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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 11, Iss. 1 — Jan. 13, 2003
  • pp: 61–67
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Polarization dependent harmonic generation in microstructured fibers

Fiorenzo G. Omenetto, Anatoly Efimov, Antoinette J. Taylor, Jonathan C. Knight, William J. Wadsworth, and Philip St. J. Russell  »View Author Affiliations


Optics Express, Vol. 11, Issue 1, pp. 61-67 (2003)
http://dx.doi.org/10.1364/OE.11.000061


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Abstract

We report on the control of visible harmonic generation in microstructured fiber through the polarization state of the fundamental radiation. By coupling λ=1.55 µm femtosecond pulses that have the same peak power into a short length (Z=20 cm) of high-Δ microstructured fiber, we observe the generation of distinct visible spectral components in the visible at the output of the fiber in dependence of the input pulse’s polarization state.

© 2002 Optical Society of America

1. Introduction

2. Experimental Results

Fig. 1. Far field mode profiles detected at the ouput of the microstructured fiber for polarization states directed along the two previously identified principal axes α and β. The input to the fiber are pulses at λ=1550 nm, τ~170 fs, with maximum average power of 25 mW (for these experiments). The two outputs are centered at (a) λ= 533 nm and (b) λ=514 nm.
Fig. 2. Plot of modal indices (N=5-25) for λ= 510 nm (black squares), λ= 520 nm (red circles), λ= 530 (green triangles), and modal index for the fundamental as a function of wavelength (black solid line). Phase matching conditions can be identified for the N=21 mode. For further details see text.

Fig. 3. Comparison of the experimentally acquired image of the near field profile of the guided λ=514 nm mode and the calculated profile of the N=21 high order mode supported by the MF in that wavelength range.

A power dependent spectral analysis is carried out on the fundamental and on the visible harmonics for the two different polarizations. The detected spectra for the fundamental pulse are illustrated in Fig. 4(a,b), whereas the results for the generated visible harmonics are shown in Fig. 5(a,b). These spectra are acquired with an infrared spectral detector (Rees E2000) with sensitivity in the 800–1700 nm range.

A comparison between the spectral features of the fundamental pulse polarized along the direction α (Fig 4a) and the direction β (Fig 4b) shows different details in the spectral dynamics as a function of power but a fundamentally similar behavior: in both cases the spectrum shifts as expected toward longer wavelengths and the magnitude of the shift (~50 nm at P=25 mW) is the same for both input polarization orientations appearing, therefore, independent from the initial polarization. Since the Raman scattering process is an intensity (i.e. pulsewidth) dependent process, this suggests that the dispersion properties are not vastly dissimilar for both polarization states. The visible spectral features are detected by means of a separate spectrometer and acquired with a 16-bit CCD camera. These images and integrated over variable time windows to insure maximum sensitivity.

Fig. 4. Detected spectra of the fundamental (λ=1550 nm)radiation at the output of the microstructured fiber as a function of power for linearly polarized light along the directions α and β. The shift at P=25 mW (indicated by the arrow) is the same for both polarization states.

The collection of spectral results shows a clear difference in dependence of the fundamental input pulse’s polarization state. In the direction α (Fig 5a) a spectral feature centered around λ=514 nm is detected for pulses of average power of 4 mW at 1550 nm. As the power of the fundamental is increased, more light is converted to the visible (with an estimated conversion efficiency of 0.2 % for a 25 mW pump) but only a feature at λ1=514 nm is observed. The relationship of this component to the fundamental wavelength is consistent with the generation of third harmonic of the fundamental yet no third harmonic from the self-shifted component is observed at these power levels.

When the input pulse polarization is rotated along the direction β (Fig 5b), however, a sharp feature centered at λ2=534 nm appears for pulses of average powers of 16 mW in addition to the λ1 component that subsequently vanishes as the power of the fundamental is further increased. Whereas for both polarizations the fundamental shifts to 1600 nm (and beyond for higher input powers, such as the ones described in [5

5. F. G. Omenetto, A. Taylor, M. D. Moores, J.C. Knight, P.St. J. Russell, and J. Arriaga, “Simultaneous generation of spectrally distinct third harmonics in a photonic crystal fiber,” Opt. Lett. 26 (15),1558, 2001 [CrossRef]

]), the shifted fundamental is converted to third harmonic radiation only when the input pulses linearly polarized along the β direction.

