Pulse generation in fiber lasers with frequency shifted feedback

Lasers with frequency shifted feedback may spontaneously generate periodic trains of short optical pulses. Frequency shifts as small as several kilohertz per roundtrip are shown to sustain pulsing at the cavity fundamental frequency in Er/sup 3+/- and Nd/sup 3+/-fiber lasers with intracavity acousto-optic frequency shifters. A numerical model based on the split step Fourier method suggests that this pulse mode of operation may be attributed to the Kerr-type nonlinearity of the optical fiber.