Circular Microcavity Research Articles

Synchronization of E. coli Bacteria Moving in Coupled Microwells.

Synchronization plays a crucial role in the dynamics of living organisms. Uncovering the mechanism behind it requires an understanding of individual biological oscillators and the coupling forces between them. Here, a single-cell assay is developed that studies rhythmic behavior in the motility of E.coli cells that can be mutually synchronized. Circular microcavities are used to isolate E.coli cells that swim along the cavity wall, resulting in self-sustained oscillations. Connecting these cavities by microchannels yields synchronization patterns with phase slips. It is demonstrated that the coordinated movement observed in coupled E.coli oscillators follows mathematical rules of synchronization which is used to quantify the coupling strength. These findings advance the understanding of motility in confinement, and open up new opportunities for engineering networks of coupled oscillators in microbial activematter.

Unidirectional emission of GaN-on-Si microring laser and its on-chip integration.

GaN-based microring lasers grown on Si are promising candidates for compact and efficient light sources in Si-based optoelectronic integration and optical interconnect due to their small footprints, low mode volume, low power consumption, and high modulation rate. However, the high symmetry of circular microcavity leads to isotropic emission, which not only reduces the light collection efficiency, but also affects other adjacent devices during data transmission. In this study, the unidirectional lasing emission of room-temperature current-injected GaN-based microring laser was realized by coating metal Ag on the microring sidewall and integrating a direct coupled waveguide. The light was efficaciously confined in the cavity and only emitted from the waveguide, which avoided optical signal crosstalk with other adjacent devices. Furthermore, we integrated a microdisk at the other end of the waveguide as a photodetector, which could effectively detect the output power of the microring laser from the direct coupled waveguide. Therefore, a preliminary on-chip integration of GaN-based microring laser, waveguide and photodetector on Si substrate was successfully demonstrated for the first time, opening up a new way for on-chip integration and optical interconnect on a GaN-on-Si platform.

Design of tunable dual-band terahertz perfect absorber base on graphene

In this paper, a novel tunable dual-band graphene-based perfect absorber which features a three-layer structure consisting of a monolayer graphene sheet and a metallic mirror separated by a thin Si layer with circular microcavity array is designed and systematically investigated. The simulation results show that the two perfect absorption peaks (99.7% and 99.5%) are achieved at 4.13 and 4.38 THz. The two resonance modes are caused by different electric and magnetic field distributions, resulting in different tuning properties. The absorption peaks could be tuned by adjusting the chemical potential of the monolayer graphene. In addition, the influences of the structural parameters such as period, thickness of the Si layer, depth and radius of the circular microcavity on the absorption characteristics of the absorber have been studied and presented.

Optical modes in the perovskite CsPbX3 semicircular and circular microcavity

In this paper, we used the finite element method to numerically study the possible optical resonance modes in the all-inorganic metal halide perovskite (CsPbX3, [Formula: see text], Br, I) semicircular and circular microcavities. For the semicircular microcavity, the quasi-three-period mode has the highest quality factor among quasi-whispering gallery mode (WGM), two-period mode and four-period mode. The quality factors of the four resonance modes all increase linearly for the larger cavity size. In addition, the circular perovskite microcavities present the WGM patterns with extremely high-quality factors, which indicates that the circular perovskite microcavity has the potential application in the optical microcavity or laser device.

Directional emission in X-cut lithium niobate microresonators without chaos dynamics

We systematically investigate the field distribution of the transverse electric modes in X-cut lithium niobate disks as an example of circular microcavities with anisotropic refractive index. A conserved quantity is discovered, which indicates the absence of chaos that generally exists in deformed microcavities and leads to a nontrivial directional emission. The emission directionality was theoretically investigated and experimentally verified by exciting high-order modes of an X-cut lithium niobate microresonator assisted with second harmonics. The field distribution analysis can enrich the knowledge in designing photonic devices that need precise control of field distribution, such as phase matching in nonlinear processes. Furthermore, the discovered emission phenomenon is momentous in enhancing and controlling communications between on-chip photonic devices.

