Transient Tap Couplers For Wafer-Level Photonic Testing Based On Optical Phase Change Materials

Wafer-level testing is crucial for process monitoring, post-fabrication trimming, and understanding system dynamics in photonic integrated circuits (PICs). Waveguide tap couplers are usually used to provide testing access to the PIC components. These tap couplers however incur permanent parasitic losses, imposing a trade-off between PIC performance and testing demands. Here we demonstrate a transient tap coupler design based on optical phase change materials (O-PCMs). In their as-fabricated "on" state, the couplers enable broadband interrogation of PICs at the wafer level. Upon completion of testing, the tap couplers can be turned "off" with minimal residual loss (0.01 dB) via a simple low-temperature (280 degrees C) wafer-scale annealing process. We further successfully demonstrated transient couplers in both Si and SiN photonics platforms. The platform-agnostic transient coupler concept uniquely combines compact footprint, broadband operation, exceptionally low residual losses, and low thermal budget commensurate with post-fabrication treatment, thereby offering a facile solution to wafer-level photonic testing without compromising the final PIC performance.