  We demonstrate that a photonic gauge potential, which arises from the phase
degree of freedom in dynamic refractive-index modulation and hence is
achormatic, can be used to achieve a broadband optical switch using the
configuration of a photonic Aharonov-Bohm interferometer (ABI). The resulting
ABI switch has a far larger bandwidth and lower cross talk than the
conventional Mach-Zehnder interferometer. Using coupled-mode theory and
full-wave numerical modeling, we compare the response of the two
interferometers in the presence of nonidealities. Our results indicate the
importance of the photonic gauge potential for broadband optical signal
processing.
