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We theoretically demonstrate a new regime of the formation of ultrashort optical solitons in spherical silica microresonators with whispering gallery modes.The solitons are driven by a coherent CW pump at the frequency in the range of normal dispersion, and the energy is transferred from this pump to the solitons via two channels: Raman amplification and the inverse Cherenkov effect. We discuss three different regimes of soliton propagation and we also show that these Raman solitons can be controlled by weak coherent CW signals.

The paper provides an analytical and numerical investigation of the dynamics of a one-dimensional chain of coupled optical resonators with conservative cubic nonlinearity and the gain saturated by nonlinear losses. The linear dependency of the resonator eigenfrequencies on their indexes makes it possible to use Wannier-Stark states as lasing modes. Numerical simulations have shown that the dependency of the resonant frequencies on the light intensity strongly affects the stability of Wannier-Stark states. To explain the observed destabilization of monochromatic lasing based on Wannier-Stark states a simple perturbation theory has been developed and compared with the data obtained in the numerical simulations.

In this work, we explore the potential of spin-based integrated devices using polariton waveguides that form codirectional couplers. For suitable coupler parameters, a transfer of condensates between the arms of the coupler, occurs leading to the observation of Josephson-like oscillations. The ability to tune the periodicity of these oscillations opens the way to the design of polaritonic circuits in which the directionality of the signal towards the output terminals can be controlled. We also investigate the response of the devices to linearly polarized excitation, delving into the dynamics of linear polarization at the output terminals of long couplers, providing valuable insights into the potential applications of spin-based polariton devices, including polariton switches and logic gates with efficient operation. Our results are supported by numerical simulations based on generalized Gross-Pitaevskii equation describing the dynamics of coherent polaritons in spatially non-uniform system. We show, how the coupling and the controllable spin degree of freedom in polariton couplers opens avenues for innovative optical architectures and functionalities., Comment: 21 pages, 7 figures

We present and experimentally study the effects of the photonic spin-orbit coupling on real space propagetion of polariton wavepackets in planar semiconductor microcavities and polaritonic analogs of graphene. In particular, we demonstrate the appearance of an analog Zitterbewegung effect, a term which translates as 'trembling motion' in english, which was originally proposed for relativistic Dirac electrons and consists of the oscillations of the center of mass of a wavepacket in the direction perpendicular to its propagation. For a planar microcavity we observe regular Zitterbewegung oscillations whose amplitude and period depend on the wavevector of the polaritons. We then extend these results to a honeycomb lattice of coupled microcavity resonators. Compared to the planar cavity such lattices are inherently more tuneable and versatile, allowing simulation of the Hamilitonians of a wide range of important physical systems. We observe an oscillation pattern related to the presence of the spin-split Dirac cones in the dispersion. In both cases the experimentally observed oscillations are in good agreement with theoretical modelling and independently measured bandstructure parameters, providing strong evidence for the observation of Zitterbewegung.

For waveguides with two separate regions of anomalous dispersion, it is possible to create a quasi-stable two-color solitary wave. In this paper we consider how those waves interact with dispersive radiation, both generation of Cherenkov radiation and scattering of incident dispersive waves. We derive the analytic resonance conditions and verify them through numeric experiments. We also report incident radiation driving the internal oscillations of the soliton during the scattering process in case of an intense incident radiation. We generalize the resonance conditions for the case of an oscillating soliton and demonstrate how one can use the scattering process to probe and excite an internal mode of two-color soliton molecules., Comment: 9 pages, 7 figures

We study the response of an optical system with the Kerr nonlinearity demonstrating Bloch oscillations to a periodic train of coherent pulses. It has been found out that the intensity of the field excited in the system by pulses resonantly depends on the train period. It is demonstrated numerically and analytically that the response of the system is stronger when the period of the driving pulses is commensurate with the period of the Bloch oscillations. Moreover, large enough pulses are capable to induce the instabilities which eventually lead to onset of chaotic Bloch oscillations of the wave-function envelope bouncing both in time and space. The analysis reveals that these instabilities are associated with period-doubling bifurcations. A cascade of such bifurcations with increase of the pulses amplitude triggers the chaotic behaviour.

We study theoretically interaction of optically-pumped excitons with acoustic waves in planar semiconductor nanostructures in the strongly nonlinear regime. We start with the multimode optomechanical lasing regime for optical pump frequency {above} the exciton resonance and demonstrate broadband chaotic-like lasing spectra. We also predict formation of propagating optomechanical domain walls driven by optomechanical nonlinearity for the optical pump {below} the exciton resonance. Stability conditions for the domain walls are examined analytically and are in agreement with direct numerical simulations. Our results apply to nonlinear sound propagation in the arrays of quantum wells or in the plane of Bragg semiconductor microcavities hosting excitonic polaritons., Comment: 8 pages, 12 figures

We report on the linear polarization of polariton condensates in a codirectional coupler that allows evanescent coupling between adjacent waveguides. We observe polarization-dependent intensity oscillations in the output terminal of the coupler that we identify as the mode beating between the linear-polarized eigenmodes.

