Researching | GZXB Volume 51 Issue 5,2022

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2022

Volume: 51 Issue 5

32 Article(s)

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Holographic Properties of Acrylate Photopolymer Materials with Double Monomers

Biao KANG, Huaqing LÜ, Yourong LIU, Shaoxin LI, and Jihong ZHENG

In recent years, due to the excellent characteristics of photopolymer recording materials such as high diffraction efficiency, high resolution and high signal-to-noise ratio, they have gradually emerged in volume holographic storage, fiber Bragg grating, waveguide, sensing and communication applications, and achieved a In recent years, due to the excellent characteristics of photopolymer recording materials such as high diffraction efficiency, high resolution and high signal-to-noise ratio, they have gradually emerged in volume holographic storage, fiber Bragg grating, waveguide, sensing and communication applications, and achieved a lot of significant results. Among them, a large number of acrylate photopolymers with stable performance, many kinds and low price have been studied. However, acrylate photopolymers have some defects, such as large shrinkage, small refractive index modulation and low stability. These problems hinder the expansion and further application of acrylate photopolymers. Based on the above research, the effects of various components in the photopolymer based on TMPTA double monomer system were studied, and a variety of photopolymer materials based on TMPTA double monomer system were compared in this paper. Combined with the diffusion movement of monomers, the effects of different film-forming resins, active monomers and photoinitiators on photopolymers were studied, and the ratio of materials was optimized. In technology, the system does not require solvent wet treatment. Just mix the medicine evenly and inject it into the mold prepared by two specific pieces of transparent glass. The thickness of the sample can be controlled by the gasket between the glasses, so it is easy to make a film with controllable thickness. Finally, bisphenol A epoxy resin and acrylate monomer TMPTA were selected in different double monomer systems. This is because the reaction activity of epoxy resin and acrylate monomer TMPTA is different, and the polymerization rate of TMPTA is much faster. When TMPTA molecules polymerize rapidly at the bright stripes, the epoxy resin is still colloidal and does not react, which is conducive to the diffusion of TMPTA molecules. Therefore, the two monomers can be separated from each other, resulting in a large refractive index difference. The network structure formed after TMPTA polymerization is combined with epoxy group to initiate epoxy group ring opening, and epoxy group is continuously inserted into it to realize chain growth, branching and crosslinking. A highly crosslinked stable structure is formed in the material. The photoinitiator is high reactive orange solid irgacure 784. Under the 532 nm laser, the ground state of irgacure 784 molecule absorbs photons rapidly, transitions to the excited state, and photodissociates. It forms a product state that is very transparent to visible light. In this system, irgacure 784 molecule first isomerized under the irradiation of coherent light to obtain the coordination unsaturated titanium central double free ground state. Then it initiated the free radical polymerization of TMPTA monomer. Finally, the ring opening polymerization of epoxy resin was carried out under the subsequent treatment. The material thus exhibits high stability and low shrinkage. By introducing double photoinitiators, the polymerization rate of active monomers was greatly accelerated, and the photosensitive sensitivity and photosensitive wavelength range of the system were improved. At the same time, the information is successfully recorded in polymer film samples, which proves that it has good holographic recording and high resolution performance. The holographic parameters are tested, which include diffraction efficiency of materials under different exposure intensity, exposure time and temperature. It shows that the double monomer system has better diffraction efficiency at exposure light intensity of 10~15 mW/cm², time of 40~80 s and temperature of 46 ℃ than at the other conditions. The experimental results show that the system with good high temperature resistance manifests that the diffraction efficiency is up to 91.5% and the refractive index is more than 2.98×10^-3, also, the transmittance is over 95.6%, which is under the conditions of a recording angle of 30°and a thickness of 70 μm. After 72 hours of high and low temperature cycling in the test chamber, the diffraction efficiency decreased to 87.2% and the decrease range was 4.7%. The temperature in the box is maintained at 80 ℃ and the humidity is 80 RH. The shrinkage of Bimonomer photopolymer system is only 0.504%.As a holographic recording medium, it can effectively record holographic information with high resolution and high diffraction efficiency. Due to the high diffraction efficiency and high stability of the polymer, the material is more suitable for other applications such as hologram and permanent storage of big data..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0509001 (2022)

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Partition and Time Division Multiplexing Retinal Projection Display Based on Human Visual Characteristics

Zichao WEI, Yimin LOU, Juanmei HU, and Fengmin WU

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0511001 (2022)

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Design of Compact Off-axis Three-mirror Afocal System Based on Freeform Surface

Junhua YAN, Zijia HU, Deyan ZHU, Yang CHEN, Yin ZHANG, and Liqian YU

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0511002 (2022)

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Three-dimensional Correlation Imaging Based on Time-of-flight Technology

