  Citation: Zhu, W.; Yang, S.; Zheng, H.; Zhan, Y.; Li, D.; Cen, G.; Tang, J.; Lu, H.; Zhang, J.; Zhao, Z.; et al. Gold Enhanced Graphene-Based Photodetector on Optical Fiber with Ultrasensitivity over Near-Infrared Bands. Nanomaterials 2022, 12, 124. https://doi.org/10.3390/nano12010124 Academic Editor: Marco Cannas Received: 2 November 2021 Accepted: 21 December 2021 Published: 30 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). nanomaterials Article Gold Enhanced Graphene-Based Photodetector on Optical Fiber with Ultrasensitivity over Near-Infrared Bands Wenguo Zhu 1,† , Songqing Yang 1,† , Huadan Zheng 1 , Yuansong Zhan 2 , Dongquan Li 2 , Guobiao Cen 3 , Jieyuan Tang 2,4 , Huihui Lu 2 , Jun Zhang 1 , Zhijuan Zhao 3 , Wenjie Mai 3 , Weiguang Xie 3 , Wenxiao Fang 5 , Guoguang Lu 5 , Jianhui Yu 2, * and Zhe Chen 2,4, * 1 Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communications, Department of Optoelectronic Engineering, Jinan University, Guangzhou 510632, China; zhuwg88@163.com (W.Z.); youngsongqing@sina.cn (S.Y.); zhenghuadan@126.com (H.Z.); ccdbys@163.com (J.Z.) 2 Key Laboratory of Optoelectronic Information and Sensing Technologies of Guangdong Higher Education Institutes, Department of Optoelectronic Engineering, Jinan University, Guangzhou 510632, China; 18507735727@163.com (Y.Z.); lidongquan1990@163.com (D.L.); tangjiey@163.com (J.T.); thuihuilu@jnu.edu.cn (H.L.) 3 Siyuan Laboratory, Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy Materials, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Energy Materials, Department of Physics, Jinan University, Guangzhou 510632, China; cgb1692190612@stu2020.jnu.edu.cn (G.C.); zz.1987@163.com (Z.Z.); wenjiemai@gmail.com (W.M.); wgxie@email.jnu.edu.cn (W.X.) 4 Key Laboratory of Visible Light Communications of Guangzhou, Jinan University, Guangzhou 510632, China 5 Science and Technology on Reliability Physics and Application of Electronic Component Laboratory, China Electronic Product Reliability and Environmental Testing Research Institute, Guangzhou 510610, China; fangwx@ceprei.com (W.F.); luguog@126.com (G.L.) * Correspondence: jianhuiyu@jnu.edu.cn (J.Y.); thzhechen@jnu.edu.cn (Z.C.) † These authors contributed equally to this work. Abstract: Graphene has been widely used in photodetectors; however its photoresponsivity is limited due to the intrinsic low absorption of graphene. To enhance the graphene absorption, a waveguide structure with an extended interaction length and plasmonic resonance with light field enhancement are often employed. However, the operation bandwidth is narrowed when this happens. Here, a novel graphene-based all-fiber photodetector (AFPD) was demonstrated with ultrahigh responsivity over a full near-infrared band. The AFPD benefits from the gold-enhanced absorption when an interdigitated Au electrode is fabricated onto a Graphene-PMMA film covered over a side-polished fiber (SFP). Interestingly, the AFPD shows a photoresponsivity of >1 × 10 4 A/W and an external quantum efficiency of >4.6 × 10 6 % over a broadband region of 980–1620 nm. The proposed device provides a simple, low-cost, efficient, and robust way to detect optical fiber signals with intriguing capabilities in terms of distributed photodetection and on-line power monitoring, which is highly desirable for a fiber-optic communication system. Keywords: graphene; photodetector; ultrasensitivity 1. Introduction As an optical to electrical signal converter, the photodetector is an indispensable el- ement in every fiber-optic communication system [1–4]. Integrating photodetectors into optical fibers to achieve all-fiber photodetection is highly desirable, owing to the intrigu- ing capabilities of distributed photodetection and on-line power monitoring, as well as their structural compactness [3,4]. Conventional photodetectors are based on Si, Ge; semi- conductors cannot be perfectly integrated with optical fiber platforms, because of their different geometries and structures. The recently developed two-dimensional (2D) materi- als provide an opportunity for the all-fiber photodetector (AFPD) [3–7]. Several AFPDs are Nanomaterials 2022, 12, 124. https://doi.org/10.3390/nano12010124 https://www.mdpi.com/journal/nanomaterials