 nm, by tuning the master laser. The seamless switch between mode-locking and Q-switching with optical injection as well as the tunability and control afforded by injection-locking could open up a range of applications, such as in multi-modal imaging. On a more fundamental level, this investigation has also generated new insights into the dynamics of quantum-dot lasers and the optical injection process.

In this letter, the viability of Artificial Neural Networks (ANNs) for widen the overall measurement range of optical sensors, based on interferometric arrangements, is demonstrated. Moreover, it is proven that by using ensembles of ANN regressions the traditional $2\pi $ ambiguity of interferometric sensors can be overcome. Here, a simple temperature sensor was implemented and from measured spectra a dataset of features was formed. For this sensor, the measurement range was increased by a factor of 2 and the achieved mean absolute error was $0.17{^{\circ }}\text{C}$. Finally, it is shown that based on numerical results it can be expected that by using these types of ensembles the measurement range and the precision of predictions can be further enhanced. [ABSTRACT FROM AUTHOR]

Pure Q-switching (self-pulsating) behaviour is shown for the first time in an optically injected two-section quantum-dot laser. Upon CW optical injection, it was possible to switch the operation regime from free-running mode-locking to locked Q-switching. Under this regime, the pulse repetition rate of around 1 GHz was tunable with injection power (by more than 100 MHz) and absorber reverse bias. Moreover, through injection-locking, the Q-switched output was spectrally tunable by around 7 nm, by tuning the master laser. The seamless switch between mode-locking and Q-switching with optical injection as well as the tunability and control afforded by injection-locking could open up a range of applications, such as in multi-modal imaging. On a more fundamental level, this investigation has also generated new insights into the dynamics of quantum-dot lasers and the optical injection process. [ABSTRACT FROM AUTHOR]

Metasurfaces can be opportunely and specifically designed to manipulate electromagnetic wavefronts. In recent years, a large variety of metasurface-based optical devices such as planar lenses, beam deflectors, polarization converters, and so on have been designed and fabricated. Of particular interest are tunable metasurfaces, which allow the modulation of the optical response of a metasurface; for instance, the variation in the focal length of a converging metalens. Response tunability can be achieved through external sources that modify the permittivity of the materials constituting the nanoatoms, the substrate, or both. The modulation sources can be classified into electromagnetic fields, thermal sources, mechanical stressors, and electrical bias. Beside this, we will consider optical modulation and multiple approach tuning strategies. A great variety of tunable materials have been used in metasurface engineering, such as transparent conductive oxides, ferroelectrics, phase change materials, liquid crystals, and semiconductors. The possibility of tuning the optical properties of these metamaterials is very important for several applications spanning from basic optics to applied optics for communications, depth sensing, holographic displays, and biochemical sensors. In this review, we summarize the recent progress on electro-optical magnetic, mechanical, and thermal tuning of metasurfaces actually fabricated and experimentally tested in recent years. At the end of the review, a short section on possible future perspectives and applications is included.

Nanomaterials with tunable optical properties have emerged as active components for advanced nanophotonic devices. Herein, the fabrication of hierarchical nanostructures through the integration of various tunable nanomaterials for diverse applications remains a challenge. Here, a two-step process consisting of the synthesis of silicon nanoparticles (Si NPs) via laser ablation followed by plasma-enhanced chemical vapor deposition of hexagonal-boron-nitride (h-BN) nanowalls has been implemented to form hierarchical Si@h-BN NPs. Experimental and numerical analyses confirm that h-BN decoration modulates the color and brightness of the hierarchical NPs (i.e., shape, intensity, and spectral width of intrinsic optical resonances). Moreover, the color palette of the resulting Si@h-BN NPs can be remotely controlled by infrared laser irradiation. We reveal that this control is related to the modification of the complex morphology of the hierarchical Si@h-BN NPs through the mutual influence of Si NP and h-BN on each other. These results open a way for utilizing hierarchical nanostructures for light manipulation at the nanometer scale for optical data storage and ink-free coloring. [ABSTRACT FROM AUTHOR]

Tunable near-infrared sources are highly demanded due to their various applications in biomedicine, printing, barcode technology, and optical storage. In this paper, widely central phase-matching wavelength tunable and high efficiency are demonstrated in theoretically and experimentally, pumped by a compact all-polarization-maintaining (PM) 9-character cavity fiber laser operating near-infrared (785 nm) based on a multiperiod grating. The wavelength tuned at about 18.2 nm as the grating period changed 1 $\mu \text{m}$ . A wide spectral tuning of 42 nm (from 776 nm to 818 nm) and high efficiency about 12.3% have been obtained. Besides, we discovered that the non-central second harmonic can also be generated from the second harmonic generation caused by strong phase mismatch, and the sum frequency generation (SFG) on account of the nonlinearity of the crystal. The result shows that the central and off-central phases match harmonics to form continuous broadband at some temperatures and grating periods, which can be widely exploited for wavelength conversion and tunable channel output.