Huiji WANG, Nan LI, Xuankui LI, Cheng ZHOU, and Lijun SONG

Different from traditional optical imaging technology, correlated imaging uses a single-pixel detector and a spatial light modulator to reconstruct object image information based on correlation calculations, having the characteristics of super-resolution, non-local, and anti-interference. Time-of-flight (TOF) technolog Different from traditional optical imaging technology, correlated imaging uses a single-pixel detector and a spatial light modulator to reconstruct object image information based on correlation calculations, having the characteristics of super-resolution, non-local, and anti-interference. Time-of-flight (TOF) technology is an effective method for optical remote sensing and three-dimensional imaging of target recognition. Compared with traditional laser correlation imaging, 3D correlation imaging can not only obtain the two-dimensional light field intensity information of the target object, but also effectively obtain the longitudinal distance information between the target objects, so that the size and position of the imaging target can be quantitatively analyzed. Three-dimensional correlation imaging technology mainly includes steroscopic vision and TOF imaging technology. To improve the image reconstruction quality of intensity 3D correlation imaging, this paper employs differential correlation imaging reconstruction algorithm and TOF technology, and the theoretical formula of intensity correlation 3D imaging is deduced. The working mode is that the short-pulse laser forms pseudothermal light through the rotating frosted glass. After passing through the beam splitter, one of the beams irradiates the target object to be measured and then is received by the Photomultiplier Tube (PMT); the other beam is detected by the array detector. The high-speed data acquisition system digitizes the peak light intensity signal detected by the PMT into discrete data points, uses the TOF technology to divide the detection signal into slice signals of different time (distance), and then integrates the signals in the respective slices to obtain the slice signal detection value, and finally the DGI algorithm is used to perform two-dimensional correlation imaging reconstruction calculation for each slice signal separately. This paper mainly investigates the influence of the light source laser power and reconstruction algorithm parameters on the imaging quality in the pseudo-thermo-optic 3D correlation imaging. The imaging results of two flat objects to be measured (the front-end target is a four-pointed star and the back-end target is the letter F) with a distance of 80 cm and a resolution of 200 pixel × 200 pixel in the numerical simulation are given. Among them, the simulation pulse laser uses the function

p (t) = e x p (- τ^{2} / σ^{2})

, the detection times is 20 000, and the sampling rate is 50%. In order to further verify its effectiveness, a pseudo-thermo-optical 3D correlation imaging experimental system is built. This paper uses a 532 nm pulsed laser as the light source and frosted glass as the spatial light modulator to build a set of pseudo-thermal light three-dimensional correlation imaging experimental system, which realizes the three-dimensional image reconstruction of a 200 pixel×200 pixel target object with a longitudinal distance of 60 cm at an absolute distance of 5.5 m in the laboratory environment. The reconstructed 3D slice images that are lower than the set threshold parameters in the simulation and experimental results are reset to zero, thereby reducing the influence of the background noise of other slice images on the quality of the reconstructed images during the 3D correlation imaging stacking process. Within a certain threshold parameter range, appropriately increasing the threshold parameter can effectively improve the reconstruction quality of 3D correlated imaging images. To further investigate the performance of the 3D correlation imaging experimental system, experimental tests are carried out for 3D correlation imaging under different laser powers, respectively. The experimental verification shows that by properly increasing the power of the laser light source, the influence of the time jitter of the echo signal on the reconstructed image quality can be effectively suppressed, and the longitudinal distance reconstruction quality and measurement accuracy of the 3D image can be further improved. The work has a reference significance for promoting the application of intensity 3D correlation imaging technology in the field of lidar imaging..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0511003 (2022)

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Noise-like Mode-locked Er：fiber Laser Based on Nonlinearity Management

Li YAN, Qimeng LIN, Yuanqi SONG, Xuzhuo JIA, Jianing TAO, Yangyang LI, Pengye SONG, and Man JIANG

Passive mode-locked fiber lasers have potential applications in fiber optic communication, fiber optic sensing, optical frequency measurement, and aerospace due to their good beam quality, compactness, small size, low fabrication cost, tunability, and easy generation of ultrashort pulses. In recent decades, several typ Passive mode-locked fiber lasers have potential applications in fiber optic communication, fiber optic sensing, optical frequency measurement, and aerospace due to their good beam quality, compactness, small size, low fabrication cost, tunability, and easy generation of ultrashort pulses. In recent decades, several types of mode-locked pulses can be generated using passive mode-locked fiber lasers, such as Gaussian pulses, self-similar pulses, soliton pulses, noise-like pulses, and so on. Among them, noise-like pulses is a special pulse generated by mode-locked lasers under certain conditions, which is widely used in low-coherence spectral interferometry, micromachining, nonlinear frequency conversion and supercontinuum spectrum generation due to its wide pulse width, high energy, and low time-domain coherence. In light of these applications, broadband noise-like pulse generation in erbium-doped fiber lasers has attracted considerable interest. The study of noise-like erbium-doped fiber lasers based on passive mode-locking technique has been reported extensively. Researchers have mostly used longer gain fibers or single-mode fibers to adjust intracavity dispersion and accumulate nonlinearity as a way to obtain the output of noise-like mode-locked pulses. So far, it has not been reported that using highly nonlinear fiber based on nonlinear polarization rotating mode-locking mechanism to manage the nonlinear in laser cavity to realize the mode-locked fiber laser with wide spectrum. In this work, we experimentally report the noise-like pulses generation in an anomalous dispersion erbium-doped fiber laser based on nonlinearity management technique. The erbium-doped mode-locked fiber laser adopt nonlinear polarization rotation technique. In the experiment, by introducing dispersion compensating fiber and highly nonlinear fiber into the nonlinear polarization rotation mode-locked erbium-doped fiber laser resonator, intracavity dispersion and non-linearity management is achieved, resulting in a stable mode-locked pulse output. When the intracavity highly nonlinear fiber length is 6 cm, corresponding to a net cavity dispersion of about -0.019 ps². An ultrashort pulse output with a central wavelength of 1 534 nm, a pulse width of 1.9 ps, a repetition frequency of 20.1 MHz, and a 40 dB spectral bandwidth of about 100 nm can be obtained. Based on this, the length of the highly nonlinear fiber in the cavity is increased to 30 cm, and the total dispersion in the cavity is -0.021 ps². This laser system can achieve noise-like pulse operation by properly adjusting the state of the wave-plate when the pump power is 1 100 mW. The output spectral coverage range of noise-like pulse is 1 280-1 850 nm, the bandwidth of 40 dB is 500 nm, the peak pulse width is as short as 70.9 fs, the base pulse width is 26.6 ps, and the repetition rate is about 19.7 MHz. The maximum output power is 2.08 mW at pump power of 1 100 mW, corresponding to an optical conversion efficiency of 0.18%. In order to verify the power stability of the noise-like mode-locked fiber laser, we monitor its output power for 2 hours, and the monitoring results showed that the output power is always maintained at about 1.01 mW, and the root mean square is calculated to be 1.14% for 2 hours, indicating that it has good environmental stability. After obtaining noise-like mode-locking pulses, we investigate the output spectra and the corresponding autocorrelation curves of noise-like pulses at different pump powers. It is found that the duration of the spike pulses decreased slightly with increasing pump power, a feature that mainly stems from the fact that the spectral bandwidth becomes progressively wider. Conversely, as the pump power increases, the pulse width of the base becomes progressively wider. And as the pumping power increases, the shape of the spectrum remains essentially the same and the output spectrum broadens in both the short and long wavelength directions, gradually increasing the spectral coverage. This is mainly due to the increasing power coupled into the highly nonlinear fiber as the pumping power increases. The present experimental study will allow subsequent optimisation of the fusion loss of the highly nonlinear fiber by tailoring the fibre device for wide bandwidth operation and selecting a higher power pump laser, resulting in a wider spectrum of noise-like mode-locked pulse output. The research in this paper provides a feasible solution for preparing a broad-spectrum noise-like mode-locked laser light source, which has great potential for applications due to its compactness, stable output, and ease of fabrication..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0514001 (2022)

