Wide‐Angle Tunable Critical Coupling in Nanophotonic Optical Coatings with Low‐Loss Phase Change Material

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 18; no. 28; pp. e2202005 - n/a
• Main Authors: Sreekanth, Kandammathe Valiyaveedu, Prabhathan, Patinharekandy, Chaturvedi, Apoorva, Lekina, Yulia, Han, Song, Zexiang, Shen, Tong Teo, Edwin Hang, Teng, Jinghua, Singh, Ranjan
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.07.2022
• Subjects: Absorbers; Coupling; critical light coupling; Electromagnetic absorption; modulators; Molybdenum disulfide; Nanotechnology; Optical coatings; Optoelectronics; perfect absorbers; Phase change materials; Photoluminescence; Refractivity; Silver; Stibnite; Thin films; transition metal dichalcogenides; Two dimensional materials; Visible spectrum
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202202005

Realizing perfect light absorption in stacked thin films of dielectrics and metals through critical light coupling has recently received intensive research attention. In addition, realizing ultra‐thin perfect absorber and tunable perfect absorber in the visible spectrum is essential for novel optoelectronics applications. However, the existing thin film stacks cannot show tunable perfect absorption in a wide‐angle range. Here, a tunable perfect absorption from normal incidence to a wide‐angle range (0° to 70°) by utilizing a two‐layer stack consisting of a high refractive index low‐loss dielectric on a high reflecting metal is proposed. This is experimentally demonstrated by depositing a thin layer of low‐loss phase change material such as stibnite (Sb2S3) on a thin layer of silver. This structure shows tunable perfect absorption with large spectral tunability in the visible wavelength. Furthermore, the absorption enhancement in 2D materials by transferring monolayer molybdenum disulfide on the stack, which shows 96% light absorption with enhanced photoluminescence, is demonstrated. In addition, the thin film stack can work as a scalable phase modulator offering a maximum phase tunability of ≈140° by changing the structural state of Sb2S3 from amorphous to crystalline. Tunable critical light coupling from normal incidence to a wide‐angle range using a thin‐film cavity consisting of a high refractive index low‐loss dielectric on a high reflecting metal is experimentally presented. The thin‐film cavity is proposed to demonstrate a 2D material‐based ultra‐thin perfect absorber operating at room temperature and a scalable phase modulator for tunable visible photonic applications.