Application of Dual-Frequency Self-Injection Locked DFB Laser for Brillouin Optical Time Domain Analysis.

Self-injection locking to an external fiber cavity is an efficient technique enabling drastic linewidth narrowing of semiconductor lasers. Recently, we constructed a simple dual-frequency laser source that employs self-injection locking of a DFB laser in the external ring fiber cavity and Brillouin lasing in the same cavity. The laser performance characteristics are on the level of the laser modules commonly used with BOTDA. The use of a laser source operating two frequencies strongly locked through the Brillouin resonance simplifies the BOTDA system, avoiding the use of a broadband electrooptical modulator (EOM) and high-frequency electronics. Here, in a direct comparison with the commercial BOTDA, we explore the capacity of our low-cost solution for BOTDA sensing, demonstrating distributed measurements of the Brillouin frequency shift in a 10 km sensing fiber with a 1.5 m spatial resolution.

Single cut technique for adjustment of doubly resonant Brillouin laser cavities.

We report a simple technical solution for precise adjustment of short fiber cavities commonly used with Brillouin fiber lasers. The technique is based on recording the Brillouin response of the cavity to the frequency scanned laser radiation. The recorded traces are used to calculate the excess cavity length that needs to be removed from the original cavity to provide its precise adjustment to the Brillouin resonance at any preselected pump laser wavelength. The adjusted laser cavity is simultaneously resonant for pump and Stokes radiation. For demonstration of the approach, fine adjustment of a 4 m long ring cavity based on standard Corning SMF-28 fiber is performed.