Deep and fast free-space electro-absorption modulation in a mobility-independent graphene-loaded Bragg resonator

Abstract

Deep and fast electro-optic modulation is critical for high-speed near infrared signal processing. We combine the electro-absorption tunability of graphene with the high-Q resonance of a Bragg-based Fabry-Perot resonator at λ=1550 nm and show that ~100% free-space signal modulation (>50 dB extinction ratio, <1 dB insertion loss) at high speed (>1 GHz) can always be achieved independently of graphene quality (mobility), provided the device is operating in reflection mode and tuned in critical coupling with graphene. Remarkably, the critical coupling mechanism produces a higher extinction ratio for lower graphene mobility. We use practical considerations to optimize the device architecture and operation as a function of graphene mobility. With a small modification this scheme can be turned into a very sensitive acousto-absorption modulator with a ~30 dB/Å extinction ratio, or an index sensor with 10 7 %/RIU sensitivity. These designs can be easily extended throughout the midIR spectrum by appropriate scaling of layer thicknesses.

Enhanced absorption and electrical modulation of graphene based on the parity-time symmetry optical structure

“…In addition to modulation depth, the operation speed is also used to describe the structure performance of the graphene modulator, which can be estimated by the formula [28] f = 1 2πRC…”

Active Modulation of Graphene Near‐Infrared Electroabsorption Employing Borophene Plasmons in a Wide Waveband

“…On one hand, borophene is a 2D metal that supports intrinsic plasmonic response with stronger field confinement than the traditional noble bulk metals in the considered nearinfrared region, significantly improving the electroabsorption of graphene. On the other hand, borophene plasmons allows us to realize the active modulation of graphene electroabsorption in a wide waveband, which is not possible for previous reported strategies that based on bulk metallic plasmons, [18] F-P cavity resonance, [26][27][28][29] guide-mode resonance [31][32][33][34][35][36][37] or magnetic polaritons. [38][39][40][41][42][43]…”

“…Such phenomenon can be attributed to the different absorption property of doped graphene at different wavelength region. [18,32,34,35,41,54] It should be mentioned that, from the ultraviolet to nearinfrared wavelength region, graphene itself is unable to excite surface plasmon resonances and its absorption is due to direct interband transitions determined by its Fermi energy E f . By plotting the real and imaginary parts of graphene permittivity in Figure 1f, it is found that there is a sharp peak in the real part and a sudden fall in the imaginary part at 1.72 µm (corresponding to the optical energy of 0.72 eV, i.e., 2E f ).…”

“…[1,2] Compared to conventional bulk electro-optic crystals, graphene [3] is a 2D material that holds is coupled with a photonic crystal slab on top of a back mirror or a Bragg reflector. [31][32][33][34][35][36][37] Recently, it is also demonstrated that increased absorption in graphene can be achieved by employing deep metallic nano-gratings [38,39] or metal-dielectric-metal multilayer structures. [40][41][42][43] These structures supported magnetic polaritons that enable a strong localized electric field around the graphene surface, which greatly enhanced the graphenelight interactions and thus the light absorption of graphene.…”

Graphene optical nonlinearity: From the third-order to the non-perturbative electrodynamic regime

“…Theoretical studies [16,31,32] and experiments [33][34][35][36][37] in integrated nonlinear waveguide devices followed, which paved the way toward voltage-tunable ultrafast absorptive and refractive nonlinearity in photonics. While the interested audience awaits for more integrated nonlinear devices and experiments, work progresses in designing new components [38][39][40][41][42][43][44][45][46][47] and extending the theoretical modeling horizons [48][49][50][51][52][53][54][55].…”