Research On Microstructure Devices In Integrated Photonics

Photonic integration is a technology that integrates integrated photonic devices with different functions on a large scale to make them have systematic functions.Photonic chips have potential to be used in the fields of neural network,quantum computing and biosensor chips.At present,the most mature field of development is optical communication chip.The optical integrated chip based on optical signal can realize high-speed optical signal transmission and communication,and can perfectly solve the challenges in the field of computing and communication.Moreover,the manufacturing process of optoelectronic integrated chip is compatible with the existing microelectronic chip technology,with low cost and low power consumption,so it has the potential to be widely used.At present,it is in the research status of system level chip composed of thousands of basic components,such as high-speed optical transceiver chip,large-scale optical switching chip and so on.But in contrast,the basic component size of photonic chip is about 400 In the long run,one of the development directions of photonic integrated chips is to improve the integration.Most of the existing integrated optoelectronic components are designed based on the principle of guided wave optics.It is impossible to control the propagation of light through the waveguide structure.In theory,it is impossible to miniaturize the existing components.In other words,after the miniaturization of the existing components,they will become more flexible It will drop sharply.Photonic chip is different from electronic chip,in the development of improving the degree of integration,the main constraint is not micro nano processing accuracy.To improve the integration of photonic chips,basic components based on new principles are needed.In recent years,scientists have proposed to use micro nano structure array to control the propagation of light,which is called integrated super surface element.The response of micro structure array to light is complex,so the design of micro structure array can realize a variety of functional devices,which has the advantages of miniaturization,high performance and high degree of freedom.But with the complexity of design,it is difficult to establish the relevant physical model.Most of the existing design methods are non physical calculation.The micro nano structure array is regarded as a two-dimensional code like distribution.The optical response of the micro nano structure array is solved by a specific algorithm,and the physical problem is transformed into an algorithm problem.However,this kind of method needs high computational power,so it needs to recalculate for different parameters,and the results of calculation can not give physical analysis.So it is necessary to establish the physical model of the response of the super surface element.Based on the principle of guided wave optics,this paper deduces the dispersion equation of optical waveguide system,introduces the content of transformation optics and metamaterials,gradually introduces the concept of gradient index element into the field of integrated photonics,and puts forward an approximate physical model for the design of super surface element.Specific super surface can be designed by simple calculationIt can provide theoretical and empirical guidance for the design of super surface elements.At the same time,it also provides a platform for the research of transformation optics,such as invisibility cloak,black hole simulation and so on.The main contents of this paper are as follows(1)The concept of gradient index element is introduced into integrated photonics system.Based on the dispersion equation and the equivalent medium theory,the functional relationship between the duty cycle and the local effective mode refractive index is fitted.In this paper,a method of using super surface element to realize gradient index element in guided wave optical system is proposed.Using this method,we design miniaturized and high performance lenburg lens,coupler and polarizing beam splitter with dimensions of about 10 nm under standard SOI parameters The lenberg lens can achieve efficient focusing,the focusing efficiency is about 87%,and the FWHM of the focus is about 0.5 ?m.The designed coupler can achieve efficient coupling between waveguides with different widths,and the coupling efficiency is much higher than that of the tapered coupler with the same length.Polarization beam splitter can realize the separation of different polarized light,and the extinction ratio can reach 20 d B.The design method can be used for different width of input and output waveguides,and can be combined with other multiplexing elements.(2)Optical switch is an important component of photonic integrated chip.At present,the most commonly used optical switch is Mach Zehnder interferometer optical switch.Most of these optical switches need phase modulators based on thermo optic or electro-optic effects,while the electro-optic and thermo optic coefficients of traditional materials are low,so the scale of traditional optical switches is mostly 300?m.In other words,in order to realize the miniaturization of optical switch elements,we need to change the existing material system.The refractive index of phase change materials varies widely.Theoretically,we can design high integrated optical switch by using phase change materials.In this paper,we design a microstructured optical switch based on phase change materials.The device size is only about 1 ?m.At 165 nm,the insertion loss is better than 1.27 d B and the modulation depth is better than0.95.This design makes full use of the characteristics of phase change materials and realizes the optical switch with low insertion loss and high extinction ratio.(3)One of the most attractive directions in photonic integration is how to make the scale of optical integration to be 10 nm,and integrate optoelectronics on the same scale.It is difficult to describe the way of photon integration,and the integration degree is reduced to sub wavelength scale,so the carrier of photon integration may need to be replaced.The possible carrier is surface plasmon,which is a kind of metal electromagnetic surface wave that can localize light in nano scale.In this paper,we also design a super surface based gradient index element,a surface plasmon lenbert lens and an efficient coupler.The performance of the designed surface plasmon lenber lens is good,and the focusing efficiency can reach 78%.The performance of the designed surface plasmon coupler is also much higher than that of the tapered coupler with the same parameters.