Temperature dependence of picosecond pulse spectra of a DFB laser

High-power distributed feedback (DFB) laser diodes are well established for continuous-wave (CW) applications. In this paper, the spectrum of high power DFB lasers under gain-switching operation is designed. For gain-switching, the laser is driven by short current pulses. During each current pulse, the laser undergoes relaxation oscillations. In this way, laser pulses with durations below 50 ps FWHM and energies above 100 pj can be generated. The power in the DFB laser mode depends on the detuning between gain peak and Bragg wavelength, which can be changed by a variation of the device temperature. The laser diodes under investigation are triple-quantum well InGaAs/AlGaAs laser diodes with a ridge waveguide structure for lateral fundamental mode operation. This work emphasizes that the spectrum of DFB lasers optimized for CW operation may degrade under pulsed operation, and can be controlled to a large extend by selecting the appropriate device temperature.