High-frequency short-pulse emissión from an erbium fiber laser generated by pump spiking

NELIDA ARACELI RUSSO; RICARDO DUCHOWICZ

Campinas, Brasil

Conferencia; 6th Iberoamerican Meeting on Optics, Lasers, and their Applications (RIAO) 2007; 2007

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Rare earth doped fibre lasers show complex temporal behaviours in spite of being pumped in a continuous regime.  Depending on the particular design and on the excitation level, auto-Q-switching and auto-modelocking operations have been reported.1,2 In this work we present the characteristics of a “continuous wave” pumped erbium fibre laser, where we have observed as output, a high frequency pulsed emission over a low power continuous radiation background. From a complete study of the system, we have related this behaviour to a particular excitation noise coming from the pump source. A correlation between measurements performed on the temporal behaviour of the pumping and the laser emission under different pump levels was performed and the complete system (pump and oscillator lasers) was characterized. At difference of a recent paper, we have analyzed the pump output at the fiber laser end and at the semiconductor output.3 Depending on the emission wavelength and on the cavity length, some train modulations were observed. When the cavity length did not adjust to a multiple of the corresponding one to the frequency of the pumping noise, the pulsed emission was modulated with a period corresponding to round-trip of the cavity. As a laser system, we employed a segment of erbium doped fibre and a pair of fibre Bragg gratings acting as reflective elements. Excitation of the active medium was performed in the 975 nm pump band with a CW semiconductor laser source through a WDM coupler. Typical output frequency was 108 MHz, while the registered pulse widths were ~1.2 ns, limited by the detection system.