With the increasingly serious energy problems and extreme climate in modern society, radiative cooling technology with zero-energy consumption has attracted much attention from the related scientific community. Since the first experimental demonstration of daytime radiative cooling in 2014, the technology has been widely studied from the perspectives of structural design, material selection, preparation process, integrated application, etc., resulting in the development of various types of devices including coatings, paintings, flexible films, fabrics, etc. New research is putting forward new requirements in terms of scene compatibility, environmental and climate adaptability. So the realization of new types of radiative cooling device that is compatible with multiple scenarios, adaptive to environmental changes, and has dynamic thermal control capabilities is of great significance to the practical application of radiative cooling technology in fields such as energy, medical, and industrial production. This paper focuses on the basic physical principles and photonics structure designs of radiative cooling technology, and summarizes the basic technology of radiative cooling devices and their progress in scene compatibility, temperature adaptive thermal regulation, etc. Firstly, the principle and basic design method of radiative cooling technology are expounded, then some typical radiative cooling structures and the main progress of realizing multi-scenario compatibility and adaptive dynamic regulation of radiative cooling devices are introduced, and at last, the development of radiative cooling devices is summarized and prospected.
The hydraulic pressure sensing technology based on photonic crystal fibers (PCFs) has important research significance and broad application prospects due to its advantages of high sensitivity, strong anti-interference ability, and adaptability to harsh environments, so it has received special attention from researchers in recent years. Based on the brief introduction of the basic principles of PCF hydraulic pressure sensing, several typical PCF hydraulic pressure sensing technologies, namely birefringent PCF hydraulic pressure sensing technology, PCF grating hydraulic pressure sensing technology, Fabry-Pérot cavity PCF hydraulic pressure sensing technology and dual-core PCF hydraulic pressure sensing technology, are mainly presented. The principles and technical schemes of these four PCF hydraulic pressure sensing technologies are introduced respectively, and their performances are analyzed, compared and summarized. Finally, the research status and future development trend of PCF hydraulic pressure sensing technology are briefly summarized.
A series of 2 at.% Dy3+ and x at.% Eu3+ (x=0,0.1,0.5,1,2,5) codoped NaY(MoO4)2 were synthesized by high-temperature solid-state reaction method. The structure of the samples was characterized by XRD, SEM and FTIR, and it is shownthat the synthesized samples have a tetragonal structure and a space group of I41/a. The excitation spectra and the emission properties under near-UV excitation of the samples were further investigated, and energy resonance transfer between Dy3+ and Eu3+ in NaY(MoO4)2 host was confirmed. The CIE coordinates of 2 at.% Dy3+ and 2 at.% Eu3+ codoped sample(x=0.659,y=0.338) are very close to the standard values specified by NTSC. Therefore, this phosphor is promising for being used as an excellent red phosphor with color rendering performance in solid-state lighting field. In addition, consideringthat NaY(MoO4)2 has the stable physicochemical properties and can be grown by Czochralski method, this study can provide a reference for exploring the single crystal growth and visible laser properties of Dy3+ and Eu3+ co-doped NaY(MoO4)2.
A method for removing ring artifacts of absorption signals in grating-based X-ray phase contrast tomography is proposed. In the method, a processing algorithm combining sinogram-domain with reconstruction image-domain is adopted. For weak artifacts, sorting and filtering are performed in the sinogram-domain. While for strong artifacts, the residual image is calculated firstly according to the performance of ring artifacts in the polar coordinate system, which is converted to Cartesian coordinate system to obtain the artifacts and the sample boundaries. Then an image segmentation method based on machine learning is used to obtain the distribution of each type of samples, and in order to protect the boundary information, the internal region of the samples is obtained through morphology operation. Finally, the distribution features of the residual images are used to locate the artifact pixels, and the mean value of adjacent non-artifact pixels are used to replace them. The experimental results show that this method can effectively remove the ring artifacts in the image without destroying the sample boundaries.
