Demonstration of 16QAM-OFDM UDWDM Transmission Using a Tunable Optical Flat Comb Source

A new approach for designing broad and flattened spectrum multicarriers optical sources is presented leading to a 32 spectral lines source by using a dual-arm Mach–Zehnder modulator (MZM) and a 41 spectral lines source from two-stage MZM. A modified simulated annealing-based optimization method is applied to derive the necessary settings allowing the optical flat comb source (OFCS) to be ultraflat. The OFCS is mooted as a technology to enhance the overall capacity of an access optical network by increasing the number of wavelength division multiplexing (WDM) channels. Here, we demonstrate an ultradense WDM (UDWDM) transmission for application to passive optical networks with ( $11 \times 12.5$ Gbps) quadrature amplitude modulation (QAM) based on a 4 b/s/Hz spectral efficiency orthogonal frequency division multiplex (16QAM-OFDM) transmitter and direct detection. We use an OFCS to generate the 11 subcarriers spaced by 6.25 GHz, made of a two-stage MZM. We study the performance of three filtered channels in terms of error vector magnitude in back-to-back (B-to-B) conditions and after propagation through 25 and 100 km standard single mode fiber.