Design,Simulation And Fabrication Of Some Photonic Integrated Devices Based On Planar Waveguide

The optical devices based on planar lightwave circuit(PLC)technology have the advantages of small size,high reliability,possibility for large scale production,and potential integration with the photonic and electronic devices.These devices are widely employed in optical telecommunications,sensing,data storage,imaging,and signal processing.This thesis is mainly devoted to study some PLC based devices, including power splitters,demultiplexer,triplexer and polarization splitter.First,the basic principle of the waveguide and the simulation methods for PLC devices are introduced.A novel effective index method is introduced to reduce a two-dimensional structure to a one-dimensional one.This method can be implemented for arbitrarily shaped waveguides.An explicit formula is obtained for the effective refractive index profile,which is determined by the modal filed and the cross-sectional refractive index of the original structure.Some numerical methods, including finite-difference mode solver,beam propagation method,finite-difference time-domain method are introduced to analysis the mode profile of the waveguides, and the propagation properties of light in devices.Multimode effects in the vertical direction which will degrade the self-imaging quality of a Multimode Interference(MMI)coupler are analyzed.Taper structures are introduced at the junction between input/output waveguides and multimode region to suppress the excitation of the undesired vertical modes and low insertion loss (0.101dB),small non-uniformity(0.102dB)are achieved.Deeply-etched SiO₂ ridge waveguides are introduced to a MMI power splitter.The strong confinement in the lateral direction of the deeply-etched SiO₂ ridge waveguides improves the quality of self-images in the MMI section.Good performances such as a low insertion loss,small non-uniformity are achieved for a 1×4 MMI power splitter and the total device size of the present MMI power splitter is reduced to about 1/16 of that based on SiO₂ buried waveguides. Some kinds of PLC based devices were studied and optimized.A polarization insensitive dual wavelength demultiplexer based on sandwiched multimode interference waveguides is presented.Firstly,polarization insensitive multimode waveguides are achieved by choosing a suitable refractive index of the SiN_x middle region.By adjusting the width and length of the multimode region,the wavelengths of 1310 nm and 1550 nm are separated successfully.Three-dimensional beam propagation method is used to simulate the whole structure.A low insertion loss and a broad bandwidth can be achieved at 1310 and 1550nm bands for both polarizations simultaneously.Two stages of directional couplers based on photonic crystal waveguides are cascaded to form an ultracompact triplexer.The special decoupling property of the PCW-based directional coupler is utilized for the design.A taper coupling region and an additional directional coupler are introduced to achieve high extinction ratios and reduce the crosstalk respectively.The total size of the present triplexer is only 50μm×20μm,and the good performance is verified with FDTD simulation.A novel polarization beam splitter is realized by combining MMI coupler and a photonic crystal.The PC structure is introduced in the multimode section of the MMI coupler working as a polarization sensitive reflector.One polarization is reflected and the other one transmits through the PC structure.The size of the proposed PBS is rather small since the length of the MMI region is no longer needed to be integer multiples of the coupling lengths for both polarizations.Finally,the fabrication procedures including electron beam lithography and etching and end-fire characterization technologies for PLC components are reviewed. Some devices are fabricated based on semiconductor clean room facilities to verify the design.