Objective . The availability of tissue-mimicking materials (TMMs) for manufacturing high-quality phantoms is crucial for standardization, evaluating novel quantitative approaches, and clinically translating new imaging modalities, such as photoacoustic imaging (PAI). Recently, a gel comprising the copolymer styrene-ethylene/butylene-styrene (SEBS) in mineral oil has shown significant potential as TMM due to its optical and acoustic properties akin to soft tissue. We propose using artists' oil-based inks dissolved and diluted in balsam turpentine to tune the optical properties. Approach . A TMM was fabricated by mixing a SEBS copolymer and mineral oil, supplemented with additives to tune its optical absorption and scattering properties independently. A systematic investigation of the tuning accuracies and relationships between concentrations of oil-based pigments and optical absorption properties of the TMM across visible and near-infrared wavelengths using collimated transmission spectroscopy was conducted. The photoacoustic spectrum of various oil-based inks was studied to analyze the effect of increasing concentration and depth. Main results . Artists' oil-based inks dissolved in turpentine proved effective as additives to tune the optical absorption properties of mineral oil SEBS-gel with high accuracy. The TMMs demonstrated long-term stability and suitability for producing phantoms with desired optical absorption properties for PAI studies. Significance . The findings, including tuning of optical absorption and spectral shape, suggest that this TMM facilitates the development of more sophisticated phantoms of arbitrary shapes. This approach holds promise for advancing the development of PAI, including investigation of the spectral coloring effect. In addition, it can potentially aid in the development and clinical translation of ultrasound optical tomography., (Creative Commons Attribution license.)

Thin films with tunable optical properties from yellow to metallic were prepared from a monolayer coating of silver nanoparticles (AgNP) onto a polyelectrolyte multilayer (PEM) thin film. The AgNP were synthesized using various concentrations of stabilizing polyelectrolytes leading to a competitive adsorption concept in which AgNP compete with excess polyelectrolytes to coat the cationic PEM top layer. The AgNP were synthesized by chemical reduction of Ag salts using poly(styrene 4-sulfonic acid-co-maleic acid) (PSS-co-MA) as stabilizing agent to produce nanoparticles coated with both a strong acid (sulfonic) and a weak acid (carboxylic) moiety. Although all the nanoparticle solutions displayed a characteristic bright yellow due to the localized surface plasmon band around 420 nm, the monolayer films of nanoparticles obtained after dipping displayed striking different optical properties. When using a high PSS-co-MA content in the solution, a pale-yellow film was obtained which color shifted to orange and metallic when the capping concentration was decreased from 0.25 to 0.001 mM. The optical properties of the AgNP film could be further changed by galvanic replacement of the Ag with gold ions to produce a gold monolayer. These results are interesting to produce surface with tunable catalytic properties, tunable optical properties, or to be used as primer for the metallization of polymeric surfaces. [ABSTRACT FROM AUTHOR]

This study aims at optimising the graphene coverage in a microresonator for the design of an efficient modulator by using a combination of graphene induced losses and phase shift. The graphene integration in the ring can provide tunability by means of altering the loss and coupling coefficient by changing the graphene coverage or its chemical potential. The fundamental parameters of graphene integrated all‐pass ring resonator are extracted based on the transmission characteristics using finite‐difference time‐domain method. As compared to conventional graphene‐oxide‐semiconductor straight waveguide, graphene integrated on an all‐pass ring resonator shows enhanced optical absorption and phase shift due to field enhancement factor. A modulator based on graphene tunable loss and phase shift is investigated taking into account the field enhancement factor. For 1.55 μm radiation and ring radius of 3.75 μm with 22% graphene coverage, a maximum modulation depth of 12.6 dB is demonstrated based on electrostatic control of graphene chemical potential. The proposed modulator can feature operational speed in the range of 10 GHz that is useful in a variety of electro‐optic applications. [ABSTRACT FROM AUTHOR]

