High-speed and high-power 1.3 mu m InGaAsP/InP selective proton-bombarded buried crescent lasers with optical field attenuation regions

High-speed and high-power InGaAsP/lnP selective proton-bombarded buried crescent (SPB-BC) lasers with optical field attenuation regions were reported. The defect of proton bombardment can not affect the lifetime of the SPB-BC laser because the optical field attenuation region obstructs the growth and propagation of defects. A CW light output over 115 mW was achieved at room temperature using a 500 mu m long cavity SPB-BC laser. The 3 dB bandwidth was 8.5 GHz, and the lifetime was about 8.5 x 10(5) h. The capacitance of four kinds of current blocking structures was first measured in our experiment, and the results shown that the capacitance of proton-bombarded pnpn structure was not only less than that of pnpn current blocking structure, but also less than that of semi-insulating Fe-InP structure.

Gamma-Ray Attenuation Technique For Measuring Void Fraction In Horizontal Gas-Liquid Two-Phase Flow

The measurement of void fraction is of importance to the oil industry and chemical industry. In this article, the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by using a single-energy gamma-ray system is described. The gamma-ray source is the radioactive isotope of Am-241 with gamma-ray energy of 59.5 keV. The time-averaged value of the void fraction in a 50.0-mm i.d. transparent horizontal pipeline is measured under various combinations of the liquid flow and gas flow. It is found that increasing the gas flow rate at a fixed liquid flow rate would increase the void fraction. Test data are compared with the predictions of the correlations and a good agreement is found. The result shows that the designed gamma-ray system can be used for measuring the void fraction in a horizontal gas-liquid two-phase flow with high accuracy.

A Wide Band Strong Acoustic Absorption in a Locally Network Anechoic Coating

Composite materials with interpenetrating network structures usually exhibit unexpected merit due to the cooperative interaction. Locally resonant phononic crystals (LRPC) exhibit excellent sound attenuation performance based on a periodical arrangement of sound wave scatters. Inspired by the interpenetrating network structure and the LRPC concept, we develop a locally network anechoic coating (LNAC) that can achieve a wide band of underwater strong acoustic absorption. The experimental results show that the LNAC possesses an excellent underwater acoustic absorbing capacity in a wide frequency range. Moreover, in order to investigate the impact of the interpenetrating network structure, we fabricate a faultage structure sample and the network is disconnected by hard polyurethane (PU). The experimental comparison between the LNAC and the faultage structure sample shows that the interpenetrating network structure of the LNAC plays an important role in achieving a wide band strong acoustic absorption.

A numerical investigation on the flow physics of koi carp (Cyprinus carpio koi) burst-and-coast swimming

Abstract—Burst-and-coast is the most common locomotion type in freely routine swimming of koi carps (Cyprinus carpio koi), which consists of a burst phase and a coast phase in each cycle and mostly leads to a straight-line trajectory. Combining with the tracking experiment, the flow physics of koi carp’s burst-andcoast swimming is investigated using a novel integrated CFD method solving the body-fluid interaction problem. The dynamical equations of a deforming body are formulated. Following that, the loose-coupled equations of the body dynamics and the fluid dynamics are numerically solved with the integrated method. The two burst modes, MT (Multiple Tail-beat) and HT (Half Tail-beat), which have been reported by the experiments, are investigated by numerical simulations in this paper. The body kinematics is predicted and the flow physics is visualized, which are in good agreement with the corresponding experiments. Furthermore, the optimization on the energy cost and several critical control mechanisms in burst-and-coast swimming of koi carps are explored, by varying the parameters in its selfpropelled swimming. In this paper, energetics is measured by the two mechanical quantities, total output power CP and Froude efficiency Fr. Results and discussion show that from the standpoint of mechanical energy, burst-and-coast swimming does not actually save energy comparing with steady swimming at the same average speed, in that frequently changing of speed leads to decrease of efficiency.

Attenuation of photosynthetically available radiation by chlorophyll, chromophoric dissolved organic matter, and tripton in lake Donghu, China

The attenuation coefficient of photosynthetically available radiation [K-d(PAR)] and three water quality parameters [chlorophyll a (chl a)], chromophoric dissolved organic matter (CDOM) and tripton] were measured at three stations in shallow, subtropical Lake Donghu from April 2003 to March 2004. The multiple regression equation of K-d(PAR) versus chl a, CDOM, and tripton was: K-d(PAR) = 0.44 + 0.019 chl a + 1.88 CDOM + 0.016 tripton, which revealed the relative contributions of the three parameters to K-d(PAR). The effects of water and CDOM on K-d(PAR) were of minor importance (19-26%), while chl a and tripton were the two greatest contributors, accounting collectively for 74-81%.

