A Study On Asymmetric Directional Coupling Power Splitter Using Silicon Subwavelength Gratings

In recent years,with the rapid development of optical network and communication technology,the speed,capacity and integration of optical communication are increasing day by day,while the technical index which can be satisfied by traditional methods has reached the bottleneck.Meanwhile,silicon-based Photonic Integrated Circuits(PICs),as a new technology compatible with CMOS manufacturing technology,have realized ultra-high integration of silicon-based photonic devices.In addition,silicon-based photonic integrated devices also have a series of significant advantages such as high performance,low coupling loss,low packaging cost and low power consumption,which play a crucial role in modern ultra-high speed and large capacity communication systems.This paper mainly introduces an important component of silicon photonic integrated circuit,namely optical power splitter.It can be used to realize the multiplexing of optical power.Firstly,this paper introduces the numerical analysis method of designing power splitter and the correlation characteristics of subwavelength grating,and then proposes a design method of power splitter by embedding subwavelength grating in asymmetric directional coupled waveguide,and analyzes and calculates the evolution process of TE and TM mode light transmission in waveguide and the power splitting ratio at the output waveguide.Finally,in this paper,two kinds of extensible power splitter design schemes are proposed.The main research content of this paper is as follows:1.A new type of high performance 2×2 power splitter is designed by combining the traditional power splitter with subwavelength grating structure.Compared with the conventional directional coupler which only relies on two straight waveguides to realize power splitting,the device has a larger working bandwidth and a more compact size.At the same time,compared with the power splitter based on subwavelength grating,the device realizes the problem of optical transmission loss in silica-based materials at 1550 nm band by using insulated silicon platform,and improves the working bandwidth of the device to a certain extent.In addition,compared with the traditional power splitters such as adiabatic evolution type and multi-mode interference type,the device size can be smaller,and finally the broadband and compact optical power splitter can be realized.With the aid of subwavelength grating structure,the device has more performance parameters that can be optimized,so that the device can maintain high performance such as compact size,large bandwidth and low loss while realizing different power beam splitting ratio.The experimental results show that if the operating bandwidth is defined as the PSR in the wavelength region of 3d B±0.55 d B,the bandwidth is up to 100 nm,the insertion loss is less than 0.3d B,and the dimension length is at least 7.4μm,and the insertion loss is less than 0.2d B when the bandwidth is greater than 90 nm and the power beam splitting ratio is 50%:50%.As a very common basic photonic device,the device can be used in many fields such as optical switch,optical phased array and multiplexer.2.According to the designed 2×2 asymmetric directional coupling power splitter has certain scalability,according to its 3d B power splitting performance,a 1×2 asymmetric directional coupling power splitter based on silicon bridge waveguide is proposed and simulated to solve the polarization sensitivity problem between TE polarization state and TM polarization state.The working principle of the design scheme,the parameter optimization method,the transmission characteristics of the device and the process tolerance are analyzed by simulation.The device performance of the 1×2 asymmetric directional coupling power splitter is better than that of the 1×2 asymmetric directional coupling power splitter under the power splitting of 3d B,which is mainly reflected in the bandwidth performance.Under the premise that the waveguide size is basically unchanged,in order to achieve a larger bandwidth,the device is cascaded through the symmetric directional coupled waveguide and the asymmetric directional coupled waveguide,and the cone waveguide is added in the middle to reduce the loss.The simulation results show that in the wavelength region where the operating bandwidth is defined as PSR located in the range of 3d B±0.55 d B,the bandwidth of 3d B power splitting device achieved by TE mode is 1480-1750 nm,up to 270 nm,and the bandwidth of 3d B power splitting device achieved by TM mode is 1530-1770 nm,up to 250 nm.The power splitting ratio of TE mode and TM mode can be kept within 3d B±0.55 d B,and the insertion loss is less than 0.2d B.In this paper,the parameters of the proposed power splitter design process are analyzed in detail and the acceptable manufacturing tolerance range is considered.It is verified that the improved device scheme can reduce the insertion loss during the proportional power conversion.It also shows that the proposed device can efficiently convert the light source mode of different power,and has compact size,good device performance,and is easy to manufacture.