We propose a novel scheme of high doped core and stairway-index trench structure to design a manufacturable graded-index 13-core 5-LP mode fiber with low inter-core crosstalk (ICXT) and large mode differential group delay (MDGD). By using the couple power theory and the finite element method (FEM), the change ICXT of with fiber parameters are investigated. The design of core graded profile and trench structure are optimized to achieve better performance and to meet the fabrication conditions. The numerical result demonstrate that this fiber achieves a low ICXT of lower than −30dB/km (Rb≤500 mm). The bending loss values satisfy the ITU-T recommendation G.655 in 195 µm cladding diameter. Furthermore, the dispersion and the MDGD dependences on wavelength are calculated. The relative core multiplicity factor (RCMF) is obtained as 75.17, which realizes the high density multiplexing. The fabrication methods of this fiber are briefly introduced. The designed fiber may be used for Space-division multiplexing (SDM) system to solve the problem of fiber capacity limitation.

The capacity of a traditional optical communication system based on single-mode fiber has approached to its theoretical limit. Multi-core few-mode fibers provide an effective way to break through the bottleneck of existing transmission capacity. In this paper, a 5-LP-mode weakly-coupled low-crosstalk 7-core fiber is designed by using a combination of trench assistance and air hole isolation structure. The fiber with a standard outer diameter achieves low crosstalk between cores and modes. The inter-core crosstalk area and the effective mode area of the core are calculated by the finite element method. After design optimization, there are 5 stable transmission LP modes in the C+L band of optical communication in this fiber. The effective refractive index difference between LP₂₁ mode and LP₀₂ mode is the smallest and is greater than 1.1 × 10^–3. The LP₃₁ mode in the optical fiber has the largest inter-core crosstalk and the loss is lower than –50 dB/km. The fiber can achieve low crosstalk transmission between modes and cores at the same time. The mode areas of the 5 LP modes in the 7 cores are larger than 86 μm², and the relative core multiplexing factor is 57.63 at a wavelength of 1550 nm. Therefore, this fiber can be used in a large-capacity high-speed fiber transmission system.

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Abstract. F10.7, the solar radiation flux at a wavelength of 10.7 cm (F10.7), is often used as an important parameter input in various space weather models and is also a key parameter for measuring the strength of solar activity levels. Therefore, it is valuable to study and forecast F10.7. In this paper, the temporal convolutional network (TCN) approach in deep learning is used to predict the daily value of F10.7. The F10.7 series from 1957 to 2019 are used, which the datasets from 1957 to 2008 are used for training and the datasets from 2009 to 2019 are used for testing. The results show that the TCN model of prediction F10.7 with a root mean square error (RMSE) from 5.03 to 5.44sfu and correlation coefficients (R) as high as 0.98 during solar cycle 24. The overall accuracy of the TCN forecasts is better than those of the widely used autoregressive (AR) models and the results of the US Space Weather Prediction Center (SWPC) forecasts especially for 2 and 3 days ahead. In addition ,the TCN model is slightly better than other neural network models like backward propagation network (BP) and long short-term memory network (LSTM) in terms of the solar radiation flux F10.7 forecast. The TCN model predicted F10.7 with a lower root mean square error, a higher correlation coefficient and the better overall model prediction.