Study On The Low-Crosstalk And Bandwidth Tunability Of Oadm

OADM (Optical Add/Drop Multiplexer) is the key of wavelength division multiplexing (WDM) Optical network elements, and plays an extremely important role in communication network to develop in the direction of high speed, large capacity and transparency. Almost all countries included in the field of modern communications network and it must solve the key technology.In this thesis, we design and demonstrate cross-connect photonic filters using micrometer-sized resonators coupled to low-loss low-crosstalk waveguide crossings in silicon-on-insulator substrate. These devices can be readily cascaded into one-dimensional and two-dimensional cross-connects as building blocks for OADM. Our designed crossing is based on the self-image property of lined-tapered multimode-interference (LTMMI). We adopt beam-propagation-method (BPM) and finite-difference time-domain (FDTD) method to simulate the optical performance of our designed LTMMI crossings in silicon-on-insulator (SOI) substrate. The simulations suggest that the LTMMI crossings exhibit only0.2dB insertion loss and this suggests significant improvement in the junction loss compared with direct crossing imposing～0.9dB insertion loss. The designed LTMMI crossing also suppresses the crosstalk and back-reflection to be below42dB. Using characteristic of slot waveguide in the coupling regions and thermal tuning, we propose and demonstrate a novel and simple design of ultra-compact microring resonator on silicon-on-insulator platform with bandwidth tunability from8.07nm to9.07nm. The detailed analysis and the design of the device are presented. The device presents an extinction ratio higher than35dB and ultra-compact size, which is very promising for practical implementations.We also introduce a vertical microring resonator with enhanced tolerance to fabrication misalignments. Both straight and microring waveguide are with relatively high refractive index difference between the core and cladding, therefore the vertical microring resonator is compact as well as confines the power efficiently. Based on coupling mode theory, the coupling coefficient is derived as a function of coupling layer thickness (d) and the offset (Δ) between the straight and microring waveguides. The analytic solutions are used to confine the range of three dimension finite-different time-domain (3D-FDTD) simulations for their efficiency. In addition, the tolerance of d and Δ is studied by taking consideration of actual fabrication technology for the vertical nano-microring resonator. The analytic solutions and simulation results show that when d=30nm, the vertical microring resonator has large coupling coefficient even Δ is varied between130nm to265nm. It is verified the vertical nano-microring resonator presented in this paper has enhanced tolerance to fabrication misalignments.