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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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Resonant Dual‐Grating Metamembranes Supporting Spectrally Narrow Bound States in the Continuum
Abstract Properties of photonic devices fashioned with dual‐grating metamaterials are reported. Enclosed by dual periodic regions, laterally propagating Bloch modes undergo radiative scattering and leaky‐mode resonance whose properties differ markedly from those with single periodicity. The resonance signatures are sensitively controlled by the relative parameters of the periodic regions. In particular, if they are physically identical and separated by a half‐wavelength, there ensues a bound state in the continuum (BIC) with extremely narrow resonance linewidth. On varying the separation between the periodic layers, the linewidth and correspondingQcan be tuned. This is confirmed experimentally via nanoimprinted dual‐grating membranes. The experimental spectra agree well with rigorously computed spectra as well with an analytical model due to Avrutsky. At grating‐depth and thickness values satisfying this model, three different types of BICs are supported by a single metamembrane. Two BICs appear at normal incidence at the Γ point with one being a quasi‐BIC on one band edge while a true symmetry‐protected BIC resides on the other edge. Moreover, a quasi‐BIC state away from the Γ point in the same device is demonstrated. Whereas these results are based on a simple model with 1D periodicity, the primary properties will carry over to general 2D/3D photonic lattices.
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- Award ID(s):
- 1809143
- PAR ID:
- 10445900
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 7
- Issue:
- 20
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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