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Relationship between Photosynthetic Fluorescence Parameters of Algae and the Initial Biomass in the Measurement of Water Quality Biological Toxicity

Min CHEN, Gaofang YIN, Nanjing ZHAO, Tingting GAN, Mengyuan GU, Peilong QI, Zhichao DING, Lu WANG, Chun FENG, and Xiaoling ZHANG

The photosynthetic fluorescence parameters of algae are easy to measure and sensitive to external stress. It is an important indicator of water quality biological toxicity measurement. However, different toxicity test schemes would lead to great differences in the toxicity data, and the stability and comparability were The photosynthetic fluorescence parameters of algae are easy to measure and sensitive to external stress. It is an important indicator of water quality biological toxicity measurement. However, different toxicity test schemes would lead to great differences in the toxicity data, and the stability and comparability were uncertain. Since fluorescence dynamics technology for measuring photosynthetic fluorescence parameters essentially uses optical detector to monitor the change of chlorophyll fluorescence signal in microalgae. In this paper, the concentration of chlorophyll was used as the measurement of biomass, and Chlorella pyrenoidosa was used as the test object to analyze the relationship between photosynthetic fluorescence parameters as the end point of toxicity test and the initial biomass of toxicity test algae samples under short-term exposure (1 h and 3 h) of diuron. The results showed that: 1) When the initial biomass changes, the correlation between photosynthetic fluorescence parameters and biomass would directly affect the stability of the toxicity test results. The photosynthetic fluorescence parameters could be divided into two categories. The first category was F_v/F_m, Yield, α, rP, σ_{PS II} and τ_es, whose values were not related to biomass changes and only represented the photosystem information of Chlorella pyrenoidosa. The toxicity test results obtained by these parameters were not affected by the change of initial biomass. When the initial chlorophyll concentration changed in the range of 20~1 000 μg·L^-1, 10 μg·L^-1 diuron stress for 1 h and 3 h, the average values of the corresponding relative standard deviations of the six parameter test results were 2.74% and 3.12% respectively, and the toxicity test results were stable. The second category of parameters was Ek, F₀, F_m, F_v and JVPⅡ. Their values were affected by biomass and contain biomass information. Among them, Ek was negatively correlated with chlorophyll concentration, and F₀, F_m, F_v and JVPⅡ were positively correlated with chlorophyll concentration. The toxicity test results of these parameter were obviously affected by biomass fluctuation and their stability became worse. When the chlorophyll concentration changed in the range of 20~1 000 μg·L^-1, the average values of relative standard deviation of the five parameter test results under 10 μg·L^-1 diuron stress for 1 h and 3 h were 14.66% and 17.27% respectively. 2) The Logistic model was selected for dose-effect analysis, and the photosynthetic fluorescence parameters F_v/F_m, Yield, α, rP, σ_PSⅡ, τ_es, F₀, F_m and F_v could establish a good dose-effect relationship with diuron. According to EC₅₀, EC₂₀ and correlation coefficient R², the optimal range of initial chlorophyll concentration of algae when photosynthetic fluorescence parameters were used as the end point of toxicity test were given. For parameters F_v/F_m, Yield, α, rP, σ_PSⅡ, and τ_es, due to population dependence, too low biomass would affect the photosynthetic physiological state of algae species, the recommended initial chlorophyll concentration range was 10~2 000 μg·L^-1; for parameters F₀, Fm and Fv, more sensitive toxicity test results (lower EC₂₀) could be obtained due to higher initial biomass, the recommended range was 200~1 000 μg·L^-1. This result provides an important basis for the establishment of a rapid detection method for water quality biological toxicity based on algal photosynthetic fluorescence parameters, and will be helpful for ecological risk assessment of the aquatic environment..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0517001 (2022)

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Preparation of ZnO Patterned Array and Its Field Emission Performance

