A Study On Etched Circular Waveguide Based On-Chip Silicon Mode-order Converters

In order to solve the problem that the transmission capacity is not enough to carry a large amount of data caused by the rapid development of Internet technology,optical interconnection has become the future development direction with its advantages of low power consumption,large capacity and high speed.The advantages of silicon-on-insulator（SOI）platforms are relatively low price,high transparency in the communication band,relatively high refractive index contrast and compatibility with complementary metal oxide semiconductor（CMOS）processes.It is very suitable for optical interconnect.Currently,mode division multiplexing（MDM）technology can be adapted to exponentially increasing optical interconnect capacity applications.The mode-order converter is the core device in the mode division multiplexing system.This paper mainly proposes and designs a circular mode-order converter based on etched grooves.The paper also analyzes its principle,introduces design ideas,calculates and analyzes the performance of the device,discuss the fabrication and analyzes the manufacturing tolerance of critical parameters.This circular mode-order converter is expected to be applied to on-chip mode division multiplexing transmission systems.Based on this,this paper first introduces the different modes of TE and the related mode field distribution,and then proposes a design method to realize mode-order converter by adding etching grooves in the circular waveguide.The article also analyzes and calculates the process of mode light transmission and evolution in the circular waveguide,as well as the mode components and their proportions at the output waveguide section.Finally,the paper proposes four scalable mode-order converter schemes.The specific research content of the paper is as follows:1.This paper proposes a circular mode-order converter based on etched grooves to realize TE₀-TE₁.The device adds two parallel etching grooves with a certain angle to the input waveguide in the circular waveguide.The angle of the etching groove and the distance between the two etching grooves are conducive to the accumulation of the required phase relationship.After optimization,the proposed TE₀-TE₁mode-order converter has a good performance,the device conversion efficiency is 99.1%at 1550 nm,the crosstalk is-25.7 d B,and the insertion loss is 0.21 d B.Finally,the paper analyzes the parameters,bandwidth and manufacturing tolerance of the device in detail.2.Based on the design concept of the TE₀-TE₁mode-order converter,since the design scheme proposed in this research has certain scalability,the paper proposes a TE₀-TE₂circular mode-order converter and a TE₀-TE₃circular mode-order converter based on the etched grooves.Similarly,a high-performance mode-order converter is also achieved by optimizing two parallel etched grooves with a certain angle to the input waveguide and matching output waveguides with different angles.After optimization,the mode conversion efficiency,crosstalk and insertion loss of the mode-order converter of TE₀-TE₂（TE₀-TE₃）are 92.5%（81.3%）,-16.1 d B（-8 d B）and 1.33 d B（1.86 d B）,respectively.Among them,the device performance of the TE₀-TE₃mode-order converter is lower than that of the TE₀-TE₂or TE₀-TE₁mode-order converter,and the insertion loss is the most obvious.On the premise that the size of the circular waveguide is not enlarged,if higher-order mode light is to be converted,the angle between the two etching grooves and the input waveguide and the distance between the two etching grooves must increase,then the mismatch in the size between the circular waveguide and the output waveguide will become more pronounced,and the insertion loss will become larger.Therefore,an additional etching area is added at the junction of the two waveguides to reduce the loss,and a new TE₀-TE₃circular mode-order converter is proposed.The conversion efficiency of the device reaches 86.6%,the modal crosstalk is-10.89 d B,and the loss is 0.997 d B.Meanwhile,the detailed parametric analysis of the proposed TE₀-TE₃mode-order converter,as well as bandwidth and acceptable manufacturing error range analysis are carried out.It is verified that the improved device scheme can reduce the insertion loss of higher-order mode-order converter,and has relatively good device and compactness.The structure of the device is easy to be fabricated and can be extended to realize a series of mode-order converter from basic modes to higher-order modes.