Ultra-selective flexible add and drop multiplexer using rectangular optical filters based on stimulated Brillouin scattering

We demonstrate an ultra-selective flexible reconfigurable add and drop multiplexer (ROADM) structure enablingseparation and aggregation operations for multi-band orthogonal frequency division multiplexing(MB-OFDM) signal with ∼2-GHz spectral granularity and 300-MHz guard band. The ROADM employs rectangular optical filters based on stimulated Brillouin effect (SBS) in fiber, which have steepedges, ∼1-dB passband ripple and tunable bandwidth from 100 MHz to 3 GHz realized by two different kinds of electrical feedback pump control approaches. The ROADM performance is measured with MB-OFDM signals inquadraturephase-shift-keying (QPSK) and 16-quadrature-amplitude-modulation (16-QAM) formats. For QPSK format signal, the SBS-ROADM induced penalty is ∼0.7 dB while the performance for 16-QAM format is also acceptable.