Advances in photonics and applications: Proceedings international workshop on photonics and application. Hanoi, 2004

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1550nm InGaAsP/InP semiconductor optical amplifier (SOA): the first study on module preparation and characterization: Semiconductor Optical Amplifier (SOA) modules based on 1550nm InGaAsP/lnP angledfacet SOA chips have been prepared and characterized. SOA amplified spontaneous emission (ASE) output power - current curves, ASE spectra and fiber - to - fiber gain curves were measured using DBR Er-dopped fiber laser as input signal source. The SOA modules have ASE bandwidths from 1530nm to 1560nm and gain coefficients of more than IOdB. Signal gain saturation was observed at SOA output power of about 7 dBm.
A compact distributed feedback solid-state dye laser for generating nearly transform-limited tunable picosecond laser pulses: An original picosecond distributed-feedback (DF) solid-state dye laser is successfully developed, its laser characteristics are presented using the excitation at 532 nm from a Q-switched Nd:YAG laser. As a result of the use of quenching-DF cavity and right-angle prisms in the pumping geometry, generation of single picosecond laser pulses and wavelength tunability are improved. Using some Pyrromethene dyes doped into Polymer or Ormosil matrices as a laser medium, nearly transform-limited picosecond laser pulses were generated and the laser wavelength was continuously tunable from 540 to 636 nm.
A hybrid algorithm to reduce the computation time of genetic algorithm for designing binary phase holograms: In order to reduce the computation time, a new approach for designing computer-generated holograms is proposed. In this new method, the authors utilized artificial neural network to initiate the genetic algorithm so that the high computation cost of genetic algorithm for synthesizing holograms is significantly reduced while the high diffraction efficiency and uniformity are still ensured. In the results, the holograms with the diffraction efficiency of 76% and uniformity of 5.8% are obtained within 200 seconds, which is 66.7% less than the GA method. Having such the properties, this method is well suited in the design of computer generated holograms and diffractive optical elements, which is computationally expensive.
A polarization-selective module for dense magneto-optical pick-up heads: A polarization-selective holographic optical element with compact dimensions of 2.4mm x 1mm x 1mm (width x length x thickness) is proposed. The element includes three modules: a holographic polarizing beam-splitter, a holographic input coupler, and a dove-prism coupler so that a simple and dense optical pick-up head can be achieved. Polarization properties of holographic volume gratings are briefly discussed. Based on the understanding, the fabrication of the element is implemented and described. The element's performance in magneto-optical pick-up heads is demonstrated by use of a differential detector.
Application of Kalman filter in tracking moving targets in a sample video sequence: A tracking moving objects in a sample video sequence software is reported. Authors describe the block diagram of the program, tracking problems and solutions, among them the automatic image filtering and automatic target association and separation are described.
Application of a low repetition rate passively mode-locked diode-pumped ND:YVO4 laser to fluorescence lifetime imaging: Many applications in biology such as fluorescence lifetime imaging measurements (FLIM) require pulsed laser sources emitting visible or ultraviolet radiations. The maximum measurable lifetime strongly depends on the repetition rate of the illuminating system, and a laser source with a repetition rate around 5 MHz or less and a pulse duration of some picoseconds is strongly needed to measure a large range of fluorescence lifetimes from one to tens of nanoseconds. The authors built an ultra-long laser cavity (the cavity length is tunable from 10 to more than 100 m) operating in a passively mode-mocked regime to obtain 16-picosecond long laser pulses with very low repetition rate (from 1 to 15 MHz). After very simple nonlinear conversion stages, the diode-pumped Nd:YVO4 laser oscillator could provide visible (532 nm) or ultraviolet (355 nm) radiation. These two excitation wavelengths allow us to cover a wide range of intrinsic fluorophores and commonly used fluorescent probes.
Applications of low power, infrared semiconductor laser into acupuncture-quantitative approach: This article discusses the electromagnetic basis of needle acupuncture, and also introduces a hypothesis explaining the phenomenon 'Dac khi' in traditional acupuncture. The proof of the equivalence between the traditional acupuncture and optoacupuncture was made by comparing the magnitude of electric and magnetic field at an acupunctures point in the tissue in case of its needling and irradiating. Applying method Monte Carlo, we developed a program called MCSKIN, simulating the propagation of photons of different wavelengths in tissues of different melanosomes concentrations.
Bistability in erbium doped fiber ring laser: An experiment on dynamical response of an Erbium-doped ring fiber laser (EDFL) and its results are reported. Modulating the pump laser at different modulation frequencies was observed the change in the behaviors of the lasers including an optical bistability, a simple bifurcation as well as chaotic behaviors. This dynamical behaviors of the laser depends on modulation index as well.
