Localized Carbon Deposition Enables Non-Invasive Trimming of Photonic Integrated Circuits

Photonic integrated circuits (PICs), widely used in optical communications and computing, require precise post-fabrication trimming due to their high sensitivity to fabrication imperfections. Focused ion beam (FIB) carbon deposition offers a promising solution, combining high spatial precision with minimal invasiveness and inherently broad material compatibility. Here, we demonstrate this technique for the first time to enable non-volatile post-fabrication trimming of PICs. To validate this approach, we use asymmetric directional couplers as representative fabrication-sensitive components. Structural characterizations verify the non-invasive nature of the localized carbon deposition, and device measurements show discrete transmission tuning levels of 1.46–16.1 dB with a trimming-induced insertion loss of only 0.3 dB. Furthermore, the optical response remains stable over two months following a brief initial settling phase. These results establish FIB carbon deposition as a robust and broadly applicable PIC trimming technique, empowering optical communications, computing, and beyond to meet rising data demands.