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Bound states in the continuum (BICs) hold significant promise in manipulating electromagnetic fields and reducing losses in optical structures, leading to advancements in fundamental research and practical applications. Despite their observation in various optical systems, the behavior of BIC in whispering-gallery-modes (WGMs) optical microcavities, essential components of photonic integrated chips, has yet to be thoroughly explored. In this study, we propose and experimentally identify a robust mechanism for generating quasi-BIC in a single deformed microcavity. By introducing boundary deformations, we construct stable unidirectional radiation channels as leaking continuum shared by different resonant modes and experimentally verify their external strong mode coupling. This results in drastically suppressed leaking loss of one originally long-lived resonance, manifested as more than a threefold enhancement of its quality (Q) factor, while the other short-lived resonance becomes more lossy, demonstrating the formation of Friedrich–Wintgen quasi-BICs as corroborated by the theoretical model and experimental data. This research will provide a practical approach to enhance theQ-factor of optical microcavities, opening up potential applications in the area of deformed microcavities, nonlinear optics, quantum optics, and integrated photonics.
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Single-peak and narrow-band mid-infrared thermal emitters driven by mirror-coupled plasmonic quasi-BIC metasurfaces
Wavelength-selective thermal emitters (WS-EMs) hold considerable appeal due to the scarcity of cost-effective, narrow-band sources in the mid-to-long-wave infrared spectrum. WS-EMs achieved via dielectric materials typically exhibit thermal emission peaks with high quality factors (Qfactors), but their optical responses are prone to temperature fluctuations. Metallic EMs, on the other hand, show negligible drifts with temperature changes, but theirQfactors usually hover around 10. In this study, we introduce and experimentally verify an EM grounded in plasmonic quasi-bound states in the continuum (BICs) within a mirror-coupled system. Our design numerically delivers an ultra-narrowband single peak with aQfactor of approximately 64 and near-unity absorptance that can be freely tuned within an expansive band of more than 10 µm. By introducing air slots symmetrically, theQfactor can be further augmented to around 100. Multipolar analysis and phase diagrams are presented to elucidate the operational principle. Importantly, our infrared spectral measurements affirm the remarkable resilience of our designs’ resonance frequency in the face of temperature fluctuations over 300°C. Additionally, we develop an effective impedance model based on the optical nanoantenna theory to understand how further tuning of the emission properties is achieved through precise engineering of the slot. This research thus heralds the potential of applying plasmonic quasi-BICs in designing ultra-narrowband, temperature-stable thermal emitters in the mid-infrared. Moreover, such a concept may be adaptable to other frequency ranges, such as near-infrared, terahertz, and gigahertz.
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- Award ID(s):
- 2143836
- PAR ID:
- 10492085
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optica
- Volume:
- 11
- Issue:
- 3
- ISSN:
- 2334-2536
- Format(s):
- Medium: X Size: Article No. 305
- Size(s):
- Article No. 305
- Sponsoring Org:
- National Science Foundation
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