Giant enhancement of emission intensity by using microcavity

We propose theoretically a tunable circular Bragg microcavity to enhance the intensity of the emission band of interest in rare-earth-doped materials and to suppress the unwanted emission bands which produce noise and diminish the efficiency of the emission of interest. The surrounding of the microcavity comprises of alternating layers of high-index and low-index materials. The luminescent ions such as neodymium Nd3+ having different emission bands in different host materials are placed in the microcavity, and single emission band with stronger intensity can be observed, and other emission bands are suppressed. The wavelength of the single emission peak can be changed from one wavelength to other wavelengths by varying the refractive index, radius of the microcavity and thus modifying the local density of states of the microcavity. The fluorescence branching ratio of emission band of interest can be enhanced from 10% to 100% due to suppression of the unwanted emission bands.

Energy action model of spark assisted chemical engraving (SACE) for improving surface quality of micro cavities in ZrO2 ceramics

ZrO2 ceramic has a wide range of applications, such as in the thermal barrier coating (TBC) of turbine blades, micro actuators, and gas sensors. However, this material is challenging to machine due to its high hardness and brittleness. Although spark assisted chemical engraving (SACE) can be used to machine ZrO2 ceramics, the traditional SACE models for glass are difficult to apply to ZrO2 ceramics since the melting point of ZrO2 is much higher than that of glass. A theoretical basis for applying the SACE process to ZrO2 ceramics is still lacking, which makes applying the SACE process to machine micro cavities with high surface quality in ZrO2 ceramics very challenging. This paper proposes an energy action model based on the processing voltage, pulse width and machining gap by analyzing the energy transfer process of SACE. The energy model expresses difference in the spark energy between physical removal and chemical removal. Through machining experiments, the contact effect of the SACE process on ZrO2 ceramics was found, and the reasons why the SACE process is sensitive to the machining gap were clarified. Furthermore, physical and chemical removal process models with or without the discharge constraint onto the end of the tool electrode were established. Using the above theoretical models, a circular ring microcavity without micro cracks on the surface was achieved in a ZrO2 ceramic workpiece by using the SACE process with the regulating energy effect trending to the chemical removal. Additionally, considering the contact effect and the process models applied in the SACE scanning process of ZrO2 ceramics, a tool electrode with a spring structure was employed to solve the bending problem of the micro tool electrode. As a result, a square micro-cavity with high surface quality was machined successfully.

Raman intensity oscillation of graphene over SiO2/Si micro-cavity

We found that the intensity of Raman scattering spatially oscillates over single- and double-layer graphene suspended over micro-fabricated silicon dioxide/silicon cavities. CVD-grown graphene sheets were transferred onto circular micro-cavities and intensities of G band and 2D band Raman peaks exhibited clear oscillation forming concentric circular patterns. We proposed the origin of oscillation as a multiple-beam interference and confirmed the model through theoretical calculations. The model well explains our experimental observations and can be applied to other laser-spectroscopy on 2D materials suspended over micro-cavities.

Manipulating spontaneous emission spectra using two-dimensional elliptical microcavities

Integrated photonics and the study of the emission spectra and efficiency of light sources are promising research directions in the optoelectronics area. Here, we present an elliptical microcavity and derive the expression for its local density of state. Theoretical analyses and numerical simulations are performed to observe the broadening of the spontaneous emission spectra (SES) when placing the emitter in circular and elliptical microcavities. The results show that an SES with a full width at half-magnitude (FWHM) of 200 nm in free space is broadened, to one with an FWHM of 400 nm, in the elliptical microcavity. This approach can be used for any modification of spontaneous emission.

InGaN/GaN microdisks enabled by nanoporous GaN cladding.

The fabrication of nanoporous (NP) GaN is proposed as a generic technique to create out-of-plane index guiding for nitride microcavities. Compared to the conventional undercut technique, the proposed technique forms uniformly a low-index NP-GaN layer beneath the entire microcavity. Therefore, it supports all cavity modes (with different cavity geometries), while the undercut technique only supports the modes that reside at the circumference of a circular microcavity. As a proof of concept, GaN microdisk cavities were fabricated with the NP-GaN as the bottom low-index medium. A cold cavity with Q>2,000 was reported under continuous-wave pumping. Lasing was demonstrated with threshold optical pumping power Pth∼60 kW/cm2 for the r=10 μm microdisk and Pth∼7 kW/cm2 for the r=50 μm microdisk. A rate equation analysis was performed to estimate the spontaneous coupling factor β∼1E-3, which was one order of magnitude higher than the previous report of a nitride microdisk laser with an InGaN quantum well active region. Therefore, NP GaN was proven to be a suitable replacement of the undercut technique for future nitride microcavities applications.

