Anisotropic Microcavity Research Articles

Trajectory tracing dynamics in anisotropic microcavities

Ray-wave correspondence has proven a powerful tool in mesoscopic optics, in particular in the description of deformed microdisc cavities with a versatile application potential ranging from microlasers to sensors. New material classes such as graphene-based systems have enriched the field by adding Dirac Fermion optics as well as anisotropic material properties as further system parameters. The trigonally warped dispersion relation in bilayer-graphene billiards generalizes the concept of birefringence and opens unconventional ways of trajectory control in the interplay of dispersion relation and the cavity geometry as we illustrate in this contribution.

Collective Excitations of Exciton-Polariton Condensates in a Synthetic Gauge Field.

Collective (elementary) excitations of quantum bosonic condensates, including condensates of exciton polaritons in semiconductor microcavities, are a sensitive probe of interparticle interactions. In anisotropic microcavities with momentum-dependent transverse-electric-transverse-magnetic splitting of the optical modes, the excitations' dispersions are predicted to be strongly anisotropic, which is a consequence of the synthetic magnetic gauge field of the cavity, as well as the interplay between different interaction strengths for polaritons in the singlet and triplet spin configurations. Here, by directly measuring the dispersion of the collective excitations in a high-density optically trapped exciton-polariton condensate, we observe excellent agreement with the theoretical predictions for spinor polariton excitations. We extract the interaction constants for polaritons of the same and opposite spin and map out the characteristic spin textures in an interacting spinor condensate of exciton polaritons.

Oscillating Motion of Exciton–Polaritons in Anisotropic Microcavities

Oscillations of the trajectory of exciton–polaritons propagating in the plane of an optical microcavity with integral quantum wells are studied. This effect is characteristic of systems with the splitting of spin states, and arises as a result of the mutual influence of the spin (polarization) degree of freedom and the translational motion of polaritons. The trajectory’s period of oscillation is determined by the splitting of the photon and exciton components of the polaritons.

Simulation method for study on outcoupling characteristics of stratified anisotropic OLEDs.

We derive explicit power dissipation functions for stratified anisotropic OLEDs based on a radiation model of dipole antennas inside anisotropic microcavity. The dipole field expressed by vector potential is expanded into plane waves whose coefficients are determined by scattering matrix method, and then an explicit expression is derived to calculate the energy flux through arbitrary interfaces. Taking advantage of the formulation, we can easily perform quantitative analysis on outcoupling characteristics of stratified anisotropic OLEDs, including outcoupling efficiency, normalized decay rate and angular emission profile. Simulations are carried out on a prototypic stratified OLED structure to verify the validity and capability of the proposed model. The dependencies of the outcoupling characteristics on various emission feature parameters, including dipole position, dipole orientation, and the intrinsic radiative quantum efficiency, are comprehensively evaluated and discussed. Results demonstrate that the optical anisotropy in different organic layers has nonnegligible influences on the far-field angular emission profile as well as outcoupling efficiency, and thereby highlight the necessity of our method. The proposed model can be expected to guide the optimal design of stratified anisotropic OLED devices, and help to solve the inverse outcoupling problem for determining the emission feature parameters.

Optically anisotropic media: New approaches to the dielectric function, singular axes, microcavity modes and Raman scattering intensities

magnified imageSix out of seven crystal systems are optically anisotropic and birefringent. We review recent insight that biaxial crystals generally exhibit four singular axes (or exceptional points) which can pairwise degenerate for special cases. Planar anisotropic microcavities are discussed as effectively biaxial systems and we predict exceptional points and demonstrate experimentally partially coalesced eigenstates. Also the general form of the dielectric function of anisotropic crystals based on individual dipole oscillators for phonon and electronic resonance is discussed. The impact of birefringence on Raman scattering intensities has been historically either ignored or modeled incorrectly. A recent theory for uniaxial and biaxial crystals explains experimental Raman scattering intensities for excitation off the principal directions without free parameters, allowing the unambiguous determination of the Raman tensor components. The above points are demonstrated and relevant in particular for the currently technologically important materials GaN, ZnO (uniaxial) and β‐Ga2O3 (biaxial). Formula for the Raman scattering intensity as a function of incoming and outgoing polarization and the Raman tensor viewed through birefringent crystal (calcite).magnified imageFormula for the Raman scattering intensity as a function of incoming and outgoing polarization and the Raman tensor viewed through birefringent crystal (calcite).

