Abstract:The 13th International Conference on Mid-Infrared Optoelectronics: Materials and Devices (MIOMD-XIII) full pdf

Abstract:A novel electrode structure for mesa-arrayed infrared detectors is proposed. A relayed electrode at the bottom of the trench is realized by depositing the electrode twice separately. Comparing with the traditional extended electrode, the novel electrode structure is not only beneficial to simplify the electrode introducing at the bottom of the trench out from the bottom to the top of the trench, but also capable of enlarging the top area on the mesa arrays for other processes and enhancing the structural integration correspondingly. The height and morphology of the relayed electrode were not changed after experiencing 200 W ultrasonic treatment for 5 mins. As shown in the cross-sectional SEM pictures of the flip-chip bonded devices, the relayed electrode at the bottom of the trench connected into a whole and reached the metallization pads on the other side. These results indicated that this new electrode structure can be applied to the mesa-arrayed infrared detectors.

Abstract:Terahertz (THz) detector work at room temperature could greatly expand the application of THz science and technology. Ultra-thin(10μm)lithium tantalate crystal (LiTaO3) material was used as sensitive layer of the detector. The responsivity could reach up to 8.38×104V/W and the noise equivalent power (NEP) could be as low as 1.26×10-10W at 20Hz operating frequency by laser radiation source at 2.52 THz. Furthermore, this processing method to fabricate the ultra-thin LiTaO3 crystal material could potentially provide a feasible approach for even higher response terahertz detectors.

Abstract:A broadband spectroscopy of anti-resonant waveguides in the terahertz region was investigated. The broadband spectral transmission properties of a poly(methylmethacrylate) (PMMA) pipe waveguide, a PMMA self-supporting waveguide, and a SiO2 pipe waveguide were studied using terahertz time domain spectroscopy (THz-TDS). The existence of the anti-resonance phenomenon was demonstrated. Additionally, the PMMA self-supporting waveguide has been experimentally shown to realize transmission bandwidth of over 2 THz without dip frequencies. Also, based on the anti-resonance mechanism, the dielectric pipe waveguide was successfully used as a terahertz refractive index sensor for liquid sensing, which offers a possible method for materials detection.

Abstract:Adopting the capacitive coupled matching structure, a Ka-band wideband three-stage power amplifier (PA) MMIC was designed by 0.1μm GaAs pHEMT process in this paper. To facilitate the design of wideband PA, a set of formulas was proposed to analyze this matching structure. This structure achieves wide operating band and high power-added efficiency (PAE) simultaneously in the presented PA. The measured saturation PAE is upon 30% over 32~40 GHz with 20 dBm output power and more than 15.5 dB power gain, which demonstrates the effectiveness of this design skill.

Abstract:Scaled AlGaN/GaN heterostructure field-effect transistors (HFETs) with a high unity current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) were fabricated and characterised on an SiC substrate. In the device, the source-to-drain distance (Lsd) was scaled to 600 nm using regrown n+-GaN Ohmic contacts. In addition, a 60-nm T-shaped gate was fabricated by self-aligned-gate technology. A recorded drain saturation current density (Ids) of 2.0 A/mm at Vgs=2 V and a peak extrinsic transconductance (gm) of 608 mS/mm were obtained in the scaled AlGaN/GaN HFETs. Moreover, in the devices with a 60-nm T-shaped gate, the maximum values of fT and fmax reached 152 and 219 GHz, respectively.

Abstract:In this paper, we present the design, numerical simulations and analysis of a metamaterial absorber with two broad and flat absorption bands, including a cavity resonance band and an electrical resonance band. The electrical resonance band reveals a blue-shift with the width of cavity (d) or spacer thickness (H) increasing, while the cavity resonance band exhibits a red-shift with d or H increasing. Furthermore, electrical and cavity resonance bands can be coupled together at the same resonance wavelength to realize a single absorption band through optimizing the structure design. Finally, the effects of the variation of angles of incidence on electrical and cavity resonance bands were simulated. This method of utilizing different resonant modes for absorption bands at different wavelengths offers a simple approach to modulate dual absorption bands to single absorption band.

