The modified Gamma distribution and Mie scattering theory were used to examine the light scattering attributes of water cloud particles to investigate the effect of water cloud on quantum interferometric radar (QIR) performance parameters, and a relationship was developed between water content and extinction coefficient of four common water cloud particles. For the polarization state of light quantum, the polarization change law of QIR detected photon under the background of water cloud particles is researched, and the mathematical model of the effect of water cloud particles on the transmission distance, resolution, bit error rate, and the survival performance of QIR detected photon is established. The theoretical analysis and experimental simulation results show that the extinction coefficient linearly increases with the increase of water content in the water cloud, causing the increase of attenuation coefficient, thus increasing the energy dissipation of the detected photon and decreasing the transmission distance of the detected photon. When the number of emitted photons remains constant, the resolution of QIR decreases with the increase in the optical thickness of water cloud particles. When the concentration of water cloud particles remains constant, the bit error rate of the system decreases with the increase of the depolarization ratio. When the number of detectable points of the target is constant, the greater the interference intensity of the water cloud to the QIR system is, the lower the survival performance of the radar is. To improve the detection performance of the system, each index parameter of the QIR system should be adjusted adaptively according to the relevant parameters of the water cloud in the design, debugging, and use of QIR.

This work improves and applies the adaptive particle swarm optimization algorithm to the study of statistical model fitting of atmospheric turbulence profiles. First, an improved adaptive particle swarm optimization algorithm is proposed to improve the speed of particle swarm optimization and avoid falling into the local optimum. The distance between the current particle and the global optimal position is used to adjust the inertia weight coefficient and make nonlinear adaptive changes. The self-learning and social learning factors are based on the concept of symmetrical linear change to realize the adaptive change of the optimization focus in each stage. Second, the improved adaptive particle swarm optimization algorithm is introduced to solve the generalized Hufnagel-Valley turbulence model in Ali region, and the turbulence model profiles of morning, evening, and four seasons in the region are fitted. The simulation results show that all the decision coefficients are greater than 0.997, which agrees well with those of the statistical average profiles obtained by radiosonde. The proposed method has similar convergence accuracy to other adaptive particle swarm optimization algorithms, but the speed is faster. This paper introduces a new method for fitting Hufnagel-Valley turbulence profile models.

The current technological development has a certain field of exploration and application for the health monitoring of building structures. As a sensor with good performance, the fiber grating sensor is widely used in civil structures. The fiber Bragg grating (FBG) Internet of Things sensing is applied in the health monitoring of special-shaped structure based on the technology. The structure principal and performance advantage of fiber gratings are mainly introduced. Combined with engineering project examples, the relevant application methods of FBG in the health monitoring of special-shaped structures is studied. and data analysis is carried out. The research shows that FBG sensors can be used in the health monitoring of special-shaped structures, and there are also certain promotion and application values for other related civil infrastructure structures.

The measurement of the traditional time difference of arrival positioning technology is not accurate. In order to improve the situation of LED indoor positioning, this paper proposes an improved position estimation algorithm based on bounded grid. The algorithm in this paper firstly uses the hyperbolic positioning method to locate the signal source by time difference of arrival (TDOA). Boundary of the area where the signal source may exist at the time to be measured was set, and the area was meshed. The grid was weighted with a prior time. Through Bayesian filtering, the probability that the signal emission source may exist at the time to be measured is obtained. Thus, the position information of the signal emission source was obtained. On this basis, the speed of the signal source was estimated by combing the arrival frequency difference. The simulation results show that compared with the least-weighted squares positioning algorithm and the Chan algorithm combined with Kalman filtering, the algorithm in this paper has obvious advantages in the accuracy and stability of position and velocity measurement.

The millimeter wave massive multiple input multiple output(MIMO) system relies on accurate channel state information. However, the high frequency of the millimeter wave shortens the time slot for channel estimation, so the previous high complexity estimation algorithms that use either the sparsity in the beam domain or the low rank property in the antenna domain alone were no longer feasible. Therefore, this paper proposes a new estimation algorithm, which combines the sparsity and low rank property. The channel estimation is regarded as a matrix complete problem. The inexact Newton method based on Augmented Lagrange alternating direction is used to solve the problem. The simulation result shows that the proposed algorithm has faster convergence speed and higher accuracy than other algorithms.

