We present a detailed theoretical investigation of claddingpumped Raman fiber amplification in an unexplored parameter space of high conversion efficiency (> 60%) and high brightness enhancement (> 1000). Fibers with large clad-to-core diameter ratios can provide a promising means for Raman-based brightness enhancement of diode pump sources. Unfortunately, the diameter ratio cannot be extended indefinitely since the intensity generated in the core can greatly exceed that in the cladding long before the pump is fully depleted. If left uncontrolled, this leads to the generation of parasitic second-order Stokes wavelengths in the core, limiting the conversion efficiency and as we will show, clamping the achievable brightness enhancement. Using a coupled-wave formalism, we present the upper limit on brightness enhancement as a function of diameter ratio for conventionally guided fibers. We further present strategies for overcoming this limit based upon depressed well core designs. We consider two configurations: (1) pulsed cladding-pumped Raman fiber amplifier (CPRFA) and (2) cw cladding-pumped Raman fiber laser (CPRFL).

© 2010 Optical Society of America

1. C. A. Codemard, J. K. Sahu, and J. Nilsson, “Cladding pumped Raman fiber amplifier for high-gain, high energy single-stage amplification,” in Optical Fiber Communications Technical Digest (Institute of Electrical and Electronics Engineers, 2005).
2. C. A. Codemard, P. Dupriez, Y. Jeong, J. K. Sahu, M. Ibsen, and J. Nilsson, “High-power continuous-wave cladding-pumped Raman fiber laser,” Opt. Lett. 31, 2290–2292 (2006). [CrossRef] [PubMed]
3. C. A. Codemard, J. K. Sahu, and J. Nilsson, “High-brightness, pulsed, cladding-pumped Raman fiber source at 1660 nm,” in Conference on Lasers and Electro-Optics, (Optical Society of America, 2007).
4. A. K. Sridharan, J. E. Heebner, M. J. Messerly, J. W. Dawson, R. J. Beach, and C. P. J. Barty, “Brightness enhancement in a high-peak-power cladding-pumped Raman fiber amplifier,” Opt. Lett. 34, 2234–2236 (2009). [CrossRef] [PubMed]
5. C. Headley, and G. P. Agrawal, Raman Amplification in Fiber Optical Communication Systems (Academic Press, Amsterdam, 2004).
6. J. W. Dawson, M. J. Messerly, R. J. Beach, M. Y. Shverdin, E. A. Stappaerts, A. K. Sridharan, P. H. Pax, J. E. Heebner, C. W. Siders, and C. P. J. Barty, “Analysis of the scalability of diffraction-limited fiber lasers and amplifiers to high average power,” Opt. Express 16, 13240–13266 (2008). [CrossRef] [PubMed]
7. A. K. Sridharan, P. H. Pax, M. J. Messerly, and J. W. Dawson, “High-gain photonic crystal fiber regenerative amplifier,” Opt. Lett. 34, 608–610 (2009). [CrossRef] [PubMed]
8. Y Ernori and S. Namiki, “100nm bandwidth flat gain Raman amplifiers pumped and gain-equalized by 12-wavelength-channel WDM high power laser diodes,” OFC, PD19 (1999).
9. G. P. Agrawal, Nonlinear Fiber optics 3rd ed. San Diego, CA (Academic Press, Amsterdam, 2001).
10. J. Ji, C. A. Codemard, M. Ibsen, J. K. Sahu, and J. Nilsson, “Analysis of the conversion to the first stokes in cladding-pumped fiber raman amplifiers,” IEEE J. Sel. Top. Quantum Electron. 15, 129–139 (2009). [CrossRef]
11. R. G. Smith, “Optical power handling capacity of low loss optical fibers as determined by stimulated Raman and Brillouin scattering,” Appl. Opt. 11, 2489–2494 (1972). [CrossRef] [PubMed]
12. J. Kim, P. Dupriez, C. Codemard, J. Nilsson, and J. K. Sahu, “Suppression of stimulated Raman scattering in a high power Yb-doped fiber amplifier using a W-type core with fundamental mode cut-off,” Opt. Express 14, 5103–5113 (2006). [CrossRef] [PubMed]
13. J. A. Yeung, and A. Yariv, “Theory of cw Raman oscillation in optical fibers,” J. Opt. Soc. Am. 69, 803–807 (1979). [CrossRef]
14. G. L. Keaton, M. A. Arbore, and T. J. Kane, “Optical wavelength filtering apparatus with depressed index claddings,” US patent 6,563,995 (2001).
15. J. S. Kim, C. Codemard, Y. Jeong, J. Nilsson, and J. K. Sahu, “High Power Continuous-Wave Yb-Doped Fiber Laser with True Single-Mode Output Using W-Type Structure,” in Conference on Lasers and Electro-Optics, (Optical Society of America, 2006).
16. M. D. Feit, and J. A. Fleck, “Computation of mode properties in optical fiber waveguides by a propagating beam method,” Appl. Opt. 19, 1154–1164 (1980). [CrossRef] [PubMed]
17. M. Heiblum, and J. H. Harris, “Analysis of curved optical waveguides by conformal transformation,” J. Quantum Electron. 11, 75–83 (1975). [CrossRef]
18. D. Marcuse, “Field deformation and loss caused by curvature of optical fibers,” J. Opt. Soc. Am. 66, 311–320 (1976). [CrossRef]

Appl. Opt.

