# Tuning of Graphene-Based Optical Devices Operating in the Near-Infrared  
[PERSON]  
1 Department of Electrical and Information Engineering, Politecnico di Bari, 4, 70126 Bari, Italy;[EMAIL_ADDRESS]
2 Centre for Advanced Photonics and Process Analysis, Munster Technological University,  
T12 T66T Kork, Ireland; [EMAIL_ADDRESS]
3 CNR-Nanofee, Department of Chemistry, University of Bari, Via Orabona, 4, 70123 Bari, Italy;[EMAIL_ADDRESS] (G.V.B. ); [EMAIL_ADDRESS] (G.B.) 4 Tyndall National Institute, T12 PX46 Cork, Ireland  
4 Correspondence: [EMAIL_ADDRESS] (A.S.V. ); [EMAIL_ADDRESS] (M.G.) [PERSON]  
3 CNR-Nanofee, Department of Chemistry, University of Bari, Via Orabona, 4, 70123 Bari, Italy;[EMAIL_ADDRESS] (G.V.B. ); [EMAIL_ADDRESS] (G.B.) [PERSON]  
3 CNR-Nanofee, Department of Chemistry, University of Bari, Via Orabona, 4, 70123 Bari, Italy;[EMAIL_ADDRESS] (G.V.B. ); [EMAIL_ADDRESS] (G.B.) [PERSON]  
1 Department of Electrical and Information Engineering, Politecnico di Bari, 4, 70126 Bari, Italy;[EMAIL_ADDRESS]  
1 Department of Electrical and Information Engineering, Politecnico di Bari, 4, 70126 Bari, Italy;antonella. by introducing doping using electrical and/or chemical gating, which shifts the Fermi energy from the Dirac point and, in turn, changes the optical response of graphene [6]. This approach opens the possibility of easily tuning graphene from a \"lossy-dielectric\" behaviour to the \"quasi-metallic\" region, which can be used to implement modulators (based on electro-optical graphene optical behaviour, Mach-Zehnder interferometers, rings, switches and Zeno-based modulators) [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23], resonators [24; 25; 26], or can be applied to a wide variety of devices that operate at a specific resonance and require wavelength tuning [27; 28; 29]. It should be noted that the use of this property of graphene is not limited only to the NIR range; in this regard, electro-optical graphene terahertz modulators can be noted [30; 31; 32]. The nonlinear photonics of graphene finds many applications, including spatial and spectral control of laser light, all-optical signal processing, ultrafast switching and probing, and frequency multiplication of the terahertz range [33; 34; 35; 36; 37; 38]. Graphene is also an affordable means for implementing a saturable absorber (SA) [39; 40; 41; 42; 43]. It is worth noting that, in addition to graphene, 2D materials such as transition metal dichalcogenides (TMD), for example MoS\({}_{2}\), WS\({}_{2}\), MoSe\({}_{2}\), ReS\({}_{2}\), WSe\({}_{2}\) and others [44; 45; 46], and black phosphorus [47; 48; 49; 50], are gaining popularity, but TMDs show a band gap of about 1 to 2.5 eV (which corresponds to frequencies from NIR to visible), and the band gap of phosphorus is highly variable depending on the number of layers: from 0.3 eV in the bulk to about 2 eV in an isolated monolayer [51; 52; 53]. Unlike the universal optical conductivity in graphene (single layer graphene absorbs \(\approx\)2.3% of vertical incident light in the FIR to UV range), semiconductor TMD can exhibit multiple absorption peaks from NIR to UV frequencies due to excitons and interband transitions (the absorption coefficients of two peaks in a TMD monolayer can reach \(\approx\)10% and \(\approx\)30%, respectively [54]), and the optical absorption of black phosphorus depends on the thickness, doping and polarization [55]. The purpose of this work is to analyse the behaviour and the integration of graphene electrodes (GEs, complete list of symbols and notations is located in Table 1) into optical devices paying particular attention on how the introduction of GEs affects the performance of the optical devices and their tunability.