Abstract:This paper presents the simulation results of DC, small-signal and noise properties of GaP based DDR IMPATT diodes. In simulation study we have considered the flat DDR structures of IMPATT diode based on GaP, GaAs, Si and GaN(wz) material. The diodes are designed to operate at the millimeter window frequencies of 94 GHz and 220 GHz. The simulation results of these diodes reveal GaP is a promising material for IMPATT applications based on DDR structure with high break down voltage (V_B) as compared to Si and GaAs IMPATTs. It is also encouraging to worth note GaP base IMPATT diode shows a better output power density of 4.9×10⁹ W/m² as compared to Si and GaAs based IMPATT diode. But IMPATT diode based on GaN(wz) displays large values of break down voltage, efficiency and power density as compared to Si, GaAs and GaP IMPATTs.

Abstract:This paper presents a 0.18 μm complementary metal-oxide-semiconductor (CMOS) technology high premature edge breakdown, extended spectrum and low dark count rate circular single-photon avalanche diode (SPAD) which together form a novel wide spectrum fluorescence correlation spectroscopy (FCS) detector. The circular device consists of a p+/deep n-well junction, a p-well guard-ring, and a poly guard-ring. Simulations on a Silvaco TCAD 3D device also show that the 10 μm-diameter circular p+/deep n-well SPAD device has high premature edge breakdown characteristics. Moreover，compared to the SPAD p+/n-well junction, the p+/deep n-well junction has a longer wavelength response and spectral expansion. The device achieves wide spectral sensitivity enabling greater than 40% photon detection probability from 490 to 775 nm wavelength at 0.5 V excess bias. The circular p+/deep n-well SPAD has fine avalanche breakdown is 15.14 V and a low dark count rate of 638 Hz at 25℃.

Abstract:In this paper, InAs-based type-II interband cascade lasers operating at the mid-infrared range were fabricated and characterized. The maximum operating temperatures under pulsed and continuous wave (CW) operating mode were determined to be 275 K and 226 K, respectively. The threshold current density was around 17 A/cm² at 80 K with an emission wavelength of approximate 3.8 μm. We analyzed the self-heating effects under CW mode and further simulated the temperature contour by the finite element method. The results indicate that the self-heating effect is a critical factor that limits the operating temperature under CW mode for our devices. Further optimization of the heat dissipation performance would be an effective way to raise the operating temperature of the devices.

Abstract:1.55 μm AlGaInAs/InP quantum well lasers with low beam divergence are theoretically designed and experimentally fabricated. An asymmetrical mode expand layer (MEL) was inserted in lower cladding to expand near field intensity distribution and decrease internal loss. Simulation results showed that the use of MEL won’t influence the laser performance negatively but dramatically decrease the vertical beam divergence at the cost of slightly increase of threshold current. And the experiment results showed high agreement to it. With a 4 μm-wide and 1000 μm-long ridge waveguide laser with MEL, the threshold current and output power of single facet without coating is 56 mA and 17.38 mw@120 mA, and the slope efficiency is 0.272 W/A. The vertical beam divergence is 29.6° and decreases about 35.3% compared to that of typical lasers.

Abstract:The simulation of transverse field sweeping system (TFSS) for a 170 GHz, MW-class gyrotron with single-stage depressed collector (SDC) is presented in this paper. The adoption of SDC aims to recover part residual kinetic energy of spent electrons as well as to improve total efficiency exceeding 55%. Transverse field sweeping system is coming into use to expand the spent electron trajectory length to 1100 mm to keep the specific heat dissipation on the collector surface within technically acceptable limits. Furthermore the modulation depth of sweeping signal and the number of transverse coils are simulated to get an optimal result 38.9% and 6 leading to an acceptable peak averaged power density . In order to ensure the safety and feasibility in actual situation, the cooling system with axial groves for collector is also designed and the thermal and fluid analysis are carried out by commercial available software ANSYS. The maximum temperature of inner and outer collector surface are and respectively. The range of water temperature at the inlet and outlet are and respectively.

Abstract:A high efficiency 220 GHz frequency doubler based on discrete diodes is presented in this paper. This doubler is realized with a 50-μm-thick, 450-μm-wide, and 2.7-mm-long quartz substrate. The conversion efficiency is better than 16% over the frequency range from 214 to 226 GHz with pumping power of 46.4~164 mW at the indoor temperature. A peak output power of 32mW at 218 GHz with an input power of 161 mW, and several frequency points with efficiency high than 20% are realized. This doubler can act as the pumping stage of the 660 GHz multiplier chain.

