In a nonreturn-to-zero format, digital-optical transmission systems clock extraction has traditionally required the use of a nonlinear electrical element (e.g., mixer or exclusive -OR gate), in the post receiver circuit to generate the missing clock frequency component in the data-frequency spectrum. For optical processing and routing applications in future multi gigabit-per-second systems, tapping of the optical highway to provide the signal power for an electronic clock extraction circuit is highly disadvantageous. Here we demonstrate a novel method of clock extraction using a split-contact semiconductor nonlinear optical amplifier (NLOA) with one gain and one saturable absorber region. The data is shaped and amplified by the NLOA, while the optical nonlinearity due to the saturable absorption generates an electrical clock frequency component at the absorber contact. Only narrow-band electrical filtering is then required to extract a stable clock signal.
© 1991 Optical Society of AmericaPDF Article