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Project Snapshot | DSPMetroNet – Digital Signal Processing functions for Simplified Coherent Transceivers in Optical Metropolitan Networks

by IT on 01-02-2022
Project snapshot Digital Signal Processing Coding information Optical Quantum Communications DSPMetroNet

By Nelson Muga


DSPMetroNetDigital Signal Processing functions for Simplified Coherent Transceivers in Optical Metropolitan Networks is a research and development (R&D) project currently running in the Optical Quantum Communications and Technologies group at the Instituto de Telecomunicações, in Aveiro.

The main objective of the DSPMetroNet project is to investigate, develop, and validate new technological paradigms in terms of optical detection schemes and (Digital Signal Processing) DSP tools to support future optical metropolitan networks. Due to the ever-increasing network traffic, the access and metropolitan optical networks are at the heart of surging demand for high bandwidth, more flexibility, and reduced cost per bit transmitted. So, there is a significant need to enhance the per wavelength data rate beyond 100 Gigabit/second. Consequently, to meet the current and future requirements for high-speed system demands, there is a need for novel advanced modulation formats coding information both in the amplitude and phase (e.g. M-ary Quadrature Amplitude Modulation (M-QAM)) and high-performance DSP algorithms.

DSPMetroNet has been focusing its research activities on high-performance, high-speed, low-cost, and simplified optical transceiver paradigms that are suitable for various applications, mainly concentrating on data center networks. In this regard, the research team has explored one such simplified coherent approach, known as the Kramers-Kronig receiver, owing to the associated benefits such as low footprint, low cost, and low-power consumption. Using the free-space-optical transmission testbed available in the optic communications lab along with complex signal modulation formats, we have successfully implemented such Kramers-Kronig receiver achieving very-high net data rates (208 Gigabit/second and 184 Gigabit/second for the 32 QAM and 16 QAM signals, respectively).

However, the Kramers-Kronig receiver implementation results in different technical challenges. For instance, its algorithm includes nonlinear mathematical operations, such as logarithmic and exponential functions, that cause spectral broadening. This, in turn, demands the digital signal to be running faster than the standard Nyquist sampling rates. Moreover, most of the usual approaches for averting the associated challenges normally require stronger powers for the optical tone signal superimposing the data signal, which brings about an increase in the nonlinear distortions and additional sensitivity penalty. To address this, the project DSPMetroNet proposed a new optical signal phase retrieval method using direct detection, which we called DC-Value (DC-V) method. A low-complexity, low-latency, and low-tone power operation are the main advantages of this new DC-V iterative method, which makes it worthy for transceivers in short-reach optical links.

Recently, we have successfully validated of the new DC-V signal phase retrieval method in the laboratory, accomplishing very-high net data rates (80 Gigabit/second over 70 km, and 50 Gigabit/second over 80 km, for the 16 QAM and QPSK signals, respectively).


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