Fabry-Perot Resonant Cavity Research Articles

Reliable fabrication of 3D freestanding nanostructures via all dry stacking of incompatible photoresist

Three-dimensional (3D) free-standing nanostructures based on electron-beam lithography (EBL) have potential applications in many fields with extremely high patterning resolution and design flexibility with direct writing. In numerous EBL processes designed for the creation of 3D structures, the multilayer resist system is pivotal due to its adaptability in design. Nevertheless, the compatibility of solvents between different layers of resists often restricts the variety of feasible multilayer combinations. This paper introduces an innovative approach to address the bottleneck issue by presenting a novel concept of multilayer resist dry stacking, which is facilitated by a near-zero adhesion strategy. The poly(methyl methacrylate) (PMMA) film is stacked onto the hydrogen silsesquioxane (HSQ) resist using a dry peel and release technique, effectively circumventing the issue of HSQ solubilization by PMMA solvents typically encountered during conventional spin-coating procedures. Simultaneously, a dry lift-off technique can be implemented by eschewing the use of organic solvents during the wet process. This pioneering method enables the fabrication of high-resolution 3D free-standing plasmonic nanostructures and intricate 3D free-standing nanostructures. Finally, this study presents a compelling proof of concept, showcasing the integration of 3D free-standing nanostructures, fabricated via the described technique, into the realm of Fabry-Perot cavity resonators, thereby highlighting their potential for practical applications. This approach is a promising candidate for arbitrary 3D free-standing nanostructure fabrication, which has potential applications in nanoplasmonics, nanoelectronics, and nanophotonics.

Enabling data-driven and bidirectional model development in Verilog-A for photonic devices.

We present a method to model photonic components in Verilog-A by introducing bidirectional signaling through a single port. To achieve this, the concept of power waves and scattering parameters from electromagnetism are employed. As a consequence, one can simultaneously transmit forward and backward propagating waves on a single wire while also capturing realistic, measurement-backed responses of photonic components in Verilog-A. We demonstrate examples to show the efficacy of the proposed technique in accounting for critical effects in photonic integrated circuits such as Fabry-Perot cavity resonance, reflections to lasers, reflection cancellation circuits, etc. Our solution makes electronic-photonic co-simulation more intuitive and accurate.

PH-Responsive, Wide Color Gamut Dynamic Color Display Enabled by PDMAEMA Brush-Based Fabry-Perot Resonant Cavity.

Dynamic color-changing materials have attracted broad interest due to their widespread applications in visual sensing, dynamic color display, anticounterfeiting, and image encryption/decryption. In this work, we demonstrate a novel pH-responsive dynamic color-changing material based on a metal-insulator-metal (MIM) Fabry-Perot (FP) cavity with a pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) brush layer as the responsive insulating layer. The pH-responsive PDMAEMA brush undergoes protonation at a low pH value (pH < 6), which induces different swelling degrees in response to pH and thus refractive index and thickness change of the insulator layer of the MIM FP cavity. This leads to significant optical property changes in transmission and a distinguishable color change spanning the whole visible region by adjusting the pH value of the external environment. Due to the reversible conformational change of the PDMAEMA and the formation of covalent bonds between the PDMAEMA molecular chain and the Ag substrate, the MIM FP cavity exhibits stable performance and good reproducibility. This pH-responsive MIM FP cavity establishes a new way to modulate transmission color in the full visible region and exhibits a broad prospect of applications in dynamic color display, real-time environment monitoring, and information encryption and decryption.

