  A fundamental road block for all-optical information processing is the
difficulty in realizing a silicon optical transistor with the ability to
provide optical gain, input output isolation and buffer action. In this work,
we demonstrate an all-optical transistor using optical nonlinearity in
microrings. By using weak light to control strong light, we observed an On/Off
ratio up to 20 dB. It can compensate losses in other optical devices and
provide fan-out capability. The device is ultra compact and is compatible with
current complementary metal-oxide-semiconductor (CMOS) processing.
