The Taiji Project is a space gravitational wave detection mission proposed by the Chinese Academy of Sciences, which uses the method of laser differential interference to detect pm-level displacement fluctuations caused by gravitational waves between satellites. In order to eliminate the phase measurement error caused by the dissynchronization of the clock between satellites, Taiji Project intends to use the sideband multiplication transfer scheme to measure and eliminate the inter-satellite clock noise. This paper discusses the requirements, principles, and methods of inter-satellite clock noise transmission of the Taiji project, and designs experiments for principle verification. By building an electronics experiment, the limit value of the clock noise of the two systems was tested, the relevant parameters of the experiment were determined, and the principle of the sideband multiplication transfer scheme was verified by further optical experiments. The experimental results show that the clock noise cancellation scheme and related parameters proposed in this paper are reasonable and feasible, and are suitable for the needs of Taiji project. Moreover, in the 0.05 Hz-1 Hz frequency band, the suppression effect of inter-satellite clock noise is better than 2π×10^-5 rad/Hz^1/2, which meets the noise requirements of Taiji pathfinder and lays an experimental and theoretical foundation for the design of clock noise transmission scheme and parameter of future Taiji Project.

Flow cytomicrographic analysis is an important development in the automatic identification of planktonic algae in the water column, where the deformation of microscopic images under rapid injection conditions affects the accuracy of automatic identification of planktonic algae. Based on a microfluidic-microscopic imaging system for planktonic algae, the effect of flow rate on the deformation of microscopic images was investigated by analysing the deformation of algal cells and image clarity at different injection flow rates.Based on the principle of deformation caused by a rolling shutter photographing a moving object, a method of image deformation correction with unidirectional offset pixels is proposed and analysed in comparison with images acquired under static conditions of algal cells.The experimental results showed that the average values of aspect ratio and sharpness of L. oocystis cell images under static conditions were 1.16 and 116.53 respectively; during the dynamic injection process, the deformation (aspect ratio) of cell images gradually increased and the sharpness decreased as the flow rate increased; the average values of aspect ratio before and after correction were 1.35 and 1.26 respectively at 95 µL/min injection flow rate, and the dispersion of deformation decreased from 0.33 before correction to 0.1. The mean value of aspect ratio before and after correction was 1.35 and 1.26 respectively at 95 µL flow rate.The results provide a method for improving the accuracy of automatic identification of planktonic algal cells in the water column.

To gain better phase measurement results in nonlinear measurement systems, a phase measurement method that uses dual-frequency grating after reducing the nonlinear effect is proposed. Firstly, the nonlinear effect of the phase measurement system is discussed, the basic reason for the existence of high-order spectra components in the frequency domain is analyzed, and the basic method used to reduce the nonlinear effect and separate fundamental frequency information is given. Then, on the basis of reducing the nonlinear effect’s influence on the system, the basic principle of phase measurement for the fringe image of a measured object using the dual-frequency grating method is analyzed. To verify the correctness and effectiveness of the proposed phase measurement method, a computer simulation and some practical experiments were implemented with good results. In the simulation, the error value of this method was 27.97% for the method with nonlinear influence, and 52.51% for that with almost no nonlinear influence. In the experiment, the effect of phase recovery produces the best results. This shows that phase measurement by the method mentioned in this paper has effective and with a small error.

We propose cosh-Pearcey-Gauss beams with uniform polarization, which are mainly modulated by a hyperbolic cosine function (n, Ω) and the angles related to uniform polarization (α, δ). Based on angular spectrum representation and the stationary phase method, the Poynting vector, spin and orbital angular momentum in the far zone are studied. The results show that a larger n or Ω in the hyperbolic cosine function can partition the longitudinal Poynting vectors, SAMs and OAMs into more multi-lobed parabolic structures. Different polarizations described by (α, δ) can distinguish their Poynting vectors and angular momentums between the TE and TM terms, though this does not affect the patterns of the whole beam. Furthermore, the weight of the left and right sides of longitudinal Poynting vectors, SAMs and OAMs in TE and TM terms can be modulated by left-handed or right-handed elliptical polarization, respectively. The results in this paper may be useful for information storage and polarization imaging.

In order to realize tunable longwave infrared laser, this paper designs a ZGP temperature tuned longwave infrared optical parametric oscillator. Using a Ho:YAG laser with the center wavelength of 2097 nm to pump ZGP crystals with different phase matching angles, the laser with a segment continuously tunable range of 7.53−8.77 μm is realized in the temperature range of 15−30°C, with a total tuning range of 1.24 μm. The output power of ZGP - OPO is greater than 1.503 W over the entire tuning range. The output power is 1.503 W at the idler wavelength of 8.77 μm, and the corresponding slope efficiency and optical conversion efficiency are 12.19% and 6.53%, respectively. The experimental results show that temperature tuning of ZGP is an effective technical method to obtain continuously tunable long-wave infrared laser. The research of this experiment has potential application value in the field of engineering of tunable long-wave laser.

