The present invention relates to an optical transmitter for transmitting data. The optical transmitter includes a pulse generator for generating N data streams overlapping in time from a de-multiplexed data source. Each respective data stream has pulses with shapes unique to that respective data stream. The transmitter also includes an optical source optically transmitting an output pulse that is generated by summing the uniquely shaped pulses from each respective data stream that are overlapping in time. Each output pulse represents N bits of the data source, where N>1.