Adaptive Modulation-Induced Reduction in Filter Concatenation Impairment for Optical OFDM Metro/Regional Systems

The impact of optical OFDM (orthogonal frequency division multiplexing) with adaptive modulation on reducing the filter concatenation effect is investigated, for the first time, in intensity modulation and direct-detection transparent metropolitan/regional network systems incorporating cascaded reconfigurable optical add/drop multiplexers (ROADMs). The ROADMs considered are based on different optical filters including fiber Bragg grating, Chebyshev, thin film and wavelength-blocker/wavelength-selective switch devices. It is shown that, in comparison with conventional identical modulation, adaptive modulation can improve the system performance by a factor of up to 60%. The utilization of adaptive modulation can also significantly enhance the network tolerance to filter loss ripple, group delay ripple and frequency dip.