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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 5 — Mar. 1, 2010
  • pp: 4428–4433
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Vector dark domain wall solitons in a fiber ring laser

H. Zhang, D. Y. Tang, L. M. Zhao, and R. J. Knize  »View Author Affiliations


Optics Express, Vol. 18, Issue 5, pp. 4428-4433 (2010)
http://dx.doi.org/10.1364/OE.18.004428


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Abstract

We observe a novel type of vector dark soliton in a fiber ring laser. The vector dark soliton consists of stable localized structures separating the two orthogonal linear polarization eigenstates of the laser emission and is visible only when the total laser emission is measured. Numerical simulations based on the coupled complex Ginzburg-Landau equations have well reproduced the results of the experimental observation.

© 2010 OSA

1. Introduction

Soliton operation of mode locked fiber lasers has been extensively investigated previously. It has been shown that the dynamics of the solitons formed in an anomalous dispersion cavity fiber laser could be well described by the nonlinear Schrödinger equation (NLSE) [1

1. I. N. Iii, “All-fiber ring soliton laser mode locked with a nonlinear mirror,” Opt. Lett. 16(8), 539–541 (1991). [CrossRef] [PubMed]

]. Generally speaking, formation of a soliton in fiber lasers is a result of the mutual nonlinear interaction among the laser gain and losses, cavity dispersion and fiber nonlinearity, as well as the cavity effects. The dynamics of the soliton should be governed by the complex Ginzburg-Landau equation (CGLE) [2

2. N. Akhmediev, J. M. Soto-Crespo, and G. Town, “Pulsating solitons, chaotic solitons, period doubling, and pulse coexistence in mode-locked lasers: complex Ginzburg-Landau equation approach,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 63(5), 056602 (2001). [CrossRef] [PubMed]

]. However, it was noticed that solitons formed in an anomalous dispersion cavity fiber laser normally have a narrow spectral bandwidth, which is far narrower than the laser gain bandwidth. Consequently, no gain bandwidth filtering effect practically exists in the laser, and the effect of laser gain is mainly to balance the cavity losses. It was confirmed experimentally when the effect of spectral filtering on the pulse shaping could no longer be ignored, dynamics of the solitons formed in a fiber laser could not be described by the NLSE but the CGLE [3

3. D. Y. Tang, L. M. Zhao, and B. Zhao, “Soliton collapse and bunched noise-like pulse generation in a passively mode-locked fiber ring laser,” Opt. Express 13(7), 2289–2294 (2005). [CrossRef] [PubMed]

]. Solitons whose dynamics are governed by the CGLE are also called the dissipative solitons. Recently, formation of dissipative solitons in fiber lasers has attracted considerable attention [4

4. H. Zhang, D. Y. Tang, L. M. Zhao, X. Wu, and H. Y. Tam, “Dissipative vector solitons in a dispersionmanaged cavity fiber laser with net positive cavity dispersion,” Opt. Express 17(2), 455–460 (2009). [CrossRef] [PubMed]

].

2. Experimental Setup

Our experiment was conducted on a fiber laser schematically shown in Fig. 1
Fig. 1 Schematic of the experimental setup. EDF: Erbium doped fiber. WDM: wavelength division multiplexer. SMF: single mode fiber. PC: polarization controller. PBS: polarization beam splitter.
. The ring cavity is made of all-anomalous dispersion fibers, consisting of 6.4 m erbium-doped fiber (EDF) with group velocity dispersion (GVD) of 10 (ps/nm)/km and an erbium-ion doping concentration of 2880 ppm, and 5.0 m single mode fiber (SMF) with GVD of 18 (ps/nm)/km. A polarization insensitive isolator was employed in the cavity to force the unidirectional operation of the ring, and an in-line polarization controller (PC) was used to fine-tune the linear cavity birefringence. A 10% fiber coupler was used to output the signal. The laser was pumped by a high power Fiber Raman Laser source of wavelength 1480 nm. An in-line polarization beam splitter (PBS) was used to separate the two orthogonal polarizations of the laser emission, and they were simultaneously measured with two identical 2GHz photo-detectors and monitored in a multi-channel oscilloscope.

