On-chip monitoring of far-field patterns using a planar diffractor in a silicon-based optical phased array

We demonstrate the on-chip monitoring of far-field patterns in a silicon-based optical phased array (OPA) using a planar diffractor and traveling-wave photodetectors (PDs) integrated at the end of the radiator array. To reproduce the diffraction patterns within a silicon slab, the planar diffractor is designed with a diffraction region surrounded by an absorptive boundary and seven discrete outlet waveguides. Each outlet waveguide is linked to the photon-assisted tunneling PD which has a silicon p-n junction and is operated under a reverse bias to detect a sub-bandgap wavelength, 1.3 µm. With the 1×16 OPA and seven detectors, the positions of the main beams aligned to specific directions in the free space were clearly monitored.