Fig. 5. Detected spectra of the visible radiation components at the output of the microstructured fiber as a function of power for both polarization states α and β. The component at 533 nm appears only in one polarization state.

Fig. 6. Scanning electron microscope image of the fiber tip used in the experiment. Various calibrated measurements performed with the microscope reveal mismatches in the 8 to 10% range between the dimensions indicated as a and b in the Figure, resulting in a slight ellipticity of the core of the microstructured fiber.

It is also interesting to note that no frequency components that could be attributed to mixing processes [7

7. R. H. Stolen, J. E. Bjorkholm, and A. Ashkin, “Phase-matched three-wave mixing in silica fiber optical waveguides,” Appl. Phys. Lett. , 24, 308, 1974 [CrossRef]

,8

8. J. Sharping, M. Fiorentino, A. Coker, P. Kumar, and R. Windeler, “Four-wave mixing in microstructure fiber,” Opt. Lett. 26 (14), 1048 (2001) [CrossRef]

] are detected for the wavelength interval covered by the fundamental and its shifted components (see Figs. 4 and 5). To further probe the detected birefringent behavior, SEM images of the microstructured fiber used were taken to verify the degree of symmetry of the structure. The resultant SEM image is shown in Fig. 6. The calibrated measurements show a slight asymmetry in the core, revealing an effective ellipticity of a solid silica core suspended in air. This mismatch is, however, quite small, yet could contribute to the different behavior seen along the two polarization axes.

3. Conclusions

These results provide an analysis of the nonlinear frequency conversion processes which occur in a high-Δ microstructured fiber when low average power femtosecond pulses at a wavelength of 1550 nm are coupled into it. The conversion of the 1550 nm light into the observed visible components occurs through a phase matched process between the fundamental mode at 1550 nm and high-order modes in the visible. The process is dependent on the linear polarization of the input pulses. This selectivity combined with Raman self-frequency shifting and third harmonic generation, provides a means to generate specific harmonics and therefore a means to control the output’s visible frequency through the input pulse polarization state. The extension of this approach can provide a basis for all-fiber signal control and ultrafast optical switching based on nonlinear phenomena in microstructured fibers.

Acknowledgements

The authors would like to greatly thank and acknowledge Jim Smith for the SEM images. This research was supported by the Los Alamos Directed Research and Development (LDRD) program by the Department of Energy. F.G.O. acknowledges the Los Alamos Office of the Director for the support received with the J. Robert Oppenheimer fellowship.

References and links

1.

J.C. Knight, T.A. Birks, P.St. J. Russell, and D.M. Atkin, “All-silica single-mode optical fiber with photonic crystal cladding,” Opt. Lett. 211547 (1996) [CrossRef] [PubMed]

2.

J. C. Knight, J. Broeng, T.A. Birks, and P. St. J. Russell., “Photonic band gap guidance in optical fibers,” Science 282, 1476 (1998) [CrossRef] [PubMed]

3.

J. K. Ranka, R. S. Windeler, and A. J. Stenz, “Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm,” Opt., Lett. 25 (1),25,2000 [CrossRef]

4.

J. K. Ranka, R. S. Windeler, and A. J. Stenz, “Optical properties of high-delta air-silica microstructure optical fibers,” Opt. Lett. 25 (11),796, 2000 [CrossRef]

5.

F. G. Omenetto, A. Taylor, M. D. Moores, J.C. Knight, P.St. J. Russell, and J. Arriaga, “Simultaneous generation of spectrally distinct third harmonics in a photonic crystal fiber,” Opt. Lett. 26 (15),1558, 2001 [CrossRef]

6.

J. Herrmann, U. Griebner, N. Zhavornokov, A. Hukasow, D. Nickel, J.C. Knight, W. J. Wadsworth, P. St. J. Russell, and G. Korn, “Experimental evidence for supercontinuum generation by fission of higher-order solitons in photonic fibers,”. Phys. Rev. Lett. 88 (17), 173901, 2002 [CrossRef] [PubMed]

7.

