Wavelength-selective micro- and nano-photonic devices for wavelength division multiplexing networks
On the road toward the information age, the enormous bandwidth demanded by the explosive growth of Internet traffic has been supplied by fiber-optic communications technology; in particular, the widespread use of Wavelength-Division Multiplexing (WDM) techniques. My research focused on Optical Add-Drop Multiplexers (OADMs) and wavelength demultiplexers, two key devices for WDM technology. Various approaches, including nanophotonic approaches based on photonic crystals, were employed in the research. First, a variety of ball lens-based OADMs were designed and implemented. The overall performance of the ball lens-based OADMs was competitive compared to that of commercial GRIN lens-based OADMs, while the former devices were more cost-effective and simpler in packaging. Optical Add-Drop Multiplexers are one of the promising applications of photonic crystals. Prior theories have been limited to devices with frequencyindependent coupling and simple mirror symmetry. Through my research, a general model was developed to understand the optical add-drop process in realistic photonic crystal-based OADMs, where the interactions between the waveguides and cavities are frequency dependent and cavity modes depart from the accidental degeneracy of frequency. Furthermore, a class of devices with more freedom in choice of symmetry were proposed. An original idea was proposed to utilize the inevitable optical loss in a way that improves device performance. The last part of my research was aimed at developing a wavelength demultiplexer based on the superprism effect in photonic crystals. In the course of this research, a general and rigorous refraction theory was developed for a photonic crystal of any lattice type, any surface orientation, and any surface termination. The theory solved some long-standing problems in grating diffraction as well. Refraction at naturally emerging quasi-periodic surfaces was treated in a unified way with the refraction on periodic surfaces. A new concept, surface-dependent mode degeneracy, was introduced and was shown to be crucial to understanding photonic crystal refraction. Arbitrary incident beam profiles were investigated. The first-ever practical demultiplexer design that has less than 3dB loss over a 25-nm spectrum is given based on this theory. The theory is anticipated to be instrumental in understanding some interesting research topics such as photonic crystal slab-based superlenses.