3. Experimental results

Figure 3(a)
Fig. 3 Vector dark polarization domain wall soliton emission of the laser. (a) Polarization resolved oscilloscope trace: horizontal axis (upper trace) and vertical axis (lower trace). (b) Total laser emission (upper trace) and one of the polarized laser emissions (lower trace). (c) The corresponding optical spectra.
shows an example of the laser emission measured along two orthogonal polarization directions. It clearly shows that along each polarization direction the laser emitted square pulses, and the square pulses between the two orthogonal polarization directions were antiphase.

Figure 3(b) shows the total laser emission and one of the polarized emissions of the laser under strong pumping. Within one cavity roundtrip time there is one square-pulse along each polarization direction. Associated with the laser emission switching from one polarization to the other, an intensity dip appeared on the total laser emission. The profile of the intensity dip is stable with the cavity roundtrips, and each dip separates the two stable linear polarization states of the laser emission. Figure 3(c) shows the corresponding optical spectra of the laser emissions. Laser emissions along the two orthogonal polarization directions have obvious different wavelengths and spectral distributions, showing that the coupling between the two polarization components is incoherent. In our experiments the cavity birefringence could be altered by rotating the paddles of the PC or carefully bending the cavity fibers, eventually the wavelength separation between the two spectral peaks could be changed. However, independent of the wavelength difference, the intensity dip could always be obtained. Moreover, the width and depth of the dip varied with both the cavity birefringence and the pumping strength. The stronger the pumping, the narrower and deeper is the dip. At even higher pump strength, splitting of the square pulse could occur. Within one cavity roundtrip another square pulse could suddenly appear. The new square pulse was found unstable. It slowly moved in the cavity and eventually merged with the old one.

4. Numerical simulation

The intensity dips possess the characteristics of vector dark PDW soliton predicted by Haelterman and Shepperd [10

10. M. Haelterman and A. P. Sheppard, “Polarization domain walls in diffractive or dispersive Kerr media,” Opt. Lett. 19(2), 96–98 (1994). [CrossRef] [PubMed]

], despite of the fact that the two stable polarization domains are now orthogonal linear polarizations instead of circular polarizations. To confirm that such PDWs could exist in our laser, we further numerically simulated the operation of the laser, using the model as described in [16

16. D. Y. Tang, L. M. Zhao, B. Zhao, and A. Q. Liu, “Mechanism of multisoltion formation and soliton energy quantization in passively mode-locked fiber lasers,” Phys. Rev. A 72(4), 043816 (2005). [CrossRef]

] but with no polarizer in cavity. To make the simulation possibly close to the experimental situation, we used the following parameters: γ=3 W−1km−1, Ωg =16 nm, k″SMF= −23 ps2/km, k″EDF= −13 ps2/km, k′′′= −0.13 ps3/km, Esat=10 pJ, cavity length L= 11.4 m, cavity linear birefringence of Lb=L, where Lb=λ/|nxny|and G=120 km−1. To favor the creation of an incoherently coupled domain wall, a polarization switching between the two orthogonal polarization components of the laser inside the simulation window was set in the initial condition. This corresponds to the initial existence of the linear polarization switching in our laser caused by the laser gain competition and cavity feedback.

A stable PDW soliton separating the two principal linear polarization states of the cavity could be numerically obtained, as shown in Fig. 4
Fig. 4 Polarization domain wall numerically calculated. Evolution of the polarization domain wall with the cavity roundtrips: (a) Horizontal polarization, (b) Vertical axis, (c) Domain wall profiles at particular roundtrip, (d) The vector domain wall soliton and its ellipticity degree at particular roundtrip.
. Figure 4(a) and Fig. 4(b) show the stable propagation of the two linear orthogonal polarization components with the cavity roundtrips. The two polarization components are conjointly trapped in the time domain. Figure 4(c) shows the domain walls along each of the polarizations and Fig. 4(d) is the total laser emission intensity. An intensity dip appears on the total laser intensity and propagates undistorted with the cavity roundtrips. We have also plotted the polarization ellipticity degree of the intensity dip in Fig. 4(d). We adopted the definition of ellipticity degree q= (μ-ν)/ (μ+ν), where q=±1 represents the two orthogonal linearly polarized states and q=0 refers to a circularly polarized state [10

