Journals >Acta Photonica Sinica
Contents
2024
Volume: 53 Issue 10
20 Article(s)
Export citation format
LD Pumped 454 nm Blue Pulsed Nd∶YLF Laser
Yinuo ZHANG, Jian MA, Junxuan ZHANG, and Xiaolei ZHU
Blue-green laser, with its high optical transmittance and low transmission loss in seawater, is currently the only spectral band capable of penetrating the air-sea interface and seawater to achieve transmission at great depths. In recent years, with the rapid development of oceanic laser remote sensing and underwater cBlue-green laser, with its high optical transmittance and low transmission loss in seawater, is currently the only spectral band capable of penetrating the air-sea interface and seawater to achieve transmission at great depths. In recent years, with the rapid development of oceanic laser remote sensing and underwater communication, there is an increasingly urgent demand for compact and high frequency repetition rate blue-green pulse laser that can be combined with airborne platform to achieve information transmission and high-precision detection of oceanic vertical profile. The blue light in the spectral band of 450 nm to 490 nm has stronger penetrating ability for open ocean than green light, making it the optimal operating spectral band for oceanic lidar. To our knowledge, the only report of quasi-three-level frequency-doubled ∶YLF laser is about its continuous operation. This study presents a blue pulse laser output at 454 nm for marine applications by intracavity frequency doubling of a pulse diode-pumped Nd∶YLF laser at 908 nm based on the quasi-three-level transition.Using 806 nm LD end-pumped Nd∶YLiF4 (Nd∶YLF) crystal, a L-shaped laser resonator is built to suppress parasitic oscillation at 1047 nm, and successfully realize the quasi-three-level Nd∶YLF laser emitting at 908 nm. The resonator of the fundamental frequency laser consists of three mirrors: a concave input coupler with a curvature radius of 200 mm, a plane mirror inserted at 45° with respect to the optical axis, and a 908 nm output coupler with output transmission of 2.7% at 908 nm. This 45° mirror is high-reflection coated at 908 nm and 454 nm, and anti-reflection coated at 1 047 nm. Thus, the resonator is singly resonant at 908 nm. Two methods, electro-optic Q-switching and gain-switching, were proposed to obtain the fundamental frequency pulse laser. Thus, for the experimental setup of Q-switching method, a polarizer and a double-RTP Pockels were inserted in the resonator as a voltage-decreased electro-optical Q-switcher. A type-Ⅰ critical phase-matched LiB3O5 (LBO) crystal with a size of 3 mm×3 mm×10 mm and phase matching cut angles of θ=90° and φ=19.3° is used to generate frequency doubled laser at 454 nm. And another 45° placed mirror with high-reflection coated at 454 nm and anti-reflection coated at 908 nm is used for the 454 nm laser output.For the gain-switched method, at a repetition rate of 100 Hz, the maximum output pulse power of the intracavity frequency-doubled 454 nm laser is 3.16 mW, with a pulse width of 418 ns. The frequency doubling efficiency is 1.1%, which is close to the theoretical calculation value of 1.3%. At different distances behind a focusing lens, the blue output laser beam diameters corresponding to the x and y direction were measured. The laser beam quality factors are calculated to be Mx2=1.07 and My2=1.12, with the beam divergence angels are measured to be 2.26 mrad in the x direction and 1.99 mrad in the y direction. For the Q-switching method, at a repetition rate of 100 Hz, the maximum output pulse power of 454 nm laser reaches 23.62 mW, with a pulse width of 66 ns, and the maximum frequency-doubling efficiency is around 3.7%. The laser beam quality factors are Mx2=1.6 and My2=1.3, and the beam divergence angels in x and y directions are separately 2.89 and 2.96. The central laser wavelength is measured to be 454.02 nm, and the FWHM of the spectral bandwidth has reached the limit of the spectrometer measurement resolution, which is less than 0.05 nm.In this paper, we present a blue pulse laser output at 454 nm by intracavity frequency doubling of a pulse diode-pumped Nd∶YLF laser at 908 nm based on the quasi-three-level transition. This study provides a new technical route for compact all-solid-state blue pulse laser, which can be used as a reference for the new laser source of ocean laser detection systems and underwater wireless optical communication systems..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1014001 (2024)
Sub-nanosecond Rising-edge Narrow Pulse Driver Circuit and Analog Simulation
Yi LI, Wenlong WEN, Qianhao WANG, Qianglong LI... and Feng LI|Show fewer author(s)
Semiconductor lasers have made great progress in theoretical research, practical application and technological development in the half century since their introduction. Today, they occupy the majority of the market share in the entire laser field, and are widely used in a variety of fields such as communication networkSemiconductor lasers have made great progress in theoretical research, practical application and technological development in the half century since their introduction. Today, they occupy the majority of the market share in the entire laser field, and are widely used in a variety of fields such as communication networks, medical aesthetics, laser sensing, and single-photon detection. Photon detection, for example, is a technique capable of detecting extremely low noise, with enhanced sensitivity enabling it to capture the smallest energy quantum of light, the photon. Not only does this technique allow for the precise counting of individual photons, which greatly enhances the accuracy and efficiency of detection, but it is also widely used in fields such as laser ranging and LIDAR to achieve high-resolution distance measurement and target detection.In laser ranging, the onset time of a laser pulse is usually defined by the rising edge of the pulse, so the steepness of the rising edge directly affects the accuracy of time-of-flight measurement. In LIDAR systems, a fast rising edge helps to shorten the laser emission time and increase the laser power, which in turn enhances the system's ability to sense the environment. Therefore, as the source of the laser signal, a semiconductor laser outputting narrow pulses with fast rising edges is crucial for improving the system accuracy.In this paper, a narrow pulse circuit with sub-nanosecond rising edge is designed, and the effects of inductance, capacitance and other parameters in the circuit on the rising edge of the output laser pulse are theoretically analyzed. The driver circuit uses a GaN integrated module with built-in driver as the main switch, and the semiconductor laser diode is driven by a reasonably designed driver circuit. At the same time, Field Programmable Gate Array (FPGA) is used as the control core to design the timing signals to realize the precise adjustment of the laser diode's pulse width and repetition frequency; and the thermoelectric cooler is driven by ADN8831 to realize the constant temperature control of the semiconductor laser.By simulating the circuit, it was found that the capacitor's ability to store and release energy increases with its value, allowing the circuit to release more charge per pulse, resulting in wider pulses and higher peak currents. Resistance only affects the peak current and an increase in resistance decreases the peak current. An increase in inductance extends the duration of the rising edge and reduces the peak current. Parasitic parameters in loop circuits, such as inductance, not only affect the speed of the pulse, but also affect the pulse waveform, making it more rounded or “dome” shaped. A relatively small capacitance has no significant effect on the overall performance. By reasonably designing the inductance and capacitance parameters and optimizing the circuit layout and wiring, sub-nanosecond rising edge laser narrow pulses can be achieved.The final experimental validation shows that the pulse front reaches 630 ps, the pulse width is adjustable from 5 ns to 15 ns, the repetition frequency is adjustable from 1 kHz to 10 kHz, the temperature of the LD is set from 25 ℃ to 26 ℃, and the RMS test value of the 12-hour power stability is 0.51%..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1014002 (2024)
[in Chinese]
Weiwei Liu, Lingling Huang, and Xing Zhao
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053400 (2024)
Instrumentation, Measurement and Metrology
A Multi-task Learning Method for 3D Reconstruction of Highly Reflective Surfaces
Mojing LI, and Changku SUN
When applying binocular Phase-Shifting Profilometry (PSP) to highly reflective surfaces, the main difficulty lies in the lack of phase in the overexposed area, based on this consideration, multi-task learning was introduced into highly reflective surface phase profiling. However, in the early stage of multi-task learniWhen applying binocular Phase-Shifting Profilometry (PSP) to highly reflective surfaces, the main difficulty lies in the lack of phase in the overexposed area, based on this consideration, multi-task learning was introduced into highly reflective surface phase profiling. However, in the early stage of multi-task learning, due to the influence of overexposed regions, the network tends to realize the correspondence retrieval of non-overexposed regions firstly, and the results obtained by the phase prediction module are not enough to constrain the stereo matching process, and the incorrect matching rate is prone to large oscillations, which reduces the network convergence speed.In order to solve this problem, considering that the fitting task of the network to the overexposed area and the non-overexposed area contains a natural priority relationship, and the traditional Pareto optimization of parallel multi-task learning is not suitable for scenarios with priority relationships, this paper proposes a multi-task learning method that dynamically updates the task priority, and controls the network to complete the learning according to above pattern.Firstly, the multi-task learning network is designed based on classic architecture UNET, which consists of phase prediction and correspondence retrieval module. In learning process, this two tasks are optimized simultaneously, thus, the correspondence retrieval process is guided by the result from phase predicting module. At the same time, a loss function consists of several parts is designed to be optimized, which concerns matching loss, prediction loss and consistency loss, corresponding to correspondence retrieval module, phase predicting module and the joint optimization respectively.Secondly, the application of Pareto optimization based on parallel multi-task learning in phase-shifting profilometry of highly reflective surfaces is derived. In this method, overexposed and non-overexposed areas are used as different data for network fitting. By introducing the multi-gradient descent method