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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 21 — Oct. 17, 2007
  • pp: 13531–13538
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End-sealing short dispersion micromanaged tapered holey fibers by hole-collapsing

Parama Pal and Wayne H. Knox  »View Author Affiliations


Optics Express, Vol. 15, Issue 21, pp. 13531-13538 (2007)
http://dx.doi.org/10.1364/OE.15.013531


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Abstract

We have recently shown that fiber dispersion can be manipulated on a sub-millimeter scale, and discussed its importance in production of low-noise supercontinuum generation. In this paper, we report the fabrication of dispersion micromanaged (DMM) holey fibers that have been structurally modified to offer greater environmental stability and have reduced sensitivity towards alignment in input coupling. Our results show that end-sealed devices can be made while retaining key features of the dispersion micromanagement.

© 2007 Optical Society of America

1. Introduction

Supercontinuum generation (SCG) is a phenomenon wherein an ultrashort pulse of light undergoes extreme spectral broadening to generate new frequency components as it propagates through a suitable nonlinear medium. Effects such as self-phase modulation, four-wave mixing (FWM) and Raman scattering [1

1. J. M. Dudley, G. Genty, and S. Coen, “Supercontinuum generation in photonic crystal fibers,” Rev. Mod. Phys. 78, 1135–1184 (2006). [CrossRef]

] play an important role. SCG is a highly nonlinear process that can be improved by more precise engineering of the waveguide dispersion of the guiding structure, which results in greater control over the dynamics of the broadening process. This ‘management’ of the dispersion can to be carried out over very small lengths that could range from a few millimeters to even sub-millimeter length scales [2

2. F. Lu and W. H. Knox, “Generation, characterization, and application of broadband coherent, femtosecond visible pulses in dispersion micromanaged holey fibers,” J. Opt. Soc. Am. B 23, 1221–1227 (2006). [CrossRef]

, 3

3. W. H. Reeves, D. V. Skryabin, F. Biancalana, J. C. Knight, P. St. J. Russell, F. G. Omenetto, A. Efimov, and A. J. Taylor, “Transformation and control of ultra-short pulses in dispersion-engineered photonic crystal fibers,” Nature 424, 511–515 (2003). [CrossRef] [PubMed]

].

We have used ‘holey’ fibers (HFs), which consist of a solid core surrounded by a lattice of air holes that constitute the cladding, and result in enhanced modal confinement and unique dispersion properties [4

4. P. Russell, “Photonic crystal fibers,” Science 299, 358–362 (2003). [CrossRef] [PubMed]

]. Supercontinuum generation has been explained on the basis of a soliton fission process that is highly nonlinear and as a consequence, the nonlinearity of the guiding structure as well as the dispersion, play crucial roles in the propagation dynamics of the solitons [5

5. A. V. Husakou and J. Herrmann, “Supercontinuum Generation of Higher-Order Solitons by Fission in Photonic Crystal Fibers,” Phys. Rev. Lett. 87, 203901 (2001). [CrossRef] [PubMed]

]. The nonlinearity, characterized through the nonlinear coefficient γ, as well as the group velocity dispersion (GVD) are parameters that can be controlled by tapering, or varying the transverse profile of the fiber along its length. Through tapering, a reduction in the core size of the fiber can be achieved which affects the nonlinearity as well as the zero-dispersion wavelength of the fiber in accordance with the eigenvalue equation for the propagation constants of the supported fiber modes of the fiber. Tapering also tunes the four-wave mixing and other phase-matching conditions required for the generation of ultra-broadband light [6

6. G. P. Agrawal, Nonlinear Fiber Optics (Academic Press, San Diego, 2001).

]. This post-processing technique provides a way to engineer or ‘micromanage’ the dispersion and waveguiding properties of a holey fiber on millimeter length scales which facilitates careful and precise modification of the generated spectrum, giving rise to the term ‘dispersion micromanagement’ (DMM) [2

2. F. Lu and W. H. Knox, “Generation, characterization, and application of broadband coherent, femtosecond visible pulses in dispersion micromanaged holey fibers,” J. Opt. Soc. Am. B 23, 1221–1227 (2006). [CrossRef]

].