Abstract:Considering the difficulty and complexity in adjusting the terahertz (THz) response of the traditional metamaterials (MMs), we proposed a novel method to adjust the THz response characteristics of MMs. Our MMs possess the same structural and material parameters as those of the traditional three-layer MMs, but differently, an additional metal strip is introduced in the middle dielectric layer. Through changing the position and line width of the additional metal strip, the response frequency and absorption for incident THz wave can be effectively adjusted. Results show that if the additional metal strip moves from near the bottom metal to the surface metal, the response frequency is red shifted. If the additional metal strip is located in the middle of the dielectric layer, the absorption reaches maximum (99.98%). If the width of the additional metal strip is enlarged, the response frequency is red shifted, and the absorption is increased. In addition, if the incident angle is ≤45o, both the central response frequencies of the traditional and novel MMs remain stable, and their absorptions are high. However, if the incident angle is >45o, their central response frequencies blue shift, and their absorptions decrease significantly. According to this novel method, the THz responses of MMs can be effectively adjusted, and the complex process for designing the MM structure can also be thus avoided..

Abstract:To enhance quantum efficiency of infrared detectors made of PtSi Schottky barrier, the flat interface of PtSi/p-silicon metal semiconductor was modified to a grating structure. The incident radiation can be coupled with the surface plasma waves within this structure, thus to improve the optical coupling efficiency of the PtSi infrared detector. Based on rigorous coupled-wave analysis method, parameters of the grating structure were optimized and electric field distributions at resonant wavelength were simulated. The quantitative relationship between the optical coupling efficiency and quantum efficiency of PtSi Schottky barrier infrared detector was discussed. Comparing with the flat structure, the average quantum efficiency is evenly increased twice in 3~5 μm wavelength range, and approximately 2.94 and 2.5 times at 3 μm and 3.4 μm, respectively.

Abstract:A new compact polarized spectrometer is reported and implemented. An array consisting of two spectrometers is employed in the proposed polarized spectrometer to enable the measurement in the entire visible spectral range, which is necessary for the measurement of different sample types. Only one polarization optical element is used in the optics system with the partially parallel optical path design, which significantly simplifies the configuration and calibration of the system. The compact polarized spectrometer utilizes the incident plane rotating effect to modulate the polarization state in space domain, which consequently reduces the measurement time. The accuracy of the proposed compact polarized spectrometer is demonstrated by measuring test samples with different thicknesses. In consideration of the advantages, such as fast speed, compact and concise structure, eases integration, the proposed instrument shows great potential to be a powerful tool for on-line measurement in thin film manufacturing.

Abstract:An efficient single-photon detector was realized using high-speed diode to eliminate the spike of InGaAs/InP avalanche photodiode (APD). The repetition rate of the single-photon detector reached up to 700 MHz. With the APD operating at the temperature of 218 K and the detection efficiency of 10%, we demonstrated that the typical dark-count and after-pulse probability was 7×10-6/pulse and 74%, respectively. This scheme provides a simple and robust method to realize high-speed single-photon detection.

Abstract:Satellite polarimetric observation is an important approach for remote sensing of atmospheric aerosols. The validity and adaptability of aerosol type model is one of key factors affecting polarimetric remote sensing of aerosol properties. For an aerosol retrieval algorithm, either neglecting coarse mode aerosols (one of common assumption of aerosol retrieval from satellite polarimetric sensors) or employing incorrect aerosol types can bring errors to the retrieval results. In this paper, the influence of aerosol modes and choice of aerosol types (six typical types: desert dust, biomass burning, background/rural, polluted continental, polluted marine, and dirty pollution) on the retrieval of aerosol optical depth (AOD) were investigated based on near-infrared polarized satellite channel at 865 nm. Based on the vector radiative transfer simulation results, the atmospheric bidirectional polarized reflection distribution functions (BPDF) of the above six aerosol types at 865 nm were analyzed. The results demonstrate that atmospheric BPDF depends greatly on aerosol particle’s size, while influence of coarse mode on atmospheric BPDF is much smaller than that of fine mode. Compared with the atmospheric BPDF associated with only one fine mode, the BPDF associated with both fine and coarse modes shows smaller BPDF. With these simulation results, AOD retrieval errors were analyzed under two circumstances, neglecting coarse mode aerosols and employing an incorrect aerosol type. The results show that: (1) Neglecting coarse mode can lead to underestimation of the retrieved fine mode AOD (AODf). The AODf errors are in the range of -12.3% to -35.7% for different aerosol types. The maximum AODf error associates with desert dust aerosol type while the minimum with polluted continental type. (2) The use of an incorrect aerosol type can bring large AOD retrieval error, which depends on bias of atmospheric BPDF related to the incorrect aerosol type. Among all six aerosol types, the maximum BPDF difference occurs between desert dust and dirty pollution aerosol types, which yields the maximum AOD retrieval errors of -60.6% and 220.3%, given mischoosing one versus another. The minimum AOD retrieval errors can be -3.0% and 7.1% occurring between background/rural and polluted continental types, which have the smallest BPDF difference. The results of this study can help to develop the next generation spaceborne polarimetric sensors and corresponding aerosol retrieval algorithms.

