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.

Depolarization is one of the most important sources of error in a quantum communication link that can be introduced by the quantum channel. Even though standard quantum process tomography can, in theory, be applied to characterize this effect, in most real-world implementations depolarization cannot be distinguished from time-varying unitary transformations, especially when the timescales are much shorter than the detectors response time. In this paper, we introduce a method for distinguishing true depolarization from fast polarization rotations by employing Hong–Ou–Mandel interference. It is shown that the results are independent of the timing resolutions of the photodetectors.

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.