Highly efficient cyan‐emitting phosphor materials are indispensable for closing the cyan gap in spectra of the traditional phosphor‐converted white light‐emitting diodes (WLEDs) to achieve high‐quality full‐spectrum white lighting. In this work, bright cyan‐emitting Ca3Ga4O9 (CGO):0.02Bi3+,0.07Zn2+ phosphor is developed to bridge the cyan gap. Such a Bi3+,Zn2+ codoping enhances the cyan emission of CGO:0.02Bi3+ by 4.1 times due to the influence of morphology and size of phosphor particles, charge compensation and lattice distortion. Interestingly, codoping La3+ ions into the current system can achieve a photoluminescence tuning of CGO:0.02Bi3+ from cyan to yellowish‐green by crystallographic site engineering. Besides, Bi3+–Eu3+ energy transfer is successfully realized in CGO:0.02Bi3+,0.07Zn2+,nEu3+ phosphors and the emission color tuning from cyan to orange is observed. The investigation of thermal quenching behaviors reveals that the incorporation of Zn2+ and La3+ improves the thermal stability of CGO:0.02Bi3+. Finally, CGO:0.02Bi3+,0.07Zn2+,0.10Eu3+ phosphor is employed to obtain a single‐phased warm WLED device. A full‐spectrum WLED device with remarkable color rendering index (Ra) of 97.4 and high luminous efficiency of 69.72 lm W−1 is generated by utilizing CGO:0.02Bi3+,0.07Zn2+ phosphor. This result suggests the important effect of CGO:0.02Bi3+,0.07Zn2+ phosphor on closing the cyan gap, providing new insights of cyan‐emitting phosphors applied in full‐spectrum white lighting. [ABSTRACT FROM AUTHOR]

In previous reports, Dalfovo et al. showed experimentally that thin films of Au nanoparticles (NP) with organic coating change their optical properties when exposed to several analytes in the vapor phase (Anal Chem 84:4886–4892 2012; J Phys Chem C 119:5098–5106 2015). This optical behavior was associated with changes in the mean distance between nanoparticles, which resulted in a displacement of their plasmon bands towards blue or red in the presence of toluene (Tol) or ethanol (EtOH) vapors, respectively. In the report by Dalfovo et al. (J Phys Chem C 119:5098–5106 2015), in-situ grazing-incidence small-angle X-ray spectroscopy (GISAXS) was performed to determine changes in the inter-NP distance within the film. In the present work, we perform theoretical calculations to interpret the results obtained by Dalfovo et al. (Anal Chem 84:4886–4892 2012; J Phys Chem C 119:5098–5106 2015). For this purpose, we employ two different theoretical approaches, a quasi-static method (QS) and the Korringa-Kohn-Rostoker method (KKR), in order to describe the plasmon resonance shift as a function of the inter-NP distance changes during exposure to Tol and EtOH vapors. Both theoretical approaches describe qualitatively the behavior observed in previous experimental results that correlate the plasmon resonant wavelength with the inter-NP distance obtained by GISAXS. Our theoretical results show that the plasmon resonant wavelength strongly depends on the ratio between the inter-particle distance and the diameter of the nanoparticles and consequently, these films could be used for optical tuning. [ABSTRACT FROM AUTHOR]

Multimode luminescence with tunable optical properties is reported in lanthanide(III) and manganese(II) co‐doped CaZnOS crystals. The materials display distinct emissions under excitations of X‐ray, ultraviolet, and near‐infrared photons as well as mechanical action, respectively. The excitation dependence of emission spectra stems from varying host‐to‐dopant and dopant‐to‐dopant energy transfer processes involved in different luminescence modes. By controlling intracrystal energy transfer through control of dopant concentration and combination, the emission spectra are precisely tuned across the visible to near‐infrared. These findings highlight a facile approach to constructing multimode luminescent materials with intrinsically encrypted emission characteristics for advanced anticounterfeiting applications. [ABSTRACT FROM AUTHOR]

Reconfigurable beam steering components are indispensable to support optical and photonic network systems operating with high adaptability and with various functions. Currently, almost all such components are made of solid parts whose structures are rigid, and hence their functions are difficult to be reconfigured. Also, optical concentration beam steering is still a very challenging problem compared to radio frequency/microwave steering. Here we show a watermill-like beam steering system that can adaptively guide concentrating optical beam to targeted receivers. The system comprises a liquid droplet actuation mechanism based on electrowetting-on-dielectric, a superlattice-structured rotation hub, and an enhanced optical reflecting membrane. The specular reflector can be adaptively tuned within the lateral orientation of 360°, and the steering speed can reach ~353.5° s−1. This work demonstrates the feasibility of driving a macro-size solid structure with liquid microdroplets, opening a new avenue for developing reconfigurable components such as optical switches in next-generation sensor networks. Adaptive elements for optical beam steering are increasingly important to support nascent optical and photonic networks. This work presents a beam steering device based on a liquid droplet actuation method, capable of providing 360 degrees lateral steering with low energy consumption and a fast response time. [ABSTRACT FROM AUTHOR]

