Bloch oscillations in plasmonic waveguide arrays.

The combination of modern nanofabrication techniques and advanced computational tools has opened unprecedented opportunities to mold the flow of light. In particular, discrete photonic structures can be designed such that the resulting light dynamics mimics quantum mechanical condensed matter phenomena. By mapping the time-dependent probability distribution of an electronic wave packet to the spatial light intensity distribution in the corresponding photonic structure, the quantum mechanical evolution can be visualized directly in a coherent, yet classical wave environment. On the basis of this approach, several groups have recently observed discrete diffraction, Bloch oscillations and Zener tunnelling in different dielectric structures. Here we report the experimental observation of discrete diffraction and Bloch oscillations of surface plasmon polaritons in evanescently coupled plasmonic waveguide arrays. The effective external potential is tailored by introducing an appropriate transverse index gradient during nanofabrication of the arrays. Our experimental results are in excellent agreement with numerical calculations.

The hybrid concept for realization of an ultra-thin plasmonic metamaterial antireflection coating and plasmonic rainbow.

We report on the design, simulation, fabrication, and characterization of a novel two layer anti-reflective coating (ARC) based on a plasmonic metamaterial and a dielectric. Promoted by the strong material dispersion of the plasmonic metamaterial, our novel concept (called hybrid ARC) combines two possible arrangements for layers in an anti-reflection coating into a single structure; albeit at two different wavelengths. This, however, causes a broadband reduction of reflection that is less sensitive against oblique incidence when compared to traditional antireflective coatings. Furthermore, we show that the current metamaterial on a metal reflector can be used for the visualization of different coloration such as plasmonic rainbow despite its sub-wavelength thickness.

Resonant metasurfaces at oblique incidence: interplay of order and disorder.

Understanding the impact of order and disorder is of fundamental importance to perceive and to appreciate the functionality of modern photonic metasurfaces. Metasurfaces with disordered and amorphous inner arrangements promise to mitigate problems that arise for their counterparts with strictly periodic lattices of elementary unit cells such as, e.g., spatial dispersion, and allows the use of fabrication techniques that are suitable for large scale and cheap fabrication of metasurfaces. In this study, we analytically, numerically and experimentally investigate metasurfaces with different lattice arrangements and uncover the influence of lattice disorder on their electromagnetic properties. The considered metasurfaces are composed of metal-dielectric-metal elements that sustain both electric and magnetic resonances. Emphasis is placed on understanding the effect of the transition of the lattice symmetry from a periodic to an amorphous state and on studying oblique illumination. For this scenario, we develop a powerful analytical model that yields, for the first time, an adequate description of the scattering properties of amorphous metasurfaces, paving the way for their integration into future applications.

Nonlinear all-photonic-crystal Fabry-Perot resonator with angle-independent bistability.

We propose a nonlinear all-photonic-crystal (PhC) Fabry-Perot cavity tuned to the subdiffractive regime of the interior PhC, and we study angular-resolved nonlinear propagation of monochromatic plane wave excitations. With rigorous numerical simulations, we show that, for sufficiently large negative pump detunings and a focusing nonlinearity, the transmitted field has a bistable dependence on the pump field. Moreover, we reveal that, in contrast to a homogeneous resonator for different inclinations, the hysteresis curve is virtually unchanged for a fairly wide angular range. This may pave the way for obtaining novel kinds of nonlinear localized solutions in driven nonlinear resonators.

Subdiffractive all-photonic crystal Fabry-Perot resonators.

We propose subdiffractive all-photonic crystal Fabry-Perot resonators and study light propagation in this novel system. The photonic crystal in the cavity is tuned to the subdiffractive regime and the mirrors to the center of the photonic bandgap. We show that such all-photonic crystal resonators exhibit a broadband angular transmission at a fixed frequency and a high Q factor, resulting in a drastic reduction of the power threshold for all-optical switching.

Direct near-field optical imaging of higher order plasmonic resonances.

We map in real space and by purely optical means near-field optical information of localized surface plasmon polariton (LSPP) resonances excited in nanoscopic particles. We demonstrate that careful polarization control enables apertureless scanning near-field optical microscopy (aSNOM) to image dipolar and quadrupolar LSPPs of the bare sample with high fidelity in both amplitude and phase. This establishes a routine method for in situ optical microscopy of plasmonic and other resonant structures under ambient conditions.

Amplitude- and phase-resolved optical near fields of split-ring-resonator-based metamaterials.

We investigate the local optical response of split-ring resonator-(SRR)-based metamaterials with an apertureless scanning near-field optical microscope. By mapping the near fields of suitably resonant micrometer-sized SRRs in the near-infrared spectral region with an uncoated silicon tip, we obtain a spatial resolution of better than lambda/50. The experimental results confirm numerical predictions of the near-field excitations of SRRs. Combining experimental near-field optical studies with near- and far-field optical simulations provides a detailed understanding of resonance mechanisms in subwavelength structures and will facilitate an efficient approach to improved designs.

