Ultimate Sensitivity for Optically Preamplified Direct-Detected OFDM Systems Using Spectrally Matched Optical Filters

We investigate the lower sensitivity bound, in terms of optical signal-to-noise ratio (OSNR), for direct-detected orthogonal frequency-division-multiplexing (DD-OFDM) systems in the presence of optically preamplified receivers. Using the spectrally matched optical filter, which is composed of two parallel filters for the carrier and sideband and has a passband matching to the signal spectrum, the ultimate sensitivity of DD-OFDM is found theoretically to approach that of coherent optical OFDM. We also investigate the effects of the filter's orders and bandwidths to the improved OSNR, and found that these effects could be effectively mitigated via the use of an optical amplifier for the carrier.