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Self-starting passively mode-locked fibre ring laser for distributed sensing

A twelve hundred meter long, passively mode-locked, fiber ring laser has been constructed using polarization preserving fiber to ensure operational stability. A short length of lo-bi spun fiber has been included to exploit non-linear polarization evolution as the mechanism for mode-locking the fiber laser. Pulses with durations in the range of 1 to 10 ns with intensities of a few Watts centered around the 1.535 (mu) wavelength were achieved. The circulating pulse within the laser cavity generates both Rayleigh and Raman scattered light. The former may be used to measure losses within the cavity, the latter permits the distributed temperature measurements of the fiber forming the cavity.