We present the machine learning inspired design of two types of GaN zero contrast subwavelength gratings (SWGs): a polynomial-shaped grating and, for reference, a conventional rectangular grating, using the differential evolution algorithm to optimize the designs for high broadband reflectivity and separately for large fabrication tolerance. Two wavelength regimes with 500 nm and 1.55 μm center wavelengths (λcenter) are investigated. Our results indicate that both polynomial and rectangular grating designs can achieve comparable stopband widths of 170 nm (Δλ) for 500 nm (Δλ/λcenter = 34%). For the 1.55 μm center wavelength, the 482 nm (Δλ/λcenter = 31%) stopband width of the polynomial grating is slightly less than that of the rectangular grating at 498 nm (Δλ/λcenter = 32%). We also demonstrate design for enhanced fabrication tolerance while placing a minimum constraint on the stopband width. Our results show the rectangular grating exhibits slightly higher fabrication tolerances for grating parameters than the polynomial-shaped grating in general. This work also outlines the technique we have adopted for the inverse design of these gratings.

中文翻译：

---

受机器学习启发的复杂形状 GaN 亚波长光栅反射器设计

我们展示了两种类型的 GaN 零对比度亚波长光栅 (SWG) 的机器学习启发设计：多项式光栅和作为参考的传统矩形光栅，使用差分进化算法优化高宽带反射率的设计，并分别用于大的制造公差。研究了具有 500 nm 和 1.55 μm 中心波长 (λcenter) 的两个波长范围。我们的结果表明，多项式和矩形光栅设计都可以实现 500 nm (Δλ/λcenter = 34%) 的可比阻带宽度 170 nm (Δλ)。对于 1.55 μm 中心波长，多项式光栅的 482 nm (Δλ/λcenter = 31%) 阻带宽度略小于矩形光栅在 498 nm (Δλ/λcenter = 32%) 的阻带宽度。我们还展示了增强制造公差的设计，同时对阻带宽度设置了最小限制。我们的结果表明，矩形光栅的光栅参数制造公差比一般的多项式光栅略高。这项工作还概述了我们为这些光栅的逆向设计所采用的技术。