Research On Integrated Silicon-based Polarization Analyzers

With the development of science and technology,polarized light has been widely used in the fields of films,communications,biomedicine and so on.Compared with other scalar parameters of light,such as power and wavelength,polarization reveals the vector characteristics of the light field.It contains more information,and is more difficult to be characterized and measured.A polarization analyzer is the instrument used to measure the polarization state of light,and plays a vital role in many fields,such as remote sensing,imaging and navigation.At present,most commercial polarization analyzers use spacial waveplates to perform different polarization manipulation on the input light,and inversely derive the polarization state by measuring the output light intensity with separate photodetectors.They often have complicated structures,poor stability and high cost.In recent years,silicon-based photonic devices have received increasing attention in the development of integrated and intelligent systems due to their small size,good stability and ease of mass production.Integrating the polarization analyzer on the silicon-based photonic chip can avoid the deficiencies of the traditional solutions and has important research value.However,it is difficult to perform polarization manipulation and light intensity detection on silicon-based chips.So far,there have been few reports of silicon-based integrated polarization analyzers.Therefore,we have deeply studied the on-chip polarization manipulation mechanism,built a silicon-based integrated device with polarization analysis function,and proposed three different on-chip polarization measurement schemes.With the help of heterogeneous integration process,silicon-germanium photodetectors are fabricated to solve the problem of on-chip light intensity detection.For the first time,a complete silicon-based integrated polarization analyzer is realized.The main contents of this thesis are summarized as follows:The working principle of time-division and light-division polarization analyzer is deduced.The calibration method of the polarization analyzer is given,and its main performance parameters are introduced.Using the full-vectorial finite-difference method,the characteristics of the polarization mode in the silicon waveguide are studied.The source of the birefringence effect of the silicon waveguide is also analyzed.The fabrication process,test platform and method of silicon devices are introduced.Drawing on the structure of a traditional time-division polarization analyzer,an equivalent silicon-based waveguide device is constructed,and the manipulation function required for polarization analysis is realized.The key devices involved are simulated,fabricated and tested.Finally,a time-division silicon-based integrated polarization analyzer chip with a size of 2 mm×0.6 mm is fabricated.The experimental results show that the root mean square error of the normalized Stokes parameter is less than 0.028.The on-chip implementation method of the key device 45° polarizer in the light-division polarization analyzer is studied,and the on-chip 45° polarizer based on cladding-etching is proposed,which verifies the feasibility of on-chip light-division polarization analysis.On this basis,the polarization analysis matrix is further studied,and is realized by using a 4×4 multimode interference coupler.Thus,a simplified light-division silicon-based integrated polarization analyzer is proposed.The size of the fabricated chip is 1.1 mm×1.5 mm,and the measured root mean square error of the normalized Stokes parameter is less than 0.041.By using the reverse design method,an ultra-small regular hexagonal polarization manipulation unit is designed with a side length of only 3.36 ?m.The device can realize the manipulation required for polarization analysis,greatly simplifying the structure of the polarization analyzer.The size of the entire chip is 1.1 mm×0.25 mm,which is only one sixth of the 4×4 multimode interference coupler scheme.The experimental results show that the root mean square error of the normalized Stokes parameter is less than 0.046.The fabricated chip is electrically and optically packaged,the supporting data acquisition circuit and visual software interface are designed,and a prototype silicon integrated polarization analyzer is constructed.