We comment on the recent paper by Zhou et al. [Appl. Opt. 45, 4433 (2006)], in which transmission losses of were claimed across the wavelength range in a high-index ( at ) SF6 glass-based photonic crystal fiber fabricated by novel die-cast technique. If confirmed, these losses are at least 1 order of magnitude lower than previous reported losses of SF6 photonic crystal fibers from other fabrication approaches. Here we present a statistic survey on the relationship between the refractive index and the bulk material attenuation, based on a large number of commercial Schott optical glasses with the ranging between 1.40 and 2.05. It shows that the loss of a high-index () glass optical fiber should be at the levels of at and at , respectively. Moreover, the material attenuation of such a high-index glass fiber should intrinsically show a large decay, from at to the level of at , which arises from the tail on the UV absorption edge of the high-index glass extending to the visible region. Therefore, we conclude that: (1) the low loss of reported in the cited paper is abnormally one or two magnitudes lower than the material attenuation that a high-index () glass optical fiber should have in the range between 420 and and that (2) the flat loss curve between 420 and in the cited paper deviates greatly from the intrinsic behavior of a high-index () glass fiber.
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