In order to meet the requirement of high-resolution dual-comb spectroscopy for the mutual coherence of optical combs, a method of dual-comb homologous frequency stabilization is proposed, that is, two optical fiber combs are locked on two frequency sidebands of the same phase modulated continuous wave laser. This method makes the two combs have the same optical reference, so there is no need for complex phase correction circuit and ultra-stable optical cavities. The coherence time is greater than 1 s. After experimental verification, this method obtains the comb-line-resolved dual-comb spectrum signal.

In this paper, the light intensity scintillations of plane wave and spherical wave are analyzed and compared for providing references for engineering design and performance evaluation of the optics system employed in turbulence medium. First, based on the classic weakly fluctuating turbulence theory, the analytical expression of the light intensity scintillation at aperture reception is derived. Then, based on the extended Rytov theory, the light intensity scintillation under nonweak fluctuation conditions is calculated. Finally, the light intensity scintillation of plane and spherical waves is simulated under various turbulence intensities and Fresnel numbers. The results show that when the Rytov variance is less than 4.8, an intersection point is present between the light intensity scintillation curves of the plane and spherical waves. The intensities of the plane and spherical wave scintillations under the Fresnel number corresponding to the intersection point are equal. When the Rytov variance is greater than 4.8, the light intensity scintillation of the plane wave is always less than that of the spherical wave. This research is of great significance for designing optical transceiver antennas and selecting beam wavelengths and waveforms in wireless optical communication systems.

Voltage control of electromagnetically induced grating is studied in an asymmetric double quantum dot system by use of quantum coherence in semiconductors. Owing to voltage tunneling effect, electromagnetically induced transparency can appear synchronously at two different frequency windows. By suitably tuning related parameters, the absorption property can be significantly modified. Therefore the intensity of a phase grating, especially its first-order diffraction intensity, can be enhanced significantly for a certain probe detuning with weak absorption. The influences of tunneling voltage, intensity of the pump field, interaction length and others on the efficiency of phase grating are investigated and the results show that the first-order diffraction efficiency of the phase grating is enhanced by 50% by simultaneously increasing the voltage tunneling rate and intensity of pump field. The results have potential applications in quantum information processing, quantum networks and optical imaging.

In the time delay estimation of chaotic spread spectra, the main peak to side lobe ratio obtained by using basic cross-correlation is not ideal, and the peak values of misjudged points are too large. Based on the advantages of generalized cross correlation (GCC) which can realize pre-filtering of signals and properly eliminate the influences of noise and interference in the received signal, we analyze three commonly used weighting functions of GCC, and we find that SCOT weighting function can suppress the noise of the transmitted signal and the received signal at the same time. Three commonly used weighting functions are applied to the Simulink simulation model of chaotic time delay estimation. The simulation results show that the results of generalized cross-correlation using SCOT weighting function are better than that of the basic cross-correlation and the other two commonly used weighting functions. Compared with the basic cross-correlation results, the main peak to side lobe ratio obtained by the generalized cross-correlation using SCOT weighting function increases by more than 0.9 dB, and the ratio of the peak value of the misjudgment point to the peak value of the fault point decreases by more than 0.2.

Optical heterodyne interference systems have high signal frequency. The tranditional oversampling demodulation method has the disadvantages of high cost and large amount of data, so it is inconvenient for real-time demodulation monitoring. In this paper, an undersampling digital orthogonal demodulation method is studied to reduce the sampling frequency of a heterodyne system, so as to meet the demands of fast demodulation and real-time monitoring in vibration sensing. Firstly, the undersampling principle of a heterodyne interference system is analyzed theoretically to obtain the condition that the sampling frequency must meet, that is, the minimum sampling frequency should be more than twice of the signal bandwidth. Then undersampling demodulation is verified experimentally. For a vibration with a 0.5 V piezoe-lectric transducer (PZT) excitation voltage and an 80 MHz heterodymium frequency, the phase could be demodulated with sampling frequency as low as 20 kHz‒10 MHz. The largest demodulation error is 0.3%, and it does not increase with the decrease of sampling frequency. The influence of sampling frequency on measurable PZT excitation voltage range is studied. Higher sampling frequency leads to larger voltage range, and the linear demodulation intervals corresponding to 50, 100, and 200 kHz sampling frequencies are 1‒7, 1‒14, and 1‒20 V, respectively. Undersampling digital orthogonal demodulation is believed to have extensive application prospects in optical heterodyne interference systems due to its low-cost and fast demodulation.

Photonic-aided millimeter-wave communication combines the advantages of optical fiber and wireless communications, and it has several applications in the next generation of wireless access network systems. Geometric shaping (GS) technology can effectively overcome the signal damage caused by the transmission channel's nonlinear effect through optimising the Euclidean distance between the constellations and can effectively improve system transmission capacity and spectrum efficiency without increasing the system hardware costs. The transmission performance of 8/16-Gbaud 80-GHz vector millimeter-wave signal in the modulation formats of 8PSK/GS-8PSK and 8QAM/GS-8QAM is studied using an optical link scheme that uses a single push-pull modulator to generate vector millimeter-wave signal, combined with GS technology. The results show that when compared with traditional modulation formats, the geometrically shaped signal has a considerable improvement in the bit error rate and optical power under back-to-back and optical fiber transmission conditions. After transmitting an 8-Gbaud GS-8PSK signal through 150 km optical fiber, the optical power is increased by approximately 1 dBm; after transmitting a 16-Gbaud GS-8QAM modulated signal through back-to-back and 80 km optical fiber, the optical power is increased by approximately 0.5 dBm.