Abstract:A bandwidth broadening and voltage reducing method for the azimuthal supported angular log-periodic strip meander line slow-wave structure has been proposed. By means of the vane-loaded technique to control the dispersion characteristics, the bandwidth of the azimuthal supported angular log-periodic strip meander line traveling-wave tube is expanded effectively. Through numerical simulation, it can be found that the 3-dB bandwidth of the structure without vane and with multi-vane loaded is 2.5 GHz and 3 GHz, respectively. The work voltage of the structure without vane and with multi-vane loaded is 5450 Vand 4650 V, respectively. As the results shown, the bandwidth and work voltage of the angular log-periodic strip meander line slow-wave structure can be expanded and reduced by means of vane-loaded method.

Abstract:On the basis of deadspace multiplication theory(DSMT) numeric model and modified deadspace multiplication theory（MDSMT）model, excess noise of multi-gain-stage avalanche photodiodes with different multiplication stage and different carrier initial energy was analyzed. The effect on excess noise of different width of impact-ionization multiplication layer and electron-heating layer and different doping of electric field control layer was also studied. At the same time, the results obtained from DSMT model were compared to with the results from Van Vliet model and McIntyre model. By adjusting the width of impact-ionization multiplication layer and electron-heating layer and the doping of electric field control layer, a structure relatively optimizing was acquired by DSMT numeric simulation, the result of excess noise on of which were was comparable to the result of Van Vliet model at k_s=0.057.

Abstract:three kinds of polarization beam splitters can be designed by using a simple metal-dielectric multilayered structure with strong nonlocality,. It is found that the equal frequency contour for the transverse electric polarization is a small circle when the average permittivity is close to zero. At the same time, the equal frequency contour for the transverse magnetic polarization turns be two branches of parabolas due to surface plasmon-induced nonlocal effect. Based on the dramatic difference between dispersions of the two polarizations, three kinds of polarization beam splitters are demonstrated, including the ultrathin ones, which may have important applications in polarization-sensitive absorbers and compact optical devices.

Abstract:Here is a transmitter for an oxygen-band differential absorption lidar that is tried for atmospheric pressure detection experiment. The laser transmitter is based on the structure of a seed-injected optical parametric oscillator and an optical parametric amplifier. As a slave oscillator, a ring cavity KTP optical parametric oscillator is used. As the master oscillator, is a continuous wave external cavity diode laser. Operating wavelength of the continuous wave external cavity diode laser was stabilized, by a PID (Proportional-Integral-Derivative) servo control loop composed of a high-precision wavelength meter. A continuous wave seed laser is injected into the optical parametric oscillator cavity, and the cavity length of the OPO (Optical Parametric Oscillator) resonator is locked by the “Ramp-Hold-Fire” technique. This laser transmitter has been proven to have the following properties: high optical frequency stability (30 MHz/rms), narrow linewidth (Fourier transform limited), and high pulse energy (≥45 mJ),which can be maintained during operation. The transmitter system operates with a single longitudinal mode, making it possible for differential absorption lidar to detect narrowband backscattering signals. Such systems therefore have the developing potential to accurately measure atmospheric pressure.

Abstract:In this study, a metal-topological insulator-metal (MTM) structure terahertz photodetector was fabricated based on a two-dimensional topological insulator Bi₂Te₃ material using a micro-nano process. The responsivity of device reaches 2×10³ A/W at 0.02 THz, the noise equivalent power (NEP) is lower than 7.5×10^-15 W/Hz^1/2, and the detectivity D* is higher than 1.62 ×10¹¹ cm?Hz^1/2 /W; The responsivity is up to 281.6 A/W at 0.166 THz, NEP is lower than 5.18×10^-14 W/Hz^1/2, D* is higher than 2.2×10¹⁰ cm?Hz^1/2/W; The responsivity is up to 7.74 A/W at 0.332 THz, NEP is lower than1.75×10^-12 W/Hz^1/2, D* is higher than 6.7×10⁸ cm?Hz^1/2 /W; at the same time, the response time of device has 7~8 μs in the terahertz band. This work breaks through the inter-band transition of traditional photon detection, and realizes terahertz detectors with room temperature operation, high response rate, high speed response and high sensitivity.

