Fabry-Perot Resonator Research Articles

High-Gain Fabry–Perot Cavity Antenna With an Artificial Magnetic Conductor Side Wall

We propose a novel design method for a Fabry–Perot (FP) cavity antenna with an artificial magnetic conductor (AMC) side wall intended to provide a high gain in the tilted target direction. However, multiple reflections in the FPC caused by the AMC side wall make it extremely difficult to design the antenna. To solve this problem, we suggest a new design method based on a more generalized image theory, which transforms our antenna into a regular FPC problem that is more straightforward to analyze. The AMC unit cells of the AMC side wall and the ground plane are deliberately designed to have the antenna satisfy the FP resonance condition, which is required to produce a high gain. As a result, the antenna provides a relatively high gain of 12.6 dBi in the target direction of 30° and has reasonable aperture efficiency of 29%, which were validated experiments.

Longitudinal Manipulation of Scalar to Vector Vortex Beams Evolution Empowered by All‐Silicon Metasurfaces

AbstractManipulating the trend of polarization profiles in the propagation direction, especially the evolution from homogeneous to inhomogeneous distribution, can provide subtle implements for light‐matter interactions. The implementation of conventional stacked structures in the terahertz (THz) band to maneuver polarization states within a finite distance will result in large insertion losses due to inherent material absorption or Fabry–Perot resonance. Metasurfaces have proved to possess many extraordinary properties and propelled the integration of THz functional devices. Herein, the evolution from scalar vortex to vector vortex beams in the longitudinal direction is experimentally demonstrated using all‐silicon metasurfaces generated by spin‐polarization multiplexing encoding techniques. The coaxial universalized phase design scheme with extended focal length provides a paradigm for polarization manipulation that is not limited to the THz band. As a conceptual investigation of the working mechanism, a series of all‐silicon samples are fabricated to experimentally evaluate the conversion capability from scalar to vortex beams, that is, homogeneous to inhomogeneous polarization profiles. The mode weight recorded in the effective region is utilized to further analyze the setting laws of topological charges in orthogonal channels, providing great opportunities for fundamental applications in emerging fields, such as singular optics and quantum science.

Disordered plasmonic nanocavity enhanced quantum dot emission

In this paper, a large-scale compatible plasmonic nanocavity design platform is utilized to achieve a nearly order of magnitude photoluminescence (PL) enhancement. The proposed design is made of multi-sized/multi-spacing gold (Au) nanounits that are uniformly wrapped with a thin aluminum oxide (Al2O3) layer, as a foreign host to form a metal–insulator–semiconductor cavity, as they are coated with semiconductor quantum dots (QDs). Our numerical and experimental data demonstrate that, in an optimal insulator layer thickness, the simultaneous formation of broadband Fabry–Perot resonances and plasmonic hot spots leads to enhanced light absorption within the QD unit. This improvement in absorption response leads to the PL enhancement of QDs. This work demonstrates the potential and effectiveness of a random plasmonic nanocavities host in the realization of lithography-free efficient emitters.

Self-Adaptive Multistage Infrared Radiative Thermo-Optic Modulators Based on Phase-Change Materials

Phase-Change Materials (PCMs) are widely applied in dynamic optical modulation due to the dramatic changes in their complex refractive index caused by temperature variation. As the functionality varies, the application of a single PCM cannot meet the compact, efficient and broadband needs of optical modulators. In this work, we combine vanadium dioxide (VO2) and a chalcogenide (Ge2Sb2Te5 (GST) or In3SbTe2 (IST)) to obtain a VO2–GST/IST multiple-stack film that is optimized by a genetic algorithm. This film has a wide spectrum and high modulation properties with three self-switchable modes varied by temperature, including transmission, absorption and reflection. The optimal results are an average normal transmittance, absorbance, and reflectance of 0.76, 0.91, 0.86 in 3–5 μm and 0.72, 0.90, 0.90 in 8–14 μm under different temperature ranges. The film enhances the transmission and absorption properties due to the formation of anti-reflective coating and Fabry–Perot resonance. Compared with GST, the film maintains high reflectance due to the metal-like interface reflection of crystalline IST, which exhibits metallic properties. For different polarization states, the film demonstrates great directional insensitivity when the incidence angles vary from 0° to 60°. The designed self-adaptive multistage infrared radiative thermo-optic modulator has promising implications for optical fuse, fiber-optic communication and energy storage fields.

