Abstract

Optical linewidth broadening through both white noise (WNS) and pseudo-random binary sequence (PBRS) phase modulation are effective techniques for suppressing stimulated Brillouin scattering (SBS) in high- power fiber amplifiers. However, detailed studies comparing both coherent beam combining and SBS suppression of these phase modulation schemes have not been reported. In this study, a passive fiber cutback experiment is performed comparing the SBS threshold enhancement factor of a PRBS and WNS broadened seed as a function of linewidth and fiber length. Particularly, assuming an optimal PRBS pattern is chosen, pseudo-random modulation provides superior SBS suppression than WNS for a given fiber length and signal linewidth. Furthermore, two WNS and PRBS modulated 150 W fiber lasers are coherently combined to measure and compare the combining efficiency, beam quality, and coherence as a function of optical path length difference. Notably, the discrete spectral density of PRBS modulation provides a re-coherence effect where the lasers periodically come back into phase. Overall, this may reduce path length matching complexity in coherently combined fiber laser systems.

© 2015 Optical Society of America

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References

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  1. A. Hadjifotiou and G. A. Hill, “Suppression of stimulated Brillouin backscattering by PSK modulation for high-power optical transmission,” IEE Proc., Optoelectron. 133(4), 256–258 (1986).
    [Crossref]
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    [Crossref] [PubMed]
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    [Crossref] [PubMed]
  5. G. D. Goodno, S. J. McNaught, J. E. Rothenberg, T. S. McComb, P. A. Thielen, M. G. Wickham, and M. E. Weber, “Active phase and polarization locking of a 1.4 kW fiber amplifier,” Opt. Lett. 35(10), 1542–1544 (2010).
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    [Crossref]
  8. C. Zeringue, I. Dajani, S. Naderi, G. T. Moore, and C. Robin, “A theoretical study of transient stimulated Brillouin scattering in optical fibers seeded with phase-modulated light,” Opt. Express 20(19), 21196–21213 (2012).
    [Crossref] [PubMed]
  9. V. R. Supradeepa, “Stimulated Brillouin scattering thresholds in optical fibers for lasers linewidth broadened with noise,” Opt. Express 21(4), 4677–4687 (2013).
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  10. T. M. Shay, V. Benham, J. T. Baker, B. Ward, A. D. Sanchez, M. A. Culpepper, D. Pilkington, J. Spring, D. J. Nelson, and C. A. Lu, “First experimental demonstration of self-synchronous phase locking of an optical array,” Opt. Express 14(25), 12015–12021 (2006).
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2014 (1)

2013 (2)

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

V. R. Supradeepa, “Stimulated Brillouin scattering thresholds in optical fibers for lasers linewidth broadened with noise,” Opt. Express 21(4), 4677–4687 (2013).
[Crossref] [PubMed]

2012 (1)

2011 (3)

2010 (1)

2006 (1)

1986 (1)

A. Hadjifotiou and G. A. Hill, “Suppression of stimulated Brillouin backscattering by PSK modulation for high-power optical transmission,” IEE Proc., Optoelectron. 133(4), 256–258 (1986).
[Crossref]

Afzal, R.

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Augst, S. J.

Baker, J. T.

Benham, V.

Brar, K.

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Culpepper, M. A.

Dajani, I.

Fan, T. Y.

Flores, A.

Gitkind, N.

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Goldizen, K. C.

Goodno, G. D.

Hadjifotiou, A.

A. Hadjifotiou and G. A. Hill, “Suppression of stimulated Brillouin backscattering by PSK modulation for high-power optical transmission,” IEE Proc., Optoelectron. 133(4), 256–258 (1986).
[Crossref]

Henrie, J.

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Hill, G. A.

A. Hadjifotiou and G. A. Hill, “Suppression of stimulated Brillouin backscattering by PSK modulation for high-power optical transmission,” IEE Proc., Optoelectron. 133(4), 256–258 (1986).
[Crossref]

Honea, E. C.

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Humphreys, R.

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Jander, D.

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Lanari, A.

Lu, C. A.

McComb, T. S.

McNaught, S. J.

Moore, G. T.

Murphy, D. V.

Naderi, S.

Nelson, D. J.

Pilkington, D.

Redmond, S. M.

Robin, C.

Rothenberg, J. E.

Sanchez, A.

Sanchez, A. D.

Savage-Leuchs, M. P.

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Shay, T. M.

Spring, J.

Supradeepa, V. R.

Thielen, P. A.

Vergien, C.

Ward, B.

Weber, M. E.

Wickham, M. G.

Yu, C. X.

Zeringue, C.

