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Zinc oxide flower-like bunches were directly synthesized on indium-doped tin oxide (ITO) glass substrates through a simple chemical bath deposition process. By adjusting precursor concentration, other morphologies (spindles and rods) were also obtained. All of them are hexagonal and single crystalline in nature and grow along the [0001] crystallographic direction. The possible growth mechanisms for these nano-and microcrystals were proposed. It was revealed that both the inherent highly anisotropic structure of ZnO and the precursor concentration play crucial roles in determining final morphologies of the products. In addition, vibrational properties of ZnO crystals with different morphologies were investigated by Raman spectroscopy.

We observed a transition from film to vertically well-aligned nanorods for ZnO grown on sapphire (0001) substrates by metalorganic chemical vapor deposition. A growth mechanism was proposed to explain such a transition. Vertically well-aligned homogeneous nanorods with average diameters of ∼30, 45, 60, and 70nm were grown with the c-axis orientation. Raman scattering showed that the E2 (high) mode shifted to high frequency with the decrease of nanorod diameters, which revealed the dependence of nanorod diameters on the stress state. This dependence suggests a stress-driven diameter-controlled mechanism for ZnO nanorod arrays grown on sapphire (0001) substrates.

We demonstrate a record-high extinction-ratio of 50.4 dB in a 2 × 2 silicon Mach-Zehnder switch equipped with a variable splitter as the front 3-dB splitter. The variable splitter is adjusted to compensate for the splitting-ratio mismatch between the front and rear 3-dB splitters. The high extinction ratio does not rely on waveguide crossings and meets a strong demand in applications to multiport circuit switches. Large fabrication tolerance will make the high extinction ratio compatible with a volume production with standard complementary metal-oxide semiconductor fabrication facilities.

We demonstrate a 32 × 32 path-independent-insertion-loss optical path switch that integrates 1024 thermooptic Mach-Zehnder switches and 961 intersections on a small, 11 × 25 mm2 die. The switch is fabricated on a 300-mm-diameter silicon-on-insulator wafer by a complementary metal-oxide semiconductor-compatible process with advanced ArF immersion lithography. For reliable electrical packaging, the switch chip is flip-chip bonded to a ceramic interposer that arranges the electrodes in a 0.5-mm pitch land grid array. The on-chip loss is measured to be 15.8 ± 1.0 dB, and successful switching is demonstrated for digital-coherent 43-Gb/s QPSK signals. The total crosstalk of the switch is estimated to be less than -20 dB at the center wavelength of 1545 nm. The bandwidth narrowing caused by dimensional errors that arise during fabrication is discussed.

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