Self-collimation of light in three-dimensional photonic crystals.

We calculate three-dimensional (3D) dispersion relations of woodpile and inverse opal photonic crystals. Inspecting the iso-frequency surfaces of the four lowest-order bands at appropriate frequencies we identify regions where self-collimation of light may be expected. These predictions are verified by means of finite-difference time-domain calculations both for high- and low-index photonic crystals.

Large-mode-area Nd-doped single-transversemode dual-wavelength microstructure fiber laser.

A novel design for a microstructure fiber (MSF) laser consisting of a large core and a single annulus of 5 air holes is described. The fiber design incorporates a silica core that was doped in the liquid phase with 1300 ppm Nd2O3. The light guiding losses in the structurally very simple MSF are approximately 0.7 dB/m. Single transverse mode emission is demonstrated with a mode field area larger than 200 microm2. The laser simultaneously emits at two groups of wavelengths centered at 1060 nm and 1090 nm. Pumped by a cw Ti:sapphire laser, the fiber laser yields a maximum output power of 280 mW (pump power limited) at a slope efficiency of 52%. Our results indicate how the advanced possibilities of MSF's can be used for optimized fiber laser designs.

Highly efficient waveguide bends in photonic crystal with a low in-plane index contrast.

We report on the realization and characterization of highly efficient waveguide bends in photonic crystals made of materials with a low in-plane index contrast. By applying an appropriate bend design photonic crystal bends with a transmission of app. 75 % per bend were fabricated.

Effects of spatial inhomogeneities on the dynamics of cavity solitons in quadratically nonlinear media.

We study the dynamics of cavity solitons under the influence of spatial inhomogeneities and derive generalized equations of motions. For perturbations large compared to the soliton size we find the modulus of the soliton velocity to be proportional to the gradient of the respective perturbation and that the proportionality coefficient changes sign when the soliton peak power drives the cavity beyond the resonance. For short scale perturbations solitons may be trapped at the extrema of the inhomogeneities. Shape and stability of these trapped solitons can be quasianalytically described by means of a perturbation theory. If both types of perturbations act solitons are either trapped or move depending on the strength of the respective perturbation. In the framework of a quasiparticle approach this dynamics is governed by a differential equation that holds for particle motion in a strongly viscous fluid under the action of a constant and harmonically varying force. We also show that in addition to acquiring a velocity the very existence conditions of the solitons (hysteresis curve) are affected by both kinds of perturbations. We find good quantitative agreement between our analytical results and numerical findings, which were obtained for a two wave interaction in a cavity filled with a quadratically nonlinear material.

Limits for interchannel frequency separation in a soliton wavelength-division multiplexing system.

We identify the required interchannel frequency separation of the input field for a soliton wavelength-division multiplexing (WDM) system. It is found that the critical frequency separation above which WDM with solitons is feasible increases with the number of transmission channels. Moreover, it is shown that a combination of time- and wavelength-division multiplexing yields the largest transmission capacity. Finally, the structure of the soliton spectra which correspond to the frequency separation smaller than the critical frequency is discussed.

Soliton generation in optical fibers for a dual-frequency input.

We analyze scenarios of soliton generation in an ideal fiber for an input that consists of either two in-phase or out-of-phase solitonlike optical pulses at different frequencies. In both cases the relationship between the structure of the emerging solitons and the frequency separation of the initial solitons is studied both analytically and numerically. Depending on the value of the frequency detuning, if the two initial solitons are in phase (symmetric input), two bound solitons with equal amplitudes (breather), a single soliton, or a pair of solitons, which have equal amplitudes and exhibit opposite velocities, can be generated. When the two initial solitons are out-of-phase (antisymmetric input), only the last scenario takes place. Also, we calculated the threshold values of the frequency separation at which the structure of the emerging solitons changes. Moreover, we demonstrated that two of these critical frequencies correspond to cusplike maxima of the energy density of the radiative modes. Finally, we show that these analytical results are entirely verified by numerical simulations.

Symmetry breaking and self-oscillations in intracavity vectorial second-harmonic generation.

We show that, in vectorial intracavity second-harmonic generation, symmetry breaking occurs if the input amplitude exceeds a critical value. The resulting asymmetric stationary solutions are characterized by a second harmonic that is independent of the input amplitude. The solutions can destabilize through Hopf bifurcations, leading to self-oscillations with pronounced antiphase dynamics. We demonstrate that symmetry breaking can be exploited for flip-flop operation.