Shuanghong Wu

Nonmechanical Infrared Beam Steering Using Blue Addressed Quantum Dot Doped Liquid Crystal Grating

We present a scheme of nonmechanical laser beam steering using ZnS/InP quantum dots doping nematic liquid crystal as the optical recording film. Because of its internal electric field generated by blue laser-induced charge carrier distribution, liquid crystal molecules are reoriented to form a phase grating which make the incident angle steer to the angle as we desire. Being a nonmechanical programmable laser beam steering, the anisotropy of the relative permittivity tensor and blue laser-induced electric carriers play a significant effect in determining the reorientable liquid crystal molecule and reconfigurable phase modulation of the gratings, that determines the steering angle and steering efficiency.

Agile Laser Beam Deflection With High Steering Precision and Angular Resolution Using Liquid Crystal Optical Phased Array

To improve the steering precision and angular resolution of liquid crystal optical phased array, in this paper, we proposed a modified periodic phase controlled method to realize a continuous scanning with a constant angular resolution of less than 20 μrad, meanwhile, its precision is less than 5 μrad (RMS). Also, another method we proposed is called sub-aperture coherence can realize even better angular resolution less than 5 μrad which is the limitation of our measurement instrument.

Theoretical model and experimental verification on the PID tracking method using liquid crystal optical phased array

Liquid crystal optical phased array (LC-OPA) has been considered with great potential on the non-mechanical laser deflector because it is fabricated using photolithographic patterning technology which has been well advanced by the electronics and display industry. As a vital application of LC-OPA, free space laser communication has demonstrated its merits on communication bandwidth. Before data communication, ATP (acquisition, tracking and pointing) process costs relatively long time to result in a bottle-neck of free space laser communication. Meanwhile, dynamic real time accurate tracking is sensitive to keep a stable communication link. The electro-optic medium liquid crystal with low driving voltage can be used as the laser beam deflector. This paper presents a fast-track method using liquid crystal optical phased array as the beam deflector, CCD as a beacon light detector. PID (Proportion Integration Differentiation) loop algorithm is introduced as the controlling algorithm to generate the corresponding steering angle. To achieve the goal of fast and accurate tracking, theoretical analysis and experimental verification are demonstrated that PID closed-loop system can suppress the attitude random vibration. Meanwhile, theoretical analysis shows that tracking accuracy can be less than 6.5μrad, with a relative agreement with experimental results which is obtained after 10 adjustments that the tracking accuracy is less than12.6μrad.

Nanoporous Palladium Films Based Resistive Hydrogen Sensors

Hydrogen sensing technology is significant in many circumstances, such as in the synthesis process of ammonia and methanol, leak detection during shuttle launches and fuel cells. Palladium (Pd) has been widely used in hydrogen sensors for its noteworthy ability to absorb a large quantity of H2 and its high selective response to H2. Pd based resistive H2 sensors have attracted much attention due to their simple device structure and fabrication process. In this chapter, nanoporous Pd films have been demonstrated for hydrogen sensors using anodic aluminum oxide (AAO) template as substrate. Nanoporous Pd films based on AAOs were found to have a quick and reversible response due to their enhanced absorption and desorption of hydrogen compared with dense Pd films that usually have very slow response. The performance of hydrogen sensors depending on different post-deposition annealing temperatures of Pd films has been investigated. A response time as short as 30 s at 1% hydrogen concentration with an anneal temperature of 200°C has been obtained. Then, the sensing performance of hydrogen sensors based on nanoporous Pd supported by AAOs was enhanced by pore-widening treatment of AAO using phosphoric acid (H3PO4) as etching solution. It is demonstrated that different concentrations of H3PO4 and different pore-widening time lead to different pore-diameters of AAO, resulting in different performance of hydrogen sensors. The optimized hydrogen sensor shows a fast response time of 19 s at hydrogen concentration of 1% and a detection range of H2 concentration from 0.1% to 2% by pore-widening treatment with a time of 30 min and 5% H3PO4 concentration. A novel carbon nanotubes and Pd nanocomposite thin films was introduced for hydrogen sensors, which exhibits very fast response speed with a response time of 8 s at 2% hydrogen gas.