An orthogonal frequency division multiplexing (OFDM) visible light communication system model based on N minimum shift keying (N-MSK) mapping is established to solve challenges related to light-emitting diode (LED) nonlinearity and carrier frequency offset caused by OFDM visible light communication. The Monte Carlo method is used to compare and analyze the differences between N-MSK and binary phase-shift keying (BPSK) mapping in the performance of signal power spectral density, constellation, carrier interference ratio, and bit error rate. The experimental results reveal that the N-MSK (N>1) mapping system has superior out-of-band attenuation characteristics. In the case of the same frequency offset, the carrier interference ratio of the system is increased by approximately 15 dB using the N-MSK (N=1) mapping mode, and the ability to suppress the intercarrier interference caused by carrier frequency offset is enhanced. For the same bit error rate (10-6), the signal-noise ratio (SNR) required by the MSK mapping system is 2 dB lower than that of BPSK mapping. The MSK mapping method can overcome the influence of LED nonlinearity on the system performance under the same SNR condition. Therefore, the proposed model has excellent signal constellation and bit error rate performance.

This study proposes a high-precisionwavelength demodulation algorithm of fiber Bragg grating (FBG) based on wavelet denoising to overcome the shortcomings of traditional wavelength demodulation algorithms in the online monitoring system of FBG, such as low detection accuracy and effectiveness. First, we perform rapid calculations on the spectral waveforms that are processed using the wavelet noise reduction method to generate a new function. Then, we obtain the center wavelength for the new function. Finally, a set of FBG transformer winding temperature online monitoring system based on a vertical-cavity surface-emitting laser is constructed; the wavelet noise reduction technique is used to demodulate the wavelength and indirectly acquire temperature data. The experiments show that the wavelet denoising technique outperforms the finding peaks directly, polynomial fitting, and Gaussian fitting algorithms in terms of speed and stability. In the temperature range of 70-90 ℃, the temperature measurement accuracy can reach ±0.04 ℃. The wavelength demodulation's highest standard deviation is less than 1.67 pm. Further, the operational efficiency of the algorithm is greater than that of the commonly used Gaussian fitting algorithm. Therefore, the algorithm may be used in the FBG's high-precision real-time online monitoring system in the industrial environment.

Relative to the collaborative task requirements of an unmanned aerial vehicle (UAV) swarms under strong electromagnetic interference, an energy efficient optimization routing algorithm for wireless ultraviolet cooperative UAV swarms is proposed. The proposed algorithm exploits the advantages of the ultraviolet scattering communication to maximize the air operation time of the UAV and the efficiency of mission completion. The proposed algorithm improves the threshold of the candidate cluster head selection of non-uniform clustering algorithm by introducing distance and energy. In the inter-cluster communication process, cluster head nodes can select the optimum data transmission route to forward the information to the lead UAV. Compared to LEACH and EEUC, the simulation results reveal that the proposed algorithm increases the energy efficiency of the UAV network by 21.02% and 3.92%, respectively. Moreover, the lifetime of the network is extended by 23.5% and 5.6%, respectively. Therefore, the proposed algorithm can efficiently balance the energy consumption of the nodes and extend the lifetime of the UAV swarms.

The strain transfer of fiber Bragg grating (FBG) strain sensor determines its accuracy when monitoring the structural strain. To study the influencing factors of strain transfer of FBG strain sensor, the mechanical model of the sensor strain transfer is developed in this paper. The theoretical derivation of the strain transfer is conducted, and the formula of strain transfer rate of the sensor is obtained. Meanwhile, to ensure proper computation the finite element simulation and calculation are performed for its special structure. Furthermore, the influencing factors and effects of the strain transfer of the sensor are analyzed, and different influencing factors are simulated using the finite element simulation, which verifies the accuracy of the theoretical derivation.

In elastic optical networks (EON), spectrum fragmentation causes a large number of requests blocked. In order to decrease fragmentation and reduce the bandwidth blocking probability of immediate reservation (IR) requests, a two-dimensional fragmentation-aware routing and spectrum allocation (RSA) algorithm is proposed. In the routing phase, the proposed algorithm considers the route hop number and the modulation format, aiming to calculate multiple candidate paths with a smaller number of hops and a higher level of modulation format offline. In spectrum allocation phase, a two-dimensional fragmentation metric namely combined fragmentation metric (CF) is designed to evaluate each candidate spectrum block, which comprehensively considers three factors: distance to frequency boundary, impact on contiguous resources, and resource consumption. Then, the proposed algorithm will allocate the candidate spectrum block with the minimum CF to IR requests. The simulation results show that compared with several well-performed benchmark algorithms, the proposed algorithm can further reduce the bandwidth blocking probability and improve the spectrum utilization.

