Zero-forcing electrical filters for direct detection optical systems

Intersymbol interference (ISI) in direct detection optical systems can limit channel spacing in frequency division multiplexing systems, and data rates, and transmission distances in long-haul transmission. It is desirable to reduce or cancel ISI in these situations, We investigate zero-forcing electrical filters to cancel ISI, and obtain tight performance bounds for minimum noise variance zero-forcing filters. We apply the results to Mach-Zehnder and Fabry-Perot filters, and to fibers with second order dispersion. We compare the performance of zero-forcing filters to that of rectangular impulse response filters and find that zero-forcing filters are advantageous in severe ISI situations with multilevel signalling.