This paper reports a digitally integrated, self-trained predistortion curve finder for linearly frequency-swept semiconductor lasers. In this method, we introduce an iteration machine to train the laser current curves by utilizing the feedback signals from the laser's output. By measuring the phase and frequency information of lasers, we find that the predistortion finder in our design can generate various high sweep velocities (THz/ms) of lasers in 1 s with phase error range less than $\boldsymbol{\pi }/2.$ This method is universal for semiconductor lasers at any sweep frequency velocity. [ABSTRACT FROM AUTHOR]

The first examples of N‐heterocyclic carbene (NHC) and cyclic(alkyl)(amino) carbene (CAAC) stabilized borepinium and borafluorenium heterocycles are reported herein. The optical properties of the heterocyclic borenium cations were tuned by varying the Lewis base and by changing the number of atoms in the ring. More importantly, functionalizing the cationic boron ring system in the NHC‐borafluorenium cation affords a temperature‐sensitive molecule with reversible colorimetric "turn off/turn on" properties in solution. Notably, this is the first report of thermochromism in these cationic species. This property, which is mediated by an intermolecular boron–oxygen bond equilibrium, was examined in detail by X‐ray crystallography, variable temperature‐UV/Vis absorption spectroscopy (VT‐UV/Vis), and density functional theory (DFT). [ABSTRACT FROM AUTHOR]

A compact plasmonic bandpass filter based on metal–insulator–metal plasmonic waveguides and a coupled U‐shaped cavity is proposed in this study. Air and silver are used as insulator and metal materials and silver is characterised by the Drude model in the simulations. By tuning the height of the designed cavity, it is found that the resonance wavelength can be easily adjusted. Furthermore, the quality factor of the designed filter can be increased by increasing the cavity numbers. One, two or three cavities can be used to generate single‐mode filters. Finally, by sweeping different structural parameters, the effect of them on transmittance spectrum is investigated. All results are obtained by the finite‐difference time domain method. The proposed structure due to its remarkable properties such as being a single‐mode filter, having a compact size, tunablity of the resonance frequency and its variable quality factor can be used in complex integrated optical structures such as demultiplexers and so on. [ABSTRACT FROM AUTHOR]

The authors theoretically propose a design for electrically tuning a metasurface based on piezoelectric actuation. The design comprises 2D gap‐plasmon elements arranged periodically on a piezoelectric substrate which controls the period between them. The technique is numerically studied for a metasurface that anomalously reflects an incident p‐polarised wave by 30° at the optical communication wavelength, 1550 nm. The dynamic behaviour of the system is investigated for two main applications; (a) steering the reflection angle and (b) retrieving the reflection angle for an incident wave of a shifted wavelength. It is demonstrated that a reflected beam can cover an angle of ∼3° upon a strain of <3.3%. It is also shown that at the same strain value, the reflection angle is retrieved for a wavelength error of ±50 nm. These results suggest a potential to design large‐bandwidth, reconfigurable metasurfaces that are integrable with planar opto‐electromechanical devices. [ABSTRACT FROM AUTHOR]

A tunable mode-locked ytterbium-doped fiber laser with a tuning range of 55 nm is demonstrated in this paper. Currently, this is the widest tuning range for all-normal dispersion (ANDi) ytterbium-doped mode-locked fiber laser based on new-material saturable absorber (SA). The combined effects of the single-walled carbon nanotubes (SWCNTs) SA and a reflective grating significantly improved laser performance: broad tuning range, superb stability, and repeatability. The experimental results indicate that SWCNTs can be a brilliant SA for achieving mode-locking operation in ANDi regime at 1 μm, with pulsewidth of 2.4 ps and optical spectral bandwidth of 1.6 nm across the full tuning range. The laser also shows that the optical spectrum can be tuned accurately and continuously, which gives possibility for various applications such as optical communications, spectroscopy, time-resolved measurement, etc. [ABSTRACT FROM AUTHOR]

