The objective of this EAGER proposal is to design, theoretically model, and experimentally demonstrate a novel class of large-area ultra-thin metasurfaces based on intersubband polaritons with giant nonlinear optical response, orders of magnitude larger than any device reported so far in the scientific literature. Proof-of-concept demonstration efforts will focus on development highly-efficient second harmonic generation mirrors in the mid-infrared regime. The proposed concept is, however, much broader and can be readily extended to other nonlinear optical phenomena. Intellectual Merits: The proposed research will introduce novel concepts in nonlinear optics and in metamaterial technology. For the first time, nonlinear response of intersubband excitations strongly coupled to optical modes in metal-dielectric-metal microcavities will be investigated. Already giant intersubband optical nonlinearities in coupled-quantum-wells systems can be further boosted by coupling intersubband transitions with ad-hoc engineered resonant modes in metal-dielectric-metal metamaterial cavities. Broader Impacts: The proposed research combines elements of metamaterial theory, optoelectronics, nonlinear optics, and semiconductor physics. This combination offers a rich, interdisciplinary educational environment for graduate and undergraduate students. Knowledge and techniques developed during our research efforts will be incorporated into focused graduate-level courses currently taught by the PI and Co-PI. The metasurfaces developed in this project are expected to find numerous industrial applications. The PI will continue his annual participation in the NNIN REU program with students involved in the proposed research and involve the co-PI in this effort. At the K-12 level, PI and co-PI will collaborate with NSF-sponsored UTeachEngineering program.
We developed a theoretical model and experimentally realized a novel class of nonlinear metasurfaces with many orders of magnitude higher nonlinear response, compared to traditional materials or metasurfaces demonstrated previously. The metasurfaces are created by coupling of electromagnetic modes in metallic nanoresonators with quantum-engineered electronic intersubband transitions in semiconductor heterostructures. Mid-infrared second-harmonic generation with up to 0.025% conversion efficiency was demonstrated in ultrathin films, 400 nm in thickness, using light intensity of only 10 kW/cm2, comparable to that of a focused laser pointer. Additionally, metasurfaces with voltage-controllable optical reflectivity were demonstrated based on giant electro-optic effect. The results were published in two peer-reviewed journal papers, Nature 5, 65-69 (2014) and Adv. Opt. Matt. 2, 1057-1063 (2014), were presented as invited and contributed talks at several leading international conferences in photonics and electromagnetics, and disseminated to the general audience through a press-release (www.utexas.edu/news/2014/07/02/meta-mirror-engineering/). The intellectual merit of this work is that it opens a new paradigm in nonlinear optics by exploiting the unique combination of exotic wave interaction in metamaterials and of quantum engineering in semiconductors. The broader impact of this work is that it unveils a pathway towards the development of ultrathin highly-nonlinear optical elements for efficient frequency conversion that will operate using low pump intensities and be free from stringent phase-matching constraints of bulk nonlinear crystals. Such elements will allow to simplify miniaturize many of the nonlinear optical systems used today for frequency conversion, spectroscopy, imaging, and optical pulse characterization.
