Erasable PCM-Assisted Probe for In Situ Monitoringof Photonic Integrated Circuits

Photonic integrated circuits (PICs) are essential for modern optoelectronics, yet fabrication-induced random phase errors often necessitate precise detection and calibration before application. Optical probing offers a direct detection method before packaging. However, conventional probes suffer from large footprints and significant inherent loss. In this work, we propose and demonstrate an ultracompact, erasable optical probe based on a phase-change-material (PCM)-assisted directional coupler. The device features a footprint of less than 14 × 6 μm2. In the ON state, the probe extracts approximately 6% of the optical power for monitoring, while in the OFF state, it exhibits a negligible residual loss of less than 0.02 dB. The probe leverages reversible phase transitions to switch between the two states. We further validate its performance by implementing in situ monitoring within a 4 × 4 optical switch array. This PCM-assisted probe provides a scalable and efficient solution for large-scale PICs.