High-Density Photonic Chip Integration with Extreme Skin-Depth Waveguides

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Nontechnical: Chip-scale photonic devices can miniaturize a bulk optical system into a single tiny chip, making it portable and allowing various optical applications outside of the laboratory. The integration of photonic chips with electronic circuitry can also lead to a broad range of applications, for example, in high-speed optical communication, chemical- and bio-sensing, high-precision spectroscopy, and light detection and ranging for driverless automobiles. As electronic devices have been revolutionized in support of high-density integrated circuits, increasing the photonic chip integration density is highly desired in many optical applications; it offers more functionality and lower power consumption in a chip. However, due to the wave nature of light, high-density photonic chip integration is extremely difficult, and the current approach relies on the index-contrast of composite semiconductor materials. Research at Texas Tech University will explore an alternative approach of using all-dielectric and highly anisotropic metamaterials, i.e. artificially engineered man-made materials, to increase the photonic chip integration density. The proposed research will be implemented on a monolithic silicon-on-insulator wafer, which is compatible with the current semiconductor foundry process and provides a low-cost solution; thus, this research would have a broader impact in industry as well, accelerating the practical use of photonic chips in many applications. Educational and outreach activities are a high priority of this project and will provide hands-on experiences for undergraduate and graduate students, especially underrepresented groups of students.Technical: Realizing a high-density photonic chip integration is highly desired in many applications, as more building blocks provide more functionalities on a single chip (analogous to electronics). However, current approaches of light confinement rely on the index-contrast of core and cladding materials and further miniaturization of photonic devices is hampered by the wave nature of light, i.e., the evanescent wave in the cladding causes waveguide crosstalk. The goal of this project is to suppress the waveguide crosstalk significantly and to devise and implement ultracompact on-chip photonic devices and circuitry. This project will pursue this goal through fundamental analysis and experimental demonstration of the exceptional coupling phenomena in the extreme skin-depth waveguides. An anisotropic coupling mechanism in the extreme skin-depth waveguides will be explored to fundamentally understand the phenomena and extremely long coupling lengths with low crosstalk will be experimentally demonstrated on a silicon chip. The fabrication tolerance of the exceptional coupling will be assessed as well, and all the characterization results will be compared with numerical and analytical results. The project will also explore the effect of active media in anisotropic claddings and will implement various passive and active ultracompact photonic devices with anisotropic metamaterials. The outcomes of this project will scientifically reveal the fundamental mechanism of an exceptional coupling that can suppress optical crosstalk and will technically advance photonic applications by providing more functionalities on a chip.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.