A 15 dB dynamic range and 4.6 cm spatial resolution tunable photon-counting optical time-domain reflectometer (PC-OTDR) is presented along with a Field Programmable Gate Array (FPGA)-based detection management system that allows several regions of the fiber to be interrogated by the same optical pulse, increasing the data acquisition rate when compared to previous solutions. The optical pulse generation is implemented by a tunable figure-8 passive mode-locked laser providing pulses with the desired bandwidth and center wavelength for WDM applications in the C-band. The acquisition rate is limited by the afterpulse effect and dead time of the employed gated avalanche single-photon detectors. The devised acquisition system not only allows for centimeter-resolution monitoring of fiber links as long as 12 km in under 20 minutes but is also readily adapted to any other photon-counting strategy for increased acquisition rate. The system provides a 20-fold decrease in acquisition times when compared with state-of-the-art solutions, allowing affordable times in centimeter-resolution long-distance fiber measurements.

Trend break detection is a fundamental problem that materializes in many areas of applied science, where being able to identify correctly, and in a timely manner, trend breaks in a noisy signal plays a central role in the success of the application. The linearized Bregman iterations algorithm is one of the methodologies that can solve such a problem in practical computation times with a high level of accuracy and precision. In applications such as fault detection in optical fibers, the length N of the dataset to be processed by the algorithm, however, may render the total processing time impracticable, since there is a quadratic increase on the latter with respect to N. To overcome this problem, the herewith proposed profile-splitting methodology enables blocks of data to be processed simultaneously, with significant gains in processing time and comparable performance. A thorough analysis of the efficiency of the proposed methodology stipulates optimized parameters for individual hardware units implementing the profile-splitting. These results pave the way for high performance linearized Bregman iteration algorithm hardware implementations capable of efficiently dealing with large datasets.

Detection of level shifts in a noisy signal, or trend break detection, is a problem that appears in several research fields, from biophysics to optics and economics. Although many algorithms have been developed to deal with such a problem, accurate and low-complexity trend break detection is still an active topic of research. The Linearized Bregman Iterations have been recently presented as a low-complexity and computationally efficient algorithm to tackle this problem, with a formidable structure that could benefit immensely from hardware implementation. In this work, a hardware architecture of the Linearized Bregman Iteration algorithm is presented and tested on a Field Programmable Gate Array (FPGA). The hardware is synthesized in different-sized FPGAs, and the percentage of used hardware, as well as the maximum frequency enabled by the design, indicate that an approximately 100 gain factor in processing time, concerning the software implementation, can be achieved. This represents a tremendous advantage in using a dedicated unit for trend break detection applications. The proposed architecture is compared with a state-of-the-art hardware structure for sparse estimation, and the results indicate that its performance concerning trend break detection is much more pronounced while, at the same time, being the indicated solution for long datasets.

Optical fibers constitute a staggering portion of the physical layer underlying modern communication networks. To extend the reach of such networks around the globe, long-haul links are necessary. In this context, establishing a connection between two remote locations is only possible due to signal booster stations interspersed along the way. Supervision of such long distance links is of the utmost importance for their reliable operation. For multiplexed networks, high-ratio optical splitters are necessary to distribute the optical signal to multiple users, diminishing severely the transmitted power for each network. In this work, an automated signal boosting remote station for monitoring signals is presented. A Field Programmable Gate Array (FPGA) is part of the remote station and grants its autonomous operation. Making use of a topology capable of reaching over-saturation amplification of semiconductor optical amplifiers (SOA), a higher portion of the optical loss experienced in the splitter is precompensated in the remote node allowing for supervision reach-extension. Approximately 0.5 dB of increased dynamic range is experimentally achieved when comparing the proposed remote station with another one using the same optical amplifier. Even though the obtained extra gain is a minor improvement, the proposed topology paves the way for scalable amplification, allowing for longer reaches.

Traditional methods for measurement of polarizing beamsplitter (PBS) parameters, especially the extinction ratio, require highly polarized light sources, alignment procedures, and/or experimental parameters that change over time, such as polarization rotations. In this work, a new method is presented that employs unpolarized light and a Faraday mirror. It is shown that precise extinction ratio and insertion loss values can be achieved in three single-sweep measurements without any alignment requirements or time-varying signals of any kind.