Abstract:Due to metallic ohmic loss， plasmonic waveguides usually have larger propagation loss. Here， an all-dielectric antislot waveguide was proposed， which can realize subwavelength mode confinement and theoretically lossless propagation simultaneously. A normalized mode area of 3.4×10^-2 was achieved in the all-dielectric antislot waveguide. Moreover， an efficient coupling scheme between the small-size antislot waveguide and input/output fiber was proposed. An overall coupling efficiency of 92.7% was attained. The misalignment tolerance for 1 dB loss penalty was about 2 μm in both y and z directions.

Abstract:In this paper， the trade-off between gain-bandwidth product （GBP） and dark current of an InAlAs/InGaAs avalanche photodiode （APD） was studied by optimizing multiplication layer. An optimized multiplication layer with 200 nm was proposed to improve the GBP and reduce the dark current. The fabricated InAlAs/InGaAs APD shows an excellent performance which is consistent with the calculated results. A high responsivity of 0.85 A/W （M=1） at 1.55 μm and a high GBP of 155 GHz was achieved， whereas the dark current is as low as 19 nA at 0.9 V_b. This study is significant to the future high-speed transmission application of the avalanche photodiodes.

Abstract:In order to obtain high power， narrow line width and near diffraction limit output semiconductor laser diodes， the high order Bragg gratings （HOBGs） and master oscillator power-amplifier （MOPA） have been fabricated in the waveguide of HOBGs-MOPA laser diodes with an emission wavelength of 980 nm. The longitudinal mode of HOBGs-MOPA was selected by the HOBGs with a period of 11.37 μm. The single-mode optical power is amplified by a tapered waveguide with an angle of 6°. In this paper， we present a single mode laser diode with continuous wave power 2.8 W at a 3 dB line-width of 31 pm. The laser diode operates in a close to diffraction-limited optical mode （M ²=2.51， laterally）.

Abstract:The epitaxial growth of GaSb on GaAs substrate was studied by using interface mismatch arrays （IMF）. The effects of growth temperature， Sb： Ga effective atomic flux ratio， thickness of AlSb transition layer and GaSb epitaxial layer on the structural quality of the material were studied. High Resolution X-ray Diffraction （HRXRD） study shows that the FWHM of the diffraction peak measured by HRXRD was very sensitive to the changes of above parameters， while the effective atomic flux ratio （EFF） of Sb： Ga was the most important factor. The FWHM value of GaSb diffraction peak changes slightly with the increase of thickness， but the structural quality of GaSb layer improves with the increase of thickness. The results show that the optimum growth temperature of GaSb is 515℃， the optimum thickness of AlSb transition layer is 5 nm. The 10 nm thick GaSb epitaxial layer was prepared and characterized specifically. The results show that the FWHM value of the diffraction peak is only about 15 arcsec， which is equivalent to that of commercial GaSb substrate. The electron mobility of the quantum Hall device is as high as 1.5×10⁵ cm²/Vs at 1.8 K under zero bias， which attains to the level of device performance on GaSb substrate.

Abstract:A millimeter wave equivalent circuit model parameters extraction method for Schottky diodes is proposed in this paper. The pad capacitance has been determined by using open circuit test structure， and the feedline inductance has been determined by using short-circuit test structure. The parasitic resistance has been extracted by using DC method and AC method respectively. An excellent fit between measured and simulated S-parameters in the frequency range of 1～40 GHz is obtained for GaAs Schottky diode．

Abstract:The concealed object detection in millimeter wave （MMW） image is of great significance in non-contact body inspection. At present， MMW radar has been able to obtain 3D images， which are simply compressed into 2D images in current methods in general. However， such a rough processing does not take the information along the depth direction into account which results in a bottleneck of detection accuracy. To address this issue， a novel framework for MMW image concealed object detection is proposed， in which a 3D image is regarded as a sequence of 2D cross-sectional images and the most of the internal logic relations of features in the crosss-sectional images can be explored along the sequential direction， i.e. the depth direction of the 3D image. The framework consists of a Convolutional Neural Network （CNN） and a Long Short-Term Memory （LSTM） network. The former is used to extract the multiscale features in each 2D cross-sectional image while the latter is used to explore the global correlation of the above features along the depth direction to achieve feature-level information fusion and improve the accuracy of 2D location prediction. Experimental results show that the proposed method achieves remarkable results comparing to the known detection method based on 2D MMW images.

