The interaction of non-monochromatic radiation with two types of arrays comprising both plasmonic and dielectric nanoparticles has been studied in detail. We have shown that dielectric nanoparticle arrays provide a complete selective reflection of an incident plane wave within a narrow spectral line of collective lattice resonance with a Q-factor of $10^3$ or larger, whereas plasmonic refractory TiN and chemically stable Au nanoparticle arrays demonstrated high-Q resonances with moderate reflectivity. The spectral position of these resonance lines is determined by the lattice period, as well as the size, shape and material composition of the particles. Moreover, the arrays, with fixed dimensional parameters make it possible to fine-tune the position of a selected resonant spectral line by tilting the array relative to the direction of the incident radiation. These effects provide possibilities for engineering of novel selective tunable optical high-Q filters in a wide range of wavelengths: from visible to middle IR. Several highly refractive dielectric nanoparticle materials with low absorption are proposed for various spectral ranges, such as LiNbO$_3$, TiO$_2$, GaAs, Si, and Ge.
We demonstrate the first functional signal processing device based on stimulated Brillouin scattering in a silicon nanowire. We use only 1 dB of on-chip SBS gain to create an RF photonic notch filter with 48 dB of suppression, 98 MHz linewidth, and 6 GHz frequency tuning. This device has potential applications in on-chip microwave signal processing and establishes the foundation for the first CMOS-compatible high performance RF photonic filter.
Optical Tamm States (OTS) are confined optical modes that can occur at the interface between two highly reflective structures. However, due to the strong reflectance required, their implemen-tation with highly processable and metal-free flexible materials has proven challenging. Herein, we develop the first structure supporting OTS based only on organic polymeric materials, demon-strating a photonic platform based on non-critical, widely available, and easily processable mate-rials. The structures fabricated present large areas and consist of a narrowband multi-layered polymeric Distributed Br…
We propose multiple approaches for controlling Wien's displacement law in the near-field leading to narrowband, tunable, spatially-coherent high temperature thermal sources. We show that narrowband super-planckian thermal emission relevant to the wavelength ranges for near-field thermophotovoltaics can be achieved by utilizing engineered plasmonic states of metals with a high melting point. Along with conventional thin film surface plasmon polaritons of high temperature plasmonic metals, we also introduce multiple different approaches to narrowband near field thermal emission a) epsilon-near-z…
Several applications in modern photonics require compact on-chip optical filters with a tailored spectral response. However, achieving sub-nanometric bandwidths and high extinction ratios is particularly challenging, especially in low-footprint device formats. Phase shifted Bragg gratings implemented by sidewall modulation of photonic nanowire waveguides are a good solution for on-chip narrowband operation with reasonable requirements in fabrication and scalability. In this work we report on their implementation and optimization in thin film lithium niobate, a photonic platform that affords re…
Tunable narrowband spectral filters with high light throughput and wide dynamic range have remarkable applications such as in optical communications, optical spectroscopy and spectral imaging. However, a cost is usually associated with the filter narrowing either in the dynamic range, in the throughput or the manufacturability. Here we report on a resonating planar multilayered structure that exhibits transparency window in reflection with a controllable full width at half maximum (sub-Angstroms till tens of nm) and tunability over wide spectral range (>500nm in the visible and near infrared).…
Here we report on a novel High Harmonic Generation (HHG) light source designed for space charge free ultrafast photoelectron spectroscopy (PES) on solids. The ultimate overall energy resolution achieved on a polycrystalline Au sample is ~22 meV at 40 K. These results have been obtained at a photon energy of 16.9 eV with a pulse bandwidth of ~19 meV, by varying, up to 200 kHz, the photon pulses repetition rate and the photon fluence on the sample. These features set a new benchmark for tunable narrowband HHG sources. By comparing the PES energy resolution and the photon pulse bandwidth with a p…
Spectral compression of femtosecond pulses by second harmonic generation in the presence of substantial group velocity dispersion provides a convenient source of narrowband Raman pump pulses for femtosecond stimulated Raman spectroscopy (FSRS). We discuss here a simple and efficient modification that dramatically increases the versatility of the second harmonic spectral compression technique. Adding a spectral filter following second harmonic generation produces narrowband pulses with a superior temporal profile. This simple modification i) increases the Raman gain for a given pulse energy, ii…
By using the formal analogy between the evolution of the state vector in quantum mechanics and the Jones vector in polarization optics, we construct and demonstrate experimentally efficient broadband half-wave polarization retarders and tunable narrowband polarization filters. Both the broadband retarders and the filters are constructed by the same set of stacked standard multi-order optical wave plates rotated at different angles with respect to their fast polarization axes: for a certain set of angles this device behaves as a broadband polarization retarder while for another set of angles it…
Many fields such as bio-spectroscopy and photochemistry often require sources of vacuum ultraviolet (VUV) pulses featuring a narrow linewidth and tunable over a wide frequency range. However, the majority of available VUV light sources do not simultaneously fulfill those two requirements, and few if any are truly compact, cost-effective and easy to use by non-specialists. Here we introduce a novel approach that goes a long way to meeting this challenge. It is based on hydrogen-filled hollow-core photonic crystal fiber pumped simultaneously by two spectrally distant pulses. Stimulated Raman sca…
In this paper, we will introduce THz graphene antennas that strongly enhance the emission rate of quantum systems at specific frequencies. The tunability of these antennas can be used to selectively enhance individual spectral features. We will show as an example that any weak transition in the spectrum of coronene can become the dominant contribution. This selective and tunable enhancement establishes a new class of graphene-based THz devices, which will find applications in sensors, novel light sources, spectroscopy, and quantum communication devices.
