Roberto Magri

Blind Adaptive Chromatic Dispersion Compensation and Estimation for DSP-Based Coherent Optical Systems

We propose an accurate and low-complexity blind adaptive algorithm for chromatic dispersion (CD) compensation and estimation in coherent optical systems. The method is based on a Frequency Domain Equalizer (FDE), a low complexity Time Domain Equalizer arranged in a butterfly structure (B-TDE) and an Optical Performance Monitoring (OPM) block in a loop configuration. The loop is such that, at each iteration, the CD value compensated by the B-TDE and estimated by the OPM is given to the FDE; according to this estimation, in the subsequent iteration, the FDE compensates also this quantity. The procedure is repeated until the majority of CD is compensated by the FDE and a small residual quantity is compensated by a low complexity B-TDE with a small number of taps. The method is extended to long haul uncompensated links exploiting the information on the mean square error (MSE) provided by the B-TDE. The proposed algorithm is then experimentally validated for a polarization multiplexed quadrature phase shift keying (PM-QPSK) signal at 112 Gbit/s propagating along 1000 km of uncompensated Z PLUS® optical fiber. A statistical analysis of the performance of the proposed solution, in terms of mean value and standard deviation of the CD estimation error, is carried out, running a set of simulations including different impairments, such as noise, polarization dependent loss, polarization mode dispersion and self-phase modulation in a line of 1000 km of uncompensated G.652 optical fiber. Our method could be used to compensate and estimate any CD quantity without increasing the number of taps in the B-TDE and exploiting devices already included in the system (TDE, FDE and OPM) arranged in a loop.

A programmable, multi-format photonic transceiver platform enabling flexible optical networks

Development of programmable photonic devices for future flexible optical networks is ongoing. To this end, an innovative, multi-format QAM transmitter design is presented. It comprises a segmented-electrode InP IQ-MZM to be fabricated in InP, which can be directly driven by low-power CMOS logic. Arbitrary optical QAM format generation is made possible using only binary electrical signals, without the need for high-performance DACs and high-swing linear drivers. The concept enables a host of Tx-side DSP functionality, including the spectral shaping needed for Nyquist-WDM system concepts. In addition, we report on the development of an optical channel MUX/DEMUX, based on arrays of microresonator filters with reconfigurable bandwidths and center wavelengths. The device is intended for operation with multi-format flexible transceivers, enabling Dense (D)WDM superchannel aggregation and arbitrary spectral slicing in the context of a flexible grid environment.

Nonlinear tolerance of 112-Gb/s DP-QPSK in a live field upgrade trial over a 848km 10G DWDM link

An in-service field trial with coherently detected DP-QPSK at 112 Gb/s was performed over a Telefónica live link of 848km, testing long term stability and determining noise margin and optimum launch power of the format.

Dense WDM-PON with 23(46) Gb/s/λ D(Q)PSK aggregation in the feeder and micro-ring resonator assisted ONUs

An aggregation scheme based on a D(Q)PSK/ASK comb transmission in the feeder is presented. A shared delay interferometer allows simple ONUs that are assisted by a ring resonator.

Detection strategies in the presence of fiber nonlinear effects

All known compensation techniques for combating fiber nonlinearities, including digital back-propagation (BP), are far from being optimal. However, it is shown that a low-complexity Viterbi detector with proper metrics is a good alternative or complement to BP for approaching optimal performance.

Blind and low complexity CD compensation and estimation method in DSP based coherent optical systems

An accurate and low complexity blind adaptive chromatic dispersion compensation and estimation algorithm for coherent optical systems is proposed and experimentally validated. The method is based on a Frequency Domain Equalizer, a low complexity Butterfly Time Domain Equalizer and an Optical Performance Monitoring in a loop configuration.

Large-scale photonic integration: a key-enabling technology for all-optical signal processing

Emerging services and applications—such as 3D TV, video on demand, and peer-to-peer applications—are driving network capacity and cost to their limit. Current research and standardization efforts are focusing on the use of advanced modulation formats such as differential-phase-shift keying (DPSK) and differential-quadrature-phase-shift keying (DQPSK) to increase optical-fiber bandwidth capacity. For the foreseeable future, these advanced modulation formats will have to co-exist with standard on-off keying (OOK) due to already-installed fibertransmission equipment. In this context, photonic integration is a key enabling technology toward the aggregation of complex functionalities for multiple modulation formats on single photonic chips. One such initiative is supported by the European Commission through the ICT-APACHE project.1 It aims to develop multi-format transmitters, receivers, and regenerators based on hybrid integration of high-performance indium phosphide (InP) monolithic elements on low-loss planar silica-on-silicon circuits. Hybrid integration has numerous advantages, such as low loss and power consumption, and a small footprint. However, the most significant benefit is easy adaptation of the silica motherboard to different circuit designs and a wide range of applications. Here, we describe a multi-format-processing chip (MFPC) that we fabricated for the first demonstration of multi-format regeneration and wavelength conversion on a single device.2 Until now, this Figure 1. (a) Multi-format-processing-chip (MFPC) layout and (b) mask design. (c) The silica motherboard. The white arrow indicates the position of the quad semiconductor optical amplifier (SOA) array. A–O: Integrated thermo-optic phase shifters. DI: Delay interferometer.

BICM and TCM Comparison in 100 Gbps Optical Coherent Links in Nonlinear Regime

The popular single-carrier QPSK modulation format is compared with 8PSK BICM and TCM schemes in 100 Gbps optical links in linear and nonlinear regime, with or without inline dispersion compensation.

Transient Control by Free Ase Light Re-Circulation in EDFA Based WDM Ring Networks

We demonstrate that a free ASE light re-circulation in EDFA based WDM ring networks provides an effective gain clamping technique. Proper network and amplifier design ensure signal power overshoots lower than 2.5 dB under 23/24 WDM channels add-drop operations.