Abstract

We study tapered fiber bundle based beam-combining structures that closely maintain their lowest supermodes in order to optimize the output beam quality. A method for efficiently producing structures with high beam quality is proposed. The method is based on monitoring the output powers of the tapered fiber bundle during fabrication and evaluating the beam properties at the central portion based on symmetry considerations. The method is demonstrated experimentally and supported by theoretical analysis. Several seven-fiber combiner configurations are demonstrated. The obtained beam qualities are close to the theoretical limits, as dictated by the brightness conservation law.

© 2010 Optical Society of America

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References

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  1. V. Gapontsev, D. Gapontsev, N. Platonov, O. Shkurikhin, “2 kW CW ytterbium fiber laser with record diffraction-limited brightness,” in IEEE 2005 Conference on Lasers and Electro Optics (2005), pp. 508.
  2. J. Dawson, M. Messerly, R. Beach, M. Shverdin, E. Stappaerts, A. Sridharan, P. Pax, J. Heebner, C. Siders, C. Barty, “Analysis and scalability of diffraction limited fiber lasers and amplifiers to high average power,” Opt. Express 16, 13240–13266 (2008).
    [CrossRef] [PubMed]
  3. M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
    [CrossRef]
  4. C. Wirth1, O. Schmidt, I. Tsybin, T. Schreiber, T. Peschel, F. Brückner, T. Clausnitzer, J. Limpert, R. Eberhardt, A. Tünnermann, M. Gowin, E. ten Have, K. Ludewigt, M. Jung, “2 kW incoherent beam combining of four narrow-linewidth photonic crystal fiber amplifiers,” Opt. Express 17, 1178–1183 (2009).
    [CrossRef]
  5. T. Y. Fan, “Laser beam combining of high power high radiance sources,” IEEE J. Sel. Top. Quantum Electron. 11, 567–577 (2005).
    [CrossRef]
  6. B. Wang, E. Mies, M. Minden, A. Sanchez, “All-fiber 50 W coherently combined passive laser array,” Opt. Lett. 34, 863–865 (2009).
    [CrossRef] [PubMed]
  7. T. H. Loftus, A. Liu, P. R. Hoffman, A. M. Thomas, M. Norsen, R. Royse, E. Honea, “522 W average power, spectrally beam-combined fiber laser with near diffraction limited beam quality,” Opt. Lett. 32, 349–351 (2007).
    [CrossRef] [PubMed]
  8. A. Carter, B. Samson, “New-technology-advances-applications-for-high-power-fiber-lasers,” in Military & Aerospace Electronics (Nufern, 2005), Vol. 16, Issue 2.
  9. IPG Photonics, “High power fiber lasers for industrial applications,” http://www.ipgphotonics.com/Collateral/Documents/English-US/HP_Brochure.pdf.
  10. OFS, “New all-fiber beam combiner from OFS enables multi-kilowatt laser applications,” www.azooptics.com/details.asp?newsID=8776.
  11. F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
    [CrossRef]
  12. A. Kosterin, V. Temianko, M. Fallahi, M. Mansuripur, “Tapered fiber bundles for combining high power diode lasers,” Appl. Opt. 43, 3893–3900 (2004).
    [CrossRef] [PubMed]
  13. K. Natterman, “Bundle of optical fibers for transmission of electromagnetic radiation of high luminous intensity,” U.S. patent 4,983,014 (October 17, 1991).
  14. A. Wetter, M. Faucher, M. Lovelady, F. Séguin, “Tapered fused-bundle splitter capable of 1kW CW operation,” Proc. SPIE 6453, 645301 (2007), doi: 10.1117/12.700466.
  15. J. D. Love, W. M. Henry, “Quantifying loss minimization in single mode fibre tapers,” Electron. Lett. 22, 912–914 (1986).
    [CrossRef]
  16. F. Payne, C. Hussey, M. Yataki, “Modeling fused single-mode-fibre couplers,” Electron. Lett. 21, 461–462 (1985).
    [CrossRef]
  17. G. Agrawal, Applications of Nonlinear Fiber Optics (Academic, 2001).
  18. K. Okamoto, Fundamentals of Optical Waveguides, 2nd ed. (Academic, 2006).
  19. M. Dietrich, Light Transmission Optics (Van-Nostrand Reinhold, 1982).
  20. R. J. Black, L. Gagnon, R. C. Youngquist, R. H. Wentworth, “Modes of evanescent 3×3 couplers and three-core fibers,” Electron. Lett. 22, 1311–1313 (1986).
    [CrossRef]
  21. A. Yariv, Optical Electronics in Modern Telecommunications (Oxford U. Press, 1997).
  22. A. J. Stevenson, J. D. Love, “Vector modes of six port couplers,” Electron. Lett. 23, 1011–1013 (1987).
    [CrossRef]
  23. T. Tamir, Guided Wave Optoelectronics (Springer-Verlag, 1988).
    [CrossRef]
  24. Y. Shamir, Y. Sintov, M. Shtaif, “Incoherent beam combining of multiple single-mode fiber lasers utilizing fused tapered bundling,” Proc. SPIE 7580, 75801R (2010), doi: 10.1117/12.841720.
    [CrossRef]
  25. R. Zhang, X. Zhang, D. Meiser, H. Giessen, “Mode and group velocity dispersion evolution in the tapered region of a single-mode tapered fiber,” Opt. Express 12, 5840–5849 (2004).
    [CrossRef] [PubMed]
  26. Y. Shamir, Y. Sintov, E. Shafir, M. Shtaif, “Beam quality output of a few mode fiber seeded by a single mode fiber source,” Opt. Lett. 32, 1975–1797 (2009).
  27. A. E. Siegman, “New developments in laser resonators,” Proc. SPIE 1224, 2–14 (1990).
    [CrossRef]