Precise control of high-frequency ultrasounds in thin crystals for the development of tunable narrowband and directional gamma-ray sources
Institute of Plasma Physics and Lasers (IPPL), Hellenic Mediterranean University（希伦尼克地中海大学等离子体物理与激光研究所）；Physical Acoustics and Optoacoustics Laboratory, Department of Music Technology and Acoustics, Hellenic Mediterranean University（希伦尼克地中海大学音乐技术与声学系物理声学与光声实验室）
Controlling the spectral and angular response of infrared (IR) radiation is a challenging task of paramount importance to various emerging photonic applications. Here, we overcome these problems by proposing and analyzing a new design of a tunable narrowband directional optical transmission filter. The presented thermally controlled multilayer filter leverages the temperature dependent phase change properties of vanadium dioxide (VO2) to enable efficient and reversible fast optical switching by using a pump-probe laser excitation setup. More specifically, transmission is blocked for high inten…
We present the model of an ultrasensitive mid-infrared (mid-IR) photodetector operating in the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) domains consisting of a hybrid heterostructure made of nanopatterned graphene (NPG) and vanadium dioxide (VO$_2$) which exhibits a large responsivity of $R\sim 10^4$ V/W, a detectivity exceeding $D^*\sim 10^{10}$ J, and a sensitivity in terms of noise-equivalent power $\mathrm{NEP}\sim 100$ fW/$\sqrt{\rm Hz}$ close to room temperature by taking advantage of the phase change of a thin VO$_2$ film. Our proposed photodetector can reach a…
Actively tunable, narrowband spectral filtering across arbitrary optical wavebands is highly desirable in a plethora of applications, from chemical sensing, hyperspectral imaging to infrared astronomy. Yet, the ability to actively reconfigure the optical properties of a solid-state narrowband filter remains elusive. Existing solutions require either moving parts, have slow response times or provide limited spectral coverage. Here, we demonstrate a continuously tunable, spectrally-agnostic, all-solid-state, narrowband phase-change metasurface filter based on a GeSbTe (GST)-embedded plasmonic na…
Dynamic radiative cooling with variable emissive power is experimentally demonstrated in this study by a wavelength-selective tunable metafilm emitter, which consists of an opaque aluminum film, a sputtered silicon spacer, and a thermochromic vanadium dioxide (VO2) layer fabricated by a furnace oxidation method. The temperature-dependent spectral emittance, experimentally obtained from spectral reflectance measurements, clearly shows a pronounced emission peak around 10 um wavelength when the VO2 experiences an insulator-to-metal phase transition near 65C. The tunable metafilm emitter achieves…
We propose a nonvolatile, reconfigurable, and narrowband mid-infrared bandpass filter based on surface lattice resonance in phase-change material Ge2Sb2Te5 (GST). The proposed filter is composed of a two-dimensional gold nanorod array embedded in a thick GST film. Results show that when GST transits from the amorphous state to the crystalline state, the narrowband reflection spectrum of the proposed filter is tuned from 3.197 μm to 4.795 μm, covering the majority of the mid-infrared regime, the peak reflectance decreases from 72.6% to 25.8%, and the corresponding Q-factor decreases from 19.6 t…
Electromagnetically induced transparency (EIT) resonances using the $5\rm{S}_{1/2}\rightarrow5\rm{P}_{3/2}\rightarrow5\rm{D}_{5/2}$ ladder-system in optically thick Rb atomic vapour are studied. We observe a strong line narrowing effect and gain at the $5\rm{S}_{1/2}\rightarrow5\rm{P}_{3/2}$ transition wavelength due to an energy-pooling assisted frequency conversion with characteristics similar to four-wave mixing. As a result it is possible to observe tunable and switchable transparency resonances with amplitude close to $100\%$ and a linewidth of 15 MHz. In addition, the large line narrowin…
Quantum information technology strongly relies on coupling of optical photons with narrowband quantum systems, such as quantum dots, color centers, and atomic systems. This coupling requires matching the optical wavelength and bandwidth to the desired system, which presents a considerable problem for most available sources of quantum light. Here we demonstrate coupling of alkali dipole transitions with a tunable source of photon pairs. Our source is based on spontaneous parametric down-conversion in a triply-resonant whispering-gallery mode resonator. For this, we have developed novel waveleng…
