The ordered titanium dioxide nanofibers (TiO2NF) are prepared using electrostatic spinning technique. A novel heterojunction structure (Se/TiO2NF) based on TiO2NF with p-type selenium (Se) nanoparticles are obtained aiming to improve the spectral selectivity of TiO2NF, inhibit the recombination of photoelectron-hole, and enhance the responsivity and response speed. The Se/TiO2NF type II band aligned heterojunction with expanded response range of 300-700 nm exhibits excellent self-powered photoelectric performance without bias voltage. Especially, the Se/TiO2NF device at 610 nm light shows the responsivity of 21 mA·W-1, the response rise time and fall time of 30 ms and 47 ms, respectively, which is faster than the response time of TiO2NF device (rise time of 45 s and fall time of 70 s). The results show that the preparation of heterojunction can achieve high performance photodetectors.

The volume holographic grating is often used as an input/output coupler in a head-mounted display, and its diffraction efficiency greatly affects the imaging quality of the system. Therefore, a new coupled grating structure is proposed to improve the diffraction efficiency of volume holographic gratings, which is composed of an optimized volume holographic grating and a blazed grating. The rigorous coupled wave analysis is used to simulate the new coupled grating structure. The results reveal that compared with the volume holographic grating, this structure increases the diffraction efficiency of transverse electric mode light by 1.5%, the diffraction efficiency of transverse magnetic mode light by 9.4%, and the diffraction efficiency of unpolarized light by 5.3%. In addition, this structure boasts an increase of 0.2° and 0.5° in the full width at half maximum of the incident angle under different polarization states (transverse electric mode light and transverse magnetic mode light), which indicates that the structure has a larger field of view angle.

The grating/nanoparticle hybrid structure is designed to improve the enhancement effect of surface-enhanced Raman scattering (SERS) substrates. The extinction characteristics and the optical field distribution of the structure are simulated through the finite-difference time-domain (FDTD) method. Meanwhile, the effect of the coupling between the propagating surface plasmons (PSPs) of gratings and localized surface plasmon resonance (LSPR) of nanoparticles are discussed. Given the LSPR wavelength of two Au nanoparticle arrays (with the interparticle spacing of 2 nm and 6 nm, respectively), when the wave vector components of PSP and LSPR of diffraction gratings along the x axis are identical in view of the matching principle of resonance wavelength of LSPR and PSP, two Au gratings with different periods are designed to match two Au nanoparticle arrays separately. When the gratings are excited by plane waves, they generate PSP to excite LSPR of nanoparticles. FDTD simulations demonstrate that the square of maximum electric field intensity in the particle gaps of the grating/nanoparticle hybrid substrate is improved by one order of magnitude compared to that of the corresponding nanoparticle array under 633 nm excitation. Meanwhile, unlike the situation where LSPR is directly excited by plane waves, the electric field intensity around the particles in the hybrid structure excited in which LSPR is excited by PSP is enhanced, and the hot spot area is largely extended, and thus more molecules are in the area of high enhancement, which is highly conducive to improving the overall SERS signal intensity of those molecules dropped on the substrate.

The broadband tunable filter is considered as one of the key equipment to break the bottleneck of the information processing technology, which can effectively improve the transmission capacity and spectrum efficiency of information networks. An ultra-broadband tunable filter based on cascaded chirped subwavelength grating assisted contra-directional coupler is proposed. The filter is based on silicon on insulator. By using subwavelength grating and introducing chirp in the contra-directional coupler, an ultra-broadband filter is obtained. The bandwidth tunability of the proposed filter is realized by cascading contra-directional couplers. The transmission function of the contra-directional coupler is analyzed, and some feasible methods to enlarge the bandwidth of the filter are proposed. The ultra-broadband filter with a bandwidth of 64.07 nm, a sidelobe suppression ratio of more than 10.5 dB and insertion loss of about 0.60 dB can be realized by using a single contra-directional coupler. The ultra-broadband tunable filter with an insertion loss of 1 dB and a bandwidth tuning range of 44.3-49.92 nm can be realized by cascading contra-directional couplers. The ultra-broadband tunable filter has the advantages of large bandwidth, tunability, high similarity with rectangular shape, small size, and uninterrupted transmission, which can be widely used in optical filtering and information transmission.

