A degenerated look-up table based perturbative nonlinearity compensation (DLUT-PNC) algorithm for probabilistically shaped 16QAM signals was proposed to compensate intra-channel fiber nonlinearity. However, this method adopts the standard 16 QAM signals without considering the influence of ASE noise to calculate the degenerated elements of table. Hence, the degenerated elements of the table are not strictly optimal. In this paper, a blind adaptive DLUT-PNC (BADLUT- PNC) method based on the gradient descent algorithm is proposed. We use the gradient descent algorithm to optimize the degenerated elements and then obtain the optimal degeneration scheme. In a single channel 70GBaud dual-polarization 16QAM transmission simulation with a 1200km link, the proposed scheme is investigated. The simulation result shows that the extra 0.15~0.45dB SNR improvements can be achieved by adopting our proposed BA-DLUT-PNC compared to the conventional DLUT-PNC method.
The paper introduces the DAS system based on advanced phase-sensitive optical time domain reflectometry (φ-OTDR) with fading noise suppressed. Besides, the DAS system based on time-gated digital optical frequency domain reflectometry (TGD-OFDR) and its improved systems are introduced. The application of DAS in railway perimeter security is introduced at the end of the paper.
KEYWORDS: Spatial resolution, Signal to noise ratio, Vibrometry, Sensors, Reflectometry, Optical fibers, Phase measurement, Magnetic sensors, Signal detection, Geometrical optics
We demonstrate a novel distributed fiber vibration sensor based on the phase extraction from time-gated digital optical frequency domain reflectometry (TGD-OFDR), which have an advantage of wide dynamic range. With the much improved signal to noise ratio (SNR) compared to conventional phase-sensitive optical time domain reflectometry (OTDR), the phase of optical signals is extracted over a long distance up to 29 km with 2.2 m spatial resolution.
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