We demonstrate for the first time a fully integrated electro-optic modulator based on locally strained silicon rib-waveguides. By depositing a Si3N4 strain layer directly on top of the silicon waveguide the silicon crystal is asymmetrically distorted. Thus its inversion symmetry is broken and a linear electro-optic effect is induced. Electro-optic characterization yields a record high value χ(2)(yyz) = 122 pm/V for the second-order susceptibility of the strained silicon waveguide and a strict linear dependence between the applied modulation voltage V(mod) and the resulting effective index change Δn(eff). Spatially resolved micro-Raman and terahertz (THz) difference frequency generation (DFG) experiments provide in-depth insight into the origin of the electro-optic effect by correlating the local strain distribution with the observed second-order optical activity.

We present detailed investigations of the local strain distribution and the induced second-order optical nonlinearity within strained silicon waveguides cladded with a Si₃N₄ strain layer. Micro-Raman Spectroscopy mappings and electro-optic characterization of waveguides with varying width w(WG) show that strain gradients in the waveguide core and the effective second-order susceptibility χ(2)(yyz) increase with reduced w(WG). For 300 nm wide waveguides a mean effective χ(2)(yyz) of 190 pm/V is achieved, which is the highest value reported for silicon so far. To gain more insight into the origin of the extraordinary large optical second-order nonlinearity of strained silicon waveguides numerical simulations of edge induced strain gradients in these structures are presented and discussed.

Photorefractive single feedback systems are known to exhibit a variety of transverse patterns [1]. In addition to predominant hexagonal patterns, stripes, squares and squeezed hexagons can be observed to coexist and compete, providing bistable parameter regions. Such co bistabilities offer the chance to directly investigate . techniques to control the pattern formation process. Ce Detuning of the counterpropagating pump beams is C known to change the linear stability [2] and can be aX employed to control the relative stability of patterns in a parameter range where a bistability between different patterns exists.-3 -2 -1 0 1 2 3We experimentally demonstrate deterministic switching between square and squeezed hexagonal patterns by pump beam detuning and investigate its suitability as a control Intensity of addressed pattern type method.(here: a squeezed hexagonal pattern) vs. control signal strength.We present an analysis of the effect of pump detuning on fundamental unstable modes under one transverse dimension and discuss its relevance for the control of twodimensional patterns. Experimental results are compared to predictions obtained by means of a linear stability analysis.

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