近日，加拿大拉瓦尔大学的Jerome Lapointe及其研究团队取得一项新进展。经过不懈努力，他们实现了用于光子电路混合集成的无需透镜和外部磁铁的无源宽带法拉第隔离器。相关研究成果已于2025年1月15日在国际知名学术期刊《自然—光子学》上发表。
本研究采用一种新的飞秒激光写入技术，在闩锁式掺铋铁氧体体块内制作波导，同时保持其磁光功能不变，从而解决了上述两大挑战。结果，研究人员成功制得一种法拉第旋转器波导，其插入损耗小于0.15dB，品质因数为346° dB-1。通过将这种法拉第旋转器置于两个30微米厚的偏振器之间，研究人员进一步展示了一种小型化的光隔离器波导，在整个光通信C波段内，其隔离度超过25dB，插入损耗小于1.5dB，可与光子电路进行混合集成，无需透镜和外部磁铁。
据悉，基于非互易效应的光隔离对于多种高性能光子器件的正常运行至关重要，这些器件应用于电信、激光雷达甚至量子平台等领域。磁光法拉第旋转是最常用的非互易效应，因为它具有独特的优势，包括宽带操作、宽输入光功率范围、低插入损耗和高光隔离度，但目前它不利于器件的小型化。法拉第隔离器直接集成到光子芯片上存在两大障碍：一是需要体积庞大的外部磁铁，二是难以制造低损耗波导以消除对自由空间耦合光学元件的需求。
附：英文原文
Title: Passive broadband Faraday isolator for hybrid integration to photonic circuits without lens and external magnet
Author: Lapointe, Jerome, Coia, Cedrik, Dupont, Albert, Valle, Ral
Issue&Volume: 2025-01-15
Abstract: Optical isolation based on a non-reciprocal effect is crucial for proper operation of several high-performance photonic devices such as in telecommunications, light detection and ranging, and even quantum platforms. The magneto-optical Faraday rotation is the most commonly used non-reciprocal effect as it offers unique advantages, including broadband operation, wide input optical power range, low insertion losses and high optical isolation, but it is currently not conducive to miniaturization. Two major impediments hinder the direct integration of Faraday isolators into photonic chips: the need for bulky external magnets and the challenging fabrication of low-loss waveguides that would eliminate the need for free-space coupling optics. Here we have addressed both challenges using a new femtosecond laser writing technique to create waveguides within the bulk of latched bismuth-doped iron garnet slabs without altering its magneto-optic functionality. As a result, we have achieved a Faraday rotator waveguide exhibiting <0.15dB insertion loss with a figure of merit of 346° dB-1. By interposing this Faraday rotator between two 30-μm-thick polarizers, we further demonstrate a miniaturized optical isolator waveguide with >25dB isolation ratio and <1.5dB insertion loss over the entire optical telecom C-band for hybrid integration to photonic circuits without lenses and external magnet.
DOI: 10.1038/s41566-024-01601-0
Source: https://www.nature.com/articles/s41566-024-01601-0