The authors propose a 2 × 2 asymmetric adiabatic coupler (AAC) indium phosphide (InP) photonic integrated circuit (PIC), suitable for tunable power applications such as all‐optical data processing. The device was idealised as the key building block in Haar transform network used for image compression, allowing to perform the necessary separate addition and subtraction of incoming input signals at its output ports. The tunable behaviour of the coupler was demonstrated experimentally for addition/subtraction and splitting (with experimental coupling ratios of 77:23/14:86 and 50:50, respectively) through phase control. The use of the developed InP PIC enables a low footprint structure design together with the high‐quality active components (lasers, photodetectors and phase modulators) of Fraunhofer Gesellschaft Heinrich Hertz Institute design toolkit. The proposed study provides a full experimental characterisation of the AAC, exploring its tuning properties and enabling further usage in a plethora of applications in high processing computing and data communications. [ABSTRACT FROM AUTHOR]

Abstract Herein, doping of methylammonium lead iodide perovskite thin films with bromine ions is successfully performed for the first time using the aerosol-assisted chemical vapour deposition process. Depending on the doping levels, photoluminescence spectra are shifted relative to their bandgap values. Detailed analysis of scanning electron microscope images showed that increasing the bromine levels linearly increased the grain sizes. The unchanged amount of detected lead provided evidence for the controlled processing conditions. Both bulk and surface compositional techniques confirmed the deposition of marginally iodine rich perovskite thin films. Graphical abstract Image 1 Highlights • Bromine doped methylammonium lead iodide perovskite thin films are deposited for the first time at atmospheric conditions using aerosol-assisted chemical vapour deposition. • Grain sizes are found to be dependent on the dopant levels. • Photoluminescent peaks are continuously blue shifted as a result of increased Br¯ concentration. • Compositional investigations confirmed slightly iodine rich thin films. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Aqueously dispersible CdTe quantum dots were synthesized by facile one-pot chemical reduction. • Optimum precursor ratio and pH facilitated particle size tunability and exceptional optical properties. • High absolute quantum yield achieved using dual capping agents namely MPA and Citric acid. • Quantum dots interacted with organic fluorophores and plasmonic nanoparticles via resonance energy transfer. Abstract We report a facile one-pot synthesis of aqueously dispersible CdTe quantum dots (QDs) with tunable optical properties by using dual capping agents namely MPA and Citric acid. Optimum precursor ratio and pH > 8 at 80 °C facilitated particle size tunability and exceptional optical properties. QDs are ∼3.7 nm as seen from HR-TEM image; highly-luminescent showing absolute quantum-yield up to 54% and bear good photostability. CdTe QDs are highly stable in water with large negative Zeta potential. Optimum ratio of Cd2+:MPA:TeO 3 2−:NaBH 4 :citric acid was 1:2:0.2:3.2:5.2, respectively. The pH dependent nucleation and growth of QDs subsequently lead to quasi CdTe/CdS structure as indicated by XRD, FTIR and particle size analysis. QDs showed excitation independent emission with tunable peak width. QDs can be stored over 6-months at 4 °C without causing agglomeration. Interaction of QDs with Rhodamine-6G and plasmonic silver nanoparticles via resonance energy transfer (RET) imply their suitability for sensors and biomedical applications. [ABSTRACT FROM AUTHOR]

Abstract The absorption and emission properties of Silicon quantum dots (Si QDs) depend largely on their surface chemistry. While the size of Si QDs is hardly controlled, delicate surface modification is relied to vary the optical properties of Si QDs. Herein, we report a one-pot synthesis of blue-emitting Si QDs followed by chromatography separation into two fractions with distinct absorption and emission properties. The polar fraction showed featureless UV–vis absorption profile and a broad photoluminescence (PL) spectrum with an enhancement in green-yellow region when compared with that of non-polar fraction, which exhibited UV-blue emission. FT-IR and XPS analyses inferred a mechanism that oxidized surfaces (SiO x) added new electronics states via which PL were red-shifted into visible region. The simple separation of easily synthesized Si QDs into colorful Si QDs is of important to deploy non-toxic Si QDs into practical applications. [ABSTRACT FROM AUTHOR]

In this letter, we introduced a novel method for the preparation of room temperature stable α-FAPbI 3 perovskite without using organic ligands and mixed cations by hydrothermal method. Structural, optical and morphology of the product were changed with respect to the temperature. Equal volume of the chlorobenzene anti-solvent was used together with perovskite solution to saturate and simply growing the perovskite crystals under hydrothermal method. Optimum temperature (140 °C) was determined from XRD and UV–vis absorption result achieving stable α-FAPbI 3 perovskite. This work favours the understanding of the large scale with stable α-FAPbI 3 perovskite with interesting morphology, and paves the way for potential applications in diverse field. [ABSTRACT FROM AUTHOR]