Lei SUN, Yipeng LIAO, Kunhua ZHU, and Xin YAN

The field emission electron source has a wide range of application value in the field of vacuum electronics, and the realization of the uniformity and patterning of the in-situ growth of the emitter material is the key technology. The traditional patterning process is complicated and the pattern has not been carefully The field emission electron source has a wide range of application value in the field of vacuum electronics, and the realization of the uniformity and patterning of the in-situ growth of the emitter material is the key technology. The traditional patterning process is complicated and the pattern has not been carefully designed, resulting in uneven electric field distribution. This paper uses ANSYS Maxwell 16.0 simulation software to study the law of electron motion trajectory, and proposes a new idea of the effective emission size of the graphical emitter array and the cathode structure of the optimal array spacing to improve the field emission performance. The simulation results show that when the array spacing d is 200 μm, the electric field distribution in the central area of the patterned array is flat, and the surrounding area of the array rises abruptly. This is mainly due to the fact that the edge part of the array exhibits the characteristics of a needle tip more than the central part of the array. When d is smaller, the field strength of the edge area between the unit arrays is superimposed, and a field strength superimposition area appears. When d slowly increases, the edge superposition effect of the field strength is weakened, and the electric field shielding effect is also weakened. Therefore, when d is larger (400 μm), the field strength of the cathode surface tends to be flat, because the edge superposition effect of the field strength and the electric field shielding effect are balanced. However, as d increases to a certain extent, when the array spacing is 600 μm, the center position of the cell array plane can be relatively far away, the field emission of the cell array is relatively independent, and the electron emission has a neutral area. It can be seen that when d is selected at a moderate value, the superposition effect of the field strength at the edge of the array is weakened, and there will be no blind areas in the surrounding electric field, and the electric field basically achieves a uniform distribution. Subsequently, according to the simulation results, the patterned seed layer is accurately positioned by inkjet printing, and then the ZnO nanorod array is hydrothermally grown. Field emission test results show that as d increases, the turn-on field strength E_on decreases from 2.95 V/μm at 200 μm to 0.57 V/μm at 400 μm, and further changes to 2.26 V/μm at 600 μm. The enhancement factor b increases first and then decreases as d increases from 200 μm to 600 μm. This is consistent with the simulation results, that is, when the effective emission size of the ZnO cathode array is 200 μm, when d is 400 μm, the field emission performance is optimal, and its turn-on field is 0.57 V/μm, and the field emission enhancement factor is 32 179. Combining the high efficiency of graphic design and inkjet printing, it is expected to realize a high-performance field emission electron source..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0525001 (2022)

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Study of Residual-time-counting Pulse Frequency Modulation Digital Readout Circuit for Ingaas Focal Plane Array

Xuquan WANG, Hongyi WANG, Yonggang ZHANG, Songlei HUANG, and Jiaxiong FANG

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0525002 (2022)

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Research on Near-infrared Spatial Heterodyne Raman Spectrometer

Bozhao FAN, Yutao FENG, Quan WANG, Chi GAO, Yang WU, Bin HAN, Chenguang CHANG, Juan LI, Yiru LI, Hengxiang ZHAO, and Di FU

Spatial Heterodyne Raman Spectroscopy (SHRS) is a new type of Raman spectroscopy detection technology, which has the advantage of high throughput, high spectral resolution, high sensitivity and no moving parts. SHRS can meet the high-sensitivity detection requirements of weak Raman scattered light, and can also obtain Spatial Heterodyne Raman Spectroscopy (SHRS) is a new type of Raman spectroscopy detection technology, which has the advantage of high throughput, high spectral resolution, high sensitivity and no moving parts. SHRS can meet the high-sensitivity detection requirements of weak Raman scattered light, and can also obtain clear and sharp Raman spectra. For Raman spectrometers, fluorescence is an inevitable background signal. The fluorescence intensity and the Raman intensity are approximately inversely proportional to the fourth power of the wavelength, so the excitation wavelength of near-infrared light has lower fluorescence than visible light. The excitation wavelengths of near-infrared light are mostly 785 nm, 830 nm and 1 064 nm, of which the shorter 785 nm has larger fluorescence. Although the 1064 nm excitation light has a weaker fluorescence, it requires the near-infrared InGaAs focal plane. Compared with visible detectors, it has higher noise, lower sensitivity and resolution. Therefore, this article chooses the wavelength of 830 nm as the excitation light for Raman spectroscopy detection, and its fluorescence is lower than that of 785 nm. On the other hand, the visible detectors can be used for high-sensitivity detection. For the excitation wavelength of 830 nm, this paper designs, simulates, develops and tests SHRS. The Littrow wavelength of the spectrometer is 842 nm, the theoretical spectral sampling interval is 2.96 cm^-1, and the theoretically Raman shift range is 171.71~3 031.04 cm^-1. The spatial heterodyne interferometer adopts integrated adhesive technology. To increase the throughput, the field-widened prisms are added to the interferometer. The field angle tolerance of the interferometer is selected to be ±2° to ensure the contrast of the interferogram in actual work, and the corresponding contrast of the ideal interferogram is better than 0.98. The fringe-imaging lens group selects a double telecentric lens group with a magnification of 1. The telecentric configuration guarantees the uniform illumination of the image surface, and the symmetrical structure can effectively balance aberrations and further enhance the stability of the system. A checkerboard target is used to test the processed fringe-imaging lens group. The measured average magnification is 1.001 9 and the relative distortion is 0.19%. The Kr lamp is used as the input light of the system to verify the design parameters of the SHRS prototype. According to the positions of the two spectral lines 877.675 nm and 892.869 nm of the Kr lamp and the corresponding Raman shift, the actual spectral sampling interval is 2.918 2 cm^-1. The smaller value compared with the design value is mainly due to the dispersion of the field-widened prism. The actual Littrow wavelength is 841.95 nm, which is close to the theoretical value. The detector selected in this paper does not respond to light with a wavelength greater than 1 000 nm, so the actual Raman shift range is 171.01~2 048.19 cm^-1. The design parameter and the simulation of the system are verified. In the Fourier transform of the interferogram to the spectrogram, apodization is needed to suppress the side lobes, and different apodization functions have different degrees of spectral line broadening, resulting in different actual spectral resolution. In rectangular function apodization, the spectral resolution is about 1.207 times the theoretical spectral sampling interval. The effective spectral resolution of the SHRS prototype is 3.35 cm^-1. An important parameter to measure the performance of Raman spectrometer is the Signal-to-Noise Ratio (SNR) of the Raman spectrum. We choose the peak intensity of the Raman spectrum after removing the baseline as the signal intensity, and the standard deviation after removing the baseline from the Raman spectrum peak area as the noise, and use the ratio of the two as SNR of the measured Raman spectrum. In the experiment, the excitation light power is 500 mW, and the integration time is 10 s. First, the standard Raman sample cyclohexane is tested. SNR of the main Raman peak at 795.5 cm^-1 is 913, and SNR of the weakest Raman peak at 1 341 cm^-1 is 15. It can be verified that the SHRS prototype has good Raman spectrum measurement capabilities, as well as high sensitivity and SNR. Secondly, the solid samples calcium carbonate, calcium sulfate and potassium sulfate are tested. These samples are all strong Raman active substances, and the Raman spectrum peaks of various substances can be accurately identified, and SNR of the main Raman spectrum peaks is greater than 300. Finally, experiments are carried out on 75% alcohol solution, glycerin and glucose powder. The Raman activity of these samples is relatively weak, and there are obvious baselines in the measured Raman spectra, indicating that there is a certain fluorescent background in the spectra. However, a clear and accurate Raman spectrum is still obtained, and the main Raman spectrum peaks of various substances can be accurately obtained, and SNR of each spectrum peak is greater than 20. In general, SHRS has higher detection sensitivity and better stability and can meet the analytical requirements of Raman spectroscopy detection. It has certain advantages in the Raman detection of high-fluorescence background substances and has certain development potential in biomedicine, food safety, geological prospecting, planetary exploration, etc..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0530001 (2022)

