Grating couplers are widely used to couple waveguide modes with the far field. Their usefulness is determined not only by energy efficiency but also by additional supported functionality. In this paper, we demonstrate a plasmonic grating on a silicon nitride slab waveguide that couples both TE and TM waveguide modes with circularly polarized light in the far field. Specifically, we experimentally confirmed that circularly polarized light excites TE and TM modes propagating in opposite directions, and the direction is controlled by the handedness. The routing efficiency for normally incident light reaches up to 95%. The same structure operates in the outcoupling regime as well, demonstrating up to 97% degree of circular polarization, where the handedness is determined by the polarization and propagation direction of outcoupled modes. Our results pave the way for the realization of polarization-division multiplexers and demultiplexers, integrated circular polarization emitters, as well as detectors of the polarization state of the incident optical field.

The temporal behavior of the lower polariton (LP) distribution in the reciprocal space, n(LP)(k), and formation of long-range spatial coherence are investigated in a nonequilibrium incoherent LP fluid generated resonantly with picosecond optical pulses at 2 K in a high-Q planar GaAs/AlAs microcavity with 12 InGaAs quantum wells. The dynamics of n(LP)(k) is found to be independent of excitation density and well described within the framework of linear Schr & ouml;dinger equations taking into account random potential disorder, delta E-LP, and finite lifetime of LPs, up to LP density n(LP)(t=0)=7x10(10)cm(-2) (3.5 orders of magnitude greater than the threshold density of Bose-Einstein condensation for LPs). This is explained by the smallness of the ratios of LP interaction energy to both the mean kinetic energy and potential disorder. The contribution of interparticle interaction to the formation of spatial coherence in the LP fluid is insignificant at E-int <<delta E-LP, but becomes noticeable already at E-int approximate to 0.2 delta E-LP, despite the fact that its effect on the k distribution of LPs remains insignificant. Coherence length L(c )in LP fluid with n(LP)(t=0)=2 and 7x1010cm-2 in the region with delta E-LP=0.15 meV at t=160 ps increases to 4.1 and 5.3 mu m, respectively, whereas in an incoherent Bose gas with the same n(LP)(k) it is equal to 3.6 mu m.

Plasmonic metasurfaces form a convenient platform for light manipulation at the nanoscale due to their specific localized surface plasmons. Even despite high intrinsic Joule losses, plasmonic nanoparticles are very effective for light manipulation. Here, we show the lattice of plasmonic nanoparticles onto a dielectric waveguide that efficiently couples oppositely propagating guided modes to circularly polarized light beams of different handedness. We demonstrate 80% degree of circular polarization for the out-coupled emission of GaAs-waveguide-embedded quantum dots. The results allow us to consider the lattice as a circular-polarization-controlled grating coupler and make this structure prospective for further implementation as an efficient coupling interface for integrated devices.

In this work, we present new experimental evidence of a nonclassical behavior of a multimode Fabry–Perot (FP) semiconductor laser by the measurements of intensity correlation functions. Due to the multimode quantum state occurrence, instead of expected correlations between the intensities of the laser modes (a semiclassical theory), their anticorrelations were revealed.

The excitation of exciton polariton spatial oscillations in coupled symmetric potential traps in GaAs/AlAs microcavities resonantly pumped by coherent and incoherent pulsed picosecond optical beams with asymmetric angular distribution has been studied. It has been found that the violation of the angular symmetry of exciting pulses, as well as the violation of their spatial symmetry, can be used to excite a mixed state of the symmetric and asymmetric modes in a coupled potential trap. With uniform resonant excitation of traps at an optimal angles to the normal to the microcavity, light pulses generate a state with a mode phase difference of π/2 and a maximal plane wavevector. It has been shown that the dynamics of the polariton system is well described by the Schrödinger equation taking into account the finite polariton lifetime and disorder potential in the barrier.

All-optical switching of the polarization of exciton polaritons is studied using a picosecond acoustic perturbation of the exciton resonance in high -Q planar GaAs/AlAs microcavities. An irreversible switch-ing of the degree of circular polarization from 22% up to 82% is realized in a microcavity pumped by a laser with a photon energy slightly exceeding the lower polariton resonance. The polarization switch is performed by a short-term, about 30-ps-long, blueshift of the exciton energy of (In, Ga)As quantum wells in the cavity active layer by a 10-ps strain pulse generated in the GaAs substrate by a violet femtosecond laser pulse and injected into the microcavity. The proposed all-optical control of light polarization using acoustic modulation of a polariton resonance opens the way for fast and easily tunable optical polarization switches.

A spiral phase plate with a topological charge of 1 is fabricated via 3D femtosecond laser submicron lithography. An optical scheme based on a Michelson interferometer is developed and assembled to check the vortex properties of a generated laser beam. Optical measurements confirm that the spiral phase plate generates an optical laser vortex with a normalized orbital angular momentum of | m | = 1. A technology for fabricating and testing spiral phase plates that transmit the required orbital angular momentum to the laser field is developed.

Nonequilibrium transitions are investigated in a plane exciton-polariton system with complex acousto-optical excitation: stationary resonant optical excitation of polaritons along the normal to the surface of the resonator and picosecond strain pulses causing reversible exciton energy perturbations. It is shown that acoustic pulses can be used for ultrafast switching of the optical response of a bistable polariton system. Switching is experimentally implemented in a high-Q GaAs microcavity.

