Efficient light couplers to topological slow light waveguides in valley photonic crystals.

We numerically and experimentally demonstrate efficient light couplers between topological slow light waveguides in valley photonic crystals (VPhCs) and wire waveguides. By numerical simulations, we obtained a high coupling efficiency of -0.84 dB/coupler on average in the slow light regime of a group index ng = 10 - 30. Experimentally, we fabricated the couplers in a Si slab and measured the transmitted power of the devices. We realized a high coupling efficiency of approximately -1.2 dB/coupler in the slow light region of ng = 10 - 30, which is close to the result from the numerical simulations. These demonstrations will lay the groundwork for low-loss photonic integrated circuits using topological slow light waveguides.

Transcriptional regulation in the early ectodermal lineage of ascidian embryos.

In ascidian embryos, ectodermal tissues derive from blastomeres in the animal hemisphere. The animal hemisphere-specific gene expression is observed as early as the 16-cell stage. Here, we characterized animal hemisphere-specific enhancers of three genes, Ci-ephrin-Ad, Ci-TGFß-NA1 and Ci-Fz4. Deletion analyses identified minimal essential elements. Although these elements contained multiple GATA sequences, electrophoretic mobility shift assays revealed that only some of them were strong binding sites for the transcription factor Ci-GATAa. On the other hand, the motif-searching software MEME identified an octamer, GA (T/G) AAGGG, shared by these enhancers. In Ci-ephrin-Ad and Ci-TGFß-NA1, the octamer was GATAAGGG, which strongly bound Ci-GATAa. The 397-bp upstream region of Ci-ephrin-Ad contained two strong Ci-GATAa-binding sites, one of which was the octamer motif. Mutation in the octamer motif, but not the other Ci-GATAa-binding site, severely affected the enhancer activity. The 204-bp upstream region of Ci-TGFß-NA1 contained four strong Ci-GATAa-binding sites, including the octamer motif. Mutation only in the octamer motif, leaving the other three Ci-GATAa-binding sites intact, abolished the enhancer activity. These results suggest a crucial role for the octamer motif.

Aspergillus oryzae type III polyketide synthase CsyB uses a fatty acyl starter for the biosynthesis of csypyrone B compounds.

Csypyrones B1, B2 and B3 are α-pyrones that can be obtained from Aspergillus oryzae expressing CsyB, which is a type III polyketide synthase. We investigated the biosynthesis of the csypyrone B compounds using [1-(13)C] and [2-(13)C] acetate feeding experiments. (13)C NMR analyses of the methyl esters of the csypyrone B compounds fed with the (13)C-labeled acetates showed that the carboxyl carbons of the csypyrone B side-chains were derived from the C-2 methyl carbon of the acetate. These results indicated that fatty acyl starters are involved in the CsyB reaction and that the csypyrone B compounds are formed by the oxidation of side-chains by the host fungus.

High Q H1 photonic crystal nanocavities with efficient vertical emission.

We report on newly-designed H1-type photonic crystal (PhC) nanocavities that simultaneously exhibit high Q factors, small mode volumes, and high external coupling efficiencies (η([perpendicular])) of light radiated above the PhC membrane. Dipole modes of the H1 PhC nanocavities, which are doubly-degenerate and orthogonally-polarized in theory, are investigated both by numerical calculations and experiments. Through modifying the sizes and positions of the air-holes near to the defect cavity, a Q factor of 62,000 is achieved, accompanied with an improved η([perpendicular]) of 0.38 (assuming an objective lens with a numerical aperture of 0.65). A further increase of η([perpendicular]) to more than 0.60 is observed at the expense of slight degradation of Q factor (down to 50,000). We further experimentally confirm the increase of both Q and η([perpendicular]), using micro-photoluminescence measurements, and demonstrate high Q factors up to 25,000: the highest value ever reported for dipole modes in H1 PhC nanocavities.

Transcriptional regulation of the retinoic acid receptor in the dorsal midline epidermis in the Ciona intestinalis embryo.

Retinoic acid regulates the spatial pattern of gene expression mainly in the epidermis in the protochordate ascidian, Ciona intestinalis. Our previous study characterized the enhancer element responsible for the activation of the retinoic acid receptor (RAR) in the dorsal midline epidermis (DME). In the present study, detailed analysis identified two small sequence elements required for the transcriptional activation in the DME. Deletion of either one of these sequences resulted in suppression of the DME enhancer, suggesting that both sites are necessary. The nucleotide sequences of these two sites were similar to the consensus recognition sequences for the Msx and Sox transcription factors, respectively. These transcription factors are expressed in the DME lineage blastomeres (b7.9 and b7.10 blastomere pairs of bilaterally symmetrical embryos of this species) at the 64-cell stage. Electrophoretic mobility shift assays revealed that recombinant Msxb and SoxB1 proteins specifically bound to these sequences. These results suggest that Msxb and SoxB1 synergistically activate the enhancer in the DME.

Room temperature continuous-wave lasing in photonic crystal nanocavity.

We demonstrate room temperature continuous-wave laser operation at 1.3 mum in a photonic crystal nanocavity with InAs/GaAs self-assembled quantum dots by optical pumping. By analyzing a coupled rate equation and the experimental light-light characteristic plot, we evaluate the spontaneous emission coupling factor of the laser to be ~ 0.22. Three-dimensional carrier confinement and a low transparent carrier density due to volume effect in a quantum dot system play important roles in the cw laser operation at room temperature as well as a high quality factor photonic crystal nanocavity.

Compact 1 x N thermo-optic switches based on silicon photonic wire waveguides.

Using silicon photonic wire waveguides, we constructed compact 1 x 1, 1 x 2, and 1 x 4 Mach-Zehnder interferometer type optical switches on a silicon-on-insulator substrate and demonstrated their switching operations through the thermo-optic effect. These switches were smaller than 140 x 65, 85 x 30, and 190 x 75 mum, respectively. At a 1550-nm wavelength, we obtained an extinction ratio larger than 30 dB, a switching power as low as 90 mW, and a switching response time of less than 100 mus. Furthermore, switching operations were successfully demonstrated for the 1 x 4 switch.