Vibrational modes prediction for water-air bubbles trapped in circular microcavities

Oscillating bubbles have proven to be a versatile tool for various microfluidic applications. Despite the existence of the extensive literature on the behavior of acoustically actuated bubbles, a ready-to-use approach, capable of predicting the oscillatory motion for the bubbles trapped in the circular microcavities, is still missing. In this study, we propose a theoretical model to quantify the resonant frequencies and viscous dissipation factors for a single trapped bubble and verify it experimentally. We further investigate an interaction of two coupled bubbles of equal and different radii. For the identical bubble pair, coupling results in controllable frequency shift from the modes of a single bubble, whereas the non-identical one can operate as a flow switch.

Optical transmission characteristics of multi-band triangular-lattice photonic crystal coupling cavity waveguide based on annular microcavity

The light localization characteristics of the near-infrared triangular-lattice photonic crystal annular microcavity are studied theoretically in this paper. The photonic crystal has a lattice constant of <i>a</i>=540 and it is composed of silicon rods each with a radius of <i>r</i>=135 immersed in air background. The two kinds of annular microcavities are obtained by removing 12 silicon rods which are located respectively at a distance of 2a and at a distance of √<span style="border-top:1px solid; padding-top:0px;">3</span><i>a</i> to the central rod. Five resonant wavelengths and the corresponding eigen mode profiles of the microcavity are studied. A coupled resonant optical waveguide is formed by integrating the microcavities with a periodic length of 7<i>a</i> in space. The group velocity of light beam propagation within multiple guiding bands are analyzed by the tight-binding approximation method. The maximum and minimum velocity of 0.0028<i>c</i> and 0.00082<i>c</i> are obtained, where <i>c</i> is the light velocity in vacuum. The light transmittance values and spatial steady distributions of the electric field's amplitude through the structure at several wavelengths within the guiding bands are studied by the finite-difference time-domain method. The results are consistent with that calculated by the plane wave expand method. Interleaving circular microcavities perpendicular to the direction of optical transmission at a lateral distance of 2√<span style="border-top:1px solid; padding-top:0px;">3</span><i>a</i>, the coupling region between the adjacent microcavities is changed, the difference in group velocity between guiding bands apparently decreases and the transmittance values of two frequency bands are enhanced.<br/>Keeping the size of silicon rods unchanged, two kinds of microcavities are constructed by removing the six rods with the distances of 2<i>a</i> and √<span style="border-top:1px solid; padding-top:0px;">3</span><i>a</i> from the center of the central silicon rod, respectively. The resonant wavelengths supported by the above two microcavities are studied. Two coupled-resonant optical waveguides with a periodic length of 7<i>a</i> are proposed. Connecting these two coupled cavity optical waveguides with the W1-typed input/output waveguides, the selecting and sharing function of guiding band are finally achieved for wavelengths within different frequency bands. Keeping the group velocity slowing down, a maximum value of one guiding band reaches 0.00047<i>c</i>.

Strain-assisted optomechanical coupling of polariton condensate spin to a micromechanical resonator

We report spin and intensity coupling of an exciton-polariton condensate to the mechanical vibrations of a circular membrane microcavity. We optically drive the microcavity resonator at the lowest mechanical resonance frequency while creating an optically trapped spin-polarized polariton condensate in different locations on the microcavity and observe spin and intensity oscillations of the condensate at the vibration frequency of the resonator. Spin oscillations are induced by vibrational strain driving, whilst the modulation of the optical trap due to the displacement of the membrane causes intensity oscillations in the condensate emission. Our results demonstrate spin-phonon coupling in a macroscopically coherent condensate.

半径5 μm的定向输出圆盘形微腔激光器

半径5 μm的定向输出圆盘形微腔激光器

Non-Hermitian Hamiltonian and Lamb shift in circular dielectric microcavity

We study the normal modes and quasi-normal modes (QNMs) in circular dielectric microcavities through non-Hermitian Hamiltonian, which come from the modifications due to system–environment coupling. Differences between the two types of modes are studied in detail, including the existence of resonances tails. Numerical calculations of the eigenvalues reveal the Lamb shift in the microcavity due to its interaction with the environment. We also investigate relations between the Lamb shift and quantized angular momentum of the whispering gallery mode as well as the refractive index of the microcavity. For the latter, we make use of the similarity between the Helmholtz equation and the Schrödinger equation, in which the refractive index can be treated as a control parameter of effective potential. Our result can be generalized to other open quantum systems with a potential term.

