Abstract:A new and upcoming application is the use of 60 GHz antennas for high date rate point-to-point connections to serve Gigabit (Gi-Fi) wireless communications. The design of Millimeter wave (MmW) antennas has to cope with the unadorned influences of manufacturing tolerances and losses at 60 GHz. In this paper, the concept of Substrate Integrated Waveguide (SIW) and Exponentially Tapered Slot (ETS) antenna were used together to design a high gain, efficient planar dielectric loaded antenna for MmW Gi-Fi wireless communications at 60 GHz. The SIW is used to feed the antenna and a dielectric is utilized in front of the antenna to increase the gain. The dielectric loaded ETS antenna and compact SIW feed were fabricated on a single substrate, resulting in low cost and easy fabrication. The antenna with elliptical shaped dielectric loaded was fabricated using printed circuit board process. The measured gain of the single element antenna is 10.2 dB, while the radiation efficiency of 96.84% is obtained at 60 GHz. The Y-junction SIW power divider is used to form a 1×4 array structure. Measured gain of the 1 × 4 array antenna is 13.3 dB, while the measured radiation pattern and gain are almost constant within the wide bandwidth of the antenna.

Abstract:The equivalent circuit model (ECM)of the folded waveguide (FW) in consistent consideration of the ohm loss on the waveguide wall was established for calculating the cold-circuit phase velocities, interaction impedance and attenuating coefficient of space harmonics of periodic TE10 mode in this slow wave structure (SWS). These results were obtained for one-dimensional (1-D) parametric model calculation of the particle-microwave interaction in the 220 GHz backward wave oscillator (BWO). When the frequency of microwave is up to terahertz regime, the ohm loss caused by surface current on rough waveguide wall is not negligible any more. Further study shows that the starting oscillation current and output power are intimately dependent upon the loss property calculation. The ECM about lossy periodic circuits was then developed from the previous loss-free model to give a more accurate analysis. Three-dimensional (3-D) Eigen mode analysis for the FW SWS was taken to verify the improved model, which shows good agreement. Additionally, based on the improved ECM, 1-D beam wave interaction calculation was conducted which is in good consistency with 3-D Particle-in-cell (PIC) method.

Abstract:To study the high-field electrical property and the drain current Ion/Ioff ratio of Al2O3/GaSb p-MOSFET, the Poisson and continuity equations with carrier velocity saturation were solved consistently with two-dimensional numerical analysis. The simulation results show that a maximum drain current of 61.2 mA/mm has been reached for 0.75-μm-gate-length GaSb p-MOSFET device. The results have been compared with that of experiment. With change of the channel length and doping-level in substrate GaSb, the drain currents exhibit little change due to the effects of gate capacitance with high-k dielectric and low-threshold voltage. In addition, a high Ion/Ioff ratio with more than three orders of magnitude and relatively low pinch-off leakage current Ioff with 10-15 A/μm are predicted in an ideal condition. The results indicate that GaSb-based MOSFET with high-k dielectric is promising for future p-channel III-V device.

Abstract:The design of a novel low-background spectrometer based on lamellar grating interferometer (LGI) is presented. Reducing background noise helps to improve the spectrometer system detectivity for detectors operating under background limited performance (BLIP) regime, and then improve the signal to noise ratio (SNR) of spectrometer. The principle is that perfect mirrors do not emit blackbody radiation since their emissivity equals zero. Therefore, a lamellar grating interferometer based on a “cold” source and a “cold” detector becomes an extremely sensitive instrument because of the reduction of background radiation. Theoretical analysis shows that the system detectivity can be improved substantially with background radiation dropping. In ideal case, for a typical HgCdTe detector, the real BLIP detectivity obtained and corresponding SNR can be improved by three orders of magnitudes when background radiation is reduced from 300 K to 77 K. Besides, without cooling the interferometer, this configuration is more compact and easier-to-build compared with previously reported low-background Michelson spectrometer. This design has important significance for infrared sensitive detection.

Abstract:By using the compact density matrix approach, the linear and nonlinear optical absorption coefficients in a GaN-based step quantum well (QW) with strong built-in electric field (BEF) have been theoretically deduced and investigated in detail. The band nonparabolicity is taken into account by using an energy-dependent effective mass (EDEM) method. The exact electronic eigen-states in the step QW with strong BEF were obtained and the simple analytical formulas for the linear and nonlinear optical absorption coefficients in the systems were also deduced. Numerical calculations on an AlN/GaN/AlxGa1-xN/AlN step QW were performed. It is found that the decreasing of well width Lw and step barrier width Lb and the doped concentration x in step barrier can result in the enhancement of the absorption coefficients. Moreover, with the decrease of Lw, Lb and x, the photon energies of absorption have blue-shift, and the full-width-at-half-maximum of the total absorption coefficient increases and the saturation absorption intensity decrease. Some results are consistent with recent experimental observations.

