The Peer review has evaluated this group as Excellent
Even if a relatively small group, the DEI Optical Communications group is the leading group (M. Martinelli Director, and A. Melloni and P. Boffi Scientific Assistants) of the CoreCom, the Politecnico di Milano Research Consortium on Optical Communication, jointly funded in the 1995 with Pirelli – the Italian leader company on optical communication technologies and systems - which counts about 20 full-time researchers and holds important instrumentation and infrastructures. In the field of Optical Communications the group activity is “vertically” organized ranging from the “system”, to the “components”, to the “technologies and devices”. Systems During the reporting period the focus was on the study and development of high spectral efficiency systems, achieved by means of communication formats able to transport more information capacity in terms of bit/s per hertz. Among the explored different formats, the attention has been focused on Differential Quadrature Phase-Shifting Keying combined with Polarization Division Multiplexing (PolDM DQPSK). Propagation experiments over 2000-km fiber link have been performed in presence of 64 WDM channels at 10 Gsample/s, hence achieving 40 Gb/s equivalent bit-rate. In connection with this topic both theoretical and experimental analysis of the main impairments in fiber propagation has been considered (XPM, SPM, FWM, etc.). Moreover, the impact of photonic statistics on the system performance has been also analyzed. Other activities in the field of optical systems concern the deployment of all-optics processing techniques for communication optical signals: wavelength conversion, optical correlation and switching. Recently, the group is involved in activities concerning the proposal of transponder-level solutions for fiber span dispersion compensation. Components The activities deal principally with aspects inherent the polarization issues in the fiber optics and in the optical system. In particular, the group achieves significant results in controlling the state of polarization of the communication signal: a polarization stabilizer operating up to 300 rad/s has been demonstrated. The same device can be employed to achieve polarization multiplexing/demultiplexing. Another significant research topic is the accurate analysis of the origin of the residual birefringence in the optical fiber: experimentation has been performed also using micro-tomographyc approach. Another important subject focused by the group in the last year has been the analysis of novel amplification techniques: in particular the signal-to-noise ratio performance in Raman and Parametric amplification has been evaluated and tested. Technologies and Devices Concerning the technologies and devices, the group expertise range from the numerical electromagnetic techniques for the analysis of high-index contrast waveguides and circuits, the synthesis of filters, (de)multiplexers, and more in general devices for the managements of channels in WDM systems, the impact of these devices in high bit rates communication systems and the characterization of waveguides and devices. One of the preferred technologies of the group is based on SiON (Silicon Oxinitride), able to realize waveguides with index contrast in the range from 164 2% to 10%. High integration scale circuits have been realized and succesfully tested (among the others a 4x4 switching matrix based on ring resonators and a DQPSK receiver with interleaver and VOAs included). Ring-based slow wave structures is the main subject of the group, for the realization of compact tunable delay lines. Actually, we have demonstrated a tunable delay of 300ps over a bandwidth of 3.3 GHz with insertion loss of only 2 dB and a footprint of 1mm2. The characterization of a delay of 1ns for 10 Gbit/s signals is in progress. The activity on slow wave structures involves also stop-light, time reverse and frequency conversion. The group own several advanced setup for the characterization of waveguides and devices. Among the others, two phase-sensitive low-coherence setup allow the characterization in time domain with femtosecond resolution. Recently, with these setup, we have demonstrated the characterization in time domain of the impact of devices on the amplitude and phase of optical pulses, discovering a superluminal behaviour in a ring resonator, Sensors Other than the researches on “optical communications”, the Research Group maintains some activities localized in a DEI dedicated lab concerning the developing of fiber-optic sensors. The activity transfers the know-how accumulated in optic communications to find novel solutions in the field of optical sensors and is mainly driven by private funding. Among the last realization, we would like to remember a Raman sensor for the detection of temperature profile in harsh environments and vibration and ultra-acoustic sensors.
Mario Martinelli (full professor)
Andrea Melloni (associate professor)
Pierpaolo Boffi (assistant professor)