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.

Spectrum enhancement of extraordinary terahertz transmission through metal-dielectric multilayer compound annular hole array metamaterial

This study presents, what we believe to be, a novel approach to enhance the spectrum of extraordinary terahertz transmission utilizing surface plasmon polaritons (SPPs) mode coupling in metal-dielectric compound annular hole array metamaterial. The transmitting properties of the structure are thoroughly assessed through a combination of theoretical analysis and numerical simulation, with a particular focus on understanding the surface plasmon mode coupling. Our investigation revealed the presence of propagating surface plasmon polaritons (PSPP), localized surface plasmon resonance (LSPR) and Fabry-Perot (FP) resonances within the compound layer. We find that the coupling of PSPP and LSPR modes plays a crucial role in determining the broadband nature of the structure. Interference theory is utilized to mitigate the FP resonance, while further optimization of the transmission bands is attained by implementing the impedance matching hypothesis. By adjusting the structure parameters, the effective coupling of the SPPs modes and numerous reflections in the dielectric cavity produced a remarkably smooth and transparent character, leading to a significant enhancement of transmission spectrum and a reduction in the incident loss of terahertz wave.

External-quantum-efficiency enhancement in quantum-dot solar cells with a Fabry–Perot light-trapping structure

In this work, we have experimentally investigated the impact of light trapping on the performance of InAs/GaAs quantum dot (QD) solar cells. To increase the amount of absorbed near-infrared photons, we fabricated a thin-film QD solar cell with a backside mirror where the positions of the QD layers were matched with the intensity peaks of one of the Fabry–Perot (FP) resonances in this structure to enable enhanced QD absorption near 1192 nm. We demonstrate that the external quantum efficiency at a given FP resonance wavelength of such an InAs/GaAs-based QD solar cell can be increased by an order of magnitude over solar cells without FP resonance by optimally positioning the QD layers.

Optical engineering of PbS colloidal quantum dot solar cells via Fabry–Perot resonance and distributed Bragg reflectors

A tradeoff between light absorption and charge transport is a well-known issue in PbS colloidal quantum dot (CQD) solar cells because the carrier diffusion length in PbS CQD films is comparable to the thickness of CQD film. We reduce the tradeoff between light absorption and charge transport by combining a Fabry–Perot (FP) resonator and a distributed Bragg reflector (DBR). A FP resonance is formed between the DBR and a dielectric-metal-dielectric film as a top transparent electrode. A SiO2-TiO2 multilayer is used to form a DBR. The FP resonance enhances light absorption near the resonant wavelength of the DBR without changing the CQD film thickness. The light absorption near the FP resonance wavelength is further boosted by coupling the FP resonance with the high reflectivity of the Ag-coated DBR. When the FP resonance and DBR are combined, the power conversion efficiency (PCE) of PbS CQD solar cells increases by 54%. Moreover, the DBR assisted FP resonance enables a very thin PbS layer to absorb near infrared light four times more. The overall PCE of the thin PbS CQD solar cell increases by 24% without sacrificing the average visible transmittance (AVT). Our results show how to overcome the inherence problem of the CQD and develop a semi-transparent solar cell where the wavelength-selective absorption and the transparency for visible light are important.

Terahertz bandpass filter with Babinet complementary metamaterial mirrors and silicon subwavelength structure.

We fabricated a rigid bandpass filter with a broad far-infrared wavelength range of high transmission using a silicon subwavelength structure with a Babinet complementary metamaterial half-mirror pair, despite its apparent light-blocking structure. The rigid one-piece filter was produced by a simple process involving photolithography, dry etching, and deposition, each performed only once. The transmission principle relies on the Fabry-Perot resonance with a metamaterial half-mirror pair that exhibits extraordinary optical transmission due to spoof surface plasmon polaritons. The transmission center wavelength was successfully predicted by the basic equation of Fabry-Perot resonance with an effective medium approximation. In contrast, a narrower bandwidth and a lower minimum transmittance than those predicted from the basic equation were provided by the subwavelength Si structure between the metamaterial mirrors, resulting in enhanced bandpass filter characteristics.

Developing a Novel Terahertz Fabry-Perot Microcavity Biosensor by Incorporating Porous Film for Yeast Sensing.

