Coherent detection in optical fiber systems
TL;DR: This work reviews detection methods, including noncoherent, differentially coherent, and coherent detection, as well as a hybrid method, and compares modulation methods encoding information in various degrees of freedom (DOF).
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Abstract: The drive for higher performance in optical fiber systems has renewed interest in coherent detection. We review detection methods, including noncoherent, differentially coherent, and coherent detection, as well as a hybrid method. We compare modulation methods encoding information in various degrees of freedom (DOF). Polarization-multiplexed quadrature-amplitude modulation maximizes spectral efficiency and power efficiency, by utilizing all four available DOF, the two field quadratures in the two polarizations. Dual-polarization homodyne or heterodyne downconversion are linear processes that can fully recover the received signal field in these four DOF. When downconverted signals are sampled at the Nyquist rate, compensation of transmission impairments can be performed using digital signal processing (DSP). Linear impairments, including chromatic dispersion and polarization-mode dispersion, can be compensated quasi-exactly using finite impulse response filters. Some nonlinear impairments, such as intra-channel four-wave mixing and nonlinear phase noise, can be compensated partially. Carrier phase recovery can be performed using feedforward methods, even when phase-locked loops may fail due to delay constraints. DSP-based compensation enables a receiver to adapt to time-varying impairments, and facilitates use of advanced forward-error-correction codes. We discuss both single- and multi-carrier system implementations. For a given modulation format, using coherent detection, they offer fundamentally the same spectral efficiency and power efficiency, but may differ in practice, because of different impairments and implementation details. With anticipated advances in analog-to-digital converters and integrated circuit technology, DSP-based coherent receivers at bit rates up to 100 Gbit/s should become practical within the next few years.
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Citations
Stealth and secured optical coherent transmission using a gain switched frequency comb and multi-homodyne coherent detection
Eyal Wohlgemuth,Yaron Yoffe,Pantea Nadimi Goki,Muhammad Imran,Francesco Fresi,Prajwal D. Lakshmijayasimha,Roi Cohen,Prince M. Anandarajah,Luca Poti,Dan Sadot +9 more
TL;DR: In this article, a novel all-optical stealth and secured transmission is proposed and demonstrated, where the covert signal is carried by multiple tones of a gain switched optical frequency comb, optically coded with spectral phase mask, and concealed below EDFA's noise.
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Applications of Machine Learning in Optical Communications and Networks
Faisal Nadeem Khan,Qirui Fan,Jianing Lu,Gai Zhou,Chao Lu,Alan Pak Tao Lau +5 more
- 08 Mar 2020
TL;DR: Various applications of machine learning techniques in different aspects of optical communications and networking including optical performance monitoring, fiber nonlinearity compensation, cognitive network failure prediction, dynamic planning and cross-layer optimization of software-defined networks, quality of transmission estimation, and physical layer design of optical communication systems are discussed.
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Real-time fast polarization tracking based on polarization phase locking least mean square algorithm
TL;DR: A fast polarization tracking scheme based on polarization phase locking least mean square (LMS) algorithm that has the advantages of no frequency/phase offset feedback requirement from the carrier recovery stage is proposed and experimentally demonstrated in real-time implementation with a quasi-feed-forward digital signal processing architecture.
17
Performance Evaluation of Phase Estimation Algorithms in Equalized Coherent Optical Systems
TL;DR: This work assesses the performance of a coherent optical system employing a phase estimation algorithm combined with a least mean square decision-directed equalizer in a feedback configuration and compares it to the constant modulus algorithm with an independent carrier phase estimation approach for 16-quadratic-amplitude-modulation transmission.
Joint-Polarization Phase-Noise Estimation and Symbol Detection for Optical Coherent Receivers
TL;DR: The problem of optimal symbol detection in the presence of laser phase noise is studied, for uncoded polarization-multiplexed fiber-optic transmission, and a pilot-based algorithm that approximates the maximum a posteriori (MAP) symbol detector is developed.
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