1. Field of the Invention
The invention relates to the field of optical fibers for wavelength division multiplex transmission networks.
2. Description of the Prior Art
Increasing information bit rates on this type of network impose compensation of chromatic dispersion and dispersion slope over bands of the spectrum other than the C band. The S band extends approximately from 1 460 nm to 1 530 nm. The C band extends approximately from 1 530 nm to 1 565 nm. The L band extends approximately from 1 565 nm to 1 625 nm. The U band extends approximately from 1 625 nm to 1 675 nm. The most widely used band is the C band. The invention relates to fibers with chromatic dispersion compensation in the S band.
In the prior art, it is known to combine certain types of dispersion shifted optical fibers reducing crossed non-linear effects, known as non-zero dispersion shifted fiber (NZ-DSF), with dispersion compensating fiber (DCF), thereby achieving a transmission line with no dispersion over a wide spectral range.
The patent application EP 1219986 discloses using an optical fiber with chromatic dispersion compensation in the S band, but the examples described with two or three slices either have a ratio between the attenuation at 1 520 nm and at 1 500 nm greater than two or a chromatic dispersion to dispersion slope ratio that renders them unsuited to the object of the invention.
The invention proposes a chromatic dispersion compensating optical fiber which, either because of profiles with at least four slices or because of profiles with three slices having structures corresponding to particular ranges of index and radius, provides effective compensation in the S band of the chromatic dispersion of a certain range of line optical fibers, combined with attenuations at 1 500 nm and at 1 520 nm that are comparable. A particularly advantageous aspect is the very deeply buried nature of the index of the first buried slice (or of the only buried slice if there is only one) relative to the index of the central slice.