Demonstration of record-low injection-current variable optical attenuator based on strained SiGe with optimized lateral pin junction.

We demonstrate a strained SiGe variable optical attenuator (VOA) with a lateral pin junction which exhibits record-low injection-current for 20-dB attenuation. We optimize the distance between the highly doped p + and n + regions in the lateral pin junction to effectively inject electrons and holes, taking into account the propagation loss. In conjunction with the enhanced free-carrier absorption in strained SiGe, the SiGe VOA with the optimized lateral pin junction exhibits 20-dB attenuation by 20-mA/mm injection current, which is 1.5 times lower current density than that of the Si VOA. The SiGe VOA also shows better RF response than the Si VOA due to the short carrier lifetime in SiGe, allowing us to achieve efficient and fast attenuation modulation simultaneously. Furthermore, 2-GHz switching and error-free transmission of 4 × 12.5 Gbps WDM signal have been also achieved.