Dynamic Propagation Characteristics of 1.55-μm Wavelength Laser in Rain and Fog Coexisting Weather
Yu Renjiao, Li Zhenhua, Lai Jiancheng, Wang Chunyong, and Wu Zhixiang
Objective The coexistence of rain and fog is a common atmospheric phenomenon in winter. When laser is transmitted in rain and fog weather, the attenuation is not only affected by rain but also by fog. Because of the small rainfall rate, fog attenuation is usually greater than rain. Globally, numerous studies have been conducted on the transmission characteristics of laser in rain and fog individually, but research on laser transmission characteristics in rain and fog coexisting weather is inadequate. To the best of our knowledge, the interaction between raindrops and fog droplets has not been considered. In this study, based on the mechanism of rain clearing fog, we improve the existing models and propose a prediction model of atmospheric attenuation in rain and fog coexisting weather, which dynamically shows the changes of atmospheric attenuation and transmittance with time in rain and fog coexisting weather. We believe that the findings of this study will have reference significance for the estimation and evaluation of atmospheric attenuation in wireless optical communication and related fields.Methods In rain and fog coexisting weather, the precipitation process has a significant effect on fog removal. As fog is removed by raindrops, the scale distribution of fog will change. In this article, we employ the general dynamic equation considering wet deposition to study the dynamic change of fog with the removal of raindrops. Then, we use the lognormal scale distribution model of raindrops and Gamma distribution model of radiation fog and advection fog to calculate the total attenuation of rain and fog after clearing. Further, we employ Lambert-Beer law to reckon the transmittance of laser after a certain distance. Finally, the numerical results are compared with the Monte-Carlo simulation results to verify the rationality of the proposed model to a certain extent.Results and Discussions The rainfall intensity positively correlates with the fog removal effect. Since the rainfall in rain and fog coexisting weather is small, the attenuation of fog gradually decreases with the removal of fog by rain (Fig. 1). When the rainfall rate is 1 mm/h, the transmittance of advection fog tends to be stable after 5 h of rainfall, whereas, the radiation of fog takes a longer time (Fig. 2). The water content of advection fog is higher than that of radiation fog, so the albedo of advection fog is higher than that of radiation fog. Owing to the obvious removal of advection fog by rain, the density of advection fog decreases, the proportion of raindrops per unit volume increases, the absorption increases, the scattering weakens, and the albedo of particle swarm increases (Tables 4 and 5). When the transmission distance is 1000 m and transmittance is less than 5%, the transmittance calculated using the Monte-Carlo method is larger than that calculated using the Lambert-Beer law, and vice versa in other cases.Conclusions In this article, we employed the lognormal scale distribution model of raindrops and Gamma distribution model of radiation fog and advection fog to study dynamic change of fog with raindrop removal using the general dynamic equation considering wet deposition. Based on the basic principle of atmospheric attenuation, the attenuation of laser propagation in the atmosphere changes with the fog scale distribution model. Because most of the radiation fog droplets are medium-sized aerosols, they are difficult to be wet removed by rainfall, so the transmittance increases slowly with time. The droplet size of the advection fog is large and quickly removed in the case of moderate and heavy rain, and then the transmittance is at a fixed value. Through Monte-Carlo simulation analysis of laser transmission in the atmosphere, in the case of small attenuation, the photon moving step is larger, the scattering times in a fixed distance range are less, the particles hardly reach the receiving plane after the collision, and the calculation results of the Monte-Carlo method are minute. With the increase in particle number density and transmission distance, the number of scattering increases, and the transmittance calculated using the Monte-Carlo method is slightly higher than that calculated using the Lambert-Beer law. Over time, owing to the removal of fog by rainfall, the droplet number density decreases, and the numerical difference between the two methods increases.
