Abstract

Although nonlinear coupling at a coupler has been widely studied for all-optical ultrafast switching, use of nonlinear coupling for logic functions has not been reported. In this paper, the phenomena of asymmetric nonlinear coupling at a fiber coupler are presented. By asymmetric nonlinear coupler, we mean a coupler in which the Kerr effects in the two waveguides are different when the same power is launched into each waveguide. The difference in Kerr effect can be implemented by controlling the nonlinear constant or waveguide thickness. Although the nonlinear effect is asymmetric in such a coupler, linear coupling is still symmetric, otherwise energy cannot be conserved. It is found that, in the chosen range of coupler asymmetry, input energy tends to appear in the waveguide of larger nonlinearity at the output end of a half beat-length coupler when only one waveguide is excited. When both waveguides are excited, the energy distribution between the two output ports depend on the relative phase of the two input signals. By appropriately choosing the coupler asymmetry and the relative phase of the input signals, nor, and, or. and xor gates are implemented using a half beat-length coupler.

© 1991 Optical Society of America