2010 (1)

Y. Shamir, Y. Sintov, M. Shtaif, “Incoherent beam combining of multiple single-mode fiber lasers utilizing fused tapered bundling,” Proc. SPIE 7580, 75801R (2010), doi: 10.1117/12.841720.
[CrossRef]

2009 (3)

2008 (1)

2007 (2)

A. Wetter, M. Faucher, M. Lovelady, F. Séguin, “Tapered fused-bundle splitter capable of 1kW CW operation,” Proc. SPIE 6453, 645301 (2007), doi: 10.1117/12.700466.

T. H. Loftus, A. Liu, P. R. Hoffman, A. M. Thomas, M. Norsen, R. Royse, E. Honea, “522 W average power, spectrally beam-combined fiber laser with near diffraction limited beam quality,” Opt. Lett. 32, 349–351 (2007).
[CrossRef] [PubMed]

2005 (1)

T. Y. Fan, “Laser beam combining of high power high radiance sources,” IEEE J. Sel. Top. Quantum Electron. 11, 567–577 (2005).
[CrossRef]

2004 (3)

1990 (1)

A. E. Siegman, “New developments in laser resonators,” Proc. SPIE 1224, 2–14 (1990).
[CrossRef]

1987 (1)

A. J. Stevenson, J. D. Love, “Vector modes of six port couplers,” Electron. Lett. 23, 1011–1013 (1987).
[CrossRef]

1986 (2)

R. J. Black, L. Gagnon, R. C. Youngquist, R. H. Wentworth, “Modes of evanescent 3×3 couplers and three-core fibers,” Electron. Lett. 22, 1311–1313 (1986).
[CrossRef]

J. D. Love, W. M. Henry, “Quantifying loss minimization in single mode fibre tapers,” Electron. Lett. 22, 912–914 (1986).
[CrossRef]

1985 (1)

F. Payne, C. Hussey, M. Yataki, “Modeling fused single-mode-fibre couplers,” Electron. Lett. 21, 461–462 (1985).
[CrossRef]

Agrawal, G.

G. Agrawal, Applications of Nonlinear Fiber Optics (Academic, 2001).

Ammons, D.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

Anderegg, J.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

Azami, N.

F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
[CrossRef]

Barty, C.

Beach, R.

Black, R. J.

R. J. Black, L. Gagnon, R. C. Youngquist, R. H. Wentworth, “Modes of evanescent 3×3 couplers and three-core fibers,” Electron. Lett. 22, 1311–1313 (1986).
[CrossRef]

Brosnan, S.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

Brückner, F.

Carter, A.

A. Carter, B. Samson, “New-technology-advances-applications-for-high-power-fiber-lasers,” in Military & Aerospace Electronics (Nufern, 2005), Vol. 16, Issue 2.

Cheung, E.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

Clausnitzer, T.

Dawson, J.

Dietrich, M.

M. Dietrich, Light Transmission Optics (Van-Nostrand Reinhold, 1982).

Eberhardt, R.

Epp, P.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

Fallahi, M.

Fan, T. Y.

