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A novel compact optical fiber concentration sensing system based on machine learning was proposed and experimentally demonstrated in this paper. The Michelson interferometer (MI) was realized by multiple arc discharge performed on the end of a section of bent bare single-mode fiber (SMF). To improve the stability and accuracy of demodulation, machine learning based on long short-term memory (LSTM) was employed and it provided an accuracy of 97.5%, which is more stable and accurate than conventional peak wavelength tracking due to the fact that LSTM can avoid the effects of dip selection, wavelength sampling rate and spectral noise on the peak wavelength tracking. Furthermore, the proposed sensing system has the advantages of compact size, low cost, high robustness, and ease of fabrication.

In this article, a high-security three-dimensional (3D) probabilistic shaping optical transmission system based on prefix-free code distribution matching (PCDM) and Polar code joint coding is proposed. The bit error rate (BER) performance of the communication system is optimized by using the probabilistic shaping effect of PCDM and the strong correction performance of Polar code. Meantime the Logistic and Lorenz chaotic models are used to mask the constellation map for multiple times to ensure the security transmission of data. The experiment verifies the transmission of 28.64Gb/s encrypted PCDM encoded signals on 2km 7-core fiber. At a BER is 1×10-3, the encrypted PCDM encoded signals improve the BER performance about 3dB compared to the conventional unencrypted 3D 32QAM signals. In terms of security performance, the key space of the proposed encryption scheme is up to 10119, and the BER of the illegal receiver is more than 0.4. The experimental results show that the proposed chaotic optical transmission scheme based on the joint encoding of PCDM and Polar can effectively improve the BER and security performance, which is a promising optical communication transmission scheme.

In this paper, a high-security probabilistic constellation shaping transmission scheme based on recurrent neural networks (RNNs) is proposed, in which the constellation point probabilistic distribution is generated based on recurrent neural network training. A 4D biplane fractional-order chaotic system is introduced to ensure the security performance of the system. The performance of the proposed scheme is verified in a 2 km seven-core optical transmission system. The RNN-trained probabilistic shaping scheme achieves a transmission gain of 1.23 dB compared to the standard 16QAM signal, 0.39 dB compared to the standard Maxwell-Boltzmann (M-B) distribution signal, and a higher net bit rate. The proposed encryption scheme has higher randomness and security than the conventional integer-order chaotic system, with a key space of 10,163. This scheme will have a promising future fiber optic transmission scheme because it combines the efficient transmission and security of fiber optic transmission systems.

This paper proposes a high-security physical layer encryption scheme for sparse code multiple access filter bank multi-carrier (SCMA-FBMC) in weakly coupled four-mode fiber. Due to the multiplexing of four modes and the overload of SCMA, the number of users connected by the proposed method is increased by six times. To improve the security of the SCMA-FBMC system, the Logistic mapping parameters are employed as the public key that is distributed to all users and is utilized for frequency masking to protect against illegal receivers' attacks. The 6D Duffing_Lu model acts as a private key of optical network units (ONUs) to prevent other ONUs from eavesdropping. A 60 Gb/s (4 × 15 Gb/s) encrypted SCMA-FBMC signal transmission over 5 km weakly coupled four-mode fiber is experimentally demonstrated. The experimental results show that there is no discernible difference in the signal's bit error rate (BER) performance before and after encryption. The sensitivity between different ONUs is less than 0.5 dB. In addition, the proposed scheme's key space can reach up to 10110, which effectively guarantee the physical layer security of the system. This scheme has application prospects in future short-distance optical access due to the growing number of connections and good security performance.

In this paper, transmission of orthogonal chirp division multiplexing (OCDM) based on asymmetric pair mapping over a seven core fiber is proposed. High-order 32 quadrature amplitude modulation (QAM) is reduced to quadrature phase-shift keying (QPSK) and 8 QAM signal employing asymmetric pair mapping, which will not affect the rate of the system. Combined with geometric shaping (GS), the average transmission power is successfully lowered, realizing signal damage suppression. In order to verify the performance of the proposed asymmetric pair mapping scheme, a 140 Gb/s asymmetric pair mapping OCDM signal transmission over 2 km seven core fiber is experimentally demonstrated. The experimental results show that the proposed transmission scheme has the best performance when the power distribution ratio (PDR) is 4 dB. Meanwhile, compared with GS 32 QAM with QPSK+rectangle 8 QAM, GS 32 QAM with QPSK+star 8 QAM and GS 32 QAM, the proposed asymmetric pair mapping OCDM signal has improved by 1.55 dB, 1.45 dB, and 0.7 dB, respectively. It has a wide range of applications in the future optical transmission system due to its outstanding performance in the suppression of high-order modulation signal degradation.

