JTh2A.178.pdf
CLEO 2018 © OSA 2018
An broadband terahertz metamaterial filter based on multiplexed metallic bar resonators Zijie Dai, Jing Yang, Qiang Su, Pengfei Qi, Dan Lu, Cheng Gong, Lu Sun, and Weiwei Liu* Institute of Modern Optics, Nankai University, Key Laboratory of Optical Information Science and Technology, Ministry of Education, Tianjin 300350, China. *Corresponding author:
[email protected]
Abstract: An ultrabroad terahertz metamaterial filter based on multiplexed metallic bar resonators is designed and fabricated. The bandwidth of terahertz filter can be significantly broadened by the h o r ( s ) multiplexed configurations. ©2018TheAut
OCIS codes: (160.3918) Metamaterials; (300.6495) Spectroscopy, terahertz; (350.2460) Filters, interference
1.Introduction Recently, metamaterials have been drawing increasing attentions due to their unique electromagnetic property not inherent in natural materials. A variety of prospective terahertz (THz) devices based on metamaterials architecture has been designed to manipulate THz wave in a desired manner, such as terahertz filters [1], modulators [2], polarizers [3]. In particular, THz filter has significant applications in wireless communication system and imaging for its spectral filtering [4]. In this work, we develop an ultrabroad metamaterial transmission filters using multiplexed metallic bar resonators in terahertz region. Samples containing a single bar and five multiplexed bars are fabricated and tested, and the multiplexed configurations show obvious broadening of the bandwidth by both simulation and measurement results. It is proved that the FWHM of this THz filter can be up to 82% with respect to the central frequency 1.26THz, which can greatly improve the applications in THz communications and imaging. 2. Sample A unit cell of the THz filter is illustrated in Fig. 1(a), where the multiple gold bars (n) with different length and equal spacing (g=30 μm) were located on the surface of quartz glass substrate. The sample were fabricated using electron beam lithography and lift-off techniques [5]. Taking five bars (n=5) as an example, Fig. 1(b) shows a microscopic image of a detail of the multiplexed gold bar structure, where the lengths of the five bars in a unit cell are l1=55 μm, l2=65 μm, l3=75 μm, l4=85 μm, and l5=95 μm, respectively.
Figure 1. Schematic of terahertz metamaterial filter. (a) A unit cell structure of the sample. (b) The microscopic image of a detail of the multiplexed gold bar array with five different length bars.
3. Results A numerical simulation of the designed filter was performed using the commercial tool – CST Microwave Studio. The experimental investigations were carried out on a home-made THz time domain spectroscopy (TDS) system, as
JTh2A.178.pdf
CLEO 2018 © OSA 2018
shown in Fig. s1 [6]. The measured relative transmittance of multiplexed gold bar structure is illustrated in Fig. 2 (black line). The relative full width at half maximum (FWHM) of the multiplexed sample (five different bars) is 82% with respect to the center frequency. The simulated result is also presented in Fig. 2 (grey line), which agree well with the experimental data. We attribute the broadening effect of filter width to the multiplexed resonance of five gold bars. As a reference, we simulated five isolated bar cases and the length of isolated bar n (n=1, 2, 3, 4, and 5) in a unit cell is corresponding to ln. As shown in Fig.2, the transmission spectra of isolated bar structures are relatively narrow and their peaks shift from 1.46 THz (n=1, l1=55 μm, red line) to 0.85 THz (n=5, l5=95 μm, orange line). Furthermore, we also simulated other cases (n=2, 3, and 4), which demonstrated that the relative FWHM of the filter can be greatly improved by adding the number of gold bars in a unit cell. The broadband filter with arbitrary wide bandwidth can be realized by assigning metallic bars with different lengths.
Figure 2. Simulated Trel of five isolated bar structures, corresponding to n=1, 2, 3, 4 and 5, respectively. Simulated and measured Trel for multiplexed gold bar structure with five different length bars.
4. Summery In conclusion, we investigate resonance characteristic of the transmission filters using multiplexed gold bar resonators in terahertz region. An ultrabroad metamaterial transmission filters can be obtained by the multiplexed configurations, which can greatly enhance the performance for broadband THz applications. 5.Acknowledgments This work is supported by National Basic Research Program of China (2014CB339802). Tianjin Special Program for Talent Development and Tianjin Research Program of Application Foundation and Advanced Technology (15JCZDJC31700). 6.References [1] Yang K, Liu S, Arezoomandan S, et al. Graphene-based tunable metamaterial terahertz filters[J]. Applied Physics Letters, 2014, 105(9): 093105. [2] Zhou Z, Wang S, Yu Y, et al. High performance metamaterials-high electron mobility transistors integrated terahertz modulator[J]. Optics Express, 2017, 25(15): 17832-17840. [3] Ren L, Pint C L, Arikawa T, et al. Broadband terahertz polarizers with ideal performance based on aligned carbon nanotube stacks[J]. Nano letters, 2012, 12(2): 787-790. [4] Sanphuang V, Yeo W G, Volakis J L, et al. THz transparent metamaterials for enhanced spectroscopic and imaging measurements[J]. IEEE Transactions on Terahertz Science and Technology, 2015, 5(1): 117-123. [5] Ueno K, Misawa H. Spectral properties and electromagnetic field enhancement effects on nano-engineered metallic nanoparticles[J]. Physical Chemistry Chemical Physics, 2013, 15(12): 4093-4099. [6] L. Liang, M. Qi, J. Yang, X. Shen, J. Zhai, W. Xu, B. Jin, W. Liu, Y. Feng, C. Zhang, H. Lu, H.-T. Chen, L.Kang, W. Xu, J. Chen, T. J. Cui, P. Wu, and S. Liu, “Anomalous terahertz reflection and scattering by flexible and conformal coding metamaterials,” Adv. Opt. Mater. 3(10), 1374– 1380 (2015).
