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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.

We have studied optical properties of site-controlled GaN nanocolumns (NCs) with an insertion of InGaN QW grown on the micro-cone patterned substrate. Time-resolved photoluminescence spectroscopy reveals two bands emission. Comparison of these spectra with the emission of a separate nanocolumn, recorded by μ-CL with high spatial resolution, allows us to ascribe the higher energy band to emission from the InGaN QW situated on the top of NCs, while the lower-energy band originates from the QW in the rest area. By the modeling of the decay times and amplitudes of PL decay curves, we have exhibited a significant enhancement of signal from the QW inside the NCs. Investigation of the NCs as a Fabry-Perot cavity at eigenfrequencies around the optical transitions has revealed that the cavity modes can provide significant enhancement of the emission from the inserted QW owing to the Purcell factor.

We report on single photon emitters for the green-yellow spectral range, which comprise a CdSe/ZnSe quantum dot placed inside a semiconductor tapered nanocolumn acting as a multimode nanoantenna. Despite the presence of many optical modes inside, such a nanoantenna is able to collect the quantum dot radiation and ensure its effective output. We demonstrate periodic arrays of such emitters, which are fabricated by focused ion beam etching from a II-VI/III-V heterostructure grown using molecular beam epitaxy. With non-resonant optical pumping, the average count rate of emitted single photons exceeds 5 MHz with the second-order correlation function g(2)(0) = 0.25 at 220 K. Such single photon emitters are promising for secure free space optical communication lines.

We show that the stacks of two-dimensional semiconductor crystals with the chiral packing exhibit optical activity and circular dichroism. We develop a microscopic theory of these phenomena in the spectral range of exciton transitions which takes into account the spin-dependent hopping of excitons between the layers in the stack and the interlayer coupling of excitons via electromagnetic field. For the stacks of realistic two-dimensional semiconductors such as transition metal dichalcogenides, we calculate the rotation and ellipticity angles of radiation transmitted through such structures. The angles are resonantly enhanced at the frequencies of both bright and dark exciton modes in the stack. We also study the photoluminescence of chiral stacks and show that it is circularly polarized., 10 pages, 6 figures

We propose to use 2D monolayers possessing optical gaps and high exciton oscillator strength as an element of one-dimensional resonant photonic crystals. We demonstrate that such systems are promising for the creation of effective and compact delay units. In transition-metal-dichalcogenide-based structures where the frequencies of Bragg and exciton resonances are close, a propagating short pulse can be slowed down by few picoseconds while pulse intensity decreases only 2–5 times. This is realized at the frequency of the “slow” mode situated within the stopband. The pulse retardation and attenuation can be controlled by detuning the Bragg frequency from the exciton resonance frequency.

Features of the propagation and slowing down of short light pulses (duration of ~0.1–2 ps) in one-dimensional resonant photonic crystals with various types of unit cells containing several quantum wells are discussed. It is established that the use of structures with a complex unit cell makes it possible to reduce the group velocity of exciton-polaritons along with the conservation of the width of the transparency window. The calculations show the possibility of the slowing down of a light pulse by a factor of 50 as compared to a pulse propagating in vacuum. The predicted delay time of the pulse is 2 ps at a damping of only 3–5 times.

We measure low-temperature micro-photoluminescence spectra along a MoS 2 nanotube, which exhibit the peaks of the optical whispering gallery modes below the exciton resonance. The energy fluctuation and width of these peaks are determined by the changes of the nanotube wall thickness and propagation of the optical modes along the nanotube axis, respectively. We demonstrate the potential of the high-quality nanotubes for realization of the strong coupling between exciton and optical modes when the Rabi splitting can reach 400 meV. We show how the formation of exciton-polaritons in such structures will be manifested in the micro-photoluminescence spectra and analyze the conditions needed to realize that.

This paper analyzes current trends in fabrication of III-nitride microresonators exploiting whispering gallery modes. Novel cup-cavities are proposed and their fabrication from GaN and InN by molec ...

InN optical cavities supporting low-order whispering-gallery modes up to room temperature are formed by molecular-beam epitaxy on patterned substrates. The observed switching of the mode type with increasing temperature is explained in terms of changes in the optical parameters due to a shift of the absorption edge and modification of its shape. Modeling taking into account a variation in the refractive index reproduces the typical distributions of the electromagnetic-field intensity in the cavities.

We study the optical properties of MoS2 nanotubes (NTs) with walls comprising dozens of monolayers. We reveal strong peaks in micro-photoluminescence (l-PL) spectra when detecting the light polarized along the NT axis. We develop a model describing the optical properties of the nanotubes acting as optical resonators which support the quantization of whispering gallery modes inside the NT wall. The experimental observation of the resonances in l-PL allows one to use them as a contactless method of the estimation of the wall width. Our findings open a way to use such NTs as polarization-sensitive components of nanophotonic devices.

Rapidly developing nanophotonics needs microresonators for different spectral ranges, formed by chip-compatible technologies. In addition, the tunable ones are much in demand. Here, we present site-controlled III-nitride monocrystal cup-cavities grown by molecular beam epitaxy. The cup-cavities can operate from ultraviolet to near-infrared, supporting quasi whispering gallery modes up to room temperature. Besides, their energies are identical in large ripened crystals. In these cavities, the refractive index variation near an absorption edge causes the remarkable effect of mode switching, which is accompanied by the spatial redistribution of electric field intensity with concentration of light into a subwavelength volume. Our results shed light on the mode behavior in semiconductor cavities and open the way for single-growth-run manufacturing the devices comprising an active region and a cavity with tunable mode frequencies. Funding Agencies|Russian Science Foundation [14-22-00107]; Swedish Research Council (VR); Swedish Energy Agency

We report on theoretical studies of short optical pulse propagation through resonant photonic crystals (RPCs) based on conventional II-VI quantum wells (QWs) and van-der-Waals (vdW) Bragg heterostructures composed of extreme-2D monolayers. The parameters needed for modelling were determined by fitting of the experimental reflectance spectra. The delay of the transmitted picosecond optical pulses is predicted to be larger in vdW structures than in the structures with QWs due to the higher radiative width of the exciton resonance. Moreover, in the vdW RPCs, the pulse shape undergoes smaller modification owing to the almost linear dispersion of the "slow" mode. High-quality extreme-2D monolayers will allow for even stronger delays without distortion and small intensity decrease, needed for nanophotonics applications.

We present original types of III-nitride monocrystal microresonators with an inserted active quantum-sized region. Modelling of microresonator's modes allows us to select right parameters of a polarized quantum well (width, composition) in the way that excitation of its optical transitions would be selectively amplified by interaction with the resonator modes. Adjustment of a GaN nanocolumn resonator to an InGaN quantum well is performed.

InN optical resonators, which can support whispering-gallery modes of low orders up to room temperature, were made by MBE on patterned substrates. The observed effect of mode switching with a temperature rise was ascribed to the change of optical parameters induced by the shift of an absorption edge and modification of its shape. The results of modelling taking into account variation of refraction index reproduce typical distribution of the intensity of electromagnetic field within the resonators.