Optical properties of III-nitride semiconductors and the applications in all-optical switching

The goal of this research was to build an Nx N all-optical WDM switch, which is indispensable for the next-generation of all-optical packet-switched networks. We started from the basic concepts of telecommunication network architectures, optical networks, WDM network elements and basic components in optical networks. We focused on the principles and applications of optical couplers, Mach-Zehnder Interferometers (MZI), arrayed waveguide gratings (AWG), and some switch architectures and techniques that have helped in the design of the optical switch.; Based on the AWG principle, we derived a general design rule for constructing an N-interleaved AWG (N-IAWG), and proposed a 1xN WDM switch consisting of two N-IAWGs and a phase shifter array. We then simplified the structure by using only one N-IAWG with total reflection implemented at the end of each phase shifter. The simplified structure significantly reduced the device size and relaxed the design tolerance. This suggests that it could be used as the fundamental building block to construct non-blocking NxN all-optical WDM switches with Spanke architecture.; The feasibility of the proposed optical switch depends on the refractive index tuning in the phase shifter array, which can be realized through the carrier-induced index tuning of semiconductors. We proposed to use III-nitride semiconductors due to their unique characteristics, and presented a theoretical study of carrier-induced refractive index change in GaN in the infrared wavelength region. Calculations verified that the magnitude of carrier-induced refractive index change is high enough for the application to the proposed optical switch.; We then prepared various devices in GaN/AlGaN material and characterized their optical properties in the 1550 nm wavelength region experimentally. We measured the refractive indices and the impact of Al concentrations. We also measured the birefringence of the GaN waveguides, which helped understand the polarization effect in the devices and would help design polarization independent optical waveguides. Among the devices we prepared, there was an eight-wavelength AWG, which was the first AWG in GaN/AlGaN material. The performance of the AWG agreed well with our design expectations and may be a foundation for the application in optical switches.