Optical encryption materials for pattern information have been widely used in anti-counterfeiting, information encryption and storage, and structural color metasurface based on anisotropic functional reuse has been developed. The optical encrypted metasurface based on one-dimensional grating diffraction requires the processing of mask or unit structure one by one, resulting in low limiting efficiency. The structure uniformity of traditional ablated LIPSS is poor, which affects the device performance. Based on the above problems, an optical metasurface machining method based on the modified structure of picosecond laser direct writing phase change material Ge₂Sb₂Te₅ is proposed. Firstly, the dispersion performance of the prepared GST modified gratings was characterized, and combined with the polarization dependence of the modified gratings, the angle-multiplexed information encryption metasurface was designed, and the metasurface prepared by the proposed method was further demonstrated. It realizes the performance of encryption under natural light, selective decryption reading and dynamic display under strong light. Compared with the traditional processing method, the proposed method can generate a series of grating structures in the form of simultaneous printing in a direct writing process, which improves the processing efficiency. At the same time, the grating structure obtained by processing is uniform and consistent, which improves the color rendering effect. The modified grating with 16° difference in orientation Angle realizes the selective information reading without crosstalk, and the obtained structure color is uniform and bright. The processing strategy proposed in this paper has a profound application prospect in the fields of anti-counterfeiting, information encryption storage and wearable flexible display devices. The processing strategy proposed in this paper has a profound application prospect in the fields of anti-counterfeiting information encryption storage and wearable flexible display devices.

In order to eliminate the uncertainty caused by the inclination of the beam, a dual polarization laser Doppler velocimetry system is established in this paper. The system uses a dual beam dual probe structure to detect the motion information of the object. Firstly, the included angle of the two beams is accurately obtained through the rotation experiment. For any beam inclination, the dual probe device is used to collect the scattered beam from the moving object surface, and the Doppler frequency shift of the two interference signals is obtained by combining the dual polarization optical path structure. Then, the refined framing algorithm is innovated to demodulate the two interference signals in real time, and the real speed of the object is obtained by synthesizing the two speed components. The experimental results show that the average error between the measured value and the theoretical value can reach 1% ~ 5% when the speed is within the range of 10 mm/min ~ 1500 mm/min. In the process of non-stationary motion, the RMSE average of V-T image corrected by thinning and framing algorithm is 1.19mm/min. The structure of the system meets the requirements of stability and reliability, high accuracy and strong anti-interference ability in speed measurement.

In this paper, a metamaterial Fano resonance design method based on deep learning is proposed to obtain high-quality factor (high-Q) resonances with desired characteristics, such as linewidth, amplitude, and spectral position.The deep neural network is used to establish the mapping between the structural parameters and the transmission spectrum curve, and the forward network is used to predict the transmission spectrum.The inverse network achieves the on-demand design of high Q resonance. The low mean square error ( MSE ) is achieved in the design process, and the mean square error of the training set is 0.007.The results indicate that compared with the traditional design process, using deep learning to guide the design can achieve faster, more accurate, and more convenient purposes.The design of Fano resonance can also be extended to the automatic inverse design of other types of metamaterials, significantly improving the feasibility of more complex metamaterial designs.

To improve the extinction ratio of a polarization beam splitter, we propose a dual-slot ultra-compact polarization splitter (PBS) consisting of a hybrid plasma horizontal slot waveguide (HSW) and a silicon nitride hybrid vertical slot waveguide (VSW). The coating material is silicon dioxide, which can prevent the oxidation of the mixed plasma and also facilitate integration with other devices. The mode characteristics of the HSW and VSW are simulated by using the finite element method (FEM). At suitable HSW and VSW widths, the TE polarization modes in HSW and VSW are phase-matched, while the TM polarization modes are phase mismatched. Therefore, the TE mode in an HSW waveguide is strongly coupled with a VSW waveguide by adopting a dual-slot, while the TM mode directly passes through the HSW waveguide. The results show that PBS achieves an extinction ratio (ER) of 35.1 dB and an insertion loss (IL) of 0.34 dB for the TE mode at 1.55 μm. For the TM mode, PBS reached 40.9 dB for ER and 2.65 dB for IL. The proposed PBS is designed for the 100 nm bandwidth, high ER, and low IL, which can be suitable for photonic integrated circuits (PICs).

The decoherence of temporal quantum correlation is explored in a voltage-controlled quantum dots molecule in a cavity. The temporal correlation in the hybrid system is studied by Leggett-Garg inequalities. The inequality violations can be interpreted as the existence of temporal quantum correlation during dynamical evolution. The temporal quantum correlation is enhanced by its electron tunnel’s strength and cavity frequency detuning. It is found that there is no temporal correlation in the regions where the values of spatial quantum correlation are zero and the maximal violations occur in conditions with high values of quantum coherence. In contrast, spatial coherence can persist at times when no violation is detected. The open quantum system approach is used to investigate the environmental effects on inequality violations. The temporal correlation is suppressed by the spontaneous decay of the quantum dots and cavity leakage. These results are serviceable in processing quantum information in hybrid quantum systems.

