Abstract

We report experimental observations of stimulated Raman scattering in a standard fiber using a directly modulated DFB semiconductor laser amplified by two erbium-doped fibers. The laser pulse width was variably controlled on a nanosecond-scale; the laser emission was separated into two distinct regimes: an initial transient peak regime, followed by a quasi steady-state plateau regime. The transient leading part of the pump pulse containing fast amplitude modulation generated a broadband Raman-induced spectral shift through the modulation instability and subsequent intra-pulse Raman frequency shift. The plateau regime amplified the conventional Stokes shifted emission expected from the peaks of the gain distribution. The output signal spectrum at the end of a 9.13 km length of fiber for the transient part extends from 1550 nm to 1700 nm for a pump pulse peak power of 65 W. We found that the Raman-induced spectral shift is measurable about 8 W for every fiber length examined, 0.6 km, 4.46 km, and 9.13 km. All spectral components of the broadband scattering appear to be generated in the initial kilometer of the fiber span. The Stokes shifted light generation threshold was higher than the threshold for the intra-pulse Raman-induced broadened spectra. This fact enables the nonlinear spectral filtering of pulses from directly modulated semiconductor lasers.

© 2005 Optical Society of America

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References

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  2. G. P. Agrawal and N. K. Dutta, Semiconductor Lasers, Second Edition, International Thompson Publishing, 1993.
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    [CrossRef]
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IEEE Photonics Tech. Lett.

N. Nishizawa and T. Goto, �??Compact System of Wavelength-Tunable Femtosecond Soliton Pulses Generation Using Optical Fiber,�?? IEEE Photonics Tech. Lett. 11, 325-327 (1999).
[CrossRef]

J. Opt. Soc. Am. B

Opt. Commun.

J. Santhanam and G. P. Agrawal, �??Raman-induced spectral shifts in optical fibers: general theory based on the moment method,�?? Opt. Commun. 222, 413-420 (2003).
[CrossRef]

L. Garcia, A. Jalili, Y. Lee, N. Poole, K. Salit, P. Sidereas, C. G. Goedde and J.R. Thompson, �??Effect of pump pulse temporal structure on long-pulse multi-order stimulated Raman scattering in optical fiber,�?? Opt. Commun. 193, 289-300 (2001).
[CrossRef]

Opt. Lett.

P. K. Shukla and J. J. Rasmussen, �??Modulation instability of short pulses in long optical fibers,�?? Opt. Lett. 11, 171-173 (1986).
[CrossRef] [PubMed]

F. M. Mitschke and L F. Molenauer, �??Discovery of the soliton self-frequency shift,�?? Opt. Lett. 11, 659-661 (1986).
[CrossRef] [PubMed]

J. P. Gordon, �??Theory of the soliton self-frequency shift,�?? Opt. Lett. 11, 662-664 (1986).
[CrossRef] [PubMed]

P. V. Mamyshev, S. V. Chernikov, E. M. Dianov and A. M. Prokhorov, �??Generation of a high-repetition-rate train of practically noninteracting solitons by using the induced modulation instability and Raman self-scattering effects,�?? Opt. Lett. 15, 1365-1367 (1990).
[CrossRef] [PubMed]

D. A. Chestnut and J. R. Taylor, �??Soliton self-frequency shift in highly nonlinear fiber with extension by external Raman pumping,�?? Opt. Lett. 28, 2512-2514 (2003).
[CrossRef] [PubMed]

A. Efimov, A. J. Taylor, F. G. Omenetto and E. Vanin, �??Adaptive control of femtosecond soliton self-frequency shift in fibers,�?? Opt. Lett. 29, 271-273 (2004).
[CrossRef] [PubMed]

A. K. Abeeluck and C. Headley, �??Continuous-wave pumping in the anomalous- and normal-dispersion regimes of nonlinear fibers for supercontinuum generation,�?? Opt. Lett. 30, 61-63 (2005).
[CrossRef] [PubMed]

G. A. Nowak, Y. H. Kao, T. J. Xia and M. N. Islam, �??Low power high-efficiency wavelength conversion based on modulation instability in high-nonlinearity fiber,�?? Opt. Lett. 23, 936-938 (1998).
[CrossRef]

D. Mahgerefteh, D. L. Butler, J. Goldhar, B. Rosenberg and G. L. Burdge, �??Technique for measurement of the Raman gain coefficient in optical fibers,�?? Opt. Lett. 21, 2026-2028 (1996).
[CrossRef] [PubMed]

Phys. Rev. A.

B. Crosignani, P. Di Porto, and S. Solimento, �??Influence of guiding structures on spontaneous and stimulated emission: Raman scattering in optical fibers.�?? Phys. Rev. A. 21, 594-598 (1980).
[CrossRef]

Other

G. P. Agrawal, Nonlinear Fiber Optics, 3d ed. (Academic, San Diego, California, 2001).

G. P. Agrawal and N. K. Dutta, Semiconductor Lasers, Second Edition, International Thompson Publishing, 1993.

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Figures (9)

Fig. 1.
Fig. 1.

Schematic of the two stage EDFA.

Fig. 2.
Fig. 2.

Typical pulse shapes at the EDFA output; (a) the power measured for a range of pulse currents, (b) the first three nanoseconds of the pulse measured with a 8-GHz photodetector and a sampling oscilloscope.

Fig. 3.
Fig. 3.

Pulse shapes for different wavelengths using the monochromator.

Fig. 4.
Fig. 4.

Stokes pulse shapes for different wavelengths taken from the output of the 9.13 km fiber.

Fig. 5.
Fig. 5.

Dependence of the pulse energy at the fiber output on wavelength. The peaks near 1660 nm and 1675 nm correspond to maxima for the Raman gain.

Fig. 6.
Fig. 6.

Output spectra for 3-ns laser diode pump pulse.

Fig. 7.
Fig. 7.

Pulse delay at the fiber output.

Fig. 8.
Fig. 8.

The ratio between the output pump peak power and the input pump peak power. The output was filtered through a monochromator to extract the energy at the pump wavelength.

Fig. 9.
Fig. 9.

Pulse shapes at the fiber output at the pump wavelength; a) the 4.46-km long fiber; b) the 9.13-km long fiber.

Equations (1)

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Δ ω R ( z ) = 8 β 2 T R z ( 15 T 0 4 )

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