Fig. 1. Diagrams of OAM photodetection and basic characterization of the MLG photodetector: (a), (b) diagrams of OAM photodetection for (a) mechanical modulation and (b) PEM modulation. (c) Optical image of the MLG photodetector. (d) Drain–source current Ids as a function of the back gate voltage Vg with a 5-mV drain-source voltage Vds, together with Ids−Vds measurements with zero back gate voltage. (e) Scanning photocurrent mapping together with (f) in situ scanning reflection mapping under the excitation of a basic mode Gaussian beam with a power of 0.9 mW at 4μm. The spatial resolution is 10μm.

Fig. 2. OPGE response of the MLG device based on mechanical modulation. (a) Schematic of polarization modulation based on a polarizer and a quarter wave plate. (b) Polarization modulation as a function of the QWP angle over a period of 180 deg. (c) Photocurrent response of the device as a function of the quarter-wave plate angle θ. The PC responses for the left and right circular polarizations are marked by blue and red dashed lines, respectively, and the CPGE component is marked by arrows, with red and blue representing positive and negative CPGE responses, respectively. (d) CPGE component JC as a function of the OAM order m. The error bars represent the standard deviation of the fit. (e) Linear fitting of JC as a function of the OAM order m.

Fig. 3. Schematic of OAM photodetection based on PEM modulation. (a) Optical part (polarization modulation with a polarizer and an optical head of the PEM). (b) Electronic part (modulating voltage, photocurrent collection, and CPGE extraction). (c) Sinusoidal modulating voltage applied to the quartz piezoelectric transducer. (d) Phase retardation introduced by the optical head of the PEM. (e) Schematic for polarization modulation in the two principal axis directions of the PEM. (f) Polarization modulation in one operation cycle of the PEM.

Fig. 4. OPGE response of the MLG device based on PEM modulation. (a) On–off measurements of the CPGE response under the excitation of OAM beams with OAM orders ±4, ±2, and ±1. (b) CPGE component JC together with its linear fit as a function of the OAM order m. The error bars represent the standard deviation of the fit. (c) Comparison of the OPGE responsivity and OAM resolution capability under mechanical and PEM modulations. (d) On-off measurements of the CPGE response with different time constants of the lock-in amplifier under the excitation of OAM beams with an OAM order of ±4. (e) Measured CPGE response together with its uncertainty as a function of the time constant of the lock-in amplifier under the excitation of OAM beams with OAM orders ±4. The dashed lines are fitting with 1/T. (f) Average signal-to-noise ratio of JC shown in Fig. (e) as function of time constant of lock-in amplifier. The average signal-to-noise ratio of JC measured with mechanical modulation is marked by red dot for reference and the dash line are fitting with T.

Fig. 5. Schematic of the PEM modulation scheme for a light OAM photodetector focal-plane-array device based on graphene. (a) Overall device structure of the focal-plane-array device. (b) Schematic of the OAM detection chip and PEM modulation module driven by the power module. (c) Schematic of the focal-plane array based on MLG photodetectors. (d) Schematic of the read-out circuit.