Back propagation neutral network based signal acquisition for Brillouin distributed optical fiber sensors.

This manuscript proposes a method based on back propagation (BP) neural network and the spectral subtraction method to quickly obtain sensing information in Brillouin fiber optics sensors. BP neural network's characteristics which can realize any complex nonlinear mapping help to determine the frequency shift section(s) information. The training function, transfer function and number of hidden layer nodes of BP neural network are determined with experimental data. The experimental results show that comparing with traditional Lorentz fitting algorithm and edge detection with Sobel operator, the BP neural network is about 1/12 in terms of time complexity with the Lorentz algorithm, about 1/9 with the edge detection based on Sobel operator; while the respective accuracy on determine the frequency shifted section(s) has improved by 79.4% and 27.9%.

Experimental investigation of all-optical nonreturn-to-zero differential phase-shift keying to return-to-zero DPSK format conversion based on nonlinear polarization rotation of semiconductor optical amplifier.

A novel all-optical nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) to return-to-zero DPSK (RZ-DPSK) format conversion scheme is proposed and experimentally demonstrated. This conversion is based on nonlinear polarization rotation of a semiconductor optical amplifier. Experimental results show that a 10 Gb/s RZ-DPSK signal with an extinction ratio over 10 dB can be converted with a tunable duty cycle from 33% to 66%, and the ER of the converted signal decreases with the increase in the duty cycle. For all cases of different duty cycles, the converted signals experience a -0.4 to -1.2 dB power penalty at a bit error rate of 10(-9) compared with the original signal. In addition, the spectra show that this format conversion is a wavelength-preserved operation.

Measurement of the linewidth enhancement factor based on nonlinear polarization rotation of semiconductor optical amplifier.

A simple measurement scheme of the linewidth enhancement factor based on the nonlinear polarization rotation of a semiconductor optical amplifier is proposed. Considering the polarization dependent gain, the relationship between the linewidth enhancement factor and the Stokes vector was derived theoretically. It is proven that the linewidth enhancement factor can be calculated directly from the Stokes parameters without any other assistant measurement system. The results demonstrate that the linewidth enhancement factor varies in a small range from 10.5 to 8.5 for TE mode and from 8.2 to 5.8 for TM mode, respectively, when the input optical power varies from 50 µW to 1 mW and the bias current varies from 90 to 170 mA.