Abstract:The VCSEL devices with high peak power at 980nm and miniaturized laser source were reported. The structure of VCSEL element devices was optimized to eliminate the non-uniform current density distribution within the VCSEL’s active region and therefore to enhance the slope efficiency. The peak power with a value of 62 W was achieved from VCSEL element deivce with 400 μm-diameter-active region. Based on the optimized element devices, VCSEL quasi array sub-mount and miniaturized laser source integrated with pulse generator circuit was demonstrated. Under the driving condition of 30 ns、2 kHz、105 A, the peak power as high as 226W was achieved. The laser pulse width, laser wavelength and the slope efficiency of the laser source were 35 ns, 979.4 nm and 2.15 W/A, respectively.

Abstract:Based on the canopy hyperspectra and derivative spectra of typical hardwoods in Mudan valley, Changbai Mountain, red edge characteristics were used to determine leaf coloring date and to establish regression models of spectra and leaf coloring date. The results show that the canopy hyperspectral reflectance can accurately reflect the change of vegetation autumn leaf coloring date. The states of the leaves of typical hardwoods can be divided into three categories: the dry leaves not falling after leaf coloring date, the leaves falling out before leave full coloring date, and the leaves falling after leaf full coloring date. The first derivative spectral curves and hyperspectral curves take clear advantage over the specific date of leaf first coloring date and leaf full coloring date. The variances of inversion models of red edge parameters and leaf coloring date are all above 0.9, and each vegetation is suitable for different forms of fitting equation. The research shows important theoretical significance and extensive application prospect on using quantitative remote sensing to monitor mountain autumn phenology.

Abstract:With a priori information of the known endmembers in hyperspectral image, there is no closed-form solution of Least Square (LS) method for linear mixing model under the Abundance Non-negativity Constraint (ANC). So many iterations which may result in big computational complexity are needed in the traditional Fully Constrained LS (FCLS) methods to obtain the optimal solution. In this paper, an analysis of impacts on abundance estimation of hyperspectal image in different simplex shapes was implemented and a fully constrained linear unmixing method based on simplex regularization was proposed which could get optimal solution under limited iteration when the hyperspectral image was spanned into a regular simplex. The proposed method was carried out by three steps. Firstly, the simplex of hyperspectral image was regularized by the known endmembers’ whitening matrix. Secondly, the analytical solution of abundance coefficients was obtained under Abundance Sum-to-one Constraint (ASC). Then for every pixel, the FCLS solution was achieved by eliminating the endmembers with negative abundance coefficients and solving the ASC equation iteratively. Experiments on simulated and real hyperspectral images indicate that the proposed method can obtain consistent results with traditional FCLS method and decrease the computational burden efficiently.