10. M. Haelterman and A. P. Sheppard, “Polarization domain walls in diffractive or dispersive Kerr media,” Opt. Lett. 19(2), 96–98 (1994). [CrossRef] [PubMed]

]. Obviously the intensity dip separates the two linear orthogonal polarization states, suggesting that it is a vector dark PDW soliton. Numerically it was observed that even with very weak cavity birefringence, e.g. Lb=100L, stable PDW soliton could still be obtained. However, if the cavity birefringence becomes too large, e.g. larger than Lb=0.5L, no stable PDWs could be obtained.

Therefore, based on the numerical simulation and the features of the experimental phenomenon, we interpret the intensity dips shown in Fig. 3(c) as a type of vector dark PDW soliton. To understand why the PDWs and vector dark soliton could be formed in our laser, we note that Malomed had once theoretically studied the interaction of two orthogonal linear polarizations in the twisted nonlinear fiber [17

17. B. A. Malomed, “Optical domain walls,” Phys. Rev. E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 50(2), 1565–1571 (1994). [CrossRef] [PubMed]

19

19. B. A. Malomed, “Domain wall between traveling waves,” Phys. Rev. E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 50(5), R3310–R3313 (1994). [CrossRef] [PubMed]

]. It was shown that PDWs between the two orthogonal linear polarizations of the fiber exist, and the fiber twist could even give rise to an effective force driving the domain walls. Considering that both the gain competition and the cavity feedback could have the same role as the fiber twist, e.g. cavity feedback also introduces linear coupling between the two orthogonal cavity polarization modes of a laser [15

15. B. Meziane, F. Sanchez, G. M. Stephan, and P. L. François, “Feedback-induced polarization switching in a Nd-doped fiber laser,” Opt. Lett. 19(23), 1970–1972 (1994). [CrossRef] [PubMed]

], not only the domain walls but also the moving of the domain walls could be explained.

4. Conclusion

In conclusion, we have reported the experimental observation of PDWs and vector dark PDW solitons in a linear birefringence cavity fiber ring laser. The domain walls and solitons are found to separate the two stable orthogonal linear principal polarization states of the laser cavity. We have further shown that the cavity feedback and the gain competition could have played an important role on the formation of such PDWs and the vector dark domain wall solitons.

Acknowledgement

Authors are indebted to Professor Boris A. Malomed, Sergei Turitsyn for useful discussions. This project is supported by the National Research Foundation Singapore under the contract NRF-G-CRP 2007-01.

References and links

1.

I. N. Iii, “All-fiber ring soliton laser mode locked with a nonlinear mirror,” Opt. Lett. 16(8), 539–541 (1991). [CrossRef] [PubMed]

2.

N. Akhmediev, J. M. Soto-Crespo, and G. Town, “Pulsating solitons, chaotic solitons, period doubling, and pulse coexistence in mode-locked lasers: complex Ginzburg-Landau equation approach,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 63(5), 056602 (2001). [CrossRef] [PubMed]

3.

D. Y. Tang, L. M. Zhao, and B. Zhao, “Soliton collapse and bunched noise-like pulse generation in a passively mode-locked fiber ring laser,” Opt. Express 13(7), 2289–2294 (2005). [CrossRef] [PubMed]

4.

H. Zhang, D. Y. Tang, L. M. Zhao, X. Wu, and H. Y. Tam, “Dissipative vector solitons in a dispersionmanaged cavity fiber laser with net positive cavity dispersion,” Opt. Express 17(2), 455–460 (2009). [CrossRef] [PubMed]

5.

C. R. Menyuk, “Stability of solitons in birefringent optical fibers. I: equal propagation amplitudes,” Opt. Lett. 12(8), 614–616 (1987). [CrossRef] [PubMed]

6.

