Printing high-quality tunable porous silicon microcavities and gradient index optics

Porous silicon (PSi) became a material of interest in the early 1990's with its ability to emit visible light. Since that time, PSi has demonstrated potential beyond light emission and gained an identity as a versatile optical material because of its inherent refractive index modulation capabilities achieved by either porosity variation or porosity infiltration. Porosity variation produces high-quality optical superlattices (e.g. microcavities), which feature optical resonances that control the light-matter interaction of light-emitters located inside the cavity and can simultaneously be tuned by pore infiltration. However, all such attempts with PSi monolithic microcavities have been fundamentally limited to emitters integrated into the porous network. Hybrid microcavities could extend the scope of compatible emitters, but grafting fragile, freestanding PSi films without damage has been an obstacle to realizing high-quality structures. Here, we demonstrate that PSi photonic components, when coupled with a modified transfer-printing technique, enable the formation of high-quality hybrid microcavities that are compatible with all forms of external emitters. Further, we provide a means to utilize PSi's refractive index modulation capabilities in the hybrid microcavity, allowing us to both globally tune and spatially modulate the resonant mode of the resulting structure.