T. Y. Fan, “Laser beam combining of high power high radiance sources,” IEEE J. Sel. Top. Quantum Electron. 11, 567–577 (2005).
[CrossRef]

Faucher, M.

A. Wetter, M. Faucher, M. Lovelady, F. Séguin, “Tapered fused-bundle splitter capable of 1kW CW operation,” Proc. SPIE 6453, 645301 (2007), doi: 10.1117/12.700466.

F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
[CrossRef]

Gagnon, L.

R. J. Black, L. Gagnon, R. C. Youngquist, R. H. Wentworth, “Modes of evanescent 3×3 couplers and three-core fibers,” Electron. Lett. 22, 1311–1313 (1986).
[CrossRef]

Gapontsev, D.

V. Gapontsev, D. Gapontsev, N. Platonov, O. Shkurikhin, “2 kW CW ytterbium fiber laser with record diffraction-limited brightness,” in IEEE 2005 Conference on Lasers and Electro Optics (2005), pp. 508.

Gapontsev, V.

V. Gapontsev, D. Gapontsev, N. Platonov, O. Shkurikhin, “2 kW CW ytterbium fiber laser with record diffraction-limited brightness,” in IEEE 2005 Conference on Lasers and Electro Optics (2005), pp. 508.

Giessen, H.

Gonthier, F.

F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
[CrossRef]

Gowin, M.

Heebner, J.

Henry, W. M.

J. D. Love, W. M. Henry, “Quantifying loss minimization in single mode fibre tapers,” Electron. Lett. 22, 912–914 (1986).
[CrossRef]

Hoffman, P. R.

Honea, E.

Hussey, C.

F. Payne, C. Hussey, M. Yataki, “Modeling fused single-mode-fibre couplers,” Electron. Lett. 21, 461–462 (1985).
[CrossRef]

Jung, M.

Komine, H.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

Kosterin, A.

Limpert, J.

Liu, A.

Loftus, T. H.

Love, J. D.

A. J. Stevenson, J. D. Love, “Vector modes of six port couplers,” Electron. Lett. 23, 1011–1013 (1987).
[CrossRef]

J. D. Love, W. M. Henry, “Quantifying loss minimization in single mode fibre tapers,” Electron. Lett. 22, 912–914 (1986).
[CrossRef]

Lovelady, M.

A. Wetter, M. Faucher, M. Lovelady, F. Séguin, “Tapered fused-bundle splitter capable of 1kW CW operation,” Proc. SPIE 6453, 645301 (2007), doi: 10.1117/12.700466.

Ludewigt, K.

Mansuripur, M.

Martineau, L.

F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
[CrossRef]

Meiser, D.

Messerly, M.

Mies, E.

Minden, M.

Natterman, K.

K. Natterman, “Bundle of optical fibers for transmission of electromagnetic radiation of high luminous intensity,” U.S. patent 4,983,014 (October 17, 1991).

Norsen, M.

Okamoto, K.

K. Okamoto, Fundamentals of Optical Waveguides, 2nd ed. (Academic, 2006).

Pax, P.

Payne, F.

F. Payne, C. Hussey, M. Yataki, “Modeling fused single-mode-fibre couplers,” Electron. Lett. 21, 461–462 (1985).
[CrossRef]

Peschel, T.

Platonov, N.

V. Gapontsev, D. Gapontsev, N. Platonov, O. Shkurikhin, “2 kW CW ytterbium fiber laser with record diffraction-limited brightness,” in IEEE 2005 Conference on Lasers and Electro Optics (2005), pp. 508.

Royse, R.

Samson, B.

A. Carter, B. Samson, “New-technology-advances-applications-for-high-power-fiber-lasers,” in Military & Aerospace Electronics (Nufern, 2005), Vol. 16, Issue 2.

Sanchez, A.

Schmidt, O.

Schreiber, T.

Seguin, F.

F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
[CrossRef]

Séguin, F.

A. Wetter, M. Faucher, M. Lovelady, F. Séguin, “Tapered fused-bundle splitter capable of 1kW CW operation,” Proc. SPIE 6453, 645301 (2007), doi: 10.1117/12.700466.

Shafir, E.

Y. Shamir, Y. Sintov, E. Shafir, M. Shtaif, “Beam quality output of a few mode fiber seeded by a single mode fiber source,” Opt. Lett. 32, 1975–1797 (2009).

Shamir, Y.