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Infrared Carbon Monoxide Sensor System for Early Fire Detection

Zhuo MA, Yafei LI, Yang LU, Fang SONG, Chuantao ZHENG, and Yiding WANG

China is not only a large agricultural country, but also one of the countries suffering from the most serious agricultural disasters in the world. Early fire detection can help to avoid greater losses. Crops have a period of smoldering before the open flame. Due to lack of oxygen, the combustion is extremely insufficie China is not only a large agricultural country, but also one of the countries suffering from the most serious agricultural disasters in the world. Early fire detection can help to avoid greater losses. Crops have a period of smoldering before the open flame. Due to lack of oxygen, the combustion is extremely insufficient, and a small amount of carbon monoxide (CO) with a relatively stable concentration will be produced. Therefore, the occurrence of early fire can be judged by detecting gas-phase CO. Non-Dispersive Infrared (NDIR) absorption spectroscopy was used in this paper. Based on the absorption band of CO gas molecules at 4.6 μm, a differential infrared CO sensor system for early fire detection was developed by using a broadband infrared thermal light source and a dual-channel pyroelectric detector. This sensor system is mainly composed of a gas pretreatment part, an optical part, an electrical part and an upper computer monitoring part. Firstly, the detection principle of the sensor system was introduced, and then the absorption band of CO in the infrared region was selected by comparing the strength of absorption lines in different absorption bands and excluding the absorption interference of other gas molecules. Through the derivation of the optical matrix, the structure of the gas cell was designed and optimized, and the optical path of gas absorption reached 180 cm . The background noise fluctuation range of the phase-locked amplifier is 38.89 μV~43.23 μV, and the lowest detection limit is 0.15 μV. Finally, the performance of the sensor system was tested through related experiments. The results show that the measurement resolution is less than 2×10^-5 and the response time is 35~38 s. The concentration level of the 0×10^-6 CO standard gas sample was dynamically monitored for 80 minutes, and its concentration fluctuation range is -1.42×10^-5~1.51×10^-5. When the integration time is 0.25 s, the detection limit of the system is 1.54 ×10^-6, and when the integration time is 300 s, the detection limit of the system can reach 3.50×10^-7. Kalman filtering algorithm was used to improve the stability of the system. Similarly, the 0×10^-6 CO standard gas sample was dynamically monitored for 80 minutes. The results show that the relative error is reduced by 40.56 %, and when the integration time is 0.25 s, the detection limit is reduced to 3.60×10^-7. Finally, fire smoldering experiments of cotton, paper and wood were carried out to study the relationship between CO concentration and smoldering time. It is proved that the change of CO concentration can be used to detect the occurrence of fire. The experimental results show that the CO sensor system has a good early fire detection capability and wide application prospects..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0530002 (2022)

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[in Chinese]

Zhiyuan Li, and Haiqing Song

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0551300 (2022)

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Instrumentation, Measurement and Metrology

A Bump Height Measurement Method Based on Optical Triangulation

Peng WANG, Fanchang MENG, Zili ZHANG, Dezhao WANG, Shan WANG, Entao YAO, Lei WANG, and Ruiqian YE