Optical matching layer structures in evanescent coupling photodiodes at a wavelength of 1.55 mu m: physics, design and simulation

We have studied the optical matching layers (OMLs) and external quantum efficiency in the evanescent coupling photodiodes (ECPDs) integrating a diluted waveguide as a fibre-to-waveguide coupler, by using the semi-vectorial beam propagation method (BPM). The physical basis of OML has been identified, thereby a general designing rule of OML is developed in such a kind of photodiode. In addition, the external quantum efficiency and the polarization sensitivity versus the absorption and coupling length are analysed. With an optical matching layer, the absorption medium with a length of 30 mu m could absorb 90% of the incident light at 1.55 mu m wavelength, thus the total absorption increases more than 7 times over that of the photodiode without any optical matching layer.

Low power-consumption and high response frequency thermo-optic variable optical Attenuators based on silicon-on-insulator materials

A novel silicon-on-insulator thermo-optic variable optical attenuator with isolated grooves based on a multimode interference coupler principle is fabricated by the inductive coupled plasma etching technology. The maximum fibre-to-fibre insertion loss is lower than 2.2 dB, the dynamic attenuation range is from 0 to 30 dB in the wavelength range 1500-1600 nm, and the maximum power consumption is only 140 mW. The response frequency of the fabricated variable optical attenuator is about 30 kHz. Compared to the variable optical attenuator without isolated grooves, the maximum power consumption decreases more than 220 mW, and the response frequency rises are more than 20 kHz.

Silicon-on-insulator based electro-optic variable optical attenuator with a series structure

An electro-optic variable optical attenuator in silicon-on-insulator is designed and fabricated. A series Structure is used to improve the device efficiency Compared to the attenuator in the single p-i-n diode Structure in the same modulating length, the attenuation range of the device in the series structure improves 2-3 times in the same injecting current density, while the insertion loss is not affected. The maximum dynamic attenuation of the device is greater than 30 dB. The response frequency is obtained to be about 2 MHz.

Field emission mechanism from a single-layer ultra-thin semiconductor film cathode

Field emission (FE) from a single-layer ultra-thin semiconductor film cathode (SUSC) on a metal substrate has been investigated theoretically. The self-consistent quantum FE model is developed by synthetically considering the energy band bending and electron scattering. As a typical example, we calculate the FE properties of ultra-thin A1N film with an adjustable film thickness from 1 to 10 nm. The calculated results show that the FE characteristic is evidently modulated by varying the film thickness, and there is an optimum thickness of about 3 nm. Furthermore, a four-step FE mechanism is suggested such that the distinct FE current of a SUSC is rooted in the thickness sensitivity of its quantum structure, and the optimum FE properties of the SUSC should be attributed to the change in the effective potential combined with the attenuation of electron scattering.

Structure tuning of line-defect waveguides based on silicon-on-insulator photonic crystal slabs

We present fabrication and experimental measurement of a series of photonic crystal waveguides. The complete devices consist of an injector taper down from 3 mu m into a triangular-lattice air-hole single-line-defect waveguide with lattice constant from 410nm to 470nm and normalized radius 0.31. We fabricate these devices on a siliconon-insulator substrate and characterize them using a tunable laser source over a wavelength range from 1510nm to 1640nm. A sharp attenuation at photonic crystal waveguide mode edge is observed for most structures. The edge of guided band is shifted about 30nm with the 10nm increase of the lattice constant. We obtain high-efficiency light propagation and broad flat spectrum response of the photonic crystal waveguides.

Optimization of mechanically induced long-period fibre grating transmission spectrum

A new double-layer grating template is designed to reduce the out-of-band loss as much as 1.8dB when the loss of LP03 reaches 10.2 dB. Meanwhile, we propose a method to remove the sidelobes in the transmission spectra by the adjustment of the thickness of pressure plates. The plate-thickness-induced shift of resonant wavelength and the attenuation of loss peak intensity when removing sidelobes can be modified by the fibre distance and contact point on the pressure plates.