An optical fiber sensor based on the parallel Vernier effect for temperature and transverse load measurement is reported in this paper. The sensor is composed of a novel compact fiber Michelson interferometer (MI) and a closed-cavity Fabry–Perot interferometer (FPI) connected in parallel. The fiber MI consists of a bent single-mode fiber (SMF) structure and a short length of hollow core silicon tube (HCST). A section of HCST is fused between two segments of SMF to form the fiber FPI. Two sensors in parallel can easily measure different physical parameters independently, thus realizing multi-parameter sensing. The fiber MI and FPI are used for temperature and transverse load measurement, respectively. Fiber optic MI and FPI are Vernier effect mutual reference interferometers. When MI is used for temperature sensing, FPI is the reference interferometer. When FPI is used for transverse load sensing, MI is the reference interferometer. It can improve the sensitivity of temperature and transverse load. Two samples were made and the sensing experiment was carried out. Through the sensing experiment, we get the maximum temperature sensitivity of 85.1 pm/°C in the temperature range of 30–80 °C and a transverse load sensitivity of −3.15 nm/N in the temperature range of 0–1.96 N. In addition, the sensor has the advantages of tiny size, low cost, and easy manufacture, which is suitable for temperature and transverse load sensing applications.

Nickel-iron alloy is broadly utilized in the industrial field due to its fabulous mechanical properties. How to prepare nickel-iron alloy with better corrosion resistance more efficiently is an important concern. Based on this, the WC particles enhanced nickel-iron coatings were fabricated by jet electrodeposition (JED) at a high current density of 100A/dm2. It was found that increasing the deposition temperature appropriately during JED is beneficial to obtain Ni-Fe-WC coating with the higher number of hard particles. Specifically, the maximum WC particles proportion reaches 4.47 wt% at 55 °C. The electrochemical corrosion behavior of coating was measured by polarization curve and electrochemical impedance spectroscopy (EIS). The polarization curve test results displayed that the Ecorr positively shifted from −0.402 to −0.281 V and the icorr reduced from 25.13 to 7.05 μA/cm2 with the increase of WC particles proportion. Meanwhile, the EIS test results exhibited that the impedance of coating enhanced from 12,720 to 59,140 Ω cm2. The neutral salt spray test (NSS) was used to simulate the corrosion of coating in a seawater environment. The NSS results showed that with the increase of WC particles, the corrosion products decreased gradually and the degree of corrosion decreased. The analysis showed that WC particles can help the grain growth and release the internal stress in the coating. Larger grain sizes reduces intergranular corrosion and smaller internal stress help to alleviate stress corrosion cracking. The above research can provide theoretical support for the efficient preparation of particle enhanced composite coating with strong corrosion resistance.

A novel optical fiber sensor based on cascade anti-resonant reflection waveguide (ARRW) and fiber ring-shaped structure (FRSS) is proposed and experimentally demonstrated for simultaneous measurement of refractive index (RI) and temperature. The sensor is very simply fabricated by splicing ARRW and FRSS based on Mach-Zehnder interference (MZI). The FRSS interference dip is sensitive to external RI and temperature changes, whereas the ARRW structure's loss dip is only sensitive to external temperature. As a result, this sensor can be used to measure both RI and temperature simultaneously. The sensor's maximum RI sensitivity is 108.61 nm/RIU and its maximum temperature sensitivity is 19 pm/ °C in the experiment. This sensor is a good choice when it is necessary to measure RI and temperature at the same time due to its compact size, high sensitivity, low cost, and good stability.

An optical fiber sensor is proposed and experimentally demonstrated for simultaneous measurement of high temperature and transverse load. The sensor is designed by splicing a silica capillary tube (SCT) to a single-mode fiber (SMF) and then heating the SCT to form an air bubble. SCT simultaneously functions as a Fabry Perot (F-P) microcavity and an anti-resonant reflection waveguide. These sensing mechanisms lead to high contrast sensitivity values of temperature and transverse load (1.89pm/°C,190.48pm/N and 24.93pm/°C, 16.68pm/N). Remarkably, the temperature sensitivity of this sensor is eleven times higher than that of the current fiber-tip micro-cavity (2.1 pm/°C). The sensor is also more advantageous in quantitative production and practical application due to its low cost, ease of fabrication, good mechanical strength, and convenient reflection probe.

