Broadband electrochromism from visible to infrared wavelengths is attractive for applications like smart windows, thermal-camouflage, and temperature control. In this work, the broadband electrochromic properties of Li4Ti5O12 (LTO) and its suitability for infrared-camouflage and thermoregulation are investigated. Upon Li+ intercalation, LTO changes from a wide band-gap semiconductor to a metal, causing LTO nanoparticles on metal to transition from a super-broadband optical reflector to a solar absorber and thermal emitter. Large tunabilities of 0.74, 0.68 and 0.30 are observed for the solar reflectance, mid-wave infrared (MWIR) emittance and long-wave infrared (LWIR) emittance respectively. The values exceed, or are comparable to notable performances in the literature. A promising cycling stability is also observed. MWIR and LWIR thermography reveal that the emittance of LTO-based electrodes can be electrochemically tuned to conceal them amidst their environment. Moreover, under different sky conditions, LTO shows promising solar heating and sub-ambient radiative cooling capabilities depending on the degree of lithiation and device design. The demonstrated capabilities of LTO make LTO-based electrochromic devices highly promising for infrared-camouflage applications in the defense sector, and for thermoregulation in space and terrestrial environments.
In this paper, a route to ultra-broadband absorption is suggested and demonstrated by a feasible design. The high absorption regime (absorption above 90%) for the suggested structure ranges from visible to mid-infrared (MIR), i.e. for the wavelength from 478 to 3,278 nm that yields an ultra-wide bandwidth of 2,800 nm. The structure consists of a top-layer-patterned metal-insulator-metal (MIM) configuration, into the insulator layer of which, an ultra-thin 5 nm layer of Manganese (Mn) is embedded. The MIM configuration represents a Ti-Al2O3-Ti tri-layer. It is shown that, without the ultra-thin…
Black phosphorous (BP), a two-dimensional (2D) material, has a direct bandgap, which fills up the bandgap lacuna left by graphene topological insulators and transition-metal dichalcogenides because of its dependence on the layers and applied strains. Theoretically, the direct and tunable band gap indicates the broadband applications in optoelectronics with high efficiencies in the spectral range from visible to mid-infrared. Here, a BP broadband optical modulator is experimentally constructed and the passively modulated lasers at 639 nm (red), 1.06 um (near-infrared) and 2.1 um (mid-infrared) …
Very recently Farhat et al. [1] have suggested that arrays of invisibility cloaks may find important applications in low-interference communication, noninvasive probing, sensing and communication networks, etc. We report on the first experimental realization of such an array of broadband invisibility cloaks, which operates in the visible frequency range. Wavelength and angular dependencies of the cloak array performance have been studied.
In the past few years, carpet cloaking attracted interests because of its feasibility at optical frequencies and potential in stealth technologies. Metasurfaces have been proposed as a method to engineer ultra-thin carpet cloaking surfaces due to their abilities to manipulate wavefronts, polarization, and phase at subwavelength scale. However, achieving broadband carpet cloaking with a significant bandwidth is one of the key remaining challenges for metasurface designs. To date, broadband carpet cloaking based on metasurfaces has not been achieved and cloaking is limited to discrete wavelength…
Broadband and tunable control of surface plasmon polaritons in the near-infrared and visible spectrum is demonstrated theoretically and numerically with a pair of phased nanoslits. We establish with simulations supported by a coupled wave model that by dividing the incident power equally between two input channels, the maximum plasmon intensity deliverable to either side of the nanoslit pair is twice that for an isolated slit. For a broadband source, a compact device with nanoslit separation of the order of a tenth of the wavelength is shown to steer nearly all the generated plasmons to one si…
Visible and near-infrared spectrum photonic integrated circuits are quickly becoming a key technology to address the scaling challenges in quantum information and biosensing. Thus far, integrated photonic platforms in this spectral range have lacked integrated photodetectors. Here, we report the first silicon nitride-on-silicon waveguide photodetectors that are monolithically integrated in a visible light photonic platform on silicon. Owing to a leaky-wave silicon nitride-on-silicon design, the devices achieved a high external quantum efficiency of > 60% across a record wavelength span from $λ…
Developing colloidal plasmonic nanomaterials with high carrier density that show optical resonances and photochemical activity extending from the visible to the mid-infrared (MIR) ranges remains a challenging pursuit. Here, we report the fabrication of titanium nitride (TiN) nanobars obtained using a two step procedure based on a wet chemical route synthesis of TiO2 nanowires and their subsequent high temperature annealing in ammonia flow. Electromagnetic simulations of the resulting TiN nanobars reveal a rich set of optical resonances featuring transverse, longitudinal and mixed transverse lo…
We present an upconversion imaging experiment from the near-infrared to the visible spectrum. Using a dedicated broadband pump laser to increase the number of resolved elements converted in the image we obtain up to 56x64 spatial elements with a 2.7 nm wide pump spectrum, more than 10 times the number of elements accessible with a narrowband laser. Results in terms of field of view, resolution and conversion efficiency are in good agreement with simulations. The computed sensitivity of our experiment favorably compares with direct InGaAs camera detection.
