On-Chip Calibration of an Optical Phased Array Through Chip Facet Reflections

We present an InP optical phased array with on-chip calibration capabilities. The on-chip calibration relies on reflecting some of the light at the optical antennas back into the OPA input waveguide and measuring the phase difference between consecutive arms through an mREV calibration algorithm. We employ a spurious low-level (<0.1%) reflection at the OPA facet, and we demonstrate that it is enough to calibrate the PIC using this method. Moreover, we calibrate following both a free-space and on-chip method and measure negligible variations of sidelobe-suppression ratio and beam width respectively, showing comparable calibration accuracies for the two methods.