Abstract:By studying two interband cascade laser (ICL) wafers with structural parameters that deviated considerably from the design, the durability of the device performance against structural variations was explored. Even with the lasing wavelength blue shifted by more than 700 nm from the designed value near 4.6 μm at 300 K, the ICLs still performed very well with a threshold current density as low as 320 A/cm² at 300 K, providing solid experimental evidence of the tolerance of ICL performance on structural variations.

Abstract:The development of uncooled IRFPA pixel structure from a single-layer structure to a double-layer structure reduces noise and improves performance. The pixel structure and its main physical parameters are introduced. It is noted that the main difference between the double-layer structure and the single-layer structure lies in the difference in the effective area of the pixel and thermal conductivity of the bridge leg. The 3-D noise model is an effective method to analyze IRFPA noise, in which spatio-temporal random noise is the main noise part of uncooled IRFPA. The mechanism of spatio-temporal random noise in uncooled IRFPA is analyzed, and a spatio-temporal random noise model is established. The relationship between spatio-temporal random noise, the effective area of the pixel, the thermal conductivity of the leg is obtained. An uncooled IRFPA with a single-layer pixel structure is improved by changing it into a double-layer pixel structure, and the noise is measured. The measured data proved the effectiveness of the uncooled IRFPA spatio-temporal random noise model.

Abstract:In order to reduce imaging spectrometer’s polarization sensitivity and improve its quantitative measurement accuracy of target’s spectral radiance, a transmission polarization-independent two-dimensional binary blazed grating was proposed. It consists of periodical groove units in both orthogonal directions and there contains 7 sub-periods within one groove unit. Duty cycles of sub-periods are independent in two orthogonal directions, so that the effective index of both TE and TM polarizations can be modulated simultaneously, and the grating’s polarization property can be optimized. Through extending the effective medium theory to the two-dimensional pattern, a two-dimensional binary blazed grating with polarization-independent high efficiency on fused silica substrate was designed for wavelength range from 0.6 to 0.8 μm. The grating periods in two orthogonal directions are 3.3 1μm and 0.473 μm, respectively. Simulation results show that, for normal incident light, diffraction efficiencies of TE and TM polarizations at reference wavelength 0.7 μm are 78.4% and 78.3%, respectively. Within wavelength range from 0.6 to 0.8 μm, diffraction efficiencies of TE and TM polarizations are both above 70% and the degree of polarization is below 2.6%. Compared with one-dimensional binary blazed grating, the two-dimensional grating has the advantages of high diffraction efficiency, low degree of polarization and easier manufacture. It is expected to be used in grating-type imaging spectrometers.

Abstract:This paper presents the fabrication and cold-test of a three-slot-staggered-ladder coupled cavity slow wave structure (CC-SWS) along with high power input-output couplers and RF windows in W-band. The SWS is fed by a rectangular waveguide coupler which is made up of a three-order step-transform rectangular waveguide placed on the short edge of the input cavity. Firstly, the dispersion, interaction impedance, transmission property and beam-wave interaction are studied using the simulation method. It is shown that the traveling wave tube (TWT) with a three-slot-staggered-ladder CC-SWS is able to provide a sat-uration output power of more than 1000 W in the frequency range of 91-96GHz, and the maximum saturated output power can reach 1125W at 94 GHz. Secondly, the CC-SWS is fabricated by the high-precision CNC milling and fixed in a nonmagnetic stainless steel housing. Test results of the fab-ricated CC-SWS with couplers and RF-windows are presented, showing the S11 < -10 dB in the frequency range of 90GHz to 100GHz. Therefore, the three-slot-staggered-ladder CC-SWS is a promising slow wave circuit of high power W-band TWT.