In this letter, a tunable filter design based on polymer and silicon layers is presented. It is shown that by taking advantage of the different thermal properties of these materials, the overall spectral and tuning characteristics can be controlled by selecting the thickness of these layers. Moreover, a mathematical model to simulate the reflectivity spectrum and the tuning behavior due to the temperature of the filter is presented. Finally, two filters were fabricated and their experimental behavior is well described by our mathematical approximation model. [ABSTRACT FROM AUTHOR]

A unique delay-dependent dynamic switching of optical nonlinearity in terms of saturation absorption (SA) and excited state absorption (ESA) in graphene oxide (GO) and reduced graphene oxide (RGO2 and RGO100) is achieved with an optical pump and white light super-continuum probe only above a threshold pump intensity. Infrared and chemical reduction are used to obtain RGO2 and RGO100 respectively. The switching regime of probe wavelength can be modulated by varying either pump wavelength or degree of reduction. When pumped at 415 nm, the threshold pump intensity to obtain switching property decreases to 9 GW/cm 2 for RGO2 from 18 GW/cm 2 in GO and the tunability range shifts from 471 to 526 nm for as grown GO to 519–623 nm in maximally reduced RGO2. Though the saturation intensity of intrinsic non-degenerate two photon absorption (nd-TPA) is found to be lower in GO (4.3 GW/cm 2 ) than RGO2 (18.2 GW/cm 2 ), nd-TPA coefficient increases from 0.0015 cm/GW (GO) to 0.0026 cm/GW (RGO2) with increasing reduction. The detailed kinetics of the scattering processes show variation as a function of pump power, probe wavelength and degree of reduction. A model band diagram based on amorphous-carbon model and a Tauc analysis are used to explain the unusual nonlinear optical properties. [ABSTRACT FROM AUTHOR]

Most carbon dots (CDs) conventional fabrication approaches produce single colored fluorescent materials, different methods are required to synthesize distinct carbon dots for specific optical applications. Herein, using one-pot hydrothermal treatment of Syringa obtata Lindl, a facile, low-cost and green assay is achieved in the controllable synthesis of blue and green fluorescent carbon dots. The fluorescent emission of CDs can be well-tuned by adding sodium hydroxide in the precursor solution. Blue fluorescent CDs are applied to Fe 3+ sensing with a low detection limit of 0.11 μM of linear range from 0.5 to 80 μM, and then further extended to analysis river water samples. Green fluorescent CDs can be applied to pH detection, which show a remarkable linear enhancement in the green fluorescence emission region when the pH is increased from 1.98 to 8.95. Eventually, the detection of Fe 3+ and pH are applied for the living cells fluorescent images in MCF-7 cells are achieved successfully, indicating as-synthesized CDs potential toward diverse application as promising candidate. [ABSTRACT FROM AUTHOR]

Optofluidics is an emerging research field that combines the two disciplines of microfluidics and optics. By using microfluidic technologies for light control, optofluidic devices can offer several advantages over solid-type optical components, including optical-grade smoothness at the fluidic interface and a high degree of optical tunability without bulky and complex mechanical moving parts. These features have made optofluidic devices more versatile and reconfigurable to improve their optical performances. In this paper, we present a novel optofluidic sunlight manipulation technology for solar indoor lighting using the electrowetting principle. Rooftop sunlight is collected by a solar concentrator and guided to individual rooms along an optical fiber (waveguide) on the bottom of which tunable liquid prisms are linearly integrated. In the light-off mode, electrowetting controls the apex angle of the prisms to be φ = 0°. Under this condition, incoming sunlight experiences total internal reflection and thus keeps propagating along the optical fiber without leaking to the prism bottom for indoor lighting. In contrast, when liquid prisms are controlled to have the angle at φ ＞ 0°, incoming sunlight is partially transmitted to the bottom surface of the arrayed prisms to contribute to interior illumination. Simulation studies validate that our electrowetting-driven solar indoor lighting (e-SIL) system is capable of variably tuning the lighting power from 0% to 98.6% of the input solar power by controlling the prism angle and varying the refractive index of prism materials. For experimental studies, we fabricated an array of 5 prisms filled with silicone oil and water. Using a fiber illuminator as a white light source that includes visible light with various incident angles, we have demonstrated two important lighting functions, (1) light on/off and (2) illumination power control. Lighting performance can be further enhanced by lowering the aspect ratio of the prism as well as increasing the number of prisms. The e-SIL technology based on tunable liquid prisms offers a new approach towards sustainable buildings that are able to reduce their electricity usage as well as provide a healthy and comfortable indoor environment under illumination of natural sunlight. [ABSTRACT FROM AUTHOR]

