Abstract

We demonstrated an efficient carrier-injection germanium (Ge) variable optical attenuator (VOA) operating at 1.95 μm on a Ge-on-insulator (GeOI) platform for mid-infrared (MIR) integrated photonics. Numerical analysis illustrated that the Ge VOA can realize a significantly higher modulation efficiency than a Si VOA owing to the larger free-carrier absorption in Ge at MIR wavelengths. We proved that by introducing phosphorus-doped spin-on-glass (P-SOG) doping technology into the formation of a Ge lateral PIN junction, we can improve the doping concentration in the n⁺ region as compared with P ion implantation, resulting in improved modulation efficiencies of 380–460 dB/A for Ge VOAs. The P-SOG-doped Ge VOA exhibited a comparable modulation efficiency to a Si VOA operating at 1.55 μm despite the shorter carrier lifetime of 0.4–0.8 ns determined by numerical fitting. Thus, the Ge VOA formed by SOG doping has promising applications in communication and sensing at MIR wavelengths.

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