In classic optical communication, intensity modulation direct detection (IM-DD) is a low-power (amplitude) system with no amplifier in the intermediate. Therefore, increasing the channel capacity becomes a challenge of signal space size and distribution at given bandwidth and maximum power (amplitude). The problem of limited power is solved by proposing a dynamic probabilistic shaping (DPS) algorithm based on the IM-DD system, which improves the system's channel capacity and bit error performance. The pulse amplitude modulation (PAM) format is used in this investigation. DPS can increase channel capacity by approximately 0.9 dB and improve bit error performance by 0.8 dB and 1 dB in PAM4 and PAM8, respectively, according to simulation data.

In this paper, a two-photon polymerization system built using a femtosecond laser was used to fabricate a microfiber long-period fiber grating (MLPG). The system uses a computer to control the three-dimensional displacement platform to complete the structure production, is programmable to realize the automatic grating production, and monitors the grating production process throughout the process. To complete the fabrication of the MLPG, the two-photon polymerization of the photoresist periodically occurs on the surface of the fiber. Compared with the traditional manufacturing method, the grating manufacturing method based on two-photon polymerization did not depend on the changes of the fiber substrate. The long-period grating can be flexibly manufactured on the outer surfaces of different types of fibers. As an example, we fabricated eight grating blocks with a 95 μm period on a microfiber with 6.9 µm diameter. At 1331 nm, a transmission spectrum loss peak of 13.5 dB is observed. The experimental results show that the temperature and refractive index sensitivities of the MLPG are as high as 1.39 nm/°C and 2207.89 nm/RIU(RIU is the unit refractive index), respectively.

In this study, an arbitrary waveform photonic generation scheme with simple structure and repeat rate tunability is proposed. The scheme consists of a dual parallel phase modulator, fiber Bragg grating, and balanced detector. The dual parallel phase modulator modulates the laser, and two optical signals obtained by fiber Bragg grating can output as square and trapezoid microwave signals via balanced detection. Meanwhile, a 90° phase shifter is used to obtain triangular and sawtooth microwave signals. By adjusting the voltage and frequency of the radio frequency drive signal, the simulation results show that the frequency of the output microwave photonic signal can achieve 10 to 25 GHz with the root mean square error (RMSE) of less than 0.33. In addition, the effects of modulation index β and 90° hybrid phase balance Δθ on microwave photonic waveform quality are analyzed experimentally. The RMSE of waveform signals is less than 0.42 when the standard value β varies by standard value ±0.15 or Δθ varies by ±3°, which verifies that the designed system has a good stability.

A pairwise maximum likelihood (ML) receiver is proposed for flip/unipolar orthogonal frequency division multiplexing (Flip/U-OFDM) system in visible light communication (VLC). Parts of Flip/U-OFDM signal are set at zero by pairwise ML in time domain, which can get some signal to noise ratio (SNR) gain. And the pairwise ML is a simple signal processing method, which will not increase the complexity for the receiver. Simulation results show that SNR gain of 2 dB can be available for the pairwise ML receiver in additive white Gaussian noise (AWGN) channel. SNR gain of 2 dB-3 dB will be achieved for the pairwise ML receiver in amplitude clipping channel and light emitting diode (LED) nonlinearity channel.

The temperature of optical fiber link is an important factor affecting the accuracy of optical fiber time synchronization, but the real-time temperature of fiber core has some problems, such as difficult measurement, large estimation error, and so on. A new method of real-time temperature measurement for optical fiber link is proposed. Through the accurate measurement of the round-trip delay sum of the optical fiber link, and filtering the delay jitter and system noise by Kalman filtering, the real-time equivalent average temperature of the fiber core of the optical fiber link can be accurately calculated. The simulation results based on the segmented temperature model verify the feasibility of proposed equivalent average temperature for the time synchronization system. The temperature control box experimental results show that the accuracy of the proposed method is about 0.015 ℃. Using the proposed method to track the core temperature in real time can improve the timing accuracy of the loopback time synchronization system by about 1 ns.

In recent years, the developed digital back-propagation (DBP) algorithm can mitigate the fiber nonlinearities significantly. However, as a noise source, the transceiver noise will remarkably degrade the effectiveness of DBP algorithm. In this paper, we investigate the transmission penalty induced by the transceiver noise in Nyquist-spaced coherent optical transmission systems over different fiber types. We show that although the pure silica core fiber exhibits the best performance without transceiver noise, it is most sensitive to the transceiver noise.

To control the two-dimensional galvanometer scanning system in light detection and ranging (LiDAR), the laser foot points can reach the detection width of 350 m or more, scanning grid point density in 1 spots/m2 or more high pointing accuracy cone scan at a flight altitude of 1000 m and a flight speed of 200 km/h airborne LiDAR to sea bottom topography mapping. According to the characteristics of the two-dimensional galvanometer structure, this study uses the improved Bresenham algorithm to generate the trigger signal of the stepping motor in the control system and compensates for the beam lateral offset error caused by the two-dimensional galvanometer system, reducing the scan angle error to 2 and scanning angle of 10°-60°, and the trigger signal derived by the algorithm is validated through experiments.

Regarding the complex adjustment problem in the field-of-view(FOV) splitting, a FOV splitting scheme using dual rhombic prisms is proposed, and a high-accuracy optical extensometer is constructed. This scheme can not only simplify the adjustment steps of FOV splitting, but also increase the gauge length of extensometer by several times, and effectively reduce the effect of out-of-plane displacement on two-dimensional digital image correlation (2D-DIC) by adopting a telecentric lens. Uniaxial tensile test and continuous loading-unloading test were carried out to verify the feasibility and accuracy of the proposed method. The results show that the strain obtained by this method is in good agreement with those obtained by the strain gauge, and the root mean square error of the strain results is no more than 3 με. Therefore, the FOV splitting optical extensometer based on the dual rhombic prisms proposed in this paper is an easy-to-implement high-accuracy strain measurement technique.