Abstract:The design and experiment of 94 GHz gyrotron with an inside quasi-optical system for the non-lethal biological effects of millimeter wave radiation are presented in this paper. The reason we chose TE_+6,2 mode as the experimental working mode is to reduce the wall heating problem at high power and high frequency. For a high-order mode, there are more neighboring modes, so mode competition affects the stability and effective operability of the experiment. The gradually tapered cavity has been designed to suppress mode competition in single cavities. In addition, the power conversion efficiency of the quasi-optical mode converter with low diffraction is 98.54%. The experimental results confirm that the output power of 50.9 kW is obtained with efficiency of 34.3%. For the non-lethal biological effects, we can draw the conclusion that the overall scheme can achieved the expected results.

Abstract:Surface plasmon polaritons (SPP) arising from the interactions between electrons and photons at the metal/semiconductor-dielectric interfaces, and spoof surface plasmons (SSP) supporting by the metamaterials or the interactions between surface electrons and terahertz/microwave waves of polyatomic crystals, are the essential foundation for breaking the diffraction limit and building integrated terahertz active/passive devices. This paper introduces the basic principles, evolution processes of conventional optical SSP, terahertz SPP and graphene surface plasmon polaritons (GSP). The detailed summary and discussion of terahertz plasmons in the applications of terahertz sources, passive devices, super-resolution imaging and so on are also presented. In the last, we discuss the developing prospects of the terahertz plasmons.

Abstract:Terahertz waves have many unique electrical and optical properties, which have significant applications in both civil and military fields, such as physics, biology, public safety inspection, local area communication, information security, environmental monitoring, non-destructive testing and defense technology etc. Terahertz detector is one of the core components in a terahertz system. Therefore, its application is usually determined by the characteristic and performance of the detector. In recent years, there are some major breakthroughs in the development of terahertz detectors. However, there are still technology challenges that limit the application of such device. For example, room temperature terahertz detectors exhibited a large noise equivalent power and low sensitivity. This is in contrast to cooled terahertz detectors, which demonstrated high response rate and low noise equivalent power, but they cannot be miniaturized and are costly. This paper provides a summary and discussion on the recent development and application of terahertz detectors from the aspect of material preparation and device configuration.

Abstract:An extended interaction oscillator(EIO) based on a single cavity composed of 12 periods of staggered double rectangular waveguide slow wave structure (SDRWSWS) is modeled and calculated on computer, those methods and steps for determining the structural parameters and the beam parameters are given. A new method called “phase re-synchronization technology” is proposed to improve electron efficiency of EIO, the method is to decrease the periods of the fifth and sixth periods of SDRWSWS counted from the entrance of the beam by 10%, so that the magnitude of the z component of electric field intensity becomes weaker in the segment which is far from the output port, but becomes stronger in the segment which is near from the output port, and such an E_z distribution is in favor of good bunching in the beam as the beam is proceeding. On the other hand, the phase of the z component of electric field intensity increases about 51.6o between the 7 to 12 periods, so that the electric field maintains synchronization with the space electric charge wave in the beam and abstracts more kinetic energy from the beam. Computer simulation results show that both power and electron efficiency become higher conspicuously, the maximum improved values are over double of unimproved ones.

Abstract:The optical properties of one-dimensional 4H-SiC gratings have been studied both theoretically and experimentally. Four optical modes are observed in the grating structure: propagating surface plasmon polaritons （PSPhPs）, dipole mode, localized surface phonon polaritons and quasi-static surface phonon polaritons. Furthermore, dielectric materials with various thicknesses were deposited on the grating surfaces by the atomic layer deposition. By utilizing the sensitivity of the PSPhPs mode to the parameters of the grating structure, a linear relation between the change of the thickness of the deposited materials and the offset of the PSPhPs peak position has been observed and deduced. These findings here could provide guidance for various applications of novel micro/nano devices, such as the nano-ruler and nano-sensor.

