Asymmetric Fabry-Perot Cavity Research Articles

Structure and Self-Modulation Features of the Superradiant States in Asymmetric Fabry–Perot Cavity

Structure and Self-Modulation Features of the Superradiant States in Asymmetric Fabry–Perot Cavity

Both enhancement and strong coupling of quantum dots on asymmetric Fabry-Perot cavity at room temperature

Abstract The interaction of light and matter is an eternal theme in optics and optoelectronics. Until now, there is almost no report about realization of both strong coupling and enhancement simultaneously. In this study, the angle-resolved photoluminescence spectra of colloidal quantum dots on the surface of SiO2/Si material are investigated. When the PL spectrum peak overlaps with the Fabry–Perot (F-P) mode of SiO2 film, the PL spectrum near emission wavelength of bare colloidal quantum dots splits into two peaks, which is Rabi splitting. Moreover, a huge enhancement factor is obtained for the PL spectra in the short-wavelength region. Both extremely huge enhancement and large Rabi splitting are obtained with colloidal quantum dots coupled low-refractive-index/high-refractive-index dielectric material system.

Polariton Phenomena in Superradiant Lasing with a Low-Q Asymmetric Fabry–Perot Cavity

Polariton Phenomena in Superradiant Lasing with a Low-Q Asymmetric Fabry–Perot Cavity

Thermally Tunable Structural Color Based on Patterned Ultra-Thin Asymmetric Fabry–Perot Cavity with Phase-Change Material

Tunable structural color has gained significant attention due to its dynamic characteristics. However, conventional devices are usually regulated only in their color capabilities by structural parameters, restricting real-time dynamic applications. In this study, we propose an ultra-thin asymmetric Fabry–Perot cavity patterned with phase-change materials (MPMP). The reversible phase transition of VO2 induces changes in the MPMP’s optical performance, enabling color mode switching through temperature control and resulting in rapid color conversion and low-temperature regulation. By adjusting relevant structural parameters of the VO2 layer and nanodiscs, the color performance range can be tailored. Through numerical investigations, we demonstrate that MPMP can produce stable transformation of dynamic structural colors by harnessing the phase-change effect. Our research unveils new possibilities for applications such as anti-counterfeiting, bio/chemical sensing, and temperature sensing.

Структура и особенности автомодуляции сверхизлучательных состояний в асимметричном резонаторе Фабри-Перо

The dependence of the structure and stability of strongly asymmetric stationary states of a superradiant laser with a slightly asymmetric low-Q Fabry-Perot cavity on its length, reflection factors of mirrors, and pumping level is studied. The states are related to a self-consistent inhomogeneous half-wavelength population inversion grating. The possibility of the existence of two dynamic phase transitions from a stationary (monochromatic) state of this type to a nonstationary one is established: 1) a dissipative superradiant transition to a regime with a quasi-continuous lasing spectrum (in a weakly asymmetric cavity) and 2) a self-modulation transition to a regime with a discrete lasing spectrum. It is shown that the latter can be caused by excitation of both polariton and electromagnetic laser modes due to resonant Rabi oscillations of active centers with a sufficiently long phase relaxation time.

To realize a variety of structural color adjustments via lossy-dielectric-based Fabry–Perot cavity structure

Abstract Structural colors with tunable properties have extensive applications in surface decoration, arts, absorbers, and optical filters. Planar structures have more advantages over other forms studied to date due to their easy manufacturability. Metal-insulator-metal-based structures are one of the known methods to fabricate structural colors where colors can be tuned mainly by the thickness of the intermediate lossless insulator layer. However, generating colors by MIM structure requires a thin metallic layer on top, and the top metals’ abrasiveness and/or oxidation may degrade the colors quickly. Thus, we propose a lossy dielectric layer to replace the top metallic layer as a solution to ensure the structure’s durability by preventing scratches and oxidation. Herein, CrON/Si3N4/Metal structures have been studied where theoretical investigations suggest that highly saturated colors can be generated in the lossy-lossless dielectric structures. Experimental data validated such simulations by revealing a range of vivid colors. Furthermore, these structures can easily achieve strong light absorption (SLA) even for a thick top layer of ∼100 nm. The colors realized by these structures are appeared due to a combination of the interference effect of the asymmetric Fabry–Perot cavity structure and the absorption rate in the CrO x N1−x layer.

