1. Technical Field
The inventions relate to optical communication systems.
2. Discussion of the Related Art
This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Some current communications systems propose the use of pulse position modulation (PPM) to achieve high sensitivity at a receiver. In PPM, a signal is transmitted during a single time slot of the M time slots within each symbol period. In each symbol period, the receiver examines each of the M time slots to identify the time slot in which the signal wits transmitted. Unfortunately, increasing the number of time slots per symbol interval causes the PPM pulses to become temporally narrow and to have correspondingly larger bandwidths. For that reason, PPM may not provide a high spectral efficiency.