High speed direct modulation of diode lasers: towards terabit communications

A novel method of directly modulating a laser is considered. The modulation is achieved through movement of a pulse of constant optical energy along the device. The average optical energy in the device remains the same, and so the photon-electron resonance limit is avoided allowing very high modulation speeds to be obtained. This principle has been illustrated with three examples: the colliding pulse mode-locked laser, the bistable self-pulsating DFB laser and the push-pull modulated DFB laser. The latter technique is of particular interest for use in future high speed systems because it allows arbitrary information to be placed on the optical output. The limiting frequency is determined by mode spacing, and hence is structurally dependant. Numerical modelling indicates that push-pull modulation of short cavity, partly gain-coupled DFB lasers can provide modulation bandwidths greater than 100 GHz