We propose a “leaf-type” hybrid metamaterial to realize bandwidth-tunable half-wave plate based on vanadium dioxide (VO₂) phase transition. The hybrid metamaterial is a hollow “leaf-type” metallic structure and regarded as a dual-band half-wave plate when VO₂ film is in the insulating phase. Within 1.01−1.17 THz and 1.47−1.95 THz, it can accomplish y− to x-polarization conversion with a polarization conversion rate over 0.9 and an average relative bandwidth of 26%. The metamaterial becomes a solid core “leaf-type” metallic structure when VO₂ is in the metallic phase. Within 1.13−2.80 THz, it can act as a broadband half-wave plate with a relative bandwidth of 85%. The working principle of the bandwidth-tunable half-wave plate is explained by the instantaneous surface current distribution and electric field theory in detail. The proposed “leaf-type” hybrid metamaterial half-wave plate has potential application prospects in THz imaging, sensing and polarization detection.

Aiming at the problem that the optical frequency scanning nonlinearity affects the phase extracting accuracy of the optical Frequency Scanning Interferometry (FSI) signal, and thus reduces the FSI ranging accuracy, a phase-extracting method based on the Complementary Ensemble Empirical Mode Decomposition and Hilbert Transform (CEEMD-HT) algorithm is proposed in this paper. Based on theoretical derivation and simulation analysis of the CEEMD-HT algorithm, the effectiveness of the algorithm in solving the phase of the non-stationary interference signal in scanning-frequency is verified by simulation. Further simulation experiments were implemented by using the real output optical frequency curve obtained with FSI ranging system as the simulation conditions. The simulation results showed that the CEEMD-HT algorithm significantly improved the phase extracting accuracy of the interference signal and that of the FSI ranging. Finally, the proposed interference signal phase-extracting method was verified via the experiment of the FSI ranging system. The results showed that the ranging repeatability of the measurement system based on the CEEMD-HT algorithm was 2.79 μm in the free space measurement range of 2 m. Compared with EMD-HT and direct measurement methods, the ranging repeatability was improved by 5.19 times and 8.28 times, respectively.

In order to improve the quality value (Q) to enhance the coupling between light and matter. In this paper, a dielectric metamaterial with simple structure, low fabrication requirements was proposed. It can excite symmetric protected bound states in the continuum (BICS). The dielectric metamaterial has a planar nanopore plate composed of tetrameric pores. By changing the position of the nanopores, the symmetrical protection BIC can be transformed into the symmetrical protection quasi BIC(QBIC), and then two high Q value Fano resonances can be induced. Through simulation calculation, the Fano resonance Q value can reach 1e⁶ when Δ=3 nm. Then, the far-field radiation of QBIC and Fano resonance is decomposed into the contributions of different multipole components. Based on the scattering power and electric field vector distribution, it can be found that the dielectric metamaterials λ₁ Fano resonance with high Q value is mainly due to magnetic quadrupole and toroidal dipole, while λ₂ Fano resonance has high Q value is mainly due to the toroidal dipole. Finally, the influence of nanopore side length and nanopore filling material on the two Fano resonances is analyzed and calculated. The research in this paper can provide theoretical guidance for the future research and preparation of high Q value optical response devices.

In this paper, the coplanar excitation of terahertz Spoof Surface Plasmon (SSP) realized by using a single-layer grating meta-surface coupling method is proposed, which overcomes the disadvantages such as the inconvenience of reflection measurement when applying the medium couplers. The periodic grating and terahertz SSP composite structure are simultaneously constructed on the monolayer metal structure. When the terahertz waves are incident vertically, the wavevector of grating structures and the wavevector of SSPs are matched, and the SSP mode can be excited. The high Q value resonant peaks can be generated in the transmission spectrum, and its factor Q can reach 1923. The effects of the structural parameters on the grating-coupled meta-surface transmission spectrum and dispersion characteristics are also analyzed. In addition, based on the high Q resonant peak in the transmission spectrum of the designed structure, the high sensing sensitivity is about 67 GHz/RIU at the resonant center frequency of 0.22 THz. The structure proposed in this paper, which realizes terahertz SSP excitation and high Q sensing by treating a single-layer meta-surface structure, exhibits great application potential in many practical applications.

In order to improve the stability of an electrowetting liquid lens’s zoom, based on the research of glass lenses, a statistical data-based index of liquid lens zoom stability and liquid lens repeated zoom accuracy is proposed. An experimental method is presented to optimize the structural parameters and materials of the liquid lens. Firstly, the main factors affecting the accuracy of a liquid lens’s repeat zoom were obtained through preliminary experimental research, including the polar solution volume, taper and non-polar solution viscosity. Secondly, taking the accuracy of the liquid lens’s repeat zoom and zoom range as evaluation indicators, it was found that the relationship between the accuracy of the liquid lens’s repeat zoom and the voltage is not monotonic, and that it rises first and then falls. On this basis, through the range analysis and comprehensive balance method, the primary and secondary factors and the optimal combination of parameters is obtained. After that, orthogonal experiments were used to optimize the design parameters. Finally, the effectiveness of this method was verified by experiments. The experimental results show that the repeat zoom accuracy of the optimized liquid lens is 0.2 m⁻¹, and the zoom range is −15.2−5.85 m⁻¹ over the voltage range of 0 to 230 V. It basically meets the requirements of stable and reliable liquid lens zoom, high precision, and large zoom range.