Fig. 1. Schematic image of (a) an untapered, unsealed HF; (b) an input and output end-sealed untapered HF; (c) an unsealed DMM HF; (d) an input end-sealed DMM, and; (e) an input and output end-sealed DMM.

2. Experimental details and results

Our initial experiment involved the investigation of the coupling sensitivity of the end-sealed HF towards input alignment for the case of the ASR generation in the visible. We took a 2m length of untapered HF (NL-3.3-850, Crystal Fibre A/S), which had a zero dispersion wavelength at 850 nm, and hole-collapsed the input-end with the fusion splicer (Ericsson FSU 995 PM). The optimum magnitude of the arc current for sealing the front-end of the HF was determined to be 12 mA applied over a duration of 0.45 seconds. The fiber was positioned with a slight offset of ~20 μm with respect to the tips of the splicer electrodes. We then placed the fiber on a motorized stepper with a step size-resolution of 0.1 μm and coupled 100-fs pulses from a mode-locked Ti:Sapphire laser (Spectra Physics’ MaiTai) at a wavelength of 880 nm and generated continuum that spanned from 400 nm to 1200 nm. This nonlinear measurement method was adopted as it was considered relevant to the use of this device as a wavelength convertor. We used an interference filter to record the power contained in the red part of the continuum at 780 nm as a function of the transverse offset of the input end with respect to the pump beam [23

23. P. Pal and W. H. Knox, “Integration of End Sealed Holey Fibers with Dispersion Micromanagement,” in Frontiers in Optics (2006), Postdeadline paper PDP-FA5.

]. Figure 2 shows the comparison of the results from the hole-collapsed fiber to those obtained with a conventionally ended fiber and the plot shows that there is indeed an enhancement of the input coupling function for the end sealed fiber implying reduced sensitivity towards input coupling. The FWHM of the input coupling function of the fiber increased from a value of 1.6 μm for the normal HF to 2.3 μm for the end-sealed HF. Although the plot shows coupled powers on a normalized scale, while carrying out the experiment, the maximum output power was identical for both cases to eliminate any inconsistency in measurement.

Fig. 2. Comparison of alignment sensitivity for normal-ended HF and end-sealed HF. Inset: Images of the end-facets of the hole-collapsed HF and the normal-ended HF

The insets on the right of Fig. 2 show microscope images of the input facets for the sealed and the unsealed fibers. The maximum coupling efficiency was ~60% for both fibers, indicating that the end-sealing did not introduce significant losses for the HF. We experimentally determined that for our fiber, the length of the collapsed section of glass needed to be under ~280 μm for the input end in order to ensure dominant fundamental mode operation.

Fig. 3. (a). Output spectrum of the hole-collapsed DMM on a log scale. Inset: Filtered ASR on a linear scale. (b) Output spectrum on a linear scale. Dotted red line indicates the pump.

We also looked at the noise characteristics for the device. Conventional ultra-broadband light generating devices, such as untapered HFs, exhibit significant spectral intensity fluctuations and broadband amplitude noise in the radio frequency range, making the resulting continuum unstable for different spectral regions. Noise seeded from the pump’s shot noise gets amplified by the nonlinear processes that occur as the pulse propagates and broadens along the length of the fiber [24

24. K. L. Corwin, N. R. Newbury, J. M. Dudley, S. Coen, S. A. Diddams, B. R. Washburn, K. Weber, and R. S. Windeler, “Fundamental amplitude noise limitations to supercontinuum spectra generated in a microstructured fiber,” Appl. Phys. B 77, 269–277 (2003). [CrossRef]

, 25

25. F. Lu and W. H. Knox, “Low noise wavelength conversion of femtosecond pulses with dispersion micro-managed holey fibers,” Opt. Express , 13, 8172 (2005). [CrossRef] [PubMed]