Transfer matrix optimization of a one-dimensional photonic crystal cavity for enhanced absorption of monolayer graphene.

The optical absorption enhancement of graphene is of significant interest due to its remarkable applications in optical devices. One of the most useful methods is placing graphene in an asymmetric Fabry-Perot cavity made of one-dimensional dielectric multilayers forming two mirrors. In that regard, using the transfer matrix method, we have explicitly calculated the required periodicity of the front photonic multilayer mirror to maximize the absorption in the graphene for any given combination of material types and number of layers. Then we studied the equivalence between these structural configurations and those with arbitrary periodicity but with defects, where the equivalence holds when ω=ξω0,ξ∈Z≥0. These defects are introduced via layer position alterations, based on which we propose an optimization algorithm to maximize absorption in structures having a cavity with an arbitrary periodicity. Numerical calculations are given for dielectric material combinations of TiO2/SiO2 and Ta2O5/SiO2, and to understand the behavior of these optimized structures for any general combination of material types, the mapping of their calculated front mirror periodicity for a range of refractive indices of the two material types has been studied.

High-sensitivity refractive index sensing with the singular phase in normal incidence of an asymmetric Fabry–Perot cavity modulated by grating

Considerable attention has been paid to the conception of point of darkness for perfect optical absorption and refractive index biochemical sensing based around phase-sensitive detection, in which the maximum change in the phase could occur at the point of darkness where the reflectivity is almost zero. To date, this has been achieved by using different material systems and complex nanopatterning under oblique-incidence conditions. In this study, a simple system consisting of an asymmetric Fabry–Perot cavity covered by a gold grating on the topside was developed to achieve perfect absorption and extreme singularity of the differential phase of reflective light under normal incidence conditions. The proposed structure was also demonstrated to function as a refractive index sensing platform based on a singular phase. It exhibits a maximum phase sensitivity of approximately 18,900 degree/RIU with a wide dynamic range during operation. This provides a more efficient alternative to the conventional oblique-incidence phase measurement system in an integrated biosensor chip.

Broadband‐Tunable Third‐Harmonic Generation Using Phase‐Change Chalcogenides

Despite remarkable progress in passive nonlinear nanophotonics, dynamically controlled ultracompact nonlinear optical sources with high efficiency remain elusive. Nonvolatility, large refractive index contrast between amorphous and crystalline phases, low thermal threshold for crystallization, and particularly high‐third‐order nonlinear optical susceptibility of phase‐change alloy Ge2Sb2Te5 (GST) make it a promising candidate for active subwavelength metaphotonic structures for realization of third‐harmonic generation (THG) devices. Herein, a GST‐based asymmetric Fabry–Perot cavity is numerically designed and experimentally demonstrated to show a dynamically reconfigurable structure with a large shift of the THG resonant band. In addition, continuous resonant spectral shifting bridged by a precisely controlled semicrystalline phase of GST is realized. Tunable THG with the fundamental wavelength ranging from 1150 to 1400 nm is presented, which corresponds to a broadband THG source in the violet‐blue visible wavelength range. Herein, the potential of GST subwavelength structures as a reliable platform for realization of the broadband‐tunable frequency‐conversion sources for applications such as THG microscopy and optical communication is indicated.

Reconfigurable and spectrally switchable perfect absorber based on a phase-change material.