Abstract:Traditional fire detection methods use the high temperature emission characteristics in mid or thermal infrared bands of the MODIS or AVHRR data to extract burning area. It is very hard for these methods to identify small fire regions such as sub-pixel due to the limitation of spatial resolution. Recently researchers have found that shortwave infrared (SWIR) data can also be used to identify and detect high temperature targets. Compared with the thermal infrared data, SWIR has a big discrimination against different features with different temperature. Thus it can identify accurately the location of high temperature targets. In this paper, we acquired fire point products by using Landsat-8 OLI data which has spatial resolution up to 30 m. The main procedure includes two steps. The improved Normalized Burning Ratio Short-wave(NBRS) is calculated at first to adaptively acquire suspected fire points based on the spectral characteristics of fire points in the near infrared and shortwave infrared. Then most false positive points are excluded based on the relationship between peak value in shortwave infrared band of fire points. This algorithm is capable of detecting the burning area around 10% in one pixel. With the premise of avoiding the interference of cloud and constructions, it can also keep a nearly 90% accuracy and low missing rate around 10%.

Abstract:Active microwave remote sensing and passive optical remote sensing have their own advantages and disadvantages in inversion of soil moisture. In order to combine the advantages of both of them to make up for shortcomings, a semi-empirical model based on Radarsat 2 data and Landsat 8 data has been presented for vegetation-covered soil moisture inversion. The model is based on water-cloud model with the vegetation water content estimated by the optical remote sensing as the key input parameter. Thus the influence of vegetation on the backscattering coefficient would be reduced. Combination of Radarsat 2 and Landsat 8 data were used to estimate the vegetation-covered soil moisture with the new coupling model in the studied area located in Eerguna City of Inner Mongolia, west of Greater Khingan. Then it was verified with the ground survey data. The research showed that the precision is high in the retrieval of vegetation water content (R2=0.89) using Landsat 8 data. The inversion accuracy of coupling model is higher than former algorithms. The R2 of HH polarization is raised from 0.27 to 0.65. These results showed that the proposed coupling model has a better inversion accuracy, and can be used in the inversion of vegetation-covered soil moisture.

Abstract:Land surface temperature and emissivity separation (TES) is a key problem in thermal infrared (TIR) remote sensing. However, because of the ill-posed problem and the at-ground radiance’s coupling with atmospheric radiance, the retrieval accuracy still needs to be improved. Through exploring the offset characteristic of atmospheric downward radiance, a temperature and emissivity retrieval algorithm based on atmospheric absorption feature was proposed from hyperspectral thermal infrared data by assuming that the land surface emissivity is equal between the adjacent channels. Furthermore, an optimal selection of channels was carried out to improve the efficiency and accuracy of method. The proposed method can reduce the influence of atmospheric correction error. The simulated results show that the accuracy is similar to the ISSTES method (Borel, 2008) for high emissivity materials. Furthermore, the proposed method can enhance the retrieval accuracy for low emissivity materials, that is approximately temperature 0.48 K and emissivity 2.1%. The results from the field measured data show that about 77% of the samples have an accuracy of LST within 1.0 K with the mean of LSEs lower than 0.01.

Abstract:Labeled Multi-Bernoulli (LMB) filter was proposed based on classic Multi-Bernoulli filter by taking label space into account. It is a true trajectory filter in comparison with other methods. The motion model and measurement model of infrared small targets were studied. The LMB Track-Before-Detect algorithm was applied to detect and track infrared small targets. In order to detect and track multiple maneuvering targets with time-varying motion models, an IMM-LMB Track-Before-Detect algorithm was proposed by integrating the interacting multiple models (IMM) with LMB Track-Before-Detect filter. The sequential Monte Carlo (SMC) implementation for IMM-LMB track-before-detect was also given. Simulation results demonstrate that the proposed algorithm can detect and track multi-targets trajectories from raw image. In addition, it can update the model probability in an online way, which detects and tracks maneuvering targets adaptively.

Abstract:In order to decrease the time and alleviate the smoothness of the adaptive sparse representation algorithm, a modified adaptive sparse representation algorithm based on difference threshold is introduced in this paper. This modified algorithm computes the difference between the current block and the previous one, then compares the difference with the threshold. When the difference is less than the threshold, the two blocks are considered having the same sparse representation vector and error. It is not needed to compute over current block again. When the difference is greater, they are considered as different. The current block contains the edge area and its position is recorded. It is then protected from averaging in reconstructing the result to alleviate the smoothness. The experimental results performed on millimeter-wave image demonstrated the effectiveness of the proposed method.