into multi-task weight search, this method can ensure that the network is optimized in a direction that can cause the loss function values of all tasks to decrease at all times, thus achieving relatively stable hyperparameter search in most cases. However, as mentioned earlier, setting two tasks as parallel priorities often leads to significant oscillations during network convergence, resulting in a decrease in network performance.To improve the reconstruction of high reflective surfaces based on parallel multi-task learning, a multi-task weight searching strategy with dynamic task priorities is proposed. On the basis of the above derivation, a key indicator is introduced, which is the proportion of pixels in non-overexposed areas that have completed stereo matching. In the early stage of network optimization, the task of fitting non overexposed area data is considered a high priority task. Once the indicator exceeds the specified threshold, it is considered that the network has basically completed the fitting of non-overexposed areas. At this time, the priority between tasks is adjusted, that is, the fitting task of the network to overexposed areas is considered a high priority task.To validate the proposed multi-task weight searching strategy, the results of manually selecting task weights and parallel multi-task weight searching strategy were compared with the results of the proposed multi-task weight searching strategy, which dynamically updates task priorities. In the comparative experiment, multiple test objects containing highly reflective areas were selected and reconstructed using three different methods. Set the incorrect matching rate as a qualitative evaluation indicator, the reconstruction results show that the multi-task weight searching strategy based on dynamic task priority proposed in this paper can achieve the most stable reconstruction performance. At the same time, compared with the parallel multi-task weight searching strategy, the network convergence speed of our method is faster and the network oscillation phenomenon is less obvious..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1012001 (2024)
Study on the Reflection Interference Spectroscopy Sensitivity Based on Nanoporous Anodic Alumina Sensing Substrate
Jianfei WANG, and Kaige WANG
Reflective Interference Spectroscopy (RIfS) technology based on porous thin film as a sensor substrate provides many advantages for biomedical molecular characterization, among which detection sensitivity is crucial. Nanoporous Anodic Aluminum (NpAA), as an effective nanostructured sensor platform, combined with RIfS tReflective Interference Spectroscopy (RIfS) technology based on porous thin film as a sensor substrate provides many advantages for biomedical molecular characterization, among which detection sensitivity is crucial. Nanoporous Anodic Aluminum (NpAA), as an effective nanostructured sensor platform, combined with RIfS technology, has practical applications in studying biomolecular properties and interactions between drug molecules and biomolecules. However, challenges will be faced, when the sample quantity is small and the refractive index of solution changes slightly, which leading to issues such as weak intensity of RIfS spectral signal, insufficient detection sensitivity, and inaccurate in judgment results. In order to improve the practicality of the reflective interference spectroscopy based on nanoporous thin films in the detection of trace samples, a model is established in this study, and various conditions affecting sensitivity and mechanisms are quantitatively investigated and analyzed by combining experiment and simulation.First, two types of NpAA sensor substrates with same pore diameter (80 nm) but different pore depths (9 μm and 11 μm) were prepared with the standard two-step anodization method with oxalic acid as the electrolyte. The morphology of NpAA was characterised with scanning electron microscope, revealing well-ordered pore structures with vertical and distinct pore walls. The material has a high porosity, with significant gaps between the pores and a periodic arrangement. This pore structure enhances the film substrate's light field capture, creating standing wave phenomenon and significantly boosting the sensing signal strength. Different concentrations of glycerol solutions, with refractive indices ranging from 1.33 to 1.60, were then applied to the two types of NpAA sensor substrates. After the solution fully penetrated into the pores, the measurement was performed. The measurement data indicated that the sensitivity of RIfS for detecting trace amounts of filling liquid is 5.60×103 nm/RIU for a 9 μm depth and 8.00×103 nm/RIU for an 11 μm depth. In porous media, as the pore depth and porosity increase, much filling liquid will be in the pores. Generally, the effective refractive index of the porous film is influenced by both the refractive index of the bulk material and the filling material. For the same range of filling liquid refractive index changes, a greater porosity results in a larger effective refractive index changes, which in turn increases the effective optical thickness changes. Therefore, the sensitivity of nanoporous anodic alumina increases with the increase of pore depth, making the RIfS with NpAA as a sensing substrate more sensitive to changes in liquid refractive index.Next, a physical model of RIfS using nanoporous anodic alumina as a sensing substrate was established, and the impacts of pore depth and inner diameter on the RIfS sensing sensitivity were numerically investigated. The simulation results showed that the different pore depths correspond to different RIfS sensitivity, with the increase of pore depth, the sensitivity of RIfS is more sensitive to the change of the filling material inside the pores. For example, sensitivity increases from 2.20×103 nm/RIU to 8.30×103 nm/RIU as the filling liquid refractive index changes increasing from 0.22 (3 μm) to 0.06 (11 μm). Similarly, the RIfS sensitivity also varies with different inner diameters of NpAA films. As the inner diameter increases, the sensitivity increases from 2.80×103 nm/RIU with a filling liquid refractive index changes of 0.18 (30 nm) to 8.30×103 nm/RIU with a filling liquid refractive index changes of 0.06 (160 nm).The simulation data are highly consistent with the experimental results. The sensitivity simulation model and experimental results in this paper will promote the practical application of the RIfS technology based on nanoporous sensing substrate in the field of non-destructive and rapid analysis of molecule characteristics and their interaction properties at the single-molecule level..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1012002 (2024)
Monitoring Method of Liquid Diffusion Process Based on High Localized FBG
Feng ZHOU, Longnan WANG, Yuqi ZENG, Xiao LUO, and Xianming LIU
Monitoring of liquid phase diffusion process in real-time is very important in many fields such as chemistry, biomedicine, environmental science and so on. The traditional methods of liquid phase diffusion measurement mainly include nuclear magnetic resonance, optical holographic interferometry, diaphragm cell, etc. FiMonitoring of liquid phase diffusion process in real-time is very important in many fields such as chemistry, biomedicine, environmental science and so on. The traditional methods of liquid phase diffusion measurement mainly include nuclear magnetic resonance, optical holographic interferometry, diaphragm cell, etc. Fiber Bragg grating (FBG) has many advantages and especially can be used in harsh environment, so it has been widely used for sensing temperature, strain and refractive index. However, for ordinary FBG, the core mode is transmitted in the fiber core, so it can't be used directly for monitoring the liquid phase diffusion process. One method is coupling the light to the fiber cladding to excite the cladding modes, which are very sensitive to the refractive index. At present, there are three types of FBGs with strong cladding modes: tilted FBG (TFBG), off-axis FBG and high localized FBG (HLFBG). HLFBG is suitable for monitoring the liquid refractive index and liquid phase diffusion process and is usually inscribed by the femtosecond laser and point-by-point method, but high accuracy motorized linear translation stages are required.In this paper, a new monitoring method of liquid phase diffusion process based on HLFBG is proposed. The HLFBG is inscribed in hydrogen-loaded fiber by femtosecond laser and phase mask method. In order to reduce the peak power of femtosecond laser and avoid damage to the phase mask, the standard single-mode fiber is hydrogen loaded under 8 MPa and 120 °C for a week before inscription of FBG. A HLFBG with grating period of 1.071 μm is successfully inscribed by using femtosecond laser with a pulse energy of 400 μJ, a phase mask with period of 2.142 μm and a cylindrical lens with focal length of 40 mm. The width of the refractive index modulation region induced by femtosecond laser is about 4 μm, which is smaller than the fiber core diameter of 9 μm, so the refractive index modulation region of FBG can't completely cover the fiber core, resulting in high localization effect. The dip corresponding to the core mode in the transmission spectrum of the HLFBG is about -17.6 dB, besides, strong cladding modes with the dip of -17.2 dB and width of 145 nm are also excited, wich are extended from 1 403.42 nm to 1 548.28 nm. If the HLFBG is placed in air, most of the cladding modes are confined and transmitted in the cladding. If it's immersed in solution, when the refractive index of the solution outside the HLFBG is larger than some higher-order cladding modes, these higher-order cladding modes will change to leaky modes which are transmissted in the solution, so the leaky modes will loss quickly, besides, there is a cut-off mode between the the cladding modes and leaky modes. The central wavelength of the cut-off mode changes linearly with the change of the refractive index, and the refractive index sensitivity is measured to be 531.69 nm/RIU, while the core mode hardly changes with the refractive index, so it is suitable for temperature compensation in the liquid phase diffusion process. Due to its large refractive index measurement range, when the HLFBG is located at the interface of two liquids, the refractive index around HLFBG will change depending on the liquid phase diffusion process. By measuring the transmission spectra of HLFBG, the liquid phase diffusion process can be monitored in real time, and the relationship between the central wavelength shift of cut-off mode and liquid phase diffusion time is obtained. Futhermore, the concentration of the solution can be calculated according to the relationships between the central wavelength of cut-off mode, refractive index and concentration. From the experimental results it can be found that the liquid phase diffusion process of glycerin-water solution showed a double exponential function relationship. With the progress of diffusion process, the concentration of the solution around HLFBG begin to rise rapidly, and the diffusion process slows down gradually with the increase of diffusion time. The concentration of the glycerol solution reaches to about 41% after 565 min. The diffusion process will continue, but the diffusion rate will become slower and slower. So if the refractive index of a measured solution is lower than that of the fiber cladding, monitoring of the liquid phase diffusion process when it is mixed with other liquids can be realized by using this method, which will provide a new measurement means for the liquid mixing process in chemistry, biomedicine and other fields..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1012003 (2024)
