Influence of chirp on optical free-space communication systems employing preamplified direct detection

Summary form only given. With the large-scale commercial deployment of Erbium-doped fiber amplifiers, optically preamplified direct detection (DD) receivers have become the technically most practicable way of achieving (nearly) quantum limited receiver performance in the 1.5 /spl mu/m wavelength range. In fiber communication systems, DD reception is affected by chirp due to fiber dispersion and nonlinear effects, but in free-space communications, narrow optical filtering changes receiver sensitivity if the input signal is chirped. We present a detailed investigation on the influence of chirp in free-space preamplified DD systems and analyze the (different!) impact in the case of non-return-to-zero (NRZ) and return-to-zero (RZ) coding. Optimizing the optical and electrical receiver bandwidths leads to improved sensitivity.