Abstract

A beam combining technique for producing a single, spatially coherent beam from two mutually incoherent (temporally and spatially) lasers is demonstrated and the spatial coherence properties of the resulting beam are characterized. The technique is based on simultaneous excitation of stimulated Brillouin scattering by two independent lasers operating at two different wavelengths in a long multimode optical fiber. Though spectrally independent, the resulting Stokes beams produce essentially identical intensity distributions corresponding to the fundamental fiber mode.

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References

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  1. B. C. Rodgers, T. H. Russell, and W. B. Roh, "Laser beam combining and cleanup by stimulated Brillouin scattering in a multimode optical fiber," Opt. Lett. 24, 1124-1126 (1999).
    [CrossRef]
  2. H. Hsu, "Multiple scattering processes in nonlinear optics," Proc. of the Symposium on Modern Optics., Polytechnic Institute of Brooklyn, XVII, 357-363 (1967)
  3. Y. Aoki, and K. Tajima, "Stimulated Brillouin scattering in a long single-mode fiber excited with a multimode pump laser," J. Opt. Soc. Am. B. 5, 358-363 (1988).
    [CrossRef]
  4. E. Lichtman, A. A. Friesem, R. G. Waarts, and H. H. Yaffe, "Stimulated Brillouin scattering excited by two pump waves in single-mode fibers," J. Opt. Soc. Am. B. 4, 1397-1403 (1987).
    [CrossRef]
  5. P. Narum, M. D. Skeldon, and R. W. Boyd, "Effect of laser mode structure on stimulated Brillouin scattering," J. of Quantum Electron. QE-22, 2161-2167 (1986).
    [CrossRef]
  6. B. Y. Zel'dovich, N. F. Pilipetskif, and V. V. Shkunov, "Phase conjugation in stimulated scattering," Sov. Phys. Usp. 25, 713-736 (1982).
    [CrossRef]
  7. C. R. Pollock, Fundamentals of Optoelectronics (Irwin, 1995).

Other

B. C. Rodgers, T. H. Russell, and W. B. Roh, "Laser beam combining and cleanup by stimulated Brillouin scattering in a multimode optical fiber," Opt. Lett. 24, 1124-1126 (1999).
[CrossRef]

H. Hsu, "Multiple scattering processes in nonlinear optics," Proc. of the Symposium on Modern Optics., Polytechnic Institute of Brooklyn, XVII, 357-363 (1967)

Y. Aoki, and K. Tajima, "Stimulated Brillouin scattering in a long single-mode fiber excited with a multimode pump laser," J. Opt. Soc. Am. B. 5, 358-363 (1988).
[CrossRef]

E. Lichtman, A. A. Friesem, R. G. Waarts, and H. H. Yaffe, "Stimulated Brillouin scattering excited by two pump waves in single-mode fibers," J. Opt. Soc. Am. B. 4, 1397-1403 (1987).
[CrossRef]

P. Narum, M. D. Skeldon, and R. W. Boyd, "Effect of laser mode structure on stimulated Brillouin scattering," J. of Quantum Electron. QE-22, 2161-2167 (1986).
[CrossRef]

B. Y. Zel'dovich, N. F. Pilipetskif, and V. V. Shkunov, "Phase conjugation in stimulated scattering," Sov. Phys. Usp. 25, 713-736 (1982).
[CrossRef]

C. R. Pollock, Fundamentals of Optoelectronics (Irwin, 1995).

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Figures (9)

Fig. 1:
Fig. 1:

Two beam incoherent combination experimental setup using a multimode fiber.

Fig. 2:
Fig. 2:

Polarimetric Stokes Power vs. Pump Power in mW. (a) SBS Power reflected into a horizontally polarized beam. (b) SBS Power reflected into a vertically polarized beam. (c) Total SBS Power.

Fig. 3:
Fig. 3:

The indicated path of figure 2c shows that the two input beams have separate thresholds.

Fig. 4:
Fig. 4:

SBS Power vs. input power at several different input powers of Laser A. The similarity of each curve indicates that the threshold and the slope efficiency of the SBS process is independent of laser A.

Fig. 5:
Fig. 5:

Dual pump and SBS spectrum generated from a Fabry-Perot interferometer with a free spectral range of 8 GHz.

Fig. 6:
Fig. 6:

Polarimetric spectrum of Laser A.

Fig. 7:
Fig. 7:

Reflected beam overlap. (a) Image of Laser A. Lighter shades indicate higher intensity. (b) Image of Laser B. Darker shades indicate higher intensity. (c) Combined laser beams showing significant mismatch between the reflected positions of laser A and laser B.

Fig. 8:
Fig. 8:

Transmitted beam overlap. (a) Image of Laser A. Lighter shades indicate higher intensity. (b) Image of Laser B. Darker shades indicate higher intensity. (c) Combined laser beams showing significant mismatch between the transmitted positions of laser A and laser B.

Fig. 9:
Fig. 9:

SBS beam overlap. (a) Image of Laser A. Lighter shades indicate higher intensity. (b) Image of Laser B. Darker shades indicate higher intensity. (c) Combined laser beams showing the two SBS beams are nearly coaxial.

Tables (1)

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Table 1. Quantitative measure of beam overlap

Equations (1)

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ε = 1 N i N [ I A ( x i ) I B ( x i ) ] 2

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