Detuned grating multisection-RW-DFB lasers for high-speed optical signal processing

We present a detailed description and a first theoretical study of an impro ved concept for high-frequency self-pulsations (SPs) in multisection (MS)-D FB lasers with an integrated phase tuning section. The DFB wavelengths of t he two DFB sections are spectrally detuned by nearly the stopband width usi ng two gratings with different grating periods. If both DFB sections are op erated at lasing conditions and an appropriate phase is chosen, we obtain b eating-type SP with a frequency given by the spectral distance of two lasin g modes. Good agreement between theory and experiment is obtained with resp ect to the role of the detuning, the role of the phase section, as well as the synchronization to external injected signals. The modeling shows a stro ng nonlinear coupling of the two involved modes via the carrier densities. This effect is important for the mutual coherence and for the observed lock ing of the beating oscillations to external signals. From the results of th e calculations, we draw the conclusion that even higher SP frequencies can be obtained based on the new concept.