In order to meet the requirements of autocollimate dynamic target tracking accuracy, an opto-mechanical system for rotating virtual targets under centrifugal conditions is established, that is, a rotating collimator is used to simulate the rotating target at infinity to complete the tracking performance detection and calibration of photoelectric tracking optical end machine. For the three auxiliary supports installed on the back of the main mirror in the collimator, the fundamental frequency of the structure can reach 167 Hz by optimal arrangement of the radial position of the auxiliary supports, and the square root (RMS) value of the main mirror surface shape error is less than λ/30 (λ is 632.8 nm) under centrifugal conditions. A 4D interferometer is used to detect the wave aberration of the collimator. The test results show that the RMS value of the collimator is better than λ/15.

An integrated technique for measuring the laser power and spectral parameters of a single bar in a kilowatt class semiconductor laser array is proposed. The beam of any single bar in the laser array is separated from the beam of other bars by the self-developed diaphragm, and the power and spectral parameters of the separated single bar beam are integrated tested by using the integrating sphere, and then compared with the results of the integrated test of the power and spectral parameters of the whole array. The experimental results show that any single bar beam in the 1 kW laser array can be separated from other bar beams by the self-developed diaphragm, and the transmittance of the diaphragm to the single bar beam is 98%.Combining with the integrating sphere integrated test system, all the bars in the laser array can be tested individually, which overcomes the traditional problem of unpacking the single bar in the stack array. In addition, the system can scan the whole stack quickly and reflect each bar in the stack directly.

In order to solve the contradiction between accuracy and radial dimension of an angle sensor, this paper derives and analyzes the axial errors of an end grating and a cylindrical grating from the aspects of radial flux and Moire fringes in detail, and the error model is also established. Based on the axial error analysis, a stereo grating angle sensor combining an end grating with a cylindrical grating is designed and the corresponding experimental system of stereo grating angle sensor is established. The experimental results show that the error of the proposed stereo grating angle sensor is 6.75" when reading head presents a uniform distribution. In contrast, when reading head presents a non-uniform distribution, the error is 4.33".These results provide a new method for the suppression of axial errors and some references for the development of compact and high precision angle sensors.

In this paper, a programmable method of laser pulse selection and amplitude control is proposed to generate pulse bursts with arbitrary time-domain waveform. A flexible and programmable pulse picker unit based on field-programmable gate array is used to drive the acousto-optic modulator to realize the fine control of each pulse's energy in bursts. Based on this innovative regulation technology of pulses' time-domain characteristics, high-energy bursts with different time-domain waveforms are realized by using ytterbium-doped chirped pulse fiber amplification system. The outputs of the system are the bursts with burst energy of 20 μJ, burst repetition rate of 1 MHz, and pulse width of less than 300 fs.

A Mach-Zehnder interferometer based on multi-core fiber, which composes of a single-mode, multi-core, multi-mode, and single-mode fiber, is proposed in this study. In the proposed interferometer, the multi-mode fiber functions as a coupler, whereas the single-mode fiber and the multi-core fiber form an asymmetric structure by offset splicing. Further, the bending and axial strain characteristics of the interferometer are studied experimentally. The experimental results show that the wavelength of the transmission spectrum of the interferometer is linearly shifted when the interferometer bends. The wavelength change can be used to modulate the curvature, and the maximum sensitivity of bending curvature is -16.88 nm/m-1. When the interferometer bends to the directions of 0° and 180°, the wave-valley wavelengths shift in the opposite direction, allowing for a preliminary determination of the bending direction. In addition, the interferometer is also sensitive to axial strain. By using the measured bending curvature and axial strain sensitivity to construct the measurement matrix, the simultaneous measurement of bending curvature and axial strain can be realized, and the cross sensitivity can be eliminated.

In this paper, a finite element model of an 808-nm high-power semiconductor laser single tube based on the actual package structure of the chip is used to obtain a reliable temperature distribution of the active layer during thermal simulation. The thermal distribution characteristics of the active layer during steady state operation are investigated by introducing various influence factors, such as ridge, copper layer on heatsink, and bonded wires. First, based on the simple finite element model, the effects of the stripe region, copper heatsink layer, and bonding wire on the average temperature of the active layer of the device were introduced and calculated. Then, these influence factors were simultaneously used to obtain the new model. The average temperatures of the active layer obtained with the simple model and the new model were 42.089 ℃ and 46.405 ℃, respectively. The average temperature of the active layer of the device calculated using experimental data of output wavelength variation with injection current was 41.708℃. Simulation results of the simple model showed an error of 11.26%. The error of simulation results of the proposed model is 0.91%. Finally, the thermal characteristics of several high-power semiconductor laser single tubes with the same package structure parameters and different conversion efficiencies and wavelengths were calculated to verify the accuracy of the simulation results.

A superhydrophobic and superoleophilic surface-based copper foam was fabricated using one-step nanosecond laser patterning and the influence of laser processing parameters on the wettability of its surface was studied. To investigate the surface morphology, elements, and wetting properties, scanning electron microscopy, energy dispersive X-ray spectroscopy, and contact angle measurement were performed. The results show that as the laser scanning speed, power, and scanning spacing increase, the rough structure of copper foam surface changes considerably. In addition, the chemical composition of the laser-ablated surface changes. Superhydrophobicity and superoleophilicity are caused by the rough structures and changes in chemical composition. The superhydrophobic and superoleophilic surface's maximum water contact angle in the air is 157.4°, while the oil contact angle is 0°. The ablated surface can successfully separate oil from water, providing oil-water separation and oil recycling practice guidelines.

