Citation: Singh, P.; Jalil, M.A.; Yupapin, P.; Ali, J.; Palomino, M.A.; Toledo-Solano, M.; Misaghian, K.; Faubert, J.; Ray, K.; Bandyopadhyay, A.; et al. Topological and Optical Properties of Passeriformes’ Feathers: Biological UV Reflector Antenna. Optics 2022, 3, 462–472. https:// doi.org/10.3390/opt3040039 Academic Editor: Thomas Seeger Received: 4 October 2022 Accepted: 22 November 2022 Published: 5 December 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 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/). Article Topological and Optical Properties of Passeriformes’ Feathers: Biological UV Reflector Antenna P. Singh 1 , M. A. Jalil 2 , P. Yupapin 3 , J. Ali 4 , M. A. Palomino 5 , M. Toledo-Solano 6 , K. Misaghian 7,8 , J. Faubert 7,8 , K. Ray 5,7,9, *, A. Bandyopadhyay 1 and J. E. Lugo 5,7,8, * 1 Advanced Key Technologies Division, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047, Japan 2 Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, Skudai 81310, Malaysia 3 Departmentof Electrical Technology, School of Industrial Technology, Sakonnakhon Technical College, Institute of Vocational Education Northeastern 2, Sakon Nakhon 47000, Thailand 4 Asia Metropolitan University, 6, Jalan Lembah, Bandar Baru Seri Alam, Johor Bahru 81750, Malaysia 5 Facultad de Ciencias Físico-Matematicas, Ciudad Universitaria, Puebla 72570, Mexico 6 Facultad de Ciencias Físico-Matematicas, CONACYT-Benemerita Universidad Autonoma de Puebla, Puebla 72570, Mexico 7 Faubert Lab, Université de Montréal, Montreal, QC H3T 1P1, Canada 8 Sage-Sentinel Smart Solutions, 1919-1 Tancha, Onna-son, Kunigami-gun, Okinawa 904-0495, Japan 9 Department of Physics Amity, School of Applied Sciences, Amity University Rajasthan, Jaipur 303002, India * Correspondence: kanadray00@gmail.com (K.R.); eduardo.lugo@sagesentinel.com (J.E.L.) Abstract: This manuscript explores the topological and optical properties of a Passeriformes bird feather. Inside the feather, the layers of keratin and melanin are responsible for light reflection, transmission, and absorption; notably, the miniature composition of melanosome barbules plays a crucial role in its reflective properties. We adopted a multilayer interference model to investigate light propagation throughout the Passeriformes plume. As a result, we obtained all necessary simulated results, such as resonance band, efficiency, and electromagnetic radiation patterns of the Passeriformes plume, and they were verified with the experimental results reported in the literature study regarding light reflectivity through its internal geometry. Interestingly, we discovered that the interior structure of the Passeriformes plume functions similarly to a UV reflector antenna. Keywords: Passeriformes; multilayer interference model; UV reflector antenna; resonance frequency 1. Introduction In the biological world, coloration and geometrical characteristics are vital for demon- strating the optical properties of bird organs [1]. For example, Huth and Burkhardt first detailed birds’ tetrachromatic features and UV perceptions of light [2]. Tetrachromatic color vision is found in many birds’ eyes, making them capable of perceiving ultraviolet light. On the other hand, it has already been shown that iridescent colors are formed due to the different refractive indexes of different layers (air, keratin, and melanin) in the bird feather. Therefore, visual communication in some birds and animals is achievable by displaying and perceiving iridescent colors. For example, iridescent color is distinguishable in the keratin layer above a single melanin layer of a Passeriformes feather [2]. In earlier studies, the unidirectional and bidirectional geometry of the barbule was described in detail in the barbs’ medullar cortex [3–5]. Moreover, one study explored the optical properties of bird feathers in the infrared region of 700–2600nm. In addition, Fox et al. determined the reflectance and transmittance of light in the visible region across the different bird species and examined the variation of light reflection and transmission in the interior morphology of barbules; these parameters vary across other species [6]. Principally, the barbules of the feather are colored by pigment, and selective interfer- ence occurs due to light reflection. Such barbules are made from different refractive (low or Optics 2022, 3, 462–472. https://doi.org/10.3390/opt3040039 https://www.mdpi.com/journal/optics