Abstract:GaSb-based InGaAsSb/AlGaAsSb type-I quantum-wells (QWs) laser diodes have been successfully fabricated. The wavelength is expanded to 2.6 μm with high output power. The device structures were grown by molecular beam epitaxy. Under the optimized QWs growth temperature of 500℃,the compressive strain of the QWs are defined to 1.3% for better optical quality. With a ridge width of 100μm and cavity length of 1.5 mm, the maximum output power of single facet without coating has reached up to 328 mW under continuous wave (CW) operation at room temperature and 700 mW under pulse condition. The threshold current density is 402 A/ cm2.

Abstract:A metamaterial band-stop filter in the Terahertz(THz) spectrum regime based on the semiconductor InSb is presented in this paper. The resonant frequency of the filter is thermally tunable due to the dielectric constant properties of InSb. Meanwhile, the effects of geometrical parameters on the performance of the filter were analyzed by the finite-integral method and equivalent LMC circuit method, respectively. The results of the two methods show good agreement with each other. The resonant frequency can be dynamically tuned across a wide band of frequencies from 0.91 to 1.28 THz in the temperature range from 220 K to 350 K, and the transmission coefficient at the resonant frequency in the stopband can be effectively suppressed. Good incidence-angle stability of the transmission characteristics up to an oblique incidence angle of 30° is demonstrated. The tunable metamaterial band-stop filter has the potential to be applied in the Terahertz wireless communication and sensing systems.

Abstract:The wavelength of the probe laser can affect the bandwidth and the efficiency of terahertz electro-optic sampling (EOS) detection method because of the relationship of velocity match between the terahertz phase velocity and the laser group velocity. An electro-optic (EO) crystal has different dispersion with different lasers, thus the wavelength of the probe laser for a given EO crystals have different influence on the EOS detection. The response functions of EOS systems based on two typical EO crystals, ZnTe and GaP, have been studied. The results show that the probe laser with wavelengths of 800 nm and 1200 nm are more suitable for the ZnTe-and GaP-based EOS system, respectively, than other selected wavelengths (600 nm, 800 nm, 1200 nm and 1600 nm). We also found that for a given thickness of an EO crystal, there exists an optimal wavelength for the probe laser pulse to obtain the broadest response function with high value.

Abstract:Single-crystalline Bi2Se3 and Bi2(TexSe1-x)3 nanowires were synthesized via Au catalytic vapor-liquid-solid (VLS) growth method. Electronic properties of the surface states in individual Bi2(TexSe1-x)3 (x=0.26) nanowire were studied by low-temperature magnetotransport measurement. Weak antilocalization (WAL) effect was found, suggesting strong spin-orbit coupling in our samples. It is indicated that the bulk effect can be suppressed effectively by the Tellurium (Te) doping. By fitting the magnetoconductance curves at magnetic field up to 7 T measured at different temperatures, the extracted dephasing length lφ decreases from 389 nm at 1.5 K to 39 nm at 20 K, which can be well described by the power law lφ∝T-0.96. It can be reasonably deduced that both the electron-electron scattering and the electron-phonon scattering play important roles in the Te-doped sample.

Abstract:We investigated the optical properties of AlN films with different thicknesses grown on sapphire by spectroscopic ellipsometry at different temperature. Based on a Tauc-Lorentz dispersion model, thickness and optical constants (the refractive index n, the extinction coefficient k) of AlN films were extracted by fitting the experimental data. Our results show that the refractive index of thicker AlN film possesses bigger values. Similar to the previous report, it was also found that the refractive index, the extinction coefficient and band gap of AlN films shift monotonously to lower energies (a redshift) with temperature increasing. Moreover, with rising temperature, varying the thicknesses of the films exhibits little influence on the shrinkage of bandgap but slight influence on the changes of the refractive index.