2D/3D integrated circuit packaging technology is adopted in the process of wafer packaging and this technology uses wafer bumps to connect active devices. Inconsistent bump heights will cause circuit break after packaging, which will cause the whole chip to fail. Therefore, on-line detection of the height consistency o 2D/3D integrated circuit packaging technology is adopted in the process of wafer packaging and this technology uses wafer bumps to connect active devices. Inconsistent bump heights will cause circuit break after packaging, which will cause the whole chip to fail. Therefore, on-line detection of the height consistency of bumps is required during wafer packaging. To meet the above requirements, a fast and high-precision bump height measurement method based on optical triangulation method is studied. Based on the basic principle of oblique incidence optical triangulation method, the line beam is projected onto the chip bump, and the reflected beam on the chip surface is collected by the camera after through the imaging system. The height of the bump is calculated according to the geometric characteristics of the light stripe in the image collected by the camera and the distance between the spot on the top of the bump and the light stripe. Compared with spectral confocal method and white light interferometry, this method has the advantages of high speed and high measurement efficiency, and can meet the needs of on-line measurement of chip packaging defects. When calibrating the parameters of the chip bump height measurement system, in order to solve the difficult problem of angle calibration of projection and imaging device in the traditional triangulation method, a new calibration method is adopted: the magnification and pixel height ratio of the imaging system are used to replace the device angle to realize the indirect calibration of angle parameters. In order to accurately calibrate the pixel height ratio, a laser interferometer is used to accurately measure the height deviation of the reference plane. The center coordinate of the light strip on the reference plane is extracted by the gray centroid method to obtain the center offset of the light strip. The pixel height ratio is calculated according to the center offset of the light strip and the height deviation of the reference plane. A high-precision circular calibration plate is used to calibrate the magnification of the imaging system. The Hough circle transformation algorithm is used to extract the center coordinates of the circular pattern, and the magnification of the imaging system is calculated according to the ratio of the center distance of adjacent circles in the image to the actual distance. By substituting the calibrated system parameters into the measurement model, the accurate measurement of chip bump height can be realized. Using this method, the chip bump height is measured, and the standard deviation of height measurement is 0.58 μm. If the same bump is measured repeatedly, the extension uncertainty is less than ±1 μm. The experimental results show the accuracy of the measurement method. Compared with the traditional optical triangulation method, the chip bump height measurement model proposed in this paper is not affected by the light strip position and width, and the measurement accuracy and speed have been further improved. The research results of this paper are of great significance to realize the rapid and accurate detection of chip bumps, and have a strong reference value for the height measurement of objects with spherical structure at the top. This measurement method combined with high-precision mobile platform can further measure the bump height of chip or wafer, so as to evaluate the bump height consistency. Therefore, this measurement method has important application value for the research of industrial on-line bump height consistency measurement system..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0512001 (2022)

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Application of Synchrotron Radiation Crystal Monochromator with Higher-harmonics in Optical Detection

Fen TAO, Lian XUE, Shangyu SI, Zhongliang LI, and biao DENG

The synchrotron is a machine which is used by physicists to produce high energy charged particles. The centripetal force acting on the relativistic electrons causes them to radiate electromagnetic radiation predominantly in vacuum ultraviolet and soft X-ray regions. The synchrotron radiation facility is a large, expens The synchrotron is a machine which is used by physicists to produce high energy charged particles. The centripetal force acting on the relativistic electrons causes them to radiate electromagnetic radiation predominantly in vacuum ultraviolet and soft X-ray regions. The synchrotron radiation facility is a large, expensive, and complex organization, devoted to the provision of electromagnetic radiation to a wide range of experimental rigs, and service a community with diverse scientific backgrounds. Synchrotron radiation has the characteristics of high photon brilliance, high collimation and high purity. Double crystal monochromator is the core splitter in synchrotron radiation beamline. The diffraction beam produced by it contains fundamental and harmonic X-rays. As monochromators select from a given spectrum a series of harmonics whose wavelengths satisfy Bragg's law for the monochromator diffracting planes, higher-order harmonics are still present in the spectrum after monochromatization with not negligible relative intensities. On the one hand, higher harmonics can reduce the monochromaticity of X-ray; on the other hand, higher harmonics have the characteristics of high resolution and high energy. In experiments, higher harmonics are usually used or suppressed according to the demands. High purity harmonics are obtained and fundamental waves are filtered by aluminum sheets of different thickness. Based on the characteristics of higher harmonics, the absorption spectrum, imaging and diffraction experiments are carried out on test beamline (09B) at Shanghai Synchrotron Radiation Facility (SSRF), which expanded the spectrum range and applications of synchrotron radiation at wavelength measurement.The lower limit of monochromator energy is an important feature for beamline. The lower limit of the monochromator energy in SSRF Beamline is 2 keV. There is no simple method to measure the lower limit of the monochromator energy at present. The lower limit of the monochromator energy can be easily measured by high order harmonic. The lower limit of 4.219 keV energy of Si(111) monochromator crystal is calibrated by measuring the K-edge absorption of element Se for third-order harmonic at 12 keV.Monochromaticity is an important criterion of beamline at synchrotron radiation, and thermal deformation of monochromator crystal affects photon energy bandwidth. The energy bandwidth of Si(333) crystal planes is 0.37"@30 keV. This value is on the same order of magnitude with the result of thermal deformation of crystal. It can be used in the detection of thermal deformation of crystal. The specular distortion of Si(333) lattice surface diffraction caused by thermal deformations of crystal Si(111) is studied by diffraction imaging with 12 keV higher harmonic.The ultrahard multifunctional X-Ray beamline in the phase II of SSRF with a photon energy range of 30~120 keV, with Laue diffraction monochromator to select from a given spectrum. It is necessary to characterize it at wavelength measurement by high-energy X-rays in this range. The rocking curve of high-energy Laue crystals is measured by Laue diffraction with 60 keV higher harmonic.Based on the test beamline at Shanghai Synchrotron Radiation Facility, studying the applications using higher-order harmonic of crystal monochromator in three aspects. First, the lower limit of the energy of the double crystal monochromator is calibrated. Second, the thermal deformation of crystal is directly observed by X-ray imaging. Third, Characterization of rocking curves of Laue crystal monochromator at high energy. Utilizing monochromator higher-harmonics, a variety of high-precision detections has been successfully realized. This work extended the applied range of Test Beamline at Shanghai Synchrotron Radiation Facility..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0512002 (2022)

