Research On Optical Pulsed Laser By Graphene-silicon Hybrid Waveguides

In order to meet the data transmission requirements of large capacity,high speed and high security,optical communication and optical interconnection technologies have emerged,and higher requirements for devices'integration have been put forward.Silicon-based optoelectronic integration is considered to be one of the most promising directions in the field of integrated optoelectronics.A variety of silicon-based passive optical devices have been implemented.However,due to the defects of silicon materials,the implementation of silicon-based active photonic devices often requires the assistance of other materials to meet the corresponding requirements.Graphene is a hexagonal lattice of single-atom two-dimensional material,which has been proven to have excellent performance in the fields of light,electricity and heat.Combining graphene and silicon can effectively improve the performance of silicon-based optoelectronic devices,such as widening the operating bandwidth or improving the response rate.And the fabrication process of the optoelectronic devices based on the graphene-silicon hybrid waveguides are compatible with the CMOS process.Graphene is also widely used in pulsed laser generation systems due to its excellent saturation absorption characteristics,which greatly promotes the development of ultrashort pulse sources.Based on the saturable absorption characteristics of graphene,a series of studies on graphene-silicon hybrid waveguide pulsed lasers are carried out.Optical pulses are directly generated in the silicon waveguide,which provides an on-chip pulsed laser source.The properties of the generated pulsed laser are characterized.The main contents are as follows:(1)The graphene-silicon hybrid waveguides are designed and fabricated.And the performance of the fabricated devices is characterized.The characteristic parameters of optical linear absorption and saturation absorption of the hybrid waveguide in the communication band are measured.It is concluded that the linear absorption coefficients of graphene on the strip waveguide and the ridge waveguide are 0.1 dB/?m and 0.045 dB/?m respectively,and the experimental measurement results agree well with the simulated values.And the saturation absorption threshold power density of the on-chip graphene saturated absorber is about 1 GW/cm~2.The carrier relaxation recovery time in the hybrid waveguide is about 48 ps.(2)The ring cavity pulse laser is designed based on the graphene-silicon hybrid waveguide.When the insertion loss of the hybrid waveguide device is~19 dB,mode-locking optical pulse with pulse width of 1.2 ps is realized.By adjusting the pump power and the intracavity polarization state,we produce stable Q-switched,mode-locked,and Q-switched mode-locked pulses in the same hybrid waveguide.After the waveguide grating coupler is optimized,the insertion loss of the hybrid waveguide is about 11 dB,and the pump power threshold of the mode-locking startup is observed to be~45 mW.(3)An integrated linear cavity pulsed laser based on hybrid waveguide is designed to realize the generation of pulsed laser with repetition frequency of 6.45 MHz.The preliminary results verify the feasibility of the experimental scheme.