Optically amplified regional and long-haul fiber optic networks employing wavelength division multiplexing (WDM) or code division multiple access (CDMA) are typically performance limited by cross-talk among different channels or users. Receiver based signal processing techniques for minimizing the resulting interference effects have been investigated in the past. In optical channels the receiver (the photo-detector) is effectively a square-law device. Combined with optical pre-amplification, this results in non-Gaussian, signal dependent noise and makes interference cancellation at the receiver difficult. In this paper we consider the design of a fiber-optic system as a whole multichannel system, using joint transmit and receive processing to minimize the performance degradation resulting from interference. Our results indicate that depending on the cross-correlation among channels or users the proposed techniques may outperform receiver based multiuser detection techniques.