Research On Optoelectronic Characterization Of Graphene-silicon Based Devices

Based on silicon on insulator(SOI)platform,silicon photonic devices have been merged as an active and fast growing technology.It meets the demands in high-speed applications and relies on the mature CMOS manufacturing technologies,thus possessing features of high speed,low cost,high stability,and large-scale scalability.However,as electro-optic modulators,the weak electro-optic(EO)effect of silicon results in large footprint as well as high power consumption.Also,the low carrier mobility in silicon limits modulation speed.Therefore,novel materials need to be explored to provide better modulation performance,including small footprint,low power consumption,and operation bandwidth.Combination of new high nonlinear materials with silicon structures could be a prospective trend.Graphene,as a new material,has attracted great interest in optical communication system according to its excellent optoelectronic characteristic since it was discovered in 2004.Also,its great performance in mobility,third-optical nonlinearity,saturation absorption and wide-band absorption make it a popular material in different research area.But the absorption rate of vertical incident light of graphene is only 2.3%,which extremely limits graphene's application in optical communication system.How to improve the absorption rate of graphene and stimulate the excellent optoelectronic properties in monolayer grapheme based silicon photonic devices have become a research hotspot in academia.The graphene on silicon waveguide structure offers the advantage of greatly increasing the interaction length compared to the geometry with light incident normal to the graphene plane.This paper mainly focused on the research of the optical and electrical characterization of grapheme-silicon based devices by transferring graphene layer to some different silicon structures.Utilizing the EO modulation mechanism of graphene,we proposed and numerically studied an on-chip graphene-silicon hybrid electro-optic(EO)modulator operating at the telecommunication band,which is implemented by a compact 1D photonic crystal nanobeam(PCN)cavity coupled to a bus waveguide with a graphene sheet on top.Through electrically tuning the Fermi level of the graphene,both the quality factor and the resonance wavelength can be significantly changed,thus the in-plane lightwave can be efficiently modulated.The proposed structure combines the merits of a 1D photonic crystal nanobeam(PCN)cavity and graphene in a single device.Based on finite-difference time-domain(FDTD)simulation results,the proposed modulator can provide a large free spectral range(FSR)of 125.6 nm,a high modulation speed of 133 GHz,and a large modulation depth of ~12.5 dB in a small modal volume.The large FSR is especially attractive for integrated WDM systems since it offers a single resonance in an ultra-wide band without being affected by adjacent resonances of the device.Besides the merits of device footprints,low consumption and mass-productivity,the proposed modulator has the advantage of high modulation speeds,high extinction ratio and large FSR,which are important for wavelength-division multiplexed(WDM)optical communication systems.