Broad Spectral Tunability Research Articles

Linear dispersion (GDD) design using grating group

Precise control of dispersion output holds paramount significance across domains such as optical fiber communication, time stretching, and spectral interferometric ranging. In comparison to other dispersion elements, like prisms, gratings are widely applied in the field of dispersion control due to their advantages of broad spectral range, tunability, and high resolution. Moreover, linear dispersion is the most desired characteristic by designers in most cases. Here, we develop a dispersion model for grating groups to determine the optimal structural parameters for achieving linear dispersion in high-order grating arrays. Based on our model, we provide corresponding parameter selection methods that allow for quantitative design of the size and slope of output dispersion by adjusting input parameters such as angle, distance, and parallelism. Additionally, we experimentally establish a dispersion interferometry structure based on the grating ensemble that validates our proposed approach's capability for linear dispersion output (linearity better than 0.9998). We believe that our approach is universally significant and contributes to enhancing the performance of dispersion interferometric measurement systems, chirp amplification systems, and other related systems.

Solution‐Processed Perovskite Quantum Dot Quasi‐BIC Laser from Miniaturized Low‐Lateral‐Loss Cavity

AbstractLaser devices produced via solution‐processed perovskite quantum dots (QDs) offer broad spectral tunability as well as ease of fabrication. Utilizing quasi‐bound states in the continuum (quasi‐BIC) modes, solution‐processed QD laser devices have been demonstrated with a nanostructure coated in a thin‐film gain media configuration. However, light leakage through thin‐film guiding from the cavity side edges becomes more pronounced when shrinking the cavity size, posing challenges for the miniaturization of quasi‐BIC‐based lasers. Here, the fabrication of well‐defined patterns of QDs via a solution process allows them to take advantage of the pattern edges to reduce losses through the cavity edges. A single‐mode BIC laser is reported by using CsPbBr3 QDs with a narrow linewidth of ≈0.1 nm. Importantly, a miniaturized quasi‐BIC laser is realized with a device size as small as 10 × 10 µm2, making it the smallest among existing solution‐processed BIC lasers. This work provides a strategy for developing ultra‐compact BIC lasers via solution‐processed gain media.

Flexible structural polyethylene films for dynamically tunable energy harvesting from the sun and outer space

Passive daytime radiative cooling (PDRC) achieves a sub-ambient temperature without any electricity input, which is of great significance for global energy savings and minimum carbon footprint, especially, in hot seasons. However, due to the static performance of most PDRC materials, it may cause overcooling and high heating energy consumption in cold seasons. Here we establish a structural surface on ubiquitous polyethylene (PE) films and demonstrate an asymmetric electromagnetic transmission with forward/backward transmittance ratios of 2.61 and 1.67 in both solar irradiance and long-wave infrared (LWIR) spectral ranges, enabling it to work as a multispectral self-adaptive window (MSW). By integrating the MSW with the PDRC material, the originally static PDRC can be transformed into a dynamic one that allows the switching between temperatures 4.3 °C lower and 3.4 °C higher than the ambient temperature of the chamber interior. The cooling and heating modes are achieved through electrically actuating the MSW, which originates from the dynamically tunable energy harvesting from the sun and outer space. The MSW features transition-temperature-independent switching, broad spectral tunability, lightweight, robust mechanical strength, low cost, and scalable manufacturability, benefiting both an in-depth insight into the dynamical interaction of terrestrial objects with nature thermodynamics resources and broad applications.

Near-IR Light-Tunable Omnidirectional Broadband Terahertz Wave Antireflection Based on a PEDOT:PSS/Graphene Hybrid Coating.

Omnidirectional broadband terahertz (THz) antireflection (AR) with an actively configurable coating promises the achievement of next-generation efficient and versatile THz components with high performance. We demonstrate a near-infrared (NIR) light-tunable and omnidirectional broadband THz AR coating based on an impedance matching method and composed of a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/graphene composite film. The omnidirectional broadband properties of the active AR coating can be efficiently achieved by tunable NIR optical excitation of less than 0.27 W·cm-2, which exhibits omnidirectional suppression of THz-wave reflection for incidence angles from 0 to 70°, concerning the broadband frequency range of 0.1-3.0 THz, with an ultrafast response time of ∼5 ps. Furthermore, we demonstrate that the active AR coating can improve the performance of a reflectance-tunable THz-wave polarization reflector by the elimination of Fabry-Pérot interference. The NIR irradiance-dependent active AR mechanism of the hybrid system is investigated, which demonstrates the essential role of the PEDOT:PSS/graphene layers in promoting the charge separation at the interface and therefore changing the photoconductivity of the composite film to achieve impedance matching under optical excitation. Several crucial advantages of the proposed and proven concept, including the wide-angle range, broad spectral range, flexible tunability, and easier fabrication, may revolutionize the AR strategy at THz frequencies for a wide range of THz applications.

