A Study On Silicon-based Passive Photonic Devices Based On Triple-Guide Directional Couplers With Subwavelength Gratings

In recent years,in order to solve various bottleneck problems in electrical interconnection,optical interconnection technology has attracted the attention of many scholars and research institutions and becomes the key technology.Benefiting from the CMOS compatibility and high refractive index difference,the photonic integrated circuit(PIC)is the basic support for the construction of the high-speed optical interconnection technology and the inevitable demand for the development of optical information processing system in the future.Optical power splitters and polarization controllers are the basic devices in PICs.The former is used for the multi-channel light splitting,while the latter is used for polarization separation and selection of different modes,having a great research significance for the realization of PICs.In this thesis,new optical power splitters and polarization controllers using subwavelength gratings based on the triple guide directional coupler are proposed and optimized in structural parameters and performance,providing the reference for the construction of high-performance PICs.Firstly,the background and significance of the research on optical interconnection technology together with the development advantages and the unsolved problems of silicon photonics are summarized.The current status of optical power splitters and polarization controllers are reviewed in detail.Several important performance parameters for designing silicon-based passive photonic devices are also given.Secondly,the principle and solving methods of the frequency domain finite difference(FDFD)and finite difference time domain(FDTD)methods are introduced in detail,which are utilized to analyze the modal characteristics and transmission properties of subwavelength gratings,respectively.Therefore,the research results can provide the theoretical basis for the analyses of subsequent silicon passive devices based on subwavelength gratings and triple guide couplers.Next,owing to the modal and transmission characteristics of the subwavelength gratings,a polarization independent power splitter based on triple-guide directional coupler assisted with subwavelength gratings is proposed and analyzed.The subwavelength grating structures are embedded on both sides of the waveguide gaps of the three-guide directional coupler to balance the coupling strength of two polarization modes,resulting in the realization of the polarization independent power splitter.The device with the advantages of low loss,balanced splitting ratio,and wide bandwidth can be applied to construct optical sensors or optical modulators.Then,a compact polarization beam splitter with high extinction ratio is proposed,based on the three-guide coupler with subwavelength gratings.The two side waveguides are replaced by subwavelength grating waveguide structures to form an asymmetric three-guide directional coupler.Thus,the TE mode can be coupled to the outer waveguide and output from this waveguide under the condition of phase matching,while the TM mode outputs directly without coupling due to the phase mismatching,thus the polarization beam splitter is realized.This device has great potential application in highly integrated polarization diversity schemes.Furthermore,a TE-pass polarizer based on the three-guide coupler using subwavelength grating structures is proposed.The subwavelength grating structures are incorporated into the middle waveguide,and the HPWs are introduced into the two outside waveguides.The input TM mode can be coupled to HPWs on both sides and gradually absorbed and attenuated via them,while the TE mode is not affected by the HPWs and directly outputs with low loss.Results show that the device with the advantages of low loss and high extinction ratio is beneficial to the building of large-scale PICs.Finally,the whole work of this thesis is summarized and the prospects for the future work are drawn.