In order to solve the problem of low pumping efficiency of terahertz wave due to the dispersion effect of femtosecond laser pulse transmission in optical fiber, aiming at the dispersion characteristics of femtosecond laser pulse in terahertz time-domain spectrum system, the mathematical models of angular dispersion and time-domain dispersion are established through theoretical analysis. The effects of grating pair spacing and incident angle of system optical path on dispersion compensation are numerically simulated by ray tracing method under three different grating constants. The results show that the dispersion of the system increases with the raise of grating pair spacing when the grating constant is given. When different grating constants are selected, the variation trend of dispersion is different with the change of incident angle, but the total dispersion increases with the increase of grating constant. The rationality of selecting a grating with a grating constant of 1200 mm-1 is verified from the two aspects of spacing and incident angle. Finally, the pulse compression effect of the grating pair is proved by experiments, which meets the pulse compression requirements of terahertz time-domain spectroscopy system.

To suppress the high-order diffraction of traditional fork gratings, a single optical element, the fork modulated groove position grating (FMGPG), is proposed, which can effectively suppress undesired high-order diffraction by adjusting the center position of grating lines. Numerical simulations and experimental results indicate that the FMGPG has a good single-order diffraction characteristic and can effectively suppress undesired high-order diffraction, which is almost consistent with the theoretical prediction. The third-order diffraction light intensity can be reduced from 24% of the required first-order diffraction light intensity to a degree less than the light intensity of the background. The suppression effects of periods, maximum movement distance, and graph areas on high-order diffraction are analyzed. Meanwhile, it is confirmed that the output beams have helical phase structures with multiple topological charges. The high-order diffraction suppression characteristic of the proposed gratings has broad application prospects in aspects such as imaging, microscopy, and particle capture.

In order to investigate the focusing characteristics of Airy beams, the theoretical formulas for the electromagnetic intensity vector and energy flux near the focusing region in cylindrical coordinate system are derived based on geometric phase, and their feasibilities are verified by vector diffraction theory. The results show that the geometric phase modulation parameter can significantly change the main lobe size, lobe spacing and energy distribution of the Airy beam. The energy and phase of the main lobe of the beam are effectively converted by introducing the vortex phase to the original cubic phase of Airy beams, and the main lobe of the beam no longer maintains its original shape. This research provides a basis for the application of Airy beams in optical sampling and manipulation, optical communication, data storage and imaging.

To improve the physical layer security of the optical communication system, an encryption-modulation integrated scheme based on the dual-drive Mach-Zehnder modulator (DD-MZM) is proposed. In this scheme, the XOR encryption operation is realized between plaintext and key in the optical domain on the basis of the vector modulation mechanism in the DD-MZM, and the function reuse of encryption and modulation is achieved. The basic working principle of the proposed scheme and the optimization process of improving the extinction ratio of encrypted signals are described, and the prototype of an encryption-modulation integrated transmitter is successfully developed based on this scheme. The experimental results reveal that the modulation and encryption of signals with a transmission speed of 32 Gb/s can be successfully realized by this scheme, and the signal extinction ratio is as high as 13.2 dB. In addition, simulation analysis indicates that compared with the common on-off keying (OOK) system, the proposed system has a better extinction ratio for its received signals.

A single sideband direct detection digital filtered multiple access-passive optical network (DFMA-PON) system is proposed to suppress the frequency selective fading effect caused by the fiber dispersion. Moreover, in order to eliminate the signal-signal beat interference (SSBI) caused by the square-law characteristic during the direct detection, a Kramers-Kronig (KK) algorithm suitable for the DFMA-PON system is designed at the receiver. The KK algorithm recovers the original signal by reconstructing the phase information from the amplitude information of the received signal, so as to eliminate the influence of SSBI on the received signal and improve the sensitivity of the receiver. The simulation results demonstrate that the performance of single sideband transmission system is significantly improved compared with that of double sideband transmission system without additional dispersion compensation algorithms. The receiver sensitivity can be increased by about 5.0 dB at most after 25 km standard single-mode fiber transmission compared with the single sideband system without KK algorithm at the receiver.

