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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 6 — Mar. 25, 2013
  • pp: 6777–6782
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Tunable CW all-fiber optical parametric oscillator operating below 1 μm

Ekaterina A. Zlobina, Sergey I. Kablukov, and Sergey A. Babin  »View Author Affiliations


Optics Express, Vol. 21, Issue 6, pp. 6777-6782 (2013)
http://dx.doi.org/10.1364/OE.21.006777


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Abstract

CW all-fiber optical parametric oscillator (FOPO) with tuning range from 950 to 1010 nm is demonstrated using birefringent photonic crystal fiber pumped by an Ytterbium-doped fiber laser (YDFL) near 1 μm. CW parametric generation with spectral linewidth of 3.7 nm at 972 nm has been obtained with slope efficiency as high as 9.4% and output power of up to 460 mW. It is also shown that the FOPO slope efficiency reaches 25% after narrowing of the pump spectrum down to 40 pm. At that the generated power exceeds 1 W, but in this case the generated radiation is modulated with 48 ns period and 50% duty factor due to pump laser power modulation which is probably caused by stimulated Brillouin back scattering.

© 2013 OSA

1. Introduction

In this paper we report on the singly resonant all-fiber OPO based on the birefringent LMA5-PM photonic crystal fiber. It generates laser radiation tunable in the wavelength range of 950 – 1010 nm at pumping by a conventional CW randomly polarized tunable YDFL.

2. Experimental setup

The experimental setup is shown in Fig. 1
Fig. 1 Schematic experimental setup.
. As a pump source we use CW YDFL that is tunable in the range from 1.04 to 1.07 μm and is generating randomly polarized radiation with output power of up to 11 W. The YDFL is pumped by multimode laser diodes and has a ring cavity which is closed by a fused fiber coupler similar to that one demonstrated in paper [14

14. S. A. Babin, S. I. Kablukov, I. S. Shelemba, and A. A. Vlasov, “An interrogator for a fiber Bragg sensor array based on a tunable erbium fiber laser,” Laser Phys. 17(11), 1340–1344 (2007). [CrossRef]

]. Tuning of operating wavelength is realized by an axial compression of a fiber Bragg grating (FBG) described in paper [15

15. S. A. Babin, S. I. Kablukov, and A. A. Vlasov, “Tunable fiber Bragg gratings for application in tunable fiber lasers,” Laser Phys. 17(11), 1323–1326 (2007). [CrossRef]

]. It was found that spectral linewidth of the YDFL Δλp is randomly changed from 30 to 200 pm at the tuning of the FBG back and forth in such mechanical configuration. We were able to obtain fixed value of Δλp after a proper re-adjustment of the FBG. Polarization controller PC1 is used to adjust a polarization state of the pump light, since the parametric process is sensitive to the polarization. The pump is coupled into the FOPO’s ring cavity via a wavelength-division-multiplexing coupler WDM1 and polarization controller PC2 and then propagates in a nonlinear fiber.

3. FOPO spectrum and tunability

Figure 2(a)
Fig. 2 FOPO tuning range with the pump wavelength near the ZDW of the fiber a) Experimental (points) and theoretical (lines) phase matching curves for two polarization modes of the pump; b) The FOPO spectra at tuning of the pump polarized along the slow axis.
shows experimental (points) and theoretical (lines) sideband wavelengths versus pump wavelength for two polarization modes of the pump radiation. Phase matching curves are plotted according to Eq. (2) for pump power Pp = 9 W. Pump wavelength λp ~1051 nm is kept near the ZDW of the fiber to provide rather small parametric shifts (up to 25 THz) to have weak influence of the fluctuations of fiber diameter on the efficiency of the parametric process. One can see that the theoretical calculations are in a good agreement with the experimental data for all wavelengths, although the parametric generation above 1010 nm is perturbed by the stimulated Raman scattering (SRS). Variations of FOPO spectra at tuning of the pump are shown in Fig. 2(b) for the slow branch only, since for parametric generation of the fast index mode the slow mode cannot be completely suppressed due to higher parametric and Raman gain. The spectra are measured at the port B by an optical spectrum analyzer (Yokogawa AQ6370). We adjusted the state of polarization for each generated wavelengths to achieve maximum output power. Spectral bandwidths of the WDM couplers are quite broad and, consequently, the generation linewidth is determined by the parametric gain bandwidth. As seen in Fig. 2(b) the gain bandwidth is reduced when the pump wavelength moves into the normal dispersion region and the sidebands move away from the pump.