To investigate the primary factors affecting the dilution rate in the laser cladding repair process and its effect on repair performance, we implement laser cladding experiments on 300M steel surface using the new 12Cr17Ni2B stainless steel powder as the laser cladding powder. To melt the powder adequately and reduce the softening degree in the heat-affected zone, the focus of the powder stream is adjusted above the substrate surface. Scanning rate and powder heat absorption rate (the ratio of laser power to powder feed rate) experiments are performed to explore the effect regularity of these process parameters on the dilution rate. The results demonstrate that these process parameters can considerably change the dilution rate. The scanning rate changes the area of the cladding layer, and the powder heat absorption rate changes the area of the fusion zone. To clarify the effect of dilution rate on the repair performance, the process of the single factor powder heat absorption rate is designed to adjust the dilution rate, and the effect of dilution rate on repair performance is analyzed. The results demonstrate that the dilution rate has little effect on the interface bonding strength of the repaired areas; however, it affects the softening degree in the heat-affected zone. The dilution of the matrix is beneficial in terms of improving hardness in the fusion zone but an overly high dilution rate will result in the cracking of the fusion zone.

Twelve types of ores were identified using laser-induced breakdown spectroscopy combined with the principal component analysis-particle swarm optimization-support vector machine (PCA-PSO-SVM) algorithm. A Savitzky-Golay filter was used to smooth the spectrum, and the segmented eigenvalue extraction method was used to perform baseline correction on the spectrum. The first 25 principal components reduced by PCA were selected as the input to the PSO-SVM classification model, and the best recognition accuracy rate for the 12 types of ore was 100%. The PCA-PSO-SVM model was compared with two classification models, i.e., principal component-linear discriminant analysis and a PCA-particle swarm optimization-error back propagation neural network. Experimental results showed that the recognition accuracy of the PCA-PSO-SVM classification model was the highest with an average recognition accuracy rate of up to 99.90%.

The single laser technology was used to weld 5-mm thick Q345B low-alloy steel and 304 stainless steel. By modifying laser power, the microstructure, microhardness, and tensile strength of welded joints made of dissimilar steel were analyzed under various process parameters. The results showed that the weld could not penetrate entirely when the laser power was less than 4 kW and the weld would collapse when the laser power was greater than 7 kW. The weld microstructure was typical strip martensite when the laser power was increased from 4 kW to 7 kW; the weld center hardness was maximum and the weld porosity was the lowest at 6 kW. The samples' tensile fracture sites were all present on the Q345B base material with no weld fracture. γ-Fe,α-Fe, Cr2Ni3, and Fe2Ni3 phases dominate in welds, with little M23C6, σ phase, and other hazardous phases.

Mold steel has excellent high temperature performance and is widely used in the field of high temperature die casting. However, conventional mechanical machining is unable to fabricate complicated conformal cooling structures. Furthermore, regular selective laser melting (SLM) is inefficient to build mold steel H13 and it usually gives rise to interval cracks and local distortion. Consequently, in terms of fabricating mold steel H13 by SLM, this paper introduces a self-developed high-temperature SLM system and the innovative hybrid spot technology, including semiconductor laser preheating spot and fiber laser melting spot. When the scanning speed is 1800-2500 mm·s-1 and the substrate is preheated at 250 °C, both individual and hybrid laser spots are used to perform the experimental study. The result indicates that the maximum density obtained under the suitable configuration of composite spot is better than that obtained by single spot with the same forming efficiency. In addition, the qualitative analysis is also performed on the action mechanism of the hybrid laser spot in view of energy input.

In this paper, 316L stainless steel samples were formed using the selective laser melting (SLM) technology to analyze the dynamic mechanical properties of the SLM 316L stainless steel under impact load. The quasistatic and dynamic compressive mechanical properties of the sample were tested using a universal experimental machine and a split Hopkinson pressure bar (SHPB) experimental device. Meanwhile, the test results of the SLM 316L samples were compared with that of the 316L stainless steel formed via traditional methods. The internal relationship between the microstructure and mechanical properties of the material was analyzed through the micromorphological observation. Finally, the Johnson-Cook (J-C) constitutive model was established to predict and characterize the dynamic mechanical behavior of SLM 316L stainless steel. The experimental results show that the SLM 316L stainless steels show typical elastic–plastic characteristics and significant strain rate hardening effects in mechanical experiments. Moreover, compared with traditional 316L, SLM 316L has a higher hardening modulus at the dynamic strengthening stage because of the cellular structure with micron size. The yield strength of the cold-rolled 316L sample is higher because of the residual stress caused by plastic deformation. By modifying the basic J-C model using the experimental data, the dynamic mechanical behavior of SLM 316L can be described more accurately.

Aiming at the problems of large temperature error and poor accuracy in infrared thermal imaging nondestructive testing system, a detection method based on nondestructive testing simulation model is proposed. Several surface temperatures at the excitation point and defect center in the same experimental environment are selected as reference values to modify and correct the simulation model. First, the temperature variation trend of both sides of the excitation point is analyzed by changing the laser excitation time to reveal the influence of defects on the temperature field of the specimen. Then, the temperature resistance effect of the defect is analyzed by comparing the temperature values of the regions on both sides of the excitation point. Finally, the fitting curve and function relationship between the excitation time and the maximum temperature difference of the temperature measuring point are obtained by using the method of data fitting. The quantitative relationship between the excitation time and the maximum temperature difference of the temperature measuring point is analyzed quantitatively. The results show that the detection method based on the simulation model of nondestructive testing has a remarkable effect on the detection of parts defects, it can solve the problems of large temperature measurement error and poor accuracy, and has a good ability to detect parts defects.

