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Photonic fiber loss plummets

19 Sep 2002

Researchers report photonic crystal fiber with record low-losses operating at telecoms wavelengths.

Scientists from Blaze Photonics, the UK spin-off from the University of Bath, claim to have made a solid-core photonic crystal fiber (PCF) with a loss of just 0.58 dB/km at a wavelength of 1.55 µms.

As well as being the lowest attenuation reported to date, the development suggests that PCF is fast approaching the transmission loss of standard singlemode optical fiber (0.2 dB/km). The result was unveiled at the annual European Conference on Optical Communication (ECOC) held in Copenhagen, Denmark, last week.

Practical applications for PCF, silica fiber riddled with holes which has unusual optical properties such as enhanced nonlinearity and dispersion, have in the past been hindered by the fiber's large optical attenuation of several dB/km.

The loss of Blaze's PCF is almost half the dB/km value of the previous best PCF which was made by scientists in Japan and exhibited a loss of 1 dB/km. Blaze's PCF design consists of a solid core made of pure undoped silica embedded in a holey cladding. The air-holes have a diameter of 1.85 µms and are spaced by 4.2 µms.

Measurements suggest the 0.58 dB/km loss is made up of three components: 0.18 dB/km from background Rayleigh scattering; 0.13 dB/km of hydroxyl absorption; and 0.27 dB/km of excess loss associated with the geometry of the fiber.

And it's not just the loss of solid-core PCF that is falling. At ECOC, Corning, the US fiber specialist, said that it had dramatically reduced the loss of a PCF with a hollow core. A 100 m length of Corning's air-core fiber exhibited a loss of 13 dB/km at a wavelength of 1500 nm, an improvement of nearly two-orders of magnitude over the 1000 dB/km value reported at ECOC 2001.

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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