The anti-Stokes wavelength goes down to 965 nm and then the generated wave vanishes. The FOPO tuning range is limited by growing attenuation at the Stokes wavelength owing to spectral properties of WDM couplers. As a result, the FOPO threshold grows with increasing frequency shift. On the other hand, the parametric generation is not limited at the small frequency shifts. However, we don’t consider in this paper the generation spectra above 1010 nm as the parametric gain there competes with the Raman gain. Moreover, the full width at half maximum exceeds 7 nm due to increase of FWM gain bandwidth thus making spectrum of parametric generation rather broad. The linewidth of the anti-Stokes sideband at the port A is measured to be 3.7 nm at 972 nm at the pump wavelength of 1050.3 nm and the input pump power of 9 W. Note that there are no signs of SRS process in Fig. 2(b) but it can be observed at some specific adjustment of the polarization controllers.

4. Output power and temporal dynamics

4.1 Pulsed operation at pump linewidth Δλp ~40 pm

The threshold of the FOPO is achieved when the parametric gain is equal to the Stokes wave losses inside the cavity. The parametric gain under exact phase matching conditions for the fiber with length L is written as G=sinh2(γPpL) [17

17. G. P. Agrawal, Nonlinear Fiber Optics, 3rd ed. (Academic Press, 2001).

]. Total cavity losses include point losses α* at splices and fiber couplers as well as distributed losses inside the fiber αL. Thereby, the FOPO threshold pump power Pth can be expressed as follows:

sinh2(γLPth)=100.1(α+αLL)
(3)

The FOPO threshold value is estimated to be Pth = 4.2 W for the following fiber parameters: γ = 10 W−1km−1, L = 0.018 km, αL = 5 dB × km−1 and the total losses α* = 1.6 dB at the Stokes wavelength.

It is known that the parametric process is more efficient when the narrowband pump is used. So we reduce the pump linewidth down to ~40 pm in order to obtain high spectral power density inside the photonic crystal fiber. The pump linewidth is changed by adjusting the tunable FBG. Figure 3(a)
Fig. 3 Power (a) and temporal (b) FOPO properties at pump linewidth Δλp = 40 pm.
presents the generated anti-Stokes power at the port A versus the pump power at the input of LMA fiber taking into account 10% splicing losses of the photonic crystal fiber with the input pigtail. In this configuration the experimentally measured threshold pump power is 5.3 W. External slope efficiency (defined as the slope of the curve in Fig. 3(a)) is equal to 25%. Output power for generation wavelength of 974 nm reaches 1.1 W at Pp ≈9.8 W. Internal slope efficiency (for intra-cavity generated power) amounts to 45%. The last value is calculated inside the cavity taking that the total anti-Stokes losses being of 2.5 dB at 970 nm.

Temporal dynamics of FOPO output radiation is detected by a fast photodetector and a digital oscilloscope. Figure 3(b) demonstrates oscillograms of pump wave from the port B and anti-Stokes wave from the port A measured simultaneously at pump parameters Pp = 9 W and Δλp = 40 pm. One can see that the FOPO operates in the pulsed regime with duty factor ~50% and modulation period of ≈48 ns corresponding to cavity round-trip time in YDFL. Modulation of the YDFL radiation is observed even below the FOPO threshold, while adjusting the polarization controller PC1. Therefore, the pulsed regime can be associated with a feedback to the YDFL, when back scattered radiation influences on the pump laser. Moreover, quite narrow pump linewidth results in stimulated Brillouin scattering (SBS) sidebands generated inside the pump laser cavity that have been observed in the output spectrum of the YDFL.

Despite the fact that the experimental data demonstrate high efficiency of the parametric conversion, the oscillator generates rather irregular pulses in this scheme. For CW operation it is necessary to raise the threshold of the SBS process. That was done by increasing the spectral linewidth of the pump.

4.2 CW operation at pump linewidth Δλp > 100 pm

The FOPO pump power threshold obtained in the experiment is 5.1 – 5.3 W that is higher than calculated value of 4.2 W. Such difference can be attributed to the partial polarization of YDFL radiation, because the parametric process is sensitive to polarization and only a part of the pump power with the appropriate polarization mode amounting to ≥ 0.5Pp is involved in the parametric generation. Additionally we should note that the horizontal axes of the Figs. 3(a) and 4(a) correspond to full pump power and thus the value of the slope efficiency is even larger than presented above.

5. Conclusion

For the narrow-band pumping of ~40 pm the pump laser starts to operate in pulsed mode due to the feedback induced by a SBS process with modulation period of 48 ns and duty factor of ~50%. As a result, the FOPO slope efficiency is increased to 25% (by 3 times compared to CW mode) and the output power becomes >1 W at 974 nm.

