Twisted black phosphorus–based van der Waals stacks for fiber-integrated polarimeters

Xiong et al., Sci. Adv. 8, eabo0375 (2022) 4 May 2022 SCIE N C E A D V A NCES | RESEA R CH A RT ICL E 1 of 8 O P T I CS Twisted black phosphorus–based van der Waals stacks for fiber-integrated polarimeters Yifeng Xiong1†, Yushu Wang1†, Runze Zhu1†, Haotian Xu1, Chenhui Wu1, Jinhui Chen2, Yang Ma1, Yuan Liu1, Ye Chen1, Kenji Watanabe3, Takashi Taniguchi4, Mengzhu Shi5,6, Xianhui Chen5,6, Yanqing Lu1, Peng Zhan7, Yufeng Hao1*, Fei Xu1* The real-time, in-line analysis of light polarization is critical in optical networks, currently suffering from complex systems with numerous bulky opto-electro-mechanical elements tandemly arranged along the optical path. Here, we design and fabricate a fiber-integrated polarimeter by vertically stacking three photodetection units based on six-layer van der Waals materials, including one bismuth selenide (Bi2Se3) layer for power calibration, two twisted black phosphorus (BP) layers for polarization detection, and three hexagonal boron nitride (hBN) layers for encap- sulation. The self-power-calibrated, self-driven, and unambiguous detection of both linearly polarized (LP) and circularly polarized (CP) light is realized by the broken symmetry–induced linear photogalvanic effects (LPGEs) and circular photogalvanic effects (CPGEs) in the two BP units. Moreover, the device enables single-pixel polari- metric imaging to acquire spatial polarization information. The ultracompact device structure, free from external optical and mechanical modules, may inspire the development of miniaturized optical and optoelectronic systems. INTRODUCTION Polarization, one of the fundamental characteristics in communication, imaging, navigation, sensing, and almost all optics-related fields (1–3), is crucial in optical networks. Traditional polarimeters used in the optical network require a series of opto-electro-mechanical elements (including lenses, prisms, polarizers, wave plates, filters, photodetectors, and mechanical parts) tandemly arranged along the optical path, which is difficult to minimize and integrate for com- pact applications (1, 4). The realization of an ultracompact polarimeter requires breakthroughs in the two main aspects: (i) the downsizing of bulky components and the compression of the optical path to nano- and micrometer scale, getting rid of any external optical and mechanical modules, and (ii)