Gain-equalizing filters for wavelength division multiplexing optical communication systems: a comparison of notch and long-period grating filters for integrated optoelectronics

Abstract

Optical notch and long-period grating (LPG) gain-equalizing filters are modeled and studied, and their performances are compared and contrasted for the case of optical waveguide amplifiers for integrated optoelectronics. The analysis is based on a 16-channel, 2.5 Gb s −1, wavelength division multiplexing communication system consisting of cascaded Er 3+-doped tellurite optical waveguide amplifiers. A tellurite-based amplifier was chosen as the amplifying element because of its broad emission bandwidth (∼80 nm), its high emission cross-section (6.44×10 −25 m 2) and its high rare-earth ion solubility. The amplifier model is based on propagation and population-rate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining finite elements and a Runge–Kutta algorithm. The analysis predicts that LPG filters show improved performance compared to notch filters, and combined with tellurite-based waveguide amplifiers reduce the deleterious gain peaking effect increasing the signal maximum transmission distance.