Bound states in the continuum (BICs) are non-radiating solutions of the wave equation with a spectrum embedded in the continuum of propagating waves of the surrounding space. The complete decoupling of BICs from the radiation continuum makes their excitation impossible from the far-field. Here, we develop a general theory of parametric excitation of BICs in nonlinear systems with Kerr-type nonlinearity via spontaneous symmetry breaking, which results in a coupling of a BIC and a bright mode of the system. Using the temporal coupled-mode theory and perturbation analysis, we found the threshold intensity for excitation of a BIC and study the possible stable and unstable solutions depending on the pump intensity and frequency detuning between the pump and BIC. We revealed that at some parameters of the pump beam, there are no stable solutions and the BIC can be used for frequency comb generation. Our findings can be very promising for use in nonlinear photonic devices and all-optical networks., Comment: 17 pages, 9 figures

Ultrafast nonlinear photonics enables a host of applications in advanced on-chip spectroscopy and information processing. These rely on a strong intensity dependent (nonlinear) refractive index capable of modulating optical pulses on sub-picosecond timescales and on length scales suitable for integrated photonics. Currently there is no platform that can provide this for the UV spectral range where broadband spectra generated by nonlinear modulation can pave the way to new on-chip ultrafast (bio-) chemical spectroscopy devices. We demonstrate the giant nonlinearity of UV hybrid light-matter states (exciton-polaritons) up to room temperature in an AlInGaN waveguide. We experimentally measure ultrafast nonlinear spectral broadening of UV pulses in a compact 100 $\mu$m long device and deduce a nonlinearity 1000 times that in common UV nonlinear materials and comparable to non-UV polariton devices. Our demonstration promises to underpin a new generation of integrated UV nonlinear light sources for advanced spectroscopy and measurement.

We study resonant radiation generated by bound solitons in a twin-core fiber near zero-dispersion wavelength, in the presence of higher order dispersion terms. We propose a theoretical description of dispersive wave generation mechanism and derive resonance conditions. The presence of third order dispersion term leads to generation of polychromatic dispersive radiation and transition from the regime of center of mass oscillations to the regime of amplitude oscillations. Such a transition is not reproduced in the case of symmetric fourth order dispersion., Comment: 7 pages, 4 figures

The scattering of weak dispersive waves (DW) on several equally spaced temporal solitons is studied. It is shown by systematic numerical simulations that the reflection of the DWs from the soliton trains strongly depends on the distance between the solitons. The dependence of the reflection and transmission coefficients on the inter-soliton distance and the frequency of the incident waves is studied in detail, revealing fascinating quasi-periodic behavior. The analogy between the observed nonlinear phenomena in temporal domain and usual Fabry-Perot and Bragg resonators is discussed., Comment: 4 pages, 4 figures

The effect of mutual interaction between dark solitons and dispersive waves is investigated numerically and analytically. The condition of the resonant scattering of dispersive waves on dark solitons is derived and compared against the results of numerical simulations. It is shown that the interaction with intense dispersive waves affects the dynamics of the soltons strongly changing their frequencies and accelerating or decelerating the solitons. It is also demonstrated that two dark solitons can form a cavity for dispersive weaves bouncing between the two dark solitons. The differences of the resonant scattering of the dispersive waves on the dark and bright solitons are discussed. In particular we demonstrate that two dark solitons and dispersive wave bouncing in between them create solitonic cavity with convex "mirrors" unlike the concave "mirror" in case of the bright solitons., Comment: 5 pages, 6 figures

We demonstrate radiation mechanism exhibited by higher order soliton. In a course of its evolution higher order soliton emits polychromatic radiation resulting in appearance of multipeak frequency comb like spectral band. The shape and spectral position of this band can be effectively controlled by the relative strength of the third order dispersion. An analytical description is completely corroborated by numerical simulations. An analogy between this radiation and the radiation of moving charges is presented. For longer pulses the described effect persists also under the action of higher order perturbations such as Raman and self-steepening.

The influence of Raman scattering and higher order dispersions on solitons and frequency comb generation in silica microring resonators is investigated. The Raman effect introduces a threshold value in the resonator quality factor above which the frequency locked solitons can not exist and, instead, a rich dynamics characterized by generation of self-frequency shift- ing solitons and dispersive waves is observed. A mechanism of broadening of the Cherenkov radiation through Hopf instability of the frequency locked solitons is also reported., Comment: 12 pages, 10 figures

We study the formation of gap solitons in the presence of parametric pump. It is shown that parametric pump can stabilize stationary solitons continuously emitting dispersive waves. The resonant interactions of the radiation and the solitons are studied and it is shown that the solitons can be effectively controlled by the radiation. In particular it is shown that the solitons can collide or to get pinned to inhomogeneities due to the interactions mediated by the resonant radiation.

We examine the existence and stability of discrete spatial solitons in coupled nonlinear lasing cavities (waveguide resonators), addressing the case of active defocusing media, where the gain exceeds damping in the low-amplitude limit. A new family of stable localized structures is found: these are bright and grey cavity solitons representing the connections between homogeneous and inhomogeneous states. Solitons of this type can be controlled by the discrete diffraction and are stable when the bistability of homogenous states is absent., Comment: 3 pages, 3 figures, accepted to Optics Letters (October 2012)