Research On Two-Dimensional Materials Hybrid Integrated Modulators And Photodetectors On Silicon-based Platform

With the advent of the "big data" era,the demand for optical-electrical data conversion has also increased exponentially.In order to fundamentally increase the communication capacity,it is necessary to improve the performance of basic components such as modulators and photodetectors.Traditional silicon-based photonic devices are difficult to meet the demands of low power consumption and high-speed response at the same time.Novel twodimensional materials,such as graphene and black phosphorus,have unique properties such as ultra-wideband spectral absorption,ultra-high carrier mobility,and adjustable Fermi energy level compared to traditional silicon-based materials,and are suitable for low power consumption,high-speed and high-efficient modulators and photodetectors.With the gradual maturity of the processing conditions of two-dimensional materials,the introduction of novel two-dimensional materials on silicon-based photonic platforms is one of the development trends of large-scale silicon-based photonic circuits in the future.From theoretical analysis to device fabrication,this article systematically studies highperformance silicon-based optical modulators,photodetectors and all-optical switches based on two-dimensional materials.Firstly,this paper proposes a slow-light-enhanced photonic crystal waveguide based on a double-layer graphene capacitor structure to realize an optical intensity modulator.By laying the double-layer graphene capacitor structure on the defect of the slow light photonic crystal waveguide,a high-speed and large modulation depth electro-optical intensity modulator can be obtained.The photonic crystal waveguide used in this design can not only increase the bandwidth of the modulator by tightly binding the optical field,but also use the slow light effect to increase the interaction time of graphene and the optical field to improve the modulation depth of the modulator.Theoretical analysis shows that the device can obtain a bandwidth of 13.6 GHz and a modulation depth of 0.5 d B/?m.The modulation depth and modulation bandwidth are 3 and 10 times higher than those of the strip waveguide doublelayer graphene modulator of the same size,respectively.After the device fabrication,the experimental results shown that the 3 d B bandwidth corresponding to the 10 ?m-long device is 12 GHz,and the modulation depth is 0.55 d B.The bandwidth of the modulator is close to the theoretical design.Although the modulation depth does not meet the theoretical expectations,the performance can be further improved by optimizing the fabrication methods.Secondly,this paper proposes a high-speed photodetector based on surface plasmon in graphene and metal slot waveguide.The core part of the photodetector is composed of graphene on the bottom layer and metal slot waveguide on the upper layer.Laying graphene on the bottom of the metal slot waveguide can significantly increase the interaction between graphene and light,and ultimately improve the responsivity of the photodetector.The contact parts between the metal slot waveguide and the two sides of the graphene are Pd and Ti respectively,which can form a built-in electric field on the two sides of the graphene to further improve the responsivity.At the same time,the metal slot waveguide can also act as contact pads,which can increase the response bandwidth by reducing electrical circuit components.Experimental results show that the 3 d B bandwidth of the photodetector can exceed 110 GHz,and the responsivity of the photodetector can reach 360 m A/W.This new type of graphene-based photodetector is expected to be applied to ultra-compact,ultra-highspeed optical interconnect circuits.Finally,this paper proposes an all-optical modulator based on heat effect by black phosphorus and silicon microring resonator.The silicon-based microring is covered with black phosphorus,achiving a high-efficient all-optical modulator in the band of 1550 nm.As a resonator device,microring can significantly increase the interaction time of light and black phosphorus.The experimental results show that the switching efficiency reaches 0.164 ?/m W,and the 3 d B bandwidth is 2.5 MHz.The rise and fall times measured by square wave are 479 ns and 113 ns,respectively,which realizes an all-optical modulator with a high-efficiency in nanosecond scale response.