IEE Proc., Optoelectron. (1)

A. Hadjifotiou and G. A. Hill, “Suppression of stimulated Brillouin backscattering by PSK modulation for high-power optical transmission,” IEE Proc., Optoelectron. 133(4), 256–258 (1986).
[Crossref]

Opt. Express (4)

Opt. Lett. (4)

Proc. SPIE (1)

E. C. Honea, R. Afzal, M. P. Savage-Leuchs, N. Gitkind, R. Humphreys, J. Henrie, K. Brar, and D. Jander, “Spectrally beam combined fiber lasers for high power, efficiency, and brightness,” Proc. SPIE 8601, 860115 (2013).
[Crossref]

Other (1)

J. W. Goodman, Statistical Optics, John Wiley & Sons (1985).

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Figures (15)

Fig. 1
Fig. 1 Two beam, actively stabilized coherent beam combining system to measure the coherence of either a WNS or PBRS phase modulated master oscillator (MO).
Fig. 2
Fig. 2 Numerical results (black dots) of SBS threshold enhancement factor vs. normalized modulation frequency for various sinusoidal modulation depths. Solid curves represent best fit for numerical results. Red dots depict experimental data points. The dashed lines are based on analytical solutions.
Fig. 3
Fig. 3 Block diagram of cutback experiment. A single-frequency seed laser is phase modulated and amplified, and the SBS threshold is measured in a passive fiber as a function of optical linewidth, phase modulation type, and fiber length.
Fig. 4
Fig. 4 Left) RF spectrum for a WNS which has been filtered by a 225 MHz low pass filter. Flatness is approximately 2dB, and suppression of higher frequencies is > 40dB. Right) Measured Gaussian spectral distribution of the phase modulated optical signal with a FWHM of 1.0 GHz. The optical bandwidth was measured using a heterodyne measurement with a fast photo-detector and RFSA.
Fig. 5
Fig. 5 Enhancement factor for phase modulation via WNS measured for the cutback experiment using a passive PM 10/125 with fiber length of 1) 70m, 2) 20m, 3) 15m.
Fig. 6
Fig. 6 Block diagram illustrating the master oscillator power amplifier system used to test the SBS threshold. In this case, the cutback was performed on the active fiber (5/130 PM Yb-doped) itself.
Fig. 7
Fig. 7 Enhancement factor measured for the cutback experiment using a WNS for phase modulation. In this case, the cutback was performed on the final stage amplifier which utilized a 5/130 PM Yb-doped fiber.
Fig. 8
Fig. 8 (Left) Illustration of a 23-1 pattern at a clock rate of 1 GHz with the (right) simulated spectral distribution of the phase modulated optical signal.
Fig. 9
Fig. 9 Cutback experiment plots showing the enhancement factor at 70m and 15m using a passive polarization maintaining 10/125 fiber with phase modulation achieved via PRBS patterns 27-1 and 215-1. Experimental data measured at 70m, 27-1 (red); 15m, 27-1 (black); 70m, 215-1 (blue); 15m, 215-1 (green).
Fig. 10
Fig. 10 Enhancement factor as a function of fiber length for ~1.7 GHz WNS and PRBS (27-1 and 215-1) phase modulated systems. A 5/130 PM Yb-doped fiber was utilized for these measurements.
Fig. 11
Fig. 11 (Left) M2 = 1.05 of combined WNS system at 273 W. (Right) M2 = 1.06 of combined PRBS system at 273 W. Insets show corresponding beam profiles.
Fig. 12
Fig. 12 Normalized visibility versus optical path difference for a 4.5 GHz WNS modulated system; experimental result (blue), expected visibility (black).
Fig. 13
Fig. 13 Visibility measurements for the PRBS 29-1 with 4.25 GHz clock rate, or FWHM spectral width of 3.78 GHz; experimental result (blue), expected visibility (black).
Fig. 14
Fig. 14 Simulated visibility vs. OPD for a filtered PRBS set at a clock rate of 4.25 GHz. Also, shown are the plots for an unfiltered PRBS and a WNS.
Fig. 15
Fig. 15 Re-coherence measurements where re-coherence distance can be controlled by modifying the pattern repitition rate. (Left) 23-1 PRBS pattern at 5GHz with re-coherence distance of 420mm. (Right) 23-1 PRBS pattern length at12GHz with re-coherence distance of 175 mm.

Equations (10)

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c n A L z + A L t = i ω γ e 2 n 2 ρ o ρ A s
c n A S z + A S t = i ω γ e 2 n 2 ρ o ρ A L
2 ρ t 2 + ( Γ B 2 i Ω B ) ρ t i Ω B Γ B ρ = ε o γ e q 2 A L A S 2 i Ω B f
A L ( z = 0 , t ) = A L 0 e i φ ( t )
I ( τ ) = I 1 + I 2 + 2 I 1 I 2 | V ( τ ) | cos ( α τ δ )
| V ( τ ) | = | + P S D ( ν ) e i ν τ d ν | = I m a x I m i n I m a x + I m i n
P S D , W N S ( ν ) 2 ln 2 π Δ ν exp [ ( 2 ln 2 v Δ ν ) 2 ]
P S D , P R B S ( ν ) = 1 ν c Sin c 2 ( π ν / ν c )
V W N S ( x ) = e π ( Δ ν ) 2 x 2 4 ln ( 2 ) c 2
V P R B S ( x ) = T r i ( x c ν C )

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