Rune Shim Jacobsen

Strained silicon as a new electro-optic material.

For decades, silicon has been the material of choice for mass fabrication of electronics. This is in contrast to photonics, where passive optical components in silicon have only recently been realized. The slow progress within silicon optoelectronics, where electronic and optical functionalities can be integrated into monolithic components based on the versatile silicon platform, is due to the limited active optical properties of silicon. Recently, however, a continuous-wave Raman silicon laser was demonstrated; if an effective modulator could also be realized in silicon, data processing and transmission could potentially be performed by all-silicon electronic and optical components. Here we have discovered that a significant linear electro-optic effect is induced in silicon by breaking the crystal symmetry. The symmetry is broken by depositing a straining layer on top of a silicon waveguide, and the induced nonlinear coefficient, χ(2) ≈ 15 pm V-1, makes it possible to realize a silicon electro-optic modulator. The strain-induced linear electro-optic effect may be used to remove a bottleneck in modern computers by replacing the electronic bus with a much faster optical alternative.

Direct experimental and numerical determination of extremely high group indices in photonic crystal waveguides.

We report on time-of-flight experimental measurements and numerical calculations of the group-index dispersion in a photonic crystal waveguide realized in silicon-on-insulator material. Experimentally group indices higher than 230 has been observed. Numerical 2D and 3D time-domain simulations show excellent agreement with the measured data.

Planar glass devices for efficient periodic poling

We demonstrate that frequency-converting devices of high quality can be realised with glass poling. The devices, made with silica-on-silicon technology, are poled with periodic, embedded electrodes, and used for second-harmonic generation. We obtain precise control of the quasi phase-matching wavelength and bandwidth, and a normalised conversion efficiency of 1.4x10-3 %/W/cm2 which, to our knowledge, is the highest obtained so far with periodic glass poling.

Poled-glass devices: influence of surfaces and interfaces

Devices in periodically poled glass must have a large periodic variation of the built-in field. We show that the periodic variation can be severely degraded by charge dynamics taking place at the external (glass-air) interface or at internal (glass-glass) interfaces if the interfaces have imperfections. The problem of the external interface can be solved by poling with periodic electrodes that are buried inside the glass, in many cases improving the poling efficiency dramatically. Internal interfaces can be addressed by the proper choice of waveguide design and processing. Without poling the device, one can reveal the existence of imperfect interfaces by use of electric field induced second-harmonic generation.

Direct numerical and experimental determination of the group index in photonic crystal waveguides

We report on direct numerical calculations and experimental measurements of the group-index dispersion in a photonic crystal waveguide fabricated in silicon-on-insulator material. The photonic crystal is defined by a triangular arrangement of holes and the waveguide is carved out by introducing a one-row line defect. Both the numerical and experimental methods are based on the time of flight approach for an optical pulse. An increase of the group index by approximately 45 times (from 4 to 155) has been observed when approaching the cutoff of the fundamental photonic bandgap mode. Numerical 2D and 3D simulations of pulse dynamics in the waveguide made by the time-domain method shows excellent agreement with measured data in most of the band. These group index values in a photonic crystal waveguide are to the best of our knowledge the largest numbers reported so far by direct tracking of pulse propagation.

Extreme group index measured and calculated in 2D SOI-based photonic crystal waveguides

The paper reports on the measurement and evaluation of the group velocity (GV) dispersion in the proximity of the cutoff wavelength for the fundamental photonic bandgap mode in a 2D photonic crystal waveguide (PCW). The PCW is created by introducing a line defect in an otherwise perfect triangular lattice of air-holes in the 216-nm thick silicon layer in an SOI material. Experimental transmission spectra show a mode cut-off around 1562.5 nm for the fundamental photonic bandgap mode. In order to measure and model the group index of modes in the PCW, a time-of-flight (ToF) method is applied

Electro-Optic Effect Induced In Glass Waveguides Containing A Charge-Trapping Layer

Abstract. Germanium-doped glass waveguides containing a thin silicon oxynitride layer as a charge trapper are thermally poled in air environment. The maximum electro-optic (EO) coefficient increases more than 20% compared to that induced in the waveguides without the trapping layer. The increased EO effect is attributed to the strength of the internal field by introducing the thin oxynitride layer in the waveguide structure. Our results demonstrate advantages of shaping the internal field to increase the optical nonlinearity in glass poling.

Correction to "Strength and Symmetry of the Third-Order Nonlinearity During Poling of Glass Waveguides"

Negative thermal poling introduces second-order nonlinear effects into silica glass. The effects are studied using the charge separation model allowing for the third-order nonlinear effect to be anisotropic. The second-order nonlinear coefficient /spl chi//sup (2)/ is found to be consistent with the results reported previously by Arentoft et al. (1999), Ren et al. (2002), and Marckmann et al. (2001) and the third-order nonlinear coefficient /spl chi//sup (3)/ is found to be anisotropic but constant during poling.