Theoretical investigation of VO2 smart window with large-scale dynamic infrared emittance adjustment for adaptive thermal management

Thermochromic windows based on vanadium dioxide (VO2) are widely used in architectural windows due to its reversible phase change process. However, traditional VO2 windows only manage solar radiative transmittance and their emittance variation trend in the mid-infrared contradicts realistic requirements, which seriously hinders the further development of thermochromic windows. To address this issue, a VO2 full-spectrum smart window based on theoretical calculations is proposed for adaptive adjustment of solar spectral transmittance and thermal emittance. We cleverly utilize a thin Ag layer to construct a Fabry-Perot (FP) resonant cavity with the VO2 layer to achieve forward modulation of the emittance in the atmospheric window. Notably, the smart window has 83.8 % emittance modulated ability, which enables effective control of radiative cooling and has greatly exceeded the reported performance of the smart windows while maintaining 72.8 % high visible transparency. Energy consumption analysis indicates that the smart window has high energy-saving potential worldwide, achieving over 60 MJ/m2 energy-saving effect. This simple and easy-to-manufacture smart window expands the research scope of windows and broadens application prospects in thermal management, infrared camouflage, and building energy conservation.

Improved optical contrast of plasmonic phase change memory using a Fabry-Perot cavity

As a promising technology to realize multilevel, non-volatile data storage and information processing, optical phase change technologies have attracted extensive attention in recent years. However, existing phase-change photonic devices face significant challenges such as limited switching contrast and high switching energy. This study introduces an innovative approach to tackle these issues by leveraging Fabry-Perot (F-P) cavity resonance and plasmon resonance techniques to enhance the modulation effect of phase change materials (PCMs) on the light. To the best of our knowledge, a novel device structure is proposed, featuring an elliptic nano-antenna placed on an F-P cavity waveguide composed of symmetric Bragg grating. This design exploits the enhanced electric field to achieve low power consumption and high contrast. The device enables crucial functions, including read, write, and erase operations, under all light conditions. Through the synergistic utilization of plasma and F-P cavity effects, an ultra-high switching contrast of around 70.6% is achieved. By varying the pulse power or duration, the proportion between the crystalline and amorphous states of the PCMs is altered, consequently modifying its refractive index. With its wide range of applications in optical storage and computing, the device holds significant potential for advancing these fields.

An ultra-thin optical polarizer based on weyl semimetals

Recently, Weyl semimetals have been extensively studied due to their unique optical responses, especially in the mid-infrared region. However, the possibility of developing optical polarizers based on Weyl semimetals remains unexplored. In this paper, under the Voigt geometry, we numerically show that an ultra-thin Weyl semimetal film with thickness L = 100 nm can achieve an impressive polarization extinction ratio (more than 40 dB) with a wide acceptance angle. Further, the proposed sandwich structure can effectively adjust the position of the TE mode transmission peak alone, thus obtaining lower insertion loss (from 0.06 dB to 0.03 dB) and wider acceptance range of angle (from 49.5∘ to 71∘). The proposed gradient Fermi level structure eliminates the Fabry-Perot cavity resonance, thus resulting a wider bandwidth (approximately 60 % improvement). Our proposed ultra-thin and wide-angle polarizer may have potential applications in optical communication and omnidirectional polarization detectors.

Extremely Stable Ag-Based Photonics, Plasmonic, Optical, and Electronic Materials and Devices Designed with Surface Chemistry Engineering for Anti-Tarnish.

Silver (Ag) metal-based structures are promising building blocks for next-generation photonics and electronics owing to their unique characteristics, such as high reflectivity, surface plasmonic resonance effects, high electrical conductivity, and tunable electron transport mechanisms. However, Ag structures exhibit poor sustainability in terms of device performance because harsh chemicals, particularly S2- ions present in the air, can damage their structures, lowering their optical and electrical properties. Here, the surface chemistry of Ag structures with (3-mercaptopropyl)trimethoxysilane (MPTS) ligands at room temperature and under ambient conditions is engineered to prevent deterioration of their optical and electrical properties owing to S2- exposure. Regardless of the dimensions of the Ag structures, the MPTS ligands can be applied to each dimension (0D, 1D, and 3D). Consequently, highly sustainable plasmonic effects (Δλ < 2nm), Fabry-Perot cavity resonance structures (Δλ < 2nm), reflectors (ΔRReflectance < 0.5%), flexible electrodes (ΔRelectrical < 0.1 Ω), and strain gauge sensors (ΔGF < 1), even in S2- exposing conditions is achieved. This strategy is believed to significantly contribute to environmental pollution reduction by decreasing the volume of electronic waste.

