There is a trend in photonic circuits to move to smaller device dimensions for improved cost efficiency and device performance. However, the trend also comes at some cost to performance, notably in the polarisation dependence of the circuits, the difficulty in coupling to the circuits, and in some cases, in increased device complexity. This paper discusses a range of Silicon-on-Insulator (SOI) based optical devices, and the advantages and disadvantages in moving to smaller waveguide dimensions. In particular optical phase modulators based upon the plasma dispersion effect and ring resonators are considered, together with a device for coupling to small waveguides, the so-called Dual Grating Assisted Directional Coupler (DGADC). The advantages of moving to small dimensions are considered, and some preliminary experimental results are given. In particular, progress of the DGADC is evaluated in the light of promising experimental results.
Waveguide based Bragg grating devices have the potential of integration with passive or active optical components. A narrow bandwidth Bragg reflection filter or Fabry-Perot resonant structures can be realised using the approach of periodic refractive index modulation in waveguide gratings to form reflective structures. Most authors have considered 1st order Bragg gratings with periods of the order of 228nm operating at 1550nm but at the expense of complexity and high cost of fabrication. This paper describes the design of Silicon-On-Insulator (SOI) rib waveguides operating in the single mode regime that exhibit low polarisation dependence. A rigorous leaky mode propagation method (LMP) has been used to investigate the influence of etch depth in 3rd order Bragg gratings on the reflectance and bandwidth in the waveguides.
Arrayed Waveguide Gratings (AWG) have gained significant popularity in Wavelength Division Multiplexing (WDM) in recent years. One of the most important characteristics of an AWG is to have a flat spectral response in order to maximize the performance of the device and reduce crosstalk. In this paper, we present a novel method of achieving a flat spectral response AWG in silicon-on-insulator (SOI). This is achieved using free carrier doping, which ultimately introduces absorption which alter the intensity field distribution at the output of the array waveguides. By applying Fourier optics to the free space region of the AWG, this field profile is the inverse Fourier transform of the output field at the AWG, hence producing a flat spectral response. The rib of the arrayed waveguides is designed to operate in singlemode condition and exhibit minimum polarization dependence. The AWG is designed to operate at a centre wavelength of 1.55μm at a grating order of 51 with path length differences of 22.61μm. Particular emphasis is paid to the theoretical analysis and development of a flat spectral response AWG, including a number of different implantation doses.