  • Jun. 15, 2021
  • Chinese Journal of Lasers
  • Vol.48 Issue, 13 1306002 (2021)
  • DOI:10.3788/CJL202148.1306002
Technology for Integrating Space Object Multidimensional Detection and Laser Communication
Xu Miao, Shi Haodong, Wang Chao, Liu Zhuang, Fu Qiang, Li Yingchao, Dong Keyan, and Jiang Huilin
Significance Humans need to observe various targets, including space, air, ground, and sea targets. Space targets include satellites, space debris, ballistic missiles, and hypersonic vehicles. Air targets include aircraft, airships, and small craft. Ground and sea targets include surface ships and ground vehicles. The past 20 years have seen an average of 12 collisions between space debris and space payloads every year. In addition, foreign ships and aircraft frequently invade our territorial waters and airspace and repeatedly spy on the activities in our important places. Therefore, the detection, identification, early warning, interception, and even striking of these abovementioned targets are an important and urgent research topic presently.Multidimensional detection based on combined polarization detection, spectrum detection, and other optical technologies can provide the shape, material, location, and other information of the target simultaneously, effectively improving the dimensions and accuracy of space target information. At the same time, with the help of space laser communication, massive information can be quickly and safely transmitted to orbiting satellites and management departments, which can provide the decision-making basis for further disposal in time.Progress In terms of space target detection, the United States has the largest and highest level of space target detection systems, followed by Russia. Europe starts late, but their system has rapidly developed in recent years. China is the latest to start and mainly performs ground-based observations. However, in recent years, China has conducted space-based observation tests and devised various detection methods, including photoelectric observation, radar monitoring, radio detection, and other detection methods.In multidimensional detection, polarization detection technology has the advantages of highlighting the target, penetrating smoke, and identifying the truth and falsehood of the target. Spectral detection technology can distinguish the physical characteristics of the target material. Intensity detection technology has high light energy utilization and resolution, but it also has its own weaknesses. The information obtained by intensity detection is less and easily disturbed by the environment. Moreover, loss of the receiving energy and decrease in imaging resolution can be introduced by polarization detection. Table 1 gives a comparison of the advantages and disadvantages of several detection technologies. Therefore, combining the three abovementioned detection methods to give full play to their own characteristics and advantages helps not only in overcoming the difficulties of space target detection but also in greatly improving the overall detection performance. Changchun University of Science and Technology conducted a multidimensional oil species differentiation test; the test results are shown in Figure 3.The X2000 flight terminal was developed in the United States from the aspect of integrating detection, imaging, and communication. It can realize the functions of bidirectional communication, bidirectional laser ranging, and high-resolution imaging. The United States also proposed the ACLAIM scheme, in which the laser communication antenna and space camera sharing a front telescope and a detector array is employed as the acquisition and tracking system and an imaging receiver. In China, satellite payloads were developed toward the direction of multifunctionality and integration to increase the system function and reduce the volume, mass, and power consumption of the load. This study proposes a new scheme for space target detection and information transmission, which integrates the four functions of laser ranging, spectral polarization imaging, super-resolution imaging, and laser communication into one. The system design and development were performed. Figure 17 depicts the system composition.Conclusions and Prospect In summary, we introduce herein the research status of the technology of multidimensional detection and laser communication integration for space objects and summarize the principle, characteristics, and application of the related technologies. The preliminary research results of our team in the related aspects are as follows: 1) for space object multidimensional detection, the detection mechanism is studied, and a large aperture and a wide field-of-view space-based telescope super-resolution imaging optical system is designed; 2) a prototype of simultaneous and time-sharing polarization imaging detection for complex space targets is developed; 3) ground and sea surface tests are conducted. As regards space laser communication, the optical principle of one-point to multipoint simultaneous space laser communication is proposed for the first time by our team at home and abroad. Accordingly, a principal prototype is developed and a demonstration test is performed. For detection and communication integration, the urgent need for this space security technology is expounded, and the system design idea and a specific implementation scheme are given.Our country should further perform an in-depth research on ultra-high-resolution imaging, full-polarization and hyperspectral multidimensional detection, space- and ground-based combined optical detection, multi-to-multi space laser communication, and integrated laser and microwave network communication to solve the problems of the incomplete detection of low-orbit targets, unclear detection of high-orbit targets, slow response of the dynamic target, and difficulties in numbering space objects, which can provide a technical guarantee for the space security in China.
