Abstract

A new class of optical fiber, the SHARC fiber, is analyzed in a high-power fiber amplifier geometry using the gain-filtering properties of confined-gain dopants. The high-aspect-ratio (~30:1) rectangular core allows mode-area scaling well beyond 10,000 μm2, which is critical to high-pulse-energy or narrow-linewidth high-power fiber amplifiers. While SHARC fibers offer modally dependent edge loss at the wide “semi-guiding” edge of the waveguide, the inclusion of gain filtering adds further modal discrimination arising from the variation of the spatial overlap of the gain with the various modes. Both methods are geometric in form, such that the combination provides nearly unlimited scalability in mode area. Simulations show that for kW-class fiber amplifiers, only the fundamental mode experiences net gain (15 dB), resulting in outstanding beam quality. Further, misalignment of the seed beam due to offset, magnification, and tilt are shown to result in a small (few percent) efficiency penalty while maintaining kW-level output with 99% of the power in the fundamental mode for all cases.

© 2012 OSA

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References

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2012 (1)

2011 (3)

2010 (4)

2009 (1)

J. R. Marciante, “Gain filtering for single-spatial-mode operation of large-mode-area fiber amplifiers,” IEEE J. Sel. Top. Quantum Electron.15(1), 30–36 (2009).
[CrossRef]

2007 (1)

2006 (4)

2005 (1)

2002 (1)

2000 (2)

1997 (1)

H. W. Bruesselbach, D. S. Sumida, R. A. Reeder, and R. W. Byren, “Low-heat high-power scaling using InGaAs diode-pumped Yb:YAG lasers,” IEEE J. Sel. Top. Quantum Electron.3(1), 105–116 (1997).
[CrossRef]

1992 (1)

G. R. Hadley, “Transparent boundary condition for the beam propagation method,” IEEE J. Quantum Electron.28(1), 363–370 (1992).
[CrossRef]

1991 (1)

J. Yamauchi, T. Ando, and H. Nakano, “Beam propagation analysis of optical fibres by alternating direction implicit method,” Electron. Lett.27(18), 1663–1666 (1991).
[CrossRef]

1990 (1)

Y. Chung and N. Dagli, “An assessment of finite difference beam propagation method,” IEEE J. Quantum Electron.26(8), 1335–1339 (1990).
[CrossRef]

Ando, T.

J. Yamauchi, T. Ando, and H. Nakano, “Beam propagation analysis of optical fibres by alternating direction implicit method,” Electron. Lett.27(18), 1663–1666 (1991).
[CrossRef]

Beach, R. J.

Bhutta, T.

Broeng, J.

Bruesselbach, H. W.

H. W. Bruesselbach, D. S. Sumida, R. A. Reeder, and R. W. Byren, “Low-heat high-power scaling using InGaAs diode-pumped Yb:YAG lasers,” IEEE J. Sel. Top. Quantum Electron.3(1), 105–116 (1997).
[CrossRef]

Byren, R. W.

H. W. Bruesselbach, D. S. Sumida, R. A. Reeder, and R. W. Byren, “Low-heat high-power scaling using InGaAs diode-pumped Yb:YAG lasers,” IEEE J. Sel. Top. Quantum Electron.3(1), 105–116 (1997).
[CrossRef]

Carstens, H.

Chen, X.

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Chung, Y.

Y. Chung and N. Dagli, “An assessment of finite difference beam propagation method,” IEEE J. Quantum Electron.26(8), 1335–1339 (1990).
[CrossRef]

Clarkson, W. A.

Dagli, N.

Y. Chung and N. Dagli, “An assessment of finite difference beam propagation method,” IEEE J. Quantum Electron.26(8), 1335–1339 (1990).
[CrossRef]

Dajani, I.

C. M. Zeringue, I. Dajani, and G. T. Moore, “Suppression of stimulated Brillouin scattering in optical fibers through phase-modulation: a time dependent model,” Proc. SPIE7914, 791409 (2011).
[CrossRef]

Deguil-Robin, N.

Demeritt, J.

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Dimarcello, F. V.

Dong, L.