To overcome the influence of statistical noise on the reconstruction quality of computational ghost imaging under the random speckle patterns illumination, a new computational ghost imaging method based on orthogonal optimization of random speckle patterns is proposed. Firstly, the effect of random speckle patterns on the reconstruction quality of the target object is analyzed based on computational ghost imaging. Then, combining the properties of a real symmetric matrix, the original random speckle patterns are orthogonalized by a spatial mapping matrix. Further, the reconstructed orthogonal speckle patterns are used to irradiate the unknown object and the transmitted light is measured by a bucket detector. A series of measured values by bucket detectorand the reconstructed speckle patterns stored in the computer are used to reconstruct the target object through second-order correlation operation. Finally, according to the covariance matrix characteristics of the reconstructed speckle patterns, the reconstruction results are compensated to further improve the reconstruction quality of the object. This method can not only effectively improve the image quality of computational ghost imaging under the action of random speckle patterns, but also has the characteristics of simple algorithm structure. The simulation results show that the method can reconstruct the target effectively and has a good performance compared with the traditional computational ghost imaging under the illumination of random speckle patterns.
A 2 μm distributed Bragg reflection (DBR) single-longitudinal-mode fiber laser with frequency tuning function is presented. The laser is based on single-mode thulium-doped silica glass fiber and pumped by 793 nm semiconductor laser pump source, and its optoelectric devices are integrated into a 1U chassis in a separate state. Fast frequency tuning of the laser can be realized through a built-in piezoelectric transducer (PZT), and the tuning range is about 6 GHz. The laser frequency can also be tuned without mode hopping in the range of 29 GHz through TEC temperature control. The output power of the single-longitudinal-mode laser is 18.2 mW, the signal-to-noise ratio is greater than 60 dB, and the pump conversion efficiency is 27%. This laser prototype is expected to play an important role in the fields of high-resolution spectroscopy, quantum information and nonlinear frequency transformation.
In order to effectively reduce the electron leakage of deep ultraviolet laser diode (DUV-LD) in the active region, a well-type ladder electron blocking layer (EBL) structure is proposed. Crosslight software is used to simulate three different structures of EBLs, namely, rectangle type, ladder type and well-type, respectively, and the energy band diagram, radiation recombination rate, electron hole concentration, P-I and V-I characteristics of the three structure devices are compared and analyzed in detail. It is found that the well-type ladder EBL has the best suppression effect on the leakage of electrons, leading to the improved optical and electrical properties of the DUV-LD device.
Excimer laser amplification technology can amplify the low-energy deep ultraviolet femtosecond pulse obtained by solid Ti:Sapphire femtosecond laser through frequency conversion into the high-energy deep ultraviolet femtosecond pulse. In order to meet therequirement of synchronization between excimer laser and femtosecond laser, a time-delay synchronization system with low jitter for excimer laser has been designed. The system adopts the method that combines field programmable gate array (FPGA) digital delay and programmable delay chip delay, uses the time measurement chip to achieve the closed-loop control of delay time to improve the stability of the system’s delay output, and finally realize the accurate delay of external trigger pulse signal. The verification experiments show thatthe system operates stably at 1-100 Hz frequency, the delay time range of output pulse signal is 56 ns-2.2 μs, the theoretical delay step is 10 ps, and the jitter is less than ±1 ns, which fully meets the requirement of synchronization between femtosecond laser and excimer laser.
In order to evaluate the effect of irradiation on the spectral properties of Cr:MgAl2O4 crystal, Raman spectra, transmittance spectra and fluorescence properties of the polished Cr:MgAl2O4 crystal were measured before and after γ irradiation with a dose of 100 Mrad, and the mechanism of the irradiation effect were analyzed. The results show that the position and intensity of Raman vibration peak are both affected by irradiation, but the number of vibration peaks does not change. And due to the absorption of color center, the transmittance in the wavelength range of 250-600 nm decreases obviously after γ irradiation. The fluorescence emission peaks of the samples after irradiation are consistent with those of before irradiation, while the fluorescence emission intensity decreases significantly and the fluorescence lifetime increases significantly after irradiation.
The detection of high-dimensional entanglement is an important challenge in both theoretical and experimental aspects of quantum information science and technology. The traditional entanglement witness based on fidelity is not suitable for detecting all kinds of entanglement states, and the number of measurement combinations is not optimal. A new algorithm based on convex optimization theory has been proposed to remedy the situation. The performance of both approaches on a bipartite time-bin-entangled qutrit is experimentally test. When the traditional entanglement witness cannot determine its entanglement property unambiguously, it’s switched to the optimization-based method. The results show that a simpler and more effective measurement scheme can be obtained by using the new method, which can efficiently and accurately verify the entanglement dimension of the target qutrit. In addition, compared with the traditional entanglement witness, the new method only requires counting 6 different pairs of coincidences instead of 15.