We present a novel terahertz (THz) Fabry-Perot (FP) microcavity biosensor that uses a porous polytetrafluoroethylene (PTFE) supporting film to improve microorganism detection. The THz FP microcavity confines and enhances fields in the middle of the cavity, where the target microbial film is placed with the aid of a PTFE film having a dielectric constant close to unity in the THz range. The resonant frequency shift increased linearly with increasing amount of yeasts, without showing saturation behavior under our experimental conditions. These results agree well with finite-difference time-domain (FDTD) simulations. The sensor's sensitivity was 11.7 GHz/μm, close to the optimal condition of 12.5 GHz/μm, when yeast was placed at the cavity's center, but no frequency shift was observed when the yeast was coated on the mirror side. We derived an explicit relation for the frequency shift as a function of the index, amount, and location of the substances that is consistent with the electric field distribution across the cavity. We also produced THz transmission images of yeast-coated PTFE, mapping the frequency shift of the FP resonance and revealing the spatial distribution of yeast.

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.

An ultrathin frequency dual-tunable Salisbury screen absorber based on graphene and strontium titanate in the terahertz region

We present a frequency dual-tunable Salisbury screen absorber (SSA) based on graphene and strontium titanate (STO) in the terahertz region. Different from the classical SSAs, the absorber is composed of an optically thick layer of gold at bottom, a high-permittivity STO spacer and a single-layer nonstructural graphene film on top, which has the advantages of high absorption, lightweight, ultrathin thickness and frequency tuning. Simulation results show that the proposed SSA can obtain a strong Fabry–Perot resonance peak with 99.96% absorbance at 1.55 THz, whose performance is comparable with metamaterial-based perfect absorbers. When changing the STO temperature from 200 to 400 K, the resonance frequency shifts from 1.22 to 1.83 THz. As varying the graphene Fermi energy level from 0 to 1 eV, the resonance frequency shifts from 1.44 to 1.65 THz. Moreover, by changing the thickness of the STO spacer from 1.5 to 5.5μm, the resonance frequency can be passively tuned from 2.96 to 0.90 THz, achieving a larger frequency tuning range under small thickness variations. Meanwhile, this SSA exhibits excellent polarization insensitivity and maintains high absorption over 90% with varied incidence angle from 0° to 58° for both TE and TM waves. Such a design would have great potential applications in the fields of detecting, thermal emitting, and imaging.

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.

The manufacture and reliability analysis of the all-rigid Fabry–Perot resonator for fiber-optic acoustic sensors

By the continuous development of aerospace, petroleum exploration, and other industrial fields, the fiber-optic acoustic sensor (FOAS) with high reliability is a desideration sensor, which can be used for noise monitoring in the extremely harsh environment. The FOAS based on the all-rigid Fabry–Perot resonator (FPR) relies on the new acoustic sensitive principle, where the change in the air refractive index is induced by sound waves and gets rid of the distortion caused by the mechanical characteristics of the acoustic sensor based on the movable parts. So, the FPR-based FOAS is very suitable for acoustic sensing in the harsh environment. In this paper, the reliability of this kind of FOASs is simulated and analyzed. The modal and anti-vibration simulation results of FPR with different sizes show that the FPR has a high natural frequency, and the external vibration environment does not affect the acoustic sensitivity of the FPR. The micro and small-batch all-rigid FPR can be manufactured by the optical contact. Moreover, the FPR can withstand the high temperature of 500°C that is verified by rapid heat treatment equipment. In order to improve the reliability of the FOAS, the metal packing shell is designed and fabricated. Moreover, the vibration and high-temperature tests of the packaged sensor are carried out. The two groups of tests show that the sensor can work normally under 10 g of acceleration vibration and 200°C high temperature, respectively. Therefore, the FOAS based on the FPR has high reliability and is very suitable for noise monitoring in the extreme harsh environment of various industrial fields. Furthermore, the research results of this paper will enhance the competitiveness and influence of the commercialized FOAS.

Balance between the diffraction efficiency and process robustness for plasmonic lithographic alignment technology considering the Fabry-Perot resonator effect.

