  Controlling the optical response of a medium through suitably tuned coherent
electromagnetic fields is highly relevant in a number of potential
applications, from all-optical modulators to optical storage devices. In
particular, electromagnetically induced transparency (EIT) is an established
phenomenon in which destructive quantum interference creates a transparency
window over a narrow spectral range around an absorption line, which, in turn,
allows to slow and ultimately stop light due to the anomalous refractive index
dispersion. Here we report on the observation of a new form of either induced
transparency or amplification of a weak probe beam in a strongly driven silicon
photonic crystal resonator at room temperature. The effect is based on the
oscillating temperature field induced in a nonlinear optical cavity, and it
reproduces many of the key features of EIT while being independent of either
atomic or mechanical resonances. Such thermo-optically induced transparency
(TOIT) will allow a versatile implementation of EIT-analogues in an integrated
photonic platform, at almost arbitrary wavelength of interest, room temperature
and in a practical, low cost and scalable system.