  • Jun. 11, 2021
  • Chinese Journal of Lasers
  • Vol.48 Issue, 12 1206002 (2021)
  • DOI:10.3788/CJL202148.1206002
Research on Routing Algorithm in Underwater Wireless Optical Communication Sensor Networks
Qin Haoran, Xie Zhibin, and Weng Zhihui
Due to the variability of the underwater environment, individual nodes in the underwater wireless optical communication sensor network cannot meet the requirements of line-of-sight transmission. In order to restore effective communication between nodes, this paper proposes a relay routing algorithm based on relay cooperative transmission method, and the bit error rate of the mixture exponential-generalized Gamma model is used as the relay selection metric. In order to ensure that the selected relay node can solve the link failure problem in the sensor network under the condition of low energy. In terms of relay selection, consider the power threshold when the node communicates successfully. The simulation results show that the relay cooperative routing algorithm for reconstructing the transmission link can guarantee low bit error rate and maximize the network lifecycle simultaneously.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1106009 (2021)
  • DOI:10.3788/LOP202158.1106009
Application of Optical Fiber Sensing Technology in State Monitoring of Superconducting Magnet
Yang Song, Liu Yanchao, Lei Xiandao, Fang Xinyu, Li Wenlong, and Fang Jin
The monitoring requirements of temperature, strain, and other physical parameters during the assembling, cooling, and operation of low-temperature and high-temperature superconducting magnets are introduced. The working principles of fiber-optic sensing technologies based on the fiber Bragg grating, Brillouin scattering, Raman scattering, and Rayleigh scattering are also introduced. The research progress of the above optical fiber sensing technologies in temperature and strain measurement of low-temperature and high-temperature superconducting magnets is reviewed. The existing problems in the above researches are summarized, and the future research is prospected. This review is helpful for researchers in the field of superconducting magnet, especially in the field of superconducting magnet stability, to understand the application progress of optical fiber sensing technology in superconducting magnet stability improvement intuitively, clearly, and comprehensively.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1106008 (2021)
  • DOI:10.3788/LOP202158.1106008
Performance of SIMO NLOS UV Communication System in a Foggy Environment
Ma Yuzhao, Cheng Feifan, Jia Huiting, and Xiong Xinglong
To study the communication performance of non-line-of-sight (NLOS) ultraviolet (UV) communication in foggy environments, we propose a new attenuation model and a simplified calculation method of asymmetric factors. These solve the problems that the common fog attenuation model is not suitable for ultraviolet atmospheric channel attenuation and the calculation of multiple scattering transmission model is complex. A single-input-multiple-output (SIMO) ultraviolet communication system is established using the diversity receiving technology. First, a UV attenuation model is developed based on the Mie scattering theory to calculate the UV attenuation parameters of two fog types at different concentrations. Second, the asymmetric factor of a droplet size is established to simplify the calculation. Finally, the equal-gain combining technique is used to combine the diversity received signals. The performance of the SIMO UV communication system is analyzed by the Monte Carlo method and compared with that of the SISO UV communication system. The results show that diversity reception can effectively improve the performance of ultraviolet communication on foggy days: on thick, medium and thin fog days, and the maximum communication distance of the SIMO communication system is about 5, 10, and 10 m longer than that of a SISO communication system, respectively. When the bit error rate of the SISO ultraviolet communication system is 10-3, the bit error rate of the SIMO communication system is reduced to about 10-5.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1106007 (2021)
  • DOI:10.3788/LOP202158.1106007
Fiber Bragg Grating Soil Pressure Sensor Based on Additive Manufacturing Technology
Liu Wenli, Hong Chengyu, Bao Chengzhi, Duan Jingchuan, and Lou Zaiming
In this study, a soil pressure sensor based on additive manufacturing (AM) technology and fiber Bragg grating (FBG) is designed. The calibration experiment results indicate that the sensitivity, minimum resolution, and measurement range of FBG soil pressure sensor are 0.2 pm/kPa, 5 kPa, and 1000 kPa, respectively, and that the sensitivity of the sensor can be adjusted as per requirement using AM parameters (filling density, filling material) to reduce measurement errors. The experimental results of the indoor model box show that, the sensor can effectively measure the internal pressure of soil during test loading and that measurement range is wide. The resolution and range can be customized according to real-world conditions, which provide a new approach for internal pressure monitoring of the soil.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1106006 (2021)
  • DOI:10.3788/LOP202158.1106006
Sensitization Method of Fabry-Perot Temperature Sensor Based on Vernier Principle
Cai Lizou, Qin Yali, Cai Xiaolei, Zheng Huan, Ren Hongliang, and Hu Yingtian
