Vol.:(0123456789) Optical and Quantum Electronics (2019) 51:169 https://doi.org/10.1007/s11082-019-1894-9 1 3 Narrow and wide band tunable absorbers based on gold squares dispersed in liquid crystal Reza Rashiditabar 1  · Najmeh Nozhat 1 Received: 22 November 2018 / Accepted: 15 May 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract In this paper, the absorption behavior of gold squares with different sizes has been inves- tigated. Our study includes gold squares in two, three and four different sizes dispersed in liquid crystal to propose an absorber with post fabrication tunability. In this case, more than 95% narrow band as well as wide band absorptions have been obtained when two and three sizes of gold squares have been used. Moreover, wide band absorption spectrum with the full width at half maximum of about 0.31 µm has been obtained when there are four different sizes of gold squares in our structure. Also, graphene has been utilized to boost the narrow band absorption from about 80 to 95%. Keywords Absorber · Liquid crystal · Localized surface plasmon resonance (LSPR) · Graphene 1 Introduction Liquid crystal (LC) is an anisotropic dielectric with unique optoelectronic properties (Yang 2014). High birefringence and liquid state of LC are two features that makes LC a suit- able candidate to be well integrated in photonic and plasmonic as well microwave devices (Khoo 2007). Mostly, optoelectronic researchers utilize LC to propose a device with post fabrication tunability. In this case, there are tunable devices such as color filters (Wang 1995), switches (Baxter et al. 2006), voltage sensors (Scherschener et al. 2006) and absorb- ers (Rashiditabar et al. 2018). Electromagnetic absorbers are indispensable blocks of photonic, terahertz and micro- wave networks. They are designed to be narrow or wide band according to their appli- cations (Tao et al. 2010; Karampour and Nozhat 2017). Also, there are electromagnetic absorbers based on the conversion of light into the surface plasmons (SPs). In Zhang et al. (2013), a narrow band absorber has been proposed to operate in mid-infrared regime. Hen- drickson et al. (2012) have fabricated a wide band plasmonic absorber by two gold squares in mid-infrared frequencies. Indeed, the mentioned absorbers suffer from post fabrication tunability. * Najmeh Nozhat nozhat@sutech.ac.ir 1 Department of Electrical Engineering, Shiraz University of Technology, Shiraz 7155713876, Iran