Fabry-Perot Nanocavities Research Articles

A perfect absorber based on a VO2-tunable Fabry–Perot cavity: an analysis of periodic oscillation absorption characteristics

Terahertz metamaterial absorbers (TMAs) have garnered significant attention as vital electromagnetic wave-absorbing devices. In this study, we designed a terahertz metamaterial absorber (TMA) utilizing an asymmetric Fabry–Perot nanocavity comprising vanadium dioxide (VO2), gold (Au), and polyimide. The TMA exhibits five perfect absorption peaks within 0.1 THz to 10 THz, with an absorption rate exceeding 97%, peaking at 99%. The absorption rate oscillates periodically between 0 and 1, and its oscillating absorption peak can be determined by f m ( fm=(2m+1)c0/(4tε2 ), while tunability of the absorption rate between 15% and 97% is achievable by adjusting the conductivity of (VO2) (2×102∼2×105S/m). The physical mechanism of the absorption peak was analyzed by simulation and compared with theoretical analysis. The results show that the absorption peak of the absorber’s absorptivity can be insensitive to polarization and has a wide absorption angle of 80% up to 40◦ or more. Importantly, the thickness of the absorber (VO2) layer can be calculated from the desired absorption frequency and dielectric constant of the interlayer medium, d=ε0/μ0/σ , thus reducing the need for redesigning different resonant layer patterns. This work provides a new perspective on terahertz absorber design.

Dynamic multicolor electrochromic skin in high-brightness flexible WO3/Au asymmetric Fabry–Perot nanocavity fabricated on Nylon 66 porous substrate

Recently, the Fabry–Perot (F–P) cavity electrochromic devices, which are constructed by combining nano-size inorganic electrochromic material WO3 and reflective metal layers, have attracted considerable attention due to their potentials in the fields of dynamic multicolor displays and active camouflage. However, in the few studies that have been reported, the peak reflectance of flexible F–P cavity multicolor electrochromic devices in the visible wavelength band is generally lower than 30 %, which limits their reflective display and camouflage effects in high-brightness environments. Thus, we have combined multicolor reflective electrochromic electrodes in WO3/Au asymmetric F–P nanocavity constructed by magnetron sputtering on a Nylon 66 porous substrate with a highly transparent UV-cured gel electrolyte and a PET plastic sealing procedure. As a result, a flexible and dynamic multicolor electrochromic skin with high reflectance (Rmax＞50 %) and excellent flexibility (bending radius of 4 mm) has been fabricated. The WO3 electrochromic layer at the top works as the dynamic dielectric layer in the broadband absorption Fabry–Perot cavity, and the inert metal Au layer at the bottom works as the reflective layer. The WO3/Au asymmetric F–P cavity can acutely capture the variation in optical constants of WO3 due to the thickness change and electric-driven effects. This cavity facilitates the selective reflection and absorption of the energy distribution of the spectrum after the induced interferometric resonance. As a result, the cavity exhibits a rich array of structural colors, including ocher, taupe, yellow, orange, green, and violet. The electrochromic skin exhibits a fast switching time and maintains 99.43 % of the optical modulation amplitude (ΔR) after 110 coloring/bleaching cycles. It provides a potential option in the field of flexible high-brightness reflective displays and dynamic camouflage in the future.

Nanoscale modeling of dynamically tunable planar optical absorbers utilizing InAs and InSb in metal-oxide-semiconductor–metal configurations

The attainment of dynamic tunability in spectrally selective optical absorption has been a longstanding objective in modern optics. Typically, Fabry–Perot resonators comprising metal and semiconductor thin films have been employed for spectrally selective light absorption. In such resonators, the resonance wavelength can be altered via structural modifications. The research has progressed further with the advent of specialized patterning of thin films and the utilization of metasurfaces. Nonetheless, achieving dynamic tuning of the absorption wavelength without altering the geometry of the thin film or without resorting to lithographic fabrication still poses a challenge. In this study, the incorporation of a metal-oxide-semiconductor (MOS) architecture into the Fabry–Perot nanocavity is shown to yield dynamic spectral tuning in a perfect narrowband light absorber within the visible range. Such spectral tuning is achieved using n-type-doped indium antimonide and n-type-doped indium arsenide as semiconductors in a MOS-type structure. These semiconductors offer significant tuning of their optical properties via electrically induced carrier accumulation. The planar structure of the absorber models presented facilitates simple thin-film fabrication. With judicious material selection and appropriate bias voltage, a spectral shift of 47 nm can be achieved within the visible range, thus producing a discernible color change.

