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Fiber and wireless optic communications have played significant roles in increasing the data capacity of modern transmission systems. Laser and channel nonlinear distortions in optical fiber systems and the inter-symbolinterference and the time-varying channel impulse response in optical wireless communication systems have deteriorated the detection and the demodulation of transmitted symbols from the received signals in corresponding systems. In the first part, we will discuss the performance of an advanced Kalman filter in mitigating the laser phase noise and the fiber nonlinearities under dispersion-unmanaged and dispersion-managed long-haul optical link conditions. In the second part, we will present two signal detection schemes in ultra-violet optical wireless communication systems by designing optimal linear and high-dimensional combinations of extracted ultra-violet signal-related geometrical features.