R. H. Stolen, J. E. Bjorkholm, and A. Ashkin, “Phase-matched three-wave mixing in silica fiber optical waveguides,” Appl. Phys. Lett. , 24, 308, 1974 [CrossRef]

8.

J. Sharping, M. Fiorentino, A. Coker, P. Kumar, and R. Windeler, “Four-wave mixing in microstructure fiber,” Opt. Lett. 26 (14), 1048 (2001) [CrossRef]

9.

N. Akhmediev and M. Karlsson, “Cherenkov radiation emitted by solitons in optical fibers,” Phys. Rev. A , 51 (3), 2602, 1995 [CrossRef] [PubMed]

10.

J. Thogersen and J. Mark, “THG in standard and erbium-doped fibers,” Optics Comm. 110 (3–4), 435, 1994

11.

A. Ferrando, E. Silvestre, J.J. Miret, P. Andres, and M.V. Andres, “Full-vector analysis of a realistic photonic crystal fiber,” Opt. Lett , 24, 276 (1999) [CrossRef]

OCIS Codes
(320.2250) Ultrafast optics : Femtosecond phenomena
(320.5550) Ultrafast optics : Pulses
(320.7140) Ultrafast optics : Ultrafast processes in fibers

ToC Category:
Research Papers

History
Original Manuscript: November 15, 2002
Revised Manuscript: January 6, 2003
Published: January 13, 2003

Citation
Fiorenzo Omenetto, Anatoly Efimov, Antoinette Taylor, Jonathan Knight, William Wadsworth, and Philip Russell, "Polarization dependent harmonic generation in microstructured fibers," Opt. Express 11, 61-67 (2003)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-11-1-61


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References

  1. J.C. Knight, T.A. Birks, P.St. J. Russell and D.M. Atkin, �??All-silica single-mode optical fiber with photonic crystal cladding,�?? Opt. Lett. 21 1547 (1996). [CrossRef] [PubMed]
  2. J. C. Knight, J. Broeng, T.A. Birks, P. St. J. Russell, �??Photonic band gap guidance in optical fibers,�?? Science 282, 1476 (1998). [CrossRef] [PubMed]
  3. J. K. Ranka, R. S. Windeler and A. J. Stenz, �??Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm,�?? Opt. Lett. 25, 25 (2000). [CrossRef]
  4. J. K. Ranka, R. S. Windeler and A. J. Stenz, �??Optical properties of high-delta air-silica microstructure optical fibers,�?? Opt. Lett. 25, 796 (2000). [CrossRef]
  5. F. G. Omenetto, A. Taylor, M. D. Moores, J.C. Knight, P.St. J. Russell, J. Arriaga, �??Simultaneous generation of spectrally distinct third harmonics in a photonic crystal fiber,�?? Opt. Lett. 26, 1558 (2001). [CrossRef]
  6. J. Herrmann, U. Griebner, N. Zhavornokov, A. Hukasow, D. Nickel, J.C. Knight, W. J. Wadsworth, P. St. J. Russell and G. Korn, �??Experimental evidence for supercontinuum generation by fission of higher-order solitons in photonic fibers,�?? Phys. Rev. Lett. 88, 173901 (2002). [CrossRef] [PubMed]
  7. R. H. Stolen, J. E. Bjorkholm and A. Ashkin, �??Phase-matched three-wave mixing in silica fiber optical waveguides,�?? Appl. Phys. Lett. 24, 308 (1974). [CrossRef]
  8. J. Sharping, M. Fiorentino, A. Coker, P. Kumar, R. Windeler, �??Four-wave mixing in microstructure fiber,�?? Opt. Lett. 26, 1048 (2001). [CrossRef]
  9. N. Akhmediev and M. Karlsson, �??Cherenkov radiation emitted by solitons in optical fibers,�?? Phys. Rev. A 51, 2602 (1995). [CrossRef] [PubMed]
  10. J. Thogersen, J. Mark, �??THG in standard and erbium-doped fibers,�?? Opt. Commun. 110, 435 (1994 ).
  11. A.Ferrando, E.Silvestre, J.J.Miret, P.Andres and M.V.Andres, �??Full-vector analysis of a realistic photonic crystal fiber,�?? Opt. Lett. 24, 276 (1999). [CrossRef]

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