Graph-optimization-based Vision/Inertial/UWB Fusion Positioning Algorithm for Indoor Environments
Bo GAO, and Baowang LIAN
Visual, inertial, and ultra-wideband (UWB) are the most commonly used sensors in indoor positioning scenarios. Visual sensors can capture environmental images and extract texture information from the scene, enabling the creation of an environment map while performing positioning. However, visual positioning technology Visual, inertial, and ultra-wideband (UWB) are the most commonly used sensors in indoor positioning scenarios. Visual sensors can capture environmental images and extract texture information from the scene, enabling the creation of an environment map while performing positioning. However, visual positioning technology has a relatively low precision, and visual sensors cannot function in strong or low light conditions. Inertial sensors have a high signal collection frequency and do not fail, providing high dynamic and accurate positioning within a short period of time. However, the positioning precision is limited by the drift of the sensors, and the positioning precision will decrease significantly over a long period of time. UWB positioning technology has a relatively high positioning precision and does not have the problem of cumulative error. It can perform positioning in a fixed global coordinate system. However, UWB positioning technology is susceptible to Non-Line-Of-Sight (NLOS) errors. If the three sensors are effectively and reasonably fused, the positioning accuracy and adaptability to indoor complex environments can be effectively improved.For this purpose, a graph-optimization-based Visual/inertial/UWB Fusion Positioning Algorithm (VIUFPA) is proposed. Firstly, visual inertial odometry based on point-line features is used to estimate the local pose, and the point-line feature extraction improves the positioning accuracy and robustness of the visual positioning system in scenes with changing lighting, weak textures, and fast camera movement. Secondly, the Robust Kalman Filtering (RKF) is designed to preprocess the UWB distance measurement values, eliminate the NLOS errors and abnormal distance measurement values, and then a UWB positioning algorithm based on RKF is constructed to provide global positioning information. Then, the UWB positioning algorithm output information is fused with the visual inertial odometry output positioning information using graph optimization to achieve high-precision indoor positioning.Finally, the validity of the proposed algorithm was verified through simulation experiments and real indoor scene experiments. First, the NLOS error suppression performance of the RKF algorithm in the presence of pedestrian interference was analyzed; second, a simulation experiment was conducted using the EuRoC dataset, where the UWB distance measurement values were simulated based on the information provided by the dataset, proving that the VIUFPA algorithm has high precision and robustness in complex environments; finally, an experimental platform was set up to conduct positioning experiments in an office with normal lighting conditions and an underground parking with weak lighting conditions, and the experimental results showed that, the proposed algorithm achieves an average positioning accuracy improvement of about 72.09% compared with the visual inertial odometry in low light, weak textures, or obstacle occlusion environments, and an average positioning accuracy improvement of about 46.15% compared with pure UWB positioning algorithm. The proposed algorithm can provide higher precision and stronger robustness positioning results in indoor environments..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1012004 (2024)
Optical Design and Fabrication
Design of Tracking Imaging Compound Axial Optical System
Tongyu XU, Xuyang LI, Zhiguang REN, Jinyang WEI... and Kaizhong YAO|Show fewer author(s)
Fast steering mirror with superior positioning accuracy and speed are essential for enhancing secondary image stabilization, which is critical for high-resolution imaging. They help in mitigating the effects of low-frequency vibrations. The continuous advancements in detectors, CPUs, and image processing algorithms havFast steering mirror with superior positioning accuracy and speed are essential for enhancing secondary image stabilization, which is critical for high-resolution imaging. They help in mitigating the effects of low-frequency vibrations. The continuous advancements in detectors, CPUs, and image processing algorithms have significantly improved the systems' ability to handle higher frame rates and detect image shifts with greater precision. As a result, composite axis optical systems that incorporate these technologies are becoming more adept at reducing image shifts caused by medium and high-frequency vibrations. This progress opens up extensive potential for applications across various fields that require high-precision imaging capabilities. This paper delves into the intricate design of a coaxial common optical path tracking and imaging composite axis optical system, which employs a Fast Steering Mirror (FSM) for secondary image stabilization. The FSM, acting as the actuator responsible for compensating image shifts, benefits from a smaller aperture, which translates into a significant enhancement in its response speed and closed-loop bandwidth. This feature is particularly advantageous in scenarios where rapid and precise adjustments are required to counteract image shifts. In the quest for the optimal front group configuration for the composite axis optical system, the paper conducts a thorough analysis of reflective and catadioptric afocal systems, weighing their respective pros and cons. The selection process culminates in the choice of a catadioptric afocal system, which is capable of achieving a larger beam expansion ratio. This system is particularly well-suited for the front group of the composite axis optical system, given its ability to meet the stringent small aperture requirement of the FSM in the optical path. The catadioptric afocal system is designed to provide a long focal length through a more compact Cassegrain configuration, while the short focal length component is delivered by a transmission system. To address the chromatic aberrations that may be introduced by the lenses, a double cemented lens is employed. Although this approach adds complexity to the optical group compared to a two-mirror system, it becomes a viable solution when the distribution of long and short focal lengths is carefully managed, allowing for a substantial beam expansion ratio. Following the selection of the appropriate front group structure, the paper employs Zemax software to validate the catadioptric afocal optical system. The validation process involves an in-depth analysis of the point spread function and optical distortion, which are obtained by placing a near-axis plane behind the afocal system. The parallel nature of the light emitted by the front group ensures that the defocusing effect caused by the rotation of the FSM remains within an acceptable range, thus minimizing its impact on image quality. Building on the understanding of the mechanism behind image rotation generation, the paper constructs a mathematical model that correlates image rotation with the Modulation Transfer Function (MTF). MATLAB is then utilized to simulate and analyze the impact of image rotation at various detector positions on the MTF, particularly when the FSM compensates for linear image shifts. This analysis identifies the position at the edge of the field of view where imaging quality is most susceptible to the effects of image rotation. By establishing the relationship between the transfer function and the rear group imaging focal length at the position most affected by image rotation, the paper explores the optimal rear group focal length that would yield the best modulation transfer function across different spatial frequencies. The results demonstrate that the impact of image rotation on image quality can be effectively reduced to an acceptable range, thus validating the theoretical feasibility of achieving secondary image stabilization through the use of a fast steering mirror. In conclusion, this paper not only underscores the theoretical viability of employing fast steering mirrors for secondary image stabilization but also for the design and development of composite axis optical systems that leverage the advantages of small aperture fast steering mirrors..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1022001 (2024)
Study on the Flexible Support Structure of the Linear Moving Mirror of the Spaceborne Michelson Interferometer
Shuai YANG, Jian SUN, Qiangqiang YAN, Yutao FENG... and Shun YAO|Show fewer author(s)