Abstract:GaSb based broad-area (BA) diode lasers with watt-class emission power and improved divergence were demonstrated using a fishbone shape microstructure. The influences of etching depth of microstructure on the emission and far-field performance were investigated. It was found that the utilization of microstructure was able to enhance the emission power evidently. Moreover, the deeply etched microstructure was more effective on the decrease of mode number and lateral far-field divergence. Compared with the device without microstructure, the deeply etched BA lasers show 57% decrease in the lateral far-field angle defined by the 95% power content, and the maximum continuous-wave (CW) output power exceeds 1.1 W.

Abstract:Infrared (IR) sub-imaging guidance technique, which combines the single detector and optical scanning device, is a transition from point-source detection technique to imaging guidance technique. Infrared rosette scan sub-imaging system (IRSSIS) is a class of sub-imaging guidance system. The IRSSIS samples part data of the field of view (FOV) according to a specific pattern and obtains a sub-image including the position information of targets. Compressive imaging in the IRSSIS was studied inspired by the single pixel camera. Compressed sensing (CS) will help to reconstruct IR image in the condition of much fewer samples. The key problem of CS applied to the IRSSIS is the measurement matrix construction. While random measurement matrix has been studied intensively, it is hard to implement. A simple deterministic measurement matrix was proposed for the IRSSIS. Furthermore, a fast and effective recovery algorithm, optimized subspace pursuit algorithm (OSP), was proposed. Simulation results show that the proposed measurement matrices can compress and reconstruct IR image prior to the random Gaussian measurement matrices and random Bernoulli measurement matrices. The proposed recovery algorithm also has a better performance.

Abstract:In this paper, we studied the relationship between dark current and baking time of mid-wavelength HgCdTe infrared photovoltaic detector. A simultaneous-mode nonlinear fitting program for n-on-p mid-wavelength HgCdTe infrared detector is reported. The curve-fitting model includes the diffusion, generation-recombination, band-to-band tunneling and trap-assisted tunneling current as dark current mechanisms. The dark current components and six characteristic parameters were obtained from the fitting of resistance-voltage(R-V) curves measured before and at different annealing time. The effects of annealing on the performance of the photodiodes were analyzed by comparing the characteristic parameters of devices at different annealing time.

Abstract:CdTe/ZnS composite passivation layers were grown with different processes, and the corresponding LW HgCdTe gate-controlled diodes were fabricated. The I-V measurement and analysis were carried out under different conditions for these devices. The results show that the polarity of the fixed interface charge is positive and interface charge density is high for the device prepared by the standard process. The large leakage current in the surface channel is formed under high reverse bias voltage, which has an important effect on the performance of the device. The fixed interface charge density is effectively reduced by improvement of the growth process of the passivation films, which changes the HgCdTe surface from weak inversion gradually to the flat band condition. The surface effect is effectively suppressed, thus the reverse characteristics of the device can be improved significantly. In addition, the number of interface traps has been greatly reduced for the device prepared by the optimized process condition, and the stability of the device is enhanced. There is no obvious change in R0A of the device with the gate voltage.

Abstract:Terahertz coded-aperture imaging is a novel imaging technique which follows the basic principles of optical coded-aperture imaging and microwave coincidence imaging. It is based on the modulation of the effective terahertz-wave spatial distribution, either amplitude or phase, over the illuminated area. The wave spatial distribution or illumination pattern is usually obtained by a reflecting antenna. Terahertz coded-aperture imaging has some significant advantages such as high frame rate, high resolution, and the ability of forward looking and staring imaging. Hence it has been regarded as one of the most important development trends of terahertz radars. In this paper, we at first introduce the proposition background of this new technique, and then expound its principles, research states of the art, an implementable setup and the key problems. Finally, the application fields including missile terminal seeking and security as well as anti-terrorism are discussed. We hope that this paper can provide some positive guidance for the study of terahertz coded-aperture imaging and the corresponding new terahertz radar.

