A Silicon Optical Transistor
  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. 
Leo T. Varghese, Li Fan, Jian Wang, Fuwan Gan, Ben Niu, Yi Xuan,   Andrew M. Weiner and Minghao Qi
physics.optics