Modulation of Thermo-TRP Channels by Temperature in Planar Lipid Bilayers

Thermal Transient receptor potential (TRP) channels belong to the large family of TRP channels. They are an important class of receptors found widely distributed throughout the mammalian central and peripheral nervous systems. They have been shown to be directly activated by heat or cold in physiologically relevant temperature ranges, but are also activated by mechano-stimulation and various ligands. Understanding the mechanisms of temperature activation could lead to the discovery of novel compounds with differing effects on ligand activation and temperature activation for the treatment of pain and other disease states, with fewer side effects.We have employed parallel planar lipid bilayer instrumentation (Orbit, Nanion) to study different reconstituted thermo-TRP channels, particularly the purified human TRP-A1, -V1, -V3 and -M8 channels. Planar lipid bilayers can be formed by painting over Micro Electrode Cavity Array (MECA) chips, a 2 by 2 array of circular micro-cavities in a highly inert polymer. The reconstitution of the proteins is achieved by adding the purified proteins directly to the bilayers.In this study, we demonstrate the activation of the different TRP channels by cold and heat in a fully controlled environment using artificial membranes and the use of a peltier element to actively cool and heat the system to the desired temperature (±1°C). Furthermore, we compared our Q10 data from purified proteins to TRP channels expressed in HEK cells (Millipore, Chantest) using an automated patch clamp platform (Patchliner, Nanion) with temperature control.Our results support the hypothesis that temperature sensitivity is located within the channels and does not require any second messengers, including calcium or accessory proteins.

Numerical Simulation of Liquid Film Evaporation in Circular and Square Microcavities

Numerical simulations are performed for liquid film evaporation in circular and square microcavities, which occurs frequently in ink-jet fabrication. The conservation equations of mass, momentum, energy, and mass fraction in the liquid and gas phases are solved using a sharp-interface level-set method, which is modified to include the effects of evaporation and dynamic contact angles. Three-dimensional computations for a square cavity are efficiently carried out in a reduced domain by introducing an effective mass transfer length for the truncated region. The liquid film evaporation pattern is observed to depend strongly on the dynamic contact angles and cavity geometry.

Microcavity Connceted with a Waveguide for Application to Optical Sensing

A high-performance microcavity sensor with a port connected with a waveguide directly is investigated numerically. With input light and output light transmitting in the same waveguide, we propose a robust coupling mechanism. For a circular microcavity with a diameter of 20μm and a refractive index of 1.45, our numerical results show that the coupled modes are excited and more than 5×104 Q-factor is calculated from the transmission spectrum. Dramatically, the spectrum shows a fano-shape resonance at specific wavelength which is useful for high-precision optical sensing on the order of 10-5.

Ultralong distance coupling between deformed circular microcavities

The ultralong distance coupling between two Asymmetric Resonant Microcavities (ARCs) is studied. Different from traditional short distance tunneling coupling between microcavities, the high efficient free space directional emission and excitation allow ultralong distance energy transfer between ARCs. In this paper, a novel unidirectional emission ARC, which shows directionality I40 = 0.54, is designed for materials of refractive index n = 2.0. Compared with regular whispering gallery microresonators, the coupled unidirectional emission ARCs show modulations of resonance frequency and linewidth even when the distance between cavities is much longer than wavelength. The performances and properties of the ultralong distance interaction between ARCs are analyzed and studied by coupling mode theory in details. The ultralong distance interaction between ARCs provides a new way to free-space based optical interconnects between components in integrated photonic circuits.

The effect of fast and continuous change of dielectric permittivity on whispering gallery modes in circular microcavity

The detailed analysis of the response of whispering gallery mode (WGM) to the permittivity change in circular microcavities made of materials with noteworthy relaxation time is presented. Continuous and mathematically well behavior function is employed to describe temporal change of resonator permittivity and the wave equation in both frequency and time domains is analyzed by means of inverse Laplace transform method. The exact transient response of cavity resonance mode with the steady state solutions are described carefully and it is shown that fast and continuous change of resonator dielectric permittivity behave like several propagating boundaries inside and outside the cavity. The transformed WGM appears after transient duration. These analyses are providing suitable tools for investigation of dynamic optical devices.