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We propose the design of a comb-shaped cavity that can support several BICs when attached to a waveguide. The cavity consists of a finite comb made of one stub of length \(d_3\) placed between two stubs of length \(d_2\) via two guides of length \(d_1\) and the whole comb is attached vertically along a waveguide. In order to classify these BICs, we compare their frequencies with those of an infinite periodic comb in the presence of a stub defect of length \(d_3\) . Therefore, we show that beyond the resonances associated with the defect stub in the gaps, there exist two types of BICs: (i) BICs induced by the upper guides of the finite system, which fall in the wide passband of the infinite system and (ii) BICs induced by the whole finite comb which coincide with the flat band domain. These latter BICs appear as anti-symmetric and symmetric modes, giving rise to a doubly-degenerate BIC (D-BIC) when they fall at the same frequency. By deviating from the BIC condition, we show that these two types of BICs transform into quasi-BICs in the shape of electromagnetically induced reflection (EIR) or electromagnetic induced transparency (EIT) resonances. The analytical results obtained by the Green’s function method are confirmed by experiments using coaxial cables operating in the radio-frequency regime. This investigation contributes to an enhanced theoretical and experimental comprehension of BICs in stubbed structures, offering valuable insights for prospective applications.

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Two Types of Bound States in the Continuum in Photonic Comb Structure

  • 会议论文

  • 发表日期：

    2025年

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  • Yamina Rezzouk,
  • Soufyane Khattou,
  • Mohamed El Ghafiani,
  • Madiha Amrani,
  • El Houssaine El Boudouti,
  • Abdelkrim Talbi,
  • Bahram Djafari-Rouhani

摘要

We propose the design of a comb-shaped cavity that can support several BICs when attached to a waveguide. The cavity consists of a finite comb made of one stub of length \(d_3\) placed between two stubs of length \(d_2\) via two guides of length \(d_1\) and the whole comb is attached vertically along a waveguide. In order to classify these BICs, we compare their frequencies with those of an infinite periodic comb in the presence of a stub defect of length \(d_3\) . Therefore, we show that beyond the resonances associated with the defect stub in the gaps, there exist two types of BICs: (i) BICs induced by the upper guides of the finite system, which fall in the wide passband of the infinite system and (ii) BICs induced by the whole finite comb which coincide with the flat band domain. These latter BICs appear as anti-symmetric and symmetric modes, giving rise to a doubly-degenerate BIC (D-BIC) when they fall at the same frequency. By deviating from the BIC condition, we show that these two types of BICs transform into quasi-BICs in the shape of electromagnetically induced reflection (EIR) or electromagnetic induced transparency (EIT) resonances. The analytical results obtained by the Green’s function method are confirmed by experiments using coaxial cables operating in the radio-frequency regime. This investigation contributes to an enhanced theoretical and experimental comprehension of BICs in stubbed structures, offering valuable insights for prospective applications.