The support structure of the moving mirror constitutes the most crucial component of the high-precision Michelson interferometer, exerting a decisive impact on the quality of the interference signal. Conventional moving mirror support is accomplished through mechanical guide rails or magnetic levitation in combination The support structure of the moving mirror constitutes the most crucial component of the high-precision Michelson interferometer, exerting a decisive impact on the quality of the interference signal. Conventional moving mirror support is accomplished through mechanical guide rails or magnetic levitation in combination with a drive motor, which is expensive, difficult to maintain, has a low life span, and has low guiding accuracy under the load of large mass and large stroke angle mirrors. To address these issues, a flexible support structure for the moving mirror of the Michelson interferometer is designed, featuring low cost, high precision, large load capacity, and large travel range. In this paper, the working principle of the Michelson interferometer is presented, and the impacts of the travel of the moving mirror, guiding accuracy, and velocity uniformity on the accuracy and stability of the interferometer are analyzed. The influence of the parasitic displacement perpendicular to the direction of motion on the parasitic path difference is quantified when the angle mirror is employed as the moving mirror. With the parallelogram guiding structure serving as the basic prototype, four parallelogram structures are nested both internally and externally to form the fundamental framework of the support structure, effectively amplifying the motion stroke of the entire structure. The flexible support structure is arranged symmetrically to counteract the parasitic displacement in the horizontal direction. Taking the load capacity, travel, and guiding accuracy of the flexible support structure as the optimization targets, the structural stiffness model is proposed. Based on the Awtar beam constraint model, the force-displacement relationship of the flexible reed with unilateral constraint is derived from the deformation mechanism of the cantilever beam, and subsequently, the stiffness formula of the flexible reed with unilateral constraint is deduced. The stiffness model of two unilateral constrained flexible reeds is obtained by means of Hooke's law. On this basis, the stiffness model of the entire flexible structure is derived in accordance with the series-parallel relationship of the flexible reeds in the flexible support structure. The finite element method combined with the stiffness model of the flexible structure is utilized to optimize the size parameters of the structure, and the transition fillet is set at the connection of the flexible reed and the rigid part to mitigate the stress concentration phenomenon. By comparing the ratios of yield strength to elastic modulus of different materials, 7075 aluminum alloy is determined as the optimal material for the structure, and the three-dimensional model design and simulation of the flexible structure are conducted. The finite element analysis results indicate that the maximum tensile stress of the flexible structure amounts to 169 MPa, the structural safety margin is 1.98, and the parasitic displacement perpendicular to the movement direction is less than 4.1 μm when the travel attains 4.5 mm under the load of 1.5 kg (angle mirror). A special test platform was established by means of a spiral micrometer, a high-precision grating scale meter, a digital dynamometer, and weights. The force-displacement relationship and parasitic displacement of the test pieces were examined, and the errors between the simulation results and the experimental results were analyzed. The results demonstrate that the parasitic displacement perpendicular to the motion direction is less than 3.2 μm and 4.7 μm, and the root-mean-square error of straightness is 0.96 μm and 1.5 μm respectively when the flexible support structure is subjected to 0.5 kg and 1.5 kg load (angle mirror) within the range of 4.5 mm travel. The test results of this structure are consistent with the design results, and can meet the support requirements of the satellite-borne Michelson interferometer for high-precision linear moving mirrors. It can also be used in other motion systems that require large stroke, large load, long life, and high guiding accuracy..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1022002 (2024)
Remote Sensing and Sensors
Remote Sensing Image Fusion Based on Joint Spectral and Spatial Dual-scale Detail Injection
Shuxiang WANG, Fei JIN, Yuzhun LIN, Jie RUI... and Xiaobing YANG|Show fewer author(s)
Remote sensing image fusion is a crucial process that significantly enhances the quality of remote sensing data by integrating multispectral and panchromatic images. However, this integration poses challenges in both spectral and spatial scales. Traditional fusion methods, such as Intensity-Hue-Saturation (IHS) transfoRemote sensing image fusion is a crucial process that significantly enhances the quality of remote sensing data by integrating multispectral and panchromatic images. However, this integration poses challenges in both spectral and spatial scales. Traditional fusion methods, such as Intensity-Hue-Saturation (IHS) transformation for Component Substitution (CS) and wavelet transform fusion for Multi-Resolution Analysis (MRA), each have their own advantages and disadvantages when striving to generate high-resolution multispectral images. The former enhances spatial resolution significantly but leads to noticeable spectral distortion, while the latter maintains spectral information well but has limited spatial resolution enhancement. To fully leverage the strengths of both types of methods, we introduce a novel fusion method that combines spectral scale detail and spatial scale detail. The proposed method consists of three stages. The first stage is the multispectral image enhancement preprocessing, which takes into consideration the different demands for spectral and spatial information of different features in remote sensing images. The panchromatic image is used as a guiding image, and guided filtering is applied to enhance the multispectral image. After enhancement, the texture-rich regions in the multispectral image are sharpened, the gradient's information of which are increased. Meanwhile the spectral-rich regions are smoothed with average filtering to preserve spectral information. The enhanced multispectral image is the foundation for controlling the amount of detail injection in the subsequent stage. The second stage is the detail injection stage, which is a key component of the proposed method and includes detail extraction, detail injection coefficient calculation, and spectral preservation coefficient calculation. Initially, spectral scale difference details and spatial scale difference details are extracted separately from the multispectral and panchromatic images using classical component substitution methods and multi-scale analysis methods. Since there is some information redundancy in the extracted details, a normalized mutual information is used to calculate the ratio of the two types of details and generate a dual-scale detail image through linear weighting. To ensure that the injected details align with the original panchromatic image, edge detection is performed using gradient operators on the enhanced multispectral image, and the resulting edge matrix serves as a constraint for detail injection. Additionally, the spectral preservation coefficient is calculated based on the spectral correlation between the original multispectral image and its intensity component to maintain the spectral relationship during the fusion process. Finally, the dual-scale detail image, edge detection matrix, and spectral preservation coefficient are multiplied to obtain the final detail injection amount. The third stage is image fusion, where the original upsampled multispectral image is pixel-wise added to the detail injection image from the second stage to generate the fused high-resolution multispectral image. To validate the effectiveness of the proposed method, experiments were conducted on four types of remote sensing datasets including IKONOS, QuickBird, WorldView4, and GF-2. The images used in the experiments contain various terrain elements such as vegetation, buildings, and water bodies to verify the requirements of different land features for spectral and spatial information. Comparing the results of the four sets of experiments, the proposed method shows color similarity to the original multispectral images in the fused true-color composite images, with clear edges and rich textures. In terms of objective quality evaluation, the experiments on IKONOS and WorldView4 datasets achieved the best or second-best results in Dλ, Ds and QNR, while in the remaining two indicators, although there was no significant advantage, the subjective visual quality was significantly better than the comparison methods. In conclusion, the proposed method, combining spectral and spatial scale detail injection, addresses the shortcomings of insufficient single-scale detail information extraction, better adapts to the characteristics of different land features, and improves the detail and accuracy of the fusion results..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1028001 (2024)
Research on the Configuration of Automatic Sharpness Detection Window in Aerial Remote Sensing Based on SFV
Hao WANG, Xiaoli WANG, Jie LI, Tao JIANG, and Xinbo WANG
The method of automatic clarity detection for aerial remote sensing based on the spatial-filtering velocimetry can effectively solve the problem of inability to focus on static targets during aerial camera flights. This method can flexibly select the type of transmission function and filter window configuration, and dyThe method of automatic clarity detection for aerial remote sensing based on the spatial-filtering velocimetry can effectively solve the problem of inability to focus on static targets during aerial camera flights. This method can flexibly select the type of transmission function and filter window configuration, and dynamically adjust the filter parameters. To address the issue of selecting the configuration of a window for detecting the clarity of aerial remote sensing based on spatial-filtering velocimetry, this study constructs typical spatial filter models from a mathematical perspective and analyzes the sinusoidal and rectangular transmission functions. Sinusoidal and rectangular transmission functions have similar low-pass filtering characteristics, but the rectangular transmission function contains high-frequency components in addition to the fundamental peak. For clarity detection, ground targets satisfy a random process, and the high-frequency components they contain are beneficial for improving detection accuracy. Therefore, theoretically, the use of a rectangular-type filter is more conducive to detection accuracy, and the parameters of the rectangular transmission function are easier to design, with a smaller computational load, making it more suitable for automatic clarity detection. The study analyzes the power spectral density functions and filtering characteristics of typical spatial filter configurations, including rectangular, circular, and Gaussian-weighted filters, and discusses the impact of different window forms of filters on the accuracy of aerial remote sensing clarity detection. From the perspective of window configuration, rectangular and circular spatial filters contain low-frequency components that are unfavorable for clarity detection, as well as high-frequency components that are beneficial for the detection results. The Gaussian-weighted spatial filter does not contain these low-frequency components, but the low-frequency components can be filtered out using a differential method, and the energy of the high-frequency components is small, which will not have a significant impact on the detection results. Therefore, there is no significant difference in the performance of these three typical window configurations when used for aerial remote sensing clarity detection. In terms of implementation difficulty, the rectangular-type spatial filter is easier to