Terchertz (THz) transmission imaging is characterized by its harmless nature to human body and high penetration capability for non-metallic materials, making it suitable for applications in security inspection and biomedical fields. The key to improve the measurement accuracy of THz line scan camera lies in the accuracy of camera parameters. This paper proposes an improved Dingo optimization algorithm (DOA) to optimize the camera parameters obtained by the Draréni calibration method. The improved DOA enhances the global search capability by modifying the feeding and survival behaviors in the traditional DOA, and introducing the individual updating strategy of particle swarm optimization algorithm and grey wolf algorithm. A THz transmission scanning imaging device is built for imaging, and 10 images from different positions are selected as test objects. The camera's initial intrinsic and extrinsic parameters are obtained using the Draréni calibration method. Finally, the particle swarm optimization algorithm, DOA, and the improved DOA proposed in this paper are used respectively for camera internal parameter optimization. The experimental results show that the proposed algorithm in this paper reduces the average reprojection error by 33.41%, 21.35%, 12.62% respectively compared with the traditional Draréni calibration method, the particle swarm optimization algorithm, and the standard DOA, which demonstrates that the proposed algorithm is stable and can significantly improve the accuracy of camera calibration.

Fourier single-pixel imaging technology is one sort of single-pixel imaging technology that provides both outstanding image quality and high imaging efficiency. When utilizing this technology, an efficient sampling approach is crucial to enhance the reconstruction quality for images with various attributes. In this work, the implementation principles and processes of three commonly used sampling methods for Fourier single-pixel imaging, namely circular sampling, Gaussian random sampling, and adaptive sampling, are studied. Taking optimal sampling as a reference, the quality of reconstructed images of the four sampling methods at various sample rate is simulated and compared, with a focus on the benefits and drawbacks of the four sampling techniques in processing images with various attributes. The results demonstrate that for images with various spectral energy distribution characteristics, the four sampling methods exhibit distinct peak signal-to-noise ratios in reconstructed images, and each sampling method has its own optimal applicability. This result will provide important reference for how to efficiently select the best sampling method to reconstruct the images with various attributes.

Ultra-narrow linewidth frequency-stabilized lasers play a crucial role in the fields of precision measurement, precision spectroscopy, atomic frequency standard and other fields, and its frequency stability depends on the performance of the reference ultra-stable cavity. The horizontally placed ultra-stable cavity is highly sensitive to external vibrations. Usually, there is a magnitude difference between actual vibration sensitivity and its theoretical design, which makes vibration noise an important factor limiting the stability of the ultra-stable cavity. This paper takes a cylindrical horizontal cavity as an example and proposes a cavity design with a low vibration-sensitive of 7.3×10-12/g (g=9.81 m·s-2) based on the finite element analysis method. Error factors affecting vibration sensitivity during processing and assembly are analyzed, and the corresponding solutions are proposed. It is indicated that the method proposed in this work is also applicable to vibration-insensitive designs of other shapes of ultra-stable cavities, and can be used in various precision measurement experiments in the future.

When high-precision laser absorption spectroscopy techniques such as cavity ring-down spectroscopy and cavity enhanced spectroscopy are used in gas measurements, the stability of laser output wavelength directly affects the accuracy of measurement results. Therefore, accurate measurement of laser wavelength is crucial to high-sensitivity laser absorption spectroscopy technology. Taking the distributed feedback (DFB) laser commonly used in the cavity ring-down absorption spectrum as an application example, a wavelength monitoring system is built in this work based on Fabry-Perot (F-P) etalon. The system utilizes the interference phenomenon of F-P etalon, and adjusts the laser driving current to scan the wavelength. And at the same time, a standared wavelength meter is used as reference, then the functional relationship between wavelength and interference light intensity can be obtained, which will be used for inversion of wavelength information in the subsequent measurement. In the experiment, a DFB laser with central wavelength of 1653 nm is used, and the F-P system has realized the wavelength measurement in the range of 1653.66160 nm to 1653.77718 nm for this laser. The linear fitting correlation between the measurement results and the reading of the reference wavelength meter is 0.9999, which proves the reliability of the F-P wavelength monitoring system. In order to further verify the stability and measurement accuracy of the system, a 10-minute continuous monitoring is carried out at the central wavelength of the laser, and the results show that the system accuracy is ± 9.12 × 10-5 nm. It is indicated that this work is of great significance for realizing high-precision atmospheric background and isotope gas measurement by cavity ring-down absorption spectroscopy technology in the future.