Abstract:Researches of RCS include computational electromagnetics and image-based measurement. Restricted by computer memory and operating time, computational electromagnetic methods are difficult to be widely applied in terahertz band. Inverse Synthetic Aperture Radar (ISAR) imaging technique has been commonly utilized in image-based measurement. The reflectivity images are usually reconstructed by back-projection (BP) algorithm. However, the RCS angular glint is significant in terahertz band, which cannot be revealed in the BP images. Thus, the sub-aperture imaging technique was employed to measure the target RCS in terahertz band in this paper. Numerical simulations were adopted to test the validity of the proposed method.

Abstract:With remarkable advantage of comprehensive cost, multicrystalline based photovoltaic module products become the most competitive and widely used PV products. A strong correlation was found between crystal defects of multicrystalline silicon and the cell efficiency thereby. The defect density at the bottom and top brick is very high, as a result, the corresponding cell efficiency is low (14.5~15.5%). The cell efficiency of the wafers from the middle position of brick is high (16.5~17.5%) due to the low defect density. However, different kinds of defects exert different influence on the cell performance. For instance, some stable defects (such as dislocation) will survive at the final cell, and some other defects (such as interstitial metal impurities) are removed during the cell process.

Abstract:A code of the terahertz wave’s atmospheric transmission and dispersive attenuation was developed with the radiation transmission theory and Van-Vleck Weisskopf line-shape based on the JPL database. The short term THz wave atmospheric transmission experimental results obtained from the THz-time domain spectroscopy (THz-TDS) technique was analyzed by this code. The absorbing attenuation characteristics and the time domain waveform of the terahertz transmission pulses were compared. The influence of the humidity on the amplitude, phase and spectrum of the transient terahertz pulse was studied. It was concluded that the maximum wireless transmission data rate exceeds 20 Gb/s between 0.1 and 0.5 THz, which is much faster than through the single mode fiber (SMF) and more suitable for short distance communication.

Abstract:The dielectric response of SBN:Ce ceremics modulating by the 532nm cw laser is investigated at room temperature by means of a terahertz time-domain spectroscopy. When the external laser field is imposed onto the SBN:Ce ceremics, the permittivity of the sample shows an appreciable modulation results, which the modulation depth reach up to 8.5% and the dielectric loss increases 15%, respectively. The experimental results show there is a linear dependency between the variation of refractive index |Δn| and the applied laser intensity. The photo-ferroelectric physical mechanisms of SBN:Ce ceramics can be attributed to the internal space field in the ceramics caused by the light excited free carries with the analytic models. The conclusion presents important references for design and selection of the teraherz tunable devices.

Abstract:This paper has designed the input and output coupler,Magnetron Injection Gun (MIG) and beam-wave interaction circuit for a W-band gyrotron traveling tube (gyro-TWT) with software simulation. The tube was manufactured according to the optimized results. The gyro-TWT is driven by a voltage of 60 kV and current of 6 A. Hot test predicts its maximum peak output power of 78 kW, 21.7% efficiency at 94 GHz with a gain of 53.9 dB. The bandwidth with peak power greater than 50 kW is about 3.8 GHz. Both the PIC simulation and hot test indicated that the gyro-TWT can work stablely. The periodic lossy dielectric loaded circuit is excellent for suppressing potential spurious oscillations and absolute oscillation.

Abstract:Synthetic Aperture Ladar(SAL) is the focus of remote sensing research in recent years with vibration as an important issue in this system. According to the research before, SAL is sensitive to the cross-trace line vibration. In order to eliminate the phase error brought by vibration, the staggered structure of two sub-apertures along range direction was proposed according to the principle of differential synthetic aperture ladar (DSAL). Using the measured POS data, the ability of eliminating the effect of line vibration of this staggered structure was analyzed in principle. Analysis was also made about the effect of angle vibration on this structure. The results show that the structure can eliminate the effect of line vibration as well as angle vibration. The results provide theoretical foundation and system choice for vibration elimination in SAL imaging in practice.

Abstract:A compact polarization splitter (PS) based on tapered cascaded multimode interference (MMI) couplers in slot waveguide structures was proposed and characterized. By utilizing two cascaded MMI couplers, the two orthogonal polarizations, quasi-TE mode and quasi-TM mode, are efficiently separated without the necessary that the total length of the MMI must be common multiple of the self-imaging lengths of the two polarizations. This greatly reduces the length of the PS and improves the design flexibility. Meanwhile, the high birefringence of slot waveguides and the tapered MMI structure can further shorten the device length. Results show that a PS with a length of 42 μm in the MMI sections can be achieved, where the polarization extinction ratios (ERs) for the quasi-TE and quasi-TM modes are 29.8 and 31.4 dB, respectively. Optical bandwidth of 43 nm is obtained for keeping the ER over 20 dB. Moreover, fabrication tolerances to the structural parameters were investigated, and field evolution along the propagation distance through the PS was also demonstrated.

Abstract:As one of the key components of high-power optically pumped THz laser, hybrid metal-mesh output coupler is critical for the output power and the beam quality. A model for the hybrid metal-mesh output coupler has been developed. The reflectance, transmittance and loss of the coupler was evaluated. Output couplers at 2.52 THz have been fabricated. The reflectance and transmittance are 70% and 11% for type I, 87% and 4% for type Ⅱ.The coupler can sustain high-power CO2 laser pump with the reflectivity over 95 %. This research provides theoretical and technical supports for developing high-power optically pumped THz laser.

