Hybrid Graphene-Silicon Based Polarization-Insensitive Electro-Absorption Modulator with High-Modulation Efficiency and Ultra-Broad Bandwidth

Abstract

Polarization-insensitive modulation, i.e., overcoming the limit of conventional modulators operating under only a single-polarization state, is desirable for high-capacity on-chip optical interconnects. Here, we propose a hybrid graphene-silicon-based polarization-insensitive electro-absorption modulator (EAM) with high-modulation efficiency and ultra-broad bandwidth. The hybrid graphene-silicon waveguide is formed by leveraging multi-deposited and multi-transferred methods to enable light interaction with graphene layers in its intense field distribution region instead of the commonly used weak cladding region, thus resulting in enhanced light–graphene interaction. By optimizing the dimensions of all hybrid graphene-silicon waveguide layers, polarization-insensitive modulation is achieved with a modulation efficiency (ME) of ~1.11 dB/µm for both polarizations (ME discrepancy < 0.006 dB/µm), which outperforms that of previous reports. Based on this excellent modulation performance, we designed a hybrid graphene-silicon-based EAM with a length of only 20 µm. The modulation depth (MD) and insertion loss obtained were higher than 22 dB and lower than 0.23 dB at 1.55 µm, respectively, for both polarizations. Meanwhile, its allowable bandwidth can exceed 300 nm by keeping MD more than 20 dB and MD discrepancy less than 2 dB, simultaneously, and its electrical properties were also analyzed. Therefore, the proposed device can be applied in on-chip optical interconnects.

Polarization-Insensitive Electro-Absorption Modulator Based on Graphene-Silicon Nitride Hybrid Waveguide

“…Accordingly, the MD for TM mode is evaluated to be 20.940 dB, which is very close to that of 20.936 dB for TE mode. As far as we know, this resulted ΔMD of 4 × 10 -3 dB is the smallest and two orders of magnitude lower than the minimum in reported single waveguide polarization-insensitive graphene modulators [39][40][41][42][43][44][45]. Furthermore, in the ON state, the propagation loss is calculated to be 0.985 dB for both modes.…”

On-Chip Reconfigurable and Ultracompact Silicon Waveguide Mode Converters Based on Nonvolatile Optical Phase Change Materials

“…The metal contacts are added on both sides of the conversion region. Then, using atom layer deposition, a 20-nm-thick Al 2 O 3 layer is deposited atop the graphene layer to prevent the graphene from oxidation [ 45 ]. Using these methods, we can realize the proposed reconfigurable silicon waveguide mode converter.…”

“…The graphene layer works as an efficient microheater because of its high thermal conductivity and low heat capacity [ 43 , 44 ]. The optical absorption loss of graphene could be quite low as the chemical potential of graphene is larger than 0.4 eV owing to the Pauli blocking mechanism [ 45 , 46 ]. The Al 2 O 3 layer is used to prevent the graphene from oxidation.…”

Symmetric Graphene Dielectric Nanowaveguides as Ultra-Compact Photonic Structures

“…Benefiting from these excellent characteristics, graphene has served as an effective nanoscale waveguiding platform in the infrared region. More importantly, the combination of graphene and silicon-on-insulator (SOI) waveguides make it possible to design graphene-based photonic integration devices [ 32 ], such as waveguides [ 33 , 34 , 35 , 36 , 37 , 38 , 39 ], sensors [ 40 , 41 ], filters [ 42 ], modulators [ 43 , 44 ], etc. Recently, graphene–SiO 2 –Si coaxial-like waveguides [ 45 ], graphene layer–SiO 2 –Si planar structures [ 46 , 47 , 48 , 49 , 50 ], and graphene-coated nanowires integrated with SiO 2 or Si substrates [ 51 , 52 , 53 , 54 , 55 , 56 ] were presented to demonstrate ultra-compact photonic integrated circuits in the mid- and far-infrared bands.…”