Abstract

The beam quality factor (or M<sup>2</sup>-parameter) for linearly polarized (LP)-modes of a step-index fiber is calculated in a closed form, as a function of the fiber V-number. It is shown that M<sup>2</sup> sharply peaks for all fiber modes when they are close to cutoff. Particularly simple expressions are derived in the limit V → ∞. Two practically important coherent superpositions of modes are considered for which the degree of degradation of the beam quality due to the higher order mode content is calculated. The reported results can be useful for designing large-core high-power fiber lasers, amplifiers, and fiber-based beam delivery systems, when preservation of the spatial beam quality is important.

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  2. N. Platonov, D. Gapontsev, V. Gapontsev and V. Shumilin, "135 W CW fibre laser with perfect single mode output," in Proc. OSA Conf. Lasers and Electro-Optics, Long Beach, CA, 2002, pp. CPDC3-1-CPDC3-4.
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Other (14)

A. Siegman, Lasers, Mill Valley, CA: Univ. Science, 1986.

N. Platonov, D. Gapontsev, V. Gapontsev and V. Shumilin, "135 W CW fibre laser with perfect single mode output," in Proc. OSA Conf. Lasers and Electro-Optics, Long Beach, CA, 2002, pp. CPDC3-1-CPDC3-4.

J. Nillson, J. Sahu, Y. Jeong, W. Clarkson, R. Selvas, A. Grudinin and S. Alam, "High power fiber lasers: New developments," in Proc. SPIE, vol. 4974, San Jose, CA, 2003, pp. 50-59.

J. Limpert, A. Liem, H. Zellmer and A. Tunnermann, "500 W continuous-wave fibre laser with excellent beam quality," Electron. Lett., vol. 39, no. 8, pp. 645-647, Apr. 2003.

J. Koplow, D. Kliner and L. Goldberg, "Single-mode operation of a coiled multimode fiber amplifier," Opt. Lett., vol. 25, no. 7, pp. 442-444, Apr. 2000.

J. Alvarez-Chavez, A. Grudinin, J. Nilsson, P. Turner and W. Clarkson, "Mode selection in high power cladding pumped fibre lasers with tapered section," in Proc. Conf. Lasers and Electro-Optics, Baltimore, MD, May 23-28 1999,Paper CWE7,. pp. 247-248.

U. Griebner, R. Koch, H. Schonnagel and R. Grunwald, "Efficient laser operation with nearly diffraction-limited output from a diode-pumped heavily Nd-doped multimode fiber," Opt. Lett., vol. 21, no. 4, pp. 266-268, Feb. 1996.

P. A. Belanger, "Beam quality factor of the LP01 mode of the step-index fiber," Opt. Eng., vol. 32, no. 9, pp. 2107-2109, Sep. 1993.

A. E. Siegman, "Defining the effective radius of curvature for a nonideal optical beam," IEEE J. Quantum Electron., vol. 27, no. 5, pp. 1146-1148, May 1991.

T. Okoshi, Optical Fibers, New York: Academic, 1982.

I. S. Gradshteyn and I. M. Ryzhik, Tables of Integrals, Series, and Products, New York: Academic, 1965.

D. Gloge, "Weakly guiding fibers," Appl. Opt., vol. 10, no. 10, pp. 2252-2258, Oct. 1971.

D. Gloge, "Optical power flow in multimode fibers," Bell Syst. Tech. J., vol. 51, no. 8, pp. 1767-1783, Oct. 1972.

D. Marcuse, "Mode conversion in optical fibers with monotonically increasing core radius," J. Lightw. Technol., vol. LT-5, no. 1, pp. 125-133, Jan. 1987.

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