Ultra-broadband spatial light modulation with dual-resonance coupled epsilon-near-zero materials
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Ultra-broadband spatial light modulation with dual-resonance coupled epsilon-near-zero materials Qin Chen1 (), Shichao Song2, Huacun Wang3, Li Liang1,3, Yajin Dong1, and Long Wen1 () 1
Institute of Nanophotonics, Jinan University, Guangzhou 511443, China Institute of Photonics Technology, Jinan University, Guangzhou 511443, China 3 Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 29 July 2020 / Revised: 5 November 2020 / Accepted: 30 November 2020
ABSTRACT It has been found that the dielectric constants of transparent conductive oxides (TCOs) can be adjusted in an extremely large range by tuning the carrier density. Due to the remarkable light confinement property of the epsilon-near-zero (ENZ) effect of TCOs, it has attracted extensive interests of light modulation. However, the operation wavelength bandwidth is usually limited by optical resonance that is applied to enhance the light-TCOs interaction. In this work, a dual-resonance light coupling scheme is proposed to expand the modulation depth-bandwidth product with almost one order-of-magnitude improvement. In a metallic subwavelength grating structure with deep trenches backed by a ground plane, the ENZ mode can be coupled to both magnetic resonance and Fabry-Perot resonance respectively by tuning the bias. Decent light modulation can be obtained in a large operation wavelength band covering two resonances by optimizing the dual-resonance configuration. Such a reconfigurable efficient broadband modulation is important for robust communication link and possesses remarkable capacity for wavelength division multiplexing.
KEYWORDS epsilon-near-zero, spatial light modulation, plasmonics, transparent conductive oxides, field effect
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Introduction
Light modulation is a key technique for optical signal processing, optical communication, optical computing, and optical imaging, etc. [1, 2]. In general, intensity, phase and polarization of light are tuned by external excitations based on various effects such as Pockel effect (LiNbO3 or electro-optical polymers) [3, 4], Kerr effect (liquid crystal) [5], phase transition (VO2) [6], MEMs [7], acousto-optic effect [8], electro-absorption (GaAs) [9] and free-carrier dispersion effect (Si) [10, 11]. Considering the system level integration with driver microelectronics, silicon-based optical modulators are the most attractive, and thus various active materials have been tried to integrate onto the silicon platform [3, 4, 12]. Both efficient modification of the material refractive index and the enhancement of lightmatter interaction have been the constant foci in light modulation. Recently, Atwater et al. found that indium tin oxide (ITO) is a promising candidate in optical modulation materials with an extraordinary large refractive index tuning range of 1.5 [13], which is at least three orders of magnitude larger than the free carrier dispersion effect of silicon. Base
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