According to the optical refraction characteristic of transparent medium, the measurement error of internal standard method is analyzed, and then an improved method of liquid refractive index measurement using laser speckle interferometry is proposed. This paper designs a double-groove structure composed of two identical rectangular grooves with one of the grooves filled with the measured liquid, and then an image speckle optical measurement system has been built, while the double-groove structure is placed between the imaging lens and CCD camera. First, adjusting the two grooves to be parallel and perpendicular to the optical axis, one speckle pattern is collected by CCD camera. Then adjusting the included angle of two grooves to make them symmetrically deflect to a small angle, another speckle pattern is collected. After that, a speckle in-plane displacement before and after the change is obtained by processing the above two speckle patterns using the digital speckle correlation method, and finally the refractive index of transparent liquid can be calculated theoretically. According to the above method, the refractive indices of water and ethanol are measured, and the results show that this improved method has the advantages of small error and high accuracy, compared with internal standard method.

Wide color gamut (WCG) and high dynamic range (HDR) display can truly replicate a real scene in a high-performance display. Light steering device based on phase modulation can change the energy distribution of a light field; thus, remarkable display performance can be realized using WCG and HDR in a display system comprising laser source and light steering technology. Light steering technology can be applied in situations demanding high performance, including cinema display and projection augmented reality. The ability to expand the dynamic range depends on the light steering modulation algorithm. Based on this, a new light steering modulation algorithm is proposed. A free-form surface lens is used to model the light steering device, the iterative algorithm is used to calculate the phase distribution, and the linearization and discrete Fourier transform are used to improve the algorithm speed. Simulation results show that the proposed algorithm can improve the maximum brightness of a picture by 10-fold and achieve more than 10 times the dynamic range via light steering modulation.

The traditional method for locating and establishing a coordinate system for fuel injection nozzle processing of automobile nozzles uses tooling fixtures. Because the manufacturing accuracy and installation error of tooling fixtures will result in a large deviation between measured aperture, hole shape, and hole position and theoretical values affecting the reliability of fuel injection nozzle; moreover, the performance of the diesel engine, stability of emission targets, and reliability of the diesel engine produce a substantial influence. Based on these, we propose a high-precision adaptive location technology based on a multifeature point matching algorithm. By measuring the spatial position of several feature points (at least six feature points) on a real automobile nozzle, the precise positioning parameters of the actual automobile nozzle and theoretical model in the machine tool's coordinate system are calculated based on the measurement date of feature points given in the three dimensional model. The automobile nozzle's all-generation hole machine parameters are then calculated. The experimental results show that the locating accuracy is less than 0.1 mm. The location technology can effectively reduce the hole machining deviation, which is an effective and feasible solution to improve the automobile nozzle location accuracy.

In this paper, combined with the principle of phase measuring deflectometry, the problem of defect detection is converted to the problem of extracting abrupt areas using absolute phase difference to solve the problem that traditional machine vision is difficult to detect surface defects of mirror-like surface. First, the coordinates and dimensions of the surface to be measured are obtained by gray projection method, and the area of the surface to be measured is segmented. Then, phase extraction and phase unwrapping are performed on the measured surface and the absolute phase distribution map is used as a difference with the absolute phase distribution of the reference surface to obtain an absolute phase difference map. Finally, the phase difference map is processed in frequency domain to filter the periodic components, and the Sobel filter is used to extract the phase difference map's abrupt areas to obtain surface defects. The experimental results show that the defect detection method based on phase measuring deflectometry can detect surface defects of mirror-like objects with a 0.180 mm detection accuracy.

We observed and investigated the phenomenon of switching between stable state and quasi-periodic state in circular-side hexagonal resonator microcavity laser with optical feedback by the Lang-Kobayashi rate equation. The influences of feedback rate and bias current on the switching between two dynamical states are analyzed, and the reason for this switching phenomenon is analyzed by bifurcation diagrams. The results show that the phenomenon of switching between these two states is more likely to occur under the conditions of high bias current and long external-cavity feedback. Finally, the difference between this switching phenomenon and the similar phenomenon of other lasers is compared and analyzed.

This paper proposes a microwave mode-locking frequency comb scheme using active mode-locking technology and photoelectric oscillator. The scheme uses traditional optoelectronic oscillators (OEO) as oscillators, and uses a mixer to add microwave modulation signals from outside to form an optoelectronic oscillator. The mode-locking of the oscillator oscillation mode realizes the microwave active mode-locking. At this time, the oscillator generates a series of frequency combs with equal frequency intervals. When the system loop cavity is 1 km long, low-phase-noise microwave comb signals with a frequency interval of 201.2 kHz are obtained through experimental analysis. The first-order carrier phase noise of the microwave comb signal is -97.2 dBc/Hz@1 kHz and -116.721 dBc/Hz@10 kHz, and the line width is approximately 10 Hz. The scheme is considerably improved in the phase-noise index compared to the conventional microwave frequency comb generation method. Furthermore, microwave frequency combs signals with a tunable frequency interval ranging from 100 kHz to 6 MHz can be obtained by changing the cavity length and modulation signal frequency of OEO.

