Dr. Yang Li Profile

Dr. Yang Li

Research Associate at Harvard John A Paulson School of Engineering and Applied Sciences

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Proceedings Article | 14 March 2018 Presentation

Monolithic CMOS-compatible zero-index metamaterials (Conference Presentation)

Daryl Vulis, Yang Li, Orad Reshef, Philip Camayd-Munoz, Mei Yin, Shota Kita, Marko Loncar, Eric Mazur

Proceedings Volume 10541, 105410X (2018) https://doi.org/10.1117/12.2290844

KEYWORDS: Metamaterials, Silicon, Photonics, Refractive index, Photonic crystals, Optical properties, Integrated optics, Photonic devices, CMOS technology, Dispersion

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Zero-index metamaterials exhibit exotic optical properties such as uniform spatial phase and infinite wavelength. These extreme properties can be utilized for integrated-optics applications. However, practical implementation of zero-index-based photonic devices requires compatibility with complementary metallic-oxide-semiconductor (CMOS) technologies. Zero-index metamaterials have been previously demonstrated in both out-of-plane and integrated configurations by taking advantage of a photonic Dirac-cone dispersion at the center of the Brillouin zone. Such metamaterials feature a square matrix of high aspect-ratio pillars and offer matched impedance through simultaneously zero effective permittivity and permeability. However, these configurations are inherently incompatible with integrated devices due to out-of-plane excitation, metallic inclusions, or high aspect-ratio structures. This work demonstrates a CMOS-compatible zero-index metamaterial consisting of a square array of air-holes in a 220-nm-thick silicon-on-insulator wafer. To experimentally verify the refractive index, we measure the angle of refraction of light through a triangular prism consisting of the metamaterial. The index is extracted using Snell's Law to verify a refractive index of zero at a wavelength of 1625 nm. Through the air-hole in silicon configuration, the proportion of silicon is increased as compared to designs based on high aspect-ratio silicon pillars. This enables a platform with low-aspect-ratio features, improved confinement of transverse electric polarized light, as well as the original benefit of matched impedance. Featuring a trivial monolithic fabrication and capacity for integration with the expansive library of existing silicon photonic devices, this metamaterial enables implementation of proposed zero-index devices and offers a powerful platform for exploring the future applications of zero-index materials.

Proceedings Article | 15 August 2017 Presentation

CMOS-compatible zero-index metamaterial (Conference Presentation)

Yang Li, Daryl Vulis, Orad Reshef, Philip Camayd-Munoz, Mei Yin, Shota Kita, Marko Loncar, Eric Mazur

Proceedings Volume 10113, 1011309 (2017) https://doi.org/10.1117/12.2252515

KEYWORDS: Metamaterials, Silicon, Silicon films, Silicon photonics, Polarization, Prisms, Photonic crystals, Optical properties, Nonlinear optics, Semiconducting wafers

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Zero-index metamaterials (ZIMs) offer exotic optical properties such as uniform spatial phase and infinite wavelength, as well as photonic applications including super-coupling and omnidirectional phase matching in nonlinear optics. Here we present an on-chip ZIM consisting of a square array of air-holes in a 220-nm-thick silicon-on-insulator (SOI) wafer. This design enables mass production of ZIM-based photonic devices at low cost and high fidelity using standard CMOS fabrication technology. To transition from the high-aspect ratio inverse case of silicon pillars under transverse magnetic (TM) polarization, our design is instead intended for a transverse electric (TE) polarization because of TE modes are, in general, better confined than TM modes for a given thin film. Furthermore, the larger volume fraction of silicon provided by the air-holes structure improves the confinement as compared with the silicon-pillars structure. We optimized the design to obtain a zero index corresponding to a finite impedance of 0.8 at 1550 nm. The bandstructure of the metamaterial shows a Dirac-cone dispersion at the center of the Brillouin zone at 1550 nm. These results indicate that this metamaterial possesses an impedance-matched, isotropic zero index at 1550 nm. To experimentally verify that the metamaterial has a zero index, we fabricated a right-triangular prism measuring twenty unit cells across. The measured effective index of this prism crosses zero linearly at 1630 nm and shows positive and negative indices at short and longer wavelengths, respectively, indicating a Dirac-cone induced zero index. This measurement is in excellent agreement with the result of full-wave simulation.

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