Non-compressive wideband spectrum sensing with sub-Nyquist sampling rates

In this paper, we propose a low complexity and reliable wideband spectrum sensing technique that operates at sub-Nyquist sampling rates. Unlike the majority of other sub-Nyquist spectrum sensing algorithms that rely on the Compressive Sensing (CS) methodology, the introduced method does not entail solving an optimisation problem. It is characterised by simplicity and low computational complexity without compromising the system performance and yet delivers substantial reductions on the operational sampling rates. The reliability guidelines of the devised non-compressive sensing approach are provided and simulations are presented to illustrate its superior performance. © 2013 IEEE.

Pixel-level tunable liquid crystal lenses for auto-stereoscopic display

Mobile video and gaming are now widely used, and delivery of a glass-free 3D experience is of both research and development interest. The key drawbacks of a conventional 3D display based on a static lenticular lenslet array and parallax barriers are low resolution, limited viewing angle and reduced brightness, mainly because of the need of multiple-pixels for each object point. This study describes the concept and performance of pixel-level cylindrical liquid crystal (LC) lenses, which are designed to steer light to the left and right eye sequentially to form stereo parallax. The width of the LC lenses can be as small as 20-30 μm, so that the associated auto-stereoscopic display will have the same resolution as the 2D display panel in use. Such a thin sheet of tunable LC lens array can be applied directly on existing mobile displays, and can deliver 3D viewing experience while maintaining 2D viewing capability. Transparent electrodes were laser patterned to achieve the single pixel lens resolution, and a high birefringent LC material was used to realise a large diffraction angle for a wide field of view. Simulation was carried out to model the intensity profile at the viewing plane and optimise the lens array based on the measured LC phase profile. The measured viewing angle and intensity profile were compared with the simulation results. © 2014 SPIE.

Dynamics of microcystins-LR and -RR in the phytoplanktivorous silver carp in a sub-chronic toxicity experiment

A sub-chronic toxicity experiment was conducted to examine tissue distribution and depuration of two microcystins (microcystin-LR and microcystin -RR) in the phytoplanktivorous filter-feeding silver carp during a course of 80 days. Two large tanks (A, B) were used, and in Tank A, the fish were fed naturally with fresh Microcystis viridis cells (collected from a eutrophic pond) throughout the experiment, while in Tank B, the food of the fish were M. viridis cells for the first 40 days and then changed to artificial carp feed. High Performance Liquid Chromatography (HPLC) was used to measure MC-LR and MC-RR in the M. viridis cells, the seston, and the intestine, blood, liver and muscle tissue of silver carp at an interval of 20 days. MC-RR and MC-LR in the collected Microcystis cells varied between 268-580 and 110-292 mug g(-1) DW, respectively. In Tank A, MC-RR and MC-LR varied between 41.5-99.5 and 6.9-15.8 mug g(-1) DW in the seston, respectively. The maximum MC-RR in the blood, liver and muscle of the fish was 49.7, 17.8 and 1.77 mug g(-1) DW, respectively. No MC-LR was detectable in the muscle and blood samples of the silver carp in spite of the abundant presence of this toxin in the intestines (for the liver, there was only one case when a relatively minor quantity was detected). These findings contrast with previous experimental results on rainbow trout. Perhaps silver carp has a mechanism to degrade MC-LR actively and to inhibit MC-LR transportation across the intestines. The depuration of MC-RR concentrations occurred slowly than uptakes in blood, liver and muscle, and the depuration rate was in the order of blood > liver > muscle. The grazing ability of silver carp on toxic cyanobacteria suggests an applicability of using phytoplanktivorous fish to counteract cyanotoxin contamination in eutrophic waters. (C) 2003 Elsevier Ltd. All rights reserved.

Sub-nanosecond silicon-on-insulator optical micro-ring switch with low crosstalk

We demonstrate a sub-nanosecond electro-optical switch with low crosstalk in a silicon-on-insulator (SOI) dual-coupled micro-ring embedded with p-i-n diodes. A crosstalk of -23 dB is obtained in the 20-mu m-radius micro-ring with the well-designing asymmetric dual-coupling structure. By optimizations of the doping profiles and the fabrication processes, the sub-nanosecond switch-on/off time of < 400 ps is finally realized under an electrical pre-emphasized driving signal. This compact and fast-response micro-ring switch, which can be fabricated by complementary metal oxide semiconductor (CMOS) compatible technologies, have enormous potential in optical interconnects of multicore networks-on-chip.

