Subwavelength-Grating Metamaterial Structures for Silicon Photonic Devices

TLDR

Subwavelength segmentation of silicon waveguides creates an effectively homogeneous medium that allows precise tuning of modal confinement, effective index, dispersion, and birefringence, and with sub‑100‑nm lithography many high‑performance devices have been demonstrated, making subwavelength engineering a core design tool in silicon photonics. This review surveys the current state of subwavelength silicon photonic structures and outlines future prospects for their impact on advanced device design. The authors first explain the fundamentals of subwavelength structures—including substrate leakage, fabrication jitter, reduced backscatter, and anisotropy engineering—then survey recent applications such as broadband couplers, high‑sensitivity sensors, low‑loss mid‑infrared devices, polarization management, spectral filters, and efficient fiber‑to‑chip couplers.

Abstract

Segmenting silicon waveguides at the subwavelength scale produce an equivalent homogenous material. The geometry of the waveguide segments provides precise control over modal confinement, effective index, dispersion and birefringence, thereby opening up new approaches to design devices with unprecedented performance. Indeed, with ever-improving lithographic technologies offering sub-100-nm patterning resolution in the silicon photonics platform, many practical devices based on subwavelength structures have been demonstrated in recent years. Subwavelength engineering has thus become an integral design tool in silicon photonics, and both fundamental understanding and novel applications are advancing rapidly. Here, we provide a comprehensive review of the state of the art in this field. We first cover the basics of subwavelength structures, and discuss substrate leakage, fabrication jitter, reduced backscatter, and engineering of material anisotropy. We then review recent applications including broadband waveguide couplers, high-sensitivity evanescent field sensors, low-loss devices for mid-infrared photonics, polarization management structures, spectral filters, and highly efficient fiber-to-chip couplers. We finally discuss the future prospects for subwavelength silicon structures and their impact on advanced device design.