The existing optical spatial modulation has some problems, such as low transmission rate, low transmitter utilization rate and undesirable bit error rate performance. A marked multi-layer optical spatial pulse position modulation (MMLOSPPM) scheme is proposed by employing the layered spatial structure and combining pulse position modulation (PPM). The timeslot of each PPM symbol is extended to distinguish layers, and the correctness of the first detection layer and its modulation symbol is improved. Besides, the theoretical bit error rate expression of the MMLOSPPM system is derived under the Gamma-Gamma turbulence model and is verified by Monte Carlo method. The simulation results show that when the spectral efficiency is 3/2 bit·s-1·Hz-1, the transmission rate of (5×4-2-2) MMLOSPPM is 3 bpcu (bit per channel use) better than that of (4×4-2) spatial PPM (SPPM) system and (3×4-2) generalized SPPM (GSPPM). When given the same transmission rate, the (5×4-2-2) MMLOSPPM system requires 2 and 11 fewer lasers than that of (7×4-4) GSPPM and (16×4-4) SPPM system respectively, and MMLOSPPM gains the best bit error rate performance in the high signal to noise ratio (SNR) region (SNR is greater than 28 dB).

This paper presents a method of deep learning-based interference-free hologram generation. In the method, simulated off-axis digital Fresnel holograms are utilized as network training samples, and an improved convolutional neural network is used to learn the feature relationships of the zero order with the positive and negative first orders of the holographic spectra. The negative first-order spectra of the holograms are thereby extracted. Experimental verification is carried out with simulated holograms and real ones, and the reconstructed images of the interference-free holograms are analyzed. The results show that the proposed method can eliminate zero-order information and interference information in a wide range in the absence of manual intervention, extract negative first-order information from the hologram, and obtain an object light field with high reconstruction quality. This means that the proposed method achieves deep learning-based interference-free hologram generation.

We present a method and a system of multifocal two-photon laser scanning microscopy (MTPLSM) based on double-helix point spread function (DH-PSF) engineering (DH-MTPLSM) to improve the imaging speed and resolution. In the excitation light path, a high-speed phase-only spatial light modulator (SLM) is employed to generate three-dimensional (3D) multifocal arrays and implement high-precision parallel digital addressing scanning of the sample surfaces. In the detection light path, a double-helix phase plate is inserted to modulate the system detection PSF to DH-PSF, which provides axial information of the sample. The aim is to reduce the number of layers scanned axially and ultimately enhance the speed of 3D imaging. Moreover, with a DH-PSF-based digital refocusing algorithm, we reconstruct the wide-field images of the sample at different depths and obtain the 3D optical sections of the sample by single 2D scanning. On this basis, we build a DH-MTPLSM system, carry out two-photon imaging experiments on mouse kidney sections with this system, and verify the ability of the proposed method in fast 3D high-resolution imaging, which is of great significance for the development of MTPLSM.

Optical three-dimensional (3D) imaging has been widely applied in fields such as medical diagnosis, remote sensing, and artificial intelligence. However, in the scattering environment, the wavefront phase of incident light is severely disturbed, which results in deteriorated performance or even failure of traditional optical 3D imaging. Moreover, the studies of imaging through scattering media mainly use expensive scientific cameras for data acquisition. Therefore, we propose a low-cost 3D imaging method through scattering media based on a common industrial camera for data acquisition. To improve the signal-to-noise ratio (SNR) of the images collected by the common industrial camera, we conduct multiple rounds of accumulative averages on the point light source speckles representing point spread function of the proposed imaging system to obtain a point spread function with an SNR as high as that by scientific cameras. Then, the deconvolution of the point spread function with the structured light speckle obtained by a single exposure is carried out to produce the deformed fringe pattern modulated by the object shape. Finally, the 3D information of the object is recovered by Fourier transform profilometry. The experimental results indicate that the proposed method can achieve an imaging effect comparable to that by scientific cameras, which provides a feasible and low-cost solution for 3D imaging through scattering media.