Abstract:We experimentally investigated the thickness-dependent magnetoresistance properties of InSb films in the temperature range of 12～300 K. The samples were grown on semi-insulating GaAs (100) substrates by molecular beam epitaxy (MBE). It was observed that the thick InSb only can show the semi-classical B2 dependence magnetoresistance resulted from the Lorentz deflection of carriers. At the same time, we found that weak antilocalization (WAL) effect can be much enhanced by reducing the sample’s thickness(with the thickness ～0.1 μm). The thin sample’s WAL magnetoresistance plot can be well fitted by Hikan-Larkin-Nagaoka (HLN) model, which demonstrates that the obseved WAL effect for thin InSb is with a 2-dimension character, which can be associated with the surface/interface states of InSb.

Abstract:In this research, we designed an MWIR optical system, which is equipped with long focal length, large zoom ratio, axis-zoom and four fields of view. The optical system is composed of seven components, including a front fixing group, a zoom focus group, an intermediate compensation group, a rear fixing group, a first mirror, a second mirror and a relay group. The optical system uses optically compensation superposition mechanical compensation method to improve the major flaws existing in previous similar optical system, that is, the single optically compensation or mechanically compensated zoom optical system cannot meet the followed requirements at the same time. The requirements includes long focal length, large zoom ratio, compact optical system, and temperature compensation for optical system under wide temperature range (-40 to 70℃), etc. The improvement achieved long focal length, large zoom ratio, axis-zoom and four fields of view. The improved design results show that the image quality of the optical system is perfect, and it can meet the requirements of the thermal imager.

Abstract:Novel spiral-shaped metamaterial absorbers (MAs) were designed. Different from the traditional MAs, the THz responses of the as-designed MAs can be effectively adjusted by altering the number of the spirals and their locations, in which the functional materials and their thicknesses remain unchanged. Results reveal that the response frequencies obtained by CST simulations agree well with those theoretically estimated by standing wave formula, suggesting high predictability of the response frequency for such MAs. In order to better understand the response mechanism of the spiral-shaped MAs, ring-shaped and split ring-shaped MAs were simultaneously investigated. Simulation results indicate that these MAs exhibit some similar response properties. However, different from the ring-shaped and split ring-shaped MAs, the as-designed spiral-shaped MAs exhibit stronger coupling effect and easier adjustment, largely due to the continuous alteration in the spiral radius for the latter. These results are helpful for promoting the theoretical study and design of metamaterials.

Abstract:The present infrared imager with unit or line detector cannot obtain wide field with high spatial resolution and high temperature sensitivity at the same time. To solve this problem, a set of wide field thermal infrared imager was developed based on uncooled array infrared detector. The system can realize the 75 ° large field of view, 0.4 mrad spatial resolution and 50 mk (NEΔT) temperature sensitivity. Furthermore, a geometric distortion correction model of array sweeping images was established to solve the low location accuracy and image mosaic crack problems.

Abstract:A reflection-mode controllable partially polarized infrared light source was designed to calibrate infrared imaging polarimeters. Theoretical calculation and measurement were carried out to verify the results. First, a theoretical calculation method was developed to calculate the polarization states of the output light based on the Mueller matrix of the aluminum coated flat mirror. Calculation results show that the output light is partially polarized with the degree of linear polarization (DoLP) smaller than 0.80 and the degree of circular polarization (DoCP) smaller than 0.60. Then a long wavelength infrared (LWIR) imaging polarimeter was employed to measure the real polarization states of the output light. Experimental results show that the output light is partially polarized with the DoLP within a range of 0.25 and 0.85 in LWIR. The relative standard deviation of DoLP is less than 6% when the incident angle for the flat mirror is less than 80°.

Abstract:In this paper, based on two-dimensional square lattice photonic crystal and twelve-fold Stampfli-type photonic quasicrystal (PQC), a single-ring-cavity add-drop filter and a double-ring-cavity-cascade add-drop filter are proposed. The dependence of the transmission efficiency of the two filters on the radius and the refractive index of the dielectric rod in the PQC were analyzed and compared. The dependence of the quality factor of the two filters on the radius and the refractive index of the dielectric rod in the center of the ring-cavity were also analyzed and compared. The results show that the performance of the double-ring-cavity-cascade add-drop filter is better than that of the single-ring-cavity add-drop filter. The research results will be helpful for the design and the fabrication of the high-quality add-drop filter devices.

