Elliptical Microcavity Research Articles

High-efficiency ultra-fast all-optical photonic crystal diode based on the lateral-coupled nonlinear elliptical defect

An all-optical Fano-like diode featuring a nonlinear lateral elliptical micro-cavity and a reflecting column in the photonic crystal waveguide is proposed. The asymmetric micro-cavity is constructed by removing one rod and changing the shape of the lateral rod from a circle to an ellipse. A reflecting pillar is also introduced into the waveguide to construct an F–P cavity with the elliptical defect and enhance the asymmetric transmission for the incident light wave transmitting rightwards and leftwards, respectively. By designing the size of the ellipse and optimizing a reflecting rod at a suitable position, a maximum forward light transmittance of −1.14 dB and a minimum backward transmittance of −57.66 dB are achieved at the working wavelength of 1550.47 nm. The corresponding response time is about 10 ps when the intensity of the pump light beam resonant at 637 nm is 3.97 W/μm2.

Polarized room-temperature polariton lasing in elliptical microcavities filled with fluorescent proteins

Organic exciton-polaritons, which arise from the strong light-matter coupling between excitons in organic molecules and cavity photons, have emerged as a versatile platform for the investigation of polariton lasing, Bose-Einstein condensation and many-body phenomena at ambient conditions. Here, we study the condensation of exciton-polaritons in fluorescent protein-filled microcavities with elliptical cross-sections. The structural anisotropy of these cavities yields a distinct optical polarization splitting, which we investigate both experimentally and numerically. In the high-density regime of exciton-polaritons, the pronounced polarization splitting of the fundamental polaritonic resonance enforces selective condensation in one linearly polarized polaritonic mode. Our findings constitute a solid basis for polarization engineering in room-temperature polariton condensates.

Optical Modes in Elliptical Microcavities for Single-Photon Sources

A theory of optical modes in an elliptical microcavity has been developed using Mathieu functions in elliptical coordinates. A key difference from the circular case is the splitting of doubly degenerate modes. Split optical modes have been numerically calculated and their symmetry has been determined. A method has been proposed to choose the parameters of a cavity for a certain wavelength. The difference between the energies of optical modes in the cavity with metallic walls and in the dielectric cavity is no more than ~20%. The dispersion relations of optical modes show the possibility of degeneracy of modes with different symmetries, which allows the spectral and polarization filtering of radiation of single-photon sources and the fabrication of sources of multiply entangled states.

Self-referred microcavity-based fused-fiber fabry-perot refractometer

In this paper, a fiber-optic Fabry-Perot microcavity sensor is presented based on splicing a catastrophic fused fiber (CFF) to a single-mode fiber (SMF) for the simultaneous measurement of the refractive index (RI) and temperature. CFF formed by the catastrophic fuse effect consists of a periodic void in the fiber core that creates a teardrop shape or elliptical air microcavity after splicing. By simulation, the elliptical microcavity sensor is selected to measure external RI changes by Fast Fourier Transform (FFT) analysis. The RI sensitivity was obtained to be −2.5 ± 0.0074/RIU with a resolution of about 4 × 10−5 RIU. Also, the experimental results showed that temperature is obtained independently from the FFT parameter without being affected by the RI. The sensor temperature was determined by tracking the wavelength shift of the interference spectrum. Consequently, the temperature sensitivity of 7 pm/°C in the range of 20 °C to 95 °C was achieved. Therefore, the RI and the temperature were simultaneously measured by analyzing the spatial frequency and wavelength shift. The proposed dual-microcavity FP sensor can compensate for any power fluctuation in the input light source.

Maximal Shannon entropy in the vicinity of an exceptional point in an open microcavity

The Shannon entropy as a measure of information contents is investigated around an exceptional point (EP) in an open elliptical microcavity as a non-Hermitian system. The Shannon entropy is maximized near the EP in the parameter space for two interacting modes, but the exact maximum position is slightly off the EP toward the weak interaction region while the slopes of the Shannon entropies diverge at the EP. The Shannon entropies also show discontinuity across a specific line in the parameter space, directly related to the exchange of the Shannon entropy as well as the mode patterns with that line as a boundary. This feature results in a nontrivial topological structure of the Shannon entropy surfaces.

Relative Entropy as a Measure of Difference between Hermitian and Non-Hermitian Systems.

We employ the relative entropy as a measure to quantify the difference of eigenmodes between Hermitian and non-Hermitian systems in elliptic optical microcavities. We have found that the average value of the relative entropy in the range of the collective Lamb shift is large, while that in the range of self-energy is small. Furthermore, the weak and strong interactions in the non-Hermitian system exhibit rather different behaviors in terms of the relative entropy, and thus it displays an obvious exchange of eigenmodes in the elliptic microcavity.

