| Summary: | Optical switches are used for signal switching in optical communication networks. Silicon photonics is a low-cost and mature technology to develop high-performance optical switches. This thesis is a theoretical and experimental study on silicon photonic switches, featuring broadband, low-power, high-speed, and low-crosstalk performance.
Broadband 3-dB couplers are fundamental building blocks for broadband switches based on Mach-Zehnder interferometer (MZI) structures. A broadband 3-dB coupler, which has a 100 nm operation bandwidth with coupling imbalance being much less than its competitors, i.e., adiabatic couplers and multimode interference couplers, has been theoretically designed and experimentally demonstrated.
Switches using thermo-optic phase tuning typically have high power consumption. In this thesis, two methods to improve the tuning efficiency of thermo-optic phase shifters have been investigated and employed: 1) using thermal isolation structures and 2) using folded waveguides structures. Accordingly, thermo-optic switches with state-of-the-art, ultra-low power consumption of down to 50μW/π have been demonstrated.
MZI switches using carrier injection phase tuning have high-speed performance but with a large switching crosstalk, due to the imbalanced tuning loss in the MZI structure. A novel carrier injection switch based on a balanced nested Mach-Zehnder interferometer (BNMZI) structure has been theoretically proposed. The BNMZI switch has balanced tuning schemes and therefore can be both high-speed and crosstalk-free. Besides, the switch has three switching states: cross, bar, and blocking.
Polarization control is necessary for single-mode switches. A high-performance polarization beamsplitter (PBS), which has a 120 nm operation bandwidth with modal isolations of more than 20 dB, has been designed and demonstrated, and it can be used for polarization control for single-mode switches.
Characterizing fabrication variability and performing yield prediction for photonic integrated circuits (PICs) are both challenging for photonics designers. We have developed an accurate and cost-efficient characterization method for fabrication variations, which extracts waveguide dimension variations from the spectral response of a single racetrack resonator. In addition, we have proposed a novel yield prediction method for PICs, which, for the first time in silicon photonics, is able to model the impacts of layout-dependent correlated manufacturing variations and take them into account in circuit simulations. === Applied Science, Faculty of === Electrical and Computer Engineering, Department of === Graduate
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