Integrated Tunable Silicon-on-insulator Filters

Book excerpt: "Silicon-on-insulator (SOI) has become an attractive material system for integrated photonic components due to its potential for integration of optical devices with complementary metal-oxide-semiconductor (CMOS) technology, and its low cost. Moreover, the high-index contrast of the SOI system enables fabrication of very compact devices. Wavelength division multiplexing (WDM) is a key technique for high-capacity telecommunication and data communication networks. Optical filters are one of the key components for implementation of photonic integrated circuits (PICs), and wavelength division multiplexed (WDM) optical communication systems.Researchers have demonstrated numerous configurations such as ring resonators, Mach-Zehnder interferometers, and integrated Bragg gratings for implementation of SOI-based optical filters. The goal of this thesis is to develop novel filter configurations for application in WDM systems and photonic integrated circuits, specifically bandwidth tunable filters and optical filters with multiple channels. To achieve this goal, first we review different possible approaches to implement bandwidth tunable filters and multi-channel filters. Contra-directional grating assisted coupler(CDGAC) is chosen to implement the chosen configurations.Using CDGACs three different configurations are chosen to implement the bandwidth tunable filters. The main drawback of all of previously demonstrated SOI integrated bandwidth tunable filters is that they have a limited bandwidth tunability range. However in this thesis by cascading two CDGACs with different periods, a bandwidth tunable add-drop filter with bandwidth tuning range of 10.6 nm is implemented. This structure has a working range limited to 17 nm. In addition to that, a fully reconfigurable add-drop filter consisting of two identical CDGACs in a loop configuration is proposed. Moreover, by omitting one of the two connecting waveguides from this structure, a bandwidth-tunable bandpass filter is realized.Finally, we propose the design, fabrication and measurement results of an add-drop filter with two drop channels which is a CDGAC with two different grating periods. The performance of proposed configuration is investigated by means of Fourier analysis which gives a thorough insight into the performance of the device and can be used to understand the behavior of similar configurations.We believe that the present thesis is a step forward towards implementation of optimal bandwidth tunable SOI filters. Moreover, the proposed two-channel optical add-drop filter can have a significant impact on the required device density to perform advanced filtering functions." --