Quantum dot micropillar laser is an excellent research platform for photonic integration and secure communication, due to its μm-scale mode volume and unique dynamics. In this study, a quantum dot micropillar laser with external cavity optical feedback is used to generate a two-mode chaotic light field. The competition between strong mode and weak mode, time delay signature, and effective bandwidth of the quantum dot micropillar laser with optical feedback are examined under various pump currents and feedback intensities. The results demonstrate that when the mode competition between strong mode and weak mode is high, i.e., the output power bifurcation between strong mode and weak mode is obvious, the output power difference between the two modes decreases at first, then decreases, as the feedback intensity increases. The chaotic light field's effective bandwidth increases at first, then decreases, and increases again as the feedback intensity increases. When the pump current is 13 μA, and the feedback intensities of the strong mode and weak mode are 4 ns-1 and 3 ns-1, the effective bandwidth of the chaotic laser of the strong mode and weak mode increases to the first peak values of 8.91 GHz and 8.49 GHz, respectively. The time delay signature of the two-mode chaotic laser first increases, then decreases, and increases again as the feedback intensity increases. When the pump current is 13 μA, the feedback intensities of the strong mode and weak mode are 16 ns-1 and 14 ns-1, respectively, the time delay signatures of the coherence-collapse chaotic laser for the strong mode and weak mode are 0.083 and 0.092, and the corresponding effective bandwidths are 11.31 GHz and 11.02 GHz.

The superhydrophobic surface can effectively improve the corrosion resistance of magnesium alloys. To this end, the preparation of superhydrophobic surfaces of magnesium alloys by laser etching combined with chemical immersion treatment. The surface structure and chemical composition of superhydrophobic magnesium alloy were characterized by laser confocal microscope and energy dispersive spectrometer. The results show that when the laser energy density is 20 J?cm-2,the superhydrophobic magnesium alloy surface with contact angle of 158.14° can be obtained, and it exhibits good durability. In addition, through potentiodynamic polarization test and carbon powder cleaning test, the surface of superhydrophobic magnesium alloy shows excellent corrosion resistance and antifouling self-cleaning performance. This excellent composite performance will promote its development in various fields in the future.

With the advent of the era of rapid information growth, the demand for data bandwidth continues to increase. Vertical-Cavity Surface-Emitting Lasers (VCSEL) have been widely used as a new type of optical communication devices. Starting from the parasitic circuit of the semiconductor laser, the internal photoelectric conversion process of the VCSEL is analyzed, and the parasitic characteristics of the intrinsic laser and the external package are considered. The large-signal and small-signal equivalent circuit models are built respectively, and the simulation is carried out using Python language and Pspice software. The influences of spontaneous emission coefficient and optical confinement factor on the threshold current are analyzed in the large-signal model, and the influence of parasitic network parameters on the modulation response bandwidth is discussed in the small-signal model. The simulation results show that the threshold current of the VCSEL device can be reduced, and the modulation bandwidth can be increased, by adjusting the spontaneous emission coefficient, optical confinement factor and parasitic network parameters.

The effect of laser remelting on the forming quality and mechanical properties of sample components during the preparation of TC4 titanium alloy using selective laser melting (SLM) is examined. According to the experimental results, the upper surface quality and densities of TC4 samples improve with increasing laser remelting iterations, and the upper surface roughness and densities improve from 13.2 μm and 98.43% without remelting to 8.7 μm and 99.23% with remelting twice, respectively. The side surface quality, however, does not alter considerably. The elongation increases and improves with laser remelting iterations, from 1.15% to 1.33%, but the tensile strength remains constant. Observing the microstructure of the TC4 sample, the acicular martensite α′ phase occupies the microstructure of the TC4 sample before and after laser remelting.

In this paper, a square symmetrical metamaterial terahertz multi-frequency absorber is designed, which can solve the problem of high frequency, multi-frequency, and high absorption rate of the absorber. The terahertz absorber is composed of a metal-dielectric-metal structure, the bottom layer is a metal film, the middle layer is a polycarbonate dielectric substrate, and the top layer is a square symmetrical metal resonance structure. The finite difference time domain method is used to simulate the transmission and reflection performance of the absorber. The finite-difference time-domain method is used to simulate the transmission and reflection performance of the absorber. Through calculation, five obvious resonant absorption peaks are obtained in the frequency range of 3-10 THz. The frequencies of the absorption peaks are 4.8 THz, 6.55 THz, 6.85 THz, 7.65 THz, and 7.88 THz, respectively. The absorption rates of these absorption peaks can reach 98.56%, 99%, 99.64%, 99%, and 90.39%, respectively. The characteristics of multi-frequency and high absorption rate are realized, and the absorber is insensitive to the incident angle. It can still maintain excellent absorption characteristics at large incident angles. The unit size of the absorber is 50 μm × 50 μm × 9.6 μm, which can be used in the fields of multi-function, multi-channel, multi-frequency communication, and plays a role in preventing electromagnetic pollution, eliminating electromagnetic interference, and improving weapon combat capability.

