C. Etrich

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.

Diffractionless propagation of light in a low-index photonic-crystal film

We experimentally demonstrate diffractionless propagation of light over 12 diffraction lengths in a two-dimensional photonic crystal film made of silicon nitride (SiNx). We show that self-guided beams may propagate for transverse electric (TE) and transverse magnetic (TM) polarized light but at slightly different frequencies. Three-dimensional calculations are used to optimize the structure for low loss and narrow beam operation in this low-index photonic crystals. Experimental and theoretical results are in good agreement.

Light propagation in a free-standing lithium niobate photonic crystal waveguide

We report on the light propagation in a one-line-defect photonic crystal waveguide (W1 PhC WG) patterned into a 450 nm thick free-standing lithium niobate membrane by ion-beam enhanced etching. The Bloch wave vectors and transmission spectrum of this PhC WG were retrieved from optical near-field images. The experimental data show good agreement with simulations performed with the three-dimensional (3D) finite-element method and the 3D finite-difference time-domain method. Those results are promising for the development of integrated optics devices operating at telecom wavelengths and based on free-standing lithium niobate PhC membranes.

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.

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.

High transmission and single-mode operation in low-index-contrast photonic crystal waveguide devices

We investigate photonic crystal films made of low-index glass materials. Polarization-sensitive waveguiding and single-mode operation (with losses as low as 1.7 dB/mm) have been observed in wide multimode photonic crystal waveguides after propagation of some millimeters. Furthermore, single-mode operation and transmission as high as about 50% per bend has been observed experimentally in low-index photonic crystal waveguide bends.

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.

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.

Bifurcations, stability, and multistability of cavity solitons in parametric downconversion

We systematically study the formation of cavity solitons in a high-finesse, doubly resonant degenerate optical parametric oscillator. Three types of cavity soliton, emanating from different plane-wave critical points, are identified. By means of amplitude equations the bifurcation dynamics of these solutions is studied and classified. We compare cavity solitons calculated from amplitude equations with the full numerical solutions near the critical points and trace their evolution numerically far from bifurcation. We found cavity soliton types previously not identified, namely, dark and oscillating solitons. These numerical studies are complemented by a linear stability analysis of cavity solitons. Various decay situations for unstable cavity solitons are discussed.