Design Of Silicon-Based Mode Converters Based On Subwavelength Grating Slots

With the rapid development of computer technology and semiconductor technology,the number of processors integrated on a single chip is increasing rapidly,which leads to a huge challenge to the transmission capacity of network on chip.At present,the optical interconnection technology based on SOI（Silicon-On-Insulator）platform is gradually replacing the traditional electrical interconnection and becoming the mainstream interconnection mode in the chip because of its advantages of large capacity,high bandwidth,low power consumption,low communication delay and low electromagnetic interference.On chip mode division multiplexing technology is considered to be a promising optical interconnection multiplexing technology.By controlling the eigenmodes propagating in the optical waveguide,it can meet the needs of great transmission capacity of on-chip network in data communication.The mode converter,which can realize the conversion between basic mode and high-order mode,as an important part of the module division multiplexing system,directly affects the total transmission capacity of the module division multiplexing system.Based on this,five silicon-based mode converters with different functions are studied in this thesis.In order to improve the performance of the device,the sub wavelength grating structure is selected and introduced in the design.The carefully designed sub wavelength grating is etched on a single silicon waveguide to realize the TE polarization mode conversion.Specific research contents are as follows:1.In this thesis,two new silicon-based mode converters based on sub wavelength grating are proposed,and the mode conversion of TE₀-TE₁ and TE₀-TE₂ is realized.Through the designed sub wavelength grating etching,the refractive index distribution of the waveguide is changed.Under the action of mode coupling,the input TE₀ mode accumulates phase difference and generates high-order mode.The conversion efficiency of TE₀-TE₁（TE₀-TE₂）converter at 1.55μm wavelength can reach 92.1（95.6）%,the modal crosstalk is-17.5（16.7）d B,the insertion loss is 0.65（0.5）d B,the device length is 3.3（4.32）μm,and the device bandwidth is 110 nm.2.The proposed TE₀-TE₁ and TE₀-TE₂ mode converters are extended,and TE₀-TE₃ and TE₀-TE₄ mode converters are designed.After considering the mode field distribution of TE₃（TE₄）,the structures of TE₀-TE₁ and TE₀-TE₂ devices are changed,and TE₃（TE₄）is generated at the output port.The conversion efficiency of TE₀-TE₃（TE₀-TE₄）converter at 1.55μm can reach 82.5（83.2）%,the modal crosstalk is-14（11）d B,the insertion loss is 1.4（1.37）d B,the device length is 10.8（9.5）μm,and the device bandwidth is 120 nm.3.A bi-directional conversion mode converter based on sub wavelength grating is innovatively proposed.Using the same device,the mutual conversion between TE₀and TE₁can be realized,and the effect of mode conversion is very close.By etching an inverted"V"structure on the waveguide,the refractive index distribution of the waveguide is no longer symmetrical along the optical input direction,and the mode conversion is realized by phase matching.When TE₀-TE₁（TE₁-TE₀）conversion is realized at the working wavelength of 1.55μm,the conversion efficiency can reach 83.4（84.5）%,the modal crosstalk is-14.6（14.17）d B,the insertion loss is 1.05（1）d B,the length of the device is only 3.3μm,and the bandwidth can reach 150 nm.