Preparation of Nano Y_2O_2S∶Eu Phosphor by Ethanol Assisted Combustion Synthesis Method

Y2O2S：Eu nano crystallines were prepared by a new ethanol assisted combustion synthesis method using sulfurcontained organic fuel in an ethanol-aqueous solution. The as-prepared nanocrystallines were characterized by X-ray diffraction, transmission electron microscope, photoluminescence spectra and X-ray luminescence spectra. It is shown that the assistant fuel ethanol has the effect of decreasing the water needed, simplifying the experiment procedure by dissolving rare earth nitrate and sulfur-contained organic fuel into an even solution, and prompting the formation of rare earth oxysulfide by igniting firstly during heating that leads to combustion decomposition reaction. Y2O2S ： Eu nano crystallines with strong photoluminescence and X-ray luminescence are obtained using thioacetamide as organic fuel. Mixtures of Y2O3 ： Eu and Y2O2S ： Eu are acquired using thiourea as fuel, and the content of Y2O2S ： Eu increases until reaches to about half of the Y2O3 ： Eu with the increasing amount of thiourea. Y2O2SO4 ： Eu emerges when S/Y = 6 and increases with increasing thiourea amount.

S-band gain flattened distributed fiber Raman amplifier with chirped fiber bragg grating filter

S-band gain flattened distributed fiber Raman amplifier with a bandwidth from 1 488 nm to 1 541 nm （53 nm in width） ,an averaged gain of 10 dB and a gain ripple of ±0.6 dB is obtained successfully, in which a single-wavelength high power fiber Raman laser with wavelength of 1 427.2 nm is used as the pump and the chirped fiber Bragg grating is used as the gain flattening filter. Besides,filter wavelength division multiplexer（FWDM） is used as the multi-signal multiplexer and 1 427 nm/1 505 nm coarse wavelength division multiplexer（OWDM） is used as the pump-signal coupler. The gain media are G652 fiber of 50 km in length and dispersion compensation fiber（DOF） of 5 km in length. Moreover, the location arrangements of different type of fibers and the effect caused by gain flattening filter as well as their solutions are discussed in detail. It is very significant to extend the range of optical fiber communication band and increase the capacity of fiber communication especially for ultra-long haul and ultra-high capacity communication system.

Optical microwave generation using two parallel DFB lasers integrated with Y-branch waveguide coupler

A new device of two parallel distributed feedback （DFB） lasers integrated monolithically with Y-branch waveguide coupler was fabricated by means of quantum well intermixing. Optical microwave signal was generated in the Y-branch waveguide coupler through frequency beating of the two laser modes coming from two DFB laser in parallel, which had a small difference in frequency. Continuous rapid tuning of optical microwave signal from 13 to 42 GHz were realized by adjusting independently the driving currents injected into the two DFB lasers.

Effect of Annealing on Optical Properties of InAs Quantum Dots Grown by MOCVD on GaAs （100） Vicinal Substrates

Thermal annealing effect on lnAs quantum dots grown on vicinal （100） GaAs substrates is studied in comparison with dots on exact （100） GaAs substrates. We find that annealing acts stronger effect on dots with vicinal substrates by greatly accelerating the degradation of material quality, as well as slightly increasing the blueshift of the emission wavelength and the narrowing of PL linewidth. It is attributed to the higher strain in the dots formed on the vicinal substrates.

The long range distributed fiber raman photon temperature sensor

A 31 km long range distributed optical fiber Raman photon temperature sensor (DOFRPTS) system have been developed based on temperature effect of the amplified spontaneous Raman scattering in fiber, and using fiber laser as a pumped source. The results show that temperature measuring uncertainty is ±2 °C, temperature resolution is 0.1 °C, measurement time is 432 s, spatial resolution is less than 4 m.

Optimization design of an electroabsorption modulator integrated with spot-size converter

A novel 1.55 μm spot-size converter integrated with electroabsorption modulator is designed and fabricated with conventional photolithography and chemical wet etching process.For the modulator,we employed a deeply-etched ridge waveguide structure with polyimide on each side of its walls.For the spot-size converter,we employed a buried double-core structure in which a ridge-based passive waveguide is incorporated.The wide and thin passive waveguide is optically combined with a laterally tapered active waveguide to control the mode size.By simulation,the figure of merit is 4.17(dB/V/(100 μm)) and the beam divergence angles in the horizontal and vertical directions are as small as 11.2°×13.0°,respectively.

