Abstract:Thin films of crystalline V2O5 nanoflakes were prepared through atomic layer deposition (ALD) process. The film thickness was verified to play a critical role in determining structural morphology, optical bandgap and Raman vibration of crystalline V2O5 thin films. Two optical bandgaps observed at about 2.8 eV and 2.4 eV result from two growth stages during ALD preparation. We expect that these results help to understand the growth control of ultrathin films and their functional devices.

Abstract:Stray light control is an important technical indicator of an optical system’s performance. The stray light in infrared optical systems includes not only external stray light, but also the internal radiation stray light. The conventional initial system design method limited to an “object-image" conjugate relationship cannot properly take account of stray light. This paper presents a triple conjugate optical system design method for “object-image”, “object-intermediate real image” and “entrance pupil-exit pupil” triple conjugate relationships that minimizes the influences of internal and external stray light to provide good stray light control performance. With this method, an off-axis three-mirror anastigmatic infrared optical system with F/# = 4, linear field of view = 7°, point source transmission less than 5×10-4, and cold iris efficiency 96% was designed and imaged good pictures in orbit.

Abstract:A cylindrical gyrotron cavity is designed and optimized with a high order mode TE34,10- to deliver an output power of megawatts level at 140 GHz. Analysis on mode competition indicates that the two adjacent modes TE33,10- and TE31,11+ involve in competition and cause significant decreasing of output power of TE34,10-. To suppress the competition hysteresis loops of TE31,11+ and TE33,10- with TE34,10- are calculated, which indicates TE34,10- can inhibit growth of the other two modes with decreasing magnetic field from its low efficiency single mode oscillation zone, while it turned out just the opposite with increasing magnetic field due to the earlier oscillation of the competitors. Based on the results, a multimode time-dependent calculation including 42 modes is carried out with magnetic field dropping from 5.59 T to 5.51 T, the results show that mode competition is successfully suppressed, the operation mode TE34,10- realizes stable single mode oscillation with an output power of 0.96 MW and an electron efficiency of 36.7% at 140 GHz.

Abstract:A theoretical study on the perfect absorbers working in the far-infrared region with SU8 based multiple-layer metamaterials has been demonstrated. The perfect absorbers consist of periodic array of metal particles, SU8 dielectric spacing layer and a thicker metallic bottom layer. Through the LC model and the finite element numerical simulation methods, we studied the performance of the absorber. With finely tuned parameters, such like the thickness of the SU8 dielectric layers, the periodicity of the metal particles array, and the length of the metal particles, the near perfect absorption up to ~100% at the wavelength range between 20 μm to 30 μm for far infrared can be achieved. Based on these results, further design for the double-resonator absorber has been provided. Dual band perfect absorption can be accurately and independently obtained by adjust the particle size of the upper and the lower metal layers. Moreover, the wavelength of the perfect absorption is also almost independent of the incident angle. These phenomena can be attributed to the multiple reflections between the thick metallic bottom layer and metal particle layers separated by SU8 dielectric layer, which can also be explained using a LC model as the resonant absorption in metal-dielectric-metal cavities.

Abstract:In this paper, a fundamental W-band monolithic microwave integrated circuit (MMIC) voltage controlled oscillator (VCO) featuring high output power and wide tuning range is proposed. The VCO is fabricated utilizing 0.8μm InP DHBT technology with peak f_Tand f_max of 170 and 250 GHz, respectively. The VCO core implements a balanced Colpitts-type topology. An additional buffer amplifier stage is connected with the VCO core to further boost output power as well as eliminate the load pulling effect. The DHBT base-collector P-N junction at reverse bias is chosen as varactor diode to realize a wide frequency tuning. The measured results demonstrate that the oscillation frequency of the proposed VCO can be tuned between 81- 97.3GHz, which is a relative tuning bandwidth of 18.3 %. Over this frequency range the maximum output power of 10.5 dBm is achieved, and the power variation is less than 3.5 dB. A phase noise of -88 dBc/Hz @1MHz is obtained at the highest oscillation frequency. To the authors’ best knowledge, this is the highest output power with such a wide tuning range reported for a W-band InP DHBT MMIC VCO.

Abstract:Active millimeter wave imaging (AMWI) is an efficient way to detect dangerous objects concealed under clothes. However, because the images acquired by AMWI are often obscure and some of concealed objects are small in size, the automatic detection and localization of the objects remain as a challenging problem. Yao[1] first employed convolutional neural networks (CNNs) and used a dense sliding window method to detect concealed objects. In this paper, we make two improvements on Yao"s work: (1) Using contextual information to suppress interference and improve detection rate; (2) Using a two-step search method instead of exhaustive search to reduce computing complexity. We firstly use one CNN in vertical direction to filter the interference and get the vertical position of the concealed object, then use another CNN to determine the horizontal position. To make use of big window containing contextual information, we use IoG (intersection-over-ground-truth) instead of IoU (Intersection-over-Union) to define positive and negative samples in training and testing process. Experimental results show that our proposed method reduce the computing time to about 30% while achieving better detection performance.