Metasurfaces have the potential to miniaturize and improve the performance of any optical element, with applications spanning telecommunications, computing and wearable optics. However, the ability to retain functionality over a continuous, broad range of wavelengths is essential for their widespread adoption. So far, efforts to achieve this have been limited to either a reflection configuration or operation at wavelengths other than the visible. Here, we show that by judicious choice of nanostructures, one can independently control both the phase and group delay, leading to broadband transmis…
We report an inverse-designed, high numerical aperture (~0.44), extended depth of focus (EDOF) meta-optic, which exhibit a lens-like point spread function (PSF). The EDOF meta-optic maintains a focusing efficiency comparable to that of a hyperboloid metalens throughout its depth of focus. Exploiting the extended depth of focus and computational post-processing, we demonstrate broadband imaging across the full visible spectrum using a 1 mm, f/1 meta-optic. Unlike other canonical EDOF meta-optics, characterized by phase masks such as a log-asphere or cubic function, our design exhibits a highly …
The most commonly used nonlinear optical process is the conversion of infrared light at 1064nm to green light at 532nm, as performed in common laser pointers. However, more relevant for future applications are nonlinear optical processes that generate a broad spectrum, a so called supercontinuum. A desirable goal is generating a spectrum that covers the whole visible range (400 -900nm), i.e., white light. Nowadays, white-light generation is usually achieved in specially designed photonic fibres requiring high laser intensities. However, in previous studies we showed that amorphous powders of $…
Ultrathin metasurfaces have recently emerged as promising materials to enable novel, flat optical components and surface-confined, miniature photonic devices. However, experimental realization of high-performance metasurfaces at visible frequencies has been a significant challenge due to high plasmonic losses and difficulties in high-uniformity nanofabrication. Here, we propose a highly-efficient yet simple metasurface design comprising of single gradient antenna as unit cell. We demonstrate visible broadband (450 - 850 nm) anomalous reflection and spectrum splitting with 85% conversion effici…
A novel phase retrieval algorithm for broadband hyperspectral phase imaging from noisy intensity observations is proposed. It utilizes advantages of the Fourier Transform spectroscopy in the self-referencing optical setup and provides, additionally beyond spectral intensity distribution, reconstruction of the investigated object's phase. The noise amplification Fellgett's disadvantage is relaxed by the application of sparse wavefront noise filtering embedded in the proposed algorithm. The algorithm reliability is proved by simulation tests and results of physical experiments on transparent obj…
In the absence of separate apertures, the size and focal length of a lens determines both its resolution and light-collection ability defined by numerical-aperture (NA) and f/#, respectively. We utilize free-form broadband-diffractive-optical elements (BDOEs) to create flat lenses that decouple NA from f#, whereby the resolution of the lens may be chosen independently from its light-collection ability. Specifically, we designed, fabricated and characterized three BDOE lenses operating in the visible band (450nm-750nm), each with f/11.25, but with NAs of 0.00075, 0.0067 and 0.054, respectively.…
The technological progress in spatial-light modulators (SLM) technology has made it possible to use those devices as programmable active focal-plane phase coronagraphic masks, opening the door to novel versatile and adaptive high-contrast imaging observation strategies. However, the scalar nature of the SLM-induced phase response is a potential hurdle when applying the approach to wideband light, as is typical in astronomical imaging. For the first time, we present laboratory results with broadband light (up to ~12pc bandwidth) for two commercially-available SLM devices used as active focal-pl…
We present a theoretical analysis of a super-resolving lens based on 1-dimensional metallo-dielectric photonic crystals composed of Ag/GaP multilayers. The lens contains a total of 10 optical skin depths of Ag, yet maintains a normal incidence transmittance of ~50% for propagating waves over the super-resolving wavelength range of 500-650 nm. The individual Ag layers are 22 nm thick and can be readily fabricated in conventional deposition systems. The importance of anti-reflection coatings for the transmission of evanescent and propagating waves is illustrated by comparison to periodic and sym…
Ultra-broadband imaging devices with high performance are in great demand for a variety of technological applications, including imaging, remote sensing, and communications. An ultra-broadband up-converter is realized based on a p-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) detector-light emitting diode (LED) device. The device demonstrates an ultra-broad response ranging from visible to terahertz (THz) with good reproducibility. The peak responsivity in the mid-infrared (MIR) region is 140 mA/W at 10.5 microns. The HIWIP-LED shows enormous potential for ultra-bro…