Chirped Fiber Bragg Gratings for Optieal Fiber Dispersion Compensation

The use of α-power chirped fiber Bragg gratings for dispersion Cancellation in an optical fiber link is discussed.Numerical and theoretical investigation of recompressing the dispersion-broadened pulse by usingα-power chirped gratings is made,which shows that,the dispersion-broadened Gaussian pulse after l00km standard fiber(with zero dispersion atλ=1.3μm)trnasmission atλ=1.55μm with initial width of T_(FWHM)=33ps(full width at half maximum)can be perfectly recompressed with the peak reflectivity of 82%by using a 30mm longα-power chirped fiber grating with properαvalue and optimal grating parameters.

Dual-Wavelength Distributed Feedback Laser for CWDM Based on Non-Identical Quantum Well

Using non-identical quantum wells as the active material, a new distributed-feedback laser is fabricated with period varied Bragg grating. The full width at half maximum of I 15 nm is observed in the amplified spontaneous emission spectrum of this material, which is flatter and wider than that of the identical quantum wells. Two wavelengths of 1.51 μm and 1.53 μm are realized under different work conditions. The side-mode suppression ratios of both wavelengths reach 40 dB. This device can be used as the light source of coarse wavelength division multiplexer communication systems.

Dependence of bimodal size distribution on temperature and optical properties of InAs quantum dots grown on vicinal GaAs （100） substrates by using MOCVD

Self-assembled lnAs quantum dots （QDs） are grown on vicinal GaAs （100） substrates by using metal-organic chemical vapour deposition （MOCVD）. An abnormal temperature dependence of bimodal size distribution of InAs quantum dots is found. As the temperature increases, the density of the small dots grows larger while the density of the large dots turns smaller, which is contrary to the evolution of QDs on exact GaAs （100） substrates. This trend is explained by taking into account the presence of multiatoinic steps on the substrates. The optical properties of InAs QDs on vicinal GaAs（100） substrates are also studied by photoluminescence （PL） . It is found that dots on a vicinal substrate have a longer emission wavelength, a narrower PL line width and a much larger PL intensity.

Gain flattened distributed fiber raman amplifiers

An S band and a C band distributed fiber Raman amplifiers (DFRAs) with flattened gain and compensated dispersion have been studied and implemented with 1427 nm and 1455 nm mono-wavelength fiber Raman lasers as the pumped sourcesrespectively. The gain of single-wave pumped S band and C band can reach 10 dB and 15 dB respectively. And a 50 nmgain flattened width was successfully obtained by using a chirp fiber Bragg grating (CFBG) gain flattened filter with gainripple of ±0.6 dB. The C band DFRA has been applied to CDMA wireless communication system successfully.

Threshold level and gain of forward stimulated Brillouin scattering in a forward pumped s-band discrete DCF fibers Raman amplifier

Amplification effect of forward stimulated Brillouin scattering (SBS) lines on the forward pumped s-band discrete DCF fiber Raman amplifier (FRA) has been studied.Pump threshold power of the forward first order Stokes SBS (FSB1- ),second order Stokes SBS (FSB2-) and third order SBS (FSB3-) in the forward pumped FRA are 1.5 mW,1.4 mW and 1.7 mW,respectively.The Stokes SBS lines are amplified by FRA and fiber Brillouin amplifier (FBA) at the same time.Gain of amplification is given as G_A=G_R·G_B,where G_R is Raman gain and G_B is Brillouin gain.Saturation gain of FSB1-,FSB2- and FSB3- are about 52 dB,65 dB and 65 dB,respectively.The saturation Raman gain of 10 km DCF forward FRA is about 14 dB,so Brillouin gain of FSB1-,FSB2- and FSB3- are about 38 dB,51 dB and 51 dB,respectively.The forward cascaded SBS lines have been observed.