In this paper, we propose a lithography-free spectrally tunable prefect absorber based on an asymmetric Fabry-Perot cavity using Ge2Sb2Te5 (GST), a phase-change material, as the cavity layer. The proposed device shows a maximum absorption of 99.7% at 1550 nm, at a particular angle of incidence and polarization when the phase of GST is in the amorphous state. The absorption spectrum is spectrally switched to longer wavelength when the phase of GST is transformed from amorphous to crystalline. The tuning range is about 866 nm, and the maximum absorption is maintained above 99% in the whole tuning range. The crystallinity ratio of GST is varied by applying voltage pulses of different amplitudes and durations. The electrothermal cosimulations show that the phase change is obtained in the whole GST layer. Furthermore, by reamorphization of GST, the absorption spectrum can be switched back, enabling a reconfigurable perfect absorber. This work shows a viable path toward achieving a tunable perfect absorber covering a 1550 nm communication wavelength window as well as an emerging optical communication window around 2 µm wavelength.

Ultrasensitive monolayer-MoS2 heterojunction photodetectors realized via an asymmetric Fabry-Perot cavity

Two-dimensional (2D) materials have attracted significant attention as a promising candidate for electronic and optoelectronic devices. However, low absorption impairs the performance of few-layer 2D material-based photodetectors (PDs). Herein, we purpose an asymmetric Fabry-Perot cavity consisting of a dielectric layer and metallic film to enhance the interactions between light and monolayer molybdenum disulfide (MoS2). The external quantum efficiency of the monolayer MoS2 heterojunction PD is enhanced by more than two orders of magnitude via optimizing the thickness of the dielectric layer. The monolayer-MoS2/nickel oxide heterojunction PD exhibits a large on/off ratio of 2 × 105, a responsivity of 703 A W−1, and an ultrahigh detectivity of 1.31 × 1015 Jones. The detectivity is the best value ever reported for monolayer-MoS2 heterojunction PDs. Our results may pave the way for high-performance 2D material-based PDs.

Dynamic Color Display with Viewing-Angle Tolerance Based on the Responsive Asymmetric Fabry-Perot Cavity.

At present, it remains challenging and desirable to prepare dynamic color-changing materials with wide viewing angles for practical applications. Herein, we proposed a responsive asymmetric metal-insulator-metal (MIM) Fabry-Perot resonance cavity to achieve dynamic color display with high viewing-angle tolerance. The responsive asymmetric MIM cavity is constructed with thermal-responsive poly(N-isopropyl acrylamide) (PNIPAm) brush as the mid-insulator layer sandwiched by two different metallic layers (Sn and Ag). The as-prepared MIM cavity shows both improved viewing-angle tolerance owing to the asymmetric architecture of the cavity and a wide tunable color gamut because of the thermal responsiveness of the mid PNIPAm layer. Remarkably, the as-prepared asymmetric MIM resonance cavity also possesses a relatively fast response rate and good repeatability. Together, with all these advantages, the proposed responsive asymmetric MIM cavity may open a new pathway to prepare high-performance color display material for future practical optical applications.

Dynamically tunable third-harmonic generation with all-dielectric metasurfaces incorporating phase-change chalcogenides.

Subwavelength nonlinear optical sources with high efficiency have received extensive attention, although strong dynamic controllability of these sources is still elusive. Germanium antimony telluride (GST) as a well-established phase-change chalcogenide is a promising candidate for the reconfiguration of subwavelength nanostructures due to the strong non-volatile change of the index of refraction between its amorphous and crystalline states. Here, we numerically demonstrate an electromagnetically-induced-transparency-based silicon metasurface actively controlled with a quarter-wave asymmetric Fabry-Perot cavity incorporating GST to modulate the relative phase of incident and reflected pump beams. We demonstrate a giant third-harmonic generation (THG) switch with a modulation depth as high as ∼70dB at the resonant band. We also demonstrate the possibility of multi-level THG amplitude modulation for the fundamental C-band by controlling the crystallization fraction of GST at multiple intermediate states. This study shows the high potential of GST-based fast dynamic nonlinear photonic switches for real-world applications ranging from communications to optical computing.

Flexible dynamic structural color based on an ultrathin asymmetric Fabry-Perot cavity with phase-change material for temperature perception.

