Large-wavelength tunability of asymmetric three-section DFB lasers under cw and pulsed bias

Abstract

We have studied wavelength tuning in three-section distributed feedback (DFB) laser diodes under pulsed and continuous biasing. In these devices the side sections are connected to each other enabling a tuning operation with two injection electrodes. The technological processes for the device fabrication are presented, emphasizing the preparation of the separation grooves. Under pulsed bias conditions we found a maximum modejump-free tuning range of 2.5 nm. The duty cycle was chosen appropriately in this case in order to isolate the nonthermal tuning effects. Under continuous biasing a maximum of total tuning range of 3.7 nm was measured in modejump-free operations. This value represents the interplay of all the wavelength tuning effects involved in these asymmetric three-section DFB lasers. Under both experimental conditions, pulsed and continuous biasing, comparably large modejump-free tuning ranges are obtained. Possible explanations of the enhanced wavelength tunability in these devices are discussed such as threshold gain modulation, plasma effect enhancement controlled by strong spatial hole burning, residual end facet phase effects, and asymmetric geometrical conditions for all section lengths and the position of the phase shift of the grating.