]. DMM devices overcome this noise limitation by essentially having small lengths which results in a truncation of all the noise-amplifying processes. When we taper the HF over small length scales, we essentially introduce a phase-matching condition that varies along the fiber as a function of the changing core size [2

2. F. Lu and W. H. Knox, “Generation, characterization, and application of broadband coherent, femtosecond visible pulses in dispersion micromanaged holey fibers,” J. Opt. Soc. Am. B 23, 1221–1227 (2006). [CrossRef]

, 26

26. F. Lu, Y. Deng, and W. H. Knox, “Generation of broadband femtosecond visible pulses in dispersion-micromanaged holey fibers,” Opt. Lett. 30, 1566–1568 (2005). [CrossRef] [PubMed]

].

Previously published results demonstrate a comparison of noise figures between DMM devices and other fibers [25

25. F. Lu and W. H. Knox, “Low noise wavelength conversion of femtosecond pulses with dispersion micro-managed holey fibers,” Opt. Express , 13, 8172 (2005). [CrossRef] [PubMed]

]. We investigated the effects of end-sealing on the noise performance of the DMM by spectrally filtering out the ASR and recording it on an RF spectrum analyzer via a fast photodetector of 1 GHz bandwidth. Our results show an imperceptible rise of the noise floor of the ASR above the baseline, leading us to conclude that the structural modifications to the DMM did not compromise the stability of the device (Fig. 4).

Fig. 4. Broadband noise for the filtered ASR at 550 nm. Inset: picture of the ASR.

Fig. 5. (a). Physical profile for the DMM generating ASR centered at 550 nm. (b) Microscope images of the hole-collapsed input and the output ends of the DMM

Figure 6 shows the spectrum obtained from an unsealed DMM, a DMM with the input end sealed, a DMM with both the input and output ends sealed, and a DMM which was not optimally sealed. The comparison shows that for the DMM that was sealed successfully, as shown in Fig. 6(c), the ASR could still be generated, albeit with a slight loss of efficiency and bandwidth which can be explained on the basis of a perturbation of the dispersion profile at the output end by the extra processing.

Fig. 6. Continuum spectra from (a) DMM with both ends sealed; (b) DMM with the input end sealed; (c) DMM with unsealed ends; (d) DMM with non-optimized sealing at both ends. Dashed lines indicate the region of the ASR.

When we cleaved the fiber incorrectly at the output end, i.e., when the sealed section was too long, we were no longer able to generate the desired ASR in the spectrum as is depicted in Figure 6(d). Further experiments to examine the specific effects of such types of processing on the nonlinear phenomena occurring inside the DMM are being carried out and will be reported elsewhere.

3. Conclusions

We developed a systematic method to hole-collapse the input and output ends of a dispersion micromanaged holey fiber. We investigated the sensitivity of coupling towards input alignment and concluded that the modified input face resulted in a more stable configuration with greater ease of coupling. We also looked at the continuum profile and broadband noise characteristics of the DMM and we concluded that the processing to the end facets of the fiber resulted in a device that was more robust and environmentally stable without compromising its spectral performance.

Acknowledgment

This project is supported by the New York state Office of Science, Technology and Academic Research (NYSTAR) contract C000073.

References and links

1.

J. M. Dudley, G. Genty, and S. Coen, “Supercontinuum generation in photonic crystal fibers,” Rev. Mod. Phys. 78, 1135–1184 (2006). [CrossRef]

2.

F. Lu and W. H. Knox, “Generation, characterization, and application of broadband coherent, femtosecond visible pulses in dispersion micromanaged holey fibers,” J. Opt. Soc. Am. B 23, 1221–1227 (2006). [CrossRef]

3.

W. H. Reeves, D. V. Skryabin, F. Biancalana, J. C. Knight, P. St. J. Russell, F. G. Omenetto, A. Efimov, and A. J. Taylor, “Transformation and control of ultra-short pulses in dispersion-engineered photonic crystal fibers,” Nature 424, 511–515 (2003). [CrossRef] [PubMed]

4.