High resolution multispectral spatial light modulators based on tunable Fabry-Perot nanocavities

Spatial light modulators (SLMs) are the most relevant technology for dynamic wavefront manipulation. They find diverse applications ranging from novel displays to optical and quantum communications. Among commercial SLMs for phase modulation, Liquid Crystal on Silicon (LCoS) offers the smallest pixel size and, thus, the most precise phase mapping and largest field of view (FOV). Further pixel miniaturization, however, is not possible in these devices due to inter-pixel cross-talks, which follow from the high driving voltages needed to modulate the thick liquid crystal (LC) cells that are necessary for full phase control. Newly introduced metasurface-based SLMs provide means for pixel miniaturization by modulating the phase via resonance tuning. These devices, however, are intrinsically monochromatic, limiting their use in applications requiring multi-wavelength operation. Here, we introduce a novel design allowing small pixel and multi-spectral operation. Based on LC-tunable Fabry-Perot nanocavities engineered to support multiple resonances across the visible range (including red, green and blue wavelengths), our design provides continuous 2π phase modulation with high reflectance at each of the operating wavelengths. Experimentally, we realize a device with 96 pixels (~1 μm pitch) that can be individually addressed by electrical biases. Using it, we first demonstrate multi-spectral programmable beam steering with FOV~18° and absolute efficiencies exceeding 40%. Then, we reprogram the device to achieve multi-spectral lensing with tunable focal distance and efficiencies ~27%. Our design paves the way towards a new class of SLM for future applications in displays, optical computing and beyond.

Electrochromic Displays Having Two‐Dimensional CIE Color Space Tunability

AbstractElectrochromic devices with a wide color gamut distribution have long been sought after for non‐emissive display technologies. The current state‐of‐the‐art multicolor electrochromic displays utilize a single electrochromic layer, which restricts their color tunability within a linear or curved segment scope in International Commission on Illumination (CIE) color space and thus leads to limited color hues. Herein, it is demonstrated vivid electrochromic displays with broadened color hues via fabricating Zn‐based multicolor electrochromic displays having 2D CIE color space tunability. In addition, it is revealed that a Fabry–Perot nanocavity structure can further tune the color hues via altering the coordinate of the 2D CIE color space. It is known that this is the first demonstration of 2D CIE color space tunability realization from a single transparent or reflective electrochromic device. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of electrochromic displays.

Vivid Coloration and Broadband Perfect Absorption Based on Asymmetric Fabry–Pérot Nanocavities Incorporating Platinum

Highly efficient color filtering and broadband perfect absorption are achieved by asymmetric Fabry–Perot nanocavities incorporating a platinum (Pt) film, which are fabricated on rigid and flexible ...

Periodic planar Fabry-Perot nanocavities with tunable interference colors based on filling density effects.

Structural colors of high performance and economically feasible fabrication are desired in various applications. Herein, we demonstrate that reflective full-color filters based on the interference effect can be realized in periodic Fabry-Perot (F-P) nanocavity arrays of the same thickness. Enabled by simply adjusting the nanocavity size and array period, the resonant wavelengths can be successively tuned in the whole visible light range, which is mainly attributed to the varied effective refractive index introduced by the different filling density of the F-P nanocavity. Compared to the plasmonic colors utilizing the similar nanostructures, the proposed interference colors offer unique advantages of higher color contrast, wider gamut, and lower fabrication requirements. Besides, these color filters do not involve modulating the vertical dimensions of the F-P nanocavities, which is conducive to the monolithic integration of multicolor optical cavities and their large-area applications in consumable products combined with replica patterning techniques, such as nanoimprinting and soft lithography.

Ultracompact gas sensor with metal-organic-framework-based differential fiber-optic Fabry-Perot nanocavities.

Refractive-index (RI)-based sensing is a major optical sensing modality that can be implemented in various spectral ranges. While it has been widely used for sensing of biochemical liquids, RI-based gas sensing, particularly small-molecule gases, is challenging due to the extremely small RI change induced by gas concentration variations. We propose a RI-based ultracompact fiber-optic differential gas sensor that employs metal-organic-framework (MOF)-based dual Fabry-Perot (FP) nanocavities. A MOF is used as the FP cavity material to enhance the sensitivity as well as the selectivity to particular gas molecules. The differential sensing scheme leverages the opposite change in the cavity-length-dependent reflection of the two FP cavities, which further enhances the sensitivity compared with single FP cavity based sensing. For proof-of-concept, a fiber-optic CO2 sensor with ZIF-8-based dual FP nanocavities was fabricated. The effective footprint of the sensor was as small as 157 µm2 and the sensor showed an enhanced sensitivity of 48.5 mV/CO2Vol%, a dynamic range of 0-100 CO2Vol%, and a resolution of 0.019 CO2Vol% with 1 Hz low-pass filtering. Although the current sensor was only demonstrated for CO2 sensing, the proposed sensor concept can be used for sensing of a variety of gases when different kinds of MOFs are utilized.

Study of disordered metallic groove arrays with a one-mode analytical model.