A periodic mid-infrared broadband chiral structure is proposed, in which each unit is composed of four indium tin oxide (ITO) helical subunits in different rotating directions. The simulation results show that the flat-topped broadband circular dichroism (CD) can be achieved in the mid-infrared waveband by optimizing the number of helical turns, the helical radius, the pitch of helix, and the wire radius of helix. Compared with the two non-rotating helical structures, the CD band of the ITO rotating helical structure is found to be broader. At the wavelength of 7.95 μm, for the ITO rotating helical structure, the maximum value of CD is 0.454 and the full width at half maximum (FWHM) of CD is 7.5 μm in the wavelength ranging from 4.1 to 11.6 μm. The broadband CD is caused by the strong coupling among the four ITO helical subunits in different rotating directions. The simulation results also show that compared with the gold and silver rotating helical structures, the proposed structure exhibits evidently better broadband CD, which provides a new idea for the design of broadband polarization state control devices in the mid-infrared band.

To reduce the weight of the large-aperture (740 mm × 480 mm) rectangular scanning mirror and ensure the surface accuracy of the mirror, this study proposes a lightweight structure design with back openings, mainly triangular lightweight holes, and a lightweight rate of 81.4% by combining the two- and three-dimensional equivalent stiffness models. Based on the principle of ball joint and flexible hinge, two types of scanning mirror components with different three-point back support modes are designed. The finite element analysis results show that under the coupling condition of Y-direction gravity and a uniform temperature difference of 40 ℃, the root-mean-square (RMS) value of the mirror surface error of the ball joint and flexible hinge support structure are 12.3 nm and 12.9 nm, respectively, which satisfies the optical design requirement of less than or equal to 0.025λ (wavelength λ=632.8 nm). Furthermore, the first-order natural frequencies are 68.1 Hz and 85.5 Hz, and the flexure hinge structure had better stiffness. The surface error of the flexure hinge scanning mirror is measured using the autocollimation method. The measurement results show that the surface error RMS value is 0.025λ. This result provides a reference for developing a large-aperture rectangular scanning mirror assembly.

In order to solve the stress concentration problem of the extension and bending deformation of the stacked PZT (Pb(Zr, Ti)O3) actuator used in piezoelectric fast steering mirror (PFSM), the extension and bending deformation model of the stacked PZT actuator was analyzed firstly based on Timoshenko model. Then, the relationships between the dynamic stress of stacked PZT actuator and the driving voltage amplitude, the driving voltage frequency and bending stiffness of flexible hinge on top of PZT actuator were analyzed by the method of piezoelectric coupling theory. Finally, the optimal design parameters of 300 mm diameter PFSM were obtained by response surface method. The research method and analysis results of this paper could provide reference for optimizing the parameters of key components of PFSM, reducing the stress concentration of stacked PZT actuator, and improving the durability and reliability of PFSM.

The optical power of the LED array was affected by thermology and electricity. The photo-electric-thermal (PET) parameters of the LED chip were coupled, and the thermal coupling relationship in the LED array was complicated, which makes it difficult to design the structure of the high-power light source. This paper proposes an optical power calculation model based on PET theory. Firstly, according to the working mechanism of the LED chip, the coupling relationship between its electrical power, junction temperature and thermal power was constructed. Secondly, by using the thermal coupling simulation result of the LED array as the training sample of the BP neural network, we obtain a BP neural network with input as layout spacing and thermal power and output as LED junction temperature. Finally, the junction temperature obtained by ANN was used as the temperature condition of the PET equation to calculate the optical power of the LED array. In order to verify the accuracy of the model, the experimental verification was performed. The maximum error was 7.6%. This model can analyze the maximum optical power operating point of the LED array under different layout parameters and heat sink temperatures. The optimization design problem of the LED array layout and heat sink structure was solved.

Based on Bi1.5Sb0.5Te1.8Se1.2 material, a grating-type ultraviolet absorber was designed. Using the finite element method, the dependence of the absorption characteristics of the absorber on structural parameters, incident angle and working wavelength was analyzed in detail. The absorption mechanism of the absorber is the magnetic polariton resonance effect. By adjusting the structural parameters, incident angle and working wavelength, the absorption characteristics of the absorber can be adjusted. With optimized parameters, the absorption rate can reach more than 80% in the wavelength range of 200~400 nm and the incident angle range of 0~75°. The work in this paper provides a theoretical basis for the design and manufacture of ultraviolet absorbers and their applications in ultraviolet detection and protection, biosensing, and ultraviolet photocatalysis.

