Antonino Nespola

Universal MEMS platforms for passive RF components: suspended inductors and variable capacitors

We propose a universal MEMS technology platform for fabricating integrable passive components for radio frequency (RF) integrated circuits. This platform is based on a novel surface-micromachined Micro-Elevator by Self-Assembly (MESA) technique. Both high-Q inductors and variable capacitors can be realized by the MESA technology. A surface-micromachined spiral inductor that is raised by 250 /spl mu/m above the Si substrate has been experimentally demonstrated. The suspended inductor has less parasitic capacitance and substrate loss, and higher quality (Q) value and resonant frequency. The inductance of a 12.5-turn inductor is measured to be 24 nH. The results show that the self-assembled passive RF elements are suitable for monolithic integration.

Fully Blind Linear and Nonlinear Equalization for 100G PM-64QAM Optical Systems

We demonstrate fully blind processing and reduced-complexity nonlinear equalization (NLE) of a 100G PM-64QAM optical channel in a 50 GHz WDM grid, achieving a maximum reach of 1524 km over pure silica core fiber at a bit error rate of 2.7 × 10-2. The equalization of linear polarization-dependent effects is performed by a radius-directed constant modulus algorithm (RD-CMA), enabled by a multiradii training stage, yielding a very small penalty (<;0.1 dB in terms of Q2 factor) relatively to data-aided CMA. Applying a simplified Volterra series nonlinear equalizer (simVSNE), operating in the frequency domain, we demonstrate a reach extension of ~27% relatively to linear equalization. Due to its lower spatial resolution requirements, the simVSNE technique is shown to provide a more efficient NLE than the well-known back-propagation split-step Fourier method, both in terms of latency and number of complex multiplications per sample. The potential benefit of NLE for fully blind processing of high-order QAM optical signals is demonstrated by an incremental reduction of the RD-CMA penalty to <;0.04 dB.

High power and highly linear monolithically integrated distributed balanced photodetectors

A distributed balanced photodetector with high saturation photocurrent and excellent linearity has been experimentally demonstrated. The maximum linear direct current (DC) photocurrent of 33 mA per branch is equivalent to 66 mA in single-ended photodetectors. A setup for investigating the alternating current (AC) linearity of the receiver is proposed and experimentally demonstrated. The receiver exhibits high AC linearity, even under high power operation. The bandwidth of the receiver remains unchanged when the effective do photocurrent is varied from 1 mA to 21 mA. The distribution of photocurrents was also measured. Device length for optimum radiofrequency performance is calculated and implemented in the design. A correlation between the dark current of the photodiodes and their failure mechanism has been established. Analyzing the failure mechanism, junction diodes are found to be more suitable for high power applications.

Optimization of Reflective FDMA-PON Architecture to Achieve 32 Gb/s Per Upstream Wavelength Over 31 dB ODN Loss

In the framework of the EU-funded research project “FABULOUS,” we experimentally demonstrate an innovative FDMA-PON architecture whose upstream transmission is based on a reflective Mach-Zehnder modulator. By a careful optimization of electrical spectrum allocation, semiconductor optical amplifier biasing point, and modulation index, we upgrade previous results over similar architectures, significantly increasing the achievable optical distribution network loss. We demonstrate an overall upstream capacity of 32 Gb/s per wavelength over 37 km of installed fiber and 31 dB loss.

Analytical and Experimental Results on System Maximum Reach Increase Through Symbol Rate Optimization

We investigated the reach increase obtained through nonlinearity mitigation by means of transmission symbol rate optimization (SRO). First, we did this theoretically and simulatively. We showed that the nonlinearity model that properly accounts for the phenomenon is the EGN model, in its version that specifically includes four-wave mixing. We then found that for PM-QPSK systems at full C-band, the reach increase may be substantial, on the order of 10-25%, with optimum symbol rates on the order of 2-6 GBd. We show that for C-band PM-QPSK systems over SMF, the potential mitigation due to SRO is greater than that ideally granted by digital backpropagation (the latter applied over a bandwidth of a 32-GBd channel). We then set up an experiment to obtain confirmation of the theoretical and simulative predictions. It consisted of 19 PM-QPSK channels, operating at 128 Gb/s per channel, over PSCF, with span length 108 km and EDFA-only amplification. We demonstrated a reach increase of about 13.5%, when going from single-carrier per channel transmission, at 32 GBd, to eight subcarrier per channel, at 4 GBd, in line with the EGN model predictions. We also extended the theoretical investigation of SRO to PM-16QAM, where we found a qualitatively similar effect to PM-QPSK, although the potential reach increase appears to be typically only about 50% to 60% that of PM-QPSK. Further investigation is, however, in order, specifically to explore the effect on PM-16QAM SRO of the removal of long-correlated phase and polarization noise.

GN-Model Validation Over Seven Fiber Types in Uncompensated PM-16QAM Nyquist-WDM Links

We report on a set of transmission experiments over seven different uncompensated fiber links carrying a 22-channel Nyquist-WDM signal comb based on polarization-multiplexed 16-quadrature amplitude modulation at RS=15.625 GBd(RB=125 Gb/s). The channel spacing was Δf=16 GHz. The experimental transmission performance was compared with analytical GN-model predictions showing a good agreement for all seven considered fiber types. Moreover, we used the experimental results for the validation of a fiber figure of merit based on the maximum reach, showing its effectiveness for approximate fiber performance prediction. Within the experimental tests, a maximum transmission distance of 3810 km at a bit error-rate of 1.5×10-2 was achieved using a pure-silica-core fiber with 150 μm2 effective area, at a net spectral-efficiency-distance product of 24700 (b·km)/(s· Hz), in a good agreement with the GN-model forecast.

Correlation between the failure mechanism and dark currents of high power photodetectors

We experimentally investigate the role of dark current on the failure mechanism of high power photodiodes. A theoretical model built to fit the experimental data indicates that the effective barrier height and the dark current are the fundamental parameters in the failure mechanism.

A New Physical Layer Capable of Record Gigabit Transmission Over 1 mm Step Index Polymer Optical Fiber

In this paper we present the latest results from the POF-PLUS EU Project, demonstrating record transmission of a Gigabit Ethernet compliant stream over 75m of 1mm PMMA SI-POF with 2.5 dB system margin, and over 50 m with 7 dB system margin, in both cases using commercial RC-LED. We believe this is an unprecedented results, showing for the first time that the target distance of 50 meters is reachable with a large system margin. The results were made possible by a careful optimization of the physical layer architecture, which is explained in detail in this paper. The system is experimentally demonstrated over realistic digital stream at the transmitter and real time processing at the receiver.

First demonstration of real-time LED-based Gigabit Ethernet transmission on 50m of A4a.2 SI-POF with significant system margin

We present the first experimental demonstration of a Gigabit Ethernet transmission system capable of reaching 50m on A4a.2 POF (standard 1mm PMMA Step-Index Plastic Optical Fiber) with high system margin (6.5 dB) under real Ethernet traffic flowing between two workstations.

Experimental Investigation of Nonlinear Interference Accumulation in Uncompensated Links

Noise due to nonlinear effects in uncompensated links has recently been shown to be Gaussian and additive. We experimentally investigate the law governing its accumulation. Our results suggest a mild super-linear accumulation versus number of spans, compatible with coherent accumulation models.