realize, with a smaller computational data volume and more convenient parameter adjustment, and is therefore more commonly used. A validation experiment was designed by fixing the camera lens on a precision guide rail and using a high-precision turntable to drive its rotation, simulating the dynamic imaging process of aerial remote sensing. The imaging characteristics of an area array CCD detector were utilized, and dynamic sampling was performed along the periodic transmittance direction of the filter to simulate the periodic modulation process of the light amplitude of moving images relative to the target speed, and interval sampling of the CCD image was performed to simulate the periodic transmittance ratio of the spatial filter, greatly simplifying the system structure compared to using physical spatial filters such as gratings. The experiment first manually calibrated the focal plane as the zero position, using the rectangular transmission function and the common spatial filter configurations, including rectangular window, circular window, and Gaussian-weighted window, to perform ground imaging automatic clarity detection experiments. For each window type, 11 positions from out-of-focus to in-focus and back to out-of-focus were captured, and evaluation curves were generated, with the peak of the curve corresponding to the best imaging clarity position of the camera. The best imaging clarity positions obtained from the experimental curves of the three filters were consistent with the manually calibrated focal plane position, and the step size between the two frames in the experiment was 60 μm, less than the optical system's half-depth of focus of 76.8 μm. The experimental results show that the clarity detection results using the three filter configurations are consistent, with single-peak and unbiased characteristics, and no significant performance differences, so the rectangular-type spatial filter, which is the easiest to implement and requires the least computational resources, can be selected..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1028002 (2024)
Special Issue for Micro/Nanophotonics
Precision Processing Technology Based on Laser Filament（Invited）
Hongzhi HE, Zhaolin CHAI, Nan ZHANG, and Weiwei LIU
With the advancement of science, traditional mechanical processing methods are no longer able to meet the processing needs of humans for various two-dimensional or three-dimensional micro nano structures. Therefore, over the past half century, a series of high-energy beam processing technologies have rapidly developed.With the advancement of science, traditional mechanical processing methods are no longer able to meet the processing needs of humans for various two-dimensional or three-dimensional micro nano structures. Therefore, over the past half century, a series of high-energy beam processing technologies have rapidly developed. For example, electron beam processing, ion beam processing, and beam processing technologies with different wavelengths from extreme ultraviolet to near-infrared. This article discusses the principle of laser filament processing, lists typical applications of laser filament processing technology, and explores the main challenges and urgent scientific problems faced by laser filament processing technology. This article provides a systematic review of the applications of laser filament in high aspect ratio microstructures, large aspect surface microstructures, biomaterial processing, and welding. Including the generation and regulation of cross medium laser filament, as well as the influence of excited state materials on the properties of laser filament. Compared with traditional laser processing technology, laser filament precision processing technology can achieve efficient preparation of micro nano structures without precise focusing while maintaining micro/nano processing accuracy.Femtosecond laser filament processing is a complex physical process involving multiple disciplines such as light, heat, force, and materials. Femtosecond laser filament processing is a complex physical process involving multiple disciplines such as light, heat, force, and materials. Femtosecond laser filament processing involves the generation and regulation of cross dielectric filaments, as well as the influence of excited state materials on filament properties and many other scientific issues that need to be addressed. Solving these fundamental scientific problems is beneficial for accurately predicting and controlling material damage in the laser action area, improving the accuracy and quality of the processed surface, reducing material loss, and also achieving an improvement in the level of femtosecond laser wire processing technology.This article introduces the application of laser filament in microstructures with large aspect ratios, large surface microstructures, biomaterial processing, and welding, revealing the principle and practical application effects of femtosecond laser filament processing technology. This article introduces several mainstream applications of precision machining technology based on femtosecond laser filament:1) For the cutting technology of transparent hard and brittle materials, the mainstream cutting technologies currently include longitudinal multi focus cutting technology, Bessel beam cutting technology, and laser filament cutting technology. After years of development, precision machining technology based on femtosecond laser filament has become an indispensable key technology in modern industry and plays an increasingly important role in fields such as microelectronics, optics, and medicine. Laser filament cutting is widely used for cutting transparent materials due to its unique advantages.2) Currently, the communication frequency used in the sixth generation wireless communication is above 90 GHz, reaching the terahertz band. However, in the manufacturing of key devices in the terahertz band, achieving large-scale, high-precision, and high-efficiency device manufacturing is currently a huge challenge. The use of laser filament effect for precision machining of three-dimensional milling surfaces of curved components effectively avoids the interference of laser defocusing caused by changes in the height of the machined surface. Its high strength and long interaction range provide a new method for processing complex surfaces.3) Due to the cumulative effect of multiple pulse incidence, high repetition rate femtosecond laser filament can cause material melting. Therefore, femtosecond laser filament can also be used as a new type of transparent material micro welding/connection technology. In the manufacturing of biomaterials, femtosecond laser filament technology can be used to separate and cut cell tissues and biomaterials without being affected by material morphology, with high separation accuracy and good quality.This article analyzes how laser filament can achieve high-precision machining in these applications and explores the main challenges faced by this technology. These challenges include the generation and regulation of cross medium laser filament, as well as the influence of excited state materials on the properties of laser filament. The solution to these basic problems is beneficial for accurately predicting and controlling material damage in the laser action area, providing stronger preparation technology support for fields such as chips and electronics. The high intensity and large aspect ratio characteristics of laser filament make laser precision machining technology based on laser filament have important applications and broad development prospects in consumer electronics, chip manufacturing, communication, and medical fields.The materials that can be processed using femtosecond laser filament processing technology in the future include transparent hard and brittle materials, polymer materials, biomaterials and tissues, as well as metal materials, which have huge application prospects in industrial technology fields such as consumer electronics, chip manufacturing, communication, and healthcare. The main market for precision laser processing in China will gradually shift from general electronic component processing to upstream materials and core components, especially in the fields of semiconductor material preparation, biomedical, polymer materials, etc. The application technology of laser filament in the semiconductor chip industry will be increasingly invented, and for high-precision chip products, non-contact laser processing is the most suitable way. With the huge demand, the chip industry is highly likely to drive the next wave of demand for precision laser processing technology..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053402 (2024)
Special Issue for Ultrafast Optics
Study on Wide Field Fiber-based Photoacoustic Functional Microscopy（Invited）
Huan CHENG, Xiaoxuan ZHONG, Sheng ZENG, Yukai XU... and Long JIN|Show fewer author(s)
The condition of blood circulation plays an important role in the development of the disease. In order to monitor the tissue microcirculation of the brain, gastrointestinal tract and other important organs in animal models with a large field of view, and obtain the blood vessel structure and oxygenation function informThe condition of blood circulation plays an important role in the development of the disease. In order to monitor the tissue microcirculation of the brain, gastrointestinal tract and other important organs in animal models with a large field of view, and obtain the blood vessel structure and oxygenation function information of target tissues with high sensitivity, high resolution and high contrast, a photoacoustic microscopic imaging technology based on optical fiber ultrasonic sensor was proposed in this paper. In this technology, the orthogonal dual-frequency fiber laser independently developed by our research group is used as the ultrasonic sensor. Different from the traditional piezoelectric ultrasonic sensor, the fiber laser ultrasonic sensor is small in size and carries out ultrasonic sensing in a non-focusing way, which can ensure the detection sensitivity while realizing the large field of view ultrasonic detection. The combined scanning mode of galvanometer and motor is designed, which can realize the large-field imaging of the vascular structure of animal model. Using 532 nm pulsed laser with high power and high repetition frequency as seed light source, on the basis of 558 nm pulsed laser obtained by optical fiber stimulated Raman scattering effect, the blood oxygen saturation information of blood vessels in animal tissues was obtained by dual-wavelength excitation method of 532 nm and 558 nm by utilizing the difference of hemoglobin absorption spectrum under different blood oxygen saturation. The imaging results were able to distinguish arteries and veins by different blood vessel colors. By vertically scanning the edge of the surgical blade, the resolution of the large-field optical