Study On Surface Plasma Light Modulator Based On Silicon Waveguide Coupling

With the continuous development of communication traffic,the bandwidth and speed of electronic devices can not meet the needs of modern high-speed communication technology,while the optical devices with larger bandwidth and faster transmission rate are affected by the diffraction limit,and the size is large,usually in the order of wavelength.Surface plasmon polariton(SPP)can break through the diffraction limit and limit the transmission of electromagnetic waves to the order of sub wavelength.Therefore,the size of plasma optical devices is small and easy to integrate.In recent years,the plasmonic modulator with horizontal metal-insulator-metal(MIM)waveguide structure is a research hotspot of nano photonics,but it is difficult to etch nano slit waveguide on metal film.Making MIM waveguide into vertical coating structure can solve this problem.In order to reduce the difficulty of the actual manufacture of the plasmonic modulator and optimize the performance of the modulator,a vertical MIM waveguide plasmonic modulator is designed based on silicon-based waveguide coupling in this thesis.It is mainly divided into three parts:polarization rotation module,coupling module and electro-optic modulation module.Each module is simulated,analyzed and optimized with COMSOL software.The main research contents are as follows:1.The related theory,excitation mode and transmission characteristics of SPP are introduced,and the transmission mode in MIM waveguide is analyzed,which provides a theoretical basis for the design of modulator.Comparing the vertical MIM waveguide with the horizontal MIM waveguide,the increase of the aspect ratio of the plasma slot will reduce the SPP transmission wavelength,which shows the advantages of the vertical MIM waveguide structure.2.The polarization rotation module and coupling module of the modulator are designed.The fully tapered plasma polarization rotator can avoid the large loss caused by the sudden change of waveguide size,and the polarization rotation length is 4.9?m.In order to optimize the device length,the taper structure is introduced at both ends of the rectangular metal strip of the polarization rotator,and the total length of polarization rotation is only 3.4?m.The polarization conversion efficiency is up to 99.6%,and the total loss of mode conversion is 1.20 d B.The TM mode after polarization rotation is coupled to the vertical MIM waveguide through the taper structure and transformed into SPP.3.The electro-optic modulation module is designed and the overall performance of the plasmonic modulator is analyzed.After optimization,the half wave voltage length product of the plasmonic modulator is only 0.025 V×mm,the extinction ratio is 31.17d B,the transmission loss is 14.48 d B,and the area of the whole device is only34.8?8?m~2.The half wave voltage length product of the modulator with the horizontal MIM waveguide structure is 0.033 V×mm.Compared with the plasmonic modulator with the horizontal MIM waveguide,the vertical MIM waveguide plasmonic modulator is not only easier to realize,but also can reduce the half wave voltage length product of the modulator by increasing the aspect ratio of the plasma slot and reducing the transmission wavelength of the SPP.The plasmonic modulator based on TM silicon waveguide does not need polarization rotation module,so the loss is lower,and the insertion loss is 12.03dB.