128-Gb/s PAM-4 Uncooled $\boldsymbol{(25^{\mathrm{o}}\mathrm{C}-70^{\mathrm{o}}\mathrm{C})}$ Direct Modulation of $\boldsymbol{1.3-\mu \mathrm{m}}$ DFB BH Lasers

High relaxation oscillation frequency of 38.1 and 25.4 GHz at
$25^{\circ}\mathrm{C}$
and
$85^{\circ}\mathrm{C}$
and small leak current with improved SR-LBH lasers were achieved. Clear eye openings of 128-Gb/s PAM-4 uncooled
$(25^{\mathrm{o}}\mathrm{C}\ \text{to}\ 70^{\mathrm{o}}\mathrm{C})$
direct modulation were demonstrated for the first time.