In this paper, based on the theory of dynamic waveguiding effect in nanodisordered KTN crystals, a detailed design and implementation of a super broadband 1x2 high speed waveguide switch is presented. The important waveguide parameters, including the dimension, the refractive index distribution, and the electric field distribution within the waveguide are quantitatively simulated and analyzed. An experimental verification of switching effect based on the design is also conducted, which confirmed the design. The broadband and high speed nature of such kind of switch can play a key role in data center networks and cloud computing, which needs low power consumption and high speed switches.
In this paper, a nanosecond speed KTN beam deflector is presented. The beam deflector is based on the combination of pre-injected space charge field and high speed (nanosecond) switching field. A beam deflection speed on the order of nanosecond was demonstrated, which was fastest beam deflection speed reported so far. The experimentally results confirmed that the speed limitation of KTN beam deflector was not limited by the electro-optic (EO) effect itself but the driving electric source and circuit. With a faster speed driving source and circuit, it is possible to develop GHz frequency beam deflector.
A high open-circuit voltage dye-sensitized solar cell (DSSC), based on a ZnO/TiO2 nanocomposite (NC) photoelectrode, was presented. This NC photoelectrode was composed of density-controlled ZnO-TiO2 core-shell nanorod arrays and dispersed TiO2 nanoparticles. The electrochemical impedance spectroscopy results confirmed that a reduced recombination loss was achieved by applying the proposed composite nanostructure. Thus, a higher open-circuit voltage of up to 0.93 V was achieved.
Dye-sensitized solar cells (DSSCs) via ZnO/TiO<sub>2</sub> nanocomposite photoanode with density-controlled abilities are presented in this paper. This nanocomposite photoanode is composed of TiO2 nanoparticles dispersed into densitycontrolled vertically aligned ZnO-TiO<sub>2</sub> core-shell nanorod arrays. The density-controlled ZnO-TiO<sub>2</sub> core-shell nanorod arrays were synthesized directly onto fluorine-doped tin oxide (FTO) substrates using an innovative two-step wet chemical route. First, the density-controlled ZnO nanorod arrays were formed by applying a ZnO hydrothermal process from a TiO<sub>2</sub> nanocrystals template. Second, the ZnO-TiO<sub>2</sub> core-shell nanorod arrays were formed by depositing a TiO<sub>2</sub> shell layer from a sol-gel process. The major advantages of a density-controlled ZnO/TiO<sub>2</sub> nanocomposite photoanode include (1) providing a better diffusion path from ZnO nanorod arrays and (2) reducing the recombination loss by introducing an energy barrier layer TiO<sub>2</sub> conformal shell coating. To validate the advantages of a density-controlled ZnO/TiO<sub>2</sub> nanocomposite photoanode, DSSCs based on a ZnO/TiO<sub>2</sub> nanocomposite photoanode were fabricated, in which N719 dye was used. The average dimensions of the ZnO nanorod arrays were 20 μm and 650 nm for the length and the diameter, respectively, while the designated spacing between each nanorod was around 5 μm. The performance of the solar cell was tested by using a standard AM 1.5 solar simulator from Newport Corporation. The experimental results confirmed that an open-circuit voltage, 0.93 V, was achieved, which was much higher than the conventional TiO<sub>2</sub> nanoparticles thin film structure for the same thickness. Thus, density-controlled ZnO/TiO<sub>2</sub> nanocomposite photoanodes could improve the performance of DSSCs by offering a better electron diffusion path.
In this paper, tunable spectrum LED based on nanostructured substrate is presented. In particular, the relationship between
the temperature distribution and the nanostructured substrate is quantitatively simulated. The simulation results suggest
that there can be a noticeable change in the temperature profile due to the existence of micro/nanostructured substrate.
Such a change in the temperature distribution can result in a change of indium composition of InGaN/GaN LED, which in
turn tune the output spectrum of LED.
In this paper, the radiation induced air fluorescence is investigated for several different types of radiation sources, including high brightness laser sources, X-ray radiation sources, and alpha radiation sources. First, the air fluorescence spectrum with three spectral bandpass filters induced by the high intensity laser was analyzed from spectrometer detector. Second, the air fluorescence intensity induced by different types of radiation are measured from photomultiplier tube detector and followed by discussion. Finally, the potential application of radiation induced air fluorescence for the radiation detection is addressed.
The method by applying the interfered femtosecond laser to create nanostructured copper (Cu) surface has been studied.
The nanostructure created by direct laser irradiation is also realized for comparison. Results show that more uniform and
finer nanostructures with sphere shape and feature size around 100 nm can be induced by the interfered laser illumination
comparing with the direct laser illumination. This offers an alternative fabrication approach that the feature size and the
shape of the laser induced metallic nanostructures can be highly controlled, which can extremely improve its
performance in related application such as the colorized metal, catalyst, SERS substrate, and etc.
A technique of enhancing terahertz (THz) wave radiation from large aperture photoconductive (PC)
antenna is presented in this paper. In this technique, the PC antenna is excited by both the optical and
previously-generated THz pulses by a laser induced air plasma created in front of PC antenna, an
enhanced THz wave signal is obtained. The technique shown in this paper can be very useful for THz
imaging and spectroscopy.
In this paper, we have reviewed our recent works on IR supercontinuum generation (SCG) and its applications. First, we
provide a brief review on the physical mechanism of the supercontinuum generation and our previous works in this field.
Second, the transmission characteristics of a new type of IR fibers is presented. Furthermore, the SCG generation in
this new type of optical fiber is experimentally demonstrated. Finally, the suggestion for the future effort is discussed.