Abstract:A sub-harmonic monolithic mixer with a center frequency of 0.825 THz is developed based on GaAs monolithic microwave integrated circuit technology. The parasitic parameters of the anti-parallel Schottky diode at the terahertz frequency are analyzed to improve the circuit design. The monolithic circuit is suitable for terahertz devices with the characteristics of high integration and little fabrication deviation. Meanwhile， the beamlead circuit is used to reduce the loss of substrate and installation position offset. Measured results show that the single-sideband （SSB） conversion loss of the mixer is lower than 33 dB in the frequency range 0.81～0.84 THz， and the minimum SSB conversion loss is 28 dB.

Abstract:Based on TE₀₁ circular electric mode， the elliptical quasi-optical mode converter is studied， and a modified formula for rapidly designing elliptical-structure quasi-optical system is proposed. The quasi-optical system designed by the modified formula is composed of an elliptical Vlasov launcher and a quasi-paraboloidal mirror. The simulation results show that the beam launched by the elliptical system has the characteristics of better launcher directionality and lower side-lobe gain， and its size is smaller than the traditional circular system.

Abstract:Materials samples of some common military coating including radar absorbing coating， high emission infrared coating， radar absorbing and high emission infrared compatible coating， radar absorbing and low emission infrared compatible coating， and aviation anticorrosive coating are prepared and their emissivity at different observation angles in Ka band is measured in this paper. An improved measurement scheme based on voltage method is proposed and used for the measurement experiments， The measurement scheme can eliminate the errors caused by antenna sidelobe and thickness difference between sample and reference bodies. In addition， the main sources of measurement uncertainty are analyzed and discussed.

Abstract:Based on the theory of open resonant cavity and quasi-optical mode conversion， a high-order quasi-optical mode generator was designed and manufactured for the cold measurement of the gyrotron oscillator. For the high-order mode generator working at 140 GHz and TE_28，8 mode， the corresponding experimental measurements were completed using the three-dimensional mobile measurement platform and the network analyzer which were controlled by computer programming. The results show that， when the simulation results related to the resonant frequency， Q factor， and the correlation of the electric field distribution with the TE_28，8 mode in the cavity are respectively 140.179 GHz， 855， and 90.9%， the corresponding cold-tested ones for resonant frequency and Q factor are respectively 140.155 GHz and 876， and the transverse electric field distribution tested is very similar to that of the TE_28，8 mode. It indicates that the quasi-optical mode generator designed in this paper can provide an effective experimental platform for the research and design process verification of the high-order body mode gyrotron oscillator.

Abstract:Here， a graphene-black arsenic van der Waals heterostructure is fabricated by the fixed-point transfer technology， realizing the broadband detection from visible light-infrared-microwave. Among them， the photoexcited electron-hole pairs generated in the black arsenic are separated and injected into the graphene under visible and infrared light radiation， which significantly reduces the potential barrier between the semiconductor black arsenic and the gold electrode， thereby realizing effective photocurrent extraction. In the microwave band， due to the difference in the Seebeck coefficient of the two materials， the non-equilibrium carriers are generated due to the photothermoelectric effect， forming the photocurrent under zero bias. The research results paved the way for bandgap engineering of two-dimensional layered materials to be applied to the fields of photonics and optoelectronics.