Characterization of Alq3-based oleds using two charge transport layers: To prepare OLEDs, tris(8-hydroxyquinolinato) aluminum (Alq3) was used as an emissive material, which emits in the green with a broad emission peaking at 530 nm. PVK played a role of a hole-transport material. An onset voltage (V ons) was obtained as low as 6.8 V for these devices, and no reverse current was observed. The enhancement in both the onset electric field (onset voltage) and the reverse current was explained due to lowering the workfunction of Al/Alq3 by the application of the super-thin LiF layer. This enable electrons better inject into the emissive Alq3 material, consequently one can have higher possibility of emissive recombination of excitons in the devices.
Copper vapor laser for biological applications: The paper describes studying of copper-vapor-laser development for applications. On the basic design of the single oscillator and the plan-plan resonator, copper vapor laser with an average output power of 8W and an efficiency of energy transfer about 1% at 8 - 10KHz repetition rate have been developed. It's being evaluated as excellent light source for Biological applications.
Development of a sensitive autocorrelator in the ultraviolet and near-infrared regions: The authors proposed herein a new method for the generntion of an ultrashort optical pulse using stimulated Raman scattering and four-wave Raman mixing. This awroach has a potential for generntion of an ultrashort optical pulse at an extremely-high repetition rate, i.e., 17 TIIz. However, it is difficult to measure the laser pulsewidth using a SHG autocorrelator, because of a low peak power of the Raman laser. Then, a sensitive autocorrelators is desirable for the measurement of the laser pulsewidth in a wide spectral region. Recently, a sensitive autocorrelator based on two-photon absorption of a photomultiplier (PMT) photocathode is reported. In the present study, a lower limit of the power density that can be measured by a PMT was studied based on the Z-scan method. It was ascertained that the power density as low as 3 kW/cm2 could be measured using IP28 PMT. The paper constructed an autocorrelator using this PMT for the measurement of the laser pulsewidth in the near-inftared region.
Development of future all-solid-state, ultraviolet, terawatt laser system using Ce:LiCAF as a gain medium: The authors have successfully demonstrated the generation of 15-uJ, 25-fs pulses at 290 nm and a coaxially pumped large-aperture Ce:LiCAF power-amplifier module to have 98-mJ output with 25% extraction efficiency. These performances of the seed pulse and the gain module are adequate for TW-class UV CPA laser systems. Such solid-state laser development will open up a new category of high-power lasers for real world applications as an alternative to Ti:sapphire CPA laser systems.
Development of nonlinear optical crystals for UV light generation in Osaka University: The article recently developed some new NLO borate crystals CsLiB6O10, GdxY1-xCa4O(BO3), CsB3O5, K2Al2B2O7, and BaAlBO3F2. CLBO is suitable for deep-UV light generation such as the fourth- and fifth-harmonic generation of aNd: YAG laser. 40- W 266-nm output could be demonstrated by using highquality crystals. Sum-frequency mixing in CLBO also enables to generate deep-UV light below 200 nm. GdYCOB realizes the noncritically phase-matched (NCPM) third-harmonic generation (THG) of a Nd:YAG laser at room temperature owing to the controllability of birefringence. CBO is suitable for high-efficiency THG of a Nd:YAG laser. An average THG power of 3.0 W was achieved using a type-II crystal, which corresponds to a conversion efficiency of 30% from the fundamental light to the third harmonic. KAB can generate 200-m W average power UV pulses at 193 nm. No degradation in the output power was observed for 50-hours continuous and more than 6-months routine operations.
Dot and ring patterns from sum frequency generation in ZnSe crystals: When using high peak power tunable femtosecond laser pulses to study the nonlinear optical properties of polycrystalline ZnSe, the authors have found sum frequency generation (SFG) dot patterns which superficially look like the Laue patterns in X-ray diffraction. They reported recently this interesting phenomenon. Further experiments were carried out to study the nature of these dot patterns. During a study of SF dot patterns in polycrystalline ZnSe samples the authors have additionally observed SFG in the form of ring patterns when changing the orientation of the sample. The paper studied SF ring patterns and SF dot pattern in the same time to understand the nature of these phenomena. Studies of second harmonic generation (SHG) dot patterns on several polycrystalline ZnSe samples showed a characteristic SH dot pattern for each sample.
Effect of size distribution in quantum dot infrared photodetectors: The article reported on effects of the size and the energy state distribution on the electrical and optical properties in self assembled InAs quantum dots. The results of characteristics measured by atomic force microscopy, photoluminescence, and dark current are analyzed by a simulation assuming a Gaussian distribution in size and related energies. The samples investigated in this study are InAs/GaAs quantum dot infrared photodet:ector structures with AIGaAs blocking layer grown by molecular beam epitaxy at different growth modes.