Abstract It is shown that electrostatic plasma wakefields can efficiently radiate at harmonics of the plasma frequency when the plasma has a positive density gradient along the propagation direction of a driver. The driver propagating at a sub-luminal group velocity excites the plasma wakefield with the same phase velocity. However, due to the positive density gradient, the wake phase velocity steadily increases behind the driver. As soon as the phase velocity becomes super-luminal, the electrostatic wakefield couples efficiently to radiative electromagnetic modes. The period of time when the …
Flexible and tensile wavelength-tunable micrometer-sized random lasers in the form of microporous polymer fiber are demonstrated. The fibers are fabricated by directly drawing from an aqueous mixture and subsequently selective chemical etching in a green solvent. Size-dependent lasing threshold and spectrum are investigated. Owing to mechanical flexibility, wavelength-tuning of 5.5 nm is achieved by stretching the fiber.
Cholesteric liquid crystals with helicoidal molecular architecture are known for their ability to selectively reflect light with the wavelength that is determined by the periodicity of molecular orientations. Here we demonstrate that by using a cholesteric with oblique helicoidal(heliconical) structure, as opposed to the classic right-angle helicoid, one can vary the wavelength of selectively reflected light in a broad spectral range, from ultraviolet to visible and infrared (360-1520 nm for the same chemical composition) by simply adjusting the electric field applied parallel to the helicoida…
Non-Hermitian lattices under semi-infinite boundary conditions sustain an extensive number of exponentially-localized states, dubbed non-Hermitian skin modes. Such states can be predicted from the nontrivial topology of the energy spectrum under periodic boundary conditions via a bulk-edge correspondence. However, the selective excitation of the system in one among the infinitely-many topological skin edge states is challenging both from practical and conceptual viewpoints. In fact, in any realistic system with a finite lattice size most of skin edge states collapse and become metastable state…
We demonstrate spectrally-tunable Fabry-Perot bandpass filters operating across the MWIR by utilizing the phase-change material GeSbTe (GST) as a tunable cavity medium between two (Ge:Si) distributed Bragg reflectors. The induced refractive index modulation of GST increases the cavity's optical path length, red-shifting the passband. Our filters have spectral-tunability of ~300 nm, transmission efficiencies of 60-75% and narrowband FWHMs of 50-65 nm (Q-factor ~70-90). We further show multispectral thermal imaging and gas sensing. By matching the filter's initial passband to a CO$_{2}$ vibratio…
Narrowband single photons that couple well to atomic ensembles could prove essential for future quantum networks, but the efficient generation of such photons remains an outstanding challenge. We realize a spatially-multiplexed heralded source of single photons that are inherently compatible with the commonly employed D2 line of rubidium. Our source is based on four-wave mixing in hot rubidium vapor, requiring no laser cooling or optical cavities, and generates single photons with high rate and low noise. We use Hong-Ou-Mandel interference to verify the indistinguishability of the photons gene…
We present how to physically realize the auxiliary source described in the recently introduced active plasmon injection loss compensation scheme for enhanced near-field superlensing. Particularly, we show that the characteristics of the auxiliary source described in the active plasmon injection scheme including tunable narrow-band and selective amplification via convolution can be realized by using a hyperbolic metamaterial functioning as a near-field spatial filter. Besides loss compensation, the proposed near-field spatial filter can be useful for real-time high resolution edge detection.
