Kim Changhyun, Bae Munseong, Choi Minho, Lee Sangbin, Lee Myunghoo, Kim Chihyeon, Jung Hojoong, Chung Haejun, Kwon Hyounghan
Center for Quantum Technology, Korea Institute of Science and Technology (KIST), Seoul 02792, South Korea.
Department of Electronic Engineering, Hanyang University, Seoul, 04763, South Korea.
Nanophotonics. 2025 Feb 6;14(11):1949-1960. doi: 10.1515/nanoph-2024-0515. eCollection 2025 Jun.
Thin-film lithium niobate (TFLN) has emerged as a promising platform for integrated photonics due to its exceptional material properties. The application of freeform topology optimization to TFLN devices enables the realization of compact designs with complex functionalities and high efficiency. However, the stringent fabrication constraints of TFLN present significant challenges for optimization, particularly in nonlinear photonic devices. In this work, we propose an inverse design methodology that successfully addresses these challenges and demonstrates the development of an efficient freeform TFLN mode converter. The numerically optimized mode converter achieves a transmission efficiency of 67.60 % and a mode purity of 84.58 %. Experimental validation through nonlinear processes, including second harmonic generation and spontaneous parametric down-conversion, shows that the fabricated devices improve the efficiency of these processes by factors of two and three, respectively, compared to devices without freeform designs. The proposed inverse design framework provides a powerful tool for advancing the development of TFLN-based devices, with broad applicability to nonlinear and quantum photonics.
薄膜铌酸锂（TFLN）因其优异的材料特性，已成为集成光子学领域一个很有前景的平台。将自由形式拓扑优化应用于TFLN器件，能够实现具有复杂功能和高效率的紧凑设计。然而，TFLN严格的制造限制给优化带来了重大挑战，尤其是在非线性光子器件中。在这项工作中，我们提出了一种逆向设计方法，成功应对了这些挑战，并展示了一种高效自由形式TFLN模式转换器的开发。通过数值优化的模式转换器实现了67.60%的传输效率和84.58%的模式纯度。通过包括二次谐波产生和自发参量下转换在内的非线性过程进行的实验验证表明，与没有自由形式设计的器件相比，所制造的器件分别将这些过程的效率提高了两倍和三倍。所提出的逆向设计框架为推进基于TFLN的器件开发提供了一个强大的工具，在非线性和量子光子学中具有广泛的适用性。