Dynamic structural color has attracted considerable attentions due to its good tunable characteristics. Here, an ultrathin asymmetric Fabry-Perot (FP)-type structural color with phase-change material VO2 cavity is proposed. The color-switching performance can be realized by temperature regulation due to the reversible monoclinic-rutile phase transition of VO2. The various, vivid structural color can be generated by simply changing the thickness of VO2 and Ag layers. Moreover, the simple structural configuration enables a large-scale, low-cost preparation on both rigid and flexible substrates. Accordingly, a flexible dynamic structural color membrane is adhered on a cup with a curved surface to be used for temperature perception. The proposed dynamic structural color has potential applications in anti-counterfeiting, temperature perception, camouflage coatings among other flexible optoelectronic devices.

Dynamic reflective color pixels based on molybdenum oxide.

Active materials which show phase transitions, usually known as Phase Change Materials (PCM), have paved the way to a new generation of reconfigurable plasmonic platforms. Tunable color devices have experienced a great development in the recent years. In particular, reflective color filters can take advantage from sunlight to select and reflect a specific resonant wavelength in the visible spectrum range. Reflective displays are usually structural color filters based on asymmetric Fabry-Perot cavities (AFPCs). For a fixed geometry, most of AFPCs filters generate static color, limiting their potential as tunable color devices. Dynamic color is achieved by introducing an active layer whose optical properties can be modulated by an external stimuli. In this paper, we propose AFPCs based on molybdenum oxide (MoOx, 2<x<3) to achieve switchable on/off color reflective pixels. On and off states of the pixels are controlled through the stoichiometry of the MoOx layer.

Reflection color tuning of a metal–insulator–metal cavity structure using arc plasma deposition of gold nanoparticles

Structural colors have diverse applications in optical filters, surface decoration, photovoltaics, and digital displays. In this study, an arc plasma deposition (APD) method was employed for fabrication of the top Au layer in the asymmetric Fabry–Perot cavity structure of Au/Si3N4/Al. With an increasing number of APD pulses (nP), the morphology of the Au layer gradually changed from a dispersion of nanoparticles (NPs) to a nanoporous film and then to a dense film, which in turn led to a change in the refractive index of the Au layer. The structural colors of the Au/Si3N4/Al structure were mainly governed by the interference effect. The optical constants of the NP-dispersed and nanoporous Au layers could be reasonably estimated based on Bruggeman's effective medium approximation. When the Au layers deposited with different nP were combined with dielectric Si3N4 layers of various thicknesses (hd), the full range of color hue with a wide range of color chroma could be realized using the Au/Si3N4/Al trilayer structure. The color hue was predominantly governed by hd, and the color chroma gradually increased with nP for a given value of hd.

Efficiently enhanced the visible-light absorption of monolayer WS2 by constructing an asymmetric Fabry-Perot cavity

Transition metal dichalcogenides (TMDCs) have been intensively researched during the past decade in consequence of their fascinating properties, such as tunable bandgap, high carrier mobility, and extraordinary luminescent efficiency. But compared with their bulk counterparts, atomically thin two-dimensional (2D) TMDCs have an intrinsic lower light absorption (∼5%), preventing them from further applications in optoelectronic area. Commonly, fabrication of high-performance TMDC nanodevices not only requires complicated or expensive process, but also is hard to simultaneously realize significant and uniform enhancement for large-scale planar integrated device applications. Herein, we provided an asymmetric Fabry–Perot (F-P) cavity method to efficiently enhance the light absorption of the monolayer tungsten disulfide (ML WS2). By constructing the F-P cavity structure of WS2/SiO2/Au with an optimal thickness of SiO2 spacer, the visible-light absorptivity of ML WS2 dramatically increased from 5% to 49%. To further testify the enhancement effect of the F-P cavity, this hybrid structure was integrated into photoconductive device and compared with pristine WS2 device. The results showed that the photoresponsivity of the hybrid F-P cavity structure (8.3 A W−1) was found to be 2 orders higher than that of pristine WS2 (0.028 A W−1). Moreover, this hybrid structure exhibited a more remarkable and uniform light-field enhancement than pristine WS2 under 532-nm excitation, attributing to the formation of the constructive interference in F-P resonance cavity. This novel F-P cavity structure can shed new light on substantially and uniformly improving the low absorptivity of 2D nanomaterials for future developments.