In this paper, a spectrophotometer is designed. The xenon lamp is used as the measuring light source of the spectrophotometer, and a mechanical structure is designed to adjust the proportion of ultraviolet energy in the luminous intensity of xenon lamp. The standard color plate determined by the proportion of fluorescent substances is used as the standard substance to calibrate the instrument and the standard instrument. The algorithm is designed to modify the instrument light source to make the ultraviolet spectral radiation intensity of the illumination light source is consistent with that of the standard instrument, so as to reduce inter-instrument agreement. In addition, experiments are designed to verify the effect of the scheme. The maximum value and average value of inter-instrument agreement ΔEab of non-fluorescent materials measured by instruments without the proposed scheme are 0.88 and 0.44 in CIELAB uniform color space, and that in the situation with fluorescence color are 13.69 and 3.46. After applying the proposed scheme, the maximum value and average value of inter-instrument agreement ΔEab of non-fluorescent materials measured by instruments are 0.88 and 0.38 in CIELAB uniform color space, and that in the situation with fluorescence color are 3.88 and 1.04. The experimental results show that the proposed scheme can improve the inter-instrument agreement level of fluorescent color measurement between different instruments.

Aiming at the stereo imaging system with Scheimpflug cameras, the calibration and epipolar rectification methods are investigated in this paper. The epipolar geometry of stereo Scheimpflug cameras is described, on the basis of which a robust and effective stepwise calibration method is proposed. Based on the calibration results of intrinsic and extrinsic parameters, the epipolar rectification model of stereo Scheimpflug cameras is presented. Furthermore, a three-dimensional digital image correlation (DIC) deformation measurement system is developed based on Scheimpflug cameras. The experimental results show that the accuracy of the three-dimensional DIC deformation measurement system is superior to 10 μm, which demonstrates the effectiveness and accuracy of the stepwise calibration and epipolar rectification of proposed stereo Scheimpflug cameras.

When the slanted-edge method is applied to measure the optical transfer function (OTF), it not only can just accurately obtain the modulation transfer function (MTF) in a single direction, but also fails to measure the Zernike aberration coefficients. In contrast, Fourier ptychography can obtain super-resolution images and reconstruct the pupil function of the optical system, thereby achieving the simultaneous measurement of Zernike aberration coefficients, and the amplitude and phase of the two-dimensional OTF. The previous macroscopic Fourier ptychography method by aperture scanning during the translation of the whole camera is not applicable to the optical path for OTF measurement. Therefore, driving lighting fibers into motion with an electronically controlled translation platform is proposed to achieve pupil translation in the frequency domain, and this method has the advantages of adjustable moving intervals, high brightness, and favorable coherence. The experimental setup is built according to the optical path for OTF measurement, and a doublet and the presence of obstruction are measured by macroscopic Fourier ptychography. The corresponding pupil function is reconstructed, and Zernike aberration coefficients and the OTF are calculated. The effects of the number of acquisition steps and the overlap rate on accuracy are analyzed by measuring high-resolution imaging lens. The experimental results show that the mean square errors of the MTF measurement results in meridian and sagittal directions relative to the measurement results of the OTF measuring equipment are in the 10-4 magnitude.

The ability of a detection system to recognize detection targets determines whether or not the functional modules connected to the laser detection system can work normally. A pulse width-intensity modulation scheme is proposed to simulate crossing target echo signals at high speed in the laboratory. This scheme can change the peak value of the output light pulse by controlling the pulse width of an input pulse signal and simulate the peak value changes of echo signals. In addition, the circuit implementation is designed to drive an 860 nm semiconductor laser for testing. The test results reveal that the input pulse signal with a pulse width of 8-16 ns corresponds to the output pulse signal with the peak power of 3.7-8.3 W. Taking the pulse width-intensity modulation module as the basic physical realization unit, we present a high-order simulation scheme of echo signals to simulate more information of target echo signals. This modulation method is simple in the principle, easy in circuit implementation, and low in costs, which provides a new direction for the design and inspection of the target recognition function of a laser detection system.