Polarization imaging, a novel photoelectric detection technology, can simultaneously acquire the contour information and polarization features of a scene. For specific application scenarios, polarization imaging has the excellent ability to distinguish different objects and highlight their outlines. Therefore, polarization imaging has been widely applied in the fields of object detection, underwater imaging, life science, environmental monitoring, 3D imaging, etc. Polarization splitting or the filtering device is the core element in a polarization imaging system. The traditional counterpart suffers from a bulky size, poor optical performance, and being sensitive to external disturbances, and can hardly meet the requirements of a highly integrated, highly functional, and highly stable polarization imaging system. A metasurface is a two-dimensional planar photonic device whose comprising units are arranged quasi-periodically at subwavelength intervals, and can finely regulate the amplitude and phase of the light field in different polarization directions. Polarization devices based on metasurface are featured with compactness, lightweight and multi-degree freedom, offering an original solution to ultracompact polarization imaging systems. Targeted at the field of polarization imaging, this paper illustrates the functional theory, developmental process and future tendency of related metasurfaces. We discuss the challenges and prospect on the future of imaging applications and systematic integrations with metasurfaces.

In order to overcome the adverse effects of near-ground turbulence on the imaging quality of the optical systems at imaging distances of tens to hundreds of meters, an optical imaging system based on a long focal length telescopic objective lens and an integrated adaptive module is designed. With a system center height of 1.9 m and the imaging distance of 50~200 m, the outdoor imaging experiment of a resolution plate is carried out. The experimental results show that the influence of turbulence on imaging quality is obvious at medium and long distances of 50~200 m near the ground. The experimental system can effectively overcome the influence of turbulence at different distances and improve the consistency of image resolution and clarity. As the imaging distance increases, the influence of turbulence increases, and the system’s correction ability and the imaging quality decrease. The imaging resolution of the system can reach 0.5 mm at an imaging distance of 100 m. Cracks on the surface of a concrete model are observed and corrected at a distance of 200 m. The experimental results show that the system can suppress the influence of turbulence and improve the clarity of the image, which verifies the practical application ability of the system.

Under conditions with large temperature differences in an infrared optical system, its imaging quality will deteriorate due to severe temperature changes. Large field-of-view medium-wave infrared cameras for airborne forest fire monitoring work in drastically changing environments. The system also has high requirements for stray radiation. In order to ensure that the optical system performs stably and with good imaging quality in the large field-of-view and the required large temperature range, a cooled medium-wave infrared optical system is designed based on athermalization and the comprehensive evaluation method of stray radiation based on noise equivalent temperature difference. The optical system consists of 6 lenses and 1 filter whose working wavelength is 3.7~4.8 μm; its F-number, focal length, and field of view are 2.5, 62.5 mm and 14.36°×10.87°, respectively. The pixel resolution of the medium-wave uncooled detector is 640×512. By using a combination of silicon and germanium materials and reasonably distributing the optical power, achromatic aberration and athermalization designs are realized. Through cold reflection optimization and cold aperture matching, stray radiation noise in the system is well-suppressed. By a bit of aspheric optimization, higher-order aberrations are corrected based on the requirements. The results show that the imaging quality of the optical system is stable and good in the temperature range of −55~+70 °C.

Multiple sub-aperture interference imaging enables the images formed by the sparse aperture imaging system to have a higher resolution after the cophasing error is corrected. In this paper, the MTF and surface target imaging of the system are analyzed with a Golay3 sparse aperture imaging system as the research object when there are different piston and tilt errors among the sub-apertures. A Golay3 sparse aperture imaging system was developed to carry out an imaging experiment with the USAF1951 resolving power test target as the area target. Three-aperture synthetic imaging is achieved by adjusting the position of the plane mirror in the light beam deflection and the adjustment module to correct the piston and tilt errors of the sub-apertures. The results of a theoretical analysis are then verified. According to calculations, the developed system’s angular resolution of 1.38 urad is close to the equivalent single-aperture imaging system’s theoretical resolution of 1.18 urad. The developed Golay3 sparse aperture imaging system can correct the cophasing errors and improve the imaging resolution.