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Optical Device

Design and Experiment of Low-voltage 4T-PPD Active Pixel

Wenjing XU, Jie CHEN, Zhangqu KUANG, Li ZHOU, Ming CHEN, and Chengbin ZHANG

The 4T Pinned Photodiode (4T-PPD) active pixel is the most widely used pixel structure for CMOS Image Sensor (CIS). In recent years, as the application of CIS has gradually expanded to the Internet of Things (IoT) and Artificial Intelligence (AI) fields, there is an increasing demand for low energy consumption. The bas The 4T Pinned Photodiode (4T-PPD) active pixel is the most widely used pixel structure for CMOS Image Sensor (CIS). In recent years, as the application of CIS has gradually expanded to the Internet of Things (IoT) and Artificial Intelligence (AI) fields, there is an increasing demand for low energy consumption. The basic theory and commonly adopted approach to reduce power consumption are to lower the power supply voltage, while the supply voltage of 4T-PPD is traditionally greater than 2.8 V. In 2016, the study published in JSSC suggested that by improving the timing, the 4T-PPD active pixels could work at 0.9 V, but the readout noise was as high as 83e^-_rms and the dynamic range was only 50 dB, which could only meet low-quality imaging.Several studies have been conducted on the charge transfer characteristics of traditional high-voltage 4T-PPD. In 2003, FOSSUM E R simulated the charge transfer from PPD to Floating Diffusion (FD) node based on thermionic emission theory. Based on this work, in 2016, HAN Liqiang et al. included non-ideal factors such as the reverse charge injection from FD to PPD. Additionally, in 2019, CAPOCCIA R et al. added an estimate of the thermionic emission barrier height based on the findings of the aforementioned studies. However, these theories were not fully applicable to low-voltage 4T-PPD, since they all assumed a complete photo-generated charge transfer inside the PPD. When the voltage drops, the electrons far away from the transfer gate lack a lateral electric field and stay in the photosensitive area, causing image lag, which will seriously affect the imaging quality.In this paper, a low-voltage 4T-PPD active pixel was designed. First, a theoretical analysis of the internal charge transfer mechanism of PPD was proposed. Three charge transfer mechanisms operate inside the PPD, namely thermal diffusion, self-induced drift, and fringe-field drift. As the charge transfer by fringe-field drift is much faster than thermal diffusion or self-induced drift, the charge transfer time inside the PPD depends predominantly on the distance where the fringing field is absent. According to the derived equations, when the photogenerated charge to the full-well chargeis less than 4%, thermal diffusion is the main mechanism for the no-fringing-field section, and the length of the no-fringing-field section is almost the same. When the photogenerated charge to the full-well chargeis larger than 4%, self-induced drift is the main mechanism for the no-fringing-field section. Moreover, when the transfer gate voltage increases, the length of the no-fringing-field section becomes shorter. As the PPD size decreases, the length of the no-fringing-field section becomes shorter significantly.When the transfer gate voltage drops, the electrons far from the transfer gate lack fringing field and could not be pulled out of the PPD within transfer time, thus resulting in image lag. To solve image lag caused by low-voltage 4T-PPD, and easily achieve it without changing the process steps and conditions, the shape of the PPD layer might be changed. In previous studies, triangle, W-shape, trapezoid, and L-shape PPD have been reported, but all these designs aim at large-sized pixels. For small-sized pixels, the PPD layer should not be cut too much, otherwise, it would affect the full-well capacity and reduce the dynamic range. Therefore, a five-finger pixel layer was proposed to replace the traditional square pixel layer. Compared with conventional rectangular PPD, the five-finger shaped PPD not only reduces the length of the no-fringing-field section but also creates an extra electrical field in the direction of the charge transfer by the narrow width effect. This causes more electrons to be pulled out of the PPD. The proposed five-finger shaped PPD not only can accelerate the electrons transfer from PPD to TG but also meets the requirements of full-well capacity and dynamic range due to the small cut-off area.A prototype sensor was fabricated using a 0.11 µm 1P3M CMOS process. The experiment results show that the residual charge of the designed five-finger 4T-PPD is reduced by 80% compared with the traditional rectangle pixel. The performance of the designed five-finger 4T-PPD with 1.5 V voltage supply is as follows, the full well capacity is 4 928e^-, the dynamic range is 67.3 dB, and the random noise is only 1.55e^-_rms, which are comparable to traditional high-voltage 4T-PPD. The findings presented in this paper provide important guidance for the design of low-voltage 4T-PPD..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0523001 (2022)

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Analysis of Dispersion Characteristics of Liquid Crystal Phased Array Devices