Aiming at the characteristics of two-dimensional silicon grating microstructure in the near infrared light absorption rate is extremely low, a micro-nano composite structure is proposed to enhance the near infrared absorption of Ag nano-pit and silicon grating by using isolators. The absorption rate of the composite structure in the wavelength range from 0.78 μm to 2.5 μm is studied based on the finite-difference time-domain method. The influence of the grating structure and Ag nano-pits on the light absorption efficiency is analyzed. The simulation results show that when Ag nano pits with a diameter of 0.1 μm are embedded in the grating gap with a period of 0.2 μm and a duty cycle of 0.5 and on the surface of the grid column, the absorptivity of the composite microstructure is above 23% in the near infrared wide band, and the average absorptivity is up to 52.3%, theoretically. When Al2O3 dielectric layer is added on the grating surface, the absorption rate of wide band is above 41.3%, and the average absorption rate is increased to 65.1%. Finally, the absorption efficiency is improved in the wide wavelength range of near infrared, which provides a new method to enhance optical absorption in photodetector, solar cell, optical communication, radar stealth, biomedical and so on.

Herein, the phase distribution characteristics of Laguerre-Gaussian (LG) beams incident on a layered topological insulator (TI) thin film are studied using the plane angular spectrum expansion method and transmission matrix theory. Numerical results show that the phase structure of LG beams in the reflected and transmitted fields is affected by the changes in topological magneto-electric polarizability. Particularly, the center axis of the phase distribution of p-wave shifts left or right. This research on the phase distribution characteristics of LG beams incident on layered topological insulator thin films has significance in wireless laser communication, optical trapping, particle manipulation, nonlinear optics, information coding, and other fields.

Plasma electromagnetic parameters are very important in development of plasma technology. In this paper, a testing method is presented based on a one-dimensional microwave photonic crystal with the cold plasma under test as a defective layer. The transfer matrix method (TMM) is used to simulate the relationship among plasma parameters, frequency offset of the defective peak, and the peak transmission intensity. The results indicate that the plasma and collision frequencies can be mapped into the frequency offset of the defective peak and the peak transmission intensity. Therefore, one can obtain the plasma electromagnetic parameter frequency by measuring the offset of the defective peak and the peak transmission intensity. This measuring approach provides a noncontact and sensitive way of sensing the electromagnetic parameters of cold plasma.

Although classical-quantum channel multiplexing technology attempts to improve the channel use of quantum secure communication, noise crosstalk severely limits the quantum channel transmission efficiency. A combined optimisation method is used to optimise the channel allocation strategy based on channel Raman noise interference analysis, and an optimal band selection algorithm suited for the quantum key distribution system is proposed. The allocation of classical and quantum channels is adjusted and optimised using the proposed combinatorial optimisation algorithm based on the correlation between the noise and channel relative position to obtain a multi-band multiplexing scheme that minimises noise. Compared with the traditional dual band multiplexing scheme, the optimal multi band multiplexing scheme can effectively reduce the interference of classical light to quantum light between different frequency bands, so as to improve the key rate of channel transmission.

Because a heat bath forming the surrounding environment of an open quantum system always contains Bosons and Fermions at the same time, it is more practical to describe the heat bath using a mixed bath rather than a single Bosonic or Fermionic bath. The dynamical evolution properties of the quantum entanglement and quantum dense encoding channel capacity of the Heisenberg XYZ spin chain model coupled with a non-Markovian Bosonic bath and Fermionic bath simultaneously were studied and compared with a non-Markovian single bath using the non-Markovian quantum state diffusion method. The numerical simulation results show that compared with a non-Markovian single bath, the Heisenberg spin chain model coupled with the non-Markovian hybrid bath has higher entanglement, better quantum dense coding, and a longer relaxation time. These results show that the non-Markovian hybrid bath has more advantages than the non-Markovian single bath. A system in the non-Markovian hybrid bath improved quantum entanglement and optimized quantum dense coding.

Aiming at the transceiver technology in wireless optical communication, this paper combs the relevant research progress from two aspects of free space optical communication and underwater optical communication, summarizes the development trend of wireless optical communication transceiver technology from communication bands, modulation modes, and photodetectors according to different scenarios, analyzes the application prospect of single photon detection in wireless optical communication. Then we report our team's results of applying superconducting series nanowire single-photon detectors to space optical communication, which is expected to provide reference and ideas for related research.