The surface of polytetrafluoroethylene (PTFE) was ablated by femtosecond laser, and then the surface enhanced Raman scattering (SERS) substrate was prepared by depositing silver nanoparticles on the surface of laser structured PTFE substrate. By adjusting the scanning path of femtosecond laser, PTFE substrates with one-dimensional grating structure and two-dimensional grating structure are obtained, respectively. After coating a thin layer of silver nanoparticles, the two-dimensional grating structure of polytetrafluoroethylene substrate can serve as a SERS substrate, which shows much better SERS enhancement, about three times higher than that based on one-dimensional grating structure.

Fiber metal laminates are widely used in large aircrafts. Debonding occurs easily at the bonding interface due to process and environmental factors, affecting its performance. It is essential to effectively detect and evaluate the bonding layer. This study proposes a method for evaluating the micro-debonding degree of adhesive interfaces using local defect resonance (LDR). Under the nonlinear mechanism of contact acoustics, the defect is regarded as a nonlinear spring oscillator, and its LDR frequency is determined. Numerical simulation is used to analyze the resonance under different excitation conditions. The experimental object is a glass fiber aluminum alloy bonding plate with different sizes of debonding defects. Piezoelectric actuator/sensor units are pasted on the surface, excitation signals with different frequencies are applied to the actuator according to the LDR frequency, and the spectral analysis of the response signals is conducted. The simulated and experimental results show that the nonlinear feature of the debonding interface can be improved based on the LDR effect. In addition, LDR frequency can be employed to determine the debonding damaged area.

It is difficult to avoid the development of nano inclusions by crucible erosion during gas atomization process. Selective laser melting equipment was used to print 18Ni300 die steel powder with nanoalumina powder. The effects of nanoalumina powder additions on microstructure and mechanical properties of 3D-printed samples were studied to determine the tolerance limit for atomization pulverization. When the nanoalumina addition (mass fraction) is less than 1%, the second phase segregation is not detected for printed or low-temperature annealed samples. When more than 1% nanoalumina is added, the Ni3(Al, Ti) and Al2O3 segregation phases appear, and the number of internal cracks and spherical pores increases, decreasing in mechanical properties. The annealed sample containing 1% nanoalumina has the maximum tensile strength of 1658 MPa.

In this study, the transfer matrix method is used to study the spin Hall effect of light on the surface of a functional photonic crystal with a defect layer. Through numerical calculations and analyses, we find that the transverse displacement of reflected light or transmitted light can be controlled by adjusting the polarization angle, incidence angle, period number of the functional photonic crystal, optical thickness of the defect layer, and circular frequency of the incident light. Numerical calculations reveal that 100-micron level transverse displacement can be achieved by adjusting the corresponding parameters. These results provide a theoretical reference for research into spin-based quantum communication and new optoelectronic devices.

High-resolution X-ray diffraction is used to measure and analyze the InAs/GaSb superlattice grown on a GaSb (100) substrate using molecular beam epitaxy to obtain satellite peak number on the rocking curve, full width at half maximum (FWHM), peak intensity, and peak position. Then, the interface strain, mismatch, and InAs/GaSb superlattice period are calculated. In the experiment, the samples’ surface morphology and surface roughness are tested and characterized using an atomic force microscope. The results show that the surface undulation and roughness of the InAs (10 ML)/GaSb(10 ML) superlattice with 50 periods are lower than other superlattice samples (such as the superlattice samples with short period or asymmetric structure). With an increase in the period, FWHM of the 1-order diffraction peak considerably decreases. Consequently, the surface morphology and continuity of the samples are improved. For the InAs (10 ML)/GaSb(10 ML) sample with 50 periods, the root-mean-square roughness is 0.31 nm, more satellite peaks (±4-order) can be observed in the rocking curve, FWHM of the 1-order diffraction peak is 0.027°, the periodic thickness is 5.59 nm, and the average strain is 0.43%.

In this study, a plasma waveguide cladded by black phosphorus/dielectric multilayer structures was theoretically proposed. By numerically solving the dispersion equation with MATLAB, the performance curves of the effective refractive index, propagation length, penetration depth, and figures of merit of the waveguide could be simulated. According to the simulation curves, the performances of the waveguide positively and negatively correlated with the electron doping rate of the black phosphorus/dielectric multilayer structure and the dielectric thickness in the element layer. Compared with the same type of metal/medium multilayer structures waveguide, the black phosphorus/dielectric multilayer structures waveguide has a larger propagation length, a smaller propagation depth and a larger figures of merit in the mid-infrared and far-infrared bands. The waveguide is tunable and has excellent performance.

Semiconductor lighting devices based on Ⅲ-nitride materials, such as AlN and GaN, have broad application prospects, but the commonly used sapphire substrates have poor heat dissipation as well as large lattice and thermal mismatches with AlN and GaN, which limit their promotion and application. Graphene is a two-dimensional layered material comprising only carbon atoms. Graphene layers are combined with van der Waals forces. Using graphene as a buffer layer can alleviate the mismatch between sapphire and Ⅲ-nitride materials. AlN and other nitrides are grown on graphene-sapphire substrates. Graphene is used to alleviate the problem of large lattice mismatch between the sapphire substrate and Ⅲ-nitride materials, which is conducive to the preparation of high-power light-emitting diodes. However, the growth of graphene on an insulating substrate is difficult. In this study, a nickel layer is coated on sapphire substrates, and nickel is used to assist the growth of graphene on the sapphire substrate, which is helpful to realize high-power light-emitting diodes using graphene.