We demonstrated a high-sensitivity liquid level sensor based on the balloon-shaped fiber Mach-Zehnder interferometer (MZI). To make an optical fiber MZI sensor, a bare single mode fiber (SMF) is bent into a balloon shape. The sensor is attached to a stiff support and linked to a buoyancy ball floating on the liquid surface via a thin thread. The change in liquid level will bend the fiber and lead to a wavelength shift of transmission spectrum. This is a novel method of measuring liquid levels. We comprehensively studied the sensing performance of the sensor, and applied the ridge regression algorithm to optimize the fitting results of the experimental data. The maximum sensitivity of liquid level and temperature are 5.245 nm/mm and 40.3 pm/°C respectively, and the sensor has a low temperature cross-sensitivity of 0.00768 mm/°C. Furthermore, the sensor has the advantages of real-time response, convenient manufacture, low cost and high reliability, which broadens the application area of balloon-shaped MZI and makes it appropriate for liquid level sensing.

Abstract The precise and effective generation and manipulation of micron‐sized droplets is crucial for chemical and biological research and applications. Normally, droplets generation and manipulation are achieved by two separate devices/systems with their respective operation strategies. Pipette, inkjet nozzle, and microfluidic channels equipped with programed syringes are commonly used for droplets generation whereas the subsequent manipulation is normally achieved by leveraging of forces originating either from optical, electric, magnetic or acoustic field and the corresponding complicated devices. Here we report a new paradigm that can realize simultaneous droplets generation and manipulation in an immiscible liquid environment using only the confined interface vibration generated by the ordinary inkjet nozzle. Droplets, ranging from femtoliter to picoliter, can be generated and manipulated without interruption since they are actuated by the same nozzle. Our strategy provides a platform for precise generation and manipulating the micro‐sized droplets that may be valuable for applications requiring simple setups and seamless connection between droplets generation and droplets manipulation.

Abstract Nanoparticle-reinforced metal matrix composite coatings have significant potential in mechanical part surface strengthening owing their excellent mechanical properties. This paper reports a phenomenon in which the grain orientation gradually evolves to (220) as the deposition current density increases when preparing nanoparticle-reinforced nickel-based composite coatings through jet electrodeposition (JED). During the preparation of the Ni-SiC composite coatings, the deposition current density increased from 180 A/dm2 to 220 A/dm2, and TC(220) gradually increase from 41.4% to 97.7%. With an increase of TC(220), the self-corrosion potential increases from −0.575 to −0.477 V, the corrosion current density decreases from 9.52 μA/cm2 to 2.76 μA/cm2, the diameter of the corrosion pits that after 10 days of immersion in a 3.5 wt% NaCl solution decreases from 278–944 nm to 153–260 nm, and the adhesion of the coating increases from 24.9 N to 61.6 N. Compared a conventional electrodeposition (CED), the Ni-SiC composite coating using JED has the advantages of a smooth surface morphology, high corrosion resistance, and strong adhesion, which are more obvious with an increase in TC(220).

We propose and demonstrate a new analog–digital combined high-secure optical communication system based on chaotic circuit driving, which achieves encryption in the analog and digital domains. A 3D chaotic system is used for analog domain phase encryption (ADPE) and digital domain time–frequency encryption (DDTFE) simultaneously. The ADPE is carried out by the privately chaotic signal driving the phase modulator (PM), which realizes chaotic phase encryption. The chaotic circuit comprehends highly complex nonlinear dynamics. Its size is 10 cm × 5 cm, which has the characteristics of small size and low cost. The DDTFE is performed by the frequency–time encryption of signals in the digital domain. The experimental results show that the optical physical layer encryption scheme based on analog and digital combination can successfully mask the original data. The driving signal of PM is that generated by the chaotic circuit and needs to be privately synchronized, so that the legal receiver may accurately decrypt the encrypted data and the eavesdropper is unable to intercept a valuable message. If the chaotic driving circuit produces a delay of 3 s, the bit error rate (BER) reaches more than 0.3 at the receiver. The results of experiment verify that the scheme can transmit 13.3 Gb/s 16 quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) signal over 25 km standard single mode fiber (SSMF). This scheme achieves low-cost, high-security communication, making it a suitable foundation for high-speed, secure optical communication at the physical layer.

In this paper, for the first time, a novel multi-level constellation compression modulation (MCCM) is proposed and applied for generalized frequency division multiplexing passive optical network (GFDM-PON). The principle of the proposed MCCM is to transfer the constellation points of the outer circle to the ones of the inner circle with different probabilities, thereby significantly reducing the average transmitted power. Also, by dynamically adjusting the compression factor, MCCM can also achieve different types of constellations to accommodate various scenarios of optical fiber transmission. In order to verify the feasibility of the proposed coded modulation technology and its transmission performance, a GFDM-PON system is set up based on intensity-modulation and direct-detection. The experimental results indicate not only that one-level constellation compression modulation (CCM) is superior to the conventional modulation technology, but also two-level CCM can significantly reduce the bit error ratio (BER) of the system. When the transmission performance is unfavorable, the system BER can be further reduced by the enhanced CCM. Therefore, the system based on the proposed MCCM technology can meet different access scenarios with robust adaptability and scalability.