The coating layer of traditional silica optical fiber is generally polymer, which is prone to thermal aging at high temperatures. This characteristic is the main reason why optical fiber is difficult to be applied in a high temperature environment. Metal materials have better high temperature resistance than polymer, which can effectively protect the surface of the optical fiber from water vapor. It is a hot research topic of high temperature optical fiber coating materials. This paper analyzes and compares five main optical fiber surface metallization coating methods (vacuum evaporation, sputtering, electroplating, electroless plating, and freezing method). The results show that electroless plating is the main method for metallization of optical fiber devices due to its economical and environmentally friendly features. Melt coating technology is the mainstream choice of metal-chemical industry production.

The magnetic properties and fluidity of a magnetic fluid have great potential applications in the field of temperature and magnetic field sensing. The combination of a magnetic fluid and an optical fiber sensing structure can modulate the light wave according to the changes in external temperature and magnetic field and obtain the sensing variation of temperature and magnetic field by demodulating the parameters of the characteristic spectra. This review summarizes the research progress of temperature and magnetic field sensors based on magnetic fluids according to different combinations of magnetic fluids and sensing structures. Furthermore, it introduces the temperature and magnetic field sensors based on mode interference, evanescent wave, fiber grating, fiber ring mirror, photonic crystal fiber, surface plasma, and Fabry-Perot interference. This review analyzes the sensing principle and sensitivity of each sensing structure and presents the future development trend. The temperature and magnetic field sensor with special fiber filled by magnetic fluid is shown to have a high sensitivity, a stable structure, and a strong anti-interference ability.

Photonic crystal lasers can further reduce the optical mode volume and the lasing threshold using the band gap effect and localized effect, which can meet the needs of device miniaturization and optoelectronic integration. Photonic crystal lasers have broad application prospects in light-emitting diodes, sensors and other aspects, so they have attracted much attention. The lasing threshold is defined as the minimum energy density of lasing oscillation and is an important index for the integrated application of laser devices. Perovskite material has the characteristics of high optical gain, which makes it an ideal gain material for realizing low threshold laser. When combined with photonic crystal laser, low threshold or no threshold pumping lasing can be realized. Based on the resonator and gain medium, the two factors (gain and loss), which are the two main factors affecting the threshold of the laser, are briefly described in terms of the resonant cavity and the gain medium, and some methods to reduce the threshold is proposed. Then, photonic crystal lasers are classified according to the dimension and structure of photonic crystals. In addition, the research progress of low threshold of perovskite photonic crystal lasers is reviewed. Finally, the development prospect of perovskite photonic crystal lasers is prospected, in order to achieve low threshold or even zero threshold, high power, high quality lasing output, and promote the integration and multi-field application of semiconductor lasers

Optical fiber has the advantages of low loss, high stability, and strong anti-interference ability, which plays an outstanding role in the construction of long-distance, high-precision, and highly reliable time-frequency transmission system. This paper combs the implementation scheme and related research results of the long-distance optical fiber time-frequency transmission system, and analyzes the influence of bidirectional delay asymmetry and various noises on the transmission accuracy, stability, and transmission distance. In addition, this paper puts forward the next development research suggestion for the fusion of optical fiber time-frequency transmission network and existing optical fiber communication network.

This work explorers the feasibility of using hyperspectral technology to estimate the chlorophyll content of long-staple cotton leaves. The spectral data and chlorophyll content of long-staple cotton were measured from field observations; original spectral data were transformed to first-order differential and continuum-removed spectra, and then four common vegetation indices and three optimized spectral indices were calculated. According to correlation analysis, we used the support vector machines (SVM) regression model to estimate the chlorophyll content of long-staple cotton leaves. The results show that the chlorophyll content is negatively correlated with spectral reflectance in the ranges of 530?560 nm and 700?750 nm, and the correlation of the first-order differential spectra passed the 0.01 significance level test. Based on the first-order differential, an SVM model was established to estimate the chlorophyll content of long-staple cotton. The coefficient of determination reached 0.72, the root mean squared error and relative error were 1.99 and 0.72, respectively. This study demonstrates that the prediction accuracy is higher than SVM model constructed by the vegetation index and optimized spectral index. The results of this study can provide a reference for the rapid detection of chlorophyll content in long-staple cotton.