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.

Highly efficient elliptical microcavity refractive index sensor with single detection unit

Here, an elliptical cavity is investigated in its vertical and horizontal arrangement as a single detection unit in a 2D hexagonal hole-type photonic crystal. The Q-factors are 3700, and 2600 for vertical and horizontally arranged cavities, respectively. The notable characteristic of the presented sensor is mainly its large detection range for refractive indices in range of n = 1 to over 2. The operation of the sensor can be divided into two distinct detection regions in separate spectra located next to lower and higher edges of photonic band gap. The design of cavities and their sensing characteristics are discussed in detail for each topology using FDTD and PWE methods.

Why elliptic microcavity lasers emit light on bow-tie-like modes instead of whispering-gallery-like modes

We study numerically a two-dimensional (2-D) elliptical microcavity laser, in the center of which a circular active region is located, modeling a focused pumped spot or an injection electrode. The object of the research is to study lasing spectra, gain-medium thresholds, and modal fields, found as solutions to a classical electromagnetic eigenvalue problem tailored to address the threshold conditions. The instrument of our study is the set of two coupled Muller boundary integral equations (BIE) on the boundaries of the cavity and the active region. These BIEs are discretized by the Nystrom technique that guarantees the convergence. Among the modes that co-exist in such a resonator, we demonstrate the whispering-gallery-like modes (WGM) and the bow-tie-like modes (BTM). We find that the threshold values of material gain of BTMs can become lower than those of nearby WGMs if the radius of the active region in the cavity center is getting sufficiently small.

Polarization switch in an elliptical micropillar – quantum dot system induced by a magnetic field in Faraday configuration

In this paper we study the effect of applying a magnetic field on an elliptical microcavity pillar with quantum dots embedded, in the presence of external laser excitation. To obtain the system dynamics we use the matrix density formalism, taking into account realistic parameters and including losses. Our results show that it is possible to use the magnetic field strength to control the polarization of the photons inside the cavity, making our system behave like a photon polarization switch. We also report the best set of parameters where this is possible. Our results also indicate that we can use the polarization of the cavity photons to look into the fine structure of the energy levels of quantum dots.

Non-Hermiticity and conservation of orthogonal relation in dielectric microcavity

Non-Hermitian properties of open quantum systems and their applications have attracted much attention in recent years. While most of the studies focus on the characteristic nature of non-Hermitian systems, here we focus on the following issue: A non-Hermitian system can be a subsystem of a Hermitian system as one can clearly see in Feshbach projective operator (FPO) formalism. In this case, the orthogonality of the eigenvectors of the total (Hermitian) system must be sustained, despite the eigenvectors of the subsystem (non-Hermitian) satisfy the bi-orthogonal condition. Therefore, one can predict that there must exist some remarkable processes that relate the non-Hermitian subsystem and the rest part, and ultimately preserve the Hermiticity of the total system. In this paper, we study such processes in open elliptical microcavities. The inner part of the cavity is a non-Hermitian system, and the outer part is the coupled bath in FPO formalism. We investigate the correlation between the inner- and the outer-part behaviors associated with the avoided resonance crossings (ARCs), and analyze the results in terms of a trade-off between the relative difference of self-energies and collective Lamb shifts. These results come from the conservation of the orthogonality in the total Hermitian quantum system.

Spectral and directional properties of elliptical quantum-dot microlasers

We have fabricated microdisk lasers of colloidal quantum dots in circular and elliptical forms with different aspect ratios. By characterizing the laser emission spectrum under optical pumping and through mode simulation calculations, we demonstrate that the elliptical resonators can display two sets of whispering-gallery modes that interact to varying degrees depending on the aspect ratio. This causes significant mode splitting in the emission spectra when the mode interaction is at maximum. We also performed angular-dependent laser emission measurements for characterizing the emission pattern of the microlasers. We found that the emission pattern becomes less isotropic and more directional as the boundary deviates further from circular symmetry. In addition, we demonstrate that the emission directional properties of these microlasers can be further tailored by coupling pairs of elliptical microcavities together in different manners, where the long or short elliptical axis interacts most strongly.

Behavior of three modes of decay channels and their self-energies of elliptic dielectric microcavity

The Lamb shift (self-energy) of an elliptic dielectric microcavity is studied. We show that the size of the Lamb shift, which is a small energy shift due to the system-environment coupling in the quantum regime, is dependent on the geometry of the boundary conditions. It shows a global transition depending on the eccentricity of the ellipsis. These transitions can be classified into three types of decay channels known as whispering-gallery modes, stable-bouncing-ball modes, and unstable-bouncing-ball modes. These modes are manifested through the Poincar\'{e} surface of section with the Husimi distribution function in classical phase space. It is found that the similarity (measured in Bhattacharyya distance) between the Husimi distributions below critical lines of two different modes increases as the difference of their self-energies decreases when the quality factors of the modes are on the same order of magnitude.

