Fabrication of semiconductor optical amplifiers and a novel gain measuring technique

The design and fabrication of 1550 nm semiconductor optical amplifiers (SOAs) and the characteristics of the fabricated SOA are reported. A novel gain measurement technique based on the integrations of the product of emission spectrum and a phase function over one mode interval is proposed for Fabry-Perot semiconductor lasers.

High-speed DFB laser and EMLs

High speed reliable 1.55 mum AlGaInAs multi-quantum well ridge waveguide (RW) DFB laser is developed with a 9GHz -3dB bandwidth. A high speed self aligned constricted mesa 1.55 mum DFB laser is achieved with a 9.1GHz -3dB bandwidth and a more than 20mW output power. A cost effective single RW electroabsorption modulated DFB laser (EMLs) is proposed and successfully fabricated by adopting selective area growth techniques:. a penalty free transmission at 2.5Gbps over 280Km normal G.652 single mode fiber is realized by using this EML as light source. For achieving a better performance EMLs. a gain-coupled DFB laser with etched quantum wells is successfully integrated with a electroabsorption modulator (EAM) for a high single mode yield. the wavelength of a EML is tuned in a 3.2nm range by a integrated thin-film heater for the wavelength routing. a buried heterostructure DFB laser is also successfully integrated with a RW EAM for a lower threshold current. lower EAM parasitic capacitance and higher output power.

Impact of wide bandgap p-type nc-Si on the performance of a-Si solar cells

This paper reports the impact of a wide bandgap p-type hydrogenated nanocrystalline silicon (nc-Si:H) on the performances of hydrogenated amorphous silicon (a-Si:H) based solar cells. The player consists of nanometer-sized Si crystallites and has a wide effective bandgap determined mainly by the quantum size-confinement effect (QSE). By incorporation of this p-layer into the devices we have obtained high performances of a-Si:H top solar cells with V-infinity=1.045 V and FF=70.3 %, and much improved mid and bottom a-SiGe:H cells, deposited on stainless steel (SS) substrate. The effects of the band-edge mismatch at the p/i-interface on the I-V characteristics of the solar cells arc discussed on the bases of the density-functional approach and the AMPS model.

Generation of 10 GHz, 1.9 ps optical pulse train using semiconductor optical amplifier and silica-based highly nonlinear fiber

We propose a simple approach to generate a high quality 10 GHz 1.9 ps optical pulse train using a semiconductor optical amplifier and silica-based highly nonlinear fiber. An optical pulse generator based on our proposed scheme is easy to set up with commercially available optical components. A 10 GHz, 1.9 ps optical pulse train is obtained with timing jitter as low as 60 fs over the frequency range 10 Hz-1 MHz. With a wavelength tunable CW laser, a wide wavelength tunable span can be achieved over the entire C band. The proposed optical pulse generator also can operate at different repetition rates from 3 to 10 GHz.

Generation of optimized wavelength-tunable optical pulse from an uncooled gain-switched Fabry-Perot semiconductor laser using optical amplifier as external light injection

We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry-Perot semiconductor laser using an optical amplifier as external light source. The timing jitter of gain-switched laser has been reduced from about 3 ps to 600 fs and the pulse width has been optimized by using our system. The stability of the system was also experimentally investigated. Our results show that an uncooled gain-switched FP laser system can feasibly produce the stable optical pulse trains with pulse width of 18 ps at the repetition frequency of 5 GHz during 7 h continuous working. We respectively proved the system feasibility under 1 GHz, 2.5 GHz and 5 GHz operation. (c) 2008 Elsevier B.V. All rights reserved.

Wide-band underwater acoustic absorption based on locally resonant unit and interpenetrating network structure

The interpenetrating network structure provides an interesting avenue to novel materials. Locally resonant phononic crystal (LRPC) exhibits excellent sound attenuation performance based on the periodical arrangement of sound wave scatters. Combining the LRPC concept and interpenetrating network glassy structure, this paper has developed a new material which can achieve a wide band underwater strong acoustic absorption. Underwater absorption coefficients of different samples were measured by the pulse tube. Measurement results show that the new material possesses excellent underwater acoustic effects in a wide frequency range. Moreover, in order to investigate impacts of locally resonant units, some defects are introduced into the sample. The experimental result and the theoretical calculation both show that locally resonant units being connected to a network structure play an important role in achieving a wide band strong acoustic absorption.

