Abstract

Recently, wavelength-division multiplexed (WDM) optical transmission systems have been intensely researched in order to increase the transmission capacity.^1,3 One of the major problems in WDM systems is gain nonuniformity of erbium-doped fiber amplifiers (EDFAs), especially when they are used in a cascade. By introducing 980-nm-pumping, gain flatness is remarkable improved,^1,2 but accumulation of the amplified spontaneous emission (ASE) around the wavelength of 1530 nm often degrades the system performance significantly. Optical notch filters¹ or long wavelength pass filters (LWPFs)^2,3 have been used for suppression of the ASE. Fiber gratings (FGs) are considered to be suitable for this use, because they have superior wavelength selectivity and can be easily fabricated with amplitude or phase masks.^1,4 In this paper, we present the chirped FGs optimally designed as ASE rejection filters for WDM transmission.

© 1996 Optical Society of America