KEYWORDS: Eye, Education and training, Picosecond phenomena, Radio over Fiber, Optical sensing, Affine motion model, Amplitude modulation, Data modeling, Machine learning, RGB color model
A designed visual geometry group (VGG)-based convolutional neural network (CNN) model with small computational cost and high accuracy is utilized to monitor pulse amplitude modulation-based intensity modulation and direct detection channel performance using eye diagram measurements. Experimental results show that the proposed technique can achieve a high accuracy in jointly monitoring modulation format, probabilistic shaping, roll-off factor, baud rate, optical signal-to-noise ratio, and chromatic dispersion. The designed VGG-based CNN model outperforms the other four traditional machine-learning methods in different scenarios. Furthermore, the multitask learning model combined with MobileNet CNN is designed to improve the flexibility of the network. Compared with the designed VGG-based CNN, the MobileNet-based MTL does not need to train all the classes, and it can simultaneously monitor single parameter or multiple parameters without sacrificing accuracy, indicating great potential in various monitoring scenarios.
A pivotal issue of the conventional optical fiber communications networks is to meet the explosively increasing requirement in data traffic. In order to meet this ever-increasing demand, there have been a lot of research and industrial development efforts to utilize the photon in various dimensions such as wavelength division multiplexing (WDM), space division multiplexing (SDM), mode division multiplexing (MDM) and so on. Fueled by emerging bandwidth-hungry applications, orbital angular momentum (OAM) modes and their multiplexing have recently gained much attention due to its special doughnut-shaped intensity distribution, as well as its unique helical phase wavefront with the theoretically infinite topological value. The OAM modes with different topological charge values are orthogonal to each other, which has provided a new degree of freedom in MDM. In this paper, we propose and design a Ge-doped air-core ring fiber, which can support numerous OAM modes. By varying the mole fraction of GeO2 and adjusting the structure parameter, including the air-core radius and the GeO2-doped ring width, we study the influence of the different fiber parameters on the total supported OAM mode number. The hollow silica fiber with a 50-μm air core and a 1.5-μm thickness of Gedoped ring is designed in simulation to support fiber eigenmodes up to HE112,1 and EH107,1. This provides 436 OAM modes at 1550 nm while maintaining radially single mode condition. Moreover, it can support more than 400 OAM modes from 1260 nm to 1625 nm, covering O, E, S, C, and L bands.
Light-carrying orbital angular momentum (OAM) has recently drawn extensive attention from researchers due to its unique field distribution. As a result of the intrinsic orthogonality among OAM modes with different topological charge values, they can be used as a modal basis in the mode-division multiplexing (MDM) optical communications systems. For fiber-based optical systems, chromatic dispersion induces temporal optical pulse broadening, which seriously limits the rate of information transmission. Consequently, dispersion compensation fiber is promising for mitigating the chromatic dispersion of the complex beam in the optical fiber. We propose and design a novel germanium-doped silica ring fiber composed of two high refractive index ring regions that can support high order OAM modes with large negative dispersion. We numerically investigate the high-order OAM modes guiding property in the proposed fiber by using a full-vector finite-element mode (FEM). Since Ge-doped silica has similar physical properties to silica, they can be easily combined with a tunable mole fraction of GeO2. Through varying the mole fraction of GeO2 and optimizing the structure parameter, we obtain a large negative dispersion of up to -99,685 ps/(nm·km) for OAM11,1 mode at the wavelength of 1614.2 nm. Furthermore, we engineer the chromatic dispersion of some other OAM modes and investigate the effects of fiber parameters on the dispersion, which indicates that the fiber we design is able to support all the OAMℓ,1 modes (∣l∣≤11) with highly negative dispersion. The designed fiber with tailorable negative dispersion can be applied to compensate for positive dispersion in the OAM-based optical systems.
In this paper, we present a stable dark soliton with its spectrum spanning about one octave generated in the silicon nitride microring resonator with normal dispersion. The dark soliton can be generated straightforwardly from noise. Then, we investigate the dependence of bandwidth and power level on pump power, the second-order dispersion, the ratio of coupling and intracavity loss coefficient and free spectral range.
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