Injection locked lasers for flexible optical comb sources

Optical transport networks will soon require channel data rates in excess of 100 Gb/s in order to continue to meet the demand for bandwidth. Bandwidth flexible optical networks, based on flex-grid ROADMs, have been proposed in the literature to support 400 Gb/s and 1 Tb/s super channels. In such systems, techniques including coherent optical OFDM and Nyquist WDM transmission may be employed to achieve channel spacing at or close to the symbol rate. Due to the reduction (or elimination) of inter-channel guard bands afforded by these techniques they are best served by optical comb sources which offer constant frequency spacing between the carriers, as opposed to independent lasers that do not. Moreover, a comb source that offers free spectral range (FSR) tunability allows a single source to be easily adapted to suit the chosen symbol rate. In order to be successfully employed in such systems, optical frequency comb sources should exhibit good spectral flatness, high frequency stability, low linewidth, and a tunable free spectral range (FSR).