Catalytic Metasurfaces Empowered by Bound States in the Continuum.

Photocatalytic platforms based on ultrathin reactive materials facilitate carrier transport and extraction but are typically restricted to a narrow set of materials and spectral operating ranges due to limited absorption and poor energy-tuning possibilities. Metasurfaces, a class of 2D artificial materials based on the electromagnetic design of nanophotonic resonators, allow optical absorption engineering for a wide range of materials. Moreover, tailored resonances in nanostructured materials enable strong absorption enhancement and thus carrier multiplication. Here, we develop an ultrathin catalytic metasurface platform that leverages the combination of loss-engineered substoichiometric titanium oxide (TiO2–x) and the emerging physical concept of optical bound states in the continuum (BICs) to boost photocatalytic activity and provide broad spectral tunability. We demonstrate that our platform reaches the condition of critical light coupling in a TiO2–x BIC metasurface, thus providing a general framework for maximizing light–matter interactions in diverse photocatalytic materials. This approach can avoid the long-standing drawbacks of many naturally occurring semiconductor-based ultrathin films applied in photocatalysis, such as poor spectral tunability and limited absorption manipulation. Our results are broadly applicable to fields beyond photocatalysis, including photovoltaics and photodetectors.

Ladder of Eckhaus instabilities and parametric conversion in chi(2) microresonators

Low loss microresonators have revolutionised nonlinear and quantum optics over the past decade. In particular, microresonators with the second order, chi(2), nonlinearity have the advantages of broad spectral tunability and low power frequency conversion. Recent observations have highlighted that the parametric frequency conversion in chi(2) microresonators is accompanied by stepwise changes in the signal and idler frequencies. Therefore, a better understanding of the mechanisms and development of the theory underpinning this behaviour is timely. Here, we report that the stepwise frequency conversion originates from the discrete sequence of the so-called Eckhaus instabilities. After discovering these instabilities in fluid dynamics in the 1960s, they have become a broadly spread interdisciplinary concept. Now, we demonstrate that the Eckhaus mechanism also underpins the ladder-like structure of the frequency tuning curves in chi(2) microresonators.

Wavelength Tunable Aqueous CsPbBr3-Based Nanoprobes with Ultrahigh Photostability for Targeted Super-Resolution Bioimaging.

Single molecule localization microscopy (SMLM) is indispensable in the visualization of cellular microstructures. However, current SMLM imaging materials, from organic fluorophores to quantum dots, still lack the requirement of increasing need for multiple targets of interest due to their broad emission. Here, by one-step encapsulating hydrophilic cesium lead bromide perovskite nanocrystals (CsPbBr3 NCs) into functionalized polyethylene glycol (PEG), a core-shell nanocomposite of CsPb(Cl(1-x)/Brx)3@PEG (0 < x < 1) was presented as a wavelength-tunable fluorescent probe with the narrow full width at half-maximum (fwhm) as 11 nm. The layer of functionalized PEG endows CsPbBr3 NCs with a broad spectral tunability from 521 to 431 nm, superior photostability for several years, and the ability to be further surface functionalized. The CsPb(Cl(1-x)/Brx)3@PEG exhibits a sub-10 nm localization precision and 10-fold enhanced spatial resolution. Using exosomes with small sizes less than 150 nm as the imaging target, CsPb(Cl(1-x)/Brx)3@PEG realized the distinction of two adjacent exosomes by SMLM. Moreover, after being modified with biotin, CsPb(Cl(1-x)/Brx)3@PEG was universally used for SMLM imaging of cellular microstructures. The excellent photostability and narrow fwhm indicated that such a CsPbBr3-based nanoprobe has great potential as a commercial dye for multitarget super-resolution bioimaging applications.

