A closed-form parametric approach to channel-estimation is provided. In one aspect, a specific parametric expression is presented for the received signal pdf that accurately models the behavior of the received signal in IM/DD optical channels. The corresponding parametric channel-estimation approach simplifies the design of MLSE receivers. The general technique lends itself well to the estimation of the signal pdf in situations where there are multiple sources of noise with different distributions, such as ASE noise, together with Gaussian and quantization noise, and signal-dependent noise, for example.