Subwavelength Phase Engineering Deep Inside Silicon

TL;DR

This paper introduces a novel method for subwavelength phase control deep inside silicon using volumetric nanostructuring, enabling advanced integrated photonics with high efficiency and compatibility with existing semiconductor processes.

Contribution

It presents the first demonstration of volumetric phase engineering within silicon, achieving full 2π phase control and high transmission efficiency through a new design approach guided by a semi-analytical model.

Findings

Achieved 2π phase control at telecommunication wavelengths

Simulated transmission efficiencies up to 90%

Focusing efficiency of 70% with array of metaatoms

Abstract

Recent advances in three-dimensional laser writing have enabled direct nanostructuring deep within silicon, unlocking a volumetric design space previously inaccessible to surface-bound nanophotonic devices. Here, we introduce subwavelength phase engineering inside crystalline silicon, offering a novel strategy for integrated photonics. We design and numerically demonstrate a volumetric metaoptic monolithically embedded within the bulk, achieving full 2$\pi$ phase control at telecommunication wavelengths, with simulated transmission efficiencies reaching 90 %. The architecture is guided by a semi-analytical Fabry-Perot model and validated through full-wave simulations. Arrays of 250-nm-wide metaatoms spaced at 300-410 nm pitch yield a focusing efficiency of 70 %. With the wafer surface left pristine, this platform can potentially enable co-integration with electronics, MEMS/NEMS, and conventional metasurfaces. Moreover, the method is directly transferable to other transparent dielectrics compatible with ultrafast laser writing. These results establish a CMOS-compatible blueprint for three-dimensional nanophotonics and multi-level integration within the wafer.