In order to improve the practicability and security of quantum key distribution (QKD) technology, it is an important research direction in the field to explore the possible security vulnerabilities in QKD system and study the corresponding defense strategies. Dead time attack is a kind of attack against QKD system with multi-channel detectors, in which the attacker uses the death time effect of single-photon avalanche photodiode to blind the designated channel to destroy the security of the key generated by QKD system. Aiming at this type of attack, a new anti-dead time attack scheme based on time measurement technology to dynamically setting dead time length is proposed. The proposed scheme uses TDC time measurement technology to ensure that the multi-channel detectors can enter and exit the dead time state simultaneously to achieve the defense goal. The feasibility of the scheme is verified on the test platform.
Quantum secure summation is the basis of quantum secure computation, which aims to compute the sum of participants′ secrets on the premise of protecting the participants′ private information. A three-party quantum secure summation protocolbased on GHZ-like states is proposed, in which only quantum center has full quantum capabilities, and the other participants can only reflect or measure the received quantum states. Theoretical analysis shows that the proposed protocol can ensure correctness, that is, multi-party can finally successfully calculate the sum of their secrets. At the same time, the protocol can also resist participant attacks and external attacks, that is, neither external attackers nor internal participants can obtain any information except their own secrets and results. Finally, how to expand the participants of the agreement from three-party to multi-party is further discussed.
Considering that the quantum key distribution protocol may be affected by the detector dead time in practical applications when the photon transmission rate is too high, the relationship between the security key generation rate based on the heralded single photon source protocol and the detector dead time is explored. First, the relationship between the security key generation rate and the detector dead time is explored with or without considering the detector dead time. The results show that when the photon transmission rate is too high, the dead time of the detector will indeed affect the generation rate of security key. Then the security key generation rate is further analyzed under different detector dead time. The results show that for the same lightsource, the greater the detector dead time is, the smaller the security key generation rate is, and the relation between the limit value of the security key generation rate and the detector dead time τ is 4.2/τ.
Canonical correlation analysis is an important data processing method for dealing with the interdependence of random vectors. However, the complexity of the classical canonical correlation analysis algorithm is polynomial dependent on the data dimension, making this type of algorithm not suitable for analyzing the data whose scale is growing exponentially in the era of big data. Aiming at the defect of classical canonical correlation analysis algorithm, a quantum canonical correlation analysis algorithm was proposed. The algorithm transformes the optimization problems involved in canonical correlation analysis into algebraic problems suitable for quantum computing technology, and uses quantum principal component analysis technology to solve it, thereby reducing the cost of canonical correlation analysis algorithms. Under certain parameter conditions, the proposed algorithm can achieve exponential acceleration in the data dimension, which meets the requirements of this algorithm for today’s actual data processing.
Micromotion induced by radio-frequency (RF) field contributes greatly to the systematic frequency shifts of optical frequency standards (OFSs). Although the micromotion is compensated to the best degree before each experiment, the influence of micromotionwill gradually appear with the shift of stray electric field during the experiment, which requires continuous compensation. To overcome this problem, indium tin oxide (ITO) conductive glass is used to optimize the vacuum system in linear ion trap system to restrain the shift of stray electric field. By measuring and calculating, the stray electric field shift is minimized to 1.63 μV·m－1·s－1, after optimization, which is around 1/40 of the previous work 57.7 μV·m－1ots－1, so that the influence of micromotion can be negligible during the long-time experiment, and the effective time of experiment can be significantly increased.
Aiming at the ubiquitous dispersion problem in optical fibers currently used, a dual-core circular liquid-doped photonic crystal fiber was designed by using the finite element method and COMSOL Multiphysics simulation software. The results show that as the ratio d1/Λ of the air hole diameter d1 to the air hole layer spacing Λ decreases, the maximum change rate and dispersion of the effective refractive index gradually move to the long wavelength direction. And with the increase of the central hole diameter d2, the maximum change rate of the effective refractive index and the minimum dispersion value also gradually move to the long wavelength direction. In addition, with the increase of the refractive index nL of the doping liquid, the maximum change rate of the effective refractive index and the minimum dispersion rate also show the same changing trend. It is shown that the large negative dispersion value of －132720 ps·nm－1·km－1 can be obtained at 1550 nm for Λ=1550μm, d1/Λ=0.7, d2/Λ=0.833, and nL=1.753.