Experimental validation of the diagonal optical path properties: mitigating phase errors in interferometric-based...

We present an efficient calibration and programming methodology in the presence of imperfections and uncertainties for Mach-Zehnder interferometer (MZI)-based optical processors, utilizing the diagonal optical path properties. This approach enables direct phase monitoring of MZI phase shifters, inherently suppressing calibration errors caused by spurious scattered light originating from non-diagonal blocks and eliminating the need for computationally intensive calibration/programming schemes. We experimentally validate these properties using a 4 × 4 interferometric mesh fabricated on a silicon-on-insulator platform, demonstrating that the calibration remains unaffected by phase-setting uncertainties in preceding or succeeding blocks on a diagonal path. We also present a benchmarking procedure to assess testbed fidelity, which is further used to confirm the effectiveness of our approach by programming two random weight matrices, where fine-tuning via the diagonal path reduces the mean error of matrix-vector multiplication by 79% compared to an offline calibration method. These results highlight diagonal path properties as a practical and scalable solution for calibrating and programming reconfigurable multiport interferometers.