Optical waveguide demultiplexer was designed and fabricated by integration of two types of gratings, namely, guided-mode-selective focusing grating couplers (GMS-FGCs) and different-guided-mode-coupling distributed Bragg reflectors (DGM-DBRs) in a slab waveguide for constructing a wavelength-division-multiplexing chip-to-chip optical interconnecting board. In the waveguide demultiplexer, guided signal waves were separated wavelength-selectively by DGM-DBRs, and coupled out by GMS-FGCs to focused free space waves. Two-channel demultiplexing with 5-nm-wavelength spacing was demonstrated at around 850-nm wavelength.
Integration of free-space-wave add-drop multiplexers that consist of focusing grating couplers (FGCs) and distributed Bragg reflectors (DBRs) in thin-film waveguides have been investigated for construction of an intraboard wavelength-division-multiplexing optical interconnection. Compact optics of a Lloyd mirror configuration and a contact-type mask aligner were combined as an interference exposure system for fabrication of DBRs of 300 microm coupling length. DBRs were integrated with FGCs on a thin-film waveguide on a glass substrate for two-channel wavelength-drop demultiplexing from guided waves to free-space waves. Measured outcoupled wavelengths of two free-space waves from two pairs of a FGC and a DBR agreed with the design values of 845 and 849 nm.
The crystal structure of NaV 6 O 11 stays hexagonal at least to 8.06 GPa at room temperature as deduced from x-ray powder and single-crystal diffraction data measured in diamond anvil cells. The material is more compressible along the c axis and the distortion of the hexagonal close packing increases on compression. Its compressibility is given by a Murnaghan equation of state with the zero-pressure bulk modulus B 0 = 177(9) GPa and the unit-cell volume at ambient pressure V 0 = 369.9(4)Å 3 (B = 4.00). The occurrence of the pressure-induced second-order P6 3 /mmc → P6 3 mc phase transition has been discussed on the basis of symmetry-mode analysis of the high-pressure single-crystal data.
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