Localized carbon deposition enables trimming of photonic integrated circuits

Abstract

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 localized trimming approach with high spatial precision. 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 confirm localized surface deposition without observable modification of the underlying waveguide core, and device measurements show discrete transmission tuning levels of 1.46–16.1 dB. Independent test structures further reveal an additional loss of 0.35 dB per π phase shift, indicating a low optical penalty at the device level. Furthermore, the optical response remains stable over two months following a brief initial settling phase. These results highlight the potential of FIB carbon deposition in device-level trimming and provide a foundation for exploring future trimming strategies toward parallel implementations.