An improved optical fiber design has been found to exhibit a relatively
low attenuation at the wavelength of 1385 nm (the "water peak"), allowing
for Raman amplification to be efficient and effective at wavelengths in
the S-band range of 1460 to 1530 nm. An ultra-dry process is used to mate
an inner core rod (core plus surrounding trench) with a cladding tube
(ring region plus cladding layers) and provide a water peak loss on the
order of 0.325 dB/km. The low water peak is combined with appropriate
dispersion values and zero dispersion wavelength to form a fiber that
supports transmission and Raman amplification in the S-, C- and L-bands
of interest for optical transmission systems.