fiber photoacoustic microimaging system was determined to be 4.2 μm. A wide range of photoacoustic functional imaging was performed on the cerebral cortex of mouselet under anesthesia, and the differential effects of different anesthetics on the hemodynamics of live animals were observed, that is, the venous oxygen saturation of live animals under isoflurane and oxygen mixed gas anesthesia was higher, while the arterial blood oxygen saturation was slightly lower than that of pentobarbtal sodium injection. In addition, the changes of microcirculation status on the intestinal surface of rats with anaphylactic shock were studied by wide-field imaging. Abnormal changes of blood circulation function were observed during anaphylactic shock, that is, the mean blood oxygen saturation of venous vessels on the surface of small intestine of rats with shock was lower than that in normal state, and the blood vessels were dilated. The mean blood oxygen saturation of arterial vessels increased, the blood vessels dilated, and the total blood vessels decreased. These results provide effective information for the study of the effect of anaphylactic shock on microcirculation. Experimental results of scanning imaging in animal models show that the system can visualize changes in microcirculatory dysfunction in living animal tissues with single-vessel spatial resolution in the range of centimeters, while obtaining hemodynamic information of blood vessel structure (including blood vessel diameter, blood vessel density), hemoglobin concentration and blood oxygen saturation. This technique provides a new technical means for clinical study of the changes of blood circulation during the occurrence, development and treatment of diseases..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053401 (2024)
Special Issue For“The 40Th Anniversary of Institute of Modern Optics Nankai University”
Research Progress of Material Detection Based on Terahertz Spectroscopy（Invited）
Jiachen WANG, Kaidi LIU, and Lu SUN
Terahertz wave refers to the electromagnetic wave with the frequency range from 0.1~ 10 THz, which shows its unique advantages in the non-destructive testing of substances due to its characteristics such as low energy and fingerprint spectrum. In this paper, we mainly take the phase state (gas, solid, liquid) of substaTerahertz wave refers to the electromagnetic wave with the frequency range from 0.1~ 10 THz, which shows its unique advantages in the non-destructive testing of substances due to its characteristics such as low energy and fingerprint spectrum. In this paper, we mainly take the phase state (gas, solid, liquid) of substances as a classification, and review the research progress of terahertz spectroscopy detection technology in recent years.Firstly, we introduce the principle of terahertz spectroscopy technology, which includes the emission and detection of terahertz waves. Currently, the optical methods commonly used to generate terahertz waves are photoconductive antennas, optical rectification, and optical filament radiation. The types of terahertz detectors are zero-difference detectors, heterodyne detectors and photodetectors. However, if you want to detect the amplitude and phase information of terahertz waves at the same time, you need to use optoelectronic technology, and the commonly used optoelectronic techniques are electro-optical sampling and photoconductive sampling. In the context of terahertz time-domain spectroscopy, terahertz spectroscopy is defined as the technique of generating and detecting terahertz pulses in a synchronised, coherent manner using visible or near-infrared laser pulses.Secondly, since the energy required for molecular rotation is on the order of millielectron volts, which corresponds exactly to the order of the single-photon energy of terahertz radiation, the purely rotational characteristic absorption peaks of many gas molecules are in the low terahertz frequency band. At the same time, due to the differences between the structures of gas molecules, the positions and intensities of their absorption peaks in the terahertz bands also differ greatly. Therefore, terahertz spectroscopy has obvious advantages in the accuracy and sensitivity of gas detection. We introduce the research progress of terahertz spectroscopy for gas detection in recent years, such as water vapour, multi-component gases and so on.Thirdly, many substances have characteristic absorption peaks in the terahertz band, which is mainly due to the fact that the energy required for intramolecular and intermolecular motions of many substances overlaps significantly with the terahertz band, such as molecular low-frequency vibrations and lattice vibrations, and thus this property can be exploited for the analysis of the composition of substances. As for the terahertz characteristic absorption peaks measured in experiments, researchers often use theoretical calculations based on density flooding to explain the origin of terahertz vibrational properties. We have introduced the detection of solid structures and compositions by terahertz spectroscopy in recent years from several applications, such as pharmaceuticals, agricultural crops, magnetic materials, etc.Fourthly, since the response frequency of hydrogen bonding corresponds to the terahertz band, when terahertz waves pass through the network structure of water molecules, the hydrogen-bonded network structure of water molecules resonates and relaxes, resulting in a strong absorption of terahertz waves. Taking advantage of this property, terahertz waves can be used for the detection of water content in liquids on the one hand, and the detection of hydrogen bonding network structures in liquids on the other. We present the research progress in recent years on the use of terahertz waves for water content detection in substances and the detection of hydrogen bonding network structures in liquids.Finally, a short summary and outlook are given. Terahertz spectroscopy has shown unique advantages in substance detection, but it still has great potential for development..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053404 (2024)
MZI/FPI Fiber Optic Dual-parameter Sensor Based on a Double Cone and Air Cavity Structure（Invited）
Tingxuan YUAN, Lilong ZHAO, Jianxin REN, Yaya MAO... and Wenchao XIA|Show fewer author(s)
This paper proposes a Mach Zehnder/Fabry Perot Interferometer (MZI/FPI) fiber sensor based on Single-mode Fiber (SMF) and Hollow-core Fiber (HCF), which has high sensitivity to temperature and lateral loads. The proposed device consists of two single-mode fiber cones formed by manually controlling the fusion splicer anThis paper proposes a Mach Zehnder/Fabry Perot Interferometer (MZI/FPI) fiber sensor based on Single-mode Fiber (SMF) and Hollow-core Fiber (HCF), which has high sensitivity to temperature and lateral loads. The proposed device consists of two single-mode fiber cones formed by manually controlling the fusion splicer and an air cavity formed by fusing a section of hollow-core fiber. The structure of the sensor is a double cone cascaded air cavity. At the beginning of the design, we compared the basic transmission spectra of single cone structure and double cone structure experimentally, and therefore chose to use double cone structure and air cavity cascade. Light undergoes its first reflection at the first interface between the single-mode fiber and the air cavity structure, and its second reflection at the second interface between the air cavity structure and the single-mode fiber. The two reflected light waves produced by the two reflections form FP interference, which can be used to measure lateral loads. The transmitted light is excited through the first cone, and a portion of the core mode light is excited to the cladding, while another portion of the core mode light continues to propagate in the core. The light couples at the second cone, and the cladding mode light couples back into the core, forming MZ interference with the core mode light, which can be used to measure temperature. The use of hollow-core fiber to form an air cavity has little effect on transmitted light, while avoiding the problem of crosstalk in dual parameter measurements. By designing temperature and lateral load experiments, this article verifies the sensitivity characteristics of this sensor to temperature and lateral loads. A significant redshift phenomenon was observed in the temperature experiment. A significant redshift phenomenon also occurred in the lateral load experiment. Through wavelength demodulation, the experimental results show that the wavelength sensitivity of the sensor to temperature is 56.29 pm/℃ in the range of 30 ℃ to 80 ℃. The wavelength sensitivity of the sensor to lateral loads is 1.123 nm/N in the range of 0~5 N. In addition, we have prepared multiple sets of fiber optic sensors with this structure and conducted repeated experiments to verify that the sensing performance of this structure of fiber optic sensors for temperature and lateral load is relatively stable. Also, the different waist diameters of cones will have a certain impact on the transmission spectrum of MZ, while the length of the air cavity will also have a certain impact on the reflection spectrum of FP. This article lists some fiber optic sensors for dual parameter measurement of temperature and lateral load. Compared with the listed sensors, the fiber optic sensor proposed in this article has better sensitivity to temperature and lateral load. And the fiber optic sensor proposed in this article has a simple manufacturing process, low production cost, and good performance, which has certain prospects in scientific research and industrial production..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053406 (2024)
Multi-dimensional Orbital Angular Momentum Holography Based on Free Lens Phase（Invited）
Xinyang YU, Fajing LI, Jiaqi LUO, Keli CHEN... and Caojin YUAN|Show fewer author(s)
