  Electromagnetically induced transparency has the unique ability to optically
control transparency windows with low light in atomic systems. However, its
practical applications in quantum physics and information science are limited
due to rigid experimental requirements. Here, we demonstrate a new mechanism of
optically induced transparency in a micro-cavity by introducing a four-wave
mixing gain to nonlinearly couple two separated resonances of the micro-cavity
in an ambient environment. A signature Fano-like resonance was observed owing
to the nonlinear interference of the two coupled resonances. Moreover, we show
that the unidirectional gain of the four-wave mixing can lead to the remarkable
effect of non-reciprocal transmission at the transparency windows. Optically
induced transparency may offer a unique platform for a compact, integrated
solution to all-optical and quantum information.