P. Russell, “Photonic crystal fibers,” Science 299, 358–362 (2003). [CrossRef] [PubMed]

5.

A. V. Husakou and J. Herrmann, “Supercontinuum Generation of Higher-Order Solitons by Fission in Photonic Crystal Fibers,” Phys. Rev. Lett. 87, 203901 (2001). [CrossRef] [PubMed]

6.

G. P. Agrawal, Nonlinear Fiber Optics (Academic Press, San Diego, 2001).

7.

N. Akhmediev and M. Karlsson, “Cherenkov radiation emitted by solitons in optical fibers,” Phys. Rev. A 51, 2602–2607 (1995). [CrossRef] [PubMed]

8.

I. Cristiani, R. Tediosi, L. Tartara, and V. Degiorgio, “Dispersive wave generation by solitons in microstructured optical fibers,” Opt. Express 12, 124–135 (2004). [CrossRef] [PubMed]

9.

F. Lu and W. H. Knox, “Generation of broadband continuum with high spectral coherence in tapered fibers”, Opt. Express 12, 347–353 (2004). [CrossRef] [PubMed]

10.

A. D. Aguirre, N. Nishizawa, J. G. Fujimoto, W. Seitz, M. Lederer, and D. Kopf, “Continuum generation in a novel photonic crystal fiber for ultrahigh resolution optical coherence tomography at 800 nm and 1300 nm,” Opt. Express 14, 1145–1160 (2006). [CrossRef] [PubMed]

11.

D. J. Jones, S. A. Diddams, J. K. Ranka, A. Stentz, R. S. Windeler, J. L. Hall, and S. T. Cundiff, “Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis,” Science 288, 635–639 (2000). [CrossRef] [PubMed]

12.

H. N. Paulsen, K. M. Hilligse, J. Thgersen, S. R. Keiding, and J. J. Larsen, “Coherent anti-Stokes Raman scattering microscopy with a photonic cystal fiber based light source,” Opt. Lett. 28, 1123–1125 (2003). [CrossRef] [PubMed]

13.

J. Ma and W. J. Bock, “Modeling of photonic crystal fibers with air holes sealed at the fiber end and its application to fluorescent light collection efficiency enhancement,” Opt. Express 13, 2385–2393 (2005). [CrossRef] [PubMed]

14.

Application Note: FEMTOWHITE 800,” http://www.crystal-fibre.com/support/Femtowhite_application_note.pdf.

15.

J. Laaegsgard and A. Bjarklev, “Reduction of coupling loss to photonic crystal fibers by controlled hole collapse: a numerical study,” Opt. Commun. 237, 431–435 (2004). [CrossRef]

16.

E. C. Mägi, H. C. Nguyen, and B. J. Eggleton, “Air-hole collapse and mode transitions in microstructured fiber photonic wires,” Opt. Express 13, 453–459 (2005). [CrossRef] [PubMed]

17.

A. T. Yablon and R. T. Bise, “Low-loss high-strength microstructured fiber fusion splices using GRIN fiber lenses,” IEEE Photonics Technol. Lett. 17, 118–120 (2005). [CrossRef]

18.

B. Bourliaguet, C. Paré, F. Émond, A. Croteau, A. Proulx, and R. Vallée, “Microstructured fiber splicing,” Opt. Express 11, 3412–3417 (2003). [PubMed]

19.

J. Villatoro, V. P. Minkovich, V. Pruneri, and G. Badeness, “Simple all-microstructured-optical-fiber interferometer built via fusion splicing,” Opt. Express 15, 1491–1496 (2007). [CrossRef] [PubMed]

20.

L. Xiao, W. Jin, and M. S. Demokan, “Fusion splicing small-core photonic crystal fibers and single-mode fibers by repeated arc discharges,” Opt. Lett. 32, 115–117 (2007). [CrossRef]

21.

J. H. Chong, M. K. Rao, Y Zhu, and Y. P. Shum, “An effective splicing method on photonic crystal fiber using CO2 laser,” IEEE Photon. Technol. Lett. 15, 942–944 (2003). [CrossRef]

22.