The photonic crystal vertical-cavity surface-emitting lasers (PCVCSEL) are the new lasers with two-dimensional photonic crystal structure based on the traditional oxide aperture confined vertical-cavity surface-emitting (VCSEL) lasers, which can achieve high-power fundamental transverse mode output. A reasonable design method for PCVCSEL structure is proposed, and a stable fundamental transverse mode output is achieved when the normalized frequency Veff is around 2.405. Through the two-dimensional equivalent refractive index model, the fundamental transverse mode PCVCSEL and the traditional VCSEL with reduced oxide aperture are compared and analyzed. The former can achieve greater lateral limitation and wider optical field width. The current distribution and temperature distribution of PCVCSEL are analyzed by thermoelectric coupling model. It is proved that the current and heat are mainly concentrated in the area corresponding to the oxide confined aperture. A PCVCSEL with a single-fundamental-mode output power of 1.6 mW with a lasing wavelength of 932 nm is successfully fabricated.

Achieving a high power fiber laser output while maintaining high beam quality is challenging due to the constraints of stimulated Raman scattering (SRS) and transverse mode instability (TMI). In this paper, based on a counter tandem pumping scheme, an output with a power of 8.38 kW and a high beam quality factor of M2=1.8 is achieved in a homemade and conventional double-clad 30 μm /250 μm Yb-doped fiber. The SRS and TMI effects are effectively suppressed, but the further power increase is restricted by the available pump power.

The unbalanced defocus blur of the left and right images leads to stereo matching failure in a binocular stereo vision system. In order to train a neural network that can deal with the image blur, this paper constructs an unbalanced defocus stereo vision dataset by adding the blur varying with the depth using a normalized blur level (NBL) based layered depth-of-field rendering algorithm and taking the FlyingThings-Stereo image pair dataset as an example. The proposed dataset can provide the unbalanced defocus stereo images and be used to train deblurring or stereo matching networks. When training the deblurring network, the dataset provides blurry and clear stereo images to the network's input and output ends. When training stereo matching network, fuzzy stereo pairs and parallax truth values are provided to the input and output ends of the network. The network is verified by synthetic and real-scene data after it is trained. Results show that the proposed dataset can effectively train the deblurring and stereo matching neural networks and enables their ability to cope with defocus blur, so as to achieve the image deblurring and stereo matching based on blurry images.

In order to improve the accuracy and robustness of visual SLAM (Simultaneous Localization and Mapping) systems in dynamic scenes, a visual SLAM algorithm based on optical flow and instance segmentation is proposed. Aiming at the inconsistency of optical flow direction between dynamic objects and static background, feature points in the dynamic region mask can be eliminated in the original tracking thread of ORB-SLAM2 in real time. We use the existing depth map and tracking thread pose estimation information to remove the optical flow related to camera motion and then cluster the optical flow amplitude generated by the dynamic object's own motion to achieve high-precision dynamic area mask detection. The dynamic landmarks in the local mapping thread are eliminated combined with epipolar geometric constraints. Finally, the test results on TUM and KITTI datasets show that in high dynamic scenes, compared with ORB-SLAM2, Detect-SLAM, and DS-SLAM, the accuracy of the proposed algorithm is improved by 97%, 64%, and 44% on average. Compared with DynaSLAM, the accuracy has an average increase of 20% in half of the high dynamic scenes, which verifies that the proposed algorithm improves the accuracy and robustness of the system in high dynamic scenes.

In crowded scenes, it is difficult for YOLOv3 to detect the objects that overlap each other heavily. Aiming at the reasons for the decline of YOLOv3 performance, three improvements are proposed. Firstly, a Tight Loss function is proposed, which optimizes the variance and mean of the coordinates of the prediction boxes to make the prediction boxes belonging to the same target more compact, thus reducing the false positive rate. Secondly, a high-resolution feature pyramid is proposed, in which the resolution of each pyramid feature is improved by upsampling, and shallow features are introduced to enhance the differences between adjacent sub-features, so as to generate distinguishing depth features for highly overlapped targets. Thirdly, a detection head based on spatial attention mechanism is proposed to reduce the number of redundant prediction boxes, so as to reduce the computational burden of the non-maximum suppression (NMS) process. The experimental results on the crowded dataset CrowdHuman show that the average accuracy and recall rate of YOLOv3 detection are improved by 2.91 percentage points and 3.20 percentage points, and the miss rate is reduced by 1.24 percentage points by using the proposed algorithms under the condition of using the traditional NMS method, which demonstrates the effectiveness of the proposed algorithms in boosting the performance in occluded pedestrian detection.