Abstract:A field of views of pyroelectric infrared sensors modulation strategy were proposed. The strategy can improve the human localization resolution, and it will not reduce the detection distance of pyroelectric infrared sensor. For the strategy, the field of views of pyroelectric infrared sensors are modulated by a mask. And the modulated field of views overlap and interleave with each other to form some sampling areas. In order to verify the proposed field of views modulation strategy, the human localization node which includes nine pyroelectric infrared sensors is fabricated. The modulated degree of the field of views of each pyroelectric infrared sensor is 36°. The degree of each sampling area is 4°. If the human moves in a sampling area, the corresponding pyroelectric infrared sensors will be triggered. The human position can be localized by using at least two nodes. According to the states of the pyroelectric infrared sensors, the human position can be estimated. In the experiment, two nodes are set in a 600 cm×600 cm square area, the theoretical error is analyzed by using least square estimation. The theoretical maximum error of the two nodes human localization equipment in a 600 cm×600 cm square area is about 70 cm. Eight human positions are estimated in experiments, and the estimation route is formed by connecting all the estimated positions. The estimation route is close to the predefined route. The minimum and maximum estimation errors are about 4.42 cm and 16.91 cm respectively.

Abstract:The structure of the polarization detector is introduced firstly, the signal response model of the detector is established. Based on the signal response model, the corresponding parameter calibration scheme is made. High-precision calculation of polarization states of incident radiation and non-uniformity correction of polarization image are realized. The experimental data show that the calculated linear polarization is 97.8% ~ 101.5% of the true value after calibration, which meets the accuracy requirements of polarization detection. The non-uniformity of intensity image and linear polarization image has been reduced by 93.64% and 93.67% respectively compared with the uncorrected image, and the image quality has been effectively improved.

Abstract:Aiming at the problem of no control point geometric correction for plane array swabbing data, a step by step geometric correction method for plane array swabbing thermal infrared image based on POS data is proposed.The main steps include image correction using the visual vector method, projection to Gaussian auxiliary plane for splicing and virtual control points are extracted. The second geometric precision correction of the global image is carried out by using the least square method to realize the geometric correction of the thermal infrared image in the research area. The validity of the proposed algorithm is verified by obtaining experimental images, the relative error of the distance between two points in the plane is 0.81%, then the relative error of the azimuth angle of two points in the plane is 0.72%, which is significantly improved in comparison with the direct application of POS correction error. The method can be applied to the geometric correction of flight images without ground control points in other plane array swallows.

Abstract:In this paper, the application of an algorithm for precipitation retrieval is studied based on the statistical analysis of the changes of brightness temperature gradient in different infrared spectra of Advanced Himawari Imager(AHI) of H8 in the field of view of “precipitation” and “non-precipitation”. Taking Anhui region as an example, when precipitation occurs, there is some change in brightness temperature gradient of AHI channel 7-16. Furthermore, dictionary learning and regularization constraints are used on precipitation retrieval. Firstly, based on the H8/AHI spectral brightness temperature data and GPM precipitation, spectral “brightness temperature” and “precipitation” dictionary are matched as historical sample databases. Secondly, K-nearest neighbor (KNN) method is used to identify “precipitation” and “non-precipitation” signals on the brightness temperature of the infrared spectrum based on the “dictionary”. Finally, precipitation retrieval for infrared data is carried out in the precipitation signal “subspace” with regularization constraints. The preliminary experimental results show that precipitation structure based on brightness temperature for H8/AHI, which was retrieved by using the Bayesian model averaging-gamma probability distribution model, has a good similarity with GPM, as well as low relative error, and the critical success index is higher than others. Furthermore, the algorithm is extended and applied to the AHI brightness temperature retrieval of typhoon “Maria” precipitation, and the spiral rain belt can be obtained.

Abstract:To solve the problem of automatic selection the segmentation scale in remote sensing image, a superpixel segmentation method of high resolution remote sensing image based on hierarchical clustering is proposed. Firstly, the watershed segmentation algorithm based on adaptive morphological reconstruction is used to segment the image into multiple superpixels. Then, the gray feature vectors of each superpixel is extracted. Finally, the hierarchical clustering method is adopted to merge the superpixels, the accurate segmentation of high-resolution remote sensing images is realized. Four sets of remote sensing images are selected in the experiment, and the experimental results are evaluated by a combination of qualitative and quantitative methods. Experimental results shown that the proposed method effectively improves the segmentation accuracy of remote sensing images, and better segmentation visual effects are obtained.