Sub-wavelength metallic grooves behave as Fabry-Perot nanocavities able to resonantly enhance the absorption of light as well as the intensity of the electromagnetic field. Here, with a one-mode analytical model, we investigate the effect of a correlated disorder on 1D groove arrays i.e., randomly shaped and positioned grooves on a metallic layer. We show that a jitter-based disorder leads to a redistribution of energy compared to the periodic case. In an extreme case, a periodic diffracting array can be converted into a highly scattering array (98% at λ = 2.8 µm with a 1 µm full width at half maximum). Eventually, we show that the optical response of combinations of variously shaped grooves can be well described by the individual sub-set behaviors.

Towards full-colour tunability of inorganic electrochromic devices using ultracompact fabry-perot nanocavities

Intercalation-based inorganic materials that change their colours upon ion insertion/extraction lay an important foundation for existing electrochromic technology. However, using only such inorganic electrochromic materials, it is very difficult to achieve the utmost goal of full-colour tunability for future electrochromic technology mainly due to the absence of structural flexibility. Herein, we demonstrate an ultracompact asymmetric Fabry-Perot (F-P) nanocavity-type electrochromic device formed by using partially reflective metal tungsten as the current collector and reflector layer simultaneously; this approach enables fairly close matching of the reflections at both interfaces of the WO3 thin layer in device form, inducing a strong interference. Such an interference-enhanced device that is optically manipulated at the nanoscale displays various structural colours before coloration and, further, can change to other colours including blue, red, and yellow by changing the optical indexes (n, k) of the tungsten oxide layer through ion insertion.

Electrically tunable perfect light absorbers as color filters and modulators

Methods for spectrally controlling light absorption in optoelectronic devices have attracted considerable attention in recent years. It is now well known that a Fabry-Perot nanocavity comprising thin semiconductor and metal films can be used to absorb light at selected wavelengths. The absorption wavelength is controlled by tailoring the thickness of the nanocavity and also by nanostructure patterning. However, the realization of dynamically tuning the absorption wavelength without changing the structural geometry remains a great challenge in optoelectronic device development. Here it is shown how an ultrathin n-type doped indium antimonide integrated into a subwavelength-thick optical nanocavity can result in an electrically tunable perfect light absorber in the visible and near infrared range. These absorbers require simple thin-film fabrication processes and are cost effective for large-area devices without resorting to sophisticated nanopatterning techniques. In the visible range, a 40 nm spectral shift can be attained by applying a reasonable bias voltage to effect the color change. It is also shown that these electrically tunable absorbers may be used as optical modulators in the infrared. The predicted (up to) 95.3% change in reflectance, transforming the device from perfectly absorbing to highly reflective, should make this technology attractive to the telecommunication (switching) industry.

Electronic Light–Matter Strong Coupling in Nanofluidic Fabry–Pérot Cavities

Electronic light–matter strong coupling has been limited to solid molecular films due to the challenge of preparing optical cavities with nanoscale dimensions. Here we report a technique to fabricate such Fabry–Perot nanocavities in which solutions can be introduced such that light–molecule interactions can be studied at will in the liquid phase. We illustrate the versatility of these cavities by studying the emission properties of Chlorin e6 solutions in both the weak and strong coupling regimes as a function of cavity detuning. Liquid nanocavities will broaden the investigation of strong coupling to many solution-based molecular processes.

High-Spectral-Contrast Symmetric Modes in Photonic Crystal Dual Nanobeam Resonators

We demonstrate accurate control of mode symmetry in suspended dual-nanobeam resonators on a silicon-on-insulator chip. Each nanobeam consists of a Fabry–Perot nanocavity bounded by tapered 1-D photonic crystals. Even and odd cavity-modes are formed due to lateral evanescent coupling between the two nanobeams. The odd cavity-mode can be excited by mode-symmetry-transforming Mach–Zehnder couplers. Modal contrasts over 27 dB are measured in fabricated structures. The influence of the optical field in the middle air slot on the background transmission and quality factors is discussed. The observed peak wavelength separations of the modes at various nanobeam spacings are in good agreement with simulation results. These nanobeam resonators are potentially useful in applications, such as ultrafast all-optical modulation, filtering, and switching.

Zeroth Order Fabry–Perot Resonance Enabled Strong Light Absorption in Ultrathin Silicon Films on Different Metals and Its Application for Color Filters

In this work, Fabry–Perot nanocavity resonance enabled strong light absorption in ultrathin single layer silicon films on different metal surfaces was investigated. It was found that the peak absorption wavelength depends on the metal underneath the silicon film in addition to the silicon film thickness. Perfect light absorption was observed in deep subwavelength ultrathin silicon films on titanium (Ti) and chromium (Cr) metal surfaces in visible spectrum, which is caused by the zeroth order Fabry–Perot resonance mode where the round-trip phase delay in the nanocavity is zero. A perfect light absorber with an ultrathin silicon film as thin as 1/27 of the absorption wavelength on titanium metal surface has been demonstrated.

