the microstructured cladding – such a bandgap, properly designed, can confine light in a lower-index core and even a hollow (air) core. Bandgap fibers with hollow cores can potentially circumvent limits imposed by available materials, for example to create fibers that guide light in wavelengths for which transparent materials are not available (because the light is primarily in the air, not in the solid materials). Another potential advantage of a hollow core is that one can dynamically introduce materials into the core, such as a gas that is to be analyzed for the presence of some substance. PCF can also be modified by coating the holes with sol-gels of similar or different index material to enhance the transmittance of light. History The term "photonic-crystal fiber" was coined by Philip Russell in 1995–1997 (he states (2003) that the idea dates to unpublished work in 1991). See also Fiber Bragg grating Fiber optics Gradient index optics Leaky mode Optical communication Optical medium Photonic crystal Subwavelength-diameter optical fiber References Further reading T. A. Birks, P. J. Roberts, P. St. J. Russell, D. M. Atkin and T. J. Shepherd, "Full 2-D photonic bandgaps in silica/air structures" Electronic Letters 31, 1941-1942 (1995). (First reported PCF proposal) P. St. J. Russell, "Photonic crystal fibers," Science 299, 358–362 (2003). (Review article.) P. St. J. Russell, "Photonic crystal fibers", J. Lightwave. Technol., 24 (12), 4729–4749 (2006). (Review article.) F. Zolla, G. Renversez, A. Nicolet, B. Kuhlmey, S. Guenneau, D. Felbacq, "Foundations of Photonic Crystal Fibres" (Imperial College Press, London, 2005). . R. F. Cregan, B. J. Mangan, J. C. Knight, T. A. Birks, P. St.J. Russell, P. J. Roberts, and D. C. Allan, "Single-mode photonic band gap guidance of light in air," Science, vol. 285, no. 5433, pp. 1537–1539, Sep. 1999. A. Bjarklev, J. Broeng, and A. S. Bjarklev, "Photonic crystal fibres" (Kluwer Academic Publishers, Boston, MA, 2003). . J. M. Dudley, G. Genty, S. Coen, "Supercontinuum Generation in Photonic Crystal Fiber," Reviews of Modern Physics 78, 1135 (2006). External links Centre for Photonics and Photonic Materials (CPPM), University of Bath Group of Prof. Philip St. John Russell at the Max Planck Institute for the Science of Light in Erlangen with some introductory material, reviews and information about current research. Encyclopedia of Laser Physics and Technology on photonic crystal fibers, with many references Steven G. Johnson, Photonic-crystal and microstructured fiber tutorials (2005). Philip Russell: Photonic Crystal Fibers, Historical