Frequency Doubled Er/Brillouin All-Fiber Laser

Introduction Nanosecond pulse laser sources with extended wavelength diversity are of great interest for numerous applications. The use of fiber lasers for second harmonic generation allows combining efficient wavelength conversion with the possibility to keep all-fiber format. Second-order nonlinear optical processes can be implemented in all-fiber configurations by using a periodically poled fiber as second-order nonlinear medium with quasi-phasematching [1,2] and a fiber laser as pump source. In the past, second-harmonic generation (SHG) was demonstrated in periodically poled fibers using solid-state lasers [1, 3] or master-oscillator-power-amplifier (MOPA) configurations as pump sources [4]. In order to fully exploit the advantages of all-fiber configurations (low-cost, robustness, compactness, flexibility) and to optimize nonlinear wavelength conversion processes in the periodically poled silica fiber (PPSF), a fiber laser with appropriate characteristics is needed. The requirements for the fiber laser (to be used as pump source for e.g. SHG) are as follows: 1) it must deliver high-peak power pulses in order to obtain high conversion efficiency of the pump; and 2) its optical spectrum must be located inside the quasi-phase-matching (QPM) resonance band of the PPSF, which is about ~1 nm for a 10 cm long device. A self-Q-switched erbium fiber laser employing stimulated Brillouin scattering (SBS) [5] can potentially meet all these requirements and, moreover, can bring simplicity of configuration and possibility of wavelength tuning. Providing a typical recovery time for the population inversion in the doped fiber as long as hundreds of microseconds (i.e. the repetition rate as low as several kHz) such lasers are able to emit nanosecond pulses with record values of the peak/average power contrast ranging up to ~10 that makes them very efficient for nonlinear conversion in fibers [6].