Optical filter analyses for demultiplexing all-optical OFDM transmission systems

Using a single optical filter to demultiplex the all-optical orthogonal frequency-division multiplexing (OFDM) system was regarded as cost-effective and simple. Here, an all-optical OFDM signal demultiplexer using sinc transfer function was analyzed. The performance difference for using optical demultiplexers with different transfer functions was also compared and discussed. Within 20 km transmission, the sinc optical filter providing orthogonality between neighbor optical subcarriers can improve the signal performance by reducing the inter-carrier interference. After 20 km transmission, the signal performance degradation may mainly be dominated by dispersion for 10 Gb/s channel capacity; hence the advantage of sinc filter becomes negligible. These analyses provide the idea for how to choose the optical demultiplexer to integrate the whole optical fast Fourier transform circuit and optical sampling circuit into a single filter. This can effectively reduce the system cost and complexity.