Effects of yttrium and ytterbium codoping on photoluminescence of erbium-doped Si02-Al203 sol-gel glass: Erbium ions (Er3+) have several important properties that make it an excellent choice for an optical amplifier. Er3+ has quantum levels that allow them to be stimulated to emit in the 1500 nm to 1600 nm widthband, which has the least power loss in most silica-based fiber. The future of optic amplifiers lies in the mediums used, as well as new methods of amplification. As additional bandwidth becomes necessary, the mediums used will switch to other elements that emit light at different bandwidths. In order to broaden the bandwidth, to flatten the gain and to increase the power, we performed the study on the properties of Er3+ ions in the novel glass mediums based in Al2O3 - SiO2 glass host doped with Y2O3 and Yb2O3.
Erbium-activated silica titania and silica-zirconia planar waveguides: Erbium-activated silica titania and silica-zirconia planar waveguides were prepared by sol- gel technique (spin on glass and dip coating). The refractive indices, the thickness of the thin films Si02- Ti02. The refractive index and the roughness of these thin film to be dependent on the thickness. The influence of the thermal annealing will be discussed. Emission of the 4 I 13/2 - 4 I 15/2 were recorded under excitation of 514 nm, 830 nm and 980 nm laser. The concentration dependent and the influence of aluminum to Silica(92)Titania(09) and Silica (83)-Zirconia (17) materials were studied . The optical and morphology properties were investigated by DTA, X ray diffraction, microraman and luminescent spectra in the third optical window of telecomm.
Fabrication and characterization of the tunable DFB fiber laser with the single wavelength and single polarization mode for optical communications: In this paper, the author reported on fabrication and characterization of the tunable DFB fiber laser with single wavelength of 1551 nm, linewidth of 30KHz, and single polarization mode. During the fabrication, experimentally demonstrated the statement on the optimal location of the phase-shift that was simulated in software by Vibeke C. Lauridsen. Finally, the testing has been carrying out on the stability of the single polarization mode of the laser while tuning the lasing wavelength by a thermal treatment method.
Fluorescence lifetime imaging of biological system under multifocal two photon excitation: Two photon microscopy is a powerful tool for biomedical applications. By using home made microscope, the authors performed intensity and lifetime measurement by timecorrelated single photon counting system. Several applications benefits of this original instrumentation: reactivity of new anti-HIV drug in cells, diagnostic of urothelial cells to 4etect diseases or cancer at an early stage However classic two photon microscopy presents the drawback of being a laser-scanning technique leading to long time acquisition for 3D images or lifetime images. The most suitable way to increase imaging speed of biological system is to illuminate several points of the sample simultaneously. The principle of 'multifocal multiphoton microscopy (MMM) has been demonstrated by several groups. To generate multiple beam, the authors has been used an original beamsplitter where the created beams have a good uniformity, a high transmission coefficient (~90 %) and it prevents from any crosstalks between the excitation beams.
Generation of 500 fs dye laser pulses by using molecular photonic processes: The paper presented the physical processes and the characteristics of a subpicosecond dye laser which is designed and operated basing on the combination use of three photonic processes of dye molecules: 1) Fast spectro-temporal evolutions in the broadband laser emissions; 2) Generation of a chain of spikes from low-Q micro-cavity laser; and 3) nonlinear resonant interaction between short laser pulses and saturable dye media. Such a laser system provides a stable generation of single 500 fs pulses with peak power of more than 250 MW at 610 nm. The whole sub-ps laser system is pumped by a single nanosecond laser (Q-switched Nd:YAG laser). The spectral and time processes involved in these pulse-shortening methods are analyzed with a rate-equation model.
Generation of ultrashort optical pulse by four-wave raman mixing: The author suggested automatic phase locking in the process of four-wave Raman mixing. This expectation is supported by the experimental result; the wave vectors of the fundamental, Stokes, and anti-Stokes beams are phase-matched in four-wave Raman mixing. For 0-hydrogen, the frequency separation is 587cm-1, which suggests the generation of a train of pulses separated by 57 fs.. The pulsewidth was reduced further in our recent works. This approach may open a new frontier in laser physics, since this method allows, in theory, the generation of an ultimately-short optical pulse at any wavelength without loss of energy by simply passing the beam through molecular hydrogen.
Holographic applications based on photopolymer materialsNam Kim: Photopolymer materials are widely used in many holographic applications because of their advantages. This paper reviews the various holographic applications which either require the high index modulation including optical demultiplexer, colordisplay filter, and polarization-selective element, or need the stability and long life such as holographic memory and security card system.