In this work, temporal correlations of radiation intensities of a multimode Fabry-Perot (FP) semiconductor laser are studied. Second- and third-order intensity correlation functions are measured both for the multimode FP laser and a pulsed Ti: Sapphire (TiSp) laser. Triple correlators of the latter demonstrate an ordinary product of double correlators (the classic case). The behavior of the multimode laser is more complex and can indicate the quantum nature of optical field correlations. We follow a specific phenomenological formula for calculation of the triple temporal correlator.

We investigate the temporal correlations of radiation intensities of a multimode Fabry–Pérot semiconductor laser. Strong intensity correlations with a fixed phase shift between different longitudinal modes of the laser are revealed. The second g(2) and third g(3) order intensity correlation functions are studied to clear the character of the intermodal coupling.

In the reported experiment, a picosecond strain pulse induces a sharp transition between the steady states in a bistable cavity-polariton system. The strain pulse of 10-ps duration, generated in the GaAs substrate and injected into a high-$Q$ GaAs/AlAs microcavity, modulates the exciton resonance energies of the embedded quantum wells and correspondingly of the polariton resonances. When the microcavity is pumped by a laser with the photon energy slightly above the lower-polariton resonance, the strain-induced energy shift triggers the irreversible switching of the bistable polariton system from the lower to the upper state. This transition is accompanied by an instant increase of the optical emission from the microcavity by more than an order of magnitude.

AbstractThe evolution of the spatial coherence and the polarization has been studied in a freely decaying polariton condensate that is resonantly excited by linearly polarized picosecond laser pulses at the lower and upper sublevels of the lower polariton branch in a high-Q GaAs-based microcavity with a reduced lateral symmetry without excitation of the exciton reservoir. It is found that the condensate inherits the coherence of the exciting laser pulse at both sublevels in a wide range of excitation densities and retains it for several dozen picoseconds. The linear polarization of the photoexcited condensate is retained only in the condensate at the lower sublevel. The linearly polarized condensate excited at the upper sublevel loses its stability at the excitation densities higher a threshold value: it enters a regime of internal Josephson oscillations with strongly oscillating circular and diagonal linear degrees of polarization. The polariton–polariton interaction leads to the nonlinear Josephson effects at high condensate densities. All the effects are well described in terms of the spinor Gross–Pitaevskii equations. The cause of the polarization instability of the condensate is shown to be the spin anisotropy of the polariton–polariton interaction.

We address dynamics of a low polariton (LP) system excited resonantly in a wide range of wave vectors by converging 2.5-ps-long Gaussian pulses. The spatial coherence in an LP system excited by incoherent light is found to form very slowly in the absence of an exciton reservoir, the coherence length at the delay time of 250 ps and T=2 K being less than 2.5 μm. The LP fluid excited by coherent linearly polarized pulses does not lose the inherited high spatial coherence and polarization and demonstrates dynamic compression to a condensate state at the LP branch bottom. In the LP fluid excited by elliptically polarized pulses the components with opposite circular polarizations are compressed almost independently of each other.

It is found that exciton-polariton systems resonantly excited in GaAs semiconductor microcavities by coherent picosecond laser pulses inherit the high coherence of the laser beam and retain it for their lifetime (>100 ps), while the coherence-formation time in polariton systems resonantly excited by incoherent pulses without excitation of the exciton reservoir exceeds 200 ps.

The dynamics of a pure low polariton (LP) system created by resonant broadband excitation in a wide range of wave vectors was investigated in a high-Q GaAs-based microcavity. The LP system is shown to inherit the high spatial coherence from the laser pulse and does not lose it during decay. As a result, its dynamics is well controlled by the spatial and momentum distributions of photons in the exciting pulse and described by the Gross-Pitaevskii equations. In particular, the purely dynamic formation of the highly populated coherent LP state was implemented at the LP band bottom in the cavity excited in a large spot by converging ps-long Gaussian laser pulses when the active region of the cavity is in front of its waist. The formed state is found to persist for several picoseconds until the LP-LP repulsion leads to the creation of high-energy LPs dissipating from the ground state with high velocities.

The possibility of the dynamic compression of a polariton system in a planar microcavity after the end of a resonant pump pulse with the formation of the ground state of a condensate on the bottom of the polariton band has been studied. The studies of dynamics of a resonantly excited polariton gas in the mean field approximation have shown that such condensate state can be formed purely dynamically at excitation by coherent convergent Gaussian light pulses with a large aperture if the active region of the cavity is ahead of the waist of the Gaussian beam. The spatial distribution of polaritons in the formed high-density condensate has sharp edges and large jumps of the violet shift and quasimomentum on these edges prevent its monotonic expansion despite the repulsive interaction between polaritons. For this reason, the further evolution of the condensate is primarily due to the discharge of particles from its boundary and is accompanied by a decrease rather than an increase in the size of the high-density region at the initial stage. Thus, the self-sustained regime of the dynamic compression of the polariton condensate can be maintained for a relatively long time.

The temporal dynamics of a spinor exciton-polariton condensate in a high-quality anisotropic GaAs microcavity under pulsed resonant excitation with light possessing a nonzero orbital angular momentum is investigated. The phenomenon of spatial separation of the spin components of the polariton condensate upon pumping with a coherent superposition of two beams with opposite circular polarizations and orbital angular momenta is observed. The key factors for the observation of this effect are the lateral anisotropy of the microcavity that causes a splitting between the linear components of the polariton ground state and the occurrence of opposite orbital angular momenta for the two spin components of the condensate. The experimental results are in qualitative agreement with the theoretical model of the phenomenon developed in JETP Lett. 104, 827 (2016).