A. Rosa

High performace silicon 2x2 optical switch based on a thermo-optically tunable multimode interference coupler and efficient electrodes.

Optical switches based on tunable multimode interference (MMI) couplers can simultaneously reduce the footprint and increase the tolerance against fabrication deviations. Here, a compact 2x2 silicon switch based on a thermo-optically tunable MMI structure with a footprint of only 0.005 mm(2) is proposed and demonstrated. The MMI structure has been optimized using a silica trench acting as a thermal isolator without introducing any substantial loss penalty or crosstalk degradation. Furthermore, the electrodes performance have significantly been improved via engineering the heater geometry and using two metallization steps. Thereby, a drastic power consumption reduction of around 90% has been demonstrated yielding to values as low as 24.9 mW. Furthermore, very fast switching times of only 1.19 µs have also been achieved.

Barium titanate (BaTiO 3 ) RF characterization for application in electro-optic modulators

Barium titanate (BaTiO3 or BTO) is currently one of the most promising ferroelectric materials for enabling Pockels modulation that is compatible with silicon photonic circuits. The relative permittivity of BTO has been characterized in thin films deposited on a silicon-on-insulator (SOI) substrate. High values between 800 and 1600 have been estimated at 20 GHz. Furthermore, no substantial difference has been obtained by using BTO grown by molecular beam epitaxy and sputtering. The obtained permittivity has been used to properly design the RF electrodes for high-speed modulation in hybrid BTO/Si devices. Electrodes have been fabricated and the possibility of achieving modulation bandwidths up to 40 GHz has been demonstrated. The bandwidth is limited by the microwave propagation losses and, in this case, different losses have been measured depending on the BTO growth process.

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.

Microwave index engineering for slow-wave coplanar waveguides

Microwave index engineering has been investigated in order to properly design slow-wave coplanar waveguides suitable for a wide range of applications in microwave, photonics, plasmonics and metamaterials. The introduction and optimization of novel capacitive and inductive elements is proposed as a design approach to increase the microwave index while keeping the impedance close to 50 Ω to ensure the compatibility with external electronic devices. The contribution of inductive and capacitive elements and their influence on the performance of the slow-wave coplanar waveguide has been systematically analyzed. As a result, a microwave index as high as 11.6 has been experimentally demonstrated in a frequency range up to 40 GHz which is, to the best of our knowledge, the largest microwave index obtained so far in coplanar waveguides.

Advanced high speed slow-light silicon modulators in the O-band for low power optical interconnects in data centers

This paper presents the design and preliminary results of a low power, compact and high-speed modulator in the O-band featuring apodized slow-light structures and a slow-wave RF design. The device is a candidate for future single mode optical interconnects in large-scale data centers.

Thermo-optical switching in hybrid VO 2 /Sİ waveguides by lateral displaced microheaters

A lateral displaced microheater is demonstrated for switching across the VO2 phase transition in ultra-short hybrid VO2/Si waveguides for both TE and TM light polarizations. Simulation and experimental results are obtained showing a very good agreement with a switching electrical power of around 10mW.

Impact of the external resistance on the switching power consumption in VO2 nano gap junctions

The influence of an external resistance on the performance of VO2 nanogap junctions is analyzed and experimentally characterized. The current-voltage response shows the reversible metal-insulator transition typical of VO2 based devices. When reaching the metallic state, the current through the VO2 junction is abruptly increased, which may result in electrical contact damage. Therefore, an external resistance in series with the VO2 junction is usually employed to limit the maximum current through the device. Our results indicate that the external resistance plays a key role in the switching power consumption showing an optimum value, which depends on the dimensions of the VO2 junction. In such a way, power consumption reductions up to 90% have been demonstrated by selecting the optimum external resistance value.

Electrical switching in hybrid VO 2 /Si photonic structures

The integration of active materials on silicon is emerging as a promising field in silicon photonics to improve the performance metrics of key photonic components, in particular active components. Active materials allow tuning their optical properties as function of external stimuli. Amongst them, vanadium dioxide (VO2) has been largely investigated for different applications due to its controllable change between an insulating and a metallic phase. For photonic applications, VO2 shows a promising performance due to the abrupt change in the refractive index between the two phases across the semiconductor to metal transition (SMT). In this work, we will present our recent results for enabling disruptive electrical switching performance in hybrid VO2/Si photonic structures. Results have been obtained in the framework of the FP7-ICT-2013-11-61456 SITOGA project.

Hybrid silicon-ferroelectric oxide platform for tunable nanophotonics on silicon

In this communication, we present strategies to implement novel or enhanced optoelectronic functionalities on silicon via the monolithic integration of functional oxides as active layers for nanophotonic devices. We focus on the use of ferroelectric oxides with naturally strong electro-optical coefficients such as BaTiO3 (BTO) on SOI for the realization of electro-optical modulators around 1.55 μm. Specifically, we present methods to monolithically integrate monocrystalline BTO on silicon and to design devices that leverage their strong Pockels coefficient for efficient and fast electro-optical modulation. We show preliminary results on the fabrication, process and characterization of a slotted BTO waveguide platform. We further discuss on first electro-optical modulation results and how to improve the current optoelectronic platform. In particular, we will explain the potential origins of optical losses in such systems and how to avoid them.

Towards high-speed electro-optical performance in a hybrid BaTiO 3 /Si Mach-Zehnder modulator

A Mach-Zehnder modulator based on a hybrid BaTiO₃/silicon optical waveguide has been designed to achieve a high modulation bandwidth with a simulated V_πL below 1V·cm and RF impedance matching. The device has been fabricated and characterized in the DC regime.