Nonlinear dielectric metasurfaces provide a promising platform to control and manipulate the optical frequency conversion at the nanoscale, suggesting new applications in imaging, lasing, and sensing. Here, we engage symmetry-broken silicon metasurfaces to enhance the second- and third-harmonic generation. We design and fabricate amorphous silicon metasurfaces supporting optical bound states in the continuum and guided-mode resonances, which greatly boost light-matter interaction resulting in several-order enhancements in both second-and third-harmonic generation.
Structural coloration generates colors by the interaction between incident light and micro- or nano-scale structures. It has received tremendous interest for decades, due to advantages including robustness against bleaching and environmentally friendly properties (compared with conventional pigments and dyes). As a versatile coloration strategy, the tuning of structural colors based on micro- and nanoscale photonic structures has been extensively explored and can enable a broad range of applications including displays, anti-counterfeiting, and coating. However, scholarly research on structural colors has had limited impact on commercial products because of their disadvantages in cost, scalability, and fabrication. In this review, we analyze the key challenges and opportunities in the development of structural colors. We first summarize the fundamental mechanisms and design strategies for structural colors while reviewing the recent progress in realizing dynamic structural coloration. The promising potential applications including optical information processing and displays are also discussed while elucidating the most prominent challenges that prevent them from translating into technologies on the market. Finally, we address the new opportunities that are underexplored by the structural coloration community but can be achieved through multidisciplinary research within the emerging research areas.
Chiral sum-frequency generation (SFG) has proven to be a versatile spectroscopic and imaging tool for probing chirality. However, due to polarization restriction, the conventional chiral SFG microscopes have mostly adopted noncollinear beam configurations, which only partially cover the aperture of microscope and strongly spoil the spatial resolution. In this study, we report the first experimental demonstration of collinear chiral SFG microscopy, which fundamentally supports diffraction-limited resolution. This advancement is attributed to the collinear focus of a radially polarized vectorial beam and a linearly polarized (LP) beam. The tightly focused vectorial beam has a very strong longitudinal component, which interacts with the LP beam and produces the chiral SFG. The collinear configuration can utilize the full aperture and thus push the spatial resolution close to the diffraction limit. This technique can potentially boost the understanding of chiral systems.
Microcavities are fundamental building blocks for on-chip integrated photonic circuits. Till now, most of the microdisks (microrings) are coupled to the waveguides via the evanescent coupling, which is strongly restricted by the nanosized gap distance (between waveguide and cavity) and narrow bandwidth to realize the phase matching condition. In this talk, we will present our recent results on a brand new coupling mechanisms. Based on the time reversal process of laser, we show that the light can be efficientyl coupled into a silicon microdisk by simply connecting a waveguide onto it. The coupling efficiency and quality (Q) factors are ~ 60% and 7*10^5, respectively. As the new mechanism doesn't rely on the phase matching considtion, the high efficiency end-fire injection can be realized within a large range of waveguide width (> 500 nm), tilt angle, and spectral range, sigificnatly reducing the costs and expanding the potential applications of potential photonic devices.
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