Mattia Mancinelli

High-frequency electro-optic measurement of strained silicon racetrack resonators

The observation of the electro-optic effect in strained silicon waveguides has been considered a direct manifestation of an induced χ(2) nonlinearity in the material. In this work, we perform high-frequency measurements on strained silicon racetrack resonators. Strain is controlled by a mechanical deformation of the waveguide. It is shown that any optical modulation vanishes, independent of the applied strain, when the applied voltage varies much faster than the carrier effective lifetime and that the DC modulation is also largely independent of the applied strain. This demonstrates that plasma carrier dispersion is responsible for the observed electro-optic effect. After normalizing out free-carrier effects, our results set an upper limit of (8±3) pm/V to the induced high-speed effective χeff,zzz(2) tensor element at an applied stress of -0.5 GPa. This upper limit is about 1 order of magnitude lower than previously reported values for static electro-optic measurements.

Optical characterization of a SCISSOR device

Here, we report on the design, fabrication and characterization of single-channel (SC-) and dual-channel (DC-) side-coupled integrated spaced sequences of optical resonators (SCISSOR) with a finite number (eight) of microring resonators using submicron silicon photonic wires on a silicon-on-insulator (SOI) wafer. We present results on the observation of multiple resonances in the through and the drop port signals of DC-SCISSOR. These result from the coupled resonator induced transparency (CRIT) which appears when the resonator band (RB) and the Bragg band (BB) are nearly coincident. We also observe the formation of high-Q (> 23000) quasi-localized modes in the RB of the drop transmission which appear when the RB and BB are well separated from each other. These multiple resonances and quasi-localized modes are induced by nanometer-scale structural disorders in the dimension of one or more rings. Finally, we demonstrate the tunability of RB (and BB) and localized modes in the DC-SCISSOR by thermo-optical or free-carrier refraction.

Coupled-resonator-induced-transparency concept for wavelength routing applications

We investigated the presence of high quality factor resonances due to Coupled Resonator Induced Transparency in complex sequences of coupled resonators devices, and proposed a new concept of wavelength router based on this effect.

Reconfigurable optical routers based on Coupled Resonator Induced Transparency resonances

The interferometric coupling of pairs of resonators in a resonator sequence generates coupled ring induced transparency (CRIT) resonances. These have quality factors an order of magnitude greater than those of single resonators. We show that it is possible to engineer CRIT resonances in tapered SCISSOR (Side Coupled Integrated Space Sequence of Resonator) to realize fast and efficient reconfigurable optical switches and routers handling several channels while keeping single channel addressing capabilities. Tapered SCISSORs are fabricated in silicon-on-insulator technology. Furthermore, tapered SCISSORs show multiple-channel switching behavior that can be exploited in DWDM applications.

Design and Implementation of an Integrated Reconfigurable Silicon Photonics Switch Matrix in IRIS Project

This paper aims to present the design and the achieved results on a CMOS electronic and photonic integrated device for low cost, low power, transparent, mass-manufacturable optical switching. An unprecedented number of integrated photonic components (more than 1000), each individually electronically controlled, allows for the realization of a transponder aggregator device which interconnects up to eight transponders to a four direction colorless-directionless-contentionless ROADM. Each direction supports 12 200-GHz spaced wavelengths, which can be independently added or dropped from the network. An electronic ASIC, 3-D integrated on top of the photonic chip, controls the switch fabrics to allow a complete and microsecond fast reconfigurability.

Optical characterization of silicon-on-insulator–based single and coupled racetrack resonators

Silicon photonics is the emerging optical interconnect technology where integrated nanophotonic components allow reaching high device density and improved optical functional- ities. One key component is the optical microresonator. A particular kind of microresonator is the racetrack resonator where straight waveguide sections are used to achieve a large value of the coupling coefficient with a bus waveguide for any light polarization state. It is our aim to study the performances of racetrack resonators fabricated on silicon on insulator via CMOS pro- cessing. We experimentally investigated different multiple resonator designs where box-shaped filter characteristic, Vernier effect, and coupled resonator induced transparency effects are ob- tained. We demonstrate that racetrack resonators are instrumental to several different functions in nanophotonics and that the actual lithographic process is fully capable of building these

Chaotic dynamics in coupled resonator sequences

We report on the generation of chaotic signals in sequences of integrated coupled silicon resonators at telecommunication wavelengths. These can pave the way to on chip all optical random bit generators naturally compatible with silicon photonics.

Reflectance Reduction in a Whiskered SOI Star Coupler

In this letter, we evaluate how the background noise is modified within a whiskered-shaped star coupler, optimized to reduce the reflectivity of its internal surfaces to reduce the back-scattered light. This letter is carried out by analyzing the Fabry-Perot interference due to the reflections between the input focal plane of the star coupler and the output facet of the waveguides. By comparing a whiskered star coupler with a standard one, we find a reduction in the star coupler reflectance of more than one order of magnitude. The experimental results are supported by a theoretical model and by numerical simulations.

Homodyne Detection of Free Carrier Induced Electro-Optic Modulation in Strained Silicon Resonators

In the last few years, strained silicon has been proposed as a potential electro-optic material, paving the way to the realization of ultrafast modulators which are compatible with the CMOS fabrication technology. The linear Pockels effect has been used for measuring the magnitude of the induced (2) components, with values reaching hundreds of pm/V. Recently, it has been shown that these values could have been overestimated due to the contribution of free carriers to the electro-optic modulation. In this work, this hypothesis is validated by a series of experimental observations, which are performed on strained silicon racetrack resonators. These are fabricated with different waveguide widths and orientations. We use a low frequency (KHz) homodyne detection technique to monitor the electro-optic response of the devices. The results indicate that the modulation strength is not dependent on the waveguide geometry or direction. A lot of anomalies are encountered in the device response, which are not compatible with a modulation mechanism of (2) origin. To this purporse, a theory based on the nonlinear injection of free carriers inside the waveguide is presented. This is able to account for all the observed anomalies.

An All Optical Method for Fabrication Error Measurements in Integrated Photonic Circuits

We propose an optical method to quantify the level of fabrication imperfections in a Silicon On Insulator wafer. The method is based on the use of Side Coupled Integrated Spaced Sequence of Resonators (SCISSOR) as test devices. Fabrication induced fluctuations of the effective index and of the coupling coefficient are mapped by comparing different spectral responses of nominally identical samples taken from different dies in the wafer. Random variations of the resonators optical path are quantified in terms of standard deviations of normally distribuited variables by finding a statistical correlation with the coupled resonator induced transparency (CRIT) phenomena. We found a strong correlation between CRIT and fabrication errors. This led us to design a SCISSOR based test structure that allows to quantify the degree of local structural imperfections in a fast, accurate and non invasive way. Performances, possible applications and limitations are investigated with the help of transfer matrix simulations.