In order to realize the non-contact high-precision measurement of high-temperature temperature fields such as the tail flame, combustion and explosion of aerospace engines, a static interferometric high-temperature temperature field imaging and detection method is studied. Firstly, a static interference high-temperature temperature field detection system is designed. Using a theoretical analysis of the measurement principle of high-temperature temperature fields, the relationship between the optical path difference and the temperature at the lowest point of high-temperature interference signal intensity is studied; Secondly, according to the response band of the visible light area array detector and the common temperature range, a static interferometric Savart prism is designed, and temperature field imaging is realized by using it for one-dimensional scanning; Finally, the optical system is designed and the corresponding relationship between the minimum optical path difference of the interference and the temperature is obtained by fitting. From this, the linear fitting formula is obtained. Simulations are conducted to verify the interference signal image where the temperature field after passing through the system reaches the area detector. The static interferometric high-temperature temperature field detection method can achieve the high-precision detection of 1000 K−3000 K temperatures. In the linear region, the temperature measurement resolution is 1.4 K and the temperature measurement relative error is better than 0.8%. This research lays the foundation for high-precision high-temperature temperature field imaging in the military and civilian fields.

In order to reduce influence of background infrared radiation, optical system temperatures below −20 °C were necessary when satellite-borne long-wave infrared imagers worked in orbit. On the base of the weak heat conduction structure, a Ω type flexible sunshield made of MLI was developed and a cryogenic optical system was achieved through direct radiation cooling. Cage-like three-dimensional heat conduction straps made of copper were developed and an isothermal design for the primary barrel was realized. The cryogenic optical system applied to space remote sensing was used for the first time in China when it was tested in orbit with satellite SJ-9B. The results showed the temperature of the whole optical system could be maintained at −35 °C~−20 °C all the time, and the temperature difference in the primary barrel was no more than 4 °C. All flight test data met the temperature requirement of the long-wave infrared imager. The thermal control method is simple and effective, which can provide a reference for the thermal design of similar satellite-borne infrared optical systems.

In order to effectively suppress the interference of CO₂ radiation from 4.3 μm attachment on 3 μm−5 μm MWiR target signal, based on the Needle random intercalation optimization algorithm, an accurate inversion correction model for the growth error of multi-layer ultra-thick Ge/Al₂O₃ films under quartz crystal monitoring is established by the electron beam evaporation method, thus realizing the design, the accurate inversion and the accurate preparation of MWiR notch filter; in order to solve the problem that the surface profile of the MWiR notch filter changes greatly, the preset substrate surface method is used to realize the low surface profile regulation of MWiR notch filter. The results show that the high refractive index Ge film has good deposition stability with the increase of coating time, while the deposition scale factor of low refractive index Al₂O₃ thin film changes up to 11.9% in a regular gradual trend. For the prepared MWiR notch filter, the average cut-off transmittance is <0.3% at 4.2 μm−4.5 μm, and the average transmittances are >95% at 3.5 μm−4.05 μm and 4.7 μm−5.0 μm. The surface profile of the substrate after coating can be effectively controlled in a small range. The film has good adaptability to complex environment, and has successfully passed the environmental test of firmness, high temperature, low temperature and damp heat specified in GJB 2485-95.

A novel photonic quasi-crystal fiber (PQF) sensor based on surface plasmon resonance (SPR) is designed for simultaneous detection of methane and hydrogen. In the sensor, Pd-WO₃ and cryptophane E doped polysiloxane films deposited on silver films are the hydrogen and methane sensing materials, respectively. The PQF-SPR sensor is analyzed numerically by the full-vector finite element method and excellent sensing performance is demonstrated. The maximum and average hydrogen sensitivities are 0.8 nm/% and 0.65 nm/% in the concentration range of 0% to 3.5% and the maximum and average methane sensitivities are 10 nm/% and 8.81 nm/% in the range between 0% and 3.5%. The sensor provides the capability of detecting multiple gases and has large potential in device miniaturization and remote monitoring.

The machining quality and detection accuracy of aero-engine blades have a very important influence on the service life of blades. Aiming at the problem of improving the accuracy of blade detection, a high-precision scanning viewpoint planning method based on structured light was proposed in this paper. Firstly, the coarse model data were obtained by coarse scanning under the overall size of the blade, and the field of view was determined according to the camera resolution and acquisition accuracy. Secondly, the improved Angle Criterion algorithm was used to extract the boundary, and the boundary segmentation points were determined according to the boundary coordinates and the range of visual field. The coarse model was sliced by the section line method of surface, and the internal segmentation points were determined according to the slice results, so as to complete the uniform segmentation of point clouds. Then, a directed bounding box was established for the segmented point cloud data to obtain the coordinates of the center point, and the normal vector was statistically analyzed to determine the orientation of the main normal, so as to generate the viewpoint coordinates of high-precision scanning. Finally, the surface morphology of the blade was tested and verified. The experimental results show that the average standard deviation of the proposed method is reduced by 0.0054mm and the collected viewpoint is reduced by 1/3 compared with the viewpoint acquisition result of the supervoxel segmentation, which has a good application prospect in machining inspection of thin-walled blades.