Homogeneous and Inhomogeneous Line Broadening in EDFA: This paper is addressed to determination of the spectroscopic key parameters which are relevant to explain broadening and flatness of gain profile of Erbium Doped Fiber Amplifier (EDFA) versus glass composition. Absorption and fluorescence of bulk glass material give a classical identification of erbium energy levels in the near infrared at 1,54um. Low temperature measurements allow to assign Stark splittings of both the ground and the excited states. Using site selective spectroscopy, homogeneous and inhomogeneous linewidths are determined by resonant and non resonant fluorescence line narrowing measurements (FLN and RFLN respectively). Knowing these parameters, it is shown a reconstruction of the spectral fluorescence profiles as a function of temperature within the 30-150K range. A comparison of all these three parameters determined for several glass compositions gives a good agreement with gain characteristics. Finally room temperature homogeneous halfheight linewidth is extrapolated from the low temperature data in agreement with Gain Spectral Hole Burning determination (GSHB).
Improvement of optical performance in InGaAsP/InGaAs MQW-LD with asymmetric separate confinement hetero-structure: The paper fabricated both symmetric and asymmetric InGaAsP/lnGaAs 1.55 um MQW-LD's with highly p-doped layers in the two-step SCH. The asymmetric structure has additional 100 nm InGaAsP layer in n-type SCH region. The symmetric and asymmetric SCH LD's show threshold current densities of 1.3 kA/cm2 and 0.7 kA/cm2, and differential slope efficiencies of 0.11 W/A and 0.10 W/A. respectively. Internal loss of the asymmetric structure was measured to be 12.7 cm-1, whereas that of symmetric structure was 20 cm-1. The reduction of internal loss in asymmetric structure indicates that the portion of the optical mode in the highly doped region is effectively reduced (calculation showed reduction from 47% to 40%). The internal quantum efficiency and the characteristic temperature also improved in asymmetric structure.
Influence of the nonlinear absorption in colliding pulse mode (CPM) dye ring lasers: The influence of the nonlinear absorption on the pulse-formation in a saturable absorber is analyzed. The relative pulse duration and pulse intensity are considered for various absorber thickness. The mechanism of ultrashort pulse formation in the passive mode locking is presented.
Infrared four-wave mixing experiments: powerful tools to study vibrational relaxation: The investigation of vibrational dynamics for molecules trapped in the condensed phase gives direct information on dynamic processes in the electronic ground state and on the effect of environment on these processes. The authors focused on model systems: W(CO)6 trapped in porous material (Xerogel) and diatomic molecule H(D)Cl embedded in van der Waals solids, at low temperature. Vibrational characteristic times Tl and T2 are obtained from one colour pump-probe experiment and time-resolved DFWM experiments respectively. These experiments were performed with the Free Electron Laser of Orsay (CLIO) or with an OPO laser.
Intramolecular interactions in gas phase peptides: Gas phase studies, with supersonic expansion condition, enable to obtain the intrinsic properties of molecules of biological interest. The strategy is to gather knowledge upon smaller parts of complex biomolecular systems in order to understand some of the intramolecular interactions at play in these systems. The study of these systems presents two majors difficulties: very low vapor pressure associated with thennal fragility and structural complexity arising from the numerous confonners allowed by the inherent flexibility of the peptide chain. These difficulties were overcome by respectively developing a laser desorption method and by using pump-probe UV-UV and UV-IR depopulation spectroscopy.
Investigating dispersion phenomenon in the one clad and the triple-clad opticlal fibre: Analyzing the effect of structure parameter on dispersion phenomenon in the optical fiber, the authors find out a set of data for structure parameters in which they have obtained the lowest dispersion at an operating wavelength or a wavelength range and show steps used to design the triple-clad optical fibre.
Investigation and manufacturing photonic active devices for communications and sensors in Vietnam: The article showed some new results of R&D on the photonic active devices such as High-concentration Er-doped fiber amplifiers and micro-cavity lasers, which have been developed for communication and sensors in Institute of Materials Science. The Er-doped silica single-mode fiber (EDF) with Er-concentration of 2500-3000 ppm and co-dopants of Al, Yb had been used as optical amplification medium of EDFA in comparison with normal 800 ppm-Er-doped fiber. The photonic active devices can be used such as booster, on-line and pre-amplifier in fiberoptic communication network and in optical sensing technique.
Laser induced shockwave plasma, its mechanism and applications for elemental analysis: Pulse laser plasma induced in ambient gas of low pressure (around 1 Torr) features a relatively large secondary plasma emitting sharp atomic lines with extremely low continuum background. It has been demonstrated experimentally that shockwave generated in the surrounding gas is responsible for the formation of this secondary plasma and the excitation of the ablated atoms in the plasma. The resulted new technique of laser-induced shockwave plasma spectroscopy (LISPS) has proved particularly favorable for practical and highly sensitive spectrochemical analysis on a wide variety of samples in different application environments.