We propose a whispering gallery mode (WGM) strain sensor formed by a polymer-wire cylindrical micro resonator for strain measurement applications.WGMs are generated by evanescently coupling light into the polymer-wire resonator from a silica fiber taper fabricated by the micro heater brushing technique. Accurate and repeatable measurements of strains up to one free spectral range shift of the WGMs (corresponding to 0.33% of the polymer-wire elongation, 3250 με) are demonstrated experimentally with the proposed sensor. Practical packaging method for the proposed strain sensor on a glass microscope slide has also been realized making the sensor portable and easy to handle. The robustness of the packaged coupling system is confirmed by vibration tests. The performance of the packaged strain sensor is evaluated and compared with that for an unpackaged sensor. [ABSTRACT FROM AUTHOR]

Abstract: Photon upconversion that is characterized by high‐energy photon emission followed by lower‐energy excitation has been conventionally studied in bulk materials for several decades. This unique nonlinear luminescence process has become a subject of great attention since 2000 when upconverted emission was demonstrated in nanostructured crystals. In comparison with their bulk counterparts, nanostructured materials provide more room for optical fine‐tuning by allowing flexible compositional integration and structural engineering. Moreover, the high colloidal stability of nanoparticles coupled with high amenability to surface functionalization opens up a number of new applications for upconversion, especially in the fields of biology and life science. In this focus review, we discuss recent developments in upconversion materials through nanostructural design and review emerging biomedical applications that involve these nanostructured upconversion materials. We also attempt to highlight challenging problems of these nanomaterials that constrain further progress in utilizing upconversion processes. [ABSTRACT FROM AUTHOR]

The authors present here designs for tuneable confined Tamm plasmons (CTPs) resonant at 1.3 μm, consisting of an AlAs/GaAs distributed Bragg reflector and gold disc. Using numerical methods they explored the effect of disc diameter on the CTP resonance and position of a dipole source (modelling a quantum dot) on emission through the disc. They found decreasing disc diameter resulted in a blue‐shifted fundamental mode and that a dipole positioned at the centre of the disc emitted with an angular distribution that collected 90% of the transmitted power within a numerical aperture of 0.7. They also explore the Purcell enhancement under the CTP as a function of dipole position. [ABSTRACT FROM AUTHOR]

We use time dependent density functional theory to study the electronic and optical properties of rectangular graphene nanoflakes with mixed armchair and zigzag edges under uniaxial strain in order to determine the role of the size and aspect ratio. Both the HOMO-LUMO and optical bandgaps are found to exhibit strong variations under uniaxial strain, unlike two-dimensional graphene. A specific 140-atom nanoflake even is subject to a transition in the energetical order of the HOMO - 1 and HOMO wavefunctions. The present work shows that through rational modifications in the aspect ratio and uniaxial strain, the electronic and optical properties of graphene nanoflakes can be favourably tuned. [ABSTRACT FROM AUTHOR]

Strongly confined and intense optical fields within the plasmonic metal nanocavities show outstanding potential for a wide range of functionalities in nanophotonics. Using time dependent density functional theory calculations, we investigate the optical response evolution as a function of the gap separation distances in nanorod-on-film systems comprised of a nanorod (NR) made of Al or Na on top of an Al film. Huge optical field modulations emerged in the chemically distinct Na NR – Al film system in comparison to the Al NR – Al film system, indicating the vital role of metals involved. We further study the optical response modifications by placing a conducting molecule in the gap region, finding strong spectral modulations via through-molecule electron tunneling. [ABSTRACT FROM AUTHOR]

Modulation of weak interlayer interactions between quasi-two-dimensional atomic planes in the transition metal dichalcogenides (TMDCs) provides avenues for tuning their functional properties. Here we show that above-gap optical excitation in the TMDCs leads to an unexpected large-amplitude, ultrafast compressive force between the two-dimensional layers, as probed by in situ measurements of the atomic layer spacing at femtosecond time resolution. We show that this compressive response arises from a dynamic modulation of the interlayer van der Waals interaction and that this represents the dominant light-induced stress at low excitation densities. A simple analytic model predicts the magnitude and carrier density dependence of the measured strains. This work establishes a new method for dynamic, nonequilibrium tuning of correlation-driven dispersive interactions and of the optomechanical functionality of TMDC quasi-two-dimensional materials. [ABSTRACT FROM AUTHOR]

