Multiwavelength line-rate-independent optical digital cross-connect system based on low-gain fiber amplifiers

Abstract

A digital cross-connect system (DCS) automatically cross connects constituent signals according to an electronically alterable memory map. Unlike a conventional circuit switch, a DCS is a nonblocking slow switch, with a connection duration of hours or months, and switches much-higher-rate signals. Present DCSs are designed to terminate a fixed-line-rate optical signal, and the cross-connect function is performed in the electrical domain. Therefore when higher line rates are required in the future, the original DCS may have to be entirely replaced. To overcome this problem we propose and demonstrate a line-rate-independent, multiwavelength optical DCS based on low-gain erbium-doped fiber amplifiers (EDFAs). This DCS provides a net optical gain, supports point-to-point, multicast, and broadcast connectivity, and uses a minimum number of basic EDFA switching units. Since fast switching is not required, switching units based on EDFAs are more suitable than those based on either semiconductor optical amplifiers1 (which may have severe saturation-induced pulse distortion and multi-wavelength cross talk) or LiNbO3 waveguide switches2 (which have high insertion loss, have high cross talk, and require high driving voltages Fig. 1.8x8 dilated Benes DCS based on low-gain EDFAs. The optical spectra of the four (small-signal) wavelengths at an input port and after the first and sixth stages of EDFA switching units are shown, respectively.