Abstract:Hyper-spectral Atmospheric Infrared Sounder (AIRS) mainly covers the CO₂ and H₂O absorption bands. Different from CO₂ channels, the brightness temperature bias of water vapor channel follows non-Gaussian statistics. In order to use AIRS channel spectral information effectively, new algorithm research is needed, two methods are presented in this paper: (1)Different from the observation error of the given spectral channel remains unchanged during the classical variational assimilation minimization iteration, the paper based on the posterior estimate of variational assimilation, namely, observation error re-estimation, re-estimating the channel observation error, which is then regarded as the weight of observation to the objective function of classical variational assimilation; Observation error re-estimation can be used to identify the reasonable observation errors which can fit variational assimilation model better. By using the weight function of M-estimators (L2-estimator, Huber-estimator, Fair-estimator and Cauchy-estimator) to couple the classical variational assimilation, and then obtain the generalized variational assimilation, make it Non-Gaussian. Re-estimated the contribution rate of observation terms to the objective function during each minimization iteration. The simulated brightness temperatures of AIRS are used to conduct ideal experiments. It is show that two methods of observation error re-estimation and Huber-estimator can provide better results than the classical method. We diagnose the impact of observations on the analysis with degrees of freedom for signal (DFS). The result of diagnosis shows that two methods can increase the available information of brightness temperatures of water vapour channels during the assimilation process. Furthermore, the analysis field obtained by using the algorithm (observation error re-estimation and Huber-estimator) in this paper is compared with the temperature field of sounding data, and it is obtained that the Huber-estimator, which generalized scale is set as 1.345 K with the best effect, which is set as 2.5 K latter, and the observation error re-estimation is better than classical variational assimilation. The effect of 200~750 hPa was relatively significant. The retrieval temperature at the surface and around the tropopause (80~200 hPa)is less than 2 K based on Huber-estimator variational assimilation. The results of this paper can lay the theoretical foundation and provide the algorithm reference for the variational assimilation of hyper-spectral data of Feng-Yun 4A and Feng-Yun 3D satellite.

Abstract:This paper presents a model for extrapolating flux from cross-matching multiple catalogues combining the data of IRAS, WISE and 2MASS, which used the Planck’s law to extrapolate flux to every band. The model simplifies the extrapolation process, and improves the extrapolation efficiency with a high precision of 3% for 70% of the stars. Our finding is in agreement with the independent long-term observation of the Vega and Sirius star reported by Cohen et al. According to the extrapolation results, more suitable multiple data of stars could be selected for star calibration.

Abstract:Based on the platform of typical SLR system, according to generation flow of SLR measurement data, extracting the difference between satellite measurement and calibration, measuring and analyzing the influence of various factors due to range bias of SLR measurement data, and technical approaches to improve the stability of SLR measurement data is provided in the paper. After applying the above research results, the long-term stability, short-term stability, and normal points accuracy of Lageos satellite at Shanghai SLR station, have been decreased from 12.7 mm, 22.7 mm and 2.0 mm in 2014 to 4.1 mm, 9.3 mm and 1.0 mm in 2015 respectively, which firstly reached the data quality standards of ILRS (10 mm, 20 mm, and 5 mm) in China ,and also improve international position in the field of SLR and the weight of observational data, with good prospects for promotion and application.

Abstract:We have demonstrated a compact, high-energy and broadly tunable monochromatic terahertz (THz) source with the dimensional size of 40 cm×25 cm, based on difference frequency generation (DFG) in DAST crystal, grown in two-zone growth method. The THz frequency was tuned randomly and rapidly in the range of 0.3~19.6 THz due to the widely tunable KTP-OPO and galvano-optical beam scanner. The highest pulse energy of 4.02 μJ was obtained at 18.6THz in our system. And the highest signal to noise ratio of 32.24 dB was realized at 4.3 THz using 4K-Bolometer detector. Furthermore, the characteristics of THz polarization and divergence angle were measured experimentally. Saturation phenomenon for THz output was observed and studied. Moreover, the transmission THz spectroscopies of materials in solid state were measured with the ultra-wideband tunable THz source based on DAST crystal.

Abstract:After comparing wide-band antenna and narrow-band antenna, a dual-frequency Terahertz antenna for wireless communication was designed. It consisted of two dipole antennas which are located on two different layers and arranged vertically to avoid connection and interaction. The two dipoles both had THz chokes to improve performance, and different sizes to operate in two different frequencies. The upper dipole use metal probe to connect the LT-GaAs substrate through the hole of substrate, and share the same photomixer with the lower dipole. The photomixer can be lighted by the same light for pumping, while the two dipole can be controlled by different circuit for bias. So they can work at different frequency and vertical direction of polarizations. They can adjust for the air’s low-loss frequency by changing the size. The dual-frequency antenna had high performance because of containing two dipole antennas. At the air’s low-loss frequency of 0.21THz, 0.35 THz, 0.41 THz, 0.68 THz, 0.85 THz and 0.93 THz, it had total efficiencies of 14.9%, 28.4%, 33.9%, 28.4% and 21.6% respectively, and max realized gain of 2.99 dB, 10.6 dB, 11.8 dB, 18.4dB, 18.2 dB and 18.3 dB respectively.

