Silicon-Based Polarization-Insensitive Optical Power Splitter

An optical power splitter is one of the fundamental devices for splitting and combining optical signals,and also the construction of more complex optical devices,such as optical switches and multiplexers.Recently,silicon-based devices have played a more and more important role in optical interconnects and optical communication due to their ultra-compact footprint,ultra-low loss and compatibility with the traditional complementary metal oxide semiconductor(CMOS)fabrication technology.Therefore,a silicon-based optical power splitter is highly required.Based on silicon integrated platform,power splitters are mainly realized through Y-branches,directional couplers(DC),and multi-mode interference couplers(MMI).However,these approaches are limited by a number of drawbacks,such as not easy to achieve 2×2 function,which is necessary in optical switches,and the high mode mismatch loss for Y-branch when the branching angle is not sufficiently small,due to the limitation of the fabrication,or the high sensitivity to wavelength and polarization for conventional DC and MMI couplers.In this thesis,we solve the polarization-dependent issue by utilizing two cascaded bent DCs.Firstly,we give a brief summary of several common optical waveguide structures and their applications.A series of eigenmode equations for the optical slab waveguide are deduced in order to describe the mode filed distribution.In addition,we also introduce the BPM and FDTD method,where are commonly used for the numerical simulation of optical waveguides.Secondly,we proposed and demonstrated a broadband and polarization-insensitive 2×2 3 dB power splitter based on cascaded bent DCs.The first bent DC is designed to split the lights of the TE polarization at 50%:50%.Since the second DC is designed to have a week coupling for TE polarization,the light of TE polarization will pass through the second DC while keeping the splitting ratio of 50%:50%.By optimizing the parameters of the second DC,the light of the TM polarization can be split with a ratio of 50%:50%.The whole 3 dB coupler can work for both polarizations in a broadband range from 1520 to 1630 nm,with an excess loss less than 1 dB.The total size of the device can be as small as 50 ?m.Thirdly,we introduce the fabrication processes of our silicon-based optical splitter,including E-beam lithography,development,etching and so on.Then we characterized our device.The results are in good agreement with the simulation.The splitter also shows good fabrication tolerance.Finally,we built a platform for the efficient coupling and packaging between the silicon waveguides and the fiber arrays.Then we introduce the alignment method and the packaging processes in detail,and demonstrate the packaged device with the fiber arrays.