At present, concentric multi-scale systems generally suffer from an unstable image plane of the sub-camera. This problem directly leads to image misalignment in subsequent image stitching, which seriously affects the imaging quality of systems. In response to this problem, this paper proposes a method based on the image-side telecentric optical path to improve the image plane stability of the sub-camera and reduce the pressure from the subsequent image stitching. The paper firstly explores the reason for misalignment and then analyzes the benefits of using the image-side telecentric optical path in the concentric multi-scale systems. Finally, it designs a concentric multi-scale imaging system based on the image-side telecentric optical path with good imaging performance. The imaging system has a focal length of 60 mm, an F number of 3, a telecentricity of less than 0.2 mrad, and the total field of view of 70°. The defocused spot radius in each field of view is smaller than the pixel size of the selected detector, and the modulation transfer function (MTF) of each field of view is greater than 0.6 at the Nyquist frequency of 108 lp/mm. The concentric multi-scale imaging system with the image-side telecentric structure can improve the image plane stability of the sub-camera from the aspect of optical structure, thereby improving the quality and efficiency of subsequent image stitching. This paper also provides more ideas and technical approaches for the future design of concentric multi-scale systems, having important theoretical and practical significance.

The application of diffractive optical elements (DOEs) in infrared dual-band and even multi-band has become a hotspot. Based on the design idea of polychromatic integral diffraction efficiency (PIDE) maximization of the double-layer DOE, the optimal working wavelength is designed in the range of working band, and the optimal microstructure height of the double-layer DOE is calculated. The mathematical analytical model of weight distribution of PIDE of a multi-band optical system is proposed. Based on this double-layer DOE, a dual-band (3.7-4.8 μm and 8.0-12.0 μm) infrared optical system with an F-number of 1.1 and a focal length of 75 mm is designed. When the system is at a spatial frequency of 29.4 lp/mm, the modulation transfer functions of the designed system are above 0.60 and 0.45 for the medium wave infrared (MWIR) and long wave infrared (LWIR), respectively, and the designed optical system realizes athermalization over the temperature range from -40 ℃ to 60 ℃. The system has shown great advantages in improving image quality, miniaturization, lightweight, and athermalization in infrared dual-band.

Compared with conventional head-up displays (HUDs), augmented reality HUDs (AR-HUDs) can display richer information, and an ideal AR-HUD requires the display of multiple virtual images at different depths to present basic and interactive information. In most traditional solutions, however, the display of information at the two depths is achieved by rotating the reflective mirror at high speed or using the optical zoom system, with lower reliability and potential safety hazards. Therefore, the optical off-axis reflective structure is proposed to achieve the dual-focal-plane display using two picture generation units (PGUs) and a single free-from surface mirror. By adding a plane mirror to increase the object distance of the far-field optical path, we achieve a display of two focal planes. Finally, a dual-focal-plane HUD is obtained, with an eye box of 130 mm×50 mm, field-of-view angles of 5°×1° and 10°×5°, and virtual image distances (VIDs) of 2.5 m and 7.5 m. The research results meet the requirement of the simultaneous display of near-field basic information and far-field interactive information, and the display effects of depth of field are enhanced.

This study develops a new ultraviolet (UV) photodetector composed of ZnO nanorods and CuCr1-xMgxO2 films. First, ZnO nanorods were grown on CuCr1－xMgxO2 films prepared by the sol-gel method under hydrothermal conditions. Then, the morphology, structure, and absorption properties of CuCr1-xMgxO2/ZnO were characterized by scanning electron microscopy (SEM), an X-ray diffractometer (XRD), and a spectrophotometer. Finally, the UV photoelectric detection performance of CuCrO2/ZnO and CuCr1-xMgxO2/ZnO was investigated. The experimental results reveal that the detector has fast response; the photo-to-dark current ratio is about 2.6 times greater than that of CuCrO2/ZnO at -10 V, and the device responsivity is 2.3 A/W higher than that of CuCrO2/ZnO. The CuCr1-xMgxO2/ZnO photodetector has excellent detection performance and the advantages of a simple preparation process, low cost, and mass production, which is an excellent photodetector with various applications in UV detection.