A novel mid-infrared thermal emitter with ultra-narrow bandwidth and large spectral tunability based on the bound state in the continuum

The development of efficient, compact and low-cost mid-infrared (MIR) sources with easy manufacturing is vital in a variety of applications including gas sensing, thermal photovoltaic power generation, infrared imaging, among others. In this work, we demonstrate that a novel type of MIR thermal emitters with ultra-narrow bandwidth and broad spectral tunability can be realized based on a new operation principle employing the concept of bound state in the continuum (BIC). Using an elaborately designed structure composed of two interdigitated gratings with the same pitch and different stripe width on a slab supported by a conducting substrate, the quasi-BIC mode with both ultra-high Q-factor (>104) and large absorbance/emittance can be achieved, resulting from the destructive interference between the couplings of two guided-mode resonances back to free space. At the operation wavelength of 7.7851 μm, even when the metal dissipation is considered, a near-unity emission at resonance with the full-width at half-maximum less than 0.3 nm is numerically presented, which is three orders of magnitude narrower than conventional metallic metamaterial based thermal emitters. By applying a geometrical scaling of the structure, the operation wavelength can be flexibly extended to other wavelengths of the MIR region. The presented novel thermal emitter with economic advantages and high performances of both ultra-narrow bandwidth and broad wavelength-tunability, will make great impact in practical applications.

Optical and electrical modulation in ultraviolet photodetectors based on organic one‐dimensional photochromic arrays

AbstractOrganic photochromic materials have drawn considerable attention for their potential applications in large‐scale and low‐cost optoelectronics owing to unique tunable physicochemical properties. For organic photodetectors, photochromic materials have realized optical and electrical engineering of semiconductor layers, which incorporate not only tunable performance, but also functionalities to optoelectronic devices. However, the essential challenge is to assemble large‐area photochromic micro‐ and nanostructure arrays with controllable geometry and precise alignment, which restricts the integration of multifunctional optoelectronic devices. Herein, we fabricate organic photochromic one‐dimensional (1D) arrays via a feasible solution process through the confined crystallization of organic molecules. By modulating and controlling the photoisomerization behaviors, these 1D photochromic arrays possess broad spectral tunability, which ensure tunable photoresponse. Furthermore, we investigate the crystallographic transition and electronic performance variation of these 1D photochromic arrays. By adjusting the dwell time of ultraviolet (UV) irradiation, the UV photochromic photodetectors realize tunable and repeatable responsivity from 85.6 to 0.709 mA/W. Our work provides new possibilities for optical and electrical engineering of photochromic microwires towards the integration of multifunctional optoelectronic devices.

Modular Zwitterion-Functionalized Poly(isopropyl methacrylate) Polymers for Hosting Luminescent Lead Halide Perovskite Nanocrystals

Inorganic lead halide perovskite nanocrystals (NCs) are an exciting class of luminescent materials with high defect tolerance and broad spectral tunability, but such NCs are vulnerable to degradati...

Water Triggered Synthesis of Highly Stable and Biocompatible 1D Nanowire, 2D Nanoplatelet, and 3D Nanocube CsPbBr3 Perovskites for Multicolor Two-Photon Cell Imaging.

Two-photon imaging in the near-infrared window holds huge promise for real life biological imaging due to the increased penetration depth. All-inorganic CsPbX3 nanocrystals with bright luminescence and broad spectral tunability are excellent smart probes for two-photon bioimaging. But, the poor stability in water is a well-documented issue for limiting their practical use. Herein, we present the development of specific antibody attached water-resistant one-dimensional (1D) CsPbBr3 nanowires, two-dimensional (2D) CsPbBr3 nanoplatelets, and three-dimensional (3D) CsPbBr3 nanocubes which can be used for selective and simultaneous two-photon imaging of heterogeneous breast cancer cells in the near IR biological window. The current manuscript reports the design of excellent photoluminescence quantum yield (PLQY), biocompatible and photostable 1D CsPbBr3 nanowires, 2D CsPbBr3 nanoplatelets, and 3D CsPbBr3 nanocubes through an interfacial conversion from zero-dimensional (0D) Cs4PbBr6 nanocrystals via a water triggered strategy. Reported data show that just by varying the amount of water, one can control the dimension of CsPbBr3 perovskite crystals. Time-dependent transition electron microscopy and emission spectra have been reported to find the possible pathway for the formation of 1D, 2D, and 3D CsPbBr3 nanocrystals from 0D Cs4PbBr6 nanocrystals. Biocompatible 1D, 2D, and 3D CsPbBr3 nanocrystals were developed by coating with amine–poly(ethylene glycol)–propionic acid. Experimental data show the water-driven design of 1D, 2D, and 3D CsPbBr3 nanocrystals exhibits strong single-photon PLQY of ∼66–88% as well as excellent two-photon absorption properties (σ2) of ∼8.3 × 105–7.1 × 104 GM. Furthermore, reported data show more than 86% of PL intensity remains for 1D, 2D, and 3D CsPbBr3 nanocrystals after 35 days under water, and they exhibit excellent photostability of keeping 99% PL intensity after 3 h under UV light. The current report demonstrates for the first time that antibody attached 1D and 2D perovskites have capability for simultaneous two-photon imaging of triple negative breast cancer cells and human epidermal growth factor receptor 2 positive breast cancer cells. CsPbBr3 nanocrystals exhibit very high two-photon absorption cross-section and good photostability in water, which are superior to those of commonly used organic probes (σ2 = 11 GM for fluorescein), and therefore, they have capability to be a better probe for bioimaging applications.