Eidam, T.

Fini, J. M.

Ghalmi, S.

Goldberg, L.

Goodno, G. D.

Gray, S.

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Hadley, G. R.

G. R. Hadley, “Transparent boundary condition for the beam propagation method,” IEEE J. Quantum Electron.28(1), 363–370 (1992).
[CrossRef]

Hädrich, S.

Jakobsen, C.

Jansen, F.

Jauregui, C.

Jiang, Z.

Kliner, D. A. V.

Koplow, J. P.

Li, J.

Li, M.-J.

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Liem, A.

Limpert, J.

Mackenzie, J. I.

Manek-Hönninger, I.

Marciante, J. R.

McComb, T. S.

McNaught, S. J.

Monberg, E.

Moore, G. T.

C. M. Zeringue, I. Dajani, and G. T. Moore, “Suppression of stimulated Brillouin scattering in optical fibers through phase-modulation: a time dependent model,” Proc. SPIE7914, 791409 (2011).
[CrossRef]

Nakano, H.

J. Yamauchi, T. Ando, and H. Nakano, “Beam propagation analysis of optical fibres by alternating direction implicit method,” Electron. Lett.27(18), 1663–1666 (1991).
[CrossRef]

Nicholson, J. W.

Nilsson, J.

Nolte, S.

Osgood, R. M.

Peng, X.

Petersson, A.

Ramachandran, S.

Rao, H.

Reeder, R. A.

H. W. Bruesselbach, D. S. Sumida, R. A. Reeder, and R. W. Byren, “Low-heat high-power scaling using InGaAs diode-pumped Yb:YAG lasers,” IEEE J. Sel. Top. Quantum Electron.3(1), 105–116 (1997).
[CrossRef]

Richardson, D. J.

Rockwell, D. A.

Roides, R. G.

Röser, F.

Rothenberg, J. E.

Rothhardt, J.

Ruffin, A. B.

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Salin, F.

Sarangan, A. M.

Scarmozzino, R.

Schreiber, T.

Shepherd, D. P.

Shkunov, V. V.

Smith, R. C. G.

Steel, M. J.

Stutzki, F.

Sumida, D. S.

H. W. Bruesselbach, D. S. Sumida, R. A. Reeder, and R. W. Byren, “Low-heat high-power scaling using InGaAs diode-pumped Yb:YAG lasers,” IEEE J. Sel. Top. Quantum Electron.3(1), 105–116 (1997).
[CrossRef]

Thielen, P. A.

Tünnermann, A.

Walton, D.

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Wang, J.

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Weber, M. E.

Wickham, M. G.

Wisk, P.

Yamauchi, J.

J. Yamauchi, T. Ando, and H. Nakano, “Beam propagation analysis of optical fibres by alternating direction implicit method,” Electron. Lett.27(18), 1663–1666 (1991).
[CrossRef]

Yan, M. F.

Zellmer, H.

Zenteno, L.

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Zeringue, C. M.

C. M. Zeringue, I. Dajani, and G. T. Moore, “Suppression of stimulated Brillouin scattering in optical fibers through phase-modulation: a time dependent model,” Proc. SPIE7914, 791409 (2011).
[CrossRef]

Zuegel, J. D.

Appl. Opt. (1)

Electron. Lett. (1)

J. Yamauchi, T. Ando, and H. Nakano, “Beam propagation analysis of optical fibres by alternating direction implicit method,” Electron. Lett.27(18), 1663–1666 (1991).
[CrossRef]

IEEE J. Quantum Electron. (2)

G. R. Hadley, “Transparent boundary condition for the beam propagation method,” IEEE J. Quantum Electron.28(1), 363–370 (1992).
[CrossRef]

Y. Chung and N. Dagli, “An assessment of finite difference beam propagation method,” IEEE J. Quantum Electron.26(8), 1335–1339 (1990).
[CrossRef]

IEEE J. Sel. Top. Quantum Electron. (2)

