We report new methods to inherently increase the flatness and bandwidth of erbium-doped silica fiber amplifiers from three perspectives: fiber design, pump-signal WDM coupler optimization, and amplifier structure. First, to achieve inherent control of the gain spectrum, a new type of composite fiber structure with an Er-doped core and a Sm-doped cladding ring is proposed and experimentally demonstrated. Interaction of the optical field with the Sm-doped cladding to produce evanescent wave filtering is modeled, which provides an in-line control of gain fluctuation in the erbium-doped fiber amplifier (EDFA) C band, 1530-1560 nm. Second, the effect of the spectral characteristics of WDM couplers over the L band of an EDFA is explored. A fused taper fiber coupler for a 1480-nm pump is optimized for signals in the wavelength range of 1570-1610 nm by measuring the small-signal gain, gain tilt, and noise figure in an L-band EDFA. Finally, a new all-fiber structure for a wide-band EDFA, where the L and C bands were coupled serially, is demonstrated with optimized pump-signal couplers. Further optimization of the new composite fiber structure and the transient effects in the serially coupled EDFAs are also discussed.
Bibliographical noteFunding Information:
Manuscript received October 31, 2000; revised October 31, 2001. This work was supported in part by the Ultra-Fast Fiber-Optical Networks (UFON), an Engineering Research Center (ERC) program sponsored by Korean Science and Engineering Foundation (KOSEF), by the BK21(Brain Korea 21) Program, supported by Ministry of Education (MOE) of Korea, and by the ITRC-CHOAN Program The authors are with the Department of Information and Communications, Kwangju Institute of Science and Technology, Kwangju 500-712, South Korea (e-mail: firstname.lastname@example.org). Publisher Item Identifier S 0018-9197(02)00621-8.
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics
- Electrical and Electronic Engineering