  We demonstrate experimentally a new form of induced transparency, i.e.,
chaos-induced transparency, in a slightly deformed microcavity which support
both continuous chaotic modes and discrete regular modes with Q factors
exceeding 3X?10^7. When excited by a focused laser beam, the induced
transparency in the transmission spectrum originates from the destructive
interference of two parallel optical pathways: (i) directly refractive
excitation of the chaotic modes, and (ii) excitation of the ultra-high-Q
regular mode via chaos-assisted dynamical tunneling mechanism coupling back to
the chaotic modes. By controlling the focal position of the laser beam, the
induced transparency experiences a highly tunable Fano-like asymmetric
lineshape. The experimental results are modeled by a quantum scattering theory
and show excellent agreement. This chaos-induced transparency is accompanied by
extremely steep normal dispersion, and may open up new possibilities a dramatic
slow light behavior and a significant enhancement of nonlinear interactions.