Iron resonance fluorescence lidar is an important means of measuring temperature and wind field in the region from the top of the intermediate layer to the bottom of the thermosphere. However, due to the presence of strong sky background noise during the daytime, the resonance fluorescence signals of iron atoms are submerged, making it impossible to detect temperature and wind field in the middle and upper atmosphere. In order to solve this problem, this paper developed a tunable narrowband filter and proposed a new filtering method of connecting two Fabry-Perot etalons with air gap in series and combining them with a narrowband interference filter. Then the filter and the method were applied in iron resonance fluorescence Doppler lidar, achieving temperature and wind field detection in the region from the top of the intermediate layer to the bottom of the thermosphere during daytime. Firstly, by defining a filter performance evaluation function, the filtering performance of the filter was quantitatively analyzed, and parameters such as bandwidth and free spectral range of the two etalons were determined. Furthermore, a control system based on PID algorithm was designed to achieve precise control of the pressure in etalon chamber. Then, the design specifications of the filter were tested through simulation. And finally, field experiments demonstrated the filtering effectiveness of the filter in the iron resonance fluorescence lidar system, achieving a signal-to-noise ratio exceeding 136 and enabling wind speed and temperature detection in the iron layer region.

The no-cloning theorem has sparked considerable interest in achieving high-fidelity approximate quantum cloning. Most of the previous studies mainly focused on the cloning of single-particle states, and cloning schemes used there are incapable of cloning quantum entangled states in multipartite systems. Few schemes were proposed for cloning multiparticle states, which consume more entanglement resources with loss of qubits, and the fidelity of the cloned state is relatively low. In this paper, cloning schemes for bipartite and tripartite entangled states based on photonic quantum walk and entanglement swapping are proposed. The results show that according to the proposed schemes, two high-fidelity (up to 0.75) cloned states can be obtained with less quantum resource consumption. Because of the simple cloning steps, few quantum resources and high fidelity, these schemes are both efficient and feasible. Moreover, this cloning machine eliminates the need for tracing out cloning machine, thereby minimizing resource waste.

The one-dimensional coinless discrete-time quantum walk is realized in optical waveguides by utilizing directional couplers between waveguides in this work, then the topological diagram of this system is obtained and the corresponding dynamic evolution behavior affected by topological edge states is studied.The results show that when the number of the lattice sites is even, there are three different topological phases, corresponding to the topological edge states with zero-energy, π-energy,zero-energy and π-energy coexistence, respectively. Whereas, when the number of the lattice sites is odd, there are only two different topological phases, corresponding to the topological edge states with zero-energy,zero-energy and π-energy coexistence, respectively. By choosing the appropriate parameter and initial state, the walkers, i.e. particles, can only be localized at the boundary of the system or oscillate on the two lattice sites of the boundary. The localization behavior of the walkers during the walking process provides a feasible scheme to realize nondestructive quantum state transmission and quantum information transmission.

In order to achieve the stable confinement of ions in ion traps, a radio frequency (RF) source based on electronic tube oscillation circuit is constructed in this work. The device can simultaneously generate two RF electric fields with equal amplitudes and opposite phases, and its output frequencies are continuously adjustable ranging from 2.15 MHz to 4.05 MHz without active impedance matching. Over a continuous measurement period of 4.68 × 104 s, the stabilities of frequency, phase difference, and dual-channel voltage peak-to-peak values of the RF source are evaluated after being installed on an ion trap, and the minimum Allan derivations of each parameter's stability are obtained to be 10-5, 10-4, and 10-4 orders of magnitude, respectively. Furthermore, calcium ions are successfully confined in the ion trap equipped with the designed RF source, and by continuous adjusting the RF frequency and amplitude without turning off the RF source, the structural variations of the calcium ion Coulomb crystal are observed by CCD camera.

Acousto-optic modulator is an important optical device, and its performance largely depends on the quality of driving power supply. Therefore, it is of great significance to develop high performance acousto-optic modulator driving power supply for different application scenarios. In order to meet the application requirement of optical parametric oscillation cavity length locking for acousto-optic modulator in vacuum squeezed light preparation in quantum optics, a high-performance acousto-optic modulator driving power supply is designed in this work. In this driving supply, the radio frequency metal-oxide-semiconductor field-effect transistor (RF MOSFET) amplifier module RA07H0608M is proposed as the core device, and the input signal is finally injected into acousto-optic modulator after passing through impedance matching circuit, high-pass filtering amplifier circuit and power amplification circuit. At the same time, the monitoring circuit monitors the working temperature and signal power in real time. The results show that the acousto-optic modulator driving supply can achieve continuous frequency and power tuning. In the operating frequency range of 75-85 MHz, the input and output signals have a good linear relationship, the output power is up to 1 W, and automatic shutdown protection of over-temperature and over-power can be achieved. It is indicated that the designed driving power supply can fully meet the requirements of long-term stable operation of acousto-optic modulator.

An integrated optical memory with a long storage lifetime based on a waveguide fabricated in a rare-earth-ion-doped crystal is developed in this work by utilizing femtosecond-laser-micromachining. This optical memory features a cross-section with 20 μm diameter and an insertion loss of 5 dB. A demonstration of long-life optical storage in the memory shows that the storage efficiency decay of the memory exhibits a multi-exponential pattern, with characteristic time constants of 4.9 ± 0.1 h and 14.2 ± 0.8 h. This optical memory has a storage efficiency of 8.1% at a storage time of 1.4 s, and a storage efficiency of 0.6% is achieved at maximum storage time of 24 hours. Such long-lived crystal waveguide based memory is potential to be extended to a 2-dimensional integration array, and is expected to be applied in integrated optical information processing.