Abstract:An innovative reflective near-infrared （NIR） fiber probe with flexibility and convenience was designed for biomedical in-situ detection. When the brand-new fiber probe structure and fiber arrangement were designed， further， a gradient-index （grin） lens was coupled to the top of the reflective NIR fiber bundles to make it have higher measurement accuracy and collection efficiency. When measuring NIR spectra of sucrose samples by coupling the grin NIR fiber probe to Fourier transform near infrared spectrometer， it was found that the grin NIR fiber probe had the advantages of convenience， high efficiency and spectral repeatability and SNR. The NIR spectra of articular cartilage at the femoral end of the canine knee joint were measured in situ by the grin NIR fiber probe and were preprocessed by first-derivative quadratic polynomials 21-point Savitzky-Golay smoothing for principal component analysis and Fisher discrimination analysis （PCA-FDA）. The correct recognition accuracies of PCA-FDA model in initial cases and cross validation cases were 97.62% and 90.47%， respectively， as well as 96.43% for the prediction set， which confirms the effectiveness of NIR fiber probe detection in situ and the feasibility of osteoarthritis recognition and lays the foundation for basic research and early clinical diagnosis of osteoarthritis.

Abstract:The phonon anharmonic effect caused by Sb in GaAsSb/InP heterojunction with different Sb components has been studied by measuring Raman spectra at 3~300 K. It is found that with the decrease of temperature， the peak position of long optical phonon moves to the high wave number， and the change tends to be gentle when the temperature is lower than 100K. The relationship between the optical phonon and temperature is simulated by using the three-phonon model and the four-phonon model， respectively. Compared with the experimental results， the four-phonon model agrees better with the experimental data， which indicates that the change of the temperature dependent Raman scattering peak position must consider the four-phonon anharmonic vibration. Compared with the lattice mismatched samples S1 （Sb=37.9%） and S3 （Sb=56.2%）， the phonon anharmonic obtained in the lattice matched sample S2 （Sb=47.7%） is the smallest， and the phonon lifetime in S2 is the longest by the study of phonon linearly. The phonon anharmonic effect and phonon lifetime of GaAsSb crystal lattice vibration are not only affected by the disordered scattering of the alloy， but also by the line defects and phonon scattering of the defects introduced by the mismatch with the substrate.

Abstract:Based on the characteristics of the FY-3 MERSI II images， an algorithm of independent sea ice segmentation based on U-ASPP-Net is proposed. The algorithm introduces the Atrous Spatial Pyramid Pooling module and Atrous Depthwise Separable Convolution on the basis of U –Net to develop a new independent sea ice segmentation network U-ASPP-Net. Meanwhile， FDWloss is used as the loss function at the back end of the network. Finally， the overlap elimination strategy is used to generate the final independent sea ice segmentation map. In order to verify the accuracy and effectiveness of U-ASPP-Net， U-Net， Deeplab v3+ and partition gradient difference and bimodal threshold segmentation method are selected as control methods for experiments. The experimental results show that the independent sea-ice fine segmentation method based on U-ASPP-NET is superior to the other methods in the four indexes of OA， Kappa coefficient， IOU， Dice coefficient. It has a strong ability to extract details and edges， and has a high degree of reduction to tiny sea ice. In addition， this algorithm can solve the problem of thin cloud interference that cannot be solved when extracting independent sea ice based on medium-resolution remote sensing images to a certain extent. It still has a good ability to extract sea ice under thin clouds and can provide more accurate technical support for the dynamic planning of the Arctic route.

Abstract:Based on the characteristic of anisotropic reflectance of nighttime TOA （top-of-atmosphere）， a new method was proposed to evaluate the accuracy of on-orbit radiometric calibration of nighttime sensors using a relative accurate simulation of the nighttime radiative transfer. Specially， the Antarctic Dome C site was selected as the study area， and the nighttime on-orbit radiance was simulated by the MT2009 （Miller-Turner 2009） TOA lunar irradiance model and TOA BRDF （Bidirectional Reflectance Distribution Function） model. After the analysis of the consistency of VIIRS DNB （Visible Infrared Imaging Radiometer Suit Day/Night Band） observed and simulated radiance under the same geometry， it was found that their differences were about 4.97×10^-10 W?cm^-2?sr^-1 one order of magnitude blow the minimum detection threshold of VIIRS DNB （3×10^-9 W?cm^-2?sr^-1） during 2018-2020. So there is good performance of on-orbit radiometric calibration of VIIRS DNB on SNPP and NOAA-20 based on the error range of acceptable instrument sensitivity. Besides， an evaluation of on-orbit radiometric calibration stability of VIIRS DNB was conducted based on the distance-corrected radiance of SNPP VIIRS DNB and NOAA-20 VIIRS DNB. And it was found that when under the same lunar phase angle， the VIIRS DNB radiance kept a good consistency within 6% between SNPP and NOAA-20.

