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Journal of Lightwave Technology

Improved Soliton Amplitude Estimation via the Continuous Spectrum

Qun Zhang, Frank R. Kschischang

Published May 27, 2019• 8 citations
Publisher

Abstract

In soliton communication systems, the continuous nonlinear spectrum, ideally zero, is conventionally ignored at the receiver. In this paper, we exploit correlation between the received continuous spectrum and perturbations of the discrete soliton eigenvalue. We propose four estimation schemes, classified into two categories, one based on the nonlinear Fourier transform (NFT) and the other based on minimum Euclidean distance. Both categories comprise two schemes, one that exploits the received continuous spectral function to achieve improved estimation and one that does not. Numerical simulations demonstrate that significant reduction in estimation error can be achieved when the continuous spectrum is exploited, translating into improved information transmission rates of up to 46% compared to the reference NFT-based scheme.

DOI
10.1109/jlt.2019.2910519

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In soliton communication systems, the continuous nonlinear spectrum, ideally zero, is conventionally ignored at the receiver. In this paper, we exploit correlation between the received continuous spectrum and perturbations of the discrete soliton eigenvalue. We propose four estimation schemes, classified into two categories, one based on the nonlinear Fourier transform (NFT) and the other based on minimum Euclidean distance. Both categories comprise two schemes, one that exploits the received continuous spectral function to achieve improved estimation and one that does not. Numerical simulations demonstrate that significant reduction in estimation error can be achieved when the continuous spectrum is exploited, translating into improved information transmission rates of up to 46% compared to the reference NFT-based scheme.
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A multistage signal estimation scheme is proposed for phase-and-amplitude modulated soliton communication systems. The estimator provides a significant mean-squared-error reduction in soliton amplitude estimation, which, in conjunction with detection of encoded phase information, results in spectral-efficiency improvements. A low-complexity version of the multistage estimation scheme is also proposed, whose performance is studied via numerical simulations under the distributed Raman amplification strategy. The achievable information rate is increased by about 1 bit/symbol for pulse bandwidth of 30 GHz, 40 GHz, and 50 GHz.
The bright solitons in quasi-1D atomic Bose-Einstein condensates are good candidates for constructing matter-wave interferometers with high sensitivity and long phase-accumulation times. Such interferometers at the mean-field level can be theoretically studied within the framework of quasi-1D Gross-Pitaevskii (GP) equation with narrow repulsive potential barriers. In this paper we present a basic proposal of using the nonlinear Fourier transform (NFT), also known as the inverse scattering transform, as an effective tool to analyze the soliton contents for those interferometers, which thanks to the nearly integrable nature of the GP equation when the normalized atom number fraction near the barrier is small. Based on typical cases, we show that the soliton components can be accurately detected from the output wave fields of the interferometers by computing the NFT spectra.
We study the quantum-noise properties of spectrally filtered solitons in optical fibers. Perturbation theory, including a quantum description of the continuum, is used to derive a complete analytical expression for the second-order correlator of the amplitude quadrature. This correlator is subsequently used to optimize the frequency response of the filter numerically in order to achieve the minimum photon-number noise. For propagation distances up to three soliton periods, the length at which the best noise reduction occurs, a square filter is found to be approximately optimum. For longer distances, more-complicated filter shapes are predicted for the best noise reduction.
With the advancement of quantum physics and deeper exploration of atomic systems, the integration of atoms into communication systems has garnered significant attention. Among these efforts, the use of Rydberg atoms as a communication receiver has emerged as a prominent area of research. In this work, we introduce a new mathematical modeling approach to more accurately establish the input-output relationship of a Rydberg atomic receiver. We categorize this relationship into three segments: one linear region and two nonlinear regions, facilitating a comprehensive analysis of the nonlinear challenges associated with Rydberg atomic receiver. Our findings indicate that adjusting the Rabi oscillation frequency of the coupling laser can effectively extend the linear operating range of the receiver. Furthermore, focusing on complex quadrature amplitude modulation, we propose a digital nonlinear distortion compensation method specifically designed for Rydberg atomic receiver. This method demonstrates a significant improvement in performance, enhancing the demodulation bit error rate compared to conventional linearization techniques.