Abstract:In this paper, the double-layer harmonic diffractive element (HDE) structure is investigated and the optimization procedure is based on the equation of diffraction efficiency of the double-layer diffractive optical element. The diffraction efficiency of the system in the designed middle and far infrared wavebands is larger than 99%, which improves the image contrast and the imagequality significantly. A new dual-band infrared double-layer HDE telescope is designed, which can work in the middle and far infrared wavebands. It is shown that the system approximately attains diffraction limit and is easy to processed.

Abstract:In this work, Ga doped ZnO (GZO)/CdS bilayer films were prepared on p-Si substrate by magnetron sputtering to form GZO/CdS/p-Si heterojunction device. The structural, optical and electrical properies of the nanocrystalline GZO/CdS bilayer films were studied by XRD, SEM, XPS, UV-VIS spectrophotometer and Hall effect measurement. The J-V curve of GZO/CdS/p-Si heterojunction device shows good rectifying behavior. And the value of IF/IR (IF and IR stand for forward and reverse current, respectively) at ±3V is found to be as high as 21. The results indicate that the nanocrystalline GZO/CdS/p-Si heterojunction possesses good diode characteristic. High photocurrent density is obtained under a reverse bias. The nanocrystalline GZO/CdS/p-Si heterojunction device exhibits clear photovoltaic effect. Because the lattice constant of CdS is between GZO and Si, it can be used for a buffer layer between GZO and Si, to effectively reduce the interface states between GZO and p-Si. Therefore, we observed the clear photovoltaic effect of GZO/CdS/p-Si heterojunction.

Abstract:In recent years, Metamaterials, artificial electromagnetic materials that are constructed by sub-wavelength units, have demonstrated unusual abilities to manipulate electromagnetic waves and promised many potential applications. One of the most intriguing applications of metamaterials is to function as high performance absorbing medium. In this work, a new type of plasmonic flexible metasurface-based super-absorber for Terahertz waves is designed, fabricated and characterized. Dependences of absorption on the optical properties of component materials and geometric parameters are optimized by full-wave numerical simulations, and then confirmed by experiments. Experimental results show that an absorption peak value of 99% is obtained at the frequency of 3 THz, which are in good agreement with numerical simulations.

Abstract:A new continuous zoom structure was described, and a new independent zoom group was added on the classical four-group-mechanical-compensation. And larger zoom ratio was achieved by the way of two zoom groups cascading. This mathematical model was deduced. Then, according to the cooled mid-wave infrared detector, a continuous-zoom infrared optical system with large zoom ratio and large relative aperture was designed. And the problem that it’s hard for a zoom optical system to achieve both large zoom ratio and large relative aperture was solved. This optical system can zoom from 6mm to 330mm, which means it can reach 55x zoom ratio while the F number is 2 constantly. The working waveband was 3.7-4.8um, the cold shield efficiency was 100%.It contains only eight lenses, three of them move in order to change the focal length. The result shows that the zoom curves are quite smooth and the image quality is quite good in the whole zoom range. The laboratory test and the out-door imaging experiment shows that the image quality is quite good in the whole zoom range. It proves the application effect of this new kind of zoom model, and shows that the system reaches its design goal.

Abstract:This brief proposes a 16-stage on-chip analog accumulation circuit architecture to realize time delay integration(TDI). The accumulation unit is based on charge amplifiers. The temporal noise on the analog signal path of the circuit structure is analyzed to enhance the noise performance, and furthermore the model of thermal noise suitable for the TDI process is given. The analysis revealed that the total thermal noise is composed of charge transfer noise and direct sampled noise, according to different stages of accumulators. The relations of each noise component versus circuit gain and corresponding method to suppress it are given. Finally, 16x256 test chip is taped out under the 0.5 μm CIS process, and test results indicate the improvement of 11.22dB in SNR at the 16 TDI stages.

Abstract:High-performance terahertz functional devices have great significance in the generation, transmission and detection of terahertz waves. This paper reports a Kagome-type low-loss terahertz waveguide and its imaging applications. Firstly, anti-resonant waveguide theory was used to design a Kagome terahertz waveguide with low loss transmission at 0.1 THz, which has a theoretical loss as low as 0.012 cm-1. Secondly, the waveguide was fabricated by 3D printing technology. The experimental loss is 0.0153 cm-1, and the beam divergence angle at the end of the waveguide is about 6±0.5 degree. Finally, a reconfigurable terahertz imaging system was set up based on the waveguide, which realizes reflection and transmission imaging for a hidden blade and ore respectively. This technology has great application prospects in the underground long-distance exploration.

Abstract:In order to detect the polarization properties of the target, a dual-polarized monopulse antenna at W band is proposed. The antenna is composed of the main-reflector, the sub-reflector, the feed horns, the orthomode transducer and the differential network. The aperture diameter of the antenna is 137mm, the feed contains five horns, the orthomode transducer is designed using the tapered waveguide, and the differential network is realized by the planer coupler. The feed horns, orthomode transducer, and differential network are integrated designed to reduce the insertion loss and compress the size of the antenna. The measured results show that the impedance bandwidth of the antenna is about 3.7GHz, the polarization isolation is greater than 35dB, the maximal gain of the sum beam is about 37.9dB, the sidelobe level is below -15dB, and the null depth of the differential beam is greater than -25dB. The antenna shows good dual-polarized monopulse performance at W band.