Abstract:Chinese ocean color and temperature （COCTS） was interfered by the unknown radiation of cold space when the satellite of HY-1B was in orbit， which causes its nine-year data to be affected to varying degrees. Using data with less impact on the two poles as samples， the response repair model based on recalibration coefficients and the non-uniform correction model based on probability distribution were established to repair the earth target signal， and the repair results were compared and optimized. The accuracy and stability of model were verified. The final results show that under the condition of the cold space radiation benchmark affected， the response repair model combined with the probability distribution correction model can obviously repair the data effectively.

Abstract:Aiming at the phenomenon of non-uniformity change caused by on-orbit temperature change of the high-orbit area array infrared earth sensor， an optical-mechanical implementation scheme for on-orbit non-uniformity calibration is proposed. The miniaturized， lightweight， and long-life optomechanical system includes calibration blackbody components and optical imaging systems. The system includes surface source blackbody， motion control mechanism， and optical imaging system. Based on the analysis of the necessity and mechanism of system non-uniformity correction， the relationship between the selection and design of surface source blackbody， motion control mechanism and optical system is studied， and the simulation design of each group of components is realized. Based on the simulation results， the effects and advantages of system heterogeneity calibration are analyzed and compared. The effect of the heterogeneity of the system is evaluated by using the orbiting earth imaging data， and the evaluation results show that the requirements for on-orbit application are met.

Abstract:A high-refractive-index contrast subwavelength grating （HCG） for 940 nm GaAs-based VCSEL is reported. The reflector is composed of GaAs and AlO_x. The effects of the grating parameters of TE-HCG on refractivity are discussed in detail. And the structural characteristics of TE-HCG and TM-HCG are analyzed， especially the influence of their topography errors on the high reflection band. The 940 nm TE-HCG has a large reflection bandwidth of up to 97 nm with its reflectivity for TE incident light more than 99.5%， and the ratio of Ratio of high reflection band to central wavelength is more than 10%. But for TM incident light its reflectivity is less than 90%. It is worth mentioning that the VCSEL with such a TE-HCG can be prepared by one-time epitaxial growth technology， which helps to improve the performance of the device. Furthermore， it greatly reduces the manufacturing difficulty and cost of a VCSEL.

Abstract:InGaAs/InP avalanche photodiodes （InGaAs/InP APDs） are capable of detecting single photons in the near infrared. With advantages of high integration and low-power consumption， they are widely used in quantum information science， laser mapping， deep space communication and other fields. In order to reduce error counts， InGaAs/InP APDs are generally operated in the gated Geiger mode， where the repetition frequency of the gating signal directly determines the detector''s working rate. Thus， we adopt a low-pass filtering scheme to build a high-performance InGaAs/InP single-photon detector with adjustable GHz repeating frequency by integrating the processing circuit with GHz sine gating signal generation， avalanche signal acquisition， temperature control， bias voltage regulation and other functions. When the frequency of GHz gating signal increases to 2 GHz， its phase noise is still better than the -70 dBc/Hz@10 kHz， and the spike noise is suppressed to the level of thermal noise. When the detection efficiency is 10%， the dark count is only 2.4×10^-6/ gate. In addition， we also verify the long-term stability of the detector under this scheme， and test the influence of working rate， bias voltage and other factors on the key performance parameters of APD， which lays a foundation for the further integration and promotion of GHz InGaAs/InP APDs.

Abstract:Based on the noise suppression effect of weighing measurement principle， a short-wave infrared spectral imaging method based on S-matrix slit array was proposed. By constructing S-matrix slit array to replace the single slit of spectral imaging system， the aliasing measurement of spatial and spectral information was realized. The detector noise and photon noise of the system were analyzed and the noise suppression effect was calculated. The simulation results show that this method can effectively reduce the noise level and improve the imaging quality of low light conditions. The principle prototype was built for imaging experiment. The imaging target was a homogeneous object. By comparing the imaging data onto a single slit， the spectral imaging method of the S-matrix slit array was used to increase the SNR by 9% and 21% respectively under 23% and 10% detector potential well light intensity.