Y. Shamir, Y. Sintov, M. Shtaif, “Incoherent beam combining of multiple single-mode fiber lasers utilizing fused tapered bundling,” Proc. SPIE 7580, 75801R (2010), doi: 10.1117/12.841720.
[CrossRef]

Y. Shamir, Y. Sintov, E. Shafir, M. Shtaif, “Beam quality output of a few mode fiber seeded by a single mode fiber source,” Opt. Lett. 32, 1975–1797 (2009).

Shkurikhin, O.

V. Gapontsev, D. Gapontsev, N. Platonov, O. Shkurikhin, “2 kW CW ytterbium fiber laser with record diffraction-limited brightness,” in IEEE 2005 Conference on Lasers and Electro Optics (2005), pp. 508.

Shtaif, M.

Y. Shamir, Y. Sintov, M. Shtaif, “Incoherent beam combining of multiple single-mode fiber lasers utilizing fused tapered bundling,” Proc. SPIE 7580, 75801R (2010), doi: 10.1117/12.841720.
[CrossRef]

Y. Shamir, Y. Sintov, E. Shafir, M. Shtaif, “Beam quality output of a few mode fiber seeded by a single mode fiber source,” Opt. Lett. 32, 1975–1797 (2009).

Shverdin, M.

Siders, C.

Siegman, A. E.

A. E. Siegman, “New developments in laser resonators,” Proc. SPIE 1224, 2–14 (1990).
[CrossRef]

Sintov, Y.

Y. Shamir, Y. Sintov, M. Shtaif, “Incoherent beam combining of multiple single-mode fiber lasers utilizing fused tapered bundling,” Proc. SPIE 7580, 75801R (2010), doi: 10.1117/12.841720.
[CrossRef]

Y. Shamir, Y. Sintov, E. Shafir, M. Shtaif, “Beam quality output of a few mode fiber seeded by a single mode fiber source,” Opt. Lett. 32, 1975–1797 (2009).

Sridharan, A.

Stappaerts, E.

Stevenson, A. J.

A. J. Stevenson, J. D. Love, “Vector modes of six port couplers,” Electron. Lett. 23, 1011–1013 (1987).
[CrossRef]

Stryckman, D.

F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
[CrossRef]

Tamir, T.

T. Tamir, Guided Wave Optoelectronics (Springer-Verlag, 1988).
[CrossRef]

Temianko, V.

ten Have, E.

Thomas, A. M.

Tsybin, I.

Tünnermann, A.

Villeneuve, A.

F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
[CrossRef]

Wang, B.

Weber, M.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

Wentworth, R. H.

R. J. Black, L. Gagnon, R. C. Youngquist, R. H. Wentworth, “Modes of evanescent 3×3 couplers and three-core fibers,” Electron. Lett. 22, 1311–1313 (1986).
[CrossRef]

Wetter, A.

A. Wetter, M. Faucher, M. Lovelady, F. Séguin, “Tapered fused-bundle splitter capable of 1kW CW operation,” Proc. SPIE 6453, 645301 (2007), doi: 10.1117/12.700466.

Wickham, M.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

Wirth1, C.

Yariv, A.

A. Yariv, Optical Electronics in Modern Telecommunications (Oxford U. Press, 1997).

Yataki, M.

F. Payne, C. Hussey, M. Yataki, “Modeling fused single-mode-fibre couplers,” Electron. Lett. 21, 461–462 (1985).
[CrossRef]

Youngquist, R. C.

R. J. Black, L. Gagnon, R. C. Youngquist, R. H. Wentworth, “Modes of evanescent 3×3 couplers and three-core fibers,” Electron. Lett. 22, 1311–1313 (1986).
[CrossRef]

Zhang, R.

Zhang, X.

Appl. Opt. (1)

Electron. Lett. (4)

J. D. Love, W. M. Henry, “Quantifying loss minimization in single mode fibre tapers,” Electron. Lett. 22, 912–914 (1986).
[CrossRef]

F. Payne, C. Hussey, M. Yataki, “Modeling fused single-mode-fibre couplers,” Electron. Lett. 21, 461–462 (1985).
[CrossRef]

R. J. Black, L. Gagnon, R. C. Youngquist, R. H. Wentworth, “Modes of evanescent 3×3 couplers and three-core fibers,” Electron. Lett. 22, 1311–1313 (1986).
[CrossRef]

A. J. Stevenson, J. D. Love, “Vector modes of six port couplers,” Electron. Lett. 23, 1011–1013 (1987).
[CrossRef]

IEEE J. Sel. Top. Quantum Electron. (1)