Growth of GaAs on Si by Using a Thin Si Film as Buffer Layer

We report a novel technique for growing high-quality GaAs on Si substrate.The process involves deposition of a thin amorphous Si film prior to the conventional two-step growth.The GaAs layers grown on Si by this technique using metalorganic chemical vapor deposition exhibit a better surface morphology and higher crystallinity as compared to the samples grown by conventional two-step method.The full width at half maximum(FWHM)of the x-ray(004)rocking curve for 2.2 μm thick GaAs/Si epilayer grown by using this new method is 160 arcsec.The FWHM of the photoluminescence spectrum main peak for this sample is 2.1 meV.These are among the best results reported so far.In addition,the mechanism of this new growth method was studied using high-resolution transmission electron microscopy.

Optical Transitions in Cubic GaN Grown by Metalorganic Chemical Vapor Deposition on GaAs (100) Substrate

Photoluminescence measurements have been performed on cubic GaN films with carrier concentration as low as 3×10^(13) cm^(-3).From the temperature and excitation intensity dependence,the emission lines at 3.268,3.150 and 3.081 eV were assigned to the excitonic,donor-acceptor pair,and free-to-acceptor transitions,respectively.Additionally,we observed two additional emission lines at 2.926 and 2.821 eV,and suggested that they belong to donor-acceptor pair transitions.Furthermore,from the temperature dependence of integral intensities,we confirmed that three donor-acceptor pair transitions(3.150,2.926,and 2.821 eV)are from a common shallow donor to three different acceptors.The excitonic emission at 3.216 eV has a full-width-at-half-maximum value of 41 meV at room temperature,which indicates a good optical quality of our sample.

The development of silicate matrix phosphors with broad excitation band for phosphor-convered white LED

This paper briefly reviews the recent progress in alkaline earth silicate host luminescent materials with broad excitation band for phosphor-convered white LED. Among them, the Sr-rich binary phases (Sr, Ba, Ca, Mg)2SiO4:Eu2+ and (Sr, Ba, Ca, Mg)3SiO5:Eu2+ are excellent phosphors for blue LED chip white LED. They have very broad excitation bands and exhibit strong absorption of blue radiation in the range of 450―480 nm. And they exhibit green and yellow-orange emission under the InGaN blue LED chip radiation, respectively. The luminous efficiency of InGaN-based (Sr, Ba, Ca, Mg)2SiO4:Eu2+ and (Sr, Ba, Ca, Mg)3SiO5:Eu2+ is about 70-80 lm/W, about 95%―105% that of the InGaN-based YAG:Ce, while the correlated color temperature is between 4600―11000 K. Trinary alkaline earth silicate host luminescent materials MO(M=Sr, Ca, Ba)-Mg(Zn)O-SiO2 show strong absorption of deep blue/near-ultraviolet radia- tion in the range of 370―440 nm. They can convert the deep blue/near-ultraviolet radiation into blue, green, and red emissions to generate white light. The realization of high-performance white-light LEDs by this approach presents excellent chromaticity and high color rendering index, and the application disadvantages caused by the mixture of various matrixes can be avoided. Moreover, the application prospects and the trends of research and development of alkaline earth silicate phosphors are also discussed.

Preparation and characterization of monodisperse spherical particles of X-ray nano-phosphors based on Gd_2O_2S:Tb

Monodisperse spherical Gd2O2S:Tb nanoparticles have been prepared using an improved homogeneous precipitation method combined with solid-gas sulfuration technology. The effects of Tb3+-doped concentration on luminescent intensity and color purity of samples were investigated, and the optimal Tb3+-doped concentration was determined. Under the excitation of X-ray, the obtained sample shows excellent luminescent properties, and its luminescent intensity is increased by about 50% under lower sulfuration temperature compared with that of the Gd2O2S:Tb nanoparticles prepared by complex precipitation method.

Up-conversion luminescence of Er^(3+) doped and Er^(3+)/Yb^(3+) co-doped YTaO_4

The synthesis and up-conversion luminescent properties of YTaO4:Er3+ and YTaO4:Er3+/Yb3+ are re- ported for the first time. According to the measurement results of up-conversion spectra, Yb3+ co-doping can remarkably enhance the green (2H11/2/4S3/2→4I15/2) and red (4F9/2→4I15/2) emissions, but de- press the infrared emission (4I9/2→4I15/2). With the increase of the Yb3+ concentration, the intensity of green emission increases, after that, when the Yb3+ concentration increases continuously, the intensity of green emission decreases, while those of the red and infrared emissions increase and decrease alternately. In addition, the up-conversion mechanisms of Er3+ doped and Er3+/Yb3+ co-doped YTaO4 are also discussed. It is found that the transform of up-conversion mechanism from two-step energy transfer to cooperating sensitization takes place when Yb3+ concentration is increased up to 12 mol%. With the further increase of Yb3+ concentration, the energy-back-transfer gradually becomes the dominant up-conversion mechanism, which results in the quenching of the green emission and slight increasing of the red and infrared emissions.

