Saturable Absorption by Vertically Inserted or Overlaid Monolayer Graphene in Optical Waveguide for All-Optical Switching Circuit

Abstract

Optical saturable absorption through a monolayer graphene vertically inserted between fibers and overlaid on an ion-exchanged waveguide was measured for picosecond switching application. In our proposed switch, complete switching is performed by controlling the signal light amplitude with the configuration of two cascaded Mach-Zehnder interferometers. To control the signal light amplitude, we use saturable absorption in graphene. For switching, the modulation depth of the amplitude is required to be 2.414, which corresponds to 7.65 dB in intensity. The modulation depth of absorption larger than 10 dB was experimentally obtained in the graphene-loaded waveguide with length of 7 mm.

All-Optical Waveguide-Type Switch Using Saturable Absorption in Graphene

“…This corresponds to the case discussed in ref. [7]. The switching conditions in Type A are derived from eqs.…”

“…We have proposed an all-optical switch controlled by Raman amplification [4,5] or by saturable absorption [6][7][8], where optical signal amplitude is controlled instead of the signal phase. In the previously proposed switches, refractive-index change induced by all optical nonlinear interactions was assumed to be small enough to be negligible [4,6] or to be adjusted at an integer multiple of 2π [7].…”

“…In the previously proposed switches, refractive-index change induced by all optical nonlinear interactions was assumed to be small enough to be negligible [4,6] or to be adjusted at an integer multiple of 2π [7]. When we assume graphene sheets as the saturable absorbing material, the induced refractive-index change cannot be ignored [9].…”

“…We confirm the switching performance by finite-difference beam-propagation-method (FD-BPM) simulation. As an experimental demonstration of saturable absorption in graphene, we also discuss measured nonlinear absorption in a graphene-loaded waveguide [7]. Nonlinear refractive-index change in graphene is also discussed to evaluate optical nonlinear phase change through vertically placed multilayer graphene based on the reported experimental results [9].…”

Microscopic Raman study of graphene on 4H-SiC two-dimensionally enhanced by surface roughness and gold nanoparticles

“…In this decade, graphene has attracted tremendous attention because of its novel electro-optic, photonic, and plasmonic properties [1][2][3][4] . Some graphene-based optical networking devices such as mode-locked fiber lasers [5][6][7][8][9][10] , optical modulators [11][12][13] , and optical switches [14][15][16][17][18][19] have been proposed, and some of these devices have practical applications. Most of the proposed devices have graphene integrated into an optical fiber or a planar waveguide 20) .…”