Electrically tunable dual-channel absorber based on a graphene integrated slanted grating cavity

In this paper, we propose a tunable dual-channel absorber based on a monolayer of graphene combined with a slanted grating. A single-channel perfect absorption of a monolayer graphene structure at 850 nm was initially achieved in a Fabry-Perot cavity resonance. The absorption rate of graphene was enhanced by nearly 24.5 times. Furthermore, the symmetry of the grating is broken to excite the quasi-bound states in the continuum (quasi-BICs) resonance mode, resulting in another absorption channel at 878.8 nm, thus achieving a perfect dual-channel absorber. The absorption half-width and absorption wavelength can be adjusted by tuning the grating thickness and the electro-optical effect of the DAST material. Furthermore, adjusting the polarization angle of the incident light enables the transition between single- and dual-channel absorbers. The proposed device has potential applications in the fields of high-performance graphene-based optoelectronic devices and optical switching systems.

Using one-step laser induced graphene to enhance the efficiency of the THz Fabry-Perot resonant cavity

The Fabry-Perot resonant cavity has been recognized as a crucial mechanism for confining Terahertz (THz) waves. However, the efficiency of the Fabry-Perot device has been hampered by the absence of lossless materials. In this study, we present a Fabry-Perot resonant cavity with enhanced efficiency, utilizing one-step laser-induced graphene without complex fabrication process. Firstly, the THz response of the samples induced by varying laser power and scanning velocity is systematically studied and measured through Terahertz frequency-domain spectroscopy (THz-FDS). Subsequently, Fourier transform is applied to facilitate quantitative analysis of the resonance intensity. Finally, the optimal resonance intensity of the device is achieved by dynamically adjusting the laser power and scanning velocity. This research introduces an innovative and technically simple approach for enhancing light-matter interactions in the THz region.

Analysis of an Ultra-Wideband, Perfectly Absorptive Fractal Absorber with a Central Square Nanopillar in a Cylindrical Structure with a Square Hollow

In this study, a fractal absorber was designed to enhance light absorptivity and improve the efficiency of converting solar energy into electricity for a range of solar energy technologies. The absorber consisted of multiple layers arranged from bottom to top, and the bottom layer was made of Ti metal, followed by a thin layer of MgF2 atop it. Above the two layers, a structure comprising square pillars formed by three layers of Ti/MgF2/Ti was formed. This pillar was encompassed by a square hollow with cylindrical structures made of Ti material on the exterior. The software utilized for this study was COMSOL Multiphysics® (version 6.0). This study contains an absorption spectrum analysis of the various components of the designed absorber system, confirming the notion that achieving ultra-wideband and perfect absorption resulted from the combination of the various components. A comprehensive analysis was also conducted on the width of the central square pillar, and the analysis results demonstrate the presence of several remarkable optical phenomena within the investigated structure, including propagating surface plasmon resonance, localized surface plasmon resonance, Fabry–Perot cavity resonance, and symmetric coupling plasma modes. The optimal model determined through this software demonstrated that broadband absorption in the range of 276 to 2668 nm, which was in the range of UV-B to near-infrared, exceeded 90.0%. The average absorption rate in the range of 276~2668 nm reached 0.965, with the highest achieving a perfect absorptivity of 99.9%. A comparison between absorption with and without outer cylindrical structures revealed that the resonance effects significantly enhanced absorption efficiency, as evidenced by a comparison of electric field distributions.

Partial Discharge Wideband Full-Band High-Gain Resonant Cavity UHF Sensor Research.

