Ultra-small GaAs-photonic-crystal-slab-waveguide-based near-infrared components:: Fabrication, guided-mode identification, and estimation of low-loss and broad-band-width in straight-waveguides, 60°-bends and Y-splitter's

We designed and fabricated ultra-small photon ic-crystal (PC)-waveguide (WG)-based components of straight-WGs, 60degrees-bends and Y-splitters, utilizing single-line-defect in the air-bridge type GaAs PC, and revealed their optical properties in detail by observing a transmittance (T) spectrum over a broad wavelength-region from 850 to 1600 nm. For this purpose, we developed a halogen-lamp-based spectrometer for an ultra-thin slab-sample, which has turned out very useful. We also calculated the corresponding T-spectrum by using three-dimensional finite-difference-time-domain method. In all cases where comparison is possible, the observed spectrum agrees essentially with the calculated one. Owing to these broad spectra, we have unambiguously identified the high-T region due to single guided-mode in the respective components. Comparisons of the spectrum between different samples or components, such as the straight-WGs with much different lengths, or the straight-WG and the sharp bend have also helped to reasonably interpret the observed spectra, allowing a comprehensive understanding of optical properties of those components. The propagation loss and the band width in each component could also be estimated from the comparison. The loss is estimated as 1.5 +/- 0.5 dB/mm for the straight-WG, while less than 1 dB/bend, if it exists, for the bend WG, and both band-widths are broader than 40 nm. We also find that the Y-splitter is capable of dividing light into two ports almost equally in intensity with a total transmittance of more than 85%; the band-width is broader than 40 nm. As a result, we have found that all those should be useful as key components in future ultra-fast planar optical integrated circuits.