Sub-nanosecond optical switch based on silicon racetrack resonator

We experimentally demonstrate a small-size and high-speed silicon optical switch based on the free carrier plasma dispersion in silicon. Using an embedded racetrack resonator with a quality factor of 7400, the optical switch shows an extinction ratio exceeding 13 dB with a footprint of only 2.2 x 10(-3) mm(2). Moreover, a novel pre-emphasis technique is introduced to improve the optical response performance and the rise and the fall times are reduced down to 0.24 ns and 0.42 ns respectively, which are 25% and 44% lower than those without the pre-emphasis.

Numerical study of sub-wavelength plasmonic waveguide

The authors present an analysis of a plasmonic waveguide, simulated using a two-dimensional finite-difference time-domain technique. With the surface structures located on the surface of the metal, the device is able to confine and guide light waves in a sub-wavelength scale. And two waveguides can be placed within 150 nm (similar to 6% of the incident wavelength) that will helpful for the optoelectronic integration. Within the 20 mu m simulation region, it is found that the intensity of the guided light at the interface is roughly two to four times the peak intensity of the incident light, and the propagation length can reach approximately 40 Pm at the wavelength of 2.44 mu m. (c) 2007 Elsevier B.V. All rights reserved.

A 1,000 Frames/s Programmable Vision Chip with Variable Resolution and Row-Pixel-Mixed Parallel Image Processors

A programmable vision chip with variable resolution and row-pixel-mixed parallel image processors is presented. The chip consists of a CMOS sensor array, with row-parallel 6-bit Algorithmic ADCs, row-parallel gray-scale image processors, pixel-parallel SIMD Processing Element (PE) array, and instruction controller. The resolution of the image in the chip is variable: high resolution for a focused area and low resolution for general view. It implements gray-scale and binary mathematical morphology algorithms in series to carry out low-level and mid-level image processing and sends out features of the image for various applications. It can perform image processing at over 1,000 frames/s (fps). A prototype chip with 64 x 64 pixels resolution and 6-bit gray-scale image is fabricated in 0.18 mu m Standard CMOS process. The area size of chip is 1.5 mm x 3.5 mm. Each pixel size is 9.5 mu m x 9.5 mu m and each processing element size is 23 mu m x 29 mu m. The experiment results demonstrate that the chip can perform low-level and mid-level image processing and it can be applied in the real-time vision applications, such as high speed target tracking.

Time-resolved photoluminescence of sub-monolayer InGaAs/GaAs quantum-dot-quantum-well heterostructures

Time-resolved photoluminescence (PL) of sub-monolayer (SML) InGaAs/GaAs quantum-dot-quantum-well heterostructures was measured at 5 K for the first time. The radiative lifetime of SML quantum dots (QDs) increases from 500 ps to 800 ps with the increase of the size of QDs, which is related to the small confinement energy of the excitons inside SML QDs and the exciton transfer from smaller QDs to larger ones through tunneling. The rise time of quantum-dot state PL signal strongly depends on the excitation power density. At low excitation power density, the rise time is about 35 ps, the mechanism of carrier capture is dominated by the emission of longitudinal-optical phonons. At high excitation power density, the rise time decreases as the excitation density increases, and Auger process plays an important role in the carrier capture. These results are very useful for understanding the working properties of sub-monolayer quantum-dot devices.

Detect the sub-wavelength data by applying a very-small-aperture laser

We present a theoretical and experimental research about applying a very-small-aperture laser (VSAL) to detect sub-wavelength data. Near-field distribution of a VSAL, which is essential for the application of such near-field devices, will be affected by the sample or fiber posited in the near-field region of the aperture. When the device is applied to detect the sub-wavelength data, the real resolution depends on the near-field spot size, the divergent angle of the beam and the distance from the aperture to the sample. Experimental results, including the near-field detection of the spot and detection of the sub-wavelength data by using the VSAL, are presented in this paper. We realize the two dimensional scanning about the sub-wavelength data (with the width 600 nm) by employing a VSAL with a 300 nm x 300 nm aperture.