Energy shell structure in a dielectric elliptic microcavity.

An energy shell structure depending on eccentricity is analyzed in a dielectric elliptic microcavity. Through the analysis, it is explicated that the energy shell structure is governed by classical constant actions of periodic orbits. For clarification, the relation between dominances of the periodic orbits and bifurcation behaviors are obtained and the length spectra based on eigenvalues computed by a numerical method are compared with the exact lengths of the periodic orbits obtained by analytic calculations. By matching effective wave numbers obtained from the periodic orbit lengths to exact wave numbers of stationary states in closed and open cavities, we find deviations provoked from the openness. We show that these deviations are caused by additional phase factors in the Einstein-Brillouin-Keller quantization.

电注入椭圆微腔半导体激光器热特性分析

电注入椭圆微腔半导体激光器热特性分析

Efficient analysis of mode profiles in elliptical microcavity using dynamic-thermal electron-quantum medium FDTD method

The dynamic-thermal electron-quantum medium finite-difference time-domain (DTEQM-FDTD) method is used for efficient analysis of mode profile in elliptical microcavity. The resonance peak of the elliptical microcavity is studied by varying the length ratio. It is observed that at some length ratios, cavity mode is excited instead of whispering gallery mode. This depicts that mode profiles are length ratio dependent. Through the implementation of the DTEQM-FDTD on graphic processing unit (GPU), the simulation time is reduced by 300 times as compared to the CPU. This leads to an efficient optimization approach to design microcavity lasers for wide range of applications in photonic integrated circuits.

Experimental measurement of gain and loss in a microcavity laser

In a microcavity laser, it is known that the quality factor obtained experimentally is much less than the one obtained numerically. This quality factor degradation in experiment is caused by various effects, such as absorption, surface roughness, flatness of the ridge boundary, and curvature. To understand the quality-factor degradation we obtain the gain and the internal loss coefficient in an elliptic microcavity laser. In the experiment, we take a triangular orbit. To confirm the triangular orbit, we measure the mode spacing and estimate the emission direction by including the Fresnel filtering. By using the Fourier transform analysis, we obtain the loss and gain coefficients because the triangular orbit can be regarded as a Fabry-Perot resonator due to the incidence angle. The obtained loss for our microcavity laser is larger than the one caused by material absorption, which is due to environmental losses, such as surface roughness and flatness of the ridge boundary.

Light propagation properties of two-dimensional photonic crystal channel filters with elliptical micro-cavities

Light propagation through a channel filter based on two-dimensional photonic crystals with elliptical-rod defects is studied by the finite-difference time-domain method. Shape alteration of the defects from the usual circle to an ellipse offers a powerful approach to engineer the resonant frequency of channel filters. It is found that the resonant frequency can be flexibly adjusted by just changing the orientation angle of the elliptical defects. The sensitivity of the resonant wavelength to the alteration of the oval rods' shape is also studied. This kind of multi-channel filter is very suitable for systems requiring a large number of output channel filters.

Light Energy Extraction From the Minor Surface Arc of an Electrically Pumped Elliptical Microcavity Laser

In this paper, the efficiency of extracting light energy from the minor surface arc of the elliptical microcavity laser is investigated for the first time using the dynamic thermal electron quantum medium finite-difference time-domain model. Light energy is extracted from the minor surface arc of the elliptical microcavity to a perpendicular waveguide. It is deduced from the field distribution that extraction efficiency of the TM polarization is higher due to wider transverse field profile. Optimum light energy is extracted when the waveguide is 0.342 ?m away from the edge of the elliptical minor arc. Higher extraction efficiency is also obtained when the waveguide index is lower than the microcavity index. It is believed that this method of extracting light energy allows for smaller device size with higher power output for building photonic integrated circuit.

Enhancement of light energy extraction from elliptical microcavity using external magnetic field for switching applications

In this letter, the extraction efficiency of light energy from an elliptically shaped microcavity laser is enhanced with external magnetic field. The magnetic field causes electrons to accumulate on the minor arc edge of the elliptical microcavity due to Lorentz force. As a result, the field amplitude at the minor arc edge is higher, and this improves light energy tunneling mechanism from the edge. The extraction efficiency from the microcavity increases by more than 30% after the application of magnetic field. Alternating the direction of the magnetic field allows the elliptical microcavity to function as a switching device.