Studies On Grating-based Planar Waveguide Demultiplexers

As the key components in a WDM system, multi/demultiplexers have a critical effect on the performance of the system. In this dissertation, grating-based integrated planar waveguide demultiplexers for high density WDM applications, including etched diffraction gratings (EDGs) and arrayed waveguide gratings (AWGs), are studied in detail. The purpose is to develop devices with better performance, lower cost and easier for fabrication.The performance of an EDG is analyzed. First, aberrations of concave gratings are investigated in detail and expressions for various orders of aberrations are developed. The design method for grating with multi-stigmatic-point is given. Secondly, the analysis of the retro-diffraction in an EDG is given by using a Finite-Difference Time-Domain (FDTD) method combined with perfectly matched layers (PML) and a periodic boundary condition. Thirdly, a statistical model to estimate the impact of phase and amplitude errors in an EDG is developed using a scalar diffraction theory.Some methods are developed to improve the performance of the demultiplexers. First, a multi-stigmatic-point method is applied in a high-channel EDG demultiplexer to improve the conventional Rowland-type design. Secondly, a two-focal-point method is introduced for an optimal design of an EDG demultiplexer with a flat-top spectral response. Thirdly, a flat-field EDG demultiplexer is designed to ease the fabrication and packaging. Finally, a simple method for fabricating a polarization-insensitive AWG device is developed by matching the thermal expansion coefficient of the overcladding layer to the silicon substrate.Experimental studies of the fabrication of the EDG and AWG devices are carried out. PECVD, ICP and lift-off technologies are used for fabricating SiO₂ devices on Si substrate. Samples of the demultiplexers are tested and the experimental results are presented.K+ - Na+ ion-exchanged waveguide devices are designed and fabricated. The ionexchange and burial process are modeled by a finite-difference method. Bending loss of a diffused buried waveguide is analyzed. The waveguide structure and fabrication conditions are optimized.In summery, theoretical and experimental studies on grating-based integrated planar waveguide demultiplexers are carried out in this dissertation. The work involves the design and fabrication of high-performance demultiplexers and the results are useful for the development and studies of integrated devices.