Multi-input signal phase stabilization in photonic processors with on-chip feedback control

Reconfigurability, coupled with stable output, is essential for scaling integrated photonic systems to large footprints and high channel counts. We address phase instability in multimode photonic processors by implementing an on-chip feedback control (FBC) scheme that stabilizes the relative phase of multi-port inputs. Following theoretical analysis and simulations for four input signals, we experimentally realize FBC in a 4 × 4 Hadamard transformation and achieve temporal output stabilization. With the feedback loop enabled, the processor maintains a normalized output-power drift below 0.006 per hour, demonstrating high long-term stability. The results align with predictions, confirming robust interference and coherent combining under active control. This method enables reliable operation of reconfigurable multimode interferometers for quantum and classical information processing and can be extended to larger processors.