Fully confined photonic band gap and guided modes in a two-dimensional photonic crystal slab

摘要

A new two-dimensional photonic crystal (2D PC) slab structure was created with a full three-dimensional light confinement. Guided modes with broad bandwidth and high transmission within the band gap are also observed. As an optical analog to electronic crystals, PC promises a revolution in the photonic world similar to the electronic revolution created by the electronic band gap engineering in semiconductor. 2D PC has an advantage of being easier to fabricate at optical wavelength ((lambda)) comparing with 3D PC. However, the light leakage in the vertical direction has been the main problem for using 2D PC in opto-electronic application. In this study, the authors solve this problem by combining traditional 2D PC with strong vertical index guiding between the waveguide layer (GaAs) and the cladding layer (Al(sub x)O(sub y)). A set of triangular lattice holes 2D PC's were fabricated with lattice constant a=460nm, hole diameter (d=0.6a) and waveguide layer thickness (t = 0.5a). Those parameters were chosen to maximize the TE photonic band gap (PBG) around (lambda) = 1.55(micro)m. The depth of etched holes is (approximately)0.6(micro) m and the 2(micro)m thick Al(sub x)O(sub y) cladding layer is obtained by thermal oxidation of Al(sub 0.9)Ga(sub 0.1)As. PC waveguides were also created by introducing line defects along (Gamma)K direction. The authors perform transmission measurement by coupling light to PC with 3(micro)m wide waveguides which extends (approximately)0.6mm on both sides of PC. An aspheric lens with NA = 0.4 is used to focus the collimated light from tunable diode laser into the input waveguide. Another identical lens is used to collect the transmitted light and focus to an infrared (IR) camera and a calibrated photo-detector with a beamsplitter. The Gaussian waveguide mode indicates that the signal detected by the photodetector comes only from the light interacting with PC and propagating along the waveguide. The absolute transmittance is obtained by normalizing the transmission with a reference measured with a nominally identical waveguide without PC.