Medeiros Correia, Marlon; von der Weid, Jean Pierre (Advisor). Modelocked fiber lasers for optical time-domain reflectometry and sensing.

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. Index Terms-Optical fiber monitoring; optical time domain reflectometry; single-photon detection.

The authors experimentally demonstrate an ultra‐low repetition rate passive mode‐locked fibre ring laser with a semiconductor optical amplifier works like as a gain medium and non‐linear polarisation rotation. A unidirectional erbium‐doped fibre amplifier provides additional gain to increase cavity power. By exploiting non‐linear polarisation rotation combined with dispersion management stable 5.18 ps optical pulses with 67.2 kHz repetition rate and energy of 1.75 nJ were generated with an extinction ratio >35 dB. The central wavelength is 1557.89 nm and the optical 3‐dB bandwidth 1.82 nm very appropriate for optical applications that often require high‐peak‐power, low repetition rate and picosecond pulses.

The authors experimentally demonstrate the operation of a lasing phase-sensitive optical time-domain reflectometer (Φ-OTDR) based on random feedback from a sensing fiber. Here, the full output of the laser provides the sensing signal, in contrast to the small backscattered signal measured in a conventional OTDR. In this proof-of-principle demonstration, the laser operates as a distributed vibration sensor with signal-to-noise ratio of 23-dB and 1.37-m spatial resolution.

The operation of a Hybrid Electronic Addressable Random laser is analyzed. The laser operates as a ϕ-OTDR distributed vibration sensor in a transform-limited mode-locked regime with 41 MHz FWHM bandwidth and <7-kHz mode linewidth.