Field enhancement within an optical fibre with a subwavelength air core


Tightly confined light enables a variety of applications ranging from nonlinear light management to atomic manipulation. Photonic-crystal fibres (PCFs) can provide strong guidance in very small cores while simultaneously offering long interaction lengths1. However, light confinement in waveguides is usually ultimately limited by diffraction2,3, which tends to spread light away from the waveguiding core, despite its higher refractive index. It was recently demonstrated that such spreading fields can be trapped by a nanometre-scale slot inside a strongly guiding silicon-on-insulator (SOI) waveguide4,5. In this letter we demonstrate the concentration of optical energy within a subwavelength-scale air hole running down the length of a PCF core. The core resembles a submicrometre-diameter tube with a bore diameter of 200 nm or less. The high intensity in an air hole, coupled with long interaction lengths, promises a new class of experiments in light–matter interaction and nonlinear fibre optics.

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Figure 1: SEM images from the fabricated PCF cross-sections.
Figure 2: Optical fields and figure of merit.
Figure 3: Group velocity dispersion of the fibres shown in Fig. 1.
Figure 4: Near-field mode patterns for PCF 3.


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The authors would like to acknowledge help from A. George in fabricating the fibres and assistance from A. Frasson and H.E.H. Figueroa in the numerical simulations. G.S.W. and C.M.B.C. acknowledge financial support of the National Council for Scientific and Technological Development (CNPq) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP). Work at Bath was funded by the UK Engineering and Physical Sciences Research Council.

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Correspondence to G. S. Wiederhecker.

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Wiederhecker, G., Cordeiro, C., Couny, F. et al. Field enhancement within an optical fibre with a subwavelength air core. Nature Photon 1, 115–118 (2007).

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