High Granularity Multiband OFDM Virtual Carrier-Assisted Direct-Detection Metro Networks

A direct-detection metropolitan (metro) network employing multiband orthogonal frequency division multiplexing (MB-OFDM) signals (MORFEUS network) is proposed. The MORFEUS network employs virtual carriers to assist the detection of each OFDM band. It represents a cost-effective network enabling high granularity and flexibility, while requiring a reduced receiver bandwidth. The MB-OFDM signal structure and their main constraints are presented. Each MB-OFDM metro node is described and discussed, with particular attention dedicated to the blocks required to insert and extract a given OFDM band of the MB-OFDM signal. Conceptual solutions for the MORFEUS insertion and extraction blocks are also proposed and discussed. The performance of a 42.8-Gb/s MORFEUS network is evaluated through numerical simulation, and the network operation design is optimized. The impact of the optical filtering effect due to band add/drop operations is assessed as well. These studies are accomplished for systems employing band selectors (BS) with different selectivity to assess the performance tolerance to interband crosstalk and in-band amplitude distortion. The studies are performed for three MORFEUS networks, with granularity of 2-, 3-, and 4-bands. A required optical signal-to-noise ratio (OSNR) of 24 dB is demonstrated in a 240-km-long MORFEUS network without optical filtering cascade effect for a bit error ratio of $10^{-3}$. This required OSNR level is achieved for the three networks with different granularity and for the two BS analyzed after suitable optimization of the MB-OFDM system parameters. Compared with an ideal MORFEUS network employing ideal rectangular BS, the analyzed networks present an OSNR penalty not exceeding 2.5 dB. A required OSNR penalty of 1 dB due to optical filtering cascade is obtained after six nodes with band filtering, for BS with a second order super-Gaussian shape.