Costanza Manganelli

Modeling of strain-induced Pockels effect in Silicon.

We propose a theoretical model to describe the strain-induced linear electro-optic (Pockels) effect in centro-symmetric crystals. The general formulation is presented and the specific case of the strained silicon is investigated in detail because of its attractive properties for integrated optics. The outcome of this analysis is a linear relation between the second order susceptibility tensor and the strain gradient tensor, depending generically on fifteen coefficients. The proposed model greatly simplifies the description of the electro-optic effect in strained silicon waveguides, providing a powerful and effective tool for design and optimization of optical devices.

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.

Thermal tuning double ring resonator filters: Experimental analysis

We present experimental results of thermally tunable double ring resonators with doped silicon and silicide heaters and different geometries. We study the effects of fabrication inaccuracies which affect the symmetry of the heating, and we show how spectra are recovered when asymmetry is electrically compensated.

Design of coupled micro-ring resonators for silicon photonic switching matrices

We present a design study and experimental results of first and second-order filters as switch elements for integrated switch matrices. A double racetrack-based filter using Bezier bends is investigated, showing a spectral response within specifications and a free spectral range higher than 2.4THz.

Silicon photonic waveguide metrology using Mach-Zehnder interferometers

We propose a procedure for characterizing fabrication deviations within a chip and among different chips in a wafer in silicon photonics technology. In particular, independent measurements of SOI thickness and waveguide width deviations can be mapped through the wafer, allowing a precise and non-destructive characterization of how these variations are distributed along the surface of the wafer. These deviations are critical for most wavelength-dependent integrated devices, like microring resonators, filters, etc. We also show that the technique allows for the characterization of proximity effects.

Automatic alignment of photonic components of massive optical switch to ITU channels (Conference Presentation)

We demonstrate the automatic thermal alignment of photonic components within an integrated optical switch. The WDM optical switch involves switching elements, wavelength de-multiplexers, interleavers and monitors each one needing independent control. Our system manages rerouting of channels coming from four different directions, each carrying 12, 200GHz spaced, wavelengths into eight add/drop ports. The integrated device includes 12 interleavers, which can act either as optical de-interleavers to split the optical signal into odd and even channels or as optical interleavers that recombine the odd and even channels coming from the switching matrix. Integrated Ge photodiodes are placed in key positions within the photonic integrated circuit (PIC) are serve for monitoring. An electronic integrated circuit (EIC) drives the photonic elements by means of dedicated heating circuits (824 on-board heater control cells, 768 for the switching elements and 56 for the interleavers and the mux/de-mux) and reads out the Ge diodes photocurrent through TIAs. We applied a stochastic optimization algorithm to align the spectral response of the interleavers to the ITU grid. We exploit the thermo-optic effect to shift the interleavers pass-band in a desired spectral position. The interleavers are provided with dedicated metallic heaters that can be operated in order to tune the interleaver response, which is typically misaligned due to fabrication inaccuracies. The experimental setup is made of a tunable laser coupled with one input port of optical switch. The optimization algorithm is implemented via a software to drive the EIC till finding the best heating configuration (on the two branches of the interleaver) on the basis of the monitor diode-feedback. This way, the even and odd wavelengths input in the interleaver are directed toward the wanted lines within the switching matrix. Our method has been used for aligning the micro-ring based switching elements in the PIC as well. In that case, the integrated Ge photodiodes have been used to align the photonic components in the PIC in order to enable different pathways for the routing or the broadcasting operation of the optical switch. With no bias applied to the heaters of the switching elements, the optical signal is expected to be maximum at the through port. When the micro-ring heaters are biased, the feedback controller finds the best set of heating values that minimize the optical power at the through port of the switching node. This way, the optical signal is coupled in the drop port and the node is enabled for switching. The algorithm, implemented in LabVIEW, converges over multiple instances and it is robust against stagnation. This work aims at enabling the automatic reconfiguration/restoration of the whole WDW optical switch.

Silicon waveguide metrology through interferometry

We present an effective technique to characterize silicon waveguide geometry by using Mach-Zehnder interferometers. The technique can independently estimate SOI thickness and waveguide width from the analysis of two simple interferometers. The results agree with standard metrology using ellipsometry and SEM microscopy, and allows the characterization of proximity effects too.