# Tuning of Graphene-Based Optical Devices Operating in the Near-Infrared
## 4 Conclusions and Future Work  
This work analysed and compared the optical behaviour in the NIR range of the graphene and its integration as an electrode into optical devices. In particular, the complex permittivity, along with the parameters of the Kubo model, was discussed. The tuning mechanisms, along with the configurations for the GE the insulator material and its thickness, were detailed.  
It is important to highlight that, during the fabrication, great attention should be paid to the process of transferring graphene into the waveguide since the transfer could lead to a deterioration in the quality of graphene, which greatly affects the ability of the device to tune the wavelength as it changes the surface conductivity. Particular attention should also be paid to the range of the supplied voltage since exceeding it leads to a breakdown of the tuning mechanism. Although the temperature of graphene does not lead to significant changes in the parameters of graphene, one should also consider its interaction with thermosensitive components (e.g., silicon waveguides). Finally, the performance of the analysed configurations was compared showing the achieved wavelength shift in the order of hundreds up to thousands of picometers.  
In conclusion, this work could help and lead the design of the tuning of graphene-based optical devices and the integration of graphene in optical resonant structures operating in the NIR.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Ref.** & \(\mathbf{t_{G}}\)**, **nm** & **TMM** & \(\mathbf{t_{\
u}}\)**, **nm** & \(\mathbf{\Gamma_{\
u}}\)**, **s\({}^{-1}\)** & **Insulator** & **V\({}_{\mathbf{G}}\)** & \(\boldsymbol{\lambda}\)**, **\(\mathbf{\mu}\)** & **Device** & **\(\boldsymbol{\Delta}\)**, **pm** \\ \hline
[7] \({}^{*}\) & - & EGWC & - & 3.8462e13 & PEO + LiClO\({}_{4}\) & \(-1.2\div 1.2\) V & 1.56907 & CNM & 800 \\ \hline
[8] \({}^{*}\) & 0.33 & GIG & 90 & 5e11 \(\div\) 1e14 & Al\({}_{2}\)O\({}_{3}\) & \(-40\div 40\) V & 1.53–1.57 & M-ZM & 140 \\ \hline
[9] \({}^{*}\) & 0.7 & GIG & 10 & 5e12 \(\div\) 1e14, & Al\({}_{2}\)O\({}_{3}\) & \(0\div 3\) V & 1.552 & M-ZM & 173/385 \\ \hline
[10] \({}^{*}\) & - & GIG & 5 & - & Al\({}_{2}\)O\({}_{3}\) & \(0\div 15\) V & 1.549 & CNM & 66/165 \\ \hline
[15] & 0.34 & GIG & 70 & 1e14 & SiO\({}_{2}\) & \(-4.95\div 4.95\) V & 1.539–1.559 & WOM & 10 \\ \hline
[19] \({}^{*}\) & 1 & EGWC & 5 & 2.2789e14 &
\begin{tabular}{c} Al\({}_{2}\)O\({}_{3}\)\(\&\) \\ ion-gel \\ \end{tabular} & \(-2\div 0\) V & 1.55 & CNM & 1000 \\ \hline
[20] \({}^{*}\) & 0.34 & EGWC & 10 & 7.5963e13 &
\begin{tabular}{c} HfO\({}_{2}\)\(\&\) \\ PEO + LiClO\({}_{4}\) \\ \end{tabular} & \(-7\div 6\) V & 1.55 & CNM & 1000 \\ \hline
[24] \({}^{*}\) & 1 & GIIW & - & - & Al\({}_{2}\)O\({}_{3}\) & \(-12.5\div 0\) V & 1.548–1.557 & MRR & 2000 \\ \hline
[25] \({}^{*}\) & 0.5 & GIIW & 25 & 1e14 & Al\({}_{2}\)O\({}_{3}\) & \(-6\div 6\) V & 1.55 & MRR & 125 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison table (\({}^{*}\) refers to fabricated devices).  
**Author Contributions:** [PERSON] performed the numerical simulations and drafted the paper. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], M.G. the authors commented, edited and reviewed the manuscript. [PERSON] supervised the work. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie, agreement No 860808 (OPTAPHI).  
**Data Availability Statement:** Not available.  
**Acknowledgments:** This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 860808 (OPTAPHI).  
**Conflicts of Interest:** The authors declare no conflict of interest.