We propose a method for improving the computational efficiency of passively mode-locked fiber laser, which is composed by symmetric split-step Fourier method (SSFM) and the global-error-local-energy (GELE) method for solving propagating equations. Our proposed method relies on the limitation of local energy increment related with global error within a certain value to control the selection of step size. This method has advantage of an automatic step adjustment mechanism. To achieve the same order of computation accuracy, the computational time of our method is 255 s, while SSFM with small constant step size method needs to calculate 3855 s. The computational time of our proposed method is one or two orders of magnitude less than that of the SSFM, which indicates our method can enhance the computational efficiency by a factor up to 10. It could be expanded with high-order algorithms, such as RK4IP, Adams, predictor–corrector, etc. for improving the accuracy.

In order to achieve accurate target ranging of weak or surface-free texture features based on a monocular camera, an improved difocus image ranging algorithm based on preserving edge spectral information is presented. By comparing two classical disfocal ranging theories with Fourier transform and Laplace transform as the calculation core, the corresponding definition evaluation function is constructed, select the method based on spectrum definition function with better sensitivity, and select the calculation range of frequency domain by retaining the information on the target edge. To verify the feasibility of the algorithm, 6 sets of different duck eggs samples were used to obtain scattered focus images of different aperture and different distances, and use the improved algorithm to solve the distance of duck eggs from the camera lens. The experimental results show that the improved algorithm based on the edge spectrum preservation has good ranging effect, with a correlation coefficient of 0.986 and Root mean square error (RMSE) of 11.39 mm, and it is found that the range ability can be effectively improved after the image rotation processing of the duck egg image taken at an oblique Angle, the root mean square error 11.39 mm to 8.76 mm, from 2.85% to 2.28% and the correlation coefficient to 0.99. It basically meets the requirements of stability and high accuracy of target ranging with weak or no surface texture features.

Non-Line-of-Sight (NLoS) imaging is a promising technique developed in recent years, which can reconstruct hidden scene by analyzing the information in the intermediate surface, and achieve "see around the corner", and has strong application value in many fields. In this paper, we review the reconstruction algorithm for NLoS imaging tasks. Firstly, considering the crossover and non-independent phenomena existing in the NLoS imaging classification, we use the different features of physical imaging model and algorithm model to reclassify it. Secondly, according to the proposed classification criteria, we respectively review the traditional and deep learning-based NLoS imaging reconstruction algorithms, summarize the state-of-the-art algorithms, and push the technical methods. And compared the results of deep learning-based and traditional NLoS imaging reconstruction algorithms for reconstruction tasks. Finally, the current challenges and the future development of NLoS imaging are summarized. Different types of NLoS imaging reconstruction algorithms are comprehensively analyzed in this review, which provides important support for the further development of NLoS imaging reconstruction algorithm.

Atmospheric turbulence affects the tracking and positioning accuracy of high-resolution remote sensing satellites seriously. This paper focuses on the effects of camera aperture, atmospheric turbulence intensity and satellite orbit height on the positioning accuracy. Firstly, we establish the turbulence model and turbulence simulation method based on Kolmogorov turbulence theory for earth observation. Then, the influence of camera aperture, satellite orbit height and atmospheric coherence length on the positioning accuracy of the satellite is simulated and analyzed, and then, the universal formula is deduced to calculate the tilt aberration of turbulence wavefront. Finally, based on this universal formula, the theoretical calculation formula of jitter is derived for earth observation. The research work can provide a theoretical basis of the influence of atmospheric turbulence for design, analysis and evaluation of very high-resolution remote sensing satellites.

In this paper, a multifunctional metamaterial device based on the phase transition properties of vanadium dioxide (VO₂) is proposed. The metamaterial structure consists of a top layer with the combined VO₂-filled SRR and metal cross, a polyimide (PI) dielectric layer, and a metal substrate. When VO₂ is in the insulating state, the cross-polarization conversion function can be realized, and the polarization conversion rate (PCR) is greater than 90% in the range of 0.48−0.87 THz. When VO₂ is in the metallic state, the device can realize dual-frequency absorption and high-sensitivity sensing functions. The absorption rates are higher than 88% at the frequencies of 1.64 THz and 2.15 THz. By changing the refractive index of the sample material, the sensing sensitivities at the two related frequencies are about 25.6 GHz/RIU and 159 GHz/RIU, and the Q-factors are 71.34 and 23.12, respectively. The proposed metamaterial multifunctional device exhibits the advantages of simple structure, switchable function, and high-efficiency polarization conversion, and provides potential application values in the future terahertz communication, imaging and other fields.

A filterless microwave photonic phase shifter (MPPS) with a tunable frequency multiplication factor (FMF) and a full 360-deg tunable range is theoretically analyzed and verified by simulation. In the scheme, two parallel Mach-Zehnder modulators (MZM), cascaded with two dual-parallel integrated Mach-Zehnder modulators (DPMZM) by a 2×2 optical coupler (OC), are used to generate the ±1st- to 4th-order sidebands adjustably, and a phase modulator (PM) is used to phase shift one of the two lightwaves. After photodetection, the 2nd- to 8th- order harmonics with a continuously tunable phase shift from 0 to 360-deg can be generated by adjusting the RF driving signal and the DC bias voltage of the DPMZM, and the DC voltage of the PM. Simulation results demonstrate that both 360-deg continuously tunable phase shift and frequency multiplication can be implemented. Large Optical Sideband Suppression Ratio (OSSR) and Electrical Spurious Suppression Ratio (ESSR) of around 20 dB can be obtained. The phase shifter wavelength insensitive performance has been also evaluated by simulation.

