Joaquim Dias Garcia

Automatic Fault Detection in WDM-PON With Tunable Photon Counting OTDR

An automatic fiber-optical fault analysis system making use of a tunable photon counting optical time-domain reflectometry (OTDR) (ν-OTDR) is proposed and demonstrated in a passive optical network testbed. The employment of the ℓ trend filter as a signal processing tool enables the minimization of the intrinsic coherent random noise impact on the acquired data and also an automatic identification of fiber faults. A feedback loop between an FPGA-based acquisition unit and the filters selections yields highly accurate automatic results and minute monitoring periods with ITU-T grid DWDM tunability, spatial resolution of 6 m and a measured 32 dB dynamic range.

A high-dimensional VARX model to simulate monthly renewable energy supply

This paper proposes a novel framework for forecasting and simulating renewable energy on a long-term horizon. In this regard, it is presented a monthly multivariate stochastic model for wind and hydro inflow as well as an efficient estimation method for high-dimensional data. Firstly, in order to model the inherent uncertainty of renewable energy supplies, this work proposes a high-dimensional VARX with periodic variance. Secondly, an estimation procedure is suggested based on the maximum likelihood criterion with endogenous variable selection. Due to the presence of multicollinearity and high-dimensionality, the estimation procedure proposed in this work has two main features: (i) a fixed-point algorithm to pursue the maximum likelihood estimators under periodic heteroskedasticity (ii) obtain a sparse solution by means of ℓ1-regularization. Simulations and forecasting results for a real case study involving fifty Brazilian renewable power plants are presented.

Adaptive Filter for Automatic Identification of Multiple Faults in a Noisy OTDR Profile

We present a novel methodology that is able to distinguish meaningful level shifts from typical signal fluctuations which, in a fiber monitoring context, is associated with the problem of identifying small losses within a noisy optical time-domain reflectometer (OTDR) profile. A two-stage regularization filtering can accurately identify the location of the significant level shifts with an efficient parameter-free algorithm. The developed methodology demands low computational effort and can easily be embedded in a dedicated processing unit. Our case studies compare the new methodology with the current available ones and show that it is the most adequate technique for fast detection of multiple unknown level shifts in a noisy OTDR profile.

An optimal polarization tracking algorithm for Lithium-Niobate-based polarization controllers

We present an optimal algorithm for the three-stage arbitrary polarization tracking using Lithium-Niobate-based Polarization Controllers: device calibration, polarization state rotation, and stabilization. The theoretical model representing the lithium-niobate-based polarization controller is derived and the methodology is successfully applied. Results are numerically simulated in the MATLAB environment.

High resolution automatic fault detection in a fiber optic link via photon counting OTDR

We present an automatic method for detecting and evaluating fault events in a fibre link. Two Photon Counting OTDR setups are presented (3.5 cm, 12 dB and 2.25 m, 29 dB) allied to a signal processing technique for automatic results.

Fast Polarization Switch for Polarization-based Quantum Communication

We present a complete optoelectronic unit for polarization visualization, switching and control. The system is based on an FPGA unit and comprises: an acquisition unit containing an analog polarimeter and digital-to-analog converters, an FPGA capable of implementing an optimal algorithm for three-stage arbitrary polarization tracking, and an electronic driver with analog-to-digital converters capable of interfacing with Lithium-Niobate-based Polarization Controllers. The results, determined via simulation of real-parameter devices, show that fast polarization switch is achievable.

Multiple Fiber Fault Location With Low-Frequency Sub-Carrier Tone Sweep

We present a monitoring technique that can be directly integrated in the sub-carrier multiplexing (SCM) transceiver for PtP and wavelength division multiplexing and sub-carrier multiplexing passive optical networks applications. The technique is based on the detection of the backscattered signal from a baseband tone (100 Hz to 100 kHz) and interpretation with the least absolute shrinkage and selection operator (LASSO) operator, a signal processing technique which identifies the fault positions based on the mathematical model of the received signal. The proposed single-ended fiber probing method enables the location of multiple faults with no a-priori knowledge of the fiber, and offers low-cost in-service operation with negligible impact on data transmission, few meters spatial resolution, and limited dynamic range. Due to all its advantages, but also considering its reach limitation, the SincLASSO method features as an ideal monitoring candidate for short reach sub-carrier multiplexed optical fiber networks, such as the ones intended for analog mobile Fronthaul based on fiber and fiber-extended copper lines.

ℓ 1 Adaptive trend filter via fast coordinate descent

Identifying the unknown underlying trend of a given noisy signal is extremely useful for a wide range of applications. The number of potential trends might be exponential, thus their search can be computationally intractable even for short signals. Another challenge is the presence of abrupt changes and outliers at unknown times which impart resourceful information regarding the signals characteristics. In this paper, we present the ℓ1 Adaptive Trend Filter, which can consistently identify the components in the underlying trend and multiple level-shifts, even in the presence of outliers. Additionally, an enhanced coordinate descent algorithm which exploits the filter design is presented. Some implementation details are discussed and a version in the Julia language is presented along with two distinct applications to illustrate the filters potential.