Blue,green,red upconversion luminescence and optical characteristics of rare earth doped rare earth oxide and oxysulfide

The cold isostatic press pretreatment process was adopted to prepare fine rare earth oxysulfide up-conversion phosphors with spherical shape, narrow size distribution and high luminescence efficiency. The upconversion optical characteristics and brightness of the blue (Y2O2SYb,Tm), green (Y2O2S: Yb,Er), red (Y2O3Yb,Er) emitter were also investigated, and a novel method was successfully developed for the brightness measurement of upconversion luminescence (UPL). It is shown that a white color can be obtained by the appropriate mixture of these primary blue, green and red emissions components. The Er3+ ions exhibit different upconversion mechanism in Y2O2S and Y2O3 host materials. The rare earth oxysulfide is an efficient upconversion matrix. The UPL brightness of Y2O2S: Yb,Er is 6.5 times higher than that of Y2O3: Yb,Er, and Y2O2S: Yb,Er shows UPL brightness of 1100 cd/m2 under 5.56 W/cm2 power density using a 980 nm laser diode.

Integration of GaN thin films with silicon substrates by fusion bonding and laser lift-off

GaN thin films grown on sapphire substrates by metalorganic chemical vapor deposition （MOCVD） are successfully bonded and transferred onto Si receptor substrates using fusion bonding and laser lift-off （LLO） technique. GaN/Al2O3 structures are joined to Si substrates by pressure bonding Ti/Au coated GaN surface onto Ti/Au coated Si receptor substrates at the temperature of 400℃. KrF excimer laser with 400-mJ/cm^2 energy density, 248-nm wavelength, and 30-ns pulse width is used to irradiate the wafer through the transparent sapphire substrates and separate GaN films from sapphire. Cross-section scanning electron microscopy （SEM） combined with energy dispersive X-ray spectrometer （EDS） measurements show that Au/Si solid solution is formed during bonding process. Atomic force microscopy （AFM） and photoluminescence （PL） measurements show that the qualities of GaN films on Si substrates degrade little after substrates transfer.

Preparation and upconversion luminescence of monodisperse Y_2O_2S:Yb/ Ho-silica/aminosilane core-shell nanoparticles

Y2O2S:Yb/Ho-silica/aminosilane core-shell nanoparticles were prepared by a solid-gas method in combination with polyvinylpyr-rolidone assisted one-step ammoniating method. The core was a single Y2O2S:Yb/Ho with 80 nm in diameter and the shell was silica/aminosilane with around 5 nm in thickness. The results of sedimentation experiment indicated that the nanoparticles could be well-dispersed in ethanol and water to form stable colloids. Since the coating weakened lattice vibration energies of the Y2O2S:Yb/Ho...

GaInN light-emitting diodes with omni-directional reflector using nanoporous SnO_2 film

Enhancement of light extraction in a GaInN light-emitting diode （LED） employing an omni-directional reflector （ODR） consisting of GaN, SnO2 nanorod and an Ag layer was presented. The ODR comprises a transparent, quarterwave layer of SnO2 nanorod claded by silver and serves as an ohmic contact to p-type GaN. Transparent SnO2 sols were obtained by sol-gel method from SnCl2·2H2O, and SnO2 thin films were prepared by dip-coating technique. The average size of the spherical SnO2 particles obtained is 200 nm. The refractive index of the nanorod SnO2 film layer is 2.01. The GaInN LEDs with GaN/SnO2/Ag ODR show a lower forward voltage. This was attributed to the enhanced reflectivity of the ODR that employs the nanorod SnO2 film layer. Experimental results show that ODR-LEDs have lower optical losses and higher extraction efficiency as compared to conventional LEDs with Ni/Au contacts and conventional LEDs employing a distributed Bragg reflector （DBR）.