Enhanced tunable plasmonic resonance in crumpled graphene resonators loaded with gate tunable metamaterials.

Graphene devices have been widely explored for photonic applications, as they serve as promising candidates for controlling light interactions resulting in extreme confinement and tunability of graphene plasmons. The ubiquitous presence of surface crumples in graphene, very less is known on how the crumples in graphene can affect surface plasmon resonance and its absorption properties. In this article, a novel approach based on the crumpled graphene is investigated to realize broadband tunability of plasmonic resonance through the mechanical reconfiguration of crumpled graphene resonators. The mechanical reconfiguration of graphene crumples combined with dual electrostatic gating (i.e. raising the Fermi level from 0.2-0.4 eV) of graphene serves as a tuning knob enabling broad spectral tunability of plasmonic resonance in the wavelength range of 14-24 µm. The crumpled region in the resonators exhibits an effective trapping potential where it extremely confines the surface plasmonic field on the surfaces of crumples providing localized surface plasmon resonance at the apices of these crumples. Finally, to achieve near-unity absorption >99% at the resonance wavelengths (17 µm and 22 µm) crumpled graphene resonators are loaded with four ring shaped metamaterials which result in the enhanced near-field intensity of ≈1.4×106. This study delivers insight into the tunability of crumpled graphene and their coupling mechanism by providing a new platform for the flexible and gate tunable graphene sensors at the infrared region.

Towards Highly Efficient Polymer Fiber Laser Sources for Integrated Photonic Sensors

Lab-on-a-Chip (LoC) devices combining microfluidic analyte provision with integrated optical analysis are highly desirable for several applications in biological or medical sciences. While the microfluidic approach is already broadly addressed, some work needs to be done regarding the integrated optics, especially provision of highly integrable laser sources. Polymer optical fiber (POF) lasers represent an alignment-free, rugged, and flexible technology platform. Additionally, POFs are intrinsically compatible to polymer microfluidic devices. Home-made Rhodamine B (RB)-doped POFs were characterized with experimental and numerical parameter studies on their lasing potential. High output energies of 1.65 mJ, high slope efficiencies of , and -lifetimes of ≥900 k shots were extracted from RB:POFs. Furthermore, RB:POFs show broad spectral tunability over several tens of nanometers. A route to optimize polymer fiber lasers is revealed, providing functionality for a broad range of LoC devices. Spectral tunability, high efficiencies, and output energies enable a broad field of LoC applications.

Observation of grating diffraction radiation at the KEK LUCX facility

The development of linac–based narrow–band THz sources with sub–picosecond, mu J-level radiation pulses is in demand from the scientific community. Intrinsically monochromatic emitters such as coherent Smith–Purcell radiation sources appear as natural candidates. However, the lack of broad spectral tunability continues to stimulate active research in this field. We hereby present the first experimental investigation of coherent grating diffraction radiation (GDR), for which comparable radiation intensity with central frequency fine–tuning in a much wider spectral range has been confirmed. Additionally, the approach allows for bandwidth selection at the same central frequency. The experimental validation of performance included the basic spectral, spatial and polarization properties. The discussion of the comparison between GDR intensity and other coherent radiation sources is also presented. These results further strengthen the foundation for the design of a tabletop wide–range tunable quasi–monochromatic or multi–colour radiation source in the GHz–THz frequency range.

Second-Harmonic Generation from Dendritic Fractal Structures

Nanostructured conductive surfaces have been exploited for a variety of applications in photonics and optical sensing due to the broad spectral tunability of the localized surface plasmon resonances and the subsequent electromagnetic field confinement in the vicinity of the structures. Herein, we report on the second-order nonlinear optical properties of dendritic fractal structures with specific geometries that were optimized to yield resonances at both the fundamental and the second-harmonic wavelengths. Using a femtosecond excitation at 800 nm, second-harmonic generation microscopy experiments were conducted on a series of gold fractal dendritic structures with and without center of inversion. The polarized second-harmonic maps reveal the local character of the second-harmonic generation (SHG) emission and even structures with center of inversion show SHG activity in the periphery of the core dendron where non-centrosymmetric features are forming the higher fractal generations. The experiments were correlated using finite-difference time-domain electromagnetic time modelling performed at both the fundamental and second-harmonic wavelengths.