Controllable preparation of TiO2 nanotube arrays on Ti foil substrates

ABSTRACT TiO2 nanotubes were prepared by anodic oxidation method using HF electrolyte solution and NH4F electrolyte solution on the titanium foil substrate. The morphology and crystal structures of the nanotube arrays were characterized. The structures of TiO2 nanotube arrays prepared by HF acid aqueous solution are not clear and regular. However, TiO2 nanotube arrays prepared by NH4F / organic ethylene glycol electrolyte are more orderly and clear. By controlling the composition of the electrolyte, anodic oxidation voltage and anodization time parameters, TiO2 nanotube arrays with a highly ordered and controllable process were obtained on the Ti foil substrate.

A novel composite hydrogen sensor based on Pd nanoclusters/TiO2 nanotube arrays

A novel composite hydrogen sensor, consisting of Pd nanoclusters/TiO2 nanotube arrays, was fabricated and evaluated at room temperature. The Pd nanoclusters layer was deposited on top surface of the nanotube arrays by using a direct current (DC) magnetron sputtering method. Resistive response of the composite sensors to 0.5% hydrogen was measured. Experimental results indicated that the Pd nanoclusters can quickly and continually form or break multiple passages by absorbing or desorbing hydrogen, so that the composite hydrogen sensors have promising hydrogen sensitivity at room temperature.

Agile laser beam deflection with high steering precision and angular resolution using liquid crystal optical phased array

To improve the steering precision and angular resolution of liquid-crystal optical phased array, in this paper, we proposed a modified periodic phase controlled method to realize a continuous scanning with a constant angular resolution of less than 20 <italic>μ</italic>rad, meanwhile, its precision is less than 5 <italic>μ</italic>rad (rms). Also, another method we proposed is called subaperture coherence that can realize even better angular resolution less than 5 <italic>μ</italic>rad, which is the limitation of our measurement instrument.

Pore-widening treatment-enhanced hydrogen sensing with nanoporous palladium films

The response of hydrogen sensor based on nanoporous palladium (Pd) supported by robust anodic aluminum oxide (AAO) substrate was enhanced by pore-widening treatment using phosphoric acid (H₃PO₄) as etching solution. It is demonstrated that different concentration of H₃PO₄ and different pore-widening time lead to different pore-diameters of AAO resulting in different performance of hydrogen sensor. The optimized hydrogen sensor shows a fast response time of 19s at H₂ concentration of 1% and a wide detection range of H₂ concentration from 0.1% to 2% by pore-widening treatment with a time of 30 minute in 5%H₃PO₄ concentration.

Characterization of NiCrO x thin films deposited by reactive sputtering at different O 2 flow rate

NiCrOx thin films were prepared by DC reactive magnetron sputtering from a NiCr metal target in Ar+O2 with the different O2 gas flow varied from 0 to 6 seem. The influence of the O2 flow rate on the deposition rate, film composition and optical properties were investigated. EDX detected a decrease in the Cr concentration with the increasing of oxygen flow rate due to the preferential oxidation of Cr to Cr2O3. The deposition rate decreases dramatically at oxygen flow of 2.6 seem, corresponding to the transition point from metal mode to compound mode on the target. Furthermore, an original numerical model, based on the standard Berg model was used to calculate the composition evaluation and deposition rate of NiCrOx films. Results show a reasonable agreement between numerical and experimental data.

Theoretical and Experimental Demonstration on Grating Lobes of Liquid Crystal Optical Phased Array

High deflection efficiency is one of the urgent requirements for practical liquid crystal optical phased array (LC-OPA). In this paper, we demonstrate that high order grating lobes induced from fringe effect are the most important issue to reduce occupation of main lobe. A novel theoretical model is developed to analyze the feature of grating lobes when the device of LC-OPA is working on the scheme of variable period grating (VPG) or variable blazing grating (VBG). Subsequently, our experiments present the relevant results showing a good agreement with the theoretical analysis.