Fault-tolerant four-dimensional constellation for coherent optical transmission systems.

We propose a 4-dimensional 2-ary amplitude ring-switched modulation format with 64 symbols, which is denoted as 4D-2A-RS64 encoded over two polarization tributaries to improve the transmission performance over long-haul optical fibers in the presence of the non-linear Kerr effect. At a spectral efficiency of 6 bits per 4D, simulation results show that this format outperforms the polarization division multiplexed (PDM) 8QAM-star modulation as well as the 4D-2A-8PSK over links without inline dispersion management. We evaluate the performance for a WDM transmission of 11 × 90~Gbaud channels over a multi-span SSMF link.

A fully digital MIMO-OFDM scheme for fading mitigation in coherent Δϕ-OTDR.

We introduce a coherent-MIMO Δϕ-OTDR based sensing technique that uses digital frequency division multiplexing of probing codes in order to mitigate the coherent fading issue in Δϕ-OTDR. Orthogonal frequency division multiplexing (OFDM) is used to probe the optical channel on several electrical subcarriers, and their responses are then combined according to specific reliability criterion to enhance the overall sensing sensitivity. This allows for a decrease of the noise floor in sensing measurements on standard single mode fiber (SSMF) and the mitigation of false alarms.

Identification of Rayleigh fading induced phase artifacts in coherent differential ϕ-OTDR.

Differential phase optical time-domain reflectometry is subject to Rayleigh fading, which locally impedes proper phase extraction. We introduce in this Letter a reliability metric derived from the measured Jones matrix estimates of the fiber sensor to discriminate between true perturbations and false alarms caused by Rayleigh backscatter fading points. The proposed soft-decision metric is also of interest for further post-processing stages exploiting artificial intelligence based classifiers.

Introducing coherent MIMO sensing, a fading-resilient, polarization-independent approach to ϕ-OTDR.

Nowadays, long distance optical fibre transmission systems use polarization diversity multiplexed signals to enhance transmission performance. Distributed acoustic sensors (DAS) use the same propagation medium, i.e.

Enhancing the performance of coherent OTDR systems with polarization diversity complementary codes.

Monitoring the optical phase change in a fiber enables a wide range of applications where fast phase variations are induced by acoustic signals or by vibrations in general. However, the quality of the estimated fiber response strongly depends on the method used to modulate the light sent to the fiber and capture the variations of the optical field. In this paper, we show that distributed optical fiber sensing systems can advantageously exploit techniques from the telecommunication domain, as those used in coherent optical transmission, to enhance their performance in detecting mechanical events, while jointly offering a simpler setup than widespread pulse-cloning or spectral-sweep based schemes with acousto-optic modulators.

Polarization-time coding for PDL mitigation in long-haul PolMux OFDM systems.

In this paper, we present a numerical, theoretical and experimental study on the mitigation of Polarization Dependent Loss (PDL) with Polarization-Time (PT) codes in long-haul coherent optical fiber transmissions using Orthogonal Frequency Division Multiplexing (OFDM). First, we review the scheme of a polarization-multiplexed (PolMux) optical transmission and the 2 × 2 MIMO model of the optical channel with PDL. Second, we introduce the Space-Time (ST) codes originally designed for wireless Rayleigh fading channels, and evaluate their performance, as PT codes, in mitigating PDL through numerical simulations.