N. N. Akhmediev, A. V. Buryak, J. M. Soto-Crespo, and D. R. Andersen, “Phase-locked stationary soliton states in birefringent nonlinear optical fibers,” J. Opt. Soc. Am. B 12(3), 434–439 (1995). [CrossRef]

7.

S. Trillo, S. Wabnitz, E. M. Wright, and G. I. Stegeman, “Optical solitary waves induced by cross-phase modulation,” Opt. Lett. 13(10), 871–873 (1988). [CrossRef] [PubMed]

8.

D. N. Christodoulides and R. I. Joseph, “Vector solitons in birefringent nonlinear dispersive media,” Opt. Lett. 13(1), 53–55 (1988). [CrossRef] [PubMed]

9.

Y. S. Kivshar and S. K. Turitsyn, “Vector dark solitons,” Opt. Lett. 18(5), 337–339 (1993). [CrossRef] [PubMed]

10.

M. Haelterman and A. P. Sheppard, “Polarization domain walls in diffractive or dispersive Kerr media,” Opt. Lett. 19(2), 96–98 (1994). [CrossRef] [PubMed]

11.

S. Pitois, G. Millot, and S. Wabnitz, “Polarization domain wall solitons with counterpropagating laser beams,” Phys. Rev. Lett. 81(7), 1409–1412 (1998). [CrossRef]

12.

E. Seve, G. Millot, S. Wabnitz, T. Sylvestre, and H. Maillotte, “Generation of vector dark-soliton trains by induced modulational instability in a highly birefringent fiber,” J. Opt. Soc. Am. B 16(10), 1642–1650 (1999). [CrossRef]

13.

C. Milián, D. V. Skryabin, and A. Ferrando, “Continuum generation by dark solitons,” Opt. Lett. 34(14), 2096–2098 (2009). [CrossRef] [PubMed]

14.

Q. L. Williams and R. Roy, “Fast polarization dynamics of an erbium-doped fiber ring laser,” Opt. Lett. 21(18), 1478–1480 (1996). [CrossRef] [PubMed]

15.

B. Meziane, F. Sanchez, G. M. Stephan, and P. L. François, “Feedback-induced polarization switching in a Nd-doped fiber laser,” Opt. Lett. 19(23), 1970–1972 (1994). [CrossRef] [PubMed]

16.

D. Y. Tang, L. M. Zhao, B. Zhao, and A. Q. Liu, “Mechanism of multisoltion formation and soliton energy quantization in passively mode-locked fiber lasers,” Phys. Rev. A 72(4), 043816 (2005). [CrossRef]

17.

B. A. Malomed, “Optical domain walls,” Phys. Rev. E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 50(2), 1565–1571 (1994). [CrossRef] [PubMed]

18.

B. A. Malomed, A. A. Nepomnyashchy, and M. I. Tribelsky, “Domain boundaries in convection patterns,” Phys. Rev. A 42(12), 7244–7263 (1990). [CrossRef] [PubMed]

19.

B. A. Malomed, “Domain wall between traveling waves,” Phys. Rev. E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 50(5), R3310–R3313 (1994). [CrossRef] [PubMed]

OCIS Codes
(060.4370) Fiber optics and optical communications : Nonlinear optics, fibers
(060.5530) Fiber optics and optical communications : Pulse propagation and temporal solitons
(140.3510) Lasers and laser optics : Lasers, fiber

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: December 10, 2009
Revised Manuscript: February 6, 2010
Manuscript Accepted: February 6, 2010
Published: February 18, 2010

Citation
H. Zhang, D. Y. Tang, L. M. Zhao, and R. J. Knize, "Vector dark domain wall solitons in a fiber ring laser," Opt. Express 18, 4428-4433 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-5-4428


