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Photonic crystal fibers | IEEE Conference Publication | IEEE Xplore

Photonic crystal fibers


Abstract:

While the field of photonic crystals has been focused on optical components, there has been a group of researchers exploring the idea of using photonic band-gaps to provi...Show More

Abstract:

While the field of photonic crystals has been focused on optical components, there has been a group of researchers exploring the idea of using photonic band-gaps to provide confinement in optical fibers. Although the precursors of this technology can be found in the mid to late 1970s (Kaiser and Astle, 1974; Yeh et al., 1978), this earlier work did not recognize the full potential of air-clad or Bragg fibers. However, the idea of a photonic crystal fiber (PCF) (Birks et al., 1995) was revived soon after the introduction of the generalized concept of photonic band gaps (Yablonovitch, 1987; John, 1987) in the late 1980s. Unlike the original all silica-based Bragg fiber, the proposed PCF generated a band gap with a silica cladding containing a periodic lattice of air holes. Although it was several years before a true photonic band-gap.fiber (PBGF) was demonstrated (Knight et al., 1998; Cregan et al.'s, 1999), the original PCFs displayed some very unusual properties (Birks et al., 1997) that generated sufficient interest to distract the research from its original goal. In this paper, we examine the relationship between the early PCFs and the more recent PBGFs.
Date of Conference: 12-13 November 2001
Date Added to IEEE Xplore: 07 August 2002
Print ISBN:0-7803-7105-4
Print ISSN: 1092-8081
Conference Location: San Diego, CA, USA

Photonic Crystal Fiber (PCF)

The original PCF or ‘holey’ fiber has relatively small air holes surrounding a solid silica core. Although the design does not produce a band gap the fiber does have the unusual property of supporting only a single transverse mode7, leading to the name endlessly single-mode (ESM) fiber. This behavior can be explained in terms of modified total internal reflection (TIR) in which the effective core-cladding index contrast is a very strong function of wavelength. In standard fibers this index contrast is only weakly dependent on wavelength and higher-order modes appear as the wavelength decreases. But in a correctly designed PCF, the index contrast decreases at shorter wavelengths preventing the onset of any higherorder modes. Because of the relationship between wavelength and core size, the ESM property can also lead to a theoretically unlimited modal area. However, for practical applications, both the endless single mode and large effective area are severely limited by bend loss just as in comparable low-contrast step-index fibers. Examples of the various air/silica micro-structured fibers. a) The original PCF design that guides using modified TIR. b) An air-clad core that, in the limit of large air holes, reduces to a silica rod suspended in air. c) The air-core PBGF that guides using a true band-gap mechanism.

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