Zhuang LIU, Qidong WANG, Haodong SHI, and Libo CHENG

Liquid crystal phased array can be widely used in space laser communication, space laser ranging and other fields. A phased array device is a diffractive optical device, which has the function of dispersion. That is, the incident light of different wavelengths has different exit angles after passing through the phased Liquid crystal phased array can be widely used in space laser communication, space laser ranging and other fields. A phased array device is a diffractive optical device, which has the function of dispersion. That is, the incident light of different wavelengths has different exit angles after passing through the phased array device., The central wavelength of the laser usually has a drift with the design value, and the laser also has a certain spectral width, which will lead to changes of the position deviation and the optical power distribution when the laser beam has large angle deflection by the phased array device. To solve this problem, the relationship between the wavelength and the coordinates of combined liquid crystal phased array devices is derived through the dispersion theory about the liquid crystal spatial light modulator and cascaded liquid crystal polarization grating. The optical power distribution formula of Gaussian beam passing through the combined liquid crystal phased array devices is derived by the combination of the optical power spectrum distribution of laser light source and the cross-sectional power distribution formula of the single-mode laser. Arming at the difficulty in formula calculation, a simple calculation method is given. The beam position deviation and the laser cross-section light power distribution of a common example are calculated. In this example, the laser wavelength is 1 064 nm, the center wavelength shift is 0.05 nm, the spectral width is 0.05 nm, the power is 1 W, the emitted light is a Gaussian beam near the basic mode, and the beam divergence angle is 20 μrad. When the beam passes through a cascade polarization grating with a designed deflection angle of (22.5°,-16.25°), the beam coordinate deviation is (26.76 m,-19.60 m) outside 1 000 km, laser beam cross-section presents an approximate elliptical distribution, the optical power distribution diagram is not rotationally symmetrical. The optical energy extends in the dispersion direction, and the system with a receiving aperture of 1.0 m can receive optical power of about 1.9 mW at the center, which is 24% different from that under the condition of uniform optical power distribution. When the beam passes through a cascade polarization grating with a designed deflection angle of (22.5°,-22.5°), the beam coordinate deviation is (30.79 m,-30.79 m) outside 1 000 km, and the light power also extends in the dispersion direction, the system with a receiving aperture of 1.0 m can receive light power of about 1.4 mW at the center, which is 36% different from that under uniform distribution. When the beam passes through a cascade polarization grating with a designed deflection angle of (27.5°,-16.25°), the beam coordinate deviation is (38.23 m,-22.84 m) outside 1 000 km, the system with a receiving aperture of 1.0 m can receive light power of about 0.97 mW at the center, which is 62% different from that under uniform distribution. It can be obtained from the data that the change caused by dispersion increases with the increase of dispersion angle, the center position deviation becomes more serious with the increase of dispersion angle, and the peak position power density decreases with the increase of dispersion angle..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0523002 (2022)

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Special Issue for Ultrafast Optics

Nanophotonic Methods for Chiral Sensing and Characterization（Invited）

Guanghao RUI, and Qiwen ZHAN

Chirality is a geometrical property where an object can not be superposed onto its mirror image via either a translational or a rotational operation. Since this type of symmetry is much harder to be maintained than to be broken, chirality exists widely in various macroscopic and microscopic structures. For example, pro Chirality is a geometrical property where an object can not be superposed onto its mirror image via either a translational or a rotational operation. Since this type of symmetry is much harder to be maintained than to be broken, chirality exists widely in various macroscopic and microscopic structures. For example, proteins and nucleic acids are built of chiral amino acids and chiral sugar. In addition, DNA double helix, sugar, quartz, cholesteric liquid crystals and biomolecules are also chiral structures. Although molecules with different handedness have the same chemical construction, usually they would possess distinct chemical behaviors. Consequently, as an essential attribute of organism, the chiral representation of matter is of great significance in the fields of pharmacology, toxicology and pharmacodynamics. When electromagnetic wave interacts with chiral materials, special optical activity phenomena will appear, such as optical rotation, circular dichroism, and chiral optical force, which become a powerful tool for material chirality detection. Since the size of chiral molecule is much smaller than the wavelength of excitation light, the chiroptical effect of molecule itself is usually very weak, which greatly limits the accuracy of detection scheme. In recent years, the progress of nanophotonic technology is expected to enhance the weak chiral optical effect between light and matter at nanoscale, making it possible to detect chirality with high sensitivity and resolution. In this paper, the developments of chiral detection technology in recent years are reviewed, which focus on the micro/nano structure based enhanced circular dichroism and optical force effect. Besides, the corresponding applications are discussed. The mechanisms of chirality sensing for various nanophotonic platforms and outlined recent advances and future opportunities of major approaches for biosensing applications are reviewed. Firstly, the microscopic origin of surface-enhanced circular dichroism, as well as the theory of superchiral near-field generation in dielectric and plasmonic substrates are discussed. Secondly, the theory and mechanistic concept of plasmon-coupled circular dichroism in plasmonic nanoparticles, as well as the examples of hotspot-enhanced plasmon-coupled circular dichroism for biosensing applications are reviewed. Thirdly, the use of chiral and achiral plasmonic and dielectric nanoantennas, as well as plasmonic-dielectric hybrid systems for enhancing the optical chirality of biomolecules are reviewed. Fourthly, the theory of the optical force exerted on chiral nanoparticle is introduced. The optical sorting of chiral material with the use of the lateral optical force of complex optical field, the enhanced chiral optical force of plasmonic nanostructure, as well as the characterization of structured chirality using photoinduced force microscopy are reviewed. Finally, the future perspective of this rapidly developing field is presented at the end of this paper..

Acta Photonica Sinica

Publication Date: May. 25, 2022
Vol. 51, Issue 5, 0551301 (2022)

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Instrumentation, Measurement and Metrology

Optical Device

Special Issue for Micro/Nanophotonics

Special Issue for Ultrafast Optics