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References

  1. I. N. Iii, “All-fiber ring soliton laser mode locked with a nonlinear mirror,” Opt. Lett. 16(8), 539–541 (1991). [CrossRef] [PubMed]
  2. N. Akhmediev, J. M. Soto-Crespo, and G. Town, “Pulsating solitons, chaotic solitons, period doubling, and pulse coexistence in mode-locked lasers: complex Ginzburg-Landau equation approach,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 63(5), 056602 (2001). [CrossRef] [PubMed]
  3. D. Y. Tang, L. M. Zhao, and B. Zhao, “Soliton collapse and bunched noise-like pulse generation in a passively mode-locked fiber ring laser,” Opt. Express 13(7), 2289–2294 (2005). [CrossRef] [PubMed]
  4. H. Zhang, D. Y. Tang, L. M. Zhao, X. Wu, and H. Y. Tam, “Dissipative vector solitons in a dispersionmanaged cavity fiber laser with net positive cavity dispersion,” Opt. Express 17(2), 455–460 (2009). [CrossRef] [PubMed]
  5. C. R. Menyuk, “Stability of solitons in birefringent optical fibers. I: equal propagation amplitudes,” Opt. Lett. 12(8), 614–616 (1987). [CrossRef] [PubMed]
  6. N. N. Akhmediev, A. V. Buryak, J. M. Soto-Crespo, and D. R. Andersen, “Phase-locked stationary soliton states in birefringent nonlinear optical fibers,” J. Opt. Soc. Am. B 12(3), 434–439 (1995). [CrossRef]
  7. S. Trillo, S. Wabnitz, E. M. Wright, and G. I. Stegeman, “Optical solitary waves induced by cross-phase modulation,” Opt. Lett. 13(10), 871–873 (1988). [CrossRef] [PubMed]
  8. D. N. Christodoulides and R. I. Joseph, “Vector solitons in birefringent nonlinear dispersive media,” Opt. Lett. 13(1), 53–55 (1988). [CrossRef] [PubMed]
  9. Y. S. Kivshar and S. K. Turitsyn, “Vector dark solitons,” Opt. Lett. 18(5), 337–339 (1993). [CrossRef] [PubMed]
  10. M. Haelterman and A. P. Sheppard, “Polarization domain walls in diffractive or dispersive Kerr media,” Opt. Lett. 19(2), 96–98 (1994). [CrossRef] [PubMed]
  11. S. Pitois, G. Millot, and S. Wabnitz, “Polarization domain wall solitons with counterpropagating laser beams,” Phys. Rev. Lett. 81(7), 1409–1412 (1998). [CrossRef]
  12. E. Seve, G. Millot, S. Wabnitz, T. Sylvestre, and H. Maillotte, “Generation of vector dark-soliton trains by induced modulational instability in a highly birefringent fiber,” J. Opt. Soc. Am. B 16(10), 1642–1650 (1999). [CrossRef]
  13. C. Milián, D. V. Skryabin, and A. Ferrando, “Continuum generation by dark solitons,” Opt. Lett. 34(14), 2096–2098 (2009). [CrossRef] [PubMed]
  14. Q. L. Williams and R. Roy, “Fast polarization dynamics of an erbium-doped fiber ring laser,” Opt. Lett. 21(18), 1478–1480 (1996). [CrossRef] [PubMed]
  15. B. Meziane, F. Sanchez, G. M. Stephan, and P. L. François, “Feedback-induced polarization switching in a Nd-doped fiber laser,” Opt. Lett. 19(23), 1970–1972 (1994). [CrossRef] [PubMed]
  16. D. Y. Tang, L. M. Zhao, B. Zhao, and A. Q. Liu, “Mechanism of multisoltion formation and soliton energy quantization in passively mode-locked fiber lasers,” Phys. Rev. A 72(4), 043816 (2005). [CrossRef]
  17. B. A. Malomed, “Optical domain walls,” Phys. Rev. E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 50(2), 1565–1571 (1994). [CrossRef] [PubMed]
  18. B. A. Malomed, A. A. Nepomnyashchy, and M. I. Tribelsky, “Domain boundaries in convection patterns,” Phys. Rev. A 42(12), 7244–7263 (1990). [CrossRef] [PubMed]
  19. B. A. Malomed, “Domain wall between traveling waves,” Phys. Rev. E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 50(5), R3310–R3313 (1994). [CrossRef] [PubMed]

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