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| Main Authors: | , , , , , |
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| Format: | Preprint |
| Published: |
2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2603.11929 |
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| _version_ | 1866911508892483584 |
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| author | Herrero-Parareda, Albert de Ceglia, Domenico Vincenti, Maria Antonietta Zilli, Attilio Shcherbakov, Maxim R. Capolino, Filippo |
| author_facet | Herrero-Parareda, Albert de Ceglia, Domenico Vincenti, Maria Antonietta Zilli, Attilio Shcherbakov, Maxim R. Capolino, Filippo |
| contents | An anomalous flat-band dispersion provided by a degenerate band edge (DBE) of longitudinal optical modes in a double-grating waveguide is used to enhance second-harmonic generation (SHG). The DBE is a fourth-order exceptional point degeneracy (EPD) in a lossless and gainless waveguide, characterized by the coalescence of four eigenmodes that establish a frozen mode in a cavity. At a DBE resonance, the cavity quality factor scales $Q\propto N^5$, where $N$ is the number of unit cells of the grating waveguide. In our numerical experiments, we observe the peak intensity of the fundamental field in the edge-excited cavity scaling as $I_1\propto N^{3.6}$. This leads to a highly efficient SHG process that is radiated vertically from the cavity (i.e., normal to the grating) without requiring collinear phase matching, with a conversion efficiency scaling as $η\propto N^{8.27}$. These results establish DBE-based waveguides as promising platforms for miniaturized efficient nonlinear photonic devices. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_11929 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Second-Harmonic Generation at a Fourth-Order Exceptional Point Degeneracy Herrero-Parareda, Albert de Ceglia, Domenico Vincenti, Maria Antonietta Zilli, Attilio Shcherbakov, Maxim R. Capolino, Filippo Optics An anomalous flat-band dispersion provided by a degenerate band edge (DBE) of longitudinal optical modes in a double-grating waveguide is used to enhance second-harmonic generation (SHG). The DBE is a fourth-order exceptional point degeneracy (EPD) in a lossless and gainless waveguide, characterized by the coalescence of four eigenmodes that establish a frozen mode in a cavity. At a DBE resonance, the cavity quality factor scales $Q\propto N^5$, where $N$ is the number of unit cells of the grating waveguide. In our numerical experiments, we observe the peak intensity of the fundamental field in the edge-excited cavity scaling as $I_1\propto N^{3.6}$. This leads to a highly efficient SHG process that is radiated vertically from the cavity (i.e., normal to the grating) without requiring collinear phase matching, with a conversion efficiency scaling as $η\propto N^{8.27}$. These results establish DBE-based waveguides as promising platforms for miniaturized efficient nonlinear photonic devices. |
| title | Second-Harmonic Generation at a Fourth-Order Exceptional Point Degeneracy |
| topic | Optics |
| url | https://arxiv.org/abs/2603.11929 |