Mar 22, 2021 |
Finding high-Q resonant modes in a dielectric nanocavity
(Nanowerk News) Optical resonators provide the foundation of modern photonics and optics. Thanks to its extreme energy confinement, the high-Q-factor optical resonator optimizes light-matter interaction and photonic device performance by enabling low-threshold laser and enhanced nonlinear harmonic generation.
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Two typical structures, the photonic crystal cavity and the whispering gallery cavity, are frequently used to obtain extremely high-Q factors. However, these structures may require dimensions that are comparable to--or several times larger than--the operating wavelength. Whether there is a general way to find out all high-Q modes in a dielectric nanocavity of arbitrary shape has been a fundamental question.
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A research team from University of New South Wales Canberra, The Australian National University, and Nottingham Trent University recently developed a robust recipe for finding high-Q modes in a single dielectric nanocavity, as reported in Advanced Photonics ("Pushing the limit of high-Q mode of a single dielectric nanocavity").
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High-Q and low-Q Mie modes of single dielectric 2D nanowire (left) and finite 3D nanoparticle (right). (Image: L. Huang et al.)
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Subwavelength high-index dielectric nanostructure
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Subwavelength high-index dielectric nanostructures are a promising platform for realizing CMOS-compatible nanophotonics. These nanostructures are based on two main factors: support of electric and magnetic Mie-type resonances and reduced dissipation.
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A single dielectric nanoresonator (e.g., a disk with finite thickness) supports the high-Q mode (also known as the quasi-bound state in the continuum). By exploring the quasi-bound state in the continuum, Huang et al. found a way to easily find many high-Q modes, using Mie mode engineering to cause a hybridization of paired leaky modes, resulting in avoided crossing of high- and low-Q modes.
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Robust, pair-wise approach
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Interestingly, both the avoided crossing, and crossing of eigenfrequencies for the paired modes, led to the discovery of high-Q modes, representing a simple yet robust way of finding high-Q modes. The team experimentally confirmed high-Q modes in a single silicon rectangular nanowire. The measured Q-factor was as high as 380 and 294 for TE(3,5) and TM(3,5), respectively (see figure). The authors attribute the resultant high Q-factors to the suppression of radiation in the limited leaky channels or minimized radiation in momentum space.
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According to senior author Andrey E. Miroshnichenko of the School of Engineering and Information Technology at University of New South Wales, "This work presents a straightforward method of finding out high-Q modes in a single dielectric nanocavity, which may find applications in integrated photonic circuits, such as ultra-low-threshold laser for on-chip light sources, strong coupling for polariton lasing, and enhanced second or third harmonic generations for night vision."
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