Silicon four-quadrant photodetector working at the 1550-nm telecommunication wavelength

In this Letter, we demonstrate a silicon four-quadrant photodetector working at the 1550-nm telecommunication wavelength and apply it to the measurements of the light-beam positions and deflection angles. Incident light changes the admittance of each quadrant photodetector through sub-bandgap optical absorption, and this change of admittance is read out through transimpedance amplification and lock-in readout circuitry. By monitoring the optical power received by the four quadrant photodetectors, we measure and track the position of the optical beam. Without any modification, the same device and associated circuit can also work at wavelengths shorter than the long-wavelength limit of silicon, for example, at 780 nm, as we demonstrate. (C) 2022 Optica Publishing Group