T. Y. Fan, “Laser beam combining of high power high radiance sources,” IEEE J. Sel. Top. Quantum Electron. 11, 567–577 (2005).
[CrossRef]

Opt. Express (3)

Opt. Lett. (3)

Proc. SPIE (4)

F. Gonthier, L. Martineau, N. Azami, M. Faucher, F. Seguin, D. Stryckman, A. Villeneuve, “High power all-fiber components: the missing link for high-power fiber lasers,” Proc. SPIE 5335, 266–276 (2004).
[CrossRef]

A. Wetter, M. Faucher, M. Lovelady, F. Séguin, “Tapered fused-bundle splitter capable of 1kW CW operation,” Proc. SPIE 6453, 645301 (2007), doi: 10.1117/12.700466.

A. E. Siegman, “New developments in laser resonators,” Proc. SPIE 1224, 2–14 (1990).
[CrossRef]

Y. Shamir, Y. Sintov, M. Shtaif, “Incoherent beam combining of multiple single-mode fiber lasers utilizing fused tapered bundling,” Proc. SPIE 7580, 75801R (2010), doi: 10.1117/12.841720.
[CrossRef]

Other (11)

T. Tamir, Guided Wave Optoelectronics (Springer-Verlag, 1988).
[CrossRef]

A. Yariv, Optical Electronics in Modern Telecommunications (Oxford U. Press, 1997).

K. Natterman, “Bundle of optical fibers for transmission of electromagnetic radiation of high luminous intensity,” U.S. patent 4,983,014 (October 17, 1991).

G. Agrawal, Applications of Nonlinear Fiber Optics (Academic, 2001).

K. Okamoto, Fundamentals of Optical Waveguides, 2nd ed. (Academic, 2006).

M. Dietrich, Light Transmission Optics (Van-Nostrand Reinhold, 1982).

A. Carter, B. Samson, “New-technology-advances-applications-for-high-power-fiber-lasers,” in Military & Aerospace Electronics (Nufern, 2005), Vol. 16, Issue 2.

IPG Photonics, “High power fiber lasers for industrial applications,” http://www.ipgphotonics.com/Collateral/Documents/English-US/HP_Brochure.pdf.

OFS, “New all-fiber beam combiner from OFS enables multi-kilowatt laser applications,” www.azooptics.com/details.asp?newsID=8776.

V. Gapontsev, D. Gapontsev, N. Platonov, O. Shkurikhin, “2 kW CW ytterbium fiber laser with record diffraction-limited brightness,” in IEEE 2005 Conference on Lasers and Electro Optics (2005), pp. 508.

M. Wickham, J. Anderegg, S. Brosnan, E. Cheung, P. Epp, D. Ammons, H. Komine, M. Weber, “Coherently coupled high power fiber arrays,” in IEEE Digest of the LEOS Summer Topical Meeting (2006), pp. 23–24.
[CrossRef]

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Figures (12)

Fig. 1
Fig. 1

(a) Schematic view of the fabrication process, demonstrated with a seven-SM fiber FTB combiner. The signal shown here is launched into the central fiber. (b) The second stage is cutting the device in the center, having two FTB combiners per one process.

Fig. 2
Fig. 2

Numbering convention in the cases of the (a) three-fiber and (b) seven-fiber combiners shown on a schematic two-dimensional cross-section of the devices.

Fig. 3
Fig. 3

BPM calculation for power oscillations along an adiabatic (a) three-fiber combiner and (b) seven-fiber combiner. The curves correspond to the power in the various cores denoted by C j with j = 1 3 or j = 1 7 consistent with the definitions in Fig. 2. The thin lines qualitatively show the FTB outline.

Fig. 4
Fig. 4

Numerical power tracking along a seven-FTB having a constant waist diameter, in the case of peripheral launch. The FTB’s outline is shown in by the dashed converging and diverging curves. The power levels within the coupled fibers (designated by different gray levels) have complex variations, caused by the multitude of beat lengths. C 1 is the power in the (outer) fiber into which light was injected, whereas C 2 7 are the powers in the other fibers.

Fig. 5
Fig. 5

Schematic of the proposed procedure for optimizing cleavage position. The power readings at the output ports are shown as a function of fiber pulling length. Light is injected into one fiber only (central fiber in the seven-bundle case), while all outputs are monitored. Solid curves show the output power in the core into which the light is injected. Dashed curves show the powers in all other outputs (which are identical). Steps (a)–(d) correspond to the stages of the gradual fusion process. Stage (d) points at the first 2 π (even) power cycle, where the central longitudinal portion (closely) contains solely one H E 11 mode. Mode distortions that may occur as a result of practical imperfections are ignored in this schematic view.

