Ioannis Lazarou

Bandpass sampling in heterodyne receivers for coherent optical access networks.

A novel digital receiver architecture for coherent heterodyne-detected optical signals is presented. It demonstrates the application of bandpass sampling in an optical communications context, to overcome the high sampling rate requirement of conventional receivers (more than twice the signal bandwidth). The concept is targeted for WDM coherent optical access networks, where applying heterodyne detection constitutes a promising approach to reducing optical hardware complexity. The validity of the concept is experimentally assessed in a 76 km WDM-PON scenario, where the developed DSP achieves a 50% ADC rate reduction with penalty-free operation.

Silicon-on-Insulator Nanowire Resonators for Compact and Ultra-High Speed All-Optical Wavelength Converters

We present the development of application-specific silicon-on-insulator SOI nanowire ring and racetrack resonators designed to assist semiconductor optical amplifier (SOA)-based all-optical wavelength conversion. We demonstrate the fabrication of fix resonance racetrack resonators exhibiting coupling gaps as low as 160 nm and tunable ring resonators with coupling gaps <; 90 nm. The resonators are cascaded after commercial 40 Gb/s SOAs to realize chirp filtering of the optical data signals through high-resolution spectral sampling. We experimentally demonstrate inverted and non-inverted SOI resonator-assisted all-optical wavelength conversion at 40 Gb/s and 160 Gb/s with power penalties <; 3 dB.

Full-Duplex 4-PAM Transmission for Capacity Upgrade in Loop-Back PONs

We report for the first time on the feasibility of quaternary (4-ary) pulse amplitude modulation (4-PAM) for both downstream (DS) and upstream (US) directions in a full-duplex passive optical network (PON) with wavelength reuse. The scheme is validated with a simple, low-cost, and colorless optical network unit (ONU) exploiting the all-optical carrier recovery scheme. The ONU employs a high-finesse optical filter with periodic frequency response for carrier extraction and data erasure of the DS signal. A cascade of two semiconductor optical amplifiers (SOAs) amplifies and modulates the recovered carrier with the 4-PAM US data-stream. The proposed scheme constitutes a migration scenario towards low-cost TDM/WDM PONs with currently deployed hardware equipment, ensuring full-duplex transmission up to 26 km, with higher spectral efficiencies and auspicious wavelength allocation.

The BOOM Project: Towards 160 Gb/s Packet Switching Using SOI Photonic Integrated Circuits and Hybrid Integrated Optical Flip-Flops

We present a 160 Gb/s optical packet switching architecture that performs label detection and packet wavelength con- version using photonic components integrated on silicon-on-insulator (SOI) waveguide boards. For label detection, we report the fabrication of a 4-channel tunable, second-order microring resonator demultiplexer using the SOI nanowire waveguide platform. For all-optical wavelength conversion we report the integration and packaging of a cascaded SOI delay interferometer (DI) structure using SOI rib waveguides. Both components were assembled with an optical flip-flop to enable 160 Gb/s optical packet switching. The power penalty after the wavelength conversion process was ~4.5 dB with error performance well above the FEC limit. This work is part of the European ICT-BOOM project which aims at building a Tb/s photonic router using hybrid and heterogeneous integration on SOI substrates. The preliminary results reported here is the initial step before the final project demonstrator.

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.

Bandwidth and Wavelength-Selective MUX/DEMUX Microresonator Elements for Flexible-Grid Applications

We propose a novel concept for a MUX/DEMUX array based on microresonators with reconfigurable bandwidth and wavelength response. Initial experimental results on a single MR element prove its suitability for flexible-grid applications.

Frequency Offset Estimation in M-QAM coherent optical systems using phase entropy

A novel approach for Frequency Offset Estimation in coherent optical M-QAM systems using the received symbol phase entropy is investigated. It is accurate, non-data-aided, oblivious to modulation format and requires no gain control.

Fabrication and experimental demonstration of the first 160 Gb/s hybrid silicon-on-insulator integrated all-optical wavelength converter

We present a hybrid integrated photonic circuit on a silicon-on-insulator substrate that performs ultra high-speed all-optical wavelength conversion. The chip incorporates a 1.25 mm non-linear SOA mounted on the SOI board using gold-tin bumps as small as 14 μm. Τhe device performs chirp filtering and signal polarity inversion with two multi-mode interference (MMI) - based cascaded delay interferometers (DIs) monolithically integrated on the same SOI substrate. Full free spectral range (FSR) tuning of the DIs is accomplished by two independently tuneable on-chip thermal heaters. We demonstrate 160Gb/s all-optical wavelength conversion with power penalties of less than 4.6dB.

A hybrid photonic integrated wavelength converter on a silicon-on-insulator substrate

We present fabrication and testing of a wavelength converter integrated on a silicon-on-insulator substrate. The chip employs a hybrid integrated SOA and delay-interferometers integrated on 4μm SOI. We demonstrate 40Gb/s error-free performance.

Flexible quadrature amplitude modulation with semiconductor optical amplifier and electroabsorption modulator.

Optical quadrature amplitude modulation (QAM) is experimentally demonstrated with a low-complexity modulator based on a semiconductor optical amplifier and electroabsorption modulator. Flexible amplitude/phase format transmission is achieved. The applicability of octary QAM for coherent optical access networks with sustainable 3 Gb/s per-user bandwidth is investigated for a long reach of 100 km, and its compatibility with a potentially high split is verified.