Modulation characteristics of tunable DFB/DBR lasers with one or two passive tuning sections

Calculation of the small-signal modulation characteristics of tunable distributed-feedback (DFB) and distributed Bragg reflector (DBR) lasers requires rate equations for the photon number, the phase of the electric field, and the carrier densities. Here, the rate equation for the photon number and phase is derived from an optical transmission-line model. Examples of the frequency- and intensity-modulation characteristics of a phase-tunable DFB laser are presented. The modulation responses exhibit the well-known relaxation resonance if either of the drive currents is modulated, but the possibility of complete removal of the resonance peak together with a perfect cancellation of spurious intensity modulation is also demonstrated. The frequency-modulation response then assumes a simple low-pass character with a cutoff frequency determined by the carrier lifetime in the passive tuning section. The importance of choosing the proper bias conditions is emphasized