A multiplexed two-wave mixing interferometer (MTWM) system has been developed, which is able to perform optical detection of ultrasonic motion for multiple points in an array simultaneously. In this MTWM system, optical phase gratings are used to create an array of detection laser beams that are directed to the specimen. The detection array can be arranged in several ways on the test object as needed. The scattered optical beams from the detection laser array are collected and mixed with a single reference beam in a photorefractive crystal to form a multiplexed two-wave mixing. Each of the output beams from the photorefractive crystal is imaged on to one of the elements in the array of photodetectors. The MTWM system is capable of providing simultaneous optical detection at several points on a test object, with high spatial resolution and sub-nanometer displacement sensitivity. The applications of this MTWM system include the crack imaging detection and quantification, material characterization analysis, and other nondestructive detection. In this paper, how to realize fast acquirement of Lamb wave dispersion curves using the MTWM system is presented. The dispersive time-position domain Lamb wave signals at multiple source-to-receiver distances are obtained. Following the algorithms of Alleyne and Cawley, these time-position domain signals are transformed to the frequency-wavenumber domain using two-dimentional fast Fourier transformation technique. This application shows the MTWM system has the ability to rapidly characterize the dispersion characteristics of Lamb waves.

In order to solve the problems of large distortion, large size, and low energy utilization of the projection system, a new small distortion projection system based on the double Gaussian structure and freeform surface lighting system is designed. The optical system is designed mainly for the freeform surface modeling method and optical path structure. According to the edge ray theory and Snell's law, a numerical iterative method is used to design the freeform surface lighting system. The simulation results show that the illumination uniformity of the lighting system can reach 87.86%, and the energy utilization rate can reach 94.38%. The imaging system is designed with a double Gaussian structure as the initial structure. The distortion of the projection system after aspheric optimization is 0.26%, and the optical transfer function is greater than 0.8 at a frequency of 93 pl/mm, and greater than at the 35° edge field of view 0.6. The imaging quality of the projection system is high, the structure is compact, and the number of lenses is small. Through the tolerance analysis, it can be known that the Q5 tolerance level meets the performance requirements of the system, and the tolerance requirements are relatively low.

This paper proposed a metasurface based on the hybrid graphene-metal which can be switched freely between a quarter wave plate and a half wave plate by adjusting the Fermi level of graphene. Numerical simulation results show that when the Fermi level of graphene is 0 eV, the proposed metasurface can realize the conversion from linearly polarized waves to right-handed circularly polarized waves in the frequency range of 1.465-3.44 THz, with a relative bandwidth of 96.5%, and the absolute bandwidth is 1.975 THz. When the Fermi energy level of graphene is 1 eV, the metasurface becomes a broadband cross-polarization converter, that is, one-half wave plate, which can achieve a polarization conversion rate greater than 80% in the frequency range of 1.173-3.44 THz. The relative bandwidth is 98.7%, and the absolute bandwidth is 2.267 THz. In addition, the proposed broadband switchable metasurface has a strong robustness to the angle of incidence. Therefore, it has a good application prospects in the fields of sensing and imaging.

In this paper, a two-dimensional photonic crystal is used to design a miniaturized, dense, scalable eight-channel multiplexer structure. The two-dimensional photonic crystal is formed by periodically arranging silicon dielectric columns in the air using a triangular lattice. The linear main waveguide, download cavity, and output waveguide structure are designed, and the coupling effect between the cavity and waveguide is used to select the wavelength. The designed cavity is composed of one inner and four outer columns, and it has a simple structure. The cavity mode can be adjusted through the diameter of the inner and outer columns to realize multiwavelength selection and the scalability structure. A quasi-dense wavelength division multiplexing structure is realized. The multiplexing of eight wavelengths, including 1542.2, 1544.2, 1546, 1548.2, 1550, 1552, 1554.4, and 1557.6 nm, achieve 2.2 nm of the average wavelength interval, and the insertion loss is -0.5, -0.25, -0.25, -0.7, -0.25, -0.5, -0.1, and -0.1 dB. respectively. The maximum channel crosstalk is -12 dB. The device size is 19.8 μm × 11 μm. It achieves miniaturization, high transmission, and high isolation. It also lays a foundation for optical integration. The design and analysis are done with the finite element method using COMSOL software.

With the distinct advantages of high-brightness, high-efficiency and wide-gamut, color-conversion with quantum dots and Micro-LED illumination holds great potentials in display domain. On the basis of the single and arrayed quantum dots model, spectrum, efficiency and viewing angle of quantum dots color-conversion procedure are characterized and demonstrated in detail. In Light Tools, simulation models is built up by Micro-LED light source, film layer of quantum dots and detector. The simulated results report color conversion efficiency from the ultraviolet Micro-LED is better than the blue source, and green, red color output light have higher conversion efficiency using corresponding quantum dots. Additionally, with the increase of viewing angle from Micro-LED, the uniformity of illuminance distribution is highly improved and the light leakage in the ultraviolet region is apparently decreased. Utilizing the newly-designed 6×6 quantum dots modality, the arrayed models with and without microstructure are investigated and compared. From the calculated true color map and illumination map,the output light from arrayed quantum dots with microstructure has obvious features of clear edges and sharp color boundaries, which is extremely applicable for high-performance display devices.