Abstract:A total of 643 farmland topsoil samples distributed in 36 counties and cities of Zhejiang Province were collected. The correlation between contents of Ni, Cu, As, Hg, Zn, Cr, Cd and Pb and that of organic matter was probed by measuring the reflectance of soil samples in visible-near infrared light band. The characteristic wave bands of heavy metal elements and organic matter were compared. The partial least squares regression (PLSR) model for the content of each heavy metal element was established. The results indicated that Ni and Cr have the best correlation with organic matter, while As has the worst, with the correlation coefficients 0.54, 0.59 and 0.20, respectively. The distance between heavy metal elements and organic matter in the first three principal components loading diagram was inversely proportional to their correlation coefficient. Degree of overlap between different heavy metal elements and organic matter at hyperspectral sensitive band and the positive and negative consistency of regression coefficients varied greatly, the greater the correlation with organic matter is, the higher degree of overlap is, and the better the positive and negative consistency. In PLSR models of heavy metals, models for Ni and Cr performed well in modeling and predicting with a good ability of quantificational prediction, with RPD values of 1.94 and 1.80 separately. The remaining models for other 6 heavy metals could only conduct distinguishing for high and low values with RPD values ranged from 1.00 to 1.4. The results of this study provide certain theoretical assistance and reference for hyperspectral remote sensing monitoring of soil contamination by heavy metals in large-scale areas.

Abstract:In space-based optical systems, during the pixel-plane tracking for closely spaced objects (CSOs), in traditional methods, pixels are partitioned after constant false alarm rate detection (CFAR), where higher false alarm rate results in more clutter measurements while lower false alarm rate results in the loss of targets’ information. To solve this problem, CSOs’ feature on pixel-plane were analyzed and a pre-detecting method using Markov random field model(MRF) was proposed. Then pixels were partitioned with k-means. Simulations indicated that detection and partition with MRF provides higher performance than traditional method, especially when signal-noise ratio is poor.

Abstract:Saline soil cause great damage not only to the agricultural production but also to the ecological environment. The general model for optical spectrum characteristics of the saline soil in Jilin Province was established and validated according to the polarized and hyperspectral spectral information. The results show that there is a strong relationship between the hyperspectral polarized information of saline soil and its physicochemical property parameters, especially for the soil line, from which we could calculate the soil with different of salinity.

Abstract:An epitaxy structure with asymmetric hetero-structure waveguide for diode laser is presented, which was optimized by selecting material system and thickness of each layer. The different designs in P-confinement and N-confinement reduce voltage loss and meet the requirement of high power and high electro-optical efficiency. Based on the theory of transportation and confinement, the principal output characteristics were analyzed and simulated. After that, a 1060 nm diode laser with single quantum well and asymmetric hetero-structure waveguide was fabricated and characterized. The measurement results show that asymmetric hetero-structure waveguide is effective to reduce voltage loss and improve the confinement of injection carriers and electro-optical efficiency.

Abstract:How to evaluate the reliabilities of different image sensors and their processing results is an important issue in the field of multi-modal fusion. In this paper, we focus on multi-modal fusion moving objects detection, in which visible light and infrared image sensors are adopted. An evaluation factor named F-BDEF (Foreground-Background Distinguishability Evaluation Factor) was proposed to evaluate the reliabilities of the detection results of two sensors. Then a multi-modal fusion moving objects detection based on F-BDEF was proposed, in which F-BDEF was used to distinguish between false positive alarm and false negative alarm, and to choose the accurate detection region from visible light result and infrared result. The experiments showed that the proposed detection method received more accurate results and could overcome many disturbances, such as sudden change of illumination, shadow, ghost, low-contrast night scene.

Abstract:The National Polar-orbiting Partnership (NPP) satellite was successfully launched in 28 October 2011. The day night band (DNB) is mounted on the Visible Infrared Imaging Radiometer Suite (VIIRS) on board the NPP to greatly improve the night time imaging capabilities. In order to cover this wide dynamic radiation range, the three gain stages are employed to view the earth at daytime, twilight and even nighttime. Especially, the radiance measured at night is relatively low, so the radiance calibration is too difficult to realize. In order to realize radiance calibration at night, the vicarious calibration method of Low-level light detection at night using the deep convection clouds is presented. The lunar irradiance model was introduced to enhance the SCIATRAN to realize the radiance transfer simulation at all time. Then, the reference values of the surface albedo, atmospheric profiles and optical properties of deep convection clouds were inputted to the enhanced model to study the sensitivity of the TOA radiance. The simulation results show that the main factors are the Cloud Optical Thickness (COT) and Effective Radius(Re) and the maximum reflectance errors are no more than 5%. In order to examine the feasibility of the calibration method, the 6 months NPP data range from August 2012 to January 2013 was used. The simulated albedos were calculated using the enhanced radiative transfer model and compared with the observed albedos. The result shows that the radiance uncertainties on a daily basis are in the range of ±10%, which means that the calibration method using Deep convection clouds is very well to calibrate the DNB high gain stage directly.