Tunable Broadband Terahertz Waveband Absorbers Based on Fractal Technology of Graphene Metamaterial.

In this paper, a metasurface Terahertz absorber based on the fractal technology of a graphene geometry resonator to realize ultra-wideband, ultrathin, adjustable double-layer cross-fractal formation is introduced. This paper proposes a dynamically tuned graphene absorbing material. The structure is composed of one- to four-level-fractal graphene pattern layers, MgF2 layers and metal reflective layers to form a two-sided mirror of an asymmetric Fabry–Perot cavity. To confine the terahertz electromagnetic wave, four different fractals are integrated into a supercell, and the coupling and superposition of adjacent resonant cavities form a broadband high-absorption absorber. Using finite element-based full-wave electromagnetic simulation software to simulate the response frequency of 0.4–2.0 THz, we found that the absorber achieves a broadband 1.26 THz range (absorption > 80%) and a relative bandwidth of 106.8%. By adjusting the Fermi energy, it can realize free switching and expand to wider broadband terahertz absorption, by adjusting the polarization angle (Φ) from 0 to 90° to prove that the structure is not sensitive to polarization, the absorber provides a 60° large angle of incidence, polarization for TE and TM the absorption pattern remains basically the same. Compared with the previous work, our proposed structure uses fractal technology to expand the bandwidth and provide dynamic adjustable characteristics with great degrees of freedom. The appearance of the fractal structure reduces the difficulty of actual processing.

人工微结构薄层红外探测器的研究进展（特邀）

The thin layer of infrared detection material guarantees the uniformity of the materials and reduces the signal noise in infrared detection. The absorption of infrared detector is limited by the thin layer of infrared detection material attributing to small volume. According to the characteristics of different infrared detection materials, artificial microstructure can effectively improve the performance of infrared detector. The strategies of enhancing the absorption of thin-layer infrared detection materials were introduced. The strategies were based on metal back plate, metal grating and asymmetric Fabry-Perot cavity. They could have an excellent performance in their own adaptive scenarios. Meanwhile, the mechanism of adjusting the absorption peak height and width by artificial microstructure was also elaborated briefly. The application of artificial microstructure in several infrared detectors was demonstrated. Finally, an artificial microstructure HgCdTe infrared detector was designed, which could achieve broadband absorption in 3.5-5.5 μm atmospheric window. The absorption peak reached 91.8% and the relative peak width was 41.8%. In most of frequency in the atmospheric window, the absorption enhancement is higher than 6. The development of artificial microstructure opens up the design idea of traditional infrared devices, and provides theoretical basis and guidance for new infrared devices.

Ultra-wideband terahertz metamaterial absorber based on Snowflake Koch Fractal dielectric loaded graphene.

In this paper, an ultra-wideband terahertz metamaterial absorber is introduced based on a Snowflake Koch Fractal (SKF) dielectric loaded on a sheet of graphene. Instead of multilayered-graphene conventional structures, a single-layered non-structured graphene absorber is presented based on gradient width modulation and cavity method. The structure of the absorber is composed of four layers, which are upper SKF dielectric and metal film layer form two mirrors of an asymmetric Fabry-Perot cavity to confine terahertz electromagnetic (EM) waves. Full wave simulations demonstrate that the proposed structure is highly efficient whereas a 161% fractional bandwidth of over 0.9 absorbance is achieved under normal incident wave considering both TE and TM polarizations. The proposed structure is polarization insensitive yielding the same absorbance for both TE and TM polarizations. The absorbance and bandwidth of the structure is almost independent of altering the incident angle θ up to 60° and 30° for TM and TE polarizations, respectively. Avoiding graphene processing and simple shape geometry are the interesting advantages of this structure resulting in feasible fabrication. The proposed structure provides much greater absorbance bandwidth in comparison to previous works.