Nanophotonics · Nonreciprocal nanophotonics: a new disruptive way to control light with nanotechnology

Nonreciprocal nanophotonics: a new disruptive way to control light with nanotechnology

Problem/issue being addressed Optics in the 21st century is undergoing revolutionary transformations driven by nanotecnology. Over just a few years we have seen a tremendous progress of tiny, nanoscale optical components from fundamental concepts to mass-fabricated consumer products. In my research I have been developing flat optical components 100 times thinner than a human hair. I was developing a the new frontiers of both fundamental and applied nano-optics research in nonlinear light-matter interactions rendered by nanoscale engineering. Nonlinearity offers a solution to a vital but largely unaddressed problem of contemporary optics and photonics: nonreciprocal optical response at the nanoscale. A nonreciprocal system exhibits different received-transmitted field ratios when their sources and detectors are exchanged. Such response requires breaking the Lorentz reciprocity theorem. Nonlinearity is one of only few fundamentally possible pathways to such behavior. Importance for society We live in an information-driven society. Our exponentially growing data exchange has well-surpassed a zettabyte per year, that’s a number with 21 zeros – a remarkable achievement of information and communication technologies (ICT). The ICT revolution started from miniaturisation of nonreciprocal electronics, semiconductor diodes and transistors. The key to the next phase of social changes brought about by the ICT is to replace electronics with photonics. Future steps are in replacing electrons with photons inside devices, their individual integrated circuits, and ultimately inside microchips. This creates a demand for miniaturisation of photonic components, with nonreciprocal components being among the most challenging to miniaturise. This project takes nonreciprocal photonics all the way to the nanoscale. The project demonstrates the first advanced manufacturing technology for nanophotonic nonreciprocal components. Overall objectives Objective 1. To develop a new avenue towards nonreciprocal control of photons at the nanoscale. Outcome: The objective was achieved in applying the concept of nonlinear metasurfaces with artificial magnetic response to nonreciprocity. In the linear regime, the metasurfaces were optimized to have strong magneto-electric copling, which in nonlinear regime was breaking the reciprocity. A 100 times transmission contrast between the "forward" and "backward" light propagation in a sub-micrometer component was achieved. Objective 2. To demonstrate design frameworks and fabrication approaches for nanoscale nonreciprocal components. Outcome: the objective was achieved using COMSOL and CST Microwave Studio software. Nanofabrication was succesfully performed using clean-room facilities at the Paderborn University, including chemical vapour deposition of thin films of materials, electron beam lithography and reactive ion etching. Designed metasurface parameters were met with 10 nm fabrication tolerance. Objective 3. To evaluate experimentally characteristics of the nanoscale nonreciprocal components. Outcome: the objective was achieved using two main types of experimental setups depending on the implemented material platform of the metasurfaces. Optical diagnostics of silicon-based and ITO-based metasurfaces was performed using tunable pulsed laser systems (256 fs -- 2 ps pulse duration, 5 MHz repetition rate, 500 mW average power, 1350-1750 nm tunability range). Optical diagnostics of VO2-based metasurfaces was performed with continuus-wave (CW) diode laser 10mW power, 1350-1750 nm tunability range. Asymmetric generation of optical harmonics and nonreciprocal transmission with an order of magnitude forward-backward contrast were measured in experiments.

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