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A Brillouin optical time-domain analysis (BOTDA) scheme based on hybrid amplification, consisting of distributed Raman amplification and lumped amplification provided by remotely pumped Erbium-doped fibers, is proposed and thorougly studied, enabling longest sensing distance among existing repeaterless techniques. First, criteria for optimizing the optical powers entering the sensing fiber are defined. Then, the walk-off effect in the forward distributed Raman amplification and associated self-phase modulation are pointed out and analyzed to describe the BOTDA pulse distortion and its impact on the balanced detection used for relative intensity noise mitigation. A compensating pulse approach is proposed to mitigate signal distortion, guaranteeing the safe use of balanced detection in an ultra-long BOTDA sensor. The combination of all approaches mentioned above is validated in two types of fiber loop configurations, with 150 km and 200 km real remoteness, both constituting record-high sensing performance in each case.

To enable optimum network transmission, the ideal is to launch as high laser power as possible into the optical fiber, to overcome the effects of fiber attenuation and maintain an acceptable signal to noise ratio. Launching high powers into a fiber however, results in unwanted nonlinear effects. Stimulated Brillouin scattering (SBS) is one of the nonlinear effects which reflects a significant proportion of the transmitted optical power back to the transmitter, degrading the system severely. This paper reports the development of a digitally selected supermode distributed Bragg reflector monolithic laser chip which can provide significant linewidth broadening using a pure frequency modulation technique by application of a dither current. By modifying a small segment of the laser chip material refractive index, it produces a modulation of the longitudinal mode and hence laser frequency; the monolithic laser chip has reduced the effects of SBS significantly with very little parasitic amplitude modulation.

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