This paper proposes a dual-control adjustable terahertz metamaterial broadband absorber based on a mixed material of graphene and vanadium dioxide (VO2). The absorber has the advantages of simple structure, switchable absorption/transmission/reflection, and large modulation depth. The absorptivity control of the absorber can be achieved by changing the phase transition characteristics of VO2 and the Fermi energy level of graphene. When VO2 is in a metallic state, the absorber can achieve broadband absorption with an absorptivity greater than 90% in the frequency range of 1.07-2.59 THz, and exhibits excellent absorption performance under a wide range of incident and polarization angles for TE and TM polarizations. By changing the Fermi energy of the graphene, the in-band absorptivity can be dynamically adjusted, and the modulation depth is greater than 67.2%. When VO2 is in an insulating state, the device behaves as an adjustable transmission mode regulated by the graphene Fermi energy level, with a transmittance modulation depth greater than 40%. Furthermore, by controlling both the VO2 phase transition characteristics and the graphene Fermi energy level, the in-band absorptivity modulation depth of the absorber can be increased to more than 90%, and the maximum modulation depth is 99.7%. The absorber realizes a terahertz dual-control absorber with good tuning characteristics through two independently controllable materials, and has potential applications in the field of terahertz smart devices (such as attenuators, reflectors, and spatial modulators).

Vortex beams have special spiral phase factors, and the communication capacity can be greatly improved by using vortex beams for communication coding. The atmospheric turbulence and haze in the actual communication environment will lead to the scattering of vortex beams and form speckles, which increases the difficulty of information decoding in the vortex optical communication. Therefore, it is of great significance to accurately and efficiently measure the topological charges of vortex beams from the speckles for their application in vortex optical communication. The characteristics of the speckle field formed after vortex beams passing through scattering medium are closely related to the topological charges. Based on the efficient feature extraction of depth neural network, the measurement of topological charges of scattered vortex beams is realized by using classified neural network, and the measurement accuracy is up to 100%.

Constructing a nanoelectrode for an individual nanoparticle and realizing the spectral characterization and modulation simultaneously have profound significances for fabricating nano-optoelectronic devices. This paper proposes and prepares the nanostructure made up of gold (Au) interdigital electrodes loaded with barium titanate (BaTiO3) nanoparticles, thereby physically couples surface plasmon polariton mode of collective grating with Mie resonance of BaTiO3 nanoparticles and local surface plasmon resonance mode at the interface of Au-BaTiO3. Therefore, the scattering modulation and characterization of individual BaTiO3 nanoparticles with a diameter less than 200 nm loaded on interdigital electrodes are realized. The platform uses the grating structure as the "background screen", which overcomes the undesired scattering signal from the whole electrode structure and solves the problem for detecting the scattering signal of individual nanoparticle when combined with electrodes. BaTiO3 nanoparticle-based nanopixels with diameters less than 200 nm exhibit tunable scattering spectra in the visible range depending on grating size and polarization, which provides an approach for further building tunable optoelectronic devices based on single nanoparticle.

A baseline correction method based on low-rank constraint and penalized least squares (LRPLS) is proposed. This paper comprehensively considers the fitted baseline's fidelity to the interferogram and its own smoothness by using the penalized least squares model. At the same time, the low-rank and sparse prior constraint conditions of the effective interferogram and noise are introduced to build a regularization framework combing the low-rank matrix recovery and penalized least squares, and the solution is carried out by an augmented Lagrangian multiplier based iterative optimization algorithm. The experiments on the data of Chang'e-1 interference imaging spectrometer (IIM) show that the proposed method can retain effective information of the interferogram while removing the baseline. Compared with existing baseline correction methods, the proposed method has better stability and anti-noise ability. In addition, the recovered hyperspectral image significantly improves after baseline correction, which has high practical significance for improving the data quality of IIM.