Fig. 6
Fig. 6

Longitudinal evolution of the fundamental H E 11 mode RMS width (dashed curves) as the taper reduces from v = 2 down to zero. The two converging thin slanted lines indicate the core-clad boundary. Below v 0.75 diffraction takes over. In order not to reach an impractical zero taper diameter, the rightmost sections have a constant of 0.25 μ m silica cylinder. Data are based on 1064 nm, 5 μ m   core / 125 μ m clad 0.14 numerical aperture (NA) SM fiber.

Fig. 7
Fig. 7

(a) MFD and the divergence angle θ versus the core down-taper v-numbers, given in the horizontal axis. Below V 3 / 4 the core is ineffective. The slanted lines show the linear taper's diameter, which is proportional to the reducing v-number. (b) The M 2 parameter, i.e., the BPP, normalized to the BPP of a standard Gaussian mode. Data are based on 1064 nm, 5 μ m   core / 125 μ m clad 0.14 NA SM fiber.

Fig. 8
Fig. 8

Numerical calculation (based on BPM computation) of beam quality along three- and seven-port FTB combiners with single fiber launch and linear down-tapered sections. In the three-port case (a), any of the three inputs yield the same pattern. In (b) only the central port is excited. Both in (a) and (b) the lowest values are around 1.15.

Fig. 9
Fig. 9

Beam quality along seven-FTB combiner with linear down-tapered sections. Here one of the outer six fibers is being injected. A rather uniform beam quality is observed. In most sections M 2 is around 3.5.

Fig. 10
Fig. 10

Photograph of the cleaved cross-section of (a) three-fiber and (b) seven-fiber combiners. Both fiber types are of 125 μ m clad. Significant coupling began at a diameter below 60 μ m , where the core v-number is roughly 1. Arrows indicate the preliminary scribe that preceded the cleavage action.

Fig. 11
Fig. 11

Intensity at the output of a three-fiber combiner, imaged into an IR CCD, when only one laser is on. The clover shape outlines the FTB tip, where the circle is the power integration boundary. Roughly one H E 11 mode is observed.

Fig. 12
Fig. 12

Intensity pattern of (a), (b) three- and (c), (d) seven-port combiners. (a) and (c) are the FTB tip near field, while (b) and (d) and far field patterns.

Tables (2)

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Table 1 Power Transfer Efficiency and Beam Quality Results with Three-Fiber FTB Combiners

Tables Icon

Table 2 Power Transfer Efficiency and Beam Quality Results with Seven-Fiber FTB Combiners

Equations (4)

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a m ( z ) = j β m ( z ) a m ( z ) + j n = 1 , n m N κ m , n ( z ) a n ( z ) .
M 7 = [ β ( z ) κ ( z ) 0 κ ( z ) 0 0 κ ( z ) κ ( z ) β ( z ) κ ( z ) κ ( z ) 0 0 0 0 κ ( z ) β ( z ) κ ( z ) κ ( z ) 0 0 κ ( z ) κ ( z ) κ ( z ) β ( z ) κ ( z ) κ ( z ) κ ( z ) 0 0 κ ( z ) κ ( z ) β ( z ) κ ( z ) 0 0 0 0 κ ( z ) κ ( z ) β ( z ) κ ( z ) κ ( z ) 0 0 κ ( z ) 0 κ ( z ) β ( z ) ] .
V ̃ 7 × 7 = [ 1 14 2 7 1 2 1 2 1 2 0 1 14 + 2 7 1 6 1 14 2 7 1 2 0 0 1 2 1 14 + 2 7 1 6 1 14 2 7 0 1 2 1 2 1 2 1 14 + 2 7 1 6 ( 7 1 ) 14 2 2 0 0 0 0 ( 1 + 7 ) 14 + 2 2 0 1 14 2 7 1 2 1 2 1 2 0 1 14 + 2 7 1 6 1 14 2 7 1 2 0 0 1 2 1 14 + 2 7 1 6 1 14 2 7 0 1 2 1 2 1 2 1 14 + 2 7 1 6 ] ,
I c = 1 14 [ 1 1 1 8 1 1 1 ] 1 14 [ 1 1 1 6 1 1 1 ] cos ( 2 7 κ z ) ,

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