L. Xiao, W. Jin, M. S. Demokan, H. L. Ho, Y. L. Ho, and C. Zhao, “Fabrication of selective injection microstructured optical fiber with a conventional fusion splicer,” Opt. Express 13, 9014–9022 (2005). [CrossRef] [PubMed]

23.

P. Pal and W. H. Knox, “Integration of End Sealed Holey Fibers with Dispersion Micromanagement,” in Frontiers in Optics (2006), Postdeadline paper PDP-FA5.

24.

K. L. Corwin, N. R. Newbury, J. M. Dudley, S. Coen, S. A. Diddams, B. R. Washburn, K. Weber, and R. S. Windeler, “Fundamental amplitude noise limitations to supercontinuum spectra generated in a microstructured fiber,” Appl. Phys. B 77, 269–277 (2003). [CrossRef]

25.

F. Lu and W. H. Knox, “Low noise wavelength conversion of femtosecond pulses with dispersion micro-managed holey fibers,” Opt. Express , 13, 8172 (2005). [CrossRef] [PubMed]

26.

F. Lu, Y. Deng, and W. H. Knox, “Generation of broadband femtosecond visible pulses in dispersion-micromanaged holey fibers,” Opt. Lett. 30, 1566–1568 (2005). [CrossRef] [PubMed]

OCIS Codes
(060.4370) Fiber optics and optical communications : Nonlinear optics, fibers
(190.7110) Nonlinear optics : Ultrafast nonlinear optics

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: August 27, 2007
Revised Manuscript: September 25, 2007
Manuscript Accepted: September 25, 2007
Published: October 1, 2007

Citation
Parama Pal and Wayne H. Knox, "End-sealing short dispersion micromanaged tapered holey fibers by hole-collapsing," Opt. Express 15, 13531-13538 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-21-13531


