20 G bps Pulse Amplitude Modulation (PAM) Format for Capacity Upgrade in Optical Communications

In the fast growing society, communication is broadening so rapidly such that internet users need to access information rapidly and amount of data flowing through internet is very huge. Various techniques for increasing capacity in data centers have drawn lots of attention in recent years. One way of addressing this demand is introduction of advanced optical modulation formats which has been motivated by the demand for high transmission capacity and better system reliability. In this work, two electrical data streams at bit rate of 10 G bps each were combined to produce 20 G bps multilevel system 4-PAM with four levels. One of the four amplitudes represents a combination of two bits (00, 01, 10, 11) per symbol. This therefore transmits two bits in parallel and therefore the data rate is doubled. The generated data was transmitted over 3.21km G.652 fiber at standard BER of 10-9. This format can be used to simultaneously transmit two bits per symbol per wavelength thereby increasing the overall link transmission speed while maintaining the channel bandwidth. We further demonstrated a digital signal processing assisted receiver to efficiently recover the transmitted signal without employing costly receiver hardware. The ability to use a single photodiode to demodulate the multilevel signal, brings a further reduction in cost on implementing the scheme. This spectral efficient modulation format will achieve even higher data rate per channel when coupled in a Dense Wavelength Division Multiplexing (DWDM) system. This will therefore lead to significant cost saving of capital investment and easing the system management and hence an efficient utilization of bandwidth.