Computer generated holography simulates the recording process of traditional optical holography by using computers to encode the amplitude and phase information of an object, and is able to achieve the information reconstruction of a virtual three-dimensional object in space, which has been widely used in the fields ofComputer generated holography simulates the recording process of traditional optical holography by using computers to encode the amplitude and phase information of an object, and is able to achieve the information reconstruction of a virtual three-dimensional object in space, which has been widely used in the fields of three-dimensional display, optical storage and optical encryption. With the increasing complexity of 3D information, the amount of information storage requirements, and the amount of encrypted data, multiplexing in computer generated holography using space, time, wavelength and polarization dimensions has become an inevitable trend. However, with the explosive growth of information, the existing dimensions are about to be exploited. OAM holographic multiplexing technology has gained the attention of researchers. Traditional multiplexing modes use OAM as the only information carrier, which is prone to crosstalk and low information multiplexing rate. In order to solve the above problems, researchers have improved the orbital angular momentum holographic encryption scheme by combining the OAM with other optical dimensions, and the corresponding research results have been numerous.Thanks to the rapid development of vortex light field modulation technology, more and more intrinsic degrees of freedom of the beam have been exploited, such as notched beams, chiral light fields, and residual optical vortices. Researchers have applied these degrees of freedom to orbital angular momentum holography and achieved remarkable results, greatly enhancing the holographic information capacity and security performance. It is found that the generalized perfect optical vortices modulated by a free-lens phase have holographic preservation and mode selection properties similar to those of the spiral phase, and it is known that this novel and unique modulated phase has not yet been applied to orbital angular momentum holography.In this paper, we propose a multidimensional holographic encryption scheme that combines optical orbital angular momentum and multiparameter tunable free-lens phase. Multiple parameters in the generalized perfect optical vortex generated based on the free lens phase modulation are used as additional channels for multiplexed holography, and their potential as new coding degrees of freedom in holographic multiplexing is demonstrated. The influence of each parameter on the beam is analyzed by simulation. It is proved that the parameters are independent of each other, and that the focal length
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053407 (2024)
Performance Test of Fabery-Perot Etalon for Radial Velocity Measurement（Invited）
Yanting LU, Huiqi YE, Liang TANG, Yang ZHAI... and dong XIAO|Show fewer author(s)
Radial velocity measurement based on high resolution spectrum of stellar is crucial to exoplanet detection. To meet the requirement of detection of small rocky type exoplanet which is similar to earth, the astronomic high resolution spectrographs need advanced wavelength calibration technology to remove the errors of iRadial velocity measurement based on high resolution spectrum of stellar is crucial to exoplanet detection. To meet the requirement of detection of small rocky type exoplanet which is similar to earth, the astronomic high resolution spectrographs need advanced wavelength calibration technology to remove the errors of instrument to reach the precision of 1 m/s or better. The white light-illuminated Fabery-Perot Etalon (FPE) is a new type of wavelength calibrator, which can supply the precision of wavelength reference at 0.1 m/s/day theoretically. Recent years, wavelength calibration for astronomic high resolution spectrograph using Fabery-Perot etalon attracts great attentions due to its high precision, flexible parameters customization for different spectrographs, ease of use and low cost. We developed one calibrator based on an air-spaced Fabery-Perot etalon inside a temperature well controlled vacuum vessel. The free spectral range, fineness and working wavelength of etalon is 30 GHz, 37 and 500~700 nm, respectively. The fineness of the calibrator reduces to about 11 due to the effects of the near-field distribution of its feeding fiber. The material of spacer is ULE 7973. A 500 nm long pass filter and a 700 nm short pass filter were used to filter out the light from a halogen tungsten lamp, the emission of which is similar to that of 2 800 K blackbody. The temperature variation coefficient close to etalon inside the Vacuum vessel is about 12 mK/℃.To test the performance of this calibrator, we feed it into the calibration system of the fiber-fed High Resolution Spectrograph (HRS) at Xinglong 2.16 meters telescope. This spectrograph is the main stellar radial velocity facility of China. The resolution is about 50 000 with the working wavelength range from 360~900 nm. The temperature and air pressure of the environment of the spectrograph are well controlled. After the upgradation in the year of 2021, the spectrograph now has 2 feed fibers, one for observation, another for simultaneous reference. Accordingly, the calibration system of spectrograph has 2 units, unit A and unit B, each of them has inputs of Flat lamp, ThAr lamp, LFC and a spare port. With the equipment of two-channel simultaneous calibration system, the drifts of HRS itself during the testing can be eliminated by feeding the reference channel with a calibrator source such as ThAr lamp, Laser Frequency Comb (LFC) or FPE calibrator. After the FPE calibrator was settled in the room of HRS, the vacuum-thermostatic control system was turned on. After 30 hours of stabilization, the calibrator was fed to HRS and a series of performance tests were conducted. With the single-channel exposures of the FPE calibrator, its parameters and spectral line profiles can be analyzed. With the series of the two-channel exposures of LFC-FPE, the stability of the FPE calibrator can be analyzed. Utilize the spectral lines produced by the FPE calibrator to recalibrate the HRS, and verify the performance of the FPE wavelength solution by the LFC equipped at HRS. For the sake of extraction of HRS data, exposures of bias, flat field, ThAr, and LFC were captured according to the HRS operation manual. The experimental data from HRS in this paper were processed by an independently developed data reduce pipeline based on the Python language.From the 1D spectra of the FPE calibrator by HRS, it can be seen that the spectral lines are dense and evenly distributed, with no obvious overlaps between the lines, and the local flux of the spectral lines is very uniform. Analysis with the wavelength solution of HRS reveals that the wavelength coverage of this calibrator is from 500~685 nm, and the flux at 500 nm is relatively weak, while the flux at 685 nm is much stronger, with a difference of approximately 10 times. Furthermore, the measured frequency spacing between lines is about 29.87 GHz. All above parameters meet the expectation of design. By comparing the profiles of measured FPE spectral lines with the simulated FPE lines, which is obtained by convolving the FPE theoretical transmission spectral lines with the thorium lines by HRS as its profiles, it can be seen that the profiles and Full Widths at Half Maximum (FWHM) of the measured spectral lines and the simulated spectral lines are well consistent, which reveals that the lines of the FPE calibrator can not be resolved by the spectrograph. The results of simultaneous calibration test of LFC-FPE shows that the FPE spectral lines still exhibited significant drifts at the beginning of the test, and became stable after more than 40 hours. Comparing with LFC-LFC tests which performed at intervals, it can be found that the stability of stabilized FPE lines is better than 0.61 m/s over 5 hours. Within its operating wavelength range, the FPE calibrator has 5 425 evenly spaced transmission peaks, which is much more than the 949 thorium lines provided by the ThAr lamp in the same wavelength range. After comparison the performances of the wavelength solutions of ThAr lamp and FPE calibrator by the LFC, it can be found that the standard deviation of the residuals of FPE solution is nearly half that of Thar solution, which reveals a higher calibration accuracy of the FPE calibrator.Utilizing the astronomical high-dispersion spectrograph HRS and the simultaneous calibration technology with LFC, the characteristics of the new wavelength calibrator developed based on FPE were studied. The wavelength range, flux distribution, line spacing, line width, and short-term stability of the spectral lines all met the design expectations. Wavelength calibration experiments on the HRS indicate that the FPE calibrator can provide higher calibration accuracy compared to the traditional ThAr lamp. The dense lines, wide spectral coverage, and good line stability indicate that white light illuminated FPE is an excellent wavelength calibration light source that can improve the accuracy of wavelength calibration and radial velocity measurement for astronomical high-dispersion spectrographs. Due to its flexible parameter customization, it is very suitable for various astronomical spectrographs with different resolutions and working ranges. Further testing and research are needed for the characteristics of long-term drifts and the performance of calibration, which are highly dependent on the stability of the working environment. Replacing a high-power white light source to improve the uniformity of the total spectral flux of the calibrator, the performance of the calibrator can be further enhanced..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053408 (2024)
Improved Dark Channel Defogging Algorithm for Underground Coal Mines Based on Adaptive Atmospheric Value Correction（Invited）
Lei SONG, Fan FENG, Xin LI, Qiang PENG... and Lipei SONG|Show fewer author(s)
In industrial production, video surveillance is a key measure to maintain the industrial production and the safety of the employees. However, in some special fields, monitoring images are often affected by dust scattering and water mist scattering that leads to fogging and blurring, and results in degraded image qualitIn industrial production, video surveillance is a key measure to maintain the industrial production and the safety of the employees. However, in some special fields, monitoring images are often affected by dust scattering and water mist scattering that leads to fogging and blurring, and results in degraded image quality, which influence the visibility of the visual observation. In addition, due to the specialty of lighting and the scenery in these working environments, commonly used dark channel dehazing algorithms have disadvantages, such as color shift, darkness, halo, etc. The traditional method is based on the atmospheric scattering model. It allocates the same value of the atmospheric light to all the pixel, which is suitable for the case of solar illumination, because the spectrum of sunlight is relatively close to the three channels of red green and blue. However, in special environments such as the presence of artificial light illumination, where the field of view and depth of field are limited, it is irrational to consider the atmospheric light of the image as the same value. Therefore, in the traditional algorithm, the dehazing image often results in color distortion, darkness, halo, etc. In order to solve these problems and better restore the image in the special environment, this paper focuses on monitoring images of underground coal mining scenery and proposes an improved fast dark channel algorithm to address these defects. This algorithm