Abstract

The light radiated from the guided mode of a hollow core photonic crystal fiber into free space is measured as a function of angle and wavelength. This enables the direct experimental visualization of the photonic band gap and the identification of localized modes of the core region.

© 2005 Optical Society of America

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References

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  3. T. A. Birks, P. J. Roberts, P. St.J. Russell, D. M. Atkin, T. J. Shepherd, �??Full 2-D photonic band gaps in silica/air structures,�?? Electron. Lett. 31, 1941 (1995).
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Electron. Lett.

T. A. Birks, P. J. Roberts, P. St.J. Russell, D. M. Atkin, T. J. Shepherd, �??Full 2-D photonic band gaps in silica/air structures,�?? Electron. Lett. 31, 1941 (1995).
[CrossRef]

M. E Lines, W. A. Reed, D. J. Di Giovanni and J. R. Hamblin, �??Explanation of anomalous loss in high delta singlemode fibers,�?? Electron. Lett. 35, 1009-1010 (1999).
[CrossRef]

J. Lightwave Technol.

Nature

C. M. Smith, N. Venkataraman, M. T. Gallagher, D. Müller, J. A. West, N. F. Borrelli, D. C. Allan, K. W. Koch, �??Low-loss hollow-core silica/air photonic band gap fiber,�?? Nature 424, 657-659 (2003).
[CrossRef] [PubMed]

J. C. Knight, �??Photonic crystal fibers,�?? Nature 424, 847-851 (2003).
[CrossRef] [PubMed]

Opt. Express

Optical Fiber Communication Conf.

B. J. Mangan, L. Farr, A. Langford, P. J. Roberts, D. P. Williams, F. Couny, M. Lawman, M. Mason, S. Coupland, R. Flea, H. Sabert, T. A. Birks, J. C. Knight and P. St. J. Russell, �??Low loss (1.7 dB/km) hollow core photonic band gap fiber,�?? postdeadline paper PDP24 in Optical Fiber Communication Conference 2004 (Los Angeles, 2004).

Phys. Rev. Lett.

A. F. Koenderink and W. L. Vos, �??Light exiting from real photonic band gap crystals is diffuse and strongly directional,�?? Phys. Rev. Lett. 91, 213902 (2003).
[CrossRef] [PubMed]

Other

H.-G. Unger, Planar Optical Waveguides and Fibers. (Clarendon Press, Oxford, England 1977).

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Figures (5)

Fig. 1.
Fig. 1.

Scanning Electron Micrograph (SEM) of the HC-PCF. The size of the hollow core is equal to 7 unit cells of the photonic crystal cladding. The pitch between adjacent holes is 3.7 µm and the air-filling fraction of the holey cladding is ~90%. The holey cladding is surrounded by a solid silica jacket to strengthen the fiber and to bring the outer diameter to 125 µm. The fiber guides light between 1400 nm and 1600 nm wavelength, with a minimum attenuation of around 20 dB/km.

Fig. 2.
Fig. 2.

Computed Density of States (DOS) for a perfect infinite cladding with an air-filling fraction of 90%. DOS values are shown relative to the vacuum level. The finger of zero DOS around n eff=1 is the fundamental photonic band gap, with regions where propagation is allowed bordering above and below. The zero-DOS region at the top defines the cladding cutoff, the lower edge of which is the effective index of the cladding.

Fig. 3.
Fig. 3.

Experimental setup. The detector is separated from the surface of the immersion cell by roughly one focal length of the cylindrical Fourier lens formed by the cell surface. An additional, orthogonally oriented cylindrical lens serves to increase the signal by covering a larger range of azimuthal angles.

Fig. 4.
Fig. 4.

(a) Scattered light signal as a function of n eff and k, normalized to the output power of the fibre and plotted in dB. The band gap manifests itself as a dark wedge in the image, corresponding to combinations of k and n eff for which no scattering is observed. The fine lines within the band gap are due to light tunneling directly out of confined modes. (b) The transmitted spectrum of the fiber, showing that the vertical white bands in (a) correspond to loss peaks (previously identified with surface-mode crossings) at specific wavelengths.

Fig. 5.
Fig. 5.

(a) Computed modal trajectories, with core modes marked as solid lines and surface modes with broken lines. Not all surface modes are shown. The HE11-like core mode is the top solid line. (b) Zoom of the experimental data to enable identification of the observed modes. Core modes and surface modes appear clearly at smaller wavenumbers.

Equations (1)

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n eff = n MF cos θ ,

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