There is a growing pressure on antenna designers to provide ever increasing operating bandwidth, efficiency, and flexibility. Emerging communications standards are requiring operation over wide frequency ranges, often with multiple, separated bands of operation. This communication proposes and demonstrates an optically tunable cavity backed slot antenna. Through the incorporation of four silicon bridging pieces and a fiber coupled laser, the operating frequency can be tuned between 4.2 and 6 GHz. Antenna efficiency has been measured and ranges between 36% and 62% depending upon the combination of frequency and tuning state, with the gain taking values between 4.3 and 6.9 dBi. An effective fabrication process for the incorporation of silicon into the antenna has been described, as well as methods for effectively simulating the optically generated conductivity. Simulations and measurements show good agreement, and several proposed improvements are proposed for this novel and flexible tuning technology. [ABSTRACT FROM AUTHOR]

Currently, the photocatalytic nanomaterials performing under solar radiation have gained worldwide attentions due to increasing environmental deterioration. For utilizing the sunlight for degradation of emerging pollutants it is important to develop visible active photocatalysts. This laboratory scale work reports magnetic and optically active nano-photocatalyst Fe x Zn 1−x O(x = 0.01, 0.03, 0.05) synthesized by solution combustion method. High resolution transmission microscopy suggests a slight degradation in the crystallite structure with Fe doping. X-ray photoelectron spectroscopy analysis shows the presence of intrinsic defects in the crystal structure. Zn resides in +2 and and Fe in +3 oxidation state. Optical band gap studies were made with band structure for each doped sample. The photoctalytic activity of the samples was tested by solar degradation of noxious pollutant Bisphenol A. 99.1% of bisphenol was degraded in 90min in presence of Fe 0.03 Zn 0.97 O under synergistic adsorption and photocatalysis. The results were analyzed in terms of total organic carbon, chemical oxygen demand, effect of scavengers, gas chromatography-mass spectrometry and reusability. In presence of Fe 0.03 Zn 0.97 O, 45.3% of total organic carbon was removed and chemical oxygen demand was reduced to 11.2%. A possible mechanism with structures of the intermediates has been given. Effect of scavengers reveal that hydroxyl radicals are major reactive oxygen species involved which is also supported by the band edge positions. The research work promises to design highly photo-active tuneable magnetic photocatalysts for solar powered degradation of contaminants of emerging concern with a simple and cost-effective approach. [ABSTRACT FROM AUTHOR]

We report analytic results on quantum capacitance (Cq) measurements and their optical tuning in a dual-gated device with potassium-doped multi-layered black phosphorous (BP) as the channel material. The two-dimensional (2D) layered BP is highly anisotropic with a semi-Dirac dispersion marked by linear and quadratic contributions. The Cq calculations mirror this asymmetric arrangement. A further increase in the asymmetry and consequently Cq is predicted by photon-dressing the BP dispersion. To achieve this and tune Cq in a field-effect transistor (FET), we suggest a configuration wherein a pair of electrostatic (top) and optical (back) gates clamp a BP channel. The back gate shines an optical pulse to rearrange the dispersion of the 2D BP. Analytic calculations are done with Floquet Hamiltonians in the off-resonant regime. The value of such Cq calculations, in addition to its role in adjusting the current drive of an FET, is discussed in the context of metalinsulator and topological phase transitions and enhancements to the thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]

Intense electromagnetic fields generated by the gold nanorods (GNRs) owing to their strong plasmon resonance make them promising candidate for applications in cancer diagnostics, photothermal therapy, single-molecule detection, drug delivery, etc. Use of GNRs in these applications as plasmon resonance probes depends on the extent to which their plasmon resonance band can be tuned into NIR region. In this study, we propose a facile seedless approach to synthesize GNRs in a cetyltrimethyammonium bromide (CTAB)-benzyledimethylhexadecylammonium chloride (BDAC) co-surfactant system with simultaneous pH regulation that yields GNRs with tunable plasmon resonance in tissue transparent NIR region. The role of binary co-surfactants, pH of the growth solution, and influence of the volume of the reducing agent on GNRs growth has been studied. Under optimized conditions, the longitudinal plasmon resonance band of GNRs can be tuned from 780-1300 nm by regulating the pH of the growth solution from 2.5 to 1.3. The role of co-surfactants and pH in the regulation of dimensions and thus plasmonic properties of GNRs synthesized by single-step seedless approach has been evaluated. [ABSTRACT FROM AUTHOR]