  We show that interference can be the principle of operation of an all-optical
switch and other nanoscale plasmonic interference devices (PIDs). The optical
response of two types of planar plasmonic waveguides is studied theoretically:
bent chains and Y-shaped configurations of closely-spaced metallic nanospheres.
We study symmetric Y-shape arrays as an example of an all-optical switch and
demonstrate that effective phase- and amplitude-sensitive control of the output
signal can be achieved due to interference effects.
