Abstract

Spatially resolved spectral interferometry is used to measure the mode content of a Yb-doped photonic-crystal fiber rod amplifier with a 2300μm2 mode area. The technique, known as S2 imaging, was adapted for the short fiber amplifier at full power and revealed a small amount of a copolarized LP11 mode. Simulations illustrate the potential for weak mode suppression in this fiber and agree qualitatively with the measurements of S2 and M2. Higher-order-mode content depends on the alignment of the input signal at injection and ranged from 18dB for optimized alignment to 13dB when the injection alignment was offset along the LP11 axis by 30% of the 55μm mode-field diameter.

© 2011 Optical Society of America

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References

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    [Crossref]
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2009 (1)

J. W. Nicholson, A. D. Yablon, J. M. Fini, and M. D. Mermelstein, “Measuring the modal content of large-mode-area fibers,” IEEE J. Sel. Top. Quantum Electron. 15, 61–70 (2009).
[Crossref]

2008 (2)

2007 (2)

2006 (1)

2005 (1)

2004 (1)

Albin, S.

Broeng, J.

Eidam, J.

Eidam, T.

Fini, J. M.

J. W. Nicholson, A. D. Yablon, J. M. Fini, and M. D. Mermelstein, “Measuring the modal content of large-mode-area fibers,” IEEE J. Sel. Top. Quantum Electron. 15, 61–70 (2009).
[Crossref]

Ghalmi, S.

Guo, S.

Hansen, K. P.

Jakobsen, C.

Li, H.

Li, L.

Limpert, J.

Mafi, A.

Mansuripur, M.

Mermelstein, M. D.

J. W. Nicholson, A. D. Yablon, J. M. Fini, and M. D. Mermelstein, “Measuring the modal content of large-mode-area fibers,” IEEE J. Sel. Top. Quantum Electron. 15, 61–70 (2009).
[Crossref]

Moloney, J. V.

Morrell, M. M.

Nicholson, J. W.

J. W. Nicholson, A. D. Yablon, J. M. Fini, and M. D. Mermelstein, “Measuring the modal content of large-mode-area fibers,” IEEE J. Sel. Top. Quantum Electron. 15, 61–70 (2009).
[Crossref]

J. W. Nicholson, A. D. Yablon, S. Ramachandran, and S. Ghalmi, “Spatially and spectrally resolved imaging of modal content in large-mode-area fibers,” Opt. Express 16, 7233–7243 (2008).
[Crossref] [PubMed]

Peyghambarian, N.

Polynkin, P.

Ramachandran, S.

Rogowski, R. S.

Röser, F.

Rothhardt, J.

Sabet, S.

Schimpf, D. N.

Schmidt, O.

Schülzgen, A.

Tai, H.

Temyanko, V. L.

Tünnermann, A.

Wielandy, S.

Wu, F.

Yablon, A. D.

J. W. Nicholson, A. D. Yablon, J. M. Fini, and M. D. Mermelstein, “Measuring the modal content of large-mode-area fibers,” IEEE J. Sel. Top. Quantum Electron. 15, 61–70 (2009).
[Crossref]

J. W. Nicholson, A. D. Yablon, S. Ramachandran, and S. Ghalmi, “Spatially and spectrally resolved imaging of modal content in large-mode-area fibers,” Opt. Express 16, 7233–7243 (2008).
[Crossref] [PubMed]

Yoda, H.

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

J. W. Nicholson, A. D. Yablon, J. M. Fini, and M. D. Mermelstein, “Measuring the modal content of large-mode-area fibers,” IEEE J. Sel. Top. Quantum Electron. 15, 61–70 (2009).
[Crossref]

J. Lightwave Technol. (1)

Opt. Express (4)

Opt. Lett. (2)

Supplementary Material (1)

» Media 1: AVI (1375 KB)     

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Figures (9)

Fig. 1
Fig. 1

Experimental setup. EFM image shows the signal beam at injection, aligned between the two SAP regions that are backlit by the pump.

Fig. 2
Fig. 2

(a) Integrated amplified spectrum. (b) Spatially resolved spectra, after normalization with the integrated spectrum, at locations of low- and high-fringe visibility (blue and red, respectively). (c) Corresponding Fourier transform magnitudes, with dashed line showing the location of the LP 11 signal.

Fig. 3
Fig. 3

(a) Input beam, as measured using the 8 bit EFM CCD camera after reflecting off the fiber face. (b) Output beam as measured using a 12 bit CCD. [(c),(d)] Modes reconstructed using the S 2 technique. The two markers in (d) correspond to the sample locations A and B for data in Fig. 2.

Fig. 4
Fig. 4

Images of the normalized field distributions for each mode. The measurement shows the expected π phase shift between the two lobes of the LP 11 mode.

Fig. 5
Fig. 5

(a) Media 1 showing spectrally resolved images that are measured by the S 2 technique. The oscillation of the beam in the y direction is due to the wavelength dependence of the phase between the LP 01 and LP 11 modes. (b) Beam centroid in the y direction as a function of wavelength.

Fig. 6
Fig. 6

(a) Model of the rodlike PCF used in simulations, where the pump-guiding double cladding has been removed. (b) Tunneling losses calculated ignoring the outer ring of holes show a narrow regime of moderate HOM suppression ( LP 01 in blue, LP 11 -like modes in red).

Fig. 7
Fig. 7

(a) Simulated double-clad geometry. (b) Fraction of power in the LP 11 mode excited by an offset Gaussian, as a function of offset y. Shows predicted reduction in LP 11 content for 5 dB and 10 dB of suppression. (c)  M 2 for a superposition of calculated LP 01 and LP 11 modes, including 5 dB of LP 11 suppression.

Fig. 8
Fig. 8

Relative power in LP 11 mode versus injection offset. Offset along the (a) x direction (across SAP axis) and (b) the y direction (along SAP axis). Also shown is the gain in decibels as a function of offset.

Fig. 9
Fig. 9

Measured M 2 for injection offsets. Offset in the (a) x direction and (b) y direction. Inset shows the offset direction relative to the orientation of the LP 11 mode.

Equations (6)

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E 2 ( x , y , ω ) = α ( x , y , ω ) E 1 ( x , y , ω ) ,
E 2 ( x , y , ω ) = α ( x , y , ω ) E 1 ( x , y , ω ) exp ( i ω Δ τ G ) .
I ( x , y , ω ) = | E 1 ( x , y , ω ) + E 2 ( x , y , ω ) | 2 = I 1 ( x , y , ω ) [ 1 + | α | 2 + 2 | α | cos ( ω Δ τ G ϕ α ) ] .
f ( x , y ) = 2 | α ¯ | exp ( i ϕ α ) 1 + | α ¯ | 2 ,
α ¯ ( x , y ) = 1 1 4 | f ( x , y ) | 2 2 f ( x , y ) .
P 2 / P 1 = I 2 ( x , y ) d x d y / I 1 ( x , y ) d x d y = I T | α ¯ | 2 / ( 1 + | α ¯ | 2 ) d x d y I T / ( 1 + | α ¯ | 2 ) d x d y .

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