Modern optical networks require broadband, high-speed, large-capacity transmission techniques. Based on the anti-resonant reflecting optical waveguiding mechanism, we propose a polarization-maintaining (PM) hollow-core optical fiber. The light is confined by four tubes, which have different thicknesses along two orthogonal directions to achieve efficient PM guidance. To enhance the PM performance while achieving low propagation loss, we investigate the effects of additional anti-resonant layers in the tubes, tube thickness, air-core size and the distance between two adjacent tubes. Numerical simulations indicate that, at 1550 nm, the proposed fiber supports two orthogonally polarized modes with the birefringence of 1.2×10-4 and the propagation losses of HE11x and HE11y modes are 0.002 dB/m and 0.013 dB/m respectively. Moreover, within 1425~1725 nm (bandwidth of 300 nm), the birefringence of the proposed fiber is no less than 1.0×10-4, the propagation losses are within 0.002 dB/m and 0.185 dB/m, and the dispersions are less than 45.51 ps?nm-1?km-1. We also show that the proposed fiber has low bend losses thanks to the air-core guidance. The proposed fiber may have applications for data centers and financial network systems that need short-range, large-capacity and low-latency transmission.

The phase grating position measurement system is the core of achieving ultraprecision manufacturing. The contrast of the self-referencing interference signal significantly influences the accuracy of measuring the position of phase gratings, which is directly determined by the polarization properties of beams. In this study, the Jones matrix and vector-form reflection law are used to trace the polarization of the transmitted beam in the self-referencing interferometer prism, and the Jones matrix model of the phase grating position measurement system is constructed; then, based on the physical light field numerical analysis software VirtualLab, the accuracy of the model is verified. Based on this model, the influence of the extinction ratio of the polarization beam splitter, the polarization state of the incident light, and the optical path difference of the prism on the contrast of the self-referencing interference signal is analyzed. The results show that to ensure that the contrast of the interference signal is better than 0.98 under the illumination beam of wavelength λ, the extinction ratio of the polarization beam splitter needs to be greater than 122; in addition, the incident light ellipticity ψ and ellipticity tan ε are (0.693 rad,0.878 rad) and (-0.093,0.093), respectively, and the prism optical path difference needs to be controlled within (-0.03λ,0.03λ). After comprehensive consideration, the value range of the incident light ellipticity is required to be 0.531δ±0.087 (δ is the phase difference from the reference interferometer prism). The analysis results can provide a theoretical basis for adjusting and compensating for the beam polarization characteristics in the phase grating position measurement system and are crucial for improving the contrast of the self-referencing interference signals and accuracy of the phase grating position measurement system.

In order to improve the performance of sending or not sending quantum key distribution (SNS-QKD), an SNS-QKD protocol based on a heralded pair-coherent source (HPCS) is proposed, named HPCS-SNS-QKD protocol. In the protocol, a weak coherent source (WCS) is replaced by HPCS. HPCS has lower ratio of vacuum state pulse than WCS. Hence the single photon error bit rate can be effectively reduced in HPCS-SNS-QKD. The relationship between the key generation rate and secure transmission distance is derived, and the expression of the key generation rate under limited pulses is given. The numerical simulation results show that the proposed HPCS-SNS-QKD protocol can exceed the upper limit of single-photon key transmission distance. Compared with WCS-SNS-QKD protocol, HPCS-SNS-QKD protocol has longer transmission distance and higher key generation rate and can endure larger misalignment error. For limited pulses in practical experiment, HPCS-SNS-QKD always has a higher key generation rate.

A simple scheme for the generation of three-qutrit singlet state is proposed, which is based on the cavity quantum electrodynamics (QED) by means of the two-photon transitions. Here a Ξ-type three-level atom originally prepared in the excited state sequentially resonates with three cavities prepared in suitable initial states (vacuum state or one-photon state). The singlet state with maximum fidelity can be obtained by selecting the interaction time between atom and cavity field and probing the atomic states. In addition, the influence of atom-cavity coupling constant on fidelity and the practical feasibility of the proposed scheme are discussed. The results show that in the case of detuning equal to zero, the fidelity is more sensitive to the atom-cavity interaction time for a larger coupling constant.

The full waveform data obtained by the geoscience laser altimeter system (GLAS) has different degrees of noise due to the system performance, the scattering of the propagation medium and the characteristics of the detection target, which affects the extraction of vertical structure parameters and the laser ranging accuracy of the GLAS. Therefore, the noise reduction effects of Gaussian filtering, wavelet threshold denoising and empirical mode decomposition (EMD) methods are analyzed and compared in this paper, and the performance of wavelet soft threshold denoising and wavelet improved threshold denoising methods as well as EMD-wavelet threshold denoising and EMD-Hurst noise reduction methods are further compared. The experimental results on six typical feature data show that the denoising results of wavelet threshold denoising and EMD-Hurst denoising methods are better than Gaussian filtering except EMD-wavelet threshold denoising. All three types of denoising methods, Gaussian filtering, wavelet threshold denoising and EMD denoising, have the best denoising effect on flat without slope. In addition, the wavelet improved threshold denoising method is better than the wavelet soft threshold denoising method, the signal-to-noise ratio (SNR) is increased by 10.70%-45.72% and root mean squared error (RMSE) is reduced by 32.04%-81.94%. The EMD-Hurst method is better than the EMD-wavelet threshold denoising method, the SNR is increased by 6.38%-65.70% and the RMSE is reduced by 13.53%-33.33%

In recent years, pulsed laser time-of-flight ranging (TOFR) has become a research hotspot topic in the field of laser ranging, which has been widely used in industrial precision measurement, robot autonomous motion, unmanned aerial vehicle control, and other fields. Due to the influences of background noise, electrical environment of measurement circuits, and rise time of echo pulses, the pulsed laser TOFR usually has certain errors, which causes the problem of distance measurement accuracy degradation. This paper firstly introduces the basic principle of pulsed laser TOFR technology, analyzes the formation causes of time-of-flight measurement errors in the pulsed laser TOFR process, and classifies the errors. Further, the various error compensation methods for time-of-flight measurement errors and the latest research results are sorted out, and finally, the current challenges of pulsed laser TOFR error compensation are summarized.

