  A rectangular potential barrier for a Bloch particle in a tight-binding
lattice is shown to become fully transparent by the application of a strong ac
field with appropriate amplitude and frequency. Such a curious phenomenon bears
some connection with the field-induced barrier transparency effect known for
freely-moving particles scattered by an ac-driven rectangular barrier; however,
for a Bloch particle transparency is not related to a resonant tunnneling
process across the cycle-averaged oscillating potential barrier, as for the
freely-moving quantum particle. The phenomenon of field-induced transparency is
specifically discussed here for photonic transport in waveguide arrays and
demonstrated by full numerical simulations of the paraxial (Schr\"{o}dinger)
wave equation beyond the tight-binding approximation.

Other Condensed Matter