We propose and theoretically verify an efficient mechanism of broadband coupling between incident light and on-chip dielectric slot waveguide by employing a tapered plasmonic nanoantenna. Nanoantenna receives free space radiation and couples it to a dielectric slot waveguide with the efficiency of up to 20% in a broad spectral range, having a small footprint as compared with the currently used narrowband dielectric grating couplers. We argue that the frequency selective properties of such nanoantennas also allow for using them as ultrasmall on-chip multiplexer/demultiplexer devices.
Tunable high-$Q$ Janus-to-chiral bound states in the continuum in bilayer PhCs
School of Physics and Optoelectronics, Xiangtan University（湘潭大学物理与光电工程学院）；School of Physics and Electronics, Hunan University（湖南大学物理学院）；State Key Laboratory of Millimeter Waves, Southeast University（东南大学毫米波国家重点实验室）；Science, Mathematics and Technology (SMT) Cluster, Singapore University of Technology and Design（新加坡科技设计大学科学、数学与技术学部）
An electronically reconfigurable dual-band-reflectarray antenna is presented in this paper. The tunable unit cell, a ring loaded square patch with a single varactor diode connected across the gap between the ring and the patch, is modeled using both a full-wave solver and an equivalent circuit. The parameters of the equivalent circuit are calculated independently of the simulation and experiment using analysis techniques employed in frequency selective surfaces. The reflection phase of the proposed unit cell is shown to provide an excellent phase range of 335$^{\circ}$ in F band and 340$^{\cir…
We investigate 1D aperiodic multilayer microstructures in order to achieve near total absorption in preselected wavelengths in a graphene monolayer. Our structures are designed by a genetic optimization algorithm coupled to a transfer matrix code. Coupled mode theory (CMT) analysis, in accordance with transfer matrix method (TMM) results, indicates the existence of a critical coupling in a graphene monolayer for perfect absorptions. Our findings show that the near-total-absorption peaks are highly tunable and can be controlled simultaneously or independently in wide range of wavelengths in the…
In this work, we numerically demonstrate an infrared frequency-tunable selective thermal emitter made of graphene covered SiC deep gratings. Full-wave simulation shows temporally-coherent emission peak associated with magnetic polariton, whose resonance frequency can be dynamically tuned within the phonon absorption band of SiC by varying graphene chemical potential. An analytical inductor-capacitor circuit model is introduced to quantitatively predict the resonance frequency and further elucidate the mechanism for the tunable emission peak. Moreover, by depositing multiple layers of graphene …
We design a photonic sphere-array nanoantenna (NA) exhibiting both strong directionality and wavelength selectivity. Although the geometric configuration of the photonic NA resembles a plasmonic Yagi-Uda NA, it has different working principles, and most importantly, reduces the inherent metallic loss from plasmonic elements. For any selected optical wavelength, a sharp Fano-resonance by the reflector is tunable to overlap spectrally with a wider dipole resonance by the sphere-chain director leading to the high directionality. The work provides design principles for directional and selective ph…
Surface plasmon resonance (SPR) has been intensively studied and widely employed for light trapping and absorption enhancement. In the mid-infrared and terahertz (THz) regime, graphene supports the tunable SPR via manipulating its Fermi energy and enhances light-matter interaction at the selective wavelength. In this work, periodic arrays of graphene rings are proposed to introduce tunable light trapping with good angle polarization tolerance and enhance the absorption in the light-absorbing materials nearby to more than one order. Moreover, the design principle here could be set as a template…
We produce transmission and reflection spectra of the anti-directional coupler (ADC) composed of linearly-coupled positive- and negative-refractive-index arms, with intrinsic Kerr nonlinearity. Both reflection and transmission feature two highly amplified peaks at two distinct wavelengths in a certain range of values of the gain, making it possible to design a wavelength-selective mode-amplification system. We also predict that a blend of gain and loss in suitable proportions can robustly enhance reflection spectra which are detrimentally affected by the attenuation, in addition to causing red…
In this study, we demonstrate first, to the best of our knowledge, robust and dynamically polarization-controlled tunable-high-Q PIT in designed nanostructures metasurface, whose sharp resonance is guaranteed by design and protected against large geometrical imperfections. By employing the explicit analysis of near-field characteristic in the reciprocal-space based on the momentum matching, and the far-field radiation features with point-scattering approach in real-space sparked from Huygens's principles, the physics of interference resonance in the spectra for plane-wave optical transmission …
