The Study On The Vertical Coupling Structure Of Waveguide Applied To Germanium-Silicon Integrated Photonic Chip

In order to achieve large-scale application of integrated optoelectronic chips,it is necessary to solve the problem of efficient optical interconnection between different devices on the chip,and taper coupler is an important structure to realize efficient vertical coupling between layers.The design of taper coupler in chip needs to follow three basic criteria,which are small device size,high coupling efficiency and large production tolerances.Due to the mutual restraint among these three criteria,achieving a compact,efficient and versatile taper coupler is still an important and difficult problem.In this thesis,the taper coupler in chip is analyzed in theory,designed in taper shape,simulated in performance and tested in experiment.Research works of realizing a compact,efficient and polarization-insensitive taper coupler are studied and innovated as follows:(1)Aiming at the Ge-SOI coupling structure,the optimization scheme is proposed.The tapered active waveguide is composed of two section with large taper angle in the front and small taper angle in the tail.It is found from FDTD algorithm simulation that the coupling efficiency can achieve more than 90% when the center width of front tapered section is equal to the resonant width of 260 nm and the width range of that is more than 200 nm.(2)A simple fabrication method of Ge-SOI coupling structure is proposed.The active germanium waveguide is sputtered in the upper layer after etching the underlying passive silicon waveguide.This method does not require etching the germanium waveguide,therefore it can reduce the difficulty of fabrication process.(3)Several types of Ge-SOI coupling structures with different taper shapes are fabricate and tested.Experimental result shows that the coupling loss is less than 3 d B,and the material absorption loss and sidewall scattering loss are the main reasons leading to the large value of total optical power loss.(4)For coupling structure applied in SiGe photonic integrated chip,an optimization scheme of compact,efficient and polarization-independent taper coupler with three section is proposed.The taper coupler is only 45-?m-long,which can achieve more than 90% coupling efficiency for both TE-and TM-polarized incident light.Its width tolerance is ±200 nm,thickness tolerance of each layer is ±100 nm,operating wavelength range is 1460~1625 nm,and can work properly under the bias of 3 V.It has large tolerance,wide wavelength range and stable performance.