Capacity and error exponent for the direct detection photon channel. I

The capacity and the lower bound on the error exponent of a direct detection optical channel are derived. The channel input in a T-second interval is a waveform satisfying certain peak and average power constraints for the optical signal. The channel output is a Poisson process with a given intensity parameter; the intensity parameter takes account of the dark-current signal component. An explicit construction for an exponentially optimum family of codes is also presented