This work models an all-optical 2-bit adder comprised of Fabry-Perot devices. Each device is composed of 2 silver mirrors on either side of a cavity made of a nonlinear Kerr material. These devices are optically bistable and suitable for fast logic operations on the order of picoseconds. We propose to use an amplifying buffer between devices to adjust the transmitted signal’s amplitude to the desired value, and to provide control for logic operations. We use the method of finite-difference time-domain (FDTD) in one-dimensional (1D) space to demonstrate the feasibility of the proposed idea.