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We propose a novel approach to the recognition of particular classes of non-conventional events in signals from phase-sensitive optical time-domain-reflectometry-based sensors. Our algorithmic solution has two main features: filtering aimed at the de-nosing of signals and a Gaussian mixture model to cluster them. We test the proposed algorithm using experimentally measured signals. The results show that two classes of events can be distinguished with the best-case recognition probability close to 0.9 at sufficient numbers of training samples., Comment: 4 pages; published version

A fiber-pumped single-frequency microchip erbium laser was developed and characterized with the aim of using it in coherent Optical Time Domain Reflectometry (OTDR) measurements and sensing. The laser is pumped by a fiber-coupled 976 nm laser diode and provides 8 mW TEM00 single frequency output power at 1.54 µm wavelength, suitable for efficient coupling to optical fibers. The amplitude and phase noise of this 200 THz oscillator were experimentally investigated and a Relative Intensity Noise (RIN) control loop was developed providing 27 dB RIN peak reduction at the relaxation oscillation frequency of 800 kHz

A new method for increasing the working range of a coherent optical time-domain reflectometer (COTDR) has been theoretically justified and experimentally demonstrated. The proposed method is based on the use of several types of optic fibers with different backscatter coefficients, in which the fiber with a higher backscatter coefficient is connected to the end of a fiber with the minimum absorption coefficient at the working wavelength, the length of which is the maximum possible in order to ensure a preset sensitivity level. It is shown that, using this approach, the COTDR working range can be increased up to 50 km.

A system based on coherent optical time domain reflectometry (OTDR) for subsea pipeline monitoring is described. The fiber sensor length is increased using erbium-doped fiber amplifier (EDFA) cascades. The sampling frequency is increased by dividing the fiber sensor into separate sensitive areas, with parallel scanning. The calculation of the erbium amplifier cascade spontaneous noise influence on the signal-to-noise ratio (SNR) is carried out.

This paper presents experimental results of a study the influence of nonlinear effects on the range of the phase-sensitive optical time-domain reflectometer. Results from measurements of the impact of the effects of stimulated Raman scattering, stimulated Brillouin scattering, self-phase modulation, and modulation instability are presented. It is shown that the power of the probe pulse for 200 ns does not exceed ≈300 mW.