Different from traditional lithography, metal material with high absorptivity and high reflectivity is introduced into plasmonic lithography technology. In particular, a silver/photo resist/silver film stack can form a Fabry-Perot (F-P) resonator structure, which can greatly change the behavior of the light reflection and transmission. Since the silver layer has a strong absorption ability to the alignment probe light with a wavelength of 532 or 633nm, the quality of the alignment signal is seriously affected. In this paper, a thin film Fourier transfer model is established to quantitatively calculate the amplitude and phase information of the diffraction light with different orders. The results show that the diffraction optical power can be enhanced by the thickness optimization of all film stacks, and the maximum wafer quality (normalized diffraction efficiency) can be increased to 25.7%. The mechanism analysis of alignment signal enhancement is based on the F-P resonator phase oscillation amplification effect. However, it can also bring the reverse of both the power and phase for the alignment probe signal when the thickness fluctuation of the F-P resonator exists, which will be a great challenge for through-the-mask moiré fringe alignment technology. To obtain the optical power distribution of the structure surface and image of moiré fringes, a transfer matrix method is given to point-by-point calculate the incidence and reflection of the probe light in the vertical direction. The finite-difference time-domain method is also used to demonstrate alignment performance. It is proved that the subtle fluctuation of the photoresist thickness can make a huge difference to moiré fringes. A balance between the diffraction efficiency and process robustness can be achieved for plasmonic lithographic alignment technology by controlling the thickness range of the F-P resonator structure. In addition, the metal-insulator-metal structure has excellent thickness sensitivity and is applicable to optical signal detection and material property monitoring.

On-chip single-mode thin-film lithium niobate Fabry-Perot resonator laser based on Sagnac loop reflectors.

We demonstrate an on-chip single-mode Er3+-doped thin-film lithium niobate (Er:TFLN) laser which consists of a Fabry-Perot (FP) resonator based on Sagnac loop reflectors (SLRs). The fabricated Er:TFLN laser has a footprint of 6.5 mm × 1.5 mm with a loaded quality (Q) factor of 1.6 × 105 and a free spectral range (FSR) of 63 pm. We generate the single-mode laser at 1544 nm wavelength with a maximum output power of 44.7 µW and a slope efficiency of 0.18%.

Bias Reconfigurable Photoresponse of an Infrared Nanocrystal Film Integrated into a Coupled Fabry-Perot Resonator

The coupling of a photonic structure to a nanocrystal film enables light focusing over a distance compatible with the charge diffusion length. This strategy has been implemented in infrared sensors based on nanocrystal films to maximize their absorption. Here, we demonstrate that the photonic structure can be further exploited to generate a bias-reconfigurable photoresponse. To reach this goal, we use a coupled Fabry-Perot structure that can be seen as a periodic grating with two different cavities per period. The two cavities are coupled and a resonance appears, increasing the effective absorption coefficient by a factor of 30 compared to standard interdigitated electrodes. When connected in the appropriate configuration, this device enables the turning-on and -off of part of the spectral response (over a factor of 25 in magnitude) simply by tuning the applied bias (<1 V). Finally, we also demonstrate that this resonator geometry is promising for integration at the focal plane array level since the resonance is maintained for a pixel size as small as 10 μm.

Ultra-broadband tunable terahertz absorber based on graphene metasurface with multi-square rings

In recent years, thinness, lightness, broadband, high absorption, and tunability have become five important elements for electromagnetic (EM) absorbers. This article proposes a novel single-layered graphene metasurface absorber (GMSA) that perfectly achieves all of the above elements. The GMSA differs from common hybrid patterns in that it adopts a graphene layer with a simple multi-square ring structure. The simulation results show that Fabry-Perot resonance (FPR) and graphene-based surface plasmon resonance (GSPR) can be combined to produce the broadband absorption of 3.04 THz in the terahertz (THz) frequency range. The proposed GMSA is completely polarization-insensitive because of its symmetrical configuration, and it exhibits wide-angle oblique incidence properties for both TE and TM-polarized waves, allowing it to achieve broadband absorption with at least 90% absorption in the range of incident angles from 0° to 45°. In addition, the chemical potential of graphene can be altered to change the effective absorption bandwidth, which can be easily tuned by the applied external voltage. The GMSA has broad application prospects in THz detection, imaging, and object cloaking due to its flexible and straightforward construction, polarization insensitive, wide-angle incident, broadband, and high absorption qualities.

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.