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Light propagation characteristics of photonic crystal waveguide for miniaturized ultrafast optical-pulse control/delay devices

Photonic crystals (PCs) having two-dimensional (2D) periodicity on a length scale of 320-450 nm were fabricated by electron beam lithography in combination with high- aspect-ratio dry etching. To achieve three-dimensional control of the optical properties, three kinds of dielectric waveguide structures based on AlGaAs heterostructures, that is, semiconductor-clad (SC), air-bridge (AB), and oxide-clad (OC) structures, were investigated. Observation of light propagating through such photonic crystal devices was employed by optical transmission measurements. Clear photonic bandgap effects resulting in 30-dB attentuation of the transmitted light could be observed in the the bandgap regions. The measured results were in good agreement with calculated band-structures and transmission spectra using a Fine-Difference Time-Domain (FDTD) method. Straight, sixty degree-bent and Y-branch defect waveguides (D-WGs) in a 2D- PC slab were fabricated, and the resulting light propagation characteristics were measured by two methods. One was measurement of transmission spectra at wavelengths ranging from 850 to 1100nm. Another was plan-view observation of the optical beam race trace along the waveguide measured with an IR-vidicon camera. Three-dimensional FDTD simulations for the band structure and transmission spectra in the air- bridge slab with and without defect waveguides resulted in the appearance of four defect propagation modes specific to the defect waveguide, between two slab modes for the defect- free PC slab. As an example of the future-promising application of the 2D-PC slab, an ultra-small and ultra-fast optical switching device including quantum dots as large optical non-linearity (%chi3+S) media is proposed. To demonstrate such a device, recent advancement of a nano- probe assisted processing of arrayed quantum dots is discussed. Achievement of this technology will provide us with a possibility of extremely miniaturized all-optical switching devices in the OTDM optical communication network.