Taking that WDMs with different spectral functions can be used, one can extend the tuning range below the obtained limit of ~960 nm. In the case of short-wavelength operation the FOPO efficiency is defined by a level of dispersion fluctuations, as the spectral width of the phase matching becomes much narrower with increasing parametric frequency shift and thus the fluctuations influence the parametric gain.

Acknowledgments

The research has been funded in part from the Russian Ministry of Education and Science and programs of Siberian Branch and Physical department of Russian Academy of Sciences.

References and links

1.

J. S. Y. Chen, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers,” Opt. Express 14(20), 9491–9501 (2006). [CrossRef] [PubMed]

2.

M. E. Marhic, K. K.-Y. Wong, L. G. Kazovsky, and T.-E. Tsai, “Continuous-wave fiber optical parametric oscillator,” Opt. Lett. 27(16), 1439–1441 (2002). [CrossRef] [PubMed]

3.

C. J. S. de Matos, J. R. Taylor, and K. P. Hansen, “Continuous-wave, totally fiber integrated optical parametric oscillator using holey fiber,” Opt. Lett. 29(9), 983–985 (2004). [CrossRef] [PubMed]

4.

M. A. Solodyankin, O. I. Medvedkov, and E. M. Dianov, “Double and single cavity CW all-fiber optical parametric oscillators at 1515 nm with pump at 1557 nm,” in Proceedings of European Conference on Optical Communications (Glasgow, UK, 2005), 47–48.

5.

Z. Luo, W.-D. Zhong, M. Tang, Z. Cai, C. Ye, and X. Xiao, “Fiber-optic parametric amplifier and oscillator based on intracavity parametric pump technique,” Opt. Lett. 34(2), 214–216 (2009). [CrossRef] [PubMed]

6.

Y. Q. Xu, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Raman-assisted continuous-wave tunable all-fiber optical parametric oscillator,” J. Opt. Soc. Am. B 26(7), 1351–1356 (2009). [CrossRef]

7.

R. Malik and M. E. Marhic, “Continuous wave fiber optical parametric oscillator with 254 nm tuning range,” in Latin America Optics and Photonics Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper MD1.

8.

R. Malik and M. E. Marhic, “Tunable continuous-wave fiber optical parametric oscillator with 1-W output power,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper JWA18.

9.

Y. Zhou, P. C. Chui, and K. K. Y. Wong, “Widely-tunable continuous-wave single-longitudinal-mode fiber optical parametric oscillator,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper OWL3.

10.

A. S. Svane, T. Lund-Hansen, L. S. Rishøj, and K. Rottwitt, “Wavelength conversion by cascaded FWM in a fiber optical parametric oscillator,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper JThA014.

11.

T. Andersen, K. Hilligsøe, C. Nielsen, J. Thøgersen, K. Hansen, S. Keiding, and J. Larsen, “Continuous-wave wavelength conversion in a photonic crystal fiber with two zero-dispersion wavelengths,” Opt. Express 12(17), 4113–4122 (2004). [CrossRef] [PubMed]

12.

R. Jiang, R. E. Saperstein, N. Alic, M. Nezhad, C. J. McKinstrie, J. E. Ford, Y. Fainman, and S. Radic, “Continuous-wave band translation between the near-infrared and visible spectral ranges,” J. Lightwave Technol. 25(1), 58–66 (2007). [CrossRef]

13.

E. A. Zlobina, S. I. Kablukov, and S. A. Babin, “Continuous-wave parametric oscillation in polarisation-maintaining optical fibre,” Quantum Electron. 41(9), 794–800 (2011). [CrossRef]

14.

S. A. Babin, S. I. Kablukov, I. S. Shelemba, and A. A. Vlasov, “An interrogator for a fiber Bragg sensor array based on a tunable erbium fiber laser,” Laser Phys. 17(11), 1340–1344 (2007). [CrossRef]

15.

S. A. Babin, S. I. Kablukov, and A. A. Vlasov, “Tunable fiber Bragg gratings for application in tunable fiber lasers,” Laser Phys. 17(11), 1323–1326 (2007). [CrossRef]

16.

E. A. Zlobina, S. I. Kablukov, and S. A. Babin, “Phase matching for parametric generation in polarization maintaining photonic crystal fiber pumped by tunable Yb-doped fiber laser,” J. Opt. Soc. Am. B 29(8), 1959–1967 (2012). [CrossRef]

17.