H. W. Bruesselbach, D. S. Sumida, R. A. Reeder, and R. W. Byren, “Low-heat high-power scaling using InGaAs diode-pumped Yb:YAG lasers,” IEEE J. Sel. Top. Quantum Electron.3(1), 105–116 (1997).
[CrossRef]

J. R. Marciante, “Gain filtering for single-spatial-mode operation of large-mode-area fiber amplifiers,” IEEE J. Sel. Top. Quantum Electron.15(1), 30–36 (2009).
[CrossRef]

J. Lightwave Technol. (2)

J. Opt. Soc. Am. B (3)

Opt. Express (5)

Opt. Lett. (4)

Proc. SPIE (2)

C. M. Zeringue, I. Dajani, and G. T. Moore, “Suppression of stimulated Brillouin scattering in optical fibers through phase-modulation: a time dependent model,” Proc. SPIE7914, 791409 (2011).
[CrossRef]

D. Walton, S. Gray, J. Wang, M.-J. Li, X. Chen, A. B. Ruffin, J. Demeritt, and L. Zenteno, “High power, narrow linewidth fiber lasers,” Proc. SPIE6102, 610205 (2006).
[CrossRef]

Other (5)

OFS Laboratories has fabricated a SHARC fiber with refractive-index uniformity of 200 ppm across the core width (Private communications with D. J. Trevor, OFS Laboratories, 2012).

P. D. Dragic, C.-H. Liu, G. C. Papen, and A. Galvanauskas, “Optical fiber with an acoustic guiding layer for stimulated Brillouin scattering suppression,” CLEO 2006, paper CThZ3.

C. Liu, G. Chang, N. Litchinitser, A. Galvanauskas, D. Guertin, N. Jabobson, and K. Tankala, “Effectively Single-Mode Chirally-Coupled Core Fiber,” ASSP 2007, paper ME2.

M. Born and E. Wolf, Principles of Optics, 6th ed. (Permagon Press, 1991), pp 127–128.

J. Oh, C. Headley, M. J. Andrejco, A. D. Yablon, and D. J. DiGiovanni, “Increased pulsed amplifier efficiency by manipulating the fiber dopant distribution,” CLEO 2006, paper CTuQ3.

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Figures (12)

Fig. 1
Fig. 1

Schematic of semi-guiding high-aspect-ratio core (SHARC) fiber in coiled configuration (not to scale). Expansion shows the schematic cross section of a SHARC fiber and the relative orientation of the fiber core with respect to the coil. The central slow-axis region of the core is doped with ytterbium to provide spatially confined gain when pumped. Similar to the definition used for semiconductor lasers, the fast and slow axes of the SHARC fiber are indicated in the figure.

Fig. 2
Fig. 2

Depiction of spatial gain saturation in fiber amplifiers: (top) conventional core filled with gain dopants; (bottom) gain-filtered fiber where only the center of the core is filled with gain dopants. Progression shows the fundamental mode with the unsaturated gain distribution (left), the saturated gain profile due to the fundamental mode, and the overlap of the next higher-order mode with the saturated gain profile (right). Red depicts the gain distribution, the black curves depict the mode of interest, and the blue curves depict the refractive index profile of the core, which is the same for all cases.

Fig. 3
Fig. 3

Relative differential gain of various slow-axis SHARC fiber modes as a function of gain width for various saturation levels (noted in figure) for flat-top (left) and Gaussian (right) gain profiles. The dashed line represents the normalized gain of the fundamental mode. The colored curves represent the higher-order modes as labeled in the top-left figure.

Fig. 4
Fig. 4

Net gain/loss analytically calculated for the first five modes as a function of the of the slow-axis cladding index step (cladding index minus core index) for an 80%-efficient, 1-kW, gain-filtered SHARC fiber amplifier using the parameters listed in Table 1 and a small-signal gain of 18.7 dB/m. The shaded region indicates the slow-axis index step for which only the fundamental mode experiences net gain through the length of the amplifier.

Fig. 5
Fig. 5

Slow-axis intensity profile along the propagation axis of the gain-filtered SHARC fiber amplifier. A uniform (flat-top) intensity profile is launched into the core of the fiber at the left side of the figure. In this and all subsequent propagation plots, the slow-axis edges of the waveguide are shown as horizontal dashed yellow lines, and the dimensions of the frame are 600 μm (vertical) × 2 m (horizontal) and are not shown to relative scale.

