Figure 2. Gate-variable properties of the all-fibre graphene device using a monolayer graphene.

(a) Optical transition properties of the device. Initial fibre-to-fibre insertion loss of the SPF was 0.5 dB (grey solid line). The insertion loss slightly increased by 0.2 and 0.27 dB for TM and TE mode, respectively, after transferring the monolayer graphene (blue and red dash lines). Blue and orange solid lines show gate-variable optical transmission for TM and TE mode, respectively, after applying the ion liquid. (b) Electrical transport properties of the device. The on–off I_D current ratio was 16.7 for the applied V_G range of ±1.8 V. The estimated V_CNP was 1.16 V (blue vertical dash line) where the Fermi level of graphene is close to zero. Inset: normalized change of optical transmission (ΔT/ΔI_D) as a function of drain current. The experimental result (black solid square) is displayed with fitted line (red solid line). Maximum of transmission change occurs at I_D of 6.55 μA (corresponding gate voltage is −0.49 V (red vertical dash line)) where the Fermi energy level shift is half the incident photon energy.