## 4 Conclusions  
This paper has presented a demultiplexer tunable in the terahertz range with three output channels designed on an MIM waveguide incorporating the LC. Based on the FP resonance of the MIM waveguide and the field distribution under different resonant modes, the operating modes as well as the locations of the three channels can be determined. By applying an external electric field across the copper plates of the MIM waveguide, the dielectric property of the LC infiltrated in the main channel of the MIM waveguide can be changed, and thus the demultiplexer can be tunable. Numerical simulations demonstrate that channels 1, 2 and 3 can demultiplex signals from the main channel at frequencies of 0.7315 THz, 1.068 THz and 1.429 THz, respectively. By applying electric field \begin{table}
\begin{tabular}{c} **Rela.** \\ **Shift** \\ **(THz)** \\ \end{tabular} \\ \hline
0 & 0.7315 & - & - & 1.068 & - & - & 1.429 & - & - \\
3 & 0.6895 & 0.042 & 5.7 & 1.038 & 0.030 & 2.8 & 1.387 & 0.042 & 2.9 \\
5 & 0.6654 & 0.066 & 9.0 & 0.996 & 0.072 & 6.7 & 1.333 & 0.096 & 6.7 \\
7 & 0.6414 & 0.090 & 12.3 & 0.966 & 0.102 & 9.6 & 1.291 & 0.138 & 9.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Shifts of spectra of the output channels due to different bias electric fields of LC. Figure 8: \(\left|H_{y}\right|\) fields in the demultiplexer with zero-biased electrical field of the LC at the resonant frequencies: **(a)** 0.7315 THz; **(b)** 1.068 THz; **(c)** 1.429 THz. Figure 7: Output spectra of the demultiplexer corresponding to channels: **(a)** 1; **(b)** 2; **(c)** 3.  
from 0 kV/cm to 7 kV/cm on the MIM waveguide, the operating frequencies of the output channels 1, 2 and 3 can be shifted relatively as large as 12.3%, 9.6% and 9.7%, respectively. Such an LC-infiltrated MIM waveguide with output channels can achieve desired demultiplexing results in the terahertz range. The demultiplexer presented here is also a meaningful reference for demultiplexing signals in the optical and microwave ranges, because the tunability of the LC material is still valid in those frequency ranges. [PERSON]-[PERSON] conceived the idea, analyzed the data, and wrote the paper. [PERSON] revised the manuscript and supervised the whole work. [PERSON]-[PERSON] analyzed the simulations and revised the manuscript. [PERSON]-[PERSON] and [PERSON] provided suggestions and revised the manuscript. This work was supported by the National Natural Science Foundation of China (61505035, 11734012, 11574218), the China Scholarship Council, the National Key Research and Development Plan (2016 YFB1200402-019), and the Guangdong Science and Technology Plan (2015B090923004). The authors declare no conflict of interest. * _[PERSON] et al. (2018)_ [PERSON]; [PERSON] Terahertz modulator a using CsPbBr3 perovskite quantum dots heterostructure. _Appl. Phys. B Lasers Opt._**2018**, _124_, 224. * _[PERSON] et al. (2018)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Ultrasensitive specific terahertz sensor based on tunable plasmon induced transparency of a graphene micro-ribbon array structure. _Opt. Express_**2018**, _26_, 30655-30666. [CrossRef]
* _[PERSON] et al. (2018)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]. Tunable ultra-wideband terahertz absorber based on graphene disks and ribbons. _Opt. Commun._**2018**, _427_, 418-425. [CrossRef]
* _[PERSON] et al. (2018)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Tunable terahertz band-stop filter based on self-gated graphene monolayers with antidot arrays. _Opt. Commun._**2018**, _427_, 21-26. [CrossRef]
* _[PERSON] et al. (2018)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Plasmon-exciton coupling interaction for surface catalytic reactions. _Chem. Rec._**2018**, _18_, 481-490. [CrossRef]
* _[PERSON] et al. (2017)_ [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Enhanced terahertz radiation generation of photoconductive antennas based on manganese ferrite nanoparticles. _Sci. Rep._**2017**, \(7\), 46261.