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References

  1. J. M. Dudley, G. Genty, and S. Coen, "Supercontinuum generation in photonic crystal fibers," Rev. Mod. Phys. 78, 1135-1184 (2006). [CrossRef]
  2. F. Lu and W. H. Knox, "Generation, characterization, and application of broadband coherent, femtosecond visible pulses in dispersion micromanaged holey fibers," J. Opt. Soc. Am. B 23,1221-1227 (2006). [CrossRef]
  3. W. H. Reeves, D. V. Skryabin, F. Biancalana, J. C. Knight, P. St. J. Russell, F. G. Omenetto, A. Efimov, and A. J. Taylor, "Transformation and control of ultra-short pulses in dispersion-engineered photonic crystal fibers," Nature 424, 511-515 (2003). [CrossRef] [PubMed]
  4. P. Russell, "Photonic crystal fibers," Science 299, 358-362 (2003). [CrossRef] [PubMed]
  5. A. V. Husakou and J. Herrmann, "Supercontinuum Generation of Higher-Order Solitons by Fission in Photonic Crystal Fibers," Phys. Rev. Lett. 87, 203901 (2001). [CrossRef] [PubMed]
  6. G. P. Agrawal, Nonlinear Fiber Optics (Academic Press, San Diego, 2001).
  7. N. Akhmediev and M. Karlsson, "Cherenkov radiation emitted by solitons in optical fibers," Phys. Rev. A 51, 2602-2607 (1995). [CrossRef] [PubMed]
  8. I. Cristiani, R. Tediosi, L. Tartara, and V. Degiorgio, "Dispersive wave generation by solitons in microstructured optical fibers," Opt. Express 12, 124-135 (2004). [CrossRef] [PubMed]
  9. F. Lu and W. H. Knox, "Generation of broadband continuum with high spectral coherence in tapered fibers", Opt. Express 12, 347-353 (2004). [CrossRef] [PubMed]
  10. A. D. Aguirre, N. Nishizawa, J. G. Fujimoto, W. Seitz, M. Lederer, and D. Kopf, "Continuum generation in a novel photonic crystal fiber for ultrahigh resolution optical coherence tomography at 800 nm and 1300 nm," Opt. Express 14, 1145-1160 (2006). [CrossRef] [PubMed]
  11. D. J. Jones, S. A. Diddams, J. K. Ranka, A. Stentz, R. S. Windeler, J. L. Hall, and S. T. Cundiff, "Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis," Science 288, 635-639 (2000). [CrossRef] [PubMed]
  12. H. N. Paulsen, K. M. Hilligse, J. Thgersen, S. R. Keiding, J. J. Larsen, "Coherent anti-Stokes Raman scattering microscopy with a photonic cystal fiber based light source," Opt. Lett. 28, 1123-1125 (2003). [CrossRef] [PubMed]
  13. J. Ma, and W. J. Bock, "Modeling of photonic crystal fibers with air holes sealed at the fiber end and its application to fluorescent light collection efficiency enhancement," Opt. Express 13, 2385-2393 (2005). [CrossRef] [PubMed]
  14. Crystal Fibre A/S, "Application Note: FEMTOWHITE 800," http://www.crystal-fibre.com/support/Femtowhite_application_note.pdf.
  15. J. Laaegsgard and A. Bjarklev, "Reduction of coupling loss to photonic crystal fibers by controlled hole collapse: a numerical study," Opt. Commun. 237, 431-435 (2004). [CrossRef]
  16. E. C. Mägi, H. C. Nguyen, and B. J. Eggleton, "Air-hole collapse and mode transitions in microstructured fiber photonic wires," Opt. Express 13, 453-459 (2005). [CrossRef] [PubMed]
  17. A. T. Yablon and R. T. Bise, "Low-loss high-strength microstructured fiber fusion splices using GRIN fiber lenses," IEEE Photonics Technol. Lett. 17, 118-120 (2005). [CrossRef]
  18. B. Bourliaguet, C. Paré, F. Émond, A. Croteau, A. Proulx, and R. Vallée, "Microstructured fiber splicing," Opt. Express 11, 3412-3417 (2003). [PubMed]
  19. J. Villatoro, V. P. Minkovich, V. Pruneri, and G. Badeness, "Simple all-microstructured-optical-fiber interferometer built via fusion splicing," Opt. Express 15, 1491-1496 (2007). [CrossRef] [PubMed]
  20. L. Xiao, W. Jin, and M. S. Demokan, "Fusion splicing small-core photonic crystal fibers and single-mode fibers by repeated arc discharges," Opt. Lett. 32, 115-117 (2007). [CrossRef]
  21. J. H. Chong, M. K. Rao, Y, Zhu, and Y. P. Shum, "An effective splicing method on photonic crystal fiber using CO2 laser," IEEE Photon. Technol. Lett. 15, 942-944 (2003). [CrossRef]
  22. L. Xiao, W. Jin, M. S. Demokan, H. L. Ho, Y. L. Ho, and C. Zhao, "Fabrication of selective injection microstructured optical fiber with a conventional fusion splicer," Opt. Express 13, 9014-9022 (2005). [CrossRef] [PubMed]
  23. P. Pal and W. H. Knox, "Integration of End Sealed Holey Fibers with Dispersion Micromanagement," in Frontiers in Optics (2006), Postdeadline paper PDP-FA5.
  24. K. L. Corwin, N. R. Newbury, J. M. Dudley, S. Coen, S. A. Diddams, B. R. Washburn, K. Weber, and R. S. Windeler, "Fundamental amplitude noise limitations to supercontinuum spectra generated in a microstructured fiber," Appl. Phys. B 77, 269-277 (2003). [CrossRef]
  25. F. Lu and W. H. Knox, "Low noise wavelength conversion of femtosecond pulses with dispersion micro-managed holey fibers," Opt. Express,  13,8172 (2005). [CrossRef] [PubMed]
  26. F. Lu, Y. Deng, and W. H. Knox, "Generation of broadband femtosecond visible pulses in dispersion-micromanaged holey fibers," Opt. Lett. 30, 1566-1568 (2005). [CrossRef] [PubMed]

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