Abstract

We have experimentally demonstrated coherent combining of 2 and then 4 fiber lasers, with respectively 99% and 95% combining efficiency. The combining method investigated here is based on a multi-arm resonator of interferometric configuration. In spite of its interferometric nature, the multi-arm laser operates without significant power fluctuations, even in an unprotected environment. This occurs when the arm length difference is large enough to introduce spectral modulations of period smaller than the laser bandwidth. We have also experimentally shown that the combining method is compatible with wavelength tuning. A Mach-Zehnder Fiber Laser was tuned over a wide spectral range of 60nm Theoretically then, we confirm that the combining method can be scaled to a large number of lasers without decreasing the combining efficiency.

© 2002 Optical Society of America

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References

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Electron. Lett. (2)

D. Sabourdy, V. Kermene, A. Desfarges-Berthelemot, L. Lefort, A. Barthelemy, C. Mahodaux and D. Pureur, "Power scaling of fibre lasers with all-fibre interferometric cavity," Electron. Lett. 38, 692-693 (2002).
[CrossRef]

P. Mollier, V. Armbruster, H. Porte, J.P. Goedgebuer, "Electrically tunable Nd 3+ -doped fibre laser using nematic liquid crystals," Electron. Lett. 31, 1248-1250, (1995).
[CrossRef]

J. Lightwave Technol. (1)

J. Opt. Soc. Am. A (1)

J. Opt. Soc. Am. B (1)

Opt. Commun. (1)

M. Auerbach, D. Wandt, C. Fallnich, H. Welling, S. Unger, "High-power tunable narrow line width ytterbium-doped double-clad fiber laser," Opt. Commun. 195, 437-441, (2001).
[CrossRef]

Opt. Express (2)

Proc. IEEE (1)

P.W. Smith, �??Mode selection in lasers,�?? Proc. IEEE 60, 422-440, (1972).
[CrossRef]

Other (1)

E. Desurvire, D. Bayart, B. Desthieux, S. Bigo, Erbium-Doped Fiber Amplifiers (Wiley, New York, 2002), chap. 4.

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Figures (15)

Fig. 1.
Fig. 1.

Interferometric resonator configurations used for power combining: a) Michelson Fiber Laser (MFL). b) Mach-Zehnder Fiber Laser (MZFL). EDF: Erbium Doped Fiber; FBG: Fiber Bragg Grating.

Fig. 2.
Fig. 2.

Experimental set-up of the Mach-Zehnder Fiber Laser (MZFL)LD1, LD2: 980nm Pump laser diodes; EDF: Erbium doped fiber; CFBG: Chirped fiber Bragg grating @ 1550nm; WDM: Wavelength-division multiplexer; PC: Polarization controller.

Fig. 3.
Fig. 3.

Power characteristics of the different fiber laser configurations: the individual fiber laser (IFL) the Mach-Zehnder fiber laser (MZFL), the 4-arm fiber laser (4AFL) ; Thr: threshold ; ηL: slope efficiency.

Fig. 4.
Fig. 4.

Theoretical and experimental MZFL combining efficiency versus the power ratio (K=P2/P1) in the two arms.

Fig. 5.
Fig. 5.

Spectra of the MZFL obtained with different arm length detuning ΔL.

Fig. 6.
Fig. 6.

Power fluctuations of the MZFL versus the path length difference ΔL compared with those of an Individual Fiber Laser (IFL).

Fig. 7.
Fig. 7.

Experimental set-up of the tunable Mach-Zehnder fiber laser; LD1, LD2: 980nm Pump laser diodes; EDF: Erbium doped fiber; WDM: Wavelength-division multiplexer; PC: Polarization controller.

Fig. 8.
Fig. 8.

Few typical spectra of the tunable Mach-Zehnder fiber laser obtained for five different adjustments of the grating orientation.

Fig. 9.
Fig. 9.

Output power versus laser wavelength. The red curve was obtained by optimizing the output power with the polarization controller at each wavelength, whereas the output power was optimized only at 1550 nm for the blue curve.

Fig. 10.
Fig. 10.

Experimental set-up of the 4-arm fiber laser (4AFL).

Fig. 11.
Fig. 11.

Scheme and nomenclature of a) the Fabry-Perot resonator; b) the Michelson interferometer.

Fig. 12.
Fig. 12.

Scheme and nomenclature of the N-arm interferometer resonator.

Fig. 13
Fig. 13

Calculated intensity spectral response of a 20-arm interferometer resonator with an average length difference ΔL = 10cm.

Fig. 14.
Fig. 14.

Calculated evolution of the highest reflectivity max(ReqN) of the spectral response, as function of the number of arms N for ΔL = 10cm.

Fig. 15.
Fig. 15.

Calculated evolution of the highest reflectivity max(ReqN) of the spectral response, as function of the average arm length difference ΔL.

Equations (7)

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r eq = E 0 r E 0 i = r 0 + r k e j 2 ω L c 1 + r 0 r k e j 2 ω L c
E S 1 i = t s . E k i ; E 1 i = e j ω L 1 c E S 1 i ; E 1 r = r 1 . E 1 i ; E S 1 r = e j ω L 1 c E 1 r
E S 2 i = r s . E k i ; E 2 i = e j ω L 2 c E S 2 i ; E 2 r = r 2 . E 2 i ; E S 2 r = e j ω L 2 c E 2 r
E k r = [ t s 2 . r 1 . e j 2 ω L 1 c + r s 2 . r 2 . e j 2 ω L 2 c ] . E k i
r k 2 = E k r E k i = 1 2 [ r 1 . e j 2 ω L 1 c + r 2 . e j 2 ω L 2 c ]
r kN = 1 N k = 1 N r k . e j 2 ω L k c
r eqN = E 0 r E 0 i = r 0 + r kN e j 2 ω L c 1 + r 0 r kN e j 2 ω L c

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