We demonstrate a diode pumped passively Q switched Tm doped double cladding silica fiber laser operating at wavelength of 1960 nm using an anti resonant Fabry Perot saturable absorber as passive modulation element. To determine a relatively preferable fiber length for stable cw Q switched operation, three active fiber simples with the length of 1.1, 5.3, and 7.0 m were employed respectively in our experiments. With 1.1 m gain fiber, we generated Q switched pulses with a pulse width of 245 ns and an average power of up to 2.2 W at a repetition rate of 620 kHz. For the longer two fiber samples, Q switched operation with longer pulse duration, Q switched mode locking and cw mode locking were observed, respectively.

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