Silicon photonics has been a rapidly growing subfield of integrated optics and optoelectronic in the last decade and is currently considered a mature technology. The main thrust behind the growth is its compatibility with the mature and low-cost microelectronic integrated circuits fabrication process. In recent years, several active and passive photonic devices and circuits have been demonstrated on silicon. Optical delay lines are among important silicon photonic devices, which are essential for a variety of photonic system applications including optical beam-forming for controlling phased-array antennas, optical communication and networking systems and optical coherence tomography. In this thesis, several types of delay lines based on apodized grating waveguides are proposed and demonstrated. Simulation and experimental results suggest that these novel devices can provide high optical delay and tunability at very high bit rate. While most of silicon photonics research has focused in the near-infrared wavelengths, extending the operating wavelength range of the technology into in the 3–5 µm, or the mid-wave infrared regime, is a more recent field of research. A key challenge has been that the standard silicon-on-insulator waveguides are not suitable for the midinfrared, since the material loss of the buried oxide layer becomes substantially high. Here, the silicon-on-sapphire waveguide technology, which can extend silicon’s operating wavelength range up to 4.4 µm, is investigated. Furthermore, silicon-on-nitride waveguides, boasting a wide transparent range of 1.2–6.7 μm, are demonstrated and iv characterized for the first time at both mid-infrared (3.39 μm) and near-infrared (1.55 μm) wavelengths.