Silicon Optical Control Devices Based On Periodic Structure

There is a history more than thirty years of Moore's Law.During this period,the develop speed of electronic integrated circuits follows this law all the time.However,because the density of integration is higher and higher,the size is smaller and smaller,it is reaching the physical limit of material.The development of electronic integrated circuits is meeting bottlenecks.People start searching for a new direction.Photonic technology is selected due to its no charge and high propagation speed.Silicon is an important semiconductor material,so there is very mature technology for the processing of silicon.It helps the development of silicon photonics very much.Silicon is indirect band gap semiconductor material,the luminous efficiency is very low,so most designs of silicon components focus on the passive components.The development of silicon waveguide,grating,filter,modulator and some others is an important support for the high efficiency propagation and conversion in silicon photonics integration.We can realize some special goals in reality by making changes based on these components.We also designed several kinds of Silicon optical control devices based on periodic structure.(1)Polarization controlled mirror based on metasurfaces.Metasurfaces mean the periodic arrangement of different micro-nano structures.By the theory of metasurfaces,every single micro-nano structure has a respond to the localized electromagnetic field,that is electric dipole moment and magnetic dipole moment in physics.We use surface equivalent current and surface equivalent magnetic current to describe the respond of the whole metasurface to the incident electromagnetic field at the macro level.These two physical parameters constitute a surface electromagnetic field on the metasurface.So the effect of incident electromagnetic field to the metasurface can be simplified to matching of this surface electromagnetic field distribution and incident electromagnetic field distribution.We can change the amplitude of electromagnetic field after reflection by the design of metasurface structure,to realize high reflection or high absorption.Metasurface can not only change the amplitude but also change the phase of electromagnetic field,this change can be from-n to ?.We designed a metasurface structure which can control the amplitude and the phase at the same time.Meeting the demand that the phase should be changed,then keep the same amplitude in x-direction and y-direction.So a left-handed rotation light will still be a left-handed rotation light after the reflection of metasurface mirror with a high reflection efficiency.(2)Vertical coupling gratings.Grating is an important component for light coupling.It is very hard to realize vertical coupling for traditional rectangle grating,while blazed grating can realize high efficiency vertical coupling.This paper designed a double-layers rectangle grating,it can control the diffractive phase of these two different layer gratings to achieve the goal of high efficiency vertical coupling.This grating can work as a blazed grating.When we etch different-sized holes in silicon,the difference of the hole size will cause the different etching speed.Then we can fabricate a double-layers grating with different effective index.Compared with other double-layers grating,this one is easier to be fabricated in technology.(3)Transient free carrier grating technology.The refractive index of silicon will change due to the effect of carrier density,a transient free carrier grating technology is given by this theory.This technology can be used for signal detection in photonics integrated chips.The bandgap of silicon is 1.12eV.We choose 850nm light which can be absorbed,two laser beams intervened on the top of silicon.So there will be different distribution of carrier density because of the absorption of light in silicon.A transient free carrier grating then be formed.This transient free carrier grating can help us export light signal from waveguides.This method is very simple and flexible,the location of transient free carrier grating can be everywhere,and there is no damage to the structure.