All Optical Nonlinearities In Semiconductor Multi Quantum Well Waveguides For Optical Switching At 155mum

Author : Yan Li
Publisher :
ISBN 13 :
Total Pages : 260 pages
Book Rating : 4.:/5 (46 download)

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Download or read book Ultrafast All-optical Switching Based on Intersubband Transitions in Gallium Nitride/aluminum Nitride Quantum-well Waveguides written by Yan Li and published by . This book was released on 2009 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Intersubband transitions in semiconductor quantum wells have been the subject of extensive research for the past several years and are nowadays used in a variety of devices operating at mid-infrared wavelengths, such as quantum-well infrared photodetectors and quantum cascade lasers. More recently near-infrared intersubband transitions have also been measured in wide-conduction-band-offset heterostructures such as GaN/AlGaN and InGaAs/AlAsSb quantum wells, at wavelengths in the low-loss transmission window of optical fibers. This opens up the possibility of utilizing the unique features of intersubband transitions for information processing applications in fiber-optic communications. In particular, due to their ultrafast relaxation lifetimes and giant optical nonlinearities, intersubband transitions are ideally well suited to nonlinear optical switching at bit rates of several hundred Gb/s. Thus they have the potential to play a key enabling role in future ultra-broadband all-optical networks, in which information is not only transmitted but also processed in the optical domain. This dissertation addresses the design, fabrication and demonstration of all-optical switching devices operating at fiber-optic communication wavelengths, based on intersubband transitions in GaN/AlN quantum-well waveguides. The intersubband absorption properties of GaN/AlN quantum wells have first been investigated via Fourier-transform infrared spectroscopy. At the same time, a self-consistent Poisson and Schrödinger equations solver has been developed to interpret the measurement results, and to design quantum well structures optimized for all-optical switching applications. The design, fabrication and characterization of waveguides based on these quantum wells are also addressed in detail in this dissertation. All-optical switching via cross absorption saturation has then been demonstrated with an optimized waveguide structure. The measured switching times are shorter than one picosecond, which indicates the suitability of these nonlinear devices for all-optical gating at bit rates of several hundred Gb/s. At the same time, relatively low control-pulse switching energies of about 40 pJ have been demonstrated. This important parameter can be further improved using a novel approach based on coupled quantum wells, which we have proposed and theoretically investigated. Finally, the intersubband refractive-index nonlinearities of GaN/AlN quantum wells have been studied both experimentally and theoretically. The results indicate that these quantum wells are also promising for all-optical switching via cross-phase modulation, an approach that may prove advantageous in terms of contrast ratio, on-state losses, and regenerative capabilities.