Integrated photonic circuits (PICs) have seen an explosion
in interest,
through to commercialization in the past decade. Most PICs rely on
sharp resonances to modulate, steer, and multiplex signals. However,
the spectral characteristics of high-quality resonances are highly
sensitive to small variations in fabrication and material constants,
which limits their applicability. Active tuning mechanisms are commonly
employed to account for such deviations, consuming energy and occupying
valuable chip real estate. Readily employable, accurate, and highly
scalable mechanisms to tailor the modal properties of photonic integrated
circuits are urgently required. Here, we present an elegant and powerful
solution to achieve this in a scalable manner during the semiconductor
fabrication process using existing lithography tools: by exploiting
the volume shrinkage exhibited by certain polymers to permanently
modulate the waveguide’s effective index. This technique enables
broadband and lossless tuning with immediate applicability in wide-ranging
applications in optical computing, telecommunications, and free-space
optics.