The generation of nanosecond square pulse and microsecond harmonic pulse in a passively mode-locked fibre ring laser is demonstrated by inserting a 20 km long single mode fibre in the cavity. The laser operates in anomalous region based on the non-linear polarisation rotation process. The square pulse generation is because of the dissipative soliton resonance effect, which clamps the peak intensity of the laser and broadens the pulse width. The pulse width can be tuned from 28.2 to 167.7 ns. It was found that the square pulse can deliver higher pulse energy compared with the harmonic pulse. The highest recorded pulse energy is 249.8 nJ under the maximum available pump power of 125 mW without pulse breaking.

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  - 1. Matsas, V.J., Newson, T.P., Zervas, M.N.: ‘Self starting passively mode-locked fiber ring laser exploiting nonlinear polarization switching’, Opt. Commun., 1992, 92, (1–3), pp. 61–66 (doi: 10.1016/0030-4018(92)90219-H).

Square pulse emission with ultra-low repetition rate utilising non-linear polarisation rotation technique

References

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