A Si-based tunable narrow-band flat-top filter with multiple-step-type Fabry-Perot cavity structure

In the optical network, the quick and accurate alignment with wavelength is an important issue during the channel detection. At this point, a filter having flat-top response characteristic is an effective solution. Based on multiple-step-type Fabry-Perot cavity structure, a novel all-Si-based thermooptical tunable flat-top filter with narrow-band has been fabricated, using our patent silicon-on-reflector bonding technology. The device demonstrated a 1-dB flat-top width of 1 nm, 3-dB band of 3 nm, free spectra range of 8 nm, and the tuning range of 4.6 nm was obtained under the applied voltage of 4 V.

Flat-top arrayed waveguide grating using a tapered multimode interferometer

A 40-channel 0.8-nm-spaced flat-top silica-based arrayed waveguide grating (AWG) with a tapered multimode interferometer (MMI) at the end of its input waveguide has been experimentally demonstrated for the first time. By adding the MMI, the 1-dB and 3-dB bandwidths are increased to 0.45 and 0.62 nm, respectively. The insertion loss (IS) of the device ranges from 3.8 to 6.8 dB. The IS uniformity is better than 3.0 dB. The crosstalk is better than -25 dB. Compared to the AWG with a rectangular MMI, the AWG with a tapered MMI shows better IS, crosstalk, and ripple. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

Temperature dependence of photoluminescence of flat and undulated SiGe/Si multiple quantum wells

Photoluminescence (PL) of strained SiGe/Si multiple quantum wells (MQW) with flat and undulated SiGe well layers was studied at different temperature. With elevated temperature from 10K, the no-phonon (NP) peak of the SiGe layers in the flat sample has firstly a blue shift due to the dominant transition converting from bound excitons (BE) to free excitons (FE), and then has a red shift when the temperature is higher than 30K because of the narrowing of the band gap. In the undulated sample, however, monotonous blue shift was observed as the temperature was elevated from 10 K to 287 K. The thermally activated electrons, confined in Si due to type-II band alignment, leak into the SiGe crest regions, and the leakage is enhanced with the elevated temperature. It results in a blue shift of the SiGe luminescence spectra.

Growth and structural properties of GaN films on flat and vicinal SiC(0001) substrates

Initial stage GaN growth by molecular-beam epitaxy (MBE) on SiC(0001) substrate is followed by in situ scanning tunneling microscopy. Comparison is made between growth on nominally flat and vicinal substrate surfaces and the results reveal characteristic differences between the two. Ex situ transmission electron microscopy (TEM) and X-ray diffraction (XRD) rocking curve measurements of the films show lower density of defects and better structural quality of the vicinal film. We suggest the improved structural quality of the vicinal film is related to the characteristic difference in its initial stage nucleation and coalescence proccsses than that of the flat film.

A Prototype X-ray Framing Camera With Variable Exposure Time Based on Double-Gated Micro-Channel Plates

We present a novel X-ray frame camera with variable exposure time that is based on double-gated micro-channel plates (MCP). Two MCPs are connected so that their channels form a Chevron-MCP structure, and four parallel micro-strip lines (MSLs) are deposited on each surface of the Chevron-MCP. The MSLs on opposing surfaces of the Chevron-MCP are oriented normal to each other and subjected to high voltage. The MSLs on the input and output surfaces are fed high voltage pulses to form a gating action. In forming two-dimensional images, modifying the width of the gating pulse serves to set exposure times (ranging from ps to ms) and modifying the delay between each gating pulse serves to set capture times. This prototype provides a new tool for high-speed X-ray imaging, and this paper presents both simulations and experimental results obtained with the camera.

Principle and analysis of the moving-optical-wedge interferometer

A new type of interferometer, the moving-optical-wedge interferometer, is presented, and its principle and properties are studied. The novel interferometer consists of one beam splitter, two flat fixed mirrors, two fixed compensating plates, one fixed optical wedge, and one moving optical wedge. The optical path difference (OPD) as a function of the displacement of the moving optical wedge from the zero path difference position is accomplished by the straight reciprocating motion of the moving optical wedge. A large physical shift of the moving optical wedge corresponds to a very short OPD value of the new interferometer if the values of the wedge angle and the refractive index of the two optical wedges are given properly. The new interferometer is not so sensitive to the velocity variation of the moving optical wedge and the mechanical disturbances compared with the Michelson interferometer, and it is very applicable to low-spectral-resolution application for any wavenumber region from the far infrared down to the ultraviolet. (C) 2008 Optical Society of America.

Temperature dependence of photoluminescence of flat and undulated SiGe/Si multiple quantum wells

Photoluminescence (PL) of strained SiGe/Si multiple quantum wells (MQW) with flat and undulated SiGe well layers was studied at different temperature. With elevated temperature from 10K, the no-phonon (NP) peak of the SiGe layers in the flat sample has firstly a blue shift due to the dominant transition converting from bound excitons (BE) to free excitons (FE), and then has a red shift when the temperature is higher than 30K because of the narrowing of the band gap. In the undulated sample, however, monotonous blue shift was observed as the temperature was elevated from 10 K to 287 K. The thermally activated electrons, confined in Si due to type-II band alignment, leak into the SiGe crest regions, and the leakage is enhanced with the elevated temperature. It results in a blue shift of the SiGe luminescence spectra.

Growth and structural properties of GaN films on flat and vicinal SiC(0001) substrates

Initial stage GaN growth by molecular-beam epitaxy (MBE) on SiC(0001) substrate is followed by in situ scanning tunneling microscopy. Comparison is made between growth on nominally flat and vicinal substrate surfaces and the results reveal characteristic differences between the two. Ex situ transmission electron microscopy (TEM) and X-ray diffraction (XRD) rocking curve measurements of the films show lower density of defects and better structural quality of the vicinal film. We suggest the improved structural quality of the vicinal film is related to the characteristic difference in its initial stage nucleation and coalescence proccsses than that of the flat film.

Flat Surface Plasmon Polariton Bands in Bragg Grating Waveguide for Slow Light

The formations of the surface plasmonpolariton (SPP) bands in metal/air/metal (MAM) sub-wavelength plasmonic grating waveguide (PGW) are proposed. The band gaps originating from the highly localized resonances inside the grooves can be simply estimated from the round trip phase condition. Due to the overlap of the localized SPPs between the neighboring grooves, a Bloch mode forms in the bandgap and can be engineered to build a very flat dispersion for slow light. A chirped PGW with groove depth varying is also demonstrated to trap light, which is validated by finite-difference time-domain (FDTD) simulations with both continuous and pulse excitations.

Origin of flat-band voltage sharp roll-off in metal gate/high-k/ultrathin- SiO2/Si p-channel metal-oxide-semiconductor stacks

The origin of the flat band voltage roll-off (V-FB roll-off) in metal gate/high-k/ultrathin-SiO2/Si metal-oxide-semiconductor stacks is analyzed and a model describing the role of the dipoles at the SiO2/Si interface on the V-FB sharp roll-off is proposed. The V-FB sharp roll-off appears when the thickness of the SiO2 interlayer diminishes to below the oxygen diffusion depth. The results derived using our model agree well with experimental data and provide insights to the mechanism of the V-FB sharp roll-off.

Crack Patterns in Ceramic Plates after Quenching

The crack patterns generated in a real ceramic plate and in a plate stacked by ceramic slabs under quenching are experimentally studied. The results here reveal that there are some distinct differences between the two crack patterns. The reasons that caused the differences are the size and boundary effects of the slabs. These crack patterns are very useful to understand the failure mechanisms of ceramic materials in thermal shock.