# Metal-Organic Hybrid Metamaterials for Spectral-Band Selective Active Terahertz Modulators
###### Abstract  
Optically controlled spectral-band selective terahertz (THz) modulators based on metal-organic hybrid metamaterials were investigated. An artificially structured material, which consists of two single split-ring resonators put together on the split gap side, was patterned on a silicon substrate to generate frequency-selective properties. An active layer of an organic thin film (fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester, also called PCBM) was deposited on the metamaterial-silicon structure for modulating the transmission of incident THz radiation. The metal-organic hybrid metamaterials enabled active control of spectral bands present in the transmission spectra of THz waves. In addition, the changes in the photo-excited carrier density due to the transfer of charges between the layers were quantitatively analyzed by simulation results.  
terahertz spectroscopy; metamaterials; modulators; active optics Article  
* [1] S. LSI Metrology & Inspection, Samsung Electronics, Yongin 17113, Korea; [EMAIL_ADDRESS]  
2]Department of Physics and Optoelectronics Convergence Research Center, Chonnam National University, Gwangju 61186, Korea; [EMAIL_ADDRESS]  
3]Department of Physics and Department of Energy Systems Research, Ajou University, Suwon 16499, Korea; [EMAIL_ADDRESS] (S.J.P.); [EMAIL_ADDRESS] (Y.H.A.)  
4]Advanced Photonics Research Institute, GIST, Gwangju 61005, Korea; [EMAIL_ADDRESS] (C.K.); [EMAIL_ADDRESS] (L-W.H.)  
5,realize active tuning of the resonant response, which enables frequency-selective filtering or spectral-band engineering [19; 20; 21; 22; 23; 24; 25; 26]. In particular, active THz filters based on metamaterial units of split-ring resonators (SRRs) offer wide variability in terms of structural dimensions for dipole and LC resonances. Moreover, while maintaining high modulation efficiency and actively controllable features of the THz waves, which are realized by an organic material-based hybrid structure, it is necessary to create THz modulators with the functions of frequency-selective filtering or spectral-band engineering.  
In this paper, we demonstrated optically controllable, spectral-band selective THz modulators, still having the property of high modulation efficiency, based on silicon-metamaterial-organic hybrid structures. The metamaterial units, which consisted of two single SRRs put together on the split gap side, fabricated on a Si substrate, exhibited frequency-selective properties over multiple spectral bands. The organic thin film, fullerene-derivative [6,6]-phenyl-C61-butyric acid methyl ester (also called PCBM), deposited on the metamaterial-Si structure acted as an active layer for modulating the transmission of incident THz radiation. By combining the organic thin film with the metamaterial-Si structure, an active control of the spectral bands present in the transmission spectra of THz waves was achieved. Furthermore, the simulations obtained to match the experimental results, by fine-tuning of the electrical conductivity values of the PCBM and Si layers, aided the understanding of the underlying mechanisms of the phenomenon, as well as estimated the amount of change in photo-induced carrier density in the tri-layer structure.