A compact frequency selective stop-band splitter by using Fabry—Perot nanocavity in a T-shaped waveguide

By utilizing a Fabry—Perot (FP) nanocavity adjacent to T-shaped gap waveguide ports, spectrally selective filtering is realized. When the wavelength of incident light corresponds to the resonance wavelength of the FP nanocavity, the surface plasmons are captured inside the nanocavity, and light is highly reflected from this port. The resonance wavelength is determined by using Fabry—Perot resonance condition for the nanocavity. For any desired filtering frequency the dimension of the nanocavity can be tailored. The numerical results are based on the two-dimensional finite difference time domain simulation under a perfectly matched layer absorbing boundary condition. The analytical and simulation results indicate that the proposed structure can be utilized for filtering and splitting applications.

High-Q/Veff gap-mode plasmonic FP nanocavity

In this paper, a high-Q/Veff gap-mode plasmonic Fabry-Perot nanocavity, which is composed of a silver nanowire on a flat silver substrate spaced by patterned dielectric distributed Bragg gratings, is investigated both analytically and numerically. The design parameters and properties of the nanocavity are exploited with the use of generalized Fabry-Perot model. The Veff ~0.0026 (λ/n)³ and Q/Veff ~1.4 × 10⁵/μm³ of the nanocavity can be achieved. Such a gap-mode plasmonic Fabry-Perot nanocavity design provides a promising realization for wide novel band filters and spaser.

Frequency Selective Propagation by Employing Fabry—Perot Nanocavities in a Subwavelength Double-slit Structure

By embedding a nanocavity adjacent to one or both of slits in a subwavelength double-slit structure, frequency selective propagation through the slits is demonstrated. When the incident light wavelength corresponds to the cavity resonance mode, the electromagnetic wave passing through the slit will be trapped within the nanocavity. Therefore, the double slit operates as a single slit and light propagation is solely allowed through the partner slit. These wavelengths are determined by applying the Fabry—Perot resonance condition for the nanocavities. Various geometrical structures result in different effective refractive indexes. Thus, the effective refractive index and consequently the attenuation wavelength can be adjusted by choosing the appropriate parameters of the nanocavity. Our theoretical predictions are in good agreement with 2D finite-difference time-domain simulation.

Sharp and asymmetric transmission response in metal-dielectric-metal plasmonic waveguides containing Kerr nonlinear media

Based on the excitation of surface plasmon polaritons (SPPs), we analytically and numerically investigate the transmission response in metal-dielectric-metal (MDM) plasmonic waveguides with a side coupled nanocavity (SCNC). By filling the nanocavity with a Kerr nonlinear medium, the position of the resonant dip in the transmission spectrum can be tuned by the incident light intensity. The oscillation of a Fabry-Perot nanocavity formed by incorporating a finite length of the same Kerr nonlinear media into the MDM waveguide acts as a background for the transmission response of the system and induces a sharp and asymmetric response line shape. As a result, the wavelength shift required for the plasmonic device to be switched from the maximum to the minimum transmission can be reduced by half in a structure less than 400 nm long. Such an effect may be potentially applied to constructing SPP-based all-optical switching with low power threshold at nanoscale.

An air-slotted nanoresonator relying on coupled high Q small V Fabry–Perot nanocavities

We study here the lateral evanescent coupling between photonic crystals cavities. The structure consists in two identical monomode Fabry–Perot nanocavities, integrated on silicon-on-insulator slot-waveguides (WG). Spectral and optical near field measurements were led and supported quantitatively by three dimensional simulations. It appears that this system produces a bimodal response: two resonances corresponding, respectively, to an even and odd mode. Particularly, the even case exhibits a field localization in the air slot inferior to λair/10. We demonstrate that merging a slotted WG structure with state-of-the-art nanocavities is a significant step toward an efficient air-slotted resonator.

Indicator immobilization on Fabry-Perot nanocavities towards development of fiber optic sensors

Two fabrications processes based on the Electrostatic Self Assembly method have been studied in order to develop a potential fibre optic sensor for detection volatile organic compounds (VOCs). A nano Fabry-Perot is constructed onto a cleaved ended fibre optic pigtail, and is doped with a vapochromic complex of formula [Au2Ag2(C6F5)4(C6H5N)2]. This material is presented in form of red powders, shows fluorescence at 585 nm when illuminated with a light at 380 nm, and suffers changes in its color and refractive index when is exposed to VOCs. Both different possibilities of doping the nano Fabry-Perot studied keep the optical properties of the sensing material. To verify the sensing ability of the final devices, they have been exposed to ethanol vapors, taking measures of their absorbance spectra and the intensity modulated reflected signal at 850 nm, employing a reflection scheme.