Airborne ambient temperature varies widely and airborne vibration is strong. And the mirror coating temperature is higher, the traditional bonding process will lead to bonding failure. Because of the difference of thermal expansion coefficient between Invar inlay and mirror material, the surface precision of mirror can not meet the requirement of system. Therefore, this paper puts forward a method of bonding the mirror after processing and coating, and designs some important parameters of the adhesive layer. In the scheme, RTV is used as the main binder, the mirror and the inlay are bonded together, and the effect of RTV curing on the structure is alleviated by good elasticity. The thickness of RTV is 1.1 mm, the width of RTV is 7.2 mm and the thickness of epoxy adhesive is 0.022 mm. The simulation results show that the RMS of the mirror shape is 25.91 nm and the first-order frequency of the mirror group mode is 242 Hz under gravity and 60 °C temperature change. The final surface detection RMS is 15.8 nm and the resonance frequency is 213 Hz. The experimental results show that the design of structure and bonding layer can meet the requirements of wide temperature and vibration condition.

3D reconstruction technology is one of the most popular research directions in machine vision, and has been widely used in the fields of unmanned driving and digital processing and production. Traditional 3D reconstruction methods include depth cameras and multi-line laser scanners, but the point clouds obtained by depth cameras have incomplete and inaccurate information, and the high cost of multi-line laser scanners hinders the application of this technology and Research. To solve the above problems, a three-dimensional reconstruction method based on a rotating two-dimensional laser scanner was proposed. First, a stepper motor was used to drive a 2D laser scanner to rotate to obtain 3D point cloud data. Then, the position of the laser scanner was calibrated by the method of multi-sensor fusion, and the point cloud data matching was completed by the coordinate system transformation. Finally, the collected point cloud data were filtered and simplified. The experimental results show: Reconstruction method compared with depth camera/IMU data fusion, the average error is reduced by 0.93 mm, the average error is 4.24 mm, the accuracy has reached the millimeter level, and the error rate is also controlled within 2%. The cost of the whole set of equipment is also greatly reduced compared to the reconstruction method of the multi-line laser scanner. It basically meets the requirements of retaining the shape characteristics of the object, high precision and low cost.

Three-dimensional reconstruction is a common method for cultural relics information conservation, mainly through point cloud alignment technology to reorganize the spatial point cloud information of cultural relics, and its alignment accuracy has an important impact on cultural relics recovery. To address the problems of low accuracy and poor robustness in the alignment of complex point cloud texture features on the surface of cultural relics, this paper proposes a local point cloud alignment method based on normal vector angle and faceted index features. Firstly, the normal vector angle and covariance matrix thresholds are set according to the point cloud planar characteristics, and the point cloud feature points satisfying both features are extracted; secondly, the K-nearest neighbor search extracts the point cloud local feature point set, and the two sets of point cloud center-of-mass positions are overlapped by rigid transformation for coarse alignment; finally, the nearest points are iterated based on ICP for fine alignment. By comparing with the traditional ICP, this method reduces the point cloud alignment error by 3% and reduces the matching time by 50%, which effectively improves the accuracy and efficiency of alignment and enhances the robustness of point cloud alignment.

Aiming at the problem of sea-sky-line detection in low-contrast infrared images being difficult and easily affected by such interference factors as clouds, strip waves and sea clutter, this paper proposes a method of using polarization difference images for sea-sky-line detection. Firstly, polarization difference imaging (PDI) is used to enhance the local contrast of the sea surface area and the signal-to-noise ratio (SNR) of the sea-sky-line. A method of large-scale local contrast accumulation of the polarization difference images is then used to determine the sea-sky-line area. Finally, the accurate detection of small-scale sea-sky-line is completed via combining the methods of gradient significance and polynomial fitting in the sea-sky-line area. Overall, the methodology integrates multi-dimensional information such as the degree of linear polarization (DOLP) and the angle of polarization (AOP) for sea-sky-line detection, and combines large-scale and small-scale detection, which can effectively overcome the interference of factors such as clouds, strip waves and sea clutter. The experimental results show that the accuracy of this algorithm for sea-sky-line detection is 98.5%, and the average time consumed is 16 ms, and that fast and accurate sea-sky-line detection can be realized through this algorithm, which in turn has wide applicability to different scenes.

