Wavelength division multiplexing of optical signals has attracted increasing interest in fiber communication and photonic switching systems for the large amount of signals that can be processed. Wavelength tunable filters are indispensable for the selection of multiplexed optical signals, with tunability one of the most significant characteristics because this limits the number of signal channels. DFB active filters have several advantages over passive filters. Their amplification exceeds 10 dB, and they have a narrow transmission bandwidth below 0.1 nm when biased just below the threshold. Electrical wavelength tunability exceeding 1 nm is achieved by using current injection and a variety of waveguide structures. The two major structures reported thus far for DFB widely tunable active filters with different tuning mechanisms are shown in Fig. 1.
This article is from 'OSA Proceedings of the International Topical Meeting on Photonic Switching Held in Salt Lake City, Utah on 6-8 March 1991. Volume 8,' AD-A253 026, p140 thru p143.