takes into account of the color pattern of the image and combines the dehazing algorithm with it to suppress the generation of color distortion. According to the theory of image color composition, the ratio of the Red, Green and Blue channels determines the hue of the pixel, and the changes of hue causes color distortion. So, to maintain the hue unchanged, it is necessary to control the ratio of the intensity values of the three channels. In this paper, the change of the pixel-based ratios between the three color channels before and after the processing of defogging with traditional dark channel prior method is analyzed to describe the generation of color distortion. Then based on this, the compensation method is proposed in which the atmospheric light value of each pixel is calculated and corrected according to the ratio of color channels in the input foggy image. Since the intensity distribution of the fog in the image is in the low frequency, the high-frequency and low-frequency parts of the image are firstly separated and the dehazing processing is only applied to the low-frequency part in order to preserve the image details. Besides this algorithm takes more measures to avoid the details of the image being destroyed, that is, the image of transmission and initial dark channel are processed by guided filtering, so that more details can be preserved. Furthermore, this algorithm proposes customized brightness and saturation enhancement functions for underground images that compensate low brightness and low saturation of the defogged images from traditional dark channel dehazing algorithm. In addition to mining images, this paper also applies the algorithm to common dehazing image datasets and compares it with some other algorithms. The comparison metric used in this article is structural similarity, which is a common measure for the similarity of two images. In addition, we also propose a new evaluation parameter, the color similarity, which is to detect the similarity between the dehazing image and the origin image in terms of color to give the evaluation of different methods on minimizing color distortion. The results show that the algorithm proposed in this paper can effectively remove fog, correct the color distortion and halo phenomenon, and improve the brightness and color saturation effectively. The algorithm provides a new means for defogging in industries such as mining and life scenarios. This algorithm provides a new idea for image processing in non-natural lighting and low brightness environments, and provides a guarantee for the smooth progress of underground production..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053409 (2024)
Monitoring of Multi-component Gas Concentration in Coal Mine Based on TDLAS Technology（Invited）
Xiaoliang SHEN, Lanxi HU, Yanxu GAO, and Lie LIN
Coal is the most important energy mineral in China, and methane gas is the main harmful gas in the mine production process, which may causes miners to be poisoned and even causes major safety accidents such as fire and gas explosion, which seriously threatens the life safety of coal miners and affects the mining progreCoal is the most important energy mineral in China, and methane gas is the main harmful gas in the mine production process, which may causes miners to be poisoned and even causes major safety accidents such as fire and gas explosion, which seriously threatens the life safety of coal miners and affects the mining progress. In order to prevent the occurrence of safety accidents caused by hazardous gases, the real-time monitoring of harmful gases in the mine is an important measurement to ensure the safety of mine production. Only by monitoring and detecting the concentrations of these harmful gases in a timely and accurate manner can problems be found early and corresponding measures taken.At present, as a new type of high-sensitivity, high-resolution, anti-electromagnetic interference sensor, tunable diode laser is widely used in various fields, and is an effective means to detect gases. In this paper, the Tunable Diode Laser Absorption Spectroscopy (TDLAS) is used. Based on the Lambert-Beale law, the relationship between gas concentration and signal intensity is analyzed. Based on TDLAS, a multi-component gas long-distance sensing system was designed to carry out remote real-time monitoring of harmful gases in the mine, so as to realize the real-time concentration monitoring of multiple gases in the mine environment from kilometers away.In this paper, four gases that may occur in the mine were calibrated, namely carbon monoxide gas (CO), carbon dioxide gas (CO2), methane gas (CH4) and ethylene gas (C2H4). The calibration curves of the four gases and lower detection limits were obtained. The coefficients of determination R2 were all greater than 0.99, indicating that the linear fittings were accurate. The lower detection limit for each gas can be less than 0.01%. Especially for methane gas , the main component of harmful gas, the calibrated linear correlation coefficient R reaches 0.995 54, and the detection limit is as lower as 2.2×10-6. The stability of the measurement is 0.137%. For the remaining three selected gases, the carbon monoxide gas reached the lower detection limit of 27.1 ×10-6, and the stability of the measurement was 0.402%; the carbon dioxide gas reached the lower detection limit of 23.2×10-6, and the stabilityof the measurement was 0.365%. The ethylene gas reached the lower detection limit of 80.7×10-6, and the stabilityof the measurement was 0.291%.After the calibration in lab, the gas detection equipment was applied in coal mine. The long-term monitoring results are consistent with the the gas detection system owned by the mine. By random sampling of the gases, detection results are compared with the third-party test results and the difference between the two is within 5%. The multi-component gas monitoring system has the advantages of high accuracy, low monitoring limit and good stability, which can provide reliable data support for mine gas safety and has a promising application in the mining industry..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053410 (2024)
Mechanism and Application of Ionizing Radiation in Modulating the Physical Properties of Two-dimensional Materials（Invited）
Tengteng GAO, Wenqi QIAN, Haiyi LIU, Xueying WANG... and Pengfei QI|Show fewer author(s)
In the post-Moore era, as traditional semiconductor technology approaches its physical limits, Two-dimensional (2D) materials have become a hot topic of research due to their unique physical properties. These materials, such as graphene, transition metal dichalcogenides, and black phosphorus, have garnered widespread aIn the post-Moore era, as traditional semiconductor technology approaches its physical limits, Two-dimensional (2D) materials have become a hot topic of research due to their unique physical properties. These materials, such as graphene, transition metal dichalcogenides, and black phosphorus, have garnered widespread attention in fields like materials science, condensed matter physics, and chemistry due to their strong exciton dipole moment, narrow linewidth, low disorder, and high binding energy. These characteristics give 2D materials potential applications in electronic devices, optoelectronics, and energy storage. Despite their excellent performance, their stability and reliability in practical applications, especially under extreme conditions, and particularly the impact of ionizing radiation on their performance, remain an issue that has not been fully resolved. Ionizing radiation, such as X-rays, gamma rays, and particle beams, can cause damage to materials, affecting their electronic structure and physical properties. Recent research has found that during the interaction between ionizing radiation and 2D materials, 2D materials undergo a series of significant changes. These changes include the formation of defects, doping at the atomic level, adjustment of interlayer spacing, and morphological transformations. These changes not only provide new possibilities for controlling the performance of 2D materials but also reveal how radiation-induced defects and doping can alter the material's electrical, optical, and mechanical properties. The occurrence of these phenomena is mainly due to the complex interactions between incident ions and the target materials. This interaction is influenced by various factors, including the type of irradiation, ion species, irradiation parameters, types of 2D materials, and substrates. This article delves into and summarizes the impact of these factors on the microstructure and performance of 2D materials. The results show that the type and energy of radiation play a crucial role in determining the performance of 2D material devices. Appropriate radiation parameters can enhance material performance, for example, by introducing beneficial doping or adjusting interlayer spacing to optimize electron mobility. However, excessive radiation may lead to a decline in performance, such as excessive defect formation that could destroy the material's electronic structure. By precisely controlling radiation parameters, effective modulation of 2D material performance can be achieved. This modulation provides a new dimension for material design, allowing researchers to optimize material performance according to specific application needs. As researchers delve into the mechanisms of radiation defect generation and regulation in 2D semiconductor materials and new types of porous materials, our understanding of the mechanisms of ionizing radiation interacting with low-dimensional materials deepens, giving rise to a series of new concepts such as radiation defect/strain engineering, bringing new research directions to the field of materials science. Compared with traditional chemical methods, ionizing radiation technology has a series of advantages, such as universality, uniformity, flexibility, non-contact, no introduction of other chemical contamination, and compatibility with integrated circuit manufacturing. These advantages make ionizing radiation technology highly promising in material modification. Modified 2D materials have significant application prospects in fields such as optics, electrocatalysis, and battery electrodes. For instance, in photolithography technology, precise control of radiation parameters can achieve fine patterning of photoresists, thus enabling the fabrication of smaller electronic devices. In the field of sensors, radiation treatment can enhance the sensitivity and selectivity of materials, allowing them to detect lower concentrations of chemical substances. Finally, the article looks forward to its application prospects and challenges in the fields of space exploration, energy, and defense..
Acta Photonica Sinica
- Publication Date: Oct. 25, 2024
- Vol. 53, Issue 10, 1053403 (2024)
© Copyright 2018-2021 | Chinese Laser Press. All Rights Reserved 沪ICP备15018463号-20