We experimentally demonstrate a novel quasi-bound state in the continuum(BIC)resonance in the mid-infrared wavelength region with the resonant electric field confined as a slot mode within a low-refractive-index medium sandwiched between high-index layers.The structures studied here comprise coupled amorphous germanium guided-mode resonance(GMR)structures with a top one-dimensional grating layer and bottom uniform layer separated by a low-index silicon nitride layer.The slot-mode profile within the silicon nitride layer with mode field confinement＞30％is achieved as a solution to the electromagnetic wave propagation through the coupled GMR structure with the dominant field component being perpendicular to the layers.The quasi-BIC resonance in symmetric 1D grating structures can be observed even at normal incidence when considering a realistic excitation beam with finite angular spread.The measured transmission peak is found to redshift(remain almost unchanged)under classical(full-conical)mounting conditions.The highest quality factor of～400 is experimentally extracted at normal incidence under a classical mounting condition with a resonance peak at 3.41 μm wavelength.Such slot-mode GMR structures with appropriately chosen low-index intermediate layers can find applications in resonantly enhanced sensing and active photonic devices.

A.S.LAL KRISHNA;SRUTI MENON;ASISH PROSAD;VARUN RAGHUNATHAN

Department of Electrical Communication Engineering,Indian Institute of Science,Bangalore 560012,India

光子学研究（英文）

[1]A.S.LAL KRISHNA;SRUTI MENON;ASISH PROSAD;VARUN RAGHUNATHAN-.Mid-infrared quasi-BIC resonances with sub-wavelength slot mode profiles in germanium-based coupled guided-mode resonance structures)[J].光子学研究（英文）,2022(01):68-75

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