The Research On Optical Modulators Based On Two Dimensional Materials

Optical modulators which is the key fu-nctional device in the optical fiber communication networks and optical interconnects have extensive and important applications in optical networks and optical interconnections.As the developing of data center and other systems,optical interconnect is moving to the inter-cabinet optical interconnection,inter-board optical interconnection,inter-chip and on-chip interconnection.The on-chip optical interconnect is the tendency in the future,and the transmission requirement will reach 10 Tb/s/cm2 in the next few years.High speed optical interconnection requires high performance optical modulator to supports.The modulation speed,footprint,power consumption,on chip integration and other features of optical modulators require higher performance in the future.However,the traditional optical modulator cannot fulfill the request.Hence the optical modulator based on new electro-optic materials has attracted a lot attention in the past decade.The traditional optical modulators,such as lithium niobate modulators,III-V compound semiconductor modulators,silicon-based modulators,and polymer modulators have performance limitations and instability issue.And it's difficult to fulfill the requirement of interconnection.The performance of conventional optical modulators is limited by the structure or the material.Therefore,it is necessary to study the optical modulator based on the new type of electro-optic functional material to realize high-speed and efficient optical modulation while compatible with the CMOS process simultaneously.The two-dimensional materials have very unique and excellent in electrical,optical,mechanical and thermal properties.There are a large number of various applications based on two-dimensional materials,such as sensors,detectors,biomedicine and so on.Hence it is to necessary to research the optical modulators based on two-dimensional materials that could meet the requirements of the optical communication network and optical interconnection.In this paper,we investigated the feasibility and the performance of optical modulator based on two-dimensional materials or the heterojunction.The working principle of modulator is studied,and the modulation speed,modulation bandwidth,power consumption,footprint of the modulators are studied in detail.This paper has made the following innovative achievements:(1)A graphene modulator based on hybrid waveguide which have field enhancement effect is proposed.The graphene-hexagonal boron nitride-graphene layer is sandwiched in the low refractive index layer of the hybrid plasmonic waveguide to form a layered stack structure.The optical properties of graphene is changed by the bias voltage through the electrodes.By computer simulation we found that the thickness of the low refractive index layer and the width of the hybrid plasmonic waveguide in the modulator have a great influence on the modulation depth.The higher the height would lead to higher loss,smaller modulation depth,while the wider width would lead to higher loss and higher modulation depth.By optimizing the geometric parameters of the structure,40 dB modulation depth could be achieved with only 3 ?m long working area,and the bandwidth of 3 dB modulation depth is up to 190 GHz.At the same time,the required voltage difference for the modulator is only 3.1 V,the energy required to transmit 1 bit information is only 7.7 fJ,and the footprint of the core area of this modulator is less than 1 ?m2.(2)A graphene modulator with hybrid waveguide resonator is proposed.We found that ehe effect of bias voltage would lead to the transmission spectrum red/blue shift or up/down shift.The red/blue shift was caused by the changes of the real part of the effective index of waveguide.While the up/down shift is mainly due to the imaginary part changes,which resulting in the loss of the resonant cavity changes.A trade-off between the modulation depth,energy and footprint was made by studying the effect of the geometrical parameters on the effective refractive index of the modulator.At the same time,the modulator can realize multi-wavelength operation.The wavelength is set from 1400 nm to 1700 nm,the modulation depth would not less than 12%,the modulation depth is up to 50%at 1600 nm,and the modulation depth can reach 18.41%at 1550 nm.Compared to the traditional resonant cavity modulator,the device area could be reduced more than 80%.(3)The optical modulator based on black phosphorus was proposed and studied for the first time.The effects of waveguide geometrical parameters on the effective refractive index with TE and TM modes along the direction of armchair and zig-zag are studied respectively since the anisotropy of black phosphorus.According to the field distribution of the waveguide and the conductivity of black phosphorus,it is found that propagation of the waveguide along the armchair direction with TM mode,has the best modulation performance.The wavelength is set to 1550 nm,an extinction ratio of about 0.166 dB/?m can be achieved,and 3 dB modulation depth can be achieved with only 18 ?m long working length.While the operating wavelength is set to 2100 nm,the extinction ratio is 0.102 dB/?m,and the 3 dB modulation depth an be achieved with only 30 ?m long working length.(4)The graphene/black phosphorus heterojunction optical modulator based on hybrid plasmonic waveguide is proposed and studied for the first time.It is found that the geometrical parameters of the waveguides can change the absorption efficiency of heterogeneous junctions.The selected geometrical parameters are different from the modulators based on graphene and hybrid plasmonic waveguide.Under the optimized parameters,the extinction ratio of the modulator is 2.51 dB/?m,and this modulation depth could achieve to 7.53 dB with only 3 ?m long working length.