This letter proposed and demonstrated a wavelet technique to reduce the time domain noise to get submeter spatial resolution in the distributed vibration sensor based on phase optical time domain reflectometry. A new wavelet shrinkage approach allows the distributed vibration measurement of 20-Hz and 8-kHz events to be detected over 1-km sensing length with a 5-ns optical pulse, which is equivalent to 50-cm spatial resolution using the single-mode sensing fiber.

Wavelet Denoising Method for Improving Detection Performance of Distributed Vibration Sensor

In this paper, we propose a novel detector for single-channel long-haul coherent optical communications, termed stochastic digital backpropagation (SDBP), which takes into account noise from the optical amplifiers in addition to handling deterministic linear and nonlinear impairments. We discuss the design approach behind this detector, which is based on the maximum a posteriori (MAP) principle. As closed-form expressions of the MAP detector are not tractable for coherent optical transmission, we employ the framework of Bayesian graphical models, which allows a numerical evaluation of the proposed detector. Through simulations, we observe that by accounting for nonlinear signal—noise interactions, we achieve a significant improvement in system reach with SDBP over digital backpropagation (DBP) for systems with periodic inline optical dispersion compensation. In uncompensated links with high symbol rates, the performance difference in terms of system reach for SDBP over DBP is small. In the absence of noise, the proposed detector is equivalent to the well-known DBP detector.

https://publications.lib.chalmers.se/records/fulltext/205073/local_205073.pdf

Stochastic Digital Backpropagation

We address the problem of efficient end-to-end network monitoring of path metrics in communication networks. Our goal is to minimize the number of measurements or monitors required to maintain an acceptable estimation accuracy. We present a framework based on diffusion wavelets and nonlinear estimation. Our procedure involves the development of a diffusion wavelet basis that is adapted to the monitoring problem. This basis exploits spatial and temporal correlations in the measured phenomena to provide a compressible representation of the path metrics. The framework employs nonlinear estimation techniques using l1 minimization to generate estimates for the unmeasured paths. We describe heuristic approaches for the selection of the paths that should be monitored, or equivalently, where hardware monitors should be located. We demonstrate how our estimation framework can improve the efficiency of end-to-end delay estimation in IP networks and reduce the number of hardware monitors required to track bit-error rates in all-optical networks (networks with no electrical regenerators).

/pdf/compressed-network-monitoring-for-ip-and-all-optical-2wk41fc0b4.pdf

Compressed network monitoring for ip and all-optical networks

A method and system for tuning channel spacing for a wavelength division multiplexing (WDM) transport system includes determining a spectrum width for a channel. A bandwidth of a group of base channels covering the spectrum width for the channel is allocated to the channel. A passband of a channel filter at a center frequency of the group is adjusted to correspond to the spectrum width of the channel.

Tunable channel spacing for wavelength division multiplexing (wdm) transport system

We demonstrate a sinusoidal-gated InGaAs/InP single photon avalanche diode (SPAD) pair with high photon detection efficiency (PDE) and low dark count rate (DCR). The photodiode pair is biased in a balanced configuration with only one of the SPADs illuminated. The advantage of balanced detectors is cancellation of the common component of the output signal, which in this case arises from sinusoidal gating. In conventional sinusoidal gating, narrow-band RF filters are used to eliminate the gating signal while imparting minimal change to the avalanche pulses. A disadvantage of this approach is that the requisite filters fix the operating frequency, whereas the balanced SPAD receiver is frequency agile. At a laser repletion rate of 1 MHz and a temperature of 240 K, the DCR and PDE are 58 kHz and 43%, respectively. The afterpulse probability is lower than a single sinusoidal-gated SPAD. Jitter of 240 ps is achieved with one photon per pulse and an excess bias of 1.6%.

Common-Mode Cancellation in Sinusoidal Gating With Balanced InGaAs/InP Single Photon Avalanche Diodes

Basic electromagnetic field concepts cylindrical waveguides lasers and optical amplifiers optical detectors receiver noise considerations optical fiber systems coherent lightwave communications detection systems wide area wave division multiplexing image channel rejection coherent detection.

Gerard Lachs

Papers

Fiber optic communications : systems, analysis, and enhancements