Diamond nanopillars can improve the photon emission efficiency of color centers and have a focusing effect on the emitted photons. By using the time-domain finite-difference method, the effects of structural changes such as diameter, height and color center position of diamond nanopillar on parameters such as Purcell factor, photon transmittance and photon extraction efficiency of color centers in the nanopillars are studied in this work, the mechanism of the nanopillar structure enhancing the luminescence of color centers is discussed, and the optimal nanopillar structure parameters are explored to obtain the maximal total fluorescence collection of color centers. It is found that the total fluorescence collection of color centers under the optimal structure is 17 times higher than that of bulk diamond, and can be effectively collected by a microscope with numerical apertureNA=0.95. Among the structural parameters, the size error of nanopillar diameter has the greatest influence on fluorescence collection, but it can also be more than 13 times than that of bulk diamond even in the range of ±20 nm. This study provides a foundation for the design and preparation of diamond color-centered luminescence-enhanced structure.

Aiming at the periodic boundary problem of phase detection in the existing turbulent random phase difference demodulation algorithms in optical fiber turbulence measurement technology, an atmospheric optical turbulent phase difference demodulation algorithm combined with phase unwrapping technology, called Phase Generated Carrier Unwrapping (PGCU), is proposed in this work based on the principle of internal modulation phase carrier technology and its signal expression. Through numerical simulation, the demodulation errors of the algorithm and the traditional Differential Cross Multiplication (DCM) algorithm under different conditions were compared and analyzed. The simulation results show that the PGCU algorithm can not only break through the periodic boundary of the detection phase, but also significantly reduce the average demodulation error by 7～11 orders of magnitude compared to the DCM algorithm under the condition of turbulence changing from strong to weak. Besides, the demodulation error has a positive correlation with the signal amplitude and frequency. And when the modulation frequency is increased from 2000 Hz to 7000 Hz, the maximum demodulation error of PGCU algorithm is reduced by 4 orders of magnitude, while that of DCM algorithm can only be reduced by 8.8%. In addition, a dynamic tracking modulation frequency algorithm is also proposed to solve the error problem caused by modulation frequency fluctuation. Finally, through the experiment of demodulating the phase difference generated by piezoelectric ceramics, it is found that the minimum relative error between the demodulated phase and the measured phase is 1.18% and the maximum relative error is 11.61%, which preliminarily verifies the reliability and accuracy of the PGCU algorithm. By introducing phase solution wrapping technology, this study has improved the detection range of turbulent random phase difference and greatly reduced the demodulation error, which provides important guidance for the practical application of fiber turbulence measurement systems.

Based on the principle of laser Doppler velocimetry, this study proposes a hybrid frequency resolution methodology combining fast Fourier transform (FFT) and continuous Fourier transform (CFT), achieving enhanced measurement accuracy for wire rod velocity. By combining autocorrelation detection, FFT spectrum estimation, CFT spectrum refinement, and energy center estimation spectrum correction, this method achieves effective noise reduction, high signal-to-noise ratio and spectral resolution, thereby improving the accuracy of wire rod speed measurement. The simulation and experimental results show that the signal-to-noise ratio of the collected signal is improved after single autocorrelation, and the average absolute error of speed measurement is less than 0.01 m/s. Compared with Welch spectrum estimation, this method has a smaller absolute error and higher accuracy in speed measurement under different speed conditions. The on-site production tests show that the speed measurements of different sections meet the requirements of high-speed wire rod production control, confirming the applicability of this method.

In response to the problem of low sensitivity of bare fiber Bragg gratings to ultrasound, the article proposes a series of polymer encapsulated fiber Bragg grating sensors. By encapsulating a polymer coating layer aroud the gratings that is much thicker than the diameter of the fiber, the strain sensitivity of the fiber Bragg gratings under ultrasound action is improved. Firstly, a fiber grating sensing model is established, and the influence of polymer Young's modulus and Poisson's ratio on fiber grating strain is analyzed based on the transfer matrix method. And then, fiber Bragg gratings are encapsulated using three polymer materials with different parameters, namely polyurethane (PU), polyacrylate (ABR), and polyvinyl chloride (PVC). The wavelength drift of the fiber Bragg grating is converted into a voltage signal using linear edge filtering method, and the sensing characteristics of the encapsulated sensors for ultrasound are measured. The results show that the decrease of Young's modulus and the increase of Poisson's ratio of polymers are helpful to improve the sensitivity of fiber gratings to ultrasonic response. And among the three materials, PU packaging has the best effect, with a peak voltage of 139.6 mV, which is about 15 times that of the bare fiber gratings. In addition, the peak voltage of the packaged sensor decays exponentially with the increasing distances from the sound source, which conforms to the attenuation trend of ultrasound in water and can restore the sound field state in space.