G. P. Agrawal, Nonlinear Fiber Optics, 3rd ed. (Academic Press, 2001).

OCIS Codes
(060.2320) Fiber optics and optical communications : Fiber optics amplifiers and oscillators
(140.3510) Lasers and laser optics : Lasers, fiber
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
(060.5295) Fiber optics and optical communications : Photonic crystal fibers

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: December 7, 2012
Revised Manuscript: January 24, 2013
Manuscript Accepted: February 5, 2013
Published: March 11, 2013

Citation
Ekaterina A. Zlobina, Sergey I. Kablukov, and Sergey A. Babin, "Tunable CW all-fiber optical parametric oscillator operating below 1 μm," Opt. Express 21, 6777-6782 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-6-6777


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References

  1. J. S. Y. Chen, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers,” Opt. Express14(20), 9491–9501 (2006). [CrossRef] [PubMed]
  2. M. E. Marhic, K. K.-Y. Wong, L. G. Kazovsky, and T.-E. Tsai, “Continuous-wave fiber optical parametric oscillator,” Opt. Lett.27(16), 1439–1441 (2002). [CrossRef] [PubMed]
  3. C. J. S. de Matos, J. R. Taylor, and K. P. Hansen, “Continuous-wave, totally fiber integrated optical parametric oscillator using holey fiber,” Opt. Lett.29(9), 983–985 (2004). [CrossRef] [PubMed]
  4. M. A. Solodyankin, O. I. Medvedkov, and E. M. Dianov, “Double and single cavity CW all-fiber optical parametric oscillators at 1515 nm with pump at 1557 nm,” in Proceedings of European Conference on Optical Communications (Glasgow, UK, 2005), 47–48.
  5. Z. Luo, W.-D. Zhong, M. Tang, Z. Cai, C. Ye, and X. Xiao, “Fiber-optic parametric amplifier and oscillator based on intracavity parametric pump technique,” Opt. Lett.34(2), 214–216 (2009). [CrossRef] [PubMed]
  6. Y. Q. Xu, S. G. Murdoch, R. Leonhardt, and J. D. Harvey, “Raman-assisted continuous-wave tunable all-fiber optical parametric oscillator,” J. Opt. Soc. Am. B26(7), 1351–1356 (2009). [CrossRef]
  7. R. Malik and M. E. Marhic, “Continuous wave fiber optical parametric oscillator with 254 nm tuning range,” in Latin America Optics and Photonics Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper MD1.
  8. R. Malik and M. E. Marhic, “Tunable continuous-wave fiber optical parametric oscillator with 1-W output power,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper JWA18.
  9. Y. Zhou, P. C. Chui, and K. K. Y. Wong, “Widely-tunable continuous-wave single-longitudinal-mode fiber optical parametric oscillator,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper OWL3.
  10. A. S. Svane, T. Lund-Hansen, L. S. Rishøj, and K. Rottwitt, “Wavelength conversion by cascaded FWM in a fiber optical parametric oscillator,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper JThA014.
  11. T. Andersen, K. Hilligsøe, C. Nielsen, J. Thøgersen, K. Hansen, S. Keiding, and J. Larsen, “Continuous-wave wavelength conversion in a photonic crystal fiber with two zero-dispersion wavelengths,” Opt. Express12(17), 4113–4122 (2004). [CrossRef] [PubMed]
  12. R. Jiang, R. E. Saperstein, N. Alic, M. Nezhad, C. J. McKinstrie, J. E. Ford, Y. Fainman, and S. Radic, “Continuous-wave band translation between the near-infrared and visible spectral ranges,” J. Lightwave Technol.25(1), 58–66 (2007). [CrossRef]
  13. E. A. Zlobina, S. I. Kablukov, and S. A. Babin, “Continuous-wave parametric oscillation in polarisation-maintaining optical fibre,” Quantum Electron.41(9), 794–800 (2011). [CrossRef]
  14. S. A. Babin, S. I. Kablukov, I. S. Shelemba, and A. A. Vlasov, “An interrogator for a fiber Bragg sensor array based on a tunable erbium fiber laser,” Laser Phys.17(11), 1340–1344 (2007). [CrossRef]
  15. S. A. Babin, S. I. Kablukov, and A. A. Vlasov, “Tunable fiber Bragg gratings for application in tunable fiber lasers,” Laser Phys.17(11), 1323–1326 (2007). [CrossRef]
  16. E. A. Zlobina, S. I. Kablukov, and S. A. Babin, “Phase matching for parametric generation in polarization maintaining photonic crystal fiber pumped by tunable Yb-doped fiber laser,” J. Opt. Soc. Am. B29(8), 1959–1967 (2012). [CrossRef]
  17. G. P. Agrawal, Nonlinear Fiber Optics, 3rd ed. (Academic Press, 2001).

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