Spectral Linewidth Reduction in Widely Wavelength Tunable DFB Laser Array

We have developed an L-band tunable distributed feedback laser array (TLA) with a new design to reduce the spectral linewidth. A wide wavelength tuning range of $sim$40 nm is obtained with a high fiber output power of 20 mW and a high side-mode suppression ratio of ?50 dB in the TLA module. A narrow linewidth of less than 580 kHz is achieved over the entire tuning range. Furthermore, we investigated the causes of linewidth variation. We found that a TLA with a longer cavity is more tolerant to external feedback, which reduces the variation in linewidth.