To meet the real demand for broadband full-band high-gain antenna sensors in the process of partial discharge (PD) Ultra-High frequency (UHF) detection test and online monitoring of power equipment, this paper builds a resonant cavity monopole UHF antenna sensor based on Fabry-Perot resonant cavity antenna technology, conducts the sensor Voltage Standing Wave Ratio (VSWR) optimization study using curved flow technology, conducts the sensor gain optimization study using slot dual resonant structure, and, finally, tests the sensor performance using the built PD detection test platform. The resonant cavity monopole antenna exhibits outstanding VSWR performance in the frequency range of 0.37 GHz-3 GHz, according to simulation and test data: the average gain in the frequency range of 0.3 GHz-3 GHz is 4.92 dBi, and the highest gain at the primary resonant frequency of 1.0 GHz is 7.16 dBi, with good radiation performance over the whole frequency spectrum. The electromagnetic pulse signal sensed by the UHF sensor developed in this paper can demonstrate the energy spectrum distribution characteristics of PD radiation electromagnetic wave signal more comprehensively, laying a firm technical foundation for thoroughly understanding the electromagnetic wave radiation characteristics of various types of PD insulation defects of various power equipment and the selection of a specific direction for its supporting optimization.

Cavity Jahn-Teller polaritons in molecules

We investigate Jahn-Teller (JT) polaritons, which emerge from the interaction of the two normal-incidence electromagnetic modes with perpendicular polarizations in a Fabry-Perot cavity resonator with JT active systems. These JT polaritons are characterized by a mixed $(+/-)$--circular electromagnetic polarization that originates from the molecular JT vibronic coupling of the material subsystem. Consequently, the exchange of photonic and vibronic angular momenta can be very efficient; exciting the cavity-JT system with short, polarized light pulses results in a dynamical and oscillatory response of the polarization in the cavity medium. Due to the photonic-vibronic coupling, we show how the cavity polarization direction becomes frequency dependent and does not necessarily coincide with the polarization direction of the external fields used to drive the system.

Three-Layered Thin Films for Simultaneous Infrared Camouflage and Radiative Cooling.

With the rapid advancements in aerospace technology and infrared detection technology, there are increasing needs for materials with simultaneous infrared camouflage and radiative cooling capabilities. In this study, a three-layered Ge/Ag/Si thin film structure on a titanium alloy TC4 substrate (a widely used skin material for spacecraft) is designed and optimized to achieve such spectral compatibility by combining the transfer matrix method and the genetic algorithm. The structure exhibits a low average emissivity of 0.11 in the atmospheric windows of 3-5 μm and 8-14 μm for infrared camouflage and a high average emissivity of 0.69 in 5-8 μm for radiative cooling. Furthermore, the designed metasurface shows a high degree of robustness regarding the polarization and incidence angle of the incoming electromagnetic wave. The underlying mechanisms allowing for the spectral compatibility of the metasurface can be elucidated as follows: the top Ge layer selectively transmits electromagnetic waves ranging from 5-8 μm while it reflects those in the ranges of 3-5 μm and 8-14 μm. The transmitted electromagnetic waves from the Ge layer are first absorbed by the Ag layer and then localized in the Fabry-Perot resonance cavity formed by Ag layer, Si layer and TC4 substrate. Ag and TC4 make further intrinsic absorptions during the multiple reflections of the localized electromagnetic waves.