Abstract:Semiconductor lasers with broad spectra are crucial for sensing, spectroscopy and biomedical imaging, etc. Currently, the broadband semiconductor lasers are majority based on the broad gain material and total interface reflection (TIR) waveguide. It is still a challenge to realize the broadband semiconductor lasers based on the simple and mature quantum well (QW) material. In this paper, a new type broadband QW laser using Bragg reflection waveguide with a deviation angle from cleaving crystal faces was demonstrated. The device consists of the InGaAs/GaAs QWs, top and bottom Bragg reflectors. It was found that it shows the characteristics of superluminescent diode (SLD) with a spectrum width of 135 nm for the device with a deviation angle of 7°. The spectrum width of 33.7 nm was achieved with an emission power of 36 mW from one facet for a deviation angle of 4.4°. This work supplies a new possible approach for the development of high performance QW broadband lasers.

Abstract:With the maturity of millimeter-wave devices, millimeter-wave imaging radar has been applied to human security check. However, the localization of forbidden objects in millimeter-wave images is still a difficult task, which greatly limits the application of millimeter-wave imaging radar. This paper adopts convolution neural network (CNN) to automatically localize forbidden objects, such as guns and knives, in millimeter-wave images. A sliding window is applied to slide over the input image. Then the probability of the existence of forbidden object in the image patch can be obtained via CNN. The image patches are overlapped with each other, and the probability values of all image patches are accumulated to obtain the probability accumulation map (PA-map). The PA-map reflects the position of forbidden objects. Due to the application of CNN and PA-map, this method achieves a high accuracy of localization in the experiment, which verifies the effectiveness of this method.

Abstract:In the experiment of HfO2/SiO2 coatings damaged by femtosecond single pulsed laser, the evolution of coating ablation along with increase of the laser energy was observed. The research shows that coating defects even in nanoscale can induce local light field intensification, which superposes on the interference field. As a result, the coating damage in threshold phase is mainly controlled by the particle defects even when irradiated by femtosecond laser. Because of the intrinsic damage characteristic of femtosecond laser to the coating materials including the defects of even distribution, the damage thresholds of these coatings are relatively deterministic. With the increase of pulse energy, the outline of damaged area becomes clearer. In this condition, the contribution of interference field is increasingly dominant compared with the local light field caused by defects, and the phenomena of coating spalling cover up the impact of defects.

Abstract:Holographic radar is well suited for the detection of concealed weapons or other contraband carried on by persons since that radio waves are nonionizing, common clothing material penetrable, and can be reflected by the human body and any concealed items. Despite the theoretical potential of holographic radar to provide a useful detection technique, this is unlikely possible in crowd circumstances. The image tends to be blured by the combined effects of multi-targets and target-motion. This paper proposes an algorithm of holographic radar imaging based on range-doppler concepts, which has some advantage in multi-moving target compensation and rapid imaging. According to the symmetry between the time-sampling and the space-sampling, the process of deducing the range-doppler holographic radar imaging algorithm is also proposed in this paper, and simulations and examination results are given to show that this algorithm has the ability to get the multi-targets image rapidly.

Abstract:In the course of maritime search and rescue, infrared image captured by helicopter airborne infrared camera has a poor image quality because of the helicopter vibration, air turbulence, high speed flight and infrared camera sweeping. According to the imaging characteristics of the helicopter airborne infrared camera, a blind restoration method for blurry images based on noise analysis and sparsity regularization was proposed. Firstly, noise distribution in the imaging process is analyzed and the noise is pre-processed. Then, according to the sparse representation theory, sparse prior information of the edges in the images is used to guide the restoration of PSF. After that, we can obtain the target image through non-blind method. The target image will be used in the next iteration. The iteration will not end until a clear image is obtained. Experiments were performed both on simulated blurry images and real blurry images. Experimental results show that our method can effectively improve the image quality.Compared with other methods, our method has a better effect on real blurry images.