In this paper, the growth of ZnO/MgZnO composite structures with a larger number of periods by pulsed laser deposition
is presented. The structural and physical properties are quantitatively characterized by field-emission scanning electron
microscopy, transmission electronic microscopy, X-ray diffraction, and photoluminescence. It is demonstrated that the
quantum confinement effect has been observed from the composite structures at room temperature. The applications of
this unique ZnO/MgZnO composite structure are also discussed.
In this paper, we present the design and the fabrication method for high DC bias voltage photoconductive semiconductor
switch (PCSS). By employing a low temperature grown molecular beam epitaxial GaAs (LT-MBE GaAs) and a proper
protection coating to prevent air breakdown, the DC bias electric field can be significantly increased. Such a PCSS
structure can effectively achieve a low DC dark current in a high voltage pulse generation system with smaller PCSS
sizes. DC bias capability also eliminates the need of complicated synchronization. The application of high DC bias field
PCSS will also be discussed.
In this paper, recent works of buried chemical detection system by stimulating and enhancing spectroscopic
signatures with multi-frequency excitations are discussed. In this detection system, those multiple excitations,
including DC electric field, microwave, CO<sub>2</sub> laser illumination and infrared radiation, are utilized and each of
them plays a unique role. The Microwave could effectively increase the buried chemicals' evaporation rate from
the source. The gradient DC electric field, generated by a Van De Graaff generator, not only serves as a vapor
accelerator for efficiently expediting the transportation process of the vapor release from the buried chemicals,
but also acts as a vapor concentrator for increasing the chemical concentrations in the detection area, which
enables the trace level chemical detection. Similarly, CO<sub>2</sub> laser illumination, which behaves as another type
vapor accelerator, could also help to release the vapors adsorbed on the soil surface to the air rapidly. Finally, the
stimulated and enhanced vapors released into the air are detected by the infrared (IR) spectroscopic fingerprints.
Our theoretical and experimental results demonstrate that more than 20-fold increase of detection signal can be
achieved by using those proposed technology.
Zinc oxide (ZnO) nano-wires have draw people's attention in recent studies. The unique structural and physical
properties offer fascinating potential for future technological applications. The state-of-the-art fabrication process of ZnO
nano-wires is based on vapor-liquid-solid (VLS) method. In this paper, the microwave assisted heating technique is
introduced for the growth of ZnO nanopillar arrays. The microwave grown ZnO nanowires were characterized by fieldemission
scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and photoluminescence
spectroscopy. It was demonstrated that (001) oriented single crystal ZnO nanowires can be grown vertically and
uniformly on a-plane sapphire wafers.
In this paper, the application of a broadband spatially coherent IR supercontinuum source to the biomedical imaging and
detection is presented. New IR material is proposed to generate Mid-IR supercontinuum above 4um, which was previously
difficult due to inherent material absorption. Broad Mid-IR supercontinuum is numerically shown to be possible
with one single wavelength pump in appropriate fiber structure.
Mid-IR broadband sources are very useful in IR Optical
Coherence Tomography (OCT) and spectroscopy in biomedical materials, due to the rich absorption structures the
Mid-IR region. Broadband Mid-IR source is better than single wavelength tunable source, such as Quantum Cascaded Lasers
(QCL), for faster analysis speed, since slow scan is not required.
In this paper, the separation of transmitted and diffused light beams in a scattering medium by a magneto-optical ultrafast
switch is investigated. The magneto-optical switch previously developed by the authors is capable of 1 ns switching
speed and has a 1 mm clear aperture. The diffused light beams and ballistic beams in a scattering medium are simulated
in the lab by two beam paths. One beam is delayed from the other to simulate the diffused light beam and the ballistic
beam, respectively. The magneto-optical switch is synchronized with the required delay to the laser pulse to keep only
the ballistic beam, acting as an ultrafast light gate. The concept is demonstrated with a 532nm Q-switched pulsed laser.
In this paper, we have reviewed our recent works on IR supercontinuum generation (SCG) and its applications. First, we
provide a brief introduction on the motivations of the proposed effort. Second, the work of SCG in single crystal
sapphire fibers is reviewed. Third, in addition to single crystal sapphire fibers, the method, the process, and the results
of fabricating other IR waveguides are presented. Fourth, a quantitative simulation on the supercontinuum generation
with the new IR waveguide is provided, which shows that it is possible to generate SCG beyond 5 microns. To the best
knowledge of authors, this is the longest SCG reported so far. Finally, more experimental results of chemical analysis
with supercontinuum source are presented.
An ultrafast light-activated magneto-optical modulator is demonstrated in this paper. This modulator is capable of 1 ns
modulation speed and has a 1 mm clear aperture. The design of the modulator incorporates a photoconductive switch and
enables a synchronized and jitter-free operation, which eliminates the need of any electrical or optical delay lines. These
features make the current design very attractive in typical free-space pulse laser applications. To the authors' knowledge,
this is so far the fastest MO modulator with such aperture size that has been reported.
In this paper, we experimentally verify that previously proposed idea of unequally spaced optical phased array can
greatly reduce grating-lobes. As the verification purpose of our previous numerical design, a laser beam is passed
through unequally-spaced slits, whose spacings are the same as the previous design. Interference patterns formed after
both 4- and 8-channel slits clearly show that the grating-lobes can be greatly minimized. To realize the beam steering
possible, optical waveguides array, which has unequally spaced design at the output ends is fabricated. The phase of
each beam can be varied using fibers array wound around PZT tubes before each beam is coupled into the waveguides
array. Interference patterns formed after the outputs of both 4- and 8-channel waveguides array show that the gratinglobes
can be greatly reduced using unequally spaced optical phased array technique.