A reference-free dual-comb spectroscopy calibrated by passive devices

Dual-comb spectroscopy has enabled new approaches for optical precision measurements. Although Doppler-limited resolution can be achieved over long-time scales across a large bandwidth, the development of dual-comb spectroscopy is hindered by strict demands for light source stability. Typically, expensive and complex self-reference systems are required to lock the carrier-envelope offset frequency (fceo) of the laser. Additionally, simply locking the repetition frequency (frep) to a radio frequency reference source still results in residual relative timing jitter between light sources. Here we extracted the relative fceo fluctuation between the frep-locked lasers from the high-precision passive notch filtering characteristics of the phase-shifted fiber Bragg grating and then eliminated it through online phase calibration. By introducing a passive broadband Fabry–Perot cavity with excellent thermal wavelength stability, we subsequently corrected residual relative timing jitter with online wavelength calibration, and the standard deviation of the relative wavelength drift was reduced to less than 0.4 pm within the full operating range. The spectral profile can also be extracted and removed by the Fabry–Perot cavity through intensity calibration. By calibrating these three dimensions, we built a reference-free post-calibration dual-comb spectroscopy and used this powerful tool to measure the Fabry–Perot cavity resonance peaks, the notch filtering narrow band of phase-shifted fiber Bragg gratings, and the absorption characteristics of hydrogen cyanide gas. The system achieves a spectral resolution of 0.8 pm over a bandwidth of more than 100 nm. This low-cost and convenient scheme provides new ideas for the application of dual-comb spectroscopy systems.

Design of embedded metamaterial solar absorber based on genetic algorithm

To effectively collect the solar energy, a metamaterial solar absorber operating in the UV to NIR wavelength range is designed, which consists of an embedded structure stacked with Ti and SiO2. The embedded structure can enhance the magnetic and electric fields to improve the absorption rate. However, the parameter space of the embedded structure is very huge to increase the optimization search time. Therefore, the absorption rate is calculated by the finite difference time domain method and the parameters of the absorber are optimized by genetic algorithm. The results show that the absorption rates of the optimized absorber are all over 95% in the 300–2500 nm and the average absorption rate is 98.7%, and the absorber is of polarization independence and the average absorption rate remains above 95% at an oblique incidence angle of 60°. By analyzing the electromagnetic field distribution of the absorber at the resonance wavelength, it can be concluded that the high absorption characteristics in the wideband are mainly achieved by the combined effects of local surface plasmon resonance, electric dipole resonance, propagating surface plasmon resonance and Fabry-Perot cavity resonance. Perfect absorber in the solar spectral range have significant value in fields such as solar energy harvesting and information detection.

Two-In-One: End-Emitting Blue LED and Self-Powered UV Photodetector based on Single Trapezoidal PIN GaN Microwire for Ambient Light UV Monitoring and Feedback.

With the continuous miniaturization and integration of the semiconductor industry, micro/nanoscale integrated photonics has received extensive attention as a key technology for optical communication, optical storage, and optical interconnection. Here, a two-in-one device is reported with both unidirectional blue light emission and UV photodetection functions based on single trapezoidal PIN GaN microwire. By constructing a Fabry-Perot resonator cavity structure, the end-emitting blue light-emitting diode with a low turn-on voltage (≈0.97V) and high color purity (full width at half maximum ≈22nm) is implemented. Furthermore, benefiting from the slow growth rate of the semipolar planes on both sides of the trapezoidal microwire and the high diffuse reflectivity of the patterned substrate, the trapezoidal microwire sides can be used as a high-performance UV photodetector. In self-driven mode, the device exhibits a large responsivity (0.218AW-1 ), high external quantum efficiency (83.31%) and fast response speed (rise/decay time of 0.48/0.98ms). Finally, the prepared two-in-one device is successfully integrated into ambient light UV monitoring and feedback system and tested. This work provides a novel strategy to combine luminescence with photodetection, demonstrating high potential for applications, such as on-chip photonic integration, energy-saving communication and ambient light monitoring and feedback system.