Rapid world wide depletion of predatory fish communities

Serious concerns have been raised about the ecological effects of industrialized fishing1, 2, 3, spurring a United Nations resolution on restoring fisheries and marine ecosystems to healthy levels4. However, a prerequisite for restoration is a general understanding of the composition and abundance of unexploited fish communities, relative to contemporary ones. We constructed trajectories of community biomass and composition of large predatory fishes in four continental shelf and nine oceanic systems, using all available data from the beginning of exploitation. Industrialized fisheries typically reduced community biomass by 80% within 15 years of exploitation. Compensatory increases in fast-growing species were observed, but often reversed within a decade. Using a meta-analytic approach, we estimate that large predatory fish biomass today is only about 10% of pre-industrial levels. We conclude that declines of large predators in coastal regions5 have extended throughout the global ocean, with potentially serious consequences for ecosystems5, 6, 7. Our analysis suggests that management based on recent data alone may be misleading, and provides minimum estimates for unexploited communities, which could serve as the ‘missing baseline’8 needed for future restoration efforts.

Large current gain and low operational voltage permeable metal-base organic transistors based on Au/Al double layer metal base

In order to realize the common-emitter characteristics of the tris(8-hydroxyquinoline) aluminium (Alq(3))-based organic transistors, we used Au/Al double metal layer as the base, thus the vertical metal-base transistors with structure of Al/n-Si/Au/Al/Alq(3)/LiF/Al were constructed. It was found that the contact properties between the base and the organic semiconductors play an important role in the device performance. The utilization of Au/Al double layer metal base allows the devices to operate at high gain in the common-emitter and common-base mode at low operational voltage.

High gain in hybrid transistors with BAlq(3)/Alq(3) isotype heterostructure emitter

We report the fabrication of permeable metal-base transistors based on bis(2-methyl-8-quinolinolato-N1,O8)-(1,1'-biphenyl-4-olato) aluminum (BAlq(3))/tri(8-hydroxyquinoline) aluminum (Alq(3)) isotype heterostructure as emitter layer. In this transistor, n-Si was used as the collector, LiF/Al as the emitter electrode, and Au/Al bilayer metal as the base. We show that the leakage current is greatly reduced in Al/n-Si/Au/Al/BAlq(3)/Alq(3)/LiF/Al devices with respect to Al/n-Si/Au/Al/Alq(3)/LiF/Al devices due to the utilization of BAlq(3)/Alq(3) isotype heterostructure emitter, leading to high common-base and common-emitter current gains at low driving voltages.

Hybrid permeable metal-base transistor with large common-emitter current gain and low operational voltage

We demonstrate the suitability of N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB), an organic semiconductor widely used in organic light-emitting diodes (OLEDs), for high-gain, low operational voltage nanostructured vertical-architecture transistors, which operate as permeable-base transistors. By introducing vanadium oxide (V2O5) between the injecting metal and NPB layer at the transistor emitter, we reduced the emitter operational voltage.

Structural evolution of tensile deformed high-density polyethylene at elevated temperatures: Scanning synchrotron small- and wide-angle X-ray scattering studies

The structural evolution of an ice-quenched high-density polyethylene (HDPE) subjected to uniaxial tensile deformation at elevated temperatures was examined as a function of the imposed strains by means of combined synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. The data show that when stretching an isotropic sample with the spherulitic structure, intralamellar slipping of crystalline blocks was activated at small deformations, followed by a stress-induced fragmentation and recrystallization process yielding lamellar crystallites with their normal parallel to the stretching direction. Stretching of an isothermally crystallized HDPE sample at 120 degrees C exhibited changes of the SAXS diagram with strain similar to that observed for quenched HDPE elongated at room temperature, implying that the thermal stability of the crystal blocks composing the lamellae is only dependent on the crystallization temperature.

Vertical structure permeable-base hybrid transistors based on multilayered metal base for stable electrical characteristics

In this work we present a permeable base transistor consisting of a 60 nm thick N,N'diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine layer or a 40 nm thick 2,6-diphenyl-indenofluorene layer as the emitter, a CalAl/Ca multilayer as the metal base, and p-Si as collector. In the base, the Ca layers are 5 nm thick and the Al layer was varied between 10 and 40 nm. the best results obtained with a 20 nm thick layer. The devices present common-base current gain with both organic layer and silicon acting as emitter, but there is only observable common-emitter current gain when the organic semiconductor acts as emitter. The obtained common-emitter current gain, similar to 2, is independent on collector-emitter voltage, base current and organic emitter in a reasonable wide interval. Air exposure or annealing of the base is necessary to achieve these characteristics, indicating that an oxide layer is beneficial to proper device operation.