Abstract:A real-time target detection method based on center points is proposed for infrared imaging systems equipped with CPUs. Following the lightweight design principles， a backbone with low computational cost is first introduced for feature extraction. Correspondingly， an efficient feature fusion module is designed to exploit spatial and contextual information extracted from multi-stages. In addition， an auxiliary background suppression module is proposed to predict foreground regions to enhance the feature representation. Finally， a simple detection head predicts the target center point and its associated properties. Evaluations on the infrared aerial target dataset show that our proposed method achieves 90.24% mAP at a speed of 21.69 ms per frame on the CPU. It surpasses the state-of-the-art Tiny-YOLOv3 by 10.16% mAP with only 21% FLOPs and 11% parameters while also runs 10.02 ms faster. The results demonstrate its great potential for real-time infrared applications.

Abstract:The whispering gallery mode （WGM） micro-resonator is an ideal platform for investigating the nonlinear light phenomenon. In this article， we achieved up to the fifth-order cascaded stimulated Brillouin scattering （SBS） light in a CaF₂ micro-disk resonator with an mm-sized 12.6 mm diameter and an ultra-high quality factor （ factor） at 1 550 nm wavelength. We found that there are multi modes of families in our large-scale micro-disk resonator when coupled to an adiabatic tapered fiber， which can easily select resonances matching the SBS frequency shift. This can eliminate the requirement that precisely controlls the scale of the resonator to match the free spectral range （FSR） with the Brillouin frequency shift. During our experiment， to solve the environmental fluctuation problem between the micro-disk resonator and tapered fiber， we designed a packaged platform that can steadily seal the resonator and tapered fiber in an N₂ atmosphere. The generated cascaded Brillouin light and the stable packaged platform can further be used to investigate the multi-wavelength Brillouin laser and Brillouin light-based gyroscope.

Abstract:The difference in projection angle leads to changes in the shape and size of objects， which limits the improvement of the detection performance of small objects by the two-dimensional （2D） concealed object detection method based on projected views of active millimeter wave （AMMW） holographic images. For this reason， a three-dimensional （3D） concealed object detection method based on point clouds was proposed for the first time. AMMW holographic images were converted into point clouds by thresholding， and then were input into the 3D object detector SECOND， which was improved by dilated convolution and multi-branch structure， to extract the 3D geometric understanding of the objects and their multi-scale context information to improve the detection ability for small objects. The experimental results showed that compared with the projection-based 2D detection methods， the average recall （AR） of this method was improved by 3.33%， which proved the effective improvement of localization accuracy. The detection rate and the average precision （AP） was relatively improved by 8.75% and 7.11%， and the false alarm was reduced by 1.78% at an intersection over union （IOU） threshold of 0.5. The average AP under different IOU thresholds was improved by 4.30%. The detection accuracy was effectively improved. The detection speed was 17.3 FPS， which reached the real-time level.

Abstract:Due to the heterogeneous characteristics of the infrared polarization focal plane， it is necessary to take into consideration the impact of the response differences in different bias channels on the overall correction effect in the process of non-uniform correction. The non-uniform correction problem of the infrared polarization focal plane is more complex than that of the ordinary homogeneous infrared focal plane. For non-uniformity correction of polarization focal plane， an algorithm based on scene-based polarization redundancy estimation is proposed. The statistical information between acquired images and estimated images from polarization redundancy is acquired， then the differences in the response of all pixels in the whole focal plane are obtained. By comparing and analyzing the differences from two directions in each polarization channel， we can obtain the updated gain correction coefficients. Then radiometric recalibration is used to suppress the ghost image caused by the static scene， and the gain correction coefficients in the current state are obtained. In this process， the gain correction coefficients are updated adaptively by evaluating the previous correction coefficients through polarization redundancy estimation. Finally， experiments on the real scene data demonstrate the effectiveness of the proposed non-uniformity correction algorithm for polarization images.