Single-step direct laser writing of halide perovskite microlasers

Halide perovskites are a family of materials with a high potential for realization of microlasers, due to their high luminescence quantum yield and broad spectral tunability. We demonstrate a single-step process for lasing microdisk fabrication from a thin film of methylammonium lead iodide (MAPbI3) perovskite through its patterning with tightly focused femtosecond (fs) laser pulses. By using kHz-scale pulse bursts destructive overheating of the material was suppressed. Perovskite microdisks fabricated under such optimized conditions showed stable lasing upon pumping with fs-laser both at lower (50 kHz) and higher (80 MHz) repetition rates and operation temperatures of 300 K and 6 K, respectively.

A colloidal quantum dot infrared photodetector and its use for intraband detection

Wavefunction engineering using intraband transition is the most versatile strategy for the design of infrared devices. To date, this strategy is nevertheless limited to epitaxially grown semiconductors, which lead to prohibitive costs for many applications. Meanwhile, colloidal nanocrystals have gained a high level of maturity from a material perspective and now achieve a broad spectral tunability. Here, we demonstrate that the energy landscape of quantum well and quantum dot infrared photodetectors can be mimicked from a mixture of mercury selenide and mercury telluride nanocrystals. This metamaterial combines intraband absorption with enhanced transport properties (i.e. low dark current, fast time response and large thermal activation energy). We also integrate this material into a photodiode with the highest infrared detection performances reported for an intraband-based nanocrystal device. This work demonstrates that the concept of wavefunction engineering at the device scale can now be applied for the design of complex colloidal nanocrystal-based devices.

TiN nanoparticles: synthesis and application as near-infrared photothermal agents for cancer therapy

We have developed TiN nanoparticles (NPs) as a novel near-infrared-activated photothermal agent. The effect of nitridation temperature on the optical property and photothermal performance of the TiN NPs were investigated. The nanoparticles nitrided at 1000 °C presented a significant absorption along the whole biological spectral range (i.e., for wavelengths above 700 nm). After coated with polystyrene sulfonate (PSS) and poly(diallyldimethylammonium chloride) (PDDA), they exhibited well-defined spherical morphology with average size of ~ 50 nm. We also demonstrated their therapeutic efficacy against SW1990 pancreatic cancer cells. The results indicated that the PSS/PDDA-coated TiN NPs offered several advantages including high photothermal conversion efficiency (44.6%), high photothermal stability, broad spectral tunability, low cytotoxicity and facile synthesis process. These features make TiN NPs promising alternative for use as a photothermal agent in cancer photothermal treatment.

Water-stable and ion exchange-free inorganic perovskite quantum dots encapsulated in solid paraffin and their application in light emitting diodes.

Perovskite quantum dots (PQDs) with high quantum efficiency and broad spectral tunability are promising luminescent materials and show potential applications in light-emitting diodes (LEDs). However, PQDs degrade rapidly in atmosphere moisture due to their easy hydrolysis and undergo undesirable spectral changes associated with ion exchanges. Herein, we encapsulated blue, green and red fluorescence-emitting all-inorganic PQDs respectively with hydrophobic solid paraffin to obtain multi-color luminescent paraffin-PQD composites (P-PQDs). The P-PQD composites not only preserve the bright luminescence, but also greatly improve the water resistance of PQDs. Moreover, the anion exchange phenomenon is effectively inhibited for the isolation of PQD nanoparticles by a solid paraffin layer. Finally, blue, green and red luminescent P-PQD microparticles have been synthesized and show promising applications in LEDs.

Highly Efficient and Stable Inorganic Perovskite Quantum Dots by Embedding into a Polymer Matrix

AbstractAll‐inorganic perovskite quantum dots (QDs) with high photoluminescence quantum yield, narrow spectral bandwidth, and broad spectral tunability have broad applications. However, perovskite QDs suffer from poor stability and the fast anion‐exchange reaction between different halide ions. Herein, we embedded green‐light‐emitting CsPbBr3 QDs and red‐light‐emitting CsPb(Br/I)3 QDs into carboxyl‐containing polymethyl methacrylate (PMMA) by the hot‐injection method. As a result, the as‐prepared perovskite@PMMA composites not only retain high luminescence but also exhibit good water resistance. Moreover, this treatment prevents anion exchange between different halide QD particles in the solid state. The applications in light‐emitting diodes and cellular labeling agents are also carried out to demonstrate their good stability.