High-harmonic generation (HHG) provides short-wavelength light that is useful for precision spectroscopy and probing ultrafast dynamics. We report efficient, phase-coherent harmonic generation up to 9th-order (333 nm) in chirped periodically poled lithium niobate waveguides driven by phase-stable $\leq$12-nJ, 100 fs pulses at 3 $μ$m with 100 MHz repetition rate. A mid-infrared to ultraviolet-visible conversion efficiency as high as 10% is observed, amongst an overall 23% conversion of the fundamental to all harmonics. We verify the coherence of the harmonic frequency combs despite the complex …
The spin-selective reflection to introduce chirality which can have a lot of applications in real life such as spectroscopy, optical setups, media industry etc. In this paper, a reflection based metasurface proposed to introduce the giant chiroptical effects at broadband visible and infrared (IR) regimes. The optimization and results of basic unit also termed as nanostructure are demonstrated here. The reflectance at the optimal parameters for the proposed nanostructure shows the inclusion of multiband giant chiroptical effects in reflection mode. The results show that this metasurface can eli…
We report here an experimental setup to perform three-pulse pump-probe measurements over a wide wavelength and temperature range. By combining two pump pulses in the visible (650-900 nm) and mid-IR (5-20 $μ$m) range, with a broadband supercontinuum white-light probe, our apparatus enables both the combined selective excitation of different material degrees of freedom and a full time-dependent reconstruction of the non-equilibrium dielectric function of the sample. We describe here the optical setup, the cryogenic sample environment and the custom-made acquisition electronics capable of referen…
A metamaterial absorber converts solar radiation into heat for applications in thermoelectric generators and solar thermophotovoltaics. A metamaterial absorber typically consists of metallic parts separated by an insulator layer which does not allow the total heat extraction via direct heat conduction. Here, we propose wide-angle and broadband metamaterial absorber comprising an insulator layer, metal grating, and metal back plane (IMM) that allows the total heat extraction via direct heat conduction. We have formulated the quasi-analytical solution (QANS) of the IMM-absorber by applying the c…
Integrating conventional optics into compact nanostructured surfaces is the goal of flat optics. Despite the enormous progress of this technology, there are still critical challenges for real world applications due to a limited efficiency in the visible, on average lower than $60\%$, which originates by absorption losses in wavelength thick ($\approx 500$nm) structures. Another issue is the realization of on-demand optical components for controlling vectorial light at visible frequencies simultaneously in both reflection and transmission, and with a predetermined wavefront shape. In this work,…
Using a hydrodynamic approach we examine bulk- and surface-induced second and third harmonic generation from semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrate resonant, broadband and highly efficient optical frequency conversion: contrary to conventional wisdom, we show that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where nonlinear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximate…
We present optimized aperiodic structures for use as broadband thermal incandescent emitters which are capable of increasing the emittance by nearly a factor of two over the visible wavelength range when compared to bulk tungsten. These aperiodic multilayer structures are designed with alternating layers of tungsten and air or tungsten and silicon carbide on top of a tungsten substrate. We investigate the properties of these structures for use as lightbulb filaments. We find that these structures greatly enhance the emittance over the visible wavelength range, while also increasing the overall…
We demonstrate imaging over the visible band using a single planar diffractive lens. This is enabled via multi-level diffractive optics that is designed to focus over a broad wavelength range, which we refer to as an achromatic diffractive lens (ADL). We designed, fabricated and characterized two ADLs with numerical apertures of 0.05 and 0.18. Diffraction-limited focusing is demonstrated for the NA=0.05 lens with measured focusing efficiency of over 40% across the entire visible spectrum (450nm to 750nm). We characterized the lenses with a monochromatic and a color CMOS sensor, and demonstrate…
Typical materials for optical Kinetic Inductance Detetectors (KIDs) are metals with a natural absorption of 30-50% in the visible and near-infrared. To reach high absorption efficiencies (90-100%) the KID must be embedded in an optical stack. We show an optical stack design for a 60 nm TiN film. The optical stack is modeled as sections of transmission lines, where the parameters for each section are related to the optical properties of each layer. We derive the complex permittivity of the TiN film from a spectral ellipsometry measurement. The designed optical stack is optimised for broadband a…
We demonstrate surface plasmon-induced enhancements in optical imaging and spectroscopy on silver coated silicon nanocones which we call black silver substrate. The black silver substrate with dense and homogeneous nanocone forest structure is fabricated on wafer level with a mass producible nanomanufacturing method. The black silver substrate is able to efficiently trap and convert incident photons into localized plasmons in a broad wavelength range, which permits the enhancement in optical absorption from UV to NIR range by 12 times, the visible fluorescence enhancement of ~30 times and the …
