Optically gated transduction enables silicon electrical readout of mid-infrared light
Silicon is the dominant platform for integrated photonics, yet its wide electronic bandgap of 1.1 eV fundamentally prevents efficient detection of mid-infrared (MIR) photons through direct valence band to conduction band excitation. Existing approaches therefore seek to enhance sub-bandgap absorption or introduce external infrared absorbers. Here we demonstrate a profoundly different detection strategy based on optically gated transduction, in which MIR photons modulate a pre-established excitation state rather than directly generating photocarriers. Our device integrates Nd3+-doped lanthanide nanoparticles with an inverse-designed Al/p-Si metasurface supporting dual resonances that simultaneously enhances optical gating in the near infrared and resonantly couples incident MIR radiation. The MIR illumination redistributes the Nd3+ emission pathways, producing an optical-state change that is converted into an electrical signal through a silicon Schottky junction. The device achieves room-temperature zero-bias detection at 6.8 um with a modulation responsivity of 103 uA/W and resolves combined gate and MIR inputs into three electrically distinguishable current states. Rather than extending silicon absorption into the infrared, this work establishes gated optical transduction as a route for reading MIR optical information on a silicon platform, opening opportunities for integrated infrared sensing, signal processing and programmable photonic systems.