Design of a switchable bifunctional terahertz metamaterial absorber from ultra-broadband to 10-band

A bifunctional absorber with hybrid graphene–vanadium dioxide (VO2) is proposed and numerically investigated in the paper. Simulation results indicate that the absorber behaves as a broadband absorber with absorptance of more than 90% from 3.15 THz to 8.45 THz, when VO2 is in the metallic state. When VO2 is in the insulating state, the design exhibits a 10-band absorber, whose peak absorptances are above 90%. Broadband absorption is investigated by the impedance matching theory, and detailed physical studies indicate that it arises from electromagnetic resonance based on VO2 patches. Ten-band absorption originates from graphene plasmon (GP) resonance and Fabry–Perot cavity resonance. By adjusting the conductivity of VO2 and the Fermi level of graphene, the designed absorber not only can be independently tuned, but also has 91.9% modulation depth under broadband absorptance. Furthermore, the effect of incident angle on absorptance is investigated, and the absorber is polarization insensitive due to the symmetry of the structure. Benefiting from the above excellent performance, the bifunctional absorber offers great potential in terahertz applications, such as modulating, switching, and electromagnetic energy harvesting.

Uncooled two-microbolometer stack for long wavelength infrared detection

We have investigated an uncooled infrared (IR) detector utilizing a dual level architecture. This was achieved by combining two-microbolometer stack in the vertical direction to achieve high IR absorption over two distinct spectral windows across the long wavelength infrared region (LWIR). In addition, we have studied amorphous silicon germanium oxide (SixGeyO1−x−y) as an IR sensitive material, and metasurface to control IR absorption/reflection in interaction with standard Fabry–Perot cavity. The bottom microbolometer uses a metasurface to selectively absorbs a portion of the spectrum and reflects radiation outside this window range. At the same time, the top microbolometer uses a conventional Fabry–Perot resonant cavity to absorb a different portion of the spectrum and transmit any unabsorbed radiation outside this window. This device can be used to measure the absolute temperature of an object by comparing the relative signals in the two spectral bands. The spectral responsivity and detectivity, and thermal response time were > 105 V/W, > 108 cm Hz1/2/W, and 1.13 ms to filtered blackbody infrared radiation between (2–16) µm. The microbolometer voltage noise power spectral density was reduced by annealing the microbolometers in vacuum at 300 °C.

Superposition Fabry-Perot filter array for a computational hyperspectral camera.

Computational hyperspectral cameras with broadband encoded filter arrays enable high precision spectrum reconstruction with only a few filters. However, these types of hyperspectral cameras have limited application, because it is difficult for conventional encoded filter arrays to balance among the spectrum regulation capacity, angle insensitivity, and processibility. This Letter presents a new, to the best of our knowledge, encoded filter composed of superposition Fabry-Perot resonance cavity (SFP) that can simultaneously take all three aspects into consideration. By learning the parameters of an SFP encoder and a neural network decoder in an end-to-end manner, a computational hyperspectral camera based on an SFP filter array presents up to 2.24 times higher spectral reconstruction accuracy, 10 times wider working angle, and can be produced with a low-cost manufacturing process.

Investigation of a Multi-Layer Absorber Exhibiting the Broadband and High Absorptivity in Red Light and Near-Infrared Region.

In this study, an absorber with the characteristics of high absorptivity and ultra-wideband (UWB), which was ranged from the visible light range and near-infrared band, was designed and numerically analyzed using COMSOL Multiphysics® simulation software (version 6.0). The designed absorber was constructed by using two-layer square cubes stacked on the four-layer continuous plane films. The two-layer square cubes were titanium dioxide (TiO2) and titanium (Ti) (from top to bottom) and the four-layer continuous plane films were Poly(N-isopropylacrylamide) (PNIPAAm), Ti, silica (SiO2), and Ti. The analysis results showed that the first reason to cause the high absorptivity in UWB is the anti-reflection effect of top TiO2 layer. The second reason is that the three different resonances, including localized surface plasmon resonance, the propagating surface plasmon resonance, and the Fabry-Perot (FP) cavity resonance, are coexisted in the absorption peaks of the designed absorber and at least two of them can be excited at the same time. The third reason is that two FP resonant cavities were formed in the PNIPAAm and SiO2 dielectric layers. Because of the combination of the anti-reflection effect and the three different resonances, the designed absorber presented the properties of UWB and high absorptivity.