Abstract:A Mach-Zehnder modulator based on photonic crystal and nanowire waveguide is proposed. The modulator consists of silicon-based photonic crystal slab waveguides, nanowire waveguides, and two photonic crystal multimode interference couplers (MMI). Designed tapered structures are working at the junction of the photonic crystal and the nanowire waveguide to reduce the loss caused by the mode mismatch. The simulation analysis by time-domain finite difference method (3D-FDTD) shows that the insertion loss and extinction ratio of the modulator with a compact size of only 46μm × 8μm × 0.22μm at the operating wavelength of 1550 nm are 0.3dB,15.1dB,respectively. The operation with a wavelength range of 20 nm are obtained at a center wavelength of 1551 nm.The 3dB bandwidth can reach 68 GHz,which allows high speed optical communication systems.

Abstract:In this paper, a thermodynamic analysis on current photovoltaics wsa given within the Shockley-Queisser model. Then the latest progresses of designing semiconductor nanowire arrays are introduced to achieve effective light trapping and reduced emission angle. Among them, non-uniform nanowire arrays with gradient shapes hold both advantages of ultralow emission angle and light trapping, therefore has attracted much research interest toward ultrahigh efficiency of solar energy conversion from visible to near-infrared wavelength.

Abstract:This paper focuses on the problem of low detection accuracy and low pixel image extraction accuracy of traditional small target detection and ship detection methods. An improved target detection algorithm based on constant false-alarm rate（ CFAR ）- dense conditional fandom fields （ DCRF）is proposed. The algorithm is based on the characteristics of small target and false alarm signal changes but different structural features. It uses the advantages of conditional fandom fields (CRF) multi-dimensional context (space, radiation) to achieve false alarm feature suppression, and introduces CFAR to improve the model and improve DCRF. Based on this model, experiments were performed under different conditions. The analysis results show that the algorithm can make full use of the global context information of the sea area, and can reduce the false alarm rate while maintaining a high detection rate.

Abstract:In order to study the noise characteristics of InGaAs focal plane arrays (FPAs), the 160×128 FPAs based on different absorber concentration materials with the same circuit structure were designed and prepared, and the noise characteristics at different temperature and integral time were tested. By studying the relationship between different material parameters, device performance and focal plane noise, the noise characteristics of short-wave infrared InGaAs FPAs are analyzed quantitatively. The results show that the noise mainly comes from the coupling noise of the focal plane and the noise of the detector. The detector noise is influenced by the dark current and operating temperature of the detector, which determines the total noise level of the focal plane in the long integral time. To manufacture photodetectors with low dark current and low capacitance is an effective way to reduce the focal plane noise.

Abstract:A several photons high accuracy multi-beam three-dimensional imaging Lidar system based on 8×8 array SiPM (Silicon photomultiplier) was introduced. The theoretical calculation and system design of laser ranging were given. According to the 64 laser beam transmitted in parallel, fiber array was used to realize the alignment of laser beam and detector. The off-axis three-mirror optical transceiver system, ultra-narrowband filter structure and 64-channel high-speed parallel readout circuit were designed, and a prototype of Lidar was built. Experimental verification result indicates that 64 channels are in good uniformity under static 21 m ranging, ranging accuracy is 1 cm and maximum distance deviation is 6 cm. In three-dimensional, imaging resolution is 512×512, imaging time is 100ms, different targets of 15 cm can be distinguished, and the thickness of plane is 5 cm.

Abstract:In order to increase the swath width and reduce the volume of hyperspectral remote sensing instruments, the compact, long-slit Wynne-Offner spectrometers suitable for wide swath width were detailedly studied. By tracing the chief ray, expressions of the astigmatism were deduced, and the astigmatism of the Offner configuration and the Wynne-Offner configuration were analyzed. It was pointed out that the anastigmatic circle domain of the Wynne-Offner configuration is larger than that of the Offner configuration, and the former was more suitable for long slit. Two examples of spectrometers were given. Length of their slits are both 70 mm, and they worked in the wavelength range of 0.5~1.0 μm and 1.0~2.5 μm respectively. The imaging quality was close to the diffraction limit, and the spectral distortion was negligible. Such Wynne-Offner spectrometers have the advantages of long slit, compact structure and high imaging quality, and it is really suitable for the remote sensing applications with wide swath width.