Fig. 6
Fig. 6

Waveguide and ytterbium doping cross-sections (top) relative to the transverse profiles of the first five fiber modes. The dashed lines denote the slow-axis edges of the waveguide and ytterbium doping regions. The dimensions of the frames are 56 μm (vertical) × 600 µm (horizontal) and are not shown to relative scale.

Fig. 7
Fig. 7

Net gain for the first five SHARC fiber modes calculated from BPM simulations (red) and the analytic model presented in Section 3 (blue).

Fig. 8
Fig. 8

(a) Higher-order mode content of the amplifier output (red) and reduction in amplifier efficiency (blue) as a function of the offset of the injected seed beam in the slow-axis direction, also cast as fundamental-mode launch efficiency (top horizontal axis). (b) Slow-axis intensity profile along the propagation axis for a fundamental-mode-matching Gaussian seed beam that is injected at the left side of the figure with a 120-µm offset in the slow-axis dimension.

Fig. 9
Fig. 9

(a) Higher-order mode content of the amplifier output (red) and reduction in amplifier efficiency (blue) as a function of magnification of the injected seed beam in the slow-axis direction, also cast as fundamental-mode launch efficiency (top horizontal axis). (b) Slow-axis intensity profile along the propagation axis for a Gaussian seed beam that is injected at the left side of the figure and is de-magnified in the slow-axis dimension to 0.65x the size that would match the fundamental mode.

Fig. 10
Fig. 10

(a) Higher-order mode content of the amplifier output (red) and reduction in amplifier efficiency (blue) as a function of relative angular misalignment of the injected seed beam in the slow-axis direction, also cast as fundamental-mode launch efficiency (top horizontal axis). The angular misalignment is normalized to the diffraction-limited far-field width of the fundamental mode. (b) Slow-axis intensity profile along the propagation axis for a Gaussian seed beam that is injected at the left side of the figure with a slow-axis angular tilt that is 1.5x greater than the diffraction-limited beam divergence of the fundamental mode.

Fig. 11
Fig. 11

Schematic diagram indicating a signal coupler spliced between an LMA fiber preamplifier and a SHARC fiber power amplifier without any free-space optics. The coupler is a passive SHARC-like fiber waveguide that propagates the signal from the LMA to the SHARC unchanged in the fast-axis dimension (perpendicular to the plane of the figure). In the slow-axis dimension, the coupler functions as a planar quarter-pitch GRIN lens, which expands the signal beam to match the SHARC slow-axis mode and collimates the signal as it enters the SHARC fiber. The red curves indicate the wavefront of the beam (propagating from left to right) while the dashed gray line indicates the classical GRIN ray trajectory path.

Fig. 12
Fig. 12

Schematic of SHARC pump coupler, which injects pump power into the thin edges of the SHARC fiber at an angle relative to the fiber axis, but well within the fiber NA. Signal claddings shown to the left guide the signal in the narrow dimension as it propagates from one section of active fiber to the next. Relative dimensions are not to scale.

Tables (2)

Tables Icon

Table 1 Parameters used to Derive Small Signal Gain Parameter

Tables Icon

Table 2 Computation Parameters used in Simulations

Equations (5)

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g k ( z ) = [ g s s ( x ) 1 + I 0 ( x , z ) / I s a t ] | Φ k ( x ) | 2 d x
d P k d z = g k ( z ) P k α k P k
I s a t m o d ( z ) = I s a t [ 1 + I p u m p ( z ) / I s a t p ]
α k = ( 1 + k ) 2 ( λ 2 n 0 w 3 ) Im ( n 0 2 n 1 2 ) | n 0 2 n 1 2 |
E ( x , y , z ) z = i 2 k 0 n c o T 2 E + i k 0 [ n 2 ( x , y ) n c o 2 2 n c o ] E + 1 2 [ g s s ( x , y ) 1 + | E | 2 / I s a t ] E

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