Stefanos Dris

ORCHESTRA - Optical performance monitoring enabling flexible networking

An optical network, like any system, has to be observable before it can become subject to optimization, and this is the main capability that ORCHESTRA project introduces. ORCHESTRAs high observability will rely on information provided by the coherent transceivers that can be extended, almost for free, to operate as software defined optical performance monitors (soft-OPM). Novel digital signal processing (DSP) OPM algorithms will be developed and combined with a novel hierarchical monitoring plane, cross-layer optimization algorithms and active-control functionalities. ORCHESTRA vision is to close the control loop, enabling true network dynamicity and unprecedented network capacity efficiency.

A 64 Gb/s PAM-4 linear optical receiver

We present a linear optical receiver realized on 130 nm SiGe BiCMOS. Error-free operation assuming FEC is shown at bitrates up to 64 Gb/s (32 Gbaud) with 165mW power consumption, corresponding to 2.578 pJ/bit.

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.

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.

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.

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.

Quaternary TDM-PAM as upgrade path of access PON beyond 10Gb/s

A 20 Gb/s quaternary TDM-PAM passive optical network with chirped and non-linear optical transmitters is experimentally demonstrated. The migration from legacy TDM-PONs and the implications of using available 10 Gb/s components are analyzed. We show that a loss budget of 27.3 dB is compatible together with a packet power ratio of 10 dB between loud and soft optical network units.

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.

112 Gb/s sub-cycle 16-QAM Nyquist-SCM for intra-datacenter connectivity

Datacenter traffic is exploding. Ongoing advancements in network infrastructure that ride on Moore’s law are unable to keep up, necessitating the introduction of multiplexing and advanced modulation formats for optical interconnects in order to overcome bandwidth limitations, and scale lane speeds with energy- and cost-efficiency to 100 Gb/s and beyond. While the jury is still out as to how this will be achieved, schemes relying on intensity modulation with direct detection (IM/DD) are regarded as particularly attractive, due to their inherent implementation simplicity. Moreover, the scaling-out of datacenters calls for longer transmission reach exceeding 300 m, requiring single-mode solutions. In this work we advocate using 16-QAM sub-cycle Nyquist-SCM as a simpler alternative to discrete multitone (DMT), but which is still more bandwidth-efficient than PAM-4. The proposed optical interconnect is demonstrated at 112 Gb/s, which, to the best of our knowledge, is the highest rate achieved in a single-polarization implementation of SCM. Off-the-shelf components are used: A DFB laser, a 24.3 GHz electro-absorption modulator (EAM) and a limiting photoreceiver, combined with equalization through digital signal processing (DSP) at the receiver. The EAM is driven by a low-swing (<1 V) arbitrary waveform generator (AWG), which produces a 28 Gbaud 16-QAM electrical signal with carrier frequency at ~15 GHz. Tight spectral shaping is leveraged as a means of maintaining signal fidelity when using low-bandwidth electro-optic components; matched root-raised-cosine transmit and receive filters with 0.1 excess bandwidth are thus employed. Performance is assessed through transmission experiments over 1250 m and 2000 m of SMF.

120 Gb/s PAM-8 and 80 Gb/s PAM-4 Optical Interconnect with a Sub-Volt Driven EAM

A record 40 Gbaud PAM-8 optical interconnect link is demonstrated using a bandwidth-limited Electro-Absorption Modulator, driven with sub-volt electrical swing. Employing digital equalization, transmission of PAM-4 and PAM-8 over 2000 m of SMF is achieved.