[18a-PA5-1~8] 3.15 Silicon photonics

▲ [18a-PA5-4] Carrier-injection Ge MIR Variable Optical Attenuator Formed by Spin-on-Glass Doping

〇(DC)Ziqiang Zhao¹, Chongpei Ho¹, Shinichi Takagi¹, Mitsuru Takenaka¹ (1.The Univ. of Tokyo)

Keywords:germanium, mid infrared, variable optical attenuator

Mid-infrared (MIR) photonics is now attracting more attention for optical communication and sensing with a wide operation wavelength from 2 μm to 15 μm. Germanium (Ge) is now emerging as a potential to broaden the application in MIR thanks to its large transparency window and superior optical properties. We have investigated a Ge-on-insulator (GeOI) platform for MIR photonic integrated circuits. In the previous study, the efficiency of a carrier-injection Ge variable optical attenuator (VOA) was limited by the poor PIN junction property due to the insufficient doping density of phosphorus in Ge. This work demonstrated an efficient Ge VOA by using spin-on-glass doping (SOG). The doping density of the n⁺-region was improved from 3.0×10¹⁷ cm^-3 to 1.9×10¹⁹ cm^-3 by applying SOG technique. As a result, an efficient Ge VOA with an improved modulation efficiency of 320 dB/A was experimentally demonstrated, which is 2.7 times larger than previous report. This result explicated that the trade-off between efficiency and lifetime can be improved using a Ge VOA, paving a way of efficient and high-speed VOA for MIR photonics.