• R. G. Smith, “Optical power handling capacity of low loss optical fibers as determined by stimulated Raman and Brillouin scattering,” Appl. Opt. 11, 2489–2494 (1972). [CrossRef] [PubMed]
• M. D. Feit, and J. A. Fleck, “Computation of mode properties in optical fiber waveguides by a propagating beam method,” Appl. Opt. 19, 1154–1164 (1980). [CrossRef] [PubMed]

IEEE J. Sel. Top. Quantum Electron.

• J. Ji, C. A. Codemard, M. Ibsen, J. K. Sahu, and J. Nilsson, “Analysis of the conversion to the first stokes in cladding-pumped fiber raman amplifiers,” IEEE J. Sel. Top. Quantum Electron. 15, 129–139 (2009). [CrossRef]

J. Opt. Soc. Am.

• J. A. Yeung, and A. Yariv, “Theory of cw Raman oscillation in optical fibers,” J. Opt. Soc. Am. 69, 803–807 (1979). [CrossRef]
• D. Marcuse, “Field deformation and loss caused by curvature of optical fibers,” J. Opt. Soc. Am. 66, 311–320 (1976). [CrossRef]

J. Quantum Electron.

• M. Heiblum, and J. H. Harris, “Analysis of curved optical waveguides by conformal transformation,” J. Quantum Electron. 11, 75–83 (1975). [CrossRef]

Opt. Express

• J. Kim, P. Dupriez, C. Codemard, J. Nilsson, and J. K. Sahu, “Suppression of stimulated Raman scattering in a high power Yb-doped fiber amplifier using a W-type core with fundamental mode cut-off,” Opt. Express 14, 5103–5113 (2006). [CrossRef] [PubMed]
• J. W. Dawson, M. J. Messerly, R. J. Beach, M. Y. Shverdin, E. A. Stappaerts, A. K. Sridharan, P. H. Pax, J. E. Heebner, C. W. Siders, and C. P. J. Barty, “Analysis of the scalability of diffraction-limited fiber lasers and amplifiers to high average power,” Opt. Express 16, 13240–13266 (2008). [CrossRef] [PubMed]

Opt. Lett.

• A. K. Sridharan, P. H. Pax, M. J. Messerly, and J. W. Dawson, “High-gain photonic crystal fiber regenerative amplifier,” Opt. Lett. 34, 608–610 (2009). [CrossRef] [PubMed]
• C. A. Codemard, P. Dupriez, Y. Jeong, J. K. Sahu, M. Ibsen, and J. Nilsson, “High-power continuous-wave cladding-pumped Raman fiber laser,” Opt. Lett. 31, 2290–2292 (2006). [CrossRef] [PubMed]
• A. K. Sridharan, J. E. Heebner, M. J. Messerly, J. W. Dawson, R. J. Beach, and C. P. J. Barty, “Brightness enhancement in a high-peak-power cladding-pumped Raman fiber amplifier,” Opt. Lett. 34, 2234–2236 (2009). [CrossRef] [PubMed]

Other

• C. Headley, and G. P. Agrawal, Raman Amplification in Fiber Optical Communication Systems (Academic Press, Amsterdam, 2004).
• C. A. Codemard, J. K. Sahu, and J. Nilsson, “High-brightness, pulsed, cladding-pumped Raman fiber source at 1660 nm,” in Conference on Lasers and Electro-Optics, (Optical Society of America, 2007).
• Y Ernori and S. Namiki, “100nm bandwidth flat gain Raman amplifiers pumped and gain-equalized by 12-wavelength-channel WDM high power laser diodes,” OFC, PD19 (1999).
• G. P. Agrawal, Nonlinear Fiber optics 3rd ed. San Diego, CA (Academic Press, Amsterdam, 2001).
• C. A. Codemard, J. K. Sahu, and J. Nilsson, “Cladding pumped Raman fiber amplifier for high-gain, high energy single-stage amplification,” in Optical Fiber Communications Technical Digest (Institute of Electrical and Electronics Engineers, 2005).
• G. L. Keaton, M. A. Arbore, and T. J. Kane, “Optical wavelength filtering apparatus with depressed index claddings,” US patent 6,563,995 (2001).
• J. S. Kim, C. Codemard, Y. Jeong, J. Nilsson, and J. K. Sahu, “High Power Continuous-Wave Yb-Doped Fiber Laser with True Single-Mode Output Using W-Type Structure,” in Conference on Lasers and Electro-Optics, (Optical Society of America, 2006).

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