|ZANETTO FRANCESCO||Cycle: XXXIII |
Tutor: FIORINI CARLO ETTORE
Advisor: SAMPIETRO MARCO Major Research topic
:Low-noise mixed-signal electronics for integrated photonics applicationsAbstract:
In the last decades, photonics became the dominant technology for long-range telecommunications, thanks to its outstanding data-rates achieved with reduced losses and power consumption. Recently, to profit of the advantages of photonics also in short-range communications, integrated optics gained a lot of relevance. In particular, Silicon Photonics emerged as a very promising technology, as it allows to integrate many optical devices in a small silicon chip fabricated with the well-consolidated manufacturing processes of the microelectronics. However, the integration density made possible by Silicon Photonics revealed the difficulty of operating complex optical architectures in an open-loop way, due to their high sensitivity to fabrication parameters and temperature variations.
In this thesis, the true potential of integrated photonics was unlocked thanks to the design of a low-noise 16-channel electronic platform, used to implement feedback control of complex optical architectures. The system exploits CLIPP detectors, that sense light in silicon waveguides in a non-invasive way by measuring their electrical conductance and can thus be integrated in many points of an optical circuit without penalties. In order to effectively use this sensor, a resolution in the conductance measurement of some picoSiemens is needed, so a two-stage mixed-signal lock-in amplifier was implemented to achieve extremely low-noise performance. The feedback loop to control photonic devices was closed in the digital domain thanks to an FPGA, providing reconfigurability to the system and allowing parallel processing of the acquired signals. The effectiveness of control platform was demonstrated in several experiments of light path tracking, reconfiguration, and thermal crosstalk compensation on a photonic routing engine for datacenters applications with Tb/s aggregate capacity and on a self-aligning beam coupler for mid-range free-space optical transmission.
Integrated optics can also be exploited for sensing applications. In collaboration with Massachusetts Institute of Technology, a gas sensing opto-electronic system was developed. The system promises to determine the chemical composition of gas mixtures thanks to optical absorption spectroscopy performed in a very small photonic chip. In order to obtain a compact multichannel electro-optical system, a custom lock-in based ASIC for low-noise readout of the gas sensing detectors was developed, featuring 6 channels operating in a frequency range between 10 kHz and 1 MHz. The ASIC was mounted on a custom PCB hosting also the photonic chip to obtain a self-sufficient gas sensing instrument.