In this study, a terahertz absorber based on graphic graphene, which exhibited tunable ultra-wideband absorption characteristics, was designed. The top, middle, and bottom of the absorber comprised ultra-thin graphene, dielectric, and gold layers, respectively. The absorber was designed and simulated by changing the thickness of the middle layer and the Fermi energy level of the top layer; the Fermi level of graphene could be controlled by changing the gate voltage. The results show that the absorber exhibits ultra-wide frequency absorption in the low-frequency region, and the absorption characteristics are optimized when the thickness of the middle layer is 30 μm; the opening and closing of the absorber can be controlled by changing the Fermi energy level of graphene, while the frequency position and bandwidth of the absorption peak are adjusted to make the absorption peak move close to 431 GHz, thus realizing a tunable function of the absorber. When the Fermi energy level of graphene is 0.4 eV, the bandwidth with an absorption rate of more than 90% is 1.8744 THz and the peak absorption rate is 99.3357%. The absorber achieves perfect absorption.

Thirty-nine yellow cigarette case samples were tested by X-ray fluorescence spectrometry, Raman spectrometry, and differential Raman spectrometry to establish a classification method for cigarette case evidence. Using the hierarchical clustering method, the samples can be classified into five categories based on X-ray fluorescence spectrum data. The Raman spectrum data and differential Raman spectrum data are analyzed by synthesis. The principal component analysis is used to reduce the dimension of the data, followed by K-Means clustering to achieve more accurate classification based on hierarchical clustering. The samples can be classified into 12 categories. The results show that the proposed method fully combines the advantages of X-ray fluorescence spectrometry and differential Raman spectrometry, and combined with chemometrics, it can achieve better classification tests for cigarette case samples and provide clues and direction for the investigation work of public security organs.

In order to achieve the accurate classification of sedative-hypnotic drugs, the infrared spectra data of 92 samples of 3 kinds of sedative-hypnotic drugs including benzodiazepine, phenothiazine, and barbital were collected. Then the classification model was constructed after data preprocessing. The experimental results show that the accuracy of series fusion is better than mean fusion and difference fusion. The random forest model was used for modeling and analysis after the fusion of the fingerprint region characteristic variables of the original spectrum and the first-order derivative spectrum. It could achieve thorough identification of three kinds of sedative-hypnotic drugs, with the accuracy up to 100%. The method is rapid and accurate, which can provide a new method and idea for the examination of hypnotics in judicial identification to a certain extent.

Cavity confinement was combined with traditional laser-induced breakdown spectroscopy (LIBS), using Ba Ⅱ 495.709 nm as the analysis line to improve the quantitative analysis and detection of Ba in the soil. A univariate calibration model based on the spectral peak integration, multivariate principal component regression (PCR), and artificial neural network (ANN) calibration model was established to quantify the metal Ba content in the soil. Compared to traditional LIBS, cavity-confinement LIBS (CC-LIBS) increased the spectral intensity and signal-to-noise ratio of the characteristic spectrum. When Ba was analyzed using the spectral peak integration method, CC-LIBS could improve the precision of univariate quantitative analysis compared to traditional LIBS. CC-LIBS combined with multivariate regression model PCR and ANN was used to improve the detection accuracy of LIBS and reduce the matrix effect in the soil on the content analysis.In addition, the correlation coefficient of calibration curve was improved from 0.63 to 0.84. The mean relative error (MRE) of the verification set was reduced from 47.52% to 23.44%, respectively. And the detection limit for Ba element was reduced from 64.73 to 37.86, respectively. CC-LIBS combined with multivariate regression model PCR and ANN was used to improve the detection accuracy of LIBS and reduce the matrix effect in the soil on the content analysis. The correlation coefficient of multivariate regression calibration curve were 0.941 and 0.999, respectively. And MREs of verification set are 9.93% and 5.35%, respectively. This research provides a new idea for the application of LIBS technology to soil quality testing.

A molybdenum cladding layer was prepared by laser cladding technology with a preset powder to improve the comprehensive properties of Nb alloy. The microstructure, crack rate, hardness, and wear resistance of the laser cladding layer with different energy densities were analyzed using a metallographic microscope, scanning electron microscope, X-ray diffraction, microhardness tester, and friction and wear tester. The findings show that when the energy density was 6.67 J/mm2, the surface of the cladding layer was smooth and the weld path was regular and continuous. The hardness of the cladding layer increased from 420 HV0.05 to 480 HV0.05 when the energy density was increased from 5.56 J/mm2 to 8.90 J/mm2, while the wear rate decreased from 12.24×10-3 mg/m to 7.59×10-3 mg/m, showing a 38% decrease. The phase of the cladding layer was mainly a Nb-Mo solid solution, with a Mo content of up to 22.3%. After 5 h of corrosion with 10% HF acid, no grain boundaries of the cladding layer were found, and the corrosion resistance of the cladding layer to HF acid showed significant improvement. In conclusion, the comprehensive performance of the niobium alloy can be improved by preparing a molybdenum cladding layer by laser cladding.