Based on the working principle of the parallel Vernier effect, a sensitization method to achieve the Vernier effect by superimposing the spectrum is proposed. The Fabry-Perot (F-P) temperature sensing interferometer is used to obtain the measured reflection spectrum. The reflection spectrum of the reference interferometer obtained using the F-P interference principle is superimposed during data processing to achieve the Vernier effect. In the range between 30 ℃ and 55 ℃, the temperature sensitivity of 5.0380 nm/℃ was achieved. Controllable temperature sensitivity can be achieved by changing the cavity length of the reference interferometer. Besides, the dip point of the Vernier envelope for measurement can be placed at any desired wavelength by changing the initial phase of the reference interferometer's incident light. A sensing interferometer with cavity length of 118.60 μm and a reference interferometer with cavity length of 96.60 μm were designed and prepared to conduct a temperature sensitization experiment based on the parallel Vernier effect. The measurement sensitivity of 2.7984 nm/℃ was obtained, which is consistent with the temperature sensitivity achieved by superimposing the F-P reflection spectrum with the same cavity length. The relative error is only 0.57%. Thus, the proposed method is feasible and effective. Besides, it solves the problem that the reference interferometer is vulnerable to the external environment.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1106004 (2021)
  • DOI:10.3788/LOP202158.1106004
On-Chip Integrated Multi-Dimensional Optical Interconnects and Optical Processing
Wang Jian, Cao Xiaoping, and Zhang Xinliang
Significance In the past half century, integrated circuits (ICs) supported by complementary metal-oxide semiconductor (CMOS) technology have developed rapidly, which promotes the continuous progress of modern information technology. As the feature size of transistors continues to decrease, the semiconductor-manufacturing process is gradually approaching its limit, resulting in slow or even stagnant improvement of integration. Meanwhile, the system performance is seriously restricted, mainly due to the electronic bottleneck. In addition, with the increase in the number of microprocessors and computing speed, power consumption and heat dissipation due to parasitic effects are becoming the main limiting factors. To break through the bottleneck of conventional IC technology in the post-Moore era, optical interconnects are considered to gradually replace conventional electrical interconnects. Compared with electrical signals, using light as the carrier for signal transmission has its unique advantages, such as large bandwidth, low loss, strong anti-electromagnetic interference capability, and high-speed parallel transmission without crosstalk. Therefore, optical interconnects will undoubtedly become the enabling technology for high-speed data transfer. Concurrently, at the network nodes, conventional optical-electrical-optical signal processing is still limited by the electronic bottleneck. Processing signals in the optical domain offer an effective strategy to increase speed. Consequently, on-chip optical interconnects and processing are paramount to the development of modern high-speed and large-capacity communication networks.The photonic integrated circuit (PIC) is paramount to realize on-chip optical interconnects and processing, which achieves rapid development in recent years. Silicon and III-V are both promising materials for the PIC platform. The main advantage of InP and other III-V materials is that they are direct bandgap materials, which can be used to fabricate semiconductor lasers, amplifiers, modulators, detectors, and other active devices. However, the cost is relatively high and size is relatively large, which limit their large-scale commercialization. By contrast, silicon materials have distinct advantages of large reserves in nature, low cost, almost transparent in the near-infrared and even mid-infrared bands, low loss, and large refractive index contrast of silicon on insulator (SOI), making them suitable for large-scale and high-density integration. Importantly, silicon materials are fully compatible with the existing mature CMOS process, which is essential for developing silicon-based PICs. Since silicon material is an indirect bandgap material, it is impossible to produce high-efficiency light sources. Monolithic integration of all active and passive devices on a single material platform is still challenging. The hybrid integration technology provides a possible solution, which enables the integration of discrete active devices, such as lasers and amplifiers, onto silicon-based passive devices through co-packaging, epitaxial bonding, and monolithic growth to realize low-cost and high-performance hybrid PICs.Although on-chip optical interconnects and processing are the development trends of high-speed communication networks, the sustainable increase of communication capacity is still crucial in the big data era with increasing capacity demand. Notably, photons have multiple physical dimensions, such as frequency/wavelength, polarization, time, complex amplitude, and spatial structure, which can be developed into multiple multiplexing and advanced modulation technologies, making it possible to realize ultra-high-capacity optical communications and interconnects. Wavelength-division multiplexing (WDM), time-division multiplexing (OTDM), polarization-division multiplexing (PDM), space-division multiplexing, and advanced modulation formats have rapidly developed in the past few decades, significantly increasing the transmission capacity of optical communication systems. Therefore, on-chip optical interconnects and processing should also exploit multiple physical dimensions of photons. Particularly, multiple