Low-loss waveguide design for full visible spectrum on-chip photonic devices
doi: 10.37188/CO.EN-2025-0036
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摘要:
将可见光集成光学器件的工作波段扩展至全可见光谱段具有重要意义，可以增强微型光谱仪的检测精度与适用性、拓宽可见光通信的带宽、使生物传感器能够同时检测复杂样品中的多种生物分子等。波导是集成光学器件的核心基础元件，然而目前对全可见光波导的研究并不完善。本文提出了一种支持全可见光谱段（435−760 nm）的波导设计，使用数值仿真方法分析了不同波导结构的传输特性，发现波导内无法实现整个可见光谱的单模传输。在多模传输条件下，通过分析波导中传播损耗与模式分布，确定了可实现低损耗传输的最佳波导尺寸、弯曲半径与波导间距等参数：对于平板波导，厚度≥1 μm可确保偏振不敏感。对于厚度为1 μm的条形波导，宽度≥2 μm可显著降低由侧壁粗糙度引起的散射损耗。对于宽1 μm、厚2 μm的条形波导，弯曲半径≥10 μm，波导间距≥0.4 μm时，辐射损耗可以忽略，且光不会耦合到相邻波导。此外，评估了制备公差对波导性能的影响。与之前主要关注可见光谱内窄波段的研究不同，本工作中提出的设计能够在单个波导中传输全可见光谱，从而促进片上全可见光谱器件的带宽扩展和性能增强。
Abstract:Extending the operational wavelength range of integrated optical devices to cover the entire visible spectrum holds significant importance, as it can enhance the detection accuracy and applicability of miniaturized spectrometers, broaden the bandwidth of visible light communication, and enable biosensors to simultaneously detect multiple biomolecules in complex samples. As the fundamental building block of integrated optical devices, waveguides have not yet been thoroughly investigated for full visible spectrum operation. This work presents a waveguide design supporting the full visible spectrum (435−760 nm). Numerical simulations were employed to analyze the transmission characteristics of various waveguide structures, revealing that single-mode propagation cannot be achieved across the entire visible spectrum. Under multimode propagation conditions, key parameters such as propagation loss and mode distribution were systematically examined to determine the optimal waveguide dimensions, bending radii, and waveguide spacings for low-loss transmission: For slab waveguides, a thickness ≥1 μm ensures polarization insensitivity. For strip waveguides with a thickness of 1 μm, a width ≥2 μm significantly reduces scattering loss induced by sidewall roughness. For strip waveguides with a width of 1 μm and thickness of 2 μm, radiation loss becomes negligible when the bending radius ≥10 μm and waveguide spacing ≥0.4 μm, while maintaining effective isolation from adjacent waveguides. Additionally, the impact of fabrication tolerances on waveguide performance was evaluated. In contrast to previous studies primarily focusing on narrow spectral bands within the visible range, the proposed design enables full visible spectrum transmission in a single waveguide, thereby facilitating bandwidth expansion and performance enhancement for on-chip full visible spectrum devices.
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Key words:
- integrated optics devices /
- waveguides /
- visible light /
- low-loss /
- silicon nitride
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Figure 1. Schematic diagrams of (a) rib waveguide, (b) rectangular waveguide, and (c) slab waveguide.
Figure 2. Effective refractive index as a function of waveguide width for the waveguide thicknesses of (a) 100 nm, (b) 200 nm, and (c) 300 nm.
Figure 3. Mode distributions in the critically dimensioned rib waveguide: (a) TE1 and (b) TM1 at 435 nm, (c) TE0 and (d) TM0 at 760 nm.
Figure 4. Variation of the effective refractive index with the thickness of the slab waveguide.
Figure 5. (a) TE0 and (b) TM0 mode distributions in the slab waveguide at 760 nm wavelength.
Figure 6. Effective refractive indices of TE0 and TM0 modes in a slab waveguide as a function of thickness at 597.5 nm wavelength.
Figure 7. (a) Transmittance, (b) output electric field, and (c) electric field propagation in the slab waveguide.
Figure 9. (a) Variation of the transmittance with the bending radius. (b) Electric field propagation at R=10 μm.
Figure 10. (a) Schematic diagram of the waveguide spacing. Electric field coupling at waveguide spacings of (b) 0.5 μm and (c) 0.1 μm. Transmittance of the (d) source waveguide and the (e) adjacent waveguide as a function of waveguide spacing.
Figure 12. (a) Variation of transmittance with the width of the waveguide at RMS=10 nm. (b) Variation of transmittance with the sidewall roughness for a 2 μm wide waveguide.
Figure 13. Variation of transmittance with (a) PML-to-edge distance and (b) PML layer count.
Figure 14. (a) Variation of transmittance with the mesh accuracy. (b) The transmittance for waveguide lengths of 20 µm and 100 µm.
Table 1. Key parameters summary of Si3N4 full visible spectrum multimode waveguides
Slab waveguide thickness Strip waveguide width
(thickness = 1 μm)Waveguide spacing Bending radius RMS roughness
(for low-loss transmission)≥ 1 μm ≥ 2 μm ≥ 0.4 μm ≥ 10 μm ≤ 10 nm 
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