Abstract:With the rapid development of graphene industry, graphene oxide has attracted much attention as an important intermediate product for the preparation of graphene. Due to its excellent physical and chemical properties, it has been widely used in multitudinous fields. Various structural models, preparation methods, properties and related applications, as well as the reduction of graphene oxide are summarized. The choice of oxidants and reduction agents were found to be important in the reaction. The basic selective principles are discussed after comparing various methods. Finally, it is pointed out that there are still some problems to be solved in the preparation and reduction of graphene oxide. The prospect of graphene oxide on its development and influence will also be evaluated.

Abstract:Graphene has a low absorption rate of light. By combining with an optical resonant cavity to restrict the light field, the absorption rate of the graphene detector element can be effectively improved. Based on the theory of electromagnetic field transmission, the optical field distribution in the bilayer graphene optical resonator is deduced, a mathematical model for the transmission matrix of the resonant enhanced photodetector is established, and a resonant enhanced photodetector for the Bernal-Stacked bilayer graphene is established. The structural parameters are numerically calculated and the detector performance is analyzed. The results show that, the optical absorption rate of bilayer graphene reaches up to 96.78% for a 1.06 μm wavelength resonant enhanced photodetector, which greatly improves the detection ability of weak optical signals.

Abstract:A photo-excited and polarization insensitive broadband tunable terahertz metamaterial absorber (MMA) based on the photo-sensitive material of silicon (Si) was proposed. The unit-cell structure of this MMA is consisting of compact split-ring resonator structure filled with silicon, mediate medium layer and metal ground-plane. The working frequency and absorption intensity of this terahertz MMA could be effectively tuned, when the conductivity of silicon was changed by the varied incident optical intensity. The simulation results demonstrate that this MMA is dynamically adjusted in the frequency range from 0.852THz to 0.442THz when the conductivity of silicon increases from 1.0×103 S/m to the 5.0×105 S/m. In addition, its relative bandwidth is as much as 63.37% and absorption modulation depth is up to 60.22%. The further simulation indicates that MMA has characteristics of polarization insensitive and wide incident angle.

Abstract:Cloud detection for remote sensing imageries is a fundamental but significant step due to the inevitable existence of large amount of clouds in the optical remote sensing data. A highly efficient cloud detection approach is capable of saving data collection cost and improving data utilization efficiency. Homomorphic filtering algorithm is one of the most commonly methods which based on single-scene image for detecting clouds. The algorithm has the advantage of fast computation and high accuracy in cloud areas detection. However, the cloud areas results are depended heavily on the cut-off frequency of the filter. The classical homomorphic filtering often uses cut-off frequency with empirical value which may not be applicable to large amount of intricate input data. Therefore, this paper aims to build the relationship between the image spectra power and the filter cut-off frequency. Based on the domestic high spatial resolution optical remote sensing data GF-1, this method makes the detection of clouds can be process to achieve a bulk deal. Our approach can self-adaptive changes the cut-off frequency rather than used empirical value when compared with the traditional homomorphic filtering, thus it could be able to meet more complicated scenarios. Further, the post-processing steps including whiteness index, spectral threshold, and morphological opening and closing operators are applied to coarse cloud mask to optimize results. We have tested on 98 GF-1 high resolution multispectral images, results indicated that our approach is capable of detecting cloud as well as haze areas with high accuracy of 93.81%. This novel self-adaptive method shows its great application potential for real-time and high efficient cloud detection, meanwhile reduced the error detection rates caused by high reflectance ground objects.

Abstract:Nonlinear unmixing can explain the nonlinear mixing effect in complex scenarios of hyperspectral imagery, but the spectral variability of ground objects is one of the difficulties. An unsupervised nonlinear unmixing algorithm dealing with spectral variability is proposed in this paper. The original hyperspectral image data is implicitly mapped into a high-dimensional feature space through a kernel function and then linear unmixing is applied for hyperspectral imagery in combination with spectral variability in this space. Further, local smoothness constraint is added on abundances and coefficients of spectral variability according to the distribution characteristics of ground objects. Experimental results on simulated and real hyperspectral data indicate that, the proposed algorithm can overcome the spectral variability problem in different nonlinear mixing scenarios and improve the unmixing accuracy.

Abstract:Infrared thermal image region of interest(ROI) extraction has important significance for fault detection, target tracking and so on. In order to solve the problems of many infrared thermal image disturbances, artificial markers and low accuracy, a ROI of infrared thermal image extraction algorithm based on fusion of multi-modal feature map was proposed. Multi-modal feature maps were constructed by contrast, entropy, and gradient features, and region filling was performed to achieve ROI extraction. Apply the new algorithm to the actual collected photovoltaic solar panel image. The results show that the new algorithm has the advantages of high average precision (93.0553%), high average recall (90.2841%), F index and J index are better than Grab Cut, less artificial marks, etc.. It can be effectively used for ROI extraction of actual infrared thermal images.