A new method for measuring the flux distribution of high-magnification convergent radiation spot is proposed. The radiation flux sensor is used to measure the flux density at different positions of the spot, and the calibration curve of the grayscale and flux density at different positions of the spot is fitted by polynomial, and finally the radiation spot is obtained. In order to verify the accuracy and feasibility of the measurement method, a high-magnification convergent radiation spot flux distribution measurement experiment was carried out, and the direct measurement results of the radiant flux sensor were compared. The results show that the measurement results of the new method are consistent with the direct measurement results, and the average deviation is < 0.54%. Through analysis, the measurement uncertainty of this measurement method is 4.35%, and the measurement accuracy is higher than the traditional measurement. The method has been improved to meet the needs of practical applications.

Vision-based measurement has good application prospects and far-reaching development significance for advanced manufacturing fields such as aerospace, the military industry and electronic chips. Among them, on-machine 3D vision detection technology based on structured light is one of the hotspots and challenges in the field of precision machining. Based on the on-machine 3D measurement process of structured light, this paper discusses and summarizes the key technologies, including its technical requirements, methods and principles involved, related research status and existing problems in the measurement calibration, phase optimization solution, on-machine 3D point cloud processing and reconstruction of different feature surfaces. Finally, according to the actual needs of relevant technologies in the future, predictions are made with regard to processing field calibration, dynamic real-time 3D reconstruction, sub-micron and nano measurement, and measurement processing integrated data transmission technology, with the corresponding research ideas put forward.

in order to save the problem of the phase solution in white light interferometry and realize the height measurement of micro morphology, white light interferometry micro measurement algorithm based on principal component analysis was proposed. White light microscopic interference system is used to collect multiple interferograms and reconstruct them into vector form. From a set of interferograms, the background illumination can be estimated by a temporal average, eliminating background light components. Then, the eigenvalues and eigenvectors representing the original data are obtained by matrix operation. Finally, the phase distribution is calculated by arctangent function. Experimental results indicate that the measurement result of standard step height of 956.05 nm by the proposed method is about 953.66 nm, the solution is approximately consistent with the iterative algorithm, in comparison to the iterative algorithm, the average time of the proposed method is 2 orders of magnitude faster. The interference fringes with surface roughness of 0.025 μm were analyzed, the mean of surface roughness calculated by the proposed method was 24.83 nm, and the sample standard deviation is 0.3831 nm. The proposed method improves the deficiency of monochromatic interferometry and has advantages of low computational requirements, fast and high accuracy.

In a distance-selected imaging system based on single-photon detection, a short-pulse laser is emitted and between the transmitter and receiver for synchronization control, and the detector operates in photon counting mode and integrates in time to complete the imaging. In this paper, in order to obtain a short pulse laser that meets the system requirements while reducing the system’s size and cost, we propose to apply these two types of narrow pulse generation circuits to single photon distance selective imaging systems. We introduce the principle and design method of both types and verify the system through simulation, physical fabrication and testing. The characteristics of the pulse generator and factors affecting its pulse width and amplitude are analyzed. The physical test results show that the transistor-based method can generate a narrow pulse with a rise time of 903.5 ps, a fall time of 946.1 ps, a pulse width of 824 ps, and an amplitude of 2.46 V; the SRD-based method can generate a narrow pulse with a rise time of 456.8 ps, a fall time of 458.3 ps, a pulse width of 1.5 ns, and an amplitude of 2.38 V; and the repetition frequency of both can reach 50 MHz. Both design methods can be used with external current-driven laser diodes to achieve excellent short pulse laser output.

Ammonia gas is an important basic industrial raw material, and realizing its non-contact detection is of great significance for the timely detection of ammonia gas leaks to avoid major safety incidents. Aiming at the shortcoming of conventional ammonia leak detection devices that can only respond when ammonia diffuses to a certain range and makes contact with a sensor, a shuffling self-attention network (SSANet) model is proposed to realize the infrared non-contact detection of ammonia leaks. Due to the high noise and low contrast of ammonia leakage images obtained by infrared cameras, an infrared detection dataset of ammonia leakage was established through non-local mean denoising and contrast-limited adaptive histogram equalization preprocessing. On the basis of YOLOv5s, the SSANet model uses the K-means algorithm to cluster and analyze the candidate frame suitable for the infrared detection of ammonia gas leakage to preset the model’s parameters. Using the lightweight ShuffleNetv2 network, the depth of 3×3 in the Shuffle Block can be adjusted. The separate convolution kernel is replaced with a 5×5 depth, and the feature extraction network is reconstructed with an SK5 Block containing a new convolution module, which makes the model size, calculation and parameters non-intensive while improving the detection accuracy. The Transformer module is used instead of its original version. The C3 module in the network bottleneck module realizes the bottom-up fusion of multi-head attention in the leake area, and further improves the detection accuracy. The experimental results show that the size and parameter requirements of the SSANet model are reduced by 76.40% and 78.30%, respectively, to 3.40 M and 1.53 M compared with the basic model of YOLOv5s; the average detection speed of a single image is increased by 1.10% to 3.20 ms; and the average detection accuracy is increased by 3.50% , reaching 96.30%. This paper provides an effective detection algorithm for the development of a non-contact detection device for ammonia leakage to ensure the safe production and stable operation of ammonia-related enterprises.