Theoretical Study Of The Switching Characteristics Of Terahertz All-optical Demultiplexer (on Toad)

In this paper, the switching characteristics of the terahertz optical asymmetric demultiplexers (TOAD) devices subject to picosecond pulses have been investigated, by taking into account of both gain saturation and nonlinear gain compression in the semiconductor optical amplifier (SOA). On the condition that the optical pulse width in OTDM system is much larger than the intra-band relaxation time, the coupling equations of gain, pulse power and phase of the SOA are derived from the SOA carrier-density rate equation and electromagnetic field equation. In a reference frame coordinate; the theoretical models of dynamical gain response of the SOA and optical pulse propagation are constructed and the dynamical gain characteristics of the SOA are studied in detail. Based on these analyses, the theoretical model of TOAD is developed by considering gain saturation and nonlinear gain compression. Furthermore, the switching characteristics of TOAD are investigated in the cases of the central frequency of the control pulse equal to and different from that of the signal pulse. Based on the modified coupling equations among the gain, pulse power and phase of the SOA, the switching characteristics of TOAD are discussed in the two cases of positive and negative frequency detuning. It is shown that, for the case of positive detuning, the switching characteristics of TOAD don't improve and begin to deteriorate while the detuning increases; but for the case of negative detuning, the switching characteristics of TOAD achieve improvement obviously and the switching contrast ratio is enhanced and however the detuning has an optimal operating range. The theoretical analysis is shown to be in good agreement with available experiment results.