The parallel structured fiber-optic Fabry-Perot interferometer (FPI) is theoretically proposed and experimentally demonstrated for transverse load measurement based on Vernier-effect. This kind of sensor consists of a hollow microsphere cavity fiber-optic FPI for sensing function and an air cavity for reference, both of which are parallel connected by a 3 dB optical fiber coupler with the functionality of Vernier-effect. Experimental results indicate that the proposed sensor can provide a high transverse load sensitivity of -3.75 nm/N, which is 3.4 times higher than single hollow microsphere cavity FPI. Moreover, with the excellent features of low cost, easy fabrication, and stable sensing, the parallel structured FPIs proposed will provide a new vision for high sensitivity transverse load sensing.

The multi-model ensemble approach is generally considered as the best way to explore the advantage and to avoid the weakness of each individual model, and ultimately to achieve the best climate projection. But the design of an optimal strategy and its practical implementation still constitutes a challenge. Here we use the random forest (RF) algorithm (from the category of machine learning) to explore the information offered by the multi-model ensemble simulations within the Coupled Model Intercomparison Project Phase 6. Our objective is to achieve a more reliable climate projection (mean climate and extremes) over China. RF is furthermore compared to two other ensemble-processing strategies of different nature, one is the basic arithmetic mean (AM), and another is the linear regression across the ensemble members. Our results indicate that RF effectively enhances the capability in capturing spatial climate characteristics. Regions with complex topography, such as the Tibetan Plateau and its periphery, show the most significant improvements. RF projects less future warming but enhanced wet conditions across China. It also produces larger spatial variability and more small-scale features. The most obvious increase of precipitation is in the northern part and the periphery of the Tibetan Plateau. The projected changes in RF for strong precipitation are almost twice higher than in AM, while in the northwestern area, weaker increases of precipitation are projected by RF, which indicates larger spatial inhomogeneity of its projection.

The tropospheric and stratospheric temperature trends and uncertainties in the fifth Coupled Model Intercomparison Project (CMIP5) model simulations in the period of 1979–2005 have been compared with satellite observations. The satellite data include those from the Stratospheric Sounding Units (SSU), Microwave Sounding Units (MSU), and the Advanced Microwave Sounding Unit-A (AMSU). The results show that the CMIP5 model simulations reproduced the common stratospheric cooling (−0.46–−0.95 K/decade) and tropospheric warming (0.05–0.19 K/decade) features although a significant discrepancy was found among the individual models being selected. The changes of global mean temperature in CMIP5 simulations are highly consistent with the SSU measurements in the stratosphere, and the temporal correlation coefficients between observation and model simulations vary from 0.6–0.99 at the 99% confidence level. At the same time, the spread of temperature mean in CMIP5 simulations increased from stratosphere to troposphere. Multiple linear regression analysis indicates that the temperature variability in the stratosphere is dominated by radioactive gases, volcanic events and solar forcing. Generally, the high-top models show better agreement with observations than the low-top model, especially in the lower stratosphere. The CMIP5 simulations underestimated the stratospheric cooling in the tropics and overestimated the cooling over the Antarctic compared to the satellite observations. The largest spread of temperature trends in CMIP5 simulations is seen in both the Arctic and Antarctic areas, especially in the stratospheric Antarctic.

In 1967, scientists used a simple climate model to predict that human-caused increases in atmospheric CO2 should warm Earth’s troposphere and cool the stratosphere. This important signature of anthropogenic climate change has been documented in weather balloon and satellite temperature measurements extending from near-surface to the lower stratosphere. Stratospheric cooling has also been confirmed in the mid to upper stratosphere, a layer extending from roughly 25 to 50 km above the Earth’s surface (S25−50). To date, however, S25−50 temperatures have not been used in patternbased attribution studies of anthropogenic climate change. Here, we perform such a “fingerprint” study with satellite-derived patterns of temperature change that extend from the lower troposphere to the upper stratosphere. Including S25−50 information increases signal-to-noise ratios by a factor of five, markedly enhancing fingerprint detectability. Key features of this global-scale human fingerprint include stratospheric cooling and tropospheric warming at all latitudes, with stratospheric cooling amplifying with height. In contrast, the dominant modes of internal variability in S25−50 have smaller-scale temperature changes and lack uniform sign. These pronounced spatial differences between S25−50 signal and noise patterns are accompanied by large cooling of S25−50 (1 to 2 ◦C over 1986 to 2022) and low S25−50 noise levels. Our results explain why extending “vertical fingerprinting” to the mid to upper stratosphere yields incontrovertible evidence of human effects on the thermal structure of Earth’s atmosphere. [ABSTRACT FROM AUTHOR]