A broadband visible blue-to-red, 10 GHz repetition rate frequency comb is generated by combined spectral broadening and triple-sum frequency generation in an on-chip silicon nitride waveguide. Ultra-short pulses of 150 pJ pulse energy, generated via electro-optic modulation of a 1560 nm continuous-wave laser, are coupled to a silicon nitride waveguide giving rise to a broadband near-infrared supercontinuum. Modal phase matching inside the waveguide allows direct triple-sum frequency transfer of the near-infrared supercontinuum into the visible wavelength range covering more than 250 THz from b…
The energy consumption of buildings is increasing at a rapid pace due to urbanization, while net-zero energy buildings powered by renewable sources offer a green and sustainable solution. However, the limited rooftop space available on skyscrapers and multi-story buildings poses a challenge for large-scale integration of solar photovoltaic modules. Conventional photovoltaics solutions such as silicon solar panels block the visible light from entering the building rending them unfeasible to cover all building surfaces. Here, we demonstrate a novel dielectric metasurface (based-on silicon nitrid…
Deep-Subwavelength and Broadband Quarter-Wave Retardation in Ultrathin Hyperbolic MoOCl2
XPANCEO；University of Rome Tor Vergata（罗马托尔维加塔大学）；University of Chemistry and Technology Prague（布拉格化工大学）；National Graphene Institute (NGI), University of Manchester（曼彻斯特大学石墨烯国家研究所）；National University of Singapore（新加坡国立大学）
Metamaterials and metasurfaces operating in the visible and near-infrared (NIR) offer a promising route towards next-generation photodetectors and devices for solar energy harvesting. While numerous metamaterials and metasurfaces using metals and semiconductors have been demonstrated, semimetals-based metasurfaces in the vis-NIR range are notably missing. Here, we experimentally demonstrate a broadband metasurface superabsorber based on large area, semimetallic, van der Waals PtSe2 thin films in agreement with electromagnetic simulations. Our results show that PtSe2 is an ultrathin and scalabl…
We demonstrate visible and near-IR image projection via non-absorbing, multi-level Broadband Diffractive-Optical Elements (BDOEs) in 1 or more planes. By appropriate design of the BDOE topography, we experimentally demonstrate: (1) different images in different spectral bands; (2) different images in different image planes; (3) image magnification by changing the distance between the illumination source and the BDOE; (4) completely flat BDOE via an index-contrast top-coating; and (5) reflective BDOEs. All of these are accomplished with broadband illumination. Furthermore, the BDOEs are highly …
We show that broadband optical magnetism can be achieved through incorporating multi-scaled 3D metallic meta-elements into Z-shaped nanohole arrays. The broadband effect arises from the excitation of multiple magnetic resonances in the meta-elements at different wavelengths. Moreover, the nanohole arrays exhibit a large transmission difference for left- and right-handed circularly polarized incident light due to the chiral arrangement of the meta-elements. More importantly, we have realized experimentally the broadband behavior for the optical range in Ag nanohole arrays fabricated by using a …
We report on the experimental realization of flat mirrors enabling the broadband generation of optical vortices upon reflection. The effect is based on the geometric Berry phase associated with the circular Bragg reflection phenomenon from chiral uniaxial media. We show the reflective optical vortex generation from both diffractive and nondiffractive paraxial light beams using spatially patterned chiral liquid crystal films. The intrinsic spectrally broadband character of spin-orbit generation of optical phase singularities is demonstrated over the full visible domain. Our results do not rely …
We demonstrate three simple cloaking devices that can hide very large spatial objects over the entire visible spectrum using only passive, off-the-shelf optics. The cloaked region for all of the devices exceeds 10^6 mm3 with the largest exceeding 10^8 mm3. Although uni-directional, these cloaks can hide the cloaked object, even if the object is transversely or self-illuminated. Owing to the small usable solid angle, but simple scaling, these cloaks may be of value in hiding small field-of-view objects such as mid- to high-earth orbit satellites.
The on-chip broadband optical spectrometers which cover the entire tissue transparency window (λ=650-1050 nm) with high resolution are highly demanded for the miniaturized bio-sensing and bio-imaging applications. Here, we propose a novel type of spatial heterodyne Fourier transform spectrometer (SHFTS) integrated with a sub-wavelength grating coupler (SWGC) for the dual-polarization bandpass sampling on the Si3N4 platform. Through tuning the coupling angles with different polarization, we experimentally demonstrated the unprecedented broadband spectrum retrieval results with the overall bandw…
In the nanophotonics community, there is an active discussion regarding the origin of the selective absorption/scattering of light by the resonances with nanorod arrays. Here we report a study of the resonances in ordered indium-tin-oxide (ITO) nanorod arrays resulted from the waveguide modes. We discover that with only 2.4% geometrical coverage, the micron-length nanorod arrays strongly interact with light across an extra-wide band from visible to mid-infrared resulting in less than 10% transmission. Simulations show excellent agreement with our experimental observation. Near-field profile ob…
