Thorsten Wahlbrink

Ultrahigh-quality-factor silicon-on-insulator microring resonator

The development of ultrahigh-quality-factor (Q) silicon-on-insulator (SOI) microring resonators based on silicon wire waveguides is presented. An analytical description is derived, illustrating that in addition to low propagation losses the critical coupling condition is essential for optimizing device characteristics. Propagation losses as low as 1.9 +/- 0.1 dB/cm in a curved waveguide with a bending radius of 20 microm and a Q factor as high as 139.000 +/- 6.000 are demonstrated. These are believed to be the highest values reported for a curved SOI waveguide device and for any directly structured semiconductor microring fabricated without additional melting-induced surface smoothing.

Pockels effect based fully integrated, strained silicon electro-optic modulator

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.

Ultrafast Kerr-induced all-optical wavelength conversion in silicon waveguides using 1.55 μm femtosecond pulses

The propagation of 300 femtosecond optical pulses in Silicon-on Insulator waveguides has been studied by means of a pump-probe set-up. The ultrafast pulses allowed the observation of large Kerr-induced red and blue shifts (9nm and 15nm, respectively) of the probe signal depending on the delay between pump (1554nm) and probe (1683nm) pulses. A numerical model taking into account the Kerr effect, Two Photon Absorption and Free Carrier Absorption is presented and provides good agreement with our experimental data and data in literature. A microring resonator based device is proposed that exploits the observed wavelength shift for sub-picosecond all-optical switching.

25ps all-optical switching in oxygen implanted silicon-on-insulator microring resonator

We present all-optical switching in oxygen ion implanted silicon microring resonators. Time-dependent signal modulation is achieved by shifting resonance wavelengths of microrings through the plasma dispersion effect via femtosecond photogeneration of electron-hole pairs and subsequent trapping at implantation induced defect states. We observe a switching time of 25 ps at extinction ratio of 9 dB and free carrier lifetime of 15 ps for an implantation dose of 7 x 10(12) cm(-2). The influence of implantation dose on the switching speed and additional propagation losses of the silicon waveguide--the latter as a result of implantation induced amorphization--is carefully evaluated and in good agreement with theoretical predictions.

Silicon-Organic Hybrid Electro-Optical Devices

Organic materials combined with strongly guiding silicon waveguides open the route to highly efficient electro-optical devices. Modulators based on the so-called silicon-organic hybrid (SOH) platform have only recently shown frequency responses up to 100 GHz, high-speed operation beyond 112 Gbit/s with fJ/bit power consumption. In this paper, we review the SOH platform and discuss important devices such as Mach-Zehnder and IQ-modulators based on the linear electro-optic effect. We further show liquid-crystal phase-shifters with a voltage-length product as low as VπL = 0.06 V·mm and sub-μW power consumption as required for slow optical switching or tuning optical filters and devices.

High-speed all-optical switching in ion-implanted silicon-on-insulator microring resonators

We demonstrate high-speed all-optical switching via vertical excitation of an electron-hole plasma in an oxygen-ion implanted silicon-on-insulator microring resonator. Based on the plasma dispersion effect the spectral response of the device is rapidly modulated by photoinjection and subsequent recombination of charge carriers at artificially introduced fast recombination centers. At an implantation dose of 1 x 10(12) cm(-2) the carrier lifetime is reduced to 55 ps, which facilitates optical switching of signal light in the 1.55 mum wavelength range at modulation speeds larger than 5 Gbits/s.

Low-Loss Silicon Strip-to-Slot Mode Converters

We demonstrate compact highly efficient broadband strip-to-slot mode converters in silicon with record-low losses of 0.02 (±0.02) dB and negligible reflections between 1480 nm and 1580 nm. The new strip-to-slot transition is logarithmically tapered, which enables a compact design. The new logarithmic tapers are compared with more conventional linearly tapered converters.

Low Power Mach–Zehnder Modulator in Silicon-Organic Hybrid Technology

We report on a silicon-organic hybrid modulator based on a Mach-Zehnder interferometer (MZI) operating at 10 Gbit/s with an energy consumption of 320 fJ/bit. The device consists of a striploaded slot waveguide covered with an electro-optic polymer cladding. The MZI modulator is poled to be driven in push-pull operation by a single coplanar RF line. Our nonlinear coefficient r33 = 15 pm/V in combination with an 80 nm narrow slot enables RF peak-to-peak drive voltages as low as 800 mVpp to suffice for an extinction ration of 4.4 dB for a 1.5 mm long modulator.

0.86-nm CET Gate Stacks With Epitaxial

In this letter, ultrathin gadolinium oxide (Gd2O3 ) high-k gate dielectrics with complementary-metal-oxide-semiconductor (CMOS)-compatible fully silicided nickel-silicide metal gate electrodes are reported for the first time. MOS capacitors with a Gd2O3 thickness of 3.1 nm yield a capacitance equivalent oxide thickness of CET=0.86 nm. The extracted dielectric constant is k=13-14. Leakage currents and equivalent oxide thicknesses of this novel gate stack meet the International Technology Roadmap for Semiconductors targets for the near term schedule and beyond

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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.