Precise control of the optical refractive index in nanolattices

Abstract

Recent developments in photonic devices, light field display, and wearable electronics have resulted from a competitive development toward new technologies to improve the user experience in the field of optics. These advances can be attributed to the rise of nanophotonics and meta-surfaces, which can be designed to manipulate light more efficiently. In these elements the performance scales are favorable to the index contrast, making the use of low-index material important. In this research, we examine the precise control of refractive indices of a low-index nanolattice material. This approach employs three-dimensional (3D) lithography and atomic layer deposition (ALD), allowing for precise control of the nanolattice geometry and its refractive index. The refractive indices of the fabricated nanolattices are characterized using spectroscopic ellipsometry and agree well with models based on effective medium theory. By controlling the unit-cell geometry by the exposure conditions and the shell thickness by the ALD process, the effective index of the nanolattice film can be precisely controlled to as low as 5 × 10−4. The proposed index control technique opens a gamut of opportunities and enables better performance in nanophotonic elements used in displays and other integrated devices.