Laser technology is extensively utilized in the field of medicine. Not only does it have different indications in vascular diseases but also its distinctive physical properties and precise biological tissue interaction effect has encouraged considerable research. This article reviews the applications of laser technology in endovascular imaging and therapy in recent years, summarizes its history and research status, and discusses its likelihood for development in the future.

Quantum cascade semiconductor lasers (QCL) that emit mid-infrared laser has promising applications in gas molecules detection, especially nitrogen oxides detection. At present, the QCLs have two major forms: pulsed and continuous light. In this study, two nitric oxide detection system using pulsed and continuous light QCLs in the same wavelength were designed. The pulsed light system uses high pulse current to generate chirp modulation; the continuous light system uses sine waves modulation and second harmonic demodulation. The spectrum resolution, measurement range, linearity, limit of detection and other indicators are compared. The results show that the measurement range of the pulsed system is 4.6 times that of the continuous light system, and the detection limit is 2.2 times that of the latter. The continuous system has better linearity. For both systems, the optical noise caused by the Etalon effect is 10 times higher than the electrical noise. So, eliminating Etalon effect will be the focus of the future instrument design.

Carbon dioxide (CO2) is produced during the fire smoldering process; thus, a fire alarm system based on non-dispersive infrared (NDIR) is employed to monitor the CO2 concentration to prevent fire accidents. Using the fundamental absorption band of CO2 molecules at 4.26 μm and mid-infrared absorption spectroscopy, the early fire alarming system uses an infrared broadband heat source and dual-channel pyroelectric detector to achieve highly sensitive CO2 detection. Using prepared CO2 gas samples, the sensor characteristics of the CO2 sensor system are studied. Early fire alarm system must work with agricultural machinery; thus, the sensor must be damped. Based on the model and application of the Duhamel integral in solving vibration system response, a vibration damping module is designed, and the damping structure is modeled and simulated. The results demonstrate that the vibration amplitude is reduced by 82%. The outdoor vibration test of the damping module demonstrates that, when using the damping module, the vibration amplitude of the instrument is reduced by 86%-87%, and the measurement variance of CO2 concentration is reduced by 50.01% and the uncertainty is reduced by 29.52% compared to the case when the damping module is not used. Simulation analysis and outdoor vibration experiment results demonstrate that the damping module provides good vibration reduction effect with the advantages of high cost-performance, simple vibration reduction structure, etc., and is of obvious value in engineering applications.

A surface-enhanced Raman scattering (SERS) substrate based on polymeric flat-plate waveguide and gold nanoparticles (AuNPs) is developed. The SERS signal of rhodamine 6G (R6G) is detected in the long range, and the enhancement performance and reproducibility of the substrate are analyzed. The experimental results show that the SERS signal increases and then decreases with increasing detection distance, reaching a maximum at a detection distance of 10 mm; the detection limit of the substrate for R6G is 10-7 mol/L and the enhancement factor is 4.3×104; the relative standard deviation (RSD) of each characteristic peak intensity of R6G is around 3% and has good repeatability. The polymeric flat-plate waveguide-AuNPs substrate can effectively detect SERS signals in a long range, laying the foundation for the non-destructive detection of molecules in biological samples.

Gaze tracking is a human-computer interaction technology, which has received extensive attention in academia and industry. Aiming at the problem of the large average error of the gaze points accuracy in non-invasive systems based on polynomial regression, a method of eye vectors calculation based on line-of-sight horizontal offset feature is proposed.On the basis of accurately extracting the coordinates of the iris center and inner corner of the eye on the face image, this method uses the inner corner coordinates as the reference point to calculate the offset of the iris center relative to the inner corner coordinates, calculates the weight of the horizontal eye movement vector through the offset, and then uses the weight to weight the horizontal eye movement vectors of the left and right eyes to synthesize new horizontal eye movement vectors. Using the data of 20 subjects with the head horizontal angle 0°from the Columbia Gaze database, this method was experimentally verified on 4 regression models. The results show that compared with the calculation method of binocular average eye vectors, this method can further reduce the horizontal of viewing angle error of the gaze points and improve the system accuracy.

The color rendering quality of RGB-LED light source is mainly evaluated by color rendering index, gamut, color discrimination ability of observer and object color saturation. However, the possible chromaticity mismatch range that all spectral reflectances metameric to one surface under standard illuminant D65 would form under a RGB-LED light source with correlated color temperature 6500 K has not been thoroughly studied. First, the peak wavelengths of blue, green, and red LED light source were changed respectively, and the simulated RGB-LED light source spectrum was generated by Gaussian distribution function. Then, chromaticity mismatch areas under RGB-LED light source formed by all spectral reflectances metameric to 12 Munsell surfaces under standard illuminant D65 were calculated. Finally, the data of five real RGB-LED light sources were analyzed. The results show that the chromaticity mismatch region corresponding to the Munsell color card was negatively correlated with the general color rendering index of RGB-LED light source, that is, the larger the general color rendering index of RGB-LED light source, the smaller the chromaticity mismatch region corresponding to the Munsell color card.