Inverse Design Validated Optimization of Lead-Free Cs$_3$Cu$_2$Cl$_5$ Visible-Light Microring Resonators Using a Coupled DFT-FDTD Framework
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866910054109675520 |
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| author | Debnath, Shoumik Saha, Sudipta |
| author_facet | Debnath, Shoumik Saha, Sudipta |
| contents | Microring resonators (MRRs) are indispensable for wavelength filtering, sensing, and on-chip signal routing in photonic integrated circuits, yet visible-wavelength implementations using environmentally benign materials remain scarce. We report a numerical design study of add-drop MRRs employing Cs$_3$Cu$_2$Cl$_5$, a lead-free all-inorganic halide with favorable optical properties in the visible spectral range. Wavelength-resolved refractive index (n) and extinction coefficient (k) of Cs$_3$Cu$_2$Cl$_5$, calculated using density functional theory (DFT), are used as direct inputs to three-dimensional finite-difference time-domain (FDTD) simulations. Independent parametric sweeps are performed over ring waveguide width (500-900 nm), coupling gap (150-300 nm), and bend radius (5-20 um). At the balanced operating point of 600 nm ring width, 200 nm gap, and 10 um radius, the device achieves a loaded quality factor Q approx 5386, a free spectral range of 11.3 nm, a drop-port extinction ratio of 32.2 dB, and a finesse of 95.8. The coupling-gap sweep reveals the full transition from over-coupled through critically coupled to under-coupled operation, with the critical point occurring near 200 nm. A pronounced bending-loss threshold is observed between 5 and 10 um, below which all performance metrics degrade rapidly. These results provide the first systematic geometry-performance map for Cs$_3$Cu$_2$Cl$_5$ based microring resonators. Cross-platform validation using Tidy3D reproduces the spectral characteristics of the optimized device, and inverse design of the bus coupling region yields an additional 3 percent improvement in drop-port power transfer. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_14931 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Inverse Design Validated Optimization of Lead-Free Cs$_3$Cu$_2$Cl$_5$ Visible-Light Microring Resonators Using a Coupled DFT-FDTD Framework Debnath, Shoumik Saha, Sudipta Optics Microring resonators (MRRs) are indispensable for wavelength filtering, sensing, and on-chip signal routing in photonic integrated circuits, yet visible-wavelength implementations using environmentally benign materials remain scarce. We report a numerical design study of add-drop MRRs employing Cs$_3$Cu$_2$Cl$_5$, a lead-free all-inorganic halide with favorable optical properties in the visible spectral range. Wavelength-resolved refractive index (n) and extinction coefficient (k) of Cs$_3$Cu$_2$Cl$_5$, calculated using density functional theory (DFT), are used as direct inputs to three-dimensional finite-difference time-domain (FDTD) simulations. Independent parametric sweeps are performed over ring waveguide width (500-900 nm), coupling gap (150-300 nm), and bend radius (5-20 um). At the balanced operating point of 600 nm ring width, 200 nm gap, and 10 um radius, the device achieves a loaded quality factor Q approx 5386, a free spectral range of 11.3 nm, a drop-port extinction ratio of 32.2 dB, and a finesse of 95.8. The coupling-gap sweep reveals the full transition from over-coupled through critically coupled to under-coupled operation, with the critical point occurring near 200 nm. A pronounced bending-loss threshold is observed between 5 and 10 um, below which all performance metrics degrade rapidly. These results provide the first systematic geometry-performance map for Cs$_3$Cu$_2$Cl$_5$ based microring resonators. Cross-platform validation using Tidy3D reproduces the spectral characteristics of the optimized device, and inverse design of the bus coupling region yields an additional 3 percent improvement in drop-port power transfer. |
| title | Inverse Design Validated Optimization of Lead-Free Cs$_3$Cu$_2$Cl$_5$ Visible-Light Microring Resonators Using a Coupled DFT-FDTD Framework |
| topic | Optics |
| url | https://arxiv.org/abs/2603.14931 |