multiplexing technologies and advanced modulation formats can be combined to effectively increase the number of signal channels and aggregate capacity of on-chip optical interconnects and processing systems.Progress Here, we give a comprehensive review of on-chip integrated multidimensional optical interconnects and processing (Fig. 1). The main characteristics of on-chip integrated multidimensional optical interconnects and processing are high integration, small footprint, high reliability, high speed, and low loss. The main contents of optical interconnects include on-chip data transmission of multidimensional optical signals (Fig. 2), on-chip multidimensional multiplexing interconnects of optical signals (Fig. 3), key integrated devices for optical interconnects (Fig. 4), heterogeneous waveguide coupling for optical interconnects (Figs. 5--7), and PICs/optical modules for optical interconnects (Fig. 8). The main contents of optical processing include on-chip wavelength conversion (Fig. 9), on-chip optical frequency comb (Fig. 10), on-chip mode processing (Fig. 11), on-chip polarization processing (Fig. 12), on-chip optical logic and computing (Figs. 13--16), on-chip reconfigurable optical processing (Fig. 17), and on-chip intelligent optical processing (Fig. 18).Conclusions and Prospects With the rapid development of cloud computing and data centers, on-chip integrated optical interconnects and processing have become the key technologies to break through the conventional electronic bottleneck with their unique advantages in integration, speed, bandwidth, power consumption, and multiple physical dimensions. In this article, we review the key technologies and recent progress of on-chip integrated multidimensional optical interconnects and processing. Looking to the future, one would expect the development trend toward multiple materials (III-V, silicon, silicon nitride, silica, polymer, lithium niobate, and 2D material), integrations (hybrid integration, monolithic integration, and integration of photonics and electronics), physical dimensions (frequency/wavelength, polarization, time, complex amplitude, and spatial structure), frequency bands (O+E+S+C+L+U, visible, mid-infrared, microwave, and terahertz), mediums (chip, fiber, free space, and underwater), functions (multifunction, reconfigurable, programmable, and intelligent), and applications (communications, sensing, measurement, imaging, computing, and quantum) (Fig. 19). One typical example would be ultrahigh capacity silicon-based on-chip multidimensional multiplexing and processing system, which consists of an integrated transmitter, integrated receiver, silicon-based multidimensional multiplexing and processing chip incorporating hybrid wavelength/polarization/mode (de) multiplexer, optical switch array, reconfigurable optical add-drop multiplexer array, variable optical attenuator array, and optical power monitor array (Fig. 20).
  • Jun. 07, 2021
  • Chinese Journal of Lasers
  • Vol.48 Issue, 12 1206001 (2021)
  • DOI:10.3788/CJL202148.1206001
All-Fiber Signal Combiner with Flat-Top Beam Output
Huang Jianbin, Chu Danping, Zhang Qunsheng, Zhang Dapeng, and Wang Xinglong
The flat-top beam output is realized through special treatment of the cone area of the optical fiber signal combiner and output fiber and the torsion treatment of the output fiber. The experimental results show that the beam intensity distribution of 4 × 1 signal combiners with a 20/130 μm (the core diameter is 20 μm, the cladding diameter is 130 μm) fiber input and 100/120/360 μm (the core diameter is 100 μm, the cladding diameter is 360 μm, the diameter of the low refractive index layer between the core and cladding is 120 μm) fiber or 200/220/360 μm fiber output is not a flat-top distribution; the strength distribution is relatively scattered. More fiber mode will be excited by twisting the output fiber. Then, a 200/220/360 μm fiber was spliced between the cone area and output fiber. The intensity distribution of 4 × 1 signal combiner is uniform and has a flat-top distribution, and presents distribution in a 4.88 mm range close to the beam waist. The calculation results show that the flatness of the beam in that range is below 0.1. It also shows that the signal combiner can handle a signal power of more than 2 kW.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1106005 (2021)
  • DOI:10.3788/LOP202158.1106005
Mode Converter of Optical Fiber Communication System Based on Space Division Multiplexing
Zhong Wenbo, Dong Zhaoda, Zhang Ling, Zhang Kefei, and Wang Yaxin
To improve limitations of bandwidth capacity of optical fiber communication system in practical engineering applications, a photonic crystal fiber core structure which is capable of transmitting fundamental and high-order modes is proposed based on space division multiplexing technology. The effective refractive index curves of the corresponding modes under different structural parameters are obtained using the finite-difference imaginary-distance beam propagation method. An asymmetric dual-core photonic crystal fiber mode converter is designed by matching the effective refractive index curves of the two modes. It demonstrates that such an LP01-to-LP02 mode converter can be achieved at the wavelength of 1550 nm. In a wider frequency range, the mode coupling efficiency is above 90%, and the coupling length is about 178.5 μm. The device diameter is 47.6 μm, and the structural design is flexible and controllable, which can meet the needs of future large-capacity communication systems.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1106003 (2021)
  • DOI:10.3788/LOP202158.1106003