| The large data age has brought a large amount of data transmission needs,and optical communication technology is expected to break through the traditional transmission bottleneck of electrical interconnection,which has been widely studied.Optical power divider and polarization divider are two very important basic components in the construction of silicon-based photon integrated circuit.The research topic of this paper is to design a power splitter and polarization beam splitter based on the principles of subwavelength grating(SWG)and multimode interference,and innovatively combine the two functions into one device.The key performance parameters of the device are analyzed and calculated.Finally,it can be used in large-scale,high integration,low loss,low cost photonic circuits on chip.Firstly,a brief review of the past and present life of PICs is made,and the core issues,future development and urgent issues of on-chip silicon photonics are introduced.The development status of optical power splitter and polarization splitter at home and abroad,and the performance index of passive optical devices in silicon-based photonics are introduced in detail.Finally,the contents of this paper are summarized and introduced.Secondly,two commonly used device numerical analysis methods,finite-difference frequency-domain(FDFD)method and finite-difference time-domain(FDTD)method,are described.Using the above two methods,the cross-section mode characteristics and transmission characteristics of subwavelength grating structure are analyzed.It is pointed out that subwavelength grating has the advantages of controllable refractive index and effective suppression of diffraction and reflection.The self mirror effect of multimode waveguide and the transmission characteristics of multimode interference guided mode are described.Then,a polarization-independent power divider based on multimode interference is presented and analyzed.Based on the multimode waveguide structure,a shallow etched region is introduced at the beginning of the multimode waveguide and a subwavelength grating structure is behind the shallow etched region.The device achieves power sharing in TE and TM modes.The total length of the device is very small(3um),the loss is maintained below 0.2d B,and the operating bandwidth of the device is very large(1300-1750nm).It basically covers the common electromagnetic frequency bands(O,E,S,C,L,U bands),and the SR is maintained in the range of 1±0.004.Then,a device based on multimode interference to achieve both polarization beam splitting and power splitting is presented and analyzed.On the basis of multimode waveguide structure,a subwavelength grating structure with gradient width is introduced in the middle of the front part of the multimode waveguide,and a shallow etching area is introduced in the middle part of the whole device,which achieves power and polarization splitting simultaneously.The overall length of the device is 40 um.The extinction ratio of TE and TM modes is greater than 16 d B.The insertion loss of TE and TM modes is less than0.85 d B.SR of TE and TM modes are all in the range of 1±0.0001.The operating bandwidth of the device is 40 nm,which can completely cover the C-band.Finally,a dual-layer silicon multimode interference device is proposed and analyzed to achieve both polarization and power splitting.The device is based on silicon nitride silicon platform,which makes the transmission of two polarization states achieve spatial isolation,and realizes TE and TM mode power bisection and polarization beam splitting at the same time.The length of the device is only 8 um,and at the center wavelength of 1.55 um,TE insertion loss is 0.51 d B,extinction ratio is 22.62 d B,reflection loss is-30.45 d B,power ratio is 1.0002;TM insertion loss 0.90 d B,extinction ratio 15.76 d B,reflection loss-31.18 d B,power fraction 1.0001;The working bandwidth can be effectively extended to 100 nm. |
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