Xuan Hu

Modeling the anisotropic electro-optic interaction in hybrid silicon-ferroelectric optical modulator

We present a numerical method to accurately model the electro-optic interaction in anisotropic materials. Specifically, we combine a full-vectorial finite-difference optical mode solver with a radio-frequency solver to analyze the overlap between optical modes and applied electric field. This technique enables a comprehensive understanding on how electro-optic effects modify individual elements in the permittivity tensor of a material. We demonstrate the interest of this approach by designing a modulator that leverages the Pockels effect in a hybrid silicon-BaTiO3 slot waveguide. Optimized optical confinement in the active BaTiO3 layer as well as design of travelling-wave index-matched electrodes is presented. Most importantly, we show that the overall electro-optic modulation is largely governed by off-diagonal elements in the permittivity tensor. As most of active electro-optic materials are anisotropic, this method paves the way to better understand the physics of electro-optic effects and to improve optical modulators.

Low-Loss and Compact Silicon Rib Waveguide Bends

Waveguide bends support intrinsically leaky propagation modes due to unavoidable radiation losses. It is known that the losses of deep-etched/strip waveguide bends increase inevitably for decreasing radius. Here, we theoretically and experimentally demonstrate that this result is not directly applicable to shallow-etched/rib waveguide bends. Indeed, we show that the total losses caused by the bends reach a local minimum value for a certain range of compact radii and rib waveguide dimensions. Specifically, we predicted the minimum intrinsic losses <;0.1 dB/90° turn within the range of 25-30 μm bend radii in a 220 nm-thick and 400 nm-wide silicon rib waveguide with 70 nm etching depth. This unexpected outcome, confirmed by experimental evidence, is due to the opposite evolution of radiation (bending) losses and losses caused by the coupling to lateral slab modes (slab leakage) as a function of the bend radius, hence creating an optimum loss region. This result may have important implications for the design of compact and low-loss silicon nanophotonic devices.

Silicon CMOS compatible transition metal dioxide technology for boosting highly integrated photonic devices with disruptive performance

In this work we will present the objectives and last results of the FP7-ICT-2013-11-619456 SITOGA project. The SITOGA project will address the integration of transition metal dioxides (TMO) materials in silicon photonics and CMOS electronics. TMOs have unique electro-optical properties that will offer unprecedented and novel capabilities to the silicon platform. SITOGA will focus on two disruptive TMO materials, barium titanate (BaTiO3) and vanadium didioxide (VO2), for developing advanced photonic integrated devices for a wide range of applications. Innovative integration processes with silicon photonics circuits and CMOS electronics will be developed. The whole technology chain will be validated by two functional demonstrators: a 40 Gbit/s DPSK transceiver and an 8×8 switching matrix with 100 Gbit/s throughput.

Integration of functional oxides on SOI for agile silicon photonics

Photonic devices enabling light modulation and switching are of major importance for modern telecommunication. Silicon-based electro-optic modulators are intensively investigated because of their direct compatibility to CMOS fabrication processes. However, the performances of Si based modulators are intrinsically limited, in terms of data transmission rate and energy consumption. To overcome this limitation, ferroelectric oxides with naturally strong electro-optical coefficients combined to small footprint could be ideal candidates for high-speed modulators. We have designed an integration scheme to implement these materials on SOI photonic platform, for 1.55 μm Datacom systems. Monolithic integration of ferroelectric oxides on SOI via SrTiO3 templates is presented. The devices are based on a horizontal (crystalline Si / ferroelectric oxide / amorphous Si) slot waveguide configuration.