23 February 2006 Stimulated Raman scattering and broadband spectrum generation of nanosecond pulses from a directly modulated DFB laser
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We report the investigation of stimulated Raman Scattering (SRS) in a standard fiber using a directly modulated DFB laser with wavelength equal to 1549 nm, amplified by a two stage Erbium-doped fiber amplifier. The amplifier provides amplification of 2-mW peak power input pulses to 100-W peak power output pulses. This setup provides a simple source of high power pulses for nonlinear investigation. However, the directly modulation of DFB lasers causes transient oscillations at the beginning of pulses. In our case pulses consisted of a 2-ns transient part followed by a steady-state plateau. We used a monochromator to measure the spectrum at the fiber output. A fast photodetector was placed at the monochromator output and pulse shapes were measured for different wavelengths. This technique allows the separate measurement of the spectrum of different parts of output pulses. We used the SMF-28 fiber with the standard dispersion of 20 ps/nm-km for our wavelength. We made measurements of the output spectra for four fiber lengths: 210 m, 600 m, 4.5 km, and 10 km. For short fiber lengths (210 m and 600 m) the spectra of the transient part and the plateau part were similar and manifest modulation instability (MI) and four-wave mixing (FWM). For 4.5-km long and 10-km long fibers we found that the transient part generates a continuous broadband spectrum while the plateau causes the Stokes wave with the spectrum maximum centered at 1656 nm.
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Jaime Gutiérrez-Gutiérrez, Roberto Rojas-Laguna, Evgeny A. Kuzin, Baldemar Ibarra-Escamilla, Sergio Mendoza-Vázquez, Julián Moisés Estudillo-Ayala, Joseph W. Haus, "Stimulated Raman scattering and broadband spectrum generation of nanosecond pulses from a directly modulated DFB laser", Proc. SPIE 6102, Fiber Lasers III: Technology, Systems, and Applications, 61021X (23 February 2006); doi: 10.1117/12.645269; https://doi.org/10.1117/12.645269

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