Intrinsic Polarization and Tunable Color of Electroluminescence from Organic Single Crystal-based Light-Emitting Devices.

A single crystal-based organic light-emitting device (OLED) with intrinsically polarized and color-tunable electroluminescence (EL) has been demonstrated without any subsequent treatment. The polarization ratio of 5:1 for the transversal-electric (TE) and transversal-magnetic (TM) polarization at the emission peak of 575 nm, and 4.7:1 for the TM to TE polarization at the emission peak of 635 nm, respectively, have been obtained. The emitting color is tunable between yellow, yellow-green and orange by changing the polarization angle. The polarized EL and the polarization-induced color tunability can be attributed to the anisotropic microcavity formed by the BP3T crystal with uniaxial alignment of the molecules.

Dipole radiation within one-dimensional anisotropic microcavities: a simulation method

We present a simulation method for light emitted in uniaxially anisotropic light-emitting thin film devices. The simulation is based on the radiation of dipole antennas inside a one-dimensional microcavity. Any layer in the microcaviy can be uniaxially anisotropic with an arbitrary orientation of the optical axis. A plane wave expansion for the field of an elementary dipole inside an anisotropic medium is derived from Maxwell's equations. We employ the scattering matrix method to calculate the emission by dipoles inside an anisotropic microcavity. The simulation method is applied to calculate the emission of dipole antennas in a number of cases: a dipole antenna in an infinite medium, emission into anisotropic slab waveguides and waveguides in liquid crystals. The dependency of the intensity and the polarization on the direction of emission is illustrated for a number of anisotropic microcavities.

Resonant Rayleigh scattering from an anisotropic organic single-crystal microcavity

Resonant Rayleigh scattering (RRS) is observed upon excitation of a microcavity containing a single crystal of the organic molecule anthracene. The RRS profile is obtained for a range of excitation energies and angles. In contrast to the circular profile observed for inorganic microcavities, the scattered light pattern is elliptical when projected normal to the sample surface. The profile shape provides a direct visual representation of the anisotropic microcavity polariton dispersion characteristic of organic crystals.

Renormalized dispersion of elementary excitations in spinor polariton condensates

We analyse the polarization of spinor polariton condensates and corresponding dispersions of elementary excitations . We have considered the effects of magnetic field induced splitting in circular polarizations and residual splitting in linear polarizations in the ground state provided by the cavity asymmetry. We show that anisotropic polariton–polariton interactions fully compensate the Zeeman splitting in circular polarizations below the critical magnetic field, thus leading to the spin-Meissner effect for the polariton condensates. We also analyzed the effect of polariton–polariton interactions on the stability of the gap in linear polarizations characteristic for anisotropic microcavities. It was shown that in realistic systems this gap increases with concentration of the particles, thus contributing to the stability of the pinning of linear polarization of photoemission in semiconductor microcavities for pump intensities above the stimulation threshold.

Secondary bifurcations and transverse standing-wave patterns in anisotropic microcavity lasers close to the first laser threshold

It is well known that in a laser--in the limit of an infinite extent of the transverse aperture--traveling tilted waves are excited at the laser threshold for positive detuning between the frequency of the gain maximum of the active medium and the cavity frequency [Phys. Rev. A 45, 8129 (1992)]. However, a transverse standing wave is unstable. In this paper, it is shown that in anisotropic lasers there can be a chain of secondary bifurcations very close to threshold, which stabilizes the standing wave and then destabilizes it again through a supercritical Hopf bifurcation. The parameter dependence of these bifurcations is discussed. The investigations are motivated by interest in pattern formation in vertical-cavity surface-emitting lasers in which the rotational symmetry is broken due to the dependence of the reflectance of the Bragg reflectors on the polarization vector of the field. The applicability of the results to other class-B lasers is discussed.