High-speed readout for direct light orbital angular momentum photodetector via photoelastic modulation

Recent progress in direct photodetection of light orbital angular momentum (OAM) based on the orbital photogalvanic effect (OPGE) provides an effective way for on-chip direct electric readout of orbital angular momentum, as well as large-scale integration focal-plane array devices. However, the recognition of OAM order from photocurrent response requires the extraction of circular polarization-dependent response. To date, the operation speed of such a detector is currently at the minute level and is limited by slow mechanical polarization modulation and low OAM recognition capability. We demonstrate that the operation speed can be greatly improved via an electrical polarization modulation strategy with a photoelastic modulator (PEM) accompanied by a phase-locked readout approach with a lock-in amplifier. We demonstrate an operation speed of up to kilohertz level with this new technology in the mid-infrared region (4 μm) on an OAM detector using multilayer graphene as photosensitive material. In principle, with a new modulation and readout scheme, we can potentially increase the operation speed to megahertz with a PEM that operates at a state-of-the-art speed. Our work paves the way toward high-speed operation of direct OAM detection devices based on the OPGE effect and pushes such technology to a more practical stage for focal plane array applications.